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Metastructures are typically composed of periodic unit cells designed to present enhanced dynamic properties in which either single or multiple resonators are periodically distributed. Even though the periodic metamaterials can obtain bandgaps with outstanding vibration attenuation, the widths of bandgaps can still be narrow for some practical applications. Rainbow metamaterials have been proposed based on gradient or random profiles to provide further improved attenuation. Nonetheless, the effects of correlated random disorder on their attenuation performance remains an open challenge. This work presents an investigation on the effects of correlated disorder on the vibration attenuation of rainbow metamaterials. An analytical model using the transfer matrix approach is used to calculate the receptance functions in a finite length metastructure composed of evenly spaced non-symmetric resonators attached to a beam with Π-shaped cross-section, thus a multi-frequency metastructure. The correlated disorder is modelled using random fields and an analytical expression of the Karhunen-Loève expansion is used such that spatial correlation on the resonator properties is modified by various correlation lengths, i.e., the level of spatial smoothness. Individual samples of random fields are used to investigate the effects of the correlated disorder in the vibration attenuation of a multi-frequency metastructure. It is shown that the bandgap can be further widened when compared to uncorrelated disorder. The obtained results indicates that a combination of the gradient profile with some level of disorder, typically resulting from random fields with larger correlation lengths, tends to give improved vibration attenuation when compared to a optimized gradient rainbow metamaterial. It opens new and innovative ways for the design of broadband rainbow metastructures for vibration attenuation.

In this paper, a thermal inkjet printing simulation model is established in the CFD simulation platform, and the influence of inkjet driver parameters and ink physical parameters on the printing process is studied by numerical simulation. The evaporation-condensation model is coupled with the VOF multiphase flow model in Fluent software to establish a thermal inkjet printing process simulation model. Based on the orthogonal test method, we investigate the influence of fluid physical parameters (ink viscosity, surface tension) and inkjet driver parameters (heater temperature value) on droplet formation by changing the physical parameters of the material and the boundary conditions of the model. Through the comparison of the results, exploring the adjustment rules of thermal inkjet technology and obtaining the optimal combination of material and process parameters for high-quality ink drop formation.

Visual images have visual features that are convenient for human observation, while infrared images have thermal features. Image fusion of visual image and the infrared image is the integration of most conductive intrinsic features by still preserving its original visual information concealed in. Image fusion has significant importance in different areas application in special environment (e.g. military, security and in surveillance) and human vision. In recent years, due to the-state-of-the-art discriminative performance, deep learning has been greatly applied in field of image fusion due to its excellent feature extraction ability. This paper employs an innovative approach for image fusion for infrared and visual images using a pre-trained dense block neural network. The model uses an isolated encoder-decoder bi-layered deep learning models, each for visual images and infrared images. An intermediary novel fusion protocols was designed using a hybrid of fusion and L1_norm strategy to infuse both visual and infrared image features. Finally, the resulting images of decoders are made subject to a weighting average to obtained fusion resulting image. Based on subjective evaluation, the proposed model, outperform all existing state of the art literature studies, via different objective evaluation indicators.

Remote sensing satellites can simultaneously capture high spatial resolution panchromatic (PAN) images and low spatial resolution multispectral (MS) images. Pan-sharpening in the fusion of remote sensing images aims to generate high-resolution MS images by integrating the spatial information of PAN images and the spectral characteristics of MS images. In this study, a novel deep perceptual patch generative adversarial network (FDPPGAN) was proposed to solve the pan-sharpening problem. First, a perception generator was constructed, it included, a matching module, which can process as input images of different resolutions, a fusion module, a reconstruction module based on the residual structure, and a module for the extracting perceptual features. Second, patch discriminator was utilized to convert the dichotomy of the sample into that multiple partial images of the same size to ensure that the generated results can retain more detailed features. Finally, the loss function of FDPPGAN comprised perceptual feature loss, content loss, generator loss, and discriminator loss. Experiments on the QuickBird and WorldView datasets demonstrated that the proposed algorithm is superior to state-of-the-art algorithms in subjective and objective indexes.

With the popular use of IoT devices, edge computing has been widely applied in the Internet of things (IoT) and regarded as a promising solution for its wide distribution, decentralization, low latency. At the same time, in response to the massive computing data and intelligent requirements of various applications in the IoT, artificial intelligence (AI) technology has also achieved rapid development. As a result, edge intelligence (EI) for the Internet of Things has attracted widespread attention. Driven by the requirement that making full use of data, machine learning (ML) models trained in EI are usually shared. However, there may be some security and privacy issues due to the openness and heterogeneity of edge intelligence. How to ensure flexible data access and data security as well as the accountability for edge nodes and users in EI model sharing have become important issues. In this article, we propose a Ciphertext Policy Attribute Based Proxy Re-encryption (CP-ABPRE) scheme with accountability to address the security and privacy issues in EI model sharing. In our scheme, a user can delegate the access right to others to make model access more flexible. Furthermore, each entity that may need to be held accountable is embedded a unique ID to achieve traceability. Finally, security analysis and performance evaluation are given to prove that our scheme is CPA secure and does not lose much efficiency with more features.

