Excess enthalpies,heat capacities,and excess heat capacities as a function of temperature in liquid mixtures of ethanol + toluene,ethanol + hexamethyldisiloxane,and hexamethyldisiloxane + toluene

The heat capacities of liquid ethanol, toluene, and hexamethyldisiloxane, and of 14 binary mixtures of these were measured at atmospheric pressure at a series of temperatures between 298 and 348 K. In addition, the excess enthalpy was measured for each of the 14 mixtures at room temperature and corrected with the aid of the heat capacities to 298.15 K. The results were represented by empirical equations of a polynomial form. From these equations, the excess heat capacity was derived and the excess enthalpy was calculated, and fitted to equations, as a function of composition at temperatures between 298 and 348 K. All the mixtures are non-ideal as evidenced by the substantial excess enthalpy. The excess enthalpy for the mixtures containing ethanol showed a strong positive temperature dependence, while the variation of temperature between 298 and 348 K had little effect on the excess enthalpy of toluene + hexamethyldisiloxane.     

Rapid and reliable method for the analysis of nucleotide pools by reversed-phase high-performance liquid chromatography

A rapid and reliable protocol for the simultaneous separation of ribo-, deoxyribo- and cyclic nucleotides has been developed using high-performance liquid chromatography on a C18 microBondapak column and isocratic elution with ammonium phosphate buffer 0.2 m, pH 5.1). Resolution of deoxyribonucleotides has been confirmed by performing resolution before and after periodate oxidation. The general order of elution is ribonucleotides, deoxyribonucleotides and cyclic nucleotides. While periodate oxidation improved the clarity of separation of deoxyribonucleotides by eliminating ribonucleotides, incorporation of methanol in the eluent shortened the retention time of cyclic nucleotides. The application of this method to a complex biological system is reported.     

CONCERNING THE ORIGIN OF CHARGE AT THE POLYSTYRENE PARTICLE/WATER INTERFACE

The electrophoretic mobility behavior of well-characterized polystyrene latex particles, carrying one type of surface functional endgroups, has been studied as a function of pH. At low pH, the interaction of protons with the functional endgroups increased in the order: Hydroxyl > carboxyl > sulfate; at high pH the order of interaction was reversed; and at intermediate pH no interactions were observed. The particles of the polystyrene latexes in their different forms at the intermediate pH range, dispersed in deionized water, all exhibited the same mobility irrespective of the functional endgroup. The origin of charge in these systems is explained as being the result of either the preferential adsorption of hydroxyl ions or an electron - injection mechanism due to the overlap of local intrinsic molecular - ion states in polystyrene and water. At low concentrations of functional endgroups, the surface properties of the polystyrene latexes are largely dependent upon the hydrophobic nature of the surface.     

Both systemic and local application of Granulocyte-colony stimulating factor (G-CSF) is neuroprotective after retinal ganglion cell axotomy

Background  

The hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) plays a crucial role in controlling the number of neutrophil progenitor cells. Its function is mediated via the G-CSF receptor, which was recently found to be expressed also in the central nervous system. In addition, G-CSF provided neuroprotection in models of neuronal cell death. Here we used the retinal ganglion cell (RGC) axotomy model to compare effects of local and systemic application of neuroprotective molecules.     

A note on the eigenvectors of Hadamard matrices of order 2n

A set of 2ⁿ mutually orthogonal eigenvectors of Hadamard matrices of order 2ⁿ are explicitly derived, and their properties are developed. An instance of Pell's equation driven by the Thue-Morse sequence is noted.     

Densities and compressibilities of aqueous HCl and NaOH from 0 to 45°C. The effect of pressure on the ionization of water

The densities and sound speeds of aqueous HCl and NaOH solutions were measured from 0.1 to 1.0m and from 0 to 45°C. These data were combined with literature data and fitted to functions of molality and temperature. The apparent molal volumes V and compressibilities K of these solutions were fitted to functions of molality and temperature. The partial molal volumes and compressibilities of HCl and NaOH solutions were used to calculate the partial molal volume V and compressibility changes for the ionization of water. Combined with literature data these values of V adn were used to calculated the effect of pressure on the ionization constant of water K _w from 0 to 200°C. The effect of pressure on K _w calculated from partial molal quantities are in reasonable agreement with that determined directly from high pressure measurements taken from the literature up to 1000 bar. It is necessary to use the pressure dependence of K ⁰ to extend the calculated pressure dependence of K _w up to 6000 bar.     

The dissociation of phosphoric acid in NaCl and NaMgCl solutions at 25°C

The pK ₁ ^* , pK ₁ ^* and pK ₃ ^* for the dissociation of H₃PO₄ have been measured in NaCl solutions from 0.5 to 6m at 25°C. The results have been used to evaluate Pitzer interaction parameters (NaClH₂PO₄)=–0.028±0.005, (NaH₃PO₄)=–0.075±0.025, (HPO₄Cl)=0.105±0.009, (PO₄Cl)=–0.59±0.02 and (NaClHPO₄)=–0.003±0.004, (PO₄NaClH)=0.110±0.008. These parameters yield values of pK ₁ ^* , pK ₂ ^* and pK ₃ ^* in NaCl that agree with the measured values with average deviations of ±0.04, ±0.03 and ±0.05 in pK ₁ ^* . Measurements of pK ₁ ^* and pK ₂ ^* were also made in NaMgCl solutions. These results have been used to evaluate ^(O)(MgH ₂ PO ₄)=–3.55±0.07,⁽¹⁾(MgH ₂ PO ₄=–16.9±0.03, ^(O)(MgH ₂ PO ₄=–17.5±0.03 and ⁽¹⁾(MgH ₂ PO ₄)=27.4±0.8 at 25°C. The results for pK ₂ ^* in NaMg–Cl solutions were also used to calculate log K _MX ^* =3.2±0.1 for the formation of the ion pair MgHPO ₄ ^o .     

An iterative estimation and validation procedure for specification of semi-Markov models with application to hospital patient flow

This article presents a methodology to identify and specify a continuous time semi-Markov model of population flow within a network of service facilities. An iterative procedure of state space definition, population disaggregation, and parameter estimation leads to the specification of a model which satisfies the underlying semi-Markov assumptions. We also present a test of the impact of occupancy upon realizations of population flows. The procedure is applied to data describing the movement of obstetric patients in a large university teaching hospital. We use the model to predict length-of-stay distributions. Finally, we compare these results with those that would have been obtained without the procedure, and show the modified model to be superior.