scholarly journals Comparison of measured and calculated scattering from surface aerosols with an average, a size-dependent, and a time-dependent refractive index

2011 ◽  
Vol 116 (D2) ◽  
Author(s):  
Yong Cai ◽  
Derek C. Montague ◽  
Terry Deshler
Keyword(s):  
Refractive Index ◽  
Time Dependent ◽  
Size Dependent

SIZE-DEPENDENT NONRESONANT THIRD-ORDER NONLINEAR SUSCEPTIBILITIES OF CdS CLUSTERS FROM 7 TO 120 Å

1992 ◽  
Vol 01 (04) ◽  
pp. 683-698 ◽  
Author(s):  
YING WANG ◽  
NORMAN HERRON
Keyword(s):  
Refractive Index ◽  
Quantum Confinement ◽  
Optical Switching ◽  
Quantum Confinement Effect ◽  
Surrounding Medium ◽  
Confinement Effect ◽  
Third Order ◽  
Size Dependent ◽  
Size Regime ◽  
Fundamental Wavelength

We report the third-order nonlinear susceptibilities χ(3) of CdS clusters (quantum dots) from 7 to 120 Å, measured by third-harmonic generation technique at a fundamental wavelength of 1.91 µm. In the size regime studied, the value of χ(3) first increases with cluster size and then levels off for cluster diameter larger than 60 Å. The volume normalized χ(3) of CdS cluster is about a factor of 2 higher than that of the bulk. These data can be explained by the enhancement in electric field inside the clusters due to the dielectric confinement effect. The size and wavelength dependences of this local field effect have been calculated for CdS clusters. Several trends in the nonresonant χ(3) can be identified: (i) In the absence of quantum confinement effect, the magnitude of χ(3) should be constant in the < 200 Å size regime. It then increases with increasing particle size until the structural resonance regime is reached. (ii) The magnitude of χ(3) can be enhanced by either lowering the refractive index of the surrounding medium or raising the refractive index of the semiconductors. (iii) Quantum confinement, which shifts the band gap to the blue and lowers the refractive index of the semiconductor clusters, reduces the nonresonant χ(3). This is in direct contrast to the resonant nonlinearity which is enhanced by the quantum-confinement effect. Finally, we discuss the size-dependent figure-of-merit of CdS composites for all-optical switching.

scholarly journals The relevance of aerosol optical depth to cumulus fraction changes: a five-year climatology at the ACRF SGP site

2007 ◽  
Vol 7 (4) ◽  
pp. 11797-11837 ◽  
Author(s):  
E. I. Kassianov ◽  
L. K. Berg ◽  
C. Flynn ◽  
S. McFarlane
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Great Plains ◽  
Value Added ◽  
Cloud Fraction ◽  
Satellite Observations ◽  
Time Dependent ◽  
Size Dependent ◽  
Cloud Properties ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. The objective of this study is to investigate, by observational means, the magnitude and sign of the actively discussed relationship between cloud fraction N and aerosol optical depth τa. Collocated and coincident ground-based measurements and Terra/Aqua satellite observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site form the basis of this study. The N–τa relationship occurred in a specific 5-year dataset of fair-weather cumulus (FWC) clouds and mostly non-absorbing aerosols. To reduce possible contamination of the aerosols on the cloud properties estimation (and vice versa), we use independent datasets of τa and N obtained from the Multi-filter Rotating Shadowband Radiometer (MFRSR) measurements and from the ARM Active Remotely Sensed Clouds Locations (ARSCL) value-added product, respectively. Optical depth of the FWC clouds τcld and effective radius of cloud droplets re are obtained from the MODerate resolution Imaging Spectroradiometer (MODIS) data. We found that relationships between cloud properties (N,τcld, re) and aerosol optical depth are time-dependent (morning versus afternoon). Observed time-dependent changes of cloud properties, associated with aerosol loading, control the variability of surface radiative fluxes. In comparison with pristine clouds, the polluted clouds are more transparent in the afternoon due to smaller cloud fraction, smaller optical depth and larger droplets. As a result, the corresponding correlation between the surface radiative flux and τa is positive (warming effect of aerosol). Also we found that relationship between cloud fraction and aerosol optical depth is cloud size dependent. The cloud fraction of large clouds (larger than 1 km) is relatively insensitive to the aerosol amount. In contrast, cloud fraction of small clouds (smaller than 1 km) is strongly positively correlated with τa. This suggests that an ensemble of polluted clouds tends to be composed of smaller clouds than a similar one in a pristine environment. One should be aware of these time- and size-dependent features when qualitatively comparing N–τa relationships obtained from the satellite observations, surface measurements, and model simulations.

