Altered Flow Research Articles

Measurement of Turbulent Kinetic Energy in Hypertrophic Cardiomyopathy Using Triple-velocity Encoding 4D Flow MR Imaging.

The turbulent kinetic energy (TKE) estimation based on 4D flow MRI has been currently developed and can be used to estimate the pressure gradient. The objective of this study was to validate the clinical value of 4D flow-based TKE measurement in patients with hypertrophic cardiomyopathy (HCM). From April 2018 to March 2019, we recruited 28 patients with HCM. Based on echocardiography, they were divided into obstructed HCM (HOCM) and non-obstructed HCM (HNCM). Triple-velocity encoding 4D flow MRI was performed. The volume-of-interest from the left ventricle to the aortic arch was drawn semi-automatically. We defined peak turbulent kinetic energy (TKEpeak) as the highest TKE phase in all cardiac phases. TKEpeak was significantly higher in HOCM than in HNCM (14.83 ± 3.91 vs. 7.11 ± 3.60 mJ, P < 0.001). TKEpeak was significantly higher in patients with systolic anterior movement (SAM) than in those without SAM (15.60 ± 3.96 vs. 7.44 ± 3.29 mJ, P < 0.001). Left ventricular (LV) mass increased proportionally with TKEpeak (P = 0.012, r = 0.466). When only the asymptomatic patients were extracted, a stronger correlation was observed (P = 0.001, r = 0.842). TKE measurement based on 4D flow MRI can detect the flow alteration induced by systolic flow jet and LV outflow tract geometry, such as SAM in patients with HOCM. The elevated TKE is correlated with increasing LV mass. This indicates that increasing cardiac load, by pressure loss due to turbulence, induces progression of LV hypertrophy, which leads to a worse prognosis.

Alteration in electroosmotic flow of couple stress fluids through membrane based microchannel

The fundamentals of electroosmosis are the most fascinating mechanism to induce flow of ionic solution under the effect of external electric field. The electroosmotic flow of the couple stress fluid in a microchannel with an active membrane pumping is analysed in the present model. The upper wall experiences membrane kinematics, generates the pressure to drive the fluid in the microchannel. Governing equations are formulated based on the mass and momentum conservation, and electric potential distribution of ions in diffuse layer. The suitable boundary conditions for the model have been considered. An analytical approach is employed to derive the solutions under the lubrication approximation, and the Debye–Hückel approximation. The effects of electric double layer thickness, couple stress parameter, and Helmholtz-Smoluchowski velocity on the velocity profile, pressure difference, net flow rate, induced streamline velocity, and local wall shear stress are computed for discussion of the physical significance of the model and its applications. Results reveal that electroosmosis mechanisms (axial electric field and electric double layer thickness) has remarkable role in modulating the fluids (Newtonian and non-Newtonian) flow driven by the rhythmic propulsion of membranes in microchannel. It is also worth mentioning that non-Newtonian fluids (couple stress fluids) need more external forces (electric force) to be pumped as compared to Newtonian fluids. Furthermore, it can be analysed that thinner electric double layers (EDLs) elevate wall shear stress, whereas stronger electric fields result in decreased wall shear stress. The results of the model help in designing smart membrane based electric pump for the use in various microscale transport phenomena of bio microfluidics systems.

Assessment of ecological flow alterations induced by hydraulic engineering projects in the Han River, China

Abstract A thorough understanding of the ecological impacts behind the hydrologic alteration is still insufficient and hinders the watershed management. Here, we used eco-flow indicators, multiple hydrological indicators, and fluvial biodiversity to investigate the ecological flow in different temporal scales. The case study in the Han River shows a decrease in high flows contributed to the decrease in eco-surplus and increase in eco-deficit in summer and autumn, while the decrease in eco-deficit can be attributed to the change of low flow in spring. An integrated hydrologic alteration was over 48% degree and was under moderate ecological risk degree in impact period I, while DHRAM scores showed the Huangzhuang station faced a high ecological risk degree in impact period II. The decrease (increase) in total seasonal eco-surplus (eco-deficit) was identified after alteration with the change in seasonal eco-flow indicators contributions. Shannon index showed a decreasing trend, indicating the degradation of fluvial biodiversity in the Han River basin. Eco-flow indicators such as eco-surplus and eco-deficit are in strong relationships with 32 hydrological indicators and can be accepted for ecohydrological alterations at multiple temporal scales. This study deepens the understanding of ecological responses to hydrologic alteration, which may provide references for water resources management and ecological security maintenance.

