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AbstractThe uncertainty of thermal protection system (TPS) is inevitable in practical engineering. In this article, the interval finite element model of TPS is established by taking the uncertainties of TPS in thermomechanical coupling analysis as interval parameters. The perturbed-based interval finite element method (PIFEM) and affine-based interval finite element method (AIFEM) are proposed to study the displacement response of uncertain TPS under thermomechanical coupling. Two numerical examples are given and compared with Monte Carlo method (MCM) to verify the effectiveness and accuracy of the PIFEM and AIFEM proposed in this article. The results show that compared with the MCM, the computational efficiency of PIFEM and AIFEM is improved by more than three orders of magnitude, and the computational efficiency of PIFEM and AIFEM is similar. In the case of considering uncertain parameters, the conservative AIFEM is more suitable for the thermomechanical coupled uncertainty analysis of TPS. The numerical results provide useful guidance for TPS design. [ABSTRACT FROM AUTHOR]

Random errors (uncertainties) in COSMIC radio occultation (RO) soundings, ERA-Interim (ERAi) reanalyses, and high-resolution radiosondes (RS) are estimated in the northeast Pacific Ocean during the MAGIC campaign in 2012 and 2013 using the three-cornered hat method. Estimated refractivity and bending angle errors peak at ∼2 km, and have a secondary peak at ∼15 km. They are related to vertical and horizontal gradients of temperature and water vapor and associated atmospheric variability at these two levels. MAGIC RS refractivity and bending angles obtained from forward models have the largest uncertainties, followed by COSMIC RO soundings. ERAi has the smallest uncertainties. The large RS uncertainties can be primarily attributed to representativeness errors (differences). Differences in space and time of the RO and model datasets from the RS observations, error correlations among datasets, and the small sample size are other possible reasons contributing to these differences of estimated error statistics. RO temperature and humidity are retrieved from refractivity using a one-dimensional variational (1D-Var) method from the COSMIC Data Analysis and Archive Center (CDAAC). The estimated errors for COSMIC temperature are comparable to those of the MAGIC RS except near 1 km, where they are much higher. The estimated errors for COSMIC specific humidity are similar to the MAGIC specific humidity errors below ∼5 km and much smaller above this level. Estimates of COSMIC random errors based on ERAi, JRA-55, and MERRA-2 reanalyses in the same region, as well as comparison with estimates from other studies, support the reliability of our estimates. [ABSTRACT FROM AUTHOR]

Total harmonic distortion (THD) plays an important role in the performance of miniature loudspeakers used in mobile phones. Traditional nonlinear models fail to predict THD in the higher frequency domain. Significant discrepancies can be found between the prediction and measurement. In this study, an extended model considering nonlinear acoustic damping is proposed to address this issue. Flow separation occurring near the orifices of the sound port is of particular interest. Two velocity-dependent parameters were derived to model the nonlinear damping effect. Based on the extended model, the dynamics of miniature loudspeakers are described using the state-space method. Experiments and calculations confirm the validity of the extended model. The influence of nonlinear acoustic damping on THD is also discussed. [ABSTRACT FROM AUTHOR]

Magnesium borohydride (Mg(BH 4) 2) is an attractive materials for solid-state hydrogen storage due to its high hydrogen content (14.9 wt%). In the present work, the dehydrogenation performance of Mg(BH 4) 2 by adding different amounts (10, 20, 40, 60 wt%) of two-dimensional layered Ti 3 C 2 MXene is studied. The Mg(BH 4) 2 -40 wt% Ti 3 C 2 composite releases 7.5 wt% hydrogen at 260 °C, whereas the pristine Mg(BH 4) 2 only releases 2.9 wt% hydrogen under identical conditions, and the onset desorption temperature decreases from 210 °C to a relative lower temperature of 82 °C. The special layered structure of Ti 3 C 2 MXene and fluorine plays an important role in dehydrogenation process especially at temperatures below 200 °C. The main dehydrogenation reaction is divided into two steps, and activation energy of the Mg(BH 4) 2 -40 wt% Ti 3 C 2 composite is 151.3 kJ mol−1 and 178.0 kJ mol−1, respectively, which is much lower than that of pure Mg(BH 4) 2. • Ti 3 C 2 MXene exhibits superior catalysis and confinement effect on Mg(BH 4) 2. • Mg(BH 4) 2 -40 wt% Ti 3 C 2 composite shows the optimal dehydriding kinetics properties. • Fluorine on the surface of Ti 3 C 2 MXene can improve the dehydrogenation performance. • Ti 3 C 2 MXene can change the decomposition behavior of Mg(BH 4) 2. [ABSTRACT FROM AUTHOR]

