Microwave surface resistance of epitaxial YBa2Cu3O7 thin films at 18.7 GHz measured by a dielectric resonator technique

We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR _s of 1×1 cm² superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE₀₁ oscillation mode the highly reproducible quality factor of about 10⁵ results in a sensitivity of ±50 forR _s measurements. The temperature dependence ofR _s can be measured up to values as high as 1 . We have investigated several YBa₂Cu₃O₇ thin films prepared by high oxygen pressure d.c. sputtering on LaAlO₃ and NdGaO₃. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivity(T) with(300K)/(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT _c , a further strong decrease ofR _s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForTT_c/2 these films exhibit an exp (–T _c/T) dependence ofR _s with-values around 0.4. These observations may be explained by a superconducting energy gap with 2/kT _c0.8 for charge carriers localized in the CuO chains for YBa₂Cu₃O₇.     

An investigation of the option space in conceptual building design for advanced building simulation

This article describes research conducted to gather empirical evidence on size, character and content of the option space in building design projects. This option space is the key starting point for the work of any climate engineer using building performance simulation who is supporting the design process. The underlying goal is to strengthen the role of advanced computing in building design, especially in the early conceptual stage, through a better integration of building performance simulation tools augmented with uncertainty analysis and sensitivity analysis. Better integration will need to assist design rather than automate design, allowing a spontaneous, creative and flexible process that acknowledges the expertise of the design team members. This research investigates and contrasts emergent option spaces and their inherent uncertainties in an artificial setting (student design studios) and in real-life scenarios (commercial design project case studies). The findings provide empirical evidence of the high variability of the option space that can be subjected to uncertainty analysis and sensitivity analysis.     

Reactivity,Selectivity, and Stability of Zeolite-Based Catalysts for Methane Dehydroaromatization

Non-oxidative dehydroaromatization is arguably the most promising process for the direct upgrading of cheap and abundant methane to liquid hydrocarbons. This reaction has not been commercialized yet because of the suboptimal activity and swift deactivation of benchmark Mo-zeolite catalysts. This progress report represents an elaboration on the recent developments in understanding of zeolite-based catalytic materials for high-temperature non-oxidative dehydroaromatization of methane. It is specifically focused on recent studies, relevant to the materials chemistry and elucidating i) the structure of active species in working catalysts; ii) the complex molecular pathways underlying the mechanism of selective conversion of methane to benzene; iii) structure, evolution and role of coke species; and iv) process intensification strategies to improve the deactivation resistance and overall performance of the catalysts. Finally, unsolved challenges in this field of research are outlined and an outlook is provided on promising directions toward improving the activity, stability, and selectivity of methane dehydroaromatization catalysts.     

Adsorption behavior and kinetics of H2S on a potassium-promoted hydrotalcite

Adsorption of H₂S and the influence of steam on its adsorption capacity and kinetics were studied on a commercial potassium-promoted hydrotalcite. The sorbent shows a very high cyclic working capacity for H₂S compared to CO₂ and H₂O, even at lower partial pressures and at different operating temperatures ranging between 300 and 500 °C. The operating temperature does not significantly influence the cyclic working capacity for half-cycle times of 30 min. The adsorption mechanism, however, changes at higher temperatures. At lower temperatures (300 °C) a fast adsorption with a fast approach to steady state was observed. At higher operating temperatures, H₂S reacts with the hydrotalcite structure, forming strongly bonded sulfuric species on the sorbent. When using dry regeneration conditions, the first cycles in cyclic operation at higher temperatures show a significantly higher adsorption of H₂S (especially the first cycle), which cannot be desorbed during regeneration with N₂. After the first fast initial adsorption rate a continuous slow adsorption of H₂S occurs, probably caused by a surface reaction between H₂S and the hydrotalcite structure. This reaction is, however, reversible if steam is used.The adsorption mechanism for H₂S and H₂O was determined using multiple cyclic experiments comparable to previous studies performed for CO₂ and H₂O adsorption. It is evident that the adsorption mechanism developed for CO₂ on the same sorbents is also valid for H₂S, indicating that the developed mechanism is consistent for sour gas adsorption on this type of sorbents. The cyclic working capacity can be significantly increased if steam is used during the regeneration step of the sorbent. The mechanistic model developed for the adsorption of CO₂ and H₂O was successfully validated with more than 160 different TGA experiments. An operating temperature of 400 °C seems to be optimal to achieve a high cyclic working capacity for H₂S, because at higher temperatures the regeneration of the formed sulfuric species seems to be hindered resulting in a significant decrease in the cyclic working capacity.     

