Onsager-Manning-Oosawa condensation phenomenon and the effect of salt

Making use of results pertaining to Painleve III type equations, we revisit the celebrated Onsager-Manning-Oosawa condensation phenomenon for charged stiff linear polymers, in the mean-field approximation with salt. We obtain analytically the associated critical line charge density, and show that it is severely affected by finite salt effects, whereas previous results focused on the no salt limit. In addition, we obtain explicit expressions for the condensate thickness and the electric potential. The case of asymmetric electrolytes is also briefly addressed.Comment: to appear in Phys. Rev. Let

Reduction of salt: will iodine intake remain adequate in The Netherlands?

Salt is the main vehicle for iodine fortification in The Netherlands. A reduction in salt intake may reduce the supply of iodine. Our aim was to quantify the effect of salt reduction on the habitual iodine intake of the Dutch population and the risk of inadequate iodine intake. We used data of the Dutch National Food Consumption Survey (1997–8) and an update of the food composition database to estimate habitual salt and iodine intake. To take into account uncertainty about the use of iodised salt (industrial and discretionary) and food supplements, a simulation model was used. Habitual iodine and salt intakes were simulated for scenarios of salt reduction and compared with no salt reduction. With 12, 25 and 50 % salt reduction in industrially processed foods, the iodine intake remained adequate for a large part of the Dutch population. For the extreme scenario of a 50 % reduction in both industrially and discretionary added salt, iodine intake might become inadequate for part of the Dutch population (up to 10 %). An increment of the proportion of industrially processed foods using iodised salt or a small increase in iodine salt content will solve this. Nevertheless, 8–35 % of 1- to 3-year-old children might have iodine intakes below the corresponding estimated average requirement (EAR), depending on the salt intake scenario. This points out the need to review the EAR value for this age group or to suggest the addition of iodine to industrially manufactured complementary food

The influence of the precipitation rate on the properties of porous chromia

The properties were studied of heated (320°C) chromia samples, prepared by two precipitation methods: \ud \ud 1. (1) addition of ammonia to chromium salt solutions,\ud 2. (2) OH− formation in chromium salt solutions through hydrolysis of urea.\ud \ud Samples formed by means of the first method are macro or mesoporous and have a lower specific surface area (~200 m2·g−1) than those formed by urea hydrolysis (~300 m2·g−1). Only in the case of a very slow addition of the ammonia solution these properties of the chromia's become equal. Experiments show that the micro porous type samples with high surface area are only formed if the pH range 5.1 to 5.7 is passed slowly. The formation of polychromium complexes of uniform size is suggested.\ud \u

Like-charge polymer-membrane complexation mediated by multivalent cations: one-loop-dressed strong coupling theory

We probe the electrostatic mechanism driving adsorption of polyelectrolytes onto like-charged membranes upon the addition of tri- and tetravalent counterions to a bathing monovalent salt solution. We develop a one-loop-dressed strong coupling theory that treats the monovalent salt at the electrostatic one-loop level and the multivalent counterions within a strong-coupling approach. It is shown that the adhesive force of the multivalent counterions mediating the like-charge adsorption arises from their strong condensation at the charged membrane. The resulting interfacial counterion excess locally maximizes the screening ability of the electrolyte and minimizes the electrostatic polymer grand potential. This translates into an attractive force that pulls the polymer to the similarly charged membrane. We show that the high counterion valency enables this adsorption transition even at weakly charged membranes. Additionally, strongly charged membranes give rise to salt-induced correlations and intensify the interfacial multivalent counterion condensation, strenghtening the complexation of the polymer with the like-charged membrane, as well as triggering the orientational transition of the molecule prior to its adsorption. Finally, our theory provides two additional key features as evidenced by previous adsorption experiments: first, the critical counterion concentration for polymer adsorption decreases with the rise of the counterion valency, and second, the addition of monovalent salt enhances the screening of the membrane charges and suppresses salt correlations. This weakens the interfacial multivalent counterion condensation and results in the desorption of the polymer from the substrate

