Minimum Head Research Articles

Assessment of Femoral Head Sphericity Using Coordinate Data through Modified Differential Evolution Approach

Coordinate measuring machines (CMMs) are utilized to acquire coordinate data from manufactured surfaces for inspection reasons. These data are employed to gauge the geometric form errors associated with the surface. An optimization procedure of fitting a substitute surface to the measured points is applied to assess the form error. Since the traditional least-squares approach is susceptible to overestimation, it leads to unreasonable rejections. This paper implements a modified differential evolution (DE) algorithm to estimate the minimum zone femoral head sphericity. In this algorithm, opposition-based learning is considered for population initialization, and an adaptive scheme is enacted for scaling factor and crossover probability. The coefficients of the correlation factor and the uncertainty propagation are also measured so that the result’s uncertainty can be determined. Undoubtedly, the credibility and plausibility of inspection outcomes are strengthened by evaluating measurement uncertainty. Several data sets are used to corroborate the outcome of the DE algorithm. CMM validation shows that the modified DE algorithm can measure sphericity with high precision and consistency. This algorithm allows for an adequate initial solution and adaptability to address a wide range of industrial problems. It ensures a proper balance between exploitation and exploration capabilities. Thus, the suggested methodology, based on the computational results, is feasible for the online deployment of the sphericity evaluation. The adopted DE strategy is simple to use, has few controlling variables, and is computationally less expensive. It guarantees a robust solution and can be used to compute different form errors.

Research on the Flow Characteristics in the Gap of a Variable-Speed Pump-Turbine in Pump Mode

A variable-speed pump-turbine is the core component of a hydraulic storage and energy generation station. When the pump-turbine operates at a constant speed, its response to the power grid frequency is poor. In order to improve the hydraulic efficiency of the pumped storage unit, variable-speed units are used. However, there has been no numerical study on the effect of the rotational flow characteristics within the gap of a variable-speed pump-turbine. This paper calculates the flow characteristics within the gap of a variable-speed pump-turbine under three typical pump modes (maximum head minimum flow condition, minimum head maximum flow condition, and maximum speed condition). The research results indicate that the rotational speed significantly affects the pressure distribution, velocity distribution, and turbulent kinetic energy distribution within the crown and band gaps. The higher the speed, the larger the area of the high-pressure region before the runner inlet compared to other operating conditions, and similarly, the low-pressure area after the runner outlet is also larger than in other operating conditions. The change in speed mainly affects the internal flow field of the crown gap, with the most noticeable changes occurring in the pressure and flow velocity at the inlet and outlet of the crown gap. There is a clear trend of pressure drop and velocity increase within the gap as the speed increases. However, with the increase in speed, the pressure distribution and flow velocity within the band gap remain almost the same. In addition to speed changes, it is observed that the pressure within the gap and the flow velocity within the passages are also related to the head, especially in the condition of maximum head, where this relationship becomes more noticeable.

Efficacy of different pesticides in suppressing yellow stem borer in spring rice (Oryza sativa) in Ratuwamai, Morang, Nepal

Rice, a staple food for over half the global population, is crucial for food security, economic stability, and cultural significance. Its production, however, is threatened by pests like the Yellow Stem Borer (YSB), which causes substantial yield losses, especially in rice-dominant regions like Nepal. This study focuses on evaluating the effectiveness of biological, botanical, and chemical pesticides against YSB in spring rice crops of Ratuwamai, Morang, Nepal. For this, we apply biological methods/pathogens like Bacillus thuringiensis, to target YSB; botanical pesticides, derived from plants like Azadirachtin and Mugworth, act as repellents; while chemical pesticides such as Cypermethrin, Chlorpyriphos and Cartap Hydrochloride offer rapid control but come with environmental risks. Among those six pesticides used, the present findings revealed that chlorpyriphos 20% EC have minimum mean dead heart with 4.92% and cypermethrin 10% EC have minimum mean white ear head with 2.44% respectively after application of first and second dose of treatments respectively. Likewise, most plant yield attributes were superior where chlorpyriphos was used. Though bacillus and azadirachtin reduced the dead heart and white ear head symptoms, they couldn’t give good yield than that of chemical pesticides. Thence, through our research we investigated the impacts of different biological, botanical and chemical pesticides in controlling YSB population densities, and influencing yield and yield attributing characters from the field experiment.

