Position Of Surface Research Articles

High-resolution sequence stratigraphy of clastic shelves IX: Methods for recognizing maximum flooding conditions in shallow-marine settings

Maximum flooding conditions in high-frequency sequences are associated with a condensed section, a generally cryptic maximum flooding surface, and with facies contacts marked by grain size changes, shell beds and bioturbation; i.e., the downlap surface and the local flooding surface. Conditions of maximum water depth usually occur above the condensed section, in the early highstand systems tract. Due to its importance in sequence stratigraphic analysis, the identification of the precise position of the maximum flooding surface, which separates the transgressive and highstand systems tracts, is critical. This is particularly true in high-resolution studies based on field and core data, where only facies contacts that are older and younger than the maximum flooding surface are recognizable. An integration of several criteria, including sedimentological (facies analysis), diagenetic, micropaleontological, geophysical and geochemical, represents the best approach to define a relatively thin uncertainty interval within high-frequency sequences, in which the cryptic MFS should lie. Among the available criteria, those sedimentological and diagenetic are the ones best suited to recognize facies contacts, whereas those micropaleontological are the most reliable ones to identify the position of the maximum flooding surface. Future studies on the integration of these methods with those geophysical and geochemical have the potential to improve the ability to identify the maximum flooding surface, and improve the available tools in the high-resolution sequence stratigraphic analysis.

Method of Stress Field and Stability Analysis of Bedding Rock Slope Considering Excavation Unloading

The stress state of a slope and its analytical solution are prerequisites for stability analysis. Currently, the limit equilibrium method cannot consider the stress state of slopes, and the solution of bedding slope stress remains in numerical simulations for a long time. In this paper, based on the theory of the elastic stress solution of the wedge top under a concentrated load, the analytical solution of the stress field was obtained using Matlab programming. Unloading stress analysis method (USAM) for determining the sliding surface of the bedding rock slope, safety factor (Fs), and reinforcement forces (Fr) were proposed. The USAM is compared with the Limit Equilibrium Method (LEM) and Finite Element Method (FEM) in terms of the Fs, Fr, sliding surface position, and sliding surface stress. The results show: 1) The analytical stress of the slope can be obtained quickly and conveniently using the USAM, while subsequent programming helps in faster completion of the stability evaluation of the bedding rock slope. Fs, Fr, sliding surface position, and sliding surface stress are all close to the results obtained by the FEM. 2) The USAM is more suitable for analyzing slopes when the angle between the slope surface and structural plane is greater than 20° (θ > 20°) and the slope angle is greater than 45° (β > 45°). 3) Through the analysis of specific engineering cases, the safety factor calculated by USAM are 0.06 and 0.02 larger than those obtained by LEM and FEM, respectively, and the required reinforcement force for the slope is closer to that obtained by FEM. The novel stress and stability analysis method allows for the rapid evaluation and optimal engineering design of bedding rock slope.

Novel tribological test rig prototype and primary results of experiments for additively manufactured test samples

This paper presents a new design of tribological test rig - (TTR), reciprocating type, with a ramp characteristic typical of computer numerical control drives. The guide temperature is measured by a series of sensors, calibrated using the triple point of water and gallium melting point methods. The uncertainty of wear measurements is provided. Experiments showed that TTR gives repeatable results of measurements with respect to wear and temperature. Each experiment was performed under different conditions: dry sliding, dry sliding with intermissions, dry sliding with a temporarily increased payload, and sliding with lubrication and with silicon oil residue. Wear rate was determined to predict the wear and compare it with established methods. Normal force and payload were predicted for a set distance and assumed wear. A set of micro-photographs helped to determine the contact surface position.

