R (gas constant)

R (gas constant) – An experimentally determined constant which is equal to the mechanical work done by the expansion of unit weight of a perfect gas at a constant pressure while heat is added to increase its temperature by one degree centigrade.

RATIO OF COMPRESSION – Ratio of final volume to the initial volume during compression.

RECIPROCATING COMPRESSOR – A compressor having a piston which is made to move to and fro, that is forward and backward and thereby compresses and delivers air.

RELATIVE HUMIDITY – Degree of saturation of the air with water vapour as determined by the use of the wet and dry bulb thermometers.

RESISTANCE – The quality of not yielding to force or external pressure, that quality of a body which acts in opposition to the pressure of another.

ROTARY COMPRESSOR – A compressor having a vane rotor or its

equivalent mounted eccentrically in a stationary casing.

RACK AND PINION STEERING GEAR – A steering gear that uses a pinion on the end of the steering shaft which is meshed with a rack on the major cross member of the steering linkage.

RADIAL BIAS TYRE – A tyre in which the plies are laid on radially, or perpendicular to the rim, with a circumferential belt on top of them. The rubber tread is vulcanized on top of the belt and plies.

RADIAL PLY TYRE – Cords running directly across the tyre carcass from bead to bead.

RADIAL SPRING RATE – The amount of radial load required to deflect a tyre (one cm) unit distance.

RADIATOR – In the cooling system, the device that removes heat from the coolant passing through it, it takes hot coolant from the engine and returns the coolant to the engine at a lower temperature. The hot coolant is cooled in the radiator for recirculation.

RADIATOR PRESSURE CAP – The cap placed on the radiator filler tube which pressurizes the cooling system for more efficient operation.

RADIATOR SHUTTER SYSTEM – A system of engine temperature control used mostly on trucks, that controls the amount of air flowing through the radiator by use of a shutter system.

REACTION CONTROL – A feedback mechanism that gives the driver a feel of the amount of input effort being applied.

REAR AXLE ASSEMBLY – A system of gears and axles that transfers power from the drive line assembly to the driving wheels of the automobile.

REAR AXLE RATIO – The ratio between the drive pinion and the ring gear in the differential assembly.

REAR END TORQUE – Reactionary torque applied to the rear axle housing as torque is applied to the wheels; rear end torque attempts to turn the axle housing in a direction opposite to wheel rotation.

REBOUND – An expansion of a suspension spring after it has been compressed as the result of jounce.

RECAPPING – A form of tyre repair in which a cap of new materials is placed on the old tread and vulcanized into place.

RECIRCULATING BALL AND NUT STEERING GEAR – A type of steering gear in which there is a nut (meshing with a gear sector) assembled on a worm, balls circulate between the nut and worm threads.

RELEASE LEVER – In the clutch, a lever that is moved by throw out bearing movement; the movement causes clutch spring pressure to be relieved so that the clutch is released or uncoupled.

RETREAD – A used tyre on which a new tread section is molded.

REVERSE FLUSHING – A method of cleaning a radiator or engine cooling system by flushing in the direction opposite to the normal coolant flow.

RIDE – The characteristic feel as one rides in a vehicle.

RIGID REAR SUSPENSION – A rear suspension system in which both wheels are attached to rigid rear axle housing.

RIM – The metal wheel on which the tyre is mounted.

RING GEAR – A large gear carried by the differential case, meshed with and driven by the drive pinion.

ROAD RESISTANCE – is the resistance of the road surface, which must be overcome when a vehicle travels along the road. This consists of friction between the tyre and road.

ROLLING RESISTANCE – is the resistance caused due to the deformation of the tyres and road, the friction of the tyres on the road surface and friction in the wheel bearings.

ROLL STEER – The steering effect as a result of body lean during a turn.

RUNOUT OF WHEEL – Lack of alignment of wheel or gear to the axle so that the wheel or gear runout or move out of alignment, as wheel or gear rotates.

RATE OF FUEL INJECTION – Amount of fuel that is injected into the combustion chamber in unit time or in one degree of crank travel.

REENTRANT COMBUSTION CHAMBER – is an open combustion chamber which has a smaller diameter (opening) at the entry than at the middle.

RESIDUAL PRESSURE – The pressure at which the fuel is retained in the fuel line when the injector needle valve and the pump delivery valve are in the closed position.

