The Structure of Isothermal, Self-gravitating Gas Spheres for Softened Gravity

A theory for the structure of isothermal, self-gravitating gas spheres in pressure equilibrium in a softened gravitational field is developed. The one parameter spline softening proposed by Hernquist & Katz (1989) is used. We show that the addition of this extra scale parameter implies that the set of equilibrium solutions constitute a one-parameter family, rather than the one and only one isothermal sphere solution for Newtonian gravity. We demonstrate the perhaps somewhat surprising result that for any finite choice of softening length and temperature, it is possible to deposit an arbitrarily large mass of gas in pressure equilibrium and with a non-singular density distribution inside of r_0 for any r_0 > 0. The theoretical predictions of our models are compared with the properties of the small, massive, quasi-isothermal gas clumps which typically form in numerical Tree-SPH simulations of 'passive' galaxy formation of Milky Way sized galaxies. We find reasonable agreement despite the neglect of rotational support in the models. We comment on whether the hydrodynamical resolution in our numerical simulation of galaxy formation is sufficient, and finally we conclude that one should be cautious, when comparing results of numerical simulations involving gravitational softening and hydrodynamical smoothing, with reality.Comment: 22 pages Latex + 12 figure

Standardization and the democratic design of information and communication technology

The way information and communication technology (ICT) develops can promote or hinder the democratic potential of this critical societal infrastructure. Concerns about the role standards development organizations (SDOs) play in this context predate the "digital age" but are reemerging amid substantial changes in the institutional landscape of standardization. This article explores the increasingly critical link between the institutional design of SDOs and the democratic design of ICT. We review some principles of democracy in terms of the design of technology, apply these to standardization, and discuss the role public policy may play here, while distinguishing between input and output legitimacy

Cosmological SPH simulations with four million particles: statistical properties of X-ray clusters in a low-density universe

We present results from a series of cosmological SPH (smoothed particle hydrodynamics) simulations coupled with the P3M (Particle-Particle-Particle-Mesh) solver for the gravitational force. The simulations are designed to predict the statistical properties of X-ray clusters of galaxies as well as to study the formation of galaxies. We have seven simulation runs with different assumptions on the thermal state of the intracluster gas. Following the recent work by Pearce et al., we modify our SPH algorithm so as to phenomenologically incorporate the galaxy formation by decoupling the cooled gas particles from the hot gas particles. All the simulations employ 128^3 particles both for dark matter and for gas components, and thus constitute the largest systematic catalogues of simulated clusters in the SPH method performed so far. These enable us to compare the analytical predictions on statistical properties of X-ray clusters against our direct simulation results in an unbiased manner. We find that the luminosities of the simulated clusters are quite sensitive to the thermal history and also to the numerical resolution of the simulations, and thus are not reliable. On the other hand, the mass-temperature relation for the simulated clusters is fairly insensitive to the assumptions of the thermal state of the intracluster gas, robust against the numerical resolution, and in fact agrees well with the analytic prediction. Therefore the prediction for the X-ray temperature function of clusters on the basis of the Press-Schechter mass function and the virial equilibrium is fairly reliable.Comment: Accepted for publication in The Astrophysical Journal. 18 pages with 7 embedded figure

Conservation Laws in Smooth Particle Hydrodynamics: the DEVA Code

We describe DEVA, a multistep AP3M-like-SPH code particularly designed to study galaxy formation and evolution in connection with the global cosmological model. This code uses a formulation of SPH equations which ensures both energy and entropy conservation by including the so-called \bn h terms. Particular attention has also been paid to angular momentum conservation and to the accuracy of our code. We find that, in order to avoid unphysical solutions, our code requires that cooling processes must be implemented in a non-multistep way. We detail various cosmological simulations which have been performed to test our code and also to study the influence of the \bn h terms. Our results indicate that such correction terms have a non-negligible effect on some cosmological simulations, especially on high density regions associated either to shock fronts or central cores of collapsed objects. Moreover, they suggest that codes paying a particular attention to the implementation of conservation laws of physics at the scales of interest, can attain good accuracy levels in conservation laws with limited computational resources.Comment: 36 pages, 10 figures. Accepted for publication in The Astrophysical Journa

Sintering and concomitant crystallization of bioactive glasses

The official meeting minutes of Bowling Green State University\u27s Board of Trustees

MCG+00-32-16: An Irregular Galaxy Close to the Lowest Redshift Absorber on the 3C 273 Line of Sight

MCG+00-32-16 is the galaxy closest in position-velocity space to the lowest redshift Ly$\alpha$ absorber along the line-of-sight to the quasar 3C 273. Its projected separation is 204 (d/19 Mpc) kpc, where d is the distance from the Milky Way to the galaxy, and the redshift difference is only 94 km/s; HI 1225+01 is slightly closer in projected separation to the absorber, but has a greater redshift difference. We present HI synthesis array mapping and CCD photometry in B and R for MCG+00-32-16. The HI disk is rotating in such a way that the side of the galaxy closer to the sight-line to the quasar has the larger velocity difference from the absorber. The absorber may be a ``failed dwarf'' member of a poor galaxy group of which MCG+00-32-16 and HI 1225+01 are the only members to have formed stars.Comment: 14 pages, 9 figures, accepted by Astrophysical Journa