Running several high-frequency underwater acoustic instruments simultaneously on board a surface or underwater platform can cause interference between the instruments. By combining ray theory and the high-frequency bistatic scattering model for water bottoms, this work presents a practical method for evaluating the relative intensities of such interference signals corresponding to different instrument-to-instrument distances. To examine this method's effectiveness, a series of lake experiments were conducted. The relative intensity of the interference signal was first evaluated by using the proposed method, and then it was measured for comparison. The experimental results showed good agreement between the evaluated and the measured intensities. [ABSTRACT FROM AUTHOR]

The seasonal prediction skill and predictability of the Northern Hemisphere storm track anomalies in boreal winter (December–January–February, DJF) is examined using seasonal ensemble reforecasts for 1982–2009 from the ECMWF Integrated Forecast System at two different atmospheric resolutions in Project Minerva. It is found that the predictable signals of storm track variations are associated with the two leading EOF modes of ensemble-averaged DJF variances of the high-pass filtered daily meridional winds at 250-hPa level derived from each of the hindcast ensemble members. These two EOF modes are highly correlated both temporarily and spatially between two sets of reforecasts. The first mode (EOF1) mainly shows a latitudinal shift of the storm tracks over the central-eastern North Pacific and the North America continent. The second mode (EOF2) is primarily the pulsing signal exerting on the mean storm track background of the North Pacific. The model predictive skill is verified against observations. The first mode has higher prediction skills and larger skillful regions than the second one. In particular, the first predictable mode is generated by the ENSO-induced wave train, starting from tropical central Pacific and propagating to North America. The skillful region lies in the North Pacific to the west of California, corresponding to the southern lobe of EOF1. The second predictable mode is generated by the North Pacific Mode, which evokes a distinctive wave train, emanating from the tropical western Pacific and propagating northeastward. Its skillful region of the storm track prediction is confined to a small area of Canada western coastlines. [ABSTRACT FROM AUTHOR]

