Separated flow demonstrated by digitized cineangiography compared with LDV

In order to demonstrate separated flow in vivo, a method for the computerized analysis of cineangiographies has been developed, tested in vitro, and compared with LDV. A pulsatile flow was created in a glass model bifurcation, and velocity profiles were obtained with LDV at several phase angles. The flow was cinefilmed during contrast injection and the images were digitized. The computer then transformed the image sequence into parametric images representing arrival times of the contrast. The separation regions demonstrated with LDV were identified as areas with delayed contrast arrival. A preliminary analysis of a cineangiography in vivo is also included.     

Development of a platelet adhesion transport equation for a computational thrombosis model

Thrombosis is a significant issue for cardiovascular device development and use. While thrombosis models are available, very few are device-related and none have been thoroughly validated experimentally. Here, we introduce a surface adherent platelet transport equation into a continuum model to account for the biomaterial interface/blood interaction. Using a rotating disc system and polyurethane-urea material, we characterize steady and pulsatile flow fields using laser Doppler velocimetry. In vitro measurements of platelet adhesion are used in combination with the LDV data to provide further experimental validation. The rotating disc system is computationally studied using the device-induced thrombosis model with the surface platelet adherent transport equation. The results indicate that the flow field is in excellent agreement to the experimental LDV data and that the platelet adhesion simulations are in good agreement with the in vitro platelet data. These results provide good evidence that this transport equation can be used to express the relationship between blood and a biomaterial if the correct platelet adhesion characteristics are known for the biomaterial. Further validation is necessary with other materials.     

Experimental technique of measuring dynamic fluid shear stress on the aortic surface of the aortic valve leaflet

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact cause and mechanism of the progression of AV calcification is unknown, although mechanical forces have been known to play a role. It is thus important to characterize the mechanical environment of the AV. In the current study, we establish a methodology of measuring shear stresses experienced by the aortic surface of the AV leaflets using an in vitro valve model and adapting the laser Doppler velocimetry (LDV) technique. The valve model was constructed from a fresh porcine aortic valve, which was trimmed and sutured onto a plastic stented ring, and inserted into an idealized three-lobed sinus acrylic chamber. Valve leaflet location was measured by obtaining the location of highest back-scattered LDV laser light intensity. The technique of performing LDV measurements near to biological surfaces as well as the leaflet locating technique was first validated in two phantom flow systems: (1) steady flow within a straight tube with AV leaflet adhered to the wall, and (2) steady flow within the actual valve model. Dynamic shear stresses were then obtained by applying the techniques on the valve model in a physiologic pulsatile flow loop. Results show that aortic surface shear stresses are low during early systole (<5 dyn/cm2) but elevated to its peak during mid to late systole at about 18-20 dyn/cm2. Low magnitude shear stress (<5 dyn/cm2) was observed during early diastole and dissipated to zero over the diastolic duration. Systolic shear stress was observed to elevate only with the formation of sinus vortex flow. The presented technique can also be used on other in vitro valve models such as congenitally geometrically malformed valves, or to investigate effects of hemodynamics on valve shear stress. Shear stress data can be used for further experiments investigating effects of fluid shear stress on valve biology, for conditioning tissue engineered AV, and to validate numerical simulations.     

Swimming in formation in krill (Euphausiacea), a hypothesis: dynamics of the flow field, properties of antennular sensor systems and a sensory-motor link

The act of swimming in formation by species such as Euphausiasuperba, Antarctic krill, is assumed to be regulated by a sensitivityto the characteristic and spatially elaborate flow field producedby this species of shrimp. We used a related species, Meganyctiphanes,North Atlantic krill, to visualize the flow field produced bytethered shrimps in an aquarium. In this situation, the propulsionjet flow some centimeters behind the shrimp is surrounded bya vortex ring of recoiling water motion from which, if the vortexis also produced by unrestrained swimming shrimp, a followingshrimp hypothetically can draw forces of lift and propulsionto decrease energy expense in long-distance migration. Two antennularsensitivities to water vibration in frequency ranges 5–40and 40–150 Hz were calibrated, and the activity of connectedinterneurons was traced into the abdominal pleopod-carryingsegments. Water oscillation of 3–10 Hz frequency, appliedto the antennules, was shown to entrain a closely synchronouspleopod beat in the stimulated specimens.     