Study on erosion characteristics of turbine in sediment-laden river

Abstract Sediment erosion of hydro turbines is prevalent and serious in the mountain river region. The effect of operating head and particle diameter on sediment erosion was investigated in this paper. A Eulerian-Lagrangian approach was applied to numerically simulate the solid-liquid flow in a Francis turbine under the minimum, design and maximum heads. Five typical diameters (0.1, 0.3, 0.5, 0.7, 0.9 mm) were firstly determined based on field measurements at a hydropower station. After tracking the trajectories of sediment particles, McLaury model was selected to predict the erosion rate. The results show that sediment erosion regions of runner blades are similar under different operating heads, while the sediment erosion rates amplify significantly with the increase of operating heads. The erosion rate of blade suction side is significantly higher than that of pressure side because of the effect of inter-blade vortices between runner blades. Sediment diameters also play an important role in accelerating erosion rate, which indicate that setting up sedimentation tanks to settle large-size sediment particles is a powerful method to alleviate sediment erosion. This study can provide a reference for erosion estimation and operational maintenance of hydro turbines in mountain river region.

Vortices Evolution Characteristics and Pressure Pulsations of Variable-speed Francis Turbine

Abstract The stability of Francis turbine under low load conditions has become the focus in the power grid dominated by variable renewable energy. In this paper, the variable-speed approach is used to explore the operating characteristics of the Francis turbine, the RANS/LES hybrid turbulent model is adopted to investigate the fluid structure evolution process, and using the Q-criterion depicts the vortex cores. The results show that the numerical simulation agrees well with the experimental data acquired from the model test. It is found that the variable-speed operation can effectively eliminate the vortex ropes in the draft tube. Unexpectedly, the vortices in the runner will evolve from the separated vortices at the runner outlet for the fixed-speed Francis turbine to the inter-blade vortices at the runner inlet for the variable-speed Francis turbine in the case of small guide vane opening. It is concluded that the optimum operating range of a variable-speed Francis turbine (VSFT) should be within ±30% rated speed and 60% to 100% opening, and the pressure pulsation coefficient in the draft tube can be reduced from 7% to 1% at minimum water head, the output and efficiency of the turbine are increased by about 30% and 10% respectively.

A Standardized Treatment Model for Head Loss of Farmland Filters Based on Interaction Factors

A head loss model for pressureless mesh filters used in farmland irrigation was developed by integrating the four basic test factors: irrigation flow, filter cartridge speed, self-cleaning flow, and initial sand content. The model’s coefficient of determination was found to be 98.61%. Among the basic factors, the total irrigation flow accounted for only 17.20% of the relatively small self-cleaning flow. The contribution of initial sand content was found to be the smallest, with a coefficient of only 0.0166. Furthermore, the contribution rate of the flow term was significantly higher than that of the initial sand content, with a value of 159.73%. In terms of quadratic interaction, the difference between the interaction term of flushing flow and filter cartridge speed, and the interaction term of filter cartridge speed and self-cleaning flow was 38.42%. On the other hand, the difference within this level for the interaction term between initial sand content and filter cartridge speed, as well as the interaction term between irrigation flow and self-cleaning flow, was 2.82%. Finally, through joint optimization of the response surface and model, the optimal values for the irrigation flow rate, filter cartridge speed, self-cleaning flow rate, and initial sand content were determined to be 121.687 m3·h−1, 1.331 r·min−1, 19.980 m3·h−1, and 0.261 g·L−1; the measured minimum head loss was found to be 21.671 kPa. These research findings can serve as a reference for enhancing the design of farmland filters and optimizing irrigation systems.

