The deterministic preparation of highly ordered single‐crystalline surfaces is a key step for studying and utilizing the physical properties of various advanced materials. This paper presents the ...fast and straightforward preparation of vicinal Al2O3(0001) surfaces with micrometer‐scale atomic order. Crisp electron‐diffraction spots up to at least 20th order evidence atomic coherence on terraces with widths exceeding 1 μm. The unique combination of three properties of Al2O3(0001) underlie this remarkable coherence: its high‐temperature stability; the differences in the ionic bonding systems of the surface as compared to the bulk; and the fact that the terraces are non‐polar whereas the step edges have a polar character. The step edges are furthermore found to have alternating configurations, which drive a step‐doubling transition. On double‐stepped surfaces, the Al‐rich (31×31)R±9$(\sqrt {31}\times \sqrt {31})\textrm {R}\pm 9$° surface reconstruction attains a singular in‐plane orientation. These results set a benchmark for high‐quality surface preparation and thus expand the scope for both fundamental studies on and the technological utilization of exciting material systems.
An extremely well‐ordered surface is obtained by annealing sapphire (0001) substrates at ultrahigh temperatures. Electron diffraction reveals micrometer‐scale atomic order on these surfaces. This order opens new avenues for engineering thin‐film quality and harnessing the unique properties of advanced materials. A highly advantageous combination of material properties ‐ ionic bonding character, high‐temperature stability, and polar step edges ‐ underlies the observed order.
Using X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM) we resolve the temperature-, time-, and flake size-dependent intercalation phases of oxygen underneath graphene on ...Ir(111) formed upon exposure to molecular oxygen. Through the applied pressure of molecular oxygen the atomic oxygen created on the bare Ir terraces is driven underneath graphene flakes. The importance of substrate steps and of the unbinding of graphene flake edges from the substrate for the intercalation is identified. With the use of CO titration to selectively remove oxygen from the bare Ir terraces the energetics of intercalation is uncovered. Cluster decoration techniques are used as an efficient tool to visualize intercalation processes in real space.
We investigate the Quaternary geology and geomorphology present around ancient fortifications across Oman to explore the ways ancient builders optimised the use of landforms and geological materials ...to plan, construct and defend from enemy attack. The study involves a review of published data and aerial images to find fort locations followed by an extensive ground reconnaissance to inspect both the building and the geology of the immediate area. Each site is characterised according to its geomorphic setting, underlying geology and the identification of the construction material according to its environment. The study examined 171 fortified structures in four geomorphic zones to show different ways forts have been sited, to maintain optimum defensibility and availability of natural resources. Alluvial and khabra deposits provide the main materials for building fortified structures with supplementary masonry from beach rock and slope deposits. Cliff forming deposits such as alluvial terraces and travertine on the mountain flanks and sabkha along the coastline were used by ancient military planners to hinder invading forces. The research presents for the first time an overview of the Quaternary deposits of Oman and their use in the building of fortifications and ancient buildings, paving the way for a more detailed study. It is hoped this manuscript motivates other researchers to embrace linking geology with historical buildings and land techniques to improve knowledge and heritage not just in Oman but elsewhere.
Se presentan los primeros resultados de los proyectos de investigación dirigidos al análisis cronoestratigráfico de las terrazas del río Tajo en el entorno de Toledo. El estudio se ha centrado en ...niveles fluviales del Pleistoceno Medio y Superior con yacimientos paleontológicos y achelenses con valoración tecnológica general similar al conjunto lítico de Pinedo (colección Máximo Martín Aguado). En el presente trabajo se incluyen las dataciones por IRSL y AAR de los niveles de terraza de +25−30 m que contienen los yacimientos achelenses de Pinedo y Cien Fanegas. Las edades IRSL obtenidas ( > 280 ka y 292±17 ka) indican que la terraza y los yacimientos que contienen se formaron durante los estadios isotópicos MIS 9 y/o MIS 8, siendo correlacionables con la Unidad Arganda II en el valle del Jarama, aunque Pinedo podría representar parcialmente a la Unidad superior de Arganda I (MIS 11–MIS 9). La datación AAR obtenida para la Unidad superior de Pinedo indica una edad de 226±37 ka. Aunque esta edad ha de tomarse con precauciones debido a la escasa contextualización estratigráfica y los bajos niveles de dentina de las muestras analizadas, podría indicar que el depósito de la terraza estudiada continuó hasta bien entrado el MIS 7, como también parece suceder en el Jarama (Valdocarros). En el tramo del valle analizado los procesos de sobre-sedimentación ligados a los procesos de subsidencia de las evaporitas del Neógeno (aguas arriba) y la existencia del nivel de base local impuesto por el Meandro Encajado de Toledo (aguas abajo), favorecieron los procesos de agradación fluvial sobre los de encajamiento. El método de datación utilizado (post IR–IRSL) ha permitido obtener la edad más antigua hasta la fecha sobre sedimentos fluviales arenosos en la Cuenca del Tajo.
