604 research outputs found
Magnetic switching in granular FePt layers promoted by near-field laser enhancement
Light-matter interaction at the nanoscale in magnetic materials is a topic of
intense research in view of potential applications in next-generation
high-density magnetic recording. Laser-assisted switching provides a pathway
for overcoming the material constraints of high-anisotropy and high-packing
density media, though much about the dynamics of the switching process remains
unexplored. We use ultrafast small-angle x-ray scattering at an x-ray
free-electron laser to probe the magnetic switching dynamics of FePt
nanoparticles embedded in a carbon matrix following excitation by an optical
femtosecond laser pulse. We observe that the combination of laser excitation
and applied static magnetic field, one order of magnitude smaller than the
coercive field, can overcome the magnetic anisotropy barrier between "up" and
"down" magnetization, enabling magnetization switching. This magnetic switching
is found to be inhomogeneous throughout the material, with some individual FePt
nanoparticles neither switching nor demagnetizing. The origin of this behavior
is identified as the near-field modification of the incident laser radiation
around FePt nanoparticles. The fraction of not-switching nanoparticles is
influenced by the heat flow between FePt and a heat-sink layer
Amixicile reduces severity of cryptosporidiosis but does not have in vitro activity against Cryptosporidium
Cryptosporidium species cause significant morbidity in malnourished children. Nitazoxanide (NTZ) is the only approved treatment for cryptosporidiosis, but NTZ has diminished effectiveness during malnutrition. Here, we show that amixicile, a highly selective water-soluble derivative of NTZ diminishes Cryptosporidium infection severity in a malnourished mouse model despite a lack of direct anticryptosporidial activity. We suggest that amixicile, by tamping down anaerobes associated with intestinal inflammation, reverses weight loss and indirectly mitigates infection-associated pathology
Dark energy and key physical parameters of clusters of galaxies
We study physics of clusters of galaxies embedded in the cosmic dark energy
background. Under the assumption that dark energy is described by the
cosmological constant, we show that the dynamical effects of dark energy are
strong in clusters like the Virgo cluster. Specifically, the key physical
parameters of the dark mater halos in clusters are determined by dark energy:
1) the halo cut-off radius is practically, if not exactly, equal to the
zero-gravity radius at which the dark matter gravity is balanced by the dark
energy antigravity; 2) the halo averaged density is equal to two densities of
dark energy; 3) the halo edge (cut-off) density is the dark energy density with
a numerical factor of the unity order slightly depending on the halo profile.
The cluster gravitational potential well in which the particles of the dark
halo (as well as galaxies and intracluster plasma) move is strongly affected by
dark energy: the maximum of the potential is located at the zero-gravity radius
of the cluster.Comment: 8 pages, 1 figur
"Dark energy" in the Local Void
The unexpected discovery of the accelerated cosmic expansion in 1998 has
filled the Universe with the embarrassing presence of an unidentified "dark
energy", or cosmological constant, devoid of any physical meaning. While this
standard cosmology seems to work well at the global level, improved knowledge
of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently
suggested repulsive-gravity scenario can account for some of the features that
are unexplained by the standard model. Through simple dynamical considerations,
we find that the Local Void could host an amount of antimatter
() roughly equivalent to the mass of a typical
supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this "dark repulsor" can explain the anomalous motion of the
Local Sheet away from the Local Void, as well as several other properties of
nearby galaxies that seem to require void evacuation and structure formation
much faster than expected from the standard model. At the global cosmological
level, gravitational repulsion from antimatter hidden in voids can provide more
than enough potential energy to drive both the cosmic expansion and its
acceleration, with no need for an initial "explosion" and dark energy.
Moreover, the discrete distribution of these dark repulsors, in contrast to the
uniformly permeating dark energy, can also explain dark flows and other
recently observed excessive inhomogeneities and anisotropies of the Universe.Comment: 6 pages, accepted as a Letter to the Editor by Astrophysics and Space
Scienc
Evolution of the nuclear spin-orbit splitting explored via the <sup>32</sup>Si<i>(d,p)</i><sup>33</sup>Si reaction using SOLARIS
The spin-orbit splitting between neutron 1p orbitals at 33Si has been deduced using the single-neutron-adding (d,p) reaction in inverse kinematics with a beam of 32Si, a long-lived radioisotope. Reaction products were analyzed by the newly implemented SOLARIS spectrometer at the reaccelerated-beam facility at the National Superconducting Cyclotron Laboratory. The measurements show reasonable agreement with shell-model calculations that incorporate modern cross-shell interactions, but they contradict the prediction of proton density depletion based on relativistic mean-field theory. The evolution of the neutron 1p-shell orbitals is systematically studied using the present and existing data in the isotonic chains of = 17, 19, and 21. In each case, a smooth decrease in the separation of the - orbitals is seen as the respective p-orbitals approach zero binding, suggesting that the finite nuclear potential strongly influences the evolution of nuclear structure in this region
Marijuana use associations with pulmonary symptoms and function in Tobacco smokers enrolled in the Subpopulations and Intermediate Outcome Measures in COPD study (SPIROMICS)
Background: Marijuana is often smoked via a filterless cigarette and contains similar chemical makeup as smoked tobacco. There are few publications describing usage patterns and respiratory risks in older adults or in those with chronic obstructive pulmonary disease (COPD). Methods: A cross-sectional analysis of current and former tobacco smokers from the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) study assessed associations between marijuana use and pulmonary outcomes. Marijuana use was defined as never, former (use over 30 days ago), or current (use within 30 days). Respiratory health was assessed using quantitative high-resolution computed tomography (HRCT) scans, pulmonary function tests and questionnaire responses about respiratory symptoms. Results: Of the total 2304 participants, 1130 (49%) never, 982 (43%) former, and 192 (8%) current marijuana users were included. Neither current nor former marijuana use was associated with increased odds of wheeze (odds ratio [OR] 0.87, OR 0.97), cough (OR 1.22; OR 0.93) or chronic bronchitis (OR 0.87; OR 1.00) when compared to never users. Current and former marijuana users had lower quantitative emphysema (P=0.004, P=0.03), higher percent predicted forced expiratory volume in 1 second (FEV1%) (P < 0.001, P < 0.001), and percent predicted forced vital capacity (FVC%) (p < 0.001, P < 0.001). Current marijuana users exhibited higher total tissue volume (P=0.003) while former users had higher air trapping (P < 0.001) when compared to never marijuana users. Conclusions: Marijuana use was found to have little to no association with poor pulmonary health in older current and former tobacco smokers after adjusting for covariates. Higher forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) was observed among current marijuana users. However, higher joint years was associated with more chronic bronchitis symptoms (e.g., wheeze), and this study cannot determine if long-term heavy marijuana smoking in the absence of tobacco smoking is associated with lung symptoms, airflow obstruction, or emphysema, particularly in those who have never smoked tobacco cigarettes
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at GeV
We report the first measurement of the opening angle distribution between
pairs of jets produced in high-energy collisions of transversely polarized
protons. The measurement probes (Sivers) correlations between the transverse
spin orientation of a proton and the transverse momentum directions of its
partons. With both beams polarized, the wide pseudorapidity () coverage for jets permits separation of Sivers functions for the valence
and sea regions. The resulting asymmetries are all consistent with zero and
considerably smaller than Sivers effects observed in semi-inclusive deep
inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the
new results with the sizable transverse spin effects seen in SIDIS and forward
hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure
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