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排序方式: 共有193条查询结果,搜索用时 265 毫秒
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Russo R Fox E Cinel C Boldini A Defeyter MA Mirshekar-Syahkal D Mehta A 《Bioelectromagnetics》2006,27(3):215-220
Recent studies have indicated that acute exposure to low level radiofrequency (RF) electromagnetic fields generated by mobile phones affects human cognition. However, the relatively small samples used, in addition to methodological problems, make the outcomes of these studies difficult to interpret. In our study we tested a large sample of volunteers (168) using a series of cognitive tasks apparently sensitive to RF exposure (a simple reaction task, a vigilance task, and a subtraction task). Participants performed those tasks twice, in two different sessions. In one session they were exposed to RFs, with half of subjects exposed to GSM signals and the other half exposed to CW signals, while in the other session they were exposed to sham signals. No significant effects of RF exposure on performance for either GSM or CW were found, independent of whether the phone was positioned on the left or on the right side. 相似文献
44.
Peroxisomes and oxidative stress 总被引:4,自引:0,他引:4
The discovery of the colocalization of catalase with H2O2-generating oxidases in peroxisomes was the first indication of their involvement in the metabolism of oxygen metabolites. In past decades it has been revealed that peroxisomes participate not only in the generation of reactive oxygen species (ROS) with grave consequences for cell fate such as malignant degeneration but also in cell rescue from the damaging effects of such radicals. In this review the role of peroxisomes in a variety of physiological and pathological processes involving ROS mainly in animal cells is presented. At the outset the enzymes generating and scavenging H2O2 and other oxygen metabolites are reviewed. The exposure of cultured cells to UV light and different oxidizing agents induces peroxisome proliferation with formation of tubular peroxisomes and apparent upregulation of PEX genes. Significant reduction of peroxisomal volume density and several of their enzymes is observed in inflammatory processes such as infections, ischemia-reperfusion injury and hepatic allograft rejection. The latter response is related to the suppressive effects of TNFalpha on peroxisomal function and on PPARalpha. Their massive proliferation induced by a variety of xenobiotics and the subsequent tumor formation in rodents is evidently due to an imbalance in the formation and scavenging of ROS, and is mediated by PPARalpha. In PEX5-/- mice with the absence of functional peroxisomes severe abnormalities of mitochondria in different organs are observed which resemble closely those in respiratory chain disorders associated with oxidative stress. Interestingly, no evidence of oxidative damage to proteins or lipids, nor of increased peroxide production has been found in that mouse model. In this respect the role of PPARalpha, which is highly activated in those mice, in prevention of oxidative stress deserves further investigation. 相似文献
45.
Kanellis J Kandane RK Etemadmoghadam D Fraser SA Mount PF Levidiotis V Kemp BE Power DA 《Immunology and cell biology》2006,84(1):6-12
AMP-activated protein kinase (AMPK) is a key energy sensor, known to regulate energy metabolism in diverse cell types. Hypoxia is encountered frequently in the microenvironments of inflammatory lesions and is a critical regulator of function in inflammatory cells. Energy deficiency is one of the consequences of hypoxia, but its potential role in modulating leucocyte function has received little attention. Using micropore chemotaxis assays to assess migratory responses of the monocyte-like cell line U937, it was found that the AMPK activators AICAR and phenformin rapidly reduced random migration (chemokinesis) as well as chemotaxis due to stromal cell-derived factor (SDF)1alpha. There was an approximate 50% reduction in both chemokinesis and chemotaxis following 30 min preincubation with both AICAR and phenformin (P < 0.01), and this continued with up to 24 h preincubation. The binding of SDF1alpha to its receptor CXCR4 was unaltered, suggesting AMPK was acting on downstream intracellular signalling pathways important in cell migration. As AMPK and statins are known to inhibit HMG CoA reductase, and both reduce cell migration, the effect of mevastatin on U937 cells was compared with AMPK activators. Mevastatin inhibited cell migration but required 24 h preincubation. As expected, the inhibitory effect of mevastatin was associated with altered subcellular localization of the Rho GTPases, RhoA and cdc42, indicating decreased prenylation of these molecules. Although the effect of AMPK activation was partially reversed by mevalonate, this was not associated with altered subcellular localization of Rho GTPases. The data suggest that activation of AMPK has a general effect on cell movement in U937 cells, and this is not due to inhibition of HMG CoA reductase. These are the first data to show an effect of AMPK on cell movement, and suggest a fundamental role for energy deficiency in regulating cellular behaviour. 相似文献
46.
