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101.
Michelle A. Meierhoefer Matthew J. Walters S. Patrick Dunn Jarrett H. Vella Bonnie J. Grant Carolyn L. Sober Nidhi S. Patel Laela M. Hajiaghamohseni Sara B. Lioi Clyde R. Metz Charles F. Beam William T. Pennington Donald G. Vanderveer N. Dwight Camper 《Journal of heterocyclic chemistry》2006,43(2):307-313
102.
A conceptually new type of electronic spark source is described. A parallel combination of a hydrogen thyratron and a diode is used as the switch element. The switch operates by providing parallel paths for current oscillating from capacitors discharging through inductive loads. The same principle is used to route current through the analytical spark gap. Either the switch current or the spark current can be adjusted in waveform from fully oscillatory to fully unidirectional simply by changing the value of a single inductor, without changing capacitance, resistance, or the voltage at which the source operates.The electrical circuitry is singularly simple, thus producing a source that is characterized by reliable, long term operation, precise ignition with low time jitter (ca. 5 nsec) and low conducted or radiated radio-frequency interference. Because of the latter, modern electronic devices (such as microprocessors and minicomputers) can be used in conjunction with and in direct control of the spark source, i.e., while the spark is conducting current. The source functions equally well for industrial spectrochemical analysis and for basic research on optical emission phenomena.A partial circuit analysis is included here. The current commutation between the hydrogen thyratron and shunt diode is characterized. Electronic circuitry appropriate for source operation at variable repetition rate is described. The types of spark current waveforms that can be obtained under electronic control are illustrated. 相似文献
103.
H. R. J. Walters H. Ast C. T. Whelan R. M. Dreizler H. Graf C. D. Schröter J. Bonfert W. Nakel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,23(4):353-357
We report here on an (e, 2e) experiment at relativistic electron energies (E 0=300 keV and 500 keV) in coplanar symmetric geometry. Absolute triple differential cross section measurements forK-shell ionisation of gold, silver and copper are compared with a number of simple first order approximations. Appreciable discrepancies between theory and experiment are found, which reduce with decreasingZ and increasing primary energy. The theoretical calculations show that spin flip effects are important in symmetric geometry, in earlier works these had been neglected. 相似文献
104.
Recently Bergelson and Leibman proved an extension to van derWaerden's theorem involving polynomials. They also generalisedthe HalesJewett theorem in a similar way. The paper presentsshort and purely combinatorial proofs of those results. 相似文献
105.
M.?KamppEmail author S.?Kawano P.?J.?P.?Roche J.?Rasch D.?H.?Madison H.?R.?J.?Walters C.?T.?Whelan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,29(1):17-19
The spin asymmetry arising in an (e,2e) process using spin-polarized incoming electrons with non-relativistic energies is shown to be dominated by the fine structure effect if a suitable kinematical regime is chosen. Calculations in the distorted wave Born approximation (DWBA) for both the triple differential cross-section and the spin asymmetry are presented for the inner shell ionization of argon. This process would provide an accessible target for existing experimental set-ups. 相似文献
106.
Dillmann I Kratz KL Wöhr A Arndt O Brown BA Hoff P Hjorth-Jensen M Köster U Ostrowski AN Pfeiffer B Seweryniak D Shergur J Walters WB;ISOLDE Collaboration 《Physical review letters》2003,91(16):162503
First beta- and gamma-spectroscopic decay studies of the N=82 r-process "waiting-point" nuclide 130Cd have been performed at CERN/ISOLDE using the highest achievable isotopic selectivity. Several nuclear-physics surprises have been discovered. The first one is the unanticipatedly high energy of 2.12 MeV for the [pi g(9/2) multiply sign in circle nu g(7/2)] 1(+) level in 130In, which is fed by the main Gamow-Teller transition. The second surprise is the rather high Q(beta) value of 8.34 MeV, which is in agreement only with recent mass models that include the phenomenon of N=82 shell quenching. Possible implications of these new results on the formation of the A approximately 130 r-process abundance peak are presented. 相似文献
107.
Kelly A. Van Houten Keith A. Walters Kirk S. Schanze Robert S. Pilato 《Journal of fluorescence》2000,10(1):35-40
The photoluminescent 1,2-enedithiolate complexes, (dppe)Pt{S2C2(2-quinoxaline)(H)}, [L2Pt{S2C2(2-pyridinium)(H)}]+ where L2 = dppm and dppe, [L2Pt{S2C2(4-pyridinium)(H)}]+, [L2Pt{2C2(N-Methyl-4-pyridinium)(H)}]+ and [L2Pt{S2C2(CH2CH2-N-2-pyridinium)}]+ where L2 = dppm, dppe, and dppp are room temperature dual emitters where the emissions have thiolate to heterocycle * intraligand charge transfer character (ILCT) singlet and triplet character. The pyridinium complexes have strong triplet-triplet absorption bands at approximately 400, 520 and 630 nm with a weaker band at 800 nm while (dppe)Pt{S2C2(2-quinoxaline)(H)} has strong triplet-triplet absorption bands at 385 and 550 nm with weaker bands at 610 and 805 nm. By fitting the decay of the transients to single exponential kinetics, the 3ILCT* lifetimes of the pyridinium complexes where determined to be 0.7 to 15.9 s (DMSO) while the 3ILCT* lifetime of (dppe)Pt{S2C2(2-quinoxaline)(H)} was determined to be 2.8 s (CH3CN). The transient absorption spectra of the complexes is affected by the appended heterocycle rather than the bulk of ancillary phosphine ligand or whether the heterocycle is protonated or alkylated. 相似文献
108.
The structure of 1,3-dehydro-5-adamantyl cation and its isoelectronic boron analogue 1,3-dehydro-5-boraadamantane as well as some related adamantane systems, hitherto unknown as persistent long-lived species, were investigated by using the density functional theory (DFT) method. (13)C and (11)B NMR chemical shifts of the compounds were also calculated using the IGLO method. Stabilization of the systems due to homoconjugation is discussed. 相似文献
109.
The crossover between thermally assisted and pure quantum tunneling has been studied in single crystals of high spin (S = 10) uniaxial molecular magnet Mn12 using micro-Hall-effect magnetometry. Magnetic hysteresis and relaxation experiments have been used to investigate the energy levels that determine the magnetization reversal as a function of magnetic field and temperature. These experiments demonstrate that the crossover occurs in a narrow ( approximately 0. 1 K) or broad ( approximately 1 K) temperature interval depending on the magnitude of the field transverse to the anisotropy axis. 相似文献
110.
Rikovska J Giles T Stone NJ van Esbroeck K White G Wohr A Veskovic M Towner IS Mantica PF Prisciandaro JI Morrissey DJ Fedoseyev VN Mishin VI Koster U Walters WB 《Physical review letters》2000,85(7):1392-1395
The first fully on-line use of the angular distribution of beta emission in detection of NMR of nuclei oriented at low temperatures is reported. The magnetic moments of the single valence particle, intermediate mass, isotopes 67Ni(nup(-1)(1/2);1/2(-)) and 69Cu(pip(1)(3/2);3/2(-)) are measured to be +0.601(5) &mgr;(N) and +2.84(1) &mgr;(N), respectively, revealing only a small deviation from the neutron p(1/2) single-particle value in the former and a large deviation from the proton p(3/2) single-particle value in the latter. Quantitative interpretation is given in terms of core polarization and meson-exchange currents. 相似文献