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1.
Charmed Deuteron     
Possible existence of bound states of a charmed baryon, Λ c , Σ c , Σ* c with a nucleon, N, as well as two charmed baryons, Λ c Λ c , etc., are examined in the meson exchange potential approach. The heavy quark spin symmetry induces a strong tensor coupling between Λ c N, Σ c N and Σ* c N states, which causes a bound state of Λ c N (J = 0+ and 1+) states. Such a bound state is also seen in the spin-singlet Λ c Λ c channel, which resembles the H dibaryon in the strange sector.  相似文献   

2.
The temperature dependences of the elastic constants, c11, c33, c44, and c66, in KCP are described. In the temperature range 10–100 K softening is observed in c44, while c66 decreases almost linearly with decreasing temperature. These results indicate the presence of a new critical region.  相似文献   

3.
The stability of large Fröhlich bipolarons in the presence of a static magnetic field is investigated with the path integral formalism. We find that the application of a magnetic field (characterized by the cyclotron frequence ω c) favors bipolaron formation: (i) the critical electronphonon coupling parameter α c (above which the bipolaron is stable) decreases with increasing ω c and (ii) the critical Coulomb repulsion strength U c (below which the bipolaron is stable) increases with increasing ω c. The binding energy and the corresponding variational parameters are calculated as a function of α, U and ω c. Analytical results are obtained in various limiting cases. In the limit of strong electron-phonon coupling (α ? 1) we obtain for ω c ? 1 that E estim ? E estim(ω c = 0) + c(u)ω c/α 4 with c(u) an explicitly calculated constant, dependent on the ratio u = U/α where U is the strength of the Coulomb repulsion. This relation applies both in 2D and in 3D, but with a different expression for c(u). For ω c ? α 2? 1 we find in 3D E estim ? ω c - α 2 A(u) ln2(ω c/α 2), (also with an explicit analytical expression for A(u)) whereas in 2D E estim 2D ? ω c - αω cπ(u-2-√2)/2. The validity region of the Feynman-Jensen inequality for the present problem, bipolarons in a magnetic field, remains to be examined.  相似文献   

4.
The theoretical shear strength (τ c ) and its temperature dependence for a series of FCC and HCP metals have been calculated. Despite the obtained differences in temperature dependences of τ c , critical deformation (γ c ), and shear modulus (G), the fact of a weak temperature dependence of ratio Gγ c c relating these quantities is established for all studied materials. The deviation of Gγ c c from the average value in the temperature ranges under consideration is no more than 12%.  相似文献   

5.
In order to elucidate the anisotropic pressure effect on superconductivity in an iron-based superconductor, magnetization measurements have been performed in Ba(Fe0.92Co0.08)2As2 single crystals under uniaxial pressures applied along the c-axis. Gigantic Tc suppression, dTc/dP//c = −15 K/GPa, was observed when the anisotropic deformation with the a-expansion and c-compression was induced by the c-pressure, which should be compared with dTc/dP < +1 K/GPa in the isotropic pressure case. This suggests that the a-axis (c-axis) compression has a positive (negative) contribution to Tc.  相似文献   

6.
The behavior of the elastic properties and their pressure derivatives near the martensitic transformation ββ′ was determined from sound velocity measurements at a frequency of 10 MHz, on a single crystal of Au-47.5 at.% Cd.The transformation of the β phase to the martensitic β' phase was obtained from the anisotropic elastic constants c11, c44 and c′, and their pressure derivatives. The behaviour of c11 and c44 is normal as a function of temperature, while the variation of c′ is positive with temperature. Before the ββ′ phase change the value of c′ is very small and exhibits high elastic anisotropy. The small value of c′ and the anisotropy were explained according to the crystallographic mechanism of the martensitic transformation and the Zener theory of instability of the b.c.c. structure. The pressure derivatives of c′ are negative and the variation of dc44dP with temperature is anomalous. This behavior can be explained by the influence of pressure on the transformation temperature, and by the instability of the β phase. It was found that the elastic constants c′ determine the mechanism of the transformation. From the pressure derivatives of c11, c44 and c′ the Grüneisen parameters for different modes of vibration were calculated. For the c′ mode the values are negative, for the c44 mode the variation of the parameter with temperature is negative. This anomalous behavior can be explained as due to the anisotropic softening of the atom bonding on the (110) planes of the cubic structure, as a consequence of the phase transformation mechanism.  相似文献   

