Geometry Response Research Articles

Long-term effects of Abay River flow regulation at Lake Tana on the geomorphic and ecological responses of the downstream river channels, Upper Blue Nile basin, Ethiopia

Alluvial rivers adjust their geometry in response to environmental and anthropogenic disturbances. Flow regulation results in a new geomorphic condition that affects the aquatic ecosystem and its nature. This paper examines the long-term effects of flow regulation on the geomorphic and ecological responses of the downstream river channels of the Abay River, which is the only natural outflow of Lake Tana, Ethiopia. Since 1996, the river’s discharge regime has been affected by constructing a head-rise weir (Chara Chara) at its natural outlet for hydropower production and dam construction on the Lake Tana tributary rivers. Hydrologic data collected at the outlet of the river, SPOT, and Google Earth images were used for the study. River banks and bed topography were extracted via ArcGIS for selected study periods. The study revealed that existing water resource development on the tributary rivers of Lake Tana modified (decreased) the outflow discharge on the Abay River, and resulted a changed morphological and moderate level ecological impact on the river system. Future ongoing and planned water resource developments will exacerbate the pressure on the lake. Without careful management, these changes are likely to have severe morphological, ecological and social consequences.

Quantifying drainage divide migration in active orogens: Insights from the eastern margin of the Tibetan Plateau

Landscape of active orogens results from a competition balance between tectonic rock uplift and erosion. Drainage divide migration is a useful approach for quantifying the landscape evolution and the underpinning drivers, because the fluvial networks adjust their geometry in response to spatiotemporal changes in rock uplift, climate and lithology. Many quantitative geomorphological metrics, such as χ-anomaly, Gilbert metrics, have been proposed to analyze the drainage divide migration. However, their interpretations often yield inconsistent results, especially in tectonically active orogens with spatial changes in rock uplift. The highly elevated and tectonically active eastern margin of the Tibetan Plateau has been studied by multiple methods of different time-scales, producing abundant structural and erosion rates determinations needed for evaluating the landscape stability and evolution. Here, we evaluated the effectiveness of χ- and Gilbert metrics in quantifying the stability of the Longmenshan-Minshan divide parallel with the plateau margin, by comparing with erosion rate data of different time scales, rock uplift predicted by upper crustal structures, bedrock lithology, precipitation. Our analyses reveal that the divide has reached dynamic steady state, as shown by the consistent cross-divide Gilbert metrics and consistent spatial changes of short, medium and long-term erosion rates, indicating the overall balance between the erosion and rock uplift. The spatial changes in rock uplift underpinned by reverse faulting along a listric upper crustal fault also explains the development of cross-divide χ-anomaly that cannot be used as an index for divide migration in regions with spatially nonuniform rock uplift. The formation of the long-term stable drainage divide in the EMTP serves as a natural laboratory for studying the divide formation and evolution in response to a phase of non-uniform rock uplift. We infer that in regions of this kind, drainage divide forms and evolves from uplift-driven to erosion-driven migration, via an intervening stable state.

Assessing channel geometry in response to land use disturbance in a low‐relief, glacially conditioned setting

AbstractBankfull stage, the highest flow elevation contained by a river channel before overbank flooding occurs, is the presumed threshold for channel morphological change. At bankfull, the channel boundary experiences the highest shear stress, producing somewhat predictable hydraulic relationships and a cross‐sectional form. However, land use and glacial conditioning can profoundly impact a channel's geomorphic responses. Two common methods characterize bankfull flow: one based on flow frequency and other based on channel form. This study considers a simplified approach to identify upstream land use relative to estimates of bankfull flow versus a channel's geometric form. The approach compares archived geomorphic surveys of 140 river reaches in southern Ontario, Canada, to 2‐year flood quantiles modelled from historical flood data of 207 gauge stations. Flood frequency analysis determines that annual maximum series (AMS) datasets, fitted to optimized probabilistic distributions, underestimate discharge for low‐magnitude, high‐frequency flood events compared to partial duration series (PDS) datasets. For smaller drainage areas (<100 km2) associated with an extensive agricultural activity and/or urbanization, the estimates of bankfull discharge (Qbf) generated by cross‐sectional channel geometry are greater than the gauge‐derived Q2 values. Channels impacted by high levels of upstream land use disturbance show statistically significant lower width‐to‐depth ratios (p < 0.001) and a trend towards a finer D50 bed material, suggesting enhanced surface runoff delivering more mobile finer sediments and channel confinement or incision. This research quantifies the formative bankfull stage to better understand the link between land use and a channel's ‘natural’ hydrogeomorphic response in a low‐relief, glacially conditioned setting.

