Bottom Layer Research Articles

Baltic Sea surface temperature analysis 2022: a study of marine heatwaves and overall high seasonal temperatures

Abstract. In 2022, large parts of the Baltic Sea surface experienced the third-warmest to the warmest temperatures over the summer and autumn months since 1997. Warm temperature anomalies can lead to marine heatwaves (MHWs), which are discrete periods of anomalous high temperatures relative to the usual local conditions. Here, we describe the overall sea surface temperature (SST) conditions observed in the Baltic Sea in 2022 and provide a spatiotemporal description of surface MHW events based on remote sensing, reanalysis, and in situ station data. The most MHWs, locally up to seven MHW events, were detected in the western Baltic Sea and the Inner Danish Straits, where maximum MHW intensities reached values of up to 4.6 °C above the climatological mean. The northern Baltic Proper and the Gulf of Bothnia were impacted mainly by two MHWs at maximum intensities of 7.3 and 9.6 °C, respectively. Our results also reveal that MHWs in the upper layer occur at a different period than at the bottom layers and are likely driven by different mechanisms. Reanalysis data from two exemplary stations, “Lighthouse Kiel (LT Kiel)” and “Northern Baltic”, show a significant increase in MHW occurrences of +0.73 MHW events per decade at LT Kiel and of +0.64 MHW events per decade at Northern Baltic between 1993 and 2022. Moreover, we discuss the expected future increased occurrence of MHWs based on a statistical analysis at both locations.

Dynamic Response Analysis of Asphalt Pavement under Pavement-Unevenness Excitation

This paper investigates and analyzes the dynamic response of asphalt pavement under pavement-unevenness excitation based on an orthogonal vector function system and efficient DVP (dual variable and position) method. Firstly, starting from the pavement unevenness of the vehicle excitation source, the pavement-unevenness excitation is established by using the filtered white-noise method, and the random load of the vehicle model is obtained by simulation. Then, based on the basic governing equation of the road-surface problem under the random load, the analytical solution of the road-surface mechanical response is obtained by using the orthogonal vector function system and DVP method. The effects of pavement-unevenness grade, vehicle speed, vehicle load, interlayer contact condition, and transverse isotropy on the mechanical response of the road surface are analyzed via the analytical results. The results show that DVP can effectively solve the dynamic response of pavements under the excitation of pavement unevenness; in addition, it can also be applied to certain situations, such as transverse isotropy of materials and interface conditions. The results show that the pavement unevenness does not affect the average stress and strain of each layer but has a significant effect on the peak value and dispersion degree. An increase in vehicle speed causes a peak in strain and a larger coefficient of variation. Poor bonding between interfaces can lead to increased stress and strain at the bottom of the surface layer.

Design and investigation of indium tin oxide-based transparent broadband microwave absorbers

This paper presents the design of a novel wideband transparent microwave absorber based on indium tin oxide (ITO). The absorber adopts a multilayer structure, with the top layer composed of a nested square structure made of ITO material, an intermediate dielectric layer of polyvinyl chloride (PVC), and a bottom layer of polyethylene terephthalate (PET) coated with ITO as the reflector. By optimizing structural parameters such as the thickness of the ITO film and the dimensions of the spacer layer, efficient broadband microwave absorption exceeding 90% is achieved within the frequency range of 2.43 to 5.67 GHz, while simultaneously meeting requirements for optical transparency and broadband performance. Simulation experiments and theoretical analyses demonstrate excellent polarization and incident angle stability of the absorber structure. Finally, samples are fabricated using screen printing technology, and free-space testing results are consistent with simulation predictions, validating the feasibility of the design.

An in‐band full‐duplex antenna for 2.4 GHz WLAN using differential‐feed based neutral coupling for isolation enhancement

