16,355 research outputs found
AN EVALUATION OF EXPECTED VALUE AND EXPECTED VALUE-VARIANCE CRITERIA IN ACHIEVING RISK EFFICIENCY IN CROP SELECTION
This article evaluates the performance of expected value and expected value-variance criteria in achieving risk efficiency in crop selection. Results indicate that the expected returns criterion achieves risk efficiency in many situations because of constraints. However, in the absence of many constraints the expected returns criterion performs poorly except when highly mean-dominant activities are present. The expected value-variance criterion achieves a high degree of risk efficiency for all situations examined. This result implies that criteria more complex than expected value-variance are not necessary for crop selection analysis, given empirical returns distributions.Crop Production/Industries,
Asymmetric Policy Interaction among Subnational Governments: Do States Play Welfare Games?
This paper explores the possibility that states respond asymmetrically to increases versus decreases in their neighboring states’ welfare benefit levels. We present a theoretical model suggesting that states respond more to decreases than to increases in their neighbors’ benefit levels. To test this proposition empirically, we use a panel of annual state-level data from 1983 to 1994 for each of the contiguous United States and the District of Columbia, and we observe changes in state demographic and economic characteristics as well as changes in state welfare benefits. We find substantial empirical evidence that uniformly supports our argument. State responses to neighbor benefit decreases tend to be at least twice as large as their responses to neighbor benefit increases. Our empirical results are robust to modeling neighbor benefits as endogenous. Our results, therefore, have substantial implications for public policy in the wake of the increased decentralization of welfare policy associated with the welfare reforms of 1996.
Science Leadership: Impact of the New Science Coordinators Academy
This article discusses the impact of the New Science Coordinators Academy (NSCA) on two cohorts of participants. The NSCA is one of four components of the Virginia Initiative for Science Teaching and Achievement (VISTA), a United States Department of Education (USED) science education reform grant. The NSCA is designed to support new school district science coordinators (with less than five years of experience) and to continue building the state science education infrastructure. Research in education leadership traditionally focuses on teacher leaders, principals, and district office personnel. Interestingly, research on district office personnel rarely distinguishes between the different roles of district personnel. This article seeks to inform the field by sharing the impact of an academy designed for new science coordinators on their learning, and to begin to understand their role and impact in their district. The five-day Academy engaged participants in a variety of experiences designed to facilitate the following: 1) build leadership skills; 2) build a common understanding and vision for hands-on science, inquiry, problem-based learning, and nature of science in the science classroom; 3) investigate data to improve student learning goals; 4) and, develop a science strategic plan. The data indicate that the NSCA was successful at meeting its goals to support the participants and to build a common language among these new coordinators. Initial data also support the variety of responsibilities of these participants and the positive impact of the Academy on their district work
FUSE, STIS, and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)
We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on
observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space
Telescope Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph.
By fitting the H I, He I, and He II lines in the Keck spectrum with non-LTE
H-He models, we obtain Teff = 36,600 K, log g = 3.95, and log N(He)/N(H) =
-0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N,
O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron
peak are observed. Both components of the N V 1240 doublet exhibit P~Cygni
profiles, indicating a weak stellar wind, but no other wind features are seen.
The star's photospheric abundances appear to have changed little since it left
the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are
consistent with published values for the red-giant stars in M3, and the
relative abundances of C, N, and O follow the trends seen on the cluster RGB.
In particular, its low C abundance suggests that the star left the asymptotic
giant branch before the onset of third dredge-up.Comment: 15 pages, 10 figures, to be published in MNRA
Thermal Performance Expectations of the Advanced Stirling Convertor Over a Range of Operating Scenarios
The Advanced Stirling Radioisotope Generator (ASRG) will enable various missions such as small body sample return, atmospheric missions around Venus, as well as long - duration deep space missions. Analysis of the temperature distributions are performed on an Advanced Stirling Convertor, and the results are compared with available experimental measurements. This analysis includes applied environmental conditions that are similar to those that will be experienced while the convertor is in operation. The applied conditions represent a potential mission profile including pre-takeoff sterilization, launch, transit, and return. The results focus on the anticipated peak temperatures of the magnets in the linear alternator. These results confirm that the ASC can support future missions to deep space targets, extreme environment landers, as well as more conventional goals
Theory of Nonequilibrium Spin Transport and Spin Transfer Torque in Superconducting-Ferromagnetic Nanostructures
Spin transport currents and the spin-transfer torques in voltage-biased
superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed.
We develop and implement an algorithm based on the Ricatti formulation of the
quasiclassical theory of superconductivity to solve the time-dependent boundary
conditions for the nonequilibrium Green's functions for spin transport through
the ferromagnetic interfaces. A signature of the nonequilibrium torque is a
component perpendicular to the plane spanned by the two ferromagnetic moments.
