Crack Monitoring in Rotating Shaft Using Rotational Speed Sensor-Based Torsional Stiffness Estimation with Adaptive Extended Kalman Filters.

In this study, we present an alternative solution for detecting crack damages in rotating shafts under torque fluctuation by directly estimating the reduction in torsional shaft stiffness using the adaptive extended Kalman filter (AEKF) algorithm. A dynamic system model of a rotating shaft for designing AEKF was derived and implemented. An AEKF with a forgetting factor (λ) update was then designed to effectively estimate the time-varying parameter (torsional shaft stiffness) owing to cracks. Both simulation and experimental results demonstrated that the proposed estimation method could not only estimate the decrease in stiffness caused by a crack, but also quantitatively evaluate the fatigue crack growth by directly estimating the shaft torsional stiffness. Another advantage of the proposed approach is that it uses only two cost-effective rotational speed sensors and can be readily implemented in structural health monitoring systems of rotating machinery.

High Density Resistive Array Readout System for Wearable Electronics.

This work presents a wearable sensing system for high-density resistive array readout. The system comprising readout electronics for a high-density resistive sensor array and a rechargeable battery, was realized in a wristband. The analyzed data with the proposed system can be visualized using a custom graphical user interface (GUI) developed in a personal computer (PC) through a universal serial bus (USB) and using an Android app in smartphones via Bluetooth Low Energy (BLE), respectively. The readout electronics were implemented on a printed circuit board (PCB) and had a compact dimension of 3 cm × 3 cm. It was designed to measure the resistive sensor with a dynamic range of 1 KΩ-1 MΩ and detect a 0.1% change of the base resistance. The system operated at a 5 V supply voltage, and the overall system power consumption was 95 mW. The readout circuit employed a resistance-to-voltage (R-V) conversion topology using a 16-bit analog-to-digital converter (ADC), integrated in the Cypress Programmable System-on-Chip (PSoC®) 5LP microcontroller. The device behaves as a universal-type sensing system that can be interfaced with a wide variety of resistive sensors, including chemiresistors, piezoresistors, and thermoelectric sensors, whose resistance variations fall in the target measurement range of 1 KΩ-1 MΩ. The system performance was tested with a 60-resistor array and showed a satisfactory accuracy, with a worst-case error rate up to 2.5%. The developed sensing system shows promising results for applications in the field of the Internet of things (IoT), point-of-care testing (PoCT), and low-cost wearable devices.

Fast synthesis of high-quality reduced graphene oxide at room temperature under light exposure.

An approach of presenting new reducing reagents, sodium-benzophenone (Na-B) or Na-B in the presence of the hydrazine (Na-B-H) system under light exposure could produce rGOs with/without N-doping at room temperature in both the solution phase and on a solid substrate. Benzophenone activated those solutions acting as a photosensitizer under light. It was assumed that the newly generated radical anions with electrons from Na-B under light can reduce GO to rGO sheets (rGONa-B1). In addition, the Na-B-H system can allow a higher degree of reduction with the doping of nitrogen atoms by the introduction of hydrazine to produce radical anions and electrons with a sodium hydrazide complex, which helps decrease the sheet resistance of the as-made rGONa-B-H2. The excellent properties (very low oxygen content (C/O ∼16.2), and low sheet resistance (∼130 Ω square(-1))) of the rGOs were confirmed by XPS, XRD, IR, Raman spectroscopy, TGA, wettability, and sheet resistance measurements. High-quality rGO films on flexible substrates could be prepared by directly immersing the GO films in these solutions for several minutes.

Mass production of graphene quantum dots by one-pot synthesis directly from graphite in high yield.

One of the most efficient and straightforward methods for production of graphene quantum dots (GQDs) could be their direct preparation from graphite powder by one-pot synthesis using high-powered microwave irradiation. It is believed that in this way, graphite can be multiply broken by repeated redox reactions, which leads to a high yield and mass production.

