Effects of hadronic potentials on elliptic flows in relativistic heavy ion collisions

Within the framework of a multiphase transport (AMPT) model that includes both initial partonic and final hadronic interactions, we show that including mean-field potentials in the hadronic phase leads to a splitting of the elliptic flows of particles and their antiparticles, providing thus a plausible explanation of the different elliptic flows between $p$ and ${\bar p}$, $K^+$ and $K^-$, and $\pi^+$ and $\pi^-$ observed in recent Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC).Comment: 5 pages, 7 figure

Revisiting compressed sensing: exploiting the efficiency of simplex and sparsification methods

We propose two approaches to solve large-scale compressed sensing problems. The first approach uses the parametric simplex method to recover very sparse signals by taking a small number of simplex pivots, while the second approach reformulates the problem using Kronecker products to achieve faster computation via a sparser problem formulation. In particular, we focus on the computational aspects of these methods in compressed sensing. For the first approach, if the true signal is very sparse and we initialize our solution to be the zero vector, then a customized parametric simplex method usually takes a small number of iterations to converge. Our numerical studies show that this approach is 10 times faster than state-of-the-art methods for recovering very sparse signals. The second approach can be used when the sensing matrix is the Kronecker product of two smaller matrices. We show that the best-known sufficient condition for the Kronecker compressed sensing (KCS) strategy to obtain a perfect recovery is more restrictive than the corresponding condition if using the first approach. However, KCS can be formulated as a linear program with a very sparse constraint matrix, whereas the first approach involves a completely dense constraint matrix. Hence, algorithms that benefit from sparse problem representation, such as interior point methods (IPMs), are expected to have computational advantages for the KCS problem. We numerically demonstrate that KCS combined with IPMs is up to 10 times faster than vanilla IPMs and state-of-the-art methods such as ℓ[subscript 1]_ℓ[subscript s] and Mirror Prox regardless of the sparsity level or problem size.National Science Foundation (U.S.) (Grant DMS-1005539

System size dependence of elliptic flows in relativistic heavy-ion collisions

The elliptic flows in both Cu+Cu and Au+Au collisions at the Relativistic Heavy Ion Collider are studied in a multi-phase transport model. For both collisions at same reduced impact parameter and minimum bias collisions, the elliptic flow of partons in Cu+Cu collisions is about a factor of three smaller than that in Au+Au collisions at same energy. The reduction factor is similar to the ratio of the sizes of the two colliding systems and is also related to the combined effects of initial energy density and spatial elliptic deformation in the two reactions. A similar system size dependence is also seen in the elliptic flow of charged hadrons from minimum bias collisions.Comment: 5 pages, 5 figures, revised version, to appear in PL

Partonic effects on higher-order anisotropic flows in relativistic heavy-ion collisions

Higher-order anisotropic flows $v_{4}$ and $v_{6}$ in heavy ion collisions at the Relativistic Heavy Ion Collider are studied in a multiphase transport model that has previously been used successfully for describing the elliptic flow $v_2$ in these collisions. We find that the same parton scattering cross section of about 10 \textrm{mb} used in explaining the measured $v_2$ can also reproduce the recent data on $v_{4}$ and $v_{6}$ from Au + Au collisions at $\sqrt{s}=200$ \textrm{AGeV}. It is further found that the $$ is a more sensitive probe of the initial partonic dynamics in these collisions than $v_{2}$. Moreover, higher-order parton anisotropic flows are nonnegligible and satisfy the scaling relation $v_{n,q}(p_{T})\sim v_{2,q}^{n/2}(p_{T})$, which leads naturally to the observed similar scaling relation among hadron anisotropic flows when the coalescence model is used to describe hadron production from the partonic matter.Comment: 5 pages, 3 figures, version to appear in PRC as a Rapid Communicatio

Pseudorapidity dependence of anisotropic flows in relativistic heavy-ion collisions

