Interferometric method for determining the sum of the flexoelectric coefficients (e1+e3) in an ionic nematic material

The time-dependent periodic distortion profile in a nematic liquid crystal phase grating has been measured from the displacement of tilt fringes in a Mach-Zehnder interferometer. A 0.2 Hz squarewave voltage was applied to alternate stripe electrodes in an interdigitated electrode geometry. The time-dependent distortion profile is asymmetric with respect to the polarity of the applied voltage and decays with time during each half period due to ionic shielding. This asymmetry in the response allows the determination of the sum of the flexoelectric coefficients (e1+e3) using nematic continuum theory since the device geometry does not possess inherent asymmetry

Modeling of Constriction Resistance in Coated Joints

Metallic coatings applied to surfaces in contact have been shown to be effective at reducing thermal contact resistance. Contact resistance is primarily caused by the constriction of heat flow as it passes through individual contact spots. Most analyses of coated constrictions have been limited to plane contacts of a semi- infinite cylinder, while an actual constriction terminates in a shape like the frustum of a cone. A numerical model has been developed to determine the constriction resistance of such a coated asperity. The gap between the cone and contact surface is considered to either be evacuated or filled with a gas, and the temperature jump phenomenon is included in the gas-gap model. The effects of radiation heat transfer are also included. The results indicate that an optimum coating thickness for minimizing constriction resistance exists in all cases. Most gases are found to reduce the coating effectiveness very slightly, especially compared to the effect of radiation. The effect of radiation on the model is shown to be highly dependent on the joint temperature, substrate and coating thermal conductivities, and constriction ratio. Contrary to current belief, radiation is shown to be important even for temperatures below 300°C when either the substrate conductivity or the constriction ratio is very low

Bend and splay elastic constants of a discotic nematic

We report the dielectric constants and the splay and bend elastic constants of hexan-dodecanoyloxy truxene in the nematic phase, which occurs between two columnar phases. The dielectric anisotropy is positive. The elastic constants are ∼10−7 dyne, which is of the same order as for nematics of rod-like molecules. Further, k33 > k11, probably as a consequence of the columnar short range order in the medium

Electrooptic soft mode response of compounds exhibiting the antiferroelectric phase

We report measurements on the electrooptic response of thin samples (~2-5 μm) of two antiferroelectric liquid crystals. All the phase transitions in these compounds can be very easily detected using this technique. We have been able to measure such an electrooptic effect for the first time in the antiferroelectric and smectic I∗ phases of a tolane compound. The response shows a relaxation at high frequencies (~10 KHz) and is at-tributed to a soft mode which produces an asymmetry in the molecular tilt in successive layers

Drosophila Activated Cdc42 Kinase Has an Anti-Apoptotic Function

Activated Cdc42 kinases (Acks) are evolutionarily conserved non-receptor tyrosine kinases. Activating somatic mutations and increased ACK1 protein levels have been found in many types of human cancers and correlate with a poor prognosis. ACK1 is activated by epidermal growth factor (EGF) receptor signaling and functions to regulate EGF receptor turnover. ACK1 has additionally been found to propagate downstream signals through the phosphorylation of cancer relevant substrates. Using Drosophila as a model organism, we have determined that Drosophila Ack possesses potent anti-apoptotic activity that is dependent on Ack kinase activity and is further activated by EGF receptor/Ras signaling. Ack anti-apoptotic signaling does not function through enhancement of EGF stimulated MAP kinase signaling, suggesting that it must function through phosphorylation of some unknown effector. We isolated several putative Drosophila Ack interacting proteins, many being orthologs of previously identified human ACK1 interacting proteins. Two of these interacting proteins, Drk and yorkie, were found to influence Ack signaling. Drk is the Drosophila homolog of GRB2, which is required to couple ACK1 binding to receptor tyrosine kinases. Drk knockdown blocks Ack survival activity, suggesting that Ack localization is important for its pro-survival activity. Yorkie is a transcriptional co-activator that is downstream of the Salvador-Hippo-Warts pathway and promotes transcription of proliferative and anti-apoptotic genes. We find that yorkie and Ack synergistically interact to produce tissue overgrowth and that yorkie loss of function interferes with Ack anti-apoptotic signaling. Our results demonstrate how increased Ack signaling could contribute to cancer when coupled to proliferative signals

Study of Dengue virus E proteingene of clinical isolates of Andhra Pradesh: in the contest to Epidemiological features

In this current article, we showed the dengue virus serotype 2 protein E gene from the clinical samples of Andhra Pradesh in an acute phase infection. The models showed positive for the protein E gene with RT-PCR techniques and cellular isolates. Two unique sequences are identified with new substrains, which are similar to the hermits of the earlier reports. This study provided the epidemiology insight of the isolated strain through the phylogenetic analyses

Elastic constants of nematic liquid crystals of uniaxial symmetry

We study in detail the influence of molecular interactions on the Frank elastic constants of uniaxial nematic liquid crystals composed of molecules of cylindrical symmetry. A brief summary of the status of theoretical development for the elastic constants of nematics is presented. Considering a pair potential having both repulsive and attractive parts numerical calculations are reported for three systems MBBA, PAA and 8OCB. For these systems the length-to-width ratio ${x_0}$ is estimated from the experimentally proposed structure of the molecules. The repulsive interaction is represented by a repulsion between hard ellipsoids of revolution (HER) and the attractive potential is represented by the quadrupole and dispersion interactions. From the numerical results we observe that in the density range of nematics the contribution of the quadrupole and dispersion interactions are small as compared to the repulsive HER interaction. The inclusion of attractive interaction reduces the values of elastic constants ratios. The temperature variation of elastic constants ratios are reported and compared with the experimental values. A reasonably good agreement between theory and experiment is observed