Abstract: This thermostatable flow cell for fluorescence measurements enables rapid thermal equilibration and precise temperature control. For a flow cell volume of less than 20 microliters, a selected temperature in the range up to 20.degree. C. above ambient can be attained within five seconds, and this selected temperature can be maintained stable within 0.1.degree. C. The cell comprises a cylindrical cavity whose walls include a metallic portion for heat conduction and a transparent window portion for light acceptance and fluorescence observation. The metallic portion of the cell is formed from a cell block to which a temperature sensing means is affixed. The window portion is affixed to the cell block by an inert bonding material. A thermoelectric device responsive to the temperature sensing means causing heating or cooling of the cell block as necessary to provide thermal equilibration at the selected temperature.

Abstract: A pressure regulating valve for use in a high-pressure fluid flow line, comprises a cylindrical needle-housing structure that is slidable within a bore in a valve body. An external spring urges the needle-housing structure toward a valve seat at a selectable pressure. Contact between the needle-housing structure and the valve seat is prevented by an annular protrusion in the bore. Conduit means through the valve body, connectable to the flow line, permits passage of the flow-line fluid into the needle-housing structure. A cylindrical needle is disposed coaxially within the needle-housing structure, and is urged toward the valve seat by a spring located in the needle-housing structure. When the pressure of the flow-line fluid entering the needle-housing structure exceeds the selected pressure urging the needle-housing structure toward the valve seat, the needle-housing structure assumes a position at which the needle remains spaced apart from the valve seat.

Abstract: In a scanning spectrophotometer, in which a narrow wavelength band of radiation can be selected from a range of wavelengths for transmission alternately through a sample cell and a reference cell, continuous automatic baseline correction is provided. A pulse train signal is generated, wherein the number of pulses represents the ratio of a parameter (e.g., intensity) of the radiation transmitted, respectively, through the sample and reference cells. A ratio of unity represents the baseline, and deviations from the baseline are indicated by changes in the number of pulses in the pulse train. Digital information indicative of baseline deviations is stored in a memory device when the spectrophotometer is being calibrated, and is retrieved from the memory device during operation of the instrument for sample analysis. The retrieved information generates a correction signal, which provides a continuous baseline correction.

Abstract: The performance of microwave tubes at very high frequencies is limited by the ability of their thermionic cathodes to provide high emission current density in combination with long life and low evaporation of active material. An improved tube uses a cathode comprising a porous metal matrix consisting of a compacted mixture of tungsten and iridium particles, impregnated with a molten barium aluminate. Other alkaline earth oxides may be used as additives. The impregnated cathode outgasses easily and has a long life because it is not dependent on thin surface films. Thermionic emission is improved compared to a tungsten matrix, and barium evporation is reduced. The combination of power and frequency obtainable from the microwave tube is thereby significantly increased.

Abstract: Chemical analysis apparatus such as a spectrophotometer including an atomizer for receiving a sample to be analyzed and being heated by resistance heating. Control means being provided to vary the voltage across the atomizer, and consequently its temperature, and a feedback circuit is connected between the atomizer and the control means and includes components which are operable to generate an electrical analogue which at least approximates the heating response characteristics of the atomizer. The feedback circuit functions as a negative feedback loop so as to modify the power input to the atomizer by application of the aforementioned electrical analogue, and in that way substantially compensates for the heating response characteristics of the atomizer such that the temperature time profile of the atomizer follows a predictable path.

Abstract: In an instrument for reconstructing computerized tomograms utilizing penetrating radiation, typically X or gamma radiation, an apparatus and technique are disclosed for removing spectral artifacts and utilizing spectral effects to create output pictures which represent facsimilies of the distribution of molecules according to atomic number and electron density within the object being pictured. Combinations of these pictorial representations are also obtained. Reconstruction errors caused by panchromaticity in the radiation source are avoided. Attenuation within the object by means of photoelectric absorption, Compton scattering and Rayleigh scattering are isolated and analyzed separately. Techniques are disclosed for treating source beams which are arbitrarily thin or of a finite thickness.

