Continuous Transfer Research Articles

The UN Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) — An ocean science-policy interface standing the test of time

Addressing the wide range of marine pollution problems facing the global ocean requires a continual transfer of credible, relevant and timely scientific information to policy and decision makers in coastal and ocean management. The United Nations GESAMP (Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection) is a long-standing scientific advisory group providing such information on a wide range of marine topics and emerging issues of concern to ten UN Sponsoring Organizations. This paper presents an overview of GESAMPs operation and examples of its current work. The group's scientific output is often cited by national governments, inter-governmental groups, and a range of non-governmental groups. Given the growing concerns about ocean health and the impacts of many stressors in an era of climate change, the development of timely and effective ocean policy and decision making would benefit from wider recognition and application of GESAMPs work.

Design of PVA/multilayer hybrid particle composite aerogel skeleton supported form-stable phase change materials with high thermal conductivity and solar-to-thermal conversion efficiency

Phase change materials (PCMs) are considered to be promising energy storage materials, but the advanced utilization of PCMs is limited by liquid phase leakage, low thermal conductivity and poor solar-to-thermal conversion ability. Herein, inspired by the structure of nacre, we used boron nitride nanosheets (BNNs) coated with polydopamine (PDA)-modified tetrapod zinc oxide (T-ZnO) to prepare multilayered BNNs/PDA@T-ZnO hybridized particles (BPT), and then employed them to reinforce the PVA aerogel to obtain a BPT/PVA skeleton. Due to the robust support of T-ZnO substrate, BPT/PVA skeleton has ordered porous structure and excellent mechanical properties, with compressive strength up to 15.7 MPa. The prepared composite PCMs of polyethylene glycol (PEG) supported by BPT/PVA skeleton (PVA/BPTs/PEG) have good heat storage capacity, thermal conductivity and solar-to-thermal conversion efficiency. The rigid BPT/PVA skeleton endows PVA/BPTs/PEG with good shape stability and durability, whereas the melting enthalpy and crystallinity of PVA/BPT/PEG reach 139.0 J·g−1 and 99.6 %, respectively. The intermediate dopamine layer of BPT acted as an adhesive for BNNs and T-ZnO and excellent solar-to-thermal conversion medium, which cause the PVA/BPTs/PEG composites to have excellent solar-to-thermal conversion efficiency (95.2 %). Meanwhile, the thermal conductivity of PVA/BPTs/PEG reach 1.34 W·m−1·K−1, benefiting from the continuous 3D heat transfer path provided by the stacked BPT particles. Considering the outstanding overall performance, the prepared composite PCMs have the potential to be suitable for the application of high efficiency thermal management and solar energy utilization.

Vapor Nanobubbles around Heated Nanoparticles: Wetting Dependence of the Local Fluid Thermodynamics and Kinetics of Nucleation.

Plasmonic nanobubbles are composite objects resulting from the interaction between light and metallic nanoparticles immersed in a fluid. Plasmonic nanobubbles have applications in photothermal therapies, drug delivery, microfluidic manipulations, and solar energy conversion. Their early formation is, however, barely characterized due to the short time and length scales relevant to the process. Here, we investigate, using molecular dynamics (MD) simulations, the effect of nanoparticle wettability on both the local fluid thermodynamics and the kinetics of nanobubble generation in water. We first show that the local onset temperature of vapor nucleation decreases with the nanoparticle/water interfacial energy and may be 100 K below the water spinodal temperature in the case of weak nanoparticle/water interactions. Second, we demonstrate that vapor nucleation may be slower in the case of weak water/nanoparticle interactions. This result, which is qualitatively at odds with the predictions of isothermal classical nucleation theory, may be explained by the competition between two antagonist effects: while, classically, hydrophobicity increases the vapor nucleation rate, it also penalizes interfacial thermal transfer, slowing down kinetics. The kinetics of heat transfer from the nanoparticle to water is controlled by the interfacial thermal conductance. This quantity turns out not only to decrease with the nanoparticle hydrophobicity but also drops down prior to phase change, yielding even longer nucleation times. Such conclusions were reached by considering the comparison between MD and continuous heat transfer models. These results put forward the role of nanoparticle wettability in the generation of plasmonic nanobubbles observed experimentally and open the path to the control of boiling using nanopatterned surfaces.