RAMMER – Tool used in a foundry for ramming the sand.

RAPPING – Tapping of the pattern with a mallet in order to loosen it as it is drawn from the mould.

RAPPING BAR – A pointed bar (or rod) made of steel or other metal, which is inserted vertically into a hole in a pattern or driven into it, then struck with a hammer on alternate sides to cause vibration and loosening of the pattern from the sand.

RELIEF SPRUE – The second sprue at opposite end of the runner to relieve pressure created during pouring operation.

RIBS – are used primarily as stiffeners and reinforcing members. If properly designed and located in difficult castings, serve to check the possibility of hot tears or cracks during solidification.

RISER – Reservoir of molten metal attached to the casting to compensate for the internal contraction of the casting during solidification.

RUNNER – The portion of the gate assembly which connects the downgate or sprue with the casting.

RADIO ACTIVE ELEMENT – An element which has at least one isotope that undergoes spontaneous nuclear disintegration to emit positive alpha particles, negative beta particles or gamma rays.

RADIO ISOTOPE – An isotope that emits ionizing radiation during its spontaneous decay.

RADIUM – A radioactive element. It is found in nature as radium 226, which has a half-life of 1620 years.

RAZOR STEEL – Steel containing 1.15-1.25% carbon. This steel is forged at 816°C, and hardened at 750-775°C. It is tempered at 230°C to straw colour.

RED BRASS – A brass containing approximately 85% copper, 5% zinc, 5% tin and 5% lead.

RED ROCK SAND – Open grain moulding sand obtained from red sand stone rocks, with good permeability but low bonding qualities.

REFRACTORY – Materials that will resist change of shape, weight, or physical properties at high temperatures say exceeding 1000oC. These materials are usually silica, fire clay, diaspore, alumina and kaolin. They are used for furnace linings.

RESIDUAL ELEMENTS – Elements present in an alloy in small quantities but not added intentionally.

RESIDUE – The material that remains after completion of a chemical or physical process, such as combustion, distillation, evaporation or filtration.

RESISTORS – Poor conductors.

ROUGHING STONE (hone) – A coarse honing stone.

RIMMED STEEL – A low carbon steel (insufficiently de-oxidized) that during solidification releases considerable quantities of gases (mainly carbon monoxide). When the mould top is not capped, a side and bottom rim of several centimetres forms. The solidified ingot has got scattered blow holes and porosity in the center but a relatively thick skin free from blow holes.

RUST – A corrosion product containing hydrated oxide of iron. Applied only to ferrous alloys.

RING LUBRICATION – Two loose rings carried by the journal rotation, being driven by frictional contact with the journal, dip into an oil bath and carry oil to the top of the journal so as to flow over the surface of the journal through oil grooves in the bearing, and finally return to the bath below.

ROLLER BEARING – An antifriction bearing consisting of hardened steel inner and outer races, separated by hardened steel rollers, which are two or three times as wide as their diameter.

ROLLING FRICTION – The force resisting the motion when a body rolls on a surface.

ROTARY OIL PUMP – An oil pump which uses an inner and outer rotor to move oil.

RADIOACTIVE – Substances that emit rays either naturally or as a result of scientific manipulation.

REFUSE – A term generally used for all solid waste materials.

RETORT – A trough or channel built into an underfeed stoker through which the stoker ram pushes green coal into the fire. The coal enters the fire from below, hence the name “underfeed”.

ROTARY BURNER – One in which the oil entering at the center of a rotary cup is whirled around very rapidly until the oil is thrown away from the cup. By centrifugal force it mixes with air and ignites.

RAM EFFECT – The effect which causes an increase of temperature and pressure of the air that enters the compressor of an aircraft gas turbine unit due to aircraft speed. Sometimes called RAM.

RAM EFFICIENCY – Actual pressure rise realized in a diffuser compared with the pressure rise possible under reversible conditions. Also called INTAKE EFFICIENCY.

REACTION TURBINE – The turbine in which the nozzles and moving blades are each made in the same general form, with the cross-section in the direction of the gas flow reduced so that both the fixed and moving blades act as expanding nozzles.

REGENERATIVE PLANT – The plant that utilizes a heat exchanger to recover heat from the turbine exhaust gases and thereby decreases the heat required to be added in the combustor.