Briquette coals with different cement contents are frequently used to study the coal body’s properties. In this study, the deformation and strength of briquette coal samples with 0, 5, 10, and 20% cement contents were experimentally and theoretically investigated using the acoustic emission (AE) characteristics monitored during the uniaxial compression tests. The results show that the uniaxial compression process of raw coal and briquette coal samples can be subdivided into compaction, elastic, plastic (yield), and brittle failure stages. With an increase in cement content, briquette coal samples undergo the elastic and plastic stages, and their postpeak stress drop rate gradually grows, and their plastic deformation is followed by brittle failure. The uniaxial compressive strength and elastic modulus of briquette coal samples show a linearly increasing relationship with cement content, while their Poisson’s ratio decreases gradually. During the uniaxial compression, raw coal and briquette coal samples produce the AE signals. The overall AE signal of briquette coal samples is relatively low, and there are no obvious AE events in raw coal samples. The uniaxial compressive strength, elastic modulus, and Poisson’s ratio of briquette coal samples with a 20% cement content and their AE signal cumulative amplitude, count, and energy values are very close to the corresponding parameters of raw coal samples. Therefore, they can be used for simulating raw coal samples in laboratory tests.

Iturin A is a natural antifungal agent that is widely used in the agriculture and food industries. In the present study, a new modified chitosan sub-micron, succinaldehydic acid (SAC) - chitosan (CS) system was synthesised by microwave irradiation and then as a carrier for capsulation of Iturin A (SAC-CS-IA). The structures of SAC-CS and SAC-CS-IA were characterised by SEM, NMR and FTIR. The size distribution suggested that the average size of SAC-CS and SAC-CS-IA was from 1.5 to 2.5 μm. An encapsulation efficiency of 92.02% under an adaptive pH (pH = 5) and time (5.5 h) was used. The study of release kinetics shows that about 80% of Iturin A was released in 25 days. An antifungal activity assay indicated that SAC-CS-IA exhibited higher antifungal activity against Ceratocystis fimbriata and Rhizopus strolonifer with 75.05 ± 3.24% and 80.54 ± 2.65%, respectively. The results indicate that the SAC-CS can improve the stability of IA on heat and pH with a wide range and tolerance most of enzymes. Actual tuber storage suggested that SAC-CS-IA can significantly inhibit pathogen fungal infection and reduce toxin product. Meanwhile, SAC-CS-IA could retain the water, starch, and soluble sugar contents. Low residue assay indicated that SAC-CS-IA could be used as an antifungal and anti-rotting agent in agriculture and food applications.

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage (SAGD) process. A mathematical approach was proposed in this research that fully couples the hydraulic, mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks. The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water. It was found that the predicted bottom hole pressures (BHPs) match closely with the field observed data. An elliptical dilation zone developed around the dual wells with relatively high pore pressure, porosity, permeability and temperature, implying good interwell hydraulic communication between both wells. The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells, though to a lesser extent. In summary, the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

Monolayer graphene with high quality was synthesized by pyrolysis of 6H-silicon carbide single crystal in a medium frequency induction heating furnace. The obtained graphene was systematically studied via Raman spectroscopy, atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM). The characterized results showed that monolayer graphene with high quality was obtained when the growth temperature, Ar flow, and growth pressure was 2000 °C, 150 sccm, and 15 Torr, respectively. Our results showed that growth temperature, Ar flow, and growth pressure had great influence on the quality of the obtained monolayer graphene. Compared with the conventional monolayer graphene preparation methods, our method is simple, controllable, and repeatable, which greatly expands the application prospect of graphene.

Because of the large earth pressure and high inner water pressure, high-stiffness segmental joints with ductile-iron joint panels (DIJPs) are needed to improve the bearing capacity of segmental joints for deep-buried drainage shield tunnels. DIJPs are always mounted in high-stiffness segmental joints to restrain deformation and reduce the joint rotation angle, thus improving the bearing capacity of segmental joints. Full-scale tensile experiments on the performance of DIJPs with different structural styles, in terms of deformation characteristic, anchorage property, and failure mode, were carried out to evaluate the applicability of DIJPs for deep-buried drainage shield tunnels. The test results show that bending deflection appears in DIJPs if the flexural rigidity of DIJPs is insufficient, which will cause bending-tensile failure for the DIJP anchor bars. The failure position is in the weak interface: the screw thread position of the anchor bars, which is the connection position between the anchor bars and DIJPs; connecting the anchor bars with the main reinforcing bars by stirrups or filling the hand hole can restrain the bending deflection of the DIJP and improve the bearing capacity of the anchor bars. When the anchor bars are connected with the main reinforcing bars, the deformation of the DIJP decreases by 5.6%, and the bearing capacity of the anchor bars increases by 31.1%; further, if the hand hole are filled with cement, the deformation of the DIJP decreases by 22.2% and the bearing capacity of the anchor bars increases by 34.1%. Considering the failure modes of the specimens, it is believed that increasing the flexural rigidity of the DIJP and improving the connection performance between the DIJP and anchor bars can improve the behavior of the DIJP and anchor bars.

