Virtual Wall Research Articles

A position control-based approach to haptic rendering of stiff objects using piece-wise linear model

In traditional force rendering approaches, it is quite popular to model a virtual stiff wall as a spring-damper system to compute the interaction force, which can easily lead to unstable behavior. In this paper, we present an approach to ensure no penetration into the wall by position control. The approach approximates the nonlinear model of a 6-DOF parallel-structure haptic device by a piece-wise linear model to improve the performance compared with a controller designed from a one-point linearized model in haptic rendering. A simulation-based performance comparison study shows that the new controller can render higher stiffness than the previous solution.

The selfie production model: Rethinking selfie taking, editing, and posting practices

With the rise of digital technologies, selfies are a contemporary and popular form of digitally produced self-expression for Saudi women. Informed by Goffman’s (1959) self-presentation theory and Hall’s (1966) proxemics theory, this study explores the process of producing and posting selfies on Instagram and Snapchat platforms, and examines how these practices are shaped by cultural norms and platform affordances. Methodologically, an ethnographic approach was employed to observe selfie practices involving: focus groups, face-to-face interviews, online observation, and photo-elicitation interviews. The sample consisted of 35 Saudi women between 18-57 years old. The results were used to develop a framework for understanding selfie production consisting of six processes: the motivation process, pre-photo process, platform affordances process, audience customization process, assessment of cultural norms process, and the process of reposting selfie. Also, the study identified a number of strategies practiced by Saudi women to present a more desirable self, including: digitally editing the selfie using beautifying filters, arranging the background, retaking the selfie, and adding digital makeup. Cultural norms were found to heavily influence selfie practices, as selfie takers carefully select particular audiences with whom to share the selfie, while blocking others from viewing the selfie using “virtual walls” depending on veiling practices, habitual proximity, and the appropriateness of the content. The model and the identified strategies make an important empirical contribution that provides a new way of thinking about selfie practices outside Euromerica.

Overlimiting convection at a heterogeneous cation-exchange membrane studied by particle image velocimetry

Electroconvection and gravitational convection are recognized as the primary mechanisms driving overlimiting currents in ion-exchange systems. Here, we use particle image velocimetry (PIV) to characterize the convection on a small piece of a commercially available heterogeneous cation-exchange membrane. We perform chronoamperometric measurements under various experimental conditions and simultaneously record the developed convection at the membrane-electrolyte solution interface using tracking particles. The convection is observed independently in horizontal and vertical planes, capturing flow fields pertinent to electroconvection and gravitational convection. PIV analysis computes velocity vector fields we employ to calculate the volumetric flow rate through a virtual semi-cylindrical wall around the membrane. The volumetric flow rate represents a way how to quantify the intensity of electroconvection. The electroconvection recorded on the horizontal plane manifests itself as a local short-range chaotic whirring localized at the membrane surface superimposed by two long-range counter-current vortices. The volumetric flow rate associated with the two counter-current vortices almost linearly increases with voltage and decreases with increasing concentration. The stagnant points of the vortices localize from 100 to 450 μm away from the membrane. The convection observed on the vertical plane occurs as a result of electroconvection and gravitational convection. We show that gravitational convection eventually dominates and produces an upward-directed intensive flow with similar values of characteristic velocities as the electroconvection. The development of the gravitational convections is approximately one order of magnitude slower (on the order of seconds) than that of electroconvection (on the order of hundreds of milliseconds).

Study on shock compression phase transition of single crystal siliconbased on molecular dynamics simulation

Crystalline silicon has a complicated phase transition mechanism, which has received extensive attention in the research field of phase diagram, and the deformation mechanism of silicon crystals under dynamic loading is the current research hotspot. In order to reveal its deformation and phase transition behaviors under intensive dynamic loading, molecular dynamics method was used to simulate the shock compression behavior of single crystal silicon along the crystal directions [001], [110] and [111] at an initial ambient temperature of 300 K, respectively. All simulations were carried out basing on the classical open-source codes LAMMPS and a Tersoff interatomic potential was adopted to describe the material responses of silicon under dynamic compression. Before shock loading, periodic boundary conditions were applied along the three independent directions, and an NPT ensemble was used to equilibrate the systems; then shock compression was applied by using the piston method, where a virtual piston wall impinges the sample such that the particle velocity in the sample is the same as the piston speed after the shock reaches a steady state. The shock particle velocities varied from 0.3 km/s to 3.2 km/s, and a timestep of 0.001 ps was adopted. During the stress wave formation and propagation, the simulation system was in the NVE ensemble with the absence of temperature control. The loading method and effect are similar to typical plane impact experiments. The results show that with the increase of shock particle velocity, the shear stress of single crystal silicon increases gradually and then decreases sharply due to the structural phase change. Both the phase transition threshold and the phase transition mechanism are anisotropic. Among them, a variety of solid-solid phase transitions and solid-liquid phase transitions are observed under shock compression along the [001] crystal direction. The phenomenon of solid-liquid coexistence is highly consistent with the recent international experiments. The research results provides new nano-scale results to support the study of phase transition of crystalline silicon under dynamic loading.

