94 research outputs found
Diffusion-limited loop formation of semiflexible polymers: Kramers theory and the intertwined time scales of chain relaxation and closing
We show that Kramers rate theory gives a straightforward, accurate estimate
of the closing time of a semiflexible polymer that is valid in cases
of physical interest. The calculation also reveals how the time scales of chain
relaxation and closing are intertwined, illuminating an apparent conflict
between two ways of calculating in the flexible limit.Comment: Europhys. Lett., 2003 (in press). 8 pages, 3 figures. See also,
physics/0101087 for physicist's approach to and the importance of
semiflexible polymer looping, in DNA replicatio
Time of life as it is in LiFeAs
The time of life of fermionic quasiparticles, the distribution of which in
the momentum-energy space can be measured by angle resolved photoemission
(ARPES), is the first quantity to look for fingerprints of interaction
responsible for the superconducting pairing. Such an approach has been recently
used for superconducting cuprates, but its direct application to pnictides was
not possible due to essential three-dimensionality of the electronic band
structure and magnetic ordering. Here, we report the investigation of the
quasiparticle lifetime in LiFeAs, a non-magnetic stoichiometric superconductor
with a well separated two-dimensional band. We have found two energy scales:
the lower one contains clear fingerprints of optical phonon modes while the
higher scale indicates a presence of strong electron-electron interaction. The
result suggests that LiFeAs is a phonon mediated superconductor with strongly
enhanced electronic density of states at the Fermi level.Comment: reevaluated electron-phonon coupling strength, added reference
Anisotropic impurities in anisotropic superconductors
Physical properties of anisotropic superconductors like the critical
temperature and others depend sensitively on the electron mean free path. The
sensitivity to impurity scattering and the resulting anomalies are considered a
characteristic feature of strongly anisotropic pairing. These anomalies are
usually analyzed in terms of s-wave impurity scattering which leads to
universal pair breaking effects depending on only two scattering parameters,
the mean free path and the impurity cross section. We investigate here
corrections coming from anisotropies in the scattering cross section, and find
not only quantitative but also qualitative deviations from universal s-wave
isotropic pairbreaking. The properties we study are the transition temperature,
the density of states, quasiparticle bound states at impurities, and pinning of
flux lines by impurities.Comment: 19 page
Social Roles and Baseline Proxemic Preferences for a Domestic Service Robot
© The Author(s) 2014. This article is published with open access at Springerlink.com. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. The work described in this paper was conducted within the EU Integrated Projects LIREC (LIving with Robots and intEractive Companions, funded by the European Commission under contract numbers FP7 215554, and partly funded by the ACCOMPANY project, a part of the European Union’s Seventh Framework Programme (FP7/2007–2013) under grant agreement n287624The goal of our research is to develop socially acceptable behavior for domestic robots in a setting where a user and the robot are sharing the same physical space and interact with each other in close proximity. Specifically, our research focuses on approach distances and directions in the context of a robot handing over an object to a userPeer reviewe
Nonadiabatic Pauli susceptibility in fullerene compounds
Pauli paramagnetic susceptibility is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of observed in fullerene
compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include
Implications of reflectance measurements on the mechanism for superconductivity in MgB
Recent optical studies in c-axis oriented superconducting MgB films
indicate that the electron-phonon coupling is weak [tu01]. We reinforce this
conclusion by examining the raw reflectance data; its frequency dependence is
incompatible with strong electron-phonon scattering. This is further
strengthened by analysis of the real part of the conductivity, and by the
temperature dependence of the effective Drude scattering rate. Using a
realistic electron-phonon spectral shape [kong01], we find , in agreement with Tu et al. [tu01]. To the extent that
, this disagrees sharply with model
calculations [kong01,kortus01,an01], and is far too low to provide the means
for K. A simple model is constructed with coupling to a high
frequency excitation, which is consistent with both the low frequency optical
data and the high .Comment: 4 pages, 4 figure
Influence of spin fluctuations on the superconducting transition temperature and resistivity in the t-J model at large N
Spin fluctuations enter the calculation of the superconducting transition
temperature T only in the next-to-leading order (i.e., in O(1/N) of the
1/N expansion of the t-J model. We have calculated these terms and show that
they have only little influence on the value of T obtained in the leading
order O(1/N) in the optimal and overdoped region, i.e., for dopings larger than
the instability towards a flux phase. This result disagrees with recent
spin-fluctuation mediated pairing theories. The discrepancies can be traced
back to the fact that in our case the coupling between electrons and spins is
determined by the t-J model and not adjusted and that the spin susceptibility
is rather broad and structureless and not strongly peaked at low energies as in
spin-fluctuation models. Relating T and transport we show that the
effective interactions in the particle-particle and particle-hole channels are
not simply related within the 1/N expansion by different Fermi surface averages
of the same interactin as in the case of phonons or spin fluctuations. As a
result, we find that large values for T and rather small scattering rates
in the normal state as found in the experiments can easily be reconciled with
each other. We also show that correlation effects heavily suppress transport
relaxation rates relative to quasiparticle relaxation rates in the case of
phonons but not in the case of spin fluctuations.Comment: 16 pages, 10 figures, will appear in Phys. Rev.
Poor screening and nonadiabatic superconductivity in correlated systems
In this paper we investigate the role of the electronic correlation on the
hole doping dependence of electron-phonon and superconducting properties of
cuprates. We introduce a simple analytical expression for the one-particle
Green's function in the presence of electronic correlation and we evaluate the
reduction of the screening properties as the electronic correlation increases
by approaching half-filling. The poor screening properties play an important
role within the context of the nonadiabatic theory of superconductivity. We
show that a consistent inclusion of the reduced screening properties in the
nonadiabatic theory can account in a natural way for the - phase
diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review
In vitro and in vivo effects of Pelargonium sidoides DC. root extract EPs® 7630 and selected constituents against SARS-CoV-2 B.1, Delta AY.4/AY.117 and Omicron BA.2
The occurrence of immune-evasive SARS-CoV-2 strains emphasizes the importance to search for broad-acting antiviral compounds. Our previous in vitro study showed that Pelargonium sidoides DC. root extract EPs® 7630 has combined antiviral and immunomodulatory properties in SARS-CoV-2-infected human lung cells. Here we assessed in vivo effects of EPs® 7630 in SARS-CoV-2-infected hamsters, and investigated properties of EPs® 7630 and its functionally relevant constituents in context of phenotypically distinct SARS-CoV-2 variants. We show that EPs® 7630 reduced viral load early in the course of infection and displayed significant immunomodulatory properties positively modulating disease progression in hamsters. In addition, we find that EPs® 7630 differentially inhibits SARS-CoV-2 variants in nasal and bronchial human airway epithelial cells. Antiviral effects were more pronounced against Omicron BA.2 compared to B.1 and Delta, the latter two preferring TMPRSS2-mediated fusion with the plasma membrane for cell entry instead of receptor-mediated low pH-dependent endocytosis. By using SARS-CoV-2 Spike VSV-based pseudo particles (VSVpp), we confirm higher EPs® 7630 activity against Omicron Spike-VSVpp, which seems independent of the serine protease TMPRSS2, suggesting that EPs® 7630 targets endosomal entry. We identify at least two molecular constituents of EPs® 7630, i.e., (−)-epigallocatechin and taxifolin with antiviral effects on SARS-CoV-2 replication and cell entry. In summary, our study shows that EPs® 7630 ameliorates disease outcome in SARS-CoV-2-infected hamsters and has enhanced activity against Omicron, apparently by limiting late endosomal SARS-CoV-2 entry
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