Soluble microbial products constitutes a major fraction of organic matters in biological wastewater treatment effluent, severely challenging downstream deep purification treatment processes. Effective control of soluble microbial products necessitate a full understanding on soluble microbial products properties in biological bioreactors, including the rapidly developing aerobic granular sludge systems. Here, we provide insights into the contents and composition dynamics of soluble microbial products during start-up and steady state of aerobic granular sludge. The effluent concentrations of soluble microbial products in the aerobic granular sludge reactor increased rapidly from 22.1 mg/L to 32.1 mg/L during the initial sludge granulation stage and declined drastically to 11.7 mg/L during granules maturing. The polysaccharides was dominant composition of soluble microbial products, which was decreased from 90% to 40% during granulation process. The ultimate effluent soluble microbial products content was lower than that in a floccular sludge reactor, indicating a higher effluent quality of the aerobic granular sludge system. This work highlights the superiority of aerobic granular sludge in improving effluent quality and implies a necessity to control soluble microbial products at the initial granulation process which has been overlooked before.

Studying the parameters of a coal and gas hole (CGOH), such as the hole shape, hole size and volume, coal quantity of CGOH, coal throw distance, calculated hole density, and gas pressure, is helpful in revealing the coal and gas outburst mechanism. In this study, we found that there were close mathematical relationships between these parameters. A nonlinear composite function relationship (CGOH parameter equation) was observed between the coal quantity, CGOH volume, and throw distance. The correctness of these relationships was verified using the Origin software. The stagnation point and inflection point of the parameter curve were obtained through the derivation of the parameter equation, and the transformation path from coal and gas outburst to coal and gas extrusion or dumping was clarified. At the same time, the equations of gas pressure, coal quantity, and throw distance are derived.

Phononic crystals (PnCs) and metamaterials are widely investigated for vibration suppression owing to the bandgaps, within which, wave propagation is prohibited or the attenuation level is above requirements. The application of PnCs and metamaterials is, however, limited by the widths of bandgaps. The recently developed rainbow structures consisting of spatially varied profiles have been shown to generate wider bandgaps than periodic structures. Inspired by this design strategy, rainbow metamaterials composed of nonperiodic mass blocks in two-dimensional (2D) space were proposed in the present study. The blocks were connected by curved beams and tessellated with internal voids to adjust their masses. In order to demonstrate the effects of the rainbow design, two 2D metamaterials, with periodic and nonperiodic units, respectively, were investigated and manufactured using additive manufacturing technologies. Receptance functions, i.e., displacement frequency response functions, of the manufactured metamaterials were calculated with finite element models and measured with a testing system containing a mechanical shaker, an impedance head, and a laser Doppler vibrometer. The obtained numerical and experimental results showed that the metamaterial with rainbow blocks has extended bandgaps compared with the periodic metamaterial.

We report a new type of three-dimensional architected polymer foams composed of perforated spherical shells and flat strut connectors, which can be precisely produced by 3D printing techniques. We investigate the effects of foam architectures, manufacturing process, and constitutive material on the deformation patterns and failure modes of the proposed architected foams. We demonstrate that flat strut connectors offer unprecedented design flexibility for controlling the mechanical performance. By tuning the geometric parameter of flat strut connectors, the stiffness of architected foams can increase about one order of magnitude while the relative density increases only by 5%. Furthermore, the failure modes can be engineered from a catastrophic one to a progressive one by using weak flat strut connectors. Our experiments elucidate the salient roles of the layer-by-layer manufacturing process and constitutive polymer on the mechanical behavior of the proposed architected foams.

Additive manufacturing has been used to propose several designs of phononic crystals and metamaterials due to the low cost to produce complex geometrical features. However, like any other manufacturing process, it can introduce material and geometrical variability in the nominal design and therefore affect the structural dynamic performance. Locally resonant metamaterials are typically designed such that the distributed resonators have the same natural frequency or, in the case of rainbow metastructures, a well-defined spatial profile. In this work, the effects of the break of periodicity caused by additive manufacturing variability on the attenuation performance of a multi-frequency metastructure is investigated. First, an experimental investigation on the manufacturing tolerances of test samples produced from a Selective Laser Sintering process are assessed and variability levels are used to propose a random field model for the metastructure. Subsequently, the stochastic model is used to investigate the vibration suppression performance of broadband multi-frequency metastructures. An analytical model based on a transfer matrix approach is used to calculate transfer receptance due to a point time harmonic force in a finite length metastructure, which is composed of evenly spaced non-symmetric resonators attached to a beam with Π-shaped cross-section. This design creates a multi-frequency metastructure, i.e. band gaps in more than one frequency band. Individual samples of the random fields are used to show that the mistuned resonators can change the vibration attenuation performance of the metastructure and that even small levels of variability, given by less than 1% for the mass and less than 3% for the Young’s modulus can have a significant effect on the overall vibration attenuation performance of the metastructure when considered together. It is also shown that different spatial profiles can have a significant effect on the vibration attenuation performance in both band gaps. Therefore, the modelling of the uncertainty metastructures has to take into account the spatial correlation of the properties of the metastructure resonators. The obtained results are expected to be useful for further robust design in mass produced industrial applications.

N-type organic semiconductors are notoriously unstable in air, requiring the design of new materials that focuses on lowering their LUMO energy levels and enhancing their air stability in organic electronic devices such as organic thin-film transistors (OTFTs). Since the discovery of the notably air stable and high electron mobility polymer poly{[N,N′-bis (2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,29-bisthiophene)} (N2200), it has become a popular n-type semiconductor, with numerous materials being designed to mimic its structure. Although N2200 itself is well-studied, many of these comparable materials have not been sufficiently characterized to compare their air stability to N2200. To further the development of air stable and high mobility n-type organic semiconductors, N2200 was studied in organic thin film transistors alongside three N2200-based analogues as well as a recently developed polymer based on a (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3 H,7 H)-dione (IBDF) core. This IBDF polymer has demonstrated promising field-effect mobility and air stability in drop-cast OTFTs. While N2200 outperformed its analogues, the IBDF-based polymer displayed superior air and temperature stability compared to N2200. Overall, polymers with more heteroatoms displayed greater air stability. These findings will support the development of new air-stable materials, and further demonstrate the persistent need for the development of novel n-type semiconductors.

