Strong Deformation Research Articles

Double-sided subduction with contrasting polarities beneath the Pamir-Hindu Kush: Evidence from focal mechanism solutions and stress field inversion

The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collision linked to two intra-continental subduction zones with different polarities. The seismicity and seismic tomography data show a steep northward subducting slab beneath the Hindu Kush and southward subducting slab under the Pamir. Here, we collect seismic catalogue with 3988 earthquake events to compute seismicity images and waveform data from 926 earthquake events to invert focal mechanism solutions and stress field with a view to characterize the subducting slabs under the Pamir-Hindu Kush region. Our results define two distinct seismic zones: a steep one beneath the Hindu Kush and a broad one beneath the Pamir. Deep and intermediate-depth earthquakes are mainly distributed in the Hindu Kush region which is controlled by thrust faulting, whereas the Pamir is dominated by strike-slip stress regime with shallow and intermediate-depth earthquakes. The area where the maximum principal stress axis is vertical in the southern Pamir corresponds to the location of a high-conductivity low-velocity region that contributes to the seismogenic processes in this region. We interpret the two distinct seismic zones to represent a double-sided subduction system where the Hindu Kush zone represents the northward subduction of the Indian plate, and the Pamir zone shows southward subduction of the Eurasian plate. A transition fault is inferred in the region between the Hindu Kush and the Pamir which regulates the opposing directions of motion of the Indian and Eurasian plates.

Weakly nonlinear shape oscillations of a Newtonian drop

Nonlinear axisymmetric shape oscillations of a Newtonian drop in a vacuum are investigated theoretically, for fundamental interest and for their relevance in transport processes across the drop surface. The weakly nonlinear analysis is carried out for, but not limited to, the modes of initial drop deformation up to m = 4. The drop Ohnesorge number covers the range between 0.01 and 1. The weakly nonlinear approach, which is carried to third order, accounts for the coupling of different oscillation modes. With increasing surface deformation, the oscillations develop an asymmetry of the times during one period the drop spends in different states of deformation, a frequency decrease below the linear value, and quasi-periodicity of the motion. In contrast to the inviscid case [D. Zrnić and G. Brenn, “Weakly nonlinear shape oscillations of inviscid drops,” J. Fluid Mech. 923, A9 (2021)], the present analysis reveals the frequency decrease and the quasi-periodicity already in the second-order approximation. The results are positively validated against relevant literature. The theory quantifies the effects of viscosity, measured by the drop Ohnesorge number, dampening the nonlinear behavior and enhancing the coupling of different oscillation modes [E. Becker et al., “Nonlinear dynamics of viscous droplets,” J. Fluid Mech. 258, 191 (1994)]. The present theory reveals the quasi-periodicity of nonlinear viscous drop shape oscillations at strong deformation. The resultant drop motion, starting from a higher-order mode of initial deformation, for which the drop exhibits aperiodic linear behavior, may turn into damped oscillatory with ongoing time due to the coupling to lower-order modes.

