Core Surface Research Articles

Antipodal Seismic Observation and Sensitivity Kernel for the Liquid Region on the Earth’s Inner Core

It is considered that a part of the inner core surface where iron in the fluid outer core is precipitated may have melted and formed a mushy region, but its position is not well understood seismologically. We recently analyzed seismic waveforms observed at the antipodal station of the seismic source and showed that there are precursors to the PKIIKP phase reflected beneath the inner core boundary. It has been found that this precursory wave can be modeled as a reflection under the liquid/solid interface at a depth of 100 km below the inner core boundary. Here, we use these precursor waves observed at the antipodal station (>179°). The sensitivity kernel of the amplitude of these precursor waves for the shear wave velocity structure on the inner core surface was calculated by the adjoint method, using theoretical seismic waveforms. Our results might be used to locate regions of the inner core surface where the shear wave velocity may be close to zero.

Nano-SiO2 enhanced slickwater fracturing fluid for improved imbibition recovery in tight gas reservoirs: Performance and mechanism

Inspired by the exceptional performance of nanomaterials in oilfield development, yet it is rarely applied in tight gas reservoir. In this study, focusing on the tight gas reservoir of the Liuyangbao, Ordos Basin, a slickwater fracturing fluid was synthesized by incorporating nano-SiO2 and surfactant to enhance its stability and activity, aiming to optimize the utilization efficiency of slickwater. The prepared SiO2-enhanced slickwater fracturing fluid exhibited excellent interfacial regulation properties involving surface tension reduction (71.65–28.31 mN/m) and wettability alteration (69.3–21.5º). In addition, SEM images indicated that the self-assembled nano-SiO2 adsorbed on the core surface, sequentially forming a large number of micro/nano structures in “spot adsorption”, “sheet adsorption”, “lobe adsorption” and “cluster adsorption” shapes, altering the original pore structure. Meanwhile, LP-N2GA results showed an upward shift in the hysteresis loop of isotherms after nano-SiO2 was adsorbed on the core samples, with a considerable increase in specific surface area (SSA) and transitional pores. Moreover, the system showed an outstanding capacity for imbibition gas production, and finally recovered 78.2 % (∼21.4 % higher than slickwater system). The underlying mechanism responsible for the system enhanced gas recovery were attributed to capillary pressure, structural disjoining pressure and Jamin effect. This work provides feasibility of the application of nano-SiO2 in the development of tight gas reservoirs.

Macau Scientific Satellite‐1 Initial Magnetic Field Model

AbstractEight months of vector magnetic field measurements from the Macau Scientific Satellite‐1 (MSS‐1), supplemented by higher latitude field intensity measurements from the Swarm satellites, are used to derive an MSS‐1 Initial Field Model (MIFM). Robust root‐mean‐square misfits between MIFM and the three components of the MSS‐1 vector field data are found to be below 3.3 nT. MIFM agrees well with the CHAOS‐7 field model and we find even better agreement with an identically parameterized model derived only from Swarm data. MSS‐1 and Swarm vector data can moreover be fit simultaneously with only a small increase in misfit (by less than 0.2 nT). We show that both lithospheric anomalies and core surface field changes can be studied using MSS‐1 data. With its fast coverage of local times MSS‐1 is a valuable addition to the global geomagnetic observing system.

