Triggered Waves Research Articles

High‐performance triboelectric nanogenerator based on a double‐spiral zigzag‐origami structure for continuous sensing and signal transmission in marine environment

AbstractWith the rapid evolution of emerging technologies like artificial intelligence, Internet of Things, big data, robotics, and novel materials, the landscape of global ocean science and technology is undergoing significant transformation. Ocean wave energy stands out as one of the most promising clean and renewable energy sources. Triboelectric nanogenerators (TENGs) represent a cutting‐edge technology for harnessing such random and ultra‐low frequency energy toward blue energy. A high‐performance TENG incorporating a double‐spiral zigzag‐origami structure is engineered to achieve continuous sensing and signal transmission in marine environment. Integrating the double‐spiral origami into the TENG system enables efficient energy harvesting from the ocean waves by converting low‐frequency wave vibrations into high‐frequency motions. Under the water wave triggering of 0.8 Hz, the TENG generates a maximum peak power density of 55.4 W m−3, and a TENG array with six units can generate an output current of 375.2 μA (density of 468.8 mA m−3). This power‐managed TENG array effectively powers a wireless water quality detector and transmits signals without an external power supply. The findings contribute to the development of sustainable and renewable energy technologies for oceanic applications and open new pathways for designing advanced materials and structures in the field of energy harvesting.

Animation tsunami modelling in 3D to determine shelter and evacuation routes

ABSTRACT Indonesia is located on the Pacific Ring of Fire, making the country prone to earthquakes and tsunamis. Indonesia, especially the southern region of Java, has the potential to be hit by a megathrust earthquake triggering waves much higher than before. Determining evacuation routes and locations as a part of disaster management is essential to avoid many fatalities. This research aims to determine evacuation routes and shelters using photogrammetry-based 3D animation. This paper applied experimental research for modelling and simulation approach with the stages of generating a 3D orthomosaic map, predicting tsunami magnitude, determining the height and distribution of waves, modelling and simulating 3D animation as well as marking evacuation routes and shelter locations. 3D orthomosaics are created based on aerial photos (UAV) drones. Future tsunami data are used to estimate the extent and depth of inundation that may occur. This research uses the Teluk Penyu area in Cilacap, Indonesia, as a study site. The tsunami disaster caused by an earthquake magnitude 7.8 centred in the south of West Java hit this city in 2006. This research produces a 3D animation model that can visualise the extent and depth of tsunami inundation to determine evacuation routes and shelter buildings.

Nonlinear Charge Transport and Excitable Phenomena in Semiconductor Superlattices.

Semiconductor superlattices are periodic nanostructures consisting of epitaxially grown quantum wells and barriers. For thick barriers, the quantum wells are weakly coupled and the main transport mechanism is a sequential resonant tunneling of electrons between wells. We review quantum transport in these materials, and the rate equations for electron densities, currents, and the self-consistent electric potential or field. Depending on superlattice configuration, doping density, temperature, voltage bias, and other parameters, superlattices behave as excitable systems, and can respond to abrupt dc bias changes by large transients involving charge density waves before arriving at a stable stationary state. For other parameters, the superlattices may have self-sustained oscillations of the current through them. These oscillations are due to repeated triggering and recycling of charge density waves, and can be periodic in time, quasiperiodic, and chaotic. Modifying the superlattice configuration, it is possible to attain robust chaos due to wave dynamics. External noise of appropriate strength can generate time-periodic current oscillations when the superlattice is in a stable stationary state without noise, which is called the coherence resonance. In turn, these oscillations can resonate with a periodic signal in the presence of sufficient noise, thereby displaying a stochastic resonance. These properties can be exploited to design and build many devices. Here, we describe detectors of weak signals by using coherence and stochastic resonance and fast generators of true random sequences useful for safe communications and storage.

