Surface Layer Research Articles

In-situ Synchrotron x-ray photoelectron spectroscopy study of medium-temperature baking of niobium for SRF application

Abstract In order to determine optimal parameters of vacuum thermal processing of superconducting radiofrequency niobium cavities exhaustive information on the initial chemical state of niobium and its modification upon a vacuum heat treatment is required. In the present work the chemical composition of the niobium surface upon ultra-high vacuum baking at 200–400 °C similar to “medium-temperature baking” and “furnace baking” of cavities is explored in-situ by synchrotron X-ray photoelectron spectroscopy (XPS). Our findings imply that below the critical thickness of the Nb2O5 layer (≈ 1 nm) niobium starts to interact actively with surface impurities, such as carbon and phosphorus. By studying the kinetics of the native oxide reduction, the activation energy and the rate-constant relation have been determined and used for the calculation of the oxygen-concentration depth profiles. It has been established that the controlled diffusion of oxygen is realized at temperatures 200–300 °C, and the native-oxide layer represents an oxygen source, while at 400 °C the pentoxide is completely reduced and the doping level is determined by an ambient oxygen partial pressure. Fluorine (F to Nb atomic ratio is 0.2) after the buffered chemical polishing was found to be incorporated into the surface layer probed by XPS (≈ 4.6 nm), and its concentration increased during the low-temperature baking (F/Nb=0.35 at 230 °C) and depleted at higher temperatures (F/Nb=0.11 at 400 °C). Thus, the influence of fluorine on the performance of mid-T baked, nitrogen-doped and particularly mild-baked (120 °C/48 h) cavities must be considered. The possible role of fluorine in the educed Nb+5 → Nb+4 reaction under the impact of an X-ray beam at room temperature and during the thermal treatment is also discussed. The range of temperature and duration parameters of the thermal treatment at which the niobium surface would not be contaminated with impurities is determined.

Combined effect of polyelectrolyte assisted interfacial polymerization and tannic acid protective surface modification to boost organic solvent nanofiltration performance

Organic solvent nanofiltration (OSN) is an effective technology for separating solute with molecular weight of 200–1000 Da (Da) from organic solvents. However, as the core of this technology, most of OSN membranes exhibit a low solvent permeance. Herein, a highly permeable OSN membrane was prepared via a poly (sodium 4-styrenesulfonate) (PSSNa)-assisted interfacial polymerization reaction using ultra-low content of aqueous monomer solution, followed by a protective modification using tannic acid (TA) grafting onto the nascent polyamide surface, and a post chemical crosslinking treatment as well as an activation treatment. PSSNa manipulates the diffusion and distribution of the m-Phenylenediamine monomers, leading to a looser and thinner polyamide layer. TA molecules successfully reacted with the remaining acyl chloride groups on the nascent polyamide layer surface and formed ester, thus preventing the surface from subsequent crosslinking reaction and also making the selective layer looser, which is beneficial for solvent permeation. Moreover, the TA modification makes the surface more hydrophilic, thus further helps to improve the solvent permeance of OSN membrane. The optimal membrane possesses an excellent ethanol permeance of 71.5 L m−2 h−1 MPa−1, an increment of 41.6 % as compared with the baseline OSN membrane, while keeping a rejection of 98.2 % for rhodamine B (RDB). Meanwhile, the surface of optimal membrane is ultra-smooth, with an average roughness of 4.4 nm, which is much beneficial for antifouling. Moreover, the OSN membrane possesses a brilliant durability performance, with only a 1.5 % decrease of the RDB rejection after being immersed in N, N-Dimethylformamide (DMF) at room temperature for 115 d, and only a further 0.3 % decrease of the RDB rejection after being further immersed in DMF at 80 °C for another 11 d, indicating its superior solvent resistance, which makes it a promising candidate for treating organic solutions from pharmaceutical and textile industries.

A cost-effective and high efficient Janus membrane for the treatment of oily brine using membrane distillation

Membrane distillation technology could utilize low-grade heat to desalinate brine, but the membrane material often suffers from disadvantages of low permeation flux and weak robustness to contaminants. To address these issues, the commercial polytetrafluoroethylene (PTFE) membrane was modified by cost-effective chemicals of tannic acid and (3-Aminopropyl)-triethoxysilane (APTES) to construct hydrophilic/underwater superoleophobic nano-rough structures on the surface to enhance its flux and oil-fouling resistance in direct contact membrane distillation. The results show that a high underwater oil contact angle of 180° is observed to the membrane surface due to the rough nanostructures functionalized by abundant hydroxyl groups. Despite the additional mass transfer resistance provided by the rough nanostructures, the flux was increased noticeably. This is mainly attributed to the strong interactions between the abundant hydroxyl groups of hydrophilic layer surface and water molecules, leading to a part of free water staying at intermediate transition state (IW). The mass transfer resistance of the hydrophilic layer itself is reduced as a consequence of decreased evaporation enthalpy of water, thereby increasing the flux. Moreover, while the flux of the pristine membrane is reduced by 84.18%, the flux of Janus membrane remains the same when treating mineral oil brine emulsions with oil concentration up to 1500 ppm in comparison with the result for 35 g l−1 brine solution, indicating that the Janus membrane is safe from the oil contamination. Our work provides a fine guidance for membrane distillation to treat high oily brine.

Impact of a floating flexible plate on the stability of double-layered falling flow

The hydrodynamic stability behavior of a two-layer falling film is explored with a floating flexible plate on the top layer surface. The stress balance at the surface is modeled using a modified membrane equation. There is an insoluble surfactant at the liquid-liquid interface of the flow system. The linear instability of perturbation waves is captured by numerically solving the generalized Orr-Sommerfeld eigenvalue problem using the Chebyshev spectral collocation technique. Four different types of linear stability modes are identified: surface mode (SM), interface mode (IM), interface surfactant mode (ISM), and shear mode (SHM). The floating flexible plate has an inferior impact on all the existing modes in the longwave zone. However, a significant influence is noticed for the finite wave numbers. The surface and interface wave instabilities can be suppressed in the smaller wavenumber zone by imposing higher structural rigidity and uniform thickness of the flexible plate. The stabilizing nature of the surface mode becomes more powerful when the top layer viscosity is dominant. A new interfacial instability emerges when the top layer is less viscous than the lower one. At moderate Reynolds numbers, the behavior of interface mode is different in two different zones mr<1 and mr>1, where m and r denote the viscosity and density ratio, respectively. Further, the unstable shear modes induced by the top and bottom layers are detected under the low inclination angles with a strong inertia force. The occurrence of the shear modes requires the viscosity and density of the lower layer to be much higher than those of the upper layer. The influence of characteristic parameters of the flexible plate on the lower layer shear mode is not very sensitive. Finally, the competition between the different modes for dominance of stability boundaries is also discussed.

High-performance thin film composite forward osmosis membrane for efficient rejection of antimony and phenol from wastewater: Characterization, performance, and MD-DFT simulation

