445 research outputs found
Model charged cylindrical nanopore in a colloidal dispersion: charge reversal, overcharging and double overcharging
Using the hypernetted-chain/mean spherical approximation (HNC/MSA) integral
equations we study the electrical double layer inside and outside a model
charged cylindrical vesicle (nanopore) immersed into a primitive model
macroions solution, so that the macroions are only present outside the
nanopore, i.e., the vesicle wall is impermeable only to the external macroions.
We calculate the ionic and local linear charge density profiles inside and
outside the vesicle, and find that the correlation between the inside and
outside ionic distributions causes the phenomena of overcharging (also referred
to as surface charge amplification) and/or charge reversal. This is the first
time overcharging is predicted in an electrical double layer of cylindrical
geometry. We also report the new phenomenon of double overcharging. The present
results can be of consequence for relevant systems in physical-chemistry,
energy storage and biology, e.g., nanofilters, capacitors and cell membranes.Comment: 10 pages, 4 figure
Ground-based dosimetry support for experiment AR002
Actinomyces levoris colonies were exposed to alpha particles at the 184-inch cyclotron, and Streptomyces levoris colonies were exposed to Ne-20 ions. A description is given of the experimental conditions for each experiment along with tables listing the doses delivered to the colonies. The doses for the Actinomyces levoris exposures came from calibrations made by the cyclotron operators, while the doses for the Streptomyces levoris exposures came in part from cave calibrations and also in part from calculations
Overcharging: The Crucial Role of Excluded Volume
In this Letter we investigate the mechanism for overcharging of a single
spherical colloid in the presence of aqueous salts within the framework of the
primitive model by molecular dynamics (MD) simulations as well as
integral-equation theory. We find that the occurrence and strength of
overcharging strongly depends on the salt-ion size, and the available volume in
the fluid. To understand the role of the excluded volume of the microions, we
first consider an uncharged system. For a fixed bulk concentration we find that
upon increasing the fluid particle size one strongly increases the local
concentration nearby the colloidal surface and that the particles become
laterally ordered. For a charged system the first surface layer is built up
predominantly by strongly correlated counterions. We argue that this a key
mechanism to produce overcharging with a low electrostatic coupling, and as a
more practical consequence, to account for charge inversion with monovalent
aqueous salt ions.Comment: 7 pages, 3 figs (4 EPS files). To appear in Europhysics Letter
Quasi-ordinary power series and their zeta functions
The main objective of this paper is to prove the monodromy conjecture for the
local Igusa zeta function of a quasi-ordinary polynomial of arbitrary dimension
defined over a number field. In order to do it, we compute the local
Denef-Loeser motivic zeta function of a quasi-ordinary
power series of arbitrary dimension over an algebraically closed field of
characteristic zero from its characteristic exponents without using embedded
resolution of singularities. This allows us to effectively represent
such that almost all the candidate poles given
by are poles. Anyway, these candidate poles give eigenvalues of the
monodromy action of the complex of nearby cycles on In particular
we prove in this case the monodromy conjecture made by Denef-Loeser for the
local motivic zeta function and the local topological zeta function. As a
consequence, if is a quasi-ordinary polynomial defined over a number field
we prove the Igusa monodromy conjecture for its local Igusa zeta function.Comment: 74 page
Quasi-ordinary singularities and Newton trees
In this paper we study some properties of the class of nu-quasi-ordinary
hypersurface singularities. They are defined by a very mild condition on its
(projected) Newton polygon. We associate with them a Newton tree and
characterize quasi-ordinary hypersurface singularities among nu-quasi-ordinary
hypersurface singularities in terms of their Newton tree. A formula to compute
the discriminant of a quasi-ordinary Weierstrass polynomial in terms of the
decorations of its Newton tree is given. This allows to compute the
discriminant avoiding the use of determinants and even for non Weierstrass
prepared polynomials. This is important for applications like algorithmic
resolutions. We compare the Newton tree of a quasi-ordinary singularity and
those of its curve transversal sections. We show that the Newton trees of the
transversal sections do not give the tree of the quasi-ordinary singularity in
general. It does if we know that the Newton tree of the quasi-ordinary
singularity has only one arrow.Comment: 32 page
On the -exponents of generic isolated plane curve singularities
In 1982, Tamaki Yano proposed a conjecture predicting how is the set of
-exponents of an irreducible plane curve singularity germ which is generic
in its equisingularity class. In 1986, Pi.~Cassou-Nogu\`es proved the
conjecture for the one Puiseux pair case. In a previous work the authors proved
the conjecture for two Puiseux pairs germs whose complex algebraic monodromy
has distinct eigenvalues. A natural problem induced by Yano's conjecture is,
for a generic equisingular deformation of an isolated plane curve singularity
germ to study how the set of -exponents depends on the topology of the
singularity. The natural generalization suggested by Yano's approach holds in
suitable examples (for the case of isolated singularites which are Newton
non-degenerated, commode and whose set of spectral numbers are all distincts).
Morevover we show with an example that this natural generalization is not
correct. We restrict to germs whose complex algebraic monodromy has distinct
eigenvalues such that the embedded resolution graph has vertices of valency at
most 3 and we discuss some examples with multiple eigenvalues.Comment: 15 page
Laser-driven plasma waves in capillary tubes
The excitation of plasma waves over a length of up to 8 centimeters is, for
the first time, demon- strated using laser guiding of intense laser pulses
through hydrogen filled glass capillary tubes. The plasma waves are diagnosed
by spectral analysis of the transmitted laser radiation. The dependence of the
spectral redshift, measured as a function of filling pressure, capillary tube
length and incident laser energy, is in excellent agreement with simulation
results. The longitudinal accelerating field inferred from the simulations is
in the range 1 -10 GV/m
Radiation mapping on Spacelab 1: Experiment no. INS006
The first attempt at mapping the radiation environment inside Spacelab is described. Measurements were made by a set of passive radiation detectors distributed throughout the volume inside the Spacelab 1 module, in the access tunnel and outside on the pallet. Measurements of the low linear energy transfer (LET) component obtained from the TLD thermoluminescent detectors (TLD) ranged from 92 to 134 mrad, yielding an average low LET dose rate of 10.0 mrads/day inside the module. Because of the higher inclination orbit, substantial fluxes of highly ionizing (HZE particles) high charge and energy galactic cosmic rays were observed for the first time on an STS flight, yielding an overall average mission dose-equivalent of 295 mrem, or 29.5 mrem/day, which is about three times higher than that measured on previous STS missions. Little correlation is found between measured average dose rates or HZE fluences and the estimates shielding throughout the volume of the module
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