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991.
Terry C. Chilcott Elicia L.S. Wong Hans G.L. Coster Michael James 《Electrochimica acta》2009,54(14):3766-6808
Electrical impedance spectroscopy characterisations of gold surfaces formed on mica templates in contact with potassium chloride electrolytes were performed at the electric potential of zero charge over a frequency range of 6 × 10−3 to 100 × 103 Hz. They revealed constant-phase-angle (CPA) behaviour with a frequency exponent value of 0.96 for surfaces that were also characterised as atomically flat using atomic force microscopy (AFM). As the frequency exponent value was only marginally less than unity, the CPA behaviour yielded a realistic estimate for the capacitance of the ionic double layer. The retention of the CPA behaviour was attributed to specific adsorption of chloride ions which was detected as an adsorption conductance element in parallel with the CPA impedance element. Significant variations in the ionic double layer capacitance as well as the adsorption conductance were observed for electrolyte concentrations ranging from 33 μM to 100 mM, but neither of these variations correlated with concentration. This is consistent with the electrical properties of the interface deriving principally from the inner or Stern region of the double layer. 相似文献
992.
介绍了中子照相技术的原理和基本装置,并将其应用于混凝土材料的检测和研究中.结果表明:中子照相能够直观地检测钢筋混凝土内部的裂缝发展情况,并能实现对混凝土中水分侵入过程的可视化研究.在成像数据的基础上,对传统的水分侵入模型进行了修正,认为在水分侵入的初始阶段,水渗透系数为常数;吸水超过4 h后,渗透系数则按指数函数衰减. 相似文献
993.
Michael Fastabend Tobias Schfers Mark Albert Hans‐Gerd Lommen 《Beton- und Stahlbetonbau》2009,104(10):657-663
Ausgehend von den kritischen Randbedingungen der Berechnung mit ganzheitlichen Gebäudemodellen werden typische und häufig anzutreffende Konstruktionsfälle diskutiert, bei denen Gesamtmodelle Vorteile für den Entwurf aufzeigen. Hier sind räumliche Tragwirkungen zu nennen, die Erfassung von Zwangsbeanspruchungen bei komplexen Grundrissen mit vielfältigen Festhaltungen sowie die Beanspruchung schlanker Gebäudestrukturen aus Windlasten und seismischen Einwirkungen. Für die genannten sinnvollen Anwendungsfälle werden die notwendigen Randbedingungen diskutiert. Die jeweiligen Anwendungsfälle werden anhand konkreter Gebäudebeispiele vorgestellt. On the reasonable use of total building models in the design of building structures Coming from the critical boundary conditions of the calculation with total building models, typical and prevalent constructions, where total models show advantages for the design, will be discussed. Here, spatial load‐bearing impact, the registration of unforced interactions of complex ground plans with various supports as well as the stressing of slender building structures resulting from wind loads and seismic impacts have to be mentioned. For the stated reasonable use cases the necessary boundary conditions will be discussed. The respective use cases will be presented by means of concrete building examples. 相似文献
994.
Aslak Fyhri Jens Kristian Steen Jacobsen Hans Tmmervik 《Landscape and urban planning》2009,91(4):202-211
European cultural landscapes have been subject to change since the middle of the twentieth century, and among the most significant alterations are general re-growth, reforestation, and overgrowth. Such changes might lead to landscape loss for locals and deterioration of vistas for sightseeing holidaymakers. This article responds to a lack of academic research on landscape perceptions among tourists. The main objective is to explore international tourists’ landscape perceptions in a coastal area in northern Scandinavia, focusing on three different concepts thought to be important for tourists’ landscape preferences: typicality, vegetation lushness, and degree of human influence. A combination of free and directed sorting procedures was employed. Quantitative and categorical data derived from the multiple sorting methods were subjected to multidimensional scaling analysis. The results indicate that foreign tourists might have an understanding of re-growth in the case area. Preference ratings gave mixed results in relation to vegetation and human influence as important features for landscape preferences, as found in previous studies. The findings emphasise the need for taking into consideration typicality of setting in future landscape research. 相似文献
995.
Dynamic stiffness and damping properties of pile groups. The dynamic stiffness and damping properties of pile‐groups have been investigated in this paper. Also, the substantial influence of these properties on an economic structure and foundation design is demonstrated. The analysis has been carried out using the “Thin‐Layer‐Method”, which is a very efficient and powerful analysis procedure in frequency domain. 相似文献
996.
