The Social Diffusion of Influence Among Adolescents: Group Interaction in a Chat Room Environment About Antidrug Advertisements

One route to influence in mass communication campaigns to reduce risky behavior is through interpersonal discussion of the content of the campaign and other behaviors pertinent to those targeted by the campaign. The goal of this study was to test the effects of online group interaction among adolescents about anti-marijuana advertisements on relevant attitudes and behaviors. A between subjects post only experimental design was used to test two crossed factors, online chat and strength of arguments in antidrug ads. A sample of 535 students was randomly assigned to one of four conditions: chat and strong argument ads, chat and weak argument ads, no chat and strong argument ads, and no chat and weak argument ads. The group interactions about antidrug ads lead to negative effects such that those who chatted reported more pro-marijuana attitudes and subjective normative beliefs than those who just viewed the ads. No support was found for the hypothesis that strong argument ads would result in more antidrug beliefs relative to weak argument ads in either the chat or the no chat conditions. Overall, these findings suggest that viewing antidrug ads and discussing them with peers may result in deleterious effects in adolescents

Black hole feedback and the evolution of massive early-type galaxies

Observationally, constraining the baryonic cycle within massive galaxies has proven to be quite difficult. In particular, the role of black hole feedback in regulating star formation, a key process in our theoretical understanding of galaxy formation, remains highly debated. We present here observational evidence showing that, at fixed stellar velocity dispersion, the temperature of the hot gas is higher for those galaxies hosting more massive black holes in their centers. Analyzed in the context of well-established scaling relations, particularly the mass-size plane, the relation between the mass of the black hole and the temperature of the hot gas around massive galaxies provides further observational support to the idea that baryonic processes within massive galaxies are regulated by the combined effects of the galaxy halo virial temperature and black hole feedback, in agreement with the expectations from the EAGLE cosmological numerical simulation.Comment: 10 pages, 5 figure, accepted for publication in MNRAS

Exact longitudinal plasmon dispersion relations for one and two dimensional Wigner crystals

We derive the exact longitudinal plasmon dispersion relations, $\omega(k)$ of classical one and two dimensional Wigner crystals at T=0 from the real space equations of motion, of which properly accounts for the full unscreened Coulomb interactions. We make use of the polylogarithm function in order to evaluate the infinite lattice sums of the electrostatic force constants. From our exact results we recover the correct long-wavelength behavior of previous approximate methods. In 1D, $\omega(k) \sim | k |\log ^{1/2} (1/k)$, validating the known RPA and bosonization form. In 2D $\omega(k) \sim \sqrt k$, agreeing remarkably with the celebrated Ewald summation result. Additionally, we extend this analysis to calculate the band structure of tight-binding models of non-interacting electrons with arbitrary power law hopping.Comment: 4 pages, 1 figure. Important typos and errors fixed, 2D dispersion adde

Hierarchy of exchange interactions in the triangular-lattice spin-liquid YbMgGaO4_{4}

The spin-1/2 triangular lattice antiferromagnet YbMgGaO$_{4}$ has attracted recent attention as a quantum spin-liquid candidate with the possible presence of off-diagonal anisotropic exchange interactions induced by spin-orbit coupling. Whether a quantum spin-liquid is stabilized or not depends on the interplay of various exchange interactions with chemical disorder that is inherent to the layered structure of the compound. We combine time-domain terahertz spectroscopy and inelastic neutron scattering measurements in the field polarized state of YbMgGaO$_{4}$ to obtain better microscopic insights on its exchange interactions. Terahertz spectroscopy in this fashion functions as high-field electron spin resonance and probes the spin-wave excitations at the Brillouin zone center, ideally complementing neutron scattering. A global spin-wave fit to all our spectroscopic data at fields over 4T, informed by the analysis of the terahertz spectroscopy linewidths, yields stringent constraints on $g$-factors and exchange interactions. Our results paint YbMgGaO$_{4}$ as an easy-plane XXZ antiferromagnet with the combined and necessary presence of sub-leading next-nearest neighbor and weak anisotropic off-diagonal nearest-neighbor interactions. Moreover, the obtained $g$-factors are substantially different from previous reports. This works establishes the hierarchy of exchange interactions in YbMgGaO$_{4}$ from high-field data alone and thus strongly constrains possible mechanisms responsible for the observed spin-liquid phenomenology

Delayed Recognition of Acute Stroke by Emergency Department Staff Following Failure to Activate Stroke by Emergency Medical Services

