双峰基面织构对Mg-2.6Nd-0.55Zn-0.5Zr合金弯曲应力及显微组织演变的影响

沿Mg-2.6Nd-0.55Zn-0.5Zr板材挤压方向(ED)和横向(TD)分别切取试样,研究双峰基面织构对其弯曲应力及显微组织演变的影响。结果显示,具有弱基面织构的ED试样比TD试样的弯曲应力低很多。这种各向异性是不同织构状态对变形机制及显微组织演变的作用所导致的。对于具有弱基面织构的ED试样,其主要的变形机制是基面滑移:内侧区域存在少量的{10■2}拉伸孪生,而外侧区域则是基面滑移和柱面滑移。相比之下,具有强基面织构的TD试样在内侧区域激活更多的{10■2}拉伸孪生,在外侧区域激活更多的柱面滑移。{10■2}拉伸孪生的激活一方面促使<0002>//压缩方向类型的织构增加,使内侧区域的织构角度限制在±30°范围内,另一方面减少高位错密度和低角度晶界的出现几率。{10■2}拉伸孪生的大量激活使TD试样保持高应变硬化能力,是该试样具有较高弯曲应力的根本原因。

Advances in low-field nuclear magnetic resonance(NMR) technologies applied for characterization of pore space inside rocks:a critical review

NMR serves as an important technique for probing rock pore space,such as pore structure characterization,fluid identification,and petrophysical property testing,due to the reusability of cores,convenience in sample processing,and time efficiency in laboratory tests.In practice,NMR signal collection is normally achieved through polarized nuclei relaxation which releases crucial relaxation messages for result interpretation.The impetus of this work is to help engineers and researchers with petroleum background obtain new insights into NMR principals and extend existing methodologies for characterization of unconventional formations.This article first gives a brief description of the development history of relaxation theories and models for porous media.Then,the widely used NMR techniques for characterizing petrophysical properties and pore structures are presented.Meanwhile,limitations and deficiencies of them are summarized.Finally,future work on improving these insufficiencies and approaches of enhancement applicability for NMR technologies are discussed.

Evolution of microstructure and mechanical properties of ZK60 magnesium alloy processed by asymmetric lowered-temperature rolling

Asymmetric lowered-temperature rolling was applied to the fabrication of fine-grained ZK60 magnesium alloy sheet with weak basal texture along the rolling direction(RD).The results showed that multi-pass lowered-temperature rolling could significantly improve the microstructure homogeneity and refine the grain size.Meanwhile,a fiber texture along the transverse direction(TD)gradually developed during rolling process.Importantly,the shear deformation along the RD made the c-axis of basal plane rotate to the RD,weakening the basal texture along this direction.Influenced by such microstructure variation,the yield strength along the TD continuously increased due to the successive grain refinement and the increased activation of prismatic slips,whereas the uniform elongation decreased owing to the decline of strain hardening ability.In contrast,the continuous weakening of basal texture along the RD increased the activation of soft basal slips,greatly offsetting the strengthening effect contributed by grain refinement and thereby causing the slight decrease of yield strength.

Configuration Design of an Under-Actuated Robotic Hand Based on Maximum Grasping Space

Capture is a key component for on?orbit service and space debris clean. The current research of capture on?orbit focuses on using special capture devices or full?actuated space arms to capture cooperative targets. However, the structures of current capture devices are complex, and both space debris and abandoned spacecraft are non?cooperative targets. To capture non?cooperative targets in space, a lightweight, less driven under?actuated robotic hand is proposed in this paper, which composed by tendon?pulley transmission and double?stage mechanisms, and always driven by only one motor in process of closing finger. Because of the expandability, general grasping model is constructed. The equivalent joint driving forces and general grasping force are analyzed based on the model and the principle of virtual work. Which reveal the relationship among tendon driving force, joint driving forces and grasping force. In order to configure the number of knuckles of finger, a new analysis method which takes the maximum grasping space into account, is proposed. Supposing the maximum grasped object is an envelope circle with diameter of 2.5m. In the condition, a finger grasping maximum envelope circle with different knuckles is modeled. And the finger lengths with corresponding knuckles are calculated out. The finger length which consists of three knuckles is the shortest among under?actuated fingers consists of not more than five knuckles. Finally, the principle prototype and prototype robotic hand which consists of two dingers are designed and assembled. Experiments indicate that the under?actuated robotic hand can satisfy the grasp requirements.

Progress in developing self-consolidating concrete(SCC)constituting recycled concrete aggregates:A review

Recycled concrete aggregate(RCA)derived from demolition waste has been widely explored for use in civil engineering applications.One of the promising strategies globally is to incorporate RCA into concrete products.However,the use of RCA in high-performance concrete,such as self-consolidating concrete(SCC),has only been studied in the past decade.This paper summarizes recent publications on the use of coarse and/or fine RCA in SCC.As expected,the high-water absorption and porous structure of RCA have posed challenges in producing a high-fluidity mixture.According to an analysis of published data,a lower strength reduction(within 23%regardless of coarse RCA content)is observed in SCC compared with vibrated concrete,possibly due to the higher paste content in the SCC matrix,which enhances the weak surface layer of RCA and interfacial transition zone.Similarly,SCC tends to become less durable with RCA substitution although the deterioration can be minimized by using treated RCA through removing or strengthening the adhered mortar.To date,the information reported on the role of RCA in the long-term performance of SCC is still limited;thus,a wide range of research is needed to demonstrate the feasibility of RCA–SCC in field applications.

