Edge Of Sheet Research Articles

Transition to marine ice cliff instability controlled by ice thickness gradients and velocity.

Portions of ice sheets grounded deep beneath sea level can disintegrate if tall ice cliffs at the ice-ocean boundary start to collapse under their own weight. This process, called marine ice cliff instability, could lead to catastrophic retreat of sections of West Antarctica on decadal-to-century time scales. Here we use a model that resolves flow and failure of ice to show that dynamic thinning can slow or stabilize cliff retreat, but when ice thickness increases rapidly upstream from the ice cliff, there is a transition to catastrophic collapse. However, even if vulnerable locations like Thwaites Glacier start to collapse, small resistive forces from sea-ice and calved debris can slow down or arrest retreat, reducing the potential for sustained ice sheet collapse.

Modeling of heat propagation processes during thermal metal cutting, taking into account the main provisions of the theory of welding deformations and stresses

The article describes the features of applying the main provisions of the theory of welding deformations and stresses to the thermal cutting of metal. The above calculation formulas allow us to pre-evaluate the temperature deformations of the sheet edges during separation heat cutting, as well as the size and configuration of the temperature field, to take into account the thermal effect on the metal and determine the size of the zone of thermal influence. These equations are considered by the authors as a basis for the development of a method for calculating thermal deformations and stresses during thermal cutting of metal, taking into account the transverse and longitudinal distribution of temperature over the sheet section, the ambient temperature and interaction with it, the parameters of the geometry of the cut sheet and its stiffness, heat capacity, thermal conductivity and other temperature characteristics.

New insight of tailor-made graphene oxide for the formation of atomic Co-N sites toward hydrogen evolution reaction

The designed synthesis of graphene oxide (GO) for the formation of nitrogen-coordinated atomic metal sites (M−N−C) is crucial for developing efficient M−N−C catalysts. Here, the effect of basal plane oxygen functional groups of GO on the adsorption of cobalt ions and their Co-N transition is investigated by tailoring the oxygen content and composition of oxygen functional groups on the basal plane of GO sheets. The tailor-made GO shows that the specific oxygen functional groups, such as hydroxyl, epoxy, and carbonyl groups, can be efficiently incorporated with formation of defected structures on the basal plane of GO sheets rather than their edge. The adsorption of cobalt ions on the GO sheets and their transition to the Co-N state are systematically investigated by XPS and XAFS analyses. Annealing temperature-controlled experiments reveal that the incorporation of nitrogen around cobalt atoms is facilitated by the increased number of oxygen functional groups on the basal plane rather than those on the edge of GO sheets, which provide energetically favorable environments for Co-N formation. The hydrogen evolution reaction (HER) activities of the resulting cobalt atom-immobilized and annealed GO (Co/GOx-T) catalysts correlate to the degree of Co-N saturation, while also demonstrating excellent HER catalytic durability.

Quenching of graphene suspension photoluminescence with saturated hydrocarbons

This paper describes a study of quenching of graphene suspension (GS) photoluminescence upon formation of an interphase interface by a saturated hydrocarbon using n-octane (С8Н18) as an example. Based on the analysed photoluminescence spectra, structural analysis, and theoretical evaluations, the paper offers a model where octane molecules are attached at the edges of composite graphene sheets by the presence of functional oxygen-containing groups. It is assumed that in the formed structure quenching of photoluminescence relates to the Anderson electron density delocalisation effect.

Oxygen Reduction Reaction on N-Doped Graphene: Effect of Positions and Scaling Relations of Adsorption Energies.

The goal of this study is to provide insight into the mechanism of the oxygen reduction reaction (ORR) on N-doped graphene surfaces. Using density functional theory and a computational hydrogen electrode model, we studied the energetics of the ORR intermediates, the effect of the position of the reaction site, and the effect of the position of the N modification relative to the active site on model graphene surfaces containing one or two N atoms. We found that scaling relations can be derived for N-doped graphenes as well, but the multiplicity of the surface should be taken into account. On the basis of the scaling relations between intermediates OOH* and OH*, the minimal overpotential is 0.33 V. Analysis of the data showed that N atoms in the meta position usually decrease the adsorption energy, but those in the ortho position aid the adsorption. The outer position on the zigzag edge of the graphene sheet also promotes the adsorption of oxygenated species, while the inner position hinders it. Looking at the most effective active sites, our analysis shows that the minimal overpotential can be approached with various doping arrangements, which also explains the contradicting results in the literature. The dissociative pathway was also investigated, but we found only one possible active site; therefore, this pathway is not really viable. However, routes not preferred thermodynamically pose the possibility of breaking the theoretical limit of the overpotential of the associative pathway.