Waves in Earth's core and geomagnetic field forecast

We use advanced numerical geodynamo series to derive a reduced stochastic model of the dynamics at the surface of Earth's core. Considering order 3 autoregressive (AR-3) processes allows to replicate the simulated spatiotemporal spectrum over a broad range of time-scales, spanning millennia to a fraction of year, including the cut-off found for periods shorter than approximately 2 years and associated with magnetic dissipation. We show how to derive such a forward model from a variety of input simulation series, and present its implementation into the pygeodyn data assimilation algorithm, based on a sequential ensemble method. The updated scheme is applied to perform magnetic field hindcasts and core flow reanalyses. For all observable length-scales, the rate of change of the observed magnetic field is most of the time accounted for within the spread of the forward model trajectories. AR-3 predictions on average supersede by about 35 % linear extrapolations on short (2 yr) time-scales, reducing high-frequency spurious variations in reanalysed flow motions. This improvement is reduced to ≈10% for 5 yr increments, with a large variability from one epoch to the other depending on the overall curvature of the magnetic field evolution. We perform a reanalysis over the period 1880–2023 covered by observatory and satellite records. We find enhanced kinetic energy in three period ranges around 12.5, 6.5 and 3.5 years. At all three periods, fluid motions share geometrical properties compatible with quasi-geostrophic magneto-Coriolis waves: equatorial symmetry, larger amplitude near the equator, flow dominated by low azimuthal wave number and modulated in longitude, phase speed much faster than the fluid velocity and decreasing with the period. At 6.5 yr period we trace back to the mid-1990's the patterns previously detected from satellite data. We also find in the 1960–70's a similar wave-train, possibly in link with the 1969 geomagnetic jerk. The AR-3 model, in conjunction with early satellite records, likely helps isolate such coherent features on interannual time-scales. Similar wave-like motions also show up at 3.5 yr period around 1970 and during the past decades. At periods around 12.5 yr we detect recurrent patterns starting as far back as 1920, and modulated over decadal time-scales. Our results show growing evidence for core dynamics governed by the presence of hydro-magnetic waves over a wide range of periods. This may allow deterministic and/or empirical descriptions of the signal that may help sound deep Earth's properties, and improve predictions of the magnetic field evolution.

Silver nanoparticle induced immunogenic cell death can improve immunotherapy

Cancer immunotherapy is often hindered by an immunosuppressive tumor microenvironment (TME). Various strategies are being evaluated to shift the TME from an immunologically ‘cold’ to ‘hot’ tumor and hereby improve current immune checkpoint blockades (ICB). One particular hot topic is the use of combination therapies. Here, we set out to screen a variety of metallic nanoparticles and explored their in vitro toxicity against a series of tumor and non-tumor cell lines. For silver nanoparticles, we also explored the effects of core size and surface chemistry on cytotoxicity. Ag-citrate-5 nm nanoparticles were found to induce high cytotoxicity in Renca cells through excessive generation of reactive oxygen species (ROS) and significantly increased cytokine production. The induced toxicity resulted in a shift of the immunogenic cell death (ICD) marker calreticulin to the cell surface in vitro and in vivo. Subcutaneous Renca tumors were treated with anti-PD1 or in combination with Ag-citrate-5 nm. The combination group resulted in significant reduction in tumor size, increased necrosis, and immune cell infiltration at the tumor site. Inhibition of cytotoxic CD8 + T cells confirmed the involvement of these cells in the observed therapeutic effects. Our results suggest that Ag-citrate-5 nm is able to promote immune cell influx and increase tumor responsiveness to ICB therapies.

Preparation, characterization and mechanism of SiO2@SiO2 core-shell microspheres through polymerization-induced colloid aggregation for fast separation using ultra performance liquid chromatography

The polymerization-induced colloid aggregation (PICA) method is commonly used to create SiO2@SiO2 core–shell silica microspheres (CSSMs), but it often encounters challenges such as incomplete shell coating and poor reproducibility. In this paper, the formation mechanism of the silica shell layer during the preparation of SiO2@SiO2 CSSMs using the PICA method was investigated. It was found that ureido modification can reduce the Zeta potential of the silica core surface, facilitating the deposition of coacervates formed by urea-formaldehyde resin (UF) and silica nanoparticles on the silica core surface to form the SiO2 shell layer when the Zeta potential of the surface is in the range of −20.1 mV to −4.8 mV. By controlling the interfacial state and surface potential of the SiO2 core, the issue of inconsistent reproducibility in preparing SiO2@SiO2 CSSMs can be overcome. Furthermore, optimization of experimental parameters such as pH, reaction temperature, water content, and reaction time can enhance the formation process. The thickness of the shell and pore size of CSSMs can be successfully adjusted by varying the reaction time and the particle size of colloidal silica sol, respectively. With optimal conditions, the semi-scale production yield of SiO2@SiO2 CSSMs can be increased to 50 g. The SiO2@SiO2 CSSMs were modified with octadecyltrichlorosilane (ODS) to be used as stationary phases in reversed phase liquid chromatography (RPLC) for fast separation of small solutes, peptides, and proteins. The superior separation efficiency indicates that the improved PICA method has the potential to be utilized as an alternative to the layer-by-layer method for large-scale production of SiO2@SiO2 CSSMs.

