Synthesis and Mechanism of Composition and Size Dependent Morphology Selection in Nanoparticles of Ag-Cu Alloys Processed by Laser Ablation Under Liquid Medium

We have synthesized Ag-Cu alloy nanoparticles of four different compositions by using the laser ablation technique with the target under aqueous medium. Following this, we report a morphological transition in the nanoparticles from a normal two-phase microstructure to a structure with random segregation and finally a core shell structure at small sizes as a function of Cu concentration. To illustrate the composition dependence of morphology, we report observations carried out on nanoparticles of two different sizes: similar to 5 and similar to 20 nm. The results could be rationalized through the thermodynamic modeling of free energy of phase mixing and wettability of the alloying phases.

Revisiting neutrino masses from Planck scale operators

Planck scale lepton number violation is an interesting and natural possibility to explain nonzero neutrino masses. We consider such operators in the context of Randall-Sundrum (RS1) scenarios. Implementation of this scenario with a single Higgs localized on the IR brane (standard RS1) is not phenomenologically viable as they lead to inconsistencies in the charged lepton mass fits. In this paper we propose a setup with two Higgs doublets. We present a detailed numerical analysis of the fits to fermion masses and mixing angles. This model solves the issues regarding the fermion mass fits but solutions with consistent electroweak symmetry breaking are highly fine-tuned. A simple resolution is to consider supersymmetry in the bulk and a detailed discussion of which is provided. Constraints from flavor are found to be strong and minimal flavor violation (MFV) is imposed to alleviate them.

Top Yukawa coupling measurement with indefinite CP Higgs in e(+)e(-) -> t(t)over-bar Phi

We consider the issue of the top quark Yukawa coupling measurement in a model-independent and general case with the inclusion of CP violation in the coupling. Arguably the best process to study this coupling is the associated production of the Higgs boson along with a t (t) over bar pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurement-assuming a Standard Model (SM)-like coupling is available in the context of the ILC-conclude that the coupling could be pinned down to about a 10% level with modest luminosity, our investigations show that the scenario could be different in the case of a more general coupling. The modified Lorentz structure resulting in a changed functional dependence of the cross section on the coupling, along with the difference in the cross section itself leads to considerable deviation in the sensitivity. Our studies of the ILC with center-of-mass energies of 500 GeV, 800 GeV, and 1000 GeV show that moderate CP mixing in the Higgs sector could change the sensitivity to about 20%, while it could be worsened to 75% in cases which could accommodate more dramatic changes in the coupling. Detailed considerations of the decay distributions point to a need for a relook at the analysis strategy followed for the case of the SM, such as for a model-independent analysis of the top quark Yukawa coupling measurement. This study strongly suggests that a joint analysis of the CP properties and the Yukawa coupling measurement would be the way forward at the ILC and that caution must be exercised in the measurement of the Yukawa couplings and the conclusions drawn from it.

Turbulence and cooling in galaxy cluster cores

We study the interplay between turbulent heating, mixing, and radiative cooling in an idealized model of cool cluster cores. Active galactic nuclei (AGN) jets are expected to drive turbulence and heat cluster cores. Cooling of the intracluster medium (ICM) and stirring by AGN jets are tightly coupled in a feedback loop. We impose the feedback loop by balancing radiative cooling with turbulent heating. In addition to heating the plasma, turbulence also mixes it, suppressing the formation of cold gas at small scales. In this regard, the effect of turbulence is analogous to thermal conduction. For uniform plasma in thermal balance (turbulent heating balancing radiative cooling), cold gas condenses only if the cooling time is shorter than the mixing time. This condition requires the turbulent kinetic energy to be a parts per thousand(3) the plasma internal energy; such high velocities in cool cores are ruled out by observations. The results with realistic magnetic fields and thermal conduction are qualitatively similar to the hydrodynamic simulations. Simulations where the runaway cooling of the cool core is prevented due to mixing with the hot ICM show cold gas even with subsonic turbulence, consistent with observations. Thus, turbulent mixing is the likely mechanism via which AGN jets heat cluster cores. The thermal instability growth rates observed in simulations with turbulence are consistent with the local thermal instability interpretation of cold gas in cluster cores.

Organic white-light emitting materials

Full-color emissive organic materials have attracted significant attention in recent years as key components in display and lighting devices based on OLEDs. An ideal white-light emitter demands simultaneous emission of red, green and blue with nearly similar distribution of intensities covering the entire region of visible spectra. However, the design of such white-light emitters is not straightforward. Mixing several emitters is seldom successful owing to the negative effects of intermolecular interactions and energy transfer processes. Nonetheless, these fundamental questions have been addressed in recent times by several research groups of vastly different expertise leading to a considerable progress in the field of organic white-light emitters. The designs cover a large area of the chemistry ranging from frustrated energy transfer to simple protonation or from designed self-assembly to simple mixing of materials. In this review, the concepts and rational approaches underlying the design of white-light emissive organic materials are described. (C) 2014 Elsevier Ltd. All rights reserved.

