Measurement of the rapidity-even dipolar flow in Pb-Pb collisions with the ATLAS detector

The rapidity-even dipolar flow v1 associated with dipole asymmetry in the initial geometry is measured over a broad range in transverse momentum 0.5 GeV<pT<9 GeV, and centrality (0-50)% in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV, recorded by the ATLAS experiment at the LHC. The v1 coefficient is determined via a two-component fit of the first order Fourier coefficient, v_{1,1}= cos \Delta\phi, of two-particle correlations in azimuthal angle \Delta\phi=\phi_a-\phi_b as a function of pT^a and pT^b. This fit is motivated by the finding that the pT dependence of v_{1,1}(pT^a,pT^b) data are consistent with the combined contributions from a rapidity-even v1 and global momentum conservation. The magnitude of the extracted momentum conservation component suggests that the system conserving momentum involves only a subset of the event (spanning about 3 units in \eta in central collisions). The extracted v1 is observed to cross zero at pT~1.0 GeV, reaches a maximum at 4-5 GeV with a value comparable to that for v3, and decreases at higher pT. Interestingly, the magnitude of v1 at high pT exceeds the value of the v3 in all centrality interval and exceeds the value of v2 in central collisions. This behavior suggests that the path-length dependence of energy loss and initial dipole asymmetry from fluctuations corroborate to produce a large dipolar anisotropy for high pT hadrons, making the v1 a valuable probe for studying the jet quenching phenomena.Comment: 9 pages, 6 figures. Proceedings for the 28th Winter Workshop on Nuclear Dynamics, Dorado Del Mar, Puerto Rico, United States Of America, 7 - 14 Apr 201

PHENIX Measurement of High-pTp_T Hadron-hadron and Photon-hadron Azimuthal Correlations

High-$p_T$ hadron-hadron correlations have been measured with the PHENIX experiment in \Cu and \pp collisions at $\sqrt{s_{NN}}=200$ GeV. A comparison of the jet widths and yields between the two colliding systems allows us to study the medium effect on jets. We also present a first measurement of direct photon-hadron correlations in \Au and \pp collisions. We find that the near-side yields are consistent with zero in both systems. By comparing the jet yields on the away side, we observe a suggestion of the expected suppression of hadrons associated with photons in \Au collisions.Comment: 5 pages, proceeding for parallel talk on Quark Matter 200

A Morphological Approach to the Pulsed Emission from Soft Gamma Repeaters

We present a geometrical methodology to interpret the periodical light curves of Soft Gamma Repeaters based on the magnetar model and the numerical arithmetic of the three-dimensional magnetosphere model for the young pulsars. The hot plasma released by the star quake is trapped in the magnetosphere and photons are emitted tangent to the local magnetic field lines. The variety of radiation morphologies in the burst tails and the persistent stages could be well explained by the trapped fireballs on different sites inside the closed field lines. Furthermore, our numerical results suggests that the pulse profile evolution of SGR 1806-20 during the 27 December 2004 giant flare is due to a lateral drift of the emitting region in the magnetosphere.Comment: 7 figures, accepted by Ap

A re-visit of the phase-resolved X-ray and \gamma-ray spectra of the Crab pulsar

We use a modified outer gap model to study the multi-frequency phase-resolved spectra of the Crab pulsar. The emissions from both poles contribute to the light curve and the phase-resolved spectra. Using the synchrotron self-Compton mechanism and by considering the incomplete conversion of curvature photons into secondary pairs, the observed phase-averaged spectrum from 100 eV - 10 GeV can be explained very well. The predicted phase-resolved spectra can match the observed data reasonably well, too. We find that the emission from the north pole mainly contributes to Leading Wing 1. The emissions in the remaining phases are mainly dominated by the south pole. The widening of the azimuthal extension of the outer gap explains Trailing Wing 2. The complicated phase-resolved spectra for the phases between the two peaks, namely Trailing Wing 1, Bridge and Leading Wing 2, strongly suggest that there are at least two well-separated emission regions with multiple emission mechanisms, i.e. synchrotron radiation, inverse Compton scattering and curvature radiation. Our best fit results indicate that there may exist some asymmetry between the south and the north poles. Our model predictions can be examined by GLAST.Comment: 35 pages, 13 figures, accepted to publish in Ap

