Voter Model Perturbations and Reaction Diffusion Equations

We consider particle systems that are perturbations of the voter model and show that when space and time are rescaled the system converges to a solution of a reaction diffusion equation in dimensions $d \ge 3$. Combining this result with properties of the PDE, some methods arising from a low density super-Brownian limit theorem, and a block construction, we give general, and often asymptotically sharp, conditions for the existence of non-trivial stationary distributions, and for extinction of one type. As applications, we describe the phase diagrams of three systems when the parameters are close to the voter model: (i) a stochastic spatial Lotka-Volterra model of Neuhauser and Pacala, (ii) a model of the evolution of cooperation of Ohtsuki, Hauert, Lieberman, and Nowak, and (iii) a continuous time version of the non-linear voter model of Molofsky, Durrett, Dushoff, Griffeath, and Levin. The first application confirms a conjecture of Cox and Perkins and the second confirms a conjecture of Ohtsuki et al in the context of certain infinite graphs. An important feature of our general results is that they do not require the process to be attractive.Comment: 106 pages, 7 figure

Secondary open angle glaucoma in a child with congenital oculodermal melanocytosis

Congenital oculodermal melanocytosis, a pigmented ocular surface lesion in children, may pose a significant diagnostic and therapeutic challenge even to the eye physician. Further, parents, care givers and non-eye care physicians are often unaware of this diagnosis and its associated potentialocular morbid conditions or the potential for malignancy thereby causing a delay in examination of such affected eyes. This article highlights an uncommon pigmented ocular surface lesion encountered in childhood. Further, a call to attention, that congenital oculodermal melanosis in childhood may harbor and coexist with an ocular morbid condition of glaucoma which develops in childhood. We report a case of congenital oculodermal melanosis with secondary open angle glaucoma in childhood.Special emphasis is placed on early identification and referral by noneye physicians. Accurate diagnosis and management of congenitaloculodermal melanosis and the associated condition of secondary open angle glaucoma in childhood by the eye care physician is important.An understanding of the natural history of pigmented eye lesions in children by non eye physicians is essential for successful outcomesand prevention of uniocular blindness and its attendant consequences.Key words: oculodermal melanocytosis; unilateral; secondary glaucoma; blindnes

Outcome of Diode Laser Cyclophotocoagulation in Neovascular Glaucoma in Nigerians: A short-term follow-up

Aim: To find out the short-term outcome of ciliary ablation with diode laser contact cyclophotocoagulation in Nigerians with neovascular glaucoma.Methods: The study is a retrospective, non-comparative, interventional case series. Demographic data, ocular and systemic history were obtained. Clinical examination included visual acuity, intraocular pressure, number ofintraocular pressure-lowering medications and type of treatment administered at the time of NVG diagnosis. Treatment with diode laser cyclophotocoagulation was instituted. Short-term outcomes were observed and patients were followed-up for three months.Results: The study included 3 eyes of 3 patients; all above 40 years, 1 female and 2 male. At the time of NVG diagnosis, all three patients presented with severe ocular pain, and had VA between PL and NPL. Intraocular pressure on the average was 33mmHg at presentation,and associated with corneal oedema. At 3 months after initial diode laser photocoagulation (DLPC), the VA remained the same in all patients. No patient required repeat treatment. Pain reduction and lowering of theintraocular pressure were achieved at 3 months followup post-DLPC without anti-glaucoma medication. Conjunctival burns and chemosis were seen. All three eyes had corneal oedema and spontaneous hyphema by the 7 day; with subsequent s th evere corneal blood stain.Conclusions: Diode laser photocoagulation can be used as an acceptable non-invasive surgical intervention for the reduction of pain and lowering of intraocular pressure in Nigerians with neovascular glaucoma. Most shortterm complications are uneventful. The presence of hyphema with corneal oedema may enhance the occurrence of corneal blood stain in black people. The presence of corneal oedema may thus be a risk factor for corneal blood staining.Key words: short-term outcome, diode laser, corneal stainin

Tunnel junctions of unconventional superconductors

The phenomenology of Josephson tunnel junctions between unconventional superconductors is developed further. In contrast to s-wave superconductors, for d-wave superconductors the direction dependence of the tunnel matrix elements that describe the barrier is relevant. We find the full I-V characteristics and comment on the thermodynamical properties of these junctions. They depend sensitively on the relative orientation of the superconductors. The I-V characteristics differ from the normal s-wave RSJ-like behavior.Comment: 4 pages, revtex, 4 (encapsulated postscript) figures (figures replaced

The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures

The spin-polarized transport is investigated in a new type of magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method and the nearly-free-electron-approximation the dependence of the tunnel magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer thickness and the applied bias voltage are studied theoretically. The TMR and spin polarization show an oscillatory behavior as a function of the spacer thickness and the bias voltage. The oscillations originate from the quantum well states in the spacer, while the existence of the magnetic barrier gives rise to a strong spin polarization and high values of the TMR. Our results may be useful for the development of spin electronic devices based on coherent transport.Comment: 15 pages, 5 figure

Midwives’ knowledge and utilization of non-pneumatic anti shock garment in reducing complication of postpartum haemorrhage in selected health care facilities in Bayelsa state Nigeria