As one of the most promising renewable energy source, biomass energy has great potential. In this case, it’s essential for the western ethnic regions in China to initiate a better use of the biomass energy, which will protect the environment, drive the economic growth, and reduce the regional disparities. With a certain industrial basis, the conditions for the development of biomass energy in China’s western ethnic regions are unique. For better development of biomass energy in these areas, the government should optimize the industrial structure of biomass energy and attach importance both to the talent training and the improvement of technical capabilities. Besides, the government should adjust measures to the local conditions and execute multi-development.

In this study, we present an optimization scheme for the resonator distribution in rainbow metamaterials that are constitutive of a Π-shaped beam with parallel plate insertions and two sets of spatially varying cantilever-mass resonators. To improve the vibration attenuation of the rainbow metamaterials at frequencies of interest, two optimization strategies are proposed, aiming at minimizing the maximum and average receptance values respectively. Objective functions for both single and multiple frequency ranges optimization are set up with the frequency response functions predicted by an analytical model. The masses of the two sets of resonators clamped at different side walls of the Π-shaped beams constitute the set of design variables. Optimization functions are solved out with the employment of the Genetic Algorithm method. Dedicate case studies are subsequently conducted to show the feasibility of the proposed scheme. The receptance values are found greatly reduced within the single and multiple optimization frequency ranges. Moreover, it is found that, the maximum value based objective function could lead to optimal structures with wider bandgaps but weaker vibration attenuation, while the optimal structure by the average value based objective function has the opposing trend with narrower bandgaps but enhanced vibration attenuation. Objective strategies should be selected according to the application requirements.

We hereby report for the first time on the design, manufacturing and testing of a three-dimensional (3D) nearly-periodic, locally resonant phononic crystal (PnC). Most of the research effort on PnCs and metamaterials has been focused on the enhanced dynamic properties arising from their periodic design. Lately, additive manufacturing techniques have made a number of designs with intrinsically complex geometries feasible to produce. These recent developments have led to innovative solutions for broadband vibration attenuation, with a multitude of potential engineering applications. The recently introduced concept of rainbow metamaterials and PnCs has shown a significant potential for further expanding the spectrum of vibration attenuation in such structures by introducing a gradient profile for the considered unit cells. Given the above, it is expected that designing non-periodic PnCs will attract significant attention from scientists and engineers in the years to come. The proposed nearly-periodic design is based on cuboid blocks connected by curved beams, with internal voids in the blocks being implemented to adjust the local masses and generate a 3D rainbow PnC. Results show that the proposed approach can produce lightweight PnCs of a simple, manufacturable design exhibiting attenuation bandwidths more than two times larger than the equivalent periodic designs of equal mass.

We experimentally and numerically investigate elastic wave propagation in a class of lightweight architected materials composed of hollow spheres and binders. Elastic wave transmission tests demonstrate the existence of vibration mitigation capability in the proposed architected foams, which is validated against the numerically predicted phononic band gap. We further describe that the phononic band gap properties can be significantly altered through changing hollow sphere thickness and binder size in the architected foams. Importantly, our results indicate that by increasing the stiffness contrast between hollow spheres and binders, the phononic band gaps are broadened and shifted toward a low-frequency range. At the threshold stiffness contrast of 50, the proposed architected foam requires only a volume fraction of 10.8% while exhibiting an omnidirectional band gap size exceeding 130%. The proposed design paradigm and physical mechanisms are robust and applicable to architected foams with other topologies, thus providing new opportunities to design phononic metamaterials for low-frequency vibration control.

Object extraction provides the basis for subsequent tasks such as object recognition, and its importance is self-evident. For this purpose, this paper proposes an object extraction algorithm based on saliency prior information. Firstly, the SIFT operator and the oriented edge forest method are used to extract the saliency points and the saliency edges respectively. Then construct a simple small convolutional neural network for the saliency fusion task, and fuse the saliency point and the saliency edge to obtain the saliency fusion map. Then the fusion map is added to the object extraction network structure as a priori information. In this paper, the residual network is used for the object extraction task, and finally the high-quality object extraction work is realized. The algorithm uses IOU parameters and Precision as the quantitative evaluation index, and uses qualitative analysis to comprehensively analyse the experimental results. Experiments show that the proposed algorithm has good results in both image quality and visual, and has good robustness.

The electron acceptor building block N,N′-dialkoxynaphthalenediimide (NDIO) has been, for the first time, used to develop an n-type polymer semiconductor, P(NDIO2OD-T). The polymer exhibits unipolar electron charge transport with an electron mobility of up to 5.4 × 10−3 cm2 V−1 s−1 in organic thin-film transistors (OTFTs) and shows good air-stability. When it is used as the acceptor in all-polymer solar cells (all-PSCs), a PCE of up to 3.25% is achieved. The performances of the OTFTs and all-PSCs based on this polymer have improved compared to its N,N′-dialkyl-substituted analogue.

