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991.
Over the past decade, the call to foster computational thinking (CT) in every child has received considerable attention. However, there is little understanding of whether children are developmentally ready to think computationally and what specific CT concepts and skills can be developed at various ages. This study explored the developmental and gender differences in CT skills of 197 Grade 4–6 students (aged 9–13) before being exposed to instruction and investigated the age–gender interaction effects on their CT acquisition in an intervention combining both programming and non-programming (unplugged) activities. Results show that students' CT skills followed a developmental progression before instruction. Gender difference across ages was insignificant in conditionals, logical operators, pattern recognition and generalization skills. Additionally, students of different ages developed CT differently during the intervention, and their CT acquisition was unaffected by gender. Implications for practice and research in CT education were discussed. 相似文献
992.
Xiangfeng Liang Dexin Ma Zhihong Jia Xiangfeng Meng 《Materials and Manufacturing Processes》2017,32(16):1887-1892
This paper studied the structural design of a ceramic core and a blade, ceramic core localization, shell preparation, casting process, core leaching technology, and the heat treatment process of a single-crystal hollow turbine blade. The results show that the single-crystal structure solidification sequence of the blade platform is consistent with the cooling sequence and the pulling-out direction of the blade. The primary dendrites were obviously enlarged with the increase of the blade thickness owing to the change in the local cooling rate. Besides, the γ′ phase had a high uniform size distribution ranging from 0.40 to 0.60?µm after heat treatment, and the cubic degree was more homogeneous in comparison with the as-cast microstructure, which are favorable for the superalloy structure. Moreover, γ′ phase size gradually increased and its quantity gradually reduced owing to the increase of the wall thickness in the growth direction. 相似文献
993.
Amanpreet Kaur 《Fullerenes, Nanotubes and Carbon Nanostructures》2017,25(5):318-326
We have demonstrated a fast, versatile, and scalable approach to synthesize high-quality few layer graphene sheets with low defect ratio and high crystallinity produced from exfoliation of graphite flakes in DMF by using probe sonication. The effect of sonication time on degree of exfoliation and number of graphene layers has been fully investigated. The degree of exfoliation of graphene sheets as a function of sonication time has been successfully analyzed by XRD, UV-Vis spectroscopy, TEM, and BET studies. The morphological changes at different sonication times have also been observed by SEM. A structural and defect characterization of graphene sheets has been discussed in detail by Raman spectroscopic technique. The shift in position of 2D Raman band and its de-convolution provided information about formation of multi to few layer graphene sheets with sonication. Moreover, Raman results are highly consistent with TEM studies as per number of graphene layers is concerned. 相似文献
994.
Shishir Gupta 《先进材料力学与结构力学》2017,24(1):64-72
The present work is concerned with a detailed illustration on the study of horizontally polarized shear waves (SH-type) propagation in a prestressed fluid saturated anisotropic porous layer sandwiched by prestressed orthotropic medium and nonhomogeneous mantles. The frequency equation for the assumed model is derived and their medium characteristics, such as porosity, prestress, anisotropy, and nonhomogeneity, are discussed. Numerical treatment is given to analyze these effects on phase velocities of SH-type waves and is plotted in various graphs. The parametric study divulges that the magnitude of wave velocities increases with the increase of nonhomogeneity parameter and prestress parameter. 相似文献
995.
Nanopore Sensing in Aqueous Two‐Phase System: Simultaneous Enhancement of Signal and Translocation Time via Conformal Coating
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Sang Jun Lee Ji Yoon Kang Wonjoon Choi Rhokyun Kwak 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(3)
Nanofluidic resistive pulse sensing (RPS) has been extensively used to measure the size, concentration, and surface charge of nanoparticles in electrically conducting solutions. Although various methods have been explored for improving detection performances, intrinsic problems including the extremely low particle‐to‐pore volume ratio (<0.01%) and fast nanoparticle translocation (10–1000 µs) still induce difficulties in detection, such as low signal magnitudes and short translocation times. Herein, we present an aqueous two‐phase system (ATPS) in a nanofluidic RPS for amplifying translocation signals and decreasing translocation speeds simultaneously. Two immiscible aqueous liquids build a liquid‐liquid interface inside nanopores. As particles translocate from a high‐affinity liquid phase into a lower‐affinity one, the high‐affinity liquid forms a conformal coating on the particles, which increases the effective particle size and amplifies the current‐blockage signal. The translocation time is also increased, as the ATPS interface impedes the particle translocation. For 20 nm particles, 7.92‐fold and 5.82‐fold enhancements of signal magnitude and translocation time can be achieved. To our knowledge, this is the first attempt to improve nanofluidic RPS by treating an interface of solution reservoirs for manipulating target particles rather than nanopores. This direct particle manipulation allows us to solve the two intrinsic problems all at once. 相似文献
996.
