1,327 research outputs found
Theory for the Interdependence of High-T Superconductivity and Dynamical Spin Fluctuations
The doping dependence of the superconducting state for the 2D one-band
Hubbard Hamiltonian is determined. By using an Eliashberg-type theory, we find
that the gap function has a symmetry in momentum
space and T becomes maximal for doping. Since we determine the
dynamical excitations directly from real frequency axis calculations, we obtain
new structures in the angular resolved density of states related to the
occurrence of {\it shadow states} below T. Explaining the anomalous
behavior of photoemission and tunneling experiments in the cuprates, we find a
strong interplay between -wave superconductivity and dynamical spin
fluctuations.Comment: 4 pages (REVTeX) with 4 figures (Postscript
Low Resolution Limits and Inaccurate Algorithms Decrease Significantly the Value of Late Loss in Current Drug-Eluting Stent Trials
Quantitative coronary and vascular angiography (QCA resp., QVA) remains the current gold standard for evaluation of restenosis. Late loss as one of the most commonly accepted parameters to highlight efficacy of the various devices has shown high correlation to clinical parameters but, surprisingly, has no impact on the evaluation of the remaining amount of restenostic tissue. The current clinical practice leads to unrealistic late loss calculations. Smaller late loss differences are usually not greater than the inherited resolution limits of QCA, which is especially the case in small differences between the various stents in the drug-eluting stent era. Late loss include additional systematic and random errors, due to the fact that measurements were taken at two different time points including the inherited resolution and calibration limits of QCA on two occasions. Due to the limited value of late loss in discriminating the small differences between the one and other DES, late lumen area loss and clearly defined calculation algorithms (e.g., MLD-relocation) should be used in future DES studies also to fulfill the more stringent regulatory requirements
The Enigmatic Young Object: Walker 90/V590 Monocerotis
We assess the evolutionary status of the intriguing object Walker 90/V590
Mon, which is located about 20 arcminutes northwest of the Cone Nebula near the
center of the open cluster NGC 2264. This object, according to its most recent
optical spectral type determination (B7), which we confirmed, is at least 3
magnitudes too faint in V for the cluster distance, but it shows the classical
signs of a young pre-main sequence object, such as highly variable Halpha
emission, Mg II emission, IR excess, UV continuum, and optical variability. We
analyzed a collection of archival and original data on Walker 90, covering 45
years including photometry, imaging, and spectroscopic data ranging from
ultraviolet to near-infrared wavelengths. According to star formation
processes, it is expected that, as this object clears its primordial
surroundings, it should become optically brighter, show a weakening of its IR
excess and present decreasing line emissions. This behavior is supported by our
observations and analysis, but timescales are expected to be longer than the
one observed here. Based on photometric data secured in 2007, we find Walker 90
at its brightest recorded optical magnitude. We document an evolution in
spectral type over the past five decades (from A2/A3 to currently B7 and as
early as B4), along with a decrease in the near-infrared K fluxes. From
near-infrared images secured in 2004, Walker 90 appears as a point source
placing an upper limit of 0.1 arcsec for its diameter. We conclude that many
observational features are explained if W90 is a flared disk system, surrounded
by an inclined optically thick accretion disk.Comment: 13 pages, 19 figure
The Impact of the Extent of Lymphadenectomy on Oncologic Outcomes in Patients Undergoing Radical Cystectomy for Bladder Cancer : A Systematic Review
Copyright © 2014 European Association of Urology. Published by Elsevier B.V. All rights reserved.Peer reviewedPostprin
Star and protoplanetary disk properties in Orion's suburbs
(Note: this is a shortened version of the original "structured" A&A format
abstract.) We performed a large optical spectroscopic and photometric survey of
the Lynds~1630N and 1641 clouds. We provide a catalog of 132 confirmed young
stars in L1630N and 267 such objects in L1641. We identify 28 transition disk
systems, 20 of which were previously unknown, as well as 42 new transition disk
candidates for which we have broad-band photometry but no optical spectroscopy.
We estimate mass accretion rates M_acc from the equivalent widths of the
H_alpha, H_beta, and HeI 5876\AA emission lines, and find a dependence on
stellar mass of M_acc propto Mstar^alpha, with alpha~3.1 in the subsolar mass
range that we probe. An investigation of a large literature sample of mass
accretion rate estimates yields a similar slope of alpha~2.8 in the subsolar
regime, but a shallower slope of alpha~2.0 if the whole mass range of 0.04
M_sun-5 Msun is included. Among the transition disk objects, the fraction of
stars that show significant accretion activity is relatively low compared to
stars with still optically thick disks (26\pm11% vs. 57\pm6%, respectively).
However, those transition disks that do show significant accretion have the
same median accretion rate as normal optically thick disks of 3-4*10^{-9}
M_sun/yr. We find that the ages of the transition disks and the WTTSs without
disks are statistically indistinguishable, and both groups are significantly
older than the CTTSs. These results argue against disk-binary interaction or
gravitational instability as mechanisms causing a transition disk appearance.
Our observations indicate that disk lifetimes in the clustered population are
shorter than in the distributed population. We propose refined Halpha
equivalent width criteria to distinguish WTTSs from CTTSs.Comment: 52 pages, 16 tables, 29 figures. Accepted by A&A. Table numbering
error correcte
Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)
We have used the LTLSM technique for a spatially resolved investigation of
the microwave transport properties, nonlinearities and material inhomogeneities
in an operating coplanar waveguide YBa_2Cu_3O_{7-\delta} (YBCO) microwave
resonator on an LaAlO_3 (LAO) substrate. The influence of twin-domain blocks,
in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform rf
current distribution were measured with a micrometer-scale spatial resolution.
