1,987 research outputs found
Electrostatic Interactions of Asymmetrically Charged Membranes
We predict the nature (attractive or repulsive) and range (exponentially
screened or long-range power law) of the electrostatic interactions of
oppositely charged and planar plates as a function of the salt concentration
and surface charge densities (whose absolute magnitudes are not necessarily
equal). An analytical expression for the crossover between attractive and
repulsive pressure is obtained as a function of the salt concentration. This
condition reduces to the high-salt limit of Parsegian and Gingell where the
interaction is exponentially screened and to the zero salt limit of Lau and
Pincus in which the important length scales are the inter-plate separation and
the Gouy-Chapman length. In the regime of low salt and high surface charges we
predict - for any ratio of the charges on the surfaces - that the attractive
pressure is long-ranged as a function of the spacing. The attractive pressure
is related to the decrease in counter-ion concentration as the inter-plate
distance is decreased. Our theory predicts several scaling regimes with
different scaling expressions for the pressure as function of salinity and
surface charge densities. The pressure predictions can be related to surface
force experiments of oppositely charged surfaces that are prepared by coating
one of the mica surfaces with an oppositely charged polyelectrolyte
Relativistic Lee Model on Riemannian Manifolds
We study the relativistic Lee model on static Riemannian manifolds. The model
is constructed nonperturbatively through its resolvent, which is based on the
so-called principal operator and the heat kernel techniques. It is shown that
making the principal operator well-defined dictates how to renormalize the
parameters of the model. The renormalization of the parameters are the same in
the light front coordinates as in the instant form. Moreover, the
renormalization of the model on Riemannian manifolds agrees with the flat case.
The asymptotic behavior of the renormalized principal operator in the large
number of bosons limit implies that the ground state energy is positive. In 2+1
dimensions, the model requires only a mass renormalization. We obtain rigorous
bounds on the ground state energy for the n-particle sector of 2+1 dimensional
model.Comment: 23 pages, added a new section, corrected typos and slightly different
titl
The 157 nm Photodissociation of OCS
The photodissociation of OCS at 157 nm has been investigated by using tunable vacuum ultraviolet radiation to probe the CO and S photoproducts. Sulfur is produced almost entirely in the 1S state, while CO is produced in its ground electronic state and in vibrational levels from v=0-3 in the appropriate ratio (v=0):(v=1):(v=2):(v=3) = (1.0):(1.0):(0.5):(0.3). The rotational distribution for each vibrational level is found to be near Boltzmann, with temperatures that decrease from 1350 K for v=0 to 780 K for v=3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from a transition of predominantly parallel character (β=1.8±0.2) and that the CO velocity and angular momentum vectors are perpendicular to one another
Electron Traps in Ag-doped Li\u3csub\u3e2\u3c/sub\u3eB\u3csub\u3e4\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e Crystals: The role of Ag Interstitial Ions
Electron paramagnetic resonance (EPR) is used to establish models for electron traps in Ag-doped lithium tetraborate (Li2B4O7) crystals. When exposed at room temperature to ionizing radiation, electrons are trapped at interstitial Ag+ ions and holes are trapped at Ag+ ions on Li+ sites. The trapped electrons occupy a 5s1 orbital on the interstitial Ag ions (some of the unpaired spin density is also on neighboring ions). Three EPR spectra are assigned to electrons trapped at interstitial Ag ions. Their g values are near 1.99 and they have resolved hyperfine structure from 107Ag and 109Ag nuclei. The spectrum representing the largest concentration of trapped electrons has the unpaired spin shared by the interstitial Ag ion and an adjacent boron ion at its regular lattice site. A 10B enriched crystal verifies this assignment and an analysis of spin-Hamiltonian parameters yields information about the Ag and B orbitals occupied by the unpaired spin. The second spectrum has the unpaired spin shared equally by two Ag ions, one at an interstitial site and the other at an adjacent Li site. The third spectrum has a large Ag hyperfine interaction and a weak Li interaction. Optical absorption bands associated with the trapped electrons are observed between 225 and 500 nm. Thermal release of electrons from these traps is responsible for a prominent thermoluminescence peak near 150 °C, whereas optical release of the electrons at room temperature produces intense optically stimulated luminescence. Radiative recombination occurs at Ag2+ ions with emission peaking near 270 nm
DNA condensation and redissolution: Interaction between overcharged DNA molecules
The effective DNA-DNA interaction force is calculated by computer simulations
with explicit tetravalent counterions and monovalent salt. For overcharged DNA
