Liquid crystal side chain polysiloxanes containing various proportions of non-mesogenic units

Recent studies have established that side chain polymeric liquid crystals composed of mesogenic and non-mesogenic side groups keep their liquid-crystalline properties even for a low proportion of mesogens. We show that the detailed structures of three kinds of new diluted liquid crystal polysiloxanes depend on the nature of the co-substituent as well as on the proportion of the silicon sites occupied by the mesogenic groups. Mixtures of these systems with low molar mass liquid crystals were also investigated in terms of compatibility and/or stabilization of smectic A phases.     

Signal averaging in gas chromatography

Ensemble or signal averaging, and the use of the technique for the solution of some unique problems with minimum sample handling, have previously been reported. The capability of the technique has been evaluated with microbore gas chromatography for the fast handling of a large number of analyses: ca 20–30 replicate injections are easily attainable in a reasonable analysis time. The implementation of the signal averaging technique with other concentration techniques for improving detection limits is also demonstrated.     

Determination in plasma of angiotensin-converting enzyme inhibitor by inhibitor-binding assay.

A method of determining a new angiotensin-converting enzyme inhibitor (CS-622) and its active metabolite (RS-5139) in plasma by inhibitor-binding assay has been developed using high-performance liquid chromatography. The assay is based on the principle that the amount of inhibitor bound to the enzyme is inversely related to the amount of hippuric acid liberated on hydrolysis from the artificial substrate (hippuryl-L-histidyl-L-leucine). Plasma was heated at 60 degrees C for 15 min, to inactivate endogenous enzyme, and preincubated with rabbit-lung angiotensin-converting enzyme at 37 degrees C for 3 min. The artificial substrate (5.75 mg/ml in pH 8.3 phosphate buffer containing sodium chloride) was added to the resulting solution, and the mixture was incubated for 30 min. The reaction was terminated by the addition of 2 M hydrochloric acid. The hippuric acid liberated on hydrolysis was extracted with ethyl acetate and determined by reversed-phase chromatography using methylparaben as an internal standard. The total concentration of the inhibitor and its metabolite were determined by this method after de-esterification by rat-plasma esterase. The standard curve was obtained by the regression analysis of log concentration against logit response. The within-day and day-to-day precision were satisfactory. The proposed method is simple, rapid and sensitive enough to determine angiotensin-converting enzyme inhibitor in plasma.     

Higher order radiative corrections to the QED Compton events at HERA

We estimate the higher order QED corrections to the QED Compton events at HERA employing the leading logarithmic approximation to all orders in α. The Compton events are events of the typee+p→e′+γ+ Hadrons, wheree′ and γ have nearly balancedp _T .     

Proton relaxation times in human red bone marrow by volume selective magnetic resonance spectroscopy

In hematological diseases the composition of red bone marrow shows alterations. The relaxation timesT ₁ andT ₂ of water and lipids in human hemopoietic bone marrow of 14 normal volunteers and 10 patients with acute leukemia and bone marrow carcinosis are determined using a double spin echo spectroscopy sequencein vivo. The volumes of interest (VOI) of (13 mm)³ in the center of vertebral bodies are examined using different measurement parameters. ForT ₁ measurements an inversion-recovery method is used.T ₂ is evaluated from spectra with differentTE. T ₁ (water) is found in a range between 1000 and 1700 ms,T ₁ (lipids) in a range between 260 and 320 ms in healthy volunteers.T ₂ (water) is determined between 32 and 65 ms. In some cases phase distortions of the water signals occur in the spectra. Water flow within the VOI may be a possible reason.T ₂ (lipids) is evaluated between 73 and 91 ms. The patients with acute leukemia exhibit clearly reduced lipid signals in their spectra. Lipid relaxation times could not be determined in these cases.T ₂ (water) is prolonged in acute leukemia to 51–98 ms.T ₁ (water) was not significantly different from values of healthy volunteers in our measurements. Results are discussed in comparison to relaxometric data from imaging and STEAM spectroscopic methods of other authors.     

Separation of screw-sensed particles in a homogeneous shear field

The Stokes motions of three-dimensional screw-sensed slender particles in a homogeneous shear field are investigated, including the effects of buoyancy. Conclusions are drawn about the possibility of achieving a separation of mixtures of right- and left-handed particles. The linearity of the Stokes equations allows complex flows to be solved by adding the effects of the several terms which describe the flow in which the particle is immersed. The homogeneous shear flow considered here consists of three such terms; solutions for a series of 12 unit motions are sufficient to determine the hydrodynamic resistance tensors. The forces and torques experienced by screw-sensed particles are calculated from these 51 resistance tensors, using slender-filament theory. The results allow an estimate of the range of buoyancy parameters for which gravitational sedimentation can be neglected. The fundamental component of the particle motion is a rotation, at approximately the same angular velocity as that of the fluid. Superimposed on this are variations, of large period, in the particle orientation. A phase plane analysis is used to find the terminal orientations. Very long calculation times are required for the phase portrait. An approximate method based on azimuthally-averaged equations is developed to avoid the requirements for long time integration.     

Dielectric relaxation of a short molecule in a liquid-crystalline solvent

Dielectric relaxation measurements of 5 mole % 4-n-hexyloxycyanobenzene (I) dissolved in 4-n-pentyloxyphenyl-trans-4-n-octylcyclohexylcarboxylate (II) were carried out from 1 kHz to 10 MHz in the nematic, smectic A and smectic B phases. The relaxation frequency of I parallel to the director is about 05 MHz in the S_Bphase and increases rapidly at the transition from S_B to S_A.