Abstract: By positioning the source and gate electrodes on the opposite faces of the active layer, these electrodes can be brought closer together and may have their adjacent edges mutually aligned or even overlapping. The series source resistance and channel resistance can be greatly reduced, because of this closer spacing, which can not be attained when the electrodes are coplanar. By also locating the drain electrode on the same side of the active layer as the source, the source-to-drain spacing can be significantly reduced, reducing channel length and improving the high frequency performance of the transistor. Further, because the electrodes are located on both sides of the active layer, it is possible to provide a large area contact on the bottom, or substrate, side of the epitaxial wafer structure which can advantageously be used to provide a low thermal and electrical resistance connection for the source contact, for example.

Abstract: Chemical analysis apparatus such as a spectrophotometer, having a carbon rod or other non-flame atomizer which is adapted to be heated by electrical resistance heating. The atomizer is included in a heater circuit, and a particular relationship exists between the electrical resistance of the atomizer and the electrical resistance of the remainder of that circuit. That relationship is such that variations in the atomizer resistance as may occur over a period of use, do not substantially affect power dissipation in the atomizer during heating. Ideally, the two resistance values are equal, but variations from the ideal are satisfactory in practice. A feed-back circuit is arranged to maintain a substantially constant voltage across the heater circuit, and that is achieved by comparing the applied voltage with a reference voltage and modifying the applied voltage as necessary to maintain a predetermined relationship between the two.

Abstract: A damper for use with a high pressure pumping system, such as a liquid chromatography system, which incorporates a reciprocating pump. The device is a generally enclosed canister including an internally formed flow volume. Inlet and outlet passages through the canister communicate with the flow volume, the inlet passage being connectable to receive the high pressure flow. A compressible body, e.g. of Teflon is positioned in the flow volume. The dimensions of the body are slightly smaller than those of the surrounding volume, whereby the high pressure flow passing between the inlet and outlet flows through the space between the body and the internal canister walls. The compression and decompression of the body in response to the pulsations in the flow dissipate the energy carried by the pulses, thereby damping same.

Abstract: Aluminum gallium arsenide is used as a transparent, conducting contact layer on the exposed surface of a gallium arsenide photovoltaic cell. Increased conductivity for the high current generated when concentrated solar radiation strikes the cell, is provided by doping the AlGaAs layer with magnesium. During the formation of the layer, Mg diffuses into the gallium arsenide to form a p-type layer and a p-n junction.

Abstract: A circuit improvement is disclosed for use in an electron capture detector of the type including an electron capture cell, means for applying polarization pulses to the cell to derive a cell current, means for varying the pulse rate to maintain the cell current constant, and means for converting the pulse frequency to an analog signal indicative of the concentration of an electron-capturing component.

Abstract: An ionization detector, such as an electron capture detector for use in pesticide residue analysis, utilizes a scandium tritide beta particle source. The scandium tritide forms a surface portion of a metallic foil. If the foil initially exhibits an unacceptably high tritium emanation rate at desired high operating temperatures, e.g., at temperatures above 250.degree. C, the foil can be treated so as to exhibit an acceptable tritium emanation rate at such temperatures. The treatment comprises heating the foil at a predetermined treatment temperature, e.g., at a selected temperature in the 300.degree. to 400.degree. C range, until the tritium emanation rate for the foil at the selected treatment temperature reaches a value which correlates with an acceptable tritium emanation rate for the foil at a particular desired operating temperature.

Abstract: A two-flame burner is used in a flame photometric detector for analyzing a sample material. The sample material is introduced via a first conduit structure into a hydrogen-rich first flame, and the combustion products and excess hydrogen from the first flame are passed via a second conduit structure into an oxygen-containing environment. A second flame is maintained at the exit end of the second conduit structure. The first and second conduit structures are composed of material that does not contribute to the coloration of the second flame during operation of the detector. Particular constituents of the sample material are detected by observing the presence of colors in the second flame indicative of the constituents. For example, the presence of sulfur is indicated by a blue coloration, and the presence of phosphorus is indicated by a green coloration.

