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The electric vehicle and energy storage markets have grown rapidly in recent years. Thermal runaway caused by malfunctioning Li-ion batteries is an urgent issue with many causes (e.g., mechanical, electrical, and thermal abuse). The most common cause of thermal runaway is the formation of an internal short circuit because of damage to the separator. There has been significant effort to improve the design of separators, but to our knowledge, only inorganic nanoparticle coatings are used in commercial Li-ion batteries. Here, hybrid organic/inorganic coating layers are synthesized in a pilot-scale process that was developed from a crosslinkable polyamide-imide synthesis technique. The fabrication process is optimized to achieve reproducible hybrid organic/inorganic coating layers that are thin (≤4 μm), permeable (≤250 s/100 cc), and thermally stable beyond 150 °C. The hybrid coating layer is applied to mini-18650 Li-ion cells to show that the discharge capacity did not change at low discharge rates, and the retention capacity after 500 cycles was better than that of the reference cells used for comparison. This work demonstrates that a novel hybrid coating layer has the potential to improve the stability of commercial Li-ion batteries. [ABSTRACT FROM AUTHOR]

A facile method is developed to improve the initial reversible capacity of hollow carbon nanofibers (HCNFs), which are manufactured via coaxial electrospinning of core/shell precursor nanofibers and their thermal treatments for stabilization and carbonization. Since the low initial reversible capacity of HCNFs is mainly caused by mesopores in the HCNFs, in our approach, the size of these mesopores is reduced by simply introducing a chemical vapor deposition (CVD) process between the stabilization and carbonization processes, thereby inducing the deposition of carbon atoms in the mesopores. The initial coulombic efficiencies of the HCNFs and the Si-encapsulated HCNFs are significantly increased by employing CVD process. The mechanism behind such improvement is revealed by morphological, microstructural, surface, and electrochemical analyses, confirming that control of the mesopores in HCNFs is an effective means to improve the electrochemical performance of HCNFs. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on Si core/C shell nanofibers as an anode material for Li-ion batteries. The Si core/C shell nanofibers are synthesized using co-axial electrospinning of Si nanoparticles in styrene-co-acrylonitrile core solution and poly(acrylonitrile) shell solution combined with subsequent thermal treatments. The microstructure and elemental composition of the nanofibers are systematically examined using FE-SEM, TEM and WAXD for confirmation of the crystalline Si core/turbostratic C shell structure. In situ observation of contact-lithiation of the Si core/C shell nanofibers is carried out to investigate their mechanical durability during the electrochemical reactions. The electrochemical performances of the nanofibers as an anode are characterized by galvanostatic charge–discharge test. Due to simple processing but a well-developed core/shell structure and good electrochemical performance, the Si core/C shell nanofibers fabricated in this study offer the potential to develop enhanced Si/C nanostructured composite anodes. [Copyright &y& Elsevier]

Abstract: This work reports on hollow carbon nanofibers (HCNFs) as anode materials for Li-ion batteries. Various HCNFs are synthesized using co-axial electrospinning of styrene-co-acrylonitrile (core) and poly(acrylonitrile) (shell) solutions and subsequent thermal treatments. The microstructures of HCNFs are examined using SEM, Raman spectroscopy, WAXD, and HR-TEM. The effect of the carbonization temperature on their turbostratic carbon structures and electrochemical properties is systematically investigated. As the carbonization temperature increases, both crystallite thickness and length significantly increases while the initial irreversible capacity decreases. These predictable microstructure and electrochemical performance of HCNFs provide important insight for the design of novel nanostructured anode materials such as Si or Sn encapsulated HCNFs. [Copyright &y& Elsevier]

Abstract: The first Korean multi-mission geostationary Earth orbit satellite, Communications, Ocean, and Meteorological Satellite (COMS) was launched by an Ariane 5 launch vehicle in June 26, 2010. The COMS satellite has three payloads including Ka-band communications, Geostationary Ocean Color Imager, and Meteorological Imager. Although the COMS spacecraft bus is based on the Astrium Eurostar 3000 series, it has only one solar array to the south panel because all of the imaging sensors are located on the north panel. In order to maintain the spacecraft attitude with 5 wheels and 7 thrusters, COMS should perform twice a day wheel off-loading thruster firing operations, which affect on the satellite orbit. COMS flight dynamics system provides the general on-station functions such as orbit determination, orbit prediction, event prediction, station-keeping maneuver planning, station-relocation maneuver planning, and fuel accounting. All orbit related functions in flight dynamics system consider the orbital perturbations due to wheel off-loading operations. There are some specific flight dynamics functions to operate the spacecraft bus such as wheel off-loading management, oscillator updating management, and on-station attitude reacquisition management. In this paper, the design and implementation of the COMS flight dynamics system is presented. An object oriented analysis and design methodology is applied to the flight dynamics system design. Programming language C# within Microsoft .NET framework is used for the implementation of COMS flight dynamics system on Windows based personal computer. [Copyright &y& Elsevier]

