Optimal design of spaced plates under hypervelocity impact

This paper presents a bumper shield design for protection of a satellite structure system subjected to hypervelocity impact (above 6 km/s) from space debris. Especially, this study is focused on the optimization of the spaced plates (the so-called Whipple shield) design using the coupled SPH and Lagrangian FEM methods. This is because the SPH is a meshless method and it is efficient in hypervelocity impact analysis involving debris caused by fragmentation and penetration under hypervelocity impact. The Whipple shield is composed of multiple spaced plates where the first bumper plate is modeled as particles for SPH simulation while the rear wall is modeled as elements for FEM. The appropriate smoothing length and mesh size were determined taking into account computational cost and accuracy and the erosion scheme is adopted to avoid numerical error due to large deformation. After verification for the comparison with previous experimental works, the optimal plate structure is proposed considering multi design objectives based on parameter optimization.     

Reliability-based robust design optimization for torque ripple reduction considering manufacturing uncertainty of interior permanent magnet synchronous motor

Journal of Mechanical Science and Technology - This study performed reliability-based robust design optimization (RBRDO) of stator and rotor shape of the IPM type electric motor to reduce the...     

Smartphone user segmentation based on app usage sequence with neural networks

The term user segmentation refers to classifying users into groups depending on their specific needs, characteristics, or behaviors. It is a key element of product development and marketing in many industries, such as the smartphone industry, which employs user segmentation to gather information about usage logs, to produce new products for such specific groups of users. However, previous studies on smartphone user segmentation have been primarily based on demographics and reported usage, which are inherently subjective and prone to skew by the observers and participants. Hamka et al. (2014) was the first to conduct a study, in which smartphone user segmentation was performed using log data collected through smartphone measurements. However, they focused only on network usage and the number of apps used, and not on characteristics or preferences. In this study, we proposed novel ways of segmenting smartphone users based on app usage sequences collected from smartphone logs. We proposed a variant of seq2seq architecture combining the advantages of previous deep neural networks: neural embedding architecture and seq2seq architecture. Furthermore, we compared the user segmentation results of the proposed method with an answer set of segmentation results conducted by domain experts. These experiments demonstrated that the proposed method effectively determines similarities between usage sequences and outperforms existing user segmentation methods.     

Pseudohalide‐Exchanged Quantum Dot Solids Achieve Record Quantum Efficiency in Infrared Photovoltaics

Application of pseudohalogens in colloidal quantum dot (CQD) solar‐cell active layers increases the solar‐cell performance by reducing the trap densities and implementing thick CQD films. Pseudohalogens are polyatomic analogs of halogens, whose chemistry allows them to substitute halogen atoms by strong chemical interactions with the CQD surfaces. The pseudohalide thiocyanate anion is used to achieve a hybrid surface passivation. A fourfold reduced trap state density than in a control is observed by using a suite of field‐effect transistor studies. This translates directly into the thickest CQD active layer ever reported, enabled by enhanced transport lengths in this new class of materials, and leads to the highest external quantum efficiency, 80% at the excitonic peak, compared with previous reports of CQD solar cells.     

A modified exhaustive search on a password system using SHA-1

In this paper, we show a method of exhaustive search on a password system that uses SHA-1 iteratively. Our method uses both the technique shown in Steube [16] and a technique for computing repetitions of SHA-1. Combining these two techniques reduces the total number of operations. We also show how to apply our method to MS Office (Microsoft Office) 2007/2010.     

Melt‐intercalation nanocomposites with fluorinated polymers and a correlation for nanocomposite formation

Various fluorinated polymers were investigated to produce polymer nanocomposites with special clays. Natural and organically treated montmorillonite clays were melt‐compounded with the polymers. Characterization by wide‐angle X‐ray scattering and transmission electron microscopy showed the separation of montmorillonite layers and the formation of polymer nanocomposites. Organically treated montmorillonite clay dispersed in poly(vinylidene fluoride) and various vinylidene fluoride copolymers and formed nanocomposites. Natural and organophilic clays were not well dispersed in other fluorinated copolymers and polyethylene. A correlation was developed for the formation of polymer–clay nanocomposite structures in chlorinated and fluorinated polymers in terms of the dielectric constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1061–1071, 2004     

Energy Saving Electrochromic Polymer Windows with a Highly Transparent Charge‐Balancing Layer

Highly transparent TiO₂ nanoparticles are explored as a non‐electrochromic (non‐EC) charge‐balancing layer for a high color contrast, bistable electrochromic window (ECW). The TiO₂ nanoparticle (TNP) layer increases the potential at the EC polymer electrode, thereby lowering the working voltage of the ECW. This leads to lower the power consumption of ECWs without loss in the high color contrast (ΔT > 72%) and to remarkably improve the cyclability (ΔT change <1% over 3000 cycles), mainly due to the low overvoltage (<0.1 V) on the electrochromic polymer layer. Furthermore, the ECWs including the non‐EC TNP layer show long‐term bistability (>2.7 h, 40% increase) and UV stability (ΔT change <1%) to provide a low‐power automatic ECW. This finding shows that the charge balanced ECP window has the potential to be used for an energy saving ECW with low‐power consumption and will be widely applied in various ECWs as well as electrochemical devices with multiple functions.     

Amine‐Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light‐Emitting Diodes

Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light‐emitting diodes (LED) are fabricated for the first time with solution‐processed polymer‐based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross‐linked PQDs. The brightest blue LED based on all inorganic CsPb(Br_1?xCl_x)₃ PQDs is also reported.