The relation between gas density and velocity power spectra in galaxy clusters: qualitative treatment and cosmological simulations

We address the problem of evaluating the power spectrum of the velocity field of the ICM using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: $(\delta\rho_k/\rho)^2 = \eta_1^2 (V_{1,k}/c_s)^2$, where $\delta\rho_k/\rho$ is the spectral amplitude of the density perturbations at wave number $k$, $V_{1,k}^2=V_k^2/3$ is the mean square component of the velocity field, $c_s$ is the sound speed, and $\eta_1$ is a dimensionless constant of order unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find $\eta_1\approx 1 \pm 0.3$. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proportional because the former are a passive scalar advected by the latter. This opens an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters, across a wide range of scales.Comment: 6 pages, 3 figures, submitted to ApJ Letter

Spherical Accretion with Anisotropic Thermal Conduction

We study the effects of anisotropic thermal conduction on magnetized spherical accretion flows using global axisymmetric MHD simulations. In low collisionality plasmas, the Bondi spherical accretion solution is unstable to the magnetothermal instability (MTI). The MTI grows rapidly at large radii where the inflow is subsonic. For a weak initial field, the MTI saturates by creating a primarily radial magnetic field, i.e., by aligning the field lines with the background temperature gradient. The saturation is quasilinear in the sense that the magnetic field is amplified by a factor of $\sim 10-30$ independent of the initial field strength (for weak fields). In the saturated state, the conductive heat flux is much larger than the convective heat flux, and is comparable to the field-free (Spitzer) value (since the field lines are largely radial). The MTI by itself does not appreciably change the accretion rate $\dot M$ relative to the Bondi rate $\dot M_B$. However, the radial field lines created by the MTI are amplified by flux freezing as the plasma flows in to small radii. Oppositely directed field lines are brought together by the converging inflow, leading to significant resistive heating. When the magnetic energy density is comparable to the gravitational potential energy density, the plasma is heated to roughly the virial temperature; the mean inflow is highly subsonic; most of the energy released by accretion is transported to large radii by thermal conduction; and the accretion rate $\dot M \ll \dot M_B$. The predominantly radial magnetic field created by the MTI at large radii in spherical accretion flows may account for the stable Faraday rotation measure towards Sgr A* in the Galactic Center.Comment: accepted in MNRAS with some modifications suggested by the referee; 15 pages, 16 figure

4-Methyl-2H-1,3-oxazine-2,6(3H)-dione

In the title compound, C5H5NO3, the planar (maximum deviation = 0.075 Å for the ring O atom) mol­ecules form N—H⋯O hydrogen bonds in a zigzag chain (C—O⋯N bond angle ≃ 140°) between glide-related mol­ecules

Therapeutic and educational objectives in robot assisted play for children with autism

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.” DOI: 10.1109/ROMAN.2009.5326251This article is a methodological paper that describes the therapeutic and educational objectives that were identified during the design process of a robot aimed at robot assisted play. The work described in this paper is part of the IROMEC project (Interactive Robotic Social Mediators as Companions) that recognizes the important role of play in child development and targets children who are prevented from or inhibited in playing. The project investigates the role of an interactive, autonomous robotic toy in therapy and education for children with special needs. This paper specifically addresses the therapeutic and educational objectives related to children with autism. In recent years, robots have already been used to teach basic social interaction skills to children with autism. The added value of the IROMEC robot is that play scenarios have been developed taking children's specific strengths and needs into consideration and covering a wide range of objectives in children's development areas (sensory, communicational and interaction, motor, cognitive and social and emotional). The paper describes children's developmental areas and illustrates how different experiences and interactions with the IROMEC robot are designed to target objectives in these areas.Final Published versio

Do Social Conditions Affect Capuchin Monkeys’ (Cebus apella) Choices in a Quantity Judgment Task?