Газопылевые структуры в окрестности рукавов спиральных галактик

A two-dimensional model of the flow of the gas-dust interstellar medium in the vicinity of the spiral arm of the galaxy is constructed. The flow in a vertical plane transverse to the disk plane is considered. The effects of nonadiabatic flow (volumetric heating and cooling of the gas by radiation) are taken into account. The balance of heating and cooling ensures the coexistence of two phases, cold parsec-sized clouds of atomic hydrogen and warm intercloud gas. The consideration includes polydisperse dust, represented by three fractions of particles of different sizes and masses. Dust particles have finite inertia, their movements do not exactly repeat the movement of gas. Turbulence in the disk and in the spiral arm is also taken into account. Models are considered that use different combinations of the location of turbulence sources in the disk and/or in the arm. The main results obtained by the methods of computer hydrodynamic modeling are as follows. Clouds undergo significant transformations as they pass through the spiral arm. A significant part of the clouds is absorbed into a thin dense cloud layer, which extends in a spiral arm along the equatorial plane in the vicinity of the center of the arm and has a size of approximately half the width of the arm. A smaller part of the clouds passes without destruction or with partial destruction through the sleeve, experiencing strong deformations along the way. The small-scale cloud component is partially restored under the action of turbulence, which perturbs the extended cloud layer inside the arm and partially destroys it into separate fragments. A wedge-shaped galactic shock wave is formed on the rear side of the arm with respect to the incoming gas flow, attached to the rear edge of the extended cloud layer. A flow limited by a shock wave has the character of a jet that performs quasi-periodic transverse oscillations. The reason for the oscillations, apparently, is the instability of the shear flow, since tangential discontinuities are formed inside the jet along the flow and at a small angle to the shock fronts. Dust particles are dragged by turbulent eddies and carried to heights of 150–200 pc above the disk plane, which naturally explains the existence of chaotic filamentous dust structures extending above the galactic disk to heights of several hundred parsecs. The grains of dust are distributed differently inside the vortices. Dust grains with sizes of 0.01-0.1 μm cluster more easily than larger dust grains with a radius of 1 μm. Turbulence serves as a mechanism to effectively trap dust particles on the front side of the spiral arm. Modeling shows that dust lanes are more pronounced on the front side of the arm.

Bionic Soft Multimodal Actuators for Fast, Large Deformation under Ultralow Magnetic Conditions

AbstractVery recently, magnetically driven soft actuators have prompted increasing interest due to their programmable deformation, swift response, and remote actuation. However, it is still challenging to trigger strong and fast actuating performances with an extremely weak magnetic field due to the difficult task of in situ programming of magnetic domains and the limited mechanical structures. Here, first a bionic sandwich structure is proposed for designing soft magnetic actuators with a specific threshold value. The crab‐like jointed structure of PDMS‐embedded NdFeB upper/lower layers is essential for generating the desirable threshold effect, while a flytrap‐inspired soft interlayer is further implemented to decrease the driving magnetic field. Theoretical analysis and numerical simulations are implemented to optimize the actuating performances of soft actuators (deformation rate, deformation angle) by modulating the structural parameters. Experimental results show that the biomimetic features yield a promptly switchable bistable state, a superior strong deformation rate of 1.93, and a maximum deformation angle of 25.5° under an ultralow magnetic field of 1 mT. Two demonstrative applications of soft actuators are investigated, including threshold switching and soft grippers, suggesting their broad applications in engineering fields. Remarkably, the magnetic soft grippers associated with the gecko‐inspired adhesion surface exhibit an improved and stable grasping ability. This work focuses on designing highly deformable actuators and functions in emerging areas of soft robotics.

A Theoretical Study on the Structural, Electronic, and Magnetic Properties of Bimetallic Pt13-nNin (N = 0, 3, 6, 9, 13) Nanoclusters to Unveil the Catalytic Mechanisms for the Water-Gas Shift Reaction.

In this work, first-principles calculations by using density functional theory at the GFN-xTB level, are performed to investigate the relative stability and structural, electronic, and magnetic properties of bimetallic Pt13−nNin (n = 0, 3, 6, 9, 13) nanoclusters by using corrected Hammer and Nørskov model. In addition, by employing the reaction path and the energetic span models, the energy profile and the turnover frequency are calculated to disclose the corresponding reaction mechanism of the water-gas shift reaction catalyzed by these nanoclusters. Our findings render that Ni causes an overall shrinking of the nanocluster’s size and misalignment of the spin channels, increasing the magnetic nature of the nanoclusters. Pt7Ni6 nanocluster is the most stable as a result of the better coupling between the Pt and Ni d-states. Pt4Ni9 maintains its structure over the reaction cycle, with a larger turnover frequency value than Pt7Ni6. On the other hand, despite Pt10Ni3 presenting the highest value of turnover frequency, it suffers a strong structural deformation over the completion of a reaction cycle, indicating that the catalytic activity can be altered.

Ti-poor high-Al chromitites of the Moa-Baracoa ophiolitic massif (eastern Cuba) formed in a nascent forearc mantle

Podiform chromitite is an important archive recording detailed information on mantle magmatism, heterogeneity and dynamics. High-Al chromitites are believed to have formed in mid-ocean ridge, back-arc, and forearc basin environments. Correlation between the geochemical composition of high-Al chromitites and their geodynamic settings is not well explored. Here, we present the petrographic, microstructural, mineral chemical, and whole-rock platinum-group element (PGE) data of the high-Al podiform chromitites from the Moa-Baracoa ophiolitic massif (MBOM) (eastern Cuba), to investigate their petrogenesis and constrain their geodynamic settings. The chromitites occur in massive and semi-massive forms enveloped in dunite within the host harzburgite. The Cr-spinels in these chromitites contain inclusions of silicates (e.g., clinopyroxene, amphibole, and phlogopite), platinum-group minerals, and base-metal sulfides. These chromitites (Cr# = 42.5–54.7, Mg# = 64.1–75.5) are poor in TiO2 (0.02–0.15 wt%), and display an obvious enrichment in IPGE (Os, Ir, and Ru) over PPGE (Rh, Pt, and Pd). Cr-spinel grains usually show low-pressure characteristics illustrated by inclusions of amphibole and phlogopite. Additionally, high-pressure/high-temperature microstructures, such as densely exsolved needles of clinopyroxene, strong crystal-plastic deformation, and overgrowth, can be found in some Cr-spinels. The coexistence of high- and low-pressure characteristics implies that some Cr-spinel grains crystallized in a relatively deep mantle while others crystallized at a shallow depth. Mineralogical and chemical features indicate that the parental magma of the chromitites was hydrous and TiO2-poor, and had high oxygen fugacity. We propose that the Ti-poor high-Al chromitite of the MBOM originated from a nascent forearc mantle during subduction initiation, in which deep-crystallized Cr-spinel were carried upward by the parental melt and deposited together with the shallow-crystallized crystals.

Nanotwins Strengthening High Thermoelectric Performance Bismuth Antimony Telluride Alloys.

Bi2Te3 based thermoelectric alloys have been commercialized in solid‐state refrigeration, but the poor mechanical properties restrict their further application. Nanotwins have been theoretically proven to effectively strengthen these alloys and could be sometimes constructed by strong deformation during synthesis. However, the obscure underlying formation mechanism restricts the feasibility of twin boundary engineering on Bi2Te3 based materials. Herein, thorough microstructure characterizations are employed on a series of Bi0.4Sb1.6Te3+ δ alloys to systematically investigate the twins’ formation mechanism. The results show that the twins belong to the annealing type formed in the sintering process, which is sensitive to Te deficiency, rather than the deformation one. The Te deficiency combined with mechanical deformation is prerequisite for constructing dense nanotwins. By reducing the δ below −0.01 and undergoing strong deformation, samples with a high density of nanotwins are obtained and exhibit an ultrahigh compressive strength over 250 MPa, nearly twice as strong as the previous record reported in hierarchical nanostructured (Bi, Sb)2Te3 alloy. Moreover, benefitting from the suppressed intrinsic excitation, the average zT value of this robust material could reach near 1.1 within 30–250 °C. This work opens a new pathway to design high‐performance and mechanically stable Bi2Te3 based alloys for miniature device development.

