Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘J’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘J’
J2-flow theory – It is also called von Mises plasticity. It is a widely used model in engineering for ductile materials (like metals) that predicts when yielding (permanent deformation) begins under complex loading, based on the principle that yielding occurs when the second deviatoric stress invariant, J2, reaches a critical value, equivalent to the material’s yield strength in simple tension. It is formulated using the scalar von Mises stress (sigma v) or equivalent stress, which represents the distortion energy, making it suitable for predicting failure in multi-axial stress states from uniaxial test data, frequently implemented through finite element analysis (FEA) with radial return algorithms.
Jaccarino-Peter effect – It is a condensed matter physics phenomenon, mainly utilized in materials engineering for designing high-field, re-entrant super-conductors. It occurs when a strong external magnetic field is applied to a material containing localized magnetic moments, resulting in the compensation of the internal exchange field, which in turn induces or restores superconductivity which has been previously suppressed.
Jack – It is a mechanical lifting device which is used to apply large forces or lift heavy loads. A mechanical jack uses a screw thread for lifting heavy equipment. A hydraulic jack uses hydraulic power.
Jack arch – It is a sprung arch in which the outer surface is horizontal and the inner surface is either horizontal or arched with a large radius.
Jack chain – It is a type of chain made of thin wire, with figure-eight-shaped links and loops at right angles to each other. Jack chains are frequently used to suspend fixtures such as lights or signs, for decorative purposes, or as part of a cable lock. Jack chain can be manufactured as either single-jack chain or as double-jack chain. If double-jack, the lower loop is formed of two strands of wire rather than just one as in a single-jack.
Jack dam drills – Jack dam drills are for drilling a hole in the skimmer plate / wall of the main trough of the blast furnace. This ensures that cast products are fully drained from the furnace. The drills are made specific to the blast furnace to meet the specific requirements such as the main trough location, foundations, columns and fixed equipment for each specific cast house. Equipment drives are either hydraulic or pneumatic and are powered by either the general pump unit of the equipment system or independently. The drills are made either portable or stationary. Jack dam drill is a useful tool for the blast furnace cast house.
Jacked piles – These piles are jacked into the soil by applying a downward force with the help of a hydraulic jack.
Jacket – It is a cavity external to the vessel which permits the uniform exchange of heat between the fluid circulating in it and the walls of the vessel. There are several types of jackets, depending on the design.
Jacket design – It refers to the engineering process of creating structures which minimize the projected area near the water surface to reduce load and foundation requirements, while considering soil conditions and foundation specifications. It involves optimizing bracing arrangements to improve load capacity and ductility.
Jacketed vessel – It is a container which is designed for controlling temperature of its contents, by using a cooling or heating ‘jacket’ around the vessel through which a cooling or heating fluid is circulated.
Jacket, mould – It is an external structural assembly which surrounds a mould, mainly used to provide structural support, rigidity, and frequently to incorporate important functional components such as cooling channels. The specific design and function of a mould jacket vary depending on the moulding process.
Jacket platform – It is a type of fixed offshore platform supported by a steel space frame, consisting of a plate girder or deck truss structure which is piled to the seafloor, typically used in water depths not exceeding 500 meters.
Jacket, shell or casing – The metal casing of the furnace enclosing the refractory brickwork. In case of cables, the term jacket is used for non-metallic coverings on the outer portions of a cable. They serve as electrical and mechanical protection for the underlying cable materials. There are several materials which can be used for cable jackets. The two broad categories are thermo-plastic and thermo-setting. For each application, the operating temperature and environment are important factors which are to be considered.
Jacket structure – It is a lattice-like framework made of steel tubular members, typically consisting of three or four vertical legs connected by horizontal and diagonal bracing, designed to provide stability and support for offshore wind turbines in deep water depths. These structures are anchored to the seabed and feature a transition piece that interfaces with the wind turbine tower, facilitating load transfer.
Jacket weight – It refers to the total mass of a large, lattice-like steel support structure (a jacket) used for offshore platforms or wind turbines, important for structural analysis, stability, and marine operations like launching and installation, where it dictates load calculations on barges and support systems. It is an important engineering parameter, differing from fabric weights, representing the immense steel framework supporting topside equipment against environmental forces.
Jack-hammer – It is a pneumatic or electro-mechanical tool which combines a hammer directly with a chisel. Hand-held jackhammers are generally powered by compressed air, but some are also powered by electric motors. Larger jackhammers, such as rig-mounted hammers used on construction machinery, are normally hydraulically powered. These tools are typically used to break up rock, pavement, and concrete. A jackhammer operates by driving an internal hammer up and down. The hammer is first driven down to strike the chisel and then back up to return the hammer to the original position to repeat the cycle. The effectiveness of the jackhammer is dependent on how much force is applied to the tool. It is normally used like a hammer to break the hard surface or rock in construction works and it is not considered under earth-moving equipment, along with its accessories (i.e., pusher leg, lubricator).
Jacking gear – It is also known as a turning gear. It is a device placed on the main shaft of an engine or the rotor of a turbine. The jacking gear rotates the shaft or rotor and associated machinery (such as reduction gears and main steam or gas turbines), to ensure uniform cool-down. Without turning, hogging or sagging can occur. Additionally, the jacking gear’s assistance in rotation can be used when inspecting the shaft, reduction gears, bearings, and turbines. As an auxiliary function, the jacking gear also helps to maintain a protective oil membrane at all shaft journal bearings.
Jacking oil pump – It is a high-pressure, motor-driven pump which supplies lubricating oil (typically at 16 mega-pascals to 300 megapascals) to the bottom of journal bearings during turbine start-up and shutdown. Its main purpose is to create a high-pressure oil film (hydrostatic lift) which causes the heavy turbine rotor shaft to ‘float’. This prevents direct metal-to-metal contact between the shaft and the Babbitt metal bearing surfaces when the rotor is turning at low speeds, where normal hydrodynamic lubrication is not yet effective.
Jack-screw – It is a type of jack that is operated by turning a leadscrew. It is normally used to lift moderate and heavy weights and as adjustable supports for heavy loads.
Jacobi elliptic functions – These are defined as generalizations of trigonometric functions which are used to solve a variety of physical problems, particularly in the context of non-linear oscillators. They have applications in areas such as the motion of pendulums, vibrations of structures, and other non-linear dynamic systems.
Jacobi method – It is a numerical technique for solving linear systems of equations, which involves decomposing a matrix into a diagonal matrix and a remainder matrix, allowing for an iterative approach to find approximations of the solution.
Jail-breaking – It is defined as the process of exploiting vulnerabilities in a software system to bypass manufacturer-imposed limitations, security guardrails, or digital rights management (DRM) controls. While originally associated with enabling root access on mobile devices, the term now also refers to techniques which trick ‘large language models’ (LLMs) into bypassing safety protocols to generate restricted content.
Jam – It takes place when materials get blocked, wedged, or stuck fast. Am causes a process to become unworkable when a movable part becomes blocked or stuck.
Jamb – It is the vertical refractory brickwork of a furnace door or any other opening. It is also a vertical structural member forming the side of an opening in a furnace wall. Jamb is also a type of refractory brick shapes, intended for use in sides of wall opening.
Jamb brick – It is a brick., normally square-shaped, with one side forming part of the oven wall and the side at right angles to it forming part of the outside wall of the battery. It is also a brick, in which one end face is completely rounded off to join one side face.
Jameson cell – It is a cylindrical device which utilizes a high-pressure jet of feed slurry to entrain air and create fine bubbles, facilitating the collision and attachment of particles, which then float to the top as froth while hydrophilic minerals sink as tailings. It operates with lower volume and without the need for agitators or compressors, ensuring stable operation through efficient particle-bubble contact.
Jamin effect – It refers to the phenomenon where a droplet entering a pore throat deforms, resulting in a smaller diameter at the advancing side than at the trailing side, which creates a higher capillary pressure at the front than at the back, hindering the droplet’s passage through the throat.
Jammer – It is a device which deliberately emits signals to disrupt communication systems, preventing the transmission or reception of data, which can result in denial of service. Jammers can be categorized into four types namely constant, deceptive, random, and reactive.
Jamming – It is the physical process by which the viscosity of some mesoscopic materials, such as granular materials, glasses, foams, polymers, emulsions, and other complex fluids, increases with increasing particle density. The jamming transition has been proposed as a new type of phase transition, with similarities to a glass transition but very different from the formation of crystalline solids.
Jam sensor – It is a specialized sensor within a conveyor system crafted to identify and signal the presence of material jams or blockages. Consistent checks are crucial to maintaining the accuracy and responsiveness of the jam sensor.
Jar ramming – It is a method of preparing sand moulds for casting. It is used to compact the sand mixture into a flask or mould box to create a sturdy mould cavity capable of withstanding the pressure of molten metal. The process typically involves (i) placing a measured quantity of tempered sand into a sample container, and (ii) applying a series of repetitive, controlled impacts or ‘jams, to the sand using a specialized machine to achieve a standard level of compaction and specific properties like green compression strength.
Jarring machine – It is a moulding machine which packs the sand by jarring.
