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High water contact angle in carbon fiber can facilitate water removal ability of gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs). Water contact angle is intensively dependent on the surface hydrophobicity of carbon fiber in GDL. In this study, the hydrophobicity of commercial GDL is enhanced through the immersion and hydrothermal methods. The porosity decreases slightly while the surface roughness and surface topology diversity increase significantly in hydrothermal GDL compared with commercial reference and immersion GDL samples. The molecular dynamics simulations show that the water contact angle increases significantly with the increasing surface roughness but varies slightly with different surface topology, indicating that the water contact angle is dominated by the surface roughness. This study's findings are expected to offer an approach that can effectively enhance the water removal capacity by tailoring the surface roughness of carbon fibers in GDL materials.

Base on the GaAs plasmonic solar cell, a three-dimensional numerical model is proposed for the photoelectrical and photothermal processes. In the model, the coupled processes of nanoparticle photothermal conversion and substrate photoelectrical conversion are accounted for with FDTD solver and DEVICE solver. The Finite-Difference-Time-Domain method is used in the FDTD solver to analyze the light absorption process. The light absorption efficiency, quantum efficiency ratio of plasmonic solar cells to bare solar cells, and temperature distributions of the nanoparticles and substrate surface are obtained. A dimensionless coefficient for the substrate temperature rise is proposed to characterize the photothermal performance of the investigated plasmonic solar cell. The nanoparticles create parasitic absorption, increase substrate light scattering, and improve light absorption. Spherical Ag nanoparticles hold a higher photoelectrical conversion efficiency than spherical Au nanoparticles with an acceptable temperature increase, while spherical Au nanoparticles have stronger thermal sensitivity than spherical Ag nanoparticles. The cylindrical nanoparticles (Au or Ag) contribute significantly to the photothermal performance but do not contribute to the enhancement of the overall integrated quantum efficiency ratio. The nanoparticle arrays have accumulated heating and interference effects that enhance the thermal response. Spherical Ag nanoparticles are recommended for photoelectrical devices, while cylindrical Ag and Au nanoparticles are suitable for the development of thermal sensors.

Sub-bottom profiling traditionally uses low-frequency signals (less than 20 kHz) to examine layered structures of the bottom sediment in large depth, but it has some limitations in deep-sea surveyi...

Summary Gas transport in nanoporous media is controlled by both the nanoscale mechanisms and complex pore structure, details of which can accurately capture the detailed gas-transport behavior. However, direct-simulation methods in large digitized samples are not feasible because of high memory and computational-time demands. Furthermore, our previous work (Landry et al. 2016) shows that when resolution of the digitized sample is not ample, the sample has to be further magnified up to five times along each linear dimension to achieve the desired accuracy. Here we propose a local-effective-viscosity multirelaxation-time lattice Boltzmann pore-network coupling model (LEV-LBM-PNM) to tackle these problems. We ran a large number of LEV-LBM simulations in high-resolution geometries with simple cross sections that had surface roughness added to them in a controlled manner. Such carefully selected geometries were run at a large number of pressure conditions to establish gas-flux correlations that depend on shape, Knudsen number, and surface roughness and can be directly used in PNM to account for all of those properties. The semianalytical gas-transport models for a single pore with various cross-sectional shapes and surface roughness were established using the LEV-LBM simulation results. The established semianalytical gas-transport model is then implemented into a 3D pore-network model to investigate the gas-transport behavior at various conditions. In an example application, the pore-network model was extracted from a Marcellus Shale focused-ion-beam scanning-electron-microscopy (FIB-SEM) image using the maximum inscribed sphere method. We found that the proposed LEV-LBM-PNM accurately predicts gas apparent permeability by accounting for gas slip in irregular pore shape and surface roughness.

Lithium ion batteries have been widely used in the power-driven system and energy storage system. While thermal safety for lithium ion battery has been constantly concerned all over the world due to the thermal runaway problems occurred in recent years. Lithium ion battery has high temperature sensitivity and the relatively narrow operating temperature range because of the complex electrochemical reactions at different temperatures. And the temperature change, including the global temperature change in different seasons and the local temperature rise that is induced by its self-heating etc., can trigger side reactions and then lead to thermal runaway, which should be further considered to ensure thermal safety of lithium ion battery. This review summarizes the inducements of thermal runaway and relevant solutions, spanning a wide temperature range. The low temperature induced issues, such as capacity fade and lithium plating and dendrite, can cause internal short circuit (ISC), while as the temperature is above the critical temperature, the speeding of side reactions and reduction of lifespan (T ​> ​40 ​°C) and thermal runaway (T ​> ​90 ​°C) will be triggered. In order to solve the thermal issues in batteries, extensive approaches have been investigated to prevent the occurrence, propagation and deterioration of thermal runaway, from the perspective of material to the battery system. The triggered mechanism at a wide temperature range, key factors for thermal safety and the effective heat dissipation strategies are concluded in this review. This review is expected to offer effective thermal safety strategies and promote the development of lithium ion battery with high-energy density.

Side-channel analysis concerns cryptanalytic attacks that exploit the physical environment of cryptographic modules by analyzing leaking emanations and obtaining the encryption key. We propose a multiple-input, multilayer-perceptron-based method for classifying power traces, in which a probability is assigned to each class, indicating the likelihood that each trace corresponds to the label for further recovering the key.

Installing blocks in cathode flow field can effectively enhance the transfer of oxygen from channel to the reaction sites of catalyst layer, thus boosting the performance of the fuel cell. In this work, an optimization methodology combined with genetic algorithm and three-dimensional fuel cell modeling is developed to optimize the design of partially blocked channel for a proton exchange membrane fuel cell (PEMFC) with parallel flow field. In the optimization, the heights of the blocks are assumed to be linearly increased and two parameters (i.e., height of the first block and the height increase between adjacent blocks) are considered. The impact of the optimized design of the blocked channel on cell performance is analyzed, and the effects of the optimized blocked channel designs with increasing-height and uniform-height block height distributions were also compared in detail. With this optimization methodology, the optimal height distribution of the blocks in the channel can be obtained for various block numbers. With varying the block numbers, the cell voltage and net cell power are firstly improved until the maximal values reached and then lowered. The maximal net cell power is reached for the block number of 16. As compared with the flow channel without adding blocks, the net power of the PEMFC can be enhanced by about 10.9%. For pressure drop behavior, with the optimized block height distribution, the total pressure drop in cathode flow field can be maintained in similar level with varying block numbers from 4 to 20. Considering both the net power and pressure drop, the optimized blocked channels with adding 8 to 16 blocks are recommended in this study. Besides, it is indicated that the performance of the optimized block design with increasing-height is higher than that of the optimized block design with uniform-height.

