Aerosol light absorption and its measurement: A review

Light absorption by aerosols contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. Aerosol light absorption in the atmosphere is dominated by black carbon (BC) with additional, significant contributions from the still poorly understood brown carbon and from mineral dust. Sources of these absorbing aerosols include biomass burning and other combustion processes and dust entrainment.For particles much smaller than the wavelength of incident light, absorption is proportional to the particle volume and mass. Absorption can be calculated with Mie theory for spherical particles and with more complicated numerical methods for other particle shapes.The quantitative measurement of aerosol light absorption is still a challenge. Simple, commonly used filter measurements are prone to measurement artifacts due to particle concentration and modification of particle and filter morphology upon particle deposition, optical interaction of deposited particles and filter medium, and poor angular integration of light scattered by deposited particles. In situ methods measure particle absorption with the particles in their natural suspended state and therefore are not prone to effects related to particle deposition and concentration on filters. Photoacoustic and refractive index-based measurements rely on the heating of particles during light absorption, which, for power-modulated light sources, causes an acoustic signal and modulation of the refractive index in the air surrounding the particles that can be quantified with a microphone and an interferometer, respectively. These methods may suffer from some interference due to light-induced particle evaporation. Laser-induced incandescence also monitors particle heating upon absorption, but heats absorbing particles to much higher temperatures to quantify BC mass from the thermal radiation emitted by the heated particles. Extinction-minus-scattering techniques have limited sensitivity for measuring aerosol light absorption unless the very long absorption paths of cavity ring-down techniques are used. Systematic errors can be dominated by truncation errors in the scattering measurement for large particles or by subtraction errors for high single scattering albedo particles. Remote sensing techniques are essential for global monitoring of aerosol light absorption. While local column-integrated measurements of aerosol light absorption with sun and sky radiometers are routinely done, global satellite measurements are so far largely limited to determining a semi-quantitative UV absorption index.     

Estimation of chemical abundance of primary cosmic-ray nuclei over Alice Springs using balloon-borne passive detectors

Summary A stack consisting of CR-39 (HCB 0.5%), nuclear emulsions and X-ray films was exposed to primary cosmic rays by a balloon lauched from Alice Springs in 1983 and was flown for 32 hours at an atmospheric depth 9.8 g cm⁻² air. The recovered plastic plates were etched in 7.5 N NaOH solution at 80°C for 96 hours. The major and minor axes of the elliptic etch pits were analysed. About 1112 elliptic etch pits were scanned. The measured integral flux of very heavy (VH) and Fe nuclei above 3.5 GeV/n are in approximate aggreement with the earlier survey of Dokeet al., but yield a flatter energy spectrum when compared to the recent high-energy extrapolated spectrum of Zatsepinet al. The charges of the detected heavy nuclei were also confirmed from delta-ray counting of heavily ionized tracks in nuclear emulsions. The energy of the incident heavy nuclei has been measured from the distribution of opening angles of alpha fragments initiated by heavy nuclei in nuclear emulsions.     

Self Replication and Signalling

It is known that if one could clone an arbitrary quantum state one could send signal faster than the speed of light. However it remains interesting to see that if one can perfectly self replicate an arbitrary quantum state, does it violate the no signaling principle? Here we see that perfect self replication would also lead to superluminal signaling.     

Mössbauer spectroscopic studies of magnesium nickel ferrites

Mössbauer spectra of magnesium nickel ferrites having spinel structure with varying percentages of nickel were obtained at room temperature. The split extreme high-resonance line could be resolved into two Lorentzians from which the cation distribution was calculated. The calculated cation distributions match very well with those obtained from magnetization measurements as well as from ferromagnetic resonance studies on the same samples. The observed quadrupole split and the hyperfine field values can be rationalized based on the obtained cation distributions.     

An Efficient Approach to Chiral Allyloxyamines by Stereospecific Allylation of Nitrosoarenes with Chiral Allylboronates

A novel and efficient approach to allyloxyamines by the allylation of nitrosoarenes with α‐chiral allylboronates is described. C? O bond formation occurs with high stereospecificity and the product allyloxyamines are easily transformed into valuable chiral building blocks such as isoxazolidines and allylic alcohols. The reaction features complete regioselectivity (O‐selectivity), high E/Z selectivity, and excellent chirality transfer.     

