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Identifying the causative agents of modified bone surfaces can be challenging, particularly in terrestrial systems where numerous biotic and abiotic factors can produce grooves, divots, and striae. This contribution focusses on fossil vertebrates in the Làng Tráng cave system in Vietnam, which preserves a diverse assemblage of middle Pleistocene mammals, and discusses criteria that can identify the agents responsible for the accumulation and degradation of the fossil accumulation. The Làng Tráng assemblage includes some postcranial elements and rare mandibles and skulls, but is dominated by isolated teeth and bones, particularly those of mid-sized (7–250 kg body weight) mammals. Rare long bone shafts exhibit grooves with U-shaped profiles attributable to the ichnotaxon Machichnus bohemicus. In contrast, flat-bottomed grooves attributable to M. multilineatus are exceptionally abundant. The size and shape of these traces are consistent with gnawing by moderate-sized to porcupines such as Atherurus macrourus and Hystrix kiangsenensis, both of which are represented in the Làng Tráng fauna. Porcupines are common contributors to cave faunas in Southeast Asia. The roots of most teeth exhibit moderate to severe biogenic modification, which resulted in common planar facets in some cases and reduction of the root bone to pyramidal wedges in others. The Làng Tráng cave system is unusual in that porcupines did not just contribute to the fauna; they were the dominant taphonomic factor in the accumulation and subsequent biogenic alteration/degradation of bone in these caves. Faceted and wedged roots are herein proposed as diagnostic attributes of porcupine-generated vertebrate bone accumulations.
Solid atmospheric particles, such as ice crystals, pollen, dust, ash and microplastics, strongly influence Earth’s climate, ecosystems and air quality. Previous studies have typically relied on analytical models valid only for very small particles or experiments in liquids, where the particle-to-fluid density ratio $R$ is much lower than values encountered in the atmosphere. We combine a novel experimental set-up with particle-resolved direct numerical simulations to study the settling of sub-millimetre ellipsoids in still air. Particle shapes span elongation and flatness values $ 0.2 \leqslant {\textit{EL}}, {\textit{FL}} \leqslant 1.0$ at a density ratio $ R = 1000$ and particle Reynolds numbers $ 2.1 \lt {\textit{Re}}_{\!p} \lt 4.5$, a regime well below the onset of wake-induced instabilities. Nonetheless, we observe unexpectedly rich dynamics: all non-spherical particles exhibit damped oscillatory motion, and some triaxial ellipsoids follow fully three-dimensional, non-planar trajectories due to rotation about all three axes. Simulations at lower density ratios ($ R = 10, 100$) confirm that these behaviours are driven by strong lateral forces happening only at $R=1000$. Key settling characteristics exhibit nonlinear and non-trivial dependencies on shape. In the two-dimensional phase space of elongation and flatness, settling velocity is symmetric about the principal diagonal ($ {\textit{EL}} = {\textit{FL}}$), while oscillation frequency and damping rate show symmetry about the anti-diagonal. Flatness strongly influences pressure drag, while elongation governs lateral drift and swept volume, which can reach up to ten times the particle diameter and four times the volume-equivalent sphere, respectively.
The right to roam – balancing inclusion and enclosure. In Norway, the right to roam is an old custom – a right to traverse and gather berries, herbs and firewood on uncultivated lands – dating back to the Viking Age. In 1957, this right was included in Norwegian laws, in the Outdoor Life Act (Friluftslova). The law transformed agrarian lands into areas for outdoor life and recreation, primarily walking and hiking. However, due to modernisation, the activities performed today are very different than those in the 1950s, involving many sorts of technical devices and installations, commercial activities and a different landscape. The law was a manifestation of the Norwegian outfields as a commons, but what is a commons for some can be an enclosure for others. This is the topic of this article: how the right to roam includes many and much but represents encroachment, displacements and enclosures and has created crowding, natural wear and tear and urges for management regimes. The article describes this as a balance between inclusion and enclosure. The article has two major parts: one presenting the academic discussion about inclusion and enclosure, the other discussing the implementation of the principle in Norway in light of this theory.
Magnetic susceptibility variations in loess–paleosol successions are widely utilized proxy records for reconstructions of global climate change during the Pleistocene. Analysis of the role of local factors in the establishment of magnetic signatures is rarely addressed. This study compares magnetic records along several adjacent profiles exposed in three open quarries near Kaolinovo (NE Bulgaria). The effect of the position of the sampled locations in the local landscape on the magnetic enhancement is revealed by differences in the thickness and degree of pedogenic magnetic enhancement. The profile, situated in a local paleo-depression, revealed disturbed sedimentation and depletion in the magnetic susceptibility. At lateral distances of 2–3 km (between quarries) the magnetic records show firmly repeatable patterns. Magnetic, geochemical, and diffuse reflectance data demonstrate a trend of increasing content of pedogenic hematites towards older paleosols, while goethite has major contribution to dithionite extractable iron phases. A representative stacked record of magnetic susceptibility for the Kaolinovo site is established using the results from mineralogical analyses. Comparison of the stacked susceptibility record from Kaolinovo with other sites from Bulgaria reveal that loess–paleosol sequences preserve reliable and repeatable magnetic records of global climate change for the last three glacial–interglacial cycles.
We investigate the energetics of mixing induced by a continuously supplied dense current (density $\rho _0$) propagating beneath a lighter ambient fluid (density $\rho _a$) along a horizontal rigid boundary within a rectangular domain. The flow fields are computed using direct numerical simulations (DNS) performed with the Nek5000 spectral element solver. Mixing is quantified through the temporal evolution of the background potential energy, which exhibits a linear increase over time. This linear trend enables the definition of a dimensionless mixing parameter $\gamma$, representing the rate of background potential energy growth. The value of $\gamma$ depends on the initial density contrast for a fixed volumetric discharge at the source, characterised by the dimensionless source Froude number. The results reveal a non-monotonic dependence of $\gamma$ on the source Froude number, highlighting a complex interaction between flow forcing and mixing efficiency. We find that, under the assumption of uniform mixing along the current’s length, a fraction $\gamma /2$ of the total supplied energy is invested in mixing along a horizontal distance equal to the height of the inlet.
Carbon-14 (14C) is an important contributor to the collective effective dose to the public due to releases from nuclear power plants (NPPs). In Sweden, only airborne emissions of 14C from NPPs are currently routinely monitored, and the existing data on waterborne 14C discharges are limited. A recent study of 14C in brown algae (Fucus spp.) in Swedish coastal waters showed higher F14C values collected at Ringhals NPP, on the Swedish west coast, than expected. Therefore, this study aimed at assessing if blue mussels (Mytilus edulis) could be used to retrospectively estimate the 14C concentration of dissolved inorganic carbon (DIC) in seawater at three sites. A method was developed to extract the fibrous layer that forms visible annual structures in the shells. All samples were analyzed with accelerator mass spectrometry and the results compared with 14C data from Fucus spp. For one of the analyzed shells (structures from 1974–1978), from the site Särdal, F14C in Fucus spp. and M. edulis agreed very well. For another shell (1972–1978), shell structures from some of the earlier years displayed up to 6% lower F14C than Fucus spp. F14C in one shell from a remote site, Båteviken, only had small annual variations (2017–2022: F14C = 1.070 ± 0.015 (1 σ)). Two shells from Ringhals NPP had higher average F14C, and a significant temporal variability (2014–2022: F14C = 1.427 ± 0.268 (1 σ)). Difficulties in unambiguous identification of the annual structures in the shells, as well as the future potential of this method, are discussed.
The present article investigates the stability of Rayleigh–Bénard convection in a composite system consisting of a horizontal fluid layer overlying a fluid-saturated Darcy porous layer subjected to a time-periodic temperature distribution. The bottom surface is heated periodically with time, whereas a Biot number-dependent thermal boundary condition represents the heat transfer at the upper surface. The Beavers–Joseph–Saffman–Jones condition describes the ‘slip’ at the interface of the domains, and the Lions interface condition governs the normal force balance, incorporating a dynamic pressure term. The Chebyshev tau method and Fourier analysis are utilised to obtain linear instability bounds, which are compared with strong global and asymptotic limits derived from the nonlinear analysis using the energy method. Four deliberately chosen configurations of superposed fluid- and porous-layer systems are investigated. Two configurations validate the analysis through the limiting cases of the classical Darcy–Bénard and Rayleigh–Bénard systems obtained by setting the fluid-to-porous depth ratio $(\hat {d})$ to zero and infinity, respectively. The other two configurations involve layers with equal depths $(\hat {d} =1)$ and a shallow fluid layer overlying a porous layer $(\hat {d} \sim 0.1)$. For these cases, modulation substantially influences the onset of convection. In the last case, the linear theory points out that modulation parameters can control the dominant convective mode (fluid/porous). Furthermore, unlike the previously reported studies, the nonlinear stability bounds are found to be significantly lower than the linear instability bounds, indicating the possibility of subcritical instabilities in the presence of modulation. The region of subcritical instabilities increases with modulation amplitude.
Some arboreal monocotyledons, such as the dragon trees (Dracaena sp.), can develop impressive trunks (>5 m perimeter) through a lateral meristem, but their ages are difficult to determine. We report here a series of calibrated radiocarbon (14C) dates obtained from a stem section of Dracaena draco (L.) L. subsp. draco growing on the island of Tenerife, Canary Islands, Spain. This radial section, about 40 cm long, was cut on October 18, 2023, from a large (∼60 cm diameter) branch that had fallen off the main stem of a privately owned dragon tree. In order to apply 14C calibration, and given the lack of clearly defined growth layers, we collected 33 sequential samples at ∼1-cm intervals along this radial section. A first attempt at wiggle-matching resulted in a calibrated dating of ∼1787 CE for the innermost sample. Because we only knew the spatial distance, but not the time interval, between 14C dates, we further applied calibration tools commonly used for sedimentary sequences. The Poisson-process deposition model in the software OxCal resulted in a calibrated age for the innermost sample of 1776–1798 CE (2σ). The classic and Bayesian age-depth deposition models available as R packages dated the innermost sample to, respectively, 1775–1862 and 1768–1813 CE. Because the branch was at a height of ∼3 m from the ground, and its section did not reach the pith, our results suggest that this dragon tree was ∼300 years old in 2023.
Supersonic jets impinging on a ground plane produce a highly unsteady jet shear layer, often resulting in extremely high noise level. The widely accepted mechanism for this jet resonance involves a feedback loop consisting of downstream-travelling coherent structures and upstream-propagating acoustic waves. Despite the importance of coherent structures, often referred to as disturbances, that travel downstream, a comprehensive discussion on the disturbance convection velocity has been limited due to the challenges posed by non-intrusive measurement requirements. To determine the convection velocity of disturbances in the jet shear layer, a high-speed schlieren flow visualisation is carried out, and phase-averaged wave diagrams are constructed from the image sets. The experiments are conducted using a Mach 1.5 jet under various nozzle pressure ratios and across a range of impingement distances. A parametric analysis is performed to examine the influence of nozzle pressure ratio on the convection velocity and phase lead/lag at specific impingement distances. The results reveal that impingement tonal frequency is nearly independent of the disturbance convection velocity, except in cases of staging behaviour. They also demonstrated that slower downstream convection velocity of the disturbance corresponds to larger coherent structures, resulting in increased noise levels. Based on the observation of acoustic standing waves, an acoustic speed-based frequency model has been proposed. With the help of the allowable frequency range calculated from the vortex-sheet model, this model can provide a good approximation for the majority of axisymmetric impingement tonal frequencies.
One-degree-of-freedom flow-induced vibration (FIV) and energy harvesting through FIV of an elastically mounted circular cylinder with mechanically coupled rotation were investigated numerically for low Reynolds number 100, mass ratio 8 and a wide range of reduced velocities. The aims of this study are to investigate the effect of the flow direction angle $\beta$ on the vibration and energy harvesting through FIV. Two types of lock-in are found: vortex-induced vibration (VIV) and galloping. The response amplitude increases with the increase of $\beta$ in both regimes. Both VIV response and galloping regimes are found for $\beta$ = 45° to $\beta$ = 90°. For $\beta$ = −90° to $\beta$ = 0°, only VIV response regimes are found. The fluid force and fluid torque play different roles in exciting/damping the vibration. In the high-amplitude gallop regime, the fluid force excites the vibration, and the torque damps the vibration. Energy harvesting at flow direction angle 90° is investigated as this flow direction has the maximum galloping amplitude. The energy harvesting is achieved by a linear electric damping coefficient in the numerical model. The maximum harvestable power in the galloping regime is significantly greater than that in the VIV regime, and it increases with the increase of the reduced velocity. When the reduced velocity is 20, the harvested power is over 20 times that in the VIV regime, and can further increase if reduced velocity further increases. The maximum efficiency over all simulated parameters is 0.424, occurring when the reduced velocity is 20, and electric damping factor is 0.04.
