2,229 research outputs found
-approximation of the integrated density of states for Schr\"odinger operators with finite local complexity
We study spectral properties of Schr\"odinger operators on \RR^d. The
electromagnetic potential is assumed to be determined locally by a colouring of
the lattice points in \ZZ^d, with the property that frequencies of finite
patterns are well defined. We prove that the integrated density of states
(spectral distribution function) is approximated by its finite volume
analogues, i.e.the normalised eigenvalue counting functions. The convergence
holds in the space where is any finite energy interval and is arbitrary.Comment: 15 pages; v2 has minor fixe
Light-cone distribution amplitudes of octet baryons from lattice QCD
We present lattice QCD results for the wave function normalization constants
and the first moments of the distribution amplitudes for the lowest-lying
baryon octet. The analysis is based on a large number of ensembles
comprising multiple trajectories in the quark mass plane including physical
pion (and kaon) masses, large volumes, and, most importantly, five different
lattice spacings down to . This allows us to perform a
controlled extrapolation to the continuum and infinite volume limits by a
simultaneous fit to all available data. We demonstrate that the formerly
observed violation of flavor symmetry breaking constraints can, indeed, be
attributed to discretization effects that vanish in the continuum limit
Expert chess memory: Revisiting the chunking hypothesis
After reviewing the relevant theory on chess expertise, this paper re-examines experimentally the finding of Chase and Simon (1973a) that the differences in ability of chess players at different skill levels to copy and to recall positions are attributable to the experts' storage of thousands of chunks (patterned clusters of pieces) in long-term memory. Despite important differences in the experimental apparatus, the data of the present experiments regarding latencies and chess relations between successively placed pieces are highly correlated with those of Chase and Simon. We conclude that the 2-second inter-chunk interval used to define chunk boundaries is robust, and that chunks have psychological reality. We discuss the possible reasons why Masters in our new study used substantially larger chunks than the Master of the 1973 study, and extend the chunking theory to take account of the evidence for large retrieval structures (templates) in long-term memory
Spectroscopic investigations of a Ti:Tm:LiNbO3 waveguide for photon-echo quantum memory
We report the fabrication and characterization of a
Ti:Tm:LiNbO optical waveguide in view of photon-echo quantum
memory applications. In particular, we investigated room- and
cryogenic-temperature properties via absorption, spectral hole burning, photon
echo, and Stark spectroscopy. We found radiative lifetimes of 82 s and 2.4
ms for the H and F levels, respectively, and a 44% branching
ratio from the H to the F level. We also measured an optical
coherence time of 1.6 s for the HH, 795 nm
wavelength transition, and investigated the limitation of spectral diffusion to
spectral hole burning. Upon application of magnetic fields of a few hundred
Gauss, we observed persistent spectral holes with lifetimes up to seconds.
Furthermore, we measured a linear Stark shift of 25 kHzcm/V. Our results
are promising for integrated, electro-optical, waveguide quantum memory for
photons.Comment: 11 pages, 14 figure
Role of Barium Swallow in Diagnosing Clinically Significant Anastomotic Leak following Esophagectomy
Background
Barium swallow is performed following esophagectomy to evaluate the anastomosis for detection of leaks and to assess the emptying of the gastric conduit. The aim of this study was to evaluate the reliability of the barium swallow study in diagnosing anastomotic leaks following esophagectomy.
Methods
Patients who underwent esophagectomy from January 2000 to December 2013 at our institution were investigated. Barium swallow was routinely done between days 5–7 to detect a leak. These results were compared to clinically determined leaks (defined by neck wound infection requiring jejunal feeds and or parenteral nutrition) during the postoperative period. The sensitivity and specificity of barium swallow in diagnosing clinically significant anastomotic leaks was determined.
Results
A total of 395 esophagectomies were performed (mean age, 62.2 years). The indications for the esophagectomy were as follows: malignancy (n=320), high-grade dysplasia (n=14), perforation (n=27), benign stricture (n=7), achalasia (n=16), and other (n=11). A variety of techniques were used including transhiatal (n=351), McKeown (n=35), and Ivor Lewis (n=9) esophagectomies. Operative mortality was 2.8% (n=11). Three hundred and sixty-eight patients (93%) underwent barium swallow study after esophagectomy. Clinically significant anastomotic leak was identified in 36 patients (9.8%). Barium swallow was able to detect only 13/36 clinically significant leaks. The sensitivity of the swallow in diagnosing a leak was 36% and specificity was 97%. The positive and negative predictive values of barium swallow study in detecting leaks were 59% and 93%, respectively.