Effects of cluster galaxies on arc statistics

We present the results of a set of numerical simulations evaluating the effect of cluster galaxies on arc statistics. We perform a first set of gravitational lensing simulations using three independent projections for each of nine different galaxy clusters obtained from N-body simulations. The simulated clusters consist of dark matter only. We add a population of galaxies to each cluster, mimicking the observed luminosity function and the spatial galaxy distribution, and repeat the lensing simulations including the effects of cluster galaxies, which themselves act as individual lenses. Each galaxy is represented by a spherical Navarro, Frenk & White (1997) density profile. We consider the statistical distributions of the properties of the gravitational arcs produced by our clusters with and without galaxies. We find that the cluster galaxies do not introduce perturbations strong enough to significantly change the number of arcs and the distributions of lengths, widths, curvature radii and length-to-width ratios of long arcs. We find some changes to the distribution of short-arc properties in presence of cluster galaxies. The differences appear in the distribution of curvature radii for arc lengths smaller than 12'', while the distributions of lengths, widths and length-to-width ratios are significantly changed only for arcs shorter than 4''.Comment: 11 pages, Latex using MN style, 6 figures enclosed. Version accepted for publication in MNRAS. Gzipped file including a full resolution version of Figures 2a, 2b, 3a, 3b, 3c can be downloaded by anonymous ftp at http://gt.pd.astro.it/~bepi/PAPERS/lensing.ps.g

Cosmological Feedback from High-Redshift Dwarf Galaxies

We model how repeated supernova explosions in high-redshift dwarf starburst galaxies drive superbubbles and winds out of the galaxies. We compute the efficiencies of metal and mass ejection and energy transport from the galactic potentials, including the effect of cosmological infall of external gas. The starburst bubbles quickly blow out of small, high-redshift, galactic disks, but must compete with the ram pressure of the infalling gas to escape into intergalactic space. We show that the assumed efficiency of the star formation rate dominates the bubble evolution and the metal, mass, and energy feedback efficiencies. With star formation efficiency f*=0.01, the ram pressure of infall can confine the bubbles around high-redshift dwarf galaxies with circular velocities v_c>52 km/s. We can expect high metal and mass ejection efficiencies, and moderate energy transport efficiencies in halos with v_c~30-50 km/s and f*~0.01 as well as in halos with v_c~100 km/s and f*>>0.01. Such haloes collapse successively from 1-2 sigma peaks in LambdaCDM Gaussian density perturbations as time progresses. These dwarf galaxies can probably enrich low and high-density regions of intergalactic space with metals to 10^-3-10^-2 Zsun as they collapse at z~8 and z<5 respectively. They also may be able to provide adequate turbulent energy to prevent the collapse of other nearby halos, as well as to significantly broaden Lyman-alpha absorption lines to v_rms~20-40 km/s. We compute the timescales for the next starbursts if gas freely falls back after a starburst, and find that, for star formation efficiencies as low as f*<0.01, the next starburst should occur in less than half the Hubble time at the collapse redshift. This suggests that episodic star formation may be ubiquitous in dwarf galaxies.Comment: Accepted for ApJ v613, 60 pages, 15 figure

Effect of action-based cognitive remediation on cognition and neural activity in bipolar disorder:Study protocol for a randomized controlled trial

Abstract Background Cognitive impairment is present in bipolar disorder (BD) during the acute and remitted phases and hampers functional recovery. However, there is currently no clinically available treatment with direct and lasting effects on cognitive impairment in BD. We will examine the effect of a novel form of cognitive remediation, action-based cognitive remediation (ABCR), on cognitive impairment in patients with BD, and explore the neural substrates of potential treatment efficacy on cognition. Methods/design The trial has a randomized, controlled, parallel-group design. In total, 58 patients with BD in full or partial remission aged 18–55 years with objective cognitive impairment will be recruited. Participants are randomized to 10 weeks of ABCR or a control group. Assessments encompassing neuropsychological testing and mood ratings, and questionnaires on subjective cognitive complaints, psychosocial functioning, and quality of life are carried out at baseline, after 2 weeks of treatment, after the end of treatment, and at a six-month-follow-up after treatment completion. Functional magnetic resonance imaging scans are performed at baseline and 2 weeks into treatment. The primary outcome is a cognitive composite score spanning verbal memory, attention, and executive function. Two complete data sets for 52 patients will provide a power of 80% to detect a clinically relevant between-group difference on the primary outcome. Behavioral data will be analyzed using mixed models in SPSS while MRI data will be analyzed with the FMRIB Expert Analysis Tool (FEAT). Early treatment-related changes in neural activity from baseline to week 2 will be investigated for the dorsal prefrontal cortex and hippocampus as the regions of interest and with an exploratory whole-brain analysis. Discussion The results will provide insight into whether ABCR has beneficial effects on cognition and functioning in remitted patients with BD. The results will also provide insight into early changes in neural activity associated with improvement of cognition, which can aid future treatment development. Trial registration Clinicaltrials.gov, NCT03295305. Registered on 26 September 2017