Bio-oil contained a large number of macromolecular compounds like asphalt, which made it difficult to obtain accurate results from direct test analysis. In this study, hydrothermal liquefaction (HTL) bio-oil of Spirulina (300 °C, 30 min, 10 MPa) was underwent column chromatography separation (CCS) process to retain the macromolecular substances in the column, which improved the accuracy of subsequent analysis results. The obtained fractions were characterized by Thermo-Gravimetric Analysis (TG), Gas Chromatography-Mass Spectrometry (GC-MS) analysis, Elemental Analysis, and Fourier Transform Infrared (FT-IR) Spectroscopy Analysis. TG analysis showed that a significant amount of components coexisting in high-boiling-range residue in bio-oil could be isolated into quasi-gasoline and quasi-kerosene species, so the low boiling-point fractions of bio-oil between 30-250 °C increased. GC-MS proved that CCS could effectively separate bio-oil and the number of detected components in bio-oil increased from 25 to 109 after CCS. The results of elemental analysis and FT-IR indicated that the components of the bio-oil were separated according to the polarity , and the higher heating values(HHVs) of each distillate oil (38.32-42.19 MJ kg−1) was significantly higher than the bio-oil before CCS (31.83-36.04 MJ kg−1). Comprehensive results of multiple analysis could help determine the market application prospects of bio-oil. In addition, tert-hexadecanethiol was studied as a representative Sulphur-compound to surmise its generation mechanism. The speculation of the conversion pathway of sulphur (S) element could provide a basis for a better understanding of the HTL reaction mechanism.

The extracellular polymeric substances (EPS) of activated sludge are a mixture of high molecular weight polymers secreted by microorganisms, which are mainly composed of proteins, polysaccharides and humic substances. It is widely accepted that EPS have a good adsorption ability for pollutants with different functional groups. However, recent studies showed the EPS had an inhibitory effect on pollutant sorption, which is contradictory to previous viewpoint. Therefore, in this study, three types of activated sludge with different EPS contents and compositions were used to investigate the role of EPS in an antibiotic-trimethoprim (TMP) sorption process at environmentally relevant concentration. The in situ experiments results showed the adsorption capacity of activated sludge for TMP were increased from 2.98, 5.37 and 28.33 μg/g VSS to 7.87, 12.93 and 150.24 μg/g VSS in nitrifying activated sludge, wastewater treatment plant activated sludge and anaerobic ammonia-oxidized activated sludge, respectively after EPS extracted. The adsorption process can be well described by the pseudo-second-order kinetic model. Results of zeta potential, contact angles and infrared spectrum showed TMP replacing proteins embedded into the cell membrane enhancing the TMP adsorption capacity of activated sludge after EPS extraction. Our results demonstrated that less proteins in EPS of activated sludge is more beneficial for TMP adsorption removal.

A semi-analytical model based on three-dimensional (3-D) periodical unit cells (PUCs) is developed to predict the sound absorption performance of sintered fiber metals as a function of porosity and fiber diameter. The PUC is developed from the most simplistic one (PUC1) to the comparatively complex one (PUC3) by taking into account the shifting of fiber position and the non-uniformity of fiber distribution. Upon numerically solving both the static Stokes (aiming at viscous flow) and diffusion-controlled reaction (aiming at inertial flow) equations defined inside the PUC, the transport parameters in the commonly used JCA (Johnson-Champoux-Allard) model for porous acoustic materials are obtained. Upon introducing the Kozeny number and pore shape factor, key transport parameters are determined as functions of fiber diameter and porosity using the proposed semi-analytical model. The theoretically predicted sound absorption coefficients are compared with experimental measurements of sintered fiber metal samples, with good agreement achieved. The validated model is then used to systematically analyze the influence of fiber diameter and porosity on sound absorption. The model reveals the physical mechanisms underlying viscous and thermal dissipation of sound energy due to fluid-structure interaction in sintered fiber metals.

The design of graphene-based composite with high thermal conductivity requires a comprehensive understanding of phonon coupling in nanosized graphene. We extended the two-temperature model to coupled groups of phonons. The study give new physical quantities, the phonon-phonon coupling factor and length, to characterize the couplings quantitatively. Besides, our proposed coupling length has an obvious dependence on system size. Our studies can not only observe the nonequilibrium between different groups of phonons but explain theoretically the thermal resistance inside nanosized graphene.

Metamaterials with multiple resonators have been widely investigated for the purpose of generating multiple stop bands or broadening the attenuation bandwidth. The multiple resonators could be connected end to end in a line, namely, in-series connection, or connected individually to the host structures, namely, in-parallel connection. This paper investigates the influence of the resonator connection methodology on the frequency response functions of metamaterial beams with multiple resonators and exhibits an approach for optimizing their resonator distribution over the structure. The receptance functions of metamaterial beams with various resonator connection architectures are calculated by a transfer matrix model, which is verified through finite element model results. It is demonstrated that resonator interconnection architectures have a great impact on the global dynamic properties of metamaterials. An optimization strategy is subsequently proposed to find out the optimal resonator connection architectures and mass distributions that could minimize the maximal receptance functions in targeted single and multiple frequency ranges. The objective functions within single targeted frequency ranges are solved by the adoption of the genetic algorithm method. The weighted sum method is used to gain an optimal solution for multi-frequency range optimization. The metamaterial beams with optimal resonator connection methods and mass distributions demonstrate greatly enhanced vibration attenuation at frequencies of interest compared with other beams. The work is expected to provide the necessary theoretical basis and incentive for future researchers working on the design of metamaterials with extended, tuned, and optimized stop bands.

