Corner Region Research Articles

Evolutionary dynamics inform management interventions of a hanging garden obligate, Carex specuicola

Uncovering the historical and contemporary processes shaping rare species with complex distributions is of growing importance due to threats such as habitat destruction and climate change. Species restricted to specialized, patchy habitat may persist by virtue of life history characteristics facilitating ongoing gene flow and dispersal, but they could also reflect the remnants of formerly widespread, suitable habitat that existed during past climate regimes. If formerly widespread species did not rely upon traits facilitating high dispersibility to persist, contemporary populations could be at high risk of extirpation or extinction. Fortunately, genomic investigations provide an opportunity to illuminate such alternative scenarios while simultaneously offering guidance for future management interventions. Herein, we test the role of these mechanisms in shaping patterns of genomic diversity and differentiation across a highly restricted and rare ecosystem: desert hanging gardens. We focus on Carex specuicola (Cyperaceae), a hanging garden obligate narrowly distributed in the Four Corners region of the southwestern United States that is listed as Threatened under the United States Endangered Species Act. Population structure and diversity analyses reveal that hanging garden populations are shaped by strong genetic drift, but that individuals in gardens are occasionally more closely related to individuals at other gardens than to individuals within the same garden. Similarly, gardens separated by long geographic distances may contain individuals that are more closely related compared to individuals in gardens separated by short geographic distances. Demographic modeling supports historical gene flow between some contemporary garden pairs, which is corroborated by low estimates of inbreeding coefficients and recent divergence times. As such, multiple lines of evidence support dispersal and gene flow across C. specuicola populations at both small and large spatial scales, indicating that even if C. specuicola was formerly more widespread, it may be well suited to persist in hanging gardens so long as suitable habitat remains available. Analyses like those demonstrated herein may be broadly applicable for understanding the short- and long-term evolutionary processes influencing rare species, and especially those having complex distributions across heterogeneous landscapes.

Exfoliation Syndrome and Exfoliation Glaucoma in the Navajo Nation.

(1) Background: Exfoliation syndrome (XFS) is a common cause of secondary open angle glaucoma. In 1971, Faulkner et al. estimated the prevalence of XFS among 50 Navajo Nation residents as 38%. Given that XFS can cause irreversible blindness secondary to glaucoma (XFG), this study aims to identify the current prevalence of XFS among Navajo Nation residents within the Four Corners region of the U.S. (2) Methods: A retrospective chart review was conducted from 2016 to 2021 for patients aged 18 and older. All patients with XFS or XFG diagnosed by slit lamp exam were identified through chart review. (3) Results: Of the 1152 patient charts available for review, eight patients (11 eyes) were diagnosed with XFS with three patients (4 eyes) demonstrating concomitant XFG. Within this XFS population, 50% of the patients identified as male, with a mean age of 73 years. The overall prevalence of XFS was 0.7% and the overall prevalence of XFG was found to be 0.26%. The rate of XFG among patients with XFS was 37.5%. (4) Conclusion: Compared to Faulkner’s study of Navajo Nation residents in 1971, our findings show a considerably lower prevalence of XFS at 0.7%. We present the largest study to date of XFS among this population.

Flexural behaviour of cold-formed steel square and rectangular hollow sections with moderate heat-treatment

This paper discusses the flexural behaviour of cold-formed square and rectangular hollow steel sections (SHSs and RHSs) with subsequent heat-treatment through experimental and numerical investigations. Firstly, an experimental programme comprising tensile coupon tests on flat and corner regions and three-point bending beam tests were conducted. A total of 12 specimens were tested under monotonic bending loads, covering a variety of section slenderness. Failure modes, moment-rotation curves and plastic hinge lengths have been evaluated highlighting the effect of the web-flange interaction on rotation capacity. Successively, experimental results were combined with numerical FE results to assess the corresponding moment and deformation capacities. Current cross-section classification limits given in Eurocode 3 and AISC 360–16 were assessed and new limits has been proposed.