AbstractThis article introduces a unique design approach for a compact in‐band full‐duplex (IBFD) antenna with good isolation in a wider bandwidth at the 2.4 GHz WLAN. The meander slot baluns are innovatively constructed in the feeding network, one balun on the top substrate layer and the other on the bottom substrate layer of the ground, to realize double differential feeding and polarization diversity. The metallic vias that connect one of the baluns in the feeding network with the co‐radiating patch further reduce the antenna's overall size. The balun's neutral coupling characteristics of differential potentials, which reduce the leakage currents by creating null potential, and differential filtering, which suppresses the leakage currents by non‐coupling fields, generate high isolation in the antenna. The designed balun offers a stable differential feed with a trivial magnitude and phase imbalances of (0.04–0.06) dB and , respectively. The antenna offers a minimum isolation of 78 dB with a wider bandwidth of 130 MHz. The far‐field measurement shows broadside radiation with low cross‐polar levels of less than −32 dB. A prototype is fabricated on FR‐4 substrate layers with an overall size of (0.8 × 0.8 × 0.012) ( is the free space wavelength of the frequency GHz) to validate the proposed design performance. The measured results of the prototype properly correlate with the simulated results.

Determination of Dynamic Stresses and Displacements under the Action of an Impact Load on a Two-Layer Structure during the Indentation Process

Introduction. Numerous researchers of the reliability of building structures pay attention to hardness, an important characteristic of the structural material. It is determined by indentation — pressing the tip of the tool into the surface. The advantages of dynamic indentation methods and the distribution of stress intensity on the surface and inside the sample are investigated. However, the condition of layered materials on impact has been poorly studied. The objective of the presented work is to consider indentation for a two-layer sample and determine the sensitivity of the top layer to the strength of the substrate. This will allow us to identify significant characteristics of the strength properties of homogeneous and heterogeneous structures.Materials and Methods. An elastoplastic model of material behavior and a shock indentation scheme were used, which took into account the masses of the indenter and the striker coupled by linear springs. The surface of the indenter was conical, the opening angle was 120°. The impact was simulated in the MATLAB system. Finite element model in Ansys APDL was used to verify the data and analyze the results of the experiment. Traditional models of elasticity theory were used for calculations. The behavior of the material in the zone of plastic deformation was described using the options of multilinear isotropic hardening and the von Mises plasticity criterion.Results. The results of comparing three versions of varying the level of yield strength in the bottom layer are presented: when the yield strength in the bottom layer is half as high as the top one, equal to it, and twice as high. Displacements at different observation points for samples with a top layer of 2 mm and 1 mm were analyzed. In the first case, under horizontal shear, the displacement indices inside the sample did not change if the yield strength level was twice lower or higher than in the top one. If these indicators were equal, the difference became noticeable. In the second case (layer 1 mm), the difference in displacement was visible at all observation points. Thus, it can be reasonably concluded that a structure with a smaller top layer is more sensitive to impact. In the course of the research, it became known that vibrations associated with the transition to the plasticity zone occurred in the 2 mm zone, and elastic damping vibrations occurred below this zone. We solved the classification problem for the top layer of the material with changing characteristics of the base. The indicator for comparison was the Brinell hardness (HB) in the range of 200–600. The results were processed using a neural network and visualized in the form of graphs. The accuracy of its calculations was 98%.Discussion and Conclusion. To determine the strength properties of homogeneous structures, it is sufficient to characterize the speed of displacement inside the sample. For an inhomogeneous structure, additional parameters should be introduced — displacements on the surface and inside the sample at fixed observation points. An integrated approach to determining the strength properties of an inhomogeneous structure improves the accuracy of calculations, and the use of neural networks increases their speed.

Research on the strength influence and crack evolution law of layered backfill based on macro and meso mechanical response

This article analyzes the effects of inclined angle (IA), filling times (FTs) and cement tailings ratio (CTR) on the uniaxial compressive strength (UCS) and crack development law of layered cemented backfill (LCB) using various research methods, including indoor experiments, numerical simulation, and computed tomography (CT) scanning. The research shows: (1) In the indoor experiments, it was observed that increasing the IA, increasing the number of FTs, and decreasing the CTR had a significant weakening effect on the UCS of the specimens. The greater the IA, the more pronounced the separation and dislocation of the layered contact surface, resulting in a significant increase in macroscopic cracks at the bottom. As the FTs increases, the center of gravity of the failure of the LCB gradually moves downwards. This causes the damage and failure time to advance, and the peak stress to change from one main crack to multiple main cracks. (2) During the numerical simulation, compressive stress accumulates and increases around the pores in the layered contact surface. Microcrack aggregation occurs on the contact surface, and downward expansion and extension. The peak strain energy decreases as the IA increases with the FTs. The number of shear cracks increased more at 20° to 30° than at 0° to 20°. The strain energy of the 0° specimen is the highest, while that of the 30° specimen is the lowest. (3) The CT scan shows that the LCB is affected by stress conduction hysteresis. When the bottom backfill is in the stage of crack evolution, the top backfill is in the stage of compaction.When the LCB reaches the peak stress, both the bottom and middle layers of the backfill lose load-bearing capacity, and the top layer of the backfill has no cracks. This paper provides reference value and research ideas for the destruction of backfill that contain layered defective structures.