We present a comprehensive analysis of a solar photovoltaic/thermal system combined with phase change material, i.e., a PV/T-PCM system. A fatty acid was chosen as the PCM with a phase transition temperature of 37 °C. A solar collector filled with PCM, which contained rectangular metal fins to enhance heat transfer, was used to cool the PV. Four-day experimental measurements were carried out under real outdoor climatic conditions in Shanghai, China. During the experiment, we examined two different intermittent thermal regulation strategies using a water circulation loop in the PV/T-PCM system to improve the overall solar energy utilization efficiency, and detailed comparisons were performed. The results indicated that the use of PCM in the solar collector could significantly mitigate the temperature fluctuation of the PV panel and improve the photoelectric efficiency. Due to the low thermal conductivity of fatty acid, the temperature stratification in the solar collector was still significant even with the addition of metal copper fins. The thermal regulation strategy of setting the temperature at 45 °C gave better performance and the overall efficiencies of Case 1 and Case 3 could reach approximately 91%. The overall efficiency of Case 3 and Case 4 was approximately 85% with the thermal regulation strategy of setting the temperature at 50 °C. More heat could be removed from the PCM in the solar collector using the relatively low temperature setting of the thermal regulation strategy. It was concluded that the overall energy utilization ratio of the PV/T-PCM system can be improved through a reasonable thermal regulation strategy; however, further work on the economics analysis of the system is still needed.

Solar–thermal water evaporation (SWE) has received much interest in recent years due to a few seminal works on materials innovation and thermal management. With many studies proposing applications ...

Maneuver models are dedicated to accurate representation of unknown motion pattern. However, for near space hypersonic jump gliding targets of high speed, diverse movement pattern, and mobility, the conventional maneuver models are difficult to describe the complex movement characteristics, and then leading to high and unstable tracking error. In order to solve this problem, a new model is proposed based on the attenuation of oscillation function. The core of the model is to consider the target acceleration as a zero mean random process with attenuation oscillation. With the model, the equations of the maneuvering target are constructed and the system dynamic error of this model was deduced taking Kalman filter as the filtering algorithm. Moreover, the corresponding relations among parameters are discussed, and an adaptive method is proposed for setting parameters appropriately in the situations when a priori information is unknown. In this way, the parameters can be adjusted online through jumping point identification. Theoretical analysis and simulation experiments are conducted to demonstrate the effectiveness of the proposed model. Comparing to commonly used models, it shows lower filtering errors tracking near space hypersonic jump gliding targets. Finally, the rationality and validity of the parameters adaptive method are explained.

Plain woven C/SiC composites have been widely applied in engineering thermal protective structures due to their excellent mechanical and physical properties. Plain woven C/SiC orthotropic composites are composed of carbon fibers, and in-yarn and out-of-yarn SiC matrixes with small air pores. Experimental studies on the effective thermal conductivities of plain woven C/SiC composites are rare due to their complex structure and costly processing technology. The effects of fiber volume fraction and porosity on the effective thermal conductivities can be revealed by numerical approach. In the present study, a finite volume numerical model at three scale levels is proposed on the basis of 3D geometric reconstructions with in-yarn and out-of-yarn porosities. The thermal conductivities of SiC matrix, woven yarn, and plain woven C/SiC composites are predicted using up-scaling approach. The proposed model is validated using available analytical and experimental results. The thermal conductivities of plain woven C/SiC composites decrease with the increment in carbon fiber volume fraction, and in-yarn and out-of-yarn porosities. The effect of out-of-yarn porosity on the thermal conductivities of the composites plays a dominant role. However, the occurrence of in-yarn porosity can lead to maximum decreases of 3.1% and 5.6% for in-plane and out-of-plane thermal conductivities respectively compared with the case without in-yarn porosity. The present work can provide a scientific guidance for the thermal design of plain woven C/SiC composites.

In the conventional vanadium redox flow battery, the bipolar plates are usually designed with flow fields to improve the battery performance by facilitating the homogeneous distribution of electrolytes. The introduction of flow field results in severer oxidation corrosion, owing to the sharp edges and corners formed on the flow fields. In this study, a modified battery structure for the vanadium redox flow battery is proposed to alleviate the oxidation corrosion of the bipolar plates and flow fields. The flow fields are segmented from the bipolar plates, and inserted between the porous electrodes and membrane as independent components. To improve the service life and processability, the flow fields are prepared with photosensitive resin by means of the three-dimensional printing technique. A battery with the modified structure is assembled to examine the battery performance and oxidation resistance. Morphology characterization and elemental composition analysis are employed to investigate the oxidization on the bipolar plate surface. The modified battery structure contributes to decreasing the contact resistance. The pressure drop and charging/discharging tests indicate that the battery with the modified structure exhibits maintained flow behavior and energy efficiency, and provides a higher Coulombic efficiency compared to the conventional vanadium redox flow battery. Moreover, the bipolar plates in the modified battery structure demonstrate a higher capacity to restrain oxidation corrosion during the charging process. The modified battery structure can enhance the service life of bipolar plates and flow fields, and is significant in the application of vanadium redox flow battery.

Arsenic (As) is a carcinogenic metalloid that poses serious health and environmental threats to human. We explored the potential of Dahlia pinnata Cav., which is a known ornamental plant, f...

