Sinusoidal Flow Research Articles

NUMERICAL INVESTIGATION OF THE EFFECT OF PULSED INJECTION ON FILM COOLING EFFECTIVENESS OF TURBINE BLADE UNDER ROTATION

The effect of rotation on temperature distribution and film cooling effectiveness for turbine blade with sinusoidal and square pulsating coolant flow is numerically investigated. The RNG k−ε turbulent model is used to simulate the turbulence effects. Four rotation speeds of 0, 500, 800 and 1000 rpm are considered. Pulsed air coolant flow at three frequencies of 2, 50, and 500 Hz is injected to the turbine blade surface. It is to consider the combined effect of both rotation and pulsation parameters on film cooling performance simultaneously. The results show that pulsed film cooling effectiveness on pressure side and around the leading edge is reduced with increasing the rotational speed. On the suction side, with increasing rotational speed, film cooling effectiveness is decreased up to a distance of near the downstream of injection hole, but the behavior is reversed for further distances. In general, the pulsed film cooling effectiveness on the pressure side is greater than that on the suction side for different rotational speeds and frequencies. For sinusoidal and square pulsation, the deviation angle was almost the same but with increasing the rotational speed and pulsation frequency, the deflection increased. For various rotational speeds and frequencies, the film cooling effectiveness for sinusoidal injection flow is higher than for square wave flow.

Least Squares Finite Element Method for Hepatic Sinusoidal Blood Flow

AbstractThe simulation of complex biological systems such as the description of blood flow in organs requires a lot of computational power as well as a detailed description of the organ physiology. We present a novel Least‐Squares discretization method for the simulation of sinusoidal blood flow in liver lobules using a porous medium approach for the liver tissue. The scaling of the different Least‐Squares terms leads to a robust algorithm and the inherent error estimator provides an efficient refinement strategy.

Design of a new turbine for OWC wave energy converters: The DDT concept

Oscillating Water Column (OWC) has attracted significant research efforts in the field of wave energy technology in the last decades. Recently, the Twin Turbines Configuration (TTC) has received attention because it is based on the use of unidirectional turbines which are much more efficient. Nevertheless, its main disadvantage with respect to classic OWC systems equipped with bidirectional turbines is the duplicity of equipment. To overcome this limitation, the Double Decker Turbine (DDT) concept is presented here as a new turbine which combines the best of both solutions, the TTC and the bidirectional turbine, in which the geometrical design of the DDT has been carried out based on a well-tested geometry taken from the bibliography. In addition, CFD modelling has been used to obtain an optimized DDT by means of a comparison between two new geometries for the outer turbine; while the inner turbine geometry has been already taken from the literature. Outer turbine has been further validated through experimental measurements of a manufactured prototype. Finally, a non-steady analysis of the proposed double turbine is carried out assuming sinusoidal flow conditions. Results demonstrate that the DDT concept can compete with the other alternatives, even envisaging high-performance characteristics to be developed in future works.

Сравнительное изучение кинетики свертывания крови и тромбообразования реологическими и электрореологическими методами.

