Hong Kong University of Science and Technology
Hong Kong University of Science and Technology Institutional RepositoryNot a member yet
162821 research outputs found
Sort by
Climate-driven hydrological and biogeochemical shifts lead to increasing dissolved organic carbon storage in a Tibetan lake of Nam Co
No full textAlpine lakes on the Tibetan Plateau are experiencing rapid hydrological and biogeochemical changes in response to climate warming, yet the associated implications for regional carbon cycling remain poorly understood. Here, we investigated the distribution and dynamics of dissolved organic matter (DOM) in Nam Co, a representative alpine lake undergoing significant expansion and increasing allochthonous input. Through large-scale sampling across vertical lake profiles and inflowing rivers, combined with in situ photochemical and microbial incubations, we characterized DOM compositional characters and transformation pathways in Nam Co. Nam Co exhibited net accumulation of dissolved organic carbon (DOC), with an estimated production of 5.55 ± 2.21 Gg C·y-1, primarily driven by enhanced autochthonous production. In contrast, we observed net losses of chromophoric and fluorescent DOM in Nam Co, which were likely driven by strong solar irradiation and effective photochemical degradation. In situ incubation experiments in Nam Co revealed that microbial and photochemical processes produced substantial molecular-level transformations. Aromatic-like molecular formulas were key in shaping microbial community composition, with their interactive dynamics strongly influenced by allochthonous DOM inputs and light availability. These findings underscore the growing importance of Tibetan lakes in regional carbon sequestration under climate warming and highlight the critical role of internal biogeochemical processes in regulating carbon cycling in alpine aquatic systems.</p
Auxiliary dual-mode rotating cylinders for energy-efficient thermal management in prosumer buildings: a coupled TRNSYS–CFD investigation
No full textThe transition toward energy-efficient prosumer buildings requires thermal management systems capable of adapting to rapidly changing seasonal loads while coordination with district heating and cooling networks. Active Heat Transfer Enhancement (AHTE) devices, such as auxiliary rotating cylinders that are integrated into the building's thermal exchange loop, offer such adaptability by providing controllable modulation of heat transfer when primary systems are insufficient. Yet, evaluating their real-world potential has been constrained by a long-standing modeling gap: CFD is needed to resolve local flow behavior within the auxiliary unit, whereas annual performance demands whole-building simulation. No existing method reliably combines these scales for prosumer-building applications. To address this challenge, this study develops a TRNSYS–CFD co-simulation framework to assess a dual-mode rotating-cylinder AHTE system serving a multi-purpose prosumer building in Ilam, Iran. The integrated model demonstrates how the controller can adjust operating conditions to navigate distinct seasonal thermofluid regimes. In winter, effective operation requires coordinated tuning of Reynolds and Rayleigh numbers to maintain strong thermal exchange and prevent buoyancy-driven performance loss. In summer, the system naturally operates in a low-Rayleigh regime, and optimal performance is achieved by regulating Reynolds-based forced convection alone. These operational patterns emerge only through the coupled framework and form the basis for a season-adaptive control strategy that enhances net energy performance. Validation against TRNSYS-CFD data indicates that incorporating the auxiliary rotating cylinder unit reduces cooling and heating loads by 3.1 % and 6.9 %, respectively. This improvement results in an overall 3.5 % reduction in annual energy consumption and a 2.8 % decrease in CO2 emissions. In addition, the computational cost is approximately 30 % lower than that incurred by a DesignBuilder simulation for the same building. The results demonstrate that rotating cylinder AHTE systems deliver significant thermal support when integrated into external prosumer energy pathways. Moreover, the TRNSYS–CFD co-simulation framework provides a robust and scalable platform for optimizing their operation within next-generation district energy networks
Metalens array for complesx-valued optical discrete fourier transform
