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This paper proposes an effective numerical method to predict welding distortion for large welded structures. To predict welding distortions, inherent strain-based methods are computationally efficient and widely used in engineering fields. However, there are some drawbacks such as the generation of undesirable longitudinal forces and the use of vector-type input variables. Equivalent loads are derived through finite element formulation considering orthotropic thermal expansion conditions. Unlike previous methods, the proposed method predicts transverse shrinkage and angular distortion accurately, removing the undesirable longitudinal forces. In addition, scalar-type input variables are employed, which results in a convenient design procedure. The performance of the proposed method is verified through various examples including complex and large welded structures.

Despite the promise of pyrenetetrone derivatives as insoluble organic cathode compounds for lithium-ion batteries, there is limited information on their electrochemical characteristics. Herein, a highly reliable computational protocol is employed to systematically explore the redox properties and theoretical performances of pyrenetetrone derivatives. This comprehensive analysis reveals that the electrochemical redox properties of pyrenetetrone derivatives at fully charged states are determined by complementary contributions from key factors, such as dopant electronegativity, electrostatic potential of the central backbone, and interatomic electronic flow. In contrast, dopant electronegativity becomes a dominant factor for tuning the redox behaviors of these organic compounds during the Li-involved discharging process, indicating the potential of boron-doped compounds for high-performance cathodes. Further investigation highlights that the entire discharging process can be summarized as Li-induced continuous reduction in electron affinity terminated by a sudden increase in solvation energy (depending on dopant electronegativity), which emphasizes the importance of solvation energy in determining cathodic deactivation.

In this work, we propose a trajectory generation method for robotic systems with contact kinematics and force constraints based on optimal control and reachability analysis tools. Normally, the dynamics and constraints of a contact-constrained robot are nonlinear and coupled to each other. Instead of linearizing the model and constraints, we solve the optimal control problem directly to obtain feasible state trajectories and their corresponding control inputs. A tractable optimal control problem is formulated and subsequently addressed by dual approaches, which rely on sampling-based dynamic programming and rigorous reachability analysis tools. In particular, a sampling-based method together with a Partially Observable Markov Decision Process solution approach are used to break down the end-to-end trajectory generation problem by generating a sequence of subregions that the system’s trajectory will have to pass through to reach its final destination. The distinctive characteristic of the proposed trajectory optimization algorithm is its ability to handle the intricate contact constraints, coupled with the system dynamics, in a computationally efficient way. We validate our method using extensive numerical simulations with two legged robots.

In this letter, we formulate a novel Markov Decision Process (MDP) for safe and data-efficient learning for humanoid locomotion aided by a dynamic balancing model. In our previous studies of biped locomotion, we relied on a low-dimensional robot model, commonly used in high-level Walking Pattern Generators (WPGs). However, a low-level feedback controller cannot precisely track desired footstep locations due to the discrepancies between the full order model and the simplified model. In this study, we propose mitigating this problem by complementing a WPG with reinforcement learning. More specifically, we propose a structured footstep control method consisting of a WPG, a neural network, and a safety controller. The WPG provides an analytical method that promotes efficient learning while the neural network maximizes long-term rewards, and the safety controller encourages safe exploration based on step capturability and the use of control-barrier functions. Our contributions include the following (1) a structured learning control method for locomotion, (2) a data-efficient and safe learning process to improve walking using a physics-based model, and (3) the scalability of the procedure to various types of humanoid robots and walking., Comment: 8 pages, 7 figures

Whilst copper and silver are the conductors of choice for myriad current and emerging applications, patterning these metals is a slow and costly process. We report the remarkable finding that an extremely thin (∼10 nm) printed layer of specific organofluorine compounds enables selective deposition of copper and silver vapour, with metal condensing only where the organofluorine layer is not. This unconventional approach is fast, inexpensive, avoids metal waste and the use of harmful chemical etchants, and leaves the metal surface uncontaminated. We have used this approach to fabricate thin films of these metals with 6 million apertures cm−2 and grids of ∼1 μm lines, through to 10 cm diameter apertures. We have also fabricated semi-transparent organic solar cells in which the top silver electrode is patterned with a dense array of 2 μm diameter apertures, which cannot be achieved by any other scalable means directly on an organic electronic device.

In this article, a layered shell element-based, elastic finite element method for predicting welding distortion in multi-pass welding is developed. The welding distortion generated in each pass can be predicted by employing layer-by-layer equivalent plastic strains as thermal expansion coefficients and using the heat-affected zone (HAZ) width as the mesh size. The final distortion can be expressed as the sum of the distortions for each pass. This study focuses on extraction of the equivalent plastic strain and HAZ width through 3D thermal elastic plastic analysis (TEPA) for each pass. The input variables extracted from each pass can be converted and added to simulate the final distortion of the multi-pass welding. A 10 mm thick, multi-pass butt-welded joint, subjected to three passes, is simulated via the proposed method. The predicted welding distortion is compared with the 3D TEPA results and the measured experimental data. The outcome indicates that good agreement can be obtained.

In this study, silicon dioxide contact holes were etched with C4F8 + CH2F2 + O2 + Ar gas plasmas, and the characteristics of the etching residue thereby generated inside the nanopatterns were investigated. The chemical composition of the etching residue formed on the sidewalls of the nano-contact patterns in the gas chemistry was investigated at various oxygen partial pressures by performing in situ Ar sputtering and X-ray photoelectron microscopy at different take-off angles. To investigate the effect of the plasma-active species (polymerizing radicals and charged species) on the formation of the etching residue, plasma diagnostics were conducted via optical emission spectroscopy and Langmuir probe measurements. It was found that as the oxygen content of the plasma increased, the thickness of the fluorocarbon (FC) polymer layer formed on the sidewalls of the nanopatterns decreased with a reduction in the FC polymer deposition rate of the plasma. In addition, at higher aspect ratios, the FC polymer layer showed a lower fluorine content.

