10,654 research outputs found
Printed circuit board with bellows rivet connection Patent
Electrical connection for printed circuits on common board, using bellows principle in rive
Coupled Mode Theory of Electron‐Beam Parametric Amplification
A theory of parametric amplification in a filamentary electron beam by transverse fields is developed in coupled mode form. Space charge effects are neglected. In addition to beam modes at the signal frequency, beam modes at frequencies ωn=ω+ω_p, n=0, ±1, ±2…, where ω_p is the pump frequency, are coupled together. A discussion of the general form of the equations is given and reveals the circumstances under which exponential gain or periodic energy transfer between various modes can occur. When applied to quadrupole electric pump fields, a description of the quadrupole amplifiers of Adler, Wade, and Gordon is obtained. This theory is then used to evaluate the noise contribution from synchronous beam modes and higher cyclotron idler modes. Coupling by axially symmetric electric fields and by axially symmetric magnetic fields is discussed, and other amplification schemes suggested. The theory of coupling by axially symmetric fields can also be used to study lens effects on noise in the gun region
Annual league tables of mortality in neonatal intensive care units: longitudinal study. International Neonatal Network and the Scottish Neonatal Consultants and Nurses Collaborative Study Group.[see comment]
OBJECTIVE: To assess whether crude league tables of mortality and league tables of risk adjusted mortality accurately reflect the performance of hospitals.
DESIGN: Longitudinal study of mortality occurring in hospital.
SETTING: 9 neonatal intensive care units in the United Kingdom.
SUBJECTS: 2671 very low birth weight or preterm infants admitted to neonatal intensive care units between 1988 and 1994.
MAIN OUTCOME MEASURES: Crude hospital mortality and hospital mortality adjusted using the clinical risk index for babies (CRIB) score.
RESULTS: Hospitals had wide and overlapping confidence intervals when ranked by mortality in annual league tables; this made it impossible to discriminate between hospitals reliably. In most years there was no significant difference between hospitals, only random variation. The apparent performance of individual hospitals fluctuated substantially from year to year.
CONCLUSIONS: Annual league tables are not reliable indicators of performance or best practice; they do not reflect consistent differences between hospitals. Any action prompted by the annual league tables would have been equally likely to have been beneficial, detrimental, or irrelevant. Mortality should be compared between groups of hospitals using specific criteria-such as differences in the volume of patients, staffing policy, training of staff, or aspects of clinical practice-after adjusting for risk. This will produce more reliable estimates with narrower confidence intervals, and more reliable and rapid conclusions
Zero field spin polarization in a 2D paramagnetic resonant tunneling diode
We study I-V characteristics of an all-II-VI semiconductor resonant tunneling
diode with dilute magnetic impurities in the quantum well layer. Bound magnetic
polaron states form in the vicinity of potential fluctuations at the well
interface while tunneling electrons traverse these interface quantum dots. The
resulting microscopic magnetic order lifts the degeneracy of the resonant
tunneling states. Although there is no macroscopic magnetization, the resulting
resonant tunneling current is highly spin polarized at zero magnetic field due
to the zero field splitting. Detailed modeling demonstrates that the local spin
polarization efficiency exceeds 90% without an external magnetic field.Comment: 7 pages, 10 figures (including supplementary information
Local magnetic divertor for control of the plasma-limiter interaction in a tokamak
An experiment is described in which plasma flow to a tokamak limiter is controlled through the
use of a local toroidal divertor coil mounted inside the limiter itself. This coil produces a local
perturbed field B_C approximately equal to the local unperturbed toroidal field B_T ≃ 3 kG, such
that when B_C adds to B_T the field lines move into the limiter and the local plasma flow to it
increases by a factor as great as 1.6, and when B_C subtracts from B_T the field lines move away
from the limiter and the local plasma flow to it decreases by as much as a factor of 4. A simple
theoretical model is used to interpret these results. Since these changes occur without significantly
affecting global plasma confinement, such a control scheme may be useful for optimizing the
performance of pumped limiters
Development of processes for the production of solar grade silicon from halides and alkali metals, phase 1 and phase 2
High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment
Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)
We have investigated the growth by molecular-beam epitaxy of the II-VI
diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates.
The growth start has been optimized by using low-temperature epitaxy. Surface
properties were assessed by Nomarski and scanning electron microscopy. Optical
properties of (Zn,Mn)Se have been studied by photoluminescence and a giant
Zeeman splitting of up to 30 meV has been observed. Our observations indicate a
high crystalline quality of the epitaxial films.Comment: To be published in Applied Physics Letter
Simulation of the Burridge-Knopoff Model of Earthquakes with Variable Range Stress Transfer
Simple models of earthquake faults are important for understanding the
mechanisms for their observed behavior, such as Gutenberg-Richter scaling and
the relation between large and small events, which is the basis for various
forecasting methods. Although cellular automaton models have been studied
extensively in the long-range stress transfer limit, this limit has not been
studied for the Burridge-Knopoff model, which includes more realistic friction
forces and inertia. We find that the latter model with long-range stress
transfer exhibits qualitatively different behavior than both the long-range
cellular automaton models and the usual Burridge-Knopoff model with nearest
neighbor springs, depending on the nature of the velocity-weakening friction
force. This result has important implications for our understanding of
earthquakes and other driven dissipative systems.Comment: 4 pages, 5 figures, published on Phys. Rev. Let
Large magnetoresistance effect due to spin-injection into a non-magnetic semiconductor
A novel magnetoresistance effect, due to the injection of a spin-polarized
electron current from a dilute magnetic into a non-magnetic semiconductor, is
presented. The effect results from the suppression of a spin channel in the
non-magnetic semiconductor and can theoretically yield a positive
magnetoresistance of 100%, when the spin flip length in the non-magnetic
semiconductor is sufficiently large. Experimentally, our devices exhibit up to
25% magnetoresistance.Comment: 3 figures, submitted for publicatio
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