Four-dimensional flow MRI for quantitative assessment of cerebrospinal fluid dynamics: Status and opportunities.

Neurological disorders can manifest with altered neurofluid dynamics in different compartments of the central nervous system. These include alterations in cerebral blood flow, cerebrospinal fluid (CSF) flow, and tissue biomechanics. Noninvasive quantitative assessment of neurofluid flow and tissue motion is feasible with phase contrast magnetic resonance imaging (PC MRI). While two-dimensional (2D) PC MRI is routinely utilized in research and clinical settings to assess flow dynamics through a single imaging slice, comprehensive neurofluid dynamic assessment can be limited or impractical. Recently, four-dimensional (4D) flow MRI (or time-resolved three-dimensional PC with three-directional velocity encoding) has emerged as a powerful extension of 2D PC, allowing for large volumetric coverage of fluid velocities at high spatiotemporal resolution within clinically reasonable scan times. Yet, most 4D flow studies have focused on blood flow imaging. Characterizing CSF flow dynamics with 4D flow (i.e., 4D CSF flow) is of high interest to understand normal brain and spine physiology, but also to study neurological disorders such as dysfunctional brain metabolite waste clearance, where CSF dynamics appear to play an important role. However, 4D CSF flow imaging is challenged by the long T1 time of CSF and slower velocities compared with blood flow, which can result in longer scan times from low flip angles and extended motion-sensitive gradients, hindering clinical adoption. In this work, we review the state of 4D CSF flow MRI including challenges, novel solutions from current research and ongoing needs, examples of clinical and research applications, and discuss an outlook on the future of 4D CSF flow.

Short-term influences of flow alteration on microbial community structure and putative metabolic functions in gravel bar hyporheic zones

Microbial communities in the hyporheic zone are important for self-purification as the riverbed is metabolically active and responsible for the retention, storage, and mineralisation of organic matter transported in the surface water. Studies exploring the response of the hyporheic microbial community to flow regime alterations remain scarce. Here, we characterised the microbial community structure over downwelling, upwelling and intermediate hyporheic zone areas within and among gravel bars at high and low discharge levels to determine flow-induced changes in a dam-regulated river using 16S rRNA gene sequencing. At low discharge, microbial composition varied across the different areas of gravel bars, reflecting heterogeneity in local abiotic conditions. However, high discharge lead to microbial community homogenisation across the three areas of the gravel bars. Microbial communities across adjacent gravel bars remained dissimilar regardless of discharge levels, likely reflecting differences in bar morphology. Our results can help better understand how anthropogenic changes in hydrologic conditions can affect microbial diversity and function in the hyporheic zone. This knowledge will help us to understand better how changes in hydrological conditions affect ecosystem functions and services in rivers affected by human impacts.

The Impact of the Covid-19 Pandemic on the Cross-Sectoral Information Flow in the U.S.

In the past decades a connection between the financial services and technology sector has evolved into a dynamic and complex relationship. However, they were not spared from the far-reaching effects that the spread of the Covid-19 pandemic brought, each responding in a distinctive manner. This paper examines the alterations in the bidirectional information flow between the financial services and technology sectors provoked by the virus outbreak by employing the concept of transfer entropy. The results document an asymmetric and modest information flow in distribution tails prior to the pandemic, with the technology sector predominating. However, as we move towards central values, the transfer intensity decreases dramatically, even reaching negative values in the flow from the financial services sector. Following the pandemic declaration, while the technology sector maintains its superior position in information transfer, its strength, shape, and symmetry are notably altered, with transmission doubling from the financial services sector, suggesting cross-sectoral contagion in market downturns and instability of the information transfer.