Introduction: Early recognition and pre-notification by emergency medical services (EMS) improves the timeliness of emergency department (ED) stroke care; however, little is known regarding the effects on care should EMS providers fail to pre-notify. We sought to determine if potential stroke patients transported by EMS, but for whom EMS did not provide pre-notification, suffer delays in ED door-to-stroke-team activation (DTA) as compared to the other available cohort of patients for whom the ED is not pre-notified-those arriving by private vehicle. Methods: We queried our prospective stroke registry to identify consecutive stroke team activation patients over 12 months and retrospectively reviewed the electronic health record for each patient to validate registry data and abstract other clinical and operational data. We compared patients arriving by private vehicle to those arriving by EMS without pre-notification, and we employed a multivariable, penalized regression model to assess the probability of meeting the national DTA goal of \u3c /=15 minutes, controlling for a variety of clinical factors. Results: Our inclusion criteria were met by 200 patients. Overall performance of the regression model was excellent (area under the curve 0.929). Arrival via EMS without pre-notification, compared to arrival by private vehicle, was associated with an adjusted risk ratio of 0.55 (95% confidence interval, 0.27-0.96) for achieving DTA \u3c /= 15 minutes. Conclusion: Our single-center data demonstrate that potential stroke patients arriving via EMS without pre-notification are less likely to meet the national DTA goal than patients arriving via other means. These data suggest a negative, unintended consequence of otherwise highly successful EMS efforts to improve stroke care, the root of which may be ED staff over-reliance on EMS for stroke recognition

Towards the use of situational information in information retrieval

This paper is an exploratory study of one approach to incorporating situational information into information retrieval systems, drawing on principles and methods of discourse linguistics. A tenet of discourse linguistics is that texts of a specific type possess a structure above the syntactic level, which follows conventions known to the people using such texts to communicate. In some cases, such as literature describing work done, the structure is closely related to situations, and may therefore be a useful representational vehicle for the present purpose. Abstracts of empirical research papers exhibit a well-defined discourse- level structure, which is revealed by lexical clues. Two methods of detecting the structure automatically are presented: (i) a Bayesian probabilistic analysis; and (ii) a neural network model. Both methods show promise in preliminary implementations. A study of users\u27 oral problem statements indicates that they are not amenable to the same kind of processing. However, from in-depth interviews with users and search intermediaries, the following conclusions are drawn: (i) the notion of a generic research script is meaningful to both users and intermediaries as a high-level description of situation; (ii) a researcher\u27s position in the script is a predictor of the relevance of documents; and (iii) currently, intermediaries can make very little use of situational information. The implications of these findings for system design are discussed, and a system structure presented to serve as a framework for future experimental work on the factors identified in this paper. The design calls for a dialogue with the user on his or her position in a research script and incorporates features permitting discourse-level components of abstracts to be specified in search strategies

Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814

We report photometry of 1RXS J232953.9+062814, a recently discovered dwarf nova with a remarkably short 64.2-minute orbital period. In quiescence, the star's light curve is that of a double sinusoid, arising from the "ellipsoidal" distortion of the Roche-lobe-filling secondary. During superoutburst, common superhumps develop with a period 3-4% longer than P_orb. This indicates a mass ratio M_2/M_1=0.19+-0.02, a surprisingly large value in so compact a binary. This implies that the secondary star has a density 2-3 times higher than that of other short-period dwarf novae, suggesting a secondary enriched by H-burning prior to the common-envelope phase of evolution. We estimate i=50+-5 deg, M_1=0.63 (+0.12, -0.09) M_sol, M_2=0.12 (+0.03, -0.02) M_sol, R_2=0.121 (+0.010, -0.007) R_sol, and a distance to the binary of 180+-40 pc.Comment: PDF, 17 pages, 3 tables, 5 figures; accepted, in press, to appear June 2002, PASP; more info at http://cba.phys.columbia.edu

Analysis of Fibrous Felts for Flexible Ablators Using Synchrotron Hard X-Ray Micro-Tomography

We analyzed the material properties of low-density felts that are used as substrates for new-generation flexible and conformal carbon/phenolic ablators, and compared them with those of a rigid carbon fiber preform that is used to manufacture rigid carbon/phenolic ablators. Micro-tomography measurements were obtained using synchrotron X-rays, allowing the characterization of the materials microstructure at the scale of the fibers. Using the tomography voxels as computational grids, we computed tortuosity and room temperature conductivity. In addition we performed micro-scale simulations of the oxidation of carbon fibers using a random walk model for oxygen diffusion and a probability law to model surface reactions