127,129 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Determining the optimum scan map strategy for Herschel-SPIRE using the SPIRE photometer simulator
No full textThe forthcoming Herschel space mission will provide an unprecedented view of the far-infrared/submillimetre Universe, with the SPIRE instrument covering the 200–670 μm wavelength range. To obtain the best quality of astronomical data from such an expensive mission the observing modes must be optimized as far as possible. This paper presents the possible scanning strategies that can be utilized by the SPIRE photometer, within the limitations imposed by the Herschel spacecraft. Each strategy is investigated for effectiveness by performing simulated observations, using the SPIRE photometer simulator. By quantifying the data quality using a simple metric, we have been able to select the optimum scanning strategy for SPIRE when it begins taking science data within the next couple of years.
Additionally, this work has led to the development of a specific SPIRE mapmaking algorithm, based on the CMB code MADmap, to be provided as part of the SPIRE data pipeline processing suite. This will allow every SPIRE user to take full advantage of the optimized scan map strategy, which requires the use of maximum likelihood mapmakers such as MADmap
In-flight calibration sources for Herschel-SPIRE
No full textSPIRE, the Spectral and Photometric Imaging Receiver, will be a bolometer instrument for ESA's Herschel satellite. The instrument comprises a three-band imaging photometer covering the 250-500 μm range, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 μm. This paper presents the requirements for and design of the photometer and spectrometer calibration/illumination sources, and the results of laboratory tests on prototypes. The photometer calibrator is an electrically heated thermal source of submillimetre radiation, the purpose of which is to provide a repeatable signal for in-flight monitoring of health and responsivity of the SPIRE photometer detectors. It is not required to provide absolute calibration or uniform illumination of the arrays, but it may be used as part of the overall calibration scheme. The spectrometer calibrator is located at a pupil at the second input port of the FTS. It is designed to enable matching of the telescope emission for a range of telescope temperature (60-90 K) and emissivity (2% - 10%). By matching the telescope emission at this port, the high background from the Herschel telescope emission can be nulled to a high degree, resulting in an interferogram in which the contribution from the astronomical source is not overwhelmed by the telescope offset. The flexibility for telescope matching inherent in the design is important, as the exact telescope parameters will be unknown until the satellite is in operation. The FTS calibrator will also be used to assist in the absolute calibration scheme for SPIRE FTS observations
Signatures of warm carbon monoxide in protoplanetary discs observed with Herschel SPIRE
No full textMHDvdW and DAN are supported by the Canadian Space Agency (CSA) and the Natural Sciences and Engineering Research Council of Canada (NSERC). IK, WFT and PW acknowledge funding from the European Union Seventh Framework Programme FP7-2011 under grant agreement no. 284405.Molecular gas constitutes the dominant mass component of protoplanetary discs. To date, these sources have not been studied comprehensively at the longest far-infrared and shortest submillimetre wavelengths. This paper presents Herschel SPIRE FTS spectroscopic observations toward 18 protoplanetary discs, covering the entire 450-1540 GHz (666-195 μm) range at v/Δv~400-1300. The spectra reveal clear detections of the dust continuum and, in six targets, a significant amount of spectral line emission primarily attributable to 12CO rotational lines. Other targets exhibit little to no detectable spectral lines. Low signal-to-noise detections also include signatures from 13CO, [CI] and HCN. For completeness, we present upper limits of non-detected lines in all targets, including low-energy transitions of H2O and CH+ molecules. The ten 12CO lines that fall within the SPIRE FTS bands trace energy levels of ~50-500 K. Combined with lower and higher energy lines from the literature, we compare the CO rotational line energy distribution with detailed physical-chemical models, for sources where these are available and published. Our 13CO line detections in the disc around Herbig Be star HD 100546 exceed, by factors of ~10-30, the values predicted by a model that matches a wealth of other observational constraints, including the SPIRE 12CO ladder. To explain the observed 12CO/13CO ratio, it may be necessary to consider the combined effects of optical depth and isotope selective (photo)chemical processes. Considering the full sample of 18 objects, we find that the strongest line emission is observed in discs around Herbig Ae/Be stars, although not all show line emission. In addition, two of the six T Tauri objects exhibit detectable 12CO lines in the SPIRE range.Peer reviewe
