Pulsar scintillations from corrugated reconnection sheets in the ISM

We show that surface waves along interstellar current sheets closely aligned with the line of sight lead to pulsar scintillation properties consistent with those observed. This mechanism naturally produces the length and density scales of the ISM scattering lenses that are required to explain the magnitude and dynamical spectrum of the scintillations. In this picture, the parts of warm ionized interstellar medium that are responsible for the scintillations are relatively quiescent, with scintillation and scattering resulting from weak waves propagating along magnetic domain boundary current sheets, which are both expected from helicity conservation and have been observed in numerical simulations. The model statistically predicts the spacing and amplitudes of inverted parabolic arcs seen in Fourier-transformed dynamical spectra of strongly scintillating pulsars with only 3 parameters. Multi-frequency, multi-epoch low frequency VLBI observations can quantitatively test this picture. If successful, in addition to mapping the ISM, this may open the door to precise nanoarcsecond pulsar astrometry, distance measurements, and emission studies using these 10AU interferometers in the sky.Comment: 9 pages, 10 figures, accepted in MNRA

High energy Scattering in 2+1 QCD: A Dipole Picture

A dipole picture of high energy scattering is developed in the 2+1 dimensional QCD, following Mueller. A generalized integral equation for the dipole density with a given separation and center of mass position is derived, and meson-meson non-forward scattering amplitude is therefore calculated. We also calculate the amplitude due to two pomeron exchange, and the triple pomeron coupling. We compare the result obtained by this method to our previous result based on an effective action approach, and find the two results agree at the one pomeron exchange level.Comment: minor typos corrected. Postscript files are available through anonymous ftp quark.het.brown.edu, in the directory /pub/preprints, file name is 9407299. Hard copy is available upon reques

Charge inversion in DNA-amphiphile complexes: Possible application to gene therapy

We study a complex formation between the DNA and cationic amphiphilic molecules. As the amphiphile is added to the solution containing DNA, a cooperative binding of surfactants to the DNA molecules is found. This binding transition occurs at specific density of amphiphile, which is strongly dependent on the concentration of the salt and on the hydrophobicity of the surfactant molecules. We find that for amphiphiles which are sufficiently hydrophobic, a charge neutralization, or even charge inversion of the complex is possible. This is of particular importance in applications to gene therapy, for which the functional delivery of specific base sequence into living cells remains an outstanding problem. The charge inversion could, in principle, allow the DNA-surfactant complexes to approach negatively charged cell membranes permitting the transfection to take place.Comment: Latex, 5 figure

Comparison of Swendsen-Wang and Heat-Bath Dynamics

We prove that the spectral gap of the Swendsen-Wang process for the Potts model on graphs with bounded degree is bounded from below by some constant times the spectral gap of any single-spin dynamics. This implies rapid mixing of the Swendsen-Wang process for the two-dimensional Potts model at all temperatures above the critical one, as well as rapid mixing at the critical temperature for the Ising model. After this we introduce a modified version of the Swendsen-Wang algorithm for planar graphs and prove rapid mixing for the two-dimensional Potts models at all non-critical temperatures.Comment: 22 pages, 1 figur

Rational-operator-based depth-from-defocus approach to scene reconstruction

This paper presents a rational-operator-based approach to depth from defocus (DfD) for the reconstruction of three-dimensional scenes from two-dimensional images, which enables fast DfD computation that is independent of scene textures. Two variants of the approach, one using the Gaussian rational operators (ROs) that are based on the Gaussian point spread function (PSF) and the second based on the generalized Gaussian PSF, are considered. A novel DfD correction method is also presented to further improve the performance of the approach. Experimental results are considered for real scenes and show that both approaches outperform existing RO-based methods

Next-to-leading-order corrections to exclusive processes in kTk_T factorization

We calculate next-to-leading-order (NLO) corrections to exclusive processes in $k_T$ factorization theorem, taking $\pi\gamma^*\to\gamma$ as an example. Partons off-shell by $k_T^2$ are considered in both the quark diagrams from full QCD and the effective diagrams for the pion wave function. The gauge dependences in the above two sets of diagrams cancel, when deriving the $k_T$-dependent hard kernel as their difference. The gauge invariance of the hard kernel is then proven to all orders by induction. The light-cone singularities in the $k_T$-dependent pion wave function are regularized by rotating the Wilson lines away from the light cone. This regularization introduces a factorization-scheme dependence into the hard kernel, which can be minimized in the standard way. Both the large double logarithms $\ln^2k_T$ and $\ln^2 x$, $x$ being a parton momentum fraction, arise from the loop correction to the virtual photon vertex, the former being absorbed into the pion wave function and organized by the $k_T$ resummation, and the latter absorbed into a jet function and organized by the threshold resummation. The NLO corrections are found to be only few-percent for $\pi\gamma^*\to\gamma$, if setting the factorization scale to the momentum transfer from the virtual photon.Comment: 13 pages; version to appear in Physical Review

Solution for the BFKL Pomeron Calculus in zero transverse dimensions

In this paper the exact analytical solution is found for the BFKL Pomeron calculus in zero transverse dimensions, in which all Pomeron loops have been included. The comparison with the approximate methods of the solution is given, and the kinematic regions are discussed where they describe the behaviour of the scattering amplitude quite well. In particular, the semi-classical approach is considered, which reproduces the main properties of the exact solution at large values of rapidity ($Y \geq 10$). It is shown that the mean field approximation leads to a good description of the scattering amplitude only if the amplitude at low energy is rather large. However, even in this case, it does not lead to the correct asymptotic behaviour of the scattering amplitude at high energies.Comment: 37 pages,19 figures and one table, the revised versio

QED-Induced Rapidity-Gap Events at the Z Peak

We study rapidity-gap events in $e^+e^-$ annihilation at the Z boson peak initiated by the emission of a virtual photon. This mechanism is suppressed by the QED coupling constant, but it is enhanced due to a large propagator term from the virtual photon. For typical kinematics, we find a smaller event rate than analogous QCD type gap events. In the small jet-pair invariant mass limit, the QED type events follow a $1+\cos^2\theta$ distribution in the jet-pair scattering angle, instead of the $\sin^2\theta$ distribution of the QCD case.Comment: 13 pages, plain TeX (needs the PHYZZX macros), 4 figures in PostScript. SLAC-PUB-6116, DOE/ER/40762-009, U of Md. PP \#93-19