25,963 research outputs found
Algorithm for astronomical, point source, signal to noise ratio calculations
An algorithm was developed to simulate the expected signal to noise ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point source signal to noise ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument
Design and development criteria for metal bellows
Experimental research describes fluid flow and the fluid-elastic mechanism causing bellows flow excitation, and aids in design of conventional bellows liner which suppresses flow-induced vibrations. Analytical models facilitate prediction of flow excitation occurrence and estimation of severity of bellows vibrations
On high-order pressure-robust space discretisations, their advantages for incompressible high Reynolds number generalised Beltrami flows and beyond
An improved understanding of the divergence-free constraint for the
incompressible Navier--Stokes equations leads to the observation that a
semi-norm and corresponding equivalence classes of forces are fundamental for
their nonlinear dynamics. The recent concept of {\em pressure-robustness}
allows to distinguish between space discretisations that discretise these
equivalence classes appropriately or not. This contribution compares the
accuracy of pressure-robust and non-pressure-robust space discretisations for
transient high Reynolds number flows, starting from the observation that in
generalised Beltrami flows the nonlinear convection term is balanced by a
strong pressure gradient. Then, pressure-robust methods are shown to outperform
comparable non-pressure-robust space discretisations. Indeed, pressure-robust
methods of formal order are comparably accurate than non-pressure-robust
methods of formal order on coarse meshes. Investigating the material
derivative of incompressible Euler flows, it is conjectured that strong
pressure gradients are typical for non-trivial high Reynolds number flows.
Connections to vortex-dominated flows are established. Thus,
pressure-robustness appears to be a prerequisite for accurate incompressible
flow solvers at high Reynolds numbers. The arguments are supported by numerical
analysis and numerical experiments.Comment: 43 pages, 18 figures, 2 table
A gas flow indicator for portable life support systems
A three-part program was conducted to develop a gas flow indicator (GFI) to monitor ventilation flow in a portable life support system. The first program phase identified concepts which could potentially meet the GFI requirements. In the second phase, a working breadboard GFI, based on the concept of a pressure sensing diaphragm-aneroid assembly connected to a venturi, was constructed and tested. Extensive testing of the breadboard GFI indicated that the design would meet all NASA requirements including eliminating problems experienced with the ventilation flow sensor used in the Apollo program. In the third program phase, an optimized GFI was designed by utilizing test data obtained on the breadboard unit. A prototype unit was constructed using prototype materials and fabrication techniques, and performance tests indicated that the prototype GFI met or exceeded all requirements
A Guide to Disability Statistics from the Panel Study of Income Dynamics
This User Guide provides information on the Panel Study of Income Dynamics (PSID). The 2003 PSID is a nationally representative sample of over 7,000 families. The PSID began in 1968 with a sample of 4,800 families and re-interviewed these families on an annual basis from 1968-1997. Since then, it has re-interviewed them biennially. Following the same families and individuals since 1968, the PSID collects data on economic, health, and social behavior. (See http://psidonline.isr.umich.edu/ for detailed information on the PSID).
Initially, the PSID identified disability by asking the head of the household whether he, or she when no adult male is present, had a physical or nervous condition that limits his or her ability to work. In 1981 the PSID began asking the head this question with respect to his spouse. Additional questions that provide an opportunity to expand this definition of disability were included in 2003. The User Guide makes use of these new questions to estimate the size of the population with disabilities and the prevalence rate of disability in the population, as well as the employment rate and level of economic well-being.
The major strength of the PSID for those interested in disability research is its long-running information on families. No other nationally representative survey has captured such detailed information on the same families over such a long time. Such longitudinal data allows researchers to better understand the dynamics of the disability process and its consequences. Here we demonstrate the comparative advantage of the PSID over traditional cross-sectional data sets. Using the PSID, we identify persons with disabilities of various lengths and show the sensitivity of alternative definitions of the population with disabilities based on the duration of a disability. We also measure how the employment and economic well-being of individuals changes following the onset of a disability. Finally, we provide examples of how the PSID has been used with the German Socio-Economic Panel (GSOEP) to compare the employment and economic well-being of working-age people with disabilities in the United States and Germany. This analysis uses the equivalized data from these longitudinal datasets contained in the Cornell University Cross-National Equivalent File (CNEF)
Energies of Quantum QED Flux Tubes
In this talk I present recent studies on vacuum polarization energies and
energy densities induced by QED flux tubes. I focus on comparing three and four
dimensional scenarios and the discussion of various approximation schemes in
view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona,
Sept. 2005. To appear in the proceeding
Partially Unbiased Entangled Bases
In this contribution we group the operator basis for d^2 dimensional Hilbert
space in a way that enables us to relate bases of entangled states with single
particle mutually unbiased state bases (MUB), each in dimensionality d. We
utilize these sets of operators to show that an arbitrary density matrix for
this d^2 dimensional Hilbert space system is analyzed by via d^2+d+1
measurements, d^2-d of which involve those entangled states that we associate
with MUB of the d-dimensional single particle constituents. The number
lies in the middle of the number of measurements needed for bipartite
state reconstruction with two-particle MUB (d^2+1) and those needed by
single-particle MUB [(d^2+1)^2].Comment: 5 page
A statistical mechanics model for free-for-all airplane passenger boarding
I present and discuss a model for the free-for-all passenger boarding which
is employed by some discount air carriers. The model is based on the principles
of statistical mechanics where each seat in the aircraft has an associated
energy which reflects the preferences of the population of air travelers. As
each passenger enters the airplane they select their seats using Boltzmann
statistics, proceed to that location, load their luggage, sit down, and the
partition function seen by remaining passengers is modified to reflect this
fact. I discuss the various model parameters and make qualitative comparisons
of this passenger boarding model with models which involve assigned seats. This
model can also be used to predict the probability that certain seats will be
occupied at different times during the boarding process. These results may be
of value to industry professionals as a useful description of this boarding
method. However, it also has significant value as a pedagogical tool since it
is a relatively unusual application of undergraduate level physics and it
describes a situation with which many students and faculty may be familiar.Comment: version 1: 4 pages 2 figures version 2: 7 pages with 5 figure
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