Formation Of Gradient Research Articles

Fabricating Cu2Zn(SnxGe1-x)Se4 thin-film solar cells with back surface Ge grading by magnetron sputtering

In this paper, an approach of forming a band gap gradient by depositing a layer of Ge between the Mo layers by magnetron sputtering is proposed. The diffusion depth of the Ge into Cu2ZnSnSe4 (CZTSe) thin film can be effectively controlled by the Mo transition layer, resulting in the formation of Cu2Zn(SnxGe1-x)Se4 (CZTGSe) thin film with a band gap grading along the back surface. To validate the formation of the Ge gradient in the absorber, energy dispersive spectrometer line scanning and grazing incidence X-ray diffraction were performed. Furthermore, the impact of Ge layer on the morphologies of CZTSe was assessed using scanning electron microscopy. As a result, the introduced Ge layer formed a Ge grading along the back surface and improved the crystal quality of the absorber. Compared to CZTSe solar cells, the power conversion efficiency (PCE) of CZTGSe solar cells with a Ge gradient improved from 5.79 % to 9.28 %.

Investigation of quantitative precursory indicators for rock failure using spatio-temporal characteristics of velocity

Stress redistribution and crack development are prominent features in rock failure. However, these processes are complex and challenging to analyze, making early warning of instability in rock engineering difficult. To characterize the rock failure process and obtain reliable precursory indicators, the imaging method that combines active and passive sources was employed to construct the velocity field during the rock failure process in this study. The micro-crack propagation law and its potential connection with the stress environment were investigated by mapping the velocity field, the acoustic emission (AE) density field, and the energy field. Moreover, the Mutation Trend Coefficient (MTC) and Deformation Coefficient (DC) were proposed as precursory indicators of instability based on the spatio-temporal correlation and directional differences of velocity evolution. Results show that the nucleation of AE sources and the release of energy accumulation are key to the formation of the velocity gradient, and progressive rock failure is accompanied by the intensification of velocity anisotropy. Additionally, low-velocity regions usually preferentially extend in the direction parallel to the principal stress, while expansion in the direction vertical to the principal stress is dominant in the plastic stage, indicating that the stress environment controls the spatial heterogeneity of the velocity field. The evolution trend of precursor indicators shows that the increase of MTC from a low value and the continuous decrease of DC can be regarded as the initiation of rock secondary cracks. The proposed indicators and method not only provide beneficial complements to the understanding of the evolution mechanism of rock damage but also have potential in the early warning and identification of the early stage of crack propagation, offering references for the safety prevention and control of rock engineering disasters.

Amplification of photothermally induced reversible actuation in non-woven fabrics compared to bulk films

The burgeoning field of soft robotics has witnessed a surge in interest, driven by the pursuit of creating precise machines with soft actuators capable of surpassing or aiding human manufacturing capabilities. This work explores light-responsive shape memory actuators derived from electrospun fibers, integrating a "push-pull" azo compound into a poly(ε-caprolactone) matrix. Driven by photothermal conversion, the resulting system exhibits reversible actuation under UV light, demonstrating rapid responses and superior performance compared to film counterparts. More specifically, the significant impact of morphology on both the photothermal behavior and the actuation performance is highlighted by comparing non-woven and bulk shape memory material. The temperature variation induced by UV light in the non-woven was notably affected by scattering effects, leading to the formation of temperature gradients throughout the material. Notably, the study establishes a unique stress-responsive range for fibrous actuators, demonstrating that their porous structure contributes to higher actuation magnitudes at lower stresses compared to conventional films. This innovation holds promise for applications in micro-robotics and biomedical fields, showcasing the potential of fibrous actuators in augmenting human-friendly robotics through their lightweight, flexible, and remotely actuated features.

A dynamically equivalent atomistic electrochemical paradigm for the larger-scale experiments.

