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61.
Using neon and its dimer as a specific example, it is shown that excited Auger decay channels that are electronically stable in the isolated monomer can relax in a cluster by electron emission. The decay mechanism, leading to the formation of a tricationic cluster, is based on an efficient energy-transfer process from the excited, dicationic monomer to a neighbor. The decay is ultrafast and expected to be relevant to numerous physical phenomena involving core holes in clusters and other forms of spatially extended atomic and molecular matter. 相似文献
62.
Pathak Madhvesh Bohra Rakesh Mehrotra Ram C. Lorenz Ingo-Peter Piotrowski Holger 《Transition Metal Chemistry》2003,28(2):187-192
Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)2Ti(OR)2] (R = Et, Pr
i
) with alkoxyalkanols (ROCH2CH2OH) (R = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)2Ti(OR)2–n
(OCH2CH2OR)
n
] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (1H- and 13C-) spectral studies, a cis-octahedral environment around TiIV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)2Ti(OEt)(OCH2CH2OBu)] for 2 weeks, orange yellow crystals of [(acac)2TiO]2 were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)2TiO]2. 相似文献
63.
Steady, nonpropagating, fronts in reaction diffusion systems usually exist only for special sets of control parameters. When varying one control parameter, the front velocity may become zero only at isolated values (where the Maxwell condition is satisfied, for potential systems). The experimental observation of fronts with a zero velocity over a finite interval of parameters, e.g., in catalytic experiments [Barelko et al., Chem. Eng. Sci., 33, 805 (1978)], therefore, seems paradoxical. We show that the velocity dependence on the control parameter may be such that velocity is very small over a finite interval, and much larger outside. This happens in a class of reaction diffusion systems with two components, with the extra assumptions that (i) the two diffusion coefficients are very different, and that (ii) the slowly diffusing variables has two stable states over a control parameter range. The ratio of the two velocity scales vanishes when the smallest diffusion coefficient goes to zero. A complete study of the effect is carried out in a model of catalytic reaction. (c) 2000 American Institute of Physics. 相似文献
64.
H. von Wenckstern M. Brandt H. Schmidt G. Biehne R. Pickenhain H. Hochmuth M. Lorenz M. Grundmann 《Applied Physics A: Materials Science & Processing》2007,88(1):135-139
We have investigated donor-like defects in ZnO substrate material grown by three different methods, and in epitaxial ZnO thin
films grown on sapphire by pulsed laser deposition. Temperature dependent Hall effect measurements yield information about
dominant donors. The thermal activation energies lie in a wide range from about 20 meV to about 370 meV. Deep level transient
spectroscopy is used to obtain parameters of deep donor-like defects. For that, a high-speed diode contact configuration was
laid out for the epitaxial thin films in order to determine the defect parameters with high precision. The identified levels
are E1, E3 and E4, though the level E4 is observed only in single crystals grown by seeded chemical vapor transport.
PACS 72.10.Fk; 72.80.Ey; 73.50.-h 相似文献
65.
A radial inhomogeneous magnetic field produced by counter-propagating currents in anti-Helmholtz configuration coils has been
superimposed to a Penning trap. The confinement properties of electrons in such a trap have been studied experimentally. Without
the radial B-field we find a number of operating conditions where instabilities occur, arising from higher order contributions
to the quadrupolar trapping field. When we apply the radial field the trap properties remain essentially unchanged until the
strength of this field at the boundary of the electron cloud is of the same order as the homogeneous Penning field. Then a
sudden breakdown in the confinement appears. The experiments have been performed in low magnetic fields. The equations of
motions of the trapped particles can be cast in a dimensionless form and our results can be considered as independent of the
field strength.
Contribution was presented at the TCP06, Vancouver Island, 2006. 相似文献
66.
R. Schmidt-Grund B. Rheinlnder C. Czekalla G. Benndorf H. Hochmut A. Rahm M. Lorenz M. Grundmann 《Superlattices and Microstructures》2007,41(5-6):360
In this paper we report on planar and microscopic cylindrical resonators with ZnO as the cavity and active medium surrounded with ZrO2/MgO Bragg reflectors. We have observed resonator behaviour of these structures and, for the planar resonators, exciton–polariton coupling with a mode splitting of about 50 meV. 相似文献
67.
68.
