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71.
Wernsdorfer W Bhaduri S Tiron R Hendrickson DN Christou G 《Physical review letters》2002,89(19):197201
The one-body tunnel picture of single-molecule magnets (SMMs) is not always sufficient to explain the measured tunnel transitions. An improvement to the picture is proposed by including also two-body tunnel transitions such as spin-spin cross relaxation (SSCR) which are mediated by dipolar and weak superexchange interactions between molecules. A Mn4 SMM is used as a model system. At certain external fields, SSCRs lead to additional quantum resonances which show up in hysteresis loop measurements as well-defined steps. A simple model is used to explain quantitatively all observed transitions. 相似文献
72.
Quantum Zeno and anti-Zeno paradoxes 总被引:1,自引:0,他引:1
Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox).
We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure
change of state: an anti-Zeno paradox. 相似文献
73.
A number of studies have investigated engineering methods of reducing forge-hammer noise by means of enclosure, blow reduction and external application of damping materials. Another alternative, in which parts and units are manufactured from metals with high internal damping, has yet to be fully investigated. In a theoretical and experimental study of sound radiation from cylindrical samples, candidate hammer materials are evaluated for potential reduction of radiated energy and energy spectrum. It is shown that the quantity of radiated sound is strongly dependent on the stiffness and damping properties of the candidate tool-steel, forged-iron and cast-iron samples. The rate of attenuation of sound radiation is also shown to be affected in a predictable manner from the (tabulated) properties of the metals. 相似文献
74.
Salima Atlas Mustapha Raihane Gregory B. Kharas Peter G. Hendrickson Hamid Kaddami Mourad Arous 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):997-1010
Copolymerization of fluorine ring-substituted 2-phenyl-1,1-dicyanoethenes, RC6H3CH?C(CN)2 (R is 2,3-F,F, 2,4-F,F, 2,5-F,F, 2,6-F,F, and 4-CF3) with 4-fluorostyrene were prepared in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the copolymers were characterized by IR, 1H and 13C-NMR, GPC, DSC, and TGA. The monomer reactivity ratios for 4-fluorostyrene (M1), r1 = 0.6 and 2-(2,4-difluorophenyl)-1,1-dicyanoethene (M2), r2 = 0 were determined from Fineman-Ross plot. The order of relative reactivity (1/r1) for difluoro-substituted monomers is 2,4-F,F (0.31) > 2,3-F,F (0.25) > 2,5-F,F (0.22) > 2,6-F,F (0.10). DSC curves showed that the copolymers were amorphous with high T g in comparison with that poly(4-fluorostyrene) indicating a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer units. From the thermogravimetric analysis, the copolymers began to degrade in the range 214–260°C. The copolymer of 4-fluorostyrene and 2-(2,4-difluorophenyl)-1,1-dicyanoethene and poly(4-fluorostyrene) were dielectrically characterized in the range 25–200°C. The dominating relaxation process detected in both materials was the α-relaxation, associated with the dynamic glass transition. The relationship polarity-permittivity was discussed. 相似文献
75.
Brian M. Ruddy Gregory T. Blakney Ryan P. Rodgers Christopher L. Hendrickson Alan G. Marshall 《Journal of the American Society for Mass Spectrometry》2013,24(10):1608-1611
Elemental composition assignment confidence in mass spectrometry is typically assessed by monoisotopic mass accuracy. For a given mass accuracy, resolution and detection of other isotopologues can further narrow the number of possible elemental compositions. However, such measurements require ultrahigh resolving power and high dynamic range, particularly for compounds containing low numbers of nitrogen and oxygen (both 15N and 18O occur at less than 0.4 % natural abundance). Here, we demonstrate validation of molecular formula assignment from isotopic fine structure, based on ultrahigh resolution broadband Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Dynamic range is enhanced by external quadrupole and internal stored waveform inverse Fourier transform (SWIFT) isolation to facilitate detection of low abundance heavy atom isotopologues. Figure
? 相似文献
76.
Nathan K. Kaiser Joshua J. Savory Christopher L. Hendrickson 《Journal of the American Society for Mass Spectrometry》2014,25(6):943-949
An auxiliary rf waveform of the same amplitude and phase applied to all the rods of an ion accumulation multipole creates an m/z-dependent axial pseudo potential. Controlled decrease of the auxiliary rf amplitude releases ions from the accumulation multipole sequentially from high to low m/z. The slope of the auxiliary rf voltage ramp is adjusted so that ions of different m/z reach the center of the ICR cell at the same time point, which mitigates the typical time dispersion observed in external source FT-ICR and extends the observable mass range for a single data acquisition by 2- to 3-fold. For complex mixture analysis, twice the number of elemental compositions are assigned when the auxiliary rf ejection is applied compared with the standard gated trapping. Figure
? 相似文献
77.
S. R. Trotman J. M. Kolthoff G. S. Buchanan S. B. Schryver A. Schotte F. Kirchhof P. Krais G. Neumann und E. C. Hendrickson 《Fresenius' Journal of Analytical Chemistry》1933,94(1-2):72-77
Ohne Zusammenfassung 相似文献
78.
粉粒体两相流的电容层析成象测量 总被引:4,自引:0,他引:4
粉粒体系统中的固相浓度分布的在线测量是十分困难的问题.电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术.它不干扰流场,不受流动中颗粒浓度、加速度、不透明等因素的制约.本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策. 相似文献
79.
ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling
behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency
conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime. 相似文献
80.