A versatile ternary ionic complex for chiral discrimination of molecules with diverse functionalities using H-1 NMR

This study reports a simple, efficient and versatile protocol developed for NMR spectroscopic enantiodiscrimination of molecules containing diverse functional -groups, such as amino alcohols, secondary alcohols, cyanohydrins, oxazolidones, diols, thiones and epoxides, using a phosphorous based three component mixture. The simple mixing and shaking of enantiopure 1,1'-binaphthyt-2,2'-diyl hydrogenphosphate (BNPA), 4-(dimethylamino)pyridine (DMAP) and a chiral analyte in the solvent CDCl3 served as a chiral solvating agent and resulted in well dispersed peaks for each enantiomer in the H-1 NMR spectrum. Discrimination could be achieved not only for the proton at the chiral centre, but also for multiple proton sites. The devised approach also permitted the precise measurement of the enantiomeric excess (ee).

Vegetation impact on stream chemical fluxes: Mule Hole watershed (South India)

The proportion of chemical elements passing through vegetation prior to being exported in a stream was quantified for a forested tropical watershed(Mule Hole, South India) using an extensive hydrological and geochemical monitoring at several scales. First, a solute annual mass balance was established at the scale of the soil-plant profile for assessing the contribution of canopy interaction and litter decay to the solute fluxes of soil inputs (overland flow) and soil outputs (pore water flow as seepages). Second, based on the respective contributions of overland flow and seepages to the stream flow as estimated by a hydrological lumped model, we assigned the proportion of chemical elements in the stream that transited through the vegetation at both flood event (End Member Mixing Analysis) and seasonal scales. At the scale of the 1D soil-plant profile, leaching from the canopy constituted the main source of K above the ground surface. Litter decay was the main source of Si, whereas alkalinity, Ca and Mg originated in the same proportions from both sources. The contribution of vegetation was negligible for Na. Within the soil, all elements but Na were removed from the pore water in proportions varying from 20% for Cl to 95% for K: The soil output fluxes corresponded to a residual fraction of the infiltration fluxes. The behavior of K, Cl, Ca and Mg in the soil-plant profile can be explained by internal cycling, as their soil output fluxes were similar to the atmospheric inputs. Na was released from soils as a result of Na-plagioclase weathering and accompanied by additional release of Si. Concentration of soil pore water by evapotranspiration might limit the chemical weathering in the soil. Overall, the solute K, Ca, Mg, alkalinity and Si fluxes associated with the vegetation turnover within the small experimental watershed represented 10-15 times the solute fluxes exported by the stream, of which 83-97% transited through the vegetation. One important finding is that alkalinity and Si fluxes at the outlet were not linked to the ``current weathering'' of silicates in this watershed. These results highlight the dual effect of the vegetation cover on the solute fluxes exported from the watershed: On one hand the runoff was limited by evapotranspiration and represented only 10% of the annual rainfall, while on the other hand, 80-90% of the overall solute flux exported by the stream transited through the vegetation. The approach combining geochemical monitoring and accurate knowledge of the watershed hydrological budget provided detailed understanding of several effects of vegetation on stream fluxes: (1) evapotranspiration (limiting), (2) vertical transfer through vegetation from vadose zone to ground surface (enhancing) and (3) redistribution by throughfalls and litter decay. It provides a good basis for calibrating geochemical models and more precisely assessing the role of vegetation on soil processes. (C) 2014 Elsevier Ltd. All rights reserved.

Electromagnetic interference shielding through MWNT grafted Fe3O4 nanoparticles in PC/SAN blends

