Small Collector Research Articles

EFFICIENCY AND UNIFORMITY OF THE LEPAAND SPRAY SPRINKLER METHODS: A REVIEW

Application efficiencies and uniformity coefficients reported for the low energy precision application (LEPA)and spray sprinkler irrigation methods are reviewed and summarized. The relative sizes of the water loss pathways forthe two sprinkler methods are also summarized. With negligible runoff and deep percolation, reported applicationefficiencies for LEPA are typically in the 95 to 98% range. Measurements such as chemical tracers, weighing lysimetercatches, and energy balance modeling are believed to be more accurate than small collector measurements forestimating spray application efficiency. Spray application efficiencies based on these other measurements exceed 90%when runoff and deep percolation are negligible. Because of the start and stop nature of mechanical move irrigationsystems, uniformity coefficients for LEPA and spray are measured both along the irrigation system mainline and in thedirection of travel. Along the mainline, reported uniformity coefficients are generally in the 0.94 to 0.97 range for LEPAand in the 0.75 to 0.85 range for spray. In the direction of travel, the uniformity coefficients are generally in the 0.75 to0.85 range for LEPA with furrow diking and in the 0.75 to 0.90 range for spray. On start and stop sprinkler systems,basin tillage on a 2 to 4 m spacing is critical for uniform LEPA irrigation because the basins prevent runoff and averagethe applications during several unequal start and stop times. Runoff is the largest potential water loss pathway for bothLEPA and spray irrigation. For the spray method, runoff can exceed either droplet evaporation and drift or nonbeneficialcanopy evaporation.

Nonlinear effects in the current-voltage characteristic of a low-density Q-machine plasma: II. Related to the electrostatic ion-cyclotron instability

In a single-ended Q-machine the current-voltage characteristic of a small collector shows a sudden jump of the current at the onset of the electrostatic ion-cyclotron instability. This jump was also accompanied by hysteresis. This is explained as an indication that the well known nonlinear potential structures that appear periodically in front of the collector during one cycle of a high-amplitude electrostatic ion-cyclotron instability, originate from collective effects of excitation and ionization interactions produced in front of the cold plate where accelerated electrons suffer inelastic collisions with the alkaline vapour present in the plasma column.

Design consideration of emitter-base junction structure for InGaP/GaAs heterojunction bipolar transistors

In this paper, the different designs of emitter-base junction including the employment of the δ-doping sheet and setback layer are presented and studied. A theoretical model is used to analyze the performances of the proposed different InGaP/GaAs heterojunction bipolar transistors (HBTs). Experimentally, a new InGaP/GaAs HBT with a δ-doping sheet and a setback layer inserting between emitter-base heterointerface is fabricated successfully. From the theoretical analysis and experimental results, it is found that the insertion of the δ-doping sheet and the setback layer can effectively eliminate the undesired potential spike at N-InGaP/p +-GaAs heterointerface. The experimental common-emitter current gain of 280 at collector current of 85 mA and a low offset voltage of 55 mV are achieved. In addition, a current gain of 11 at very small collector current of 0.5 μA without passivation is obtained.

Current Jumps and Hysteresis in a Single‐ended Q‐Machine in Connection with the Electrostatic Ion‐Cyclotron Instability

AbstractWe report on an investigation in a single‐ended Q‐machine where the current‐voltage characteristic of a small collector showed some interesting new features. The most interesting of these was a sudden jump of the current at the onset of the electrostatic ion‐cyclotron instability. This jump was also accompanied by hysteresis. Besides that, the characteristic showed another trivial type of hysteresis that was only due to a temporary covering of the collector by alkaline metal from the plasma. The former phenomenon could be an indication that the well‐known nonlinear potential structures that appear periodically in front of the collector during a cycle of a high‐amplitude electrostatic ion‐cyclotron instability, are related to inelastic collisions of accelerated electrons with alkaline vapour present in the plasma column.

Influence of the -doping sheet and setback layer on the performance of an InGaP/GaAs heterojunction bipolar transistor

In this paper, we demonstrate the qualitative influence of a -doping sheet and setback layer on the performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). The results of a theoretical simulation show that the potential spike is reduced by the simultaneous employment of an appropriate setback layer and -doping sheet. Due to the reduction in the potential spike, a high current gain, even at a small collector current regime, and small offset voltage can be attained. Experimentally, an offset voltage as small as 55 mV and current gain of 11 at collector current of A are obtained without a passivation structure.

