50,946 research outputs found
Prediction of gas leakage of environmental control systems
Mathematical models of leakage configurations and various flow theories are presented with the substantive experimental test data to provide background material for future design and failure analysis. Normal-rate leakage and emergency, high-rate leakage are considered
Hole tunneling times in GaAs/AlAs double-barrier structures
We have calculated hole tunneling times in GaAs/AlAs double-barrier structures taking quantum well band-mixing effects into account. Our results indicate that for sufficiently high hole temperatures and concentrations, band-mixing effects reduce average hole tunneling times from the pure heavy hole value to values comparable to electron tunneling times in the same structure. For very low hole temperatures and concentrations, band mixing is less important and average hole tunneling times should approach the pure heavy hole value. These results provide an explanation for previously reported experimental results in which electrons and holes were found to be characterized by very similar tunneling times
Strategy for designing broadband epsilon-near-zero metamaterial with loss compensation by gain media
A strategy is proposed to design the broadband gain-doped epsilon-near-zero
(GENZ) metamaterial. Based on the Milton representation of effective
permittivity, the strategy starts in a dimensionless spectral space, where the
effective permittivity of GENZ metamaterial is simply determined by a pole-zero
structure corresponding to the operating frequency range. The physical
structure of GENZ metamaterial is retrieved from the pole-zero structure via a
tractable inverse problem. The strategy is of great advantage in practical
applications and also theoretically reveals the cancellation mechanism
dominating the broadband near-zero permittivity phenomenon in the spectral
space
Legacy data and cosmological constraints from the angular-size/redshift relation for ultra-compact radio sources
We have re-examined an ancient VLBI survey of ultra-comact radio sources at
2.29 GHz, which gave fringe amplitudes for 917 such objects with total flux
density >0.5 Jy approximately. A number of cosmological investigations based
upon this survey have been published in recent years. We have updated the
sample with respect to both redshift and radio information, and now have full
data for 613 objects, significantly larger than the number (337) used in
earlier investigations. The corresponding angular-size/redshift diagram gives
Omega_m=0.25+0.04/-0.03, Omega_\Lambda=0.97+0.09/-0.13 and K=0.22+0.07/-0.10.
In combination with supernova data, and a simple-minded approach to CMB data
based upon the angular size of the acoustic horizon, our best figures are
Omega_m=0.298+0.025/-0.024, Omega_\Lambda=0.702+0.035/-0.036 and K=
0.000+0.021/-0.019. We have examined simple models of dynamical vacuum energy;
the first, based upon a scalar potential V(phi)=omega_C^2 phi^2/2, gives
w(0)=-1.00+0.06/-0.00, (dw/dz)_0=+0.00/-0.08; in this case conditions at z=0
require particular attention, to preclude behaviour in which phi becomes
singular as z -->infinity. For fixed w limits are w=-1.20+0.15/-0.14. The above
error bars are 68% confidence limits.Comment: 24 pages, 9 figure
Electron tunneling time measured by photoluminescence excitation correlation spectroscopy
The tunneling time for electrons to escape from the lowest quasibound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 and 62 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≈12 ps) to 34 Å(≈800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy hole carrier densities are observed to decay at the same rate, indicating a coupling between the two decay processes
Mammographic image restoration using maximum entropy deconvolution
An image restoration approach based on a Bayesian maximum entropy method
(MEM) has been applied to a radiological image deconvolution problem, that of
reduction of geometric blurring in magnification mammography. The aim of the
work is to demonstrate an improvement in image spatial resolution in realistic
noisy radiological images with no associated penalty in terms of reduction in
the signal-to-noise ratio perceived by the observer. Images of the TORMAM
mammographic image quality phantom were recorded using the standard
magnification settings of 1.8 magnification/fine focus and also at 1.8
magnification/broad focus and 3.0 magnification/fine focus; the latter two
arrangements would normally give rise to unacceptable geometric blurring.
Measured point-spread functions were used in conjunction with the MEM image
processing to de-blur these images. The results are presented as comparative
images of phantom test features and as observer scores for the raw and
processed images. Visualization of high resolution features and the total image
scores for the test phantom were improved by the application of the MEM
processing. It is argued that this successful demonstration of image
de-blurring in noisy radiological images offers the possibility of weakening
the link between focal spot size and geometric blurring in radiology, thus
opening up new approaches to system optimization.Comment: 18 pages, 10 figure
Amplified Dispersive Fourier-Transform Imaging for Ultrafast Displacement Sensing and Barcode Reading
Dispersive Fourier transformation is a powerful technique in which the
spectrum of an optical pulse is mapped into a time-domain waveform using
chromatic dispersion. It replaces a diffraction grating and detector array with
a dispersive fiber and single photodetector. This simplifies the system and,
more importantly, enables fast real-time measurements. Here we describe a novel
ultrafast barcode reader and displacement sensor that employs
internally-amplified dispersive Fourier transformation. This technique
amplifies and simultaneously maps the spectrally encoded barcode into a
temporal waveform. It achieves a record acquisition speed of 25 MHz -- four
orders of magnitude faster than the current state-of-the-art.Comment: Submitted to a journa
Architectural design of an Algol interpreter
The design of a syntax-directed interpreter for a subset of Algol is described. It is a conceptual design with sufficient details and completeness but as much independence of implementation as possible. The design includes a detailed description of a scanner, an analyzer described in the Floyd-Evans productions, a hash-coded symbol table, and an executor. Interpretation of sample programs is also provided to show how the interpreter functions
Reply to Comment on "Reevaluation of the parton distribution of strange quarks in the nucleon"
A Comment on the recently published reevaluation of the polarization-averaged
parton distribution of strange quarks in the nucleon using final data on the
multiplicities of charged kaons in semi-inclusive deep-inelastic scattering is
reviewed. Important features of the comparison of one-dimensional projections
of the multidimensional HERMES data are pointed out. A test of the
leading-order extraction of xS(x) using the difference between charged-kaon
multiplicities is repeated. The results are consistent with leading-order
predictions within the uncertainties in the input data, and do not invalidate
the earlier extraction of xS(x).Comment: Reply Comment to arXiv:1407.372
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