Teachers’ Opinion About Collaborative Virtual Walls and Massive Open Online Course During the COVID-19 Pandemic

During the COVID-19 pandemic, Mexican universities incorporated technological tools to update the activities of the courses under the distance modality. This quantitative research analyzes the teachers' perception about Collaborative Virtual Walls (CVWs) and Massive Open Online Courses (MOOCs) through data science. The participants are 54 professors from the National Autonomous University of Mexico who completed the International Diploma “Innovation in University Teaching 2021”. The results of machine learning indicate that CVWs and MOOCs positively influence the learning and participation of the students. Likewise, the decision tree technique identifies 4 predictive models about these technological tools. This study recommends the incorporation of ICTs in the educational field because teachers can organize and carry out creative activities under the distance modality. Even universities can include in their strategic planning the incorporation of CVWs and MOOCs in the educational process. The limitations of this research are the sample and analysis about the perception of the teachers in a Mexican university. Therefore, future research can analyze CVWs and MOOCs considering the development of skills and satisfaction of the students in the middle schools, high schools and universities. In conclusion, teachers rely on technological advances such as CVWs and MOOCs to create new school activities under the distance modality and improve the teaching-learning conditions during the COVID-19 pandemic.

Compact eighth‐mode ridged substrate integrated waveguide filter

In this letter, a novel eighth-mode ridged substrate integrated waveguide (EMRSIW) is proposed by bisecting the RSIW resonator along the virtual magnetic walls. The EMRSIW shows a size of nearly one-eighth of a conventional RSIW resonator and a significant size reduction compared to the conventional eighth-mode SIW resonator. A prototype of a third-order bandpass filter with transmission zeros has been designed and tested.

Single-Ended Band-Notched Vivaldi Antenna With Common Mode Suppression and Low Cross Polarization

In this letter, a differential-fed band-notched Vivaldi antenna with common-mode (CM) suppression and low cross polarization is proposed. Under CM excitation, the antenna cannot be excited as the CM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field is not supported by the virtual magnetic wall, realizing a high level of CM suppression. Under differential mode excitation, the antenna could radiate effectively with a broadside beam. Moreover, the cross-polarized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field component is reduced due to the symmetric configuration with differential feeding arrangement, which gives rise to lower cross polarization. Meanwhile, the notched band can be obtained by simply turning the microstrip feeding stubs, without extra structure. To achieve a single-ended differential-fed antenna structure, spatial reversal is applied to the feeding arrangement for 180° phase difference, no need of the phase-shift circuit. Finally, the proposed antenna is fabricated and measured. It is demonstrated that the proposed antenna with simple configuration supplies high level of CM suppression, better cross-polarization characteristic below −30dB and a notched band from 3.75 to 4.3 GHz.

Formation of Group Creative Thinking When Working with Virtual Walls

Formation of Group Creative Thinking When Working with Virtual Walls

Virtual walls for dielectric fluid manipulation through controllable charge deposition

Fluid transportation is a basic physical process in various engineering applications, and solid walls are most commonly used to confine fluid flows. Solid walls, however, have some disadvantages, including large pressure drops and plaguing by fouling. Here we experimentally demonstrate a method of controlling dielectric fluid flows on planar surfaces by virtual (not solid) walls through a spatially controlled charge deposition. Acting on the three-phase contact line, an electrically induced pressure has the same function as solid sidewalls. Dielectric fluids can be confined within designated areas, or flow directionally with the aid of contactless masks. Dielectric fluids can also move on planar surfaces by moving contactless masks. Due to the virtual wall effect of this novel method, an open channel can be developed to continuously transport fluids. The method may provide a new perspective to manipulating dielectric liquid flows and can be an alternative way of open fluidic devices.

