Outer Side Research Articles

A New Concept of Horizontal Bone Augmentation Using Collagen Bovine Bone Blocks Without Membrane at Implant Placement: A Preliminary Study.

A buccal bone thickness (BBT) of at least 1.8-2mm is necessary to ensure long-term implant stability, and a bone grafting procedure is commonly needed to restore this BBT. This study aims to prove the effectiveness of a novel bone augmentation technique in which minero-organic bone substitutes are solely used to restore adequate BBT, excluding the need for coverage membranes. Fifty partially edentulous patients having a residual bone width ranging between 5 and 6mm were enrolled in this study. The horizontal buccal defects were grafted simultaneously at implant placement. Minero-organic collagen bovine bone blocks (CBBB) were placed on the outer side of the buccal bone wall, and adapted to the defect morphology through slow compressive movements. The grafted sites were not covered with any type of membrane nor stabilized with fixation pins. Cone-beam computed tomography scans were obtained pre-operatively, immediately post-surgery, and four months later. Scans were superimposed on the ITK-Snap software to measure the amount of bone gain and assess the percentage of CBBB resorption. Measurements were effectuated at four different levels apically to crestal level. Radiographic findings showed BBT increase and CBBB resorption in all cases, four months post-grafting. A mean horizontal bone gain of 1.39mm was calculated at a crestal level. Based on these findings, it appears that this novel and user-friendly bone grafting technique can achieve positive outcomes from both clinical and radiographic perspectives.

Improving the maneuverability of vehicles by using front swivel axles with separate electric wheels

There is a need for vehicles to maneuver when there are traffic jams, to overcome narrow streets and various obstacles. This leads to increased requirements for dynamism and maneuverability of vehicles.
 The authors present the results of the development and research of the steering control of the vehicle, which provides increased maneuverability. Such circumstances significantly affect the increase in maneuverability of wheeled vehicles, including tractors, for which the use of front suspension axles is possible in terms of layout. The use of a front swing axle with electric motor-wheels with separate control will increase the maneuverability of a two-axle vehicle and minimize the steering effort when turning.
 When solving the task, a mathematical model of the movement of the vehicle on a turn was created. The forces in the contact of the wheels with the road surface were determined, which made it possible to determine the forces and moments of resistance to the rotation of the front axle. Rational laws of control of turning the front axle, providing minimal resistance to the movement of the vehicle, were obtained.
 A vehicle turning control option is proposed, in which the wheels of the outer and inner sides are alternately braked when the vehicle enters and exits the turn. In addition, it is possible to alternately create a torque difference on the wheels of the outer and inner sides of the front axle. Using the proposed turn control options, it is possible to create a multi-axle vehicle with a rocking axle.
 The materials of the article on the controllability of vehicles depending on the design of the steering and front axle are of interest to researchers, designers of mobile equipment, graduate students and students of engineering specialties

Experimental simulation of seepage field distribution for small interval tunnel under varying-head infiltration

In complex hydrogeological environments, it is difficult to achieve a dynamic equilibrium state for the recharge, seepage, and discharge of tunnel groundwater. Especially in case of reservoir flood discharge, local heavy rainfall, extreme dry climate or other emergency situations, the groundwater level will rapidly change, and the tunnel will be under the action of hydrodynamic head height within a certain period of time. Therefore, as urban tunnels in water-rich areas develop towards large cross-section, small spacing and complex sensitive stratum, studying the spatial distribution characteristics of seepage and stress fields in small interval tunnels under variable water head infiltration conditions is an urgent problem to be solved. In this paper, using the self-developed seepage model testing equipment, tunnel seepage tests under different hydrodynamic head heights and heavy rainfall conditions are carried out on the Kexuecheng Tunnel, which is a typical small interval tunnel in complex hydrogeological environment of Chongqing, China. According to the test results, as the burial depth and water level increase, the water pressure at each monitoring point gradually increases. Benefiting from the superimposed drainage effect of adjacent hole, the average water pressure at the inner side is 8 ∼ 12% lower than that on the outer side. The grouting circle and high groundwater level will further aggravate the asymmetric distribution of hydrodynamic pressure on the lining structure. However, as the hydrodynamic head height increases, the effective stress of the stratum decreases, and the earth pressure on the tunnel decreases by 24 ∼ 40%. Under heavy rainfall conditions, the evolution of lining structure pressure can be divided into initial infiltration stage, rapid growth stage, gradually stable stage and slowly decreasing stage. Suffered by the influence of rainstorm on seepage field and stress field, the overall pressure acting on the vault, left haunch, right haunch and bottom of lining structure increase by 45.4%, 132.3%, 117.4% and 147.4%, respectively.

