Efficient thermal energy harvesting using phase‐change materials (PCMs) has great potential for cost‐effective thermal management and energy storage applications. However, the low thermal ...conductivity of PCMs (KPCM) is a long‐standing bottleneck for high‐power‐density energy harvesting. Although PCM‐based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m−1 K−1) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase‐change composites (PCCs) by compression‐induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter‐sized graphite sheet consists of lateral van‐der‐Waals‐bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance KPCM in the range of 4.4–35.0 W m−1 K−1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high‐power‐density and low‐cost applications of PCMs in large‐scale thermal energy storage, thermal management of electronics, etc.
A method for synthesizing high‐performance thermally conductive phase‐ change composites is demonstrated. Large aligned graphite sheets inside the composite are generated from worm‐like expanded graphite. The aligned and interconnected graphite framework enhances KPCM up to 4.4–35.0 W m−1 K−1 at graphite loadings below 40.0 wt%, which may accelerate the high‐power‐density, low‐cost, and large‐scale applications of phase‐change materials.
In this study, we investigate the differences between two transient, three-dimensional, thermomechanically coupled ice-sheet models, namely, a first-order approximation model (FOM) and a ‘full’ ...Stokes ice-sheet model (FSM) under the same numerical framework. For all numerical experiments, we take the FSM outputs as the reference values and calculate the mean relative errors in the velocity and temperature fields for the FOM over 100 years. Four different boundary conditions (ice slope, geothermal heat flux, basal topography and basal sliding) are tested, and by changing these parameters, we verify the thermomechanical behavior of the FOM and discover that the velocity and temperature biases of the FOM generally increase with increases in the ice slope, geothermal heat flux, undulation amplitude of the ice base, and with the existence of basal sliding. In addition, the model difference between the FOM and FSM may accumulate over time, and the spatial distribution patterns of the relative velocity and temperature errors are in good agreement.
Satellite altimetry is a primary method for monitoring dynamic changes in polar ice and snow. However, recent studies on extreme melting events have revealed the notable impact of radar altimeter ...signals penetrating through snow, challenging previous assumptions that monitoring imparted negligible effects. Current approaches for mitigating penetration errors offer only partial alleviation instead of complete elimination. This study estimates the penetration values of Greenland satellite monitoring from February 2004 to November 2020 by comparing the temporal sequence of elevation changes obtained from laser altimetry and radar altimetry. We investigated the temporal and spatial evolution characteristics of penetration, particularly focusing on the extreme melting event in 2019. Interestingly, laser altimeter signals are also determined to penetrate water bodies, introducing a potential source of inaccuracy in laser altimeter measurements during the melting season. Furthermore, the analysis estimated the impact of time-variable penetration depths on Greenland's mass balance, revealing that regions with severe mass loss have the potential to exceed loss rates of 10 Gt/yr. These findings enhance our understanding of the impact of penetration errors in satellite altimetry and emphasize the crucial need for their correction to ensure accurate mass balance calculations in Greenland.
Deglaciation of the northwestern Laurentide Ice Sheet in the central Mackenzie Valley opened the northern portion of the deglacial Ice-Free Corridor between the Laurentide and Cordilleran ice sheets ...and a drainage route to the Arctic Ocean. In addition, ice sheet saddle collapse in this section of the Laurentide Ice Sheet has been implicated as a mechanism for delivering substantial freshwater influx into the Arctic Ocean on centennial timescales. However, there is little empirical data to constrain the deglaciation chronology in the central Mackenzie Valley where the northern slopes of the ice saddle were located. Here, we present 30 new .sup.10 Be cosmogenic nuclide exposure dates across six sites, including two elevation transects, which constrain the timing and rate of thinning and retreat of the Laurentide Ice Sheet in the area. Our new .sup.10 Be dates indicate that the initial deglaciation of the eastern summits of the central Mackenzie Mountains began at â¼15.8 ka (17.1-14.6 ka), â¼1000 years earlier than in previous reconstructions. The main phase of ice saddle collapse occurred between â¼14.9 and 13.6 ka, consistent with numerical modelling simulations, placing this event within the Bølling-Allerød interval (14.6-12.9 ka). Our new dates require a revision of ice margin retreat dynamics, with ice retreating more easterly rather than southward along the Mackenzie Valley. In addition, we quantify a total sea level rise contribution from the Cordilleran-Laurentide ice saddle region of â¼11.2 m between 16 and 13 ka.
Display omitted
•3D mesoporous black TiO2-x/Ag sphere and 2D g-C3N4 sheet heterojunction is fabricated.•The narrowed bandgap extends the photoresponse to visible light region.•It exhibits excellent ...visible light photocatalytic performance.•It is ascribed to Ti3+ doping, Ag and g-C3N4 coupling, and the mesoporous network.
3D mesoporous black TiO2-x/Ag nanosphere coupled with 2D g-C3N4 sheet ternary heterojunctions are successfully fabricated through a facile evaporation-induced self-assembly (EISA) process and photodeposition method, followed by a mild calcination (350°C) under an argon atmosphere after an in situ solid-state chemical reduction strategy. The resultant mesoporous black TiO2-x/Ag/g-C3N4 ternary heterojunctions with narrow band gap of∼2.27eV possess a relative high specific surface area of∼100m2g−1, main pore size of 6.2nm and the highest visible-light-driven photocatalytic property for degradation of methyl orange (97%) and methylene blue (99%). The apparent reaction rate constants (k) of mesoporous black TiO2-x/Ag/g-C3N4 for methyl orange and methylene blue are∼9 and 11 times higher than that of pristine TiO2. The possible mechanism is proposed, and the excellent photocatalytic property can be ascribed to the introduction of Ti3+ self-doping and g-C3N4, which favor the visible light absorption and the separation of electron-hole pairs, the surface plasma resonance effect of Ag nanoparticle, and the mesoporous networks offer more surface active sites.
