696 research outputs found
Probing protein-protein interactions by dynamic force correlated spectroscopy (FCS)
We develop a formalism for single molecule dynamic force spectroscopy to map
the energy landscape of protein-protein complex (). The joint
distribution of unbinding lifetimes and
measurable in a compression-tension cycle, which accounts for the internal
relaxation dynamics of the proteins under tension, shows that the histogram of
is not Poissonian. The theory is applied to the forced unbinding of
protein , modeled as a wormlike chain, from . We propose a new
class of experiments which can resolve the effect of internal protein dynamics
on the unbinding lifetimes.Comment: 12 pages, 3 figures, accepted to Phys. Rev. Let
Optically bound microscopic particles in one dimension
Counter-propagating light fields have the ability to create self-organized
one-dimensional optically bound arrays of microscopic particles, where the
light fields adapt to the particle locations and vice versa. We develop a
theoretical model to describe this situation and show good agreement with
recent experimental data (Phys. Rev. Lett. 89, 128301 (2002)) for two and three
particles, if the scattering force is assumed to dominate the axial trapping of
the particles. The extension of these ideas to two and three dimensional
optically bound states is also discussed.Comment: 12 pages, incl. 5 figures, accepted by Phys. Rev.
On the equivalence of the Ashkin-Teller and the four-state Potts-glass models of neural networks
We show that for a particular choice of the coupling parameters the
Ashkin-Teller spin-glass neural network model with the Hebb learning rule and
one condensed pattern yields the same thermodynamic properties as the
four-state anisotropic Potts-glass neural network model. This equivalence is
not seen at the level of the Hamiltonians.Comment: 3 pages, revtex, additional arguments presente
Optical binding of particles with or without the presence of a flat dielectric surface
Optical fields can induce forces between microscopic objects, thus giving
rise to new structures of matter. We study theoretically these optical forces
between two spheres, either isolated in water, or in presence of a flat
dielectric surface. We observe different behavior in the binding force between
particles at large and at small distances (in comparison with the wavelength)
from each other. This is due to the great contribution of evanescent waves at
short distances. We analyze how the optical binding depends of the size of the
particles, the material composing them, the wavelength and, above all, on the
polarization of the incident beam. We also show that depending on the
polarization, the force between small particles at small distances changes its
sign. Finally, the presence of a substrate surface is analyzed showing that it
only slightly changes the magnitudes of the forces, but not their qualitative
nature, except when one employs total internal reflection, case in which the
particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl
Dynamic Critical Behavio(u)r of a Cluster Algorithm for the Ashkin--Teller Model
We study the dynamic critical behavior of a Swendsen--Wang--type algorithm
for the Ashkin--Teller model. We find that the Li--Sokal bound on the
autocorrelation time ()
holds along the self-dual curve of the symmetric Ashkin--Teller model, but this
bound is apparently not sharp. The ratio
appears to tend to infinity either as a logarithm or as a small power (0.05
\ltapprox p \ltapprox 0.12).Comment: 51062 bytes uuencoded gzip'ed (expands to 111127 bytes Postscript); 4
pages including all figures; contribution to Lattice '9
Investigation of superconducting interactions and amorphous semiconductors
Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements
Resonant radiation pressure on neutral particles in a waveguide
A theoretical analysis of electromagnetic forces on neutral particles in an
hollow waveguide is presented. We show that the effective scattering cross
section of a very small (Rayleigh) particle can be strongly modified inside a
waveguide. The coupling of the scattered dipolar field with the waveguide modes
induce a resonant enhanced backscattering state of the scatterer-guide system
close to the onset of new modes. The particle effective cross section can then
be as large as the wavelength even far from any transition resonance. As we
will show, a small particle can be strongly accelerated along the guide axis
while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure
Multidrug Resistant Pulmonary Tuberculosis Treatment Regimens and Patient Outcomes: An Individual Patient Data Meta-analysis of 9,153 Patients
Dick Menzies and colleagues report findings from a collaborative, individual patient-level meta-analysis of treatment outcomes among patients with multidrug-resistant tuberculosis.
Background: Treatment of multidrug resistant tuberculosis (MDR-TB) is lengthy, toxic, expensive, and has generally poor outcomes. We undertook an individual patient data meta-analysis to assess the impact on outcomes of the type, number, and duration of drugs used to treat MDR-TB
Towards an on-chip platform for the controlled application of forces via magnetic particles: A novel device for mechanobiology
In-vitro tests and analyses are of fundamental importance for investigating biological mechanisms in
cells and bio-molecules. The controlled application of forces to activate specific bio-pathways and
investigate their effects, mimicking the role of the cellular environment, is becoming a prominent
approach in this field. In this work, we present a non-invasive magnetic on-chip platform which allows
for the manipulation of magnetic particles, through micrometric magnetic conduits of Permalloy patterned
on-chip. We show, from simulations and experiments, that this technology permits to exert a
finely controlled force on magnetic beads along the chip surface. This force can be tuned from few to
hundreds pN by applying a variable external magnetic field
- …