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31.
电刺激兔延髓腹侧化学敏感区和压力敏感区对呼吸、血压,的影响及其中枢递质机制 总被引:1,自引:0,他引:1
电刺激麻醉兔延髓腹侧化学敏感区头端区引起潮气量(V_T)增加,呼吸频率(f)增快;电刺激压力敏感区(中间区)则使V_T减小,f亦增快。弱刺激时,两者均产生降压反应;刺激增强可诱发双相或升压反应。在出现周期性呼吸时,电刺激化学敏感区可使呼吸节律正常化、V_T增大,而电刺激压力敏感区则导致呼吸暂停。电刺激压力敏感区时,吸气时间(TI)和呼气时间(T_E)均缩短,以T_E变化更明显;由于V_T减小和T_I缩短,V_T/T_I保持相对不变,提示吸气终止的中枢阈值降低。在准备刺激的相应局部预先应用阿托品,可使电刺激化学敏感区产生的通气增强效应翻转,而对电刺激压力敏感区引起的通气抑制无明显影响;用印防己毒素则可选择性消除电刺激压力敏感区的通气抑制和降压效应。本工作表明延髓腹侧存在两个不同的中枢机制,其中化学敏感区产生的通气增强与胆碱能系统有关;压力敏感区产生的通气减弱效应与GABA系统有关。 相似文献
32.
Takashi Kohyama 《Journal of plant research》1988,101(2):207-212
A simple relation (v-lnB) (u-lnx)=c was recognized betweenx as dbh (or individual basal area) andB as the cumulative basal area abovex, for various stands of warm-temperate rain forests of Yakushima Island, southern Japan (v, u andc, parameters). The model parameters explained a difference in the pattern of stand development between secondary succession
after clear-felling and gap regeneration within primary forests. 相似文献
33.
Markus Riederer Kathrin Kurbasik Rainer Steinbrecher Andreas Voss 《Trees - Structure and Function》1988,2(3):165-172
Summary A method for the rapid determination of the lengths and surface areas of very large samples of needles of Picea abies (L.) Karst. using a computer-aided image analysis system was developed. Two independent methods for measuring non-destructively the volumes of individual needles and of all needles attached to a twig were devised. The surface areas and lengths of about 38000 needles sampled from the three youngest needle age-classes (1986, 1985, 1984) of 48 trees approximately 130 years old at four sites in the Fichtelgebirge mountains (N. E. Bavaria, FRG) were measured. The frequency distributions of lengths and areas for each site and age-class are given. Variability of needle size was fairly large. Even though the sites differed in climate, soil, and air pollution levels no consistent effect of these factors on needle size could be detected. Needle lengths and surface areas did not correlate with either the total chlorophyll content of the needles or the degree of crown thinning. The needle surface area (in mm2) of fully developed P. abies needles can be estimated by the empirical equation surface area = 4.440 x needle length -24.8 (r = 0.937), and the needle volume (in mm3) by needle volume = 0.208 x projected needle area
1.353 (r = 0.969). 相似文献
34.
Summary Two alternative estimators of individual tree leaf area (A1) area are used to derive estimates of leaf-area index (L) for 40 plots in Pinus contorta Dougl. stands. One estimator of A1 is based on the common assumption of a constant ratio between A1 and sapwood cross-sectional area at breast height (As). The second estimator of A1 accounts for tree-to-tree variation in the relation between A1 and As. The apparent relationship between stand growth and leaf-area index is strongly dependent on the way leaf area is estimated. When L is derived from a constant A1As ratio, stand growth appears to be strongly correlated with L. However, when L is based on estmates of A1 that account for tree-to-tree variation in the A1 — As relation, stand growth is seen to be only weakly related to L. Stand structure, quantified as percent live-crown, accounts for a great deal of the observed variation in leaf-area efficiency. These contrasting relationships illustrate the importance of unbiased estimates of L in interpreting the link between stand-level processes and leaf area.Utah Aggriculural Experiment Station Journal Paper No. 3333 相似文献
35.