Coupled multi-objective optimization of water distribution network design and partitioning: a spectral graph-theory approach

ABSTRACT This paper proposes a novel method that integrates a tailored spectral graph metric and economic aspects within a coupled bi-objective optimization framework for the simultaneous pipe sizing and partitioning of water distribution networks (WDNs). Besides minimum pressure head and topological WDN connectivity, the telescopic diameter distribution criterion is applied through a new algorithm in the sizing phase to help the optimization converge towards sound engineering solutions. The application of the proposed method to a synthetic layout and a real Italian case study proves the superiority of the solutions obtained with the novel method from hydraulic and managerial/operational viewpoints in comparison with those obtained with a traditional decoupled method (separate pipe sizing and partitioning) in terms of i) compliance with service pressure constraints and ii) ease of management following WDN partitioning into district metered areas (DMAs).

Feasibility analysis and nail planning ofS2 iliac crest screw placement in children

To evaluate the feasibility of S2 alar iliac screw insertion in Chinese children using computerized three-dimension reconstruction and simulated screw placement technique, and to optimize the measurement of screw parameters. A total of 83 pelvic CT data of children who underwent pelvic CT scan December 2018 to December 2020 were retrospectively analyzed, excluding fractures, deformities, and tumors. There were 44 boys and 39 girls, with an average age of (10.66±3.52) years, and were divided into 4 groups based on age (group A:5 to 7 years old;group B:8 to 10 years old;group C:11-13 years old;group D:14 to 16 years old). The original CT data obtained were imported into Mimics software, and the bony structure of the pelvis was reconstructed, and the maximum and minimum cranial angles of the screws were simulated in the three-dimensional view with the placement of 6.5 mm diameter S2 alar iliac screws. Subsequently, the coronal angle, sagittal angle, transverse angle, total length of the screw, length of the screw in the sacrum, width of the iliac, and distance of the entry point from the skin were measured in 3-Matic software at the maximum and minimum head tilt angles, respectively. The differences among the screw parameters of S2 alar iliac screws in children of different ages and the differences between gender and side were compared and analyzed. In all 83 children, 6.5 mm diameter S2 iliac screws could be placed. There was no significant difference between the side of each screw placement parameter. The 5 to 7 years old children had a significantly smaller screw coronal angle than other age groups, but in the screw sagittal angle, the difference was more mixed. The 5 to 7 years old children could obtain a larger angle at the maximum head tilt angle of the screw, but at the minimum cranial angle, the larger angle was obtained in the age group of 11 to 13 years old. There were no significant differences among the age groups. The coronal angle and sagittal angle under maximum cephalic angle and minimum cranial angle of 5 to 7 years old male were (40.91±2.91)° and (51.85±3.75)° respectively, which were significantly greater than in female. The coronal angle under minimum cranial angle was significantly greater in girls aged 8-10 years old than in boys. For the remaining screw placement angle parameters, there were no significant differences between gender. The differences in the minimum iliac width, the screw length, and the length of the sacral screws showed an increasing trend with age in all age groups. The distance from the screw entry point to the skin in boys were significantly smaller than that of girls. The minimum width of the iliac in boys at 14 to 16 years of age were significantly wider than that in girls at the same stage. In contrast, in girls aged 5 to 7 years and 11 to 13 years, the screw length was significantly longer than that of boys at the same stage. The pelvis of children aged 5 to 16 years can safely accommodate the placement of 6.5 mm diameter S2 alar iliac screws, but the bony structures of the pelvis are developing and growing in children, precise assessment is needed to plan a reasonable screw trajectory and select the appropriate screw length.