The model fidelity in simulating the Northern Hemisphere storm track interannual variability and the connections of this variability to the low frequency atmospheric variations and oceanic variations are examined based on the atmospheric European Centre for Medium-Range Weather Forecasts (ECMWF) model and coupled NCAR Community Climate System Model (CCSM) systems at different horizontal resolutions. The atmospheric general circulation model (AGCM) runs are forced by observed sea surface temperatures (SST) with varying atmospheric resolutions, while the coupled general circulation model (CGCM) runs have a fixed atmospheric resolution but varying oceanic resolutions. The phases, between the North Pacific (NP) and North Atlantic (NA) sectors, of the simulated hemisphere-scale Empirical Orthogonal Function (EOF) modes of the storm track fluctuations change with the model resolution, suggesting the storm track variability in NP and NA basins are largely independent. The models can qualitatively reproduce the basin-scale EOFs of both NP and NA storm track variability. These EOFs are not sensitive to either atmospheric or oceanic model horizontal resolutions, but their magnitudes from the CGCM runs are substantially underestimated. The storm track variations over NP basin are hybrid of internal atmospheric variations and external forcing from the underlying conditions, but the fluctuations over the NA basin are merely atmospheric internal variability. The NP storm track variability from SST forcing accounts for 4.4% of the total variance in observations, while it only has less than 2% of the total in all AGCM simulations. The external forcing to the storm track variations is more realistically reproduced in the higher atmospheric resolution runs. The air–sea coupling makes the SST feedbacks to the atmospheric internal variability, absent in the atmospheric ECMWF model hindcasts, emerge in the coupled CCSM simulations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The nanopores provided binding sites for exactly-sized Co nanoparticles. • This porous structure strengthened anchoring force between PGO and Co. • Co/PGO exhibited a high HGR of 5955 m L H 2 ⋅ min − 1 ⋅ g M − 1 for NaBH 4 hydrolysis. • Co/PGO catalyst exhibited stability in NaBH 4 hydrolysis. Abstract Non-noble metal Co nano catalyst anchored on novel nanoporous graphene oxide (PGO) was successfully prepared for hydrolysis of NaBH 4. The PGO was obtained by calcinating graphene oxide (GO) and Na 2 MoO 4. During calcination, Na 2 MoO 4 etched GO planes and plenty of nanopores with an average size of 20 nm was imported on the surface of GO. The nanopores provided binding sites for exactly-sized Co nanoparticles (NPs) to locate in GO, which could strengthen interaction between the Co NPs and PGO. The as-prepared Co/PGO exhibited a glorious catalytic activity on NaBH 4 hydrolysis in alkaline condition, with a high hydrogen generation rate (HGR) 5955 m L H 2 ⋅ min − 1 ⋅ g M − 1 at room temperature. Furthermore, The PGO facilitated reusability of the catalyst Co particles, with a retention rate 73% in HGR after five cycles. This work provided a potential strategy for preparing an efficient and non-noble catalyst for hydrogen generation from NaBH 4 hydrolysis. [ABSTRACT FROM AUTHOR]

Changes in precipitation amount, intensity and frequency in response to global warming are examined using global high‐resolution (16 km) climate model simulations based on the European Centre for Medium‐range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) conducted under Project Athena. Our study shows the increases of zonal‐mean total precipitation in all latitudes except the northern subtropics (15°–30°N) and southern subtropics‐to‐midlatitudes (30°–40°S). The probability distribution function (PDF) changes in different latitudes suggest a higher occurrence of light precipitation (LP; ≤1 mm/day) and heavy precipitation (HP; ≥30 mm/day) at the expense of moderate precipitation reduction (MP; 1–30 mm/day) from Tropics to midlatitudes, but an increase in all categories of precipitation in polar regions. On the other hand, the PDF change with global warming in different precipitation climatological zones presents another image. For all regions and seasons examined, there is an HP increase at the cost of MP, but LP varies. The reduced MP in richer precipitation zones resides in the PDF peak intensities, which linearly increase with the precipitation climatology zones. In particular in the Tropics (20°S to 20°N), the precipitation PDF has a flatter distribution (i.e. HP and LP increases with MP reduction) except for the Sahara Desert. In the primary precipitation zones in the subtropics (20°–40°) of both hemispheres, precipitation over land switches toward higher intensity (HP increases, but MP and LP decrease) in both winter and summer, while precipitation over ocean in both seasons shows a flattening trend in the intensity distribution. For the major precipitation zones of the mid‐to‐high latitude belt (40°–70°), PDF of precipitation tends to be flatter over ocean in summer, but switches toward higher intensities over land in both summer and winter, as well as over ocean in winter. Heavy precipitation frequency increases over all latitudes. between 40°N and 60°S excluding the equatorial region, precipitation PDFs tend to increase in light precipitation and heavy precipitation but decrease in moderate precipitation, while within the latitudinal bands of 40°N–70°N and 60°S–80°S, light precipitation decreases but moderate precipitation and heavy precipitation increase in frequency. Poleward of 70°, precipitation of all intensities increases. [ABSTRACT FROM AUTHOR]