REHEAT CYCLE – The unit in which the expansion of the hot gases is carried out in two stages, and reheating of the working fluid to the upper limit of temperature takes place between the stages of expansion.

ROCKET – A self propelled unit in which the fuel and the oxidant are contained within the shell.

RECRYSTALLIZATION – A process in which the distorted grain structure of metals that are subjected to mechanical deformation is replaced by a new strain free grain structure during annealing.

RUST PROOFING – Treatment of iron and steel parts to render them resistant to rust, implies a more permanent form of protection.

RADIATOR – A heat exchanger which reduces coolant temperature in a liquid cooling system.

RADIUS RIDE – In a reground crankshaft, if the radius of the journal, where it comes up to the crank cheek, is not cut away enough, the journal will ride on the edge of the bearing. The contact is called radius ride.

REBORE – To bore out a cylinder larger than its original size.

RECIPROCATING ENGINE – Also called piston engine. An engine in which the piston moves up and down or back and forth, as a result of combustion in the top of the cylinder.

RING EXPANDER – A special tool used to expand piston rings for installation on the piston.

RING LAND – Solid area of piston which supports rings, located between ring grooves.

RING RIDGE – A ridge left at the top of a cylinder as the cylinder wall below it is worn by piston ring movement.

RING RIDGE REMOVER – A special tool used for removing the ring ridge from the cylinder.

ROCKER ARM – In an I head engine, a device that rocks on a shaft or pivots on a stud as the cam actuates the push rod causing the valve to open.

ROD BOLTS – Special bolts used on the connecting rod to attach the cap. Sometimes lock nuts are provided.

ROD SMALL END – The end of the connecting rod through which a piston pin passes to connect the piston to the connecting rod.

ROD BIG END – The end of the connecting rod that attaches around the crankpin.

RPM – Revolutions per minute.

REVERSE FLUSHING – A method of cleaning a radiator or an engine cooling system by flushing in the direction opposite to normal coolant flow.

RADIUS GAUGE – Tool used for checking the radius of small fillets or rounded corners.

RECORDING INSTRUMENTS – Instruments which provide a permanent record of readings such as steam pressure, steam flow, air flow, flue gas temperature, feed water temperature, fuel flow and fuel temperature.

RING GAUGE – A gauge in which the inside measuring surfaces are circular in form. A ring gauge may be cylindrical or conical, plain or threaded.

RACK – A straight metal strip having teeth that mesh with those of a gear to convert rotary motion into reciprocating motion or just the opposite.

RATCHET – A gear with triangular shaped teeth to be engaged by a pawl which gives it intermittent motion or locks it against backward movement.

RELIEVING ATTACHMENT – A device or mechanism fastened to the cross feed of a lathe to provide a reciprocating motion to the cutting tool, to obtain a clearance in the back of the cutting edges of the teeth when making taps, milling cutters or hobs.

REVERSE LEVER – A lever on the machine tool for changing the direction of some movable part such as the lead screw on a lathe.

REVOLVING LATHE CENTRE – It is fitted in the tailstock instead of the fixed type of loose head centre, in some cases, so that the high speeds of work revolutions become possible.

RIGHT HAND THREAD – A screw thread which advances into the mating part when turned clockwise or to the right.

RIVET – A one piece fastener consisting of a head and a body and used for fastening two or more pieces together by passing the body through a hole in each piece and then forming a second head on the body end. It cannot be removed except by taking off the head.

ROLLER STEADY – Type of steady fitted with roller points to support long or slender work in a lathe.

ROTARY TABLE – An attachment for the milling machine consisting of a round work holding table provided with T slots and operated by a handwheel attached to a worm or worm gear for rotating the table. A scale graduated in degrees permits the work to be moved any number of degrees for spacing holes or milling radii. Also called CIRCULAR MILLING ATTACHMENT.

RACK – A straight metal strip having teeth that mesh with those of a gear to convert rotary into reciprocating motion or just the opposite.

RATCHET – A gear with triangular shaped teeth to be engaged by a pawl which gives it intermittent motion or locks it against backward movement.

RECESS – A groove cut below the normal surface of a workpiece.

RIGHT HAND THREAD – A screw thread which advances into the mating part when turned clockwise or to the right.

RADIAL DRILLING MACHINE – Machine with the drill head working on an arm which has a rotary movement in the horizontal plane. In this the drill spindle could be moved to the positions required instead of moving the work for each hole to be drilled.

