Tunable temperature‐ and shear‐responsive hydrogels based on poly(alkyl glycidyl ether)s

We describe the synthesis, characterization and direct‐write 3D printing of triblock copolymer hydrogels that have a tunable response to temperature and shear stress. In aqueous solutions, these polymers utilize the temperature‐dependent self‐association of poly(alkyl glycidyl ether) ‘A’ blocks and a central poly(ethylene oxide) segment to create a physically crosslinked three‐dimensional network. The temperature response of these hydrogels was dependent upon composition, chain length and concentration of the ‘A’ block in the copolymer. Rheological experiments confirmed the existence of sol–gel transitions and the shear‐thinning behavior of the hydrogels. The temperature‐ and shear‐responsive properties enabled direct‐write 3D printing of complex objects with high fidelity. Hydrogel cytocompatibility was also confirmed by incorporating HeLa cells into select hydrogels resulting in high viabilities over 24 h. The tunable temperature response and innate shear‐thinning properties of these hydrogels, coupled with encouraging cell viability results, present an attractive opportunity for additive manufacturing and tissue engineering applications. © 2018 Society of Chemical Industry     

Lead halide perovskite nanowires stabilized by block copolymers for Langmuir-Blodgett assembly

The rapid development of solar cells based on lead halide perovskites (LHPs) has prompted very active research activities in other closely-related fields. Colloidal nanostructures of such materials display superior optoelectronic properties. Especially, one-dimensional (1D) LHPs nanowires show anisotropic optical properties when they are highly oriented. However, the ionic nature makes them very sensitive to external environment, limiting their large scale practical applications. Here, we introduce an amphiphilic block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-P4VP), to chemically modify the surface of colloidal CsPbBr₃ nanowires. The resulting core-shell nanowires show enhanced photoluminescent emission and good colloidal stability against water. Taking advantage of the stability enhancement, we further applied a modified Langmuir-Blodgett technique to assemble monolayers of highly aligned nanowires, and studied their anisotropic optical properties.

     

Comparison in composite performance after thermooxidative aging of injection molded polyamide 6 with glass fiber,talc, and a sustainable biocarbon filler

Degradation is an unavoidable part of a material's life making it important to both monitor and control the aging behavior of plastics. This study compares thermooxidative degraded composites of a novel bio-based and sustainable filler, Biocarbon (MBc), against that of traditional and commercially available fillers (glass fiber and talc) used in the automotive industry. The influence of thermooxidative degradation on the composites was studied under accelerated heat aging for 1000 h at 140°C. The mechanical properties of the composites were evaluated using notched Izod impact as well as both tensile and flexural tests. Morphological structure of the composites was investigated using a scanning electron microscopy. Dynamic mechanical analysis and differential scanning calorimetry were used to evaluate the physical transitions both before and after aging. The glass-filled composites displayed the best performance; while, both the talc and biocarbon composites possessed similar strength and ductility performances. Advantageously, the biocarbon composites experienced an 11% reduction in density as compared to talc-filled composites with similar weight content. After aging, all composites exhibited reduced tensile and flexural strengths ranging from 5 to 67% partly due to chain scission. Whereas, the modulus of all composites increased with a range of 1–24% due to an annealing effect. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48618.     

Cylindrical lithium-ion structural batteries for drones

The low cost, simplicity, and easy use of battery-powered multirotor aircraft has led to their adoption in commercial, industrial, agricultural, and military applications. These aircraft, however, have limited payloads and shorter endurance and range than fuel-powered conventional aircraft. To extend these key performance metrics, a structural battery is developed that uses commercially available battery cells as load bearing and power source elements for weight critical applications. The cylindrical structural battery is tested in three-point bending and is found to have four times higher stiffness and two times higher yield strength than the structure without battery reinforcement. Simulations of a quadcopter, redesigned with the proposed cylindrical structural batteries, demonstrate 41% longer hover time.     

