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61.
Monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) were determined in natural water samples by aqueous phase ethylation with sodium tetraethylborate (STEB), room temperature trapping of the resulting volatile derivatives on Tenax TA®, followed by gas chromatography-quartz furnace atomic absorption spectrometry (GC-QFAAS). Recoveries of butyltin spikes from natural water samples were 90-109% at concentrations of ∼100 ng Sn/l. The method precision at ∼100 ng Sn/l was ≤6% RSD for butyltins spiked into natural waters. The detection limits for 1 l water samples were <1 ng Sn/l for all butyltin species. Sample throughput of the method is high (greater than three samples per hour) due to the two-stage nature of the procedure, which allows derivatisation/trapping and GC-QFAAS quantitation to be performed separately. Off-line trapping is also advantageous as it extends the life of the GC column and quartz furnace to at least 12 months due to minimisation of carry-over of co-purged material. 相似文献
62.
TX Liu T Wei SE Zhu GW Wang M Jiao S Yang FL Bowles MM Olmstead AL Balch 《Journal of the American Chemical Society》2012,134(29):11956-11959
The reaction of an organic azide with an endohedral metallofullerene has been investigated for the first time. Isomeric [5,6]- and [6,6]-azafulleroids can be obtained from the thermal reaction of Sc(3)N@I(h)-C(80) with 4-isopropoxyphenyl azide, while photoirradiation leads exclusively to the [6,6]-azafulleroid. An unprecedented thermal interconversion between the two isomeric azafulleroids has also been discovered. 相似文献
63.
Liu J Mendenhall MP Holley AT Back HO Bowles TJ Broussard LJ Carr R Clayton S Currie S Filippone BW García A Geltenbort P Hickerson KP Hoagland J Hogan GE Hona B Ito TM Liu CY Makela M Mammei RR Martin JW Melconian D Morris CL Pattie RW Pérez Galván A Pitt ML Plaster B Ramsey JC Rios R Russell R Saunders A Seestrom SJ Sondheim WE Tatar E Vogelaar RB VornDick B Wrede C Yan H Young AR;UCNA Collaboration 《Physical review letters》2010,105(18):181803
A precise measurement of the neutron decay β asymmetry A? has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A? = -0.119?66±0.000?89{-0.001?40}{+0.001?23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275?90{-0.004?45}{+0.004?09}. 相似文献
64.
Malonic acid derivatives undergo unusually mild decarboxylation when treated with N,N'-carbonyldiimidazole (CDI) at room temperature to generate the carbonyl imidazole moiety in high yield, which can be reacted further with a variety of nucleophiles in an efficient one-pot process. 相似文献
65.
The heterogeneous condensation of a Lennard-Jones vapor onto a nanoscale seed particle is studied using molecular dynamics simulations. Measuring the nucleation rate and the height of the free energy barrier using the mean first passage time method shows that the presence of a weakly interacting seed has little effect on the work of forming very small cluster embryos but accelerates the rate by lowering the barrier for larger clusters. We suggest that this results from a competition between the energetic and entropic features of cluster formation in the bulk and at the heterogeneity. As the interaction is increased, the free energy of formation is reduced for all cluster sizes. We also develop a simple phenomenological model of film formation on a small seed that captures the general features of the nucleation process for small heterogeneities. A comparison of our simulation results with the model shows that heterogeneous classical nucleation theory provides a good estimate of the critical size of the film but significantly overestimates the size of the barrier. 相似文献
66.
Ahmad QR Allen RC Andersen TC Anglin JD Bühler G Barton JC Beier EW Bercovitch M Bigu J Biller S Black RA Blevis I Boardman RJ Boger J Bonvin E Boulay MG Bowler MG Bowles TJ Brice SJ Browne MC Bullard TV Burritt TH Cameron K Cameron J Chan YD Chen M Chen HH Chen X Chon MC Cleveland BT Clifford ET Cowan JH Cowen DF Cox GA Dai Y Dai X Dalnoki-Veress F Davidson WF Doe PJ Doucas G Dragowsky MR Duba CA Duncan FA Dunmore J Earle ED Elliott SR Evans HC Ewan GT Farine J Fergani H Ferraris AP Ford RJ 《Physical review letters》2001,87(7):071301
Solar neutrinos from (8)B decay have been detected at the Sudbury Neutrino Observatory via the charged current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The flux of nu(e)'s is measured by the CC reaction rate to be straight phi(CC)(nu(e)) = 1.75 +/- 0.07(stat)(+0.12)(-0.11)(syst) +/- 0.05(theor) x 10(6) cm(-2) s(-1). Comparison of straight phi(CC)(nu(e)) to the Super-Kamiokande Collaboration's precision value of the flux inferred from the ES reaction yields a 3.3 sigma difference, assuming the systematic uncertainties are normally distributed, providing evidence of an active non- nu(e) component in the solar flux. The total flux of active 8B neutrinos is determined to be 5.44+/-0.99 x 10(6) cm(-2) s(-1). 相似文献
67.
