Coulomb corrections and multiple e+e- pair production in ultra-relativistic nuclear collisions

We consider the problem of Coulomb corrections to the inclusive cross section. We show that these corrections in the limiting case of small charge number of one of the nuclei coincide with those to the exclusive cross section. Within our approach we also obtain the Coulomb corrections for the case of large charge numbers of both nuclei.Comment: 7 pages, REVTeX

On the nature of Coulomb corrections to the e^+e^- pair production in ultrarelativistic heavy-ion collisions

We manifest the origin of the wrong conclusion made by several groups of authors on the absence of Coulomb corrections to the cross section of the e^+e^- pair production in ultrarelativistic heavy-ion collisions. The source of the mistake is connected with an incorrect passage to the limit in the expression for the cross section. When this error is eliminated, the Coulomb corrections do not vanish and agree with the results obtained within the Weizs\"acker-Williams approximation.Comment: 7 pages, LaTe

Theory of Nonlinear Dispersive Waves and Selection of the Ground State

A theory of time dependent nonlinear dispersive equations of the Schroedinger / Gross-Pitaevskii and Hartree type is developed. The short, intermediate and large time behavior is found, by deriving nonlinear Master equations (NLME), governing the evolution of the mode powers, and by a novel multi-time scale analysis of these equations. The scattering theory is developed and coherent resonance phenomena and associated lifetimes are derived. Applications include BEC large time dynamics and nonlinear optical systems. The theory reveals a nonlinear transition phenomenon, ``selection of the ground state'', and NLME predicts the decay of excited state, with half its energy transferred to the ground state and half to radiation modes. Our results predict the recent experimental observations of Mandelik et. al. in nonlinear optical waveguides

Exact Z2Z^2 scaling of pair production in the high-energy limit of heavy-ion collisions

The two-center Dirac equation for an electron in the external electromagnetic field of two colliding heavy ions in the limit in which the ions are moving at the speed of light is exactly solved and nonperturbative amplitudes for free electron-positron pair production are obtained. We find the condition for the applicability of this solution for large but finite collision energy, and use it to explain recent experimental results. The observed scaling of positron yields as the square of the projectile and target charges is a result of an exact cancellation of a nonperturbative charge dependence and holds as well for large coupling. Other observables would be sensitive to nonperturbative phases.Comment: 4 pages, Revtex, no figures, submitted to PR

Optogenetic manipulation of medullary neurons in the locust optic lobe

The locust is a widely used animal model for studying sensory processing and its relation to behavior. Due to the lack of genomic information, genetic tools to manipulate neural circuits in locusts are not yet available. We examined whether Semliki Forest virus is suitable to mediate exogenous gene expression in neurons of the locust optic lobe. We subcloned a channelrhodopsin variant and the yellow fluorescent protein Venus into a Semliki Forest virus vector and injected the virus into the optic lobe of locusts (Schistocerca americana). Fluorescence was observed in all injected optic lobes. Most neurons that expressed the recombinant proteins were located in the first two neuropils of the optic lobe, the lamina and medulla. Extracellular recordings demonstrated that laser illumination increased the firing rate of medullary neurons expressing channelrhodopsin. The optogenetic activation of the medullary neurons also triggered excitatory postsynaptic potentials and firing of a postsynaptic, looming-sensitive neuron, the lobula giant movement detector. These results indicate that Semliki Forest virus is efficient at mediating transient exogenous gene expression and provides a tool to manipulate neural circuits in the locust nervous system and likely other insects

Structural expression of a fading rift front: a case study from the Oligo-Miocene Irbid rift of northwest Arabia

