Flow Stretch Research Articles

Passive leg movement enhances interstitial VEGF protein, endothelial cell proliferation, and eNOS mRNA content in human skeletal muscle

The present study used passive limb movement as an experimental model to study the effect of increased blood flow and passive stretch, without enhanced metabolic demand, in young healthy male subjects. The model used was 90 min of passive movement of the leg leading to a 2.8-fold increase (P < 0.05) in blood flow without a significant enhancement in oxygen uptake. Muscle interstitial fluid was sampled with microdialysis technique and analyzed for vascular endothelial growth factor (VEGF) protein and for the effect on endothelial cell proliferation. Biopsies obtained from the musculus vastus lateralis were analyzed for mRNA content of VEGF, endothelial nitric oxide synthase (eNOS), and matrix metalloproteinase-2 (MMP-2). The passive leg movement caused an increase (P < 0.05) in interstitial VEGF protein concentration above rest (73 +/- 21 vs. 344 +/- 83 pg/ml). Addition of muscle dialysate to cultured endothelial cells revealed that dialysate obtained during leg movement induced a 3.2-fold higher proliferation rate (P < 0.05) than dialysate obtained at rest. Passive movement also enhanced (P < 0.05) the eNOS mRNA level fourfold above resting levels. VEGF mRNA and MMP-2 mRNA levels were unaffected. The results show that a session of passive leg movement, elevating blood flow and causing passive stretch, augments the interstitial concentrations of VEGF, the proliferative effect of interstitial fluid, and eNOS mRNA content in muscle tissue. We propose that enhanced blood flow and passive stretch are positive physiological stimulators of factors associated with capillary growth in human muscle.

New resource augmentation analysis of the total stretch of SRPT and SJF in multiprocessor scheduling

This paper studies online job scheduling on multiprocessors and, in particular, investigates the algorithms Shortest Remaining Processing Time First (SRPT) and Shortest Job First (SJF) for minimizing total stretch, where the stretch of a job is its flow time (response time) divided by its processing time. SRPT is perhaps the most well-studied algorithm for minimizing total flow time or stretch. This paper gives the first resource augmentation analysis of the total stretch of SRPT, showing that it is indeed O ( 1 ) -speed 1-competitive. This paper also gives a simple lower bound result showing that SRPT is not s-speed 1-competitive for any s < 1.5 . This paper also makes contribution to the analysis of SJF. Extending the work of [L. Becchetti, S. Leonardi, A. Marchetti-Spaccamela, K. Pruhs, Online weighted flow time and deadline scheduling, in: RANDOM-APPROX, 2001, pp. 36–47], we are able to show that SJF is O ( 1 ) -speed 1-competitive for minimizing total stretch. More interestingly, we find that the competitiveness of SJF can be reduced arbitrarily by increasing the processor speed (precisely, SJF is O ( s ) -speed ( 1 / s ) -competitive for any s ⩾ 1 ). We conjecture that SRPT also admits a similar result.

A 2D constrained mixture model for arterial adaptations to large changes in flow, pressure and axial stretch

Soft tissue growth and remodelling (G&R) are achieved through highly complex, temporally regulated mechanisms that lead to the adaptation of structurally significant cells and extracellular matrix proteins. Herein we present a constrained mixture model to describe vascular adaptations in response to large perturbations in luminal flow rate, transmural pressure and axial extension. In the associated simulations, G&R occur in evolving loaded (i.e. current) configurations. Although several hypotheses are employed with regard to vasoregulatory mechanisms and rates of growth and turnover of individual constituents, the main hypothesis is that each structural constituent is produced within a range of homeostatic stresses (or stretches). As a result, although material that was produced in one configuration may have the same mechanical behaviour as that produced in another configuration, these materials will possess different natural configurations and contribute a different structural response to the mixture. Our simulations illustrate how, by simply evolving the reference states of individual constituents, blood vessels can adapt their structure and function to restore wall stresses.

