Radial distribution function of freely jointed hard-sphere chains in the solid phase

Monte Carlo simulation is used to generate the radial distribution function of freely jointed tangent-bonded hard-sphere chains in the disordered solid phase for chain lengths of three, four, six, and eight segments. The data are used to create an accurate analytical expression of the total radial distribution function of the hard-sphere chains that covers a density range from the solidification point up to a packing fraction of 0.71. It is envisioned that the correlation will help further progress toward molecular thermodynamic treatment of the solid phase in general and toward perturbed chain theories for the solid phase, in particular.     

Synthesis and characterization of soluble low‐bandgap oligothiophene‐[all]‐S,S‐dioxides‐based conjugated oligomers and polymers

The synthesis and characterization of a new family of soluble oligothiophene‐S,S‐dioxides and their use as building blocks to form polythiophene‐S,S‐dioxides via microwave‐assisted Stille coupling polymerization are described. Incorporation of the sulfone group into the polythiophene backbone leads to narrowing of the polymer bandgap, and while the energies of both Frontier orbitals in polythiophene‐S,S‐dioxide are lower with respect to polythiophenes, this tendency is considerably stronger for the lowest unoccupied molecular orbital than for the highest occupied molecular orbital, resulting in greater electron‐accepting ability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chlorobiphenyl (PCB) composition of extracts of subsurface soil, superficial dust and air from a contaminated landfill

Samples of 3 matrices (air, superficial dust and subsurface soil) from an aged PCB-containing landfill were extracted and the extracts refined for bioassay. Acetone:hexane extraction was modestly selected for non-planar compounds. Coplanar PCBs and PCDFs were enriched about 2-fold in the subsequent benzene:methylene chloride extracts of the soil. Extract refinement with Florisil slurry and alumina column chromatography did not appreciably change the composition of the extracts. CB 28 (2,4,4′-triCB) dominated in all extracts. The congener composition of soil and air were surprisingly similar, being enriched in tri- and tetraCBs while dust retained higher proportions of congeners with 4 and 5 chlorines. It is postulated that anaerobic dechlorination in the moist subsurface soil depleted the higher chlorinated congeners; more volatile congeners escaped into the atmosphere while moderately chlorinated congeners were trapped in the superficial dust and debris. The refined extracts represent distinct compositions of environmental PCB mixtures suitable for bioassay. Received: 21 November 1995 / Revised: 9 April 1996 / Accepted: 14 April 1996     

Tandem Pummerer-Diels-Alder Reaction Sequence. A Novel Cascade Process for the Preparation of 1-Arylnaphthalene Lignans

The alpha-thiocarbocation generated from the Pummerer reaction of an o-benzoyl-substituted sulfoxide is intercepted by the adjacent keto group to produce an alpha-thio isobenzofuran as a transient intermediate which undergoes a subsequent Diels-Alder cycloaddition with added dienophiles. Acid-catalyzed ring-opening of the cycloadduct followed by aromatization gave an arylnaphthalene derivative. With acetylenic dienophiles, the tandem cyclization-cycloaddition sequence provided tetralones which result from a pinacol-type rearrangement of the primary cycloadducts. The versatility of the approach is highlighted through the synthesis of taiwanin C and E and justicidin E. The alpha-thiocarbocation generated from the Pummerer reaction of benzo[1,3]dioxol-5-yl-[6-[(ethylsulfinyl)methyl]benzo[1,3]dioxol-5-yl)methanone is intercepted by the adjacent keto group to produce an alpha-thioisobenzofuran as a transient intermediate which undergoes a subsequent Diels-Alder cycloaddition with dimethyl maleate. The initially formed Diels-Alder cycloadduct was readily converted to 5-benzo[1,3]dioxol-5-yl-8-(ethylthio)naphtho[2,3-d][1,3]dioxole-6,7-dicarboxylic acid dimethyl ester by loss of water on treatment with p-toluenesulfonic acid. Desulfurization of the thionaphthalene with Ra/Ni followed by hydrolysis of the less hindered methyl ester afforded 5-benzo[1,3]dioxol-5-ylnaphtho[2,3-d][1,3]dioxole-6,7-dicarboxylic acid 6-methyl ester which was further transformed into taiwanin C and justicidin E in good yield. Oxidation of the initial Diels-Alder cycloadduct with NaIO(4) in the presence of RuCl(3) followed by extrusion of ethyl sulfinate gave a naphthol derivative which can be converted into taiwanin E.     