Assessment of crack severity of asphalt pavements using deep learning algorithms and geospatial system

Applications of Artificial Intelligence (AI), Deep Learning (DL), and Machine Learning (ML) are becoming common in the field of civil and infrastructure engineering. This paper proposes an innovative asphalt pavement health monitoring framework based on state-of-the-art deep learning algorithms, a convenient data collection strategy, a novel crack width calculation algorithm, and a novel geolocation-based crack visualization method. Furthermore, this paper introduces a 2000-image (1440 × 1440) dataset for crack classification, an 8000 image dataset (360 × 360) dataset and another dataset with manually segmented images. Transfer learning based DL model achieved a validation accuracy of 99%. A novel crack width calculation algorithm is proposed based on the skeletonization and gradient calculation on binary images to quantify the severity of the crack. Locations of the cracked surface positions were identified using geotagged images, and a geospatial mapping method was proposed to visualize the crack locations for health monitoring and maintenance purposes.

Timing Differences in Stride Cycle Phases in Retired Racehorses Ridden in Rising and Two-Point Seat Positions at Trot on Turf, Artificial and Tarmac Surfaces.

Injuries to racehorses and their jockeys are not limited to the racetrack and high-speed work. To optimise racehorse-jockey dyads' health, well-being, and safety, it is important to understand their kinematics under the various exercise conditions they are exposed to. This includes trot work on roads, turf and artificial surfaces when accessing gallop tracks and warming up. This study quantified the forelimb hoof kinematics of racehorses trotting over tarmac, turf and artificial surfaces as their jockey adopted rising and two-point seat positions. A convenience sample of six horses was recruited from the British Racing School, Newmarket, and the horses were all ridden by the same jockey. Inertial measurement units (HoofBeat) were secured to the forelimb hooves of the horses and enabled landing, mid-stance, breakover, swing and stride durations, plus stride length, to be quantified via an in-built algorithm. Data were collected at a frequency of 1140 Hz. Linear Mixed Models were used to test for significant differences in the timing of these stride phases and stride length amongst the different surface and jockey positions. Speed was included as a covariate. Significance was set at p < 0.05. Hoof landing and mid-stance durations were negatively correlated, with approximately a 0.5 ms decrease in mid-stance duration for every 1 ms increase in landing duration (r2 = 0.5, p < 0.001). Hoof landing duration was significantly affected by surface (p < 0.001) and an interaction between jockey position and surface (p = 0.035). Landing duration was approximately 4.4 times shorter on tarmac compared to grass and artificial surfaces. Mid-stance duration was significantly affected by jockey position (p < 0.001) and surface (p = 0.001), speed (p < 0.001) and jockey position*speed (p < 0.001). Mean values for mid-stance increased by 13 ms with the jockey in the two-point seat position, and mid-stance was 19 ms longer on the tarmac than on the artificial surface. There was no significant difference in the breakover duration amongst surfaces or jockey positions (p ≥ 0.076) for the ridden dataset. However, the mean breakover duration on tarmac in the presence of a rider decreased by 21 ms compared to the in-hand dataset. Swing was significantly affected by surface (p = 0.039) and speed (p = 0.001), with a mean swing phase 20 ms longer on turf than on the artificial surface. Total stride duration was affected by surface only (p = 0.011). Tarmac was associated with a mean stride time that was significantly reduced, by 49 ms, compared to the turf, and this effect may be related to the shorter landing times on turf. Mean stride length was 14 cm shorter on tarmac than on grass, and stride length showed a strong positive correlation with speed, with a 71 cm increase in stride length for every 1 m s-1 increase in speed (r2 = 0.8, p < 0.001). In summary, this study demonstrated that the durations of the different stride cycle phases and stride length can be sensitive to surface type and jockey riding position. Further work is required to establish links between altered stride time variables and the risk of musculoskeletal injury.

Combination of Cross-Correlation-Based Analysis and Ultrasonic GW Tomography for Barely Visible Impact Damage Detection Preliminary Assessment

Statistical based reconstruction methods and signal processing tooling techniques are implemented and used to detect delaminations or debondings within composite complex items with very high precision. From the literature, it appears that although a single procedure for the estimation of structural health is a fast solution, multiple analyses based on different reconstruction methods or different damage parameters are the way to achieve maturation assessments of the methodology. This highlights the fact that the hardware and software parts of an SHM system need two different assessment and maturation ways. This work focuses on the software part by proposing a way to start assessing the outcomes. In this paper, the damage detection and localization strategy in CFRP plate-like structures with elastic guided waves excited and acquired with a circular array PWAS network is considered. Previous outcomes are compared by new analyses using a new post-processing approach based on a cross-correlation-based technique in terms of the BVID (Barely Visible Impact Damage) surface position and its center of mass. The advantage of this specific study is hopefully to enable confidence in the transition from R&amp;D to field implementation. In addition, this work tries to evidence an improvement in terms of cost efficiency and reduced complexity while maintaining the same accuracy.

