Microscopic model of critical current noise in Josephson junctions

We present a simple microscopic model to show how fluctuating two-level systems in a Josephson junction tunnel barrier of thickness L can modify the potential energy of the barrier and produce critical current noise spectra. We find low frequency 1/f noise that goes as L5. Our values are in good agreement with recent experimental measurements of critical current noise in Al/AlOx/Al Josephson junctions. We also investigate the sensitivity of the noise on the nonuniformity of the tunnel barrier.     

Tribological durability of silane monolayers on silicon

We report the frictional performance and long-term tribological stability of various alkyl silane monolayer films on silicon by using pin-on-disk tribometry at ambient conditions. We show that the durability of monolayers derived from n-alkyltrichlorosilanes on silicon increases exponentially with the chain length of the silane precursor, which we relate to the cohesive energy of these monolayers through molecular dynamics simulations. X-ray photoelectron spectroscopy (XPS) was used to show that tribological damage consisted of the loss of molecular components that could be partially replaced upon exposure to a solution containing perfluorinated silane precursors. For monolayers derived from n-octadecyltrichlorosilane, a critical load was identified to be approximately 250 mN (200 MPa), above which failure of films occurred within 100 cycles of testing. Monolayers with hydroxyl surfaces exhibited reduced stabilities due to stronger tip-surface interactions. Monolayers with the capability for cross-linking exhibited much greater stabilities than monolayers where cross-linking was limited or prevented. Collectively, these results demonstrate that the mechanical durability of monolayers when subjected to a tribological load is greatly enhanced by maximizing dispersional interactions and cross-linking and minimizing tip-surface interactions.     

LiCoO(2) Concaved Cuboctahedrons from Symmetry-Controlled Topological Reactions

Morphology control of functional materials is generally performed by controlling the growth rates on selected orientations or faces. Here, we control particle morphology by "crystal templating": by choosing appropriate precursor crystals and reaction conditions, we demonstrate that a material with rhombohedral symmetry-namely the layered, positive electrode material, LiCoO(2)-can grow to form a quadruple-twinned crystal with overall cubic symmetry. The twinned crystals show an unusual, concaved-cuboctahedron morphology, with uniform particle sizes of 0.5-2 μm. On the basis of a range of synthetic and analytical experiments, including solid-state NMR, X-ray powder diffraction analysis and HRTEM, we propose that these twinned crystals form via selective dissolution and an ion-exchange reaction accompanied by oxidation of a parent crystal of CoO, a material with cubic symmetry. This template crystal serves to nucleate the growth of four LiCoO(2) twin crystals and to convert a highly anisotropic, layered material into a pseudo-3-dimensional, isotropic material.     

Effect of excess methanol addition on the morphology of sonogel-derived silica

Sonochemical processing techniques may be used to create fully miscible sols without the initial addition of a solvent. However, by intentionally adding excess alcohol to a sol produced by sonication, it is possible to manipulate the porosity of the resulting sonogel. Sonogels of systematically varied methanol content were prepared using a two-step process with subsequent drying at 60°C. The as-prepared sol with no excess methanol produced a purely microporous solid. The addition of excess methanol to the sol resulted in the formation of mixed microporosity and mesoporosity as revealed by nitrogen gas adsorption and transmission electron microscopy.     

Search for charged Higgs,scalar tau's and a test of technicolor models

We have used our measurements of final states from e⁺e^? containing an isolated muon and a hadronic or electron shower to search for new spin 0 charged particles. We exclude (95% CL) a supersymmetric partner of the τ with a mass less than 14 GeV/c². We obtain upper limits on the branching ratio to τv_τ for charged Higgs particles or technipions with masses up to 14 GeV/c². This disagrees with some technicolor model predictions.     

Determination of the optical second harmonic response of pharmaceutical solid–solid mixtures

We report on a new method for characterising crystallinity and polymorphism of pharmaceutical drugs and excipients in the solid state. The optical nonlinearity of certain crystalline structures allows under certain circumstances the quantitative determination of polymorphism or crystallinity. An apparatus was set up to measure the second harmonic response of powdered samples when irradiated with a pulsed laser source. Here we present experimental results from various pharmaceutically interesting materials. This rapid, novel technique has potential for industrial monitoring of pharmaceutical manufacturing processes.     

Applications of synthetic oligoribonucleotide analogues in studies of RNA structure and function

The study of RNA structure and function has been considerably aided by the development of methods for the chemical synthesis of oligoribonucleotides into which have been incorporated modified nucleosides carrying site-specific alterations. Such modifications are designed to eliminate or alter individual functional groups in the RNA which potentially can take part in hydrogen-bonding or other non-covalent interactions. Comparison of the properties of the modified RNA with unmodified RNA models allows conclusions to be drawn concerning the importance or otherwise of specific functional groups within the RNA. The methods have been applied to studies of RNA structure, RNA catalysis, and interactions of RNA with proteins.     

Tests of quantum chromodynamics and a direct measurement of the strong coupling constant αs at √s=30 GeV

We report the measurement of the reaction e⁺ + e^? → hadronic jets at a center-of-mass energy √s=30 GeV using the MARK-J detector at PETRA. By measuring the energy and angular distribution of both neutrals and charged particles we were able to isolate unambiguously the three-jet events in a kinematic region where the backgrounds from q$\text{q}$ and phase space contributions and other processes are small. Various comparisons of the data with quantum chromodynamics were made. The relative yield of three-jet events and the shape distribution of the events enable us to determine α_s = 0.23 ± 0.02 (statistical error) with a systematic error of ± 0.04.     

Contra-Hofmeister anion extraction by cyclosteroidal receptors

Steroid-based receptors with enclosed binding sites, formed from quaternary ammonium and macrocyclic bis-urea units, can substantially override the Hofmeister series in anion phase transfer experiments.