Abstract: The first Korean multi-mission geostationary satellite, Communication, Ocean, and Meteorological Satellite (COMS) will be launched in 2010. The missions of this satellite will be Ka-band communications, ocean color monitoring, and meteorological imaging. The satellite was designed with only one solar array on the south panel. This novel configuration will keep imaging instruments on the north side from heating up. Asymmetry of the spacecraft configuration requires twice-a-day thruster-based Wheel Off-Loading (WOL) operations to keep the satellite attitude for imaging and communication. Thruster firings during the WOL operations cause the satellite orbit to change two times a day. Weekly East–West Station-Keeping (EWSK) and North–South Station-Keeping (NSSK) maneuver operations are planned for the COMS satellite in order to maintain the satellite in ±0.05° box at 128.2°E longitude. The EWSK maneuver is planned to be performed two days after the NSSK maneuver to correct small side effects in East–West direction due to plume impingement against the solar array during NSSK maneuver. Normally thruster firings during the WOL operation affect the satellite orbit only in the North–South direction, but there are also small perturbations in the East–West direction. In this paper, EWSK maneuver strategy for the COMS satellite is presented. This strategy takes twice-a-day thruster-based WOL operations and plume impingement effect of the NSSK maneuver into account. And an iterative process to calculate the velocity changes and maneuver time for the EWSK maneuver is applied. One year of the EWSK and NSSK maneuver simulations are performed with twice-a-day WOL to verify the proposed strategy. The proposed strategy showed that the mean longitude of the satellite is controlled at 128.2°±0.007° which is three times tighter than that of non-iterative process. Required Delta velocity (ΔV) for EWSK maneuver is also slightly smaller for iterative process. Tightly controlled mean longitude guarantees a better quality of satellite communications and Earth imaging when the spacecraft attitude is well maintained by on-board control. [Copyright &y& Elsevier]

Abstract: In this paper, Global Positioning System-based (GPS) Orbit Determination (OD) for the KOrea-Multi-Purpose-SATellite (KOMPSAT)-2 using single- and double-differenced methods is studied. The requirement of KOMPSAT-2 orbit accuracy is to allow 1m positioning error to generate 1-m panchromatic images. KOMPSAT-2 OD is computed using real on-board GPS data. However, the local time of the KOMPSAT-2 GPS receiver is not synchronized with the zero fractional seconds of the GPS time internally, and it continuously drifts according to the pseudorange epochs. In order to resolve this problem, an OD based on single-differenced GPS data from the KOMPSAT-2 uses the tagged time of the GPS receiver, and the accuracy of the OD result is assessed using the overlapping orbit solution between two adjacent days. The clock error of the GPS satellites in the KOMPSAT-2 single-differenced method is corrected using International GNSS Service (IGS) clock information at 5-min intervals. KOMPSAT-2 OD using both double- and single-differenced methods satisfies the requirement of 1-m accuracy in overlapping three dimensional orbit solutions. The results of the SAC-C OD compared with JPL’s POE (Precise Orbit Ephemeris) are also illustrated to demonstrate the implementation of the single- and double-differenced methods using a satellite that has independent orbit information available for validation. [Copyright &y& Elsevier]

Abstract: A GPS-based orbit determination system for the KOMPSAT-2 has been developed. Two types of orbit determination software such as operational orbit determination and precise orbit determination are designed and implemented. GPS navigation solutions from on-board the satellite are used for the operational orbit determination, and raw measurements data such as C/A code pseudorange and L1 carrier phase are processed for the precise orbit determination. Operational concept, architectural design, and performance test are described. [Copyright &y& Elsevier]

GPS navigation solutions and GPS-related telemetry points are analyzed using one-day playback data from the KOMPSAT-1 Spacecraft. Then, the GPS navigation solutions are reconstructed using simulated GPS raw measurements such as pseudo-ranges between the KOMPSAT-1 and GPS satellites constellation. GPS data generation and preprocessing computer programs are developed and used for the generation of the GPS raw measurement and reconstruction of the GPS navigation solutions. The playback GPS data and the reconstructed data are compared with each other. [Copyright &y& Elsevier]

