心肌电兴奋传导速度对心律失常影响的仿真研究

心电场是由心肌的电活动产生的。心肌细胞的电特性及心肌细胞间的传导关系决定了体表电位的分布及心电图的变化。心肌电兴奋传导速度则是影响心肌间兴奋传导关系的重要参数之一。由于很难通过实验方法来人为改变电兴奋传导速度,因而临床上有关该参数对心律影响的定量知识相当缺乏。本文采用真实三雏躯干模型及心脏模型,对心肌电兴奋传导速度与心律变化的关系进行定量仿真研究。结果表明,兴奋传导速度决定了整个心电图的变化,而局部普通心肌的传导速度在相当范围内变化似乎对心电图影响不明显,但传导速度超过一定范围后可能产生突变。     

Global vegetation models: incorporating transient changes to structure and composition

Abstract. We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.     

Chromosome translocations in wild populations of tetraploid emmer wheat in Israel and Turkey

Translocation frequencies (as compared to the standard chromosome arrangement typified by that in Chinese Spring) in 9 or more genotypes from each of 15 populations of Triticum dicoccoides in Israel were determined. Data also were obtained from 2 genotypes of the southernmost population (Jaba). A single population from Turkey was also investigated. There were 119 genotypes with translocations in the sample of 171 genotypes investigated (70%). The frequency of translocations in different populations varied from 0.27 to 1.00, and all populations had 1 or more genotypes with one or more translocations. Some populations such as Qazrin appeared to be homogeneous for translocations, but most populations were heterogeneous. A sample of 17 genotypes from 12 of the populations were crossed with the Langdon D-genome disomic substitutions to determine the identity of the chromosomes involved in the translocations. There were nine genotypes with translocations and with the exception of a 2A/2B translocation, none of them involved the same chromosomes. The B-genome chromosomes were involved in translocations more frequently than the A-genome chromosomes. Translocation frequencies (TF) of the various populations were correlated with environmental variables, primarily with water availability and humidity, and possibly also with soil type. In general, TF was higher in peripheral populations in the ecologically heterogeneous frontiers of species distribution than in the central populations located in the catchment area of the upper Jordan valley.     

Larval habitat preference of the endemic Hawaiian midge,Telmatogeton torrenticola Terry (Telmatogetoninae)

Telmatogeton torrenticola Terry is a large endemic chironomid (lastinstar >20 mm) commonly found in high gradient Hawaiian streams on smoothrock surfaces with torrential, shallow flow and in the splash zones ofwaterfalls. We have quantified benthic water flow in larval habitat in a 50m segment of Kinihapai Stream, Maui using a thermistor-based microcurrentmeter. Under base flow conditions at sites suitable for larval attachment,depth was measured and bottom water velocity measurements were made 2 mmabove populations. Larval densities ranged from 386.9–1178m^–2, habitat bottom water velocities from 13.4–64.2 cms^–1, and water depths from 1.5–50 cm. Bottom velocitiesof sites with zero larvae ranged from 20.8–21.8 cm s^–1with depths from 50 to >160 cm. Larval densities were greatest inareas with high bottom water velocities and shallow depths. Stepwisemultiple regression analyses showed that density could be confidentlypredicted best by Froude number (r=0.81; p=0.008). In the absence of Froudenumber as a regression term, the best variable to predict larval density wasbottom velocity ratio: relative depth ratio (r=0.75; p=0.019). In addition,the torrential habitat of the larvae was always characterized by aperiphyton community that appeared to be the primary food resource for thelarvae. These data suggest that torrential flows over appropriate substratesare important factors regulating habitat availability for T. torrenticolaand that reduced discharge (e.g. affected by water diversions) couldsignificantly reduce the amount of available habitat for this organism andother flow sensitive stream fauna.     

