Chemical interactions at noble metal nanoparticle surfaces - catalysis, sensors and devices

In this paper, a summary of some of the recent research efforts in our laboratory on chemical interactions at noble metal nanoparticle surfaces is presented. The article is divided into five sections, detailing with (i) interactions of simple halocarbons with gold and silver nanoparticle surfaces at room temperature by a new chemistry and the exploitation of this chemistry in the extraction of pesticides from drinking water, (ii) interaction of biologically important proteins such as Cyt c, hemoglobin and myoglobin as well as a model system, hemin with gold and silver nanoparticles and nanorods forming nano-bio conjugates and their surface binding chemistry, (iii) formation of polymer-nano composites with tunable optical properties and temperature sensing characteristics by single and multi-step methodologies, (iv) nanomaterials-based flow sensors and (v) composites of noble metal nanoparticles and metallic carbon nanotubes showing visible fluorescence induced by metal-semiconductor transition

On the evolution of tachyonic perturbations at super-Hubble scales

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a non-canonical scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations can be enhanced or suppressed at super-Hubble scales if there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations during the fast roll regime proves to be responsible for the change in the amplitude of the curvature perturbations at super-Hubble scales. Furthermore, following the earlier analysis for the canonical scalar field, we show that the power spectrum evaluated in the long wavelength approximation matches the exact power spectrum obtained numerically very well. Finally, we briefly comment on an application of this phenomenon.Comment: v1: 15 pages, 4 figures; v2: 16 pages, 5 figures, power spectrum included, discussion in section 5 enlarged, references added; v3: 17 pages, 5 figures, enhancement AS WELL AS suppression of modes at super-Hubble scales pointed out, title changed, discussions enlarged, references added, to appear in JCA

Can slow roll inflation induce relevant helical magnetic fields?

We study the generation of helical magnetic fields during single field inflation induced by an axial coupling of the electromagnetic field to the inflaton. During slow roll inflation, we find that such a coupling always leads to a blue spectrum with $B^2(k) \propto k$, as long as the theory is treated perturbatively. The magnetic energy density at the end of inflation is found to be typically too small to backreact on the background dynamics of the inflaton. We also show that a short deviation from slow roll does not result in strong modifications to the shape of the spectrum. We calculate the evolution of the correlation length and the field amplitude during the inverse cascade and viscous damping of the helical magnetic field in the radiation era after inflation. We conclude that except for low scale inflation with very strong coupling, the magnetic fields generated by such an axial coupling in single field slow roll inflation with perturbative coupling to the inflaton are too weak to provide the seeds for the observed fields in galaxies and clusters.Comment: 33 pages 6 figures; v4 to match the accepted version to appear in JCA

Occurrence of a rare lambridiform fish, Desmodema polystictum (Ogilby, 1898) from Andaman coast of India

The present study reveals the first documented distribution record of Desmodema polystictum (Ogilby, 1898) from the Andaman coast, eastern Indian Ocean. The species is rare in nature and the knowledge regarding the taxonomy, ecology and distribution is still limited. Only few records have been come from the Indian Ocean. The study is based on a single specimen (34 cm total length) collected from the northeastern region of Andaman Islands, India. The present record of D. polystictum from Andaman waters provides greater latitude and depth distribution than previously acknowledged from the Indian Exclusive Economic zone. Along with the comparative morphometric and meristic data from previous reports, description of present specimen as well as distributional information are also provided and discussed

Resonant magnetic fields from inflation

We propose a novel scenario to generate primordial magnetic fields during inflation induced by an oscillating coupling of the electromagnetic field to the inflaton. This resonant mechanism has two key advantages over previous proposals. First of all, it generates a narrow band of magnetic fields at any required wavelength, thereby allaying the usual problem of a strongly blue spectrum and its associated backreaction. Secondly, it avoids the need for a strong coupling as the coupling is oscillating rather than growing or decaying exponentially. Despite these major advantages, we find that the backreaction is still far too large during inflation if the generated magnetic fields are required to have a strength of order 10^{-15} Gauss today on observationally interesting scales. We provide a more general no-go argument, proving that this problem will apply to any model in which the magnetic fields are generated on subhorizon scales and freeze after horizon crossing.Comment: 13 pages + 7 pages of appendices and references, 3 figures, matches published versio

Recent Ancestry of Kyasanur Forest Disease Virus

Clinicians in Asia should consider this disease when diagnosing acute febrile illnesses