Biporous structures at the nano–microscale are promising candidates for controlling phase change heat transfer, through their enhanced capillary wicking and fluid transportation. However, existing methods for fabricating biporous structures involve complex process which is not suitable for small-scale thermal devices such as heat pipes, owing to their confined and non-flat inner structures. Herein, we report the biporous structures inside copper-sintered heat pipes, enabled by layer-by-layer (LbL) assembled multi-walled carbon nanotube (MWCNT)-polyethyleneimine (PEI) coating for enhanced thermal performance. The repetitive filling and removing of the oppositely charged solutions with MWCNT-PEI and carboxylic-functionalized MWCNTs assembled the nanoporous MWCNT-PEI coatings (10, 20, and 40 bilayers) on the microporous copper-sintered inner surfaces. The fiber-like MWCNT networks structurally manipulated morphology and thickness of biporous structures, while the hydrophilic PEI shells chemically optimized wettability. A reduced thermal resistance (∼14.3%) was observed for MWCNT-PEI coating in 10 bilayers, due to the enhanced capillary wicking, interfacial contact areas, and bubble dynamics, whereas the 40 bilayers did not exhibit improved thermal performance owing to the redundant nanoporous layers causing reduced volume of microporous structures and increased thermal resistance. The LbL-assembled MWCNT-PEI coatings would act as functional layers to improve the performance of miniaturized and thin-film-based thermal devices.

Silver nanowire networks can offer exceptionally high performance as transparent electrodes for stretchable sensors, flexible optoelectronics, and energy harvesting devices. However, this type of electrode suffers from the triple drawbacks of complexity of fabrication, instability of the nanowire junctions, and high surface roughness, which limit electrode performance and utility. Here, a new concept in the fabrication of silver nanowire electrodes is reported that simultaneously addresses all three of these drawbacks, based on an electrospun nanofiber network and supporting substrate having silver vapor condensation coefficients of one and near‐zero, respectively. Consequently, when the whole substrate is exposed to silver vapor by simple thermal evaporation, metal selectively deposits onto the nanofiber network. The advantage of this approach is the simplicity, since there is no mask, chemical or dry metal etching step, or mesh transfer step. Additionally, the contact resistance between nanowires is zero and the surface roughness is sufficiently low for integration into organic photovoltaic devices. This new concept opens the door to continuous roll‐to‐roll fabrication of high‐performance fused silver nanowire electrodes for myriad potential applications.\ud \ud

This paper proposes an MPC-based controller to efficiently execute multiple hierarchical tasks for underactuated and constrained robotic systems. Existing task-space controllers or whole-body controllers solve instantaneous optimization problems given task trajectories and the robot plant dynamics. However, the task-space control method we propose here relies on the prediction of future state trajectories and the corresponding costs-to-go terms over a finite time-horizon for computing control commands. We employ acceleration energy error as the performance index for the optimization problem and extend it over the finite-time horizon of our MPC. Our approach employs quadratically constrained quadratic programming, which includes quadratic constraints to handle multiple hierarchical tasks, and is computationally more efficient than nonlinear MPC-based approaches that rely on nonlinear programming. We validate our approach using numerical simulations of a new type of robot manipulator system, which contains underactuated and constrained mechanical structures., Comment: 8 pages, 5 figures

For a nonlinear system (e.g. a robot) with its continuous state space trajectories constrained by a linear temporal logic specification, the synthesis of a low-level controller for mission execution often results in a non-convex optimization problem. We devise a new algorithm to solve this type of non-convex problems by formulating a rapidly-exploring random tree of barrier pairs, with each barrier pair composed of a quadratic barrier function and a full state feedback controller. The proposed method employs a rapid-exploring random tree to deal with the non-convex constraints and uses barrier pairs to fulfill the local convex constraints. As such, the method solves control problems fulfilling the required transitions of an automaton in order to satisfy given linear temporal logic constraints. At the same time it synthesizes locally optimal controllers in order to transition between the regions corresponding to the alphabet of the automaton. We demonstrate this new algorithm on a simulation of a two linkage manipulator robot., Comment: 6 pages, 5 figures. Accepted for publication in IEEE Conference on Decision and Control (CDC) copyright 2020 IEEE

The study of InP etching kinetics as well as the evaluation of InP etching mechanism in HBr + Cl2 + Ar inductively coupled plasma were carried out. Experiments on the measurements of the etching rates for InP, SiO2, and SiNx as well as plasma diagnostics using Langmuir probes and optical emission spectroscopy were conducted at a fixed total gas pressure (10 mTorr, or 1.33 Pa), input power (800 W), and bias power (200 W), and the variable parameter was the HBr/Cl2 mixing ratio. Zero-dimensional (global) plasma modeling provided data regarding the densities of the plasma active species as well as on the particle and energy fluxes to the etched surface. An increase in the Cl2 fraction in the feed gas yielded a non-monotonic InP etching rate with a maximum of ~120 nm/min at 35% Cl2. Model-based analysis of the InP etching kinetics revealed that 1) the InP etching process is mainly provided by the chemical etching pathway; 2) the non-monotonic change in the InP etching rate cannot be explained by the chemical effects of Br and Cl atoms; and 3) the HCl molecules may have sufficiently contributed to the chemical etching pathway.

Conductive polymers are exceptionally promising for modular electrochemical applications including chemical sensors, bioelectronics, redox-flow batteries, and photo-electrochemical systems due to considerable synthetic tunability and ease of processing. Despite well-established structural heterogeneity in these systems, conventional macroscopic electroanalytical methods – specifically cyclic voltammetry – are typically used as the primary tool for structure-property elucidation. This work presents an alternative correlative multi-microscopy strategy; data from laboratory and synchrotron-based micro-spectroscopies, including conducting-atomic force microscopy and synchrotron nanoscale infrared spectroscopy, is combined with potentiodynamic movies of electrochemical fluxes from scanning electrochemical cell microscopy (SECCM) to reveal the relationship between electrode structure and activity. A model conductive polymer electrode system of tailored heterogeneity is investigated, consisting of phase-segregated domains of poly(3-hexylthiophene) (P3HT) surrounded by contiguous regions of insulating poly(methyl methacrylate) (PMMA), representing an ultramicroelectrode array. Isolated domains of P3HT are shown to retain bulk-like chemical and electronic structure when blended with PMMA, and possess approximately equivalent electron-transfer rate constants compared to pure P3HT electrodes. The nanoscale electrochemical data are used to model and predict multiscale electrochemical behavior, revealing that macroscopic cyclic voltammograms should be much more kinetically facile than observed experimentally. This indicates that parasitic resistances rather than redox kinetics play a dominant role in macroscopic measurements in these conducting polymer systems. SECCM further demonstrates that the ambient degradation of the P3HT electroactivity within P3HT/PMMA blends is spatially heterogeneous. This work serves as a roadmap for benchmarking the quality of conductive polymer films as electrodes, emphasizing the importance of nanoscale electrochemical measurements in understanding macroscopic properties.\ud \ud

Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm2) and 20.9% (large-area, ~1 cm2). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C. Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole-transporting layer that is better matched to the surrounding layers, and show high-efficiency and high-stability devices.

An efficient approach to predicting the welding angular distortion of large structures by using scalar input variables with no restriction on the mesh size near the welding region is proposed. To transform the input variables according to the mesh size, the explicit form of the force matrix is derived based on finite element theory. The proposed method is easily applied and requires only the measured distortion rate of a unit welded specimen and a user-designed mesh system to conduct the welding distortion analysis. The proposed method was applied to various case studies for verification, and the results show that the proposed method can effectively predict the welding angular distortion.

This paper presents a methodology for estimating the minimum design vapor pressure of prismatic pressure vessels for on-ship application. Engineering authorities guide the codes for a novel concept design such as a prismatic pressure vessel using a design by analysis (DBA). DBA methods enable high efficiency because they directly calculate the loads to avoid inherent conservativeness that exists in a design by rule (DBR). However, in DBA methods, the designer should conduct a finite element analysis (FEA) and evaluate the results iteratively to meet the design criteria. In this paper, we propose a new approach to estimating the minimum vapor pressure of a prismatic pressure vessel that follows the design philosophy of an IMO Type C independent tank. The procedure of the proposed method was demonstrated based on a case study. An FEA was also conducted for verification purposes. The results show that the proposed method can effectively estimate the required minimum shell thickness and designed vapor pressure without conducting an iterative FEA. In addition, minimization of the tank shell thickness is made possible because the proposed method directly calculates the crack propagation rate to avoid an unnecessary margin while satisfying the fatigue crack propagation criteria.

We report an influence of abnormal mixing effect of host systems having undesirable energy level and transport level in the emission layer (EML). Rather, we focused on their device performance and stability (e.g. driving lifetime) when it was prepared by solution-process. The resultant green phosphorescent organic light emitting diodes (s-OLEDs) showed reasonable device performance and interesting photo-physical properties, which revealed that we can achieve good performance if an appropriate compromise between the factors which govern a charge transport and an energy transfer processes can be realized albeit the EML has undesirable host systems with both bad energy level matching (e.g., HOMO, LUMO levels) and charge transport properties. In this study, a high performance of the s-OLEDs by controlling photo-physical pathways such as exciton quenching process (e.g. triplet-triplet annihilation). Besides, such kind of change in photo-physical pathway may be optimized by controlling the charge balance (i.e. carrier transport behaviour) where we intentionally selected N- and P-type host materials (denote NH and PH, respectively) with abnormal HOMO and LUMO energy levels.

In this work, we investigated how the CF4/C4F8 and CF4/CH2F2 mixing ratios in CF4+C4F8+Ar and CF4+CH2F2+Ar inductively coupled plasmas influence plasma parameters, densities and fluxes of plasma active species and etching characteristics (process kinetics, etching rates and selectivities, etching residues) for both Si and SiO2. For this purpose, we employed surface diagnostics by x-ray photoelectron spectroscopy (XPS), plasma diagnostics by Langmuir probes and 0-dimensional plasma model. It was found that the substitution of CF4 for CH2F2 causes the stronger decreases in both F atom flux and ion energy flux compared with the effect of C4F8. Accordingly, the CF4+CH2F2+Ar mixture provides the deeper fall of both Si and SiO2 etching rates, leaves the higher amount of the fluorocarbon polymer on the etched surface (especially in the case of Si) and results in a bit higher SiO2/Si etching selectivity. It was shown also that, in both gas systems, the etching process appears in the steady-state regime. The mechanisms influencing the etching/polymerization balance were discussed based on the correlation between Si and SiO2 etching rates with fluxes of plasma active species.

Solution processing, especially printing of OLEDs is an issue of current research. Among various types of printing, nozzle printing does not require complicated experimental procedures, and therefo...

The deposition of SiOC thin films via remote plasma atomic layer deposition was investigated. Octamethylcyclotetrasiloxane (OMCTS) and O2, Ar, H2 plasmas were respectively used as a precursor and reactants during the deposition process at 400 °C. Plasma and deposition temperatures had a significant effect on the physical and electrical characteristics of the films. When Ar and H2 plasma was respectively used during the deposition process, films exhibited low dielectric constants while incorporating carbon; however, O2 plasma yielded carbon free SiO2 films. Low dielectric constants resulted in low film densities and the presence of carbon within the films. When Ar and H2 plasma was used as the reactant gas, pores within the films with loose structures and Si C bonds served to lower the dielectric constant. As a result, Ar and H2 plasma conditions exhibited low dielectric constants of 2.7 and 3.1 at 100 °C, respectively. Meanwhile, the presence of carbon and low film densities caused leakage paths within the films. X-ray photoelectron spectroscopy supported analyses demonstrating the bonding characteristics of Si, C, O components.

The purpose of this study is to investigate the effect of layer-by-layer (LbL) assembled carbon nanotube (CNT) coatings on dropwise condensation heat transfer under steam–air mixture conditions. To promote dropwise condensation, an additional hydrophobic coating was added to the LbL-assembled CNT coatings, which resulted in a 16% enhanced condensation heat transfer coefficient (HTC) compared to that of the bare surface under saturated steam conditions. Despite the existence of the nanostructures on the CNT-layered surface, the larger droplet size was observed from the high-speed images than that of the bare surface due to flooding condensation phenomenon. Considering that the HTC was enhanced without smaller droplet size, it is evident that this enhancement was mainly attributed to the reduced constriction resistance driven by the high thermal conductivity of the CNT layers. A new HTC model for dropwise condensation incorporating constriction resistance was developed to better predict the measured condensation HTC. Although the enhancement of the condensation HTC on the LbL-assembled CNT coatings was diminished with the air mass fraction, this work reports a new perspective to enhance the dropwise condensation heat transfer performance by controlling the constriction resistance using a highly thermally conductive coating.

Computation offloading enables mobile devices to execute rich applications by using the abundant computing resources of powerful server systems. The distributed shared memory based (DSM-based) computation offloading approach is expected to be especially popular in the near future because it can dynamically migrate running threads to computing nodes and does not require any modifications of existing applications to do so. The current DSM-based computation offloading scheme, however, has focused on efficiently offloading computationally intensive applications and has not considered the significant performance degradation caused by processing the I/O requests issued by offloaded threads. Because most mobile applications are interactive and thus yield frequent I/O requests, efficient handling of I/O operations is critically important. In this paper, we quantitatively analyze the performance degradation caused by I/O processing in DSM-based computation offloading schemes using representative commodity applications. To remedy the performance degradation, we apply a remote I/O scheme based on remote device support to computation offloading. The proposed approach improves the execution time by up to 43.6% and saves up to 17.7% of energy consumption in comparison with the existing offloading schemes. Selective compression of the remote I/O scheme reduces the network traffic by up to 53.5%.

This paper proposes design principles of a new concept prismatic pressure vessel that is primarily constructed of plane surfaces. These principles were compared with those of conventional pressure vessel which is primarily constructed of revolutionary surfaces. Considering structural characteristics of prismatic pressure vessel, membrane force and bending moment were calculated individually. Formulas including maximum bending moment and membrane force effects were illustrated by applying Levy's method and superposition method. For total stress at the plate of the pressure vessel, membrane force effects obtained from the shear loads of adjacent plates were included to enable to get more accurate solutions. The proposed simplified formulas for prismatic pressure vessel were suggested so that they can be applied for all dimensions and thicknesses. Case studies were conducted to verify the formulas by comparing with FEM results. By providing an overview of the stress relations of a non-stiffened type prismatic pressure vessel, the design principle of a prismatic pressure vessel shows distinctive concept to the conventional cylindrical pressure vessel. The membrane force effect studied in this research will be useful in the design of larger pressure vessels that require stiffeners.

We synthesized a novel wide bandgap polymer, PDTFBT, forming a weak donor (WD)-weak acceptor (WA) structure for use in organic photodetectors (OPDs) and organic solar cells (OSCs). The fluorination in the D unit and the alkoxy substitution in the A unit induced WD and WA properties, respectively. The WD-WA structure of PDTFBT effectively broadened the bandgap compared to typical D-A structures, and the S-F and S-O dipole-dipole interactions induces a highly planar backbone structure with excellent π-π stacking in the vertical direction. In OPDs, conformationally less disordered PDTFBT polymer retained the constant responsivity and significantly improved the detectivity of PDTFBT:PC71BM devices even with a thick active layer of 470 nm, contrary to the variation in the responsivity of P3HT:PC61BM devices depending on the thickness. In OSCs, the deep HOMO energy level (−5.57 eV) of PDTFBT led to high Voc of 0.92 V in PDTFBT:PC71BM devices, which was 0.3 eV higher than that of P3HT:PC61BM devices (0.62 V), resulting in 1.8-fold enhanced power conversion efficiency. We demonstrated that the WD-WA structure with S-F and S-O interactions is highly promising strategy to make wide bandgap polymers for organic photodetectors and for the bottom cell of tandem architecture.