Learning geodesic-aware local features from RGB-D images

Most of the existing handcrafted and learning-based local descriptors are still at best approximately invariant to affine image transformations, often disregarding deformable surfaces. In this paper, we take one step further by proposing a new approach to compute descriptors from RGB-D images (where RGB refers to the pixel color brightness and D stands for depth information) that are invariant to isometric non-rigid deformations, as well as to scale changes and rotation. Our proposed description strategies are grounded on the key idea of learning feature representations on undistorted local image patches using surface geodesics. We design two complementary local descriptors strategies to compute geodesic-aware features efficiently: one efficient binary descriptor based on handcrafted binary tests (named GeoBit), and one learning-based descriptor (GeoPatch) with convolutional neural networks (CNNs) to compute features. In different experiments using real and publicly available RGB-D data benchmarks, they consistently outperforms state-of-the-art handcrafted and learning-based image and RGB-D descriptors in matching scores, as well as in object retrieval and non-rigid surface tracking experiments, with comparable processing times. We also provide to the community a new dataset with accurate matching annotations of RGB-D images of different objects (shirts, cloths, paintings, bags), subjected to strong non-rigid deformations, for evaluation benchmark of deformable surface correspondence algorithms.

Characteristics and Main Controlling Factors of Fractures within Highly-Evolved Marine Shale Reservoir in Strong Deformation Zone

Based on the systematical observations of cores, thin sections, and scanning electron microscope (SEM) sections, together with the testing data and characteristic parameters, this paper discussed the characteristics and controlling factors of fractures, and their control on shale gas accumulation in the Lower Cambrian Niutitang Formation black shale reservoir of Well YX1 in the northern Guizhou Province. The results show that macro structural fractures are common in the Niutitang Formation, which can be divided into shear fractures (e.g., high dip-angle shear fractures and low dip-angle slip fractures), tensional fractures, and tension-shear fractures. Non-structural fractures in microfractures can be divided into organic-related fractures and inorganic mineral-related fractures. Most of the structural fractures were filled and the types of fillings are diverse. The staggered relationships of fractures confirm the complexity of tectonic movement in the study area. The formation of structural fractures in Well YX1 is mainly controlled by the major fault. The influence of mineral composition and content, mechanical properties, brittleness, and organic matter content of rocks on the characteristics of the fractures are from the external manifestation of sedimentary environment. Affected by diagenetic evolution, organic matter-related fractures are not common. Compared with other shale gas reservoirs in China and abroad, the organic-rich shale reservoir of Well YX1 is characterized by both “geological sweet spots” and “engineering sweet spots”; however, strong deformation and faulting have led to the loss of shale gas and damage of the overpressure environment. Therefore, it is suggested that small-scale fractures, caused by tectonic movements but without large penetrating faults, are the most favorable for shale gas reservoirs. Based on the complicated tectonic setting in northern Guizhou, the formation pressure should be taken into account.

Mode II interlaminar fracture toughness enhancement of fine z‐pin reinforced carbon fiber composite with low fraction of pins

AbstractThis article aims to improve the shear delamination resistance of composite laminate and minimize implantation damage on fiber orientation by using fine z‐pins. The z‐pins with the diameters as small as 0.1 and 0.2 mm were prepared by using different carbon fibers. The results show that z‐pinning method significantly improves the mode II interlaminar fracture toughness, and the GIIC value becomes larger with the decrease in z‐pin diameter. Compared with the control sample, the precracked GIIC values of (carbon fiber‐reinforced polymer composite) CFRP(0.5CF4X−pin), CFRP(0.2CF4X−pin), and CFRP(0.1CF4X−pin) increase by 67%, 142%, and 176%, respectively. As z‐pin diameter decreases from 0.5 to 0.1 mm, the failure mode changes from z‐pin pullout to shear fracture. The evolution of failure mode greatly enhances the resistance to crack propagation and the final GIIC value. The carbon fiber type of pin(0.5mm) has no obvious influence on the delamination sliding resistance. For pin(0.1mm) and pin(0.2mm), the strong deformation resistance of z‐pin is the dominant factor driving the improvement of the GIIC values though providing high‐shear traction load. In addition, the z‐pins with large shear deformation capacity can also enhance the crack sliding resistance.