Sparse array design (SAD) optimizes the geometrical configuration of the loudspeaker array. It provides possibilities for further improving the performance of personal sound zone (PSZ). In this paper, the SAD problem in PSZ is formulated as a sparse multi-objective optimization problem, which takes multiple performance metrics into consideration during the sparsity promotion procedure. A swap-based group search algorithm is designed and proposed for solving the formulated non-convex and combinatorial problem to near-optimality. An approximate form is also proposed for reducing computational burden when there exist multiple target sound fields in bright zone. Simulation and experimental results suggest that the proposed method is more suitable in PSZ for controlling over trade-offs and achieving the same good or even better performances, and the proposed approximate form is effective. [ABSTRACT FROM AUTHOR]

In this work, Al2O3 nanoceramics were prepared by spark plasma sintering of amorphous powders and polycrystalline powders with similar particle sizes. Effective comparisons of sintering processes and ultimate products depending on starting powder conditions were explored. To ensure near-full density higher than 98% of the Al2O3 nanoceramics, the threshold temperature in SPS is 1450 °C for polycrystalline Al2O3 powders and 1300 °C for amorphous powders. The low SPS temperature for amorphous powders is attributed to the metastable state with high free energy of amorphous powders. The Al2O3 nanoceramics prepared by amorphous powders display a mean grain size of 170 nm, and superior mechanical properties, including high bending strength of 870 MPa, Vickers hardness of 20.5 GPa and fracture toughness of 4.3 MPa∙m1/2. Furthermore, the Al2O3 nanoceramics prepared by amorphous powders showed a larger dynamic strength and dynamic strain. The toughening mechanism with predominant transgranular fracture is explained based on the separation of quasi-boundaries. [ABSTRACT FROM AUTHOR]

Using climate simulations from coupled and uncoupled general circulation models, this study investigates the influence of horizontal resolution in both atmospheric and oceanic model components on the mean precipitation over the Gulf Stream (GS) region. For this purpose, three sets of model experiments are analyzed. The first two examine the effects of increasing horizontal resolution of an atmospheric general circulation model (AGCM) gradually from 100 to 10 km under fixed oceanic settings. Specifically, the AGCM is either forced with prescribed observed sea surface temperature (SST) (the first case) or coupled to a non-eddy-resolving ocean general circulation model (OGCM) at a fixed horizontal resolution near 100 km (the second case). The third set of experiments examines the effects of the oceanic resolution with a pair of long-term simulations by another coupled ocean-atmosphere general circulation model (CGCM), in which the OGCM is run respectively at non-eddy-resolving (100 km) and eddy-resolving (10 km) resolutions, while the AGCM resolution remains fixed at 50 km for both runs. In general, all simulations qualitatively reproduce the gross features of the mean GS precipitation and its annual cycle. At similar AGCM resolutions, the uncoupled models produce a GS rain band that is more realistic in both structure and strength compared to the coupled models with non-eddy-resolving oceans. This is because the prescribed observed SST better represents the gradient near the oceanic front than the non-eddy-resolving OGCMs simulate. An increase from the baseline AGCM resolution produces enhanced climatological GS precipitation, both large-scale and convective, with the latter more tightly confined to the oceanic front. The enhancement, however, is moderate and further increases in resolution achieves diminishing results. On the other hand, an increase in oceanic resolution from non-eddy-resolving to eddy resolving scheme results in more consistent simulations with observations in both intensity and structure of the rain band. The major increase is in the convective precipitation near the much-tightened SST gradient associated with the oceanic front. Therefore, the intensity improvement caused by oceanic resolution increases is more effective than that from atmospheric resolution increases. Further analyses show that the improvement of Gulf Stream precipitation climatology due to model horizontal resolution increases can be understood in terms of the atmospheric surface pressure adjustment to the sharper SST gradient near the oceanic front, which leads to stronger atmospheric surface convergence and upper level divergence. The associated ascending motion contributes to the precipitation band located in the Gulf Stream. [ABSTRACT FROM AUTHOR]

The secondary-edge-source method (SESM) has found widespread application in predicting edge diffraction. The method, however, is limited to point sources. Based on the concept of weighted summation of diffractive contribution from each propagation path, this letter extends the SESM to directional sources with equivalent acoustic centers. The validity of the proposed method is demonstrated by comparing theoretical results to those obtained using the omnidirectional monopole superposition method. [ABSTRACT FROM AUTHOR]

