Angular distribution and azimuthal asymmetry for pentaquark production in proton-proton collisions

Angular distributions for production of the $\Theta^+$ pentaquark are calculated for the collisions of polarized protons with polarized target protons. We compare calculations based on different assumptions concerning spin and parity ($J=1/2^\pm,3/2^\pm$) of the $\Theta^+$ state. For a wide class of interactions the spin correlation parameters describing the asymmetric angular distributions are calculated up to 250 MeV above production threshold. The deviations from the near threshold behavior are investigated.Comment: 8 pages, 5 figure

Thermal Properties of a Hot Pion Gas beyond the Quasiparticle Approximation

Within the Matsubara formalism we derive expressions for the pion self-energy and the two-pion propagator in a hot pion gas. These quantities are used to selfconsistently calculate the in-medium $\pi\pi$ amplitude beyond the quasiparticle approximation (QPA). The results are shown to differ significantly from QPA-based calculations. We also examine the impact of chiral constraints on the $\pi\pi$ interaction in a chirally improved version of the J\"ulich $\pi\pi$ model.Comment: 12 pages LaTex (3 figures uuencoded

Pion Properties in a Hot ΠNΔ\Pi N \Delta Gas

Based on a recent meson-exchange model for the vacuum $\pi\pi$ interaction we compute selfconsistently the in-medium $\pi\pi$ scattering amplitude and pion selfenergy in a hot $\pi N\Delta$ gas. The contributions to the pion selfenergy are calculated from the $\pi\pi$ T-matrix as well as from p-wave interaction with nucleons and thermally abundant $\Delta$'s. Results are presented for two scenarios believed to be realized in the relativistic heavy ion collisions performed at the GSI-SIS and the CERN-SpS. Possible implications for the observed soft pion enhancement at both SIS and SpS are indicated.Comment: 20 pages in Latex, 5 figures available on request from the authors, UIUC preprint P-93-11-09

Thermal Hadron Production in High Energy Heavy Ion Collisions

We provide a method to test if hadrons produced in high energy heavy ion collisions were emitted at freeze-out from an equilibrium hadron gas. Our considerations are based on an ideal gas at fixed temperature $T_f$, baryon number density $n_B$, and vanishing total strangeness. The constituents of this gas are all hadron resonances up to a mass of 2 GeV; they are taken to decay according to the experimentally observed branching ratios. The ratios of the various resulting hadron production rates are tabulated as functions of $T_f$ and $n_B$. These tables can be used for the equilibration analysis of any heavy ion data; we illustrate this for some specific cases.Comment: 12 pages (not included :13 figures + tables) report CERN-TH 6523/92 and Bielefeld preprint BI-TP 92/0

Image Classification With Small Datasets: Overview and Benchmark

Image classification with small datasets has been an active research area in the recent past. However, as research in this scope is still in its infancy, two key ingredients are missing for ensuring reliable and truthful progress: a systematic and extensive overview of the state of the art, and a common benchmark to allow for objective comparisons between published methods. This article addresses both issues. First, we systematically organize and connect past studies to consolidate a community that is currently fragmented and scattered. Second, we propose a common benchmark that allows for an objective comparison of approaches. It consists of five datasets spanning various domains (e.g., natural images, medical imagery, satellite data) and data types (RGB, grayscale, multispectral). We use this benchmark to re-evaluate the standard cross-entropy baseline and ten existing methods published between 2017 and 2021 at renowned venues. Surprisingly, we find that thorough hyper-parameter tuning on held-out validation data results in a highly competitive baseline and highlights a stunted growth of performance over the years. Indeed, only a single specialized method dating back to 2019 clearly wins our benchmark and outperforms the baseline classifier

Nuclear liquid-gas phase transition within the lattice gas model

We study the nuclear liquid-gas phase transition on the basis of a two-component lattice gas model. A Metropolis type of sampling method is used to generate microscopic states in the canonical ensemble. The effective equation of state and fragment mass distributions are evaluated in a wide range of temperatures and densities. A definition of the phase coexistence region appropriate for mesoscopic systems is proposed. The caloric curve resulting from different types of freeze-out conditions are presented.Comment: 13 pages including 4 figure

Electrokinetic optimization of a micromixer for lab-on-chip applications

This paper is concerned with the optimization of an electrokinetic micromixer suitable for Lab-on-Chip and other microfluidic applications. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house Finite-Element-Method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e. frequency and amplitude, for a given waveform. The simulation results of two optimized electrical excitations featuring a discrete and a continuous waveform are compared and discussed. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly

Coulomb Effects on Particle Spectra in Relativistic Nuclear Collisions

Coulomb effects on $\pi^\pm$ and $K^\pm$ spectra in relativistic nuclear collisions are investigated. At collision energies around 1 GeV the ratio of at ultrarelativistic energies. We describe the ratios at SIS, AGS and SPS energies with simple analytic models as well as more elaborate numerical models incorporating the expansion dynamics. The Coulomb effect depends on the properties of the source after the violent collision phase and provides information on source sizes, freeze-out times, and expansion velocities. Comparison with results from HBT analyses are made. Predictions for $\pi^\pm$ and $K^\pm$ at RHIC and LHC energies are given