Ethics and digital collections: a selective overview of evolving complexities

PurposeDigital collections are becoming more commonplace at libraries, archives and museums around the world, creating potential for improved accessibility to information that may otherwise remain hidden and further support for intellectual exploration. As a result of the growing potential for digital collections to inform and influence, the conversation surrounding ethics and digital collections needs to be continually examined and adapted as technologies evolve, user expectations change and digital information plays an increasing role in our everyday lives. In this context, this paper presents an overview of multifaceted ethical realities that impact the how, why and what digital information is created, accessed and preserved.Design/methodology/approachWritten from the perspective of a digital collections librarian, this paper relies on existing research in presenting ethical considerations and complements that research with professional observations in providing subsequent reflections on addressing challenges in the age of digital information.FindingsThere are and should be considerations given to not only what information is contained in a given collection, but also how that information is selected, accessed and consumed by the public. The conclusions offered are designed to provoke reflection on the evolving and interconnected nature of information and ethics in the context of digital collections.Originality/valueInformation ethics is multifaceted, with one of those facets relating directly to digital collections. This paper demonstrates that digital collections are more complex than simply a collection of digitized documents and photographs. As the field of information management continually evolves and adapts, so, too, do the ethical realizations identified in this paper, all of which go beyond the (virtual) walls of a library, archive or museum, and carry the potential to have a long-term impact concerning information and its integrity, equity and access.

Modelling of three-dimensional particle rebound from an anisotropic rough wall

In gas-solid confined flows, particle rebound on a rough wall may have a great influence on the macroscopic properties of both phases. Existing simulation methods use simplified approaches where surface roughness is modelled as two-dimensional or isotropic. To improve the accuracy of such simulations, an anisotropic virtual rough wall statistical approach and the corresponding Lagrangian stochastic particle-wall collision model are proposed. From deterministic simulations of the impact of particles on the anisotropic virtual wall given as correlated bi-Gaussian surface, wall-normal vector angle statistics are used for model development. Rebound angle statistics computed from deterministic simulations and using the proposed stochastic model are in very good agreement. Incident particles in vertical planes not collinear with one of the principal directions of the anisotropic rough surface are bouncing with a mean transverse angle towards the principal direction of lower roughness.

Special Issue: Teaching and Learning Anthropology in the Time of COVID-19

This special issue results from email conversations begun in the summer of 2020 concerning COVID-19’s effects on the teaching and learning of anthropology in higher education. The Society for Applied Anthropology’s Higher Education Thematic Interest Group listserv functioned as a networking tool, bringing together questions, authors, editors, and the journal. The resulting commentaries, project showcases, and research articles published here offer analyses of teaching and learning within the virtual walls of the academy during the pandemic. They reveal much about student and professor experiences with online tools and digital anthropology as well as the preexisting inequalities in higher education uncovered by the pandemic. Collectively, the essays in this issue offer insights and perspectives that can help guide anthropological teaching and learning in the future.&nbsp;

Formation of group creative thinking when working with virtual walls

The problem and the aim of the study. Preparing a graduate capable of individual creative thinking, ready to work in a team, and to manage changes, projects, teams is one of the most important tasks that digital school teachers face. The effectiveness of its solution depends on the experience of collaboration, tools of virtual interaction, the formation of group thinking. The authors propose to use collective virtual walls to form group creative thinking as an important skill corresponding to the conditions of uncertainty of the future. Research methods. To activate cognition, create favorable conditions for creativity and discoveries when working together, methods of group interactive learning are used (demonstration in a remote mode of interaction, online discussion, project presentations, work on a collective virtual wall). The study was carried out on the basis of gymnasium No. 2 in Kirovo-Chepetsk. As a software tool to support online collaboration and co-creative discovery, the Trello service (https://trello.com/) was used. As a method for statistical processing of the experimental data, the Pearson’s χ2 (chi-square) criterion was used. Results. In the experimental group, students used collective virtual walls to obtain theoretical information, complete practical tasks in an interactive online environment, creative search and experience of collective discovery, group reflection and presentation of team projects. The assessment of the levels of formation of group creative thinking was carried out and statistically significant differences in the qualitative changes that occurred in the pedagogical system were revealed, χ2 emp. 2 &gt; χ2crit0.05 (6.89 &gt; 5.99). In conclusion, the authors generalized the conditions under which joint activity over a collective virtual wall contributes to the formation of group creative thinking. The conditions are: awareness of the meaning and motives of joint activity; the need for self-expression and active participation in the discussion; work according to a general plan; analysis of the progress of an individual task and the entire collective project; control and self-control; direct interpersonal communication, virtual communication, etc.

