The stability of the spectator, Dirac, and Salpeter equations for mesons

Mesons are made of quark-antiquark pairs held together by the strong force. The one channel spectator, Dirac, and Salpeter equations can each be used to model this pairing. We look at cases where the relativistic kernel of these equations corresponds to a time-like vector exchange, a scalar exchange, or a linear combination of the two. Since the model used in this paper describes mesons which cannot decay physically, the equations must describe stable states. We find that this requirement is not always satisfied, and give a complete discussion of the conditions under which the various equations give unphysical, unstable solutions

Break-up fragment topology in statistical multifragmentation models

Break-up fragmentation patterns together with kinetic and configurational energy fluctuations are investigated in the framework of a microcanonical model with fragment degrees of freedom over a broad excitation energy range. As far as fragment partitioning is approximately preserved, energy fluctuations are found to be rather insensitive to both the way in which the freeze-out volume is constrained and the trajectory followed by the system in the excitation energy - freeze-out volume space. Due to hard-core repulsion, the freeze-out volume is found to be populated un-uniformly, its highly depleted core giving the source a bubble-like structure. The most probable localization of the largest fragments in the freeze-out volume may be inferred experimentally from their kinematic properties, largely dictated by Coulomb repulsion

Two-pion exchange potential and the πN\pi N amplitude

We discuss the two-pion exchange potential which emerges from a box diagram with one nucleon (the spectator) restricted to its mass shell, and the other nucleon line replaced by a subtracted, covariant $\pi N$ scattering amplitude which includes $\Delta$, Roper, and $D_{13}$ isobars, as well as contact terms and off-shell (non-pole) dressed nucleon terms. The $\pi N$ amplitude satisfies chiral symmetry constraints and fits $\pi N$ data below $\sim$ 700 MeV pion energy. We find that this TPE potential can be well approximated by the exchange of an effective sigma and delta meson, with parameters close to the ones used in one-boson-exchange models that fit $NN$ data below the pion production threshold.Comment: 9 pages (RevTex) and 7 postscript figures, in one uuencoded gzipped tar fil

Continuous phase transitions with a convex dip in the microcanonical entropy

The appearance of a convex dip in the microcanonical entropy of finite systems usually signals a first order transition. However, a convex dip also shows up in some systems with a continuous transition as for example in the Baxter-Wu model and in the four-state Potts model in two dimensions. We demonstrate that the appearance of a convex dip in those cases can be traced back to a finite-size effect. The properties of the dip are markedly different from those associated with a first order transition and can be understood within a microcanonical finite-size scaling theory for continuous phase transitions. Results obtained from numerical simulations corroborate the predictions of the scaling theory.Comment: 8 pages, 7 figures, to appear in Phys. Rev.

Thermal fluctuations in the lattice Boltzmann method for non-ideal fluids

We introduce thermal fluctuations in the lattice Boltzmann method for non-ideal fluids. A fluctuation-dissipation theorem is derived within the Langevin framework and applied to a specific lattice Boltzmann model that approximates the linearized fluctuating Navier-Stokes equations for fluids based on square-gradient free energy functionals. The obtained thermal noise is shown to ensure equilibration of all degrees of freedom in a simulation to high accuracy. Furthermore, we demonstrate that satisfactory results for most practical applications of fluctuating hydrodynamics can already be achieved using thermal noise derived in the long wavelength-limit.Comment: 15 pages, 5 figure

spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models

The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagome, pyrochlore, and other lattices with flat bands in their one-particle density of states.Comment: 7 pages, 1 figur

Mode 2 fatigue crack growth specimen development

A Mode II test specimen was developed which has potential application in understanding phemonena associated with mixed mode fatigue failures in high performance aircraft engine bearing races. The attributes of the specimen are: it contains one single ended notch, which simplifiers data gathering and reduction; the fatigue crack grous in-line with the direction of load application; a single axis test machine is sufficient to perform testing; and the Mode I component is vanishingly small

Witness Recantation Study: Preliminary Findings

In September 2012, the National Registry of Exonerations began a research study of all the cases in our database that involve post-conviction recantations by witnesses or victims. This is the first systematic study of recantations ever conducted. Its purpose is to identify patterns and trends among these cases, with a particular focus on the circumstances that first elicit the false testimony, and on the official reactions to the recantations by judges and other authorities. Our data set includes all the cases in the Registry as of February 28, 2013 – a total of 1,068 cases, 250 of which involve recantations. We developed a coding system to track various features of these cases, from the crime (or alleged crime) and initial investigation through the conviction, post-conviction proceedings, re-investigation, and exoneration of the defendant. In early April, we finished coding the cases, and we presented initial findings at the Innocence Network Conference on April 20th. This memo provides background on the project and a brief summary of our findings thus far

Witness Recantation Study: Preliminary Findings

In September 2012, the National Registry of Exonerations began a research study of all the cases in our database that involve post-conviction recantations by witnesses or victims. This is the first systematic study of recantations ever conducted. Its purpose is to identify patterns and trends among these cases, with a particular focus on the circumstances that first elicit the false testimony, and on the official reactions to the recantations by judges and other authorities. Our data set includes all the cases in the Registry as of February 28, 2013 – a total of 1,068 cases, 250 of which involve recantations. We developed a coding system to track various features of these cases, from the crime (or alleged crime) and initial investigation through the conviction, post-conviction proceedings, re-investigation, and exoneration of the defendant. In early April, we finished coding the cases, and we presented initial findings at the Innocence Network Conference on April 20th. This memo provides background on the project and a brief summary of our findings thus far