Enthalpies of Dilution of Aqueous Solutions of HCl, MgCl2}, CaCl2, and BaCl2 at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of BaCl₂ at 300°C and 11.0 MPa, MgCl₂, CaCl₂, and BaCl₂ at 325°C and 14.8 MPa, and at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of MgCl₂ and CaCl₂ at 300°C and 10.3 MPa and for aqueous solutions of HCl at 250, 275, and 300°C at 10.3 MPa and 320°C at 12.8 MPa were included with the new data at 300°C and 11.0 MPa and at 350°C and 17.6 MPa when fitting the Pitzer parameters. The concentration range of the chloride solutions was 0.5 to 0.02 molal. Parameters for the Pitzer excess Gibbs ion–interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat-capacity changes for the association of alkaline earth metal ions and H⁺ with chloride ion were estimated from the heat data. For all systems, the enthalpy and entropy changes are positive and show accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

The Stochastically Subordinated Poisson Normal Process for Modelling Financial Assets

The method of stochastic subordination, or random time indexing, has been recently applied to Wiener process price processes to model financial returns. Previous emphasis in stochastic subordination models has involved explicitly identifying the subordinating process with an observable quantity such as number of trades. In contrast, the approach taken here does not depend on the specific identification of the subordinated time variable, but rather assumes a class of time models and estimates parameters from data. In addition, a simple Markov process is proposed for the characteristic parameter of the subordinating distribution to explain the significant autocorrelation of the squared returns. It is shown, in particular, that the proposed model, while containing only a few more parameters than the commonly used Wiener process models, fits selected financial time series particularly well, characterising the autocorrelation structure and heavy tails, as well as preserving the desirable self-similarity structure, and the existence of risk-neutral measures necessary for objective derivative valuation. Also, it will be shown that the model proposed fits financial times series data better than the popular generalised autoregressive conditional heteroscedasticity (GARCH) models. Additionally, this paper will develop a skew model by replacing the normal variates with Lévy stable variates.     

A method for treating the passage of a charged hard sphere ion as it passes through a sharp dielectric boundary

In the implicit solvent models of electrolytes (such as the primitive model (PM)), the ions are modeled as point charges in the centers of spheres (hard spheres in the case of the PM). The surfaces of the spheres are not polarizable which makes these models appropriate to use in computer simulations of electrolyte systems where these ions do not leave their host dielectrics. The same assumption makes them inappropriate in simulations where these ions cross dielectric boundaries because the interaction energy of the point charge with the polarization charge induced on the dielectric boundary diverges. In this paper, we propose a procedure to treat the passage of such ions through dielectric interfaces with an interpolation method. Inspired by the "bubble ion" model (in which the ion's surface is polarizable), we define a space-dependent effective dielectric coefficient, ε(eff)(r), for the ion that overlaps with the dielectric boundary. Then, we replace the "bubble ion" with a point charge that has an effective charge q/ε(eff)(r) and remove the portion of the dielectric boundary where the ion overlaps with it. We implement the interpolation procedure using the induced charge computation method [D. Boda, D. Gillespie, W. Nonner, D. Henderson, and B. Eisenberg, Phys. Rev. E 69, 046702 (2004)]. We analyze the various energy terms using a spherical ion passing through an infinite flat dielectric boundary as an example.     

Boden

Ohne Zusammenfassung     

Capillary ion chromatography of inorganic anions on octadecyl silica monolith modified with an amphoteric surfactant