The indoor environment and the integrated design of homes for older people with dementia

There are currently about 6 million – mainly older – people with dementia in the European Union. With ageing, a number of sensory changes occur. Dementia syndrome exacerbates the effects of these sensory changes and alters perception of stimuli. People with dementia have an altered sensitivity for indoor environmental conditions, which can induce problematic behaviour with burdensome symptoms to both the person with dementia and the family carer. This paper, based on literature review, provides an overview of the indoor environmental parameters, as well as the integrated design and implementation of relevant building systems. The overview is presented in relation to the intrinsic ageing of senses, the responses of older people with dementia and the impact on other relevant stakeholders through the combined use of the International Classification of Functioning, Disability and Health, and the Model of Integrated Building Design. Results are presented as indicators of the basic value, functional value and economic value, as well as a synthesis of building-related solutions. Results can help designers and building services engineers to create optimal environmental conditions inside the living environments for people with dementia, and can be used to raise awareness among health care professionals about of the influence of the indoor environment on behaviour of the person with dementia.     

Uncertainty in airflow rate calculations due to the use of surface-averaged pressure coefficients

Mean wind pressure coefficients (C_p) are key input parameters for air infiltration and ventilation studies. However, building energy simulation and stand-alone airflow network programs usually only provide and/or use a limited amount of C_p data, which are based on several assumptions. An important assumption consists of using surface-averaged C_p values instead of local C_p values with a high resolution in space. This paper provides information on the uncertainty in the calculated airflow rate due to the use of surface-averaged C_p data. The study is performed using published empirical data on pressure coefficients obtained from extensive wind tunnel experiments. The uncertainty is assessed based on the comparison of the airflow rate (?) calculated using the surface-averaged C_p values (?_AV) and the airflow rate calculated using local C_p values (?_LOC). The results indicate that the uncertainty with a confidence interval of 95% is high: 0.23 ?_AV < ?_LOC < 5.07 ?_AV. In cases with the largest surface-averaged ΔC_p, the underestimation or overestimation is smaller but not negligible: 0.52 ?_AV < ?_LOC < 1.42 ?_AV. These results provide boundaries for future improvements in C_p data quality, and new developments can be evaluated by comparison with the uncertainty of the current methods.     

On the applicability of the laminar flow index when selecting surgical lighting

In modern operating rooms ultraclean air is supplied through the ceiling to prevent bacteria from entering an operating wound and cause infections. Operating lamps can disturb this flow of clean air. In this paper the accuracy of some aspects of the Laminar Flow Index of operating lamps was tested. The disturbance of the airflow was determined for different shapes and sizes of operating lamps in an isothermal situation. To accomplish this, an experimental study and a simulation study of a small room with an operating lamp were performed. The infection risk was found to be proportional to the projected surface area of the lamp. Although different lamp shapes resulted in a distinctly different flow pattern in the room, this did not affect the infection risk in a significant way. Operating lamps with a projected area smaller than 0.1 m² do not disturb the airflow at all in this particular setup.     

The Precision of the Swift Stability Test

The precision of the automated version of the oxidation stability test on oils and fats was investigated. Nine laboratories were involved in this ring test, testing 5 different oil and fat samples of the same origin according to a standard procedure. A standard graphical interpretation of the results was developed, resulting in a strict definition of the induction period. Its repeatability equals 0.99 h and the within-laboratory standard deviation 1.45 h.     

Overview of HVAC system simulation

The paper gives an overview of heating, ventilation and air-conditioning (HVAC) system modeling and simulation. The categorization of tools for HVAC system design and analysis with respect to which problems they are meant to deal with is introduced. Each categorization is explained and example tools are given. Further, the paper summarizes current approaches used for modeling (i) HVAC components, (ii) HVAC control and (iii) HVAC systems in general. After giving an overview of solution techniques for HVAC system simulation, the paper provides suggestions on how one should select an HVAC modeling approach relative to the simulation objective at hand.     

Literature review on thermal comfort in transient conditions

The conventional theory of thermal comfort in conditions characteristic for dwellings and offices (for example, that of Fanger) assumes steady-state conditions. Yet thermal conditions in buildings are seldom steady, due to the interaction between building structure, climate, occupancy, and HVAC system. This article reviews work on thermal comfort specifically undertaken to examine what variations in indoor temperatures may be acceptable.

Following an account of man's thermoregulatory system, some experimental findings on periodic and on ramp (or drift) variation in room temperature are presented.

It is concluded that the results for cyclic variations uphold the present ASHRAE standard, but those for drifts may not.