The impact of the peaked edge currents and rf field penetration into weak links
on the linear device performance were studied as well. The LTLSM capabilities
and its future potential for non-destructive characterization of the microwave
properties of superconducting circuits are discussed.Comment: 8 pages, 9 figures, 2-column format, presented at High Temperature
Superconductors in High Frequency Fields 2004, Journal of Superconductivity
(in press
Is pain sensitivity altered in people with Alzheimer's disease? A systematic review and meta-analysis of experimental pain research
Background: Clinical studies suggest people with Alzheimer's disease (AD) have altered pain sensitivity. Experimental pain research is equivocal.
Objective: Conduct a meta-analysis to investigate if people with AD have altered pain sensitivity compared to healthy controls (HCs).
Methods: Three authors searched electronic databases from inception till November 2015 for experimental pain studies in AD vs. HCs. Outcome measures were pain threshold, tolerance, pain ratings, heart rate response to nox- ious stimuli and the Facial Action Coding System (FACS). Random effect meta-analysis calculating Hedges' g ± 95% confidence intervals (CI) was conducted.
Results: Thirteen studies were identified, including 256 people with AD (74.6 (±5.6) years, 59% females with a mean mini mental state examination (MMSE) score of 19.2) and 260 HCs. Meta-analysis demonstrated no signif- icant difference in pain threshold (g = 0.025, 95% CI â0.315-0.363, p = 0.88, n AD = 135, n HCs = 157), pain tolerance (g = â0.363, 95% CI â2.035-1.309, p = 0.67, n AD = 41, n HCs = 53) or pain intensity ratings (g = 0.03, p = 0.89, n AD = 138, n HCs = 135). Heart rate response to pain was less pronounced in AD but not significant (g = â0.746, p = 0.11). People with AD (n = 90) had significantly higher FACS scores versus HCs (n = 109) (g = 0.442, p = 0.03) indicating increased pain. Meta-regression demonstrated that an increasing percentage of AD female participants moderated pain threshold (p = 0.02) whilst MMSE scores did not (p = 0.19).
Conclusion: People with AD have a greater sensitivity to pain when validated observer ratings of facial expres- sions are used. Verbal response to painful stimuli, even under experimental conditions, may mean pain is not identified in people with AD. Clinically useful observer rated pain tools may be the most appropriate way to as- sess pain in AD
Low Frequency Nonlinear Magnetic Response of an Unconventional Superconductor
We consider an unconventional superconductor in a low frequency harmonic
magnetic field. In the Meissner regime at low T a nonlinear magnetic response
arises from quasiparticle excitations near minima in the energy gap. Various
physical quantities then acquire higher harmonics of the frequency of the
applied field. We discuss how examination of the field and angular dependence
of these harmonics allows determination of the structure of the energy gap. We
show how to distinguish nodes from small finite minima ("quasinodes"). Gaps
with nodal lines give rise to universal power law field dependences for the
nonlinear magnetic moment and the nonlinear torque. They both have separable
temporal and angular dependences. In contrast, when there are quasinodes these
quantities have more complicated and nonseparable field, temporal, and angular
dependences. We illustrate this on the example of an s+id gap. We discuss how
to perform measurements so as to maximize the nonlinear signal and how to
investigate in detail the properties of the superconducting minima, thus
determining the gap function symmetry.Comment: To appear in Phys Rev B. Ten figures, 13 text page
Timescale of Mass Accretion in Pre-Main-Sequence Stars
We present initial result of a large spectroscopic survey aimed at measuring
the timescale of mass accretion in young, pre-main-sequence stars in the
spectral type range K0 - M5. Using multi-object spectroscopy with VIMOS at the
VLT we identified the fraction of accreting stars in a number of young stellar
clusters and associations of ages between 1 - 50 Myr. The fraction of accreting
stars decreases from ~60% at 1.5 - 2 Myr to ~2% at 10 Myr. No accreting stars
are found after 10 Myr at a sensitivity limit of Msun yr-1. We
compared the fraction of stars showing ongoing accretion (f_acc) to the
fraction of stars with near-to-mid infrared excess (f_IRAC). In most cases we
find f_acc < f_IRAC, i.e., mass accretion appears to cease (or drop below
detectable level) earlier than the dust is dissipated in the inner disk. At 5
Myr, 95% of the stellar population has stopped accreting material at a rate of
> 10^{-11} Msun yr-1, while ~20% of the stars show near-infrared excess
emission. Assuming an exponential decay, we measure a mass accretion timescale
(t_acc) of 2.3 Myr, compared to a near-to-mid infrared excess timescale
(t_IRAC) of 2.9 Myr. Planet formation, and/or migration, in the inner disk
might be a viable mechanism to halt further accretion onto the central star on
such a short timescale.Comment: Accepted for publicatio
High-Tc Cuprate Superconductivity in a Nutshell
Since the discovery of high-Tc cuprate superconductivity in 1986 many new
experimental techniques and theoretical concepts have been developed. In
particular it was shown that the BCS theory of d-wave superconductivity
describes semi-quantitatively the high-Tc superconductivity. Furthermore, it
was demonstrated that Volovik's approach is extremely useful for finding the
quasiparticle properties in the vortex state. Here we survey these developments
and forecast future directions.Comment: 11 pages, 3 figure
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