261 research outputs found
Transport properties of the metallic state of overdoped cuprate superconductors from an anisotropic marginal Fermi liquid model
We consider the implications of a phenomenological model self-energy for the
charge transport properties of the metallic phase of the overdoped cuprate
superconductors. The self-energy is the sum of two terms with characteristic
dependencies on temperature, frequency, location on the Fermi surface, and
doping. The first term is isotropic over the Fermi surface, independent of
doping, and has the frequency and temperature dependence characteristic of a
Fermi liquid. The second term is anisotropic over the Fermi surface (vanishing
at the same points as the superconducting energy gap), strongly varies with
doping (scaling roughly with , the superconducting transition
temperature), and has the frequency and temperature dependence characteristic
of a marginal Fermi liquid. Previously it has been shown this self-energy can
describe a range of experimental data including angle-dependent
magnetoresistance (ADMR) and quasi-particle renormalisations determined from
specific heat, quantum oscillations, and angle-resolved photo-emission
spectroscopy (ARPES). Without introducing new parameters and neglecting vertex
corrections we show that this model self-energy can give a quantitative
description of the temperature and doping dependence of a range of reported
transport properties of Tl2201 samples. These include the intra-layer
resistivity, the frequency dependent optical conductivity, the intra-layer
magnetoresistance, and the Hall coefficient. The temperature dependence of the
latter two are particularly sensitive to the anisotropy of the scattering rate
and to the shape of the Fermi surface. In contrast, the temperature dependence
of the Hall angle is dominated by the Fermi liquid contribution to the
self-energy that determines the scattering rate in the nodal regions of the
Fermi surface.Comment: 17 pages, 16 figure
Holon-Doublon Binding as the Mechanism for the Mott transition
We study the binding of a holon to a doublon in a half-filled Hubbard model
as the mechanism of the zero-temperature metal-insulator transition. In a spin
polarized system and a non-bipartite lattice a single holon-doublon (HD) pair
exhibits a binding transition (e.g., on a face-centred cubic lattice), or a
sharp crossover (e.g., on a triangular lattice) corresponding well to the
standard Mott transition in unpolarized systems. We extend the HD-pair study
towards non-polarized systems by considering more general spin background and
by treating the finite HD density within a BCS-type approximation. Both
approaches lead to a discontinuous transition away from the fully polarized
system and give density correlations consistent with numerical results on a
triangular lattice.Comment: 6 pages, 4 figure
The role of the maximum involvement of biopsy core in predicting outcome for patients treated with dose-escalated radiation therapy for prostate cancer
Abstract
Purpose
To evaluate the influence of the maximum involvement of biopsy core (MIBC) on outcome for prostate cancer patients treated with dose-escalated external beam radiotherapy (EBRT).
Methods and materials
The outcomes of 590 men with localized prostate cancer treated with EBRT (≥75 Gy) at a single institution were retrospectively analyzed. The influence of MIBC on freedom from biochemical failure (FFBF), freedom from metastasis (FFM), cause-specific survival (CSS), and overall survival (OS) was compared to other surrogates for biopsy tumor volume, including the percentage of positive biopsy cores (PPC) and the total percentage of cancer volume (PCV).
Results
MIBC correlated with PSA, T-stage, Gleason score, NCCN risk group, PPC, PCV, and treatment related factors. On univariate analysis, MIBC was prognostic for all endpoints except OS; with greatest impact in those with Gleason scores of 8–10. However, on multivariate analysis, MIBC was only prognostic for FFBF (hazard ratio [HR] 1.9, p = 0.008), but not for FFM (p = 0.19), CSS (p = 0.16), and OS (p = 0.99).
