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31.
C C Rindt A A van Steenhoven J D Janssen R S Reneman A Segal 《Journal of biomechanics》1990,23(5):461-473
A finite element approximation of steady flow in a rigid three-dimensional model of the carotid artery bifurcation is presented. A Reynolds number of 640 and a flow division ratio of about 50/50, simulating systolic flow, was used. To limit the CPU- and I/O-times needed for solving the systems of equations, a mesh-generator was developed, which gives full control over the number of elements into which the bifurcation is divided. A mini-supercomputer, based on parallel and vector processing techniques, was used to solve the system of equations. The numerical results of axial and secondary flow compare favorably with those obtained from previously performed laser-Doppler velocity measurements. Also, the influence of the Reynolds number, the flow division ratio, and the bifurcation angle on axial and secondary flow in the carotid sinus were studied in the three-dimensional model. The influence of the interventions is limited to a relatively small variation in the region with reversed axial flow, more or less pronounced C-shaped axial velocity contours, and increasing or decreasing axial velocity maxima. 相似文献
32.
E J Ottevanger C W Spoor J L van Leeuwen A A Sauren J D Janssen A Huson 《Journal of biomechanics》1989,22(8-9):957-962
An experimental setup was developed for statically measuring seven vertical and three horizontal reaction forces on the foot. In the setup, the leg can be simultaneously loaded (1) by a vertical force, (2) by an externally applied axial moment, and (3) by simulated muscle forces. The foot is free to invert under influence of the external loads. Statical analysis and test experiments were used for evaluation. The setup can be used in combination with Roentgen photogrammetry to measure bone positions simultaneously with forces. 相似文献
33.
Summary In a two-phase system of D-sorbitol in water and decanoic acid the esterification is catalyzed by lipase fromCandida rugosa. The initial esterification rate is 3.0 mmole/g.h and is strongly dependent on the water content of the reaction mixture. In a two-phase membrane reactor the initial esterification rate is 6.8 mmole/g.h. After 570 hours this reaction rate is reduced by 15%, which indicates a fairly good stability of lipase in this membrane system. 相似文献
34.
Localized transient expression of GUS in leaf discs following cocultivation with Agrobacterium 总被引:15,自引:0,他引:15
A chimaeric gene has been constructed that expresses -D-glucuronidase (GUS) in transformed plant tissues, but not in bacterial cells. This gene has proved extremely useful for monitoring transformation during the period immediately following gene transfer from Agrobacterium tumefaciens. GUS expression was detectable 2 days after inoculation, peaked at 3–4 days and then declined; if selection was imposed expression increased again after 10–14 days. The extent of transient expression after 4 days correlated well with stable integration as measured by kanamycin resistance, hormone independence, and gall formation. Histochemical staining of inoculated leaf discs confirmed the transient peak of GUS expression 3–4 days after inoculation. The most surprising result was that the blue staining was concentrated in localized zones on the circumference of the disc; within these zones, essentially all the cells appeared to be expressing GUS. We suggest that the frequency of gene transfer from Agrobacterium is extremely high within localized regions of leaf explants, but that the frequency of stable integration is several orders of magnitude lower. 相似文献
35.
Physiological changes and alk gene instability in Pseudomonas oleovorans during induction and expression of alk genes. 总被引:4,自引:0,他引:4
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The alk genes of Pseudomonas oleovorans, which is able to metabolize alkanes and alkenes, are organized in alkST and alkBFGHJKL clusters, in which the expression of alkBFGHJKL is positively regulated by AlkS. Growth of the wild-type strain GPo1 and P. oleovorans GPo12 alk recombinants on octane resulted in changes of cellular physiology and morphology. These changes, which included lower growth rates and a reduction of the number of CFU due to filamentation, were also seen when the cells were grown on aqueous medium, and the alk genes were induced with dicyclopropylketone, a gratuitous inducer of the alk genes. These effects were seen only for recombinants carrying both alkST and alkBFGHJKL operons. Deletion of parts of either alkB or alkJ, which encode two major Alk proteins located in the cytoplasmic membrane, modified but did not eliminate the effects described above, suggesting that they were due to induction and expression of several alk genes. Continuous growth of the cells in the presence of dicyclopropylketone for about 10 generations led to inactivation, but not elimination, of the alk genes. This resulted in a return of the recombinants to normal physiology and growth. 相似文献
36.