Effective material model for cold-formed rectangular hollow sections in beam element-based advanced analysis

This study develops and validates an effective material model for cold-formed rectangular hollow sections. Advanced design methods utilize non-linear finite element analysis in design. An accurate calculation model, which is usually beam element-based, is crucial such that the design outcome is safe but economical. Unfortunately, cold-formed sections have non-linear residual stress distribution over the material thickness, that cannot be explicitly modelled in general-purpose beam elements. Additionally, corner regions of cold-formed sections have higher material strength compared to flat regions. This beneficial feature is usually disregarded by assuming the flat region properties for the entire cross-section. This study develops an effective material model that replicates a stress-strain curve that would be obtained if the tensile test was made for the entire cross-section instead of a separate tensile coupon. Consequently, the effects of residual stresses and corner strength enhancements are included in the effective material model such that their consideration in beam element-based advanced design method is effortless. The effective material model is validated for the steel grade S700 against numerical shell element buckling tests and excellent modelling accuracy is achieved.

Fabrication and quality analysis of angle composite part by vacuum-bag-only process with interleaved woven fiber/prepreg layup

This study used the vacuum-bag-only (VBO) process to fabricate angle composite parts with interleaved layup of prepreg and dry fibers. The quality of angle parts is investigated by statistical methods, which are divided into two parts: geometric characteristics and internal characteristics. The results indicated that the part fabricated by the convex mold presented higher dimension stability and uniformity as compared to that by the concave mold. According to the results, increasing the laminate thickness and decreasing the angle mold could effectively reduce the corner thickness deviation and angle deviation percentages. In addition, the lead caul plate could effectively improve the thickness change in the corner area in both the concave and convex molds, and both the lead and Si-rubber caul plates could significantly reduce the angle deviation. For the internal characteristics, to quantify the void content of the laminate, we propose a scoring mechanism to analyze angle part. The part fabricated by the convex mold has a higher score than that by the concave mold. In order to fully understand the thickness variation of the part at the corner region, a semi-empirical model was proposed to calculate the corner thickness deviation in different mold geometry and stacking thickness. In this study, the prediction errors of the semi-empirical model for the parts by the concave and convex molds are 17.6% and 16.1%, respectively. The results of this research can also be extended to other VBO processes with more complicated geometries and provide advice and guideline on mold design and process conditions.

Effects of Surface-Attached Vertical Ribs on Wind Loads and Wind-Induced Responses of High-Rise Buildings

Façade design tends to be diverse with increasing requirements for architectural functions in modern high-rise buildings, leading to various aerodynamic roughness conditions of the building surface. A typical practice is setting vertical ribs on the building façade. This study aims to clarify the effects of vertical ribs on the wind loads and wind-induced responses of high-rise buildings. The models with four vertical rib configurations were tested in the open and suburban exposures using the High-Frequency Force Balance (HFFB) technique in a wind tunnel. The base overturning moments and corresponding responses are demonstrated and compared between models and exposures. Results show that the vertical ribs with a relative width of 4% can not only reduce the mean force coefficients in the along-wind direction but also attenuate the cross-wind vibration by disrupting the regular vortex shedding. Moreover, the half-distributed and full-distributed rib configurations have almost indistinguishable benefit, indicating that the ribs in the corner region of the building façade play a dominant role in reducing the wind-induced responses. Although the cross-wind responses of the building would be less severe in the suburban exposure than those in the open exposure, the reduction rate of the wind-induced responses by the vertical ribs remains almost unchanged.

Experimental Investigation of Terminal Shock/Boundary-Layer Interaction with and without Upstream Lateral Confinement

A generic external-compression inlet test model is designed and fabricated to investigate the flow characteristics of terminal shock/boundary-layer interaction for inlet applications with and without upstream lateral confinement. When the leading edge of the sidewall is positioned 150 mm upstream of the duct entrance, the bifurcation height of the shock, the centerline separation length, and the pressure rise ratio at are close to reported values in the literature, although the corner separation herein is minor as compared with previous experiments with thick sidewall boundary layers. However, when the leading edge of the sidewall is aligned with the duct entrance, an obvious increase in the bifurcation point height can be observed, and an increase in centerline separation can be inferred from schlieren photographs. The significantly intensified separation is verified directly by surface oil flow visualization. In addition, the focus previously present in the corner region is replaced by a reattachment node located near the junction region of the bottom plate and sidewall leading edge. The intensification of the separation is attributed to a local high-pressure region caused by the impingement of the postshock subsonic flow onto the sidewalls.