RADIATOR – A heat exchanger in which cooling water gives up heat without coming into direct contact with air.

RAM (pump) – Hydraulic ram, also termed a water ram, by which water is raised by its own momentum from a lower to a higher level.

RECTIFIER – A device, made of a diode or series of diodes, used in a welding machine, for converting alternating current to direct current.

RELAY – An electromagnetic switch which utilizes variation in the strength of an electric circuit to effect the operation of another circuit.

RELIEF VALVE – An automatic valve which is held shut by a spring of correct strength. Excessive pressure opens the valve and releases some of the gas or liquid.

RELIEVING LATHE – Machine for backing off the teeth of milling cutters to facilitate machining of metals.

REVERBERATORY FURNACE – Furnace in which ore or metal is melted by contact with the flame, but is not in contact with the fuel.

RHEOSTAT – A device to regulate current flow by varying the resistance in the circuit.

RIGBY HAMMER – Steam hammer used for a wide range of forging work.

RIVETING MACHINE – Power operated machine used to form rivet heads. May be classified according to the method of operation hydraulic, pneumatic, or steam and the manner in which the rivet head is formed.

ROLLING MILL – Mill in which ingots, bars, blooms, billets etc., of steel or other metals, are rolled to reduce or alter their sections.

ROLL TURNERS LATHE – Special design of lathe adapted for machining rolls employed for printing machines, calendars or rolling mills.

ROOTS BLOWER – An air pump or blower similar in principle to a gear type pump.

ROTARY BLOWER – Pump or compressor used to supply air or gas to a furnace, forge, internal combustion engine or similar application. This may be a vane, geared rotor, centrifugal or turbine type depending on the particular application and the volume of air or gas or the pressure required.

ROTARY PUMP – Pump used for liquid or gas, in which a rotating impeller is used, may be vane type, gear type centrifugal and turbine type.

RACK – A storage place for individual items or palletized loads.

RAIL ROAD CRANE – Crane mounted on a truck meeting railroad requirements and supported by axles of varying number used for load handling and wreckage clearing purposes, carry a power unit which is a combination of a diesel, a generator and a number of electric motors.

REACH OF CRANE – Distance of the load from the axis of the rotary part of the crane, decided by crane stability, decreases with an increase in the load to be handled.

REVERSIBLE PALLET – A pallet with an identical top and bottom deck.

REVOLVING CRANE – A crane which can lift up the load and transfer it to any point of a circle with a radius equal to the reach, being thus suitable for loading the rail road flat cars and lorries, for construction site works etc. e.g., travelling revolving crane, fixed revolving crane.

RIGHT HAND LAY ROPES – Ropes in which the strands bend round to the right.

ROW PATTERN – A pallet pattern used for the arrangement of items of unequal length or width.

RADIOACTIVITY – The spontaneous nuclear disintegration with emission of corpuscular or electromagnetic radiation.

RESIDUAL STRESS – Stress induced within the structure of a material by cold working, machining, and heat treatments.

RESILIENCE – Ability of a material to store elastic energy without permanent deformation.

RETENTIVITY – The capacity of a material to retain a portion of the magnetic field set up in it after the magnetizing force is removed.

ROCKWELL HARDNESS – Hardness test that uses a penetrator and known weights. Several scales are used to cover very soft to very hard materials. The Rockwell C scale is used mostly for steel.

REFINING OF METAL – Process of removal of impurities from metals or alloys, resulting in improved properties or a different product. Also refers to the refining of the grain of a coarse grained metal or alloy.

REFLEX PROCESS – Photo printing process enabling copies to be made from opaque originals.

RESISTANCE WELDING – Uniting two pieces of metal by the passage of a heavy electrical current (high amperage current) while the surfaces are pressed together.

RIVETING – A hammering operation in which the end of a metal pin (i.e., a rod or rivet) is pressed over or spread out. It may be either a hot or cold working process.

ROLL FORMING – Process of passing strip stock between driven rollers that form the strip to the shape desired.

ROLL GRINDING – The operation of grinding large rolls of steel mills or calendars.

ROLL THREADING – A method of threading a part by pressing and rolling between serrated dies.

RUBBER METAL BONDING – Bonding of natural rubber or synthetic rubber to metal surfaces.

