692 research outputs found
High Temperature Matter and Gamma Ray Spectra from Microscopic Black Holes
The relativistic viscous fluid equations describing the outflow of high
temperature matter created via Hawking radiation from microscopic black holes
are solved numerically for a realistic equation of state. We focus on black
holes with initial temperatures greater than 100 GeV and lifetimes less than 6
days. The spectra of direct photons and photons from decay are
calculated for energies greater than 1 GeV. We calculate the diffuse gamma ray
spectrum from black holes distributed in our galactic halo. However, the most
promising route for their observation is to search for point sources emitting
gamma rays of ever-increasing energy.Comment: 33 pages, 13 figures, to be submitted to PR
Dynamics of liquid 4He in Vycor
We have measured the dynamic structure factor of liquid 4He in Vycor using
neutron inelastic scattering. Well-defined phonon-roton (p-r) excitations are
observed in the superfluid phase for all wave vectors 0.3 < Q < 2.15. The p-r
energies and lifetimes at low temperature (T = 0.5 K) and their temperature
dependence are the same as in bulk liquid 4He. However, the weight of the
single p-r component does not scale with the superfluid fraction (SF) as it
does in the bulk. In particular, we observe a p-r excitation between T_c =
1.952 K, where SF = 0, and T_(lambda)=2.172 K of the bulk. This suggests, if
the p-r excitation intensity scales with the Bose condensate, that there is a
separation of the Bose-Einstein condensation temperature and the superfluid
transition temperature T_c of 4He in Vycor. We also observe a two-dimensional
layer mode near the roton wave vector. Its dispersion is consistent with
specific heat and SF measurements and with layer modes observed on graphite
surfaces.Comment: 3 pages, 4 figure
Development and characterization of a Yucatan miniature biomedical pig permanent middle cerebral artery occlusion stroke model
BACKGROUND: Efforts to develop stroke treatments have met with limited success despite an intense need to produce novel treatments. The failed translation of many of these therapies in clinical trials has lead to a close examination of the therapeutic development process. One of the major factors believed to be limiting effective screening of these treatments is the absence of an animal model more predictive of human responses to treatments. The pig may potentially fill this gap with a gyrencephalic brain that is larger in size with a more similar gray-white matter composition to humans than traditional stroke animal models. In this study we develop and characterize a novel pig middle cerebral artery occlusion (MCAO) ischemic stroke model. METHODS: Eleven male pigs underwent MCAO surgery with the first 4 landrace pigs utilized to optimize stroke procedure and 7 additional Yucatan stroked pigs studied over a 90Â day period. MRI analysis was done at 24Â hrs and 90Â days and included T2w, T2w FLAIR, T1w FLAIR and DWI sequences and associated ADC maps. Pigs were sacrificed at 90Â days and underwent gross and microscopic histological evaluation. Significance in quantitative changes was determined by two-way analysis of variance and post-hoc Tukeyâs Pair-Wise comparisons. RESULTS: MRI analysis of animals that underwent MCAO surgery at 24Â hrs had hyperintense regions in T2w and DWI images with corresponding ADC maps having hypointense regions indicating cytotoxic edema consistent with an ischemic stroke. At 90Â days, region of interest analysis of T1 FLAIR and ADC maps had an average lesion size of 59.17Â cc, a loss of 8% brain matter. Histological examination of pig brains showed atrophy and loss of tissue, consistent with MRI, as well as glial scar formation and macrophage infiltration. CONCLUSIONS: The MCAO procedure led to significant and consistent strokes with high survivability. These results suggest that the pig model is potentially a robust system for the study of stroke pathophysiology and potential diagnostics and therapeutics
Excitations in confined helium
We design models for helium in matrices like aerogel, Vycor or Geltech from a
manifestly microscopic point of view. For that purpose, we calculate the
dynamic structure function of 4He on Si substrates and between two Si walls as
a function of energy, momentum transfer, and the scattering angle. The
angle--averaged results are in good agreement with the neutron scattering data;
the remaining differences can be attributed to the simplified model used here
for the complex pore structure of the materials. A focus of the present work is
the detailed identification of coexisting layer modes and bulk--like
excitations, and, in the case of thick films, ripplon excitations. Involving
essentially two--dimensional motion of atoms, the layer modes are sensitive to
the scattering angle.Comment: Phys. Rev. B (2003, in press
Gamer Girls: Navigating a Subculture of Gender Inequality
Purpose
Video gaming, which remains culturally embedded in masculine ideals, is increasingly becoming a leisure activity for female consumers. Guided by social dominance theory, this paper examines how female gamers navigate the masculine-oriented gaming consumption context.
Methodology/approach
Eight avid female gamers (ages 20â29) participated in-depth interviews, following a phenomenological approach to better understand their lived experiences with video gaming. Data were analyzed using phenomenological procedures.
