Geometric Invariant Theory in a Model-Independent Analysis of Spontaneous Symmetry and Supersymmetry Breaking

Functions which are covariant or invariant under the transformations of a reductive linear algebraic group can be advantageously expressed in terms of functions defined in the orbit space of the group, i.e. as functions of a finite set of basic invariant polynomials. This fact and the tools of geometric invariant theory can be exploited in many physical contexts where the study of covariant or invariant functions is important, for instance in the determination of patterns of spontaneous symmetry and/or supersymmetry breaking in possibly supersymmetric quantum field theories of elementary particles, in the analysis of phase spaces and structural phase transitions in solid state physics (Landau's theory), in covariant bifurcation theory, in crystal field theory and in most areas of solid state theory where use is made of symmetry adapted functions. We shall present some elements of geometric invariant theory and illustrate some of the possible applications in the study of spontaneous symmetry and supersymmetry breaking.     

Modulation of the cosmogenic nuclide production expected from the galactovertical motion of the solar system

Summary A variable cosmogenic-production rate model is proposed which takes account of the changes in galactic-cosmic-ray irradiation conditions arising from the vertical oscillation of the solar system about the galactic plane. The model incorporates and substantiates several ideas and suggestions previously put forward in the literature. The time distribution of the¹⁰Be concentration predicted by the model appears to be consistent with the data of the deep-sea sediment core RC 12-65. A comparison of our model with the conventional constant-production rate model is carried out, especially with reference to time-integrated concentrations in meteorites.

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Riassunto Si propone un modello di produziones variabile di nuclidi cosmogenici che tiene conto del cambiamento nelle condizioni di esposizione ai raggi cosmici galattici derivante dal moto verticale del sistema solare rispetto al pianogalattico. Il modello sviluppa alcune idee avanzate di recente da vari autori. La distribuzione differenziale della concentrazione di¹⁰Be in riserve terrestri prevista dal modello è consistente con i dati del sedimento marino RC 12-65. Si confrontano le previsioni del modello a produzione variabile con quelle del modello tradizionale a produzione costante, con particolare attenzione alle concentrazioni, integrate sul tempo d'irradiazione cosmica, di nuclidi cosmogenici in meteoriti.

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Резюме Предлагается модель переменной интенсивности космогенного образования, которая учитывает изменения в условиях космического облучения, возникающие от вертикальных осцилляций солнечной системы относительно галактической плоскости. Эта модель включает и подтверждает некоторые идеи и предположения, ранее выдвинутые в литературе. Временное распределение концентрации¹⁰Be, предсказннное в рамках этой модели, согласуется с данными RC 12-65 для глубоководных отложений. Проводится сравнение предложенной модели с общепринятой моделью постоянной интенсивности образования, особое внимание уделяется интегральным по времени концентрациям космогенных нуклидов в метеоритах.

     

Development and validation of a fast RP-HPLC method for determination of methotrexate entrapment efficiency in polymeric nanocapsules

A rapid and effective isocratic chromatographic procedure is successfully developed to determinate methotrexate (MTX) entrapment efficiency (EE) in polymeric nanocapsules using reversed-phase high-performance liquid chromatography. The method employed a RP-C(18) Shimadzu Shim-pack CLC-ODS (150 mm x 4.6 mm, 5 microm) column with mobile phase constituted by a mixture of water-acetonitrile-tetrahydrofuran (65:30:5 v/v/v; pH 3.0) at a flow rate of 0.8 mL/min. The eluate is monitored with a UV detector set at 313 nm. The parameters used in the validation process are: linearity, specificity, precision, accuracy, and limit of quantitation (LOQ). The linearity is evaluated by a calibration curve in the concentration range of 10-50 microg/mL and presented a correlation coefficient of 0.9998. The polymers (PLA or PLA-PEG), oil, and surfactants used in the nanocapsule formulation did not interfere with analysis and the recovery was quantitative. The intra and inter-day assay relative standard deviation were less than 0.72%. Results are satisfactory, and the method proved to be adequate for the determination of methotrexate in nanocapsules formulations.     

The role of adsorbates in electrocatalytic systems: An analysis of model systems with single crystals

The use of single crystal electrodes as model catalysts has been widely applied for the study of several reactions. The known structure of the surface provides a system with controlled electronic properties that helps in the understanding of the mechanism of reactions. In this model system, any modification, including the adsorption of anions, organic molecules or foreign atoms, generate changes in the electronic properties of the surface and, thus, in the adsorption energy of the species involved in the studied reaction. The adsorbate can hinder the surface and diminish the activity or prevent the oxidation of the surface and improve the catalysis. The changes in electronic properties can modify the adsorption energy and enhance or worsen the catalytic activity. The effect of any adsorbed species will depend on the structure of the surface, the nature of the species and the studied reaction.     

