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21.
Equations are written for the velocities of rotation and translation of rigid rod-like particles suspended in arbitrary Stokes flows. These make use of the first approximation from slender body theory for the evaluation of drag forces parallel and transverse to the particle axis, and neglect couples induced by shear stress at the particle surface. They are therefore asymptotically valid as the particle axis ratio becomes large. Simple forms of the equations, applying in constant viscosity flows, are solved, where possible analytically and otherwise numerically, and results obtained for particle motion in planar Poiseuille and sink flows. These are discussed and displayed in terms of appropriate dimensionless groups in a comprehensive set of plots, that can conveniently be used to provide information on translational and rotational velocities, and orientation and displacement as a function of time, including particle slip along and across streamlines, for a wide range of cases. In this way the effects of non-homogeneity in the flow fields are quantified. 相似文献
22.
Mitsuru Ueda Toshihisa Kumakura Yoshio Imai Charles U. Pittman Easley Wallace 《Journal of polymer science. Part A, Polymer chemistry》1984,22(1):85-96
The effect of solvent in homo- and copolymerizations of methacryloyl fluoride (MAF) was investigated in various aromatic solvents. In these solvents, there is a significant effect on the rate of polymerization, on the tacticity of the resulting poly(methacryloyl fluoride), and on the copolymerization of MAF with methyl methacrylate (MMA). The equilibrium constants between MAF and aromatic solvents were determined from NMR spectroscopic measurements. These results indicated that the solvent effect on the MAF polymerization stems from changes in reactivity of MAF induced by the strong MAF–solvent interaction as well as stabilization of the MAF radical by solvents. Copolymerization of MAF with both p-methoxystyrene (MSt) and p-nitrostyrene (NSt) was also studied. 相似文献
23.
A minimum thickness gate valve design for mass spectrometry is described in detail. The ion optics required to transmit ions from the source to the ICR cell are integrated into the design to minimize fringe field effects on the ions as they travel through the gate valve. The total thickness of the complete gate valve assembly is 1.03 in. (26.2 mm) with a maximum fringe field distance of 0.065 in. (1.7 mm). The gate valve is able to maintain a vacuum of <10(-10) mbar at the ICR cell when the source is vented to atmosphere and the estimated ion transfer efficiency is >95%. 相似文献
24.
25.
D. W. Bardayan K. A. Chipps R. P. Fitzgerald J. C. Blackmon K. Y. Chae A. E. Champagne U. Greife R. Hatarik R. L. Kozub C. Matei B. H. Moazen C. D. Nesaraja S. D. Pain W. A. Peters S. T. Pittman J. F. Shriner Jr. M. S. Smith 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):457-460
There are a number of astrophysical environments in which the path of nucleosynthesis proceeds through proton-rich nuclei. These nuclei have traditionally not been available as beams, and thus proton-capture reactions on these nuclei could only be studied indirectly. At the Holifield Radioactive Ion Beam Facility (HRIBF), some of the first direct measurements of (p, $ \gamma$ ) cross-sections on radioactive beams have been made. The Daresbury Recoil Separator (DRS) has been used to separate the recoils of interest from the unreacted primary beam and identify them in an isobutane-filled ionization counter. First data from 17F (p, $ \gamma$ 18Ne and 7Be (p, $ \gamma$ 8B measurements are presented. 相似文献
26.