High-gain, low offset voltage, and zero potential spike by InGaP/GaAs δ-doped single heterojunction bipolar transistor (δ-SHBT)

We report on fabrication, characterization, and comparison of InGaP/GaAs single heterojunction bipolar transistors (SHBT's) and heterostructure-emitter bipolar transistors (HEBT's). The SHBT with a /spl delta/-doped sheet located at the E-B heterointerface (/spl delta/-SHBT) exhibits a common-emitter current gain as high as 410 and an extremely low offset voltage of 55 mV. Even though at the small collector current density of 1/spl times/10/sup -3/ A/cm/sup 2/, the current gain is still larger than 20. Theoretical derivations show that the zero potential spike exists near the E-B junction under +1.5 V forward bias. However, an HEBT with a 700-/spl Aring/ narrow energy-gap emitter shows a small current gain and a collector current density due to the charge storage and bulk recombination effect. On the other hand, the increase of the CB capacitance in our /spl delta/-SHBT is very small as compared with conventional HBT's.

Measurement of the Isotopic Composition of Manganese, Iron, and Nickel in the Galactic Cosmic Rays

view Abstract Citations (16) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of the Isotopic Composition of Manganese, Iron, and Nickel in the Galactic Cosmic Rays Westphal, A. J. ; Afanasyev, V. G. ; Price, P. B. ; Solarz, M. ; Akimov, V. V. ; Rodin, V. G. ; Shvets, N. I. Abstract Using the small collector of the Trek experiment, a nuclear track-etch detector deployed on board the Russian space station Mir, we have made a measurement of the isotopic composition of manganese, iron, and nickel in the Galactic cosmic rays (GCR) at energies between 150 and 400 A MeV. We find that the isotopic composition of iron and nickel in the GCR source is consistent with solar system values; in particular, [60Ni]/[58Ni] is 0.78+-0.280.29 times the solar value, in contradiction to two previous results. The measurements were made in 1991-1992, during a maximum in solar activity and unusually strong solar modulation; we estimate that the analyzed GCR ions had kinetic energies between 550 and 1200 A MeV outside of the heliosphere. Based on our upper limit for the abundance of 56Ni, we place a lower limit of ∼24 days on the time between nucleosynthesis and acceleration of GCR material; the lack of significant enhancements in 54Fe or 60Ni excludes the possibility of major contributions of neutron- rich supernova zones to the GCR source. We do not find a strong depletion of 54Mn, indicating that this isotope does not completely decay during propagation. We also place upper limits on the abundances of 54Fe, 57Fe, 58Fe, 62Ni, and 64Ni. Our limit on the abundance of 58Fe is nearly a factor of 3 lower than previously reported upper limits. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177725 Bibcode: 1996ApJ...468..679W Keywords: ISM: COSMIC RAYS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; ISM: ABUNDANCES full text sources ADS |

Investigation of control and simulation of solar process heat plants using a flexible test facility

An advanced control system for the operation of solar process heat plants and a simulation program for the design were developed. A flexible test facility was installed in order to qualify the control system and the simulation model. It consists of different small collector fields, two storage tanks, an auxiliary electric heater and an adjustable heat sink for simulating any load profile. The advanced control system provided a fast control of the necessary collector field outlet temperatures and an effective compensation for any disturbances. The simulation program based on TRNSYS was extended to meet the requirements for the design of solar process heat plants.

Fully Radiative Current Path Structure (FRACS) for sub-0.1 μm emitter transistor

A new structure is proposed for bipolar transistors - FRACS (Fully Radiative Current Path Structure). A FRACS transistor has a line emitter and a cylindrical base and collector or a point emitter and a spherical base and collector. Device parameters of the FRACS transistor is obtained by extending the conventional one-dimensional transistor model to a two- or three-dimensional model. In this structure, base transit time is reduced as the emitter size is reduced by radiative collector current flow. Using this model, a general bipolar transistor with a shallow link base is found to increase the cutoff frequency as the emitter size is reduced. The Kirk effect is suppressed in this structure because of the small collector current density at the collector-base junction. The effect was experimentally examined. A cylindrical base was fabricated by thermal diffusion of boron to achieve the FRACS transistor. Cutoff frequency was observed to increase as the emitter size was reduced. Maximum cut-off frequency of 64 GHz was achieved by this transistor with a 25-nm thick base formed by rapid vapor-phase diffusion. >

