978 research outputs found
Experimental gas-fired pulse-combustion studies
Experimental studies conducted at Argonne National Laboratory on a gas-fired, water-cooled, Helmholtz-type pulse combustion burner are discussed. In addition to the experimental work, information is presented on the evolution of pulse combustion, the types of pulse combustion burners and their applications, and the types of fuels used. Also included is a survey of other pertinent studies of gas-fired pulse combustion. The burner used in the Argonne research effort was equipped with adjustable air and gas flapper valves and was operated stably over a heat-input range of 30,000 to 200,000 Btu/h. The burner's overall heat transfer in the pulsating mode was 22 to 31% higher than when the unit was operated in the steady mode. Important phenomena discussed include (1) effects on performance produced by inserting a corebustor to change tailpipe diameter, (2) effects observed following addition of an air-inlet decoupling chamber to the unit, and (3) occurrence of carbon monoxide in the exhaust gas
Estimating the Social Value of Higher Education: Willingness to Pay for Community and Technical Colleges
Much is known about private returns to education in the form of higher earnings. Less is known about social value, over and above the private, market value. Associations between education and socially-desirable outcomes are strong, but disentangling the effect of education from other causal factors is challenging. The purpose of this paper is to estimate the social value of one form of higher education. We elicit willingness to pay for the Kentucky Community and Technical College System directly through a stated-preferences survey and compare our estimate of total social value to our estimates of private value in the form of increased earnings. Our earnings estimates are based on two distinct data sets, one administrative and one from the U.S. Census. The difference between the total social value and the increase in earnings is our measure of the education externality. Our work differs from previous research by eliciting values directly in a way that yields a total value including any external benefits and by focusing on education at the community college level. Our preferred estimate indicates the social value of expanding the system substantially exceeds private value by approximately 50 percent.social returns, education externalities, contingent valuation, earnings
Diffraction and boundary conditions in semi-classical open billiards
The conductance through open quantum dots or quantum billiards shows
fluctuations, that can be explained as interference between waves following
different paths between the leads of the billiard. We examine such systems by
the use of a semi-classical Green's functions. In this paper we examine how the
choice of boundary conditions at the lead mouths affect the diffraction. We
derive a new formula for the S-matrix element. Finally we compare
semi-classical simulations to quantum mechanical ones, and show that this new
formula yield superior results.Comment: 7 pages, 4 figure
Geometry-dependent scattering through quantum billiards: Experiment and theory
We present experimental studies of the geometry-specific quantum scattering
in microwave billiards of a given shape. We perform full quantum mechanical
scattering calculations and find an excellent agreement with the experimental
results. We also carry out the semiclassical calculations where the conductance
is given as a sum of all classical trajectories between the leads, each of them
carrying the quantum-mechanical phase. We unambiguously demonstrate that the
characteristic frequencies of the oscillations in the transmission and
reflection amplitudes are related to the length distribution of the classical
trajectories between the leads, whereas the frequencies of the probabilities
can be understood in terms of the length difference distribution in the pairs
of classical trajectories. We also discuss the effect of non-classical "ghost"
trajectories that include classically forbidden reflection off the lead mouths.Comment: 4 pages, 4 figure
- …