Variational Approach to Molecular Kinetics

The eigenvalues and eigenvectors of the molecular dynamics propagator (or transfer operator) contain the essential information about the molecular thermodynamics and kinetics. This includes the stationary distribution, the metastable states, and state-to-state transition rates. Here, we present a variational approach for computing these dominant eigenvalues and eigenvectors. This approach is analogous the variational approach used for computing stationary states in quantum mechanics. A corresponding method of linear variation is formulated. It is shown that the matrices needed for the linear variation method are correlation matrices that can be estimated from simple MD simulations for a given basis set. The method proposed here is thus to first define a basis set able to capture the relevant conformational transitions, then compute the respective correlation matrices, and then to compute their dominant eigenvalues and eigenvectors, thus obtaining the key ingredients of the slow kinetics

A DYNAMOMETRIC SYSTEM FOR STUDIES OF BALANCE WHILE QUIET STANDING (PROTOTYPE)

Studies on balance while quiet standing are frequently conducted through the measurement of the Center of Pressure (COP). Usually, a triaxial force platform is used in such studies, where the horizontal forces can be considered negligible. However, the cost of such instrument is a high limitation for research in this field. Considering that vertical reactions are significant they can be used to measure COP oscillations. This work describes the development of an inexpensive uniaxial dynamometric system to be used in balance studies

SURFBOARD INSTRUMENTATION

The measurement of biomechanics activities of surfers is a challenge for researchers. The aquatic environment is hostile for electronic equipments, which makes difficult the measurement of related variables. Therefore, the aim of this work is to construct an electronic system (M32C Mitsubishi single-chip microcomputer based) embedded in a surfboard for displacement measurements

Anharmonic dynamics in crystalline, glassy, and supercooled-liquid glycerol: A case study on the onset of relaxational behavior

10 págs.; 8 figs.The temperature dependence of the spectral distributions of the glass, crystalline, and supercooled-liquid phases of glycerol is investigated by means of neutron inelastic scattering. The importance of anharmonic effects is quantified by the temperature dependence of reduced spectral frequency moments. The onset of relaxational (i.e., stochastic, zero-frequency) motions in the supercooled liquid state is monitored by neutron quasielastic scattering. A substantial deviation of the observed linewidths from the hydrodynaimc prescription is observed and is interpreted at a microscopic level, by comparison with the crystalline phase. ©1998 American Physical SocietyWork supported in part by DGICYT ~Spain! Grant No. PB95-0075-c03-01. Dr. O. Randl of the Institute Laue Langevin is acknowledged for the help given during the measurements at the IN10 spectrometer. The work at ANL was supported by the U.S. Department of Energy, BESMaterials Sciences, under Contract No. W-31-109-ENG-38.Peer Reviewe

CAPRIN E BRUCELLOSIS IN THREE DISTRICTS OF THE CAÑETE PROVINCE, LIMA

El objetivo del presente estudio epidemiológico fue estimar la prevalencia de brucelosis en cabras criadas bajo un sistema semi-estabulado, en los distritos de San Vicente, Nuevo Imperial y San Luis de la provincia de Cañete, en Lima. Se colectaron muestras de sangre de 385 cabras de tres o más meses de edad, procedentes de 21 hatos y no vacunados contra brucelosis caprina. Hubo cuatro cabras serorreactoras con la prueba Rosa de Bengala, y sólo una fue confirmada mediante la prueba de Fijación de Complemento, dando una prevalencia de brucelosis caprina de 0.26 ± 0.04%. Esta baja prevalencia podría deberse al efecto positivo del Programa de Control y Erradicación de Brucelosis Caprina conducido por el Ministerio de Salud del Perú (MINSA) y el Servicio Nacional de Sanidad Agraria (SENASA) desde el año 2000 en la provincia de Cañete.The objective of the present epidemiological study was to determine the prevalence of brucellosis in raised goats under a barn-feeding system in the districts of San Vicente, Nuevo Imperial and San Luis, Cañete Province, Lima. Blood samples were collected from 385 goats of three or more months of age, not vaccinated against caprine brucellosis and belonging to 21 herds. Results showed four sero-positive goats to the Rose Bengal test and only one to the Complement Fixation test. The prevalence of caprine brucellosis was estimated at 0.26 ± 0.04%. This low prevalence could be due to the positive effect of the Control and Eradication Program of Caprine Brucellosis conducted by the Peruvian Ministry of Health and the National Service of Agrarian Health (SENASA) since the year 2000 in the province of Cañete

