28,484 research outputs found
Introducing Asymmetric Separability in the FAST Multistage Demand System
This paper determines the set of parametric restrictions required to maintain flexibility under asymmetric weak separability for the flexible and separable translog (FAST) multistage demand system. Because there is not a unique set of parametric restrictions that ensures separability and the values of the unconditional price and expenditure elasticities depend on the parametric restrictions imposed, the appropriateness of a chosen set of parametric restrictions should be tested empirically. An empirical example that illustrates how the choice of parametric restrictions affects the estimation results and the functional form of the price and expenditure elasticities is provided.Research Methods/ Statistical Methods,
Survival, Development and Population Dynamics of \u3ci\u3eEmpoasca Fabae\u3c/i\u3e (Homoptera: Cicadellidae) on Three Legume Hosts
Survival and development of potato leafhopper, Empoasca fabae, nymphs were measured on alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), and red clover (Trifolium pratense). Survival was not significantly different among host plants (mean = 62%). There was no interaction between sex and host plant for developmental time. Males developed significantly faster than females. Developmental time was fastest on alfalfa, intermediate on trefoil, and slowest on red clover. Plots of alfalfa, trefoil, and red clover were planted to compare the seasonal abundance of the potato leafhopper in the three forages. Nymphs were more abundant in trefoil than in alfalfa and red clover late in July, but no differences occurred on the other sample dates. At their peak, adults were more abundant in alfalfa than in trefoil and red clover
Diagnostics of the structure of AGN's broad line regions with reverberation mapping data: confirmation of the two-component broad line region model
We re-examine the ten Reverberation Mapping (RM) sources with public data
based on the two-component model of the Broad Line Region (BLR). In fitting
their broad H-beta lines, six of them only need one Gaussian component, one of
them has a double-peak profile, one has an irregular profile, and only two of
them need two components, i.e., a Very Broad Gaussian Component (VBGC) and an
Inter-Mediate Gaussian Component (IMGC). The Gaussian components are assumed to
come from two distinct regions in the two-component model; they are Very Broad
Line Region (VBLR) and Inter-Mediate Line region (IMLR). The two sources with a
two-component profile are Mrk 509 and NGC 4051. The time lags of the two
components of both sources satisfy ,
where and are the lags of the two components while
and represent the mean gas velocities of the two regions,
supporting the two-component model of the BLR of Active Galactic Nuclei (AGN).
The fact that most of these ten sources only have the VBGC confirms the
assumption that RM mainly measures the radius of the VBLR; consequently, the
radius obtained from the R-L relationship mainly represent the radius of VBLR.
Moreover, NGC 4051, with a lag of about 5 days in the one component model, is
an outlier on the R-L relationship as shown in Kaspi et al. (2005); however
this problem disappears in our two-component model with lags of about 2 and 6
days for the VBGC and IMGC, respectively.Comment: 7 pages, 5 figures. Accepted for publication in the Special Issue of
Science in China (G) "Astrophysics of Black holes and Related Compact
Objects
Low Cost Dewatering of Waste Slurries
The U.S. Bureau of Mines has developed a technique for dewatering mineral waste slurries which utilizes polymer and a static screen. A variety of waste slurries from placer gold mines and crushed stone operations have been successfully treated using the system. Depending on the waste, a number of polymers have been used successfully with polymer costs ranging from 0.15 per 1,000 gal treated. The dewatering is accomplished using screens made from either ordinary window screen or wedge wire. The screens used are 8 ft wide and 8 ft long. The capacity of the screens varies from 3 to 7 gpm/sq. ft. The water produced is acceptable for recycling to the plant or for discharge to the environment. For example, a fine grain dolomite waste slurry produced from a crushed stone operation was dewatered from a nominal 2.5 pct solids to greater than 50 pct solids using 0.15 worth of polymer per 1,000 gal of slurry. The resulting waste water had a turbidity of less than 50 NTU and could be discharged or recycled. The paper describes field tests conducted using the polymer-screen dewatering system
Random Boolean Network Models and the Yeast Transcriptional Network
The recently measured yeast transcriptional network is analyzed in terms of
simplified Boolean network models, with the aim of determining feasible rule
