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61.
Oxygen can be determined in a perfluorotributylamine emulsion used as a blood substitute by coulometry and polarography. The oxygen uptake of the emulsion (4.3 × 10?3 mol l?1 or 11 ml-% at 25°C and PO2 = 760 mm Hg) is about three times greater than that of water. The adsorption of surfactant on a dropping mercury electrode changes the electrochemical parameters E, α and k3. The marked difference between the diffusion coefficients of oxygen and hydrogen peroxide (ratio 2.6) seems to be proceed from the ejection of oxygen molecules from the perfluorotributylamine droplets and from the insolubility of hydrogen peroxide molecules in the droplets. The constant rate of oxygen release by these droplets was estimated to be 104 s?1 by a stopped-flow spectrophotometric method. This constant rate seems to be linked with the particle diameter (0.2 μm) and the diffusion coefficient in the perfluorotributylamine droplets (1.6 × 10?6 cm2 s?1). 相似文献
62.
Background
Subjective tinnitus is characterized by an auditory phantom perception in the absence of any physical sound source. Consequently, in a quiet environment, tinnitus patients differ from control participants because they constantly perceive a sound whereas controls do not. We hypothesized that this difference is expressed by differential activation of distributed cortical networks. 相似文献63.
Gabriella Josefsson Fredrik Berthold E. Kristofer Gamstedt 《International Journal of Solids and Structures》2014
Nanocomposites, reinforced by different types of cellulose fibrils, have gained increased interest the last years due to the promising mechanical properties. There is a lack of knowledge about the mechanical properties of the cellulose fibrils, and their contribution to the often claimed potential of the impressive mechanical performance of the nanocomposites. This paper investigates the contribution from different types of cellulose nanofibril to the overall elastic properties of composites. A multiscale model is proposed, that allows back-calculation of the elastic properties of the fibril from the macroscopic elastic properties of the composites. The different types of fibrils used were nanofibrillated cellulose from wood, bacterial cellulose nano-whiskers and microcrystalline cellulose. Based on the overall properties of the composite with an unaged polylactide matrix, the effective longitudinal Young’s modulus of the fibrils was estimated to 65 GPa for the nanofibrillated cellulose, 61 GPa for the nano whiskers and only 38 GPa for the microcrystalline cellulose. The ranking and absolute values are in accordance with other studies on nanoscale morphology and stiffness estimates. Electron microscopy revealed that in the melt-processed cellulose nanofibril reinforced thermoplastics, the fibrils tended to agglomerate and form micrometer scale platelets, effectively forming a microcomposite and not a nanocomposite. This dispersion effect has to be addressed when developing models describing the structure–property relations for cellulose nanofibril composites. 相似文献
64.
Image-potential states in front of a clean Cu (100) surface were investigated by time- and angle-resolved two-photon photo-emission
(2PPE). We observe a previously unknown quasi-elastic relaxation channel, which efficiently couples states with different
quantum numbers, n, and parallel momenta, k∥. This process of resonant interband scattering (RIS) is independent of sample temperature and shows a close relationship
to the pure dephasing of image-potential states.
Received: 1 October 2001 / Revised version: 24 October 2001 / Published online: 23 November 2001 相似文献
65.
The first total synthesis of the chlorinated 1‐oxo‐β‐carboline alkaloid bauerine C based on a Japp–Klingemann reaction is reported. An intermediate of this synthesis was converted to the fully aromatic β‐carboline bauerine B, and the related alkaloid bauerine A was prepared in an analogous manner. 相似文献
66.
Let X1,…, Xn be i.i.d. random variables symmetric about zero. Let Ri(t) be the rank of |Xi − tn−1/2| among |X1 − tn−1/2|,…, |Xn − tn−1/2| and Tn(t) = Σi = 1nφ((n + 1)−1Ri(t))sign(Xi − tn−1/2). We show that there exists a sequence of random variables Vn such that sup0 ≤ t ≤ 1 |Tn(t) − Tn(0) − tVn| → 0 in probability, as n → ∞. Vn is asymptotically normal. 相似文献
67.
Berthold Stech 《Zeitschrift fur Physik C Particles and Fields》1997,75(2):245-251
An explicit model is presented which gives the momentum transfer-dependent ratios of form factors of hadronic currents. For the unknown Isgur-Wise function and its generalization for transitions to light particles a simple phenomenological Ansatz is added. The model allows a calculation of all form factors in terms of mass parameters only. It is tested by comparison with experimental data, QCD sum rules and lattice calculations. 相似文献
68.
Matzanke Berthold F. Bill Eckard Müller Gertraud I. Winkelmann Günther Trautwein Alfred X. 《Hyperfine Interactions》1989,47(1-4):311-327
Hyperfine Interactions - Iron limited growth of microbes results in derepression of siderophore receptor and transport-systems which can be utilized for controlled and specific siderophore... 相似文献
69.
Yanqing Deng Roland Kersting Victor Roytburd Jingzhou Xu Ricardo Ascazubi Kai Liu Xi-Cheng Zhang Michael S. Shur 《International Journal of Infrared and Millimeter Waves》2004,25(2):215-228
We describe a method to determine the radiation spectrum of terahertz sources using a transmitted Fabry-Perot interferometer and a bolometer detector. Our novel Fabry-Perot spectrometer can measure the spectrum of an unknown broadband sub-terahertz and terahertz source. The spectrometer does not need to be pre-tuned. We develop a new algorithm to support the measurements using this spectrometer. Our technique allows us to measure the spectrum over more than an octave, and our numerical algorithm is very stable and robust, providing for an accurate spectrum determination. Two Gunn oscillation sources with the main frequencies at 200 GHz and 600 GHz are used to test the proposed method. The spectrum extracted from the measured data shows that this method is accurate and reliable. 相似文献
70.