Casimir Energy and Entropy between perfect metal Spheres

We calculate the Casimir energy and entropy for two perfect metal spheres in the large and short separation limit. We obtain nonmonotonic behavior of the Helmholtz free energy with separation and temperature, leading to parameter ranges with negative entropy, and also nonmonotonic behavior of the entropy with temperature and with the separation between the spheres. The appearance of this anomalous behavior of the entropy is discussed as well as its thermodynamic consequences.Comment: 10 pages and 8 figures. Accepted for publication in the Proceedings of the tenth conference on Quantum Field Theory under the influence of external conditions - QFEXT'1

Formation of a carcinogenic aromatic amine from an azo dye by human skin bacteria in vitro

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Azo dyes represent the major class of dyestuffs. They are metabolised to the corresponding amines by liver enzymes and the intestinal microflora following incorporation by both experimental animals and humans. For safety evaluation of the dermal exposure of consumers to azo dyes from wearing coloured textiles, a possible cleavage of azo dyes by the skin microflora should be considered since, in contrast to many dyes, aromatic amines are easily absorbed by the skin. A method for measuring the ability of human skin flora to reduce azo dyes was established. In a standard experiment, 361011 cells of a culture of Staphylococcus aureus wereincubatedinsyntheticsweat (pH 6.8, final volume 20 mL) at 288C for 24 h with Direct Blue 14 (C.I. 23850, DB 14). The reaction products were extracted and analysed using HPLC. The reduction product o-tolidine (3,3'-dimethylbenzidine, OT) could indeed be detected showing that the strain used was able to metabolise DB 14 to the corresponding aromatic amine. In addition to OT, two further metabolites of DB 14 were detected. Using mass spectrometry they were identified as 3,3'-dimethyl-4-amino-4'-hydroxybiphenyl and 3,3'-di methyl-4-aminobiphenyl. The ability to cleave azo dyes seems to be widely distributed among human skin bacteria, as, under these in vitro conditions, bacteria isolated from healthy human skin and human skin bacteria from strain collections also exhibited azo reductase activity. Further studies are in progress in order to include additional azo dyes and coloured textiles. At the moment, the meaning of the results with regard to consumer health cannot be finally assessed

Quantal Consequences of Perturbations Which Destroy Structurally Unstable Orbits in Chaotic Billiards

Non-generic contributions to the quantal level-density from parallel segments in billiards are investigated. These contributions are due to the existence of marginally stable families of periodic orbits, which are structurally unstable, in the sense that small perturbations, such as a slight tilt of one of the segments, destroy them completely. We investigate the effects of such perturbation on the corresponding quantum spectra, and demonstrate them for the stadium billiard

The Generation of Successive Unmarked Mutations and Chromosomal Insertion of Heterologous Genes in Actinobacillus pleuropneumoniae Using Natural Transformation

We have developed a simple method of generating scarless, unmarked mutations in Actinobacillus pleuropneumoniae by exploiting the ability of this bacterium to undergo natural transformation, and with no need to introduce plasmids encoding recombinases or resolvases. This method involves two successive rounds of natural transformation using linear DNA: the first introduces a cassette carrying cat (which allows selection by chloramphenicol) and sacB (which allows counter-selection using sucrose) flanked by sequences to either side of the target gene; the second transformation utilises the flanking sequences ligated directly to each other in order to remove the cat-sacB cassette. In order to ensure efficient uptake of the target DNA during transformation, A. pleuropneumoniae uptake sequences are added into the constructs used in both rounds of transformation. This method can be used to generate multiple successive deletions and can also be used to introduce targeted point mutations or insertions of heterologous genes into the A. pleuropneumoniae chromosome for development of live attenuated vaccine strains. So far, we have applied this method to highly transformable isolates of serovars 8 (MIDG2331), which is the most prevalent in the UK, and 15 (HS143). By screening clinical isolates of other serovars, it should be possible to identify other amenable strains

Density of states of helium droplets

Accurate analytical expressions for the state densities of liquid He-4 droplets are derived, incorporating the ripplon and phonon degrees of freedom. The microcanonical temperature and the ripplon angular momentum level density are also evaluated. The approach is based on inversions and systematic expansions of canonical thermodynamic properties.Comment: 20 pages, 5 figure

Social roles and aging from a life-span perspective

Este trabalho investigou os papéis sociais e as tarefas evolutivas desempenhados por adultos. O local escolhido para investigação foi um assentamento de famílias de baixa renda do Distrito Federal criado em 1989. Utilizou-se um questionário contendo 17 questões abertas e 15 questões fechadas, preenchido pela primeira autora durante uma visita domiciliar. Participaram 98 respondentes (73 F e 25 M), sendo 51 entre 50 e 59 anos e 47 a partir de 60 anos. Os resultados apontaram que este grupo é heterogêneo e que seus papéis sociais são influenciados pelas variáveis demográficas (idade, sexo, escolaridade, ocupação, naturalidade e estado civil) e também pelas variáveis relativas à moradia atual. Concluiu-se também que as expectativas sociais, o suporte social e a escolarização são fatores de suma importância para oferecer recursos para a otimização e compensação necessárias a um envelhecimento bem sucedido. __________________________________________________________________________________________________________ ABSTRACTThis study investigated the social roles and developmental tasks of adults. The study took place in a settlement of low-income families, created in The Federal District in 1989. Data were collected through a questionnaire composed of 17 open and 15 closed questions, administered by the first author during a home visit. There were 98 respondents, 73 female and 25 male, being 51 between 50 to 59 years old and 47 elders above the age of 60. The result indicated that this group is heterogeneous and that its social roles are influenced by the demographic variables - age, sex, educational level, work, place of the birth and marital status, as well for the relative variables to current residence. The data allow the conclusion that social expectations, social support and the educational level are important resources for the optimization and necessary compensation to successful aging

Quantum Chaos of Bogoliubov Waves for a Bose-Einstein Condensate in Stadium Billiards

We investigate the possibility of quantum (or wave) chaos for the Bogoliubov excitations of a Bose-Einstein condensate in billiards. Because of the mean field interaction in the condensate, the Bogoliubov excitations are very different from the single particle excitations in a non-interacting system. Nevertheless, we predict that the statistical distribution of level spacings is unchanged by mapping the non-Hermitian Bogoliubov operator to a real symmetric matrix. We numerically test our prediction by using a phase shift method for calculating the excitation energies.Comment: minor change, 4 pages, 4 figures, to appear in Phys. Rev. Let

Sonoluminescence: Nature's Smallest BlackBody

The Spectrum of the light emitted by a sonoluminescing bubble is extremely well fit by the spectrum of a blackbody. Furthermore the radius of emission can be smaller than the wavelength of the light. Consequences, for theories of sonoluminescence are discussed.Comment: 8 pages, 3 Figure

Discrete Symmetries in the Weyl Expansion for Quantum Billiards

We consider two and three-dimensional quantum billiards with discrete symmetries. We derive the first terms of the Weyl expansion for the level density projected onto the irreducible representations of the symmetry group. As an illustration the method is applied to the icosahedral billiard. The paper was published in J. Phys. A /27/ (1994) 4317-4323Comment: 8 printed pages Latex fil