Lateral flow assays (LFAs) have been extensively used as point-of-care testing platforms because they are inexpensive, portable, simple, and rapid, which particularly improve their availability in resource-poor settings. However, the poor sensitivity of LFAs restricts their further applications. Herein, we proposed a novel and simple method to enhance the detection sensitivity of LFAs by embedding cotton thread-based barriers into paper and further integrating them into strips to decrease the flow rate of sample and extend the reaction time. The number and hydrophilicity of the embedded cotton threads were sequentially optimized. The flow rate of liquid in cotton thread-embedded LFAs was mathematically simulated using a circuit-like model and the simulation results are consistent with the experimental results. With using human immunodeficiency virus nucleic acid as a model target, the cotton thread-embedded LFAs presented a fourfold enhancement in detection sensitivity compared to that of the unmodified LFAs. The strategy of embedding cotton threads into paper possesses great potential for fabricating other paper-based microfluidic devices in the future.

The micro-scale effect of Al 2 O 3 particle on the deformation behaviors of the copper matrix was investigated using nanoindentation. Moderate strengthening effects were produced by the Al 2 O 3 as indicated from the mechanical deformation evolutions. Specifically, the displacement recovery ratio and elastic work ratio is 6% and 9% higher for the Cu-5 wt% Al 2 O 3 (C5A) composite material compared with that of the pure copper (PC) material, respectively. While for the indentation hardness and indentation modulus, the increment is 36% and 75%, respectively. Notably, the moderate strengthening effects were quantitatively illuminated from the power law index m for the C5A indent (1.2) and PC indent (1.1–1.3). In addition, synergetic strengthening effects were proposed from the microstructure evolutions in the C5A composite material. Specifically, the increment in yield strength deduced from the grain refinement is 120 MPa, which is 67% higher than that of the Al 2 O 3 particle dispersion strengthening. The synergetic strengthening effects revealed from the microstructure evolutions are expected to provide new strengthening approaches for the ceramic particle reinforced metal matrix composite materials.

The effects of compression deformation of gas diffusion layer (GDL) on the performance of a proton exchange membrane fuel cell (PEMFC) with serpentine flow field were numerically investigated by coupling two-dimensional GDL mechanical deformation model based on Finite Element Analysis and three-dimensional two-phase PEMFC model with incorporating the deformation impacts. Emphasis is located on exploring the influences of assembly pressure on the non-uniform geometric deformation and distributions of transport properties in the GDL, flow behaviors and local distributions of oxygen and current density, cell polarization curves and net power densities of the PEMFC. It was indicated that the non-uniform deformation of GDL results in inhomogeneous distributions of porosity and permeability in the GDL due to the presence of rib-channel pattern, and the transport properties in the under-rib region are greatly reduced with increasing the assembly pressure, consequently weakening the gas flow and oxygen transport in the under-rib region and increasing the non-uniformity of local current density distribution. As for the overall cell performance, however, attributed to the tradeoff between the adverse impacts of GDL compression on mass transport loss and positive effects on reducing ohmic loss, the overall cell performance is firstly increased and then decreased with increasing assembly pressure from 0 MPa to 5.0 MPa, and the maximum cell performance can be achieved at the assembly pressure of about 1.0 MPa for all cases studied. As compared with the case for zero assembly pressure, the maximum net power density of the cell can be improved by about 7.7%, 9.9%, 10.5% and 10.7% for the cathode stoichiometry ratios of 2.0, 3.0, 4.0 and 5.0@iref = 1 A·cm−2, respectively. Practically, it is suggested that the assembly pressure is controlled in an appropriate range of 0.5 MPa–1.5 MPa such that the cell net power can be boosted and pressure head requirement for the pump can be maintained in a appropriate level.

Battery warming at low temperature is a critical issue affecting battery thermal management. In this study, the pulse self–heating strategy is proposed to enable quick and safe warming of lithium–ion battery at low temperature. The battery is heated up using pulse self–discharge. This strategy can heat up 18,650 commercial battery with a control circuit and alleviate the battery degradation during heating. Compared with continuous direct current self–heating, the battery can be heated up from −10 °C to 10 °C by pulse heating within 175 s while the direct current heating consumes 280 s with approximating polarization voltage. The effects of ambient temperature, switching interval, and initial state–of–charge on heating performance are further investigated. Heating duration is found to be insensitive to the switching interval in the studied range. Conversely, battery internal resistance and off–period voltage at different ambient temperatures and initial state–of–charges are found to be the predominant factors that influence heating duration. Heating duration in the range of 150–180 s is achieved at ambient temperature ranging from −10 °C to 0 °C. In real applications, pulse heating is recommended to be performed at higher initial state–of–charge (>0.8), at which heating duration is within 200 s.

Plasmonic solar cells include metal nanoparticles deposited on the top surface of substrate, whose output performance is constrained by self-heating, light induced heating, and environmental conditions. In this study, a numerical model for coupled optical-thermal-electrical processes was developed for GaAs based plasmonic solar cells with nanoparticles (Ag, Au). Temperature fluctuation due to hotspots and thermalization was observed. Light absorption, thermalization power, and electric performance of the solar cells at various angles of incident irradiation were analyzed. Results show that the hot spot makes a significant uneven temperature distribution in the layers of plasmonic solar cells. Varied angles of incident irradiance can cause more fluctuation in thermalization power and electrical performance for plasmonic solar cells than for non-plasmonic ones. Ag nanoparticles can enhance the broad-spectrum light absorption (0.3–0.87 μm), and Au nanoparticles can enhance the light absorption near the cutoff wavelength of GaAs (0.7–0.87 μm). It was concluded that plasmonic solar cells with Ag nanoparticles have higher efficiency of optical-electrical conversion at wide angles (of incidence), whereas plasmonic solar cells with Au nanoparticles provide higher efficiency of optical-electrical conversion at a specific angle. Thus, by properly designing the nanoparticle properties, the thermalization loss can be reduced, and the electrical performance can be improved.

