Strangeness contribution to the vector and axial form factors of the nucleon

The strangeness contribution to the vector and axial form factors of the nucleon is presented for momentum transfers in the range $0.45<Q^2<1.0$ GeV$^2$. The results are obtained via a combined analysis of forward-scattering parity-violating elastic $\vec{e}p$ asymmetry data from the $G^0$ and HAPPEx experiments at Jefferson Lab, and elastic $\nu p$ and $\bar{\nu} p$ scattering data from Experiment 734 at Brookhaven National Laboratory. The parity-violating asymmetries measured in elastic $\vec{e}p$ scattering at forward angles establish a relationship between the strange vector form factors $G_E^s$ and $G_M^s$, with little sensitivity to the strange axial form factor $G_A^s$. On the other hand, elastic neutrino scattering at low $Q^2$ is dominated by the axial form factor, with still some significant sensitivity to the vector form factors as well. The combination of the two data sets allows the simultaneous extraction of $G_E^s$, $G_M^s$, and $G_A^s$ over a significant range of $Q^2$ for the very first time.Comment: 3 pages, 1 figure, will appear in AIP Conference Proceedings for PANIC 200

Cylindrical, periodic surface lattice — theory, dispersion analysis, and experiment

A two-dimensional surface lattice of cylindrical topology obtained via perturbing the inner surface of a cylinder is considered. Periodic perturbations of the surface lead to observation of high-impedance, dielectric-like media and resonant coupling of surface and non-propagating volume fields. This allows synthesis of tailored-for-purpose "coating" material with dispersion suitable, for instance, to mediate a Cherenkov type interaction. An analytical model of the lattice is discussed and coupled-wave equations are derived. Variations of the lattice dispersive properties with variation of parameters are shown, illustrating the tailoring of the structure's electromagnetic properties. Experimental results are presented showing agreement with the theoretical model

Simulation of transient energy distributions in sub-ns streamer formation

Breakdown and streamer formation is simulated in atmospheric pressure nitrogen for a 2D planar electrode system. A PIC code with multigrid potential solver is used to simulate the evolution of the non-equilibrium ionization front on sub-nanosecond timescales. The ion and electron energy distributions are computed, accounting for the inclusion of inelastic scattering of electrons, and collisionally excited metastable production and ionization. Of particular interest is the increased production of metastable and low-energy ions and electrons when the applied field is reversed during the progress of the ionization front, giving insight into the improved species yields in nanosecond pulsed systems

The evolution of electron overdensities in magnetic fields

When a neutral gas impinges on a stationary magnetized plasma an enhancement in the ionization rate occurs when the neutrals exceed a threshold velocity. This is commonly known as the critical ionization velocity effect. This process has two distinct timescales: an ion–neutral collision time and electron acceleration time. We investigate the energization of an ensemble of electrons by their self-electric field in an applied magnetic field. The evolution of the electrons is simulated under different magnetic field and density conditions. It is found that electrons can be accelerated to speeds capable of electron impact ionization for certain conditions. In the magnetically dominated case the energy distribution of the excited electrons shows that typically 1% of the electron population can exceed the initial electrostatic potential associated with the unbalanced ensemble of electrons

Corrections to Gravity due to a Sol Manifold Extra Dimensional Space

The corrections to the gravitational potential due to a Sol extra dimensional compact manifold, denoted as $M_A^3$, are studied. The total spacetime is of the form $M^4\times M_A^3$. The range of the Sol corrections is investigated and compared to the range of the $T^3$ corrections.Comment: 13 pages, 10 figures, published versio

Strange form factors of the nucleon in a two-component model

The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0 collaborations shows a good overall agreement. The strange magnetic moment is found to be positive, 0.315 nm.Comment: 11 pages, 2 tables, 5 figures, accepted for publication in J. Phys. G. Revised version, new figures, extra table, new results, updated reference

Excitation and coupling of volume and surface fields on complex electrodynamic surfaces at Mm-wave and THz frequencies

The analytical theory describing the resonant excitation and coupling of volume and surface fields on the surface of two-dimensional complex electrodynamic structures is presented. The theoretical analysis is valid over a broad frequency spectrum from mm-wave frequencies through THz and even optical frequencies. An experimental study of planar periodic structures has been carried out using a vector network analyser calibrated to operate in the 140-220 GHz frequency range. Experimental results compare resonant eigenmode formation in two periodic surface lattice structures designed to operate within the 140-220 GHz frequency band; one periodic surface lattice etched onto a metal-backed substrate and the other arranged to have an equivalent air separation. Dispersion diagrams derived from the analytical theory are presented. The results and theory are fundamental to some of the routes to the innovation of high-power, mm-wave and THz sources, solar cells, and novel sub-wavelength absorbers

Symbolic Manipulators Affect Mathematical Mindsets

Symbolic calculators like Mathematica are becoming more commonplace among upper level physics students. The presence of such a powerful calculator can couple strongly to the type of mathematical reasoning students employ. It does not merely offer a convenient way to perform the computations students would have otherwise wanted to do by hand. This paper presents examples from the work of upper level physics majors where Mathematica plays an active role in focusing and sustaining their thought around calculation. These students still engage in powerful mathematical reasoning while they calculate but struggle because of the narrowed breadth of their thinking. Their reasoning is drawn into local attractors where they look to calculation schemes to resolve questions instead of, for example, mapping the mathematics to the physical system at hand. We model the influence of Mathematica as an integral part of the constant feedback that occurs in how students frame, and hence focus, their work