Radiative effects of aerosols at an urban location in southern India: Observations versus model

The radiative impact of aerosols is one of the largest sources of uncertainty in estimating anthropogenic climate perturbations. Here we have used independent ground-based radiometer measurements made simultaneously with comprehensive measurements of aerosol microphysical and optical properties at a highly populated urban site, Bangalore (13.02 degrees N, 77.6 degrees E) in southern India during a dedicated campaign during winter of 2004 and summer and pre-monsoon season of 2005. We have also used longer term measurements carried out at this site to present general features of aerosols over this region. The aerosol radiative impact assessments were made from direct measurements of ground reaching irradiance as well as by incorporating measured aerosol properties into a radiative transfer model. Large discrepancies were observed between measured and modeled (using radiative transfer models, which employed measured aerosol properties) radiative impacts. It appears that the presence of elevated aerosol layers and (or) inappropriate description of aerosol state of mixing are (is) responsible for the discrepancies. On a monthly scale reduction of surface irradiance due to the presence of aerosols (estimated using radiative flux measurements) varies from 30 to 65 W m(-2). The lowest values in surface radiative impact were observed during June when there is large reduction in aerosol as a consequence of monsoon rainfall. Large increase in aerosol-induced surface radiative impact was observed from winter to summer. Our investigations re-iterate the inadequacy of aerosol measurements at the surface alone and importance of representing column properties (using vertical profiles) accurately in order to assess aerosol-induced climate changes accurately. (C) 2010 Elsevier Ltd. All rights reserved.

An infrared spectroscopic study of the low-spin-high-spin transition in FexMn1-x(Phen)2(NCS)2: A composition-induced change in the order of the spin-state transition

Infrared spectroscopy provides a valuable tool to investigate the spin-state transition in Fe(II) complexes of the type Fe(Phen)2(NCS)2. With progressive substitution of Fe by Mn, the first-order transition changes over to a second-order transition, with a high residual population of the high-spin state even at very low temperatures

Synthesis, infrared spectra and thermoanalytical properties of transition metal sulfite hydrazine hydrates

Transition metal sulfite hydrazine hydrates, MSO3·xN2H4·yH2O whereM=Mn, Fe, Co, Ni and Zn have been prepared and characterized by chemical analysis, infrared spectra, thermoanalytical and combustion studies. The colours,x andy parameters of the complexes varied depending upon the preparation conditions. Thermal decomposition characteristics differ from metal to metal yielding metal oxides at relatively low temperatures.Mittels chemischer Analyse, IR-Spektren, thermoanalytischen und Verbrennungsstudien wurden die Hydrazinhydrate der hergestellten Übergangsmetallsulfite MSO3·xN2H4·yH2O mitM=Mn, Fe, Co, Ni und Zn beschrieben. Farbe sowie die Parameterx undy der Komplexe hängen von den Herstellungsbedingungen ab. Die thermische Zersetzung, bei der bei relativ niedrigen Temperaturen Metalloxide entstehen, ist von Metall zu Metall verschieden.

Analytical and numerical solutions of inward spherical solidification of a superheated melt with radiative-convective heat transfer and density jump at freezing front

Analytical and numerical solutions of a general problem related to the radially symmetric inward spherical solidification of a superheated melt have been studied in this paper. In the radiation-convection type boundary conditions, the heat transfer coefficient has been taken as time dependent which could be infinite, at time,t=0. This is necessary, for the initiation of instantaneous solidification of superheated melt, over its surface. The analytical solution consists of employing suitable fictitious initial temperatures and fictitious extensions of the original region occupied by the melt. The numerical solution consists of finite difference scheme in which the grid points move with the freezing front. The numerical scheme can handle with ease the density changes in the solid and liquid states and the shrinkage or expansions of volumes due to density changes. In the numerical results, obtained for the moving boundary and temperatures, the effects of several parameters such as latent heat, Boltzmann constant, density ratios, heat transfer coefficients, etc. have been shown. The correctness of numerical results has also been checked by satisfying the integral heat balance at every timestep.

A Photoelectron Spectroscopic Study Of The Interaction Of Oxygen, Nitrogen And Transition-Metals With C-60 Films

Evidence is presented for the strong interaction of oxygen and nitrogen with solid films of buckminsterfullerene based on core-level spectroscopic studies. Cr, Ni and Cu deposited on C60 films interact strongly giving rise to large changes in the C(Is) and C(2p) binding energies as well as the (2p) binding energies of the transition metals.

Electronic Structure of and the Metal-Insulator Transition in La1-xSrxCoO3-δ: A Soft-X-Ray Absorption Study

We report the soft-X-ray absorption spectra at the oxygen K-edge of La1-xSrxCoO3-δ (x = 0.0, 0.1, 0.2, 0.3 and 0.4) series with experimentally determined δ values. We show that the doping of holes by replacing La3+ with Sr2+ induces states within the band gap of the insulating undoped compound for small x and these doped states have a very substantial oxygen 2p character. This indicates that the insulating compounds belong to the charge transfer insulator regime. With increasing Sr content, the doped states broaden into a band overlapping the top of the primarily oxygen p-derived band, leading to an insulator-metal transition at x ≥ 0.2.

