Alloying behavior and characterization of(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy alloy(HEA)powders fabricated by mechanical alloying were studied.The CoCrFeNiMn)_(90)Al_(10) powders have duplex solid-solution structures.In contrast,nanocrystalline HfNi_(3) anchoring in amorphous structures is found in the(CoCrFeNiMn)_(90)Hf_(10) powders.The(CoCrFeNiMn)_(90)Al_(10) powders show better ferromagnetic behaviors,mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases.Combined with our previous work,the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed.It is found that,compared with the as-cast HEA reported previously,the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader.Moreover,the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.

融合仿真模型与深度强化学习的离心压缩机控制优化方法

作为一种复杂的工业系统,离心压缩机具有强耦合、强非线性、大滞后的特点。由于控制参数较多,且参数之间相互影响、关系复杂,加之其控制优化需要综合考虑输出性能、整机效率、可靠性等因素,离心压缩机调控的难度非常大。本文提出了一种融合仿真模型与深度强化学习的离心压缩机控制优化方法,对避免流体机械工作点漂移、提高系统可靠性、降低能耗具有一定的意义。首先,分析离心压缩机典型结构,建立离心压缩机Greitzer仿真模型。然后,根据流体机械性能优化需求,设计优化评价指标,提出基于异步优势演员-评论家(A3C)深度强化学习的智能控制优化方法。最后,通过气动试验台实验验证了方法在压缩机系统中的应用效果。

Lamb wave signal selective enhancement by an improved design of meander-coil electromagnetic acoustic transducer

In this paper, we investigate a method of selectively enhancing the single mode signal of a Lamb wave by using a meander-coil electromagnetic acoustic transducer （EMAT） with a new magnetic configuration. We use the Lamb antisym- metric （A0） mode and symmetric （SO） mode as an example for analysis. The analytical expression of the magnitude of the spatial Fourier transform of the Lorentz force generated by different meander coils is used to determine the optimal driving frequency for single mode generation. The numerical calculation is used to characterize the new magnetic configuration and the conventional EMAT magnet. Experimental examinations of each meander coil in combination with the conventional and new magnetic configuration show that the Lamb wave signal can be selectively enhanced by choosing the appropriate driving frequency and coil parameters through using the improved meander-coil EMAT.

Simulation research on effect of magnetic nanoparticles on physical process of magneto–acoustic tomography with magnetic induction

Magneto–acoustic tomography with magnetic induction（MAT-MI） is a multiphysics coupled imaging technique that is combined with electrical impedance tomography and ultrasound imaging. In order to study the influence of adding magnetic nanoparticles as a contrast agent for MAT-MI on its physical process, firstly, we analyze and compare the electromagnetic and acoustical properties of MAT-MI theoretically before and after adding magnetic nanoparticles, and then construct a two-dimensional（2 D） planar model. Under the guidance of space-time separation theory, we determine the reasonable simulation conditions and solve the electromagnetic field and sound field physical processes in the two modes by using the finite element method. The magnetic flux density, sound pressure distribution, and related one-dimensional（1 D）, 2 D, and three-dimensional（3 D） images are obtained. Finally, we make a qualitative and quantitative analysis based on the theoretical and simulation results. The research results show that the peak time of the time item separated from the sound source has a corresponding relationship with the peak time of the sound pressure signal. At this moment, MAMPTMI produces larger sound pressure signals, and the sound pressure distribution of the MAMPT-MI is more uniform, which facilitates the detection and completion of sound source reconstruction. The research results may lay the foundation for the MAT-MI of magnetically responsive nanoparticle in subsequent experiments and even clinical applications.

Influence exerted by bone-containing target body on thermoacoustic imaging with current injection

Thermoacoustic imaging with current injection(TAI-CI) is a novel imaging technology that couples with electromagnetic and acoustic research, which combines the advantages of high contrast of the electrical impedance tomography and the high spatial resolution of sonography, and therefore has the potential for early diagnosis. To verify the feasibility of TAI-CI for complex bone-containing biological tissues, the principle of TAI-CI and the coupling characteristics of fluid and solid were analyzed. Meanwhile, thermoacoustic(TA) effects for fluid model and fluid–solid coupling model were analyzed by numerical simulations. Moreover, we conducted experiments on animal cartilage, hard bone and biological soft tissue phantom with low conductivity(0.5 S/m). By injecting a current into the phantom, the thermoacoustic signal was detected by the ultrasonic transducer with a center frequency of 1 MHz, thereby the B-scan image of the objects was obtained. The B-scan image of the cartilage experiment accurately reflects the distribution of cartilage and gel, and the hard bone has a certain attenuation effect on the acoustic signal. However, compared with the ultrasonic imaging, the thermoacoustic signal is only attenuated during the outward propagation. Even in this case, a clear image can still be obtained and the images can reflect the change of the conductivity of the gel. This study confirmed the feasibility of TAI-CI for the imaging of biological tissue under the presence of cartilage and the bone. The novel TAI-CI method provides further evidence that it can be used in the diagnosis of human diseases.

Electrochemical properties of LiNi_(0.5)Mn_(1.3)Ti_(0.2)O_4/Li_4Ti_5O_(12)cells

Spinel compounds LiNi0.5Mn1.3Ti0.2O4（LNMTO） and Li4Ti5O12 （LTO） were synthesized by different methods. The particle sizes of LNMTO and LTO are 0.5-2 and 0.5-0.8 μm, respectively. The LNMTO/LTO cell exhibits better electrochemical properties at both a low current rate of 0.2C and a high current rate of 1C. When the specific capacity was determined based on the mass of the LNMTO cathode, the LNMTO/LTO cell delivered 137 mA.h.g-1 at 0.2C and 118.2 mA-h-g-l at 1C, and the corresponding capacity retentions after 30 cycles are 88.5% and 92.4%, respectively.

Seed caching and cache pilferage by three rodent species in a temperate forest in the Xiaoxinganling Mountains

Although differences in food-hoarding tactics both reflect a behavioral response to cache pilferage among rodent species and may help explain their coexistence,differentiation in cache pilfering abilities among sympatric rodents with different hoarding strategies is seldom addressed.We carried out semi-natural enclosure experiments to investigate seed hoarding tactics among three sympatric rodent species(Tamias sibiricus,Apodemus peninsulae and Clethrionomys rufocanus)and the relationship of their pilfering abilities at the inter-and intraspecific levels.Our results showed that T.sibiricus exhibited a relatively stronger pilfering ability than A.peninsulae and C.rufocanus,as indicated by its higher recovery rate of artificial caches.Meanwhile A.peninsulae showed a medium pilfering ability and C.rufocanus displayed the lowest ability.We also noted that both cache size and cache depth significantly affected cache recovery in all three species.T.sibiricus scatter-hoarded more seeds than it larder-hoarded,A.peninsulae larder-hoarded more than scatter-hoarded,and C.rufocanus acted as a pure larder-hoarder.In T.sibiricus,individuals with lower pilfering abilities tended to scatter hoard seeds,indicating an intraspecific variation in hoarding propensity.Collectively,these results indicated that sympatric rodent species seem to deploy different food hoarding tactics that allow their coexistence in the temperate forests,suggesting a strong connection between hoarding strategy and pilfering ability.

