National Air Traffic Services

National Air Traffic Services (NATS) are concerned with ensuring low probabilities of errors in determining aircraft positions. In general, error probabilities depend on the tails of some probability distributions for which there has been no theoretical model. Analysis of radar performance is regularly undertaken by NATS to ensure radar performance is within safety limits, with the maximum range being dependent on the declared separation between aircraft. NATS brought two questions to the Study Group, involving the horizontal (azimuthal) errors in radar data and the vertical errors in altimetry system data. In both cases, NATS asked the Study Group to analyse the data and assess whether the probability distributions that are currently used are good models for the errors

Mathematical and numerical modelling of peristaltic flow and absorption in the small intestine

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Amphibole compositional trends in oversaturated and undersaturated alkaline plutonic ring-complexes

ABsrRAcr Amphiboles from different alkaline ring-complexes, representing both silica-oversaturated and silica-undersaturated petrographic associations, have been studied in relation to their host rocks. Textural, optical and chemical evidence emphasizes major amphibole compositional trends related to host-rock chemistry. In rocks whose agpaitic coefficient is less than 0.9, the Ca + Alt" content of amphiboles is more than 2.5, whereas it is less than 2.5 in agpaitic rocks (NazO*K2O,/ALO" > 0.9). This feature is shown firstly by the presence of solid-solution series from kaersutite to hornblende or hastingsite with substitutions I Ti € NaAAl. Ti + O <+ Fe3* + OH-and CaAl <= NaSi predominating in silica-undersaturated rock series and NaAl = n Si in basic and intermediate rocks from silica-oversaturated series. Secondly, this feature is shown by tbe presence of solid-solution series from actinolite or barroisite to winchite. with CaA|" P Na Si substitution or to katophorite, richterite and then arfvedsonite with balanced substitutions as n Fes" c> NaFe2+ and CaAlt" <2 Na Si. The first trends are related to early magmatic stages, and the second to late magmatic stages. The absence of (Ca + Alb)-rich amphiboles in agpaitic rocks and an observed break between (Ca + Alr")-rich amphiboles and (Ca .-1-Ali")-poor amphiboles suggest that (Ca + Alt')-rich amphibole stability is controlled by magma alkalinity. One argument is based on the description of a reaction, involving hastingsite and a residual liquid, which results in the crystallization of clinopyroxene and Ti-magnetite, and in the addition of potential analcime to the residual liquid. This alkalinization of the liquid ultimately produces a peralkaline concentrate

A Spherical Model for "Starless" Cores of Magnetic Molecular Clouds and Dynamical Effects of Dust Grains

In the standard picture of isolated star formation, dense ``starless'' cores are formed out of magnetic molecular clouds due to ambipolar diffusion. Under the simplest spherical geometry, I demonstrate that ``starless'' cores formed this way naturally exhibit a large scale inward motion, whose size and speed are comparable to those detected recently by Taffala et al. and Williams et al. in ``starless'' core L1544. My model clouds have a relatively low mass (of order 10 $M_\odot$) and low field strength (of order 10 $\mu$G) to begin with. They evolve into a density profile with a central plateau surrounded by a power-law envelope, as found previously. The density in the envelope decreases with radius more steeply than those found by Mouschovias and collaborators for the more strongly magnetized, disk-like clouds. At high enough densities, dust grains become dynamically important by greatly enhancing the coupling between magnetic field and the neutral cloud matter. The trapping of magnetic flux associated with the enhanced coupling leads, in the spherical geometry, to a rapid assemblage of mass by the central protostar, which exacerbates the so-called ``luminosity problem'' in star formation.Comment: 27 pages, 4 figures, accepted by Ap

safety run in evaluation of the phase i trial of trifluridine tipiracil ftd tpi in combination with oxaliplatin and a monoclonal antibody bevacizumab or nivolumab in patients pts with metastatic colorectal cancer mcrc

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Probing the evolutionary status of starless cores through N2H+ and N2D+ observations

We have undertaken a survey of N2H+ and N2D+ towards 31 low-mass starless cores using the IRAM 30m telescope. Our main objective has been to determine the abundance ratio of N2D+ and N2H+ towards the nuclei of these cores and thus to obtain estimates of the degree of deuterium enrichment, a symptom of advanced chemical evolution according to current models. We find that the N(N2D+)/N(N2H+) ratio is larger in more "centrally concentrated cores" with larger peak H2 and N2H+ column density than the sample mean. The deuterium enrichment in starless cores is presently ascribed to depletion of CO in the high density (> 3*10^4 cm-3) core nucleus. To substantiate this picture, we compare our results with observations in dust emission at 1.2 mm and in two transitions of C18O. We find a good correlation between deuterium fractionation and N(C18O)/N(H2) for the nuclei of 14 starless cores. We, thus, identified a set of properties that characterize the most evolved, or "pre-stellar", starless cores. These are: higher N2H+ and N2D+ column densities, higher N(N2D+)/N(N2H+), more pronounced CO depletion, broader N2H+ lines with infall asymmetry, higher central H2 column densities and a more compact density profile than in the average core. We conclude that this combination of properties gives a reliable indication of the evolutionary state of the core. Seven cores in our sample (L1521F, OphD, L429, L694, L183, L1544 and TMC2) show the majority of these features and thus are believed to be closer to forming a protostar than are the other members of our sample. Finally, we note that the subsample of Taurus cores behaves more homogeneously than the total sample, an indication that the external environment could play an important role in the core evolution.Comment: 42 pages, 17 figures, 12 tables, published in ApJ. Figures 8 to 15 available in gif format; full resolution version can be downloaded at http://cfa-www.harvard.edu/~acrapsi/publications/ Replaced with final version as published on the journa

Far-infrared to millimeter astrophysical dust emission I: A model based on physical properties of amorphous solids

We propose a new description of astronomical dust emission in the spectral region from the Far-Infrared to millimeter wavelengths. Unlike previous classical models, this description explicitly incorporates the effect of the disordered internal structure of amorphous dust grains. The model is based on results from solid state physics, used to interpret laboratory data. The model takes into account the effect of absorption by Disordered Charge Distribution, as well as the effect of absorption by localized Two Level Systems. We review constraints on the various free parameters of the model from theory and laboratory experimental data. We show that, for realistic values of the free parameters, the shape of the emission spectrum will exhibit very broad structures which shape will change with the temperature of dust grains in a non trivial way. The spectral shape also depends upon the parameters describing the internal structure of the grains. This opens new perspectives as to identifying the nature of astronomical dust from the observed shape of the FIR/mm emission spectrum. A companion paper will provide an explicit comparison of the model with astronomical data.Comment: accepted in A&A, 21 pages, 9 figure

The Second Data Release of the Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg2 of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ≈ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 Å at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them