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On the milliarcsecond scale structural properties of low and high redshift quasars 低红移和高红移类星体的毫弧秒尺度结构特性。
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00018-4
S. Frey , L.I. Gurvits
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引用次数: 2
Feature subset selection based on relevance 基于相关性的特征子集选择
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00043-3
Hui Wang, David Bell, Fionn Murtagh
{"title":"Feature subset selection based on relevance","authors":"Hui Wang,&nbsp;David Bell,&nbsp;Fionn Murtagh","doi":"10.1016/S0083-6656(97)00043-3","DOIUrl":"10.1016/S0083-6656(97)00043-3","url":null,"abstract":"<div><p>In this paper an axiomatic characterisation of feature subset selection is presented. Two axioms are presented: sufficiency axiom—preservation of learning information, and necessity axiom—minimising encoding length. The sufficiency axiom concerns the existing dataset and is derived based on the following understanding: any selected feature subset should be able to describe the training dataset without losing information, i.e. it is consistent with the training dataset. The necessity axiom concerns the predictability and is derived from Occam's razor, which states that the simplest among different alternatives is preferred for prediction. The two axioms are then restated in terms of relevance in a concise form: maximising both the <em>r</em>(<em>X</em>; <em>Y</em>) and <em>r</em>(<em>Y</em>; <em>X</em>) relevance. Based on the relevance characterisation, four feature subset selection algorithms are presented and analysed: one is exhaustive and the remaining three are heuristic. Experimentation is also presented and the results are encouraging. Comparison is also made with some well-known feature subset selection algorithms, in particular, with the built-in feature selection mechanism in C4.5.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 387-396"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00043-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81010372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 11
Timing the sun in Egypt and Mesopotamia 埃及和美索不达米亚的太阳计时
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(96)00069-4
John Fermor
{"title":"Timing the sun in Egypt and Mesopotamia","authors":"John Fermor","doi":"10.1016/S0083-6656(96)00069-4","DOIUrl":"10.1016/S0083-6656(96)00069-4","url":null,"abstract":"<div><p>By the 5th Century B.C. three great cultures were in contact in the Eastern Mediterranean area. The newest of these, the Greek, began by borrowing and improving on the discoveries of Babylonians and Egyptians. The knowledge of the gnomon is attested as one such borrowing. An overview is attempted of the state of timekeeping, with particular emphasis on the measure of shadows, in these two older cultures, revealing the uncertainties as to just what they had to offer the Greeks, and how they had come to their conclusions.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 157-167"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(96)00069-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81471637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Multiscale image fusion in astronomy 天文学中的多尺度图像融合
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00040-8
Albert Bijaoui, Yves Bobichon, Benoît Vandame
{"title":"Multiscale image fusion in astronomy","authors":"Albert Bijaoui,&nbsp;Yves Bobichon,&nbsp;Benoît Vandame","doi":"10.1016/S0083-6656(97)00040-8","DOIUrl":"10.1016/S0083-6656(97)00040-8","url":null,"abstract":"<div><p>Image fusion techniques are increasingly applied to astronomical images in order to improve sensitivity or to compare images. We discuss in this paper the ability of multiscale transforms for many applications: geometrical and photometrical registrations, co-addition and compression. A strategy for multiscale image fusion is derived.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 365-372"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00040-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80738343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 8
The cycles of Selene Selene的循环
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(98)00004-X
B.A. Steves
{"title":"The cycles of Selene","authors":"B.A. Steves","doi":"10.1016/S0083-6656(98)00004-X","DOIUrl":"https://doi.org/10.1016/S0083-6656(98)00004-X","url":null,"abstract":"<div><p>The discovery and use of the Saros, a lunar cycle of 18 years and 10 or 11 days, is reviewed from its earliest origins two millennia ago to the present day, when it is known with precision and enables the accurate prediction of both time and type of solar and lunar eclipses. The theoretical basis for the Saros is discussed, along with other historically known lunar cycles. The geometry of the Sun-Moon-Earth system is found to repeat itself after one Saros, not only at eclipses but also at any phase of the cycle, indicating that the Moon moves in a nearly periodic orbit. The search for periodic orbits using the Saros has led to the discovery of a set of eight periodic orbits of period equal to one Saros whose time evolutions closely resemble that of the real Moon. Finally, the potential of the Saros in studying the dynamics and stability of the Earth-Moon system is examined and the existence of other Saros-like cycles of longer periods in the present, past and future of the Earth-Moon-Sun system is explored.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 4","pages":"Pages 543-571"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(98)00004-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91694755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 2
Point object recognition — Some single- and multi-channel applications 点对象识别。一些单通道和多通道应用
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00047-0
Peter Linde, Ralph Snel, Stefan Spännare