RUNNING FIT – Term used of parts which are assembled so that they are free to rotate a type of clearance fit.

RACK – A portion of a gear wheel which has an infinitely large number of teeth.

RACHETS – Mechanisms used to transform motion of rotation or translation into intermittent rotation or translation.

RECTILINEAR MOTION – A motion wherein all points of the body move in straight line paths (e.g., piston motion).

RELATIVE INSTANTANEOUS CENTER – In the case of two bodies, it is the point about which either of them appears to turn (at that instant) if the other is considered fixed (e.g., if two links in a mechanism are pinned together, the pin becomes the relative instantaneous center, if the two bodies are in pure rolling contact, the point of contact is the relative instantaneous center).

RELATIVE MOTION – A body has motion relative to another body only if there is a difference in their absolute motions.

RESOLUTION OF VECTORS – Resolution refers to the breaking down of a vector into any number of component vectors.

REVERTED GEAR TRAIN – The compound gear train in which the first and the last gears are coaxial (e.g., units used in automobile transmission, lathe back gears, industrial speed reducers and in clocks).

ROLLING CONTACT – In a direct contact mechanism, rolling contact exists only if there is no sliding and hence the tangential components of velocities of the contact point on the two bodies are equal in magnitude and direction.

ROTATION – In rotation all points in a body remain at fixed distances from a line which is perpendicular to the plane of motion. This line is the AXIS OF ROTATION.

REFRIGERANT – Substance which is circulated in a refrigeration system to transfer heat.

REFRIGERANT FAMILY – Safest group of refrigerants produced by manipulating the atoms of carbon tetrachloride with those of fluorine and hydrogen.

REFRIGERATING CAPACITY – The ability of a system to remove heat as compared with the cooling effect produced by the melting of ice, expressed as a rate of heat removal, kcal/ hr or tons/ 24 hrs.

REFRIGERATION SYSTEM – The part of the refrigeration/ air conditioning system that includes compressor, condenser, evaporator, control valves and switches and tubing. It absorbs the heat from air in the duct housing/space and transfers it to the outdoors.

RELATIVE HUMIDITY – The percentage of moisture in the air compared with the maximum amount that the air can hold, at the prevailing temperature. Also expressed as the ratio of the pressure of the water vapour present to the maximum possible water pressure at the prevailing temperature.

RESISTIVE CRYOGENIC SYSTEM – Uses nitrogen to cool the electrical conductors to temperatures where their electrical resistance is very low.

REVERSE CYCLE REFRIGERATION – Uses rejected heat to produce warmth.

ROTARY COMPRESSOR – Compressor which consists of a cylindrical casing containing a shaft whose axis is eccentric to that of the cylinder, the shaft carries a rotor having radial slots in which blades slide and the tip of the blades press against the casing by their inertia or with the aid of springs.

REED VALVE – A type of valve used in the crankcase of some two cycle engines. Air fuel mixture enters the crankcase through the reed valve, which then closes as pressure builds up in the crankcase.

RESISTOR SPARK PLUG – A spark plug incorporating a resistor to shorten the spark duration. This suppresses radio interference and lengthens plug life.

RICH MIXTURE – An air fuel mixture with high proportion of fuel.

RISE TIME – The length of time between the begining of the voltage at the plug and the begining of the spark.

RUN ON – Condition when a SI engine continues to run, even when the ignition key is turned off. Also called DIESELING.

RADIAL STAYS – Long threaded rods used in locomotive boilers, screwed through both the firebox crown sheet and wrapper sheet and the ends riveted.

REDUCING VALVE – An automatic throttle valve for use where low pressure steam for heating or process is taken from high pressure mains.

REGENERATIVE AIR HEATER – A type of air heater containing a rotor which comes in contact alternately with hot gases and air thereby transfers heat from hot gases to the air.

REHEATER – A superheater that heats steam which is let out from a high pressure turbine and after heating sends the steam to a low pressure turbine thereby increases the plant efficiency.

RETARDERS – Also called Spinners-These are helical strips or ribbons of metal centered in horizontal or vertical fire tubes of a fire tube boiler for increasing the wiping effect on the inner surfaces of the tubes, by the flue gases on their way to the chimney stack. The tubes cannot be cleaned by scraping or brushing until these strips are removed. Retarders also increase the boiler frictional resistance to the flue gases.