Jars – These are glassware which are used in chemical laboratories. These are cylindrical containers with wide openings which can be sealed. Bell jars are used to contain vacuums.
Jasper – It is a type of quartz which can be brown, yellow, or green, but is very frequently a mottled, brick red colour.
Java – In software engineering, it is a high-level, object-oriented programming language and computing platform known for its ‘write once, run anywhere’ (WORA) capability, allowing code to run on any device with a Java virtual machine (JVM). It is used to build diverse applications, from enterprise software and web apps to Android apps, providing a reliable, portable, and secure foundation for large-scale systems, emphasizing classes and objects for organized, maintainable code.
Java byte code – It is the intermediate representation of a Java programme which is produced by the Java compiler, allowing the programme to be executed by the Java runtime interpreter on different devices and operating systems.
Javadpour model – It is a theoretical framework which integrates viscous flow and Knudsen diffusion within a single nano-tube, focusing on the concept of apparent permeability.
Java virtual machine – It is a crucial engineering component which acts as a runtime engine, creating a platform-independent environment to execute Java bytecode, enabling ‘write once, run anywhere’ (WORA) by abstracting underlying hardware and operating system (OS), and handling key tasks like memory management (garbage collection), class loading, and bytecode verification / execution through interpreters/JIT (just in time) compilers for performance. It is a virtual machine specification which defines an abstract machine with its own instruction set, registers, and memory, interpreted by specific implementations for different platforms.
Jaw crusher – Jaw crusher is used as primary crusher. It uses compressive force for breaking the material. This mechanical pressure is achieved by the two jaws of the crusher. Reduction ratio is usually 6:1. The jaw crusher is consisting of two vertical jaws installed to a ‘V’ form, where the top of the jaws is further away from each other than the bottom. One jaw is kept stationary and is called a fixed jaw while the other jaw, called a swing jaw, moves back and forth relative to it, by a cam or pitman mechanism. The volume or cavity between the two jaws is called the crushing chamber. The movement of the swing jaw can be quite small, since complete crushing is not performed in one stroke. The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap. Jaw crusher is used for the primary disintegration of metal pieces, ores, or agglomerates into coarse powder. In jaw crusher rock is broken by the action of steel plates.
Jaw plate – It is a replaceable, wear-resistant component within a jaw crusher, forming the crushing surfaces (a fixed and a movable plate) which use compressive force to break down hard materials like rock or ore, typically made from high-strength manganese steel for durability against abrasion and impact.
Jeffries’ method – It is a method for determining grain size based on counting grains in a prescribed area.
Jerk – It is the rate of change of acceleration with respect to time, basically the third derivative of position, measured in meters per second cubed. It quantifies how abruptly acceleration changes, impacting smoothness, comfort (elevators), structural dynamics (vibrations), and efficiency in motion control systems like 3D printers and vehicles. Lower jerk means smoother motion, while high jerk causes uncomfortable bumps or can lead to component failure.
Jerky movement – It is a sudden, spasmodic, or abrupt motion which can be unpredictable. It can also refer to a condition where someone makes fast, uncontrollable movements.
Jet – It is a stream of fluid which is projected into a surrounding medium, normally from some kind of a nozzle, aperture or orifice. Jets can travel long distances without dissipating. Jet fluid has higher speed compared to the surrounding fluid medium. In the case that the surrounding medium is assumed to be made up of the same fluid as the jet, and this fluid has viscosity, some of the surrounding fluid is carried along with the jet in a process called entrainment.
Jet actuators – These are devices which produce control jets from fluidic sources, which can be either steady or unsteady, and need mechanical energy to operate. They can vary in complexity and can include configurations such as synthetic jets which do not necessitate a pressure source, hence simplifying the system.
Jet boundary – It refers to the interface where a jet of fluid interacts with surrounding fluid or surfaces, influencing parameters such as pressure distribution, momentum, and entrainment effects, particularly in the context of boundary layer dynamics and control.
Jet cooling – It uses a high-pressure jet of steam to cool water or other fluid media. Typical uses include industrial sites, where a suitable steam supply already exists for other purposes.
Jet drilling – It uses high-velocity fluid (water, acid, or abrasive slurry) or plasma streams from specialized nozzles to cut into rock or difficult materials, creating small holes or extensive lateral channels for resource extraction or precision machining, offering alternatives to traditional methods like mechanical drilling or hydraulic fracturing, particularly in complex formations. Key types include ‘radial jet drilling’ (RJD) for well stimulation and ‘electro jet drilling’ for micro-holes in superalloys.
Jet electrolyte – It is a high-conductivity jet of electrolyte which is impinged under pressure on a work-piece to achieve anodic dissolution, facilitating processes like the generation of small diameter holes and micro-grooves in materials.
Jet engine – It is a type of reaction engine, discharging a fast-moving jet of heated gas (normally air) which generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
Jet engine disk – It is turbine disk. It is a crucial, high-strength rotating component which connects turbine blades, withstanding extreme heat, pressure, and centrifugal forces to extract energy from hot gases to power the engine’s compressor and fan. These disks are complex structures, frequently made from superalloys, designed to prevent catastrophic failures like rotor burst by managing severe low-cycle fatigue and thermal stress, ensuring engine safety and reliability.
Jet engine disk, process modeling for – It involves a multi-disciplinary approach, combining CAD (computer aided design) design, finite element analysis (FEA), and material behaviour simulations to create high-performance, lightweight rotating components. These disks are required to withstand extreme thermal and centrifugal loads during operation.
Jet flow rate – It refers to the volume of fluid injected through a jet per unit time, which influences flow behaviour, pressure distribution, and turbulence profiles in configurations such as slot jets and impinging jets.
Jet hardening – It is also called ‘impinging jet quenching’ (IJQT). It is an engineering process used for the localized hardening of metal components, particularly steel, by utilizing high-velocity water jets to achieve rapid, controlled cooling. This method creates a hardened, wear-resistant surface layer (frequently martensite) over a tougher, more ductile core.
Jet impact force – It is the reaction force exerted by a high-velocity fluid stream (a ‘jet’) when it strikes a surface (like a plate, vane, or turbine blade), caused by the fluid’s substantial change in momentum, calculated using the impulse-momentum principle (Force = mass flow rate × change in velocity). It is fundamental in fluid mechanics for designing turbines, waterjet cutters, and understanding hydro-entanglement, quantifying how much force is generated when water or air hits a surface.
Jet impingement cooling – It works by spraying a working fluid onto a surface being cooled.
Jet interaction – It describes how multiple fluid jets influence each other, creating complex flow structures, shockwaves, and pressure changes which affect performance, seen in systems like scramjets, nozzles, or combustion engines, impacting thrust, mixing, and stability by merging, deflecting, or generating unique flow patterns. It is important in combustion (fuel spray mixing), where careful analysis predicts forces and flow fields for optimized performance.
Jet Kote surfacing system – It is a high-pressure combustion thermal spray process in which a spray gun burns a fuel e.g., methyl acetylene propadiene mixture (MAPP) gas, or propane, with a high volume of oxygen within a combustion chamber. Using a nitrogen carrier gas, the powder is injected into the combustion products and is rapidly heated and accelerated to impact at high speed against the work surface to be coated. Unlike the detonation gun process, the jet Kote system is based on continuous combustion within the gun.
Jet nozzle – It is a specialized device which converts a fluid’s (liquid or gas) pressure and thermal energy into high-velocity, directed kinetic energy, creating a focused, powerful stream for applications like propulsion, cutting, or cleaning. It works by constricting the flow, accelerating the fluid as it exits, and controlling its speed, direction, and shape, making them critical in jet engines, industrial manufacturing, and fluid dynamics.
Jet producing apparatus – It is a device which produces a jet of air or inert gas which impinges on the stream of molten metal and disintegrates it into small particles. These irregularly shaped (nodular) particles, together with a substantial volume of cooling air, are drawn through a chiller chamber and into a cyclone and / or bag filter collecting system. The atomized powers are then graded by screening.
Jet pulverizer – It is an equipment which comminutes metal pieces or agglomerates by means of pressurized air or steam injected into a chamber.
Jet Reynolds number (Re) – It quantifies the ratio of a fluid’s inertial forces to its viscous forces in a jet, determining if the flow is smooth (laminar, low Re) or chaotic (turbulent, high Re). It is calculated as Re = u0 x Dv (jet velocity × diameter / kinematic viscosity) and is important for predicting flow behaviour, mixing, and heat transfer in applications like nozzles, combustion, and fluid dynamics.
Jet scrubber – It is a high velocity water jet directed into the throat of a venture section of a cupola to separate out particulates in air pollution control.
Jet tapping – It is a method of tapping a melting furnace by firing a small explosive charge instead of using an oxygen lance. The tapper consists of an explosive charge enclosed in a plastic case surrounded by a hollow bullet-shaped body.
Jet vapour deposition – It is a vacuum deposition method in which evaporated atoms or molecules are ‘seeded’ into a supersonic jet flow of inert gas into a rapidly pumped vacuum chamber. The jet flow transports the atoms and molecules to the substrate surface, where they are deposited.
Jet velocity – It is the speed at which a fluid (like water, air, or gas) exits a confined opening (a nozzle or orifice) into a surrounding environment, representing the conversion of pressure energy to high kinetic energy, important for applications from cooling to propulsion, and characterized by its decay as it mixes with ambient fluid. It is a fundamental parameter in fluid dynamics, measured as a vector (magnitude and direction), determining a jet’s force, momentum, and thermal effects.
Jewel bearing – It is a bearing which is made of diamond, sapphire, or a hard substitute metal.
Jewelry application, powder metallurgy – Powder metallurgy allows for higher precision and consistency in the production of metal components. Metal powders are used in the production of a wide range of jewelry items, including rings, necklaces, earrings, bracelets and brooches.
JFET – It is a field effect transistor with a reverse-biased PN junction between gate and channel.
J-groove – It is also called J-bevel. It is a type of joint preparation where the edge of one work-piece is machined to a concave, radius-shaped profile (resembling the letter ‘J’). It is used in butt or corner joints, typically with the mating piece left square, to create a strong, deep-penetration weld, especially on thick materials.
J-groove weld – It is a type of groove weld. It is a specialized groove preparation for butt or edge joints, where one edge is machined with a curved, J-shaped profile (like half a ‘U’) and the other edge remains flat, allowing for deep, strong, and efficient full-penetration welds, especially in thicker materials, by providing good access and better heat distribution to reduce cracking.
J-hook – It is a J-shaped fastener or connector used to support, suspend, or anchor items in several applications, ranging from cable management to structural construction and industrial lifting.
Jib – It is the projecting part of crane from which lifting chain or gear is suspended.
Jib crane – It is a type of crane where a horizontal member (jib or boom), supporting a moveable hoist, is fixed to a wall or to a floor mounted pillar. Jib cranes are used in industrial premises and on vehicles. The jib can swing through an arc, to give additional lateral movement, or be fixed.
JIC fittings – These are a type of flare fitting machined with a 37-degree flare seating surface. JIC (Joint Industry Council) fittings are widely used in fuel delivery and fluid power applications, especially where high pressure (up to 69 MPa) is involved.
Jig – It is a mechanism for holding a part and guiding the tool during machining or assembly operation. It is also a piece of milling equipment which is used to concentrate an ore on a screen submerged in water, either by the reciprocating motion of the screen or by the pulsation of water through it.
Jig borer – It resembles a specialized kind of milling machine which provides tool and die makers with a higher degree of positioning precision (repeatability) and accuracy than those provided by general machines. Although capable of light milling, a jig borer is more suited to highly accurate drilling, boring, and reaming, where the quill or headstock does not see the significant side loading that it would with mill work. The result is that it is a machine which is designed more for location accuracy than heavy material removal.
Jig boring – It is the boring with a single-point tool where the work is positioned upon a table which can be located so as to bring any desired part of the work under the tool. Hence, holes can be accurately spaced. This type of boring can be done on milling machines or jig borers.
Jig concentrators – These are devices which are used mainly in the mining industry for mineral processing, to separate particles within the ore body, based on their specific gravity (relative density. The particles normally of a similar size, frequently crushed and screened prior to being fed over the jig bed. There are several variations in design, however, the basic principles are constant. The particles are introduced to the jig bed (normally a screen) where they are thrust upward by a pulsing water column or body, resulting in the particles being suspended within the water. As the pulse dissipates, the water level returns to its lower starting position and the particles once again settle on the jig bed. As the particles are exposed to gravitational energy whilst in suspension within the water, those with a higher specific gravity (density) settle faster than those with a lower count, resulting in a concentration of material with higher density at the bottom, on the jig bed. The particles are now concentrated as per the density and can be extracted from the jig bed separately. In the mining of majority of the heavy minerals, the denser material is the desired mineral and the rest is discarded as floats (or tailings).
Jiggering – It is a plastic forming process used with clay-based ceramics in which a plastic mass is pressed under relatively low pressure into a plaster die, and the final shape is achieved by rotating the die and shaping the plastic mass with a fixed tool. Jiggering is a mechanical version of the potter’s wheel and produces shapes with circular cross sections.
Jigging bed – It is made of water and mineral particles. The bed moves in two sections namely pulsion stroke and suction stroke alternately so that the hydro-dynamic properties of the jigging bed vary alternately.
Jigging process – It is an ore concentration process which is carried out in any fluid whose effectiveness depends on differences in the density of the granular mineral particles. It consists of separation of the particles into layers of different specific gravities followed by the removal of the separated layers. It is the process of sorting different materials in the ore in a fluid by stratification, based upon the movement of a bed of particles, which are intermittently fluidized by the pulsation of the fluid in a vertical plane. The stratification causes particles to be arranged in layers with increasing density from the top to the bottom. This particle arrangement is developed by several continuously, varying forces acting on the particles, and is more related to particle density than most other gravity concentrating methods. In the jigging process, the particles are introduced to the jig bed (normally a screen) where they are thrust upward by a pulsating water column or body, resulting in the particles being suspended within the water. As the pulse dissipates, the water level returns to its lower starting position and the particles once again settle on the jig bed. As the particles are exposed to gravitational energy whilst in suspension within the water, those with a higher density settle faster than those with a lower density, resulting in a concentration of material with higher density at the bottom, on the jig bed. The particles are now concentrated according to density and can be extracted from the jig bed separately. In case of the beneficiation of the iron ore, the denser material is the desired enriched ore and the rest is needed to be discarded as floats (or tailings).
Jig grinder – It is a machine tool which is used for grinding complex shapes and holes where the highest degrees of accuracy and finish are needed. The jig grinder is very similar to a jig borer, in that the table positioning and spindles are very accurate.
Jig quenching – It is a specialized heat treatment process where a heated metal part is held, clamped, or constrained in a specialized fixture (jig or die) while being quenched in a liquid medium. It is a critical engineering technique used mainly to prevent distortion, warpage, or cracking in complex or delicate geometries while ensuring maximum hardness.
Jig tailings – These are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore in the jigging process.
J-integral – It is a mathematical expression. It is a line or surface integral which encloses the crack front from one crack surface to the other, used to characterize the fracture toughness of a material having appreciable plasticity before fracture. The J-integral eliminates the need to describe the behaviour of the material near the crack tip by considering the local stress-strain field around the crack front. ‘JIc’ is the critical value of the J-integral needed to initiate growth of a preexisting crack.
Jishu-Hozen – It means ‘autonomous maintenance’. It is a core ‘total productive maintenance’ (TPM) pillar where machine operators take responsibility for basic upkeep (cleaning, lubrication, tightening, inspection) of their own equipment, preventing break-downs, increasing efficiency, and fostering operator ownership by training them to detect and address issues early, shifting from reactive to pro-active maintenance.
Jitter – It is the deviation from true periodicity of a presumably periodic signal, frequently in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significant, and normally undesired, factor in the design of almost all communications links. Jitter can be quantified in the same terms as all time-varying signals, e.g., root mean square (RMS), or peak-to-peak displacement. Also, like other time-varying signals, jitter can be expressed in terms of spectral density.
Jittered dot-plot – In a simple dot plot, the dots can overlap. In some cases, they can coincide completely, so obscuring some of the points. A solution is to randomly move the dots perpendicularly from the axis, to separate them from one another. This is called jittering. It results in a jittered dot-plot.
Jobbing foundry – It is a foundry engaged in the manufacture of several types of castings and is not a part of a manufacturing plant, and produces castings for sale that normally makes a wide variety of castings in small lots or quantities.
Jobbing workshop – It is also called job shop. It is a manufacturing facility which specializes in producing custom-made or unique items in small quantities as per a customer’s specific design and specifications. This is known as job production or one-off production, in contrast to mass production or batch production.
Job injury – It is also called occupational injury. It is physical or psychological harm to a worker directly resulting from an accident or exposure at work, caused by work-place events like machinery malfunction, falls, over-exertion, or unsafe conditions, differing from occupational diseases which develop over time. Engineering plays a key role in preventing these by designing safer equipment, processes, and protective measures (like PPE), addressing risks from tools, lifting, and environmental factors.
Job involvement – It is the extent to which an individual identifies with their job and considers it a material component of their self-worth.
Job production – It is a specific type of production system. It involves production of special type of products which vary in nature and size. In this type of production system, products are produced as per the order and specifications of the customers.
Job satisfaction – It reflects the feelings an employee has about his or her job or facets of the job, such as pay or supervision.
Job title – It refers to a specific designation within an occupation which encompasses different activities and responsibilities associated with that role. It serves as a label for the overall duties expected of an individual in a particular position.
Jog – It means inching movement. It is a function which provides momentary operation of an actuator to achieve a small movement of the valve.
Jog control – It is a control mechanism enabling manual adjustments or precise movement of conveyor components in small increments. Regular inspections are necessary to ensure the effective functionality and safety of the jog control.
Jogging – It means momentarily energizing a motor with short bursts of power (full voltage) to make small, controlled movements for precise positioning, like nudging a conveyor belt or crane, contrasting with inching (reduced voltage for slower, finer adjustments) and distinct from the physical exercise. It is a motor control function using push-buttons to quickly start and stop the motor to move machine parts into exact spots, often limited to about 5 times per minute to prevent overheating.
Joggle – It is a small, deliberate offset or step bend in a material (like sheet metal or rebar) which allows for flush, overlapping joints, maintains smooth surfaces, creates space for other parts (like in gutters or structural beams), or aligns components for better load transfer in construction, preventing slipping and reinforcing connections.
Jog-pairs – These are structural defects on a dislocation line consisting of two closely spaced atomic-level offsets (jogs) which lie outside the main slip plane. When a dislocation cuts through another, it can form these jogs, which are characterized by a specific height (frequently multiples of interplanar spacing) and separation distance.
Johansen method – It is frequently referred to as the Johansen yield model or European yield model. It is a plastic design approach used to determine the ultimate load-carrying capacity of timber-to-timber or steel-to-timber connections utilizing dowel-type fasteners (e.g., bolts, nails, screws). This method forms the theoretical basis for modern structural design standards such as Eurocode 5 (EN 1995-1-1).
Johansen’s test – In statistics, the Johansen test is a procedure for testing cointegration of several time series. It is a way to determine if three or more time series are cointegrated. More specifically, it assesses the validity of a cointegrating relationship, using a maximum likelihood estimates (MLE) approach. It is also used to find the number of relationships and as a tool to estimating those relationships. There are two types of Johansen’s test namely one uses trace (from linear algebra), the other a maximum eigenvalue approach (an eigenvalue is a special scalar, when one multiplies a matrix by a vector and get the same vector as an answer, along with a new scalar, the scalar is called an eigenvalue).
Johnson-Cook equation – It is a phenomenological model in engineering which describes a metal’s flow stress (resistance to deformation) under high strain, strain rate, and temperature conditions, normally used in finite element analysis (FEA) for high-velocity impacts, like explosions or machining, by combining terms for strain hardening, strain rate hardening, and thermal softening. It is popular for its simple, closed-form formula which needs few material parameters determined experimentally, predicting material behaviour when traditional models fail.
Johnson-Kendall-Roberts theory – It describes the adhesive contact between two elastic bodies, extending Hertz contact theory by incorporating surface energy and van der Waals forces, leading to a non-zero contact area even without load and predicting a distinct pull-off force, important for understanding adhesion in nano-scale to macro-scale applications like surface coatings, MEMS (micro-electromechanical systems). It provides formulas to relate contact radius, applied force, and material properties like surface energy and elastic modulus, enabling measurement of surface energy from experiments.
Johnson-Mehl-Avrami kinetics (JMAK) model – It describes the rate of solid-state phase transformations (like crystallization, melting, or precipitation) by quantifying how a new phase forms from a parent phase through random nucleation and growth, expressed as X = 1 – exp(-k x t to the power n), where ‘X’ is the transformed fraction, ‘k’ is a rate constant, ‘t’ is time, and ‘n’ (the Avrami exponent) reflects nucleation / growth dimensionality. This model is important in materials science for understanding processes like solidification, recrystallization, and even polymer curing, helping predict material properties and micro-structure evolution.
Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation – It is a fundamental kinetic model in materials engineering and science used to describe the progression of phase transformations (such as crystallization, recrystallization, and precipitation) as a function of time and temperature. It models how a new, lower-energy phase nucleates and grows within a parent phase, accounting for the impingement of growing grains as they consume the material.
Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory – It frequently referred to as the Avrami equation. It is a mathematical model used in material science, including foundry and metallurgy, to describe the kinetics of phase transformations (such as solidification, crystallization, or recrystallization) under isothermal conditions.
Johnson noise – It is also known as Johnson-Nyquist noise. It is the unavoidable electrical noise from the random thermal motion of charge carriers (electrons) within any electrical conductor, creating random voltage fluctuations. It is present even without applied voltage, is proportional to absolute temperature, and limits the sensitivity of electronic devices, needing cooling for extreme precision.
Joining – It is the process of permanently or temporarily connecting two or more solid components to form a single unit, creating assemblies, structures, or products, frequently using techniques like welding, fasteners, adhesives, soldering, or brazing, which is important for complex designs and repairs where direct manufacturing is not feasible or economical.
Joining pipes – It refers to the methods used to connect lengths of pipe together, which include butt-welded, screwed, and socket-weld connections. Each method involves specific techniques to ensure a secure and effective assembly, accommodating different pipe materials and sizes.
Joining processes – Joining processes, include (i) metallurgical joining, such as welding and diffusion bonding, and (ii) mechanical joining, such as riveting, shrink fitting, and mechanical assembly. Metallurgical joining processes, such as welding, brazing, and soldering, form a permanent and robust joint between components. Mechanical joining processes, such as riveting and mechanical assembly, bring two or more parts together to build a sub-assembly which can be disassembled conveniently. Joining processes are necessary for different various engineering activities and in the development of virtually every manufactured product. These processes frequently appear to consume higher fractions of the product cost and to create more of the production difficulties than normally expected. There are a number of reasons for this. First reason is that the joining is multifaceted, both in terms of process variations and in the disciplines needed for problem solving (such as mechanics, materials science, physics, chemistry, and electronics etc.). An engineer with unusually broad and deep training is needed to bring these disciplines together and to apply them effectively to a variety of processes. The second reason is that joining difficulties normally occur far into the manufacturing process, where the relative value of scrapped parts is high. The third reason is that a very large percentage of product failures occur at joints since they are normally located at the highest stress points of an assembly and are hence the weakest parts of the assembly. Careful attention to the joining processes can produce high incentives in manufacturing economy and product reliability.
Joining technology – It refers to the science and methods used to permanently or temporarily connect two or more separate parts into an assembled product, encompassing processes like welding, brazing, soldering, mechanical fastening (bolts, rivets), and adhesive bonding, crucial for creating everything from vehicles to electronics by overcoming material limitations and ensuring structural integrity. It involves selecting the right technique (fusion, solid-state, liquid-solid) for materials like metals, polymers, or composites to achieve desired strength, function, and cost-effectiveness.
Joint – It is the location where two or more members are to be or have been fastened together mechanically or by welding, brazing, soldering, or adhesive bonding. It is also junction of members or the edges of members which are to be joined or have been joined. In case of refractory lining, joint is a space between refractory bricks normally filled with refractory mortar / cement.
Joint, adhesive – The location at which two adherends or substrates are held together with a layer of adhesive. The general area of contact for a bonded structure.
Joint alteration number – It is an important parameter in rock mass classification systems which quantifies the condition or alteration of rock joint surfaces, indicating the nature and thickness of filling material or surface weathering, ranging from 1 for unaltered joints (no filler) to values as high as 10-20 for thick, clay-filled zones, considerably affecting the joint’s shear strength and overall rock mass stability.
Joint authorization – It is the process where multiple authorizing officials, stakeholders, or organizations collectively share responsibility and accountability for accepting the security risks and approving the operation of a system.
Joint, ball – This joint has two degrees of rotational freedom, i.e., pitch and yaw. Pitch allows components to rotate around the ‘z’ axis. Yaw rotates components around the ‘x’ axis.
Joint bar – It is also called a fishplate or splice bar. It is a steel component used to connect the ends of two rails, creating a continuous, stable track for smooth train passage. Bolted to the sides of the rail ends, joint bars ensure alignment, distribute wheel loads, and provide necessary space for rails to expand and contract with temperature changes, though modern mainlines frequently use welded track instead.
Joint, bolted – It is a joint in which a connection is made between two or more parts by using a bolt and a nut to join them together. It is one of the most common elements in construction and machine design. It consists of a male threaded fastener (e. g., a bolt) which captures and joins other parts, secured with a nut having matching female screw thread. There are two main types of bolted joint designs namely tension joints and shear joints. While simple in design, the bolted joint is one of the most common ways in which objects are joined.
Joint brazing – It is a joint made by the process of brazing. Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Joint, bridge – It is a type of joint used in railway engineering. This joint is almost similar to the suspended joint. The only difference is that the two sleepers on both sides of the bridge joint are joined by a flat metal or corrugated plate. This plate is also called a bridge plate.
Joint, butt – It is a type of edge joint in which the edge faces of the two adherends are at right angles to the other faces of the adherends.
Joint classification – It categorizes connections (like bolts, welds, or friction-based) between structural members (beams, braces, panels) based on load transfer, geometry, and function, mainly differentiating between X-joints, K-joints, and T-joints in structures, determining how forces (tension, compression, shear) distribute through the chord and brace members for design integrity and stability, important for areas like pipeline or offshore platform design.
Joint clearance – It is the distance between the faying surfaces of a joint. In brazing, this distance is referred to as that which is present before brazing, at the brazing temperature, or after brazing is completed.
Joint cognitive system -It is the unified whole formed by humans and technology working together as a single cognitive entity to perform complex tasks, emphasizing their inter-dependent, collaborative cognition rather than viewing humans and machines as separate parts. Cognitive systems engineering (CSE) studies joint cognitive system (JCS) to design systems which effectively manage complexity and support this human-machine teamwork, focusing on distributed cognition, shared understanding, and coordinated action in safety-critical domains.