Robust and fast stochastic 4D Flow Vector-field signature technique for quantifying composite flow dynamics from 4D Flow MRI: Application to left atrial flow in atrial fibrillation

4D flow MRI is an emerging imaging modality that maps voxel-wise blood flow information as velocity vector fields that is acquired in 7-dimensional image volumes (3 spatial dimensions + 3 velocity directions + time). Blood flow in the cardiovascular system is often complex and composite involving multiple flow dynamics and patterns (e.g., vortex flow, jets, stagnating flow) that occur and interact simultaneously. The spectrum of such complex flow dynamics is embedded in the velocity vector field dynamics derived from 4D Flow MRI. However, current flow metrics cannot fully measure high-dimensional vector-field data and embedded complex composite flow data. Instead, these methods need to break down the vector-field data into secondary scalar fields of individual flow components using fluid dynamics operators. These methods are gradient-based and sensitive to data uncertainties, and only focus on individual flow components of the overall composite flow, therefore potentially underestimating the severity of overall flow changes associated with cardiovascular diseases. To address these limitations, in MICCAI 2021, we introduced a novel comprehensive stochastic 4D Flow vector-field signature technique that works directly on the entire spatiotemporal velocity vector field. This technique uses efficient stochastic gradient-free interrogation of multi-million flow vector-pairs per patient to derive the patient's unique flow profile of the complex composite flow alterations and in real-time processing. The signature technique's probabilistic gradient-free formulation should allow for highly robust quantification despite inherent errors in 4D flow MRI acquisitions. Here, we extend the application of the 4D flow vector-field signature technique to the left atrium to analyze complex composite flow changes in patients with atrial fibrillation. In 128 subjects, we performed extensive sensitivity testing and determined that the vector-field signature technique is highly robust to typical sources of data uncertainties in 4D flow MRI: degradation in spatiotemporal resolution, added gaussian noise, and segmentation errors. We demonstrate the excellent generalizability of the stochastic convergence from the aorta to the left atrium and between different 4D Flow MRI acquisition protocols. We compare the robustness of our technique to existing advanced flow quantification metrics of kinetic energy, vorticity, and energy loss demonstrating a superior performance of up-to 14-fold. Our results show the potential diagnostic and clinical utility of our signature technique in identifying distinctly altered composite flow signatures in atrial fibrillation patients independent of existing flow metrics.

Post-occlusive reactive hyperemia variables can be used to diagnose vascular dysfunction in hemorrhagic shock

IntroductionLaser doppler flowmetry (LDF) allows non-invasive assessment of microvascular functions. The combination of LDF with an occlusion functional test enables study of post-occlusive reactive hyperemia (PORH), providing additional information about vasomotor function, capillary blood flow reserve, and the overall reactivity of the microvascular system. AimTo identify early alterations of PORH variables in the skin of a rat in hemorrhagic shock (HS). Material and methodsMale Wistar rats (n = 14) weighing 400–450 g were anesthetized with a combination of tiletamine/zolazepam (20 mg/kg) and xylazine (5 mg/kg). The animals breathed on their own, and were placed on a heated platform in the supine position. A PE-50 catheter was inserted into the carotid artery to measure the mean arterial pressure (MAP). The optical probe of the Laser Doppler device was installed on the plantar surface of the hind limb of a rat; a pneumatic cuff was applied proximal to the same limb. The occlusion time was 3 min. The following physiological variables were measured at baseline and 30 min after blood loss: MAP, mmHg; mean cutaneous blood flow (M, PU); cutaneous vascular conductance (CVC = M/MAP); peak hyperemia (Mmax, PU) and maximum cutaneous vascular conductance (CVCmax) during PORH. In the HS group (n = 7), 30 % of the estimated blood volume was taken within 5 min. There was no blood loss in the group of sham-operated animals (Sham, n = 7). The results are presented as Me [25 %;75 %]. The U-Mann-Whitney criterion was used to evaluate intergroup differences. Differences were considered statistically significant at p < 0.05. ResultsThe groups did not differ at baseline. Blood loss led to a significant decrease in MAP (43 [31;46] vs. 94 [84;104] mmHg), M (11.5 [16.9;7.8] vs 16.7 [20.2;13.9]) and Mmax (18.1 [16.4;21.8] vs. 25.0 [23.0;26.2]) in the HS group compared to the Sham group, respectively. At the same time, both CVC (0.25 [0.23;0.30] vs. 0.16 [0.14;0.21]) and CVCmax (0.55 [0.38;0.49] vs 0.24 [0.23; 0.29]) increased after blood loss in the HS group compared to the Sham group. Arterial blood gas analysis revealed metabolic lactic acidosis in the HS group. ConclusionIn this rat model of HS, alterations in cutaneous blood flow are manifested by a decrease in perfusion (M) and the intensity of PORH (Mmax) with a simultaneous increase in vascular conductance (CVC and CVCmax).