7.
Antiproton-proton elastic scattering data at 6.2 GeV/c in the range 0.3 (GeV/c)2 ? ?t ? 10.0 (GeV/c)2 is presented. The experiment, using spark chambers and proportional chambers, was performed at the CERN Proton Synchroton.The dip at about ?t = 0.5 and the structure at about ?t = 2.2 (GeV/c)2 are equally strong at 6.2 GeV/c as they are at 5.0 GeV/c. The differential cross sections around 90° c.m. are not very different at 5.0 GeV/c and at 6.2 GeV/c, whereas in the backward region there is a decrease of the order of one magnitude.  相似文献   

8.
The symmetry breaking corrections to the pion?Cbaryon couplings vanish to first order in 1/N c, where N c is the number of colours. Loop graphs with octet and decuplet intermediate states cancel to various orders in N c as a consequence of the large-N c spin-flavour symmetry of QCD baryons. The baryon axial vector current is computed at one-loop order in heavy baryon chiral perturbation theory in the large N c limit. 1/N c corrections in the case of g A in QCD are presented here.  相似文献   

9.
A unified model of the superconducting mechanism has been put forward. The model suits not only to high-Tc but also to low-Tc superconductors. It is found that there are superconducting domains (SD) in crystal. When TTc, all the SD’s in the whole crystal are connected with one another. We have obtained the formula of Tc. On the basis of the formula and theory of quantum mechanics, the different behaviours of isotopic effects in low- and high-Tc superconductors as well as C60, the triangular peak of Tc of transition metals, Matthias rules, and other effects are explained. New superconductors with higher Tc are predicted.  相似文献   

10.
The statistical behaviour of the variances, covariance and gradients of the reaction progress variable (c), and the mixture fraction (ξ) have been analysed in a pulverised coal jet flame using a three-dimensional carrier phase direct numerical simulation (DNS) dataset. It has been observed that the Favre-probability density functions (PDFs) of c and ξ can be parametrised by the standard β function. Furthermore, the log-normal distribution has been found to accurately represent |?c| and |?ξ|. It is also found that ?c and ?ξ remain aligned throughout the flame brush. Finally the joint PDF of |?c| and |?ξ| has been compared with the product of the PDF of |?c| and PDF of |?ξ| extracted from carrier phase DNS, and it has been found that |?c| and |?ξ| are not statistically independent in the case investigated.The bivariate log-normal distributions with and without correlation have also been considered, and the former is found to be in better agreement with the carrier phase DNS data.  相似文献   

11.
In this work, it is theoretically discussed the magnetocaloric effect in the Laves phase doped compounds (Ho1?c Er c )Co2 and (Ho1?c Dy c )Co2. To this end, it has been used a model Hamiltonian of localized states and itinerant 3d-electrons, including the crystalline electrical field and the magnetoelastic interaction. The theoretical calculations show that composite materials made up of several samples of the doped compounds (Ho1?c Er c )Co2 and (Ho1?c Dy c )Co2 exhibit large values of the magnetocaloric potentials in a wide range of temperatures.  相似文献   

12.
We studied the electromagnetic form factors(EMFFs) of Λ_c and the contributions of the quark and diquark currents to the EMFFs of Λ_c in the space-like region in the Bethe–Salpeter equation approach with instantaneous approximation. In this picture, baryon Λ_c can be regarded as a two-body c(ud) system. We found that for different values of parameters the contribution of quark and diquark currents to the EMFFs of Λ_c is very different,while their total contribution to the EMFFs of Λ_c is similar. The EMFFs of Λ_c are similar to those of other baryons(proton, Ξ~-, and Σ~+) with a peak at ω = 1, where ω = v′·v is the velocity transfer between the initial state(with velocity v) and the final state(with velocity v′) of Λ_c.  相似文献   

13.
It is shown that the Toxen relationship Δ/kTc = Tc/Hc(0) (dHc/dT)Tc can be used to obtain Δ/kTc as a function of pressure from critical field curves taken at high pressures. Data for Sn, In, Zn, Al, Cd, Ga, and Th are analyzed and Δ(p)/kTc are tabulated. For Sn and In a comparison was made of energy gaps so determined with those measured directly by tunnelling.  相似文献   

14.
With the neutron interferometer, measurements of the coherent neutron scattering lengths by various gases have been performed. We get the following numbers for the bound coherent scattering lengths for atoms (in fm):b c (H) =?3.64(3),b c (D)=6.55(8),b c (He?3)=5.74(7),b c (He)=3.26(3),b c (N)=9.30(8),b c (O)=5.83(5),b c (Ne) =4.63(4),b c (Ar)=2.07(2),b c (Kr)=7.52(6),b c (Xe)=4.69(4). In some cases greater accuracy is achieved in comparison with recommended values from the literature. The absolute values for hydrogen and deuterium measured with gaseous samples, are about 2% smaller than the values measured with liquids and other reference values.  相似文献   

