A new class of bent‐shaped mesogens exhibiting unusual mesophase behaviour

Examples of a new class of bent‐core compounds are presented, the central fragment of which consists of a benzoyl derivative of a secondary cyclic amine. The mesophase behaviour has been studied by differential scanning calorimetry, polarizing optical microscopy, X‐ray diffraction and electro‐optical measurements. It was found that the five‐ring compounds form smectic CP or B₁ phases which are typical for bent‐core mesogens. The six‐ring compounds exhibit, in some cases, only conventional non‐polar smectic phases; in other cases non‐polar smectic phases as well as banana phases are seen. Of particular interest is the occurrence of a switchable uniaxial semectic A‐like phase with an antiferroelectric structure.     

The Cayley Method and the Inverse Eigenvalue Problem for Toeplitz Matrices

Despite the fact that symmetric Toeplitz matrices can have arbitrary eigenvalues, the numerical construction of such a matrix having prescribed eigenvalues remains to be a challenge. A two-step method using the continuation idea is proposed in this paper. The first step constructs a centro-symmetric Jacobi matrix with the prescribed eigenvalues in finitely many steps. The second step uses the Cayley transform to integrate flows in the linear subspace of skew-symmetric and centro-symmetric matrices. No special geometric integrators are needed. The convergence analysis is illustrated for the case of n = 3. Numerical examples are presented.     

Intermediate frequency modes in Raman spectra of Ar+‐irradiated single‐wall carbon nanotubes

We study the effect of Ar⁺ irradiation on the intermediate frequency modes (IFM) in Raman spectra of single‐wall carbon nanotubes. We observe new features in the intermediate frequency region from 386 to 635 cm^–1 as the defect concentration increases, whereas at the same time there is a decrease of other IFM modes. After annealing in vacuum, the IFM modes recover and become similar to those of the nanotubes before irradiation. We interpret the new features in the Raman spectra as originating from the phonon density of states that becomes visible in the Raman process due to the presence of defects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Intermediate nematic phases in binary systems with complex formation

The phase diagrams of some binary systems of smectogenic compounds are presented in which intermediate nematic phases occur over a large concentration range. An attempt has been made to interpret this behaviour in terms of structural differences between the smectic A phases of the components.     

On the structure of the thermotropic cubic mesophases

Two new substances, glycosides, with an optically isotropic mesophase were investigated. Using measurements of the refractive index, the optical isotropy of the thermotropic phases was proved. X-ray diffraction experiments provided information about the structure of the cubic mesophase. Similarly to the lyotropic cubic phases, here too structures of space group la-3d are present.     

Conductivity study of stretch-oriented new polyacetylene

Oriented polyacetylene samples were synthetized and doped with iodine and FeCl₃. Their electric conductivity and anisotropy were measured within the temperature range 4-300 K. The results were described using the Ping Sheng model. It is concluded that the factors limiting the conductivity parallel and perpendicular to the stretching direction are the same and thus no interfibrillar conduction occurs. Some processes related to the mechanical stretching are discussed. © 1994 John Wiley & Sons, Inc.