7,710 research outputs found
Restoration of isotropy on fractals
We report a new type of restoration of macroscopic isotropy (homogenization)
in fractals with microscopic anisotropy. The phenomenon is observed in various
physical setups, including diffusions, random walks, resistor networks, and
Gaussian field theories. The mechanism is unique in that it is absent in spaces
with translational invariance, while universal in that it is observed in a wide
class of fractals.Comment: 11 pages, REVTEX, 3 postscript figures. (Compressed and encoded
figures archived by "figure" command). To appear in Physical Review Letter
Non-Fermi liquid, unscreened scalar chirality and parafermions in a frustrated tetrahedron Anderson model
We investigate a four-impurity Anderson model where localized orbitals are
located at vertices of a regular tetrahedron and find a novel fixed point in
addition to the ordinary Fermi liquid phase. That is characterized by
unscreened scalar chirality of a tetrahedron. In this phase, parafermions
emerges in the excitation spectrum and quasiparticle mass diverges as 1/|T
log^3 T| at low temperatures (T). The diverging effective mass is a
manifestation of singular Fermi liquid states as in the underscreened Kondo
problem. Between the two phases, our Monte Carlo results show the existence of
a non Fermi liquid critical point where the Kondo effects and the intersite
antiferromagnetic interactions are valanced. Singular behaviors are prominent
in the dynamics and we find that the frequency (omega) dependence of the
self-energy (Sigma) is the marginal Fermi liquid like, -Im Sigma \sim |omega|.Comment: 7 pages, 4 figures, 1 table, published versio
Flow properties of concentrated suspensions
The viscosity and flow behavior of a concentrated suspension, with special emphasis on fresh concrete containing a superplasticizer, is analyzed according to Newton's law of viscosity. The authors interpreted Newton's law in a new way, and explain non-Newton flow from Newton's law. The outline of this new theory is given. Viscosity of suspensions, and the effect of dispersants are analyzed
Quantum impurity in a Tomonaga-Luttinger liquid: continuous-time quantum Monte Carlo approach
We develop a continuous-time quantum Monte Carlo (CTQMC) method for quantum
impurities coupled to interacting quantum wires described by a
Tomonaga-Luttinger liquid. The method is negative-sign free for any values of
the Tomonaga-Luttinger parameter, which is rigorously proved, and thus,
efficient low-temperature calculations are possible. Duality between electrons
and bosons in one dimensional systems allows us to construct a simple formula
for the CTQMC algorithm in these systems. We show that the CTQMC for
Tomonaga-Luttinger liquids can be implemented with only minor modifications of
previous CTQMC codes developed for impurities coupled to non-interacting
fermions. We apply this method to the Kane-Fisher model of a potential
scatterer in a spin-less quantum wire and to a single spin coupled with the
edge state of a two-dimensional topological insulator assuming an anisotropic
XXZ coupling. Various dynamical response functions such as the electron Green's
function and spin-spin correlation functions are calculated numerically and
their scaling properties are discussed.Comment: 15 pages, 11 figure
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 , we
find that 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
Effective Hamiltonian of Three-orbital Hubbard Model on Pyrochlore Lattice: Application to LiV_2O_4
We investigate heavy fermion behaviors in the vanadium spinel LiV_2O_4. We
start from a three-orbital Hubbard model on the pyrochlore lattice and derive
its low-energy effective Hamiltonian by an approach of real-space
renormalization group type. One important tetrahedron configuration in the
rochlore lattice has a three-fold orbital degeneracy and spin S=1, and
correspondingly, the effective Hamiltonian has spin and orbital exchange
interactions of Kugel-Khomskii type as well as correlated electron hoppings.
Analyzing the effective Hamiltonian, we find that ferromagnetic double exchange
processes compete with antiferromagnetic superexchange processes and various
spin and orbital exchange processes are competing to each other. These results
suggest the absence of phase transition in spin and orbital spaces down to very
low temperatures and their large fluctuations in the low-energy sector, which
are key issues for understanding the heavy fermion behavior in LiV_2O_4.Comment: 26 pages, 26 figure
Perception and production of English /r/-/l/ by adult Japanese speakers
This dissertation examines perception and production of English /r/-/l/ by adult Japanese speakers. This programme of research is organized into three sections, termed Study 1, Study2, and Study 3. The first study examined whether category assimilation between English /r/-/l/ and Japanese /ɾ/ was predictive of /r/-/l/ identification accuracy using an individual difference approach. Japanese speakers were assessed in terms of /r/-/l/ identification and assimilation of English /r/-/l/ into Japanese /ɾ/, /r/-/l/ production, and perceptual best exemplars for /r/, /l/, and /ɾ/. The results demonstrated that, although Japanese speakers strongly assimilated /l/ to /ɾ/, category assimilation was not predictive of English /r/-/l/ identification accuracy, and that only Japanese speaker’s representations for F3 in /r/ and /l/ was predictive of /r/-/l/ identification ability. The second study similarly took an individual difference approach and examined whether there is a relationship between perception and production of /r/-/l/ measuring perception accuracies (i.e., identification, discrimination, and perceptual best exemplars) and production accuracies (i.e., acoustic measurements, and recognition accuracy by English speakers). The results demonstrated that perception and production of /r/-/l/ were moderately related. However, not all aspects of /r/-/l/ perception were incorporated into /r/-/l/ production. The third study examined whether one-to-one pronunciation training leads to improvement in production and perception of English /r/-/l/ using a multipronged approach (i.e., explicit instructions, real-time spectrograms, and feedback with signal-processed versions of their own productions). The results demonstrated that Japanese speakers could be trained to produce native-like English /r/-/l/, improving to the point that they approached a 100% accuracy ceiling in terms of how well native speakers could identify their productions. However, the training did not improve their English /r/-/l/ perception at all
Spin Susceptibility in the Superconducting state of Ferromagnetic Superconductor UCoGe
In order to determine the superconducting paring state in the ferromagnetic
superconductor UCoGe, ^{59}Co NMR Knight shift, which is directly related to
the microscopic spin susceptibility, was measured in the superconducting state
under magnetic fields perpendicular to spontaneous magnetization axis:
^{59}K^{a, b}. ^{59}K^{a, b} shows to be constant, but does not decrease below
a superconducting transition. These behaviors as well as the invariance of the
internal field at the Co site in the superconducting state exclude the
spin-singlet pairing, and can be interpreted with the equal-spin pairing state
with a large exchange field along the c axis, which was studied by Mineev
[Phys. Rev. B 81, 180504 (2010)].Comment: 5 pages, 4 figures, to be appear in PR
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