37,048 research outputs found
Undulatory swimming in fluids with polymer networks
The motility behavior of the nematode Caenorhabditis elegans in polymeric
solutions of varying concentrations is systematically investigated in
experiments using tracking and velocimetry methods. As the polymer
concentration is increased, the solution undergoes a transition from the
semi-dilute to the concentrated regime, where these rod-like polymers entangle,
align, and form networks. Remarkably, we find an enhancement in the nematode's
swimming speed of approximately 65% in concentrated solutions compared to
semi-dilute solutions. Using velocimetry methods, we show that the undulatory
swimming motion of the nematode induces an anisotropic mechanical response in
the fluid. This anisotropy, which arises from the fluid micro-structure, is
responsible for the observed increase in swimming speed.Comment: Published 1 November 2013 in Europhysics Letter
Symmetry of the Gap in Bi2212 from Photoemission Spectroscopy
In a recent Letter, Shen et al have detected a large anisotropy of the
superconducting gap in Bi2212, consistent with d-wave symmetry, from
photoemission spectroscopy. Moreover, they claim that the change in their
spectra as a function of aging is also consistent with such an intrepretation.
In this Comment, I show that the latter statement is not entirely correct, in
that the data as a function of aging are inconsistent with a d-wave gap but are
consistent with an anisotropic s-wave gap.Comment: 3 pages (Plain TeX with macros), plus 1 postscript figur
Calibration of shielded microwave probes using bulk dielectrics
A stripline-type near-field microwave probe is microfabricated for microwave
impedance microscopy. Unlike the poorly shielded coplanar probe that senses the
sample tens of microns away, the stripline structure removes the stray fields
from the cantilever body and localizes the interaction only around the
focused-ion beam deposited Pt tip. The approaching curve of an oscillating tip
toward bulk dielectrics can be quantitatively simulated and fitted to the
finite-element analysis result. The peak signal of the approaching curve is a
measure of the sample dielectric constant and can be used to study unknown bulk
materials.Comment: 10 pages, 3 figure
Underlying Fermi surface of SrCaCuO in two-dimensional momentum space observed by angle-resolved photoemission spectroscopy
We have performed an angle-resolved photoemission study of the two-leg ladder
system SrCaCuO with = 0 and 11. "Underlying Fermi
surfaces" determined from low energy spectral weight mapping indicates the
quasi-one dimensional nature of the electronic structure. Energy gap caused by
the charge density wave has been observed for =0 and the gap tends to close
with Ca substitution. The absence of a quasi-particle peak even in =11 is in
contrast to the two-dimensional high- cuprates, implying strong carrier
localization related to the hole crystalization.Comment: 5 pages, 3 figure
Evidence of Electron Fractionalization from Photoemission Spectra in the High Temperature Superconductors
In the normal state of the high temperature superconductors
Bi_2Sr_2CaCu_2O_{8+delta} and La_{2-x}Sr_{x}CuO_4, and in the related ``stripe
ordered'' material La_1.25Nd_0.6Sr_0.15CuO_4, there is sharp structure in the
measured single hole spectral function A(k,w) considered as a function of k at
fixed small binding energy w. At the same time, as a function of w at fixed k
on much of the putative Fermi surface, any structure in A(k,w), other than the
Fermi cutoff, is very broad. This is characteristic of the situation in which
there are no stable excitations with the quantum numbers of the electron, as is
the case in the one dimensional electron gas.Comment: Published versio
Thermodynamics with density and temperature dependent particle masses and properties of bulk strange quark matter and strangelets
Thermodynamic formulas for investigating systems with density and/or
temperature dependent particle masses are generally derived from the
fundamental derivation equality of thermodynamics. Various problems in the
previous treatments are discussed and modified. Properties of strange quark
matter in bulk and strangelets at both zero and finite temperature are then
calculated based on the new thermodynamic formulas with a new quark mass
scaling, which indicates that low mass strangelets near beta equilibrium are
multi-quark states with an anti-strange quark, such as the pentaquark
(u^2d^2\bar{s}) for baryon nmber 1 and the octaquark (u^4d^3\bar{s}) for
dibaryon etc.Comment: 14 pages, 12 figures, Revtex4 styl
Low-Energy Electronic Structure of the High-Tc Cuprates La2-xSrxCuO4 Studied by Angle-resolved Photoemission Spectroscopy
We have performed a systematic angle-resolved photoemission spectroscopy
(ARPES) study of the high-Tc cuprates La2-xSrxCuO4, ranging from the underdoped
insulator to the superconductor to the overdoped metal. We have revealed a
systematic doping evolution of the band dispersions and (underlying) Fermi
surfaces, pseudogap and quasi-particle features under the influence of strong
electron-electron interaction and electron-phonon interaction. The unusual
transport and thermodynamic properties are explained by taking into account the
pseudogap opening and the Fermi arc formation, due to which the carrier number
decreases as the doped hole concentration decreases.Comment: 27 pages, 17 figures, accepted in Journal of Physics Condensed Matte
Direct observation of the mass renormalization in SrVO by angle resolved photoemission spectroscopy
We have performed an angle-resolved photoemission study of the
three-dimensional perovskite-type SrVO. Observed spectral weight
distribution of the coherent part in the momentum space shows cylindrical Fermi
surfaces consisting of the V 3 orbitals as predicted by
local-density-approximation (LDA) band-structure calculation. The observed
energy dispersion shows a moderately enhanced effective mass compared to the
LDA results, corresponding to the effective mass enhancement seen in the
thermodynamic properties. Contributions from the bulk and surface electronic
structures to the observed spectra are discussed based on model calculations.Comment: 5 pages, 5 figure
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