On the equivalence of the cokriging and kriging systems

Simple cokriging of components of a p-dimensional second-order stationary random process is considered. Necessary and sufficient conditions under which simple cokriging is equivalent to simple kriging are given. Essentially this condition requires that it should be possible to express the cross-covariance at any lag h using the cross-covariance at \h\ = 0 and the auto-covariance at lag h. The mosaic model, multicolocated kriging and the linear model of coregionalization are examined in this context. A data analytic method to examine whether simple kriging of components of a multivariate random process is equivalent to its cokriging is given

A characterization of symmetric isofactorial models

The paper examines symmetric isofactorial models. A necessary and sufficient condition for a bivariate stationary random function to be isofactorial is given. Using this characterization, a procedure for checking whether an isofactorial model is appropriate is outlined. If data indicates that an isofactorial model is adequate, the procedure also provides a method for identifying the factors of the model. The paper concentrates on the case where Z(x) takes values 0, 1, 2,..., N and the general case is discussed briefly

Data configurations and the cokriging system: Simplification by screen effects

Large cokriging systems arise in many situations and are difficult to handle in practice. Simplifications such as simple kriging, strictly collocated and multicollocated cokriging are often used and models under which such simplifications are, in fact, equivalent to cokriging have recently received attention. In this paper, a two-dimensional second-order stationary random process with known mean is considered and the redundancy of certain components of the data at certain locations vis-a-vis the solution to the simple cokriging system is examined. Conditions for the simple cokriging weights of these components at these locations are set to zero. The conditions generalise the notion of the autokrigeability coefficient and can, in principle, be applied to any data configuration. In specific sampling situations such as the isotopic and certain heterotropic configurations, models under which simple kriging, strictly collocated, multicollocated and dislocated cokriging are equivalent to simple cokriging are readily identified and results already available in the literature are obtained. These are readily identified and the results are already available in the literature. The advantage of the approach presented here is that it can be applied to any data configuration for analysis of permissible simplifications in simple cokriging

Thermal expansion of irradiated polyvinyl chloride from 10 K to 340 K

The coefficient of thermal expansion is measured for irradiated Polyvinyl Chloride (PVC) from 10K to 340K. The samples of PVC are irradiated, up to 500 Mrad in steps of 100 Mrad, in air at room temperature by using Co gamma rays with a dose rate of 0.3 Mrad/h. The PVC is an amorphous sample which is confirmed by X-ray diffraction. The coefficient of thermal expansion is found to decrease with radiation dose from 10K to 110K and it increaseswith radiation dose from 110K to 340K. The results are explained on the basis of radiation induced degradation of the sample

Thermal Expansion of Irradiated Polyethylene from 10 to 340 K

The coefficient of thermal expansion of $\gamma$-irradiated polyethylene has been measured from 10 to 340 K by using the three-terminal capacitance technique. The samples are irradiated to 500 Mrad in steps of 100 Mrad in air at room temperature with $\gamma$-rays from a $Co^{60}$ source at a dose rate of 0.3 Mrad/h. The crystallinity of the sample is measured by x-ray diffraction. The crystallinity is found to decrease with radiation dose. The thermal expansion coefficient is found to be constant with radiation doses from 10 to 110 K and decreases with doses from 110 to 340 K

Thermal expansion of irradiated polypropylene from 10-340 K

The coefficient of thermal expansion of gamma-irradiated polypropylene (PP) has been measured from 10-340 K by using the three-terminal capacitance technique. The samples were irradiated to 500 Mrad in air at room temperature with gamma rays from a $^{60}Co$ source at a dose rate of 0.26 Mrad $h ^{-1}$. The crystallinity of the sample was measured by X-ray diffraction technique. The crystallinity was found to decrease with radiation dose from 55% at 0 Mrad to 44.7% at 500 Mrad. The thermal expansion coefficient was found to be almost constant with radiation dose from 10-125 K and decreases with radiation dose from 125-34O K

Thermal expansion of gamma irradiated nylon 66 from 10 K to 340 K

Study of the thermal properties of irradiated poly-mers is very important from both a scientific and a technological point of view. Very little information is available on the thermal properties of irradiated polymers. Thermal expansion of technologically important irradiated polymers was measured by Subramanyam and colleagues [1-3]. Here we have made an attempt to measure the thermal expansion of gamma irradiated nylon 66 from 10 K to 340 K

Thermal expansion of irradiated nylon-6 from 10 K to 340 K

Thermal expansion of irradiated nylon-6 has been studied in the temperature range 10 to 340 K using a three-terminal capacitance bridge technique. Irradiation is carried out using cobalt-60 gamma-rays up to 500 Mrad dosage. Radiation enhances chain scission over crosslinking. alpha increases from 0 to 250 Mrad between 10 to 340 K and not much variation is observed between 250 to 500 Mrad for samples from 10 to 250 K