Search

Quantitative identification of water utilization characteristics of xerophytic shrubs is an important prerequisite for the selection and optimization of a regional artificial sand-fixing vegetation system. In this study, a hydrogen (δD) stable isotope technique was used to study the changes in water use characteristics of four typical xerophytic shrubs, Caragana korshinskii, Salix psammophila, Artemisia ordosica, and Sabina vulgaris in the Hobq Desert under light (4.8 mm after 1 and 5 days) and heavy (22.4 mm after 1 and 8 days) rainfall events. Under light rainfall, C. korshinskii and S. psammophila primarily used the 80–140 cm layer of soil water (37–70%) and groundwater (13–29%), and the water use characteristics did not change significantly after the light rainfall event. However, the utilization ratio of A. ordosica to soil water in the 0–40 cm layer increased from less than 10% on the first day after rain to more than 97% on the fifth day after rain, whereas the utilization ratio of S. vulgaris to soil water in the 0–40 cm layer also increased from 43% to nearly 60%. Under heavy rainfall, C. korshinskii and S. psammophila still used the 60–140 cm layer (56–99%) and groundwater (~15%), while the main water utilization depth of A. ordosica and S. vulgaris expanded to 0–100 cm. Based on the above results, C. korshinskii and S. psammophila primarily use the soil moisture of the 80–140 cm layer and groundwater, while A. ordosica and S. vulgaris use the soil moisture of the 0–100 cm layer. Therefore, the co-existence of A. ordosica and S. vulgaris will increase the competition between artificial sand-fixing plants, while the combination of the two plants with C. korshinskii and S. psammophila will avoid competition between artificial sand-fixing plants to some extent. This study provides important guidance for regional vegetation construction and sustainable management of an artificial vegetation system.

Waves and tidal currents can interact to produce strong seabed shear stress and mobilization of sediments on continental shelves. Modelled wave and tidal current data for a 3-year period were used in a combined-flow sediment transport model to simulate the seabed shear stresses and the mobilization of uniform medium sand on the continental shelves of Canada. The modelling results are presented to establish the first national framework of seabed disturbance and sediment mobility on the continental shelves of Canada. Strong waves and tidal currents on the Canadian continental shelves produce mean bed shear velocity >5 cm * [s.sup.-1]. Medium sand can be mobilized >50% of the time over many areas on the shelves. The mobilization by tidal currents occurs over 36% and by waves over 50% of the shelf area, demonstrating that mobilization of sediments is dominated by waves on the Canadian continental shelves. Combined shear stresses due to wave and tidal current interaction further increase sediment mobilization to over 68% of the shelf area. The spatial variation of the relative importance of wave and tidal disturbances allows classification of the continental shelves into six disturbance types. Innovative Seabed Disturbance (SDI) and Sediment Mobility (SMI) indices are proposed to quantify the seabed exposure to oceanographic processes and sediment mobilization, incorporating both the magnitude and frequency of these processes. The proposed SDI and SMI, together with the disturbance type classification, can be used as standard parameters to best quantify seabed disturbance and sediment mobility on other shelves of the world. Key words: tidal current and waves, shear stresses, sediment mobilization, seabed disturbance, continental shelves, Canada. Les vagues et courants de maree peuvent interagir pour produire de fortes contraintes de cisaillement sur le fond marin et la mobilisation de sediments sur les plateaux continentaux. Des donnees modelisees sur les vagues et les courants de maree pour une periode de trois ans ont ete utilisees dans un modele de transport de sediments a ecoulement combine pour simuler les contraintes de cisaillement sur le fond marin et la mobilisation de sable moyen uniforme sur les plateaux continentaux du Canada. Les resultats de la modelisation sont presentes dans le but d'etablir le premier cadre national de perturbations du fond marin et de mobilite des sediments sur les plateaux continentaux du Canada. De forts courants de maree et vagues sur les plateaux continentaux canadiens produisent des vitesses de cisaillement moyennes sur le fond de >5 cm * [s.sup.-1]. Le sable moyen peut etre mobilise >50 % du temps sur de nombreux secteurs des plateaux. La mobilisation par des courants de maree se produit sur plus de 36 %, et par les vagues, sur plus de 50 % de la superficie des plateaux, ce qui demontre que les vagues constituent l'agent dominant de mobilisation de sediments sur les plateaux continentaux canadiens. Les contraintes de cisaillement combinees dues a l'interaction des vagues et des courants de maree accroissent egalement la mobilisation de sediments sur 68 % de la superficie des plateaux. Les variations spatiales de l'importance relative des perturbations par les vagues et les marees permettent la categorisation des plateaux continentaux selon six types de perturbations. Des indices novateurs de perturbation du fond marin (SDI) et de mobilite des sediments (SMI) sont proposes pour quantifier l'exposition des fonds marins a des processus oceanographiques et a la mobilisation de sediments, incorporant a la fois la magnitude et la frequence de ces processus. Les indices proposes, combines a la categorisation des types de perturbations, peuvent etre utilises comme parametres normalises pour quantifier le mieux les perturbations du fond marin et la mobilite des sediments sur d'autres plateaux du monde. [Traduit par la Redaction] Mots-cles : courant de maree et vagues, contraintes de cisaillement, mobilisation de sediments, perturbation du fond marin, plateaux continentaux, Canada., Introduction The impacts on the seafloor exerted by waves and currents, and the sediment responses to this forcing, directly affect the cost and safety of seabed installations for offshore engineering [...]

Summary: This research deals with a frame‐supported shear wall for urban over‐track building of vehicle depot in Chisha, Guangzhou, China, which is characterized by its remarkable height of 160.8 m. Technical issues are commonly encountered in these kinds of buildings due to discontinuous vertical structural rigidity, large podium, and structural transition. These challenges significantly impact the engineering process, especially when the rigidity difference between transfer story exceeding the threefold, as well as the building height exceeds limit as in code. In this paper, a shaking table test was developed based on a 1:10 scaled model of the structure. Using similarity theory, the dynamic similarity relationship was established for the design of the model. Subsequently, the experimental model was constructed with the configuration of critical parameters such as mass design, sensor placement, and seismic test conditions. This was followed by in‐depth analysis, recording component failures and investigating key aspects such as dynamic characteristics, that is, acceleration and displacement responses and shear force distribution under different earthquake intensities. A theoretical seismic response of the prototype structure was derived from the test results. The shaking table tests confirmed that the structure met the stringent seismic design requirements as prescribed in the Chinese standards, with no damage under minor earthquakes, repairability under moderate earthquakes, and collapse prevention under rare earthquakes. The results of the study provide valuable insights along with improvement measures for the design and development of similar urban over‐track buildings, potentially contributing to more efficient land use in urban China. [ABSTRACT FROM AUTHOR]

Local scour around piers is one of the primary causes of collapse of bridges that cross rivers. The most severe scouring occurs in cold regions where ice cover significantly changes the velocity profile. Having an accurate estimation of the maximum scour depth around bridge piers, especially in cold regions, is necessary for a safer design of piers. In this study, 3D numerical models are compared to laboratory experiments to examine the process of local scour around bridge piers with and without smooth and rough ice cover. By using the equation of Meyer-Peter and Muller, the sediment transport model is validated to approximate the transport of the sediment particles. Numerical results showed good agreements with experimental observations where the maximum scour depth and turbulent kinetic energy around bridge piers were the highest under rough ice cover conditions. Key words: bridge pier, ice-covered flow, local scour, numerical simulation, sediment transport, turbulent flow. L'affouillement local autour des piles est l'une des principales causes d'effondrement de ponts qui traversent les rivieres. L'affouillement le plus grave se produit dans les regions froides ou la couverture de glace modifie considerablement le profil de vitesse. Il est necessaire d'avoir une estimation precise de la profondeur d'affouillement maximale autour des piles de pont, surtout dans les regions froides, afin d'assurer une conception plus sure des piles. Dans le cadre de cette etude, des modeles numeriques 3D sont compares a des experiences en laboratoire afin d'examiner le processus d'affouillement local autour des piles de pont avec et sans couverture de glace lisse et rugueuse. En utilisant l'equation de Meyer-Peter et Muller, le modele de transport de sediments est valide pour estimer le transport des particules de sediments. Les resultats numeriques ont montre une bonne concordance avec les observations experimentales ou la profondeur d'affouillement maximale et l'energie cinetique turbulente autour des piles du pont etaient les plus elevees dans des conditions de couverture de glace rugueuse. [Traduit par la Redaction] Mots-cles : pile de pont, ecoulement sous la glace, affouillement local, simulation numerique, transport de sediments, ecoulement turbulent., Introduction Worldwide, local scour is a major cause of bridge failure. Local scour is created by horseshoe and wake vortices at the base of bridge piers, which increase in magnitude [...]

GaN materials have attracted great interest and have demonstrated remarkable potential in many fields. When growing GaN materials, substrate selection is of great importance. By virtue of their nominally unlimited size, easy removal, and excellent thermal conduction, metal substrates have been suggested as an alternative to the commonly used substrates such as sapphire. GaN growth on metal substrates, however, is still quite rare, and many aspects remain unexplored. This paper uses computational fluid dynamics to perform a three‐dimensional numerical simulation of the GaN‐ MOCVD reaction chamber. We investigated the influence of the graphite containers' rotational velocity and the metal matrix's temperature at various locations. When the pressure within the MOCVD chamber remains constant, increasing the graphite tray's rotational velocity enhances the temperature field distribution within the chamber. However, the flow field becomes unstable when the rotation rate exceeds 1000 rpm. Our findings serve as a crucial benchmark for the future parameter optimization of MOCVD growth of GaN on metals. [ABSTRACT FROM AUTHOR]