Influences of Sediment Particles on Air Vessel Water Hammer Protection Effect in the Long-Distance Water Supply Systems

Abstract Long-distance water supply systems are important measures to improve the water resources distribution, and the water hammer protection devices such as air vessels are usually added in the project to ensure the safety and stable operation. However, the sediment particles are always ignored in the design. Hence, a numerical model and program were established for sediment laden water hammer based on the method of characteristics (MOC). Using the proposed model, the water hammer protection influences of sediment particles parameters are simulated for the same pipeline system of a water supply project. The result shows that the resistance loss of sediment-laden water in pipelines is larger than that of water, and the initial head of pump needed to be increased to ensure the water levels of downstream reservoirs are consistent. After power failure and pump stopping, the negative pressure wave of sediment-laden water is 2.97 m higher than that of water, and the theoretical minimum internal pressure along pipelines is 7.8 m lower. With the same air vessel protection, the lowest minimum internal pressure heads along pipelines decrease with the increase of quantities of sediment, while the results show no obvious influence by changes of median particle diameters. The lowest absolute pressure of pipeline could reach −0.69 m under the condition of 50 kg/m3 quantity of sediment and 0.05 mm median particle diameter. The relevant research results are of great significance sediment-laden water hammer numerical simulation and water hammer protection design.

Assessing the energy recovery potential at district metered areas inlets of water supply systems: A Spanish case study

The energy required for various processes in the water cycle can have significant economic and environmental impacts. Therefore, efficient energy management in urban water supply systems is crucial for a sustainable operation. By installing energy recovery technologies in these facilities, it is possible to reap the benefits of the infrastructure design by saving energy. In this study, a new methodology to assess the energy recovery at the inlets of district metered areas is presented, considering the city of Murcia (Spain) as case study. This methodology is based on creating a detailed model of city water supply system and calibrating such model with an experimental campaign of measurements. Then, the assessment of the hydraulic potential recovery is analysed through two different energy estimators, one considering the minimum available net head and the other assuming a variable net head. Results show that there are several points where turbines could be installed, most of them recovering in between 1000–5000 kWh, which could be used to cover the yearly energy consumption of about 24–120 m2 of a school or 10–50 traffic lights of such area. Moreover, in some points it could be recovered up to 14500 kWh. Even though these values are not high, the energy recovered could be used for self-consumption of nearby electrical loads, at the time that reduces the pressure in the system, thus leading to leak reductions. Moreover, this kind of energy recovery does not reduce the potential of other proposals for upstream energy recovery, such as replacing pressure reduction valves with turbines instead. The scripts developed to apply the proposed methodology are available in EPANET-Octave file exchange for the researcher community.

Micro hydro power generation in water distribution networks through the optimal pumps-as-turbines sizing and control

Sustainable use of water and energy sources is a crucial challenge for smart and resilient urban water infrastructure. At this aim, this study presents a methodology for implementing and selecting pumps-as-turbines (PaTs) in water distribution networks (WDNs) to minimise leakage losses and maximise energy recovery. A novel dynamic control algorithm for PaTs is proposed, which optimises the pressure dissipation while granting a minimum pressure head in the network. The digital hydraulic model of a WDN, which incorporates the developed control strategy, outputs the available pressure heads and flow rates of each PaT for an extended period simulation. The entire simulated data series are fed into a new algorithm to select the best machine to be installed to achieve a reliable solution under realistic and varying conditions. Finally, this methodology is applied to a real test case, improving the sustainability and energy efficiency of a mountainous WDN by enhancing the water-energy nexus.

