QCD effective action with a most general homogeneous field background

We consider one-loop effective action of SU(3) QCD with a most general constant chromomagnetic (chromoelectric) background which has two independent Abelian field components. The effective potential with a pure magnetic background has a local minimum only when two Abelian components H_{\mu\nu}^3 and H_{\mu\nu}^8 of color magnetic field are orthogonal to each other. The non-trivial structure of the effective action has important implication in estimating quark-gluon production rate and p_T-distribution in quark-gluon plasma. In general the production rate depends on three independent Casimir invariants, in particular, it depends on the relative orientation between chromoelectric fields.Comment: 6 pages, 3 figures (9 pages in published version

Universal Robotic Gripper based on the Jamming of Granular Material

Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multi-fingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where. Here we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of granular material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the granular material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback. We find that volume changes of less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight. We show that the operating principle is the ability of granular materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. We delineate three separate mechanisms, friction, suction and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.Comment: 10 pages, 7 figure

Probing the isospin dependent mean field and nucleon nucleon cross section in the medium by the nucleon emissions

We study the isospin effects of the mean field and two-body collision on the nucleon emissions at the intermediate energy heavy ion collisions by using an isospin dependent transport theory. The calculated results show that the nucleon emission number $N_{n}$ depends sensitively the isospin effect of nucleon nucleon cross section and weakly on the isospin dependent mean field for neutron-poor system in higher beam energy region . In particular, the correlation between the medium correction of two-body collision and the momentum dependent interaction enhances the dependence of nucleon emission number $N_{n}$ on the isospin effect of nucleon nucleon cross section. On the contrary, the ratio of the neutron proton ratio of the gas phase to the neutron proton ratio of the liquid phase, i.e., the degree of isospin fractionation $_{b}/_{b}$ depends sensitively on the isospin dependent mean field and weakly on the isospin effect of two-body collision for neutron-rich system in the lower beam energy region. In this case, $N_{n}$ and $_{b}/_{b}$ are the probes for extracting the information about the isospin dependent nucleon nucleon cross section in the medium and the isospin dependent mean field,respectively.Comment: 4 pages,4 figure

Azimuthal anisotropy: transition from hydrodynamic flow to jet suppression

Measured 2nd and 4th azimuthal anisotropy coefficients v_{2,4}(N_{part}), p_T) are scaled with the initial eccentricity \varepsilon_{2,4}(N_{part}) of the collision zone and studied as a function of the number of participants N_{part} and the transverse momenta p_T. Scaling violations are observed for p_T \alt 3 GeV/c, consistent with a $p_T^2$ dependence of viscous corrections and a linear increase of the relaxation time with $p_T$. These empirical viscous corrections to flow and the thermal distribution function at freeze-out constrain estimates of the specific viscosity and the freeze-out temperature for two different models for the initial collision geometry. The apparent viscous corrections exhibit a sharp maximum for p_T \agt 3 GeV/c, suggesting a breakdown of the hydrodynamic ansatz and the onset of a change from flow-driven to suppression-driven anisotropy.Comment: 5 pages, 4 figs; submitted for publicatio

Constraints on models for the initial collision geometry in ultra relativistic heavy ion collisions

Monte Carlo (MC) simulations are used to compute the centrality dependence of the collision zone eccentricities ($\epsilon_{2,4}$), for both spherical and deformed ground state nuclei, for different model scenarios. Sizable model dependent differences are observed. They indicate that measurements of the $2^{\text{nd}}$ and $4^{\text{th}}$ order Fourier flow coefficients $v_{2,4}$, expressed as the ratio $\frac{v_4}{(v_2)^2}$, can provide robust constraints for distinguishing between different theoretical models for the initial-state eccentricity. Such constraints could remove one of the largest impediments to a more precise determination of the specific viscosity from precision $v_{2,4}$ measurements at the Relativistic Heavy Ion Collider (RHIC).Comment: 4 pages, 3 figs - version accepted for publicatio

