3,606 research outputs found
Pressure Treated Wood
Discusses chemical treatments to increase wood's fire resistance and protect it from rot and termites
Damped Lyman alpha systems and disk galaxies: number density, column density distribution and gas density
We present a comparison between the observed properties of damped Lyman alpha
systems (DLAs) and the predictions of simple models for the evolution of
present day disk galaxies, including both low and high surface brightness
galaxies. We focus in particular on the number density, column density
distribution and gas density of DLAs, which have now been measured in
relatively large samples of absorbers. From the comparison we estimate the
contribution of present day disk galaxies to the population of DLAs, and how it
varies with redshift. Based on the differences between the models and the
observations, we also speculate on the nature of the fraction of DLAs which
apparently do not arise in disk galaxies.Comment: 11 pages, 10 figures, accepted in MNRA
Sea turtle nesting in the Ten Thousand Islands of Florida
Loggerhead sea turtles (Caretta caretta) nest in numerous substrate and beach
types within the Ten Thousand Islands (TTl) of southwest Florida. Nesting beach
selection was analyzed on 12 islands within this archipelago. Numerous physical
characteristics were recorded to identify the relatedness of these variables and determine
their importance for nesting beach selection in C. caretta. These variables were chosen
after evaluating the islands, conducting literature searches and soliciting personal
communications. Along transects, data were collected, on the following: height of
canopy, beach width, overall slope (beach slope and slope of offshore approach) and sand
samples analyzed for pH, percentage of water, percentage of organic content, percentage
of carbonate and particle size (8 size classes). Data on ordinal aspect of beaches and
beach length were also recorded and included in the analysis. All of the variables were
analyzed by tree regression, incorporating the nesting data into the analysis. In the TTl,
loggerheads appear to prefer wider beaches (p< 0.001; R2
= 0.56) that inherently have less
slope, and secondarily, wider beaches that have low amounts of carbonate (p< O.00 1). In
addition, C. caretta favors nest sites within or in close proximity to the supra-littoral
vegetation zone of beaches in the TTl (p< 0.001). (86 page document
Carbureting conditions characteristics of aircraft engines
Tests were conducted at the altitude laboratory erected at the Bureau of Standards for the National Advisory Committee for Aeronautics to determine the changes in engine performance with changes in atmospheric temperature and pressure at various levels above the earth's surface, with special reference to (a) the variables affecting the functioning of the carburetor and (b) the changes in performance resulting from variables in the carburetor itself. This report constitutes a concise statement of the difficulties to be encountered in this branch of carburetion
Sewing sound quantum flesh onto classical bones
Semiclassical transformation theory implies an integral representation for
stationary-state wave functions in terms of angle-action variables
(). It is a particular solution of Schr\"{o}dinger's time-independent
equation when terms of order and higher are omitted, but the
pre-exponential factor in the integrand of this integral
representation does not possess the correct dependence on . The origin of
the problem is identified: the standard unitarity condition invoked in
semiclassical transformation theory does not fix adequately in a
factor which is a function of the action written in terms of and
. A prescription for an improved choice of this factor, based on
succesfully reproducing the leading behaviour of wave functions in the vicinity
of potential minima, is outlined. Exact evaluation of the modified integral
representation via the Residue Theorem is possible. It yields wave functions
which are not, in general, orthogonal. However, closed-form results obtained
after Gram-Schmidt orthogonalization bear a striking resemblance to the exact
analytical expressions for the stationary-state wave functions of the various
potential models considered (namely, a P\"{o}schl-Teller oscillator and the
Morse oscillator).Comment: RevTeX4, 6 page
From Heisenberg matrix mechanics to EBK quantization: theory and first applications
Despite the seminal connection between classical multiply-periodic motion and
Heisenberg matrix mechanics and the massive amount of work done on the
associated problem of semiclassical (EBK) quantization of bound states, we show
that there are, nevertheless, a number of previously unexploited aspects of
this relationship that bear on the quantum-classical correspondence. In
particular, we emphasize a quantum variational principle that implies the
classical variational principle for invariant tori. We also expose the more
indirect connection between commutation relations and quantization of action
variables. With the help of several standard models with one or two degrees of
freedom, we then illustrate how the methods of Heisenberg matrix mechanics
described in this paper may be used to obtain quantum solutions with a modest
increase in effort compared to semiclassical calculations. We also describe and
apply a method for obtaining leading quantum corrections to EBK results.
Finally, we suggest several new or modified applications of EBK quantization.Comment: 37 pages including 3 poscript figures, submitted to Phys. Rev.
Ultimate decoherence border for matter-wave interferometry
Stochastic backgrounds of gravitational waves are intrinsic fluctuations of
spacetime which lead to an unavoidable decoherence mechanism. This mechanism
manifests itself as a degradation of the contrast of quantum interferences. It
defines an ultimate decoherence border for matter-wave interferometry using
larger and larger molecules. We give a quantitative characterization of this
border in terms of figures involving the gravitational environment as well as
the sensitivity of the interferometer to gravitational waves. The known level
of gravitational noise determines the maximal size of the molecular probe for
which interferences may remain observable. We discuss the relevance of this
result in the context of ongoing progresses towards more and more sensitive
matter-wave interferometry.Comment: 4 page
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