Search

The Bacillus velezensis strain NBNZ-0060 was isolated from the bottom sediment samples of the lake Jin in Wuhan, China. This strain is an aerobic denitrifying bacterium and able to promote growth of submerged macrophytes. The 3,929,784 bp entire genome contains 3,781 coding sequences (CDS), 27 rRNAs, 85 tRNAs, 5 ncRNAs, with an average G + C content of 46.5%. The average nucleotide identity and digital DNA-DNA values between strain NBNZ-0060 and Bacillus velezensis NRRL B-41580T were 98.28% and 84.5%, respectively. The genome data have been deposited in NCBI with the accession number CP133277.1.

ObjectivesUnder the condition of considering the influence of the sea surface, the relationships between the induced current of a whip antenna on a large ship under the incidence of high-altitude nuclear electromagnetic pulse (HEMP) and the incident angle of the pulse and antenna position are studied.Methods The half-space finite different time domain (FDTD) method is used to consider the influence of the sea surface; the thin wire algorithm is used to solve the problems of huge computational grid and low efficiency caused by the fine structure; the lumped element FDTD method is used to consider the influence of the load behind the antenna on the induced current; and a parallel algorithm based on MPI is used to speed up the calculation.ResultsThe results show that the induced current on the whip antenna of an aircraft carrier model is related to the antenna position and incident angle in the HEMP incident case. The peak value of the induced current at the antenna port is 5.6 A in typical cases.ConclusionsThe analysis shows that the magnitude of the induced current at the antenna port mainly depends on the antenna position and has little relationship with the incident angle of the pulse. The research provides an algorithm basis for the calculation and analysis of induced current in the case of the incident pulse electromagnetic wave of large ships, and the research results provide a theoretical support for the analysis of ship electromagnetic compatibility problems.

In this work, a molybdenum carbide coating on the surface of short carbon fibers prepared using molten salt method was proposed to ameliorate the interfacial bonding and improve the performance of carbon fiber/Al composites. The carbon fiber/Al composites were produced using vacuum hot pressing. The characteristics of molybdenum carbide coating were analyzed. Besides, the microstructures, bending strength and thermal properties of the carbon fiber/Al composites were explored. Furthermore, the interfacial thermal resistance of the composites was investigated in relation to theoretical evaluations derived from the combined Maxwell-Garnett effective medium approach and acoustic mismatch model schemes. The results indicated that a homogeneous Mo _2 C coating with a thickness of 0.5 μ m was obtained by proper molar ratio of carbon fibers, MoO _3 and chloride salts mixture and heated at 1000 °C for 60 min. The Mo _2 C coating greatly enhanced the bond between the aluminum matrix and carbon fiber, leading to improvements in the densification behavior and bending strength of the coated composites. The enhanced thermal properties including improved thermal conductivity and reduced coefficient of thermal expansion (CTE) were also achieved by the Mo _2 C coating. The in-plane thermal conductivity of 60 vol.% Mo _2 C-coated carbon fiber/Al composite was 221 W·m ^−1 ·K ^−1 enhanced by 92% compared to that of uncoated composite and the CTE was 6.0 × 10 ^–6 K ^−1 which was suitable for electronic packaging materials.

Due to the low density of the green part produced by selective laser sintering (SLS), previous reports mainly improve the sample’s density through the infiltration of low-melting metals or using isostatic pressing technology. In this study, the feasibility of preparing high-density 316L stainless steel using 316L and epoxy resin E-12 as raw materials for SLS combined with debinding and sintering was investigated. The results indicated that in an argon atmosphere, high carbon and oxygen contents, along with the uneven distribution of oxygen, led to the formation of impurity phases such as metal oxides, including Cr2O3 and FeO, preventing the effective densification of the sintered samples. Hydrogen-sintered samples can achieve a high relative density exceeding 98% without losing their original design shape. This can be attributed to hydrogen’s strong reducibility (effectively reducing the carbon and oxygen contents in the samples, improving their distribution uniformity, and eliminating impurity phases) and hydrogen’s higher thermal conductivity (about 10 times that of argon, reducing temperature gradients in the sintered samples and promoting better sintering). The microstructure of the hydrogen-sintered samples consisted of equiaxed austenite and ferrite phases. The samples exhibited the highest values of tensile strength, yield strength, and elongation at 1440 °C, reaching 513.5 MPa, 187.4 MPa, and 76.1%, respectively.