The role of a Ti nano-layer embedded in TaO x -based devices operating with conductive filaments consisting of oxygen vacancies was investigated. The Ti nano-layer was embedded in three different positions: the top interface (Au/TaO x ), bottom interface (TaO x /TiN), and both interfaces. The embedded Ti nano-layer serves as not only an oxygen reservoir but also a tunneling barrier in the case of the top interface. The position of the Ti nano-layer and its thickness play important roles in the resistive switching behaviors. In addition, the effect of the current compliance on the resistive switching behaviors was evaluated. The different resistive switching behaviors were investigated using current-voltage sweep measurements and X-ray photoelectron spectroscopy. The non-linear behavior of the low resistance state could be controlled by the top interface and current compliance. The current of the high resistance state could be controlled by the bottom interface. It is noteworthy that only 1.5-nm-thick Ti nano-layer can adjust the non-linear behavior of the low resistance state at top interface and the current of the high resistance state at bottom interface.

We synthesized the conjugated polymers PT2OBT, PVT2OBT, and PFBT2OBT for use in organic photodetecting devices. An octyloxy benzothiadiazole (OBT) moiety was used as a weak electron-accepting building block in the polymer system to cause the dominant absorption in the green-light region via weakening the intramolecular charge transfer (ICT) interactions between adjacent electron-donating moieties. In particular, indirect X-ray detection using a scintillator requires a low leakage current; thus, we focused on designing a molecular structure that can enhance the detectivity. The difluorobenzene-incorporated PFBT2OBT polymer showed a strong edge-on orientation both in the pristine film and in the blend film; however, PT2OBT and PVT2OBT have no preferred molecular orientation in the blend film. In the edge-on structure, the alkyl side chains of PFBT2OBT align on the surface of the electrode, forming an insulating layer, which decreases the tunneling leakage current, whereas in the latter cases, the interface between the semiconducting polymer backbone and PC70BM can come into contact with the electrode, forming a pathway for the leakage current. Consequently, the PFBT2OBT:PC70BM devices showed promising detectivities of over 1013 Jones over a wide range of reverse biases of up to −2 V, resulting from their low dark current density of less than 2.3 × 10−9 A cm−2.

It is widely considered that charge carrier extraction in bulk‐heterojunction organic photovoltaics (BHJ OPVs) is most efficient when the area of contact between the semiconductor layers and the electrodes is maximized and the electrodes are electrically homogeneous. Herein, it is shown that ≈99% of the electrode surface can in fact be insulating without degrading the efficiency of charge carrier extraction, provided the spacing of the conducting areas is less than or equal to twice the optimal thickness of the BHJ layer. This striking result is demonstrated for BHJ OPVs with both conventional and inverted device architectures using two different types of BHJ OPVs, namely, PCDTBT:PC70BM and the ternary blend PBDB‐T:ITIC‐m:PC70BM. This finding opens the door to the use of a large pallet of materials for optical spacers and charge transport layers, based on a low density of conducting particles embedded in a wide bandgap insulating matrix.

Curcumin is a polyphenol compound derived from the rhizomes of Curcuma longa that exhibits antioxidant, anti-inflammatory, anticancer, and antimicrobial properties. However, its low solubility in aqueous solutions, low absorption following oral administration, and rapid degradation limit its use as a functional food material. In this study, a hydroxypropyl methylcellulose-based solid dispersion of curcumin (DW-CUR 20) was prepared and its bioavailability was evaluated. In addition, its therapeutic efficacy as a hepatoprotective agent was investigated using the model of tert-butyl hydroperoxide (t-BHP)-induced hepatocyte damage. The rat plasma pharmacokinetic study showed that the oral curcumin bioavailability of DW-CUR 20 significantly increased compared to that of non-formulated curcumin. DW-CUR 20 showed a concentration-dependent hepatocyte protective effect on t-BHP-induced HepG2 cells. DW-CUR 20 inhibited the release of lactate dehydrogenase and decreased apoptosis-related proteins such as Poly (ADP-ribose) polymerase, cleaved caspase-7 and cleaved caspase-8 on t-BHP-treated HepG2 cells. These findings suggest that DW-CUR 20 could be a promising formulation for enhancing the therapeutic efficiency of curcumin and for improving the safety.

Graphene-based carbon nanostructures with nanometer dimensions have been of great interest due to the existence of a bandgap. So far, well-ordered edge structure and uniformly synthesized graphene quantum dots (GQDs) with a hexagonal single-crystalline structure have not been directly observed owing to the limited precision of current synthesis approaches. Herein, we report on a novel approach not just for the synthesis of the size-controlled single-crystalline GQDs with hexagonal shape but also for a new discovery on constructing 2D and 3D graphene single crystal structures from d-glucose via catalytic solution chemistry. With size-controlled single-crystalline GQDs, we elucidated the crucial role of edge states on luminescence from the correlation between their crystalline size and exciton lifetime. Furthermore, blue-emissive single-crystalline GQDs were used as an emitter on light-emitting diodes and exhibit stable deep-blue emission regardless of the voltage and doping level.

A novel approach to fabricate flexible organic solar cells is proposed without indium tin oxide (ITO) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using junction‐free metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin‐film devices without planarization by conductive materials such as PEDOT:PSS. A highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) is fabricated on PEDOT‐free and ITO‐free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).

