共查询到20条相似文献,搜索用时 15 毫秒
1.
Satoshi Watamura 《Physics letters. [Part B]》1984,136(4):245-250
We examine the compactification of D=4+2N, Einstein-Maxwell-Dirac theory. It is shown that the manifold CPN × M4 is a solution of the equations of motion. The structure of the fermions, gauge bosons and their couplings in the four-dimensional effective theory is investigated. The scale of CPN is quantized by a generalized Dirac condition. When the results are applied to the solution with internal space CP1×CP2, the weak mixing angle and the ratio of the couplings of SU(3) (g3) and SU(2) (g2) are defined by two integers and a hypercharge. An SU(3)-triplet chiral fermion can appear in four-dimensional effective theory. 相似文献
2.
H.Vernon Smith 《Nuclear Physics A》1974,224(3):561-572
We investigate the 40Ca(d, α0, 1, 2, 4)38K reactions for Ed = 4.00–4.61 MeV. The α1 and α4 transitions are isospin forbidden. The resonant-like structures observed in the α0, α1, α2, and α4 transitions are consistent with Ericson theory. In addition we can fit a portion of the α1, data with a few interfering Breit-Wigner resonances. The level parameters for the corresponding 42Sc levels are given. 相似文献
3.
C.S. Guo 《Solid State Communications》2006,137(10):549-552
The structural and electronic properties of the armchair Cx(BN)y nanotubes are studied using the density functional theory with a generalized gradient approximation. The results show that the properties of the Cx(BN)y nanotubes are intermediate between those of carbon nanotubes and BN nanotubes, and also adjustable by their radius, ratio of carbon component, and configurations. 相似文献
4.
Kentaro Onabe 《Journal of Physics and Chemistry of Solids》1982,43(11):1071-1086
An improved theory based on the pair approximation is given for the thermodynamic properties of type A1?xBxC1?yDyIII–V quaternary solid solutions. The theory takes into account the quasi-chemical nature of the nearest neighbor pair distribution, which has been neglected or inadequately treated in previous work. With a suitable thermodynamic treatment, a quasi-chemical equilibrium relation for the nearest neighbor pair distribution is derived. Numerical calculations using available thermodynamic data show that the distribution will deviate appreciably from random mixing values in the In1?xGaxP1?yAsy and Al1?xGaxAs1?ySby systems due to a short-range clustering effect of nearest neighbor pairs with strong bond energy, whereas the deviation will be small in the Al1?xGaxP1?yASy system. The expressions for the chemical potentials and the activity coefficients of the binary compound components are given. These are readily applicable to phase diagram calculations. 相似文献
5.
As a perturbation to the P(?)2 theory we consider interaction densities of the form V(?(x)), where ?(x) is a scalar hermitian boson field and V(α) is a bounded real continuous function. It is proved that the asymptotic fields exist and are equal to the asymptotic fields of the P(?)2 theory. The connection with non-polynomial theories of rational type is indicated. Furthermore the consequences of a bounded perturbation for the S-matrix and the spectral properties are discussed. 相似文献
6.
The susceptibilities of polycrystalline samples of various antiferromagnetic linear-chain compounds ANiX3 (A =Tl, NH4, Rb, Cs and X = Cl, Br) have been measured in the temperature region 2–200 °K. The results, amongst which the already known data for RbNiCl3 and CsNiCl3, are interpreted in terms of a theory, developed by Weng, for antiferromagnetic Heisenberg linear-chain systems with spin S = 1. By means of Oguchi's Green function theory and the experimentally determined transition temperatures TN the order of magnitude of the ratio between inter- and intra-chain interaction is obtained. 相似文献
7.
The k-linear intravalence and intraconduction band coupling terms along the 〈111〉 directions are shown to explain the anomalously large strength of the E′1 structure relative to E′1 + Δ′1 and also the large energy separation between them. Quantitative agreement between theory and experiment is obtained using intraband coupling values calculated from k · p perturbation theory. 相似文献
8.
