Time-resolved spectroscopy of the excited electronic state of reaction centers of Rhodopseudomonas viridis

The spectral properties of the excited electronic state of the reaction centers of Rhodopseudomonas (Rps.) viridis are studied by dichroic transient absorption spectroscopy with sub-picosecond time resolution. The theoretical analysis of the experimental results allows the assignment of the transient absorption from two dimer bands of the special pair and show its excitonic coupling to other pigments

Detection & identification of hazardous narcotics and new psychoactive substances using Fourier transform infrared spectroscopy (FTIR)

According to the latest World Drug Report, released by the United Nations Office on Drugs and Crime (UNODC), drug use is up 30% over the past decade and there are more drugs, and more types of drugs, than ever. Herein we use Fourier Transform Infrared Spectroscopy (FTIR) for the rapid ID of narcotics in a range of concentrations – from pure forms (as it is likely to be smuggled & transported) to street forms, often mixed with conventional cutting agents. Using FTIR, 75% of “street sample” narcotics were rapidly identified, and the effects of cutting agents on identification (ID) were also investigated. The limit of detection of MDMA was assessed, with a correct ID shown from 25% w/v. Concentration was correlated with Hit Quality Index, showing the capability of FTIR use in concentration estimation

Crossover effects in the Wolf-Villain model of epitaxial growth in 1+1 and 2+1 dimensions

A simple model of epitaxial growth proposed by Wolf and Villain is investigated using extensive computer simulations. We find an unexpectedly complex crossover behavior of the original model in both 1+1 and 2+1 dimensions. A crossover from the effective growth exponent $\beta_{\rm eff}\!\approx\!0.37$ to $\beta_{\rm eff}\!\approx\!0.33$ is observed in 1+1 dimensions, whereas additional crossovers, which we believe are to the scaling behavior of an Edwards--Wilkinson type, are observed in both 1+1 and 2+1 dimensions. Anomalous scaling due to power--law growth of the average step height is found in 1+1 D, and also at short time and length scales in 2+1~D. The roughness exponents $\zeta_{\rm eff}^{\rm c}$ obtained from the height--height correlation functions in 1+1~D ($\approx\!3/4$) and 2+1~D ($\approx\!2/3$) cannot be simultaneously explained by any of the continuum equations proposed so far to describe epitaxial growth.Comment: 11 pages, REVTeX 3.0, IC-DDV-93-00

A numerical study of the development of bulk scale-free structures upon growth of self-affine aggregates

During the last decade, self-affine geometrical properties of many growing aggregates, originated in a wide variety of processes, have been well characterized. However, little progress has been achieved in the search of a unified description of the underlying dynamics. Extensive numerical evidence has been given showing that the bulk of aggregates formed upon ballistic aggregation and random deposition with surface relaxation processes can be broken down into a set of infinite scale invariant structures called "trees". These two types of aggregates have been selected because it has been established that they belong to different universality classes: those of Kardar-Parisi-Zhang and Edward-Wilkinson, respectively. Exponents describing the spatial and temporal scale invariance of the trees can be related to the classical exponents describing the self-affine nature of the growing interface. Furthermore, those exponents allows us to distinguish either the compact or non-compact nature of the growing trees. Therefore, the measurement of the statistic of the process of growing trees may become a useful experimental technique for the evaluation of the self-affine properties of some aggregates.Comment: 19 pages, 5 figures, accepted for publication in Phys.Rev.

Dynamic renormalization group study of a generalized continuum model of crystalline surfaces

We apply the Nozieres-Gallet dynamic renormalization group (RG) scheme to a continuum equilibrium model of a d-dimensional surface relaxing by linear surface tension and linear surface diffusion, and which is subject to a lattice potential favoring discrete values of the height variable. The model thus interpolates between the overdamped sine-Gordon model and a related continuum model of crystalline tensionless surfaces. The RG flow predicts the existence of an equilibrium roughening transition only for d = 2 dimensional surfaces, between a flat low-temperature phase and a rough high-temperature phase in the Edwards-Wilkinson (EW) universality class. The surface is always in the flat phase for any other substrate dimensions d > 2. For any value of d, the linear surface diffusion mechanism is an irrelevant perturbation of the linear surface tension mechanism, but may induce long crossovers within which the scaling properties of the linear molecular-beam epitaxy equation are observed, thus increasing the value of the sine-Gordon roughening temperature. This phenomenon originates in the non-linear lattice potential, and is seen to occur even in the absence of a bare surface tension term. An important consequence of this is that a crystalline tensionless surface is asymptotically described at high temperatures by the EW universality class.Comment: 22 pages, 5 figures. Accepted for publication in Physical Review

