166 research outputs found
CONDUCTIVITY OF LAYERED STRUCTURES WITH A STRONGLY DEGENERATE ELECTRON GAS
The conductivity of periodical multilayer structures with a degenerate electron gas is calculated. It is shown that for smooth tunnelly transparent barriers the resistivity of structure coincides with the corresponding value of
the bulk material. In the presence of a random potential at the interface
between the layers, the conductivity of the system decreases with the increase of a ratio of the mean free path to the period of the structure.Обчислена електропровiднiсть перiодичних багатошарових структур
з виродженим електронним газом. Показано, що для гладких тунельно прозорих бар’єрiв опiр структури спiвпадає з вiдповiдним значенням для об’ємного матерiалу. У випадку, коли на границях роздiлу iснує випадковий розсiюючий потенцiал, провiднiсть системи зменшується зi збiльшенням вiдношення довжини вiльного пробiгу електронiв до перiоду структури
Conductivity of layered structures with a strongly degenerate electron gas
The conductivity of periodical multilayer structures with a degenerate electron gas is calculated. It is shown that for smooth tunnelly transparent barriers the resistivity of structure coincides with the corresponding value of
the bulk material. In the presence of a random potential at the interface
between the layers, the conductivity of the system decreases with the increase of a ratio of the mean free path to the period of the structure.Обчислена електропровiднiсть перiодичних багатошарових структур
з виродженим електронним газом. Показано, що для гладких тунельно прозорих бар’єрiв опiр структури спiвпадає з вiдповiдним значенням для об’ємного матерiалу. У випадку, коли на границях роздiлу iснує випадковий розсiюючий потенцiал, провiднiсть системи зменшується зi збiльшенням вiдношення довжини вiльного пробiгу електронiв до перiоду структури
SU Aur: A deep fading event in Visible and near-infrared bands
In three seasons of 2015-2018 we carried out a series of visible and near
infrared (NIR) photometry of SU Aur. In course of this photometric monitoring
we detected an event of a deep fading of the star in spring of 2018. In this
paper we present preliminary analysis of our photometry.Comment: 4 pages, 2 figure
The formation of planetary disks and winds: an ultraviolet view
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure
About Bianchi I with VSL
In this paper we study how to attack, through different techniques, a perfect
fluid Bianchi I model with variable G,c and Lambda, but taking into account the
effects of a -variable into the curvature tensor. We study the model under
the assumption,div(T)=0. These tactics are: Lie groups method (LM), imposing a
particular symmetry, self-similarity (SS), matter collineations (MC) and
kinematical self-similarity (KSS). We compare both tactics since they are quite
similar (symmetry principles). We arrive to the conclusion that the LM is too
restrictive and brings us to get only the flat FRW solution. The SS, MC and KSS
approaches bring us to obtain all the quantities depending on \int c(t)dt.
Therefore, in order to study their behavior we impose some physical
restrictions like for example the condition q<0 (accelerating universe). In
this way we find that is a growing time function and Lambda is a decreasing
time function whose sing depends on the equation of state, w, while the
exponents of the scale factor must satisfy the conditions
and
, i.e. for all equation of state relaxing in this way the
Kasner conditions. The behavior of depends on two parameters, the equation
of state and a parameter that controls the behavior of
therefore may be growing or decreasing.We also show that through
the Lie method, there is no difference between to study the field equations
under the assumption of a var affecting to the curvature tensor which the
other one where it is not considered such effects.Nevertheless, it is essential
to consider such effects in the cases studied under the SS, MC, and KSS
hypotheses.Comment: 29 pages, Revtex4, Accepted for publication in Astrophysics & Space
Scienc
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Assessing the viability of successful reconstruction of the dynamics of dark energy using varying fundamental couplings
We assess the viability of successful reconstruction of the evolution of the
dark energy equation of state using varying fundamental couplings, such as the
fine structure constant or the proton-to-electron mass ratio. We show that the
same evolution of the dark energy equation of state parameter with cosmic time
may be associated with arbitrary variations of the fundamental couplings.
Various examples of models with the same (different) background evolution and
different (the same) time variation of fundamental couplings are studied in the
letter. Although we demonstrate that, for a broad family of models, it is
possible to redefine the scalar field in such a way that its dynamics is that
of a standard quintessence scalar field, in general such redefinition leads to
the breakdown of the linear relation between the scalar field and the variation
of fundamental couplings. This implies that the assumption of a linear coupling
is not sufficient to guarantee a successful reconstruction of the dark energy
dynamics and consequently additional model dependent assumptions about the
scalar field responsible for the dark energy need to be made.Comment: 7 pages, 2 figures, published versio
Measurement of the View the tt production cross-section using eμ events with b-tagged jets in pp collisions at √s = 13 TeV with the ATLAS detector
This paper describes a measurement of the inclusive top quark pair production cross-section (σtt¯) with a data sample of 3.2 fb−1 of proton–proton collisions at a centre-of-mass energy of √s = 13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron–muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously σtt¯ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be:
σtt¯ = 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb,
where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented
Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at sqrt [ s ] = 13TeV
A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb−1 of proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at √s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions
The performance of the jet trigger for the ATLAS detector during 2011 data taking
The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton–proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon–nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction
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