An optimization method for sound absorption of gradient (multi-layered) sintered metal fiber felts is presented. The theoretical model based on dynamic flow resistivity is selected to calculate the sound absorption coefficient of the sintered metal fiber felts since it only requires three key morphological parameters: fiber diameter, porosity and layer thickness. The model predictions agree well with experimental measurements. Objective functions and constraint conditions are then set up to optimize separately the distribution of porosity, fiber diameter, and simultaneous porosity and fiber diameter in the metal fiber. The optimization problem for either a sole frequency or a pre-specified frequency range is solved using a genetic algorithm method. Acoustic performance comparison between optimized and non-optimized metal fibers is presented to confirm the effectiveness of the optimization method. Gradient sintered metal fiber felts hold great potential for noise control applications particularly when stringent restriction is placed on the total volume and/or weight of sound absorbing material allowed to use.

The influence of surface roughness such as short fibers on sound propagation in cylindrical micro-tubes is investigated, both theoretically and numerically. Based on the calculated velocity and temperature fields, a theoretical model is developed to evaluate the sound propagation performance of composite micro-tubes containing periodical fibrous surface roughness elements. Finite element models are developed to validate the theoretical model, with good agreements achieved. The sound propagation performance of micro-tubes with surface roughness is compared with that of micro-tubes without surface roughness, with the influence of roughness geometry on sound propagation systematically investigated. Surface roughness can dramatically increase the sound energy consumed by viscous effect and decrease the sound energy consumed by thermal effect, resulting enlarged sound absorption.

In this study, we propose a ‘rainbow’ metamaterial to achieve broadband multi-frequency vibration attenuation. The rainbow metamaterial is constituted of a Π-shaped beam partitioned into substructures by parallel plates insertions with two attached cantilever-mass acting as local resonators. Both resonators inside each substructure can be non-symmetric such that the metamaterial can have multi-frequency bandgaps. Furthermore, these cantilever-mass resonators have a progressively variant design along the beam, namely rainbow-shaped, for the purpose of achieving broader energy stop bands. Π-shaped beams partitioned by parallel plate insertions can be extended to honeycomb sandwich composites, hence the proposed rainbow metamaterial can serve as a precursor for future honeycomb composites with superior vibration attenuation for more industrial applications. A mathematical model is first developed to estimate the frequency response functions of the metamaterial. Interaction forces between resonators and the backbone structure are calculated by solving the displacement of the cantilever-mass resonators. The plate insertions are modeled as attached masses with both their translational and rotational motion considered. Subsequently, the mathematical model is verified by comparison with experimental results. Metamaterials fabricated through an additive manufacturing technique are tested with a laser doppler receptance measuring system. After the validation of the mathematical model, a numerical study is conducted to explore the influences of the resonator spatial distributions on the frequency response functions of structures. Results show that for metamaterials with both symmetric and non-symmetric resonators, rainbow-shaped resonators can introduce inertial forces inside wider frequency range when compared to the periodic resonators of the same total mass, hence broader bandgaps. Meanwhile, the attenuation inside the bandgaps decreases when the bandgap become broader. Metamaterials with broadband multi-frequency range vibration attenuation can be achieved with non-symmetric sinusoidally varying resonators.

Single layer molybdenum disulfide (SLMoS2), a semiconductor possesses intrinsic bandgap and high electron mobility, has attracted great attention due to its unique electronic, optical, mechanical and thermal properties. Although thermal conductivity of SLMoS2 has been widely investigated recently, less studies focus on molybdenum disulfide nanotube (MoS2NT). Here, the comprehensive temperature, size and strain effect on thermal conductivity of MoS2NT are investigated. Thermal conductivity is obtained as 16 Wm−1 K−1 at room temperature, and it has a ∼T−1 dependence on temperature from 200 to 400 K and a ∼Lβ dependence on length from 10 to 320 nm. Interestingly, a chirality-dependent strain effect is identified in thermal conductivity of zigzag nanotube, in which the phonon group velocity can be significantly reduced by strain. This work not only provides feasible strategies to modulate the thermal conductivity of MoS2NT, but also offers useful insights into the fundamental mechanisms that govern the thermal conductivity, which can be used for the thermal management of low dimensional materials in optical, electronic and thermoelectrical devices.

Solid-state lithium-ion batteries (SSLIBs) become the new generation of devices for energy storage due to better performance and safety. Poly (ethylene oxide) (PEO) based material is an alternative promising candidate for solid electrolytes, while its thermal conductivity is crucial to heat dissipation inside batteries. In this work, we study the thermal conductivity of PEO by molecular dynamics simulation. Interestingly, by enhancing the structure order, thermal conductivity of crystalline PEO is obtained as high as 60 Wm−1 K−1 at room temperature, which is two orders higher than the value (0.37 Wm−1 K−1) of amorphous PEO. Moreover, thermal conductivity of crystalline PEO shows a significant stepped negative temperature dependence, which is attributed to the temperature-induced morphology change. Our study offers useful insights into the fundamental mechanisms that govern the thermal conductivity of PEO but not hinder the ionic transport, which can be used for the thermal management and further optimization of high-performance SSLIBs.

