Explore the vast range of titles available.

In-situ stress plays a pivotal role in influencing the desorption, adsorption, and transportation of coalbed methane. The reservoir gas content represents a pivotal physical parameter, encapsulating both the coalbed methane enrichment capacity and the underlying enrichment law of the reservoir. This investigation collates, computes, and consolidates data concerning pore pressure, breakdown pressure, closure pressure, triaxial principal stress, gas content, lateral pressure coefficient, and other pertinent variables from coal reservoirs within several coal-bearing synclines in the Liupanshui coalfield, China. This study elucidates the characteristics of longitudinal stress development in the study area, the gas content of the longitudinal reservoirs and their interrelationships. The study area is situated within the middle-high stress zone, exhibiting discernible evolution patterns from reverse fault mechanism to strike-slip fault mechanism to normal fault mechanism, progressing from shallow to deep. In the deeper stratigraphy, a strike-slip-normal fault mechanism emerges. The relationship between burial depth and triaxial principal stress is subjected to linear regression, resulting in the proposal of a simplified model for vertical in-situ stress. The hyperbolic regression algorithm was employed in order to derive both the envelope and median formulas for lateral pressure coefficient ( k values). The k value displays discrete behavior along the vertical axis in shallow depths, gradually converging in deeper strata and ultimately stabilising at approximately 0.65 with increasing depth. A comprehensive examination of the k value substantiates the efficacy of the simplified in-situ stress model along the vertical axis, offering profound insights into the vertical interrelationships and evolving patterns of the triaxial principal stresses. The mean gas content in the study area was found to be 11.89 m³/t, exhibiting a general increase in depth, followed by a subsequent decrease. The pore pressure ( P p ) displays a discernible positive correlation with gas content. This study comprehensively elucidates the developmental patterns of the stress field, the simplified model of vertical in-situ stress, the attributes of the stress ratio ( K H , k h , lateral pressure coefficient k ), the characteristics of reservoir gas content, and the corresponding and transformative relationships between coupled geostress field parameters and gas content. The lateral pressure coefficient conversion depth, in-situ stress conversion depth, and gas inversion depth are delineated, accompanied by a detailed exposition of their definition process, physical significance, and interrelations. Within the study area, the lateral pressure coefficient conversion depth is estimated to range between 450 and 500 m, while the critical depth for in-situ stress conversion is approximately 670 m. Moreover, the critical depth for gas content conversion falls within the range of 700–800 m. It is noteworthy that the critical depth for deep coalbed methane within the Liupanshui coalfield has been identified as approximately 800 m. Subsequently, a vertical “in-situ stress-gas content mode” relationship model for coalbed methane development was formulated, thereby providing a structured framework for understanding the dynamic interactions between vertical in-situ stress and gas content.

The Critical Depth Hypothesis formalized by Sverdrup in 1953 posits that vernal phytoplankton blooms occur when surface mixing shoals to a depth shallower than a critical depth horizon defining the point where phytoplankton growth exceeds losses. This hypothesis has since served as a cornerstone in plankton ecology and reflects the very common assumption that blooms are caused by enhanced growth rates in response to improved light, temperature, and stratification conditions, not simply correlated with them. Here, a nine-year satellite record of phytoplankton biomass in the subarctic Atlantic is used to reevaluate seasonal plankton dynamics. Results show that (1) bloom initiation occurs in the winter when mixed layer depths are maximum, not in the spring, (2) coupling between phytoplankton growth (μ) and losses increases during spring stratification, rather than decreases, (3) maxima in net population growth rates ( r ) are as likely to occur in midwinter as in spring, and (4) r is generally inversely related to μ. These results are incompatible with the Critical Depth Hypothesis as a functional framework for understanding bloom dynamics. In its place, a \"Dilution-Recoupling Hypothesis\" is described that focuses on the balance between phytoplankton growth and grazing, and the seasonally varying physical processes influencing this balance. This revised view derives from fundamental concepts applied during field dilution experiments, builds upon earlier modeling results, and is compatible with observed phytoplankton blooms in the absence of spring mixed layer shoaling.

