The Second Moments of the Line Shapes of Multiple Quantum NMR Coherences in One-Dimensional Systems

The second moments of the line shapes of the zeroth- and second-order multiple quantum NMR coherences determined by the dipole–dipole interactions of nuclear spins in crystals have been calculated. The second moments determined by the zz part of the dipole–dipole interaction have been derived both by a direct calculation and based on the exact solution (in terms of the zz model) for the decay of the multiple quantum coherence intensities on the evolution period of a multi-quantum NMR experiment. The decay of the multiple quantum NMR coherence intensities in a single crystal of calcium fluorapatite is well described by the Gaussian curves with the calculated second moments.     

Monte Carlo simulation in the theory of wave propagation in random media: II. Scintillation index, second and fourth moments

The purpose of this article (comprising parts I and II) is to develop and test the approach of combining a path-integral technique and a complex-valued Monte Carlo method to calculate the highest moments of the Green function of the stochastic wave equation for media with random small-scale inhomogeneities against the background of large-scale inhomogeneities. In part II calculations of the second and fourth moments of the Green function and the scintillation index have been performed for 1D and 2D cases in the framework of three models: a model of the stochastic wave equation and models of parabolic and Markov approximations. The finiteness of the correlation radius of inhomogeneities has been shown to be the reason for the significant difference between the Markov approximation and the other two. The results obtained prove that the applicability of the parabolic approximation (without the Markov approximation) is much wider than might be expected. A comparison has been made showing good agreement with reliable results for 1D media. The Monte Carlo results have exhibited the singularities existing at the localization centres and forming exponential decay of the second moment from distances of about one wavelength. The unexpected sharp oscillations interrupting the exponential decay of the Green function moments have been obtained at distances from the localization centre of several tens of times the average distance between scatterers. The effect of weak large-scale inhomogeneities on the behaviour of the second moment has also been investigated.     

Statistical bootstrap of fireball decay spectra

We propose a generalized statistical bootstrap equation for the generating functional of the fireball decay spectra which includes the bootstrap of the hadronic mass spectrum. In the form of an integral representation a solution is given for some n-particle distributions as well as multiplicity moments in the case of identical particles. Within this formalism we are able to discuss decay-chain end effects and to treat quantum number conservation explicity. The general equation is approximated by a simpler bootstrap equation for the linear decay chain with quantum-number conservation. An asymptotic solution for the single particle distributions according to this equation is discussed.     

Distribution of film orientations in free and strained foams

We show that the distribution of film orientations in a free (i.e., unstrained) foam cluster, though in general not uniform, has the same second moments as a uniform distribution. This is, however, in general not true of its other moments, which reflects the internal order of film orientations imposed by Plateau's laws. For a strained cluster, we relate the deviations of the second moments of the orientation distribution from their values for an unstrained cluster, to the stresses acting on the cluster. Our predictions are corroborated by experimental results for free and strained two-dimensional clusters, allowing us to find the force on a cluster bounded by two parallel walls.     

Spectroscopic factors within the dinuclear-system model

A model of the cluster radioactivity of even—even nuclei is presented. In this model, zero-point vibrations in the charge-asymmetry coordinate determine spectroscopic factors, while tunneling in the coordinate of the relative separation of the centers of mass of the cluster and the daughter nucleus determine the penetrability of the barrier of the nucleus-nucleus potential. The conservation of the total spin and energy in the decay process is taken into account. The potential of the model for describing experimental half-lives is demonstrated. A number of predictions for possible cluster-emission reactions in the regions of lead and tin radioactivities are made.     

Magnetic enhancement in cobalt-manganese alloy clusters

Magnetic moments of Co(N)Mn(M) and Co(N)V(M) clusters (N < or = 60; M < or = N/3) are measured in molecular beams using the Stern-Gerlach deflection method. Surprisingly, the per atom average moments of Co(N)Mn(M) clusters are found to increase with Mn concentration, in contrast to bulk CoMn. The enhancement with Mn doping is found to be independent of cluster size and composition in the size range studied. Meanwhile, Co(N)V(M) clusters show reduction of average moments with increasing V doping, consistent with what is expected in bulk CoV. The results are discussed within the virtual bound states model.     

