Long-distance Propagation Research Articles

Ultraviolet spectral broadening by stimulated rotational Raman scattering on nitrogen pumped with signal laser injection

We present experimental results on kilojoule ultraviolet laser output with 1% spectral broadening. Through stimulated rotational Raman scattering (SRRS) with signal laser injection, we achieve effective spectral broadening in short-range propagation, with good retention of the original near-field distribution and time waveform. Theoretical calculations show that 2% bandwidth spectral broadening can be achieved by injecting 20 kW/cm2 signal light at 2.2 GW/cm2 flux of the pump laser. In addition, high-frequency modulation in the near field can be effectively avoided through replacement of the original random noise signal light by the controllable signal light. The SRRS in the atmospheric environment excited with signal laser injection can provide wide-band light output with controllable beam quality without long-distance propagation, representing an important potential route to realization of broadband laser drivers.

Efficient Fourth-Order PSTD Algorithm with Moving Window for Long-Distance EMP Propagation.

Satellite-borne electromagnetic pulse (EMP) detection technology plays an important role in military reconnaissance, space environment monitoring, and early warning of natural disasters. However, the complex ionosphere greatly distorts the waveform during propagation and poses a challenge to EMP detection. Therefore, it is necessary to conduct theoretical research on EMP propagation in the ionosphere. Conventional second-order pseudo-spectral time-domain (PSTD-2) algorithm has difficulties in keeping the stability and accuracy of waveforms in calculations over hundreds of kilometers of propagation. To overcome the difficulties, a fourth-order PSTD algorithm incorporating the moving window technique (MWPSTD-4) is proposed. In the numerical examples, the performance of MWPSTD-4 is compared with PSTD-4 and PSTD-2 in the long-distance propagation of EMP. The results show that the MWPSTD-4 improves efficiency while guaranteeing accuracy and is suitable for large-scale electromagnetic field simulation. The proposed method provides a basic algorithm to eliminate the numerical dispersion interference for calculating the long-distance propagation of EMP in complex spaces and is helpful for the design and calibration of satellite-borne EMP detectors.

Domination based graph neural networks

Graph Neural Networks (GNNs) have emerged as a widely used and effective method across various domains for learning from graph data. Despite the abundance of GNN variants, many struggle with effectively propagating messages over long distances. This paper introduces a novel hierarchical message passing framework for graph learning, specifically designed to address the challenge of long-distance message propagation in graphs. By constructing smaller graphs from the main graph using the concept of domination, a fundamental principle in graph theory, we facilitate more efficient message passing within each subgraph. Subsequently, we employ a Graph Attention Network (GAT) to aggregate these features and propagate them to distant nodes across the graph. Experimental results on standard node classification datasets validate that the proposed architecture achieves performance comparable to or better than conventional GNNs. Additionally, our model consistently performs better on graphs with missing edges.

A distributed PD detection method for high voltage cables based on high precision clock synchronization

Partial discharge (PD) is a crucial cause of high voltage (HV) cable failures. Detecting and locating PD efficiently and effectively is paramount for HV cable maintenance. However, the attenuation of the PD signal after long-distance propagation makes it challenging to identify. This paper presents a distributed PD detection method that significantly reduces the propagation distance of PD signals before the sensor captures them. The technique uses the time-of-arrival to locate PD, whose localization accuracy is directly linked to the clock synchronization (CS) accuracy. CS between different sensors is achieved through three times interactions of the CS signal. The linear frequency modulation (LFM) signal is selected as the CS signal, which can generate a significant gain after pulse compression. It ensures that the CS signal can be effectively recognized after the attenuation of long-distance propagation. The paper also introduces a signal discrimination method based on the short-time Fourier transform that eliminates the influence of the LFM signal on PD identification. The cableless CS method makes it easier to set up before the onsite test. A prototype was implemented and tested. The CS accuracy was measured within 4 ns in the laboratory. An onsite test was carried out to evaluate the performance of the distributed PD detection system. A defect was found at a joint location, which was also confirmed by an additional ultrasonic PD test.

