899 research outputs found
Sympathetic Cooling Simulations with a Variable Time Step
In this paper we present a new variable time step criterion for the
velocity-Verlet algorithm allowing to correctly simulate the dynamics of
charged particles exchanging energy via Coulomb collisions while minimising
simulation time. We present physical arguments supporting the use of the
criterion along with numerical results proving its validity. We numerically
show that ions with 18 meV initial energy can be
captured and sympathetically cooled by a Coulomb crystal of
and in less than 10 ms, an important result for the GBAR
project.Comment: LEAP 2016 proceedin
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Passive infrared bullet detection and tracking
An apparatus and method for passively detecting a projectile such as, for example, a bullet using a passive infrared detector. A passive infrared detector is focused onto a region in which a projectile is expected to be located. Successive images of infrared radiation in the region are recorded. Background infrared radiation present in the region is suppressed such that second successive images of infrared radiation generated by the projectile as the projectile passes through the region are produced. A projectile path calculator determines the path and other aspects of the projectile by using the second successive images of infrared radiation generated by the projectile. The present invention, in certain embodiments, also determines the origin of the path of the projectile and takes a photograph of the area surrounding the origin and/or fires at least one projectile at the area surrounding the origin of the path of the projectile
A Field Theory of Extended Particles Based on Covariant Harmonic Oscillator Wavefunctions
We attempt to combine the covariant harmonic oscillator (CHO)
quark model with second quantized field theory. We review the CHO
formalism for a system of two quarks (meson). We introduce a mesonic
field Φ(x1 ,x2) that depends on the position of both quarks, and then
derive the field equations from a covariant lagrangian L(x1, x2).
The CHO equation allows a complete separation of the average meson
coordinate X from the relative quark coordinate ξ. The CHO wavefunction
in the field expresses the extended size and internal structure
of the meson. Φ, describes mesons in the ground state and any excited
state , with angular momentum ∞ mass^2. From Φ we construct conserved
tensors like P^μ the meson momentum. We second quantize Φ in the
X variable only and discuss the extended particle commutation relations.
We investigate a Φ^3-type meson interaction where the vertex
function is an overlap integral of the wavefunctions entering the
interaction region. We derive a nonlinear integrodifferential
equation for the U matrix , linearize and solve it by perturbation
theory. The result is simple diagramatic rules for the S matrix.
The S matrix is covariant and unitary. We do not find any contradiction
between the principles of QFT and the CHO quark model. The
Φ field theory includes scalar meson(point particle)theory as a special
case, while its greater generality illuminates the difference between
point and extended particles
A Case–Crossover Study of Wintertime Ambient Air Pollution and Infant Bronchiolitis
We examined the association of infant bronchiolitis with acute exposure to ambient air pollutants. DESIGN: We employed a time-stratified case–crossover method and based the exposure windows on a priori, biologically based hypotheses. PARTICIPANTS: We evaluated effects in 19,901 infants in the South Coast Air Basin of California in 1995–2000 with a hospital discharge record for bronchiolitis in the first year of life (International Classification of Diseases, 9th Revision, CM466.1). EVALUATIONS/MEASUREMENTS: Study subjects’ ZIP code was linked to ambient air pollution monitors to derive exposures. We estimated the risk of bronchiolitis hospitalization associated with increases in wintertime ambient air pollutants using conditional logistic regression. RESULTS: We observed no increased risk after acute exposure to particulate matter ≤ 2.5 μm in aerodynamic diameter (PM(2.5)), carbon monoxide, or nitrogen dioxide. PM(2.5) exposure models suggested a 26–41% increased risk in the most premature infants born at gestational ages between 25 and 29 weeks; however, these findings were based on very small numbers. CONCLUSIONS: We found little support for a link between acute increases in ambient air pollution and infant bronchiolitis except modestly increased risk for PM(2.5) exposure among infants born very prematurely. In these infants, the periods of viral acquisition and incubation concurred with the time of increased risk. RELEVANCE TO PROFESSIONAL PRACTICE: We present novel data for the infant period and the key respiratory disease of infancy, bronchiolitis. Incompletely explained trends in rising bronchiolitis hospitalization rates and increasing number of infants born prematurely underscore the importance of evaluating the impact of ambient air pollution in this age group in other populations and studies
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