Pit Structure Research Articles

Micro-Raman analysis of HVPE grown etched GaN epilayer with porous formation

The GaN epilayer grown by hydride vapor phase epitaxy was wet etched by phosphoric acid as the etchant. X-ray diffraction confirms that the GaN has a wurtzite structure. Scanning electron microscopy shows various sizes of hexagonal pits for different times of etchant reactions. Atomic force microscopy shows increase in surface roughness with different etchant rate. The photoluminescence gives a 3.4 eV luminescence for the pristine GaN epilayer. In the etched films, the deep-level defect belonging to yellow and green luminescence was found. The deconvoluted Ga 3d peaks of etched samples show Ga-rich epilayers. Micro-Raman spectroscopy is a non-destructive method for measuring carrier concentration, phonon lifetime and strain using A 1 (LO) spectra of Raman vibration mode was utilized via the Lorentz fitting method. The carrier concentration increases while the phonon lifetime decreases with etching rate. Overall, in the 9 min reaction, the epilayer was etched heavily with a perfect hexagonal etch pit structure.

Morphology of the north-western wall of Eos Chaos, Valles Marineris: Evidence for glaciation during late Amazonian high obliquity

Glacial landforms have been reported from various regions on Mars; most notably from the mid-to-high latitude regions. We studied Eos Chaos, located towards the eastern boundary of Valles Marineris, for the possible glacial processes occurring in the low-latitude areas on Mars. A thorough investigation of the morphology of the north-western wall of Eos Chaos was carried out using planetary datasets such as context camera (CTX) and High-resolution Imaging Science Experiment (HiRISE) images from NASA's Mars Reconnaissance Orbiter (MRO) mission and Mars Color Camera (MCC) images from ISRO's Mars Orbiter Mission-1 (MOM-1). We identified various geomorphological features that may have resulted from diverse geological processes. The glacial processes are manifested by the morphological features such as tongue-shaped lobate flows, alternative dark and light strata (~10-15 m thick), light-toned fragmented sediments, kettle lake-like structures, surface striations, sublimation hollows, and pit and knob structures. The flow features correspond to three stages of evolution: developing (~0.3 km length), intermediate size (1.5 km length), and mature (~15 km length). These three stages culminated in developing a model depicting the evolution of the glacial landforms of the region based on morphological features. We deduce that the glacial landforms of the region were formed during episodes of higher planetary spin axis obliquity during the late Amazonian.

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Preparation of multi-layered microcapsule-shaped activated biomass carbon with ultrahigh surface area from bamboo parenchyma cells for energy storage and cationic dyes removal

There has been a vast interest in recent years in developing convenient, cost-effective, and greener ways to use abundant natural resources with renewable qualities to alleviate problems associated with energy storage and polluted water sources. Biomass carbon materials have attracted much attention because of the advantages such as abundant resources, relatively low cost, developed pore structure, etc. Present work demonstrates the versatility, effectiveness, and potential of a biomass-derived electrode and adsorbent from bamboo parenchyma cells activated at relatively low temperature (650 °C). The multi-layer microcapsule shape of bamboo parenchyma cells and abundant pit structure enable this biomass material to have an ultrahigh surface area (3973 m2 g−1) and pore volume (2.076 cm3 g−1) after activation. The supercapacitor made of biomass carbon has the high specific capacitance of 276 F g−1 at 0.1 A g−1, exhibiting good capacity retention (89.48%) after 15000 cycles at 10 A g−1. Moreover, the biomass carbon has a maximum adsorption capacity of 1750 mg g−1 in methylene blue dye and demonstrates excellent continuous adsorption performance of continuous flow method. These results confirm that the biomass carbon from bamboo parenchyma cells has great potential for energy storage and cationic dyes removal.

