DNA-psoralen: single-molecule experiments and first principles calculations

The authors measure the persistence and contour lengths of DNA-psoralen complexes, as a function of psoralen concentration, for intercalated and crosslinked complexes. In both cases, the persistence length monotonically increases until a certain critical concentration is reached, above which it abruptly decreases and remains approximately constant. The contour length of the complexes exhibits no such discontinuous behavior. By fitting the relative increase of the contour length to the neighbor exclusion model, we obtain the exclusion number and the intrinsic intercalating constant of the psoralen-DNA interaction. Ab initio calculations are employed in order to provide an atomistic picture of these experimental findings.Comment: 9 pages, 4 figures in re-print format 3 pages, 4 figures in the published versio

Strongly coupled matter near phase transition

In the Hartree approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism of the real scalar field theory, we show that for the strongly coupled scalar system near phase transition, the shear viscosity over entropy density is small, however, the bulk viscosity over entropy density is large. The large bulk viscosity is related to the highly nonconformal equation of state. It is found that the square of the sound velocity near phase transition is much smaller than the conformal value 1/3, and the trace anomaly at phase transition deviates far away from 0. These results agree well with the lattice results of the complex QCD system near phase transition.Comment: 6 pages, 2 figures, 1 table, contributed to the International Conference on Strangeness in Quark Matter 2008, Beijing, China, 6-10 October 200

The role of the equation of state and the space-time dimension in spherical collapse

We study the spherically symmetric collapse of a fluid with non-vanishing radial pressure in higher dimensional space-time. We obtain the general exact solution in the closed form for the equation of state ($P_r = \gamma \rho$) which leads to the explicit construction of the root equation governing the nature (black hole versus naked singularity) of the central singularity. A remarkable feature of the root equation is its invariance for the three cases: (${D+1}, {\gamma = -1}$), (${D}, {\gamma = 0}$) and (${D - 1}, {\gamma = 1}$) where $D$ is the dimension of space-time. That is, for the ultimate end result of the collapse, $D$-dimensional dust, ${D+1}$ - AdS (anti de Sitter)-like and ${D-1}$ - dS-like are absolutely equivalent.Comment: 4 Pages, RevTeX, no figures, minor changes, new references added, Detailed version to follo

Hidden Consequence of Active Local Lorentz Invariance

In this paper we investigate a hidden consequence of the hypothesis that Lagrangians and field equations must be invariant under active local Lorentz transformations. We show that this hypothesis implies in an equivalence between spacetime structures with several curvature and torsion possibilities.Comment: Some misprints appearing in the published version have been correcte

Asymmetric I-V characteristics and magnetoresistance in magnetic point contacts

We present a theoretical study of the transport properties of magnetic point contacts under bias. Our calculations are based on the Keldish's non-equilibrium Green's function formalism combined with a self-consistent empirical tight-binding Hamiltonian, which describes both strong ferromagnetism and charging effects. We demonstrate that large magnetoresistance solely due to electronic effects can be found when a sharp domain wall forms inside a magnetic atomic-scale point contact. Moreover we show that the symmetry of the $I$-$V$ characteristic depends on the position of the domain wall in the constriction. In particular diode-like curves can arise when the domain wall is placed off-center within the point contact, although the whole structure does not present any structural asymmetry.Comment: 7 figures, submitted to PR

Looking for a varying α\alpha in the Cosmic Microwave Background

We perform a likelihood analysis of the recently released BOOMERanG and MAXIMA data, allowing for the possibility of a time-varying fine-structure constant. We find that in general this data prefers a value of $\alpha$ that was smaller in the past (which is in agreement with measurements of $\alpha$ from quasar observations). However, there are some interesting degeneracies in the problem which imply that strong statements about $\alpha$ can not be made using this method until independent accurate determinations of $\Omega_b h^2$ and $H_0$ are available. We also show that a preferred lower value of $\alpha$ comes mainly from the data points around the first Doppler peak, whereas the main effect of the high-$\ell$ data points is to increase the preferred value for $\Omega_b h^2$ (while also tightening the constraints on $\Omega_0$ and $H_0$). We comment on some implications of our results.Comment: 15 pages; submitted to Phys. Rev.

Protein kinase C inhibitor and irradiation-induced apoptosis: Relevance of the cytochrome c-mediated caspase-9 death pathway

Caspases are a family of cysteine proteases that constitute the apoptotic cell death machinery, We report the importance of the cytochrome c-mediated caspase-9 death pathway for radiosensitization by the protein kinase C (PKC) inhibitors staurosporine (STP) and PKC-412. In our genetically defined tumor cells, treatment with low doses of STP or the conventional PKC-specific inhibitor PKC-412 in combination with irradiation (5 Gy) potently reduced viability, enhanced mitochondrial cytochrome c release into the cytosol, and specifically stimulated the initiator caspase-9. Whereas treatment with each agent alone had a minimal effect, combined treatment resulted in enhanced caspase-3 activation. This was prevented by broad-range and specific caspase-9 inhibitors and absent in caspase-9-deficient cells. The tumor suppressor p53 was required for apoptosis induction by combined treatment but was dispensable for dose-dependent STP-induced caspase activation. These results demonstrate the requirement for an intact caspase-9 pathway for apoptosis-based radiosensitization by PKC inhibitors and show that STP induces apoptosis independent of p53

Linear theory and violent relaxation in long-range systems: a test case

In this article, several aspects of the dynamics of a toy model for longrange Hamiltonian systems are tackled focusing on linearly unstable unmagnetized (i.e. force-free) cold equilibria states of the Hamiltonian Mean Field (HMF). For special cases, exact finite-N linear growth rates have been exhibited, including, in some spatially inhomogeneous case, finite-N corrections. A random matrix approach is then proposed to estimate the finite-N growth rate for some random initial states. Within the continuous, $N \rightarrow \infty$, approach, the growth rates are finally derived without restricting to spatially homogeneous cases. All the numerical simulations show a very good agreement with the different theoretical predictions. Then, these linear results are used to discuss the large-time nonlinear evolution. A simple criterion is proposed to measure the ability of the system to undergo a violent relaxation that transports it in the vicinity of the equilibrium state within some linear e-folding times

Collapsing Perfect Fluid in Higher Dimensional Spherical Spacetimes

The general metric for N-dimensional spherically symmetric and conformally flat spacetimes is given, and all the homogeneous and isotropic solutions for a perfect fluid with the equation of state $p = \alpha \rho$ are found. These solutions are then used to model the gravitational collapse of a compact ball. It is found that when the collapse has continuous self-similarity, the formation of black holes always starts with zero mass, and when the collapse has no such a symmetry, the formation of black holes always starts with a mass gap.Comment: Class. Quantum Grav. 17 (2000) 2589-259