Hydrodynamics of Internal Shocks in Relativistic Outflows

We study the hydrodynamical effects of two colliding shells, adopted to model internal shocks in various relativistic outflows such as gamma-ray bursts and blazars. We find that the density profiles are significantly affected by the propagation of rarefaction waves. A split-feature appears at the contact discontinuity of the two shells. The shell spreading with a few ten percent of the speed of light is also shown to be a notable aspect. The conversion efficiency of the bulk kinetic energy to internal one shows deviations from the widely-used inelastic two-point-mass-collision model. Observational implications are also shortly discussed.Comment: 6 pages, 4 figures, Proceeding of International Symposium on High Energy Gamma-ray Astronomy (July 26-30, 2004, Heidelberg, Germany

Metastability of R-Charged Black Holes

The global stability of R-charged AdS black holes in a grand canonical ensemble is examined by eliminating the constraints from the action, but without solving the equations of motion, thereby constructing the reduced action of the system. The metastability of the system is found to set in at a critical value of the chemical potential which is conjugate to the R-charge. The relation among the small black hole, large black hole and the instability is discussed. The result is consistent with the metastability found in the AdS/CFT-conjectured dual field theory. The "renormalized" temperature of AdS black holes, which has been rather ad hoc, is suggested to be the boundary temperature in the sense of AdS/CFT correspondence. As a byproduct of the analysis, we find a more general solution of the theory and its properties are briefly discussed.Comment: 36 pages, 7 figures, v2 is the published version. the exposition is made slightly shorter and hopefully cleare

The Grounds For Time Dependent Market Potentials From Dealers' Dynamics

We apply the potential force estimation method to artificial time series of market price produced by a deterministic dealer model. We find that dealers' feedback of linear prediction of market price based on the latest mean price changes plays the central role in the market's potential force. When markets are dominated by dealers with positive feedback the resulting potential force is repulsive, while the effect of negative feedback enhances the attractive potential force.Comment: 9 pages, 3 figures, proceedings of APFA

Fabrication and characterization of Si3N4 ceramics without additives by high pressure hot pressing

High pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and alpha-beta phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high-temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder. The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39 MN/m to the 3/2 power and independent of temperature up to 1400 C

Open Problems in α\alpha Particle Condensation

$\alpha$ particle condensation is a novel state in nuclear systems. We briefly review the present status on the study of $\alpha$ particle condensation and address the open problems in this research field: $\alpha$ particle condensation in heavier systems other than the Hoyle state, linear chain and $\alpha$ particle rings, Hoyle-analogue states with extra neutrons, $\alpha$ particle condensation related to astrophysics, etc.Comment: 12 pages. To be published in J. of Phys. G special issue on Open Problems in Nuclear Structure (OPeNST

Electronic phase diagram of La1.875_{1.875}Ba0.125−x_{0.125-x}Srx_xCuO4_4

We performed systematic measurements of magnetic susceptibility on single crystals of La$_{1.875}$Ba$_{0.125-x}$Sr$_x$CuO$_4$. The dependence of the superconducting transition temperature on Sr-concentration demonstrates a step-like pattern upon doping at {\it x}$\sim$0.08 as the crystal structure changes from low-temperature tetragonal (LTT) to low-temperature orthorhombic (LTO) phase at low temperature. Upon cooling, an anomalous upturn in the susceptibility was observed at the structural phase transition between the LTT-LTO phases under the magnetic field parallel to {\it c}-axis.Comment: 6 pages, 4 figures, Proceeding paper of the Stripes2000 conference in Roma, Ital

Effects of Superconductivity and Charge Order on the sub-Terahertz reflectivity of La1.875_{1.875}Ba0.125−y_{0.125-y}Sry_{y}CuO4_4

The reflectivity $R (\omega)$ of both the $ab$ plane and the c axis of two single crystals of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$ has been measured down to 5 cm$^{-1}$, using coherent synchrotron radiation below 30 cm$^{-1}$. For $y$ = 0.085, a Josephson Plasma Resonance is detected at $T \ll T_c$ = 31 K in $R_{c} (\omega)$, and a far-infrared peak (FIP) appears in the optical conductivity below 50 K, where non-static charge ordering (CO) is reported by X-ray scattering. For $y$ = 0.05 ($T_c$ = 10 K), a FIP is observed in the low-temperature tetragonal phase below the ordering temperature $T_{CO}$. At 1/8 doping the peak frequency scales linearly with $T_{CO}$, confirming that the FIP is an infrared signature of CO, either static or fluctuating.Comment: v2: longer version, 9 pages, 6 color figure

Forced convection heat transfer simulation using dissipative particle dynamics with energy conservation

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Dissipative particle dynamics (DPD) with energy conservation was applied to simulate forced convection in parallel-plate channels with boundary conditions of constant wall temperature (CWT) and constant wall heat flux (CHF). DPD is a coarse-grained version of molecular dynamics. An additional governing equation for energy conservation was solved along with conventional DPD equations where inter-particle heat flux accounts for changes in mechanical and internal energies when particles interact with surrounding particles. The solution domain was considered to be two-dimensional with periodic boundary condition in the flow direction. Additional layers of particles on top and bottom of the channel were utilized to apply no-slip velocity and temperature boundary conditions. The governing equations for energy conservation were modified based on periodic fully developed velocity and temperature conditions. The results were shown via temperature profiles across the channel cross section. The Nusselt numbers were calculated from the temperature gradient at the wall using a second order accurate forward difference technique. The results agreed well with the exact solutions to within 2.3%.This work is supported by the National Science Foundation grant (NSF-OISE-0530203)