Physical Layer Properties Research Articles

Finite Element Analysis of Interface Dependence on Nanomechanical Sensing

Nanomechanical sensors and their arrays have been attracting significant attention for detecting, discriminating and identifying target analytes. The sensing responses can be partially explained by the physical properties of the receptor layers coated on the sensing elements. Analytical solutions of nanomechanical sensing are available for a simple cantilever model including the physical parameters of both a cantilever and a receptor layer. These analytical solutions generally rely on the simple structures, such that the sensing element and the receptor layer are fully attached at their boundary. However, an actual interface in a real system is not always fully attached because of inhomogeneous coatings with low affinity to the sensor surface or partial detachments caused by the exposure to some analytes, especially with high concentration. Here, we study the effects of such macroscopic interfacial structures, including partial attachments/detachments, for static nanomechanical sensing, focusing on a Membrane-type Surface stress Sensor (MSS), through finite element analysis (FEA). We simulate various macroscopic interfacial structures by changing the sizes, numbers and positions of the attachments as well as the elastic properties of receptor layers (e.g., Young’s modulus and Poisson’s ratio) and evaluate the effects on the sensitivity. It is found that specific interfacial structures lead to efficient sensing responses, providing a guideline for designing the coating films as well as optimizing the interfacial structures for higher sensitivity including surface modification of the substrate.

Real-space light-reflection mapping of atomically thin WSe2 flakes revealing the gradient local strain

The spatially continuous control of the physical properties in semiconductor materials is an important strategy in increasing electron-capturing or light-harvesting efficiencies, which is highly desirable for the application of optoelectronic devices including photodetectors, solar cells and biosensors. Unlike the multi-layer growth of chemical composition modulation, local strain offers a convenient way to continuously tune the physical properties of a single semiconductor layer, and open up new possibility for band engineering within the 2D plane. Here, we demonstrate that the gradient refractive index and bandgap can be generated in atomically thin transition metal dichalcogenide flakes due to the effect of thermal strain difference. A highly resolved confocal scanning optical microscopy is used to perform a real-space light-reflection mapping of suspended atomically thin WSe2 flakes at the low temperature of 4.2 K, in which the parabolic light-reflection profiles have been observed on suspended monolayer and bilayer WSe2 flakes. This finding is corroborated by our theoretical model which includes the effect of strain on both the refractive index and bandgap of nanostructures. The inhomogeneous local strain observed here will allow new device functionalities to be integrated within 2D layered materials, such as in-plane photodetectors and photovoltaic devices.

Comparative structural investigations of nuclear waste glass alteration layers and sol-gel synthesized aerogels

While various glass alteration layer formation mechanisms have been debated in recent years, the glass alteration community generally agrees that more information on physical properties of the alteration layers is needed to further the understanding of their impacts on overall glass alteration. In this work, pore volumes and solid structures of glass (International Simple Glass, ISG) alteration layers formed in solutions of various pH conditions in initially dilute conditions at 90 °C are evaluated with positron annihilation spectroscopy, small-angle X-ray scattering, and scanning transmission electron microscopy. Pore volumes of alteration layers formed at pH 9 were found to be at their lowest near the surfaces of the alteration layers. Solid structures of alteration layers are compared with those of synthetic aerogels of comparable compositions produced under various pH conditions. Alteration layers formed at pH 11 on ISG were shown to contain large structures (>10 nm) similar to synthetic aerogels created under neutral and basic conditions whereas alteration layers formed at pH 9 did not. Available dissolved silica species defined by silica solubility were proposed to have the greatest impact on alteration layer structure.

How Dissociation of Carboxylic Acid Groups in a Weak Polyelectrolyte Brush Depend on Their Distance from the Substrate.

