Bounds on the possible evolution of the Gravitational Constant from Cosmological Type-Ia Supernovae

Recent high-redshift Type Ia supernovae results can be used to set new bounds on a possible variation of the gravitational constant $G$. If the local value of $G$ at the space-time location of distant supernovae is different, it would change both the kinetic energy release and the amount of $^{56}$Ni synthesized in the supernova outburst. Both effects are related to a change in the Chandrasekhar mass $M_{Ch} \propto G^{-3/2}$. In addition, the integrated variation of $G$ with time would also affect the cosmic evolution and therefore the luminosity distance relation. We show that the later effect in the magnitudes of Type Ia supernovae is typically several times smaller than the change produced by the corresponding variation of the Chandrasekhar mass. We investigate in a consistent way how a varying $G$ could modify the Hubble diagram of Type Ia supernovae and how these results can be used to set upper bounds to a hypothetical variation of $G$. We find G/G_0 \la 1.1 and G'/G \la 10^{-11} yr^{-1} at redshifts $z\simeq 0.5$. These new bounds extend the currently available constrains on the evolution of $G$ all the way from solar and stellar distances to typical scales of Gpc/Gyr, i.e. by more than 15 orders of magnitudes in time and distance.Comment: 9 pages, 4 figures, Phys. Rev. D. in pres

Genetic population structure of marine fish: mismatch between biological and fisheries management units

An essential prerequisite of a sustainable fisheries management is the matching of biologically relevant processes and management action. In fisheries management and assessment, fish stocks are the fundamental biological unit, but the reasoning for the operational management unit is often indistinct and mismatches between the biology and the management action frequently occur. Despite the plethora of population genetic data on marine fishes, to date little or no use is made of the information, despite the fact that the detection of genetic differentiation may indicate reproductively distinct populations. Here, we discuss key aspects of genetic population differentiation in the context of their importance for fisheries management. Furthermore, we evaluate the population structure of all 32 managed marine fish species in the north-east Atlantic and relate this structure to current management units and practice. Although a large number of studies on genetic population structure have been published in the last decades, data are still rare for most exploited species. The mismatch between genetic population structure and the current management units found for six species (Gadus morhua, Melanogrammus aeglefinus, Merlangius merlangus, Micromesistius poutassou, Merluccius merluccius and Clupea harengus), emphasizes the need for a revision of these units and questions the appropriateness of current management measures. The implementation of complex and dynamic population structures into novel and less static management procedures should be a primary task for future fisheries management approache

Risk aversion, exchange-rate uncertainty, and the law of one price: Insights from the market for online air-travel tickets

We argue that risk aversion driven by exchange-rate uncertainty causes a wedge between the domestic and foreign prices of a homogeneous good. We test our hypothesis using a unique micro-data set from a market with minimum imperfections. The empirical findings validate our hypothesis, as accounting for exchange-rate uncertainty we are able to explain a significant proportion of deviations from the law of one price. Overall, our analysis suggests the possibility of a new solution to the purchasing power parity puzzles.© Canadian Economics Association

Development of copper sulfide/cadmium sulfide thin film solar cell s : fourth technical progress report, April 13 - July 12, 1980 /

"Work Performed Under Contract No. AC02-77CH00178.""February 27, 1981."Includes bibliographical references (page 61).Mode of access: Internet

Development of copper sulfide/cadmium sulfide thin-film solar cell s : third technical progress report, January 13 - April 12, 1980 /

"Work Performed Under Contract No. AC02-77CH00178.""July 23, 1980."Includes bibliographical references (page 30).Mode of access: Internet

A Multivariate Multilevel Approach to the Modeling of Accuracy and Speed of Test Takers

speed, accuracy, IRT, response times,