Цель исследования: изучить механизмы формирования и тромбодинамические свойства кровяного сгустка при тромбообразовании in vitro и представить сравнительное исследование кинетики тромбообразования с помощью реологических и электрореологических методов в условиях постоянного и осциллирующего сдвигового вискозиметрического течения; оценить свертывание цельной и консервированной крови, ее вязкоупругие свой ства и влияние фибриногена и декстранов на формирование сгустка. Материалы и методы. Вязкость и удельную электропроводимость нормальной и консервированной с CPD-A1-адениновым раствором крови измеряли ротационным вискозиметром Low Shear 30 Contraves (LS30) с коаксиальными цилиндрами и копией измерительной системы MS1/1 со встроенными электродами (разработана на базе LS30) в условиях постоянного сдвигового потока и в электрическом поле. Вязкоупругие свойства нормальной цельной крови исследовали с помощью реометра Physica MCR 301 (Anton Paar, Austria) в условиях осциллирующего синусоидального потока. Результаты. Представлены результаты кинетики динамической вязкости и удельной электропроводимости консервированной крови в процессе коагуляции в условиях постоянного сдвигового потока и в электрическом поле. Исследованы вязкоупругие свойства цельной крови в условиях синусоидального осциллирующего вискозиметрического течения и представлены зависимости упругого модуля G' (storage modulus) и модуля потерь G'' (loss modulus), а также нормальных сил как функция времени при свертывании. Приводятся данные эффекта фибриногена и декстрана на упругий модуль G' и на модуль потерь G'' цельной крови в процессе коагуляции. Заключение. В условиях вискозиметрического течения при низких скоростях сдвига кинетика тромбообразования характеризуется начальным этапом постепенного увеличения кажущейся вязкости и уменьшения удельной электропроводимости крови и периодом интенсивной коагуляции, характеризирующимся экспоненциальным ростом вязкости и параллельным уменьшением удельной электропроводимости исследуемого образца. Установлено, что коагулирующая цельная кровь обладает нелинейными вязкоупругими свойствами. Кинетика образования сгустка в условиях осциллирующего вискозиметрического течения крови характеризуется увеличением упругого модуля G' и модуля потерь G'' со временем. Одновременно зарегистрирована и отрицательная нормальная сила исследуемого образца в зазоре между пластинами при постоянной толщине зазора. Повышение содержание фибриногена ускоряет коагуляцию и увеличивает значения упругого модуля G' и модуля потерь G'', а также и нормальной силы коагулирующей цельной крови. Objectives: to study the mechanisms of thrombus formation and thrombodynamic properties of a blood clot during coagulation in vitro and to present a comparative study of clot kinetics formation under conditions of steady and oscillating shear viscometric flow and at electric field by rheological and electrorheological methods; to evaluate the coagulation of whole and preserved blood, its viscoelastic properties and the effect of fi brinogen and dextrans on clot formation. Materials/ Methods. The viscosity and electrical conductivity of normal blood and blood preserved with CPD-A1-adenine solution were measured with a Low Shear 30 Contraves (LS30) rotational viscometer with coaxial cylinders and with a copy of the measuring system MS1 / 1 with builtin electrodes at a steady viscometric shear flow and in an electric field too. The viscoelastic properties of normal whole blood were investigated using a Physica MCR 301 rheometer (Anton Paar, Austria) at an oscillating sinusoidal flow. Results. Kinetics of the dynamic viscosity and electrical conductivity of preserved blood during coagulation at a steady shear flow and at electric field were obtained. The viscoelastic properties of whole blood were investigated under conditions of sinusoidal oscillating viscometric flow. The dependences of the elastic (storage) modulus G' and the loss modulus G'', as well as the normal coagulation forces as a function of time are presented. The effect of fibrinogen and dextran on the elastic modulus G' and the loss modulus G'' of whole blood during coagulation are presented. Conclusions. The kinetics of blood coagulation at low shear rates is characterized by a gradual increase of the apparent viscosity and a decrease in blood conductivity at the initial stage and an exponential increase in viscosity during intensive coagulation and a parallel decrease of conductivity too. It was established that coagulating whole blood exhibit nonlinear viscoelastic properties under conditions of sinusoidal blood flow. The kinetics of thrombus formation is characterized by increasing the elastic modulus G' (storage modulus) and the loss modulus G'' with time. The negative normal force in the gap between the plates is also registered at a constant thickness of the gap. An increase in fibrinogen content accelerates coagulation and increases the values of elastic modulus G' and loss modulus G', as well as of the normal force of coagulating whole blood.

Bile Acids and GPBAR-1: Dynamic Interaction Involving Genes, Environment and Gut Microbiome.