No full textPhotonic computing has emerged as a promising platform for accelerating computational tasks requiring high degrees of parallelism, ranging from signal and image processing to neural network tasks. This study presents meta-DFT (discrete Fourier transform), a single-layer metasurface device, designed to perform optical complex-to-complex DFT with (Formula presented.) digital time complexity. A key challenge in free-space optical computing lies in digital error control. This approach addresses this by spatially separating light into discrete focal spots, enabling complex phase reconstruction via an interferometric method with an integrated reference metalens, alongside an error mitigation scheme. The device's performance is systematically evaluated using input vectors with random complex amplitudes and phases, demonstrating error mitigation capability to reduce the error by half with as few as five pixels per output focal spot. These findings pave the way toward the advancement of metasurface-based optical computation, offering a robust framework readily extensible to arbitrary complex-valued matrix-vector multiplication (MVM).</p
Trimethylolethane-mediated electric double layer engineering for dendrite-free zinc anodes
No full textElectrolyte additives are a key strategy for stabilizing zinc anodes and interfaces in aqueous zinc ion batteries (AZIBs). However, conventional additives often affect both the electric double layer (EDL) and the solvated sheath of Zn2+, resulting in ambiguous mechanistic interpretations. Here, we introduce trimethylolethane (TME) as an additive that selectively modifies the EDL architecture without altering the Zn2+ solvation structure, enabling precise elucidation of EDL-mediated anode stabilization. TME preferentially adsorbs onto the zinc anode surface over water molecules, enabling dual-functional regulation: it reduces Zn2+ adsorption on the Zn (101) crystal facet while enhancing adsorption on the Zn (002) facet, thereby promoting uniform Zn2+ distribution. More importantly, TME molecules penetrate the EDL to form a stable, water-deficient interface, reducing active H2O molecules and suppressing parasitic reactions. Concurrently, the EDL-embedded TME increases zinc ion nucleation overpotential, creating abundant nucleation sites and promoting the formation of compact, dendrite-free Zn deposits. The Zn\\Zn symmetric cell with TME additive remarkably achieved a cycle life of up to 1495 h at 1 mA cm−2 (1 mAh cm−2), outperforming most reported electrolyte systems. This work establishes a new paradigm in EDL-oriented electrolyte engineering, providing critical insights for the rational design of next-generation high-performance AZIBs.</p
Quantifying groundwater level variability and annual slope failure probability using multi-year groundwater level observations
No full textThe variation in groundwater level (GL) has been recognized as an important triggering factor of landslides and often exhibits high uncertainty. Most existing slope reliability analysis and landslide risk assessment studies ignored the uncertainty of GL and focused on estimating slope failure probability that is not related to a time period. This study proposes a rigorous method for quantifying the annual failure probability (PFA) of slopes considering both uncertainties in GL and soil properties. Multi-year groundwater monitoring data are utilized to quantify the annual exceedance probability of GL through a statistical analysis. A series of GL scenarios corresponding to different return periods or exceedance probabilities is generated and used to estimate the corresponding conditional slope failure probabilities. These conditional probabilities are combined using the Total Probability Theorem to estimate PFA. The results from a real slope indicate that the conditional slope failure probability increases exponentially as GL rises. The variability in GL dominates PFA when the variability of soil properties is relatively low (e.g., coefficient of variation, COV = 0.1). Conversely, when the variability of soil properties is relatively high (e.g., COV ≥ 0.3), PFA is dominated by soil uncertainties, and the conditional failure probability becomes insensitive to GL fluctuations. This highlights the importance of monitoring groundwater conditions in quantifying and mitigating landslide risks. Preliminary validation indicates that GL scenarios corresponding to a return period of 10 to 15 years can be used as representative GL conditions for evaluating PFA, offering a practical guidance for slope design engineering.</p
Past, present and future perspectives on the science of aging
No full textAs Nature Aging celebrates its fifth anniversary, the journal asks some of the researchers who contributed to the journal early on to reflect on the past and the future of aging and age-related disease research, the impact of the field on human health now and in the future, and what challenges need to be addressed to ensure sustained progress.</p
Strong and deformable high-Al/Ti medium entropy alloy with good thermal stability via multiple coherent-precipitation