The effective removal of heavy metals and phenolic pollutants from aqueous solutions has received widespread attention in the field of wastewater treatment. In this work, a novel PAN/CNTs/UiO-66-NH2 modified forward osmosis (FO) membrane was prepared for efficient removal of antimony (Sb) and phenol from wastewater. The membrane was synthesized using a facile and cost-effective method. The PAN/CNTs substrate membrane was prepared using electrospinning technology, and UiO-66-NH2 MOF particles were loaded onto the surface of the active layer during the interfacial polymerization (IP) process. The presence of CNTs in the spinning solution regulated the pore structure and properties of nanofibers. Characterization of the membrane confirmed its unique structure and enhanced properties. When the CNTs addition was 0.01 g, and UiO-66-NH2 addition was 0.05 wt%, the FO membrane exhibited the optimal operational performance. In the AL-FS mode, the water flux, reverse salt flux (RSF), and Js/Jw ratio were 14.68 LMH, 0.17 gMH, and 0.01 g/L, respectively. As a comparison, the water flux, RSF, and Js/Jw ratio were 21.19 LMH, 0.65 gMH, and 0.032 g/L in the AL-DS mode, respectively. Simultaneously, efficient removal of antimony and phenol was achieved in both modes, with antimony removal efficiencies of 99.26 % and 97.98 %, and phenol removal efficiencies of 96.61 % and 93.18 %, respectively. The modified membrane exhibited excellent performance in rejecting Sb and phenol. Molecular dynamics simulations and density functional theory calculations provide theoretical support for the excellent performance of membranes. The membrane demonstrated a high water flux, making it promising for practical applications. Additionally, it exhibited remarkably low reverse salt flux, highlighting its suitability for desalination processes. The exceptional removal efficiency of Sb and phenol, coupled with the membrane's impressive hydraulic performance, makes it a promising candidate for the treatment of industrial effluents containing these challenging contaminants. The results presented in this study underscore the potential of PAN/CNTs/UiO-66-NH2 FO membranes as an advanced solution for addressing water pollution challenges.

Revealing roles of S-layer protein (SlpA) in Clostridioides difficile pathogenicity by generating the first slpA gene deletion mutant.

Clostridioides difficile infection (CDI) with high morbidity and high mortality is an urgent threat to public health, and C. difficile pathogenesis studies are eagerly required for CDI therapy. The major surface layer protein, SlpA, was supposed to play a key role in C. difficile pathogenesis; however, a lack of isogenic slpA mutants has greatly hampered analysis of SlpA functions. In this study, the whole slpA gene was successfully deleted for the first time via CRISPR-Cas9 system. Deletion of slpA in C. difficile resulted in smaller, smother-edged colonies, shorter bacterial cell size, and aggregation in suspension. For life cycle, the mutant demonstrated lower growth (changes of optical density at 600 nm, OD600) but higher cell density (colony-forming unit, CFU), decreased toxins production, and inhibited sporulation. Moreover, the mutant was more impaired in motility, more sensitive to vancomycin and Triton X-100-induced autolysis, releasing more lactate dehydrogenase. In addition, SlpA deficiency led to robust biofilm formation but weak adhesion to human host cells.IMPORTANCEClostridioides difficile infection (CDI) has been the most common hospital-acquired infection, with a high rate of antibiotic resistance and recurrence incidences, become a debilitating public health threat. It is urgently needed to study C. difficile pathogenesis for developing efficient strategies as CDI therapy. SlpA was indicated to play a key role in C. difficile pathogenesis. However, analysis of SlpA functions was hampered due to lack of isogenic slpA mutants. Surprisingly, the first slpA deletion C. difficile strain was generated in this study via CRISPR-Cas9, further negating the previous thought about slpA being essential. Results in this study will provide direct proof for roles of SlpA in C. difficile pathogenesis, which will facilitate future investigations for new targets as vaccines, new therapeutic agents, and intervention strategies in combating CDI.

Improvement of fatigue life of Ti-6Al-4V alloy treated by double-sided symmetric oblique laser shock peening

To improve the anti-foreign object damage (FOD) ability of Ti-6Al-4V alloy blisk blades, a blade simulation specimen was designed and subjected to double-sided symmetrical oblique laser shock peening (DSOLSP) treatment. Surface roughness, residual stress distribution, and microstructural evolution of simulated specimens of Ti-6Al-4V alloy without and with DSOLSP were investigated, and the strengthening effect was evaluated by flexural fatigue test. The results showed that after DSOLSP treatment, surface roughness of simulated specimens was reduced from Ra0.97 µm to Ra0.6 µm. DSOLSP treatment generated a compressive residual stress (CRS) field along the entire thickness direction of the simulated specimen. Nanostructures with a depth of ∼500 nm was observed at topmost surface layer, and the average size of the nanograins was about 35.2 nm. Compared with the base material, the flexural average fatigue life of the simulated specimen was increased by 8.45 times. Moreover, mathematical statistical analysis confirms that DSOLSP has a significant effect on the fatigue life of simulated samples. The development of CRS fields throughout the entire thickness direction, the grain refinement on the surface, and the reduction of surface roughness are primarily responsible for the enhancement of the flexural fatigue life of the DSOLSP simulated specimen.

