13,206 research outputs found
Improvement of Fourier Polarimetry for applications in tomographic photoelasticity
The use of the Fourier Polarimetry method has been demonstrated to extract the three characteristic parameters in integrated photoelasticity. In contrast to the phase-stepping method, it has been shown that the Fourier method is more accurate. However, the Fourier method isn't very efficient as it requires that a minimum of nine intensity images be collected during a whole revolution of a polarizer while the phase-stepping method only needs six intensity images. In this paper the Fourier transformation is used to derive the expression for determination of the characteristic parameters. Four Fourier coefficients are clearly identified to calculate the three characteristic parameters. It is found that the angular rotation ratio could be set arbitrarily. The angular rotation ratio is optimized to satisfy the requirements of efficiency and proper data accuracy, which results in data collection about three times faster than the methods suggested by previous researchers. When comparing their performance in terms of efficiency and accuracy, the simulated and experimental results show that these angular rotation ratios have the same accuracy but the optimized angular rotation ratio is significantly faster. The sensitivity to noise is also investigated and further improvement of accuracy is suggested
Simulating the impact of the Smith Cloud
We investigate the future evolution of the Smith Cloud by performing
hydrodynamical simulations of the cloud impact onto the gaseous Milky Way
Galactic disk. We assume a local origin for the cloud and thus do not include a
dark matter component to stabilize it. Our main focus is the cloud's influence
on the local and global star formation rate (SFR) of the Galaxy and whether or
not it leads to an observable event in the far future. Our model assumes two
extremes for the mass of the Smith Cloud, an upper mass limit of 10
M and a lower mass limit of 10 M, compared to the
observational value of a few 10 M. In addition, we also make the
conservative assumption that the entirety of the cloud mass of the extended
Smith Cloud is concentrated within the tip of the cloud. We find that the
impact of the low-mass cloud produces no noticeable change in neither the
global SFR nor the local SFR at the cloud impact site within the galactic disk.
For the high-mass cloud we find a short-term (roughly 5 Myr) increase of the
global SFR of up to 1 M yr, which nearly doubles the normal
Milky Way SFR. This highly localized starburst should be observable.Comment: 14 pages, 5 figure
Relationship of management factors with prevalence of respiratory problems in beira antelope (Dorcotragus megalotis)
Most of the Beira antelopes (Dorcatragus megalotis) that ever lived at Al Wabra Wildlife Preservation (AWWP) showed respiratory signs and since winter 2005/2006 many Beiras have diedfrom a Fibrinous Pleuropneumonia Syndrome (FPPS) with Mycoplasma spp. as suspectedcausative agent. Neither therapies with different drugs nor vaccinations yielded a sustained success against the respiratory disease so far. This study aimed to test if there is a relationship between management factors and the prevalence of respiratory problems, in order to find indications whether changes in management might decrease the risk of respiratory diseases. For this reason, environmental factors such as temperature and humidity as well as individual appearance (coughing, nasal discharge etc.) and feeding of vitamin/mineral supplements were recorded daily for over a year. There was a noticeable increase of affected Beiras during winter months
Signatures of few-body resonances in finite volume
We study systems of bosons and fermions in finite periodic boxes and show how
the existence and properties of few-body resonances can be extracted from
studying the volume dependence of the calculated energy spectra. Using a
plane-wave-based discrete variable representation to conveniently implement
periodic boundary conditions, we establish that avoided level crossings occur
in the spectra of up to four particles and can be linked to the existence of
multi-body resonances. To benchmark our method we use two-body calculations,
where resonance properties can be determined with other methods, as well as a
three-boson model interaction known to generate a three-boson resonance state.
Finding good agreement for these cases, we then predict three-body and
four-body resonances for models using a shifted Gaussian potential. Our results
establish few-body finite-volume calculations as a new tool to study few-body
resonances. In particular, the approach can be used to study few-neutron
systems, where such states have been conjectured to exist.Comment: 13 pages, 10 figures, 2 tables, published versio
Is a Trineutron Resonance Lower in Energy than a Tetraneutron Resonance?