Prediction of edge fracture during hole-flanging of advanced high-strength steel considering blanking pre-damage

The stretch-flangeability of advanced high-strength steel (AHSS) sheets after blanking highly depends on the stress states as well as the edge pre-damage inherited from the initial blanking process. It cannot be predicted by using conventional forming limit diagram methods. To solve this issue, in this study, a numerical simulation model of the two-step hole cutting-hole expansion tests for the TRIP800 sheet was established by considering the initial surface irregularities induced by hole fabrication into the hole expansion process. Two methods, punching and wire-cut electrical discharge machining with low speed were adopted to cut holes. The modified Mohr–Coulomb fracture model together with post-failure softening was utilized to predict the fracture initiation and crack propagation during two forming processes. The results manifested that the WEDM-LS cutting method brought negligible damage to the hole edge and the sheet edge fabricated by this method can be assumed without pre-damage. Multiple finer notches were detected at the surface of the punched hole. These features triggered stress states with higher stress triaxiality up to 0.6 and thus accelerated the edge fracture occurrence during the hole expansion deformation. The measured hole expansion ratio of the punched hole was 26.1%, which was correctly predicted by the proposed model by considering edge pre-damage. As a comparison, the ideal model without pre-damage overestimated the value by about 100%.

Hydrogen Evolution on Reduced Graphene Oxide-Supported PdAu Nanoparticles

Hydrogen evolution reaction (HER) was investigated on reduced graphene oxide (rGO)-supported Au and PdAu nanoparticles in acid solution. The graphene spread over glassy carbon (rGO/GC) was used as a support for the spontaneous deposition of Au and Pd. The resulting Au/rGO and PdAu/rGO electrodes were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Phase AFM images have shown that the edges of the rGO sheets were active sites for the deposition of both Au and Pd. XPS analysis revealed that the atomic percentages of both Au and PdAu nanoparticles were slightly higher than 1%. The activity of the PdAu/rGO electrode for the HER was remarkably high, with the overpotential close to zero. HER activity was stable over a 3 h testing time, with a low Tafel slope of approx. −46 mV/dec achieved after prolonged hydrogen evolution at a constant potential.

N-methylene phosphonic acid chitosan/graphene sheets decorated with silver nanoparticles as green antimicrobial agents

A green and scalable approach for the preparation of few-layered graphene utilizing the biowaste of potato peels has been developed. The potato peels have been dried and carbonized to obtain a new graphite structure that has been exfoliated in N-methylene phosphonic acid chitosan (MPC). The exfoliation process assisted the formation of graphene sheets with a high size diameter and quality of 50% based on the weight of graphite structure. The graphene sheets were green decorated with silver nanoparticles using microwave power to obtain new nanocomposites. The mass ratio between the graphite and silver nitrate was optimized and observed to change the morphology and size diameter of silver nanoparticles. The as-prepared MPC structure, graphene, and silver decorated graphene nanocomposites were characterized using 1HNMR, FTIR, XRD, UV/Vis spectrophotometer, SEM, and TEM besides tested as antimicrobial agents. The bacterial performance was also controlled by changing the number of AgNPs distributed on graphene sheets based on the mass ratios of graphite/AgNO3. The inhibition diameter of silver decorated graphene was considerably increased to 24.8, and 20.1 mm as in the case of MPC-GRP-Ag30 composite compared to the pure graphene (11.2, 13.5 mm) for E. coli and S. aureus, consecutively proposing that the blade edge of graphene sheets can destroy the bacteria membrane and release silver cations promptly that are directed for the interaction with the cytoplasmic parts of the bacteria cell. Such findings offer green and biocompatible antibacterial agents based on the graphene derived from the biowaste products.

Simulation Research on Roll Forming in Container Roof

The finite element simulation of the roll forming process of the container roof is carried out, and the stress, strain, and history curves of key nodes are analyzed. It is proved that the rolling process will produce edge wave and wrinkle defects in the flat section, and the influence of parameters on the edge wave wrinkle is studied. Studies have shown that: the length of the transition section increases, the number of wrinkle decreases; the distance between the arches increases, which suppresses the generation of side wave defects, but after more than 350mm, the effect on the side wave remains unchanged; the width of the sheet edge increases, and the side wave defects follow the increase.

