Concave Valleys Research Articles

Machinability and mechanism of abrasive flow machining ultra-precision surface with orientated grinding marks

The loud noise in electric automobile caused by the overlap between orientated grinding marks with meshing line on ground gear tooth surface becomes a big problem for both drivers and manufacturers. Relying on the excellent self-deformation features and trace material removal, the abrasive flow machining (AFM) process exhibited potential machinability for above ultra-precision ground surface. Benefiting by the pseudo network structure, the abrasive media would possess both excellent elasticity and fluid capability, which could be quantitatively reflected by storage modulus, loss modulus and shear thinning nature in rheological properties. Meanwhile, deriving from the CFD simulation, the media exhibited the steady flow velocity and shear stress at the finishing channel, potentially contributing to the finishing uniformity on the target ground channel, which was subsequently confirmed by the change of ground surface morphology and profiles at the initial and finished state. Most convex peaks and concave valleys have been effectively subdued and whittled, leading to a rather smoother surfaces than initial ones. Besides, on account of the different collision position between grains with convex peaks, the finishing mechanism on ground surfaces with orientated marks could be elaborated as the transition effect from directly fractured material removal on convex peak cusp into plastic deformation on residual convex peaks. Combining with the interaction between continuous matrix and discrete grains in flow field, the mechanics on single grain was systematically investigated to establish the material removal theoretical model. Generally, the AFM technique exhibited the stunning machinability on ultra-precision ground surface.

In silico analysis shows that dynamic changes in curvature guide cell migration over long distances.

In vitro experiments have shown that cell scale curvatures influence cell migration; cells avoid convex hills and settle in concave valleys. However, it is not known whether dynamic changes in curvature can guide cell migration. This study extends a previous in-silico model to explore the effects over time of changing the substrate curvature on cell migration guidance. By simulating a dynamic surface curvature using traveling wave patterns, we investigate the influence of wave height and speed, and find that long-distance cell migration guidance can be achieved on specific wave patterns. We propose a mechanistic explanation of what we call dynamic curvotaxis and highlight those cellular features that may be involved. Our results open a new area of study for understanding cell mobility in dynamic environments, from single-cell in vitro experiments to multi-cellular in vivo mechanisms.

Shaping of topography by topographically-controlled vegetation in tropical montane rainforest.

Topography is commonly viewed as a passive backdrop on which vegetation grows. Yet, in certain circumstances, a bidirectional feedback may develop between the control of topography and the spatial distribution of vegetation and landform development, because vegetation modulates the erosion of the land surface. Therefore, if reinforcing feedbacks are established between erosion and land cover distribution over timescales relevant to landform development, then the interactions between vegetation and topography may create distinctive landforms, shaped by vegetation. We expose here a strong correlation between the spatial distribution of vegetation, erosion rates, and topography at a characteristic length scale of 102-103m (mesoscale topography) in the Luquillo Experimental forest (LEF) of Puerto Rico. We use high-resolution LiDAR topography to characterize landforms, satellite images to classify the vegetation into forest types, and in-situ produced cosmogenic 10Be in the quartz extracted from soils and stream sediments to document spatial variations in soil erosion. The data document a strong correlation between forest type and topographic position (hilltop vs. valleys), and a correlation between topographic position and 10Be-derived erosion rates over 103-104 years. Erosion is faster in valleys, which are mostly covered by monocot Palm Forest, and slower on surrounding hills mostly covered by the dicot Palo Colorado Forest. Transition from one forest type to the next occurs across a break-in-slope that separates shallowly convex hilltops from deeply concave valleys (coves). The break-in-slope is the consequence of a longer-lasting erosional imbalance whereby coves erode faster than hills over landscape-shaping timescales. Such a deepening of the coves is usually spurred by external drivers, but such drivers are here absent. This implies that cove erosion is driven by a process originating within the coves themselves. We propose that vegetation is the primary driver of this imbalance, soil erosion being faster under Palm forest than under Palo Colorado forest. Concentration of the Palm forest in the deepening coves is reinforced by the better adaptation of Palm trees to the erosive processes that take place in the coves, once these develop steep slopes. At the current rate of landscape development, we find that the imbalance started within the past 0.1-1.5 My. The initiation of the process could correspond to time of settlement of these mountain slopes by the Palm and Palo Colorado forests.

Meniscus-Induced Directional Self-Transport of Submerged Bubbles on a Slippery Oil-Infused Pillar Array with Height-Gradient.