In this study, multiwall carbon nanotubes (MWNTs) were chemically grafted onto dopamine anchored iron oxide (Fe3O4) nanoparticles via diazotization reaction to design electromagnetic (EM) shielding materials based on PC (polycarbonate)/SAN poly (styrene-co-acrylonitrile)] blends. A two step mixing protocol was adopted to selectively localize the nanoparticles in a given phase of the blends. In the first step, MWNT-g-Fe3O4 nanoparticles were solution blended with PC, followed by dilution with SAN during melt mixing in the subsequent step. This strategy, besides improving the quality of dispersion of MWNTs in the blends, facilitated enhanced EM interference shielding effectiveness (SE). Both, the MWNTs and the modified MWNTs, selectively localized in the PC phase and led to high electrical conductivity, in striking contrast to PC filled MWNT composites. The SE was measured on toroidal samples over a broad range of frequencies; X-band (8.2-12 GHz) and K-u-band (12-18 GHz). It was observed that the shielding mechanism mostly involved reflection in the blends with MWNTs, whereas absorption dominated in the case of blends with MWNT-g-Fe3O4. To realize the efficacy of this strategy, a few compositions were prepared by physical mixing MWNTs with Fe3O4 nanoparticles. Intriguingly, blends with MWNT-g-Fe3O4 nanoparticles manifested enhanced microwave absorption over physically mixed nanoparticles. An SE of -32.5 dB was observed (at 18 GHz) for MWNT (3 wt%)-g-Fe3O4 (3 vol%) in PC/SAN blends.

Poly(vinylidene fluoride)-Based Flexible and Lightweight Materials for Attenuating Microwave Radiations

Two unique materials were developed, like graphene oxide (GO) sheets covalently grafted on to barium titanate (BT) nanoparticles and cobalt nanowires (Co-NWs), to attenuate the electromagnetic (EM) radiations in poly(vinylidene fluoride) (PVDF)-based composites. The rationale behind using either a ferroelectric or a ferromagnetic material in combination with intrinsically conducting nanoparticles (multiwall carbon nanotubes, CNTs), is to induce both electrical and magnetic dipoles in the system. Two key properties, namely, enhanced dielectric constant and magnetic permeability, were determined. PVDF/BT-GO composites exhibited higher dielectric constant compared to PVDF/BT and PVDF/GO composites. Co-NWs, which were synthesized by electrodeposition, exhibited saturation magnetization (M-s) of 40 emu/g and coercivity (Hc) of 300 G. Three phase hybrid composites were prepared by mixing CNTs with either BT-GO or Co-NWs in PVDF by solution blending. These nanoparticles showed high electrical conductivity and significant attenuation of EM radiations both in the X-band and in the Ku-band frequency. In addition, BT-GO/CNT and Co-NWs/CNT particles also enhanced the thermal conductivity of PVDF by ca. 8.7- and 9.3-fold in striking contrast to neat PVDF. This study open new avenues to design flexible and lightweight electromagnetic interference shielding materials by careful selection of functional nanoparticles

New insights of superoxide dismutase inhibition of pyrogallol autoxidation

Autoxidation of pyrogallol in alkaline medium is characterized by increases in oxygen consumption, absorbance at 440 nm, and absorbance at 600 nm. The primary products are H2O2 by reduction of O-2 and pyrogallol-ortho-quinone by oxidation of pyrogallol. About 20 % of the consumed oxygen was used for ring opening leading to the bicyclic product, purpurogallin-quinone (PPQ). The absorbance peak at 440 nm representing the quinone end-products increased throughout at a constant rate. Prolonged incubation of pyrogallol in alkali yielded a product with ESR signal. In contrast the absorbance peak at 600 nm increased to a maximum and then declined after oxygen consumption ceased. This represents quinhydrone charge-transfer complexes as similar peak instantly appeared on mixing pyrogallol with benzoquinones, and these were ESR-silent. Superoxide dismutase inhibition of pyrogallol autoxidation spared the substrates, pyrogallol, and oxygen, indicating that an early step is the target. The SOD concentration-dependent extent of decrease in the autoxidation rate remained the same regardless of higher control rates at pyrogallol concentrations above 0.2 mM. This gave the clue that SOD is catalyzing a reaction that annuls the forward electron transfer step that produces superoxide and pyrogallol-semiquinone, both oxygen radicals. By dismutating these oxygen radicals, an action it is known for, SOD can reverse autoxidation, echoing the reported proposal of superoxide:semiquinone oxidoreductase activity for SOD. The following insights emerged out of these studies. The end-product of pyrogallol autoxidation is PPQ, and not purpurogallin. The quinone products instantly form quinhydrone complexes. These decompose into undefined humic acid-like complexes as late products after cessation of oxygen consumption. SOD catalyzes reversal of autoxidation manifesting as its inhibition. SOD saves catechols from autoxidation and extends their bioavailability.