Seed caching and cache pilferage by three rodent species in a temperate forest in the Xiaoxinganling Mountains

Although differences in food-hoarding tactics both reflect a behavioral response to cache pilferage among rodent species and may help explain their coexistence, differentiation in cache pilfering abilities among sympatric rodents with different hoarding strategies is seldom addressed. We carried out semi-natural enclosure experiments to investigate seed hoarding tactics among three sympatric rodent species (Tamias sibiricus, Apodemus peninsulae and Clethrionomys rufocanus) and the relationship of their pilfering abilities at the inter- and intraspecific levels. Our results showed that T. sibiricus exhibited a relatively stronger pilfering ability than A. peninsulae and C. rufocanus, as indicated by its higher recovery rate of artificial caches. Meanwhile A. peninsulae showed a medium pilfering ability and C. rufocanus displayed the lowest ability. We also noted that both cache size and cache depth significantly affected cache recovery in all three species. T. sibiricus scatter-hoarded more seeds than it larder-hoarded, A. peninsulae larder-hoarded more than scatter-hoarded, and C. rufocanus acted as a pure larder-hoarder. In T. sibiricus, individuals with lower pilfering abilities tended to scatter hoard seeds, indicating an intraspecific variation in hoarding propensity. Collectively, these results indicated that sympatric rodent species seem to deploy different food hoarding tactics that allow their coexistence in the temperate forests, suggesting a strong connection between hoarding strategy and pilfering ability.

Magnetoacoustic position imaging for liquid metal in animal interstitial structure

Magnetoacoustic tomography with magnetic induction(MAT-MI),as a new kind of in-vivo imaging method,has potential application value in interstitial fluid research.In this paper,we propose the application of MAT-MI with liquid metal serving as a tracer of the interstitial structure to study its fluid behavior,and use it to implement the positional imaging of the spatial distribution of liquid metal.Owing to the particularity of liquid metal magnetoacoustic pressure(MAP)signals,we propose an envelope analysis method to extract the rising edge of the amplitude envelope of the detected waveform as effective position data.And for the first time,we propose the method of superpositing pixel matrix to achieve the position imaging of liquid metal.Finally,the positional imaging of the liquid metal sample embedded in the gel is achieved to have relatively accurate results.This study provides a method of effectively extracting data and implementing the position imaging for liquid metal in the interstitial structure in the frame of MAT-MI.

Lorentz Force Electrical Impedance Detection Using Step Frequency Technique

Lorentz force electrical impedance tomography(LFEIT)inherits the merit of high resolution by ultrasound stimulation and the merit of high contrast through electromagnetic field detection.To reduce the instantaneous peak power of the stimulating signal to the transducer,the sinusoidal pulse and step-frequency technique is investigated in LFEIT.The theory of application of step-frequency technique in LFEIT is formulated with the direct demodulation method and the in-phase quadrature demodulation method.Compared with the in-phase quadrature demodulation method,the direct demodulation method has simple experimental setup but could only detect half of the range.Experiments carried out with copper foils confirmed that LFEIT using the step-frequency technique could detect the electrical conductivity variations precisely,which suggests an alternative method of realization of LFEIT.

Synthesis and properties of Na_(0.8)Ni_(0.4)Mn_(0.6)O_2 oxide used as cathode material for sodium ion batteries

A new P2-structured oxide Na0.8Ni0.4Mn0.6O2was synthesized using a solid reaction method in which Na2CO3, MnO2and NiO were used as starting materials.This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions, including good rate capability and good cycle performance at both room temperature and elevated temperature. It displays two apparent voltage plateaus at about 3.6 and 3.3 V, and its discharge capacity reaches92 mAh·g-1at 0.1 C in the voltage range of 2.0-4.0 V. At1.0 C, its discharge capacity reaches 85.3 mAh·g-1. After80 cycles at different current rates, the as-prepared sample exhibits good capacity retention. At elevated temperature of 55 ℃, the discharge capacity remains the same at low current rate of 0.1 C, but at high current rate of 1.0 C, the discharge capacity is a little lower than that at room temperature.