Yves Leterrier Jérémy Thivolle Fabiane Oliveira Jan‐Anders Månson Lorenz Gubler Hicham Ben youcef Lukas Bonorand Günther Scherer 《Journal of Polymer Science.Polymer Physics》2013,51(15):1139-1148
The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)‐based proton‐conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion® NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 °C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion®. Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power‐law behavior with exponent equal to ?0.04 ± 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power‐law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH ≥ 70% and 30 °C. The general behavior of grafted films observed at 30 °C was also obtained at 50 °C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 °C when compared with 30 °C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time‐dependent behavior, from power‐law scaling to exponential scaling. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139–1148 相似文献
69.
Y. Xu W. Lorenz G. Pfister M. Bahadir F. Korte 《Fresenius' Journal of Analytical Chemistry》1986,325(4):377-380
Summary Two methods for the determination of triazines in soil were developed and compared. After extraction of the residues with methanol and clean-up by gel permeation chromatography, the samples evaporated were analysed for triazines by splitless capillary gas-chromatography with NP-detector (GC-NPD) and microbore high performance liquid chromatography with UV detector (HPLC-UV) at 222 nm. Both methods gave similar results. The microbore HPLC method was suitable for the analysis of a number of triazines at 10 ppb whereas capillary GC method was used for the analysis of triazines at 5 ppb. Satisfactory average recoveries for the two methods were obtained at 80 ppb and 20 ppb, respectively.
On leave from: Institute of Hydrobiology, Academia Sinica, Wuhan, P. R. China 相似文献
Rückstandsanalytik von Triazin-Herbiciden im Boden: Vergleich zwischen einer capillar-gas-chromatographischen und einer hochleistungs-flüssig-chromatographischen Methode
Zusammenfassung Zwei Methoden zur Bestimmung von Triazinen im Boden wurden entwickelt und miteinander verglichen. Nach der Extraktion der Rückstände mit Methanol und clean-up durch Gelpermeations-Chromatographie wurden die Proben eingeengt und auf Triazin-Rückstände hin untersucht. Zur Detektion wurden die splitlose Capillar-Gas-Chromatographie mit NP-Detektor (GC-NPD) und die Microbore-Hochdruckflüssig-Chromatographie mit UV-Detektor (HPLC-UV) bei 222 nm verwendet. Beide Methoden ergaben vergleichbare Ergebnisse bei einem Minimum an Zeit- und Materialaufwand und der Möglichkeit der Automatisation der Rückstandsanalytik. Die Microbore-HPLC-Methode erreichte nach einfachem GPC clean-up eine Nachweisgrenze von 10 ppb im Vergleich zu 5 ppb bei der Capillar-GC-Methode. Zufriedenstellende Wiederfindungsraten wurden für beide Methoden bei 80 ppb und 20 ppb ermittelt.
On leave from: Institute of Hydrobiology, Academia Sinica, Wuhan, P. R. China 相似文献
70.
Different fiber materials (hemp, linen, viscose rayon, polyamide and dyneema twine) were tested for their suitability as fiber
phantoms for diffusion tensor imaging (DTI) calibration on clinical magnetic resonance imaging systems with common diffusion-weighted
echo planar imaging sequences. Additionally, the potential for fiber tracking validation of these fiber phantoms was investigated.
For phantom manufacturing the fibers were wound up into a bundle of parallel fibers enwrapped by plastic ribbon. The most
homogenously distributed fractional anisotropy (FA) values (0.63 ± 0.10) were determined in the dyneema and polyamide (0.3
± 0.1) fiber phantom. FA values in the viscose, linen and hemp bundles were at high variations (about 0.2 ± 0.10). The dispersion
of the direction of the principal eigenvector in the polyamide and dyneema phantom was less than 7°, for the other fiber phantoms
it was over 30°. Thus, the presented results may indicate that polyamide- and dyneema-based fiber phantoms provide the opportunity
for verification and validation of DTI sequences on clinical scanner. Additionally, they can be applicable for testing the
accuracy of fiber tracking algorithms. A strong parallel alignment of the fibers with a constant compression grade of the
fiber bundles could be achieved by machine-made production. This could also provide highly reproducible diffusion properties
within the anisotropic fiber phantoms.
Authors' address: Kamil A. Il'yasov, Physics Department, Kazan State University, Kremlevskaya ulitsa 18, Kazan 420008, Russian
Federation 相似文献