Astronomical Review最新文献

{"title":"Particle Swarm Optimization and regression analysis – II","authors":"S. Mohanty","doi":"10.1080/21672857.2012.11519708","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519708","url":null,"abstract":"Abstract In the first part of this article, Particle Swarm Optimization (PSO) was applied to the problem of optimizing knot placement in the regression spline method. Although promising for broadband signals having smooth, but otherwise unknown, waveforms, this simple approach fails in the case of narrowband signals when the carrier frequency as well as the amplitude and phase modulations are unknown. A method is presented that addresses this challenge by using PSO based regression splines for the in-phase and quadrature amplitudes separately. It is thereby seen that PSO is an effective tool for regression analysis of a broad class of signals.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117247981","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}

{"title":"Radio Emission From Low Mass Young Stellar Objects","authors":"A. Scaife","doi":"10.1080/21672857.2012.11519709","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519709","url":null,"abstract":"Abstract Compact radio emission provides a reliable method for the detection of low luminosity young stellar objects (YSOs), and is particularly useful for detecting the earliest stages of protostellar evolution where the source itself may still be heavily embedded in its natal dust envelope. For such Class 0 and Class I objects the dominant radio emission mechanism is expected to be free-free, however unlike massive YSOs the way in which this radio emission is produced remains a subject of debate. As larger samples of radio YSOs become available the relationship between the radio luminosity of the Class 0/I population and their wider global properties is now being clarified. Furthermore, the broader scientific applications of such samples are also becoming increasingly apparent. These improved constraints on the nature of the radio emission from YSOs are now contributing to our understanding of not only the evolutionary physics of protostars themselves but also their wider impact on their surroundings. Here we discuss the physics of the radio emission, the emerging relationship between this emission and other properties of YSOs and some of the applications for studies exploiting this emission.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115028625","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}

{"title":"Pulsations and Hydrodynamics of Luminous Blue Variable Stars","authors":"J. Guzik, C. Lovekin","doi":"10.1080/21672857.2012.11519705","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519705","url":null,"abstract":"Abstract The Luminous Blue Variable stars exhibit behavior ranging from light curve 'microvariations' on timescales of tens of days, to ‘outbursts’ accompanied by mass loss of ~10−3 Msun occurring decades apart, to ‘giant eruptions’ such as seen in Eta Carinae, ejecting one or more solar masses and recurring on timescales of centuries. Here we review the work of the Los Alamos group since 1993, to investigate pulsations and instabilities in massive stars using linear pulsation models and non-linear hydrodynamic models. The models predict pulsational variability that may be associated with the microvariations. We show using a nonlinear pulsation hydrodynamics code with a time-dependent convection treatment, that in some circumstances the Eddington limit is exceeded periodically in the pulsation driving region of the stellar envelope, accelerating the outer layers, and perhaps initiating mass loss or the LBV outbursts. We discuss how pulsations and mass loss may be responsible for the location of the Humphreys-Davidson Limit in the H-R diagram. The ‘giant eruptions’, however, must involve much deeper regions in the stellar core to cause such large amounts of mass to be ejected. We review and suggest some possible explanations, including mixing from gravity modes, secular instabilities, the epsilon mechanism, or the SASI instability as proposed for Type II supernovae. We outline future work and required stellar modeling capabilities to investigate these possibilities.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115426196","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}

{"title":"The Solar Photon Sail Comes of Age","authors":"G. Matloff","doi":"10.1080/21672857.2012.11519704","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519704","url":null,"abstract":"Abstract Solar photon sailing, spacecraft propulsion by the pressure of sunlight, has long been a theoretical concept. During 2010, two successful missions—one in Earth orbit and one in deep space—demonstrated the utility of the concept and advanced its technological readiness level. This paper reviews the history of the solar sail, near term mission possibilities and possible far-future developments. Both recent missions: the NASA Earth-orbital Nanosail D2 drag sail and the Japanese JAXA Ikaros interplanetary technology demonstrator are discussed. Used with close solar flybys or solar-orbital laser power stations, the photon sail is one of our few candidates for extrasolar and interstellar propulsion. It may also have application to Earth defense from asteroid impacts and terrestrial climate control.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129649747","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}

