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排序方式: 共有41条查询结果,搜索用时 15 毫秒
31.
We have employed a classical molecular dynamics simulation to investigate the energy transfer of a heavy projectile ion to a surface, i.e. Cs+ impacting onto Pt(1 1 1), for incidence energies between 25 and 100 eV and an incidence angle of 45°. The in-plane scattering results show a continuous increase of the final energy with increasing scattering angle. All scattering intensities have a main supraspecular peak and scattering into subspecular angles increases with increasing incidence energy. The large projectile/target mass ratio causes a high energy loss and a strong angular dependence of the final energy distribution. The trends of the energy transfer and its angular dependence can be understood in terms of a binary collision model, augmented with double collisions and an the image charge correction. Backscattering at high incidence energies leads to a distribution of very low final energies, indicating the onset of surface sputtering. Peaks in the energy spectra arise from impact site dependent scattering and can be assigned to single, double, triple or sputtering type collisions. 相似文献
32.
Negative electrospray ionization mass spectrometry: a method for sequencing and determining linkage position in oligosaccharides from branched hemicelluloses 下载免费PDF全文
Bernard Quéméner Jacqueline Vigouroux Estelle Rathahao Jean Claude Tabet Aleksandra Dimitrijevic Marc Lahaye 《Journal of mass spectrometry : JMS》2015,50(1):247-264
Xyloglucans of apple, tomato, bilberry and tamarind were hydrolyzed by commercial endo β‐1‐4‐D‐endoglucanase. The xylo‐gluco‐oligosaccharides (XylGos) released were separated on CarboPac PA 200 column in less than 15 min, and, after purification, they were structurally characterized by negative electrospray ionization mass spectrometry using a quadrupole time‐of‐flight (ESI‐Q‐TOF), a hybrid linear ion trap (LTQ)/Orbitrap and a hybrid quadrupole Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometers. In order to corroborate the fragmentation routes observed on XylGos, some commercial galacto‐manno‐oligosaccharides (GalMOs) and glucurono‐xylo‐oligosaccharides were also studied. The fragmentation pathways of the ionized GalMos were similar to those of XylGos ones. The product ion spectra were mainly characterized by prominent double cleavage (D) ions corresponding to the entire inner side chains. The directed fragmentation from the reducing end to the other end was observed for the main glycosylated backbone but also for the side‐chains, allowing their complete sequencing. Relevant cross‐ring cleavage ions from 0,2Xj ‐type revealed to be diagnostic of the 1‐2‐linked‐ glycosyl units from XylGos together with the 1‐2‐linked glucuronic acid unit from glucuronoxylans. Resonant activation in the LTQ Orbitrap allowed not only determining the type of all linkages but also the O‐acetyl group location on fucosylated side‐chains. Moreover, the fragmentation of the different side chains using the MSn capabilities of the LTQ/Orbitrap analyzer also allowed differentiating terminal arabinosyl and xylosyl substituents inside S and U side‐chains of XylGos, respectively. The CID spectra obtained were very informative for distinction of isomeric structures differing only in their substitution pattern. These features together makes the fragmentation in negative ionization mode a relevant and powerful technique useful to highlight the subtle structural changes generally observed during the development of plant organs such as during fruit ripening and for the screening of cell wall mutants with altered hemicellulose structure. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
33.
G. Wlodarczak F. Herlemont J. Demaison A. Fayt J.G. Lahaye 《Journal of Molecular Spectroscopy》1985,112(2):401-412
The ν6 fundamental of CH335Cl has been remeasured by using a Stark-Lamb-dip technique. These Stark resonances were combined with the zero-field microwave spectra to give determinable combinations of the vibration-rotation parameters and the dipole moments: μ″ = 1.89628(23)D and μ′ = 1.89738(19)D. 相似文献
34.
C. T. W. Lahaye W. Hogervorst W. Vassen 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,7(1):37-45
In a CW laser-atomic beam experiment Stark manifolds in barium originating from the Rydberg states 6s40f 1 F 3, 6s40g 1,3 G 4,3 G 5 and 6s40h 1,3 H 5 have been studied. Accurate quantum defect values for higher orbital angular momentum states (l=6, 7) have been determined. The Stark manifolds are also calculated by diagonalization of the energy matrix in the presence of an external electric field. Good agreement between experiment and calculations is obtained. 相似文献
35.
