3,918 research outputs found
Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves
The long-time thermal relaxation of (TMTTF)Br, SrCuO
and SrCaCuO single crystals at temperatures below 1 K
and magnetic field up to 10 T is investigated. The data allow us to determine
the relaxation time spectrum of the low energy excitations caused by the
charge-density wave (CDW) or spin-density wave (SDW). The relaxation time is
mainly determined by a thermal activated process for all investigated
materials. The maximum relaxation time increases with increasing magnetic
field. The distribution of barrier heights corresponds to one or two Gaussian
functions. The doping of SrCaCuO with Ca leads to
a drastic shift of the relaxation time spectrum to longer time. The maximum
relaxation time changes from 50 s (x = 0) to 3000 s (x = 12) at 0.1 K and 10 T.
The observed thermal relaxation at x=12 clearly indicates the formation of the
SDW ground state at low temperatures
Multi-photon effects in energy losses spectra
Effect of radiation of many photons by a single electron traversing a target
is discussed. When the summary energy of emitted photons (the energy losses
spectrum) is measured only, the photon spectrum is distorted comparing with the
photon spectrum in one interaction. Influence of this effect is discussed for
the cases (1) bremsstrahlung (described by Bethe-Heitler formula), (2) the
strong Landau-Pomeranchuk-Migdal effect and (3) transition radiation.
Qualitative picture of the phenomenon is discussed in detail. Comparison with
the recent SLAC experiment in relatively thick target (2.7% of the radiation
length), where the effect of emission of many photons by a projectile is very
essential, shows perfect agreement of the theory and data.Comment: LaTeX2.09, 19 pages, 5 PostScript figure
Inner Polar Rings and Disks: Observed Properties
A list of galaxies with inner regions revealing polar (or strongly inclined
to the main galactic plane) disks and rings is compiled from the literature
data. The list contains 47 galaxies of all morphological types, from E to Irr.
We consider the statistics of the parameters of polar structures known from
observations. The radii of the majority of them do not exceed 1.5 kpc. The
polar structures are equally common in barred and unbarred galaxies. At the
same time, if a galaxy has a bar (or a triaxial bulge), this leads to the polar
disk stabilization - its axis of rotation usually coincides with the major axis
of the bar. More than two thirds of all considered galaxies reveal one or
another sign of recent interaction or merging. This fact indicates a direct
relation between the external environment and the presence of an inner polar
structure.Comment: 12 pages, 3 figures, accepted to Astrophysical Bulletin. Minor
changes and corrections are still possibl
Group Analysis of Variable Coefficient Diffusion-Convection Equations. I. Enhanced Group Classification
We discuss the classical statement of group classification problem and some
its extensions in the general case. After that, we carry out the complete
extended group classification for a class of (1+1)-dimensional nonlinear
diffusion--convection equations with coefficients depending on the space
variable. At first, we construct the usual equivalence group and the extended
one including transformations which are nonlocal with respect to arbitrary
elements. The extended equivalence group has interesting structure since it
contains a non-trivial subgroup of non-local gauge equivalence transformations.
The complete group classification of the class under consideration is carried
out with respect to the extended equivalence group and with respect to the set
of all point transformations. Usage of extended equivalence and correct choice
of gauges of arbitrary elements play the major role for simple and clear
formulation of the final results. The set of admissible transformations of this
class is preliminary investigated.Comment: 25 page
Energy distributions of field emitted electrons from carbon nanosheets: manifestation of the quantum size effect
We emphasize the importance of experiments with voltage dependent field
emission energy distribution analysis in carbon nanosheets. Our analysis shows
the crucial influence of the band structure on the energy distribution of field
emitted electrons in few-layer graphene. In addition to the main peak we found
characteristic sub-peaks in the energy distribution. Their positions strongly
depend on the number of layers and the inter-layer interaction. The discovery
of these peaks in field emission experiments from carbon nanosheets would be a
clear manifestation of the quantum size effect in these new materials.Comment: accepted for publication in JETP Letter
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter
An in-situ calibration of a logarithmic periodic dipole antenna with a
frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of
a radio station system used for detection of cosmic ray induced air showers at
the Engineering Radio Array of the Pierre Auger Observatory, the so-called
Auger Engineering Radio Array (AERA). The directional and frequency
characteristics of the broadband antenna are investigated using a remotely
piloted aircraft (RPA) carrying a small transmitting antenna. The antenna
sensitivity is described by the vector effective length relating the measured
voltage with the electric-field components perpendicular to the incoming signal
direction. The horizontal and meridional components are determined with an
overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} %
respectively. The measurement is used to correct a simulated response of the
frequency and directional response of the antenna. In addition, the influence
of the ground conductivity and permittivity on the antenna response is
simulated. Both have a negligible influence given the ground conditions
measured at the detector site. The overall uncertainties of the vector
effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in
the square root of the energy fluence for incoming signal directions with
zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is
unchanged with respect to v2. 39 pages, 15 figures, 2 table
Measurement of event shapes in deep inelastic scattering at HERA
Inclusive event-shape variables have been measured in the current region of
the Breit frame for neutral current deep inelastic ep scattering using an
integrated luminosity of 45.0 pb^-1 collected with the ZEUS detector at HERA.
The variables studied included thrust, jet broadening and invariant jet mass.
The kinematic range covered was 10 < Q^2 < 20,480 GeV^2 and 6.10^-4 < x < 0.6,
where Q^2 is the virtuality of the exchanged boson and x is the Bjorken
variable. The Q dependence of the shape variables has been used in conjunction
with NLO perturbative calculations and the Dokshitzer-Webber non-perturbative
corrections (`power corrections') to investigate the validity of this approach.Comment: 7+25 pages, 6 figure
Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
We report a multi-resolution search for anisotropies in the arrival
directions of cosmic rays detected at the Pierre Auger Observatory with local
zenith angles up to and energies in excess of 4 EeV ( eV). This search is conducted by measuring the angular power spectrum
and performing a needlet wavelet analysis in two independent energy ranges.
Both analyses are complementary since the angular power spectrum achieves a
better performance in identifying large-scale patterns while the needlet
wavelet analysis, considering the parameters used in this work, presents a
higher efficiency in detecting smaller-scale anisotropies, potentially
providing directional information on any observed anisotropies. No deviation
from isotropy is observed on any angular scale in the energy range between 4
and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no
other deviation from isotropy is observed for moments beyond the dipole one.
The corresponding -values obtained after accounting for searches blindly
performed at several angular scales, are in the case of
the angular power spectrum, and in the case of the needlet
analysis. While these results are consistent with previous reports making use
of the same data set, they provide extensions of the previous works through the
thorough scans of the angular scales.Comment: Published version. Added journal reference and DOI. Added Report
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