Effect of temperature and pressure on the sparking voltage

This report presents the results of an investigation which was to determine how the voltage necessary to produce the proper spark discharge varies with the pressure and temperature of the gas in which the discharge takes place

Moving boundary approximation for curved streamer ionization fronts: Solvability analysis

The minimal density model for negative streamer ionization fronts is investigated. An earlier moving boundary approximation for this model consisted of a "kinetic undercooling" type boundary condition in a Laplacian growth problem of Hele-Shaw type. Here we derive a curvature correction to the moving boundary approximation that resembles surface tension. The calculation is based on solvability analysis with unconventional features, namely, there are three relevant zero modes of the adjoint operator, one of them diverging; furthermore, the inner/outer matching ahead of the front has to be performed on a line rather than on an extended region; and the whole calculation can be performed analytically. The analysis reveals a relation between the fields ahead and behind a slowly evolving curved front, the curvature and the generated conductivity. This relation forces us to give up the ideal conductivity approximation, and we suggest to replace it by a constant conductivity approximation. This implies that the electric potential in the streamer interior is no longer constant but solves a Laplace equation; this leads to a Muskat-type problem.Comment: 22 pages, 6 figure

Heat energy of various ignition sparks

This report describes a method developed at the Bureau of Standards for measuring the total energy liberated as heat in a spark gap by an ignition system. Since this heat energy is obtained from the electromagnetic energy stored in the windings of the magneto or coil, it is a measure of the effectiveness of the device as an electric generator. Part 2 gives the results of measurements in absolute units of the total heat supplied to a spark gap by ignition systems of different types operating at various speeds, under conditions substantially equivalent to those in the cylinder of a high-compression aviation engine

Computer Components and Systems

Contains reports on two research projects.United States Navy Bureau of Ships (Contract NObsr 77603

The Electric Double Layer Structure Around Charged Spherical Interfaces

We derive a formally simple approximate analytical solution to the Poisson-Boltzmann equation for the spherical system via a geometric mapping. Its regime of applicability in the parameter space of the spherical radius and the surface potential is determined, and its superiority over the linearized solution is demonstrated.Comment: 7 pages, 5 figure

Giant slip lengths of a simple fluid at vibrating solid interfaces

It has been shown recently [PRL 102, 254503 (2009)] that in the plane-plane configuration a mechanical resonator vibrating close to a rigid wall in a simple fluid can be overdamped to a frozen regime. Here, by solving analytically the Navier Stokes equations with partial slip boundary conditions at the solid fluid interface, we develop a theoretical approach justifying and extending these earlier findings. We show in particular that in the perfect slip regime the above mentioned results are, in the plane-plane configuration, very general and robust with respect to lever geometry considerations. We compare the results with those obtained previously for the sphere moving perpendicularly and close to a plane in a simple fluid and discuss in more details the differences concerning the dependence of the friction forces with the gap distance separating the moving object (i.e., plane or sphere) from the fixed plane. Finally, we show that the submicron fluidic effect reported in the reference above, and discussed further in the present work, can have dramatic implications in the design of nano-electromechanical systems (NEMS).Comment: submitted to PRE (see also PRL 102, 254503 (2009)

On the Detectability of the Hydrogen 3-cm Fine Structure Line from the EoR

A soft ultraviolet radiation field, 10.2 eV < E <13.6 eV, that permeates neutral intergalactic gas during the Epoch of Reionization (EoR) excites the 2p (directly) and 2s (indirectly) states of atomic hydrogen. Because the 2s state is metastable, the lifetime of atoms in this level is relatively long, which may cause the 2s state to be overpopulated relative to the 2p state. It has recently been proposed that for this reason, neutral intergalactic atomic hydrogen gas may be detected in absorption in its 3-cm fine-structure line (2s_1/2 -> 2p_3/2) against the Cosmic Microwave Background out to very high redshifts. In particular, the optical depth in the fine-structure line through neutral intergalactic gas surrounding bright quasars during the EoR may reach tau~1e-5. The resulting surface brightness temperature of tens of micro K (in absorption) may be detectable with existing radio telescopes. Motivated by this exciting proposal, we perform a detailed analysis of the transfer of Lyman beta,gamma,delta,... radiation, and re-analyze the detectability of the fine-structure line in neutral intergalactic gas surrounding high-redshift quasars. We find that proper radiative transfer modeling causes the fine-structure absorption signature to be reduced tremendously to tau< 1e-10. We therefore conclude that neutral intergalactic gas during the EoR cannot reveal its presence in the 3-cm fine-structure line to existing radio telescopes.Comment: 7 pages, 4 figures, MNRAS in press; v2. some typos fixe