Temporal evolution of mechanical stimuli from vascular remodeling in response to the severity and duration of aortic coarctation in a preclinical model

Coarctation of the aorta (CoA) is one of the most common congenital cardiovascular diseases. CoA patients frequently undergo surgical repair, but hypertension (HTN) is still common. The current treatment guideline has revealed irreversible changes in structure and function, yet revised severity guidelines have not been proposed. Our objective was to quantify temporal alterations in mechanical stimuli and changes in arterial geometry in response to the range of CoA severities and durations (i.e. age of treatment) seen clinically. Rabbits were exposed to CoA resulting in peak-to-peak blood pressure gradient (BPGpp) severities of ≤ 10, 10–20, and ≥ 20 mmHg for a duration of ~ 1, 3, or 20 weeks using permanent, dissolvable, and rapidly dissolvable sutures. Elastic moduli and thickness were estimated from imaging and longitudinal fluid–structure interaction (FSI) simulations were conducted at different ages using geometries and boundary conditions from experimentally measured data. Mechanical stimuli were characterized including blood flow velocity patterns, wall tension, and radial strain. Experimental results show vascular alternations including thickening and stiffening proximal to the coarctation with increasing severity and/or duration of CoA. FSI simulations indicate wall tension in the proximal region increases markedly with coarctation severity. Importantly, even mild CoA induced stimuli for remodeling that exceeds values seen in adulthood if not treated early and using a BPGpp lower than the current clinical threshold. The findings are aligned with observations from other species and provide some guidance for the values of mechanical stimuli that could be used to predict the likelihood of HTN in human patients with CoA.

Diving into the optoelectronic properties of Cu(II) and Zn(II) curcumin complexes: a DFT and wavefunction benchmark.

Curcumin is a popular food additive around the world whose medicinal properties have been known since ancient times. The literature has recently highlighted several biological properties, but besides the health-related usages, its natural yellowish color may also be helpful for light-harvesting applications. This research aims to close a knowledge gap regarding the photophysical description of curcumin and its metallic complexes. We conducted benchmark experiments comparing NEVPT calculations with several DFT functionals (B3LYP, M06-L, M06-2X, CAM-B3LYP, and ωB97X-D) for describing the UV spectra of curcumin and its metallo-derivative, curcumin-copper(II). Once we determined the most suitable functional, we performed tests with different basis sets and conditions, such as solvation and redox state, to identify their impact on excited state properties. These results are also reported for the curcumin-zinc(II) derivative. We found that the accuracy of DFT functionals depends strongly on the nature of curcumin's excitations. Intra-ligand transitions dominate the absorption spectra of the complexes. Curcumin absorption is marginally affected by solvation and chelation, but when combined with redox processes, they may result in significant modifications. This is because copper cation changes its coordination geometry in response to redox conditions, changing the spectrum. We found that, compared to a NEVPT reference, B3LYP is the best functional for a general description of the compounds, despite not being appropriate for charge transfer transitions. M06-L was the best for LMCT transitions. However, compared with NEVPT2 and PNO-LCCSD(T)-F12 results, no functional achieved acceptable accuracy for MLCT transitions.

Feedforward Control System Development and Implementation for Longitudinal and Lateral Motion of a Four-Wheeled Robot

The work presented in this paper advances through a series of physics-based increasing fidelity models that are used to design robot controllers that respect the robot's capabilities. It also develops a reference simple controller that is applicable to a large subset of tracking conditions, most of which involve non-invasive or highly dynamic movements, defines path geometry in response to the control problem, and develops both a simple geometric control and a dynamic model predictive control approach. In this research, we propose the mathematical modeling of the longitudinal and lateral movements utilizing PID with a feed-forward controller for a nonlinear model with disturbance impact. A feed-forward controller is suggested in this work to get rid of the disturbance effect.

