636 research outputs found
Determination of the composition of rarefied neutral atmospheres by mass spectrometers carried on high-speed spacecraft
The quantitative measurement of atomic and molecular O2 in rarefied atmospheres by mass spectrometers onboard high speed spacecraft is reported. Data are also given on instrument performance in high speed molecular beams and in the fly through mode
An explicit model for the adiabatic evolution of quantum observables driven by 1D shape resonances
This paper is concerned with a linearized version of the transport problem
where the Schr\"{o}dinger-Poisson operator is replaced by a non-autonomous
Hamiltonian, slowly varying in time. We consider an explicitly solvable model
where a semiclassical island is described by a flat potential barrier, while a
time dependent 'delta' interaction is used as a model for a single quantum
well. Introducing, in addition to the complex deformation, a further
modification formed by artificial interface conditions, we give a reduced
equation for the adiabatic evolution of the sheet density of charges
accumulating around the interaction point.Comment: latex; 26 page
Optimal non-reversible linear drift for the convergence to equilibrium of a diffusion
We consider non-reversible perturbations of reversible diffusions that do not
alter the invariant distribution and we ask whether there exists an optimal
perturbation such that the rate of convergence to equilibrium is maximized. We
solve this problem for the case of linear drift by proving the existence of
such optimal perturbations and by providing an easily implementable algorithm
for constructing them. We discuss in particular the role of the prefactor in
the exponential convergence estimate. Our rigorous results are illustrated by
numerical experiments
Mass spectrometer with magnetic pole pieces providing the magnetic fields for both the magnetic sector and an ion-type vacuum pump
A mass spectrometer (MS) with unique magnetic pole pieces which provide a homogenous magnetic field across the gap of the MS magnetic sector as well as the magnetic field across an ion-type vacuum pump is disclosed. The pole pieces form the top and bottom sides of a housing. The housing is positioned so that portions of the pole pieces form part of the magnetic sector with the space between them defining the gap region of the magnetic sector, through which an ion beam passes. The pole pieces extend beyond the magnetic sector with the space between them being large enough to accommodate the electrical parts of an ion-type vacuum pump. The pole pieces which provide the magnetic field for the pump, together with the housing form the vacuum pump enclosure or housing
How Dissociated Are Implicit and Explicit Racial Attitudes? A Bogus Pipeline Approach
The current study examined the implicit and explicit attitudes of White Americans toward African-Americans. A variation of the Bogus Pipeline procedure was employed to determine if the apparent dissociation between implicit and explicit measures of racial attitudes that is reported in previous research might be exaggerated. The results indicated that the relationship between implicit and explicit attitudes was only significant under Bogus Pipeline conditions, while implicit and explicit attitudes were largely dissociated when they were measured under normal circumstances. Thus, it appeared that as the motivation to accurately report explicit attitudes increased, the implicit-explicit relationship strengthened and the dissociation between implicit and explicit racial attitudes was substantially reduced. The results indicate that Whites’ implicit and explicit attitudes toward African-Americans may not be as greatly dissociated as some theories of racial attitudes have presumed
Mean field limit for bosons and propagation of Wigner measures
We consider the N-body Schr\"{o}dinger dynamics of bosons in the mean field
limit with a bounded pair-interaction potential. According to the previous work
\cite{AmNi}, the mean field limit is translated into a semiclassical problem
with a small parameter , after introducing an
-dependent bosonic quantization. The limit is expressed as a
push-forward by a nonlinear flow (e.g. Hartree) of the associated Wigner
measures. These object and their basic properties were introduced in
\cite{AmNi} in the infinite dimensional setting. The additional result
presented here states that the transport by the nonlinear flow holds for rather
general class of quantum states in their mean field limit.Comment: 10 page
A study of the feasibility of employing a magnetic mass spectrometer for the analysis of the Martian atmosphere
Magnetic-sector mass spectrometer for Mars atmosphere analysi
Ardis H. Nier, 1921–2009
Ardis Hovland Nier died on December 16, 2009.
Ardis was a great friend of the Meteoritical Society and
endowed its Nier Prize in celebration of the remarkable
contributions of Alfred Nier to meteorite research. She
very much enjoyed meeting many interesting and
friendly people at the society’s meetings. She was by
nature curious, intelligent, and good spirited, and she
tried to find humor and optimism in whatever situation
or condition she faced throughout her 88 years
Vortex distribution in the Lowest Landau Level
We study the vortex distribution of the wave functions minimizing the Gross
Pitaevskii energy for a fast rotating condensate in the Lowest Landau Level
(LLL): we prove that the minimizer cannot have a finite number of zeroes thus
the lattice is infinite, but not uniform. This uses the explicit expression of
the projector onto the LLL. We also show that any slow varying envelope
function can be approximated in the LLL by distorting the lattice. This is used
in particular to approximate the inverted parabola and understand the role of
``invisible'' vortices: the distortion of the lattice is very small in the
Thomas Fermi region but quite large outside, where the "invisible" vortices
lie.Comment: 4 pages, 1 figur
Dynamical phase transition for a quantum particle source
We analyze the time evolution describing a quantum source for noninteracting
particles, either bosons or fermions. The growth behaviour of the particle
number (trace of the density matrix) is investigated, leading to spectral
criteria for sublinear or linear growth in the fermionic case, but also
establishing the possibility of exponential growth for bosons. We further study
the local convergence of the density matrix in the long time limit and prove
the semiclassical limit.Comment: 24 pages; In the new version, we added several references concerning
open quantum systems and present an extended result on linear particle
production in the fermionic cas
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