Uniform electron gases

We show that the traditional concept of the uniform electron gas (UEG) --- a homogeneous system of finite density, consisting of an infinite number of electrons in an infinite volume --- is inadequate to model the UEGs that arise in finite systems. We argue that, in general, a UEG is characterized by at least two parameters, \textit{viz.} the usual one-electron density parameter $\rho$ and a new two-electron parameter $\eta$. We outline a systematic strategy to determine a new density functional $E(\rho,\eta)$ across the spectrum of possible $\rho$ and $\eta$ values.Comment: 8 pages, 2 figures, 5 table

The role of recombination in the emergence of a complex and dynamic HIV epidemic

<p>Abstract</p> <p>Background</p> <p>Inter-subtype recombinants dominate the HIV epidemics in three geographical regions. To better understand the role of HIV recombinants in shaping the current HIV epidemic, we here present the results of a large-scale subtyping analysis of 9435 HIV-1 sequences that involve subtypes A, B, C, G, F and the epidemiologically important recombinants derived from three continents.</p> <p>Results</p> <p>The circulating recombinant form CRF02_AG, common in West Central Africa, appears to result from recombination events that occurred early in the divergence between subtypes A and G, followed by additional recent recombination events that contribute to the breakpoint pattern defining the current recombinant lineage. This finding also corrects a recent claim that G is a recombinant and a descendant of CRF02, which was suggested to be a pure subtype. The BC and BF recombinants in China and South America, respectively, are derived from recent recombination between contemporary parental lineages. Shared breakpoints in South America BF recombinants indicate that the HIV-1 epidemics in Argentina and Brazil are not independent. Therefore, the contemporary HIV-1 epidemic has recombinant lineages of both ancient and more recent origins.</p> <p>Conclusions</p> <p>Taken together, we show that these recombinant lineages, which are highly prevalent in the current HIV epidemic, are a mixture of ancient and recent recombination. The HIV pandemic is moving towards having increasing complexity and higher prevalence of recombinant forms, sometimes existing as "families" of related forms. We find that the classification of some CRF designations need to be revised as a consequence of (1) an estimated > 5% error in the original subtype assignments deposited in the Los Alamos sequence database; (2) an increasing number of CRFs are defined while they do not readily fit into groupings for molecular epidemiology and vaccine design; and (3) a dynamic HIV epidemic context.</p

Speiseröhrendivertikel (ohne krikopharyngeale Divertikel)

Speiseröhrendivertikel bilden sich in der Regel auf dem Boden einer vorbestehenden Motilitätsstörung. Durch die veränderten intraösophagealen Druckverhältnisse kommt es zu einer Aussackung der Mukosa und Submukosa durch Lücken im Muskelmantel. Man spricht in diesen Fällen daher auch von Pulsions- oder „falschen“ Divertikeln. Erheblich seltener sind die sog. „echten“ oder Traktionsdivertikel der Speiseröhre, die als Folge entzündlicher Verklebungen der Speiseröhre mit trachealen und bronchialen Lymphknotenkonglomeraten entstehen. Grundsätzlich können Divertikel im Verlauf der gesamten Speiseröhre auftreten, am häufigsten ist jedoch eine distale Lokalisation im unteren Speiseröhrendrittel. Diese Befunde werden auch als epiphrenische Divertikel bezeichnet. Beide Entitäten bedürfen einer individuellen internistisch-chirurgischen Abstimmung des therapeutischen Prozedere. Aufgrund der nicht unerheblichen perioperativen Morbidität sollte eine chirurgische Versorgung nur unter strenger Indikationsstellung bei entsprechender Symptomatik erfolgen