Cerebral blood flow and white matter alterations in adults with phenylketonuria

BackgroundPhenylketonuria (PKU) represents a congenital metabolic defect that disrupts the process of converting phenylalanine (Phe) into tyrosine. Earlier investigations have revealed diminished cognitive performance and changes in brain structure and function (including the presence of white matter lesions) among individuals affected by PKU. However, there exists limited understanding regarding cerebral blood flow (CBF) and its potential associations with cognition, white matter lesions, and metabolic parameters in patients with PKU, which we therefore aimed to investigate in this study. MethodArterial spin labeling perfusion MRI was performed to measure CBF in 30 adults with early-treated classical PKU (median age 35.5 years) and 59 healthy controls (median age 30.0 years). For all participants, brain Phe levels were measured with 1H spectroscopy, and white matter lesions were rated by two neuroradiologists on T2 weighted images. White matter integrity was examined with diffusion tensor imaging (DTI). For patients only, concurrent plasma Phe levels were assessed after an overnight fasting period. Furthermore, past Phe levels were collected to estimate historical metabolic control. On the day of the MRI, each participant underwent a cognitive assessment measuring IQ and performance in executive functions, attention, and processing speed. ResultsNo significant group difference was observed in global CBF between patients and controls (F (1, 87) = 3.81, p = 0.054). Investigating CBF on the level of cerebral arterial territories, reduced CBF was observed in the left middle and posterior cerebral artery (MCA and PCA), with the most prominent reduction of CBF in the anterior subdivision of the MCA (F (1, 87) = 6.15, p = 0.015, surviving FDR correction). White matter lesions in patients were associated with cerebral blood flow reduction in the affected structure. Particularly, patients with lesions in the occipital lobe showed significant CBF reductions in the left PCA (U = 352, p = 0.013, surviving FDR correction). Additionally, axial diffusivity measured with DTI was positively associated with CBF in the ACA and PCA (surviving FDR correction). Cerebral blood flow did not correlate with cognitive performance or metabolic parameters. ConclusionThe relationship between cerebral blood flow and white matter indicates a complex interplay between vascular health and white matter alterations in patients with PKU. It highlights the importance of considering a multifactorial model when investigating the impact of PKU on the brain.

Blood-brain Barrier Permeability May Influence Vasopressor Effects in Anesthetized Patients With Brain Tumor: An Analysis of Magnetic Resonance Imaging Data

Objective: This is a secondary analysis of data from a previous study of anesthetized brain tumor patients receiving ephedrine or phenylephrine infusions. 18 patients with magnetic imaging verified tumor contrast enhancement were included. We hypothesized that vasopressors induce microcirculatory flow changes, characterized by increased capillary transit time heterogeneity (CTH) and decreased mean transit time (MTT), in brain regions exhibiting BBB leakage. Methods: This is a secondary analysis of data from a previous study of anesthetized brain tumor patients receiving ephedrine or phenylephrine infusions. 18 patients with magnetic imaging verified tumor contrast enhancement were included. Postvasopressor to prevasopressor ratios of CTH, MTT, relative transit time heterogeneity (RTH), cerebral blood flow (CBF), cerebral blood volume, and oxygen extraction fraction (OEF) were calculated in tumor, peritumoral, hippocampal, and contralateral grey matter regions. Comparisons were made between brain regions and vasopressors. Results: During phenylephrine infusion, ratios of CTH, RTH, and CBF were greater, and ratios of MTT and OEF were lower, in the tumor region with contrast leakage compared with corresponding contralateral grey matter ratios. During ephedrine infusion, ratios of CTH, MTT, RTH, CBF, and cerebral blood volume were higher in the tumor region with leakage compared with contralateral grey matter ratios. In addition, the ratio of CBF was higher in all regions, the ratio of RTH was lower in the leaking tumor region, and the ratio of OEF was lower in peritumoral, hippocampal, and grey matter regions with ephedrine compared with phenylephrine. Conclusions: Vasopressors can induce distinct microcirculatory flow alterations in regions with compromised brain tumor barrier or BBB. Ephedrine, a combined α and β-adrenergic agonist, appears to result in fewer flow alterations and less impact on tissue oxygenation compared with phenylephrine, a pure α-adrenergic agonist.