Electrochemical systems possess a considerable part of modern technologies, such as the operation of rechargeable batteries and the fabrication of electronic components, which are explored both experimentally and computationally. The largest gap between the experimental observations and atomic-level simulations is their orders-of-magnitude scale difference. While the largest computationally affordable scale of the atomic-level computations is ∼ns and ∼nm, the smallest reachable scale in the typical experiments, using very high-precision devices, is ∼s and ∼μm. In order to close this gap and correlate the studies in the two scales, we establish an equivalent simulation setup for the given general experiment, which excludes the microstructure effects (i.e., solid-electrolyte interface), using the coarse-grained framework. The developed equivalent paradigm constitutes the adjusted values for the equivalent length scale (i.e., lEQ), diffusivity (i.e., DEQ), and voltage (i.e., VEQ). The time scale for the formation and relaxation of the concentration gradients in the vicinity of the electrode matches for both smaller scale (i.e., atomistic) equivalent simulations and the larger scale (i.e., continuum) experiments and could be utilized for exploring the cluster-level inter-ionic events that occur during the extended time periods. The developed model could offer insights for forecasting experiment dynamics and estimating the transition period to the steady-state regime of operation.

Heparan sulfate-dependent phase separation of CCL5 and its chemotactic activity

Secreted chemokines form concentration gradients in target tissues to control migratory directions and patterns of immune cells in response to inflammatory stimulation; however, how the gradients are formed is much debated. Heparan sulfate (HS) binds to chemokines and modulates their activities. In this study, we investigated the roles of HS in the gradient formation and chemoattractant activity of CCL5 that is known to bind to HS. CCL5 and heparin underwent liquid–liquid phase separation and formed gradient, which was confirmed using CCL5 immobilized on heparin-beads. The biological implication of HS in CCL5 gradient formation was established in CHO-K1 (wild-type) and CHO-677 (lacking HS) cells by Transwell assay. The effect of HS on CCL5 chemoattractant activity was further proved by Transwell assay of human peripheral blood cells. Finally, peritoneal injection of the chemokines into mice showed reduced recruitment of inflammatory cells either by mutant CCL5 (lacking heparin-binding sequence) or by addition of heparin to wild-type CCL5. Our experimental data propose that co-phase separation of CCL5 with HS establishes a specific chemokine concentration gradient to trigger directional cell migration. The results warrant further investigation on other heparin-binding chemokines and allows for a more elaborate insight into disease process and new treatment strategies.

Heparan sulfate-dependent phase separation of CCL5 and its chemotactic activity.

Secreted chemokines form concentration gradients in target tissues to control migratory directions and patterns of immune cells in response to inflammatory stimulation; however, how the gradients are formed is much debated. Heparan sulfate (HS) binds to chemokines and modulates their activities. In this study, we investigated the roles of HS in the gradient formation and chemoattractant activity of CCL5 that is known to bind to HS. CCL5 and heparin underwent liquid-liquid phase separation and formed gradient, which was confirmed using CCL5 immobilized on heparin-beads. The biological implication of HS in CCL5 gradient formation was established in CHO-K1 (wild-type) and CHO-677 (lacking HS) cells by Transwell assay. The effect of HS on CCL5 chemoattractant activity was further proved by Transwell assay of human peripheral blood cells. Finally, peritoneal injection of the chemokines into mice showed reduced recruitment of inflammatory cells either by mutant CCL5 (lacking heparin-binding sequence) or by addition of heparin to wild-type CCL5. Our experimental data propose that co-phase separation of CCL5 with HS establishes a specific chemokine concentration gradient to trigger directional cell migration. The results warrant further investigation on other heparin-binding chemokines and allows for a more elaborate insight into disease process and new treatment strategies.

Receptor binding and tortuosity explain morphogen local-to-global diffusion coefficient transition

Morphogens are intercellular signaling molecules providing spatial information to cells in developing tissues to coordinate cell fate decisions. The spatial information is encoded within long-ranged concentration gradients of the morphogen. Direct measurement of morphogen dynamics in a range of systems suggests that local and global diffusion coefficients can differ by orders of magnitude. Further, local diffusivity can be large, which would potentially abolish any concentration gradient rapidly. Such observations have led to alternative transport models being proposed, including transcytosis and cytonemes. Here, we show that accounting for tissue architecture combined with receptor binding is sufficient to hinder the diffusive dynamics of morphogens, leading to an order of magnitude decrease in the effective diffusion coefficient from local to global scales. In particular, we built a realistic in silico architecture of the extracellular spaces of the zebrafish brain using light and electron microscopy data. Simulations on realistic architectures demonstrate that tortuosity and receptor binding within these spaces are sufficient to reproduce experimentally measured morphogen dynamics. Importantly, this work demonstrates that hindered diffusion is a viable mechanism for gradient formation, without requiring additional regulatory control.