For decode-and-forward (DF) multiple-input multiple-output (MIMO) relay communication systems, we present a scheme for joint symbol and channel estimation. In this scheme, symbols at source and relay are coded by Khatri-Rao Space-Time codes and then received signals are formulated as two parallel factor (PARAFAC) models in relay and destination respectively. We also analyze the uniqueness of decomposition for the constructed PARAFAC model. On the assumption that channel state information (CSI) is unknown at source, relay and destination, all signal matrices and CSI can be jointly estimated by designing relevant algorithm to fit the parallel factor (PARAFAC) model. Simulation results indicate that proposed scheme has higher accuracy in channel estimation and better performance in signal detection.

A hybrid acoustic metamaterial is proposed as a new class of sound absorber, which exhibits superior broadband low-frequency sound absorption as well as excellent mechanical stiffness/strength. Based on the honeycomb-corrugation hybrid core (H-C hybrid core), we introduce perforations on both top facesheet and corrugation, forming perforated honeycomb-corrugation hybrid (PHCH) to gain super broadband low-frequency sound absorption. Applying the theory of micro-perforated panel (MPP), we establish a theoretical method to calculate the sound absorption coefficient of this new kind of metamaterial. Perfect sound absorption is found at just a few hundreds hertz with two-octave 0.5 absorption bandwidth. To verify this model, a finite element model is developed to calculate the absorption coefficient and analyze the viscous-thermal energy dissipation. It is found that viscous energy dissipation at perforation regions dominates the total energy consumed. This new kind of acoustic metamaterials show promising engineering applications, which can serve as multiple functional materials with extraordinary low-frequency sound absorption, excellent stiffness/strength and impact energy absorption.

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption.

The multi-layered coal strata in Lin-Xing block of China is rich in tight sandstone gas and the coalbed methane (CBM). The feasibility of multi-gas production and the optimal layer for fracturing in multi-layers requires a better understanding of fracture vertical extension mechanism through sandstone coal interbedding. To analyze the problems, six true tri-axial experiments were conducted on the multi-layered specimens of sandstone and coal outcrops. The transition zone was simulated by the cement with certain strength and thickness. In the experiments, the perforation position, fluid viscosity, and lithological difference were discussed. The results showed that the effect of viscosity exhibited a stepped manner as a function of fracture complexity. High-viscosity fluid significantly improved the fracture penetration ability when fracturing in coal layer. The results also show that when indirectly fracturing in sandstone, low-viscosity fluid was under the risk of natural fracture activation near wellbore to cause fracturing failure. When both layers were perforated, complex fracture network was easily formed as multi-layers were fractured. Perforation in both sandstone and coal layers were the best method based on the fracture penetration ability and the overall fracture complexity. T-shaped and step-wise fractures were found in the interface. The transition zone made it easier for fracture vertical extension through layers. The field production data was in good agreement with the experimental results. These results provide a guideline for the optimal perforation position selection and fracturing parameters in coal strata.

The particle size of coal particles is an important factor affecting the physical and mechanical properties of coal. In this study, uniaxial and triaxial compression tests were conducted to investigate the effects of coal particle size on the physical and mechanical properties of briquettes and their impact mechanism using a rock mechanics test-150B servo system (RMT-150B). The results showed that the uniaxial compression strength, elastic modulus and deformation modulus of briquettes increase when particle size is decreased. The deformation characteristics of the briquettes directly prepared by raw tectonic coal were similar to those of coal specimens with a particle size of 0.18&ndash, 0.25 mm. The cohesion and strength of coal specimens increased when particle size was decreased, and the plastic deformation capacity decreased when particle size was decreased, showing a strong correlation. The f briquette directly prepared by the raw tectonic coal had a strength between that of coal specimens with a particle size of 2&ndash, 6 mm and those with a particle size of 0.18&ndash, 0.25 mm. The mechanical properties of briquettes mainly depend on the meshing force between the coal particles. The smaller the particles, the greater the mechanical meshing force. The &ldquo, floating particles&rdquo, generated in the voids between coal particles during the preparation process, are a significant factor affecting the plasticity characteristics. The research results may be used as a basic reference in the study of the mechanical properties of tectonic coal, gas migration and coal and gas outburst mechanisms.

Image degradation caused by shadows is likely to cause technological issues in image segmentation and target recognition. In view of the existing shadow removal methods, there are problems such as small and trivial shadow processing, the scarcity of end-to-end automatic methods, the neglecting of light, and high-level semantic information such as materials. An end-to-end deep convolutional neural network is proposed to further improve the image shadow removal effect. The network mainly consists of two network models, an encoder&ndash, decoder network and a small refinement network. The former predicts the alpha shadow scale factor, and the latter refines to obtain sharper edge information. In addition, a new image database (remove shadow database, RSDB) is constructed, and qualitative and quantitative evaluations are made on databases such as UIUC, UCF and newly-created databases (RSDB) with various real images. Using the peak signal-to-noise ratio (PSNR) and the structural similarity (SSIM) for quantitative analysis, the algorithm has a big improvement on the PSNR and the SSIM as opposed to other methods. In terms of qualitative comparisons, the network shadow has a clearer and shadow-free image that is consistent with the original image color and texture, and the detail processing effect is much better. The experimental results show that the proposed algorithm is superior to other algorithms, and it is more robust in subjective vision and objective quantization.

