4,165 research outputs found
Guiding of Rydberg atoms in a high-gradient magnetic guide
We study the guiding of Rb 59D Rydberg atoms in a linear,
high-gradient, two-wire magnetic guide. Time delayed microwave ionization and
ion detection are used to probe the Rydberg atom motion. We observe guiding of
Rydberg atoms over a period of 5 ms following excitation. The decay time of the
guided atom signal is about five times that of the initial state. We attribute
the lifetime increase to an initial phase of -changing collisions and
thermally induced Rydberg-Rydberg transitions. Detailed simulations of Rydberg
atom guiding reproduce most experimental observations and offer insight into
the internal-state evolution
Time and energy constraints and the relationships between currencies in foraging theory
Measured foraging strategies often cluster around values that maximize the ratio of energy gained over energy spent while foraging (efficiency), rather than values that would maximize the long-term net rate of energy gain (rate). The reasons for this are not understood. This paper focuses on time and energy constraints while foraging to illustrate the relationship between efficiency and rate-maximizing strategies and develops models that provide a simple framework to analyze foraging strategies in two distinct foraging contexts. We assume that while capturing and ingesting food for their own use (which we term feeding), foragers behave so as to maximize the total net daily energetic gain. When gathering food for others or for storage (which we term provisioning), we assume that foragers behave so as to maximize the total daily delivery, subject to meeting their own energetic requirements. In feeding contexts, the behavior maximizing total net daily gain also maximizes efficiency when daily intake is limited by the assimilation capacity. In contrast, when time available to forage sets the limit to gross intake, the behavior maximizing total net daily gain also maximizes rate. In provisioning contexts, when daily delivery is constrained by the energy needed to power self-feeding, maximizing efficiency ensures the highest total daily delivery. When time needed to recoup energetic expenditure limits total delivery, a low self-feeding rate relative to the rate of energy expenditure favors efficient strategies. However, as the rate of self-feeding increases, foraging behavior deviates from efficiency maximization in the direction predicted by rate maximization. Experimental manipulations of the rate of self-feeding in provisioning contexts could be a powerful tool to explore the relationship between rate and efficiency-maximizing behavio
Quantum simulation of the Klein paradox with trapped ions
We report on quantum simulations of relativistic scattering dynamics using
trapped ions. The simulated state of a scattering particle is encoded in both
the electronic and vibrational state of an ion, representing the discrete and
continuous components of relativistic wave functions. Multiple laser fields and
an auxiliary ion simulate the dynamics generated by the Dirac equation in the
presence of a scattering potential. Measurement and reconstruction of the
particle wave packet enables a frame-by-frame visualization of the scattering
processes. By precisely engineering a range of external potentials we are able
to simulate text book relativistic scattering experiments and study Klein
tunneling in an analogue quantum simulator. We describe extensions to solve
problems that are beyond current classical computing capabilities.Comment: 3 figures, accepted for publication in PR
Intrinsic anomalous Hall effect in nickel: An GGA+U study
The electronic structure and intrinsic anomalous Hall conductivity of nickel
have been calculated based on the generalized gradient approximation (GGA) plus
on-site Coulomb interaction (GGA+U) scheme. It is found that the intrinsic
anomalous Hall conductivity () obtained from the GGA+U
calculations with eV and eV, is in nearly perfect agreement
with that measured recently at low temperatures while, in contrast, the
from the GGA calculations is about 100% larger than the
measured one. This indicates that, as for the other spin-orbit interaction
(SOI)-induced phenomena in 3 itinerant magnets such as the orbital magnetic
magnetization and magnetocrystalline anisotropy, the on-site electron-electron
correlation, though moderate only, should be taken into account properly in
order to get the correct anomalous Hall conductivity. The intrinsic
and the number of valence electrons () have also been
calculated as a function of the Fermi energy (). A sign change is
predicted at eV (), and this explain qualitatively
why the theoretical and experimental values for Fe and Co are
positive. It is also predicted that fcc NiCo(Fe,Cu) alloys with
being small, would also have the negative with the
magnitude being in the range of cm. The most
pronounced effect of including the on-site Coulomb interaction is that all the
-dominant bands are lowered in energy relative to the by about 0.3 eV,
and consequently, the small minority spin X hole pocket disappears. The
presence of the small X hole pocket in the GGA calculations is attributed
to be responsible for the large discrepancy in the between
theory and experiment.Comment: 7 pages, 3 figures; Accepted for publication in Physical Review
The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode
We undertook a time-series photometric multi-site campaign for the rapidly
oscillating Ap star HD 99563 and also acquired mean light observations over two
seasons. The pulsations of the star, that show flatter light maxima than
minima, can be described with a frequency quintuplet centred on 1557.653
microHertz and some first harmonics of these. The amplitude of the pulsation is
modulated with the rotation period of the star that we determine with 2.91179
+/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the
mean light data. We break the distorted oscillation mode up into its pure
spherical harmonic components and find it is dominated by the l=1 pulsation,
and also has a notable l=3 contribution, with weak l=0 and 2 components. The
geometrical configuration of the star allows one to see both pulsation poles
for about the same amount of time; HD 99563 is only the fourth roAp star for
which both pulsation poles are seen and only the third where the distortion of
the pulsation modes was modelled. We point out that HD 99563 is very similar to
the well-studied roAp star HR 3831. Finally, we note that the visual companion
of HD 99563 is located in the Delta Scuti instability strip and may thus show
pulsation. We show that if the companion was physical, the roAp star would be a
2.03 solar mass object, seen at a rotational inclination of 44 degrees, which
then predicts a magnetic obliquity of 86.4 degrees.Comment: 10 pages, 6 figures, accepted for publication by MNRA
Pharmacokinetics of Micafungin in Critically Ill Patients
We investigated covariates of pharmacokinetics of micafungin in critically ill patients. After application of micafungin, plasma samples were collected. Non-linear mixed effects modelling (NONMEM 7.3) was used to develop the pharmacokinetic model. Using this model, the adequacy of a fixed 100 mg dosing regimen was evaluated in the study cohort. A two-compartment model with linear elimination was found to describe the obtained data. SOFA score was identified as a significant covariate on both clearance and central volume of distribution, respectively. Patients in highly critical condition, represented by a SOFA above 10 showed a 30.8% lower central volume of distribution than the less critically ill patients. For patients with bilirubin levels above 4 mg/dl, clearance was decreased by 21.1%. Renal replacement therapy (RRT) did not influence micafungin clearance or the volumes of distribution. In a posthoc evaluation of the modeled population, 100 mg micafungin was suitable when assessing the PKPD targets (AUC/MIC) for C. albicans and C. glabrata, with insufficient target attainment for C. parapsilosis. Micafungin pharmacokinetics appear not to be influenced by the status of RRT. A dose of 100 mg micafungin is suitable for infections with C. albicans and C. glabrata in critically ill patients
Properties of 3-manifolds for relativists
In canonical quantum gravity certain topological properties of 3-manifolds
are of interest. This article gives an account of those properties which have
so far received sufficient attention, especially those concerning the
diffeomorphism groups of 3-manifolds. We give a summary of these properties and
list some old and new results concerning them. The appendix contains a
discussion of the group of large diffeomorphisms of the -handle 3-manifold.Comment: 20 pages. Plain-TeX, no figures, 1 Table (A4 format
The Strange Prospects for Astrophysics
The implications of the formation of strange quark matter in neutron stars
and in core-collapse supernovae is discussed with special emphasis on the
possibility of having a strong first order QCD phase transition at high baryon
densities. If strange quark matter is formed in core-collapse supernovae
shortly after the bounce, it causes the launch of a second outgoing shock which
is energetic enough to lead to a explosion. A signal for the formation of
strange quark matter can be read off from the neutrino spectrum, as a second
peak in antineutrinos is released when the second shock runs over the
neutrinosphere.Comment: 10 pages, 8 figures, invited talk given at the international
conference on strangeness in quark matter (SQM2008), Beijing, October 6-10,
Beijing, China, version to appear in J. Phys.
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