20,196 research outputs found
DETERMINANTS OF LENDER RESPONSE TO SHORT-TERM CREDIT NEEDS OF SMALL COMMERCIAL FARMERS
Agricultural Finance,
CROSS-SECTIONAL ESTIMATION OF U.S. DEMAND FOR BEEF PRODUCTS: A CENSORED SYSTEM APPROACH
Demands for beef products are investigated using the U.S. Department of AgricultureÂ’'s 1987-88 Nationwide Food Consumption Survey data. The censored translog demand system is estimated with full-information and simulated maximum-likelihood procedures. These procedures represent different approaches to evaluation of multiple probability integrals in the likelihood function, but produce very similar parameter and elasticity estimates. Findings suggest sociodemographic variables play important roles in the demand for beef, and that demand for different cuts of beef should be treated differently.Demand and Price Analysis,
HOUSEHOLD DEMAND FOR FINFISH: A GENERALIZED DOUBLE-HURDLE MODEL
This study estimates household demand for finfish in the United States using a limited dependent variable model that accounts for both participation and consumption decisions and also accommodates nonnormal heteroskedastic errors. Results suggest that own-price elasticity is near unitary and income elasticity is small. Price of finfish, shopping frequency, Northeast, Black and other non-Whites, and the life-cycle variable “"young, single, no children”" are they key factors that affect significantly both the probability of participation and the level of finfish consumption. Furthermore, a variable may exert opposite effects on the probability and level of consumption.Consumer/Household Economics, Demand and Price Analysis,
ESTIMATION OF A DEMAND SYSTEM WITH LIMITED DEPENDENT VARIABLES
The study employs the full-information maximum-likelihood method to estimate a censored translog demand system. U.S. household consumption of steak, roast, and ground beef are used to demonstrate the application of the estimation procedure. The proposed methodology produces more efficient estimates than the popular two-step procedures found in demand literature.Demand and Price Analysis,
Characterizing small-scale migration behavior of sequestered CO2 in a realistic geological fabric
For typical reservoir conditions, buoyancy and capillary forces grow dominant over viscous forces within a few hundred meters of the injection wells as the pressure gradient due to injection decreases, resulting in qualitatively different plume migration regimes. The migration regime depends on two factors: the capillary pressure of the leading edge of the plume and the range of
threshold entry pressures within the rock at the leading edge of the plume. A capillary channel regime arises when these two factors have the same magnitude. Flow patterns within this regime vary from finger-like structures with minimal rock contact to back-filling structures with compact volumes of saturation distributed between fingers. Reservoir heterogeneity is one of the
principal factors influencing CO2 migration pathway in the capillary channel regime. Here we characterize buoyancy-driven migration in a natural 2D geologic domain (1 m × 0.5 m peel from an alluvium) in which sedimentologic heterogeneity has been resolved at sub-millimeter (depositional) resolution. The relevant features of the heterogeneity are grain size distribution, which determines the mean and range of threshold pressures and correlation lengths of threshold pressures in horizontal and vertical directions. The relevant physics for this migration regime is invasion percolation, and simulations indicate that CO2 migrates through the peel in a few narrow pathways which cannot be captured by conventional coarse-grid simulations. The storage
efficiency of the capillary channel regime would be low and consequently CO2 would also migrate greater distances than expected from models or simulations that neglect the capillary channel flow regime.Bureau of Economic Geolog
Tunable negative permeability in a three-dimensional superconducting metamaterial
We report on highly tunable radio frequency (rf) characteristics of a
low-loss and compact three dimensional (3D) metamaterial made of
superconducting thin film spiral resonators. The rf transmission spectrum of a
single element of the metamaterial shows a fundamental resonance peak at
24.95 MHz that shifts to a 25 smaller frequency and becomes
degenerate when a 3D array of such elements is created. The metamaterial shows
an \emph{in-situ} tunable narrow frequency band in which the real part of the
effective permeability is negative over a wide range of temperature, which
reverts to gradually near-zero and positive values as the superconducting
critical temperature is approached. This metamaterial can be used for
increasing power transfer efficiency and tunability of electrically small
rf-antennas.Comment: 6 pages, 4 figure
State-space model identification and feedback control of unsteady aerodynamic forces
Unsteady aerodynamic models are necessary to accurately simulate forces and
develop feedback controllers for wings in agile motion; however, these models
are often high dimensional or incompatible with modern control techniques.
Recently, reduced-order unsteady aerodynamic models have been developed for a
pitching and plunging airfoil by linearizing the discretized Navier-Stokes
equation with lift-force output. In this work, we extend these reduced-order
models to include multiple inputs (pitch, plunge, and surge) and explicit
parameterization by the pitch-axis location, inspired by Theodorsen's model.
Next, we investigate the na\"{\i}ve application of system identification
techniques to input--output data and the resulting pitfalls, such as unstable
or inaccurate models. Finally, robust feedback controllers are constructed
based on these low-dimensional state-space models for simulations of a rigid
flat plate at Reynolds number 100. Various controllers are implemented for
models linearized at base angles of attack , and . The resulting control laws are
able to track an aggressive reference lift trajectory while attenuating sensor
noise and compensating for strong nonlinearities.Comment: 20 pages, 13 figure
ESTIMATING THE VALUE OF SEQUENTIAL UPDATING SOLUTIONS FOR INTRAYEAR CROP MANAGEMENT
Results of comparing updating versus nonupdating modeling assumptions call into question the use of models based on nonupdating strategies as valid representations of actual farmer actions. If farmers are sequential updaters, the results indicate that models assuming no updating are inaccurate. The degree of this inaccuracy ranges between 4% and 10% of profits for the study area. Further, the results indicate that updating appears to be important for both descriptive and prescriptive studies of farmer behavior.Crop Production/Industries,
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