11,450 research outputs found
Material and doping dependence of the nodal and anti-nodal dispersion renormalizations in single- and multi-layer cuprates
In this paper we present a review of bosonic renormalization effects on
electronic carriers observed from angle-resolved photoemission spectra in the
cuprates. We specifically discuss the viewpoint that these renormalizations
represent coupling of the electrons to the lattice, and review how the wide
range of materials dependence, such as the number of CuO layers, and the
doping dependence can be straightforwardly understood as arising due to novel
electron-phonon coupling.Comment: 9 pages and 6 figures. Submitted as a review article for Advances in
Condensed Matter Physic
Doping evolution of spin and charge excitations in the Hubbard model
To shed light on how electronic correlations vary across the phase diagram of
the cuprate superconductors, we examine the doping evolution of spin and charge
excitations in the single-band Hubbard model using determinant quantum Monte
Carlo (DQMC). In the single-particle response, we observe that the effects of
correlations weaken rapidly with doping, such that one may expect the random
phase approximation (RPA) to provide an adequate description of the
two-particle response. In contrast, when compared to RPA, we find that
significant residual correlations in the two-particle excitations persist up to
hole and electron doping (the range of dopings achieved in the
cuprates). These fundamental differences between the doping evolution of
single- and multi-particle renormalizations show that conclusions drawn from
single-particle processes cannot necessarily be applied to multi-particle
excitations. Eventually, the system smoothly transitions via a
momentum-dependent crossover into a weakly correlated metallic state where the
spin and charge excitation spectra exhibit similar behavior and where RPA
provides an adequate description.Comment: 5 pages, 4 figures, plus supplementary materia
The Complex Wind Torus and Jets of PSR B1706-44
We report on Chandra ACIS imaging of the pulsar wind nebula (PWN) of the
young Vela-like PSR B1706-44, which shows the now common pattern of an
equatorial wind and polar jets. The structure is particularly rich, showing a
relativistically boosted termination shock, jets with strong confinement, a
surrounding radio/X-ray PWN and evidence for a quasi-static `bubble nebula'.
The structures trace the pulsar spin geometry and illuminate its possible
relation to SNR G343.1-2.3. We also obtain improved estimates of the pulsar
flux and nebular spectrum, constraining the system age and energetics.Comment: To appear in the Astrophysical Journal. 15pp, 4 figures in 7 file
Experimental and numerical investigations of flow structure and momentum transport in a turbulent buoyancy-driven flow inside a tilted tube.
Buoyancy-driven turbulent mixing of fluids of slightly different densities [At = Δρ/(2〈ρ〉) = 1.15×10−2] in a long circular tube tilted at an angle θ = 15° from the vertical is studied at the local scale, both experimentally from particle image velocimetry and laser induced fluorescence measurements in the vertical diametrical plane and numerically throughout the tube using direct numerical simulation. In a given cross section of the tube, the axial mean velocity and the mean concentration both vary linearly with the crosswise distance z from the tube axis in the central 70% of the diameter. A small crosswise velocity component is detected in the measurement plane and is found to result from a four-cell mean secondary flow associated with a nonzero streamwise component of the vorticity. In the central region of the tube cross section, the intensities of the three turbulent velocity fluctuations are found to be strongly different, that of the streamwise fluctuation being more than twice larger than that of the spanwise fluctuation which itself is about 50% larger than that of the crosswise fluctuation. This marked anisotropy indicates that the turbulent structure is close to that observed in homogeneous turbulent shear flows. Still in the central region, the turbulent shear stress dominates over the viscous stress and reaches a maximum on the tube axis. Its crosswise variation is approximately accounted for by a mixing length whose value is about one-tenth of the tube diameter. The momentum exchange in the core of the cross section takes place between its lower and higher density parts and there is no net momentum exchange between the core and the near-wall regions. A sizable part of this transfer is due both to the mean secondary flow and to the spanwise turbulent shear stress. Near-wall regions located beyond the location of the extrema of the axial velocity (|z|≳0.36 d) are dominated by viscous stresses which transfer momentum toward (from) the wall near the top (bottom) of the tube
Phaselocked patterns and amplitude death in a ring of delay coupled limit cycle oscillators
We study the existence and stability of phaselocked patterns and amplitude
death states in a closed chain of delay coupled identical limit cycle
oscillators that are near a supercritical Hopf bifurcation. The coupling is
limited to nearest neighbors and is linear. We analyze a model set of discrete
dynamical equations using the method of plane waves. The resultant dispersion
relation, which is valid for any arbitrary number of oscillators, displays
important differences from similar relations obtained from continuum models. We
discuss the general characteristics of the equilibrium states including their
dependencies on various system parameters. We next carry out a detailed linear
stability investigation of these states in order to delineate their actual
existence regions and to determine their parametric dependence on time delay.
