A corresponding states approach to Small-Angle-Scattering for polydisperse ionic colloidal fluids

Approximate scattering functions for polydisperse ionic colloidal fluids are obtained by a corresponding states approach. This assumes that all pair correlation functions $g_{\alpha \beta}(r)$ of a polydisperse fluid are conformal to those of an appropriate monodisperse binary fluid (reference system) and can be generated from them by scaling transformations. The correspondence law extends to ionic fluids a {\it scaling approximation} (SA) successfully proposed for nonionic colloids in a recent paper. For the primitive model of charged hard spheres in a continuum solvent, the partial structure factors of the monodisperse binary reference system are evaluated by solving the Orstein-Zernike (OZ) integral equations coupled with an approximate closure. The SA is first tested within the mean spherical approximation (MSA) closure, which allows analytical solutions. The results are found in good overall agreement with exact MSA predictions up to relevant polidispersity. The SA is shown to be an improvement over the ``decoupling approximation'' extended to the ionic case. The simplicity of the SA scheme allows its application also when the OZ equations can be solved only numerically. An example is then given by using the hypernetted chain (HNC) closure. Shortcomings of the SA approach, its possible use in the analysis of experimental scattering data and other related points are also briefly addressed.Comment: 29 pages, 7 postscript figures (included), Latex 3.0, uses aps.sty, to appear in Phys. Rev. E (1999

Thermodynamic properties of polydisperse fluid mixtures

We present a systematic study of the thermodynamic properties of a polydisperse fluid mixture. The size of the particles, σ , is assumed to be distributed according to a continuous distribution function fΣ(σ) , for which we have chosen a Γ -distribution. The interatomic potentials are given by a hard core repulsion plus an adjacent attractive tail in the form of a squarewell or a Yukawa potential; for the size-dependence of the attraction strength we have assumed different models. The properties of the mixture are calculated using the optimized random phase approximation (ORPA), a thermodynamic perturbation theory which is known to give reliable results in the case of simple liquids. To take into account polydispersity we combine the ORPA with the orthogonal decomposition technique where all σ -dependent functions (i.e., the correlation functions and the interatomic potentials) are expanded in terms of orthogonal polynomials pi(σ) associated with the weight function fΣ(σ) .Представлено систематичне дослідження термодинамічних властивостей полідисперсної рідкої суміші. Розмір частинок σ вважається розподіленим згідно з неперервною функцією розподілу fΣ(σ) , для якої ми вибрали Γ -розподіл. Міжатомні потенціали задаються відштовхуванням типу твердих кульок та приєднаним притяганням у формі квадратної ями або потенціалу Юкави; для залежності сили притягання від розміру частинокми приймаємо різні моделі. Властивості суміші розраховуються за допомогою оптимізованого наближення хаотичних фаз (ОНХФ), термодинамічної теорії збурень, яка, яквідомо, дає надійні результати для випадку простих рідин. З метою врахування полідисперсності ми комбінуємо ОНХФ з технікою ортогонального розкладу, в як ій всі σ -залежні функції (тобто кореляційні функції та міжатомні потенціали) розкладаються за ортогональними поліномами pi(σ) , пов’язаними з ваговими функціями fΣ(σ)

Identification of two new protective pre-erythrocytic malaria vaccine antigen candidates

<p>Abstract</p> <p>Background</p> <p>Despite years of effort, a licensed malaria vaccine is not yet available. One of the obstacles facing the development of a malaria vaccine is the extensive heterogeneity of many of the current malaria vaccine antigens. To counteract this antigenic diversity, an effective malaria vaccine may need to elicit an immune response against multiple malaria antigens, thereby limiting the negative impact of variability in any one antigen. Since most of the malaria vaccine antigens that have been evaluated in people have not elicited a protective immune response, there is a need to identify additional protective antigens. In this study, the efficacy of three pre-erythrocytic stage malaria antigens was evaluated in a <it>Plasmodium yoelii</it>/mouse protection model.</p> <p>Methods</p> <p>Mice were immunized with plasmid DNA and vaccinia virus vectors that expressed one, two or all three <it>P. yoelii </it>vaccine antigens. The immunized mice were challenged with 300 <it>P. yoelii </it>sporozoites and evaluated for subsequent infection.</p> <p>Results</p> <p>Vaccines that expressed any one of the three antigens did not protect a high percentage of mice against a <it>P. yoelii </it>challenge. However, vaccines that expressed all three antigens protected a higher percentage of mice than a vaccine that expressed PyCSP, the most efficacious malaria vaccine antigen. Dissection of the multi-antigen vaccine indicated that protection was primarily associated with two of the three <it>P. yoelii </it>antigens. The protection elicited by a vaccine expressing these two antigens exceeded the sum of the protection elicited by the single antigen vaccines, suggesting a potential synergistic interaction.</p> <p>Conclusions</p> <p>This work identifies two promising malaria vaccine antigen candidates and suggests that a multi-antigen vaccine may be more efficacious than a single antigen vaccine.</p

Gas barrier design for the WIPP

The Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, is planned as the first mined repository for transuranic (TRU) wastes generated by defense programs of the United States Department of Energy (DOE). In coming years, tests with radioactive wastes are planned to be conducted at the WIPP. Potential tests include evaluation of gases generated by wastes emplaced in mined alcoves. Barriers must be installed in the entries to the test alcoves to limit gas release during testing. This paper discusses several rock mechanics issues involved in the design of an Alcove Gas Barrier (AGB) for use in these potential tests. The unique requirements placed on a gas barrier, when coupled with the geologic setting and strict regulations, make the AGB design challenging from several perspectives of rock mechanics. The AGB structure will be placed in the WIPP underground, which comprises a layered evaporite sequence of rock. A schematic of the design as it might appear in the WIPP underground is shown in Figure 1. The underlying requirement is that the AGB reduce gas leakage from a test alcove to an acceptable limit. The most likely route for gas leak-age is through a disturbed rock zone (DRZ), which develops in response to the excavation. Among other effects, the loading on the structure is a function of the geometrical arrangement and time, including considerations of installation and service life. Resolution of design issues also requires a defensible measure of conservatism. These considerations give rise to several issues in rock mechanics which are the emphases of this paper

Two Promoter Rearrangements in a Drug Efflux Transporter Gene Are Responsible for the Appearance and Spread of Multidrug Resistance Phenotype MDR2 in <i>Botrytis cinerea</i> Isolates in French and German Vineyards

In French and German vineyards, Botrytis cinerea isolates with multiple fungicide resistance phenotypes have been observed with increasing frequencies. Multidrug resistance (MDR) results from mutations that lead to constitutive overexpression of genes encoding drug efflux transporters. In MDR2 and MDR3 strains, overexpression of the major facilitator superfamiliy transporter gene mfsM2 has been found to result from a rearrangement in the mfsM2 promoter (type A), caused by insertion of a retroelement (RE)-derived sequence. Here, we report the discovery of another, similar RE-induced rearrangement of the mfsM2 promoter (type B) in a subpopulation of French MDR2 isolates. MDR2 isolates harboring either type A or type B mutations in mfsM2 show the same resistance phenotypes and similar levels of mfsM2 overexpression. RE sequences similar to those in mfsM2 were found in low copy numbers in other but not all B. cinerea strains analyzed, including non-MDR2 strains. Population genetic analyses support the hypothesis that the two rearrangement mutations have only occurred once, and are responsible for the appearance and subsequent spread of all known MDR2 and MDR3 strains in French and German wine-growing regions. </jats:p