Hydrophilic acrylamide‐based hydrogels are emerging platforms for numerous applications, but the resources to fully exploit these materials are currently limited. A deep understanding of the molecular‐level structure/property relationships in hydrogels is crucial to progressing these efforts. Such relationships can be challenging to elucidate on the basis of experimental data alone. Here, molecular simulations are used as a complementary strategy to reveal the molecular‐level phenomena that govern the thermo‐mechanical properties of hydrogels. The focus is on acrylamide‐based hydrogels cross‐linked with N,N′‐methylenebisacrylamide, generated using previously established computational cross‐linking procedure. The water content is found to be a key determinant in the elastic response of these hydrogels, with enhanced tensile and shear properties at low water content. However, it is also found that increasing water content enhances the hydrogel's thermal conductivity, with the dominant contribution arising from the non‐bonded contributions to the heat flux. In addition, chemical cross‐linking improves the heat transfer properties of the hydrogel, whereas a reduction in convective heat transfer is predicted with an increase in hydrogel cross‐linking. These simulations provide a rational basis for designing and testing customized hydrogel formulations for maximizing both thermal conductivity and mechanical properties.

An effective strategy is proposed to enhance the oxygen reduction reaction (ORR) performance of multiwall carbon nanotubes (MWCNTs) in both acid and alkaline electrolytes by coating them with a layer of biomass derivative N-doped hydrothermal carbons. The N-doped amorphous carbon coating plays triple roles: it (i) promotes the assembly of MWCNTs into a 3D network therefore improving the mass transfer and thus increasing the catalytic activity; (ii) protects the Fe-containing active sites, present on the surface of the MWCNTs, from H2O2 poisoning; (iii) creates nitrogenated active sites and hence further enhances ORR activity and robustness.

Wave effects of phonons can give rise to controllability of heat conduction beyond that by particle scattering at surfaces and interfaces. In this work, we propose a new class of 3D nanostructure: a silicon-nanowire-cage (SiNWC) structure consisting of silicon nanowires (SiNWs) connected by nano-cross-junctions (NCJs). We perform equilibrium molecular dynamics (MD) simulations, and find an ultralow value of thermal conductivity of SiNWC, 0.173 Wm-1K-1, which is one order lower than that of SiNWs. By further modal analysis and atomistic Green's function calculations, we identify that the large reduction is due to significant phonon localization induced by the phonon local resonance and hybridization at the junction part in a wide range of phonon modes. This localization effect does not require the cage to be periodic, unlike the phononic crystals, and can be realized in structures that are easier to synthesize, for instance in a form of randomly oriented SiNWs network., Nano-cross-junction, silicon-nanowires-cage, thermal conductivity, local phonon resonance, random network of silicon nanowires

Reaction of BiCl3 with 2-(2-hydroxy-3-methoxyphenyl)benzimidazole (HL) in tetrahydrofuran (THF) under reflux gave mononuclear complex of formula [Bi(HL)2Cl3·H2O]. The binding interaction of the complex with bovine serum albumin (BSA) was investigated using the fluorescence quenching method. The experimental results showed that the complex could bind to BSA in the proportion of about 1:1. The binding reaction was spontaneous and hydrophobic force played major role in the reaction. The binding of the complex to BSA could change the microenvironment and conformation of BSA.

An ultrathin (subwavelength) hierarchy multi-slit metamaterial with simultaneous negative effective density and negative compressibility is proposed to absorb sound over a wide frequency range. Different from conventional acoustic metamaterials having only negative real parts of acoustic parameters, the imaginary parts of effective density and compressibility are both negative for the proposed metamaterial, which result in superior viscous and thermal dissipation of sound energy. By combining the slit theory of sound absorption with the double porosity theory for porous media, a theoreticalmodel is developed to investigate the sound absorption performance of the metamaterial. To verify the model, a finite element model is established to calculate the effective density, compressibility, and sound absorption of the metamaterial. It is theoretically and numerically confirmed that, upon introducing micro-slits into the meso-slits matrix, the multi-slit metamaterial possesses indeed negative imaginary parts of effective density and compressibility. The influence of micro-slits on the acoustical performance of the metamaterial is analyzed in the context of its specific surface area and static flow resistivity. This work shows great potential of multi-slit metamaterials in noise control applications that require both small volume and small weight of sound-absorbing materials.

Robust Stable Marriage (RSM) is a variant of the classical Stable Marriage problem, where the robustness of a given stable matching is measured by the number of modifications required for repairing it in case an unforeseen event occurs. We focus on the complexity of finding an (a,b)-supermatch. An (a,b)-supermatch is defined as a stable matching in which if any 'a' (non-fixed) men/women break up it is possible to find another stable matching by changing the partners of those 'a' men/women and also the partners of at most 'b' other couples. In order to show deciding if there exists an (a,b)-supermatch is NP-Complete, we first introduce a SAT formulation that is NP-Complete by using Schaefer's Dichotomy Theorem. Then, we show the equivalence between the SAT formulation and finding a (1,1)-supermatch on a specific family of instances., Comment: Accepted for publication in COCOA'17