Embryoid bodies (EBs) are primitive embryonic structures derived from differentiating embryonic stem cells (ESCs). Many techniques
have been used to obtain EBs. Improving the technique of EB formation can help in achieving better results in ESCs differentiation
into neurons, myocardiocytes, haemopoeitic cells, and others. We evaluated the use of Sigmacote™ as a hydrophobic substrate
to improve EB formation. CCE and P19 cell lines were used to obtain EBs and retinoic acid was used to induce neural differentiation.
The results revealed that Sigmacote™, as a hydrophobic substrate, can improve EB formation from ESCs. Our results demonstrate
that the silicon-coating of glass petri dishes by Sigmacote™ is an easy and reproducible technique to enhance EB formation
from murine ESCs and EC cells. 相似文献
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Indole-3-Acetic Acid (IAA) Production in Symbiotic and Non-Symbiotic Nitrogen-Fixing Bacteria and its Optimization by Taguchi Design 总被引:1,自引:0,他引:1
Production of Indole-3-acetic acid (IAA) in 35 different symbiotic and non-symbiotic nitrogen-fixing bacteria strains isolated
from soil and plant roots was studied and assayed by chromatography and colorimetric methods. These bacteria included Agrobacterium, Paenibacillus, Rhizobium, Klebsiella
oxytoca, and Azotobacter. The best general medium and synergism effects of isolates for IAA production were investigated. Effects of different variables
containing physical parameters and key media components and optimization of condition for IAA production were performed using
the Design of Experiments. Qualitek-4 (W32b) software for automatic design and analysis of the experiments, both based on
Taguchi method was used. The results showed that Rhizobium strains, symbiotic, and Paenibacillus non-symbiotic bacteria yielded the highest concentrations of IAA (in the range of 5.23–0.27 and 4.90–0.19 ppm IAA/mg biomass,
respectively) and IAA production was increased by synergism effect of them. Yeast Extract Mannitol medium supplemented with
l-tryptophan was the best general medium for IAA production. The analysis of experimental data using Taguchi method indicated
that nitrogen source is very prominent variable in affecting the yield and mannitol as carbon source, potassium nitrate (1%),
and l-tryptophan (3 g/l) as nitrogen sources after 72-h incubation at 30°C were the optimum conditions for production of IAA. 5.89 ppm
IAA/mg biomass was produced under these optimal conditions. 相似文献
49.
A simple control strategy is proposed and applied to a class of non-linear systems that have abundant sensory and actuation channels as in living systems. The main objective is the independent control of constrained trajectories of motion, and control of the corresponding constraint forces. The peripheral controller is a proportional, derivative and integral (PID) controller. A central controller produces, via pattern generators, reference signals that are the desired constrained position and velocity trajectories, and the desired constraint forces. The basic tenet of the this hybrid control strategy is the use of two mechanisms: 1. linear state and force feedback, and 2. non-linear constraint velocity feedback - sliding mode feedback. The first mechanism can be envisioned as a high gain feedback systems. The high gain attribute imitates the agonist-antagonist co-activation in natural systems. The strategy is applied to the control of the force and trajectory of a two-segment thigh-leg planar biped leg with a mass-less foot cranking a pedal that is analogous to a bicycle pedal. Five computational experiments are presented to show the effectiveness of the strategy and the performance of the controller. The findings of this paper are applicable to the design of orthoses and prostheses to supplement functional electrical stimulation for support purposes in the spinally injured cases. 相似文献
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