The perpendicular component is absent in normal-metal-ferromagnetic nanopillars
(NFNFN) contacts, but is shown to have the same order of magnitude as the
in-plane torque for non-equilibrium SFNFS contacts. The out-of-plane torque is
due to the rotation of quasiparticle spin by the exchange fields of the
ferromagnetic layers. In the ballistic limit the equilibrium torque is related
to the spectrum of spin-polarized Andreev bound states, while the {\sl ac}
component, for small bias voltages, is determined by the nearly adiabatic
dynamics of the Andreev bound states. The nonlinear voltage dependence of the
non-equilibrium torque, including the subharmonic gap structure and the
high-voltage asymptotics, is attributed to the interplay between multiple
Andreev reflections, spin filtering and spin mixing. These properties of spin
angular momentum transport may be exploited to control the state of
nanomagnets.Comment: 15 pages, 14 figure
Incoherent Scatter Measurements of F-Region Density, Temperatures, and Vertical Velocity at Millstone Hill
The Millstone Hill Thomson (incoherent) scatter radar system has been operated routinely since 1963 to perform a synoptic study of F-region electron densities, and electron and ion temperatures. This report describes system changes made in 1968 which considerably increased the accuracy of the measurements and allowed their extension to higher altitudes. These changes have also made it impossible to measure the vertical velocity of the plasma over the altitude range 450 to 900 km to an accuracy on the order of 5 to 10 m/sec, depending upon altitude and time of day.
Of even greater significance, complete machine reduction of the results is now possible so that considerable savings in time and effort have been secured in analyzing the data. The new system permits all the radar data to be gathered in the digital computer in real time, thereby eliminating the need for post real-time processing of magnetic-tape recordings of the signals. Furthermore, it is now possible to transmit the data to other workers in computer-usable form.
This report describes the main functions of the computer program required to analyze the measurements, and lists the times of all measurements made with the new system prior to 1 January 1970. Examples of these results are presented and discussed
Constraining the History of the Sagittarius Dwarf Galaxy Using Observations of its Tidal Debris
We present a comparison of semi-analytic models of the phase-space structure
of tidal debris with observations of stars associated with the Sagittarius
dwarf galaxy (Sgr). We find that many features in the data can be explained by
these models. The properties of stars 10-15 degrees away from the center of Sgr
--- in particular, the orientation of material perpendicular to Sgr's orbit
(c.f. Alard 1996) and the kink in the velocity gradient (Ibata et al 1997) ---
are consistent with those expected for unbound material stripped during the
most recent pericentric passage ~50 Myrs ago. The break in the slope of the
surface density seen by Mateo, Olszewski & Morrison (1998) at ~ b=-35 can be
understood as marking the end of this material. However, the detections beyond
this point are unlikely to represent debris in a trailing streamer, torn from
Sgr during the immediately preceding passage ~0.7 Gyrs ago, but are more
plausibly explained by a leading streamer of material that was lost more that 1
Gyr ago and has wrapped all the way around the Galaxy. The observations
reported in Majewski et al (1999) also support this hypothesis. We determine
debris models with these properties on orbits that are consistent with the
currently known positions and velocities of Sgr in Galactic potentials with
halo components that have circular velocities v_circ=140-200 km/s. The best
match to the data is obtained in models where Sgr currently has a mass of ~10^9
M_sun and has orbited the Galaxy for at least the last 1 Gyr, during which time
it has reduced its mass by a factor of 2-3, or luminosity by an amount
equivalent to ~10% of the total luminosity of the Galactic halo. These numbers
suggest that Sgr is rapidly disrupting and unlikely to survive beyond a few
more pericentric passages.Comment: 19 pages, 5 figures, accepted to Astronomical Journa
Amino Acid Supplementation of Opaque-2 Corn for Growing Pigs
The purpose of this research was to study the adequacy of the essential amino acids lysine, methionine, typtophan, threonine and isoleucine in opaque-2 corn diets for young pigs. Rate of gain, feed efficiency and plasma amino acid levels were criteria used to evaluate the diets
Imaging the Ionized Disk of the High-Mass Protostar Orion-I
We have imaged the enigmatic radio source-I (Orion-I) in the Orion-KL nebula
with the VLA at 43 GHz with 34 mas angular resolution. The continuum emission
is highly elongated and is consistent with that expected from a nearly edge-on
disk. The high brightness and lack of strong molecular lines from Orion-I can
be used to argue against emission from dust. Collisional ionization and H-minus
free-free opacity, as in Mira variables, require a central star with >10^5
Lsun, which is greater than infrared observations allow. However, if
significant local heating associated with accretion occurs, lower total
luminosities are possible. Alternatively, photo-ionization from an early B-type
star and p+/e- bremsstrahlung can explain our observations, and Orion-I may be
an example of ionized accretion disk surrounding a forming massive star. Such
accretion disks may not be able to form planets efficiently.Comment: 16 pages, 1 table, 3 figure
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