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31.
Buoyancy effect on forced convection in the leaf boundary layer 总被引:1,自引:0,他引:1
Abstract. Mixed convection (forced convection plus free convection) in the leaf boundary layer was examined by air flow visualization and by evaluation of the boundary layer conductance at different leaf-air temperature differences ( T L - T A ) under low wind velocities. The visualized air flow was found to become more unstable and buoyant at higher T L - T A . An ascending longitudinal plume was induced along the upper surface, and the air flow along the lower surface ascended after passing the trailing leaf edge. The air flow modified by buoyancy was considered to result in an increase in boundary layer conductance ( G A ) for mixed convection, which became higher with higher T L - T A as compared with the conductance for pure forced convection without buoyancy. This increase in G A appeared larger at larger Grashof number (Gr) and at smaller Reynolds number (Re). The dependences of buoyancy effect on Gr and Re were related to 'edge-effects'. 相似文献
32.
Ignacio García-De La Torre Mario Salazar-Páramo Gerardo Salmón-De La Torre 《Molecular biology reports》1996,23(3-4):153-157
Mixed connective tissue disease (MCTD) was described as a distinct clinical syndrome in 1972. Since then many cases have been reported in the literature worldwide. In this study we present our experience with a group of 17 Mexican patients with this syndrome, and we analyze their clinical and serological features, as well as the causes of death in these patients. The patients are Mexican mestizos living in Guadalajara and most of them have been followed-up at Hospital General de Occidente for a period of 1–10 years. The female/male ratio was 16:1, and their age ranged from 14–55 years with a mean of 29 years. The disease duration has ranged from 1–17 years, with a mean of 6 years. Among the clinical manifestations we have found a high frequency of lymphadenopathy when compared with published series (13/17 or 76%), and the laboratory findings in our patients included a very high polyclonal increase of gammaglobulins (93%), lymphopenia (76%), direct immunofluorescence speckled nuclear epidermal deposits in skin biopsies (75%) and positive rheumatoid factor (65%). Other clinical and serological features were similar to those reported in other series of patients with MCTD. Six of the 17 patients have died (35%), and in 3 of them (17.5%) the cause of death was due to an infectious disease that suddenly presented, and apparently was not related to a concomitant high dose of steroids or malnutrition in the patients. It seems that in addition to the already well known autoimmune abnormalities that occur in MCTD, there are other features like the presence of lymphadenopathy, the high polyclonal increase of gammaglobulins, and the lymphopenia, that reflect the profound disturbance of the immune system in this syndrome, possibly contributing to the sudden appearance of a severe infectious disease in some of our patients.Abbreviations ANA
antinuclear antibody
- CIE
counterimmunoelectrophoresis
- MCTD
mixed connective tissue disease
- PHA
passive hemagglutination
- PM
polymyositis
- RF
rheumatoid factor
- SLE
systemic lupus erythematosus
- SS
systemic sclerosis (SS) 相似文献
33.
Soil P resources,plant growth and rooting characteristics in nutrient poor upland grasslands 总被引:1,自引:1,他引:0
A. E. S. Macklon L. A. Mackie-Dawson A. Sim C. A. Shand A. Lilly 《Plant and Soil》1994,163(2):257-266
A field study was undertaken to establish the demand for P by mixed herbage, manipulated by cutting regimes, and the extent to which orthophosphate alone in soil solution could meet this demand from three cambisols derived from different parent materials. Differences in soil types were sufficient to produce significantly different rooting patterns at each site. Yields for 7-and 10-cm treatments generally exceeded those for swards cut to 2-and 4-cm. The highest yields were from plots cut once at the end of the season, or when herbage was cut in June and October only. Yields fell in the second season by an average of 30%. Two cuts in the season resulted in almost twice the P uptake compared with other treatments, leading to the view that a silage cut stimulated root growth. Rooting was deepest in Tarves Association soil (Dystric cambisol), densest in Insch Association soil (Eutric cambisol) and intermediate in Foudland Association soil (Dystric cambisol) but herbage yield at each site was similar. Whole season mean P and N content in roots ranged from 1.0 to 3.4 and from 8.1 to 27.9 mg g–1 dry weight, respectively. The lowest values were in once cut herbage and were half those in herbage cut in June and October only. Data for the total P resources of the soils, extractable P, and shoot and root P at each site are presented together with data for P in soil solution (principally organic) from an associated soil solution study. There was a disparity between daily uptake and orthophosphate in soil solution. These findings suggested that it was probable that soluble organic forms of P are important for P nutrition in these nutrient poor soils, and could account for the excess of observed P uptake (from soils low in P) over that predicted by mechanistic mathematical models. 相似文献
34.
Ch. Sasikala Ch. V. Ramana G. S. Prasad 《World journal of microbiology & biotechnology》1994,10(2):221-223
Production of H2 from glucose by an anoxygenic phototrophic bacterium (Rhodobacter sphaeroides), a cyanobacterium (Synechococcus cedrorum) and a heterotrophic bacterium (Pseudomonas fluorescens) was tested individually and in mixed cultures of various combinations in light. H2 production was maximal with a mixed culture of R. sphaeroides and P. fluorescens, which could be further enhanced by immobilization of the bacteria in alginate gel. Inhibition of H2 photoproduction was observed in a mixture of S. cedrorum and P. fluorescens and a co-culture of all the three organisms.Ch. Sasikala and Ch. V. Ramana are and G. S. Prasad was with the Microbial Biotechnology Laboratory, Department of Botany, Osmania University, Hyderabad-500 007, India. G. S. Prasad is now with the Microbial Type Culture Collection Centre (MTCC), IMTECH, Chandigar, India. 相似文献
35.
