Near-zero Values Research Articles

A refined model for the mechanisms of Precambrian phosphorite formation

Despite the economic and scientific importance of Precambrian phosphorites, our understanding of the mechanism leading to their formation remains limited, including for the largest phosphogenic episode in the late Neoproterozoic. To improve our understanding of Precambrian phosphorite formation, we combined sedimentology, petrography, and elemental, and Fe-C isotopic analyses to study the two main phosphorite beds (the lower and upper phosphorite beds) in the Ediacaran Doushantuo Formation, Zhangcunping area, South China. The phosphorites consist mainly of granular textures characterized by densely packed grains, some of which are coated with secondary phosphate growth. However, there are notable differences in the mineralogy, microfossil assemblages, and elemental contents of the two beds. The lower phosphorites have no Ce anomaly, and relatively low Y/Ho ratios and positive δ56Fe values (0.04–0.30 ‰, average of 0.19 ‰). In contrast, the upper phosphorites have negative Ce anomalies and higher Y/Ho ratios and near-zero δ56Fe values (−0.29–0.19 ‰ (average of −0.01 ‰). These observations suggest that the lower phosphorites formed in anoxic-suboxic environments, whereas the upper phosphorites formed in relatively oxygenated environments. The δ13Ccarb values of the phosphorites range from −3.97 ‰ to 1.71 ‰ (average of −1.56 ‰), and are lighter than values in dolostones (−0.52 ‰ to 4.39 ‰, average of 2.02 ‰). This suggesting that formation of the Doushantuo phosphorites was influenced by degradation of organic matter in an ocean with high primary productivity. The lower phosphorites, which were also regulated by Fe redox pumping, have positive δ56Fe values, along with the presence of pyrite framboids and iron oxides, suggesting deposition near the Fe-redox boundary where extensive Fe cycling. The upper phosphorites show positive correlations between Mn and Fe, and Mn/Fe and P2O5, suggesting formation near the Mn boundary with extensive Mn cycling, primarily mediated by Mn redox pumping. Sedimentological observation indicate that primary phosphates were concentrated into granular phosphorites by winnowing processes following primary precipitation. Accordingly, we propose a refined model for Precambrian phosphorite formation in which degradation of organic matter, Fe and Mn pumping, and physical reworking of deposits co-evolve and interact within a dynamic Precambrian redox environment. Our model provides a reasonable explanation for the distribution of global phosphorite deposits throughout geological history.

Spatiotemporal disparity of volcanogenic mercury records in the southwestern Neo-Tethys Ocean during the Permian–Triassic transition

The Permian–Triassic (P-Tr) transition marks a vital period in Earth's history, characterized by major environmental perturbations and the largest mass extinction event of the Phanerozoic, with volcanic activities playing a key role. Previous investigations of mercury (Hg) anomalies in over 50 marine and terrestrial sections spanning the P-Tr boundary (PTB) have suggested a predominant volcanogenic influence. However, there remains ongoing debate regarding the exact timing and primary sources of these anomalies in different regions. In this study, we present stratigraphically high-resolution (∼7× higher compared to the previous work in the same section) Hg records from the shallow marine strata of the Qubu section, located at the Himalayan Tethys Zone of southern Tibet, Southwest China. Our analysis reveals peak Hg concentrations of approximately 80 to 100 ng/g and Hg/TOC ratios of 111 to 263 (ppb/wt%) at the uppermost Permian. Notably, new measurements of Hg isotopes, characterized by ∼0‰ of Δ199Hg values, provide unambiguous evidence supporting the prevailing volcanic influence. Our results are consistent with similar observations of Hg anomalies in proximal shallow-marine sections around the Neo-Tethys Ocean, including those in northern India and western Australia. However, we found that relatively shallower marine settings (shelf, lagoon or inshore) tend to exhibit Hg spikes in the latest Permian, whereas deeper sections (outer-shelf or deep carbonate ramp) show peaks in the Early Triassic. Since Hg anomalies for all the sections have been verified to be volcanogenic based on their near-zero values of Δ199Hg, the discrepancies among them concerning timing and water depth may be attributed to prolonged volcanic influences extending into the Triassic period. Our findings underscore the complexity of sedimentary Hg records and further raise questions about the spatiotemporal consistency of Hg anomalies during the P-Tr transition. Additionally, the most negative Δ199Hg value (−0.20‰) in the uppermost black shale in the Qubu section likely resulted from photic zone euxinia consistent with globally developed P-Tr shallow-marine anoxic conditions, while other low values of Δ199Hg with low Hg concentrations were derived from some moderate terrestrial influx.

