Revealing the atomic-scale deformation mechanisms of metallic nanowires (NWs) is important for their practical application. However, there are few reports providing direct atomic-scale experimental ...elucidation on those metallic NWs. Here, we conduct serial in situ deformation tests on silver (Ag) nanowires with diameters of 3–11 nm. The in situ atomic-scale observations reveal a transition in the deformation mechanism with a decrease in the diameter of Ag NWs. For the 55¯4 and 001 oriented NWs with diameters of ∼11 nm, the plastic deformation is dominated by full dislocation that involves leading and trailing partial dislocations, whereas the full or extended dislocations are rarely observed in the NWs with diameters in the range of ∼ 5–8 nm, and their plastic deformation is governed by SF generation and annihilation. Moreover, for the 1¯11 oriented NWs, 60° mixed and pure edge dislocations are frequently observed when the diameter is approximately 5 nm and the plastic deformation is accommodated by relative slip between two adjacent {111} planes for NWs with diameters below ∼ 3 nm. These results indicate that the plastic deformation not only depends on the size of NWs but also can be significantly impacted by the loading orientation.
•We provide in situ atomic-scale deformation process of Ag NWs (d < ∼10 nm).•Plastic deformation mechanism of Ag NWs is different from high SF energy metal.•There is a transition from extend dislocation to SF for 55¯4 and 001 NWs.•There is a transition from full dislocation to {111} planes slip in 1¯11 NWs.•Plastic deformation is impacted by size, SF energy and loading direction.
The deformation activities near crack tips of submicron-sized single-crystalline Mo were investigated using in situ transmission electron microscopy (TEM) with mixed mode I-II loading. Results show ...that dislocations in multiple slip systems were activated in front of crack tips. These dislocations glided on the uncommon slip planes of {123}, forming dislocation arrays. These dislocations moved at velocities of 3–5 nm/s with spacing of ∼10–34 nm in the zone of ∼50–300 nm away from crack tips. Dislocation velocity and spacing were influenced by the force from elastic crack stress field. Additionally, phase transformation from body-centered cubic to face-centered cubic was also activated in front of crack tips, and high densities of interface dislocations were observed at the semicoherent phase interfaces. Two kinds of phase transformation mechanisms were uncovered. One is the Pitsch mechanism, which is rarely accessed, while the other is the Nishiyama-Wasserman/Kurdjumov-Sachs mechanism.
•Unusual slip planes of {123} types are activated in front of crack tip in bcc Mo.•Dislocations are in arc shape, parallel forming a dislocation array.•The spacing and speed of dislocations in each array depend on the force.•Infrequent relationship of bcc-to-fcc phase transformation is observed.
Twin crystal structured Al-10 wt.% Mg alloys that were grown over a broad solidification velocity range were prepared and studied for the first time. The high thermal gradient (G) and growth velocity ...(V) of directional solidification resulted in the dominant solidification of twins: the twinned dendrite trunks at constant high Vs curved in the G direction with large angles in 7 mm diameter crucibles and invaded regular columnar grains because of a distinct kinetics growth advantage. Transitive deceleration experiments were designed to produce twin crystals that evolved with lower values of V (100, 10, and 0.5 μm/s) and had a structural coarsening trend. Twin cell growth in the absence of arms occurred at a growth velocity of 10 μm/s. A coherency loss was observed at a growth velocity of 0.5 μm/s with straight coherent twin boundaries turning into curved incoherent boundaries. Linear theoretical analyses were performed to understand the structural evolution of the twins. These results demonstrate the possibility of producing dense and controlled twin crystals in the Al-Mg system under most industrial production conditions; thus, this approach can be a new structural choice for designing Al-Mg-based alloys that have widespread commercial applications.
Polymorphism (and its extended form – pseudopolymorphism) in solids is ubiquitous in mineralogy, crystallography, chemistry/biochemistry, materials science, and the pharmaceutical industries. Despite ...the difficulty of controlling (pseudo‐)polymorphism, the realization of specific (pseudo‐)polymorphic phases and associated boundary structures is an efficient route to enhance material performance for energy conversion and electromechanical applications. Here, this work applies the pseudopolymorphic phase (PP) concept to a thermoelectric copper sulfide, Cu2‐xS (x ≤ 0.25), via CuBr2 doping. A peak ZT value of 1.25 is obtained at 773 K in Cu1.8S + 3 wt% CuBr2, which is 2.3 times higher than that of a pristine Cu1.8S sample. Atomic‐resolution scanning transmission electron microscopy confirms the transformation of pristine Cu1.8S low digenite into PP‐engineered high digenite, as well as the formation of (semi‐)coherent interfaces between different PPs, which is expected to enhance phonon scattering. The results demonstrate that PP engineering is an effective approach for achieving improved thermoelectric performance in Cu‐S compounds. It is also expected to be useful in other materials.
