We conduct numerical investigations on turbulent Rayleigh–Bénard (RB) convection modulated by oscillating filaments, where an array of active filaments is adhered to the bottom surface. Our study ...focuses on the dependence of global heat transfer, quantified by the Nusselt number (Nu), on the rigidity (B) of the active filaments under various oscillation frequencies (ω). We reveal two critical filament rigidities, Bc1 and Bc2, delineating distinct heat transfer regimes: (I) Soft regime (B<Bc1), where negligibly small filament rigidity allows for obvious bending, and Nu decreases with increasing rigidity B in this regime. (II) Elastic bending regime (Bc1<B<Bc2), where elastic bending of filament takes place, inducing swaying motion near the filament root and subsequently perturbing the boundary layers to favor thermal plumes emission. In this regime, Nu noticeably increases with rising rigidity. (III) Stiff regime (B>Bc2), characterized by minimal deformation induced by filament–fluid interaction and the saturation of heat transfer enhancement. Furthermore, we analyze the competition between bending and inertial forces experienced by the filaments through comparing their relative magnitude, from which we theoretically determine both critical rigidities Bc. Our study offers valuable insights into the intricate dynamics of active filaments in turbulent convection, advancing our understanding of heat transfer modulation in active environments with dynamically driving agents.
•Mechanism of heat transfer modulation by active filament has been elucidated.•Three heat transfer regimes are identified depending on filament rigidity.•Critical filament rigidity is determined by the competition between bending and inertial forces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, we report that reversals of the large-scale circulation in two-dimensional Rayleigh–Bénard (RB) convection can be suppressed by imposing sinusoidally distributed heating to the bottom ...plate. We examine how the frequency of flow reversals depends on the dimensionless wavenumber $k$ of the spatial temperature modulation with various modulation amplitude $A$. For sufficiently large $k$, the flow reversal frequency is close to that in the standard RB convection under uniform heating. However, when $k$ decreases, the frequency of flow reversal gradually becomes lower and can even be largely reduced. Furthermore, we examine the growth of the corner roll and the global flow structure based on Fourier mode decomposition, and reveal that the size of the corner roll diminishes as the wavenumber decreases. The reason is that the regions occupied by the cold phase can absorb heat from the hot plumes and thus lower their temperature, which reduces the corner roll's kinetic energy input provided by the buoyancy force, and weakens the feeding process of the corner rolls. This results in the locking of the corner roll into a smaller region near the corner, making it harder for a reversal to occur. Using the concept of horizontal convection caused by non-uniform heating, we find a relevant parameter $k/A$ to describe briefly how the reversal frequency depends on wavenumber and modulation amplitude. The present work provides a new way to control the flow reversals in RB convection through modifying temperature boundary conditions.
Kagome materials have been reported to possess abundant and peculiar physical properties, which provide an excellent platform to explore exotic quantum states. We present a discovery of ...superconductivity in van der Waals material Pd3P2S8 composed of Pd kagome lattice under pressure. Pd3P2S8 displays superconductivity for those pressures where the semiconducting-like temperature dependence of the resistivity turns into a metallic one. Moreover, it is found that the increased pressure results in a gradual enhancement of superconducting transition temperature, which finally reaches 6.83 K at 79.5 GPa. Combining high-pressure x-ray diffraction, Raman spectroscopy and theoretical calculations, our results demonstrate that the observed superconductivity induced by high pressure in Pd3P2S8 is closely related to the formation of amorphous phase, which results from the structural instability due to the enhanced coupling between interlayer Pd and S atoms upon compression.
The structure, stability, charge transfer, and chemical bonding properties of palladium-doped magnesium clusters, PdMg n (n = 2–20), are comprehensively researched by CALYPSO software within ...first-principles DFT computations. It is shown that the cluster structure evolved from a tetrahedral-based structure to a cage-like structure, and interestingly, the single Pd atom always immerses in the Mg n clusters except for PdMg2 and PdMg3. Stability studies indicate that PdMg4, PdMg7, PdMg10, and PdMg15 clusters have relative robust stability and can be identified as ‘magic’ clusters. Most importantly, chemical bonding studies reveal that Pd–Mg is always non-covalent bond (closed-shell) interaction in all PdMg n (n = 2–20) clusters, and PdMg6 and PdMg7 are the critical sizes at which Mg–Mg covalent interactions occur. The geometric structure database of transition metal-doped Mg clusters will be enriched by this study, and it also provides, at least theoretically, new members of cage-like structures for magnesium-based hydrogen storage nanomaterials.
The mechanism behind osteonecrosis of the femoral head (ONFH) remains unclear. The aim of this study was to explore the pathogenesis of ONFH from a biomechanical standpoint to provide a theoretical ...basis for improved treatments. We compared the bone structure of fractured femoral heads with that of necrotic femoral heads by Micro-CT scanning and histological evaluation. In addition, we compared the biomechanical properties of each zone in fractured femoral heads with those in necrotic femoral heads by using biomechanical tests. Compared with fractured femoral heads, bone microarchitecture and bone morphometry in necrotic zone and sclerotic zone of necrotic femoral heads have altered markedly. In addition, the biomechanical properties of the necrotic zone in femoral heads weaken markedly, while those of the sclerotic zone strengthen. We hypothesize that discordance between bone structure and function of the femoral head may be involved in the pathogenesis of ONFH and that more attention should be paid to the prevention and treatment of such discordance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Two new open-chain cytochalasins, xylarchalasins A and B (1 and 2), together with six known analogues (3-8), were isolated from the endophytic fungus Xylaria sp. GDGJ-77B from the Chinese medicinal ...plant Sophora tonkinensis. Their structures were elucidated on the basis of comprehensive spectroscopic analysis. Compound 2 displayed moderate antibacterial activities against Bacillus subtilis and Escherichia coli with MIC values of 25 and 12.5 μg/mL, respectively.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The scientific aspects of hydrogen storage in a single Mg atom have been investigated using density functional theory (DFT) calculations on gas-phase MgHn (n = 1–20) clusters. It is found, at least ...theoretically, that MgH7 and MgH12 gas-phase clusters have saturation sizes for the attraction of one Mg atom to odd and even numbered H atoms. Their hydrogen storage capacities reach an impressive 22.69 wt% and 33.47 wt%, respectively, which is a significant breakthrough from the insight into the hydrogen storage capacity of MgH2 (7.65 wt%). It is shown that there are two modes of cluster structure growth, alternating between odd and even H-atoms. Stability studies reveal that Mg stores even H atoms which are always more stable than odd H atoms. Electronic structure property studies indicate that Mg and H atoms contribute regularly to molecular orbitals. Finally, a clear and interesting odd-even mode mechanism for Mg-stored H atoms is established by atomic charge distribution, topological property studies of bond critical points, including bonding paths of bond critical points, electron density, Laplacian of electron density, electron localization function and interaction region indicator analysis. The specificity of such a mechanism is that the van der Waals interaction of Mg–H enhances the hydrogen storage capacity of the Mg atom. We believe that this research points to an extremely promising future for the assembly of potential hydrogen storage materials based on magnesium-based clusters.
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