Electric Deflection of Rotating Molecules

We provide a theory of the deflection of polar and non-polar rotating molecules by inhomogeneous static electric field. Rainbow-like features in the angular distribution of the scattered molecules are analyzed in detail. Furthermore, we demonstrate that one may efficiently control the deflection process with the help of short and strong femtosecond laser pulses. In particular the deflection process may by turned-off by a proper excitation, and the angular dispersion of the deflected molecules can be substantially reduced. We study the problem both classically and quantum mechanically, taking into account the effects of strong deflecting field on the molecular rotations. In both treatments we arrive at the same conclusions. The suggested control scheme paves the way for many applications involving molecular focusing, guiding, and trapping by inhomogeneous fields

Seven Steps Towards the Classical World

Classical physics is about real objects, like apples falling from trees, whose motion is governed by Newtonian laws. In standard Quantum Mechanics only the wave function or the results of measurements exist, and to answer the question of how the classical world can be part of the quantum world is a rather formidable task. However, this is not the case for Bohmian mechanics, which, like classical mechanics, is a theory about real objects. In Bohmian terms, the problem of the classical limit becomes very simple: when do the Bohmian trajectories look Newtonian?Comment: 16 pages, LaTeX, uses latexsy

Relationship between daytime sleepiness and blood pressure in healthy older adults

Background: Some sleep disorders have been linked to hypertension, but few studies have examined the relationship between daytime sleepiness and blood pressure (BP). This study attempted to determine whether scores on a short questionnaire assessing daytime sleepiness (Epworth Sleepiness Scale [ESS]) were associated with BP and could be used to predict hypertension after 5 years in healthy older adults who had not previously been diagnosed with hypertension. Methods: A group of 157 healthy men and women 55 to 80 years of age completed an extensive medical examination, a series of psychosocial tests, and two 24-h ambulatory BP sessions. After 5 years the procedures were repeated in 133 (85%) of the subjects. Psychosocial variables and BP were compared in subjects scoring high (score of 10) and low (10) on the ESS. Results: Compared to individuals with low ESS sores, those scoring high had increased casual and sleep BP as well as higher systolic BP levels and diastolic BP variability during waking hours, and reported higher levels of anger, depression, anxiety, and intensity of psychological symptoms as well as lower defensiveness. Individuals with high ESS scores were more likely to be diagnosed with hypertension 5 years later. Groups with high and low ESS scores did not differ significantly on any other variables. Conclusions: The ESS, a simple measure of daytime sleepiness, identified individuals at risk for hypertension. Future studies should investigate the possibility that diagnosis and treatment of daytime sleepiness could aid in BP reduction and ultimately in decreased morbidity and mortality from cardiovascular disorders. Am J Hypertens 2004;17:787–792 © 2004 American Journal of Hypertension, Ltd

Mixing by Swimming Algae

In this fluid dynamics video, we demonstrate the microscale mixing enhancement of passive tracer particles in suspensions of swimming microalgae, Chlamydomonas reinhardtii. These biflagellated, single-celled eukaryotes (10 micron diameter) swim with a "breaststroke" pulling motion of their flagella at speeds of about 100 microns/s and exhibit heterogeneous trajectory shapes. Fluorescent tracer particles (2 micron diameter) allowed us to quantify the enhanced mixing caused by the swimmers, which is relevant to suspension feeding and biogenic mixing. Without swimmers present, tracer particles diffuse slowly due solely to Brownian motion. As the swimmer concentration is increased, the probability density functions (PDFs) of tracer displacements develop strong exponential tails, and the Gaussian core broadens. High-speed imaging (500 Hz) of tracer-swimmer interactions demonstrates the importance of flagellar beating in creating oscillatory flows that exceed Brownian motion out to about 5 cell radii from the swimmers. Finally, we also show evidence of possible cooperative motion and synchronization between swimming algal cells.Comment: 1 page, APS-DFD 2009 Gallery of Fluid Motio

Sewing sound quantum flesh onto classical bones

Semiclassical transformation theory implies an integral representation for stationary-state wave functions $\psi_m(q)$ in terms of angle-action variables ($\theta,J$). It is a particular solution of Schr\"{o}dinger's time-independent equation when terms of order $\hbar^2$ and higher are omitted, but the pre-exponential factor $A(q,\theta)$ in the integrand of this integral representation does not possess the correct dependence on $q$. The origin of the problem is identified: the standard unitarity condition invoked in semiclassical transformation theory does not fix adequately in $A(q,\theta)$ a factor which is a function of the action $J$ written in terms of $q$ and $\theta$. A prescription for an improved choice of this factor, based on succesfully reproducing the leading behaviour of wave functions in the vicinity of potential minima, is outlined. Exact evaluation of the modified integral representation via the Residue Theorem is possible. It yields wave functions which are not, in general, orthogonal. However, closed-form results obtained after Gram-Schmidt orthogonalization bear a striking resemblance to the exact analytical expressions for the stationary-state wave functions of the various potential models considered (namely, a P\"{o}schl-Teller oscillator and the Morse oscillator).Comment: RevTeX4, 6 page

Bohmian Mechanics and Quantum Information

Many recent results suggest that quantum theory is about information, and that quantum theory is best understood as arising from principles concerning information and information processing. At the same time, by far the simplest version of quantum mechanics, Bohmian mechanics, is concerned, not with information but with the behavior of an objective microscopic reality given by particles and their positions. What I would like to do here is to examine whether, and to what extent, the importance of information, observation, and the like in quantum theory can be understood from a Bohmian perspective. I would like to explore the hypothesis that the idea that information plays a special role in physics naturally emerges in a Bohmian universe.Comment: 25 pages, 2 figure

Thermodynamic entropy production fluctuation in a two dimensional shear flow model

We investigate fluctuations in the momentum flux across a surface perpendicular to the velocity gradient in a stationary shear flow maintained by either thermostated deterministic or by stochastic boundary conditions. In the deterministic system the Gallavotti-Cohen (GC)relation for the probability of large deviations, which holds for the phase space volume contraction giving the Gibbs ensemble entropy production, never seems to hold for the flux which gives the hydrodynamic entropy production. In the stochastic case the GC relation is found to hold for the total flux, as predicted by extensions of the GC theorem but not for the flux across part of the surface. The latter appear to satisfy a modified GC relation. Similar results are obtained for the heat flux in a steady state produced by stochastic boundaries at different temperatures.Comment: 9 postscript figure

Development of Simulators for Electrochemical Responses: Experimental and Pedagogical Applications

The work carried out in this CRADA addressed the development of computational algorithms to simulate the response for commonly used electrochemical techniques. The goal was the incorporation of these algorithms into DigiSimR, a generalized simulator for cyclic voltammetry (CV). CV, a ubiquitously applied electroanalytical technique used by nonelectrochemists as well as electrochemists, is sometimes referred to as "electrochemical spectroscopy". The latest version, DigiSimR 2.1, is now being sold by the industrial partner, Bioanalytical Systems, Inc. The response of the electrochemical community to this latest program (as well as its predecessors, DigiSimR 2.0 and the DOS version; versions 2.0 and 2.1 are for Windows), has been uniformly positive and numerous publications are now appearing which feature its application