arXiv subjects

Yi Gu

Publications and source records attributed to Yi Gu.

101 records · Page 6Linked to original sources

arXiv2016

Optimizing Top Precision Performance Measure of Content-Based Image Retrieval by Learning Similarity Function

In this paper we study the problem of content-based image retrieval. In this problem, the most popular performance measure is the top precision measure, and the most important component of a retrieval system is the similarity function used to compare a query image against a database image. However, up to now, there is no existing similarity learning method proposed to optimize the top precision measure. To fill this gap, in this paper, we propose a novel similarity learning method to maximize the top precision measure. We model this problem as a minimization problem with an objective function as the combination of the losses of the relevant images ranked behind the top-ranked irrelevant image, and the squared Frobenius norm of the similarity function parameter. This minimization problem is solved as a quadratic programming problem. The experiments over two benchmark data sets show the advantages of the proposed method over other similarity learning methods when the top precision is used as the performance measure.

cs.CV↗

arXiv2015

CEI: a new indicator measuring City Commercial Credit Risk initiated in China

Aiming at quantifying and evaluating the regional commercial environment along with the level of economic development among cities in mainland China, the concept of China City Commercial Environment Credit Index(CEI) was first introduced and established in 2010. In this manuscript, a historical review and detailed introduction of CEI is included, followed by statistical studies. In particular, an independent statistical cross-check for the existing CEI-2012 is performed and significant factors that play the most in influential roles are discussed.

q-fin.RM↗

arXiv2014

On algebraic surfaces of general type with negative c2

We prove that for any prime number $p\ge 3$, there exists a positive number $κ_p$ such that $χ(\mathcal{O}_X)\ge κ_pc_1^2$ holds true for all algebraic surfaces $X$ of general type in characteristic $p$. In particular, $χ(\mathcal{O}_X)>0$. This answers a question of N. Shepherd-Barron when $p\ge 3$.

math.AG↗

arXiv2014

On Pluri-canonical Systems of Arithmetic Surfaces

Let $S$ be a Dedekind scheme with perfect residue fields at closed points, let $f: X\rightarrow S$ be a minimal regular arithmetic surface of fibre genus at least $2$ and let $f': X'\rightarrow S$ be the canonical model of $f$. It is well known that $ω_{X'/S}$ is relatively ample. In this paper we prove that $ω_{X'/S}^{\otimes n}$ is relative very ample for all $n\geq 3$.

math.AG↗

arXiv2014

Digital Logarithmic Airborne Gamma Ray Spectrometer

A new digital logarithmic airborne gamma ray spectrometer is designed in this study. The spectrometer adopts a high-speed and high-accuracy logarithmic amplifier (LOG114) to amplify the pulse signal logarithmically and to improve the utilization of the ADC dynamic range, because the low-energy pulse signal has a larger gain than the high-energy pulse signal. The spectrometer can clearly distinguish the photopeaks at 239, 352, 583, and 609keV in the low-energy spectral sections after the energy calibration. The photopeak energy resolution of 137Cs improves to 6.75% from the original 7.8%. Furthermore, the energy resolution of three photopeaks, namely, K, U, and Th, is maintained, and the overall stability of the energy spectrum is increased through potassium peak spectrum stabilization. Thus, effectively measuring energy from 20keV to 10MeV is possible.

physics.ins-det↗

arXiv2013

Acoustic scaling of anisotropic flow in shape-engineered events: implications for extraction of the specific shear viscosity of the quark gluon plasma

It is shown that the acoustic scaling patterns of anisotropic flow for different event shapes at a fixed collision centrality (shape-engineered events), provide robust constraints for the event-by-event fluctuations in the initial-state density distribution from ultrarelativistic heavy ion collisions. The empirical scaling parameters also provide a dual-path method for extracting the specific shear viscosity $(η/s)_\mathrm{QGP}$ of the quark-gluon plasma (QGP) produced in these collisions. A calibration of these scaling parameters via detailed viscous hydrodynamical model calculations, gives $(η/s)_\mathrm{QGP}$ estimates for the plasma produced in collisions of Au+Au ($\sqrt{s_{NN}}= 0.2$ TeV) and Pb+Pb ($\sqrt{s_{NN}}= 2.76$ TeV). The estimates are insensitive to the initial-state geometry models considered.

nucl-ex↗

arXiv2013

Is anisotropic flow really acoustic?