Synergistic Improvement of Dielectric and Thermal Conductivity Properties for Polymers Filled with Multifunctional Modified Nanowires.

Dielectric composites are widely used in power electronics, power systems, aerospace, and other fields due to their extremely high power density. However, if their energy density can be further increased, the application range will be greatly improved. Improving the dielectric constant of composites is one of the most effective ways to increase the energy density. In this study, a preparation method for copper calcium titanate nanowires (CCTO-NWs) with adjustable aspect ratio was investigated. Upon incorporation of these CCTO-NWs into the polymer matrix, the nanocomposites exhibit a significantly higher dielectric constant and a lower dielectric loss. In addition, a thin layer of Al2O3 with excellent thermal conductivity is coated on the surface of the CCTO-NWs to form a core-shell structure nanowire CCTO-NW@Al2O3. The introduction of the thermal conductive layer of Al2O3 not only creates a continuous heat transfer path within the dielectric composite, increasing the thermal conductivity of the composite from 0.11 W/(m·K) of pure HIPS to 1.12 W/(m·K), but also serves as a buffer layer between HIPS and CCTO-NWs, effectively alleviating the electric field distortion caused by the large difference in the dielectric constant between them, thereby optimizing the dielectric properties of the composite and reducing the dielectric permeability threshold from 30 to 20 vol %. This work provides an effective strategy for synergistically improving the dielectric constant and thermal conductivity of dielectric composites while also taking into account the good flexibility of polymer/ceramic nanocomposites.

FMDL: Federated Mutual Distillation Learning for Defending Backdoor Attacks

Federated learning is a distributed machine learning algorithm that enables collaborative training among multiple clients without sharing sensitive information. Unlike centralized learning, it emphasizes the distinctive benefits of safeguarding data privacy. However, two challenging issues, namely heterogeneity and backdoor attacks, pose severe challenges to standardizing federated learning algorithms. Data heterogeneity affects model accuracy, target heterogeneity fragments model applicability, and model heterogeneity compromises model individuality. Backdoor attacks inject trigger patterns into data to deceive the model during training, thereby undermining the performance of federated learning. In this work, we propose an advanced federated learning paradigm called Federated Mutual Distillation Learning (FMDL). FMDL allows clients to collaboratively train a global model while independently training their private models, subject to server requirements. Continuous bidirectional knowledge transfer is performed between local models and private models to achieve model personalization. FMDL utilizes the technique of attention distillation, conducting mutual distillation during the local update phase and fine-tuning on clean data subsets to effectively erase the backdoor triggers. Our experiments demonstrate that FMDL benefits clients from different data, tasks, and models, effectively defends against six types of backdoor attacks, and validates the effectiveness and efficiency of our proposed approach.

Fast continuous patch-based artistic style transfer for videos

Fast continuous patch-based artistic style transfer for videos

An Ultrahigh‐Rectification‐Ratio WSe2 Homojunction Defined by High‐Efficiency Charge Trapping Effect