Large-Scale Laboratory Experiments On The Wave Generation Due To The Collapse Of Partially And Fully Submerged Granular Columns

Landslides that occur in coastal environments can drive cascading consequences such as wave forces, flooding, and infrastructure damage to coastal communities. It can be difficult to classify these slides as subaerial or submarine, and the mechanics of wave generation associated with partially submerged failures are not well understood. Limited physical modelling has been conducted that encompasses both the triggering of granular landslides and subsequent waves associated with partially and fully submerged mass movements. To date, laboratory work investigating tsunamis generated by submarine landslides has focused on the wave formed in the direction of the mass movement (seaward direction) for rigid block experiments (eg. Rzadkiewicz, 1997) and deformable slide masses (e.g. Grilli et al., 2017, Takabatake, 2020, Bullard et al., 2023). From these experimental data sets, predictive relationships connecting slide acceleration, mass, and initial submergence depth to the amplitude of the wave formed have been presented for the seaward wave. Such relationships have not been presented for the landward directed wave, which propagates in the opposite direction of the submarine landslide motion. Further, not all landslides are easily classified as either subaerial or submarine. Consider the 2018 Anak Krakatoa landslide in which the sliding surface was estimated to be 100 m below sea level (Pakoksung et al., 2020), resulting in one third of the total collapse being submerged. In comparison to the end-member conditions of subaerial and submarine failures, the mechanics of wave generation associated with partially submerged failures is much less clear. Granular column collapse experiments provide an idealized experimental framework to explore momentum transfer processes and the resulting waves generated in partially submerged and fully submerged conditions. Work by Cabrera et al., (2020) made use of granular collapse experiments of partially to fully submerged columns to derive a continuous momentum-based function to estimate the maximum seaward wave amplitude based on the initial column submergence ratio (Hw/Ho). However, these experiments were conducted at a small-scale (Ho = 0.15 m) with a width of one particle (2.4 mm diameter). To address this research gap, a series of 22 large-scale granular collapse experiments were conducted by releasing columns of river stone (0.75 m and 0.50 m high) into a laboratory flume reservoir with water depths ranging up to 1.10 m to explore the wave generation and runup processes in both seaward and landward directions. The columns were released by a rapid pneumatically actuated vertical rising gate designed to enable the near instantaneous loss of support of the source volumes resulting in granular collapse. The failure mechanics were captured with high-speed cameras (Figure 1a,b) and wave amplitudes were measured using wave capacitance gauges (Figure 1c,d). This work also provides the first experimental data set of the landward propagating wave and runup associated with submerged granular collapse experiments. Overall, the seaward wave amplitudes measured in these highly-instrumented, large-scale physical models agree with empirical relationships developed in a previous study using smaller-scale models.

Motion measurements of explosive shock waves based on an event camera

Shock wave measurement is vital in assessing explosive power and designing warheads. To obtain satisfactory observation data of explosive shock waves, it is preferable for optical sensors to possess high-dynamic range and high-time resolution capabilities. In this paper, the event camera is first employed to observe explosive shock waves, leveraging its high dynamic range and low latency. A comprehensive procedure is devised to measure the motion parameters of shock waves accurately. Firstly, the plane lines-based calibration method is proposed to compute the calibration parameters of the event camera, which utilizes the edge-sensitive characteristic of the event camera. Then, the fitted ellipse parameters of the shock wave are estimated based on the concise event data, which are gained by utilizing the characteristics of the event triggering and shock waves’ morphology. Finally, the geometric relationship between the ellipse parameters and the radius of the shock wave is derived, and the motion parameters of the shock wave are estimated. To verify the performance of our method, we compare our measurement results in the TNT explosion test with the pressure sensor results and empirical formula prediction. The relative measurement error compared to pressure sensors is the lowest at 0.33% and the highest at 7.58%. The experimental results verify the rationality and effectiveness of our methods.

Holocene gigascale rock avalanches in Vaigat strait, West Greenland—Implications for geohazard

Abstract Rock avalanche–triggered displacement waves (also termed tsunamis) have recently occurred in Greenland and Alaska, and they illustrate the presence of such hazards in polar regions. To improve understanding of the magnitude of this hazard for these areas, we investigated gigascale subaerial rock avalanches impacting a partially confined water body within the Vaigat strait (western Greenland). We present a new combined subaerial to subaqueous digital elevation model, alongside a new compilation of seismic data, which revealed nine deglacial to Holocene rock avalanche complexes that are between one and two orders of magnitude larger than nearby historical rock avalanches. The three largest complexes have deposit thicknesses up to 300 m, runout distances reaching 19 km, and best-estimate volumes from 1.7 to 8.4 km3. Based on the morphology and the volume–angle of reach relations, it is likely that each complex represents a single or few events, thus making them among the largest displacement wave–generating subaerial to submarine rock avalanches on Earth. We estimated displacement wave magnitude up to 280 m on the opposite shore. The ages of the deposits are poorly constrained but the main rock avalanche activity is referable to early Holocene times. With significant climatic changes predicted in the Arctic, we recommend that hazard assessments account for events not only from the historical record but also those from the recent geological past.

Achieving High Power Density and Durability of Multilayered Swing‐Structured Triboelectric Nanogenerator toward Marine Environmental Protection

AbstractProtecting marine environment is an important and urgent task to maintain marine ecological balance. As a promising blue energy harvesting technology, triboelectric nanogenerator (TENG) can provide electrical energy for marine environmental protection. Previous reported swing‐structured TENGs have advantages of low driving force in low‐frequency water waves and strong durability, but the space utilization and volume power density are relatively low. Here, a multilayered swing‐structured TENG (MS‐TENG) with low wear is designed to increase the space utilization rate, and thereby enhance the output performance. The MS‐TENG generates the highest peak power density of 15.18 W m−3 Hz−1 and average power density of 3.56 W m−3 Hz−1 under water wave triggering at 0.8 Hz. By coupling the charge pumping and non‐contact mode of main TENGs, the MS‐TENG achieves strong performance stability, exhibiting little attenuation of electric output after 240 000 cycles. Furthermore, the MS‐TENG has successfully powered a water quality detector for self‐powered ballast water quality monitoring, and an application is presented about electrical dehydration of water‐in‐oil emulsions driven by the MS‐TENG with a dehydration rate of 99.6%. This work promotes the development of high power density MS‐TENG and demonstrates its application potential for self‐powered marine environmental protection.

Arguments for the physical nature of the triggered ion-acoustic waves observed on the Parker Solar Probe

Arguments for the physical nature of the triggered ion-acoustic waves observed on the Parker Solar Probe

Shuttering Schools in the Gateway City: School District Viability and Black Community Relations After Mass K-12 School Closures in St. Louis, MO

ABSTRACT Since 1990, over 40% of schools have closed in the St. Louis Public Schools District (SLPSD) because of steep enrollment decline. Tracing educational trends over 30 years, I examine when, where, and why K-12 public schools closed in St. Louis in order to highlight the social conditions and policy decisions that contract contemporary urban education. I ask: What key social factors influence K-12 school closure patterns in St. Louis, Missouri? This mixed methods study summarizes analyses of data from the U.S. Department of Education, the St. Louis Public Schools District, and local news coverage to describe trends, determinants, and consequences of K-12 public school closures in St. Louis, Missouri (1990–2020). Findings demonstrated that closures in the city district were concentrated in majority-Black neighborhoods, with limited evidence of benefits to youth and communities. Findings also indicated that attempts to create educational change through the desegregation transfers program, charter school expansion, and administrative restructuring all triggered waves of closures. Drawing from community relations perspectives, I interpret mass closures as racialized policy practices that strain Black community relations and contract city districts. I argue that recurrent closures undermine youth and community development and disengage Black communities in ways that threaten district viability. Conclusions weigh whether the closure practices in the district have caused irreparable damage to Black community relations or if new policy objectives can foster long-term growth.