Mechanical response and texture evolution prediction of AZ31 magnesium alloy during CVCDE process using crystal plasticity finite element method

Continuous variable channel direct extrusion (CVCDE) is one of the effective methods for the fabrication of high-performance light alloy, which can realize the cooperative control of the shape and properties of extruded components with short process in a single pass. However, in consideration of the closed cavity in CVCDE, it is difficult to observe the microstructure in real time, and it is characterized by strong nonlinear and complex deformation path. Therefore, CPFEM (Crystal Plasticity Finite Element Method) was established based on VPSC-PTR to study texture evolution under complex conditions. The texture evolution law under different forming conditions was stated, and the experiments data were compared with the simulation results. The results were consistent with the simulation results. By means of crystal plasticity simulation, the material deformation and strain distribution at different positions in the CVCDE process were revealed. The simulation results based on this model show that during the 2-interim CVCDE process, the edge region of AZ31 magnesium alloy is subjected to obvious shear strain, which promotes the initiation of non-basal plane <c+a> slip system, and the basal axis orientation of grain is deflated, and the material texture is significantly different from that in the center deformation region.

Non-destructive wear analysis of aged polyethylene hip inserts: Comparison of gravi-metric investigations with three-dimensional microstructure analysis in micro-CT after 10 million cycles

The hip joint is the most frequently implanted artificial joint in humans. The most important parameter is the durability, i.e. the time until a replacement operation. The most common reason for material failure is mechanical abrasion/wear as a limiting factor and significantly determines the survival time of the implant. [1, 2]. In the case of the acetabular cup, the plastic insert is often the most affected. The hip model examined here is characterized by a metal sleeve into which the plastic insert is pressed. This assumes an optimal fit of the insert in the cup in order to create conditions for the lowest possible abrasion. Unfortunately, it is not yet possible to test the abrasion of this system non-destructively. The abrasion of the hip is tested on so-called simulators by biomechanical loading according to ISO standard 14 242 over 5 million cycles [3, 4]. Additional scenarios with increased loading of the cup are required, such as artificial aging of the plastic as a "worst-case" scenario. A non-destructive analysis of the polyethylene has not been possible so far; up to now, the plastic has been knocked out of the metal sleeve with a hammer blow (with force) under strong deformation (Fig.1: destroyed back side by mechanical deformation on the left, plastic insert on the right). This study is the first to enable non-destructive testing of the plastic after aging and biomechanical stress by X-ray microcomputed tomography (XCT) examination. This will be compared to conventional gravimetric examinations and surface scanning results and tested for routine use. The second goal is to test wear abrasion not after 5 million cycles but after 10 million cycles.

First-principles prediction of structure and mechanical properties of TM5SiC2 ternary silicides

Although transition metal silicides are promising advanced functional materials, the adjustment of strength and ductility behavior is a great challenge. It is believed that the introduction of C element maybe improved the overall properties of transition metal silicides. Similar to the TM5SiB2, the structure, elastic properties and ductility of TM5SiC2(TM = Cr, Mo, Nb and W) ternary silicides are studied by the first-principles calculations. The results show that four novel TM5SiC2 ternary silicides are firstly predicted. Compared to TM5Si3, these TM5SiC2 ternary silicides have strong elastic deformation resistance due to the role of C element. In particular, these TM5SiC2 ternary silicides also exhibit better ductility compared to the brittle TM5Si3 phases. The calculated electronic structure shows that these TM5SiC2 ternary silicides have electronic properties because of the band overlap of C-2p state and TM-d state near the Fermi level. Therefore, this work can provide a new path to improve the mechanical properties of TM-Si-C ternary silicides high-temperature materials.

