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The present study experimentally investigates the onset of ventilation of surface-piercing hydrofoils. Under steady-state conditions, the depth-based Froude number $\textit{Fr}$ and the angle of attack $\alpha$ define regions in which distinct flow regimes are either locally or globally stable. To map the boundary between these stability regions, the parameter space $(\alpha , \textit{Fr})$ was systematically surveyed by increasing $\alpha$ until the onset of ventilation while maintaining a constant $\textit{Fr}$. Two simplified model hydrofoils were examined: a semi-ogive with a blunt trailing edge and a modified NACA 0010-34. Tests were conducted in a towing tank under quasi-steady-state conditions for aspect ratios of $1.0$ and $1.5$, and for $\textit{Fr}$ ranging from $0.5$ to $2.5$. Ventilation occurred spontaneously for all test conditions as $\alpha$ increased. Three distinct trigger mechanisms were identified: nose, tail and base ventilation. Nose ventilation is prevalent at $\textit{Fr} \lt 1.0$ and $\textit{Fr} \lt 1.25$ for aspect ratios of $1.0$ and $1.5$, respectively, and is associated with an increase in the inception angle of attack. Tail ventilation becomes prevalent at higher $\textit{Fr}$, and the inception angle of attack exhibits a negative trend. Base ventilation was only observed for the semi-ogive profile, but it did not lead to the development of a stable ventilated cavity. Notably, the measurements indicate that the boundary between bistable and globally stable regions is not uniform and extends to significantly higher $\alpha$ than previously estimated. A revised stability map is proposed to reconcile previously published and current data, demonstrating how two alternative paths to a steady-state condition can lead to different flow regimes.
A low-density jet is known to exhibit global self-excited axisymmetric oscillations at a discrete natural frequency. This global mode manifests as large-scale periodic vortex ring structures in the near field. We experimentally investigate the effectiveness of axial and transverse forcing in controlling such global vortical structures. We apply acoustic forcing at a frequency ($f_{\!f}$) around the natural global frequency of the jet ($f_n$) leading up to and beyond lock-in. Using time-resolved stereoscopic particle image velocimetry, we find that the jet synchronises to $f_{\!f}$ when forced sufficiently strongly. When forced purely axially, the jet exhibits in-phase roll-up of the shear layers, producing axisymmetric vortex ring structures. When forced purely transversely, the jet exhibits anti-phase roll-up of the shear layers, producing tilted vortex ring structures. We find that the former produces relatively strong oscillations, while the latter produces oscillations that are even weaker than those of the unforced case due to asynchronous quenching. We show that the transverse forcing breaks the jet axisymmetry by altering the topology of the coherent structures in the near field, leading to global instability suppression. We also find that the wavelength of the applied forcing has a notable influence on the evolution of vortical structures, thereby modifying the forced response of the jet. The efficacy of transverse forcing and the influence of the forcing wavelength in suppressing the global mode of a self-excited low-density jet present new possibilities for the open-loop control of a variety of globally unstable flows.
Deception Island is an active, caldera-forming volcano whose surveillance is critically constrained by its extreme Antarctic isolation, scarce resources and limited seasonal human access. This study addresses these challenges by presenting an innovative Global Navigation Satellite Systems (GNSS) geodetic surveillance framework specifically adapted for such a remote environment. Our approach establishes a key operational distinction between non-real-time monitoring and near-real-time surveillance via a semi-continuous wireless network. We effectively resolve the inherent trade-off between promptness and precision by applying signal enhancement methods (e.g. Kalman filtering) to maintain millimetric accuracy in deformation detection, even when utilizing the high sampling rates (1 Hz) essential for rapid assessment. The resulting model allows for the rigorous isolation of the local volcanic signal from the complex regional tectonic kinematics. Crucially, data analysis reveals recurrent 3 year cycles of inflation and deflation in the magmatic system, strongly correlated with seismicity, which validates ground deformation as a reliable volcanic precursor. The primary practical advance is the validation of a dual-term hazard forecasting system: 1) mid-term (months) forecasts based on long-term time-series analysis to facilitate safe inter-campaign operations and 2) short-term (days) forecasting during periods of unrest using ground displacement acceleration, complemented by a magma injection model to predict the spatial location of potential vent openings. This validated and technologically adjusted framework provides an optimized and transferable template for continuous geodetic surveillance in other isolated, active polar volcanoes.
The cell body of flagellated microalgae is commonly considered to act merely as a passive load during swimming, and a larger body size would simply reduce the speed. In this work, we use numerical simulations based on a boundary element method to investigate the effect of body–flagella hydrodynamic interactions (HIs) on the swimming performance of the biflagellate Chlamydomonas reinhardtii. We find that body–flagella HIs significantly enhance swimming speed and efficiency. As body size increases, the competition between the enhanced HIs and the increased viscous drag leads to an optimal body size for swimming. Based on the simplified three-sphere model, we further demonstrate that the enhancement by body–flagella HIs arises from an effective non-reciprocity: the body affects the flagella more strongly during the power stroke, while the flagella affect the body more strongly during the recovery stroke. Our results have implications for both microalgal swimming and laboratory designs of biohybrid microrobots.
Blastoids have three primary systems providing entrances to blastoid hydrospires, the primary organ for respiration: (1) exposed hydrospire slits formed across the width of the radiodeltoid suture; (2) hydrospire pores formed at the aboral ends of the ambulacra; and (3) hydrospire tubules formed as invaginations along the radiodeltoid suture, becoming openings that pierce the radials and deltoids ontogenetically. Blastoid classification historically divided the blastoids into two groups—the Fissiculata and Spiraculata. The Fissiculata comprised those blastoids that have exposed hydrospire slits or spiracular slits. The Spiraculata had hydrospire pores and spiracles that connect internally to hydrospires. Spiraculate classification focused on the configuration of the spiracles and anispiracle in combination with thecal form. Spiracles are the adoral consequence of the ambulacra infilling the radial sinus and covering the hydrospires by the lancet and the side plates and are found in all spiraculate blastoids. In this revision of blastoid classification, we place primacy on the three mechanisms by which water is drawn into the hydrospires—hydrospire slits open to seawater, hydrospire pores, and hydrospire tubules. Hydrospire tubules are formed along the radiodeltoid suture, a very different ontogenetic position from hydrospire pores, which are formed at the aboral end of the ambulacrum, and a fundamental phylogenetic difference. We herein abandon the term Spiraculata and refer to the spiraculate grade as being the Stomatoblastida, new superorder for spiraculates with hydrospire pores and the Tubuloblastida, new superorder for spiraculates with hydrospire tubules. The Fissiculata is elevated to superordinal status.
In the present study, we introduce a new temperature transformation for compressible turbulent boundary layers with adiabatic and isothermal walls. Unlike existing transformations that rely on a single invariant function for the non-dimensional temperature gradient across the entire inner layer, a composite transformation strategy is proposed by leveraging two newly proposed Mach-number and wall-temperature invariant functions for the mean temperature field. This approach not only deploys appropriate Mach-number invariant functions in the viscous sublayer and the logarithmic region, but also introduces an improved solution to the long-standing singularity challenge inherent in single invariant function models. The performance of this composite transformation is verified by extensive direct numerical simulation (DNS) datasets (26 cases) of compressible turbulent boundary-layer flows. The results demonstrate that the proposed transformation maps the mean temperature profiles to the incompressible reference without case-specific parameter tuning, exhibiting significantly reduced scatter when compared with the existing temperature transformations.
An important question in evolutionary biology and macroecology is whether taxa show systematic trajectories in occupancy, the proportion of geographic area occupied, over macroevolutionary timescales. Past studies have used fossils to document these trajectories, showing a symmetric rise and fall. In this study, I focus on several biases in the analyses of fossil occupancy trajectories that have been unaccounted for. First, better sampling of boundary bins in a taxon’s stratigraphic range, paradoxically, results in lower mean occupancy of taxa in those bins. This is because better sampling allowed more taxa with low occupancies to be included in the mean occupancies of those bins compared with intermediate bins. Second, the possibility that taxa may have incomplete durations within boundary bins could also lower occupancies in those bins. Finally, a bias can also exist when the number of sampled sites is not constant throughout a taxon’s stratigraphic range. I use simulations to show that the first bias can be corrected by conditioning these boundary bins to be sampled in the same way as intermediate bins. To mitigate the second bias, I use higher-resolution time bins to constrain the intervals over which taxa’s occupancies are measured so that they are comparable between boundary and intermediate time bins. I also present an approach that can correct for the last bias by subsampling geographic sites, testing its impact in a simulation. Considering these factors, the occupancy trajectories of marine animal genera look to be a relatively gradual rise post-origination with a sudden decline before extinction.
