288 research outputs found
RISK PERCEPTIONS AND MANAGEMENT RESPONSES: PRODUCER-GENERATED HYPOTHESES FOR RISK MODELING
Farm level risk analyses have used price and yield variability almost exclusively to represent risk. Results from a survey of 149 agricultural producers in 12 states indicate that producers consider a broader range of sources of variability in their operations. Significant differences exist among categories with respect to the importance of the sources of variability in crop and livestock production. Producers also used a variety of management responses to variability. There were significant difference among categories in the importance given to particular responses and their use of them. These results have implications for research, extension, and policy programs.Risk and Uncertainty,
IDENTIFICATION OF ERRORS IN COTTON FIBER DATA SETS USING BAYESIAN NETWORKS
Cotton fiber is graded on a series of parameters based on physiological factors (strength, length, and thickness), lint color, and presence of non-lint matter such as leaves, stems or other foreign materials. Cotton lint is graded by the USDA-AMS after harvest and ginning, and the grade determines the price of the lint. Given the importance of cotton fiber quality to the value of the crop, the spatial variability of cotton fiber properties is of particular interest to researchers and producers in developing management scenarios for optimal profitability. Previous research studies have relied on hand-harvesting the cotton at intervals throughout the field to obtain a measure of the cotton fiber quality and the extent of spatial variability. However, hand-harvested cotton has different qualities than that harvested by machine and ginned in the large-scale production gins. Part of this arises from the difference in efficiency of harvest between machine and humans, and part results from the different gins used for the smaller sample sizes. While these studies have demonstrated the extent of spatial variability of fiber properties, handharvesting is not amenable to large-scale or production research efforts. Moreover, the differences in fiber properties limit the extension of the results to the production setting. We have developed a mechanism of sampling cotton from the cotton chute during mechanical harvest. The samples are then ginned on a research gin. This study was undertaken to develop a method of translating these small-scale researcher level results to full-scale production level results. The research reported here is the first step in that effort, and demonstrates the use of Bayesian networks to detect erroneous entries in cotton fiber data sets
Infrared receivers for low background astronomy: Incoherent detectors and coherent devices from one micrometer to one millimeter
The status of incoherent detectors and coherent receivers over the infrared wavelength range from one micrometer to one millimeter is described. General principles of infrared receivers are included, and photon detectors, bolometers, coherent receivers, and important supporting technologies are discussed, with emphasis on their suitability for low background astronomical applications. Broad recommendations are presented and specific opportunities are identified for development of improved devices
FUSE and HST STIS Observations of Hot and Cold Gas in the AB Aurigae System
We present the first observations of a Herbig Ae star with a circumstellar
disk by the Far Ultraviolet Spectroscopic Explorer (FUSE), as well as a
simultaneous observation of the star obtained with the Hubble Space Telescope
Space Telescope Imaging Spectrograph (STIS). The spectra of AB Aurigae show
emission and absorption features arising from gasses that have a wide range in
temperature, from hot OVI emission to cold molecular hydrogen and CO
absorption. Emissions from the highly ionized species OVI and CIII present in
the FUSE spectrum are redshifted, while absorption features arising from
low-ionization species like OI, NI, and SiII are blueshifted and show
characteristic stellar wind line-profiles. We find the total column density of
molecular hydrogen toward AB Aur from the FUSE apectrum, N(H_2) = (6.8 +/- 0.5)
x 10^19 cm^-2. The gas kinetic temperature of the molecular hydrogen derived
from the ratio N(J=1)/N(J=0) is 65 +/- 4 K. The column density of the CO
observed in the STIS spectrum is N(CO) = (7.1 +/- 0.5) x 10^13 cm^-2, giving a
CO/H_2 ratio of (1.04 +/- 0.11) x 10^-6. We also use the STIS spectrum to find
the column density of HI, permitting us to calculate the total column density
of hydrogen atoms, the fractional abundance of H_2, and the gas-to-dust ratio.Comment: 5 pages, including 6 figures. LaTex2e (emulateapj5.sty). Accepted for
publication in ApJ Letter
Spin relaxation in (110) and (001) InAs/GaSb superlattices
We report an enhancement of the electron spin relaxation time (T1) in a (110)
InAs/GaSb superlattice by more than an order of magnitude (25 times) relative
to the corresponding (001) structure. The spin dynamics were measured using
polarization sensitive pump probe techniques and a mid-infrared, subpicosecond
PPLN OPO. Longer T1 times in (110) superlattices are attributed to the
suppression of the native interface asymmetry and bulk inversion asymmetry
contributions to the precessional D'yakonov Perel spin relaxation process.
