Turbulence and Mixing in the Intracluster Medium

The intracluster medium (ICM) is stably stratified in the hydrodynamic sense with the entropy $s$ increasing outwards. However, thermal conduction along magnetic field lines fundamentally changes the stability of the ICM, leading to the "heat-flux buoyancy instability" when $dT/dr>0$ and the "magnetothermal instability" when $dT/dr<0$. The ICM is thus buoyantly unstable regardless of the signs of $dT/dr$ and $ds/dr$. On the other hand, these temperature-gradient-driven instabilities saturate by reorienting the magnetic field (perpendicular to $\hat{\bf r}$ when $dT/dr>0$ and parallel to $\hat{\bf r}$ when $dT/dr<0$), without generating sustained convection. We show that after an anisotropically conducting plasma reaches this nonlinearly stable magnetic configuration, it experiences a buoyant restoring force that resists further distortions of the magnetic field. This restoring force is analogous to the buoyant restoring force experienced by a stably stratified adiabatic plasma. We argue that in order for a driving mechanism (e.g, galaxy motions or cosmic-ray buoyancy) to overcome this restoring force and generate turbulence in the ICM, the strength of the driving must exceed a threshold, corresponding to turbulent velocities $\gtrsim 10 -100 {km/s}$. For weaker driving, the ICM remains in its nonlinearly stable magnetic configuration, and turbulent mixing is effectively absent. We discuss the implications of these findings for the turbulent diffusion of metals and heat in the ICM.Comment: 8 pages, 2 figs., submitted to the conference proceedings of "The Monster's Fiery Breath;" a follow up of arXiv:0901.4786 focusing on the general mixing properties of the IC

Immersive Learning Research Network

Computer games have now been around for over three decades and the term serious games has been attributed to the use of computer games that are thought to have educational value. Game-based learning (GBL) has been applied in a number of different fields such as medicine, languages and software engineering. Furthermore, serious games can be a very effective as an instructional tool and can assist learning by providing an alternative way of presenting instructions and content on a supplementary level, and can promote student motivation and interest in subject matter resulting in enhanced learning effectiveness. REVLAW (Real and Virtual Reality Law) is a research project that the departments of Law and Computer Science of Westminster University have proposed as a new framework in which law students can explore a real case scenario using Virtual Reality (VR) technology to discover important pieces of evidence from a real-given scenario and make up their mind over the crime case if this is a murder or not. REVLAW integrates the immersion into VR as the perception of being physically present in a non-physical world. The paper presents the prototype framework and the mechanics used to make students focus on the crime case and make the best use of this immersive learning approach

Daytime ClO over McMurdo in September 1987: Altitude profile retrieval accuracy

During the 1987 National Ozone Expedition, mm-wave emission line spectra of the 278.6 GHz rotational stratospheric ClO were observed at McMurdo Station, Antarctica. The results confirm the 1986 discovery of a lower stratospheric layer with approximately 100 times the normal amount of ClO; the 1987 observations, made with a spectrometer bandwidth twice that used in 1986, make possible a more accurate retrieval of the altitude profile of the low altitude component of stratospheric ClO from the pressure broadened line shape, down to approximately 16 km. The accuracy of the altitude profile retrievals is discussed, using the daytime (09:30 to 19:30, local time) data from 20 to 24 September, 1987 as an example. The signal strength averaged over this daytime period is approx. 85 percent of the midday peak value. The rate of ozone depletion implied by the observed ClO densities is also discussed

Quantitative observations of the behavior of anomalous low altitude ClO in the Antarctic spring Stratosphere, 1987

During the second National Ozone Expedition ground-based observations at McMurdo Station Antarctica were performed which resulted in a second season's measurement of abnormally large amounts of ClO in the Antarctic spring stratosphere. The original measurements of 1986, in which the presence of this anomalous layer was first discovered, were limited in low altitude recovery of the ClO mixing ratio profile by the restrictions of the spectral bandwidth (256 MHz) which was used to measure the pressure-broadened ClO emission line shape. The 1987 measurements were marked by the use of twice the spectral bandpass employed the previous year, and allow a better characterization of the ClO mixing ratio profile in the critical altitude range 18 to 25 km. In-situ aircraft measurements of ClO made over the Palmer Peninsula during Aug. and Sept. of 1987 by Anderson, et al. effectively determined the important question of the ClO mixing ratio profile at altitudes inaccessible to our technique, below approximately 18 to 18.5 km. These flights did not penetrate further than 75 deg S, however, (vs 78 deg S for McMurdo) and were thus limited to coverage near the outer boundaries of the region of severest ozone depletion over Antarctica in 1987, did not reach an altitude convincingly above that of the peak mixing ratio for ClO, and were not able to make significant observations of the diurnal variation of ClO. The two techniques, and the body of data recovered by each, thus complement one another in producing a full picture of the anomalous ClO layer intimately connected with the region of Antarctic spring ozone depletion. An analysis is presented of the mixing ratio profile from approximately 18 to 45 km, the diurnal behavior, and the secular change in ClO over McMurdo Station during Sept. and early Oct. 1987

