New Classes of Exact Causal Viscous Cosmologies

Two particular exact solutions of thegravitational field equations for a homogeneous flatFriedmann-Robertson-Walker universe filled with a causalbulk viscous fluid in the framework of the fullIsrael-Stewart-Hiscock theory are presented. The dynamics of theuniverse is entirely determined in the present models byits thermal behavior. The solutions of the fieldequations are expressed in an exact closed parametric form and correspond to an inflationarytransition between a singular state and a Minkowskianspace-time and a quasi-Minkowskian era and aninflationary state, connected by a noninflationaryphase, respectively. The inflationary era of the first solution isassociated with an increase in temperature and energydensity (a heating period), but with a decrease of thecomoving entropy. The evolutionary period described by the second solution leads during itsnoninflationary phase to a rapid decrease in thetemperature, the energy density, and the comovingentropy of the corresponding universe.     

Relativistic compact objects in isotropic coordinates

We present a matrix method for obtaining new classes of exact solutions for Einstein’s equations representing static perfect fluid spheres. By means of a matrix transformation, we reduce Einstein’s equations to two independent Riccati-type differential equations for which three classes of solutions are obtained. One class of the solutions corresponding to the linear barotropic-type fluid with an equation of statep =γρ is discussed in detail.     

Development of an HPLC-Method for the Determination of E-2-Nonenal in Beer using Column Switching Techniques

Abstract

E-2-nonenal is an important compound formed during ageing of beer. It has a flavour threshold value of about 0.1 μg/l. A method is described for isolation of E-2-nonenal from beer by solid phase extraction. After extraction E-2-nonenal is derivatized with dansylhydrazine and analyzed with reversed phase HPLC using column switching techniques. The combination of on-line preconcentration of the derivative and heartcutting enables the analysis of E-2-nonenal in beer at natural levels.     

Improved analysis by liquid chromatography of iso-alpha acids

This paper shows that the liquid chromatography (LC) methods so far described in the literature for iso-alpha acids analysis are unsatisfactory. The main reasons for this are the failure of the advocated eluent systems to completely suppress trace metal activity of commercial LC columns and the lack of a stable reference iso-alpha acid. The trace metal problem can be solved by using a column packing material specifically designed for “Hop Acid” analysis and by adding ethylenediaminetetraacetate (EDTA) to the eluent. The reference problem is more difficult, but possibly a formulation of the iso-alpha acids in their acid form may be the answer. Chromatographic conditions changing the elution pattern of the individual iso-alpha acids are studied. This leads to better control of their co-elution in the analytical procedure.     

Food-induced esterase electromorphs in Carinarion spp. and their effects on taxonomic data analysis (Gastropoda, Pulmonata, Arionidae)

Nonspecific esterases (EST) are often used to measure genetic variation, yet they may be influenced by environmental factors such as food, climate and age. This may produce misleading similarity indices and genetic diversity estimates (i.e., clone or strain diversities in uniparental organisms). Therefore, polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing (IEF) were used to investigate environmental effects on the EST variation in natural Carinarion populations, as well as in 45 individuals that were raised individually on carrots to produce offspring by selfing. Food effects on EST profiles in these progenies were examined by raising them on different food items (lettuce, nettle, or paper). Our results indicated that: (i) Arion (Carinarion) fasciatus and A. (C.) silvaticus show species-specific EST profiles, (ii) A. fasciatus-like outcrossers most probably are conspecific with A. fasciatus s.s., (iii) not all EST variation has a Mendelian basis since lettuce and nettle altered EST profiles, and (iv) food effects on EST profiles differed strongly between individuals. Although food-induced EST profiles did not affect taxonomic interpretations, they did inflate genetic diversity estimates and thus provided misleading population-genetic data.     

Modified gravity with arbitrary coupling between matter and geometry

The field equations of a generalized f(R)$f(R)$ type gravity model, in which there is an arbitrary coupling between matter and geometry, are obtained. The equations of motion for test particles are derived from a variational principle in the particular case in which the Lagrange density of the matter is an arbitrary function of the energy-density of the matter only. Generally, the motion is non-geodesic, and takes place in the presence of an extra force orthogonal to the four-velocity. The Newtonian limit of the model is also considered. The perihelion precession of an elliptical planetary orbit in the presence of an extra force is obtained in a general form, and the magnitude of the extra gravitational effects is constrained in the case of a constant extra force by using Solar System observations.