A general software defect-proneness prediction framework

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.BACKGROUND - Predicting defect-prone software components is an economically important activity and so has received a good deal of attention. However, making sense of the many, and sometimes seemingly inconsistent, results is difficult. OBJECTIVE - We propose and evaluate a general framework for software defect prediction that supports 1) unbiased and 2) comprehensive comparison between competing prediction systems. METHOD - The framework is comprised of 1) scheme evaluation and 2) defect prediction components. The scheme evaluation analyzes the prediction performance of competing learning schemes for given historical data sets. The defect predictor builds models according to the evaluated learning scheme and predicts software defects with new data according to the constructed model. In order to demonstrate the performance of the proposed framework, we use both simulation and publicly available software defect data sets. RESULTS - The results show that we should choose different learning schemes for different data sets (i.e., no scheme dominates), that small details in conducting how evaluations are conducted can completely reverse findings, and last, that our proposed framework is more effective and less prone to bias than previous approaches. CONCLUSIONS - Failure to properly or fully evaluate a learning scheme can be misleading; however, these problems may be overcome by our proposed framework.National Natural Science Foundation of Chin

Ultrasonic tracking of a sinking ball in a vibrated dense granular suspension

Observing and understanding the movement of an intruder through opaque dense suspensions such as quicksand remains a practical and conceptual challenge. Here we use an ultrasonic probe to investigate the dynamics of a steel ball sinking in a 3D dense glass bead packing saturated by water. We show that the frictional model developed for dry granular media can be used to describe the ball motion induced by horizontal vibration. From this rheology we infer the static friction coefficient and effective viscosity that decrease when increasing the vibration intensity. Our main finding is that the vibration-induced reduction of the yield stress and increase of the sinking depth are presumably due to induced slipping at the grain contacts but without visible plastic rearrangements of grains, in contrast to dry granular packings. To explain these results, we propose a mechanism of acoustic lubrication that reduces the inter-particle friction and leads to a decrease of the yield stress. This scenario is different from the mechanism of liquefaction usually invoked in loosely packed quicksands where the vibration-induced compaction increases the pore pressure and decreases the confining pressure on the solid skeleton, thus reducing the granular resistance to external load.Comment: 9 pages and 5 figures, plus the supplemental information (1 page, 2 movies, 1 figure

Magnetotransport and spin dynamics in an electron gas formed at oxide interfaces

We investigate the spin-dependent transport properties of a two-dimensional electron gas formed at oxides' interface in the presence of a magnetic field. We consider several scenarios for the oxides' properties, including oxides with co-linear or spiral magnetic and ferroelectric order. For spiral multiferroic oxides, the magnetoelectric coupling and the topology of the localized magnetic moments introduce additional, electric field controlled spin-orbit coupling that affects the magneto-oscillation of the current. An interplay of this spin-orbit coupling, the exchange field, and of the applied magnetic field results in a quantum, gate-controlled spin and charge Hall conductance

Deprojection technique for galaxy cluster considering point spread function

We present a new method for the analysis of Abell 1835 observed by XMM-Newton. The method is a combination of the Direct Demodulation technique and deprojection. We eliminate the effects of the point spread function (PSF) with the Direct Demodulation technique. We then use a traditional depro-jection technique to study the properties of Abell 1835. Compared to that of deprojection method only, the central electron density derived from this method increases by 30%, while the temperature profile is similar.Comment: accepted for publication in Sciences in China -- G, the Black Hole special issu

Probing viscoelastic properties of a thin polymer film sheared between a beads layer and quartz crystal resonator

We report measurements of viscoelastic properties of thin polymer films of 10-100 nm at the MHz range. These thin films are confined between a quartz crystal resonator and a millimetric bead layer, producing an increase of both resonance frequency and dissipation of the quartz resonator. The shear modulus and dynamic viscosity of thin films extracted from these measurements are consistent with the bulk values of the polymer. This modified quartz resonator provides an easily realizable and effective tool for probing the rheological properties of thin films at ambient environment.Comment: submitted to ap