Study on Bonding Properties of Different Surfacing Layer Metals with 45 Steel Base Metal

Study on Bonding Properties of Different Surfacing Layer Metals with 45 Steel Base Metal

Optimizing Green Synthesis of Hydrotalcite - Silver Nanoparticles using Syzygium Nervosum based Reducing Agent.

This work aimed to assess the effect of Syzygium nervosum leaf extract as a reducing agent for green synthesis of AgNPs on HT through an optimizing process using response surface methodology (RSM) and the Box-Benken model. The optimal conditions for synthesis of AgNPs on HT include reaction time of 6.15 hours, reaction temperature of 50 oC and the ratio of diluted Syzygium nervosum leaf extract to reduce AgNO3 of 50.37 mL/mg. Under the optimal conditions, the yield of reduction reaction reached 77.54 %, close to the theoretical value of 76.97 %.Besides, the morphology, density, and characteristics of AgNPs on the surface of HT layers have been determined by using Ultraviolet-visible spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, selected area diffraction, X-ray diffraction, Dynamic light scattering, Infraredspectroscopy, Fluorescence emission spectroscopy, Brunauer-Emmett-Teller methods. The spherical AgNPs were synthesized successfully on the surface of HT with the average particle size of 13.0 ± 1.1 nm. Interestingly, HT-Ag hybrid materials can inhibit strongly the growth of E. coli, S. aureus as well as two antibiotic resistance bacterial strains, P. stutzeri B27 and antibiotic resistance E. coli. Overall, the HT-Ag hybrid materials are very promising for application in practice.

Polyethylene Film Surface Modification via Benzoic Acid Grafting.

A polyethylene (PE) film surface modification method is proposed via benzoic acid (BA) alkylation grafting to improve the surface affinity to polar substances. The procedure involves sequentially spraying AlCl3 and BA onto the heat-softened PE surface. The occurrence of the alkylation reaction was evaluated through comparative chemical, morphological, and thermal analyses. It was demonstrated that the grafting reaction of BA onto the PE film surface took place, limited to the surface layer, while preserving the bulk properties of PE. The reaction resulted in the formation of aluminum benzoate complexes, which improved the surface affinity to polar compounds. The impact of grafting on the surface properties of PE was further assessed by comparing the behavior of PE films treated with BA and untreated PE films when painted with watercolors. The PE film grafted with BA exhibited increased affinity towards watercolors, providing strong evidence of a change in surface polarity from hydrophobic to hydrophilic. These findings indicate that the proposed methodology effectively renders the PE surface paintable, even with non-toxic water-based inks, making it suitable for applications such as packaging.

Morphological Characterization of Native Isolates of Hypocreale Fungi Metarhizium rileyi (Farl.) Samson from Maize Fall Armyworm

The Present studies indicates the collection of entomopathogenic fungi from the roving survey in Northeastern region of Karnataka, India to know the diversity of M. rileyi distribution and also its growth pattern. Different morphological parameters used for describing the growth pattern which indicates diversity and uniqueness of M. rileyi i.e., colony colour which was white during initial stage and then during sporulating stage the colour changed into malachite green colour. The conidiophores were in compact patches. Conidia were aseptate, hyaline, round or ovoid in shape and elongate by forming chains. Conidiophores were short, which bears round to ovoid aseptate conidia in different isolates. The conidia size on its ratio found that, the highest size ratio was recorded in UASRBC Mr-20 2.19 then remaining isolates which has shown less than 2.0. The radial growth found only in Mr-20 and Mr-22nd Isolates, colony diameter ranged from 0.3 to 2.23 cm, concentric rings of colonies found in all the isolates except Mr-19 and Mr-20th isolates. The colony surface layer was white cottony growth to pale yellow color was found in all the isolates, the colony pigmentation in most of the isolates was light brown colored pigmentation. The growth appearance was irregular patchy growth was observed in most of the isolates. Among six different isolates the highest width was recorded in isolate UASRBC Mr-20 (6.46) followed by UASRBC Mr-22 (5.73) which was significantly superior than remaining isolates. The highest colony diameter was recorded in UASRBC Mr-18 (19 mm).