Tidal barrage operation optimization using moment-based control


 As decarbonization of energy systems becomes an imperative and the deployment of intermittent renewables increases, the operation of electrical grids becomes challenging. In this sense, tidal barrage schemes can supply clean and predictable energy with more flexibility than the more traditional wind and solar plants. However, the high infrastructure costs associated with tidal barrage plants hinders its deployment. An optimal operation is key to maximize energy output and assure the project’s feasibility.
 Recently, Ringwood and Faedo [3] introduced a novel approach to tidal barrage control by applying wave energy control techniques, with promising results. The model consists on a two-way tidal barrage scheme, where an analogy is made between latching/declutching algorithms applied in WEC control and holding/sluicing from tidal barrage. The optimization was done using the moment-based framework developed in [1] and [2], which can formulate linear and non-linear problems in a concave quadratic environment, thus allowing the application of efficient numerical solution algorithms. This preliminary study has a number of simplifying assumptions, leaving a pathway to further examine the optimal control problem.
 This paper extends the results of the analysis from [3] by adding complexities to the model. Crucially, the basin is modeled such as the area is a polynomial function of the water level, instead of assuming constant surface area. This will affect the operational head of the optimal solution, as the volume of water at the top of the basin will be higher than at the bottom. Another added constraint will be the minimum head that the turbine requires to generate electricity. Furthermore, a cost function is introduced to penalize the energy consumption of the sluice gates, as shown in figures 1.a) and 1.b). This not only increases the accuracy of the model, but in many cases improves the convergence of the algorithm by adding a quadratic term. Figure 2 shows the value of the overall energy yield (as a fraction of the energy output without penalty) and simulation run time (as a fraction of the run time without penalty) with different penalty coefficients.
 1.a) Sluice gate area without considering cost function
 1.b) Sluice gate area with penalty factor of 3
 
 
 2. Energy and run time variations with penalty
 
 

Efficacy of eco-friendly insecticides against yellow stem borer under spring rice crop ecosystem of Saptari district, Nepal

The study aimed to assess the effectiveness of eco-friendly insecticides in controlling yellow stem borer in spring rice crops of Hardinath-1 variety in Saptari district, Nepal. For this experiment, a Randomized Block Design was used with seven different treatments and an untreated control group. The treatments tested included Bacillus thuringiensis var kurtaski, Beauveria bassiana, Azadiractin 2.00%, garlic extract, tobacco extract, larvosin, and an untreated plot. The plots used were 3 × 4 meters in size and the plants were spaced 20 centimeters apart in both rows and between plants. The crop was sprayed twice, once during the vegetative stage and once during the reproductive stage, when the pest population reached a certain level. The incidence of dead heart was observed on ten randomly selected hills from each plot before and after the insecticide application, and observations on yellow stem borer incidence were recorded. Results showed that B. thuringiensis var kurtaski had the lowest dead heart infestation (0.4889%) and the minimum white head infestation (0.367%), as well as the highest mean yield (5.755mt/ha). Neembicide and B. bassiana also showed promising results.

Computational Analysis of Bifurcation of Raghuganga Hydropower Project

Computational analysis is the modern design optimization tool used widely for determining the effect of different loading parameters where operating conditions and geometry are complex for manual solutions to execute. This study has great significance in the design and optimization of penstock branches as the ancient technology used for the design has least chance of having minimum head loss and good structural strength at the same time. Bifurcation of Raghuganga Hydropower Project of 40 MW installed capacity is chosen for this study in which, head loss, velocity and pressure distribution and stress distribution around the branching regions have been observed by varying the angle of cone of bifurcation. Upon varying the cone angles gradually starting from 3 degrees up to 15 degrees, the values of head loss have been reduced from 0.972 m to 0.086 m till 13-degree angle of cone and upon further increasing the angle to 15 degrees, the head loss increased sharply to 2.201 m. Also, for the structural analysis on the optimized cone angle profile, pipe thickness was varied from 25 mm till the values of stress was in the acceptable range. Upon simulations, it was found that optimum pipe thickness is 40 mm and sickle reinforcement of 75 mm with the value of maximum stress (Von-Mises) at the branching to be 167 MPa and minimum factor of safety of 1.49 for the material chosen i.e. E 250 corresponding to I S 2062.