We compare the random error statistics (uncertainties) of COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate, C1) and COSMIC-2 (C2) radio occultation (RO) bending angles and refractivities for the months of August 2006 and 2021 over the tropics and subtropics using the three-cornered hat method. The uncertainty profiles are similar for the two RO missions in the troposphere. However, a higher percentage of C2 profiles reach close to the surface in the moisture-rich tropics, an advantage of the higher signal-to-noise ratio (SNR) in C2. C2 uses signals from both GPS (Global Positioning System) and GLONASS Global Navigation System Satellites (GNSS). The GPS occultations show smaller uncertainties in the stratosphere and lower mesosphere (30–60 km) than the GLONASS occultations, a result of more accurate GPS clocks. Therefore, C2 (GPS) uncertainties are smaller than C1 uncertainties between 30–60 km while the C2 (GLONASS) uncertainties are larger than those of C1. The uncertainty profiles vary with latitude at all levels. We find that horizontal gradients in temperature and water vapor, and therefore refractivity, are the major cause of uncertainties in the tropopause region and troposphere through the violation of the assumption of spherical symmetry in the retrieval of bending angles and refractivity. [ABSTRACT FROM AUTHOR]

The multimodal method is used to develop an approach for optimizing the shape of axisymmetric acoustic horns for both well-controlled directivity and high radiation efficiency over a wide frequency range. A horn with an arbitrary profile can be efficiently modeled with the multimodal method by projecting the wave field over transverse modes in connected short cylinders; the radii of the cylinders are used directly as design variables. Many design variables are employed in the optimization process to ensure design flexibility and computational accuracy. The relative weights for the design objectives of constant directivity, high radiation efficiency, and acceptable shape smoothness are adjusted by two coefficients in the objective function. The optimization problem is solved with a gradient-based algorithm, which takes advantage of algebraic gradient expressions. Numerical experiments demonstrate that the optimization procedure generates smooth horn contours that exhibit considerably improved performance over the target frequency band. Interestingly, a high-quality horn produced with moderate weight coefficients is similar in shape to constant-directivity horns invented earlier while having good low-frequency loading properties. The proposed method provides an attractive alternative to conventional horn design approaches. [ABSTRACT FROM AUTHOR]

The spectral division method (SDM) is one of several sound field synthesis techniques of spatial sound reproduction. The synthesis accuracy of SDM is usually higher than that of wave field synthesis (WFS). However, existing SDM-based sound field synthesis methods are developed for virtual sources moving uniformly along a straight trajectory. This Letter proposes a 2.5-dimensional SDM driving function for arbitrary moving sources. Numerical simulations have validated the driving function. The results indicate that the synthesis error of the SDM with the proposed driving function is lower than that of WFS, especially when the virtual source is close to the secondary sources. [ABSTRACT FROM AUTHOR]

Uncertainties are unavoidable in practical engineering, and phononic crystals are no exception. In this paper, the uncertainties are treated as the interval parameters, and an interval phononic crystal beam model is established. A perturbation-based interval finite element method (P-IFEM) and an affine-based interval finite element method (A-IFEM) are proposed to study the dynamic response of this interval phononic crystal beam, based on which an interval vibration transmission analysis can be easily implemented and the safe bandgap can be defined. Finally, two numerical examples are investigated to demonstrate the effectiveness and accuracy of the P-IFEM and A-IFEM. Results show that the safe bandgap range may even decrease by 10% compared with the deterministic bandgap without considering the uncertainties. [ABSTRACT FROM AUTHOR]

Personal Sound Zone (PSZ) allows listeners to enjoy their individual sound without being disturbed by sound from other zones. Acoustic contrast, signal distortion, and array effort are the most frequently used metrics for measuring the performance of a PSZ system. However, usually, the three metrics cannot be optimized at the same time. A trade-off between the three metrics has to be made when designing a PSZ system. In this paper, two generalized methods based on multi-objective optimization are proposed for dealing with all possible trade-off problems between the three metrics in PSZ. Optimality analysis of the two proposed methods is taken, and the relationship between the two proposed methods is investigated. Numerical simulations are presented to validate the efficacy and flexibility of the two proposed methods. [ABSTRACT FROM AUTHOR]

