Effects of Gamma Ray Bursts in Earth Biosphere

We continue former work on the modeling of potential effects of Gamma Ray Bursts on Phanerozoic Earth. We focus on global biospheric effects of ozone depletion and show a first modeling of the spectral reduction of light by NO2 formed in the stratosphere. We also illustrate the current complexities involved in the prediction of how terrestrial ecosystems would respond to this kind of burst. We conclude that more biological field and laboratory data are needed to reach even moderate accuracy in this modelingComment: Accepted for publication in Astrophysics & Space Scienc

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

Clamping of the Linewidth Enhancement Factor in Narrow Quantum-Well GRINSCH Semiconductor Lasers

The linewidth enhancement factor in single quantum-well GRINSCH semiconductor lasers is investigated theoretically and experimentally. For thin wells a small linewidth enhancement factor is obtained which clamps with increasing carrier density, in contrast to the monotonous increase observed for thicker wells. Microscopic many-body calculations reproduce the experimental observations attributing the clamping to a subtle interplay between excitation dependent gain shifts and carrier population distributions

Dataset for the Incorporation of Climate Change into a Multiple Stressor Risk Assessment for the Chinook Salmon (Oncorhynchus tshawytscha) Population in the Yakima River, Washington USA

Data files available below This data set is in support of Landis et al (in press 2024). A key question in understanding the implications of climate change is how to integrate ecological risk assessments that focus on contaminants with the environmental alterations from climate projections. This article summarizes the results of integrating selected direct and indirect effects of climate change into an existing Bayesian network previously used for ecological risk assessment. The existing Bayesian network Relative Risk Model (BN-RRM) integrated the effects of organophosphate pesticides concentrations, water temperature, and dissolved oxygen levels on the Chinook salmon population in the Yakima River Basin, Washington, USA, with the endpoint being no net loss to the population described by a three patch metapopulation age structured model. Climate change-induced changes in water quality parameters (temperature and dissolved oxygen levels) were incorporated into the model based on projected climatic conditions in the 2050s and 2080s. Pesticide concentrations in the original model were modified assuming different bounding scenarios of pest control strategies in the future, as climate change may alter pest numbers and species and thus the required emission of pesticides. Our results suggest that future direct and indirect changes to the Yakima River Basin result in a high probability (62%) that the salmon population will drop below the management goal of no net loss. The key driver in salmon population risk was found to be increases in temperature levels, with pesticide concentrations playing little to no role, as indicated by the sensitivity analysis. However, indirect effects to community structure and dynamics, such as changes in the food web, were not considered. Our study demonstrates the feasibility of incorporating the direct effects of climate change and its indirect effects on chemical emissions into an integrated Bayesian network relative risk framework. It also highlights the value of using Bayesian networks for identifying key drivers of ecological risk and elucidating possible mitigation measures to avoid unacceptable changes in risk. Future research needs are also described for incorporating climate change projections into exposure-driven ecological risk assessments. The Netica file can be opened and read with the free download version of Netica available at https://www.norsys.com/netica.html. The structure of the model and the notes for each node and the conditional probability tables can then be accessed. A licensed version of Netica can run and modify the file

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

Nonlinear localized waves in a periodic medium

We analyze the existence and stability of nonlinear localized waves in a periodic medium described by the Kronig-Penney model with a nonlinear defect. We demonstrate the existence of a novel type of stable nonlinear band-gap localized states, and also reveal an important physical mechanism of the oscillatory wave instabilities associated with the band-gap resonances.Comment: 4 pages, 5 figure