Thermal management of lithium–ion battery has become a critical issue in recent years. In this study, a thermal management module with a sandwich structure consisting of a battery, phase change material, and heat pipe is assembled. The battery temperature response is experimentally investigated for battery, heat pipe and phase change material composite with three discharge and charge cycles. A lumped thermal model is built to consider the coupling of battery heat generation, phase change material melting, and transient thermal response of heat pipe. The underlying coupling mechanism of battery temperature and phase change process is revealed at different environmental temperatures, heat transfer coefficients at condensation section, and thickness ratios of phase change material and battery. The model is validated with the experimental data in one discharge/charge cycle. A continuous safe cycling is difficult to maintain for battery with the air convection and only phase change material. The utilization of heat pipe can recover the latent heat of phase change material with an appropriate melting point at the end of each cycle to ensure a low battery temperature for long-time cycling. Four stages, namely, sensible heat, latent heat, solidification, and steady stage, are found in each cycle for the proposed cooling module. Then, the coupling mechanism of battery heat generation and heat transfer in heat pipe and phase change material is identified. The condensation section for heat pipe may operate at the unsustainable, sustainable, and uneconomic regions. To guarantee safe battery temperature, low energy consumption, and sufficient module energy density in long-time cycling simultaneously, the phase change material melting point is recommend to be at least 3 °C higher than environmental temperature, and the heat transfer coefficient in the condenser is recommended to range from 30 W/m2·K to 60 W/m2·K with an optimum thickness ratio of 0.17 associated with a phase change ratio of approximately 0.55.

Ionic wind generators have shown significant application potential in devices for cooling, air actuation, and flow control. In this study, a needle-to-ring electrode ionic wind generator with optimized parameters was employed to cool a heated copper plate. A three-dimensional numerical simulation was conducted to obtain the electric, flow, and temperature fields of the ionic wind generator. To verify the ionic wind generator's capacity to cool the heated plate, an ionic wind generator prototype was fabricated and experimentally tested. The temperature distribution of the plate heated by a uniform distributed heat flux and non-uniform heat flux with a local hot spot was analyzed. Results show that the applied voltage should be less than the threshold voltage of spark discharge to ensure effective and stable operation of the ionic wind generator. When the plate is heated by a uniform heat flux, the temperature distribution in most areas around the center of the plate is relatively uniform. If a hot spot exists, the temperature of the central plate is higher than that of the surrounding areas, and the radial temperature difference gradually increases with the increase of the hot-spot heat flux. Moreover, the high-temperature area in the center of the plate gradually expands with increasing hot-spot radius. Besides, the increase in the copper plate thickness has little influence on the final temperature distribution. The heated plate with a uniform heat flux below 2 kW/m2 could be cooled to below 80 °C by the ionic wind generator at an applied voltage of 11 kV. When the plate is heated by a non-uniform heat flux with a hot spot, compared with the experimental results of natural convection, ionic wind can effectively reduce the temperature of the plate (a temperature drop of at least 45 °C was observed). This study provides a potential solution for commercial chip cooling with needle-to-ring-type ionic wind generators.

The heat transfer mechanism in the gas adsorption of a Cu-benzene- 1, 3, 5-tricarboxylic acid particle adsorption bed is investigated by a model combining the lattice Boltzmann method with the grand canonical Monte Carlo method. The effects of distribution and thermal conductivity of the adsorption particle and types of adsorbates (CO2, CH4, and H2) on gas adsorption are discussed. The results indicate that in the fluid region, the temperature peak in the particle random range, low particle thermal conductivity, and CH4 adsorption are higher than those in other cases. In the solid region, the temperature peak is independent of the particle range, whereas the temperature peak in low particle thermal conductivity and CO2 adsorption are higher than those in other cases. In the case of high thermal conductivity of the adsorbate and particle, the adsorbent with low adsorption heat is recommended to improve the adsorption performance of the adsorption bed.

Shale is a kind of heterogeneous porous medium consisting of organic matter (OM), inorganic matter (IM), and interparticle pores. A modified lattice Boltzmann model is developed at the pore-scale to accurately predict the effective mass diffusivity of the heterogeneous shale structure by fully considering the multicomponent and irregular morphological features. The model is validated by the classic empirical formulas and numerical results of the shale with regular IM and OM skeletons. The effects of average gain diameter, irregular structural morphology, porosity, OM volume fraction, and OM diffusivity on the effective mass diffusivity are investigated. The effect of average gain diameter can be ignored. The Nield formula is capable of predicting the effective mass diffusivity of a random OM structure. The formula of Comiti and Renaud can be extended to predict the effective mass diffusivity of a random IM structure by modifying the empirical coefficient to 1.6. The effective mass diffusivity of the heterogeneous shale structure with random OM and IM is between that of pure IM and OM. This effective mass diffusivity increases with the increment of porosity, OM volume fraction, and OM diffusivity. A general empirical formula is proposed to calculate the effective mass diffusivity effectively and conveniently.

Heat leak (HL) has a significant influence on the thermal performance of loop heat pipes. It is difficult to measure the HL properties inside the evaporator through proper experiments. In this study, a one-dimensional numerical study is conducted for the HL simulation. A two-phase HL model is proposed, which takes into account the effects of the bubble generation on HL properties and systemic operations. Compared with the traditional conductive HL equation, the present model can clearly describe the two-phase transport characteristics in an evaporator core. The present model is validated by the experimental data of the loop heat pipe (LHP) at different heat loads and heat sink temperatures. The present model improves the prediction accuracy for radial HL in the variable-conductance mode of LHP. By coupling the one-dimensional two-phase HL model with the global LHP model, the two-phase transport properties in the evaporator core, the vapor temperatures, and the HL characteristics are investigated. Due to the existence of bubble generation, the equivalent thermal conductance between the evaporator and reservoir is increased. The HL amount is also induced to increase, which results in an increased vapor temperature especially in the variable-conductance region. The evaporator core contains the subcooled and saturated zones. The variation trends of the fluid temperature, heat transfer coefficient, equilibrium vapor quality, and void fraction are different in the two zones. The subcooled zone in the evaporator core is suggested to be enlarged in order to weaken the effects of bubbles on the system operation.

An ionic wind pump is an energy-saving device that can produce a volume flow when electrodes are applied with high voltage. Compared to the traditional methods, ionic wind pumps possess the advantages of low energy consumption, no moving parts, compact structure and flexible design. In this study, a large-size ionic wind pump, consisting of many single regular hexagonal needle-ring ionic wind generators, was developed as the preliminary model. However, its experimental performance was not as good as our expectations. In order to improve this preliminary model, a simulation method was used to investigate the configuration factors of the single ionic wind pump. In the optimized model, mesh gap is 6 mm, eccentricity is 0.26, section area is 238.44 mm2 and needle electrode number is 3. In subsequent experiments, the final optimized large-size ionic wind pump showed a great promotion in velocity, and the maximum average velocity of the optimized pump was higher than the preliminary model by 13.3%. Our numerical simulation and experiment results have practical significance in designing ionic wind pumps.

