Fast and slow climate responses to CO2 and solar forcing: A linear multivariate regression model characterizing transient climate change

Climate change in response to a change in external forcing can be understood in terms of fast response to the imposed forcing and slow feedback associated with surface temperature change. Previous studies have investigated the characteristics of fast response and slow feedback for different forcing agents. Here we examine to what extent that fast response and slow feedback derived from time-mean results of climate model simulations can be used to infer total climate change. To achieve this goal, we develop a multivariate regression model of climate change, in which the change in a climate variable is represented by a linear combination of its sensitivity to CO2 forcing, solar forcing, and change in global mean surface temperature. We derive the parameters of the regression model using time-mean results from a set of HadCM3L climate model step-forcing simulations, and then use the regression model to emulate HadCM3L-simulated transient climate change. Our results show that the regression model emulates well HadCM3L-simulated temporal evolution and spatial distribution of climate change, including surface temperature, precipitation, runoff, soil moisture, cloudiness, and radiative fluxes under transient CO2 and/or solar forcing scenarios. Our findings suggest that temporal and spatial patterns of total change for the climate variables considered here can be represented well by the sum of fast response and slow feedback. Furthermore, by using a simple 1-D heat-diffusion climate model, we show that the temporal and spatial characteristics of climate change under transient forcing scenarios can be emulated well using information from step-forcing simulations alone.

A dendrimer facilitates resonance energy transfer between hydrophobic aromatic guest molecules in water

A water soluble third generation poly(alkyl aryl ether) dendrimer was examined for its ability to solubilize hydrophobic polyaromatic molecules in water and facilitate non-radiative resonance energy transfer between them. One to two orders of magnitude higher aqueous solubilities of pyrene (PY), perylene (PE), acridine yellow (AY) and acridine orange (AO) were observed in presence of a defined concentration of the dendrimer. A reduction in the quantum yield of the donor PY* emission and a partial decrease in lifetime of the donor excited state revealed the occurrence of energy transfer from dendrimer solubilized excited PY to ground state PE molecules, both present within a dendrimer. The energy transfer efficiency was estimated to be similar to 61%. A cascade resonance energy transfer in a three component system, PY*-to-PE-to-AY and PY*-to-PE-to-AO, was demonstrated through incorporation of AY or AO in the two component PY-PE system. In the three-component system, excitation of PY resulted in emission from AY or AO via a cascade energy transfer process. Careful choice of dye molecules with good spectral overlap and the employment of dendrimer as the medium enabled us to expand absorption-emission wavelengths, from similar to 330 nm to similar to 600 nm in aqueous solution. (C) 2015 Elsevier B.V. All rights reserved.

Region-of-interest diffuse optical tomography system

Diffuse optical tomography (DOT) using near-infrared light is a promising tool for non-invasive imaging of deep tissue. This technique is capable of quantitative reconstruction of absorption (mu(a)) and scattering coefficient (mu(s)) inhomogeneities in the tissue. The rationale for reconstructing the optical property map is that the absorption coefficient variation provides diagnostic information about metabolic and disease states of the tissue. The aim of DOT is to reconstruct the internal tissue cross section with good spatial resolution and contrast from noisy measurements non-invasively. We develop a region-of-interest scanning system based on DOT principles. Modulated light is injected into the phantom/tissue through one of the four light emitting diode sources. The light traversing through the tissue gets partially absorbed and scattered multiple times. The intensity and phase of the exiting light are measured using a set of photodetectors. The light transport through a tissue is diffusive in nature and is modeled using radiative transfer equation. However, a simplified model based on diffusion equation (DE) can be used if the system satisfies following conditions: (a) the optical parameter of the inhomogeneity is close to the optical property of the background, and (b) mu(s) of the medium is much greater than mu(a) (mu(s) >> mu(a)). The light transport through a highly scattering tissue satisfies both of these conditions. A discrete version of DE based on finite element method is used for solving the inverse problem. The depth of probing light inside the tissue depends on the wavelength of light, absorption, and scattering coefficients of the medium and the separation between the source and detector locations. Extensive simulation studies have been carried out and the results are validated using two sets of experimental measurements. The utility of the system can be further improved by using multiple wavelength light sources. In such a scheme, the spectroscopic variation of absorption coefficient in the tissue can be used to arrive at the oxygenation changes in the tissue. (C) 2016 AIP Publishing LLC.

White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved.

White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved.

Tuning Photoluminescence Response by Electric Field in Electrically Soft Ferroelectrics

We show that an electrically soft ferroelectric host can be used to tune the photoluminescence (PL) response of rare-earth emitter ions by external electric field. The proof of this concept is demonstrated by changing the PL response of the Eu3+ ion by electric field on a model system Eu-doped 0.94(Na1/2Bi1/2TiO3)-0.06(BaTiO3). We also show that new channels of radiative transitions, forbidden otherwise, open up due to positional disorder in the system, which can as well be tuned by electric field.