384 research outputs found
The electrical double layer for a fully asymmetric electrolyte around a spherical colloid: an integral equation study
The hypernetted chain/mean spherical approximation (HNC/MSA) integral
equation is obtained and solved numerically for a totally asymmetric primitive
model electrolyte around a spherical macroparticle. The ensuing radial
distribution functions show a very good agreement when compared to our Monte
Carlo and molecular dynamics simulations for spherical geometry and with
respect to previous anisotropic reference HNC calculations in the planar limit.
We report an analysis of the potential vs charge relationship, radial
distribution functions, mean electrostatic potential and cumulative reduced
charge for representative cases of 1:1 and 2:2 salts with a size asymmetry
ratio of 2. Our results are collated with those of the Modified Gouy-Chapman
(MGC) and unequal radius Modified Gouy-Chapman (URMGC) theories and with those
of HNC/MSA in the restricted primitive model (RPM) to assess the importance of
size asymmetry effects. One of the most striking characteristics found is
that,\textit{contrary to the general belief}, away from the point of zero
charge the properties of an asymmetric electrical double layer (EDL) are not
those corresponding to a symmetric electrolyte with the size and charge of the
counterion, i.e. \textit{counterions do not always dominate}. This behavior
suggests the existence of a new phenomenology in the EDL that genuinely belongs
to a more realistic size-asymmetric model where steric correlations are taken
into account consistently. Such novel features can not be described by
traditional mean field theories like MGC, URMGC or even by enhanced formalisms,
like HNC/MSA, if they are based on the RPM.Comment: 29 pages, 13 figure
Ion pairing in model electrolytes: A study via three particle correlation functions
A novel integral equations approach is applied for studying ion pairing in
the restricted primitive model (RPM) electrolyte, i. e., the three point
extension (TPE) to the Ornstein-Zernike integral equations. In the TPE
approach, the three-particle correlation functions are obtained. The TPE results are compared to molecular
dynamics (MD) simulations and other theories. Good agreement between TPE and MD
is observed for a wide range of parameters, particularly where standard
integral equations theories fail, i. e., low salt concentration and high ionic
valence. Our results support the formation of ion pairs and aligned ion
complexes.Comment: 43 pages (including 18 EPS figs) - RevTeX 4 - J. Chem. Phys. (in
press
Electrophoresis of a rod macroion under polyelectrolyte salt: Is mobility reversed for DNA?
By molecular dynamics simulation, we study the charge inversion phenomenon of
a rod macroion in the presence of polyelectrolyte counterions. We simulate
electrophoresis of the macroion under an applied electric field. When both
counterions and coions are polyelectrolytes, charge inversion occurs if the
line charge density of the counterions is larger than that of the coions. For
the macroion of surface charge density equal to that of the DNA, the reversed
mobility is realized either with adsorption of the multivalent counterion
polyelectrolyte or the combination of electrostatics and other mechanisms
including the short-range attraction potential or the mechanical twining of
polyelectrolyte around the rod axis.Comment: 8 pages, 5 figures, Applied Statistical Physics of Molecular
Engineering (Mexico, 2003). Journal of Physics: Condensed Matters, in press
(2004). Journal of Physics: Condensed Matters, in press (2004
Charge Fluctuation Forces Between Stiff Polyelectrolytes in Salt Solution: Pairwise Summability Re-examined
We formulate low-frequency charge-fluctuation forces between charged
cylinders - parallel or skewed - in salt solution: forces from dipolar van der
Waals fluctuations and those from the correlated monopolar fluctuations of
mobile ions. At high salt concentrations forces are exponentially screened. In
low-salt solutions dipolar energies go as or ; monopolar
energies vary as or , where is the minimal separation
between cylinders. However, pairwise summability of rod-rod forces is easily
violated in low-salt conditions. Perhaps the most important result is not the
derivation of pair potentials but rather the demonstration that some of these
expressions may not be used for the very problems that originally motivated
their derivation.Comment: 8 pages and 1 fig in ps forma
Controlling the spectrum of x-rays generated in a laser-plasma accelerator by tailoring the laser wavefront
By tailoring the wavefront of the laser pulse used in a laser-wakefield
accelerator, we show that the properties of the x-rays produced due to the
electron beam's betatron oscillations in the plasma can be controlled. By
creating a wavefront with coma, we find that the critical energy of the
synchrotron-like x-ray spectrum can be significantly increased. The coma does
not substantially change the energy of the electron beam, but does increase its
divergence and produces an energy-dependent exit angle, indicating that changes
in the x-ray spectrum are due to an increase in the electron beam's oscillation
amplitude within the wakefield.Comment: 7 pages, 2 figures, submitted to Appl. Phys. Let
High-gradient plasma and laser accelerators
Novel high-gradient accelerators have demonstrated acceleration of electrons and positrons with electric field strengths of 1 to > 100 GeV/m. This is about 10 to 1000 times higher than achieved in RF-based accelerators, and as such they have the potential to overcome the limitations associated with RF cavities. Plasma-based accelerators have produced multi-GeV bunches with parameters approaching those suitable for a linear collider. These accelerators offer the prospect of near term, compact and cost-effective particle physics experiments that provide new physics possibilities supporting precision studies and the search for new particles.
