616 research outputs found
Durability Tests of a Fiber Optic Corrosion Sensor
Steel corrosion is a major cause of degradation in reinforced concrete structures, and there is a need to develop cost-effective methods to detect the initiation of corrosion in such structures. This paper presents a low cost, easy to use fiber optic corrosion sensor for practical application. Thin iron film is deposited on the end surface of a cleaved optical fiber by sputtering. When light is sent into the fiber, most of it is reflected by the coating. If the surrounding environment is corrosive, the film is corroded and the intensity of the reflected signal drops significantly. In previous work, the sensing principle was verified by various experiments in laboratory and a packaging method was introduced. In this paper, the method of multiplexing several sensors by optical time domain reflectometer (OTDR) and optical splitter is introduced, together with the interpretation of OTDR results. The practical applicability of the proposed sensors is demonstrated in a three-year field trial with the sensors installed in an aggressive marine environment. The durability of the sensor against chemical degradation and physical degradation is also verified by accelerated life test and freeze-thaw cycling test, respectively
Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders
Top quark pair production at photon-photon colliders is studied in low scale
quantum gravity scenario. From the dependence of the cross sections on the spin
configuration of the top quark and anti-quark, we introduce a new observable,
top spin asymmetry. It is shown that there exists a special top spin basis
where with the polarized parent electron beams the top spin asymmetry vanishes
in the standard model but retains substantial values with the large extra
dimension effects. We also present lower bounds of the quantum gravity scale
from total cross sections with various combinations of the laser,
electron beam, and top quark pair polarizations. The measurements of the top
spin state with unpolarized initial beams are
shown to be most effective, enhancing by about 5% the bounds with respect
to totally unpolarized case.Comment: 18 pages, 4 figures, ReVTe
Mode oscillation and harmonic distortions associated with sinusoidal modulation of semiconductor lasers
This paper investigates mode dynamics, operation characteristics and signal distortions associated with sinusoidal modulation of semiconductor lasers. The study is based on intensive integrations of the multimode rate equation model of semiconductor lasers over wide ranges of the modulation frequency and depth. The rate equations take into account both spectral symmetric and asymmetric suppressions of modal gain. The higher harmonic distortions as well as the half harmonic distortion associated with the period doubling effect are investigated. The study is applied to both cases of single-mode and multimode oscillations of the non-modulated laser. The obtained results showed that the modulated signal has six distinct waveforms depending on the modulation conditions; three types have continuous periodic waveforms and the others have periodic pulsing waveforms. The modulated laser is found to oscillate in a single mode under weak modulation where the modulated signal is continuous, whereas the pulsing signals are associated with multimode oscillation. The higher harmonic distortions of single-mode laser are lower than those of two-mode lasers, and become serious at modulation frequencies around the relaxation oscillation frequency. These distortions are highest when the laser output is pulsating and the pulses are superposed by relaxation oscillations. Š EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012
Kaluza-Klein gravitino production with a single photon at e^+ e^- colliders
In a supersymmetric large extra dimension scenario, the production of
Kaluza-Klein gravitinos accompanied by a photino at e^+ e^- colliders is
studied. We assume that a bulk supersymmetry is softly broken on our brane such
that the low-energy theory resembles the MSSM. Low energy supersymmetry
breaking is further assumed as in GMSB, leading to sub-eV mass shift in each KK
mode of the gravitino from the corresponding graviton KK mode. Since the
photino decays within a detector due to its sufficiently large inclusive decay
rate into a photon and a gravitino, the process e^+ e^- -> photino + gravitino
yields single photon events with missing energy. Even if the total cross
section can be substantial at sqrt(s)=500 GeV, the KK graviton background of
e^+ e^- -> photon + graviton is kinematically advantageous and thus much
larger. It is shown that the observable, sigma(e^-_L)-sigma(e^-_R), can
completely eliminate the KK graviton background but retain most of the KK
gravitino signal, which provides a unique and robust method to probe the
supersymmetric bulk.Comment: Reference added and typos correcte
Diversidade e Estrutura GenĂŠticas de Bryconamericus aff. Iheringii (Characiformes: Characidae) na Ărea de InfluĂŞncia do ReservatĂłrio da Itaipu
Trabalho de ConclusĂŁo de Curso apresentado ao Instituto Latino-Americano de CiĂŞncias da Vida e Natureza da Universidade Federal da Integração Latino-Americana, como requisito parcial Ă obtenção do tĂtulo de Bacharel em CiĂŞncias BiolĂłgicas â Ecologia e Biodiversidade.A diversidade genĂŠtica ĂŠ necessĂĄria para que as populaçþes evoluam e se adaptem Ă s mudanças ambientais, e comumente, estĂĄ distribuĂda em um padrĂŁo dentro e entre populaçþes que ĂŠ referido como estrutura genĂŠtica. O isolamento e a existĂŞncia de poucos caminhos migratĂłrios entre ĂĄguas doces implicam na estruturação genĂŠtica, principalmente, para peixes que possuem baixa mobilidade. Peixes de pequeno porte (⤠15 cm de comprimento), que habitam riachos, representam, no mĂnimo 50% de toda a ictiofauna sul-americana e apresentam um alto grau de endemismo, devido, em parte, Ă sua baixa capacidade de deslocamento. Neste contexto, o presente trabalho objetivou avaliar a diversidade e a estrutura genĂŠticas do caracĂdeo Bryconamericus aff. iheringii na ĂĄrea de influĂŞncia do reservatĂłrio da Itaipu Binacional. Para isto, foram analisados 47 espĂŠcimes, 23 coletados em riachos da margem direita (Paraguai) e 24 coletados em riachos da margem esquerda (Brasil) do reservatĂłrio da Itaipu. Para acessar sua diversidade genĂŠtica, foi empregado o marcador molecular D-loop, sendo estimado o nĂşmero de haplĂłtipos, os Ăndices de diversidade haplotĂpica e nucleotĂdica e o nĂvel de estruturação entre as diferentes amostras. B. aff. iheringii apresentou nĂveis de diversidade genĂŠtica dentro do padrĂŁo relatado para a espĂŠcie, com moderados (amostras do Paraguai) a altos (amostras do Brasil) nĂveis de diversidade, o que se deve, sobretudo, ao fato de que quase todos os riachos paraguaios analisados sĂŁo de uma Ăşnica microbacia, enquanto os riachos brasileiros sĂŁo de quatro microbacias diferentes. As populaçþes nĂŁo parecem ter respondido a eventos drĂĄsticos recentes, pois mesmo as presentes em regiĂľes sob a pressĂŁo de atividades agrĂcolas, mostram variaçþes no DNA mitocondrial. Foram encontrados altos nĂveis de estruturação genĂŠtica entre o conjunto de amostras paraguaio e brasileiro e entre as microbacias dentro de cada paĂs, o que se deve, principalmente, aos processos de colonização destas drenagens, os quais possivelmente envolvem fundadores com diferentes linhagens haplotĂpicas. AlĂŠm disso, parece plausĂvel que o rio ParanĂĄ (reservatĂłrio da Itaipu) funciona como uma barreira ao fluxo gĂŞnico entre as diferentes margens e entre suas microbacias. Deste modo, a identificação de linhagens ĂŠ de grande importância, pois a manutenção da diversidade genĂŠtica de uma espĂŠcie depende de sua preservação. Considerando a importância de estudos genĂŠtico-populacionais para a conservação de espĂŠcies, espera-se que este trabalho possa servir como base para futuros estudos mais amplos com peixes de riachos
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
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