Consistency Analysis of Kaluza-Klein Geometric Sigma Models

Geometric -models are purely geometric theories of scalar fields coupled to gravity. Geometrically, these scalars represent the very coordinates of spacetime, and, as such, can be gauged away. A particular theory is built over a given metric field configuration which becomes the vacuum of the theory. Kaluza-Klein theories of the kind have been shown to be free of the classical cosmological constant problem, and to give massless gauge fields after dimensional reduction. In this paper, the consistency of dimensional reduction, as well as the stability of the internal excitations, are analyzed. Choosing the internal space in the form of a group manifold, one meets no inconsistencies in the dimensional reduction procedure. As an example, the SO(n) groups are analyzed, with the result that the mass matrix of the internal excitations necessarily possesses negative modes. In the case of coset spaces, the consistency of dimensional reduction rules out all but the stable mode, although the full vacuum stability remains an open problem.     

Structure and supramolecular organization of tri-n-butyl(octadecyl)phosphonium tetrafluoroborate and its influence on catalytic activity of stabilized palladium nanoparticles

Russian Chemical Bulletin - A crystal structure and aggregation properties of tri-n-butyl(octadecyl)phosphonium tetrafluoroborate were studied. Palladium nanoparticles stabilized by this...     

Decyl(Tri-Tert-Butyl)Phosphonium Tetrafluoroborate/Palladium Acetate: An Effective Catalyst for Cross-Coupling Reaction of Arylbromides with Phenylacetylene in Copper-Free Conditions

Abstract

The phosphonium salts with sterically hindered cation and noncoordinating anion can be used as phase-transfer reagent in the Sonogashira cross-coupling reaction allowing copper- and amine-free protocol. The reactions proceed under mild conditions with good yields.     

Chitosan-Based Ciprofloxacin Extended Release Systems: Combined Synthetic and Pharmacological (In Vitro and In Vivo) Studies

Ciprofloxacin is one of the most effective antibiotics, but it is characterized by a range of side effects. Elaboration of drug-releasing systems which allow to diminish toxicity of ciprofloxacin is a challenging task in medicinal chemistry. The current study is focused on development of new ciprofloxacin releasing systems (CRS). We found that ultrasound efficiently promotes N,N′-dicyclohexyl carbodiimide-mediated coupling between COOH and NH₂ functionalities in water. This was used for conjugation of ciprofloxacin to chitosan. The obtained ciprofloxacin/chitosan conjugates are capable of forming their self-assembled nanoparticles (SANPs) in aqueous medium. The SANPs can be additionally loaded by ciprofloxacin to form new CRS. The CRS demonstrated high loading and encapsulation efficiency and they are characterized by extended release profile (20 h). The elaborated CRS were tested in vivo in rats. The in vivo antibacterial effect of the CRS exceeded that of the starting ciprofloxacin. Moreover, the in vivo acute and subacute toxicity of the nanoparticles was almost identical to that of the chitosan, which is considered as the non-toxic biopolymer.     

Specific features of the chemical behavior of sodium 3,4,5-tris(2-thienyl)-1,2-diphosphacyclopentadienide

A new representative of 1,2-diphosphacyclopentadienide anions containing 2-thienyl substituents at carbon atoms was synthesized by the reaction of sodium polyphosphides with cyclopropenylphosphonium salts. The specific features of the chemical behavior of this compound were revealed by studying the reactions with organic and heteroorganic electrophiles and with pentacarbonylmanganese bromide.

     

Trace enrichment of chlorophenols in human urine by C18 reversed-phase adsorption and by n-hexane extraction

Summary The efficiency and sensitivity of C₁₈ reversed-phase adsorption of free chlorophenols and of n-hexane extraction of either free or acetylated chlorophenols from human urine were compared. All procedures were found to be efficient for the trace enrichment of 2,4-dichlorophenol, 2,4,6- and 2,4,5-trichlorophenols, 2,3,4,6- and 2,3,4,5-tetrachlorophenols and pentachlorophenol. The recoveries of chlorophenols from non-hydrolysed and acid hydrolysed urine samples were comparable. By treatment of 1 ml urine sample detection limits of 1–2 ng/ml were achieved, while the treatment of 5 ml samples enhanced the detection sensitivity to less than 1 ng/ml. The n-hexane extraction of acetylated chlorophenols from 1 ml urine samples is the simplest and fastest procedure because the acetylation and extraction of chlorophenols are performed simultaneously in one step. The C₁₈ adsorption seems to be more suitable than n-hexane extraction for accumulation of chlorophenols from a urine volume of 5 ml and higher because the elution is performed always with the same small volume of acetone. Both C₁₈ adsorption and n-hexane extraction procedures were applied for analysis of chlorophenols in general population and in persons with possible occupational exposure to organochlorine compounds.     

Asymptotic Stability in Geometric σ–models

Geometric –models have been defined as purely geometric theories of scalar fields in interaction with gravity. By construction, these theories possess soliton solutions with topologically nontrivial scalar sectors. We perform a detailed analysis of the stability of the effective scalar field theory far from the soliton core. It is shown that the requirement for the asymptotic stability is consistent with the existence of massive, static, spherically symmetric soliton solutions.     

Extraction chromatographic separation of Y, REE, Bi, Th, and U from the matrix suitable for their determination in pure iron and Low-Alloyed steels by ICP-MS and ICP-AES

The possibilities of tetraphenylmethylene-diphosphineoxide as stationary phase in extraction chromatography separation of REE, as well as Y, Bi, Th, and U from solutions of iron and microamounts of many other elements have been studied. The optimal conditions of separation are determined. The proposed procedure of chromatographic separation is quite applicable to the on- and off-line modes of ICP-MS and ICP-AES analyses of high-purity iron and low-alloyed steels.