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A C Crawford - One of the best experts on this subject based on the ideXlab platform.
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unprecedented quality factors at accelerating gradients up to 45 mvm 1 in niobium superconducting resonators via low temperature nitrogen infusion
Superconductor Science and Technology, 2017Co-Authors: Anna Grassellino, A Romanenko, Y Trenikhina, Mattia Checchin, Martina Martinello, Oleksandr Melnychuk, Saravan Kumar Chandrasekaran, Dmitri Sergatskov, S Posen, A C CrawfordAbstract:We report the finding of new Surface treatments that permits one to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis–Bardeen Surface resistance and residual resistance accordingly. In particular, we find Surface 'infusion' conditions that systematically (a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; (b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art Surface Processing. Cavities subject to the new Surface Process have more than two times the state-of-the-art Q at 2 K for accelerating fields >35 MVm−1. Moreover, very high accelerating gradients ~45 MVm−1 are repeatedly reached, which correspond to peak magnetic Surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the Surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity Surface.
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unprecedented quality factors at accelerating gradients up to 45 mv m in niobium superconducting resonators via low temperature nitrogen infusion
arXiv: Accelerator Physics, 2017Co-Authors: Anna Grassellino, A Romanenko, Y Trenikhina, Mattia Checchin, Martina Martinello, Oleksandr Melnychuk, Saravan Kumar Chandrasekaran, Dmitri Sergatskov, S Posen, A C CrawfordAbstract:We report the finding of new Surface treatments that permit to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen Surface resistance and residual resistance accordingly. In particular, we find Surface infusion conditions that systematically a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art Surface Processing. Cavities subject to the new Surface Process have larger than two times the state of the art Q at 2K for accelerating fields > 35 MV/m. Moreover, very high accelerating gradients ~ 45 MV/m are repeatedly reached, which correspond to peak magnetic Surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the Surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity Surface.
C Quijada - One of the best experts on this subject based on the ideXlab platform.
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electrochemical behaviour of aqueous so2 at polycrystalline gold electrodes in acidic media a voltammetric and in situ vibrational study part 1 reduction of so2 deposition of monomeric and polymeric sulphur
Electrochimica Acta, 2000Co-Authors: C Quijada, F Huerta, Emilia Morallon, J L Vazquez, L E A BerlouisAbstract:The electro-reduction of SO2 has been monitored by using cyclic voltammetry, FT-IR spectroscopy and SER spectroscopy. Prior to the bulk reduction, SO2 is reduced to yield a monomeric sulphur adlayer at a maximum coverage of about 0.25. The sulphur adlayer undergoes a reversible redox Surface Process at E<0.0 V (RHE), which implies a change in the frequency of the Au---S stretching mode from 270 to 300/310 cm−1. In the potential region encompassing the bulk reduction voltammetric peak, infrared spectra display a band at 2585 cm−1 attributable to a S---H vibration from a soluble species. Accordingly, H2S or H2Sx were proposed as tentative bulk reduction products. In positive sweeps a broad anodic wave develops between 0.2 and 0.6 V that leaves polymeric sulphur species adsorbed at multilayer level, with a S---S stretching mode at 460 cm−1 and a S---S---S bending vibration at 218 cm−1. Multilayer sulphur can be removed reductively under a sharp cathodic peak. According to literature of the S(-II)/Au system, removal proceeds to yield soluble S(-II) species, via intermediate polysulphides.
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electrochemical behaviour of aqueous sulphur dioxide at polycrystalline pt electrodes in acidic medium a voltammetric and in situ ft ir study part ii promoted oxidation of sulphur dioxide reduction of sulphur dioxide
Journal of Electroanalytical Chemistry, 1995Co-Authors: C Quijada, J L Vazquez, A Rodes, J M Perez, A AldazAbstract:The promoted electro-oxidation of aqueous sulphur dioxide at platinum electrodes has been studied in acidic medium with the aid of cyclic voltammetry and in-situ FT-IR spectroscopy. Promotion of SO2 oxidation is achieved when adsorbed SO2 is reduced previously to adsorbed sulphur. On a platinum Surface covered by sulphur in this way, an enhancement of SO2 oxidation is attained. Spectroscopic evidence demonstrates that, like oxidation of SO2 in the oxygen adsorption region, soluble S(VI) is the ultimate reaction product of the catalysed SO2 oxidation. The electroreduction of SO2 has been dealt with by using the same techniques. Besides a Surface Process converting adsorbed SO2 into adsorbed sulphur, bulk SO2 reduces irreversibly giving rise to a diffusion-limited voltammetric peak. The absence of significant IR bands in the potential region at which reduction of bulk SO2 takes place, allows discarding the generation of S-H containing species. A sulphur + polysulphide mixture is suggested as the ultimate product, yet whether this mixture is formed directly in the electron-transfer step or stems from chemical decomposition of sulphur-oxygen short lifetime intermediates is not clear. Reduction of SO2 leads to a progressive accumulation of sulphur on the platinum Surface. An excess of adsorbed sulphur negatively affects the kinetic stages of both oxidation and reduction of bulk SO2.
Anna Grassellino - One of the best experts on this subject based on the ideXlab platform.
