Exact scalar field cosmologies in a higher derivative theory

We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR ² in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity. Some new and interesting potentials are noted in the presence of R ² term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover approximation.     

Crystallization of potassium sulfate from pure aqueous solution and in presence of surfactants

The use of surfactants offers an interesting possibility to control the crystallization from solutions. There are already some applications in technical scale. Yet, little knowledge exists on the mechanism of the effect and his dependence on surfactant concentration. Therefore, the displacement rates of selected single crystal faces of K₂SO₄ in pure aqueous solutions and in presence of different amounts of tensides have been measured. Furthermore, in order to get insight into the state of surfactant solutions existing in the interesting concentration interval, the critical micelle concentrations have been determined. In comparison with growth from pure solution, the admixtures caused at concentrations below 10⁻⁵ mol/l no drastic alterations. On the contrary, above a transition region characterized by a very irregular growth, a practically totally inhibition of growth as well as of dissolution was observed. The changes of surface morphology induced by surfactants have been investigated using the phase contrast microscopy.     

Synthesis of D-Erythro- and D-Threo-Sphingosine Derivatives From L-Serine

The protected serine aldehyde 10 was converted to the crystalline N-Boc-protected sphingosines 6 – 9 by a three-step reaction sequence. Compound 10 was transformed with high diastereoselectivity (95%) either to the erythro- or threo-alkynols, 17 and 18 , respectively. The erythro-isomer 17 is formed by the addition to 10 of lithium pentadecyne 16 in THF/HMPT at ?78°, whereas the corresponding threo-isomer 18 is produced in the presence of ZnBr² in Et₂O. Deprotection of the acetal moiety afforded 1,3-diols 19 and 20 . These diols were selectively reduced with Red-Al to the (E)-sphingosines 6 and 8 , or the (Z)-isomers 7 and 9 by partial hydrogenation over Lindlar's catalyst. Cleavage of the N-Boc group and further transformation to ceramides were readily achieved as demonstarted by the conversion of 6 to N-octadecanoyl-D -erythro-sphingosine 5 .     

Determination of isotope ratios of chromium nickel,zinc and copper by gas chromatography-mass spectrometry by using volatile metal chelates

A gas chromatographic-mass spectrometric (GC-MS) method involving thermally stable, volatile chelates was investigated for measurements of isotope ratios of chromium, nickel, zinc and copper. The chelating agents acetylacetone, trifluoroacetylacetone, sodium diethyldithiocarbamate and lithium bis (trifluoroethyl)dithiocarbamate [Li(FDEDTC])] were used. Experimental conditions for the preparation of chelates and the mass spectrometric operating parameters for precise and accurate measurement of isotope ratios were optimized using a general-purpose mass spectrometer. Imprecision values of 1–4% were obtained for measurements of different isotope ratios using chelates containing about 10 ng of metal. The capability of this technique for the accurate determination of natural and altered isotope ratios was also evaluated for these elements using Li(FDEDTC) as a chelating agent. This GC-MS method obviates the need for a more specialized mass spectrometer such as a thermal ionization or inductively coupled plasma mass spectrometer for trace metal determination. The technique gives detection limits down to parts per 10⁹ levels and offers considerable potential for isotope dilution measurements.     

An ESR investigation of triple ions derived from 1,2,4,5-tetramesitoylbenzene

Stable triple ions were obtained in MTHF solution from the ion pairs of 1,2,4,5-tetramesitoylbenzene (TMB) radical anion and alkali metal cations by reaction with soluble alkali metal salts. Their ESR spectra are highly resolved. MO calculations with parameters which lead to spin density values as nearly as possible equal to the experimental ones allow estimates of the oxygen-metal distances. The relatively most stable triple ions are the ones with the smallest estimated oxygen metal distances.     

Synthesis and molecular structure of novel 4‐aryloctahydropyrido‐[1,2‐c]pyrimidine derivatives

A series of new 4‐aryloctahydropyrido[1,2‐c]pyrimidine‐1,3‐diones 6a,b,d‐h and j were synthesized by intramolecular cyclization of α‐aryl‐α‐(1‐ethoxycarbonyl‐2‐piperidyl)‐acetamide derivatives 5a,b,d‐h and j . The structures of compounds were determined by ¹H and ¹³C nmr spectroscopy. Nmr and X‐ray diffraction data indicate that the configuration at the C4, C4a stereocenters constitute RR and SS pair.