Homonuclear vanadium-51 dipolar couplings in inorganic solids obtained via hahn spin echo decay NMR spectroscopy

Dipolar dephasing of the magnetization following a Hahn spin echo pulse sequence potentially provides a quantitative means for determining the dipolar second moment in solids. In this work, the possibility of employing Hahn spin echo decay spectroscopy to obtain quantitative ⁵¹V–⁵¹V dipolar second moments is explored. Theoretical spin echo response curves are compared to experimental ones for a collection of crystalline vanadium-containing compounds. This work suggests that ⁵¹V dipolar second moments can be obtained by selectively exciting the central m = 1/2 → −1/2 by a Hahn echo sequence for vanadate compounds with line broadening no greater than approximately 220 ppm. For vanadates with greater broadening of the central transition due to chemical shift, second-order quadrupolar, and dipolar interactions, off-resonance effects lead to an oscillatory time dependence of the spin echo. Experimentally determined second moments of the normalized echo decay intensities lie within 10–33% of the calculated values if the second moments are extrapolated to zero evolution time due to the time scale dependence of spin exchange among neighboring vanadium nuclei. Alternatively, the second moments can be obtained to within 10–25% of the calculated values if the broadening of the central transition due to chemical shift and second-order quadrupolar effects can be estimated.     

Angular momentum non-conserving decays in isotropic media

Various processes that are forbidden in vacuum due to angular momentum conservation can occur in a medium that is isotropic and does not carry any angular momentum. We illustrate this by considering explicitly two examples. The first one is the decay of a spin-0 particle into a photon and another spin-0 particle, using a model involving the Yukawa interactions of the scalar particles with a charged fermion field. The second one involves the decay of a neutrino into another neutrino and a graviton, in the standard model of particle interactions augmented with the linearized gravitational couplings.     

Abelian and non-Abelian anomalies in monopole-fermion interactions

Taking an example of the standard SU(5) theory, the monopole-fermion system is reduced to an effective 2-dimensional model. This is a generalized Schwinger model containing four Abelian gauge fields interacting with N generations of massless fermions through vector and axialvector couplings. We quantize such a system exactly in the canonical operator formalism. Then, analyzing the cluster property of operators carrying various chiral charges, the roles of the Abelian and non-Abelian anomalies are studied in monopole-induced baryon decay. We demonstrate that the Abelian anomaly and the charge-mixing boundary condition are the driving forces for monopole-induced baryon decay, though the conservation law suggests the importance of the non-Abelian anomaly.     

Negative binomial multiplicity distribution from binomial cluster production

Two step interpretation of negative binomial multiplicity distribution as a compound of binomial cluster production and negative binomial like cluster decay distribution is proposed. In this model we can expect the average multiplicity for the cluster production increases with increasing energy, different from a compound Poisson-Logarithmic distribution in [4, 5].     

Two-particle Pseudorapidity Correlations in pp Collisions at 400GeV/c

The pseudorapidity distributions of charged produced in pp collisions at 400GeV/c have been measured using LEBC films.Two-particle pseudorapidity correlations at fixed multiplicity have been studied.The experimental data was fitted by cluster model.It is found that the average cluster multiplicities as well as the cluster decay widths both vary slightly with charged multiplicity.     

Bombarding energy dependence of angular momentum transfer in deep inelastic collisions

Measurements of first and second moments of γ-ray multiplicity distributions from deep inelastic collisions of ⁸⁶Kr + ¹⁵⁴Sm are reported. A global systematics of the angular momentum distributions from deep inelastic reactions with projectile masses ? 40 is presented. The average angular momentum is found to depend linearly on the incident channel average angular momentum, while no simple systematics for the second moment appears obvious. In order to illuminate the question whether the angular momentum transfer process reaches statistical equilibrium in deep inelastic collisions, numerical calculations have been performed on two models: a two-sphere classical model including the collective modes of twisting, bending, wriggling and tilting, and a statistical equilibrium Fermi-gas model. The two-sphere classical model is not able to account for the observed second moments, and neither does the Fermi-gas model give an explanation of the deep inelastic multiplicity data.     

Restrictions on the cluster decay multiplicity distribution in the independent cluster emission model due to crossing symmetry and isospin invariance

We discuss multiparticle production in high energy proton-proton scattering under the assumption that all produced secondaries are pions. We take into account the pion isospin but neglect the isospin of the protons. In the first part of the paper it is shown that the multiplicity distribution of the independent cluster emission model can be derived from a unitary, crossing symmetric, isospin invariant, impact parameter model. This part is a straight forward generalization of a previous work where similar results were obtained for isospin-zero mesons. In the second part of the paper we shall discuss the restrictions on the cluster decay multiplicity distribution due to crossing symmetry in the meson variables and to isospin invariance. In particular, we shall derive a non-trivial lower bound for the dispersion of the charged particles in the cluster decay multiplicity distribution.     