Based on the theoretical model of a soil plug column, the stress analysis of the soil plug column during the spinning process of steel casing is carried out, and the critical depth of the soil column is determined using the stress and torsional shear ratio of the soil column. The effect of factors such as casing wall thickness, surface load, and steel casing spinning speed on the critical depth of soil columns has been explored, and more reasonable construction process parameters have been obtained quantitatively. Combined with the construction of small net distance test piles at a distance of 2.5 m from the tunnel, the impact of the construction process on the existing shield tunnel has been explored. The results indicate that during the construction process, when the wall thickness of the steel casing does not exceed 0.012 m, the surface load does not exceed 15 kPa, the spinning speed of the steel casing is maintained at 5/4/2/4 m/h or 5/3/2/3 m/h (corresponding to soil depths of 2.5/9.5/6/14 m), and the soil height of the soil column is controlled within 11 m, it is not easy to generate soil plug inside the steel casing, and the soil column has strong torsional shear resistance. According to the measured data of adjacent tunnels, it has been found that the construction method of fully rotating steel casing bored pile can effectively reduce the impact on adjacent shield tunnels, and has a good microdisturbance effect, which can control tunnel deformation not exceeding 1 mm and maintain within the warning value range.

Since their first observation in metallic alloys, quasicrystals have remained highly intriguing ubiquitous physical structures, sharing properties of ordered and disordered media. They can be created in various ways, including optically induced or technologically fabricated structures in photonic and phononic systems. Understanding the wave propagation in such two-dimensional structures attracts considerable attention, with strikingly different localization properties observed in various quasicrystalline systems. Direct observation of localization in purely linear photonic quasicrystals remains elusive, and the impact of varying rotational symmetry on localization is yet to be understood. Here, using sets of interfering plane waves, we create photonic two-dimensional quasicrystals with different rotational symmetries. We demonstrate experimentally that linear localization of light does occur even in clean linear quasicrystals. We found that light localization occurs above a critical depth of optically induced potential and that this critical depth rapidly decreases with increasing order of the discrete rotational symmetry of the quasicrystal. These findings pave the way for achieving wave localization in a wide variety of aperiodic systems obeying discrete symmetries, with possible applications in photonics, atomic physics, acoustics and condensed matter. Localization of light is observed in photonic quasicrystals with various orders of rotational symmetry.

Although the global environmental impact of Laurentide Ice-Sheet destabilizations on glacial climate during Heinrich Events is well-documented, the mechanism driving these ice-sheet instabilities remains elusive. Here we report foraminifera-based subsurface (~150 m water depth) ocean temperature and salinity reconstructions from a sediment core collected in the western subpolar North Atlantic, showing a consistent pattern of rapid subsurface ocean warming preceding the transition into each Heinrich Event identified in the same core of the last 27,000 years. These results provide the first solid evidence for the massive accumulation of ocean heat near the critical depth to trigger melting of marine-terminating portions of the Laurentide Ice Sheet around Labrador Sea followed by Heinrich Events. The repeated build-up of a subsurface heat reservoir in the subpolar Atlantic closely corresponds to times of weakened Atlantic Meridional Overturning Circulation, indicating a precursor role of ocean circulation changes for initiating abrupt ice-sheet instabilities during Heinrich Events. We infer that a weaker ocean circulation in future may result in accelerated interior-ocean warming of the subpolar Atlantic, which could be critical for the stability of modern, marine-terminating Arctic glaciers and the freshwater budget of the North Atlantic. The mechanism driving past Laurentide Ice-Sheet instabilities remains elusive Here, the authors present a sediment record from the subpolar western North Atlantic and show that massive warming of the upper interior ocean was the likely trigger for repeated collapses of the Laurentide Ice-Sheet and iceberg discharge into the North Atlantic, known as Heinrich Events.

The effect of biomass dynamics on the estimation of watercolumn primary production is analysed, by coupling a primary production model to a simple growth equation for phytoplankton. The production model is formulated with depth- and time-resolved biomass, and placed in the context of earlier models, with emphasis on the canonical solution for watercolumn production. A relation between the canonical solution and the general solution for the case of an arbitrary depth-dependent biomass profile was derived, together with an analytical solution for watercolumn production in case of a depth dependent biomass profile described with the shifted Gaussian function. The analysis was further extended to the case of a time-dependent, mixed-layer biomass and two additional analytical solutions to this problem were derived, the first in case of increasing mixed-layer biomass and the second in case of declining biomass. The solutions were tested with Hawaii Ocean Time-series data. The canonical solution for mixed-layer production has proven to be a good model for this data set. The shifted Gaussian function was demonstrated to be an accurate model for the measured biomass profiles and the shifted Gaussian parameters extracted from the measured profiles were further used in the analytical solution for watercolumn production and results compared with data. The influence of time-dependent biomass on mixed-layer production was studied through analytical solutions. Re-examining the Critical Depth Hypothesis we derived an expression for the daily increase in mixed-layer biomass. Finally, the work was placed in a remote sensing context and the time-dependent model for biomass related to the remotely sensed-biomass.