Directional manipulation of submerged bubbles is fundamental for both theoretical research and industrial production. However, most current strategies are limited to the upward motion direction, complex surface topography, and additional apparatuses. Here, we report a meniscus-induced self-transport platform, namely, a slippery oil-infused pillar array with height-gradient (SOPAH) by combining femtosecond laser drilling and replica mold technology. Owing to the unbalanced capillary force and Laplace pressure difference, bubbles on SOPAH tend to spontaneously transport along the meniscus gradient toward a higher elevation. The self-transport performances of bubbles near the pillars depend on the complex meniscus shape. Significantly, to understand the underlying transport mechanism, the 3D meniscus profile is simulated by solving the Young-Laplace equation. It is found that the concave valleys formed between the adjacent pillars can change the gradient direction of the meniscus and lead to the varied transport performances. Finally, by taking advantage of a water electrolysis system, the assembled SOPAH serving as a bubble-collecting device is successfully deployed. This work should not only bring new insights into the meniscus-induced self-transport dynamics but also benefit potential applications in the field of intelligent bubble manipulation.

Forest canopy height variation in relation to topography and forest types in central Japan with LiDAR

Spatial variations of maximum canopy height are key indicators of many ecosystem processes such as above-ground biomass and productivity. With rapid advances in remote sensing techniques, such as airborne laser scanning (ALS), we can now measure canopy height, tree density, and canopy gaps from local to large scales. But these data are yet to be fully exploited for a better understanding of canopy height variations in relation to fine topographical heterogeneities and neighborhood conditions at the landscape level (>100 km2). In this study, we analyzed ALS data to extract spatial variations in canopy height and topographic features for a forest-dominated area of 230 km2 in Kyoto, Japan. The study area spanned an elevational range from 70 to 1000 m a.s.l and included four forest types, i.e., cedar or cypress plantations (PL), natural evergreen needle leaf forests (ENF), deciduous broadleaved forests (DBF), and evergreen broadleaved forests (EBF). PL had a greater mean canopy height than ENF, both of which were taller than DBF and EBF. Canopy height exhibited a hump-shaped relationship with elevation with the peak value at mid-altitude (461–560 m) in all forest types. Canopy height was greater by 5-10 m in the concave valleys than on the convex slopes and ridges. Trees were taller at greater distances from forest gaps and with lower tree density in the neighborhood. Local tree density, distance from the nearest canopy gap, and topographic curvatures were the most significant predictors in the best-fitted model (Random Forest: R2 = 0.41). The analytical approach developed in this study provides a useful tool for planning proper land use and maintaining a healthy forest stand at the regional scale.

Geomorphology, soils and palaeosols of the Chencha area (Gamo Gofa, south western Ethiopian Highlands)

The landscape of the Chencha Highland (south western Ethiopia) is characterized by flat plateau bordered by steep slopes affected by landslides and dissected by concave valleys and gullies. Coalescing alluvial fans are found along the eastern piedmont at the transition to the Lake Abaya shores. A major rift-plateau escarpment, with minor synthetic and antithetic faults, is located along the eastern slopes of the highlands. Soil erosion is a widespread process and the soil cover is usually thin and discontinuous. Immature Cambisols formed on colluvial deposits containing lithic tools, pottery fragments and charcoal represent the most recent phase of soil formation. They are related to the clearance of the original forest cover and the introduction of extensive agricultural and pastoral practices. On the slopes these soils locally unconformably overlie reddish, strongly weathered buried Nitisols and Luvisols that can be classified as Palaeoedlisols with formation of saprolite. Thicker and better preserved Palaeoeldisols can be found on the summit plateau, due to reduced runoff erosion. Different generations of clay illuviation indicate that they underwent polycyclic processes, recording soil processes probably older than Holocene. Along the slopes, gully erosion exhumed a palaeo-gully system infilled by colluviums of soils and buried soils containing Middle Stone Age artifacts suggesting that important slope degradational processes occurred also during the Late Pleistocene. Buried brownish soils in these infillings show moderate clay illuviation that indicates short-lived climatic amelioration and phases of slope stability.

