25,321 research outputs found
Data management study, volume 5. Appendix B - Contractor data package Planetary Quarantine /PQ/ Final report
Contractor data management package for Voyager spacecraft sterilization projec
Trade Restrictions and Trade Reversal: Lessons from the U.S.-Canada Herring Dispute
This paper analyzes international trade in value added products when free trade and perfect competition in the market for an intermediate product, such as raw fish, are the exception rather than the rule. Current evidence from the General Agreement on Tariffs and Trade (GATT) regarding disputes between countries, such as the V.S.-Canada dispute over trade in raw herring, suggests that bilateral trade in raw fish among major exporters of seafood products may not be completely free of structural and political barriers. The study presents models showing that restrictions on the exportation of raw fish from an exporting country can make possible monopsony behavior by fish processors in a rival exporting country and they outline the market behavior of the players under such circumstances. The analysis illustrates how, under such conditions, economic forces contribute to the creation of trade disputes. It further demonstrates how expansion of the demand for final product may, through trade reversal pressures, dilute the market power of the processor monopsony and make trade restriction policies irrelevant.roe herring, trade reversal, trade restrictions, monopsony, trade dispute, GATT, market imperfection, free trade, fishery management, comparative advantage reversal, Environmental Economics and Policy, International Relations/Trade,
Magnetic, Transport, and Thermal Properties of Single Crystals of the Layered Arsenide BaMn2As2
Growth of BaMn2As2 crystals using both MnAs and Sn fluxes is reported. Room
temperature crystallography, anisotropic isothermal magnetization M versus
field H and magnetic susceptibility chi versus temperature T, electrical
resistivity in the ab plane rho(T), and heat capacity C(T) measurements on the
crystals were carried out. The tetragonal ThCr2Si2-type structure of BaMn2As2
is confirmed. After correction for traces of ferromagnetic MnAs impurity phase
using M(H) isotherms, the inferred intrinsic chi(T) data of the crystals are
anisotropic with chi_{ab}/chi_{c} \approx 7.5 at T = 2 K. The temperature
dependences of the anisotropic chi data suggest that BaMn2As2 is a collinear
antiferromagnet at room temperature with the easy axis along the c axis, and
with an extrapolated Neel temperature T_N \sim 500 K. The rho(T) decreases with
decreasing T below 310 K but then increases below \sim 50 K, suggesting that
BaMn2As2 is a small band-gap semiconductor with an activation energy of order
0.03 eV. The C(T) data from 2 to 5 K are consistent with this insulating ground
state, exhibiting a low temperature Sommerfeld coefficient gamma = 0.0(4)
mJ/mol K^2. The Debye temperature is determined from these data to be theta_D =
246(4) K. BaMn2As2 is a potential parent compound for ThCr2Si2-type
superconductors.Comment: 7 pages, 6 figures; v2: typos corrected, additional data and
discussion, accepted for publication in Phys. Rev.
The neutral gas in the environs of the Geminga gamma-ray pulsar
We present a high-resolution (24 arcsec) study of the HI interstellar gas
distribution around the radio-quiet neutron star Geminga. Based on Very Large
Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field
around Geminga. These observations have revealed the presence of a neutral gas
shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which
surrounds Geminga at a radial velocity compatible with the kinematical distance
of the neutron star. In addition, morphological agreement is observed between
the internal face of the HI shell and the brightest structure of Geminga's tail
observed in X-rays.We explore the possibility that this morphological agreement
is the result of a physical association.Comment: One tarfile including a Latex file (7 pages) and two figures. Paper
accepted for publication in Advances in Space Research; typos corrected;
changes in section Results and Discussion after referee's suggestions. S.
Johnston's affilation correcte
Applications of radio interferometry to navigation
Radio astronomy experiments have demonstrated the feasibility of making precise position measurements using interferometry techniques. The application of this method to navigation and marine geodesy is discussed, and comparisons are made with existing navigation systems. The very long baseline technique, with a master station, can use either an artificial satellite or natural sources as position references; a high-speed data link is required. A completely ship-borne system is shown to be feasible, at the cost of poorer sensitivity for natural sources. A comparison of Doppler, delay and phase-track modes of operating a very long baseline configuration is made, as that between instantaneous measurements and those where a source can be tracked from horizon to transit. Geometric limitations in latitude and longitude coverage are discussed. The characteristics of natural radio sources, their flux, distribution on the sky, and apparent size are shown to provide a limit on position measurements precision. The atmosphere and frequency standard used both contribute to position measurement uncertainty by affecting interferometric phase
Detecting Pulsars with Interstellar Scintillation in Variance Images
Pulsars are the only cosmic radio sources known to be sufficiently compact to
show diffractive interstellar scintillations. Images of the variance of radio
signals in both time and frequency can be used to detect pulsars in large-scale
continuum surveys using the next generation of synthesis radio telescopes. This
technique allows a search over the full field of view while avoiding the need
for expensive pixel-by-pixel high time resolution searches. We investigate the
sensitivity of detecting pulsars in variance images. We show that variance
images are most sensitive to pulsars whose scintillation time-scales and
bandwidths are close to the subintegration time and channel bandwidth.
Therefore, in order to maximise the detection of pulsars for a given radio
continuum survey, it is essential to retain a high time and frequency
resolution, allowing us to make variance images sensitive to pulsars with
different scintillation properties. We demonstrate the technique with
Murchision Widefield Array data and show that variance images can indeed lead
to the detection of pulsars by distinguishing them from other radio sources.Comment: 8 papes, 9 figures, accepted for publication in MNRA
The Urban Food Question in the Context of Inequality and Dietary Change: A Study of Schoolchildren in Accra
Diets are changing globally, as agricultural and food systems have become globalised. Understanding how patterns of globalisation affect welfare is a key development question, but we know little about the way that the globalisation of food systems impacts different groups. This study explores food security and consumption among schoolchildren in Accra. We use a novel approach based on triangulation of primary data on food consumption and a synthesis of secondary literature on food trade, policy and urban food environment. Thus, we bridge a divide between micro-level analyses of food consumption and macro-level studies of food systems. We find that socio-economic status is a critical dimension, with poorer children more vulnerable to food insecurity and narrow dietary diversity. However, the consumption of packaged and processed foods, often sugar-rich and nutrient-poor, cuts across wealth groups. We argue that the urban food question today is defined by two intersecting phenomena: inequality and dietary change. The urban poor continue to face the fundamental challenge of adequate food access amidst a food environment that provides consumers with unhealthy and cheap food options. Therefore, food policy needs to regulate imports of cheap, unhealthy and enticing food
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