Detailed turbulent structures investigation around piers group induced flow

This paper aims to investigate the mean velocities and turbulence characteristics, which include Reynolds shear stresses (RSS) and turbulent intensities, in order to study temporal and spatial flow patterns around a complex three square-piers group. Measurements have been performed by acoustic Doppler velocimeter (ADV) to identify turbulence flow structures alteration and vortices formation in longitudinal, transverse, and vertical directions. In total, 164 locations around the bridge piers have been measured, while each location consists of no lesser than 15 vertical depth ADV data point measurements. To investigate the flow turbulence, critical locations have been observed from high vortex-influenced regions. The impacted mean velocity profiles have been compared to that at the unaffected region to study the flow alteration caused by piers group. The result reveals that the log-law layer near wall has been enhanced by the installation of pier. Furthermore, as identified from the most critical locations of turbulent structures across different measurement rows, the accelerated flow will result in lower observed turbulent structures. Although flow after each pier has been influenced by strong reversal velocities, vortices have managed to form at near wake. Analysis has been divided into inner and outer flow regions (IFR and OFR) based on flow depth to enhance the understanding of how bridge piers contribute to the development of flow turbulence.

Numerical Modeling Prediction of Vegetation Trajectories Under Different Flow Regimes in New Zealand Braided Rivers

AbstractWe use two‐dimensional physics‐based numerical modeling to study multi‐decadal evolution of vegetation and morphology under different flow regimes in real‐world gravel‐bed braided rivers. To assess model realism, we focus on two rivers in Canterbury (New Zealand) that, despite having been subjected to the introduction of similar invasive vegetation species in the last ∼100 years, show very different trajectories of vegetation presence due to their different flow regimes: the Lower Waitaki River and the Waimakariri River. The former, featuring a naturally damped flow regime—and having experienced further artificial flow damping due to hydropower generation from the 1930s, experienced vegetation encroachment; while the latter, featuring a flashy flow regime, retains an unvegetated braided planform. We propose an innovative calibration and validation procedure to determine an optimal setup of vegetation parameters that allows the model to robustly reproduce the trajectories of both rivers, thereby proving that the model responds sensibly to different hydrological conditions. Then, we isolate the impact of hydropower‐related flow regime modifications on vegetation encroachment in the Lower Waitaki by running the calibrated model with a natural flow regime that does not feature the effect of hydropower generation, and find that vegetation encroachment would have happened even without flow alteration, albeit to a milder degree. Finally, we apply to simulation results a conceptual framework based on a synthetic parameter that compares the relative strength of hydrological and vegetation controls, and discuss the use of this parameter as a predictor of vegetation presence across flow regimes.