Understanding Low-Speed Streaks and Their Function and Control through Movable Shark Scales Acting as a Passive Separation Control Mechanism.

The passive bristling mechanism of the scales on the shortfin mako shark (Isurus oxyrinchus) is hypothesized to play a crucial role in controlling flow separation. In the hypothesized mechanism, the scales are triggered in response to patches of reversed flow at the onset of separation occurring in the low-speed streaks that form in a turbulent boundary layer. The two goals of this investigation were as follows: (1) to measure the reversing flow occurring within the low-speed streaks in a separating turbulent boundary layer; (2) to understand the passive flow control mechanism of movable shark skin scales that inhibit reversing flow within the low-speed streaks. Experiments were conducted using digital particle image velocimetry (DPIV). DPIV was used to analyze the flow in a turbulent boundary layer subjected to an adverse pressure gradient formation over both a smooth flat plate and a flat plate on which shark skin specimens were affixed. The experimental analysis of the flow over the smooth flat plate corroborated the findings of previous direct numerical simulation studies, which indicated that the average spanwise spacing of the low-speed streaks increases in the presence of adverse pressure gradients upstream of the point of separation. However, the characteristics of the flow over the shark skin specimen more closely resemble that of a zero-pressure gradient turbulent boundary layer. A comparative analysis of the width and velocity of the reversed streaks between flat plate and shark skin cases reveals that the mean spanwise spacing decreases, and thus, the number of streaks increases over the shark skin. Additionally, the reversed streaks observed over shark scales are thinner and the highest negative velocity within the streaks falls within the range required to bristle the scales.

Multi-gradient structures by cold extrusion of strongly textured continuously cast commercially pure aluminum

During extrusion, the material is subjected to a heterogeneous deformation that results in the formation of gradients of microstructure and thus mechanical properties. In this study, using continuously cast commercially pure aluminum as a reference material, we show how a cast structure with coarse columnar grains affects the formation of these gradients during extrusion at room temperature. Characterization of the initial material as well as the extruded round bars by optical and electron microscopy, X-ray diffraction as well as by means of mechanical testing documents the formation of four characteristic annular sections. For extrusion along the casting direction there is a <100>/<111> double-fiber textured center with lowest hardness, followed by a <111> single-fiber textured ring with a hardness plateau, a double-fiber textured region with grains arranged alternatingly in an iris-like shape, and an (ultra-)fine grained surface layer with highest hardness. For extrusion opposite to the casting direction we find similar characteristics of the center section. With increasing distance from the center follow another double-fiber textured section with increasing hardness, a <111> single-fiber textured ring with nearly homogeneous hardness and a surface layer with a slightly rotated <111> fiber and highest hardness. The key finding is that the macroscopic anisotropy of the cast material, resulting from the grain size, crystal orientation and growth direction of the columnar grains, determines the local material flow during extrusion and thus leads to the formation of these different complex multi-gradient macrostructures that may provide unique properties for complex applications such as light-weight safety-relevant components.

Molecular mechanism of BMP signal control by Twisted gastrulation

Twisted gastrulation (TWSG1) is an evolutionarily conserved secreted glycoprotein which controls signaling by Bone Morphogenetic Proteins (BMPs). TWSG1 binds BMPs and their antagonist Chordin to control BMP signaling during embryonic development, kidney regeneration and cancer. We report crystal structures of TWSG1 alone and in complex with a BMP ligand, Growth Differentiation Factor 5. TWSG1 is composed of two distinct, disulfide-rich domains. The TWSG1 N-terminal domain occupies the BMP type 1 receptor binding site on BMPs, whereas the C-terminal domain binds to a Chordin family member. We show that TWSG1 inhibits BMP function in cellular signaling assays and mouse colon organoids. This inhibitory function is abolished in a TWSG1 mutant that cannot bind BMPs. The same mutation in the Drosophila TWSG1 ortholog Tsg fails to mediate BMP gradient formation required for dorsal-ventral axis patterning of the early embryo. Our studies reveal the evolutionarily conserved mechanism of BMP signaling inhibition by TWSG1.

