The influence of surface oxides on photocurrents at anthracene electrodes

The photoelectric work function was measured for six faces of a molybdenum single crystal. The crystal was cleaned by repeated cycles of ion bombardment and annealing at 920K under ultrahigh vacuum conditions. The work functions were found to be:

$\text{Φ}{}_{110}\text{=4.95±0.02}\text{eV}\text{,}\text{Φ}{}_{111}\text{=4.55±0.02}\text{eV}\text{,}\text{Φ}{}_{332}\text{=4.55±0.02}\text{eV}\text{,}\text{Φ}{}_{100}\text{=4.53±0.02}\text{eV}\text{,}\text{Φ}{}_{114}\text{=4.50±0.04}\text{eV}\text{,}\text{Φ}{}_{112}\text{=4.36±0.03}\text{eV}\text{.}$

The homogeneity of the surfaces was tested by the Schottky effect of work function lowering at high collecting fields. Effects of adsorption from the ambient atmosphere at pressures of p<2×10^?10torr, thermal segregation of bulk impurities, and of Ne⁺ bombardment dosage and energy, were investigated under identical conditions for each crystal face. The anisotropic character of the surface was clearly revealed.     

Long- and short-range order in the mesophases of laterally substituted calamitic mesogens and their radial octapodes

The mesomorphic behavior of a calamitic mesogen (4'-undecyloxybiphenyl-4-yl-4-octyloxy-2-(pent-4-en-1-yloxy)benzoate) and of a supermesogenic octapode formed by the side-on attachment of the mesogen to a octasilsesquioxane central core is studied by X-ray diffraction and polarizing optical microscopy. The calamitic compound is found to have a nematic phase that has biaxial domains (cybotactic clusters) of tilted layers throughout its entire temperature range. Domains of analogous structure are also found in both the nematic and the hexagonal columnar mesophases exhibited by the obctapode compound. The spacing of the layers forming the domains is found to have the same, essentially temperature independent value for the calamitic monomer and for the octapode, in both its mesophases. Comparison with compounds of analogous structure shows that this value is determined by the length of the rigid part of the mesogenic unit. Variation of the latter length is shown to have no effect on the size of the hexagonal lattice of the octapode columnar phase or on the stacking distance within the columns. The presence of the biaxial domains in the nematic phase is discussed in connection with the phase biaxiality that has been observed in structurally related tetrapode compounds and the possibility of field induced macroscopic biaxial nematic order.     

Eigenvalue perturbation theory of classes of structured matrices under generic structured rank one perturbations

udy the perturbation theory of structured matrices under structured rank one perturbations, and then focus on several classes of complex matrices. Generic Jordan structures of perturbed matrices are identified. It is shown that the perturbation behavior of the Jordan structures in the case of singular J-Hamiltonian matrices is substantially different from the corresponding theory for unstructured generic rank one perturbation as it has been studied in [18, 28, 30, 31]. Thus a generic structured perturbation would not be generic if considered as an unstructured perturbation. In other settings of structured matrices, the generic perturbation behavior of the Jordan structures, within the confines imposed by the structure, follows the pattern of that of unstructured perturbations.     

Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field

Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.     

Perturbation theory of selfadjoint matrices and sign characteristics under generic structured rank one perturbations

For selfadjoint matrices in an indefinite inner product, possible canonical forms are identified that arise when the matrix is subjected to a selfadjoint generic rank one perturbation. Genericity is understood in the sense of algebraic geometry. Special attention is paid to the perturbation behavior of the sign characteristic. Typically, under such a perturbation, for every given eigenvalue, the largest Jordan block of the eigenvalue is destroyed and (in case the eigenvalue is real) all other Jordan blocks keep their sign characteristic. The new eigenvalues, i.e. those eigenvalues of the perturbed matrix that are not eigenvalues of the original matrix, are typically simple, and in some cases information is provided about their sign characteristic (if the new eigenvalue is real). The main results are proved by using the well known canonical forms of selfadjoint matrices in an indefinite inner product, a version of the Brunovsky canonical form and on general results concerning rank one perturbations obtained.     