Anisotropic Scaling in Threshold Critical Dynamics of Driven Directed Lines

The dynamical critical behavior of a single directed line driven in a random medium near the depinning threshold is studied both analytically (by renormalization group) and numerically, in the context of a Flux Line in a Type-II superconductor with a bulk current $\vec J$. In the absence of transverse fluctuations, the system reduces to recently studied models of interface depinning. In most cases, the presence of transverse fluctuations are found not to influence the critical exponents that describe longitudinal correlations. For a manifold with $d=4-\epsilon$ internal dimensions, longitudinal fluctuations in an isotropic medium are described by a roughness exponent $\zeta_\parallel=\epsilon/3$ to all orders in $\epsilon$, and a dynamical exponent $z_\parallel=2-2\epsilon/9+O(\epsilon^2)$. Transverse fluctuations have a distinct and smaller roughness exponent $\zeta_\perp=\zeta_\parallel-d/2$ for an isotropic medium. Furthermore, their relaxation is much slower, characterized by a dynamical exponent $z_\perp=z_\parallel+1/\nu$, where $\nu=1/(2-\zeta_\parallel)$ is the correlation length exponent. The predicted exponents agree well with numerical results for a flux line in three dimensions. As in the case of interface depinning models, anisotropy leads to additional universality classes. A nonzero Hall angle, which has no analogue in the interface models, also affects the critical behavior.Comment: 26 pages, 8 Postscript figures packed together with RevTeX 3.0 manuscript using uufiles, uses multicol.sty and epsf.sty, e-mail [email protected] in case of problem

Renormalization group study of one-dimensional systems with roughening transitions

A recently introduced real space renormalization group technique, developed for the analysis of processes in the Kardar-Parisi-Zhang universality class, is generalized and tested by applying it to a different family of surface growth processes. In particular, we consider a growth model exhibiting a rich phenomenology even in one dimension. It has four different phases and a directed percolation related roughening transition. The renormalization method reproduces extremely well all the phase diagram, the roughness exponents in all the phases and the separatrix among them. This proves the versatility of the method and elucidates interesting physical mechanisms.Comment: Submitted to Phys. Rev.

Training software developers for electronic medical records in Rwanda

Also published in Studies in health technology and informatics (2010), volume: 160, issue: pt 1, p. 585-589.This paper describes a training program in Rwanda that enables local computer science graduates to play a significant role in the country’s implementation of a national electronic medical record (EMR) system. This training program is unique in the region. The paper discusses the challenges inherent in such an undertaking which produces local software developers familiar with medical informatics. Successful and sustainable eHealth implementations in the developing world will rely on local talent

Glassy Vortex State in a Two-Dimensional Disordered XY-Model

The two-dimensional XY-model with random phase-shifts on bonds is studied. The analysis is based on a renormalization group for the replicated system. The model is shown to have an ordered phase with quasi long-range order. This ordered phase consists of a glass-like region at lower temperatures and of a non-glassy region at higher temperatures. The transition from the disordered phase into the ordered phase is not reentrant and is of a new universality class at zero temperature. In contrast to previous approaches the disorder strength is found to be renormalized to larger values. Several correlation functions are calculated for the ordered phase. They allow to identify not only the transition into the glassy phase but also an additional crossover line, where the disconnected vortex correlation changes its behavior on large scales non-analytically. The renormalization group approach yields the glassy features without a breaking of replica symmetry.Comment: latex 12 pages with 3 figures, using epsf.sty and multicol.st

Physics of Solar Prominences: II - Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape