Abstract: A radiotherapy machine beam treats a region of a subject while the region and volumes abutting the region are imaged by a magnetic resonance imaging system. The beam and an excitation coil assembly of the imaging system are arranged so the beam is not incident on the coil assembly and magnetic fields derived from the coil assembly do not interact with the beam. The excitation coil assembly includes two spaced winding segments for producing a main DC magnetic field; the segments are located on opposite sides of the region. In one embodiment, wherein the excitation coil assembly is mounted independently of movement of an axis of the beam, the winding segments have a common axis generally aligned with an axis about which the beam axis turns. A treatment couch for the subject fits within aligned central openings of the winding segments. The coil produces main magnetic field lines that extend generally in the same direction as the axis about which the beam turns.

Abstract: A radiotherapy machine beam treats a region of a subject while the region and volumes abutting the region are imaged by a magnetic resonance imaging system. The beam and an excitation coil assembly of the imaging system are arranged so the beam is not incident on the coil assembly and magnetic fields derived from the coil assembly do not interact with the beam. The excitation coil assembly includes two spaced winding segments for producing a main DC magnetic field; the segments are located on opposite sides of the region. In one embodiment, wherein the excitation coil assembly is mounted independently of movement of an axis of the beam, the winding segments have a common axis generally aligned with an axis about which the beam axis turns. A treatment couch for the subject fits within aligned central openings of the winding segments. The coil produces main magnetic field lines that extend generally in the same direction as the axis about which the beam turns.

Abstract: High quality epitaxial layers can be grown on a multi-layer substrate which has a crystalline pseudomorphic layer with an exposed surface used for the epitaxial growth. The pseudomorphic layer of the substrate has a thickness at or below the pseudomorphic limit so it will be deformed as stress forces are developed during epitaxial growth of heteroepitaxial structures. A plastically deformable layer is bonded to the pseudomorphic layer, This plastically deformable layer is made of material that plastically flows at epitaxial growth temperatures.

Abstract: A heater for an indirectly heated vacuum tube cathode is formed of anisotropic pyrolytic graphite in which current passes through the graphite in the "c" direction.

Abstract: A vacuum tube for amplifying an r.f. signal includes an assembly containing a cathode and grid for current modulating an electron beam derived from the cathode. One of the electrodes of the assembly includes a slow wave structure approximately resonant to the frequency of the signal. A cavity resonant to the frequency of the signal, positioned between the grid and a collector for the beam, is coupled to the beam. In one embodiment, the slow-wave structure is mounted in a support for the grid, while in a second embodiment, the grid is configured as plural, parallel meander lines forming the slow-wave structure. In the latter embodiment, the beam is preferably annular and the meander line geometry, in certain modifications, is adjusted so that there is a relatively small electric-field variation with radius over the portion of the grid through which the annular beam passes. In a further embodiment, the grid is configured as two interlaced spirals, driven by complementary replicas of the r.f.

Abstract: Compounds of the formula Bi.sub.1 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.

Abstract: A calibrator supplying electric parameters (viz voltage, current and resistances) over plural ranges to a meter to be calibrated comprises internal components for deriving each parameter over the plural ranges, an internal voltage reference, a DAC, a memory, an analog comparator and analog-to-digital converter. The internal components are connected in circuit with the internal voltage reference, analog-to-digital converter, comparator and memory for writing data signals into the memory indicative of calibration correction factors for the internal components. The internal components are connected in circuit with the memory and DAC so the DAC responds to the stored data signals indicative of the calibration correction factors to enable the value of the parameter supplied to the device by the internal components to be modified and corrected in accordance with the calibration correction for the parameter.

Abstract: A mechanism for locking and unlocking a reciprocating shaft includes a plate fixed to the shaft having an inclined surface. A housing surrounds the shaft and plate having a wall surrounding the inclined surface. A set of balls is located between the inclined surface and the housing wall. An assembly is translatable relative to the shaft and is biased by a spring to jam the balls between the inclined surface and the housing wall to lock the shaft against reciprocation. The assembly is movable against the force of the spring by a fluid pressure actuated cylinder to move the balls away from the inclined surface to unlock the shaft.

Abstract: Calibrating errors of a variable gain amplifier used in an AC calibrator or a meter for measuring AC are determined for a gamut of frequencies. The gain of the variable gain amplifier is varied by adjusting the value of a variable resistor in discrete steps. A variable amplitude signal is applied to the amplifier while the resistor is adjusted in discrete steps so the amplifier derives a gamut of variable amplitude signals that are supposed to have predetermined values. The amplitudes of the gamut of variable amplitude signals derived by the amplifier are detected and compared with the values that the signals are supposed to have to derive a calibrating error signal of the amplifier for each variable resistor value. A gamut of variable frequency, constant amplitude signals is applied to the amplifier while the amplifier gain is constant. The amplifier has a tendency to derive an AC output signal having a different amplitude in response to different ones of the frequencies.