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unprecedented quality factors at accelerating gradients up to 45 mvm 1 in niobium superconducting resonators via low temperature nitrogen infusion
Superconductor Science and Technology, 2017Co-Authors: Anna Grassellino, A Romanenko, Y Trenikhina, Mattia Checchin, Martina Martinello, Oleksandr Melnychuk, Saravan Kumar Chandrasekaran, Dmitri Sergatskov, S Posen, A C CrawfordAbstract:We report the finding of new Surface treatments that permits one to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis–Bardeen Surface resistance and residual resistance accordingly. In particular, we find Surface 'infusion' conditions that systematically (a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; (b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art Surface Processing. Cavities subject to the new Surface Process have more than two times the state-of-the-art Q at 2 K for accelerating fields >35 MVm−1. Moreover, very high accelerating gradients ~45 MVm−1 are repeatedly reached, which correspond to peak magnetic Surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the Surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity Surface.
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unprecedented quality factors at accelerating gradients up to 45 mv m in niobium superconducting resonators via low temperature nitrogen infusion
arXiv: Accelerator Physics, 2017Co-Authors: Anna Grassellino, A Romanenko, Y Trenikhina, Mattia Checchin, Martina Martinello, Oleksandr Melnychuk, Saravan Kumar Chandrasekaran, Dmitri Sergatskov, S Posen, A C CrawfordAbstract:We report the finding of new Surface treatments that permit to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen Surface resistance and residual resistance accordingly. In particular, we find Surface infusion conditions that systematically a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art Surface Processing. Cavities subject to the new Surface Process have larger than two times the state of the art Q at 2K for accelerating fields > 35 MV/m. Moreover, very high accelerating gradients ~ 45 MV/m are repeatedly reached, which correspond to peak magnetic Surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the Surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity Surface.
Zhiyuan Zheng - One of the best experts on this subject based on the ideXlab platform.
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inclusion of solar elevation angle in land Surface albedo parameterization over bare soil Surface
Journal of Advances in Modeling Earth Systems, 2017Co-Authors: Zhiyuan Zheng, Zhigang Wei, Zhiping Wen, Wenjie Dong, Xiaohang Wen, Xian Zhu, Chen Chen, Dongdong YanAbstract:Land Surface albedo is a significant parameter for maintaining a balance in Surface energy. It is also an important parameter of bare soil Surface albedo for developing land Surface Process models that accurately reflect diurnal variation characteristics and the mechanism behind the solar spectral radiation albedo on bare soil Surfaces and for understanding the relationships between climate factors and spectral radiation albedo. Using a data set of field observations, we conducted experiments to analyze the variation characteristics of land Surface solar spectral radiation and the corresponding albedo over a typical Gobi bare soil underlying Surface and to investigate the relationships between the land Surface solar spectral radiation albedo, solar elevation angle, and soil moisture. Based on both solar elevation angle and soil moisture measurements simultaneously, we propose a new two-factor parameterization scheme for spectral radiation albedo over bare soil underlying Surfaces. The results of numerical simulation experiments show that the new parameterization scheme can more accurately depict the diurnal variation characteristics of bare soil Surface albedo than the previous schemes. Solar elevation angle is one of the most important factors for parameterizing bare soil Surface albedo and must be considered in the parameterization scheme, especially in arid and semiarid areas with low soil moisture content. This study reveals the characteristics and mechanism of the diurnal variation of bare soil Surface solar spectral radiation albedo and is helpful in developing land Surface Process models, weather models, and climate models.
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simulation and improvement of common land model on the bare soil of loess plateau underlying Surface
Environmental Earth Sciences, 2012Co-Authors: Zhigang Wei, Zhiyuan Zheng, Chao Wang, Hong Wei, Hui LiuAbstract:Climate model has become an irreplaceable tool for the study and prediction of climate changes. The land Surface Process, as one of the important parts of all climate models, must be considered so that the simulative ability of climate models could be improved. Using the common land model (CoLM) that is driven by the LOPEX experiment data, the characteristics of land Surface Processes of the Loess Plateau are simulated. Furthermore, based on the comparison of the field observation data with the simulated results, the simulative performance of CoLM in the Loess Plateau region is also examined. The results show that, CoLM can be used in the Loess Plateau, and it perfectly simulates net radiations and net short-wave radiations. However, the simulated land-Surface temperature is slightly higher than actual measured value, while the simulated soil temperature values in lower layers (5, 10, 20, 40 cm) are relatively less and the variety phase of these also lag. Moreover, the simulated sensible heat flux is a little larger, while the simulated soil thermal conductivity value is obviously lower. By modifying the calculation plan of soil thermal conductivity, the simulated result has been greatly improved. As a whole, if CoLM is applied in the Loess Plateau of Northwestern China, the parameterization of soil thermal conductivity should be ameliorated, which can improve its simulative capacity in the Loess Plateau regions.
Ismail Elkhrachy - One of the best experts on this subject based on the ideXlab platform.
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vertical accuracy assessment for srtm and aster digital elevation models a case study of najran city saudi arabia
Ain Shams Engineering Journal, 2017Co-Authors: Ismail ElkhrachyAbstract:Abstract Digital Elevation Model is imperative to many earth Surface Process analyses. In this study, the quality of DEMs acquired by SRTM ver.3 and ASTER ver.2 is evaluated. The reference levels produced from GPS elevations, and the topographic map is used to assess the vertical accuracy of SRTM and ASTAR DEMs in Najran city, Saudi Arabia. The GPS reference elevations gave us the values of ±5.94 m and ±5.07 m for used SRTM and ASTER DEMs. Also, by using elevation from the topographic map as a reference elevations the obtained accuracy was ±6.87 m and ±7.97 m for SRTM and ASTER DEMs. For our study area, the 30 m SRTM elevations data featured a much greater absolute vertical accuracy than the absolute vertical accuracy value of ±16 m, which published in the SRTM data specification.