Electromagnetic Reconfiguration Using Stretchable Mechanical Metamaterials.

Response to environmental thermomechanical inputs in applications that range from wearable electronics to aerospace structures necessitates agile communication systems driven by reconfigurable electromagnetic structures. Antennas in these systems must dynamically preserve acceptable radiation characteristics while enabling on-demand performance reconfiguration. However, existing reconfiguration mechanisms through stretchable conductors rely on high-strain behavior in soft substrates, which limits their applicability. Herein, this work demonstrates the use of mechanical metamaterials for stretchable conductors and dielectrics in antennas. Metamaterials allow conductor stretching up to 30% with substrate base material tensile moduli ranging from 26MPa to 44GPa. It is shown, through several antenna designs, that mechanical metamaterials enable similar frequency reduction upon stretching as monolithic conductors, while simultaneously providing a miniaturization effect. The conductor patterning, furthermore, provides control over coupling between mechanical stretching and electromagnetic reconfiguration. This approach enables designing reconfigurable antenna functionality through metamaterial geometry in response to arising needs in applications ranging from body-adapted electronics to space vehicles.

A Comprehensive Assessment of Right Ventricular Function in Chronic Thromboembolic Pulmonary Hypertension.

While chronic thromboembolic pulmonary hypertension (CTEPH) results from macroscopic and microscopic obstruction of the pulmonary vascular bed, the function of the right ventricle (RV) and increased RV afterload are the main determinants of its symptoms and prognosis. In this review, we assess RV function in patients diagnosed with CTEPH with a focus on the contributions of RV afterload and dysfunction to the pathogenesis of this disease. We will also discuss changes in RV function and geometry in response to treatment, including medical therapy, pulmonary endarterectomy, and balloon pulmonary angioplasty.

A novel MRI-based three-dimensional model of stomach volume, surface area, and geometry in response to gastric filling and emptying.

Gastric motility and accommodation have a critical role in maintaining normal gastrointestinal homeostasis. Different modalities can be adopted to quantify those processes, that is, scintigraphy to measure emptying time and intragastric Barostat for accommodation assessment. However, magnetic resonance imaging (MRI) can assess the same parameters noninvasively without ionizing radiation. Our study aimed to develop a detailed three-dimensional (3D) MRI model of the stomach to describe gastric volumes, surface areas, wall tension distribution, and interobserver agreement. Twelve healthy volunteers underwent an MRI protocol of six axial T2-weighted acquisitions. Each dataset was used to construct a 3D model of the stomach: First, the volumes of the whole stomach, gastric liquid, and air were segmented. After landmark placing, a raw 3D model was generated from segmentation data. Subsequently, irregularities were removed, and the model was divided into compartments. Finally, surface area and 3D geometry parameters (inverse curvatures) were extracted. The inverse curvatures were used as a proxy for wall tension distribution without measuring the intragastric pressure. The model was able to describe changes in volume and surface geometry for each compartment with a distinct pattern in response to filling and emptying. The surface tension was distributed nonhomogeneously between compartments and showed dynamical changes at various time points. The presented model offers a detailed tool for evaluating gastric volumes, surface geometry, and wall tension in response to filling and emptying and will provide insights into gastric emptying and accommodation in diseases such as diabetic gastroparesis.

Molecular dynamics investigation of the structural flexibility of H2O2 and H2S2 in response to medium polarity