J. N. Abdurashitov E. P. Veretenkin V. M. Vermul V. N. Gavrin S. V. Girin V. V. Gorbachev P. P. Gurkina G. T. Zatsepin T. V. Ibragimova A. V. Kalikhov T. V. Knodel I. N. Mirmov N. G. Khairnasov A. A. Shikhin V. E. Yants T. J. Bowles W. A. Teasdale J. S. Nico J. F. Wilkerson B. T. Cleveland S. R. Elliott 《Journal of Experimental and Theoretical Physics》2002,95(2):181-193
We present measurements of the solar neutrino capture rate on metallic gallium in the Soviet-American gallium experiment (SAGE) over a period of slightly more than half the 22-year solar cycle. A combined analysis of 92 runs over the twelve-year period from January 1990 until December 2001 yields a capture rate of 70.8 ?5.2 +5.3 (stat) ?3.2 +3.7 (sys) SNU for solar neutrinos with energies above 0.233 MeV. This value is slightly more than half the rate predicted by the standard solar model, 130 SNU. We present the results of new runs since April 1998 and analyze all runs combined by years, months, and bimonthly periods beginning in 1990. A simple analysis of the SAGE results together with the results of other solar neutrino experiments gives an estimate of (4.6±1.2)× 1010 neutrinos cm?2 s?1 for the flux of the electron pp neutrinos that reach the Earth without changing their flavor. The flux of the pp neutrinos produced in thermonuclear reactions in the Sun is estimated to be (7.6 ± 2.0) × 1010 neutrinos cm?2 s?1, in agreement with the value of (5.95±0.06)×1010 neutrinos cm?2 s?1 predicted by the standard solar model. 相似文献
68.
V. V. Gorbachev J. N. Abdurashitov T. J. Bowles M. L. Cherry B. T. Cleveland R. Davis Jr. S. R. Elliott V. N. Gavrin S. V. Girin P. P. Gurkina T. V. Ibragimova A. V. Kalikhov N. G. Khairnasov T. V. Knodel K. Lande I. N. Mirmov J. S. Nico A. A. Shikhin W. A. Teasdale E. P. Veretenkin V. M. Vermul D. L. Wark P. S. Wildenhain J. F. Wilkerson V. E. Yants G. T. Zatsepin 《Physics of Atomic Nuclei》2002,65(12):2156-2160
The solar neutrino capture rate measured by the Russian-American Gallium Experiment on a metallic gallium target SAGE during the time from January 1990 through December 2000 is 77.0 ?6.2 ?3.0 +6.2 +3.5 SNU, where the uncertainties are statistical and systematic, respectively. The experimental procedures and data analysis are presented. 相似文献
69.
R. A. Mendelson W. A. Bowles F. L. Finger 《Journal of Polymer Science.Polymer Physics》1970,8(1):127-141
The investigation of the effect of molecular structural variables on the melt viscosity of polyethylene was extended to the shear dependent region by application of a reduced variables treatment following, in a formal sense, that of Bueche. Viscosity–shear rate data were obtained for a series of experimentally polymerized linear polyethylene samples having a range of molecular weights and molecular weight distributions as characterized primarily by gel permeation chromatography. These data could be superimposed on a single reduced variables flow curve using parameters which were a function only of temperature, limiting Newtonian viscosity, M?w, and M?w/M?n. The same treatment was successfully applied also to branched (low-density) fraction data discussed in a previous paper, with additional correction for long-chain branching. However, different reduced variables curves were obtained for the branched and linear cases. 相似文献
70.
[reaction: see text] Simple bis(bromoethynyl)arenediynes are easily prepared by the desilylative halogenation of the corresponding trimethylsilyl derivatives. Cycloaromatization of these halogenated enediynes leads to the otherwise difficult to prepare 2,3-dibromoarenes in good yield. Alkynylation of the resulting haloaromatic compound regenerates the soluble enediyne system, homologated by one aromatic ring. This iterative methodology can be terminated by the cycloaromatization of the unsubstituted enediyne, providing the simple acene hydrocarbon. 相似文献