Analysis of the mechanical behavior of asphalt pavement under multiple coupling effects

To reveal the damage mechanism of asphalt pavement caused by the spatial rotation of the stress principal axis, and the influence range of excess pore water pressure on the pavement under the coupling action of multiple fields, the finite element software was used to build the three-dimensional highway asphalt pavement models. Under the consideration of gravity's impact on dynamic computation results, the study investigated the variation patterns of the direction cosines of the principal stress axes of asphalt structural pavement elements under the action of moving loads, as well as the distribution laws of excess pore water pressure. The results indicate that the influence of gravity on dynamic computation results increases gradually with the depth of the pavement, reaching an error of first principal stress of 40.1 % at the bottom of the lower layer. During the movement of loads, the pavement elements directly under the load undergo rotation of the principal stress axes in the xy, xz, and yz planes under different physical fields. With increasing pavement depth, the angle between the first principal stress and the z-axis primarily fluctuates between −90° to 0° and 90° to 180°. The cosine of the angle between the first principal stress and the x-axis and z-axis undergoes instantaneous positive and negative conversion, which can easily lead to transverse and longitudinal cracks on the road surface. The influence widths of excess pore water pressure along the longitudinal and transverse directions of the pavement increase with the pavement depth, with maximum widths of 5.426 m and 2.075 m, respectively. These findings offer new insights into the mechanisms behind the formation of transverse and longitudinal cracks on asphalt pavement and hold significant implications for the improvement of asphalt design methods.

Studies of Hydrogen Sulfide Contamination of the Deep-Water Basin of the Middle Caspian Sea During Cruise of the R/V “Issledovatel Kaspiya” September 2022

Results of the comprehensive studies of hydrological and chemical structure of the Middle and Northern Caspian Sea carried out aboard r/v “Issledovatel Kaspiya” in September 2022 are presented. It is shown, despite the continuing decrease in sea level, there is no aeration of the deep layers, the hydrogen sulfide layer persists with a tendency to increase the concentration of hydrogen sulfide in the bottom layer. There is an increase of the oxygen minimum zone. The changes of the Caspian Sea ecosystem have led to a weakening of the removal of nutrients from the photic layer into the bottom layers and, as a consequence, a decrease in the concentration of silicon in the bottom layer. The results obtained will allow to evaluate the trends of ongoing changes.

Hydrothermal coupling model between wellbore and permafrost for drilling in arctic cold regions

The abundant oil and natural gas resources in the Arctic cold regions have driven people to conduct drilling operations in these harsh environments. During drilling operations in Arctic permafrost regions, the linear heat source effect generated by the flow of drilling fluid in the wellbore continuously melts the surrounding permafrost, which can lead to wellhead settlement and instability of the wellbore wall, among other accidents. In order to provide guidance for drilling engineering in cold regions, there is an urgent need to study the coupled heat transfer between the wellbore and the permafrost in Arctic drilling. Due to the significant influence of hydrothermal coupling process in permafrost on temperature transfer, conventional wellbore heat transfer models are not suitable. Therefore, this paper proposes a hydrothermal coupling model between the wellbore and permafrost for drilling in Arctic cold regions and analyzes the heat transfer in the wellbore and the hydrothermal processes of the formation using numerical methods. By applying this model, the insulation effects of existing main wellbore temperature control and insulation technologies were studied. The main research findings indicate that drilling process can cause the permafrost around the wellbore to thaw, and the thawed permafrost around the wellbore presents a “horn” shape that expands from the wellhead to the bottom of permafrost layer; Without insulation measures, the volume of thawed permafrost around the wellbore can reach 315 m³ after 7 days of circulation; During the drilling process, moisture migration occurs. Under the effect of gravitational seepage, unfrozen water content in the thawed permafrsot around the wellbore increases from the wellhead to the bottom of the permafrsot layer; Vacuum insulated tubing has almost negligible impact on the temperature of the drilling fluid in the wellbore, while it can reduce the volume of thawed permafrost around the wellbore by 62.5 % to 88 % or even higher; Drilling fluid cooling systems can significantly lower the temperature of the drilling fluid in the wellbore but cannot effectively prevent the thawing of permafrost around the wellbore. Therefore, in practical drilling operations, priority should be given to using high-quality vacuum insulated tubing or combining both methods simultaneously.

