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Search Results: 1 - 10 of 409898 matches for " L. P. SILVA "
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Determining the Penguin Effect on CP Violation in $B^0 \rightarrow π^+ π^-$
Joao P. Silva,L. Wolfenstein
Physics , 1993, DOI: 10.1103/PhysRevD.49.1151
Abstract: A major goal in B physics is measuring the CP-violating asymmetry in the decay $B^0 \rightarrow \pi^+ \pi^-$. In order to determine one of the phase angles in the CKM matrix from this decay it is necessary to determine the influence of the penguin amplitude. Here we show how, using $SU(3)$ symmetry, the penguin effect can be approximately determined from the ratio of the decay rates of $B^0 \rightarrow K^+ \pi^-$ and $B^0 \rightarrow \pi^+ \pi^-$.
Detecting New Physics from CP-violating phase measurements in B decays
Joao P. Silva,L. Wolfenstein
Physics , 1996, DOI: 10.1103/PhysRevD.55.5331
Abstract: The standard CKM model can be tested and New Physics detected using only CP-violating phase measurements in B decays. This requires the measurement of a phase factor which is small in the Standard Model, in addition to the usual large phases $\beta$ and $\gamma$. We also point out that identifying violations of the unitarity of the CKM matrix is rather difficult, and cannot be done with phase measurements alone.
Fundamental CP-violating quantities in a SU(2)$ \otimes $U(1) model with many Higgs doublets
L. Lavoura,Joao P. Silva
Physics , 1994, DOI: 10.1103/PhysRevD.50.4619
Abstract: We consider a SU(2)$ \otimes $U(1) gauge theory with many scalar doublets, but without fermions. We devise a systematic method of constructing quantities which are invariant under changes of basis of the scalar fields, but acquire a minus sign under a general CP transformation. Those quantities provide a basis-independent way of checking for the existence of CP violation.
Disentangling violations of CPT from other new-physics effects
L. Lavoura,Joao P. Silva
Physics , 1999, DOI: 10.1103/PhysRevD.60.056003
Abstract: We analyze the prospects for observing CPT violation using neutral-meson P0-P0bar systems. Before one can claim a measurement of CPT violation, one must be able to rule out the possibility that its result is due to simpler new-physics effects. In particular, one must be able to separate the CPT-violating quantities from parameters violating the Delta P = \Delta Q rule of semileptonic decays, and from new-physics contributions to the production mechanism of the neutral mesons. One can isolate CPT violation using the semileptonic decays of single, tagged neutral mesons; unfortunately, this situation cannot be implemented at the Upsilon(4S). For P0-P0bar pairs produced in a correlated parity-odd state we show that, by combining the di-lepton with the single-lepton decays, it is in principle possible to extract unambiguously one CPT-violating parameter. Finally, we develop the formalism necessary for describing new-physics effects in the production mechanism; this includes both cascade decays and violations of the rule of associated production.
Performance of tetraploid alfalfa genotypes as exposed to aluminum toxicity  [PDF]
Le?nidas P. Passos, Maurício Marini K?pp, Francisco J. Silva Lédo
Agricultural Sciences (AS) , 2012, DOI: 10.4236/as.2012.32027
Abstract: A study was carried out to evaluate the development of 12 tetraploid alfalfa cultivars exposed to Al toxicity in nutrient solution. Newly germinated seedlings of cultivars Alfa 200, Alto, Araucana, Costera, Crioula, Esmeralda, Falcon, F-708, Rio, Romagnola, Valley Plus, and Victoria, were exposed to either 0, 4, 8 or 12 mg·L-1 Al3+. Plants were analyzed regarding root length (RL) and dry matter (RDM), aerial part length (APL), and dry matter (APDM), hypocotyl length (HypL) and dry matter (HypDM), epicotyl length (EpiL) and dry matter (EpiDM), and petiole length (PetL), and dry matter (PetDM). Results indicated that, although all genotypes exhibited detectable sensitivity to such a stress, cvs. Crioula, Victoria and Alpha-200 were tolerant to 4 mg·L-1 Al3+ toxicity. It was also concluded that Al3+ levels up to the 4 mg·L-1 will be effective for screening tetraploid alfalfa genotypes regarding this type of stress, when evaluations are made in nutrient solution. Finally, RL is the most suitable variable for conducting such evaluations, but all variables related to dry matter in the aerial part are also recommended.
