Black-Hole Mass Measurements

The applicability and apparent uncertainties of the techniques currently available for measuring or estimating black-hole masses in AGNs are briefly summarized.Comment: 6 pages. Invited review at `AGN Physics with the Sloan Digital Sky Survey' conference (July 2003), eds. G. Richards and P. Hall (ASP Conf. Series, 2004

The G20 has served its purpose and should be replaced with a Global Economic Council on a firmer constitutional foundation

Robert Wade and Jakob Vestergaard argue that by permanently excluding 172 countries, the G20 deprives the large majority of nations of voice on matters that may crucially affect them. They believe it should be replaced by a Global Economic Council (GEC) based on a delegated voting system, and here they provide details of what this might look like

Temporal Gillespie algorithm: Fast simulation of contagion processes on time-varying networks

Stochastic simulations are one of the cornerstones of the analysis of dynamical processes on complex networks, and are often the only accessible way to explore their behavior. The development of fast algorithms is paramount to allow large-scale simulations. The Gillespie algorithm can be used for fast simulation of stochastic processes, and variants of it have been applied to simulate dynamical processes on static networks. However, its adaptation to temporal networks remains non-trivial. We here present a temporal Gillespie algorithm that solves this problem. Our method is applicable to general Poisson (constant-rate) processes on temporal networks, stochastically exact, and up to multiple orders of magnitude faster than traditional simulation schemes based on rejection sampling. We also show how it can be extended to simulate non-Markovian processes. The algorithm is easily applicable in practice, and as an illustration we detail how to simulate both Poissonian and non-Markovian models of epidemic spreading. Namely, we provide pseudocode and its implementation in C++ for simulating the paradigmatic Susceptible-Infected-Susceptible and Susceptible-Infected-Recovered models and a Susceptible-Infected-Recovered model with non-constant recovery rates. For empirical networks, the temporal Gillespie algorithm is here typically from 10 to 100 times faster than rejection sampling.Comment: Minor changes and updates to reference

An Empirical Ultraviolet Iron Spectrum Template Applicable to Active Galaxies

Iron emission is often a severe contaminant in optical-ultraviolet spectra of active galaxies. Its presence complicates emission line studies. A viable solution, already successfully applied at optical wavelengths, is to use an empirical iron emission template. We have generated FeII and FeIII templates for ultraviolet active galaxy spectra based on HST archival 1100 - 3100 A spectra of IZw1. Their application allows fitting and subtraction of the iron emission in active galaxy spectra. This work has shown that in particular CIII] lambda 1909 can be heavily contaminated by other line emission, including iron transitions. Details of the data processing, generation, and use of the templates, are given by Vestergaard & Wilkes (2001).Comment: 4 pages, including 1 figure, to appear in "Spectroscopic Challenges of Photoionized Plasmas", ASP Conf. Series, Eds. Gary Ferland and Daniel Wolf Savi

A Hubble Space Telescope Imaging Study of Four FeLoBAL Quasar Host Galaxies

We study the host galaxies of four Iron Low-Ionization Broad Absorption-line Quasars (FeLoBALs) using Hubble Space Telescope imaging data, investigating the possibility that they represent a transition between an obscured AGN and an ordinary optical quasar. In this scenario, the FeLoBALs represent the early stage of merger-triggered accretion, in which case their host galaxies are expected to show signs of an ongoing or recent merger. Using PSF subtraction techniques, we decompose the images into host galaxy and AGN components at rest-frame ultraviolet and optical wavelengths. The ultraviolet is sensitive to young stars, while the optical probes stellar mass. In the ultraviolet we image at the BAL absorption trough wavelengths so as to decrease the contrast between the quasar and host galaxy emission. We securely detect an extended source for two of the four FeLoBALs in the rest-frame optical; a third host galaxy is marginally detected. In the rest-frame UV we detect no host emission; this constrains the level of unobscured star formation. Thus, the host galaxies have observed properties that are consistent with those of non-BAL quasars with the same nuclear luminosity, i.e., quiescent or moderately starforming elliptical galaxies. However, we cannot exclude starbursting hosts that have the stellar UV emission obscured by modest amounts of dust reddening. Thus, our findings also allow the merger-induced young quasar scenario. For three objects, we identify possible close companion galaxies that may be gravitationally interacting with the quasar hosts.Comment: 33 pages, 15 figures. Accepted for publication in MNRA

