Supported metal catalysts, particularly noble metals supported on SiO2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO2/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO2 films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon. 相似文献
Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes. 相似文献
Abstract This article presents a study of a large scale incorporation of one data acquisitionsystem into physics teaching in Israel. By 1994 about 30% of the schools throughout the country used the V-scope, a 3-D multibody motion tracing system, in their lab programme. The views and reactions of post-training teachers, experienced teachers and students on various aspects of using the system are described, analysed and compared. 相似文献
We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a 55Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology. 相似文献
We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer Tc control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented. 相似文献
1. 1. System design optimization and validation for single-speed heat pump by S.K. Fischer and C.K. Rice, Oak Ridge National Laboratories.
2. 2. Analysis of on/off cycling for an air-to-air heat pump operating in the heating mode by W.A. Miller, Oak Ridge National Laboratories.
3. 3. Field measured cycling, frosting and defrosting losses for a high efficiency air source heat pump by V.D. Baxter and J.C. Moyers, Oak Ridge National Laboratories.
4. 4. Design and available energy analysis of a heating-only residential heat pump for the Western Pacific Northwest by D.E. Elger, C.M. Reistad and S. Lang, Oregon State University.
5. 5. A study of heat pump service life by Nance C. Lovvorn, Alabama Power Company and Carl C. Hiller, Electric Power Research.
Résumé
1. 1. Optimisation de la conception des systèmes et application à la pompe à chaleur à une seule vitesse;
2. 2. analyse du cycle par tout ou rien d'une pompe à chaleur air-air fonctionnant en mode de chauffage;
3. 3. pertes en fonctionnement cyclique, par givrage et dégivrage mesurées sur place pour une pompe à chaleur de grand rendement dont la source est l'air;
4. 4. conception et analyse de l'énergie disponible d'une pompe à chaleur uniquement pour le chauffage de locaux résidentiels sur la côte du Pacifique nord-ouest occidental;
5. 5. étude de la durée de vie d'une pompe à chaleur.
Les noms et les addresses des auteurs se trouvent dans le sommaire anglais. 相似文献
A mathematical model of evaporation process from a laminar falling liquid film on a vertical plate of constant temperature is presented. The model is developed with and without interfacial shear stress due to the vapor flow at the liquid film surface. The vapor pressure drop, vapor exit velocity and cooling rate are calculated for different liquid mass flow values. It is shown that lower liquid mass flow produces higher cooling rate. The results also show that the interfacial shear stress has a considerable negative effect on the cooling rate. It is proved that there exists an optimum distance between the plates, which gives the maximum volumetric cooling rate. 相似文献
This paper reports densities of compressed R134a (1,1,1,2-tetrafluoroethane) determined by using a contiuously weighed pycnometer at 20 K intervals between 180 and 380 K at pressures from slightly greater than the vapour pressure to 70 MPa. The results are accurate to within ±0.1%. Saturated liquid densities derived by extrapolation from the experimental values agree with other reported values to within ±0.3%. 相似文献
Abstract This paper looks at some of the problems of existing courseware authoring systems, and advocates the use of knowledge-based techniques to resolve these problems and to form the basis of future authoring environments. The prototype knowledge-based representation language, GTE, is presented as an example of a knowledge-based language which might form the basis of such environments. The final part of the paper discusses some of the developments in GTE which must take place if it is to be used within a full and flexible authoring environment. The paper will focus particularly on the question of instructional strategies, but many of the observations can be taken as relevant to all the knowledge involved in a teaching interaction. 相似文献