A weak polyelectrolyte brush is composed of a layer of polyacids or polybases grafted by one end of their chains to a substrate surface. For such brush layers immersed in an aqueous solution, the dissociation behavior of the acidic or basic groups and the structural and physical properties of the brush layer will thus be strongly dependent on the environmental conditions. For a polyacid brush layer consisting of, e.g., poly(acrylic acid), this means that the chains in the brush layer will be charged at high pH and uncharged at low pH. However, theoretical scaling laws not only foresee the structural changes occurring in response to the pH-induced dissociation behavior but also how the dissociation behavior of the brush layer depends on the ionic strength of the aqueous solution and the density of acidic groups within the brush layer. We have herein employed spectroscopic ellipsometry and a quartz crystal microbalance with dissipation monitoring (QCM-D) to experimentally evaluate the theoretically predicted dissociation and structural behavior of PAA brushes. Spectroscopic ellipsometry allows us to study the brush thickness as a function of pH and ionic strength, while QCM-D gives us an opportunity to investigate the swelling behavior of PAA brushes at various penetration depths of propagating acoustic waves. Our studies show that the dissociation degree of the carboxylic acid groups in a PAA brush increases with increasing distance from the substrate. Moreover, the ionic strength enhances carboxylic acid dissociation, such that a higher ionic strength leads to a narrower distribution and higher average dissociation degree. In conclusion, our results provide an experimental verification of the theoretically predicted gradient in the degree of dissociation of the acid groups in weak polyacid brush layers and shows that at a pH value equal to approximately the average pKa value of the brush, the state of the acid groups varies from being almost uncharged to almost fully dissociated depending on the ionic strength and vertical position in the brush.

Physical and mechanical properties of the overburden layer on gas hydrate-bearing sediments of the South China sea

Gas hydrate exploitation may trigger the destruction of the overburden structure and settlement of the overburden layer on the gas hydrate-bearing sediments. It is extremely urgent to explore the basic laws governing the physical and mechanical properties of the overburden layers before performing commercial exploitations of hydrates. However, relatively few studies have focused on the physical and mechanical properties of the overburden layer (uppermost ~10 m) on the gas hydrate-bearing sediments of the South China Sea. In this research, we studied the physical and mechanical properties of the overburden sediments from this area, including the particle size distribution, the specific surface area, the pore size distribution, the water content, the liquid/plastic limits, and the mineral and chemical compositions of the particles, as well as the strength and deformation characteristics. According to the results, we found that the overburden sediments of the Shenhu area are characterized as well-graded clayey silts and considered to be internally stable and self-filtering. The isothermal adsorption-desorption curve is a Type H3 hysteretic loop, indicating that the shape of the particles occurs primarily in a plate form, and most of the pores are slit-shaped. The plasticity index in this area is relatively lower than that in other areas, which suggests that there is a risk of overburden collapse during the production process of hydrates. The mineral composition of the overburden sediment particles is primarily quartz, plagioclase, calcite and some accessory clay minerals, which can provide guidance for remolding the overburden sediments in the laboratory. The sediments show strain hardening and shear contraction behavior upon shearing; in addition, the established strength criterion will contribute to the formulation of constitutive equations for the overburden sediments, which can be used as essential input parameters in gas hydrate production simulations.

Surabaya earthquake hazard soil assessment

The vulnerability of land in an area to earthquake ground motions is one of the factors causing damage caused by the earthquakes. The city of Surabaya, which is crossed by two active fault segments, needs an assessment to reduce the risk of being affected by an earthquake that might occur. The aims of this study are (1) to find out the distribution of Seismic Site Classes, (20 to know the distribution of the value of Seismic Amplification, and (3) to know the potential of liquefaction in the city of Surabaya. Surabaya city, which is geologically dominated by alluvium deposits, consists of soft soil (SE) and medium (SD) sites based on N-SPT30 and Vs30 data. The level of soil amplification against earthquakes ranging from 1 to 4. This occurs because the physical properties of the Surabaya City soil layer are dominated by alluvium deposits. Regions with more than 2 amplification values are located around the coastline on the North and East coasts of Surabaya City. Based on the potential liquefaction index value, Surabaya City is included in the region with a high potential for liquefaction with a potential liquefaction index value of more than 5.

Modification of aluminum surfaces by supersonic plasma sputtering

Surface engineering allows you to change the physical and chemical properties of the surface layers of materials by modifying or applying protective coatings using various methods. Plasma technologies are widely used in various branches of engineering to produce hardening, wear-resistant, heat-resistant, corrosion-resistant, protective and decorative and other types of coatings that significantly improve the performance properties of products. In this work the results of laboratory studies of the physical and mechanical properties of Ni-B-Cr-Si coatings deposited by supersonic plasma deposition on an aluminum substrate are presented. It is shown that the use of this method of modification of metal surfaces is advisable.

Growth features of rare species of the Fabaceae l. family on sod-carbotate soils in the flora of the Novgorod region

The results of geobotanical description of natural landscapes are provided in this paper. The agrochemical characteristics of soils on the studied areas are given. The habitats of rare and genetically significant species of legumes in the flora of the Novgorod region were identified. The soil cover of the Novgorod region is extremely complex and diverse, which is due to the large heterogeneity of the terrain, the diversity of soil-forming rocks and the difference in the bioclimatic situation in its areas. Millennial anthropogenic activity also left its strong imprint on the soil pattern. In the soils of the region, depending on the features of the parent rocks and other conditions, the nature of the horizon also changes. In some cases, it is metamorphic, in others - eluvial-illuvial or illuvial. Morphological differences are reflected in the chemical and physical properties of the respective layers. The development of sod-podzolic soils on carbonate moraine, common in all natural areas of the region and known as sod-podzolic residual carbonate, is characterized by varying degrees of secondary saturation of the bases of the upper horizons or only weak unsaturation with distinct morphological podzol content. The deceleration rate of the podzolic process depends both on the intensity and method of cultivation, and on the saturation degree of rock carbonate content, the depth of the carbonate occurrence and its nature. The features of formation, structure, properties and classification of sod-carbonate soils of the Novgorod region are observed in this research. Data on agricultural use of various subtypes of sod-carbonate soils in comparison with sod-podzolic soils are presented below.

Plastic Performance and Coordinated Design of Surface-Reinforced Sandwich Beams

In this work, a surface-reinforced sandwich configuration with variable material layer is proposed to improve the plastic performance of sandwich structures in limited-space with the least cost, which is promoted by the hierarchy of human bone with multi-stiff layers outside the cellular core. First, a generalized yielding criterion and an analytical model for the large deflection of the fully clamped surface-reinforced sandwich beams under transverse loading are developed. Then, the comparison between finite element (FE) simulations and experimental results for surface-reinforced sandwich beams with varied geometric and physical properties of each material layers is presented, which verifies the accuracy of the theoretical solutions. Finally, the coordinated design of the surface-reinforced sandwich beam in limited-space is investigated and the synergistic effects of each material layer on the load carrying and energy absorption ability of the structure are discussed in detail. The results given in this paper provide theoretical guidance in plastic design of sandwich structures with multi-cover sheets as well as the selection of the face-sheet, the core and the reinforced skin.

Laboratory and Field Experimental Study on the Vacuum Preloading Method with Pumping and Discharging

