Results 1 - 10 of 133
Results 1 - 10 of 133. Search took: 0.02 seconds
|Sort by: date | relevance|
[en] Recently, engineering applications have started to adopt solutions inspired by nature. The peculiar adhesive properties of gecko skin are an example, as they allow the animal to move freely on vertical walls and even on ceilings. The high adhesive forces between gecko feet and walls are due to the hierarchical microscopical structure of the skin. In this study, the effect of metal coatings on the adhesive strength of synthetic, hierarchically structured, dry adhesives was investigated. Synthetic dry adhesives were fabricated using PDMS micro-molds prepared by photolithography. Metal coatings on synthetic dry adhesives were formed by plasma sputtering. Adhesive strength was measured by pure shear tests. The highest adhesion strengths were found with coatings composed of 4 nm thick layers of Indium, 8 nm thick layers of Zinc and 6 nm thick layers of Gold, respectively
[en] The interaction between different lightshelf geometries combined with a curved ceiling was investigated using radiance to maximize the daylight performance of a lightshelf. Two main performance parameters were investigated; illuminance level and distribution uniformity in a large space located in a sub-tropical climate region like Jordan. It was found that a curved lightshelf could improve the daylight level by 10% compared to a horizontal lightshelf. A curved lightshelf help to bounce more daylight deep into a space thus improve the illuminance level and uniformity level. The best lightshelf shapes found are curved and chamfered lightshelves compared to horizontal lightshelves.
[en] In this paper, computer simulation of smoke spread dynamics in industrial hall is investigated. A set of simulations of fire in three industrial halls with the same geometry varying in the height of ceiling is realized using the FDS fire simulator, version 6. The obtained simulation results are described focusing on the impact of the ceiling height and fire barriers on the fire course and smoke spread dynamics
[en] The effect of the ceiling-mounted radiation shielding on the amount of the scatter radiation was assessed under conditions simulating obese patients for clinically relevant exposure parameters. Measurements were performed in different projections and with different positions of the ceiling-mounted shielding: without shielding; shielding closest to the patient; and shielding closest to the physician performing the procedure. The protection provided by the shielding was assessed for cardiology when the femoral access is used and for radiology when the physician performs the procedure in the abdominal area. The results show that the use of the ceiling-mounted shielding can decrease the dose from the scatter radiation by 95% at the position of the performing physician. In cardiology, the impact is more pronounced when the left oblique projection is used. In radiology, a large decrease was observed for right oblique projections, compared to cardiology. The ceiling-mounted shielding should be placed as close to the physician as possible. The idea of creating the largest radiation shadow by placing the radiation shielding as close to the patient as possible does not provide as effective radiation protection of the operator as it might be thought
[en] In this study, in a floor heated room, natural convection heat transfer over the floor is analysed numerically for different thermal conditions. An equation relevant to Nusselt number over the floor has been obtained by using the numerical data. Different equations are given in the literature. They consider the effect of floor Rayleigh number while neglecting the effect of wall and ceiling thermal conditions. Numerical data obtained in this study show that the Nusselt number over the floor depends on not only the floor Rayleigh number but also the wall Rayleigh number (for insulated ceiling conditions). The equations given in the literature are different from each other due to their not considering the effect of wall and ceiling Rayleigh numbers. This difference between the equations may be eliminated by obtaining an equation containing the effect of floor, wall and ceiling Rayleigh numbers. In this new approach, an equation relevant to the floor Nusselt number that depends on the floor and wall Rayleigh numbers has been obtained in the floor heating system for insulated ceiling conditions. The equation obtained in this study has been compared with the equations given in the literature. It has been seen that the equation obtained in this study matches the numerical values under more extensive thermal conditions than the equations given in the literature. The maximum deviation for the equations given in the literature is 35%, but in the current study, the maximum deviation has been found to be 10%. As a result, it is more convenient to use the equation found in the new approach as a function of Rayleigh number over the floor and wall for insulated ceiling conditions