In this paper, a novel blind source separation (BSS) method drawing on the framework of Multivariate nonlinear chirp mode decomposition (MNCMD) termed as Nonlinear Chirp Component Analysis (NCCA) is proposed. In contrast to other BSS methods, NCCA is designed to separate the non-stationary sources in an elegant variational optimization framework. Firstly, the source signals are modeled as wide-band nonlinear chirp modes (NCMs) which could be transformed into narrow-band signals with demodulation techniques. Afterwards, the objective function is represented as the summation of source signals bandwidths fulfilling the constraint that the multivariate observed signal is the linear combination of the source signals. Finally, the alternate direction method of multipliers (ADMM) algorithm is employed to solve this optimization problem without more predefined parameters than MNCMD. After that, the source signals including their instantaneous frequency (IF), instantaneous amplitude (IA), the mixing matrix are updated to the optimal values. The merits of NCCA inherited from MNCMD like mode-aligned, filter bank structure, Quasi-orthogonality of modes and its unique attribute of identifying the BSS model and undetermined blind source separation (UBSS) model are testified through a series of synthetic signal. Its anti-noise property and convergence property get verified too. The performance of NCCA in the analysis of vibration analysis through simulation and experimental vibration system is highlighted in the end. [ABSTRACT FROM AUTHOR]

• High-performance Al-Si-Mg samples were successfully fabricated by Wire-arc DED. • The precipitation strengthening induced by nanoscale β'' phases. • The addition of Mn element inhibits the development of detrimental Fe-rich phases. In this study, a novel high-performance Al-Si-Mg alloy was fabricated using wire-arc directed energy deposition (wire-arc DED), resulting in remarkable mechanical properties, including a yield strength of 299.2 ± 1.3 MPa, an ultimate tensile strength of 376.5 ± 8.1 MPa and an elongation an elongation of 6.9 ± 0.3 %. The heat-treated samples exhibited a uniform distribution of a significant quantity of nanoscale β'' phases, serving as the primary strengthening phase and contributing to substantial precipitation strengthening. The addition of Mn facilitates the formation of Al 6 (Mn, Fe) phase, effectively suppressed the formation of detrimental Fe-rich phases. However, the presence of numerous pores and the lack of fusion regions emerged as significant factors impacting mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, an integrated analytical and experimental study on a type of one-dimensional periodic acoustic metamaterial with mass-in-mass unit cells is presented. Then, this paper proposes an antioptimization strategy to study the effect of the design parameters of the local resonators of the mass-in-mass acoustic metamaterial model on the band gap behavior. In this antioptimization strategy, the interval model is used to deal with the inner mass, spring stiffness and damping coefficient of the local resonators, and an interval mass-in-mass acoustic metamaterial model is established. Both the rational series expansion-interval perturbation finite element method (RSE-IPFEM) and interval affine finite element method (IAFEM) are used to evaluate the lower and upper bounds of the dynamic response interval vector, based on which an interval vibration transmission analysis can be implemented. Meanwhile, Monte Carlo method and experiments are also presented to demonstrate the efficiency and accuracy of the RSE-IPFEM and IAFEM. Results show that the design parameters of the local resonators significantly affect the beginning frequency of the band gap. Compared with the traditional optimization algorithm, the calculation accuracy of the antioptimization algorithm based on RSE-IPFEM and IAFEM can meet the engineering requirements, and the calculation efficiency is also significantly improved. Since IAFEM is more effective than RSE-IPFEM in suppressing conservatism, IAFEM is a better antioptimization strategy for dealing with the interval mass-in-mass acoustic metamaterial model. Therefore, the proposed antioptimization scheme is expected to inspire future researchers to analyze regulation rules of the band gap following the same procedures. [ABSTRACT FROM AUTHOR]

