Tavis-Cummings model and collective multi-qubit entanglement in trapped ions

We present a method of generating collective multi-qubit entanglement via global addressing of an ion chain following the guidelines of the Tavis-Cummings model, where several qubits are coupled to a collective motional mode. We show that a wide family of Dicke states and irradiant states can be generated by single global laser pulses, unitarily or helped with suitable postselection techniques.Comment: 6 pages, 3 figures. Accepted for publication in Physical Review

Precovery of near-Earth asteroids by a citizen-science project of the Spanish Virtual Observatory

This article describes a citizen-science project conducted by the Spanish Virtual Observatory (SVO) to improve the orbits of near-Earth asteroids (NEAs) using data from astronomical archives. The list of NEAs maintained at the Minor Planet Center (MPC) is checked daily to identify new objects or changes in the orbital parameters of already catalogued objects. Using NEODyS we compute the position and magnitude of these objects at the observing epochs of the 938 046 images comprising the Eigth Data Release of the Sloan Digitised Sky Survey (SDSS). If the object lies within the image boundaries and the magnitude is brighter than the limiting magnitude, then the associated image is visually inspected by the project's collaborators (the citizens) to confirm or discard the presence of the NEA. If confirmed, accurate coordinates and, sometimes, magnitudes are submitted to the MPC. Using this methodology, 3,226 registered users have made during the first fifteen months of the project more than 167,000 measurements which have improved the orbital elements of 551 NEAs (6% of the total number of this type of asteroids). Even more remarkable is the fact that these results have been obtained at zero cost to telescope time as NEAs were serendipitously observed while the survey was being carried out. This demonstrates the enormous scientific potential hidden in astronomical archives. The great reception of the project as well as the results obtained makes it a valuable and reliable tool for improving the orbital parameters of near-Earth asteroids.Comment: 9 pages, 5 figures. Accepted in Astron. Nach

Automated supervised classification of variable stars I. Methodology

The fast classification of new variable stars is an important step in making them available for further research. Selection of science targets from large databases is much more efficient if they have been classified first. Defining the classes in terms of physical parameters is also important to get an unbiased statistical view on the variability mechanisms and the borders of instability strips. Our goal is twofold: provide an overview of the stellar variability classes that are presently known, in terms of some relevant stellar parameters; use the class descriptions obtained as the basis for an automated `supervised classification' of large databases. Such automated classification will compare and assign new objects to a set of pre-defined variability training classes. For every variability class, a literature search was performed to find as many well-known member stars as possible, or a considerable subset if too many were present. Next, we searched on-line and private databases for their light curves in the visible band and performed period analysis and harmonic fitting. The derived light curve parameters are used to describe the classes and define the training classifiers. We compared the performance of different classifiers in terms of percentage of correct identification, of confusion among classes and of computation time. We describe how well the classes can be separated using the proposed set of parameters and how future improvements can be made, based on new large databases such as the light curves to be assembled by the CoRoT and Kepler space missions.Comment: This paper has been accepted for publication in Astronomy and Astrophysics (reference AA/2007/7638) Number of pages: 27 Number of figures: 1

SOCIAL RELATIONS AND SEED TRANSACTIONS AMONG SMALLSCALE MAIZE FARMERS IN THE CENTRAL VALLEYS OF OAXACA, MEXICO; PRELIMINARY FINDINGS

This paper explores social arrangements associated with seed transactions among small-scale maize farmers in the Central Valleys of Oaxaca, Mexico, a centre of crop genetic diversity. A formal seed distribution system has yet to develop in the region and when seed loss occurs, farmers are faced with costs and difficulties identifying, locating, and obtaining seed of desired varieties. For these reasons, it was hypothesized that there were strong incentives for collective action among farmers to facilitate seed supply. The study found, however, no evidence of collective action with regards to seed supply in the three study communities-San Pablo Huitzo, San Lorenzo Albarradas, Santa Ana Zegache. Instead, farmers acquired seed using a variety of networks of social relations and different types of seed transactions. The results suggest that seed flow among farmers in the Central Valleys of Oaxaca is a complex process of negotiation and reciprocity, influenced by a variety of agroecological, socioeconomic, and cultural factors.Farm Management,