Calculations using a nonperturbative 14-band nanostructure model give good
agreement with experiment and indicate that possible structural inversion
asymmetry contributions to T1 associated with compositional mixing at the
superlattice interfaces may limit the observed spin lifetime in (110)
superlattices. Our findings have implications for potential spintronics
applications using InAs/GaSb heterostructures.Comment: 4 pages, 2 figure
Moving beyond physical education subject knowledge to develop knowledgeable teachers of the subject
All knowledge is socially constructed, including physical education teachers’ knowledge of their subject. It is acquired from other people either formally and deliberately (e.g. by being taught) or informally and casually (e.g. by interacting with physical education teachers or playing in a sports team). The social aspects of learning appear to be particularly strong in physical education. This has implications for the development of knowledge for teaching, with trainee teachers focusing on the development of subject, and particularly content, knowledge. Focusing on subject knowledge reinforces a traditional view of physical education as it is, not as it might be to meet the needs of young people today. It is argued that attention needs to be given not only to the knowledge, skills and competencies that trainee teachers ought to develop but also to the social aspects of their learning and development and the context in which they learn. Attention also needs to be given to how the ability to think critically can be developed so that trainee teachers can become reflective practitioners able to challenge and, where appropriate, change the teaching of the subject. Only by doing this can the particularly strong socialisation which shapes the values and beliefs of physical education teachers begin to be challenged. However, as the process of developing knowledgeable teachers is ongoing it is also necessary to look beyond teacher training to continuing professional development
Moving beyond physical education subject knowledge to develop knowledgeable teachers of the subject
All knowledge is socially constructed, including physical education teachers’ knowledge of their subject. It is acquired from other people either formally and deliberately (e.g. by being taught) or informally and casually (e.g. by interacting with physical education teachers or playing in a sports team). The social aspects of learning appear to be particularly strong in physical education. This has implications for the development of knowledge for teaching, with trainee teachers focusing on the development of subject, and particularly content, knowledge. Focusing on subject knowledge reinforces a traditional view of physical education as it is, not as it might be to meet the needs of young people today. It is argued that attention needs to be given not only to the knowledge, skills and competencies that trainee teachers ought to develop but also to the social aspects of their learning and development and the context in which they learn. Attention also needs to be given to how the ability to think critically can be developed so that trainee teachers can become reflective practitioners able to challenge and, where appropriate, change the teaching of the subject. Only by doing this can the particularly strong socialisation which shapes the values and beliefs of physical education teachers begin to be challenged. However, as the process of developing knowledgeable teachers is ongoing it is also necessary to look beyond teacher training to continuing professional development
Sub-millimeter to centimeter excess emission from the Magellanic Clouds. I. Global spectral energy distribution
In order to reconstruct the global SEDs of the Magellanic Clouds over eight
decades in spectral range, we combined literature flux densities representing
the entire LMC and SMC respectively, and complemented these with maps extracted
from the WMAP and COBE databases covering the missing the 23--90 GHz (13--3.2
mm) and the poorly sampled 1.25--250 THz (240--1.25 micron). We have discovered
a pronounced excess of emission from both Magellanic Clouds, but especially the
SMC, at millimeter and sub-millimeter wavelengths. We also determined accurate
thermal radio fluxes and very low global extinctions for both LMC and SMC.
Possible explanations are briefly considered but as long as the nature of the
excess emission is unknown, the total dust masses and gas-to-dust ratios of the
Magellanic Clouds cannot reliably be determined.Comment: Accepted for publication by A&
Spin relaxation of conduction electrons in bulk III-V semiconductors
Spin relaxation time of conduction electrons through the Elliot-Yafet,
D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is calculated theoretically for
bulk GaAs, GaSb, InAs and InSb of both - and -type. Relative importance
of each spin relaxation mechanism is compared and the diagrams showing the
dominant mechanism are constructed as a function of temperature and impurity
concentrations. Our approach is based upon theoretical calculation of the
momentum relaxation rate and allows understanding of the interplay between
various factors affecting the spin relaxation over a broad range of temperature
and impurity concentration.Comment: an error in earlier version correcte
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