Evidence for a folded conformation of the cell wall protein fromAcetabularia (Polyphysa) cliftonii

Summary The cell wall protein fromAcetabularia has a non-random structure in aqueous solution at pH 5.3, as determined on the basis of intrinsic viscosity, sedimentation velocity and small angle X-ray scattering experiments. This non-random structure is stable in a pH range of 4.5–6.8, as observed on the basis of circular dichroism and viscosity measurements, supporting that the cell wall protein has a specific folded structure. All hydrodynamic measurements, including small angle X-ray scattering in solution, in this pH range are consistent with a prolate ellipsoid model for the shape of this protein, with overall dimensions ofc=86.0 Å,b=7.0 Å, anda=7.5 Å, and with a radius of gyration ofR=39.5 Å. The possibility of a coiled shape was investigated using a worm-like chain model, but it was inconsistent with the experimental data. Instead, a filled particle with uniform density which is equivalent in the scattering behavior is proposed. By a comparison of the observed radius of gyration, R_g=39.5 Å, and the radius of gyration of the cross section,R _c =7.5 Å, we were able to describe the cell wall protein in terms of a prolate ellipsoid of revolution. Comparisons of the experimental scattering curve, plotted as logl (h) versus logh, with the corresponding plots of normalized intensities, calculated for particles of particular shape and various axial ratios indicate a very asymmetric shape for the cell wall protein fromAcetabularia.This research was supported by a grant of the Deutsche Forschungsgemeinschaft.     

ATP-dependent calcium transport and its correlation with Ca2+-ATPase activity in basolateral plasma membranes of rat duodenum

Isolated basolateral plasmamembrane vesicles from rat duodenum epithelial cells exhibit ATP-dependent calcium-accumulation and Ca²⁺-dependent ATPase activity. Calcium accumulation stimulated by ATP is prevented by the calcium ionophore A23187, inhibited 80% by 0.1 mM orthovanadate but is not effected by oligomycin. Calcium accumulation is not observed with the substrate β-γ-(CH₂)-ATP, ADP and p-nitrophenyl phosphate. Kinetic studies reveal an apparent K_m of 0.2 μM Ca²⁺ and a V_max of 5.3 nmol Ca²⁺/min per mg protein for the ATP-dependent calcium-uptake system. Calmodulin and phenothiazines have no effect on calcium accumulation in freshly prepared membranes, but small effects are inducable after a wash with a 5 mM EGTA. The kinetic parameters of Ca²⁺-ATPase are: K_m = 0.25 μM Ca²⁺ and V_max = 19.2 nmol P_i/min per mg protein. Three techniques, osmotic shock, treatment with Triton X-100 or the channel-forming peptide alamethacin, reveal that about 40% of the vesicles are resealed. Assuming that half of the resealed vesicles have an inside-out orientation, the V_max of ATP-dependent calcium uptake amounts to 25 nmol Ca²⁺/min per mg protein and of the Ca²⁺-ATPase to 23 nmol P_i/min per mg protein. The close correlation between kinetic parameters of Ca²⁺-ATPase and ATP-dependent calcium-transport strongly suggests that both systems are expressions of a Ca²⁺-pump located in duodenal basolateral plasma membranes.     

中国柯属5种资源植物潜在地理分布及其对气候变化的响应

利用最大墒模型和地理信息系统软件对柯属（Lithocarpus）5种资源植物在我国的适宜分布区进行了定量预测,并对未来不同气候情景下其分布区的变化进行了分析。结果显示：木姜叶柯（L.litseifolius（Hance）Chun.）在我国秦岭淮河以南广泛分布,短尾柯（L.brevicaudatus（Skan）Hay.）主要分布在我国亚热带中东部区域;木姜叶柯在未来气候（2061-2080年）RCP2.6、RCP8.5两种情景下适生区面积分别减少了5.1%和3.0%,而短尾柯却分别增加了0.5%和1.5%。白柯（L.dealbatus（Hook.f.et Thoms.ex DC.）Rehd.）适宜区主要分布在云南北部、四川南部,烟斗柯（L.corneus（Lour.）Rehd.）主要分布在两广省份的南亚热带地区。白柯和烟斗柯在RCP2.6情景下适生区面积分别减少了12.1%和17.8%,在RCP8.5情景下分别减少了3.5%和15.9%,这两个种的适宜区面积减少较多。厚斗柯（L.elizabethae（Tutch.）Rehd.）主要分布于广西,在两种情景下适宜区面积分别增加了7.3%和6.3%。研究结果表明,由于分布区存在差异,同属不同物种的未来分布对气候变化的响应不同。     