AbstractAlthough 2D material van der Waals heterostructures (vdWHs) exhibit many novel properties and applications, 2D homojunctions have unique advantages in interface lattice matching, band continuity, and charge transfer efficiency. However, the rectification performances of 2D homojunction diodes are severely limited by the small junction barrier, mainly due to inefficient charge doping. In this work, an ultrahigh‐rectification‐ratio WSe2 homojunction diode achieved by the semi‐floating gate doping of graphdiyne oxide (GDYO) is reported. Utilizing the WSe2/GDYO direct charge trapping mode can free the inhibition of charge capturing efficiency by removing conventional insulating barriers and thus improve the rectification ratio. The C─C(sp) and oxygen‐containing functional groups in the GDYO layer can provide outstanding charge‐trapping ability due to their unsaturation. Furthermore, the oxygen plasma treatment used for oxidizing graphdiyne (GDY) into GDYO can make GDYO a flatter surface, thus creating strong‐coupling WSe2/GDYO interfaces to improve the charge transfer efficiency and enhance the electrostatic doping effect. Besides, the WSe2/GDYO interfaces are confirmed to possess a higher junction barrier than that of the WSe2/GDY interfaces. This research proposes a brand‐new approach to building p–n junctions via charge trapping and the homojunction diode with a record‐highest rectification ratio of up to 106 is obtained.

Rapid Charge Transfer Enabled by Noncovalent Interaction through Guest Insertion in Supercapacitors based on Covalent Organic Frameworks.

Covalent organic frameworks (COFs) have been proposed for electrochemical energy storage, although the poor conductivity resulted from covalent bonds limits their practical performance. Here, we propose to introduce noncovalent bonds in COFs through a molecular insertion strategy for improving the conductivity of the COFs as supercapacitor. The synthesized COFs (MI-COFs) establish equilibriums between covalent bonds and noncovalent bonds, which construct a continuous charge transfer channel to enhance the conductivity. The rapid charge transfer rate enables the COFs to activate the redox sites, bringing about excellent electrochemical energy storage behavior. The results show that the MI-COFs exhibit much better performance in specific capacitance and capacity retention rate than those of most COFs-based supercapacitors. Moreover, through simply altering inserted guests, the mode and strength of noncovalent bond can be adjusted to obtain different energy storage characteristics. The introduction of noncovalent bonds is an effective and flexible way to enhance and regulate the properties of COFs, providing a valuable direction for the development of novel COFs-based energy storage materials.

Rapid Charge Transfer Enabled by Noncovalent Interaction through Guest Insertion in Supercapacitors based on Covalent Organic Frameworks

AbstractCovalent organic frameworks (COFs) have been proposed for electrochemical energy storage, although the poor conductivity resulted from covalent bonds limits their practical performance. Here, we propose to introduce noncovalent bonds in COFs through a molecular insertion strategy for improving the conductivity of the COFs as supercapacitor. The synthesized COFs (MI−COFs) establish equilibriums between covalent bonds and noncovalent bonds, which construct a continuous charge transfer channel to enhance the conductivity. The rapid charge transfer rate enables the COFs to activate the redox sites, bringing about excellent electrochemical energy storage behavior. The results show that the MI−COFs exhibit much better performance in specific capacitance and capacity retention rate than those of most COFs‐based supercapacitors. Moreover, through simply altering inserted guests, the mode and strength of noncovalent bond can be adjusted to obtain different energy storage characteristics. The introduction of noncovalent bonds is an effective and flexible way to enhance and regulate the properties of COFs, providing a valuable direction for the development of novel COFs‐based energy storage materials.

Performance evaluation of sulfidated nanoscale iron for hexavalent chromium removal from groundwater in sequential batch study.

Chromium [Cr] contamination in groundwater is one of the serious environmental concerns due to the carcinogenicity of its water-soluble and mobile hexavalent [Cr(VI)] form. In spite of the existence of multiple precipitation and adsorption-based Cr(VI) remediation technologies, the usage of sulfidated nano zerovalent iron (S-nZVI) has recently attracted researchers due to its high selectivity. Although S-nZVI effectively immobilized Cr(VI), its long-term performance in multiple shifted equilibrium has not been explored. In this contribution, influences of S-nZVI dosage, initial concentration of Cr(VI), pH, ionic strength, total hardness, sulfate, carbonate, and silicate were probed in ultrapure water. Further experiments were performed in synthetic groundwater to investigate the effects of initial concentration of Cr(VI) in the pH range of 4-8 for 1g L-1 S-nZVI dosage. Cr(VI) removal rate was quantified in groundwater without pH fixation. Finally, a comparative study between conventional nano zerovalent iron (nZVI) and S-nZVI was conducted in sequential batch reactors to investigate their respective efficiencies during repeated usage. Mechanistic interpretation of the processes governing the immobilization of Cr(VI) was done by integrating the results of these experiments with the metadata. While aggregation due to magnetic properties and rapid oxidation of Fe decreased the efficiency of nZVI with repeated usage, sulfidation minimized the passivation and favored an extended reducing environment because of continuous electron transfer from iron and sulfur components.