We present quantum Monte Carlo calculations of few-neutron systems confined
in external potentials based on local chiral interactions at
next-to-next-to-leading order in chiral effective field theory. The energy and
radial densities for these systems are calculated in different external
Woods-Saxon potentials. We assume that their extrapolation to zero
external-potential depth provides a quantitative estimate of three- and
four-neutron resonances. The validity of this assumption is demonstrated by
benchmarking with an exact diagonalization in the two-body case. We find that
the extrapolated trineutron resonance, as well as the energy for shallow well
depths, is lower than the tetraneutron resonance energy. This suggests that a
three-neutron resonance exists below a four-neutron resonance in nature and is
potentially measurable. To confirm that the relative ordering of three- and
four-neutron resonances is not an artifact of the external confinement, we test
that the odd-even staggering in the helium isotopic chain is reproduced within
this approach. Finally, we discuss similarities between our results and
ultracold Fermi gases.Comment: 6 pages, 5 figures, version compatible with published lette
Ascent control studies of the 049 and ATP parallel burn solid rocket motor shuttle configurations
The control authority approach is discussed as a major problem of the parallel burn soil shuttle configuration due to the many resulting system impacts regardless of the approach. The major trade studies and their results, which led to the recommendation of an SRB TVC control authority approach are presented
Molecular Weight Dependence of Polymersome Membrane Elasticity and Stability
Vesicles prepared in water from a series of diblock copolymers and termed
"polymersomes" are physically characterized. With increasing molecular weight
, the hydrophobic core thickness for the self-assembled bilayers
of polyethyleneoxide - polybutadiene (PEO-PBD) increases up to 20 -
considerably greater than any previously studied lipid system. The mechanical
responses of these membranes, specifically, the area elastic modulus and
maximal areal strain are measured by micromanipulation. As expected
for interface-dominated elasticity, ( 100 ) is found to be
independent of . Related mean-field ideas also predict a limiting
value for which is universal and about 10-fold above that typical of
lipids. Experiments indeed show generally increases with
, coming close to the theoretical limit before stress relaxation is
opposed by what might be chain entanglements at the highest . The
results highlight the interfacial limits of self-assemblies at the nano-scale.Comment: 16 pages, 5 figures, and 1 tabl
Analytic structure and power-series expansion of the Jost function for the two-dimensional problem
For a two-dimensional quantum mechanical problem, we obtain a generalized
power-series expansion of the S-matrix that can be done near an arbitrary point
on the Riemann surface of the energy, similarly to the standard effective range
expansion. In order to do this, we consider the Jost-function and analytically
factorize its momentum dependence that causes the Jost function to be a
multi-valued function. The remaining single-valued function of the energy is
then expanded in the power-series near an arbitrary point in the complex energy
plane. A systematic and accurate procedure has been developed for calculating
the expansion coefficients. This makes it possible to obtain a semi-analytic
expression for the Jost-function (and therefore for the S-matrix) near an
arbitrary point on the Riemann surface and use it, for example, to locate the
spectral points (bound and resonant states) as the S-matrix poles. The method
is applied to a model simlar to those used in the theory of quantum dots.Comment: 42 pages, 9 figures, submitted to J.Phys.
Potential Energy Surface for H_2 Dissociation over Pd(100)
The potential energy surface (PES) of dissociative adsorption of H_2 on
Pd(100) is investigated using density functional theory and the full-potential
linear augmented plane wave (FP-LAPW) method. Several dissociation pathways are
identified which have a vanishing energy barrier. A pronounced dependence of
the potential energy on ``cartwheel'' rotations of the molecular axis is found.
The calculated PES shows no indication of the presence of a precursor state in
front of the surface. Both results indicate that steering effects determine the
observed decrease of the sticking coefficient at low energies of the H_2
molecules. We show that the topology of the PES is related to the dependence of
the covalent H(s)-Pd(d) interactions on the orientation of the H_2 molecule.Comment: RevTeX, 8 pages, 5 figures in uufiles forma
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