Engineered substrates incapable of induction of chondrogenic differentiation compared to the chondrocyte imprinted substrates

It is well established that surface topography can affect cell functions. However, finding a reproducible and reliable method for regulating stem cell behavior is still under investigation. It has been shown that cell imprinted substrates contain micro- and nanoscale structures of the cell membrane that serve as hierarchical substrates, can successfully alter stem cell fate. This study investigated the effect of the overall cell shape by fabricating silicon wafers containing pit structure in the average size of spherical-like chondrocytes using photolithography technique. We also used chondrocyte cell line (C28/I2) with spindle-like shape to produce cell imprinted substrates. The effect of all substrates on the differentiation of adipose-derived mesenchymal stem cells (ADSCs) has been studied. The AFM and scanning electron microscopy images of the prepared substrates demonstrated that the desired shapes were successfully transferred to the substrates. Differentiation of ADSCs was investigated by immunostaining for mature chondrocyte marker, collagen II, and gene expression of collagen II, Sox9, and aggrecan markers. C28/I2 imprinted substrate could effectively enhanced chondrogenic differentiation compared to regular pit patterns on the wafer. It can be concluded that cell imprinted substrates can induce differentiation signals better than engineered lithographic substrates. The nanostructures on the cell-imprinted patterns play a crucial role in harnessing cell fate. Therefore, the patterns must include the nano-topographies to have reliable and reproducible engineered substrates.

Influence of groundwater level change on deep foundation pit and its control technology

During the construction of deep foundation pits with rich water straight grooves, instability of deep foundation pits due to groundwater frequently occurs, posing a huge challenge to construction safety and economy. Based on the deep foundation pit of the intercity connecting line of Beijing New Airport, the technical method of combining theoretical analysis and on-site monitoring is adopted to analyze the influencing factors of groundwater on the retaining structure of deep foundation pit, and control and analyze the influencing factors. The deformation control technology for deep foundation pit is proposed. The following conclusions are obtained: (1) Based on the on-site geological conditions and the mechanism of groundwater level change, the deformation and failure forms and precipitation forms of deep foundation pits are obtained through theoretical analysis. (2) Based on the Deformation monitoring technology of deep foundation pit, the change of groundwater level and Deformation monitoring of retaining structure are carried out. (3) Combining on-site monitoring with theoretical calculation, conducting comparative analysis of data, summarizing the influencing factors of deep foundation pit damage, obtaining targeted deformation control technology for deep foundation pit, guiding the construction of practical projects, and providing reference for similar projects.

A Practical Method for Calculating Soil Mixing Wall Retaining Structure by Means of a “Simple Beam Method”

SMW is the abbreviation of soil mixing wall. H‐type steel, also known as the new cement mixing pile wall, is inserted into the cement pile, which combines the bearing load with the impervious water retaining, and has the two functions of stress and impervious retaining wall of the supporting structure. In the design of conventional foundation pit engineering, the active Earth pressure calculated by Rankine’s theory is not consistent with the engineering practice because the soil behind the retaining structure has not reached the limit equilibrium state. The embedded depth and the horizontal supporting force of the retaining structure are usually calculated with the equivalent beam method, but the method is complicated. Taking the supporting structure of a foundation pit called “soil mixing wall retaining wall and bolt” as a case, in this paper, the lateral pressure is used to calculate the active Earth pressure at any depth, and the “simple beam method” is used to calculate the embedded depth, the horizontal supporting force, and the internal force of the SMW continuous wall, which intends to find out the first and second supporting points as the pivots of the “simple beam method” under the most unfavorable conditions. When the first pivot is used as the supporting point of the “simple beam method,” the soil pressure is ignored because it is within the critical depth of the Rankine active Earth pressure; while the second pivot is used as the supporting point of the “simple beam method,” the forces on it are balanced to the torque of the second pivot, only considering the moment balance of the active and passive Earth pressure on the isolation body under the second pivot point. The results are in good agreement with the results of the equivalent beam method and the measured values, and they are much closer to the measured values, which provides a practical method for designing SMW retaining structures.

A liquid metal-fluoropolymer artificial protective film enables robust lithium metal batteries at sub-zero temperatures.

Batteries that are both high-energy-density and durable at sub-zero temperatures are highly desirable for deep space and subsea exploration and military defense applications. Our design incorporates a casting membrane technology to prepare a gallium indium liquid metal (LM)/fluoropolymer hybrid protective film on a lithium metal anode. The LM not only spontaneously forms a passivation alloy layer with lithium but also reduces the nucleation potential barrier and homogenizes the Li+ flux on the surface of the lithium anode. The fluoropolymer's polar functional groups (-C-F-) effectively induce targeted dispersion of gallium indium seeds, and the unique pit structure on the surface provides oriented sites for lithium plating. By implementing these strategies optimally, the protected lithium metal anode remains in operation at a current density of 20 mA cm-2 with an over-potential of about 50.4 mV after 500 h, and the full cells have a high capacity retention rate of up to 98.5% at a current density of 0.5 C after 100 cycles. Furthermore, the battery shows improved low temperature performance at -30 °C, validating the potential of the protective film to enable battery operation at sub-zero temperatures.

Assessing the impact of the process of constructing foundation pit enclosure structures on surrounding building

An important issue in the calculations of retaining structures of pits and their interaction with the foundation and existing structures is taking into account the features of their installation technology. Quite often, during calculations, this factor is ignored or taken into account by introducing correction factors, which are somehow based on the statistical processing of observation data during the construction of similar objects.
 The development of numerical methods has enabled designers to use detailed finite-element models in calculations to more accurately predict the behavior of bases and structures, without spending excessive amounts of time.
 In this work, numerical modeling methods are used to reproduce the process of installation of the pit enclosure structures using the trench method "wall in soil" to determine its impact on existing buildings. For this, a numerical model of a 9-floor building with a soil massif was created. Modeling of the foundation pit and enclosure structures, which is installed next to the building, was done. At the same time, the use of a three-dimensional formulation of the problem made it possible to take into account the length of the wall panel and the technological sequence of the construction.
 The existing methods of trench excavation modeling were analyzed and one of them was implemented in the calculation scheme.
 The impact of various factors on the formation of additional deformations of the existing building was investigated, such as: L - distance from the foundation pit to the building; Нст - the depth of laying the sole "wall in the ground"; Lзхв - the length of the wall panel; ρг.р - is the density of the clay slurry.
 Within each task, the settlement of the foundation of the building is determined with different input parameters: L={1,2; 3; 5; 10m}, Нст={12; 18; 24m}, Lзхв={3; 4; 5m}, ρг.р={1.05; 1.10; 1.30t/m3}. The results are presented in the form of graphs.
 The results of the research show that the most determining factors affecting the «technological settlements» of the slab foundation of the building are the distance from the pit to the building and the depth of laying the sole of the "wall in the soil". With different combinations of these parameters, the values of calculated vertical deformations of the building can differ up to several times.

Structural optimization and hydraulic performance analysis of bionic pit flow channels based on a genetic algorithm

Orthogonal experiments have mostly been used in the structural optimization of drip irrigation emitter flow channels. To further improve the efficiency of the optimal design, this study used a genetic algorithm to optimize the structure of the bionic pit flow channel. Based on the structural similarity and performance optimization of the torus-margo bordered pit structure, the constitutive equation of the flow channel unit was constructed. The selection, crossover and mutation operators were set by the genetic algorithm, and the objective function value was calculated. The design variables and known variables that met the requirements were put into the computational domain model, and the pit flow channel structure was simulated and optimized. The results showed that there were large low-velocity regions at the junctions and corners of the pit flow channel units at a working pressure of 50 kPa, and no complete low-velocity vortices were observed, indicating that the flow channels had good anti-clogging performance. The distribution of flow velocity on the same cross-section was quite different, which made the flow layers collide and mix, which intensified the loss of energy, indicating that it had a good energy dissipation effect. The multivariate linear regression analysis showed that the four variables of tooth stagger value (j), flow channel angle (θ), tooth spacing (l) and inner and outer boundary spacing (h) had a decreasing degree of influence on the flow index (x). The flow index (x) was negatively correlated with the tooth stagger value (j), flow channel angle (θ) and tooth spacing (l), and positively correlated with the inner and outer boundary spacing (h). The test results of physical samples showed that the average error between the simulation results and the real values was 3.4%, indicating that the accuracy was high, which can provide a basis for the structural optimization design of related pit drip irrigation emitters.

Bacteria with a mouth: Discovery and new insights into cell surface structure and macromolecule transport.

A bacterium with a "mouth"-like pit structure isolated for the first time in the history of microbiology was a Gram-negative rod, containing glycosphingolipids in the cell envelope, and named Sphingomonas sp. strain A1. The pit was dynamic, with repetitive opening and closing during growth on alginate, and directly included alginate concentrated around the pit, particularly by flagellins, an alginate-binding protein localized on the cell surface. Alginate incorporated into the periplasm was subsequently transferred to the cytoplasm by cooperative interactions of periplasmic solute-binding proteins and an ATP-binding cassette transporter in the cytoplasmic membrane. The mechanisms of assembly, functions, and interactions between the above-mentioned molecules were clarified using structural biology. The pit was transplanted into other strains of sphingomonads, and the pitted recombinant cells were effectively applied to the production of bioethanol, bioremediation for dioxin removal, and other tasks. Studies of the function of the pit shed light on the biological significance of cell surface structures and macromolecule transport in bacteria.

RESEARCH ON THE STRUCTURE AND CONNECTIONS OF PITS IN DIFFERENT CELLS OF MOSO BAMBOO (PHYLLOSTACHYS PUBESCENS)

The plant grows within the transportation of water and nutrients, including radial and longitudinal, but bamboo only exists pits inthe radial, so it plays anirreplaceable role at this moment. This study aims at giving rise to further understanding of the biological functions of pits in bamboo.Light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to investigate the structure and connections of bamboo pits. The results show that the arrangement of pits is significantly different, including alternate,scalariform and opposite arrangements. The presence or absence of the bordered on different cells is also displayed distinctively, these characteristicsextremely affect thetransportation of water and nutrients in bamboo.

ANALIZA ZAŠTITNE KONSTRUKCIJE GRAĐEVINSKE JAME SPO GREEN CITY U SARAJEVU

As part of the development of the Main Design of Residential – Business complex Green City in Sarajevo, the construction of three underground floors along the entire complex is planned. The very location of the facility from the aspect the construction pit is very challenging. During the design of the retaining structure of the construction pit, the complex geological structure and the proximity of the railway represented a special challenge. As part of this paper, the selected solution for the retaining structure of the construction pit will be presented, the impact of the excavation on the surrounding buildings and the railway will be analyzed, and the phased construction of the underground floors of the building and the construction pit retaining structure will be presented in order to obtain the most rational solution.

Water Transport Characteristics of Multiple Structures of Xylem Vessels in Magnolia

The multiple structures of xylem vessels in Magnolia provide stable and efficient water transport channels. The structural parameters of xylem vessels were studied in wood sections and in macerated materials. The results showed that the xylem vessels of Magnolia contained a helical thickening structure and a pit structure of a secondary wall, and the end walls had a scalariform perforation plate. The helical thickening and scalariform perforation plate increased the flow resistance of the vessel, and the pit structure decreased the flow resistance of the vessel. There was a close positive correlation between the flow resistance of the vessels and the helical width, the helical height, the thickness of the scalariform perforation plate, the number of holes in the scalariform perforation plate, the length of the pit canal, and the pit spacing. In addition, there was a negative correlation between the flow resistance of the vessels and the helical spacing, the pit vertical diameter, and the pit domain length. Among these structural parameters, the helical height, the number of holes, and the length of pit canal had a greater influence on the flow resistance. The pit structure caused the vessel to produce radial water transport. The radial transmission efficiency increased with the increase in the pit domain length. With no pit membrane in the pit structure of Magnolia, the radial transmission efficiency would be between 43.99% and 53.21%.

Study on Design and Deformation Law of Pile-Anchor Support System in Deep Foundation Pit

In this study, a deep foundation pit project of Nanlishi Road in the Xicheng District of Beijing was taken as the engineering background. Based on the monitoring method of that project and referring to its design scheme principle, this study applied advanced monitoring technology methods such as anchor axial force and deep horizontal displacement monitoring. The mechanism of pile–soil interaction, the stress change and deformation law of the three-pile and two-anchor support systems of deep foundation pits, and the stability of deep foundation pit support in an anhydrous sandy pebble stratum, were studied in depth. Results show: The axial force of the anchor rod had great loss in the early stage of prestressed tension locking; with the deepening of foundation pit excavation, the lateral pressure of stratum increased gradually, and the prestress of the anchor increased until the end of excavation, where it tended to be stable; the maximum horizontal displacement of the pile was smaller than the design value, and the maximum horizontal displacement was not at the top of the pile; the axial force of the prestressed anchor varied with the formation pressure and surrounding load; the tension of the lower anchor had a certain influence on the axial force of the upper anchor. Except for the east side of the foundation pit, the anchors of the first layer were all stabilized at about 140 kN, and the anchors of the second layer were stabilized at about 150 kN. The third row of anchors on the north side was stable at around 170 kN. By analyzing the variation law of stress and deformation of the supporting structure of the foundation pit, the timeliness of the data during the construction process was improved, and a reference is provided for the informatization construction of related working conditions.

Relationships between Xylem Transport, Anatomical, and Mechanical Traits at Organ Level of Two Cupressaceae Species

Compared to arid regions, forests in humid regions can be more vulnerable to drought as they are not used to, and thus not adapted to, water stress. Therefore, it is vital to understand the drought responses of woodland species in humid areas. Xylem structures and functions of species growing in the humid regions are the key to their drought responses. Two Cupressaceae species (including three taxa: Sequoia sempervirens, Taxodium distichum and its variety Taxodium distichum var. imbricatum) grown in a mesic common garden were targeted, and their xylem hydraulic function (hydraulic conductivity, Ks; cavitation resistance, P50), anatomical structure (tracheid and pit structure), and mechanical support (wood density, WD; tracheid thickness-to-span ratio, Ttob) were measured. Likewise, we analyzed the differences in hydraulic function and anatomical structure of xylem in branches and roots, and the quantitative relationship between xylem water transport, anatomical structure, and mechanical support. Our results showed that roots had a higher hydraulic conductivity and a weaker cavitation resistance than branches. There was no safety–efficiency trade-off in the branches and roots within species. Tracheid mechanical support had a trade-off relationship with Ks or P50 (negative correlation appeared in branch Ks ~ WD and root Ks ~ Ttob of S. sempervirens, root P50 ~ Ttob of T. distichum var. imbricatum, and branch P50 ~ WD). There was no trade-off in anatomical structure, which led to no safety–efficiency trade-off in xylem function. Our results suggest that the two species exhibit both low efficiency and low safety in xylem, and that there is no safety–efficiency trade-off in branches and roots. The reason behind this is that the structural demand for high safety and high efficiency differs (i.e., the root Ks of S. sempervirens was strongly controlled by Dh; in contrast, the root P50 of S. sempervirens was strongly determined by tracheid density, N). Namely, the structural basis for a safety–efficiency trade-off does not exist and therefore trade-offs cannot be achieved.