Intense erosion processes are widespread in the Mediterranean region, and include sheet wash erosion, rilling, gullying, shallow landsliding, and the development of large and active badlands in both ...subhumid and semi-arid areas. This review analyses the main environmental and human features related to soil erosion processes, and the main factors that explain the extreme variability of factors influencing soil erosion, particularly recent land use changes. The importance of erosion in the Mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation, the occurrence of intense rainstorms and long-lasting droughts, high evapotranspiration, the presence of steep slopes and the occurrence of recent tectonic activity, together with the recurrent use of fire, overgrazing and farming. These factors have resulted in a complex landscape in which intensification and abandonment, wealth and poverty can co-exist. The changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes, including farmland abandonment in mountain areas, the expansion of some subsidized crops to marginal lands, and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events. The occurrence of human-related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the Mediterranean basin. Here, we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the Mediterranean region: 1) to reduce the effects and extent of forest fires, and restructure the spatial organization of abandoned landscapes; 2) to provide guidance for making the EU agricultural policy more adapted to the complexity and fragility of Mediterranean environments; 3) to develop field methods and models to improve the identification of runoff and sediment contributing areas; 4) to contribute to the conservation of landscapes (i.e. bench-terraced fields) having high cultural and productivity values; 5) to improve knowledge of the hydrological and geomorphological functioning of badlands, with the aim of reducing sediment yield and accessibility; 6) to better understand the effect of climate change on soil erosion in the Mediterranean region; and 7) to improve quantitative information on long-term soil erosion.
•Recent land uses contribute to soil erosion in marginal lands.•Long history of human activity explains many landscape characteristics.•Intensification and extensification/wealth and poverty increase spatial complexity.
Effect of paddy terraces topography on landslide reduction NAKASHIMA, Atsushi; NAKANO, Shinji; Ganeindran, Rainoo Raj ...
Journal of the Japanese Society of Revegetation Technology,
2017, 2017-00-00, 20170101, Letnik:
43, Številka:
1
Journal Article
•Surface runoff and erosion were analysed using a portable rainfall simulator.•Surface runoff is land use-related.•Surface runoff and infiltration capacity are influenced by soil water ...repellency.•Only on abandoned terraces, surface runoff causes a strong increase in soil erosion.•Abandoned terraces are instable due to the increase in soil erosion susceptibility.
In mountain regions, soil landscapes are highly vulnerable against soil loss. Moreover, these environments are particularly affected by land use changes, which influence soil properties and related processes like surface runoff generation and soil erosion. These processes are in turn amplified by extreme climatic events and intensive geomorphological dynamics. The objective of this study is to quantitatively assess the effects of land use changes on surface runoff and soil erosion in a southern Alpine valley (Onsernone valley, Switzerland) characterized by a former intense land use followed by a progressive abandonment in the last decades. Surface runoff and related sediment transport has been analysed under controlled and reproducible conditions using a portable rainfall simulator device (1 m2). The results show a statistically significant increase in surface runoff when the soil gets water repellent reducing the surface infiltration capacity and generating preferential flow paths, which prevent a homogeneous wetting of the soil. However, the documented high sensitivity of surface runoff to land use changes does not result in an equally high sensitivity to soil erosion processes. Instead, soils display a high aggregate stability leading to very low sediment transports except for abandoned and reforested agricultural terraces. There, the lack of maintenance and progressive collapse of terrace dry walls locally increase slope angles and directly exposes the soil to atmospheric agents and surface runoff, which causes soil erosion rates beyond the customary natural level.