Whole-body control (WBC) is a generic task-oriented control method for feedback control of loco-manipulation behaviors in humanoid robots. The combination of WBC and model-based walking controllers has been widely utilized in various humanoid robots. However, to date, the WBC method has not been employed for unsupported passive-ankle dynamic locomotion. As such, in this article, we devise a new WBC, dubbed the whole-body locomotion controller (WBLC), that can achieve experimental dynamic walking on unsupported passive-ankle biped robots. A key aspect of WBLC is the relaxation of contact constraints such that the control commands produce reduced jerk when switching foot contacts. To achieve robust dynamic locomotion, we conduct an in-depth analysis of uncertainty for our dynamic walking algorithm called the time-to-velocity-reversal (TVR) planner. The uncertainty study is fundamental as it allows us to improve the control algorithms and mechanical structure of our robot to fulfill the tolerated uncertainty. In addition, we conduct extensive experimentation for: (1) unsupported dynamic balancing (i.e., in-place stepping) with a six-degree-of-freedom biped, Mercury; (2) unsupported directional walking with Mercury; (3) walking over an irregular and slippery terrain with Mercury; and 4) in-place walking with our newly designed ten-DoF viscoelastic liquid-cooled biped, DRACO. Overall, the main contributions of this work are on: (a) achieving various modalities of unsupported dynamic locomotion of passive-ankle bipeds using a WBLC controller and a TVR planner; (b) conducting an uncertainty analysis to improve the mechanical structure and the controllers of Mercury; and (c) devising a whole-body control strategy that reduces movement jerk during walking.

As interest in autonomous driving system has increased recently, variety of ADAS technologies that are responsible for safety of passengers are receiving attention. Realtime analysis and robust vehicle detection are essential for ADAS technology to cope with rapidly changing road conditions. In this paper, we propose a real-time vehicle detection system based on correlation filter.

Slab-like copper films with a thickness of 9 nm (∼70 atoms) and sheet resistance of ≤9 Ω sq−1 are shown to exhibit remarkable long-term stability toward air-oxidation when passivated with an 0. 8 nm aluminium layer deposited by simple thermal evaporation. The sheet resistance of 9 nm Cu films passivated in this way, and lithographically patterned with a dense array of ∼6 million apertures per cm2, increases by

A novel experimental technique for sidewall analysis of plasma-etched nano-patterns using tilted X-ray photoelectron spectroscopy (XPS) combined with in-situ ion sputtering was investigated. Complete removal of the residue layer (on the mask surface) and the mask layer using in-situ ion sputtering in the XPS chamber was conducted to reveal the sidewall information of the plasma-etched hole in SiO2 in addition to the trench in Si, after anisotropic plasma etching. The influence of the measured profile depth changes after adjusting the take-off angle in the sidewall chemistry of the plasma-etched hole in SiO2 and the trench in Si was examined. To demonstrate the analysis results, the sidewall compositions of the plasma-etched hole in SiO2 with various oxygen contents in the plasma were comparatively analyzed using XPS and Auger electron spectroscopy. It was observed that fluorinated carbon polymer (C-Fx, x ≤ 3) and SixOy (x ≤ 2, y ≤ 3) residue layers were formed on the hole in SiO2 and trench in Si sidewalls after C4F8/CH2F2/O2/Ar and HBr/Cl2 plasma etching, respectively. Thus, changes in the chemical characteristics of these sidewall etching residues were realized, revealing their dependency on the pattern size and type, plasma gas chemistry, and mask material. In addition, effectiveness of the dry cleaning process was evaluated using the tilted XPS combined with in-situ Ar ion sputtering.

In this paper, we report flexible transparent conducting electrode (TCE) film using a silver grid (Ag grid)/silver nanowire (AgNW) hybrid structure (AG/NW-GFRHybrimer). The AG/NW-GFRHybrimer consists of an AgNW-embedded glass-fabric reinforced plastic film (AgNW-GFRHybrimer) and an electroplated Ag grid. The AgNW-GFRHybrimer is used as a flexible transparent substrate and a seed layer for electroplating. The Ag grid is fabricated via an all-solution-process; the grid pattern is formed using conventional photolithography, and Ag is deposited through electroplating. The AG/NW-GFRHybrimer exhibits excellent opto-electrical properties (transparency = 87%, sheet resistance = 13 Ω/□), superior thermal stability (250 °C for 720 min and 85 °C/85% RH for 100 h), and outstanding mechanical flexibility (bending radius = 1 mm for 2000 cycles). Finally, a touch-screen panel (four-wire resistive type) was fabricated using the AG/NW-GFRHybrimer to demonstrate its potential for use in actual optoelectronic applications.

The bio-immobilization efficiency of single-walled carbon nanotube (SWCNT) thin films treated in NH3/Ar/N2 inductively coupled plasmas with different Ar/N2 gas mixing ratios was studied. The plasma parameters as well as the densities and fluxes of the plasma active species were controlled using both plasma diagnostics (Langmuir probes, optical emission spectroscopy) and modeling. The surface morphology of the SWCNT thin films was observed by field-emission scanning electron microscopy (FE-SEM). The structural changes on the treated surfaces were detected by Raman spectroscopy. The changes in atomic composition for plasma-treated and pristine SWCNT film surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). Fluorescence analysis of the plasma-functionalized SWCNT surfaces was performed with green fluorescent proteins (GFPs). It was found that the transition from NH3/Ar to NH3/N2 gas system at other constant processing conditions resulted in increasing the CNT surface roughness, the degree of structural defects, the number of NH2-functional groups connected to the CNT surface and the bio-immobilization capability. It was proposed that all these effects are connected to the chemical etching and modification of SWCNTs due to the increased flux of NHx (x

This study developed a high-level conceptual design of a Pressurized Liquefied Natural Gas (PLNG) supply chain with marine production, transportation, and utilization steps and estimated the life cycle cost (LCC) of the chain to assess its economic feasibility. The PLNG supply chain consisted of a Floating Liquefied Natural Gas Unit (FLNG) and a LNG Shuttle-and-Regasification Vessel (SRV). Because PLNG was produced, stored, and transported at a higher temperature and pressure than ambient-pressure LNG (ALNG), the PLNG supply chain reduced production (liquefaction) and regasification costs while increasing storage and shipping costs relative to those for ALNG, mainly due to the requirement for heavy containment systems to carry the PLNG. To reduce PLNG storage and shipping costs by improving the volume efficiency of the pressure containment system, a novel concept for a prismatic pressure vessel was employed for the pressure cargo tanks. An assessment of economic feasibility estimated the normalized LCC for a range of product pressures and shipping distances. The assessment showed that PLNG was economically feasible when the PLNG pressure was 5 bar and at short shipping distances. The cost of the pressure containment system proved to be the critical cost component. A sensitivity study demonstrated that a decrease in the material cost for the containment system could significantly increase the breakeven shipping distance. Under optimum conditions, the cost for transporting PLNG was 6% less than that of transporting ALNG.