Testing of a full-scale flat slab building for gravity and lateral loads

Full-scale testing of a two-storey flat slab structure is reported, undertaken in the SlabSTRESS research project; the construction and testing were planned and carried out at the ELSA laboratory of the European Commission’s Joint Research Centre. The dimensions are three bays by two, spans 4.5 and 5 m, slab thickness 0.2 m, interstorey height 3.2 m. Two different longitudinal reinforcement details were considered; welded studs shear reinforcement was provided only in the second floor slab. The testing program included seismic tests for service and ultimate actions, using the pseudodynamic technique with virtual walls. To this aim a building structure was designed with primary walls and the flat slab frame as secondary element. Cyclic loading tests followed up to ultimate drift capacity of the structure. The sequence of tests included strengthening of a set of damaged connections using bolted bars in holes drilled through the slab, followed by cyclic testing to failure. The instrumentation was provided for the global response and the connections with local rotations in the columns and slab; cracking around the columns was measured with through-crack sensors; a measurement system for internal forces and moments was included within the columns. The results show the response with deformations and damage for the different loading conditions up to failure. The results obtained on a full-scale structure extend and confirm the knowledge in the literature, mainly based on isolated connections and/or small-scale samples.

Effect of staggered array structure on the flow field of micro gas chromatographic column

A new design of staggered array semi-packed micro gas chromatographic column was presented based on the micro electromechanical system (MEMS) technology. It was a sensor for gas sample analysis. The internal velocity fields of ten types of semi-packed micro gas chromatographic column were studied. The effects of array spacing and dislocation spacing on the flow field distribution were investigated. The results show that on the basis of ensuring the formation of virtual wall, with the increase of array spacing, the maximum velocity difference between the flow channels in the vertical direction decreases gradually, but the velocity difference in the flow channels a and b increases. When the inlet velocity was set to be 0.18 m/s, the maximum velocity difference in the channel of the staggered semi-packed micro gas chromatography column 3 (CSAC3) was 0.05610 m/s. The maximum velocity difference in the channel a was 0.09160 m/s. The maximum velocity difference in the channel b was 0.02401 m/s. CSAC3 had a more uniform velocity field distribution, which can effectively suppress the laminar flow effect during chromatographic separation, and had a smaller pressure distribution, which puts forward lower requirements for carrier gas system. The staggered array semi-packed micro gas chromatography column proposed in this paper can effectively improve the velocity field distribution and pressure distribution in the channel, and provide a theoretical basis for the design of the new micro gas chromatography column structure.

Rapid Fabrication of Superhydrophobic Virtual Walls for Microfluidic Gas Extraction and Sensing.

Based on the virtual walls concept, where fluids are guided by wettability, we demonstrate the application of a gas phase extraction microfluidic chip. Unlike in previous work, the chip is prepared using a simple, rapid, and low-cost fabrication method. Channels were cut into double-sided adhesive tape (280 µm thick) and bonded to hydrophilic glass slides. The tape was selectively made superhydrophobic by ‘dusting’ with hydrophobic silica gel to enhance the wettability contrast at the virtual walls. Finally, the two glass slides were bonded using tape, which acts as a spacer for gas transport from/to the guided liquids. In our example, the virtual walls create a stable liquid–vapor–liquid flow configuration for the extraction of a volatile analyte (ammonia), from one liquid stream to the other through the intermediate vapor phase. The collector stream contained a pH indicator to visualize the mass transport. Quantitative analysis of ammonium hydroxide in the sample stream (<1 mM) was possible using a characteristic onset time, where the first pH change in the collector stream was detected. The effect of gap length, flow rates, and pH of the collector stream on the onset time is demonstrated. Finally, we demonstrate the analysis of ammonium hydroxide in artificial human saliva to show that the virtual walls chip is suitable for extracting volatile analytes from biofluids.