Light-induced changes of the refractive indices in a colloid of gold nanoparticles in a nematic liquid crystal

It was shown that irradiation of a nematic liquid crystal doped with metal nanoparticles in the visible near the plasmon resonance band led to strong thermal changes of the refractive indices. The effect was studied by recording of dynamic optical gratings in the colloid. Nanoparticles "worked" as effective nano-heaters in a matrix causing the order parameter decrease around the particles. A large nonlinearity parameter (n (2) ≈ 10(-2) cm(2)/kW and fast response (≈ 0.7 ms), with no detectable particles' aggregation and excellent photo- thermo-stability make these colloids potentially attractive nonlinear optical media. Application of a dynamic holography technique allowed measuring the coefficients of thermal conductivity of the liquid crystal along the director k (||) = (0.4 ± 0.02) W m(-1)K(-1) and perpendicular to the director k (⊥) = (0.2 ± 0.01) W m(-1)K(-1).     

Role of external flow and frame invariance in stochastic thermodynamics

For configurational changes of soft matter systems affected or caused by external hydrodynamic flow, we identify applied work, exchanged heat, and entropy change on the level of a single trajectory. These expressions guarantee invariance of stochastic thermodynamics under a change of frame of reference. As criterion for equilibrium versus nonequilibrium, zero versus nonzero applied work replaces detailed balance versus nonvanishing currents, since both latter criteria are shown to depend on the frame of reference. Our results are illustrated quantitatively by calculating the large deviation function for the entropy production of a dumbbell in shear flow.     

Effect-Directed Profiling of Monofloral Honeys from Ethiopia by High-Performance Thin-Layer Chromatography and High-Resolution Mass Spectrometry

Ethiopian honey is used not only as food but also for treatment in traditional medicine. For its valorization, bioactive compounds were analyzed in nine types of monofloral Ethiopian honey. Therefore, a non-target effect-directed profiling was developed via high-performance thin-layer chromatography combined with multi-imaging and planar effect-directed assays. Characteristic bioactivity profiles of the different honeys were determined in terms of antibacterial, free-radical scavenging, and various enzyme inhibitory activities. Honeys from Hypoestes spp. and Leucas abyssinica showed low activity in all assays. In contrast, others from Acacia spp., Becium grandiflorum, Croton macrostachyus, Eucalyptus globulus, Schefflera abyssinica, Vernonia amygdalina, and Coffea arabica showed more intense activity profiles, but these differed depending on the assay. In particular, the radical scavenging activity of Croton macrostachyus and Coffea arabica honeys, the acetylcholinesterase-inhibiting activity of Eucalyptus globulus and Coffea arabica honeys, and the antibacterial activity of Schefflera abyssinica honey are highlighted. Bioactive compounds of interest were further characterized by high-resolution mass spectrometry. Identifying differences in bioactivity between mono-floral honey types affects quality designation and branding. Effect-directed profiling provides new insights that are valuable for food science and nutrition as well as for the market, and contributes to honey differentiation, categorization, and authentication.     

Cooperative,Reversible Self‐Assembly of Covalently Pre‐Linked Proteins into Giant Fibrous Structures

We demonstrate a simple bioconjugate polymer system that undergoes reversible self‐assembling into extended fibrous structures, reminiscent of those observed in living systems. It is comprised of green fluorescent protein (GFP) molecules linked into linear oligomeric strands through click step growth polymerization with dialkyne poly(ethylene oxide) (PEO). Confocal microscopy, atomic force microscopy, and dynamic light scattering revealed that such strands form high persistence length fibers, with lengths reaching tens of micrometers, and uniform, sub‐100 nm widths. We ascribe this remarkable and robust form of self‐assembly to the cooperativity arising from the known tendency of GFP molecules to dimerize through localized hydrophobic patches and from their covalent pre‐linking with flexible PEO. Dissipative particle dynamics simulations of a coarse‐grained model of the system revealed its tendency to form elongated fibrous aggregates, suggesting the general nature of this mode of self‐assembly.     

Quantum chaos

A quantum system which is allowed to interact with its boundary in a self-consistent way is shown to exhibit chaos. We conjecture that in general genuine wave chaos (decaying autocorrelation functions, exponential sensitivity of wavefunctions to initial wavefunction configurations) can be obtained whenever a wavefield is allowed to modify its confining boundaries in a self-consistent way. We suggest to test this conjecture in the acoustic regime.