Spheroidal force-free neutron star magnetospheres

Context. Fast rotating and self-gravitating astrophysical objects suffer strong deformations from centrifugal forces. If, moreover, they are magnetised, they generate an electromagnetic wave that is perturbed accordingly. When stellar objects are also surrounded by an ideal plasma, a magnetosphere is formed. For neutron stars, a relativistic magnetised wind is launched, efficiently extracting rotational kinetic energy flowing into particle creation and radiation. Aims. We study the electromagnetic configuration of a force-free magnetosphere encompassing an ideal spheroidal rotating conductor as an inner boundary. We put special emphasis on millisecond period neutron star magnetospheres, that is those showing a significant oblate shape. For completeness, we also investigate the effect of prolate stars. Methods. Force-free solutions were computed by numerical integration of the time-dependent Maxwell equations in spheroidal coordinates using pseudo-spectral techniques. Relevant quantities such as the magnetic field structure, the spin-down luminosity, the polar cap rims, and the current density are shown and compared to the force-free spherical star results. Results. We find that the force-free magnetic field produced by spheroidal stars remains very similar to their spherical counterpart. However, the spin-down luminosity slightly decreases with increasing oblateness or prolateness. Moreover, the polar cap area increases and, for the most part, always encompasses the equivalent spherical star polar cap rims. The polar cap current density is also drastically affected. Conclusions. Neutron stars are significantly distorted by either rotational effects such as millisecond pulsars or by magnetic pressure such as magnetars and high magnetic field pulsars. An observational interpretation of and fitting a thermal X-ray pulsation will greatly benefit from an accurate and quantitative analysis similar to the one presented in this paper. However, even for the fastest possible rotation, the effect would certainly be unobservable, in the sense that we cannot predict what feature of the light curve would supposedly reveal the neutron star deformation due to fast rotation.

Nanopore Structure and Mechanical Properties in Brittle Tectonically Deformed Coals Explored by Atomic Force Microscopy

Tectonically deformed coals (TDCs) are of great importance to coalbed methane exploitation and coal mining safety. Compared to primary coals, reservoir properties of TDCs have been transformed greatly by tectonic stress. Here, the pore structure and mechanical properties of primary coal and brittle TDCs were obtained with atomic force microscopy and software. The results showed that tectonic stress generally promotes pore development and Young’s modulus of brittle TDCs. According to the variation in pore structure and Young’s modulus, two stages were identified: weak brittle deformation stage (primary coal–cataclastic coal–schistose coal–mortar coal) and strong brittle deformation stage (mortar coal–granulitic coal–flaky coal). The extent of tectonic impact varies greatly between these two stages. In weak brittle deformation stage, tectonic stress has little impact on coal pore structure. The mean pore number increases slowly, and the mean pore size decreases slowly. In this stage, half of the pore number increment is provided by macropores of 100–200 nm diameter. In strong brittle deformation stage, tectonic stress has a major impact on coal pore structure. The mean pore number increases quickly, and the mean pore size decreases quickly. Most of the pore number increment comes from mesopores of 10–50 nm diameter and macropores of 50–100 nm diameter. In addition, the Young’s modulus of primary coal and different brittle TDCs varies from 1.5 to 2.0 GPa. In weak brittle deformation stage, the Young’s modulus of different samples levels off. While in strong brittle deformation stage, the Young’s modulus increases gradually. Combined with former studies, it is inferred that tectonic stress can influence coal’s Young’s modulus by transforming its chemical structure.

Influence of the droplet trajectory on the resulting droplet deformation and droplet size distribution in high‐pressure homogenizer orifices