Ensuring the Stability of Channel Linings Under Unsteady Filtration

When assessing the stability of the slopes of the banks of reservoirs and channels, the filtration regime that occurs with a rapid decrease in the water level in the upstream, which is due to the nature of the operation of structures before floods, discharges, emergency situations, is of particular interest. A change in the water levels in the upstream causes a change in the position of the depression surface and the parameters of the filtration flow (pressure gradients, filtration rates and flow rates) in the coastal massif. At the same time, unsteady filtration occurs in the coastal massif and the stability of the slopes is reduced significantly due to the action of hydrodynamic forces directed towards the slope. The most reliable anchors of channel slopes in similar conditions are those that, under normal channel operation, when there is no groundwater support, the lining should exclude filtration from the channel, ie filtration losses of irrigated water, and if there is a backwater and with a rapid decrease in the water level in the channel, it should provide free access of the ground stream into the channel channel or its diversion in the other direction. This eliminates the occurrence of significant hydrodynamic pressures, and the destruction of the channel slope fasteners. The article presents the results of studies of 4 designs of channel linings operating under conditions of unsteady filtration. In the course of the study, we considered the following variants of structural schemes of linings. Fastening with combined deformation and filtration seams; fastening with self-collapsing seams; fastening with discharge tubular drains with water discharge into the channel; fastening with filtration and discharge holes arranged during the appearance of groundwater backup in the channel area. The results of calculating the stability of the fastening plates for overturning and surfacing are presented. According to the results of the calculation, the most acceptable fastening options are determined, their advantages and disadvantages are given. The proposed fastening design meets the above requirements and thereby ensures the strength and stability of the linings during the operation of the channel.

Accumulation of thick fluvial sediments in the Shinano River incised-valley fills: implications for sequence stratigraphy and alluvial architecture

ABSTRACTThe relationship between fluvial systems and base-level changes, controlled mainly by sea-level fluctuations and tectonic activity, on time scales of 103–104 years, is important for evaluating and improving nonmarine sequence stratigraphy and numerical and physical alluvial architecture models. However, there are not enough quantitative data available from field studies, especially for periods of rapid base-level rise. The Echigo Plain, Japan, is a fluvial–coastal lowland where the tidal range is very small and where a very deep valley was incised by the Shinano River during the latest Pleistocene. The depth of the incised valley near the shoreline, 160 m below mean sea level, is greater than the amount of sea-level fall during the Last Glacial Maximum (LGM) because of tectonic subsidence. We studied an approximately 100-m-long borehole sediment core obtained from the landward part of the plain, where thick fluvial deposits have accumulated since the LGM. Sediment facies, diatom assemblages, sulfur content, carbon to sulfur ratios, and radiocarbon age dates indicate that most of the core sediments were deposited in a fluvial environment during the past 12 kyr. Sediment accumulation rates were 10–15 m/kyr between 12 and 8 cal kyr BP, and relatively low (less than 5 m/kyr) subsequently, mainly because of glacio-eustatic sea-level rise. The timing of the reduction in the accumulation rate is one possible indicator of the position of the maximum-flooding surface in a sequence composed only of fluvial sediments. The presence of many thin layers of very fine to fine-grained sand (20–80 cm thick), interpreted as crevasse-splay deposits, that formed between 11 and 8 cal kyr BP, when the base level was rising rapidly, implies that crevasse-splay deposits are characteristic of aggrading fluvial sediments and the transgressive systems tract in nonmarine sequence stratigraphy. Tectonic subsidence at approximately 2 m/kyr has contributed markedly to the larger accumulation rate of fluvial sediments of the highstand systems tract on the Echigo Plain, compared with rates in other fluvial–coastal lowlands, since 5–6 cal kyr BP, when the eustatic sea-level rise had mostly ceased.

