Physical Properties of (2) Pallas

We acquired and analyzed adaptive-optics imaging observations of asteroid (2) Pallas from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km (image scales 13-20 km/pix). We improve our determination of the size, shape, and pole by a novel method that combines our AO data with 51 visual light-curves spanning 34 years of observations as well as occultation data. The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky and light-curve behavior at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5 deg. of [long, lat] = [30 deg., -16 deg.] in the ECJ2000.0 reference frame, indicating a high obliquity of ~84 deg., leading to high seasonal contrast. The best triaxial-ellipsoid fit returns radii of a=275 km, b= 258 km, and c= 238 km. From the mass of Pallas determined by gravitational perturbation on other minor bodies [(1.2 +/- 0.3) x 10-10 Solar Masses], we derive a density of 3.4 +/- 0.9 g.cm-3 significantly different from the density of C-type (1) Ceres of 2.2 +/- 0.1 g.cm-3. Considering the spectral similarities of Pallas and Ceres at visible and near-infrared wavelengths, this may point to fundamental differences in the interior composition or structure of these two bodies. We define a planetocentric longitude system for Pallas, following IAU guidelines. We also present the first albedo maps of Pallas covering ~80% of the surface in K-band. These maps reveal features with diameters in the 70-180 km range and an albedo contrast of about 6% wrt the mean surface albedo.Comment: 16 pages, 8 figures, 6 table

Simultaneous NIR/sub-mm observation of flare emission from SgrA*

We report on a successful, simultaneous observation and modeling of the sub-millimeter to near-infrared flare emission of the Sgr A* counterpart associated with the super-massive black hole at the Galactic center. Our modeling is based on simultaneous observations that have been carried out on 03 June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and the LABOCA bolometer at the APEX telescope. Inspection and modeling of the light curves show that the sub-mm follows the NIR emission with a delay of 1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion of the source components.Comment: 12 pages, 9 figures, 3 tables, in press with A&

OBJECTIVE: a benchmark for object-oriented active database systems

Cataloged from PDF version of article.Although much work in the area of Active Database Management Systems (ADBMSs) has been done, it is not yet clear how the performance of an active DBMS can be evaluated systematically. In this paper, we describe the OBJECTIVE Benchmark for object-oriented ADBMSs, and present experimental results from its implementation in an active database system prototype. OBJECTIVE can be used to identify performance bottlenecks and active functionalities of an ADBMS, and to compare the performance of multiple ADBMSs. (C) 1999 Published by Elsevier Science Inc. All rights reserved

A language and an execution model for the detection of active situations

This paper presents a thesis about a language and an execution model for the detection of situations aimed at reducing the complexity of active applications. This work has been motivated by the observation that in many cases, there is a gap between current tools that enable to react to a single event (following the ECA: Event – condition – action paradigm), and the reality, in which a single event may not require any reaction, however the reaction should be given to patterns over the event history. The concept of situation presented in this paper, extends the concept of composite event, in its expressive power, flexibility, and usability. This paper motivates the work, surveys other efforts in this are, and presents preliminary ideas for both the language and the execution model

Collaborative software agents support for the texpros document management system

This dissertation investigates the use of active rules that are embedded in markup documents. Active rules are used in a markup representation by integrating Collaborative Software Agents with TEXPROS (abbreviation for TEXt PROcessing System) [Liu and Ng 1996] to create a powerful distributed document management system. Such markup documents with embedded active rules are called Active Documents. For fast retrieval purposes, when we need to generate a customized Internet folder organization, we first define the Folder Organization Query Language (FO-QL) to solve data categorization problems. FO-QL defines the folder organization query process that automatically retrieves links of documents deposited into folders and then constructs a folder organization in either a centralized document repository or multiple distributed document repositories. Traditional documents are stored as static data that do not provide any dynamic capabilities for accessing or interacting with the document environment. The dynamic and distributed nature of both markup data and markup rules do not merely respond to requests for information, but intelligently anticipate, adapt, and actively seek ways to support the computing processes. This outcome feature conquers the static nature of the traditional documents. An Office Automation Definition Language (OADL) with active rules is defined for constructing the TEXPROS \u27s dual modeling approach and workflow events representation. Active Documents are such agent-supported OADL documents. With embedded rules and self-describing data features, Active Documents provide capability of collaborative interactions with software agents. Data transformation and data integration are both data processing problems but little research has focused on the markup documents to generate a versatile folder organization. Some of the research merely provides manual browsing in a document repository to find the right document. This browsing is time consuming and unrealistic, especially in multiple document repositories. With FO-QL, one can create a customized folder organization on demand

