806 research outputs found
Collective excitations of atomic Bose-Einstein condensates
We apply linear-response analysis of the Gross-Pitaevskii equation to obtain
the excitation frequencies of a Bose-Einstein condensate confined in a
time-averaged orbiting potential trap. Our calculated values are in excellent
agreement with those observed in a recent experiment.Comment: 11 pages, 2 Postscript figures, uses psbox.tex for automatic figure
inclusion. More info at http://amo.phy.gasou.edu/bec.htm
Enhancement of the Deuteron-Fusion Reactions in Metals and its Experimental Implications
Recent measurements of the reaction d(d,p)t in metallic environments at very
low energies performed by different experimental groups point to an enhanced
electron screening effect. However, the resulting screening energies differ
strongly for divers host metals and different experiments. Here, we present new
experimental results and investigations of interfering processes in the
irradiated targets. These measurements inside metals set special challenges and
pitfalls which make them and the data analysis particularly error-prone. There
are multi-parameter collateral effects which are crucial for the correct
interpretation of the observed experimental yields. They mainly originate from
target surface contaminations due to residual gases in the vacuum as well as
from inhomogeneities and instabilities in the deuteron density distribution in
the targets. In order to address these problems an improved differential
analysis method beyond the standard procedures has been implemented. Profound
scrutiny of the other experiments demonstrates that the observed unusual
changes in the reaction yields are mainly due to deuteron density dynamics
simulating the alleged screening energy values. The experimental results are
compared with different theoretical models of the electron screening in metals.
The Debye-H\"{u}ckel model that has been previously proposed to explain the
influence of the electron screening on both nuclear reactions and radioactive
decays could be clearly excluded.Comment: 22 pages, 12 figures, REVTeX4, 2-column format. Submitted to Phys.
Rev. C; accepte
Modulation of Variation by Response-Reward Spatial Proximity
There has been a recent surge in the experimental investigation of the control of behavioral variability. Currently, it is understood that variability in behavior is predictably modulated by reinforcement parameters (e.g., a probability of reward delivery and reward magnitude). In two experiments, we investigated how spatial proximity between response and reward locations impacts the production of behavioral variability in both response rate and lever press duration. Rats were trained to lever press on two levers in a standard operant chamber that only differed from one another in their proximity to a food niche (i.e., Near vs. Far); a second experimental factor, the probability of reward, was signaled by an auditory cue. In Experiment 1, trials with a high-probability stimulus terminated with reward on 100% of trials, while trials with a low-probability stimulus terminated with reward 25% of the time. We used a similar procedure in Experiment 2, but reduced the likelihood of reward on low-probability trials to 10% and collected data in a post-acquisition extinction test. Overall, proximity and probability were inversely related to variation of response rate, whereas only the probability factor affected variation in lever press duration. Proximity also interacted with probability to influence variation in response rate. These findings extend the factors modulating behavioral variability to include the spatial proximity between a response and reward
The 198Au beta-half-life in the metal Au revisited
The half-life of the beta-decay of 198Au has been measured for room
temperature and 12 K. The resulting values of T(RT) = 2.684 +- 0.004 d and T(12
K) = 2.687 +- 0.005 d agree well within statistical uncertainties. An evidence
for a temperature dependence of the half-life was not observed.Comment: accepted for publication in Eur. Phys. J.
evidence from cerebrospinal fluid analysis
Background The diagnosis of multiple sclerosis (MS) is currently based solely
on clinical and magnetic resonance imaging features. However,
histopathological studies have revealed four different patterns of lesion
pathology in patients diagnosed with MS, suggesting that MS may be a
pathologically heterogeneous syndrome rather than a single disease entity.
