A simple oxidative procedure for the removal of ruthenium residues from metathesis reaction products

Ruthenium residues can be easily and rapidly removed from Grubbs metathesis products by washing with 15% aqueous hydrogen peroxide, which converts any ruthenium complexes into highly insoluble ruthenium dioxide, which then catalyzes the conversion of excess peroxide into water and oxygen. Ruthenium levels lower than 2 ppm can be routinely obtained; an additional advantage is that any phosphines are also rapidly oxidized to the corresponding, more polar phosphine oxides thereby facilitating their removal as well in many cases.     

Analysis of Airborne Particulates by Electron Spectroscopy for Chemical Analysis (ESCA)

Environmental pollution is one of the greatest challenges facing today's technological society. Our knowledge of the elemental composition and toxicology of pollutants increased substantially over the last decade. But efforts aimed at molecular characterization of these pollutants have not kept pace. The knowledge of the exact chemical form of a pollutant is quite important because some elements are much more toxic in one chemical form than in another. Mercury in the form of calomel is used as medication, but other forms of mercury, such as methyl mercury, are highly poisonous.     

Articulatory-acoustic kinematics: the production of American English /s/

Due to its aerodynamic, articulatory, and acoustic complexities, the fricative /s/ is known to require high precision in its control, and to be highly resistant to coarticulation. This study documents in detail how jaw, tongue front, tongue back, lips, and the first spectral moment covary during the production of /s/, to establish how coarticulation affects this segment. Data were obtained from 24 speakers in the Wisconsin x-ray microbeam database producing /s/ in prevocalic and pre-obstruent sequences. Analysis of the data showed that certain aspects of jaw and tongue motion had specific kinematic trajectories, regardless of context, and the first spectral moment trajectory corresponded to these in some aspects. In particular contexts, variability due to jaw motion is compensated for by tongue-tip motion and bracing against the palate, to maintain an invariant articulatory-aerodynamic goal, constriction degree. The change in the first spectral moment, which rises to a peak at the midpoint of the fricative, primarily reflects the motion of the jaw. Implications of the results for theories of speech motor control and acoustic-articulatory relations are discussed.     

High-pressure synthesis, amorphization, and decomposition of silane

By compressing elemental silicon and hydrogen in a diamond anvil cell, we have synthesized polymeric silicon tetrahydride (SiH(4)) at 124 GPa and 300 K. In situ synchrotron x-ray diffraction reveals that the compound forms the insulating I4(1)/a structure previously proposed from ab initio calculations for the high-pressure phase of silane. From a series of high-pressure experiments at room and low temperature on silane itself, we find that its tetrahedral molecules break up, while silane undergoes pressure-induced amorphization at pressures above 60 GPa, recrystallizing at 90 GPa into the polymeric crystal structures.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Enhancement of the Photoresponse in Organic Field‐Effect Transistors by Incorporating Thin DNA Layers

A mechanistic study of the DNA interfacial layer that enhances the photoresponse in n‐type field‐effect transistors (FET) and lateral photoconductors using a solution‐processed fullerene derivative embedded with disperse‐red dye, namely PCBDR, is reported. Incorporation of the thin DNA layer simultaneously leads to increasing the electron injection from non‐Ohmic contacts into the PCBDR active layer in dark and to increasing the photocurrent under irradiation. Such features lead to the observation of the enhancement of the photoresponsivity in PCBDR FETs up to 10³. Kelvin probe microscopy displays that in the presence of the DNA layer, the surface potential of PCBDR has a greater change in response to irradiation, which is rationalized by a larger number of photoinduced surface carriers. Transient absorption spectroscopy confirms that the increase in photoinduced carriers in PCBDR under irradiation is primarily ascribed to the increase in exciton dissociation rates through the PCBDR/DNA interface and this process can be assisted by the interfacial dipole interaction.     

Steering by transient destabilization in piecewise-holonomic models of legged locomotion

We study turning strategies in low-dimensional models of legged locomotion in the horizontal plane. Since the constraints due to foot placement switch from stride to stride, these models are piecewise-holonomic, and this can cause stride-to-stride changes in angular momentum and in the ratio of rotational to translational kinetic energy. Using phase plane analyses and parameter studies based on experimental observations of insects, we investigate how these changes can be harnessed to produce rapid turns, and compare the results with dynamical cockroach data. Qualitative similarities between the model and insect data suggest general strategies that could be implemented in legged robots.      

Product partial orders with the sperner property

Sufficient conditions are established for the product of two ranked partially ordered sets to have the Sperner property. As a consequence, it is shown that the class of strongly Sperner rank-unimodal rank-symmetric partially ordered sets is closed under the operation of product. Counterexamples are given which preclude most small variations in the hypotheses or conclusions of the two main results.     

Perturbed nonlinear differential equations

The existence of a solution defined for all t and possessing a type of boundedness property is established for the perturbed nonlinear system y = f(t, y) + F(t, y). The unperturbed system x = f(t, x) has a dichotomy in which some solutions exists and are well-behaved as t increases to ∞ and some solution exists and are well-behaved as t decreases to ? ∞. A similar study is made for a perturbed nonlinear differential equation defined on a half line, say, R⁺, and the existence of a family of solutions with special boundedness properties is established. Finally, the ideas are applied to the study of integral manifolds. Examples are given.