3,055 research outputs found
Study of neutron response and n-gamma discrimination by charge comparison method for small liquid scintillation detector
The study of the neutron response and n-gamma discrimination for small
(18x26x8) mm3 liquid scintillator BC501A (Bicron) detector was carried out by
digital charge comparison method. Three ranges of neutron energies were used:
uniform distribution from 0.95 MeV to 1.23 MeV, continuous spectra of AmBe
source and monoenergetic 16.2 MeV neutrons. The obtained results are compared
with those for cylindrical liquid scintillation detector (40 mm diameter, 60 mm
length) at the same energies of neutrons. A dramatic fall of the neutron
response function at 400 keVee for small detector at 16.2 MeV neutron energy
was measured. For (0.95 - 1.23) MeV neutron energy range such fall takes place
at 260 keVee. The greater slope of neutron locus at (0.95 - 1.23) MeV neutron
energy comparing to 16.2 MeV for both detectors is explained by longer tail of
pulse from proton recoils within (0.1-1.23) MeV energy range.Comment: submitted to Nuclear Instruments and Methods in Phys. Res. Sect.
Arabidopsis Tetraspanins Are Confined to Discrete Expression Domains and Cell Types in Reproductive Tissues and Form Homo- and Heterodimers When Expressed in Yeast
Tetraspanins are evolutionary conserved transmembrane proteins present in all multicellular organisms. In animals, they are known to act as central organizers of membrane complexes and thought to facilitate diverse biological processes, such as cell proliferation, movement, adhesion, and fusion. The genome of Arabidopsis (Arabidopsis thaliana) encodes 17 members of the tetraspanin family; however, little is known about their functions in plant development. Here, we analyzed their phylogeny, protein topology, and domain structure and surveyed their expression and localization patterns in reproductive tissues. We show that, despite their low sequence identity with metazoan tetraspanins, plant tetraspanins display the typical structural topology and most signature features of tetraspanins in other multicellular organisms. Arabidopsis tetraspanins are expressed in diverse tissue domains or cell types in reproductive tissues, and some accumulate at the highest levels in response to pollination in the transmitting tract and stigma, male and female gametophytes and gametes. Arabidopsis tetraspanins are preferentially targeted to the plasma membrane, and they variously associate with specialized membrane domains, in a polarized fashion, to intercellular contacts or plasmodesmata. A membrane-based yeast (Saccharomyces cerevisiae) two-hybrid system established that tetraspanins can physically interact, forming homo- and heterodimer complexes. These results, together with a likely genetic redundancy, suggest that, similar to their metazoan counterparts, plant tetraspanins might be involved in facilitating intercellular communication, whose functions might be determined by the composition of tetraspanin complexes and their binding partners at the cell surface of specific cell types.Marie Curie International Reintegration grant: (no. IRG–256602), U.S. Department of Agriculture-Agricultural Research Service Current Research Information System grant: (5335–21000–030–00D), Fundação
Ciência e Tecnologia Postdoctoral Fellowship: (SFRH/BPD/43584/2008), China Scholarship Council fellowship, UC-Berkeley College of Natural Resources SPUR
Revising the age for the Baptistina asteroid family using WISE/NEOWISE data
We have used numerical routines to model the evolution of a simulated
Baptistina family to constrain its age in light of new measurements of the
diameters and albedos of family members from the Wide-field Infrared Survey
Explorer. We also investigate the effect of varying the assumed physical and
orbital parameters on the best-fitting age. We find that the physically allowed
range of assumed values for the density and thermal conductivity induces a
large uncertainty in the rate of evolution. When realistic uncertainties in the
family members' physical parameters are taken into account we find the
best-fitting age can fall anywhere in the range of 140-320 Myr. Without more
information on the physical properties of the family members it is difficult to
place a more firm constraint on Baptistina's age.Comment: 27 pages, 16 figures, accepted to Ap
Physical and dynamical characterization of the Euphrosyne asteroid Family
The Euphrosyne asteroid family occupies a unique zone in orbital element
space around 3.15 au and may be an important source of the low-albedo
near-Earth objects. The parent body of this family may have been one of the
planetesimals that delivered water and organic materials onto the growing
terrestrial planets. We aim to characterize the compositional properties as
well as the dynamical properties of the family. We performed a systematic study
to characterize the physical properties of the Euphrosyne family members via
low-resolution spectroscopy using the IRTF telescope. In addition, we performed
smoothed-particle hydrodynamics (SPH) simulations and N-body simulations to
investigate the collisional origin, determine a realistic velocity field, study
the orbital evolution, and constrain the age of the Euphrosyne family. Our
spectroscopy survey shows that the family members exhibit a tight taxonomic
