409 research outputs found
Extension of the LDA-1/2 method to the material class of bismuth containing III-V semiconductors
The LDA-1/2 method is employed in density functional theory calculations for
the electronic structure of III-V dilute bismide systems. For the
representative example of Ga(SbBi) with Bi concentrations below , it is
shown that this method works very efficiently, especially due to its reasonably
low demand on computer memory. The resulting bandstructure and wavefunctions
are used to compute the interaction matrix elements that serve as input to
microscopic calculations of the optical properties and intrinsic losses
relevant for optoelectronic applications of dilute bismides
Gain spectroscopy of a type-II VECSEL chip
Using optical pump-white light probe spectroscopy the gain dynamics is
investigated for a VECSEL chip which is based on a type-II heterostructure. The
active region the chip consists of a GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs
multiple quantum well. For this structure, a fully microscopic theory predicts
a modal room temperature gain at a wavelength of 1170 nm, which is confirmed by
experimental spectra. The results show a gain buildup on the type-II chip which
is delayed relative to that of a type-I chip. This slower gain dynamics is
attributed to a diminished cooling rate arising from reduced electron-hole
scattering.Comment: 4 pages, 4 figure
Investigating the effects of ebselen, a potential new lithium mimetic, on glutamate transmission
Self-assembly of the general membrane-remodeling protein PVAP into sevenfold virus-associated pyramids
This is the final version of the article. Available from National Academy of Sciences via the DOI in this record.Viruses have developed a wide range of strategies to escape from the host cells in which they replicate. For egress some archaeal viruses use a pyramidal structure with sevenfold rotational symmetry. Virus-associated pyramids (VAPs) assemble in the host cell membrane from the virus-encoded protein PVAP and open at the end of the infection cycle. We characterize this unusual supramolecular assembly using a combination of genetic, biochemical, and electron microscopic techniques. By whole-cell electron cryotomography, we monitored morphological changes in virus-infected host cells. Subtomogram averaging reveals the VAP structure. By heterologous expression of PVAP in cells from all three domains of life, we demonstrate that the protein integrates indiscriminately into virtually any biological membrane, where it forms sevenfold pyramids. We identify the protein domains essential for VAP formation in PVAP truncation mutants by their ability to remodel the cell membrane. Self-assembly of PVAP into pyramids requires at least two different, in-plane and out-of-plane, protein interactions. Our findings allow us to propose a model describing how PVAP arranges to form sevenfold pyramids and suggest how this small, robust protein may be used as a general membrane-remodeling system.D.P. and T.E.F.Q. received financial support from L’Agence Nationale de la Recherche. W.K. and B.D. received financial support from the Max Planck Society
Influence of Coulomb and Phonon Interaction on the Exciton Formation Dynamics in Semiconductor Heterostructures
A microscopic theory is developed to analyze the dynamics of exciton
formation out of incoherent carriers in semiconductor heterostructures. The
carrier Coulomb and phonon interaction is included consistently. A cluster
expansion method is used to systematically truncate the hierarchy problem. By
including all correlations up to the four-point (i.e. two-particle) level, the
fundamental fermionic substructure of excitons is fully included. The analysis
shows that the exciton formation is an intricate process where Coulomb
correlations rapidly build up on a picosecond time scale while phonon dynamics
leads to true exciton formation on a slow nanosecond time scale.Comment: 18 pages, 7 figure
Concurrent multiple sclerosis and amyotrophic lateral sclerosis: where inflammation and neurodegeneration meet?
The concurrence of multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS) is exceedingly rare and the pathological features have not been examined extensively. Here we describe the key pathological features of a 40 year old man with pathologically confirmed concurrent MS and ALS
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