Indian Institutes of Technology

About: Indian Institutes of Technology is a based out in . It is known for research contribution in the topics: Dielectric & Population. The organization has 28600 authors who have published 40156 publications receiving 652996 citations. The organization is also known as: IITs & Indian Institute of Technology.

Three-level spin system under decoherence-minimizing driving fields: Application to nitrogen-vacancy spin dynamics

Abstract: Within the framework of a general three-level problem, the dynamics of the nitrogen-vacancy (NV) spin is studied for the case of a special type of external driving consisting of a set of continuous fields with decreasing intensities. Such a set has been proposed for minimizing coherence losses. Each new driving field with smaller intensity is designed to protect against the fluctuations induced by the driving field at the preceding step with larger intensity. We show that indeed this particular type of external driving minimizes the loss of coherence, using purity and entropy as quantifiers for this purpose. As an illustration, we study the coherence loss of an NV spin due to a surrounding spin bath of $^{13}\mathrm{C}$ nuclei.

Metal Bioremediation by Thermophilic Microorganisms

Abstract: Environmental pollution with toxic metals is a severe threat to biota and human health. Microbe-mediated bioremediation of such contaminants has emerged as a potential alternative to conventional treatment methods. Thermophilic microorganisms, owing to their natural ability to survive and flourish under elevated temperatures along with other stressful environmental conditions including high concentrations of heavy metals, have developed various adaptation strategies to cope with harsh environments, which may offer enormous opportunities for bioremediation of heavy metals at higher temperatures. Thermophilic microorganisms, being common in geological and anthropogenic thermal environments with high concentrations of dissolved metal, possess unique cell wall structures and metabolic and enzymatic properties that may contribute in metals–thermophiles interactions. Biosorption/bioaccumulation of metals is most effective and widely used approach for the bioremediation. The nature and extent of metal biosorption onto thermophilic bacteria may differ greatly from the mesophilic organisms. Microbial transformation of metal through oxidation/reduction reactions plays a critical role in metal speciation, distribution, and thus altered toxicity in the ecosystems, which may be implemented in metal recovery and remediation. Both sulfate- and metal-reducing bacteria have profound application in metal bioremediation. Thermophilic bacteria with higher metal tolerance and metabolic characteristics at high temperature may exhibit enhanced metal solubilization through sulfur- or iron-oxidizing processes. Thermophilic microbial community can perform both degradative and productive functions through coupling of metal reduction with oxidation of a variety of organic and inorganic substrates. Thermophilic bacteria are also able to reduce a wide spectrum of metals including Mn (IV), Cr (VI), U (VI), Tc (VII), Co (III), Mo (VI), Au (I, III), and Hg (II) which can be used for the immobilization of toxic metals/radionuclides during bioremediation of hot wastewater of disposal sites of radioactive wastes having temperature range favorable for thermophiles for a long period of time. This chapter discusses various modes of metal-microbe interactions in thermophilic bacteria for their promising application in bioremediation.

Oblique wave interaction with porous, flexible barriers in a two-layer fluid

Abstract: Oblique wave scattering by multiple porous, flexible barriers is studied in a two-layer fluid in both the cases of surface-piercing and bottom-standing partial barriers in water of finite depth. The mathematical problem is handled for a solution using a generalized orthogonal relation suitable for a two-layer fluid along with the least square approximation method for single and double barriers. Various characteristics of the eigensystem, including convergence of the eigenfunction expansions for the velocity potentials associated with surface gravity waves in two-layer fluid, are derived. Wave scattering by multiple barriers is studied using a wide-spacing approximation method and compared with the solution obtained through the least square approximation method in the case of double barriers. The effectiveness of the barrier system on wave scattering is analyzed in different cases by analyzing the scattering coefficients in surface and internal modes, surface and interface wave elevations, deflection of the flexible barriers under wave action, and wave loads on the barriers. It is observed that multiple zeros in wave reflections occur for waves in surface and internal modes for various values of nondimensional barrier spacing and an oblique angle of incidence. Further, the condition for Bragg resonance is derived in the case of multiple barriers in a two-layer fluid. In the case of wave scattering by double barriers, for certain combinations of barrier spacing and porous-effect parameter, optimum wave forces are exerted for the same angle of incidence. The findings of the present study are likely to play a significant role in the protection of marine facilities from wave action.

Well-Defined Fluorinated Copolymers: Current Status and Future Perspectives

Abstract: Well-defined fluoropolymers exhibit unique properties such as excellent oil and water repellency, satisfactory thermal stability, a low refractive index, and low surface energy. The origin of these properties is attributed to the presence of a strong electronegative and low polarizable fluorine atom in the backbone of such polymers, which leads to a strong C–F bond (with a high bond dissociation energy of 485 kJ mol–1). Because of these features, these polymers have found applications as functional coatings, thermoplastics, biomedical items, separators, and binders for Li ion batteries, fuel cell membranes, piezoelectric devices, high-quality wires and cables, and so forth. Usually, fluoropolymers are synthesized by the conventional radical (co)polymerization of fluoroalkenes, which leads to the production of (co)polymers with an ill-defined end group, uncontrolled molar mass, and high dispersity values. In the last two decades, significant developments of various reversible deactivation radical polymerization (RDRP) techniques have helped the design of macromolecular architectures (including block, graft, star, and dendrimers) on demand. However, for relevant new applications, well-defined fluoropolymers with controlled macromolecular architectures (e.g., block copolymers as thermoplastic elastomers and electroactive polymers or graft copolymers for fuel cell membranes) are required. Several RDRP methods, developed in the last two decades, have paved the way for the synthesis of (co)polymers with well-defined molar mass, dispersity, chain end-functionality, and macromolecular architectures. Some of these RDRP techniques have been successfully employed for the synthesis of well-defined fluorinated copolymers. These techniques include iodine-transfer polymerization (ITP), reversible addition–fragmentation chain-transfer (RAFT) polymerization, organometallic-mediated radical polymerization (OMRP), and, to a lesser extent, nitroxide-mediated polymerization (NMP). Impressive control of the molar mass parameters of the fluoropolymers synthesized via these techniques also encouraged the researchers to combine these techniques with other postpolymerization strategies, leading to innovative novel polymeric materials. Thus, synthesized well-defined fluoropolymers exhibited a unique combination of properties (such as excellent weather resistance, high thermal/chemical/aging resistance, morphological versatility, and a low dielectric constant/flammability/refractive index). These led to the application of such developed materials in various high-technology applications such as high-performance elastomers, coatings for marine antifouling applications, fluorinated surfactants, fuel cell membranes, and gel polymer electrolytes for Li ion batteries. Newer advances in the field of polymer synthesis techniques are the need of the hour in order to synthesize more advanced fluorinated materials which may change the use of such polymers in engineering and biomedical fields in the current century. However, it should be kept in mind that success in this regard shall heavily depend on a deeper understanding of the polymerization process and structure–activity relationships.