Hydrogen peroxide (H2O2) and hydrogen persulfide (H2S2) are the simplest members of the peroxide and persulfide families, and both are signaling molecules that regulate several biological functions. Rotation about the O–O and S–S bonds impacts the strength of these molecules as H-bond donors or acceptors and tunes their polarity and stability by converting the polar equilibrium skewed structure (ϕHOOH ~ 112°, ϕHSSH ~ 91°) to the nonpolar less stable trans (ϕ = 180°) or the most polar and least stable cis (ϕ = 0°) conformers. The change in geometry in response to the structure and polarity of the microenvironment is an important feature that would influence how these molecules interact with or permeate through biological systems. Consistent with larger energy barriers for rotation about the S–S bond, quantum chemical calculations with MP2(full)/6–311++G(3df,3pd) reveal that when interacting with a single water, ethanol, or n-pentane molecule in the gas phase, the geometry of H2S2 is more rigid (ϕHSSH = 91 ± 3°) than that of H2O2 (ϕHOOH = 112 ± 8°). Molecular dynamics simulations of a single H2O2 or H2S2 in liquid water (ε = 80), ethanol (ε = 25), or n-pentane (ε = 2) reveal that, compared to the gaseous monomer, H2O2 maintains a more polar geometry in ethanol and water. Interestingly, the distribution of ϕHOOH significantly shifts towards the nonpolar conformation as solvent polarity decreases; the fraction of structures with ϕHOOH ≥ 160° is 0.10, 0.14, and 4.30% in water, ethanol, and n-pentane, respectively. The high-energy cis conformation of H2O2 was negligible in all solvents, especially in n-pentane. The equilibrium geometry of H2S2 is hardly influenced by solvent polarity and both cis and trans conformations are essentially absent in the three solvents. In contrast to rigid H2S2, H2O2 is thus a flexible molecule whose geometry depends on the environment polarity, a property that enables stabilizing H2O2 in different microenvironments and possibly plays a role in how biological systems discriminate between H2O2 and the rigid and polar close analog, H2O.

Soft Spiral‐Shaped Microswimmers for Autonomous Swimming Control by Detecting Surrounding Environments

In nature, most microorganisms have motility, which is essential for their survival or reproduction. To move, some microorganisms have evolved soft spiral‐shaped flagella, which rotate through specialized motors. Many of these microorganisms can change the morphology of their spiral‐shaped flagella to control their motility. Herein, by mimicking these flagella, spiral‐shaped microswimmers are developed for various applications, such as target drug delivery, micro‐object transport, and micro‐fluid manipulation. In previous studies, numerous fabrication methods of spiral‐shaped microswimmers are developed. However, the swimming direction and velocity are controlled only by external systems, such as magnetic fields, because the spiral body is not able to deform. Therefore, this soft spiral‐shaped microswimmer for autonomous swimming control by detecting surrounding stimuli is proposed. The velocity of microswimmer largely depends on the geometry of the microswimmer's body. Through usage of a stimuli‐responsive hydrogel in the microswimmer, the geometry autonomously changes in response to the surrounding stimuli. Using finite‐element simulation, it is revealed that the pattern angle is an important parameter for acceleration/deceleration of the microswimmer. The dimensionless velocity of the fabricated bilayered spiral swimmer changes by deforming the geometry in response to the surrounding thermal stimuli.

Homeostatic Plasticity Shapes the Retinal Response to Photoreceptor Degeneration.

Homeostatic plasticity stabilizes input and activity levels during neural development, but whether it can restore connectivity and preserve circuit function during neurodegeneration is unknown. Photoreceptor degeneration is the most common cause of blindness in the industrialized world. Visual deficits are dominated by cone loss, which progresses slowly, leaving a window during which rewiring of second-order neurons (i.e., bipolar cells) could preserve function. Here we establish a transgenic model to induce cone degeneration with precise control and analyze bipolar cell responses and their effects on vision through anatomical reconstructions, invivo electrophysiology, and behavioral assays. In young retinas, we find that three bipolar cell types precisely restore input synapse numbers when 50% of cones degenerate but one does not. Of the three bipolar cell types that rewire, two contact new cones within stable dendritic territories, whereas one expands its dendrite arbors to reach new partners. In mature retinas, only one of four bipolar cell types rewires homeostatically. This steep decline in homeostatic plasticity is accompanied by reduced light responses of bipolar cells and deficits in visual behaviors. By contrast, light responses and behavioral performance are preserved when cones degenerate in young mice. Our results reveal unexpected cell type specificity and a steep maturational decline of homeostatic plasticity. The effect of homeostatic plasticity on functional outcomes identify it as a promising therapeutic target for retinal and other neurodegenerative diseases.

