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Detailed flow patterns in the nasal cavity. 总被引:9,自引:0,他引:9
The human nasal cavity filters and conditions inspired air while providing olfactory function. Detailed experimental study of nasal airflow patterns has been limited because of the complex geometry of the nasal cavity. In this work, particle image velocimetry was used to determine two-dimensional instantaneous velocity vector fields in parallel planes throughout a model of the nasal cavity that was subjected to a nonoscillatory flow rate of 125 ml/s. The model, which was fabricated from 26 computed tomography scans by using rapid prototyping techniques, is a scaled replica of a human right nasal cavity. The resulting vector plots show that the flow is laminar and regions of highest velocity are in the nasal valve and in the inferior airway. The relatively low flow in the olfactory region appears to protect the olfactory bulb from particulate pollutants. Low flows were also observed in the nasal meatuses, whose primary function has been the subject of debate. Comparison of sequentially recorded data suggests a steady flow. 相似文献
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Divergence time estimates of mammals from molecular clocks and fossils: Relevance of new fossil finds from India 总被引:1,自引:0,他引:1
G. V. R. Prasad 《Journal of biosciences》2009,34(5):649-659
This paper presents a brief review of recent advances in the classification of mammals at higher levels using fossils and
molecular clocks. It also discusses latest fossil discoveries from the Cretaceous — Eocene (66–55 m.y.) rocks of India and
their relevance to our current understanding of placental mammal origins and diversifications. 相似文献
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Sudha Rao Gopalakrishna Kamath Gururaj Maralihalli Anil S. Bhagwat 《Photosynthesis research》1987,12(2):155-164
The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD
-aminolevulinic acid dehydratase
- FMN
flavin mononucleotide
- O2
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superoxide
- H2O2
hydrogen peroxide
- 102
singlet oxygen
- LA
levulinic acid
- PBG
porphobilinogen
- BSA
bovine serum albumin
- BME
2-mercaptoethanol
- SOD
superoxide dismutase
- pHMB
para-hydroxymercuribenzoate
- DTT
dithiothreitol
- FAD
flavin adenine dinucleotide
- NADH
nicotinamide adenine dinucleotide 相似文献
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The Role of Gravity in Apical Dominance : Effects of Clinostating on Shoot Inversion-Induced Ethylene Production, Shoot Elongation, and Lateral Bud Growth
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Shoot inversion-induced release of apical dominance in Pharbitis nil is inhibited by rotating the plant at 0.42 revolutions per minute in a vertical plane perpendicular to the axis of rotation of a horizontal clinostat. Clinostating prevented lateral bud outgrowth, apparently by negating the restriction of the shoot elongation via reduction of ethylene production in the inverted shoot. Radial stem expansion was also decreased. Data from experiments with intact tissue and isolated segments indicated that shoot-inversion stimulates ethylene production by increasing the activity of 1-aminocyclopropane-1-carboxylic acid synthase. The results support the hypothesis that shoot inversion-induced release of apical dominance in Pharbitis nil is due to gravity stress and is mediated by ethylene-induced retardation of the elongation of the inverted shoot. 相似文献