36.
M. Kawasaki 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,174(2):133-144
Gymnarchus niloticus, a wave-type African electric fish, performs its jamming avoidance response by relying solely upon afferent signals and does not use corollary discharges from the pacemaker nucleus in the medulla which generates the rhythmicity of electric organ discharges. This is in sharp contrast to the mode of sensory processing found in closely related African pulse-type electric fishes where afferent signals are gated by corollary discharges from the pacemaker for the distinction of exafferent and reafferent stimuli. Does Gymnarchus still possess a corollary discharge mechanism for other behavioral tasks but does not use it for the jamming avoidance response? In this study, I recorded from and labeled medullary neuronal structures that either generate or convey the pacemaker signal for electric organ discharges to examine whether this information is also sent directly to any sensory areas. The pacemaker nucleus was identified as the site of generation of the pacemaking signal. The pacemaker neurons project exclusively to the lateral relay nucleus which, in turn projects exclusively to the medial relay nucleus. Neurons in the medial relay nucleus send unbranched axons to the spinal electromotoneurons. These neurons are entirely devoted to drive the electric organ discharges, and no axon collaterals from these neurons were found to project to any sensory areas. This indicates that Gymnarchus does not possess the neuronal hardware for a corollary discharge mechanism. 相似文献
37.
Pyridine and its derivatives have been found as pollutants in the environment. Although alkylpyridines constitute the largest class of pyridines contaminating the environment, little information is available concerning the fate and transformation of these compounds. In this investigation ethylpyridines have been used as model compounds for investigating the biodegradability of alkylpyridines. A mixed culture of ethylpyridine-degrading microorganisms was obtained from a soil that had been exposed to a variety of pyridine derivatives for several decades. The enrichment culture was able to degrade 2-, 3-, and 4-ethylpyridine (100 mg/L) at 28° C and pH 7 within two weeks under aerobic conditions. The degradation rate was greatest for 2-ethylpyridine and least for 3-ethylpyridine. Transformation of ethylpyridines was dependent on substrate concentration, pH, and incubation temperature. Studies on the metabolic pathway of 4-ethylpyridine revealed two products; these chemicals were identified by MS and NMR analyses as 4-ethyl-2(1H)-pyridone and 4-ethyl-2-piperidone. 6-Ethyl-2(1H)-pyridone was determined to be a product of 2-ethylpyridine degradation. These results indicate that the transformation mechanism of ethylpyridines involves hydroxylation and reduction of the aromatic ring before ring cleavage. 相似文献
38.
田林老山中山两类森林凋落物研究 总被引:15,自引:2,他引:13
田林老山中山两类森林凋落物研究梁宏温(广西农学院林学分院,南宁530001)StudiesontheLitterfallofTwoForestTypcsinMid—AltitudeofLaoshanMountaininTianlinCounty.¥L... 相似文献
39.
Kinetics of microbial growth with mixtures of carbon sources 总被引:11,自引:0,他引:11
40.
Krešimir Begović Jonathan S. Schurman Marek Svitok Jakob Pavlin Thomas Langbehn Kristyna Svobodová Martin Mikoláš Pavel Janda Michal Synek William Marchand Lucie Vitková Daniel Kozák Ondrej Vostarek Vojtech Čada Radek Bače Miroslav Svoboda 《Global Change Biology》2023,29(1):143-164
In a world of accelerating changes in environmental conditions driving tree growth, tradeoffs between tree growth rate and longevity could curtail the abundance of large old trees (LOTs), with potentially dire consequences for biodiversity and carbon storage. However, the influence of tree-level tradeoffs on forest structure at landscape scales will also depend on disturbances, which shape tree size and age distribution, and on whether LOTs can benefit from improved growing conditions due to climate warming. We analyzed temporal and spatial variation in radial growth patterns from ~5000 Norway spruce (Picea abies [L.] H. Karst) live and dead trees from the Western Carpathian primary spruce forest stands. We applied mixed-linear modeling to quantify the importance of LOT growth histories and stand dynamics (i.e., competition and disturbance factors) on lifespan. Finally, we assessed regional synchronization in radial growth variability over the 20th century, and modeled the effects of stand dynamics and climate on LOTs recent growth trends. Tree age varied considerably among forest stands, implying an important role of disturbance as an age constraint. Slow juvenile growth and longer period of suppressed growth prolonged tree lifespan, while increasing disturbance severity and shorter time since last disturbance decreased it. The highest age was not achieved only by trees with continuous slow growth, but those with slow juvenile growth followed by subsequent growth releases. Growth trend analysis demonstrated an increase in absolute growth rates in response to climate warming, with late summer temperatures driving the recent growth trend. Contrary to our expectation that LOTs would eventually exhibit declining growth rates, the oldest LOTs (>400 years) continuously increase growth throughout their lives, indicating a high phenotypic plasticity of LOTs for increasing biomass, and a strong carbon sink role of primary spruce forests under rising temperatures, intensifying droughts, and increasing bark beetle outbreaks. 相似文献