Dynamic measurements of roots hydraulic conductance using a high-pressure flowmeter in the laboratory and field

A new high-pressure flowmeter(HPFM)is described which is capableof rapid water-flow measurements. The HPFM permits dynamic determinationof hydraulic conductance of roots, K_r, and can be used in tehlaboratory or field. The base of a root is connected to theHPFM and water is perfused into the root system opposite tothe normal direction of flow during trnaspiration. The perfusionpressure is changed at a constant rate of 3–7 kPa s^–1while measuring the flow into the root every 2–4 s. Theslope of the plot of flow versus applied pressure is K_r. This paper describes the HPFM, presnents the theory of dynamicflow measurements, discusses sources of error, presnets evidencethat dynamic measurements of K_r in Ficus maclellandi (and sixother tropical species from Panama) yield the correct result,and demonstrates the use of the method under field conditionsin Panama on Cecropia obtusifolia and Palicourea guianensis. Key words: High-pressure flowmeter, root and shoot hydraulic conductance, Ficus maclellandi, Cecropia obtusifolia, Palicourea guianensis     

Development of Sinks as an Autocatalytic Feed-back Process: a Test using the Asymmetric Growth of Leaves in Mestha (Hibiscus cannabinus L.)

Differential development of sinks that depend on a common resourcepool has been viewed as a consequence of an autocatalytic feedbackprocess of flow of resource units into them. The feed-back processimplies that the stronger a sink is relative to its competitors,the greater is its probability of getting further resourcesas a non-linear function of its resource drawing ability andsink size. We show that this model contrasts with that of thesink-strength dependent model in its prediction of the subsequentdevelopment of the initial asymmetry of growing leaves whentheir resource drawing ability is enhanced. By artificiallyenhancing the resource drawing ability of the leaves of Mestha(Hibiscus cannabinus L.) by external application of growth regulators,we test these predictions and show that the results are in conformitywith the autocatalytic model proposed by Ganeshaiah and UmaShaanker.Copyright 1995, 1999 Academic Press Autocatalytic growth, resource flow, leaf asymmetry, sink-strength, self-organization, Hibiscus cannabinus (L.)     

Optimal Regulation of Gas Exchange: Evidence from Field Data

Since the work of Cowan in 1977 it has been assumed that plantsregulate their stomata in a way that maximizes photosynthesisat a constant average rate of transpiration. The approach wasfurther developed by Hari et al. (1986) by introducing additionalassumptions which enabled the mathematical solution of the optimizationproblem using the Lagrangian method. The solution is testedfor Scots pine seedlings against field data. The results supportthe optimization hypothesis.Copyright 1993, 1999 Academic Press Pinus sylvestris (L.), stomatal conductance, photosynthesis, transpiration, optimization, field measurements, mathematical model, Lagrangian method     

Suppression of acute anti-friend virus CD8+ T-cell responses by coinfection with lactate dehydrogenase-elevating virus

Friend virus (FV) and lactate dehydrogenase-elevating virus (LDV) are endemic mouse viruses that can cause long-term chronic infections in mice. We found that numerous mouse-passaged FV isolates also contained LDV and that coinfection with LDV delayed FV-specific CD8⁺ T-cell responses during acute infection. While LDV did not alter the type of acute pathology induced by FV, which was severe splenomegaly caused by erythroproliferation, the immunosuppression mediated by LDV increased both the severity and the duration of FV infection. Compared to mice infected with FV alone, those coinfected with both FV and LDV had delayed CD8⁺ T-cell responses, as measured by FV-specific tetramers. This delayed response accounted for the prolonged and exacerbated acute phase of FV infection. Suppression of FV-specific CD8⁺ T-cell responses occurred not only in mice infected concomitantly with LDV but also in mice chronically infected with LDV 8 weeks prior to infection with FV. The LDV-induced suppression was not mediated by T regulatory cells, and no inhibition of the CD4⁺ T-cell or antibody responses was observed. Considering that most human adults are carriers of chronically infectious viruses at the time of new virus insults and that coinfections with viruses such as human immunodeficiency virus and hepatitis C virus are currently epidemic, it is of great interest to determine how infection with one virus may impact host responses to a second infection. Coinfection of mice with LDV and FV provides a well-defined, natural host model for such studies.     