Physics-Informed Approximation of Internal Thermal History for Surface Deformation Predictions in Wire Arc Directed Energy Deposition

Abstract This work presents a physics-informed fusion methodology for deformation detection using multi-sensor thermal data. A challenge with additive manufacturing (AM) is that abnormalities commonly occur due to rapid changes in the thermal gradient. Different non-destructive in-situ thermal sensors capture parts of the thermal history but are limited by the visible temperature spectrum and sensor field of view of the fabrication process. Various sensors mitigate problems with the loss of thermal history information; however, it brings forth challenges with integrating different data streams and the need to interpolate the internal thermal history. This study develops a thermal data-informed heat flux methodology that fills the gap in fusing numerical temperature approximation with data-driven knowledge of the surface of additive manufactured components. First, this study fuses infrared (IR) thermal data complexities during the AM process with the Goldak double ellipsoidal heat flux to model the energy input into the component. Second, a thermal physics-informed model input (PIMI) is created with thermal data-informed heat flux to capture internal thermal history. Lastly, a regression convolutional neural network (CNN) captures the relationship between the three-dimensional thermal gradient and the resulting surface deformation. The rapid thermal gradient formation and identification of deformation is a key step toward using thermal history data and machine learning to improve quality control in AM. The proposed surface deformation detection model achieved an mean squared error of 1.14 mm and an R2 of 0.89 in the case study when fabricating thin-walled structures.

Modern Trends in Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Multi-layered Microfluidic Drug Screening Platform Enabling Simultaneous Generation of Linear and Logarithmic Concentration Gradients

Since many microfluidic devices have limited drug dose order of gradients and incorporate 2D cell culture, we here present a multi-layered platform with linear and logarithmic gradients with 3D-cell culturing chambers. By employing Hagen–Poiseuille flow resistance equation and the parallel electric schematics, we determined the appropriate channel dimensions to achieve the desired target concentrations (100%, 50%, 20%, 10%, 5%, 2%, 1%, 0%). To validate the gradient formation against theoretical values, we introduced a solution containing fluorescein into the microfluidic chip. Moreover, cell culturing chambers were spaced out laterally for every 9 mm, aligning with the dimensions with the standard plate reader, providing enhanced usability. Vertical layout of the chip minimized the lateral dimension required for housing various components while maintaining a favorable height for imaging. By preventing the need to use external tubing to connect concentration gradient generator and cell culturing chamber modules, our platform holds promise in facilitating the integration of microfluidics into drug evaluation processes. To demonstrate use of this flexible platform, we tested two chemotherapy drugs against human bladder cancer cells (T24) embedded in 3D fibrin gel and evaluated their cell viability and proliferation rate. IC50 values were extracted for cells exposed to varying doses of cisplatin, gemcitabine, and gemcitabine with a fixed cisplatin dose, confirming the enhanced apoptosis of the bladder cancer cells and the advantages of combination chemotherapy. This simple multi-layered device may accelerate screening of anti-cancer drugs for a specific cell type by extracting optimal dosage for two drugs.

Prevalence, causes, and consequences of agricultural land abandonment: A case study in the Region of Murcia, Spain

Agricultural land abandonment has received increasing attention from the scientific community and decision makers in recent years. In this study, we aimed to identify the current status of agricultural land abandonment in Europe, investigate its main causes and consequences, and propose management solutions based on future projections. We selected the Region of Murcia (RM) in southeastern Spain as the study area as it has been identified as a hotspot of agricultural land abandonment. A large number of areas with severe erosion (gullies and piping) attributed to abandonment have been identified in the Neogene and Quaternary basins. Morphometric analyses of various fields and estimates of soil loss were performed in 57 abandoned land areas in the RM. Additionally, physical and chemical soil analyses were performed in 15 selected areas. The results showed that abandoned crop terraces in loam soil promote piping processes owing to their flat surfaces and the formation of a hydraulic gradient. Furthermore, soils with a poor structure, fine texture, and low organic matter content are vulnerable to erosion processes. Additionally, increased exchange sodium percentage (ESP), electrical conductivity (EC), sodium absorption ratio (SAR), and soluble sodium percentage (SSP) contribute to these processes. The results of this study confirmed the detrimental effects of abandoning agricultural land. We found that multiple contributing factors led to severe erosion on abandoned land in the RM. Therefore, efficient land use planning and management are required, especially for land abandonment in Neogene and Quaternary basins in semi-arid regions.

Hydrogen Peroxide Signaling in the Maintenance of Plant Root Apical Meristem Activity.