structures, given the requirement of stable solutions of the generated Boolean
networks. We find that for ensembles of generated models, those with canalyzing
Boolean rules are remarkably stable, whereas those with random Boolean rules
are only marginally stable. Furthermore, substantial parts of the generated
networks are frozen, in the sense that they reach the same state regardless of
initial state. Thus, our ensemble approach suggests that the yeast network
shows highly ordered dynamics.Comment: 23 pages, 5 figure
A Variational Approach for Minimizing Lennard-Jones Energies
A variational method for computing conformational properties of molecules
with Lennard-Jones potentials for the monomer-monomer interactions is
presented. The approach is tailored to deal with angular degrees of freedom,
{\it rotors}, and consists in the iterative solution of a set of deterministic
equations with annealing in temperature. The singular short-distance behaviour
of the Lennard-Jones potential is adiabatically switched on in order to obtain
stable convergence. As testbeds for the approach two distinct ensembles of
molecules are used, characterized by a roughly dense-packed ore a more
elongated ground state. For the latter, problems are generated from natural
frequencies of occurrence of amino acids and phenomenologically determined
potential parameters; they seem to represent less disorder than was previously
assumed in synthetic protein studies. For the dense-packed problems in
particular, the variational algorithm clearly outperforms a gradient descent
method in terms of minimal energies. Although it cannot compete with a careful
simulating annealing algorithm, the variational approach requires only a tiny
fraction of the computer time. Issues and results when applying the method to
polyelectrolytes at a finite temperature are also briefly discussed.Comment: 14 pages, uuencoded compressed postscript fil
Analytical and experimental investigation of gas bearing tilting pad pivots Final report
Fretting damage in gas bearing tilting pad pivot
Development of a simplified procedure for rocket engine thrust chamber life prediction with creep
An analytical method for predicting engine thrust chamber life is developed. The method accounts for high pressure differentials and time-dependent creep effects both of which are significant in limiting the useful life of the shuttle main engine thrust chamber. The hot-gas-wall ligaments connecting adjacent cooling channels ribs and separating the coolant flow from the combustion gas are subjected to a high pressure induced primary stress superimposed on an alternating cyclic thermal strain field. The pressure load combined with strain-controlled cycling produces creep ratcheting and consequent bulging and thinning of these ligaments. This mechanism of creep-enhanced ratcheting is analyzed for determining the hot-gas-wall deformation and accumulated strain. Results are confirmed by inelastic finite element analysis. Fatigue and creep rupture damage as well as plastic tensile instability are evaluated as potential failure modes. It is demonstrated for the NARloy Z cases analyzed that when pressure differentials across the ligament are high, creep rupture damage is often the primary failure mode for the cycle times considered
The Importance of Broad Emission-Line Widths in Single Epoch Black Hole Mass Estimates
Estimates of the mass of super-massive black holes (BHs) in distant active
galactic nuclei (AGNs) can be obtained efficiently only through single-epoch
spectra, using a combination of their broad emission-line widths and continuum
luminosities. Yet the reliability and accuracy of the method, and the resulting
mass estimates, M_BH, remain uncertain. A recent study by Croom using a sample
of SDSS, 2QZ and 2SLAQ quasars suggests that line widths contribute little
information about the BH mass in these single-epoch estimates and can be
replaced by a constant value without significant loss of accuracy. In this
Letter, we use a sample of nearby reverberation-mapped AGNs to show that this
conclusion is not universally applicable. We use the bulge luminosity (L_Bulge)
of these local objects to test how well the known M_BH - L_Bulge correlation is
recovered when using randomly assigned line widths instead of the measured ones
to estimate M_BH. We find that line widths provide significant information
about M_BH, and that for this sample, the line width information is just as
significant as that provided by the continuum luminosities. We discuss the
effects of observational biases upon the analysis of Croom and suggest that the
results can probably be explained as a bias of flux-limited, shallow quasar
samples.Comment: 10 text pages + 4 Figures + 1 Table. Accepted for publication in ApJ
Letter
- …