Measurement of the registration temperature effect in BP-1 glass

In order to determine its effect on mass measurements and charge measurements for the cosmic-ray experiments ANTIPODE and TREK, I have measured the change in detector response with temperature (the so-called registration temperature effect, or RTE) for BP-1 glass responding to relativistic gold ions and to stopping argon ions. I measure a small but finite RTE for relativistic gold, and conclude that thermal regulation is necessary for the large collector of TREK, which is being exposed outside of the Russian space station Mir. I set a small upper limit for the magnitude of RTE for stopping argon, and conclude that the thermal variations experienced by ANTIPODE in its balloon flight over Antarctica were not large enough to degrade its mass resolution; I further conclude that the thermal variations that we anticipate for the small collector of TREK, which is being exposed inside the Russian space station, will not degrade its mass resolution.

Silicon vibration amplitude determined by energy-filtered CBED

The frozen phonon method was recently developed to include the effects of thermal vibrations in the multislice calculation. In this method, each atom in the simulated specimen is displaced by a random amount which follows a Gaussian distribution with a standard deviation equal to the atomic vibration amplitude. Convergent beam electron diffraction (CBED) patterns calculated by this technique contain Kikuchi bands and a thermal diffuse background which were matched quantitatively to experimental Si (100) CBED patterns for scattering angles up to the first order Laue Zone. In this paper, we report the measurement of the room temperature silicon vibration amplitude from comparison of energy filtered CBED with frozen phonon calculations.The energy filtered Si (100) patterns were obtained with a VG HB501A STEM in microdiffraction mode by fixing a convergent probe (7.5mrad half angle, probe size ≈ 40Å) on the specimen and scanning the post specimen electrons over a small axial collector aperture (1.6mrad).

AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) prepared by molecular beam epitaxy

A novel AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT) has been fabricated and demonstrated. The problems of conventional single heterojunction bipolar transistors (SHBTs) such as graded Al x Ga 1- x Ax emitter and the precise alignment of emitter-base junction are avoided. The proposed HEBT device exhibits significant advantages as (i) ease of fabrication, (ii) extremely small collector offset voltage. The common-emmiter current gain up to 180 with an offset voltage about 80 mV has been obtained in the nonoptimized device. Furthermore, an interesting controllable S-shaped negative-differential-resistance (NDR) phenomenon is observed under reverse operation mode. Therefore, the proposed HEBT may be employed as a multiple-function device which provides the transistor and switch actions on the same wafer, simultaneously.

Characteristics of impact-ionization current in the advanced self-aligned polysilicon-emitter bipolar transistor

Using an algorithm to calculate the base current increase due to local thermal effects, the authors show that one can accurately measure the impact ionization current over the full range of collector current. From the measured impact ionization ratio, it was possible to quantitatively describe the characteristics of the space-charge modulation and base push-out effect over a wide range of collector current. Computer simulation results support the measured data. It is also shown that one can use the measured impact ionization ratio to distinguish small collector concentration variations and thickness differences. The characterization was performed for self-aligned polysilicon-emitter transistors in an advanced BiCMOS technology. >

Miniband Base Transistor

A new type of transistor called the miniband base transistor is proposed and fabricated. The miniband base transistor uses, as an entire base layer, a superlattice of the same conduction type as an emitter and a collector. The superlattice base is designed so that the injected electrons are in the first excited miniband, while base current carriers are in the ground miniband. The minigap between these two minibands is expected to suppress LO-phonon scatterings and to increase the current gain. The transistor is fabricated using an AlGaAs/GaAs superlattice. Electrical measurements indicate that the superlattice base is effective for improving the current gain of the hot-electron transistor at small collector voltage.

