593 research outputs found
Channeling of Electrons in a Crossed Laser Field
In this article a new analytical description of the effective interaction
potential for a charged particle in the field of two interfering laser beams is
presented. The potential dependence on the lasers intensities, orientation and
parameters of the particle entering the considered system is analyzed. It is
shown for the case of arbitrary lasers crossing angle that for different values
of projectile velocity the attracting potential becomes a scattering one so
that the channel axes and borders interchange each other. In addition the
projectile radiation spectral distribution is given and general estimations on
the expected beam radiation yield are outlined
Adaptive extensions of the Nelder and Mead Simplex Method for optimization of stochastic simulation models
We consider the Nelder and Mead Simplex Method for the optimization of stochastic simulation models. Existing and new adaptive extensions of the Nelder and Mead simplex method designed to improve the accuracy and consistency of the observed best point are studied. We compare
the performance of the extensions on a small microsimulation model, as well as on five test functions. We found that gradually decreasing the noise during an optimization run is the most preferred approach for stochastic objective functions. The amount of computation effort needed for successful optimization is very sensitive to the timing of noise reduction and to the rate of decrease of the noise. Restarting the algorithm during the optimization run, in the sense that the algorithm applies a fresh simplex at certain iterations during an optimization run, has adverse effects in our tests for the microsimulation model and for most test functions
Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states
We demonstrate the first experimental violation of a spin-1 Bell inequality.
The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and
Holt formalism. For entangled spin-1 particles the maximum quantum mechanical
prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden
variables. We obtained an experimental value of 2.27 using the
four-photon state generated by pulsed, type-II, stimulated parametric
down-conversion. This is a violation of the spin-1 Bell inequality by more than
13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve
Comparison of response surface methodology and the Nelder and Mead simplex method for optimization in microsimulation models
Microsimulation models are increasingly used in the evaluation of cancer screening. Latent parameters of such models can be estimated by optimization of the goodness-of-fit. We compared the efficiency and accuracy of the Response Surface Methodology and the Nelder and Mead Simplex Method for optimization of microsimulation models. To this end, we tested several automated versions of both methods on a small microsimulation model, as well as on a standard set of test functions. With respect to accuracy, Response Surface Methodology performed better in case of optimization of the microsimulation model, whereas the results for the test functions were rather variable. The Nelder and Mead Simplex Method performed more efficiently than Response Surface Methodology, both for the microsimulation model and the test functions
Finite Temperature QCD with Two Flavors of Non-perturbatively Improved Wilson Fermions
We study QCD with two flavors of non-perturbatively improved Wilson fermions
at finite temperature on the lattice. We determine the transition
temperature at lattice spacings as small as fm, and study string
breaking below the finite temperature transition. We find that the static
potential can be fitted by a two-state ansatz, including a string state and a
two-meson state. We investigate the role of Abelian monopoles at finite
temperature.Comment: 29 pages, 22 figures, Late
Chewing lice (phthiraptera) of magpie (pica pica l.) (aves: passeriformes: corvidae) in turkey
Magneto-thermal evidence of a partial gap at the Fermi surface of UPt_2Si_2
Motivated by the observation of a giant Nernst effect in URu_2Si_2, the
thermoelectric response of the related system UPt_2Si_2 was investigated using
thermal and electric transport properties such as the Nernst and Seebeck
effects, thermal conductivity, Hall effect and electrical resitivity. Unlike
URu_2Si_2, UPt_2Si_2 is neither superconducting nor exhibits a ``hidden-order''
state. Nevertheless a pronounced Nernst effect anomaly is found to coincide
with the onset of the antiferromagnetic order in UPt_2Si_2. Although the
absolute values are substantially lower, its appearance and characteristics can
favorably be compared to the giant Nernst effect in URu_2Si_2 indicating the
common feature of a partial Fermi surface gap.Comment: 4 pages, 4 figure
The role of extracerebral cholesterol homeostasis and ApoE e4 in cognitive decline
AbstractWe examined the associations between extracerebral markers of cholesterol homeostasis and cognitive decline over 6 years of follow-up, and studied the modifying effect of apolipoprotein E (ApoE) e4. Data were collected in the Longitudinal Aging Study Amsterdam (n = 967, with longitudinal data on cognition, ages ≥ 65 years) and analyzed using linear mixed models. General cognition (Mini-Mental State Examination; MMSE), memory (Auditory Verbal Learning Test), and information processing speed (Coding task) were measured. The results show that ApoE e4 was a significant effect modifier. Significant associations were found only in ApoE e4 noncarriers (n = 718). We found a nonlinear negative association between the ratio of lanosterol to cholesterol (≤ 189.96 ng/mg), a marker for cholesterol synthesis, and general cognition. Lower cholesterol absorption, i.e., lower ratios of campesterol and sitosterol to cholesterol, as well as a higher rate of cholesterol synthesis relative to absorption were associated with lower information processing speed. In ApoE e4 carriers, the negative association between the ratio of campesterol to cholesterol and memory reached borderline significance. Future research should focus on the interaction between (disturbed) cholesterol homeostasis and ApoE e4 status with respect to dementia
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