Upper limit on the cosmic-ray photon flux above 10(19) eV using the surface detector of the Pierre Auger Observatory

A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature of the shower front. Applying this method to the data, tipper limits on the flux of photons of 3.8 x 10(-3), 2.5 x 10(-3), and 2.2 x 10(-3) km(-2) sr(-1) yr(-1) above 10(19) eV, 2 x 10(19) eV, and 4 x 10(19) eV are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results also show that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination from photons. (C) 2008 Elsevier B.V. All rights reserved.

Measurement of the energy spectrum of cosmic rays above 10(18) eV using the Pierre Auger Observatory

We report a measurement of the flux of cosmic rays with unprecedented precision and Statistics using the Pierre Auger Observatory Based on fluorescence observations in coincidence with at least one Surface detector we derive a spectrum for energies above 10(18) eV We also update the previously published energy spectrum obtained with the surface detector array The two spectra are combined addressing the systematic uncertainties and, in particular. the influence of the energy resolution on the spectral shape The spectrum can be described by a broken power law E(-gamma) with index gamma = 3 3 below the ankle which is measured at log(10)(E(ankle)/eV) = 18 6 Above the ankle the spectrum is described by a power law with index 2 6 followed by a flux suppression, above about log(10)(E/eV) = 19 5, detected with high statistical significance (C) 2010 Elsevier B V All rights reserved

Stirring, charging, and picking: hunting tactics of potamotrygonid rays in the upper Paraná River

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity. (C) 2005 Elsevier Ltd. All rights reserved.

MEASURING HYSTERESIS LOOPS OF FERROELECTRIC POLYMERS USING THE CONSTANT CHARGING CURRENT CORONA TRIODE

A novel method is proposed for measuring the hysteresis loops of ferroelectric polymers. The samples need to have only one electrode and are poled by corona discharge in a constant current corona triode. It is shown how the sample surface potential and the charging current are related to the remanent polarization and coercive field, so that the hysteresis loops can be obtained. An illustrative example is given for samples of beta-PVDF for which the hysteresis cycles were remarkably close to those obtained with the traditional Sawyer-Tower circuit. Values of 80 MV/m and 70 mC/m2 were estimated for the coercive field and remanent polarization, respectively.

Effect of different methods of cutting fluid application on turning of a difficult-to-machine steel (SAE EV-8)

In this study, different methods of cutting fluid application are used in turning of a difficult-to-machine steel (SAE EV-8). Initially, a semisynthetic cutting fluid was applied using a conventional method (i.e. overhead flood cooling), minimum quantity of cutting fluid, and pulverization. A lubricant of vegetable oil (minimum quantity of lubricant) was also applied using the minimum quantity method. Thereafter, a cutting fluid jet under high pressure (3.0 MPa) was singly applied in the following regions: chip-tool interface, top surface of the chip (between workpiece and chip) and tool-workpiece contact. Moreover, two other methods were used: an interflow between conventional application and chip-tool interface jet (combined method) and, finally, three jets simultaneously applied. In order to carry out these tests, it was necessary to set up a high-pressure system using a piston pump for generating a cutting fluid jet, a venturi for fluid application (minimum quantity of cutting fluid and minimum quantity of lubricant) and a nozzle for cutting fluid pulverization. The output variables analyzed included tool life, surface roughness, cutting tool temperature, cutting force, chip form, chip compression rate and machined specimen microstructure. Among the results, it can be observed that the tool life increases and the cutting force decreases with the application of cutting fluid jet, mainly when it is directed to the chip-tool interface. Excluding the methods involving jet fluid, the conventional method seems to be more efficient than other methods of low pressure, such as minimum quantity of volume and pulverization, when considering just the cutting tool wear. © 2013 IMechE.

Carregamento ótimo de veículos elétricos considerando as restrições das redes de distribuição de média tensão

Pós-graduação em Engenharia Elétrica - FEIS

An MILP model for the plug-in electric vehicle charging coordination problem in electrical distribution systems

A new mixed-integer linear programming (MILP) model is proposed to represent the plug-in electric vehicles (PEVs) charging coordination problem in electrical distribution systems. The proposed model defines the optimal charging schedule for each division of the considered period of time that minimizes the total energy costs. Moreover, priority charging criteria is taken into account. The steady-state operation of the electrical distribution system, as well as the PEV batteries charging is mathematically represented; furthermore, constraints related to limits of voltage, current and power generation are included. The proposed mathematical model was applied in an electrical distribution system used in the specialized literature and the results show that the model can be used in the solution of the PEVs charging problem.

Ellipsometric Study of Single-Crystal γ-Inse From 1.5 To 9.2 Ev

We report the component E ┴ c of the pseudodielectric-function tensor <ε(E)> = <ε1(E)> + i< ε2(E)> of γ-phase single-crystal InSe, obtained from 1.5 to 9.2 eV by vacuum-ultraviolet spectroscopic ellipsometry with the sample at room temperature. Overlayer artifacts were reduced as far as possible by measuring fresh surfaces prepared by cleavage. Accurate critical-point energies of observed structures were obtained by a combined method of spectral analysis.