The Annealing Effect of Welding on the Strength of Cold‐worked Stainless Steel

AbstractCold‐working can occur during the production of flat sheet products and the fabrication of structural cross‐sections. In both cases, when the material is cold‐worked, plastic deformations result in material strength enhancements. These strength enhancements are particularly significant for materials such as stainless steel, which exhibit rounded stress‐strain behaviour and pronounced strain hardening, and for hollow cross‐sections, where the strength increases arise in both the corner and flat regions of the cross‐section. Numerous studies have shown the importance of utilising this strength enhancement in design, and expressions to predict the strength enhancements have been established. However, if cold‐worked material is welded, some enhanced strength can be lost due to partial annealing in the heat affected zone (HAZ). The extent of this strength loss is investigated experimentally herein. The experimental programme comprised ten tensile coupon tests, with central welds parallel and transverse to the direction of cold‐rolling, as well as twelve full cross‐section tensile tests. Digital imaging correlation was utilised to determine the local constitutive properties of the base metal, the HAZ, and the weld metal. The microhardness and microstructure of the welded coupons, along with the widths of the weld and HAZ, were also characterised.

Water Level Change Monitoring Based on a New Denoising Algorithm Using Data from Landsat and ICESat-2: A Case Study of Miyun Reservoir in Beijing

Inland lakes or reservoirs are the main surface water resources, related to people’s survival and social development. On-site water level data are critical for water resource management, while satellite laser and remote sensing data are a significant tool for long-term change monitoring. In this study, we took the Miyun Reservoir, the most important source of drinking water in Beijing, as the research area. We used Landsat images and the Ice, Cloud, and Land Elevation Satellite (ICESat-2) for small-scale water level change monitoring and inversion across unrecorded periods. First, we proposed a new two-step denoising method based on local statistics to denoise the ATL03 single photon data from 2018 to 2020, and extracted the effective elevation information of Miyun Reservoir. Second, based on Landsat images from 1984 to 2020, the MNDWI index was used to extract the water area and generated a percentage map of water occurrence. Finally, the water and land boundary elevation were selected from the effective photon elevation information according to the boundary position under each percentage of the water generation percentage graph, the area, and the water level elevation model (A–E model) was established, and the water level values of unrecorded periods were inverted. The denoising results showed that the denoising accuracy of all data is higher than 95%. The area of Miyun Reservoir has changed greatly in the past 37 years, especially in the northeast corner and northern region. The inverted water level elevation had a strong correlation with the measured value, the correlation coefficient reached 0.97, the root mean square error (RMSE) was 0.553 m, and the estimated water level value was highly consistent with the recorded value and fluctuated dramatically from 1984 to 2020. This method complements the traditional water level mapping method, provides a new idea for the monitoring of water level changes in lakes or reservoirs without field records, and also contributes to the timely and effective monitoring and management of global lake and reservoir water level and time changes.

Study of the factors influencing load displacement curve of energy absorbing device by area division simulation

A pre folded energy absorbing device, which is the key device of energy absorption anti impact for roadway support, is tested by quasi-static compression and simulated. The energy absorbing device is divided into zones, and the influence of the area on the load displacement curve of the energy absorbing device is studied according to the area. It is found that the error of numerical simulation is within 5%, indicating that the finite element modeling procedure is appropriate for the problem analyzed here. The device crushes following the pre folded origami pattern in a stable progressive. The device was divided into four areas: the upper and lower opening region of the concave surface four corner parts; the other areas of opening regions; the middle fold edge; the surrounding four sides edge. Each area has effect on the first drop stage and the second rise stage of the load displacement curve. The middle fold edge area has an effect on the peak load value of load displacement curve. Four indicators of peak load, average load, load efficiency, and specific energy absorption were generated from the results of numerical simulation. The strength enhancement of corner region can ensure the energy absorbing device with low peak load and high mean crushing load. The other areas of opening regions affect the first descending and second ascending of the curve. The first rising stage bears the load from the middle edge.