Ground-based simulation of laser link acquisition for inter-satellite laser interferometry

Laser link acquisition and pointing technique is one of the essential techniques for the inter-satellite laser interferometry for space-based gravitational waves detection and next-generation Earth gravity measurement missions. The first step of building up inter-satellite laser link is using an acquisition camera to capture the inter-satellite laser beam signals within a pre-scanning uncertain cone. Subsequently, high-precision angle measurement technology, namely differential wavefront sensing, is used to achieve a high pointing precision required. Due to the distance constraint of a ground-based simulation experiment, it is difficult to verify directly the feasibility of an inter-satellite laser link acquisition and pointing control scheme. By means of controlling the optical properties of the received laser beam, the long-distance beam propagation is simulated with two optical benches of an inter-satellite interferometer, and the process of a laser link acquisition experiment has been demonstrated. The experimental results show that the inter-satellite laser beams could establish the dual-way locking successfully. The fluctuation of the laser beam pointing direction (in-loop) can be suppressed to about 5 µrad in atmospheric environment. The results verify the feasibility of the laser link acquisition scheme. The experimental setup can be extended to conduct experiments with various parameters, providing technical support for further testing of the inter-satellite laser link acquisition and pointing control methods.

Multi-Wave Structures of Traveling Ionospheric Disturbances Associated with the 2022 Tonga Volcanic Eruptions in the New Zealand and Australia Regions

Using dense global navigation satellite system data and brightness temperature data across the New Zealand and Australia regions, we tracked the propagation of traveling ionospheric disturbances (TIDs) associated with the 15 January 2022 Tonga volcanic eruptions. We identified two shock wave-related TIDs and two Lamb wave-related TIDs following the eruptions. The two shock wave-related TIDs, propagating with velocities of 724–750 and 445–471 m/s, respectively, were observed around New Zealand and Australia within a distance of 3500–6500 km from the eruptive center. These shock wave-related TIDs suffered severe attenuation during the propagation and disappeared more than 6500 km from the eruptive center. Based on the TEC data from the nearest ground-based receivers, we estimated the onset times of two main volcanic explosions at 04:20:54 UT ± 116 s and 04:24:37 UT ± 141 s, respectively. The two shock wave-related TIDs were most likely generated by these two main volcanic eruptions. The two Lamb wave-related TIDs propagated with velocities of 300–370 and 250 m/s in the near-field region. The Lamb wave-related TIDs experienced minimal attenuation during their long-distance propagation, with only a 0.17% decrease observed in the relative amplitudes of the Lamb wave-related TIDs from the near-field to far-field regions.

Guided Wave Behavior in Type IV Composite Overwrapped Pressure Vessels Under Fatigue Loading

Innovative Ultrasonic Guided Wave Approach for Structural Health Monitoring of Type IV Composite Overwrapped Pressure Vessels Seyedreza Hashemi, Jan Heimann, Amir Charmi, Eric Duffner, Jens Prager Abstract: The digitalization of quality control processes and the use of digital data infrastructures is a novel idea that can be applied for ensuring the operational safety and reliability of pressure vessels, particularly in the context of hydrogen storage at high pressure. Despite the critical role these pressure vessels play, current safety regulations lack an established concept for Structural Health Monitoring (SHM). This research addresses this gap by presenting a study on the application of ultrasonic guided waves (GWs) for SHM of Type IV Composite Overwrapped Pressure Vessels (COPVs). The study focuses on the development of a reliable measurement system to transition from conventional periodic inspections to SHM and predictive maintenance, prolonging the remaining lifetime of the vessels. A sensor network is employed, consisting of fifteen piezoelectric wafers arranged in three rings, which are mounted on the outer surface of the COPV. Deploying GWs, known for their long-distance propagation and ability to cover complex structures, the study explores GW behavior under different environmental and operational conditions, including periodic pressure fluctuations and temperature loadings. Meticulous analysis of GW signals by utilizing various features and damage indices, underscores their suitability for an effective SHM under realistic working conditions. The project aims to localize defects by considering temperature, and internal pressure. Mimicking the continuous monitoring of Type IV COPVs in H2 refueling gas stations under authentic operational conditions, the COPV underwent thousands of pressure load cycles in our special test facility . The implemented methodology facilitates early damage detection, showcasing the efficacy of the designed method in effective safety assurance.