Oil is an important strategic material and civil energy. Accurate prediction of oil consumption can provide basis for relevant departments to reasonably arrange crude oil production, oil import and export, and optimize the allocation of social resources. Therefore, a new grey model FENBGM(1,1) is proposed to predict oil consumption in China. Firstly, the grey effect of the traditional GM(1,1) model was transformed into a quadratic equation. Four different parameters were introduced to improve the accuracy of the model, and the new initial conditions were designed by optimizing the initial values by weighted buffer operator. Combined with the reprocessing of the original data, the scheme eliminates the random disturbance effect, improves the stability of the system sequence, and can effectively extract the potential pattern of future development. Secondly, the cumulative order of the new model was optimized by fractional cumulative generation operation. At the same time, the smoothness rate quasi-smoothness condition was introduced to verify the stability of the model, and the particle swarm optimization algorithm (PSO) was used to search the optimal parameters of the model to enhance the adaptability of the model. Based on the above improvements, the new combination prediction model overcomes the limitation of the traditional grey model and obtains more accurate and robust prediction results. Then, taking the petroleum consumption of China's manufacturing industry and transportation, storage and postal industry as an example, this paper verifies the validity of FENBGM(1,1) model, analyzes and forecasts China's crude oil consumption with several commonly used forecasting models, and uses FENBGM(1,1) model to forecast China's oil consumption in the next four years. The results show that FENBGM(1,1) model performs best in all cases. Finally, based on the prediction results of FENBGM(1,1) model, some reasonable suggestions are put forward for China's oil consumption planning.

This study aims to develop a finite difference time-domain (FDTD) modeling method for complex terrain using a paper contour map. First, the image preprocessing technology is employed to segment, denoise, and number the drawing area to arrive at independent figures and curve matrices. Subsequently, the support vector machine (SVM) classifier is implemented to identify the number and obtain the elevation value pertinent to the curve in the figure. Finally, the scattered points in the curve matrix are meshed by the Delaunay triangulation algorithm, and a three-dimensional triangular mesh model is established according to the recognition results. The FDTD calculation model is established by the method of intersection of Yee cell grid lines and triangle projection. The simulation results reveal that the recognition rate of the SVM classification model in this study is close to 100% for printed numerals. This approach is capable of quickly and accurately establishing the FDTD-based calculation model for complex terrain on the basis of the paper contour map.

A new hybrid Finite-Difference Time-Domain (hybrid FDTD) algorithm is proposed in this paper. This hybrid FDTD method combines the superiorities of explicit unconditionally stable FDTD (US-FDTD) and traditional FDTD methods to achieve unconditional stability and high calculation efficiency. US-FDTD is used in fine grids and the adjacent coarse grids subdomain and it breaks the Courant-Friedrich-Levy (CFL) condition. Traditional FDTD is used in the remaining coarse grids subdomain and it is a matrix free method. A compensation scheme is used on the subdomain boundary without compromising accuracy. Hybrid FDTD makes the explicit time marching with a uniform time step determined by the size of coarse grid in whole domain, which reduces the iteration time. In addition, because US-FDTD is only used in one of the subdomains, compared with global US-FDTD method, the matrix dimension of hybrid FDTD is reduced, which saves the time for eigenvalue solution. Numerical results show high efficiency and accuracy of the proposed method.