Objective The aim of this study was to investigate whether patients with
pattern I MS differ from patients with pattern II or III MS with regard to
cerebrospinal fluid (CSF) findings, especially with reference to intrathecal
IgG synthesis, which is found in most patients with MS but is frequently
missing in MS mimics such as aquaporin-4-IgG-positive neuromyelitis optica
spectrum disorders and myelin oligodendrocyte glycoprotein-IgG-positive
encephalomyelitis. Methods Findings from 68 lumbar punctures in patients who
underwent brain biopsy as part of their diagnostic work-up and who could be
unequivocally classified as having pattern I, pattern II or pattern III MS
were analysed retrospectively. Results Oligoclonal bands (OCBs) were present
in 88.2% of samples from pattern I MS patients but in only 27% of samples from
patients with pattern II or pattern III MS (P < 0.00004); moreover, OCBs were
present only transiently in some of the latter patients. A polyspecific
intrathecal IgG response to measles, rubella and/or varicella zoster virus
(so-called MRZ reaction) was previously reported in 60–80% of MS patients, but
was absent in all pattern II or III MS patients tested (P < 0.00001 vs.
previous cohorts). In contrast, the albumin CSF/serum ratio (QAlb), a marker
of blood–CSF barrier function, was more frequently elevated in samples from
pattern II and III MS patients (P < 0.002). Accordingly, QAlb values and
albumin and total protein levels were higher in pattern II and III MS samples
than in pattern I MS samples (P < 0.005, P < 0.009 and P < 0.006,
respectively). Conclusions Patients with pattern II or pattern III MS differ
significantly from patients with pattern I MS as well as from previous,
histologically non-classified MS cohorts with regard to both intrathecal IgG
synthesis and blood–CSF barrier function. Our findings strongly corroborate
the notion that pattern II and pattern III MS are entities distinct from
pattern I MS
Excited states of a dilute Bose-Einstein condensate in a harmonic trap
The low-lying hydrodynamic normal modes of a dilute Bose-Einstein gas in an
isotropic harmonic trap determine the corresponding Bogoliubov amplitudes. In
the Thomas-Fermi limit, these modes have large low-temperature occupation
numbers, and they permit an explicit construction of the dynamic structure
function . The total noncondensate number at zero
temperature increases like , where is the condensate radius measured
in units of the oscillator length. The lowest dipole modes are constructed
explicitly in the Bogoliubov approximation.Comment: 15 pages, REVTE
Parareal with a Learned Coarse Model for Robotic Manipulation
A key component of many robotics model-based planning and control algorithms is physics predictions, that is, forecasting a sequence of states given an initial state and a sequence of controls. This process is slow and a major computational bottleneck for robotics planning algorithms. Parallel-in-time integration methods can help to leverage parallel computing to accelerate physics predictions and thus planning. The Parareal algorithm iterates between a coarse serial integrator and a fine parallel integrator. A key challenge is to devise a coarse model that is computationally cheap but accurate enough for Parareal to converge quickly. Here, we investigate the use of a deep neural network physics model as a coarse model for Parareal in the context of robotic manipulation. In simulated experiments using the physics engine Mujoco as fine propagator we show that the learned coarse model leads to faster Parareal convergence than a coarse physics-based model. We further show that the learned coarse model allows to apply Parareal to scenarios with multiple objects, where the physics-based coarse model is not applicable. Finally, we conduct experiments on a real robot and show that Parareal predictions are close to real-world physics predictions for robotic pushing of multiple objects. Code (https://doi.org/10.5281/zenodo.3779085) and videos (https://youtu. be/wCh2o1rf-gA) are publicly available
Grundlegende Untersuchungen zur Fertigung gestufter Mikrostrukturen aus fluorierten Polymeren nach dem LIGA-Verfahren
Pulverspritzgiessen keramischer Mikrobauteile - Entwicklung von Prototypen- und Massenfertigungsverfahren
Dynamics of a Bose-Einstein Condensate in an Anharmonic Trap
We present a theoretical model to describe the dynamics of Bose-Einstein
condensates in anharmonic trapping potentials. To first approximation the
center-of-mass motion is separated from the internal condensate dynamics and
the problem is reduced to the well known scaling solutions for the Thomas-Fermi
radii. We discuss the validity of this approach and analyze the model for an
anharmonic waveguide geometry which was recently realized in an experiment
\cite{Ott2002c}
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