Enhanced Multi-Beam Echo Sounder Simulation through Distance-Aided and Height-Aided Sound Ray Marching Algorithms

The study proposes two innovative algorithms in the field of multi-beam echo sounder (MBES) simulation: distance-aided sound ray marching (DASRM) and height-aided sound ray marching (HASRM). These algorithms aim to enhance the efficiency and accuracy of MBES simulations, particularly when dealing with long-distance propagation and real-time processing limitations. DASRM addresses issues related to simulation accuracy by efficiently utilizing the KD-tree for spatial indexing and intersection detection instead of the signed distance field (SDF). Building upon the further analysis of DASRM, HASRM is proposed, which improves the search strategy for ray intersections and utilizes a height field pyramid for sampling and retrieval, thereby reducing memory usage while enhancing indexing efficiency. The experimental results demonstrate that both algorithms significantly outperform traditional methods in terms of simulation time, with HASRM exhibiting particular advantages in parallel computing due to its data structure and improved strategies. Additionally, DASRM is well suited for applications requiring complex scene construction, while HASRM proves especially effective in simulating MBES with a focus on underwater terrain due to its effectiveness in handling large incident angles and long-distance propagation.

MEMS flexible conformal hydrophone based on heterogeneous integration technology

PurposeHuman-induced marine environmental noise, such as commercial shipping and seismic exploration, is concentrated in the low-frequency range. Meanwhile, low-frequency sound signals can achieve long-distance propagation in water. To meet the requirements of long-distance underwater detection and communication, this paper aims to propose an micro-electro-mechanical system (MEMS) flexible conformal hydrophone for low-frequency underwater acoustic signals. The substrate of the proposed hydrophone is polyimide, with silicon as the piezoresistive unit.Design/methodology/approachThis paper proposes a MEMS heterojunction integration process for preparing flexible conformal hydrophones. In addition, sensors prepared based on this process are non-contact flexible sensors that can detect weak signals or small deformations.FindingsThe experimental results indicate that making devices with this process cannot only achieve heterogeneous integration of silicon film, metal wire and polyimide, but also allow for customized positions of the silicon film as needed. The success rate of silicon film transfer printing is over 95%. When a stress of 1 Pa is applied on the x-axis or y-axis, the maximum stress on Si as a pie-zoresistive material is above, and the average stress on the Si film is around.Originality/valueThe flexible conformal vector hydrophone prepared by heterogeneous integration technology provides ideas for underwater acoustic communication and signal acquisition of biomimetic flexible robotic fish.

Study on vibration attenuation of three-component local resonant pile with low-frequency attenuation zone

The paper explores the increasing concern over environmental vibrations resulting from machine operation and rail transit. Notably, low-frequency vibrations generate surface waves with characteristics like significant energy carrying capacity, long-distance propagation, and slow attenuation. The primary challenge in ground vibration attenuation lies in addressing low-frequency vibrations. The study employs the finite element method to investigate the vibration attenuation of a three-component local resonance pile in three-dimensional space. The analysis delves into the impact of the unit cell structure’s geometry size on bandgaps, and the influences of the period number on the Attenuation Zones (AZs) are also discussed. Furthermore, a comparison is made regarding the vibration attenuation performance of a two-component local resonance pile. The findings reveal that the appropriate design of a three-component local resonance pile can generate low-frequency complete bandgap. The concrete radius, rubber layer thickness, and buried depth of the pile significantly affect Rayleigh wave bandgap. Frequency domain analysis indicates that an increase in period number expands AZs into the bandgap range. Time domain analysis demonstrates a noticeable decrease in ground acceleration amplitude within the bandgap range. The research results presented in this paper offer a novel approach to address the low-frequency vibration attenuation.

PLC-γ-Ca2+ pathway regulates axonal TrkB endocytosis and is required for long-distance propagation of BDNF signaling.