Titanium (Ti) and its alloys are attracting special attention in the field of dentistry and orthopedic bioengineering because of their mechanical adaptability and biological compatibility with the natural bone. The dental implant is subjected to masticatory forces in the oral environment and transfers these forces to the surrounding bone tissue. Therefore, by simulating the mechanical behavior of implants and surrounding bone tissue we can assess the effects of implants on bone growth quite accurately. In this study, dental implants with different gradient pore structures that consisted of simple cubic (structure a), body centered cubic (structure b) and side centered cubic (structure c) were designed, respectively. The strength of the designed gradient porous implant in the oral environment was simulated by three-dimensional finite element simulation technique to assess the mechanical adaptation by the stress-strain distribution within the surrounding bone tissue and by examining the fretting of the implant-bone interface. The results show that the maximum equivalent stress and strain in the surrounding bone tissue increase with the increase of porosity. The stress distribution of the gradient implant with a smaller difference between outer and inner pore structure is more uniform. So, a-b type porous implant exhibited less stress concentration. For a-b structure, when the porosity is between 40 and 47%, the stress and strain of bone tissue are in the range of normal growth. When subject to lingual and buccal stresses, an implant with higher porosity can achieve more uniform stress distribution in the surrounding cancellous bone than that of low porosity implant. Based on the simulated results, to achieve an improved mechanical fixation of the implant, the optimum gradient porous structure parameters should be: average porosity 46% with an inner porosity of 13% (b structure) and outer porosity of 59% (a structure), and outer pore sized 500 μm. With this optimized structure, the bone can achieve optimal ingrowth into the gradient porous structure, thus provide stable mechanical fixation of the implant. The maximum equivalent stress achieved 99 MPa, which is far below the simulation yield strength of 299 MPa.

The tungsten (W)-plated diamond process was explored and optimized. A dense and uniform tungsten coating with a thickness of 900 nm was successfully prepared by the powder covering sintering method. The Diamond-WC-Cu composite with high density and high thermal conductivity were successfully prepared by cyclic vacuum pressure infiltration. The microstructure and composition of the W-plated diamond particles were analyzed. The effect of tungsten coating on the microstructure and thermal conductivity of the Diamond-WC-Cu composite was investigated. After calculation, the interface thermal resistance of the composite forming the tungsten carbide transition layer is 2.11 × 10−8 m2∙K∙W−1. The thermal conductivity average value of the Diamond-WC-Cu composite with a diamond volume fraction of 60% reaches 874 W∙m−1∙K−1, which is close to the theoretical prediction value of Hasselman-Johnson (H-J) model and differential effective medium (DEM) model. Moreover, the Maxwell-Eucken (M-E) model, H-J model, and DEM model were used to evaluate the thermal conductivity of the Diamond-WC-Cu composite.

Abstract In the present work, for the first time, we reported the exploration of mesoporous 3C-SiC hollow fibers via single-spinneret electrospinning of polyureasilazane (PSN) and polyvinylpyrrolidone (PVP) solution followed by high-temperature pyrolysis treatment. The resultant products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and N2 adsorption. The as-prepared hollow fibers with totally mesoporous walls were uniformly sized in diameter and high purity in morphology. They were composed of single-crystalline 3C-SiC nanoparticles with a surface area of 21.75 m2/g and average pore diameter of ~34 nm. The PSN concentration played a determined role on the formation of hollow fibers rather than the conventional solid counterparts, enabling their growth in a tunable manner. A possible mechanism was proposed for the formation of mesoporous SiC hollow fiber.

Sub-solvus dynamic recrystallization (DRX) mechanisms in an advanced γ-γ’ nickel-based superalloy GH4151 were investigated by isothermal compression experiments at 1040 °C with a strain rate of 0.1 s−1 and various true strain of 0.1, 0.3, 0.5, and 0.7, respectively. This has not been reported in literature before. The electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) technology were used for the observation of microstructure evolution and the confirmation of DRX mechanisms. The results indicate that a new dynamic recrystallization mechanism occurs during hot deformation of the hot-extruded GH4151 alloy. The nucleation mechanism can be described as such a feature, that is a primary γ’ (Ni3(Al, Ti, Nb)) precipitate embedded in a recrystallized grain existed the same crystallographic orientation, which is defined as heteroepitaxial dynamic recrystallization (HDRX). Meanwhile, the conventional DRX mechanisms, such as the discontinuous dynamic recrystallization (DDRX) characterized by bulging grain boundary and continuous dynamic recrystallization (CDRX) operated through progressive sub-grain merging and rotation, also take place during the hot deformation of the hot-extruded GH4151 alloy. In addition, the step-shaped structures can be observed at grain boundaries, which ensure the low-energy surface state during the DRX process.