A material consisting of the same substance can crystalize in different structural phases with (or without) identical composition, termed “(pseudo)polymorphic phases” (PPs). This work applies this PP concept to copper sulfides to improve thermoelectric performance. The resulting PPs maintain electron transport and enhance phonon scattering. A peak ZT value of 1.25 is obtained, which is 2.3 times higher than that of pristine copper sulfide.
Ni-based superalloys rely on high volume fractions of L12 ordered γ' phase precipitates for strength against creep deformation at elevated temperatures. However, under certain conditions dislocations ...existing in the FCC γ matrix may enter the L12 γ' phase in pairs. The shear motion of different combinations of dislocation pairs creates different planar defects in the γ' phase, including anti-phase boundaries (APB) or stacking faults. The formation of an APB requires the shear distortion associated with an a/2 dislocation and the formation of a stacking fault requires the shear distortion associated with a k dislocation. Given that the native dislocations in FCC structure are a/2 , the formation mechanism of k dislocations remains to be clarified. Different mechanisms have been suggested for the formation of stacking faults in the γ' phase in the literature. In this study, the shearing motions of various partial dislocation pairs and the planar defects formed in the γ' phase were investigated by means of transmission electron microscopy and the mechanisms were analyzed in terms of their crystallographic and energetic implications.
Recently, blended learning has attracted more and more attention by the educational researchers. They often focus on how to combine blended learning with advanced technology to serve the teaching. In ...this paper, we proposed a novel learning pattern of "blended plus flipped". The pattern combined blended learning with flipped classroom, which integrated with offline learning, online learning, and study in class and out of class,. This achieves seamless integration of time and space. We test this idea using the course of "Educational Technology Research Method" and the experimental result demonstrates that blended learning pattern outperforms the traditional learning pattern. It is found that the time length of online learning and the active degree of the forum are the major factors affecting the blended learning pattern.
Blockchain is being pursued by a growing number of people with its characteristics of openness, transparency, and decentralization. At the same time, how to secure privacy protection in such an open ...and transparent ledger is an urgent issue to be solved for deep study. Therefore, this paper proposes a protocol based on Secure multi-party computation, which can merge and sign different transaction messages under the anonymous condition by using Pedersen commitment and Schnorr Signature. Through the rationality proof and security analysis, this paper demonstrates the private transaction is safe under the semi-honest model. And its computational cost is less than the equivalent multi-signature model. The research has made some innovative contributions to the privacy computing theory.
In this paper, we present a computer-assisted teaching system for digital signal recognition using the computer as an interactive partner in problem solving activities. The software is designed to ...help students solve problems according to their own decision, or those arranged by their instructor. It can be used as a tool for digital signal course learning, spectrum recognition training, optical data processing, and providing feedbacks and advice upon request. The system includes an interactive interface, a spectrum simulator for graphical display of students' spectrum, a database which contains data of chemical groups and related information. The results showed that the developed system was effective in improving students' ability in spectrum interpretation.
In this paper, we propose an improvement on LEACH (Low Energy Adaptive Clustering Hierarchy) protocol in order to monitor the large-scale environment longer and stably with wireless sensor networks. ...Since being proposed, the LEACH protocol has been regard as a perfect routing protocol of wireless sensor networks (WSNs) while the system was used to monitor large-scale area, and we have never stop improving this classic routing protocol all the time. There has been lots of improvement on LEACH protocol now such as LEACH-C etc. But nearly all of those advanced protocol based on LEACH protocol continue using a primal function of LEACH to set a fixed optimum number of clusters in each round during the whole lifetime of the system, and the nodes computes their own probability to be cluster head mostly in terms of this optimum number of clusters. In our experiment, we found it will seriously damage the system's lifetime and stability that the nodes reckon the probability to be cluster head relying on the fixed optimum number of clusters. As we known, the nodes will die during the system life; it means the total number of the nodes in network must be decreasing along with the system-life. In the LEACH protocol, we know the optimum number of clusters in each round depend on the total number of the nodes in the network. Theoretically while the total number of the nodes is deceased, the optimum number of cluster should be upgraded too. In this improvement, we introducing a special method which let the system choose the dynamic optimum number of clusters during the system's set-up state, and the dynamic optimum number of clusters were decided base on the real time total sum of nodes in the whole network. As the experiment results shown, the improvement can not only prevent the system from seriously energy consumption, and obviously extend the lifetime but also advance the quality of our monitoring system.
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