The Ploučnice River system, located in the central Bohemian Massif, is draining an area almost not covered by continental ice sheets but instead archiving the fluvial deposits. The fluvial style ...changes from a high-energy braided to a long-bend meandering river in the upper terrace levels (36 to 29 m above present floodplain). The middle terrace levels (22 to 14 m above present floodplain) indicate a fluvial style changing from a high- to medium-energy braided river. In the lower terrace levels (13 to 5 m above present floodplain), the terrace deposits indicate high-energy braided to long-bend meandering river environments. To provide greater details on the timing of fluvial terrace formation, this study applied 26Al and 10Be isochron burial and optically stimulated luminescence (OSL) dating methods to terraces of the Ploučnice River system. Terrace fluvial infills are dated with isochron burial dating in relative altitude 34, 29, and 14 m above present floodplain (apf); whereas terrace accumulations in relative altitude 19, 12, and 6 m apf are dated with OSL. Because of differences in age results between the two dating methods, we propose two different evolution models: the first is based on isochron burial and OSL dating, and the second model is on OSL dating results only. The time span represented by the river terraces remains unclear and varies from Eburonian to Weichselian (1680 to 56 ka) or from Saalian to Weichselian (138 to 56 ka) with the estimation of the highest terrace (248 ka) respectively. The former river evolution model is based on tectonic activity at least since 1000 ka. Morphotectonic analysis recognized new lineaments of which the general direction corresponds with the main direction of the Ohře fault zone (NE- to ENE-striking) and Lužice fault zone (NW-striking). Based on dated terrace ages of 1153 ± 123 ka at 14 m apf and 138 ± 21 ka at 19 m above present floodplain, we propose a normal fault being active from at least 1153 ka. The second river evolution model assumes possible remobilization of clasts analyzed by isochron burial dating before their final deposition. From three OSL ages we calculated a mean incision rate and estimated an age of upper terrace levels at 34 m apf to be 248 ± 38 ka (Saalian age). As remobilization of clasts in high-energy fluvial and glaciofluvial environments is very likely, age determination is challenging. Nevertheless, we interpret the terrace record in the Ploučnice River system as a product of Quaternary climatic changes influenced by tectonic processes.
•Dating by isochron burial and OSL dating methods shows discrepancy.•Due to differences in age results, we establish two different evolution models.•Remobilization of gravel in high-energy fluvial environments is very likely.•The Ploučnice fluvial system belongs to glacially-fed river with periodical changes of the sediment supply.
Steady progress in integrated circuit design has forced basic metrology to adopt silicon lattice parameter as a secondary realization of the SI meter that lacks convenient physical gauges for precise ...surface measurements at a nanoscale. To employ this fundamental shift in nanoscience and nanotechnology, we propose a set of self-organized silicon surface morphologies as a gauge for height measurements within the whole nanoscale (0.3–100 nm) range. Using 2 nm sharp atomic force microscopy (AFM) probes, we have measured the roughness of wide (up to 230 μm in diameter) singular terraces and the height of monatomic steps on the step-bunched and amphitheater-like Si(111) surfaces. For both types of self-organized surface morphology, the root-mean-square terrace roughness exceeds 70 pm but has a little effect on step height measurements having 10 pm accuracy for AFM technique in air. We implement a step-free 230-μm-wide singular terrace as a reference mirror in an optical interferometer to reduce the systematic error of height measurements from >5 nm to about 0.12 nm, which allows visualizing 136-pm-high monatomic steps on the Si(001) surface. Then, using a “pit-patterned” extremely wide terrace with dense but counted monatomic steps in a pit wall, we have optically measured mean Si(111) interplanar spacing (313.8 ± 0.4 pm) that agrees well with the most precise metrological data (313.56 pm). This opens up avenues for the creation of silicon-based height gauges using bottom-up approaches and advances optical interferometry among techniques for metrology-grade nanoscale height measurements.
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