Carbon dioxide as a working fluid in drying heat pumpsLe dioxyde de carbone comme fluide actif dans des séchoirs à pompe à chaleur

Carbon dioxide as a working fluid in refrigeration and heat pump systems is increasingly important in view of the CFC substitution problem. It is both under ecological and economical aspects an attractive alternative to the HFC working fluids at present in practical use. The thermophysical properties and characteristics of carbon dioxide are quite different from those of refrigerants used in conventional vapour compression cycles. Its application in conventional vapour compression refrigerating systems is limited by its critical parameters (t_c=31.1°C and p_c=73.8 bar). The possibility to use carbon dioxide also beyond these limits in high temperature processes, e.g. heat pumps, is given by the application of a trans-critical process. The design and construction of a commercial drying heat pump system (batch type cabinet dryer with 12 kW heating capacity and closed air circuit) using the natural working fluid carbon dioxide is shown and experimental results of investigations carried out are presented. Energy savings are given compared to manufacturer's data of energy consumption.     

Brillouin and raman spectra anomalies in knsbn with the tungsten bronze structure

Abstract

The Brillouin and Raman scattering from a complex single crystal from the tungsten-bronze family, (K_0.5Na_0.5)_0.2(Sr_0.75Ba_0.25)_0.9Nb₂O₆ doped with Cu²⁺ (KNSBN:Cu), have been comparatively studied in a wide temperature range around the ferroelectric transition. Step-like anomalies in hypersonic velocity and damping confirm the first-order structural transition. These anomalies look like some perturbations on the high-temperature slopes of both a broad dip in sound velocity and a broad maximum in damping that develop in a wide temperature range. The acoustic behavior of KNSBN:Cu does not simply follow the Landau theory prediction valid for many ferroelectrics except relaxors, to which the KNSBN:Cu behavior is intrinsically analogous. The total intensity of the Raman spectra as well as the intensity of separate internal and external vibrations and their width correlate with acoustic anomalies, namely there are step-like drops at the same temperature of the first-order transition and a broad range where the intensity is drastically increased.     

Increase in Generation of Poly-Crystalline Silicon by Atmospheric Pressure Plasma-Assisted Excimer Laser Annealing

In this work, a novel atmospheric pressure plasma-assisted excimer laser annealing method for increasing the generation efficiency of poly-crystalline silicon from amorphous silicon layers is presented. Here, both the plasma and the laser propagate coaxially in order to generate energetic synergies. The influence of different process gases and plasma discharge modes as well as the working distance were investigated. Depending on the particularly applied plasma, the crystalline area was increased by a factor of approx. 1.1 to 1.9, where the highest efficiency was observed when introducing an argon plasma beam to the annealing process.     

Role of geometry, substrate and atmosphere on performance of OFETs based on TTF derivatives

We report a comparative study of OFET devices based on zone-cast layers of three tetrathiafulvalene (TTF) derivatives in three configurations of electrodes in order to determine the best performing geometry. The first testing experiments were performed using SiO₂/Si substrates. Then the optimum geometry was employed for the preparation of flexible OFETs using Parylene C as both substrate and dielectric layer yielding, in the best case, to devices with μ_FET = 0.1 cm²/V s. With the performed bending tests we determined the limit of curvature radius for which the performance of the OFETs is not deteriorated irreversibly. The investigated OFETs are sensitive to ambient atmosphere, showing reversible increase of the source to drain current upon exposition to air, what can be explained as doping of TTF derivative by oxygen or moisture.     

Transversely compressed bonded joints

The load capacity of bonded joints can be increased if transverse pressure is applied at the interface. The transverse pressure is assumed to introduce a Coulomb-friction contribution to the cohesive law for the interface. Response and load capacity for a bonded single-lap joint was derived using non-linear fracture mechanics. The results indicated a good correlation between theory and tests. Furthermore, the model is suggested as theoretical base for determining load capacity of bonded anchorages with transverse pressure, in externally reinforced concrete structures.     

Distributed SIP conference management with autonomously authenticated sources and its application to an H.264 videoconferencing software for mobiles

The design of conferencing systems for achieving efficient and flexible communication in a fully distributed, infrastructure-independent fashion is a promising direction, both in terms of research and practical development. In the particular case of video communication, the seamless adaptation to heterogeneous mobile devices poses an additional strong challenge to those seeking for interoperable and easy-to-deploy solutions. In this paper, we make several contributions towards a generic peer-to-peer (P2P) videoconferencing solution that extends into the mobile realm. We describe the essential building blocks for conference management and media distribution that are necessary for a distributed conferencing approach. Establishing a distributed SIP conference focus, participants share the conference according to their individually given capabilities and resources in terms of bandwidth and processing power rather than in a centralized and fixed way. Overall concepts and SIP-primitives for such an autonomous organization are presented. Security issues that derive from this decentralized identity management are resolved by so-called Overlay AuthoCast, a novel use of cryptographically generated identifiers. Furthermore, this work is dedicated to the development of a software-based H.264 video codec implementation and the specific aspects resulting from tuning such a highly resource-intensive software codec to the given target platform of a standard consumer smartphone.