用生态模式建设城市河流防护工程刍议

在城市河流防护工程实践中,传统砌石、混凝土等护砌方式在达到一定的功能目的的同时,产生了许多消极后果。针对用生态模式建设城市河流防护工程,恢复并保护自然水环境进行研究与探讨,可为山东三大工程提供有关技术的可行性与技术支持,做好科技服务。     

Results of a 90-day toxicity study on 1,2,3- and 1,1,2-trichloropropane administered via the drinking water

Trichloropropanes have been identified as environmental contaminants in sediments of the Great Lakes region of North America. Since these chemicals had the potential to find their way into drinking water, a 90-day feeding study was carried out in order to determine their subchronic toxicity. Groups of 10 male and 10 female weanling Sprague-Dawley rats were supplied drinking water ad libitum, containing 1,2,3- or 1,1,2-trichloropropane at concentrations of 1, 10, 100 or 1000 mg/L for 13 weeks. Emulphor (0.5%) was used to solubilize the chemicals. At the end of the study, the animals were killed and examined for gross and microscopic changes. Heart, liver, brain, kidney and spleen were excised and weighed. Blood was collected and subjected to a comprehensive hematological analysis. Serum was collected and profiled for changes in 12 biochemical parameters and a portion of liver was used to determine mixed function oxidase activity. Although three animals died during the study, their deaths could not be related to treatment. Decreased growth rate was observed in both sexes of the group receiving 1000 mg/L 1,2,3-trichloropropane. There was an increase in liver, kidney and brain weights (relative to body weight) in rats of both sexes fed 1000 mg/L 1,2,3-trichloropropane. Fatty livers were observed in some of the treated animals but a clear dose-relationship was not evident. An elevation in serum cholesterol was observed in female rats fed the highest dose of 1,2,3-trichloropropane. This chemical also induced hepatic aminopyrine demethylase and aniline hydroxylase activities in male rats at the highest dose. Administration of both isomers produced only mild histological changes in the liver, thyroid and kidney of rats at the highest dose. The changes in the liver consisted of an increase in cytoplasmic eosinophilia in the periportal area together with vesiculation of biliary epithelial nuclei. Morphological changes were characterized by increased anisokaryosis in the proximal epithelium and occasional pyknosis associated with the accumulation of large eosinophilic inclusions. Changes in the thyroid consisted of a mild reduction in follicular size associated with an increased epithelial height. In general, these changes were more severe in the males than females, but were still mild overall. It was concluded that the no-effect level for both chemicals was 100 mg/L (15–20 mg/kg bw/day) and based on effects on growth rate and other changes, the 1,2,3- isomer was judged to be slightly more toxic than the 1,1,2- isomer.     

Growth temperature dependence of low-noise MESFET in molecular-beam epitaxy

The substrate growth temperature dependence of electrical properties for a low-noise MESFET fabricated on MBE-grown material has been demonstrated. The optimum noise figure and its associated gain were attributed to the higher epilayer quality and mobility at a growth temperature of 650°C between temperatures of 550°C and 700°C.     

A novel endonuclease from kinetoplastid hemoflagellated protozoan parasite Leishmania

A nuclease activity has been purified from the nuclei-kinetoplast fraction of Leishmania. This enzyme, termed endonuclease M (Endo M), is shown by electrophoresis in a denaturing polyacrylamide gel to be associated with a single polypeptide of molecular mass 52 kDa. Physical analysis of the enzyme indicates that it has a sedimentation coefficient S20,w of 4.5S, a Stoke's radius of 32.5 A, and a native molecular mass of 53 kDa. The final Mono Q purified Endo M possesses both DNase and RNase activities. It acts as an endonuclease by introducing random single-stranded nicks into the supercoiled DNA molecules, that often leads to its linearization due to nicking at the opposite strands, and subsequent degradation of the DNA with further incubation. Single-stranded DNA is twice preferred to double-stranded DNA as substrate. Single-stranded RNA is also degraded rapidly and is competitive as a substrate with single-stranded DNA. RNA:DNA hybrids, however, are largely resistant to the Endo M digestion.     