Paleoenvironmental characterization and historical trends of polycyclic aromatic hydrocarbons (PAHs) of Nutrias Lagoon, Uruguay

Concentrations of polycyclic aromatic hydrocarbons were assessed in a sediment core retrieved from Nutrias Lagoon, located within the Rocha Lagoon Protected Area along the SE Uruguayan coast. Using a 210Pb chronology, we reconstructed the historical accumulation of polycyclic aromatic hydrocarbons over the past 123 years (1895-2018). This study, the first of its kind in Uruguay, fills a research gap in understanding historical PAH accumulation and source changes. Our examination of dating, geochemical, and sedimentological data unveiled four main events, with minor instances in 1956±5 and 1964±4, and more significant occurrences in 1914±9 and 1997±2. Additionally, two prominent trend shifts were identified, one predating 1900 and the other in 1986±2. Before 1900, a dry spell was apparent, supported by all proxies, alongside a notable surge in heavy polycyclic aromatic hydrocarbons, likely attributed to fires during this arid period. Post-1986±2, a rise in sedimentation rates in the lagoon was observed, possibly due to increased rainfall. Also, the eutrophication of the lagoon over the years can be observed. Furthermore, a recent increase in polycyclic aromatic hydrocarbons influx at the core's surface was linked to the construction of a nearby lagoon bridge and associated roadwork. Our findings suggest that atmospheric deposition constitutes the primary source of polycyclic aromatic hydrocarbons in the lagoon, offering insights into its recent environmental history and basin dynamics. This study establishes a critical baseline for future research in the region and facilitates the development of effective and sustainable environmental management strategies.

Fabrication of Mo-encapsulated stainless steel by powder metallurgy and assessment of localized corrosion resistance

As a source of corrosion inhibitors, 2.5% Mo powder was mixed with Type 304L stainless steel powder and spark-plasma sintered to a fabricate Mo-encapsulated Type 304L stainless steel. The Mo particles formed a core/shell structure. The localized corrosion resistance of the fabricated Mo-encapsulated Type 304L stainless steel was compared with those of spark-plasma-sintered Type 304L and Type 316L stainless steels. Potentiodynamic polarization in 0.1 M NaCl suggested that the Mo cores could release molybdate, which acts as an inhibitor. However, the shells did not dissolve, preventing the Mo-enriched particles from acting as pit initiation sites. Similarly, the surface of the Mo core dissolved during dip-and-dry cycles using 0.1 M NaCl, but the shell was less prone to dissolution. Although the fabricated Mo-encapsulated stainless steel did not contain Mo as a solid solution, its rust resistance was equivalent to that of spark-plasma-sintered Type 316L stainless steel. In potentiodynamic polarization, the initiation potential for localized corrosion of the Mo-encapsulated Type 304L stainless steel was remarkably higher than those of the sintered Type 304L and Type 316L stainless steels. The corrosion inhibition mechanism of the Mo-encapsulated Type 304L stainless steel was discussed from three viewpoints: (1) passive film modification on the steel matrix, (2) cathodic protection of the steel matrix by the Mo core dissolution, and (3) corrosion inhibition by molybdate dissolved from the Mo-enriched particles, and the last one appeared to be the most likely.

Resistance of a PdAu12(8e) Core to Growth in Collision-Induced Sequential Reductive Elimination of (C≡CR)2 from [PdAu24(C≡CR)18]2.

