34 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 quantitative analysis of complexity of human pathogen-specific CD4 T cell responses in healthy M. tuberculosis infected South Africans
No full textAuthor Summary: Human pathogen-specific immune responses are tremendously complex and the techniques to study them ever expanding. There is an urgent need for a quantitative analysis and better understanding of pathogen-specific immune responses. Mycobacterium tuberculosis (Mtb) is one of the leading causes of mortality due to an infectious agent worldwide. Here, we were able to quantify the Mtb-specific response in healthy individuals with Mtb infection from South Africa. The response is highly diverse and 66 epitopes are required to capture 80% of the total reactivity. Our study also show that the majority of the identified epitopes are restricted by multiple HLA alleles. Thus, technical advances are required to capture and characterize the complete pathogen-specific response. This study demonstrates further that the approach combining identified epitopes into "megapools" allows capturing a large fraction of the total reactivity. This suggests that this technique is generally applicable to the characterization of immunity to other complex pathogens. Together, our data provide for the first time a quantitative analysis of the complex pathogen-specific T cell response and provide a new understanding of human infections in a natural infection setting
Urban Infrastructure Damage Detection and Mapping Using Sentinel 1
No full textNatural or man-made disasters can have a drastic impact on social, economic and environmental aspects of an affected population. Specifically, earthquakes are one of the most potent natural hazards, which cause a disproportionate amount of fatalities, primarily due to a) unexpected building collapses, b) restricted or limited access to basic amenities and c) potential hazards following earthquakes such as landslides, tsunamis etc. It is crucial to have an overview of the infrastructural damage caused following a disaster for search and rescue services to assess the extent of the damage. For the purpose of this research, Sentinel 1 imagery is used to map the building damage in an urban area after a disaster. A combination of parameters such as persistent scatterers, pixel amplitude and phase is used with a timeseries of full-resolution and spatially averaged radar images. Points that are stable in amplitude over a long timeseries, also known as Persistent Scatterers, are extracted from a stack of full-resolution images. The amplitudes of persistent scatterers, along with amplitude and coherence of pixels derived from a stack of spatially-averaged images, are statistically analysed to check the trends of the parameters pre- and post the disaster. A change detection algorithm is applied to this stack in order to localise the areas of building damage. The results are superimposed on Google Earth for easy interpretation using a graded damage scale. The analysis shows that exploiting the persistent scatterer amplitudes in the manner used in this research provides a novel way of locating building damage. This technique can be used effectively in urban areas. Using a combination of pixel amplitudes and coherence along with the persistent scatterers helps correctly find new and unique points of damage for each parameter used. The results were validated using reference Grading and crowd-sourced maps. The results illustrate that the proposed approach can be used for detecting and producing informative maps on infrastructural damage detection in urban areas
Speaking the Same Language: How Ethnonationalism and Hindutva Seep into the Adjudication of Citizenship in Assam
No full textIn the border state of Assam, questions of security, identity and citizenship have long shaped its politics. This essay focuses on the evolving jurisprudence of citizenship in the Indian border state of Assam. The author analyses 1,444 judgments of the Gauhati High Court, passed between 2013 and 2019, to study how courts interpret and enforce the laws of citizenship
Speaking the Same Language: How Ethnonationalism and Hindutva Seep into the Adjudication of Citizenship in Assam
No full textIn the border state of Assam, questions of security, identity and citizenship have long shaped its politics. This essay focuses on the evolving jurisprudence of citizenship in the Indian border state of Assam. The author analyses 1,444 judgments of the Gauhati High Court, passed between 2013 and 2019, to study how courts interpret and enforce the laws of citizenship
Experimental Study of Cement Stabilized Fiber Reinforced Compressed Earth Blocks as an Alternative Building Material
No full textabstract: Concern and interest about the environment and ecologic systems have promoted the usage of earth as a construction material. Technology advancement has resulted in the evolution of adobe into compressed stabilized earth blocks (CSEB). CSEB’s are prepared by compressing the soil-stabilizer mixture at a particular stress. In order to accomplish the required strength, cement has been used in a regular basis as stabilizing agent. It is of interest to find means to reduce the cement used in their construction without affecting its dry strength and durability. In this study, natural fibers were used along with lower proportions of cement to stabilize soil with varying fine content. Blocks were compacted at 10MPa stress and prepared by using 7%, 5% and 3% cement along with fiber content ranging from 0.25% to 2%. The effect of fine content, cement and fibers on strength and durability of the CSEB blocks were studied. Different sand/fine fractions of a native Arizona soil were used to fabricate the blocks. Results indicate that the compressive strength reaches a maximum value for blocks with 30% fine content and inclusion of fibers up to 0.5% increased the dry compressive strength. The use of 0.25% fiber by weight and 5% cement content showed comparable dry compressive strength to that of the 7% cement blocks with no fibers. The dry strength of the blocks reached an optimal condition when the combination of materials was 30% fines, 5% cement and 0.5% fibers, which satisfied the strength requirement given by the ASTM C62 and ASTM C216 standards for construction material. The CSEB’s with 0.5% fiber had higher toughness. The durability was determined by subjecting the CSEBs to wetting and drying cycles. The blocks with 5% cement withstand the durability test as the dry strength was higher than that required for construction use.
The blocks were also submitted to heating and cooling cycles. After 12 cycles, the specimens showed a reduction in strength, which further increased as the number of cycles increased. Finally, the thermal resistivity of fiber reinforced CSEB was found to be higher than that for clay bricks.Dissertation/ThesisMasters Thesis Civil and Environmental Engineering 201
Author response
No full textGiant lipid vesicles are closed compartments consisting of semi-permeable shells, which isolate femto- to pico-liter quantities of aqueous core from the bulk. Although water permeates readily across vesicular walls, passive permeation of solutes is hindered. In this study, we show that, when subject to a hypotonic bath, giant vesicles consisting of phase separating lipid mixtures undergo osmotic relaxation exhibiting damped oscillations in phase behavior, which is synchronized with swell–burst lytic cycles: in the swelled state, osmotic pressure and elevated membrane tension due to the influx of water promote domain formation. During bursting, solute leakage through transient pores relaxes the pressure and tension, replacing the domain texture by a uniform one. This isothermal phase transition—resulting from a well-coordinated sequence of mechanochemical events—suggests a complex emergent behavior allowing synthetic vesicles produced from simple components, namely, water, osmolytes, and lipids to sense and regulate their micro-environment.MOE (Min. of Education, S’pore)Published versio
Implementation of Boost PFC in the Induction Heating System for EMI–RFI Suppression
No full textThe present work deals with the design and performance analysis of a high frequency resonant inverter based Induction Heating (IH) system employing Boost Power Factor Correction (PFC) technique to overcome the problems due to EMI and RFI. Most of the existing techniques use passive filters for harmonics attenuation that fail to meet the present day requirements because of drawbacks like considerably high THD, poor dynamic performance, etc. This paper presents a new control approach for boost PFC based on inner and outer loops to eliminate the problems due to harmonics in the IH system. The equivalent circuit parameter model of the IH system has been used to analyze the presence of harmonics, and the incorporation of boost PFC at the input of the system shows its elimination as per the stringent EMI-RFI regulations. Moreover, attention has been paid to the design algorithm of the boost PFC, and a detailed mathematical analysis has been done to outline an approach for its parameter selection. A comparative analysis of the IH system with and without the incorporation of the boost PFC has been done in terms of the THD in the input current waveform. The findings of the present work show that the incorporation of Boost PFC eliminates the harmonics in the IH system in a better manner than the existing techniques. Doi: 10.28991/HIJ-2021-02-02-05 Full Text: PD