Three-dimensional numerical simulation of the interaction between high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth metal

The rupture accident of the steam generator heat transfer tube of the lead-bismuth cooled fast reactor causes a high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth, and the interaction mechanism between water and liquid lead-bismuth needs to be studied clearly. In this paper, based on the volume of fluid method, the LES turbulence model and the Lee phase transition model, a three-dimensional numerical model is developed to study the multiphase flow and heat transfer mechanism of water and lead-bismuth interaction. The effects of sub-cooled water temperature, inlet pressure, and nozzle diameter on the distribution of phase state, pressure, temperature, and generated steam volume are studied in detail. The results indicate that the water jet can be divided into the jet water zone, the water-steam mixed zone, and the multiphase flow zone, respectively. Among them, the appearance of water-steam mixed zone depends on the internal boiling of the jet, and this zone tends to appear under the condition of low inlet pressure, small nozzle diameter and high sub-cooled water temperature. For multiphase flow zone, the temperature increases with sub-cooled water temperature, decreases with nozzle diameter and is almost not influenced by inlet pressure; The pressure increases with sub-cooled water temperature, inlet pressure and nozzle diameter. When nozzle diameter is large enough, however, it no longer has any effect on the temperature and pressure distribution within the jet. The volume of steam generated by water boiling is positively correlated with all three factors. Overall, the steam migrates upward through the outer side of the jet, absorbing heat and expanding during the migration process, and forming a high-temperature area at the top of the jet.

Thermal performance and energy saving using phase change materials (PCM) integrated in building walls

One of the new strategies lately used in energy efficient building (EEB) is the integration of phase change materials (PCM) into the building structure. This study examines the long-term thermal behavior of a building wall that contains different types and thicknesses of PCM in the hot summer season according to the climate of Aswan in Egypt. The building wall is studied with and without the PCM layer under different exterior weather conditions. ANSYS 2020 R1 is used to design and simulate a 2D simplified thermal model. The influences of PCM types (RT-27, RT-31, RT-42, RT-35HC, RT-44HC, and lauric acid), thickness (1, 2, 3, 4, 6, and 8 cm), and location inside the wall (outer side, inner side, and the middle), as well as different cities on the inner wall temperature are studied. The results show that, using PCM in the wall structure reduces the indoor heat flux and reaches the temperature of internal walls closer to the desired levels. Additionally, RT-35HC has the highest thermal performance and the optimal place of the PCM location is 1.5 cm from the inside and outside of the wall. The average expected indoor wall temperature reached 31.1 °C, and 27.7 °C for the wall without and with PCM, respectively, based on three-month model simulations. The use of 1.5 cm inner and outer of RT35HC-PCM in the wall structure results in a 66 % reduction in the overall energy gain throughout the summer.

Experimental investigation on flow boiling heat transfer characteristics of water and circumferential wall temperature inhomogeneity in a helically coiled tube

Helically coiled tubes (HCTs) have been widely used in chemical industry and nuclear engineering because of its compact structure and excellent heat transfer performance. This paper designed and built an experimental platform to study the flow boiling heat transfer (FBHT) of subcritical water with high temperature and high pressure in an HCT. The results showed that the wall temperature on the inner side is higher and it gradually decreases when moving to the outer side along the circumferential direction. The variation law of circumferential wall temperature inhomogeneity (CWTI) under different pressures, mass velocities, heat fluxes and vapour qualities was obtained. The distribution of circumferential wall temperature varies greatly in the single-phase region while it varies slightly and is relatively uniform in the two-phase boiling region. As the vapour quality increases, the CWTI decreases first, and maintains at a low value when the vapour quality is about 0.0 ∼ 0.9. When the vapour quality reaches about 0.9, the CWTI increases rapidly. When the vapour quality is less than 0.5, the heat flux and mass velocity have little effect on the CWTI. When the vapour quality is larger than 0.5, reducing the heat flux or increasing the mass velocity can effectively reduce the CWTI. In addition, the flow pattern of two-phase boiling flow in the HCT is divided into four regions, namely bubble flow, slug flow, annular flow and mist flow, and the transition vapour quality xt1 = 0.2, xt2 = 0.5 and xt3 = 0.93 are respectively selected according to the sudden abrupt change of the wall temperature or the differential pressure. Finally, the existing FBHT correlations are collected and evaluated and the calculation accuracy needs to be improved for more accurate calculation. Therefore, a new FBHT correlation with better accuracy is proposed for calculating the heat transfer coefficient of two-phase flow boiling in the HCT.

Model experiment and support optimization analysis of primary support arch cover excavation of large-section metro station in sandy mudstone stratum

The span and height of the Xietaizi metro station of Chongqing Rail Transit Line 18 are all larger than 20 m. The concept of “primary support arch cover” is adopted in the construction method, which aims to give full play to the bearing capacity of sandy mudstone, greatly improve the construction efficiency, and reduce the economic cost. In this paper, the model experiment of primary support arch cover excavation of large-section metro station in sandy mudstone stratum was carried out and the progressive failure process of the initial arch cover was revealed. It is found that the ground surface settlement is not strictly symmetrical about the station center, which is more significant in the case of the measuring points are far away from the central axis of the cavern. Since the support structure installed, the steel arch stresses and anchor axial forces at the inner and outer sides are in a rapid growth stage, and then shows a slow growth trend until stable. For the stresses at the inner and outer sides, the steel arch at the left arch shoulder is characterized by overall compression. The vertical displacements and convergence of the station are more prominent than the horizontal displacements and convergence, which indicates that the significance of control the settlement of the arch crown. The vertical convergence of the station is mainly caused by the settlement of the crown. When the level of loading is large, the number of longitudinal cracks will be increased as penetrating crack and the bulging phenomena will occur at the left arch shoulder of the secondary lining structure. Based on the numerical simulation, the whole dynamic procedure of construction is optimized from the demolition timing of temporary support. The vertical displacements and horizontal convergences for overall demolition schemes are smaller than those for stepping demolition with the excavation of middle guide holes.

A‐DA’D‐A Type Pentacyclic Small Molecule Acceptors to Exceed 16.5% Efficiency by Heteroatom Effect at the Outer Side Chain

Comprehensive SummaryIn this work, we adopt a “heteroatom side‐chains” modification strategy to modify the thiophene units in A‐DA'D‐A (acceptor‐donor‐acceptor’‐donor‐acceptor) type pentacyclic SMAs (small molecule acceptors), that is, introducing branched alkyl chain at the β‐position of thiophene instead of straight alkyl chain, and then introducing oxygen atom at the third‐position on the basis of branched chain. Two new pentacyclic SMAs (BZ4F‐EH and BZ4F‐OEH) were synthesized, and the influence of the heteroatom side‐chains on photoelectric properties of A‐DA'D‐A type pentacyclic SMAs was systematically studied. Compared with our previously reported BZ4F (Y26), BZ4F‐EH shows slightly blue‐shifted absorption, while BZ4F‐OEH has obvious red‐shifted absorption. As a result, BZ4F‐OEH‐based binary device achieved a high power conversion efficiency (PCE) of 16.56% with a fill factor (FF) of 79.3%, which is the highest efficiency of pentacyclic SMAs to date. The results indicated that the modification of hetero‐atomization on the β‐position of thiophene is a simple and efficient way to improve the PCE of A‐DA'D‐A type SMAs, and this work provides an important guideline for future molecular design.

Investigation on seepage field distribution and structural safety performance of small interval tunnel in water-rich region

The complicated interaction between seepage field and stress field of tunnels in water-rich region has an important impact on the stratum deformation stability, structural safety performance, groundwater resources and ecological environment protection, etc. Especially for large-span urban tunnel with small spacing, the seepage funnels of the two holes will partially overlap and affect each other, making the seepage field distribution much more complex, and the difficulties in prediction water drainage and safety performance of supporting structure increase sharply. In this paper, in order to investigate the seepage field distribution and its influence on the structural mechanical behavior of small interval tunnel in water-rich region, using the self-developed seepage model test equipment, tests under different hydrostatic head heights were carried out on the Kexuecheng Tunnel, which is a typical small interval tunnel under complex hydrogeological environment in Chongqing, China. According to the test results, with the increase of buried depth and water level, the water pressure at each monitoring point gradually increased. For small interval tunnel, the average water pressure on the inner side decreased by 10–15 % compared with the outer side. Benefiting from the grouting circle can effectively block the supply of pore water in the rock mass, the water pressure behind the lining can be significantly reduced by 32 %–42 %. But with the increase of the hydrostatic height, the proportion of water pressure that can be shared by the grouting circle decreased gradually, and further aggravated the asymmetric distribution of the water pressure on lining structure. Meanwhile, the water pressure evolution curve shown a W-shaped distribution in horizontal direction and a V-shaped descend funnel along the tunnel axis, the predicted seepage influence range may increase to over 60–70 m under high water pressure. Contrary to the asymmetric distribution of water pressure, the earth pressure at the inner side was about 10 % higher than that at the outer side. Influenced by the tunnel excavation unloading effect, the closer to the tunnel face, the smaller the surrounding rock pressure. The minimum safety factors of the lining structure under water level of 0, 30, 40 and 50 m were 4.28, 3.85, 3.41 and 2.98, the structural safety performance significantly decreased with the increase of the hydrostatic head height.

Thermo-Hydrodynamic Lubrication Analysis of Slipper Pair Considering Wear Profile

The profile of sealing land is a sensitive factor affecting the thermo-hydrodynamic lubrication characteristics of the slipper pair. In this paper, the non-uniform wear of the running surface under the slipper was presented and defined as the boundary condition. Based on the finite volume method and the successive over-relaxation iteration method, a discrete numerical model coupled with the temperature, pressure, and thickness of the oil film was constructed. The Newton and sequential circulation methods were used to solve the coupling equations. The influence of the wear profile on the film thickness, sliding attitude, and leakage were discussed. The analyzed results show that the control of the wear on the outer side of sealing land and the contour vertex position, and the avoidance of the wear on the inner side of sealing land could improve the thermo-hydrodynamic lubrication performance of the slipper pair.

Analysis of Factors Influencing the Flow Characteristics of Paste Backfill in Pipeline Transportation

The continuous accumulation of tailings in tailings reservoirs not only causes environmental pollution but may also cause geological disasters. The paste-filling mining method is an effective way to address the accumulation of tailings, and it is necessary to study the flow characteristics of the pipeline transportation process—a core process of this method. However, limited by factors such as test conditions, equipment, and cost, the research in this field mainly focuses on the flow performance of conveying materials and the influence of single conveying conditions on the resistance of filling pipelines. The pipeline transportation of paste is a systematic project, and its pipeline transportation characteristics are not only determined by the characteristics of the slurry itself but also related to the geometric characteristics of the pipeline. In this study, an orthogonal test and numerical simulation were used to study the influence of five parameters—i.e., the filling gradient, the curvature radius of the elbow, the inner diameter of the pipeline, the paste flow rate, and the paste concentration—on pipeline transportation characteristics, and they were sorted according to their levels of influence. The results show that, during the pipeline transportation process, the slurry concentration has the greatest influence on the resistance loss and the maximum wall shear stress of the pipeline, and the slurry flow rate has the greatest influence on the maximum flow rate at the elbow. The numerical simulation results were compared and analyzed using rheological theory. The maximum difference rate was 11%, and the average difference rate was 6%. Numerical simulation results indicate that the pipe wall near the outer diameter side of the inlet section and the center of the elbow section wears easily during the paste-conveying process. The results enrich the theory of paste pipeline transportation, improve the understanding of the influence of various parameters on paste transportation characteristics, and provide a reference for paste pipeline design.

