899 research outputs found
Multiple scattering of matter waves: an analytic model of the refractive index for atomic and molecular gases
We present an analytic model of the refractive index for matter waves
propagating through atomic or molecular gases. The model, which combines a WKB
treatment of the long range attraction with the Fraunhofer model treatment of
the short range repulsion, furnishes a refractive index in compelling agreement
with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)]
on Li atom matter waves passing through dilute noble gases. We show that the
diffractive contribution, which arises from scattering by a two dimensional
"hard core" of the potential, is essential for obtaining a correct imaginary
part of the refractive index.Comment: 5 pages, 1 figure, 2 table
An analytic model of rotationally inelastic collisions of polar molecules in electric fields
We present an analytic model of thermal state-to-state rotationally inelastic
collisions of polar molecules in electric fields. The model is based on the
Fraunhofer scattering of matter waves and requires Legendre moments
characterizing the "shape" of the target in the body-fixed frame as its input.
The electric field orients the target in the space-fixed frame and thereby
effects a striking alteration of the dynamical observables: both the phase and
amplitude of the oscillations in the partial differential cross sections
undergo characteristic field-dependent changes that transgress into the partial
integral cross sections. As the cross sections can be evaluated for a field
applied parallel or perpendicular to the relative velocity, the model also
offers predictions about steric asymmetry. We exemplify the field-dependent
quantum collision dynamics with the behavior of the Ne-OCS() and
Ar-NO() systems. A comparison with the close-coupling calculations
available for the latter system [Chem. Phys. Lett. \textbf{313}, 491 (1999)]
demonstrates the model's ability to qualitatively explain the field dependence
of all the scattering features observed
Quasiparticle Interference on the Surface of Topological Crystalline Insulator Pb(1-x)Sn(x)Se
Topological crystalline insulators represent a novel topological phase of
matter in which the surface states are protected by discrete point
group-symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy
is one possible realization of this phase which undergoes a topological phase
transition upon changing the lead content. We used scanning tunneling
microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe
the surface states on (001) PbSnSe in the topologically
non-trivial (x=0.23) and topologically trivial (x=0) phases. We observed
quasiparticle interference with STM on the surface of the topological
crystalline insulator and demonstrated that the measured interference can be
understood from ARPES studies and a simple band structure model. Furthermore,
our findings support the fact that PbSnSe and PbSe have
different topological nature.Comment: 5 pages, 4 figure
The nonlinear time-dependent response of isotactic polypropylene
Tensile creep tests, tensile relaxation tests and a tensile test with a
constant rate of strain are performed on injection-molded isotactic
polypropylene at room temperature in the vicinity of the yield point. A
constitutive model is derived for the time-dependent behavior of
semi-crystalline polymers. A polymer is treated as an equivalent network of
chains bridged by permanent junctions. The network is modelled as an ensemble
of passive meso-regions (with affine nodes) and active meso-domains (where
junctions slip with respect to their positions in the bulk medium with various
rates). The distribution of activation energies for sliding in active
meso-regions is described by a random energy model. Adjustable parameters in
the stress--strain relations are found by fitting experimental data. It is
demonstrated that the concentration of active meso-domains monotonically grows
with strain, whereas the average potential energy for sliding of junctions and
the standard deviation of activation energies suffer substantial drops at the
yield point. With reference to the concept of dual population of crystalline
lamellae, these changes in material parameters are attributed to transition
from breakage of subsidiary (thin) lamellae in the sub-yield region to
fragmentation of primary (thick) lamellae in the post-yield region of
deformation.Comment: 29 pages, 12 figure
High-Energy Approach for Heavy-Ion Scattering with Excitations of Nuclear Collective States
A phenomenological optical potential is generalized to include the Coulomb
and nuclear interactions caused by the dynamical deformation of its surface. In
the high-energy approach analytical expressions for elastic and inelastic
scattering amplitudes are obtained where all the orders in the deformation
parameters are included. The multistep effect of the 2 rotational state
excitation on elastic scattering is analyzed. Calculations of inelastic cross