Bile acids (BA) are amphiphilic molecules synthesized in the liver from cholesterol. BA undergo continuous enterohepatic recycling through intestinal biotransformation by gut microbiome and reabsorption into the portal tract for uptake by hepatocytes. BA are detergent molecules aiding the digestion and absorption of dietary fat and fat-soluble vitamins, but also act as important signaling molecules via the nuclear receptor, farnesoid X receptor (FXR), and the membrane-associated G protein-coupled bile acid receptor 1 (GPBAR-1) in the distal intestine, liver and extra hepatic tissues. The hydrophilic-hydrophobic balance of the BA pool is finely regulated to prevent BA overload and liver injury. By contrast, hydrophilic BA can be hepatoprotective. The ultimate effects of BA-mediated activation of GPBAR-1 is poorly understood, but this receptor may play a role in protecting the remnant liver and in maintaining biliary homeostasis. In addition, GPBAR-1 acts on pathways involved in inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity, and sinusoidal blood flow. Recent evidence suggests that environmental factors influence GPBAR-1 gene expression. Thus, targeting GPBAR-1 might improve liver protection, facilitating beneficial metabolic effects through primary prevention measures. Here, we discuss the complex pathways linked to BA effects, signaling properties of the GPBAR-1, mechanisms of liver damage, gene-environment interactions, and therapeutic aspects.

Aerodynamic pressures on a 5:1 rectangular cylinder in sinusoidal streamwise oscillatory flows with non-zero mean velocities

In this paper, the aerodynamic pressures on a 5:1 rectangular cylinder in sinusoidal streamwise oscillatory flows (SSOFs) with non-zero mean velocities are studied through wind tunnel experiments. First, the mean and fluctuating pressure coefficients are determined based on the measurements in SSOFs with different reduced frequencies and gust amplitudes. The results are compared with those of smooth flow and grid-generated turbulent flow. Next, the power spectral densities of surface pressures are presented to study their energy distributions in the frequency domain. Then, the spanwise correlations of surface pressures in SSOFs are compared with those of smooth flow to explore their three-dimensional characteristics. The testing results show that the reduced frequency, varying from 0.012 to 0.032 has little effect on the streamwise pressure distributions of the 5:1 rectangular cylinder, and the influences of the gust amplitude of SSOFs are significant. The maximum RMS pressure coefficient increases and the separation bubble length reduces to a large degree as the gust amplitude increases. The spectral analysis demonstrates that the energy of fluctuating pressures in SSOFs is primarily from oscillatory streamwise gusts, while it is mainly provided by vortex shedding in smooth flow. The SSOF can accelerate the vortex shedding process and the Strouhal number increases as the increased gust amplitude. The spanwise correlations of pressures are strong in the majority region of the side surface of the 5:1 rectangular cylinder in SSOFs.

Hot deformation analysis and microstructure evolution of Al–Mg–Mn-Sc-Zr alloy by isothermal compression

In this work, a new type of Al–Mg–Mn-Sc-Zr alloy was compressed under different temperatures (300 °C–450 °C) and different strain rates (0.0001 S-1 to 10 S−1). The hyperbolic sinusoidal Arrhenius flow stress constitutive equation and the constitutive equation of flow stress related with Z parameter have been calculated. In addition, the processing maps based on dynamic material model (DMM) at different strains have been established. The results show that deformation behavior and microstructure evolution of the alloy are significantly affected by deformation temperature and strain rate. The flow stress decreases with the increase of the temperature or the decrease of strain rate. Meanwhile, increasing the temperature or decreasing the strain rate, the average grain boundary (GB) angle and the high angle grain boundary (HAGB) fraction will rise and it is beneficial for dynamic recrystallization (DRX) or dynamic recovery (DRV). The dislocation density of the 1 S−1- 300 °C, 0.0001 S-1- 300 °C, 1 S−1- 450 °C and 0.0001 S-1- 450 °C samples are 1.19 × 1014/m2, 5.97 × 1013/m2, 6.52 × 1013/m2 and 2.03 × 1013/m2 respectively. Moreover, under very low strain rate, some grains would combine together and the morphology of the Al3(Sc, Zr) particles would change. In the 0.0001 S-1- 450 °C sample, some particles have lost the coherency. This is due to the co-effect of the high temperature and the very low strain rate.

Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

Far field of turbulent spots

The proliferation of turbulence in subcritical wall-bounded shear flows involves spatially localised coherent structures. Turbulent spots correspond to finite-time nonlinear responses to pointwise disturbances and are regarded as seeds of turbulence during transition. The rapid spatial decay of the turbulent fluctuations away from a spot is accompanied by large-scale flows with a robust structuration. The far field velocity field of these spots is investigated numerically using spectral methods in large domains in four different flow scenarios (plane Couette, plane Poiseuille, Couette-Poiseuille and a sinusoidal shear flow). At odds with former expectations, the planar components of the velocity field decay algebraically. These decay exponents depend only on the symmetries of the system, which here depend on the presence of an applied gradient, and not on the Reynolds number. This suggests an effective two-dimensional multipolar expansion for the far field, dominated by a quadrupolar flow component or, for asymmetric flow fields, by a dipolar flow component.

Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation.

Endothelin-1 in portal hypertension: The intricate role of hepatic stellate cells.

Portal hypertension is pathologically defined as increase of portal venous pressure, mainly due to chronic liver diseases such as fibrosis and cirrhosis. In fibrotic liver, activated hepatic stellate cells increase their contraction in response to endothelin-1 (ET-1) via autocrine and paracrine stimulation from liver sinusoidal endothelial cells and injured hepatocytes. Clinical studies are limited with ET receptor antagonists in cirrhotic patients with portal hypertension. Hence, studies are needed to find molecules that block ET-1 synthesis. Accumulation of extracellular matrix proteins in the perisinusoidal space, tissue contraction, and alteration in blood flow are prominent during portal hypertension. Therefore, novel matrix modulators should be tested experimentally as well as in clinical studies. Specifically, tumor necrosis factor-α, transforming growth factor-β1, Wnt, Notch, rho-associated protein kinase 1 signaling antagonists, and peroxisome proliferator-activated receptor α and γ, interferon-γ and sirtuin 1 agonists should be tested elaborately against cirrhosis patients with portal hypertension.

Filtration performance of glass fibrous air filter media under sinusoidal flow condition

Air filter is one of the key equipments for sustainable built environment. However, the variation of incoming air velocity is usually neglected in previous studies. Therefore, we applied computational fluid dynamics techniques at micro-scale to study the filtration performance of a glass fibrous media under sinusoidal flow condition. The effects of different flow rates, fluctuation frequencies, fluctuation amplitudes and particle sizes on filtration performance were investigated. Results show that changing the incoming flow field can weaken the Brownian diffusion of particles, resulting in reduced capture efficiency for particles smaller than 0.1 μm. The ratio of particle penetration between sinusoidal flow condition and constant flow condition is calculated. When the fluctuating frequency of the airflow changes for particles less than 0.1 μm, the smaller the particle size is, the larger the ratio of particle penetration is. When the particle size is near the Most Penetrating Particle Size (MPPS), the fluctuating airflow with large amplitude makes the particles more easily trapped by the fiber. The fluctuating airflow with large amplitude will result in a significant reduction in the capture efficiency for particles larger than 1 μm, and the penetration ratio will be greater than that under constant flow condition by three times. For particles with size smaller than 0.1 μm and larger than 1 μm, the amplitude of 0.4 u‾ and smaller has little effect on the capture efficiency. The capture efficiency of particles with size near MPPS value is less susceptible to changes in sinusoidal gas velocity with small amplitude.

Generation and application of sub-kilohertz oscillatory flows in microchannels

We present a user-friendly and versatile experimental technique that generates sub-kilohertz sinusoidal oscillatory flows within microchannels. The method involves the direct interfacing of microfluidic tubing with a loudspeaker diaphragm to generate oscillatory flow in microchannels with frequencies ranging from $10-1000$ Hz and amplitudes ranging from $10 - 600 \ \mu$m. The speaker-based apparatus allows independent control of frequency and amplitude that is unique to the speaker's manufacturing specifications. The performance of our technique is evaluated by Fourier spectral analysis of oscillatory motion of tracer particles, obtained by particle tracking velocimetry, as well as by comparing oscillatory flow profiles against theoretical benchmarks such as Stokes flow in a square channel and Stokes' second problem near a solid boundary. Applications that utilize both the oscillatory flow and the associated steady rectified flows are demonstrated in prototypical microfluidic configurations. These include inertial focusing and mixing at low Reynolds numbers, respectively.

