1,223 research outputs found

### Electron Mass Enhancement due to Anharmonic Local Phonons

In order to understand how electron effective mass is enhanced by anharmonic
local oscillation of an atom in a cage composed of other atoms, i.e., {\it
rattling}, we analyze anharmonic Holstein model by using a Green's function
method. Due to the evaluation of an electron mass enhancement factor $Z$, we
find that $Z$ becomes maximum when zero-point energy is comparable with
potential height at which the amplitude of oscillation is rapidly enlarged.
Cooperation of such quantum and rattling effects is considered to be a key
issue to explain the electron mass enhancement in electron-rattling systems.Comment: 3 pages, 3 figures, to appear in J. Phys. Soc. Jpn. Suppl.
(Proceedings for International Conference on Heavy Electrons

### Shock propagation through a bubbly liquid in a deformable tube

Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid–structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments
are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure
on the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves
in a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds

### Realization of Strong Coupling Fixed Point in Multilevel Kondo Models

Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen

### Electric Dipolar Susceptibility of the Anderson-Holstein Model

The temperature dependence of electric dipolar susceptibility \chi_P is
discussed on the basis of the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) technique. Note that P is related with
phonon Green's function D. In order to obtain correct temperature dependence of
P at low temperatures, we propose a method to evaluate P through the Dyson
equation from charge susceptibility \chi_c calculated by the NRG, in contrast
to the direct NRG calculation of D. We find that the irreducible charge
susceptibility estimated from \chi_c agree with the perturbation calculation,
suggesting that our method works well.Comment: 4 pages, 4 figure

### Kondo Effect in an Electron System with Dynamical Jahn-Teller Impurity

We investigate how Kondo phenomenon occurs in the Anderson model dynamically
coupled with local Jahn-Teller phonons. It is found that the total angular
moment composed of electron pseudo-spin and phonon angular moments is screened
by conduction electrons. Namely, phonon degrees of freedom essentially
contribute to the formation of singlet ground state. A characteristic
temperature of the Kondo effect due to dynamical Jahn-Teller phonons is
explained by an effective $s$-$d$ Hamiltonian with anisotropic exchange
interaction obtained from the Jahn-Teller-Anderson model in a non-adiabatic
region.Comment: 5 pages, 3 figure

### Universality in heavy-fermion systems with general degeneracy

We discuss the relation between the T^{2}-coefficient of electrical
resistivity $A$ and the T-linear specific-heat coefficient $\gamma$ for
heavy-fermion systems with general $N$, where $N$ is the degeneracy of
quasi-particles. A set of experimental data reveals that the Kadowaki-Woods
relation; $A/\gamma^{2} = 1*10^{-5} {\mu\Omega}(K mol/mJ)^{2}$, collapses
remarkably for large-N systems, although this relation has been regarded to be
commonly applicable to the Fermi-liquids. Instead, based on the Fermi-liquid
theory we propose a new relation; $\tilde{A}/\tilde{\gamma}^2=1\times10^{-5}$
with $\tilde{A} = A/(1/2)N(N-1)$ and $\tilde{\gamma} = \gamma/(1/2)N(N-1)$.
This new relation exhibits an excellent agreement with the data for whole the
range of degenerate heavy-fermions.Comment: 2 figures, to appear in Phys. Rev. Let

### Signal Detection Performance of Overlapped FFT Scheme with Additional Frames Consisting of Non-continuous Samples in Indoor Environment

Overlapped FFT has been proposed as a signal detection scheme in dynamic spectrum access to reduce the variance of the noise and improve the detection probability. However, the improvement of the detection probability in the conventional overlapped FFT is bounded with the upper limit of the overlap ratio. This paper proposes a new overlapped FFT scheme using additional frames. In the proposed scheme, in addition to the original FFT frames, new frames that consist of multiple subframes with non-continuous samples are constructed and included. It can realize the increase of the number of the FFT frames and the improvement of the detection probability compared with the conventional scheme. Numerical results through computer simulation show that the proposed scheme improves the detection probability by up to 0.07. On indoor channel models the proposed scheme also improves the detection probability. In addition, it is clarified that as the delay spread increases the detection probability reduces due to the correlation between the frames

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