Dynamic analysis of VVER type nuclear power plants using different procedures for consideration of soil-structure interaction effects

The dynamic response of structures due to seismic loadings is conventionally analyzed in the time domain using substructure methods (decoupled system models). This procedure uses frequency-independent impedances to represent capabilities of the soil underneath the structure. The soil parameters are tuned to the fundamental frequencies of the soil-structure system. This is a common procedure widely used in the preliminary design of power plant structures which provides conservative results. However, parallel to the rapid progress being made in upgrading the capability of data processing systems, methods and software tools have become available which work also in the frequency domain using complex models (for the soil and the structure) or models in which the soil is represented by frequency-dependent impedances. This procedure (coupled system models) also allows realistic treatment of kinematic interaction effects and especially consideration of the embedment parameters of the building structure. The main goal of the study presented here was to demonstrate the effects of different procedures for consideration of soil-structure interaction on the dynamic response of the structures mentioned above. The analyses were based on appropriate mathematical models of the coupled vibrating structures (reactor building, turbine hall, intermediate building structures of a VVER 440/213 as well as the main building of the VVER 1000) and the layered soil. On the basis of this study, it can be concluded that substructure methods using frequency-independent impedances (equivalent dashpots) and cut-off of modal damping usually provide conservative results. Coupled system models which allow the soil-structure interaction effects to be realistically represented (by coupled models of the soil and the structure or by frequency-dependent impedances) provide more accurate results. The advantage of the analysis using coupled system models will be demonstrated and discussed, based on results obtained for the VVER 440/213 PAKS and VVER 1000 Kozloduy.     

How dry are dried samples? Water adsorption measured by STM

When operating scanning probe microscopes, like STM or AFM, under ambient conditions, the presence of water on the sample and the tip always plays an important role. The water not only influences the structure of the sample itself, but also the imaging process; in the case of the STM using a wet etched w-tip, by interfering with the electron transfer process, and in the case of the AFM, due to the capillary forces in the micro Newton range that dominate the tip surface interaction forces. In this paper, the distribution and the amount of adsorbed water on different surfaces is investigated with the help of the STM, which can provide information by imaging and by current/distance spectroscopy. Hydrophilic and hydrophobic surfaces like titanium, gold, and graphite were studied at a relative humidity between 10 and 90%. Under very dry conditions with relative humidity below 15%, the presence of water was only detectable by the longer decay length of the measured current with distance compared to samples prepared in UHV completely free of water. At less dry conditions on gold surfaces, water was found as droplets. With increasing humidity, the quantity and the size of these droplets increased until the whole surface became covered with water. Above 55% humidity, the thickness of the water film increased with increasing humidity up to several 10 nm. On titanium and graphite, water was always present in the form of closed layers growing in thickness with increasing humidity.     

The surface impedance of superconductors and normal conductors: The Mattis-Bardeen theory

The contribution of the Mattis-Bardeen theory to the understanding of the surface impedance of superconductors and normal conductors is reviewed. The early theoretical and experimental studies of the surface impedance of conductors are sketched to provide the context in which the Mattis-Bardeen theory and, independently, the Abrikosov-Gor'kov-Khalatnikov theory were developed. The Mattis-Bardeen theory is described along with the methods for numerical calculation of the surface impedance from their expression for the current density. Extensions to include the effects of anisotropy and strong coupling are briefly discussed. Theory is compared with representative measurements of the surface impedance, demonstrating excellent agreement in absolute magnitude and in the dependences on frequency, temperature, and material parameters.     

Optical channel switching algorithm for continuously tunable lasers

A novel idea and realisation of a control algorithm to switch the wavelength of continuously tunable lasers is presented. The concept allows the switching of a defined number of dense wavelength division multiplexed (DWDM) channels up or down by employing a broadband wavelength locker. The switching algorithm is implemented and demonstrated for a micro-electro-mechanically tunable vertical-cavity surface emitting laser (MEM-VCSEL).     

Micro-mechanically tunable long wavelength VCSEL with buried tunnel junction

A novel two-chip concept for an electrically pumped and micro-electro-mechanically tunable vertical-cavity surface-emitting laser, with an emission wavelength in the 1.5 /spl mu/m range, is presented. Continuous tuning over 30 nm in singlemode operation has been shown.     

Nonlinear surface impedance in “low” and “high”T c superconductors

The degradation of the surface impedanceZ = R + iX with rf power is a principal limit for measurements and applications. Such nonlinearities occur for normal conducting cavities by heating or electron loading. But superconductors show a much richer spectrum of causes for nonlinearities. The nonlinearities in the surface resistance δR ∞ γ H ⁿ and surface reactance δR ∞ α H ⁿ can be classified by the ratior = δX/δ R. This ratio differs in value, temperature, or frequency dependence for the different mechanisms, allowing a unique identification of those mechanisms. This identification is a prerequisite for an improved rf cavity design and improvement of superconducting materials.     

Chirp and linewidth enhancement factor of tunable, optically-pumped long wavelength VCSEL

Small-signal frequency modulation response and chirp characteristics of a tunable, optically-pumped 1.6 /spl mu/m vertical cavity surface emitting laser (VCSEL) based on microelectromechanical at wavelength tuning are presented for the first time. From the measurements the linewidth enhancement factor /spl alpha//sub H/ has been derived and is discussed.     

Continuously tunable 1.55-/spl mu/m VCSEL implemented by precisely curved dielectric top DBR involving tailored stress

We present an optically pumped and continuously tunable 1.55-/spl mu/m vertical-cavity surface-emitting laser (VCSEL). The device shows 26-nm spectral tuning range, 400-/spl mu/W maximum output power, and 57-dBm side-mode suppression ratio. The VCSEL is implemented using a two-chip concept. The movable top mirror membrane is precisely designed to obtain a tailored air-gap length (L'=16 /spl mu/m) and a radius of curvature (ROC=4.5mm) in order to efficiently support the fundamental optical mode of the plane-concave resonator. It consists of a distributed Bragg reflector (DBR) with periodic, differently stressed silicon nitride and silicon dioxide multilayers implemented by plasma-enhanced chemical vapor deposition. The lower InP-based part, comprising the InP-InGaAsP bottom DBR and the active region, is grown monolithically using metal-organic vapor phase epitaxy.     

Dual polymer bonding of thermoplastic composite structures

This paper describes a process that facilitates fusion bonding of thermoplastic composite components without the need for complex fixtures and without disrupting the fiber alignment in the component laminates. The dual polymer bonding process, Thermabond, requires that an interlayer polymer be fused to the surface of each laminate prior to bonding. The characteristics of the interlayer polymer allow for joining of the components at a temperature below the softening/melting point of the reinforced polymer in the composite laminates. This leads to significant processing advantages without significant loss in mechanical performance. Discussions of resin compatibility, the effect of process conditions on mechanical performance, and the application of the APC-2/PEI Thermabond system to various structural components are included.