Internal stresses, normal modes, and nonaffinity in three-dimensional biopolymer networks

We numerically investigate deformations and modes of networks of semiflexible biopolymers as a function of crosslink coordination number z and strength of bending and stretching energies. In equilibrium filaments are under internal stress, and the networks exhibit shear rigidity below the Maxwell isostatic point. In contrast to two-dimensional networks, ours exhibit nonaffine bending-dominated response in all rigid states, including those near the maximum of z=4 when bending energies are less than stretching ones.     

Torque scaling in turbulent Taylor-Couette flow with co- and counterrotating cylinders

We analyze the global transport properties of turbulent Taylor-Couette flow in the strongly turbulent regime for independently rotating outer and inner cylinders, reaching Reynolds numbers of the inner and outer cylinders of Re(i) = 2×10(6) and Re(o) = ±1.4×10(6), respectively. For all Re(i), Re(o), the dimensionless torque G scales as a function of the Taylor number Ta (which is proportional to the square of the difference between the angular velocities of the inner and outer cylinders) with a universal effective scaling law G ∝ Ta(0.88), corresponding to Nu(ω) ∝ Ta(0.38) for the Nusselt number characterizing the angular velocity transport between the inner and outer cylinders. The exponent 0.38 corresponds to the ultimate regime scaling for the analogous Rayleigh-Bénard system. The transport is most efficient for the counterrotating case along the diagonal in phase space with ω(o) ≈ -0.4ω(i).     

Every orientable Seifert 3-manifold is a real component of a uniruled algebraic variety

We show that any orientable Seifert 3-manifold is diffeomorphic to a connected component of the set of real points of a uniruled real algebraic variety, and prove a conjecture of János Kollár.     

Observation of sub-Bragg diffraction of waves in crystals

We investigate the diffraction conditions and associated formation of stop gaps for waves in crystals with different Bravais lattices. We identify a prominent stop gap in high-symmetry directions that occurs at a frequency below the ubiquitous first-order Bragg condition. This sub-Bragg-diffraction condition is demonstrated by reflectance spectroscopy on two-dimensional photonic crystals with a centered rectangular lattice, revealing prominent diffraction peaks for both the sub-Bragg and first-order Bragg conditions. These results have implications for wave propagation in 2 of the 5 two-dimensional Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as centered rectangular, triangular, hexagonal, and body-centered cubic.     

Base induced rearrangements of α-halosulfones α-sulfonyl carbanions with bridgehead electrofugal centre

The KOtBu-induced Ramberg-Bäcklund reaction of the trans bicyclic halosulfones 1 and 2 is studied in DME and DMSO. Strong indications are obtained that the reaction proceeds via the intermediate Z-episulfone with retention-inversion (involving exo-S-geometry).¹ Base induced epimerization at the nucleofugal centre (from axial to equatorial halogen) is demonstrated in DMSO.     

Electrochemical formation and reduction of silver oxides in alkaline media

The anodic oxidation of silver electrodes in NaOH solution and the reduction of the silver oxides formed were studied by potential step chronoamperometry. Oxidation of Ag to Ag₂O is a diffusion-controlled reaction, the diffusion control being established in the solid phase. Oxidation of Ag₂O to AgO proceeds via a nucleation and growth-controlled process. The amount of AgO decreased with increasing step height. The current—time curves for this reaction have been analysed with the Kolmogoroff—Avrami equation. Reduction of AgO to Ag₂O occurs initially on the outside of the electrode, and the rate of the reaction is limited by diffusion of ions across the thickening layer of Ag₂O. Reduction of Ag₂O to Ag proceeds via a nucleation and growth reaction.     

2,7,15,16-tetramethyl-trans-15,16-dihydropyrene

The synthesis of 2,7,15,16-tetramethyl-trans-15,16-dihydropyrene has been accomplished by two different routes. The compound is of interest in providing a better understanding of the ESR spectra of 15,16-dihydropyrenes.     

Separation of normal and abnormal hemoglobin chains by reversed-phase high-performance liquid chromatography

A review is presented of the elution patterns on reversed-phase columns of the normal and abnormal globin chains of different hemoglobin types, including 16 beta-chain variants, 7 alpha-chain variants, 9 gamma-chain variants, and 4 variants with fusion or hybrid chains. Separations appear to be based primarily on differences in hydrophobicity. The method is ideally suited for the detection of abnormal globin chains, their quantitation and their isolation. Semi-quantitative data based on the calculation of the delta/non-alpha ratios allow the detection of beta-thalassemic conditions in situations where the quantitation of hemoglobin A2 by other procedures is impossible or complicated.     

Modules over twisted group rings and vector bundles over the anisotropic real conic

We prove, in an elementary way, that a locally free sheaf of finite rank over the anisotropic real conic is the direct sum of indecomposable locally free sheaves of rank 1 or 2. Our proof is purely algebraic, and is based on a classification of graded ?[X, Y]-modules endowed with a certain action of the cyclic group ?/4?.     

Formation of high-quality self-assembled monolayers of conjugated dithiols on gold: base matters

This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases and studied the quality of the resulting SAMs on gold. We found that the optimal conditions to reproducibly form dense, high-quality monolayers are 9-15% triethylamine (Et(3)N) in THF. The deprotection base tetrabutylammonium hydroxide (Bu(4)NOH) leads to less dense SAMs and the incorporation of Bu(4)N into the monolayer. Furthermore, our results show the importance of the equilibrium concentrations of (di)thiolate in solution on the quality of the SAM. To demonstrate the relevance of these results for molecular electronics applications, large-area molecular junctions were fabricated using no base, Et(3)N, and Bu(4)NOH. The magnitude of the current-densities in these devices is highly dependent on the base. A value of β=0.15 ?(-1) for the exponential decay of the current-density of OPEs of varying length formed using Et(3)N was obtained.