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      Volume 25, Issue 6

      June 2020,   pages  741-886

    • Editorial

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    • Science Smiles

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    • Louis Nirenberg (1925–2020)

      Kaushal Verma

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    • Estimating a Genius – Louis Nirenberg

      Vamsi Pritham Pingali

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      Louis Nirenberg (1925–2020) made monumental contributions to partial differential equations and related areas of mathe-matics. This article attempts to present aspects of his life as well as his works to mathematically mature laymen without doing justice to either.

    • The Maximum Principle and the Moving Plane Method

      Mousomi Bhakta

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      In this article we discuss the maximum principle and it’s ap-plication to the study of symmetry of solutions of nonlinear partial differential equations, which was one of the main re-search topics of Louis Nirenberg. The central question in symmetry that we discuss is the following if a domain Ω ⊂ RN and the given boundary data on ∂Ω have some symmetry, for example radial symmetry, axial symmetry or symmetry with respect to some hyperplane, then when we can say that posi-tive solution of a given nonlinear partial differential equation on Ω inherit these symmetries.

    • Physics with Coffee and Doughnuts: Understanding the Physics Behind Topological Insulators Through Su-Schrieffer-Heeger Model

      Navketan Batra Goutam Sheet

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      Topological insulators are a new class of materials that have attracted significant attention in contemporary condensed mat-ter physics. They are different from regular insulators, and they display novel quantum properties that involve the idea of ‘topology’, an area of mathematics. Some of the fundamental concepts behind topological insulators, particularly in low-dimensional condensed matter systems such as poly-acetylene chains, can be understood using a simple one-dimensional toy model popularly known as the Su-Schrieffer-Heeger (SSH) model. This model can also be used as an introduction to the topological insulators of higher dimensions. Here, we give a concise description of the SSH model along with a brief re-view of the background physics and attempt to understand the ideas of topological invariants, edge states, and bulk-boundary correspondence using the model.

    • Thermodynamic and Kinetic Aspects of the Stability of Sir P. C. Ray’s Mercurous Nitrite Compound

      Asim K Das

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      Different thermodynamic and kinetic aspects of the stability of mercurous nitrite discovered accidentally in 1896 by P. C. Ray’s group have been critically analysed in this review arti-cle. It has been concluded that mercurous nitrite is thermody-namically unstable but it gains the kinetic stability which may originate from the overpotential factor in the gas evolution in its redox decomposition. It may also arise from strengthen-ing the HgI–HgI bond which undergoes cleavage at the rate determining step (rds) in the disproportionation of Hg22+ orits oxidation by the one-electron oxidant like NO2−. TheHgI–HgI bond is strengthened through the formation of the rela-tively weaker HgI–O bond (i.e. nitrito linkage) compared to the HgI–N bond (i.e. nitro linkage) in mercurous nitrite.

    • Rewriting the Genome of the Model Eukaryote Saccharomyces cerevisiae

      Vijayan Sambasivam Desirazu N Rao Srinivasan Chandrasegaran

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      An international consortium of scientists has embarked on the total design and synthesis of all the 16 yeast chromosomes of the laboratory organism, Saccharomyces cerevisiae.Once constructed, the 16 synthetic chromosomes will be consoli-dated into a single yeast strain along with a new 17th yeast chromosome called the “neochromosome” which contains all the tRNA genes, to generate a designer eukaryotic genome, Sc2.0. The key criterion for the stream-lined yeast (Sc2.0) is that it should retain the same cell fitness and phenotype of the wild-type (Sc1.0), but show increased genetic stabil-ity and flexibility to enable future studies. All the 16 syn-thetic yeast chromosomes have been designed using BioStu-dio, an open-source framework that was developed specifi-cally to design and construct chromosome-size fragments in silico. The completely redesigned Sc2.0 genome is a highly modified version of the S. cerevisiaegenome, with a reduction in the size of ∼1.1 million base pairs, which is about 8% of the native genome. In 2017, the Sc2.0 consortium reported the complete synthesis and assembly of 6.5 individual yeast chromosomes in discrete strains and showed consolidation of 2.5 synthetic chromosomes (synIII/synVI/synIXR) into a sin-gle yeast strain that bodes well for the successful completion of the Sc2.0 genome.

    • How to Design Experiments in Animal Behaviour: 12. Male Frogs Sing for Sex but Why Don’t They Do Their Best?

      Raghavendra Gadagkar

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      Charles Darwin proposed a separate theory of sexual selec-tion, as distinct from his theory of natural selection, to ac-count for adaptations that confer success in finding a mate, which may sometimes be quite the opposite of what is best for survival. Darwin’s proposal that females have a sense of beauty and choose mating partners that appear beautiful to them was met with much scepticism. But today we have a rather detailed understanding of what animals find beauti-ful and why. In this article, I will describe a few very sim-ple experiments performed by Michael J. Ryan, in collabora-tion with A. Stanley Rand, herpetologist extraordinaire and Merlin D Tuttle of the Bat Conservation International fame, that laid the foundation for our current understanding of the meaning and evolution of beauty. Studying the t´ungara frog on Barro Colorado Island, a research station of the Smithso-nian Tropical Research Institute in Panama, they showed that (1) male t´ungara frogs can produce both simple calls, consist-ing of just a whine, or complex calls in which one or more chucks are added to the whine, (2) female t´ungara frogs have a decided preference to mate with males giving complex calls,(3) males are nevertheless reluctant to add chucks to their calls and generally do so only when they hear other males calling, and (4) the local predatory fringe-lipped bat also has a decided preference to eat males giving complex calls. Male t´ungara frogs thus face a trade-off between sex and survival. These experiments not only answered the question of why males don’t do their best when it comes to singing, but they also set the stage for many more sophisticated investigations that have led to an understanding of how and why natural selection has favoured this particular sexual aesthetic in the frogs and this particular culinary aesthetic in the bats.

    • A Window into the World of Nucleon-nucleon Interactions

      Indulekha K

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    • A Versatile Ace at Bridge Building: M.S. Narasimhan in Conversation with Sudhir Rao

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    • Congratulations to the Newly Elected Members

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    • Indian Paradise Flycatcher

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