Although lithium-ion batteries have already had a considerable impact on making our lives smarter, healthier, and cleaner by powering smartphones, wearable devices, and electric vehicles, demands for significant improvement in battery performance have grown with the continuous development of electronic devices. Developing novel anode materials offers one of the most promising routes to meet these demands and to resolve issues present in existing graphite anodes, such as a low theoretical capacity and poor rate capabilities. Significant improvements over current commercial batteries have been identified using the electrospinning process, owing to a simple processing technique and a wide variety of electrospinnable materials. It is important to understand previous work on nanofiber anode materials to establish strategies that encourage the implementation of current technological developments into commercial lithium-ion battery production, and to advance the design of novel nanofiber anode materials that will be used in the next-generation of batteries. This review identifies previous research into electrospun nanofiber anode materials based on the type of electrochemical reactions present and provides insights that can be used to improve conventional lithium-ion battery performances and to pioneer novel manufacturing routes that can successfully produce the next generation of batteries. [ABSTRACT FROM AUTHOR]

Abstract This work reports the design strategy of mechanically robust yarn electrodes having high areal capacity (ca. 14 mAh/cm2) as building blocks for microbatteries. Lithium iron phosphate (LiFePO 4) was embedded into poly(acrylonitrile) nanofibers (NFs) via electrospinning. The obtained NFs were assembled into yarns via a yarning process, and were then thermally treated to produce carbon NF yarns. A hot-stretching process was used between the yarning and thermal treatment processes, improving the mechanical (tensile modulus of 1.03 GPa and strength of 38 MPa) and electrical (43.1 S/cm) properties of the yarn electrodes. The free-standing yarn electrodes with different mass loadings showed stable cycling performances with reasonable reversible capacity (ca. 112 mAh/g) up to 30 cycles. These mechanically robust and electrochemically excellent yarn electrodes could serve as building blocks for various structures in advanced microbatteries requiring high areal density. Graphical abstract Unlabelled Image Highlights • Twisted nanofiber yarn was designed as a building block electrode for microbatteries. • Yarn electrodes revealed excellent mechanical (tensile strength of 38 MPa) and electrical (43.1 S/cm) properties. • Free-standing yarn electrodes showed high areal capacity (ca. 14 mAh/cm2) and cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: ZnO nanotubes with a wall thickness on the order of nanometers were produced by utilizing an organic template and atomic layer deposition (ALD). The organic template was removed by an O2 plasma process and a thermal annealing process, with the wall structure of the ZnO nanotubes maintained during the removal of the template. We investigated the response of a ZnO nanotube to ethanol gas as a function of its wall thicknesses. The ZnO nanotubes with a wall thicknesses of 10nm showed the highest gas response (defined as the ratio of electrical resistances, R air/R gas, under air atmosphere to the mixed air atmosphere with ethanol vapor) of 1184 toward 100ppm at 450°C. The ZnO nanotube with a wall thickness of 10nm was wholly depleted and thus highly responds to the adsorption of chemical species on its surface. Accurate control of the wall thickness of the ZnO nanotubes is crucial to make ZnO nanotube sensors with high response. [Copyright &y& Elsevier]

Abstract: Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25m (1σ) and 0.5m/s (1σ), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40×40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge–Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user’s discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites. The comparison of the orbit determination results using EKF and UKF shows that orbit determination using the UKF yields better results than that using the EKF. In addition, the estimation of the accuracy using the C/A code pseudorange is better than that using the navigation solutions. The absolute position and velocity accuracies of the UKF using GPS C/A code pseudorange were 12.098m and 0.0159m/s in the case of the CHAMP satellite, and 8.172m and 0.0085m/s in the case of the KOMPSAT-2 satellite. Moreover, the abnormal excursions of navigation solutions can be eliminated. These results verify that onboard orbit determination using GPS C/A code pseudorange, which is based on the UKF can provide more stable and accurate orbit information in the spaceborne GPS receiver. [Copyright &y& Elsevier]

Although polyacrylonitrile (PAN)-based carbon fibers have been successfully commercialized owing to their excellent material properties, their actual mechanical performance is still much lower than the theoretical values. Meanwhile, there is a growing demand for the use of superior carbon fibers. As such, many studies have been conducted to improve the mechanical performance of carbon fibers. Among the various approaches, designing a strong precursor fiber with a well-developed microstructure and morphology can constitute the most effective strategy to achieve superior performance. In this review, the efforts used to modulate materials, processing, and additives to deliver strong precursor fibers were thoroughly investigated. Our work demonstrates that the design of materials and processes is a fruitful pathway for the enhancement of the mechanical performance of carbon fibers. [ABSTRACT FROM AUTHOR]