A new method of rapid-intelligent assessment for the dynamic service performance in high-speed railway subgrade

ABSTRACT There is a lack of a rapid, advanced, and comprehensive method for assessing the dynamic service performance in high-speed railway subgrade, which leads to an inability to pre-assess the health state of the subgrades in advance. In this paper, an innovative method of rapid-intelligent assessment for the dynamic service performance (RADSP) in high-speed railway subgrade was proposed. Firstly, a large-scale exciter was used to simulate the train loading effect, which could rapidly obtain the assessment metrics for subgrade dynamic service performance, including subgrade dynamic response (SDR) and subgrade cumulative deformation (SCD), where the SDR includes dynamic stress and acceleration. Then, to explore the future development trend of SCD during operation, an intelligent and advanced prediction of SCD was conducted using the optimal machine learning (ML) prediction model. Finally, by combining the results of the SDR and SCD assessments to achieve the RADSP in high-speed railway subgrade. Moreover, the method was applied to assess the dynamic service performance of diatomaceous earth subgrade structures with four different waterproofing structure layers (WSL): the middle of subgrade surface layer (WSL-1), the bottom of subgrade surface layer (WSL-2), the middle of subgrade bottom layer (WSL-3), and the bottom of subgrade bottom layer (WSL-4). The results indicate that: 1) During the excitation experiments, the maximum values for SDR (dynamic stress, acceleration) and SCD exceed the respective limits of 50 kPa, 10 m/s2, and 15 mm under WSL-1 and WSL-4. 2) The ensemble model, AdaBoost-GPR, is selected as the optimal ML model to predict the SCD values. Notably, the prediction SCD value exceeds the 15 mm limit under WSL-3, indicating that the SCD during future operation does not meet the requirements for pre-assessment. 3) Under WSL-2, both SDR and SCD assessments satisfy the limit value requirements, indicating that the dynamic service performance is better. Based on the proposed method, it is found that when designing waterproof-drainage subgrade structures in diatomaceous earth areas, it is recommended to position the WSL at the bottom of subgrade surface layer. The research findings serve as a crucial reference and valuable lesson for the health monitoring of high-speed railway subgrades.

Performance evaluation of proton exchange membrane fuel cells adopting rectangular-baffle and tapered flow channels with an equivalent average depth

ABSTRACT Optimizing the flow channel structures can improve the efficiency of proton exchange membrane fuel cells and promote the efficient utilization of clean energy. This study investigates the impacts of rectangular-baffle and tapered flow channels on electrical performance, temperature distribution and mass transfer of proton exchange membrane fuel cells, based on a 3D, multi-physical model. The equivalent average depth is adopted as the reference benchmark to mitigate the influence of channel depth. Results indicate that adopting variable-depth channels enhances convective mass transfer on the porous layer surface under higher voltage. The convective mass transfer of oxygen is dominant in the activation polarization region, while diffusion is dominant in the concentration polarization region. Variable-depth channels enhance heat and mass transfer in comparison to the straight channel. The tapered channel can improve the mass transfer flux in oxygen starvation region, and the drainage ability of the rectangular baffle channel is inferior to the tapered channel. The rectangular baffle channel demonstrates better convective heat transfer performance and temperature uniformity. A rectangular-baffle channel can increase net power by 4.31%, while a tapered channel can achieve a maximum increase of 9.27% when the pumping power is considered. Therefore, incorporating a tapered channel is an optimal strategy to boost cell efficiency.