The flow harmonics for charged hadrons ($v_{n}$) and their ratios $(v_n/v_2)_{n\geq 3}$, are studied for a broad range of transverse momenta ($p_T$) and centrality ($\text{cent}$) in Pb+Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV. They indicate characteristic scaling patterns for viscous damping consistent with the dispersion relation for sound propagation in the plasma produced in the collisions. These scaling properties are not only a unique signature for anisotropic expansion modulated by the specific shear viscosity ($η/s$), they provide essential constraints for the relaxation time, a distinction between two of the leading models for initial eccentricity, as well as an extracted $\left< η/s \right>$ value which is insensitive to the initial geometry model. These constraints could be important for a more precise determination of $η/s$.

nucl-ex↗

arXiv2013

Beam energy dependence of the viscous damping of anisotropic flow

The flow harmonics $v_{2,3}$ for charged hadrons, are studied for a broad range of centrality selections and beam collision energies in Au+Au ($\sqrt{s_{NN}}= 7.7 - 200$ GeV) and Pb+Pb ($\sqrt{s_{NN}}= 2.76$ TeV) collisions. They validate the characteristic signature expected for the system size dependence of viscous damping at each collision energy studied. The extracted viscous coefficients, that encode the magnitude of the ratio of shear viscosity to entropy density $η/s$, are observed to decrease to an apparent minimum as the collision energy is increased from $\sqrt{s_{NN}}= 7.7$ to approximately 62.4 GeV; thereafter, they show a slow increase with $\sqrt{s_{NN}}$ up to 2.76 TeV. This pattern of viscous damping provides the first experimental constraint for $η/s$ in the temperature-baryon chemical potential ($T, μ_B$) plane, and could be an initial indication for decay trajectories which lie close to the critical end point in the phase diagram for nuclear matter.

nucl-ex↗

arXiv2012

PHENIX Measurements of Higher-order Flow Harmonics for Identified Charged Hadrons in Au+Au collisions at $\sqrt{s_{NN}}=39-200$ GeV

The azimuthal anisotropy coefficients $v_{2,3,4}$, characterizing collective flow in Au+Au collisions, are presented for identified particle species as a function of transverse momentum ($p_T$), centrality ($\rm{cent}$) and beam collision energy ($\sqrt{s_{NN}}=0.039-0.20$ TeV). The $v_n$ values for each particle species, show little, if any, change over the measured beam energy range, and ${v_n}/{(n_q)^{n/2}}$ vs. $KE_T/n_q$ scales to a single curve (constituent quark number ($n_q)$ scaling) for each $n$, over a broad range of transverse kinetic energies ($KE_T$). A comparison of $v_2(p_T)$ for individual particle species obtained in Au+Au collisions at $\sqrt{s_{NN}}=0.20$ TeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV (LHC), indicate stronger collective flow at the LHC. These flow measurements and their scaling patterns, can provide important additional constraints for extraction of the specific viscosity $η/s$.

nucl-ex↗

arXiv2012

Does quark number scaling breakdown in Pb+Pb collisions at Root_s = 2.76 TeV?

The anisotropy coefficient $v_2$, for unidentified and identified charged hadrons [pions ($π$), kaons ($K$) and protons ($p$)] measured in Au+Au collisions at $\sqrt{s_{NN}}= 0.20$ TeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV (LHC), are compared for several collision centralities ($\text{cent}$) and particle transverse momenta $p_T$. In contrast to the measurements for charged hadrons, the comparisons indicate a sizable increase of $v_2(p_T)$ for $π,K$ and $p$, as well as a blueshift of proton $v_2(p_T)$, from RHIC to LHC. When this blueshift is accounted for, the LHC data [for $π$, $K$, $p$] show excellent scaling of $v_2({KE}_T)$ with the number of valence quarks ($n_q$), for a broad range of transverse kinetic energies (${KE}_T$) and collision centralities. These observations suggest a larger mean sound speed $ $ for the plasma created in LHC collisions, and significant radial flow generation after its hadronization.

nucl-ex↗

arXiv2011

Bright six-partite continuous variable entanglement using cascaded four-wave mixing processes in a four-level atomic system

We theoretically show that bright six-partite continuous-variable entanglement can be generated using cascaded four-wave mixing effects of third-order nonlinearity atomic systems above threshold. The six-partite continuous-variable entanglement among the six cavity fields with different frequencies is analyzed by applying optimized inseparability criteria proposed by Van Loock and Furusawa.

quant-ph↗