Single-particle Fragmentation Research Articles

Monitoring of single-particle fragmentation process under static loading using acoustic emission

The fragmentation of single particle is one of the common observations in stressed soils. Individual particles are generally randomly shaped and exhibit twisted and discrepant fracture features. Conventional descriptions based on either strength prediction or comminution energy estimation are more or less statistical, which inevitably brings difficulties to understand the physical mechanism of fragmentation. As an attempt to overcome such limitations, this study presents an Acoustic Emission (AE) testing method to monitor the process of the single-particle fragmentation. AE testing is considered as an effective non-destructive technique and is capable of detecting micro-level defects inside a material. In the tests, the activity and the frequency characteristics of the AE signals were recorded and analyzed. It was found that the process of particle fragmentation was highly distinguished by AE characteristics. The AE activity was relatively low at first, followed by an inactive period. Finally, the AE signals tended to be significant active and exhibited a clustering of high frequency AEs before the impending fracture failure. This feature provides a useful insight to clarify the inner crack initiation and growth during the process of particle fragmentation. The technique is also promising for further applications such as particle fracture issues in granular systems which consist of numerous single grained particles.

Single particle fragmentation in ultrasound assisted impact comminution

Impact fragmentation is the underlying principle of comminution milling of dry, bulk solids. Unfortunately the outcome of the fragmentation process is more or less determined by the dimensionality of the impactor and its impact velocity. Since fragmentation is dominated by interfering shock waves, manipulating traveling shock waves and adding energy to the system during its fragmentation could be a promising approach to manipulate fragment mass distributions and energy input. In a former study we explored mechanisms in impact fragmentation of spheres, using a three-dimensional Discrete Element Model (DEM) Carmona et al. (Phys Rev E 77:051302, 2008). This work is focused on studying how single spheres fragment when impacted on a planar vibrating target.

Effects of ground state correlations on the structure of odd-mass spherical nuclei

It is well known that the Pauli principle plays a substantial role at low energies because the quasiparticle and phonon operators, used to describe them, are built of fermions and as a consequence they are not ideal bosons. The correct treatment of this problem requires calculation of the exact commutators between the quasiparticle and phonon operators and in this way to take into account the Pauli principle corrections. In addition to the correlations due to the quasiparticle interaction in the ground-state influence the single-particle fragmentation as well. In this article, we generalize the basic equations of the quasiparticle-phonon nuclear model to account for both effects mentioned above. As an illustration of our approach, calculations of the structure of the low-lying states in the odd-mass nuclei $^{131\ensuremath{-}137}\mathrm{Ba}$ have been performed.

Ground state correlations and structure of odd spherical nuclei

It is well known that the Pauli principle plays a substantial role at low energies because the phonon operators are not ideal boson operators. Calculating the exact commutators between the quasiparticle and phonon operators, one can take into account the Pauli principle corrections. Besides, the ground state correlations due to the quasiparticle interaction in the ground state influence the single-particle fragmentation as well. In this paper, we generalize the basic equations of the quasiparticle-phonon nuclear model to account for both effects mentioned. As an illustration of our approach, calculations on the structure of the low-lying states in 133Ba have been performed.

On the Drell–Levy–Yan relation to O(α2)

We study the validity of a relation by Drell, Levy and Yan (DLY) connecting the deep inelastic structure (DIS) functions and the single-particle fragmentation functions in e^+e^- annihilation which are defined in the spacelike (q^2<0) and timelike (q^2>0) regions respectively. Here q denotes the momentum of the virtual photon exchanged in the deep inelastic scattering process or the annihilation process. An extension of the DLY-relation, which originally was only derived in the scaling parton model, to all orders in QCD leads to a connection between the two evolution kernels determining the q^2-dependence of the DIS structure functions and the fragmentation functions respectively. In relation to this we derive the transformation relations between the space-and time-like splitting functions up to next-to-leading order (NLO) and the coefficient functions up to NNLO both for unpolarized and polarized scattering. It is shown that the evolution kernels describing the combined singlet evolution for the structure functions F_2(x,Q^2), F_L(x,Q^2) where Q^2=|q^2| or $F_2(x,Q^2), \partial F_2(x,Q^2)/\partial \ln(Q^2)$ and the corresponding fragmentation functions satisfy the DLY relation up to next-to-leading order. We also comment on a relation proposed by Gribov and Lipatov.