High-resolution measurements of the KL2,3L2,3 radiative Auger edge in Mg and Al are reported. The theory of soft X-ray absorption thresholds by Flynn and Lipari is modified to account for the KL2,3L2,3 threshold energies. The calculated energies are in excellent agreement with the experimental results including previous measurements on Si. 相似文献
9.
We give the complete asymptotic reggeon field theory (RFT) scaling law for the elastic cross section in O(?2), extending previous results to include the 3-pomeron cut. This provides the most detailed realistic test of this theory. Numerically we find the encouraging result that the small-t SPS collider data for dσel/dt are in agreement with these new asymptotic RFT predictions. However, ISR data are not compatible with this theory, either in s or t dependence. Previous positive ISR results were largely due to the existence of a j = 1 fixed cut which is not present here. Our results, coupled with the observation that critical RFT fits to σtot require large non-leading terms, imply that a lower bound for the RFT asymptotic scale in single renormalized propagator processes (σtot,dσel/dt) lies around SPS-collider energies. The asymptotic scale for multi-propagator processes (the rapidity plateau, ab→aX reactions, multiplicity distributions etc.) is expected to be well beyond the SPS collider. A possible global RFT picture is them that perturbation theory (including finite rapidity scale effects due to the excitation of new quantum numbers) is applicable through ISR and up to the SPS collider, consistent with recent observations. The critical RFT can become the relevant diffractive theory for σtot and dσel/dt at larger t at and above the SPS collider. Predictions for dσel/dt at larger t at the SPS collider are given in this paper and we urge experimentalists to test them. 相似文献
10.
M. Hamedoun R. Masrour K. Bouslykhane A. Hourmatallah N. Benzakour 《Journal of magnetism and magnetic materials》2008
By using mean field theory, we have evaluated the nearest-neighbour and the next-neighbour super-exchange J1(x) and J2(x), respectively, for Zn1−xCuxCr2Se4 in the range 0?x?1. The intraplanar and the interplanar interactions are deduced. High-temperature series expansions are derived for the magnetic susceptibility and two-spin correlation functions for a Heisenberg ferromagnetic model on the B-spinel lattice. The calculations are developed in the framework of the random phase approximation. The magnetic phase diagram is deduced. A spin glass phase is predicted for intermediate range of concentration. The results are comparable with those obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) have been deduced. The values are comparable to those of the 3D Heisenberg model, and are insensitive to the dilution x. 相似文献
11.
Four-photon mixing is used to measure spin resonance of conduction electrons in Hg1?xCdxTe (x = 0.23). The magnetic tuning rate and the motionally narrowed linewidth are studied experimentally below and through the quantum limit and comparison is made with theory. 相似文献
12.
The temperatures at which the cooperative Jahn-Teller phase transitions occur in TbcGd1?cVO4 have been determined from Raman and optical birefringence measurements. Over a narrow range of c there are two transition temperatures; between these temperatures the crystal is distorted, but a higher and lower temperatures the crystal has the same undistorted structure. This unusual behaviour was predicted earlier, and is accurately described by molecular field theory. 相似文献
13.
Electronic structure calculations were performed for substitutional erbium rare-earth impurity in cubic GaN using density-functional theory calculations within the LSDA+U approach (local spin-density approximation with Hubbard-U corrections). The LSDA+U method is applied to the rare-earth 4f states. The ErxGa1−xN is found to be a semiconductor, where the filled f-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty f-states are also shown to shift downwards and upwards in the valence and conduction bands, respectively, with increase in the U potentials. 相似文献
14.
G. LalithaP. Venugopal Reddy 《Physica B: Condensed Matter》2011,406(19):3568-3575
With a view to understand the elastic behaviour of a material system, La0.67Sr0.33−xBaxMnO3 (where x=0, 0.1, 0.2, and 0.33) especially in the vicinity of their magnetic transition temperature TC, a systematic investigation of ultrasonic velocity over a temperature range 300-400 K has been carried out. The materials prepared by citrate gel route, were characterized structurally by XRD and on analyzing the XRD patterns, it has been concluded that all the samples are having rhombohedral structure with space group of R3?c. The magnetic (TC) transition temperatures determined by AC susceptibility measurements are found to decrease continuously with increasing barium concentration. Finally, the ultrasonic longitudinal velocities of all the samples are found to exhibit considerable softening in the vicinity of their magnetic transition temperatures, TC and the observed behaviour is explained using mean field theory and Jahn-Teller theorem. 相似文献
15.