molecules, the interaction force shows a double-minimum structure. The
positions and depths of these minima are regulated by the counterion density in
the bulk. Using two-dimensional lattice sum and free energy perturbation
theories, the coexisting phases for DNA bundles are calculated. A
DNA-condensation and redissolution transition and a stable mesocrystal with an
intermediate lattice constant for high counterion concentration are obtained.Comment: 26 pages, 10 figure
Structural and Electrostatic Characterization of Pariacoto Virus: Implications for Viral Asembly
This is the peer reviewed version of the following article:Devkota, B., Petrov, A., Lemieux, S., Boz, M. B., Tang, L., Schneemann, A., … Harvey, S. C. (2009). Structural and Electrostatic Characterization of Pariacoto Virus: Implications for Viral Asembly. Biopolymers, 91(7), 530–538. http://doi.org/10.1002/bip.21168, which has been published in final form at doi.org/10.1002/bip.21168. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingWe present the first all-atom model for the structure of a T=3 virus, pariacoto virus (PaV), which is a non-enveloped, icosahedral RNA virus and a member of the Nodaviridae family. The model is an extension of the crystal structure, which reveals about 88% of the protein structure but only about 35% of the RNA structure. Evaluation of alternative models confirms our earlier observation that the polycationic protein tails must penetrate deeply into the core of the virus, where they stabilize the structure by neutralizing a substantial fraction of the RNA charge. This leads us to propose a model for the assembly of small icosahedral RNA viruses: nonspecific binding of the protein tails to the RNA leads to a collapse of the complex, in a fashion reminiscent of DNA condensation. The globular protein domains are excluded from the condensed phase but are tethered to it, so they accumulate in a shell around the condensed phase, where their concentration is high enough to trigger oligomerization and formation of the mature virus
Transistor behavior via Au clusters etched from electrodes in an acidic gating solution: metal nanoparticles mimicking conducting polymers
We report that the electrical conductance between closely-spaced gold
electrodes in acid solution can be turned from off [insulating; I] to on
[conducting; C] to off again by monotonically sweeping a gate voltage applied
to the solution. We propose that this ICI transistor action is due to an
electrochemical process dependent on nanoparticles etched from the surface of
the gold electrodes. These measurements mimic closely the characteristics of
nanoscale acid-gated polyaniline transistors, so that researchers should guard
against misinterpreting this effect in future molecular-electronics
experiments.Comment: 17 pages, 4 figure
The chromium site in doped glassy lithium tetraborate
Using extended X-ray absorption fine structure (EXAFS) spectroscopy, we find that Cr substitutes primarily in the LiĂľ site as a dopant in lithium tetraborate Li2B4O7 glasses, in this case 98.4Li2B4O7e1.6Cr2O3 or nominally Li1.98Cr0.025B4O7. This strong preference for a single site is nonetheless accompanied by site distortions and some site disorder, helping explain the optical properties of chromium doped Li2B4O7 glasses. The resulting O coordination shell has a contraction of the Cr-O bond lengths as compared to the Li-O bond lengths. There is also an increase in the O coordination number
The chromium site in doped glassy lithium tetraborate
Using extended X-ray absorption fine structure (EXAFS) spectroscopy, we find that Cr substitutes primarily in the LiĂľ site as a dopant in lithium tetraborate Li2B4O7 glasses, in this case 98.4Li2B4O7e1.6Cr2O3 or nominally Li1.98Cr0.025B4O7. This strong preference for a single site is nonetheless accompanied by site distortions and some site disorder, helping explain the optical properties of chromium doped Li2B4O7 glasses. The resulting O coordination shell has a contraction of the Cr-O bond lengths as compared to the Li-O bond lengths. There is also an increase in the O coordination number
Attraction between DNA molecules mediated by multivalent ions
The effective force between two parallel DNA molecules is calculated as a
function of their mutual separation for different valencies of counter- and
salt ions and different salt concentrations. Computer simulations of the
primitive model are used and the shape of the DNA molecules is accurately
modelled using different geometrical shapes. We find that multivalent ions
induce a significant attraction between the DNA molecules whose strength can be
tuned by the averaged valency of the ions. The physical origin of the
attraction is traced back either to electrostatics or to entropic
contributions. For multivalent counter- and monovalent salt ions, we find a
salt-induced stabilization effect: the force is first attractive but gets
repulsive for increasing salt concentration. Furthermore, we show that the
multivalent-ion-induced attraction does not necessarily correlate with DNA
overcharging.Comment: 51 pages and 13 figure
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