346 research outputs found
Crossover from Luttinger liquid to Coulomb blockade regime in carbon nanotubes
We develop a theoretical approach to the low-energy properties of 1D electron
systems aimed to encompass the mixed features of Luttinger liquid and Coulomb
blockade behavior observed in the crossover between the two regimes. For this
aim we extend the Luttinger liquid description by incorporating the effects of
a discrete single-particle spectrum. The intermediate regime is characterized
by a power-law behavior of the conductance, but with an exponent oscillating
with the gate voltage, in agreement with recent experimental observations. Our
construction also accounts naturally for the existence of a crossover in the
zero-bias conductance, mediating between two temperature ranges where the
power-law behavior is preserved but with different exponent.Comment: 5 pages, 3 figure
Az alvĂĄsidĆ felmĂ©rĂ©se MagyarorszĂĄgon Ă©s RomĂĄniĂĄban Ă©lĆ iskolĂĄskorĂș gyermekek körĂ©ben
Introduction: Children's sleep duration is decreasing in the last decade. Despite of the well known negative consequences, there are no data on children's sleep duration in Hungary and Romania. Aim: The aim of the authors was to assess sleep duration of school-age children in Hungary and Romania. Method: A self-edited questionnaire was used for the study. 2446 children were enrolled. All elementary and secondary schools in a Hungarian city, and one elementary and secondary school in a Romanian city took part in the study. Results: Mean sleep duration was 8.3+/-1.2 hours on weekdays. There was a significant difference between the two countries (Hungary vs. Romania, 8.5+/-1.2 hours vs. 7.8+/-0.9 hours, p = 0.001). Age correlated with sleep duration on weekdays (r= -0.605, p = 0.001), but not during weekend. Conclusions: this is the first study on children's sleep duration in Hungary and Romania. The difference between countries may be due to the difference in mean age or cultural and/or geographical differences. Orv. Hetil., 2013, 154, 1592-1596
Coulomb Gaps in One-Dimensional Spin-Polarized Electron Systems
We investigate the density of states (DOS) near the Fermi energy of
one-dimensional spin-polarized electron systems in the quantum regime where the
localization length is comparable to or larger than the inter-particle
distance. The Wigner lattice gap of such a system, in the presence of weak
disorder, can occur precisely at the Fermi energy, coinciding with the Coulomb
gap in position. The interplay between the two is investigated by treating the
long-range Coulomb interaction and the random disorder potential in a
self-consistent Hartree-Fock approximation. The DOS near the Fermi energy is
found to be well described by a power law whose exponent decreases with
increasing disorder strength.Comment: 4 pages, revtex, 4 figures, to be published in Phys. Rev. B as a
Rapid Communicatio
Enhanced Local Moment Formation in a Chiral Luttinger Liquid
We derive here a stability condition for a local moment in the presence of an
interacting sea of conduction electrons. The conduction electrons are modeled
as a Luttinger liquid in which chirality and spin are coupled. We show that an
Anderson-U defect in such an interacting system can be transformed onto a
nearly-Fermi liquid problem. We find that correlations among the conduction
electrons stabilize the local moment phase. A Schrieffer-Wolff transformation
is then performed which results in an anisotropic exchange interaction
indicative of the Kondo effect in a Luttinger liquid. The ground-state
properties of this model are then equivalent to those of the Kondo model in a
Luttinger liquid.Comment: 11 pages, no figure
Spin-charge separation at small lengthscales in the 2D t-J model
We consider projected wavefunctions for the 2D model. For various
wavefunctions, including correlated Fermi-liquid and Luttinger-type
wavefunctions we present the static charge-charge and spin-spin structure
factors. Comparison with recent results from a high-temperature expansion by
Putikka {\it et al.} indicates spin-charge separation at small lengthscales.Comment: REVTEX, 5 pages, 5 figures hardcopies availabl
Renormalization group approach to Fermi Liquid Theory
We show that the renormalization group (RG) approach to interacting fermions
at one-loop order recovers Fermi liquid theory results when the forward
scattering zero sound (ZS) and exchange (ZS) channels are both taken into
account. The Landau parameters are related to the fixed point value of the
``unphysical'' limit of the forward scattering vertex. We specify the
conditions under which the results obtained at one-loop order hold at all order
in a loop expansion. We also emphasize the similarities between our RG approach
and the diagrammatic derivation of Fermi liquid theory.Comment: 4 pages (RevTex) + 1 postcript file, everything in a uuencoded file,
uses epsf (problem with the figure in the first version
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Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR
DC745 is a commercially available silicone elastomer consisting of dimethyl, methylphenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is generally considered to age gracefully and to be resistant to chemical and thermally harsh environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static {sup 1}H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. {sup 1}H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. {sup 1}H multiple quantum NMR was used to assess changes in the network structure and observed the presence of a bimodal distribution of residual dipolar couplings, <{Omega}{sub d}>, that were dose dependent. The domain with the lower <{Omega}{sub d}> has been assigned to the polymer network while the domain with the higher <{Omega}{sub d}> has been assigned to polymer chains interacting with the inorganic filler surfaces. In samples exposed to radiation, the residual dipolar couplings in both reservoirs were observed to increase and the populations were observed to be dose dependent. The NMR results are compared to Differential Scanning Calorimetry (DSC) and a two-step solvent swelling technique. The solvent swelling data lend support to the interpretation of the NMR results and the DSC data show both a decrease in the melt temperature and the heat of fusion with cumulative dose, consistent with radiative crosslinking. In addition, DSC thermograms obtained following a 3 hr isothermal soak at -40 C showed the presence of a second melt feature at T{sub m} {approx} -70 C consistent with a network domain with significantly reduced segmental motion
Quasi-Particles in Two-Dimensional Hubbard Model: Splitting of Spectral Weight
It is shown that the energy and momentum dependences of
the electron self-energy function are, where is some
constant, being the band energy,
and the critical exponent , which depends on the curvature of the
Fermi surface at , satisfies, . This leads to a
new type of electron liquid, which is the Fermi liquid in the limit of but for has a split
one-particle spectra as in the Tomonaga-Luttinger liquid.Comment: 8 pages (LaTeX) 4 figures available upon request will be sent by air
mail. KomabaCM-preprint-O
Coulomb gap in one-dimensional disordered electron systems
The density of states of one-dimensional disordered electron systems with
long range Coulomb interaction is studied in the weak pinning limit. The
density of states is found to follow a power law with an exponent determined by
localization length, and this power law behavior is consistent with the
existing numerical results.Comment: RevTeX4 file, 5 pages, no figures To appear in Physical Reviews
Renormalization group study of interacting electrons
The renormalization-group (RG) approach proposed earlier by Shankar for
interacting spinless fermions at is extended to the case of non-zero
temperature and spin. We study a model with -invariant short-range
effective interaction and rotationally invariant Fermi surface in two and three
dimensions. We show that the Landau interaction function of the Fermi liquid,
constructed from the bare parameters of the low-energy effective action, is RG
invariant. On the other hand, the physical forward scattering vertex is found
as a stable fixed point of the RG flow. We demonstrate that in and 3, the
RG approach to this model is equivalent to Landau's mean-field treatment of the
Fermi liquid. We discuss subtleties associated with the symmetry properties of
the scattering amplitude, the Landau function and the low-energy effective
action. Applying the RG to response functions, we find the compressibility and
the spin susceptibility as fixed points.Comment: 11 pages, RevTeX 3.0, 2 PostScript figure
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