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Chandrasekhar T. Ashok N. M. Tej Anandamayee Mondal Soumen Watson P. V. 《Earth, Moon, and Planets》1998,81(2):111-121
During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J,
H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature
of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived
in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains
with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain
the unusual brightness of comet Hale—Bopp.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Multivariate Spatial Modeling for Geostatistical Data Using Convolved Covariance Functions 总被引：1，自引：0，他引：1
Soil pollution data collection typically studies multivariate measurements at sampling locations, e.g., lead, zinc, copper
or cadmium levels. With increased collection of such multivariate geostatistical spatial data, there arises the need for flexible
explanatory stochastic models. Here, we propose a general constructive approach for building suitable models based upon convolution
of covariance functions. We begin with a general theorem which asserts that, under weak conditions, cross convolution of covariance
functions provides a valid cross covariance function. We also obtain a result on dependence induced by such convolution. Since,
in general, convolution does not provide closed-form integration, we discuss efficient computation.
We then suggest introducing such specification through a Gaussian process to model multivariate spatial random effects within
a hierarchical model. We note that modeling spatial random effects in this way is parsimonious relative to say, the linear
model of coregionalization. Through a limited simulation, we informally demonstrate that performance for these two specifications
appears to be indistinguishable, encouraging the parsimonious choice. Finally, we use the convolved covariance model to analyze
a trivariate pollution dataset from California. 相似文献
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