6,035 research outputs found
Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy
Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.Comment: 21 pages, 7 figure
The pasta phase within density dependent hadronic models
In the present paper we investigate the onset of the pasta phase with
different parametrisations of the density dependent hadronic model and compare
the results with one of the usual parametrisation of the non-linear Walecka
model. The influence of the scalar-isovector virtual delta meson is shown. At
zero temperature two different methods are used, one based on coexistent phases
and the other on the Thomas-Fermi approximation. At finite temperature only the
coexistence phases method is used. npe matter with fixed proton fractions and
in beta-equilibrium are studied. We compare our results with restrictions
imposed on the the values of the density and pressure at the inner edge of the
crust, obtained from observations of the Vela pulsar and recent isospin
diffusion data from heavy-ion reactions, and with predictions from spinodal
calculations.Comment: 15 pages, 11 figures and 7 table
Electron beam shaping via laser heater temporal shaping
Active longitudinal beam optics can help FEL facilities achieve cutting edge
performance by optimizing the beam to: produce multi-color pulses, suppress
caustics, or support attosecond lasing. As the next generation of
superconducting accelerators comes online, there is a need to find new elements
which can both operate at high beam power and which offer multiplexing
capabilities at Mhz repetition rate. Laser heater shaping promises to satisfy
both criteria by imparting a programmable slice-energy spread on a shot-by-shot
basis. We use a simple kinetic analysis to show how control of the slice energy
spread translates into control of the bunch current profile, and then we
present a collection of start-to-end simulations at LCLS-II in order to
illustrate the technique.Comment: 12 pages, 11 figure
Twist Mode in Spherical Alkali Metal Clusters
A remarkable orbital quadrupole magnetic resonance, so-called twist mode, is
predicted in alkali metal clusters where it is represented by
low-energy excitations of valence electrons with strong M2 transitions to the
ground state. We treat the twist by both macroscopic and microscopic ways. In
the latter case, the shell structure of clusters is fully exploited, which is
crucial for the considered size region (). The
energy-weighted sum rule is derived for the pseudo-Hamiltonian. In medium and
heavy spherical clusters the twist dominates over its spin-dipole counterpart
and becomes the most strong multipole magnetic mode.Comment: 8 pages, 4 figures, to be published in Phys. Rev. Lett., v.85, n.15,
200
Assessment of the stability of exogenous gamma hydroxybutyric acid (GHB) in stored blood and urine specimens
OBJECTIVE: The aim of this work
is to test the stability of exogenous GHB in whole
blood and urine samples collected from living and
deceased GHB free-users, spiked with known
concentrations of GHB and stored at different
temperatures (–20°C, 4°C and 20°C) up to 4 weeks.
MATERIALS AND METHODS: GHB was added
to GHB-free ante-mortem blood and urine samples
at the concentration of 5 and 10 mg/L, respectively
whereas in post-mortem blood and urine specimens at 50 and 10 mg/L respectively. All samples
were stored at three different temperatures: –20°C,
4°C and 20°C and extracted and analyzed at three
days, 1 week, 2 weeks, 3 and 4 weeks in duplicate.
No preservatives were added. GHB was quantified
by GC-MS after LLE according to a previously published method.
RESULTS: Post-mortem blood specimens
showed a reduction of GHB levels higher than 10%
only after a period of 4 weeks of storage for samples kept at +4°C and +20°C, whereas samples
stored at –20°C showed a mean reduction of 8.7%.
In post-mortem urine samples, there was a mean
reduction of GHB levels higher than 20% at all storage temperatures, after 4 weeks of storage. Antemortem blood samples showed a reduction of GHB
levels lower than 10% only after 3 days of storage
at –20°C and at +4°C (samples stored at +20°C
showed a mean reduction of 10.4%). After 4 weeks
of storage, there was a mean reduction of GHB
concentrations higher than 20% at all storage temperatures. Ante-mortem urine samples showed a
reduction of GHB levels higher than 10% after just
3 days of storage for samples kept at all tested temperatures. After 4 weeks of storage, there was a
mean reduction of GHB concentrations higher than
25% at all storage temperatures.
CONCLUSIONS: According to our findings, it
would be useful to perform GHB analysis both in
blood and urine specimens within 3 days of
sampling and the specimens should be stored at
–20°C or 4°C in order to avoid instability issues
The effect of verbal encouragement on performance and muscle fatigue in swimming
Background and Objectives: Verbal encouragement (VE) can be used to enhance performance in several sports, even though no studies have been conducted among swimmers and only a few effects have been reported in elite athletes. Besides influencing motor performance, VE is also known to enhance the physical load, thus potentially increasing the probability of developing fatigue. With this in mind, this study aimed to explore the effects of VE in swimmers in order to fill in the knowledge gap concerning the aquatic environment. Materials and Methods: Each athlete swam a maximal 200 m freestyle trial under two different conditions: one trial with VE and the other without VE. The two main outcome measures were: (1) performance velocity (m/s); and (2) muscle fatigue, investigated by means of surface electromyography. Sixty swimmers were recruited, aged 18.63 ± 3.46 years (median 18 years), 28 men (47%), and 32 women (53%), with 7.03 ± 3.9 years of experience. Results: With VE, performance significantly improved in the swim trial (p < 0.001, effect size (ES) −0.95, large). When breaking the results down into the first half (first (0–100 m) vs. the second half (100–200 m)), the ES was large in the first part (−1.11), indicating an improvement in performance. This worsened, however, in the second part of the trial (ES 0.63). In the multivariate analysis, years of experience were found to be a significant predictor of the change in overall performance (p = 0.011). There was a significant increase in muscle fatigue induced by VE, overall, and during the second half, but not during the first half of the trial. Conclusions: The present study indicates that VE during a middle-distance event (200 m) increases performance most in swimmers with little experience. However, it has a negative impact on fatigue
Reexamining the neutron skin thickness within a density dependent hadronic model
We calculate the skin thickness, binding energy, surface energy and density
profiles within the Dirac solution of a density dependent hadronic model and
compare with the NL3 parametrization results of the non-linear Wallecka model.
The asymmetry for polarized electron scattering is also obtained using a
partial wave expansion calculation. Results for 208Pb, 40Ca, 48Ca, 66Ni and
90Zr are shown and discussed.Comment: 7 pages, 6 figures and 2 tables. Accepted for publication in Physical
Review
Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser
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