Big continuous data: dealing with velocity by composing event streams

International audienceThe rate at which we produce data is growing steadily, thus creating even larger streams of continuously evolving data. Online news, micro-blogs, search queries are just a few examples of these continuous streams of user activities. The value of these streams relies in their freshness and relatedness to on-going events. Modern applications consuming these streams need to extract behaviour patterns that can be obtained by aggregating and mining statically and dynamically huge event histories. An event is the notification that a happening of interest has occurred. Event streams must be combined or aggregated to produce more meaningful information. By combining and aggregating them either from multiple producers, or from a single one during a given period of time, a limited set of events describing meaningful situations may be notified to consumers. Event streams with their volume and continuous production cope mainly with two of the characteristics given to Big Data by the 5V’s model: volume & velocity. Techniques such as complex pattern detection, event correlation, event aggregation, event mining and stream processing, have been used for composing events. Nevertheless, to the best of our knowledge, few approaches integrate different composition techniques (online and post-mortem) for dealing with Big Data velocity. This chapter gives an analytical overview of event stream processing and composition approaches: complex event languages, services and event querying systems on distributed logs. Our analysis underlines the challenges introduced by Big Data velocity and volume and use them as reference for identifying the scope and limitations of results stemming from different disciplines: networks, distributed systems, stream databases, event composition services, and data mining on traces

Intrinsic Near-Infrared Properties of the Variable Source Sagittarius A*

This thesis on observational astronomy focuses on the highly variable near-infrared source Sagittarius A* (Sgr A*) at the center of the Milky Way, associated with the central super-massive black hole. It is divided in two parts: a comprehensive data description of Ks-band measurements of Sgr A*, covering the last seven years of observations with the Very Large Telescope and the state-of-the-art instrument NAOS/CONICA, and an effort in polarimetric instrumentation, the calibration of the instrumental polarization properties of NAOS/CONICA in the Ks-band. In the first part I characterize the statistical properties of the near-infrared variability of Sgr A*, the electromagnetic manifestation of the Galactic Center super-massive black hole, and find the flux density to be power-law distributed. I cannot confirm the evidence of a two state process with different flux density distributions behind the variability, as reported in other publications. I find a linear rms-flux relation for the flux density range up to 12 mJy on a timescale of 24 minutes. This and the power- law flux density distribution imply a phenomenological, formally non-linear statistical variability model with which I can simulate the observed variability and extrapolate its behavior to higher flux levels and longer timescales. I can show that a bright outburst within the last 400 years, that has been discussed as the possible reason for the X- ray emission from massive molecular clouds surrounding the Galactic Center, can be expected as an extreme value of our statistics without the need for a cosmic event. I give arguments, why data with our time support cannot be used to decide on the question whether the power spectral density of the underlying random process shows more structure at timescales below 100 min compared to what is expected from a red noise random process, as discussed in the context of orbiting hot spots in the accretion flow of the black hole. In the second part I report on the results of calibrating and simulating the instrumental polarization properties of the Very Large Telescope adaptive optics camera system NAOS/CONICA (NACO) in the Ks-band. Here my goal was to understand the influence of systematic calibration effects on the time-resolved polarimetric observations of Sgr A*. I used the Stokes/Mueller formalism for metallic reflections to describe the instrumental polarization. The model is compared to standard-star observations and time-resolved observations of bright sources in the Galactic Center. I simulated the differences between calibration methods and tested their influence on three examples of polarimetric Ks-band light curves of Sgr A*. I find the instrumental polarization to be highly dependent on the pointing position of the telescope and about 4% at maximum. I report a polarization angle offset of 13.2° due to a position angle offset of the λ /2-wave plate with respect to the data-header value that affects the calibration of NACO data taken before autumn 2009. With the new model of the instrumental polarization of NACO it is possible to measure the polarization with an accuracy of 1% in polarization degree. The uncertainty of the polarization angle is ≤ 5° for polarization degrees ≥ 4%. For densely sampled polarimetric time series I find that the improved understanding of the polarization properties gives results that are consistent with the previously used method to derive the polarization of Sgr A*. The difference between the derived and the previously employed polarization calibration is well within the statistical uncertainties of the measurements, and for Sgr A* they do not affect the results from our relativistic modeling of the accretion process