Fredholm Property of Matrix Wiener-Hopf plus and minus Hankel Operators with Semi-Almost Periodic Symbols
Castro,L. P; Silva,A. S.;
Cubo (Temuco) , 2010, DOI: 10.4067/S0719-06462010000200014
Abstract: we will present sufficient conditions for the fredholm property of wiener-hopf plus and minus hankel operators with different fourier matrix symbols in the c*-algebra of semialmost periodic elements. in addition, under such conditions, we will derive a formula for the sum of the fredholm indices of thesewiener-hopf plus hankel and wiener-hopf minus hankel operators. some examples are provided to illustrate the results of the paper.
Extens?o de Cadeia em Poli(Naftalato de Etileno) pelo Fosfito de Trifenila
Dias, Marcos L.;Silva, Alexandre P. F.;
Polímeros , 2001, DOI: 10.1590/S0104-14282001000300008
Abstract: the reactive processing of poly(ethylene naphthalate) (pen) in presence of triphenylphosphite (tpp) was investigated. an internal mixer coupled to a torque rheometer was used to monitor changes of molecular mass and temperature during processing. the torque curves revealed that chain extension reactions took place. during the processing, there is an increase in the molecular weight of the polyester, which reaches a maximum and then decreases due to molecular degradation, accelerated by the presence of chain extention by-products. the intensity of the chain extention reaction increases when tpp content, temperature and shear rate rise. chain extension and degradation rate are slower in pen than in poly(ethylene terephthalate). the presence of low molecular weight by-products of chain extension in pen causes changes in the tg, due to plasticization effects, and increase the crystallization rate.
Visits of bats to flowers of Lafoensia glyptocarpa KOEHNE (LYTHRACEAE)
Revista Brasileira de Biologia , 1999, DOI: 10.1590/S0034-71081999000100003
Abstract: in the present study visits of phyllostomid bats to the lafoensia glyptocarpa kohne flowers were observed at federal rural university of rio de janeiro, itaguaí municipality, rio de janeiro state. this tree species present floral characteristics to fit the "chiropterophilous syndrome", encouraging the visit of four species of bats which showed different behavior patterns, according to their size, weight and access to the food resources. glossophaga soricina (pallas, 1766) showed hovering behavior. phyllostomus hastatus (pallas, 1767) and platyrrhinus lineatus (geoffroy, 1810) showed landing behavior and artibeus lituratus (olfers, 1818) fed during the quick flight, without a real landing.
Temperatura base, coeficientes de cultura e graus-dia para cafeeiro arábica em fase de implanta??o
Lima, Edson P.;Silva, Elio L. da;
Revista Brasileira de Engenharia Agrícola e Ambiental , 2008, DOI: 10.1590/S1415-43662008000300007
Abstract: this paper had as its purpose the determination of the inferior base temperature - tb, and superior - tb, for arabic coffee plants. the cultivars "acaiá cerrado" (mg-1474) and "rubi" (mg-1192) were evaluated, associating crop coefficients - kc, to growing degrees-day - gdd. the trial was carried out in the "universidade federal de lavras" - ufla, from march 2003 to september 2004. for statistical analysis, a study with regression and comparisons among regressions using the procedure described in snedecor & cochran (1989) were used. the values of gdd were obtained with the methodology presented by ometto (1981), and were compared to the methods presented by arnold (1959), snyder (1985) and dufault (1997); tb = 12.9 °c and tb = 32.4 °c were obtained after comparisons among the methods: least standard deviation in degrees-day and days, coefficient of variation in degrees-day, regression coefficient and analysis of kc versus gdd were found. for both cultivars, up to 4200 gdd, values of 0.20, 0.89 and 0.48 were found, for kc minimum, maximum and mean, respectively.
Electron paramagnetic resonance in the CoIn2-2xCr2xS4 semiconductor system
Silva, P;Zamora L, C;Sagredo, V;
Revista mexicana de física , 2006,
Abstract: we report electron paramagnetic resonance (epr) measurements in the diluted magnetic semiconductor (dms) coin2-2xcr2xs4, 0.05 < x < 1. the resonance field (hr) is obtained from the spectra, and we have found oscillations around 410 mt. when temperature decreases hr decreases also, this behavior is in agreement with a paramagnetism-ferromagnetism phase transition. in the sample x = 0.05, hr increases from 400 mt until very high values while temperature is decreasing. the linewidth δ hpp, for all the samples increases as the temperature decreases. near liquid nitrogen temperatures, the epr spectra is not observed. the behavior observed below the transition temperature is explained in terms of the exchange interaction between chromium ions. the ferrimagnetic behaviour is the responsible for the poor epr signal at low temperatures.
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