AbstractHigh‐pressure homogenization is a commonly used process to produce emulsions with a droplet size of less than 1 μm. During the process, a pre‐emulsion is pumped with a pressure of several mega Pascal through a disruption unit, where the droplets are deformed and subsequently broken up in the turbulent area of the disruption unit. The scope of this investigation is to determine the influence of the droplet trajectory on the droplet size distribution of emulsions of different viscosity ratios or interfacial tension. Measurements of the droplet deformation prior to the droplet breakup using image‐processing tools complemented the observations. In addition, computational fluid dynamics simulations were performed to determine the stress history on the droplet trajectories. It was found that droplets on a trajectory close to the wall are more deformed when leaving the disruption unit compared to droplets on the centreline. The deformation of droplets at the edge of the jet increases downstream the disruption unit until it is finally disrupted. The simulation results support the experimental data, as it can be shown that shear and strain stresses on the trajectories close to the wall significantly exceed the stresses on the trajectories on the centreline. For an emulsion with a viscosity ratio greater than 3, droplets on a trajectory close to the wall resulted in smaller droplets and narrower droplet size distribution, while no significant influence was found for smaller viscosity ratios. Lowering the interfacial tension results in a stronger deformation, which was more pronounced for lower viscosity ratios (λ ≈ 3).

Effects of Plate Velocity Slowdown on Altering Continental Collision Patterns and Crustal-Lithospheric Deformation During the Collision Process

Continental collision zones are widely distributed across the earth’s surface with diverse types of tectonic processes. Even the same collision zone shows significant lateral tectonic variations along its strike. In this study, we systematically investigated how plate velocity slowdown after the closure of the ocean influences the continental collision evolution, as well as the effects of kinematic characteristics and continental rheology on varying the continental collision modes in a plate velocity slowdown model. From the comparison between the constant plate velocity system (CVS) and the plate velocity-dropping system (VDS), we can conclude the following: Plate velocity dropping promotes the extension inside the slab by decreasing the movement of the surface plate, whereas slab pull increases as subduction continues. The timing of the subducting slab break-off and the polarity alteration was initiated earlier in the plate velocity drop models than in the constant plate velocity models, and fast convergence may have triggered multiple episodes of slab break-off and caused strong deformation adjacent to the collision zone. Parametric tests of the initial subducting angle, plate convergence velocity, and continental crustal rheological strength in VDS indicated the following: (1) Three end members of the continental lithospheric mantle deformation modes were identified from the VDS; (2) models with a low subducting angle, fast continental convergence velocity, and medium-strength overriding crust were more likely to evolve into a polarity reversed mode, whereas steep-subducting-angle, slow-plate-velocity, weak-overriding-crust models tended toward a two-sided mode; (3) a strong overriding continent is more liable to develop a stable mode; and (4) overriding crustal rheological strength plays a significant role in controlling changes in continental collision modes.

Distribution Prediction of Shale Deformation Structures in Tectonically Complex Area Based on Relationship Between Geological Structures and Shale Deformation

The alteration of shale structures and properties induced by tectonic activities is an important factor restricting the efficient utilization of shale gas resources. Predicting the distributions of shale deformation structures is of significance for the potential evaluation and favorable area optimization of shale resources in tectonically complex areas. Taking the Wufeng–Longmaxi shale of the southern Sichuan Basin as the research object, deformation observations of shale outcrops and shale core samples were conducted to reveal the distribution patterns of shale deformation structures in fault and fold structures. On this basis, the distribution rules of shale deformation structures in the unexposed areas were predicted by considering the structural framework of the study area. Our research indicated that faults can cause structural deformation in a limited area and that the influences of reverse faults were relatively more significant. Shale near the fault planes of reverse faults usually showed intense folding deformations, with well-developed bedding-parallel and crumpled cleavages. Strong deformation structures (crumpled, mylonitized, scaly, fractured-crumpled, and flaky structure) were distributed. Structural deformations in shale near normal faults were mainly characterized by the increase of tectonic fractures, and shale usually showed cataclastic structure. In the areas affected by strike-slip faults, bedding-perpendicular fractures and the fractures high-angle oblique to bedding planes were well developed. Folds can cause shale to deform in a larger area than faults. Shale in core zones usually displayed strong deformation structures. In the core–limb transitional areas of folds, shale mainly developed bedding-parallel and bedding-perpendicular fractures, and shale usually displayed platy and cataclastic structure. The observed structural deformations in fold limbs were generally weak, and shale usually showed primary structure and weak brittle deformation structures. According to the structural framework of the study area, it is predicted that strong deformation structures are mainly distributed in the core zones of anticlines (especially the tight and closed ones) and near the fault planes of large-scale reverse faults, while medium-intensity brittle deformation structures (platy and cataclastic structure) are distributed in core–limb transitional areas of anticlines and near the normal and strike-slip faults. In the limbs of anticlines and the areas controlled by synclines (mostly wide and gentle), shale mainly shows primary structure and weak brittle deformation structures.

