Solving for Micro- and Macro- Scale Electrostatic Configurations Using the Robin Hood Algorithm

We present a novel technique by which highly-segmented electrostatic configurations can be solved. The Robin Hood method is a matrix-inversion algorithm optimized for solving high density boundary element method (BEM) problems. We illustrate the capabilities of this solver by studying two distinct geometry scales: (a) the electrostatic potential of a large volume beta-detector and (b) the field enhancement present at surface of electrode nano-structures. Geometries with elements numbering in the O(10^5) are easily modeled and solved without loss of accuracy. The technique has recently been expanded so as to include dielectrics and magnetic materials.Comment: 40 pages, 20 figure

Bloom-Gilman duality of the nucleon structure function and the elastic peak contribution

The occurrence of the Bloom-Gilman duality in the nucleon structure function is investigated by analyzing the Q**2-behavior of low-order moments, both including and excluding the contribution arising from the nucleon elastic peak. The Natchmann definition of the moments has been adopted in order to cancel out target-mass effects. It is shown that the onset of the Bloom-Gilman duality occurs around Q**2 ~ 2 (GeV/c)**2 if only the inelastic part of the nucleon structure function is considered, whereas the inclusion of the nucleon elastic peak contribution leads to remarkable violations of the Bloom-Gilman duality.Comment: in Proc. of the XVI European Conference on Few-body Problems in Physics, Autrans (France), July 199

The Kinetic Interpretation of the DGLAP Equation, its Kramers-Moyal Expansion and Positivity of Helicity Distributions

According to a rederivation - due to Collins and Qiu - the DGLAP equation can be reinterpreted (in leading order) in a probabilistic way. This form of the equation has been used indirectly to prove the bound $|\Delta f(x,Q)| < f(x,Q)$ between polarized and unpolarized distributions, or positivity of the helicity distributions, for any $Q$. We reanalize this issue by performing a detailed numerical study of the positivity bounds of the helicity distributions. To obtain the numerical solution we implement an x-space based algorithm for polarized and unpolarized distributions to next-to-leading order in $\alpha_s$, which we illustrate. We also elaborate on some of the formal properties of the Collins-Qiu form and comment on the underlying regularization, introduce a Kramers-Moyal expansion of the equation and briefly analize its Fokker-Planck approximation. These follow quite naturally once the master version is given. We illustrate this expansion both for the valence quark distribution $q_V$ and for the transverse spin distribution $h_1$.Comment: 38 pages, 27 figures, Dedicated to Prof. Pierre Ramond for his 60th birthda

Shadowing Effects on the Nuclear Suppression Factor, R_dAu, in d+Au Interactions

We explore how nuclear modifications to the nucleon parton distributions affect production of high transverse momentum hadrons in deuteron-nucleus collisions. We calculate the charged hadron spectra to leading order using standard fragmentation functions and shadowing parameterizations. We obtain the d+Au to pp ratio both in minimum bias collisions and as a function of centrality. The minimum bias results agree reasonably well with the BRAHMS data while the calculated centrality dependence underestimates the data and is a stronger function of p_T than the data indicate.Comment: 18 pages, 3 figures, final version, Phys. Rev. C in pres

Interaction of small size wave packet with hadron target

We calculate in QCD the cross section for the scattering of an energetic small-size wave packet off a hadron target. We use our results to study the small-$\sigma$ behaviour of $P_{\pi}(\sigma)$, the distribution over cross section for the pion, in the leading $\alpha_{s}$-order.Comment: Revised version of the report CEBAF-TH-96-0

Families of N=2 Strings

In a given 4d spacetime bakcground, one can often construct not one but a family of distinct N=2 string theories. This is due to the multiple ways N=2 superconformal algebra can be embedded in a given worldsheet theory. We formulate the principle of obtaining different physical theories by gauging different embeddings of the same symmetry algebra in the same ``pre-theory.'' We then apply it to N=2 strings and formulate the recipe for finding the associated parameter spaces of gauging. Flat and curved target spaces of both (4,0) and (2,2) signatures are considered. We broadly divide the gauging choices into two classes, denoted by alpha and beta, and show them to be related by T-duality. The distinction between them is formulated topologically and hinges on some unique properties of 4d manifolds. We determine what their parameter spaces of gauging are under certain simplicity ansatz for generic flat spaces (R^4 and its toroidal compactifications) as well as some curved spaces. We briefly discuss the spectra of D-branes for both alpha and beta families.Comment: 66+1 pages, 2 tables, latex 2e, hyperref. ver2: typos corrected, reference adde

Symmetry breaking effect on determination of polarized and unpolarized parton distributions

We perform a new extraction for unpolarized and polarized parton distribution functions considering a flavor decompositions for sea quarks and applying very recent deep inelastic scattering (DIS) and semi inclusive deep inelastic scattering (SIDIS) data in the fixed flavor number scheme (FFNS) framework. In the new symmetry breaking scenario the light quark and antiquark densities are extracted separately and new parametrization forms are determined for them. The heavy flavors contribution, including charm and bottom quarks, are also taken to be account for unpolarized distributions.Comment: Talk presented at 16th International QCD Conference (QCD12), Montpellier, France, July 2- 7, 2012. Submitted to Nuc. Phys. (Proc. Suppl.), 4 pages, 4 figure

NLO photon parton parametrization using ee and ep data

An NLO photon parton parametrization is presented based on the existing $F_2^\gamma$ measurements from $e^+e^-$ data and the low-$x$ proton structure function from $ep$ interactions. Also included in the extraction of the NLO parton distribution functions are the dijets data coming from $\gamma p \to j_1 + j_2 +X$. The new parametrization is compared to other NLO parametrizations.Comment: 22 pages, 7 figures, 2 table

ABC's of Writing Medical Papers in English

Publishing medical papers in English is important as English remains the predominant language for most medical papers (both electronic and traditional journal publications). In addition, journals with the highest impact factors are published in English and a publication in English thus enhances the visibility of authors and their institutions, and is important for promotion in some academic centers. This article reviews the basic principles that will help you successfully publish a manuscript in English. Although other books and articles are available on this subject, there are relatively few references. The present article is based on this author's experience of publishing nearly 400 articles in English. It will emphasize writing original articles, but the principles can be applied to virtually any type of manuscript