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C sar Ovalles Carlos Vallejos Tito Vasquez Iraima Rojas Ursula Ehrman Jose Luis Benitez Ronald Martinez 《Petroleum Science and Technology》2003,21(1):255-274
An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive under steam injection conditions (280-315°C and residence times of at least 24-h). Laboratory experiments showed a 4° increase in the API gravity (from 9 to 12°) of the upgraded product, a two-fold reduction in the viscosity and, an approximately 8% decrease in the asphaltene content with respect to the original crude. Further increases on the temperature led to products with improved properties reaching 15°API at 315°C. It was found that the presence of the natural formation (catalysts) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. From GC and GC-MS results a reaction pathway is proposed that involves hydrogen transfers from tetralin to the extra-heavy crude oil resulting in the formation of 1,2-dihydronaphthalene. This compound is then transformed into naphthalene, further upgrading of crude oil through hydrogen donation. The results of the experiments carried out in the presence and absence of the mineral formation and with an inert solid (SiC) strongly indicate that the former acts as a catalyst and not as a heat transfer matrix. Isotopic labeling studies (CD4 and 13CH4) give evidences that, most probably, methane is involved in the upgrading reactions. 相似文献
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E. P. M. Leiva C. Vázquez M. I. Rojas M. M. Mariscal 《Journal of Applied Electrochemistry》2008,38(8):1065-1073
In this work, the structural and energetic properties of two typical catalytic surfaces, Na/Pt(111) and O/Pt(111), are studied
by means of quantum mechanical calculations and Monte Carlo Grand Canonical simulations. The simulations were performed with
electrostatic potentials at different truncation schemes. In order to elucidate the modification of catalyst surfaces produced
by the backspillover of ionic species onto Pt(111), the electrostatic field at the interface due to the electric double layer
was also analyzed. 相似文献
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The successful initiation and execution of a virtual team is gaining increasing attention in the design and construction community. From opportunities to integrate international and multidisciplinary teams to the opportunity to leverage the best resources in an organization on a given project, virtual teams can transform the concept of project planning and execution. However, potential barriers exist in several areas to the successful implementation of virtual teams. The needs of increased management emphasis, social and cultural understanding, and emphasis on common goals are only a few of the nontechnical factors that can turn successful virtual teaming into virtual frustration. When combined with traditional technical challenges including compatibility of systems, security, and the selection of appropriate technologies, the line between leveraging virtual technologies for enhanced solutions and introducing additional complications into the project process is one that can be easily crossed. This paper presents the findings of research that addresses the opportunities and potential barriers to successful virtual teams in the engineering, procurement, and construction industry. Combining results from current research, industry practices, and early results from nonconstruction industries, the research findings provide an initial path to successful virtual team implementation. 相似文献
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DP Kiel RH Myers LA Cupples XF Kong XH Zhu J Ordovas EJ Schaefer DT Felson D Rush PW Wilson JA Eisman MF Holick 《Canadian Metallurgical Quarterly》1997,12(7):1049-1057
Previous studies of the vitamin D receptor (VDR) polymorphisms and bone mineral density (BMD) have suggested that there may be differences in calcium absorption among groups of women with different VDR genotypes, and that the association may be stronger in younger women. To investigate the association between the VDR polymorphisms and BMD, this study was undertaken in the Framingham Study Cohort and a group of younger volunteers. Subjects from the Framingham Study (ages 69-90 years) included those who underwent BMD testing and who had genotyping for the VDR alleles (n = 328) using polymerase chain reaction methods and restriction fragment length polymorphisms with BsmI (B absence, b presence of cut site). A group of younger volunteer subjects (ages 18-68) also underwent BMD testing and VDR genotyping (n = 94). In Framingham Cohort subjects with the bb genotype, but not the Bb or BB genotypes, there were significant associations between calcium intake and BMD at five of six skeletal sites, such that BMD was 7-12% higher in those with dietary calcium intakes greater than 800 mg/day compared with those with intakes < 500 mg/day. The data also suggested that BMD was higher in persons with the bb genotype only in the group with calcium intakes above 800 mg/day. No significant differences were found in the Framingham Cohort for age-, sex-, and weight-adjusted BMD at any skeletal site between those with the BB genotype and those with the bb genotype regardless of 25-hydroxyvitamin D levels or country of origin. In the younger volunteers, BMD of the femoral neck was 5.4% higher (p < 0.05) in the bb genotype group compared with the BB group and 11% higher (p < 0.05) in males with the bb genotype compared with the BB group. There were no significant differences at the lumbar spine. In this study, the association between calcium intake and BMD appeared to be dependent upon VDR genotype. The findings of an association between dietary calcium intake and BMD only in the bb genotype group suggests that the VDR genotype may play a role in the absorption of dietary calcium. Studies that do not consider calcium intake may not detect associations between VDR genotype and BMD. In addition, the association between VDR alleles and BMD may become less evident in older subjects. 相似文献
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Starting with total RNA from spermatogenic cells of Mytilus trossulus and using random priming, we have cloned and sequenced the c-DNAs corresponding to two variants of the sperm-specific protein PLII* (phi 2B). DNA sequencing in conjunction with mass spectrometry and protein sequence data have allowed us to establish that of the three sperm-specific proteins present in the sperm of Mytilus (PL-II*(phi 2B), PL-III (phi 1), PL-IV (phi 3)), the first and the last one are the result of post-translational cleavage of a common precursor. This common precursor is a member of the histone H1 family, and it exhibits inter- and intraspecific microheterogeneity. 相似文献
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