On the phase equilibrium Stockmayer fluids

The fluid phase equilibrium of the Stockmayer fluid is investigated using a thermodynamic perturbation theory approach. The reference and the perturbation potential are the Lennard–Jones potential and the dipolar–dipolar interactions, respectively. They are assumed to be represented by the modified Benedict–Webb–Rubin equation of state [J.K. Johnson, J.A. Zollweg, K.E. Gubbins, Mol. Phys. 78 (1993) 591–618] and the Padé approximant [G. Stell, J.C. Rasaiah, H. Narang, Mol. Phys. 27 (1974) 1393–1414], respectively. The asymmetry found in an analogous study [M.E. van Leeuwen, B. Smit, E.M. Hendriks, Mol. Phys. 78 (1993) 271–283] based on the BWR equation of state [J.J. Nicolas, K.E. Gubbins, W.B. Streett, D.J. Tildesley, Mol. Phys. 37 (1979) 1429–1454] is now not observed on the vapour–liquid equilibrium coexistence curves of Stockmayer fluids with dipolar strength of μ^*2 = 1, 2, 3, and 4. Results agree with computer simulations for dipolar strength of μ^*2 = 1; however as strength dipole increases, liquid densities are over-estimated.     

Identification of 11-Nor-delta9-tetrahydrocannabinol-9-carboxylic acid in urine by ion trap GC-MS-MS in the context of doping analysis

The purpose of this study is to develop a sensitive and specific alternative to current gas chromatography (GC)-mass spectrometry (MS) selected ion monitoring confirmation methods of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid (cTHC) in human urine samples, in the context of doping analysis. An identification procedure based on the comparison, among suspicious and control samples, of the relative abundances of cTHC selected product ions obtained by GC-tandem MS in an ion trap is presented. The method complies with the identification criteria for qualitative assays established by sports authorities; the comparison procedure is precise, reproducible, specific, and sensitive, thus indicating that it is fit for the purpose of identification accordingly to World Antidoping Agency requirements.     

Weighted Inequalities for Multilinear Potential Operators and their Commutators

We prove weighted strong inequalities for the multilinear potential operator T_f{\cal T}_{\phi} and its commutator, where the kernel ϕ satisfies certain growth condition. For these operators we also obtain Fefferman-Stein type inequalities and Coifman type estimates. Moreover we prove weighted weak type inequalities for the multilinear maximal operator M_j,L^B\mathcal{M}_{\varphi,L^{B}} associated to an essentially nondecreasing function φ and to the Orlicz space L ^B for a given Young function B. This result allows us to obtain a weighted weak type inequality for the operator T_f{\cal T}_{\phi}.     

Self-doping effect in poly(o-methoxyaniline)/poly(3-thiopheneacetic acid) layer-by-layer films

Nanostructured films from two conducting polymers, poly(o-methoxyaniline) (POMA) and poly(3-thiopheneacetic acid) (PTAA), were fabricated with the layer-by-layer (LBL) technique. The electrochemical response of the LBL films differs from that of a POMA cast film, even in a potential range where PTAA is inactive. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated by quartz crystal microbalance measurements. The results show that the transport properties of conducting polymers can be changed by alternation with layers of appropriate materials in LBL films.     

Novel Applications of Raney Nickel/Isopropanol: Efficient System for the Reduction of Organic Compounds

Catalytic hydrogenation of various organic substrates with Raney nickel in isopropanol proceeds under mild conditions of temperature and pressure. Comparison with other catalysts systems evidenced the superiority of Raney nickel/isopropanol.     

Some Aspects of the Spontaneous Solubility Equilibria of Solid Carbonates

In order to adequately carry out the laboratory procedures usually taught in a general analytical chemistry course, students must master the subject of multiple equilibria in aqueous solution, both conceptually and mathematically. The use of a computer program to solve the concentrations of all species at equilibrium with a slightly soluble compound is frequently recommended in the chemical education literature, due to its simplicity and quickness. But, when this calculation procedure fails to consider other important reactions aside from the solubility equilibrium itself, significant differences in the numerical results may be obtained. For several metal carbonates, the usual procedure to calculate their solubilities is to consider carbonate ion hydrolysis as the only additional reaction.In this paper it is shown numerically and graphically that for magnesium and silver carbonates, the precipitation reaction of metal (hydr)oxides would occur at the pH value calculated from the carbonate dissolution plus the anion hydrolysis equilibria. An analytical procedure to solve these complex multiple equilibria system is presented. The final solution to the problem is obtained through a high-order equation that is easily solved by a simple iterative method. The correct solubility-pH curve for the metal carbonates is calculated, and the pH values for the metal hydroxide precipitation onset for several important representative and transition metal carbonates are shown. It is concluded that the overall procedures to solve these multiple equilibria problems are not beyond the comprehension of any chemistry student with a acceptable background in general, inorganic, and analytical chemistry, and that by focusing on tasks such as these, important critical-thinking skills can be obtained.     

Comparing the catalytic efficiency of ring substituted 1-hydroxybenzotriazoles as laccase mediators

A series of ring substituted 1-hydroxybenzotriazoles (6-X-HBTs) have been tested as mediators in the laccase-promoted oxidation of 4-methoxybenzyl alcohol, 3,4-dimethoxybenzyl alcohol, and the dimeric lignin model 1-(3,4-dimethoxyphenyl)-2-phenoxyethanol. The effect of the aryl substituents on the yields of oxidation products is remarkable. The catalytic mediation efficiency increases as the electron releasing (ER) properties of the substituent increases up to a maximum value for 6-CH₃-HBT, which resulted a very efficient mediator. Both the oxidation of the 6-X-HBTs to the N-oxyl radicals (6-X-BTNO) by laccase and the hydrogen atom transfer (HAT) process from the benzylic C–H to the 6-X-BTNO contribute to the overall reactivity. The former process is favored by ER substituents that lower the mediator redox potentials. On the other hand, ER substituents decrease the 6-X-BTNO reactivity in the HAT process due to a decrease in the NO–H BDE value, as assessed in this study through a radical equilibration technique.     

Finite objects and automorphisms

We show that every K-finite decidable object X of an elementary topos E is Dedekind-finite, i.e., that every monic endomorphism of X is an automorphism. As an easy corollary, every epic endomorphism of X is likewise an automorphism. The proof depends in part on an analysis of the finite cardinals of E and in part on the equivalence, in any Boolean tbpos, of Kfiniteness and Tarski-finiteness (Theorem 6). Here X is Tarski-finite iff every inhabited collection of arbitrary elements of ω ^X (subobjects of X ) contains a ¨—minimal element.