27,224 research outputs found
Detailed design specification for the Yield Estimation Subsystem Data Management System (YESDAMS)
There are no author-identified significant results in this report
Chiral effective theory predictions for deuteron form factor ratios at low Q^2
We use chiral effective theory to predict the deuteron form factor ratio
G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are
calculated to next-to-next-to-leading order. At this order the chiral expansion
for the NN isoscalar charge operator (including consistently calculated 1/M
corrections) is a parameter-free prediction of the effective theory. Use of
this operator in conjunction with NLO and NNLO chiral effective theory wave
functions produces results that are consistent with extant experimental data
for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment
G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance
contributions to this quantity. The variation is of the same size as the
discrepancy between the theoretical result and the experimental value. This
motivates the renormalization of G_Q via a two-nucleon operator that couples to
quadrupole photons. After that renormalization we obtain a robust prediction
for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise,
model-independent predictions for the values of this ratio that will be
measured at the lower end of the kinematic range explored at BLAST. We also
present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure
Muon production in low-energy electron-nucleon and electron-nucleus scattering
Recently, muon production in electron-proton scattering has been suggested as
a possible candidate reaction for the identification of lepton-flavor violation
due to physics beyond the Standard Model. Here we point out that the
Standard-Model processes and can cloud potential beyond-the-Standard-Model signals in
electron-proton collisions. We find that Standard-Model cross
sections exceed those from lepton-flavor-violating operators by several orders
of magnitude. We also discuss the possibility of using a nuclear target to
enhance the signal.Comment: 24 pages. Additional figure showing energy-dependence of total cross
section, minor changes to text. Conclusions unaltered. This version to appear
in Physical Review
X-ray photoelectron spectroscopy measurement of valence-band offsets for Mg-based semiconductor compounds
We have used x-ray photoelectron spectroscopy to measure the valence-band offsets for the lattice matched MgSe/Cd0.54Zn0.46Se and MgTe/Cd0.88Zn0.12Te heterojunctions grown by molecular beam epitaxy. By measuring core level to valence-band maxima and core level to core level binding energy separations, we obtain values of 0.56+/-0.07 eV and 0.43+/-0.11 eV for the valence-band offsets of MgSe/Cd0.54Zn0.46Se and MgTe/Cd0.88Zn0.12Te, respectively. Both of these values deviate from the common anion rule, as may be expected given the unoccupied cation d orbitals in Mg. Application of our results to the design of current II-VI wide band-gap light emitters is discussed
Minimizing Induced Drag with Weight Distribution, Lift Distribution, Wingspan, and Wing-Structure Weight
Because the wing-structure weight required to support the critical wing section bending moments is a function of wingspan, net weight, weight distribution, and lift distribution, there exists an optimum wingspan and wing-structure weight are presented for rectangular wings with four different sets of design constraints. These design constraints are fixed lift distribution and net weight combined with 1) fixed maximum stress and wing loading, 2) fixed maximum deflection and wing loading, 3) fixed maximum stress and stall speed and 4) fixed maximum deflection and stall speed. For each of these analytic solutions, the optimum wing-structure weight is found to depend only on the net weight, independent of the arbitrary fixed lift distribution. Analytic solutions for optimum weight and lift distributions are also presented for the same four sets of design constraints. Depending on the design constraints, the optimum lift distribution can differ significantly from the elliptic lift distribution. Solutions for two example wing designs are presented, which demonstrate how the induced drag varies with lift distribution, wingspan, and wing-structure weight in the design space near the optimum solution. Although the analytic solutions presented here are restricted to rectangular wings, these solutions provide excellent test cases for verifying numerical algorithms used for more general multidisciplinary analysis and optimization
A Direct Measurement of the Total Gas Column Density in Orion KL
The large number of high-J lines of C^(18)O available via the Herschel Space Observatory provide an unprecedented ability to model the total CO column density in hot cores. Using the emission from all the observed lines (up to J = 15-14), we sum the column densities in each individual level to obtain the total column after correcting for the population in the unobserved states. With additional knowledge of source size, V_(LSR), and line width, and both local thermodynamic equilibrium (LTE) and non-LTE modeling, we have determined the total C^(18)O column densities in the Extended Ridge, Outflow/Plateau, Compact Ridge, and Hot Core components of Orion KL to be 1.4 × 10^(16) cm^(–2), 3.5 × 10^(16) cm^(–2), 2.2 × 10^(16) cm^(–2), and 6.2 × 10^(16) cm^(–2), respectively. We also find that the C^(18)O/C^(17)O abundance ratio varies from 1.7 in the Outflow/Plateau, 2.3 in the Extended Ridge, 3.0 in the Hot Core, and to 4.1 in the Compact Ridge. This is in agreement with models in which regions with higher ultraviolet radiation fields selectively dissociate C^(17)O, although care must be taken when interpreting these numbers due to the size of the uncertainties in the C^(18)O/C^(17)O abundance ratio
The slowly expanding envelope of CRL618 probed with HC3N rotational ladders
Lines from HC3N and isotopic substituted species in ground and vibrationally
excited states produce crowded millimeter and submillimeter wave spectra in the
C-rich protoplanetary nebula CRL618. The complete sequence of HC3N rotational
lines from J=9-8 to J=30-29 has been observed with the IRAM 30m telescope
toward this object. Lines from a total of 15 different vibrational states
(including the fundamental), with energies up to 1100 cm^-1, have been detected
for the main HC3N isotopomer. In addition, the CSO telescope has been used to
complement this study in the range J=31-30 to J=39-38, with detections in five
of these states, all of them below 700 cm^-1. Vibrationally excited HC3N
rotational lines exhibit P-Cygni profiles at 3 mm, evolving to pure emission
lineshapes at shorter wavelengths. This evolution of the line profile shows
little dependence on the vibrational state from which they rotational lines
arise. The absorption features are formed against the continuum emission, which
has been successfully characterized in this work due to the large frequency
coverage. The HC3N column density in front of the the continuum source has been
determined by comparing the output of an array of models to the data. The best
fits are obtained for column densities in the range 2.0-3.5 10$^17 cm^-2,
consistent with previous estimates from ISO data, and TK in the range 250 to
275 K, in very good agreement with estimates made from the same ISO data.Comment: 24 pages, 7 figures, accepted in ApJ part I (Jul. 8, 2004
Elastic energy of polyhedral bilayer vesicles
In recent experiments [M. Dubois, B. Dem\'e, T. Gulik-Krzywicki, J.-C.
