Almost Hermitian 6-Manifolds Revisited

A Theorem of Kirichenko states that the torsion 3-form of the characteristic connection of a nearly K\"ahler manifold is parallel. On the other side, any almost hermitian manifold of type $\mathrm{G}_1$ admits a unique connection with totally skew symmetric torsion. In dimension six, we generalize Kirichenko's Theorem and we describe almost hermitian $\mathrm{G}_1$-manifolds with parallel torsion form. In particular, among them there are only two types of $\mathcal{W}_3$-manifolds with a non-abelian holonomy group, namely twistor spaces of 4-dimensional self-dual Einstein manifolds and the invariant hermitian structure on the Lie group \mathrm{SL}(2, \C). Moreover, we classify all naturally reductive hermitian $\mathcal{W}_3$-manifolds with small isotropy group of the characteristic torsion.Comment: 26 pages, revised versio

Ecological niches of open ocean phytoplankton taxa:Niches of open ocean phytoplankton

International audienceWe characterize the realized ecological niches of 133 phytoplankton taxa in the open ocean based on observations from the MAREDAT initiative and a statistical species distribution model (MaxEnt). The models find that the physical conditions (mixed layer depth, temperature, light) govern large-scale patterns in phyto-plankton biogeography over nutrient availability. Strongest differences in the realized niche centers were found between diatoms and coccolithophores. Diatoms (87 species) occur in habitats with significantly lower temperatures, light intensity and salinity, with deeper mixed layers, and with higher nitrate and silicate concentrations than coccolithophores (40 species). However, we could not statistically separate the realized niches of coccolithophores from those of diazotrophs (two genera) and picophytoplankton (two genera). Phaeocystis (two species) niches only clearly differed from diatom niches for temperature. While the realized niches of diatoms cover the majority of niche space, the niches of picophytoplankton and coccolithophores spread across an intermediate fraction and diazotroph and colonial Phaeocystis niches only occur within a relatively confined range of environmental conditions in the open ocean. Our estimates of the realized niches roughly match the predictions of Reynolds' C-S-R model for the global ocean, namely that taxa classified as nutrient stress tolerant have niches at lower nutrient and higher irradiance conditions than light stress tolerant taxa. Yet, there is considerable within-class variability in niche centers, and many taxa occupy broad niches, suggesting that more complex approaches may be necessary to capture all aspects of phytoplankton ecology

Statistical Mechanics of Horizontal Gene Transfer in Evolutionary Ecology

The biological world, especially its majority microbial component, is strongly interacting and may be dominated by collective effects. In this review, we provide a brief introduction for statistical physicists of the way in which living cells communicate genetically through transferred genes, as well as the ways in which they can reorganize their genomes in response to environmental pressure. We discuss how genome evolution can be thought of as related to the physical phenomenon of annealing, and describe the sense in which genomes can be said to exhibit an analogue of information entropy. As a direct application of these ideas, we analyze the variation with ocean depth of transposons in marine microbial genomes, predicting trends that are consistent with recent observations using metagenomic surveys.Comment: Accepted by Journal of Statistical Physic

Linguistic Naturalism and Natural Style. From Varro and Cicero to Dionysius of Halicarnassus

NWO276-30-009Classics and Classical Civilizatio

Fixed-term contracts and labour market efficiency in the European Union

Summary in GermanSIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel W 813 (95.207) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Education, labor market segment, and growth in wages: experiences of West German men in the post-war period

SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 159754 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Beschaeftigungsdynamik und Arbeitslosigkeit in der Europaeischen Union Abschlussbericht eines Projektes des 'Systems zur gegenseitigen Interrichtung ueber beschaeftigungspolitische Massnahmen - MISEP' (Multual Information System on Employment Policies) fuer die Europaeische Kommission, Generaldirektion V