Data from two surveys by multi-beam sonar and two by marine/terrestrial LiDAR are used to evaluate the geomorphology of the seafloor in littoral areas of the Canadian Arctic Channels, near King William Island, Nunavut. Submarine terrains show well-preserved glacial landforms (drumlins, mega-scale glacial lineations, iceberg-turbated terrain, recessional moraines, and glaciofluvial landforms) with only slight modification by modern processes (wave action and sea-ice activity). At Gjoa Haven the seafloor is imprinted by fields of pits 2 m wide and 0.15 m deep. They may result from gas hydrate dissolution triggered by falling relative sea levels. The Arctic Archipelago displays what might be termed inverted terrains: marine terrains, chiefly beach ridge complexes, exist above modern sea level and well-preserved glacial terrains are present below modern sea level. This is the inverse of the submerging regimes of Atlantic Canada, where glacial terrains exist on land, but below sea level they have been effaced and modified by marine processes down to the lowstand depth. Key words: Canadian Arctic Archipelago, LiDAR, multi-beam sonar, littoral zone. Les donnees de deux leves par sonar multifaisceaux et de deux leves par LiDAR marin/terrestre sont utilisees pour evaluer la geomorphologie du fond marin dans des zones littorales des chenaux du Grand Nord canadien pres de l'lle King William (Nunavut). Les terrains sous-marins montrent des formes de relief glaciaires (drumlins, lineations glaciaires megascopiques, terrain perturbe par des icebergs, moraines de retrait et formes de relief fluvioglaciaires) bien preservees que des processus recents (action des vagues et activite de la banquise) n'ont que tres legerement modifie. A Gjoa Haven, le fond marin est recouvert de champs de petites depressions de 2 m de largeur et 0,15 m de profondeur qui pourraient etre le resultat de la dissolution d'hydrates de gaz declenchee par la baisse des niveaux de la mer relatifs. Les iles de l'Arctique presentent ce qui pourrait etre decrit comme des << terrains inverses>>, soit des terrains marins, principalement des complexes de cretes de plage, presents au-dessus du niveau actuel de la mer et des terrains glaciaires bien preserves presents sous le niveau actuel de la mer. Il s'agit de la situation inverse des regimes d'immersion du Canada atlantique, ou des terrains glaciaires sont presents sur terre, alors que, sous le niveau de la mer, ils ont ete attenues et modifies par des processus marins jusqu'a la profondeur du bas niveau. [Traduit par la Redaction] Mots-cles: iles de l'Arctique canadien, LiDAR, sonar multifaisceaux, zone littorale., Introduction Since 2003 the Ocean Mapping Group, University of New Brunswick, has been collecting depth, backscatter, and sub-bottom data from the Canadian Arctic Archipelago using the CCGS Amundsen. These data [...]

The inner shelf off southwest Newfoundland, bordering the Laurentian Channel, was mapped with multi-beam sonar between depths of 200 and ~20 m, overlapping with coverage by marine/terrestrial LiDAR from maximum depths of 30 m to above sea level. The new data provide the first clear view of linkages between terrestrial and nearshore coastal systems and the inner shelf. Offshore sand reservoirs associated with adjacent sandy coastal barriers and spits are thin (~2 m), and isolated from one another, so that bedrock is the dominant seafloor terrain on the inner most shelf. The offshore sand reservoirs link with complex nearshore bar systems, from which it is inferred that sediment exchange with terrestrial systems can occur. Several isolated sand bodies are interpreted as residuals from former coastal systems destroyed during the Holocene transgression. The new data reveal the unexpected existence of a submarine canyon that facilitates transport of sediment from the inner shelf into the deep glacial trough of the Laurentian Channel. Key words: LiDAR, multi-beam sonar, nearshore bars, Newfoundland. La plateforme interne de la cote sud-ouest de Terre-Neuve, qui borde le chenal Laurentien, a ete cartographiee par sonar multifaisceaux entre les profondeurs de 200 et ~20 m, chevauchant la couverture par LiDAR marin/terrestre qui va d'une profondeur maximum de 30 m jusqu'au-dessus du niveau de la mer. Les nouvelles donnees fournissent le premier portrait clair des liens entre les systemes cotiers terrestres et littoraux et la plateforme interne. Des reservoirs de sable extracotiers associes a des barrieres et fleches de sable cotieres attenantes sont minces (~2 m) et isoles les uns des autres, de sorte que le substrat rocheux est le type de terrain dominant du fond marin dans la partie la plus interne de la plateforme. Les reservoirs de sable extracotiers sont relies a des systemes littoraux complexes de barres, ce qui permet d'inferer qu'un echange de sediments avec des systemes terrestres peut se produire. Plusieurs depots de sable isoles sont interpretes comme etant des restes d'autres systemes cotiers detruits durant la transgression holocene. Les nouvelles donnees revelent l'existence non anticipee d'un canyon sous-marin qui facilite le transport de sediments de la plateforme interne jusque dans la fosse glaciaire profonde du chenal Laurentien. [Traduit par la Redaction] Mots-cles: LiDAR, sonar multifaisceaux, barres littorales, Terre-Neuve., Introduction On the glaciated coasts of Newfoundland, Canada, coastal systems such as beaches, barrier beaches, forelands, and beach-ridge complexes are derived from remobilized glacial sediments (Shaw and Potter 2015). These [...]