Charge profile of surface doped C60

We study the charge profile of a C60-FET (field effect transistor) as used in the experiments of Schoen, Kloc and Batlogg. Using a tight-binding model, we calculate the charge profile treating the Coulomb interaction in a mean-field approximation. The charge profile behaves similarly to the case of a continuous space-charge layer, in particular it is confined to a single interface layer for doping higher than ~0.3 electron (or hole) per C60 molecule. The morahedral disorder of the C60 molecules smoothens the structure in the density of states.Comment: 6 pages, 9 figure

Common and Fundamental Factors in Stock Returns of Canadian Oil and Gas Companies

In this paper, we assess the determinants of Canadian oil and gas stocks returns. We find that the stock return of Canadian energy stock is positively associated with returns on the Canadian stock market, appreciations of crude oil and natural gas prices, growth in internal cash flows and proven reserves, and negatively with interest rates. Surprisingly, however, production volume and a weakening of the Canadian dollar against the U.S. dollar have a negative impact. This latter impact is more pronounced for oil producers than for integrated energy companies. Finally, we find that the influence of the exchange rate, the market return and prices of natural gas on Canadian oil and gas stocks changes significantly over the years 1995-1998 and 2000-2002. Le but de cet article est de mesurer ce qui influence le rendement des actions d'entreprises pétrolières et gazières canadiennes. Nous trouvons que le rendement des actions de ces entreprises énergétiques est influencé positivement par le rendement du marché canadien dans son ensemble, par une appréciation du prix du pétrole et du gaz naturel, par une croissance dans les flux monétaires discrétionnaires de l'entreprise, par la quantité de réserves prouvées de l'entreprise. Nous trouvons également que le volume de production et une dépréciation du dollar canadien par rapport à la devise américaine réduit sensiblement le rendement des titres énergétiques, ce qui va à l'encontre de notre hypothèse initiale. L'impact du taux de change est encore plus marqué pour les producteurs indépendants que pour les entreprises intégrées. En dernier lieu, nous montrons que le marché a subi une cassure significative entre les années 1995-1998 et 2000-2002, spécialement pour ce qui est de l'impact du taux de change, du rendement de marché et du pris du gaz naturel.stock return valuation, panel data analysis, oil and gas industry, rendement des actions, analyse de données transversales, industrie pétrolière et gazière

Towards an Understanding of the Atmospheres of Cool White Dwarfs

Cool white dwarfs with Teff < 6000 K are the remnants of the oldest stars that existed in our Galaxy. Their atmospheres, when properly characterized, can provide valuable information on white dwarf evolution and ultimately star formation through the history of the Milky Way. Understanding the atmospheres of these stars requires joined observational effort and reliable atmosphere modeling. We discuss and analyze recent observations of the near-ultraviolet (UV) and near-infrared (IR) spectrum of several cool white dwarfs including DQ/DQp stars showing carbon in their spectra. We present fits to the entire spectral energy distribution (SED) of selected cool stars, showing that the current pure-hydrogen atmosphere models are quite reliable, especially in the near-UV spectral region. Recently, we also performed an analysis of the coolest known DQ/DQp stars investigating further the origin of the C2 Swan bands-like spectral features that characterize the DQp stars. We show that the carbon abundances derived for DQp stars fit the trend of carbon abundance with Teff seen in normal cool DQ stars. This further supports the recent conclusion of Kowalski A&A (2010) that DQp stars are DQ stars with pressure distorted Swan bands. However, we encounter some difficulties in reproducing the IR part of the SED of stars having a mixed He/H atmosphere. This indicates limitations in current models of the opacity in dense He/H fluids.Comment: 6 pages, 4 figures, to appear in the proceedings of the "18th European White Dwarf Workshop" in Krakow, Poland (2012

Techno-economic analysis of residential thermal flexibility for demand side management

The continuing rise in solar and wind production leads to an increasing demand of flexibility to stabilize the electricity grid. Furthermore, we can assume a gradual but intensive rise in the use of electrical heatpumps for household spatial heating, for different reasons. Therefore, this paper investigates the feasibility and viability of entering the flexibility market by aggregating residential thermal loads. For this research, a dataset of 200 dwellings in the Netherlands, equipped with a heatpump and smart metering infrastructure, is analysed. By means of a greybox modeling approach, a thermal model and control framework have been set up for every house, in order to identify the load shift potential and the accompanying cost of providing flexibility for the houses. We find that thermal flexibility is asymmetric: downwards flexibility is, apart from much more dependent on outdoor temperature than upwards flexibility, strictly lower than upwards flexibility. The cost for downwards flexibility is strictly negative in terms of the prosumer. Concerning upwards flexibility, the cost is most of the time positive. Moreover, it can be concluded that there is a potentially viable business case for the flexibility aggregator

Controlling percolation with limited resources

Connectivity - or the lack thereof - is crucial for the function of many man-made systems, from financial and economic networks over epidemic spreading in social networks to technical infrastructure. Often, connections are deliberately established or removed to induce, maintain, or destroy global connectivity. Thus, there has been a great interest in understanding how to control percolation, the transition to large-scale connectivity. Previous work, however, studied control strategies assuming unlimited resources. Here, we depart from this unrealistic assumption and consider the effect of limited resources on the effectiveness of control. We show that, even for scarce resources, percolation can be controlled with an efficient intervention strategy. We derive this strategy and study its implications, revealing a discontinuous transition as an unintended side-effect of optimal control.Comment: 5 pages, 4 figures, additional supplemental material (19 pages

Exploiting the user interaction context for automatic task detection

Detecting the task a user is performing on her computer desktop is important for providing her with contextualized and personalized support. Some recent approaches propose to perform automatic user task detection by means of classifiers using captured user context data. In this paper we improve on that by using an ontology-based user interaction context model that can be automatically populated by (i) capturing simple user interaction events on the computer desktop and (ii) applying rule-based and information extraction mechanisms. We present evaluation results from a large user study we have carried out in a knowledge-intensive business environment, showing that our ontology-based approach provides new contextual features yielding good task detection performance. We also argue that good results can be achieved by training task classifiers `online' on user context data gathered in laboratory settings. Finally, we isolate a combination of contextual features that present a significantly better discriminative power than classical ones

Protein crops: Food and feed for the future [Editorial]

Peer reviewedPeer Reviewe

A comparison of broad iron emission lines in archival data of neutron star low-mass X-ray binaries

Relativistic X-ray disk-lines have been found in multiple neutron star low-mass X-ray binaries, in close analogy with black holes across the mass-scale. These lines have tremendous diagnostic power and have been used to constrain stellar radii and magnetic fields, often finding values that are consistent with independent timing techniques. Here, we compare CCD-based data from Suzaku with Fe K line profiles from archival data taken with gas-based spectrometers. In general, we find good consistency between the gas-based line profiles from EXOSAT, BeppoSAX and RXTE and the CCD data from Suzaku, demonstrating that the broad profiles seen are intrinsic to the line and not broad due to instrumental issues. However, we do find that when fitting with a Gaussian line profile, the width of the Gaussian can depend on the continuum model in instruments with low spectral resolution, though when the different models fit equally well the line widths generally agree. We also demonstrate that three BeppoSAX observations show evidence for asymmetric lines, with a relativistic disk-line model providing a significantly better fit than a Gaussian. We test this by using the posterior predictive p-value method, and bootstrapping of the spectra to show that such deviations from a Gaussian are unlikely to be observed by chance.Comment: 13 pages, 9 figures, accepted to Ap