A methodology for selective removal of orbital debris

Earth-orbiting objects, large enough to be tracked, were surveyed for possible systematic debris removal. Based upon the statistical collision studies of others, it was determined that objects in orbits approximately 1000 km above the Earth's surface are at greatest collisional risk. Russian C-1B boosters were identified as the most important target of opportunity for debris removal. Currently, more than 100 in tact boosters are orbiting the Earth with apogees between 950 km and 1050 km. Using data provided by Energia USA, specific information on the C-1B booster, in terms of rendezvous and capture strategies, was discussed

Radiation leukaemogenesis: is virus really necessary?

Generalized lymphosarcomatosis (leukaemia) of non-thymic type occurs in mice bearing 90Sr or 239Pu or 226Ra. Tumours passaged from such mice have been tested for tumour-associated transplantation antigens that could provoke a protective immunity which would be expected if such antigens were determined by virus activated by the irradiation. Sub-threshold doses of living syngeneic tumour, large doses of living allogeneic tumour and large doses of killed syngeneic tumour were without protective effect. This suggests that viruses observed electron micrographically in such tumours are passengers and not causative

Timed Consistent Network Updates

Network updates such as policy and routing changes occur frequently in Software Defined Networks (SDN). Updates should be performed consistently, preventing temporary disruptions, and should require as little overhead as possible. Scalability is increasingly becoming an essential requirement in SDN. In this paper we propose to use time-triggered network updates to achieve consistent updates. Our proposed solution requires lower overhead than existing update approaches, without compromising the consistency during the update. We demonstrate that accurate time enables far more scalable consistent updates in SDN than previously available. In addition, it provides the SDN programmer with fine-grained control over the tradeoff between consistency and scalability.Comment: This technical report is an extended version of the paper "Timed Consistent Network Updates", which was accepted to the ACM SIGCOMM Symposium on SDN Research (SOSR) '15, Santa Clara, CA, US, June 201

It Takes More Than an Apple a Day

http://dx.doi.org/10.1126/science.337.6101.146

On estimating tropical forest carbon dynamics in Papua New Guinea

One of the few initiatives to address ongoing global warming that did not completely stall at the UNFCCC climate change negotiations was the reduction emissions from deforestation and forest degradation (REDD). REDD has a focus on the forests of the tropics. Unfortunately forest mensuration in most tropical countries has been inadequate to accurately determine forest carbon stocks, much less the effects of land use and changes in land use on them (Houghton et al. 2009; Bryan et al. 2010a). Whilst tropical logging is known to be widespread, the exact areas of tropical forest subject to logging have not been accurately mapped (Asner et al. 2009) or mapped with sufficient regularity to provide adequate data on the areas subject to this activity. Biomass losses due to logging have usually been derived from limited plot data, or derived via various models from estimates of regional biomass and timber extraction volumes (Houghton et al. 2009) and thus encapsulate considerable uncertainty. For these reasons the carbon impact of tropical logging remains an open question, and one that needs to be closed before any international institutional arrangement considers promoting forms of timber extraction as a tool for controlling carbon emissions. Here, we examine the current state of forest carbon research in Papua New Guinea (PNG) to illustrate the problems that can arise by developing forest management policy prematurely from incomplete forest research

Affective Life and Cultural Economy: Payday Loans and the Everyday Space-Times of Credit-Debt in the UK

Analysing the affective geographies of digitally mediated payday loans in the UK, this paper advocates and exemplifies an approach to cultural economy that focuses on how economic worlds are affectively animated and lived. Supplementing the two versions of ‘culture’ that cultural economy approaches have to date been organised around – culture as signifying system, or culture as assembled effect ‐ we propose a cultural economy of everyday space‐times which is attuned to the affective composition of forms of living. Drawing on empirical work with forty users of digitally mediated payday loans, we employ this approach to trace how their loans become part of three intersecting forms of living: relief, as a pressing concern is deferred to the immediate future; separation, as private spaces are created within ordinary life and obligations are felt as individual responsibilities; and pressure, as demands to pay intensify the sense that debt is spiralling out of control and already ongoing precarity cannot be sustained. In conclusion, we pose further questions for a cultural economy approach orientated to the analysis of forms of living

The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel

We report new radial velocity observations of GP Vel/HD77581, the optical companion to the eclipsing X-ray pulsar Vela X-1. Using data spanning more than two complete orbits of the system, we detect evidence for tidally induced non-radial oscillations on the surface of GP Vel, apparent as peaks in the power spectrum of the residuals to the radial velocity curve fit. By removing the effect of these oscillations (to first order) and binning the radial velocities, we have determined the semi-amplitude of the radial velocity curve of GP Vel to be K_o=22.6+/-1.5 km/s. Given the accurately measured semi-amplitude of the pulsar's orbit, the mass ratio of the system is 0.081+/-0.005. We are able to set upper and lower limits on the masses of the component stars as follows. Assuming GP Vel fills its Roche lobe then the inclination angle of the system, i=70.1+/-2.6 deg. In this case we obtain the masses of the two stars as M_x=2.27 +/-0.17 M_sun for the neutron star and M_o=27.9+/-1.3 M_sun for GP Vel. Conversely, assuming the inclination angle is i=90 deg, the ratio of the radius of GP Vel to the radius of its Roche lobe is beta=0.89+/-0.03 and the masses of the two stars are M_x=1.88+/-0.13 M_sun and M_o=23.1+/-0.2 M_sun. A range of solutions between these two sets of limits is also possible, corresponding to other combinations of i and beta. In addition, we note that if the zero phase of the radial velocity curve is allowed as a free parameter, rather than constrained by the X-ray ephemeris, a significantly improved fit is obtained with an amplitude of 21.2+/-0.7 km/s and a phase shift of 0.033+/-0.007 in true anomaly. The apparent shift in the zero phase of the radial velocity curve may indicate the presence of an additional radial velocity component at the orbital period.Comment: Accepted for publication in Astronomy & Astrophysic

Many Roads to Synchrony: Natural Time Scales and Their Algorithms

We consider two important time scales---the Markov and cryptic orders---that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the epsilon-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the epsilon-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.Comment: 17 pages, 16 figures: http://cse.ucdavis.edu/~cmg/compmech/pubs/kro.htm. Santa Fe Institute Working Paper 10-11-02

Toward a Structure Determination Method for Biomineral-Associated Protein Using Combined Solid- State NMR and Computational Structure Prediction

SummaryProtein-biomineral interactions are paramount to materials production in biology, including the mineral phase of hard tissue. Unfortunately, the structure of biomineral-associated proteins cannot be determined by X-ray crystallography or solution nuclear magnetic resonance (NMR). Here we report a method for determining the structure of biomineral-associated proteins. The method combines solid-state NMR (ssNMR) and ssNMR-biased computational structure prediction. In addition, the algorithm is able to identify lattice geometries most compatible with ssNMR constraints, representing a quantitative, novel method for investigating crystal-face binding specificity. We use this method to determine most of the structure of human salivary statherin interacting with the mineral phase of tooth enamel. Computation and experiment converge on an ensemble of related structures and identify preferential binding at three crystal surfaces. The work represents a significant advance toward determining structure of biomineral-adsorbed protein using experimentally biased structure prediction. This method is generally applicable to proteins that can be chemically synthesized