Negative vacuum pressure hardly reaches deep soils due to the drain board bending and serious blockage with the existing vacuum preloading methods (VPMs), thus resulting in poor reinforcement relative to practical engineering applications. To address this issue, this paper proposes a vacuum preloading method with pumping and discharging (a new dredger filling foundation processing technique based on vacuum preloading). This new VPM is developed through technological improvement and plastic drain board innovations in traditional VPMs. The new VPM uses a plastic vertical drainage board with double drainage channels, and the core board is in a “tic‐tac‐toe” shape with a hollow centre and square pipeline channels. It can execute air and water drainage. Vacuum transfer holes were set at two grooves, every 2‐3 m from the central pipeline of the core board. Grooves at two sides of the core board and filter membrane were rolled together to improve drainage. In addition, the vacuum pipe, tube connector, and core board centre of the vertical plastic drainage board were connected directly and securely. A stereoscopic vacuum transmission system composed of a horizontal and vertical drainage system was built. In this vacuum transmission system, the transfer route was shortened, and the loss of vacuum along the route was decreased. The negative vacuum pressure was transferred to different soil depths through the central pipeline of the core board to accelerate the dissipation of pore pressure in soil mass and prevent vacuum pressure loss caused by drainage board bending, thus improving the reinforcement effect. Dredger filling silt foundation reinforcement by VPM and VPM with pumping and drainage were compared in laboratory simulations and field tests with different drainage boards. Test results show that the loss of vacuum pressure along the drainage path was relatively smaller in the new physical vapor deposition (PVD), and the pressure transfer efficiency was increased. Deep soil mass was reinforced effectively by using the new PVD. After reinforcement, the physical and mechanical properties of soil layers were improved. Moreover, soil strengths were remarkably improved, with sharp reductions in natural moisture content and porosity. Then, the transfer law of vacuum on different drainage boards and the reinforcement mechanism of VPM with pumping and drainage were analysed. Research conclusions show the superiority of VPM with pumping and drainage in terms of effectiveness and soft foundation reinforcement. This study provides a theoretical basis for the application and development of the new VPM.

METALLOGRAPHIC STUDIES OF SAMPLES MADE OF 65G STEEL SUBJECTED TO COMPLEX TREATMENT BY ELECTROSPARK AND VIBRATION ARC DISCHARGES USING CERMET POWDERS

In this paper, some physical and mechanical properties of the surface layer of widely used steel 65G in mechanical engineering and agriculture, subjected to plasma treatment. The research is aimed at increasing the service life of parts and friction units of machinery and equipment. It is shown that vibroplasma surface treatment with the use of metal-ceramic powders allows to increase the hardness of the surface layer by more than 3 times. The elemental composition and microstructure of the sample surface were studied. The microstructure of the base material of the coated samples corresponds to the structure of the reference sample. The microstructure of the reference sample corresponds to the microstructure of low-carbon (pre-eutectoid) steel after annealing. Grained ferrite-pearlite structure with a predominance of ferrite. In the process of vibro plasma treatment in the surface layer of the sample is formed of 3 zones: the zone of deposited metal-ceramic material, a hardened area of the surface layer mixed with elements of the base and filler material and heat affected zone.

Accelerated key generation and distribution using polarization scrambling in optical fiber.

The physical-layer properties of the classical optical fiber channel provide an inherent, unique, random and reciprocal source for secure key generation and distribution (SKGD). However, the key generation rate (KGR) is generally less than kbit/s in the reported SKGD schemes. In this paper, an accelerated SKGD scheme based on active polarization scrambling is proposed in the classical optical fiber channel. A combination of unique birefringence distribution of optical fiber channel and active scrambling of instant state of polarization (SOP) enables a fast and random SOP fluctuation to be securely shared between the legitimate users for accelerated SKGD. The proposed SKGD scheme is experimentally demonstrated over 24-km standard single-mode fiber (SSMF), where a KGR of 200-kbit/s with an error-free operation is achieved after the post-processing procedure. Moreover, the possible fiber-tapping attacks are theoretically and experimentally analyzed for the security robustness of the proposed scheme. The results imply that a faster SKGD scheme could be achieved by incorporating an active polarization scrambling mechanism into the random properties of the fiber channel.

Scaling laws and snap-through events in indentation of perforated membranes

We revisit the classical theory of indentation for very soft materials. Many experiments consist in extracting the stiffness of a membrane from the cubic answer of the force versus indentation depth. However, this law is restricted to a perfect membrane under a sharp point loading. In biophysical experiments, where this technique recovers some success at low scales thanks to AFM, the thin samples are highly deformable, hyper-elastic, pre-stretched and often attached to a substrate which cannot be neglected. In addition microscopic tiny pores may exist or may be created by the indenter. This diversity requires specific studies with the correct elasticity: here we choose the neo-Hookean elastic model at large membrane deformations. We show that, the weak loading regime is extremely sensitive to any physical properties of the thin layer but also of the indenter geometry. In addition, when a hole exists, at finite forcing or finite indentation depth, we discover a topological bifurcation with abrupt dynamical jump variation of typical quantities such as the hole size. This bifurcation is similar to the famous catenoid instabilities which are also due to a topological bifurcation, when the two rings of support are pulled apart. This bifurcation is robust in the sense that it always exists whatever the physical properties of the sample.

Research on Optimized Penetration Ratio Fracturing Technology for Transition Zone

The geological reserves of the Sazhong transition zone are 10046×104t, accounting for 12.5% of the Sazhong development zone. The effect of fracturing stimulation in this block is of great significance for the stable production of the Sazhong oilfield. The transition zone has the characteristics of low porosity, low permeability and low oil saturation. The crude oil has three high and one low characteristics: high viscosity, high wax content, high freezing point and low sulfur content. In the transition zone, due to poor physical properties of the oil layer, unbalanced formation pressure, high proportion of low-yield and low-efficiency wells, and energy replacement of thin oil layers, it is difficult to tap the potential of the production increase measures, and the effect of the measures is getting worse year by year. According to statistics, since the transition zone has 40 fractured oil wells since 2009, the fracturing process is general pressure and multi-crack, and the average pressure is 3 layers and 1 slit. The average average sand volume of single seam is 7.1m3, the average sand ratio is 25.7%, and the penetration ratio is only 14.1%. The average initial liquid increase after fracture is 20.4t, and the average initial daily oil increase is only 2.5t. Therefore, the study of transition zone fracturing technology can improve the overall development effect of the block, which is of great significance for the sustainable high yield and stable production of the Sazhong Oilfield.

Optical and Physical Characteristics of the Lowest Aerosol Layers over the Yellow River Basin

Studying the presence of aerosols in different atmospheric layers helps researchers understand their impacts on climate change, air quality, and human health. Therefore, in the present study, the optical and physical properties of aerosol layers over the Yellow River Basin (YERB) were investigated using the CALIPSO Level 2 aerosol layer products from January 2007 to December 2014. The Yellow River Basin was divided into three sub-regions i.e., YERB1 (the plain region downstream of the YERB), YERB2 (the Loess Plateau region in the middle reaches of the YERB), and YERB3 (the mountainous terrain in the upper reaches of the YERB). The results showed that the amount (number) of aerosol layers (N) was relatively large (>2 layers) in the lower part of the YERB (YERB1), which was mainly caused by atmospheric convection. The height of the highest aerosol layer top (HTH) and the height of the lowest aerosol layers base (HB1) varied significantly with respect to the topography of the YERB. High and low values of aerosol optical depth (AOD) were observed over the YERB1 (plain area) and YERB3 (elevated area) regions, respectively. Population, economy, and agricultural activities might be the possible reasons for spatial variations in AOD. AOD values for the lowest aerosol layer were high—between 0.7 and 1.0 throughout the year—indicating that aerosols were mainly concentrated at the bottom layer of the atmosphere. In addition, the integrated volume depolarization ratio (0.15–0.2) and the integrated attenuated total color ratio (~0.1) were large during spring for the lowest aerosol layer due to the presence of dust aerosols. The thicknesses of the lowest aerosol layers (TL1) did not vary with respect to the topographic features of the YERB. Over the sub-regions of the YERB, a significant positive correlation between the AOD of the lowest aerosol layer (AOD1) and the thickness of the lowest aerosol layer (TL1) was found, which indicates that TL1 increases with the increase of AOD1. In the whole YERB, a positive linear correlation between the N and HTH was observed, whereas a negative correlation between N and the portion of AOD for the lowest aerosol layer (PAOD1) was found, which revealed that the large value of N leads to the small value of PAOD1. The results from the present study will be helpful to further investigate the aerosol behavior and their impacts on climate change, air quality, and human health over the YERB.