Not all continental rifts mature to form a young ocean. The mechanism and duration of their cessation depend on the crustal structure, modifications in plate kinematics, lithospheric thermal response, or the intensity of subcrustal flow (e.g., plume activity). The cessation is recorded in the structure and stratigraphy of the basins that develop during the rifting process. This architecture is lost due to younger tectonic inversion, severe erosion, or even burial into greater depths that forces their detection by low-resolution geophysical imaging. The current study focuses on a uniquely preserved Oligo-Miocene rift that was subsequently taken over by a crossing transform fault system and, mostly due to that, died out. We integrate all geological, geophysical, and previous study results from across the southern Galilee to unravel the structural development of the Irbid failing rift in northwest Arabia. Despite tectonic, magmatic, and geomorphologic activity postdating the rifting, its subsurface structure northwest of the Dead Sea fault is preserved at depths of up to 1&thinsp;km. Our results show that a series of basins subsided at the rift front, i.e., rift termination, across the southern Galilee. We constrain the timing and extent of their subsidence into two main stages based on facies analysis and chronology of magmatism. Between 20 and 9&thinsp;Ma grabens and half-grabens subsided within a larger releasing jog, following a NW direction of a deeper presumed principal displacement zone. The basins continued to subside until a transition from the transtensional Red Sea to the transpressional Dead Sea stress regime occurred. With the transition, the basins ceased to subside as a rift, while the Dead Sea fault split the jog structure. Between 9 and 5&thinsp;Ma basin subsidence accentuated and an uplift of their margins accompanied their overall elongation to the NNE. Our study provides for the first time a structural as well as tectonic context for the southern Galilee basins. Based on this case study we suggest that the rift did not fail but rather faded and was taken over by a more dominant stress regime. Otherwise, these basins of a failing rift could have simply died out peacefully.</p

Approximating k-Forest with Resource Augmentation: A Primal-Dual Approach

In this paper, we study the $k$-forest problem in the model of resource augmentation. In the $k$-forest problem, given an edge-weighted graph $G(V,E)$, a parameter $k$, and a set of $m$ demand pairs $\subseteq V \times V$, the objective is to construct a minimum-cost subgraph that connects at least $k$ demands. The problem is hard to approximate---the best-known approximation ratio is $O(\min\{\sqrt{n}, \sqrt{k}\})$. Furthermore, $k$-forest is as hard to approximate as the notoriously-hard densest $k$-subgraph problem. While the $k$-forest problem is hard to approximate in the worst-case, we show that with the use of resource augmentation, we can efficiently approximate it up to a constant factor. First, we restate the problem in terms of the number of demands that are {\em not} connected. In particular, the objective of the $k$-forest problem can be viewed as to remove at most $m-k$ demands and find a minimum-cost subgraph that connects the remaining demands. We use this perspective of the problem to explain the performance of our algorithm (in terms of the augmentation) in a more intuitive way. Specifically, we present a polynomial-time algorithm for the $k$-forest problem that, for every $\epsilon>0$, removes at most $m-k$ demands and has cost no more than $O(1/\epsilon^{2})$ times the cost of an optimal algorithm that removes at most $(1-\epsilon)(m-k)$ demands

Structure of the Coulomb and unitarity corrections to the cross section of e+e−e^+e^- pair production in ultra-relativistic nuclear collisions

We analyze the structure of the Coulomb and unitarity corrections to the single pair production as well as the cross section for the multiple pair production. In the external field approximation we consider the probability of $e^+e^-$ pair production at fixed impact parameter $\rho$ between colliding ultra-relativistic heavy nuclei. We obtain the analytical result for this probability at large $\rho$ as compared to the electron Compton wavelength. We estimate also the unitary corrections to the total cross section of the process.Comment: 10 pages, 2 figures, RevTeX, references correcte

Optogenetic manipulation of medullary neurons in the locust optic lobe

The locust is a widely used animal model for studying sensory processing and its relation to behavior. Due to the lack of genomic information, genetic tools to manipulate neural circuits in locusts are not yet available. We examined whether Semliki Forest virus is suitable to mediate exogenous gene expression in neurons of the locust optic lobe. We subcloned a channelrhodopsin variant and the yellow fluorescent protein Venus into a Semliki Forest virus vector and injected the virus into the optic lobe of locusts (Schistocerca americana). Fluorescence was observed in all injected optic lobes. Most neurons that expressed the recombinant proteins were located in the first two neuropils of the optic lobe, the lamina and medulla. Extracellular recordings demonstrated that laser illumination increased the firing rate of medullary neurons expressing channelrhodopsin. The optogenetic activation of the medullary neurons also triggered excitatory postsynaptic potentials and firing of a postsynaptic, looming-sensitive neuron, the lobula giant movement detector. These results indicate that Semliki Forest virus is efficient at mediating transient exogenous gene expression and provides a tool to manipulate neural circuits in the locust nervous system and likely other insects