4,521 research outputs found
Incoherent pion photoproduction on the deuteron with polarization observables I: Formal expressions
Formal expressions are developed for the general five-fold differential cross
section of incoherent -photoproduction on the deuteron including beam and
target polarization. The polarization observables of the cross section are
described by various beam, target and beam-target asymmetries for polarized
photons and/or polarized deuterons. They are given as bilinear hermitean forms
in the reaction matrix elements divided by the unpolarized cross section. In
addition, the corresponding observables for the semi-exclusive reaction are also given.Comment: 11 pages, 1 figur
Annihilation of edge dislocations in smectic A liquid crystals
This paper presents a theoretical study of the annihilation of edge dislocations in the same smectic plane in a bulk smectic-A phase. We use a time-dependent Landau-Ginzburg approach where the smectic ordering is described by the complex order parameter psi( r--> ,t) =eta e(iphi) . This quantity allows both the degree of layering and the position of the layers to be monitored. We are able to follow both precollision and postcollision regimes, and distinguish different early and late behaviors within these regimes. The early precollision regime is driven by changes in the phi ( r--> ) configuration. The relative velocity of the defects is approximately inversely proportional to the interdefect separation distance. In the late precollision regime the symmetry changes within the cores of defects also become influential. Following the defect collision, in the early postcollision stage, bulk layer order is approached exponentially in time. At very late times, however, there seems to be a long-time power-law tail in the order parameter fluctuation relaxation
NbS: A unique quasi one-dimensional conductor with three charge density wave transitions
Through transport, compositional and structural studies, we review the
features of the charge-density wave (CDW) conductor of NbS (phase II). We
highlight three central results: 1) In addition to the previously reported CDW
transitions at = 360\,K and = 150\,K, another CDW transition
occurs at a much higher temperature = 620-650\,K; evidence for the
non-linear conductivity of this CDW is presented. 2) We show that CDW
associated with the - transition arises from S vacancies acting as
donors. Such a CDW transition has not been observed before. 3) We show
exceptional coherence of the -CDW at room-temperature. Additionally, we
report on the effects of uniaxial strain on the CDW transition temperatures and
transport.Comment: 16 pages, 18 figure
Phase formation and relaxor properties of lead-free perovskite ceramics on the base of sodium-bismuth titanate
The work was supported by the Russian Foundation for Basic Research (Projects 16-53-48009, 17-03-00542)
Depth-dependent scaling of axial distances in light microscopy
In volume fluorescence microscopy, refractive index matching is essential to minimize aberrations. There are, however, common imaging scenarios where a refractive index mismatch (RIM) between immersion and a sample medium cannot be avoided. This RIM leads to an axial deformation in the acquired image data. Over the years, different axial scaling factors have been proposed to correct for this deformation. While some reports have suggested a depth-dependent axial deformation, so far none of the scaling theories has accounted for a depth-dependent, non-linear scaling. Here, we derive an analytical theory based on determining the leading constructive interference band in the objective lens pupil under RIM. We then use this to calculate a depth-dependent re-scaling factor as a function of the numerical aperture (NA), the refractive indices n1 and n2, and the wavelength λ. We compare our theoretical results with wave-optics calculations and experimental results obtained using a measurement scheme for different values of NA and RIM. As a benchmark, we recorded multiple datasets in different RIM conditions, and corrected these using our depth-dependent axial scaling theory. Finally, we present an online web applet that visualizes the depth-dependent axial re-scaling for specific optical setups. In addition, we provide software that will help microscopists to correctly re-scale the axial dimension in their imaging data when working under RIM
A separation of electrons and protons in the GAMMA-400 gamma-ray telescope
The GAMMA-400 gamma-ray telescope is intended to measure the fluxes of gamma
rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to
several TeV. Such measurements concern with the following scientific goals:
search for signatures of dark matter, investigation of gamma-ray point and
extended sources, studies of the energy spectra of Galactic and extragalactic
diffuse emission, studies of gamma-ray bursts and gamma-ray emission from the
active Sun, as well as high-precision measurements of spectra of high-energy
electrons and positrons, protons, and nuclei up to the knee. The main
components of cosmic rays are protons and helium nuclei, whereas the part of
lepton component in the total flux is ~10E-3 for high energies. In present
paper, the capability of the GAMMA-400 gamma-ray telescope to distinguish
electrons and positrons from protons in cosmic rays is investigated. The
individual contribution to the proton rejection is studied for each detector
system of the GAMMA-400 gamma-ray telescope. Using combined information from
all detector systems allow us to provide the proton rejection from electrons
with a factor of ~4x10E5 for vertical incident particles and ~3x10E5 for
particles with initial inclination of 30 degrees. The calculations were
performed for the electron energy range from 50 GeV to 1 TeV.Comment: 19 pages, 10 figures, submitted to Advances and Space Researc
The GAMMA-400 space observatory: status and perspectives
The present design of the new space observatory GAMMA-400 is presented in
this paper. The instrument has been designed for the optimal detection of gamma
rays in a broad energy range (from ~100 MeV up to 3 TeV), with excellent
angular and energy resolution. The observatory will also allow precise and high
statistic studies of the electron component in the cosmic rays up to the multi
TeV region, as well as protons and nuclei spectra up to the knee region. The
GAMMA-400 observatory will allow to address a broad range of science topics,
like search for signatures of dark matter, studies of Galactic and
extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission,
gamma-ray bursts and charged cosmic rays acceleration and diffusion mechanism
up to the knee
Surface Deposition and Imaging of Large Ag Clusters Formed in He Droplets
The utility of a continuous beam of He droplets for the assembly and surface
deposition of Ag clusters, ~ 300 - 6 000, is studied with transmission
electron microscopy. Images of the clusters on amorphous carbon substrates
obtained at short deposition times have provided for a measure of the size
distribution of the metal clusters. The average sizes of the deposited clusters
are in good agreement with an energy balance based estimate of Ag cluster
growth in He droplets. Measurements of the deposition rate indicate that upon
impact with the surface the He-embedded cluster is attached with high
probability. The stability of the deposited clusters on the substrate is
discussed.Comment: 24 pages, 5 figure
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