{"title":"Particle Swarm Optimization and regression analysis – II","authors":"S. Mohanty","doi":"10.1080/21672857.2012.11519703","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519703","url":null,"abstract":"Abstract In the first part of this article, Particle Swarm Optimization (PSO) was applied to the problem of optimizing knot placement in the regression spline method. Although promising for broadband signals having smooth, but otherwise unknown, waveforms, this simple approach fails in the case of narrowband signals when the carrier frequency as well as the amplitude and phase modulations are unknown. A method is presented that addresses this challenge by using PSO based regression splines for the in-phase and quadrature amplitudes separately. It is thereby seen that PSO is an effective tool for regression analysis of a broad class of signals.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122138279","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}

{"title":"Radiation as Self-Action via a Cosmological Mirror","authors":"M. Ibison","doi":"10.1080/21672857.2012.11519706","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519706","url":null,"abstract":"Abstract Expressed in conformal coordinates, the cosmological scale factor is anti-symmetric about the conformal singularity. Does this imply the existence of a post-singularity ‘image’ universe?. If so, what degree of reality should be conferred on the image? Is it a mathematically redundant copy of our (real) presingularity universe, or something more substantial? This paper initially considers these questions in the light of the behavior of matter and radiation at and just beyond the singularity. We draw attention to the fact that the conformal singularity presents no barrier to radiation, so that a post-singularity universe, if it exists, must be electromagnetically coupled to our own. Further, the time-reversed scale factor, taken literally, predicts this radiation is destined to be progressively blue-shifted after passing through the singularity event. Consistency appears to demand the existence of a substantial mirror universe, fully populated with matter and radiation so as to be compatible with the time-reversed scale factor. Either that, or there is deadwood in the mathematics. Motivated by these considerations, we argue a role for a mirror universe which depends on electromagnetic coupling through the singularity, in which it appears as essential rather than optional. We point out that the post-singularity universe provides the missing absorbers required by the Wheeler-Feynman absorber theory in the framework of direct particle interaction. This theory explains radiation in terms of particle-particle interactions, without appeal to independent degrees of freedom of an electromagnetic field. The proposed mechanism involving two universes ties the electromagnetic arrow of time to the cosmological arrow associated with expansion. We conclude with suggestions about why this is perhaps just the first step toward a fuller integration, wherein both universes are recognized necessary parts of theories and phenomena in other areas of physics.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130536886","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}

{"title":"Toward a Unified AGN Structure","authors":"D. Kazanas, Kelgo Fukumura, E. Behar, I. Contopoulos, C. Shrader","doi":"10.1080/21672857.2012.11519707","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519707","url":null,"abstract":"Abstract We present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries to luminous quasars, with emphasis on AGN and their phenomenology. Central to this model is the notion of MHD winds launched from the accretion disks that power these objects. These winds provide the matter that manifests as blueshifted absorption features s in the UV and X-ray spectra of a large fraction of these sources; furthermore, their density distribution in the poloidal plane determines the “appearance” (i.e. the column and velocity structure of these absorption features) as a function of the observer inclination angle. This work focuses on just the broadest characteristics of these objects; nonetheless, it provides scaling laws that allow one to reproduce within this model the properties of objects spanning a very wide luminosity range and viewed at different inclination angles, and trace them to a common underlying dynamical structure. Its general conclusion is that the AG phenomenology can be accounted for in terms of three parameters: The wind mass flux in units of the Eddington value,ṁ, the observer’s inclination angle θ And the logarithmic slope between the O/UV and X-ray fluxes αox· However, because of a significant correlation between αox and UV luminosity, we conclude that the AGN structure depends on only two parameters. Interestingly, the correlations implied by this model appear to extend to and consistent with the, characteristics of galactic X-ray sources, suggesting the presence of a truly unified underlying structure for accretion powered sources.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125937253","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}