Spark Plug Defects and Tests

The successful operation of the spark plug depends to a large extent on the gas tightness of the plug. Part 1 of this report describes the method used for measuring the gas tightness of aviation spark plugs. Part 2 describes the methods used in testing the electrical conductivity of the insulation material when hot. Part 3 describes the testing of the cold dielectric strength of the insulation material, the resistance to mechanical shock, and the final engine test

DO IT Trial: vitamin D Outcomes and Interventions in Toddlers - a TARGet Kids! randomized controlled trial.

BackgroundVitamin D levels are alarmingly low (&lt;75 nmol/L) in 65-70% of North American children older than 1 year. An increased risk of viral upper respiratory tract infections (URTI), asthma-related hospitalizations and use of anti-inflammatory medication have all been linked with low vitamin D. No study has determined whether wintertime vitamin D supplementation can reduce the risk of URTI and asthma exacerbations, two of the most common and costly illnesses of early childhood. The objectives of this study are: 1) to compare the effect of 'high dose' (2000 IU/day) vs. 'standard dose' (400 IU/day) vitamin D supplementation in achieving reductions in laboratory confirmed URTI and asthma exacerbations during the winter in preschool-aged Canadian children; and 2) to assess the effect of 'high dose' vitamin D supplementation on vitamin D serum levels and specific viruses that cause URTI.Methods/designThis study is a pragmatic randomized controlled trial. Over 4 successive winters we will recruit 750 healthy children 1-5 years of age. Participating physicians are part of a primary healthcare research network called TARGet Kids!. Children will be randomized to the 'standard dose' or 'high dose' oral supplemental vitamin D for a minimum of 4 months (200 children per group). Parents will obtain a nasal swab from their child with each URTI, report the number of asthma exacerbations and complete symptom checklists. Unscheduled physician visits for URTIs and asthma exacerbations will be recorded. By May, a blood sample will be drawn to determine vitamin D serum levels. The primary analysis will be a comparison of URTI rate between study groups using a Poisson regression model. Secondary analyses will compare vitamin D serum levels, asthma exacerbations and the frequency of specific viral agents between groups.DiscussionIdentifying whether vitamin D supplementation of preschoolers can reduce wintertime viral URTIs and asthma exacerbations and what dose is optimal may reduce population wide morbidity and associated health care and societal costs. This information will assist in determining practice and health policy recommendations related to vitamin D supplementation in healthy Canadian preschoolers

Is a Classical Language Adequate in Assessing the Detectability of the Redshifted 21cm Signal from the Early Universe?

The classical radiometer equation is commonly used to calculate the detectability of the 21cm emission by diffuse cosmic hydrogen at high redshifts. However, the classical description is only valid in the regime where the occupation number of the photons in phase space is much larger than unity and they collectively behave as a classical electromagnetic field. At redshifts z<20, the spin temperature of the intergalactic gas is dictated by the radiation from galaxies and the brightness temperature of the emitting gas is in the range of mK, independently from the existence of the cosmic microwave background. In regions where the observed brightness temperature of the 21cm signal is smaller than the observed photon energy, of 68/(1+z) mK, the occupation number of the signal photons is smaller than unity. Neverethless, the radiometer equation can still be used in this regime because the weak signal is accompanied by a flood of foreground photons with a high occupation number (involving the synchrotron Galactic emission and the cosmic microwave background). As the signal photons are not individually distinguishable, the combined signal+foreground population of photons has a high occupation number, thus justifying the use of the radiometer equation.Comment: 4 pages, Accepted for publication in JCA