Evolution of water wave packets by wind in shallow water

We use the Korteweg–de Vries (KdV) equation, supplemented with several forcing/friction terms, to describe the evolution of wind-driven water wave packets in shallow water. The forcing/friction terms describe wind-wave growth due to critical level instability in the air, wave decay due to laminar friction in the water at the air–water interface, wave stress in the air near the interface induced by a turbulent wind and wave decay due to a turbulent bottom boundary layer. The outcome is a modified KdV–Burgers equation that can be a stable or unstable model depending on the forcing/friction parameters. To analyse the evolution of water wave packets, we adapt the Whitham modulation theory for a slowly varying periodic wave train with an emphasis on the solitary wave train limit. The main outcome is the predicted growth and decay rates due to the forcing/friction terms. Numerical simulations using a Fourier spectral method are performed to validate the theory for various cases of initial wave amplitudes and growth and/or decay parameter ranges. The results from the modulation theory agree well with these simulations. In most cases we examined, many solitary waves are generated, suggesting the formation of a soliton gas.

FamLink2 – A comprehensive tool for likelihood computations in pedigrees analyses involving linked DNA markers accounting for genotype uncertainties

There is an increasing demand for software that can handle an arbitrary number of linked markers in forensic genetics; primarily with application to inference of relationships and direct matching but also in applications such as ancestry inference and mixture interpretation. With the emergence of sequencing technologies, denser sets of SNP markers are generated and analyzed. Additionally, sequence data of low quality and quantity DNA generate uncertainty about the underlying true genotype. We provide an efficient implementation of a general model for pedigree likelihood computations with genetic marker data using a three-layered approach. The top and first layer is the population model where allele frequencies and population substructure are accounted for. The second layer is the inheritance model which efficiently handles linked markers using an IBD model. The third and bottom layer is the observational level where we model the likelihood of the true genotype given underlying reads as well as parameters for errors. We exemplify the utility of our implementation as well as provide validation according to guidelines established by the ISFG using a combination of two published SNP panels. We demonstrate that computations are feasible for panels encompassing 10,000 markers and we argue that, due to the properties of the underlying algorithm, extending the number of markers will result in a linear increase in computation time. In addition we study the impact of parameters used in our model and suggest some guidelines pertaining to their values. The results demonstrate that a probabilistic model for low coverage sequence read data is needed instead of relying on an a threshold based genotype and applying our general model for inference of relationships on a real case can be superior, i.e. higher information content, to other methods relying on either fixed genotypes with low quality sequence data or simple pair wise relationship tests. In summary, the implementation, FamLink2 (freely available at https://famlink.se), can jointly handle genetic linkage, genotype uncertainty and population substructure for an arbitrary pedigree with data for any number of individuals. Whereas the current study will focus on calculations disregarding mutations, FamLink2 has the ability to model mutations for certain built-in pedigrees.

Self‐Powered and 3D Printable Soft Sensor for Human Health Monitoring, Object Recognition, and Contactless Hand Gesture Recognition

AbstractA new galvanic cell design of a self‐powered and 3D‐printable soft sensor showing health monitoring, object recognition, and contactless hand gesture recognition, is reported. The soft sensor consists of a 3D‐printed poly(acrylic acid) (PAA) hydrogel electrolyte layer, a soft anode layer, and a soft cathode layer. The anode layer is a 3D‐printed and Cu2+ cross‐linked poly(N,N‐dimethylacrylamide‐co‐3‐alanine‐2‐hydroxypropylmethacrylate) (PDA) hydrogel dispersed with Cu metal particles (PDA/Cu2+/Cu hydrogel), while the cathode layer is a bottom thin layer of the PAA hydrogel containing MnO2 (PAA/MnO2). Using graphite films as the soft electrodes, the soft sensor is finally assembled. The soft sensor has high force and temperature sensitivities. It gives different electric current responses under stretching, bending, pressing, and impact loading. The soft sensor is demonstrated to be useful in detecting human motion and physiological activities, e.g., breath. Based on the force and contactless temperature sensitivities, the soft sensor is used to recognize human hand gestures and plastic balls with different diameters. This 3D printable soft sensor with self‐powering, contactless motion capturing, and multi‐pimulus sensing capabilities illustrates a new pathway to make soft sensory devices for healthcare and human‐machine interaction applications.