Detecting slender objects with uncertainty based on keypoint-displacement representation

Slender objects are long and thin objects. Existing object detection networks are not specially designed for detecting slender objects. We propose a method to detect slender objects. We represent slender objects with a keypoint-displacement pattern instead of using axis-aligned bounding boxes, avoiding problems like orientation confusion and wrong elimination. In our network, three parallel branches predict keypoint heatmaps, displacement vector field, and displacement uncertainty heatmap respectively. We add the uncertainty branch to enable our network to give uncertainty together with detection results. The predicted uncertainty provides a continuous criterion to evaluate whether detection results are reliable. In addition, the uncertainty branch can lower the weight of ambiguous training samples, leading to more accurate detection results. We employ our proposed method in two typical practical applications. Edges of electrode sheets and pins of electronic chips are correctly detected as slender objects. Manufacturing quality is evaluated through analyzing the detection results, including keypoint number, displacement property, and uncertainty value.

A Method for Simultaneous Optimization of Blank Shape and Forming Tool Geometry in Sheet Metal Forming Simulations

This paper presents a numerical method for simultaneous optimization of blank shape and forming tool geometry in three-dimensional sheet metal forming operations. The proposed iterative procedure enables the manufacturing of sheet metal products with geometry fitting within specific tolerances (surface and edge deviations less than 0.5 or 1.0 mm, respectively) that prescribe the maximum allowable deviation between the simulated and desired geometry. Moreover, the edge geometry of the product is affected by the shape of the blank and by an additional trimming phase after the forming process. The influences of sheet metal thinning, edge geometry, and springback after forming and trimming are considered throughout the blank and tool optimization process. It is demonstrated that the procedure effectively optimizes the tool and blank shape within seven iterations without unexpected convergence oscillations. Finally, the procedure thus developed is experimentally validated on an automobile product with elaborated design and geometry which prone to large springback amounts owning to complex-phase advanced high strength steel material selection.

Catalysts with single metal atoms for the hydrogen production from formic acid

ABSTRACT Formic acid is a liquid organic hydrogen carrier. Metal and metal-complex catalysts are known to catalyze the hydrogen production from formic acid and hydrogen transfer reactions with formic acid as a hydrogen donor. In this review, we will show that heterogeneous catalysts with single metal atoms are promising for these reactions. The main emphasis is done to the catalysts with single atoms stabilized by pyridinic nitrogen atoms on the edge or vacancy sites of graphene sheets. The activity of the catalysts containing these sites often exceeds that of the catalysts with nanoparticles. We consider application of different physical methods and density functional theory calculations to establish the nature of single-atom active sites and reaction mechanism. Coordination of these sites significantly affects their performance in the mentioned reactions. This review could be useful for development of novel efficient catalysts.

Role of cations on the dissolution mechanism of kaolinite in high alkaline media

Kaolinite and its dehydroxylated forms are widely used in industry, including the growing field of geopolymers. Until now, a deep understanding of the dissolution mechanism of kaolinite particles in alkaline media is still lacking. This work aims to investigate the dissolution mechanisms through aluminum and silicon leaching of two references kaolinites (KGa-1b and KGa-2) regarding various 2 M alkali treatment (KOH, NaOH and 50/50 NaOH + KOH) as a function of time and at 80 °C. For this, a wide range of methods have been used, from the determination of [Si] and [Al] in solution to the analysis of solids by combining X-ray diffraction (XRD), Fourier Transformed Infrared (FTIR), X-ray Absorption Near Edge Structure (XANES) and Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopies and Transmission Electronic Microscopy (TEM) observations. The results evidence a higher dissolution rate with poorly crystallized kaolinites, confirming the role of the crystallinity of the samples toward reactivity in an alkaline media. In addition, the nature of the cation significantly affect the degree of dissolution following the sequence KOH < NaOH + KOH < NaOH. This process is combined with a change in Al speciation from 6-coordinated to 4-coordinated sites, as evidenced by XAS and MAS-NMR experiments. Altogether, these results allow to propose different dissolution mechanisms at the particle scale depending on the cations. The dissolution in presence of KOH proceeds uniformly from the edges, starting from the edges of the octahedral sheet, whereas in the case of NaOH, the edges dissolution is oriented with respect to areas of less coherence starting from the tetrahedral sheet.