In dem Beitrag werden Beschaeftigung und Arbeitslosigkeit in der Europaeischen Union mit einem dynamischen Ansatz untersucht. Ausgehend von der Theorie der Uebergangsarbeitsmaerkte werden die vielfaeltigen Bruecken in Beschaeftigung, aber auch der Verlust von Beschaeftigung untersucht. Jaehrliche Zustroeme in und Abstroeme aus Beschaeftigung und Arbeitslosigkeit in den EU-Mitgliedslaendern werden mit Daten der Europaeischen Arbeitskraeftestichprobe ermittelt. Diese 'natuerlichen' Stroeme werden ergaenzt durch Teilnehmer an Massnahmen der Arbeitsmarktpolitik. Die Stroeme zwischen Arbeitslosigkeit und Beschaeftigung werden ins Verhaeltnis zu allen anderen Uebergaengen in Beschaeftigung - aus Inaktivitaet, Bildungsaktivitaeten und Selbstaendigkeit - gesetzt. Maximal zwei Drittel aller Stroeme in abhaengige Beschaeftigung kommen aus Arbeitslosigkeit. Die Uebergangsarbeitsmaerkte aus abhaengiger Beschaeftigung oder Arbeitslosigkeit in selbstaendige Taetigkeit weisen eine interessante positive Dynamik auf. Nach den Uebergangsbilanzen berechnen die Autoren individuelle Uebergangswahrscheinlichkeiten zwischen Beschaeftigung und Arbeitslosigkeit sowie fuer die Rueckkehr aus Arbeitslosigkeit in abhaengige Beschaeftigung. Basierend auf gepoolten logistischen Regressionen zwischen 1988 und 1996 zeigt sich der bedeutende Einfluss von Alter, Qualifikationsniveau und Geschlecht in den Mitgliedslaendern. Abschliessend werden Vorschlaege fuer ein verbessertes Monitoring und eine verbesserte Evaluation des Arbeitsmarktes und der Arbeitsmarktpolitik eroertert und Schlussfolgerungen fuer die Arbeitsmarktpolitik gezogen. (HH)'In this paper we apply a dynamic perspective to investigate employment and unemployment in the European Union. Based on the theory of transitional labour markets, we analyse the process of finding and loosing employment for individuals and for aggregrate flows. The European Labour Force Survey allows to analyse employment transitions only from one year to another. These 'natural' flows between labour market statuses are increasingly supplemented by participants in labour market programmes in the form of transitional labour market arrangements. Labour market policies, therefore, play an important role in labour market mobility and overall labour market dynamics. In labour market analyses it is important to consider flows in both directions: flows out of unemployment are matched by flows into unemployment. A one-eyed focus on flows out of unemployment is unlikely to be successful if there is a simultaneous increase in the flows into unemployment. The difference between the flows is the more interesting indicator in the evaluation of success of labour market policies. The study investigates flows between unemployment and dependent employment in relationship to other transitions into employment from inactivity, education or self-employment. Only between one third or up to two thirds of persons enter employment directly from unemployment compared to all flows into employment. Differences in the employment transitions of men and women, as well as age-specific and other demographic factors which have an impact on the transition balance are presented in more detail. Transitions from education to dependent employment, the first entry into the labour market, as well as exit from the labour market into retirement are analysed using the transition balance approach in the country comparisons. The transitional labour market from dependent employment and unemployment to self-employment show an interesting positive transition balance in recent years for most countries. The analysis of major transition balances is complemented by micro-level estimates of transition probabilities from dependent employment into unemployment and the return from unemployment to employment. Based on a pooled logistic regression of the transition probabilities between 1988 and 1996 we find the important impact of age, level of qualifications and gender in each country. Changes over the years reflect largely the influence of macroeconomic conditions on these transition probabilities. Finally, we propose improvements for monitoring and the evaluation of. the labour markets and labour market policies. Our conclusions emphasise the role of labour market policies in shaping the transition balance and the high potential to develop transitional labour markets in the European Union.' (author's abstract)SIGLEAvailable from UuStB Koeln(38)-991102711 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman