Intermediate Flow Research Articles

Evaluation of flow of chorioretinal capillaries in healthy black and white subjects using optical coherence tomography angiography

This study compared macular capillary parameters between healthy black and white subjects using optical coherence tomography angiography (OCTA). We measured vessel density (VD) of superficial (SCP), intermediate (ICP), and deep (DCP) capillary plexuses and choriocapillaris blood flow area (BFA) of the fovea, parafovea and total 3 mm-diameter circular area centered on the fovea, as well as the foveal avascular zone (FAZ) parameters, controlling for axial length. Black subjects had lower foveal and parafoveal VD in the SCP (p = 0.043 and p = 0.014) and the ICP (p = 0.014 and p = 0.002). In the DCP, black subjects had a trend toward lower foveal and parafoveal VD. Black subjects had decreased choriocapillaris BFA in the total 3 mm area (p = 0.011) and the parafovea (p = 0.033), larger FAZ area (p = 0.006) and perimeter (p = 0.014), and a higher capillary density in a 300 μm wide region around the FAZ (FD-300) (p = 0.001). There was no significant difference in FAZ acircularity index. To our knowledge, this is the first report analyzing the three distinct retinal capillary plexuses and identifying differing baseline VD, choriocapillaris and FAZ parameters in healthy young black compared to white subjects. Larger studies are needed to validate these findings and better understand racial differences in vulnerability to ocular diseases.

Effect of particle mass inhomogeneity on the two-dimensional Rayleigh–Bénard system of Yukawa liquids: A molecular dynamics study

The effect of particle mass inhomogeneity on the evolution of macroscale fluid flow in the Rayleigh–Bénard system of two-dimensional Yukawa liquids is studied using “first principles” classical molecular dynamics simulations. We find that Rayleigh–Bénard convection cells (RBCCs) formed in the quasi-steady-state become unstable at later times as a result of introducing a small fraction (≤2% of the total particles) of particle mass inhomogeneity in a Yukawa system made up of point particles of uniform charges. The unstable RBCCs, after passing through several intermediate states, give rise to a unidirectional shear flow in the direction perpendicular to the external gravity. Depending on the fraction and phase space of the particle mass inhomogeneity introduced in the system, the unidirectional shear flow further evolves to give shearless parallel flow. We use single or dual particle mass distributions of various forms, such as Gaussian distribution, Dirac-delta distribution, or a combination of both, around different mean values in order to introduce particle mass inhomogeneity. The role of system size on the emergence of various intermediate fluid flow states is also investigated. Furthermore, by introducing an inhomogeneity in charge commensurate with mass inhomogeneity, we demonstrate the robustness of our findings. Finally, for the case of decreasing correlation strength and for otherwise identical parameters, it is shown that the particle mass inhomogeneity fails to generate shear flows from RBCCs in 2D Yukawa liquids.

Impact of water source dynamics on dissolved reactive phosphorus loadings in heterogenous karst agroecosystems with phosphatic limestones

AbstractKarst landscapes underlain with phosphatic limestones are now recognized to be an important contributor of fluvial phosphorus (P) to coastal waters. Specifically, karst agroecosystems may be a hotspot for dissolved reactive P (DRP) due to chronic over‐application of organic and inorganic fertilizers that create legacy P accumulation in surface soils. Nevertheless, few studies have assessed the hydrologic controls on DRP transport in these systems at the watershed scale, which is the focus of this study. We analysed soil moisture, soil water extractable P, and storm event hydrologic and water quality data from a small heterogenous karst watershed (10.7 km2) in the Inner‐Bluegrass Region of Central Kentucky, USA. Four storm events were sampled in winter, 2020 and were analysed for flow pathways using hydrograph recession analysis and water source connectivity using a tracer‐based unmixing model. Based on hydrograph separation results, multiple linear regression analysis was performed to assess drivers of DRP concentrations and loadings. Soil water extractable P results showed stark vertical gradients with greater concentrations at both the surface and deeper soil zones, and minimum concentrations in the root zone. Results for the storm event analysis showed that water source connectivity provided superior prediction of DRP concentrations over the flow pathway analysis, which reflected the heterogeneity of karst maturity masking intermediate flow pathways. Findings from the MLR and loading analysis suggest waters sourced from the soil/epikarst produced significantly higher loadings compared with phreatic and precipitation water source in the three largest events, although concentrations fell between the phreatic (low) and precipitation (high) sources. Findings highlight variable activation of matrix‐macropore exchange at different depths throughout the event. Collectively these results suggest existing models and approaches to assess karst hydrology need revision to improve management strategies in this critical landscape.

The prediction of fluidelastic forces in triangular tube bundles subjected to a two-phase flow: The effect of the flow approach angle

The U-bend region in a typical steam generator is characterized by two-phase flow conditions and susceptible to damage due to fluidelastic instability excitation. To prevent such a destructive fluid–structure mechanism, numerous experimental and numerical works have been done to investigate, understand, and devise techniques to mitigate it. The effect of the flow approach angle on fluidelastic instability remains one of the topics which has not been fully resolved. This work aims to utilize flow numerical modeling techniques to gain an understanding of such an effect in a two-phase air–water flow. Various flow approach angles ranging from normal to parallel triangular arrays were investigated for various void fractions ranging from water to air flows. The results obtained revealed that the effect of a homogeneous air void fraction is very critical at very high values (99% and above). Moreover, at any intermediate flow approach angle between a normal and a parallel triangular array, the flow inside the array carries features of both normal and parallel triangular flow patterns. Based on this, a new FEI force-approach angle, semi analytical model is proposed to calculate the fluidelastic forces at any flow approach angle. The data obtained from this model were validated against information extracted from flow simulations and showed a good agreement.

Groundwater flow patterns, hydrogeochemistry and metals background levels of shallow hard rock aquifer in a humid tropical urban area in sub-Saharan Africa- A case study from Olézoa watershed (Yaoundé-Cameroon)

Study regionOlézoa watershed, Yaoundé-Cameroon, Central Africa Study FocusThis study aimed to determine the hydrogeological characteristics of shallow hard rock aquifer and the environmental levels of heavy metals in an urbanized equatorial region. Physico-chemical parameters and heavy metals were determined on 25 groundwater samples and analyzed using conventional hydrochemical methods, multivariate analysis, heavy metal pollution index (HPI) and natural background levels (NBL). New Hydrological Insights for the RegionHydrogeological functioning is not marked by a mass of basal groundwater with a low hydraulic gradient Hydrochemical facies were predominantly Ca-Mg-Cl, HCO3-Ca-Mg and Ca-Cl type, which were controlled water-rock interaction, cation exchange, dissolution of silicates and anthropogenic activities. Multivariate analysis did not show very significant hydrochemical spatial zonation but the first major component can be used as an indication of the groundwater flow direction. Vertically, a three-part structure around depths of 1 m and 3−7 m were identified and associated with local and intermediate flow systems at the Olézoa watershed-scale.HPI showed short range variations similar to that of EC, suggesting compartmentalization of the shallow aquifer on a small scale. Thus, a preliminary conceptual model describing groundwater dynamics has been proposed. NBL and median HPI values indicate a serious concern in terms of groundwater qualitative potential and the urgency of regular monitoring of heavy metals in groundwater in this urbanized part of sub-Saharan Africa.

Nested Recharge Systems in Mountain Block Hydrology: High-Elevation Snowpack Generates Low-Elevation Overwinter Baseflow in a Rocky Mountain River

The majority of each year′s overwinter baseflow (i.e., winter streamflow) in a third-order eastern slopes tributary is generated from annual melting of high-elevation snowpack which is transmitted through carbonate and siliciclastic aquifers. The Little Elbow River and its tributaries drain a bedrock system formed by repeated thrust faults that express as the same siliciclastic and carbonate aquifers in repeating outcrops. Longitudinal sampling over an 18 km reach was conducted at the beginning of the overwinter baseflow season to assess streamflow provenance. Baseflow contributions from each of the two primary aquifer types were apportioned using sulfate, δ34SSO4, and silica concentrations, while δ18OH2O composition was used to evaluate relative temperature and/or elevation of the original precipitation. Baseflow in the upper reaches of the Little Elbow was generated from lower-elevation and/or warmer precipitation primarily stored in siliciclastic units. Counterintuitively, baseflow generated in the lower-elevation reaches originated from higher-elevation and/or colder precipitation stored in carbonate units. These findings illustrate the role of nested flow systems in mountain block recharge: higher-elevation snowmelt infiltrates through fracture systems in the cliff-forming—often higher-elevation—carbonates, moving to the lower-elevation valley through intermediate flow systems, while winter baseflow in local flow systems in the siliciclastic valleys reflects more influence from warmer precipitation. The relatively fast climatic warming of higher elevations may alter snowmelt timing, leaving winter water supply vulnerable to climatic change.

A unified immersed boundary-lattice Boltzmann flux solver (UIB-LBFS) for simulation of flows past porous bodies

A novel numerical method named the unified immersed boundary-lattice Boltzmann flux solver (UIB-LBFS) for simulating incompressible flows past homogeneous porous bodies is proposed in this paper. A diffuse layer through which the porosity is smoothly changed is introduced. As a consequence, the governing equations in the porous domain and the pure-fluid domain can be unified. The solutions to each domain can be smoothly transitioned from one to the other through the diffuse layer around the domain interface. A fractional-step technique is employed to split the computational procedure into the predictor step and the corrector step, respectively. In the predictor step, an intermediate flow field is first predicted without considering the domain interface by the unified lattice Boltzmann flux solver. Then, the physical conditions at the fluid–porous interface are implemented through the immersed boundary method to correct the flow field in the corrector step. All the flow quantities are evaluated at the cell centers, while the viscous and the inviscid numerical fluxes are locally reconstructed at each cell interface simultaneously. Numerical validations are carried out, and excellent agreements between the present and published results are achieved. The accuracy and the reliability of the UIB-LBFS are thus proven.

Evaluation of Groundwater Quality for Human Consumption and Irrigation in Relation to Arsenic Concentration in Flow Systems in a Semi-Arid Mexican Region.

The supply of drinking water to the population is an important challenge facing humanity, since both surface and underground sources present a great variability of water storage with respect to space and time. This problem is further aggravated in arid and semi-arid areas where rainfall is low and torrential, which makes groundwater the main source of supply; therefore, it is necessary to carry out studies that allow evaluating the evolution of the quantity and quality of water. This study addresses the behavior of groundwater in a semi-arid region, considering the theory of flow systems to identify movement as well as water quality, es determined by a water quality index (WQI), calculated considering arsenic and fluorine. In addition, a quality irrigation classification is used, employing the norms in accordance with international standards and the Mexican Norm, which allows for a comparison. Local, regional, intermediate and mixed flow systems are identified, and the evolution of cations and anions in addition to temperature is examined. It is observed that the drinking water quality index classifies them as excellent in most of the monitored wells (<50), but with a negative evolution. Regarding irrigation, most of the water samples are classified without restriction for the establishment of any type II crop (C2S1) and with restrictions for horticultural crops. It is observed that arsenic had values between 0.49 and 61.40 (µg/L) in 2005, while in 2015 they were between 0.10 and 241.30 (µg/L). In addition, fluoride presented values between 0.00 and 2.6 (mg/L) in 2005, while in 2015 they were between 0.28 and 5.40 (mg/L). The correlations between arsenic and fluorine are noted as well as WQI and SAR. A finding in this research was to include arsenic and fluorine in the calculation of the WQI allowing a better interpretation of the quality of water for both human consumption and for agricultural use to based on this make the best decision to control any harmful effects for the population, in addition to identifying the appropriate purification treatment required to control pollutants. It is concluded that arsenic is an element of utmost importance when considering water quality, so it is necessary to examine its evolution and continue to monitor its levels constantly.

Effect of Flow Rate Scaling on SAE-InAs Crystal Phase and Integration of Self-Catalyzed InAs/InSb Heterostructure Nanowires on Si (111) Substrate by MOCVD

The effect of III-V molar flow scaling on crystal quality of selectively grown InAs nanowires on patterned Si (111) substrate is investigated by metal organic chemical vapor deposition. We found the correlations between molar flow rate scaling and selectivity and InAs crystal structure have been investigated. When the molar flow rate is higher, nanowire follows random nucleation and exhibits zincblende crystal structure, whereas growth selectivity increases to 97% at intermediate molar flow rates and nanowire exhibits wurtzite dominant crystal phase with occasional stacking faults. Once the molar flow rate is scaled-down aggressively, nanowire exhibits polytype crystal structure with small degradation in selectivity. The resistivity calculated from current-voltage curve of moderate molar flow rate InAs nanowires showed 15.9 × 10–3 Ωcm, which was significantly (1.6 times) lower than typical InAs nanowires with low molar flow rate (25.31 × 10–3 Ωcm). Finally, we integrate axial InSb heterostructure nanowire with two different crystal structures on InAs stem by self-catalyzed selective area epitaxy for the V/III ratio of 2. This study further offers good opportunity to tune the crystal structure of InSb with the help of In-catalyzed growth technique.

Geomorphological Controls on Groundwater Transit Times: A Synthetic Analysis at the Hillslope Scale

AbstractWe investigated how geomorphological structures shape Transit Time Distributions (TTDs) in shallow aquifers. Extensive three‐dimensional simulations were performed to determine the TTDs for synthetic convergent, straight, and divergent hillslopes with a constant slope. The uniform recharge applied on top of the aquifer is transferred to the receiving stream through steady‐state groundwater flows, return flows and saturation excess overland flows. Without seepage, TTDs evolve from uniform‐ to power law‐like‐ distributions depending on the average distance of the groundwater volume to the river (barycenter). Remarkably, the coefficient of variation (ratio of the standard deviation to the mean) of the TTDs scales linearly with the barycenter in agreement with a theoretical prediction based on three analytical approximations derived for specific cases. With seepage, the TTD has three separate modes corresponding to rapid saturation excess overland flows, to the intermediate flow paths ending in seepage area and to the slower flow paths going all the way to a discharge in the river. The coefficient of variation additionally depends on the extent of the seepage area. For a natural hillslope in the crystalline basement of Normandy (France), the same synthetic analysis demonstrates that the coefficient of variation is not only determined by the extent of the seepage zone but also by its structure in relation to the local and global geomorphological organization. The results suggest the possibility to assess the variability of transit times by combining geomorphological analysis, surface soil saturation observations and environmental tracers.

Effect of Ar/N2 flow ratio on the microstructure and mechanical properties of Ti-Cr-N coatings deposited by DC magnetron sputtering on AISI D2 tool steels

Ti-Cr-N coatings were deposited on Si (100) and AISI D2 tool steel substrates by reactive DC magnetron co-sputtering technique from titanium and chromium target in mixed Ar/N2 atmosphere. The Ar/N2 ratio effects on the chemical composition, structure, morphology, intrinsic stress and mechanical properties of the Ti-Cr-N coatings were investigated. The growing process of Ti-Cr-N coatings can be divided into three stages: Stage I, in poisoning mode (low flow ratio 1 < Ar/N2 ≤ 1.4), Stage II, in transition mode (intermediate flow ratio 1.4 ≤ Ar/N2 ≤ 3) and Stage III in metallic mode (Ar/N2 > 3). For all samples, XRD analysis shown the formation of mixed nitrides phases. In stage I, Ti2N, TiN0.3, and hexagonal-Cr2N phases were observed. In Stage II, TiN0.3, Cr2N, and cubic-TiN phases were formed, while only TiN and Cr2N are observed in stage III. The coatings deposited with Ar/N₂ ratio of 3 shows the largest hardness of 24 GPa which is attribute to the dense structure and smoother surface morphology. The properties of the films are discussed in terms of evolution growth stages resulting by the variation of Ar/N2 flow ratios.

Dripping and jetting of semi-dilute polymer solutions co-flowing in co-axial capillaries

This work is focused on the mechanisms of the dripping and jetting flow modes of viscoelastic semi-dilute polyacrylamide aqueous solutions co-flowing with silicone oil in co-axial capillaries. A phase diagram of the dripping, jetting, and intermediate flow modes is established. It was found that in the dripping mode, the elongation velocity of the filament between the terminal droplet and the inner capillary is controlled solely by the continuous phase rate. At the same time, the decrease in the filament diameter is due to both stretching and outflow of the polymer solution into the terminal droplet. In the jetting mode, the thread diameter was found to evolve in three stages. In the first stage, the average jet velocity increases, whereas in the second and third stages, it becomes constant and corresponds to the velocity of the continuous phase. The transition from the second to the third stage is defined by the appearance of capillary waves resulting in the formation of the beads-on-string structure. In the third stage, the filament diameter between the neighbor beads decreases exponentially and is governed by the relaxation time, which strongly depends on polymer concentration, but does not depend on the continuous phase flow rate. A simple physical model was proposed for describing the evolution of dimensions of filaments and beads during development of jet capillary instability. The universal character of the evolution of filaments and beads sizes, which is independent of concentration of semi-diluted polymer solutions and flow rates of the continuous phase, is revealed.

The impact of closed perforation zones and damaged sections on flow dynamics and pressure behaviors of horizontal wells

Horizontal wells with multiple completion parts have become a common completion technique in the oil and gas industry. Sand and asphalt production problems, damaged zones and water cresting or gas coning are the main reasons for using this technique to sustain or improve oil and gas recovery. However, using such completion technique introduces negative effects on pressure behavior of horizontal wells.This paper introduces new mathematical models for horizontal well containing several closed completed sections acting in finite and infinite reservoirs. These models can be used to evaluate the impact of the completion techniques on both pressure behaviors and flow regimes either in the vicinity of wellbore or at the outer boundary of reservoirs. They can be used also to investigate the change in productivity index that would result due to the usage of certain type of completion technique. In this research, the completed sections (cemented or isolated parts) and the places where packers are installed are considered as no-flow sections. These sections are expected to increase pressure drop required for flowing reservoir fluid toward wellbore. They are also expected to change flow regimes mainly in the vicinity of wellbore.Several models have been developed and solved in this study for different completion techniques, wellbore conditions and reservoir configuration. It has been found that the great impact of completion techniques is observed on flow regimes that commonly develop in the drainage area close to wellbore. This impact shows similar trends to the skin factor. Several new flow regimes have been observed, one of them has been developed due to the existence of closed completed sections which is intermediate or second radial flow regime. This flow regime can be found for some cases of long wellbore having multi-short perforated sections. The study will introduce the mathematical models for known and newly developed flow regimes for horizontal well including the completion technique.

Effect of body stiffness distribution on larval fish-like efficient undulatory swimming.

Energy-efficient propulsion is a critical design target for robotic swimmers. Although previous studies have pointed out the importance of nonuniform body bending stiffness distribution (k) in improving the undulatory swimming efficiency of adult fish-like robots in the inertial flow regime, whether such an elastic mechanism is beneficial in the intermediate flow regime remains elusive. Hence, we develop a class of untethered soft milliswimmers consisting of a magnetic composite head and a passive elastic body with different k These robots realize larval zebrafish-like undulatory swimming at the same scale. Investigations reveal that uniform k and high swimming frequency (60 to 100 Hz) are favorable to improve their efficiency. A shape memory polymer-based milliswimmer with tunable k on the fly confirms such findings. Such acquired knowledge can guide the design of energy-efficient leading edge-driven soft undulatory milliswimmers for future environmental and biomedical applications in the same flow regime.

Multiscale calculation results of the flow behavior in micro/nano porous filtration membrane with the adsorbed layer-fluid interfacial slippage

The paper presents the multiscale calculation results for the multiscale flow in micro/nano porous filtration membranes where the adsorbed layer effect is involved, by considering the adsorbed layer-fluid interfacial slippage. The analysis consists of the molecular scale analysis for the adsorbed layer flow and the continuum analysis for the intermediate fluid flow. The calculation results are respectively compared with the classical flow theory calculations and those based on the solid layer assumption. The adsorbed layer flow rate is also compared with the flow rate of the intermediate continuum fluid. It is shown that for a strong fluid-pore wall interaction or for a large adsorbed layer-fluid interfacial slippage the adsorbed layer can be treated as a solid layer; otherwise it should be treated as a flowing layer. The large interfacial slippage results in the flow rate through the pore far greater than the classical Hagen-Poiseuille equation calculation; it largely propels the flow of the intermediate continuum fluid and makes the adsorbed layer flow negligible particularly for the medium and strong fluid-pore wall interactions. The increasing fluid-pore wall interaction strength significantly reduces the flow rate through the pore.

Watershed hydrological modelling in data scarce regions; integrating ecohydrology and regionalization for the southern Caspian Sea basin, Iran

The aim of this study is to evaluate an alternative approach to indicate how hydrological processes behave in a given watershed, and to test whether this approach can replace traditional calibration, particularly under data deficient conditions. Therefore, a regional calibration method (RC) was adapted to characterize “parameter-based hydrologic processes” as a function of watershed ecologic attributes. The methodological process included (1) temporal phase, (2) correlation analysis and (3) spatial phase. The defined methodology was carried out on a 4160 km2 area containing 21 watersheds laying in the southern coastal line of the Caspian Sea, Iran. By implementing the RC, regional models were specified corresponding to each hydrological process defined in the Tank model. Testing the reliability of the transferring process of hydrological parameters was conducted using multi-level accuracy comparison (MAC) benefiting from descriptive statistics, scatter-plots and T-test.Both temporal and spatial phases have shown acceptable outputs backed by their ecologic significance, but as an alternative approach to traditional calibration, the standalone RC still needs development to achieve a more robust basis covering all the parameters of the hydrologic model. According to the post-processor MAC, the transferability of six out of twelve regional models (height of lower outlet at the first tank, intermediate flow, deep-percolation, infiltration, surface flow, height of outlet at the second tank) was accepted with respect to the given tests. As such, our method outperformed the number of transferable parameters by an outstanding regional model predicting the surface flow in comparison with similar studies.Although the RC could not achieve total perfection, nevertheless it could still help users by providing more information about the contribution of ecologic variables in the prediction of the hydrological processes of a certain watershed.

Effects of External Flow on Resonant Absorption of Coronal Loop Kink Oscillations Driven by an External Fast Wave: Selective Excitation Problem

Abstract Resonant absorption is considered to be a crucial mechanism for the damping of the coronal loop oscillations and plasma heating. We study resonant absorption of the coronal loop kink oscillations excited by such external drivers as flares, assuming that there is an intermediate shear flow region surrounding the loop. We find that for long coronal loops resonant absorption can be highly enhanced or reduced depending sensitively on the magnitude and direction of the flow and the spatial extent of the flow region when the transitional layer is thin. For short coronal loops, high flow speed and a thick transitional layer are needed to have a substantial resonant absorption. We provide a potential picture to explain the results where the external Alfvén speed and phase speed of the wave are important parameters. These results imply that the transport of the external wave energy into the loop is significantly changed by the shear flow region, which may cause the selective excitation of the coronal loop oscillations.

Controllable preparation of double emulsion droplets in a dual-coaxial microfluidic device

This article investigates the formation process of double emulsions, controlling their sizes, and manipulating the encapsulation process in a three nested microcapillary tube configuration. In the proposed geometry, as a result of the interaction of liquids using dripping instability, double emulsions are generated. Governing equations are discretized using the finite-element method utilizing COMSOL Multiphysics 5.4 software, employing axisymmetric assumption, and the interface position is tracked by solving additional transport equations of the phase-field method. Influence of phase flow rates in the form of inner phase Weber number, Wein, intermediate phase capillary number, Caint, and outer phase capillary number, Caout, are studied on the flow regimes and characteristics of double emulsions. Results exhibit that the outer phase flow rate has the most influence among other phase flow rates. Additionally, three distinct regimes, named single emulsion, decussate, and double emulsion, are observed by changing intermediate phase flow rare. Furthermore, satellite droplets are detected at relatively high flow rates of the outer phase due to the second instability induced by the continuous phase to the intermediate phase jet. A comparison between the formation frequency of the present study with some similar works, including both capillary-based and channel-based devices, unveils that the existing configuration has a higher throughput of double emulsion generation in a broad range of flow rates.

Rheology of a dense granular bed penetrated by a rotating impeller

Understanding of the rheological behaviour of fully three-dimensional and non-uniform particle flow is of great interest. We analyse the resistance exhibited by a granular bed as a rotating impeller is penetrated into it, from which the rheological characteristics of the bed are deduced. For this end, the transient rheological response of both spherical and rodlike particles is simulated by Discrete Element Method. Transition from quasi-static to intermediate flow regime of rodlike particles is found to occur at a much larger shear strain rate than that of spherical particles. The relationship between the bulk friction coefficient and the inertial number is not monotonic. The viscosity of particle flow is inferred from the blade torque and is related to the inertial number and granular temperature, for which a power law is obtained covering both quasi-static and intermediate flow regimes. It can be used for obtaining flow field in complex geometry and dynamics using continuum mechanics by Computational Fluid Dynamics.

Состояние гемодинамики и вариабельность сердечного ритма у тяжелобольных COVID‑19 в разгар заболевания и в процессе реабилитации

Введение. Состояние системы гемостаза при COVID-19 детально исследовано. Вместе с тем совершенно не изучено состояние гемодинамики и вариабельность сердечного ритма (ВСР) у больных COVID-19 в разгар заболевания и в процессе реабилитации. Цель исследования: изучить состояние микроциркуляции и ВСР у больных с тяжелым течением COVID-19 в процессе заболевания, после выписки из стационара и после прохождения курса реабилитации. Материалы и методы. Наши наблюдения проведены на 43 пациентах, получавших лечение в ГУЗ «ГКБ № 1» (Чита), перепрофилированной для терапии больных COVID-19, а также на курорте «Дарасун» (Забайкальский край), предназначенном для реабилитации больных, перенесших COVID-19. Контрольную группу составили 69 человек, сопоставимых по полу возрасту и сопутствующим заболеваниям. Состояние кровотока и ВСР изучали с помощью датчика mDLS (Dynamic Light Scattering, Rehovot, Israel) и использования оригинального алгоритмического подхода. При этом сигнал разлагался на частотные компоненты, связанные с гемодинамическими источниками различной скорости сдвига слоев крови (гемодинамические индексы), в значительной степени отражающих состояние системы гемостаза. Результаты. У больных COVID‑19 абсолютные значения гемодинамических индексов оказались значительно выше, чем в контроле, что свидетельствует об усилении микроциркуляторной динамики. Особенно резко возрастали значения HI1и HI2, что связано с усилением пристеночного (эндотелиального) и промежуточного кровотока. Об этом же свидетельствует увеличение у тяжелобольных почти в 4 раза соотношения HI1/HI3, которое не восстанавливалось после выздоровления, а также после реабилитации. Одновременно в разгар заболевания происходило значительно усиление пульсовых (PULSE 1 и 2) и резкое снижение респираторных (RESP1, 2 и 3) осцилляторных индексов, значения которых оставались стабильными как у выздоровевших пациентов, так и у прошедших курс реабилитации. Заключение. У больных COVID-19 в разгар заболевания отмечаются выраженные сдвиги со стороны микроциркуляции и ВСР, обусловленные повышением тонуса симпатического отдела автономной нервной системы, и сохраняющееся после выписки из стационара и прохождения курса реабилитации. Background. Hemostasis in COVID‑19 has been studied in detail. The state of hemodynamics and heart rate variability (HRV) in patients with COVID‑19 at the height of the disease and during rehabilitation has not been fully studied. Objectives: to study microcirculation and HRV in patients with severe COVID-19 during the course of the disease, after discharge from the hospital and after rehabilitation course. Patients/Methods. We examined 43 patients with COVID‑19 treated at City Clinical Hospital № 1 (Chita) and underwent rehabilitation at Darasun resort (Trans-Baikal Territory). The control group consisted of 69 people of same sex, age and concomitant diseases. Blood flow and HRV were studied using mDLS sensor (Dynamic Light Scattering, Rehovot, Israel) and an original algorithmic approach. The signal was decomposed into frequency components associated with hemodynamic sources of different shear rates of blood layers (hemodynamic indexes) that largely reflected hemostasis state. Results. In patients with COVID-19, the absolute values of hemodynamic indexes were significantly higher than in controls, it was the evidence of microcirculatory intensification. The HI1 and HI2 values increased especially sharply, that was associated with increased endothelial and intermediate blood flow. This was also evidenced by an almost 4‑fold increase in the HI1/HI3 ratio in seriously ill patients that does not restored after recovery, as well as after rehabilitation. At the same time, at the height of the disease, there was a significant increase of pulse (PULSE 1 and 2) and a sharp decrease of respiratory (RESP1, 2 and 3) oscillatory indexes, that remained stable both in recovered patients and in those who underwent a course of rehabilitation. Conclusions. In patients with COVID-19 at the height of the disease pronounced shifts in microcirculation and HRV are noted due to increased tonus of sympathetic nervous system that persisted after discharge and rehabilitation.