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31.
Knippels G.M.H. van der Meer A.F.G. Oepts D. van Amersfoort P.W. 《Quantum Electronics, IEEE Journal of》1997,33(1):10-17
We have investigated the optical output of the free-electron laser for infrared experiments (FELIX) when it is driven by an electron beam with a ramped energy. We show that the applied slow ramp on the electron beam energy leads to a frequency chirp on each picosecond optical pulse. Typical values for the chirp are 0.2% frequency sweep across a 1.5-ps-long optical pulse. The optical pulses were analyzed with a double-grating pair and with a second-order autocorrelator. The pulse duration was reduced in the double-grating pair by 20%. A linear dependence of the chirp on the cavity desynchronization was measured 相似文献
32.
The sequence proline-proline-glycine-proline is highly conserved in cytochrome P450 families 1 and 2, and similar proline rich sequences are found in other cytochromes P450. Since this sequence immediately follows the NH2-terminal hydrophobic membrane insertion signal, it potentially could function as a signal either for retention of cytochrome P450 in the endoplasmic reticulum or for its correct orientation in the membrane. To test this possibility, DNA sequence coding for this tetrapeptide was deleted from cytochrome P450 2C2 cDNA. Translation of the mutated mRNA in a reticulocyte cell-free system containing canine microsomal membranes resulted in the insertion of the protein into the membrane with a topology indistinguishable from that of normal cytochrome P450 2C2. The mutated protein was expressed in COS1 cells and its distribution, assayed by immunofluorescence, was similar to that of cytochrome P450 2C2. Furthermore, if a short peptide containing a potential glycosylation site was fused to the N-terminus of the mutant protein, the new hybrid protein was glycosylated in COS1 cells and the carbohydrate moiety remained sensitive to cleavage by endoglycosidase H. These results indicate that the protein was inserted and retained in the endoplasmic reticulum membrane. Pulse-chase studies showed that the mutated protein was degraded about four times as fast as cytochrome P450 2C2. In contrast to cytochrome P450 2C2, no (omega-1) hydroxylase activity was detected in COS1 cells expressing the mutated protein at similar steady-state levels as the wild-type protein. These results indicate that, although the conserved PPGP tetrapeptide is not required for cellular localization of cytochrome P450 in the endoplasmic reticulum membrane, its deletion decreases the stability of the protein and abolishes enzymatic activity. 相似文献
33.
Surgical thrombectomy is not a rational approach to neonatal renal vein thrombosis since the occlusion mainly involves intrarenal branches rather than the main renal vein, which is even patent in some instances. Conservative management combines supportive therapy for renal failure and systemic hypertension, if needed, and either heparin or thrombolytic agents. Streptokinase has proven difficult to handle in neonates and should not be used. Urokinase has been used in 18 patients but results are difficult to interpret because these cases occurred over an 18-year period. Plasminogen tissue activator, the latest thrombolytic agent developed, has been used in few pediatric patients. An international task force is currently studying whether or not a randomized study is warranted to provide data for standardizing thrombolytic therapy in pediatric renal vein thrombosis. 相似文献
34.
35.
A short-pulse 1.444-μm laser based on Nd:YAG technology has been demonstrated. The 1.444-μm is eye-safe. With the cavity-dump technique, a pulse of 50 m× and 14 ns was obtained. The beam quality was excellent with an M2 of 1.6 by the use of a telescopic resonator. Silicon-window polarizers were used to suppress the 1.06-μm radiation but showed 1.444-μm absorption as well 相似文献
36.
37.
The effect of caseinate and soy protein in the diet on the mutagenicity induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was assessed in-vivo and ex-vivo in the DNA-repair host-mediated assay and liquid suspension assay, respectively. Of the two proteins only casein showed a strong antimutagenic activity over the whole digestive tract, except in the stomach. It is suggested that the molecular structure of a protein determines its protective effect against mutagens: casein lacks secondary and tertiary structure so that amino acids are more readily available for interaction with the mutagen than with the amino acids in soy protein which is a globular protein. 相似文献
38.
Cancer invasion and metastasis are associated with matrix degradation. We describe a novel in vivo model of invasion by squamous epithelial neoplastic cells derived from transgenic mice grown on acellular human dermis. Human dermis was subjected to multiple freeze-thaw cycles to render it acellular, maintaining the basement membrane of the former dermal-epidermal junction. Cells representing discrete stages of a multistep transgenic mouse model of epidermal carcinogenesis (neonatal transgenic keratinocytes, moderately/poorly differentiated squamous cell carcinoma, and lymph node metastasis) were seeded onto the basement membrane surface, grown in culture for 4 days, grafted in a subpannicular pocket of athymic mice, and harvested after 3 weeks. Histological analysis demonstrated that neonatal transgenic keratinocytes did not degrade the basement membrane or invade the underlying dermis. In contrast, malignant cells derived from both a moderately differentiated squamous carcinoma and a lymph node metastasis were highly invasive. Immunohistochemical analysis revealed collagenase only in nests of invading malignant cells in contact with the dermal matrix, but not in the tumor mass remaining above the basement membrane, suggesting that this proteinase may be required for stromal invasion. This novel model recapitulates the events seen in malignant invasion: transgenic keratinocytes are unable to penetrate the dermis while cells from a moderately differentiated carcinoma and from lymph node metastasis consistently invade. 相似文献
39.
M Hessing D Kanters H Takeya C van 't Veer TM Hackeng S Iwanaga BN Bouma 《Canadian Metallurgical Quarterly》1993,317(3):228-232
Human C4b-binding protein (C4BP) functions as a cofactor to factor I in the degradation of C4b and accelerates the decay rate of the C4b2a complex. In this study we describe a monoclonal antibody directed against the alpha-chain of C4BP that inhibits the binding of C4b to C4BP. In order to identify the structural domain of the alpha-chain of C4BP that interacts with C4b, tryptic fragments of C4BP were generated. Amino acid sequence analysis of the fragments revealed that the residues Ser333-Arg356 of the alpha-chain of C4BP contain the epitope of this antibody, and as a consequence, that this part of the alpha-chain of C4BP is likely to be involved in the interaction with C4b. 相似文献
40.
Measuring knowledge transfer between fields of science 总被引:4,自引:2,他引:2
Rinia Ed J. van Leeuwen Thed N. Bruins Eppo E. W. van Vuren Hendrik G. van Raan Anthony F. J. 《Scientometrics》2002,54(3):347-362
In this paper we report on the results of an exploratory study of knowledge exchange between disciplines and subfields of
science, based on bibliometric methods. The goal of this analysis is twofold. Firstly, we consider knowledge exchange between
disciplines at a global level, by analysing cross-disciplinary citations in journal articles, based on the world publication
output in 1999. Among others a central position of the Basic Life Sciences within the Life Sciences and of Physics within
the Exact Sciences is shown. Limitations of analyses of interdisciplinary impact at the journal level are discussed. A second
topic is a discussion of measures which may be used to quantify the rate of knowledge transfer between fields and the importance
of work in a given field or for other disciplines. Two measures are applied, which appear to be proper indicators of impact
of research on other fields. These indicators of interdisciplinary impact may be applied at other institutional levels as
well.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献