Fisheries Management with Multiple Market Failures

Within fisheries it is well-known that several market failures exist. However, fisheries economists analyse these market failures separately despite the fact that the market failures arise simultaneously. In this paper several market fail-ures that arise simultaneously are analysed. A resource stock tax and a tax on self-reported harvest are considered as a solution to problems associated with the stock externality, measuring individual catches and stock uncertainty. Within a fisheries economic model it is shown that it will be in the interest of risk-averse fishermen to report a part of their catch even without a control pol-icy. In addition, it is shown that this tax structure can secure optimal expected individual catches and simulations show that the tax payment is very low. Thus, the tax system may be useful in practical fisheries management.Prices regulation, Quantity regulation, Asymmetric Information, Self-Reporting, Stock Tax and Harvest Tax

A Bioeconomic Analysis of the Greenland Shrimp Fishery in the Davis Strait

This paper presents a bioeconomic analysis determining the resource rent and optimum effort of the shrimp (Pandalus borealis) fishery in the Davis Strait, taking into account the discard behaviour of the fleet. It is demonstrated that, from an economic point of view, the shrimp stock in the Davis Strait is substantially overfished. In order to obtain the maximum economic yield, the effort must be reduced by at least 40% compared to the effort level of 1991. The gain in resource rent by reducing effort is estimated to be at least 20% compared to the resource rent of 1991.Bioeconomics, rent, discard, shrimp, Greenland, Environmental Economics and Policy, Production Economics,

Regulation of Renewable Resources in Federal Systems: The Case of Fishery in th EU

The EU regulation of fisheries is decided in two levels. The level of the total allowable catch (TAC) for the most important species is decided every year by the Council of Minsters. The TACs are allocated to the Member States as quotas. The Member States determine who is going to harvest the quota. There is, however, an information problem associated with this structure. It does not take into account how efficient fishermen in different countries are. In this paper we model the information problem as an adverse selection problem and analyse an EU tax coupled to effort as an alternative to the TAC system. We work with the hypothesis that EU suffers from a fiscal illusion and includes tax revenue in the objective function in order to finance other, also inefficient, operations. Even in the light of these imperfections there are at least two reasons for recommending an EU tax. First, it can be used to correct part of the market failure associated with fishery. Second, it can be used to secure correct revealation of types in the light of asymmetric information.

Meat quality of hull calves fed only grass or only herbs for 8 weeks prior to slaughter matches that of concentrate-fed bull calves

The organic rules require that bull calves are raised outdoor at least 6 months a year in Denmark and are fed at least 60% roughage of the total diet. These rules are a constraint for an organic production of beef based on the bull calves born in the organic dairy herds because of extra labor costs, expected lower growth rate, difficulties in raising bull calves outdoor, possibly lower meat quality and lack of sufficiently high organic premium payment for the carcass. Thus, the bull calves are sold for conventional fattening. The supply of organic beef from young cattle is concomitantly very limited. However, in order to obtain the necessary higher payment for beef from organic-raised young cattle, it is important that consumers like the beef from grass- and herb-fed young cattle

A Sample of Quasars with Strong Nitrogen Emission Lines from the Sloan Digital Sky Survey

We report on 293 quasars with strong NIV] lambda 1486 or NIII] lambda 1750 emission lines (rest-frame equivalent width > 3 \AA) at 1.7 < z < 4.0 selected from the Sloan Digital Sky Survey (SDSS) Fifth Data Release. These nitrogen-rich (N-rich) objects comprise ~1.1% of the SDSS quasars. The comparison between the N-rich quasars and other quasars shows that the two quasar subsets share many common properties. We also confirm previous results that N-rich quasars have much stronger Lya and NV lambda 1240 emission lines. Strong nitrogen emission in all ionization states indicates high overall nitrogen abundances in these objects. We find evidence that the nitrogen abundance is closely related to quasar radio properties. The radio-loud fraction in the NIII]-rich quasars is 26% and in the NIV]-rich quasars is 69%, significantly higher than ~8% measured in other quasars with similar redshift and luminosity. Therefore, the high nitrogen abundance in N-rich quasars could be an indicator of a special quasar evolution stage, in which the radio activity is also strong.Comment: 8 pages, 4 figures; accepted by ApJ (ApJ June 10, 2008, v680 n1 issue