3,525 research outputs found
A selected bibliography on physical education for the Winthrop public schools
Thesis (Ed. M.)--Boston University, 194
An evaluation of the effects of blue crab (Callinectes sapidus) behavior on the efficacy of crab pots as a tool for estimating population abundance
Crab traps have been used extensively in studies on the population dynamics of blue crabs to provide estimates of catch per unit of effort; however, these estimates have been
determined without adequate consideration of escape rates. We examined the ability of the blue crab (Callinectes
sapidus) to escape crab pots and the possibility that intraspecific crab interactions have an effect on catch
rates. Approximately 85% of crabs that entered a pot escaped, and 83% of crabs escaped from the bait chamber
(kitchen). Blue crabs exhibited few aggressive behavioral interactions in and around the crab pot and were
documented to move freely in and out of the pot. Both the mean number and size of crabs caught were significantly
smaller at deeper depths. Results from this study show that
current estimates of catch per unit of effort may be biased given the high escape rate of blue crabs documented
in this study. The results of this paper provide a mechanistic view of trap efficacy, and reveal crab behavior in and around commercial crab pots
A General-Equilibrium Analysis of Public Policy for Pharmaceutical Prices
Retail sales of prescription drugs totaled 400 billion by the year 2010. This paper analyzes the welfare and distributional effects of two policy families that could be used to cope with high and rising pharmaceutical costs. We employ a general-equilibrium approach to contrast the current patented-monopoly system with a) a price ceiling imposed on the pharmaceutical sector of the economy; and b) a universal insurance program covering pharmaceutical purchases. We use a version of the Kelton and Wallace (1995) monopoly production environment: a two-good general-equilibrium model in which a license is required to produce one of the goods. Individuals in the model are heterogeneous with respect to preferences, but have identical production technologies and labor resources. Results indicate potential welfare gains for both the price-ceiling and universal-insurance policies, with very distinct distributional effects.
Local structure of liquid carbon controls diamond nucleation
Diamonds melt at temperatures above 4000 K. There are no measurements of the
steady-state rate of the reverse process: diamond nucleation from the melt,
because experiments are difficult at these extreme temperatures and pressures.
Using numerical simulations, we estimate the diamond nucleation rate and find
that it increases by many orders of magnitude when the pressure is increased at
constant supersaturation. The reason is that an increase in pressure changes
the local coordination of carbon atoms from three-fold to four-fold. It turns
out to be much easier to nucleate diamond in a four-fold coordinated liquid
than in a liquid with three-fold coordination, because in the latter case the
free-energy cost to create a diamond-liquid interface is higher. We speculate
that this mechanism for nucleation control is relevant for crystallization in
many network-forming liquids. On the basis of our calculations, we conclude
that homogeneous diamond nucleation is likely in carbon-rich stars and unlikely
in gaseous planets
Heterogeneous critical nucleation on a completely-wettable substrate
Heterogeneous nucleation of a new bulk phase on a flat substrate can be
associated with the surface phase transition called wetting transition. When
this bulk heterogeneous nucleation occurs on a completely-wettable flat
substrate with a zero contact angle, the classical nucleation theory predicts
that the free energy barrier of nucleation vanishes. In fact, there always
exist a critical nucleus and a free energy barrier as the first-order
pre-wetting transition will occur even when the contact angle is zero.
Furthermore, the critical nucleus changes its character from the critical
nucleus of surface phase transition below bulk coexistence (undersaturation) to
the critical nucleus of bulk heterogeneous nucleation above the coexistence
(oversaturation) when it crosses the coexistence. Recently, Sear [J.Chem.Phys
{\bf 129}, 164510 (2008)] has shown by a direct numerical calculation of
nucleation rate that the nucleus does not notice this change when it crosses
the coexistence. In our work the morphology and the work of formation of
critical nucleus on a completely-wettable substrate are re-examined across the
coexistence using the interface-displacement model. Indeed, the morphology and
the work of formation changes continuously at the coexistence. Our results
support the prediction of Sear and will rekindle the interest on heterogeneous
nucleation on a completely-wettable substrate.Comment: 11pages, 9 figures, Journal of Chemical Physics to be publishe
AN ENERGY-INTEGRATED ANALYSIS FOR MEASURING THE ANOMALOUS PRECESSION FREQUENCY FOR THE MUON \u3ci\u3eg\u3c/i\u3e − 2 EXPERIMENT AT FERMILAB
In the search for physics beyond the Standard Model, the Muon g − 2 Experiment at Fermilab (E989) will make the most precise measurement of the anomalous magnetic moment of the muon, aμ. Improvements in precision come from both increased statistics and new techniques to significantly reduce previous systematic uncertainties. The muon aμ is determined by extracting both the anomalous spin precession frequency, ωa, and the average magnetic field sampled by the muons, B. Traditionally an energy threshold analysis method which requires reconstruction of decay positrons from the muon decay, μ+ → e+νeνμ has been used to extract ωa. This thesis will describe a novel, energy-integrated analysis method for ωa extraction that does not require full reconstruction of positron hits and lowers the energy threshold therefore sampling more of the stored muons. This new technique has different sensitivities to effects like gain fluctuations and positron pulse pile-up. The analysis results will focus on data taken in 2019, the second year of running the experiment
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