Stimuli-responsive micro/nanoporous hairy skin for adaptive thermal insulation and infrared camouflage

A smart hairy skin with hiearchical micro/nanoporous shape memory polymer enables dynamically adaptive thermal insulation.

Root Plasticity in the Pursuit of Water.

One of the greatest challenges of terrestrial vegetation is to acquire water through soil-grown roots. Owing to the scarcity of high-quality water in the soil and the environment’s spatial heterogeneity and temporal variability, ranging from extreme flooding to drought, roots have evolutionarily acquired tremendous plasticity regarding their geometric arrangement of individual roots and their three-dimensional organization within the soil. Water deficiency has also become an increasing threat to agriculture and dryland ecosystems due to climate change. As a result, roots have become important targets for genetic selection and modification in an effort to improve crop resilience under water-limiting conditions. This review addresses root plasticity from different angles: Their structures and geometry in response to the environment, potential genetic control of root traits suitable for water-limiting conditions, and contemporary and future studies of the principles underlying root plasticity post-Darwin’s ‘root-brain’ hypothesis. Our increasing knowledge of different disciplines of plant sciences and agriculture should contribute to a sustainable management of natural and agricultural ecosystems for the future of mankind.

Engineering a Bacterial Flagella Forest for Sensing and Actuation – A Progress Report

Flagella can be used to make magnetically-controlled microfluidic and nanoscale devices for biomedical applications in both vitro and vivo environments. They are capable of operating with high precision on the cellular and subcellular level. So far, scientists and engineers have successfully used monolithic inorganic materials or photoactive polymers [1] to mimic the helical bacterial flagella whose rotary-propulsion mechanism effectively overcomes the dominant viscous forces that prevail in a low Reynolds-number environment. Here, we focus on bacterial flagella and their rotary motion. The bacterial flagellum is an ideal biomaterial for constructing self-propelling nanoswimmers because it can reversibly change its geometry in response to different environmental stimuli such as pH, the local concentration of certain organic solvents, and mechanical force on the flagella. The bacterial flagellum is very easy to manipulate because it is composed of flagellin which can be mechanically isolated through vortexing and centrifugation, which enables flagella to be used as nanoscale sensors and mechanical transducers. Our project focuses on fabricating a bacterial flagella forest which consists of an ordered array of flagella on a glass substrate. Flagella are attached to magnetic nanobeads via biotin-avidin bonding for actuation by oscillating magnetic field.

Flame Curvature Distribution in High Pressure Turbulent Bunsen Premixed Flames

The flame curvature statistics of turbulent premixed Bunsen flames have been analysed in this paper using a Direct Numerical Simulation (DNS) database of turbulent Bunsen flames at ambient and elevated pressures. In order to be able to perform a large parametric study in terms of pressure, heat release parameter, turbulence conditions and nozzle diameter, a single step Arrhenius type irreversible chemistry has been used for the purpose of computational economy, where thermo-chemical parameters are adjusted to match the behavior of stoichiometric methane-air flames. This analysis focuses on the characterization of the local flame geometry in response to turbulence and hydro-dynamic instability. The shape of the flame front is found to be consistent with existing experimental data. Although the Darrieus Landau instability promotes cusp formation, a qualitatively similar flame morphology can be observed for hydro-dynamically stable flames. A criterion has been suggested for the curvature PDF to become negatively skewed.

Bacteria-inspired nanorobots with flagellar polymorphic transformations and bundling

Wirelessly controlled nanoscale robots have the potential to be used for both in vitro and in vivo biomedical applications. So far, the vast majority of reported micro- and nanoscale swimmers have taken the approach of mimicking the rotary motion of helical bacterial flagella for propulsion, and are often composed of monolithic inorganic materials or photoactive polymers. However, currently no man-made soft nanohelix has the ability to rapidly reconfigure its geometry in response to multiple forms of environmental stimuli, which has the potential to enhance motility in tortuous heterogeneous biological environments. Here, we report magnetic actuation of self-assembled bacterial flagellar nanorobotic swimmers. Bacterial flagella change their helical form in response to environmental stimuli, leading to a difference in propulsion before and after the change in flagellar form. We experimentally and numerically characterize this response by studying the swimming of three flagellar forms. Also, we demonstrate the ability to steer these devices and induce flagellar bundling in multi-flagellated nanoswimmers.