Brain-derived neurotrophic factor (BDNF) and its tropomyosin receptor kinase B (TrkB) are important signaling proteins that regulate dendritic growth and maintenance in the central nervous system (CNS). After binding of BDNF, TrkB is endocytosed into endosomes and continues signaling within the cell soma, dendrites, and axon. In previous studies, we showed that BDNF signaling initiated in axons triggers long-distance signaling, inducing dendritic arborization in a CREB-dependent manner in cell bodies, processes that depend on axonal dynein and TrkB activities. The binding of BDNF to TrkB triggers the activation of different signaling pathways, including the ERK, PLC-γ and PI3K-mTOR pathways, to induce dendritic growth and synaptic plasticity. How TrkB downstream pathways regulate long-distance signaling is unclear. Here, we studied the role of PLC-γ-Ca2+ in BDNF-induced long-distance signaling using compartmentalized microfluidic cultures. We found that dendritic branching and CREB phosphorylation induced by axonal BDNF stimulation require the activation of PLC-γ in the axons of cortical neurons. Locally, in axons, BDNF increases PLC-γ phosphorylation and induces intracellular Ca2+ waves in a PLC-γ-dependent manner. In parallel, we observed that BDNF-containing signaling endosomes transport to the cell body was dependent on PLC-γ activity and intracellular Ca2+ stores. Furthermore, the activity of PLC-γ is required for BDNF-dependent TrkB endocytosis, suggesting a role for the TrkB/PLC-γ signaling pathway in axonal signaling endosome formation.

Impact of multiple weak layers on deformation of the interior of Qaidam Basin, northern Tibetan Plateau

The Qaidam Basin is the largest sedimentary basin within the Tibetan Plateau, with up to ∼15-km-thick deposits accumulated in the Cenozoic. Understanding how it deformed in response to the far-field effects of India-Eurasia collision is critical to improving our knowledge of the mechanism underlying northward plateau growth. Unlike typical compressional basins, where upper-crustal deformation concentrates at their margins, the Qaidam Basin features the development of many NW- to WNW-striking folds across the entire basin. Why crustal shortening occurred in the interior of Qaidam Basin, ∼100 km away from the margins, together with the underground geometries beneath these folds, remains unknown. Herein, based on newly acquired three- and two-dimensional (3-D and 2-D) seismic reflection data, borehole logging, and scaled physical analog modeling, we investigated the geometries, kinematics, and formation mechanisms of the folds within the interior of Qaidam Basin. For the first time, we reveal three local weak layers in the Lulehe, Upper Xiaganchaigou, and Shangyoushashan Formations, respectively. They consist mainly of mudstone intercalated with evaporites and limestones, and they have different spatial distributions that are likely confined by major faults and folds. These mechanically weak layers became locally thickened or thinned in response to tectonic loading and/or facilitated detachment slip to form many décollement folds that were observed at the surface. The shallow deformation above the weak layers is largely decoupled from underlying basement-involved faulting and folding, which mostly terminate upward in these weak layers. Analog modeling results suggest that the lowermost and widely distributed décollement layer in the Lulehe Formation likely facilitated long-distance rapid propagation of deformation into the basin interior. In sum, our study highlights the significance of multiple weak layers during Cenozoic deformation in the Qaidam Basin interior.

Photon-assisted ultrafast electron–hole plasma expansion in direct band semiconductors

Abstract Time-resolved terahertz spectroscopy is used to investigate formation and ultrafast long-distance propagation of electron–hole plasma in strongly photoexcited GaAs and InP. The observed phenomena involve fundamental interactions of electron–hole system with light, which manifest themselves in two different regimes: a coherent one with the plasma propagation speeds up to c/10 (in GaAs at 20 K) and an incoherent one reaching up to c/25 (in InP at 20 K), both over a macroscopic distance >100 μm. We explore a broad range of experimental conditions by investigating the two materials, by tuning their band gap with temperature and by controlling the interaction strength with the optical pump fluence. Our interpretation suggests that the observed phenomena should occur in most direct band semiconductors upon strong photoexcitation with low excess energy.