Two forms of Pf1 Inovirus: X-ray diffraction studies on a structural phase transition and a calculated libration normal mode of the asymmetric unit

Inovirus is a helical array of alpha-helical protein asymmetric units surrounding a DNA core. X-ray fibre diffraction studies show that the Pf1 species of Inovirus can undergo a reversible temperature-induced transition between two similar structural forms having slightly different virion helix parameters. Molecular models of the two forms show no evidence for altered interactions between the protein and either the solvent or the viral DNA; but there are significant differences in the shape and orientation of the protein asymmetric unit, related to the changes in the virion parameters. Normal modes involving libration of whole asymmetric units are in a frequency range with appreciable entropy of libration, and the structural transition may be related to changes in libration.

A Theory of the Lifted Temperature Minimum on Calm Clear Nights

Numerous reports from several parts of the world have confirmed that on calm clear nights a minimum in air temperature can occur just above ground, at heights of the order of $\frac{1}{2}$ m or less. This phenomenon, first observed by Ramdas & Atmanathan (1932), carries the associated paradox of an apparently unstable layer that sustains itself for several hours, and has not so far been satisfactorily explained. We formulate here a theory that considers energy balance between radiation, conduction and free or forced convection in humid air, with surface temperature, humidity and wind incorporated into an appropriate mathematical model as parameters. A complete numerical solution of the coupled air-soil problem is used to validate an approach that specifies the surface temperature boundary condition through a cooling rate parameter. Utilizing a flux-emissivity scheme for computing radiative transfer, the model is numerically solved for various values of turbulent friction velocity. It is shown that a lifted minimum is predicted by the model for values of ground emissivity not too close to unity, and for sufficiently low surface cooling rates and eddy transport. Agreement with observation for reasonable values of the parameters is demonstrated. A heuristic argument is offered to show that radiation substantially increases the critical Rayleigh number for convection, thus circumventing or weakening Rayleigh-Benard instability. The model highlights the key role played by two parameters generally ignored in explanations of the phenomenon, namely surface emissivity and soil thermal conductivity, and shows that it is unnecessary to invoke the presence of such particulate constituents as haze to produce a lifted minimum.

Electron spectroscopic investigation of the semiconductor-metal transition in La1-xSrxMnO3

We study the electronic structure of La1-xSrxMnO3+δ, x=0, 0.1, 0.2, 0.3, and 0.4, across the semiconductor-metal transition, using various electron spectroscopy techniques. The negligible intensity seen at EF using ultraviolet photoemission spectroscopy and bremsstrahlung isochromat spectroscopy (BIS) indicate an unusual semiconductor-metal transition observed for x≥0.2, consistent with the resistivity data. The BIS spectra show doped hole states developing about 1.4 eV above EF as a function of x. Auger electron spectroscopy gives an estimate of the intra-atomic Coulomb energy in the O 2p manifold to be about 6.8 eV. The Mn 2p core-level spectrum of LaMnO3, analyzed in terms of a configuration-interaction calculation, gives parameter values of the charge-transfer energy Δ=5.0 eV, the hybridization strength between Mn 3d and O 2p states, t=3.8 eV, and the on-site Coulomb energy in Mn 3d states Udd=4.0 eV, suggesting a mixed character for the ground state of LaMnO3.

Two forms of PF1 INOVIRUS: X-ray diffraction studies on a structural phase transition and a calculated libration normal mode of the assymetric unit

Inovirus is a helical array of agr-helical protein asymmetric units surrounding a DNA core. X-ray fibre diffraction studies show that the Pf1 species of Inovirus can undergo a reversible temperature-induced transition between two similar structural forms having slightly different virion helix parameters. Molecular models of the two forms show no evidence for altered interactions between the protein and either the solvent or the viral DNA; but there are significant differences in the shape and orientation of the protein asymmetric unit, related to the changes in the virion parameters. Normal modes involving libration of whole asymmetric units are in a frequency range with appreciable entropy of libration, and the structural transition may be related to changes in libration.

Nonlinear hydrodynamics of a hard-sphere fluid near the glass transition

We conduct a numerical study of the dynamic behavior of a dense hard-sphere fluid by deriving and integrating a set of Langevin equations. The statics of the system is described by a free-energy functional of the Ramakrishnan-Yussouff form. We find that the system exhibits glassy behavior as evidenced through a stretched exponential decay and a two-stage relaxation of the density correlation function. The characteristic times grow with increasing density according to the Vogel-Fulcher law. The wave-number dependence of the kinetics is extensively explored. The connection of our results with experiment, mode-coupling theory, and molecular-dynamics results is discussed.

Observations on transition in plane bubble plumes

Flow visualization studies of plane laminar bubble plumes have been conducted to yield quantitative data on transition height, wavelength and wave velocity of the most unstable disturbance leading to transition. These are believed to be the first results of this kind. Most earlier studies are restricted to turbulent bubble plumes. In the present study, the bubble plumes were generated by electrolysis of water and hence very fine control over bubble size distribution and gas flow rate was possible to enable studies with laminar bubble plumes. Present observations show that (a) the dominant mode of instability in plane bubble plumes is the sinuous mode, (b) transition height and wavelength are related linearly with the proportionality constant being about 4, (c) wave velocity is about 40 % of the mean plume velocity, and (d) normalized transition height data correlate very well with a source Grashof number. Some agreement and some differences in transition characteristics of bubble plumes have been observed compared to those for similar single-phase flows.