109 research outputs found
Roles of two successive phase transitions in new spin-Peierls system TiOBr
In this sturdy, we determine the roles of two successive phase transitions in
the new spin-Peierls system TiOBr by electron and synchrotron X-ray diffraction
analyses. Results show an incommensurate superstructure along the h- and
k-directions between Tc1=27K and Tc2=47K, and a twofold superstructure which is
related to a spin-Peierls lattice distortion below Tc1. The diffuse scattering
observed above Tc2 indicates that a structural correlation develops at a high
temperature. We conclude that Tc2 is a second-order lock-in temperature, which
is related to the spin-Peierls lattice distortion with the incommensurate
structure, and that Tc1 is from incommensurate to commensurate phase transition
temperature accompanying the first-order spin-Peierls lattice distortion.Comment: 4 pages, 5 figure
Spin-Peierls transition in TiOCl
Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2
quantum magnet TiOCl shows that the phase transition at T_{c2} = 90 K
corresponds to a lowering of the lattice symmetry. Below T_{c1} = 66 K a
twofold superstructure develops, that indicates the formation of spin-singlet
pairs via direct exchange between neighboring Ti atoms, while the role of
superexchange is found to be negligible. TiOCl thus is identified as a
spin-Peierls system of pure 1D chains of atoms. The first-order character of
the transition at T_{c1} is explained by the competition between the
structurally deformed state below T_{c2} and the spin-Peierls state below
T_{c1}.Comment: Phys. Rev. B (Rapid Communications) in pres
GPUVerify: A Verifier for GPU Kernels
We present a technique for verifying race- and divergence-freedom of GPU kernels that are written in mainstream ker-nel programming languages such as OpenCL and CUDA. Our approach is founded on a novel formal operational se-mantics for GPU programming termed synchronous, delayed visibility (SDV) semantics. The SDV semantics provides a precise definition of barrier divergence in GPU kernels and allows kernel verification to be reduced to analysis of a sequential program, thereby completely avoiding the need to reason about thread interleavings, and allowing existing modular techniques for program verification to be leveraged. We describe an efficient encoding for data race detection and propose a method for automatically inferring loop invari-ants required for verification. We have implemented these techniques as a practical verification tool, GPUVerify, which can be applied directly to OpenCL and CUDA source code. We evaluate GPUVerify with respect to a set of 163 kernels drawn from public and commercial sources. Our evaluation demonstrates that GPUVerify is capable of efficient, auto-matic verification of a large number of real-world kernels
Spin gap formation in the quantum spin systems TiOX, X=Cl and Br
In the layered quantum spin systems TiOCl and TiOBr the magnetic
susceptibility shows a very weak temperature dependence at high temperatures
and transition-induced phenomena at low temperatures. There is a clear
connection of the observed transition temperatures to the distortion of the
octahedra and the layer separation. Band structure calculations point to a
relation of the local coordinations and the dimensionality of the magnetic
properties. While from magnetic Raman scattering only a small decrease of the
magnetic exchange by -5-10% is derived comparing TiOCl with TiOBr, the
temperature dependence of the magnetic susceptibility favors a much bigger
change.Comment: 5 figures, 15 pages, further information see
http://www.peter-lemmens.d
High yield synthesis of electrolyte heating assisted electrochemically exfoliated graphene for electromagnetic interference shielding applications
Herein, we demonstrate a facile one pot synthesis of graphene nanosheets by electrochemical exfoliation of graphite. In the present study, we report a significant increase in the yield of graphene by electrolyte heating assisted electrochemical exfoliation method. The obtained results of heating assisted electrochemically exfoliated graphene (utilizing H2SO4 + KOH + DW) synthesis clearly exhibit that the yield increases similar to 4.5 times i.e. from similar to 17% (room temperature) to similar to 77% (at 80 degrees C). A plausible mechanism for the enhanced yield based on lattice expansion and vibration of intercalated ions has been put forward and discussed in details. The quality of graphene was examined by Raman, XPS, FTIR, AFM, SEM, TEM/HRTEM and TGA techniques. The Raman as well as morphogenesis results confirm the quality of the graphene nanosheets. We have used this graphene as electromagnetic interference shielding material where a comparatively large quantity of graphene is required. This graphene exhibits enhanced shielding effectiveness (46 dB at 1 mm thickness of stacked graphene sheets in frequency region 12.4 to 18 GHz) as compared to conventional electromagnetic interference shielding materials, which is greater than the recommended limit (similar to 30 dB) for techno-commercial applications. Thus the present work is suggestive for future studies on enhancement of yield of high quality graphene by proposed method and the use of synthesized graphene in electromagnetic interference shielding and other possible applications