In the present paper, the sloshing flow in a cuboid tank forced to oscillate horizontally is investigated with both experimental and numerical approaches. The filling depth chosen is $h/L=0.35$ (with h the water depth and L the tank height), which is close to the critical depth. According to Tadjbakhsh & Keller (J. Fluid Mech., vol. 8, issue 3, 1960, pp. 442–451), as the depth passes through this critical value the response of the resonant sloshing dynamics changes from ‘hard spring’ to ‘soft spring’. The experimental tank has a thickness of $0.1L$, reducing three-dimensional effects. High-resolution digital camera and capacitance wave probes are used for time recording of the surface elevation. By varying the oscillation period and the amplitude of the motion imposed on the tank, different scenarios are identified in terms of free-surface evolution. Periodic and quasi-periodic regimes are found in most of the frequencies analysed but, among these, sub-harmonic regimes are also identified. Chaotic energetic regimes are found with motions of greater amplitude. Typical tools of dynamical systems, such as Fourier spectra and phase maps, are used for the regime identification, while the Hilbert–Huang transform is used for further insight into doubling-frequency and tripling-period bifurcations. For the numerical investigation, an advanced and well-established smoothed particle hydrodynamics method is used to aid the understanding of the physical phenomena involved and to extend the range of frequencies investigated experimentally.

∼90% of gas hydrates occur as pore‐filling or fracture‐filling morphology in clay‐rich marine sediments. Their dissociation releases gas with distinct environmental fates interacting with climate change. A well‐constrained model of hydrate distribution with different morphologies is urgently needed. We present a novel one based on drilling data worldwide. We identified a geomechanics‐controlled critical depth, typically several hundred meters below the seafloor, which limits the maximum occurrence depth of fracture‐filling hydrates. This relative positioning of critical depth and bottom of the gas hydrate stability zone (BGHSZ) determines hydrate distribution with various morphologies: pore‐filling hydrates develop and predominate below critical depth only when critical depth lies above BGHSZ, while only fracture‐filling hydrates occur above BGHSZ when critical depth exceeds BGHSZ. Critical depth increases with higher clay‐sized fractions or water depths, causing varying hydrate morphologies at specific depths along continental margins. This model is essential for evaluating hydrates' roles in global carbon cycle.

The paper fully answers a long standing open question concerning the stability/instability of pure gravity periodic traveling water waves—called Stokes waves—at the critical Whitham–Benjamin depth h WB = 1.363 . . . and nearby values. We prove that Stokes waves of small amplitude O ( ϵ ) are, at the critical depth h WB , linearly unstable under long wave perturbations. The same holds true for slightly smaller values of the depth h > h WB - c ϵ 2 , c > 0 , depending on the amplitude of the wave. This problem was not rigorously solved in previous literature because the expansions degenerate at the critical depth. To solve this degenerate case, and describe in a mathematically exhaustive way how the eigenvalues change their stable-to-unstable nature along this shallow-to-deep water transient, we Taylor-expand the computations of Berti et al. (Arch Ration Mech Anal 247:91, 2023) at a higher degree of accuracy, starting from the fourth order expansion of the Stokes waves. We prove that also in this transient regime a pair of unstable eigenvalues depict a closed figure “8”, of smaller size than for h > h WB , as the Floquet exponent varies.

Mesoscale eddies can alter the propagation of wind-generated near-inertial waves (NIWs). Different from previous studies, the subsurface mooring observed NIWs are generated outside an anticyclonic eddy (ACE) and then interact with the arriving ACE. It is found that with the arrival of the ACE, the NIWs accelerate to propagate downward and the maximum vertical wavelength and group velocity of NIWs reach ∼500 m and ∼35 m day −1 , respectively. When entering the core of the ACE, the near-inertial energy is trapped and finally stalls at a critical depth, which basically corresponds to the base of the ACE located at around 750-m depth. Through a ray-tracing model and dynamic analyses, this critical depth is much deeper than that of NIWs generated directly inside an ACE. By using depth–time varying stratification and relative vorticity, ray-tracing experiments further demonstrate that NIWs generated outside and passed over by an ACE can propagate to deep depths. Furthermore, energy budget analyses indicate that the net energy transfer from the ACE to NIWs plays an important role in the enhancement of downward-propagating near-inertial energy and its long-term persistence (∼45 days) in the critical layer. Within the critical layer, the enhancement of shear instability and nonlinear interactions among internal waves account for the loss of the trapped near-inertial energy and provide energy for furnishing deep ocean mixing.