Analysis and Modeling of Ground Operations at Hub Airports

Building simple and accurate models of hub airports can considerably help one understand airport dynamics, and may provide quantitative estimates of operational airport improvements. In this paper, three models are proposed to capture the dynamics of busy hub airport operations. Two simple queuing models are introduced to capture the taxi-out and taxi-in processes. An integer programming model aimed at representing airline decision-making attempts to capture the dynamics of the aircraft turnaround process. These models can be applied for predictive purposes. They may also be used to evaluate control strategies for improving overall airport efficiency.This research was supported in part by Honeywell, by an MIT teaching fellowship, and by NASA under grant NAG 2-1128 and through the National Center of Excellence for Aviation Operations Research (NEXTOR)

Bio-catalyzed electrode reactions: from biocorrosion to biofuel celles

International audienceWhereas corrosion of metallic materials by bacteria is a process dreaded by metallurgists, the mechanisms of such corrosion, involving specific biofilms or enzymes as they do, are of great interest as regards fuel cells. Indeed, developing biofilms or adding enzymes having the ability to reproduce biocorrosion phenomena enables enhanced rates to be achieved for the reactions occurring at the anode and cathode areas of metallic materials leading to biocorrosion. Bio-catalyzed reactions at the anode and cathode are nearly identical in microbial fuel cells leading to electricity production. Demonstration of such biocatalysis processes on conductor materials hints at new prospects, with the highlighting of an electrochemical connection between materials and microorganisms. Biofilms, owing to the bacteria and/or enzymes they contain, are electrochemically active, thus conferring on conducting materials unexpected behavior, including corrosion protection effects

Nuclear corrosion and materials: achievements and challenges

International audienceCorrosion and material sciences face challenges which involved and still need increases of knowledge and understanding in light water nuclear power plants.In pressurized water reactors (PWRs), the performances of the two first barriers for the plant safety (cladding for the fuel and steam generator tubing for the primary circuit) have key importance and their performances have been improved through the better knowledge of their corrosion behaviors. This leads for cladding to the evolution of zirconium alloy composition with addition of niobium. Stress corrosion cracking of nickel base alloys has been a great challenge for PWRs which has been solved progressively by evolutions of Alloy 600 from Meal Annelled (MA) to thermally treated (TT) materials and then to evolution of the alloy composition with less nickel and more chromium (Alloy 690), based on corrosion results. SCC mechanisms are still in progress for a better prediction of the nickel base alloy susceptibility, linked to the extension of the service time of nuclear power plants from 40 years, as initially planned, to 60 years and probably more as expected now, In secondary circuits of PWRs, like for boiling water reactors, flow accelerated corrosion (FAC) has been and is still an industrial challenge linked to the design of the apparatus, thermohydraulics and water chemistry. The chemical composition of low alloyed steels (chromium content) is a major parameter for FAC. These 3 corrosion phenomena (general corrosion of cladding alloys, stress corrosion cracking of nickel base alloys and flow accelerated corrosion) sustain researches and developments to model corrosion phenomena at various scales, from atoms to components

Modeling the Images of Relativistic Jets Lensed by Galaxies with Different Mass Surface Density Distributions

The images of relativistic jets from extragalactic sources produced by gravitational lensing by galaxies with different mass surface density distributions are modeled. In particular, the following models of the gravitational lens mass distribution are considered: a singular isothermal ellipsoid, an isothermal ellipsoid with a core, two- and three-component models with a galactic disk, halo, and bulge. The modeled images are compared both between themselves and with available observations. Different sets of parameters are shown to exist for the gravitationally lensed system B0218+357 in multicomponent models. These sets allow the observed geometry of the system and the intensity ratio of the compact core images to be obtained, but they lead to a significant variety in the Hubble constant determined from the modeling results.Comment: 26 pages, 9 figures, will be published in the Astronomy Letters, 2011, v.37, N4, pp. 233-24

Gut microbiota-derived propionate reduces cancer cell proliferation in the liver

Peer reviewedPublisher PD

Cooperative coupling of ultracold atoms and surface plasmons

Cooperative coupling between optical emitters and light fields is one of the outstanding goals in quantum technology. It is both fundamentally interesting for the extraordinary radiation properties of the participating emitters and has many potential applications in photonics. While this goal has been achieved using high-finesse optical cavities, cavity-free approaches that are broadband and easy to build have attracted much attention recently. Here we demonstrate cooperative coupling of ultracold atoms with surface plasmons propagating on a plane gold surface. While the atoms are moving towards the surface they are excited by an external laser pulse. Excited surface plasmons are detected via leakage radiation into the substrate of the gold layer. A maximum Purcell factor of $\eta_\mathrm{P}=4.9$ is reached at an optimum distance of $z=250~\mathrm{nm}$ from the surface. The coupling leads to the observation of a Fano-like resonance in the spectrum.Comment: 9 pages, 4 figure

Numerical Modeling of Evanescent-Wave Atom Optics

We numerically solve the time-dependent Schrodinger equation for a two-level atom interacting with an evanescent light field. The atom may be reflected or diffracted. Using the experimental parameter values we quantitatively model the evanescent field dopplerons (velocity-tuned resonances) observed by Stenlake et al. [Phys. Rev. A 49, 16 (1994)]. Besides successfully modeling the experiment, our approach provides complementary insights to the usual solution of the time-independent Schrodinger equation. We neglect spontaneous emission

Role of AMP-activated protein kinase in regulating hypoxic survival and proliferation of mesenchymal stem cells

Aims Mesenchymal stem cells (MSCs) are widely used for cell therapy, particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity, critical elements for their survival and differentiation, have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and, more generally, to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation. Methods and results MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes, a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand, A-769662, a well-characterized AMPK activator, was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice, providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation, we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved, whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation. Conclusion MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation, p27 being involved in this regulatio

Methods for in-flight robustness evaluation

The goal of this program was to combine modern control concepts with new identification techniques to develop a comprehensive package for estimation of 'robust flutter boundaries' based on experimental data. The goal was to use flight data, combined with a fundamental physical understanding of flutter dynamics, to generate a prediction of flutter speed and an estimate of the accuracy of the prediction. This report is organized as follows: the specific contributions of this project will be listed first. Then, the problem under study will be stated and the general approach will be outlined. Third, the specific system under study (F- 18 SRA) will be described and a preliminary data analysis will be performed. Then, the various steps of the flutter boundary determination will be outlined and applied to tile F-18 SRA data and others