A Model for Evaluating Time Constraints on Short-term Reproductive Success in Altricial Birds

SYNOPSIS. We develop a simple single dimension model incorporatingthe time and energy commitments of breeding altricial birdsin an effort to understand the evolutionary constraints on parentalcare. We chose time as the dimension of preference, becauseit is a naturally bounded constraint, e.g., length of day orbreeding season. The utility of the model was evaluated by comparingsimulations of time allocation of various breeding scenariosfor the European starling (Sturnus vulgaris) to field data.The structure of the model may prove useful in determining theevolutionary constraints on parental care imposed by the developmentalpattern of chicks.     

Convection in ice-covered lakes: effects on algal suspension

Convection occurs in ice-covered lakes if solar radiation warmsnear-surface water from the freezing point towards the temperatureof maximal density. One effect of convective mixing may be tosuspend non-motile phytoplankton in the upper water column,providing cells with enough light for growth during ice-coveredperiods. Observations of the diatom Aulacoseira baicalensisunder the ice cover of Lake Baikal, Siberia, support the hypothesisthat convective mixing causes net suspension of cells. Thispaper presents a theoretical examination of the conditions underwhich convective flow fields can suspend algae in the photiczone of the upper water column. It is shown that the efficiencyof algal suspension depends on the ratio of the still-wateralgal sinking rate, W_p, to convective updraft speed, W_u. Thesuspension efficiency is also shown to be affected by asymmetriesin the flow field and night-time cessation of convection, butonly if W_p and W_u are comparable in value. It is concluded thatconvection in Lake Baikal should be vigorous enough to increasethe mixed-layer residence time of A.baicalensis from a few daysto over a month, at least during years with thin snow cover.     

Seasonal Periodicity in Germination of Seeds of Chenopodium album L.

Seeds of Chenopodium album L. were buried under field and controlledconditions. The germination capacity of these seeds was testedover a range of conditions at regular intervals. Seed buriedin the field only showed small seasonal changes in germinationcapacity when tested at constant temperatures in incubators.However, when germination was tested at field temperatures,seasonal changes in germination were more obvious. Nitrate andlight always promoted germination. There was a strong positiveinteraction between the effects of the two factors. When nitrateand light were combined, exhumed seeds germinated over a muchlonger period of the year than in water with or without light.Desiccation only stimulated under particular conditions, forexample, when germination was tested in nitrate in darkness.A regression model was developed with the data from the germinationtests in incubators. The model describes the changes in dormancyand germination and estimates germination at field temperaturesaccurately throughout the year. Despite the absence of clearseasonal changes in the temperatures suitable for germination(computed with the model), germination in the field showed seasonalperiodicity, because the field temperature and the germination-temperaturerange only overlapped from spring to late summer.Copyright 1993,1999 Academic Press Chenopodium album, lamb's quarters, dormancy pattern, germination, regression model, temperature, light, nitrate, desiccation     

Apple Fruit Bud Development and Growth; Analysis and an Empirical Model

Analysis of the information available on apple bud developmentand growth after dormancy leads to an empirical model of growthto full bloom. The analysis and model are set in the frameworkof the physiological mechanisms considered to be responsiblefor dormancy and subsequent bud growth. It is necessary to introducean arbitrary ‘growth unit’ scale to describe theseprocesses quantitatively, which is done by the equation G = A/(I+be^–k(I).P) where G and A are in growth units, the value of k is controlledby a dormancy index I and P is a temperature summation. Themodel fulfils the main requirements laid down for it and thevalues of P at full bloom, derived from controlled environmentwork and field observations, are very similar.     

Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

不同地理种群尖音库蚊复组抗性动态和遗传多样性

通过生物测定、蛋白质电泳和等位酶分析等方法对5个不同地区的尖音库蚊复组蚊虫Culex pipiens complex的抗性水平、种群中非特异性酯酶基因表型分布和种群遗传多样性进行了研究。不同地理种群的抗性检测结果表明：5个种群分别对敌敌畏、对硫磷、氯菊酯和溴氰菊酯的抗性较高,对残杀威、巴沙和胺菊酯的抗性较低;朝阳种群对敌敌畏抗性最高（55.7倍）,武汉种群次之;佛山种群对氯菊酯和溴氰菊酯的抗性比率高达123倍和23.9倍。酯酶电泳结果显示：5个种群间酯酶多态性存在差异,广州和佛山两个库蚊种群酯酶表型多态性最高,有B1,A2-B2,A8-B8,A9-B9,B10和A11-B11等6种酯酶表型,提示高活性酯酶是主要的抗性机制。群体遗传学研究表明：每位点平均等位基因数（A）为2.76,平均多态位点百分率（P）为64.45％,平均预期杂合度（He）为0.1943,种群间遗传分化系数（Fst）值为0.10,平均基因流(Nm)＝2.57,说明5个种群有较丰富的遗传多样性,种群内遗传多样性高于种群之间。据此推测,种群间可以通过迁徙等方式进行基因交流,使得遗传结构、抗性水平朝一致性方向变化。本研究对我国尖音库蚊复组蚊虫的综合治理有一定指导意义。     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

Modelling and Measuring Transpiration from Scots Pine with Increased Temperature and Carbon Dioxide Enrichment

Starting in 1996, individual trees of Scots pine (Pinus sylvestrisL.) aged 30 years, were grown in closed-top chambers and exposedto either normal ambient conditions (CON), elevated CO₂(approx.700 µmol mol^-1; Elev. C), elevated temperature (approx.2 °C and approx. 6 °C above the outside ambient temperatureduring the ‘growing season’ and ‘off season’,respectively; Elev. T) or a combination of elevated CO₂and warmertemperature (Elev. CT). Sap flow was monitored simultaneouslyby the constant-power heat balance method in a total of 16 trees,four for each treatment, over a 32 d period in summer 1998 (afterthe completion of needle expansion and branch elongation). Toquantify the contributions of crown and physical environmentalvariables to total crown transpiration, a ‘sun/shade model’was developed and used to partition the changes in transpirationto different sources. The results of the sap flow measurementsindicate that (1) total daily sap flow (E_tree.d) varied from0.15–3.41 kg per tree; (2) the treatment effect on E_tree.ddependedgreatly on the weather conditions; (3) the cumulative E_tree.dforthe 32 d dropped significantly by 22% relative to CON (P =0.038)under Elev. C and increased significantly by 21% (P =0.043)and 16% (P =0.048) under Elev. T and Elev. CT, respectively.In general, the modelled transpiration gave good agreement withthe sap flow results. The model computations showed that, ona typical sunny day in summer, the effect of treatment on crownstomatal conductance was responsible for approx. 80% of thechange inE_tree.d , while the increase in needle area and theeffect on total radiation absorption contributed only a smallpercentage. Furthermore, sunlit needles were responsible forover 60% of change in transpiration. The effect of the treatmentson E_tree.dwas larger at high temperature and vapour pressuredeficit but was not sensitive to incident daily radiation. Copyright2000 Annals of Botany Company Transpiration model, sap flow, CO₂and temperature elevation, environment-controlled chamber, Pinus sylvestris L.     

An Optical Model for Phototactic Orientation in Dictyostelium discoideum Slugs

The optical properties of an enlarged optical model of the tipof a slug (a glass tube filled with sucrose solution) of Dictyosteliumdiscoideum were studied to validate the hypothesis that theorganism orients itself with respect to lateral light usinga lens effect: Light is focussed by refraction onto the distalside of the slug where the higher "signal" compared to the frontside causes a turn toward the light. Light was effectively focusedeven when the model deviated only as little as 10° fromthe light direction. Slugs of D. discoideum strains HO596 and HO813 show bidirectionalphototaxis: They orient themselves at some angle on either sideof the incident light beam. This angle is {small tilde}80°in HO596 and {small tilde}70° in HO813. We suggest thatthis phenomenon can be explained by the optical properties ofthe slug such as absorption and scattering, shape of the tipor location and extension of the light-sensitive zone. The angleof orientation with respect to light is regulated by a balancebetween a turn toward and a turn away from the light direction. (Received October 15, 1985; Accepted February 10, 1986)     