Evolución del crecimiento en salmuera, a bajas temperaturas y diferentes acidulantes, de levaduras aisladas de aceitunas de mesa

The evolution of the main yeast species related to table olives ( Pichia anomala, Pichia membranaefaciens, Pichia minuta, Saccharomyces cerevisiae, Candida diddensii, Candida famata , and Debaryomyces hansenii ) at low temperature ( 7 ºC ) and different physico-chemical brine conditions was studied, using the log of the relative growth as response. In general, the NaCl concentration had a reduced effect, which was slightly greater at pH 3.5, although it was never significant. The effects of pH and type of acid were significant: the presence of acetic acid always diminished the yeast population with time; however the population was maintained, or even slightly increased, in the presence of lactic acid. Such effects were higher at pH 3.5 than at pH 4.0. The behaviour of the yeast species was diverse. Sacch. cerevisiae , P. nmembranaefaciens , C. famata y Deb. hansenii diminished with time in 8 % NaCl. The yeast population markedly decreased at pH 3.5, mainly in the case of Sacch. cerevisiae and C. famata. The presence of acetic acid decreased the yeast population in most species and always lead to a progressive diminution of it with time. No differences between species due to lactic acid was observed. These results can be of interest for the development of commercial presentations of table olives to be preserved at low temperature and with a reduced level of sodium.Se ha estudiado la evolución de las principales especies de levaduras relacionadas con las aceitunas de mesa ( Pichia anomala, Pichia membranaefaciens, Pichia minuta, Saccharomyces cerevisiae, Candida diddensii, Candida famata , y Debaryomyces hansenii ) a baja temperara ( 7 ºC ) y en diversas condiciones físico-químicas en las salmueras, utilizando el log del crecimiento relativo como respuesta. En general, la concentración de sal tiene un efecto muy limitado, que se aprecia algo más a pH 4, pero sin llegar a ser significativo. Los efectos del tipo de ácido y pH fueron significativos; la presencia de acético disminuye la población con el tiempo, mientras que con el láctico se mantiene e, incluso, se eleva ligeramente. Estos efectos se acentúan a pH 3,5. El comportamiento de cada levadura frente a las diferentes variables ha sido diverso. La población relativa de las especies Sacch. cerevisiae , P. membranaefaciens , C. famata y Deb. hansenii disminuyó con el tiempo en presencia del 8 % de NaCl. A pH 3,5 disminuye muy sensiblemente la población inicial en todos los casos, siendo tal influencia más destacada en Sacch. cerevisiae y C. famata. La presencia de acético disminuye de forma importante la población inicial inoculada en la mayoría de los casos y provocó siempre un descenso paulatino en las mismas. No se observó diferencias entre las especies debido al ácido láctico. Estos estudios pueden ser de interés para el desarrollo de presentaciones comerciales de aceitunas de mesa refrigeradas y con reducido nivel de sodio

A weak characterization of slow variables in stochastic dynamical systems

We present a novel characterization of slow variables for continuous Markov processes that provably preserve the slow timescales. These slow variables are known as reaction coordinates in molecular dynamical applications, where they play a key role in system analysis and coarse graining. The defining characteristics of these slow variables is that they parametrize a so-called transition manifold, a low-dimensional manifold in a certain density function space that emerges with progressive equilibration of the system's fast variables. The existence of said manifold was previously predicted for certain classes of metastable and slow-fast systems. However, in the original work, the existence of the manifold hinges on the pointwise convergence of the system's transition density functions towards it. We show in this work that a convergence in average with respect to the system's stationary measure is sufficient to yield reaction coordinates with the same key qualities. This allows one to accurately predict the timescale preservation in systems where the old theory is not applicable or would give overly pessimistic results. Moreover, the new characterization is still constructive, in that it allows for the algorithmic identification of a good slow variable. The improved characterization, the error prediction and the variable construction are demonstrated by a small metastable system