Joint compound – It is also known as drywall mud. It is a gypsum-based, paste-like material used to fill, seal, and finish the joints between panels of drywall or gypsum board. It is engineered to harden, allowing it to be sanded into a smooth, seamless surface for painting. It is frequently used in combination with paper or fibre-glass mesh tape to reinforce joints and prevent cracking.
Joint coordinates – These define the location and orientation of connected components (joints) within a structure or mechanism, important for defining geometry and motion, frequently using global ‘XYZ’ or local cylindrical systems, especially in robotics (joint angles) to describe complex movements and forces.
Joint, corner – When pieces are joined at 90-degree and take the shape of an ‘L’, they form a corner joint. These joints are easy to assemble and need very little if any edge preparation. These joints are frequently used for projects or applications which need a square frame. The two types of corner joints are open corner and closed corner. When the edge of one piece lies flush against the edge of another, it is a closed corner joint. An open corner joint is when two edges meet at their corners and there is an opening where the thickness of each metal can be seen.
Joint, cylindrical – This joint provides two degrees of freedom, i.e., one translational and one rotational. Components joined with a cylindrical joint always rotate around the same axis.
Joint density – It is the measurement of the number of joints in a given area or along a drill core, expressed as a function of the intersection angles between the joints and the observation plane or drill hole. It can be calculated using weighted joint density methods to provide more accurate assessments of joint spacing and distribution in rock formations.
Joint design – It is the arrangement and configuration of components in adhesive bonding, which influences the strength, reliability, and durability of the bond. Effective joint design is to consider the stresses on the part and the mechanical properties of both the adhesive and adherends, with larger bond surface areas typically yielding higher strength.
Joint distribution – It describes the probabilities of two or more variables occurring together, modeling their interdependence, important for analyzing systems where outcomes are not isolated, using functions like ‘joint probability density’ (PDF) for continuous variables or ‘joint probability mass’ (PMF) for discrete ones, to predict system behaviour like component failures or production variations.
Joint domain – It refers to analyzing systems by integrating multiple perspectives (like time / frequency, or domains such as land, sea, air, space, cyber) for a holistic understanding, frequently seen in advanced areas or complex signal processing, emphasizing combined insights beyond single-domain views for better solutions, contrasting with standard single domain analysis. It is about connecting different functional areas (like material science, design, simulation) to solve complex problems, ensuring reliability in mechanical joining, or unifying AI (artificial intelligence) training across distinct data sets.
Jointed frame – It is a structural system of interconnected members (bars / beams) linked by joints, analyzed for load distribution; it can be a pin-jointed frame (truss) where members only take tension / compression (axial force) through frictionless pins, or a rigid-jointed frame (like building skeletons) where joints transfer axial force, shear, and bending moments, allowing rotation but not relative movement between members. The type of joint (pin against rigid) dictates how loads are transferred and analyzed, with trusses being simpler (only axial) and frames like building columns / beams handling complex forces.
Joint, edge – It is a joint made by bonding the edge faces of two adherends. An edge joint is created when fit-up of the work-pieces leaves the edges parallel or nearly parallel to one another. These joints are frequently used when the work-pieces are not to be subjected to any added stress. An edge joint is not to be used if one or both of the pieces are subject to impact or other types of stress.
Jointed rock mass – It is a natural rock formation fractured by discontinuities (joints, faults, bedding planes) into inter-connected blocks, considerably reducing its strength and altering its behaviour compared to solid rock, needing assessment for stability in civil projects based on block size, joint orientation, spacing, roughness, and infill. Its engineering properties depend on the intact rock strength and these structural features, making different classification systems vital for design.
Joint efficiency – It is the ratio of the strength of a welded joint to the strength of the base metal, expressed in percent.
Joint efficiency factor – It is a parameter which quantifies the reduction in strength of components because of the presence of joints, such as riveted joints, and is incorporated into equations to account for the efficiency of these connections in structural analysis.
Joint estimation – It refers to the simultaneous determination of two or more coupled system states, parameters, or variables, rather than estimating them independently. It is a model-based approach, frequently utilized in dynamic, complex, and non-linear systems to achieve higher accuracy and robustness by updating coupled variables together (e.g., in battery management, vehicle dynamics, and structural monitoring).
Joint estimator – It is an algorithm, filter, or observer designed to simultaneously determine multiple unknown, coupled, or interrelated system variables (states, parameters, or inputs) using a single, unified, or cascaded framework. Unlike independent estimators which can struggle with strongly coupled systems, joint estimators improve robustness and precision by considering the inter-dependencies between variables, or system states and external input forces.
Joint, expansion – It is an assembly to allow it to expand and contract as the environment conditions move from hot to cold and helps to ensure that the system remains functional.
Joint fastener – It is a dedicated device which is utilized to securely connect and fasten the ends of conveyor belts. Routine checks are required to verify and uphold the strength and integrity of the joint fastener.
Joint filler powder – It is a chemical compound which is used to fill the gap between two parts of a structure or two adjacent structures.
Joint, flexible – It connects two non-aligned sections. It allows a wide range of motion.
Joint health and safety committee – The joint health and safety committee is a committee in work-place. The responsibilities and powers of joint committee can include obtaining information on work-place hazards, identifying work-place hazards, and recommending how to make the work-place safer and healthier.
Joint force – It is also called joint reaction force. It refers to the internal forces within a connection (like a hinge, or bolted flange) which balance all external loads, and inertia, important for stability and movement, frequently analyzed using methods like the ‘method of Joints’ in structural mechanics. These forces, acting between connected bodies, can be calculated to ensure structures, or mechanisms remain in equilibrium, preventing failure.
Joint, hinge – It is a joint between two objects which allows movement only in one plane. For example, hinge joints on doors.
Joint histogram – It is a multi-dimensional frequency map showing the relationship between two or more sets of data (like pixel intensities in images or sensor readings), where each bin counts how frequently specific combinations of values occur together, widely used in image analysis for segmentation, texture analysis, and image registration. Basically, it is a co-occurrence matrix which reveals correlations, frequently by plotting values from one dataset (e.g., Image A) against another (Image B) to find patterns like intensity-to-intensity relationships, helping understand data fusion or underlying structures.
Joint implementation – It is the mechanism which defined in Article 6 of the Kyoto Protocol. It allows a country with an emission reduction or limitation commitment under the Kyoto Protocol (Annex B Party) to earn emission reduction units (ERUs) from an emission-reduction or emission removal project in another Annex B Party, each equivalent to one ton of carbon di-oxide, which can be counted towards meeting its Kyoto target. Joint implementation offers Parties a flexible and cost-efficient means of fulfilling a part of their Kyoto commitments, while the host Party benefits from foreign investment and technology transfer. A joint implementation project is required to provide a reduction in emissions by sources, or an improvement of removals by sinks, i.e., is additional to what would otherwise have occurred. Projects are to have approval of the host Party and participants have to be authorized to participate by a Party involved in the project.
Jointing accessories, cable – Several types of jointing accessories are mainly used for jointing all types of low voltage and medium voltage power cables. Every jointing kit is provided with an instruction manual supplied by the manufacturer. Joints are to be made as per the guidelines given in the instruction manual. The cable jointing has (i) heat shrinkable jointing kit (preferred), (ii) cold shrinkable jointing kit, (iii tapex tape type jointing kit, (iv) push on type jointing kit, and (v) cast resin jointing kit.
Jointing, cable – Cable joint is a device used to join two or more cables together for extension of lengths or to branch. These joints are made to perform at the same voltage class and ratings of the intended cables and are able to withstand the normal and emergency loading conditions. Selection of the proper cable accessories, proper jointing techniques, skill and workmanship is important. The quality of joint is to be such that it does not add any resistance to the circuit. All underground cable joints are to be mechanically and electrically sound and it is protected against moisture and mechanical damage. The joint is to be further resistant to corrosion and chemical effects. The basic types of cable joints are (i) straight through joint which is used to connect two cables lengths together (simple straight through joints which are for jointing same type of cables and transition straight through joints which are for jointing two different type cables), and (ii) tee joint / branch joint which is normally used for jointing a service cable to the main distribution cable in distribution network.
Jointing kit – It is also called cable jointing kit. It is a comprehensive set of materials and components specifically designed to join and insulate electrical cables, ensuring a secure and reliable connection.
Jointing material refractory – It is the refractory material which is intended for laying and jointing brick(s) or block(s) by troweling, grouting in the joints or dipping. These materials are mixtures of fine aggregate and bond, supplied in the dry state or mixed with suitable liquids ready for use.
Joint interface – It defines the boundary and interaction between two assembled components, important for transmitting loads, motion, and energy, needing detailed specification to manage complex behaviours, microscopic roughness, and potential failure modes (e.g., friction, wear, delamination) using techniques like FEA (finite element analysis) and specialized joint elements for accurate modeling. It involves physical connections (bolts, gaskets) and conceptual interactions, where defining precise requirements prevents system integration issues.
