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Background: Crocodiles are semi-aquatic animals well adapted to hear both on land and under water. Currently, there is limited information on how their amphibious hearing is accomplished. Here, we describe, for the first time, the ear anatomy in the living crocodile using photon-counting detector computed tomography (PCD-CT) and 3D rendering. We speculate on how crocodiles, despite their closed ear canals, can use tympanic hearing in water that also provides directional hearing. Material and Methods: A Cuban crocodile (Crocodylus rhombifer) underwent photon-counting detector computed tomography (PCD-CT), under anesthesia and spontaneous respiration. In addition two seven-month-old C. rhombifer and a juvenile Morelet´s crocodile (Crocodylus moreletii) underwent micro-computed tomography (µCT) and endoscopy. One adult Cuviérs dwarf caiman (Paleosuchus palpebrosus) was micro-dissected and video-recorded. Aeration, earflap, and middle ear morphology were evaluated and compared after 3D modeling. Results and Discussion: PCD-CT and µCT with 3D rendering and segmentation demonstrated the anatomy of the external and middle ears with high resolution in both living and expired crocodiles. Based on the findings and comparative examinations, we suggest that the superior earflap, by modulating the meatal recess together with local bone conduction, may implement tympanic hearing in submerged crocodiles, including directional hearing. [ABSTRACT FROM AUTHOR]

Some marine animals form long‐lived luminescence for predation, communication, camouflage, and anti‐predation. These marine animals demonstrate soft nature, sustainable glowing, and underwater emission, which are difficult to achieve in synthetic room temperature phosphorescence (RTP) materials. Inspired by these marine animals, here the study reports RTP hydrogels that show long‐lived phosphorescence (lifetime >500 ms and afterglow >10 s) in water. Exceptional underwater mechanical properties are simultaneously achieved, including tensile strength of 5.1 MPa, tensile strain of 452%, and toughness of 19.3 MJ m−3. The key to this achievement lies in the in situ phase separation microarchitecture formed between polyacrylamide (PAM) and its partial hydrolysates, which confines the motions of polymer chains and protects vulnerable triplet excitons from quenching of water. Such a strategy shows the merits of facile fabrication without laborious synthesis. In addition, these RTP hydrogels offer repeatable photoprinting and highly stability in water, providing a versatile platform for underwater applications of RTP materials, including information encryption and camouflage of marine animals. [ABSTRACT FROM AUTHOR]

Ensuring effective and reliable communication within underwater sensor networks (UWSNs) is a formidable challenge due to their unique characteristics, which include offshore exploration, underwater surveillance and monitoring. UWSNs have proven to be a promising approach in various fields, including research investigations, surveillance operations and underwater disaster response. To advance this field, numerous researchers have dedicated themselves to developing new protocols tailored to UWSNs or refining existing protocols, all with the goal of improving research. One important aspect that continues to attract the attention of researchers is the reliability factor in the underwater environment, leading to constant efforts to improve the overall efficiency of the network and optimize energy consumption. In this work, a machine learning based node reliability calculation algorithm (MRNQ) has been proposed, which takes into account numerous parameters such as the success rate, transmission time, node efficiency, and the network efficiency. The proposed approach outperforms CSLT and TMHCV across key metrics with notable percentage improvements. It achieves a 5.16% higher packet delivery rate, a 22.06% reduction in packet drop rates, a 42.4% extension in network lifetime, and a 0.87676% improvement in malicious node detection. [ABSTRACT FROM AUTHOR]

Corrosion and biofouling are wetting‐related phenomena that limit the effective use of metals in aqueous media. Nonwettable surfaces can mitigate the adverse effects of wetting by minimizing contact with water. However, current achievements in this field fall short of meeting industrial requirements due to the short lifetime of plastrons. This study proposes a method to measure the protective sustainability of plastron. Superhydrophobic (SHS) and aerophilic (APhS) surfaces are constructed on lightweight aluminum and are initially analyzed by conventional goniometry, which show comparable values. However, the plastron that develops underwater is substantially different. While SHS exhibit unevenly broken plastron, APhS show uniform, continuous plastron. As an example of the sustained protective performance of plastron, the corrosion resistance of SHS and APhS is presented. Potentiodynamic polarization, impedance spectroscopy, and long‐term immersion in seawater show a drastic enhancement in corrosion resistance, exclusively for APhS. In fact, almost no electrochemical signals are measurable, and no pitting corrosion is observed after 415 days of immersion in seawater. Conversely, SHS show no noticeable improvement and corrode faster than bare Al due to plastron loss. Since goniometric measurements do not provide information on plastron, it is essential to analyze the plastron for any non‐wettable surface utilized underwater. [ABSTRACT FROM AUTHOR]

Simple Summary: The advent of underwater endoscopic resection techniques has served as an add-on for both basic and advanced procedures, since its first report in 2012 till its inclusion into the European Society of Gastrointestinal Endoscopy guidelines. Hence, we aimed to perform a comprehensive update on the state of the art about the feasibility of underwater basic and advanced techniques for GI endoscopy. Underwater endoscopic mucosal resection represents a standard for treating intermediate-size colonic and non-ampullary duodenal lesions. Promising results have been shown in third-space endoscopy studies, even though further prospective studies are awaited to standardise the technique for both endoscopic submucosal dissection and peroral endoscopic myotomy. The endoscopic resection of gastrointestinal tract lesions embraces different types of techniques, ranging from conventional polypectomy/endoscopic mucosal resection (EMR) to the field of third-space endoscopy, including endoscopic submucosal dissection (ESD), full-thickness resection and peroral endoscopic myotomy (POEM). Parallelly, the advent of underwater techniques has served as an add-on for both basic and advanced procedures, since its first report in 2012. We aimed to provide a comprehensive update on the state of the art about the feasibility of underwater basic and advanced techniques for GI endoscopy. Underwater EMR (U-EMR) has proved effective and safe in treating > 10 mm sessile or flat or all-size recurrent colonic lesions. Conversely, although data show good effectiveness and safety for <10 mm lesions, it is preferred when high-grade dysplasia is suspected, favouring cold snare polypectomy for all other cases. Moreover, promising data are emerging regarding the feasibility of U-ESD for difficult-to-resect colonic lesions. U-EMR represents a standard of care for treating < 25 mm superficial non-ampullary duodenal epithelial tumours. Data regarding oesophageal, gastric and ampullary lesions remains limited to small cohorts. Finally, using water immersion for POEM has shown a reduction in procedure time compared to the CO2 insufflation technique for vessel coagulation, albeit in a single-centre experience. Based on these results, U-EMR has become a standard for treating intermediate-size colonic and non-ampullary duodenal lesions, as highlighted also in the European Society of Gastrointestinal Endoscopy guidelines. Promising results have been shown in third-space endoscopy studies, even though further prospective studies are awaited to standardise the technique for both ESD and POEM. [ABSTRACT FROM AUTHOR]

AbstractThis paper shows how and why it is ‘im-possible’—i.e. simultaneously possible and impossible—for humans to travel and stay underwater by narrating the story of how Jules’ Undersea Lodge was designed and how its guests can remain there for relatively long periods of time. Drawing from interviews with its designer, Ian Koblick, reflexive ethnographic material collected at Key Largo’s (Florida) Jules’ Undersea Lodge in the early spring of 2024, and an interview with Joseph Dituri—who in 2023 set a world record for the longest time spent in an underwater habitat – we conceptualize im-possibility as a dialectical tension between possibility and impossibility. [ABSTRACT FROM AUTHOR]

Underwater wireless optical communication (UOWC) systems have lately garnered a significant amount of attention for both academic purposes and trial applications. Although the idea is not new, the fact that seawater has a smaller window of absorption for blue-green light has reawakened interest in it, and it has grown an essential attraction because of its high bandwidth, it can cover a wide variety of underwater activities as compared to radio frequency and acoustic technologies. To monitor pollution, maintain oil pipelines, monitor climate change, conduct offshore investigations, and conduct oceanography research, the wireless transmission of information underwater technology is of importance to the military, industrial, and scientific organizations all around the world. The use of wavelengths of visible light to transmit secure data across point-to-point connections in underwater optical wireless communication (UOWC) compares well with the usage of free-space optical (FSO) communications. However, UWOC systems also have a huge amount of absorption and scattering introduced by the aquatic channels. Different from standard terrestrial free-space optical communication, many unique system design strategies have been investigated in recent years to solve these technological issues. This article presents a vision as well as various obstacles in the domain of underwater optical wireless communication, a detailed overview, and comparison of underwater communications techniques (UOWC) links, basic modulation technique techniques, and c pursuits on UWOC. [ABSTRACT FROM AUTHOR]

Underwater multicell single-layer thin metal plate corner reflectors can’t form a relatively stable TS in a large space because of its strong frequency characteristics. To solve the problem, the paper designs the underwater multicell cavity corner reflectors. Then using FEM coupled DBEM solver to simulated its scattering acoustic field in incident wave frequence varies from 5.0 kHz to 15.0 kHz. The results show that the underwater multicell cavity corner reflectors has weak frequency characteristics, obvious decoupling effect and strong scattering ability. Underwater multicell cavity corner reflectors can maintain stable target strength in a large space, and has better reflection ability, so it is an ideal underwater acoustic reflection device.

As human exploration of marine continues to expand, the demand for underwater devices is also increasing. The unique properties of hydrogel materials make them well‐suited for underwater applications. We propose a multi‐functional polyvinyl alcohol (PVA) – NaCl @ Polyaniline (PANI) (PNP) hydrogel, which is characterized by easy fabrication, integrated structure, and flexibility, and can be directly applied in the fields of underwater energy storage and underwater sensing. Solid‐state supercapacitors fabricated by the PNP hydrogel, due to integrated and all‐solid‐state design, can be charged and discharged underwater without encapsulation. What's more, the PNP supercapacitor can maintain a capacitance retention rate of over 90 % after 5,000 cycles in simulated seawater, eliminating concerns about the hydrogel's dehydration when used underwater. The PNP hydrogel with an integrated three‐layer structure can also be applied to the capacitive pressure sensors, which can also be directly used in underwater environments without the need for encapsulation, significantly reducing the structural complexity and preparation steps of the device. Finally, we demonstrate a “supercapacitor module” with a voltage window greater than 1.6 V created by directly connecting multiple PNP supercapacitors in series, as well as an underwater intelligent glove, providing new solutions for underwater energy storage and underwater wearable sensing applications. [ABSTRACT FROM AUTHOR]

Aluminium alloys are widely employed across numerous thanks to their superior combination of strength, lightweight characteristics and corrosion resistance. In recent years, Friction stir processing (FSP) has come up as a promising technique for machining aluminium alloys, enabling greater control over microstructural evolution and mechanical properties. This paper provides an in-depth exploration the impact of process parameters on the microstructure and mechanical properties of aluminium alloys processed by FSP. The study focuses on the systematic investigation of the influence of the principle process parameters, including rotational speed, machining speed and applied pressure, on the microstructure and resulting mechanical performance of FSP machined aluminium alloys. Furthermore, the mechanical properties of FSP treated aluminium alloys are measured by a comprehensive set of tests, including tensile tests, hardness measurements and fracture tests. The relationship between process parameters and the mechanical behaviour of the alloys is analysed in detail to identify the optimum conditions for achieving the desired properties. Findings show that process parameters plays a significant role in defining the microstructure and mechanical properties of alloys. [ABSTRACT FROM AUTHOR]

This study pioneers a breakthrough in sustainable energy solutions by developing a cutting-edge system for powering autonomous Smart Ocean surface vehicles. The research delves into the exploration of renewable energy harvesting techniques, specifically focusing on solar and hydro flow energy systems, with the aim of creating a self-sustaining power infrastructure. Through rigorous experimentation and modeling, we design and implement a versatile test rig setup to analyze the efficacy of these techniques under varying surface water conditions. Additionally, we investigate and assess distributed solar power systems ranging from 100W to 700W, as well as hydro flow power systems within the same power range, to ascertain their viability for real-world applications. Furthermore, we engineer and optimize the necessary electronic hardware utilizing IoT and industry-grade components, enabling efficient harnessing of dual renewable energy sources to power propulsion systems for our autonomous vehicles. This research introduces novel approaches to energy sustainability for autonomous ocean surface vehicles. The study disregards traditional methods and instead aims to unveil unconventional solutions for powering these vehicles. Through a series of experimental investigations, we seek to redefine the boundaries of renewable energy utilization in marine environments. By leveraging cutting-edge technologies and industry-grade components, our work aims to establish a new paradigm in the propulsion systems of autonomous oceanic vehicles. [ABSTRACT FROM AUTHOR]

Water covers about 71% of the Earth's surface, which is crucial for transportation, climate regulation, and the production of pharmaceuticals. The Internet of Underwater Things (IoUT) can detect valuable items such as minerals, metals, corals, and coral reefs. One of the crucial purposes is preventing damage from natural disasters. IoT principles helped advance plans for a new underwater network. Underwater networks suffer from some issues, including a lack of dependability, constrained capacity, long propagation delays, high processing requirements, high energy costs, and node detection with encrypted communication. Along with node identification and dynamic network setup, real-time, secure data exchange is one of our main research interests. These problems provide significant challenges for IoUT. Our proposed scheme involves a dynamic graph for network design, an Artificial fish swarm algorithm (AFSA) based on AI for node recognition, and Elliptic Curve Cryptography (ECC) for a secure communication mechanism. For underwater objects, this proposed approach is more trustworthy, safe, and resilient, preventing damage from natural disasters and being helpful for design and secure communication in maritime engineering. [ABSTRACT FROM AUTHOR]

Aiming at the demand for long-range and high-resolution imaging detection of small targets such as submerged submarine markers in shallow coastal waters, research on single-photon lidar imaging technology is carried out. This paper reports the sequential two-mode fusion imaging algorithm, which has a strong information extraction capability and can reconstruct scene target depth and reflection intensity images from complex signal photon counts. The algorithm consists of four steps: data preprocessing, extremely large group value estimation, noise sieving, and total variation smoothing constraints to image the target with high quality. Simulation and test results show that the imaging performance and imaging characteristics of the method are better than the current high-performance first-photon group imaging algorithm, indicating that the method has a great advantage in sparse photon counting imaging, and the method proposed in this paper constructs a clear depth and reflectance intensity image of the target scene, even in the 50,828 Lux ambient strong light and strong interference, the 0.1 Lux low-light environment, or the underwater high-attenuation environment. [ABSTRACT FROM AUTHOR]

The ability to switch adhesion strength is a highly desirable property for adhesives applied in a wet environment. The major challenges involve the presence of a water layer between the substrate and adhesive, and the incorporation of efficient switching mechanisms. Despite the recent progresses in devising such systems, there exist several intrinsic limitations in the current strategies, such as high residual adhesion, the use of solid–liquid transition, or thin film configurations. Herein, a channeled poly(N‐isopropylacrylamide) (PNIPAm) hydrogel containing bio‐inspired dopamine‐comonomers is reported, which undergoes temperature‐controlled reversible switching of underwater adhesion on both hydrophilic and hydrophobic surfaces. The introduction of microscopic channels inside the hydrogel, achieved by removing a sacrificial agarose network, greatly facilitates water removal from the interface and thus promotes underwater adhesive strength. On glass, the maximum adhesive stress of the channeled hydrogel can reach six times that of hydrogels without channels. Additionally, high switching efficiency and low residual adhesion can be achieved by the thermal phase transition of the PNIPAm network, also demonstrated by the capture and release of lightweight, irregular, fragile, and biological objects using the hydrogel. The channeling strategy provides implications for designing future underwater adhesive systems for, e.g., soft robotics or biomedical applications. [ABSTRACT FROM AUTHOR]

Within the domain of multi-label classification for micro-videos, utilizing terrestrial datasets as a foundation, researchers have embarked on profound endeavors yielding extraordinary accomplishments. The research into multi-label classification based on underwater micro-video datasets is still in the preliminary stage. There are some challenges: the severe color distortion and visual blurring in underwater visual imaging due to water molecular scattering and absorption, the difficulty in acquiring underwater short video datasets, the sparsity of underwater short video modality features, and the formidable task of achieving high-precision underwater multi-label classification. To address these issues, a bilayer graph convolution learning network based on constrained codec (BGCLN) is established in this paper. Specifically, modality-common representation is constructed to complete the representation of common information and specific information based on the constrained codec network. Then, the attention-driven double-layer graph convolutional network module is designed to mine the correlation information between labels and enhance the modality representation. Finally, the combined modality representation fusion and multi-label classification module are used to obtain the category classifier prediction. In the underwater video multi-label classification dataset (UVMCD), the effectiveness and high classification accuracy of the proposed BGCLN have been proved by numerous experiments. [ABSTRACT FROM AUTHOR]

Underwater multicell single-layer thin metal plate corner reflectors can't form a relatively stable TS in a large space because of its strong frequency characteristics. To solve the problem, the paper designs the underwater multicell cavity corner reflectors. Then using FEM coupled DBEM solver to simulated its scattering acoustic field in incident wave frequence varies from 5.0 kHz to 15.0 kHz. The results show that the underwater multicell cavity corner reflectors has weak frequency characteristics, obvious decoupling effect and strong scattering ability. Underwater multicell cavity corner reflectors can maintain stable target strength in a large space, and has better reflection ability, so it is an ideal underwater acoustic reflection device. [ABSTRACT FROM AUTHOR]

This review is a comprehensive overview of recent advancements in underwater in situ heavy metal voltammetric analyzers (UIHVAs). It explores various types of in situ voltammetric analyzers, including the voltammetric in situ profiling system, submersible integrated multi-channel trace metal sensing probes, vibrating gold microwire electrode voltammetric analyzers, and electrochemical analyzers designed for on-site flow measurements. It also covers electrochemical sensors based on flexible liquid crystal polymers, deep-sea mercury sensors, and other in situ electrochemical analyzers. This review systematically examines the research and development progress of microelectrode arrays, screen-printed, carbon, bismuth, antimony, and lab-on-a-chip electrodes. The final section looks at key trends in the research and development of voltammetric analyzers, highlighting the exploration of novel working electrodes, the integration of smart monitoring and data analysis technologies, and the promotion of interdisciplinary collaboration and innovation. From a global perspective, in situ heavy metal voltammetric analysis technology has demonstrated significant applicability in various fields, such as environmental monitoring, marine science, and biogeochemistry. This technology holds considerable potential for further development. However, extensive research and continuous improvement are required to improve detection performance. We are convinced that with continued technological advances and dedicated research efforts, these challenges can be overcome and will pave the way for the widespread application of UIHVAs. [ABSTRACT FROM AUTHOR]

The taphonomy and diagenesis of bone and teeth recovered from any environments provide crucial information for forensic sciences and investigations. This leads to the estimation of the postmortem interval (PMI) and the postmortem submersion interval (PMSI) of the organism/s. Aquatic taxa can induce macroscopic and microscopic alterations in biomineralized tissues (e.g., grooves) or can colonize them by attachment (e.g., Bryozoa). Bryozoa are tiny invertebrates that form colonies in freshwater and saltwater. They can survive for years as suspension feeders in all climates. Most marine Bryozoa species have a biomineralized exoskeleton that can be preserved after their death. This research analyzes eight fragments of archeological elephant ivory with a known PMSI of 314 years, which were inhabited by three distinct bryozoan colonies. The variations in the preservation of the bryozoan exoskeletons and the overgrowth of different marine taxa reveal that one colony (lichenoporid cyclostomatid) was alive at the time of the ivory collection from the submerged archeological site while the two other colonies (cheilostomatid) had previously died at different times. The primary objective of this observation is to contribute to the understanding of the taphonomy of terrestrial mammalian biomineralized tissues recovered in marine environments. Additionally, the study discusses the potential forensic implications of this association, such as the evidence of marine submersion and the PMSI. A secondary objective is to present the Bryozoa colonies within a distinctive depositional context, considering that many bryozoan species of the Western Australian coast remain undescribed. The complexity of the Bryozoa ecobiology is also highlighted, with the need of further research (e.g., minimum time for colonization). Finally, this study highlights the urgency of multidisciplinary collaboration to advance aquatic forensic capabilities. [ABSTRACT FROM AUTHOR]

There are eight underwater hotels in the world. Drawing from our on-site observations and reflections, in this paper we discuss how one of them, Singapore's Equarius Hotel, may at first be understood as a heterotopia – a concept coined by Michel Foucault to denote a fully realized utopia. However, we will argue that our original concept of alloútopia (from the Greek alloú, for elsewhere, and topia, for place) is better suited to make sense of the more-than-human dynamics shaping underwater hotel rooms and the human-animal encounters taking place therein. We develop our original concept by drawing from contemporary geographical literature on heterotopias, and more-than-human geographies of aquatic animal encounters. We further outline the usefulness of the concept for a variety of applications across tourist geographies and more-than-human geographies. [ABSTRACT FROM AUTHOR]

We developed an inexpensive light instrument (ILI) and protocol for the measurement of photosynthetically active radiation (PAR) at discrete depths underwater. We tested the accuracy of the ILI against a submersible radiometer (RAD) and a Secchi disk method. The ILI consists of a PAR sensor (HOBO MX2202; Onset) attached to a flat disk that ensures that the sensor faces upwards when lowered through the water column. The flat disk is attached to a rope marked at 1-m increments (to 20 m) that allows for the measurement of PAR at discrete depths. A weight is attached to the bottom of the flat disk to prevent it from drifting. The ILI is much cheaper (US $130), less bulky, and lighter (1.1 kg) than the RAD (US $40,000, weight 9 kg). We tested our method in a mesotrophic lake and in an oligotrophic lake in summer and fall 2023. The correlations between the RAD and ILI measurements of irradiance at depth (as a percentage of surface irradiance), and the depth to which 1% of the PAR at the surface penetrated the water (Z1%PAR), were high and did not significantly differ. There was a difference of 8% in the Z1%PAR determined by the ILI compared with that determined by the RAD. However, the estimated Z1%PAR based on the Secchi disk data was 37% deeper than that calculated with the RAD data. Our method should enable the study of underwater PAR in remote regions where transporting bulky and expensive equipment is impossible due to logistic and/or financial constraints. Moreover, our method can be used for the direct measurement of PAR at discrete depths. [ABSTRACT FROM AUTHOR]

In recent years, the immense potential for MEMS devices in the biomedical industry has been understood. It has been determined that, among their many plausible functions, their use may also extend to single human red blood cell diagnostics, whereby biomarkers of quantifiable magnitudes may be detected. Without a doubt, the mechanical and thermal specifications by which potential devices must be able to function are very strict. Among them is the ability to operate while fully submerged in aqueous solutions. In this work, six devices were modelled numerically in deionised (DI) water and 0.9 wt% NaCl solution, the results of which were validated experimentally. The mechanical performance of the different devices when fully submerged in 0.9 wt% NaCl solution is hereby discussed. With the exception of one, all the devices in their current configuration are confirmed to be suitable candidates for biomedical applications. [ABSTRACT FROM AUTHOR]

In this article, we designed an experimental system for underwater wireless optical communications. A function generation device sent frequencies (1–500 kHz) by amplitude shift key modulation technology, and these frequencies were loaded over light-emitting diode to propagate through a glass water tank with a length of 1 m, width of 40 cm, and height of 30 cm containing clean water of 80 L. These frequencies were received by a photodiode (BPX61), and the received signal was displayed through a digital storage oscilloscope device. Four techniques, single input–single output (SISO), single input–multiple output, multiple input–single output, and multiple input–multiple output (MIMO), were applied under the same optical conditions to know the quality of receiving the optical signal and the difference between them. Finally, the parameter values of signal-to-noise ratio, peak-to-peak voltage, and voltage gain were checked for each technique, and they were the lowest values for the SISO technique and the highest values for the MIMO technique. [ABSTRACT FROM AUTHOR]

Underwater visibility is often very poor due to low contrast and colour distortion due to the absorption and scattering of light in water. Enhancing the quality of these underwater images is crucial for marine researchers and divers, and for applications such as underwater robotics and navigation. However, implementing advanced image enhancement algorithms on resource- constrained devices can be challenging due to limited computational power and memory. This research presents an investigation of traditional image enhancement algorithms - such as gamma cor, Gamma Correction, Histogram Equalization, Contrast Limited Adaptive Histogram Equalization (CLAHE), and Unsupervised Colour Correction Model (UCM) - applied to the Enhancing Underwater Visual Perception (EUVP) dataset and analyzes the feasibility of deploying these algorithms on resource constrained devices such as Raspberry Pi 3 and Raspberry Pi 4, which can be used to build a real-time edge device for underwater workers to enhance their visibility. [ABSTRACT FROM AUTHOR]

BackgroundCrocodiles are semi-aquatic animals well adapted to hear both on land and under water. Currently, there is limited information on how their amphibious hearing is accomplished. Here, we describe, for the first time, the ear anatomy in the living crocodile using photon-counting detector computed tomography (PCD-CT) and 3D rendering. We speculate on how crocodiles, despite their closed ear canals, can use tympanic hearing in water that also provides directional hearing.Material and MethodsA Cuban crocodile (Crocodylus rhombifer) underwent photon-counting detector computed tomography (PCD-CT), under anesthesia and spontaneous respiration. In addition two seven-month-old C. rhombifer and a juvenile Morelet´s crocodile (Crocodylus moreletii) underwent micro-computed tomography (µCT) and endoscopy. One adult Cuviérs dwarf caiman (Paleosuchus palpebrosus) was micro-dissected and video-recorded. Aeration, earflap, and middle ear morphology were evaluated and compared after 3D modeling.Results and DiscussionPCD-CT and µCT with 3D rendering and segmentation demonstrated the anatomy of the external and middle ears with high resolution in both living and expired crocodiles. Based on the findings and comparative examinations, we suggest that the superior earflap, by modulating the meatal recess together with local bone conduction, may implement tympanic hearing in submerged crocodiles, including directional hearing.

In base-station-based underwater wireless acoustic networks (B-UWANs), effective handover mechanisms are necessary to ensure seamless data services for mobile nodes such as autonomous underwater vehicles (AUVs). Unlike terrestrial base stations (BSs), moored buoy BSs in B-UWANs experience motion responses due to wave loads under environmental conditions, posing unique challenges to the handover process. This study examines how BS motion affects handover decision errors, which arise when AUVs incorrectly initiate handovers to unintended BSs due to BS motion. By utilizing the AUV–BS distance as a handover triggering parameter, our analysis reveals a significant increase in decision errors within the overlapping regions when both the current and target BSs are in motion, especially when moving in the same direction. In addition, these errors intensify with the magnitude of BS motion and are exacerbated by smaller BS network radii. Based on these simulation results, we present an analytical framework that not only measures the influence of BS motion on the AUV–BS distance but also provides strategic insights for refining underwater handover protocols, thereby enhancing operational reliability and service continuity in B-UWANs. [ABSTRACT FROM AUTHOR]

Assessment of compressive strength is crucial for ensuring the safety of concrete structures. However, existing works mainly focus on wet concrete rather than fully saturated concrete underwater and neglect the influences of mix parameters. To this end, this study develops a testing system to measure ultrasonic waves underwater and investigates the influence of water-cement (W/C) ratio (ranging from 0.35 to 0.54), sand-aggregate (S/A) ratio (ranging from 0.57 to 0.87), and average diameter (Da) of coarse aggregate (ranging from 7.5 to 17.44) on the relationships between compressive strength and the velocities of pressure (P) and Rayleigh (R) waves. Ultrasonic and destructive experiments are performed on 96 concrete blocks with 32 mix parameters. The W/C and S/A ratios have a more significant influence on the relationship than the Da. Therefore, a set of formulas is developed to assess compressive strength based on the velocity of P and R waves considering the influence of W/C and S/A ratios. The developed formulas improve the accuracy by 32% to 57% compared to existing formulas, guiding the assessment of underwater infrastructures. [ABSTRACT FROM AUTHOR]

The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) has been researched in both fiber and atmospheric channels. However, the wavelength attack may also pose a threat to the case of ocean turbulent channels, which are vital for the secure communication of both ocean sensor networks and submarines. In this work, we propose two wavelength attack schemes on underwater discrete modulated (DM) CV-QKD protocol, which is effective for the case with and without local oscillator (LO) intensity monitor, respectively. In terms of the transmittance properties of the fused biconical taper (FBT) BS, two sets of wavelengths are determined for Eve's pulse manipulation, which are all located in the so-called blue–green band. The derived successful criterion shows that both attack schemes can control the estimated excess noise of Alice and Bob close to zero by selecting the corresponding condition parameters based on channel transmittance. Additionally, our numerical analysis shows that Eve can steal more bits when the wavelength attack controls the value of the estimated excess noise closer to zero. [ABSTRACT FROM AUTHOR]

Answering Huijbens and Jóhannesson's call to investigate tourist destination development through a relational ontology marked by a vital materialism, this paper focuses on the creation of the Muraka. The Muraka is the underwater villa of the Conrad Maldives Rangali Island—an ultra-luxury resort located in Alifu Dhaalu Atoll. No social scientific research has ever been conducted at underwater hotels. Drawing upon fieldwork at the Muraka—part of a broader project on three underwater hotels (conducted in Singapore, Tanzania, and the Maldives), we aim to contribute original knowledge to more-than-human geographies and tourist studies by bringing attention to the architectural relations that entangle underwater hotels with their environments. In doing so we become attuned to more-than-human lives and create narratives that can help us imagine new relations with the planet both within and beyond the realm of tourist encounters. By focusing in particular on the creation of the Muraka through the lens of the original concept of alloutopia, we contribute to non-representational and more-than-human perspectives on tourism [ABSTRACT FROM AUTHOR]

The current scallop fishery sector allows many scallops to remain in specified fishing zones, and this process leads to heavy losses in the sector. Scallop fishermen aim to harvest the remaining scallops to reduce their losses. To achieve this, a fisherman must understand the scallop ecology on the seafloor. In our previous study, we proposed a method for measuring scallops using wheeled robots. However, a wheeled robot must be able to resist disturbance from the sea to achieve high measurement accuracy. Strong anchoring of wheels against the seafloor is necessary to resist disturbance. To better understand anchoring performance, we confirmed the wheel anchoring capacity in water-containing sand in an experiment. In this experiment, we towed fixed wheels on water-containing sand and measured the resistance force acting between the wheel and the sand. Afterward, we considered the resistance force as the wheel anchoring capacity on the water-containing sand. The experimental results capture the tendency for the anchoring capacity of sand with/without water to increase with sinkage. The results also demonstrate that the anchoring capacity of water-containing sand is lower than that of non-water-containing sand. However, the results indicate that when the wheels possess lugs, their presence tends to increase the wheels' anchoring capacity in water. [ABSTRACT FROM AUTHOR]

The purpose of the present study was twofold: (i) to compare the kinematic characteristics of individual and relay swimming starts; and (ii) to relate the kinematic variables to 5 m performance for both starts. Twelve elite-level swimmers performed 2 × 25 m at maximal effort (one with an individual and one with a relay start randomly). Two-dimensional direct linear transformation algorithms were used to calculate swimmers' centre of mass (CM) kinematics during each subphase. The results indicated moderate to much faster 5 m, 10 m 15 and 15 m times (29.4, 10.7 and 6.5%) for relay than individual starts as well as the differences at specific parameters, but no differences in take-off horizontal velocity between start techniques. Large correlations to performance times were found in block time, horizontal take-off velocity, take-off velocity and entry angle (r = 0.77 to 0.83) 20 for individual start, but in changeover time, take-off height and entry distance (r = 0.69 to 0.90) for relay start. Differences on swim start regulations between individual and relay events were in line with different key parameters related to start performances in each event. This should be considered by swimmers and coaches when addressing the starting improvement. [ABSTRACT FROM AUTHOR]

This article relies on an ethnography of commercial divers that involves the author's training, certification, and activity underwater to propose an ecofeminist analysis of the undersea (furthermore with the undersea). It presents how feminist environmental theory engages with the ethnographic method of immersion and how underwater fieldwork grounded in feminist theory contributes, in turn, to reflections on the role of embodiment in the production of ethnographic knowledge. This article emphasizes the role of experiencing risky situations (gender-based violence and life-threatening situations) in the research process to address the reproduction of masculinity that is part of the commercial diving training supported by the profession's equipment and technologies. By doing so, the article unveils how participating in underwater activities as part of fieldwork raises issues for feminist ethics, especially regarding multispecies relationality. Overcoming these ethical limits and reconciling ecofeminism and ethnography in the study of underwater ecologies can, as the article concludes, rely on creative methods. [ABSTRACT FROM AUTHOR]

With their unique capability to deal with a considerable geographic area, satellite–ground–underwater optical wireless communication (OWC) systems are an appealing alternative to meet the ever-increasing demand for end-to-end broadband services. Using four different Laguerre–Gaussian (LG) modes, an orbital angular momentum (OAM) multiplexing method was developed to enhance the spectral efficiency and system capacity of the satellite–ground–underwater OWC system. At an aggregate throughput of 160 Gbps, LG[0,0], LG[0,2], LG[0,4], and LG[0,8] were realized. Various atmospheric conditions, water types, and scintillation effects were used to evaluate the performance of two separate OWC links for satellite-to-ground and ground-to-underwater communication. A maximum OWC range of 21,500–30,000 km has been obtained under weak-to-strong turbulence for satellite-to-ground scenarios, and a range of 12–27 m underwater for ground-to-underwater scenarios under various scintillation effects. At LG[0,0], in pure sea, the maximum gain is −75.02 dB, the noise figure is 75.02 dB, the output signal is −78.32 dBm, and the signal-to-noise ratio is 21.67 dB. In comparison with other works in the literature, this system shows a superior performance. [ABSTRACT FROM AUTHOR]