Understanding hydrogen jet dynamics for direct injection hydrogen engines

The energy paradigm is shifting toward carbon-free and low-emission alternative fuels. Among the many candidates, hydrogen is considered a promising option thanks to its favorable fuel properties, including zero carbon content, high gravimetric energy density, and fast flame speed, despite its technical fuel production and storage challenges. Direct injection technology has been identified as the best approach for applying hydrogen in combustion engines to overcome the accompanying issues, such as backfire and low energy density. However, studies have yet to be conducted on hydrogen jet behavior in direct injection systems, specifically, studies that elucidate engine design and injection parameter optimization in the combustion system. Therefore, we aimed to assess hydrogen jet behavior through experiments and computational approaches comprehensively. Hydrogen was injected at 10 MPa using the direct injection method into a constant volume chamber under a quasi-steady ambient condition. Z-type high-speed Schlieren imaging was performed using a high-speed camera to visualize the hydrogen jet structure, which depicted the hydrogen jet’s vapor intermittency and vortex structure. We also performed a computational fluid dynamics (CFD) simulation to understand the aerodynamics of the jet. The results showed the formation of vortical flow in the inner core region, where the pressure was comparatively lower than that on the outer side of the jet. Our further investigation of the injection strategy showed that multiple injections were more beneficial in forming a favorable hydrogen-air mixture near the spark plug than a single injection case.

Proposal of defect inspection method of steel plate by full-wave rectified magnetic field

The large-diameter steel pipes are often used in petrochemical plants. In this large-diameter steel pipe, there are many cases where corrosion in the steel pipe is inspected from the outside of the steel pipe. In particular, there is a demand for a method for detecting defects inside or outside the steel pipe from the outer side of the steel pipe at high speed. Therefore, the electromagnetic inspection method is useful for detecting these defects. In the electromagnetic inspection method, using both static (DC) magnetic field and alternating (AC) magnetic field is proposed for inspecting inner side defects as well as outside defects. On the other hand, the Fourier series expansion of the full-wave rectified wave of the stationary AC magnetic field shows that it is a composite of the DC component and the AC component due to the cosine wave. Therefore, in this research, an inspection method using full-wave rectified AC magnetic field is proposed for inspecting inner side defects as well as surface defects. In this paper, the usefulness of the proposed method is demonstrated by electromagnetic field analysis using the “play model” that takes into account minor loop magnetic properties. In addition, a verification experiment is also carried out.

Performance enhancement of adhesive joints of additive manufactured parts by using different types of fibre reinforcements

The main objective of this study was to investigate experimentally the mechanical performance of adhesive joints made of additive manufactured (AM) polymeric parts reinforced with different types of fibres. PLA (PolyLactic Acid) and ABS (acrylonitrile butadiene styrene) AM adherends were fabricated by fused deposition modelling (FDM). Further, natural (jute and curauá) and synthetic (glass) fibre reinforcement fabrics were laminated on the outer sides of the AM parts using an epoxy resin via compression moulding. The type of reinforcement (natural or synthetic) and the effect of the number of the layers (1 and 2 layers) on the performance of the bonded joints was studied by testing single lap joints (SLJs) bonded with an epoxy structural adhesive. It was found that the mechanical performance of adhesively bonded SLJs is improved by using different types of fibre reinforcements to the 3D printed core adherends. The failure load varied as a function of fibre type and number of layers used as reinforcement, as well as the material used for the core of the adherends. The ABS SLJs presented lower strength compared to PLA SLJs, mainly due to the ABS adherend inferior mechanical properties. In addition, the PLA core specimens presented a better interface adhesion with the epoxy resin used in this study to laminate the reinforcements, when compared to the ABS core reinforced specimens. The best results in terms of improvement in failure load were obtained for the curauá fibre reinforced PLA 3D printed SLJ specimens (the average joint strength was more than 1.5 times higher than the neat-PLA SLJ specimens).

Endowment of omniphobicity and exceptional bendability to a wear-resistant POSS coating

Coating of a new polyhedral oligomeric silsesquioxane, GMPOSS bearing two 3-glycidyloxypropyl (G) and six 3-methacryloxypropyl (M) groups, is highly wear-resistant but has no oil- or water-repellency and limited bendability. To render omniphobicity, perfluorinated poly(propylene oxide) (FP) bearing a terminal carboxyl group (FP-COOH) is grafted onto a fraction of the GMPOSS molecules to yield F-GMPOSS, a mixture of GMPOSS and GMPOSS-FP. Subsequent photocuring of a liquid film of F-GMPOSS that contains 2.6 wt% of fluorine produces a highly transparent coating with superior dynamic de-wetting properties. To improve the coating’s bendability, an innovative method for composite making is developed. A flexible porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFP) scaffold is prepared first on a poly(ethylene terephthalate) (PET) substrate. F-GMPOSS containing photoinitiators are then infused into the PVDFP pores and photocured to produce a composite coating. At a thickness of 20 μm, the composite can fold, without crack or peel, 500 times on either the inner or outer side of its PET substrate around a rod of a diameter of 2 mm. The coating also has a transmittance of 95 ± 2% at 500 nm, a low surface energy of 11.8 ± 1.6 mJ/m2, and an impressive hardness of 0.80 ± 0.02 GPa. Its superior ink contraction capability remains intact after 100 abrasions with steel wool. While the methods for rendering antismudge properties and flexibility can be used to prepare other materials and coatings, the F-GMPOSS coating and the F-GMPOSS/PVDFP composite coating are of practical value and may be used as the encapsulating layer for foldable touchscreens, for example.

Response of Extratropical Transitioning Tropical Cyclone Size to Ocean Warming: A Case Study for Typhoon Songda in 2016

This study attempts to investigate how future sea surface temperature increases will affect the size (radius of gale-force [17 m s−1] wind at 10 m height; i.e., R17) evolution of tropical cyclones that undergo extratropical transition (ET) through sensitivity experiments of sea surface temperature (SST) for Typhoon Songda (2016) in the northwestern Pacific. Two numerical experiments were carried out, including a control simulation (control) and a sensitivity experiment (SST4.5) with SST increased by 4.5 degrees in the entire domain. The results showed that Songda tended to be stronger and larger with projected higher SSTs. Moreover, the momentum equation for tangential wind was utilized to study the mechanism of R17 evolution in different SST scenarios, in which the radial absolute vorticity flux term played a dominant role in generating a positive tendency of tangential wind. The results indicate that before ET, higher SSTs in the entire domain led to more active rainbands in both inner-core and outer-core regions. As a result, stronger secondary circulation and low-level inflow extended outward, and the absolute angular momentum (AAM) importing from the outer region increased, which led to a larger R17 in SST4.5. During the ET, the peripheral baroclinically driven frontal convection induced extensive boundary layer inflow, which accelerated the tangential flow in the outer frontal region through strong inward AAM transport. However, due to the lower latitude of the cyclone and the strong frontolysis at the outer side of the cold pool in SST4.5, the peripheral frontal convection reached the location of R17 later; thus, the increase in the cyclone size lagged behind that in the control.

Influence of Small Radius Curved Shield Tunneling Excavation on Displacement of Surrounding Soil

In contrast to straight tunnels, the mechanisms of displacement of surrounding soil induced by shield excavation of small radius curved tunnels are more complex. Based on field monitoring data of surface settlement and horizontal displacement of a small radius curved shield tunnel in a section of Zhengzhou Metro Line 3, a numerical model using three-dimensional a finite element method is established to evaluate factors of the displacement of surrounding soil. The results verify the validity of numerical simulation by comparison with field monitoring data and the influence of unbalanced additional thrust at tail jacks, curvature radius of a tunnel and tail grouting pressure on surface settlement and horizontal displacement of surrounding soil. Maximum surface settlement and horizontal displacement of surrounding soil at the outer side and inner side of curved tunnel axes are positively related to thrust ratio, while negatively related to curvature radius and grouting pressure. The ultimate objective of this study is to ascertain factors of displacement of surrounding soil induced by small radius shield excavation and provide a theoretical basis and technical support for the design and construction of similar tunnel.

Dynamic Response and Failure Mechanism of Deep-Buried Tunnel with Small Net Distance under Blasting Load

Under blasting load, a series of safety problems, such as lining cracking and surrounding rock instability, are prone to occur in deep-buried tunnels with a small net distance. It is significant to understand the dynamic response and failure mechanism of tunnels under blasting. The blasting attenuation formula is optimized through theoretical analysis and field experiments. The measuring point vibration is monitored in real time and the tunnel blasting model is established by ANSYS/LS-DYNA software. The model was set as having no reflective boundary and an uncoupled charge structure was used. The attenuation law of blasting seismic waves is studied from the adjacent tunnel lining and the direction of the tunnel cross-section and length. The inner and outer sides of the tunnel lining are investigated, respectively. The displacement and acceleration of lining measuring point are also analyzed. The dynamic response of the tunnel lining under blasting excavation is analyzed from multiple angles. The results show that the arch foot on the inner side of the lining (the side in contact with the tunnel headroom) is the first to generate vibration. On the outside of the lining (the side in contact with the rock),the peak vibration velocity is reached after blasting load unloading. There is little difference in the vibration velocity at different positions of the transverse section, but great difference in the vibration velocity of the longitudinal section. The influence of the horizontal displacement was greater than that of the vertical displacement. The vibration acceleration of the measuring point at the arch foot of the section is the largest and the detonation is also the largest.