Pre-eruptive intracoronal resorption in orthodontic patients: A retrospective analysis of 3,143 patients

ObjectivesThe aim of this retrospective study was to analyze the occurrence and characteristics of pre-eruptive intracoronal resorptions in a clinical orthodontic patient population. Materials and methodsPatients treated in an orthodontic department (University of Pécs, Pécs, Hungary) were included. Unerupted teeth on panoramic radiographs were analyzed for intracoronal radiolucent lesions. For each patient, the demographic data, jaw localization, number of unerupted teeth with pre-eruptive intracoronal resorption lesions, number of lesions per tooth, size and localization of pre-eruptive intracoronal resorption defects, affected tooth's surface, pulp involvement and ectopic position of the tooth with defects were recorded. ResultsIn the 3,143 patients investigated, 55 teeth in 49 patients showed pre-eruptive intracoronal resorption lesions (subject incidence: 1.56%). The incidence on unerupted teeth was 0.25%. Pre-eruptive intracoronal resorption was significantly more common in mandibles (43 mandibular vs. 12 maxillary lesions) with an odds ratio of 12.84 (95% Confidence Interval: 5.19–31.74) and no gender differences were found (p = 0.746). The occurrence of pre-eruptive intracoronal resorption was highest in the youngest (7–10 years) mixed dentition status group (p < 0.001). Most of the lesions (44 of 55, or 80.0%) were localized in the dentin, occupying two-third or less of the dentin thickness. Only 12.73% (7/55) of the lesions were not localized on the occlusal surface. Of the lesions, 89.1% (49/55) showed no obvious size increase over an average follow-up of 36.4 ± 8.1 months. ConclusionsPre-eruptive intracoronal resorption may occur mainly in the mixed dentition stage in orthodontic patients. Careful and attentive radiographic evaluations may facilitate early detection and follow-up of the lesions’ possible dimensional changes, especially when resorption influences orthodontic extraction therapy.

Simulation of the Pressure Bonding Process Using the Phase-field Crystal Method

The present study simulated the pressure bonding process by the phase-field crystal method for a two-dimensional system. Two crystals with different orientations and sinusoidal surfaces were placed relative to each other, and their uppermost and lowermost layers were gradually approached as chuck regions. The dependencies of the atomic structure and energy of the system on the relative position of the sinusoidal surface, relative azimuth angle of the two crystals and the moving velocity of the chuck (V), were investigated. The voids at the interface remained when V was slow, suggesting that there was an upper limit to the chuck moving velocity to obtain a good bonding state. This would be the optimum value of the chuck moving velocity from an engineering viewpoint. The relative position of the upper and lower crystals had no significant effects on the atomic structure and energy of the system, while the relative azimuth angle between the crystals had a crucial effect on the change in the atomic structure and energy of the system, i.e., a smaller orientational difference was necessary for good bonding.

Catalytic effects of magnesium-transition metal (Fe and Ni) hydrides on oxygen and nitrogen reduction: A case study of explosive characteristics and their environmental contaminants

The catalytic effects of magnesium-transition metal (Mg–TM) hydrides on O2 and N2 reduction were examined. The results indicated that magnesium hydrides (MHs) combustion process primarily occurred in three stages: dehydrogenation, active Mg combustion, and residual Mg combustion. After the dehydrogenation stage, the active Mg particles and released H atoms became more likely to be oxidised and nitrified in MgFeH than in MgH2. Moreover, a large quantity of NH3 was observed after the combustion of MgFeH. Fe has a rich electronic structure and an active surface position, which enables it to activate N2 and thus facilitate the catalytic reduction of N2. Due to the lower temperature and pressure requirements of the initial reaction in the MgFeH combustion or explosion process, compared to those of the Haber-Bosch process, the combustion and explosion of MgFeH can result in the release of significant amounts of NH3. However, the addition of Ni can prevent the activation of O2 and N2, thereby inhibiting their reduction. This means that Ni not only inhibits N2 reduction but also enhances the dehydrogenation capacity of MHs. Therefore, to develop and design hydrogen storage materials for MHs, Ni is a safer and more environmentally friendly catalyst than Fe.