distribution, suggesting a homogeneous composition of the parent body. Our SPH
simulations are consistent with the Euphrosyne family having formed via a
reaccumulation process instead of a cratering event. Finally, our N-body
simulations indicate that the age of the family is 280 Myr +180/-80 Myr, which
is younger than a previous estimate.Comment: 10 pages, 13 figures, accepted to be published in A&
The Effectiveness of Monetary Policy Anchors: Firm-Level Evidence
Abstract Analyses of monetary policy posit that exchange-rate pegs, inflation targets, and central bank independence can help anchor private-sector inflation expectations+ Yet there are few direct tests of this argument+ We offer cross-national, microlevel evidence on the effectiveness of monetary anchors in controlling private-sector inflation concerns+ Using firm-level data from eighty-one countries~approximately 10,000 firms!, we find evidence that "international" anchors~exchange-rate commitments! correlate significantly with a substantial reduction in private-sector concerns about inflation while "domestic" anchors~inflation targeting and central bank independence! do not+ Our conjecture is that private-sector inflation expectations are more responsive to exchange-rate anchors because they are more transparent, more constraining, and more costly than domestic anchoring arrangements+ The literature on monetary policy highlights the role of monetary institutions in stabilizing private-sector inflation expectations+ Central bank independence~CBI!, inflation targeting~IT!, and fixed exchange rates~pegs! are widely viewed as institutions that have the capacity to mitigate private-sector concerns that policymakers will exploit them after they have locked in their price, wage, and investment decisions+ While other empirical research explores the institutional correlates of inflation and its variability-yielding mixed results-we use firm-level data in our study to directly assess the impact of monetary anchors on private-sector inflation concerns+ We find evidence that pegs mitigate firm owners' concerns with inflation, but that domestic anchors such as IT and CBI are uncorrelated with our microindicators of inflation expectations+ Considerable research has investigated the use of IT, CBI, and pegs as institutions that establish monetary policy credibility+ Whereas these anchors are expected
GSDMD membrane pore formation constitutes the mechanism of pyroptotic cell death
Pyroptosis is a lytic type of cell death that is initiated by inflammatory caspases. These caspases are activated within multi-protein inflammasome complexes that assemble in response to pathogens and endogenous danger signals. Pyroptotic cell death has been proposed to proceed via the formation of a plasma membrane pore, but the underlying molecular mechanism has remained unclear. Recently, gasdermin D (GSDMD), a member of the ill-characterized gasdermin protein family, was identified as a caspase substrate and an essential mediator of pyroptosis. GSDMD is thus a candidate for pyroptotic pore formation. Here, we characterize GSDMD function in live cells and in vitro We show that the N-terminal fragment of caspase-1-cleaved GSDMD rapidly targets the membrane fraction of macrophages and that it induces the formation of a plasma membrane pore. In vitro, the N-terminal fragment of caspase-1-cleaved recombinant GSDMD tightly binds liposomes and forms large permeability pores. Visualization of liposome-inserted GSDMD at nanometer resolution by cryo-electron and atomic force microscopy shows circular pores with variable ring diameters around 20 nm. Overall, these data demonstrate that GSDMD is the direct and final executor of pyroptotic cell death
Statistical Mechanics of Nonuniform Magnetization Reversal
The magnetization reversal rate via thermal creation of soliton pairs in
quasi-1D ferromagnetic systems is calculated. Such a model describes e.g. the
time dependent coercivity of elongated particles as used in magnetic recording
media. The energy barrier that has to be overcome by thermal fluctuations
corresponds to a soliton-antisoliton pair whose size depends on the external
field. In contrast to other models of first order phase transitions such as the
phi^4 model, an analytical expression for this energy barrier is found for all
values of the external field. The magnetization reversal rate is calculated
using a functional Fokker-Planck description of the stochastic magnetization
dynamics. Analytical results are obtained in the limits of small fields and
fields close to the anisotropy field. In the former case the hard-axis
anisotropy becomes effectively strong and the magnetization reversal rate is
shown to reduce to the nucleation rate of soliton-antisoliton pairs in the
overdamped double sine-Gordon model. The present theory therefore includes the
nucleation rate of soliton-antisoliton pairs in the double sine-Gordon chain as
a special case. These results demonstrate that for elongated particles, the
experimentally observed coercivity is significantly lower than the value
predicted by the standard theories of N\'eel and Brown.Comment: 21 pages RevTex 3.0 (twocolumn), 6 figures available on request, to
appear in Phys Rev B, Dec (1994
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