Light Distribution and Photosynthesis in Field Crops

In a new model of light distribution in field crops a parameters is the fraction of light passing through unit leaf layer withoutinterception. Radiation profiles measured with solarimetersand photocells give values of s from 0.7 for grasses to 0.4for species with prostrate leaves. Knowing s, leaf transmissionT and leaf-area index L the light distribution in a field cropmay be described by a binomial expansion of the form {s+(I-s)T)^L.To calculate crop photosynthesis at given light intensity thisexpansion is combined with two parameters describing the shapeof the light-response curve of single leaves. Finally, the assumptionthat solar radiation varies sinusoidally allows daily totalphotosynthesis to be estimated from daylength and insolation. The theory predicts about the same potential photosynthesisin a cloudy temperte climate with long days as in a more sunnyequatorial climate with short days. When L < 3 photosynthesisincreases as s decreases, i.e. as leaves become more prostrate;but when L > 5, photosynthesis increases as s increases,i. e. as leaves become more erect. Assuming that respirationis proportional to leaf area, estimated dry-matter productionagrees well with field measurements on sugar-beet, sugar-cane,kale, and subterranean clover. Estimates of maximum gross photosynthesis(for sugar-cane and maize) range from 60 to 9 g m^–2 day^–1depending on insolation.     

Effects of adenosine on pressure-flow relationships in an in vitro model of compartment syndrome

Shrier, Ian, Ari Baratz, and Sheldon Magder. Effects ofadenosine on pressure-flow relationships in an in vitro model ofcompartment syndrome. J. Appl.Physiol. 82(3): 755-759, 1997.Blood flow throughskeletal muscle is best modeled with a vascular waterfall at thearteriolar level. Under these conditions, flow is determined by thedifference between perfusion pressure (Pper) and the waterfall pressure(Pcrit), divided by the arterial resistance (Ra). By pump perfusing anisolated canine gastrocnemius muscle(n = 6) after it was placed within anairtight box, with and without adenosine infusion, we observed aninteraction between the pressure surrounding a muscle (as occurs incompartment syndrome) and baseline vascular tone. Wetitrated adenosine concentration to double baseline flow. We measuredPcrit and Ra at box pressures (Pbox), which resulted in 100 (Pbox = 0),90, 75, and 50% flow without adenosine; and 200, 180, 150, 100, and50% flow with adenosine. Without adenosine, each 10% decline in flowwas associated with a 5.7 mmHg increase in Pcrit(P < 0.01). With adenosine, the samedecrease in flow was associated with a 2.6-mmHg increase in Pcrit(P < 0.01). Values of Pcrit at 50%of flow were almost identical. Each 10% decrease in flow was alsoassociated with 2.2% increase in Ra with or without adenosine(P < 0.001). Ra decreased withadenosine infusion (P < 0.05), andthere was no interaction between adenosine and flow (P > 0.9). We conclude thatincreases in pressure surrounding a muscle limit flow primarily throughchanges in Pcrit with and without adenosine-induced vasodilation. Theinteraction between Pbox and adenosine with respect to Pcrit but not Rasuggests that Pbox affects the tone of the vessels responsible forPcrit but not Ra.

     

Dual-fiber laser Doppler velocimeter and its application to the measurements of coronary blood velocity

To obtain a smaller sample volume and a suitable sample position for the measurement of blood velocity, we fabricated a laser Doppler velocimeter (LDV) with a dual-fiber pickup. The two fibers (clad: 62.5 micron and core: 50 micron) were placed side by side. An He-Ne laser was introduced into the blood through one fiber and the backscattered light was collected by the other fiber. The Doppler signal was analyzed by a spectrum analyzer. The spectrum of the Doppler shift frequency showed a sharp peaked pattern for both forward and reverse flows and exhibited an excellent correlation with the known blood velocity. The blood velocity in the poststenotic portion of canine coronary artery was successfully measured by the dual-fiber LDV. These results indicate that the dual-fiber LDV is useful for measuring blood velocity accurately with a small sample volume even in disturbed flow fields.