22,579 research outputs found
Auger electron intensity variations in oxygen-exposed large grain polycrystalline silver
Auger electron spectroscopic studies of the grains in oxygen-charged polycrystal-line silver show significant intensity variations as a function of crystallographic orientation. These intensity variations were observed by studies of the Auger images and line scans of the different grains (randomly selected) for each silver transition energy. The results can be attributed to the diffraction of the ejected Auger electrons and interpreted by corresponding changes in the electron mean-free path for inelastic scattering and by oxygen atom accumulation in the subsurface. The subsurface (second layer) octahedral sites increased in size because of surface relaxation and serve as a stable reservoir for the dissolved oxygen
Events, processes, and the time of a killing
The paper proposes a novel solution to the problem of the time of a killing (ToK), which persistently besets theories of act-individuation. The solution proposed claims to expose a crucial wrong-headed assumption in the debate, according to which ToK is essentially a problem of locating some event that corresponds to the killing. The alternative proposal put forward here turns on recognizing a separate category of dynamic occurents, viz. processes. The paper does not aim to mount a comprehensive defense of process ontology, relying instead on extant defenses. The primary aim is rather to put process ontology to work in diagnosing the current state of play over ToK, and indeed in solving it
Collisional decay of a strongly driven Bose-Einstein condensate
We study the collisional decay of a strongly driven Bose-Einstein condensate
oscillating between two momentum modes. The resulting products of the decay are
found to strongly deviate from the usual s-wave halo. Using a stochastically
seeded classical field method we simulate the collisional manifold. These
results are also explained by a model of colliding Bloch states.Comment: 4 pages, 4 figure
Topology and Phases in Fermionic Systems
There can exist topological obstructions to continuously deforming a gapped
Hamiltonian for free fermions into a trivial form without closing the gap.
These topological obstructions are closely related to obstructions to the
existence of exponentially localized Wannier functions. We show that by taking
two copies of a gapped, free fermionic system with complex conjugate
Hamiltonians, it is always possible to overcome these obstructions. This allows
us to write the ground state in matrix product form using Grassman-valued bond
variables, and show insensitivity of the ground state density matrix to
boundary conditions.Comment: 4 pages, see also arxiv:0710.329
Facilitating Transformations in a Human Genome Project Database
Human Genome Project databases present a confluence of interesting database challenges: rapid schema and data evolution, complex data entry and constraint management, and the need to integrate multiple data sources and software systems which range over a wide variety of models and formats. While these challenges are not necessarily unique to biological databases, their combination, intensity and complexity are unusual and make automated solutions imperative. We illustrate these problems in the context of the Human Genome Database for Chromosome 22 (Chr22DB), and describe a new approach to a solution for these problems, by means of a deductive language for expressing database transformations and constraints
Voltage-dependent Block of the Cystic Fibrosis Transmembrane Conductance Regulator Cl- Channel by Two Closely Related Arylaminobenzoates
The gene defective in cystic fibrosis encodes a Cl- channel, the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is blocked by diphenylamine-2-carboxylate (DPC) when applied extracellularly at millimolar concentrations. We studied the block of CFTR expressed in Xenopus oocytes by DPC or by a closely related molecule, flufenamic acid (FFA). Block of whole-cell CFTR currents by bath-applied DPC or by FFA, both at 200 µM, requires several minutes to reach full effect. Blockade is voltage dependent, suggesting open-channel block: currents at positive potentials are not affected but currents at negative potentials are reduced. The binding site for both drugs senses ~40% of the electric field across the membrane, measured from the inside. In single-channel recordings from excised patches without blockers, the conductance was 8.0 ± 0.4 pS in symmetric 150 mM Cl^-. A subconductance state, measuring ~60% of the main conductance, was often observed. Bursts to the full open state lasting up to tens of seconds were uninterrupted at depolarizing membrane voltages. At hyperpolarizing voltages, bursts were interrupted by brief closures. Either DPC or FFA (50 µM) applied to the cytoplasmic or extracellular face of the channel led to an increase in flicker at V_m =-100 mV and not at V_m = +100 mV, in agreement with whole-cell experiments. DPC induced a higher frequency of flickers from the cytoplasmic side than the extracellular side. FFA produced longer closures than DPC; the FFA closed time was roughly equal (~ 1.2 ms) at -100 mV with application from either side. In cell-attached patch recordings with DPC or FFA applied to the bath, there was flickery block at V_m = -100 mV, confirming that the drugs permeate through the membrane to reach the binding site. The data are consistent with the presence of a single binding site for both drugs, reached from either end of the channel. Open-channel block by DPC or FFA may offer tools for use with site-directed mutagenesis to describe the permeation pathway
Damping of bulk excitations over an elongated BEC - the role of radial modes
We report the measurement of Beliaev damping of bulk excitations in cigar
shaped Bose Einstein condensates of atomic vapor. By using post selection,
excitation line shapes of the total population are compared with those of the
undamped excitations. We find that the damping depends on the initial
excitation energy of the decaying quasi particle, as well as on the excitation
momentum. We model the condensate as an infinite cylinder and calculate the
damping rates of the different radial modes. The derived damping rates are in
good agreement with the experimentally measured ones. The damping rates
strongly depend on the destructive interference between pathways for damping,
due to the quantum many-body nature of both excitation and damping products.Comment: 5 pages, 4 figure
Reconstructing Seesaws
We explore some aspects of "reconstructing" the heavy singlet sector of
supersymmetric type I seesaw models, for two, three or four singlets. We work
in the limit where one light neutrino is massless. In an ideal world, where
selected coefficients of the TeV-scale effective Lagrangian could be measured
with arbitrary accuracy, the two-singlet case can be reconstructed, two three
or more singlets can be differentiated, and an inverse seesaw with four
singlets can be reconstructed. In a more realistic world, we estimate \ell_\a
\to \ell_\b \gamma expectations with a "Minimal-Flavour-Violation-like"
ansatz, which gives a relation between ratios of the three branching ratios.
The two singlet model predicts a discrete set of ratios.Comment: 14 page
On the QCD corrections to the charged Higgs decay of a heavy quark
Using dimensional regularization for both infrared and ultraviolet
divergences, we confirm that the QCD corrections to the decay width
are equal to those to in the limit of a
large quark mass.Comment: 6 pages, report Alberta Thy-25-9
Feasibility of Comparing the Results of Pancreatic Resections between Surgeons: A Systematic Review and Meta-Analysis of Pancreatic Resections
Background. Indicators of operative outcomes could be used to identify underperforming surgeons for support and training. The feasibility of identifying HPB surgeons with poor operative performance ("outliers") based on the results of pancreatic resections is not known. Methods. A systematic review of Medline, Embase, and the Cochrane library was performed to identify studies on pancreatic resection including at least 100 patients and published between 2004 and 2014. Proportions that lay outside the upper 95% and 99.8% confidence intervals based on results of the systematic reviews were considered as "outliers." Results. In total, 30 studies reporting on 10712 patients were eligible for inclusion in this review. The average short-term mortality after pancreatic resections was 3.1% and proportion of patients with procedure-related complications was 47.0%. None of the classification systems assessed the long-term impact of the complications on patients. The surgeon-specific mortality should be 5 times the average mortality before he or she can be identified as an outlier with 0.1% false positive rate if he or she performs 50 surgeries a year. Conclusions. A valid risk prognostic model and a classification system of surgical complications are necessary before meaningful comparisons of the operative performance between pancreatic surgeons can be made
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