Masayuki Nishida Hirotaka Nishijima Kazuya Yonezawa Isao Sato Teisuke Anzai Kohichi Okita Hisakazu Yasuda 《European journal of applied physiology and occupational physiology》1992,64(6):528-533
To assess exercise energy metabolism of forearm flexor muscles in rowers, six male student rowers and six control subjects matched for age and sex were studied using phosphorus-31 magnetic resonance spectroscopy (31P-MRS). Firstly, to adjust for the effect of differences in cross-sectional muscle area, the maximal cross-sectional area (CSAmax) of the forearm flexor muscles was estimated in each individual using magnetic resonance imaging. Multistage exercise was then carried out with an initial energy production of 1 J.cm-2 CSAmax for 1 min and an increment of 1 J.cm-2 CSAmax every minute to the point of muscle exhaustion. A series of measurements of 31P-MRS were performed every minute. The CSAmax was significantly greater in the student rowers than in the control subjects [19.8 (SD 2.2) vs 17.1 (SD 1.2) cm2, P less than 0.05]. The absolute maximal exercise intensity (J.min-1) was greater in the rowers than in the control subjects. However, the maximal exercise intensity per unit of muscle cross sectional area (J.min-1.cm-2) was not significantly different between the two groups. During mild to moderate exercise intensities, a decrease in phosphocreatine and an increase in inorganic phosphate before the onset of acidosis were significantly less in the rowers, indicating a requirement of less adenosine 5'-diphosphate to drive adenosine 5'-triphosphate production. The onset of acidosis was also significantly delayed in the rowers. No difference was observed in forearm blood flow between the two groups at the same exercise intensity (J.min-1.cm-2).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
36.
Toshiyuki Sato 《Ecological Research》1992,7(1):1-7
Gametophyte populations inAthyrium brevifrons were analysed with respect to population size and surviving area (%) of individual thalli in a transplant garden at Sapporo
during 5–26 April 1983, to study the safe-microsite for gametophyte establishment in nature. Spores dispersed in August 1982
germinated and grew into thalli of various widths (<10 mm); 10.3% of the thalli matured by early October 1982. Maturation
was attained by gametophytes of width 4–7 mm. The number of gametophytes gradually decreased with increasing width. By April
1983, 20.5% of total gametophytes were mature with a mode of 5–6 mm in width. The relative number of gametophytes with surviving
area of 2–20% increased and that of 85–100% decreased in accordance with collection days delayed until after snow-melt. Surviving
area (%) on gametophyte of all widths decreased with decreasing soil moisture contents. In particular, immature gametophytes
of 2–4 mm width showed a significant correlation (P<0.01) between soil moisture content and relative number of gametophytes with 0–20% surviving area and mean surviving area
(%) of every width of thalli. The spring desiccation might be a factor that reduces or limits gametophyte populations in nature. 相似文献
37.
阔叶树的叶形曲线方程:—适于叶面积计算的数学模型 总被引:3,自引:0,他引:3
树木的叶形可以看作一个平面几何图形。这种几何图形可用解析方程给予表达,我们把这种解析方程称为叶形曲线方程。由于叶形是一个左右对称,而上下不对称的图形,也就是说叶的最宽处绝大多数不在叶的中部,少数在 相似文献
38.
电刺激乌拉坦麻醉的大鼠下丘脑外侧区(LH)可使缰核(Hb)内51.0%的单位兴奋,15.7%的单位抑制,其中发生兴奋反应的单位有15.4%可被逆行激活。双侧Hb内微量注射利多卡因,电刺激LH引起的升压反应可被阻断42.0±28.0%;反之,双侧LH内微量注射利多卡固,电刺激Hb引起的升压反应可被阻断62.0±26.4%。结果表明,LH与Hb在血压调节中相互依赖,具有协同作用。 相似文献
39.
黄淮海平原高产田作物群体结构特征 总被引:9,自引:5,他引:4
本文利用实测资料分析了高产田作物群体结构特征。精播高产栽培麦田春季最大蘖数12×10~6/ha,群体最大叶面积指数5.5—6.0,成穗4.5—5.25×10~6/ha。传统高产栽培麦田春季最大蘖数15—18×10~6/ha,群体最大叶面积指数6.0—6.5,成穗6.0—7.5×10~6/ha。小麦营养生长与生殖生长期叶日积比,精播高产栽培麦田是1∶0.89,传统高产栽培麦田为1∶0.73。夏玉米种植密度主要受叶倾角的影响。紧凑型玉米品种的叶倾角大于65°,种植密度7.5—8.25×10~4/ha;平展型玉米品种的叶倾角小于50°,种植密度5.25—6.0×10~4/ha。 相似文献
40.
A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and
maximum depth is 167 m. The surface area covers 9.8 km2, and the lake contains 0.98 km3 volume of water.
Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient
was 8.3 × 10−2. The concentration of Chl.-a was in the range of 0.06–0.46 mg m−3, and total nitrogen was 18–30 μg 1−1. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks
and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity,
and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely
low.
The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species
of Copepoda. The zooplankton density range was 6200–16200 individuals m−3. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983. 相似文献