共查询到20条相似文献,搜索用时 31 毫秒
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The mass spectra of the excited heavy baryons consisting of two light (u,d,s) and one heavy (c,b) quarks are calculated in the heavy-quark–light-diquark approximation within the constituent quark model. The light quarks, forming the diquark, and the light diquark in the baryon are treated completely relativistically. The expansion in v/c up to the second order is used only for the heavy (b and c) quarks. The internal structure of the diquark is taken into account by inserting the diquark–gluon interaction form factor. An overall good agreement of the obtained predictions with available experimental data is found. 相似文献
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C. Carimalo N. Arteaga-Romero S. Ong 《The European Physical Journal C - Particles and Fields》1999,11(4):685-693
We present predictions for exclusive photoproduction of a meson on proton at large transfer, where we use a quark–diquark structure model for the proton. Extrapolation from our results
to lower transfers is comparable in magnitude with available data in that range. This may support the diquark model in its
ability to provide, for that process, an appropriate link between diffractive physics at low transfer and the standard semiperturbative
approach of hard exclusive processes at very large transfer, in which the proton recovers its three-quark structure.
Received: 5 November 1998 / Revised version: 13 July 1999 / Published online: 3 November 1999 相似文献
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We check a commonly used approximation in which a baryon with a heavy quark is described as a heavy quark–light diquark system. The heavy quark influences the diquark internal motion reducing the average distance between the two light quarks. Besides, we show how the average distance between the heavy quark and any of the light quarks, and that between the heavy quark and the center of mass of the light diquark, are smaller than the distance between the two light quarks, which seems to contradict the heavy quark–light diquark picture. This latter result is in agreement with expectations from QCD sum rules and lattice QCD calculations. Our results also show that the diquark approximations produces larger masses than the ones obtained in a full calculation. 相似文献
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A. Nogová 《Czechoslovak Journal of Physics》1985,35(12):1325-1330
Results are presented on baryon production in ¯vn and ¯vp collisions obtained within the framework of Monte Carlo quark-parton model. The inclusive distributions of protons and lambdas are compared with data. It is shown that the model which does not introduce diquarks can give satisfactory results on the distributions of baryons both in the target and fragmentation regions.The author is indebted to J. Piút for valuable suggestion and advices and to P. Lichard for help in computing and for discussions. 相似文献
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I. M. Narodetskii Yu. A. Simonov V. P. Yurov 《Zeitschrift fur Physik C Particles and Fields》1992,55(4):695-700
Color-magnetic interaction with a smearing function found from the fit to the - splitting is strong enough to support a bound state of a single
pair. We present some piloting calculations in order to illustrate the eigenenergy dependence on the cutoff parameter for different choices of the smearing function. In the threequark system the spin-spin interaction can lead to the existence of the short-range correlations in each1
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qq subsystem, thereby providing the dynamical mechanism for the quark-diquark picture of the proton. 相似文献
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J. D. Betancur-Rios K. Nomura C. J. Wang G. A. Pérez Alcazar J. A. Tabares 《Hyperfine Interactions》2008,187(1-3):43-48
The purpose of this paper is to investigate the isothermal behavior of Fe–27.3Mn–7.6Al–C–6.5Cr–0.25Si–0.88Mo (Mo(0)) and Fe–27.3Mn–7.6Al–1.0C–6.5Cr–0.25Si (Mo(1)) alloys and compare it against Fe–9Cr–1Mo (FCR) commercial alloy. The experiments were carried out at 600°C, 700°C, 750°C and 850°C, each one during 72 h in static air. The oxidation kinetics was measured as a function of time using a Thermogravimetry analyzer (TGA). The structure and composition of the oxide scale were characterized by X-ray diffraction (XRD) and Integral Conversion Electron Mössbauer Spectroscopy (CEMS). The TGA results show that at all oxidation temperatures the sample FCR exhibit the lowest kinetic corrosion and the lowest weight gain, whereas Mo(0) the highest. By CEMS technique it were found a broad magnetic sextet, which has been fit by one hyperfine field distribution with mean hyperfine field characteristic to ferritic/martensite phase, one Fe3?+? doublet and one singlet for the Mo(0) and Mo(1) alloys. Samples oxidized at highest temperatures exhibit a strong paramagnetic line, probably due that the Cr or Mn oxides may be enriched on the surface. Then, the magnetic phase can be converted partially into austenite phase at highest temperatures. 相似文献
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The performance of a CMOS-compatible electro-optic Mach-Zehnder plasmonic modulator is investigated using electromagnetic and carrier transport simulations. Each arm of the Mach-Zehnder device comprises a metal–insulator–semiconductor–insulator–metal (MISIM) structure on a buried oxide substrate. Quantum mechanical effects at the oxide/semiconductor interfaces were considered in the calculation of electron density profiles across the structure, in order to determine the refractive index distribution and its dependence on applied bias. This information was used in finite element simulations of the electromagnetic modes within the MISIM structure in order to determine the Mach-Zehnder arm lengths required to achieve destructive interference and the corresponding propagation loss incurred by the device. Both inversion and accumulation mode devices were investigated, and the layer thicknesses and height were adjusted to optimise the device performance. A device loss of <8 dB is predicted for a MISIM structure with a 25 nm thick silicon layer, for which the device length is <3 μm, and <5 dB loss is predicted for the limiting case of a 5 nm thick silicon layer in a 1.2 μm long device: in both cases, the maximum operating voltage is 7.5 V. 相似文献