SIGNIFICANCE FOR INTERNATIONAL CORRELATION OF THE PERAPERTÚ FORMATION IN NORTHERN PALENCIA, CANTABRIAN MOUNTAINS. TECTONIC/STRATIGRAPHIC CONTEXT AND DESCRIPTION OF MISSISSIPPIAN AND UPPER BASHKIRIAN GONIATITES

Small ammonoid assemblages are recorded from the Perapertú Formation in northern Palencia. This is a mudstone unit with local platform limestones characterised by carbonate debris flows on the limestone margins. This unit, of Late Bashkirian to Early Moscovian age, participates in a series of southwards verging thrust slicesNorth of a major fault zone which originated as the head (leading edge) of a large thrust sheet with an internal deformation consisting of thrust slices and at least one nappe structure. Opposed vergencies at the head of this major thrust sheet (Carrionas Thrust Front) and the Ruesga Fault which locally modifies its trace, mark the position where the northern branch of the Cantabric-Asturian arcuate fold belt has overridden the southern branch in early Westphalian (Langsettian) times. The chronostratigraphic significance of the Perapertú Formation is discussed in the context of marine-terrestrial correlations for the Late Bashkirian-Early Moscovian time interval. It is concluded that the evidence from NW Spain suggests a position of the base of the Moscovian at the level of basal Westphalian or even within the highest Namurian. A brief analysis of the literature shows this position to be different to some of the correlations admitted in recent publications.A newly discovered goniatite fauna from the lower part of the Perapertú Formation contains Brannerocera ssp. indicating Late Bashkirian to earliest Moscovian, and Deleshumardites cantabricus Kullmann gen. et sp. nov. This fauna is figured and described in conjunction with the new subfamily Dombaritinae Kullmann (family Delepinoceratidae).

The Origin of Terraces in Buried Valleys in the Northwest of the East European Plain

Abstract —The paper considers the origin of terraces that often complicate the slopes of abnormally deep buried valleys in the northwest of the East European Plain. The Izborsk–Maly valley (Pskov Region, Russia), which is half filled with Quaternary sediments, was chosen as the object of study. Since the upper part of the valley remains unfilled, it is possible to study in detail both geologic and geomorphologic structures of its terraced slopes being of particular interest in the context of the origin of buried valleys and the role of substrate in it. The four denudation-terrace levels that have been identified on the slopes of the Izborsk–Maly valley at absolute elevations of 53, 56–58, 70–72, and 75–77 m formed during the destruction of the preglacial karst landscape under the influence of Pleistocene glaciations. The formation of the terraces was probably linked with several stages of overdeepening of the valley and its expansion by the glacial erosion processes, which corresponded to at least two stages of the ice sheet advance in this area. The last stage may have been the beginning of the Late Valdai (Weichselian) glaciation or the activation of the edge of an ice sheet during its Luga phase (~15.7 cal kyr BP). Results of the study suggest that the Izborsk–Maly valley formed in subglacial conditions. The degree of glacial erosion was determined primarily by the coherence of Devonian carbonate-terrigenous rocks hosting the valley and the degree of the area transformation by karst processes. The cirque shape of slopes is the evidence of karst processes expression in pre-glacial time. Analysis of literature data shows that the origin of denudation terraces in the buried valleys in the northwest of the East European Plain has been paid little attention. The obtained data contribute to the study of this problem and provide insights into the origin of buried valleys.

Carbon Based Polymeric Nanocomposites for Dye Adsorption: Synthesis, Characterization, and Application.

Agglomeration and restacking can reduce graphene oxide (GO) activity in a wide range of applications. Herein, GO was synthesized by a modified Hummer’s method. To minimize restacking and agglomeration, in situ chemical oxidation polymerization was carried out to embed polyaniline (PANI) chains at the edges of GO sheets, to obtain GO-PANI nanocomposite. The GO-PANI was tested for the adsorptive removal of brilliant green (BG) from an aqueous solution through batch mode studies. Infrared (FT-IR) analysis revealed the dominance of hydroxyl and carboxylic functionalities over the GO-PANI surface. Solution pH-dependent BG uptake was observed, with maximum adsorption at pH 7, and attaining equilibrium in 30 min. The adsorption of BG onto GO-PANI was fit to the Langmuir isotherm, and pseudo-second-order kinetic models, with a maximum monolayer adsorption capacity (qm) of 142.8 mg/g. An endothermic adsorption process was observed. Mechanistically, π-π stacking interaction and electrostatic interaction played a critical role during BG adsorption on GO-PANI.