Microstructures and mechanical properties of in-situ TiB2/Al−xSi−0.3Mg composites

In-situ 2 vol.%TiB2 particle reinforced Al−xSi−0.3Mg(x=7,9,12,15 wt.%)composites were prepared by the salt−metal reaction,and the microstructures and mechanical properties were investigated.The results show that the TiB2 particles with a diameter of 20−80 nm and the eutectic Si with a length of 1−10μm are the main strengthening phases in the TiB2/Al−xSi−0.3Mg composites.The TiB2 particles promote grain refinement and modify the eutectic Si from needle-like to short-rod shape.However,the strengthening effect of TiB2 particles is weakened as the Si content exceeds the eutectic composition,which can be attributed to the formation of large and irregular primary Si.The axial tensile test results and fractography observations indicate that these composites show more brittle fracture characteristics than the corresponding alloy matrixes.

Analysis of the geomorphology surrounding the Chang'e-3 landing site

Chang＇e-3 （CE-3） landed on the Mare Imbrium basin in the east part of Sinus Iridum （19.51°W, 44.12°N）, which was China＇s first soft landing on the Moon and it started collecting data on the lunar surface environment. To better understand the environment of this region, this paper utilizes the available high-resolution topography data, image data and geological data to carry out a detailed analysis and research on the area surrounding the landing site （Sinus Iridum and 45 km×70 km of the landing area） as well as on the topography, landform, geology and lunar dust of the area surrounding the landing site. A general topographic analysis of the surrounding area is based on a digital elevation model and digital elevation model data acquired by Chang＇e-2 that have high resolution; the geology analysis is based on lunar geological data published by USGS; the study on topographic factors and distribution of craters and rocks in the surrounding area covering 4km^4km or even smaller is based on images from the CE-3 landing camera and images from the topographic camera; an analysis is done of the effect of the CE-3 engine plume on the lunar surface by comparing images before and after the landing using data from the landing camera. A comprehensive analysis of the results shows that the landing site and its surrounding area are identified as typical lunar mare with flat topography. They are suitable for maneuvers by the rover, and are rich in geological phenomena and scientific targets, making it an ideal site for exploration.

A High-Randomness and High-Stability Electronic Quantum Random Number Generator without Post Processing

Random numbers are one of the key foundations of cryptography.This work implements a discrete quantum random number generator(QRNG)based on the tunneling effect of electrons in an avalanche photo diode.Without any post-processing and conditioning,this QRNG can output raw sequences at a rate of 100 Mbps.Remarkably,the statistical min-entropy of the 8,000,000 bits sequence reaches 0.9944 bits/bit,and the min-entropy validated by NIST SP 800-90B reaches 0.9872 bits/bit.This metric is currently the highest value we have investigated for QRNG raw sequences.Moreover,this QRNG can continuously and stably output raw sequences with high randomness over extended periods.The system produced a continuous output of 1,174 Gbits raw sequence for a duration of 11,744 s,with every 8 Mbits forming a unit to obtain a statistical min-entropy distribution with an average value of 0.9892 bits/bit.The statistical min-entropy of all data(1,174 Gbits)achieves the value of0.9951 bits/bit.This QRNG can produce high-quality raw sequences with good randomness and stability.It has the potential to meet the high demand in cryptography for random numbers with high quality.

Spin glassy behavior and large exchange bias effect in cubic perovskite Ba0.8Sr0.2FeO3-δ

A single-phase iron oxideBa0.8Sr0.2FeO3-δwith a simple cubic perovskite structure in Pm-3 m symmetry is successfully synthesized by a solid-state reaction method in O2 flow. The oxygen content is determined to be about 2.81, indicating the formation of mixed Fe3+and Fe4+charge states with a disorder fashion. As a result, the compound shows small-polaron conductivity behavior, as well as spin glassy features arising from the competition between the ferromagnetic interaction and the antiferromagnetic interaction. Moreover, the competing interactions also give rise to a remarkable exchange bias effect in Ba0.8 Sr0.2 FeO2.81, providing an opportunity to use it in spin devices.

Device-Free Through-the-Wall Activity Recognition Using Bi-Directional Long Short-Term Memory and WiFi Channel State Information

Activity recognition plays a key role in health management and security.Traditional approaches are based on vision or wearables,which only work under the line of sight(LOS)or require the targets to carry dedicated devices.As human bodies and their movements have influences on WiFi propagation,this paper proposes the recognition of human activities by analyzing the channel state information(CSI)from the WiFi physical layer.The method requires only the commodity:WiFi transmitters and receivers that can operate through a wall,under LOS and non-line of sight(NLOS),while the targets are not required to carry dedicated devices.After collecting CSI,the discrete wavelet transform is applied to reduce the noise,followed by outlier detection based on the local outlier factor to extract the activity segment.Activity recognition is fulfilled by using the bi-directional long short-term memory that takes the sequential features into consideration.Experiments in through-the-wall environments achieve recognition accuracy>95%for six common activities,such as standing up,squatting down,walking,running,jumping,and falling,outperforming existing work in this field.