Abstract: An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Abstract: A baffle divides a housing into first and second compartments. The first compartment includes a chromatography oven having a fan for circulating heated air over the columns while the oven is closed and for sucking ambient temperature cooling air in the first compartment into the oven while the oven is open. Ambient air is sucked into a tortuous path in the first compartment. Cooling air from the second compartment flows into the first compartment via openings in the baffle. The cooling air flows over the oven exterior and is at least partially sucked into the oven by an oven fan while the oven is open. The oven heater, coaxial with the blades, is located between an oven wall and blades. A ring baffle, having approximately the same diameter as and coaxial with the blades, is located between the wall and the blades. A fan outside of the oven sucks air from the oven through an outlet while the oven is open.

Abstract: A DC-DC converter includes first and second switches to be opened and closed at mutually exclusive times at a predetermined frequency. The first switch is connected to an inductor and a transformer primary winding so that a first current component from a DC input supply flows through it via the inductor. A second current component having a sinusoidal component flows through the first switch in response to discharge of energy stored in a resonant circuit coupled to the transformer. The second component begins approximately simultaneously with closure of the first switch. The second switch, when closed, is connected so that a bi-directional current component flows through it in response to energy stored in the inductor. The rectifier is connected between the secondary winding and the load so the secondary winding supplies substantial current to the load.

Abstract: A shielded transformer of the type particularly used as an isolation transformer, has a greatly reduced interwinding capacitance. Metallic overlap is provided, completely across a juncture of the metallic shield with faces of the windows in the core, and completely across a juncture of the metallic shield with the metallic case. This metallic overlap is tolerant to misalignments and variations in fit, completely eliminating gaps that cannot be economically made small with the butt joint of present art. The overlap comprises grooves in faces of the window or in the case. In a second embodiment, the overlap comprises grooves in channels on faces of the window and on the case. The shield fits into the grooves.

Abstract: The d.c. power supplied by a photovoltaic solar panel to a load is controlled by monitoring the slope of the panel voltage vs. current characteristic and adjusting the current supplied by the panel to the load so that the slope is approximately unity. The slope is monitored by incrementally changing the panel load and indicating whether the resulting change in current derived from the panel is above or below a reference value, indicative of the panel voltage. In response to the change in the monitored current being above the reference value, the slope of a voltage vs. current curve is greater than unity and the load is adjusted to decrease the current supplied by the panel to the load. Conversely, in response to the current being less than the reference value, the slope of the voltage vs. current curve is less than unity and the load is adjusted to increase the current supplied by the panel to the load.

Abstract: A transistor having a selectively saturated emitter collector path is protected.The emitter collector voltage level is sensed as being greater than a predetermined level to indicate saturation as is the presence and absence of drive current to the base. In response to the transistor not being activated to saturation while the drive current is applied to the base, a fault indication is derived. In response to the fault being indicated, the transistor is prevented from conducting by decoupling a source of operating voltage and current from the emitter collector path and/or decoupling the drive current from the base.

Abstract: A method and apparatus for applying a reverse bias voltage to the base-emitter junction of a transistor, for turning off the transistor from a normal conduction state, or for connecting a relatively low impedance current path between the base and emitter electrodes for turning off the transistor from a fault conduction state.

Abstract: A diffusion pump for a leak detector of helium or other light gases includes a foreline, responsive to gases from vacuum equipment being monitored for leak detection, and an inlet, connected to a mass spectrometer or other similar high vacuum gas measuring instrument. The diffusion pump includes two diffusion stages. The second stage has a diffuser throat with a relatively narrow width and small cross-sectional area so that the velocity of diffusion oil vapor flowing through it causes the light gases to be easily back diffused from the foreline to the inlet, while substantially preventing the flow of air or other relatively heavy gases between the foreline and the inlet. Fluid is returned to the pool by a conduit having a vertically extending, longitudinal axis aligned substantially with the center of the pool and an outlet orifice in proximity to the bottom of the pool, whereby the oil is returned to the coolest part of the pool at its bottom, central portion.

Abstract: In one embodiment of the invention, a switching circuit is provided by connecting the main current paths of a plurality of relatively low voltage transistors in series for switching a relatively high level of voltage, with zener diodes being connected across the main current paths of each one of the transistors, the zeners having a breakdown voltage rating no greater than the inverse voltage rating of their respective transistor, and polarized for breaking down whenever the inverse voltage rating of the transistor is exceeded, the zener diodes also providing a voltage divider circuit for applying appropriate levels of bias voltage to the common connections between the transistors for ensuring the inverse voltage ratings of the transistors are not exceeded at times that the transistors are all turned off, or non-conductive.

Abstract: A high-power, solid-state switching circuit includes in a preferred embodiment a first switching device susceptible to damage from excessive peak power dissipation at times of turn-on and turn-off in switching high currents from a relatively high-voltage supply, the first switching device having its main current path connected in parallel with the main current path of a second switching device that is substantially less susceptible to such damage from excessive peak power dissipation, but which has a substantially higher impedance in its main current path than the first device when turned on, the devices complementing one another via the operation of said switching circuit for turning on the second device before the first device, thereby substantially lowering the voltage across the main current path of the first device, allowing the latter to be turned on and turned off with substantially reduced peak power dissipation via the snubbing effect of the second device, and the first device relative to the second

Abstract: A protection circuit for a switching amplifier having a plurality of serially stacked switching transistors includes a voltage breakdown device and a current responsive device for sensing the voltage developed between the emitter and collector electrodes of each conducting switching transistor. The base drive for any transistor is removed in response to Vce of a switching transistor exceeding a predetermined value.