3,445 research outputs found
Non-sequential double ionization of molecules in a strong laser field
We consider the final stage of double ionization of molecules by
short linearly polarized laser pulses. The saddles of the effective adiabatic
potential energy close to which simultaneous escape of electrons from a
molecule takes place are identified. The analysis of the saddles and numerical
simulations of the ionization indicate that to observe clear signatures of
simultaneous electron escape in double ionization of molecules
stronger and much shorter laser pulses than those used in the recent experiment
[E. Eremina, {\it et al}, Phys. Rev. Lett. {\bf 92}, 173001 (2004)] should be
applied.Comment: 5 pages, 3 figures, Conference proceedings from 13th International
Laser Physics Workshop, Triest, Italy, July 12-16, 200
Pace Environmental Law Review 2015 Symposium: Reconceptualizing the Future of Environmental Law
Pace Environmental Law Review\u27s 2015 Symposium, entitled Reconceptualizing the Future of Environmental Law, can be traced back to over a year ago when a few Pace Environmental Law faculty members approached me and Katie Hatt, the Managing Editor of the law review, with an idea.1 No, not an idea, rather a question. They simply asked us, “what do you think the future holds for environmental law?” This question transformed into an extensive conversation about the past, the present, and the future of environmental law
Non-sequential double ionization of molecules
Double ionization of diatomic molecules by short linearly polarized laser
pulses is analyzed. We consider the final stage of the ionization process, that
is the decay of a highly excited two electron molecule, which is formed after
re-scattering. The saddles of the effective adiabatic potential energy close to
which simultaneous escape of electrons takes place are identified. Numerical
simulations of the ionization of molecules show that the process can be
dominated by either sequential or non-sequential events.
In order to increase the ratio of non-sequential to sequential ionizations
very short laser pulses should be applied.Comment: 7 pages, 7 figures, submitted to PR
Bypass transition and spot nucleation in boundary layers
The spatio-temporal aspects of the transition to turbulence are considered in
the case of a boundary layer flow developing above a flat plate exposed to
free-stream turbulence. Combining results on the receptivity to free-stream
turbulence with the nonlinear concept of a transition threshold, a physically
motivated model suggests a spatial distribution of spot nucleation events. To
describe the evolution of turbulent spots a probabilistic cellular automaton is
introduced, with all parameters directly fitted from numerical simulations of
the boundary layer. The nucleation rates are then combined with the cellular
automaton model, yielding excellent quantitative agreement with the statistical
characteristics for different free-stream turbulence levels. We thus show how
the recent theoretical progress on transitional wall-bounded flows can be
extended to the much wider class of spatially developing boundary-layer flows
Double ionization of a three-electron atom: Spin correlation effects
We study the effects of spin degrees of freedom and wave function symmetries
on double ionization in three-electron systems. Each electron is assigned one
spatial degree of freedom. The resulting three-dimensional Schr\"odinger
equation is integrated numerically using grid-based Fourier transforms. We
reveal three-electron effects on the double ionization yield by comparing
signals for different ionization channels. We explain our findings by the
existence of fundamental differences between three-electronic and truly
two-electronic spin-resolved ionization schemes. We find, for instance, that
double ionization from a three-electron system is dominated by electrons that
have the opposite spin
On statistically stationary homogeneous shear turbulence
A statistically stationary turbulence with a mean shear gradient is realized
in a flow driven by suitable body forces. The flow domain is periodic in
downstream and spanwise directions and bounded by stress free surfaces in the
normal direction. Except for small layers near the surfaces the flow is
homogeneous. The fluctuations in turbulent energy are less violent than in the
simulations using remeshing, but the anisotropy on small scales as measured by
the skewness of derivatives is similar and decays weakly with increasing
Reynolds number.Comment: 4 pages, 5 figures (Figs. 3 and 4 as external JPG-Files
Lagrangian tracers on a surface flow: the role of time correlations
Finite time correlations of the velocity in a surface flow are found to be
important for the formation of clusters of Lagrangian tracers. The degree of
clustering characterized by the Lyapunov spectrum of the flow is numerically
shown to be in qualitative agreement with the predictions for the white-in-time
compressible Kraichnan flow, but to deviate quantitatively. For intermediate
values of compressibility the clustering is surprisingly weakened by time
correlations.Comment: 4 pages, 5 figures, to be published in PR
Metabolic Imaging to Assess Treatment Response to Cytotoxic and Cytostatic Agents
For several decades, cytotoxic chemotherapeutic agents were considered the basis of anti-cancer treatment for patients with metastatic tumors. A decrease in tumor burden, assessed by volumetric computed tomography (CT) and magnetic resonance imaging (MRI), according to the Response Evaluation Criteria in Solid Tumors (RECIST), was considered as a radiological response to cytotoxic chemotherapies. In addition to RECIST-based dimensional measurements, a metabolic response to cytotoxic drugs can be assessed by positron emission tomography (PET) using 18F-fluoro-thymidine (FLT) as a radioactive tracer for drug-disrupted DNA synthesis. The decreased 18FLT-PET uptake is often seen concurrently with increased apparent diffusion coefficients (ADC) by diffusion weighted imaging (DWI) due to chemotherapy-induced changes in tumor cellularity. Recently, the discovery of molecular origins of tumorogenesis led to the introduction of novel signal transduction inhibitors (STIs). STIs are targeted cytostatic agents; their effect is based on a specific biological inhibition with no immediate cell death. As such, tumor size is not anymore a sensitive end-point for a treatment response to STIs; novel physiological imaging end-points are desirable. For receptor tyrosine kinase inhibitors as well as modulators of the downstream signaling pathways, an almost immediate inhibition in glycolytic activity (the Warburg effect) and phospholipid turnover (the Kennedy pathway) has been seen by metabolic imaging in the first 24 hours of treatment. The quantitative imaging end-points by magnetic resonance spectroscopy (MRS) and metabolic PET (including 18F-fluoro-deoxy-glucose, FDG, and total choline) provide an early treatment response to targeted STIs, before a reduction in tumor burden can be seen
Approach to ergodicity in quantum wave functions
According to theorems of Shnirelman and followers, in the semiclassical limit
the quantum wavefunctions of classically ergodic systems tend to the
microcanonical density on the energy shell. We here develop a semiclassical
theory that relates the rate of approach to the decay of certain classical
fluctuations. For uniformly hyperbolic systems we find that the variance of the
quantum matrix elements is proportional to the variance of the integral of the
associated classical operator over trajectory segments of length , and
inversely proportional to , where is the Heisenberg
time, being the mean density of states. Since for these systems the
classical variance increases linearly with , the variance of the matrix
elements decays like . For non-hyperbolic systems, like Hamiltonians
with a mixed phase space and the stadium billiard, our results predict a slower
decay due to sticking in marginally unstable regions. Numerical computations
supporting these conclusions are presented for the bakers map and the hydrogen
atom in a magnetic field.Comment: 11 pages postscript and 4 figures in two files, tar-compressed and
uuencoded using uufiles, to appear in Phys Rev E. For related papers, see
http://www.icbm.uni-oldenburg.de/icbm/kosy/ag.htm
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