Beyond a Richardson-Gaudin Mean-Field: Slater-Condon Rules and Perturbation Theory.

Richardson-Gaudin states provide a basis of the Hilbert space for strongly correlated electrons. In this study, optimal expressions for the transition density matrix elements between Richardson-Gaudin states are obtained with a cost comparable with the corresponding reduced density matrix elements. Analogues of the Slater-Condon rules are identified based on the number of near-zero singular values of the RG state overlap matrix. Finally, a perturbative approach is shown to be close in quality to a configuration interaction of Richardson-Gaudin states while being feasible to compute.

Co-existence of magmatic- and metamorphic-hydrothermal gold deposits in the northern margin of the North China Craton and their genetic link to Paleo-Pacific plate subduction: Insights from in-situ analyses of sulfur isotopes and trace elements

Mid-Mesozoic gold deposits, whose metallogeny was coincident with subduction of the Paleo-Pacific plate, are widely distributed in the northern margin of the North China Craton (NCC). The genesis of these deposits is currently debated with magmatic- and metamorphic-hydrothermal models. In-situ analyses of sulfur isotopes and trace elements provide an opportunity to clarify such a debate. Here, the two techniques were used to determine the trace elements and sulfur isotopes of sulfides from three mid-Mesozoic gold deposits (Jiapigou, Jinchangyu, and Jinchanggouliang) in the northern margin of NCC. The Co/Ni ratios of pyrites suggest that Jiapigou and Jinchanggouliang deposits are of magmatic-hydrothermal origin, whereas the Jinchangyu deposits receive ore-forming materials mainly from crustal-hydrothermal fluids. In addition, gold-bearing sulfides display positive (5.60 ± 1.87 ‰, SD), near-zero (−0.31 ± 1.27 ‰, SD) and negative δ34SV-CDT values (−3.84 ± 2.97 ‰, SD) in the Jiapigou, Jinchangyu, and Jinchanggouliang, respectively. The results suggest that mid-Mesozoic gold deposits in the northern margin of NCC have variable sources of sulfur and metals. The Jiapigou deposit, representative of the arc settings, received sulfur and metals mainly from the subducting ocean crust. The Jinchanggouliang deposit, representative of cratonic destruction settings, received sulfur and metals mainly from the metasomastized mantle. The Jinchangyu deposit, representative of the back-arc settings, received sulfur and metals mainly from the metamorphic basement. We infer that subduction of the Paleo-Pacific plate in the mid-Mesozoic not only led to direct metallogeny of magmatic-hydrothermal gold deposits at arc settings and cratonic destruction settings, but also triggered the release of ore-forming fluids from the basement at back-arc, favoring metallogeny of crustal-hydrothermal gold deposits. Thus, mid-Mesozoic gold deposits in the northern margin of NCC cannot be exclusively explained by a single model.

A Two-Axis Orthogonal Resonator for Variable Sensitivity Mode Localization Sensing.

This paper experimentally demonstrates a mode localization sensing approach using a single two-axis orthogonal resonator. The resonator consists of concentric multi-rings connected by elliptic springs that enable two orthogonal oscillation modes. By electrostatically tuning the anisotropic stiffness between the two axes, the effective coupling stiffness between the modes can be precisely controlled down to near-zero values. This allows the sensitivity of mode localization sensing to be tuned over a wide range. An order of magnitude enhancement in sensitivity is experimentally achieved by reducing the coupling stiffness towards zero. The resonator's simple single-mass structure offers advantages over conventional coupled resonator designs for compact, tunable mode localization sensors. Both positive and negative values of coupling stiffness are demonstrated, enabling maximum sensitivity at the point where coupling crosses through zero. A method for decomposing overlapping resonance peaks is introduced to accurately measure the amplitude ratios of the localized modes even at high sensitivities. The electrostatic tuning approach provides a new option for realizing variable sensitivity mode localization devices using a simplified resonator geometry.