One-step method for fabrication of bioinspired hierarchical superhydrophobic surface with robust stability

Functional surfaces provided by nature, especially some typical examples, such as lotus leaf, legs of water spiders, and shells of beetles, which inspire the study of biomimetic superhydrophobic surfaces. These natural surfaces exhibit fantastic wetting behavior with spatially, micro-nano hierarchical structures. Inspired by this, a one-step, facile electrodeposition process was developed for the fabrication of superhydrophobic surface on aluminum alloy. A Danxia-landform-like morphology surface is obtained by electrodeposition, with micro-nano-binary scale structure and low surface energy coating. The surface with convex microscale pillars and fractals in nanoscale, which are the key points of superhydrophobicity. Also, wettability is controlled by changing the anodization voltages, and roughness of the surface increased with a higher voltage. Due to the spatially, hierarchical morphology, the as-prepared surface possessed robust mechanically stability, for the nano coating layer located in ‘concave valleys’ is well protect. Experiments results verified that the prepared superhydrophobic surface have good performances of mechanical durability, as well as corrosion resistance. Thus, such a fabrication method would flourish approaches of water-repellence surface on aluminum alloy engineering materials.

Curvotaxis directs cell migration through cell-scale curvature landscapes

Cells have evolved multiple mechanisms to apprehend and adapt finely to their environment. Here we report a new cellular ability, which we term “curvotaxis” that enables the cells to respond to cell-scale curvature variations, a ubiquitous trait of cellular biotopes. We develop ultra-smooth sinusoidal surfaces presenting modulations of curvature in all directions, and monitor cell behavior on these topographic landscapes. We show that adherent cells avoid convex regions during their migration and position themselves in concave valleys. Live imaging combined with functional analysis shows that curvotaxis relies on a dynamic interplay between the nucleus and the cytoskeleton—the nucleus acting as a mechanical sensor that leads the migrating cell toward concave curvatures. Further analyses show that substratum curvature affects focal adhesions organization and dynamics, nuclear shape, and gene expression. Altogether, this work identifies curvotaxis as a new cellular guiding mechanism and promotes cell-scale curvature as an essential physical cue.

Hurricane Camille 1969 and Storm-Triggered Landslides in the Appalachians and a Perspective in a Warmer Climate

This study analyzes storm-triggered landslides in the US Appalachians, in the current geological setting. Concave valleys that favor the convergence of surface runoff are the primary locales for landslides. If the slopes are weathered to the same degree and have the same vegetation coverage, slope orientation (azimuthal) is not critical for slope stability. However, it is found that for the region south of the Black Mountains (North Carolina), north-facing slopes are more prone to slide, because, for the regions not limited by water availability (annual precipitation), the northern slopes usually are grass slopes. For the slopes of the Blue Ridge Mountains, south facing slopes are more prone to slide. Gravity measurements over the past decade reveal that geological conditions, the chute system and underground cracks over the region are stable. Future changes in storm-triggered landslide frequency are primarily controlled by changes in extreme precipitation. Thus, a series of ensemble climate model experiments is carried out to investigate possible changes in future extreme precipitation events, using a weather model forced by atmospheric perturbations from ensemble climate models. Over 50 locations are identified as prone to future landslides. Many of these locales are natural habitats to the Appalachian salamanders. In a future warmer climate, more severe extreme precipitation events are projected because of increased atmospheric water vapor and more frequent passages of tropical cyclone remnants. There is also a likely shift of tropical cyclone tracks and associated extreme precipitations, and the cluster center of Appalachians’s scarps is expected to move westward, with ecological consequences for the endemic salamanders.

Structure and mechanical properties of pincers of lobster (Procambarus clarkii) and crab (Eriocheir Sinensis)

The structure and mechanical properties of the pincer exoskeletons (cuticles) of lobster (Procambarus clarkii) and crab (Eriocheir Sinensis) were investigated, respectively. The microstructures and inorganic materials of the pincer exoskeletons were observed and determined using a scanning electron microscope and X-ray diffraction. The mechanical properties of the pincer exoskeletons were evaluated by nano-indentation tests and tensile tests under different conditions. The results showed that the inorganic materials in the lobster claw exoskeleton exhibited an amorphous structure, while those in the crab claw exoskeleton were crystallized as calcium carbonate with a calcite crystal structure and were stable at the temperature below 250 °C. The surfaces of the pincers were biologically unsmooth. Many concave valleys with setae near the tip and many convex domes far off the tip were observed on the surface of the lobster pincer, while many micro-spines were seen on the surface of crab pincer. The microstructures of the pincer exoskeleton exhibited highly mineralized chitin–protein fibers arranged in a twisted plywood structure. The surface hardness and elastic modulus of the crab claws were 0.33 GPa and 8.18 GPa, respectively, higher than those of the lobster claw (0.27 and 5.44 GPa). The transition in the mechanical properties and structure between the exocuticle and the endocuticle was discontinuity. The tensile strength of the crab pincer was two times higher than that of the lobster pincer, and the dry specimen was fractured more easily than the fresh specimen.