Synergistic Antimicrobial Activity of Berberine Hydrochloride, Baicalein and Borneol against Candida albicans

Objective To determine the synergistic effects of berberine hydrochloride, baicalein,and borneol in different combinations on Candida albicans. Methods The broth microdilution method was used to determine the minimal inhibitory concentration（MIC） and minimal bactericidal concentration（MBC） of the three agents, and the checkerboard method was simultaneously used to determine the MIC and fractional inhibitory concentration index（FICI） of the combination of three antimicrobial agents to study their extracorporeal effects. Results Berberine hydrochloride was the most potent inhibitor of C. albicans（MIC and MBC of 0.160 and 0.640 mg/mL）, followed by borneol（MIC and MBC of 0.320 and 0.640 mg/mL） and baicalein（MIC and MBC of 1.28 and 20.48 mg/mL）. Moreover, the antifungal effect of the combination was significantly stronger than that tested alone. Further in vivo study showed that the mortality rate of tainted mice reduced over 50% compared with the control group. Conclusion The results of experiments in vitro and in vivo indicate the synergistic effect of the combination of three antimicrobial agents on C. albicans, which can make reference for the future clinical treatment.

Subtle Alignment of Organic Semiconductors at the Donor/Acceptor Heterojunction Facilitates the Photoelectric Conversion Process

The aligned molecular packing structure is vital to the anisotropic charge transport in conjugated polymer and small molecule thin films.However,how this molecular packing motif influences the photoelectric conversion process at the donor/acceptor heterojunction is still mysterious.Herein,we employed a PM6/Y6 bilayer model to investigate the long-range alignment of molecular packing induced photoelectric conversion process.Both PM6 and Y6 layers were properly controlled to exhibit the uniaxially oriented molecular packing compared to their as-cast counterparts,as revealed by the polarized absorption spectra and transmission electron microscopy.After analyzing the photovoltaic performance of bilayer devices,the smaller energy loss,lower energetic disorder,and longer charge carrier lifetime can be observed in the bilayer devices with aligned Y6 molecules,which contribute to a higher power conversion efficiency(PCE)than the as-cast devices.While the molecular packing structure of PM6 layer exhibited negligible influence on the device performance,probably resulting from the intrinsic semicrystalline nature of PM6 molecules.Our results indicate that the alignment of small molecular acceptor at the donor/acceptor interfaces should be a powerful strategy to facilitate the photoelectric conversion process,which will definitely pave the way to highly efficient bulk heterojunction photovoltaic device.

Effect of Ni-P content on microstructure and mechanical properties of Fe-Ni-P alloy

A series of Fe-Ni-P alloys with different Ni-P contents were prepared by micro-press sintering,and the influence of the contents on the final microstructure and mechanical properties was evaluated.Sample Fe-34(Ni,P)contains the highest Ni-P content(34.18 wt.%)and its relative density reaches 98.75%,which is attributed to the introduction of an appropriate amount of liquid phase during the sintering process.The main phase of the sample is transformed from a to c phase under the gradual increment of Ni-P content.Simultaneously,a large number of phosphides that have strong inhibition on the migration and expansion of grain boundaries are precipitated on the matrix,and synergistic effect with low-temperature sintering results in partial grain refinement.The samples with high Ni-P content have a high volume of c phase,which makes the sample show the optimal plasticity under the maximum compressive load.And the fracture mode has also changed from brittle fracture to a mixed mode of brittle and ductile fracture.The decrease in the proportion of a phase has a weakening effect on the strength,but the refinement of the grain and the increase in the phosphide are the factors that increase the strength,so that the degree of manifestation varies in different Ni-P levels.

Preparation and compression behavior of Fe-Ni-P/porous-Fe/Fe-Ni-P composites

Porous-Fe-N alloys designed for light weight or energy absorption are inevitably facing the compromise of deteriorated mechanical properties. To optimize their mechanical properties, here a novel Fe-Ni-P/porous-Fe/Fe-Ni-P composite with sandwich structure was fabricated by spark plasma sintering and further strengthened via cryogenic treatment. Based on the principle of solid phase sintering and transient liquid phase sintering, porous core and dense outer layers formed simultaneously after co-sintering. The as-fabricated samples show excellent compressive strength of 1708 MPa, and after cryogenic treatment, due to the sufficient martensitic transformation, Fe-Ni-P outer layers show substantially increased hardness from 246.7 to 386.6 HV_(0.1)while the porous-Fe core remains unchanged. And the compressive strength maintains 1424 MPa despise the aggravated incongruity of deformation. The ratio of constituent microhardness R has been proposed to represent the hardness matching, and with decreasing R, the incongruity of deformation is intensified, and the nominal compressive strength is reduced.