Polygonal complexes

Ian Leary inquires whether a class of hyperbolic finitely presented groups are residually finite. We answer in the affirmative by giving a systematic version of a construction in his paper, which shows that the standard 2-complexes of these presentations have a VH-structure. This structure induces a splitting of these groups, which together with hyperbolicity, implies that these groups are residually finite

Gravity from a fermionic condensate of a gauge theory

The most prominent realization of gravity as a gauge theory similar to the gauge theories of the standard model comes from enlarging the gauge group from the Lorentz group to the de Sitter group. To regain ordinary Einstein-Cartan gravity the symmetry must be broken, which can be accomplished by known quasi-dynamic mechanisms. Motivated by symmetry breaking models in particle physics and condensed matter systems, we propose that the symmetry can naturally be broken by a homogenous and isotropic fermionic condensate of ordinary spinors. We demonstrate that the condensate is compatible with the Einstein-Cartan equations and can be imposed in a fully de Sitter invariant manner. This lends support, and provides a physically realistic mechanism for understanding gravity as a gauge theory with a spontaneously broken local de Sitter symmetry.Comment: 16 page

First study of B→πB \to \pi semileptonic decay form factors using NRQCD

We present a quenched calculation of the form factors of the semileptonic weak decay $B \to \pi l \bar{\nu}$ with $O(1/m_Q)$ NRQCD heavy quark and Wilson light quark on a $16^3 \times 32$ lattice at $\beta=5.8$. The form factors are evaluated at six heavy quark masses, in the range of $m_Q \sim 1.5-8$ GeV. $1/m_Q$ dependence of matrix elements are investigated and compared with HQET predictions. We observe clear signal for the form factors near $q^2_{max}$, even at the $b$-quark mass range. $f^0(q^2_{max})$ is compared with $f_B/f_{\pi}$ based on the soft pion theorem and significant difference is observed.Comment: 3 pages, 5 ps figures, uses espcrc2.sty and epsf.sty, Talk presented at Lattice'9

Chiral Perturbation Theory for phi -> rho gamma gamma and phi -> omega gamma gamma

We predict differential decay distributions for phi->rho gamma gamma and phi -> omega gamma gamma using chiral perturbation theory. We also consider the isospin violating decay phi -> omega pi^0. Experimental information on these decays can be used to determine couplings in the heavy vector meson chiral Lagrangian.Comment: It was shown by P. Ko et al., hep-ph/9510205 (Phys. Lett. B366 (1996) 287), that there is a etaprime pole contribution that dominates over what we calculate

Quasi-hydrostatic intracluster gas under radiative cooling

Quasi-hydrostatic cooling of the intracluster gas is studied. In the quasi-hydrostatic model, work done by gravity on the inflow gas with dP \neq 0, where P is the gas pressure, is taken into account in the thermal balance. The gas flows in from the outer part so as to compensate the pressure loss of the gas undergoing radiative cooling, but the mass flow is so moderate and smooth that the gas is considered to be quasi-hydrostatic. The temperature of the cooling gas decreases toward the cluster center, but, unlike cooling flows with dP = 0, approaches a constant temperature of \sim 1/3 the temperature of the non-cooling ambient gas. This does not mean that gravitational work cancels out radiative cooling, but means that the temperature of the cooling gas appears to approach a constant value toward the cluster center if the gas maintains the quasi-hydrostatic balance. We discuss the mass flow in quasi-hydrostatic cooling, and compare it with the standard isobaric cooling flow model. We also discuss the implication of \dot{M} for the standard cooling flow model.Comment: 5 pages, 1 figure, accepted for publication in A&

Severe multidirectional instability of the gleno-humeral joint

The article presents a case study of a 22 year-old female college athlete with multidirectional instability (MDI) of the glen-humeral (GH) joint. The athlete participated in overhead sports activities such as softball, basketball and swimming, and her presenting symptoms included decreased function, crepitus and spontaneous subluxation. Clinical management and range of motion (ROM) measurement are also discussed

Correlation of physical properties with molecular structure for some dicyclic hydrocarbons having high thermal-energy release per unit volume

As part of a program to study the correlation between molecular structure and physical properties of high-density hydrocarbons, the net heats of combustion, melting points, boiling points, densities, and kinematic viscosities of some hydrocarbons in the 2-n-alkylbiphenyl, 1,1-diphenylalkane, diphenylalkane, 1,1-dicyclohexylalkane, and dicyclohexylalkane series are presented

The Thalamus and Brainstem Act As Key Hubs in Alterations of Human Brain Network Connectivity Induced by Mild Propofol Sedation

Despite their routine use during surgical procedures, no consensus has yet been reached on the precise mechanisms by which hypnotic anesthetic agents produce their effects. Molecular, animal and human studies have suggested disruption of thalamocortical communication as a key component of anesthetic action at the brain systems level. Here, we used the anesthetic agent, propofol, to modulate consciousness and to evaluate differences in the interactions of remote neural networks during altered consciousness. We investigated the effects of propofol, at a dose that produced mild sedation without loss of consciousness, on spontaneous cerebral activity of 15 healthy volunteers using functional magnetic resonance imaging (fMRI), exploiting oscillations (<0.1 Hz) in blood oxygenation level-dependent signal across functionally connected brain regions. We considered the data as a graph, or complex network of nodes and links, and used eigenvector centrality (EC) to characterize brain network properties. The EC mapping of fMRI data in healthy humans under propofol mild sedation demonstrated a decrease of centrality of the thalamus versus an increase of centrality within the pons of the brainstem, highlighting the important role of these two structures in regulating consciousness. Specifically, the decrease of thalamus centrality results from its disconnection from a widespread set of cortical and subcortical regions, while the increase of brainstem centrality may be a consequence of its increased influence, in the mildly sedated state, over a few highly central cortical regions key to the default mode network such as the posterior and anterior cingulate cortices