Star formation and chemical evolution in SPH simulations: a statistical approach

In Smoothed Particles Hydrodynamics (SPH) codes with a large number of particles, star formation as well as gas and metal restitution from dying stars can be treated statistically. This approach allows to include detailed chemical evolution and gas re-ejection with minor computational effort. Here we report on a new statistical algorithm for star formation and chemical evolution, especially conceived for SPH simulations with large numbers of particles, and for parallel SPH codes. For the sake of illustration, we present also two astrophysical simulations obtained with this algorithm, implemented into the Tree-SPH code by Lia & Carraro (2000). In the first one, we follow the formation of an individual disc-like galaxy, predict the final structure and metallicity evolution, and test resolution effects. In the second one we simulate the formation and evolution of a cluster of galaxies, to demonstrate the capabilities of the algorithm in investigating the chemo-dynamical evolution of galaxies and of the intergalactic medium in a cosmological context.Comment: 17 pages, 20 figures, accepted for publication on MNRA

A Parallel Tree-SPH code for Galaxy Formation

We describe a new implementation of a parallel Tree-SPH code with the aim to simulate Galaxy Formation and Evolution. The code has been parallelized using SHMEM, a Cray proprietary library to handle communications between the 256 processors of the Silicon Graphics T3E massively parallel supercomputer hosted by the Cineca Supercomputing Center (Bologna, Italy). The code combines the Smoothed Particle Hydrodynamics (SPH) method to solve hydro-dynamical equations with the popular Barnes and Hut (1986) tree-code to perform gravity calculation with a NlogN scaling, and it is based on the scalar Tree-SPH code developed by Carraro et al(1998)[MNRAS 297, 1021]. Parallelization is achieved distributing particles along processors according to a work-load criterion. Benchmarks, in terms of load-balance and scalability, of the code are analyzed and critically discussed against the adiabatic collapse of an isothermal gas sphere test using 20,000 particles on 8 processors. The code results balanced at more that 95% level. Increasing the number of processors, the load-balance slightly worsens. The deviation from perfect scalability at increasing number of processors is almost negligible up to 32 processors. Finally we present a simulation of the formation of an X-ray galaxy cluster in a flat cold dark matter cosmology, using 200,000 particles and 32 processors, and compare our results with Evrard (1988) P3M-SPH simulations. Additionaly we have incorporated radiative cooling, star formation, feed-back from SNae of type II and Ia, stellar winds and UV flux from massive stars, and an algorithm to follow the chemical enrichment of the inter-stellar medium. Simulations with some of these ingredients are also presented.Comment: 19 pages, 14 figures, accepted for publication in MNRA

Coupling Chemical Evolution with SPH

We present a new statistical algorithm of Chemical Evolution implemented into the Tree-SPH code developed by Lia & Carraro (2000 MNRAS 314, 145)

Google Votes: A Liquid Democracy Experiment on a Corporate Social Network

This paper introduces Google Votes, an experiment in liquid democracy built on Google\u27s internal corporate Google+ social network. Liquid democracy decision-making systems can scale to cover large groups by enabling voters to delegate their votes to other voters. This approach is in contrast to direct democracy systems where voters vote directly on issues, and representative democracy systems where voters elect representatives to vote on issues for them. Liquid democracy systems can provide many of the benefits of both direct and representative democracy systems with few of the weaknesses. Thus far, high implementation complexity and infrastructure costs have prevented widespread adoption. Google Votes demonstrates how the use of social-networking technology can overcome these barriers and enable practical liquid democracy systems. The case-study of Google Votes usage at Google over a 3 year timeframe is included, as well as a framework for evaluating vote visibility called the Golden Rule of Liquid Democracy

Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy injection in the gas around a fading AGN

We present deep Chandra X-ray observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp and hosting a fading AGN. We find extended soft X-ray emission from hot gas around the low intrinsic luminosity (unobscured) AGN ($L_{\rm bol} \sim 10^{42}-10^{44}$ erg s$^{-1}$). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN (\mbox{E_{\rm bub}} \sim 10^{54} - 10^{55} erg). A possible scenario is that this bubble is inflated by the fading AGN, which after changing accretion state is now in a kinetic mode. Other possibilities are that the bubble has been inflated by the past luminous quasar ($L_{\rm bol} \sim 10^{46}$ erg s$^{-1}$), or that the temperature gradient is an indication of a shock front from a superwind driven by the AGN. We discuss the possible scenarios and the implications for the AGN-host galaxy interaction, as well as an analogy between AGN and X-ray binaries lifecycles. We conclude that the AGN could inject mechanical energy into the host galaxy at the end of its lifecycle, and thus provide a source for mechanical feedback, in a similar way as observed for X-ray binaries.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Pengaruh Hedonic Shopping Motivation Terhadap Impulse Buying Pada Toko Online: Studi Pada Toko Online Zalora

Online shopping, including shopping for fashion goods, has become a trend in Indonesia. One of buyer's motivations to do online-fashion-shopping is hedonic shopping motivation. This research aims to examine the influence of hedonic shopping motivation on impulse buying process. Using 100 buyers of Zalora (an online shop) as the respondents, this study confirms that hedonic shopping motivation has a significant influence on the impulse buying process

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

The Wisconsin H Alpha Mapper has been used to set the first deep upper limits on the intensity of diffuse H alpha emission from warm ionized gas in the Local Group dwarf spheroidal galaxies (dSphs) Draco and Ursa Minor. Assuming a velocity dispersion of 15 km/s for the ionized gas, we set limits for the H alpha intensity of less or equal to 0.024 Rayleighs and less or equal to 0.021 Rayleighs for the Draco and Ursa Minor dSphs, respectively, averaged over our 1 degree circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of approximately less than 10% of the stellar mass, or approximately 10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star forming episodes more than 8 Gyr in the past, without violating these limits on the mass of ionized gas.Comment: 10 pages, 2 figures, AASTeX two-column format. Accepted for publication in The Astrophysical Journa

Oportunidades Program Participation and Body Mass Index, Blood Pressure, and Self-Reported Health in Mexican Adults

IntroductionGovernments around the world are seeking to address the increasing prevalence of obesity and hypertension. Our objective was to evaluate the effect of an incentive-based development program (Oportunidades, formerly Progresa) on body mass index (BMI), blood pressure, and self-reported health.MethodsAn intervention group of low-income (below the 20th percentile nationally), rural, Mexican adults (aged 30-65 years) (n = 5280) received program benefits (cash transfers contingent on positive changes in health behavior such as regular health checkups) for 3.5 to 5.0 years. They were compared with a newly recruited control group of adults (n = 1063) who had not yet begun receiving benefits. Analyses were adjusted for almost 50 social and economic covariates.ResultsAge- and sex-adjusted BMI was lower in adults from intervention communities than in those from control communities (26.57 kg/m(2) vs 27.16 kg/m(2), P < .001), as was the prevalence of obesity (20.28% vs 25.31%, P < .001) and overweight (59.24% vs 63.04%, P = .03); these results were attenuated after covariates were included. Adults in intervention communities had a lower combined prevalence of uncontrolled hypertension (33.80% vs 34.52%, P = .008) when adjusting for all covariates. Mean systolic (beta = -2.60, P < .001) and diastolic (beta = -2.84, P < .001) blood pressures were significantly lower in the intervention communities after all covariates were included, and self-reported health outcomes were better.ConclusionParticipation in Oportunidades, a large-scale cash-transfer program, was associated with lower prevalence of obesity and hypertension and better self-reported health in adults in rural Mexico