Coverage Analysis of mmWave and THz-Enabled Aerial and Terrestrial Heterogeneous Networks

Heterogeneous networks (HetNets) are becoming a promising solution for future wireless systems to satisfy the high data rate requirements. This paper introduces a stochastic geometry framework for the analysis of the downlink coverage probability in a multi-tier HetNet consisting of a macro-base station (MBS) operating at sub-6 GHz, millimeter wave (mmWave)-enabled unmanned aerial vehicles (UAVs) operating at 28 GHz, and small BSs operating both at mmWave and THz frequencies. The analytical expressions for the coverage probability for each tier have been derived in the paper. Monte Carlo simulations are then performed to validate the analytical expressions. The effectiveness of the HetNet is analyzed on various performance metrics including association and coverage probabilities for different network parameters. We show that the mmWave and THz-enabled cells provide significant improvement in the achievable data rates because of their high available bandwidths, however, they have a degrading effect on the coverage probability due to their high propagation losses

Gamma Ray Bursts as Probes of Quantum Gravity

Gamma ray bursts (GRBs) are short and intense pulses of $\gamma$-rays arriving from random directions in the sky. Several years ago Amelino-Camelia et al. pointed out that a comparison of time of arrival of photons at different energies from a GRB could be used to measure (or obtain a limit on) possible deviations from a constant speed of light at high photons energies. I review here our current understanding of GRBs and reconsider the possibility of performing these observations.Comment: Lectures given at the 40th winter school of theretical physics: Quantum Gravity and Phenomenology, Feb. 2004 Polan

Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons

We extract at redshift z=0 a Milky Way sized object including gas, stars and dark matter (DM) from a recent, high-resolution cosmological N-body simulation with baryons. Its resolution is sufficient to witness the formation of a rotating disk and bulge at the center of the halo potential. The phase-space structure of the central galactic halo reveals the presence of a dark disk component, that is co-rotating with the stellar disk. At the Earth's location, it contributes to around 25% of the total DM local density, whose value is rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations from pure Gaussian and Maxwellian distributions, with a sharper drop of the high velocity tail. We give a detailed study of the impact of these features on the predictions for DM signals in direct detection experiments. In particular, the question of whether the modulation signal observed by DAMA is or is not excluded by limits set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and compared to the case of a standard Maxwellian halo, in both the elastic and the inelastic scattering scenarios. We find that the compatibility between DAMA and the other experiments is improved. In the elastic scenario, the DAMA modulation signal is slightly enhanced in the so-called channeling region, as a result of several effects. For the inelastic scenario, the improvement of the fit is mainly attributable to the departure from a Maxwellian distribution at high velocity.Comment: 39 page

Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO

Gamma-ray bursts are believed to originate in core-collapse of massive stars. This produces an active nucleus containing a rapidly rotating Kerr black hole surrounded by a uniformly magnetized torus represented by two counter-oriented current rings. We quantify black hole spin-interactions with the torus and charged particles along open magnetic flux-tubes subtended by the event horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii) aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al. 2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating LIGO/Virgo detectors enables searches for nearby events and their spectral closure density 6e-9 around 250Hz in the stochastic background radiation in gravitational waves. At current sensitivity, LIGO-Hanford may place an upper bound around 150MSolar in GRB030329. Detection of Egw thus provides a method for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49

Relativistic Hydrodynamic Evolutions with Black Hole Excision

We present a numerical code designed to study astrophysical phenomena involving dynamical spacetimes containing black holes in the presence of relativistic hydrodynamic matter. We present evolutions of the collapse of a fluid star from the onset of collapse to the settling of the resulting black hole to a final stationary state. In order to evolve stably after the black hole forms, we excise a region inside the hole before a singularity is encountered. This excision region is introduced after the appearance of an apparent horizon, but while a significant amount of matter remains outside the hole. We test our code by evolving accurately a vacuum Schwarzschild black hole, a relativistic Bondi accretion flow onto a black hole, Oppenheimer-Snyder dust collapse, and the collapse of nonrotating and rotating stars. These systems are tracked reliably for hundreds of M following excision, where M is the mass of the black hole. We perform these tests both in axisymmetry and in full 3+1 dimensions. We then apply our code to study the effect of the stellar spin parameter J/M^2 on the final outcome of gravitational collapse of rapidly rotating n = 1 polytropes. We find that a black hole forms only if J/M^2<1, in agreement with previous simulations. When J/M^2>1, the collapsing star forms a torus which fragments into nonaxisymmetric clumps, capable of generating appreciable ``splash'' gravitational radiation.Comment: 17 pages, 14 figures, submitted to PR

Fermi acceleration in astrophysical jets

We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGNs, GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur.Comment: 6 pages, one figure; based on talk at "The multimessenger approach to unidentified gamma-ray sources", Barcelona/Spain, July 2006; accepted for publication in Astrophysics and Space Scienc

Techno-econo-environmental feasibility of retrofitting urban transportation system with optimal solar panels for climate change mitigation – A case study

Two novel solar buses are proposed to mitigate climate change in urban settings. Operational problems of solar power harnessing in cities such as high land costs and dust accumulation on the panels are obviated by installing solar panels on the otherwise rooftop area of the urban buses. Furthermore, the fuel consumption and hazardous emissions of buses decrease by improving their aerodynamic performance. An integrated solar power and aerodynamic model is developed, validated, and employed in a multi-objective optimization algorithm to compare proposed single-part (SiPS) and separate-part (SePS) systems. A multi-level stochastic procedure is applied to obtain a robust plan, calculate the economic payback, and study the feasibility of the optimal system's application using a novel combined economic-environmental ratio in Tabriz metropolitan city. The results showed that the costs of energy and vehicle-specific power were 0.922 $/kWh and 0.864$/kWh, and −12.71 kW/t and −17.53 kW/t for the optimal SiPS and SePS, respectively. Moreover, 233.76 MWh/year green energy could be generated, 1132 tCO2-eq/year hazardous emissions could be reduced, and 398,400 US$land costs could be saved by retrofitting the bus rapid transport routes in Tabriz with the SePS. Although the project was recommended if the energy unit price was greater than 0.25$/kWh in the case study, it was profitable under almost all probable conditions considering the combined economic-environmental revenue

Fatores de risco para o desenvolvimento de distúrbios alimentares: um estudo em universitárias Risk factors in the development of eating disorders: study in a group of college women

Este trabalho buscou identificar, em mulheres universitárias, aquelas que apresentavam fatores de risco para o desenvolvimento de distúrbios alimentares. Aplicou-se o questionário Eating Attitudes Test em 221 mulheres (114 estudantes de nutrição e 107 estudantes de outras áreas não relacionadas à saúde). Os resultados indicaram que 22,17% das estudantes apresentaram fatores de risco para o desenvolvimento de distúrbio alimentar, sendo que no grupo de alunas da nutrição o percentual foi maior (25,43%) do que no grupo de estudantes de outros cursos (18,69%). Embora a diferença não tenha sido significativa, as futuras nutricionistas podem estar inseridas em um ambiente mais favorável ao desenvolvimento de distúrbios alimentares.<br>This work studied a group of 221 college women, to identify those who presented risk factors compatible with the development of eating disorders. The Eating Attitudes Test was applied to 221 women (114 nutrition students and 107 students from other areas, unrelated to the health field). Results indicated that 22.17% of the group presented risk factors in the development of an eating disorder. Nutrition students presented a higher percentage (25.43%) than the other students (18.69%), but this difference was not significant. However, women who study nutrition may be exposed to an environment more propitious to the development of eating disorders