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41.
Arthur R. Butz 《Journal of statistical physics》1972,4(2-3):199-216
Letu() be an absolutely integrable function and define the random process where thet
i are Poisson arrivals and thes
i, are identically distributed nonnegative random variables. Under routine independence assumptions, one may then calculate a formula for the spectrum ofn(t), S
n(), in terms of the probability density ofs, ps(). If any probability density ps() having the property ps() I for small is substituted into this formula, the calculated Sn() is such that Sn() 1 for small . However, this is not a spectrum of a well-defined random process; here, it is termed alimit spectrum. If a probability density having the property ps()
for small , where > 0, is substituted into the formula instead, a spectrum is calculated which is indeed the spectrum of a well-defined random process. Also, if the latter ps is suitably close to the former ps, then the spectrum in the second case approximates, to an arbitrary, degree of accuracy, the limit spectrum. It is shown how one may thereby have 1/f noise with low-frequency turnover, and also strict 1/f
1– noise (the latter spectrum being integrable for > 0). Suitable examples are given. Actually, u() may be itself a random process, and the theory is developed on this basis. 相似文献
42.
We investigated the181Ta nuclear quadrupole interaction (NQI) in crystals of Cux TaS2 by time differential perturbed angular correlation (TDPAC) both in situ during galvanostatic intercalation at 300 K and subsequently
between 11 K and 813 K. During electrointercalation the spectra show broad frequency distributions due to slowly diffusing
Cu+ in the van der Waals gap.
The line narrowing upon heating to 813 K can be described by a simple two site jump model. Within this model we derive an
activation enthalpy for Cu+ jumps of about 290 meV. 相似文献
43.
Using time differential perturbed angular correlation we probed the incommensurate 2D-plane wave charge density wave in 1T-TaS2 via the181Ta nuclear quadrupole interaction. For the interpretation of the observed line profiles a non-local treatment of the ICDW-perturbation is required. Taking the tensorial character of the electric field gradient into account the wavelength of the CDW-modulation can be derived from the line profiles within an accuracy of better than 5%. 相似文献
44.
Quadrupole-interaction nuclear orientation experiments have been performed on182Ta (jπ=3?1; T1/2=115d) in 2H-TaS2. γ-anisotropies up to ~ 30 % have been observed at a temperature of ~ 8 mK, which, however, is only about half of the value expected taking into account known results of TDPAC measurements on181Ta in 2H-TaS2. In principle, matrices of dichalcogenides could be well suited for nuclear quadrupole resonance on oriented nuclei (NQR-ON) experiments. 相似文献
45.
G. Biro H. Butz A. Gadow und M. R. Möller 《Fresenius' Journal of Analytical Chemistry》1988,330(4-5):460-461
46.
Pure LiMn2O4 and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCoxMn2−xO4, were prepared. The effect of extended cycling on the crystal structure was investigated. A capacity decrease with increasing
cobalt content was observed in the potential range about 4100 mV vs. Li/Li+. Cycling behavior is significantly improved, compared to LiMn2O4. LiCoxMn2−xO4 is discharged in a single phase reaction in the upper potential range around 4100 mV vs. Li/Li+, whereas pure LiMn2O4 shows a two phase behavior. LiMn2O4 shows a significant broadening of peaks in plots of differential capacity and change in shape of the voltage profile upon
extended cycling. LiCoxMn2−xO4 shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared
to spinels with lithium substitution, Li1+xMn2−xO4. In contrast to Li1+xMn2-xO4, LiCoxMn2-xO4 is discharged in a two step process in the range of 0 ≤ × ≤ 0,5.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
47.
We report on the measurement of the nuclear quadrupole interaction by TDPAC on a single crystal of 1T-TaS2 before and after bombardment with 70 MeV16O6+ ions. In 1T-TaS2, two groups of inequivalent Ta-sites are observed at 298 K due to the presence of a nearly commensurate charge density wave
(CDW) Upon16O6+ bombardment a single slightly broadened line is observed which resembles closely the incommensurate CDW state. 相似文献
48.
Three different types of low frequency internal motions in biomolecules are illustrated by representative modern applications of hyperfine spectroscopic techniques: (1) the rotation of aromatic amino acid residues is studied by1H nuclear magnetic resonance via chemical shift averaging; (2) confined diffusion is studied by57Fe Mössbauer-spectroscopy via the variation of the recoilfree fraction and via the appearance of very broad resonance absorption lines; (3) large-scale intramolecular reorientational motion is studied by perturbed angular correlation of γ-rays emitted from radioactive 199mHg labels via the loss of anisotropy. 相似文献
49.
The quadrupole interaction (QI) at substitutional Ta atoms in a Re matrix has been investigated by TDPAC between 1.2 K and 450 K. It was found to depend only weakly on temperature with a minium around 200 K. No change in the QI was observed when the sample was cooled into the superconducting state. The QI was found to increase with pressure with the coefficient (? lnq/?P)T=+0.93(23)10?3 kbar?1 at 300 K. A discussion of the temperature and pressure variations in connection with published Mössbauer data reveals the role of the conduction electron contribution to the electric field gradient. 相似文献
50.
Electron microprobe analysis has been performed on W, Nb, Mo, and Al layers of 2 to 300A?thickness deposited on refractory metals. For this thickness range a linear relation is found between layer thickness and characteristic X-ray intensity. The importance of a correct background measurement and its influence on the accuracy of the determination of the layer thickness is demonstrated. Additional effects arising from the backscatter coefficient of the substrate material and the fluorescence excitation within the layer are investigated. It is found that the highest sensitivity in the thickness measurement occurs at primary electron energies of 2.5 to 3 times the excitation energy of the used characteristic X-ray line of the layer material. This experimental finding is discussed in terms of the dependence of the X-ray background intensity and the ionization probability on the energy of the primary electrons. 相似文献