Coulomb effects on growth of instabilities in asymmetric nuclear matter

We study the effects of the Coulomb interaction on the growth of unstable modes in asymmetric nuclear matter. In order to compare with previous calculations we use a semiclassical approach based on the linearized Vlasov equation. Moreover, a quantum calculation is performed within the R.P.A.. The Coulomb effects are a slowing down of the growth and the occurrence of a minimal wave vector for the onset of the instabilities. The quantum corrections cause a further decrease of the growth rates.Comment: 10 pages, revtex, 4 ps figures, to appear in Phys. Rev. C e-mail: [email protected], [email protected]

Impaired M3 and enhanced M2 muscarinic receptor contractile function in a streptozotocin model of mouse diabetic urinary bladder

We investigated the contractile roles of M2 and M3 muscarinic receptors in urinary bladder from streptozotocin-treated mice. Wild-type and M2 muscarinic receptor knockout (M2 KO) mice were given a single injection of vehicle or streptozotocin (125 mg kg−1) 2–24 weeks prior to bladder assays. The effect of forskolin on contractions elicited to the muscarinic agonist, oxotremorine-M, was measured in isolated urinary bladder (intact or denuded of urothelium). Denuded urinary bladder from vehicle-treated wild-type and M2 KO mice exhibited similar contractile responses to oxotremorine-M, when contraction was normalized relative to that elicited by KCl (50 mM). Eight to 9 weeks after streptozotocin treatment, the EC50 value of oxotremorine-M increased 3.1-fold in urinary bladder from the M2 KO mouse (N = 5) compared to wild type (N = 6; P < 0.001). Analogous changes were observed in intact bladder. In denuded urinary bladder from vehicle-treated mice, forskolin (5 µM) caused a much greater inhibition of contraction in M2 KO bladder compared to wild type. Following streptozotocin treatment, this forskolin effect increased 1.6-fold (P = 0.032). At the 20- to 24-week time point, the forskolin effect increased 1.7-fold for denuded as well as intact bladders (P = 0.036, 0.01, respectively). Although streptozotocin treatment inhibits M3 receptor-mediated contraction in denuded urinary bladder, muscarinic contractile function is maintained in wild-type bladder by enhanced M2 contractile function. M2 receptor activation opposes forskolin-induced relaxation of the urinary bladder, and this M2 function is enhanced following streptozotocin treatment

Near-Infrared Molecular Hydrogen Emission from the Central Regions of Galaxies: Regulated Physical Conditions in the Interstellar Medium

The central regions of many interacting and early-type spiral galaxies are actively forming stars. This process affects the physical and chemical properties of the local interstellar medium as well as the evolution of the galaxies. We observed near-infrared H2 emission lines: v=1-0 S(1), 3-2 S(3), 1-0 S(0), and 2-1 S(1) from the central ~1 kpc regions of the archetypical starburst galaxies, M82 and NGC 253, and the less dramatic but still vigorously star-forming galaxies, NGC 6946 and IC 342. Like the far-infrared continuum luminosity, the near-infrared H2 emission luminosity can directly trace the amount of star formation activity because the H2 emission lines arise from the interaction between hot and young stars and nearby neutral clouds. The observed H2 line ratios show that both thermal and non-thermal excitation are responsible for the emission lines, but that the great majority of the near-infrared H2 line emission in these galaxies arises from energy states excited by ultraviolet fluorescence. The derived physical conditions, e.g., far-ultraviolet radiation field and gas density, from [C II] and [O I] lines and far-infrared continuum observations when used as inputs to photodissociation models, also explain the luminosity of the observed H2 v=1-0 S(1) line. The ratio of the H2 v=1-0 S(1) line to far-IR continuum luminosity is remarkably constant over a broad range of galaxy luminosities; L_H2/L_FIR = about 10^{-5}, in normal late-type galaxies (including the Galactic center), in nearby starburst galaxies, and in luminous IR galaxies (LIRGs: L_FIR > 10^{11} L_sun). Examining this constant ratio in the context of photodissociation region models, we conclude that it implies that the strength of the incident UV field on typical molecular clouds follows the gas density at the cloud surface.Comment: Accepted for ApJ, 24 pages, 17 figures, for complete PDF file, see http://kao.re.kr/~soojong/mypaper/2004_pak_egh2.pd