Showing papers by "Varian Associates published in 1990"

Dynamics and physiology of saxitoxin production by the dinoflagellates Alexandrium spp.

Abstract: Toxin content (fmol cell−1) and a suite of elemental and macromolecular variables were measured in batch cultures of the dinoflagellatesAlexandrium fundyense, A. tamarense andAlexandrium sp. from the southern New England region, USA. A different perspective was provided by semicontinuous cultures which revealed sustained, steady-state physiological adaptations by cells to N and P limitation. Two types of variability were investigated. In batch culture, changes in nutrient availability with time caused growth stage variability in toxin content, which often peaked in mid-exponential growth. A second type of variability that could be superimposed on growth stage differences is best exemplified by the high toxin content of cells grown at suboptimal temperatures. Calculations of the net rate of toxin production (R tox ; fmol cell−1 d−1) for these different culture treatments and modes made it possible to separate the dynamics of toxin production from cell division. Over a wide range of growth rates, cells produced toxin at rates approximating those needed to replace “losses” to daughter cells during division. The exception to this direct proportionality was with P limitation, which was associated with a dramatic increase in the rate of toxin production as cells stopped dividing due to nutrient limitation in batch culture. Growth stage variability in batch culture thus reflects small imbalances (generally within a factor of two) between the specific rates of toxin production and cell division. N limitation and CO2 depletion both affect pathways involved in toxin synthesis before those needed for cell division; P limitation does the opposite. The patterns of toxin accumulation were the same as for major cellular metabolites or elemental pools. The highest rates of toxin production appear to result from an increased availability of arginine (Arg) within the cell, due to either a lack of competition for this amino acid from pathways involved in cell division or to increased de novo synthesis. There were no significant changes in toxin content with either acclimated growth at elevated salinity, or with short term increases or decreases of salinity. These results demonstrate that toxin production is a complex process which, under some conditions, is closely coupled to growth rate; under other conditions, these processes are completely uncoupled. Explanations for the observed variability probably relate to pool sizes of important metabolites and to the differential response of key biochemical reactions to these pool sizes and to environmental conditions.

Growth and properties of LPCVD titanium nitride as a diffusion barrier for silicon device technology

Abstract: Chemical vapor deposition has been used to deposit titanium nitride (TiN) on silicon wafers at low pressures in a cold-wall single-wafer reactor. Experiments are reported for pressures in the range of 100-300 mtorr and temperatures between 450{degrees}-700{degrees}C, with titanium tetrachloride and ammonia as reactants. Both hydrogen and nitrogen are evaluated as diluents. Deposition rates as high as 1000 {angstrom}/min have been achieved. The chemical nature of the films are evaluated by Auger and RBS techniques, while the morphology is depicted by SEM. For the most part, the films are stoichiometric and contain small quantities of oxygen, chlorine, and hydrogen.

Sputtering apparatus with a rotating magnet array having a geometry for specified target erosion profile

Abstract: A magentron sputtering apparatus includes a rotatable magnet which is either concave or convex. For one magnet structure, at least a portion of the centerline of the magnet lies along a curve defined by ##EQU1## where ξ(r) is a preselected erosion profile. When stationary, the magnet generates a localized magnetic field of approximately constant width. In operation, when the magnet is rotated, it generates the preselected erosion profile in the target. The preselected erosion profile may be constant.

Spiral microstrip hyperthermia applicators: Technical design and clinical performance

Abstract: Spiral microstrip microwave (MW) antennas have been developed and adapted for use as clinical hyperthermia applicators. The design has been configured in a variety of forms including single fixed antenna applicators, multi-element arrays, and mechanically scanned single or paired antennas. The latter three configurations have been used to allow an expansion of the effective heating area. Specific absorption rate (SAR) distributions measured in phantom have been used to estimate the depth and volume of effective heating. The estimates are made using the bioheat equation assuming uniformly perfused tissue. In excess of 500 treatments of patients with advanced or recurrent localized superficial tumors have been performed using this applicator technology. Data from clinical treatments have been analyzed to quantify the heating performance and verify the suitability of these applicators for clinical use. Good microwave coupling efficiency together with the compact applicator size have proved to be valuable clinical assets.

