522 research outputs found
Efficient adaptive importance sampling for time-dependent reliability analysis of structures
Various methods have been used by researchers to evaluate the time-dependent reliability of structures. Among them, the stochastic-process-based method is theoretically the most rigorous but also computationally the most expensive. To enable the wide application of the stochastic-process-based method in the time-dependent reliability analysis of complex problems, an efficient importance sampling method is presented. This new method, extended from an existing method for time-independent reliability analysis, offers an efficient solution for time-dependent problems of structural systems with multiple important regions. Furthermore, to enhance the efficiency and robustness of the proposed method, a number of numerical measures are proposed. The capability and efficiency of the proposed method are demonstrated through two numerical examples
Unified cyclic stress–strain model for normal and high strength concrete confined with FRP
Fiber reinforced polymer (FRP) has become increasingly popular as a confining material for concrete, both in the strengthening of existing columns where FRP wraps with fibers oriented completely or predominantly in the hoop direction are typically used, and in new construction where filament-wound FRP tubes with fibers oriented at desired angles to the longitudinal axis are typically used. For both types of applications, the stress-strain behavior of FRP-confined concrete under cyclic axial compression needs to be properly understood and modeled for the accurate simulation of such columns under seismic loading. This paper presents an improved cyclic stress-strain model for FRP-confined concrete on the basis of a critical assessment of an earlier model proposed by Lam and Teng in 2009 by making use of a database containing new test results of both concrete-filled FRP tubes (CFFTs) and concrete cylinders confined with an FRP wrap. The assessment reveals several deficiencies of Lam and Teng\u27s model due to the limited test results available to them. The proposed model corrects these deficiencies and is shown to provide reasonably accurate predictions for both concrete in CFFTs and concrete confined with an FRP wrap and for both normal strength concrete (NSC) and high strength concrete (HSC)
A CsI(Tl) Scintillating Crystal Detector for the Studies of Low Energy Neutrino Interactions
Scintillating crystal detector may offer some potential advantages in the
low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed
near the core of Nuclear Power Station II in Taiwan is being constructed for
the studies of electron-neutrino scatterings and other keV-MeV range neutrino
interactions. The motivations of this detector approach, the physics to be
addressed, the basic experimental design, and the characteristic performance of
prototype modules are described. The expected background channels and their
experimental handles are discussed.Comment: 34 pages, 11 figures, submitted to Nucl. Instrum. Method
Endothelial junctional membrane protrusions serve as hotspots for neutrophil transmigration
Upon inflammation, leukocytes rapidly transmigrate across the endothelium to enter the inflamed tissue. Evidence accumulates that leukocytes use preferred exit sites, alhough it is not yet clear how these hotspots in the endothelium are defined and how they are recognized by the leukocyte. Using lattice light sheet microscopy, we discovered that leukocytes prefer endothelial membrane protrusions at cell junctions for transmigration. Phenotypically, these junctional membrane protrusions are present in an asymmetric manner, meaning that one endothelial cell shows the protrusion and the adjacent one does not. Consequently, leukocytes cross the junction by migrating underneath the protruding endothelial cell. These protrusions depend on Rac1 activity and by using a photo-activatable Rac1 probe, we could artificially generate local exit-sites for leukocytes. Overall, we have discovered a new mechanism that uses local induced junctional membrane protrusions to facilitate/steer the leukocyte escape/exit from inflamed vessel walls
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
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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