Giant Room-Temperature Power Factor in p-Type Thermoelectric SnSe under High Pressure.

Materials that can efficiently convert heat into electricity are widely utilized in energy conversion technologies. The existing thermoelectrics demonstrate rather limited performance characteristics at room temperature, and hence, alternative materials and approaches are very much in demand. Here, it is experimentally shown that manipulating an applied stress can greatly improve a thermoelectric power factor of layered p‐type SnSe single crystals up to ≈180 µW K−2 cm−1 at room temperature. This giant enhancement is explained by a synergetic effect of three factors, such as: band‐gap narrowing, Lifshitz transition, and strong sample deformation. Under applied pressure above 1 GPa, the SnSe crystals become more ductile, which can be related to changes in the prevailing chemical bonding type inside the layers, from covalent toward metavalent. Thus, the SnSe single crystals transform into a highly unconventional crystalline state in which their layered crystal stacking is largely preserved, while the layers themselves are strongly deformed. This results in a dramatic narrowing in a band gap, from E g = 0.83 to 0.50 eV (at ambient conditions). Thus, the work demonstrates a novel strategy of improving the performance parameters of chalcogenide thermoelectrics via tuning their chemical bonding type, stimulating a sample deformation and a band‐structure reconstruction.

Improvements in ultra‐light and flexible epitaxial lift‐off GaInP/GaAs/GaInAs solar cells for space applications

AbstractA thin, lightweight, flexible solar cell is developed that maximizes the power‐to‐mass ratio under AM0 illumination and has a competitive efficiency after typical high energy electron irradiation. The inverted metamorphic triple junction (IMM3J) solar cells with Ga0.51In0.49P/GaAs/Ga0.73In0.27As subcells are grown on GaAs substrates and have a total epitaxy thickness of about 10 μm. After epitaxial growth, the inverted layer stack is metallized, with the metal serving as back‐contact, back reflector and support layer for the ultra‐thin solar cells before the GaAs substrate is separated by an epitaxial lift‐off (ELO) process. The nondestructive nature of the ELO process makes multiple reuses of the GaAs substrate possible. The solar cell structure is optimized for maximum EOL efficiency, that is, after 1‐MeV electron irradiation with a fluence of 1 × 1015 cm−2, by means of simulations that include the irradiation induced defects in the various semiconductor alloys. Assuming realistic charge carrier lifetime in the materials, we predict a near‐term efficiency potential for the IMM3J ELO of 30.9% under AM0 illumination before and 26.7% after irradiation. Several IMM3J ELO solar cells with an area of approximately 20 cm2 from different development stages were tested under AM0 illumination. The newest solar cells (generation III) with a mass density of only 13.2 mg/cm2 reach conversion efficiencies of 30.2% at 25°C. The resulting power‐to‐mass ratio of 3.0 W/g for the bare solar cell is one of the highest published ratios. After irradiation, a conversion efficiency of 25.4% was measured for “generation II” devices under AM0 illumination, which corresponds to a power‐to‐mass ratio of 2.6 W/g. IMM3J ELO solar cells from “generation I” were also tested for mechanical stability as “de‐risking” test of this new cell technology. No degradation of the cell performance was found after dipping the cell in liquid N2 and then heating up to 25°C for five times, despite of strong deformation of the flexible cell during the temperature cycle.