The Brain Kidney Axis Vascular Cross Talk

AbstractChronic kidney disease (CKD) is associated with cognitive impairment and dementia; 87% of patients on chronic dialysis have some degree of cognitive impairment. The prevalence of CKD increases with age and approximately 40% of persons aged &gt;60 years have CKD. With increasing life expectancy, prevalence of both CKD and dementia are expected to increase.CKD and Alzheimer’s disease (AD) share common risk factors. Patients with CKD are older, and have multiple comorbidities such as hypertension, diabetes mellitus, dyslipidemia, metabolic syndrome, and obesity, making CKD a model for accelerated aging, inflammation, and vascular dysregulation. Inflammation and vascular dysregulation can disrupt blood brain barrier, decreased kidney function can influence amyloid clearance, an important AD biomarker. Patients with CKD have alterations in cerebral blood flow, brain white matter integrity, brain neurochemicals, and blood brain barrier permeability‐ findings that are similar to those seen in AD.We investigated brain alterations seen in CKD before and after successful kidney transplant and found reversibility of brain alterations, and improvement in cognitive function after kidney transplantation. Further, we examined whether the cognitive impairment in CKD is due to comorbidities such as hypertension or due to decreased kidney function. In addition, for the first time, we have shown evidence for disruption of blood brain barrier in patients with CKD. With the high prevalence of CKD in the older population, and the strong association between decreased glomerular filtration rate and cognitive impairment, understanding the mechanisms underlying cognitive impairment and developing strategies to mitigate the risks in the CKD population is important.The potential reversibility in brain alterations seen in CKD after a kidney transplant indicate an opportunity to develop strategies for management of cognitive impairment.

Enhanced arterial spin labeling in mild cognitive impairment phenotypes

AbstractBackgroundArterial spin labeling perfusion MRI is increasingly proving to be a promising tool for exploring neurovascular changes in neurodegenerative conditions. Using an advanced 3D pseudo‐continuous arterial spin labeling sequence with Hadamard‐encoded multiple post‐labeling delays (eASL), this study evaluated both cerebral blood flow (CBF) and arterial transit time (ATT) alterations in mild cognitive impairment (MCI) phenotypes.MethodMCI patients (N = 19;Mage = 74.63±5.65) and controls (N = 20;Mage = 70.04±7.06) underwent a 3T MR scan with the eASL sequence. ATT and CBF were simultaneously measured. Voxel‐wise group comparisons of CBF and ATT were performed. Results were thresholded at a cluster‐size corrected p&lt;0.001 (a&lt;0.05). A region of interest (ROI) was defined as the overlap of clusters showing a significant difference in CBF and ATT between MCI and controls. Independent t‐tests between MCI phenotypes (amnestic, non‐amnestic) and controls on CBF and ATT ROIs were conducted. Pearson correlations of ROIs with measures of cognition, including executive functioning, were calculated. Correlations informed regression analysis.ResultsVoxelwise analyses (Figure1) demonstrated decreased CBF in MCI compared to controls in the default mode network, middle and superior frontal gyri, inferior parietal lobule, and temporal lobe. Increased ATT was seen in similar regions, with clusters centered in inferior and middle temporal lobe and visual cortex. T‐tests using created ROIs (as described above) revealed group differences between controls and MCI phenotypes in both CBF and ATT (ps≤.01); there was a non‐significant trend for higher ATT in naMCI versus aMCI. The highest correlational values emerged between CBF and ATT ROIs with a measure of executive functioning (TrailsB). IVs in regression analysis were age (step 1) and ATT and CBF overlapping ROI values (step 2, stepwise); TrailsB = DV . Across the entire cohort, CBF (R2 change = .239, p&lt;.001), not ATT, was included in the model.ConclusionAdvanced 3D pCASL with Hadamard encoded multiple PLDs (eASL) can be used to simultaneously measure CBF and ATT in MCI and controls. MCI patients showed different patterns of reduced CBF and prolonged ATT. While CBF and ATT values were significantly correlated with TrailsB, regression analysis revealed that CBF was a more robust predictor of TrailsB. Future research should examine eASL as a biomarker for MCI phenotypes.

