Abstract: Apparatus for detection and measurement of agglutinations of magnetic particles employing Hall sensors. A low frequency AC signal is employed to excite or bias the Hall sensors which reside in a DC magnetic field. The particles are moved into operative relationship with the Hall sensors in order to generate a signal representing the number of particles on the substrate. The method for such detection and measurement is also part of the invention.

Abstract: Apparatus for detection and measurement of agglutinations of magnetic particles employing Hall sensors. A low frequency AC signal is employed to excite or bias the Hall sensors which reside in a DC magnetic field. The particles are moved into operative relationship with the Hall sensors in order to generate a signal representing the number of particles on the substrate. The method for such detection and measurement is also part of the invention.

Abstract: A dual capillary inlet cryogenic test chamber having the ability to continuously regulate temperature between about 1.5 K. and 400 K. A controllably heated capillary tube is located in the cryogenic reservoir, spaced from the test chamber and thermally insulated from the cryogen. This capillary tube has a characteristic impedance to fluid flow. A second low temperature, high impedance capillary tube inlet is also in the cryogenic reservoir and is connected between the cryogen reservoir and the test chamber. The combination of a control system with pressure and temperature feedback, combined with the two inlet tubes of different impedance, enables the apparatus to operate continuously and stably at any temperature within its operating range, or to smoothly sweep through any predetermined temperature range.

Abstract: A stochastic excitation, SQUID detection system for determining the frequency response of a sample. A pair of counterwound detection coils are adjacent to an excitation coil. The sample is selectively placed in one of the detection coils for taking measurements. The SQUID sensor is a broadband, high sensitivity device which enables the frequency response of the sample to be determined over a wide bandwidth with a single measurement.

Abstract: An apparatus and method for regulating the temperature in a cryogenic test chamber. Liquid helium is drawn into a test chamber located in a cryogenic vessel through a capillary tube which is spaced apart from the test chamber. The capillary tube is thermally insulated from the liquid helium. In a high temperature mode, a heater element heats the capillary tube to a temperature just high enough to boil the liquid helium as the helium is drawn through the capillary tube into the test chamber, thereby insuring that only gaseous helium enters the test chamber and preventing any tendency of the temperature in the test chamber to oscillate when the test chamber is warmed to temperature only slightly higher than the temperature of the liquid helium.

Abstract: A method for controlling the flow of a cooling medium such as helium into an insulated chamber surrounding a region to establish a stable thermal environment in the region over a wide range of cryogenic temperatures. A thermally insulated capsule surrounds a variable temperature capillary to precondition the helium before it flows into the insulated chamber. The capillary can be operated in different modes, depending upon the heating or lack of heating of the capillary. At low temperatures the capillary can pass the helium in its liquid phase, at high temperatures only a small amount of gaseous helium is passed, and at certain intermediate temperatures there is an ample flow of gaseous helium only.