Hydrogen peroxide (H2O2) is a prevalent reactive oxygen species (ROS) found in cells and takes a central role in plant development and stress adaptation. The root apical meristem (RAM) has evolved strong plasticity to adapt to complex and changing environmental conditions. Recent advances have made great progress in explaining the mechanism of key factors, such as auxin, WUSCHEL-RELATED HOMEOBOX 5 (WOX5), PLETHORA (PLT), SHORTROOT (SHR), and SCARECROW (SCR), in the regulation of RAM activity maintenance. H2O2 functions as an emerging signaling molecule to control the quiescent center (QC) specification and stem cell niche (SCN) activity. Auxin is a key signal for the regulation of RAM maintenance, which largely depends on the formation of auxin regional gradients. H2O2 regulates the auxin gradients by the modulation of intercellular transport. H2O2 also modulates the expression of WOX5, PLTs, SHR, and SCR to maintain RAM activity. The present review is dedicated to summarizing the key factors in the regulation of RAM activity and discussing the signaling transduction of H2O2 in the maintenance of RAM activity. H2O2 is a significant signal for plant development and environmental adaptation.

Segregation-dependent mechanical stability of reverted austenite and resultant tensile properties of Co-free maraging steel fabricated by wire-arc directed energy deposition

The segregation-dependent mechanical stability of reverted austenite (RA) and resultant tensile properties was investigated on Co-free maraging steel fabricated by wire-arc directed energy deposition (DED). The results showed that the segregation in the interdendritic regions enabled the formation of gradient reverted austenite in Co-free maraging steel fabricated by wire-arc DED when subjected to aging heat treatment. The content and mechanical stability of reverted austenite and resultant tensile properties were strongly dependent on the degree and compositional gradient of segregation in the interdendritic regions as well as the post heat treatment process. The reverted austenite with compositional gradient inherited from the segregation, transformed into martensite successively from the edge to the interior within individual reverted austenite grain at different strain levels. Besides, the variations in the degree and compositional gradient of segregation in the interdendritic regions widened the range the mechanical stability of the reverted austenite and thereby activating martensite transformation over a broad strain regime. Annealing process prior to aging could modify the degree and compositional gradient of segregation in the interdendritic regions and accordingly tune the content and the range of mechanical stabilities of reverted austenite grains, thus attaining a gradual and consistent transformation induced plasticity effect over whole deformation regime and thereby increasing ductility without sacrificing strength of Co-free maraging steel fabricated by wire-arc DED.

In vitro co-culture of Clostridium scindens with primary human colonic epithelium protects the epithelium against Staphylococcus aureus.

A complex and dynamic network of interactions exists between human gastrointestinal epithelium and intestinal microbiota. Therefore, comprehending intestinal microbe-epithelial cell interactions is critical for the understanding and treatment of intestinal diseases. Primary human colonic epithelial cells derived from a healthy human donor were co-cultured with Clostridium scindens (C. scindens), a probiotic obligate anaerobe; Staphylococcus aureus (S. aureus), a facultative anaerobe and intestinal pathogen; or both bacterial species in tandem. The co-culture hanging basket platform used for these experiments possessed walls of controlled oxygen (O2) permeability to support the formation of an O2 gradient across the intestinal epithelium using cellular O2 consumption, resulting in an anaerobic luminal and aerobic basal compartment. Both the colonic epithelial cells and C. scindens remained viable over 48h during co-culture. In contrast, co-culture with S. aureus elicited significant damage to colonic epithelial cells within 24h. To explore the influence of the intestinal pathogen on the epithelium in the presence of the probiotic bacteria, colonic epithelial cells were inoculated sequentially with the two bacterial species. Under these conditions, C. scindens was capable of repressing the production of S. aureus enterotoxin. Surprisingly, although C. scindens converted cholic acid to secondary bile acids in the luminal medium, the growth of S. aureus was not significantly inhibited. Nevertheless, this combination of probiotic and pathogenic bacteria was found to benefit the survival of the colonic epithelial cells compared with co-culture of the epithelial cells with S. aureus alone. This platform thus provides an easy-to-use and low-cost tool to study the interaction between intestinal bacteria and colonic cells in vitro to better understand the interplay of intestinal microbiota with human colonic epithelium.