1-3 connectivity piezoelectric ceramic-polymer composite transducers made with viscous polymer processing for high frequency ultrasound

Potential applications of high frequency ultrasound exist because of the high spatial resolution consequent upon short wavelength. The frequencies of interest, typically from 25 MHz upwards, are easily supported by modern instrumentation but the capabilities of ultrasonic transducers have not kept pace and the transducers in high frequency commercial ultrasonic systems are still made with single-phase crystal, ceramic or piezopolymer materials. Despite potential performance advantages, the 1-3 connectivity piezoelectric ceramic-polymer composite materials now widely used at lower ultrasonic frequencies have not been adopted because of manufacturing difficulties. These difficulties are centred on fabrication of the 1-3 piezoceramic bristle-block comprising tall, thin pillars upstanding from a supporting stock. Fabrication techniques which have been explored already include injection moulding, mechanical dicing, and laser machining. Here, we describe an alternative technique based on viscous polymer processing (VPP) to produce net shape ceramic bristle-blocks. VPP produces green-state ceramic with rheological properties suitable for embossing. We outline how this can be created then report on our work to fabricate PZT bristle-blocks with lateral pillar dimensions of the order of 50 microm and height-to-width ratios of the order of 10. These have been backfilled with low pre-cure viscosity polymer and made into complete 1-3 piezocomposite transducer elements. We outline the performance of the transducers in terms of electrical impedance and pulse-echo behaviour and show that it corresponds well with computer modelling. We conclude that VPP is a promising technique to allow the established advantages of piezocomposite material to be exploited at higher frequencies than have been possible so far.     

Quasielastic 3He(e,e'p)2H reaction at Q2 = 1.5 GeV2 for recoil momenta up to 1 GeV/c

We have studied the quasielastic 3He(e,e(')p)2H reaction in perpendicular coplanar kinematics, with the energy and the momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e(')p)2H cross section was measured for missing momenta up to 1000 MeV/c, while the A(TL) asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/c, the cross section is described by variational calculations using modern 3He wave functions. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The A(TL) asymmetry displays characteristic features of broken factorization with a structure that is similar to that generated by available models.     

Temperature dependent lineshape changes in solid H2 for low oH2 concentrations

The nmr lineshape due to unpaired oH₂ molecules in solid pH₂ changes significantly below 0.2 K. A deconvolution of lineshape based on a mitional narrowing model yields the relative amplitude of the part of the signal showing resolved structure as well as the temperature dependence of the frequency determining parameter. Both the relative amplitude of this signal and the temperature at which structure appears decrease with increasing oH₂ concentration.     

Improved detectability and signal strength for rotating phase fluorescence immunoassays through image processing

Fluorescence immunoassays based on rotating solid phase have shown promise of lowered detection limits, among other advantages. However, intrinsic background distortion effects have limited their utility. Here, novel image processing strategies are used to minimize these effects and improve the estimate of concentration and lower the detection limit. This initial demonstration of a new processing capability is performed on data for a protein, myoglobin, which is a biomarker for acute myocardial infarction. For these data, compared with published results, the detection limit is improved by a factor of approximately one hundred (to 700 fM), which is competitive with or better than other immunoassay strategies (ELISA, for example) that are fully developed. This work suggests that image and video processing technologies can provide a valuable alternative approach to biochemical detection and concentration estimation.