63 research outputs found
Polyelectrolyte Adsorption on Charged Substrate
The behavior of a polyelectrolyte adsorbed on a charged substrate of
high-dielectric constant is studied by both Monte-Carlo simulation and
analytical methods. It is found that in a low enough ionic strength medium, the
adsorption transition is first-order where the substrate surface charge still
keeps repulsive. The monomer density at the adsorbed surface is identified as
the order parameter. It follows a linear relation with substrate surface charge
density because of the electrostatic boundary condition at the charged surface.
During the transition, the adsorption layer thickness remains finite. A new
scaling law for the layer thickness is derived and verified by simulation.Comment: Proceedings of the 3rd Symposium on Slow Dynamics in Complex Systems,
3-8 November 2003, Sendai, Japa
Stretching a double-stranded DNA: Nature of the B-form to the S-form transition
[[abstract]]The abrupt extension of the contour length and the self-unwinding of the double helix in the transition from the B-form to S-form of a double-stranded DNA under a stretching force is investigated in the framework of the model with basepair interactions and bending @Phys. Rev. Lett.
22, 4560 ~1999!#. In the region where thermal fluctuations can be neglected the classical mechanical approach is employed and equations governing the detail structure of the DNA are derived with some analytical results obtained. The transition from the B-form to S-form can be understood in
terms of an effective potential with a barrier separating these two states and resulting in a first-order transition. The double helix of the DNA is almost fully unwound across the transition. Detail
structural configurations, such as the loci of the two strands, relative extension, linear extension coefficient, and the threshold stretching force are calculated. The mean torque release as the dsDNA
untwist across the transition is also estimated. These results are in agreement with various experimental data.[[notice]]補正完畢[[booktype]]紙
Scaling Theory of Polyelectrolyte Adsorption on Repulsive Charged Surface
We studied polyelectrolyte adsorption on a repulsive charged surface by
scaling analysis. At low ionic strength and low surface charge density in which
a single polyelectrolyte is able to be adsorbed onto the surface, different
regimes in the phase diagram are identified. The possibility of multi-layer
structure formed by polyelectrolytes of like charge is also investigated.Comment: 4 pages, 2 figure
Optically induced electrostriction modes in a nanoparticle of a uniformly charged electret
The electromagnetic response of a nanoparticle of an ion-doped polymeric
elastic insulator, commonly called as an electret, is considered in the
continuum model of a uniformly charged elastic sphere. The spectral formulae
for the frequency of optically induced spheroidal and torsional shear
oscillations driven by bulk force of elastic and dielectric stresses are
obtained in analytic form. Particular attention is given to relaxation
dielectric mode of the electrostriction response and its stability in the
lowest quadrupole mode. The practical usefulness of ultrafine particles of
electrets as a biolabels capable of accumulating likely-charged inclusions
uniformly dispersed over the spherical volume of an elastic matrix is briefly
discussed.Comment: International Journal of Nanoscience, 2008, Vol.7, No.6, pp.291-29
Activity-assisted barrier-crossing of self-propelled colloids over parallel microgrooves
We report a systematic study of the dynamics of self-propelled particles
(SPPs) over a one-dimensional periodic potential landscape, which is fabricated
on a microgroove-patterned polydimethylsiloxane (PDMS) substrate. From the
measured non-equilibrium probability density function of the SPPs, we find that
the escape dynamics of the slow-rotating SPPs across the potential landscape
can be described by an effective potential, once the self-propulsion force is
included into the potential under the fixed angle approximation. This work
demonstrates that the parallel microgrooves provide a versatile platform for a
quantitative understanding of the interplay among the self-propulsion force,
spatial confinement by the potential landscape, and thermal noise, as well as
its effects on activity-assisted escape dynamics and transport of the SPPs
Short-Range Ising Spin Glass: Multifractal Properties
The multifractal properties of the Edwards-Anderson order parameter of the
short-range Ising spin glass model on d=3 diamond hierarchical lattices is
studied via an exact recursion procedure. The profiles of the local order
parameter are calculated and analysed within a range of temperatures close to
the critical point with four symmetric distributions of the coupling constants
(Gaussian, Bimodal, Uniform and Exponential). Unlike the pure case, the
multifractal analysis of these profiles reveals that a large spectrum of the
-H\"older exponent is required to describe the singularities of the
measure defined by the normalized local order parameter, at and below the
critical point. Minor changes in these spectra are observed for distinct
initial distributions of coupling constants, suggesting an universal spectra
behavior. For temperatures slightly above T_{c}, a dramatic change in the
function is found, signalizing the transition.Comment: 8 pages, LaTex, PostScript-figures included but also available upon
request. To be published in Physical Review E (01/March 97
25th annual computational neuroscience meeting: CNS-2016
The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong
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