The gas flow field design has a significant influence on the overall performance of a proton exchange membrane fuel cell (PEMFC). A single-channel PEMFC with wedge-shaped fins in the cathode channel was proposed, and the effects of fin parameters such as volume (0.5 mm3, 1.0 mm3, and 1.5 mm3), number (3, 5, and 9), and porosity of the gas diffusion layer (GDL) (0.2, 0.4, 0.6, and 0.8) on the performance of PEMFC were numerically examined based on the growth rate of power density (GRPD) and polarization curve. It was shown that wedge-shaped fins could effectively improve the PEMFC performance. With an increase in fin volume, the distributions of oxygen mass fraction in the outlet area of the cathode channel were lower, the drainage effect of the PEMFC improved, and GRPD also increased accordingly. Similar results were obtained as the number of fins increased. The GDL porosity had a greater effect than the wedge-shaped fins on the improvement in PEMFC performance, but the influence of GDL porosity weakened and the GRPD of porosity decreased as the porosity increased. This study provides an effective guideline for the optimization of the cathode channel in a PEMFC.

When nanoparticles (NPs) enter into the biological system, a wide range of proteins will coat on their surfaces forming protein corona, which changes the initial synthetic characteristics of NPs to the biological identity, resulting in the loss of their targets or specially designed properties. Although pre-coating with proteins would reduce the protein corona formation, they may diminish the targeting moieties in the transport process. Patchy NPs can offer unique advantages of asymmetry, heterogeneity, and multi-functions. This has inspired us to use the asymmetry to realize the versatility of NPs, to accommodate stealth and targeting functions. In this study, we performed molecular dynamics simulations to investigate the adsorption mechanism between patchy NPs and human serum albumin, and the interaction mechanism between NP–HSA and the membrane. The results show that there is a high probability for HSA to interact with the hydrophobic, or charged brushes of patchy NPs. The adsorption sites, as calculated through the contact probability between NPs and the residues, depend on the NP surface properties. Furthermore, the HSA adsorption on NPs could improve the NP-membrane interaction. The simulation results provide deep understanding of the NP interaction mechanism, which would help the NP design for their biomedical applications.

Exploring thermally robust single atom catalysts (SACs) is of great significance. Here, we develop a universal strategy for stabilizing Pt atoms on the mono-oxygen vacancies of CeO2 with diverse exposed facets. The stabilization mechanism was proposed that the formed Pt-O-Ce interface will be taken into distortion spontaneously to keep thermodynamics stable through strong metal-support interactions. The highest degree of Pt-O-Ce distortion is achieved over Pt1-CeO2{100} material, which exhibits exceptional efficiency and thermal stability for oxygenated hydrocarbon removal. The enhanced adsorption capacity of O2 and methanol confirmed in the distortion interface is seen as another crucial reason for improving the stability of SACs. Methanol oxidation on Pt1-CeO2{100} obeys the L-H mechanism under relatively low temperature and then goes through to the MVK mechanism with temperature increasing. We believe that these results would bring new opportunities in the fabrication of SACs and applications of them in thermal reactions.

The traditional sound absorption problem has not been completely resolved over the last 200 years. At every stage, its research has changed depending on practical requirements and current technologies. Phononic crystals (PCs) and acoustic metamaterials (AMs) have gained attention because of their extensive investigation and development over the past 30 years. Especially, the use of these materials brings new vitality into the traditional sound absorption problem to figure out broad working band and low-frequency absorption. This review highlights recent progress in sound absorption—from airborne to waterborne absorption—and gradient-index AMs. Progress in gradient-index AMs is singled out because of their favorable impedance matching, good viscous and thermal dissipation, and lengthened propagation paths compared with those of other materials. The progress in sound absorption of PCs and AMs is promising to serve as the next-generation sound absorbing materials, trap and reuse acoustic energy, and attenuate earthquake/tsunami wave in the future., Graphical Abstract, Acoustics; Materials Design; Materials Structure; Metamaterials

In this experimental study, the after-treatment characteristics of urea-based selective catalytic reduction (urea-SCR) in a diesel engine was investigated at a low engine exhaust temperature (250 °C). This represented the idle state of diesel vehicles during road congestion. Detailed experimental work was performed on a heavy-duty diesel engine test bench under the World Harmonized Transient Cycle. The influence of the ammonia/nitrogen ratio was first investigated using vanadium-based SCR (V-SCR) catalyst. When the ammonia/nitrogen ratio was 1.0, the influences of space velocity on the after-treatment characteristics of two different configurations of V-SCR catalysts were investigated in terms of NOX emission, NH3 slip and NOX conversion efficiency. Small SV resulted in reduction of the NH3 slip and the coated-type catalyst indicated more NH3 slip than the extruded-type catalyst at equal catalyst dimensions. It was concluded that the extruded-type V-SCR catalyst showed better operating characteristics than did the coated-type V-SCR catalyst.

Since the good application of quantum mechanism in the field of communication, quantum secure communication has become a research hotspot. The existing quantum secure communication protocols usually assume that the quantum channel is noise-free. But the inevitable quantum noise in quantum channel will greatly interferes the transmission of quantum bits or quantum states, seriously damaging the security and reliability of the quantum system. This paper analyzes and discusses the performance of a $\chi$ state based steganography protocol under four main quantum noises, i.e., Amplitude Damping (AD), Phase damping (Phs), Bit Flip (BF) and Depolarizing (D). The results show that the protocol is least affected by amplitude damping noise when only the sender's first transmission in quantum channel is affected by quantum noise. Then, we analyze the performance of the protocol when both the sender's two transmissions are affected by quantum noise, and find that the specific combination of different noises will increase the performance of the protocol in quantum noisy channel. This means that an extra quantum noise can be intentionally added to quantum channel according to the noise intensity, so that the protocol can improve performance under the influence of quantum noises. Finally, the detailed mathematical analysis proves the conclusions.