A coupling interaction between localised surface plasmon resonance of metal nanoparticles (NPs) and emitting materials has been shown to improve the internal quantum efficiency in organic light-emitting diodes. In this research, Ag NPs were introduced into blue polymer light-emitting diodes (PLEDs), which suffer from low efficiency. Ag NPs were attached to the indium tin oxide (ITO) surface through a ligand-exchange process, which guarantees well-dispersed Ag NPs, to maximise resonant coupling and to prevent optical and electrical side effects. Mercaptoacid molecules not only function as a coupling agent between ITO and Ag NPs, but also aid the transfer of holes by increasing the work function of ITO, as confirmed by tests on hole-only devices and by ultraviolet photoelectron spectroscopy. Maximum current efficiencies of blue PLEDs improved by 25% with thioglycolic acid (TGA) only and by 48% with 0.302 nM Ag NPs attached to TGA. We confirmed from time-resolved photoluminescence spectra and normalised electroluminescence spectra that the enhancement mechanism is the resonant interaction between Ag NPs and the blue light-emitting polymer, SPB-02T.

Nanostructured heterojunction semiconductor/metal oxide electrodes are desired for use in efficient photoelectrochemical (PEC) water splitting. We introduced a mesoscopic IO (meso-IO) structure and sensitized the TiO2 IO structure using a CdSe/CdS nanoparticle bilayer for use as PEC water splitting electrodes. The CdS nanoparticle shell was deposited on the IO surface using successive ionic layer absorption and reaction and subsequently, the CdSe layer was grown by chemical bath deposition. The CdSe/CdS double layer sensitization revealed the extension of visible light absorption up to 680 nm. The meso-IO structures provide an ideal geometry for highly compact composite materials; the CdSe/CdS meso-IO TiO2 structure produced a highly compact film with a volume fraction of approximately 82%. Thus, upon application as a PEC water splitting electrode, due to this highly compact structure, the CdSe/CdS meso-IO TiO2 electrodes exhibit a high volumetric photocurrent density of 1.95 mA cm−2 μm−1, which was higher than any previous reports in the literature. Moreover, we obtained improved long-term stability during water splitting: the CdSe/CdS meso-IO TiO2 electrode that was decorated using 3 at% iridium oxide colloidal particles displayed a photocurrent of 98% of the initial photocurrent for 2 h.

A series of novel carbazole-based materials, DPACz1 , DPACz2 and DPACz3 having diphenylamino moieties at 1- and 8-positions of carbazole have been synthesized and characterized for the first time. The introduction of diphenylamino substituents at 1- or 1,8-positions of carbazole resulted into increase of the band-gap compared with the previously reported 3,6- or 2,7-substituted ones. The HOMO levels increased from DPACz1 to DPACz2 with the addition of one additional diphenylamino unit, and further increased in case of DPACz3 , a dimer of DPACz1 having a benzidine moiety. The materials have high triplet energy levels of 2.68, 2.60 and 2.45 eV, respectively. Based on suitable HOMO levels and high triplet energies, the newly synthesized diphenylaminocabazoles were investigated for their potential as solution-processable host materials for green phosphorescent OLEDs with the device configuration, [ITO/PEDOT:PSS/Emitting layer/TPBi/CsF/Al]. All the devices emitted typical green light with high luminance and had low turn-on voltages along with good luminous efficiencies which were further improved by adjusting charge balance using PBD, as a co-host. The basic characteristics and the preliminary OLED results showed the usefulness of our new materials, and this kind of 1-/1,8-substitution of carbazole would open a new way of materials design.

The effect of deposition pattern on the temperature and global distortion of Direct Metal Tooling (DMT) based Additive Manufactured (AM) is investigated through the experimental results of laser deposited SUS316. DMT is one of the Directed Energy Deposition (DED) processes. In situ temperature measurements were used to monitor the temperature of the substrates and global distortion patterns were analyzed using CMM (coordinate Measuring Machine) after the deposition. Six different patterns combining long raster and short raster patterns were considered for the case studies. The results showed that the deposition pattern affects the temperature gradient and that the peak temperature of each layer can increase or decrease according to the sequence of the deposition pattern. Also, the pattern of the first layer had a dominant influence on the longitudinal bending deflection that occurs. Based on these results, appropriate tool path schedule can be utilized to control not only the distortion but also the peak temperature of the DMT-based AM parts.

In this study, modified equivalent load method for welding distortion analysis is suggested to improve its accuracy. To avoid the excessive computational time for welding distortion analysis of large welded structures, shell element-based elastic analysis methods are widely used, applying the inherent deformation approach. Equivalent nodal forces are commonly used in common FE (Finite Element) codes to enter these inherent deformation values. However, the conventional method cannot estimate precise longitudinal bending following the conventional equation. In this study, the problem of the existing equivalent load method is analyzed by a case study, and the modified equivalent load method that can estimate angular distortion, transverse shrinkage, and longitudinal bending is presented based on the FEM principle. The results show that by applying the proposed method, the shell element-based elastic FE approach for the welding distortion analysis can be achieved with improved accuracy.