Nucleon-nucleus reactions at ultrarelativistic energies.

In order to discern coherent processes from incoherent and collective processes in nucleon-nucleus reactions at high energies, we study these reactions with an incoherent-multiple-collision model. In this model, the projectile nucleon makes successive inelastic collisions with nucleons in the target nucleus, the probability of such collisions being given by the thickness function and the nucleon-nucleon inelastic cross section. It is assumed that each baryon-baryon collision produces particles and degrades momenta just as a baryon-baryon collision in free space, and that there are no secondary collisions between the produced particles and the nucleons. We found that the inelastic proton data, the pseudorapidity distribution data ${\mathrm{dN}}^{\mathrm{pA}}$/d\ensuremath{\eta}, and the total nucleon-nucleus absorption data can be well explained by the incoherent-multiple-collision model. However, the single-particle fragmentation data for nonleading particles indicate that there is a reduction of the fragmentation cross section because of subsequent collisions of the leading baryon along the collision chain. Modification of the incoherent-multiple-collision model is suggested. The modified model gives cross sections for the reactions pA\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$X, pA\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$X, pA\ensuremath{\rightarrow}${K}^{+}$X, pA\ensuremath{\rightarrow}${K}^{\mathrm{\ensuremath{-}}}$X, and pA\ensuremath{\rightarrow}p\ifmmode\bar\else\textasciimacron\fi{}X in the projectile fragmentation region in good agreement with experiment.

The breaking of intrinsic reflection symmetry in nuclear ground states

Negative-parity excited states of doubly even nuclei have earlier been attributed to vibrational excitations. This paper shows that an interpretation starting from a reflection asymmetric intrinsic state is more appropriate for certain nuclei in the radium region. Theoretical evidence for stable octupole deformation comes from a deformed shell-model calculation in which we use a single-particle potential with a realistic radial shape and a finite-range interaction for the surface energy. The octupole effect systematically improves the agreement between theoretical and experimental masses. The low-lying O + excitations observed in experiment are compatible with the calculated collective octupole potentials. The possibility of obtaining further evidence from the spectroscopy of odd-mass nuclei is considered in an exactly solvable model, which shows that the smaller energy splitting observed in odd- A parity doublets mainly reflects single-particle fragmentation of the collective mode. The systematics of theoretical shell structure and experimental spectroscopy suggests the presence of other regions of octupole collectivity near the limits of stability.

Two-particle distributions ine+e−jets

We apply the jet calculus of Konishi, Ukawa, and Veneziano (KUV) to the two-particle spectra of ${e}^{+}{e}^{\ensuremath{-}}$ jets. This computation uses single-particle fragmentation functions and the KUV analysis of leading logarithms to predict the multiparticle spectra entirely from the single-particle data. The effects of charm and heavier flavors are discussed and a simple prescription for inverting the necessary double moments is given. The double-differential cross section $\frac{d\ensuremath{\sigma}}{d{x}_{1}d{x}_{2}}$ is displayed for various combinations of mesons and the antiproton.

Self-consistent exchange-degeneracy relations and «accidental» early scaling in inclusive reactions

A set of self-consistent exchange-degeneracy relations for single-particle fragmentation vertices is derived from the exoticity criterion of Chanet al. and factorization of secondary Regge exchanges. It is shown that there are many reactions with (ab\(\bar c\))-channel nonexotic but which will exhibit early scaling owing to the exact cancellation of the contributions from the secondary Regge exchanges («accidental» early scaling). Existing data are found to be in agreement with predictions from these exchange-degeneracy relations. Further tests are suggested. Predictions for early scaling in two-body inclusive reactions are also discussed.

Characteristics of an inelastic vertex from Hadron-Hadron scattering

Inelastic π−p events at 25 GeV/c are selected to enhance the likehood of single-particle fragmentation. The fragmentation vertex is studied as a function of momentum transfer, effective mass and multiplicity. The t-dependence of the inelastic vertex suggests a point-like interaction, and the triple Regge-formalism shows promise for describing the M∗ dependence.