Previous studies have reported that [PdAu24(PAF)18]2- (PAF = 3,5-(CF3)2C6H3C≡C) with an icosahedral superatomic PdAu12(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PAF)2 ( J. Phys. Chem. C 2020, 124, 19119). The most likely scenario after the CISRE of (PAF)2 is the growth of the PdAu12(8e) core via the fusion of the Au(0) atoms produced from the Au2(PAF)3 units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu24(PAF)18-2n]2- (n = 1-6) revealed that the electronically closed PdAu12(8e) core does not grow to a single superatom with (8 + 2n)e but assembles with Au2(2e) units. Characterization of the CISRE products of other alkynyl-protected Au clusters suggested that even the non-superatomic Au17(8e) core was resistant to growth due probably to rigidification by PA ligands. We propose that there is a kinetic bottleneck in the growth process of protected Au clusters at the stage where they are electronically closed and/or lose their structural fluxionality by ligation.

Improvement and effectiveness analysis of dynamic/static imbibition experiments.

In low-permeability fractured reservoirs, there is a generalized fluid displacement between the replacement fluid in the fracture and the matrix crude oil. This imbibition behavior plays a crucial role in the development of this type of reservoir. The experimental devices for studying static imbibition behavior are generally susceptible to air pollution on the surface of the test core and a long testing period; the experimental devices for studying dynamic imbibition behavior are generally unable to eliminate the driving action. A dual-purpose experimental setup and an experimental method for dynamic or static imbibition that can avoid the above defects were designed. A method of fracture fluid flow rate calculation and motor speed conversion is proposed, and the method is used to assist in setting the parameters of dynamic imbibition experiments. The device was applied to compare the experimental effects with the static imbibition bottle and the dynamic replacement imbibition, respectively, and the effect of fracture width on the dynamic imbibition of repellent oil was investigated. The results show that: the static imbibition recovery rate of the dynamic/static imbibition experimental device is 1.55 percentage points higher than that of the imbibition bottle; the dynamic imbibition recovery rate is 3-6 percentage points lower than that of the driving dynamic imbibition method, and it can reflect the influence of a single flow rate condition on the imbibition; imbibition in low-permeability fractured reservoirs is more likely to take place in the fracture in the interval of 50-100 μm in the width.

Gas sensing properties of Ti0.2V1.8CTx/V2O5 nanocomposite

A method for the preparation of nanocomposite containing Ti0.2V1.8CTx MXene core and titanium-doped vanadium oxide surface layers as a result of relatively low-temperature partial oxidation of MXene multilayer - two-dimensional vanadium-titanium carbide has been developed. It is shown that during oxidation in air atmosphere of initial Ti0.2V1.8CTx at temperature 250°С, in general, the microstructure of accordion-like aggregates with some increase in porosity of their constituent layers and increase in their thickness due to the formation of V2O5 is preserved. At the same time, preservation of the MXene structure with a decrease in the interplanar spacing from 10.3 (initial powder Ti0.2V1.8CTx) to 7.3 Å was observed. Raman spectroscopy confirmed the formation of vanadium oxide. Kelvin-probe force microscopy data revealed that the formation of Ti0.2V1.8CTx/V2O5 nanocomposite results in a decrease in the work function from 4.88 (Ti0.2V1.8CTx) to 4.68 eV. The chemosensor properties towards a range of gaseous analytes (H2, CO, NH3, NO2, C6H6, C3H6O, CH4, C2H5OH and O2) have been comprehensively studied for Ti0.2V1.8CTx/V2O5 layers coated using the microplotter printing. At increased detection temperatures (125–200°С), high sensitivity to oxygen (10% O2) and NO2 (100 ppm) is observed; there are notable responses to humidity (50% RH) throughout the 25–200°С temperature range. At room temperature, good response to acetone, ethanol and ammonia is observed.