Region specific and subimage based neighbour gradient feature extraction for robust periocular recognition

This paper proposes a Periocular recognition algorithm that uses region-specific and sub-image-based neighbor gradient feature extraction to achieve better recognition results. This approach initially segments the periocular region into four sub-regions such as eyebrow, eye corner regions, upper and lower eye fold regions after detecting the left and right eye corner points. KAZE feature extraction algorithm is used to extract the features from the upper eye fold region, while the HOG feature extraction algorithm is used to extract the feature from the eyebrow and eye corner regions. This approach also estimates the shape of the eyebrow by estimating the distance from N points on the eyebrow region to the eye corner midpoint. The eyebrow shape feature also contains the width and height measures through N points on the eyebrow that give its shape. The proposed approach also proposes a sub-image-based neighbor gradient (SING) feature extraction that extracts the neighbor gradient features from a 3×3 sub-image. Finally, the extracted features are trained using the Naïve Bayes classifier. The experimental evaluation was done using the AR dataset, CASIA Iris distance dataset, and UBIPr dataset using the metrics such as rank-1, rank-5 recognition accuracies, the area under the ROC curve (AUC), and equal error rate (EER). The proposed scheme provides a rank-1 recognition rate of 92.32 %, 97.41 %, and 97.87 % for the dataset UBIPr, CASIA-Iris, and AR datasets respectively. The experimental results reveal that the proposed method outperforms the traditional periocular recognition algorithms.

A novel zipper shape joint for improving microstructure and mechanical property of electron beam welded TiAl joint

TiAl alloy is sensitive to welding cracks and exhibits brittle nature at room temperatures. The formation of the α2-Ti3Al phase coupled with high welding residual stress has been proved to be the key factor triggering the cracking of the joint. To improve the microstructure of the weld, a zipper shape joint is designed to decrease the cooling rate of the joint. Finite element simulation analysis of the traditional line-shape joint and the zipper shape joint was carried out. The results reveal that the special zipper shape design effectively decreases the cooling rate of the joint than the straight-line shape joint. The zipper shape can play a role in preheating and post-heat treatment during the welding process. Compared with the straight-line shape joint, the high temperature (above 750 °C) dwelling time of the zipper shape joint is greatly prolonged, which promoted the α → γ phase transformation. However, such weld path also causes stress concentration in the corner region of zipper shape weld bead. Though welding cracks still exist, the crack frequency of the zipper shape joint is decreased obviously. The tensile tests also exhibit that the strength of the zipper shape joint reaches 417 MPa, 40.4 % higher than that of the straight-line shape joint of 297 MPa. Hence, joint shape design can be regarded as a promising direction for further investigations referring to crack control of TiAl joints.

Significance of eigenstresses and curling stresses for total thermal stresses in a concrete slab, as a function of subgrade stiffness

ABSTRACT Thermally induced stresses of a concrete slab are quantified based on in situ temperature measurements. PT100A sensors recorded the temperature at four specific depths during 23 days in autumn. Best-fit quadratic polynomials are used to extrapolate the measured temperatures to the top and the bottom of the slab. The obtained surface temperature histories are used as boundary conditions for the solution of the transient heat conduction problem in thickness direction. Postprocessing the thermal eigenstrains provides access to the eigencurvatures of the plate and to the eigendistortions of the plate-generators. Stresses resulting from the constrained eigencurvatures of the plate are computed numerically, for values of the modulus of subgrade reaction amounting to 50, 100, 200, and 300 MPa/m. Self-equilibrated eigenstresses resulting from the prevented eigendistortions of the plate-generators are quantified analytically. Daily maxima of tensile stresses in corner regions at the top of the slab, and in the central region at its bottom, are found in the early morning and in the early afternoon, respectively. Disregarding the eigenstresses leads to an underestimation of tensile stresses in corner regions by at least 33 % and an overestimation in the central region by at least 26 % . The misestimations increase with decreasing modulus of subgrade reaction.

Large eddy simulation and combined control of corner separation in a compressor cascade

Due to the demand for higher aerodynamic performance of compressors, thoroughly investigating the high-loss flow in the corner region and effectively controlling it are important. In this paper, a novel parameterization method based on the extended free form deformation (EFFD) technique and the constraints for EFFD's control points is proposed. Then, considering the features of typical control techniques and the degrees of freedom of both the blade and hub geometries, the combined control approach is implemented in the corner region of a linear cascade. Furthermore, large eddy simulation is used to simulate the flow, verify the effects of the combined control approach, and explore the underlying physical mechanisms of corner separation. The numerical results show that the combined control can significantly decrease the mean total pressure loss. The loss reduction at the design point reaches 6.05%, while it decreases by almost 2.5% near the stall/blockage operating conditions. The combined control increases the radial pressure gradient at the rear of the blade by depressing the hub and stretching the suction surface. Consequently, although the radial flow slightly increases the mixing loss in the mainstream at large incidences, the accumulation of low-energy flow in the boundary layer and the corresponding development of the corner vortex are significantly restrained. Moreover, by redistributing the static pressure on the hub, the combined control weakens the migration of crossing flow and obstructs the low-velocity flow from the pressure side involved in the separation. Overall, the combined control contributes to reducing the corner separation and improving the aerodynamic performance.