Based on quantum identity authentication, a novel continuous variable quantum steganography protocol is proposed in this paper. It can effectively transmit deterministic secret information in the public quantum channel by taking full advantage of entanglement properties of continuous variable GHZ state. Compared with the existing quantum steganography results, this protocol has the advantages of good imperceptibility and easy implementation. Finally, the detailed performance analysis proves that the proposed protocol has not only these advantages, but also good security and information transmission efficiency, even under eavesdropping attacks, especially to the spectroscopic noise attack.

Thermal cloaks can thermally hide an object without disturbing background thermal field. The coordinate transformation method for designing conventional thermal cloaks face some challenges that the physical properties of metamaterials are required to be anisotropic and inhomogeneous. Furthermore, the coordinate transformation is not applicable for complex geometrical conditions. In this study, a proactive thermal cloak is proposed. The cloak contains two concentric annular zones: one with high thermal conductivity and another with adaptive heat source. The cloaked zone is surrounded by the high thermal conductivity zone. The high thermal conductivity zone keeps the object in the cloaked zone from thermally being affected by outside zones. The heat source zone adjusts the background thermal field without any distortion. The thermal cloak with an analytical heat source distribution is presented for the 2D and 3D background thermal fields with uniform gradient. The adaptive heat source in the thermal cloak is designed by inverse problem theory of a numerical method for the 2D arbitrary background thermal field. This proactive thermal cloak can avoid the issue of anisotropic physical properties for the conventional thermal cloak designed with coordinate transformation method. The heat source thermal cloak with relatively easy implementation can manipulate temperature field proactively without contact. This thermal cloak is applicable for arbitrary background thermal fields and complex geometrical conditions by a numerical design approach. The proposed thermal cloak opens a new strategy to manipulate the thermal field with adaptive heat source.

A method that combines finite volume method (FVM) and grand canonical Monte Carlo (GCMC) method is proposed to investigate the direct air capture of low concentration CO2 by 5A zeolites in an adsorption bed of a space shuttle. In the FVM, the multicomponent Langmuir model and linear fitting formula are used to calculate saturation adsorption capacities and adsorption heat at macro-scale level, respectively. The GCMC method is used to obtain the parameters of the multicomponent Langmuir model and linear fitting formula at micro-scale level. The combined method overcomes the shortcomings of the saturation adsorption capacities and adsorption heat restricted by experiments or empirical formulas. The effects of inlet velocity, particle size, and porosity on heat and mass transfer in the adsorption bed are predicted. The saturation adsorption time for N2 is faster than that for CO2. The competitive adsorption process between CO2 and N2 is divided into three stages, namely, primary, intermediate, and saturation stage. The location of temperature difference peak between solid and gas phase moves toward the outlet of the adsorption bed with increasing velocity, porosity, adsorption time or decreasing particle size. An adsorption bed with high inlet velocity and porosity and small particle size is recommended to achieve improved performance.

Experimental investigations of the heat transfer characteristics during charging were performed for a 25 wt% microencapsulated phase change material (MPCM), which was synthesized by polymerization. The shell and core were urea-formaldehyde and hexadecane (C16H34), respectively. The shell–core ratio of the MPCM was 3:7 by weight. A direct mixing stratified water storage tank was installed in the experimental system to decrease the chilled supply water temperature fluctuation. The influences of different stirring rates on the heat transfer performance of the MPCM slurry was also compared. The experimental results indicated that the volumetric thermal energy storage capacity of the MPCM slurry was 1.74 times that of pure water at 200 rpm. The charging rate and heat transfer coefficient increased rapidly in the phase transition region, however, there is no significant improvement compared with pure water during the whole charging process.

Shale gas is becoming an increasingly promising alternative energy resource because of its high efficiency and environment-friendly characteristic. The amount of adsorbed gas on the shale matrix surfaces and dissolved gas in the shale matrix bulk is the dominant factor in the long-term productivity of shale reservoir. Although experimental measurements have been extensively carried out to investigate the gas adsorption and diffusion properties in the shale matrix, they cannot provide the detailed information on the microscopic transport mechanism of shale gas during the gas production process. Molecular simulation can accurately visualize the gas adsorption/desorption and diffusion processes in the shale matrix. In the present study, the recent research advances of molecular simulation on gas adsorption/desorption and diffusion in the shale matrix are reviewed. Firstly, the density functional theory (DFT) for shale gas molecule desorption/adsorption on the surface of the matrix crystal is illustrated. Then, the grand canonical Monte Carlo (GCMC) method predicting the amount of shale gas desorption/adsorption in the shale matrix crystal is introduced. Finally, molecular dynamics simulation (MD) for gas diffusion in the shale matrix is elucidated. Further developments of the molecular simulation method in shale gas production are also discussed.

In some pressure-based methods, inner iteration processes are introduced to achieve efficient solutions. However, number of the inner iteration is fixed as 2 or 4 for different computations. In thi...

The cryogenic loop heat pipe is an effective and reliable heat transfer system in the space technology. A global model of cryogenic loop heat pipe is developed by full consideration of the subcooled effect and the mass flow rate variation of the working fluid along the evaporator core. The heat leak is calculated on the basis of one-dimensional temperature distributions in the evaporator core. The calculation of the proposed model improves the prediction accuracy relative to traditional zero-dimensional models. The effects of filling pressure, parasitic heat load, auxiliary heat load, and use of bayonet on the CLHP performance are investigated. A normal “U-shape” of the evaporating temperature curve appears at a low filling pressure (1.45 MPa). At moderate and high filling pressures (1.465 MPa and 1.5 MPa, respectively), two new evaporating temperature curves with “flat bottom U-shape” and “L-shape”, which shows the unique operating characteristics of cryogenic loop heat pipes, are found. The two new profiles are attributed to the coupling of mass and energy between gas reservoir and primary compensation chamber. The determinant factor for the minimum working heat load is the void fraction of the primary compensation chamber. By contrast, the maximum working heat load is determined by the void fraction at a low filling pressure (below 1.4 MPa) and the maximum capillary pressure at a high filling pressure (above 1.4 MPa). The use of a bayonet can decrease the maximum vapor quality in the evaporator core and effectively avoid burnout.