Ultrasensitive detection of TNT in soil, water, using enhanced electrogenerated chemiluminescence 总被引:1,自引:0,他引:1
Tommie L. Pittman 《Analytica chimica acta》2009,632(2):197-32
The ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) was accomplished on the basis of sandwich-type TNT immunoassay combined with electrogenerated chemiluminescence (ECL) technology. Biotinylated anti-TNT species were attached to the surface of 1-μm diameter streptavidin-coated magnetic beads (MB) and 10-μm diameter avidin-coated polystyrene microspheres/beads (PSB) pre-loaded with ECL labels (∼7 billion hydrophobic ruthenium(II) tris(2,2′-bipyridine) (RuII) molecules per bead) to form anti-TNT ↔ MB and anti-TNT ↔ PSB(RuII) conjugates, respectively. Sandwich-type PSB(RuII) ↔ anti-TNT < TNT > anti-TNT ↔ MB aggregates were formed when PSB(RuII) ↔ anti-TNT was mixed with anti-TNT ↔ MB conjugates in the presence of analyte TNT and 2.0% bovine serum albumin blocking agent. The newly formed aggregates were magnetically separated from the aqueous reaction media and dissolved in acetonitrile containing 0.10 M tri-n-propylamine ECL coreactant-0.055 M trifluoroacetic acid-0.10 M tetrabutylammonium tetrafluoroborate electrolyte. ECL as well as cyclic voltammetric measurements were carried out with a potential scan from 0 to 2.8 V vs Ag/Ag+, and the integrated ECL intensity was found to be linearly proportional to the analyte TNT concentration over the range of 0.10-1000 ppt (pg mL−1). The limit of detection (≤0.10 ± 0.01 ppb) is about 600× lower as compared with the most sensitive TNT detection method in the literature, and the absolute detection limit in mass (∼0.1 pg) is only ∼0.5% of that from mass spectroscopy. The approach coupled with the standard addition method was applied to measure the TNT contaminations in soil and creek water samples collected from a military training base. 相似文献
27.
Debbie J. Beard Chandler R. Pace Charles U. Pittman Jr. Svein Saebø 《Structural chemistry》2009,20(6):961-967
Cyclic ketene acetals are a class of organic molecules characterized by a nucleophilic exo-methylene carbon attached to a
carbon with two adjacent O, N, or S atoms. We have carried out a systematic computational study of a series of five-membered
cyclic acetals like 2-methylene-1,3-dioxolane and its OS, SS, NO, NS, and NN analogs as well as all the protonated species. The calculations were performed at the MP2 level using a triple zeta plus
polarization basis set. The nucleophilicity was discussed in terms of geometrical factors, calculated atomic charges, calculated
chemical shifts, and proton affinities. All the six neutral species were strong nucleophiles. The NN analog was predicted to be the strongest and the SS analog the weakest nucleophile. 相似文献
28.
Pittman JJ Manard BT Kowalski PJ Marcus RK 《Journal of the American Society for Mass Spectrometry》2012,23(1):102-107
Polypropylene (PP) capillary-channeled polymer (C-CP) films have parallel, μm-sized channels that induce solution wicking
via capillary action. Efficient mass transport from the solution phase to the channel surface leads to adsorption of hydrophobic
protein solutes. The basic premise by which C-CP films can be used as media to manipulate analyte solutions (e.g., proteins
in buffer), for the purpose of desalting or chromatographic separation prior to MALDI-MS analysis is presented here. Cytochrome
c and myoglobin prepared in a Tris-HCl buffer, and ribonuclease A, lysozyme, and transferrin prepared in phosphate buffered
saline (PBS), are used as the test solutions to demonstrate the desalting concept. Protein analysis is performed after deposition
on a C-CP film with and without a water washing step, followed by spray deposition of a typical sinapinic acid matrix. Extracted
MALDI mass spectra exhibit much improved signal-to-noise characteristics after water washing. A mixture of cytochrome c and myoglobin (2 μL of 2.5 μM each in Tris-HCl buffer) was applied, washed with water and spatially separated via simple
capillary action (wicking) using a reversed-phase solvent composition of 0.1% trifluoroacetic acid (TFA) in 50:50 acetonitrile
(ACN):H2O. Subsequent application of sinapinic acid followed by imaging of the film using MALDI-MS reveals that as the protein solution
is wicked down the film, separation occurs. 相似文献
29.
Peter C. Zhu Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1996,34(1):73-80
Stable polymers were made by the cationically initiated 1,2-polymerization of cyclic ketene acetals employing heterogeneous, activated carbon-supported sulfuric acid catalysts. A methodology has been established for the preparation of the carbon black of different acidic strengths. By adjusting either the acid strength or the amount of carbon black used, cyclic ketene acetals with different activities can be polymerized efficiently to form stable high molecular weight polymers. This methodology will be a useful tool for polymerization, copolymerization, and studies of the relative reactivities of the cyclic ketene acetals. The polymer structures were determined by FTIR, 13C-NMR, and 1H-NMR studies. © 1996 John Wiley & Sons, Inc. 相似文献
30.
Reduction of -fluorosulfides with sodium in alcohol results in the formation of fluoroalkanes. 相似文献