85,870 research outputs found

    Main-Belt Comet 238P/Read Revisited

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    We present a series of observations of the return of activity in main-belt comet 238P/Read. Using data obtained in July and August 2010 when 238P appeared to be largely inactive, we find best-fit IAU phase function parameters of H=19.05+/-0.05 mag, corresponding to a nucleus radius of r_n ~ 0.4 km (assuming an albedo of p_R=0.05), and G=-0.03+/-0.05. Observations from September 2010 onward show a clear rise in activity, causing both a notable change in visible morphology and increasing photometric excesses beyond what would be expected based on bare nucleus observations. By the end of the observing period reported on here, the dust mass in the coma shows indications of reaching a level comparable to that observed in 2005, but further observations are highly encouraged once 238P again becomes observable from Earth in mid-2011 to confirm whether this level of activity is achieved, or if a notable decrease in activity strength compared to 2005 can be detected. Comet 238P is now the second main-belt comet (after 133P/Elst-Pizarro) observed to exhibit recurrent activity, providing strong corroboration for the conclusion that it is a true comet whose active episodes are driven by sublimation of volatile ice.Comment: 13 pages, 3 figures, accepted for publication in ApJ Letter

    The Return of Activity in Main-Belt Comet 133P/Elst-Pizarro

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    Comet 133P/Elst-Pizarro is the first-known and currently best-characterised member of the main-belt comets, a recently-identified class of objects that exhibit cometary activity but which are dynamically indistinguishable from main-belt asteroids. We report here on the results of a multi-year monitoring campaign from 2003 to 2008, and present observations of the return of activity in 2007. We find a pattern of activity consistent with the seasonal activity modulation hypothesis proposed by Hsieh et al. (2004, AJ, 127, 2997). Additionally, recomputation of phase function parameters using data in which 133P was inactive yields new IAU parameters of H_R=15.49+/-0.05 mag and G_R=0.04+/-0.05, and linear parameters of m_R(1,1,0)=15.80+/-0.05 mag and Beta=0.041+/-0.005 mag/deg. Comparison between predicted magnitudes using these new parameters and the comet's actual brightnesses during its 2002 and 2007 active periods reveals the presence of unresolved coma during both episodes, on the order of ~0.20 of the nucleus cross-section in 2002 and ~0.25 in 2007. Multifilter observations during 133P's 2007 active outburst yield mean nucleus colours of B-V=0.65+/-0.03 mag, V-R=0.36+/-0.01 mag, and R-I=0.32+/-0.01 mag, with no indication of significant rotational variation, and similar colours for the trail. Finally, while 133P's trail appears shorter and weaker in 2007 than in 2002, other measures of activity strength such as dust velocity and coma contamination of nucleus photometry are found to remain approximately constant. We attribute changes in trail strength to the timing of observations and projection effects, thus finding no evidence of any substantial decrease in activity strength between 2002 and 2007.Comment: 31 pages, 13 figures, accepted for publication in MNRA

    The Interdependence of Taiwanese and Japanese Stock Prices

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    This paper empirically analyzes the relationship among the prices of Taiwanese stocks, Japanese stocks, and crude oil from January 1980 to July 2008. It provides some interesting results: (1) crude oil prices made an impact on Japanese stock prices, while the latter exerted a strong influence on Taiwanese stock prices during the period of Japan's economic growth; (2) however, no causality was observed among the variables during the Japanese economy's "lost decade"; and (3) causality from Japanese stock prices and crude oil prices to Taiwanese stock prices was observed during the period of Japan's economic recovery.Taiwanese stock prices, Japanese stock prices, LA-VAR

    The interdependence of Taiwanese and Japanese stock prices

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    This paper empirically analyzes the relationship among the prices of Taiwanese stocks, Japanese stocks, and crude oil from January 1980 to July 2008. It provides some interesting results: (1) crude oil prices made an impact on Japanese stock prices, while the latter exerted a strong influence on Taiwanese stock prices during the period of Japan’s economic growth; (2) however, no causality was observed among the variables during the Japanese economy’s "lost decade"; and (3) causality from Japanese stock prices and crude oil prices to Taiwanese stock prices was observed during the period of Japan’s economic recovery.Taiwanese stock prices; Japanese stock prices; LA-VAR

    From patterned response dependency to structured covariate dependency: categorical-pattern-matching

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    Data generated from a system of interest typically consists of measurements from an ensemble of subjects across multiple response and covariate features, and is naturally represented by one response-matrix against one covariate-matrix. Likely each of these two matrices simultaneously embraces heterogeneous data types: continuous, discrete and categorical. Here a matrix is used as a practical platform to ideally keep hidden dependency among/between subjects and features intact on its lattice. Response and covariate dependency is individually computed and expressed through mutliscale blocks via a newly developed computing paradigm named Data Mechanics. We propose a categorical pattern matching approach to establish causal linkages in a form of information flows from patterned response dependency to structured covariate dependency. The strength of an information flow is evaluated by applying the combinatorial information theory. This unified platform for system knowledge discovery is illustrated through five data sets. In each illustrative case, an information flow is demonstrated as an organization of discovered knowledge loci via emergent visible and readable heterogeneity. This unified approach fundamentally resolves many long standing issues, including statistical modeling, multiple response, renormalization and feature selections, in data analysis, but without involving man-made structures and distribution assumptions. The results reported here enhance the idea that linking patterns of response dependency to structures of covariate dependency is the true philosophical foundation underlying data-driven computing and learning in sciences.Comment: 32 pages, 10 figures, 3 box picture

    On the shock transition, the hydraulic jump, and vortex breakdown

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    The normal shock, hydraulic jump, and vortex breakdown have a common feature: they are all marked by a transition from a supercritical to a subcritical flow state. These phenomena are due to the nonlinearity of the flow, and it will be shown that viscosity also plays an essential role. This paper demonstrates explicitly how viscosity enters into these flows, The treatment of normal shock served a starting illustration. Then an equation governing the phenomenon of hydraulic jump is derived with the inclusion of the effect of viscosity. It is explicitly shown that supercritical flow is not stable and has to go through a transition to a conjugate subcritical flow state downstream. Similar treatment is also applied to vortex breakdown with largely similar results
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