Synthesis and characterization of guest-host azo dyes with broad absorption bands

Abstract

Three groups of dyes were synthesized and characterized in order to examine their solubility, absorption spectrum, and order parameter in liquid crystal hosts. Our synthesis method allowed the formation of the diazonium salts and the diazo coupling in ethyl acetate instead of an aqueous medium, permitting the formation of long and neutral azo dyes. In the liquid crystal BDH-E7, they showed order parameters in the range of 0.52 to 0.76. The two dyes with the longest molecular lengths were particularly interesting due to their very broad absorption spectra in the visible region. Each of these two compounds behave as single component black dye guest/host systems, which generally require a mixture of two or three dyes in the liquid crystal host. These dyes were also evaluated for use in polymer dispersed liquid crystal films.     

Cyanobacterial Polyketide Synthase Docking Domains: A Tool for Engineering Natural Product Biosynthesis

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Theory of spin noise in nanowires

We develop a theory of spin noise in semiconductor nanowires considered as prospective elements for spintronics. In these structures, spin-orbit coupling can be realized as a random function of a coordinate correlated on a spatial scale of the order of 10?nm. By analyzing different regimes of electron transport and spin dynamics, we demonstrate that the spin relaxation can be very slow, and the resulting noise power spectrum increases algebraically as the frequency goes to zero. This effect makes spin phenomena in nanowires best suitable for studies by rapidly developing spin-noise spectroscopy.     

Measurement of the cross section of the reaction pp → pp π0 in the region of dibaryon resonances

The energy dependence of the cross section of the neutral pion production is measured in the range 600÷900 MeV. No unambiguous evidences for the existence of broad isovector dibaryon resonances were obtained. The isoscalar cross section of the pion production does not reveal any structure, predicted by the theory with resonances.     

Asymptotic statistical properties of AR spectral estimators forprocesses with mixed spectra

The influence of a point spectrum on large sample statistics of the autoregressive (AR) spectral estimator is addressed. In particular, the asymptotic distributions of the AR coefficients, the innovations variance, and the spectral density estimator of a finite-order AR(p) model to a mixed spectrum process are presented. Various asymptotic results regarding AR modeling of a regular process with a continuous spectrum are arrived at as special cases of the results for the mixed spectrum setting. Finally, numerical simulations are performed to verify the analytical results     

The synergistic effect of polysorbate 80 upon the toxicity of tri-n-butyltin chloride

Polysorbate 80 (Tween 80) was used as an emulsifying agent for administering tri-n-butyltin chloride (TBTCl) to rats below, at and above the LD₅₀ for the compound. Tween 80 greatly enhanced the toxicity of the organotin compound. The LD₅₀ in the presence of Tween 80 (16% of the emulsion) is less than half of the LD₅₀ when the TBTCl was administered in corn oil.     

On the identification of harmonic signal fields convergence methodin an arbitrary noise field using the 1-D MV spectrum

This paper considers the recovery of a multichannel harmonic signal field corrupted by a possibly unknown homogeneous noise field. An approach is presented using the convergence-based spectra developed by Foias et al. (1990) in the random process setting. This technique has the advantage of discerning between the point and narrowband noise spectrum based on the monotonically decreasing convergence properties of a sequence of minimum variance (MV) spectra. For the proposed technique, the random field is reduced to a sequence of random processes using a set of condensing functions. An additional advantage of the proposed technique is that these condensing functions can be used to reflect a priori information and, hence, improve the effective signal-to-noise ratio (SNR). This technique uses information from all dimensions. Traditional techniques would separately apply a spectral algorithm to each dimension of the random field and thereby lose joint information from other dimensions     

Nonlinear interaction of s.a.w.s in piezoelectric crystals with secondary electrons

Some new experimental results and a simple theoretical model of nonlinear interaction of s.a.w.s in piezoelectric crystals with electron beams are presented.