A note on the cylindrical collapse of counter-rotating dust

We find analytical solutions describing the collapse of an infinitely long cylindrical shell of counter-rotating dust. We show that--for the classes of solutions discussed herein--from regular initial data a curvature singularity inevitably develops, and no apparent horizons form, thus in accord with the spirit of the hoop conjecture.Comment: 8 pages, LaTeX, ijmpd macros (included), 1 eps figure; accepted for publication in Int. J. Mod. Phys.

No-horizon theorem for spacetimes with spacelike G1 isometry groups

We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike $G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on ${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent horizons. Given any (3+1) spacetime with spacelike translational isometry, the no-horizon condition can be readily tested without the need for dimensional reduction. This provides thus a useful and encompassing apparent horizon test for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence towards the validity of the hoop conjecture, and signals possible violations of strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra

Self-assembled nanoparticles of dextrin substituted with hexadecanethiol

The amphiphilic molecule dextrin-VA-SC16 (dexC16) was synthesized and studied in this work. DexC16 has a hydrophilic dextrin backbone with grafted acrylate groups (VA) substituted with hydrophobic 1- exadecanethiol (C16). A versatile synthetic method was developed allowing control of the dextrin degree of substitution with the hydrophobic chains (DSC16, number of alkyl chains per 100 dextrin glucopyranoside residues). Materials with different DSC16 were prepared and characterized using 1H NMR. DexC16 self-assembles in water through association of the hydrophobic alkyl chains, originating nanoparticles. The nanoparticles properties were studied by dynamic light scattering (DLS), fluorescence spectroscopy, and atomic force microscopy (AFM)

Human dynamics revealed through Web analytics

When the World Wide Web was first conceived as a way to facilitate the sharing of scientific information at the CERN (European Center for Nuclear Research) few could have imagined the role it would come to play in the following decades. Since then, the increasing ubiquity of Internet access and the frequency with which people interact with it raise the possibility of using the Web to better observe, understand, and monitor several aspects of human social behavior. Web sites with large numbers of frequently returning users are ideal for this task. If these sites belong to companies or universities, their usage patterns can furnish information about the working habits of entire populations. In this work, we analyze the properly anonymized logs detailing the access history to Emory University's Web site. Emory is a medium size university located in Atlanta, Georgia. We find interesting structure in the activity patterns of the domain and study in a systematic way the main forces behind the dynamics of the traffic. In particular, we show that both linear preferential linking and priority based queuing are essential ingredients to understand the way users navigate the Web.Comment: 7 pages, 8 figure

Avaliação de cultivares de alface crespa sob cultivo protegido no município de Iranduba/AM.

O objetivo deste trabalho foi avaliar o desempenho de cultivares de alface crespa sob cultivo protegido no município de Iranduba/AM.Suplemento. Trabalho apresentado no 52. Congresso Brasileiro de Olericultura, Salvador, 2012

A closer look at the U(1)B−LU(1)_{B-L} explanation of the ATOMKI nuclear anomalies

We revisit the gauged $U(1)_{B-L}$ explanation of the ATOMKI nuclear anomalies, in which the new gauge boson is the hypothetical $X(17)$ particle. It is known that the vanilla $B-L$ scenario is unable to account for appropriate couplings, namely the suppression of the couplings of $X(17)$ to neutrinos, which motivates adding vector-like leptons. The simplest case, in which the new fields have $B-L$ charges equal to $1$, is highly disfavoured since it requires large mixing with the Standard Model fields. One solution recently put forward is to consider large $B-L$ charges to counterbalance small mixing. We show that, in this scenario, and after taking into account several phenomenological constraints, the dominant contribution to the muon anomalous magnetic moment $(g-2)_\mu$ is expected to be extremely large and with a negative sign, being thus excluded by experiment.Comment: 15 LaTeX pages, 4 figure

Modelling of thermoelectric generator with heat pipe assist for range extender application

Recent trends towards electrification of vehicles favour the adoption of waste energy recovery into electricity. Battery-only Electric Vehicles (BEV) need a very large energy storage system so the use of a Range Extender (RE) may allow a significant downsizing of these bulky components. The Internal Combustion Engines (ICE) have two major discarded energy fluxes, engine cooling and exhaust gas. In Extended Range Electric Vehicles (EREV) and hybrids the potential for heat conversion into electricity is particularly convenient. The direct conversion of thermal energy into electricity, using Thermoelectric Generators (TEG) is very attractive in terms of complexity. However, current commercial TEG modules based on Seebeck effect are temperature limited, so they are unable to be in direct contact with the exhaust gases. A way to downgrade the temperature levels without reducing its potential is to interpose Heat Pipes (HP) between the exhaust gas and the modules. This control of maximum temperature at the modules is achieved by regulating the pressure of phase change of the HP fluid. Such design is convenient for engines with large thermal load variations, such as the RE being developed by the team, with a low (15kW) and a high (40kW) power mode of operation. This system will be able to operate efficiently in both modes. The present work presents the thermal modelling of such a system in order to assess the suitability of this approach. This work is complemented with the experimental work being carried out by the team in this subject, already with some published results. The model was validated with experimental data with a good correlation. Therefore, it was possible to demonstrate the potential of this system for wasted heat recovery.MIT Portugal, Fundação para a Ciência e a Tecnologia (FCT

Temperature controlled exhaust heat thermoelectric generation

The amount of energy wasted through the exhaust of an Internal Combustion Engine (ICE) vehicle is roughly the same as the mechanical power output of the engine. The high temperature of these gases (up to 1000°C) makes them intrinsically apt for energy recovery. The gains in efficiency for the vehicle could be relevant, even if a small percentage of this waste energy could be regenerated into electric power and used to charge the battery pack of a Hybrid or Extended Range Electric Vehicle, or prevent the actuation of a conventional vehicle's alternator.SFRH / BPD / 51048 / 2010MIT-Pt/EDAM-SMS/0030/200

Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse

We study the occurrence, visibility, and curvature strength of singularities in dust-containing Szekeres spacetimes (which possess no Killing vectors) with a positive cosmological constant. We find that such singularities can be locally naked, Tipler strong, and develop from a non-zero-measure set of regular initial data. When examined along timelike geodesics, the singularity's curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for publication in Class. Quantum Gra