This study presents a multimodal-based method to optimize the boundary shape of a rectangular horn for optimum impedance matching, assuming that the horn is mounted in an enclosure to adapt to practical applications. An infinite rectangular waveguide with a perfectly matched layer is introduced to solve the multimodal radiation impedances of the horn. The throat impedance of the horn is then calculated using the mode matching method. The optimum impedance matching properties over a wide frequency range are obtained by performing gradient-based shape optimization. The results show that the choice of target frequency band can significantly affect the optimization results. The numerical model is verified by the finite element method. The impedance matching performance of an optimal horn design is also experimentally validated. • Shape optimization of a rectangular horn using the multimodal method is studied. • A rectangular horn mounted in a practical finite-sized enclosure is considered. • The optimized horns exhibit wideband near-perfect impedance matching properties. • A judicious choice of the target frequency band is crucial for achieving desirable performance. • Experimental evidence is made for wideband minimum reflection coefficients. [ABSTRACT FROM AUTHOR]

Co-Mo particles were loaded on three dimensional graphene oxide (3DGO) carrier via a chemical reduction method to get a composite catalyst, Co-Mo/3DGO, for hydrogen generation from NaBH 4 hydrolysis. Hydrolysis measurement shows that the ratio Co:Mo = 0.7:0.3 realizes a much higher hydrogen generation rate (HGR) of 7023.3 mL H 2 ⋅ min − 1 ⋅ g M − 1 , about 1.6 times of that for the Mo element undoped Co/3DGO (4394 m L H 2 . min − 1. g M − 1 ) catalyst. And the reaction activation energy is as low as 35.6 kJ mol − 1. The as prepared Co 0.7 Mo 0.3 /3DGO catalyst disperses on 3DGO surface as smaller particles than Co/3DGO, and presents a waxberry like structure with more active sites for catalysis reaction, which enables the catalyst a superior catalytic activity. Besides abundant active sites, MoO 3 supported active blend of Co and CoO is another reason for the higher activity. Image 1 • Co-Mo/3DGO, catalyst for NaBH 4 hydrolysis was prepared. • The Co-Mo/3DGO catalyst presented a waxberry like structure with more active sites. • The catalyst had a superior catalytic activity, and HGR was 7023.3 mL H 2 ⋅ min − 1 ⋅ g M − 1 [ABSTRACT FROM AUTHOR]

Herein, the cobalt-molybdenum bimetallic sulfide catalysts supported on nitrogen-doped graphene (CoMoS 2 /NGO) were facilely synthesized by a one-pot hydrothermal route. These composites exhibit various special nanostructures, rich in abundant edge site exposure and defects, which play an important role in providing active sites for catalyzing hydrogen evolution reaction (HER). When hydrogen peroxide (H 2 O 2) was used as an additive in hydrothermal process, the as-fabricated composite exhibited more efficiency towards HER, showing as low onset overpotential (η on) as −54 mV in 0.5 M H 2 SO 4. Typical H 2 O 2 -assisted composite realized a remarkable cathodic current density of 30 mA cm−2 at an overpotential η = −137 mV and it possessed a small Tafel slope of 34.13 mV dec−1. Moreover, it exhibited an excellent cycling stability and superior electronic exchange rate. The results prove that CoMoS 2 /NGO catalysts have great potential for electrochemical HER. Image 1 • N element was doped onto graphene oxide surface, forming N-doped GO. • Additives contributed to formation of CoMoS 2 with special morphology. • Synergistic effect between CoS 2 and MoS 2 was beneficial to electrocatalysis. [ABSTRACT FROM AUTHOR]