Vertical alignments of graphene sheets spatially and densely piled for fast ion diffusion in compact supercapacitors.

Supercapacitors with porous carbon structures have high energy storage capacity. However, the porous nature of the carbon electrode, composed mainly of carbon nanotubes (CNTs) and graphene oxide (GO) derivatives, negatively impacts the volumetric electrochemical characteristics of the supercapacitors because of poor packing density (<0.5 g cm(-3)). Herein, we report a simple method to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes. Because of their vertically aligned and opened-edge graphene structure, VArGO electrodes displayed high packing density and highly efficient volumetric and areal electrochemical characteristics, very fast electrolyte ion diffusion with rectangular CV curves even at a high scan rate (20 V/s), and the highest volumetric capacitance among known rGO electrodes. Surprisingly, even when the film thickness of the VArGO electrode was increased, its volumetric and areal capacitances were maintained.

Facile preparation of an n-type reduced graphene oxide field effect transistor at room temperature.

We introduce a facile method to prepare an n-type reduced graphene oxide field effect transistor at room temperature via a typical Benkeser reduction using lithium and ethylenediamine.

Highly hydrophilic and insulating fluorinated reduced graphene oxide.

A facile method for the synthesis of highly fluorinated reduced graphene oxide from graphene oxide using BF3-OEt2 solution and alkylthiol/alkylamine on the Gram scale has been described using a detailed mechanism. The maximum fluorination was as high as 38 wt% and the fluorinated reduced graphene oxide produced has great wettability and high insulating properties.

Anti-solvent derived non-stacked reduced graphene oxide for high performance supercapacitors.

An anti-solvent for graphene oxide (GO), hexane, is introduced to increase the surface area and the pore volume of the non-stacked GO/reduced GO 3D structure and allows the formation of a highly crumpled non-stacked GO powder, which clearly shows ideal supercapacitor behavior.

High-quality reduced graphene oxide by a dual-function chemical reduction and healing process.

A new chemical dual-functional reducing agent, thiophene, was used to produce high-quality reduced graphene oxide (rGO) as a result of a chemical reduction of graphene oxide (GO) and the healing of rGO. Thiophene reduced GO by donation of electrons with acceptance of oxygen while it was converted into an intermediate oxidised polymerised thiophene that was eventually transformed into polyhydrocarbon by loss of sulphur atoms. Surprisingly, the polyhydrocarbon template helped to produce good-quality rGOC (chemically reduced) and high-quality rGOCT after thermal treatment. The resulting rGOCT nanosheets did not contain any nitrogen or sulphur impurities, were highly deoxygenated and showed a healing effect. Thus the electrical properties of the as-prepared rGOCT were superior to those of conventional hydrazine-produced rGO that require harsh reaction conditions. Our novel dual reduction and healing method with thiophene could potentially save energy and facilitate the commercial mass production of high-quality graphene.

Nitrogen-doped partially reduced graphene oxide rewritable nonvolatile memory.

As memory materials, two-dimensional (2D) carbon materials such as graphene oxide (GO)-based materials have attracted attention due to a variety of advantageous attributes, including their solution-processability and their potential for highly scalable device fabrication for transistor-based memory and cross-bar memory arrays. In spite of this, the use of GO-based materials has been limited, primarily due to uncontrollable oxygen functional groups. To induce the stable memory effect by ionic charges of a negatively charged carboxylic acid group of partially reduced graphene oxide (PrGO), a positively charged pyridinium N that served as a counterion to the negatively charged carboxylic acid was carefully introduced on the PrGO framework. Partially reduced N-doped graphene oxide (PrGODMF) in dimethylformamide (DMF) behaved as a semiconducting nonvolatile memory material. Its optical energy band gap was 1.7-2.1 eV and contained a sp2 C═C framework with 45-50% oxygen-functionalized carbon density and 3% doped nitrogen atoms. In particular, rewritable nonvolatile memory characteristics were dependent on the proportion of pyridinum N, and as the proportion of pyridinium N atom decreased, the PrGODMF film lost memory behavior. Polarization of charged PrGODMF containing pyridinium N and carboxylic acid under an electric field produced N-doped PrGODMF memory effects that followed voltage-driven rewrite-read-erase-read processes.