Supramolecular motif and macroscopic pattern in alpha-methylferrocenemethanol films cast from organic solution

The macroscopic patterns were formed in alpha-methylferrocenemethanol films cast from organic solutions. The macroscopic pattern was composed of concentric rings in the solid film. The concentric rings consist of convex ridges and concave valleys; the ordered phase constitutes the convex ridges, while the concave valleys barely contain anything. It has been found that, as for the solvent which can form hydrogen bonding with the solute and has suitable evaporation rate, macroscopic pattern could be observed in the solid film; while as for the solvent that cannot form hydrogen bonding with the solute, no macroscopic pattern would appear. It was suggested that, intermolecular hydrogen bonding and aromatic π stacking interactions of the solute is responsible for the formation of the microscopic crystalline structure; while the hydrogen bonding between the solute and the solvent, and the solvent-evaporation-induced crystallization process, as well as the solvent-evaporation-induced convections are responsible for the formation of the macroscopic pattern. The results could offer a facile way to the electronic material films with well-defined spatial alignment.

Photoinduced Formation of Microscopic Ordering and Macroscopic Pattern in Spiropyran-Containing Polyacrylate−Tetraoctylammonium Bromide Films

In this study, photoisomerizable polyacrylate containing spiropyran moieties was synthesized. By taking advantage of the photoinduced structural transformations of the spiropyran moieties, photoinduced microscopic ordering and eventually macroscopic patterns were formed in the polymer films consisting of spiropyran-containing polyacrylate (SPPA) and tetraoctylammonium bromide (TOAB). The patterns thus obtained are composed of concentric rings, which alternatively consist of macroscopic convex ridges and concave valleys, with the former being amphormous phases and the latter being ordered mesomorphous ones. It was found that the open-ring protonated merocyanine (MC) form of the spiropyran moieties, which is triggered by UV illumination, was crucial to the formation of mesomorphous structure and macroscopic patterns for this polymer−surfactant system. It is possible that the interaction between the MC form and TOAB leads to the formation of the microscopic ordering and macroscopic pattern in the polymer−TOA...

Mesomorphous Structure and Macroscopic Patterns Formed by Polymer and Surfactant from Organic Solutions

Ordered mesomorphous structures were obtained from the ternary system of organic solvent, polymer, and surfactant, and this microscopic ordering could lead to unique water-wave-like macroscopic patterns in solid polymer−surfactant film. The mesomorphous structures and macroscopic patterns were obtained by dissolving a nonpolyelectrolyte polymer and cationic surfactant in organic solvents and casting the solutions on glass substrates. The patterns thus obtained are composed of concentric rings, and these concentric rings, with their diameters up to centimeters, alternatively consist of macroscopic convex ridges and concave valleys, with the former being amphormous phase and the latter being ordered mesomorphous one. This macroscopic patterning in a solid polymer−surfactant system could offer a new way for fabricating ordered supramolecular structure in macroscopic dimensions.

Slope Deposits in the Northern Margin of Kitakami Massif, Northeast Japan

Several types of slope deposits were observed in undulating lands near the northern margin of Kitakami Massif. Stratigraphic relations of the deposits were investigated tephrochronologically. The radiocarbon ages of several tephra layers have already been known. The processes by which the slope deposits were formed were studied from their facies, their relations to landforms and lithology, and paleoenvironmental data including pollen analysis. As the result, the following four periods were discerned as 'periods of slope instability' when mass-movements on slope surfaces were more active than at the other periods.The period I: It is earlier than the late Pleistocene and might be warmer. Piedmont gentle slopes composed of removed materials of granodiorite were built at the foot of the mountains of the same rock.The period II: It is the cooler late Pleistocene when gentle slopes composed of screes were formed, smoothly continuing to or covering terrace surfaces.The period III: It is the latest Pleistocene and is subdivided into the subperiod III-1 about 30, 000 years B. P. and the subperiod III-2 about 15, 000 or 20, 000 years B. P.. Palynological data suggest colder climate of those days which is concordant to common knowledge. The same landforms as those of the period II were formed during the subperiod III-1, and derasional valleys were configurated through the subperiod III-1 and III-2. Those shallow concave valleys were terraced and flat-floored valleys were excavated in the Holocene. The morphological evidence suggests the intensification of fluvial action at about the time of the Pleistocene-Holocene boundary. Rocks were deeply weathered on the summits of the residual mountains and tali were formed at the foot of steep slopes during the period III.The period IV is in the Holocene and was the least unstable among the four periods of slope instability.