Lightweight aerial image object detection algorithm based on improved YOLOv5s

YOLOv5 is one of the most popular object detection algorithms, which is divided into multiple series according to the control of network depth and width. To realize the deployment of mobile devices or embedded devices, the paper proposes a lightweight aerial image object detection algorithm (LAI-YOLOv5s) based on the improvement of YOLOv5s with a relatively small amount of calculation and parameter and relatively fast reasoning speed. Firstly, to better detect small objects, the paper replaces the minimum detection head with the maximum detection head and proposes a new feature fusion method, DFM-CPFN(Deep Feature Map Cross Path Fusion Network), to enrich the semantic information of deep features. Secondly, the paper designs a new module based on VoVNet to improve the feature extraction ability of the backbone network. Finally, based on the idea of ShuffleNetV2, the paper makes the network more lightweight without affecting detection accuracy. Based on the VisDrone2019 dataset, the detection accuracy of LAI-YOLOv5s on the mAP@0.5 index is 8.3% higher than that of the original algorithm. Compared with other series of YOLOv5 and YOLOv3 algorithms, LAI-YOLOv5s has the advantages of low computational cost and high detection accuracy.

Air vessel sizing approach for pipeline protection using artificial neural networks

Water hammer is the unsteady flow in conduits due to sudden change of velocities in pipelines and poses it to danger. Sensitivity analysis is performed to show the effect of pump and pipeline parameters on the maximum and minimum head just downstream the pump after pump power failure. A new approach to find the required gas volume in a hydropneumatic tank (air vessel) to protect the pipeline using artificial neural networks (ANNs) is introduced. About 760 runs were generated using Bentley Hammer v8i. For each run, the maximum and minimum head just downstream the pump were calculated for a pump power failure. Two MATLAB codes are written to use networks for finding the best design that guarantees the pressure in the pipeline is within the allowable range. The results showed that pump inertia and wave celerity have a very small effect on the maximum and minimum heads.

FINITE ELEMENT METHOD OF SEEPAGE AND STABILITY ANALYSIS OF SAURA-KEFFI EARTH DAM

Finite element method (FEM) based analysis using the SEEP/W and SLOPE/W sub-programme options of a GEOSTUDIO software was used to analyze Saura-Keffi earth dam in Nasarawa State, Nigeria with the view to analyze the dam seepage and its stability. The created dam geometry was assigned material properties and boundary conditions at reservoir water levels of: minimum (3 m), normal (6 m) and maximum (7 m). The analysis was conducted under the cases that the dam was without and with seepage measures (SCM). The results of the analyzed semi-permeable homogenous dam revealed a percentage reduction inseepage flux to 28.3% when the dam was considered with a central core and complete cut-off trench along the dam crest axis. see figure 7. The pore-water (PWP) revealed a decrease in value from (12 to 11.2) kPa at minimum water head with SCM. The PWP further increased by 18.9% as water rises from 6 m to 7m with SCM. The exit gradient showed an insignificant increase in value of 1.2% with the construction of SCM which indicates less flow at the exit end of the dam leading to increase in stability. The horizontal filter drain at the downstream lower and kept the phreatic line within the dam body to allow for adequate embankment and foundation drainage as shown in figure (5&6). The F.S at the maximum water level revealed an increase in value from 1.27 to 1.52 when a horizontal filter was considered. The Morgenstern-priced method of slope stability was used to estimate an acceptable minimum F.S of 1.52 at 0.5 lambda value with the introduction of horizontal filter.

Morphometric study of the radius bone in a KwaZulu-Natal population: Laterality and sexual dimorphism

Radius is sexually dimorphic bone, a relevant feature in biological profiling necessary in forensic investigations. This study aimed to record the radius morphometry and compare the radius morphometric parameters in terms of sex and laterality. Ninety-six dry-human radii bones were collected, and a total of nine morphometric measurements were recorded viz: Maximum radial length (MRL), Distal Breath (DB), Sagittal Diameter at Mid-shaft (SDM), Transverse Diameter at Mid-shaft, Vertical Head Height (HH), Minimum Head Diameter (MinHD), Maximum Head Diameter (MaxHD), Radial Head (CRH), Circumference at Radial Tuberosity (CRT). Circumference at the mean and maximum values in males was consistently higher than the female values for all parameters measured except the values in SDM and TD, where the minimum values of females + were greater on the right-hand side. For laterality, only DB (p 0.001) for both males and females, SDM for both males (p 0.013) and females (p 0.012), HH for males (p 0.042), and CRT for males (p 0.025) were statistically different. Sex and laterality remained unchanged when age was introduced as a confounding factor. This effectively means that age has no bearing on the sexual dimorphism as well as laterality of this sample. The right side consistently had greater values than the left except for HH and CRT for males without age, as well as CRT for males with age. The study concluded that the radius bone of people of the KwaZulu-Natal region is sexually dimorphic and can be used for sex determination.