Quantification of surface layer turbulence using sensible heat values from energy balance versus aerodynamic methods

Surface layer optical turbulence values in the form of the refractive index structure function C n 2 are often calculated from surface layer temperature, moisture, and wind characteristics and compared to measurements from sonic anemometers, differential temperature sensors, and imaging systems. A key derived component needed in the surface layer turbulence calculations is the sensible heat value. Typically, the sensible heat is calculated using the bulk aerodynamic method that assumes a certain surface roughness and a friction velocity that approximates the turbulence drag on temperature and moisture mixing from the change in the average surface layer vertical wind velocity. These assumptions/approximations generally only apply in free convection conditions. To obtain the sensible heat, a more robust method, which applies when free convection conditions are not occurring, is via an energy balance method such as the Bowen ratio method. The use of the Bowen ratio––the ratio of sensible heat flux to latent heat flux––allows a more direct assessment of the optical turbulence-driving surface layer sensible heat flux than do more traditional assessments of surface layer sensible heat flux. This study compares surface layer C n 2 values using sensible heat values from the bulk aerodynamic and energy balance methods to quantifications from sonic anemometers posted at different heights on a sensor tower. The research shows that the sensible heat obtained via the Bowen ratio method provides a simpler, more reliable, and more accurate way to calculate surface layer C n 2 values than what is required to make such calculations from bulk aerodynamic method-obtained sensible heat.

DISTINCTIVE FEATURES OF CELLULOSE NANOCRYSTALLITES

In this paper, a set of methods was used to study the structural characteristics and properties of cellulose nanocrystallites and free cellulose nanocrystalline particles (CNCs). It was shown that cellulose nanocrystallites have three main distinctive features. The first distinctive feature of cellulose nanocrystallites is their rod-like shape with a quite high aspect ratio and a low percolation threshold. The second distinctive feature of nanocrystallites is their highly developed specific surface area that leads to the spontaneous crystallization and aggregation of rod-like crystallites by their lateral planes. This aggregation process is thermodynamically favorable because it leads to a decrease in the specific surface area of nanocrystallites and a reduction of the thermodynamic potential. The third distinctive feature of cellulose nanocrystallites is the paracrystalline structure of their surface layers, which significantly affects structural characteristics such as lattice distortion, interplanar spacings, parameters, and volume of the crystalline unit cell, etc. Along with structure, the paracrystalline fraction affects also important physical and physical-chemical properties of cellulose, such as accessibility to deuteration, the content of CII-allomorph after cellulose alkalization, melting point of nanocrystallites, etc. Correlation equations were derived that provide to predict the structural characteristics and properties of nanocrystallites using the content of the paracrystalline fraction.

Layer‐Controllable “2.5D” DNA Origami Crystals Synthesized by a Hierarchical Assembly Strategy

AbstractThe finite periodic arrangement of functional nanomaterials on the two‐dimensional scale enables the integration and enhancement of individual properties, making them an important research topic in the field of tuneable nanodevices. Although layer‐controllable lattices such as graphene have been successfully synthesized, achieving similar control over colloidal nanoparticles remains a challenge. DNA origami technology has achieved remarkable breakthroughs in programmed nanoparticle assembly. Based on this technology, we proposed a hierarchical assembly strategy to construct a universal DNA origami platform with customized layer properties, which we called 2.5‐dimensional (2.5D) DNA origami crystals. Methodologically, this strategy divides the assembly procedure into two steps: 1) array synthesis, and 2) lattice synthesis, which means that the layer properties, including layer number, interlayer distance, and surface morphology, can be flexibly customized based on the independent designs in each step. In practice, these synthesized 2.5D crystals not only pioneer the expansion of the DNA origami crystal library to a wider range of dimensions, but also highlight the technological potential for templating 2.5D colloidal nanomaterial lattices.