Joint, investigation – It is the investigation of a failure which is carried out by two parties normally the organization and the supplier.
Joint kinematics – It describes the motion of connected parts (links) in a mechanism, focusing on position, velocity, and acceleration without considering the forces causing the movement, Important for designing robots, or engines, using kinematic joints to constrain degrees of freedom like sliding, rolling, and spinning. A kinematic joint is the connection between these links, limiting their relative freedom (e.g., a pin joint allowing rotation but blocking translation).
Joint, lap – It is a joint made by placing one adherend partly over another and bonding the overlapped portions. The weld is deposited in the joint where the two intersect. A lap joint shows good mechanical properties, especially when a person welds both sides of the overlapped pieces, which provides extra reinforcement.
Joint liability – It denotes the obligation of two or more partners be responsible for satisfying a liability. A joint liability allows parties to share the risks associated with the contract and to protect themselves in the event of lawsuits.
Joint, mechanical – It is a type of connection used in composite structures that involves fastening components together using bolts, screws, or other mechanical means. These joints allow for disassembly and inspection but can add weight and can lead to stress concentrations causing potential failure.
Joint penetration – It is the depth which a weld extends from its face into a joint, exclusive of reinforcement.
Joint, pin slot – This joint also allows two degrees of freedom, but components can rotate around different axes.
Joint, planar – This joint allows three degrees of freedom. It allows two directions of translation in a plane and a single rotational direction normal to that plane. It is useful for joining two components so they can rotate while sliding across the plane.
Joint preparation – It is the important process of shaping, cleaning, and aligning parts (like pipes or plates) before they are joined (normally by welding or bonding) to create a strong, defect-free connection which meets design specifications, involving edge profiling (‘V,’ ‘U’, ‘J’ grooves), cleaning surfaces, and achieving precise fit-up. Proper preparation ensures good fusion, penetration, and mechanical strength, preventing weld defects like cracking or porosity.
Joint probability – The joint probability is the joint density function of two random variables, or bivariate density.
Joint probability density function, f(x, y) – It describes the likelihood of two (or more) continuous random variables, ‘x’ and ‘y’, occurring simultaneously, representing the probability density over a 2D space. It is non-negative everywhere, and its total integral over all space is to be equal to 1, allowing calculation of probabilities for regions by double integration.
Joint programme – It is a collaborative agenda aimed at establishing a coordinated plan of action among different stakeholders to support the development and implementation of specific initiatives, such as research, development, and innovation in a particular industry.
Joint publication – It is an official document, often developed collaboratively by different several organizations in the industry, to establish shared principles, guidance, or knowledge, ensuring unified understanding and coordinated action towards common goals. Key aspects include mutual benefit, shared ownership, transparency, and establishing common perspectives for planning, training, and operations, even if the final authority rests with a lead organization.
Joint responsibility – It takes place when two or more parties share responsibility for action or a contract.
Joint, revolute – It has a single rotational degree of freedom, much like a hinge. This joint can rotate around the standard ‘x’, ’y’, ‘z’ axis, or around an edge in the model (a custom axis).
Joint, rigid – It fixes two components to one another. It is a connection between two components which prevents them from moving relative to each other. It provides no degrees of freedom.
Joint root – It is that portion of a joint which is to be welded where the members approach closest to each other. In cross section, the joint root can be either a point, a line, or an area.
Joint rotation – It refers to the angular displacement or relative turning movement between two connected structural members (like beams, or links) at their interface, caused by applied loads, forces, or inherent flexibility, important for analyzing structural behaviour, or mechanism movement, frequently measured as the angle of one segment’s coordinate system relative to the other. It quantifies how much a connection ‘yields’ or rotates beyond rigid-body movement, impacting stiffness and performance.
Joint, scarf – It is a joint made by cutting away similar angular segments on two adherends and bonding the adherends with the cut areas fitted together.
Joint sets – These refer to groups of joints in rock which have the same dip angle and strike angle. The number of joint sets can indicate the rock’s strength, with a higher count suggesting weaker rock for construction purposes.
Joint set number (Jn) – It is a specific value in rock mass classification systems (like the Q-system), representing the number of joint sets in a rock mass, with higher numbers (e.g., 1 for zero sets, 2 for one, 4 for two, 9 for three, 15 for four or more) indicating more joint sets and normally weaker rock for construction because of increased discontinuity. It helps quantify rock mass structure, where multiple joint sets create weaker blocks, affecting stability for tunnels, slopes, and foundations.
Joint, slider – It has a single translational degree of freedom. It is used for components which slide along one another. Options are similar to revolute joint options, except that components slide along the selected axis rather than rotating around it.
Joint, soldered – It is a joint in which solder is used as jointing material. These joints consist of a very thin layer of solder between the substrate and the joining component. Soldering is a process whereby metal components are joined together using a low-temperature filler metal, which is normally a tin-containing alloy. To assist in the wetting of the basis metal by molten solder, a flux, which is a weak acid, is to be present to dissolve the thin oxide films already present on the surface of the components and to prevent further oxidation during heating of the joint. Solder joints are the backbone of any electronic device. They connect components, allow electricity to flow, and hold everything in place.
Joint square – It is a type of joint used in railway engineering. In this type of joint, the joints in the two different rails are exactly opposite to each other.
Joints, structural components – These are the mechanical connections which join simple structural elements, such as trusses and panels, together through means like bolts, rivets, and adhesions, ensuring functional integrity and load transmission within the assembly.
Joint, staggered – It is a type of joint used in railway engineering. In staggered joints, the joints in one rail are staggered and are not exactly opposite to the joints in the other rail. These joints are normally used on curved tracks as they reduce the centrifugal force pushing the track in the outward direction. These are advantages of staggered joint. In case of first advantage, since the centrifugal force on the curved tracks has a tendency of pushing the tracks out of the alignment, a staggered joint is the most suitable rail joint as it reduces centrifugal force on curves. The second advantage is that it provides a smooth running as compared to a square joint.
Joint strength – It is the maximum load or stress a connection (like a weld, bolt, or adhesive bond) can withstand before failing, frequently compared to the base material’s strength, and is important for designing safe, reliable structures by assessing load-bearing capacity, failure modes (shear, tension, bearing), and efficiency relative to the parent material. It is a complex property influenced by the joint type, materials, geometry, and manufacturing quality, quantified using formulas or testing for different stresses.
Joint, supported – It is a type of joint used in railway engineering. In this joint, the rail ends are directly supported on the sleeper. This joint is expected to reduce the wear and tear in rails by preventing a cantilever action. However, the support still tends to raise the height of the ends of the rail. This makes the run on the supported joints hard. This joint also suffers from major wear and tear from the sleeper that supports the joint. The maintenance of this joint is challenging.
Joint surface – It refers to the interface where two components meet, important for function, movement, or separation, structural connections (bolts / welds) in structures, and even geological fractures (joints) in rock, defining load paths, permeability, or material continuity. Key aspects include surface texture (rough / smooth), geometry (planar / undulating), and function (load transfer, sealing, movement).
Joint, suspended – It is a type of joint used in railway engineering. In a suspended joint, the rail ends are suspended between the sleepers, with some rail portion being cantilevered. Because of the cantilever action, the sleeper packing becomes loose due to a hammering action by the loads from the moving trains. These are the most commonly used joints on railway systems.
Joint, ‘T’ – A T-joint is created when the edges of two work-pieces meet at around 90-degree and take the shape of a ‘T’. The edge of one work-piece to the flat surface of another is welded. T-joints possess good mechanical strength, especially when welded from both sides. One can find these joints in many fabrication applications, including structural steel, tubing and equipment applications. T-joints normally need little or no joint preparation and are easily welded when the correct parameters and techniques are used. One can leave the edges of the joint unaltered, or one can prepare them by cutting, machining or grinding.
Joint task force – It is a temporary, multi-department team formation assembled under one team leader for a specific task, integrating elements from different departments for coordinated effort, with engineering roles organized within its structure for specialized support, frequently focusing on infrastructure, logistics, or technical challenges.
Joint technical committee – It is a collaborative, consensus-based body established by two or more parent organizations to develop, prepare, maintain, and promote technical standards in a shared field of interest.
Joint test action group – It is an Institute of Electrical and Electronics Engineers standard IEEE 1149.1 for testing and debugging electronic circuits, especially complex printed circuit boards (PCBs) and embedded systems, by providing a serial interface to access internal device logic, allowing for fault detection, boundary scan testing, and in-system programming without direct physical access to every pin. It uses a dedicated ‘test access port’ (TAP) and specific pins to control test registers, enabling communication with chips like processors and ‘field-programmable gate arrays’ (FPGAs) for functions like checking for shorts, verifying connections, and loading firmware.
Joint transmission – It mainly refers to a cellular network technique where multiple base stations simultaneously send data to a single user, boosting signal quality and throughput for edge users, frequently through ‘coordinated multi-point’ (CoMP). It is a form of coordinated data delivery, like advanced MIMO (multiple-input and multiple-output), improving performance by constructively combining signals or spatial streams from distributed points, distinct from single-point transmission.
