3,039 research outputs found
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
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
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
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
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
Recommended from our members
Evaluation of Non-photorealistic 3D Urban Models for Mobile Device Navigation.
Systems, interactions and macrotheory
A significant proportion of early HCI research was guided by one very clear vision: that the existing theory base in psychology and cognitive science could be developed to yield engineering tools for use in the interdisciplinary context of HCI design. While interface technologies and heuristic methods for behavioral evaluation have rapidly advanced in both capability and breadth of application, progress toward deeper theory has been modest, and some now believe it to be unnecessary. A case is presented for developing new forms of theory, based around generic “systems of interactors.” An overlapping, layered structure of macro- and microtheories could then serve an explanatory role, and could also bind together contributions from the different disciplines. Novel routes to formalizing and applying such theories provide a host of interesting and tractable problems for future basic research in HCI
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
- …