Quantum image steganography is the art and science of hiding secret information into quantum carrier images. This paper proposes a novel quantum image steganography algorithm based on an efficient embedding technique of exploiting modification direction. For convenience, this embedding technique is referred to the EMD embedding. In the EMD embedding, it is clear that each carrier pixel-group of the carrier image contains N pixels and each secret digit of secret information belongs to the (2N + 1)-ary notational system, where N is a system parameter. The embedding process is that at most only one pixel of the carrier pixel-group will be either increased by 1 or decreased by 1. The new algorithm takes advantage of the EMD embedding owning high embedding efficiency that the (2N + 1) different modifications to N carrier pixels represent the value of the secret digit. In addition, designing the dedicated quantum circuit for the EMD embedding contributes to better understanding the process of the new algorithm. Experimental simulation based on MATLAB shows that the new algorithm has good performance on imperceptibility, security, embedding efficiency and embedding capacity.

Rechargeable lithium–ion batteries (LIBs) have improved significantly over the past 20 years; however, the micro-scale working mechanism of these batteries, especially the influence of electrode microstructures on battery performance, still requires further study. The relationship between the electrode microstructure and battery performance is studied in detail by developing a two-dimensional (2D) lattice Boltzmann model to reveal the ion and electron transport within an LIB porous electrode. The present model is established by using randomly reconstructed electrode geometry and the coupling of the electrochemical reaction and ion and electron transport under complex boundary conditions. The influences of the micro-scale morphological features of the battery electrode on the local lithium concentration distribution, electric potential and macroscopic discharge performance are revealed. The randomness of the particle distribution and particle shape result in a heterogeneous distribution of the lithium concentration and electrode potential. In electrode particles, lithium exchanges are enhanced for small particles and improved at the edges and corners for large irregular particles. Regions with low lithium concentration produce a high electric potential. A large particle size and low porosity in an anode improve battery performance. Likewise, a small particle size and high porosity in a cathode also improve battery performance.

Multilayer graphene reinforced copper matrix (Cu-MLG) composites were fabricated via molecular-level mixing combined with vacuum hot-pressing (VHP). The MLG displayed a preferred orientation in the copper matrix, with the in-plane surface perpendicular to the hot-pressing direction, resulting in significant anisotropy in the thermal properties of Cu-MLG composites. Theoretical predictions were made using four models (Schapery, Kerner, Turner and mixture rule) to investigate the effect of the preferential orientation of MLG on the CTE anisotropy of Cu-MLG composites. The CTE anisotropy was further analyzed by carrying out molecular dynamics (MD) simulations to determine the variation in bond lengths for copper and MLG in different directions in the interface regions. The MLG bond length increased gradually with increasing temperatures in the in-plane direction, while in the out-plane directions, it increased significantly at first and then decreased at higher temperatures. The variations of bond lengths for MLG are consistent with the CTE anisotropy of the Cu-MLG composites in the same direction.

Highlights • We find out that the sources for preparing entangled OAM states based on a Vogel spiral with the same Fibonacci numbers, which can prepare two types of entangled states. • The distribution of significantly different probabilities to the entangled state photons and measurement bases during both transmission and reception, thus reducing the fraction of discarded data. • We use the close relations among Lucas sequence, Chebyshev maps and k-Chebyshev maps to greatly enhance the capacity of per entangled particle for key generation without the limit of spiral and OAM bandwidths. • We divide the accepted data into different subsets in terms of the types of measurements chosen and estimate an error rate for each subset separately to guarantee the security of our proposed scheme. Abstract The conjugation relation between Lucas sequence and Fibonacci sequence lead us to devise some simple modifications which essentially increases the efficiency and the capacity of quantum key distribution scheme proposed by Simon et al. (Phys. Rev. A. 87, 032312 (2013)). The first major ingredient of our scheme is the sources for preparing entangled OAM states based on a Vogel spiral with the same Fibonacci numbers, which can prepare two types of entangled states. The second major ingredient is the distribution of significantly different probabilities to the entangled state photons and measurement bases during both transmission and reception, thus reducing the fraction of discarded data. The third major ingredient is that we use the close relations among Lucas sequence, Chebyshev maps and k-Chebyshev maps to greatly enhance the capacity of per entangled particle for key generation without the limit of spiral and OAM bandwidths. Lastly, combined the ideas proposed by Lo et al. (e-print arXiv:quant-ph/0011056) and Xue et al. (Phys. Rev. A. 65, 022317 (2002)), we divide the accepted data into different subsets in terms of the types of measurements chosen and estimate an error rate for each subset separately to guarantee the security of our proposed scheme.

Electrode compression is an effective approach to enhance the performance of vanadium redox flow battery (VRFB). Electrode compression can decrease the contact resistance between the electrode and the current collector. Porous electrode compression and deformation are not uniform because of the rib-channel patterns and part of the fibers pressed into the channel. The effects of the non-uniform deformation of a compressed electrode on the performance of a VRFB with flow field are not fully analyzed. In this study, a non-uniform model is proposed to consider the electrode shape deformation and non-uniformity of physical properties inside a compressed electrode. Morphological features of a deformed electrode including the intrusion ratio and local porosities under compression are investigated. Non-uniformly compressed electrodes with different local porosity and permeability are obtained. The predicted cell performance is initially validated using experiment data. The performance of VRFB with non-uniformly compressed electrode and serpentine flow field are investigated under different compression ratios (CRs). The non-uniform model can reasonably predict the charge/discharge and flow behavior. The velocity profile, local current density, and overpotential fluctuation along the rib and channel regions are obtained. The bulk velocity associated with species transport is improved because of the decreased cross-section areas of the flow channel inside the compressed electrode. An appropriate compression can improve the VRFB performance because of the enhanced species transport and increased reaction area when the intrusion part is considered. An optimized electrode CR of 55.7% is found to exhibit the maximum concentration uniformity as well as the minimum current density and overpotential. The present model can guide the VRFB design when the compressed electrode is considered.

