Synthesis of α-arylnaphthalenes from diphenylacetaldehydes and 1,1-diphenylacetones

Condensation of diphenylacetaldehydes and 1,1-diphenylacetones with malonodinitrile and cyclization of obtained aryl-ylidenemalonodinitriles in concentrated sulfuric acid leads to 1-amino-4-arylnaphthalene-2-carbonitriles. The benzannulation reaction is accompanied by a quasi-aromatic rearrangement. Preliminary tests of some synthesized aminonitriles have revealed their considerable biological activity against phytopathogenic fungi.     

DCMDS-RV: density-concentrated multi-dimensional scaling for relation visualization

Journal of Visualization - This paper proposes a novel unsupervised multi-dimensional scaling (MDS) method to visualize high-dimensional data and their relations in a low-dimensional (e.g., 2D)...     

Evidence for the spin-dependent scattering of conduction electrons on Mn2+ ions in Hg1−xMnxTe and Cd1−xMnxSe mixed crystals

Changes in the resistivity of Hg_1?xMn_xTe and Cd_1?xMn_xSe mixed crystals associated with paramagnetic resonance of the Mn²⁺ ions have been observed at liquid helium temperature in a strong magnetic field. The effect was recorded by monitoring the submillimeter radiation induced photoconductivity in a swept magnetic field. An increase in the resistivity associated with EPR of the Mn²⁺ ions is interpreted in terms of the spin- dependent scattering of electrons on magnetic impurities, the spins of which are selectively depolarised by means of paramagnetic resonance. Some additional effects influencing the experiments are also discussed.     

g-factor tuning and manipulation of spins by an electric current

We investigate the Zeeman splitting of the two-dimensional electron gas in an asymmetric silicon quantum well, performing electron-spin-resonance (ESR) experiments. Applying a small dc current we observe a shift in the resonance field due to the additional current-induced Bychkov-Rashba type of spin-orbit field. We also show that a high frequency current may induce electric dipole spin resonance very efficiently. We identify different contributions to this type of ESR signal.     

SPE–TLC Profiling of Impurities in 1-(3,4-Methylenedioxyphenyl)-2-nitropropene, an Intermediate in 3,4-Methylenedioxy- methamphetamine (MDMA) Synthesis

Impurity profiling of 1–(3,4-methylenedioxyphenyl)-2-nitropropene, an intermediate in the synthesis of 3,4-methylenedioxymethamphetamine (MDMA), has been studied by SPE combined with TLC. Extraction of impurities was performed on C₁₈ columns. TLC separation was performed on 0.2 mm silica gel 60 plates, with fluorescent indicator F₂₅₄, in a horizontal developing chamber. To improve the quality of the profile (increase the TLC sensitivity) SPE extracts were concentrated by evaporation in a stream of nitrogen. The usefulness of methanol, ethanol, ethyl acetate, chloroform, acetonitrile, and their mixtures as mobile phases was tested by use of Gibbss triangle. Spots of the separated impurities were observed under UV light (_exc=254 and 366 nm). The proposed characteristics of profile quality (optimization criteria) are based on matrix presentation of the TLC pattern. They take into account, simultaneously, the number of spots revealed, differences between R_F values, and the intensity of fluorescence.     

Collective character of spin excitations in a system of Mn2+ spins coupled to a two-dimensional electron gas

We have studied the low energy spin excitations in n-type CdMnTe based dilute magnetic semiconductor quantum wells. For magnetic fields for which the energies for the excitation of free carriers and Mn spins are almost identical, an anomalously large Knight shift is observed. Our findings suggest the existence of a magnetic-field-induced ferromagnetic order in these structures, which is in agreement with recent theoretical predictions [Phys. Rev. Lett. 91, 077202 (2003)]].     

A Robust Identification Technique for Time-Varying ARMA Processes Based on Variable Structure Systems Theory

In this paper, a novel method for extracting the values of the coefficients of time-varying ARMA processes is proposed. The approach discussed assumes solely that the orders of the numerator and the denominator polynomials are known. The algorithm is demonstrated to be stable in the sense of Lyapunov, furthermore, it is shown in the paper that the evolution in the parameter space takes place in a finite volume. The proposed method is cost effective and is based on the variable structure systems theory, which is well known with its robustness to uncertainties. In the simulation example, the coefficients of a second order ARMA process is extracted by the use of the algorithm presented. The results confirm the prominent features of the proposed technique.     

Electron spin resonance and Rashba field in GaN-based materials

We discuss problem of Rashba field in bulk GaN and in GaN/Al_xGa_1−xN two-dimensional electron gas, basing on results of X-band microwave resonance experiments. We point at large difference in spin-orbit coupling between bulk material and heterostructures. We observe coupled plasmon-cyclotron resonance from the two-dimensional electron gas, but no spin resonance, being consistent with large zero-field spin splitting due to the Rashba field reported in the literature. In contrast, small anisotropy of g-factor of GaN effective mass donors indicates rather weak Rashba spin-orbit coupling in bulk material, not exceed 400 G, α_BIA<4×10⁻¹³ eVcm. Furthermore, we observe new kind of electron spin resonance in GaN, which we attribute to surface electron accumulation layer. We conclude that the sizable Rashba field in GaN/Al_xGa_1−xN heterostructures originates from properties of the interface.