Quéméner B Désiré C Lahaye M Debrauwer L Negroni L 《European journal of mass spectrometry (Chichester, England)》2003,9(1):45-60
The off-line coupling of high-performance anion-exchange chromatography (HPAEC) to electrospray ionisation/ion trap mass spectrometry (ESI-ITMS) is described. The Dionex carbohydrate membrane desalter (CMD) has been assessed as an on-line chromatographic desalting system to remove the high sodium concentration necessary for the HPAEC separation of partially methyl-esterified oligogalacturonides. The developed HPAEC configuration proved to be suitable for indirect coupling with ESI-ITMS. This paper provides some interesting features of positive- and negative-ion multistage tandem mass spectrometry (MS(n)) analysis of these acidic oligosaccharides. The spectra acquired in both negative- and positive-ion modes show characteristic fragment ions resulting from glycosidic bond and cross-ring cleavages. Some new mass spectrometric fragmentation routes are also described. The positive-ion mode gave more complex spectra but was as informative as the negative-ion mode. ESI-ITMS was revealed to be, as previously reported from direct use on an unseparated enzymatic digest, a powerful sequencing technique for the determination of linkage type and the methyl ester distribution of partially methyl-esterified oligogalacturonides. Moreover, unlike matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF MS), it gives valuable information on the elution behaviour of these oligomers in relation to their structure, namely the HPAEC co-elution of isomeric structures. 相似文献
36.
Walter Nielsch und Lieselotte Giefer 《Fresenius' Journal of Analytical Chemistry》1955,146(5):323-326
Zusammenfassung In der vorliegenden Arbeit wird gezeigt, daß Pyrophosphat-Ion bei Ph 4,1 als Mangansalz gefällt und durch Titration der dem Pyrophosphat äquivalenten Menge Mangan mit Idranal III-lösung komplexometrisch bestimmt werden kann. Hierbei muß die Konzentration mindestens 0,2 mg P2O7
4–/ml Lösung betragen und die Mn-Ionen müssen mindestens im 5 fachen Überschuß vorliegen.Dieses Verfahren erfordert wesentlich weniger Zeit als die gravimetrische Bestimmung oder die Überführung in Orthophosphat und dessen Bestimmung. Diese Methode ist für die Betriebsüberwachung von ausreichender Genauigkeit. 相似文献
37.
Lahaye T Metz J Fröhlich B Koch T Meister M Griesmaier A Pfau T Saito H Kawaguchi Y Ueda M 《Physical review letters》2008,101(8):080401
We investigate the collapse dynamics of a dipolar condensate of 52Cr atoms when the s-wave scattering length characterizing the contact interaction is reduced below a critical value. A complex dynamics, involving an anisotropic, d-wave symmetric explosion of the condensate, is observed. The atom number decreases abruptly during the collapse. We find good agreement between our experimental results and those of a numerical simulation of the three-dimensional Gross-Pitaevskii equation, including contact and dipolar interactions as well as three-body losses. The simulation indicates that the collapse induces the formation of two vortex rings with opposite circulations. 相似文献
38.
39.
T.?Lahaye D.?Guéry-OdelinEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,33(1):67-75
We present a theoretical analysis of the evaporative
cooling of a magnetically guided atomic beam by means of discrete
radio-frequency antennas. First we derive the changes in flux and
temperature, as well as in collision rate and phase-space density,
for a single evaporation step. Next we show how the occurrence of
collisions during the propagation between two successive antennas
can be probed. Finally, we discuss the optimization of the
evaporation ramp with several antennas to reach quantum
degeneracy. We estimate the number of antennas required to
increase the phase-space density by several orders of magnitude.
We find that at least 30 antennas are needed to gain a factor
108 in phase-space density. 相似文献
40.
Joachim Nölte Lieselotte Moenke-Blankenburg Thomas Schumann 《Fresenius' Journal of Analytical Chemistry》1994,349(1-3):131-135
Solid sampling with laser vaporization has been coupled to an ICP emission spectrometer with an Echelle optical system and a solid-state-detector for the analysis of steel and soil samples. Pulsation of the vaporized material flow was compensated by real-time background correction and internal standardization, resulting in good accuracy and precision. 相似文献