Multi-orbit lunar GNSS constellation design with distant retrograde orbit and Halo orbit combination

The Moon is the closest natural satellite to mankind, with valuable resources on it, and is an important base station for mankind to enter deep space. How to establish a reasonable lunar Global Navigation Satellite System (GNSS) to provide real-time positioning, navigation, and timing (PNT) services for Moon exploration and development has become a hot topic for many international scholars. Based on the special spatial configuration characteristics of Libration point orbits (LPOs), the coverage capability of Halo orbits and Distant Retrograde Orbit (DRO) in LPOs is discussed and analyzed in detail. It is concluded that the Halo orbit with a period of 8 days has a better coverage effect on the lunar polar regions and the DRO has a more stable coverage effect on the lunar equatorial regions, and the multi-orbital lunar GNSS constellation with the optimized combination of DRO and Halo orbits is proposed by combining the advantages of both. This multi-orbital constellation can make up for the fact that a single type of orbit requires a larger number of satellites to fully cover the Moon, using a smaller number of satellites for the purpose of providing PNT services to the entire lunar surface. We designed simulation experiments to test whether the multi-orbital constellations meet the full lunar surface positioning requirements, and compare the coverage, positioning, and occultation effects of the four constellation designs that pass the test, and finally obtain a set of well-performing lunar GNSS constellations. The results indicate that the multi-orbital lunar GNSS constellation combining DRO and Halo orbits can cover 100% of the Moon surface, provides there are more than 4 visible satellites at any time on the Moon surface, which meets the navigation and positioning requirements, and the Position Dilution of Precision (PDOP) value is stable within 2.0, which can meet the demand for higher precision Moon surface navigation and positioning.

Investigation on surface quality in micro milling of additive manufactured Ti6Al4V titanium alloy

The additive manufactured technology is widely applied to produce titanium alloy parts with complex structures. The subsequent machining operations are necessary for additive manufactured parts to achieve the required machining quality. In this paper, the theoretical surface roughness model in micro milling was established. The model indicated the theoretical milled roughness mainly depends on the feed per tooth, tool nose radius and bottom edge inclination angle. Then, micro milling experiments are conducted on additive manufactured titanium alloy using PCD micro end mill. The surface roughness on milled surface was measured and investigated. At the middle position of micro milled surface, the distribution curves of surface roughness Ra and Sa show the same variation trend under different milling parameters. Moreover, the measured surface roughness results on different transverse positions of milled surface showed that the difference value between the actual and theoretical surface roughness of milled surface is mostly induced by the unstable cutting behaviors, which is also mainly responsible for the surface roughness size effect. The transverse distribution of surface roughness on milled surface exhibited a W shape because of the variation of the instantaneous undeformed chip thickness and material removal mode at different transverse positions.

Acoustic Roughness Measurement of Railway Tracks: Running Surface Detection and Compensation of Lateral Movements for Optical Measurements on a Train.

Rolling noise is a significant contributor to railway noise. Wheel and rail roughness are decisive for the emitted noise level. An optical measurement method installed on a moving train is suitable for closer monitoring of the rail surface condition. A measurement setup based on the chord method requires the sensors to be positioned in a straight line along the direction of measurement and in a stable lateral position. Measurements should always be performed within the shiny and uncorroded running surface, even when there are lateral movements of the train. In this study, concepts for the detection of the running surface and the compensation of lateral movements are investigated in a laboratory setting. The setup consists of a vertical lathe with a ring-shaped workpiece that incorporates an implemented artificial running surface. The detection of the running surface based on laser triangulation sensors and a laser profilometer is investigated. It is shown that the running surface can be detected using a laser profilometer that measures the intensity of the reflected laser light. It is possible to detect the lateral position and the width of the running surface. A linear positioning system is proposed to adjust the lateral position of the sensors based on the running surface detection of the laser profilometer. When the lateral position of the measuring sensor is disturbed by a movement with a wavelength of 18.85 m, the linear positioning system can keep the laser triangulation sensor inside the running surface for 98.44% of the measured data points at a velocity of approximately 7.5 km h-1. The mean positioning error is 1.40 mm. By implementing the proposed system on the train, future studies can be conducted to examine the lateral position of the running surface as a function of the various operational parameters of the train.