Internationalization of Indonesian Language Towards World Language

The aim to be achieved in this study is to describe efforts to internationalize Indonesian for Indonesian citizens domiciled in the Netherlands. This research is categorized into descriptive research types. The population of this study is an entire Indonesian citizen domiciled in the Netherlands, especially in Denhag City and its surroundings. Data collection was carried out through the distribution of questionnaires to 20 respondents who became research samples, while data analysis was carried out using percentage techniques. The results showed that efforts to internationalize Indonesian in the Netherlands follow five aspects that cause a language to survive its speakers. First, it has a large number of speakers of the language; this was evident for Indonesian in the Netherlands. Second, language loyalty that encourages the people of a language to maintain their language, and if necessary prevent the influence of other languages; This can be seen from the frequency of Indonesian citizens using Indonesian, especially in the family and workplace environment. Third, language pride that encourages people to develop their language and use it as a symbol of community identity and unity; This can be proven clearly through various activities carried out by Indonesian citizens while still using Indonesian. Fourth, awareness of the norm that encourages people to use their language carefully and politely. Fifth, there is a continuous transfer of spoken language from the previous generation to the next; This has been proven by Indonesian citizens by getting used to the use of Indonesian in the household environment so that their sons and daughters can still speak Indonesian and fluent in Indonesian

Exploring the origin of wear in cemented carbides via molecular dynamics simulations

In this work, the experimentally observed tribological phenomena of WC-Co cemented carbides were interpreted on the atomic scale using molecular dynamics simulations. It was demonstrated that the friction-induced deformation was mainly coordinated by dislocations slip in both Co and WC phases, along with the local rotation of WC grains adjacent to the Co binder. The dislocation motion within the subsurface Co phase was crucial for the continuous transfer of stress across WC/Co interfaces. The fracture of WC grains, which frequently occurs in various friction processes, was found to result from interactions between the internal partial dislocations. This caused formation of atomic-scale micro-voids early at the intersection. Significantly higher tensile stress existed at the WC/WC grain boundaries, which resulted in a higher risk of intergranular cracking compared to that at the WC/Co interfaces during the friction process. The findings in the present study facilitate to understand the tribological behavior of a variety of cermet materials hence to improve their wear resistance.

Highly conductive diamond skeleton reinforced Cu-matrix composites for high-efficiency thermal management

The weak interfacial bonding strength between diamond and copper intrinsically restricts the enhancement of the thermal conductivity of diamond particles/copper composites (abbreviated as DP/Cu). This work first proposed the diamond skeleton (DS) as the reinforcement element rather than dispersed diamond particles. The tungsten (W) transition layer (c.a. ∼300 nm thick) having adequate thermal expansion coefficient was sputtered onto the surface of DS via vacuum evaporation technology, aiming to improve the wettability between diamond and copper and accordingly increase the thermal conductivity of DS/copper composites extruded by gas pressure infiltration technique. The experimental results show that the coated W layer can effectively improve the wettability of the diamond surface and reduce the wettability angle from 108.6° to 13.2°. Raman and XRD spectra show that the W layer can, to a great extent, prevent the graphitization of the diamond surface. SEM and EDX evidence a continuous heat transfer path of DS inside the composites. The thermal conductivity of the DS/Cu composite with low diamond loading of 18.4 vol% reaches 575 W/mK, 43.3% higher than that of pure Cu. Finite element simulations show that DS exhibits excellent heat transfer characteristics, agreeing well with the thermal conductivity simulation results.

