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21.
We investigate the connections between extremal indices on the one hand and stability of Markov chains on the other hand.
Both theories relate to the tail behaviour of stochastic processes, and we find a close link between the extremal index and
geometric ergodicity. Our results are illustrated throughout with examples from simple MCMC chains.
相似文献
22.
S. P. Sethi W. P. Drews R. G. Segers 《Journal of Optimization Theory and Applications》1982,36(1):93-109
This paper briefly reviews the literature on necessary optimality conditions for optimal control problems with state-variable inequality constraints. Then, it attempts to unify the treatment of linear optimal control problems with state-variable inequality constraints in the framework of continuous linear programming. The duality theory in this framework makes it possible to relate the adjoint variables arising in different formulations of a problem; these relationships are illustrated by the use of a simple example. This framework also allows more general problems and admits a simplex-like algorithm to solve these problems.This research was partially supported by Grant No. A4619 from the National Research Council of Canada to the first author. The first author also acknowledges the support provided by the Brookhaven National Laboratory, where he conducted his research. 相似文献
23.
C. Dauwe M. Dorikens L. Dorikens-Vanpraet D. Segers 《Applied Physics A: Materials Science & Processing》1974,5(2):117-120
Measurements of positron annihilation lifetime and lineshape factors in deformed OFHC copper, for 14 different pairs of specimen, ranging up to 66% deformation, are discussed. The influence of annihilation in the source is carefully examined and the data are consequently corrected. The lifetime varies from (124±2) ps for annealed copper to (179±2) ps for dislocation saturated samples. Trapping cross sections and trapping efficiencies are calculated. The possibility of interference of vacancies formed during the deformation is discussed. 相似文献
24.
Debajyoti Choudhury Rahul Sinha S Arunagiri Gautam Bhattacharyya Debrupa Chakraverty Debajyoti Choudhury Amitava Datta Anindya Datta Aseskrishna Datta Amol Dighe Dilip Kumar Ghosh Anjan Giri Stephen King Anirban Kundu Rukmani Mohanta Biswarup Mukhopadhyaya Sreerup Raychaudhuri Saurabh Rindani Probir Roy DP Roy Sourov Roy AI Sanda Nita Sinha Rahul Sinha K Sridhar H Yamamoto 《Pramana》2000,55(1-2):335-345
This report summarises the work done during WHEPP-6 (Institute of Mathematical Sciences, Chennai, India, Jan 3–15, 2000) in
Working group on ‘B and collider physics’. 相似文献
25.
D. Segers F. Van Brabander L. Dorikens-Vanpraet M. Dorikens 《Applied Physics A: Materials Science & Processing》1982,27(3):129-132
Positron-annihilation lineshape parameter measurements were performed during isothermal annealing of room temperature deformed iron. An isothermal annealing effect is seen in impure iron while in pure iron no effect is measured. 相似文献
26.
Motoko-Kwete D. Segers M. Dorikens L. Dorikens-Vanpraet P. Clauws D. Geshef 《Physics letters. A》1990,150(8-9):413-416
Positron annihilation studies have been carried out on Si-n irradiated with He+ ions at the V.U.B. cyclotron, to a dose of 4×1017 He/cm2. No temperature dependence on the S-parameter and lifetimes is seen below the irradiation temperature. The positron lifetime associated to the created defects is 290 ps. During the isochronal annealing, this lifetime stays constant up to 700 K. It is attributed to the annihilation of positrons from large vacancy-clusters filled with He atoms. From the isochronal annealing results, only one annealing stage is seen. This annealing stage which extends over a long range of temperature 700–1000 K, is ascribed to the degassing of helium atoms from defects and the growth of vacancy-clusters. The lifetime of positrons in those defects reaches a value of about 530±30 ps at 1000 K, indicating that the vacancy-clusters formed have a mean size of more than 8 vacancies. 相似文献
27.
Study of the effect of annealing on defects in Fe-Mn-Si-Cr-Ni-C alloy by slow positron beam 总被引:1,自引:0,他引:1
FeMnSi shape memory alloys (SMAs) have received much attention as one-way SMAs due to their cost-effectiveness. Variable-energy (0-30 keV) positron beam studies have been carried out on a Fe-Mn-Si-Cr-Ni-C alloy with different degrees of deformation. Doppler broadening profiles of the positron annihilation as a function of incident positron energy were shown to be quite sensitive to defects introduced by deformation. The variation of the nature and the concentration of defects are studied as a function of isochronal annealing temperature. These results are correlated with the data measured with the positron annihilation lifetime spectroscopy (PALS). The positron annihilation results are compared to XRD and optical microscopy (OM). 相似文献
28.
Steven Van Petegem Danny Segers Charles Dauwe Florian dalla Torre Helena Van Swygenhoven 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):829-836
Summary. Nanostructured Ni3Al was produced by the inert gas condensation and in situ compaction technique and characterized by means of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction,
and density measurements. The defect structure was investigated using positron annihilation lifetime spectroscopy (PALS).
It is shown that in some samples besides the cubic also the martensitic phase can be present. The defect structure can be
divided into three major components: vacancy-like defects in the grain boundaries and nano-voids with a size of 1 nm as seen
with PALS, and large pores with sizes up to 8 nm as seen with HRTEM. Furthermore, it is shown that an increasing compaction
temperature leads to significantly smaller nano-voids.
Received October 5, 2001. Accepted (revised) November 12, 2001 相似文献
29.
M. Dorikens L. Dorikens-Vanpraet D. Segers I. Lemahieu 《Applied Physics A: Materials Science & Processing》1987,43(4):257-259
A target and converter set-up for production of slow positrons on linear electron accelerators is described. It makes use not only of the pair-production processes but also of a positron source created on-line by nuclear reactionThis paper is based upon a poster presented at the International Symposium Production of Low-Energy Positrons with Accelerators and Applications (Justus-Liebig-Universität Giessen, FRG, 25–27 September, 1986) 相似文献
30.
In 1835 Joseph Plateau (1801?C1883) was appointed Professor of Physics and Applied Physics at Ghent University, Belgium. By then he was well known for his groundbreaking work on the aftereffect of light on the human retina, and he would go on to become the first person to produce moving images, for which he is considered to be the Father of Film. His greatest scientific achievement, however, was his discovery of surface tension. 相似文献