Mercury isotopes of the Late Ordovician to Middle Triassic tuff layers in South China link the fate of ancient volcanism and the mass extinction

Mercury (Hg) anomalies in sedimentary records are a newly developed proxy of large volcanism in the geological past. Tuff layers host abundant volcanic ash and record key information on the type of volcanic emission (e.g., arc volcanism and large igneous province eruptions). Here, we measured the Hg isotopic compositions of several tuff layers in South China. Tuff samples in the Late Ordovician Wufeng Formation and the Middle Triassic Guanling Formation mostly show positive Δ199Hg values of – 0.01 to 0.10‰ and – 0.06 to 0.16‰, respectively, suggesting arc volcanism occurred during these two periods. Tuff samples in the Middle Permian Dachang Layer mostly show near-zero Δ199Hg values (– 0.08 to 0.00‰), suggesting volcanism was driven by the Emeishan large igneous province eruption. Results of this study verify Hg isotopes as a useful proxy in revealing the type of volcanism in geological history.

Amphistomy: stomata patterning inferred from 13C content and leaf-side-specific deposition of epicuticular wax.

The benefits and costs of amphistomy (AS) vs. hypostomy (HS) are not fully understood. Here, we quantify benefits of access of CO2 through stomata on the upper (adaxial) leaf surface, using 13C abundance in the adaxial and abaxial epicuticular wax. Additionally, a relationship between the distribution of stomata and epicuticular wax on the opposite leaf sides is studied. We suggest that the 13C content of long-chain aliphatic compounds of cuticular wax records the leaf internal CO2 concentration in chloroplasts adjacent to the adaxial and abaxial epidermes. This unique property stems from: (1) wax synthesis being located exclusively in epidermal cells; and (2) ongoing wax renewal over the whole leaf lifespan. Compound-specific and bulk wax 13C abundance (δ) was related to amphistomy level (ASL; as a fraction of adaxial in all stomata) of four AS and five HS species grown under various levels of irradiance. The isotopic polarity of epicuticular wax, i.e. the difference in abaxial and adaxial δ (δab - δad), was used to calculate the leaf dorsiventral CO2 gradient. Leaf-side-specific epicuticular wax deposition (amphiwaxy level) was estimated and related to ASL. In HS species, the CO2 concentration in the adaxial epidermis was lower than in the abaxial one, independently of light conditions. In AS leaves grown in high-light and low-light conditions, the isotopic polarity and CO2 gradient varied in parallel with ASL. The AS leaves grown in high-light conditions increased ASL compared with low light, and δab - δad approached near-zero values. Changes in ASL occurred concomitantly with changes in amphiwaxy level. Leaf wax isotopic polarity is a newly identified leaf trait, distinguishing between hypo- and amphistomatous species and indicating that increased ASL in sun-exposed AS leaves reduces the CO2 gradient across the leaf mesophyll. Stomata and epicuticular wax deposition follow similar leaf-side patterning.

Wavefront rotator with near-zero mean polarization change

A K-mirror is a device that rotates the wavefront of an incident optical field. It has recently gained prominence over the Dove prism, another commonly used wavefront rotator, due to the fact that while a K-mirror has several controls for adjusting the internal reflections, a Dove prism is made of a single glass element with no additional control. Thus, one can obtain much lower angular deviations of transmitting wavefronts using a K-mirror than with a Dove prism. However, the accompanying polarization changes in the transmitted field due to rotation persist even in the commercially available K-mirrors. A recent theoretical work [Appl. Opt. 61, 8302 (2022)APOPAI0003-693510.1364/AO.472543] shows that it is possible to optimize the base angle of a K-mirror for a given refractive index such that the accompanying polarization changes are minimum. In contrast, we show in this paper that by optimizing the refractive index it is possible to design a K-mirror at any given base angle and with any given value for the mean polarization change, including near-zero values. Furthermore, we experimentally demonstrate a K-mirror with an order-of-magnitude lower mean polarization change than that of the commercially available K-mirrors. This can have important practical implications for OAM-based applications that require precise wavefront rotation control.