Rayleigh–Taylor instability in porous media under sinusoidal time-dependent flow displacements

Linear stability analysis and nonlinear simulations have been carried out to analyze the Rayleigh–Taylor instability in homogeneous porous media under time-dependent flow displacements. The flow processes consist of a sinusoidal time-dependent velocity characterized by its period (T) and amplitude (Γ) and ensure that the same amount of fluid is injected over a full flow period. A new, more efficient approach to determine instability characteristics has been developed for the stability analysis of these time-dependent injection flows and showed a growth rate that varies in time like the displacement velocity. The effects of the period T and amplitude Γ as well as the fluids’ viscosity (R) and density differences (ΔG) have been analyzed. Consistent with constant injection displacements, a larger ΔG leads to stronger instabilities. Furthermore, it is found that a larger R tends to attenuate the instability during extraction and soaking periods and to enhance it during injection. This study also revealed that for a given total injection time, the time-dependent flow can be less or more unstable than its constant injection counterpart. In particular, for Γ < −1, larger periods lead to stronger instabilities with longer more developed fingers. For Γ > 1, on the other hand, it is found that larger periods tend to attenuate the instability resulting in a smaller number of fingers and a more diffused front. Flows with unit amplitude (Γ = 1) exhibit the same qualitative trends as but are overall more unstable than their counterparts with Γ > 1.

Single-Phase to Three-Phase Unified Power Quality Conditioner for Power Factor Improvement Using Fuzzy Logic Controller

This paper manages the arrangement of a nearby three stage four wire (3P4W) electrical power appropriation framework (EPDS), utilizing a solitary to three stage bound together power quality conditioner (UPQC) topology with fluffy controller , called UPQC 1Ph to 3Ph. The topology is shown for applications in country or remote zones in which, for financial reasons, just EPDS with single wire earth return are open to the buyer. Since the utilization of three stage loads is expanding in these regions, access to a three stage dispersion framework ends up dominant. By embracing a double pay methodology, the proposed UPQC 1Ph to 3Ph is capable of depleting from the single stage electrical framework a sinusoidal flow and in stage with the voltage, coming about high power factor. Moreover, the framework is likewise ready to stifle lattice voltage sounds, just as to make up for different aggravations, for example, voltage lists. In this proposed topology we are utilizing fluffy rationale controller to Single-Phase To Three-Phase Unified Power Quality Conditioner to decrease of the music and execution will be expanded. Along these lines, a 3P4W framework with fluffy managed, offset and sinusoidal voltages with low consonant substance is accommodated single and three stage loads. An examination of the power move through the arrangement and parallel converters is performed so as to help the structuring of the power converters. Reenactment results are exhibited for approving the proposition of fluffy, just as assessing the static and dynamic exhibitions of the proposed topology.

Flow-induced vibration attenuation of a viscoelastic pipe conveying fluid under sinusoidal flow using a nonlinear absorber

In this paper, the dynamics of a viscoelastic pipe conveying fluid attached to a nonlinear energy sink (NES) subjected to a sinusoidal flow is studied, aiming at performance improvement of such fluid-interaction systems. The NES has an essentially nonlinear cubic stiffness and a nonlinear cubic damping. Complexification-averaging and fourth-order Runge-Kutta methods are applied to solve the equations of the motion. The conditions of flow-induced instability, the weak modulated response (WMR), and the strongly modulated response (SMR) are investigated. The influence of the internal fluid velocity, the external flow velocity, the viscoelastic damping coefficient, the NES stiffness, location, and damping on the system efficiency is elucidated. The Poincare-Bendixson theorem implies that there are no closed trajectories in the phase diagram of the system response. The results revealed that the occurrence probability of the SMR and jump phenomenon in the system response increases by ascending the internal fluid velocity. Besides, it is shown that at high external fluid velocities or low viscoelastic damping coefficients, the detached resonance curve (DRC) emerges in the frequency-response curves, and simultaneously the unstable regions expand. Furthermore, by approaching the NES installation location to the pipe supports, the occurrence probability of the SMR, DRC, and WMR descends, the divergence regions are enlarged and the transient response lasts longer.

