67 research outputs found
Obstacles, slopes and tic-tac-toe: an excursion in discrete geometry and combinatorial game theory
No full textThe minimum number of slopes used in a straight-line drawing of G is called the slope number of G. We show that every cubic graph can be drawn in the plane with straight line edges using only the four basic slopes {0, π/4, π/2,−π/4}. We also prove that four slopes have this property if and only if we can draw K4 with them. Given a graph G, an obstacle representation of G is a set of points in the plane representing the vertices of G, together with a set of obstacles (connected polygons)
such that two vertices of G are joined by an edge if and only if the corresponding points can be connected by a segment which avoids all obstacles. The obstacle number of G is the minimum number of obstacles in an obstacle representation of G. We show that there are graphs on n vertices with obstacle number (n/log n). We show that there is an m = 2n + o(n), such that, in the Maker-Breaker game played on Zd where Maker needs to put at least m of his marks consecutively in one
of n given winning directions, Breaker can force a draw using a pairing strategy. This improves the result of Kruczek and Sundberg who showed that such a pairing strategy exits if m ≥ 3n. A simple argument shows that m has to be at least 2n+1 if Breaker is only allowed to use a pairing strategy, thus the main term of our bound is optimal.Ph. D.Includes bibliographical referencesIncludes vitaby V S Padmini Mukkamal
Risk management through social networks among male and female pastoralists in Karamoja, Uganda
No full textEnvironmental volatility, resource-related risks, and the overall uncertainty about the future fundamentally shape behavioral strategies and are critical to understanding the evolution of human social behavior. One of the central ways in which humans in subsistence economies manage risk and uncertainty is through pooling or sharing risk with other individuals, such as central place food sharing among forager populations. Among pastoralists in East Africa, risk pooling takes the form of ‘stock friendships’: an informal insurance system in which male herders form mutually beneficial partnerships through livestock transfers. Networks of stock friends are critical to recouping short term losses such as food shortage, as well as to ensuring long-term sustainability through the rebuilding of herds. This dissertation investigates risk pooling friendships and other risk management strategies of pastoralists in Karamoja, Uganda. Risk management is a central concern for pastoralists in Karamoja because of the unreliable climate, recent volatile history, and lack of institutional support. Consequently, social networks of livestock and food exchange, such as stock friendships, play a significant role in minimizing the adverse effects of disasters. During fourteen months of fieldwork, I collected qualitative and quantitative data on men’s stock friendship networks, women’s close friendship networks, and individuals’ exchange networks during a prolonged drought. I use these data to present the following: 1) an ethnographic investigation of friendship contracts among men and women; 2) an examination of the characteristics of friendship networks, including size, composition, geographical spread, and relational content; 3) a study of how individual level and external factors influence friendship networks; and 4) an analysis of which social exchange networks are activated during drought induced stress. Based on data on norms and transfers within friendship networks, I argue that risk pooling friendships in Karamoja are characterized by needbased transfers and ‘demand sharing’ rather than account-keeping reciprocity. Further, I show that during periods of extreme stress, need-based transfers of food, livestock, and money are acquired not only from kin and friendship networks (‘strong ties’), but also from ‘weak tie’ friends within the neighborhood. I, thus, contend that engaging in risk pooling relationships and need based transfers are a necessity in an environment characterized by unpredictability. Lastly, I present results from an experimental economic game that explores participants’ risk attitudes and time preference—variables critical to understanding decision-making under conditions of chronic risk and uncertainty.Ph.D.Includes bibliographical referencesby K. Padmini Iye
A green and efficient protocol for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives via a one-pot, four component reaction by grinding method
No full textAbstractAn efficient grinding protocol for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives from acetylene ester, hydrazine hydrate, aryl aldehydes and malononitrile under solvent free conditions has been achieved with excellent yields. The structures of the synthesized compounds were deduced by spectroscopic techniques and the compounds were further evaluated for their in vitro antioxidant and antimicrobial activities
Evaluation of antimicrobial activity of glycinate and carbonate derivatives of cholesterol: Synthesis and characterization
No full textAbstractA series of glycinate and carbonate derivatives of cholesterol (4a–t) were synthesized, characterized and assessed for their in vitro antimicrobial activity. Our results revealed that the compounds exerted inhibitory activities against gram-negative bacteria and fungi
Synthesis and biological evaluation of new benzofuran carboxamide derivatives
No full textAbstractA series of new 3-(glycinamido)-benzofuran-2-carboxamide and 3-(β-alanamido)-benzofuran-2-carboxamide derivatives (5a–o) were synthesized for the purpose of developing the new bioactive chemical entities and evaluated for their in vitro antimicrobial, anti-inflammatory and DPPH radical scavenging activities. The synthesized compounds were characterized by NMR, IR, Mass and X-ray crystallographic techniques
Synthesis and biological evaluation of new benzofuran carboxamide derivatives
No full textA series of new 3-(glycinamido)-benzofuran-2-carboxamide and 3-(β-alanamido)-benzofuran-2-carboxamide derivatives (5a–o) were synthesized for the purpose of developing the new bioactive chemical entities and evaluated for their in vitro antimicrobial, anti-inflammatory and DPPH radical scavenging activities. The synthesized compounds were characterized by NMR, IR, Mass and X-ray crystallographic techniques
Synthesis and characterization of curcumin-sulfonamide hybrids: Biological evaluation and molecular docking studies
No full textStereo-selective green protocol for the synthesis of highly substituted 1-phenyl-tetrahydro indeno [1, 2-b]pyrroles
No full textChemInform Abstract: One‐Pot Synthesis of N‐Aryl 1,4‐Dihydropyridine Derivatives and Their Biological Activities.
No full textChemInform Abstract: A One‐Pot Sequential Five‐Component Domino Reaction for the Expedient Synthesis of Polysubstituted Pyrroles
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