Self-assembled nanostructures of fully hydrated monoelaidin-elaidic acid and monoelaidin-oleic acid systems

In recent years, there has been a surge of interest in exploring the effect of trans-fatty acids (TFAs) on biological membrane properties. The research studies are motivated by an increasing body of evidence suggesting that the consumption of TFAs increases the risk of developing negative health effects such as coronary heart disease and cancer. The ultimate goal of studying the lipid-fatty acid interactions at the molecular level is to predict the biological role of fatty acids in cells. In this regard, it is interesting to elucidate the effect of loading TFAs and their counterpart cis-fatty acids (CFAs) on the physical properties of lipid model membranes. Here, the present study focuses on discussing the following: (1) the effect of mixing monoelaidin (ME, TFA-containing lipid) with its counterpart monoolein (MO, CFA-containing lipid) on modulating the fully hydrated self-assembled structure, and (2) the influence of solubilizing oleic acid (OA) and its trans counterpart elaidic acid (EA) on the fully hydrated ME system. The ME model membrane was selected due to its sensitivity to variations in lipid composition and temperature. Synchrotron small-angle X-ray scattering (SAXS) was applied for studying the temperature-dependent structural behavior of the fully hydrated ME/MO-based system prepared with an equal ME/MO weight ratio and also for characterizing the fully hydrated OA- and EA-loaded ME systems. Wide-angle X-ray (WAXS) experiments were also performed for characterizing the formed crystalline lamellar phases at ambient temperatures. The results demonstrate the significant influence of the partial replacement of ME by MO on the phase behavior. The addition of MO induces the lamellar-nonlamellar phase transitions at ambient temperatures and promotes the formation of the inverted type hexagonal (H(2)) phase above 72 °C. The fully hydrated ME/EA and ME/OA systems with their rich polymorphism exhibit an interesting temperature-dependent complex behavior. The experimental findings show that the temperature-induced phase transitions are dictated by the solubilized fatty acid concentration and its configuration. Both EA and OA have a significant impact on the fully hydrated ME system. Similar to previous published studies, OA induces a significantly stronger mean negative membrane curvature as compared to EA. The two phase diagrams are discussed in terms of water-lipid and lipid-fatty acid interactions, membrane bending, and lipid packing concepts. A newly observed interesting epitaxial relationship for the lamellar-hexagonal phase transition in the EA-loaded ME system is illustrated and discussed in detail.     

Conformational and Electronic Interaction Studies of P-Substituted α-Phenoxyacetones

The v_co analysis of p-substituted α-phenoxy-acetones X-θ-O-CH₂-C(O)-Me (1-6) indicates the existence of the cislgauche rotational isomerism. The nearly constant increase in the cislgauche population ratios for the whole series, on going from carbon tetrachloride to acetonitrile, and the small sensitivity of the carbonyl frequency shifts (Δv_c) for the cis rotamer, on going from electron-attracting to electron-donating substituents, are interpreted as an interplay of the Field (F) and the Inductive (-I) Effects, which originates an almost constant carbonyl bond order, and suggests that the cis rotamers have almost the same energy in the whole series. The decrease in the cislgauche population ratios, in all solvents, and the deshielding effects on the carbonyl carbon atom, and on the methylene carbon atom in a weaker extent, observed in the ¹³C NMR spectra, on going from electron-attracting to electron-donating substituents, are discussed in terms of φ*CO/ⁿO orbital and Ar^δ+ -O^δ- — C^δ+ =O^δ- Coulombic interactions, which stabilize the gauche rotamers of the investigated compounds.     

Facile Synthesis of Pentacarbonyltungsten(0) Complexes with Oxaphosphirane Ligands

Facile synthesis of tungsten(0) complexes of the type 7a – g (R¹ = C₅Me₅) and 8a – g (R¹ = CH(SiMe₃)₂) using transient Li/Cl phosphanylidenoid tungsten(0) complexes 4 , 5 and carbonyl derivatives 6a – g is reported; furthermore, for all complexes NMR, IR spectroscopic, mass spectrometric investigations and, in addition, single‐crystal X‐ray structures of complexes 7b , d – g and 8b , d are presented.