687 research outputs found
A dedicated algorithm for calculating ground states for the triangular random bond Ising model
In the presented article we present an algorithm for the computation of
ground state spin configurations for the 2d random bond Ising model on planar
triangular lattice graphs. Therefore, it is explained how the respective ground
state problem can be mapped to an auxiliary minimum-weight perfect matching
problem, solvable in polynomial time. Consequently, the ground state properties
as well as minimum-energy domain wall (MEDW) excitations for very large 2d
systems, e.g. lattice graphs with up to N=384x384 spins, can be analyzed very
fast. Here, we investigate the critical behavior of the corresponding T=0
ferromagnet to spin-glass transition, signaled by a breakdown of the
magnetization, using finite-size scaling analyses of the magnetization and MEDW
excitation energy and we contrast our numerical results with previous
simulations and presumably exact results.Comment: 5 pages, 5 figure
Heavy mineral analysis by ICP-AES a tool to aid sediment provenancing
Correlation and provenancing of sediments/sedimentary rocks can be achieved by several techniques; a common approach is through the identification and quantification of heavy minerals using a petrological microscope. This can be time consuming, the analysis of heavy minerals by inductively coupled plasma atomic emission spectroscopy offers a faster alternative, by determining key elements associated with specific heavy minerals. Here we outline a method for determining heavy mineral species though ICP-AES using high temperature fusion with a lithium metaborate flux to ensure complete dissolution of resistate minerals. The method was tested in a provenance study of desert sands from the United Arab Emirates. The results are compared with those derived from traditional optical microscopy. These show good agreement for minerals with specific geochemical signatures, whilst the overall geochemistry of the heavy mineral concentrate was diagnostic of potential sediment sources. This geochemical approach is capable of processing large numbers of samples rapidly and is advocated as a screening technique. A combination of geochemical and mineralogical data produced by these techniques provides a powerful diagnostic tool for studies of heavy mineral signatures in sediments frequently used in mineral reconnaissance, paleogeographic reconstruction and reservoir characterisation in the petroleum industry
Near optimal configurations in mean field disordered systems
We present a general technique to compute how the energy of a configuration
varies as a function of its overlap with the ground state in the case of
optimization problems. Our approach is based on a generalization of the cavity
method to a system interacting with its ground state. With this technique we
study the random matching problem as well as the mean field diluted spin glass.
As a byproduct of this approach we calculate the de Almeida-Thouless transition
line of the spin glass on a fixed connectivity random graph.Comment: 13 pages, 7 figure
Distributed phase-covariant cloning with atomic ensembles via quantum Zeno dynamics
We propose an interesting scheme for distributed orbital state quantum
cloning with atomic ensembles based on the quantum Zeno dynamics. These atomic
ensembles which consist of identical three-level atoms are trapped in distant
cavities connected by a single-mode integrated optical star coupler. These
qubits can be manipulated through appropriate modulation of the coupling
constants between atomic ensemble and classical field, and the cavity decay can
be largely suppressed as the number of atoms in the ensemble qubits increases.
The fidelity of each cloned qubit can be obtained with analytic result. The
present scheme provides a new way to construct the quantum communication
network.Comment: 5 pages, 4 figure
Stress corrosion cracking in Al-Zn-Mg-Cu aluminum alloys in saline environments
Copyright 2013 ASM International. This paper was published in Metallurgical and Materials Transactions A, 44A(3), 1230 - 1253, and is made
available as an electronic reprint with the permission of ASM International. One print or electronic copy may
be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via
electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or
modification of the content of this paper are prohibited.Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack (“pop-in” vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies (E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under- and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak- and over-aged tempers, and for high-copper alloys in under- and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor
Autoregulation of von Willebrand factor function by a disulfide bond switch
Force-dependent binding of platelet glycoprotein Ib (GPIb) receptors to plasma von Willebrand factor (VWF) plays a key role in hemostasis and thrombosis. Previous studies have suggested that VWF activation requires force-induced exposure of the GPIb binding site in the A1 domain that is autoinhibited by the neighboring A2 domain. However, the biochemical basis of this “mechanopresentation” remains elusive. From a combination of protein chemical, biophysical, and functional studies, we find that the autoinhibition is controlled by the redox state of an unusual disulfide bond near the carboxyl terminus of the A2 domain that links adjacent cysteine residues to form an eight-membered ring. Only when the bond is cleaved does the A2 domain bind to the A1 domain and block platelet GPIb binding. Molecular dynamics simulations indicate that cleavage of the disulfide bond modifies the structure and molecular stresses of the A2 domain in a long-range allosteric manner, which provides a structural explanation for redox control of the autoinhibition. Significantly, the A2 disulfide bond is cleaved in ~75% of VWF subunits in healthy human donor plasma but in just ~25% of plasma VWF subunits from heart failure patients who have received extracorporeal membrane oxygenation support. This suggests that the majority of plasma VWF binding sites for platelet GPIb are autoinhibited in healthy donors but are mostly available in heart failure patients. These findings demonstrate that a disulfide bond switch regulates mechanopresentation of VWF.: This study was supported by grants from the National
Health and Medical Research Council of Australia (P.J.H.), Royal College of Pathologists
Foundation Kanematsu/Novo Nordisk Research Award (F.P. and L.J.), Diabetes Australia
Research Trust grant G179720 and Sydney Medical School Early-Career Researcher Kickstart
Grant (L.J.), National Heart Foundation of Australia Postdoctoral Fellowship (101285) (L.J.)
and British Heart Foundation Intermediate Basic Science Research Fellowship (FS/11/51/28920)
(B.M.L.), Deutsche Forschungsgemeinschaft (research unit FOR 1543 to C.A.-S., C.B., and F.G.),
the Center for Modelling and Simulation in the Biosciences postdoctoral program of
the Heidelberg University (A.B.), and the Klaus Tschira Foundation (F.G.). B.L. was supported
by the Dutch Thrombosis Foundation through grant number 2016-03.
Translating Message Sequence Charts to other Process Languages Using Process Mining
Message Sequence Charts (MSCs) are often used by software analysts when discussing the behavior of a system with different stakeholders. Often such discussions lead to more complete behavioral models in the form of, e.g., Event-driven Process Chains (EPCs), Unified Modeling Language (UML), activity diagrams, Business Process Modeling Notation (BPMN) models, Petri nets, etc. Process mining on the other hand, deals with the problem of constructing complete behavioral models by analyzing event logs of information systems. In contrast to existing process mining techniques, where logs are assumed to only contain implicit information, the approach presented in this paper combines the explicit knowledge captured in individual MSCs and the techniques and tools available in the process mining domain. This combination allows us to discover high-quality process models. To constructively add to the existing work on process mining, our approach has been implemented in the process mining framework ProM (www.processmining.org)
A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses
We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
Measurements of long-range near-side angular correlations in TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a
nucleon-nucleon centre-of-mass energy of TeV, collected
with the LHCb detector at the LHC. The analysis is based on data recorded in
two beam configurations, in which either the direction of the proton or that of
the lead ion is analysed. The correlations are measured in the laboratory
system as a function of relative pseudorapidity, , and relative
azimuthal angle, , for events in different classes of event
activity and for different bins of particle transverse momentum. In
high-activity events a long-range correlation on the near side, , is observed in the pseudorapidity range . This
measurement of long-range correlations on the near side in proton-lead
collisions extends previous observations into the forward region up to
. The correlation increases with growing event activity and is found
to be more pronounced in the direction of the lead beam. However, the
correlation in the direction of the lead and proton beams are found to be
compatible when comparing events with similar absolute activity in the
direction analysed.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-040.htm
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