Conclusions
In patients undergoing dose-escalated EBRT, MIBC had the greatest influence in those with Gleason scores of 8–10 but provided no additional prognostic data as compared to PPC and PCV, which remain the preferable prognostic variables in this patient population.http://deepblue.lib.umich.edu/bitstream/2027.42/112858/1/13014_2012_Article_631.pd
Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals
The femtosecond optical pump-probe technique was used to study dynamics of
photoexcited electrons and coherent optical phonons in transition metals Zn and
Cd as a function of temperature and excitation level. The optical response in
time domain is well fitted by linear combination of a damped harmonic
oscillation because of excitation of coherent phonon and a
subpicosecond transient response due to electron-phonon thermalization. The
electron-phonon thermalization time monotonically increases with temperature,
consistent with the thermomodulation scenario, where at high temperatures the
system can be well explained by the two-temperature model, while below
50 K the nonthermal electron model needs to be applied. As the
lattice temperature increases, the damping of the coherent phonon
increases, while the amplitudes of both fast electronic response and the
coherent phonon decrease. The temperature dependence of the damping of
the phonon indicates that population decay of the coherent optical
phonon due to anharmonic phonon-phonon coupling dominates the decay process. We
present a model that accounts for the observed temperature dependence of the
amplitude assuming the photoinduced absorption mechanism, where the signal
amplitude is proportional to the photoinduced change in the quasiparticle
density. The result that the amplitude of the phonon follows the
temperature dependence of the amplitude of the fast electronic transient
indicates that under the resonant condition both electronic and phononic
responses are proportional to the change in the dielectric function.Comment: 10 pages, 9 figures, to appear in Physical Review
A consistent picture for large penguins in D -> pi+ pi-, K+ K-
A long-standing puzzle in charm physics is the large difference between the
D0 -> K+ K- and D0 -> pi+ pi- decay rates. Recently, the LHCb and CDF
collaborations reported a surprisingly large difference between the direct CP
asymmetries, Delta A_CP, in these two modes. We show that the two puzzles are
naturally related in the Standard Model via s- and d-quark "penguin
contractions". Their sum gives rise to Delta A_CP, while their difference
contributes to the two branching ratios with opposite sign. Assuming nominal
SU(3) breaking, a U-spin fit to the D0 -> K+ pi-, pi+ K-, pi+ pi-, K+ K- decay
rates yields large penguin contractions that naturally explain Delta A_CP.
Expectations for the individual CP asymmetries are also discussed.Comment: 24 pages, 8 figure
Coupled-resonator optical waveguides: Q-factor and disorder influence
Coupled resonator optical waveguides (CROW) can significantly reduce light
propagation pulse velocity due to pronounced dispersion properties. A number of
interesting applications have been proposed to benefit from such slow-light
propagation. Unfortunately, the inevitable presence of disorder, imperfections,
and a finite Q value may heavily affect the otherwise attractive properties of
CROWs. We show how finite a Q factor limits the maximum attainable group delay
time; the group index is limited by Q, but equally important the feasible
device length is itself also limited by damping resulting from a finite Q.
Adding the additional effects of disorder to this picture, limitations become
even more severe due to destructive interference phenomena, eventually in the
form of Anderson localization. Simple analytical considerations demonstrate
that the maximum attainable delay time in CROWs is limited by the intrinsic
photon lifetime of a single resonator.Comment: Accepted for Opt. Quant. Electro
An oomycete NLP cytolysin forms transient small pores in lipid membranes
Microbial plant pathogens secrete a range of effector proteins that damage host plants and consequently constrain global food production. Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) are produced by numerous phytopathogenic microbes that cause important crop diseases. Many NLPs are cytolytic, causing cell death and tissue necrosis by disrupting the plant plasma membrane. Here, we reveal the unique molecular mechanism underlying the membrane damage induced by the cytotoxic model NLP. This membrane disruption is a multistep process that includes electrostatic-driven, plant-specific lipid recognition, shallow membrane binding, protein aggregation, and transient pore formation. The NLP-induced damage is not caused by membrane reorganization or large-scale defects but by small membrane ruptures. This distinct mechanism of lipid membrane disruption is highly adapted to effectively damage plant cells.Peer reviewe
Determining using with multibody D decays
We propose a method for determining using decays
followed by a multibody decay, such as , and . The main advantages of the method is
that it uses only Cabibbo allowed decays, and that large strong phases are
expected due to the presence of resonances. Since no knowledge about the
resonance structure is needed, can be extracted without any hadronic
uncertainty.Comment: 17 pages, 1 figur
Two component dark matter
We explain the PAMELA positron excess and the PPB-BETS/ATIC e+ + e- data
using a simple two component dark matter model (2DM). The two particle species
in the dark matter sector are assumed to be in thermal equilibrium in the early
universe. While one particle is stable and is the present day dark matter, the
second one is metastable and decays after the universe is 10^-8 s old. In this
model it is simple to accommodate the large boost factors required to explain
the PAMELA positron excess without the need for large spikes in the local dark
matter density. We provide the constraints on the parameters of the model and
comment on possible signals at future colliders.Comment: 6 pages, 2 figures, discussion clarified and extende
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