Charge distribution and screening in layered graphene systems

The charge distribution induced by external fields in finite stacks of graphene planes, or in semiinfinite graphite is considered. The interlayer electronic hybridization is described by a nearest neighbor hopping term, and the charge induced by the self consistent electrostatic potential is calculated within linear response (RPA). The screening properties are determined by contributions from inter- and intraband electronic transitions. In neutral systems, only interband transitions contribute to the charge polarizability, leading to insulating-like screening properties, and to oscillations in the induced charge, with a period equal to the interlayer spacing. In doped systems, we find a screening length equivalent to 2-3 graphene layers, superimposed to significant charge oscillations.Comment: 8 page

Timelike self-similar spherically symmetric perfect-fluid models

Einstein's field equations for timelike self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure

The effects of deformation and pairing correlations on nuclear charge form factor

A set of moderately deformed $s-d$ shell nuclei is employed for testing the reliability of the nuclear ground state wave functions which are obtained in the context of a BCS approach and offer a simultaneous consideration of deformation and pairing correlations effects. In this method, the mean field is assumed to be an axially symmetric Woods-Saxon potential and the effective two-body interaction is a monopole pairing force. As quantities of main interest we have chosen the nuclear form factors, the occupancies of the active (surface) orbits and the Fermi sea depletion, which provide quite good tests for microscopic descriptions of nuclei within many body theories. For our comparisons with results emerging from other similar methods, an axially deformed harmonic oscillator field is also utilized.Comment: 20 pages, 12 figures, 2 table

The Low-level Spectrum of the W3W_3 String

We investigate the spectrum of physical states in the $W_3$ string theory, up to level 2 for a multi-scalar string, and up to level 4 for the two-scalar string. The (open) $W_3$ string has a photon as its only massless state. By using screening charges to study the null physical states in the two-scalar $W_3$ string, we are able to learn about the gauge symmetries of the states in the multi-scalar $W_3$ string.Comment: 31 pages, Plain Tex, CTP TAMU-70/92, Goteborg ITP 92-43, Imperial/TP/91-92/22, KCL-TH-92-

Role of low-ll component in deformed wave functions near the continuum threshold

The structure of deformed single-particle wave functions in the vicinity of zero energy limit is studied using a schematic model with a quadrupole deformed finite square-well potential. For this purpose, we expand the single-particle wave functions in multipoles and seek for the bound state and the Gamow resonance solutions. We find that, for the $K^{\pi}=0^{+}$ states, where $K$ is the $z$-component of the orbital angular momentum, the probability of each multipole components in the deformed wave function is connected between the negative energy and the positive energy regions asymptotically, although it has a discontinuity around the threshold. This implies that the $K^{\pi}=0^{+}$ resonant level exists physically unless the $l=0$ component is inherently large when extrapolated to the well bound region. The dependence of the multipole components on deformation is also discussed

Event display: can we see what we want to see?

Due to the complexity of HEP detectors and their data the graphical representation of events is necessary, but also very demanding. The paper covers physiological aspects, e.g. choice of colours, human pattern recognition and 3D vision. For the unbiased understanding of the data realistic 2D and 3D projections, schematic projections and abstract 2D and 3D projections are discussed