Quantitative analysis of the tropospheric delay differences for 1–300 GHz microwave signals with ground-based microwave radiometric profiles

Tropospheric delay is a significant source of error in various microwave measurement technologies. As the tropospheric delay differences associated with the signal frequency can be neglected for signals near the L band, the Global Navigation Satellite System (GNSS) is frequently used to assist other microwave measurements on tropospheric delay correction for its high precision and all-weather capabilities. However, when the signal frequency differences are significant, further analysis of tropospheric delay related to signal frequency is required for higher accuracy in long-distance propagation. This study quantitatively analyzed the tropospheric delay differences from L-band to millimeter band (1–300 GHz) affected by dry air, water vapor, and liquid water, based on Microwave Radiometer (MWR) measurement profiles and the Millimeter-wave Propagation Model93 (MPM93) at Shanghai. Relative to the GNSS L-band signal of 1.2 GHz, the RMS of tropospheric delay differences over 1–300 GHz varies from 0.033 mm to 9.436 mm, with the maximum tropospheric delay differences up to 18.03 mm at 300 GHz. Tropospheric delay differences strongly correlate with surface temperature and surface pressure, except for some of the atmosphere absorption bands. These quantitative analyses are helpful for the comprehensive application of GNSS to assist other microwave measurement techniques.

Interdecadal changes in the frequency of winter extreme cold events in North China during 1989–2021

How extreme weather and climate events change is an intriguing issue under global warming. By investigating the frequency of extreme cold events (Frexces) in winter over North China (NC), this paper presents robust interdecadal changes in Frexces in NC since the late 1980s. Two shift points are detected at about 2003 and 2013 through a Mann–Kendall test. Three periods are then identified as 1989–2002 (P1), 2003–2012 (P2), and 2013–2021 (P3). Frexces increases from P1 to P2 and then decreases from P2 to P3. Correspondingly, the winter mean Siberian–Ural High (SUH), polar jet stream (PJS), and North Atlantic Oscillation (NAO) show interdecadal changes. The winter SUH gets stronger and the PJS and NAO weaker during P2, while the SUH is weakened and the PJS and NAO strengthened in P3. The stronger SUH and weaker PJS is favourable for cold-air intrusion into NC in P2, and the opposite is true for the weaker SUH and stronger PJS in P1 and P3. The weaker NAO in P2 relates to long-distance wave propagation to Eurasia to strengthen the SUH, while wave activity accompanying the stronger NAO in P3 is confined to western Eurasia. For the all-extreme cold events composite, the area affected by the cold air inducing extreme cold events in NC enlarges northwestward to the West Siberian Plain, and the intensity of the cold air also gets strengthened from P1 to P3.摘要全球变暖背景下, 极端天气气候事件的变化受到关注. 本文研究发现, 1989–2021年期间, 华北地区极端冷日数在2003和2013年发生了年代际变化. 极端冷日数先增加后减少. 2003–2012年, 西伯利亚–乌拉尔高压偏强, 极地西风急流偏弱, 有利于冷空气南下入侵华北地区, 华北极端冷日数偏多. 而在1989–2002年和2013–2021年, 情况相反. 虽然三个时段华北极端冷日的强度没有显著差异, 但与其相联系的冷空气强度变得更强, 2013–2021年冷空气中心区域往西北扩张到了贝加尔湖以西地区.

Rapid Propagation of Ca2+ Waves and Electrical Signals in the Liverwort Marchantia polymorpha.

In response to both biotic and abiotic stresses, vascular plants transmit long-distance Ca2+ and electrical signals from localized stress sites to distant tissues through their vasculature. Various models have been proposed for the mechanisms underlying the long-distance signaling, primarily centered around the presence of vascular bundles. We here demonstrate that the non-vascular liverwort Marchantia polymorpha possesses a mechanism for propagating Ca2+ waves and electrical signals in response to wounding. The propagation velocity of these signals was approximately 1-2 mm s-1, equivalent to that observed in vascular plants. Both Ca2+ waves and electrical signals were inhibited by La3+ as well as tetraethylammonium chloride, suggesting the crucial importance of both Ca2+ channel(s) and K+ channel(s) in wound-induced membrane depolarization as well as the subsequent long-distance signal propagation. Simultaneous recordings of Ca2+ and electrical signals indicated a tight coupling between the dynamics of these two signaling modalities. Furthermore, molecular genetic studies revealed that a GLUTAMATE RECEPTOR-LIKE (GLR) channel plays a central role in the propagation of both Ca2+ waves and electrical signals. Conversely, none of the three two-pore channels were implicated in either signal propagation. These findings shed light on the evolutionary conservation of rapid long-distance Ca2+ wave and electrical signal propagation involving GLRs in land plants, even in the absence of vascular tissue.