Flow augmentation from off‐channel storage improves salmonid habitat and survival

AbstractObjectiveIn the western United States, juvenile salmon Oncorhynchus spp. and steelhead O. mykiss are especially vulnerable to streamflow depletion in the dry season. Releasing water from off‐channel storage into small streams is a novel restoration strategy to offset impacts from anthropogenic flow alteration on salmonid fishes. To date, no studies have evaluated the ecological effects of small‐scale flow augmentations. Here, we quantify the effects of one such augmentation project on habitat connectivity, water quality, invertebrate drift, and juvenile salmonid movement and survival.MethodsOur study took place in a northern California stream and included an unusually wet summer (2019) and a more typical dry summer (2020). We used categorical and time‐series analyses in a before–after, control–impact (BACI) design, along with capture–mark–recapture methods to evaluate the ecological impacts of a 13.9‐L/s flow augmentation.ResultWe found that differences in ambient streamflows between the two years mediated the physical and ecological effects of the flow augmentation treatment. In the dry year, habitat connectivity and dissolved oxygen markedly increased at sites over 1.5 km downstream from the point of augmentation, whereas during the wet year, the effects on those variables were negligible. In both years, invertebrate drift marginally increased after augmentation. Interpool movement of wild juvenile steelhead and stocked Coho Salmon O. kisutch increased after augmentation during the dry summer but not during the wet summer. Flow augmentation increased the survival probability for salmonids, with a larger effect during the dry summer (24% higher survival for Coho Salmon and 20% higher survival for steelhead) than during the wet summer (no effect was observed for steelhead survival, and Coho Salmon survival increased by 11%).ConclusionThis study indicates that appropriately designed small‐scale flow augmentations can improve conditions for rearing salmonids in small streams, particularly during dry years. More broadly, it provides empirical evidence that efforts to restore summer streamflow in small, salmon‐bearing streams can yield significant ecological benefits.

Molecular Mechanisms Associated with Aging Kidneys and Future Perspectives

The rapid growth of the elderly population is making the need for extensive and advanced information about age-related organ dysfunction a crucial research area. The kidney is one of the organs most affected by aging. Aged kidneys undergo functional decline, characterized by a reduction in kidney size, decreased glomerular filtration rate, alterations in renal blood flow, and increased inflammation and fibrosis. This review offers a foundation for understanding the functional and molecular mechanisms of aging kidneys and for selecting identifying appropriate targets for future treatments of age-related kidney issues.

Study of the electroosmotic flow of a structured fluid with a new generalized rheological model

The electroosmotic flow of a viscoelastic fluid in a capillary system was investigated analytically. The rheology of the fluid was characterized by a novel generalized exponential model equation. The charge density obeys the Boltzmann distribution, which governs the electrical double-layer field and body force generated by the applied electrical field. Mathematically, this scenario can be modeled by the Poisson-Boltzmann partial differential equation, by assuming that the zeta potential is small, i.e., less than 25 mV (Debye-Hückel approximation). Considering a pulsating electric field, the shear viscosity and the alteration in the volumetric flow were presented as a function of the material parameters through the characteristic dimensionless numbers by using an exponential-type generalized rheological model. Thixotropy, shear thinning, yield stress mechanisms, and weight concentration were analyzed through numerical results. Finally, the flow properties and rheology were predicted using experimental data reported elsewhere for worm-like micellar solution of cetyl trimethyl ammonium tosilate (CTAT). The rheological equation of state proposed in this study describes the alterations in the structure resulting from applied forces (tangential and normal). These forces induced a structural evolution (kinetic model) due to the relaxation processes caused by shear strain. It is important to mention that in electroosmotic flows, complex behavior such as (i) thixotropy, (ii) rheopexy, and (iii) shear banding flow is scarcely explained in terms of the change in the structure of the fluid under flow.Graphical

Assessing environmental flow alterations induced by dams and climate change using a distributed hydrological model at catchment scale

Abstract Hydrological alterations by dams and climate change can reduce aquatic biodiversity by disrupting the life cycles of organisms. Here, we aimed to evaluate and compare the hydrological alterations caused by dams and climate change throughout the Omaru River catchment, Japan, using a distributed hydrological model (DHM). First, to assess the impacts of dam and climate change independently, we performed runoff analyses using either dam discharge or future climatic data (two future periods, 2031–2050 and 2081–2100 × three representative concentration pathways). Subsequently, we derived indicators of hydrologic alterations (IHA) to quantify changes in flow alterations by comparing them to IHA under natural conditions (i.e., without dam or climate change data). We found that dams altered IHAs more than climate change. However, on a catchment-scale standpoint, climate change induced wider ranges of flow alterations, such as a further decrease in low flow metrics along the tributaries and uppermost main stem, suggesting a catchment-level shrinkage in important corridors of aquatic organisms. We also observed that the altered flow by water withdrawals was ameliorated by the confluence of tributaries and downstream hydropower outflows. Our approach using a DHM captured the various patterns of flow alterations by dams and climate change.