{"title":"Point object recognition — Some single- and multi-channel applications","authors":"Peter Linde,&nbsp;Ralph Snel,&nbsp;Stefan Spännare","doi":"10.1016/S0083-6656(97)00047-0","DOIUrl":"10.1016/S0083-6656(97)00047-0","url":null,"abstract":"<div><p>High-precision photometric analysis of images of crowded stellar fields needs sophisticated algorithms. The photometric precision is, however, a strong function of the completeness of source detection. We discuss several aspects of this problem, both with relation to single- and multi-channel applications. In single images, we separate detection into two phases, source image enhancement and actual detection. Comparative tests show a point spread function pixel fitting technique to give the best results. For the fraction of undetectable stars still affecting image statistics, we have developed a technique to extract information about their effect on the faint-end luminosity function. We give two examples of multi-channel image fusion applications: (1) a combination of low- and high-resolution images and (2) removal of undersampling effects by sub-pixel image displacements. Preliminary results show considerable potential for these techniques.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 419-426"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00047-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78155470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Soft computing: A new perspective for some data mining problems 软计算:一些数据挖掘问题的新视角
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00042-1
M.A. Vila, J.C. Cubero, J.M. Medina, O. Pons
{"title":"Soft computing: A new perspective for some data mining problems","authors":"M.A. Vila,&nbsp;J.C. Cubero,&nbsp;J.M. Medina,&nbsp;O. Pons","doi":"10.1016/S0083-6656(97)00042-1","DOIUrl":"10.1016/S0083-6656(97)00042-1","url":null,"abstract":"<div><p>Databases in the real world are often dynamic, incomplete, noisy and very large and most of the problems which appear in the Data Mining field are caused by these characteristics. However, it is often unnecessary to obtain results (rules, clusters, etc.) with a high degree of precision since the input data is itself imprecise. For these reasons, we propose a new approach to cope with these situations. We refer to the “Soft Computing” methodology which combines the ability of Fuzzy Logic to represent and manage imprecise data and knowledge together with the accepted capacities for learning and heuristic computation of Neural Networks and Genetic Algorithms. The aim of the paper is to present some of the possiblities offered by the use of Soft Computing.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 379-386"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00042-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81186788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 8
MERLIN and VLBA observations of Cygnus X-3 MERLIN和VLBA对天鹅座X-3的观测
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(96)00063-3
S.J. Newell , R.E. Spencer , M.A. Garrett
{"title":"MERLIN and VLBA observations of Cygnus X-3","authors":"S.J. Newell ,&nbsp;R.E. Spencer ,&nbsp;M.A. Garrett","doi":"10.1016/S0083-6656(96)00063-3","DOIUrl":"10.1016/S0083-6656(96)00063-3","url":null,"abstract":"<div><p>We present new results from a radio mapping campaign on the X-ray binary (XRB), Cygnus X-3 using both MERLIN and the VLBA. This has produced two significant results. Firstly, observations using MERLIN at 5 GHz during a quiescent phase in June 1995 showed the presence of N and S radio lobes associated with a bright core. The position angle and separation of these lobes are consistent with the idea of a large scale jet in this source. Secondly, observations with the VLBA at 15 GHz during a period of small scale flaring have shown the source to be expanding at apparently superluminal velocities. This expansion was then followed by a period of <em>apparent</em> contraction with similar superluminal speeds.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 57-63"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(96)00063-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73243700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Geodetic VLBI observations of the gamma-bright blazar PKS 0528 + 134 伽玛亮耀变体PKS 0528 + 134的大地测量VLBI观测
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00019-6
S. Britzen, T.P. Krichbaum
{"title":"Geodetic VLBI observations of the gamma-bright blazar PKS 0528 + 134","authors":"S. Britzen,&nbsp;T.P. Krichbaum","doi":"10.1016/S0083-6656(97)00019-6","DOIUrl":"10.1016/S0083-6656(97)00019-6","url":null,"abstract":"<div><p>With a time sampling of up to one observation per month, the analysis of geodetic VLBI data can reveal a detailed picture of the kinematics in numerous compact radio sources. The database comprises simultaneous observations obtained at two frequencies (8.4 and 2.3 GHz) which have been collected over a period of about 15 years. For our analysis of short-time structural variability in the jets of AGN we selected several sources, mainly on the basis of their flux density variability in the radio and, in case of correlated outbursts and intra-day variability, also in the optical regime. These sources are generally found to be active in the γ-ray regime as well. This fact enables us to study possible correlations between the structural properties seen at radio wavelengths and the flux-density behaviour in the γ-ray regime. The results for the γ-active quasar PKS 0528 + 134 are presented.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 275-279"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00019-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75258783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Information fusion in remote sensing 遥感中的信息融合
Vistas in Astronomy Pub Date : 1997-01-01 DOI: 10.1016/S0083-6656(97)00036-6
Torfinn Taxt , Anne H. Schistad Solberg
{"title":"Information fusion in remote sensing","authors":"Torfinn Taxt ,&nbsp;Anne H. Schistad Solberg","doi":"10.1016/S0083-6656(97)00036-6","DOIUrl":"10.1016/S0083-6656(97)00036-6","url":null,"abstract":"<div><p>A short review of data fusion in remote sensing with emphasis on statistically based data fusion methods is given. The introductory part defines data fusion and image registration, and provides a historical background and some general references. Multivariate data are the necessary basis for any data fusion algorithm. The possible levels of data fusion and the frequent occurrence of various types of multivariate data in remote sensing are discussed. Finally, the paper presents a number of statistically based data fusion methods and discusses data fusion in the Bayesian framework.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 337-342"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00036-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79385440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 9
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