The observation of avalanche-like transport during confinement power degradation in Heliotron J

In this study, we observe avalanche-like electron thermal transport in Heliotron J under plasma conditions that exhibit power degradation to the central electron cyclotron heating (ECH). The newly installed GHz sampling electron cyclotron emission diagnostic allows for the observation of the long-distance radial propagation of electron temperature fluctuations. We find that the electron temperature fluctuations are associated with avalanches, because the Te fluctuations (i) propagate from the core to the edge with a speed comparable to the diamagnetic drift velocity, (ii) exhibit a 1/f power-law scaling in the frequency spectrum and a Hurst exponent close to 1, and (iii) dominate in the ECH deposition location and spread to the edge as the heating power increases. Furthermore, the electron heat avalanches can spread to the scrape off layer region when they are enhanced, i.e., the Te fluctuations correlate with the Dα emission, which also has a frequency spectrum that scales with a 1/f power law.

Self-healing properties of optical pin beams

In some situations, the beam is partially blocked by an obstacle during propagation, and the influence of the obstacle and ways to decrease the influence have been studied for practical applications. The self-healing effect of Bessel beams is considered as one potential technology for this. The optical pin beam (OPB) can evolve into a Bessel-like beam and can retain its robust property after long-distance propagation. In this paper, we study the propagation property of an OPB after it is partially blocked by an obstacle. We observe the self-healing effects of the OPB and find that it exhibits robust self-healing abilities. An experiment is conducted to confirm the self-healing effect of the OPB. As one example of the application of the self-healing effect, the radiation forces of an obstructed OPB are calculated. Our findings may have important applications in various fields such as micro-imaging, trapping, and long-distance optical communication under disturbance conditions.

Enhanced fracture toughness stability of (B,Y)-contained TiAl-based alloy prepared by cold crucible directional solidification

Cold crucible directional solidification (CCDS) can be used to prepare the well-DS TiAl-based alloys with good mechanical properties. However, when the DS columnar grains are coarsened, the stability of fracture toughness will not be guaranteed due to the internal random-direction (α2+γ) lamellas. In this study, in order to improve the fracture toughness stability of CCDS TiAl-based alloys, (B,Y) refinement element was added, and the model alloys Ti–44Al–6Nb–1Cr–2V and Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) were used. The two alloys were fabricated by CCDS under the same parameters, and their macro/microstructure and fracture toughness were studied. The results showed that the B/Y compounds hindered the growth of dendrites, narrowed the DS window, and significantly refined the columnar grains. The fracture toughness of well-DS Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) alloy with the refined columnar grains was still at a higher level, and the key was that the stability of its fracture toughness was significantly improved comparing with that of the well-DS Ti–44Al–6Nb–1Cr–2V alloy with the coarsened columnar grains. It was found that the well-DS Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) alloy could provide more longitudinal grain boundary barriers for the radial crack propagation, create more crack deflection when the crack entered the next columnar grain (lamella colony) and avoid the crack long-distance propagation along the bad-orientation (α2+γ) lamellas.

Detecting the Kauai source beacon with ocean observatories innitiative hydrophones

In March of 2023, a sound source off the coast of Kauai began regularly transmitting a 75 Hz signal into the ocean, six times a day, every fourth day. The regular transmission of this signal allows for the long-term measurements of ocean basin scale temperature changes using the technique of acoustic tomography, as well as further investigations of long-distance acoustic propagation. The Ocean Observatory Initiative (OOI) has, as part of its suite of oceanographic sensors, 11 hydrophones that are continually recording ambient sound. These hydrophones are in various diverse environments in the north-east pacific including bottom mounted in shallow environments, deep environments, on top of seamounts, and moored at 200 m below the ocean surface. In this talk, we present preliminary results of acoustic propagation modeling and data analysis towards receiving the Kauai signal with the OOI hydrophones. The diverse environments of the hydrophones allow us to investigate how different levels of ambient sound and environmental factors, such as proximity to the sound channel affect the ability to detect a positive reception of the Kauai source across the ocean basin. [Work supported by ONR.]