Experiments and Modeling of a Compliant Wall Response to a Turbulent Boundary Layer with Dynamic Roughness Forcing

The response of a compliant surface in a turbulent boundary layer forced by a dynamic roughness is studied using experiments and resolvent analysis. Water tunnel experiments are carried out at a friction Reynolds number of Reτ≈410, with flow and surface measurements taken with 2D particle image velocimetry (PIV) and stereo digital image correlation (DIC). The narrow band dynamic roughness forcing enables analysis of the flow and surface responses coherent with the forcing frequency, and the corresponding Fourier modes are extracted and compared with resolvent modes. The resolvent modes capture the structures of the experimental Fourier modes and the resolvent with eddy viscosity improves the matching. The comparison of smooth and compliant wall resolvent modes predicts a virtual wall feature in the wall normal velocity of the compliant wall case. The virtual wall is revealed in experimental data using a conditional average informed by the resolvent prediction. Finally, the change to the resolvent modes due to the influence of wall compliance is studied by modeling the compliant wall boundary condition as a deterministic forcing to the smooth wall resolvent framework.

Extracting boundary conditions for sound propagation calculations using augmented reality

The number of air-to-water heat pumps has increased over the last years, resulting in a rising number of installed outdoor units. These objects constantly emit noise into the environment during the heat pumps’ runtime. To avoid conflicts with neighbors or even a relocation of the already placed heat pump, an app is developed to estimate the emitted sound of the virtual heat pump on site. This publication presents adapted sound calculation methods suitable for outdoor use and on mobile devices. Based on this, boundary conditions are specified that must be met by the sound data of the respective sound source and the objects recorded on site using augmented reality in real time. Both the determination of the sound data and the identification of objects using AR are explained in detail. Furthermore, different virtual objects that alter the sound propagation can be placed in the real environment and configured with sound-relevant properties. This allows the estimation of the usefulness of sound-reducing measures already before realization. An example of the identification of individual objects, the placement of virtual walls and heat pumps, and the final visualization of the sound propagation in different ways on the mobile device is presented.

Learning Optimal Impedance Control During Complex 3D Arm Movements

Humans use their limbs to perform various movements to interact with an external environment. Thanks to limb's variable and adaptive stiffness, humans can adapt their movements to the external unstable dynamics. The underlying adaptive mechanism has been investigated, employing a simple planar device perturbed by external 2D force patterns. In this work, we will employ a more advanced, compliant robot arm to extend previous work to a more realistic 3D-setting. We study the adaptive mechanism and use machine learning to capture the human adaptation behavior. In order to model human's stiffness adaptive skill, we give human subjects the task to reach for a target by moving a handle assembled on the end-effector of a compliant robotic arm. The arm is force controlled and the human is required to navigate the handle inside a non-visible, virtual maze and explore it only through robot force feedback when contacting maze virtual walls. By sampling the hand's position and force data, a computational model based on a combination of model predictive control and nonlinear regression is used to predict participants' successful trials. Our study shows that participants selectively increased the stiffness within the axis direction of uncertainty to compensate for instability caused by a divergent external force field. The learned controller was able to successfully mimic this behavior. When it is deployed on the robot for the navigation task, the robot arm successfully adapt to the unstable dynamics in the virtual maze, in a similar manner as observed in the participants’ adaptation skill.

The AudioMaze: An EEG and motion capture study of human spatial navigation in sparse augmented reality.

Spatial navigation is one of the fundamental cognitive functions central to survival in most animals. Studies in humans investigating the neural foundations of spatial navigation traditionally use stationary, desk-top protocols revealing the hippocampus, parahippocampal place area (PPA), and retrosplenial complex to be involved in navigation. However, brain dynamics, while freely navigating the real world remain poorly understood. To address this issue, we developed a novel paradigm, the AudioMaze, in which participants freely explore a room-sized virtual maze, while EEG is recorded synchronized to motion capture. Participants (n=16) were blindfolded and explored different mazes, each in three successive trials, using their right hand as a probe to "feel" for virtual maze walls. When their hand "neared" a virtual wall, they received directional noise feedback. Evidence for spatial learning include shortening of time spent and an increase of movement velocity as the same maze was repeatedly explored. Theta-band EEG power in or near the right lingual gyrus, the posterior portion of the PPA, decreased across trials, potentially reflecting the spatial learning. Effective connectivity analysis revealed directed information flow from the lingual gyrus to the midcingulate cortex, which may indicate an updating process that integrates spatial information with future action. To conclude, we found behavioral evidence of navigational learning in a sparse-AR environment, and a neural correlate of navigational learning was found near the lingual gyrus.