Therapeutic mask adapter.  A calibrated orifice in the mask  adapter for a continuous-flow oxygen system that increases  the flow of oxygen to a mask being used by a passenger who  is known to have a heart or respiratory problem. Thermal dimpling.  See hot dimpling. Thermal relief valve.  A relief valve in a hydraulic system  that relieves pressure that builds up in an isolated part of the  system because of heat. Thermal relief valves are set at a  higher pressure than the system pressure relief valve. Thermistor.  A special form of electrical resistor whose  resistance varies with its temperature. Thermistor material.  A material with a negative temperature  coefficient that causes its resistance to decrease as its  temperature increases. Thermocouple.  A loop consisting of two kinds of wire, joined  at the hot, or measuring, junction and at the cold junction in the  instrument. The voltage difference between the two junctions  is proportional to the temperature difference between the  junctions. In order for the current to be meaningful, the  resistance of the thermocouple is critical, and the leads are  designed for a specific installation. Their length should not  be altered. Thermocouples used to measure cylinder head  temperature are usually made of iron and constantan, and  thermocouples that measure exhaust gas temperature for  turbine engines are made of chromel and alumel. Thermocouple fire-detection system.  A fire-detection  system that works on the principle of the rate-of-temperature  rise. Thermocouples are installed around the area to be  protected, and one thermocouple is surrounded by thermal  insulation that prevents its temperature changing rapidly. In  the event of a fire, the temperature of all the thermocouples  except the protected one will rise immediately and a fire  warning will be initiated. In the case of a general overheat  condition, the temperature of all the thermocouples will rise  uniformly and there will be no fire warning. Thermoplastic resin.  A type of plastic material that becomes  soft when heated and hardens when cooled. Thermosetting resin.  A type of plastic material that, when once  hardened by heat, cannot be softened by being heated again. Total air temperature.  The temperature a column of moving  air will have if it is stopped. Toroidal coil.  An electrical coil wound around a ring-shaped  core of highly permeable material. TMC.  Thrust management computer. Total air pressure.  The pressure a column of moving air  will have if it is stopped. Torsion rod.  A device in a spring tab to which the control  horn is attached. For normal operation, the torsion rod acts as  a fixed attachment point, but when the control surface loads  are high, the torsion rod twists and allows the control horn  to deflect the spring tab. Torque tube.  A tube in an aircraft control system that  transmits a torsional force from the operating control to the  control surface. Torque links.  The hinged link between the piston and cylinder  of an oleo-type landing gear shock absorber. The torque links  allow the piston to move freely in and out of the landing  gear cylinder, but prevent it rotating. The torque links can be  adjusted to achieve and maintain the correct wheel alignment.  Torque links are also called scissors and nutcrackers. Torque.  A force that produces or tries to produce rotation. Toe-out.  A condition of landing gear alignment in which  the front of the tires are further apart than the rear. When the  aircraft rolls forward, the wheels try to move farther apart. Toe-in.  A condition of landing gear alignment in which the  front of the tires are closer together than the rear. When the  aircraft rolls forward, the wheels try to move closer together. TIG welding.  Tungsten inert welding is a form of electric arc  welding in which the electrode is a nonconsumable tungsten  wire. TIG welding is now called GTA (gas tungsten arc) welding. Thixotropic agents.  Materials, such as microballoons, added  to a resin to give it body and increase its workability. Thermostatic expansion valve (TEV).  The component  in a vapor-cycle cooling system that meters the refrigerant  into the evaporator. The amount of refrigerant metered by  the TEV is determined by the temperature and pressure of  the refrigerant as it leaves the evaporator coils. The TEV  changes the refrigerant from a high-pressure liquid into a  low-pressure liquid.  G-36