The expert panel has defined a long term R&D roadmap towards a compact collider with attractive intermediate experiments and studies. A delivery plan for the required R&D has been developed and includes work packages, deliverables, a minimal plan, connections to ongoing projects and an aspirational plan
Spectral analysis and zeta determinant on the deformed spheres
We consider a class of singular Riemannian manifolds, the deformed spheres
, defined as the classical spheres with a one parameter family of
singular Riemannian structures, that reduces for to the classical metric.
After giving explicit formulas for the eigenvalues and eigenfunctions of the
metric Laplacian , we study the associated zeta functions
. We introduce a general method to deal with some
classes of simple and double abstract zeta functions, generalizing the ones
appearing in . An application of this method allows to
obtain the main zeta invariants for these zeta functions in all dimensions, and
in particular and . We give
explicit formulas for the zeta regularized determinant in the low dimensional
cases, , thus generalizing a result of Dowker \cite{Dow1}, and we
compute the first coefficients in the expansion of these determinants in powers
of the deformation parameter .Comment: 1 figur
Characterizing, modelling and understanding the climate variability of the deep water formation in the North-Western Mediterranean Sea
Observing, modelling and understanding the climate-scale variability of the deep water formation (DWF) in the North-Western Mediterranean Sea remains today very challenging. In this study, we first characterize the interannual variability of this phenomenon by a thorough reanalysis of observations in order to establish reference time series. These quantitative indicators include 31 observed years for the yearly maximum mixed layer depth over the period 1980â2013 and a detailed multi-indicator description of the period 2007â2013. Then a 1980â2013 hindcast simulation is performed with a fully-coupled regional climate system model including the high-resolution representation of the regional atmosphere, ocean, land-surface and rivers. The simulation reproduces quantitatively well the mean behaviour and the large interannual variability of the DWF phenomenon. The model shows convection deeper than 1000 m in 2/3 of the modelled winters, a mean DWF rate equal to 0.35 Sv with maximum values of 1.7 (resp. 1.6) Sv in 2013 (resp. 2005). Using the model results, the winter-integrated buoyancy loss over the Gulf of Lions is identified as the primary driving factor of the DWF interannual variability and explains, alone, around 50 % of its variance. It is itself explained by the occurrence of few stormy days during winter. At daily scale, the Atlantic ridge weather regime is identified as favourable to strong buoyancy losses and therefore DWF, whereas the positive phase of the North Atlantic oscillation is unfavourable. The driving role of the vertical stratification in autumn, a measure of the water column inhibition to mixing, has also been analyzed. Combining both driving factors allows to explain more than 70 % of the interannual variance of the phenomenon and in particular the occurrence of the five strongest convective years of the model (1981, 1999, 2005, 2009, 2013). The model simulates qualitatively well the trends in the deep waters (warming, saltening, increase in the dense water volume, increase in the bottom water density) despite an underestimation of the salinity and density trends. These deep trends come from a heat and salt accumulation during the 1980s and the 1990s in the surface and intermediate layers of the Gulf of Lions before being transferred stepwise towards the deep layers when very convective years occur in 1999 and later. The salinity increase in the near Atlantic Ocean surface layers seems to be the external forcing that finally leads to these deep trends. In the future, our results may allow to better understand the behaviour of the DWF phenomenon in Mediterranean Sea simulations in hindcast, forecast, reanalysis or future climate change scenario modes. The robustness of the obtained results must be however confirmed in multi-model studies
Aspirado traqueal de cavalos clinicamente sadios da raça Quarto de Milha apĂłs prova de trĂȘs tambores