The superplastic deformation of a hot-extruded GH4151 billet was investigated by means of tensile tests with the strain rates of 10−4 s−1, 5 × 10−4 s−1 and 10−3 s−1 and at temperatures at 1060 °C, 1080 °C and 1100 °C. The superplastic deformation of the GH4151 alloy was reported here for the first time. The results reveal that the uniform fine-grained GH4151 alloy exhibited an excellent superplasticity and high strain rate sensitivity (exceeded 0.5) under all experimental conditions. It was found that the increase of strain rate resulted in an increased average activation energy for superplastic deformation. A maximum elongation of 760.4% was determined at a temperature of 1080 °C and strain rate of 10−3 s−1. The average activation energy under different conditions suggested that the superplastic deformation with 1 × 10−4 s−1 in this experiment is mainly deemed as the grain boundary sliding controlled by grain boundary diffusion. However, with a higher stain rate of 5 × 10−4 s−1 and 1 × 10−3 s−1, the superplastic deformation is considered to be grain boundary sliding controlled by lattice diffusion. Based on the systematically microstructural examination using optical microscope (OM), SEM, electron backscatter diffraction (EBSD) and TEM techniques, the failure and dynamic recrystallization (DRX) nucleation mechanisms were proposed. The dominant nucleation mechanism of dynamic recrystallization (DRX) is the bulging of original grain boundaries, which is the typical feature of discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) is merely an assistant mechanism of DRX. The main contributions of DRX on superplasticity elongation were derived from its grain refinement process.

The near fields of electric dipole are commonly used in wide-band analysis of complex electromagnetic problems. In this paper, we propose new near field time-domain expressions for electric dipole. The analytical expressions for the frequency-domain of arbitrarily oriented electric dipole are given at first; next we give the time-domain expressions by time-frequency transformation. The proposed expressions are used in hybrid TDIE/DGTD method for analysis of circular antenna with radome. The accuracy of the proposed algorithm is verified by numerical examples.

In this work, TiC coating was successfully deposited on a graphite flake surface via molten salt technique, for the purpose of promoting the interfacial connection between Cu and graphite flake. Vacuum hot pressing was then employed to prepare TiC-coated graphite flake/Cu composite. The results indicate that introducing TiC coating on graphite flake surface can evidently reduce the pores and gaps at the interface, resulting in a significant improvement on the bending strength. When the TiC-coated graphite flake content is 60 vol%, the bending strength is increased by 58% compared with the uncoated one. The coefficient of thermal expansion dropped from 6.0 ppm·K−1 to 4.4 ppm·K−1, with the corresponding thermal conductivity as high as 571 W·m−1·K−1. The outstanding thermal conductivity, apposite coefficient of thermal expansion, as well as superior processability, make TiC-coated graphite flake/Cu composite a satisfactory electronic packaging material with vast prospect utilized in microelectronic industry.

In this study, diamond-copper composites were prepared with ZrC/Zr-coated diamond powders by spark plasma sintering. The magnetron sputtering technique was employed to coat the diamond particles with a zirconium layer. After heat treatment, most of the zirconium reacted with the surface of diamond and was transformed into zirconium carbide. The remaining zirconium on the zirconium carbide surface formed the outer layer. Owing to the method used to produce the ZrC/Zr-coated diamond in this study, the maximum thermal conductivity (TC) of 609 W·m−1·K−1 was obtained for 60 vol. % diamond-copper composites and the corresponding coefficient of thermal expansion (CTE) reached as low as 6.75 × 10−6 K−1. The bending strength of 40 vol. % ZrC/Zr-coated diamond-copper composites reached 255.95 MPa. The thermal and mechanical properties of ZrC/Zr-coated diamond-copper composites were substantially superior to those of uncoated diamond particles. Excellent properties can be attributed to the strengthening of the interfacial combination and the decrease in the interfacial thermal resistance due to the improvement associated with the ZrC/Zr coating. Theoretical analysis was also proposed to compare the thermal conductivities and CTE of diamond-copper composites fabricated with these two kinds of diamond powders.