Comparative study on cavernous weathering features formed by coastal processes and acidic alteration: Implications for rounded pits on Martian rocks

Surface images taken by rovers and landers show the existence of rounded pits with diameter of centimeters on Martian rock surfaces. These pits seem to be similar to terrestrial cavernous weathering features, generated by salt weathering (e.g., alveoli), or by stream flow erosion (e.g., potholes), found near coastal areas. Alternatively, if the weathered rocks contained carbonate minerals, the pits might have been formed by acidic weathering. Here, we compare geomorphology of cavernous weathering features formed by coastal processes on Earth and by laboratory experiments simulating acidic weathering of carbonate. Our field observations for coastal areas of the Japanese islands show that a high cavity number density and small cavities characterize cavernous features formed by salt weathering as compared with those formed by stream flow. Our experimental results show that acidic weathering can generate cavernous features, with high number densities and small diameters. Based on principal component analysis, cavernous weathering features formed by salt weathering, stream flow, and acidic alteration can be distinguished mainly by the number density and diameter. By applying our approach to Martian rocks, we find that the morphological characteristics of rounded pits on Jezero Crater rocks are different from the above cavernous weathering features, and that the Martian pits are categorized as being intermediate between cavernous features formed by salt weathering and acidic weathering. If the pits on Jezero Crater rocks were formed by salt weathering, salt weathering on Mars could have been less effective (possibly, due to a difference in water salinity or salt composition) than those found in coastal areas of Earth. Alternatively, these Martian pits might be formed by other processes (e.g., vesicles in volcanic breccia, eolian processes, or freeze-thaw cycles of porewater).

Spatio-temporal variability of streamflow in major and medium rivers of Nepal

Study regionWe selected six (three on each) major and medium river basins of Nepal as a study domain for the analysis. The study areas were so selected that they represent the river basins across the country from East (Kankai basin) to West (Karnali basin). Study focusThis study focuses on the long-term hydrologic alteration in the river flow of Nepal's medium and major rivers of different river basins. The overarching objective of the study is to evaluate the spatio-temporal change in flow magnitude, duration, frequency, timing, and rate of change in the major and medium rivers in Nepal. With continuity in the development activities, it is imperative to analyze the potential impact of human activities in the hydrologic regimes. For this, we used a set of 33 indicators from the indicator of hydrologic alteration (IHA) developed by The Nature Conservancy for the pre and post-impact period. The pre and post-impact period is defined here as the time before and after which the substantial alteration occurred, possibly due to multiple reasons. The pre and post impact periods were determined using the Pettitt statistical test carried out at the most downstream of the hydrological gauge station of each river basin. Further, the trends in the annual flow were estimated using the Mann-Kendall test, and the slope of the trend was estimated using Sen’s slope. New hydrological insights for the regionThe results showed that in the post-impact period, the mean annual discharge in major and medium rivers of Nepal was found to decrease by 5.86% and 7.94%, respectively. Except for the West Rapti River (−14.3%), the hydrologic change of 1-day maximum flow is observed to have increased in the medium rivers and decreased in the major rivers. Moreover, except for the Kankai River (+14.29%), the hydrologic change of 1-day minimum flow is observed to be reduced in both the major and medium rivers. In major rivers, the overall degree of alteration ranges from 28.7% to 38.0%, which resembles the low to mid variability range. Similarly, the result of the hydrologic alteration showed that for the medium rivers, the overall degree of alteration varied from 35.8% to 46.7%, representing the medium range of variability. This suggests that the river systems undergoing moderate hydrologic alteration have experienced moderate alteration. These rivers might be capable of sustaining a healthy ecosystem, however, could be more susceptible to other stressors like drought.