Agent Street: An Environment for Exploring Agent-Based Models in Second Life

Urban models can be seen on a continuum between iconic and symbolic. Generally speaking, iconic models are physical versions of the real world at some scaled down representation, while symbolic models represent the system in terms of the way they function replacing the physical or material system by some logical and/or mathematical formulae. Traditionally iconic and symbolic models were distinct classes of model but due to the rise of digital computing the distinction between the two is becoming blurred, with symbolic models being embedded into iconic models. However, such models tend to be single user. This paper demonstrates how 3D symbolic models in the form of agent-based simulations can be embedded into iconic models using the multi-user virtual world of Second Life. Furthermore, the paper demonstrates Second Life\'s potential for social science simulation. To demonstrate this, we first introduce Second Life and provide two exemplar models; Conway\'s Game of Life, and Schelling\'s Segregation Model which highlight how symbolic models can be viewed in an iconic environment. We then present a simple pedestrian evacuation model which merges the iconic and symbolic together and extends the model to directly incorporate avatars and agents in the same environment illustrating how \'real\' participants can influence simulation outcomes. Such examples demonstrate the potential for creating highly visual, immersive, interactive agent-based models for social scientists in multi-user real time virtual worlds. The paper concludes with some final comments on problems with representing models in current virtual worlds and future avenues of research.Agent-Based Modelling, Pedestrian Evacuation, Segregation, Virtual Worlds, Second Life

Small Solutions to the Large Telescope Problem: A Massively Replicated MEMS Spectrograph

In traditional seeing-limited observations the spectrograph aperture scales with telescope aperture, driving sizes and costs to enormous proportions. We propose a new solution to the seeing-limited spectrograph problem. A massively fiber-sliced configuration feeds a set of small diffraction-limited spectrographs. We present a prototype, tunable, J-band, diffraction grating, designed specifically for Astronomical applications: The grating sits at the heart of a spectrograph, no bigger than a few inches on a side. Throughput requirements dictate using tens-of-thousands of spectrographs on a single 10 to 30 meter telescope. A full system would cost significantly less than typical instruments on 10m or 30m telescopes.Comment: 9 pages, 5 figures, presented at SPIE Astronomical Telescopes and Instrumentation, 23 - 28 June 2008, Marseille, France. See http://www.ucolick.org/~npk/MEMS for video

Effects of flavor-symmetry violation from staggered fermion lattice simulations of graphene

We analyze the effects of flavor splitting from staggered fermion lattice simulations of graphene. Both the unimproved action, and the tadpole improved action with a Naik term show significant flavor symmetry breaking in the spectrum of the Dirac operator. We also measure the average plaquette term and describe how it calls for a reinterpretation of previous lattice Monte Carlo simulation results, due to tadpole improvement. From this we infer that the simulations are indicative of a semi-metal phase for suspended graphene.Comment: 7 pages, 5 figures; v2. added results for noncompact gauge action; v3. added results for stout smearing, corrected rescaling of coupling, published versio

Prison officer\u27s beliefs regarding self-harm in prisoners : an empirical investigation

The prevention of self-harm and suicide in prisoners depends on good interaction between the individual prisoner and prison staff. Staff perceptions of prisoner self-harm are likely to be a crucial factor influencing this interaction. The aim of the present study was to determine correctional officers\u27 perception of the causes and functions of self-harm, and the effects of incident severity and repetitiveness on perceptions. A sample of 76 correctional officers was presented with a vignette depicting a self-harm in which the severity and repetitiveness of the incident was systematically altered. Officers\u27 rated both the causes and functions of the behaviour. Four attributional dimensions were identified by factor analysis. These factors related primarily to personal factors about the individual prisoner. Staff perceived the functions of self-harm to be communicative rather than to commit suicide. Perceptions were not affected by severity or repetitiveness information, except for high severity leading to a greater perception of suicidal intent. Initiatives to help staff work more effectively and therapeutically with distressed prisoners are therefore likely to impact positively upon rates of self-harm.<br /

New Complexity Bounds for Certain Real Fewnomial Zero Sets

Consider real bivariate polynomials f and g, respectively having 3 and m monomial terms. We prove that for all m>=3, there are systems of the form (f,g) having exactly 2m-1 roots in the positive quadrant. Even examples with m=4 having 7 positive roots were unknown before this paper, so we detail an explicit example of this form. We also present an O(n^{11}) upper bound for the number of diffeotopy types of the real zero set of an n-variate polynomial with n+4 monomial terms.Comment: 8 pages, no figures. Extended abstract accepted and presented at MEGA (Effective Methods in Algebraic Geometry) 200

Magnetic phase diagram of a spin-1 condensate in two dimensions with dipole interaction

Several new features arise in the ground-state phase diagram of a spin-1 condensate trapped in an optical trap when the magnetic dipole interaction between the atoms is taken into account along with confinement and spin precession. The boundaries between the regions of ferromagnetic and polar phases move as the dipole strength is varied and the ferromagnetic phases can be modulated. The magnetization of the ferromagnetic phase perpendicular to the field becomes modulated as a helix winding around the magnetic field direction, with a wavelength inversely proportional to the dipole strength. This modulation should be observable for current experimental parameters in $^{87}$Rb. Hence the much-sought supersolid state, with broken continuous translation invariance in one direction and broken global U(1) invariance, occurs generically as a metastable state in this system as a result of dipole interaction. The ferromagnetic state parallel to the applied magnetic field becomes striped in a finite system at strong dipolar coupling.Comment: 11 pages, 7 figures;published versio

Arsenic uptake by beets (Beta Vulgaris) cultivated in a roxarsone-contaminated medium

Arsenic (As) is a global toxicant that negatively impacts human health. Roxarsone (ROX) is an organoarsenical administered to poultry to control internal parasites. ROX is excreted from poultry unchanged and the waste may be used for vegetable fertilizer. This experiment was conducted with beets (Beta vulgaris) by adding 0, 1, 10, and 100 mg/kg As (T1, T2, T3, and T4 respectively, with ROX, presented as As concentrations) to a growing medium prepared with topsoil and other ingredients in a greenhouse pot experiment. The study aimed to determine effects of As-contaminated soils on biomass production, uptake of As by beets, and allocation of As to tissues. Results showed that biomass production of beets was negatively correlated with As concentrations in the growing medium (r = -0.3286, p \u3c 0.0001). As uptake by beets was positively correlated with As concentrations in the growing medium (roots, rs= 0.7577, p \u3c 0.0001; shoots, rs = 0.8406, p \u3c 0.0001). As uptake by beets was observed with median values in the roots of 0.267 ± 0.004 mg/kg, 0.271 ± 0.001 mg/kg, 0.271 ± 0.289 mg/kg, and 3.76 ± 1.92 mg/kg for T 1 , T 2 , T 3 , and T 4 respectively ; the shoots took up 0.259 ± 0.006 mg/kg, 0. 263 ± 0.313 mg/kg, 0.271 ± 0.373 mg/kg, and 3.94 ± 0.72 mg/kg for the respective treatments. Beets took up 4.3 ± 2.3% of available As and distributed it equally into tissues. The results suggest that As could be transferred to humans through the food chain via beet consumption