Graphite flake (GF)/Cu composites have received much attention as a promising thermal management material. This work provides a homogenization method to examine the effect of interfacial characteristics on the thermal conductivity of GFs/Cu composite. The finite element homogenization method is used to establish models of representative volume elements of material microstructure and interfacial layers, respectively, considering the distribution morphology and thermophysical properties of interface compositions. The interfacial layers are considered equivalent heat conduction materials, including interface compositions, pores, and Kapitza thermal resistances between compositions. The results of the thermal conductivity obtained by the approach were compared with the experimental results in the literature, and it shows good agreement. The results have indicated that the thermal conductivity of GFs/Cu composites is strongly affected by graphite sizes, graphite volume contents, interface contents, pore shapes, the relative density of interfacial layers, and whether the interface component is continuous has a significant influence. [ABSTRACT FROM AUTHOR]

Diamond/copper composites possess excellent thermal physical properties, and its near-net-shape preparation can be successfully realized by means of melt in- filtration. The relevant process and the influencing factors of porous diamond preforms infiltrated by copper were studied. Research results showed that, it is advantageous for the infiltration process in condition that the copper blocks were placed at both the top and the bottom of porous preforms. Composite density could reach 99.3% which was near to full density, meanwhile the thermal conductivity could reach 628 W m-1 K-1, when the melt infiltration was carried out at 1230°C with the pressure of 20 MPa for 30 min. The density was not obviously increased by further improving the infiltration temperature and extending the heat holding time, however the thermal conductivity dropped, which was associated with the variation of interfacial thermal resistance due to the change of interface structure. There was an incubation period in the infiltration process, which brought that the composite density was lower and even that the infiltration cannot be completed, when infiltration temperature was below 1130°C or pressure was less than 20 MPa. [ABSTRACT FROM AUTHOR]

The supernova remnant HESS J1731-347 is a young supernova remnant (SNR) that displays a nonthermal X-ray and TeV shell structure. A molecular cloud at a distance of ∼3.2 kpc is spatially coincident with the western part of the SNR, and it was likely hit by the SNR. The X-ray emission from this part of the shell is much lower than from the rest of the SNR. Moreover, a compact GeV emission region coincident with the cloud has been detected with a soft spectrum. These observations seem to imply a shock-cloud collision scenario at this area, where the stalled shock can no longer accelerate super-TeV electrons or maintain strong magnetic turbulence downstream, while the GeV cosmic rays (CRs) are released through this stalled shock. To test this hypothesis, we have performed a detailed Fermi-LAT reanalysis of the HESS J1731-347 region with over nine years of data. Two distinct GeV components are found, one displaying a soft spectrum is from the compact GeV emission region, the other one displaying a hard spectrum is from the rest of the SNR (excluding the cloud region). A hadronic model involving a shock-cloud collision scenario is built to explain the γ-ray emission from this area. It consists of three CR sources: run-away super-TeV CRs that have escaped from the fast shock, leaked GeV CRs from the stalled shock, and the local CR sea. The X-ray and γ-ray emission of the SNR excluding the shock-cloud interaction region is explained in a one-zone leptonic model. Our shock-cloud collision model explains the GeV–TeV observations from the clouds around HESS J1731-347, i.e., a cloud in contact with the SNR and a distant cloud in spatial coincidence to the TeV source HESS J1729-345. We find however that the leaked GeV CRs from the shock-cloud collision do not necessarily dominate the GeV emission from the clouds, due to a comparable contribution from the local CR sea. [ABSTRACT FROM AUTHOR]