173,765 research outputs found
Recommended from our members
Semiparametric estimation for a class of time-inhomogenous diffusion processes
Copyright @ 2009 Institute of Statistical Science, Academia SinicaWe develop two likelihood-based approaches to semiparametrically estimate a class of time-inhomogeneous diffusion processes: log penalized splines (P-splines) and the local log-linear method. Positive volatility is naturally embedded and this positivity is not guaranteed in most existing diffusion models. We investigate different smoothing parameter selections. Separate bandwidths are used for drift and volatility estimation. In the log P-splines approach, different smoothness for different time varying coefficients is feasible by assigning different penalty parameters. We also provide theorems for both approaches and report statistical inference results. Finally, we present a case study using the weekly three-month Treasury bill data from 1954 to 2004. We find that the log P-splines approach seems to capture the volatility dip in mid-1960s the best. We also present an application to calculate a financial market risk measure called Value at Risk (VaR) using statistical estimates from log P-splines
The c-axis charge traveling wave in coupled system of Josephson junctions
We demonstrate a manifestation of the charge traveling wave along the c-axis
(TW) in current voltage characteristics of coupled Josephson junctions in
high- superconductors. The branches related to the TW with different
wavelengths are found for the stacks with different number of Josephson
junctions at different values of system's parameters. Transitions between the
TW branches and the outermost branch are observed. Time dependence of the
electric charge in the superconducting layers and charge-charge correlation
functions for TW and outermost branches show different behavior with bias
current. We propose an experimental testing of the TW by microwave irradiation.Comment: Supplement : http://theor.jinr.ru/~hamdipur/lambda0.av
One-electron spectral functions of the attractive Hubbard model at intermediate coupling
We calculate the one-electron spectral function of the attractive-U Hubbard
model in two dimensions. We work in the intermediate coupling and low density
regime and evaluate analytically the self-energy. The results are obtained in a
framework based on the self-consistent T-matrix approximation. We also
calculate the chemical potential of the bound pairs as a function of
temperature. On the basis of this calculation we analyze the low-temperature
resistivity and specific heat in the normal state of this system. We compare
our results with recent beautiful tunneling experiments in the underdoped
regime of HTSC-materials.Comment: 2 pages, LT22 Conference paper, phbauth and elsart style files
include
Phase diffusion and charging effects in Josephson junctions
The supercurrent of a Josephson junction is reduced by phase diffusion. For
ultrasmall capacitance junctions the current may be further decreased by
Coulomb blockade effects. We calculate the Cooper pair current by means of
time-dependent perturbation theory to all orders in the Josephson coupling
energy and obtain the current-voltage characteristic in closed form in a range
of parameters of experimental interest. The results comprehend phase diffusion
of the coherent Josephson current in the classical regime as well as the
supercurrent peak due to incoherent Cooper pair tunneling in the strong Coulomb
blockade regime.Comment: 4 pages, 3 figures, RevTe
Photodisintegration of light nuclei for testing a correlated realistic interaction in the continuum
An exact calculation of the photodisintegration cross section of 3H, 3He and
4He is performed using as interaction the correlated Argonne V18 potential,
constructed within the Unitary Correlation Operator Method (VUCOM).
Calculations are carried out using the
Lorentz Integral Transform method in conjunction with an hyperspherical
harmonics basis expansion. A comparison with other realistic potentials and
with available experimental data is discussed. The VUCOM potential leads to a
very similar description of the cross section as the Argonne V18 interaction
with the inclusion of the Urbana IX three-body force for photon energies 45< w
< 120 MeV, while larger differences are found close to threshold.Comment: 9 pages, 6 figure
- ā¦