Performance of an integrated array of solar collector modules for different air flow rates and flow organizations

A 20 m 2 integrated flat plate solar air heating module has been developed at IIT, Kharagpur, India to match with a grain dryer of capacity 0.5 t paddy/day. Based on some statistical, physical and operational parameters, an iterative procedure has been followed for designing this integrated array system. It consists of 10 small collectors (2 × 5) with a number of common partitions among themselves. Under identical conditions, any compartment of the integrated array of collectors shows higher thermal efficiency and temperature rise of air compared to that for any exactly similar small collector whose four side edges are directly exposed to the outside environment. The temperature rise and efficiency of the system vary nonlinearly with both air flow rate and collector area. A second degree multiple regression equation has been developed for the present system relating temperature rise to air flow rate and collector area. The performance of the integrated array system also varies with air flow organization. Combined flow organization gives the best performance followed by parallel and series flow organizations. The results of the iterative procedure have been compared with some observed parameters.

Radiation damage study of bipolar devices in x-ray lithography

The radiation damage of bipolar transistors has been investigated using the vacuum ultraviolet (VUV) storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The bipolar devices under investigation were exposed to the x-ray radiation in the range of 1–2 keV. The device parameters were measured before and after irradiation, and were measured again after the devices were annealed in forming gas at 400 °C for 30 min. The study shows that x-ray radiation degrades the common emitter current gain. At small collector currents, the current gain is reduced by about 20%. This change is primarily due to the interface states generated by irradiation at the interface between Si and SiO2 in the base region. Upon annealing, current gain recovers its initial value. The C–V (capacitance–voltage) measurements on MOS capacitors indicate that x-ray radiation increases interface state density from its initial order of magnitude of 1010/cm2 eV to 1012/cm2 eV. The C–V curves also clearly indicate the generation of positive trapped charges in the silicon oxide. Upon annealing, the interface state density is reduced back to its initial value.

Common-emitter current gain of Al/sub x/Ga/sub 1-x/As/GaAs/GaAs heterojunction bipolar transistors operating at small collector current

A recently developed current gain model, which accounts for high-current effects and can adequately characterize the current gain at high collector current, is improved by including both interfacial and bulk space-charge-region recombination currents, resulting in a comprehensive model that predicts the current gain more accurately at small collector currents. Comparison of the model and measured data for an Al/sub 0.25/Ga/sub 0.75//GaAs/GaAs heterojunction bipolar transistor is included in support of the model. >

Introduction of a small dry dust collector for drying drums

Introduction of a small dry dust collector for drying drums

Numerical models of the raingauge exposure problem, field experiments and an improved collector design

AbstractA new design of conventional raingauge is proposed that minimizes the most important source of systematic error in point rainfall measurements: that due to the interaction of the wind with the gauge (the ‘raingauge exposure’ problem). Basic physical principles, numerical simulations and extensive field trials in England and Denmark are also used to provide a consistent quantitative description of the wind‐induced errors of conventional cylindrical gauges.It is shown that an inverted conical collector with a large semi‐vertical angle may provide the basis of an adequate solution of the raingauge exposure problem. The need to minimize outsplash demands that the collector should have a fairly large diameter and take the form of a flat champagne glass. A small diameter flat champagne glass collector has been tested for over 31/2 years against a standard 5′’ cylindrical gauge, a 5′ pit gauge and an inverted conical gauge at the Institute of Hydrology, Wallingford. The insensitivity of the losses of the ‘flat champagne glass’‐shaped collector to wind speed at low rates of rainfall is confirmed, as well as the need for a larger collector diameter to minimize outsplash. A combination of a ‘steep champagne glass’ gauge and a ‘flat champagne glass’ gauge might lead to even better estimates of rainfall in high winds, notably on ships, and could provide a low‐cost approach to improving snowfall measurements on land.

Properties of molecular-beam-epitaxy-grown and O+-implanted GaAs and their application to the formation of a buried collector of an AlGaAs/GaAs heterojunction bipolar transistor

Changes in properties of molecular-beam-epitaxy-grown GaAs by oxygen-ion (O+) implantation and annealing, such as crystallinity, carrier concentration, and sheet resistance, are investigated. Using these results, we developed a method of O+ implantation through an external base area to form a small buried collector and to minimize the product, RbCbc, of the base-collector capacitance Cbc and the base resistance Rb in an AlGaAs/GaAs heterojunction bipolar resistance Rb in an AlGaAs/GaAs heterojunction bipolar transistor (HBT) fabricated by a multiple self-alignment process with one mask. High-frequency properties of HBT’s are improved by this method remarkably.