Mid-late holocene accretional history of low-lying, coral-reef rim islets, South-Marutea Atoll, Tuamotu, central South Pacific: The key role of marine hazard events

South-Marutea Atoll is located in the Gambier Island Group, at the south-eastern end of the Tuamotu Archipelago, French Polynesia, central South Pacific. Understanding the modalities of islet building from low-lying atolls over the mid to late Holocene, in relation to sea-level changes and cycles of marine hazard events, is a prerequisite for better anticipate future geomorphic changes to which the islets will likely be faced in the next decades under global climate warming. Herein is presented the depositional history of two selected atoll islets, based on chronostratigraphic analysis of sedimentary, coral-dominated sequences from six excavations. Identified as Motu Aramu and Motu Vainono, these islets are located respectively in north-north-east and due south of the atoll rim. Additional surficial sampling was conducted on modern ocean-facing shingle ridges, respectively on north-north-west (Motu Oire), west (Motu Aranui) and east (Motu Tekava) rim areas, in order to date the latest ridge-emplacement stages. Oire and Aranui sites, located along the leeward atoll sites, are protected from trade winds, Aramu, Vainono and Tekava are located on the windward sides, directly exposed to northeasterly and southeasterly storm swells respectively. A total of 88 coral clasts were collected to be U/Th dated. The excavated sequences range between 2.50 ​m and 0.90 ​m in thickness, from the outer islet sides lagoonwards. Five lithofacies, including two subfacies, were recognized based on texture and biological composition: a coral boulder-cobble-dominated, a coral pebble-dominated – pebble-supported and sand-supported subfacies – and a foraminifera-rich, sand-dominated and an organic-rich, pebble to sand facies. These facies tend to be distributed from ocean sides landwards according to a decreasing grain-size gradient. A model of atoll-island accretion emerges in relation with changes in frequency and intensity of marine hazard events. The islet foundations consist of conglomerate platforms, locally up to 1.0 ​m thick, deposited from about 5,000 to 1,000 ​calendar year (cal yr) BP. Islets began to accrete from 5,000 ​yr cal BP. While at Motu Vainono, islet building occurred continuously over the last 5,000 years, at Motu Aramu, there is an apparent non-depositional episode, from 4,000 to 2,000 ​yr cal BP, interpreted as caused by a marked decreased in enso-related cyclone activity. The outer shingle ridges in all studied sites were regularly reshaped during the last millennium. During the last 5,000 years, the major accretion-islet episodes occurred irrespective of the course of sea level, indicating that sea-level change was not a driver of islet accretion. Periodical, marine high-energy events clearly appear to be the key controls of islet shaping. Shifts of cyclone source areas further south and increasing cyclone intensity, but lower frequency, due to enhanced enso variability throughout the 21st century, is postulated to expose the Gambier island Group to stronger, but fewer disturbance events when compared to the last millennia.

3D characterization of vascular bundle in moso bamboo node and its effect on compressive properties

Abstract The structure of the bamboo node obviously differs from that of the internode and largely affects the mechanical properties of bamboo. However, the node structure of moso bamboo, an important economic and ecologic bamboo species, was still unclear. Thus, in this study, the 3D structural changes of the vascular bundle (VB) in the moso bamboo node were visualized and quantified. The compressive properties and failure mechanisms of the bamboo node were discussed based on the structural changes. The results showed that the horizontal VB in bamboo node was classified into three types: branching, cross-linking, and thickening. The cross-sectional area of the vertical VB in bamboo node increased, and the vertical VBs shifted to the outer side after passing through the node. Due to the “wire hoop” effect of the horizontal VBs, the longitudinal compressive strength of the node was greater than that of the internode. The deflection of VBs caused slippage between VBs and resulted in the decrease of the node’s transversal compressive strength. This research provided key information for a deeper understanding of the structure and mechanical properties of bamboo for potential applications.