11,079 research outputs found
The Base Engine for Solar Stirling Power
A new concept in Stirling engine technology is embodied in the base engine now being developed at Stirling Thermal Motors, Inc. This is a versatile energy conversion unit suitable for many different applications and heat sources. The base engine, rated 40 kW at 2800 RPM, is a four-cylinder, double-acting variable displacement Stirling engine with pressurized crankcase and rotating shaft seal. Remote-heating technology is incorporated with a stacked-heat-exchanger configuration and a liquid metal heat pipe connected to a distinctly separate combustor or other heat source. High efficiency over a wide range of operating conditions, long life, low manufacturing cost and low material cost are specifically emphasized. The base engine, its design philosophy and approach, its projected performance, and some of its more attractive applications are described
Sorption (kinetic and capacity) and desorption of trace elements in volcanic soils of Italy and the Azores
Investigating invariant item ordering in the Mental Health Inventory : an illustration of the use of different methods
Invariant item ordering is a property of scales whereby the items are scored in the same order across a wide range of the latent trait and across a wide range of respondents. In the package ‘mokken’ in the statistical software R, the ability to analyse Mokken scales for invariant item ordering has recently been available and techniques for inspecting visually the item response curves of item pairs, have also been included. While methods to assess invariant item ordering are available, there have been indications that items representing extremes of distress in mental well-being scales, such as suicidal ideation, may lead to claiming invariant item ordering where it does not exist. We used the Mental Health Inventory to see if invariant item ordering was indicated in any Mokken scales derived and to see if this was being influenced by extreme items. A Mokken scale was derived indicating invariant item ordering. Visual inspection of the item pairs indicated that the most difficult item (suicidal ideation) was located far from the remaining cluster of items. Removing this item lowered invariant item ordering to an unacceptable level
Phase Space Manipulation of Cold Free Radical OH Molecules
We report bunching, slowing, and acceleration of a supersonically cooled beam
of diatomic hydroxyl radicals (OH). \textit{In situ} observation of
laser-induced fluorescence along the beam propagation path allows for detailed
characterization of longitudinal phase-space manipulation of OH molecules
through the Stark effect by precisely sequenced inhomogeneous electric fields.Comment: 5 pages, 4 color figure
The influence of the presence of deviant item score patterns on the power of a person-fit statistic
Studies investigating the power of person-fit statistics often assume that the item parameters that are used to calculate the statistics are estimated in a sample without misfitting item score patterns. However, in practical test applications calibration samples likely will contain such patterns. In the present study, the influence of the type and the number of misfitting patterns in the calibration sample on the detection rate of the ZU3 statistic was investigated by means of simulated data. An increase in the number of misfitting simulees resulted in a decrease in the power of ZU3. Furthermore, the type of misfit and the test length influenced the power of ZU3. The use of an iterative procedure to remove the misfitting patterns from the dataset was investigated. Results suggested that this method can be used to improve the power of ZU3. Index terms: aberrance detection, appropriateness measurement, nonparametric item response theory, person fit, person-fit statistic ZU3
The number of Guttman errors as a simple and powerful person-fit statistic
A number of studies have examined the power of several statistics that can be used to detect examinees with unexpected (nonfitting) item score patterns, or to determine person fit. This study compared the power of the U3 statistic with the power of one of the simplest person-fit statistics, the sum of the number of Guttman errors. In most cases studied, (a weighted version of) the latter statistic performed as well as the U3 statistic. Counting the number of Guttman errors seems to be a useful and simple alternative to more complex statistics for determining person fit. Index terms: aberrance detection, appropriateness measurement, Guttman errors, nonparametric item response theory, person fit
Forming the Moon from terrestrial silicate-rich material
Recent high-precision measurements of the isotopic composition of lunar rocks
demonstrate that the bulk silicate Earth and the Moon show an unexpectedly high
degree of similarity. This is inconsistent with one of the primary results of
classic dynamical simulations of the widely accepted giant impact model for the
formation of the Moon, namely that most of the mass of the Moon originates from
the impactor, not Earth.
Resolution of this discrepancy without changing the main premises of the
giant impact model requires total isotopic homogenisation of Earth and impactor
material after the impact for a wide range of elements including O, Si, K, Ti,
Nd and W. Even if this process could explain the O isotope similarity, it is
unlikely to work for the much heavier, refractory elements. Given the
increasing uncertainty surrounding the giant impact model in light of these
geochemical data, alternative hypotheses for lunar formation should be
explored. In this paper, we revisit the hypothesis that the Moon was formed
directly from terrestrial mantle material. We show that the dynamics of this
scenario requires a large amount of energy, almost instantaneously generated
additional energy. The only known source for this additional energy is nuclear
fission. We show that it is feasible to form the Moon through the ejection of
terrestrial silicate material triggered by a nuclear explosion at Earths
core-mantle boundary (CMB), causing a shock wave propagating through the Earth.
Hydrodynamic modelling of this scenario shows that a shock wave created by
rapidly expanding plasma resulting from the explosion disrupts and expels
overlying mantle and crust material.Comment: 26 pages, 5 figures, 1 tabl
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