493 research outputs found
Transverse optical Josephson plasmons, equations of motion
A detailed calculation is presented of the dielectric function in
superconducttors consisting of two Josephson coupled superconducting layers per
unit cell, taking into account the effect of finite compressibility of the
electron fluid. From the model it follows, that two longitudinal, and one
transverse optical Josephson plasma resonance exist in these materials, for
electric field polarization perpendicular to the planes. The latter mode
appears as a resonance in the transverse dielectric function, and it couples
directly to the electrical field vector of infrared radiation. A shift of all
plasma frequencies, and a reduction of the intensity of the transverse optical
Josephson plasmon is shown to result from the finite compressibility of the
electron fluid.Comment: 17 pages, ReVTeX, 7 figures in eps forma
Two-Dimensional Electron Gases at Oxide Interfaces
Two-dimensional electron gases (2DEGs) based on conventional semiconductors such as Si or GaAs have played a pivotal role in fundamental science and technology. The high mobilities achieved in 2DEGs enabled the discovery of the integer and fractional quantum Hall effects and are exploited in high-electron-mobility transistors. Recent work has shown that 2DEGs can also exist at oxide interfaces. These electron gases typically result from reconstruction of the complex electronic structure of the oxides, so that the electronic behavior of the interfaces can differ from the behavior of the bulk. Reports on magnetism and superconductivity in oxide 2DEGs illustrate their capability to encompass phenomena not shown by interfaces in conventional semiconductors. This article reviews the status and prospects of oxide 2DEG
Assessment of Financial Risk Prediction Models with Multi-criteria Decision Making Methods
A wide range of classification models have been explored for financial risk prediction, but conclusions on which technique behaves better may vary when different performance evaluation measures are employed. Accordingly, this paper proposes the use of multiple criteria decision making tools in order to give a ranking of algorithms. More specifically, the selection of the most appropriate credit risk prediction method is here modeled as a multi-criteria decision making problem that involves a number of performance measures (criteria) and classification techniques (alternatives). An empirical study is carried out to evaluate the performance of ten algorithms over six real-life credit risk data sets. The results reveal that the use of a unique performance measure may lead to unreliable conclusions, whereas this situation can be overcome by the application of multi-criteria decision making techniques
Massive stars as thermonuclear reactors and their explosions following core collapse
Nuclear reactions transform atomic nuclei inside stars. This is the process
of stellar nucleosynthesis. The basic concepts of determining nuclear reaction
rates inside stars are reviewed. How stars manage to burn their fuel so slowly
most of the time are also considered. Stellar thermonuclear reactions involving
protons in hydrostatic burning are discussed first. Then I discuss triple alpha
reactions in the helium burning stage. Carbon and oxygen survive in red giant
stars because of the nuclear structure of oxygen and neon. Further nuclear
burning of carbon, neon, oxygen and silicon in quiescent conditions are
discussed next. In the subsequent core-collapse phase, neutronization due to
electron capture from the top of the Fermi sea in a degenerate core takes
place. The expected signal of neutrinos from a nearby supernova is calculated.
The supernova often explodes inside a dense circumstellar medium, which is
established due to the progenitor star losing its outermost envelope in a
stellar wind or mass transfer in a binary system. The nature of the
circumstellar medium and the ejecta of the supernova and their dynamics are
revealed by observations in the optical, IR, radio, and X-ray bands, and I
discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry"
Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna
Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure
Effective Actions and Phase Fluctuations in d-wave Superconductors
We study effective actions for order parameter fluctuations at low
temperature in layered d-wave superconductors such as the cuprates. The order
parameter lives on the bonds of a square lattice and has two amplitude and two
phase modes associated with it. The low frequency spectral weights for
amplitude and relative phase fluctuations is determined and found to be
subdominant to quasiparticle contributions. The Goldstone phase mode and its
coupling to density fluctuations in charged systems is treated in a
gauge-invariant manner. The Gaussian phase action is used to study both the
-axis Josephson plasmon and the more conventional in-plane plasmon in the
cuprates. We go beyond the Gaussian theory by deriving a coarse-grained quantum
XY model, which incorporates important cutoff effects overlooked in previous
studies. A variational analysis of this effective model shows that in the
cuprates, quantum effects of phase fluctuations are important in reducing the
zero temperature superfluid stiffness, but thermal effects are small for .Comment: Some numerical estimates corrected and figures changed. to appear in
PRB, Sept.1 (2000
Mass Splitting and Production of and Measured in N Interactions
From a sample of decaying to the
final state, we have observed, in the hadroproduction experiment E791 at
Fermilab, and through
their decays to . The mass difference ) is measured to be ; for
, we find .
The rate of production from decays of the triplet is
(22\pm 2\pm 3) {%} of the total production assuming equal rate
of production from all three, as measured for and .
We do not observe a statistically significant baryon-antibaryon
production asymmetry. The and spectra of from
decays are observed to be similar to those for all 's
produced.Comment: 15 pages, uuencoded postscript 3 figures uuencoded, tar-compressed
fil
JINGLE – IV. Dust, H I gas and metal scaling laws in the local Universe
Scaling laws of dust, Hi gas and metal mass with stellar mass, specific star formation rate and metallicity are crucial to our understanding of the buildup of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (MHI/M?) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multi-dimensional parameter space. We find that these scaling laws for galaxies with −1.0 . logMHI/M? . 0 can be reproduced using closed-box models with high fractions (37-89%) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (=30-40), and long dust lifetimes (1-2Gyr). The models have present-day dust masses with similar contributions from stellar sources (50-80%) and grain growth (20-50%). Over the entire lifetime of these galaxies, the contribution from stardust (>90%) outweighs the fraction of dust grown in the interstellar medium (<10%). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth timescales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
Measurement of charm production at central rapidity in proton-proton collisions at TeV
The -differential production cross sections of the prompt (B
feed-down subtracted) charmed mesons D, D, and D in the rapidity
range , and for transverse momentum GeV/, were
measured in proton-proton collisions at TeV with the ALICE
detector at the Large Hadron Collider. The analysis exploited the hadronic
decays DK, DK, DD, and their charge conjugates, and was performed on a
nb event sample collected in 2011 with a
minimum-bias trigger. The total charm production cross section at TeV and at 7 TeV was evaluated by extrapolating to the full phase space
the -differential production cross sections at TeV
and our previous measurements at TeV. The results were compared
to existing measurements and to perturbative-QCD calculations. The fraction of
cdbar D mesons produced in a vector state was also determined.Comment: 20 pages, 5 captioned figures, 4 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/307
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