Joint type – It is a weld joint classification based on the five basic arrangements of the component parts such as butt joint, corner joint, edge joint, lap joint, and T-joint.
Joint variable – It normally defines the configuration of a mechanical system using angles for rotational joints or distances for prismatic (linear) joints, forming coordinates in ‘joint space’. In statistics, a ‘joint variable’ refers to two or more random variables (like ‘X’ ‘Y’) described by a joint probability distribution, showing their simultaneous likelihood. A third meaning, joint variation, describes a relationship where one quantity changes proportionally with the product of two or more others, like area (A) varying jointly with length (L) and width (W) (A =k x L x W).
Joint, welded – It implies joining two or more metal or non-metal parts together to form a single unit, by using a specific technique and geometry. A welded joint is a connection between two or more pieces of metal or non-metal which are fused together using heat. Welding joints are used to create strong, durable structures and components.
Joint welding – It is production welding used to weld cast components together to obtain an integral unit.
Joint working group – It is a temporary or semi-permanent team with members from different organizations, committees, or departments, formed to tackle specific, shared technical challenges, develop standards, or coordinate complex projects, pooling diverse expertise for defined goals, frequently involving standard setting or research and development across institutional lines.
Joist – It is a horizontal structural member used in framing to span an open space, frequently between beams which subsequently transfer loads to vertical members. Steel joists can take on various shapes, resembling the Roman capital letters ‘C’, ‘I’, ‘L’ and ‘S’.
Jolt – It means to raise the flask filled with sand and allow it to drop, thereby compacting the sand against the pattern.
Jolt machine – It is a moulding machine which packs or rams the sand around the pattern by raising the table on which the flask, sand, and pattern are mounted a few inches and allowing the whole to drop suddenly. The table is raised pneumatically, and the operation is repeated until the desired sand density is reached.
Jolt rammer – It is a mechanical device used to compact sand around a pattern inside a flask (mould box) through rapid vertical vibrations or jolting. By lifting the table holding the flask, sand, and pattern, and letting it drop suddenly, the inertia causes the sand to settle densely, ensuring a firm, well-packed mould for metal casting.
Jolt ramming – It consists of packing sand in a mould by raising and dropping the sand, pattern, and flask on a table. Jolt-type, jolt squeezers, jarring machines, and jolt rammers are machines using this principle. It is also called jar ramming.
Jolt squeeze moulding machine – It creates high-quality sand moulds for metal casting by combining rapid, repeated jolting (impact) with pressure (squeezing) to uniformly compact moulding sand around a pattern, ensuring density, strength, and dimensional accuracy for defect-free castings. This process removes air and fills deep pockets effectively, improving upon simpler jolt or squeeze methods.
Jolt-squeezer machine – It is a combination machine which uses a jolt action followed by a squeezing action to compact the sand around the pattern.
Jolting – It means pushing or shaking something abruptly and roughly.
Jolting screen – It is a vibrating screen which uses mechanical vibrations to separate materials. It is frequently used to screen coal, ore, or other fine, dry materials.
Jominy bar – It is a standardized steel sample (typically 100 millimeters long, and 25 millimeters diameter) used in the Jominy end-quench test, an important method to measure steel’s hardenability (how deep it can harden) by creating a cooling-rate gradient from a rapid end-quench to slow air-cooling, revealing hardness variations along its length.
Jominy end – It refers to the water-quenched end of a standardized steel bar in the Jominy end-quench test, which experiences the most rapid cooling, creating a gradient of cooling rates along the bar’s length, hence indicating the material’s hardenability (how deep it hardens). Hardness is measured at increasing distances from this intensely cooled Jominy end, revealing the steel’s capacity to form hard micro-structures like martensite as cooling slows further from the end.
Jominy end quench test – It is used to measure the hardenability of a steel, which is a measure of the capacity of the steel to harden in depth under a given set of conditions. It is a standardized method according to ISO 642. The test sequence can be broken down into four steps namely (i) creation of the mold and preparation of the sample, (ii) heating of the sample to a specified temperature in the austenitic range for a defined duration, (iii) quenching of the sample on the front surface with a water jet under predefined conditions, and (iv) testing the hardness at defined points in the longitudinal direction of the ground specimen test surface.
Jominy equivalent cooling rate – It is the cooling rate at 704 deg C for each Jominy position for which there is a cooling time–temperature curve.
Jominy hardenability – It refers to the measurement of a steel’s ability to harden to a specific depth, determined by the Jominy end-quench test, where a standard bar is quenched from one end and hardness is measured along its length, showing how far the hard martensitic structure penetrates from the quenched surface. It is important for predicting a steel’s mechanical properties in large parts, as higher hardenability means martensite forms deeper, resisting softer phases like pearlite and ferrite.
Jominy hardenability test – It is a laboratory procedure for determining the hardenability of a steel or other ferrous alloy. It is also referred to as the end-quench hardenability test. Hardenability is determined by heating a standard sample above the upper critical temperature, placing the hot sample in a fixture so that a stream of cold water impinges on one end, and, after cooling to room temperature is completed, measuring the hardness near the surface of the sample at regularly spaced intervals along its length. The data are normally plotted as hardness against distance from the quenched end.
Jones matrix – It is a 2×2 complex matrix used in Jones calculus to describe how a perfectly polarized light wave’s electric field (represented as a 2×1 Jones vector) is transformed by a linear optical component, like a polarizer or waveplate. It mathematically models the change in the light’s amplitude and phase in the ‘x’ and ‘y’ directions as it passes through optical elements, important for analyzing polarization in lasers, optical communications, and interferometry.
Jones matrix method – It is a comprehensive polarization mode dispersion (PMD) measurement technique for optical fibers and passive optical components. It uses a 2×2 complex matrix to represent the transfer function of an optical device, relating input and output Jones vectors of a light-wave signal.
Jones vector – It is a 2×1 complex column vector representing the polarization state of a mono-chromatic, fully polarized light wave, capturing the amplitudes and relative phases of its orthogonal electric field components (Ex, Ey) in a 2D space. It i’s a core tool in Jones calculus, used to mathematically describe how light interacts with optical components (polarizers, waveplates) by multiplying the vector by corresponding Jones matrices, revealing the output polarization’s shape (linear, circular, elliptical) and orientation.
Josephson effect – It is the tunneling of a current across a thin insulator (Josephson junction) between two superconductors, which occurs because of the relative phase between their quantum states. This effect allows for the generation of direct current (DC) when the voltage is zero, and alternating current (AC) when a voltage is applied, with the alternating current frequency dependent on the voltage difference.
Josephson junction – It is a quantum mechanical device consisting of two super-conducting electrodes separated by a thin, non-super-conducting barrier. This barrier can be a variety of materials, including insulators, semi-conductors, or even ferromagnets. The junction’s ability to allow electrons to tunnel through the barrier gives rise to unique properties, including the flow of a supercurrent in the absence of a voltage.
Joule (J) – It is the derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.
Joule heating – It is the process by which the passage of an electric current through a conductor produces heat.
Joule heating effect – It is the physical effect by which the pass of current through an electrical conductor produces thermal energy. This thermal energy is then evidenced through a rise in the conductor material temperature, hence the term ‘heating’.
Joule-Thomson coefficient (Mjt) – It measures a fluid’s temperature change per unit pressure drop during an isenthalpic (constant enthalpy) expansion, typically through a constriction like a valve. It is mathematically defined as Mjt = (delta T /delta P)H, indicating whether a gas cools (positive Mjt) or heats (negative Mjt) as it expands, important for refrigeration, liquefaction, and avoiding freezing in gas pipelines.
Joule-Thomson effect – It is a change in temperature in a gas undergoing Joule-Thomson expansion.
Joule-Thomson expansion – It is the adiabatic, irreversible expansion of a gas flowing through a porous plug or partially open valve.
Journal – It is the part of a shaft or axle which is in contact with or enclosed by a bearing. The journal of the shaft (the part in contact with the bearing) slides over the bearing surface.
Journal bearing – in this, the bearing pressure is exerted at right angles to the axis of the axis of the shaft. The portion of the shaft lying within the bearing is known as journal. Shaft is normally made of mild steel.
Journal failure, rolls – The journal of the roll can suffer a cross-sectional failure. It normally starts at the bottom of the radius adjacent to the barrel. The fracture face follows the radius and then continues into the side of the barrel, and shears away a portion of the barrel end face. Under shock load conditions the peak load can exceed the ultimate bending strength of the core material and fracture occurs, normally at the most highly stressed cross-sectional area. The failure of the journal can take place because of the bending fracture. Fracture lines start from the outside and spread over the whole cross-section, particularly starting in the fillet area and very frequently after fatigue crack propagation. This failure arises from high bending loads which exceed either the ultimate bending strength or fatigue strength of the journal. This kind of breakage can be caused by (i) high rolling loads combined with a weak roll design, (ii) rolling abnormalities with extreme bending forces, (iii) inadequate roll quality as far as journal strength is concerned, and (iv) a notch effect as a consequence of too small a fillet radius, circumferential grooves, and fatigue cracks induced by corrosion etc.
