A new approach to reduction of the Neumann problem in acoustic scattering to a non-hypersingular integral equation

The Neumann problem for the propagative Helmholtz equation inthe exterior of several bodies (obstacles) is studied in twoand three dimensions by a special modification of the boundaryintegral equation method. This modification can be called the'method of interior boundaries', because additional boundariesare introduced inside scattering bodies. The solution of theproblem is obtained in the form of a single layer potentialon the whole boundary. The density in the potential satisfiesthe uniquely solvable Fredholm equation of the second kind andcan be computed by standard codes. In fact our method holdsfor any positive wave numbers.     

Morphology and properties of polycaprolactone-poly(dimethyl siloxane)-polycaprolactone triblock copolymers

The molecular structure, crystallization, solid-state morphology, thermal properties, and phase behavior of two copolymers consisting of a poly(dimethylsiloxane) (PDMS) mid-block coupled to polycaprolactone (PCL) end-blocks were investigated. Both copolymers (which differ only in the molecular lengths of the PCL end-blocks) were found to be lamellar systems, whose core consists of PCL chains having the same crystal structure as PCL homopolymer, and whose amorphous interlayers contain the PDMS blocks and the PCL noncrystalline segments. From x-ray and electron-microscopy results, it is expected that the PCL blocks may be folded once in the longer copolymer and not at all in the shorter. As a result of their differing PCL lengths, the former crystallizes as regular PCL spherulites (at a growth rate reduced with respect to PCL homopolymer), whereas the latter yields only defective, immature axialites of low overall crystallinity. Electron diffraction showed that these spherulites grow preferentially along b crystallographic axis and that the PCL crystalline stems are arranged perpendicularly to their lamellae. © 1993 John Wiley & Sons, Inc.     

Structure of peptides on metal oxide surfaces probed by NMR

Peptides that bind inorganic surfaces and template the formation of nanometer-sized inorganic particles are of great interest for the self- or directed assembly of nanomaterials for sensors and diagnostic applications. These surface-recognizing peptides can be identified from combinatorial phage-display peptide libraries, but little experimental information is available for understanding the relationship between the peptide sequence, structure at the nanoparticle surface, and function. We have developed NMR methods to determine the structures of peptides bound to inorganic nanoparticles and report on the structure of three peptides bound to silica and titania surfaces. Samples were prepared under conditions leading to rapid peptide exchange at the surface such that solution-based nuclear Overhauser experiments can be used to determine the three-dimensional structure of the bound peptide. The binding motif is defined by a compact "C"-shaped structure for the first six amino acids in the 12-mer. The orientation of the peptide on the nanoparticle surface was determined by magnetization transfer from the nanoparticle surface to the nearby peptide protons. These methods can be applied to a wide variety of abiotic interfaces to provide an insight into the relationship between the primary sequence of peptides and their functionality at the interface.     

Decoherence via the dynamical casimir effect

We derive a master equation for a mirror interacting with the vacuum field via radiation pressure. The dynamical Casimir effect leads to decoherence of a superposition state in a time scale that depends on the degree of "macroscopicity" of the state components, and which may be much shorter than the relaxation time scale. Coherent states are selected by the interaction as pointer states.     

EFFECT OF COMPOSITION AND PROCESSING CONDITION ON MICROSTRUCTURAL PROPERTIES AND DURABILITY OF FLUOROPOLYMER/ACRYLIC BLENDS

Fluoropolymer blends have been widely used as binders for exterior coatings because of their excellent resistance to ultra-violet (UV) radiation as well as to many corrosive chemical agents.It is known that the fluorinated component usually has a lower glass transition temperature and easily crystallizes in the final structure depending upon the blend composition and sample annealing condition.We investigated the effect of blend composition and annealing process (slow and fast cooling) on the surface mor...     

WIM/WISE NMR studies of chain dynamics in solid polymers and blends

Wideline separation (WISE) NMR with window-less isotropic mixing (WIM) is developed as a method to study the dynamics of polymers and blends. This experiment is designed to measure the dynamics of polymers through the proton lineshapes that are correlated with the carbon chemical shifts in two-dimensional NMR experiments. If the atoms experience large amplitude fluctuations that are fast compared to the dipolar broadening, then the proton lines will be narrowed relative to rigid solids. We have modified the WISE experiment by replacing the cross polarization step with WIM to quench spin diffusion during the cross polarization so that the proton linewidths can be directly related to the chain dynamics. Two-dimensional WIM/WISE has been used to measure the main-chain and side-chain dynamics in poly(n-butyl methacrylate) and blends of polystyrene and poly(vinyl methyl ether).     

The two-dimensional NMR spectroscopy of macromolecules

Two-dimensional (2D) NMR is a versatile technique which exists in many versions. Two broad classes of 2D techniques are (1) correlated spectroscopy and (2) J-resolved spectroscopy. The first of these may be divided into two further subdivisions: COSY, which permits correlations of resonances via J-coupling, and NOESY, which allows direct measurement of intenuclear (usually interproton) distances by the nuclear Overhauser effect. COSY greatly facilitates the interpretation of complex spectra and spectral interpretation in terms of stereochemical sequences is placed on a firmer foundation. NOESY provides direct information concerning the local conformations of polymers in solution. By use of J-resolved 2D NMR, we can separate J-couplings and chemical shifts on different axes and thus achieve a degree of resolution of both these parameters far beyond what is attainable in the 1D spectrum. Finally, we may combine correlated and J-resolved spectroscopy and achieve the benefits of both in 3D NMR, in which the 2D cross peaks exhibit J-coupling fine structure. These techniques are illustrated for a variety of polymers including poly(methyl methacrylate), poly(vinyl fluoride), poly-y-benzyl L-glutamate, and poly(propylene oxide).