3,438 research outputs found
Making Sense of Non-Binding Retail-Price Recommendations
We model non-binding retail-price recommendations (RPRs) as a communication device facilitating coordination in vertical supply relations. Assuming both repeated vertical trade and asymmetric information about production costs, we show that RPRs may be part of a relational contract, communicating private information from manufacturer to retailer that is indispensable for maximizing joint surplus. We show that this contract is self-enforcing if the retailer’s profit is independent of production costs and punishment strategies are chosen appropriately. We also extend our analysis to settings where consumer demand is variable or depends directly on the manufacturer’s RPRs.vertical relationships, relational contracts, asymmetric information, price recommendations
The interstellar gas experiment
The Interstellar Gas Experiment (IGE) exposed thin metallic foils to collect neutral interstellar gas particles. These particles penetrate the solar system due to their motion relative to the sun. Thus, it is possible to entrap them in the collecting foils along with precipitating magnetospheric and perhaps some ambient atmospheric particles. For the entire duration of the Long Duration Exposure Facility (LDEF) mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectroscopic analysis of the noble gas component of these particles, we have detected the isotopes of He-3, He-4, Ne-20, and Ne-22. In the foil analyses carried out so far, we find a distribution of particle arrival directions which shows that a significant part of the trapped particles are indeed interstellar atoms. The analysis needed to subtract the competing fluxes of magnetospheric and atmospheric particles is still in progress
The Interstellar Gas Experiment: Analysis in progress
The Interstellar Gas Experiment (IGE) exposed thin metallic foils aboard the LDEF spacecraft in low Earth orbit in order to collect neutral interstellar particles which penetrate the solar system due to their motion relative to the sun. By mechanical penetration these atoms were imbedded in the collecting foils along with precipitating magnetospheric ions and, possibly, with ambient atmospheric atoms. During the entire LDEF mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. After the foils were returned to Earth, a mass spectrometric analysis of the noble gas component of the trapped particles was begun. The isotopes of He-3, He-4, Ne-20, and Ne-22 were detected. We have given a first account of the experiment. In order to infer the isotopic ratios in the interstellar medium from the concentrations found in the foils, several lines of investigation had to be initiated. The flux of ambient atmospheric noble gas atoms moving toward the foils due to the orbital motion of LDEF was estimated by detailed calculations. Any of these particles which evaded the baffles in the IGE collector could be entrapped in the foils as a background flux. However, the calculations have shown that this flux is negligible, which was the intent of the experiment hardware design. This conclusion is supported by the measurements. However, both the concentration of trapped helium and its impact energy indicate that the flux of magnetospheric ions which was captured was larger than had been expected. In fact, it appears that the magnetospheric particles constitute the largest fraction of the particles in the foils. Since little is known about this particle flux, their presence in the IGE foils appears fortunate. The analysis of these particles provides information about their isotropic composition and average flux
The new surprising behaviour of the two "prototype" blazars PKS 2155-304 and 3C 279
Recent VHE observations have unveiled a surprising behaviour in two
well-known blazars at opposite sides of the blazar sequence. PKS 2155-304 have
shown for the first time in an HBL a large Compton dominance, high gamma-ray
luminosities and a cubic relation between X-ray and VHE fluxes. 3C 279 is the
first FSRQ detected at VHE. The high luminosity required to overcome the
significant absorption caused by the BLR emission cannot be easily reconciled
with the historical and quasi-simultaneous SED properties. Both cases shed a
new light on the structure and ambient fields of blazars. Contrary to previous
claims, it is also shown that 3C 279 --as any FSRQ-- cannot in general provide
robust constraints on the EBL.Comment: Proceedings of "4th Heidelberg International Symposium on High Energy
Gamma-Ray Astronomy 2008" (Gamma 2008), July 7-11, 2008. Slightly refined
text with updated reference
A GENERAL COMPUTATIONAL APPROACH FOR MAGNETOHYDRODYNAMIC FLOWS USING THE CFX CODE: BUOYANT FLOW THROUGH A VERTICAL SQUARE CHANNEL
The buoyancy-driven magnetoconvection in the cross
section of an infinitely long vertical square duct is investigated
numerically using the CFX code package. The
implementation of a magnetohydrodynamic (MHD) problem
in CFX is discussed, with particular reference to the
Lorentz forces and the electric potential boundary conditions
for arbitrary electrical conductivity of the walls.
The method proposed is general and applies to arbitrary
geometries with an arbitrary orientation of the magnetic
field. Results for fully developed flow under various thermal
boundary conditions are compared with asymptotic
analytical solutions. The comparison shows that the asymptotic
analysis is confirmed for highly conducting walls
as high velocity jets occur at the side walls. For weakly
conducting walls, the side layers become more conducting
than the side walls, and strong electric currents flow
within these layers parallel to the magnetic field. As a
consequence, the velocity jets are suppressed, and the core
solution is only corrected by the viscous forces near the
wall. The implementation of MHD in CFX is achieved
Age and environment affect constitutive immune function in Red Knots (Calidris canutus)
We studied subspecies, age and environmental effects on constitutive immune function (natural antibody and complement titres, haptoglobin activity and leukocyte concentrations) in Red Knots (Calidris canutus). We compared C. c. islandica and C. c. canutus in the Wadden Sea and found no difference in immune function between subspecies. However, C. c. canutus on their wintering grounds in Banc d’Arguin had higher natural antibody and lower complement levels than C. c. canutus or C. c. islandica in the Wadden Sea. This suggests that immune function is determined more by the surrounding environment than by subspecies. We also compared age classes in the Wadden Sea and found that first year birds had significantly lower natural antibody levels than adults, but that second year birds no longer differed from adults. Finally, we examined the interaction of age and environment in Banc d’Arguin. We found that first year birds (but not adults) in a low quality habitat had higher leukocyte concentrations than first year birds or adults in a high quality habitat. Differences in available resources and defence needs between environments, and differences among individuals differentially distributed between sites, are likely important contributors to the variation in immune function we report. Future studies, which examine these factors on wild birds, will be important for our understanding of how animals function in their natural environment.
Mechanics of collagen-hydroxyapatite model nanocomposites
Bone is a hierarchical biological composite made of a mineral component (hydroxyapatite crystals) and anorganic part (collagen molecules). Small-scale deformation phenomena that occur in bone are thought tohave a significant influence on the large scale behavior of this material. However, the nanoscale behaviorof collagen–hydroxyapatite composites is still relatively poorly understood. Here we present a molec-ular dynamics study of a bone model nanocomposite that consist of a simple sandwich structure ofcollagen and hydroxyapatite, exposed to shear-dominated loading. We assess how the geometry of thecomposite enhances the strength, stiffness and capacity to dissipate mechanical energy. We find that H-bonds between collagen and hydroxyapatite play an important role in increasing the resistance againstcatastrophic failure by increasing the fracture energy through a stick-slip mechanism
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