Investigation on interphase mass transfer coefficient of a deformable bubble with density contrast using phase-field lattice Boltzmann method

The gas–liquid mass transfer process with density contrast is modeled in this paper using a phase-field Lattice Boltzmann (LB) method. In this method, the phase-field model used to calculate the flow field and the continuous species transfer model used to calculate the concentration distribution are coupled by introducing the divergence condition of the velocity in the presence of mass transfer into the Allen-Cahn equation. For a deformable bubble rising in stagnant liquid, a two-dimensional parameter dependence study is conducted and the results indicate that an increase in initial diameter, as well as a decrease in liquid diffusion coefficient or liquid viscosity, can improve the steady-state value for the Sherwood number, whereas the distribution coefficient has a little impact on this steady-state value. Furthermore, a correlation originally proposed by Takemura and Yabe (1998) modified with a shape factor can be used to predict the steady-state Sherwood number in the numerical results.

Towards continual knowledge transfer in modeling manufacturing processes under non-stationary data streams

Towards continual knowledge transfer in modeling manufacturing processes under non-stationary data streams

Effect of the laser-wire relative position on the wire-based laser-directed energy deposition of in-situ synthesis Ti/TiB/TiC composite coatings

Laser-directed energy deposition (LDED) with a Ti-B4C cored wire was utilized to synthesize the TiB- and TiC-reinforced titanium matrix composite coatings for enhancing the tribological performance of Ti alloys. The wire transfer behaviors, microstructural characteristics and wear performance of the coatings were investigated at two different laser-wire relative positions. The wire deposition better adapted to varying processing parameters when the wire tip was placed in the anterior portion of the laser-irradiated region, which resulted in the continuous bridging transfer mode. This enabled favorable process stability, track formability, and microstructure homogenization. The representative LDEDed coatings were dominated by TiB/TiC composite structures characterized by the embedding of TiC dendrites into TiB hollow prisms. The formation of TiB/TiC composite structures was related with the heterogeneous nucleation on the coherent (010)TiB//(101)TiC interface, of which the two-dimensional lattice mismatch was only 5.500%. A well-defined three-phase orientation relationship between the α-Ti matrix and reinforcements of TiB and TiC was identified as [112¯1]α-Ti//[01¯0]TiB//[101]TiC. This relationship improved interface stability and restrained the interfacial debonding under an imposed load. The typical LDEDed coating produced by the continuous bridging transfer mode possessed the desired combination of high hardness and low wear rate, which was primary attributable to the direct load-bearing effect of the tightly combined TiB/TiC intergrowth structures and the indirect load-sharing effect of the TiBw/TiCp eutectic phases.

Numerical thermomechanical modelling of lava dome growth during the 2007–2009 dome-building eruption at Volcán de Colima

SUMMARY Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007–2009. The mathematical model treats the lava dome extrusion dynamics as a thermomechanical problem. The equations of motion, continuity and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e. the distributions of the temperature, crystal content, viscosity and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome–air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermomechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyse effusive eruptions, dome morphology and carapace evolution including its failure potentially leading to pyroclastic flow hazards.

Deep operator learning-based surrogate models with uncertainty quantification for optimizing internal cooling channel rib profiles

