The effect of olefinic terminal chains on the mesomorphic properties of 4,4'-disubstituted diphenyldiacetylenes

New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1-4; and X = C n H 2n + 1 , F, CF 3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF 3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices.

Four of the diacetylenes with m = 1 ( A, B = H) were also prepared ( X = C 6 H 13 , F, n = 2, 3). When X was C 6 H 13 ( n = 2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X = F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X = C 6 H 13 and n = 2 had a melting temperature below room temperature.     

Ultrashort pulse laser osteotomy

Laser treatment of bone tissue has already been the subject of many studies to find substitutes for mechanical instruments that are nowadays used in implantology and orthopaedics. Mainly lasers with pulse durations in the μs region have been tested leaving surface features that are not always satisfactory. Therefore, in the present study laser osteotomy has been performed with a 330 fs Yb:glass laser, λ = 1040 nm, at a pulse repetition rate of 1 kHz. For bovine spongiosa, compacta, and cartilage, the ablation thresholds as well as the ablation rates for various pulse energies have been determined. Additionally, quadratic areas have been ablated in bone tissue. The remaining morphology has been analyzed via scanning electron microscopy. Laser ablation has also been performed with an Er, Cr:YSGG laser, λ = 2780 nm, PRR = 20 Hz, τ ～ 50 μs. The results of USPL and Erbium laser ablation are compared.     

Vortex ring generation due to the coalescence of a water drop at a free surface

 Results are presented of an experimental investigation of vortex ring formation by a fluid drop contacting a free surface with negligible velocity. The pool fluid is mixed with fluorescein dye, and a laser sheet is used to illuminate a plane of the flow. A series of representative images is recorded by a CCD camera and speculation is made regarding specific sources of vorticity flux through the free surface. Two scaling analyses previously presented by other investigators are demonstrated to be equivalent under the assumptions of this experiment, and they provide the motivation for a series of test runs in which the duration of the coalescence process, τ_*, is related to variations in drop diameter L and fluid surface tension σ. Experimental results are in agreement with the analyses, showing τ_*∼σ^-1/2 and τ_*∼L ^3/2. Received: 22 December 1995 / Accepted: 15 October 1996     

Exact solutions of a nonlinear sigma-model in a curved space and the theory of magnetically ordered media with variable saturation magnetization

Stationary solitons are found to occur in two-dimensional media with a variable saturation magnetization whose square is a harmonic function of the coordinates. It is shown in this case that the Landau-Lifshits equation can be reduced to the integrable O(3) sigma-model in curved space. Some properties of the solutions obtained are discussed. Bibliography: 15 titles. Translated by V. D. Lipovskii.     

Solution of a singular Cauchy problem of implicit form

Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 6, pp. 755–760, June, 1991.     

Relevance of Reflection in Static and Dynamic Light Scattering Experiments

Using a monodisperse PMMA dispersion, it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influcence of reflection on DLS measurements was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from the basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the static and dynamic light scattering technique.