Time delay is found to expand the range of possible phaselocked patterns and to
contribute favorably toward their stability. The amplitude death state is
studied in the parameter space of time delay and coupling strength. It is shown
that death island regions can exist for any number of oscillators N in the
presence of finite time delay. A particularly interesting result is that the
size of an island is independent of N when N is even but is a decreasing
function of N when N is odd.Comment: 23 pages, 12 figures (3 of the figures in PNG format, separately from
TeX); minor additions; typos correcte
ASCA observations of the young rotation-powered pulsars PSR B1046-58 and PSR B1610-50
We present X-ray observations of two young energetic radio pulsars, PSRs
B1046-58 and B1610-50, and their surroundings, using archival data from the
Advanced Satellite for Cosmology and Astrophysics (ASCA).
The energetic pulsar PSR B1046-58 is detected in X-rays with a significance
of 4.5 sigma. The unabsorbed flux, estimated assuming a power-law spectrum and
a neutral hydrogen column density N_H of 5E21 cm^-2 is (2.5 +/- 0.3) x 10E-13
ergs/cm^2/s in the 2-10 keV band. Pulsed emission is not detected; the pulsed
fraction is less than 31% at the 90% confidence level for a 50% duty cycle. We
argue that the emission is best explained as originating from a pulsar-powered
synchrotron nebula. The X-ray counterpart of the pulsar is the only hard source
within the 95% error region of the previously unidentified gamma-ray source 3EG
J1048-5840. This evidence supports the results of Kaspi et al. (1999), who in a
companion paper, suggest that PSR B1046-58 is the counterpart to 3EG
J1048-5840.
X-ray emission from PSR B1610-50 is not detected. Using similar assumptions
as above, the derived 3 sigma upper limit for the unabsorbed 2-10 keV X-ray
flux is 1.5E-13 ergs/cm^2/s. We use the flux limit to estimate the pulsar's
velocity to be less than ~170 km/s, casting doubt on a previously reported
association between PSR B1610-50 and supernova remnant Kes 32. Kes 32 is
detected, as is evident from the correlation between X-ray and radio emission.
The ASCA images of PSR B1610-50 are dominated by mirror-scattered emission from
the X-ray-bright supernova remnant RCW 103, located 33' away.
We find no evidence for extended emission around either pulsar, in contrast
to previous reports of large nebulae surrounding both pulsars.Comment: Accepted for publication in the ApJ (v.528, pp.436-444) Correcting
typo in abstract of .tex fil
Dietary Strategies to Optimize Wound Healing after Periodontal and Dental Implant Surgery: An Evidence-Based Review
Methods to optimize healing through dietary strategies present an attractive option for patients, such that healing
from delicate oral surgeries occurs as optimally as possible with minimal patient-meditated complications through improper
food choices. This review discusses findings from studies that have investigated the role of diet, either whole foods
or individual dietary components, on periodontal health and their potential role in wound healing after periodontal surgery.
To date, research in this area has largely focused on foods or individual dietary components that may attenuate inflammation
or oxidant stress, or foster de novo bone formation. These studies suggest that a wide variety of dietary components,
including macronutrients and micronutrients, are integral for optimal periodontal health and have the potential to
accelerate oral wound healing after periodontal procedures. Moreover, this review provides guidance regarding dietary
considerations that may help a patient achieve the best possible outcome after a periodontal procedure
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