Study of Wear Resistance of Cylindrical Parts by Electromechanical Surface Hardening

The work scientifically substantiates the use of an effective technology for increasing the wear resistance of cylindrical parts, using the example of protective sleeves of cantilever pumps, due to electromechanical surface hardening. A review of research was carried out and it was established that the achievement of the highest values of microhardness of the surface layer at a depth of up to 1.2 mm is possible during electromechanical processing of protective sleeves of cantilever pumps. The application of various modes and schemes of electromechanical surface hardening (EMSH) is accompanied by a change in structure and, as a result, an increase in the hardness of the surface layer of the bushings. The actual contact area of the tool roller with the processed surface and the depth of the temperature-deformation effect depend on the physical and mechanical properties of the materials and the pressing force. The formation of a temperature gradient in the hardened zone at a depth of up to 1.2 mm from the surface has been proven. Metallographic analysis of the surfaces of the sleeves treated by EMSH shows the formation of a white layer with reduced etchability and increased hardness in the hardening zones. The results of the X-ray structural analysis confirmed the formation of the martensite phase in the hardening zone. The microhardness of the hardened steel zone increased by 2.6...3.6 times compared to the initial values at a depth of up to 1 mm from the surface, depending on the materials. In the case of their overlap, the alternation of a fully hardened zone, a partially hardened zone, and a self-relief zone is observed. At the same time, the microhardness of steels along the surface depends on the hardening scheme.&#x0D; Wear tests under friction conditions of parts of cantilever pumps paired with stuffing boxes showed that the wear resistance of protective sleeves after EMSH increased by 3.1 times for 45 steel, 1.9 times for U8 steel, 2.5 times for SHKH15 steel, for cast iron by 1.9 times compared to the initial values. The use of U8 steel samples after EMSH, instead of serial bushings made of steel 45, allows to increase the wear resistance of parts by 6.1 times, which allows us to recommend U8 steel for use in the manufacture of protective bushings for console pumps. On the basis of the research, recommendations are given for the application of EMSH for the formation of a surface layer with increased wear resistance of protective sleeves during their production and during repair of console pumps in workshops or service centers of agribusiness companies.

Coupled study on in-situ synchrotron high-energy X-ray diffraction and in-situ EBSD on the interfacial stress gradient in layered metals

As one of the heterostructures, the layered structure has attracted extensive research interest as it achieves superior properties to individual components. The layer interface is considered a critical factor in determining the mechanical properties of layered metals, where heterogeneity across the interface results in the strengthening of the soft layer and forming an interfacial stress gradient in the hard layer. However, there is still limited research associated with the formation of interfacial stress gradients in the hard layer, as stress measurement at high spatial resolution remains technically challenging. In the present study, we experimentally quantified the formation of interfacial stress gradients in the Ti layer of Ti/Al layered metal upon tension using in-situ high-energy X-ray diffraction (XRD). The analysis coupling in-situ high-energy XRD and in-situ electron back-scattered diffraction (EBSD) suggested that the interfacial stress gradient in the Ti layer rapidly rose as the Al layer was insufficient to accommodate the deformation of Ti. During the later deformation stage, collective effects of dislocation motion and geometrically necessary dislocation (GND) accumulation in the Al layer determined the evolution of interfacial stress gradients. The maximum interfacial stress gradient is below 0.4 MPa/μm in Ti layers, with a constant range width of 35 μm independent of the macroscopic strain. The present study therefore opens a new window to local stress modification using incompatible component deformation, which is instructive for the design and fabrication of high-performance layered metals.

Subsurface acoustic ducts in the Northern California current system.

This study investigates the subsurface sound channel or acoustic duct that appears seasonally along the U.S. Pacific Northwest coast below the surface mixed layer. The duct has a significant impact on sound propagation at mid-frequencies by trapping sound energy and reducing transmission loss within the channel. A survey of the sound-speed profiles obtained from archived mooring and glider observations reveals that the duct is more prevalent in summer to fall than in winter to spring and offshore of the shelf break than over the shelf. The occurrence of the subsurface duct is typically associated with the presence of a strong halocline and a reduced thermocline or temperature inversion. Furthermore, the duct observed over the shelf slope corresponds to a vertically sheared along-slope velocity profile, characterized by equatorward near-surface flow overlaying poleward subsurface flow. Two potential duct formation mechanisms are examined in this study, which are seasonal surface heat exchange and baroclinic advection of distinct water masses. The former mechanism regulates the formation of a downward-refracting sound-speed gradient that caps the duct near the sea surface, while the latter contributes to the formation of an upward-refracting sound-speed gradient that defines the duct's lower boundary.