Quantitative consideration in selection of breakwater concrete armor unit based on unit’s internal tensile stress response

Concrete armor units are essential for the protection of rubble mound breakwaters, yet their selection is generally not based on structural integrity considerations. In this study, the authors used static finite element simulations, as implemented by Ansys software, to compare the structural integrity of five armor units: Accropode, A-Jack, BPPT-Lock, tetrapod, and dolos. All armor units have a mass of around 11,500 kg and have the same quality of concrete at f’c of 30 MPa. The study involves two different loading cases: Armor units were (1) arranged on a breakwater slope subjected to their own weight and (2) placed on a horizontal ground subjected to idealized wave attacks. In Case #1, the armor units were modelled fixed to the ground and bonded to each other. In Case #2, the wave attack was modelled as a unidirectional and uniform pressure. From the simulation results, the authors compare the highest tensile stresses which could be found on the corner regions of the armor units—their most vulnerable region. In both cases, armor units with stocky shapes experience lower tensile stresses compared to those with slender shapes. These results confirm that Accropode, BPPT-Lock, and tetrapod are structurally safer than dolos and A-Jack.

Life at Mesa Verde: An Analysis of Health and Trauma from Wetherill Mesa, Mesa Verde National Park

Many Mesa Verde cliff dwellings were occupied during the thirteenth century in the final decades before the Four Corners region was depopulated. Deposits in such cliff dwellings offer unique opportunities to research motivations for migration and to understand living conditions in these unusual locations. In compliance with NAGPRA, bioarchaeological data were collected from Wetherill Mesa burials in 1995; this study is the first systematic analysis of these data. Skeletal health indicators demonstrate increased physiological stress for residents of Pueblo III cliff dwellings. Worsening health related to resource availability and distribution, aggregation, and unsanitary living conditions might have influenced migration from the region. Skeletal fracture data indicate decreased trauma during the Pueblo III, contrasted with the possibility of culturally mediated violence or violent attack at Long House. This pattern of violence was likely a response to insecurity during the late thirteenth century and ultimately might have provided another motivation for migration.

Experimental quality assessment of thermoplastic composite corner regions manufactured using laser-assisted tape placement

Over the past 25 years, interest in thermoplastic composites in aircraft has steadily increased. Combining winding and laser-assisted tape placement is a promising method to manufacture thermoplastic structures using in-situ consolidation, as shown recently by manufacturing a variable stiffness, unitized, integrated-stiffener thermoplastic wingbox at the University of Limerick. The corner regions are a critical point of the structure and require in-depth characterization studies, for example by unfolding L-shaped samples in a 4-point bend test. In this work, samples with radii varying from 2 to 10 mm were manufactured and tested. Two manufacturing parameters were varied: the rotational speed and acceleration of the tool. Test data show that decreasing the radius increases the corner strength, but an optimum radius exists to withstand a maximum unfolding force/moment. In addition, the slowest deposition rate with least acceleration of the head used during manufacturing lead to the highest corner strength for the same radius.

Topology optimization of thin-walled tubes filled with lattice structures

Thin-walled tubes filled with ultra-light materials have attracted much attention due to excellent energy absorption characteristics. With the development of additive manufacturing technology, it is allowed to manufacture structures with complex geometry shapes as new filled materials. In this study, complex proportional assessment (COPRAS) and discrete optimization algorithm were proposed to design and optimize the topology of thin-walled tubes filled with lattice structures. Firstly, the finite element model verified by experiment was adopted to investigate the influence of cross-sectional configurations and octet truss lattice filling distributions on crashworthiness of hybrid structures. The results show that the cross-sectional configuration has a greater effect on specific energy absorption (SEA) and the lattice filling distribution has a greater effect on peak crushing force (PCF). Then, COPRAS was used to sort the crashworthiness of hybrid structures with different topologies and select the optimal solution. It was found that C3-L4 structure had the best crashworthiness among all design schemes, indicating that the better crashworthiness can be obtained by filling the lattice in the four corner regions of tube or increase the number of cells in corner regions. Finally, the discrete optimization algorithm based on successive orthogonal arrays was adopted to further improve the crashworthiness of hybrid structure. It was found that the thin-walled tubes with different thickness had greater energy absorption capacity than those with the same thickness. Hence, the method proposed in this paper can become an effective way for topology optimization of crashworthiness.

