PHENIX and the Reaction Plane: Recent Results

During the past several years, experiments at RHIC have established that a dense partonic medium is produced in Au+Au collisions at sqrt(s)=200 GeV. Subsequently, a primary goal of analysis has been to understand and characterize the dynamics underlying this new form of matter. Among the many probes available, the measurements with respect to the reaction plane has proven to be crucial to our understanding of a wide range of topics, from the hydrodynamics of the initial expansion of the collision region to high-pt jet quenching phenomena. Few tools have the ability to shed light on such a wide variety of observables as the reacion plane. In this article, we discuss recent PHENIX measurements with respect to the reaction plane, and the implications for understanding the underlying physics of RHIC collisions.Comment: 9 pages, 13 figures, Submitted for proceedings to the Winter Workshop on Nuclear Dynamics 2010, Ocho Rios, Jamaic

Development of an alpha scattering instrument for heavy element detection in surface materials

The development and characteristics of a portable instrument for detecting and measuring the amounts of lead in painted surfaces are discussed. The instrument is based on the ones used with the alpha scattering experiment on the Surveyor lunar missions. The principles underlying the instrument are described. It is stated that the performance tests of the instrument were satisfactory

Incommensurate magnetic structure of CeRhIn5

The magnetic structure of the heavy fermion antiferromagnet CeRhIn5 is determined using neutron diffraction. We find a magnetic wave vector q_M=(1/2,1/2,0.297), which is temperature independent up to T_N=3.8K. A staggered moment of 0.374(5) Bohr magneton at 1.4K, residing on the Ce ion, spirals transversely along the c axis. The nearest neighbor moments on the tetragonal basal plane are aligned antiferromagnetically.Comment: 4 pages, 4 figures There was an extra factor of 2 in Eq (2). This affects the value of staggered moment. The correct staggered moment is 0.374(5) Bohr magneton at 1.4

Minimax mean estimator for the trine

We explore the question of state estimation for a qubit restricted to the $x$-$z$ plane of the Bloch sphere, with the trine measurement. In our earlier work [H. K. Ng and B.-G. Englert, eprint arXiv:1202.5136[quant-ph] (2012)], similarities between quantum tomography and the tomography of a classical die motivated us to apply a simple modification of the classical estimator for use in the quantum problem. This worked very well. In this article, we adapt a different aspect of the classical estimator to the quantum problem. In particular, we investigate the mean estimator, where the mean is taken with a weight function identical to that in the classical estimator but now with quantum constraints imposed. Among such mean estimators, we choose an optimal one with the smallest worst-case error-the minimax mean estimator-and compare its performance with that of other estimators. Despite the natural generalization of the classical approach, this minimax mean estimator does not work as well as one might expect from the analogous performance in the classical problem. While it outperforms the often-used maximum-likelihood estimator in having a smaller worst-case error, the advantage is not significant enough to justify the more complicated procedure required to construct it. The much simpler adapted estimator introduced in our earlier work is still more effective. Our previous work emphasized the similarities between classical and quantum state estimation; in contrast, this paper highlights how intuition gained from classical problems can sometimes fail in the quantum arena.Comment: 18 pages, 3 figure

The ELAV RNA-stability factor HuR binds the 5′-untranslated region of the human IGF-IR transcript and differentially represses cap-dependent and IRES-mediated translation

The type I insulin-like growth factor receptor (IGF-IR) is an integral component in the control of cell proliferation, differentiation and apoptosis. The IGF-IR mRNA contains an extraordinarily long (1038 nt) 5′-untranslated region (5′-UTR), and we have characterized a diverse series of proteins interacting with this RNA sequence which may provide for intricate regulation of IGF-IR gene expression at the translational level. Here, we report the purification and identification of one of these IGF-IR 5′-UTR-binding proteins as HuR, using a novel RNA crosslinking/RNase elution strategy. Because HuR has been predominantly characterized as a 3′-UTR-binding protein, enhancing mRNA stability and generally increasing gene expression, we sought to determine whether HuR might serve a different function in the context of its binding the IGF-IR 5′-UTR. We found that HuR consistently repressed translation initiation through the IGF-IR 5′-UTR. The inhibition of translation by HuR was concentration dependent, and could be reversed in trans by addition of a fragment of the IGF-IR 5′-UTR containing the HuR binding sites as a specific competitor, or abrogated by deletion of the third RNA recognition motif of HuR. We determined that HuR repressed translation initiation through the IGF-IR 5′-UTR in cells as well, and that siRNA knockdown of HuR markedly increased IGF-IR protein levels. Interestingly, we also found that HuR potently inhibited IGF-IR translation mediated through internal ribosome entry. Kinetic assays were performed to investigate the mechanism of translation repression by HuR and the dynamic interplay between HuR and the translation apparatus. We found that HuR, occupying a cap-distal position, significantly delayed translation initiation mediated by cap-dependent scanning, but was eventually displaced from its binding site, directly or indirectly, as a consequence of ribosomal scanning. However, HuR perpetually blocked the activity of the IGF-IR IRES, apparently arresting the IRES-associated translation pre-initiation complex in an inactive state. This function of HuR as a 5′-UTR-binding protein and dual-purpose translation repressor may be critical for the precise regulation of IGF-IR expression essential to normal cellular homeostasis

Optimization of ground and excited state wavefunctions and van der Waals clusters

A quantum Monte Carlo method is introduced to optimize excited state trial wavefunctions. The method is applied in a correlation function Monte Carlo calculation to compute ground and excited state energies of bosonic van der Waals clusters of upto seven particles. The calculations are performed using trial wavefunctions with general three-body correlations

The Yang-Lee zeros of the 1D Blume-Capel model on connected and non-connected rings

We carry out a numerical and analytic analysis of the Yang-Lee zeros of the 1D Blume-Capel model with periodic boundary conditions and its generalization on Feynman diagrams for which we include sums over all connected and non-connected rings for a given number of spins. In both cases, for a specific range of the parameters, the zeros originally on the unit circle are shown to departure from it as we increase the temperature beyond some limit. The curve of zeros can bifurcate and become two disjoint arcs as in the 2D case. We also show that in the thermodynamic limit the zeros of both Blume-Capel models on the static (connected ring) and on the dynamical (Feynman diagrams) lattice tend to overlap. In the special case of the 1D Ising model on Feynman diagrams we can prove for arbitrary number of spins that the Yang-Lee zeros must be on the unit circle. The proof is based on a property of the zeros of Legendre Polynomials.Comment: 19 pages, 5 figure

Universal Properties of the Four-Body System with Large Scattering Length

Few-body systems with large scattering length have universal properties that do not depend on the details of their interactions at short distances. We study the universal bound state properties of the four-boson system with large scattering length in an effective quantum mechanics approach. We compute the four-body binding energies using the Yakubovsky equations for positive and negative scattering length. Moreover, we study the correlation between three- and four-body energies and present a generalized Efimov plot for the four-body system. These results are useful for understanding the cluster structure of nuclei and for the creation of weakly-bound tetramers with cold atoms close to a Feshbach resonance.Comment: 14 pages, 4 ps figures, minor changes, version to appear in EPJ