Sharks are the most dangerous predators of people in the sea, resulting in people being mauled and killed each year. A shark
repellent could help to diminish this danger. The aglycone of the shark repellent pavoninin-5, (25R)-cholest-5-en-3β,15α,26-triol (5a), was synthesized from diosgenin (9). Removing mercury from the Clemmensen reduction of 9 gave a higher yield of (25R)-cholest-5-en-3β,16β,26-triol, 10a, and was also more environmentally friendly. Attempted methods for the transposition of the C-16β hydroxyl to the 15α position
are described. A successful method for this transposition via the 15α-hydroxy-16-ketone, 8a, using the Barton deoxygenation reaction on the 16-alcohol 14b, is reported. 相似文献
To evaluate the influence of various Cr(VI) concentrations (0.05, 0.25, 0.50, 1.00 and 2.00 g/kg) on the activity of soil
enzymes, the activities of catalase, polyphenol oxidase, dehydrogenase, alkaline phosphatase in soils were investigated in
the incubation experiment with a period of 35 d. The results indicate that all the tested Cr(VI) concentrations significantly
inhibit dehydrogenase activity by over 70% after 35 d. The activity of alkaline phosphatase is slightly inhibited during the
whole experiment except for on the day 7. Cr(VI) has no obvious effect on the activity of catalase in soil. On the contrary,
Cr(VI) stimulates the activity of polyphenol oxidase. The results suggest that dehydrogenase activity can be used as an indicator
for assessing the severity of chromium pollution.
Foundation item: Projects(2006AA06Z374, 2007AA021304) supported by the National High-Tech Research and Development Program of China; Project(2008SK2007)
supported by the Key Program of Science and Technology of Hunan Province, China 相似文献
Based on the structural characteristic of metal drill collar for induction logging while drilling, we have given the analytical
formulae of lengthways fields Ez and Hz when the tool is located in a fan-ring shaped slot of drill collar by the boundary conditions of electromagnetic field, and
derived the other components of electromagnetic field in and out the fan-ring slot from Ez and Hz. In the other intervals of formation, where the drill collar is a solid cylinder, the analytical formulae of field are educed
through the method of variable coefficient. The total analytical solutions of field in whole space have been obtained. With
the help of the analytical formulae, we have also given numerical examples and analyzed the distributive characteristic of
electromagnetic field. From the computational results we find that the secondary scattering field Hz is in a linear relation with the conductivity of stratum. The characteristic of field is very useful for induction logging
while drilling, which can be used to measure and analyze the logging responses of the stratum conductivity. This paper sets
up a theoretical foundation for us to study the distrbutions of field and to direct the design of logging instruments.
Supported by the National Natural Science Foundation of China (Grant No. 10705049), the Beijing Natural Science Foundation
(Grant No.1083011) and Funding Project for Academic Human Resources Development in Institutions of Higher Learning [PHR(IHLB)] 相似文献
The traditional unified viscoplasticity constitutive model can be only applied to metal materials. The study of the unified
constitutive theory for metal materials has discovered the correlation between the classical plasticity theory and the unified
viscoplasticity constitutive model, thus leading to the concepts of the classic plastic potential and yield surface in the
unified constitutive model. Moreover, this research has given the continuous expression of the classical plastic multiplier
and presented the corresponding constructive method, which extends its physical significance and lays down a good foundation
for the application of the unified constitutive theory to the material analysis in more fields. This paper also introduces
the unified constitutive model for metal materials and geo-materials. The numerical simulation indicates that the construction
should be both reasonable and practical.
Supported by the National Natural Science Foundation of China (Grant No. 90410012) 相似文献
A new type counter electrode for dye-sensitized solar cells (DSCs) was proposed which consists of substrate, aluminum film
and platinum film. The new type counter electrode can obviously improve the photoelectric conversion efficiency of DSCs from
3.46% to 7.07% under the standard AM1.5 irradiation condition. Advantages and shortcomings of this new type counter electrode
in terms of electrical properties, optical properties and anti-corrosive properties were analyzed. As a result, some improvements
were proposed.
Supported by the Key Foundation for Fundamental Research of Tianjin Municipal Science & Technology Commission in China ( Grant
No. 06YFJZJC01700) and the National Basic Research Program of China (“973“ Project) (Grant Nos. 2006CB20260, 2006CB202603) 相似文献
The survivability is usually critical for wireless sensor networks,which are often deployed in the unattended harsh environment.Lots of technical schemes to improve the survivability depend on the redundant resources of the sensor networks.The amount of resources is usually determined by the node density during the deployment phase.For the random deployment and random node failures,the quantitative relation between the survivability and the node density is studied.Based on the conditional survivability,the node density to meet the required survivability level is presented.Finally,the survivability for unpredictable failures and the optimal node density to maximize the price–performance ratio are also discussed. 相似文献
A mesoporous membrane for selective separation of hydrogen was prepared usingthe sol-gel method. Some metal salts such as RuCl3, Pd(NH3)4Cl2, RhCl3,, and H 2PtCl6, were added to the boehmite sol and coated on a porous alumina substrate before firing at 500°C. It was foundthat the permeability of hydrogen and the separation factor for a hydrogen-nitrogen gaseous mixture of these metaldispersed membranes exceeded the limitations of the Knudsen diffusion mechanism. Although the gas permeation through a neat alumina membrane is governed by the Knudsen diffusion, the metals dispersed in alumina membranes were effective in promoting hydrogen permeation. These metaldispersed alumina membranes were also used in a membrane reactor for methane steam reforming at low temperature. In the temperature range of 300 to 500°C, the membrane reactor attained a methane conversion twice as high as the equilibrium value of the packed bed catalytic reactor system as a result of the selective removal of hydrogen from the reaction system. 相似文献
As recent cyber-attacks have been increasing exponentially, the importance of security training for employees also has become growing ever than before. In addition, it is suggested that security training and education be an effective method for discerning cyber-attacks within academia and industries. Despite the importance and the necessity of the training, prior study did not investigate the quantitative utility of security training in an organizational level. Due to the absence of referential studies, many firms are having troubles in making decisions with respect to arranging optimal security training programs with limited security budgets. The main objective of this study is to find out a relationship between cybersecurity training and the number of incidents of organizations. Thus, this study quantified the effectiveness of security training on security incidents as the first study. This research examined the relationship among three main factors; education time, education participants, and outsourcing with numbers of cybersecurity incidents. 7089 firm level data is analyzed through Poisson regression method. Based on analysis results, we found that the negative relationship between security trainings and the occurrence of cybersecurity incidents. This study sheds light on the role of security training and education by suggesting its positive association with reducing the number of incidents in organizations from the quantitative perspective. The result of this study can be used as a referential guide for information security training decision-making procedure in organizations.