Beran et al. (2012) reported that capuchin monkeys closely matched the performance of humans in a quantity judgment test in which information was incomplete but a judgment still had to be made. In each test session, subjects first made quantity judgments between two known options. Then, they made choices where only one option was visible. Both humans and capuchin monkeyswere guided by past outcomes, as they shifted from selecting a known option to selecting an unknown option at the point at which the known option went from being more than the average rate of return to less than the average rate of return from earlier choices in the test session. Here, we expanded this assessment of what guides quantity judgment choice behavior in the face of incomplete information to include manipulations to the unselected quantity.We manipulated the unchosen set in two ways: first, we showed the monkeys what they did not get (the unchosen set), anticipating that “losses” would weigh heavily on subsequent trials in which the same known quantity was presented. Second, we sometimes gave the unchosen set to another monkey, anticipating that this social manipulation might influence the risk-taking responses of the focal monkey when faced with incomplete information. However, neither manipulation caused difficulty for the monkeys who instead continued to use the rational strategy of choosing known sets when they were as large as or larger than the average rate of return in the session, and choosing the unknown (riskier) set when the known set was not sufficiently large. As in past experiments, this was true across a variety of daily ranges of quantities, indicating that monkeys were not using some absolute quantity as a threshold for selecting (or not) the known set, but instead continued to use the daily average rate of return to determine when to choose the known versus the unknown quantity

Management Issues and Their Relative Priority within State Fisheries Agencies

For researchers and managers to work together for greatest mutual benefit, researchers must understand what issues fisheries managers consider most important. To assess management priorities, we conducted a mail survey asking U.S. state fisheries agencies to identify the priority, based on personnel time, they place on 12 fisheries management issues. Based on an 88% response rate, we determined relative emphases across (1) management issues, (2) geographic regions, and (3) freshwater or marine orientations. Issues directly linked to sport and commercial fishers, i.e., stocking, harvest regulations, fishing pressure, and exploring recruitment, were of paramount importance in all agency time budgets. The issue that included conflict, policy, and human dimensions concerns also was identified as "high priority." Six other issueshabitat restoration, hydropower licensing, instream flow, contaminants, introduced species, and nongame species-were of "moderate priority" nationwide. Approximately 50% of the issues varied in emphases across geographic region, and five issues were differentially emphasized in agencies with freshwater and marine responsibilities. To solve persistent problems that plague fisheries management, agencies must clearly identify high-priority management concerns and communicate their specific problem-solving needs to researchers. Results of this survey should provide a first step in identifying these management priorities and research needs

4-Bromo-2H-1,3-oxazine-2,6(3H)-dione

The title compound, C4H2BrNO3, is one of a series of three substituted oxauracils prepared as precursors in the preparation of 1-aza-1,3-butadienes. Although each structure has identical potential for N—H⋯O inter­molecular hydrogen bonds, each forms a distinctive inter­molecular network. In the title compound, there are two independent mol­ecules in the asymmetric unit, with a non-crystallographic twofold screw-like relationship between them. The two indpendent mol­ecules are linked by an inter­molecular N—H⋯O hydrogen bond. In the crystal structure, this hydrogen-bonded pair is linked to translationally related mol­ecules through further inter­molecular N—H⋯O hydrogen bonds, forming one-dimensional chains along [100]. The crystal structure also has short Br⋯O=C inter­molecular contacts with distances of 2.843 (4) and 2.852 (4) Å

Art+Politics

For the exhibition Art + Politics, students worked closely with the holdings of Gettysburg College\u27s Special Collections and College Archives to curate an exhibition in Schmucker Art Gallery that engages with issues of public policy, activism, war, propaganda, and other critical socio-political themes. Each of the students worked diligently to contextualize the objects historically, politically, and art-historically. The art and artifacts presented in this exhibition reveal how various political events and social issues have been interpreted through various visual and printed materials, including posters, pins, illustrations, song sheets, as well as a Chinese shoe for bound feet. The students\u27 essays that follow demonstrate careful research and thoughtful reflection on the American Civil War, nineteenth-century politics, the First and Second World Wars, World\u27s Fairs, Dwight D. Eisenhower\u27s campaign, Vietnam-War era protests, and the Cultural Revolution in China. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1009/thumbnail.jp