The Dodge City Tornadoes on 24 May 2016: Understanding Cycloidal Marks in Surface Damage Tracks and Further Analysis of the Debris Cloud

Abstract Mobile, polarimetric radar data were collected on a series of tornadoes that occurred near Dodge City, Kansas. A poststorm survey revealed a series of tornadic debris swaths in several dirt fields and high-resolution pictures of the tornado documented the visual characteristics of the tornado and the lofted debris cloud. The main rotational couplet associated with the tornado was identified in the single-Doppler velocities; however, no secondary rotational couplets were resolved in the low-level data performed during two consecutive volume scans. Numerical simulations have suggested that cycloidal damage swaths can result when debris is deposited as the low-level inflow turns upward in the corner region of the updraft annulus of the tornado core. This mechanism can dominate even when suction vortices are present in the simulations and can produce these swaths in the absence of these smaller-scale vortices. It is hypothesized that the observed cycloidal damage swaths were a result of the low-level inflow in the corner region of the tornado and not by the existence of suction vortices. Polarimetric data were combined with photographs of the tornado in order to document the lofted debris cloud and its relationship with the funnel. This analysis provided an opportunity to investigate whether recent findings describing the cross-correlation coefficient ρhv and differential reflectivity ZDR signatures of the lofted debris cloud could be replicated. Regions of low ρhv at the periphery of the funnel cloud suggesting high debris loading and a column of negative ZDR centered on the tornado believed to be produced by common debris alignment were noted. Significance Statement It is well known that some tornadoes produce smaller-scale vortices that rotate around the central axis of the main circulation. In addition, numerous aerial photographs have documented cycloidal debris marks within tornado damage tracks that traverse open fields. The prevailing theory shown in numerous textbooks is that these marks are produced by these vortices. The current study suggests that this widely accepted model for producing these marks may be incorrect. It is suggested that these cycloidal marks are produced by the main tornado circulation and not by the smaller-scale vortices in this case.

Transient nature of secondary vortices in an axial compressor stage with a tandem rotor

An efficient and compact design of a compressor continues to be a challenging area of research. The unavoidable streamwise adverse pressure gradient together with passage transverse pressure gradient restricts the maximum allowable blade turning. Tandem blading is an interesting concept for increasing the pressure rise by permitting a higher blade turning angle. The energized flow through the tandem blade nozzle gap helps to minimize the possibility of flow separation over the suction surface of the aft blade. However, a coherent transient analysis of a tandem rotor stage in an axial compressor is yet to be well explored. In the present paper, the complex flow field over a tandem rotor and the succeeding stator passage is analyzed in detail. Although the tandem rotor increases the flow turning and diffusion effect, the presence of separate trailing edge wakes and hub corner vortex causes early onset of flow separation over the stator suction. The flow structures developed within the rotor and the stator passages at different time instances are highlighted with the help of limiting streamlines and iso-surface Q-criterion superimposed with entropy contours. The results indicate that within the rotor passage, transient flow features are observed near the hub corner region close to the aft blade trailing edge rather than the tip region. When the rotor passes the stator leading edge, the rotor trailing edge leakage flow at the hub is entrained into the stator leading edge reverse flow region. This is then further circumferentially dragged into the mid-passage region. The interference of multiple rotor wakes with the stator leading edge leads to the formation of longitudinal and arch like separation vortices at the stator-hub and the stator-casing regions, respectively. These separation vortices grow in size while being convected downstream. Eventually, as time progresses, the vortices split and shed periodically from the stator surface. The present investigation highlights the requirement of a new stator design in a tandem rotor–conventional stator configuration. Such designs could further magnify the significant aerodynamic performance obtained using a tandem configuration.