Cosmic ray driven dynamo in galactic disks. A parameter study

We present a parameter study of the magnetohydrodynamical dynamo driven by cosmic rays in the interstellar medium (ISM) focusing on the efficiency of magnetic field amplification and the issue of energy equipartition between magnetic, kinetic and cosmic ray (CR) energies. We perform numerical CR-MHD simulations of the ISM using the extended version of ZEUS-3D code in the shearing box approximation and taking into account the presence of Ohmic resistivity, tidal forces and vertical disk gravity. CRs are supplied in randomly distributed supernova (SN) remnants and are described by the diffusion-advection equation, which incorporates an anisotropic diffusion tensor. The azimuthal magnetic flux and total magnetic energy are amplified depending on a particular choice of model parameters. We find that the most favorable conditions for magnetic field amplification correspond to magnetic diffusivity of the order of 3\times 10^{25} \cm^2\s^{-1}, SN rates close to those observed in the Milky Way, periodic SN activity corresponding to spiral arms, and highly anisotropic and field-aligned CR diffusion. The rate of magnetic field amplification is relatively insensitive to the magnitude of SN rates in a rage of spanning 10% up to 100% of realistic values. The timescale of magnetic field amplification in the most favorable conditions is 150 Myr, at galactocentric radius equal to 5 kpc. The final magnetic field energies fluctuate near equipartition with the gas kinetic energy. In all models CR energy exceeds the equipartition values by a least an order of magnitude, in contrary to the expected equipartition. We suggest that the excess of cosmic rays can be attributed to the fact that the shearing-box does not permit cosmic rays to leave the system along the horizontal magnetic field.Comment: 12 papges, 11 figures, accepted for publication in Astronomy and Astrophysic

Development and Optimization of Computational Chemistry Algorithms

The challenges specific to the development of computational chemistry software are discussed. Selected solutions are presented, including examples of algorithmic optimizations and improved load-balancing for parallel calculations. A software framework for development of new quantum-chemical algorithms is proposed. Key design points are discussed. Optimization techniques are briefly described. Important implementation aspects, like automatic code generation, are highlighted

Reconnection Studies Under Different Types of Turbulence Driving

We study a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional direct numerical simulations. The model has been already successfully tested in Kowal et al. (2009) confirming the dependencies of the reconnection speed $V_{rec}$ on the turbulence injection power $P_{inj}$ and the injection scale $l_{inj}$ expressed by a constraint $V_{rec} \sim P_{inj}^{1/2} l_{inj}^{3/4}$ and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in order to drive turbulence, we injected velocity fluctuations in Fourier space with frequencies concentrated around $k_{inj}=1/l_{inj}$, as described in Alvelius (1999). In this paper we extend our previous studies by comparing fast magnetic reconnection under different mechanisms of turbulence injection by introducing a new way of turbulence driving. The new method injects velocity or magnetic eddies with a specified amplitude and scale in random locations directly in real space. We provide exact relations between the eddy parameters and turbulent power and injection scale. We performed simulations with new forcing in order to study turbulent power and injection scale dependencies. The results show no discrepancy between models with two different methods of turbulence driving exposing the same scalings in both cases. This is in agreement with the Lazarian and Vishniac (1999) predictions. In addition, we performed a series of models with varying viscosity $\nu$. Although Lazarian and Vishniac (1999) do not provide any prediction for this dependence, we report a weak relation between the reconnection speed with viscosity, $V_{rec}\sim\nu^{-1/4}$.Comment: 19 pages, 9 figures. arXiv admin note: text overlap with arXiv:0903.205

A neural-network controlled dynamic evolutionary scheme for global molecular geometry optimization

A novel, neural network controlled, dynamic evolutionary algorithm is proposed for the purposes of molecular geometry optimization. The approach is tested for selected model molecules and some molecular systems of importance in biochemistry. The new algorithm is shown to compare favorably with the standard, statically parametrized memetic algorithm

Effective Resource Allocation in Parallel Quantum-Chemical Calculations

Key factors affecting the parallel efficiency of archetypical quantum-chemical calculations are discussed. Effective load balancing schemes are proposed. Introduction of the memory affinity to the balancing process is shown to result in super-linear scaling

Czy odstąpienie od ratowania życia jest etycznie usprawiedliwione?

Podejmując próbę odpowiedzi na pytanie postawione w tytule, wypada zacząć od istotnego rozróżnienia pomiędzy (1) ratowaniem życia osoby nieumierającej i niewyniszczonej skrajnie chorobą terminalną (znajdującej się na wczesnym etapie opieki paliatywnej) a (2) zaniechaniem technicznego odsuwania w czasie momentu śmierci pacjenta w schyłkowej fazie nieuleczalnej choroby. O ile odstąpienie od interwencji ratującej życie w pierwszej sytuacji z reguły nie będzie etycznie usprawiedliwione, o tyle w drugiej widzieć je należy nie tylko jako dopuszczalną opcję, ale wręcz jako moralną powinność. Rozumna (roztropna) aplikacja takich pojęć bioetycznych, jak daremność medyczna, uporczywość terapeutyczna, środki proporcjonalne i nieproporcjonalne, dobro pacjenta, wydaje się niezbędna przy podejmowaniu etycznie usprawiedliwionych decyzji o odstąpieniu od ratowania życia (zaprzestaniu interwencji przedłużających życie) pacjentów paliatywnych