Breakup of thin liquid sheets through hole–hole and hole–rim merging

Abstract

Mechanical clinching and self-pierce riveting for sheet combination of 780-MPa high-strength steel and aluminium alloy A5052 sheets and durability on salt spray test of joints

To increase the usage of high-strength steel and aluminium alloy sheets for lightweight automobile body panels, the joinability of sheet combinations including a 780-MPa high-strength steel and an aluminium alloy A5052 sheets by mechanical clinching and self-pierce riveting was investigated for different tool shapes in an experiment. All the sheet combinations except for the two steel sheets by self-pierce riveting, i.e., the two steel sheets, the two aluminium alloy sheets, and the steel-aluminium alloy sheets, were successfully joined by both the joining methods without the gaps among the rivet and the sheets. Then, to show the durability of the joined sheets, the corrosion behaviour and the joint strength of the aged sheets by a salt spray test were measured. The corrosion and the load reduction of the clinched and the riveted two aluminium alloy sheets were little. The corrosion of the clinched two steel sheets without the galvanized layer progressed, and then the load after 1176 h decreased by 85%. In the clinched two galvanized steel sheets, the corrosion progress slowed down by 24%. In the clinched steel and aluminium alloy sheets, the thickness reduction occurred near the minimum thickness of the upper sheet and in the upper surface on the edge of the lower aluminium alloy sheet, whereas the top surface of the upper sheet and the upper surface of the lower sheet were mainly corroded in the riveted joint. The load reduction was caused by the two thickness reductions, i.e., the reduction in the minimum thickness of the upper sheet and the reduction in the flange of the aluminium alloy sheet. Although the load of the clinched steel without the galvanized coating layer and aluminium alloy sheets decreased by about 20%, the use of the galvanized steel sheet brought the decrease by about 11%. It was found that the use of the galvanized steel sheets is effective for the decrease of strength reduction due to corrosion.

Auroral Arcs: The Fracture Theory Revisited

AbstractThe fracture theory for auroral arcs, developed by the author since 1980, compares the decoupling of the magnetic field from the ionosphere by the auroral acceleration region (AAR) with the breaking of a solid rod. In the latter elastic energy stored by the bending is converted into kinetic energy of the stress release motion. Similarly, magnetic energy stored in sheared magnetic fields is temporarily converted into stress release motions and finally transported as Poynting flux into the AAR. The fracture theory has been especially applied to arcs embedded in the convection of the evening auroral oval. The present study subjects the different steps in the fracture process to a critical analysis in the light of new physical insights. This boils down to a revision of the illustrating cartoon used in the earlier publications, without having affecting the quantitative evaluations. The first revision concerns the height extent of the AAR. It must be largely increased. The second revision introduces a nearly 2‐D magnetohydrodynamics (MHD) turbulence into the state of the AAR. This is supported by high‐altitude electric field data and leads to new view of auroral rays. The third revision describes the transition from the AAR to the ionosphere as structured by so‐called potential fingers, which contain substantial fractions of the total field‐parallel potential drop. The most important modification pertains to the average U‐shaped potential of a spontaneously propagating AAR. While the leading edge of the auroral current sheet is structured by stress release motions, the reverse flow in the rear section escapes simple interpretation. It is proposed that this flow is driven by a turbulent transport of reversed momentum from front to rear in response to the incompressibility of the magnetic field in the acceleration region. This leads to a revision of the field‐aligned currents and wavefield in the rear of the arc.

Basement-involved thrusting, salt migration and intramontane conglomerates: a case from the Southern Pyrenees

The northern margin of the Organyà basin (Southern Pyrenees) has a complex structure in which syn-rift Lower Cretaceous carbonates flank a wide Keuper evaporite province, featuring the leading edges of the basement-involved thrust sheets of the Pyrenean antiformal stack. Recent studies show that Keuper diapirs and salt walls grew during the Cretaceous extensional episode, conditioning the development of differentiated depocenters and minibasins. The role of salt tectonics during the Pyrenean orogeny has not been addressed in previous structural studies, but present-day cross-sections indicate a Keuper evaporite-bearing vertical thickness of up to 3000 m in the Senterada-Gerri de la Sal area. We infer that salt migration was a determinant mechanism in triggering a gentle northward tilting of the Organyà basin during the Eocene-Oligocene, recorded in the La Pobla de Segur and Gurp syn-tectonic conglomerates in a large north-directed onlap, opposite to the main sedimentary influx direction. Contemporaneously, we interpret that salt migration, promoted by conglomerate differential loading, enabled the sinking and rotation of the unrooted Nogueres thrust units (têtes plongeantes). We use new and published structural data for the Lower Cretaceous margin of the Organyà basin, combined with structural and clast provenance data from the Cenozoic alluvial fan conglomerates of La Pobla and Gurp, to understand the Lutetian to late Oligocene evolution of the northern margin of the Central South-Pyrenean Unit. The tectono-sedimentary evolution of this area and the salt evacuation patterns are closely related to the exhumation history of the stacked Paleozoic thrust sheets of the Pyrenean hinterland to the north. In this study, we correlate the movements over a mobile substratum and the paleogeographic changes of conglomeratic basins at the toe of an exhuming orogenic interior.