Evolving turbulence and magnetic fields in galaxy clusters

We discuss, using simple analytical models and MHD simulations, the origin and parameters of turbulence and magnetic fields in galaxy clusters. Three physically distinct regimes can be identified in the evolution of cluster turbulence and magnetic fields. Firstly, the fluctuation dynamo will produce microgauss-strong, random magnetic fields during cluster formation and major mergers. Turbulent velocity of about 300 km/s can be maintained at scales 100-200 kpc. The magnetic field is intermittent, has a smaller scale of 20-30 kpc and average strength of 2 microgauss. Secondly, when major mergers end, turbulent speed and magnetic field undergo a power-law decay, decreasing in strength but increasing in scale by a factor of about two. Thirdly, smaller-mass subclusters and cluster galaxies produce turbulent wakes, with turbulent speeds and magnetic field strengths similar to those quoted above. The velocity scales are about 200 kpc and 10 kpc respectively, and the magnetic field scale is about 6 times smaller. Although these wakes may fill only a small fraction of the cluster volume, their area covering factor can be close to unity. So one can potentially reconcile observations that indicate the coexistence of turbulence with ordered filamentary gas structures, as in the Perseus cluster. Random Faraday rotation measure is estimated to be typically 100-200 rad/m^2, in agreement with observations. We predict detectable synchrotron polarization from cluster radio halos at wavelengths 3-6 cm, if observed at sufficiently high resolution (abridged).Comment: 20 pages, 9 figures, Replaced to match version accepted by MNRA

Public choices between lifesaving programs : how important are lives saved?

In developing and industrial countries alike, there is concern that health and safety policy may respond to irrational fears - to the"disaster of the month"- rather than address more fundamental problems. In the United States, for example, some policymakers say the public worries about trivial risks while ignoring larger ones and that funding priorities reflect this view. Many public health programs with a low cost per life saved are underfunded, for example, while many environmental regulations with a high cost per life saved are issued each year. Does the existing allocation of resources reflect people's preoccupation with the qualitative aspects of risks, to the exclusion of quantitative factors (lives saved)? Or can observed differences in the cost per life saved of environmental and public health programs be explained by the way the two sets of programs are funded? The authors examine the preferences of U.S. citizens for health and safety programs. They confronted a random sample of 1,000 U.S. adults with choices between environmental health and public health programs, to see which they would choose. The authors then examined what factors (qualitative and quantitative) seem to influence these choices. Respondents were asked about pairs of programs, among them: smoking education or industrial pollution control programs, industrial pollution control or pneumonia vaccine programs, radon eradication or a program to ban smoking in the workplace, and radon eradication or programs to ban pesticides. The survey results, they feel, have implications beyond the United States. They find that, while qualitative aspects of the life-saving programs are statistically significant in explaining people's choices among them, lives saved matter, too. Indeed, for the median respondent in the survey, the rate of substitution between most qualitative risk characteristics and lives saved is inelastic. But for a sizable minority of respondents, choice among programs appears to be insensitive to lives saved. The interesting question for public policy is what role the latter group plays in the regulatory process.Health Monitoring&Evaluation,Public Health Promotion,Insurance&Risk Mitigation,Insurance Law,Water Conservation,Health Monitoring&Evaluation,Insurance&Risk Mitigation,Insurance Law,Water Conservation,Environmental Economics&Policies

Global logistics indicators, supply chain metrics, and bilateral trade patterns

Past research into the determinants of international trade highlighted the importance of the basic spatial gravity model augmented by additional variables representing sources of friction. Studies modeled many sources of friction using various proxies, including indices based on expert judgment in some cases. This paper focuses on logistics friction and draws on a data set recently compiled by the World Bank with specific quantitative metrics of logistics performance interms of time, cost, and variability in time. It finds that the new variables that relate directly to logistics performance have a statistically significant relationship with the level of bilateral trade. It also finds that a single logistics index can capture virtually all of the explanatory power of multiple logistics indicators. The findings should spur public and private agencies that have direct or indirect power over logistics performance to focus attention on reducing sources of friction so as to improve their country's ability to compete in today's global economy. Moreover, since the logistics metrics are directly related to operational performance, countries can use these metrics to target actions to improve logistics and monitor their progress.Common Carriers Industry,Transport and Trade Logistics,Economic Theory&Research,Free Trade,Trade Policy