Paleoecological reconstructions provide valuable insights into the impacts of environmental change on key functions of wetland ecosystems. Here, we integrate biological and sedimentological proxies to provide a baseline of vegetation and hydrological change since the Middle Holocene at a riparian marsh, with the goal of informing wetland restoration within a regional biodiversity hotspot in the Great Lakes coastal zone. Four stages of wetland development are identified, reflecting the combined impacts of Lake Erie fluctuations, fluvial processes, regional paleoclimate, and anthropogenic influence. Wetland establishment took place ∼6000 cal yr BP during a Lake Erie high stand, and pollen assemblages indicate that the site was initially a forested wetland. Subsequently, water levels remained elevated as a transition to an emergent marsh with silty, organic-rich sediments took place ∼5300 cal yr BP. Once water levels stabilized in the Late Holocene, a thicket swamp established in sandier sediments, suggesting closer proximity to the meandering channel. The intensification of European settlement from 1850 CE marked a major transition, resulting from disturbances caused by land clearance and hydrological alterations, including higher rates of sediment accretion, novel diatom communities, and increases in herbaceous vegetation. These paleoecological records demonstrate the importance of considering whole-watershed measures in restoration planning, including controls on mineral sediment influxes, maintenance of local water tables, and management of invasive species producing high biomass.
Chapter 3 examines the history of the clean energy regime complex, which sets the stage to delve into questions of its effectiveness in later chapters. This chapter traces the role played by states, multilateral and bilateral organizations, transnational initiatives, and norm diffusion in driving regime complex emergence over the three periods of analysis (Period 1: 1980–2001, Period 2: 2002–2008, Period 3: 2009–2023). The chapter demonstrates that diverging state interests alone do not explain the regime complex’s emergence, but that organizational expansion, transnational actor agency, normative change, and institutional interplay all contribute to its formation.
Chapter 6 transitions to the case of the Philippines to provide a comparative analysis of regime complex effectiveness. The chapter begins with a political economy analysis of the domestic actors and interests involved in the energy sector in the Philippines, then delves into the history of geothermal development with an analysis of the impacts of the clean energy regime complex actors on barriers to geothermal development over time. The major findings of this chapter indicate that early domestic political support for geothermal development under the Marcos and Ramos regimes was a response to the exogenous shocks of energy crises. This response to exogenous shocks opened pathways of change that were key in catalyzing geothermal development in the country that later placed the Philippines as the world’s second largest producer for several decades. In the Philippines, an embrace of the energy transition enabled the positive impact of the clean energy regime complex on geothermal development. In Indonesia, domestic political resistance to the energy transition limited regime complex effectiveness.
The book concludes in Chapter 8 with a summary of the major theoretical and empirical findings on the clean energy regime complex’s emergence and effectiveness across Indonesia and the Philippines, and a discussion of the theory’s broader generalizability, further research opportunities, and policy implications and recommendations for fostering energy transitions in a world of complex governance.
Understanding biotic responses to environmental changes will help identify extinction risks and direct conservation efforts to mitigate negative effects associated with anthropogenic-induced environmental changes. Here we use the Quaternary fossil record of mole salamanders (Ambystoma) from the southwestern United States and northern Mexico to reveal geographic patterns of extirpation since the Pleistocene. Ambystoma are known to have previously inhabited regions of central Texas on the Edwards Plateau; however, they are largely absent from the region today. We used a well-dated fossil record of Ambystoma from Hall’s Cave combined with other fossil sites in the region to deduce why Ambystoma was ultimately extirpated from the Edwards Plateau and to test hypotheses related to temperature-driven body-size changes in line with the temperature–size rule. We propose that Ambystoma was likely extirpated from the region due to changing temperature and precipitation regimes that caused increased mortality and disruptions to breeding and larval development. We found some support for decreased body size in Ambystoma with increased temperature during the late Pleistocene, suggesting that body size may be an important feature to monitor in modern populations of Ambystoma as salamanders become subjected to increasingly hotter temperatures in the coming decades.