Frost quakes in wetlands in northern Finland during extreme winter weather conditions and related hazard to urban infrastructure

Abstract. The paper reports the first results of an experiment in northern Finland during winter 2022–2023 that aimed at studying seismic events caused by seasonal freezing in the so-called critical zone (CZ) of the Earth. These events have attracted public attention recently, as multiple reports about them from local inhabitants in Arctic and sub-Arctic areas appeared on social networks. To make an instrumental study of such events, to reveal the relationship between their occurrence and winter weather conditions, and to evaluate the possible hazard, we installed two high-resolution seismic arrays with co-located soil temperature stations at two sites in Finland, one of them being in the city of Oulu in the sub-Arctic area (65.04° N, 25.61° E) and the other one above the polar circle in the municipality of Sodankylä (67.36° N, 26.63° E). The equipment recorded continuous seismic and soil temperature data during November 2022–April 2023. Based on reports from the inhabitants of Talvikangas (Oulu) about the ground shaking and unusual noises on 6 January 2023 and their observations of new fractures on the roads there, we selected the time interval for the identification of frost quakes that originated during that day from continuous seismic records in Talvikangas and in Sodankylä. During the selected time interval, the extremely rapid air temperature drops of about −1.4 °C h−1 in Talvikangas and −0.88 °C h−1 in Sodankylä were observed. We identified and located two types of seismic events – namely, frost quakes with frequencies of about 10–20 Hz, with waveforms like those of tectonic events, and irregularly shaped frost tremors with frequencies of about 120–180 Hz. The sources of frost quakes in Talvikangas are mainly located on irrigated wetland, while in Sodankylä, about 50 % of registered frost quakes were caused by ice fracturing on the Kitinen River. However, several relatively strong events, with their origin in the wetlands, were also recorded. A significant number of sources of frost tremors are confined to wetland areas cut by irrigation channels and to roads cleaned from snow during winter both in Talvikangas and in Sodankylä. We calculated ground accelerations and ground velocities for the strongest events from both groups and compared them to equivalent properties of other seismic signals, like distant local earthquakes in the area, mining production blasts, and cargo train vibration. Our study shows that high-frequency frost tremors corresponding to surface fracture opening in the uppermost frozen surface layer of a thickness of up to 5 cm can directly damage infrastructure objects like roads and basements of buildings. Surface waves, produced by frost quakes and propagating inside the shallow soil layer, have large enough ground accelerations at epicentral distances of hundreds of metres. Therefore, frost quakes should be considered a phenomenon that can potentially damage infrastructures, and they have to be taken into account in seismic hazard assessments. Our research is the first instrumental study of seismic events originating from wetland areas. These events occur as a result of the interaction between the uppermost layer of the solid Earth's CZ and atmosphere processes that deserves further study.

Flexible SERS substrates with gradient porous Cu structure dealloying from the thermal diffusion couples of Al/Cu stacking foils

Accurate and sensitive surface-enhanced Raman scattering (SERS) substrates are urgently demanded for the various analytic techniques. The SERS substrates with multimodal and gradient porous structure, utilized for the Rhodamine 6G (R6G) detection, have been designed and successfully fabricated from the thermal diffusion couples of Al and Cu foils via chemical dealloying. The structural inheritance of the initial microstructure of thermal diffusion couple precursors governs the formation of the final layer-by-layer gradient porous Cu with different characteristic pore sizes and morphology. An outmost surface layer of disordered lipstick-like porous structure on the SERS substrates enhances SERS effects as has been expected. The SERS activity of R6G Raman probes on gradient porous Cu is evaluated as a SERS enhancement factor of 6.63 × 1012 and limit of detection of 2.10 × 10−17 mol/L, higher than other porous SERS substrates. Meanwhile, the present SERS substrates are flexible and exhibit good bending properties due to the unreacted Cu layer as a supporting skeleton and other gradient porous Cu layers. The superior SERS performances are considered to result from the synergetic effects of the surface scattering of porous Cu rods and enhancements of the high electromagnetic fields between the small gaps between the nanopores.

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer

Approximation of the statistical distributions of atmospheric air density in the surface layer