Dynamic Tunable Color Display Based on Metal-Insulator-Metal Resonator with Polymer Brush Insulator Layer as Signal Transducer.

Dynamic color-changing nanomaterials have been widely investigated for applications in fields like optical sensors, wearable activity monitors, smart electronic devices, and anticounterfeiting materials due to the excellent ability to change their optical properties with external variation. Here, a simple metal-insulator-metal (MIM) trilayer Fabry-Perot resonance cavity with a poly(N-isopropylacrylamide) (PNIPAm) brush layer as a responsive element is reported as a thermal-induced colorimetric response platform. The dynamic changes of conformation and physical properties of PNIPAm brush layer in response to external signals give rise to a significant color change of the MIM Fabry-Perot resonance cavity. This MIM Fabry-Perot resonance cavity shows the advantages of dynamic color change, rapid response, good repeatability, and simple construction. Additionally, the as-prepared MIM cavity shows great potential in various applications such as color printing, multicolor indicator, and information anticounterfeiting.

Characterization of the Agilkia region through discrete-element simulation of Philae’s rebound

Context. The cold gas system and anchoring harpoons that were designed to hold Philae down after it landed on the Agilkia region of comet 67P/Churyumov-Gerasimenko (67P) failed. This caused the lander to move on a complex trajectory that comprised multiple impacts and rebounds. The motion of Philae was mainly dominated by the gravitational environment and the physical properties of the surface on Agilkia. This allows us to determine the physical properties of the surface layer by high-fidelity discrete-element simulations of Philae’s rebounds. Aims. We explore the surface physical properties of the Agilkia region on comet 67P by minimizing the difference in Philae’s rebound status between observational data and simulations based on the assumption of a granular-boulder hybrid surface material. Methods. We first developed an efficient gravity model to accurately approximate the high-resolution polyhedral shape of the comet. This allowed us to run many simulations for the landing trajectory. We developed a complete dynamical model of the motion of Philae, including a mechanical model of the lander and the hybrid surface model. This focused in particular on the interaction of discrete elements in Philae and the granular regolith layer with a boulder added on top of it. We used mixed discrete optimization to determine the input physical variables on Agilkia to fit the rebound observational data (Philae’s rebound velocity). Results. The discrete-element simulation constrained by Philae’s rebound velocity implies that Philae first impacted on a boulder and scratched it with the landing gear. After this, its three soles interacted with the granular regolith, which consists of particles with a mean diameter of 0.014 ± 0.004 cm. The thickness of the region interaction is estimated to be 0.272 ± 0.062 m with a corresponding density of 1443 ± 231 kg m−3. The Young modulus for each particle is estimated to be 108 Pa. Based on a porosity of 0.75, the friction of the surface of particles is derived to be moderate, with a friction coefficient of about 0.6.

Improving Reactant and Proton Transport in Catalyst Layers for Direct Alcohol Fuel Cells