A comprehensive study on crystal structure, phase compositions of the BiVO4-LaVO4 binary dielectric ceramic system and a typical design of dielectric resonator antenna for C-band applications

Novel multi-component (Bi1-xLax)VO4 (BLVOx) (0.05 ≤ x ≤ 0.9) solid-solution/composite ceramics crystal structures, phase compositions as well as its applications in the C-band dielectric resonator antenna have been designed and investigated. With the increased substitution of La3+, phase transitions among the monoclinic scheelite (mBiVO4), tetragonal zircon (zt(La,Bi)VO4) and monoclinic monazite (mLaVO4), driven by the compositional changes, were detected. La3+ played an essential role in the optimization of the dielectric properties of BLVOx. The measured Q × f values at the microwave band are considerably larger around the range of compositions forming the zircon phase and reached the maximum value (12,800 GHz) at pure zircon phase (x = 0.5), demonstrating that the impact of zircon structure on the intrinsic loss should not be disregarded and is beneficial for low dielectric loss. Meanwhile, the εr and TCF values could be tuned by regulating the concentration ratio of Bi3+/La3+ to obtain composites or solid-solutions with appropriate εr and near-zero TCF values. Additionally, a cylindrical dielectric resonator antenna (CDRA) of BVLO0.5 ceramic was designed with high simulated radiation efficiency (99.8%) and gain (4.58 dBi) at the center frequency (6.73 GHz), indicating its potential application in C-band because of its tunable permittivity and low-loss.

Runoff generation in a semiarid environment: The role of rainstorm intra-event temporal variability and antecedent soil moisture

Rainfall intensity and antecedent soil moisture are key variables affecting the initiation and accumulation of runoff, and therefore, impact on the occurence flood events. We used time series of rainfall intensities characterizing rainstorms with different mean, standard deviation, and skewness to simulate runoff response of a sealed loamy soil profile under various initial soil moisture conditions. We found that shifting from wet to dry initial soil moisture leads to a 300 % increase in ponding time and a 350 % decrease in total runoff. Intense rainfall events catalyze runoff development and runoff occurs earlier with increasing mean, maximum intensity, and variance of rainfall. Higher variance in intra-event storm-intensity temporal distribution yields more runoff. Earlier runoff formation aligned with negatively skewed storm structures, but largest cumulative runoff resulted from storms displaying near-zero skewness values. The combination between rainfall intensification and extended dry periods between storms might reduce potential runoff. These insights improve our understanding of anticipated impacts of climate variations on floods and may also contribute to ecosystem health evaluations, and bolster predictive capabilities of surface processes.

Two K20 microwave dielectric ceramics SrLnAlO4 (Ln = Eu, Gd) with near-zero τf and contrasting Q×f

K20 microwave dielectric ceramics SrLnAlO4 (Ln = Eu, Gd, and Ho) were prepared at 1440–1520 °C. SrEuAlO4 and SrGdAlO4 crystallized into tetragonal K2NiF4-type structures. While SrHoAlO4 was a mixture (SrHo2Al2O7, Ho2O3, and Sr3HoAl2O7.5) due to the too-small radius of Ho3+ to bond in [HoO9] dodecahedron. SrEuAlO4 and SrGdAlO4 exhibited near-zero τf values of +1.7 and +4.3 ppm/°C and low εr (19.37 and 19.14) along with contrasting Q×f values (70,030 and 5560 GHz). Compared with the modified molecular polarizability (αCorr) based on the bond valence deviation, the αobs values of SrEuAlO4 and SrGdAlO4 are much higher, indicating that their dielectric polarizabilities were underestimated, and this phenomenon was mainly influenced by rattling cations, which also causes their τf with near-zero values. Due to the magnetic subsystem adversely affecting microwave dielectric losses, the worsened Q×f value of SrGdAlO4 compared to that of SrEuAlO4 is due to the high magnetic moment of Gd3+ (7.94 μB).