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Microstructure, electrical, mechanical and thermal properties of quenched bismuth–tin eutectic, Rose (Bi50Sn22.9Pb27.1) and Wood’s (Bi50Sn12.5Pb25Cd12.5) alloys have been investigated using scanning electron microscopy, X-ray diffraction analysis, the double bridge method, the dynamic resonance method, Vickers hardness measurement and thermal analysis. Wood’s alloy (Bi–Pb–Sn–Cd) has low electrical resistivity and melting point but a high elastic modulus and internal friction when compared with the Rose (Bi–Pb–Sn) alloy. The presence of cadmium in Wood’s alloy decreases its melting point and electrical resistivity with an increase in its elastic modulus, which improves the mechanical properties. Wood’s alloy (Bi–Pb–Sn–Cd) has better properties, which make it useful in various applications such as in protection shields for radiotherapy, locking of mechanical devices and welding at low temperature. 相似文献
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We construct and study a new topological field theory in three dimensions. It is a hybrid between Chern–Simons and Rozansky–Witten theory and can be regarded as a topologically-twisted version of the N=4d=3 supersymmetric gauge theory recently discovered by Gaiotto and Witten. The model depends on a gauge group G and a hyper-Kähler manifold X with a tri-holomorphic action of G. In the case when X is an affine space, we show that the model is equivalent to Chern–Simons theory whose gauge group is a supergroup. This explains the role of Lie superalgebras in the construction of Gaiotto and Witten. For general X, our model appears to be new. We describe some of its properties, focusing on the case when G is simple and X is the cotangent bundle of the flag variety of G. In particular, we show that Wilson loops are labeled by objects of a certain category which is a quantum deformation of the equivariant derived category of coherent sheaves on X. 相似文献
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Variations of Vickers hardness were observed in Al–Mg–Mn alloy and Al–Mg–Mn–Sc–Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al–Mg–Mn–Sc–Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1−xZrx and also block-shaped Al3Sc precipitates growing along <1 0 0>Al with facets {1 0 0} and {1 1 0} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc. 相似文献
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We have investigated the plastic deformation properties of single-phase Zr–Nb–Ti–Ta–Hf high-entropy alloys from room temperature (RT) up to 300 °C. Uniaxial deformation tests at a constant strain rate of 10?4?s?1 were performed, including incremental tests such as stress relaxations, strain-rate changes, and temperature changes in order to determine the thermodynamic activation parameters of the deformation process. The microstructure of deformed samples was characterized by transmission electron microscopy. The strength of the investigated Zr–Nb–Ti–Ta–Hf phase is not as high as the values frequently reported for high-entropy alloys in other systems. At RT we measure a flow stress of about 850 °C. We find an activation enthalpy of about 1 eV and a stress dependent activation volume between 0.5 and 2 nm3. The measurement of the activation parameters at higher temperatures is affected by structural changes evolving in the material during plastic deformation. 相似文献
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We study a novel five-species system on two-dimensional lattices when each species have two superior and two inferior partners. Here we simplify the huge parameter space of predation probability to only two parameters. Both of Monte Carlo simulation and Mean Field Theory reveal that two of strategies may die out when the ratio of the two parameters is close to the golden point 0.618, and the remaining three strategies are provided a cyclic dominance system. 相似文献
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We show how the Hintermann–Merlini–Baxter–Wu model (which is a generalization of the well-known Baxter–Wu model to a general Eulerian triangulation) can be mapped onto a particular infinite-coupling-limit of the Ashkin–Teller model. We work out some mappings among these models, also including the standard and mixed Ashkin–Teller models. Finally, we compute the phase diagram of the infinite-coupling-limit Ashkin–Teller model on the square, triangular, hexagonal, and kagome lattices. 相似文献
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Microwave induced d.c. voltage due to inverse a.c. Josephson effect has been observed across bulk samples of Y-Ba-Cu-O and Y-Ba-Sr-Cu-O. The d.c. voltage is found to vary with microwave power, frequency and also with small external magnetic fields. Although the resistivity curve of Y-Ba-Cu-O does not show any appreciable resistance drop around 230 K, the microwave induced d.c. voltage due to the inverse a.c. Josephson effect has been found to exist upto 230 K. The resistivity behaviour of Y-Ba-Sr-Cu-O shows a sharp resistivity drop above 230 K. In this sample the inverse Josephson effect is found to exist upto +26 °C, indicating the presence of a phase having a superconducting onset around this temperature. 相似文献
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V. Bhat A. K. Ganguli K. S. Nanjundaswamy R. A. Mohan Ram J. Gopalakrishnan C. N. R. Rao 《Phase Transitions》2013,86(1-2):87-95
Abstract High-TC superconducting oxides of nominal La1.85Ba0.15 CuO4 and YBa2 Cu3 O7 have been prepared by using nitrate, carbonate, oxalate/malonate and citrate precursors. While the samples in the Y-system are generally monophasic YBa2Cu3O7?δ with TC around 90K, the preparations in the La-system are biphasic containing K2NiF4-like La1.85Ba0.15 CuO4 (TC = 30K) and a perovskite-like phase with' a much higher TC (200–300K). Effect of Ca, Zr, Ce as well as S substitution in YBa2Cu3O7?δ has also been investigated 相似文献
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We study the geodesic motion of pseudo-classical spinning particles in the NUT–Reissner–Nordstrom space–time. We investigate the generalized Killing equations for spinning space and derive the constants of the motion in terms of the solutions of these equations. We give an analysis of the motion on a cone and on a plane. 相似文献