Isospin in Reaction Dynamics. The Case of Dissipative Collisions at Fermi Energies

A key question in the physics of unstable nuclei is the knowledge of the $EOS$ for asymmetric nuclear matter ($ANM$) away from normal conditions. We recall that the symmetry energy at low densities has important effects on the neutron skin structure, while the knowledge in high densities region is crucial for supernovae dynamics and neutron star properties. The $only$ way to probe such region of the isovector $EOS$ in terrestrial laboratories is through very dissipative collisions of asymmetric (up to exotic) heavy ions from low to relativistic energies. A general introduction to the topic is firstly presented. We pass then to a detailed discussion on the $neck-fragmentation$ process as the main dissipative mechanism at the Fermi energies and to the related isospin dynamics. From Stochastic Mean Field simulations the isospin effects on all the phases of the reaction dynamics are thoroughly analysed, from the fast nucleon emission to the mid-rapidity fragment formation up to the dynamical fission of the $spectator$ residues. Simulations have been performed with an increasing stiffness of the symmetry term of the $EOS$. Some differences have been noticed, especially for the fragment charge asymmetry. New isospin effects have been revealed from the correlation of fragment asymmetry with dynamical quantities at the freeze-out time. A series of isospin sensitive observables to be further measured are finally listed.Comment: 16 pages, 6 figures, Contribution to the 5th Italy-Japan Symposium, Recent Achievements and Perspectives in Nuclear Physics, Naples Nov.3-7 2004, World Sci. in press. Latex in WorldSci/proc/styl

The Affine Structure of Gravitational Theories: Symplectic Groups and Geometry

We give a geometrical description of gravitational theories from the viewpoint of symmetries and affine structure. We show how gravity, considered as a gauge theory, can be consistently achieved by the nonlinear realization of the conformal-affine group in an indirect manner: due the partial isomorphism between $CA\left( 3,1\right)$ and the centrally extended $Sp\left( 8\right)$, we perform a nonlinear realization of the centrally extended (CE)$Sp\left( 8\right)$ in its semi-simple version. In particular, starting from the bundle structure of gravity, we derive the conformal-affine Lie algebra and then, by the non-linear realization, we define the coset field transformations, the Cartan forms and the inverse Higgs constraints. Finally we discuss the geometrical Lagrangians where all the information on matter fields and their interactions can be contained.Comment: 21 pages. arXiv admin note: text overlap with arXiv:0910.2881, arXiv:0705.460

The Proteus Effect and Gaming: The Impact of Digital Actors and Race in a Virtual Environment

Race and racial identity is a frequently discussed topic in the media today. This topic is driven by what oftentimes amounts to culture clashes, and a system that claims impartiality yet is rampant with implicit bias demonstrating favorable treatment of one race over another. An example of this favoritism resides within video game design, where over 50% of player-controlled game characters are White, and less than 40% are Black (Leonard, 2007). Leonard also wrote that Black game characters are more likely to conform to Black stereotypes (e.g. play sports, or involved in gangs) than Whites (e.g. middle class citizen or unhygienic). Minimal research exists on understanding what information a video game character, or avatar, conveys to a game player, and whether this information is platform dependent or not. Furthermore, limited information exists on what the personification of agency really means within a digital environment. The purpose of this study was to examine the relationship that race may exert within video game play and, by extension, video game design in regards to the control of in-game avatars. Moreover, the goal is to determine if the Proteus effect, the central psychological theory under analysis, exists for console video game players in regards to race and skin color. Originating from the world of virtual reality, the Proteus effect emphasizes conformity to an avatar’s identity cues (Yee & Bailenson, 2007). Specifically, this study examines how the similarity or mismatch between in game avatars and the individual controlling them affects game-world behaviors. Ninety male university students comprised of 3 different races (Middle Eastern, African American, and Caucasian American) played Grand Theft Auto V (GTAV) on PlayStation 3 with an assignment of either White (Michael) or Black (Franklin) game character condition. Data were collected on a behavioral metric with two primary categories: Crime against people and crimes against property. They also completed a personality inventory (HEXACO), and performed an implicit association task to further scientific exploration of the Proteus effect. The results indicated that behavioral outcomes between the Middle-Eastern and Caucasian Americans contained significant differences, and this was regardless of their digital actor (DA) assignment. However, African American gamers had significant performance differences between the two DA conditions (White, Black); there were more crimes committed against in-game people and in-game property when playing as a White DA than when playing as a Black DA when compared against the other two groups. For the game play itself, no significant performance differences were observed between the White and Black DA conditions when collapsed across race conditions indicating that the platform selected offered equal opportunity for all gamers, and that one DA did not facilitate extra crimes above and beyond the other DA. Personality factors were controlled for through the use of the HEXACO model and demonstrated that the three faces did not significantly differ in terms of personality. However, when considering game play and crime specifically, individuals scoring high in the Honesty-Humility dimension of the personality inventory committed fewer crimes against property during their gameplay as indicated by a significant regression analysis. The Proteus effect exists for console video games, and was observed within this study because a change in self representation via the DA caused an observable change in behavior. The African American participants experimentally depicted this in that they committed significantly less crimes while playing as a Black DA than the crimes they committed while playing as a White DA that did not occur for the other two races. The significance of this finding lies in the fact that this discovery bolsters understanding of DA-man relationships, and the nature of agency within digital environments. This study also demonstrates that DAs can alter gameplay, and the gaming community needs richer designs incorporating racial inclusivity within video games

From Seed to Sky: Impacts of explosive compounds on vegetation across spatial and developmental scales