Methane flames in a jet impinging onto a wall

Traditionally, research has focused on positive stretch in the stagnation flow and negative stretch along the Bunsen flame. Only a very limited amount of research has been devoted to studying the behavior of a conical Bunsen flame established in a stagnation flow, which is significantly affected by the combined effects of the curvature stretch and the aerodynamic straining. This investigation is aimed at studying the characteristics of laminar conical premixed flames in an impinging jet flow experimentally and theoretically. First, we analyze the transport processes of a nonreactive impinging jet flow numerically. For lower burner-to-plate distance, the potential core becomes concave at the top. Hence, a conical Bunsen flame established in such a flow field may suffer positive flow stretch. The predicted flame shapes using a simple model incorporated with the numerical results agree well with the experimental observations. Flame shapes exhibit double-solution characteristics in a certain range of methane concentrations. Experimentally, by following different paths of adjusting methane concentration (decreasing from rich to lean or increasing from lean to rich), two different flame configurations (planar or conical flame) may exist at the same flow conditions, namely burner-to-plate distance, inlet velocity, and methane concentration. At the higher (or lower) critical methane concentration, the transition from a flat flame to a conical flame (or from a conical flame to a flat flame) occurs. The calculation of stretch and measurement of flame temperature for the low inlet velocity, 0.8 m/s, show that the stretch of a conical flame established in a stagnation flow is negative (dominated by the flame curvature). However, it is important to emphasize that at high velocity, e.g., U in = 1.6 m/s, a negatively stretched flame tip can suffer positive flow stretch. This significant finding has been verified in the experiment since the conical flame tip is higher than the positively stretched flat flame.

Extinction and flame bifurcations of stretched dimethyl ether premixed flames

Extinction limits and flame bifurcation of lean premixed dimethyl ether–air flames are numerically investigated using the counterflow flame with a reduced chemistry. Emphasis is paid to the combined effect of radiation and flame stretch on the extinction and flammability limits. A method based on the reaction front is presented to predict the Markstein length. The predicted positive Markstein length agrees well with the experimental data. The results show that flow stretch significantly reduces the flame speed and narrows the flammability limit of the stretched dimethyl ether–air flame. It is found that the combined effect of radiation and flow stretch results in a new flame bifurcation and multiple flame regimes. At an equivalence ratio slightly higher than the flammability limit of the planar flame, the distant flame regime appears at low stretch rates. With an increase in the equivalence ratio, in addition to the distant flame, a weak flame isola emerges at moderate stretch rates. With a further increase in the equivalence ratio, the distant flame and the weak flame branches merge together, resulting in the splitting of the weak flame branch into two weak flame branches, one at low stretch and the other at high stretch. Flame stability analysis demonstrates that the high stretch weak flame is also stable. Furthermore, a K-shaped flammability limit diagram showing various flame regimes and their extinction limits is obtained.

An experimental study on combustion characteristics of flames in a coaxial flow with a stagnation point

By using a stagnation-point coaxial flow generated by a lower coaxial burner and an upper quartz plate, an inner (or outer) premixed flame influenced by outer (or inner) oxygen content is experimentally developed to simulate and study double-flame burning structures modified by interactions of flamelets in turbulent combustible flows. In the experiments, fuel–air and oxygen–nitrogen mixtures are therefore introduced into outer (or inner) and inner (or outer) flows, respectively. This experimental arrangement allows either the inner flame or the outer flame to be located at different planes by separately adjusting the compositions and injection velocities of the inner and outer flows. An inner (or outer) planar premixed flame with a small outer (or inner) lifted tail or an inner (or outer) nonplanar premixed flame and an outer (or inner) trumpet-shaped diffusion flame can be developed in the flow field. The lifted tail and the trumpet-shaped diffusion flame are stabilized along the interface between the inner and outer jets in the coaxial flow. The inner (or outer) premixed flame influenced by the outer (or inner) oxygen content may experience transports of mass and thermal diffusion parallel to the flame surface. It endures the flow stretch tangent to the flame surface. Furthermore, in the flow field, the directions of flow convection for both inner and outer flows are the same (both divergent). The combustion characteristics, including extinction, blow off, flashback, the transition from the flat flame to the hat-shaped flame, and the ignition and development of diffusion flame are reported and discussed. Finally, the measurements of flame shape and temperature distribution are involved.

Upstream migration of Atlantic salmon at a power station on the River Nidelva, Southern Norway

AbstractThe upstream migration of 17 radio‐tagged adult Atlantic salmon, Salmo salar L., past hydroelectric developments on the River Nidelva, Southern Norway, was examined. Salmon migrated quickly from the site of release in the lower part of the river up to the tunnel outlet of Rygene power station, but were substantially delayed at the outlet. The salmon stayed in the outlet area for 0–71 days (median = 20), and mainly took up a position inside the dark power station tunnel. Water discharge in the tunnel was 57–176 m3 s−1, while residual flow in the river between the outlet and the dam 2.5 km further upstream was 3 m3 s−1. Ten salmon passed the outlet and entered the residual flow stretch, but none passed the dam. Six of the 10 salmon returned to the tunnel outlet. No major migration barriers were identified in the residual flow stretch, suggesting lack of motivation among the salmon to migrate due to either low water discharge compared with the main river, or several minor migration barriers along the river stretch.

Modeling the Initial Growth of the Plasma and Flame Kernel in SI Engines

The initial size and growth of the plasma and flame kernel just after spark discharge in S.I. engines determines if the flame becomes self-sustainable or extinguishes. On the other hand, the development of the kernel during the initial phases has non-negligible influences on the further combustion. For example, cyclic variations often find their origin in the beginning of combustion and determine the working limits of the engine and the driving behavior of the vehicle. These factors demonstrate the crucial importance of the knowledge of the initial growth of the plasma and flame kernel in S.I. engines. A complete model is developed for the growth of the initial plasma and flame kernel in S.I. engines, which takes into account the fundamental properties of the ignition system (electrical energy and power, geometry of the spark plug, heat losses to the electrodes and the cylinder wall), the combustible mixture (pressure, temperature, equivalence ratio, fraction of residual gasses, kind of fuel), and the flow (average flow velocity, turbulence intensity, stretch, characteristic time and length scales). The proposed model distinguishes three phases: the pre-breakdown, the plasma, and the initial combustion phase. The model of the first two phases is proposed in a previous article of the same authors [1], the latter is exposed in this article. A thermodynamic model based on flamelet models and which takes stretch into account, is used to describe the initial combustion phase. The difference between heat losses to the electrodes and the cylinder wall is considered. The burning velocity varies from the order of the laminar velocity to the fully developed burning velocity. The evolution is determined as well by the life time as by the size of the kernel. The stretch (caused by turbulence and by the growth of the kernel), the nonadiabatic character of the flame, and instabilities have influence on the laminar burning velocity. Validation of this model is done using measurements of the expansion in a propane-air mixture executed by Pischinger [2] at M.I.T. The agreement seems very good.

Three-dimensional velocity field for wavy Taylor–Couette flow

The stability of wavy supercritical cylindrical Couette flow has been studied extensively, but few measurements of the velocity field in flow have been made. Particle image velocimetry was used to measure the azimuthal and radial velocities in latitudinal planes perpendicular to the axis of rotation for wavy cylindrical Couette flow in the annulus between a rotating inner cylinder and a fixed outer cylinder. These measurements were matched to previous measurements of the axial and radial velocity measured in several meridional planes resulting in an experimentally measured, time-resolved, three-dimensional, three-component velocity field for wavy cylindrical Couette flow. Using this complete velocity field it is possible to evaluate details of the flow field. The vortical motion transports azimuthal momentum radially while the axial exchange of fluid between vortices in wavy flow transports azimuthal momentum axially. As the Reynolds number increases, these effects strengthen. Streams of net axial flow stretch axially along the length of the annulus and wind around the vortices from the inner cylinder to the outer cylinder and back while also winding azimuthally in the annulus. The azimuthal velocity measured at the center of a vortex is similar to the azimuthal wave speed. Measurements of the azimuthal velocity in cylindrical surfaces concentric with the axis of rotation suggest that the origin of the waviness is related to a jet-like azimuthal velocity profile rather than the radial outflow jet. Near both cylinder walls, the shear stress is quite large, decreasing to near zero at the middle of the annular gap.

The Quenching of Spray Flames by Stretch and Heat Loss.

The extinction of stretched premixed flames propagating in a stagnation-point flow under the influences of dilute fuel spray, preferential diffusion and upstream external heat loss is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. The liquid fuel loading and the initial droplet size of the spray indicate the internal heat gain and heat loss for the lean and rich sprays, respectively. The flow stretch coupled with Lewis number (Le) intensifies the burning intensity of the Le>1 flame, but weakens that of the Le 1 flame can be quenched with or without external heat loss, and that both the external heat loss and the flow stretch strongly dominate the trend for flame extinction characterized by a C-shaped extinction curve. In the absence of external heat loss, no extinction occurs under the influence of flow stretch for the Le<1 flame enduring completely prevaporized burning sprays. However, it can be extinguished by the external heat loss characterized by a C-shaped extinction curve if the flow stretch is small. Under the condition of Le<1 flames experiencing a small flow stretch and enduring a partially prevaporized spray composed of a large enough liquid loading and sufficiently large droplet size, a W-shaped extinction curve is obtained. The W-shaped extinction curve in distinction from the C-shaped one points out that the flame extinction is governed by the internal heat loss.