Gyrotrons for ECH applications

Abstract: Gyrotron oscillators have served as effective sources for electron cyclotron heating (ECH) applications in the area of magnetic confinement fusion Successful development programs at frequencies at 28 GHz, 60 GHz, and 140 GHZ, have led to the availability of wide-range gyrotron sources with high-average-power capabilities Since 1975, over 100 pulsed and CW gyrotrons with typical power levels of 200 kW at frequencies ranging from 28–106 GHz have been used by various fusion laboratories Present development activity is aimed at providing sources that will generate power levels up to 1 MW CW at frequencies in the range 100–140 GHz for the ECH experiments that are currently being planned Initial experimental efforts in this area have verified many of the concepts to be employed in forthcoming 1-MW CW test vehicles Source requirements, that are even more formidable, are foreseen for the next generation magnetic fusion facilities Frequencies ranging from 200–300 GHz with power generation capabilities of 1–2 MW CW per tube are being considered for these future applications To this end, various gyrotron designs have been conceived that address these demanding specifications

Dual track handling and processing system

Abstract: A dual track substrate handling and processing system (1) includes an entrance load lock station (L1), an exit load lock station (L2) and a plurality of substrate processing stations (S1-S6), all positioned above a transfer vacuum chamber (30). The load lock station and each processing station are configured to hold two vertically oriented workpieces (w). A transport system conveys workpieces, two at a time, from parallel input cassettes (C1, C2) to the entrance load lock station (L1). The transport system includes a transport assembly that simultaneously advances two workpieces from each station to the next station; thus workpieces are processed two at a time in the same environment in each processing station and system throughput is correspondingly increased.

Method and apparatus for temperature measurements

Abstract: Remote measurement of temperature of a process chamber provided with a substrate exhibiting a temperature dependent band gap which substrate is illuminated by a source of continuous spectrum light with a spectrum which overlaps the band gap edge of the substrate. The light which exits the substrate is focused by a lens and is picked up by a fiber optic which takes it to a spectrometer where the spectrum is analyzed to ascertain the intensity versus wavelength histograph for exit rays in the wavelength region of the equivalent band gap of the substrate. The wavelength at the point of infection in the region of band gap edge of the substrate in the histograph of the wavelength versus intensity characteristic of exit rays determines the real time substrate temperature from predetermined calibration data which correlates the wavelength at the point of inflection to actual temperature of the substrates.

Characterization of surface-undoped In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/InP high electron mobility transistors

Abstract: High-performance 0.3- mu m-gate-length surface-undoped In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g/sub m//g/sub 0/ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-*150- mu m-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB+or-1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures. >

Double tuned bird cage coil

Abstract: A multiply tuned bird cage results from the combination of low pass and high pass filter elements to yield a band reject network (A1', A2'...Ai', B1', B2'...Bi) behaving as a low pass network at a low frequency and a high pass network at a high frequency. A band pass bird cage coil is obtained by adding a parallel LC combination to each leg of a bird cage coil to create additional poles in the impedance curve z(f).

Spectroscopic plasma torch for microwave induced plasmas

Abstract: A spectroscopic plasma torch suitable for use at atmospheric pressure disclosed. The torch utilizes a microwave induced helium plasma confined in a plasma discharge tube. The plasma is suspended and stabilized by a vortex flow of helium. The torch includes a high velocity gas jet for introducing sample materials into the plasma The design avoids the formation of carbon deposits in the plasma discharge tube caused by the premature pyrolysis of organic materials outside the plasma and prevents other sample materials from being adsorbed on the surface of the plasma tube. Because of these characteristics, the torch is particularly well suited for use as a component in a gas chromatography detector which employs helium as the plasma support gas.

Production of ion beams by chemically enhanced sputtering of solids

Abstract: A method for producing an ion beam for ion implantation by chemically enhanced bombardment of solids. The method is carried out in a reaction chamber having an anode and cathode and a cathode liner rich in a selected element, namely boron, arsenic, phosphorus or antimony. A non-poisonous feed gas is introduced into the reaction chamber and energy is supplied to the feed gas to generate a plasma in the reaction chamber. The constituents of the plasma react chemically with the selected element in the cathode liner and an electrical potential is established between the anode and the cathode so that ions in the plasma bombard the cathode liner. The chemical reaction and bombardment together generate an ion species in the plasma containing the selected element. A beam of ions containing the selected species is then extracted from the plasma.

Wafer arm handler mechanism

Abstract: A wafer handler arm conveys a wafer from a horizontal orientation to a vertical orientation for wafer processing. The arm includes a wafer holding member which is rigidly attached to a first shaft. The first shaft is rotatable about its longitudinal axis and the first shaft is rotatable about a second axis perpendicular to the first axis.

