A volumetric display for visual, tactile and audio presentation using acoustic trapping.

Science-fiction movies portray volumetric systems that provide not only visual but also tactile and audible three-dimensional (3D) content. Displays based on swept-volume surfaces1,2, holography3, optophoretics4, plasmonics5 or lenticular lenslets6 can create 3D visual content without the need for glasses or additional instrumentation. However, they are slow, have limited persistence-of-vision capabilities and, most importantly, rely on operating principles that cannot produce tactile and auditive content as well. Here we present the multimodal acoustic trap display (MATD): a levitating volumetric display that can simultaneously deliver visual, auditory and tactile content, using acoustophoresis as the single operating principle. Our system traps a particle acoustically and illuminates it with red, green and blue light to control its colour as it quickly scans the display volume. Using time multiplexing with a secondary trap, amplitude modulation and phase minimization, the MATD delivers simultaneous auditive and tactile content. The system demonstrates particle speeds of up to 8.75 metres per second and 3.75 metres per second in the vertical and horizontal directions, respectively, offering particle manipulation capabilities superior to those of other optical or acoustic approaches demonstrated until now. In addition, our technique offers opportunities for non-contact, high-speed manipulation of matter, with applications in computational fabrication7 and biomedicine8.

Sustainable Fabrication of Luminescent Zinc Oxide Nanoparticles From Cucumis melo Fruit Peel Extract as Prospective Photocatalytic and Antigermicidal Agent.

The focus of current advances in nanotechnology has shifted significantly towards environmentally conscious methods that use harmless ingredients and moderated reaction circumstances to promote equitable development. Zinc oxide nanoparticles (NPs) currently grabbed attention of multiple medical fields owing to their unique ability to safeguard against cellular damage and alleviate serious human diseases via processes related to metabolism. This work focused on the generation of ZnO NPs using the peel of Cucumis melo fruit. The NPs were then analyzed and characterized using UV-Vis spectroscopy. The results indicated that at a wavelength of 352 nm, it was proven that the biosynthesis of ZnO NPs had occurred. The XRD pattern indicated the presence of dense crystal structures. The field emission scanning electron microscope (FE-SEM) picture confirmed the existence of polygonal-shaped ZnO NPs. The findings indicate that the produced ZnO NPs possess tough antibacterial properties against Gram-positive and Gram-negative microorganisms. When the ZnO NPs were exposed to direct sunshine for 80 min, they showed an 89% dye breakdown efficiency. This research specifically focused on the decomposition of reactivity dyes, with methylene blue dye being used as the target dye. The work demonstrates that the biosynthesis of ZnO NPs has a crucial and versatile role in the biological and environmental sectors.

Electrically Induced Liquid Metal Droplet Bouncing.

Liquid metals, including eutectic gallium-indium (EGaIn), have been explored for various planar droplet operations, including droplet splitting and merging, promoting their use in emerging areas such as flexible electronics and soft robotics. However, three-dimensional (3D) droplet operations, including droplet bouncing, have mostly been limited to nonmetallic liquids or aqueous solutions. This is the first study of liquid metal droplet bouncing using continuous AC electrowetting through an analytical model, computational fluid dynamics simulation, and empirical validation to the best of our knowledge. We achieved liquid metal droplet bouncing with a height greater than 5 mm with an actuation voltage of less than 10 V and a frequency of less than 5 Hz. We compared the bouncing trajectories of the liquid metal droplet for different actuation parameters. We found that the jumping height of the droplet increases as the frequency of the applied AC voltage decreases and its amplitude increases until the onset of instability. Furthermore, we model the attenuation dynamics of consecutive bouncing cycles of the underdamped droplet bouncing system. This study embarks on controlling liquid metal droplet bouncing electrically, thereby opening a plethora of new opportunities utilizing 3D liquid metal droplet operations for numerous applications such as energy harvesting, heat transfer, and radio frequency (RF) switching.

First results on transient plasma-based remediation of nanoscale particulate matter in restaurant smoke emissions.

Recent studies have shown that nanoscale particulate matter produced in commercial charbroiling processes represents a serious health hazard and has been linked to various forms of cancer and cardiopulmonary disease. In this study, we propose a highly effective method for treating restaurant smoke emissions using a transient pulsed plasma reactor produced by nanosecond high voltage pulses. We measure the size and relative mass distributions of particulate matter (PM) produced in commercial charbroiling processes (e.g., cooking of hamburger meat) both with and without the plasma treatment. Here, the plasma discharge is produced in a 3" diameter cylindrical reactor with a 5-10 ns high voltage (17 kV) pulse generator. The distribution of untreated nanoparticle sizes is peaked around 125-150 nm in diameter, as measured using a scanning mobility particle sizer (SMPS) spectrometer. With plasma treatment, we observe up to a 55-fold reduction in relative particle mass and a significant reduction in the nanoparticle size distribution using this method. The effectiveness of the nanoscale PM remediation increases with both the pulse repetition rate and pulse voltage, demonstrating the scalability of this approach for treating particulate matter at higher flow rates and larger diameter reactors.