Downregulation of endocardial nitric oxide synthase expression and nitric oxide production in atrial fibrillation: potential mechanisms for atrial thrombosis and stroke.

In the arterial endothelium, laminar flow and cyclical stretch induce expression of NO synthase (NOS). We hypothesized that atrial fibrillation (AF) causes a downregulation of atrial endocardial NOS expression and NO* production. Because NO* has antithrombotic properties, this may contribute to thromboembolism in AF. In pigs, AF was produced with rapid atrial pacing at 600 bpm for 1 week, whereas controls had atrial pacing at 100 bpm. All animals production from freshly isolated tissue was measured by a NO*-specific microelectrode. Left atrial basal and stimulated NO* production was decreased in AF by 73% and 71% (P<0.01). Endocardial NOS expression, determined by Western analysis, was also significantly decreased by 46%. Expression of the prothombotic protein plasminogen activator inhibitor 1 (PAI-1) is known to be regulated by NO* and was increased in the left atrium by 1.8-fold in AF (P<0.05). NO* concentration was decreased in the left atrial appendage, although NOS expression was not affected. Neither NOS concentration, NO* levels, nor PAI-1 expression were altered in the aortas or right atria of animals with AF. AF is associated with a marked decrease in endocardial NOS expression and NO* bioavailability and an increase in PAI-1 expression in the left atrium. These data suggest that organized atrial contraction is needed to maintain normal endocardial expression of NOS. It is likely that loss of this antithrombotic enzyme contributes to the thromboembolic phenomena commonly observed in AF.

The interaction between internal heat loss and external heat loss on the extinction of stretched spray flames with nonunity Lewis number

The influences of flow stretch, preferential diffusion, internal heat transfer and external heat loss on the extinction of dilute spray flames propagating in a stagnation-point flow are analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. The internal heat transfer, associated with the liquid fuel loading and the initial droplet size of the spray, provides heat loss for rich sprays but heat gain for lean sprays. The flow stretch respectively weakens and intensifies the burning intensity of the lean methanol-spray flame ( Le>1) and rich methanol-spray flame ( Le<1). Results show that the Le>1 flame can be extinguished with or without external heat loss. Flame extinction characterized by a C-shaped curve is dominated by the external heat loss or the flow stretch. For the Le<1 flame without external heat loss, no extinction occurs under the influence of flow stretch. However, the Le<1 flame with completely prevaporized fuel sprays enduring a small amount of flow stretch can be extinguished by the external heat loss and this behavior is characterized by a C-shaped curve. Note that the W-shaped extinction curve is mainly governed by the internal heat loss. Flame extinction characterized by a W-shaped curve occurs when the Le<1 spray flame with external heat loss endures a positive stretch and experiences a partially prevaporized spray with sufficiently large liquid fuel loading and droplet size.

313 PAH 生成挙動に及ぼす拡散火炎燃焼状態変化の影響

PAH production of counterflow diffusion flame has been investigated experimentally. In particular, effect of variation of flame characteristics such as flow stretch, stoichiometric mixture fraction, and molar stoichiometry, on PAH production is discussed in the present study. PAH production is strongly correlated with the flow stretch. For larger flow stretch condition, PAH production is clearly enhanced. Effect of stoichiometric mixture fraction variation is also clarified. To increase the stoichiometric mixture fraction reduces PAH formation. A simple numerical analysis for counterflow diffusion flame with GRI-Mech shows that those results are reasonably explained based on the laminar flamelet concept. Concerning the formation mechanism of measured PAH, reaction path of benzene and PAH via propargyl has a key roll in the present experimental condition.

Turbulent Non-Premixed Flame Structure near Extinction Caused by Flame Stretch.

An experimental study was made on the structure of the turbulent counter flow non-premixed flame established in the forward stagnation region of a porous cylinder. Stable-species-concentration profiles were measured in detail for propane flames at atmospheric pressure. These distributions were analyzed to make clear the effects of flame stretch and turbulence intensity on the flame structure. The non-premixed flames are extinguished by flame stretch caused by the flow field. For the turbulent flow, effects of the flow field can be separated into those of the bulk flow and fluctuating flow. Therefore, the flame stretch consists of the bulk flow stretch and turbulent stretch. In the present study, the turbulent stretch was estimated by the inverse of the Kolmogorov time scale. With increasing the flame stretch, thickness of the turbulent flame zone decreased and spatial gradient of the species become steeper. The main reaction generating the intermediate species occurred on the fuel side of the turbulent flame zone. With the strong stretch, leakage of the intermediate species is large compared to the weak stretch. With the strong turbulence, the profiles of the intermediate species are rather flat, whereas the Gaussian distributions are observed for the case of weak turbulence. Based on the mixture fraction, the effects of flame stretch and turbulence intensity cannot be discernible.

Effects of internal heat transfer and preferential diffusion on stretched spray flames

The extinction of dilute spray flames propagating in a stagnation-point flow under the influence of flow stretch, preferential diffusion, and internal heat transfer is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. The internal heat transfer, associated with the liquid fuel loading and the initial droplet size of the spray, provides heat loss and heat gain for rich and lean sprays, respectively. It is found that the flow stretch coupled with Lewis number ( Le) reduces and enhances the burning intensity of the lean methanol-spray flame ( Le>1) and rich methanol-spray flame ( Le<1), respectively; and that the flame extinction characterized by a C-shaped curve for the Le>1 flame is dominated by the flow stretch, while the S-shaped extinction curve for the Le<1 flame is mainly influenced by the internal heat loss associated with the droplet gasification process.

Extinction of stretched spray flames with nonunity Lewis numbers in a stagnation-point flow

The extinction of stretched premixed flames under the influence of dilute fuel sprays is studied using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Three parameters for flame extinction in the analysis consist of the mass fraction of liquid fuel and the initial droplet size of the spray, indicating the internal heat loss and heat gain for rich and lean sprays, respectively, and the flow stretch coupled with Lewis number (Le) that intensifies and weakens the burning strength of the Le<1 and Le>1 flame, respectively. The study presents sample calculations on lean ethanol-spray flames (Le>1), rich ethanol-spray flames (Le>1), and rich methanol-spray flames (Le<1). Results show that the burning intensity of a spray flame with Le>1 is weakened by the flow stretch: however, it is enhanced (further reduced) when the lean (rich) spray has a larger amount of liquid fuel loading or a smaller initial droplet size. It is generally found that the external heat loss associated with the flow stretch dominates the trend for flame extinction. The coupling effects of flow stretch and internal heat gain result in that there exists flame flashback instead of flame extinction for rich methanol-spray flames (Le<1).

Effects of mechanical forces on signal transduction and gene expression in endothelial cells.

Fluid shear stress and circumferential stretch play important roles in maintaining the homeostasis of the blood vessel, and they can also be pathophysiological factors in cardiovascular diseases such as atherosclerosis and hypertension. The uses of flow channels and stretch devices as in vitro models have helped to elucidate the mechanisms of signal transduction and gene expression in cultured endothelial cells in response to shear stress, which is a function of blood flow and vascular geometry, or mechanical strain, which is a function of transmural pressure and the mechanical properties and geometry of the vessel. Shear stress has been found to increase the activities of a number of kinases to modulate the phosphorylation of many signaling proteins in endothelial cells, eg, the proteins in focal adhesion sites and the proteins in the mitogen-activated protein kinase pathways. Downstream to such signaling cascades, multiple transcription factors such as AP-1, NF-kappaB, Sp-1, and Egr-1 are activated. The actions of these transcription factors on the corresponding cis-elements result in the induction of genes encoding for vasoactivators, adhesion molecules, monocyte chemoattractants, and growth factors in endothelial cells, thus modulating vascular structure and function. Some of the effects of mechanical strain on endothelial cells are similar to those by shear stress, eg, the signaling pathways and the genes activated, but there are differences, eg, the time course of the responses. Studies on the effects of mechanical forces on signal transduction and gene expression provide insights into the molecular mechanisms by which hemodynamic factors regulate vascular physiology, and pathophysiology.

Numerical simulation of a counterflow diffusion flame in supersonic airflow

A counterflow diffusion flame of hydrogen, developed in the forward stagnation-flow region of a porous cylinder in supersonic airflow (which can be considered as a flame of the “Tsuji-burner” in supersonic airflow), was analyzed numerically by solving the two-dimensional Navier-Stokes equations for multispecies. A counterflow diffusion flame, having a temperature distribution and concentration distributions of species in the direction of the burner surface, can be established in the very thin region behind a detached shock wave. It is shown that thermal quenching occurs when the flame approaches the surface of a porous cylindrical burner as in the case of a normal “Tsuji-burner.” The decrease of static temperature or March number (equivalent to the flow velocity) of airflow causes flame extinction, in contrast to the case of subsonic airflow. Flame temperature approaches the stagnation temperature in the region of high static temperature and has maximum heat release at a certain static temperature. This is due to the increase of flow velocity and stretch rate based on the increase of static temperature, but appreciable flame extinction does not occur even if the stretch rate becomes much higher: because the stagnation temperature exceeds the critical temperature, which has previously been discussed for a high-temperature subsonic airflow system.

Mechanotransduction and the functional response of bone to mechanical strain.

Mechanotransduction plays a crucial role in the physiology of many tissues including bone. Mechanical loading can inhibit bone resorption and increase bone formation in vivo. In bone, the process of mechanotransduction can be divided into four distinct steps: (1) mechanocoupling, (2) biochemical coupling, (3) transmission of signal, and (4) effector cell response. In mechanocoupling, mechanical loads in vivo cause deformations in bone that stretch bone cells within and lining the bone matrix and create fluid movement within the canaliculae of bone. Dynamic loading, which is associated with extracellular fluid flow and the creation of streaming potentials within bone, is most effective for stimulating new bone formation in vivo. Bone cells in vitro are stimulated to produce second messengers when exposed to fluid flow or mechanical stretch. In biochemical coupling, the possible mechanisms for the coupling of cell-level mechanical signals into intracellular biochemical signals include force transduction through the integrin-cytoskeleton-nuclear matrix structure, stretch-activated cation channels within the cell membrane, G protein-dependent pathways, and linkage between the cytoskeleton and the phospholipase C or phospholipase A pathways. The tight interaction of each of these pathways would suggest that the entire cell is a mechanosensor and there are many different pathways available for the transduction of a mechanical signal. In the transmission of signal, osteoblasts, osteocytes, and bone lining cells may act as sensors of mechanical signals and may communicate the signal through cell processes connected by gap junctions. These cells also produce paracrine factors that may signal osteoprogenitors to differentiate into osteoblasts and attach to the bone surface. Insulin-like growth factors and prostaglandins are possible candidates for intermediaries in signal transduction. In the effector cell response, the effects of mechanical loading are dependent upon the magnitude, duration, and rate of the applied load. Longer duration, lower amplitude loading has the same effect on bone formation as loads with short duration and high amplitude. Loading must be cyclic to stimulate new bone formation. Aging greatly reduces the osteogenic effects of mechanical loading in vivo. Also, some hormones may interact with local mechanical signals to change the sensitivity of the sensor or effector cells to mechanical load.

Macrozoobenthos in some rapids in a lowland river in Finland before and after the construction of a hydroelectric power plant

AbstractIn the beginning of the 1980s a hydroelectric power plant was constructed in the middle course of the lowland river Perhonjoki in western Finland. Some shallow lakes upstream of the power plant were enlarged for use as a reservoir and some rapids downstream were dredged and remodelled. As a consequence of the construction, the flow was almost completely diverted from a 2.5 km stretch of the river and the former rapids in this area were remodelled with weirs. The discharge from the power plant was regulated in the short term during low flow seasons in winter and summer. The effects of this project on the stream bottom fauna has been studied. The sampling started in 1980 before any major impact took place and has continued until 1992.In the low flow stretch of the river the lotic fauna of the former rapids has withdrawn to small rivulets and several species have disappeared, including the large caddisfly Arctopsyche ladogensis. In the remodelled rapids downstream from the power plant large numbers of black fly larvae have appeared every spring since the power plant was completed. The reason for this was probably dredging of the rapids, which wiped out the natural moss vegetation on the stones in the rapids and generated large areas of bare stone surfaces in places with suitable current velocities for the larvae. A lake outlet effect might also be part of the reason, even if samples of the phytoplankton could not demonstrate higher amounts of plankton downstream of the power plant reservoir than upstream. In late summer the number of filter‐feeding trichopterans has increased and the species composition has changed. Neurclipsis bimaculata and Ceratopsyche nevae have become more abundant and Arctopsyche ladogensis as well as several species commonly found among water moss have disappeared.