Vacuum tube with an electron beam that is current and velocity-modulated

Abstract: A high-frequency amplifier tube includes a grid that responds to an r.f. input signal to current modulate a linear electron beam derived from a cathode. A resonant structure establishes an electric field in a region between the grid and cathode. First and second resonant cavities downstream of the grid in the named order are coupled to the modulated electron beam. The first cavity responds to the r.f. signal to velocity modulate the current-modulated beam. The second cavity is coupled to the current- and velocity-modulated beam for deriving an output signal. An AC connection from a source of the input signal is established to transformer coupling in the first cavity. A phase-shift circuit adjusts the relative phase of the modulation on the beam as it passes through the first cavity and the phase of the r.f. signal as coupled to the first cavity so that fields induced in the cavity by the modulated beam are optimally phased with respect to fields established in the first cavity by the transformer coupling. The phase-shift circuit is connected between the first cavity and the resonant structure or between the second cavity and the resonant structure. A resonant slow-wave circuit is included in the electron-permeable or in an electrically conductive support structure for the grid.

Circuit for coupling energy to pulse forming network or capacitor

Abstract: A pulse forming network or capacitor load is charged to a precise voltage from an energy storing device with a circuit including a transformer having a primary connected in series with a switch and storage device and a secondary connected in series with the load and a monitor circuit. The monitor circuit develops an output signal indicative of the load voltage and current. In response to the output signal increasing to a predetermined value the switch is opened. The transformer, having a substantial leakage inductance, releases its stored energy when the switch is opened. The transformer stored energy is coupled to the load and to a capacitor connected to the primary. Charge stored in the capacitor after the load requirements have been satisfied is transferred back to the energy storage device.

Screening of trihalomethanes by direct aqueous injection using electron capture detection

Abstract: The disinfection of drinking water with chlorine produces carcinogenic by-products called trihalomethanes or (THM's). These compounds are formed when the chlorine reacts with the organic matter in the raw water. The four major THM's are chloroform, bromodichloromethane, dibromochromethane, and bromoform. Direct aqueous injection is used for the rapid screening THM's and other volatile organic compounds (VOC's) in water by direct on column injection of the water sample in to wide bore capillary columns, to which is attached an electron capture detector.

Chemical indicators of decomposition for raw surimi and flaked artificial crab

Abstract: Raw surimi and a surimi-derived flaked artificial crab were stored at 4°C, 10°C and 22°C until advanced decomposition occurred. The raw surimi and the flaked artificial crab remained at an acceptable level of quality based on sensory analysis for approximately 2–4 days and 6–8 days, respectively, when stored at 10°C. Both products were of acceptable quality for at least 13 days when stored at 4°C. The potentials of total volatile acids (TVA) and total volatile bases (TVB) determined by flow injection analysis, ethanol determined by head-space gas chromatography and the amines, cadaverine, putrescine, and histamine all determined by high performance liquid chromatography, were evaluated as chemical indicators of decomposition for those products. TVA and TVB appeared to have the most potential as indicators of decomposition.

Imaging GaAs vacuum photodiode with 40% quantum efficiency at 530 nm

Abstract: This paper will describe a high quantum efficiency imaging phosphor diode optimized for 500-700 nm sensitivity. Potential applications for this tube include undersea imaging and detection of 530-nm laser light. The tube is designed to function as a low noise factor optical amplifier. The tube consists of an 18-mm CsO activated GaAs/AlGaAs photocathode and a high resolution P46 phosphor screen enclosed in a Kovar/ceramic vacuum envelope. Measured results for quantum efficiency (QE), MTF, dark current, noise factor, operating life, response time and gain are presented. Finally, the paper discusses the engineering tradeoffs associated with fabricating a GaAs/AlGaAs cathode with high short wavelength QE.

Uptake and metabolism as mechanisms of selective herbicidal activity of the 1,2,4‐triazolo[1,5‐a] pyrimidines

Abstract: In order to identify the factors providing the triazolopyrimidines with a wide range of selectivity amongst agriculturally important plant species, studies were made on the uptake and metabolism of a representative compound, N-(2,6-dichlorophenyl)-5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine- 2-sulfonamide. This compound is much more phytotoxic to dicots than to monocots. Experiments showed that variations in leaf morphologies and geometries relative to spray applications resulted in different herbicide dosages applied to plant species used in selectivity evaluations. However, this parameter did not have a statistically significant correlation to herbicide selectivity measurements. Characterization of the metabolic pathways showed that the major herbicide metabolites involved methyl hydroxylation or hydroxylation of the aniline ring followed by glucose conjugation. Since these metabolites were not exclusive to either monocots or dicots, herbicide selectivity does not appear dependent on the pathway of metabolism. Studies on the kinetics of metabolism suggest instead that metabolic rate was important. Monocots metabolized the herbicide rapidly and generally were tolerant while the opposite was true of dicots.