Explosive compounds are broadly distributed across the globe as a result of nearly two centuries of munitions use in warfare and military activities. Two explosive compounds have seen disproportionate use; RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and TNT (2-methyl- 1,3,5-trinitrobenzene), being the most commonly found explosives in the environment. The effects of explosives on biota have been studied in great detail; however, there is a general lack of understanding with regard to broader ecological impacts of these contaminants. My dissertation objective was to follow the impacts of explosive compounds on vegetation across scales. Impacts on vegetation at the species scale alter community composition via species-specific and age-specific responses to explosives. Results presented here showed that contaminated soils induced a variety of responses in vegetation, yet impacts to water relations were similar regardless of species. Use of novel metrics in monitoring plant responses to explosives compounds aided in delineation of reference and treatment groups. At the community scale the presence of explosives induced species and functional composition shifts. The observed shifts are likely due to physiological impairment as individuals in the field exhibited significant impacts to physiological functions. Effects of explosives contamination also detectable using remote sensing techniques. Impacts to plant morphology and physiology are directly related to community level shifts observed in long contaminated areas. This highlights the long lasting impacts that these largely overlooked contaminants can have on a system and opens avenues for new, at range, vegetation based contaminant detection systems

Pathology and Motivation in Players of Grand Theft Auto IV

Intrinsically motivated behavior is defined as a behavior that is performed for pure enjoyment (Ryan, Rigby & Przybylski, 2006). Video game playing is a form of intrinsically motivated behavior (Frederick & Ryan, 1995). Popular media commonly claims the act of playing video games leads individuals to behave in deviant and antisocial ways outside the confines of the gaming environment (Grossman & Christensen, 2008). Psychopathy is a primary feature of Antisocial Personality Disorder, according to the American Psychiatric Association (2013), and psychopathic criminals commit the greatest variety of crimes and more crimes of any type than the average criminal (Lynam, Whiteside & Jones, 1999,). The present study assessed 80 male college students on their level of psychopathy and the virtual crimes they committed while playing Grand Theft Auto IV to determine if game players with naturally high levels of psychopathy performed differently than their non-psychopathic counterparts, and subsequently to determine if the crimes committed during game play were modified and/or qualified by psychopathic scores. Correlational analysis revealed psychopathy scores positively relate to virtual crimes against people, but not to crimes against property. Results also showed that virtual crimes against property were negatively correlated to the intrinsic motivation subscale of Relatedness, with crimes against people having no significant self-reported intrinsic motivational outcome. A regression analysis revealed the subscale of Effort/Importance positively related to the psychopathy scores of the participants. Results are reasonably set forth in the vastly unexplored environment of human behavior, motivation, and expectations in video gaming

"Magic" numbers in Smale's 7th problem

Smale's 7-th problem concerns N-point configurations on the 2-dim sphere which minimize the logarithmic pair-energy V_0(r) = -ln r averaged over the pairs in a configuration; here, r is the chordal distance between the points forming a pair. More generally, V_0(r) may be replaced by the standardized Riesz pair-energy V_s(r)= (r^{-s} -1)/s, which becomes - ln r in the limit s to 0, and the sphere may be replaced by other compact manifolds. This paper inquires into the concavity of the map from the integers N>1 into the minimal average standardized Riesz pair-energies v_s(N) of the N-point configurations on the 2-sphere for various real s. It is known that v_s(N) is strictly increasing for each real s, and for s<2 also bounded above, hence "overall concave." It is (easily) proved that v_{-2}(N) is even locally strictly concave, and that so is v_s(2n) for s<-2. By analyzing computer-experimental data of putatively minimal average Riesz pair-energies v_s^x(N) for s in {-1,0,1,2,3} and N in {2,...,200}, it is found that {v}_{-1}^x(N) is locally strictly concave, while v_s^x(N) is not always locally strictly concave for s in {0,1,2,3}: concavity defects occur whenever N in C^{x}_+(s) (an s-specific empirical set of integers). It is found that the empirical map C^{x}_+(s), with s in {-2,-1,0,1,2,3}, is set-theoretically increasing; moreover, the percentage of odd numbers in C^{x}_+(s), s in {0,1,2,3}, is found to increase with s. The integers in C^{x}_+(0) are few and far between, forming a curious sequence of numbers, reminiscent of the "magic numbers" in nuclear physics. It is conjectured that the "magic numbers" in Smale's 7-th problem are associated with optimally symmetric optimal-energy configurations.Comment: 109 pages, of which 30 are numerical data tables. Thoroughly revised version, to appear in J. Stat. Phys. under the different title: `Optimal N point configurations on the sphere: "Magic" numbers and Smale's 7th problem

Test beam Characterizations of 3D Silicon Pixel detectors

3D silicon detectors are characterized by cylindrical electrodes perpendicular to the surface and penetrating into the bulk material in contrast to standard Si detectors with planar electrodes on its top and bottom. This geometry renders them particularly interesting to be used in environments where standard silicon detectors have limitations, such as for example the radiation environment expected in an LHC upgrade. For the first time, several 3D sensors were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip and readout electronics. Devices with different electrode configurations have been characterized in a 100 GeV pion beam at the CERN SPS. Here we report results on unirradiated devices with three 3D electrodes per 50 x 400 um2 pixel area. Full charge collection is obtained already with comparatively low bias voltages around 10 V. Spatial resolution with binary readout is obtained as expected from the cell dimensions. Efficiencies of 95.9% +- 0.1 % for tracks parallel to the electrodes and of 99.9% +- 0.1 % at 15 degrees are measured. The homogeneity of the efficiency over the pixel area and charge sharing are characterized.Comment: 5 pages, 7 figure