Simulation of stellar instabilities with vastly different timescales using domain decomposition

Strange mode instabilities in the envelopes of massive stars lead to shock waves, which can oscillate on a much shorter timescale than that associated with the primary instability. The phenomenon is studied by direct numerical simulation using a, with respect to time, implicit Lagrangian scheme, which allows for the variation by several orders of magnitude of the dependent variables. The timestep for the simulation of the system is reduced appreciably by the shock oscillations and prevents its long term study. A procedure based on domain decomposition is proposed to surmount the difficulty of vastly different timescales in various regions of the stellar envelope and thus to enable the desired long term simulations. Criteria for domain decomposition are derived and the proper treatment of the resulting inner boundaries is discussed. Tests of the approach are presented and its viability is demonstrated by application to a model for the star P Cygni. In this investigation primarily the feasibility of domain decomposition for the problem considered is studied. We intend to use the results as the basis of an extension to two dimensional simulations.Comment: 15 pages, 10 figures, published in MNRA

Anisotropic valence-->core x-ray fluorescence from a [Rh(en)3][Mn(N)(CN)5]·H2O single crystal: Experimental results and density functional calculations

High resolution x-ray fluorescence spectra have been recorded for emission in different directions from a single crystal of the compound [Rh(en)3][Mn(N)(CN)5]·H2O. The spectra are interpreted by comparison with density functional theory (DFT) electronic structure calculations. The Kbeta[double-prime] line, which is strongly polarized along the Mn–N axis, can be viewed as an N(2s)-->Mn(1s) transition, and the angular dependence is understood within the dipole approximation. The so-called Kbeta2,5 region has numerous contributions but is dominated by Mn(4p) and C(2s)-->Mn(1s) transitions. Transition energy splittings are found in agreement with those of calculated occupied molecular orbitals to within 1 eV. Computed relative transition probabilities reproduce experimentally observed trends

Peat decomposition indicators of two contrasting bogs in the Eastern Alps, Austria

Since carbon (C) in peatlands is labile and sensitive to disturbances, peatlands have the potential to release high C amounts by land use changes and to accelerate global warming. Therefore, adequate peat decomposition indicators (PDI) are necessary to assess the peatland degradation status and potential for CO2 release. In order to assess the peat degradation status of nine sites in Alpine bogs (Enns valley, Austria), we compared PDI of two peat bogs with contrasting land-use histories. The conventional PDI: loss on ignition, bulk density, C:N ratios, water table depths (WTD) were compared with the recently introduced PDI: stable carbon isotope signature (d13C) and nitrogen isotope signature (d15N). The most PDI were different between the two bogs and the study sites with contrasting WTD and degree of peat decomposition. We demonstrated strong relationships and similar depth profiles of variables: Loss of ignition of strongly degraded peat decreases from the acrotelm to the catotelm, but remains stable at less degraded peat. Bulk density generally increases with depth, and was lowest in the acrotelm of the central bog area and highest in the catotelm of the former peat cutting areas. C:N ratios increased slightly with the degree of peat decomposition. d13C and d15N increased from the top to the depths of -24 to -42 cm at all study sites. In the catotelm, dC13 were significantly lower in strongly decomposed peat compared to the less degraded sites. Higher d15N values in acrotelm and catotelm of strongly degraded peat may be evidence for more pronounced N fractionation during decomposition compared to less degraded sites. Decomposers tend to preferably use substances with 12C for respiration, resulting in a relative enrichment of 13C in the residual organic matter. Accordingly, the increase of d13C with depth in the acrotelm in strongly decayed peat may be assigned to 12C loss by respiration

A portable 3D printer system for the diagnosis and treatment of multidrug-resistant bacteria

Summary: Multidrug-resistant bacteria are a major threat to human health, but broad-spectrum antibiotics are losing efficacy. There is a need to screen a given drug against a bacterial infection outside of the laboratory. To address this need, we have designed and built an inexpensive and easy-to-use 3D-printer-based system that allows easily readable quantitative tests for the performance of antibacterial drugs. The platform creates a sterile diagnostic device by using 3D printing, and the device is filled automatically with growth medium, and then antibiotics are sprayed onto the medium by ink-jet technology. The sample for testing can be introduced via a fluid port, and the printer hot bed is used to incubate the device, allowing operation in the field. Combining advantages from various established tests of antibacterial performance, this allows the comparison of a specific antibiotics and bacteria. Also, this system can create and test several antibiotic formulations for therapeutic use, and we demonstrate this potential by investigating a mixture of pathogens that are only killed by a mixture of drugs

Instabilities of captured shocks in the envelopes of massive stars

The evolution of strange mode instabilities into the non linear regime has been followed by numerical simulation for an envelope model of a massive star having solar chemical composition, M=50M_sun, T_eff=10^4K and L=1.17*10^6 L_sun. Contrary to previously studied models, for these parameters shocks are captured in the H-ionisation zone and perform rapid oscillations within the latter. A linear stability analysis is performed to verify that this behaviour is physical. The origin of an instability discovered in this way is identified by construction of an analytical model. As a result, the stratification turns out to be essential for instability. The difference to common stratification instabilities, e.g., convective instabilities, is discussed.Comment: 16 pages, 6 figures, accepted for publication in MNRA

Efficient chemotherapy of rat glioblastoma using Doxorubicin-loaded PLGA nanoparticles with different stabilizers

Background: Chemotherapy of glioblastoma is largely ineffective as the blood-brain barrier (BBB) prevents entry of most anticancer agents into the brain. For an efficient treatment of glioblastomas it is necessary to deliver anti-cancer drugs across the intact BBB. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with poloxamer 188 hold great promise as drug carriers for brain delivery after their intravenous injection. In the present study the anti-tumour efficacy of the surfactant-coated doxorubicin-loaded PLGA nanoparticles against rat glioblastoma 101/8 was investigated using histological and immunohistochemical methods. Methodology: The particles were prepared by a high-pressure solvent evaporation technique using 1% polyvinylalcohol (PLGA/PVA) or human serum albumin (PLGA/HSA) as stabilizers. Additionally, lecithin-containing PLGA/HSA particles (Dox-Lecithin-PLGA/HSA) were prepared. For evaluation of the antitumour efficacy the glioblastoma-bearing rats were treated intravenously with the doxorubicin-loaded nanoparticles coated with poloxamer 188 using the following treatment regimen: 3×2.5 mg/kg on day 2, 5 and 8 after tumour implantation; doxorubicin and poloxamer 188 solutions were used as controls. On day 18, the rats were sacrificed and the antitumour effect was determined by measurement of tumour size, necrotic areas, proliferation index, and expression of GFAP and VEGF as well as Isolectin B4, a marker for the vessel density. Conclusion: The results reveal a considerable anti-tumour effect of the doxorubicin-loaded nanoparticles. The overall best results were observed for Dox-Lecithin-PLGA/HSA. These data demonstrate that the poloxamer 188-coated PLGA nanoparticles enable delivery of doxorubicin across the blood-brain barrier in the therapeutically effective concentrations