839 research outputs found
A comparison of high temperature fatigue crack propagation in various sub-solvus heat treated turbine disc alloys
The microstructure and fatigue performance of three sub-solvus heat treated nickel based disc superalloys for turbine disc applications are reported. The alloy variants studied are RR1000, N18 and Udimet 720 Low Interstitial (U720Li), with the latter tested both in a standard and large grain variant (LG). Their microstructures are examined in terms of grain and gamma prime size. Fatigue crack growth (FCG) rates for all materials at 650ÂşC show that RR1000 provides the best performance, followed by U720Li-LG, N18 and U720Li. In general, the failure modes become increasingly intergranular with increasing ?K. Some of the variations in FCG rate between the alloys are due to reduction in grain boundary oxidation processes with increased grain size, but more subtle interplays between grain boundary character, alloy composition and slip character are also importan
Sudden switch of generalized Lieb-Robinson velocity in a transverse field Ising spin chain
The Lieb-Robinson theorem states that the speed at which the correlations
between two distant nodes in a spin network can be built through local
interactions has an upper bound, which is called the Lieb-Robinson velocity.
Our central aim is to demonstrate how to observe the Lieb-Robinson velocity in
an Ising spin chain with a strong transverse field. We adopt and compare four
correlation measures for characterizing different types of correlations, which
include correlation function, mutual information, quantum discord, and
entanglement of formation. We prove that one of correlation functions shows a
special behavior depending on the parity of the spin number. All the
information-theoretical correlation measures demonstrate the existence of the
Lieb-Robinson velocity. In particular, we find that there is a sudden switch of
the Lieb-Robinson speed with the increasing of the number of spin
Hysteretic behavior of the vortex lattice at the onset of the second peak for HgBaCuO superconductor
By means of local Hall probe ac and dc permeability measurements we
investigated the phase diagram of vortex matter for the HgBaCuO superconductor in the regime near the critical temperature. The second peak
line, , in contrast to what is usually assumed, doesn't terminate
at the critical temperature. Our local ac permeability measurements revealed
pronounced hysteretic behavior and thermomagnetic history effects near the
onset of the second peak, giving evidence for a phase transition of vortex
matter from an ordered qausilattice state to a disordered glass
Weakly coupled one-dimensional Mott insulators
We consider a model of one-dimensional Mott insulators coupled by a weak
interchain tunnelling . We first determine the single-particle Green's
function of a single chain by exact field-theoretical methods and then take the
tunnelling into account by means of a Random Phase Approximation (RPA). In
order to embed this approximation into a well-defined expansion with a small
parameter, the Fourier transform of the interchain coupling is
assumed to have a small support in momentum space such that every integration
over transverse wave vector yields a small factor . When
\tp(0) exceeds a critical value, a small Fermi surface develops in the form of
electron and hole pockets. We demonstrate that Luttinger's theorem holds both
in the insulating and in the metallic phases. We find that the quasi-particle
residue increases very fast through the transition and quickly reaches a
value of about . The metallic state close to the transition retains
many features of the one-dimensional system in the form of strong incoherent
continua.Comment: 14 pages, 13 figure
Evidence of Final-State Suppression of High-p_T Hadrons in Au + Au Collisions Using d + Au Measurements at RHIC
Transverse momentum spectra of charged hadrons with 6 GeV/c have
been measured near mid-rapidity (0.2 1.4) by the PHOBOS experiment
at RHIC in Au + Au and d + Au collisions at . The spectra for different collision centralities are compared to collisions at the same energy. The resulting nuclear modification
factor for central Au + Au collisions shows evidence of strong suppression of
charged hadrons in the high- region ( GeV/c). In contrast, the d +
Au nuclear modification factor exhibits no suppression of the high-
yields. These measurements suggest a large energy loss of the high-
particles in the highly interacting medium created in the central Au + Au
collisions. The lack of suppression in d + Au collisions suggests that it is
unlikely that initial state effects can explain the suppression in the central
Au + Au collisions.Comment: 3 pages, 4 figures, International Europhysics Conference on High
Energy Physics EPS (July 17th-23rd 2003) in Aachen, German
Talented suppliers? Strategic change and innovation in the UK aerospace industry
The 1990s marked the start of extensive re-structuring in the aerospace industry throughout the world. While the ensuing consolidation among prime contractors has been widely researched, the changes affecting the aerospace supply chain have received less attention. This study focuses on the re-structuring taking place within the supply chain of the UK aerospace industry. The findings point to extensive re-structuring. Unlike most earlier studies the lean supply model was found to be a powerful influence, with suppliers moving away from subcontractor status and instead taking on the mantle of âtalentedâ suppliers. While some of the implications of lean supply, in terms of the dynamics of innovation, were not apparent, there were modest signs of increased process innovation on the part of some suppliers
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Variation in Target Attainment of Beta-Lactam Antibiotic Dosing Between International Pediatric Formularies.
