Behaviour of the anchoring strength coefficient near a structural transition at a nematic-substrate interface

A nearly symmetric alkoxyphenylbenzoate monomer is found to exhibit a transition from perpendicular to tilted alignment at a lecithin-treated glass substrate several degrees below the nematic-isotropic phase transition. By means of the Freedericksz transition the coefficient B of the anchoring energy has been obtained. It is found that B rapidly decreases, and the tilt susceptibility increases on approaching this transition.     

Structural and optical properties of DNA layers covalently attached to diamond surfaces

Label-free detection of DNA molecules on chemically vapor-deposited diamond surfaces is achieved with spectroscopic ellipsometry in the infrared and vacuum ultraviolet range. This nondestructive method has the potential to yield information on the average orientation of single as well as double-stranded DNA molecules, without restricting the strand length to the persistence length. The orientational analysis based on electronic excitations in combination with information from layer thicknesses provides a deeper understanding of biological layers on diamond. The pi-pi* transition dipole moments, corresponding to a transition at 4.74 eV, originate from the individual bases. They are in a plane perpendicular to the DNA backbone with an associated n-pi* transition at 4.47 eV. For 8-36 bases of single- and double-stranded DNA covalently attached to ultra-nanocrystalline diamond, the ratio between in- and out-of-plane components in the best fit simulations to the ellipsometric spectra yields an average tilt angle of the DNA backbone with respect to the surface plane ranging from 45 degrees to 52 degrees . We comment on the physical meaning of the calculated tilt angles. Additional information is gathered from atomic force microscopy, fluorescence imaging, and wetting experiments. The results reported here are of value in understanding and optimizing the performance of the electronic readout of a diamond-based label-free DNA hybridization sensor.     

Analysis of biosensors by chemically specific optical techniques. Chemiluminescence-imaging and infrared spectroscopic mapping ellipsometry

The standard methods currently used to read out microarrays are fluorescent and chemiluminesent imaging techniques. These methods require labeling of a component with a marker and, usually, only the concentration of the marker molecule is detected. A label-free imaging method that also enables quantitative spectroscopic analysis of the composition and component interaction would be of great advantage. In this article it is shown for the first time that IR mapping ellipsometry enables label-free imaging of a biochip before and after incubation with peptide solution. The measurements prove that IR ellipsometry is a sensitive tool for laterally resolved identification of the different materials and determination of the composition of a biochip. The lateral resolution required was achieved by using radiation from an infrared synchrotron beamline.      

The structure and stability of Si60 and Ge60 cages: a computational study

Structural studies of fullerene-like Si(60) and Ge(60) cages using ab initio methods were augmented by density functional tight-binding molecular dynamics (DFTB-MD) simulations of finite temperature effects. Neither the perfect I(h) symmetry nor the distorted T(h) structures are true minima. The energies of both are high relative to distorted, lower symmetry minima, C(i) and T, respectively, which still preserve C(60)-type connectivity. Both Si(60) and Ge(60) favor C(i) symmetry cages in which Si and Ge vertexes exhibit either near-trigonal or pyramidal geometries. These structural variations imply significant reactivity differences between different positions. The small magnetic shielding effects (NICS) indicate that aromaticity is not important in these systems. The inorganic fullerene cages have lower stabilities compared with their carbon analogs. Si(60) is stable towards spontaneous disintegration up to 700 K according to DFTB-MD simulations, and thus has potential for experimental observation. In contrast, Ge(60) preserves its cage structure only up to 200 K.     

Effect of Molecular Structure on Mesomorphism: 5. Comparison of Methyl and Trifluoromethyl as Lateral Substituents in the Solid and Nematic Phases.1

Two laterally-substituted nematogenic liquid crystals, methyl-p-phenylene-di-p-butoxybenzoate and trifluoromethyl-p-phenylene-di-p-butoxybenzoate, have been studied by differential scanning calorimetry, powder x-ray diffraction, and polarized light microscopy (hot stage microscopy and hot-wire stage microscopy). Comparison of thermodynamic data for the nematicisotropic transitions of these two compounds suggests a strongly repulsive electronic interaction between molecules in the nematic phase of the trifluoromethyl compound. Detailed molecular structural augments are presented to rationalize the thermodynamic data. The room temperature solid phases of the two compounds were found to have different crystal structures. However, the high temperature solid phases were found, by a novel application of hot-wire stage microscopy, to be isomorphous.     

Diode-end-pumped Tm:GdVO4 laser operating at 1818 and?1915?nm

High power operation at 1818 and 1915 nm has been demonstrated from a Tm:GdVO₄ laser operating in quasi-continuous-wave mode with a maximum measured power of 8.7 W and a laser output energy of 175 mJ was observed in a 20 ms pulse at 1.9 μm. The operation at 1818 nm is the shortest wavelength achieved at multi-watt power levels for a Tm-doped solid-state laser without intra-cavity tuning elements. It has been shown that by careful analysis of the emission spectra, the Tm:GdVO₄ laser can be tuned over a 100 nm wavelength range simply by appropriate selection of the reflectivity of the output coupler.     

From Metacyclophanes to Cyclacenes: Synthesis and Properties of [6.8]3Cyclacene

Conjugated belts : [6.8]₃cyclacene as the first hydrocarbon cyclacene was synthesized in a de novo strategy. Various [2₃]metacyclophanes are described as intermediates. The synthetic approach was extended to larger cyclacenes, and [2₄]metacyclophanes as precursors of [6.8]₄cyclacene were synthesized.

     

Algebraic construction of static axially symmetric self-dual gauge fields for an arbitrary group

It is suggested that the Higgs and the Yukawa couplings of the standard model possess two global U(1)-symmetries: independent chiral rotations of quarks and leptons. The model requires the existence of two axions, one of which (massive) does not interact with leptons, whereas the second one interacts both with leptons and quarks.