Optimal electrode compression can efficiently reduce electrode contact resistance and enhance species mass transfer so that the performance of vanadium redox flow battery (VRFB) is consequently improved. New designs of VRFB with a serpentine flow field on the current collector and compressed thin electrodes are investigated to increase its power density. In this study, the intrusion ratio, porosity, strain–stress, area specific resistance, hydrodynamic characteristics, and charge/discharge performance of VRFBs are comprehensively characterized under different compression ratios (CRs) which can be adjusted by changing the assembly force. Then, VRFBs using carbon felts with different CRs are tested by experiments, and the influence of electrode compression on VRFB cell performance is quantitatively evaluated. The in-homogeneous compression of carbon felt electrode in a VRFB with a flow field leads to a non-uniform porosity distribution of the electrodes under the channel, intrusion, and rib regions. The intrusion ratio, local average porosity, and permeability at different CRs are obtained. The Kozney–Carman constant of carbon fiber felt is modified by measuring the flow pressure drop through the electrode. The charge/discharge curves are acquired and the corresponding energy efficiencies are calculated under different CRs. It is shown that the charge/discharge time increases with the CR, and the energy efficiency can be improved to a maximum of 19.4% when the CR varies from 0.3% to 41.8%.

A fully dynamic model for mixture gas separation is built in Cu-BTC membranes. A multi-scale method that couples the lattice Boltzmann method with grand canonical Monte Carlo (GCMC) is proposed to investigate the mass transfer process of CO2/CH4 mixture gases in Cu-BTC membranes. The convection and diffusion in the interparticle flow field and the intraparticle diffusion and adsorption in the particle interior are simultaneously considered. The membrane morphology is reconstructed by a sphere-based simulated annealing method. The effects of membrane porosity and particle size on the mass transfer and selectivity of CO2/CH4 mixture gases are predicted. Results show that the selectivity of CO2/CH4 is mainly determined by interparticle and intraparticle mass transfer resistances. Meanwhile, the time of saturation adsorption for CO2 and CH4 both decrease with an increase in porosity but decreases for CO2 and increases for CH4 with an increase in particle size. The selectivity of CO2/CH4 in Cu-BTC membranes decreases with an increase in porosity and particle size. Therefore, membranes with small porosity and particle size should be utilized. Compared with the traditional binary GCMC and ISAT methods based on saturation adsorption, the proposed coupled method is closer to the physical essence of the process because it considers dynamic competitive adsorption. The present method can be helpful in the design of efficient metal–organic framework (MOF) membranes.

A modified lattice Boltzmann method (LBM) is established to predict effective thermal conductivity of aerogel materials for insulation performance. A stochastic generation method based on mesoscopic solid-phase growth principle is adopted to reconstruct and mimic aerogel porous structure. The modified LBM scheme introduces an additional coefficient to regulate significant differences in inherent thermal conductivity between solid and gas phases, and a converged solution is guaranteed. The modified model is validated with experimental data, and it offers improved prediction accuracy than conventional theoretical models. Investigations are performed to determine the effects of density, ambient pressure, and characteristic temperature on effective thermal conductivity. When temperature is lower than 500 K, an optimal density of 110 kg/m3 minimizes effective thermal conductivity. When temperature is higher than 500 K, the effective thermal conductivity decreases monotonously with increasing density. At fixed temperature, the variation in effective thermal conductivity can be divided into three typical stages based on pressure. Separate contributions of gas-phase conduction, solid-phase conduction, and radiative heat transfer are discussed and analyzed.

A two-dimensional quasi-steady-state model is applied to investigate charge/discharge behavior and performance of a VRFB. Emphasis is focused on exploring the influences of various strategies of soc-dependent operating current density on battery performance. For constant-current operation, with the increase of current density, although the system mean power density is significantly boosted, the system capacity and net discharge energy in a cycle are obviously decreased. It is quite difficult to give consideration to both the system capacity and system power simultaneously such that overall battery performance can be improved. Applying the strategy of soc-dependent operating current (i.e., low current at the end of charge/discharge process while high current for the rest time), the system capacity, power density and net discharge energy in a cycle can be simultaneously boosted while comparable efficiencies can be achieved. Optimally, at the mean operating current density of about 70 mA cm−2, the system capacity is maximally improved by 9.3% and the net discharge energy is maximally increased by 7.9% as compared with that under constant-current operation. As the same time, the energy-based system efficiency can be maintained over 78%, which is comparable with that for constant-current operation.

The traditional image authentication technique generally determines the image attribution by extracting specific features and combining the similarity calculation algorithm. Because of the selected features dimensions, characterization and other factors, the accuracy and speed of image authentication have been restricted. In this paper, Recog-Net, an end-to-end image authentication model based on convolution neural network has been proposed. Deep residual network is chosen as the features extractor. Mahalanobis distance and threshold method are used to complete the image authentication. Experiments show that the performance of the extractor's features, compared with the traditional features and the features of other convolution neural network architectures, is more excellent, with a high degree of generality, recognition rate and robustness, still having these advantages even after a substantial compression. The Recog-Net for image authentication is able to accurately authenticate the images tampered with certain range.

A solar pond is a simple and reliable system that collects and stores solar energy for applications with low-grade heat supply. The main obstacle to the long-term stable operation of a solar pond is interface erosion induced by double-diffusive convection. In this study, an active method of using an external magnetic field is proposed to repress the intense convection region and improve its corresponding operating stability. A two-dimensional transient model is developed and solved using the lattice Boltzmann method with multiple-relaxation-time collisions. The double-diffusive convection, variation of solar energy absorption to depth, and changes in solution electrical conductivity are considered in the model. The fluid flow, heat, and mass transfer characteristics were investigated under continuous high illumination with or without an external magnetic field. When magnetic control is exerted on a solar pond, the decrease in the nonconvective zone thickness caused by interface erosion changes from 14.75% to 0. The state of the solar pond is transformed from a thermally unstable state to a theoretically stable state after 35 h of continuous high illumination. Further, the external magnetic field can delay concentration homogenization and improve the heat storage performance of a lower convective zone. A Hartmann number above 56.67 is recommended to enhance the stability of the solar pond. This research sheds new light on methods to improve the long-term stability of solar ponds.