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141.
M. Cameron Sullards Jeanette Adams 《Journal of the American Society for Mass Spectrometry》1995,6(7):608-610
The use of sector mass spectrometers to study metastable ion decompositions of peptide metal-ion complexes formed by electrospray ionization is discussed. Products that are formed by charge-separation reactions are characterized by large kinetic energy release distributions. This causes scans at a constant B/E to give incorrect product ion abundances and possibly incorrect mass assignments. Two instrumental methods exist that can be used either to detect the ions or to estimate relative ion abundances: a floated collision cell or mass-analyzed ion kinetic energy spectrometry (MIKES) scans. The floated collision cell, by virtue of an altered B/E scan law, however, discriminates against important metastable ion reactions that occur outside the cell. MIKES scans provide a clearer estimate of product ions that arise by metastable ion charge-separation reactions. Problems with pseudotandem (first field-free region) experiments are also discussed. 相似文献
142.
143.
D. Sarkisyan A. Sargsyan J. Keaveney C. S. Adams 《Journal of Experimental and Theoretical Physics》2014,119(1):8-14
It is shown that high-contrast resonance of electromagnetically induced transparency (EIT) in a ladder Ξ-system of 5S 1/2-5P 3/2-5D 5/2 levels can be formed in optical cells containing a column of rubidium vapor with thickness L in an interval of 100 nm ≤ L ≤ 780 nm. Using bichromatic laser radiation with certain parameters, an 83% contrast of the EIT resonance (or dark resonance, DR) has been achieved for a vapor column thickness of L = 780 nm. An important condition for the formation of high-contrast DR is that the frequency of the coupling laser radiation must be resonant with the frequency of the corresponding 5P 3/2-5D 5/2 transition (for the probe radiation frequency scanned over the 5S 1/2-5P 3/2 transition). It is also shown that a DR can be formed at a record small vapor column thickness of L ≈ 100 nm. Expressions that can be used to estimate the expected DR width at small L values are presented. 相似文献
144.
Bennett GR Cuneo ME Vesey RA Porter JL Adams RG Aragon RA Caird JA Landen OL Rambo PK Rovang DC Ruggles LE Simpson WW Smith IC Wenger DF 《Physical review letters》2002,89(24):245002
An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system. 相似文献
145.
De Vita R Anghinolfi M Burkert VD Dodge GE Minehart R Taiuti M Weller H Adams G Amaryan MJ Anciant E Armstrong DS Asavapibhop B Asryan G Audit G Auger T Avakian H Bagdasaryan H Ball JP Barrow S Battaglieri M Beard K Bektasoglu M Bianchi N Biselli AS Boiarinov S Bonner BE Bosted P Bouchigny S Branford D Brooks WK Bueltmann S Calarco JR Capitani GP Carman DS Carnahan B Cazes A Ciciani L Cole PL Coleman A Connelly J Cords D Corvisiero P Crabb D Crannell H Cummings JP De Sanctis E Degtyarenko PV 《Physical review letters》2002,88(8):082001
The double spin asymmetry in the (-->)e(-->)p --> e(prime)pi(+)n reaction has been measured for the first time in the resonance region for four-momentum transfer Q2 = 0.35-1.5 GeV(2). Data were taken at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH3 target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with Q(2) of the helicity asymmetry A1 for the F(15)(1680) resonance than expected from the analysis of the unpolarized data. 相似文献
146.
Abazov VM Abbott B Abdesselam A Abolins M Abramov V Acharya BS Adams DL Adams M Ahmed SN Alexeev GD Alves GA Amos N Anderson EW Arnoud Y Baarmand MM Babintsev VV Babukhadia L Bacon TC Baden A Baldin B Balm PW Banerjee S Barberis E Baringer P Barreto J Bartlett JF Bassler U Bauer D Bean A Beaudette F Begel M Belyaev A Beri SB Bernardi G Bertram I Besson A Beuselinck R Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Blazey G Blessing S Boehnlein A Bojko NI Borcherding F Bos K Brandt A Breedon R 《Physical review letters》2002,88(17):171802
We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of pp events corresponding to 108.3 pb(-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, t-->b chi+1 and t-->blnu, no evidence for signal is found. We derive cross-section limits as a function of stop ( t ), chargino ( chi+1), and sneutrino ( nu) masses. 相似文献
147.