Direct alcohol fuel cells (DAFC) produce electricity from liquid fuels such as methanol, ethanol etc., where the alcohol is oxidized at the anode and oxygen is reduced on the cathode side of the fuel cell. Operation of alcohol fuel cells is attractive because of the exceptionally high volumetric energy density and easy handling of liquid fuels in comparison to pressurized hydrogen. [1] Especially direct methanol fuel cells (DMFC) have been widely investigated as portable power sources. However, even with these relatively simple fuels, the reaction kinetics of the electro-oxidation are slow in comparison to hydrogen oxidation. Furthermore, DAFC suffer from severe reactant crossover through the membrane, leading to low open circuit voltages and poor overall performance. [2] In order to solve crossover issues, manufacturing of various composite membranes and additional alcohol blocking layers become more and more important in this research field. [3] Nonetheless, also understanding and improving reactant and proton transport in catalyst layers for DAFCs is very important in order to improve current densities and reduce costs, as less expensive platinum group metal catalysts are needed. Commonly, very high loadings on the anode side of DAFC result in thick catalyst layers, which suffer from poor reactant transport and high proton resistances and flooding, especially in the high current density regions. Our work to be presented is focused on novel architectures of membrane electrode assemblies (MEAs) for applications in direct alcohol fuel cells to target these problems and improve the physical properties of the catalyst layer with a focus on different ionomers, different ionomer contents, and pore size distribution. [1] R. P. O'Hayre, F. B. Prinz, S.-W. Cha, W. G. Colella, Fuel cell fundamentals, Third edition ed., Wiley, Hoboken, 2016. [2] C. Xu, A. Faghri, X. Li, T. Ward, International Journal of Hydrogen Energy 2010, 35, 1769–1777. [3] P. Prapainainar, N. Pattanapisutkun, C. Prapainainar, P. Kongkachuichay, International Journal of Hydrogen Energy 2019, 44, 362–378.

Determining the Subnanometer Thickness of the Water-Depletion Layer at the Interface between Water and the Hydrophobic Substrate.

Surface plasmon resonance (SPR) is one of the most popular and powerful techniques for label-free detecting and quantitatively analyzing the interfacial refractive index (RI). So far, most of the SPR measurements are mainly applied to detect the relative change of RI upon biological and chemical events occurring at the interface, while the determinations on the absolute value of RI remains challenging. However, the absolute value of RI has become increasingly urgent in some cases, such as the existence and physical properties of the water depletion layer (WDL). WDL refers to a subnanometer-thick layer with reduced density between water and the hydrophobic substrate. The detailed explanations of how water meets hydrophobic surface have been studied by several kinds of techniques for decades but it remains under debate. In this work, we successfully established a method to measure the absolute RI at a gold-liquid interface by surface plasmon resonance microscopy (SPRM) and 2D Fourier transformation image processing and further applied this method to study the existence and physical nature of WDL. It was found that a 0.6 nm thick WDL existed at the interface of water and the hydrophobic substrate, leading to a reduced refractive index of 1.3295 ± 0.0006 compared with the standard value of 1.3325. Our results further indicated that the WDL consisted of a uniform layer rather than numerous isolated surface nanobubbles that distributed at the interface with high density.

Physical Properties of Soils Altered by Invasive Pheretimoid Earthworms: Does Their Casting Layer Create Thermal Refuges?

Pheretimoid earthworms are invasive in hardwood forests of formerly glaciated regions in the USA. They alter the forest floor structure by creating an extensive, several cm-deep casting layer comprising loose macro-aggregates. Little is known about the physical properties of the casting layer and how they relate to earthworm ecology. Here, thermal and macropore properties of three forest soil textures (clay, silt, and sandy soils, with and without pheretimoids) were measured and compared to explore the possible relationships to their ecology. Thermal properties were significantly different between the casting layer (CAST) and original soil (NOCAST). Results indicate that CAST soils dampen temperature fluctuations occurring at the surface more than NOCAST soil. The increased dampening may be of particular importance to pheretimoid survival in forest fires and during spring when surface fluctuations could expose the hatchlings to fatal temperatures. Macropore volume, an indicator of ease of movement of pheretimoids, was significantly greater in CAST than NOCAST soil. Together, the ease of movement and greater temperature dampening of CAST soils may provide thermal refuges to pheretimoids from temperature variations outside the optimal range. This may improve their chances of survival in newly colonized areas where the climate differs from the original range.