The Effect of Groundwater Level on Forced Convection Heat Transfer from a Buried Cylinder

The effect of groundwater level on forced convection heat transfer from a cylinder of 1 m in diameter buried at a depth of 10 m is studied numerically. The porosity and permeability of the soil are fixed at 0.5 and 1.0 × 10–11 m2, respectively, throughout the present study, while the inlet velocity U0 and the position of the phreatic surface (h), measured from the center of the cylinder, are varied in the ranges from 10–9 to 10–3 m s−1 and from − 4 to 4 m, respectively. Under these conditions, the heat fluxes on the cylinder are computed numerically. Various approximate solutions are also proposed and compared with those obtained numerically. The heat transfer results are also presented in nondimensional form for generality. The paper is divided into three parts, depending on the relative positions of the phreatic surface to the heated cylinder. First, the heat transfer rates are analyzed when the phreatic surface is above the cylinder, so that the cylinder is completely submerged in the water. In the second case, the phreatic surface is assumed to lie below the cylinder, so that the cylinder is left in the water-free space. In the third case, the phreatic surface is in contact with the cylinder surface, so that the cylinder is partially submerged in groundwater. For the above respective cases, three different approximate analyses are presented, and their validities and limitations are evaluated in comparison with the numerical calculations.

Low-Loss Pogo Pin Probe Card with a Coupling Isolation Structure up to 50 GHz

A design for a millimeter wave RF probe card that removes resonance is proposed. The designed probe card optimizes the position of the ground surface and the signal pogo pins to resolve the resonance and signal loss issues that occur when connecting a dielectric socket and a PCB. At millimeter wave frequencies, the height of the dielectric socket and pogo pin matches the length of half a wavelength, allowing the socket to act as a resonator. When the leakage signal from the PCB line is coupled to the 2.9 mm high socket with pogo pins, resonance at a frequency of 28 GHz is generated. The probe card uses the ground plane as a shielding structure to minimize this resonance and radiation loss. The importance of the signal pin location is verified via measurements in order to address the discontinuity caused by field polarity switching. A probe card fabricated using the proposed technique exhibits an insertion loss performance of −8 dB up to 50 GHz and eliminates resonance. A signal with an insertion loss of −3.1 dB can be transmitted to a system-on-chip in a practical chip test.

Research on the influence of foundation pit excavation on the lateral force and deformation of side shield tunnels based on full-scale experiments

To explore the internal force and deformation response law of the Hangzhou subway shield segment under the influence of the excavation and unloading of the side foundation pit, the self-developed “shield segment hydraulic loading system” was used to carry out full-scale loading tests on the three-ring staggered assembled segments. A preloading loading test were performed before the formal experiment to determine the loading method of the initial confining pressure. Analyzed the change mechanism of the internal force and deformation of the segment structure are influenced by factors such as the foundation pit and the tunnel clear distance. A numerical model is established based on the experimental results, and the influencing parameters that are difficult to complete in the experiment, such as the depth of the tunnel, are analyzed in detail. The research results show that the equal load maintains a balanced state of the segment to the greatest extent, and its internal force and deformation results are large, which is suitable for this experiment. After the excavation of the foundation pit, the maximum positive and negative bending moment increases, while the maximum axial force decreases. The average maximum recovery rate of tunnel section is 15.6%. Moreover, the additional internal force and deformation of the segment will increase with increasing deformation parameters of the envelope structure and decrease with increasing clear distance between the foundation pit and the tunnel. The bending moment of the segment is more sensitive to changes in the confining pressure, the convergence change can be controlled within a limited range, and the trend of the change in the internal force of the bolt shows differences. The numerical model established in this paper can better analyze the stress state of the tunnel. When the tunnel is buried deep in the slightly upper position of the excavation surface of the foundation pit, the unloading effect that is received is largest.