Joo K Smith LC Burkert VD Minehart R Aznauryan IG Elouadrhiri L Stepanyan S Adams GS Amaryan MJ Anciant E Anghinolfi M Armstrong DS Asavapibhop B Audit G Auger T Avakian H Barrow S Bagdasaryan H Battaglieri M Beard K Bektasoglu M Bertozzi W Bianchi N Biselli AS Boiarinov S Bonner BE Brooks WK Calarco JR Capitani GP Carman DS Carnahan B Cole PL Coleman A Cords D Corvisiero P Crabb D Crannell H Cummings J De Sanctis E De Vita R Degtyarenko PV Demirchyan RA Denizli H Dennis LC Deppman A 《Physical review letters》2002,88(12):122001
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma*p-->Delta(+)-->p pi(0) transition. We report new experimental values for the ratios E(1+)/M(1+) and S(1+)/M(1+) over the range Q2 = 0.4-1.8 GeV2, extracted from precision p(e,e(')p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role. 相似文献
148.
Low-molecular-weight organoiodine and organobromine compounds released by polar macroalgae--the influence of abiotic factors 总被引:1,自引:0,他引:1
Laturnus F Giese B Wiencke C Adams FC 《Fresenius' Journal of Analytical Chemistry》2000,368(2-3):297-302
The influence of temperature, light, salinity and nutrient availability on the release of volatile halogenated hydrocarbons was investigated in the Antarctic red macroalgal species Gymnogongrus antarcticus Skottsberg. Compared to standard culture condition, an increase in the release rates of iodocompounds was generally found for the exposure of the alga to altered environmental conditions. Macroalgae exhibited higher release rates after adaptation for two months to the changed factors, than after short-term exposure. Monitoring the release rates during a 24 h incubation period (8.25 h light, 15.75 h darkness) showed that changes between light and dark periods had no influence on the release of volatile halocarbons. Compounds like bromoform and 1-iodobutane exhibited constant release rates during the 24 h period. The formation mechanisms and biological role of volatile organohalogens are discussed. Although marine macroalgae are not considered to be the major source of biogenically-produced volatile organohalogens, they contribute significantly to the bromine and iodine cycles in the environment. Under possible environmental changes like global warming and uncontrolled entrophication of the oceans their significance may be increase. 相似文献
149.
We explore possible effects of vacuum energy on the evolution of black holes. If the universe contains a cosmological constant, and if black holes can absorb energy from the vacuum, then black hole evaporation could be greatly suppressed. For the magnitude of the cosmological constant suggested by current observations, black holes larger than 4×1024 g would accrete energy rather than evaporate. In this scenario, all stellar and supermassive black holes would grow with time until they reach a maximum mass scale of 6×1055 g, comparable to the mass contained within the present day cosmological horizon. 相似文献
150.
M.J.A. Van craen F.C. Adams L.J.A. Van Beek R.A.L. Vanden Berghe 《Spectrochimica Acta Part B: Atomic Spectroscopy》1984,39(12):1579-1581
Corrosion phenomena of Al-1 % Si bond wires, observed after life testing of certain transistors, are studied. The following information is derived from laboratory simulation tests: the kinetics of the corrosion process, information about the corrosion mechanism and critical parameters, especially the influence of the environmental gas and Si content and finally the identification of the corrosion products and their comparison with those found for the transistor. It is demonstrated, using a combination of several surface analytical techniques, that the A1 pitting corrosion is induced and enhanced by the presence of water as a transport medium and surface electrolyte in an oxygen-rich atmosphere, with chloride ions as a stimulating and activating species. The effect of 1 % Si in the wire consists in acceleration of the corrosion rate, and is probably due to grain boundary effects. All critical corrosion parameters could be traced in the transistor system by electron microscopy, laser microprobe mass analysis and residual gas (and moisture) analysis by mass spectrometry. 相似文献