Electronic and magnetothermal properties of ferromagnetic clusters

The electronic structures and the magnetothermal properties of nickel clusters have been investigated. Their effective magnetic moments and specific heat capacities have been calculated assuming that the clusters undergo superparamagnetic relaxation. The average magnetic moments are computed adopting Friedel's model of ferromagnetic clusters. The surface effect and the cluster size effect on the thermodynamic properties of these clusters have been analysed based on the mean field theory approximation. The specific heat capacity of Ni clusters for N=300, where N is the number of atoms in the cluster, shows the peak value at T=550 K and exhibits a steady increase with N. The effective potentials and energy eigen values of the clusters as a function of the number of atoms and radius of the cluster have also been calculated self-consistently using the local density approximation (LDA) of the density functional theory (DFT); this has been performed within the framework of the spherical jellium background model (SJBM). The results of this study have been compared with the Stern-Gerlach experimental data and other theoretical results already reported in literature     

Nucleation theorems applied to the Ising model

We use Monte Carlo simulations to study a single cluster of "up" spins in a sea of "down" spins in the three-dimensional Ising model. We evaluate the growth and decay rates for clusters of different sizes, identify the critical size for which these rates are equal, and obtain the internal energy of the critical size cluster. The results of the simulations at different temperatures and magnetic fields are used together with the first and second nucleation theorems to predict how the cluster nucleation rate changes when the external magnetic field and the temperature are changed. Our results are in agreement with literature values, but our method requires significantly less computational effort than the simulations reported earlier and avoids the difficult evaluation of free energies.     

Spectroscopic factors and barrier penetrabilities in cluster radioactivity

The cold cluster decay model is presented in the framework of a dinuclear system concept. Spectroscopic factors are extracted from barrier penetrabilities and measured half-lives. The deformation of the light cluster and residual nucleus is shown to affect the nucleus-nucleus potential and decay characteristics. Half-lives are predicted for neutron-deficient actinides and intermediate-mass nuclei. The connection between spontaneous fission and cluster radioactivity is discussed.     

Structural Dependence of Electronic and Magnetic Properties of the Cr13 Cluster

A tight-binding effective potential has been employed, in conjunction with a genetic algorithm, to fully optimize the Cr₁₃ cluster geometry without imposing any symmetry constraints. The minimum energy structure of this cluster is found to be a slightly distorted icosahedron. Based on the optimized structure and three assumed geometries (icosahedron,bcc-like and fcc-like), the structural dependence of electronic and magnetic properties of the Cr₁₃ cluster is discussed by using a d-band Hubbard-like Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment and local magnetic moments. It is found that for all considered geometries the Cr₁₃ cluster exhibits antiferromagnetic behavior. Results are also given for the cohesive energy, average coordination number, and local electronic densities of states. The results indicate that the average coordination number per atom in the cluster geometry is a significant factor to affect the magnetism.Also, the local density of states is a sensitive function of geometry.     

Vector and Tensor Coupling Constants of SU(3) Baryons in a Chiral Soliton Model

We report in the present talk a recent investigation on the vector properties of SU(3) baryons, based on a chiral soliton model. All relevant parameters from the model are adjusted to the experimental data of the masses and magnetic moments of the baryon octet. We compute the electromagnetic transitions for the baryon octet, the decuplet, and the antidecuplet. The numerical predictions for transition magnetic moments and radiative partial decay widths are in a very good agreement with all data of existing experiment and the vector meson dominance being used, the coupling constants for the vector mesons and antidecuplet baryon vertices are determined from the calculated transition magnetic moments.     

Charged particle correlations in\bar pp collisions at c.m. energies of 200, 546 and 900 GeV

We present data on two-particle pseudorapidity and multiplicity correlations of charged particles for non single-diffractive \(p\bar p - collisions\) at c.m. energies of 200, 546 and 900 GeV. Pseudorapidity correlations interpreted in terms of a cluster model, which has been motivated by this and other experiments, require on average about two charged particles per cluster. The decay width of the clusters in pseudorapidity is approximately independent of multiplicity and of c.m. energy. The investigations of correlations in terms of pseudorapidity gaps confirm the picture of cluster production. The strength of forward-backward multiplicity correlations increases linearly with ins and depends strongly on position and size of the pseudorapidity gap separating the forward and backward interval. All our correlation studies can be understood in terms of a cluster model in which clusters contain on average about two charged particles, i.e. are of similar magnitude to earlier estimates from the ISR.