On thermally driven fluid flows arising in astrophysics

We investigate a potential model for an unbounded celestial bodies of finite mass composed of a solid core and a gaseous atmosphere. The system is governed by the Navier–Stokes–Fourier–Poisson equations, incorporating no-slip boundary conditions for velocity and a specified temperature distribution on the surface of the solid core. Additionally, a positive far-field condition is imposed on the temperature. This manuscript extends the mathematical theory of open fluid systems to unbounded exterior domains addressing these physically motivated yet highly challenging combination of boundary conditions. Notably, we establish the existence of global-in-time weak solutions and demonstrate the weak–strong uniqueness principle

Human mesenchymal stem/stromal cell-derived extracellular vesicle transport in meniscus fibrocartilage.

Extracellular vesicles (EVs) derived from endometrial-derived mesenchymal stem/stromal cells (eMSC) play a crucial role in tissue repair due to their immunomodulatory and reparative properties. Given these properties, eMSC EVs may offer potential benefits for meniscal repair. The meniscus, being partly vascularized, relies on diffusivity for solute trafficking. This study focuses on EVs transport properties characterization within fibrocartilage that remains unknown. Specifically, EVs were isolated from Crude and CD146+ eMSC populations. Green fluorescence-labeled EVs transport properties were investigated in three structurally distinct layers (core, femoral, and tibial surfaces) of porcine meniscus. Diffusivity was measured via custom fluorescence recovery after photobleaching (FRAP) technique. Light spectrometry was used to determine EVs solubility. Both Crude and CD146+ eMSC EVs exhibited high purity (>90% CD63CD9 marker expression) and an average diffusivity of 10.924 (±4.065) µm²/s. Importantly, no significant difference was observed between Crude and CD146+ eMSC EV diffusivity on the meniscal layer (p > 0.05). The mean partitioning coefficient was 0.2118 (±0.1321), with Crude EVs demonstrating significantly higher solubility than CD146+ EVs (p < 0.05). In conclusion, this study underscores the potential of both Crude and CD146+ eMSC EVs to traverse all layers of the meniscus, supporting their capacity to enhance delivery of orthobiologics for cartilaginous tissue healing.

Improved flux pinning properties of Mg exceed MgB2 ceramics with B4C and Dy2O3 additions

In this study, MgB2 polycrystals were synthesized via the addition of B4C and Dy2O3. X-ray diffraction confirmed that MgB2 was the predominant phase in all the samples. The superconducting properties of the samples were characterized by in-field temperature-dependent resistivity and magnetization measurements. The upper critical field (Hc2) and the critical current density (Jc) of each sample were estimated. The results indicate significant enhancements in Hc2 and Jc with the optimal addition levels of B4C and Dy2O3. According to collective pinning theory, δl pinning was identified as the dominant pinning type in the fabricated samples. The dominant pinning mechanism was determined to be core surface pinning induced by grain boundaries, which is consistent with predictions made by the Dew–Hughes model.

Study on gas–liquid–solid multiphase flow and erosion in ball valves

In industrial processes involving ball valves, gas–liquid–solid multiphase flows with continuous carrier and discrete particle phases are characterised by erosion challenges. These challenges reduce sealing performance and can lead to leakage and valve failure. To explore the characteristics of gas–liquid–solid multiphase flow and flow-induced erosion in ball valves, we conducted a combination of computational fluid dynamics numerical simulations and experimental testing. Results indicate that an increase in the gas content increases the flow coefficient, accelerates both liquid flow and particle movement and exacerbates erosion. In addition, particles are less concentrated in regions with higher gas concentrations. Erosion is primarily observed on the upstream surface and rear wall of the valve core as well as the upper side of the downstream pipeline. Severe erosion occurs more at smaller valve openings, and affected regions expand as the valve opening increases.