Salt-induced changes of colloidal interactions in critical mixtures

We report on salt-dependent interaction potentials of a single charged particle suspended in a binary liquid mixture above a charged wall. For symmetric boundary conditions (BC) we observe attractive particle-wall interaction forces which are similar to critical Casimir forces previously observed in salt-free mixtures. However, in case of antisymmetric BC we find a temperature-dependent crossover from attractive to repulsive forces which is in strong contrast to salt-free conditions. Additionally performed small-angle x-ray scattering experiments demonstrate that the bulk critical fluctuations are not affected by the addition of salt. This suggests that the observed crossover can not be attributed alone to critical Casimir forces. Instead our experiments point towards a possible coupling between the ionic distributions and the concentration profiles in the binary mixture which then affects the interaction potentials in such systems.Comment: 5 pages, 4 Figure

Salt marsh harvest mouse abundance and site use in a managed marsh

The salt marsh harvest mouse (Reithrodontomys raviventris) is a federal and California listed endangered mammal endemic to the San Francisco Bay. The objectives of this research were to determine habitat use of endangered salt marsh harvest mice in a managed marsh in Fremont California, and to evaluate whether managed flooding of the marsh provides favorable habitat conditions for the mice. In addition, this research explores the effectiveness of using mark-recapture model selection analysis to estimate capture probability, survival, and population growth rate for salt marsh harvest mice. Mice were captured for four nights per month between May and August, 2008. Thirty-six unique salt marsh harvest mice were captured for a catch per 100 nights of trap effort of 1.9. The sex ratio of male to female mice was skewed towards males with a sex of 2.3:1. Salt marsh harvest mice were distributed randomly throughout the marsh and no relationships were found between mice distribution and pickleweed salinity, pickleweed height, distance to levees, distance to dry or filled water bodies, percent cover of vegetation, or sympatric rodents. The findings of this study indicate that catch-per-trap-effort, the current standard method to estimate salt marsh harvest mice populations, may not be accurate. The results of this study can be used by managers of salt marsh harvest mice habitat to manage and estimate mouse populations

Why is the condensed phase of DNA preferred at higher temperature? DNA compaction in the presence of a multivalent cation

Upon the addition of multivalent cations, a giant DNA chain exhibits a large discrete transition from an elongated coil into a folded compact state. We performed single-chain observation of long DNAs in the presence of a tetravalent cation (spermine), at various temperatures and monovalent salt concentrations. We confirmed that the compact state is preferred at higher temperatures and at lower monovalent salt concentrations. This result is interpreted in terms of an increase in the net translational entropy of small ions due to ionic exchange between higher and lower valence ions.Comment: 4pages,3figure

Epsomite as flame retardant treatment for wood: Preliminary study

The effect of epsomite as flame retardant for wood has been investigated and compared with a commercial boron salt. Both flame retardants have been introduced into wood samples by vacuum impregnation. Epsomite is a hydrated sulphate salt with a water solubility of 731 g L-1 at room temperature. Thanks to this high solubility it was possible to obtain elevated epsomite loadings in comparison with the borax salt. Flame retardancy was evaluated by means of the limiting oxygen index, the dripping test and the exposition to a direct flame (Bunsen test). The results showed that the addition of epsomite increases the limiting oxygen index, delays the time to ignition and the evolution of the temperatures trough the wood. © 2016 Elsevier LtdPeer ReviewedPostprint (author's final draft

Environmentally Friendly Pervious Concrete for Treating Deicer-Laden Stormwater: Phase I

A graphene oxide-modified pervious concrete was developed by using low-reactivity, high-calcium fly ash as sole binder and chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of this pervious concrete were measured against three control groups. The test results indicate that graphene oxide modified fly ash pervious concrete is comparable to Portland cement pervious concrete. While the addition of 0.03% graphene oxide (by weight of fly ash) noticeably increased the compressive strength, split tensile strength, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of fly ash pervious concrete, it reduced the void ratio and infiltration rate. The fly ash pervious concrete also showed unfavorable high initial loss during the freeze-deicer salt scaling test, which may be attributed to the low hydration degree of fly ash at early age. It is recommended that durability tests for fly ash concrete be performed at a later age