A Census of the Carina Nebula -- II. Energy Budget and Global Properties of the Nebulosity

The first paper in this series took a direct census of energy input from the known OB stars in the Carina Nebula, and in this paper we study the global properties of the surrounding nebulosity. We find that the total IR luminosity of Carina is about 1.2E7 Lsun, accounting for only about 50-60% of the known stellar luminosity from Paper I. Similarly, the ionizing photon luminosity -- (abridged; many important details omitted). Synchronized star formation around the periphery of Carina provides a strong case that star formation here was indeed triggered by stellar winds and UV radiation. This second generation appears to involve a cascade toward preferentially intermediate- and low-mass stars, but this may soon change when eta Car and its siblings explode. If the current reservoir of atomic and molecular gas can be tapped at that time, massive star formation may be rejuvinated around the periphery of Carina much as if it were a young version of Gould's Belt. Also, when these multiple SNe occur, the triggered second generation will be pelted repeatedly with SN ejecta bearing short-lived radioactive nuclides. Carina may therefore represent the most observable analog to the cradle of our own Solar System.Comment: MNRAS accepted, 14 pages, fig 1 in colo

Analysis and test evaluation of the dynamic response and stability of three advanced turboprop models

Results of dynamic response and stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. One model was also tested using a semi-span wing and fuselage configuration for response to realistic aircraft inflow. Stability tests were performed using tunnel turbulence or a nitrogen jet for excitation. Measurements are compared with predictions made using beam analysis methods for the model with straight blades, and finite element analysis methods for the models with swept blades. Correlations between measured and predicted rotating blade natural frequencies for all the models are very good. The IP dynamic response of the straight blade model is reasonably well predicted. The IP response of the swept blades is underpredicted and the wing induced response of the straight blade is overpredicted. Two models did not flutter, as predicted. One swept blade model encountered an instability at a higher RPM than predicted, showing predictions to be conservative

Low EUV Luminosities Impinging on Protoplanetary Disks

The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the EUV luminosity impinging on 14 disks around young (~2-10Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10$^{42}$ photons/s for all sources without jets and lower than $5 \times 10^{40}$ photons/s for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [NeII] 12.81 micron luminosities from three disks with slow [NeII]-detected winds. This indicates that the [NeII] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.Comment: Accepted for publication to The Astrophysical Journa

An Optimal Linear Time Algorithm for Quasi-Monotonic Segmentation

Monotonicity is a simple yet significant qualitative characteristic. We consider the problem of segmenting a sequence in up to K segments. We want segments to be as monotonic as possible and to alternate signs. We propose a quality metric for this problem using the l_inf norm, and we present an optimal linear time algorithm based on novel formalism. Moreover, given a precomputation in time O(n log n) consisting of a labeling of all extrema, we compute any optimal segmentation in constant time. We compare experimentally its performance to two piecewise linear segmentation heuristics (top-down and bottom-up). We show that our algorithm is faster and more accurate. Applications include pattern recognition and qualitative modeling.Comment: This is the extended version of our ICDM'05 paper (arXiv:cs/0702142

ASK FOR INFORMATION RETRIEVAL: PART II. RESULTS OF A DESIGN STUDY

In \u27ASK for Information Retrieval: Part P1, we discussed the theory and background to a design study for an information retrieval (IR) system based on the attempt to represent the anomalous states of knowledge (ASKs) underlying information needs. In Part 11, we report the methods and results of the design study, and our conclusions

ASK FOR INFORMATION RETRIEVAL: PART I. BACKGROUND AND THEORY

We report the results of a British Library Research and Development Department funded design study for an interactive information retrieval system which will determine structural representations of the anomalous states of knowledge (ASKs) underlying information needs, and attempt to resolve the anomalies through a variety of retrieval strategies performed on a database of documents represented in compatible structural formats. Part I discusses the background to the project and the theory underlying it, Part II (next issue) presents our methods, results and conclusions. Basic premises of the project were: that information needs are not in principle precisely specifiable; that it is possible to elicit problem statements from information system users from which representations of the ASK underlying the need can be derived; that there are classes of ASKs; and, that all elements of information retrieval systems ought to be based on the user\u27s ASK. We have developed a relatively freeform interview technique for eliciting problem statements, and a statistical word co-occurrence analysis for deriving network representations of the problem statements and abstracts. Structural characteristics of the representations have been used to determine classes of ASKs, and both ASK and information structures have been evaluated by, respectively, users and authors. Some results are: that interviewing appears to be a satisfactory technique for eliciting problem statements from which ASKs can be determined; that the statistical analysis produces structures which are generally appropriate both for documents and problem statements; that ASKs thus represented can be usefully classified according to their structural characteristics; and, that of thirty-five subjects, only two had ASKs for which traditional \u27best match\u27 retrieval would be intuitively appropriate. The results of the design study indicate that at least some of our premises are reasonable, and that an ASK-based information retrieval system is at least feasible

Magnetoresistance and magnetic breakdown in the quasi-two-dimensional conductors (BEDT-TTF)2_2MHg(SCN)4_4[M=K,Rb,Tl]

The magnetic field dependence of the resistance of (BEDT-TTF)$_2$MHg(SCN)$_4$[M=K,Rb,Tl] in the density-wave phase is explained in terms of a simple model involving magnetic breakdown and a reconstructed Fermi surface. The theory is compared to measurements in pulsed magnetic fields up to 51 T. The value implied for the scattering time is consistent with independent determinations. The energy gap associated with the density-wave phase is deduced from the magnetic breakdown field. Our results have important implications for the phase diagram.Comment: 5 pages, RevTeX + epsf, 3 figures. To appear in Physical Review B, Rapid Communications, September 15, 199

Comment on ``Two Time Scales and Violation of the Fluctuation-Dissipation Theorem in a Finite Dimensional Model for Structural Glasses''

In cond-mat/0002074 Ricci-Tersenghi et al. find two linear regimes in the fluctuation-dissipation relation between density-density correlations and associated responses of the Frustrated Ising Lattice Gas. Here we show that this result does not seem to correspond to the equilibrium quantities of the model, by measuring the overlap distribution P(q) of the density and comparing the FDR expected on the ground of the P(q) with the one measured in the off-equilibrium experiments.Comment: RevTeX, 1 page, 2 eps figures, Comment on F. Ricci-Tersenghi et al., Phys. Rev. Lett. 84, 4473 (2000