Dedieu, C. Vautrin, S. D\'esert, E. Perez, and T. Zemb, Nature (London) Vol.
411, 672 (2001)] the spontaneous formation of hollow bilayer vesicles with
polyhedral symmetry has been observed. On the basis of the experimental
phenomenology it was suggested [M. Dubois, V. Lizunov, A. Meister, T.
Gulik-Krzywicki, J. M. Verbavatz, E. Perez, J. Zimmerberg, and T. Zemb, Proc.
Natl. Acad. Sci. U.S.A. Vol. 101, 15082 (2004)] that the mechanism for the
formation of bilayer polyhedra is minimization of elastic bending energy.
Motivated by these experiments, we study the elastic bending energy of
polyhedral bilayer vesicles. In agreement with experiments, and provided that
excess amphiphiles exhibiting spontaneous curvature are present in sufficient
quantity, we find that polyhedral bilayer vesicles can indeed be energetically
favorable compared to spherical bilayer vesicles. Consistent with experimental
observations we also find that the bending energy associated with the vertices
of bilayer polyhedra can be locally reduced through the formation of pores.
However, the stabilization of polyhedral bilayer vesicles over spherical
bilayer vesicles relies crucially on molecular segregation of excess
amphiphiles along the ridges rather than the vertices of bilayer polyhedra.
Furthermore, our analysis implies that, contrary to what has been suggested on
the basis of experiments, the icosahedron does not minimize elastic bending
energy among arbitrary polyhedral shapes and sizes. Instead, we find that, for
large polyhedron sizes, the snub dodecahedron and the snub cube both have lower
total bending energies than the icosahedron
DiFX2: A more flexible, efficient, robust and powerful software correlator
Software correlation, where a correlation algorithm written in a high-level
language such as C++ is run on commodity computer hardware, has become
increasingly attractive for small to medium sized and/or bandwidth constrained
radio interferometers. In particular, many long baseline arrays (which
typically have fewer than 20 elements and are restricted in observing bandwidth
by costly recording hardware and media) have utilized software correlators for
rapid, cost-effective correlator upgrades to allow compatibility with new,
wider bandwidth recording systems and improve correlator flexibility. The DiFX
correlator, made publicly available in 2007, has been a popular choice in such
upgrades and is now used for production correlation by a number of
observatories and research groups worldwide. Here we describe the evolution in
the capabilities of the DiFX correlator over the past three years, including a
number of new capabilities, substantial performance improvements, and a large
amount of supporting infrastructure to ease use of the code. New capabilities
include the ability to correlate a large number of phase centers in a single
correlation pass, the extraction of phase calibration tones, correlation of
disparate but overlapping sub-bands, the production of rapidly sampled
filterbank and kurtosis data at minimal cost, and many more. The latest version
of the code is at least 15% faster than the original, and in certain situations
many times this value. Finally, we also present detailed test results
validating the correctness of the new code.Comment: 28 pages, 9 figures, accepted for publication in PAS
Time scale separation and heterogeneous off-equilibrium dynamics in spin models over random graphs
We study analytically and numerically the statics and the off-equilibrium
dynamics of spin models over finitely connected random graphs. We identify a
threshold value for the connectivity beyond which the loop structure of the
graph becomes thermodynamically relevant. Glauber dynamics simulations show
that this loop structure is responsible for the onset of dynamical features of
a local character (dynamical heterogeneities and spontaneous time scale
separation), consistently with previous (experimental and numerical) studies of
glasses and spin glasses in their approach to the low temperature phase.Comment: 5 pages, latex, 2 postscript figure
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