B. Hölldobler E. Janssen H. J. Bestmann F. Kern I. R. Leal P. S. Oliveira W. A. König 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(1):47-53
The Neotropical species Pachycondyla marginata conducts well-organized predatory raids on the termite species Neocapritermes opacus and frequently emigrates to new nest sites. During both activities the ants employ chemical trail communication. The trail pheromone orginates from the pygidial gland. Among the substances identified in the pygidial gland secretions, only citronellal was effective as a trail pheromone. Isopulegol elicited an increase in locomotory activity in the ants and may function as a synergist recruitment signal. The chemical signal is enhanced by a shaking display performed by the recruiting ant. 相似文献
37.
Gerhard Bringmann Klaus-Peter Gulden Daniel Vitt Klaus Birken Clemens Helf 《Journal of molecular modeling》1995,1(3):161-175
AdaptivSearch is the first adaptive strategy based algorithm for the rational and economical construction of n-dimensional hypersurfaces. AdaptivSearch works iteratively: At each step it parcels out the definition range into several triangles, evaluates the worst according to a built-in error criterion, and refines the approximation to the unknown function by choosing the barycenter of this partial area as the node to be calculated next. Based upon the error criterion, AdaptivSearch selectively approaches those parts of the hypersurface in which the curvature exhibits the strongest changes. Some examples of AdaptivSearch applications for both analytical functions and chemical model surfaces are given in order to demonstrate the behavior of the algorithm. These show its broad applicability and the usefulness, especially for chemical problems. 相似文献
38.
Prediction of the Reaction Equilibrium of Biocatalytic Reactions in Aqueous-Organic Two-Phase Systems 总被引:1,自引:0,他引:1
Anja E. M. Janssen Albert Van Der Padt Klaas Van't Riet 《Biocatalysis and Biotransformation》1995,12(4):223-240
Biocatalytic reactions can be carried out in aqueous-organic two-phase systems. Several models to describe the thermodynamically-determined equilibrium position in such systems have appeared in the literature. Some of these models are only valid for dilute systems, whereas others can also be used for nondilute systems. In this paper, these models are described and compared. It is explained in what way the equilibrium constants of each model can be used to predict the product concentration in different organic solvents. 相似文献
39.
J. J. van der Waarde R. Kok D. B. Janssen 《Applied microbiology and biotechnology》1994,42(1):158-166
The biodegradation of chloroallyl alcohols by pure and mixed bacterial cultures was investigated. Only 2-chloroallyl alcohol and cis- and trans-3-chloroallyl alcohol served as growth substrate for pure cultures. The other chloroallyl alcohols could be cometabolically degraded during growth on 2-chloroallyl alcohol. Cometabolic degradation of trichloroallyl alcohol, which was the most recalcitrant congener, by a Pseudomonas strain isolated on 2-chloroallyl alcohol resulted in 60% dechlorination. Efficient degradation of a mixture of chloroallyl alcohols in continuous culture could only be achieved in the presence of a satellite population. The mixed culture degraded 99% of the total chloroallyl alcohols added with 71% chloride release. The culture contained strains with a new catabolic potential. The results indicate the importance of mixed cultures and genetic adaptation for efficient chloroallyl alcohol removal. 相似文献
40.
Reconstitution of a surface transferrin binding complex in insect form Trypanosoma brucei. 总被引:9,自引:1,他引:8
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M J Ligtenberg W Bitter R Kieft D Steverding H Janssen J Calafat P Borst 《The EMBO journal》1994,13(11):2565-2573
In the bloodstream of the mammalian host, Trypanosoma brucei takes up host transferrin by means of a high-affinity uptake system, presumably a transferrin receptor. Transferrin-binding activity is seen in the flagellar pocket and is absent in insect form trypanosomes. By transfection we have reconstituted a transferrin-binding complex in insect form trypanosomes. Formation of this complex requires the products of two genes that are part of a variant surface glycoprotein expression site, expression site-associated gene (ESAG) 6 (encoding a protein with GPI-anchor) and ESAG 7 (encoding a protein without any obvious membrane attachment). This complex can be precipitated by transferrin-Sepharose and by an antibody directed only against the ESAG 6 protein. Transfection of ESAG 6 or 7 alone did not result in transferrin binding. In the transfected trypanosomes, the products of ESAG 6 alone and the combination of ESAG 6 and 7 did not exclusively localize to the flagellar pocket, but were present all over the surface of the trypanosome. The reconstituted transferrin-binding complex also did not result in the uptake of transferrin. Additional proteins present in bloodstream trypanosomes, but not in sufficient amounts in insect form trypanosomes, may therefore be required for the correct routing of the transferrin-binding complex to the flagellar pocket, and for its rapid internalization after ligand binding. 相似文献