7,177 research outputs found
Application of numerical methods to planetary radiowave scattering
Get PDFExisting numerical techniques for the solution of scattering problems were investigated to determine those which might be applicable to planetary surface studies, with the goal of improving the interpretation of radar data from Venus, Mars, the Moon, and icy satellites. The general characteristics of the models are described along with computational concerns. In particular, the Numerical Electrogmatics Code (NEC) developed at the Lawrence Livermore Laboratory is discussed. Though not developed for random rough surfaces, the NEC contains elements which may be generalized and which could be valuable in the study of scattering by planetary surfaces
Avery Final Report: Identification and Cross-Directional Control of Coating Processes
Get PDFCoating refers to the covering of a solid with a uniform layer of liquid. Of special industrial interest is the cross-directional control of coating processes, where the cross-direction refers to the direction perpendicular to the substrate movement. The objective of the controller is to maintain a uniform coating under unmeasured process disturbances.
Assumptions that are relevant to coating processes found in industry are used to develop a model for control design. We show how to identify the model from input-output data. This model is used to derive a model predictive controller to maintain flat profiles of coating across the substrate by varying the liquid flows along the cross direction.
The model predictive controller computes the control action which minimizes the predicted deviation in cross-directional uniformity. The predictor combines the estimate obtained from the model with the measurement of the cross-directional uniformity to obtain a prediction for the next time step. A filter is used to obtain robustness to model error and insensitivity to measurement noise. The tuning of the noise filter and different methods for handling actuator constraints are studied in detail. The three different constraint-handling methods studied are: the weighting of actuator movements in the objective function, explicitly adding constraints to the control algorithm, i.e. constrained model predictive control, and scaling infeasible control actions calculated from an unconstrained control law to be feasible.
Actuator constraints, measurement noise, model uncertainty, and the plant condition number are investigated to determine which of these limit the achievable closed loop performance. From knowledge of how these limitations affect the performance we find how the plant could be modified to improve the process uniformity. Also, because identification of model parameters is time-consuming and costly, we study how accurate the identification must be to achieve a given level of performance.
The theory developed throughout the paper is rigorously verified though simulations and experiments on a pilot plant. The effect of interactions on the closed loop performance is shown to be negligible for this pilot plant. The measurement noise and the actuator constraints are shown to have the largest effect on closed loop performance
The Mystery of the Cosmic Diffuse Ultraviolet Background Radiation
Full text linkThe diffuse cosmic background radiation in the GALEX far ultraviolet (FUV,
1300 \AA\ - 1700 \AA) is deduced to originate only partially in the
dust-scattered radiation of FUV-emitting stars: the source of a substantial
fraction of the FUV background radiation remains a mystery. The radiation is
remarkably uniform at both far northern and far southern Galactic latitudes,
and it increases toward lower Galactic latitudes at all Galactic longitudes. We
examine speculation that it might be due to interaction of the dark matter with
the nuclei of the interstellar medium but we are unable to point to a plausible
mechanism for an effective interaction. We also explore the possibility that we
are seeing radiation from bright FUV-emitting stars scattering from a "second
population" of interstellar grains---grains that are small compared with FUV
wavelengths. Such grains are known to exist (Draine 2011) and they scatter with
very high albedo, with an isotropic scattering pattern. However, comparison
with the observed distribution (deduced from their m emission) of
grains at high Galactic latitudes shows no correlation between the grains'
location and the observed FUV emission. Our modeling of the FUV scattering by
small grains also shows that there must be remarkably few such "smaller" grains
at high Galactic latitudes, both North and South; this likely means simply that
there is very little interstellar dust of any kind at the Galactic poles, in
agreement with Perry & Johnston (1982). We also review our limited knowledge of
the cosmic diffuse background at ultraviolet wavelengths shortward of Lyman
---it could be that our "second component" of the diffuse
far-ultraviolet background persists shortward of the Lyman limit, and is the
cause of the re-ionization of the Universe (Kollmeier et al. 2014).Comment: 73 pages, 31 figures, ApJ accepte
Who Benefits from Obtaining a GED? Evidence from High School and Beyond
Get PDFThis paper examines the value of the GED credential and the conventional high school diploma in explaining the earnings of 27-year-old males in the early 1990s. The data base is the High School & Beyond sophomore cohort. We replicate the basic findings of prior studies that implicitly assume the labor market value of the GED credential does not depend on the skills with which dropouts left school. We show that these average effects mask a more complicated pattern. Obtaining a GED is associated with higher earnings at age 27 for those male dropouts who had very weak cognitive skills as tenth graders, but not for those who had stronger cognitive skills as tenth graders.
Do the Cognitive Skills of School Dropouts Matter in the Labor Market?
Get PDFDoes the U.S. labor market reward cognitive skill differences among high school dropouts, the members of the labor force with the least educational attainments? This paper reports the results of an exploration of this question, using a new data set that provides information on the universe of dropouts who last attempted the GED exams in Florida and New York between 1984 and 1990. The design of the sample reduces variation in unmeasured variables such as motivation that are correlated with cognitive skills. We examine the labor market returns to basic cognitive skills as measured by GED test scores. We explore whether the returns differ by gender and race. The results indicate quite large earnings returns to cognitive skills for both male and female dropouts, and for white and non-white dropouts. The earnings payoff to skills increases with age.
Interplay of Superconductivity and Spin-Dependent Disorder
Full text linkThe finite temperature phase diagram for the 2D attractive fermion Hubbard
model with spin-dependent disorder is considered within Bogoliubov-de Gennes
mean field theory. Three types of disorder are studied. In the first, only one
species is coupled to a random site energy; in the second, the two species both
move in random site energy landscapes which are of the same amplitude, but
different realizations; and finally, in the third, the disorder is in the
hopping rather than the site energy. For all three cases we find that, unlike
the case of spin-symmetric randomness, where the energy gap and average order
parameter do not vanish as the disorder strength increases, a critical disorder
strength exists separating distinct phases. In fact, the energy gap and the
average order parameter vanish at distinct transitions, and
, allowing for a gapless superconducting (gSC) phase. The gSC
phase becomes smaller with increasing temperature, until it vanishes at a
temperature .Comment: 9 pages, 7 figure
Antebellum Southampton County, Virginia, 1840-1860
Get PDFThis thesis is a descriptive account of life in antebellum Southampton. Established by the Virginia House of Burgesses in 1749, Southampton County gained notoriety as the site of Nat Turner\u27s slave rebellion. Fears of another armed slave revolt prompted the Virginia General Assembly to enact a series of stringent slave codes, which remained in effect until the Civil War. Primary sources consulted in the preparation of this thesis include corporate records, church manuscripts, court order books, reports of county and state officers, tax journals, and personal papers of the county\u27s contemporary citizens
Other Constituency Statutes
Get PDFThis Article will use the Missouri experience as a point of departure to consider what the legal effect of other constituency statutes might be. Recognizing that other constituency statutes were adopted along with other statutes clearly aimed at deterring unwanted takeovers, those other statutes will also be discussed. First, the Missouri law relating to corporate governance prior to the enactment of the package of Missouri legislation that includes the other constituency statute will be examined, including the legislative history of these statutes and the sources from which they seem to have been drawn. Next, this Article will consider whether, and to what extent, the changing nature of the corporate shareholder population should affect the interpretation of such statutes. This will require some digression into the nexus of contracts approach to corporate theory and some counter-arguments to this approach
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