Journal radius – It refers to the constant radius of a cylindrical shaft (the journal) within a journal bearing system, basically half its diameter (D/2), important for calculating load, pressure, and motion in rotating machinery, where it defines the bearing’s supporting surface. It is a fundamental parameter for the shaft which rotates, supporting radial loads and enabling smooth motion within the bearing shell, impacting friction and system life.
Joystick – It is an input device consisting of a stick which pivots on a base and reports its angle or direction to the device it is controlling. Joysticks are also used for controlling machines such as cranes, mining trucks, and excavators. Joysticks has virtually replaced the traditional mechanical control lever in nearly all modern hydraulic control systems. Joysticks for industrial applications are also produced using Hall effect (contactless sensing) technology. Another technology used in joystick design is the use of strain gauges to build force transducers from which the output is proportional to the force applied rather than physical deflection. Miniature force transducers are used as additional controls on joysticks for menu selection functions.
JPEG (Joint Photographic Experts Group) – It refers to a standard algorithm and file format for lossy compression of digital images, mainly for photos, using techniques like ‘discrete cosine transform’ (DCT) to reduce file size by discarding visually imperceptible data, making it efficient for web and storage by trading quality for smaller size, supporting colour / grayscale, and frequently including metadata (‘exchangeable image file format’, EXIF).
J-R curve – It is a graph of crack-extension resistance as a function of stable crack extension, which is the difference between either the physical crack size or the effective crack size and the original crack size. J-R curves normally depend on sample thickness and, for some materials, on temperature and strain rate.
Judder – It is an intermittent motion arising from design features that allow an increase in tangential force or displacement to produce an increase in normal force.
Jth component – It normally refers to the ‘j-th’ element in a set, vector, or matrix which defines a system’s properties, such as in structural analysis, stress tensors, or numerical simulations. It represents a specific, indexed, or position-dependent variable within a larger dataset, usually denoted by ‘i’ (for row) and ‘j’ (for column).
Judgment – In engineering, it is the essential ability to apply scientific principles, experience, and critical thinking to make sound, context-sensitive decisions in complex, ambiguous situations where data is incomplete, leading to practical, safe, and effective real-world solutions, frequently involving creating alternative designs (like firestop engineering judgments or EJs) when standard tested methods do not apply. It blends technical knowledge with ethical responsibility and practical wisdom, going beyond pure calculation to solve unique problems and ensure safety.
Jump instruction – It is defined as a programming command which alters the flow of execution by directing the programme to a specified location, often used in calling subroutines.
Jump phenomenon – It refers to abrupt changes in a system’s response, frequently seen in non-linear vibrations (where amplitude rapidly increases or decreases) or mechanical systems like cam-followers (follower losing contact with the cam) or fluid dynamics (hydraulic jumps), indicating instability or critical speed transitions, leading to sudden shifts in motion or energy states.
Junction – It consists of the points or surfaces in structures where different elements or components come together. It is also a point (as in a thermocouple) at which dissimilar metals make contact. It is also an interface in a semiconductor device between regions with different electrical characteristics.
Junction box – It is an enclosure specifically designed to protect electrical connections in a conveyor system. Ongoing checks become essential to safeguard the integrity of electrical connections and prevent issues such as shorts or malfunctions.
Junction depth (Xj) – It is the critical vertical distance from a semiconductor’s surface to the point where the implanted or diffused dopant concentration drops to a specific, low background level (e.g., 10 to the power m16 to 10 to the power 18 atoms per cubic centimeter), defining the boundary of the p-n junction important for transistors and diodes. This depth, measured in nano-meters, dictates device performance, with shallower junctions (ultra-shallow junctions or USJs) enabling smaller, faster, and more power-efficient modern integrated circuits (ICs).
Junction, electrical – It is a point or area where (i) two or more conductors or (ii) different semi-conducting regions of differing electrical properties make physical contact. Electrical junction types include thermo-electricity junctions, metal–semiconductor junctions and p–n junctions. Junctions are either rectifying or non-rectifying. Non-rectifying junctions comprise ohmic contacts, which are characterized by a linear current–volage relation. Electronic components using rectifying junctions include p–n diodes, Schottky diodes and bipolar junction transistors.
Junction formation – It is the important process of creating a boundary between different materials, normally two types of semiconductors (P-type and N-type) to form a p-n junction, which controls charge flow in diodes and transistors. This interface allows charge carriers (electrons and holes) to diffuse, creating a depletion region with an internal electric field, fundamental for electronic device operation. It also applies to forming single-molecule connections between electrodes or adhesive contacts in tribology.
Junction growth – It is the increase in the real contact area between two surfaces because of the material flow (plastic deformation and adhesion) when subjected to both normal load and tangential (sliding / shear) forces, frequently leading to increased friction. It is explained by Bowden and Tabor’s theory, where the initial contact points yield and spread out to accommodate the extra shear stress from sliding, effectively enlarging the area where adhesion and ploughing occur, sometimes considerably.
Junction point – It is a fundamental concept defining a point where two or more paths, elements, or components connect, such as wires in an electrical circuit (also called a node), or polymer chains in materials science, serving as a critical location for analysis, current flow, or structural interaction. It is where distinct segments meet and signals, forces, or materials are shared or redirected, differing from simple connections by normally involving multiple (frequently three or more) branches.
Junction potential – It is the voltage which forms at the boundary between two different materials (like electrolytes or semi-conductors) because of the differing ion / charge carrier movement, causing charge separation and creating an electric field which opposes further net flow, crucial in electro-chemical sensors (liquid junction potential) and semi-conductor devices (p-n junction). It is basically a built-in voltage preventing immediate equilibrium, impacting measurement accuracy in analytical systems and fundamental to diode / transistor function in electronics.
Junction roller – It is a roller strategically positioned at conveyor junctions to facilitate and guide material flow. Regular inspections are critical to ensuring the proper alignment and functional reliability of junction rollers.
Junctions, metal casting – Junctions are areas of natural localized thickness – like T-Junction or an X-Junction. Hence, it is necessary to take care when designing features which result in these ‘Junction’. Typical examples of junctions are internal features, ribs and webs or external protrusions such as fins or brackets. Less obvious junctions can appear when external and internal geometry, which are functionally unrelated are located on the same part of the casting wall. For example, a boss or lug on the outside of the casting occupying the same part of the casting wall as an internal rib.
Junction solar cells – These are the devices which utilize multiple p-n semi-conductor junctions coupled in series to absorb a range of wave-lengths from the solar spectrum, enabling light conversion efficiencies which surpass the theoretical Shockley-Queisser limit.
Junction temperature (Tj) – It is the highest temperature reached at the actual semi-conductor junction (where n-type and p-type materials meet) within an electronic component, considerably higher than the case or ambient temperature, and is critical for predicting device reliability and life-span, as exceeding maximum limits causes failure. It is a key parameter in thermal management, calculated using power dissipation, ambient temperature, and thermal resistances, with lower junction temperatures leading to better performance and longevity.
Junction transistor – It is a three-layer, three-terminal semiconductor device (emitter, base, collector) which amplifies or switches electronic signals by controlling current flow between its junctions, basically acting like two p-n diodes in close proximity to form either an n-p-n or p-n-p structure, utilizing both electrons and holes as charge carriers.
Jurassic rock – It refers to sedimentary formations which has been deposited during the Jurassic period, which play a vital role in reservoir engineering by influencing reservoir performance and characteristics. These rocks are analyzed for their properties to support the development and production of petroleum reservoirs.
Justified for development – In case of mineral deposits, justified for development needs that the project has been demonstrated to be technically feasible and viable, and there is a reasonable expectation that all necessary approvals / contracts for the Project to proceed to development is forthcoming.
Just noticeable difference – It is as the smallest detectable difference between two levels of a particular sensory stimulus, particularly in the context of perceived image quality. It refers to the minimum variation in a stimulus which can be perceived by an observer, impacting the overall quality assessment. It is the minimum change in a sensory stimulus (like light, sound, or touch) which a human observer can detect at least 50 % of the time, important for designing systems where human perception matters.
Just-in-time (JIT) – It is an inventory management method in which goods are received from suppliers only as they are needed. The main objective of this method is to reduce inventory holding costs and increase inventory turnover.
Just-in-time manufacturing – It is a system to produce goods only as needed, synchronizing raw material orders with production schedules to eliminate waste, reduce inventory costs, and increase efficiency, frequently using pull systems like Kanban, focusing on continuous flow and precise delivery of ‘what is needed, when it is needed, in the quantity needed’. It needs strong supplier relationships, high quality, reliable equipment, and meticulous planning to achieve goals like zero defects, zero inventory, and zero stoppages, mirroring Lean principles.
J-values – These refer to the coupling constants in nuclear magnetic resonance (NMR) spectroscopy, defined as the separation between signals in ppm (parts per million) multiplied by the operating frequency of the NMR instrument in mega-hertz, resulting in a value expressed in hertz. They indicate the number of bonds between coupling nuclei, with superscripts denoting the bond count, such as 1J for one bond, 2J for two bonds, and 3J for three bonds.
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