FIRST-SPIRE spectrometer: a novel imaging FTS for the submillimeter
No full textThe SPIRE instrument for the FIRST mission will consist of a three band imaging submillimeter photometer and a two band imaging Fourier Transform Spectrometer (FTS) optimized for the 200 - 400 micrometers range, and with extended coverage out to 670 micrometers. The FTS will be used for follow-up spectroscopic studies of objects detected in photometric surveys by SPIRE and other facilities, and to perform medium resolving power (R approximately 500 at 250 micrometers ) imaging spectroscopy on galactic and nearby extra-galactic sources
Erratum : Herschel/SPIRE observations of the TWA brown dwarf disc 2MASSW J1207334-393254
No full textWe have revised our analysis of the SPIRE observations of 2MASSW J1207334–393254 (2M1207). Recent PACS observations show a bright source located ∼25 arcsec east of 2M1207. There are issues in terms of the detection/non-detection of the bright source when comparing the Spitzer, WISE and PACS observations. The object's detection/non-detection is apparently inconsistent, perhaps due to variability or low signal-to-noise ratio of the data. We have looked into the possible misidentification of the target, and have revised the measured SPIRE fluxes and the disc parameters for 2M1207. We have also reviewed which among the various formation mechanisms of this system would still be valid
HerMES: point source catalogues from Herschel-SPIRE observations II
No full textThe Herschel Multi-tiered Extragalactic Survey (HerMES) is the largest Guaranteed Time Key Programme on the Herschel Space Observatory. With a wedding cake survey strategy, it consists of nested fields with varying depth and area totalling ∼380 deg2. In this paper, we present deep point source catalogues extracted from Herschel-Spectral and Photometric Imaging Receiver (SPIRE) observations of all HerMES fields, except for the later addition of the 270 deg2 HerMES Large-Mode Survey (HeLMS) field. These catalogues constitute the second Data Release (DR2) made in 2013 October. A sub-set of these catalogues, which consists of bright sources extracted from Herschel-SPIRE observations completed by 2010 May 1 (covering ∼74 deg2) were released earlier in the first extensive data release in 2012 March. Two different methods are used to generate the point source catalogues, the sussextractor point source extractor used in two earlier data releases (EDR and EDR2) and a new source detection and photometry method. The latter combines an iterative source detection algorithm, starfinder, and a De-blended SPIRE Photometry algorithm. We use end-to-end Herschel-SPIRE simulations with realistic number counts and clustering properties to characterize basic properties of the point source catalogues, such as the completeness, reliability, photometric and positional accuracy. Over 500 000 catalogue entries in HerMES fields (except HeLMS) are released to the public through the HeDAM (Herschel Database in Marseille) website (http://hedam.lam.fr/HerMES)
The SPIRE Instrument
No full textSPIRE, the Spectral and Photometric Imaging Receiver, is Herschel's submillimetre camera and spectrometer. It comprises a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier Transform Spectrometer (FTS) covering 194–672 μm. The design of SPIRE is described, and the expected scientific performance is summarised, based on modelling and flight instrument test results
Evaluating Transatlantic Flight Emissions and Inefficiencies Using Space-Based ADS-B Data
No full textThe increasing demand for global air travel has intensified the urgency to mitigate aviation’s carbon emissions. Continuous monitoring of aircraft fuel efficiency and emissions has become an important task in aviation. One of the main challenges has been the lack of surveillance data for flights across oceans, specifically in the North Atlantic region, where numerous flights occur. Recently, space-based ADS-B data has been made available by new space companies like Spire Global, enabling flight surveillance for aircraft in remote regions, including transatlantic flights. In this study, we utilize several months of space-based ADS-B data from Spire, combined with groundbased ADS-B data from the OpenSky Network, to demonstrate increased accuracy in flight trajectory and emission estimations. We introduce the use of wind data to improve emission quantification. Utilizing these accurate trajectories, we quantify excess emissions by comparing actual flight paths with their optimal alternatives. Our approach provides a robust methodology that benefits future policy for carbon emissions assessments.Control & Simulatio
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