[en] A new initiative has been implemented at the Sunshine Hospital Radiation Therapy Centre, to provide a calming and comforting environment for patients attending radiation therapy treatment. As part of this initiative, the department's computed tomography (CT) room and radiation therapy bunkers were designed to incorporate ceiling art that replicates a number of different visual scenes. The study was undertaken to determine if ceiling art in the radiation therapy treatment CT and treatment bunkers had an effect on a patient's experience during treatment at the department. Additionally, the study aimed to identify which of the visuals in the ceiling art were most preferred by patients. Patients were requested to complete a 12-question survey. The survey solicited a patient's opinion/perception on the unit's unique ceiling display with emphasis on aesthetic appeal, patient treatment experience and the patient's engagement due to the ceiling display. The responses were dichotomised to ‘positive’ or ‘negative’. Every sixth patient who completed the survey was invited to have a general face-to-face discussion to provide further information about their thoughts on the displays. The results demonstrate that the ceiling artwork solicited a positive reaction in 89.8% of patients surveyed. This score indicates that ceiling artwork contributed positively to patients’ experiences during radiation therapy treatment. The study suggests that ceiling artwork in the department has a positive effect on patient experience during their radiation therapy treatment at the department
[en] Highlights: • Nonlinear mathematical model of a hydro-turbine governing system with sloping ceiling tailrace tunnel is presented. • A novel control strategy using nonlinear state feedback with polynomial functions is proposed. • Hopf bifurcation control of a hydro-turbine governing system using the proposed control strategy is described. • Application and functional mechanism of the proposed control strategy are analyzed. - Abstract: Aiming at improving the regulation quality of a hydro-turbine governing system with sloping ceiling tailrace tunnel, Hopf bifurcation control using nonlinear state feedback is studied. Firstly, the nonlinear mathematical model of a hydro-turbine governing system with sloping ceiling tailrace tunnel is presented. Then, a novel control strategy using nonlinear state feedback with polynomial functions is proposed, and Hopf bifurcation control of a hydro-turbine governing system using the proposed control strategy is described. Finally, the application and functional mechanism of the proposed control strategy are analyzed by comparison with the PID strategy. The results indicate that: The proposed nonlinear state feedback control strategy is able to make the frequency of a hydro-turbine unit return to the initial value (i.e. rated frequency), and the regulation quality and the response speed are obviously better than those under the PID strategy. The effect of the linear term of nonlinear state feedback control strategy is to modify the system's linear stability, in order to eliminate or delay an existing bifurcation. Altering the nonlinear term can change the stability of bifurcation solutions, for example, converting a Hopf bifurcation from subcritical to supercritical.
[en] In this study, the relation between radiative and convective heat transfer coefficient at the ceiling is determined for a cooled ceiling room of which floor surface is isolated. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces (εw = εc = 0) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (Tc = 0-25 deg. C, Tw = 28-36 deg. C). Then, radiative heat transfer is calculated theoretically for different surface emissivities (εw = εc = 0.7, 0.8 and 0.9). Numerical data are compared with the results of correlations based on experimental data given in literature. New correlations for convective and radiative heat transfer coefficients at the ceiling are found in the current study. The ratio of radiative heat transfer coefficients to convective heat transfer coefficients (hcr/hcc) is determined. It was seen that the ratios range from 0.7 to 2.3 depending on the temperature difference. The ratios increase as the temperature differences increase. Therefore, a new correlation between the coefficients is developed depending on temperature difference at the ceiling
[en] Heating and cooling systems based on the use of hot or cold floors or ceilings meet increasing favour. In such systems, moreover, radiant temperature gains a far greater importance than in traditional systems; and therefore the importance of measurement and control techniques grow; but at the same time, in presence of these systems, unavoidably the radiant field tends to become asymmetrical. In this work a theoretical study and an experimental check on the most common radiant temperature measurement tool, the globe thermometer, when used in conditions of asymmetrical radiant temperature, are described. The results point out the necessity of a more complete definition of the features of the globe thermometers designed to operate in non-symmetric radiative fields, especially with reference to covering material and thickness, to temperature sensor position and to radiative properties of the inner surface.