In forming processes, friction is a local phenomenon influenced by the contact conditions at the tool-sheet metal interface. A multi-scale friction model applicable for coated sheets is developed for ...the boundary lubrication regime which accounts for the physical behavior of coating and measured surface topographies of sheet and tools. The contact patches and therefore the real area of contact is determined at the tool-sheet metal interface for different contact loading conditions. A single asperity micro-scale ploughing model is adapted at each contact patch to determine the friction force from which the overall coefficient of friction is determined. The friction model is validated using different sets of lab-scale friction tests and cup drawing experiments on zinc coated (GI) steel sheets.
•1.A multi-scale friction model is developed for the boundary lubrication regime.•2.Applicable for coated sheets and accounts for physical behavior of the coatings.•3.Surface topographies of sheet and tools are used as the input in the model.•4.Single asperity ploughing model is adopted at macro-scale deformed sheet surface.•5.The model is validated using lab-scale friction tests and cup drawing experiments.
Display omitted
Two-dimension (2D) MXene materials have increasingly attracted attentions in improving the photocatalytic conversion of solar-to-chemical energy over graphitic carbon nitride ...(g-C3N4). In this work, Pt nanoparticles modified few-layer Ti3C2 MXene sheet (MXene@Pt) was successfully prepared by chemical reduction, which was used as efficient co-catalysts to enhance the photocatalytic hydrogen evolution over porous g-C3N4 (PCN). The high work function of MXene@Pt and the tight 2D/2D interfacial contact between MXene@Pt and PCN significantly promoted the transfer and separation of photogenerated electron-hole. Besides, the MXene@Pt could enhance the light-harvesting of PCN and provide plentiful active sites for hydrogen evolution reaction. The hydrogen evolution activity of optimum 2D/2D MXene@Pt modified PCN (PCN/MPt-5) composite was dramatically enhanced, even higher than that of equal Pt mass modified PCN. Besides, overall water splitting was realized via a two-electron pathway with H2O2 and H2 generation. This work may provide the fabrication strategy for developing MXene-based co-catalyst in photocatalysis.
This paper presents the deformation of a joined sheet after the clinch riveting process. The DX51D steel sheet with zinc coating was used. The samples to be joined with clinch riveting technology had ...a thickness of 1 ± 0.05 mm and 1.5 ± 0.1 mm. The sheet deformation was measured before and after the joining process. The rivet was pressed in the sheets with the same dimension between the rivet axis and three sheet edges: 20, 30, and 40 mm. For fixed segments of the die, from the rivet side close to the rivet, the sheet deformation was greater than that of the area with movable segments. The movement of the die’s sliding element caused more sheet material to flow in the space between the fixed part of the die and movable segments. Hence, the sheet deformation in these places was smaller than for the die’s fixed element—the sheet material was less compressed. For sheet thickness values of 1.5 mm and a width value of 20 mm, the bulk of the sheet was observed. For a sheet width of 20 mm, it was observed that the deformation of the upper and lower sheets in the area of the rivet was greater than for sheet width values of 30 or 40 mm.
Current sheets are an essential element of the planetary magnetotails, where strong plasma currents self‐consistently support magnetic field gradients. The current sheet configuration is determined ...by plasma populations that contribute to the current density. The most commonly investigated configuration is supported by diamagnetic cross‐field currents of hot ions, typical for the magnetospheres of magnetized planets. In this study, we examine a new type of the current sheet configuration supported by field‐aligned currents from electron streams in the Jovian magnetodisk. Such bi‐directional streams increase the electron thermal anisotropy close to the fire‐hose instability threshold and lead to strong magnetic field shear. The current sheet configuration supported by electron streams is nearly force‐free, with |B| ≈ const across the sheet. Using Juno plasma and magnetic field measurements, we investigate the internal structure of such current sheets and discuss possible mechanisms for their formation.
Key Points
We report Juno observations of thin anisotropic current sheets in the Jovian magnetodisk
The contribution of electron streams to the current sheet stress balance is estimated
We show force‐free current sheet configuration supported by strong electron field‐aligned currents
Constrained groove pressing (CGP) is a modern technique for developing ultrafine grain structures in sheet metals for inducing superior material properties. In CGP, the sheet metal specimens are ...subjected to repetitive corrugating and straightening under the plane strain deformation condition by utilizing alternate pressing with the asymmetrically grooved dies and flat dies. This induces a great amount of plastic strain in the sheet metal specimen without changing its initial dimensions. Over the last few years, CGP has gained significant importance for it being one of the most suitable techniques to fabricate sheet metals with superior and attractive properties. CGP can effectively refine the grain structure to a sub-micrometre level and at times, even to a nanometer level. Materials processed by CGP exhibit very high strength, high hardness and many other desirable properties. Numerous investigations were made on different materials like aluminium, copper, low carbon steel and nickel, and their properties were well documented in the scientific literature. This review summarizes most of the scientific results that were obtained by applying CGP to various materials and gives an outline of the applications of CGP in various industries. This review also discusses about the future scope of research on CGP and its benefits.
PDF
