Objective: The dosimetric characteristics for linear accelerators with the same model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer's original specif...Objective: The dosimetric characteristics for linear accelerators with the same model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer's original specifications. In this preliminary study, a quantitative investigation of the similarity in the basic photon and electron dosimetry data from the Siemens Oncor linear accelerators at our hospital(Children's Cancer Hospital, Cairo, Egypt) was reported. Methods: The output factor(OF), wedge factors(WF), percentage depth dose(PDD), and beam profile for the 6 and 10 MV photon beams were measured. Results: The measured output factors varied by less than about 1% for each field size. The difference between the maximum and minimum PDD values at each depth was less than about 1%. The difference between the beam flattnes and symetry was no more than 1% at all off-axis distances. For electron the results showed that the PDD, OF, and the beam profiles were matched within 1% differences. Conclusion: These results strongly suggest that it is feasible to establish one reference photon and electron dosimetry data set for the two machines and nominal energies.展开更多
The aim of this work is to study the interaction of spoken words and images that are used within programs targeted to popularize knowledge among teenagers. We will look into the program Bit@bit developed by Television...The aim of this work is to study the interaction of spoken words and images that are used within programs targeted to popularize knowledge among teenagers. We will look into the program Bit@bit developed by Television de Catalunya, which is intended to disseminate computer concepts, tools and procedures. In this kind of program, one can find spoken language （on/off screen voices, interviews, etc.）, other oral material （sounds, music, songs）, written language （descriptions, title sequences, inserts and Uniform Resource Locator, or electronic addresses）, and other visual material （film cut images, advertising, other TV programs, cartoons, films, both location or studio images, depicting reality, or computer screens, or logotypes）. The profusion of multimodal elements used in this program helps to keep the young audience＇s attention. The use of references to their world or knowledge, as a target group, is based on interplay among different semiotic strategies. At the same time, the entire program＇s multi-segmentation into short video clips, combined with a fast paced sound track helps its audience to understand the specialized explanations presented. Of all the multimodal wealth that the program presents, we will concentrate only on the relationship between the words and the images （leaving other secondary semiotics to one side）, the main strategy for achieving the objective of transmitting knowledge and winning adolescent audiences.展开更多
A series of experiments were performed on indigenously synthesized catalyst pallets of cobalt as a very active metal on ceramic support like SiC, A1203 ＆ TiO2 in a fixed bed reactor configuration with an aim to study...A series of experiments were performed on indigenously synthesized catalyst pallets of cobalt as a very active metal on ceramic support like SiC, A1203 ＆ TiO2 in a fixed bed reactor configuration with an aim to study the catalyst activity ＆ selectivity, chemical kinetics, design flexibility, temperature, pressure by characteristics diffusion distance. Catalyst pallets were prepared and then characterized by N2 adsorption, X-ray Diffraction, Scanning Electron Microscope, and Temperature Programmed Reduction. The results showed the Brunaner, Emmett and Teller area of SiC was the lowest among the three supports prepared for testing. However, its reducibility showed improvement with use of cobalt acetate, as a precursor, rather than cobalt nitrates. Mechanical strength and behavior was checked by the hardness testing machine. Fischer Tropsch （FT） synthesis experiments were performed in the fixed bed reactor set at 450-500 K and 2.3-2.5 MPa using synthetic gas having HJCO ration = 2.0. FT synthesis showed that cobalt/silicon carbide catalyst gives high CO conversion and lower methane selectivity, compared to Co/A1203 and Co/TiO2, as well as high C5＋ selectivity of almost 90%. Moreover, its stability was enhanced by the addition of Zr02, as without this addition, the Co/SiC interactions are weaker and can cause carbon sintering, and thus, the deactivation rate to increase.展开更多
文摘Objective: The dosimetric characteristics for linear accelerators with the same model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer's original specifications. In this preliminary study, a quantitative investigation of the similarity in the basic photon and electron dosimetry data from the Siemens Oncor linear accelerators at our hospital(Children's Cancer Hospital, Cairo, Egypt) was reported. Methods: The output factor(OF), wedge factors(WF), percentage depth dose(PDD), and beam profile for the 6 and 10 MV photon beams were measured. Results: The measured output factors varied by less than about 1% for each field size. The difference between the maximum and minimum PDD values at each depth was less than about 1%. The difference between the beam flattnes and symetry was no more than 1% at all off-axis distances. For electron the results showed that the PDD, OF, and the beam profiles were matched within 1% differences. Conclusion: These results strongly suggest that it is feasible to establish one reference photon and electron dosimetry data set for the two machines and nominal energies.
文摘The aim of this work is to study the interaction of spoken words and images that are used within programs targeted to popularize knowledge among teenagers. We will look into the program Bit@bit developed by Television de Catalunya, which is intended to disseminate computer concepts, tools and procedures. In this kind of program, one can find spoken language （on/off screen voices, interviews, etc.）, other oral material （sounds, music, songs）, written language （descriptions, title sequences, inserts and Uniform Resource Locator, or electronic addresses）, and other visual material （film cut images, advertising, other TV programs, cartoons, films, both location or studio images, depicting reality, or computer screens, or logotypes）. The profusion of multimodal elements used in this program helps to keep the young audience＇s attention. The use of references to their world or knowledge, as a target group, is based on interplay among different semiotic strategies. At the same time, the entire program＇s multi-segmentation into short video clips, combined with a fast paced sound track helps its audience to understand the specialized explanations presented. Of all the multimodal wealth that the program presents, we will concentrate only on the relationship between the words and the images （leaving other secondary semiotics to one side）, the main strategy for achieving the objective of transmitting knowledge and winning adolescent audiences.
文摘A series of experiments were performed on indigenously synthesized catalyst pallets of cobalt as a very active metal on ceramic support like SiC, A1203 ＆ TiO2 in a fixed bed reactor configuration with an aim to study the catalyst activity ＆ selectivity, chemical kinetics, design flexibility, temperature, pressure by characteristics diffusion distance. Catalyst pallets were prepared and then characterized by N2 adsorption, X-ray Diffraction, Scanning Electron Microscope, and Temperature Programmed Reduction. The results showed the Brunaner, Emmett and Teller area of SiC was the lowest among the three supports prepared for testing. However, its reducibility showed improvement with use of cobalt acetate, as a precursor, rather than cobalt nitrates. Mechanical strength and behavior was checked by the hardness testing machine. Fischer Tropsch （FT） synthesis experiments were performed in the fixed bed reactor set at 450-500 K and 2.3-2.5 MPa using synthetic gas having HJCO ration = 2.0. FT synthesis showed that cobalt/silicon carbide catalyst gives high CO conversion and lower methane selectivity, compared to Co/A1203 and Co/TiO2, as well as high C5＋ selectivity of almost 90%. Moreover, its stability was enhanced by the addition of Zr02, as without this addition, the Co/SiC interactions are weaker and can cause carbon sintering, and thus, the deactivation rate to increase.