Formation of ammonite concretions through organic decomposition in the iron-reduction zone

ABSTRACT The ammonites in spherical carbonate concretions often preserve their original three-dimensional (3-D) shell shapes and detailed fragile structures. However, the formation process of spherical ammonite concretions is not fully understood. Herein, the ammonite concretions identified in the Cretaceous (Campanian) Osoushinai Formation, Yezo Group, Japan, are examined to understand their formation process during soft-tissue decomposition after burial in marine sediments. In the Osoushinai Formation, almost all observed ammonites in concretions preserve their 3-D form without phragmocone deformation. The calcite filling in the remaining body chamber of ammonites (BC1) shows that shells were buried with soft tissues. These occurrences, negative δ13C values, and the near-zero δ18O values of BC1 as well as the concretions indicate that both BC1 and concretions rapidly formed from dissolved inorganic carbon derived from organic matter, including the soft tissue of dead organisms, in the shallow part of the sediments. The increasing Fe concentration in BC1 shows that BC1 formed in the iron-reduction (FeR) zone, where organic matter was decomposed owing to the activity of iron-reducing microorganisms. The similarity of the elemental and isotopic compositions of BC1 and concretions show that they concurrently formed in the FeR zone. In the Osoushinai Formation, an abundant influx of Fe(III) and intense bioturbation during the deposition of the formation promoted organic decomposition in the FeR zone, causing rapid formation of BC1 and concretions. Such rapidly formed calcite fillings and concretions protected fossils from deformation and dissolution during diagenesis to preserve their 3-D form. Overall, the findings of this study provide new insight into the relation between sedimentary environments and the fossil preservation process via rapid concretion formation.

Inhibitory Components in Muscle Synergies Factorized by The Rectified Latent Variable Model from Electromyographic Data.

Non-negative matrix factorization (NMF), widely used in motor neuroscience for identifying muscle synergies from electromyographical signals (EMGs), extracts non-negative synergies and is yet unable to identify potential negative components (NegCps) in synergies underpinned by inhibitory spinal interneurons. To overcome this constraint, we propose to utilize rectified latent variable model (RLVM) to extract muscle synergies. RLVM uses an autoencoder neural network, and the weight matrix of its neural network could be negative, while latent variables must remain non-negative. If inputs to the model are EMGs, the weight matrix and latent variables represent muscle synergies and their temporal activation coefficients, respectively. We compared performances of NMF and RLVM in identifying muscle synergies in simulated and experimental datasets. Our simulated results showed that RLVM performed better in identifying muscle-synergy subspace and NMF had a good correlation with ground truth. Finally, we applied RLVM to a previously published experimental dataset comprising EMGs from upper-limb muscles and spike recordings of spinal premotor interneurons (PreM-INs) collected from two macaque monkeys during grasping tasks. RLVM and NMF synergies were highly similar, but a few small negative muscle components were observed in RLVM synergies. The muscles with NegCps identified by RLVM exhibited near-zero values in their corresponding synergies identified by NMF. Importantly, NegCps of RLVM synergies showed correspondence with the muscle connectivity of PreM-INs with inhibitory muscle fields, as identified by spike-triggered averaging of EMGs. Our results demonstrate the feasibility of RLVM in extracting potential inhibitory muscle-synergy components from EMGs.

Predicting River Discharge in the Niger River Basin: A Deep Learning Approach

Across West Africa, the River Niger is a major source of freshwater. In addition, the river system also provides services such as aquaculture, transportation, and hydropower. The river network plays a critical role in the hydropolitics and hydroeconomics of the region. Therefore, River Niger is integral to the development of West Africa, hence, there is a need to ensure that the river’s ecosystem is a healthy one. In light of the changing climate and its associated threats such as droughts and floods, constant monitoring and measurements of the the river’s flow system cannot be overemphasized. This study investigates temporal variations in annual river discharge characteristics at eight stations (Koulikoro, Dioila, Kirango, Douna, Mopti, Dire, Ansongo, and Niamey) in the Niger River basin, presenting detailed quantitative findings. Analyzing discharge data of River Niger from 1950 to 1990, the minimum discharge measures (minimum and 10th percentile) exhibit a consistent decreasing trend post-1960, persisting into the 1990s at several stations. Central tendency measures (mean and 50th percentile) also consistently reduced since 1950, with near-zero median values observed in Diola and Douna. Recovery in mean discharge is evident in Ansongo after 1980. Extreme values (maximum and 90th percentile) show decreasing trends across all stations, with some locations exhibiting a slight recovery after 1980. The decreasing trend in annual minimum, mean, and maximum values has implications for water resources, affecting hydroelectric generation, fish farming, and dry season irrigation. Machine learning algorithms (MLAs) are deployed to predict the prediction of monthly river discharge, with LSTM identified as the best-performing model overall. However, model performance varies across locations, with TCN excelling in Diola but underperforming in Koulikoro. This study emphasizes the chaotic nature of time series data and external drivers limiting the long-term predictive capabilities of MLAs. Quantitative evaluation of MLA performance reveals specific strengths and weaknesses at each station. This study underscores the importance of predicting the 10th percentile of annual river discharge for water resource planning. Models exhibit diverse performance across basins, emphasizing the need for tailored approaches. Further analysis considers measures of central tendencies, predicting the 50th percentile (Q50) and mean discharge values. TCN emerges as the best model for Q50 prediction, showcasing superior performance over other models. Additionally, the study delves into predicting high and low extreme discharges, crucial for understanding potential flood events and preparing for meteorological and hydrological droughts. This study concludes by emphasizing the necessity for location-specific studies in the River Niger basin to facilitate an enhanced integrated river management system.