The Antarctic Peninsula is one of the regions in Antarctica that has experienced notable and extensively studied warming since the mid-twentieth century. Meteorological data, although limited and mostly dating back to the International Geophysical Year (1957–1958), reveal dramatic climate changes in both the Antarctic Peninsula and West Antarctica, with the Antarctic Peninsula showing the highest warming trends on the continent. One major manifestation of this warming is the increasing frequency and intensity of extreme warm events. This study utilizes temperature data from the Artigas Antarctic Scientific Base provided by National Weather Service, Uruguayan Institute of Meteorology (INUMET), which have not previously been used or quality-controlled. Data were processed and analysed, and a quality hourly database was built for the period 1 January 1998 to 11 December 2016 for the surface temperature, constructing a complete time series interpolating the data with two other nearby Antarctic stations (C.M.A. Eduardo Frei Montalva and King Sejong). Temperature presented an annual cycle with marked interannual and seasonal variability, with the cold season being the one with the highest variability and the largest anomalies, both positive and negative. No significant trend was found for the monthly mean temperature. A study of warm temperature events was conducted at three points on King George Island, defining warm events and extreme warm events as those in which the mean daily temperature was above the 90th and 99th percentile, respectively, for at least 3 consecutive days. A high frequency of occurrence was found (all years except 2015) mostly in the cold season of the year, and with large interannual variability. In turn, it was found that certain atmospheric dynamics favour the generation of these extreme warm events, and that their occurrence is higher during La Niña years. Although the majority of the extreme warm events occurred during positive phases of the Southern Annular Mode, the statistical correlations were not significant.
Over the past half century, paleobiologists have advanced the estimation of phylogenetic relationships among fossil taxa to explore evolutionary patterns in deep time. This study employs a breadth of phylogenetic analyses, specifically divergence time estimations and character rate evolution, within three blastozoan echinoderm clades: Diploporita, Eublastoidea, and Paracrinoidea. Utilizing reversible jump Markov chain Monte Carlo (rjMCMC) and fossilized birth–death (FBD) models, we investigated evolutionary rates through anatomical subunit partitioning. Results suggest similar rates among the three groups, although Paracrinoidea exhibits elevated rates in several anatomical subunits. The inferred trees largely agree with other recently published analyses, in that the current taxonomy of the group does not reflect true evolutionary relationships. Thus, this study adds to a growing body of literature that highlights the need to revise echinoderm taxonomy. We tested different clock models for each group and found that model choice had strong effects on resulting trees; our findings suggest linked clocks (i.e., the same clocks for all character partitions) had more support than unlinked clocks (i.e., different clocks for different character partitions). These findings indicate a need to carefully consider model choice and rates of evolution when utilizing these types of analyses.
Garnet-bearing silicic volcanic rocks are rare in fossil orogens and usually record a transient stage from regional compression to extension. This study reports newly identified 839 ± 3 Ma garnet-bearing dacitic volcanic rocks associated with the Fuchuan ophiolite complex (FOC) in the eastern Jiangnan Orogen (JO), Southeast China. The presence of these unusual rocks provides new constraints on the late Neoproterozoic tectonic evolution of the orogen.
The garnet-bearing dacitic volcanic rocks of the garnets are weakly peraluminous and exhibit trace element and Nd isotopic signatures similar to those of post-orogenic, strongly peraluminous granites in the eastern JO, indicating a similar crustal source. The garnets are almandine-rich (76–79 wt%) and characterized by low CaO (<2.5 wt%), MnO (<2.6 wt%) and TiO2 (<0.1 wt%), consistent with garnets in peraluminous S-type volcanic rocks globally. Integrated petrological, geochemical and zircon Hf isotopic evidence indicates that the primary magma originated from partial melting of a heterogeneous lower-crustal source, comprising both juvenile basaltic and ancient pelitic components. High zircon saturation temperatures (>900°C) further imply the heating of coeval underplating mantle-derived mafic magma, analogous to the mechanism forming ‘hot granites’.
Integrating our findings with regional geology, we propose that the garnet-bearing dacitic volcanic rocks associated with the FOC formed in an ensialic back-arc basin along the southeastern margin of the Yangtze Craton. The occurrence of the garnet-bearing magmatism records the onset of back-arc extension, likely following the ∼880–860 Ma arc–continent collision and subsequent subduction polarity reversal.
We evaluate the systematic position of Shundeagrion cheni Huang, Lia, and Nel, 2024 and transfer it to the odonate suborder Cephalozygoptera and family Dysagrionidae.
This study conducted theoretical analysis and direct numerical simulations (DNS) of vertical natural convection in a two-dimensional cavity filled with porous media, where the imposed temperature gradient is oriented perpendicular to the direction of gravity. Three regimes characterised by distinct flow states and the angle $\theta$ of the isothermal layer are identified. In the steady regime I with $\theta \approx \pi /2$, the flow is weak and heat transfer is dominated by conduction. In the transitional regime II with rapidly increasing $\theta$, kinetic and thermal boundary layers gradually develop. In the turbulent regime III with $\theta \approx 0$, clear boundary layers arise and turbulent thermal convection prevails. Corresponding to these flow states, theoretical analysis is performed to derive the scaling laws of the Nusselt number $\textit{Nu}-1\sim Ra_{D}^{\gamma _1 }\textit{Pr}^{\eta _1}$ and Reynolds number $\textit{Re}\sim Ra_{D}^{\gamma _2 }\textit{Pr}^{\eta _2}$ with respect to Rayleigh–Darcy number $Ra_D$ and Prandtl number $\textit{Pr}$. We derive $(\gamma _1,\gamma _2,\eta _1,\eta _2)=(2,1,0,-1)$ for the steady regime and $(1/3,4/9,0,-2/3)$ for the turbulent regime. All theoretical scaling exponents in these two regimes are validated by DNS results. Furthermore, we find that the influence of the Darcy number $Da$ becomes almost negligible when it is sufficiently small. Unified models for $\textit{Pr}=1$ are proposed to integrate the three regimes and are applicable across a broad range of $\phi$ and $Ra_D$, which are satisfactorily verified by DNS results. The unified models provide a predictive framework for heat transport and flow intensity in porous-medium thermal convection, thereby offering practical values for thermal engineering applications.
Studying social behaviour of mobile and cryptic marine mammals is challenging, particularly for small species like harbour porpoises whom in many areas tend to be challenging to initially spot and then gain repeated observations. Recently, there has been a rise in the number of observations of harbour porpoises occurring in atypical group sizes that are larger than the typical size of two to three individuals. This behaviour, in conjunction with the evolving availability and usability of Unmanned Aerial Vehicle (UAV) technology, is supporting and improving the capture of information on social behaviours. Around Shetland, Scotland, harbour porpoises are sighted from land via opportunistic and systematic surveys year-round with atypical group sizes also observed. To capture information on group size, opportunistic and systematically collected UAV footage were collated and analysed. This revealed sexual approach behaviours in typical group sizes of small groups (two to four individuals), as well as atypical group sizes of medium groups (five to nine individuals), large groups (10 to 19 individuals), and aggregations (≥20 individuals) occur in multiple bays around Shetland. This is the first insight into group sizes and behaviours for the region which was recently designated as an Important Marine Mammal Area (IMMA). Further insight into these social behaviours and group size (e.g. seasonality, site fidelity) could aid harbour porpoise conservation and management within the IMMA and elsewhere.
The suitability of marine limpet shells for radiocarbon dating may depend on potential offsets due to diet and habitat, especially with regard to grazing mollusks on carbonate substrates (Dye 1994; England et al. 2013). A previous study on one grazing limpet species on the coast of Ireland found no offsets from carbonate substrates (Allen et al. 2019), but a similar study from mediterranean coasts found significant offsets on carbonate substrates (Ferguson et al. 2011). We carried out a new study of radiocarbon and stable carbon isotopes, using multiple species of mollusks collected live from the coasts of Gibraltar and Sardinia, from both carbonate and non-carbonate substrates. The 14C results indicate that one species, inhabiting the upper shore, has a significant offset at the carbonate locations. This species, Patella rustica, has adapted to tolerate desiccation and may have biological traits that result in higher metabolic-derived carbon incorporated in its shell. The results of this preliminary study imply that selected species of grazing mollusks are suitable for radiocarbon dating, even in areas of carbonate geology.
Radiocarbon dating by accelerator mass spectrometry (AMS) requires transforming samples into graphite, a step that typically depends on liquid nitrogen and high-purity carrier gases, increasing both cost and operational complexity. We present μGRAPHILINE, a fully automated, modular combustion–graphitization line that removes these dependencies by combining dual-zone combustion with iron–zinc reduction. Performance was evaluated on more than 180 standards and reference materials targets measured on two independent AMS systems. The μGRAPHILINE consistently achieved >90% graphitization yields, stable backgrounds of ∼0.24 pMC (≈48,500 BP), and sample throughput of ∼3.5 hours per target. Reliable operation was demonstrated for a broad sample-size range, from routine 1 mg C down to ∼0.2 mg C, with ion currents sufficient for precise AMS analysis. The system’s automation, modularity, and low memory effect support improved laboratory throughput and operator efficiency. These results indicate that μGRAPHILINE provides a robust and efficient approach to radiocarbon sample preparation with broad potential applications.