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61.
Moss CL Chung TW Wyer JA Nielsen SB Hvelplund P Tureček F 《Journal of the American Society for Mass Spectrometry》2011,22(4):731-751
Electron transfer and capture mass spectra of a series of doubly charged ions that were phosphorylated pentapeptides of a
tryptic type (pS,A,A,A,R) showed conspicuous differences in dissociations of charge-reduced ions. Electron transfer from both
gaseous cesium atoms at 100 keV kinetic energies and fluoranthene anion radicals in an ion trap resulted in the loss of a
hydrogen atom, ammonia, and backbone cleavages forming complete series of sequence z ions. Elimination of phosphoric acid was negligible. In contrast, capture of low-energy electrons by doubly charged ions
in a Penning ion trap induced loss of a hydrogen atom followed by elimination of phosphoric acid as the dominant dissociation
channel. Backbone dissociations of charge-reduced ions also occurred but were accompanied by extensive fragmentation of the
primary products. z-Ions that were terminated with a deaminated phosphoserine radical competitively eliminated phosphoric acid and H2PO4 radicals. A mechanism is proposed for this novel dissociation on the basis of a computational analysis of reaction pathways
and transition states. Electronic structure theory calculations in combination with extensive molecular dynamics mapping of
the potential energy surface provided structures for the precursor phosphopeptide dications. Electron attachment produces
a multitude of low lying electronic states in charge-reduced ions that determine their reactivity in backbone dissociations
and H- atom loss. The predominant loss of H atoms in ECD is explained by a distortion of the Rydberg orbital space by the
strong dipolar field of the peptide dication framework. The dipolar field steers the incoming electron to preferentially attach
to the positively charged arginine side chain to form guanidinium radicals and trigger their dissociations. 相似文献
62.
Feng Zheng Akella Sivaramakrishna John R. Moss 《Journal of organometallic chemistry》2011,696(11-12):2457-2465
Thermal decomposition studies on platinacycloalkanes of the type Pt(CH2)mL2 (where m = 6,7,8,10 and L2 = dppp {1,3-bis(diphenylphosphino)propane}, dppe {1,2-bis(diphenylphosphino)ethane} or L = PPh3, tBu3P) are described. The results reveal that the organic product distribution depends on various factors such as the nature of ligand, the metal system, the mode of decomposition, the ring size and the temperature. Possible mechanistic pathways for the formation of various products are discussed. These platinacycloalkanes can be used as models for metallacycloalkane intermediates in catalytic reactions. 相似文献
63.
Lu Z Moss RA Warmuth R Krogh-Jespersen K 《The journal of physical chemistry. A》2011,115(47):13799-13803
Laser flash photolysis of fluorophenyldiazirine incarcerated in hemicarcerand 2 affords incarcerated fluorophenylcarbene [2⊙3], which forms a metastable, innermolecular π-complex with aryl moieties of 2. This carbene complex can be observed spectroscopically. Extensive computational studies provide insights into the structure, spectroscopy, energetics, and kinetics of the 2⊙3 carbene complex. 相似文献
64.
Replacement of one hydrogen atom by deuterium in the negative ion of cyclo-octatetraene, makes no significant difference to the electron spin densities at the hydrogen nuclei. This result contrasts with a recent observation that mono-deuteration produces a measurable change in the spin distribution in the benzene negative ion. The difference between the two systems is interpreted in terms of the Jahn-Teller effect. 相似文献
65.
Ian G. Moss 《Contemporary Physics》2013,54(4):468-476
The discovery of the Standard Model Higgs boson opens up a range of speculative cosmological scenarios, from the formation of structure in the early universe immediately after the big bang, to relics from the electroweak phase transition one nanosecond after the big bang, on to the end of the present-day universe through vacuum decay. Higgs physics is wide ranging, and gives an impetus to go beyond the Standard Models of particle physics and cosmology to explore the physics of ultra-high energies and quantum gravity. 相似文献
66.
Kaleb C. Burrage Christopher S. Perreault Eric K. Moss Jeffrey S. Pigott Blake T. Sturtevant Jesse S. Smith 《高压研究》2013,33(3):489-498
ABSTRACTThe isothermal compression of transition metal tantalum (Ta) was studied in a diamond anvil cell by X-ray diffraction utilizing rhenium (Re) and gold (Au) as internal X-ray pressure standards. The Re pressure marker was employed during non-hydrostatic compression to pressures up to 310?GPa while the Au pressure marker was used during quasi-hydrostatic compression in a neon pressure-transmitting medium to 80?GPa. Two ultra-high pressure experiments were conducted on Ta and Re mixtures utilizing focused-ion beam machined toroidal diamond anvils with central flats varying from 8 microns to 16 microns in diameter. The Ta metal was observed to be stable in the body-centered-cubic phase to a volume compression V/V0?=?0.581. The measured equations of state (EOS) of Ta using two different calibrations of the Re pressure marker are compared with the ambient temperature isotherm derived from shock compression data. We provide a detailed analysis of EOS fit parameters for Ta under quasi-hydrostatic and non-hydrostatic conditions. 相似文献
67.
J. P. Moss A. D. Linney S. R. Grindrod C. A. Mosse 《Optics and Lasers in Engineering》1989,10(3-4):179-190
A no contact system based on laser scanning, which records 20 000 facial surface coordinates with a dynamic resolution of approximately 0·9mm in 30s, has been developed for the study of facial changes following facial reconstructive surgery. Individual profiles are recorded with a resolution better than 0·5mm. The system is based on the analysis of the output from a video camera which obliquely views a laser line projected vertically onto the face. In order to sample the whole face, the subject sits on a chair which rotates at six degrees per second under computer control. Examples of applications of the system are given. 相似文献
68.
This article presents a review of the strategies that have been both demonstrated and proposed for the multiplexing of multiple noninterferometric optical fiber point sensors to form a sensor network. The focus, which avoids consideration of interferometric sensor types, enables discussion of conventional multiplexing tech niques, namely, spatial, time division, frequency division, and wavelength division prior to dealing with combined or hybrid schemes, which exhibit the potential for increased multiplexing gain. Specific advantages and potential drawbacks of the different strategies are provided together with an indication of the number of point sensors that each multiplexing scheme can support. 相似文献
69.
Steven C. Moss John F. Knudsen Robert C. Bowman Jr. Paul M. Adams Duane D. Smith 《Applied Surface Science》1991,50(1-4):337-340
We have used picosecond transient reflectance techniques to measure the near-surface characteristics of ion-implanted GaAs. These non-destructive laser-based diagnostic techniques allow measurement of the modification of near-surface properties at relatively low implant fluences. Photothermal phenomena dominate these results and yield important information concerning the extent of implant-induced materials modification. 相似文献
70.
T. J. Greytak D. Kleppner D. G. Fried T. C. Killian L. Willmann D. Landhuis S. C. Moss 《Physica B: Condensed Matter》2000,280(1-4):20-26
The addition of atomic hydrogen to the set of gases in which Bose–Einstein condensation can be observed expands the range of parameters over which this remarkable phenomenon can be studied. Hydrogen, with the lowest atomic mass, has the highest transition temperature, 50 μK in our experiments. The very weak interaction between the atoms results in a high ratio of the condensate to normal gas densities, even at modest condensate fractions. Using cryogenic rather than laser precooling generates large condensates. Finally, two-photon spectroscopy is introduced as a versatile probe of the phase transition: condensation in real space is manifested by the appearance of a high-density component in the gas, condensation in momentum space is readily apparent in the momentum distribution, and the phase transition line can be delineated by following the evolution of the density of the normal component. 相似文献