Combustion characteristics of oxymethylene dimethyl ether-diesel blends: An experimental investigation using a constant-volume combustion chamber

The combustion characteristics of oxymethylene dimethyl ether (OMEx) and its blends with diesel have been investigated using a multi-hole injector in a constant-volume combustion chamber. The results show OMEx addition can reduce the ignition delay, especially when blends of more than 50 vol% are used, at low chamber temperature. Two individual heat-release peaks are observed for OMEx during premixed combustion at 750 K, due to a pronounced low-temperature heat-release phase. The chamber temperature of 800 K can be regarded as a transition point for the behavior of burn duration as well as maximum ROHR peak, mostly caused by combustion regime transition from premixed- to diffusion combustion. It appears that there is an approximate linear relation between maximum ROHR peak and the time at which this peak occurs with injection pressure. The ignition delay of OMEx is almost insensitive to a decrease in ambient oxygen concentration. And the premixed ROHR profile, due to its high oxygen content, is very similar and only ignition delay and burn duration increase slightly. Additionally, comparisons of natural luminosity results for OMEx and diesel indicate that OMEx produces near-zero soot values. Luminosity is expected to be caused by chemiluminescence alone, which increases with injection pressure.

Design, simulation, and measurement of near-zero-index shells for electromagnetic beam generation

We present design and simulation of three-dimensional (3D) shell structures, which generate directional radiation patterns from isotropic sources thanks to their near-zero-index (NZI) characteristics, as well as realizations of these shells via low-cost 3D printing. Throughout the design process of NZI beam generators, both homogenized structures, for which near-zero relative permittivity and/or permeability values are enforced, and actual models involving periodic arrangements of dielectric rods are considered. Solutions of the electromagnetic problems are obtained by using rigorous implementations of the state-of-the-art surface-integral-equation (SIE) formulations in frequency domain. Iterative solutions of matrix equations derived from SIEs are accelerated by different forms of the multilevel fast multipole algorithm (MLFMA) and suitable preconditioners, when necessary. In the design process of NZI shells, alternative strategies are employed to obtain customized radiation patterns. In this context, various cavities with strong resonance behaviors are designed as source regions. At the same time, outer surfaces are modified to either enhance or suppress outgoing electromagnetic fields. In addition to comprehensive simulations and analyses of NZI beam generators, their capabilities are verified by measurements, specifically at 10.3 GHz, on different prototypes fabricated via 3D printing. Measurements of diverse NZI shell structures are presented to demonstrate that NZI properties can successfully be achieved by well-designed arrangements of dielectric rods with proper materials. The results demonstrate the feasibility of efficient, effective, low-cost, and reconfigurable NZI shells to generate alternative beam configurations that can be useful in a plethora of microwave applications.

