61 research outputs found
Coherent vs incoherent interlayer transport in layered metals
The magnetic-field, temperature, and angular dependence of the interlayer
magnetoresistance of two different quasi-two-dimensional (2D) organic
superconductors is reported. For -(BEDT-TTF)I we find a
well-resolved peak in the angle-dependent magnetoresistance at (field parallel to the layers). This clear-cut proof for the coherent
nature of the interlayer transport is absent for
''-(BEDT-TTF)SFCHCFSO. This and the non-metallic
behavior of the magnetoresistance suggest an incoherent quasiparticle motion
for the latter 2D metal.Comment: 4 pages, 4 figures. Phys. Rev. B, in pres
Capture of Solar and Higher-Energy Neutrinos by Iodine 127
We discuss and improve a recent treatment of the absorption of solar
neutrinos by I, in connection with a proposed solar neutrino
detector. With standard-solar-model fluxes and an in-medium value of -1.0 for
the axial-vector coupling constant , we obtain a B-neutrino cross
section of 3.3, about 50\% larger than in our previous work,
and a Be cross section that is less certain but nevertheless also larger
than before. We then apply the improved techniques to higher incoming energies
that obtain at the LAMPF beam dump, where an experiment is underway to finalize
a calibration of the I with electron neutrinos from muon decay. We
find that forbidden operators, which play no role in solar-neutrino absorption,
contribute nonnegligibly to the LAMPF cross section, and that the preliminary
LAMPF mean value is significantly larger than our prediction.Comment: 13 pages + 3 postscript figures (attached), in RevTex 3 , submitted
to Phys. Rev.
Nuclear Skins and Halos in the Mean-Field Theory
Nuclei with large neutron-to-proton ratios have neutron skins, which manifest
themselves in an excess of neutrons at distances greater than the radius of the
proton distribution. In addition, some drip-line nuclei develop very extended
halo structures. The neutron halo is a threshold effect; it appears when the
valence neutrons occupy weakly bound orbits. In this study, nuclear skins and
halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov
and relativistic Hartree-Bogoliubov theories for spherical shapes. It is
demonstrated that skins, halos, and surface thickness can be analyzed in a
model-independent way in terms of nucleonic density form factors. Such an
analysis allows for defining a quantitative measure of the halo size. The
systematic behavior of skins, halos, and surface thickness in even-even nuclei
is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical
Review
Can tonne-scale direct detection experiments discover nuclear dark matter?
Models of nuclear dark matter propose that the dark sector contains large
composite states consisting of dark nucleons in analogy to Standard Model
nuclei. We examine the direct detection phenomenology of a particular class of
nuclear dark matter model at the current generation of tonne-scale liquid noble
experiments, in particular DEAP-3600 and XENON1T. In our chosen nuclear dark
matter scenario distinctive features arise in the recoil energy spectra due to
the non-point-like nature of the composite dark matter state. We calculate the
number of events required to distinguish these spectra from those of a standard
point-like WIMP state with a decaying exponential recoil spectrum. In the most
favourable regions of nuclear dark matter parameter space, we find that a few
tens of events are needed to distinguish nuclear dark matter from WIMPs at the
level in a single experiment. Given the total exposure time of
DEAP-3600 and XENON1T we find that at best a distinction is
possible by these experiments individually, while sensitivity is
reached for a range of parameters by the combination of the two experiments. We
show that future upgrades of these experiments have potential to distinguish a
large range of nuclear dark matter models from that of a WIMP at greater than
.Comment: 23 pages, 7 multipanel figure
Dark Matter Search with CUORE-0 and CUORE
The Cryogenic Underground Observatory for Rare Events (CUORE) is a ton-scale experiment made of TeO2 bolometers that will probe the neutrinoless double beta decay of 130Te. Excellent energy resolution, low threshold and low background make CUORE sensitive to nuclear recoils, allowing a search for dark matter interactions. With a total mass of 741 kg of TeO2, CUORE can search for an annual modulation of the counting rate at low energies. We present data obtained with CUORE-like detectors and the prospects for a dark matter search in CUORE-0, a 40-kg prototype, and CUORE
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
Effects of the SSRL wiggler on the SPEAR beam
A wiggler for SSRL has been built, is now undergoing magnetic testing, and is scheduled to be installed in SPEAR in time for the October turn-on. This wiggler is a 7-pole (5 full- and 2 half-pole), 3-period design, approximately 1 m effective length, and designed to reach 18 kG peak field. It will be placed in the short straight section just counterclockwise from the south symmetry point. In this note, the effects of this wiggler on the beam are estimated by means of the computer program MAGIC and various matching schemes are investigated. 4 refs., 2 tabs
Emittance in a FODO-cell lattice
Several PEP Notes give formulas and curves for the variation of beam parameters in a FODO lattice as functions of focal length. However, because of approximations, the results for emittance are not accurate when the focusing is too strong. We give here the emittance calculation correct for any phase advance per cell between 0 and . 3 refs., 1 fig
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