Upstream Shift of Generation Region of Whistler‐Mode Rising‐Tone Emissions in the Magnetosphere

AbstractWe have performed a series of simulation runs for whistler‐mode wave‐particle interaction in a parabolic magnetic field with 12 different frequencies of triggering waves and 3 different plasma frequencies specifying cold plasma densities. Under a given plasma condition, a specific frequency range of the triggering wave exists that can generate rising‐tone emissions. The generation region of rising‐tone emission shifts upstream. The velocity of the wave generation region is dependent on duration of the subpacket, which is controlled by the formation of the resonant current in the generation region. When the source velocity, which is a sum of the resonance and group velocities, is approximately the same as the velocity of the wave generation region, a long‐sustaining rising‐tone emission is generated. When the spatial and temporal gap between subpackets exists due to damping phase of short subpacket generation, resonant electrons in the gap of the subpackets are carried at the resonance velocity to the upstream region, and the velocity of the wave generation region becomes large in magnitude. When formation of resonant currents is delayed, the velocity of the generation region becomes smaller than the source velocity in magnitude. Below one quarter of the cyclotron frequency, coalescence of subpackets takes place, suppressing formation of the resonant current in the generation region. Since gradual upstream shift of the generation region is necessary for the wave to grow locally, the source velocity should be a small negative value.

Triggering of Whistler‐Mode Rising and Falling Tone Emissions in a Homogeneous Magnetic Field

AbstractWe perform a self‐consistent one‐dimensional electromagnetic particle simulation with a uniform magnetic field and open boundaries. The plasma environment consists of cold isotropic electrons, energetic electrons, and immobile ions. The energetic electrons are initialized with a subtracted‐Maxwellian distribution with temperature anisotropy. By oscillating external currents with a constant frequency 0.2 fce, where fce is the electron cyclotron frequency, a whistler‐mode wave is injected as a triggering wave from the center of the simulation system, and we investigated the process of interactions between the triggering wave and energetic electrons. We find that both rising‐tone and falling‐tone emissions are triggered through the formation of an electron hole and an electron hill in the velocity phase space consisting of a parallel velocity and the gyro‐phase angle of the perpendicular velocities. The rising‐tone emission varies from 0.2 fce to 0.4 fce, while the falling‐tone varies from 0.2 fce to 0.15 fce. The generation region of the rising‐tone triggered emission starts near the injection point of the triggering wave and moves upstream generating new subpackets. The generation region of the falling‐tone triggered emission also moves upstream generating new subpackets. The simultaneous formation of the electron hole and hill is identified by separating small and large wavenumber components corresponding to lower and higher frequencies, respectively, by applying the discrete Fourier transformation to the waveforms in space. Based on the simulation results of the whistler‐mode triggered emissions, we conclude that the mechanism of frequency variation of whistler‐mode chorus emissions works even in a uniform magnetic field.

Micromachined Tools Using Acoustic Wave Triggering for the Interaction with the Growth of Plant Biological Systems

A plant biological system is exposed to external influences. In general, each plant has its characteristics and needs with specific interaction mechanisms adapted to its survival. Interactions between systems can be examined and modeled as energy exchanges of mechanical, chemical or electrical variables. Thus, each specific interaction can be examined by triggering the system via a specific stimulus. The objective of this work was to study a specific stimulus (mechanical stimulation) as a driver of plants and their interaction with the environment. In particular, the experimental design concerns the setting up and testing of an automatic source of mechanical stimuli at different wavelengths, generated by an electromechanical transducer, to induce a micro-interaction in plants (or in parts of them) that produces a specific behavior (hypothesis) of plants. Four different experimental setups were developed for this work, each pursuing the same objective: the analysis of the germination process induced by stimulation by sound waves in the audible range. It can be said that the introduction of sound waves as a stimulant or a brake for the growth of plants can offer significant advantages when used on a large scale in the primary sector, since these effects can be used instead of polluting chemical solutions.

Nanofiber-Enhanced "Lucky-Bag" Triboelectric Nanogenerator for Efficient Wave Energy Harvesting by Soft-Contact Structure.