Clinical features of adult patients with secondary hemophagocytic lymphohistiocytosis from causes other than lymphoma: an analysis of treatment outcome and prognostic factors.

Although hemophagocytic syndrome (HS) featuring secondary hemophagocytic lymphohistiocytosis (HLH) has a grave prognosis, little is known about the natural course of the disease. Patients who showed the clinical features of HLH as well as tissue-proven hemophagocytosis when seen at Asan Medical Center between 1999 and 2010 were included in this analysis. Patients with proven lymphoma were excluded. The median age of our 23 study patients was 49 years. Epstein-Barr virus was suspected to have caused HS in 16 (70%) patients and hepatitis A virus in one patient. Twenty-two patients were treated, 13 according to the HLH protocol and nine using immunosuppressive agents such as corticosteroid and/or cyclosporine. Five patients undertook allogeneic hematopoietic cell transplantation (HCT) during their treatment-dependent relapse (n = 4) or responsive status (n = 1). After the median follow-up of 180 days, 17 (74%) died and six (26%) were alive. The median time from initial presentation until death was 41 days among those patients who died. The serum fibrinogen level ≥166 mg/dL determined at the initial visit was significantly associated with the survival time according to univariate analysis. The low histiocyte proportion in bone marrow and early initiation of treatment tended to correlate with a favorable outcome. On multivariate analysis, serum fibrinogen ≥166 mg/dL (hazard ratio, 0.175, P = 0.018) was an independent clinical factor for determining the patient survival time. Despite appropriate patient management, the outcome of HS featuring HLH was grave. The serum fibrinogen level at the initial presentation was significant, and selected patients obtained some benefit from allogeneic HCT.

Pyrolysis kinetics and decomposition characteristics of pine trees.

Pine trees comprise over 35% of the forests in Korea, since 1989, pine wilt disease introduced via the Japanese pine sawyer has been infecting many of these trees. As a renewable resource, pine can be converted to bio-oil, gas, and char through pyrolysis. In this study, the pyrolysis characteristics of pine trees were investigated using thermogravimetric analyzer, with most of the materials decomposing between 330 and 370 degrees C at heating rates of 5-20 degrees C/min. The apparent activation energy increased from 145 to 302 kJ mol(-1) with increasing pyrolysis conversion. The kinetics of pine tree pyrolysis were experimentally and mathematically evaluated. The kinetic parameters were determined using nonlinear least-squares regression of the experimental data assuming first-order kinetics. It was found from the kinetic rate constants that the predominant reaction pathway was A (pine) to gas (C(1)-C(4)) rather than A to bio-oil at temperatures of 330-370 degrees C.

Pyrolysis characteristics and kinetics of oak trees using thermogravimetric analyzer and micro-tubing reactor.

In this work, pyrolysis characteristics were investigated using thermogravimetric analysis (TGA) at heating rates of 5-20 degrees C/min. Most of the materials were decomposed between 330 degrees C and 370 degrees C at each heating rate. The average activation energy was 236.2 kJ/mol when the pyrolytic conversion increased from 5% to 70%. The pyrolysis kinetics of oak trees was also investigated experimentally and mathematically. The experiments were carried out in a tubing reactor at a temperature range of 330-370 degrees C with a reaction time of 2-8 min. A lump model of combined series and parallel reactions for bio-oil and gas formation was proposed. The kinetic parameters were determined by nonlinear least-squares regression from the experimental data. It was found from the reaction kinetic constants that the predominant reaction pathway from the oak trees was to bio-oil formation rather than to gas formation at the investigated temperature range.