Dynamics of circular arrangements of vorticity in two dimensions

The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical co-rotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long-lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to a break down into individual vortices. In the pre-annular stage, vortical structures in a viscous flow are found here to tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Interestingly at higher Reynolds numbers, the merger of an odd number of vortices is found to proceed very differently from that of an even number. The former process is rapid and chaotic whereas the latter proceeds more slowly via pairing events. The annular vortex takes the form of a generalised Lamb-Oseen vortex (GLO), and diffuses inwards until it forms a standard Lamb-Oseen vortex. For lower Reynolds number, the numerical (fully nonlinear) evolution of the GLO vortex follows exactly the analytical evolution until merger. At higher Reynolds numbers, the annulus goes through instabilities whose nonlinear stages show a pronounced difference between even and odd mode disturbances. It is hoped that the present findings, that multiple vortex merger is qualitatively different from the merger of two vortices, will motivate studies on how multiple vortex interactions affect the inverse cascade in two-dimensional turbulence.Comment: Abstract truncated. Paper to appear in Physical Review

EUROPEAN UNION ENLARGEMENT: WHAT ARE THE AGRICULTURAL TRADE MODELS MISSING?

This paper quantifies the potential impact of European Union enlargement and the consequences of ignoring the non-agricultural component of this integration. We find that agriculture-focused studies offer sound estimates of agriculture-specific production and trade changes, but the estimates of trade volume changes, and welfare gains are far too low.International Relations/Trade,

RECENT APPROACHES INVOLVED IN COLONIC DRUG TARGETING FOR THE TREATMENT OF INFLAMMATORY BOWEL DISEASE: A REVIEW

The objective of the review is to present the contemporary approaches involved in colonic drug targeting for the therapy of inflammatory bowel disease (IBD). The adverse reactions and side-effects of the conventional drug delivery systems are largely on account of the systemic absorption of the drugs from the small intestine. Moreover, in current drug delivery systems, the drug has to be frequently administered and also in larger doses which greatly reduces patient compliance. Various approaches which are being described here mainly target the colonic region specifically for improved therapy of IBD, by increasing localization and accessibility of the drug to the target site. Also, these approaches will result in the reduction of dose and minimization of adverse effects combined with the use of conventional drug delivery systems

Trivially extendable graphs

Let G be a simple graph. Let k be a positive integer. G is said to be k-extendable if every independent set of cardinality k is contained in a maximum independent set of G. G is said to be trivially extendable if G is not k-extendable for 1 ≤ k ≤ (β0(G) − 1). A well covered graph is one in which every maximal independent set is maximum. Study of k-extendable graphs has been made in [7,8,9]. In this paper a study of trivially extendable graphs is made. Characterization of graphs with β0(G) = (n − 3) and which is trivially extendable has been done. Similarly graphs with β0(G) = (n − 2) is also studied for trivial extensibility.Publisher's Versio

Barriers to expansion of mass literacy and primary schooling in West Bengal : a study based on primary data from selected villages

This paper examines factors affecting literacy and access to school education in West Bengal, India, and reports the results of a binomial probit model estimated with primary data from ten villages of West Bengal. In the analysis of adult literacy, the significant variables were sex, caste and occupational status and village location. In the probit results for educational achievements of children of ages 6 to 16 years in the same villages, however, occupational status was not statistically significant. In contemporary West Bengal, we argue, class barriers to school attendance have become less significant; other features of educational deprivation persist. Key words: Education, literacy, India, West Bengal JEL Classification: I