Ion-induced multiply reentrant liquid-liquid transitions and the nature of criticality in ethanol-water mixture

We report a quite unusual feature of four liquid-liquid reentrant transitions in ethanol (E)+water (W)+ammonium sulfate mixture by meticulous tuning of the ammonium sulfate concentration in a narrow range, as a function of temperature, at atmospheric pressure. Detailed exploration of the intricate phase behavior in terms of E/W sections shows that the range of triple reentrance shrinks with increasing E/W. The behavior of osmotic susceptibility is investigated by light scattering, near the critical point, in the one-phase region by varying the temperature at fixed concentration of the components, in a particular E/W section. The critical exponent of susceptibility (gamma) and correlation length (nu) are observed to have Fisher renormalized Ising values [Phys. Rev. 176, 237 (1968)], with gamma(r)=1.41 and nu(r)=0.718. The effective susceptibility exponent, gamma(eff), exhibits a sharp, nonmonotonic crossover from Ising to mean-field critical behavior, which is completed outside the critical regime. The amplitude of the correlation length, xi(o)(=21.2+/-0.4 A), deduced from light scattering experiment, is an order of magnitude larger than the typical values in usual aqueous electrolyte systems. This value of xi(o) is further verified from small-angle x-ray scattering (SAXS) experiments and found to be consistent. SAXS experiments on the critical sample reveal the presence of long-ranged intermolecular correlations, leading to supramolecular structuring, at a temperature far away from the critical point. These results convincingly demonstrate that the finite length scale arising due to the structuring competes with the diverging correlation length of critical concentration fluctuations, which influences the nonasymptotic critical behavior in this aqueous electrolyte system. The sulphate ions play a dominant role in both structuring and the complex phase behavior.     

Developmental cognitive neuroscience of arithmetic: implications for learning and education

In this article, we review the brain and cognitive processes underlying the development of arithmetic skills. This review focuses primarily on the development of arithmetic skills in children, but it also summarizes relevant findings from adults for which a larger body of research currently exists. We integrate relevant findings and theories from experimental psychology and cognitive neuroscience. We describe the functional neuroanatomy of cognitive processes that influence and facilitate arithmetic skill development, including calculation, retrieval, strategy use, decision making, as well as working memory and attention. Building on recent findings from functional brain imaging studies, we describe the role of distributed brain regions in the development of mathematical skills. We highlight neurodevelopmental models that go beyond the parietal cortex role in basic number processing, in favor of multiple neural systems and pathways involved in mathematical information processing. From this viewpoint, we outline areas for future study that may help to bridge the gap between the cognitive neuroscience of arithmetic skill development and educational practice.     

Synthesis of electron energy loss spectra for the quantification of detection limits.

We describe a method for predicting detection limits of minority elements in electron energy loss spectroscopy (EELS), and its implementation as a software package that gives quantitative predictions for user-specified materials and experimental conditions. The method is based on modeling entire energy loss spectra, including shot noise as well as instrumental noise, and taking into account all the relevant experimental parameters. We describe the steps involved in modeling the entire spectrum, from the zero loss up to inner shell edges, and pay particular attention to the contributions to the pre-edge background. The predicted spectra are used to evaluate the signal-to-noise ratios (SNRs) for inner shell edges from user-specified minority elements. The software also predicts the minimum detectable mass (MDM) and minimum mass fraction (MMF). It can be used to ascertain whether an element present at a particular concentration should be detectable for given experimental conditions, and also to quickly and quantitatively explore ways of optimizing the experimental conditions for a particular EELS analytical task. We demonstrate the usefulness of the software by confirming the recent empirical observation of single atom detection using EELS of phosphorus in thin carbon films, and show the effect on the SNR of varying the acquisition parameters. The case of delta-doped semiconductors is also considered as an important example from materials science where low detection limits and high spatial resolution are essential, and the feasibility of such characterization using EELS is assessed.     

COMPARISON OF THE EFFECTS OF UV-VISIBLE IRRADIATION OF MELANINS and MELANIN-HEMATOPORPHYRIN COMPLEXES FROM HUMAN BLACK and RED HAIR

Clinical evidence indicates that people with light skin and red hair have a higher incidence of UV radiation-induced diseases including cancer. It is not known whether this is because of the lower protection due to the smaller amounts of eumelanin present in the skin of these people or whether the presence of pheomelanin in their skin is responsible for the higher susceptibility to carcinogenesis. Irradiation of melanoproteins from red hair with UV-visible light has been reported to produce superoxide. Comparative studies on the formation of superoxide during the irradiation of the melanins isolated from human black and red hair (BHM and RHM, respectively) are reported in this paper. These showed that no superoxide formation could be detected in the case of the BHM. whereas the formation of superoxide during the irradiation of RHM could be definitely demonstrated. Irradiation of the RHM with NADH resulted in the oxidation of more NADH than the irradiation of NADH with BHM. The observation that RHM is an active photosensitizer indicates that this property of pheomelanin present in light skin may at least partly be responsible for the harmful effect of radiation on people with light skin and/or red hair. Administration of hematoporphyrin followed by visible irradiation is a currently used mode of therapy for cancer. The present studies have shown that hematoporphyrin is bound to both BHM and RHM. The binding of hematoporphyrin to the melanins increased the formation of superoxide by RHM and the oxidation of NADH by both the melanins. The binding of porphyrins to melanins may have an influence upon the photosensitivity in diseases such as porphyrias and may also affect the therapeutic efficacy of hematoporphyrin.     

Synthesis of Hydrophilic and Hydrophobic High Surface Area Xerogels at pHs Below Silica Iso-electric Point

The synthesis of hydrophilic and hydrophobic high surface area (up to 1087 m²/cc) silica xerogels at pHs below 2 is demonstrated in this work. High surface area xerogels exhibit extremely fine microstructural features and fast gelation times (less than one hour). Contrary to conventional generalization that xerogels synthesized at low pH are polymeric, it is demonstrated that particulate xerogels can also be synthesized at pHs below 2. These xerogels are synthesized by the addition of large amounts of NH₄OH and have relatively lower surface areas. The particulate nature of these xerogels is indicated by their opacity and from their coarse microstructural features as observed by TEM.     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

Nonequilibrium states of driven disordered polymorphic solids

Condensed matter systems, when driven far from equilibrium, often exhibit a far more varied set of phases than their equilibrium counterparts. The existence of non-equilibrium analogs of ‘solids’ and ‘liquids’ has been demonstrated earlier in the context of models for driven disordered vortex lattices in superconductors. Here we study the effects of a structural (polymorphic) transition in a driven two-dimensional crystal placed in a quenched random background. Such a polymorphic crystal is shown to exhibit a complex sequence of unusual dynamical phases as the external drive is varied, including some which have no analog in the undriven pure system. We propose that such states should be accessible in experiments.     

Processing and characterization of porous electrochemical cells for flue gas purification

In the present work, porous electrode materials lanthanum strontium manganate (LSM)-gadolinium-doped cerium oxide (CGO) and electrochemical cells LSM-CGO + CGO were fabricated via the processes of slurry preparation, tape casting and lamination, and sintering. Graphite, wheat starch, and polyamide powders were used as pore formers, respectively, in order to investigate their effects on shrinkage, flow rate, porosity, and average pore size of the sintered samples. The observation from scanning electronic microscope (SEM) revealed different microstructures caused by different pore formers. Porous, flat, and crack-free electrochemical cells were successfully achieved using the present ceramic processing route. The produced cells could potentially be used for flue gas purification.