Search For Oxygen in Cool DQ White Dwarf Atmospheres

We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective dredge-up from their C/O interiors. Recent model calculations predict that oxygen should also be present in DQ atmospheres in detectable amounts. Our synthetic spectra calculations for He-rich white dwarfs with traces of C and O indicate that CO should be easily detected in the cool DQ atmospheres if present in the expected amounts. Determination of the oxygen abundance in the atmosphere will reveal the C/O ratio at the core/envelope boundary, constraining the important and uncertain ^{12}C(alpha,gamma)^{16}O reaction rate.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European Workshop on White Dwarf

Sonic levitation apparatus

A sonic levitation apparatus is disclosed which includes a sonic transducer which generates acoustical energy responsive to the level of an electrical amplifier. A duct communicates with an acoustical chamber to deliver an oscillatory motion of air to a plenum section which contains a collimated hole structure having a plurality of parallel orifices. The collimated hole structure converts the motion of the air to a pulsed. Unidirectional stream providing enough force to levitate a material specimen. Particular application to the production of microballoons in low gravity environment is discussed

Dual Fronts Propagating into an Unstable State

The interface between an unstable state and a stable state usually develops a single confined front travelling with constant velocity into the unstable state. Recently, the splitting of such an interface into {\em two} fronts propagating with {\em different} velocities was observed numerically in a magnetic system. The intermediate state is unstable and grows linearly in time. We first establish rigorously the existence of this phenomenon, called ``dual front,'' for a class of structurally unstable one-component models. Then we use this insight to explain dual fronts for a generic two-component reaction-diffusion system, and for the magnetic system.Comment: 19 pages, Postscript, A

Systematic derivation of a rotationally covariant extension of the 2-dimensional Newell-Whitehead-Segel equation

An extension of the Newell-Whitehead-Segel amplitude equation covariant under abritrary rotations is derived systematically by the renormalization group method.Comment: 8 pages, to appear in Phys. Rev. Letters, March 18, 199

New exact fronts for the nonlinear diffusion equation with quintic nonlinearities

We consider travelling wave solutions of the reaction diffusion equation with quintic nonlinearities $u_t = u_{xx} + \mu u (1 -u ) ( 1 +\alpha u + \beta u^2 +\gamma u^3)$. If the parameters $\alpha , \beta$ and $\gamma$ obey a special relation, then the criterion for the existence of a strong heteroclinic connection can be expressed in terms of two of these parameters. If an additional restriction is imposed, explicit front solutions can be obtained. The approach used can be extended to polynomials whose highest degree is odd.Comment: Revtex, 5 page

Front propagation into unstable and metastable states in Smectic C* liquid crystals: linear and nonlinear marginal stability analysis

We discuss the front propagation in ferroelectric chiral smectics (SmC*) subjected to electric and magnetic fields applied parallel to smectic layers. The reversal of the electric field induces the motion of domain walls or fronts that propagate into either an unstable or a metastable state. In both regimes, the front velocity is calculated exactly. Depending on the field, the speed of a front propagating into the unstable state is given either by the so-called linear marginal stability velocity or by the nonlinear marginal stability expression. The cross-over between these two regimes can be tuned by a magnetic field. The influence of initial conditions on the velocity selection problem can also be studied in such experiments. SmC$^*$ therefore offers a unique opportunity to study different aspects of front propagation in an experimental system

Renormalization Group Theory for Global Asymptotic Analysis

We show with several examples that renormalization group (RG) theory can be used to understand singular and reductive perturbation methods in a unified fashion. Amplitude equations describing slow motion dynamics in nonequilibrium phenomena are RG equations. The renormalized perturbation approach may be simpler to use than other approaches, because it does not require the use of asymptotic matching, and yields practically superior approximations.Comment: 13 pages, plain tex + uiucmac.tex (available from babbage.sissa.it), one PostScript figure appended at end. Or (easier) get compressed postscript file by anon ftp from gijoe.mrl.uiuc.edu (128.174.119.153), file /pub/rg_sing_prl.ps.

The Renormalization Group and Singular Perturbations: Multiple-Scales, Boundary Layers and Reductive Perturbation Theory

Perturbative renormalization group theory is developed as a unified tool for global asymptotic analysis. With numerous examples, we illustrate its application to ordinary differential equation problems involving multiple scales, boundary layers with technically difficult asymptotic matching, and WKB analysis. In contrast to conventional methods, the renormalization group approach requires neither {\it ad hoc\/} assumptions about the structure of perturbation series nor the use of asymptotic matching. Our renormalization group approach provides approximate solutions which are practically superior to those obtained conventionally, although the latter can be reproduced, if desired, by appropriate expansion of the renormalization group approximant. We show that the renormalization group equation may be interpreted as an amplitude equation, and from this point of view develop reductive perturbation theory for partial differential equations describing spatially-extended systems near bifurcation points, deriving both amplitude equations and the center manifold.Comment: 44 pages, 2 Postscript figures, macro \uiucmac.tex available at macro archives or at ftp://gijoe.mrl.uiuc.edu/pu

The Speed of Fronts of the Reaction Diffusion Equation

We study the speed of propagation of fronts for the scalar reaction-diffusion equation $u_t = u_{xx} + f(u)$\, with $f(0) = f(1) = 0$. We give a new integral variational principle for the speed of the fronts joining the state $u=1$ to $u=0$. No assumptions are made on the reaction term $f(u)$ other than those needed to guarantee the existence of the front. Therefore our results apply to the classical case $f > 0$ in $(0,1)$, to the bistable case and to cases in which $f$ has more than one internal zero in $(0,1)$.Comment: 7 pages Revtex, 1 figure not include

Understanding parental concerns related to their child’s development and factors influencing their decisions to seek help from health care professionals: Results of a qualitative study.

Background: Early identification of children at risk of developmental delay is crucial to promote healthy development. Assessing parental concerns about development is often part of identification processes. However, we currently do not understand well how and why parents become concerned, and, how and why they access early identification and intervention services. The purpose of this study was to explore parental perceptions about their child’s development, and the factors influencing their reported professional help-seeking behaviours. Methods: This exploratory study was part of a larger study describing child development in children aged 2-5 in a small Canadian city. We conducted semi-structured interviews with 16 parents whose children were at risk of developmental delay to examine their perceptions of their child’s development, their use of community services promoting development, and their recommendations to optimize those services. Results: Four themes were identified: 1) Vision of child development influencing help-seeking behaviours: Natural or Supported?, 2) Internal and external sources contributing to parents’ level of developmental concern, 3) Using internal resources and struggling to access external resources, and 4) Satisfaction with services accessed and recommendations to access more support. Parents’ vision of child development along with sources of parental concern appeared to influence the level of concern, enhancing our understanding of how parents become concerned. The level of concern, and parents’ knowledge and perceived access to resources seemed to influence their decision whether or not to consult health care professionals. Parents provided many suggestions to improve services to promote child development and support families. Discussion: Results highlight the importance of supporting parents in recognizing if their child is at risk of delay, and increasing awareness of available resources. It appears particularly important to ensure health care professionals and community-based support services are accessible to provide parents with the support they need, especially when they have concerns