Prediction of s^{±}-Wave Superconductivity Enhanced by Electronic Doping in Trilayer Nickelates La_{4}Ni_{3}O_{10} under Pressure.

Motivated by the recently reported signatures of superconductivity in trilayer La_{4}Ni_{3}O_{10} under pressure, we comprehensively study this system using abinitio and random-phase approximation techniques. Without electronic interactions, the Ni d_{3z^{2}-r^{2}} orbitals show a bonding-antibonding and nonbonding splitting behavior via the O p_{z} orbitals inducing a "trimer" lattice in La_{4}Ni_{3}O_{10}, analogous to the dimers of La_{3}Ni_{2}O_{7}. The Fermi surface consists of three electron sheets with mixed e_{g} orbitals, and a hole and an electron pocket made up of the d_{3z^{2}-r^{2}} orbital, suggesting a Ni two-orbital minimum model. In addition, we find that superconducting pairing is induced in the s^{±}-wave channel due to partial nesting between the M=(π,π) centered pockets and portions of the Fermi surface centered at the Γ=(0,0) point. With changing electronic density n, the s^{±} instability remains leading and its pairing strength shows a domelike behavior with a maximum around n=4.2 (∼6.7% electron doping). The superconducting instability disappears at the same electronic density as that in the new 1313 stacking La_{3}Ni_{2}O_{7}, correlated with the vanishing of the hole pocket that arises from the trilayer sublattice, suggesting that the high-T_{c} superconductivity of La_{3}Ni_{2}O_{7} does not originate from a trilayer and monolayer structure. Furthermore, we confirm the experimentally proposed spin state in La_{4}Ni_{3}O_{10} with an in-plane (π, π) order and antiferromagnetic coupling between the top and bottom Ni layers, and spin zero in the middle layer.

Prevalence and distribution of dissolved paralytic shellfish toxins in seawater in the Yellow Sea and the Bohai Sea, China

Paralytic shellfish toxins (PSTs) could be secreted by PSTs-producing microalgae or released by ruptured cells in seawater. In this study, the distribution of dissolved PSTs in the Yellow Sea and the Bohai Sea, China, was investigated by two cruises in April and July 2023. Seawater samples were collected from the surface, middle and bottom layers, and the profiles of PSTs were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the spatial distribution characteristics of dissolved PSTs and their correlation with environmental factors were explored. Results showed that C1/2, GTX1/4, GTX2/3 and dcGTX2/3, were detected in seawater samples in both spring and summer, with the detection rates 100 % and 97.6 %, respectively. The total PST (ΣPSTs) concentrations ranged in 12 ∼ 590 pmol L−1, 9.3 ∼ 546 pmol L−1, 12 ∼ 2,452 pmol L−1, and not detected (nd) ∼ 188 pmol L−1 in seawater samples collected from the surface, middle and bottom layers in spring, and the surface layer in summer, respectively. Concentrations of PSTs markedly varied in the vertical water column in different sea regions. Generally, concentrations of ΣPSTs in the bottom seawater were higher than those in the surface and middle layers in the Bohai Sea and the North Yellow Sea, but no significant difference in the different water layers in the South Yellow Sea. In addition, concentrations of ΣPSTs in surface waters were much lower in summer than those in spring. In both spring and summer, dissolved PSTs in surface seawater were mainly distributed in the South Yellow Sea. These results indicate that PSTs were prevalent in the Yellow Sea and the Bohai Sea, of which the potential hazard to marine organisms should be highly concerned.

Effect of Current Waveform on Microstructure Evolution and Mechanical Properties of GH4169 High-Temperature Alloy Tungsten Inert Gas Additive Manufacturing.

