644 research outputs found
Superconducting gap variations induced by structural supermodulation in BSCCO
We discuss the possibility that the strain field introduced by the structural
supermodulation in Bi-2212 and certain other cuprate materials may modulate the
superconducting pairing interaction. We calculate the amplitude of this effect,
visible in scanning tunneling spectroscopy experiments, and thereby relate a
change in the local superconducting gap with the change in the local dopant
displacements induced by the supermodulation. In principle, since this
modulation is periodic, sufficiently accurate x-ray measurements or ab initio
calculations should enable one to determine which atomic displacements enhance
pairing and therefore T_c.Comment: 4 pages, 3 figure
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
Investigating the Effectiveness of the Tutorials in Introductory Physics in Multiple Instructional Settings
This paper examines the educational impact of the implementation of "Changes
in Energy and Momentum" from the Tutorials in Introductory Physics in five
different instructional settings. These settings include (1) a completely
computer-based learning environment and (2) use of cooperative learning groups
with varying levels of instructor support. Pre- and post-tests provide evidence
that a computer-based implementation falls significantly short of classroom
implementations which involve both collaborative learning groups and
interactions with a teaching assistance. Other findings provide insight into
the importance of certain elements of instructor training and the appropriate
use of the tutorial as an initial introduction to a new concept.Comment: 8 Pages, 3 figures, 4 table
Structure and dynamics of the Shapley Supercluster
We present results of our wide-field redshift survey of galaxies in a 285
square degree region of the Shapley Supercluster (SSC), based on a set of 10529
velocity measurements (including 1201 new ones) on 8632 galaxies obtained from
various telescopes and from the literature. Our data reveal that the main plane
of the SSC (v~ 14500 km/s) extends further than previous estimates, filling the
whole extent of our survey region of 12~degrees by 30~degrees on the sky (30 x
75~h-1 Mpc). There is also a connecting structure associated with the slightly
nearer Abell~3571 cluster complex (v~ 12000km/s. These galaxies seem to link
two previously identified sheets of galaxies and establish a connection with a
third one at V= 15000 km/s near R.A.= 13h. They also tend to fill the gap of
galaxies between the foreground Hydra-Centaurus region and the more distant
SSC. In the velocity range of the Shapley Supercluster (9000 km/s < cz < 18000
km/s), we found redshift-space overdensities with b\_j < 17.5 of ~5.4 over the
225 square degree central region and ~3.8 in a 192 square degree region
excluding rich clusters. Over the large region of our survey, we find that the
intercluster galaxies make up 48 per cent of the observed galaxies in the SSC
region and, accounting for the different completeness, may contribute nearly
twice as much mass as the cluster galaxies. In this paper, we discuss the
completeness of the velocity catalogue, the morphology of the supercluster, the
global overdensity, and some properties of the individual galaxy clusters in
the Supercluster.Comment: Accepted for publication in Astronomy and Astrophysic
Pancreatic cysts suspected to be branch duct intraductal papillary mucinous neoplasm without concerning features have low risk for development of pancreatic cancer.
BackgroundThe risk of developing pancreatic cancer is uncertain in patients with clinically suspected branch duct intraductal papillary mucinous neoplasm (BD-IPMN) based on the "high-risk stigmata" or "worrisome features" criteria proposed in the 2012 international consensus guidelines ("Fukuoka criteria").MethodsRetrospective case series involving patients referred for endoscopic ultrasound (EUS) of indeterminate pancreatic cysts with clinical and EUS features consistent with BD-IPMN. Rates of pancreatic cancer occurring at any location in the pancreas were compared between groups of patients with one or more Fukuoka criteria ("Highest-Risk Group", HRG) and those without these criteria ("Lowest-Risk Group", LRG).ResultsAfter exclusions, 661 patients comprised the final cohort (250 HRG and 411 LRG patients), 62% female with an average age of 67 years and 4 years of follow up. Pancreatic cancer, primarily adenocarcinoma, occurred in 60 patients (59 HRG, 1 LRG). Prevalent cancers diagnosed during EUS, immediate surgery, or first year of follow up were found in 48/661 (7.3%) of cohort and exclusively in HRG (33/77, 42.3%). Using Kaplan-Meier method, the cumulative incidence of cancer at 7 years was 28% in HRG and 1.2% in LRG patients (P<0.001).ConclusionsThis study supports using Fukuoka criteria to stratify the immediate and long-term risks of pancreatic cancer in presumptive BD-IPMN. The risk of pancreatic cancer was highest during the first year and occurred exclusively in those with "high-risk stigmata" or "worrisome features" criteria. After the first year all BD-IPMN continued to have a low but persistent cancer risk
Spectral Properties of Holstein and Breathing Polarons
We calculate the spectral properties of the one-dimensional Holstein and
breathing polarons using the self-consistent Born approximation. The Holstein
model electron-phonon coupling is momentum independent while the breathing
coupling increases monotonically with the phonon momentum. We find that for a
linear or tight binding electron dispersion: i) for the same value of the
dimensionless coupling the quasiparticle renormalization at small momentum in
the breathing polaron is much smaller, ii) the quasiparticle renormalization at
small momentum in the breathing polaron increases with phonon frequency unlike
in the Holstein model where it decreases, iii) in the Holstein model the
quasiparticle dispersion displays a kink and a small gap at an excitation
energy equal to the phonon frequency w0 while in the breathing model it
displays two gaps, one at excitation energy w0 and another one at 2w0. These
differences have two reasons: first, the momentum of the relevant scattered
phonons increases with increasing polaron momentum and second, the breathing
bare coupling is an increasing function of the phonon momentum. These result in
an effective electron-phonon coupling for the breathing model which is an
increasing function of the total polaron momentum, such that the small momentum
polaron is in the weak coupling regime while the large momentum one is in the
strong coupling regime. However the first reason does not hold if the free
electron dispersion has low energy states separated by large momentum, as in a
higher dimensional system for example, in which situation the difference
between the two models becomes less significant.Comment: 11 pages, 10 figure
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
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