94,502 research outputs found
The inside-out view on neutron-star magnetospheres
No full textWe construct hydromagnetic neutron star equilibria which allow for a non-zero electric current distribution in the exterior. The novelty of our models is that the neutron star's interior field is in equilibrium with its magnetosphere, thus bridging the gap between previous work in this area, which either solves for the interior assuming a vacuum exterior or solves for the magnetosphere without modelling the star itself. We consider only non-rotating stars in this work, so our solutions are most immediately applicable to slowly rotating systems such as magnetars. Nonetheless, we demonstrate that magnetospheres qualitatively resembling those expected for both magnetars and pulsars are possible within our framework. The ‘inside-out’ approach taken in this paper should be more generally applicable to rotating neutron stars, where the interior and exterior regions are again not independent but evolve together
Magnetic fields in axisymmetric neutron stars
No full textWe derive general equations for axisymmetric Newtonian magnetohydrodynamics and use these as the basis of a code for calculating equilibrium configurations of rotating magnetized neutron stars in a stationary state. We investigate the field configurations that result from our formalism, which include purely poloidal, purely toroidal and mixed fields. For the mixed-field formalism, the toroidal component appears to be bounded at less than 7 per cent. We calculate distortions induced both by magnetic fields and by rotation. From our non-linear work, we are able to look at the realm of validity of perturbative work: we find for our results that perturbative-regime formulae for magnetic distortions agree to within 10 per cent of the non-linear results if the ellipticity is less than 0.15 or the average field strength is less than 10^17 G. We also consider how magnetized equilibrium structures vary for different polytropic indices
Adopt a moratorium on heritable genome editing
No full textEric Lander, Françoise Baylis, Feng Zhang, Emmanuelle Charpentier, Paul Berg and specialists from seven countries call for an international governance framework
RSS James Clark Ross Cruise 221, 26 May – 05 Jun 2010. PAP observatory development
No full textThis very short cruise was primarily to deploy a novel moored observatory at PAP (NE Atlantic), a long term study site at which a variety of observations have been made over the past 20 years with increasing levels of intensity and sophistication. This new design was in collaboration with the UK Met Office.In addition to this, a benthic lander was to be deployed which would transmit data by an acoustic link to the surface buoy and hence to land by satellite link. Unfortunately this was lost due to an imploding sphere.A number of equipment trials were also carried out to good effect. In addition studies were made on the effects of high CO2 of calcifying phytoplankton. A team of photographers were present to in order to increase public awareness of observational oceanography and numerous interviews were completed. In addition a daily web diary was maintained by the EuroSITES outreach team
Battery and Fuel Cell Development Goals for the Lunar Surface and Lander
No full textNASA is planning a return to the moon and requires advances in energy storage technology for its planned lunar lander and lunar outpost. This presentation describes NASA s overall mission goals and technical goals for batteries and fuel cells to support the mission. Goals are given for secondary batteries for the lander s ascent stage and suits for extravehicular activity on the lunar surface, and for fuel cells for the lander s descent stage and regenerative fuel cells for outpost power. An overall approach to meeting these goals is also presented
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Descent, Touchdown and Repositioning of a hopping planetary lander on Enceladus
No full textThis report deals with the design of a complete guidance, navigation and control system for a planetary lander on Enceladus, for both descent and repositioning. A basic lander model with a main engine, attitude thrusters and a landing gear is presented, for which the equations of motion in different reference frames are derived, including the effects of third body perturbations and non-homogeneous gravity fields. The guidance system incorporates a gravity-turn guidance logic for a flat and a spherical moon model for the initial descent phase, a quadratic guidance logic for both pinpoint landing and repositioning, a velocity nullifying logic for the terminal guidance phase and a ballistic guidance logic for a more fuel-efficient repositioning. The control system consists of a linear quaternion controller combined with a pulse-width-pulse-frequency modulator. The navigation system is build around an Inertial Measurement Unit with an extended Kalman filter to fuse the attitude and position measurements. The on-board software incorporates a basic hazard avoidance system, which uses a simulated LIDAR scan of the target area to generate a hazard map. The retargeting is based on a reachability and fuel consumption analysis. The spacecraft is capable of fully autonomous landings. This guidance, navigation and control system is combined in a simulation software written in C++ to test the system performance in presence of various error sources. All program elements have been tested with results from literature. The Monte Carlo simulations of the full GNC system include variances of the lander's state vector and of the GNC configuration parameters. The success rate is 90% for the descent phase, and 98% for the repositioning phase. The mean landing precision is in the order of 1m, with velocity and pointing errors of 0.2 m/s and 1.4°, respectively. Stricter requirements on the lander's mass distribution, and the implementation of a feedback velocity nullifying guidance scheme can increase the mission success rate even further. The thesis work shows, that a landing mission to Enceladus is possible with current technology. The Enceladus Lander Simulator is comprehensive software package for descent and repositioning simulations, and its modularity allows extensions in the future.Astrodynamics and Space MissionsEarth Observation and Space SystemsAerospace Engineerin
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Benthic fluxes measured with a lander at station USC-SC
No full textBenthic fluxes measured with a lander at station USC-S
Securing XML documents with author-X
No full textAuthor-X is a Java-based system that addresses the security issues of access control and policy design for XML document administration. Author-X supports the specification of policies at varying granularity levels and the specification of user credentials as a way to enforce access control. Access control is available according to both push and pull document distribution policies, and document updates are distributed through a combination of hash functions and digital signature techniques. The Author-X approach to distributed updates allows a user to verify a document's integrity without contacting the document server
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