sections for the O ions scattered on different nuclei at about hundred
Mev/nucleon are compared with experimental data, and important role of the
Coulomb excitation is established.Comment: 9 pages; 3 figures. Submitted to the Physics of Atomic Nucle
Quasiparticle interference on the surface of the topological crystalline insulator Pb_(1−x)Sn_xSe
Topological crystalline insulators represent a novel topological phase of matter in which the surface states are protected by discrete point group symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy is one possible realization of this phase, which undergoes a topological phase transition upon changing the lead content. We used scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe the surface states on (001) Pb_(1−x)Sn_xSe in the topologically nontrivial (x=0.23) and topologically trivial (x=0) phases. We observed quasiparticle interference with STM on the surface of the topological crystalline insulator and demonstrated that the measured interference can be understood from ARPES studies and a simple band structure model. Furthermore, our findings support the fact that Pb_(0.77)Sn_(0.23)Se and PbSe have different topological nature
Short-range oscillators in power-series picture
A class of short-range potentials on the line is considered as an
asymptotically vanishing phenomenological alternative to the popular confining
polynomials. We propose a method which parallels the analytic Hill-Taylor
description of anharmonic oscillators and represents all our Jost solutions
non-numerically, in terms of certain infinite hypergeometric-like series. In
this way the well known solvable Rosen-Morse and scarf models are generalized.Comment: 23 pages, latex, submitted to J. Phys. A: Math. Ge
Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations
Abstract The dual-spacecraft Van Allen Probes mission has provided a new window into mega electron volt (MeV) particle dynamics in the Earth\u27s radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different timescales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization and abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 ± 0.5). This reveals graphically that both competing mechanisms of multi-MeV electron energization are at play in the radiation belts, often acting almost concurrently or at least in rapid succession. Key Points Clear observations to higher energy than ever before Precise detection of where and how acceleration takes place Provides new eyes on megaelectron Volt
ПОВЫШЕНИЕ КАЧЕСТВА ШАРЖИРОВАНИЯ ПОВЕРХНОСТИ НАКАТНЫМ РОЛИКОМ ПУТЕМ СООБЩЕНИЯ ЕМУ УЛЬТРАЗВУКОВЫХ КОЛЕБАНИЙ
The paper contains results of experimental investigations reflecting the impact of technological and acoustic parameters on abrasive ability and resistance period of diamond-containing coating. Such coating has been obtained on the disk surface as a result of its charging with a knurling tool under normal conditions and imparting ultrasonic oscillations to it. Приведены результаты экспериментальных исследований, отражающие влияние технологических и акустических параметров на абразивную способность и период стойкости алмазосодержащего покрытия, полученного на поверхности диска в результате его шаржирования накатным роликом в обычных условиях и при сообщении ему ультразвуковых колебаний
Early Observations and Analysis of the Type Ia SN 2014J in M82
We present optical and near infrared (NIR) observations of the nearby Type Ia
SN 2014J. Seventeen optical and twenty-three NIR spectra were obtained from 10
days before (10d) to 10 days after (+10d) the time of maximum -band
brightness. The relative strengths of absorption features and their patterns of
development can be compared at one day intervals throughout most of this
period. Carbon is not detected in the optical spectra, but we identify CI
1.0693 in the NIR spectra. We find that MgII lines with high
oscillator strengths have higher initial velocities than other MgII lines. We
show that the velocity differences can be explained by differences in optical
depths due to oscillator strengths. The spectra of SN 2014J show it is a normal
SN Ia, but many parameters are near the boundaries between normal and
high-velocity subclasses. The velocities for OI, MgII, SiII, SII, CaII and FeII
suggest that SN 2014J has a layered structure with little or no mixing. That
result is consistent with the delayed detonation explosion models. We also
report photometric observations, obtained from 10d to +29d, in the
and bands. SN 2014J is about 3 magnitudes fainter than a normal SN Ia at
the distance of M82, which we attribute to extinction in the host. The template
fitting package SNooPy is used to interpret the light curves and to derive
photometric parameters. Using = 1.46, which is consistent with previous
studies, SNooPy finds that for mag.
The maximum -band brightness of mag was reached on
February 1.74 UT days and the supernova had a decline parameter of
mag.Comment: 6 figures, 6 tables, submitted to the Ap
- …