Background: Non-pneumatic anti-shock garment (NASG) is a first-aid lower-body pressure device that reverses hypovolaemic shock and decreases obstetric hemorrhage thereby decreasing maternal morbidity and mortality due to post-partum haemorrhage (PPH).This study assessed the knowledge and utilization of non-pneumatic anti shock garment in the management of postpartum hemorrhage among midwives in selected health care facilities in Bayelsa state.  Methods: This is a descriptive cross-sectional study in which a sample size of 112 nurses were selected using purposive sampling technique. The instrument for data collection was questionnaire and data collected were analyzed using descriptive and inferential statistics.  Results: The study revealed that majority of the respondents regardless of their educational level had good knowledge of the description, mechanism of action, and uses of NASG. It was also revealed that majority of the respondents do not use NASG in their centers and its application in management of post-partum hemorrhage was not part of the protocols in these centers, which was a clear indication of underutilization of the NASG in the primary health care centers. There was no significant association found between years of working experience of respondents and their utilization of NASG with (X2 = 8.577, df = 2, P = 0.114) as well as between the level of knowledge of midwives and their utilization of the NASG with (X2 = 0.387, df = 1, P = 0.534).Conclusions: It was recommended that non-pneumonic antishock garment should be made available by government and its utilization should be included in all health care centers policy as a management protocol for post-partum hemorrhage.

Synchrotron Facilities and Free Electron Lasers

Synchrotron radiation (SR) is electromagnetic radiation emitted when a charged particle travels along a curved trajectory. Initially encountered as a nuisance around orbits of high energy synchrotron accelerators, it gradually became an indispensable research tool in many applications: crystallography, X-ray lithography, micromechanics, structural biology, microprobe X-ray experiments, etc. So-called first generation SR sources were exploiting SR in parasitic mode at electron accelerators built to study particle collisions. The second generation of SR sources was the first facilities solely devoted to SR production. They were optimized to achieve stable high currents in the accelerator ring to achieve substantially higher photon flux and to provide a large number of SR beam lines for users. Third generation sources were further optimized for increased brilliance, i.e. with photons densely packed into a beam of very small cross-sectional area and minimal angular divergence (see the Appendix for more detailed definitions of flux, brightness and brilliance) and makes extensive use of the insertion devices such as wigglers and undulators. Free Electron Lasers (FELs), the fourth generation SR sources, open new research possibilities by offering extremely short pulses of extremely bright and coherent radiation. The number of SR sources around the world now probably exceeds 100. These facilities vary greatly in size, energy of the electron (or positron) beams, range of photon energies and other characteristics of the photon beams produced. In what follows we will concentrate on describing some common aspects of SR facilities, their operation modes and specific radiation protection aspects

Exclusive W^+ + photon production in proton-antiproton collisions II: results

We present results for total cross sections, single and double differential distributions and correlations between pairs of outgoing particles in the reactions p + antip --> W^+ + photon and p + antip --> W^+ + photon + jet at sqrt(S)=1.8 TeV. Order alpha-strong QCD corrections and leading logarithm photon bremsstrahlung contributions are included in the MS-bar mass factorization scheme for three experimental scenarios: 1) 2-body inclusive production of W^+ and photon, 2) exclusive production of W^+, photon and 1 jet and 3) exclusive production of W^+ and photon with 0 jet. The latest CTEQ parton distribution functions, which fit the newly released HERA data, are used in our analysis. The dependence of our results on the mass factorization scale is used to place error bars on our predictions for the single differential distributions and correlations.Comment: 15 pages (LateX). 50 pages of postscript figures available via ftp anonymous from max.physics.sunysb.edu in the directory preprints/mendoza/EXCLUSIVE_W_GAMMA_II.dir (files named fig_*.ps) ITP-SB-93-80. ([email protected])([email protected]

Gel-Electrophoresis and Diffusion of Ring-Shaped DNA

A model for the motion of ring-shaped DNA in a gel is introduced and studied by numerical simulations and a mean-field approximation. The ring motion is mediated by finger-shaped loops (hernias) that move in an amoeba-like fashion around the gel obstructions. This constitutes an extension of previous reptation tube treatments. It is shown that tension is essential for describing the dynamics in the presence of hernias. It is included in the model as long range interactions over stretched DNA regions. The mobility of ring-shaped DNA is found to saturate much as in the well-studied case of linear DNA. Experiments in polymer gels, however, show that the mobility drops exponentially with the DNA ring size. This is commonly attributed to dangling-ends in the gel that can impale the ring. The predictions of the present model are expected to apply to artificial 2D obstacle arrays (W.D. Volkmuth, R.H. Austin, Nature 358,600 (1992)) which have no dangling-ends. In the zero-field case an exact solution of the model steady-state is obtained, and quantities such as the average ring size are calculated. An approximate treatment of the ring dynamics is given, and the diffusion coefficient is derived. The model is also discussed in the context of spontaneous symmetry breaking in one dimension.Comment: 8 figures, LaTeX, Phys. Rev. E - in pres

Exclusive W + photon production in proton-antiproton collisions I: general formalism

We present a detailed computation of the fully exclusive cross section of p + antip --> W + photon + X with X = 0 and 1 jet in the framework of the factorization theorem and dimensional regularization. Order alpha-strong and photon bremsstrahlung contributions are discussed in the MS-bar mass factorization scheme. The resulting expressions are ready to be implemented numerically using Monte Carlo techniques to compute single and double differential cross sections and correlations between outgoing pairs of particles.Comment: ITP-SB-93-72, 40 pages, LateX. 3*4 figures in separate file. ([email protected]) ([email protected]