Influence of the composition of the polymer matrix on the electrooptical properties of films with a dispersed liquid crystal

Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.     

PERIODIC ENVIRONMENTS AND PERIODIC HARVESTING

ABSTRACT. We consider autonomous population models under periodic harvesting and population models in periodic environments and seek conditions under which there is an asymptotically stable periodic solution.     

Electrohydrodynamic instability in some nematic cyanobiphenyls in an a.c. electric field

Electrohydrodynamic instability in homeotropically oriented nematic samples of 4'-n-octyl-4-cyano-biphenyl and 4'n-alkyloxy-4-cyanobiphenyl, (n = 8.9) have been studied in an a.c. electric field. The domain patterns during the instability in these compounds in a very low frequency a.c. field are very similar to those in a d.c. field. The domain patterns observed at higher frequencies have been identified as 'maltese crosses' or 'crossed isogyres'. The electro-convective 'isotropic' flows near the electrode play an important role in the observed instability.     

Combined supercritical-fluid chromatography/mass spectrometry in the analysis of diuron in plasma using on-line phase-system switching

On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL.     

Burning Voltage in Atmospheric and Vacuum Short Arcs of Vanishing Length

The stepwise increase of the burning voltage of short break arcs has been found not only in a gas but also in vacuum. It is suggested that the effect is associated with the occurrence of a positive anode fall which enhances ionisation phenomena near the anode. This view is supported by the simultaneous registration of arc current, burning voltage, light emission from the anode region, of spectral lines of ions, atoms and continuum from the near anode plasma. The phenomena occur beyond a critical gap distance which can be related to the characteristic geometry of the discharge.     

Direct numerical simulation of settling of a large solid particle during bioconvection

Settling of a large solid particle in bioconvection flow caused by gyrotactic microorganisms is investigated. The particle is released from the top of the bioconvection chamber; its settling pattern depends on whether it is released in the centre of the bioconvection plume or at its periphery. The Chimera method is utilized; a subgrid is generated around a moving particle. The method suggested by Liu and Wang (Comput. Fluid 2004; 33 :223–255) is further developed to account for the presence of a moving boundary in the streamfunction‐vorticity formulation using the finite‐difference method. A number of cases for different release positions of the particle are computed. It is demonstrated that bioconvection can either accelerate or decelerate settling of the particle depending on the initial position of the particle relative to the plume centre. It is also shown that the particle impacts bioconvection plume by changing its shape and location in the chamber. Copyright © 2005 John Wiley & Sons, Ltd.     

A transform method for linear evolution PDEs on a finite interval

We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series.     

Banana-shaped mesogens: a new homologous series of compounds exhibiting the B7 mesophase

The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B₇ mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.