Conclusion
Barium swallow is an insensitive but specific test for detecting leaks at the cervical anastomotic site after esophagectomy
Obesity, unhappiness, and the challenge of affluence : theory and evidence
Is affluence a good thing? The book "The Challenge of Affluence" by Avner Offer (2006) argues that economic prosperity weakens self-control and undermines human well-being. Consistent with a pessimistic view, we show that psychological distress has been rising through time in modern Great Britain. Taking over-eating as an example, our data reveal that half the British population view themselves as overweight, and that happiness and mental health are worse among fatter people in Britain and Germany. Comparisons also matter. We discuss problems of inference and argue that longitudinal data are needed. We suggest a theory of obesity imitation where utility depends on relative weight
Exploration and Exploitation of Victorian Science in Darwin's Reading Notebooks
Search in an environment with an uncertain distribution of resources involves
a trade-off between exploitation of past discoveries and further exploration.
This extends to information foraging, where a knowledge-seeker shifts between
reading in depth and studying new domains. To study this decision-making
process, we examine the reading choices made by one of the most celebrated
scientists of the modern era: Charles Darwin. From the full-text of books
listed in his chronologically-organized reading journals, we generate topic
models to quantify his local (text-to-text) and global (text-to-past) reading
decisions using Kullback-Liebler Divergence, a cognitively-validated,
information-theoretic measure of relative surprise. Rather than a pattern of
surprise-minimization, corresponding to a pure exploitation strategy, Darwin's
behavior shifts from early exploitation to later exploration, seeking unusually
high levels of cognitive surprise relative to previous eras. These shifts,
detected by an unsupervised Bayesian model, correlate with major intellectual
epochs of his career as identified both by qualitative scholarship and Darwin's
own self-commentary. Our methods allow us to compare his consumption of texts
with their publication order. We find Darwin's consumption more exploratory
than the culture's production, suggesting that underneath gradual societal
changes are the explorations of individual synthesis and discovery. Our
quantitative methods advance the study of cognitive search through a framework
for testing interactions between individual and collective behavior and between
short- and long-term consumption choices. This novel application of topic
modeling to characterize individual reading complements widespread studies of
collective scientific behavior.Comment: Cognition pre-print, published February 2017; 22 pages, plus 17 pages
supporting information, 7 pages reference
Physicochemical analysis of rotavirus segment 11 supports a 'modified panhandle' structure and not the predicted alternative tRNA-like structure (TRLS)
.Rotaviruses are a major cause of acute gastroenteritis, which is often fatal in infants. The viral genome consists of 11 double-stranded RNA segments, but little is known about their cis-acting sequences and structural elements. Covariation studies and phylogenetic analysis exploring the potential structure of RNA11 of rotaviruses suggested that, besides the previously predicted "modified panhandle" structure, the 5' and 3' termini of one of the isoforms of the bovine rotavirus UKtc strain may interact to form a tRNA-like structure (TRLS). Such TRLSs have been identified in RNAs of plant viruses, where they are important for enhancing replication and packaging. However, using tRNA mimicry assays (in vitro aminoacylation and 3'- adenylation), we found no biochemical evidence for tRNA-like functions of RNA11. Capping, synthetic 3' adenylation and manipulation of divalent cation concentrations did not change this finding. NMR studies on a 5'- and 3'-deletion construct of RNA11 containing the putative intra-strand complementary sequences supported a predominant panhandle structure and did not conform to a cloverleaf fold despite the strong evidence for a predicted structure in this conserved region of the viral RNA. Additional viral or cellular factors may be needed to stabilise it into a form with tRNA-like properties
BNip3 regulates mitochondrial function and lipid metabolism in the liver
BNip3 localizes to the outer mitochondrial membrane, where it functions in mitophagy and mitochondrial dynamics. While the BNip3 protein is constitutively expressed in adult liver from fed mice, we have shown that its expression is superinduced by fasting of mice, consistent with a role in responses to nutrient deprivation. Loss of BNip3 resulted in increased lipid synthesis in the liver that was associated with elevated ATP levels, reduced AMP-regulated kinase (AMPK) activity, and increased expression of lipogenic enzymes. Conversely, there was reduced β-oxidation of fatty acids in BNip3 null liver and also defective glucose output under fasting conditions. These metabolic defects in BNip3 null liver were linked to increased mitochondrial mass and increased hepatocellular respiration in the presence of glucose. However, despite elevated mitochondrial mass, an increased proportion of mitochondria exhibited loss of mitochondrial membrane potential, abnormal structure, and reduced oxygen consumption. Elevated reactive oxygen species, inflammation, and features of steatohepatitis were also observed in the livers of BNip3 null mice. These results identify a role for BNip3 in limiting mitochondrial mass and maintaining mitochondrial integrity in the liver that has consequences for lipid metabolism and disease
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