The aim of the present study wasto evaluate through endoscopy the trachealaspiration cytology in twenty seven Quarter Horsesfrom Curitiba and surroundings, following theThree Barrel Competittion. Upper respiratory tractsecretion was obtained by tracheal aspiration usinga polyethylene catheter introduced through theendoscopic fiberoptic working channel, at the level oftracheal bifurcation. Cytologic slides were preparedby smear and stained by diff-quick technique andthe differential was performed in 500 cells countingby 1,000X optic microscopy. None of the horsespresented abnormality, including epixtasis, at theclinical examination. However, hemosiderophageswere detected at cytology in three animals,suggesting that some may be suffering of subclinicalpulmonary hemorrhage. Differential cell countingof tracheal aspiration results were, in average:44.09 ± 35.68% of epithelial cells; 1.10 ± 2.18%of Globet cells; 23.10 ± 35.93% of neutrophils;0.13 ± 0.37% of lymphocytes; 0.91 ± 2.81% ofeosinophils; 30.57 ± 23.62% of macrophages and0.13 ± 0.93% of hemosiderophages. In conclusion,based in the present study, the evaluation of cellularpopulations with the tracheal aspiration may offerimportant additional information to the clinician,particularly about the inflammatory processes oflower respiratory tract and pulmonary bleeding.O objetivo do presente estudo foi avaliar,com o auxĂlio de endoscopia, a citologia do aspiradotraqueal em vinte sete cavalos da raça Quartode Milha, provenientes de Curitiba e RegiĂŁo Metropolitana,apĂłs prova de TrĂȘs Tambores. Foi obtidasecreção das vias aĂ©reas por aspirado traquealcom cateter de polietileno introduzido no canal detrabalho do endoscĂłpio, na altura da bifurcação traqueal.As lĂąminas citolĂłgicas foram preparadas poresfregaço e coradas pela tĂ©cnica de panĂłtico rĂĄpidoe a contagem diferencial foi realizada em 500cĂ©lulas atravĂ©s de microscopia Ăłptica com aumentode 1000 vezes. Nenhum dos cavalos apresentouanormalidade, incluindo epistaxe, ao exame clĂnico.Entretanto, Ă citologia detectou-se hemossiderĂłfagosem trĂȘs animais, sugerindo que alguns delespoderiam estar sofrendo de hemorragia pulmonarsubclĂnica. A contagem diferencial de cĂ©lulas do aspiradotraqueal foi em mĂ©dia de: 44,09 ± 35,68% decĂ©lulas epiteliais; 1,10 ± 2,18% de cĂ©lulas caliciformes;23,10 ± 35,93% de neutrĂłfilos; 0,13 ± 0,37%de linfĂłcitos; 0,91 ± 2,81% de eosinĂłfilos; 30,57 ±23,62% de macrĂłfagos e 0,13 ± 0,93% de hemossiderĂłfagos.Em conclusĂŁo, baseado no presentetrabalho, a avaliação das populaçÔes celularescom o aspirado traqueal pode fornecer ao clĂnicoimportantes informaçÔes adicionais, especialmenteacerca de processos inflamatĂłrios das vias aĂ©reasinferiores e hemorragia pulmonar
The combinatorics of plane curve singularities. How Newton polygons blossom into lotuses
This survey may be seen as an introduction to the use of toric and tropical
geometry in the analysis of plane curve singularities, which are germs
of complex analytic curves contained in a smooth complex analytic surface .
The embedded topological type of such a pair is usually defined to be
that of the oriented link obtained by intersecting with a sufficiently
small oriented Euclidean sphere centered at the point , defined once a
system of local coordinates was chosen on the germ . If one
works more generally over an arbitrary algebraically closed field of
characteristic zero, one speaks instead of the combinatorial type of .
One may define it by looking either at the Newton-Puiseux series associated to
relative to a generic local coordinate system , or at the set of
infinitely near points which have to be blown up in order to get the minimal
embedded resolution of the germ or, thirdly, at the preimage of this
germ by the resolution. Each point of view leads to a different encoding of the
combinatorial type by a decorated tree: an Eggers-Wall tree, an Enriques
diagram, or a weighted dual graph. The three trees contain the same
information, which in the complex setting is equivalent to the knowledge of the
embedded topological type. There are known algorithms for transforming one tree
into another. In this paper we explain how a special type of two-dimensional
simplicial complex called a lotus allows to think geometrically about the
relations between the three types of trees. Namely, all of them embed in a
natural lotus, their numerical decorations appearing as invariants of it. This
lotus is constructed from the finite set of Newton polygons created during any
process of resolution of by successive toric modifications.Comment: 104 pages, 58 figures. Compared to the previous version, section 2 is
new. The historical information, contained before in subsection 6.2, is
distributed now throughout the paper in the subsections called "Historical
comments''. More details are also added at various places of the paper. To
appear in the Handbook of Geometry and Topology of Singularities I, Springer,
202
- âŠ