Fiddling while the ice melts? How organizational scholars can take a more active role in the climate change debate
The debate over anthropogenic climate change or the idea that human activities are altering the physical climate of the planet continues to rage amid seemingly irreconcilable differences, both within the developed world and between developed and less developed countries. With high uncertainty, rival worldviews, and wide diversity of meaning attached to the expression, climate change has become a key narrative within which local and transnational issues – economic, social, and political – are framed and contested. The field is fraught with controversies regarding causes and consequences, as well as different attitudes toward risks, technologies, and economic and social well-being for different groups. Parties also dispute how to share responsibility for reducing emissions – whether the issue primarily needs market, regulatory, technological, or behavioral solutions. Climate change is many things to many people. Competing interests negotiate over its interpretation and utilize various strategies to promote practices that advance their own understandings regarding climate change and its governance
Constructing a climate change logic: An institutional perspective on the "tragedy of the commons"
Despite increasing interest in transnational fields, transnational commons have received little attention. In contrast to economic models of commons, which argue that commons occur naturally and are prone to collective inaction and tragedy, we introduce a social constructionist account of commons. Specifically, we show that actor-level frame changes can eventually lead to the emergence of an overarching, hybrid "commons logic" at the field level. These frame shifts enable actors with different logics to reach a working consensus and avoid "tragedies of the commons." Using a longitudinal analysis of key actors' logics and frames, we tracked the evolution of the global climate change field over 40 years. We bracketed time periods demarcated by key field-configuring events, documented the different frame shifts in each time period, and identified five mechanisms (collective theorizing, issue linkage, active learning, legitimacy seeking, and catalytic amplification) that underpin how and why actors changed their frames at various points in time-enabling them to move toward greater consensus around a transnational commons logic. In conclusion, the emergence of a commons logic in a transnational field is a nonlinear process and involves satisfying three conditions: (1) key actors view their fates as being interconnected with respect to a problem issue, (2) these actors perceive their own behavior as contributing to the problem, and (3) they take collective action to address the problem. Our findings provide insights for multinational companies, nation-states, nongovernmental organizations, and other stakeholders in both conventional and unconventional commons
Effects of Blood Products on Inflammatory Response in Endothelial Cells In Vitro
BACKGROUND: Transfusing blood products may induce inflammatory reactions within the vascular compartment potentially leading to a systemic inflammatory response. Experiments were designed to assess the inflammatory potential of different blood products in an endothelial cell-based in vitro model and to compare baseline levels of potentially activating substances in transfusion products.
METHODS: The inflammatory response from pre-activated (endotoxin-stimulated) and non-activated endothelial cells as well as neutrophil endothelial transmigration in response to packed red blood cells (PRBC), platelet concentrates (PC) and fresh frozen plasma (FFP) was determined. Baseline inflammatory mediator and lipid concentrations in blood products were evaluated.
RESULTS: Following incubation with all blood products, an increased inflammatory mediator release from endothelial cells was observed. Platelet concentrates, and to a lesser extent also FFP, caused the most pronounced response, which was accentuated in already pre-stimulated endothelial cells. Inflammatory response of endothelial cells as well as blood product-induced migration of neutrophils through the endothelium was in good agreement with the lipid content of the according blood product.
CONCLUSION: Within the group of different blood transfusion products both PC and FFP have a high inflammatory potential with regard to activation of endothelial cells. Inflammation upon blood product exposure is strongly accentuated when endothelial cells are pre-injured. High lipid contents in the respective blood products goes along with an accentuated inflammatory reaction from endothelial cells
MHC class I–specific antibody binding to nonhematopoietic cells drives complement activation to induce transfusion-related acute lung injury in mice
In a manner partially independent of activating Fcγ receptors, antibody-mediated production of complement component C5a and recruitment of macrophages elicit transfusion-related acute lung injury in mice
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