The pseudorapidity dependence of anisotropic flows $v_{1}$, $v_{2}$, $v_{3}$ , and $v_{4}$ of charged hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider is studied in a multi-phase transport model. We find that while the string melting scenario, in which hadrons that are expected to be formed from initial strings are converted to their valence quarks and antiquarks, can explain the measured $p_{T}$-dependence of $v_{2}$ and $v_{4}$ of charged hadrons at midrapidity with a parton scattering cross section of about 10 \textrm{mb}, the scenario without string melting reproduces better the recent data on $v_{1}$ and $v_{2}$ of charged hadrons at large pseudorapidity in Au + Au collisions at $\sqrt{s}=200$ AGeV . Our results thus suggest that a partonic matter is formed during early stage of relativistic heavy ion collisions only around midrapidity and that strings remain dominant at large rapidities. The $p_{T}$-dependence of $v_{1}$, $v_{2}$, $v_{3}$ and $v_{4}$ for charged hadrons at forward pseudorapidity is also predicted, and we find that while $v_{1}$ and $v_{2}$ are appreciable at large pseudorapidity the higher-order anisotropic flows $v_{3}$ and $v_{4}$ are essentially zero.Comment: 5 pages, 4 figures, revised version, to appear in PL

Hydrodynamic condition and suspended sediment diffusion in the Yellow Sea and East China Sea

Based on monthly averaged current, temperature, and salinity, we analyzed the changes of suspended sediment concentration (SSC) and the relationship with the warm current, coastal current, and cold water mass (CWM) in the East China Seas (ECSs). The result shows that the coastal current and surface diluted water are the route for transporting suspended sediment. The Kuroshio and its derived warm current branches play the important role of the continental shelf circulation system and control the diffusion of suspended sediment. High SSC has been mainly concentrated in coastal current and CWM. Two sedimentary dynamic patterns have been identified. The winter‐half‐year pattern lasts almost 7 months. The coastal currents off the Shandong Peninsula, northern Jiangsu, Zhejiang‐Fujian coast are the main routes for diffusion and deposition of the suspended sediment from the Yellow River and Changjiang River. The summer‐half‐year pattern is characterized by the well‐developed CWM. All CWMs have a unique function to trap suspended sediment under the thermocline due to weakening tidal current and residual current there. These CWMs in the Yellow Sea (YS) and north ECS are connected together. The layer above the thermocline is characterized by diluted water with low salinity, high temperature. Suspended sediment can be transported into the Okinawa Trough and the South Korea coast during this period. A strong eddy always occur nearby the Kuroshio bend at northeast Taiwan, which has promoted the exchange between the ECS shelf and Okinawa Trough, and the development of the shelf edge current and Taiwan warm current (TWC)

Soft X-ray induced oxidation on acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum

Water soluble acrylic acid grafted luminescent silicon quantum dots (Si-QDs) were prepared by a simplified method. The resulting Si-QDs dissolved in water and showed stable strong luminescence with peaks at 436 and 604?nm. X-ray photoelectron spectroscopy (XPS) was employed to examine the surface electronic states after the synthesis. The co-existence of the Si2p and C1s core levels infers that the acrylic acid has been successfully grafted on the surface of silicon quantum dots. To fit the Si2p spectrum, four components were needed at 99.45, 100.28, 102.21 and 103.24?eV. The first component at 99.45?eV (I) was assigned to Si–Si within the silicon core of the Si-QDs. The second component at 100.28?eV (II) was from Si–C. The third at 102.21?eV (III) was a sub-oxide state and the fourth at 103.24?eV (IV) was from SiO2 at Si-QDs surface. With an increase in exposure to soft X-ray photons, the intensity ratio of the two peaks within the Si2p region A and B increased from 0.5 to 1.4 while the peak A intensity decreased, and eventually a steady state was reached. This observation is explained in terms of photon-induced oxidation taking place within the surface dangling bonds. As the PL profile for Si-QDs is influenced by the degree of oxidation within the nanocrystal structure, the inducement of oxidation by soft X-rays will play a role in the range of potential applications where such materials could be used – especially within biomedical labelling