Direct current (DC) and pulsed DC tungsten inert gas (TIG) additive manufacturing processes were employed to fabricate GH4169 high-temperature alloy specimens. Upon comparing and analysing the two additive manufacturing methods, the evolution of microstructure and mechanical properties of the additively manufactured specimens were discussed. It provided a useful reference for the engineering application of pulsed DC TIG technology. The results showed that the overall forming process of the specimen was relatively stable under the DC TIG additive manufacturing and pulsed DC TIG additive manufacturing processes. The aspect ratio of the deposited layer of the pulsed DC-deposited specimen was relatively low, and the deposited layer of the pulsed DC specimen became flatter, which was conducive to maintaining the stability of the molten pool during the deposition process and improving forming accuracy. The microstructure distribution of the deposited layer from bottom to top was relatively uneven, with columnar dendrites in the bottom layer, cellular crystals in the middle layer, and equiaxed crystals in the top layer. Compared with the DC TIG additive manufacturing of GH4169 high-temperature alloy specimens, the Laves phase of the pulsed DC specimens was significantly reduced, which improved the plasticity and brittleness of the material.

On the patterns and mechanisms of residual currents and suspended sediment transport in the Lingdingyang of the Pearl River Delta

Tide-averaged current, i.e., Eulerian residual current (ERC), indicates net transport of sediment and pollutants in coastal and estuarine regions. In this paper, we examine the dynamics of tidal currents and associate residual currents (RCs), suspended sediment transport and its governing mechanisms in the Lingdingyang (LDY) of the Pearl River Delta based on field data and numerical modeling. Results indicate that seaward ERCs dominate throughout the LDY. The ERCs are greater in the wet seasons than that in the dry seasons. The ERCs are smaller in the middle layer of the water column over the shoals, whereas they ware are larger in the middle layers in deep channels. The ERCs mainly discharge into the sea through the deep channel and west shoal, forming a slack water zone in the middle shoal. Vertical circulation structures of ERCs are controlled by the channel-shoal structure. A dual ERC circulation structure was observed between the channels, which is characterized with seaward and landward ERCs at the surface and bottom layers, respectively. As a result, the residual sediment transports are seaward, with large rates at the shoal than in the channel. Seaward ERCs explain residual sediment transport in the deep channel. Both ERCs and Stokes RCs (SRCs) are important over the shoal. Tidal pumping is of secondary importance and its direction varies over time and in space. These findings provide a scientific basis for understanding the channel-shoal evolution and maintenance of the navigational waterway in the LDY.

Sediment oxygen uptake and hypoxia in coastal oceans, the Pearl River Estuary region

Hypoxia is increasing in coastal oceans due to high oxygen consumption and weak ventilation. Quantifying biological oxygen uptake and how its effects on hypoxia respond to stratification is important for management and predicting future trends. This work introduces a simple analysis to quantify and compare the biological and physical drivers of hypoxia, by using an example from the Pearl River Estuary (PRE) region (10–70 m deep). We show that in the PRE region, sediment respires ∼50 % of organic matter produced in the water column and oxidizes ∼88 % of the ammonium produced from sediment organic matter degradation. These processes lead to high sediment oxygen uptake (SOU; 41.1 ± 16.3 mmol m-2d-1). Under stratification, sediment's effect on the bottom oxygen is strongly regulated by the thickness of the bottom boundary layer (BBL), and the robust relationships can be used to parameterize SOU. We then construct a simple and generic mass-balance model to estimate the water column oxygen uptake in the BBL (WOUBBL) and quantify the total oxygen loss. By comparing model results to observations in the PRE and other similar systems, we show that the sensitivity of oxygen levels to SOU is largely controlled by the duration of stratification, while the organic matter settling velocity controls the contributions of SOU to total oxygen consumption. We further demonstrate how the model can help evaluate the primary drivers of hypoxia (stratification versus high oxygen consumption), determine the time scale of stratification required to develop hypoxia, and explain the within and across system variabilities.

