Time scale of entropic segregation of flexible polymers in confinement: Implications for chromosome segregation in filamentous bacteria

We report molecular dynamics simulations of the segregation of two overlapping chains in cylindrical confinement. We find that the entropic repulsion between the chains can be sufficiently strong to cause segregation on a time scale that is short compared to the one for diffusion. This result implies that entropic driving forces are sufficiently strong to cause rapid bacterial chromosome segregation.Comment: Minor changes. Added some references, corrected the labels in figure 6 and reformatted in two columns. Also added reference to published version in PR

A study of the stress wave factor technique for nondestructive evaluation of composite materials

The acousto-ultrasonic method of nondestructive evaluation is an extremely sensitive means of assessing material response. Efforts continue to complete the understanding of this method. In order to achieve the full sensitivity of the technique, extreme care must be taken in its performance. This report provides an update of the efforts to advance the understanding of this method and to increase its application to the nondestructive evaluation of composite materials. Included are descriptions of a novel optical system that is capable of measuring in-plane and out-of-plane displacements, an IBM PC-based data acquisition system, an extensive data analysis software package, the azimuthal variation of acousto-ultrasonic behavior in graphite/epoxy laminates, and preliminary examination of processing variation in graphite-aluminum tubes

Modelling Molecular Motors as Folding-Unfolding Cycles

We propose a model for motor proteins based on a hierarchical Hamiltonian that we have previously introduced to describe protein folding. The proposed motor model has high efficiency and is consistent with a linear load-velocity response. The main improvement with respect to previous models is that this description suggests a connection between folding and function of allosteric proteins.Comment: 5 pages RevTeX, 2 Postscript figures, replaced due to LaTeX proble

Magnetic Diode Effect in Double Barrier Tunnel Junctions

A quantum statistical theory of spin-dependent tunneling through asymmetric magnetic double barrier junctions is presented which describes $both$ ballistic and diffuse tunneling by a single analytical expression. It is evidenced that the key parameter for the transition between these two tunneling regimes is the electron scattering. For these junctions a strong asymmetric behaviour in the I-V characteristics and the tunnel magnetoresistance (TMR) is predicted which can be controlled by an applied magnetic field. This phenomenon relates to the quantum well states in the middle metallic layer. The corresponding resonances in the current and the TMR are drastically phase shifted under positive and negative voltage.Comment: 10 pages, 4 Postscript figures, submitted to Europhys. Let

A Comparative Survey of Leguminous Plants as Sources of the Isoflavones, Genistein and Daidzein: Implications for Human Nutrition and Health

Over 80 taxa of mostly agriculturally important legumes were surveyed as sources of the metabolites, genistein and daidzein. Remarkably high concentrations (over 2 g · kg–1 dry weight) of the anticancer metabolite, genistein, were found in the leaves of Psoralea corylifolia (Indian bread root). All other legumes, with the exception of fermented soybean miso, had genistein levels <400 mg · kg–1 dry weight. Concentrations of over 1 g · kg–1 dry weight and 0.95 g · kg–1 dry weight of the anticancer metabolite, daidzein, were found in the stems of the fava bean (Vicia faba) and roots of kudzu vine (Pueraria lobata)' respectively. From this survey, our results indicate that the legumes, lupine (Lupinus spp.), fava bean, (Vicia faha), soybeans (Glycine max), kudzu (Pueraria lobata), and psoralea (Psoralea corylifolia), are excellent food sources for both genistein and daidzein. Miso, a fermented soybean product, is also a rich source of both isoflavones.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63131/1/acm.1997.3.7.pd

Report of the Terrestrial Bodies Science Working Group. Volume 4: The moon

A rationale for furture exploration of the moon is given. Topics discussed include the objectives of the lunar polar orbiter mission, the mission profile, and general characteristics of the spacraft to be used

Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions

Application of Bardeen's tunneling theory to magnetic tunnel junctions having a general degree of atomic disorder reveals the close relationship between magneto-conduction and voltage-driven pseudo-torque, as well as the thickness dependence of tunnel-polarization factors. Among the results: 1) The torque generally varies as sin theta at constant applied voltage. 2) Whenever polarization factors are well defined, the voltage-driven torque on each moment is uniquely proportional to the polarization factor of the other magnet. 3) At finite applied voltage, this relation predicts significant voltage-asymmetry in the torque. For one sign of voltage the torque remains substantial even when the magnetoconductance is greatly diminished. 4) A broadly defined junction model, called ideal middle, allows for atomic disorder within the magnets and F/I interface regions. In this model, the spin dependence of a state-weighting factor proportional to the sum over general state index of evaluated within the (e.g. vacuum) barrier generalizes the local state density in previous theories of the tunnel-polarization factor. 5) For small applied voltage, tunnel-polarization factors remain legitimate up to first order in the inverse thickness of the ideal middle. An algebraic formula describes the first-order corrections to polarization factors in terms of newly defined lateral auto-correllation scales.Comment: This version no. 3 is thoroughly revised for clarity. Just a few notations and equations are changed, and references completed. No change in results. 17 pages including 4 figure

Gel-Electrophoresis and Diffusion of Ring-Shaped DNA

A model for the motion of ring-shaped DNA in a gel is introduced and studied by numerical simulations and a mean-field approximation. The ring motion is mediated by finger-shaped loops (hernias) that move in an amoeba-like fashion around the gel obstructions. This constitutes an extension of previous reptation tube treatments. It is shown that tension is essential for describing the dynamics in the presence of hernias. It is included in the model as long range interactions over stretched DNA regions. The mobility of ring-shaped DNA is found to saturate much as in the well-studied case of linear DNA. Experiments in polymer gels, however, show that the mobility drops exponentially with the DNA ring size. This is commonly attributed to dangling-ends in the gel that can impale the ring. The predictions of the present model are expected to apply to artificial 2D obstacle arrays (W.D. Volkmuth, R.H. Austin, Nature 358,600 (1992)) which have no dangling-ends. In the zero-field case an exact solution of the model steady-state is obtained, and quantities such as the average ring size are calculated. An approximate treatment of the ring dynamics is given, and the diffusion coefficient is derived. The model is also discussed in the context of spontaneous symmetry breaking in one dimension.Comment: 8 figures, LaTeX, Phys. Rev. E - in pres

Colloidal transport through optical tweezer arrays

Viscously damped particles driven past an evenly spaced array of potential energy wells or barriers may become kinetically locked in to the array, or else may escape from the array. The transition between locked-in and free-running states has been predicted to depend sensitively on the ratio between the particles' size and the separation between wells. This prediction is confirmed by measurements on monodisperse colloidal spheres driven through arrays of holographic optical traps.Comment: 4 pages, 4 figure