On the internal velocity structure of sub-aqueous, gravity-driven granular flow: Measurements using MHz frequency sound

The vertical structure of downslope velocity within sub-aqueous gravity-driven flows of (smoother) glass beads and (rougher) natural sand is investigated for both fixed roughness and erodible beds using high-resolution, MHz-frequency acoustics. The observed velocity profiles within the O(1) cm thick, O(10) cm/s flows exhibit a negative shear layer extending downward from the sediment–water interface to a velocity maximum at ∼ 9 grain diameters depth within the layer, below which the velocities decrease to near-zero values at the pre-flow bed location for fixed roughness beds and to non-zero values for mobile beds. The attenuation of sound transmitted through the moving layer is used to constrain the depth-averaged solids concentration to a value of ∼ 0.52. The observed negative shear at the interface indicates that, unlike the sub-aerial case, interfacial friction is dynamically important in gravity-driven sub-aqueous granular flows. It is shown that the observed vertical structure of velocity within the layer can be well represented by continuum viscous flow models. Solids concentration and effective viscosity are estimated from the best-fit model parameters using the Zarraga–Hill–Leighton (2000) empirical relation for suspensions of negatively buoyant particles, yielding vertically averaged values ∼ 0.57. While the sub-millimeter vertical resolution of the measurements is too coarse to provide precise estimates of the friction velocity at the interface, the model-data comparisons nevertheless indicate that the vertical structure of the downslope flow consists of a weakly stratified dense layer and a thin, dilute transition layer between the dense flow and the overlying water.

Evidence for high-frequency oxygenation of Ediacaran shelf seafloor during early evolution of complex life

Increasing oxygenation of the early Ediacaran Ocean is thought to have been responsible for the emergence of early animals. Although geochemical studies have suggested periods of oceanic oxygenation in the Ediacaran, direct evidence for seafloor oxygenation has been lacking. Here, we report frequent occurrences of distinctive, sub-millimetric, and early diagenetic pyrite-marcasite rosettes in phosphorites from the lower Ediacaran Doushantuo Formation (Weng’an, South China). They typically consist of a nucleus of framboidal pyrite, a cortex of radiating marcasite blades intergrown with quartz, and a rim of second-generation pyrite, recording partial oxidative dissolution of pyrite and co-precipitation of marcasite and quartz. This inference is further supported by near-zero carbon isotope values of the host dolostone, similarly low sulfur isotope values for pyrite and marcasite, and evident Fe-isotope fractionation between marcasite and pyrite. Collectively, our findings reveal intermittent bottom-water and porewater oxygenation events, providing direct evidence of high-frequency oxygenation of Ediacaran continental shelves.

Analysis of the energy transfer process for multiple scattering problems involving lossy media

The energy transfer process for acoustic propagation and scattering in inhomogeneous, lossy media is rigorously investigated. Two problems are considered: an arbitrarily composed cluster of lossy scatterers, excited by a single point source and a layered, lossy medium excited by an internal point-source distribution. Energy conservation laws and optical theorems are established. The connection of active intensity with the scattering cross section and the relation between reactive intensity and Lagrangian density are determined. Furthermore, the influence of the losses of the involved media to the kinetic energy is unveiled. Reductions to lossless media and near-zero frequency values are derived.

The structural characteristics and microwave dielectric properties of (Mg0.5Ti0.5)3+ substituted Sr0.6Ca0.4LaAlO4 ceramics

Achieving both high Qf and near-zero τf values for microwave dielectric ceramics in the microwave frequency band is challenging. In this work, the effect of (Mg0.5Ti0.5)3+ substitution on the structural characteristics and microwave dielectric properties of Sr0.6Ca0.4LaAlO4 ceramics was systematically investigated. The Sr0.6Ca0.4LaAl1-x(Mg0.5Ti0.5)xO4 (x = 0–0.5) ceramics were successfully synthesized. The average bond length of Sr/Ca/La–O for Sr0.6Ca0.4LaAl1-x(Mg0.5Ti0.5)xO4 ceramics is related to the dielectric constant (εr). The relative density of the ceramics and FWHM of the Raman peak have strong effects on the Qf values. There is a dependence of the [AlO6] octahedral distortion on the τf values, which provides new possibilities for tuning the temperature coefficient of the K2NiF4-type ceramics. When x is 0.4, the excellent microwave dielectric properties are obtained as following: εr = 20.52, Qf = 103,600 GHz (at 7.79 GHz), and τf = −3.77 ppm/°C. The above work provides a deeper insight into the relationship between the crystal structure characteristics and the microwave dielectric properties of the K2NiF4-type ceramics.