Requirements for a virtual environment to support the social participation education of low-literates

People of low literacy experience difficulties while participating in society. Learning support software could help alleviate these difficulties. However, there is currently no overview of theoretically and empirically sound requirements for this kind of support. This paper uses the situated cognitive engineering method to create a requirements baseline for a virtual environment to support the societal participation education of low-literates (VESSEL), based on an analysis of the domain, human factors, and current applications. Four major outcomes are presented. First, a comprehensive overview is collected of the operational demands and human factors knowledge relevant to societal participation learning for low-literate citizens. Second, this overview is translated into a list of eight functional requirements: focused on low-literate learners, set in the context of societal participation, and supported by claims of cognitive, affective, and social benefits to learning. Third, a sample of Dutch societal participation learning support programs is assessed using these requirements, to highlight both current technology best practices and discrepancies between theory and practice. Fourth, virtual learning environment technology is suggested as an ‘enabling’ technology; an overview is shown of how virtual environments, actors, and objects can beneficially enable meeting the requirements baseline. Finally, directions for future study are discussed.

     

High‐Performance Integrated ZnO Nanowire UV Sensors on Rigid and Flexible Substrates

Due to the large surface area‐to‐volume ratio and high quality crystal structure, single nanowire (NW)‐based UV sensors exhibit very high on/off ratios between photoresponse current and dark current. Practical applications require a large‐scale and low‐cost integration, compatibility to flexible electronics, as well as reasonably high photoresponse current that can be detected without high‐precision measurement systems. In this paper, NW‐based UV sensors were fabricated in large‐scale by integrating multiple NWs connected in parallel via the contact printing method. Linear scaling of the photoresponse current with the number of NWs is demonstrated. Integrated ZnO NW UV sensors were fabricated on rigid glass and flexible polyester (PET) substrates at the macroscopic scale. The flexible and rigid sensors performed comparably, exhibiting on/off current ratios approximately three orders of magnitude higher than sensors made from polycrystalline ZnO thin films. Under UV irradiance of 4.5 mW cm^?2 and 3 V bias, photoresponse currents and on/off current ratios for the rigid and flexible UV sensors reached 12.22 mA and 82 000, and 14.1 mA and 120 000, respectively. This result suggests that lateral integration of semiconductor NWs is an effective approach to large‐scale fabrication of flexible NW sensors that inherit the merits of single‐NW‐based systems with unaffected performance compared to using rigid substrate.     

风景园林设计项目的经济绩效评估 德克萨斯州案例研究的经验与教训

通过研究德克萨斯州5个项目/案例的经济绩效成果,评估了风景园林与经济活动之间的关系。5个项目/案例分别为:克莱德沃伦公园(Klyde Warren Park)、凯蒂步道(Katy Trail)、德州大学达拉斯分校校园特色景观概念性规划(UT Dallas Campus Identity and Landscape Framework Plan)、阿狄森公园(Addison Circle)和布法罗河湾散步道(Buffalo Bayou Promenade)。研究采用了定量和定性相结合的实证调查法,首先评价了风景园林设计及相关设计领域的经济评估和绩效研究情况。之后重点研究了所选项目的景观类型、过程和结果,以突出在经济绩效研究中,确定统一标准和全面框架的重要性。最后,讨论了通过实证证据和系统性调查对经济活动进行研究的价值,并将经济活动作为景观绩效的一部分。总之,综合标准、方法与案例研究的结果来说明不同城市风景园林设计类型项目的经济影响,还讨论了通过统一标准方法来获得可靠实证结果的价值。结果表明,从案例中可以看到,经济绩效并不总是容易被量化的,同样也并非所有的设计改进均与经济活动直接相关。因此,这项研究强调了记录指定的景观项目中所有直接、间接和连锁的经济效应,并突出其经济价值的重要性。这也表明,未来的风景园林设计将对社会产生更大的经济影响和价值。