Anisotropic Si nano-trench structures were fabricated using inductively coupled HBr + Cl2 plasmas for sidewall etching residue analysis. The sidewall etching residues formed inside the Si nano-trench patterns were analyzed via tilted X-ray photoelectron spectroscopy. The changes in the chemical composition and binding state of the etching residues formed on the Si nano-trench sidewalls were investigated with various gas mixing ratios in HBr + Cl2 plasma etching processes. The sidewall chemistry of the plasma-etched Si nano-trench patterns was examined at various take-off angles. SiO2 and suboxide groups (SixOy, x ≤ 2, y ≤ 3) were formed on the Si nano-trench sidewalls after the plasma etching. An increase in the chlorine content of the gas plasma resulted in the increased formation of SiO2 and suboxide residual groups on the Si nano-trench sidewalls. Additionally, the changes in the chemical states of the Si nano-trench sidewalls after a wet-cleaning process were examined using our designed experimental technique.

In this paper, we devise methods for the multiobjective control of humanoid robots, a.k.a. prioritized whole-body controllers, that achieve efficiency and robustness in the algorithmic computations. We use a form of whole-body controllers that is very general via incorporating centroidal momentum dynamics, operational task priorities, contact reaction forces, and internal force constraints. First, we achieve efficiency by solving a quadratic program that only involves the floating base dynamics and the reaction forces. Second, we achieve computational robustness by relaxing task accelerations such that they comply with friction cone constraints. Finally, we incorporate methods for smooth contact transitions to enhance the control of dynamic locomotion behaviors. The proposed methods are demonstrated both in simulation and in real experiments using a passive-ankle bipedal robot.

This paper presents a trajectory generation method for contact-constrained robotic systems such as manipulators and legged robots. Contact-constrained systems are affected by the interaction forces between the robot and the environment. In turn, these forces determine and constrain state reachability of the robot parts or end effectors. Our study subdivides the trajectory generation problem and the supporting reachability analysis into tractable subproblems consisting of a sampling problem, a convex optimization problem, and a nonlinear programming problem. Our method leads to significant reduction of computational cost. The proposed approach is validated using a realistic simulated contact-constrained robotic system., Comment: 8 pages, 6 figures

This paper proposes a novel control method to minimize muscle energy for power-assistant robotic systems that support the intended motions of a user under unknown external perturbations, using surface electromyogram (sEMG) signals. Conventional control methods based on force/torque (F/T) sensors have limitations to detect human intentions and could, presumably, misunderstand or distort such intentions because of external perturbations of the interaction forces, such as those found in activities of daily living. F/T sensors measure the sum of the applied force, including unknown external forces and human intention; thus, a power-assistant robot controller cannot exactly decompose the real human force. In this paper, we describe a counterexample that cannot be supported by conventional force-sensor-based control methods. We also verify why these control methods may guide human behavior in the wrong direction, and thus, have limitations under unknown external perturbations. We then propose a new control method to minimize the muscle energy indicated by sEMG signals. The proposed control approach is fundamentally based on the concept of power-assistance, in which a robot can reduce the users expended muscle energy while performing given tasks. The proposed control approach is verified through experiments using a power-assistant robotic system for the upper limbs under external perturbations.

In this paper, we investigate the feasibility of energy harvesting from the mouse click motion using a piezoelectric energy transducer. Specifically, we use a robotic finger to realize repeatable mouse click motion. The robotic finger wears a glove with a pocket for including the piezoelectric material as an energy transducer. We propose a model for the energy harvesting system through the inverse kinematic framework of parallel joints in the finger and the electromechanical coupling equations of the piezoelectric material. Experiments are performed to elucidate the effect of the load resistance and the mouse click motion on energy harvesting.

The distributed shared memory (DSM)-based computation offloading scheme allows collaborative multiple threads to dynamically migrate and execute across a mobile device and computing nodes. Despite this strong advantage, it misses a significant portion of the potential performance gain because the traditional DSM model is suboptimal for computation offloading. This paper proposes an enhanced DSM model that aims to enable multiple computing nodes to efficiently and reliably offload concurrent multiple threads from a mobile device. To achieve this design goal, we propose the following novel schemes: a) selective object tracking minimizes the set of objects to be monitored by the DSM layer; b) lock-thread repartitioning dynamically relocates threads and locks in order to reduce remote lock acquisitions and inter-node synchronizations; and c) thread-state checkpointing protects the data and context upon unexpected system failures. We implemented METEOR, which is a prototype based on the proposed schemes, and evaluated it with diverse applications. The evaluation showed that METEOR, with four computing nodes, improved the performance by up to 109% and reduced energy consumption by up to 52% in comparison with the previous DSM-based offloading scheme.

Recently, supply voltage has been reduced for low power applications, and near threshold computing (NTC) is considered as a promising solution for optimal energy efficiency. However, NTC suffers a significant performance degradation, which is prone to timing errors. Thus, in order to improve the reliability of NTC operations, error-resilient techniques are indispensable, though they cause area and power overheads. In this paper, we propose a design methodology which provides an optimal implementation of error-resilient circuits. A modified Quine-McCluskey (Q-M) algorithm is exploited to earn the minimum set of error-resilient circuits without any loss of detection ability. From the proposed design flow, benchmark results show that optimal design reduces up to 72% of required flip-flops to be changed to error-resilient circuits without compromising an error detection ability.