This paper focuses on designing surrogate models that have uncertainty quantification capabilities to effectively improve the thermal performance of rib-turbulated internal cooling channels. To construct the surrogate, we use the deep operator network (DeepONet) framework, a novel class of neural networks designed to approximate mappings between infinite-dimensional spaces using relatively small datasets. The proposed DeepONet takes an arbitrary rib geometry as input and outputs continuous detailed pressure and heat transfer distributions around the profiled ribs. The datasets needed to train and test the proposed DeepONet framework were obtained by simulating a 2D rib-roughened internal cooling channel. To accomplish this, we continuously modified the input rib geometry by adjusting the control points according to a simple random distribution with constraints, rather than following a predefined path or sampling method. The studied channel has a hydraulic diameter, Dh, of 66.7 mm, and a length-to-hydraulic diameter ratio, L/Dh, of 10. The ratio of rib center height to hydraulic diameter (e/Dh), which was not changed during the rib profile update, was maintained at a constant value of 0.048. The ribs were placed in the channel with a pitch-to-height ratio (P/e) of 10. In addition, we provide the proposed surrogates with effective uncertainty quantification capabilities. This is achieved by converting the DeepONet framework into a Bayesian DeepONet (B-DeepONet). B-DeepONet samples from the posterior distribution of DeepONet parameters using the novel framework of stochastic gradient replica-exchange MCMC. Finally, we demonstrate the performance of the proposed DeepONet-based surrogate models with uncertainty quantification by incorporating them into a constrained, gradient-free optimization problem that enhances the thermal performance of the rib-turbulated internal cooling channel.

In-situ engineering of 3D porous Co nanoparticles incorporated in B/N Co-doped carbon nanotube/nanofiber networks as integrated cathode materials for Zn-air batteries

Rational design and construction of low-cost and highly efficient bifunctional catalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for the commercialization of the rechargeable Zn-air batteries (ZABs). Herein, a 3D self-standing bifunctional catalytic electrode has been successfully achieved by in-situ confinement of Co nanoparticles into B/N co-doped carbon nanotube/nanofiber well-integrated networks (Co-B/N-CNTs@CFs). The purpose of designing such a 3D network structure is to optimize the electronic structure of the active sites for high electrocatalytic activity, ensure continuous and fast electron and charge transfer for high utilization of active sites, and avoid the abscission and aggregation of nanocatalysts for high electrocatalytic stability, which is confirmed by a series of experimental, characterization, and theoretical studies. As a result, the Co-B/N-CNTs@CFs as integrated cathode materials deliver efficient and stable OER/ORR performance with a ΔE of 0.59 V, largely outperforming the benchmark Pt/C-RuO2 electrode (0.71 V), and hence leading to appealing applications in both the assembled aqueous and flexible solid-state ZABs. This study forges a new path for the production of integrated cathode while enhancing their superiority, allowing for the construction of energy storage devices.

Pore‐Scale Modeling of Coupled CO2 Flow and Dissolution in 3D Porous Media for Geological Carbon Storage

AbstractDissolution trapping is one of the crucial trapping mechanisms for geological carbon storage in deep saline aquifers. The injected supercritical CO2 (scCO2) flow and dissolution processes are coupled and interact with each other. Therefore, we performed direct numerical simulations in three‐dimensional micro‐CT images of sandstones using the volume of fluid and continuous species transfer method. We investigated the coupled scCO2 flow and dissolution processes at pore‐scale under different rock structures, capillary numbers, and rock wettability conditions. The dynamic evolution of the scCO2/brine phase distribution and scCO2 concentration distribution occurring during the injection period were presented and analyzed. Complicated coupling mechanisms between scCO2‐brine two‐phase flow and interphase mass transfer were also revealed. Our results showed that the scCO2 dissolution was highly dependent on the local distribution of scCO2 clusters. The rock with relatively high porosity and permeability would have more capacity for scCO2 injection resulting in a faster and greater dissolution of scCO2 in brine. The effect of capillary number on the scCO2 dissolution process was related to the range of capillary number. The effective upscaled (macro‐scale) mass transfer coefficient (kA) during scCO2 dissolution was evaluated, and the power‐law relationship between kA and Péclet number was obtained. Rock wettability was found to be another factor controlling the scCO2 dissolution process by affecting the scCO2‐brine interfacial area. Our pore‐scale study provides a deep understanding of the scCO2 dissolution trapping mechanism, which is important to enhance the prediction of sequestration risk and improve sequestration efficiency.