Aging characterization of dielectric materials using microstrip spiral resonator sensor: application in high frequency range, up to 18 GHz

This current work aims to propose a complete microwave procedure for dielectric materials aging characterization. To achieve this aim, a microstrip spiral resonator sensor, based on printed circuit board (PCB) technology, is designed to attend polyvinyl chloride (PVC) aging behavior through microwave measurements. The resonator is composed of a spiral microstrip, excited by coupling 50-Ohm transmission line on the top layer of the substrate; meanwhile a rectangular slot is etched in the bottom layer, behind the spiral shape to achieve high inductive effect. Structure optimization was conducted using high-frequency structure simulator (HFSS). The sensor is then used as a holder of the UV-aged PVC material while reflection (S11) and transmission (S21) coefficients are measured by vector network analyzer (VNA) in high frequency range, up to 18 GHz. The aging effect is finally perceived by observing the frequency shift of the resonance frequency between the empty and the aged-PVC loaded sensor, together with a variation in the S21 parameter amplitude. It is then found that for 864 h of UV-exposure is provided more than 0.45% frequency shift and about 4.67% decrease in electromagnetic energy transmission. Moreover, comparison between S11 and S21 results reveals that using S11 parameter is more practical to investigate material aging as it allows for simple visual checking of the frequency shift.

Hydrophobic and positively charged magnetic nanoparticles for enhanced oil recovery from concentrated emulsion wastewaters

With the development of petroleum industry, a large amount of oil-in-water (O/W) emulsion wastewaters were produced, resulting in serious environmental pollution and resource waste. Up till now, magnetic nanoparticles (MNPs) were frequently reported in emulsion wastewater treatment and mainly focused on the water purification, but little effort was devoted to the facile recovery of oil resource. In the present work, a class of hydrophobic and positively charged MNPs, namely dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DOTAC)-coated MNPs (M−DOTAC), was carefully synthesized by regulating DOTAC anchoring density on Fe3O4@SiO2, and then employed to treat the concentrated emulsion wastewaters stabilized by anionic sodium dodecyl benzene sulfonate (SDBS) or nonionic Tween-80. M−DOTAC with relatively high DOTAC density (M−DOTAC 1.8) exhibited higher positive charge density and hydrophobicity, and hence could significantly promote the oil droplet coalescence and mergence via the electrostatic attraction and hydrophobic adsorption bridging as well as the hydrophilic-lipophilic transition of interfacial adsorption layer. Accordingly, with addition of moderate dosage of M−DOTAC 1.8, the emulsion was broken and divided into three layers: (1) a continuous oil layer was formed in the upper layer which could be directly recycled; (2) the middle layer was composed of MNPs-tagged oil droplets/flocs; (3) the bottom layer was the clearer water phase. The optimal recovery rate of oil resource reached ∼ 60 % in SDBS stabilized system, and further increased to ∼ 98 % in Tween-80 stabilized system. However, the oil recovery rate was declined at an excessive dosage of M−DOTAC 1.8 due the formation of double emulsion. Besides, M−DOTAC 1.8 exhibited good reusability. These results indicated the fabricated M−DOTAC had great application prospect in treating emulsion wastewaters containing high oil content.

Permeability characteristics, structural failure characteristics, and triggering process of loess landslides in two typical strata structures

Landslides occurring at the interface of strata are among the most common forms of loess landslides in China. Statistics indicate that significant loess-red silty clay interface landslides induced by irrigation in the Heifangtai Platform than loess-paleosol interface landslides in the South Jingyang Platform. To uncover the permeability characteristics, structural failure patterns, and triggering processes of two typical strata structures. This study employs Nuclear Magnetic Resonance (NMR) and Scanning Electron Microscopy (SEM) techniques to investigate the permeability and structural failure of two soil combination types: loess-red silty clay and loess-paleosol. The results revealed a positive correlation between the stagnant water effect and flow rate, but a negative correlation with the initial water content. Notably, these two typical strata exhibited distinct differences in the stagnant water effect. In loess-red silty clay, continuous filling of mesopores and macropores by fine clay particles, while at the same time the agglomerates disintegration at the interface, thereby enhancing the stagnant water effect. In contrast, loess-paleosol exhibited good connectivity between the mosaic pores at the interface. This facilitated the formation of several elongated microcracks, which acted as dominant channels for infiltration and weakened the stagnant water effect. However, the macroscopic triggering mechanism for loess landslides in both loess-red silty clay and loess-paleosol combination strata remains similar. Irrigation water stagnates within the relatively impermeable layers, saturating and structurally damaging the bottom of loess layer, ultimately inducing landslides. These findings provide a scientific basis for the future study of loess landslide hazards in different strata structures, which is of great significance.