Structural reconstruction synthesis of highly luminous water-stable CsPbBr3@CsPb2Br5@DSPE core-shell perovskite nanocrystals for bioimaging, pattering, and LEDs

Lead halide perovskite (LHP) nanocrystals (NCs) suffer from poor stability against environmental factors (heat, moisture, oxygen, etc.), which seriously hinders their practical application. Constructing a core-shell structure could be an effective approach to improve the stability and optical properties of the LHP NCs. Herein, a novel strategy of water-triggered phase transformation and phospholipid (DSPE) micelle encapsulation is proposed, generating highly luminescent water-dispersed CsPbBr3@CsPb2Br5@DSPE core-shell-shell nanocrystals. The epitaxial growth of the CsPb2Br5 shell is induced by the in-situ reconstruction of the CsPbBr3 surface by water erosion, and the lattice mismatch with the CsPbBr3 core is small (3.8%). The further amphipathic phospholipid encapsulation guarantees their excellent water dispersity and stability. Revealed by the femtosecond transient absorption spectroscopy, the dense CsPb2Br5@DSPE shell effectively passivates the surface of the CsPbBr3 core, thus improving its stability and luminescence performance. The resulting CsPbBr3@CsPb2Br5@DSPE nanoparticles exhibit excellent performance as fluorescent probes for bioimaging, aqueous inks for high-resolution pattering, and light conversion layers for LEDs, demonstrating their promising potential in multiple applications.

Characterization of hydromagnetic waves propagating over a steady, non-axisymmetric background magnetic field

Motivated by recent observations of rapid (interannual) signals in the geomagnetic data, and by advances in numerical simulations approaching the Earth’s outer core conditions, we present a study on the dynamics of hydromagnetic waves evolving over a static base state. Under the assumption of timescales separation between the rapid waves and the slow convection, we linearize the classical magneto-hydrodynamics equations over a steady non-axisymmetric background magnetic field and a zero velocity field. The initial perturbation is a super-rotating pulse of the inner core, which sets the amplitude and length scales of the waves in the system. The initial pulse triggers axisymmetric, outward propagating torsional Alfvén waves, with characteristic thickness scaling with the magnetic Ekman number as E k M 1 / 4 . Because the background state is non-axisymmetric, the pulse also triggers non-axisymmetric, quasi-geostrophic (QG) Alfvén waves. As these latter waves propagate outwards, they turn into QG, magneto-Coriolis (QG-MC) waves as the Coriolis force supersedes inertia in the force balance. The period of the initial wave packet is preserved across the shell but the QG-MC wavefront disperses and a westward drift is observed after this transformation. Upon reaching the core surface, the westward drift of the QG-MC waves presents an estimated phase speed of about 1100 k m y − 1 . This analysis confirms the QG-MC nature of the rapid magnetic signals observed in geomagnetic field models near the Equator.

Optimum Size and Heat Transfer and Velocity Correlations of the Outer and Inner Surfaces of Vertical Hollow Polygonal Cylinders in Natural Convection

Abstract Laminar natural convection heat transfer from vertical hollow polygonal cylinders with a wide range of cross-sectional areas is investigated. The buoyancy-driven three-dimensional (3D) flow around hollow polygonal cylinders immersed in quiescent ambient air with equal outer and inner surface temperatures is analyzed. The governing equations are numerically solved in nondimensional variables using the finite volume method. The numerical solution is validated using available experimental and numerical data. Results of the mean Nusselt number for the outer (Nu¯ho) and inner (Nu¯hi) surfaces are obtained by varying a number of key parameters. These parameters are the Rayleigh number based on the cylinder height (Rah) in the range 103≤ Rah≤ 107, the nondimensional cross-sectional area (AC) in the range 0.006 ≤ AC≤ 0.5, and the number of sides of the polygon (N) in the range 6 ≤ N ≤∞. In all cases, a Prandtl number (Pr) of 0.7 has been assumed. The study shows that at a certain Rayleigh number and a certain number of sides, the heat transfer rate from the inner surface decreases (by as much as 79.8%) as the polygon area decreases (by as much as 83.32%), whereas the heat transfer rate on the outer surface increases (by as much as 133.3%) as the polygon area decreases (by as much as 83.32%). It has also been found that the behavior of the buoyancy-driven flow in the vicinity of the outer surface is fundamentally different than that near the inner surface. Additional details about this fundamental difference are presented in the Results and Discussion section of the paper. New correlations to calculate the average velocity at the exit surface of the cylinder inner core and the mean Nusselt number for both the outer and inner surfaces have also been developed. Also, correlations have been developed for selecting the optimal cross-sectional area for purposes of identifying the regions where the thermal and velocity boundary layers overlap within the inner core of the cylinder.

