An analytical model with temporal variable eddy diffusivity applied to contaminant dispersion in the atmospheric boundary layer

In this work, we present a new analytical model for the prediction of pollutant dispersion in the atmospheric boundary layer incorporating either the spatial and temporal continuous dependence of the eddy diffusivity. For such, we solve the time-dependent three-dimensional advection–diffusion equation combining the Decomposition and GILTT approaches. In fact, applying the idea of Decomposition method, we reduce the advection–diffusion equation with temporal dependence of the eddy diffusivity into a set of recursive advection–diffusion equations with eddy diffusivity just depending on the spatial variable z$z$, which is then directly solved by the GILTT method. To our knowledge this sort of model has not been part of the literature yet.     

Analysis of the NF1 gene by temperature gradient gel electrophoresis reveals a high incidence of mutations in exon 4b

A total of 196 unrelated patients with neurofibromatosis type 1 (NF1) was screened for mutations in exons 4a-c of the NF1 gene by temperature gradient gel electrophoresis (TGGE) of polymerase chain reaction (PCR)-amplified genomic DNA fragments using intron-based primers. DNA samples with abnormal TGGE band patterns were subjected to sequence analysis. Sequence alterations were identified in ten patients (5.1%): 496delGT (1), 499delTGTT (4), T528A = D176E (2), T539A = L180X (1), 540insA (1), C574T = R192X (1). Thus, a total of six different mutations was identified in exon 4b but none in exons 4a and 4c. Only the missense mutation D176E, which we assume to be a nonpathogenic polymorphism, and the 4-base pair (bp) deletion 499delTGTT have been described before. The reason for the high incidence of mutations in exon 4b is obviously a tetranucleotide tandem repeat comprising nucleotides 495-502 (TGTTTGTT) that may give rise to slipped mispairing and subsequent deletion of one repeat unit during replication. Additionally, the recurrent 4 bp deletion was found as a second hit in a malignant schwannoma of a further NF1 patient, suggesting that microlesions may be as frequent among somatic as among germline mutations. This is the first report of a systematic study of NF1 exons 4a-c in a large group of NF1 patients.     

Diffraction analysis of aberrated laser resonators

A numerical analysis of laser resonators with aberrations is presented. The analysis shows that aberrations lead to large diffraction losses of laser resonators which are laid out to produce diffraction-limited beam quality. Static or dynamic compensation of the aberrations is possible and would yield much higher output power. PACS 42.15.Fr; 42.55.Ah; 42.55.Px, Rz     

Divergence of geometrical optics series at the boundary of its applicability: An analytical example in elementary functions (2D Gaussian beam in free space)

An analytical example in elementary functions is presented (2D Gaussian beam diffraction in free space), which demonstrates the divergence of the geometrical optics (GO) series when the conditions for its applicability are violated. This example shows that accounting for higher terms in GO power series leads to divergence and therefore becomes completely useless beyond the boundaries of GO applicability.     

Estimating statistical parameters of an elastic random medium from traveltime fluctuations of refracted waves

Traveltime fluctuations of diving-type refracted waves are studied in the framework of geometrical optics in order to estimate the statistical parameters of an elastic random medium. A stratified background medium is considered in which the velocity increases linearly with depth. Smooth and strongly anisomeric (statistically anisotropic) inhomogeneities are embedded in this medium. The covariance and the variance of traveltime fluctuations are derived and subsequently used to estimate the standard deviation of the medium fluctuations and the inhomogeneity scale lengths in horizontal and vertical directions. The theoretical estimation procedure is verified by performing numerical calculations and it is observed that, under the considered conditions, the traveltime variance decreases at large offsets. This new phenomenon has not been observed before either in acoustics and optics, or in radio wave propagation.     

Atomic force microscopy and transmission electron microscopy of biocompatible magnetic fluids: A comparative analysis

The present study provides a comparative analysis of the size dispersity of magnetic nanoparticles (MNPs) within magnetic fluids as obtained from atomic force microscopy (AFM) and transmission electron microscopy (TEM). Whereas the mean particle diameter obtained from the AFM data presented a reduction of about 34% as compared to the value obtained from the TEM data, the standard deviation obtained from the AFM data is twice the value found from the TEM data. Similarities and differences in the size dispersity parameters are discussed in terms of sample preparation and tip characteristics. A two-dimensional mode for the deposition of the MNPs on top of the mica substrate is discussed as well.     

Boron-mediated aldol reaction of carboxylic esters: complementary anti- and syn-selective asymmetric aldol reactions

The boron-mediated aldol reaction of carboxylic esters is described in detail. Contrary to the general belief that carboxylic esters are inert under the condition of the boron enolate formation, propionate esters are enolized with certain combinations of a boron triflate and an amine. More importantly, the stereochemical course of the aldol reaction can be controlled by the judicious selection of the enolization reagents. Treatment of propionate esters with c-Hex2BOTf and triethylamine produces anti-aldol products, and that with Bu2BOTf and diisopropylethylamine gives syn-aldol products selectively after reaction with aldehydes. Complementary anti- and syn-selective asymmetric aldol reactions with structurally related, readily available chiral norephedrine-derived propionate esters are developed.