LARGE-SCALE DISTRIBUTION OF ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE 10(18) eV AT THE PIERRE AUGER OBSERVATORY

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 10(18) eV at the Pierre Auger Observatory is presented. This search is performed as a function of both declination and right ascension in several energy ranges above 10(18) eV, and reported in terms of dipolar and quadrupolar coefficients. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Assuming that any cosmic-ray anisotropy is dominated by dipole and quadrupole moments in this energy range, upper limits on their amplitudes are derived. These upper limits allow us to test the origin of cosmic rays above 10(18) eV from stationary Galactic sources densely distributed in the Galactic disk and predominantly emitting light particles in all directions.

Discovery of the Persistent Luminescence Mechanism of CdSiO3:Tb3+

The persistent luminescence of CdSiO3:Tb3+ was investigated with photoluminescence, thermoluminescence (TL), synchrotron radiation X-ray absorption (XANES and EXAFS) and UV-VUV spectroscopies. Only the typical intraconfigurational 4f(8)-4f(8) transitions of the Tb3+ ion were observed with no traces of band emission in either the conventional UV excited or persistent luminescence spectra. The trap structure from TL with three traps from 0.65 to 0.85 eV is ideal for room-temperature persistent luminescence similar to, e.g., Sr2MgSi2O7:Eu2+,R3+. Despite the rather low band gap energy, 5.28 eV, the persistent luminescence from Tb3+ is produced only under UV irradiation due to the inauspicious position of the F-7(6) ground level deep in the band gap of CdSiO3. This confirms the role of electrons as the charge carriers in the mechanism of Tb3+ persistent luminescence. The XANES spectra indicated the presence of only the trivalent Tb3+ species, thus excluding the direct Tb3+ -> Tb-IV oxidation during the charging process of persistent luminescence. Eventually, a unique persistent luminescence mechanism for Tb3+ in CdSiO3 was constructed based on the comprehensive experimental data.

Constraints on the origin of cosmics rays above '10 POT. 18' eV from large-scale anisotropy searches in data of the Pierre Auger observatory

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above '10 POT. 18' eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments.Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above '10 POT. 18' eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.

Suche nach einem leichten Higgs-Boson im Kanal WH ev e bb in pp-Kollisionen bei s=1.96 TeV am DO-Detektor des Tevatron

Eine wichtige Komponente des Standardmodells der Teilchenphysik bildet der Higgs-Mechanismus, der benötigt wird um den vom Standardmodell beschriebenen Teilchen Masse zu verleihen. Dieser Mechanismus beinhaltet jedoch ein weiteres schweres Elementarteilchen das bislang noch nich beobachtet werden konnte. Die Suche nach diesem Teilchen ist eines Hauptziele der derzeitigen Forschung an Teilchenbeschleunigern. Diese Arbeit untersucht die vom D0-Detektor am Tevatron des Fermi National Accelerator Laboratory (FNAL) aufgezeichneten Daten von ppbar-Kollisionen bei einer Schwerpunktsenergie von sqrt{s}=1.96 TeV, um im Kanal WH -> enu bb nach einem leichten Higgs-Boson zu suchen. Darüber hinaus wird der Produktionswirkungsquerschnitt der Wbb-Produktion ermittelt. Für die Analyse stand eine integrierte Luminosität von L=255pb^{-1} zur Verfügung. Zur Selektion dieser Prozesse, werden Ereignisse ausgewählt, die Elektronen und fehlenden Transversalimpuls enthalten, sowie mindestens zwei Jets, die sich als b-Jets identifizieren lassen. Um eine effiziente Selektion zu erhalten, wurden Schnitte auf verschiedene Kenngrößen entwickelt, getestet und optimiert. Aus den selektierten Ereignissen wird der Wbb-Wirkungsquerschnitt ermittelt, der für Ereignisse angegeben wird, in denen die b-Quarks p_T>8 GeV und |eta|<3 erfüllen. Der unter Berücksichtigung des Verzweigungsverhältnisses BR(W->enu)=0.108 errechnete Wert ist sigma(Wbb)=21.8 pb (+15.5; -20.0 pb(sys+stat)). Wegen der geringen Signifikanz der Messung von etwa 1.2sigma wurden die Ereigniszahlen auch zur Berechnung einer oberen Grenze auf den Wirkungsquerschnitt verwendet, die sich bei einem Konfidenzniveau von 95% zu sigma^95(Wbb)=60.9pb ergibt. Ebenso wurden Grenzen auf den WH-Produktionswirkungsquerschnitt ermittelt. Dafür wurde die statistische Methode von Feldman und Cousins angewandt, nachdem sie nach den Vorschlägen von Conrad et al. erweitert worden war, um systematische Unsicherheiten zu berücksichtigen. Für ein Standardmodell Higgs-Boson der Masse 115 GeV kann eine obere Grenze auf den Produktionswirkungsquerschnitt von sigma^{95} (WH)=12.2pb angegeben werden. Für höhere Massen bis 135 GeV werden ähnliche Grenzen ermittelt.