Arizona’s Rising STEM Occupational Demands and Declining Participation in the Scientific Workforce: An Examination of Attitudes among African Americans toward STEM College Majors and Careers

According to the Bureau of Labor Statistics (2008), science, technology, engineering, and math (STEM) occupations constitute a growing sector of Arizona’s economy. However, the number of African Americans earning degrees related to these occupations has not kept pace with this growth. Increasing the participation of African Americans in STEM education fields and subsequent related occupations in Arizona is vital to growing and maintaining the state’s economic stature. This objective is made even more compelling given that each year, from 2008– 2018, there are 3,671 projected job openings in STEM fields in Arizona. This study explores the extent to which the attitudes held by African Americans in Arizona toward STEM related majors and careers influence their likelihood of joining the state’s scientific workforce. Our analyses reveal the importance of career consideration, confidence in one’s ability to be successful in a STEM related field, and family support of the pursuit of STEM education and careers.Educatio

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

Inherent noise can facilitate coherence in collective swarm motion

Among the most striking aspects of the movement of many animal groups are their sudden coherent changes in direction. Recent observations of locusts and starlings have shown that this directional switching is an intrinsic property of their motion. Similar direction switches are seen in self-propelled particle and other models of group motion. Comprehending the factors that determine such switches is key to understanding the movement of these groups. Here, we adopt a coarse-grained approach to the study of directional switching in a self-propelled particle model assuming an underlying one-dimensional Fokker–Planck equation for the mean velocity of the particles. We continue with this assumption in analyzing experimental data on locusts and use a similar systematic Fokker–Planck equation coefficient estimation approach to extract the relevant information for the assumed Fokker–Planck equation underlying that experimental data. In the experiment itself the motion of groups of 5 to 100 locust nymphs was investigated in a homogeneous laboratory environment, helping us to establish the intrinsic dynamics of locust marching bands. We determine the mean time between direction switches as a function of group density for the experimental data and the self-propelled particle model. This systematic approach allows us to identify key differences between the experimental data and the model, revealing that individual locusts appear to increase the randomness of their movements in response to a loss of alignment by the group. We give a quantitative description of how locusts use noise to maintain swarm alignment. We discuss further how properties of individual animal behavior, inferred by using the Fokker–Planck equation coefficient estimation approach, can be implemented in the self-propelled particle model to replicate qualitatively the group level dynamics seen in the experimental data

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

Phenotypic properties of transmitted founder HIV-1

Defining the virus–host interactions responsible for HIV-1 transmission, including the phenotypic requirements of viruses capable of establishing de novo infections, could be important for AIDS vaccine development. Previous analyses have failed to identify phenotypic properties other than chemokine receptor 5 (CCR5) and CD4+ T-cell tropism that are preferentially associated with viral transmission. However, most of these studies were limited to examining envelope (Env) function in the context of pseudoviruses. Here, we generated infectious molecular clones of transmitted founder (TF; n = 27) and chronic control (CC; n = 14) viruses of subtypes B (n = 18) and C (n = 23) and compared their phenotypic properties in assays specifically designed to probe the earliest stages of HIV-1 infection. We found that TF virions were 1.7-fold more infectious (P = 0.049) and contained 1.9-fold more Env per particle (P = 0.048) compared with CC viruses. TF viruses were also captured by monocyte-derived dendritic cells 1.7-fold more efficiently (P = 0.035) and more readily transferred to CD4+ T cells (P = 0.025). In primary CD4+ T cells, TF and CC viruses replicated with comparable kinetics; however, when propagated in the presence of IFN-α, TF viruses replicated to higher titers than CC viruses. This difference was significant for subtype B (P = 0.000013) but not subtype C (P = 0.53) viruses, possibly reflecting demographic differences of the respective patient cohorts. Together, these data indicate that TF viruses are enriched for higher Env content, enhanced cell-free infectivity, improved dendritic cell interaction, and relative IFN-α resistance. These viral properties, which likely act in concert, should be considered in the development and testing of AIDS vaccines