Field amplified polarity switching sample injection in capillary zone electrophoresis

Abstract: An improved electroinjection method of introducing a sample having positive and negative ions into a capillary column for CE or CZE process by introducing a short plug of a low concentration buffer before introducing the sample into the column which results in increasing amount of charged ions of the sample introduced in the capillary column due to increasing the electric field at the injection point. A method for efficiently introducing both positive and negative ions is also shown.

Optical switching apparatus and method

Abstract: An apparatus and method for switching unpolarized light are provided. The apparatus includes GaInAs/GaAs optical switching devices which can be fabricated using conventional processes on a single wafer in matrix arrangement to provide an n×m cross bar switch. Switching is accomplished by shifting the band gap of the GaInAs material of a device using electrical or optical power to heat the material. Each switching device may comprise two-polarity (n/p) or single polarity (n or p) semiconductor materials.

Vacuum tube including grid-cathode assembly with resonant slow-wave structure

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. signal so the beam is formed at twice the frequency of the r.f. signal. Focusing electrodes configured as a perforated sheet, contacting the cathode, or as electrodes just downstream of the control grid, or both, collimate ,the beam, whether hollow or not.

Fast warm-up cathode for high power vacuum tubes

Abstract: of the Disclosure In order to bring a high power vacuum tube to full power in a few seconds, it is necessary to heat the cathode quickly to 1100°C. In large tubes, prior art structures cannot be simply enlarged. A novel cathode structure in which the heater element is anisotropic pyrolytic graphite coated with anisotropic pyrolytic boron nitride for insulation and then sintered to the cathode avoids these problems.

Process for manufacturing an impeller by electrical discharge machining and articles so obtained

Abstract: A process for manufacturing impellers of turbine pumps provides for subjecting disks corresponding to the impeller to be obtained to electrical discharge machining, using tools in form of plates provided with radial slits extending along at least an arc of circumference and opening into hollow areas. A combined motion of rotation and translation is imparted to the disks, thus generating twisted blades having a profile with defined geometric characteristics. A one-piece rotor can be manufactured employing open tools with slits formed along a semicircumference, and two passages in succession of the workpiece through the tools, moving the workpiece with a combined motion of rotation and translation. An advantageous application of the articles manufactured by this process is for rotors of turbomolecular pumps, since the compression ratio and the pumping speed are optimized and a considerable structural sturdiness of the article is obtained.

Quasi-passive, non-radioactive receiver protector device

Abstract: A receiver protector device includes a sealed discharge chamber containing one or more pairs of spaced-apart, conical electrodes and an ionizable gas. A field emission array is mounted in the discharge chamber to provide a source of free electrons which assist in initiating a discharge when an RF input signal exceeds a desired threshold power level. The field emission array includes a substrate, a plurality of generally conical emitters distributed on the substrate, a conductive gate layer for extracting electrons from the emitters and a dielectric layer between the gate layer and the substrate. When a bias voltage is applied to the gate layer, electrons are extracted from the emitters. The field emission array can be mounted adjacent to the electrodes or in a recess in one of the electrodes. The bias voltage can be supplied by a battery mounted on the receiver protector device external to the discharge chamber.

Background correction method for use in gas chromatography

Abstract: A method of correcting for background changes in a plasma emission detector comprising a photodetector array is disclosed. In the photodetector array a plurality of sensors are used to detect the emission lines from a discrete number of selected elements including carbon. It is shown that, to the first order, there is a correlation between the response at detectors other than the carbon detector with the response at a carbon detector. The exact extent of this correlation is highly dependent on the amount of nitrogen present in the carrier gas used in the system. A calibration curve can be generated which allows compensation at a frequency of interest as a function of the magnitude of the carbon signal. This curve will depend on the level of nitrogen in the carrier gas and can be empirically determined each time a new bottle of gas is connected to the system. In a preferred embodiment, the calibration curve is not referred to unitl the carbon response reaches a preselected threshold value corresponding to the point on the calibration curve where there is a measurable spurious reading.