Automatic tractography and segmentation using finsler geometry based on higher-order tensor fields

Background and objective: We focus on three-dimensional higher-order tensorial (HOT) images using Finsler geometry. In biomedical image analysis, these images are widely used, and they are based on the diffusion profiles inside the voxels. The diffusion information is stored in the so-called diffusion tensor D. Our objective is to present new methods revealing the architecture of neural fibers in presence of crossings and high curvatures. After tracking the fibers, we achieve direct 3D image segmentation to analyse the brain’s white matter structures. Methods: To deal with the construction of the underlying fibers, the inverse of the second-order diffusion tensor D, understood as the metric tensor D−1, is commonly used in DTI modality. For crossing and highly curved fibers, higher order tensors are more relevant, but it is challenging to find an analogue of such an inverse in the HOT case. We employ an innovative approach to metrics based on higher order tensors to track the fibers properly. We propose to feed the tracked fibers as the internal initial contours in an efficient version of 3D segmentation. Results: We propose a brand-new approach to the inversion of a diffusion HOT, and an effective way of fiber tracking in the Finsler setting, based on innovative classification of the individual voxels. Thus, we can handle complex structures with high curvatures and crossings, even in the presence of noise. Based on our novel tractography approach, we also introduce a new segmentation method. We feed the detected fibers as the initial position of the contour surfaces to segment the image using a relevant active contour method (i.e., initiating the segmentation from inside the structures). Conclusions: This is a pilot work, enhancing methods for fiber tracking and segmentation. The implemented algorithms were successfully tested on both synthetic and real data. The new features make our algorithms robust and fast, and they allow distinguishing individual objects in complex structures, even under noise.

Impacts of a beaver dam analogue complex on streambed vertical hydraulic gradients in a 1.2‐km stream reach in Wyoming, USA

AbstractBeaver dam analogues (BDAs) have seen growing use as restoration structures across the western United States. This study investigates the patterns in streambed upwelling and downwelling along a 1.2‐km stream reach in Red Canyon Creek (RCC), Wyoming before and after the installation of 31 new BDAs and the upgrade of four existing BDAs in July 2021. Over 100 mini‐piezometers were used to measure upwelling and downwelling in low‐flow, summer periods as quantified by vertical hydraulic gradient (VHG). Both before and after BDA installation, the stream reach was dominated by downwelling patterns, suggesting that RCC was a net losing stream during this summer period, with and without BDAs. While there were spatial variations in VHG before BDA installation, this variation was not dependent on stream depth, water surface concavity, sediment characteristics, and position relative to meanders, suggesting that unobservable subsurface properties may be a control on VHG or that there are attributes that were not captured due to the 10‐m spacing of mini‐piezometers. After BDA installation, VHGs were primarily related to the magnitude of the elevation gradient across the BDA. VHGs were highest near the BDAs and diminished once moving more than a few metres from the BDAs. When VHGs were averaged over the full reach length, BDAs appeared to slightly enhance net stream loss, albeit we could not control for possible seasonal differences in water table gradient during the observtion period.

Modelling Time-Dependent Flow through Railway Ballast

In this study, a numerical simulation of fluid flow through railway ballast in the time domain is presented, providing a model for unsteady-state flow. It is demonstrated that the position of the free surface with respect to time can also be used to solve the steady flow case. The effect of ballast fouling is included in the model to capture the realistic behavior of railway ballast, which is critical to understanding the impact of flooding. A thorough comparison with a range of previous studies, including theoretical and experimental approaches, is made, and very close agreement is obtained. The significant impact of ballast fouling on fluid flow and its potential consequences for railway infrastructure are highlighted by the simulation. Valuable insights into the behavior of water flow through porous media and its relevance to railway ballast management are offered by this study.