6,438 research outputs found
Outsourcing labour to the cloud
Various forms of open sourcing to the online population are establishing themselves as cheap, effective methods of getting work done. These have revolutionised the traditional methods for innovation and have contributed to the enrichment of the concept of 'open innovation'. To date, the literature concerning this emerging topic has been spread across a diverse number of media, disciplines and academic journals. This paper attempts for the first time to survey the emerging phenomenon of open outsourcing of work to the internet using 'cloud computing'. The paper describes the volunteer origins and recent commercialisation of this business service. It then surveys the current platforms, applications and academic literature. Based on this, a generic classification for crowdsourcing tasks and a number of performance metrics are proposed. After discussing strengths and limitations, the paper concludes with an agenda for academic research in this new area
Geometric derivation of the microscopic stress: a covariant central force decomposition
We revisit the derivation of the microscopic stress, linking the statistical mechanics of particle systems and continuum mechanics. The starting point in our geometric derivation is the Doyle-Ericksen formula, which states that the Cauchy stress tensor is the derivative of the free-energy with respect to the ambient metric tensor and which follows from a covariance argument. Thus, our approach to define the microscopic stress tensor does not rely on the statement of balance of linear momentum as in the classical Irving-Kirkwood-Noll approach. Nevertheless, the resulting stress tensor satisfies balance of linear and angular momentum. Furthermore, our approach removes the ambiguity in the definition of the microscopic stress in the presence of multibody interactions by naturally suggesting a canonical and physically motivated force decomposition into pairwise terms, a key ingredient in this theory. As a result, our approach provides objective expressions to compute a microscopic stress for a system in equilibrium and for force-fields expanded into multibody interactions of arbitrarily high order. We illustrate the proposed methodology with molecular dynamics simulations of a fibrous protein using a force-field involving up to 5-body interactions
Nuevos datos sobre la sedimentaciĂłn terciaria en La Mancha (Ciudad Real)
Los datos obtenidos de la investigaciĂłn geofĂsica y perforaciĂłn de sondeos en la parte occidental de La Mancha han permitido determinar la estructura del sustrato del NeĂłgeno: un conjunto de fosas controladas por fallas, que se generaron en periodos de tectĂłnica distensiva. Se han separado tres unidades litoestratigrĂĄficas: Unidad detrĂtica de la base, Unidad lutĂtica roja intermedia y Unidad carbonatada superior
Nondiffractive sonic crystals
We predict theoretically the nondiffractive propagation of sonic waves in
periodic acoustic media (sonic crystals), by expansion into a set of plane
waves (Bloch mode expansion), and by finite difference time domain calculations
of finite beams. We also give analytical evaluations of the parameters for
nondiffractive propagation, as well as the minimum size of the nondiffractively
propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A
Retrograde filling material in periapical surgery: a systematic review
Background: Periapical surgery focuses on the treatment of teeth with persistent periapical lesions when orthograde root canal treatment fails. Although MTAÂź is the gold standard material for retrograde filling, BiodentineÂź - a tricalcium silicate-based cement - has been proposed in order to resolve several of its limitations. A systematic review has been carried out to compare the physicochemical properties of BiodentineÂź versus MTAÂź as root-end filling material in periapical surgery. Material and methods: An electronic search was conducted by two independent examiners during March 2020 in the Cochrane, PubMed-MEDLINE and Scopus databases. In addition, a manual search was made in specialized journals. Comparative human or in vitro studies that evaluated bond strength, the presence of marginal gap and sealing ability were included. No restriction on publication date was applied. Animal studies, clinical cases, cases series and expert opinions were excluded. Results: After analyzing 147 initially selected studies, 13 publications were included. Regarding bond strength, the studies seemed to evidence better performance of BiodentineÂź in both acidic and blood contaminated environments. In relation to the presence of marginal gap and sealing ability, the studies yielded contradictory results. According to some authors, the sealing ability of BiodentineÂź is greater than that of MTAÂź during the first 24 hours, though both materials prove equal after one week. Other authors recorded no significant differences. Conclusions: Considering the limitations and heterogeneity of the studies included, there is not sufficient evidence to confirm the clinical superiority of BiodentineÂź as a root-end filling material in periapical surgery
Combined molecular/continuum modeling reveals the role of friction during fast unfolding of coiled-coil proteins
Coiled-coils are filamentous proteins that form the basic building block of important force-bearing cellular elements, such as intermediate filaments and myosin motors. In addition to their biological importance, coiled-coil proteins are increasingly used in new biomaterials including fibers, nanotubes, or hydrogels. Coiled-coils undergo a structural transition from an a-helical coil to an unfolded state upon extension, which allows them to sustain large strains and is critical for their biological function. By performing equilibrium and out-of-equilibrium all-atom molecular dynamics (MD) simulations of coiledcoils in explicit solvent, we show that two-state models based on Kramers’ or Bell’s theories fail to predict the rate of unfolding at high pulling rates. We further show that an atomistically informed continuum rod model accounting for phase transformations and for the hydrodynamic interactions with the solvent can reconcile two-state models with our MD results. Our results show that frictional forces, usually neglected in theories of fibrous protein unfolding, reduce the thermodynamic force acting on the interface, and thus control the dynamics of unfolding at different pulling rates. Our results may help interpret MD simulations at high pulling rates, and could be pertinent to cytoskeletal networks or protein-based artificial materials subjected to shocks or blasts
On the interaction between Autonomous Mobility-on-Demand systems and the power network: models and coordination algorithms
We study the interaction between a fleet of electric, self-driving vehicles
servicing on-demand transportation requests (referred to as Autonomous
Mobility-on-Demand, or AMoD, system) and the electric power network. We propose
a model that captures the coupling between the two systems stemming from the
vehicles' charging requirements and captures time-varying customer demand and
power generation costs, road congestion, battery depreciation, and power
transmission and distribution constraints. We then leverage the model to
jointly optimize the operation of both systems. We devise an algorithmic
procedure to losslessly reduce the problem size by bundling customer requests,
allowing it to be efficiently solved by off-the-shelf linear programming
solvers. Next, we show that the socially optimal solution to the joint problem
can be enforced as a general equilibrium, and we provide a dual decomposition
algorithm that allows self-interested agents to compute the market clearing
prices without sharing private information. We assess the performance of the
mode by studying a hypothetical AMoD system in Dallas-Fort Worth and its impact
on the Texas power network. Lack of coordination between the AMoD system and
the power network can cause a 4.4% increase in the price of electricity in
Dallas-Fort Worth; conversely, coordination between the AMoD system and the
power network could reduce electricity expenditure compared to the case where
no cars are present (despite the increased demand for electricity) and yield
savings of up $147M/year. Finally, we provide a receding-horizon implementation
and assess its performance with agent-based simulations. Collectively, the
results of this paper provide a first-of-a-kind characterization of the
interaction between electric-powered AMoD systems and the power network, and
shed additional light on the economic and societal value of AMoD.Comment: Extended version of the paper presented at Robotics: Science and
Systems XIV, in prep. for journal submission. In V3, we add a proof that the
socially-optimal solution can be enforced as a general equilibrium, a
privacy-preserving distributed optimization algorithm, a description of the
receding-horizon implementation and additional numerical results, and proofs
of all theorem
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