Remote chance of recontact

The ejection of appendages with uncertain drag characteristics presents a concern for eventual recontact. Recontact shortly after release can be prevented by avoiding ejection in a plane perpendicular to the velocity. For ejection tangential to the orbit, the likelihood of recontact within a year is high in the absence of drag and oblateness. The optimum direction of ejection of the thermal shield cable and an overestimate of the recontact probability are determined for the Cosmic Background Explorer (COBE) mission when drag, oblateness, and solar/lunar perturbations are present. The probability is small but possibly significant

A Graphical Model Formulation of Collaborative Filtering Neighbourhood Methods with Fast Maximum Entropy Training

Item neighbourhood methods for collaborative filtering learn a weighted graph over the set of items, where each item is connected to those it is most similar to. The prediction of a user's rating on an item is then given by that rating of neighbouring items, weighted by their similarity. This paper presents a new neighbourhood approach which we call item fields, whereby an undirected graphical model is formed over the item graph. The resulting prediction rule is a simple generalization of the classical approaches, which takes into account non-local information in the graph, allowing its best results to be obtained when using drastically fewer edges than other neighbourhood approaches. A fast approximate maximum entropy training method based on the Bethe approximation is presented, which uses a simple gradient ascent procedure. When using precomputed sufficient statistics on the Movielens datasets, our method is faster than maximum likelihood approaches by two orders of magnitude.Comment: ICML201

Social Network for Veterans

poster abstractThe purpose of the Social Network for Veterans is to find an informal method to help Veterans stay in contact, engage in social interaction, discover areas for assistance, develop an awareness of health behavior issues concerning Veterans. The Social Network for Veterans will use animated characters (avatars) similar to characters used in Second Life or Metaverse. The Social Network will be for Veterans only. It is a collective online shared space where the Veteran can explore, meet other Veterans, socialize and participate in activities as a group or individually while chatting in real-time. Veterans are more likely to seek help from other Veterans and with a Social Network in play Veterans can offer each other help and advice no matter where their location on the planet. The Social Network will offer informative games, pet therapy, music therapy etc., social interaction, help channels, help links, health information and other basic information while providing an entertaining, safe and pleasant atmosphere

Finito: A Faster, Permutable Incremental Gradient Method for Big Data Problems

Recent advances in optimization theory have shown that smooth strongly convex finite sums can be minimized faster than by treating them as a black box "batch" problem. In this work we introduce a new method in this class with a theoretical convergence rate four times faster than existing methods, for sums with sufficiently many terms. This method is also amendable to a sampling without replacement scheme that in practice gives further speed-ups. We give empirical results showing state of the art performance

SAGA: A Fast Incremental Gradient Method With Support for Non-Strongly Convex Composite Objectives

In this work we introduce a new optimisation method called SAGA in the spirit of SAG, SDCA, MISO and SVRG, a set of recently proposed incremental gradient algorithms with fast linear convergence rates. SAGA improves on the theory behind SAG and SVRG, with better theoretical convergence rates, and has support for composite objectives where a proximal operator is used on the regulariser. Unlike SDCA, SAGA supports non-strongly convex problems directly, and is adaptive to any inherent strong convexity of the problem. We give experimental results showing the effectiveness of our method.Comment: Advances In Neural Information Processing Systems, Nov 2014, Montreal, Canad

GOES-I/M ascent maneuvers from transfer orbit to station

The Geostationary Operational Environmental Satellite (GOES)-I/M station acquisition sequence consists nominally of three in-plane/out-of-plane maneuvers at apogee on the line of relative nodes and a small in-plane maneuver at perigee. Existing software to determine maneuver attitude, ignition time, and burn duration required modification to optimize the out-of-plane parts and admit the noninertial, three-axis stabilized attitude. The Modified Multiple Impulse Station Acquisition Maneuver Planning Program (SENARIO2) was developed from its predecessor, SCENARIO, to optimize the out-of-plane components of the impulsive delta-V vectors. Additional new features include commputation of short term J sub 2 perturbations and output of all premaneuver and postmaneuver orbit elements, coarse maneuver attitudes, propellant usage, spacecraft antenna aspect angles, and ground station coverage. The output data are intended to be used in the launch window computation and by the maneuver targeting computation (General Maneuver (GMAN) Program) software. The maneuver targeting computation in GMAN was modified to admit the GOES-I/M maneuver attitude. Appropriate combinations of ignition time, burn duration, and attitude enable any reasonable target orbit to be achieved

Guarding International Borders Against HIV: A Comparative Study in Futility

Back in 1985, when knowledge of HIV began to spread, governments reacted by passing immigration laws to restrict the entry of HIV positive individuals. These laws required such individuals to either declare their HIV status or undergo mandatory HIV testing to secure entry. As justification for these initiatives, many countries claimed to be preserving the public health and their domestic economy. The United States, China, and Russia are three countries that have had, or still have, some form of HIV immigration restrictions. Initially, it may seem logical that preventing HIV positive individuals from entering a country will cut down on the spread of HIV and save the economy from health care costs. Nevertheless, an analysis of the HIV travel restrictions of these three countries will show that the public health and economic reasoning behind such laws is flawed because HIV is not spread by casual contact and because economic goals can be accomplished with less restrictive means. Moreover, this article will further reveal that HIV travel restrictions contribute to several health concerns and create issues with confidentially and stigmatization. In the end, a comparative analysis of these three countries, with specific attention paid to their successes and failures, reveals that the best system is one that works on both an international and domestic level. On the international level, border *90 testing must be voluntary, confidential, and informed. It should also utilize pre and post test counseling, and not be used to restrict entry. On the domestic level, individual countries need to educate the public and create programs to address high-risk groups responsible for the rapid spread of HIV. In doing so, society will find not only that it is more effectively protecting itself from the spread of HIV, but also that it is protecting the HIV community from the stigma and discrimination that contributed to the rapid spread of HIV in the first place