A theory of 1/f noise

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, p_s(). If any probability density p_s() having the property p_s() I for small is substituted into this formula, the calculated S_n() is such that S_n() 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 p_s() 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 p_s is suitably close to the former p_s, 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.     

Electrointercalation of Cu into 2H-TaS2: in situ monitoring of reaction and Cu mobility

We investigated the¹⁸¹Ta nuclear quadrupole interaction (NQI) in crystals of Cu_x 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.     

The 2D-electric-field gradient profile in the incommensurate charge density wave state of 1T-TaS2

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%.     

Nuclear orientation study of182Ta in 2H-TaS2

Quadrupole-interaction nuclear orientation experiments have been performed on¹⁸²Ta (j^π=3^?1; T_1/2=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.     

Chemiluminescenzimmunoassays zum Nachweis von Arzneimitteln und Suchtstoffen in der Forensischen Analytik

Ohne Zusammenfassung

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Detection of drugs of abuse by chemiluminescence immunoassay

     

Structural and electrochemical effects of cobalt doping on lithium manganese oxide spinel

Pure LiMn₂O₄ and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCo_xMn_2−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. LiCo_xMn_2−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. LiCo_xMn_2−xO₄ shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared to spinels with lithium substitution, Li_1+xMn_2−xO₄. In contrast to Li_1+xMn_2-xO₄, LiCo_xMn_2-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     

Suppression of the charge density waves in 1T-TaS2 by 70 MeV16O6+ bombardment

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.     

Hyperfine interaction investigations of the internal dynamics of biomolecules

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.     

The temperature and pressure dependence of the electric field gradient at tantalum in rhenium

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.     

The determination of thin layer thicknesses with an electron microprobe

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.