Femoral morphology in Ortolani's anatomical collection of developmental dysplasia of the hip: Anteversion is unrelated to severity of infantile dysplasia.

This study evaluated and quantified femoral anteversion and femoral head sphericity in healthy and dysplastic hips of post-mortem infant specimens from Ortolani's collection. Healthy hips and hips with cases of dysplasia, with a large variety of severity, were preserved. Morphological measurements were taken on 14 specimens (28 hips), with a mean age of 4.68 months. The degree of dysplasia was classified as mild (A) to severe (D); 11 hips were Grade A, 6 hips were Grade B, 7 hips were Grade C, and 4 hips were Grade D. The femoral anteversion angle, the minimum femoral head diameter, and the maximum femoral head diameter were measured. The minimum and maximum femoral head diameters were used to estimate femoral head sphericity. The mean femoral anteversion angle was 30.81 degrees ± 11.07 degrees in cases and 29.69 degrees ± 12.69 degrees in controls. There were no significant differences between the normal-to-mild group and moderate-to-severe group when comparing the femoral anteversion angle (p = 0.836). The mean estimated sphericity was 1.08 mm ± 0.50 mm in cases and 0.81 mm ± 0.65 mm in controls, with no statistically significant difference between the groups (p = 0.269). Ortolani's collection showed no significant differences between healthy and dysplastic hips in specimens under 1 year of age. While the femoral head appeared slightly more flattened in dysplastic hips, it was not statistically significant. The findings in the unique collection add to the knowledge of the pathoanatomy of infantile hip dysplasia. Femoral anteversion may not play a role in the etiology and pathogenesis of DDH.

Virtual Big Heads in Extended Reality: Estimation of Ideal Head Scales and Perceptual Thresholds for Comfort and Facial Cues

Extended reality (XR) technologies, such as virtual reality (VR) and augmented reality (AR), provide users, their avatars, and embodied agents a shared platform to collaborate in a spatial context. Although traditional face-to-face communication is limited by users’ proximity, meaning that another human’s non-verbal embodied cues become more difficult to perceive the farther one is away from that person, researchers and practitioners have started to look into ways to accentuate or amplify such embodied cues and signals to counteract the effects of distance with XR technologies. In this article, we describe and evaluate the Big Head technique, in which a human’s head in VR/AR is scaled up relative to their distance from the observer as a mechanism for enhancing the visibility of non-verbal facial cues, such as facial expressions or eye gaze. To better understand and explore this technique, we present two complimentary human-subject experiments in this article. In our first experiment, we conducted a VR study with a head-mounted display to understand the impact of increased or decreased head scales on participants’ ability to perceive facial expressions as well as their sense of comfort and feeling of “uncannniness” over distances of up to 10 m. We explored two different scaling methods and compared perceptual thresholds and user preferences. Our second experiment was performed in an outdoor AR environment with an optical see-through head-mounted display. Participants were asked to estimate facial expressions and eye gaze, and identify a virtual human over large distances of 30, 60, and 90 m. In both experiments, our results show significant differences in minimum, maximum, and ideal head scales for different distances and tasks related to perceiving faces, facial expressions, and eye gaze, and we also found that participants were more comfortable with slightly bigger heads at larger distances. We discuss our findings with respect to the technologies used, and we discuss implications and guidelines for practical applications that aim to leverage XR-enhanced facial cues.