732 research outputs found
Microprogram scheme for automatic recovery from computer error
Microprogram scheme enables computer to recover from failure in one of its two central processing units during time duration of instruction in which failure occurs. Microprogram advantages include - /1/ built-in interpretive capability, /2/ selection of processing interrupts by priority, and /3/ economical use of bootstrap sequence
Regional hydrology controls stream microbial biofilms: evidence from a glacial catchment
International audienceGlaciers are highly responsive to global warming and important agents of landscape heterogeneity. While it is well established that glacial ablation and snowmelt regulate stream discharge, linkage among streams and streamwater hydrogeochemistry, the controls of these factors on stream microbial biofilms remain insufficiently understood. We investigated glacial (metakryal, hypokryal), groundwater-fed (krenal) and snow-fed (rhithral) streams ? all of them representative for alpine stream networks ? and present evidence that these hydrologic and hydrogeochemical factors differentially affect sediment microbial biofilms. Average microbial biomass and bacterial carbon production were low in the glacial streams, whereas bacterial cell size, biomass, and carbon production were higher in the tributaries, most notably in the krenal stream. Whole-cell in situ fluorescence hybridization revealed reduced detection rates of the Eubacteria and higher abundance of ?-Proteobacteria in the glacial stream, a pattern that most probably reflects the trophic status of this ecosystem. Our data suggest low flow during the onset of snowmelt and autumn as a short period (hot moment) of favorable environmental conditions with pulsed inputs of allochthonous nitrate and dissolved organic carbon, and with disproportional high microbial growth. Krenal and rhithral streams with more constant and favorable environments serve as possible sources of microbes and organic matter to the main glacial channel during periods (e.g. snowmelt) of elevated hydrologic linkage among streams. Ice and snow dynamics have a crucial impact on microbial biofilms, and we thus need better understanding of the microbial ecology and enhanced consideration of critical hydrological episodes in future models predicting alpine stream communities
Forward Symplectic Integrators and the Long Time Phase Error in Periodic Motions
We show that when time-reversible symplectic algorithms are used to solve
periodic motions, the energy error after one period is generally two orders
higher than that of the algorithm. By use of correctable algorithms, we show
that the phase error can also be eliminated two orders higher than that of the
integrator. The use of fourth order forward time step integrators can result in
sixth order accuracy for the phase error and eighth accuracy in the periodic
energy. We study the 1-D harmonic oscillator and the 2-D Kepler problem in
great details, and compare the effectiveness of some recent fourth order
algorithms.Comment: Submitted to Phys. Rev. E, 29 Page
Mirror formation control in the vicinity of an asteroid
Two strategies are presented for the positioning and control of a spacecraft formation designed to focus sunlight onto a point on the surface of asteroid, thereby sublimating the material and ejecting debris creating thrust. In the first approach, the formation is located at artficial equilibrium points around the asteroid and controlled using the force from the solar radiation pressure. The second approach determines the optimal periodic formation orbits, subject to the gravitational perturbations from the asteroid, the solar radiation pressure and the control acceleration derived from a control law
A Tentative Modeling Study of the Effect of Wall Reactions on Oxidation Phenomena
This paper gives details of a tentative modeling study that investigates the
inhibiting effect of internal reactor walls treated with acid..
Benthic Biofilm Controls on Fine Particle Dynamics in Streams
Este artĂculo contiene 15 páginas, 7 figuras, 3 tablas.Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter
and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall
biomass in headwater streams, and they present a primary control on the transformation and export of
labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a
feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We
quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental
stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to
obtain a range of biofilm characteristics. Fluorescent, 8 mm particles were introduced to each flume, and
their concentrations in the water column were monitored over a 30 min period. We measured particle
concentrations using a flow cytometer and mesoscale (10 mm to 1 cm) biofilm structure using optical
coherence tomography. Particle deposition-resuspension dynamics were determined by fitting results to a
stochastic mobile-immobile model, which showed that retention timescales for particles within the
biofilm-covered streambeds followed a power-law residence time distribution. Particle retention times
increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest
that biofilm structural parameters are key predictors of particle retention in streams and rivers.This study was
funded by a Marie Curie Intra-
European Fellowship to WRH (FP7-
PEOPLE-2011-IEF-302297) and an
Austrian Science Fund grant to T.J.B.
(START Y420-B17). K.R.R. was
supported by a CUAHSI Pathfinder
fellowship and U.S. NSF Graduate
Research Fellowship. J.D.D. was
supported by a Fulbright-Spain
fellowship. The modeling effort was
supported by U.S. NSF grants EAR-
1215898 and EAR-1344280 to AIP.
Supporting data are provided at
doi:10.6084/m9.figshare.4252193.Peer reviewe
Accurate analytical approximation of asteroid deflection with constant tangential thrust
We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection mission
Pulsar Timing and its Application for Navigation and Gravitational Wave Detection
Pulsars are natural cosmic clocks. On long timescales they rival the
precision of terrestrial atomic clocks. Using a technique called pulsar timing,
the exact measurement of pulse arrival times allows a number of applications,
ranging from testing theories of gravity to detecting gravitational waves. Also
an external reference system suitable for autonomous space navigation can be
defined by pulsars, using them as natural navigation beacons, not unlike the
use of GPS satellites for navigation on Earth. By comparing pulse arrival times
measured on-board a spacecraft with predicted pulse arrivals at a reference
location (e.g. the solar system barycenter), the spacecraft position can be
determined autonomously and with high accuracy everywhere in the solar system
and beyond. We describe the unique properties of pulsars that suggest that such
a navigation system will certainly have its application in future astronautics.
We also describe the on-going experiments to use the clock-like nature of
pulsars to "construct" a galactic-sized gravitational wave detector for
low-frequency (f_GW ~1E-9 - 1E-7 Hz) gravitational waves. We present the
current status and provide an outlook for the future.Comment: 30 pages, 9 figures. To appear in Vol 63: High Performance Clocks,
Springer Space Science Review
Towards a framework for work package allocation for GSD
Proceeding of: Proceeding of: OTM 2011 Workshops: Confederated International Workshops and Posters: EI2N+NSF ICE, ICSP+INBAST, ISDE, ORM, OTMA, SWWS+MONET+SeDeS, and VADER 2011, Hersonissos, Crete, Greece, October 17-21, 2011Global software development is an inexorable trend in the software industry. The impact of the trend in conventional software development can be found in many of its aspects. One of them is task or work package allocation. Task allocation was traditionally driven by resource competency and availability but GSD introduces new complexities to this process including time-zones differences, costs and cultural differences. In this work a report on the construction of a framework for work-package allocation within GSD projects is presented. This framework lies on three main pillars: individual and organizational competency, organizational customization and sound assessment methods.This work is supported by the Spanish Centro para el Desarrollo
TecnolĂłgico Industrial (CDTI) under the Eureka Project E! 6244 PROPS-Tour and
the national cooperation project SEM-IDi (IDI-20091150)
On the Deterrent Effect of Individual Versus Collective Liability in Criminal Organizations
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