A reversed-phase monolithic silica based capillary column (Onyx C(18), 150 mm x 0.1 mm) was modified with the amphoteric surfactant, N-dodecyl-N,N-(dimethylammonio)undecanoate (DDMAU) and evaluated for the separation and determination of inorganic anions using on-column capacitively coupled contactless conductivity detection (C(4)D). The chromatographic performance of the column was evaluated and under optimal conditions separation efficiencies of 56,200 plates per meter or 7025 plates per column (at detection point) were observed (for iodide). Direct plumbing of the capillary column to the micro-injector and on-column detection eliminated extra-column band broadening, thus allowing accurate analysis of van Deemter curves obtained for the monolithic capillary column. The calculated value for the C-term in the obtained van Deemter curve was between 3 and 4 ms for inorganic anions, allowing for the utilisation of relatively high flow rates without significant losses in efficiency. The performance of the C(4)D detector was investigated and compared for detection on an open tubular capillary column and on the modified monolithic silica capillary column. The on-column detection approach did not result in any significant decrease in peak sensitivity for the monolith compared to responses recorded for open tubular capillary columns, and in addition meant the system could be applied to rapid separations by simple variation in apparent column length. The proposed chromatographic system allowed for detection of common anions at sub-ppm level with a 10 nL injection volume. Additionally, on-column detection allowed visualisation of the development of the separation at any point in time and evaluation of the longitudinal uniformity of the ion-exchange coating.     

Use of contactless conductivity detection for non-invasive characterisation of monolithic stationary-phase coatings for application in capillary ion chromatography

A capacitively-coupled contactless conductivity detector (C4D) has been utilised as an on-capillary detector within a capillary ion chromatograph, incorporating a reversed-phase monolithic silica capillary column semi-permanently modified with a suitable ionic surfactant. The monolithic capillary column (150 x 0.1 mm i.d.) was modified using sodium dioctyl sulfosuccinate (DOSS), an anionic surfactant, for the separation of small inorganic and organic cations. With the use of the on-capillary conductivity detector, the longitudinal homogeneity and temporal stability of the coating were investigated. The approach allowed a detailed non-invasive observation of the nature of the ion-exchange coating over time, and an example of an application of the technique to produce a longitudinal stationary-phase charge gradient is shown. An investigation of the basis of the measured on-capillary conductivity was carried out with a counter ion study, clearly showing the on-capillary detection technique could also distinguish between chemical forms of the immobilised ion exchanger. The above method was used to produce a stable and homogeneously-modified monolithic ion-exchange capillary column, for application to the separation of inorganic alkaline earth cations and amino acids.     

Carbon nanotube amplification strategies for highly sensitive immunodetection of cancer biomarkers

We describe herein the combination of electrochemical immunosensors using single-wall carbon nanotube (SWNT) forest platforms with multi-label secondary antibody-nanotube bioconjugates for highly sensitive detection of a cancer biomarker in serum and tissue lysates. Greatly amplified sensitivity was attained by using bioconjugates featuring horseradish peroxidase (HRP) labels and secondary antibodies (Ab(2)) linked to carbon nanotubes (CNT) at high HRP/Ab(2) ratio. This approach provided a detection limit of 4 pg mL(-)(1) (100 amol mL(-)(1)), for prostate specific antigen (PSA) in 10 microL of undiluted calf serum, a mass detection limit of 40 fg. Accurate detection of PSA in human serum samples was demonstrated by comparison to standard ELISA assays. PSA was quantitatively measured in prostate tissue samples for which PSA could not be differentiated by the gold standard immunohistochemical staining method. These easily fabricated SWNT immunosensors show excellent promise for clinical screening of cancer biomarkers and point-of-care diagnostics.     

Chemistry and Logical Structures

The utility of the basic structures of modern mathematics for chemistry is discussed; general set theory, topology, and group theory are shown to pervade almost all static and dynamic aspects of chemistry. Chemical analogy, the systematic classification of molecules and a corresponding nomenclature system, conformational transformations, polyhedral rearrangements, and the relations between starting materials, transition complexes, and final products of chemical reactions are examples of where we apply the elements of modern mathematics to the solution of chemical problems.     

Packing and counting arbitrary Hamilton cycles in random digraphs

We prove packing and counting theorems for arbitrarily oriented Hamilton cycles in (n, p) for nearly optimal p (up to a factor). In particular, we show that given t = (1 ? o(1))np Hamilton cycles C₁,…,C_t, each of which is oriented arbitrarily, a digraph ～(n, p) w.h.p. contains edge disjoint copies of C₁,…,C_t, provided . We also show that given an arbitrarily oriented n‐vertex cycle C, a random digraph ～(n, p) w.h.p. contains (1 ± o(1))n!pⁿ copies of C, provided .