Ground-based time-guidance algorithm for control of airplanes in a time-metered air traffic control environment: A piloted simulation study

The rapidly increasing costs of flight operations and the requirement for increased fuel conservation have made it necessary to develop more efficient ways to operate airplanes and to control air traffic for arrivals and departures to the terminal area. One concept of controlling arrival traffic through time metering has been jointly studied and evaluated by NASA and ONERA/CERT in piloted simulation tests. From time errors attained at checkpoints, airspeed and heading commands issued by air traffic control were computed by a time-guidance algorithm for the pilot to follow that would cause the airplane to cross a metering fix at a preassigned time. These tests resulted in the simulated airplane crossing a metering fix with a mean time error of 1.0 sec and a standard deviation of 16.7 sec when the time-metering algorithm was used. With mismodeled winds representing the unknown in wind-aloft forecasts and modeling form, the mean time error attained when crossing the metering fix was increased and the standard deviation remained approximately the same. The subject pilots reported that the airspeed and heading commands computed in the guidance concept were easy to follow and did not increase their work load above normal levels

C1,αC^{1,\alpha} regularity of solutions of degenerate fully non-linear elliptic equations

In the present paper, a class of fully non-linear elliptic equations are considered, which are degenerate as the gradient becomes small. H\"older estimates obtained by the first author (2011) are combined with new Lipschitz estimates obtained through the Ishii-Lions method in order to get $C^{1,\alpha}$ estimates for solutions of these equations.Comment: Submitte

Repeated games for eikonal equations, integral curvature flows and non-linear parabolic integro-differential equations

The main purpose of this paper is to approximate several non-local evolution equations by zero-sum repeated games in the spirit of the previous works of Kohn and the second author (2006 and 2009): general fully non-linear parabolic integro-differential equations on the one hand, and the integral curvature flow of an interface (Imbert, 2008) on the other hand. In order to do so, we start by constructing such a game for eikonal equations whose speed has a non-constant sign. This provides a (discrete) deterministic control interpretation of these evolution equations. In all our games, two players choose positions successively, and their final payoff is determined by their positions and additional parameters of choice. Because of the non-locality of the problems approximated, by contrast with local problems, their choices have to "collect" information far from their current position. For integral curvature flows, players choose hypersurfaces in the whole space and positions on these hypersurfaces. For parabolic integro-differential equations, players choose smooth functions on the whole space

On the Numerical Approximations of an Optimal Correction Problem

The numerical solution of an optimal correction problem for a damped random linear oscillator is studied. A numerical algorithm for the discretized system of the associated dynamic programming equation is given. To initiate the computation, we adopt a numerical scheme derived from the deterministic version of the problem. Next, a correction-type algorithm based on a discrete maximum principle is introduced to ensure the convergence of the iteration procedure

Are dentists enough aware of infectious risk associated with dental unit waterlines?

Environmental conditions in DU encourage biofilm development. This biofilm may represent a risk for patients and dental staff exposed to water and aerosols generated during dental cares, particularly for immunocompromised persons. A survey was conducted on the 175 dental surgeons of the department of Vienne (France) to investigate the motivations of dental practitioners to renew their DU, their awareness levels with respect to infectious risks related to water circulating within DU, and methods used for the maintenance of DU waterlines. These dentists were only partially aware of the need for maintaining DU waterlines. For this maintaining, chemical treatments and purges of pipes were carried out by 88% and 91.5% of dentists respectively ; chemical treatments were usually on a continous mode and dentists seemed to have complete confidence in their DU supplier regarding the choice and the use of chemical treatments. Flushes were performed only once per day in most cases (63%). This survey also highlighted that dentists were not enough aware of water related infectous risk, even though 68% estimated that the development of a biofilm within DU waterlines was an actual risk. Finally, very positively, dentists strongly indicated their wish to be more informed regarding all these risks. Although these results are based on a relatively small sample, corresponding to dentists of a French department, they clearly suggest that awareness of dental surgeons is still insufficient and must be performed to permit an effective prevention of infectious risk related to DU waterlines

V(RI)sub(c) Photometry of Cepheids in the Magellanic Clouds

We present V(RI)sub data for thirteen Cepheids in the Large Magellanic Cloud ans fifty-five in each wavelength band. The median uncertainty in the photometry iy Moffett, Gieren & Barnes (1998) which contained 1000 measures ($\pm 0.01$ mag) in each wavelength band on 22 variables with periods in the range 8--133 days.Comment: LaTeX file (9 pages), LaTeX table (1 page), 2 figures of 3 panels eacs PASP (July

The Search for Stellar Companions to Exoplanet Host Stars Using the CHARA Array

Most exoplanets have been discovered via radial velocity studies, which are inherently insensitive to orbital inclination. Interferometric observations will show evidence of a stellar companion if it sufficiently bright, regardless of the inclination. Using the CHARA Array, we observed 22 exoplanet host stars to search for stellar companions in low-inclination orbits that may be masquerading as planetary systems. While no definitive stellar companions were discovered, it was possible to rule out certain secondary spectral types for each exoplanet system observed by studying the errors in the diameter fit to calibrated visibilities and by searching for separated fringe packets.Comment: 26 pages, 5 tables, 8 figure

Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling

The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l'Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and non-monotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales