Search for the Chiral Magnetic Effect in Au+Au collisions at sNN=27\sqrt{s_{_{\rm{NN}}}}=27 GeV with the STAR forward Event Plane Detectors

A decisive experimental test of the Chiral Magnetic Effect (CME) is considered one of the major scientific goals at the Relativistic Heavy-Ion Collider (RHIC) towards understanding the nontrivial topological fluctuations of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is expected to result in a charge separation phenomenon across the reaction plane, whose strength could be strongly energy dependent. The previous CME searches have been focused on top RHIC energy collisions. In this Letter, we present a low energy search for the CME in Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}}=27$ GeV. We measure elliptic flow scaled charge-dependent correlators relative to the event planes that are defined at both mid-rapidity $|\eta|<1.0$ and at forward rapidity $2.1 < |\eta|<5.1$. We compare the results based on the directed flow plane ($\Psi_1$) at forward rapidity and the elliptic flow plane ($\Psi_2$) at both central and forward rapidity. The CME scenario is expected to result in a larger correlation relative to $\Psi_1$ than to $\Psi_2$, while a flow driven background scenario would lead to a consistent result for both event planes[1,2]. In 10-50\% centrality, results using three different event planes are found to be consistent within experimental uncertainties, suggesting a flow driven background scenario dominating the measurement. We obtain an upper limit on the deviation from a flow driven background scenario at the 95\% confidence level. This work opens up a possible road map towards future CME search with the high statistics data from the RHIC Beam Energy Scan Phase-II.Comment: main: 8 pages, 5 figures; supplementary material: 2 pages, 1 figur

Numerical simulation study of the strain rate effect on concrete in compression considering material heterogeneity

The behaviour of brittle materials is generally known to be strain rate sensitive. There are different theories about the mechanisms under which the rate dependency of the material behaviour develops. Some recent studies suggest that the experimentally observed dynamic increase factor (DIF) in the compressive strength of concrete could be attributable to the dynamic response within the sample specimens, rather than a rate sensitive material property. This paper is aimed to provide another perspective from a mesoscale heterogeneity point of view. To this end, a robust mesoscale concrete model is employed to carry out numerical experiments at high strain rates. To best represent the loading conditions in actual dynamic tests, a numerical split Hopkinson pressure bar (SHPB) apparatus is set up, and the numerical experiment is performed in a similar fashion as a physical SHPB test. To allow for a direct observation of the relative contribution of the mesoscale heterogeneity, a companion homogeneous concrete model is also simulated. Comparison between the dynamic behaviour of the mesoscale and homogeneous models indicates that the heterogeneity in the concrete composite plays an important role, in addition to the dynamic inertia effect, in the dynamic enhancement of the apparent compressive strength of concrete

A Novel Genetic Algorithm with Orthogonal Prediction for Global Numerical Optimization

Abstract. This paper proposes a novel orthogonal predictive local search (OPLS) to enhance the performance of the conventional genetic algorithms. OPLS operation predicts the most promising direction for the individuals to explore their neighborhood. It uses the orthogonal design method to sample orthogonal combinations to make the prediction. The resulting algorithm is termed the orthogonal predictive genetic algorithm (OPGA). OPGA has been tested on eleven numerical optimization functions in comparison with some typical algorithms. The results demonstrate the effectiveness of the proposed algorithm for achieving better solutions with a faster convergence speed