Developing clean and renewable ocean wave energy is a top priority and an effective way to achieve carbon neutrality. Triboelectric nanogenerators (TENGs) have emerged as promising green and clean energy-harvesting devices. To harvest low-frequency wave energy efficiently, much effort has been made on the modification of the contact surface, which leads to a higher fabrication cost. In this work, we designed a novel “Lucky-Bag” core (LBC) for spherical TENGs with a low-cost and easy fabricating process. The nanofiber/silicone hybrid porous outer layer of the LBC can switch freely from plane to surface and improve the output performance of both the plane and spherical TENGs. Several factors, such as the input frequency, direction, and resistive load, together with the thickness were systematically investigated; the unique porous soft-contact structure increased the triboelectric contact area, and the working mechanism was studied by using the COMSOL software. The experimental results showed that the peak-to-peak open-circuit voltage (V) and short-circuit current (I) could reach 580 V and 23.5 A at 1.5 Hz, even under 2D linear motion. Besides, the maximum output power of the spherical TENGs reached 9.10 mW, which can fully power electronic devices such as capacitors and LEDs under water wave triggering. These findings provide useful guidance for optimizing the performance of spherical TENGs for practical applications in harvesting water wave energy.

Nonlinear triggering process of whistler-mode emissions in a homogeneous magnetic field

We perform an electromagnetic particle simulation of triggered emissions in a uniform magnetic field for understanding of nonlinear wave–particle interaction in the vicinity of the magnetic equator. A finite length of a whistler-mode triggering wave packet with a constant frequency is injected by oscillating an external current at the equator. We find that the first subpacket of triggered emissions is generated in the homogeneous magnetic field. By analyzing resonant currents and resonant electron dynamics in the simulation, we find that the formation of an electron hole in a velocity phase space results in resonant currents, and the currents cause wave amplification and frequency increase. We obtain the interaction time of counter-streaming resonant electrons in a triggering wave packet with a finite width. By changing the duration time of the triggering pulse, we evaluate the interaction time necessary for formation of an electron hole. We conduct 4 runs with different duration times of the triggering pulse, 980, 230, 105, 40 Omega _e^{-1}, which correspond to cases with interaction times, 370%, 86%, 39%, and 15% of the nonlinear trapping period, respectively. We find generation of triggered emissions in the three cases of 370%, 86%, and 39%, which agrees with the conventional nonlinear model that the nonlinear transition time, which is necessary for formation of resonant currents, is about a quarter of the nonlinear trapping period.Graphic

Impacts of the January 2022 Tonga Volcanic Eruption on the Ionospheric Dynamo: ICON‐MIGHTI and Swarm Observations of Extreme Neutral Winds and Currents

AbstractThe eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 triggered atmospheric waves at all altitudes. The National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON) and European Space Agency Swarm satellites were well placed to observe its impact on the ionospheric wind dynamo. After the Lamb wave entered the dayside, Swarm A observed an eastward and then westward equatorial electrojet (EEJ) on two consecutive orbits, each with magnitudes exceeding the 99.9th percentile of typically observed values. ICON simultaneously observed the neutral wind (90–300 km altitude) at approximately the same distance from Tonga. The observed neutral winds were also extreme (>99.9th percentile at some altitudes). The covariation of EEJ and winds is consistent with recent theoretical and observational results, indicating that the westward electrojet is driven by strong westward winds in the Pedersen region (∼120–150 km). These observations imply that the dynamo is a key mechanism in the ionospheric response to the Tonga disturbance.

LED multispectral imaging based on frequency-division modulation of square wave and synchronous triggering

The ultimate goal of LED illumination-based multispectral imaging (LEDMSI) is higher image accuracy, more band spectrum information, and faster acquisition speed. The inherent square wave integral sampling mode limits the image accuracy and sampling speed of LEDMSI based frequency-division modulated with a sine wave as the carrier. A LED multispectral imaging combining square wave frequency-division modulation and camera external triggering is proposed. Experiments were conducted with five LEDs of different wavelengths and a monochrome camera as examples. The experimental design follows: the microprocessor generates a series of square waves whose frequency is twice the ratio relationship to modulate the light source of different wavelengths and control the camera to acquire synchronously. The camera sets the delay time and exposure time to acquire multispectral images synchronously. Then the single-band image is obtained through the differential accumulation algorithm. Use objective image quality evaluation indicators to evaluate the obtained images. The results show that this method can quickly acquire images of more wavelengths, maintain good image quality, and has good anti-interference ability, which provides a new idea for LEDMSI technology. The acquisition method is not limited to LEDMSI and the improved method can be widely used in signal acquisition systems with integration sampling mode.