As antimicrobial susceptibility of common bacterial pathogens decreases, ensuring optimal dosing may preserve the use of older antibiotics in order to limit the spread of resistance to newer agents. Beta-lactams represent the most widely prescribed antibiotic class, yet most were licensed prior to legislation changes mandating their study in children. As a result, significant heterogeneity persists in the pediatric doses used globally, along with quality of evidence used to inform dosing. This review summarizes dosing recommendations from the major pediatric reference sources and tries to answer the questions: Does beta-lactam dose heterogeneity matter? Does it impact pharmacodynamic target attainment? For three important severe clinical infections-pneumonia, sepsis, and meningitis-pharmacokinetic models were identified for common for beta-lactam antibiotics. Real-world demographics were derived from three multicenter point prevalence surveys. Simulation results were compared with minimum inhibitory concentration distributions to inform appropriateness of recommended doses in targeted and empiric treatment. While cephalosporin dosing regimens are largely adequate for target attainment, they also pose the most risk of neurotoxicity. Our review highlights aminopenicillin, piperacillin, and meropenem doses as potentially requiring review/optimization in order to preserve the use of these agents in future
The role of skeletal micro-architecture in diagenesis and dating of Acropora palmata
Past variations in global sea-level reflect continental ice volume, a crucial factor for understanding the Earth's climate system. The Caribbean coral Acropora palmata typically forms dense stands in very shallow water and therefore fossil samples mark past sea-level. Uranium-series methods are commonly used to establish a chronology for fossil coral reefs, but are compromised by post mortem diagenetic changes to coral skeleton. Current screening approaches are unable to identify all altered samples, whilst models that attempt to correct for 'open-system' behaviour are not applicable across all diagenetic scenarios. In order to better understand how U-series geochemistry varies spatially with respect to diagenetic textures, we examine these aspects in relation to skeletal micro-structure and intra-crystalline amino acids, comparing an unaltered modern coral with a fossil A. palmata colony containing zones of diagenetic alteration (secondary overgrowth of aragonite, calcite cement and dissolution features). We demonstrate that the process of skeletogenesis in A. palmata causes heterogeneity in porosity, which can account for the observed spatial distribution of diagenetic features; this in turn explains the spatially-systematic trends in U-series geochemistry and consequently, U-series age. We propose a scenario that emphasises the importance of through-flow of meteoric waters, invoking both U-loss and absorption of mobilised U and Th daughter isotopes. We recommend selective sampling of low porosity A. palmata skeleton to obtain the most reliable U-series ages. We demonstrate that intra-crystalline amino acid racemisation (AAR) can be applied as a relative dating tool in Pleistocene A. palmata samples that have suffered heavy dissolution and are therefore unsuitable for U-series analyses. Based on relatively high intra-crystalline concentrations and appropriate racemisation rates, glutamic acid and valine are most suited to dating mid-late Pleistocene A. palmata. Significantly, the best-preserved material in the fossil specimen yields a U-series age of 165 Âą 8 ka, recording a paleo sea-level of -35 Âą 7 msl during the MIS 6.5 interstadial on Barbados
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
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