Hans‐A. Gülich 《Bautechnik》2009,86(5):285-293
Schutzeinrichtungen am Rand von Autobahnbrücken sollen Durchbruch und Absturz von Fahrzeugen verhindern. Die Zielsetzung ist ehemals durch Unfälle auf Talbrücken der Sauerlandlinie verdeutlicht und durch den folgenreichen Unfall auf der Wiehltalbrücke verschärft worden. Eine erneute Häufung von Lkw‐Durchbrüchen verweist auf unzureichende Richtlinien und untaugliche Absturzsicherungen. Das Unfallgeschehen der letzten Jahre zwingt zu Sorgfalt bei der Anwendung von Schutzeinrichtungen, Regelungen und Prüfverfahren. Nicht zuletzt auf Autobahnbrücken müssen die Randbedingungen der Verkehrssituation entsprechen. Highway bridges with inadequate guardrails – breakthroughs of trucks in sight. Safety devices at the borders of highway bridges are to prevent vehicles from breakthrough and crash. By accidents on viaducts of Sauerland‐route the objective has been demonstrated formerly and it was intensified by the momentous accident on Wiehltal viaduct in 2004. A recent amount of trucks breaking through guardrails is indicating insufficient guidelines as well as inadequate devices against plunge. The occurrence of accidents during last years forces careful application of safety devices, guidelines, and methods of testing. Not least on highway bridges conditions at the borders must correspond with the traffic situation. 相似文献
997.
998.
How much fluoride is good for a strong electron‐withdrawing effect? In this review we summarize recent results on the use of perfluoroalkanesulfonates, in particular of the cost effective nonafluorobutanesulfonates (nonaflates), in transition metal‐catalyzed reactions and a few other typical transformations. During the last decade many advantages over the commonly used triflates have been discovered. The generation of alkenyl and (het)aryl nonaflates and their applications in metal‐catalyzed processes such as Heck, Suzuki, Sonogashira, Stille, and Negishi couplings or amination reactions are described. Although far from a systematic investigation, all the presented results clearly demonstrate the many advantages of nonaflates and of similar higher fluorinated sulfonates in laboratory and industrial scale organic synthesis. 相似文献
999.
Hokland SL Pedersen M Salomir R Quesson B Stødkilde-Jørgensen H Moonen CT 《IEEE transactions on medical imaging》2006,25(6):723-731
Focused ultrasound is very well suited for inducing noninvasive local hyperthermia. Since magnetic resonance imaging (MRI) may be employed to obtain real-time temperature maps noninvasively the combination of these two technologies offers great advantages specifically aimed toward oncological studies. Real-time identification of the target region and accurate control of the temperature evolution during the treatment has now become possible. Thermal ablation of pathological tissue, local drug delivery using thermosensitive micro-carriers and controlled transgene expression using thermosensitive promoters have recently been demonstrated with this unique technology. Based on these experiments combined focused ultrasound and MRI thermometry holds promise for future oncological diagnostics and treatment. In this paper, we review some of the recent methodological developments as well as experimental and first clinical studies using this approach. 相似文献
1000.
Nielen MW Bovee TF van Engelen MC Rutgers P Hamers AR van Rhijn JH Hoogenboom LR 《Analytical chemistry》2006,78(2):424-431
New anabolic steroids show up occasionally in sports doping and in veterinary control. The discovery of these designer steroids is facilitated by findings of illicit preparations, thus allowing bioactivity testing, structure elucidation using NMR and mass spectrometry, and final incorporation in urine testing. However, as long as these preparations remain undiscovered, new designer steroids are not screened for in routine sports doping or veterinary control urine tests since the established GC/MS and LC/MS/MS methods are set up for the monitoring of a few selected ions or MS/MS transitions of known substances only. In this study, the feasibility of androgen bioactivity testing and mass spectrometric identification is being investigated for trace analysis of designer steroids in urine. Following enzymatic deconjugation and a generic solid-phase extraction, the samples are analyzed by gradient LC with effluent splitting toward two identical 96-well fraction collectors. One well plate is used for androgen bioactivity detection using a novel robust yeast reporter gene bioassay yielding a biogram featuring a 20-s time resolution. The bioactive wells direct the identification efforts to the corresponding well numbers in the duplicate plate. These are subjected to high-resolution LC using a short column packed with 1.7-microm C18 material and coupled with electrospray quadrupole time-of-flight mass spectrometry (LC/QTOFMS) with accurate mass measurement. Element compositions are calculated and used to interrogate electronic substance databases. The feasibility of this approach for doping control is demonstrated via the screening of human urine samples spiked with the designer anabolic steroid tetrahydrogestrinone. Application of the proposed methodology, complementary to the established targeted urine screening for known anabolics, will increase the chance of finding unknown emerging designer steroids, rather then being solely dependent on findings of the illicit preparations themselves. 相似文献