Measurement uncertainty of shear wave velocity: A case study of thirteen alluvium test sites in Taipei Basin

Field seismic methods are widely applied to site investigations for seismic design. The most often used ones are cross-hole, down-hole, SCPT, suspension P–S logging, and surface wave methods. The choice of seismic methods has a variety of technical and cost considerations. However, the measurement uncertainty among resulting shear wave velocities by above methods are rarely statistically characterized with mathematical models and sound database in the literature, even though it is an important factor to consider before choosing a method. In this study, thirteen alluvium sites in Taipei Basin were chosen and carefully planned to simultaneously measure the velocity profiles using each of the five most common seismic methods with conventional shear wave triggering techniques. Using the data from the test and statistical models, the differences between seismic methods were quantified as the calibrated measurement uncertainty, which can be used as a reference for selecting an appropriate method for measuring shear wave velocity. Finally, the effect of measurement uncertainty on seismic site classification and simplified soil liquefaction potential evaluations based on shear wave velocity was investigated.

Phylogenomic analyses highlight innovation and introgression in the continental radiations of Fagaceae across the Northern Hemisphere

Northern Hemisphere forests changed drastically in the early Eocene with the diversification of the oak family (Fagaceae). Cooling climates over the next 20 million years fostered the spread of temperate biomes that became increasingly dominated by oaks and their chestnut relatives. Here we use phylogenomic analyses of nuclear and plastid genomes to investigate the timing and pattern of major macroevolutionary events and ancient genome-wide signatures of hybridization across Fagaceae. Innovation related to seed dispersal is implicated in triggering waves of continental radiations beginning with the rapid diversification of major lineages and resulting in unparalleled transformation of forest dynamics within 15 million years following the K-Pg extinction. We detect introgression at multiple time scales, including ancient events predating the origination of genus-level diversity. As oak lineages moved into newly available temperate habitats in the early Miocene, secondary contact between previously isolated species occurred. This resulted in adaptive introgression, which may have further amplified the diversification of white oaks across Eurasia.

Core Electron Heating by Triggered Ion Acoustic Waves in the Solar Wind

Abstract Perihelion passes on Parker Solar Probe orbits 6–9 have been studied to show that solar wind core electrons emerged from 15 solar radii with a temperature of 55 ± 5 eV, independent of the solar wind speed, which varied from 300 to 800 km s−1. After leaving 15 solar radii and in the absence of triggered ion acoustic waves at greater distances, the core electron temperature varied with radial distance, R, in solar radii, as 1900R −4/3 eV because of cooling produced by the adiabatic expansion. The coefficient, 1900, reproduces the minimum core electron perpendicular temperature observed during the 25 days of observation. In the presence of triggered ion acoustic waves, the core electrons were isotropically heated as much as a factor of two above the minimum temperature, 1900R −4/3 eV. Triggered ion acoustic waves were the only waves observed in coincidence with the core electron heating. They are the dominant wave mode at frequencies greater than 100 Hz at solar distances between 15 and 30 solar radii.

Nonlinear Signatures of VLF‐Triggered Emissions: A Simulation Study

AbstractWe conduct a particle‐in‐cell simulation reproducing triggering process of whistler‐mode rising‐tone emissions by injecting a wave with a fixed frequency at the equator. Rising‐tone elements with multiple subpackets with monotonically increasing frequencies are generated from the triggering wave. Generation regions of the subpackets move upstream or downstream depending on the group velocities and resonance velocities for different frequencies. Because of the motion of a source region to the upstream, a long rising‐tone subpacket is generated self‐sustainingly through formation of an electron hole in velocity phase space stretched over the generation region. The long rising‐tone subpacket is modulated with increasing magnitude, splitting into smaller subpackets through propagation. The amplitude modulations in the subpacket arise from two different processes; resonant trapping oscillation of electrons at the equatorial region and enhancement of amplitude variations through propagation in the downstream.