We synthesized four novel red azo dyes for use in a low-temperature-cured white organic light-emitting diode color conversion layer. The various substituents were introduced into the synthesized dyes to induce steric strain within the base compound for enhancing their solubility. All synthesized dyes exhibited excellent maximum absorption peaks at 521 nm, and AR4, in particular, displayed the highest molar absorptivity of 42 500. Via optimal mixing, the synthesized dyes were used to form red color resists for use in microdisplay color conversion layers. As a white backlight was applied to the optimized spin-coated films, the AR3 and AR4 films, with large dihedral angles between their substituents and diazonium planes, exhibited excellent color coordinates and transmittances, as intermolecular aggregation was inhibited. The color resists fabricated using the AR3 and AR4 dyes also displayed clear micropatterning results, confirming their high compatibility with low-temperature curing binders for use in future display production. [Display omitted] • Four novel azo dyes were synthesized and suitably fabricated into color conversion layers. • Their solubility, stability, optical properties, and chromatic properties were optimized. • Synthesized dyes with bulky substituents showed the superior color reproduction ranges. • They were successfully adopted for low-temperature curing top emission OLED displays. [ABSTRACT FROM AUTHOR]

High rate and long lifespan were enabled by the layered oxide cathode active material inspired carbon secondary microsphere. [Display omitted] • Monodisperse secondary carbon microsphere was designed. • Diameters of the secondary particles were highly controllable with the composition. • High rate capability was achieved with the primary particles of ca. 100 nm. • Long lifespan over 500 cycles was achieved with high capacity retention of 83.8%. A new anode material that will provide lithium ion (Li-ion) batteries with high energy and power density is urgently needed. In this work, a layered oxide cathode-inspired secondary hard carbon microsphere (CMS) anode material was designed, and exhibited excellent rate performance and long cyclability. Polyacrylonitrile/poly(styrene- co -acrylonitrile) (PAN/SAN) compositions displaying the meatball-like shape of the PAN precursor were carbonized into CMSs having turbostratic microstructures. The CMS carbonized at 1,000 °C (CMS1000) displayed high specific capacity at the highest current density of 1,000 mA g−1, i.e. , 77.6 % of its average charge capacity at 100 mA g−1, and considerable cycling retention after 500 cycles, i.e. , 83.8 % of the specific capacity at cycle 25. Our work demonstrates that the design of new anode materials is a fruitful route to improve commercial Li-ion batteries. [ABSTRACT FROM AUTHOR]

This work reports a novel design strategy for a strong polyacrylonitrile (PAN) fiber using an electrochemical wet-spinning process. First, a spinning dope was prepared using PAN copolymer containing methyl acrylate. This was spun using a conventional wet-spinning setup, but with a special nozzle spinneret whereby an electric potential could be applied. In situ electrochemical oxidation of methyl acrylate was then induced within the nozzle, resulting in electrochemical demethylation of the PAN copolymer. The subsequently endowed hydrophilic and hygroscopic properties of the PAN fibers improved the chain mobility of the PAN molecules and reduced void formation during wet-spinning. Investigation of the quantitative relationships between the degree of electrochemical demethylation and the mechanical properties of the PAN fibers clarified the in situ plasticization effect of absorbed water induced by the electrochemical demethylation. The Young's modulus and tensile strength of the PAN fibers were improved by 23.4% and 23.5%, respectively, and the breaking strain was increased by 28.1%. These results demonstrate the innovativeness of our new electrochemical wet-spinning process. Image 1 • A new strategy for improving mechanical properties of carbon fiber precursor. • In situ induced plasticizing effect by electrochemical reaction. • Increased mechanical properties of a fiber via decreased size of internal voids. [ABSTRACT FROM AUTHOR]

This report describes a new twist-spinning process for the manufacture of piezoelectric yarn without the need for additional poling processes. Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) nanofibers were first electrospun and organized into a web structure. Using rotational and translational motors, the nanofibers of the web were pulled and stretched and, finally, twisted into piezoelectric yarns. The crystallinity, β phase ratio, and mechanical and piezoelectric properties of these twist-spun piezoelectric yarns were characterized to assess the effects of the twist-spinning operation on their microstructure and performance. Twist-spun piezoelectric yarns that had undergone high degrees of stretching exhibited enhancements in both crystallinity and β phase ratio by 83% and 12%, respectively. In contrast, high stretching reduced the tensile strength and modulus of the yarns due to small surface angles. The twist-spun piezoelectric yarn with the highest β phase ratio and lowest modulus attained in this study yielded a piezoelectric potential and piezoelectric voltage constant of 500 mV and 0.412 mVm/N, respectively. Unlabelled Image • Poling-free spinning process was designed for piezoelectric nanofiber yarns. • PVDF-TrFE nanofibers were enhanced in both crystallinity (by 83%) and β phase ratio (by 12%) after yarn spinning process. • Piezoelectric yarn showed high mechanical (tensile strength of ~25 MPa) and piezoelectric (potential of 500 mV and g 33 of 0.40) properties. [ABSTRACT FROM AUTHOR]