351 research outputs found
Measurement of cosmic-ray low-energy antiproton spectrum with the first BESS-Polar Antarctic flight
The BESS-Polar spectrometer had its first successful balloon flight over
Antarctica in December 2004. During the 8.5-day long-duration flight, almost
0.9 billion events were recorded and 1,520 antiprotons were detected in the
energy range 0.1-4.2 GeV. In this paper, we report the antiproton spectrum
obtained, discuss the origin of cosmic-ray antiprotons, and use antiprotons to
probe the effect of charge sign dependent drift in the solar modulation.Comment: 18 pages, 1 table, 5 figures, submitted to Physics Letters
Measurements of Atmospheric Antiprotons
We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4
GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to
26 g/cm^2. The observed energy spectra, including our previous measurements at
mountain altitude, were compared with estimated spectra calculated on various
assumptions regarding the energy distribution of antiprotons that interacted
with air nuclei.Comment: Accepted for publication in PL
Balloon Measurements of Cosmic Ray Muon Spectra in the Atmosphere along with those of Primary Protons and Helium Nuclei over Mid-Latitude
We report here the measurements of the energy spectra of atmospheric muons
and of the cosmic ray primary proton and helium nuclei in a single experiment.
These were carried out using the MASS superconducting spectrometer in a balloon
flight experiment in 1991. The relevance of these results to the atmospheric
neutrino anomaly is emphasized. In particular, this approach allows
uncertainties caused by the level of solar modulation, the geomagnetic cut-off
of the primaries and possible experimental systematics to be decoupled in the
comparison of calculated fluxes of muons to measured muon fluxes. The muon
observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886
g/cmsquared, respectively. The proton and helium primary measurements cover the
rigidity range from 3 to 100 GV, in which both the solar modulation and the
geomagnetic cut-off affect the energy spectra at low energies.Comment: 31 pages, including 17 figures, simplified apparatus figure, to
appear in Phys. Rev.
Interaction of quasilocal harmonic modes and boson peak in glasses
The direct proportionality relation between the boson peak maximum in
glasses, , and the Ioffe-Regel crossover frequency for phonons,
, is established. For several investigated materials . At the frequency the mean free path of the
phonons becomes equal to their wavelength because of strong resonant
scattering on quasilocal harmonic oscillators. Above this frequency phonons
cease to exist. We prove that the established correlation between
and holds in the general case and is a direct consequence of
bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur
Measurements of Proton, Helium and Muon Spectra at Small Atmospheric Depths with the BESS Spectrometer
The cosmic-ray proton, helium, and muon spectra at small atmospheric depths
of 4.5 -- 28 g/cm^2 were precisely measured during the slow descending period
of the BESS-2001 balloon flight. The variation of atmospheric secondary
particle fluxes as a function of atmospheric depth provides fundamental
information to study hadronic interactions of the primary cosmic rays with the
atmosphere.Comment: 21 pages, 11 figures, 4 table
On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope
The Fermi-LAT experiment recently reported high precision measurements of the
spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV.
The spectrum shows no prominent spectral features, and is significantly harder
than that inferred from several previous experiments. Here we discuss several
interpretations of the Fermi results based either on a single large scale
Galactic CRE component or by invoking additional electron-positron primary
sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that
while the reported Fermi-LAT data alone can be interpreted in terms of a single
component scenario, when combined with other complementary experimental
results, specifically the CRE spectrum measured by H.E.S.S. and especially the
positron fraction reported by PAMELA between 1 and 100 GeV, that class of
models fails to provide a consistent interpretation. Rather, we find that
several combinations of parameters, involving both the pulsar and dark matter
scenarios, allow a consistent description of those results. We also briefly
discuss the possibility of discriminating between the pulsar and dark matter
interpretations by looking for a possible anisotropy in the CRE flux.Comment: 29 pages, 12 figures. Final version accepted for publication in
Astroparticle Physic
Propagation of secondary antiprotons and cosmic rays in the Galaxy
Recent measurements of the cosmic ray (CR) antiproton flux have been shown to
challenge existing CR propagation models. It was shown that the reacceleration
models designed to match secondary to primary nuclei ratios (e.g., B/C) produce
too few antiprotons. In the present paper we discuss one possibility to
overcome these difficulties. Using the measured antiproton flux AND B/C ratio
to fix the diffusion coefficient, we show that the spectra of primary nuclei as
measured in the heliosphere may contain a fresh local "unprocessed" component
at low energies perhaps associated with the Local Bubble, thus decreasing the
measured secondary to primary nuclei ratio. The independent evidence for SN
activity in the solar vicinity in the last few Myr supports this idea. The
model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni
(Z<=28). Calculated isotopic distributions of Be and B are in perfect agreement
with CR data. The abundances of three "radioactive clock" isotopes in CR, 10Be,
26Al, 36Cl, are all consistent and indicate a halo size z_h~4 kpc based on the
most accurate data taken by the ACE spacecraft.Comment: 6 pages, 5 ps-figures, cospar.sty; Proc. of 34th COSPAR Scientific
Assembly (Houston, 10-19 October 2002). Submitted to Advances in Space
Research. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Design, Commissioning and Performance of the PIBETA Detector at PSI
We describe the design, construction and performance of the PIBETA detector
built for the precise measurement of the branching ratio of pion beta decay,
pi+ -> pi0 e+ nu, at the Paul Scherrer Institute. The central part of the
detector is a 240-module spherical pure CsI calorimeter covering 3*pi sr solid
angle. The calorimeter is supplemented with an active collimator/beam degrader
system, an active segmented plastic target, a pair of low-mass cylindrical wire
chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole
detector system is housed inside a temperature-controlled lead brick enclosure
which in turn is lined with cosmic muon plastic veto counters. Commissioning
and calibration data were taken during two three-month beam periods in
1999/2000 with pi+ stopping rates between 1.3*E3 pi+/s and 1.3*E6 pi+/s. We
examine the timing, energy and angular detector resolution for photons,
positrons and protons in the energy range of 5-150 MeV, as well as the response
of the detector to cosmic muons. We illustrate the detector signatures for the
assorted rare pion and muon decays and their associated backgrounds.Comment: 117 pages, 48 Postscript figures, 5 tables, Elsevier LaTeX, submitted
to Nucl. Instrum. Meth.
Stochastic Production Of Kink-Antikink Pairs In The Presence Of An Oscillating Background
We numerically investigate the production of kink-antikink pairs in a
dimensional field theory subject to white noise and periodic driving.
The twin effects of noise and periodic driving acting in conjunction lead to
considerable enhancement in the kink density compared to the thermal
equilibrium value, for low dissipation coefficients and for a specific range of
frequencies of the oscillating background. The dependence of the kink-density
on the temperature of the heat bath, the amplitude of the oscillating
background and value of the dissipation coefficient is also investigated. An
interesting feature of our result is that kink-antikink production occurs even
though the system always remains in the broken symmetry phase.Comment: Revtex, 21 pages including 7 figures; more references adde
Comportamento à flexão de vigas eco-eficientes de ultra elevada durabilidade
Atualmente, o ecossistema mundial tem vindo a ser confrontado com problemas de grande
importância, a elevada poluição do meio ambiente e a limitação dos recursos energéticos. Estes
problemas têm contribuído para que a sustentabilidade da construção seja uma prioridade cada
vez maior no presente e no futuro. A manutenção e a reabilitação do património construído
surge como uma das medidas mais eficazes para prevenir ou reduzir o consumo de energia no
setor da construção. No caso da construção nova, a tendência é para verificar-se um aumento
da utilização de elementos estruturais pré-fabricados com partes betonadas em obra, obtendose
uma maior rapidez de execução associada a um maior controlo de qualidade.
O betão de ultra elevada durabilidade, reforçado com fibras metálicas, é considerado um
material inovador desenvolvido nas últimas décadas, apresentando um conjunto de
caraterísticas especiais, como a durabilidade, a facilidade de aplicação, as elevadas resistências
mecânicas, tornando-o num produto particularmente atraente para a reabilitação e reforço de
estruturas de betão. No entanto, este betão não deve ser produzido em grandes quantidades
devido ao elevado consumo de cimento e adições, resultando em elevados custos económicos
e ambientais. Considerando estas desvantagens é proposto que o betão de ultra elevada
durabilidade seja usado apenas na camada de recobrimento, formando-se assim uma superskin
que protege o elemento estrutural dos ambientes mais agressivos, isto é, aumenta a durabilidade
das estruturas de betão sem que, no entanto, seja criado um impacte ambiental muito
significativo (a quantidade de CO2 libertada para a atmosfera é menor devido ao menor
consumo de cimento e adições).
A presente dissertação pretende explorar o conceito de superskin do ponto de vista do
comportamento estrutural, nomeadamente, estudar o comportamento de vigas sujeitas a
esforços de flexão, compostas por uma camada exterior de betão de ultra elevada durabilidade,
associado a um núcleo com betão eco-eficiente, com baixa dosagem de cimento, de modo a
obter uma solução mais durável e ao mesmo tempo, ecologicamente mais eficiente.
Foram realizadas oito vigas com diferentes taxas de armadura: quatro vigas produzidas apenas
com betão com baixa dosagem de cimento (usadas como vigas de referência) e quatro vigas
produzidas com um betão de ultra elevada durabilidade na camada de recobrimento e com um
betão com baixa dosagem de cimento no núcleo. As diferentes taxas de armadura longitudinal
permitem avaliar a influência da superskin em vigas com roturas dúcteis e frágeis. Com base
nos dados recolhidos durante os ensaios experimentais estudou-se: (i) relação cargadeslocamento;
(ii) os valores teóricos e experimentais do momento resistente; (iii) a evolução
da curvatura nas secções críticas; (iv) a evolução da rigidez à flexão com a carga aplicada; (v)
a ductilidade; e (vi) a fendilhação e o tipo de rotura. Da análise de resultados foi possível
verificar que o recobrimento em betão de ultra elevada durabilidade é uma solução com aspetos
muito positivos, nomeadamente, aumenta a resistência à flexão das vigas
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