No full textBCC-based high/medium-entropy alloys (H/MEAs) possess prominent high-temperature strength, low thermal expansion, and high thermal conductivity, making them a promising candidate for elevated-temperature applications. However, their limited deformability at room temperature (RT) hinders industrial implementation. Here, we report a novel cost-effective (FeCrNi)85(AlTi)15 MEA featuring a multiple-phase microstructure with BCC/L21, L21/BCC, and FCC/L12 coherent interfaces in the as-cast state. The strategic incorporation of L12-strengthened FCC matrix phase within brittle BCC and L21 matrices can activate hetero-deformation-induced (HDI) hardening effect, achieving an attractive compressive plasticity of 35 % at room temperature. The well-controlled L21-Ni2AlTi, BCC, and L12-Ni3(Al, Ti) nanoparticles coherently precipitate in BCC, L21, and FCC matrix phases, respectively, resulting in a super-high yield strength of 1850 MPa, outperforming existing B2/L21-strengthened BCC H/MEAs. The triple-coherent interface system demonstrates exceptional thermal stability, maintaining yield strengths of 850 MPa at 700 °C and 395 MPa at 800 °C. Moreover, this alloy exhibits a dynamic phase transformation-induced hardening effect during long-term aging due to the precipitation of σ-FeCr phase. These results provide a new strategy for overcoming the drawback of inadequate deformability in BCC-based alloys and developing novel advanced as-cast materials for high-temperature applications under compressive loading.</p
Homochiral Metal–Organic Framework Featuring Transformable Helical and Sheeted Structures
No full textPursuing artificial mimics of natural protein structures is a critical research area with broad implications in biochemistry, synthesis, and materials science. A key objective is to understand and validate the chirality transfer process from small molecules, such as amino acids, to complex three-dimensional (3D) architectures. Despite significant progress, only a limited number of artificial materials with well-defined, protein-like crystalline structures have been reported due to the inherent challenge of balancing structural rigidity and flexibility. Typically, rigidity enhances structural integrity and facilitates characterization, whereas flexibility enables greater functional versatility. In this study, by using a cysteine-derived linker that integrates both rigid and flexible motifs, we report the synthesis of homochiral metal–organic frameworks L/D-Zn-PDT-α and L/D-Zn-PDT-β, featuring helical and pleated-sheet structures, respectively. An in situ crystal transformation from Zn-PDT-α to Zn-PDT-β is closely monitored, disclosing a transition pathway from a relatively rigid to a more flexible crystalline phase. Systematic crystallographic analyses demonstrate how the coordination mode (bidentate versus monodentate) dictates the rigidity or flexibility of the resulting 3D structure. Owing to their structural adaptability, L/D-Zn-PDT-β frameworks serve as homochiral hosts capable of accommodating achiral organic dyes, thereby inducing notable chiroptical activities. The insights obtained from the structural study may have broader implications for the design of other chiral assemblies beyond this work.</p
MnSi<sub>2</sub>Te<sub>4</sub>: A van der Waals Antiferromagnetic Semiconductor with Large Negative Magnetoresistance
No full textMagnetism in van der Waals semiconductors offers significant potential for fundamental research on low-dimensional magnetism and the development of high-performance two-dimensional spintronic devices. Here, we report the growth, physical properties, and first-principles calculations of a new dual-octahedral transition metal chalcogenide (DTMC) MnSi2Te4. MnSi2Te4 features a layered structure with an intralayer heterostructure, where the metal octahedra and nonmetal dimeric octahedra form zigzag chains alternately. Property characterization reveals that MnSi2Te4 is a collinear G-type antiferromagnetic semiconductor, with a Néel temperature TN of 18.6 K and a significant unsaturated negative magnetoresistance (NMR) reaching −42.5% at 9 T and 100 K. First-principles calculations on the electronic band structure demonstrate that the large NMR primarily originates from the spin splitting due to parity-time symmetry breaking. This study not only discovers a new member of DTMCs with a unique crystal structure and large NMR, but also establishes a promising platform for investigating next-generation spintronic devices.</p
Observation of W+W−γ production in pp collisions at √s = 13 TeV with the ATLAS detector and constraints on anomalous quartic gauge-boson couplings
No full textThis Letter reports the observation of W+W−γ triboson production in 140 fb−1 of data collected by the ATLAS detector from proton–proton collisions at a centre-of-mass energy of s = 13 TeV at the LHC. Events with an opposite-charge eμ pair, a high transverse-momentum photon, and significant missing transverse momentum are considered. The observed (expected) significance of the signal is 5.9 (6.0) standard deviations. The measured fiducial cross-section, defined for the W+W−γ→e±μ∓νν¯γ final state is 6.2 ± 0.8 (stat.) ± 0.6 (sys.) fb, in good agreement with the Standard Model prediction of 6.1−0.7+1.0 fb. Constraints on the Wilson coefficients of 13 dimension-8 operators describing physics beyond the Standard Model through anomalous quartic gauge-boson couplings are derived using the effective field theory framework.</p