Design of bionic tire tread compounds with pit structures and the improvement mechanism of wear and wet grip resistance

Design of bionic tire tread compounds with pit structures and the improvement mechanism of wear and wet grip resistance

Enlightening the darkness: The potential of charcoal analysis for the study of vegetation dynamics and relative exploitation at Krania during the Iron Age Greece

In the framework of the NWO project “What went into the melting pot? Land-use, agriculture, and craft production as indicators for the contributions of Greek migrants and local inhabitants to the so-called Greek colonization in Italy (ca. 850–550 BC)”, science-based methods are employed to analyze and compare the organization of subsistence strategies in the Greek motherland and in the indigenous and colonial milieus of Italy (Crielaard et al. 2020). As a part of the subproject ‘Flora & Fauna’, which focuses on farming practices, subsistence strategies and surplus production, Iron Age material from the settlement of Krania in the Pieria region of Greece was analyzed. The site was excavated in 2001 and revealed occupation phases from the 3rd millennium BC to the Hellenistic period. The amount of ceramics recovered demonstrates the importance of trade with the rest of Greece, in particular Corinth, providing evidence for long-standing contacts and networks. Two pit structures contained a high concentration of material, notably charcoal and ceramics dating to the 9th-8th centuries BC. This material constitutes an interesting case study in itself but also as a regional comparandum with other Greek assemblages. This paper discusses how anthracological analysis can contribute to our understanding of human-environment interactions, anthropogenic practices and environmental management.

Centrifuge Model Investigation of Interaction between Successively Constructed Foundation Pits

A series of centrifuge model tests were conducted to study the interaction between successively constructed adjacent foundation pits. The stress, deformation, and earth pressure on retaining structures and the settlement of the soil between the two adjacent foundation pits during successive construction were investigated by a comprehensive instrumentation program. To reveal the effect of the construction sequence, both the stress and deformation of successively constructed foundation pits were compared. The results showed that the stress and deformation of the retaining structure in the foundation pit constructed first were larger than those in the foundation pit constructed later. Due to the inward displacement of the soil around the foundation pits excavated first, the first strut of the foundation pit constructed later underwent high tension during the construction of the first foundation pit. The lateral deformation of the retaining structure of the foundation pit excavated first increased with the increase of the excavation depth. However, the excavation of the second foundation pit reduced the earth pressure on the retaining wall between the two excavations, thus leading to the recovery of the inward deformation in the first excavation. However, the top of the retaining wall deformed into the first foundation pit during the whole construction. The settlement of the soil between the two foundation pits showed a superposition effect. During the construction of the two foundation pits, the settlement of the soil between them kept increasing. The active earth pressure on the middle wall of the foundation pit constructed later was lower than that on the middle wall of the first foundation pit. The excavation of the foundation pit constructed later had no significant effect on the passive earth pressure of the first foundation pit.

Modification strategies for improving antibacterial properties of polyetheretherketone

AbstractPolyetheretherketone (PEEK) is a semi‐crystalline thermoplastic polymer that has been gradually used in the repair of bone defects because of its well chemical stability, reliable biocompatibility, excellent X‐ray radiolucency, and low modulus. However, PEEK is a biologically inert material, and planktonic bacteria can adhere to its surface and eventually form biofilms, allowing for the rapid development of implant‐related infections. This review mainly introduces two important antibacterial modification strategies: antibacterial coating and surface morphology modification. Antibacterial coating include antibiotics, natural extracts, antimicrobial peptides, polymers, metals and metal oxides, selenium, fluoride, silicon nitride, and graphene oxide. These coatings can exert their antibacterial effect by inhibiting bacterial adhesion, killing bacteria by contact, or actively releasing antimicrobial substances. In terms of antibacterial surface topography, different surface microstructures have their respective antibacterial functions. Conical or cylindrical structures can exert stress on the bacterial surface causing the rupture of the cell membrane to kill bacteria. Nano protrusions or particles smaller than the size of bacteria can inhibit the adhesion of bacteria by reducing the contact area of bacteria and PEEK. The pit structure close to the size of bacteria can prevent the contact between adjacent bacteria and delay or prevent the formation of biofilm.