K. Ragavendran 《Physica B: Condensed Matter》2009,404(2):248-250
Density functional theory is used to understand the response of the transition metal-oxygen octahedra in LixMn2O4 and LixNi0.5Mn1.5O4 to lithium intercalation and de-intercalation. Electronic structure computations on these compounds for x=0, 0.5 and 1 indicate that the 3d DOS of Mn is almost unaffected to variations in x. On the other hand, the oxygen 2p-DOS and to a lesser extent Ni 3d DOS are found to be sensitive to perturbation. The observations are explained on the grounds of self-regulating response, characteristic of systems having localized d states that communicate with a covalent manifold. 相似文献
16.
The magnetic contribution to the thermoelectric power was separated for the metallic glass Fe20Ni60B10Si10 which exhibits the ferro-paramagnetic transition at Tc = 455 K remarkably below the crystallization threshold Tx = 670 K. Results are compared with the predictions of the Kasuya theory. 相似文献
17.
The magnetic properties of the Ca1−xMnxO systems in the range 0?x?1 have been studied by mean field theory and high-temperature series expansions (HTSEs). By using the first theory, we have evaluated the nearest neighbour and the next-neighbour super-exchange interaction J1(x) and J2(x) respectively, in the range 0.45?x?1. The corresponding classical exchange energy for magnetic structure is obtained for the Ca1−xMnxO systems. The HTSEs combined with the Padé approximants (PA) method is applied to the Ca1−xMnxO systems; we have obtained the magnetic phase diagrams (TN or TSG versus dilution x) in the range 0?x?1. The obtained theoretical results are in agreement with experimental ones obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) are deduced in the range 0?x?1. 相似文献
18.
M.G. Albrow D. Aston D.P. Barber L. Bird R.J. Ellison C.H. Halliwell R.E.H. Jones A.D. Kanaris F.K. Loebinger P.G. Murphy M.G. Strong J. Walters D.D. Yovanovich R.F. Templeman 《Nuclear Physics B》1973,58(1):22-30
In a study of charged KL0 three-body decays a sample of 6668 KL0 → π±e?ν candidates has been obtained. The Dalitz plot distribution is in agreement with V ? A theory, and limits are presented for scalar and tensot contributions to the weak current. Using a conventional expansion for the form factor f+ we find λ+ = 0.055 ± 0.010 with systematic effects estimated at ± 0.01. 相似文献
19.
The lattice and electronic properties for 5d-shells Ir substituted Fe-based superconductor SmOFe1−xIrxAs (x=0,0.2,0.25,0.3) are investigated based on the density functional theory (DFT) with a spin generalized gradient approximation SGGA+U method. The electronic density of states (DOS) of SmOFe1−xIrxAs is studied and well compared with the results of experimental X-ray photoemission spectroscopy (XPS). The calculation indicated that iridium substitution at the Fe site induced a modification of the FeAs4 tetrahedron and suppressed the magnetic ordering corresponding to the Fe-3d, which may be the main cause of inducing superconductivity in Ir-doped SmOFeAs system. 相似文献
20.
M. Bezi JavanN. Tajabor 《Journal of magnetism and magnetic materials》2012,324(1):52-59
We studied the structural, electronic and magnetic properties of small Fen clusters (n=2-7) endohedrally doped in icosahedral C60 and C80 fullerenes using first principles calculations based on the density functional theory. It is found that the encapsulated Fen clusters inside icosahedral C80 are energetically favorable while Fen@C60 metallofullerene nano-cages are not. The binding energies of the Fen encapsulated in C60 are positive and increase with the number of iron atoms (n) while those of the Fen@C80 are negative and their absolute values increase up to n=6. The encapsulation does not significantly change the enclosed cluster structure, but the total magnetic moment of the larger clusters reduces due to a stronger Fe-C hybridization. 相似文献