Role of natural fractures in damage evolution around tunnel excavation in fractured rocks

This paper studies the role of pre-existing fractures in the damage evolution around tunnel excavation in fractured rocks. The length distribution of natural fractures can be described by a power law model, whose exponent a defines the relative proportion of large and small fractures in the system. The larger a is, the higher proportion of small fractures is. A series of two-dimensional discrete fracture networks (DFNs) associated with different length exponent a and fracture intensity P21 is generated to represent various scenarios of distributed pre-existing fractures in the rock. The geomechanical behaviour of the fractured rock embedded with DFN geometry in response to isotropic/anisotropic in-situ stress conditions and excavation-induced perturbations is simulated using the hybrid finite-discrete element method (FEMDEM), which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of natural fractures, and the propagation of new cracks. An excavation damaged zone (EDZ) develops around the man-made opening as a result of reactivation of pre-existing fractures and propagation of wing cracks. The simulation results show that when a is small, the system which is dominated by large fractures can remain stable after excavation given that P21 is not very high; however, intensive structurally-governed kinematic instability can occur if P21 is sufficiently high and the fracture spacing is much smaller than the tunnel size. With the increase of a, the system becomes more dominated by small fractures, and the EDZ is mainly created by the coalescence of small fractures near the tunnel boundary. The results of this study have important implications for designing stable underground openings for radioactive waste repositories as well as other engineering facilities that are intended to generate minimal damage in the host rock mass.

Sexual dimorphism in bone–muscle relationship in young adults

ABSTRACTThe purpose of this study was to analyse associations between lean soft tissue (LST), a surrogate of skeletal muscle mass and key fracture-related geometric characteristics of the proximal femur. Moreover, we examined the role that muscle played on the proximal femur geometry in response to physical activity (PA). Participants were 83 young adults. Leg LST (exposure) was assessed by dual energy X-ray absorptiometry (DXA). Proximal femur geometry was derived from a left hip DXA scan. Geometric variables (outcomes) included the femoral neck axis length (FNAL), the femoral neck width (FNW), the neck–shaft angle and FNW|FNAL (an index of robustness). PA was evaluated by accelerometry. Linear regression was used to analyse relationships. Additional exposure variables included body height and mass. In males, leg LST explained 17.4% of variation in FNAL (P < 0.001) and 15% in FNW (P = 0.015). In females, it explained 8.8% of the variance in FNAL (P = 0.020). Associations remained significant in males, but not in females, when vigorous PA was added to the models. These results suggest that public health approaches to promote PA may be particularly important in females since vigorous PA seems to convey advantages in femur geometry and consequently in bone strength.

Actin cytoskeleton differentially alters the dynamics of lamin A, HP1α and H2B core histone proteins to remodel chromatin condensation state in living cells.

Cells in physical microenvironments regulate their functioning and geometry in response to mechanical stimuli. Recent studies have demonstrated the influence of the integrated actin cytoskeleton on nuclear integrity and chromatin organization. However, the mechanisms underlying the mechanotransduction of their physical coupling to nuclear protein dynamics are not well understood. In this study, we take advantage of micropatterned geometric substrates in NIH3T3 mouse fibroblasts to probe the functional influence of actin organization on nuclear lamina and chromatin assembly. Fluorescence correlation spectroscopy studies demonstrate that stabilization of perinuclear actin strengthens the transient interactions of lamin A with the chromatin. Correspondingly, fluorescence recovery after photobleaching studies reveal enhanced mobility of these nuclear lamina proteins when actin organization is perturbed. Combining these fluorescence dynamics assays, we also demonstrate an actin-driven differential modulation of core histone H2B and heterochromatin HP1α protein dynamics with chromatin. These altered dynamics are reflected structurally by concomitant changes in the architecture of the heterochromatin foci as seen by immunofluorescence assays. Taken together, our study provides a demonstration of the differential mechanical control of perinuclear actin on the dynamics of the nuclear lamina, euchromatin and heterochromatin regimes of the nucleus, and suggests an actin-mediated route to spatially and structurally tune chromatin organization and dynamics.