Switchable ultrastrong coupling in circuit QED

Superconducting quantum circuits possess the ingredients for quantum information processing and for developing on-chip microwave quantum optics. From the initial manipulation of few-level superconducting systems (qubits) to their strong coupling to microwave resonators, the time has come to consider the generation and characterization of propagating quantum microwaves. In this paper, we design a key ingredient that will prove essential in the general frame: a swtichable coupling between qubit(s) and transmission line(s) that can work in the ultrastrong coupling regime, where the coupling strength approaches the qubit transition frequency. We propose several setups where two or more loops of Josephson junctions are directly connected to a closed (cavity) or open transmission line. We demonstrate that the circuit induces a coupling that can be modulated in strength and type. Given recent studies showing the accessibility to the ultrastrong regime, we expect our ideas to have an immediate impact in ongoing experiments

Evaluation of a two-phase extraction system of carbohydrates and proteins from chlorella vulgaris utex 1803

Microalgae are a valuable source of high-value products and biofuels, however the high-energy cost required for the extraction of their metabolites has kept questioning on possible industrial upgrading. The aim of this study was to evaluate the effect of temperature, solvent/biomass, NaOH concentration and thermal pretreatment of the biomass in a 2-cycle carbohydrate and protein extraction system. Results shown that best conditions for carbohydrates extraction are achieved at a solvent concentration of 3.67 M, 55°C and a solvent/biomass ratio of 30mL/g. On the other side, the best conditions for protein were 3 M, 85°C and 45 mL/g. The efficiencies achieved under these conditions were 95% for carbohydrates and 98% for proteins. Using the best extraction conditions for each metabolite a thermal pre-treatment was performed at 25°C, 75°C and 105°C. Results indicate that highest efficiencies were achieved with dry biomass pretreated at 105°C, with values of 95% for carbohydrates and 98% for proteins

Quantum computation with trapped ions in an optical cavity

Two-qubit logical gates are proposed on the basis of two atoms trapped in a cavity setup. Losses in the interaction by spontaneous transitions are efficiently suppressed by employing adiabatic transitions and the Zeno effect. Dynamical and geometrical conditional phase gates are suggested. This method provides fidelity and a success rate of its gates very close to unity. Hence, it is suitable for performing quantum computation.Comment: 4 pages, 5 figures, REVTEX, second part modified, typos correcte

Decarbonizing the EU energy system by 2050: an important role for BECCS

This article examines the implications for the EU’s energy system if an 80% reduction in CO2 emissions is to be achieved by 2050 against 1990 levels, using the European TIMES Model (ETM-UCL) to project a least-cost pathway that meets this CO2 constraint (‘Policy Success’), along with milestone targets for 2020. A Reference scenario (no CO2 constraints post-2020) was analysed to allow for comparison. The key conclusions are as follows: (a) the achievement of negative emissions in the power sector via the use of biomass with carbon capture and storage (BECCS) allows for much more limited decarbonization in the buildings and transport sectors; (b) CCS is also extensively used for decarbonization of the industrial sector; (c) because of the absence in the model of options for transport mode-switching and building fabric efficiency improvements, the transport and buildings sectors achieve relatively little abatement by 2050 – the inclusion of these options could considerably reduce the need for BECCS and the cost of abatement; (d) decarbonization of the EU’s energy system by 2050 would increase energy system costs by 14% compared to a Reference scenario with no CO2 constraints; and (e) average EU-wide marginal CO2 abatement costs in Policy Success reach $300/tCO2 in 2050. Such a value is within the (wide) range of marginal carbon prices produced by comparable scenarios in other studies. / Policy relevance: The EU has set itself a target of reducing its greenhouse gas emissions by at least 80% by 2050, against 1990 levels. This will require a reduction of at least 80% in CO2 emissions from the energy system. This article, using results from the European TIMES Model (ETM-UCL), demonstrates that in the absence of significant decarbonization in the buildings and road transport sectors, substantial negative emissions in the power sector must be achieved, through as-yet unproven technologies (involving BECCS) . Therefore, a comprehensive strategy to reduce emissions across all energy-using sectors is required if this outcome is to be avoided. In addition, this article adds further evidence to the notion that substantial decarbonization of the EU’s energy system may be achieved through a relatively small additional investment above that required anyway