A Phase‐Separation Route to Synthesize Porous CNTs with Excellent Stability for Na+ Storage
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Zhi Chen Taihong Wang Ming Zhang Guozhong Cao 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(22)
Porous carbon nanotubes (CNTs) are obtained by removing MoO2 nanoparticles from MoO2@C core@shell nanofibers which are synthesized by phase‐segregation via a single‐needle electrospinning method. The specific surface area of porous CNTs is 502.9 m2 g?1, and many oxygen‐containing functional groups (C? OH, C?O) are present. As anodes for sodium‐ion batteries, the porous CNT electrode displays excellent rate performance and cycling stability (110 mA h g?1 after 1200 cycles at 5 A g?1). Those high properties can be attributed to the porous structure and surface modification to steadily store Na+ with high capacity. The work provides a facile and broadly applicable way to fabricate the porous CNTs and their composites for batteries, catalysts, and fuel cells. 相似文献
997.
Qiyi Fang Zhepeng Zhang Qingqing Ji Siya Zhu Yue Gong Yu Zhang Jianping Shi Xiebo Zhou Lin Gu Qian Wang Yanfeng Zhang 《Nano Research》2017,10(8):2761-2771
Molybdenum ditelluride (MoTe2),which is an important transition-metal dichalcogenide,has attracted considerable interest owing to its unique properties,such as its small bandgap and large Seebeck coefficient.However,the batch production of monolayer MoTe2 has been rarely reported.In this study,we demonstrate the synthesis of large-domain (edge length exceeding 30 μm),monolayer MoTe2 from chemical vapor deposition-grown monolayer MoS2 using a chalcogen atom-exchange synthesis route.An in-depth investigation of the tellurization process reveals that the substitution of S atoms by Te is prevalently initiated at the edges and grain boundaries of the monolayer MoS2,which differs from the homogeneous selenization of MoS2 flakes with the formation of alloyed Mo-S-Se hybrids.Moreover,we detect a large compressive strain (approximately-10%) in the transformed MoTe2 lattice,which possibly drives the phase transition from 2H to 1T'at the reaction temperature of 500 ℃.This phase change is substantiated by experimental facts and first-principles calculations.This work introduces a novel route for the templated synthesis of two-dimensional layered materials through atom substitutional chemistry and provides a new pathway for engineering the strain and thus the intriguing physics and chemistry. 相似文献
998.
Wei Zheng Biao Xu Lin Zhou Yilong Zhou Haimei Zheng Chenghan Sun Enzheng Shi Tanner Dale Fink Yue Wu 《Nano Research》2017,10(5):1498-1509
Thermoelectric materials,which can convert waste heat into electricity,have received increasing research interest in recent years.This paper describes the recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures.We start our discussion with the strategies of improving the power factor of a given material by using nanoheterostructures.Then we discuss the methods of decreasing thermal conductivity.Finally,we highlight a way of decoupling power factor and thermal conductivity,namely,incorporating phase-transition materials into a nanowire heterostructure.We have explored the lead telluride-copper telluride thermoelectric nanowire heterostructure in this work.Future possible ways to improve the figure of merit are discussed at the end of this paper. 相似文献
999.
Tuomas Haggren Ali Shah Anton Autere Joona-Pekko Kakko Veer Dhaka Maria Kim Teppo Huhtio Zhipei Sun Harri Lipsanen 《Nano Research》2017,10(8):2657-2666
Light management and electrical isolation are essential for the majority of optoelectronic nanowire (NW) devices.Here,we present a cost-effective technique,based on vapor-phase deposition of parylene-C and subsequent annealing,that provides conformal encapsulation,anti-reflective coating,improved optical properties,and electrical insulation for GaAs nanowires.The process presented allows facile encapsulation and insulation that is suitable for any nanowire structure.In particular,the parylene-C encapsulation functions as an efficient antireflection coating for the nanowires,with reflectivity down to <1% in the visible spectrum.Furthermore,the parylene-C coating increases photoluminescence intensity,suggesting improved light guiding to the NWs.Finally,based on this process,a NW LED was fabricated,which showed good diode performance and a clear electroluminescence signal.We believe the process can expand the fabrication possibilities and improve the performance of optoelectronic nanowire devices. 相似文献
1000.