Pulse diffusion welding of female joints

Special feature of operation of electrovacuum tubes, in particular the cathode assembly, is constant heating due to bombardment of its surface with electrons. Stable characteristics and durability of the cathode assembly depend on high-quality connection (welding) of the core surfaces with the emitter over the entire area of ​​the overlapped conjugation. The use of diffusion welding for joining a cathode assembly made of dissimilar materials is not possible due to the occurrence of poor welding fusion due to the presence of gaps in the ring sectors of the equipment, and, consequently, a decrease in the service life of the cathode assembly. The authors proposed to implement the process by combining magnetic pulse welding with diffusion welding. The originality of the work is the possibility of remote action on the joint through a dielectric quartz cup, which is a part of the technological vacuum chamber. The inductor system is outside the quartz cup, which allows heating the assembled unit without heating the tool – an inductor made of dissimilar materials – to a temperature of 700 ° C and higher. The authors determined the main parameters of the process of pulse diffusion welding in vacuum: pressure in the working chamber is В=0.66·10−2Pa (5·10−5mmHg); preheating temperature is T=700–1250°C; magnetic field pulse energy is W=5÷17kJ; operating frequency of current pulse discharge is fd=5–15kHz; magnetic pressure is Pm∙107N/m2. In this way, cathode assemblies of a wide range of metal pair combinations with a base diameter of d=20mm and a sample length of L=40mm were produced. The proposed technology has been successfully implemented and introduced at Tantal (Open Joint Stock company). The economic effect consists in reducing labor intensity and obtaining joints of stable quality.

In-situ prediction of soil organic carbon contents in wheat-rice rotation fields via visible near-infrared spectroscopy

Visible near-infrared (VNIR) spectroscopy is a reliable method for estimating soil properties. However, its effectiveness in accurately predicting soil organic carbon (SOC) contents, particularly in wheat-rice rotation fields, remains uncertain. In this study, we collected 202 samples from wheat-rice fields (0–20 ​cm) in southeastern China and measured in-situ spectra of the vertical surface of the soil cores and the laboratory spectra of the dried and sieved soil samples. Our study focused on evaluating three algorithms - external parameter orthogonalization (EPO), direct standardization (DS), and piecewise direct standardization (PDS) - to address the influence of external factors, particularly soil moisture. To carry out our analysis, the dataset was divided into calibration (141 samples) and validation (61 samples) sets via the Kennard-Stone algorithm. A subset of the corresponding in-situ and laboratory spectra in the calibration set (transfer set) was used to derive the transfer matrix for EPO, DS, and PDS, enabling the conversion of in-situ spectra to laboratory spectra by characterizing their differences. Four machine learning models, including cubist, partial least squares regression (PLSR), random forest (RF), and memory-based learning (MBL), were used to predict the SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) contents based on the laboratory, in-situ, and corrected in-situ spectra. The results revealed that the laboratory spectra outperformed the non-corrected in-situ spectra, with coefficients of determination (R2) of 0.91, 0.75, and 0.80 for SOC, POC, and MAOC, respectively. Among the models, MBL and PLSR exhibited the highest average R2 at 0.85–0.86. EPO marginally improved the prediction accuracy (R2 increased from 0.85 to 0.87 for SOC, 0.64 to 0.69 for POC, and 0.75 to 0.82 for MAOC). These promising prediction accuracies underscore the potential of VNIR spectra for in-situ predictions in wheat-rice fields in Southeast China, offering insights for predicting SOC contents via in-situ spectroscopy.