Abstract: In a wide tuning range nuclear magnetic resonance spectrometer, the probe structure includes a series resonant pick-up coil circuit disposed in RF magnetic field exchanging relation with the sample under analysis for detecting nuclear magnetic resonance of the sample. A variable capacitor is series resonated with the inductance of the pick-up coil and the capacitor is arranged for tuning the series resonance of the pick-up coil over a wide tuning range, for example, from 6 to 32 megahertz. The low series resonant impedance of the pick-up coil, as of 1.5 to 5 .OMEGA., is matched to the relatively high input impedance, as of 50 ohms, of a low noise RF amplifier by means of a pair of series connected transmission line transformers for transforming the 50 ohm input impedance of the amplifier to the low series resonance impedance of the pick-up coil.

Abstract: In a nuclear magnetic resonance spectrometer, the probe structure includes an analysis channel RF magnetic coil disposed in RF magnetic field exchanging relation with a sample of gyromagnetic resonators under analysis for detecting nuclear magnetic resonance of the sample. A control group of nuclear magnetic resonators is also disposed in the sample region and nuclear magnetic resonance of the control group is excited and detected by a second RF magnetic coil. The control RF coil is formed and arranged relative to the sample RF magnetic coil to minimize cross coupling between the sample and control channels. In a preferred embodiment, the control RF magnetic coil is coaxially disposed of the analysis RF coil and is further segmented into a pair of axially spaced portions disposed at opposite ends of the analysis coil and connected in magnetic field bucking relation relative to each other so that the RF magnetic field generated by the control RF coil cancels in the region of the analysis RF coil.

Abstract: In a nuclear magnetic resonance spectrometer a gate is employed for time share multiplexing of the resonance and transmitter signals. An improved gate circuit is connected in series between the receiver and the resonance detecting circuit employed for picking up resonance of the sample. The improved gate circuit includes a pair of parallel connected branches of PIN diodes connected between the input and output terminals of the gate. The diodes in each parallel branch are poled toward an intermediate control node in such a manner so that a positive control potential applied to the control of one branch node turns that branch on and conversely a negative control potential applied to the other control node turns on the other branch. Equal magnitude and opposite sign control pulses are applied to the control nodes so that transient switching signals, tending to leak through the gate, cancel on the output line to the RF receiver.

Abstract: A gyromagnetic resonance spectrometer employing a spinning sample in a magnetic field, the spinning sample being affixed to a gas driven turbine which is supported by a gas bearing. Means are provided for firmly holding and centering the sample at more than one axial position thereby aligning the sample tube with the turbine axis irrespective of variations in sample tube diameter and straightness.

Abstract: A vortex restraining plug for an NMR spinning sample tube which floats partially submerged in the sample and which restrains vortexing.

Abstract: In a chromatographic column oven, a particular arrangement of a fan, heater and baffles provides low thermal gradients and rapid oven cool-down. Low thermal gradients are obtained by providing an air circulation pattern that promotes optimum mixing of the air within the oven enclosure. A fast cool-down time is obtained by providing a high-velocity air flow along the walls of the oven enclosure. A fan is mounted substantially at the geometric center of a first wall of the oven enclosure. A second wall of the enclosure, which faces the first wall, comprises a door for providing access to the oven enclosure. An elongate heating element is mounted on the first wall so as to substantially surround the periphery of the fan. A plurality of baffles are mounted symmetrically around the periphery of the fan on and extending perpendicularly from the first wall. A gap is provided between each particular baffle and the wall or walls intersecting the first wall nearest that particular baffle.

Abstract: An improved technique is disclosed for forming two- or three-dimensional images of a macroscopic sample by means of gyromagnetic resonance. A train of free induction decay transient resonance signals are induced and detected from a sample in a region to be imaged. A sequence of pulsed magnetic field gradients are applied during the series of free induction decay signals to derive sets of gyromagnetic resonance data as a function of the changing magnetic field gradients. Two- or three-dimensional images are reconstructed from the sets of resonance data by two- or three-dimensional Fourier transformation.