Modular divergent creation of dual-cocatalysts integrated semiconducting sulfide nanotriads for enhanced photocatalytic hydrogen evolution

Heteronanostructures(HNs)with precise components and interfaces are important for many applications,such as designing efficient and robust solar-to-fuel catalysts via integrating specific semiconductors with favorable band alignments.However,rationally endowing such features with rigorous framework control remains a synthetic bottleneck.Herein,we report a modular divergent creation of dual-cocatalysts integrated semiconducting sulfide nanotriads(NTds),comprising both isolated Pd_(x)S oxidation(ox)and MoS_(2) reduction(red)domains within each single CdS counterpart,which exhibit superior photocatalytic activity and stability for hydrogen evolution reaction(HER).The stepwise constructed Pd_(x)S_((ox))−CdS−MoS_(2(red)) NTds possess dualinterfaces facilitating continuous charge separation and segregated active sites accelerating redox reactions,respectively,achieving the HER rate up to 9 mmol·h^(−1)·g^(−1),which is about 60 times higher than that of bare CdS,and show no evidence of deactivation after long-term cycling.This design principle and transformation protocol provide predictable retrosynthetic pathways to HNs with increased degree of complexity and more elaborate functionalities that are otherwise inaccessible.

Anti-photocorrosive photoanode with RGO/PdS as hole extraction layer

Photoelectrochemical(PEC)hydrogen production is of great interest as an ideal avenue towards clean and renewable energy.However,the instability and low energy conversion efficiency of photoanodes hinder their practical applications.Here we address these issues by introducing a hole extraction layer(HEL)which could rapidly transfer and consume photogenerated holes.The HEL is constructed by reduced graphene oxide(RGO)and other cocatalysts that enable rapid transfer and subsequent consumption of holes,respectively.Specifically,we showcase a high-stability photoanode composed of CdSeTe nanowires(CST NWs)and RGO/PdS nanoparticles(PdS NPs)based HEL.The photoanode achieves excellent photocorrosion resistance,which allows stable hydrogen evolution for>2 h at 0.5 VRHE.

Magnetic field enhanced thermal conductivity and origin of large thermopower in layered cobaltates

Cobalt oxide,as one of the most fascinating examples of correlated electronic system,exhibits several exotic transport characteristics,such as superconductivity,charge ordering,and topological frustration.In this study,we are reporting the observation of another intriguing transport phenomenon in calcium cobaltates.Specifically,under a large magnetic field of 7 T,we observed an anomalously enhanced thermal conductivity that was accompanied with a largely suppressed thermopower.This observation reveals a hitherto undiscovered correlation between the two transport factors.Within the premise of Heisenberg model,we have shown that the observed experimental results can be explained consistently only if the magnon excitation is taken into account.Our study offers an insight into the puzzling origin of large thermopower observed in layered cobaltates and provides a specific strategy for further optimization of thermopower.

Anomalous Thermopower and High ZT in GeMnTe2 Driven by Spin’s Thermodynamic Entropy

NaxCoO_(2)was known 20 years ago as a unique example in which spin entropy dominates the thermoelectric behavior.Hitherto,however,little has been learned about how to manipulate the spin degree of freedom in thermoelectrics.Here,we report the enhanced thermoelectric performance of GeMnTe_(2)by controlling the spin’s thermodynamic entropy.The anomalously large thermopower of GeMnTe_(2)is demonstrated to originate from the disordering of spin orientation under finite temperature.Based on the careful analysis of Heisenberg model,it is indicated that the spin-system entropy can be tuned by modifying the hybridization between Te-p and Mn-d orbitals.As a consequent strategy,Se doping enlarges the thermopower effectively,while neither carrier concentration nor band gap is affected.The measurement of magnetic susceptibility provides a solid evidence for the inherent relationship between the spin’s thermodynamic entropy and thermopower.By further introducing Bi doing,the maximum ZT in Ge_(0.94)Bi_(0.06)MnTe_(1.94)Se_(0.06)reaches 1.4 at 840 K,which is 45%higher than the previous report of Bi-doped GeMnTe_(2).This work reveals the high thermoelectric performance of GeMnTe_(2)and also provides an insightful understanding of the spin degree of freedom in thermoelectrics.