scholarly journals Pesticide Encapsulation at the Nanoscale Drives Changes to the Hydrophobic Partitioning and Toxicity of an Active Ingredient

Nanomaterials ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 81 ◽  
Author(s):  
Matthew Slattery ◽  
Bryan Harper ◽  
Stacey Harper
Keyword(s):  
Active Ingredient ◽  
Large Fraction ◽  
Ceriodaphnia Dubia ◽  
Time Dependent ◽  
Hydrodynamic Diameter ◽  
Dependent Manner ◽  
Size Dependent ◽  
Pesticide Formulations ◽  
Dependent Inhibition ◽  
Time Dependent Inhibition

Given the costs associated with designing novel active ingredients, new formulations focus on the use of other ingredients to modify existing formulations. Nanosized encapsulated pesticides offer a variety of enhanced features including controlled release and improved efficacy. Despite the presence of nanosized capsules in current-use pesticide formulations, the analytical and toxicological implications of encapsulation are uncertain. To explore this issue quantitatively, we fractionated the capsules of a commercially available encapsulated insecticide formulation (γ-cyhalothrin active ingredient) into two size ranges: a large fraction (LF), with an average hydrodynamic diameter (HDD) of 758 nm, and a small fraction (SF), with an average HDD of 449 nm. We developed a novel extraction method demonstrating a time-dependent inhibition of γ-cyhalothrin from capsules for up to 48 h. An acute immobilization test with a freshwater macroinvertebrate (Ceriodaphnia dubia) revealed that the SF was significantly more toxic than both the LF and the free γ-cyhalothrin treatment (EC50 = 0.18 µg/L, 0.57 µg/L, and 0.65 µg/L, respectively). These findings highlight that encapsulation of γ-cyhalothrin mitigates hydrophobic partitioning in a time-dependent manner and influences toxicity in a size-dependent manner. Recognizing the analytical and toxicological nuances of various nanosized capsules can contribute to innovation in pesticide formulations and may lead to more comprehensive pesticide regulation.

Optical excitation waves in a molecular crystal

1964 ◽  
Vol 282 (1390) ◽  
pp. 433-445 ◽  
Keyword(s):  
Refractive Index ◽  
Quantum Theory ◽  
Excited States ◽  
Molecular Crystal ◽  
Optical Excitation ◽  
Time Dependent ◽  
Hartree Approximation ◽  
Quasi Particle ◽  
Quantum Theory Of Radiation ◽  
Classical Picture

We have used the quantum theory of radiation, within the time-dependent Hartree approximation, to study exciton states of a van der Waals molecular crystal. The radiation variables are eliminated to give a semi-classical picture of molecular dipoles interacting through a retarded potential, and the solutions of the Hartree equations are closely connected with the quasi-particle excited states in Agranovich’s theory. In the Lorentz-Lorenz approximation the crystal has excited states which correspond to both longitudinal and transverse exciton weaves, and the refractive index behaves classically. The paper concludes with a brief discussion of metallic reflexion by dye crystals.

Mode-locking observation of a CO2 laser by intracavity plasma injection

1980 ◽  
Vol 58 (6) ◽  
pp. 840-844 ◽  
Author(s):  
P. K. John ◽  
M. Dembinski
Keyword(s):  
Refractive Index ◽  
Shock Tube ◽  
Plasma Density ◽  
Co2 Laser ◽  
Mode Locking ◽  
Time Dependent ◽  
Electromagnetic Shock ◽  
Plasma Injection ◽  
Phase Perturbation ◽  
Underdense Plasma

A TEA CO2 laser was simultaneously Q-switched and mode-locked when an underdense plasma was injected into the cavity. The plasma was produced in an electromagnetic shock tube. Plasma density and temperature were Ne ~ 1017 cm−3 and Te ~ 2 eV, respectively. Phase perturbation of the cavity due to the time dependent plasma refractive index could account for the observed mode-locking.

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