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961.
>Vidal Alonso Salvatore De Vincenzo 《International Journal of Theoretical Physics》2000,39(6):1483-1498
The problem of a relativistic free particle on a line with a hole, which ischaracterized in terms of boundary conditions for a one-dimensional DiracHamiltonian perturbed at one point, is reviewed. We show that the generalfour-parameter family of point interactions earlier obtained by Falkensteiner andGrosse can be written in two forms: In one of them three subfamilies of boundaryconditions are obtained. In the nonrelativistic limit one of these subfamiliescoincides with those given by Carreau et al. and Carreau. In the other form, threesubfamilies of boundary conditions are also obtained, two of which coincide withthose studied by Benvegnu;ag and Dabrowski. In the nonrelativistic limit all thesesubfamilies coincide with those studied by Albeverio et al. The most generalsubfamilies for which the Dirac Hamiltonian is invariant under space inversionP as well as under time reversal T and PT are obtained. Only these subfamiliesrepresent delta-type Dirac point interactions. Typical relativistic andnonIrelativistic boundary conditions are therein included. 相似文献
962.
Turini N Ukegawa F Valls J Vejcik S Velev G Vidal R Vilar R Vologouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ Watanabe T Watts T Webb R Wenzel H Wester WC Wicklund AB Wicklund E Williams HH Wilson P 《Physical review letters》2000,84(8):1663-1668
We have studied the production of B hadrons in 1.8-TeV pp[over ˉ] collisions. We present measurements of the fragmentation fractions, f_{u}, f_{d}, f_{s}, and f_{baryon}, of produced b quarks that yield B^{+}, B^{0}, B_{s}^{0}, and Λ[over ˉ]_{b}^{0} hadrons. Reconstruction of five electron-charm final states yields f_{s}/( f_{u}+f_{d})=0.213±0.068 and f_{baryon}/( f_{u}+f_{d})=0.118±0.042, assuming f_{u}=f_{d}. If all B hadrons produced in pp[over ˉ] collisions cascade to one of these four hadrons, we determine f_{u}=f_{d}=0.375±0.023, f_{s}=0.160±0.044, and f_{baryon}=0.090±0.029. If we do not assume f_{u}=f_{d}, we find f_{d}/f_{u}=0.84±0.16. 相似文献
963.
Trischuk W de Troconiz JF Tseng J Turini N Ukegawa F Vaiciulis T Valls J Vejcik S Velev G Vidal R Vilar R Volobouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ Watanabe T Waters D Watts T Webb R Wenzel H 《Physical review letters》2000,85(10):2062-2067
We use 106 pb (-1) of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an antitop quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to t&tmacr; are presented. At the 95% confidence level, we exclude the existence of a leptophobic Z' boson in a model of top-color-assisted technicolor with mass M(Z')<480 GeV/c(2) for natural width gamma = 0.012M(Z'), and M(Z')<780 GeV/c(2) for gamma = 0.04M(Z'). 相似文献
964.
Tipton P Tkaczyk S Tollefson K Tollestrup A Toyoda H Trischuk W de Troconiz JF Tseng J Turini N Ukegawa F Vaiciulis T Valls J Vejcik III Velev G Vidal R Vilar R Volobouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ 《Physical review letters》2000,85(10):2056-2061
We report the results of a search for second and third generation leptoquarks using 88 pb(-1) of data recorded by the Collider Detector at Fermilab. Color triplet technipions, which play the role of scalar leptoquarks, are investigated due to their potential production in decays of strongly coupled color octet technirhos. Events with a signature of two heavy flavor jets and missing energy may indicate the decay of a second (third) generation leptoquark to a charm (bottom) quark and a neutrino. As the data are found to be consistent with standard model expectations, mass limits are determined. 相似文献
965.
Barium Ferrite (BaFe12O19) films have been successfully deposited on high silica glass substrates using an inductively coupled plasma source. Precursor of the metals used was a barium acetate and ferric nitrate solution of controlled concentration which was injected into the hot region of the plasma using a nebulizer. Variables studied included molar ratio of precursor liquid, substrate to plasma distance, plasma torch power, and oxygen concentration in plasma and carrier gas. Films were characterized for microstructure, composition and magnetic properties using scanning and transmission electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and vibrating sample magnetrometry. Results indicate that barium ferrite forms under certain conditions of oxygen content in the plasma and substrate temperature above 800°C. Magnetic properties indicate that there is some degree of preferred orientation of the barium ferrite crystals on the substrate, and coercivity and magnetization correspond to that of a hard magnetic material. 相似文献
966.
Picón Zamora D Martı́nez Vidal JL Martı́nez Galera M Garrido Frenich A López González JL Arahal MR 《Talanta》2003,60(2-3):335-344
This paper addresses an attempt to overcome the deviation that results from the use of a solid phase extraction (SPE) procedure for extracting trace levels of three benzimidazole pesticides (carbendazim, fuberidazole and thiabendazole) from water samples, for their subsequent quantitative determination by spectrofluorimetry, using univariate calibration. The deviation is due to an attenuation effect originating in the C(18) cartridge used in the SPE step. The approach developed is based on the calculation of a correction factor (fc) that is dependent on the signal measured after the SPE step. In order to calculate fc a study of the intermediate precision of two calibration graphs (with and without SPE) was performed. The fc was added to the predicted concentrations for the analytes using a calibration graph for pure solvent, built every time that the analysis is done. In addition, predictions were made using both average calibration graphs obtained from the intermediate precision study. In this study, the first of these three options was shown to improve the accuracy of predictions in the presence of matrix effects. 相似文献
967.
M José Campello Luis Castedo José M Saá Rafael Suau M.Carmen Vidal 《Tetrahedron letters》1982,23(2):239-240
The first two cancentrine-type cularines, namely sarcocapnine and oxosarcocapnine were isolated from (D.C.). Their structure has been proposed on chemical and spectroscopic data. 相似文献
968.
Graham Hungerford Mário Rui Pereira João A. Ferreira Teresa M. R. Viseu Anabela F. Coelho M. Isabel C. Ferreira Klaus Suhling 《Journal of fluorescence》2002,12(3-4):397-417
The photophysical behavior of several probes incorporated in sol-gel–derived matrices (both monoliths and thin films) has been studied using steady-state and time-resolved fluorescence, along with fluorescence anisotropy to study the matrix structure and to elucidate probe-matrix interactions. The probes studied include laser and solvatochromic dyes along with porphyrins and phthalocyanines. It was found that spectral shifts, time-resolved decays, and quantum yields depend on the type of matrix and its preparation conditions combined with the drying time and the nature of retained solvent, which can be added to act as an anticracking agent. The differences between the results in the TiO2 matrix, where electron transfer is most probably present, and SiO2 are shown. 相似文献
969.
R. V. Valqui Vidal 《Journal of Optimization Theory and Applications》1987,54(3):583-589
This note presents a family of linear maximum principles for the discrete-time optimal control problem, derived from the saddle-point theorem of mathematical programming. Some simple examples illustrate the applicability of the main theoretical results. 相似文献
970.