Elucidating the mechanism of nucleation near the gas-liquid spinodal

We have constructed a multidimensional free energy surface of nucleation of the liquid phase from the parent supercooled and supersaturated vapor phase near the gas-liquid spinodal. In particular, we remove the Becker-Doring constraint of having only one growing cluster in the system. Close to the spinodal, the free energy, as a function of the size of the largest cluster, develops surprisingly a minimum at a subcritical cluster size. It is this minimum at intermediate size that is found to be responsible for the barrier towards further growth of the nucleus at large supersaturation. An alternative free energy pathway involving the participation of many subcritical clusters is found near the spinodal where the growth of the nucleus is promoted by a coalescence mechanism. The growth of the stable phase becomes collective and spatially diffuse, and the significance of a "critical nucleus" is lost for deeper quenches.     

Effect of cyclodextrin nanocavity confinement on the photophysics of a beta-carboline analogue: a spectroscopic study

Interaction of a beta-carboline based biologically active molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueous solution has been studied using steady state and time-resolved fluorescence and steady-state fluorescence anisotropy techniques. Polarity dependent intramolecular charge transfer (ICT) process is responsible for the remarkable sensitivity of this biological fluorophore to the CD environments. Upon encapsulation, the CT fluorescence exhibits hypsochromic shift along with enhancements in the fluorescence yield, fluorescence anisotropy (r), and fluorescence lifetime. The reduction in the nonradiative deactivation rate of the fluorophore within the CD nanocavities leads to an increase in both fluorescence yield and lifetime. Among the three CDs, gamma-CD shows the most spectacular confinement effect. The results establish the formation of 1:1 AODIQ:CD inclusion complexes in alpha- and beta-CDs. In aqueous gamma-CD solutions, however, depending on the concentration of the gamma-CD, formation of both 1:1 and 1:2 complexes have been revealed. Hydrodynamic radii of the 1:1 and 1:2 probe-gamma-CD supramolecular complexes have also been determined.     

Photophysics of a cationic biological photosensitizer in anionic micellar environments: combined effect of polarity and rigidity

A steady-state and time-resolved photophysical study of a cationic phenazinium dye, phenosafranin (PSF), has been investigated in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain lengths, namely, sodium decyl sulfate (S(10)S), sodium dodecyl sulfate (S(12)S), and sodium tetradecyl sulfate (S(14)S). In all these micellar environments, the charge transfer fluorescence of PSF shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield as compared to that in aqueous medium. A reduction in the nonradiative deactivation rate within the hydrophobic interior of micelles led to an increase in the fluorescence yield and lifetime. The present work shows the degree of accessibility of the fluorophore toward the ionic quencher in the presence of surfactants of different surfactant chain lengths. The fluorometric and fluorescence quenching studies suggest that the fluorophore resides at the micelle-water interfacial region. The enhancements in the fluorescence anisotropy and rotational relaxation time of the probe in all the micellar environments from the pure aqueous solution suggest that the fluorophore binds in motionally restricted regions introduced by the micelles. Polarity and viscosity of the microenvironments around the probe in the micellar systems have been determined. The work has paid proper attention to the hydrophobic effect of the surfactant chain length on photophysical observations.     

Surfactant chain-length-dependent modulation of the prototropic transformation of a biological photosensitizer: norharmane in anionic micelles

A photophysical study of norharmane (NHM), an efficient cancer cell photosensitizer, has been undertaken in well-characterized biomimetic micellar nanocavities formed by anionic surfactants of varying chain length, namely, sodium decyl sulfate (S10S), sodium dodecyl sulfate (S12S), and sodium tetradecyl sulfate (S14S), using steady-state and time-resolved fluorescence spectroscopy. The effect of the hydrophobic chain length on the structural dynamism of the fluorophore has been reported. Experimental results demonstrate that the equilibrium of this dynamism is sensitive to the environment. Variation in the surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. A striking feature of the present study is that an increase in the surfactant chain length (hydrophobicity) favors the cationic species of NHM. This has been rationalized on the basis of changes in the local pH and the aggregation number of the micelles. A fluorescence quenching study of the micelle-bound probe using ionic quencher Cu2+ corroborates this.