RINGLEMANN CHART – The chart used for comparing the smokes density when no instrument is available.

RIVETED JOINT EFFICIENCY – Ratio of the strength of a unit section of the joint to the same unit length of solid plate. Unit length usually taken is the pitch of the rivets (distance from centre to centre) in the row having the greatest pitch.

RIVETED STAYS – Stays in which the threaded ends are riveted instead of having a nut at each end.

RADIAL FLOW TURBINE – A steam turbine in which the blades are so arranged to cause the flow of steam radially inwards or outwards.

RANKINE EFFICIENCY OF TURBINE – Ratio of the adiabatic heat drop to the heat supplied.

REAMED NOZZLE – A round nozzle used primarily in the high pressure impulse stage steam turbines. They have lower efficiency and somewhat greater in length.

REHEAT CYCLE – A system in which steam is initially expanded through a turbine and then reheated before further expansion in the turbine.

REHEAT FACTOR – In a multistage steam turbine it is the ratio of the sum of the individual heat drops (cumulative drop) in the different stages to the direct or adiabatic drop in a single step for the whole pressure drop that occurs.

RELATIVE EFFICIENCY – Ratio of the overall thermal efficiency of the actual plant to the thermal efficiency of the ideal Rankine cycle.

RIM HORSE POWER – Power developed by steam in passing over the blade as obtained from the velocity diagrams.

R – An experimentally determined constant which is equal to the mechanical work done by the expansion of unit weight of a perfect gas at a constant pressure while heat is added to increase its temperature through one degree.

RADIATION – Continuous form of interchange of heat energy from one body to another by means of electromagnetic waves without causing a change in the temperature of the medium between the two bodies involved. These energy waves may be reflected, penetrate the material or be absorbed.

REAL GAGES – are those that deviate from the characteristic gas relation, Pv = RT.

REFLECTIVITY – Ability of a material to reflect radiant heat.

REFRIGERATOR – Maintains a body at a temperature lower than that of the surroundings while operating in a cycle. External work is supplied for realizing it.

RENAULT’S LAW – The two specific heats of a gas Cv and Cp do not change with the temperature and pressure.

REVERSIBLE PROCESS – Any process performed so that the system and all its surroundings can be restored to their initial states by performing the process in reverse.

RUDOLF CLAUSIUS STATEMENT – Heat can flow from a hot body to a cold body unaided, but it cannot flow from a cold body to a hotter body without the expenditure or supply of mechanical work.

RADICAL PORT TIMING – Ports open for a relatively long period of time.

REED CAGE – An aluminium frame providing a mounting place for reed petals in a two stroke cycle engine.

REED PETALS – Movable part of a reed valve assembly.

REED VALVE SYSTEM – A two stroke intake system that uses thin flapper valves that are opened by vacuum and closed by pressure.

REAR SUSPENSION – The suspension system that consists of the swing arm, rear shock absorbers, springs and linkage.

RIM BAND – A strip of soft rubber that protects the inner tube from the spoke nipples.

RIM OFFSET – The deliberate lacing of spokes off center to the hub to achieve rear chain or front brake clearance.

ROLLER CHAIN – A chain made up of pins, side plates, bushings and rollers. Roller links are connected by pin links to achieve desired length. The ends are usually connected by a pin link which has a removable side plate, called master link.

ROTARY VALVE – A two stroke engine intake system that uses a partially cut away rotating disc to open and close the intake passage into the crankcase.

RANDOM INTERMITTENT WELDS – Intermittent welds on one or both sides of a joint in which the weld increments are made without regard to spacing.

REDUCING ATMOSPHERE – A chemically active protective atmosphere which at elevated temperature will reduce metal oxides to their metallic state.

REDUCING FLAME – A gas flame having a reducing effect owing to excess fuel gas.

RESIDUAL STRESS – Stress present in a member that is free to external forces or thermal gradients.

RESISTANCE BRAZING – is an electric brazing process wherein the heat is obtained by passing an electric current through the parts being brazed.

RESISTANCE WELDING – In this, the metal parts to be joined are heated by their resistance to the flow of an electric current e.g., spot welding, seam welding.

ROLL WELDING – A solid state welding process that produces coalescence of metals by heating and by applying pressure with rolls sufficient to cause deformation at the faying surfaces.