Many-body approach to infinite non-periodic systems: application to the surface of semi-infinite jellium

A method to implement the many-body Green function formalism in the GW approximation for infinite non periodic systems is presented. It is suitable to treat systems of known ``asymptotic'' properties which enter as boundary conditions, while the effects of the lower symmetry are restricted to regions of finite volume. For example, it can be applied to surfaces or localized impurities. We illustrate the method with a study of the surface of semi-infinite jellium. We report the dielectric function, the effective potential and the electronic self-energy discussing the effects produced by the screening and by the charge density profile near the surface.Comment: 11 pages, 4 figure

Correlation energies of inhomogeneous many-electron systems

We generalize the uniform-gas correlation energy formalism of Singwi, Tosi, Land and Sjolander to the case of an arbitrary inhomogeneous many-particle system. For jellium slabs of finite thickness with a self-consistent LDA groundstate Kohn-Sham potential as input, our numerical results for the correlation energy agree well with diffusion Monte Carlo results. For a helium atom we also obtain a good correlation energy.Comment: 4 pages,1 figur

Differential expression of genes involved in iron metabolism in Aspergillus fumigatus

The ability of fungi to survive in many environments is linked to their capacity to acquire essential nutrients. Iron is generally complexed and available in very limited amounts. Like bacteria, fungi have evolved highly specific systems for iron acquisition. Production and uptake of iron-chelating siderophores has been shown to be important for certain human bacterial pathogens, as well as in fungal pathogens such as Cryptococcus neoformans and Fusarium graminearum. This system also enables the opportunistic fungal pathogen Aspergillus fumigatus to infect and subsequently colonize the human lung. In this study, advantage was taken of genome sequence data available for both Aspergillus nidulans and A. fumigatus either to partially clone or to design PCR primers for 10 genes putatively involved in siderophore biosynthesis or uptake in A. fumigatus. The expression of these genes was then monitored by semi-quantitative and quantitative real-time PCR over a range of iron concentrations. As expected, the putative biosynthetic genes sidA, sidC and sidD were all strongly up-regulated under iron starvation conditions, although the variable degree of induction indicates complex regulation by a number of transcriptional factors, including the GATA family protein SreA. In contrast, the gene sidE shows no iron-regulation, suggesting that SidE may not be involved in siderophore biosynthesis. The characterisation of the expression patterns of this subset of genes in the iron regulon facilitates further studies into the importance of iron acquisition for pathogenesis of A. fumigatus. [Int Microbiol 2006; 9(4):281-287

Many-body GW calculations of ground-state properties: Quasi-2D electron systems and van der Waals forces

We present GW many-body results for ground-state properties of two simple but very distinct families of inhomogeneous systems in which traditional implementations of density-functional theory (DFT) fail drastically. The GW approach gives notably better results than the well-known random-phase approximation, at a similar computational cost. These results establish GW as a superior alternative to standard DFT schemes without the expensive numerical effort required by quantum Monte Carlo simulations

Multipole strength function of deformed superfluid nuclei made easy

We present an efficient method for calculating strength functions using the finite amplitude method (FAM) for deformed superfluid heavy nuclei within the framework of the nuclear density functional theory. We demonstrate that FAM reproduces strength functions obtained with the fully self-consistent quasi-particle random-phase approximation (QRPA) at a fraction of computational cost. As a demonstration, we compute the isoscalar and isovector monopole strength for strongly deformed configurations in $^{240}$Pu by considering huge quasi-particle QRPA spaces. Our approach to FAM, based on Broyden's iterative procedure, opens the possibility for large-scale calculations of strength distributions in well-bound and weakly bound nuclei across the nuclear landscape.Comment: 5 pages, 3 figure

Exchange and Correlation Kernels at the Resonance Frequency -- Implications for Excitation Energies in Density-Functional Theory

Specific matrix elements of exchange and correlation kernels in time-dependent density-functional theory are computed. The knowledge of these matrix elements not only constraints approximate time-dependent functionals, but also allows to link different practical approaches to excited states, either based on density-functional theory, or on many-body perturbation theory, despite the approximations that have been performed to derive them.Comment: Submitted to Phys. Rev. Lett. (February 4, 1999). Other related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Premating behavioral tactics of Columbian ground squirrels

In polygynous and polygynandrous mating systems males possess a variety of behavioral tactics that increase their access to reproductive females. In addition to overt combat or defending resources that attract mates, males use premating tactics that provide them with subsequent opportunities to copulate with receptive females. For Columbian ground squirrels, Urocitellus columbianus, we report that co-occupation of a burrow system by a reproductive male and a female on the night before the female exhibits diurnal estrus is an example of such a tactic. Our hypothesis was that nocturnal underground association results in successful consortships and therefore constitutes a mating tactic that is complementary to other mating behaviors exhibited during a female's estrus. Under this hypothesis appropriate predictions are that: males co-occupying a burrow system with a female at night should mate first with that female; males co-occupying a burrow system with a female overnight should sire more of her offspring than her subsequent mates; and the reproductive success of males co-occupying a burrow system with females should be higher than the reproductive success of mates that do not. To test our predictions we used a combination of field observations on nocturnal underground consortships (NUCs) and microsatellite DNA analyses of paternity. Males copulated with females during NUCs, as evidenced by inseminations. These males sired more offspring than males that did not participate in NUCs. Males ≥3 years old participated in more NUCs than sexually mature 2-year-old males. Our results supported the hypothesis that entrance into NUCs with a female before she exhibits estrus was a premating tactic that increased male reproductive success when exhibited in concert with other mating tactics such as territorial defens

Enhanced mtDNA repair and cellular survival following oxidative stress by targeting the hOGG repair enzyme to mitochondria.

Oxidative damage to mtDNA has been implicated as a causative factor in many disease processes and in aging. We have recently discovered that different cell types vary in their capacity to repair this damage, and this variability correlates with their ability to withstand oxidative stress. To explore strategies to enhance repair of oxidative lesions in mtDNA, we have constructed a vector containing a mitochondrial transport sequence upstream of the sequence for human 8-oxoguanine glycosylase. This enzyme is the glycosylase/AP lyase that participates in repair of purine lesions, such as 8-oxoguanine. Western blot analysis confirmed this recombinant protein was targeted to mitochondria. Enzyme activity assays showed that mitochondrial extracts from cells transfected with the construct had increased enzyme activity compared to cells transfected with vector only, while nuclear enzyme activity was not changed. Repair assays showed that there was enhanced repair of oxidative lesions in mtDNA. Additional studies revealed that this augmented repair led to enhanced cellular viability as determined by reduction of tetrazolium compound to formazan, Trypan blue dye exclusion, and clonogenic assays. Therefore, targeting of DNA repair enzymes to mitochondria may be a viable approach for the protection of cells against some of the deleterious effects of oxidative stress

Gene patents in the US - focusing on what really matters

With new technologies, concerns about gene patent claims regarding isolated DNA are becoming less relevant, but broad method claims could be more problematic