Optimal design and implementation of a half-cycle generator with the range of 400 A and 100 kHz frequency

In this paper, a double-layer half-cycle generator (HCG) has been designed and built. The proposed HCG creates sinusoidal flow with 400 A peak and 5 µs pulse width which feeds RLC load with 100 kHz work frequency, within resonance mode. Previous HCGs have been designed based on saturable reactor (SR). It should be noted that SR is a nonlinear element, and it will be distanced from its desirable performance upon change of temperature and under impact; however, a double-layer HCG has been proposed with no such defects. In proposed HCG, thyristor has been used instead of SR which is controllable, and it has none of aforementioned problems. Also, when SR is eliminated, its reverse retrieval needs no minority carriers. This way, sweep-out circuit may be also eliminated. From among other advantages of proposed HCG, reduction in number of circuit layers may be referred to, comparing to previous HCG. This results in reduction in number of equipment which in turn optimizes proposed HCG, in terms of volume and manufacturing costs. Finally, proposed HCG has been simulated in Matlab, while it has been implemented practically. Comparing simulation results and laboratory sample confirms correctness of relationships, in analytical design of HCG.

Turbulent viscosity and magnetic Prandtl number from simulations of isotropically forced turbulence

Context.Turbulent diffusion of large-scale flows and magnetic fields plays a major role in many astrophysical systems, such as stellar convection zones and accretion discs.Aims.Our goal is to compute turbulent viscosity and magnetic diffusivity which are relevant for diffusing large-scale flows and magnetic fields, respectively. We also aim to compute their ratio, which is the turbulent magnetic Prandtl number, Pmt, for isotropically forced homogeneous turbulence.Methods.We used simulations of forced turbulence in fully periodic cubes composed of isothermal gas with an imposed large-scale sinusoidal shear flow. Turbulent viscosity was computed either from the resulting Reynolds stress or from the decay rate of the large-scale flow. Turbulent magnetic diffusivity was computed using the test-field method for a microphysical magnetic Prandtl number of unity. The scale dependence of the coefficients was studied by varying the wavenumber of the imposed sinusoidal shear and test fields.Results.We find that turbulent viscosity and magnetic diffusivity are in general of the same order of magnitude. Furthermore, the turbulent viscosity depends on the fluid Reynolds number (Re) and scale separation ratio of turbulence. The scale dependence of the turbulent viscosity is found to be well approximated by a Lorentzian. These results are similar to those obtained earlier for the turbulent magnetic diffusivity. The results for the turbulent transport coefficients appear to converge at sufficiently high values of Re and the scale separation ratio. However, a weak trend is found even at the largest values of Re, suggesting that the turbulence is not in the fully developed regime. The turbulent magnetic Prandtl number converges to a value that is slightly below unity for large Re. For small Re we find values between 0.5 and 0.6 but the data are insufficient to draw conclusions regarding asymptotics. We demonstrate that our results are independent of the correlation time of the forcing function.Conclusions.The turbulent magnetic diffusivity is, in general, consistently higher than the turbulent viscosity, which is in qualitative agreement with analytic theories. However, the actual value of Pmtfound from the simulations (≈0.9−0.95) at large Re and large scale separation ratio is higher than any of the analytic predictions (0.4−0.8).

Hepatocyte HIF‐1alpha mediates obesity‐induced decreased incretin effects

The decrease in incretin effects is an important etiologic component of type 2 diabetes with unknown mechanisms. In an attempt to understand obesity‐induced changes in liver oxygen homeostasis and its metabolic consequence, we came across a novel finding that liver HIF‐1α expression was increased mainly by soluble factors released from obese adipocytes, leading to decreased incretin effects. In‐depth mouse metabolic phenotyping revealed that obesity increased first‐pass degradation of an incretin hormone GLP‐1 with increased liver DPP4 expression and decreased sinusoidal blood flow rate, reducing active GLP‐1 levels in peripheral circulation. Deletion of hepatocyte HIF‐1α KO blocked these changes induced by obesity: hepatocyte HIF‐1α KO mice were protected from obesity‐induced glucose intolerance without changes in body weight, liver steatosis, or insulin resistance. Deletion of hepatocyte HIF‐2α did not change liver DPP4 expression but improved hepatic steatosis. Our results identify a previously unknown pathway for obesity‐induced impaired beta cell glucose response (incretin effects) and the development of glucose intolerance through inter‐organ communications.