{"title":"Electromagnetic Control of Spacetime and Gravity: The Hard Problem of Interstellar Travel","authors":"L. Williams","doi":"10.1080/21672857.2012.11519699","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519699","url":null,"abstract":"Abstract This review considers the hard problem of interstellar travel: overcoming fundamental limits set by the nature of space and time. The prospects for a solution to this problem are discussed in terms of the mathematical form of extensions to the classical equations of electrodynamics and general relativity, extensions which offer some prospect of faster-than-light interstellar travel with terrestrial engineering. This is tantamount to the electromagnetic control of gravity. Extensions are considered which preserve invariance under general coordinate transformations, but which relax Lorentz invariance in the limit of flat spacetimes. Such extensions describe undiscovered couplings between gravity and electromagnetism, and can be understood to unify them at the classical level. Of course, only extensions consistent with past tests of Lorentz invariance are contemplated. Among the suite of effects which arises from coupling between gravity and electromagnetism, at least two are of interest for faster-than-light travel. One is a non-Lorentzian invariant interval with its prospect of spacelike geodesics and a corresponding relaxation of the limiting speed of light. The second effect is control of the coupling constant for mass-energy to warp spacetime, which would seem to be necessary to allow terrestrial engineering of interesting space warps, such as wormholes or Alcubierre warps. Both effects are mediated by as-yet-undiscovered force fields, perhaps just a single scalar field. New forces in the equations of motion, and new sources of stress-energy in the Einstein equations, are auxiliary e ects which may be of interest for falsifying such extensions to general relativity and electrodynamics. An example theory is presented which exhibits such extensions to the laws of gravity and electromagnetism: five-dimensional general relativity, developed between 1920 and 1960. In this theory, the faster-than-light limiting speed and the control of the coupling constant, as well as the extra forces in the equations of motion and the extra stress-energy source, all originate from a single scalar field. There is a particularly alluring identification of electric charge as a sort of momentum in the fifth dimension. It can be perilous to speculate about undiscovered physics, but the discoveries contemplated here will apparently be necessary if our civilization, or any civilization, is to reach the stars and explore the galaxy.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129868360","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}

{"title":"Quantum Mechanics, Gravity, and the Multiverse","authors":"Y. Nomura","doi":"10.1080/21672857.2012.11519701","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519701","url":null,"abstract":"Abstract The discovery of accelerating expansion of the universe has led us to take the dramatic view that our universe may be one of the many universes in which low energy physical laws take different forms: the multiverse. I explain why/how this view is supported both observationally and theoretically, especially by string theory and eternal inflation. I then describe how quantum mechanics plays a crucial role in understanding the multiverse, even at the largest distance scales. The resulting picture leads to a revolutionary change of our view of spacetime and gravity, and completely unifies the paradigm of the eternally inflating multiverse with the many worlds interpretation of quantum mechanics. The picture also provides a solution to a long-standing problem in eternal inflation, called the measure problem, which I briefly describe.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127469827","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}

{"title":"Particle Swarm Optimization and regression analysis – I","authors":"S. Mohanty","doi":"10.1080/21672857.2012.11519700","DOIUrl":"https://doi.org/10.1080/21672857.2012.11519700","url":null,"abstract":"Abstract Particle Swarm Optimization (PSO) is now widely used in many problems that require global optimization of high-dimensional and highly multi-modal functions. However, PSO has not yet seen widespread use in astronomical data analysis even though optimization problems in this field have become increasingly complex. In this two-part article, we first provide an overview of the PSO method in the concrete context of a ubiquitous problem in astronomy, namely, regression analysis. In particular, we consider the problem of optimizing the placement of knots in regression based on cubic splines (spline smoothing). The second part will describe an in-depth investigation of PSO in some realistic data analysis challenges.","PeriodicalId":204186,"journal":{"name":"Astronomical Review","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124883413","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}