Impact of diurnal forcing on intraseasonal sea surface temperature oscillations in the Bay of Bengal

The diurnal cycle is an important mode of sea surface temperature (SST) variability in tropical oceans, influencing air-sea interaction and climate variability. Upper ocean mixing mechanisms are significant at diurnal time scales controlling the intraseasonal variability (ISV) of SST. Sensitivity experiments using an Ocean General Circulation Model (OGCM) for the summer monsoon of the year 2007 show that incorporation of diurnal cycle in the model atmospheric forcings improves the SST simulation at both intraseasonal and shorter time scales in the Bay of Bengal (BoB). The increase in SST-ISV amplitudes with diurnal forcing is approximate to 0.05 degrees C in the southern bay while it is approximate to 0.02 degrees C in the northern bay. Increased intraseasonal warming with diurnal forcing results from the increase in mixed layer heat gain from insolation, due to shoaling of the daytime mixed layer. Amplified intraseasonal cooling is dominantly controlled by the strengthening of subsurface processes owing to the nocturnal deepening of mixed layer. In the southern bay, intraseasonal variability is mainly determined by the diurnal cycle in insolation, while in the northern bay, diurnal cycle in insolation and winds have comparable contributions. Temperature inversions (TI) develop in the northern bay in the absence of diurnal variability in wind stress. In the northern bay, SST-ISV amplification is not as large as that in the southern bay due to the weaker diurnal variability of mixed layer depth (MLD) limited by salinity stratification. Diurnal variability of model MLD is not sufficient to create large modifications in mixed layer heat budget and SST-ISV in the northern bay.

Limiting two-Higgs-doublet models

We update the constraints on two-Higgs-doublet models (2HDMs) focusing on the parameter space relevant to explain the present muon g - 2 anomaly, Delta alpha(mu), in four different types of models, type I, II, ``lepton specific'' (or X) and ``flipped'' (or Y). We show that the strong constraints provided by the electroweak precision data on the mass of the pseudoscalar Higgs, whose contribution may account for Delta alpha(mu), are evaded in regions where the charged scalar is degenerate with the heavy neutral one and the mixing angles alpha and beta satisfy the Standard Model limit beta - alpha approximate to pi/2. We combine theoretical constraints from vacuum stability and perturbativity with direct and indirect bounds arising from collider and B physics. Possible future constraints from the electron g - 2 are also considered. If the 126 GeV resonance discovered at the LHC is interpreted as the light CP-even Higgs boson of the 2HDM, we find that only models of type X can satisfy all the considered theoretical and experimental constraints.

Iterated stochastic filters with additive updates for dynamic system identification: Annealing-type iterations and the filter bank

A nonlinear stochastic filtering scheme based on a Gaussian sum representation of the filtering density and an annealing-type iterative update, which is additive and uses an artificial diffusion parameter, is proposed. The additive nature of the update relieves the problem of weight collapse often encountered with filters employing weighted particle based empirical approximation to the filtering density. The proposed Monte Carlo filter bank conforms in structure to the parent nonlinear filtering (Kushner-Stratonovich) equation and possesses excellent mixing properties enabling adequate exploration of the phase space of the state vector. The performance of the filter bank, presently assessed against a few carefully chosen numerical examples, provide ample evidence of its remarkable performance in terms of filter convergence and estimation accuracy vis-a-vis most other competing filters especially in higher dimensional dynamic system identification problems including cases that may demand estimating relatively minor variations in the parameter values from their reference states. (C) 2014 Elsevier Ltd. All rights reserved.

Highly efficient WO3-ZnO mixed oxides for photocatalysis

Monoclinic nanocuboid WO3 enhanced the photocatalyst efficiency of quasi nanobelt zinc oxide for dye degradation in the presence of visible light radiation. Combustion synthesized ZnO resulted in a belt-like morphology through in situ cluster formation of near spherical particles but homogenously disperses and strongly adheres to nanocuboid WO3 during physical mixing. Cationic methylene blue (MB) and anionic orange G (OG) undergo degradation through a charge transfer mechanism in the presence of WO3-ZnO (1 : 9 weight percentage ratio) mixture. The photocatalytic reaction was enhanced due to the reduction in the recombination of photogenerated electron-holes. The high degree of 90% degradation of both dyes is due to the activity of the mixed oxides, which is much higher than that obtained either with WO3 or ZnO individually.

Highly efficient WO3-ZnO mixed oxides for photocatalysis

Monoclinic nanocuboid WO3 enhanced the photocatalyst efficiency of quasi nanobelt zinc oxide for dye degradation in the presence of visible light radiation. Combustion synthesized ZnO resulted in a belt-like morphology through in situ cluster formation of near spherical particles but homogenously disperses and strongly adheres to nanocuboid WO3 during physical mixing. Cationic methylene blue (MB) and anionic orange G (OG) undergo degradation through a charge transfer mechanism in the presence of WO3-ZnO (1 : 9 weight percentage ratio) mixture. The photocatalytic reaction was enhanced due to the reduction in the recombination of photogenerated electron-holes. The high degree of 90% degradation of both dyes is due to the activity of the mixed oxides, which is much higher than that obtained either with WO3 or ZnO individually.