Findings
Findings reveal an undercurrent of gender-based consumer vulnerability, driven by stereotypical perceptions of âgamer girlsâ in the masculine-oriented gaming subculture. Further, the findings highlight the multilayered, multidimensional nature of gaming as a vulnerable consumption environment, at individual, marketplace, and cultural levels.
Social implications
The culturally embedded gamer girl stereotype provides a foundation upon which characteristics of consumer vulnerability flourish, including a culture of gender-based consumer harassment, systematic disempowerment in the marketplace, and conflicting actions and attitudes toward future cultural change.
Originality/value
This research suggests female gamers struggle to gain a foothold in gaming due to the socially and culturally constructed masculine dominance of the field. Our research study provides a stepping-stone for future scholars to explore gendered subcultures and begins to address the dynamic interplay of power, gender, technology, and the market
Phase phonon spectrum and melting in a quantum rotor model with diagonal disorder
We study the zero-temperature () quantum rotor model with on-site
disorder in the charging energy. Such a model may serve as an idealized
Hamiltonian for an array of Josephson-coupled small superconducting grains, or
superfluid He in a disordered environment. In the approximation of
small-amplitude phase fluctuations, the Hamiltonian maps onto a system of
coupled harmonic oscillators with on-site disorder. We study the effects of
disorder in this harmonic regime, using the coherent potential approximation
(CPA), obtaining the density of states and the lifetimes of the spin-wave-like
excitations for several choices of the parameters which characterize the
disorder. Finally, we estimate the parameters characterizing the
quantum melting of the phase order, using a suitable Lindemann criterion.Comment: 8 pages, 5 figures. To be published in Phys. Rev. B. Minor change
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Bias in data-driven artificial intelligence systems - An introductory survey
Artificial Intelligence (AI)-based systems are widely employed nowadays to make decisions that have far-reaching impact on individuals and society. Their decisions might affect everyone, everywhere, and anytime, entailing concerns about potential human rights issues. Therefore, it is necessary to move beyond traditional AI algorithms optimized for predictive performance and embed ethical and legal principles in their design, training, and deployment to ensure social good while still benefiting from the huge potential of the AI technology. The goal of this survey is to provide a broad multidisciplinary overview of the area of bias in AI systems, focusing on technical challenges and solutions as well as to suggest new research directions towards approaches well-grounded in a legal frame. In this survey, we focus on data-driven AI, as a large part of AI is powered nowadays by (big) data and powerful machine learning algorithms. If otherwise not specified, we use the general term bias to describe problems related to the gathering or processing of data that might result in prejudiced decisions on the bases of demographic features such as race, sex, and so forth. This article is categorized under: Commercial, Legal, and Ethical Issues > Fairness in Data Mining Commercial, Legal, and Ethical Issues > Ethical Considerations Commercial, Legal, and Ethical Issues > Legal Issues
Bias in data-driven artificial intelligence systemsâAn introductory survey
Artificial Intelligence (AI)-based systems are widely employed nowadays to make decisions that have far-reaching impact on individuals and society. Their decisions might affect everyone, everywhere, and anytime, entailing concerns about potential human rights issues. Therefore, it is necessary to move beyond traditional AI algorithms optimized for predictive performance and embed ethical and legal principles in their design, training, and deployment to ensure social good while still benefiting from the huge potential of the AI technology. The goal of this survey is to provide a broad multidisciplinary overview of the area of bias in AI systems, focusing on technical challenges and solutions as well as to suggest new research directions towards approaches well-grounded in a legal frame. In this survey, we focus on data-driven AI, as a large part of AI is powered nowadays by (big) data and powerful machine learning algorithms. If otherwise not specified, we use the general term bias to describe problems related to the gathering or processing of data that might result in prejudiced decisions on the bases of demographic features such as race, sex, and so forth. This article is categorized under: Commercial, Legal, and Ethical Issues > Fairness in Data Mining Commercial, Legal, and Ethical Issues > Ethical Considerations Commercial, Legal, and Ethical Issues > Legal Issues
Regionalizing the infrastructure turn : a research agenda
An interdisciplinary âinfrastructure turnâ has emerged over the past 20 years that disputes the concept of urban infrastructure as a staid or neutral set of physical artefacts. Responding to the increased conceptual, geographical and political importance of infrastructure â and endemic issues of access, expertise and governance that the varied provision of infrastructures can cause â this intervention asserts the significance of applying a regional perspective to the infrastructure turn. This paper forwards a critical research agenda for the study of âinfrastructural regionalismsâ to interrogate: (1) how we study and produce knowledge about infrastructure; (2) how infrastructure is governed across or constrained by jurisdictional boundaries; (3) who drives the construction of regional infrastructural imaginaries; and (4) how individuals and communities differentially experience regional space through infrastructure. Analysing regions through infrastructure provides a novel perspective on the regional question and consequently offers a framework to understand better the implications of the current infrastructure moment for regional spaces worldwide
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