广义Foster定理

利用Ｍａｘｗｅｌｌ方程组导出了适用于有耗网络的广义Ｆｏｓｔｅｒ定理，得到了一些有关电抗斜率以及Ｑ值的有用公式及结论。     

Cleavage of Müllerian inhibiting substance activates antiproliferative effects in vivo

Müllerian inhibiting substance (MIS), an inhibitor of growth and development of the female reproductive ducts in male fetuses, requires precise proteolytic cleavage to yield its biologically active species. Human plasmin is now used to cleave and, thereby, activate immunoaffinity-purified recombinant human MIS at its monobasic arginine-serine site at residues 427-428. To avoid the need for exogenous enzymatic cleavage and to simplify purification, we created an arginine-arginine dibasic cleavage site (MIS RR) using site-directed mutagenesis to change the serine at position 428 (AGC) to an arginine (cGC). The mutant cDNA was then stably transfected into a MIS-responsive ocular melanoma cell line, OM431, followed by cloning for amplified expression to test its biological activity in vitro and in vivo. Media from each clone were assayed for production of MIS RR by a sensitive ELISA for holo-MIS, and high- and low-producing clones were selected for further study. Media from the highest MIS RR producer caused Müllerian duct regression in an organ culture bioassay. Other transfections were done with an empty vector (pcDNAI Neo) or a construct lacking the leader sequence and thus failing to secrete MIS, to serve as controls. The OM431 clones containing the MIS RR mutant were growth inhibited in monolayer culture. The high- and low-producing MIS RR OM431 clones, along with transfected OM431 controls, were injected into the tail veins of immunosuppressed severe combined immunodeficiency mice for in vivo analyses. Four to 6 weeks later, pulmonary metastases were counted in uniformly inflated lungs. OM431 clones containing the more easily cleaved MIS RR displayed a significant dose-dependent reduction in pulmonary metastases when compared to the lungs of animals given injections of OM431 clones containing empty vector, leaderless MIS, or wild-type MIS that requires activation by plasmin cleavage. Since the purification protocol of MIS RR is less complicated than that for wild-type MIS, which requires subsequent enzymatic activation, MIS RR can be used for scale-up production with increased yields for further therapeutic trials against MIS-sensitive tumors.     

One-stage sternal stenting with homograft bone after cardiac operation in pediatric patients

Low cardiac output after open heart operations in neonates and infants carries a high mortality. Delayed sternal closure may be life-saving but may prolong hospital stay and increase costs. To circumvent these issues, we shaped homograft bone and interposed it between the sternal edges to allow primary wound closure in 2 pediatric patients. Midterm results are satisfactory.     

Synthesis and Properties of the Bi-Based Superconducting Powder Prepared by the Pechini Process

Bi-based superconductors are of great interest in high-temperature superconductors. We describe what is believed to be the first synthesis of these materials using the Pechini process, a low-temperature synthetic method that often yields inorganic oxide of excellent phase purity and well-controlled stoichiometry. Using this process, it has been possible to synthesize phase-pure Bi-2223 phase by calcining the appropriate polymeric precursors in air at 800°C for several hours. The superconductivity studies show that the Pechini-synthesized materials appear to offer high-quality performance.     

The synthesis of symmetrical and unsymmetrical P1/P1' cyclic ureas as HIV protease inhibitors

Cyclic urea SD146, a potent HIV protease inhibitor bearing a flat resistance profile, possessed poor solubility and bioavailability, which precluded further development of the compound. In an effort to improve upon the pharmacokinetic profile of the compound, several analogs modified at the P1/P1' residues were prepared and evaluated. Several of those compounds displayed significant improvement of physical properties.     

A knowledge-based approach for retrieving images by content

A knowledge based approach is introduced for retrieving images by content. It supports the answering of conceptual image queries involving similar-to predicates, spatial semantic operators, and references to conceptual terms. Interested objects in the images are represented by contours segmented from images. Image content such as shapes and spatial relationships are derived from object contours according to domain specific image knowledge. A three layered model is proposed for integrating image representations, extracted image features, and image semantics. With such a model, images can be retrieved based on the features and content specified in the queries. The knowledge based query processing is based on a query relaxation technique. The image features are classified by an automatic clustering algorithm and represented by Type Abstraction Hierarchies (TAHs) for knowledge based query processing. Since the features selected for TAH generation are based on context and user profile, and the TAHs can be generated automatically by a clustering algorithm from the feature database, our proposed image retrieval approach is scalable and context sensitive. The performance of the proposed knowledge based query processing is also discussed