Quasirandom Load Balancing

We propose a simple distributed algorithm for balancing indivisible tokens on graphs. The algorithm is completely deterministic, though it tries to imitate (and enhance) a random algorithm by keeping the accumulated rounding errors as small as possible. Our new algorithm surprisingly closely approximates the idealized process (where the tokens are divisible) on important network topologies. On d-dimensional torus graphs with n nodes it deviates from the idealized process only by an additive constant. In contrast to that, the randomized rounding approach of Friedrich and Sauerwald (2009) can deviate up to Omega(polylog(n)) and the deterministic algorithm of Rabani, Sinclair and Wanka (1998) has a deviation of Omega(n^{1/d}). This makes our quasirandom algorithm the first known algorithm for this setting which is optimal both in time and achieved smoothness. We further show that also on the hypercube our algorithm has a smaller deviation from the idealized process than the previous algorithms.Comment: 25 page

Scale-dependence of magnetic helicity in the solar wind

We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. (1982, Phys. Rev. Lett. 48, 1256) by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k~2 AU^{-1} (or frequency nu~2 uHz) at distances below 2.8 AU and at k~30 AU^{-1} (or nu~25 uHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10^{45} Mx^2/cycle at large scales and to a 3 times lower value at smaller scales.Comment: 8 pages, 6 figures, ApJ (in press

A Unified treatment of small and large- scale dynamos in helical turbulence

Helical turbulence is thought to provide the key to the generation of large-scale magnetic fields. Turbulence also generically leads to rapidly growing small-scale magnetic fields correlated on the turbulence scales. These two processes are usually studied separately. We give here a unified treatment of both processes, in the case of random fields, incorporating also a simple model non-linear drift. In the process we uncover an interesting plausible saturated state of the small-scale dynamo and a novel analogy between quantum mechanical (QM) tunneling and the generation of large scale fields. The steady state problem of the combined small/large scale dynamo, is mapped to a zero-energy, QM potential problem; but a potential which, for non-zero mean helicity, allows tunneling of bound states. A field generated by the small-scale dynamo, can 'tunnel' to produce large-scale correlations, which in steady state, correspond to a force-free 'mean' field.Comment: 4 pages, 1 figure, Physical Review Letters, in pres

Self- resistance in Dina Mehta’s Getting Away with Murder

Dina Mehta is an Indian writer belonging to the Parsi community. Among the Indian writers belonging to the community of Parsi\u27s, Dina Mehta is prominent. Generally, the Parsi novelists who write in English are differentiated into two categories; expatriate writers and stay-at-home writers and Dina Mehta falls into the category of stay-at-home writers. Other Parsi novelists like Firdaus Kanga, Rohinton Mistry, Farrukh Dhondy and Bapsi Sidhwa are included in the list of expatriate novelists. The work of these novelists reflects the life of their community and the history of India. Their works also portray their ethnic identity and relationships like motherhood, intricate baffling relationship of men and women, incest and adultery. Dina Mehta\u27sGetting Away With Murderdeals with various issues like child abuses, rape, female feticide, and blind superstitious belief that are the hindrance in the development of human development, but this play voices against foeticide, infanticide, rape, inequality, and gender discrimination. This play portrays the independent thinking modern women who work to rise up herself and world around with her conscience thoughts, and harmony. Getting away with murder is one of the three plays in the collection entitled “Body blows- women violence and survival” published by Seagull books, Calcutta in 2000. The play was first performed by Indus International, a socio-cultural group for women at British Council Theatre in Mumbai in 1990. The play seeks to portray the lives of three friends Mallika, Sonali and Raziya who are connected perhaps by the strain of suffering that they undergo in the hands of male hypocritic and dominating human. The private world outside so corrupted that women have to face childhood sexual abuse, differential treatment on the male and the female child, infidelity partners with whom they have an utterly insecure relationship, sexual harassment at workplace and elsewhere, and a disheveled life despite having been educated