Photoinduced dichroism in additively coloured KCl: Na at room temperature

Spectral and kinetic investigations of the reversible photoinduced dichroism in KCl : Na containing F_A and F_A + F_B centers are done. It is suggested that in presence of F_B centers the observed 〈100〉 and 〈110〉 dichroism is connected with the F_B(II) centers.     

Relativistically invariant equations (βμ∂μ+ϱ)Ψ(x)=0 with singular ϱ, and detβ0 ≠ 0

We study relativistically invariant equations (β^μ?_μ+?)Ψ(x)=0 with a singular ?. The absence of a simple relation between these equations and their “conjugate” $\text{((β}{}^{\mathrm{\mu }}\text{)}{}^1\text{?}{}_{\mathrm{\mu }}\text{? ?}{}^1\text{)?(x) = 0}$ is pointed out. Assuming that Ψ(x) transforms under an arbitrary finite-dimensional representation of ISL(2,C), the problem of existence is investigated. It is shown that the assumption detβ⁰ ≠ 0 implies: all β^μ are invertible and the representation of ISL(2,C) is even- dimensional. The difficulties in the general treatment of the problem are discussed. A particular class of equations is illustrated by several examples.     

Photoinduced macroscopic chiral structures in a series of azobenzene copolyesters

A study of the propagation of elliptically polarized light and the resulting formation of macroscopic chiral structures in a series of azobenzene side-chain copolyesters, in which the morphology is varied from liquid crystalline to amorphous, is reported. Real-time measurements are presented, showing the dynamic behavior of the photoinduced rotation of the polarization ellipse in the different samples. The relationship between the ellipticity of the recording light and the linear birefringence induced is studied. A numerical solution that takes into account the influence of the photoinduced linear dichroism on the light propagation through the samples is presented. Received: 10 June 2002 / Revised version: 26 July 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +45-4677/4588, E-mail: lian.nedelchev@risoe.dk RID="**" ID="**"Permanent address: Department of Chemistry and Physics, The Nottingham Trent Unversity, Clifton Lane, Nottingham NG11 8NS, England     

Synthesis of 1,3-aminonaphthols by diastereoselective Betti-type aminoalkylation of dihydroxy naphthalenes; diastereoselectivity,absolute configuration,and application

Dihydroxy naphthalenes have been applied in Betti-type solventless condensation between aldehydes and (S)-phenylethylamine as a chiral auxiliary. A series of chiral 1,3-aminonaphthols has been synthesized and isolated in diastereoisomerically pure form. The absolute configurations of the aminonaphthols synthesized have been determined by means of advanced NMR experiments and confirmed by X-ray crystallography. The new chiral aminonaphthols have been tested as pre-catalysts for the addition of diethyl zinc and alkynyl-Zn-reagents to aldehydes with enantioselectivities of up to 98% ee.     

Design of designs

Representing a design graphically can make certain properties of a design obvious that otherwise would require tedious reasoning. This holds for symmetries, resolvability, and subdesign inclusion in appropriate cases. We describe how a graphical representation can be achieved in many cases and show several examples, in particular visualizations of the biplanes on up to 16 vertices and subdesigns of the large Witt design. © 2011 Wiley Periodicals, Inc. J Combin Designs 20:1–22, 2012     

On the Possibility of Chaos in a Generalized Model of Three Interacting Sectors

In this study we extend a model, proposed by Dendrinos, which describes dynamics of change of influence in a social system containing a public sector and a private sector. The novelty is that we reconfigure the system and consider a system consisting of a public sector, a private sector, and a non-governmental organizations (NGO) sector. The additional sector changes the model’s system of equations with an additional equation, and additional interactions must be taken into account. We show that for selected values of the parameters of the model’s system of equations, chaos of Shilnikov kind can exist. We illustrate the arising of the corresponding chaotic attractor and discuss the obtained results from the point of view of interaction between the three sectors.     

Gas absorption in a thin liquid film flow on a horizontal rotating disk

An analytical model for the rate of gas absorption into laminar non-wavy film flow on a horizontal rotating disk is obtained assuming short contact times. Literature data for the oxygen mass transfer coefficient in a wavy film is correlated by means of the dimensionless numbers deriving from the model. The rate enhancement due to waves is found to vary from 6 to 13 times. It is established that the absorption process in the film on the disk as compared to that in a gravitational wavy film flow can be intensified up to 14 times by means of a moderate rotation speed.     

[PbAsSiiPr3]6 — the First Structurally Characterized Compound with Chemical Bonds between Lead and Arsenic

The compound [PbAsSiiPr₃]₆ ( 1 ) could be obtained by the reaction of PbCl₂ with iPr₃SiAs(SiMe₃)₂ in THF at 0 °C. Central structural motif is a hexagonal prism built by six lead and six arsenic atoms. The average Pb—As bond length is 281 pm. The cluster crystallizes in the monoclinic space group C2/c, the lattice constants are: a = 4460.8(9) b = 2296.6(5), c = 2734.4(6) pm, β = 117.57(3)°. The thermogravimetric analysis in vacuum shows the tendecy of 1 to decompose under formation of elementary lead and volatile arsenic compounds.     

High-sensitivity material with reversible photo-induced anisotropy

A new high-sensitivity material with reversible photo-induced anisotropy, suitable for real-time recording, is investigated. The material (methyl-red dye introduced in a polymer layer) requires low recording intensities (tens of mW cm^-2) and possesses excellent reusability.