CoPt-Co hybrids were successfully supported on amino modified SiO 2 nanospheres by a chemical reduction method at a temperature of 278 K. The solid carrier i.e. amino modified SiO 2 , provides numerous anchoring sites for the metal nanoparticles (NPs) to improve the dispersion while reducing the size of metal NPs. The supported NPs displayed a narrow particle size distribution on the SiO 2 surface with an average diameter of 12 nm. The XRD results alongside with the binary alloy phase diagram suggest that the resulted NPs are bimetallic, composed of CoPt and amorphous Co. Among the prepared materials, the solid with the specific composition of SiO 2 @Pt 0.1 Co 0.9 was proved to be effective catalyst for ammonia borane (AB) hydrolysis in aqueous solution. The turnover frequency (TOF) value of the supported nanocatalyst was 25.59 mol H 2 ⋅ min − 1 ⋅ mol M − 1 , almost twice as that of unsupported Pt 0.1 Co 0.9 NPs while the activation energy was 37.05 kJ mol−1. Furthermore, the SiO 2 @Pt 0.1 Co 0.9 composite manifested high catalytic activity even after five cycles of reuse. fx1 • SiO 2 nanospheres are modified with amino groups that offer plenty of bonding sites. • CoPt-Co NPs form on the SiO 2 through chelation between [PtCl 6 ]2-, Co2+ and amino. • Co and CoPt nanoparticles play synergistic role for catalytic AB hydrolysis. • Hydrolysis of AB with SiO 2 @Pt 0.1 Co 0.9 reveals high TOF of 25.59 mol H 2 ⋅ min − 1 ⋅ mol M − 1 . • SiO 2 @Pt 0.1 Co 0.9 catalyst exhibits good reusability for AB hydrolysis. [ABSTRACT FROM AUTHOR]

Based on the three-dimensional sono-elasticity theory for ship structures, the Green's function is incorporated and an integrated calculation method of acoustic radiation and propagation for floating bodies in shallow water considering the sound velocity profile is proposed. The near-field and arbitrary far-field acoustic radiation problem can be efficiently calculated. A numerical example of a rigid sphere is given and the results are compared with the finite element method solution to validate the reliability and demonstrate improvements in efficiency. The method is applied to an elastic capsular shell, verifying the applicability of the method for any elastic floating bodies. [ABSTRACT FROM AUTHOR]

In this study polyaniline (PANI) was coated on Nd Mg Ni-based alloy surface via an evaporation-polymerization method. SEM-EDX results show that PANI coats on the alloy particle surface, and remains stable during charging/discharging cycles. With assistance of PANI in improving kinetics, high rate dischargeability at 1500 mA/g increases by 12.7% (The treating time is 45 min). Cyclic voltammogram and infrared tests on charged and discharged electrodes shows that transformation between benzene-quinone oxidation species and benzene-benzene reduction species in the charging/discharging electrochemical windows of metal hydride electrodes helps to improve high rate dischargeability by facilitating charge transfer and subsequent hydrogen diffusion. The PANI not only works as an electro-catalytic layer but also as a protective layer to improve cycling stability of Nd Mg Ni-based alloy electrodes. [ABSTRACT FROM AUTHOR]

Understanding hydraulic fracturing mechanisms in heterogeneous laminated rocks is important for designing and optimizing well production, as well as for predicting shale gas production. In this study, a micromechanics-based numerical approach was used to understand the physical processes and underlying mechanisms of fracking for different strata orientations, in-situ stresses, rock strengths, and injection parameters. The numerical experiments revealed a very strong influence of the pre-existing weakness planes on fracking. Geological models for rock without weakness planes and laminated rock behave very differently. Most simulated fractures in the rock without weakness planes were caused by tensile failure of the rock matrix. In an intact rock model, although a radial damage zone was generated around the injection hole, most of the small cracks were isolated, resulting in poor connectivity of the fracture network. For rock models with pre-existing weakness planes, tension and shear failure of these structural planes formed an oval-shaped network. The network was symmetrically developed around the injection well because the strength of the pre-existing weakness planes is generally lower than the rock matrix. The research shows that the angular relations between the orientation of the structural planes and the maximum horizontal stress, as well as the in-situ stress ratios, have significant effects on the morphology and extent of the networks. The strength of the pre-existing weakness planes, their spacing, and the injection rate can dramatically influence the effectiveness of hydraulic fracturing treatments. [ABSTRACT FROM AUTHOR]