Correction: Predicting Mental Imagery-Based BCI Performance from Personality, Cognitive Profile and Neurophysiological Patterns.

[This corrects the article DOI: 10.1371/journal.pone.0143962.].

Transmissive Labyrinthine Acoustic Metamaterial-Based Holography for Extraordinary Energy Harvesting.

Conventional energy sources are continuously depleting, and the world is actively seeking new green and efficient energy solutions. Enormous amounts of acoustic energy are dissipated daily, but the low intensity and limited efficiency of current harvesting techniques are preventing its adoption as a ubiquitous method of power generation. Herein, a strategic solution to increase acoustic energy harvesting efficiency using a specially designed metamaterial is implemented. A scalable transmissive labyrinthine acoustic metamaterial (LAM) is designed, developed, and employed to maximize ultrasound (40 kHz) capture over its large surface area (>27 k mm2), which is focused onto a piezoelectric film (78.6 mm2), thus magnifying incident sound pressure by 13.6 times. Three different piezoelectric films - two commercial and one lab-made nanocomposite film are tested with LAM in the acoustic energy harvesting system. An extraordinary voltage gain of 157-173% and a maximum power gain of 272% using the LAM compared to the case without the LAM are achieved. Multipoint focusing using holographic techniques, showcasing acoustic patterning to allow on-demand simultaneous harvesting in separate locations, is demonstrated. Our versatile approach for high-intensity acoustic energy harvesting opens future opportunities to exploit sound energy as a resource to contribute toward global sustainability.

Investigation of independent reinforcement learning algorithms in multi-agent environments.

Independent reinforcement learning algorithms have no theoretical guarantees for finding the best policy in multi-agent settings. However, in practice, prior works have reported good performance with independent algorithms in some domains and bad performance in others. Moreover, a comprehensive study of the strengths and weaknesses of independent algorithms is lacking in the literature. In this paper, we carry out an empirical comparison of the performance of independent algorithms on seven PettingZoo environments that span the three main categories of multi-agent environments, i.e., cooperative, competitive, and mixed. For the cooperative setting, we show that independent algorithms can perform on par with multi-agent algorithms in fully-observable environments, while adding recurrence improves the learning of independent algorithms in partially-observable environments. In the competitive setting, independent algorithms can perform on par or better than multi-agent algorithms, even in more challenging environments. We also show that agents trained via independent algorithms learn to perform well individually, but fail to learn to cooperate with allies and compete with enemies in mixed environments.

High-speed acoustic holography with arbitrary scattering objects.

Recent advances in high-speed acoustic holography have enabled levitation-based volumetric displays with tactile and audio sensations. However, current approaches do not compute sound scattering of objects' surfaces; thus, any physical object inside can distort the sound field. Here, we present a fast computational technique that allows high-speed multipoint levitation even with arbitrary sound-scattering surfaces and demonstrate a volumetric display that works in the presence of any physical object. Our technique has a two-step scattering model and a simplified levitation solver, which together can achieve more than 10,000 updates per second to create volumetric images above and below static sound-scattering objects. The model estimates transducer contributions in real time by reformulating the boundary element method for acoustic holography, and the solver creates multiple levitation traps. We explain how our technique achieves its speed with minimum loss in the trap quality and illustrate how it brings digital and physical content together by demonstrating mixed-reality interactive applications.

The sense of agency in emerging technologies for human-computer integration: A review.

Human-computer integration is an emerging area in which the boundary between humans and technology is blurred as users and computers work collaboratively and share agency to execute tasks. The sense of agency (SoA) is an experience that arises by a combination of a voluntary motor action and sensory evidence whether the corresponding body movements have somehow influenced the course of external events. The SoA is not only a key part of our experiences in daily life but also in our interaction with technology as it gives us the feeling of "I did that" as opposed to "the system did that," thus supporting a feeling of being in control. This feeling becomes critical with human-computer integration, wherein emerging technology directly influences people's body, their actions, and the resulting outcomes. In this review, we analyse and classify current integration technologies based on what we currently know about agency in the literature, and propose a distinction between body augmentation, action augmentation, and outcome augmentation. For each category, we describe agency considerations and markers of differentiation that illustrate a relationship between assistance level (low, high), agency delegation (human, technology), and integration type (fusion, symbiosis). We conclude with a reflection on the opportunities and challenges of integrating humans with computers, and finalise with an expanded definition of human-computer integration including agency aspects which we consider to be particularly relevant. The aim this review is to provide researchers and practitioners with guidelines to situate their work within the integration research agenda and consider the implications of any technologies on SoA, and thus overall user experience when designing future technology.

Unified Representation of Twitter and Online News Using Graph and Entities.

To improve consumer engagement and satisfaction, online news services employ strategies for personalizing and recommending articles to their users based on their interests. In addition to news agencies' own digital platforms, they also leverage social media to reach out to a broad user base. These engagement efforts are often disconnected with each other, but present a compelling opportunity to incorporate engagement data from social media to inform their digital news platform and vice-versa, leading to a more personalized experience for users. While this idea seems intuitive, there are several challenges due to the disparate nature of the two sources. In this paper, we propose a model to build a generalized graph of news articles and tweets that can be used for different downstream tasks such as identifying sentiment, trending topics, and misinformation, as well as sharing relevant articles on social media in a timely fashion. We evaluate our framework on a downstream task of identifying related pairs of news articles and tweets with promising results. The content unification problem addressed by our model is not unique to the domain of news, and thus can be applicable to other problems linking different content platforms.

Metamaterial bricks and quantization of meta-surfaces.

Controlling acoustic fields is crucial in diverse applications such as loudspeaker design, ultrasound imaging and therapy or acoustic particle manipulation. The current approaches use fixed lenses or expensive phased arrays. Here, using a process of analogue-to-digital conversion and wavelet decomposition, we develop the notion of quantal meta-surfaces. The quanta here are small, pre-manufactured three-dimensional units-which we call metamaterial bricks-each encoding a specific phase delay. These bricks can be assembled into meta-surfaces to generate any diffraction-limited acoustic field. We apply this methodology to show experimental examples of acoustic focusing, steering and, after stacking single meta-surfaces into layers, the more complex field of an acoustic tractor beam. We demonstrate experimentally single-sided air-borne acoustic levitation using meta-layers at various bit-rates: from a 4-bit uniform to 3-bit non-uniform quantization in phase. This powerful methodology dramatically simplifies the design of acoustic devices and provides a key-step towards realizing spatial sound modulators.

Predicting Mental Imagery-Based BCI Performance from Personality, Cognitive Profile and Neurophysiological Patterns.

Mental-Imagery based Brain-Computer Interfaces (MI-BCIs) allow their users to send commands to a computer using their brain-activity alone (typically measured by ElectroEncephaloGraphy-EEG), which is processed while they perform specific mental tasks. While very promising, MI-BCIs remain barely used outside laboratories because of the difficulty encountered by users to control them. Indeed, although some users obtain good control performances after training, a substantial proportion remains unable to reliably control an MI-BCI. This huge variability in user-performance led the community to look for predictors of MI-BCI control ability. However, these predictors were only explored for motor-imagery based BCIs, and mostly for a single training session per subject. In this study, 18 participants were instructed to learn to control an EEG-based MI-BCI by performing 3 MI-tasks, 2 of which were non-motor tasks, across 6 training sessions, on 6 different days. Relationships between the participants' BCI control performances and their personality, cognitive profile and neurophysiological markers were explored. While no relevant relationships with neurophysiological markers were found, strong correlations between MI-BCI performances and mental-rotation scores (reflecting spatial abilities) were revealed. Also, a predictive model of MI-BCI performance based on psychometric questionnaire scores was proposed. A leave-one-subject-out cross validation process revealed the stability and reliability of this model: it enabled to predict participants' performance with a mean error of less than 3 points. This study determined how users' profiles impact their MI-BCI control ability and thus clears the way for designing novel MI-BCI training protocols, adapted to the profile of each user.

Holographic acoustic elements for manipulation of levitated objects.

Sound can levitate objects of different sizes and materials through air, water and tissue. This allows us to manipulate cells, liquids, compounds or living things without touching or contaminating them. However, acoustic levitation has required the targets to be enclosed with acoustic elements or had limited manoeuvrability. Here we optimize the phases used to drive an ultrasonic phased array and show that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter. Furthermore, we introduce the holographic acoustic elements framework that permits the rapid generation of traps and provides a bridge between optical and acoustical trapping. Acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation. Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically controlled micro-machines that do not interfere with magnetic resonance imaging.

Dexterous ultrasonic levitation of millimeter-sized objects in air.

Acoustic levitation in air has applications in contactless handling and processing. Here a first-order Bessel function-shaped acoustic field, generated using an 8-element circular array operating at 40 kHz, traps millimeter-sized objects against gravity. The device can manipulate objects in a vertical plane over a few millimeters with an accuracy of ± 0.09 mm.