Head tube: a simple device for estimating velocity in running water

Construction and operation of a head tube are described. A head tube is an inexpensive, easily-built alternative to a current meter for measuring water velocity in streams and rivers. When water flowing in a channel is obstructed by an object, its depth increases at the point of zero velocity (stagnation zone). The difference between the flowing-water depth and depth in the stagnation zone is the head (h). A head tube consists of a clear, hollow, 2.5 cm diameter acrylic tube and a sliding sleeve made of clear plastic. The tube is placed vertically on the river bottom. The difference (head) between water level inside the tube and the height of water against the tube's upstream face is measured against a scale (cm s^–1) drawn on the sleeve, which provides a direct reading of velocity. Graduations of the scale are calculated from a hydrodynamic equation relating mean velocity () to head (h): = (2gh)^0.5, whereg is acceleration due to gravity. When tested in a laboratory flume, the head tube gave very precise estimates of velocity (R ² of relationship = 0.98), although the original calibration scale overestimated current meter-measured velocity by 22 percent. The relationship between head tube and current meter estimates of mean velocity determined in a river with stony substrate was less precise than the correspondence observed in the laboratory (R ² = 0.81). However, estimates of discharge based on head tube measurements were within 8 percent of estimates based on current meter readings.     

Interpretation of sedimentation data measured in a former tidal channel Lake Volkerak

In Lake Volkerak, situated in the southwest of the Netherlands, downward settling fluxes are related to external inputs of suspended solids and wind action. The settling fluxes, measured using sediment traps, were 55 g (dw) m ^–2 d ^–1 on average. The ratio of metal concentration to scandium concentration was used to discriminate between external (polluted) suspended solids and internal (relatively clean) suspended solids. Generally, the contribution of the river suspended solids was small compared to that of resuspended material; the river-transported material was mainly deposited in the centre and to the east of the lake. The amount of material trapped increased substantially with increasing wind velocity.A simple model was used to interpretate the data. This model does not have a predictive capacity, but can be used to interpret and assess the significance of material retained in the sediment traps. Erosion was related to the wind velocity, using an empirical relationship between the orbital velocity of the wind-generated waves at the bottom and the wind velocity. The critical wind velocity for erosion to occur was estimated to be 5.5 m s^–1. The extremely high amounts retained in the sediment traps in shallow areas during storms emphasised the importance of these wind conditions for the transport of fine sediments.     

Anisakis simplex and Anisakis physeteris: physicochemical properties of larval and adult hemoglobins

To resolve the taxonomic relationship between two types of parasitic nematode larvae (Type I and II) and two species of parasitic nematode adults (Anisakis simplex and A. physeteris) of the aquatic ascarid genus Anisakis, collected in Japanese coastal water, a comparison was made of their hemoglobins' physicochemical properties. The larval hemoglobins were more similar to each other in electrophoretic pattern than to either adult, indeed there were few similarities whatsoever in these patterns of larval and adult hemoglobins. However, isoelectric points were 6.2 for the Type I larva and for A. simplex and 5.4 for the Type II larva and for A. physeteris. All samples showed identical patterns in spectrophotometric scanning. The circular dichroic spectra of the samples were also virtually identical, although slight differences were noted in the oxygenated hemoglobins; the Type II larva and A. physeteris exhibited a small positive peak at 575 nm but the Type I larva and A. simplex exhibited a much smaller peak (negative position). The sedimentation coefficients of the samples possessed essentially identical values (11.2–12.4). The molecular weights of the samples were estimated, roughly, to be in the range 33 to 43 × 10⁴ by thin-layer chromatography on Sephadex G-200. The evidence suggests that a relationship may exist between the Type I larva and A. simplex, and between the Type II larva and A. physeteris.