15.
Motivated by the recent experimental observation of exclusive χ c events at the Tevatron, we revisit earlier studies of central exclusive scalar χ c0 meson production, before generalising the existing formalism to include χ c1 and χ c2 mesons. Although χ c0 production was previously assumed to be dominant, we find that the χ c1 and χ c2 rates for the experimentally considered χ c J/ψ γμ + μ ? γ decay process are in fact comparable to the χ c0 rate. We have developed a new Monte Carlo event generator, SuperCHIC, which models the central exclusive production of the three χ c states via this decay chain, and have explored possible ways of distinguishing them, given that their mass differences are not resolvable within the current experimental set-up. Although we find that the severity of current experimental cuts appears to preclude this, the acceptance does not change crucially between the three states and so our conclusions regarding the overall rates remain unchanged. This therefore raises the interesting possibility that exclusive χ c1 and χ c2 production has already been observed at the Tevatron.  相似文献   

16.
The a, b, c, and β crystallographic parameters of the (CH3)2NH2Al(SO4)2 · 6H2O crystal (DMAAS) have been measured by x-ray diffraction in the 90–300-K temperature range. The thermal expansion coefficients along the principal crystallographic axes αa, αb, and αc have been determined. It was shown that, as the temperature is increased, the parameter α decreases and b increases, whereas c decreases for T<T c (where T c is the transition temperature) and increases for T>T c, so that one observes a minimum in the c=f(T) curve in the region of the phase transition (PT) temperature T c ~ 152 K. The thermal expansion coefficients αa, αb, and αc vary in a complicated manner with increasing temperature, more specifically, αa and αc assume negative values at low temperatures, and the αa=f(T), αb=f(T), and αc=f(T) curves exhibit anomalies at the PT point. The crystal has been found to be substantially anisotropic in thermal expansion.  相似文献   

17.
The Tc and Hc2 of hexagonal single crystals Rb0.2WO3 were measured. Upper critical field rotation data in the plane perpendicular to the c-axis showed a large anisotropy with a 60° periodicity. Rotation in a plane containing the c-axis showed an even larger anisotropy having 180° symmetry.  相似文献   

18.
Evidence for the quasi-elastic production of the doubly charged charmed barron Σ++c has been observed in a vp interaction in BEBC. The mass of the Σ++c and of its decay product, the Λ+c, are 2454±5 MeV and 2288±5 MeV, respectively. The mass difference M(Σ++c)? M(Λ+c) is 166±1 MeV. Combining the Λ+c mass value obtained here with the values obtained in the two Λ+c events previously observed in this experiment, thevalue M(Λ+c)=2283±3 MeV is deduced.  相似文献   

19.
《Physica A》1995,216(3):316-332
In disordered anisotropic square +/− J Ising models SQ(p, q) at groundstates we investigate the pairs (pc, qc) of critical concentrations of antiferromagnetic bonds with concentrations p,q, respectively in orthogonal coordinate directions. We are led to pc(q) ≈ π(q) with π(q) from the so-called adjoined problem. This approach is well supported by simulations for different values of q on the basis of minimal matchings of frustrated plaquettes. In particular, pc(0) ≈ 0.21 from simulations and π(0) = 0.2113248 …, with the conjecture that pc(0) = π(0). The concept of the adjoined problem is extended to d-dimensional (hyper-) cubic lattices. We hereby obtain for pc,d especially in the sotropic case: pc,3 ≈ 0.154, pc,4 ≈ 0.170, pc,5 ≈ 0.178, pc,6 ≈ 0.182. Moreover, in analogy to SQ(p,q) we used the approach also for honeycomb Ising models HC(p,q,r) with no antiferromagnetic bonds in the third plaquette direction (r = 0).  相似文献   

20.
The room-temperature isomer shifts of iron in nickel aluminides have been measured. A single Mössbauer-resonance line is observed for alloys of composition (NiAl)100-cFec, 0 ? c ? 5 at. %, and Al50Ni50-cFec, 2 ? c ? 50 at. %. The isomer shift for dilute Fe concentration in stoichiometric NiAl is compared with that for FeAl at stoichiometric composition.  相似文献   

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