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We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition. Using electron microscopy, the microstructural evolution upon varying the process parameters, especially laser power and powder feed rate, was investigated in relation with crack formation. Cladding layers showing dilution rates of more than 5% contained cracks due to the formation of the brittle Co2Ti intermetallic phase. The observed cracks could be ascribed to a mismatch in thermal expansion and a resulting stress of more than 440 MPa acting on the Co2Ti phase, as determined by density functional theory and nanoindentation. Furthermore, an excess laser energy caused chemical inhomogeneity and unmelted Ti powder particles, while a deficient laser energy resulted in lack of fusion. Neither cracks nor partially melted powders were observed for a powder feed rate of 3 g/min and a laser power of 225-300 W, for which the dilution rate was minimized to less than 5%. For such samples the cladding layers comprised pure α-Ti and a uniform CoTi interface with Co2Ti islands.

Damage to nuclear power plants causes human casualties and environmental disasters. There are electrical facilities that control safety-related devices in nuclear power plants, and seismic performance is required for them. The 2016 Gyeongju earthquake had many high-frequency components. Therefore, there is a high possibility that an earthquake involving many high frequency components will occur in South Korea. As such, it is necessary to examine the safety of nuclear power plants against an earthquake with many high-frequency components. In this study, the shaking table test of electrical facilities was conducted against the design earthquake for nuclear power plants with a large low-frequency components and an earthquake with a large high-frequency components. The response characteristics of the earthquake with a large high-frequency components were identified by deriving the amplification factors of the response through the shaking table test. In addition, safety of electrical facility against the two aforementioned types of earthquakes with different seismic characteristics was confirmed through limit-state seismic tests. The electrical facility that was performed to the shaking table test in this study was a motor control center (MCC).

Using a facile hydrothermal procedure, hydrophilic NaYF4: Yb3+/Er3+ nanoparticles (NPs) have been prepared as lanthanide-doped upconversion (UC) materials exhibiting different morphologies, crystal phases and luminescence intensity. The upconversion nanoparticles (UCNP) were characterized by means of electron microscopy and spectroscopy, X-ray diffraction (XRD) and photoluminescence analysis. The molar concentration of reactants and volumes of NaF affect the shapes and uniformity of the synthesized NPs. These parameters also have influence on crystal phase and luminescence intensity of the NPs. Adjusting hydrothermal reaction time and dopant concentration also enable the synthesis of NPs with strong UC luminescence. The as-prepared UCNP showed cellular nontoxicity to HeLa cells, and thus they are capable as promising agents for biological imaging.

We prepared a high-concentration suspension of boron nitride (BN) nanoplates stabilized with benzyl alcohol (B-BN) in epoxy resin as a polymer composite adhesive for a highly efficient heat dissipation. At a BN concentration of 40 wt%, the polymer composite with B-BN exhibited a high thermal conductivity (κ = 1.51 W/m·K at 25 °C) comparable to that of a composite with bulk BN and significantly higher than that of a composite with a chemically modified BN (S-BN). Furthermore, the concentration of B-BN in the epoxy resin was increased to 46 wt% without a significant increase in viscosity, leading to a further improvement in the thermal conductivity to 2.11 W/m·K. The epoxy resin with B-BN exhibited a low coefficient of thermal expansion and high effective modulus owing to the strong affinity to the epoxy. Finally, we recycled benzyl alcohol more than 10 times for the preparation of B-BN, which may reduce the manufacturing cost and environmental pollution. Therefore, B-BN could be a promising filler for heat dissipation as well as starting material for additional modification.

This study presents a combined strategy of bidisperse boron nitride (BN) and surface modification to improve the thermal conductivity (κ) of the BN-epoxy composite. Surface modification of hexagonal BN was carried out with benzoic acid (BA). The optimal weight ratio of large and small BN (BNl and BNs) was 8:2 for their connectivity in the epoxy matrix. For 50 wt% filler content, the BNl8s2-BA composite has a much higher κ of 2.71 W/m K (out-plane direction), which is 12.3, 1.32, and 1.50 times higher than that of the pure epoxy, and its composite with BNl10s0-BA and BNl8s2, respectively. The chemical-sensitive analyses indicate that carboxyl-carboxylate interaction occurred in partially deprotonated benzoic acid on BN during the epoxy curing process, resulting in in-situ formation of a continuously thermal conductive pathway, which is responsible for the improved κ.

Multifunctional nanocomposite has a huge potential for cell imaging, drug delivery, and improving therapeutic effect with less side effects. To date, diverse approaches have been demonstrated to endow a single nanostructure with multifunctionality. Herein, we report the synthesis and application of core-shell nanoparticles composed with upconversion nanoparticle (UCNP) as a core and a graphene oxide quantum dot (GOQD) as a shell. The UCNP was prepared and applied for imaging-guided analyses of upconversion luminescence. GOQD was prepared and employed as promising drug delivery vehicles to improve anti-tumor therapy effect in this study. Unique properties of UCNPs and GOQDs were incorporated into a single nanostructure to provide desirable functions for cell imaging and drug delivery. In addition, hypocrellin A (HA) was loaded on GOQDs for photo-dynamic therapy (PDT). HA, a commonly used chemotherapy drug and a photo-sensitizer, was conjugated with GOQD by π-π interaction and loaded on PEGylated UCNP without complicated synthetic process, which can break structure of HA. Applying these core-shell nanoparticles to MTT assay, we demonstrated that the UCNPs with GOQD shell loaded with HA could be excellent candidates as multifunctional agents for cell imaging, drug delivery and cell therapy.

A cross-stacking MoS2/graphene hybrid patterns for the application to advanced flexible opto-electronic devices have been demonstrated by soft-lithographic patterning method. Well-defined MoS2/graphene hybrid pattern was fabricated simply by a soft lithographic patterning technique. In-depth exploration for the optical properties of diverse cross-stacking photodetectors based on MoS2/graphene patterns was carried out. In addition, cross-stacking MoS2/graphene was demonstrated onto a flexible polyethylene terephthalate (PET) substrate for the analysis of physical properties of devices. Substantially, this method should pave the way for realistic applications of transparent and flexible nano-electronic devices based on 2D materials.

The chemical and ultrastructural properties of cell walls were investigated to determine the effect of dilute acid pretreatment on the hydrolysis of lignocellulosic biomass. Confocal Raman microscopy was used to gain a clear understanding of how dilute acid pretreatments destroy lignocellulosic cell walls. Total fermentable sugar (glucose and xylose) was high in oxalic acid hydrolysate (26.18 g/L) compared to that in sulfuric acid hydrolysate (24.34 g/L). Chemical composition of the pretreated biomass differed slightly according to the acid catalyst used. Oxalic acid pretreatment was effective for enzymatic hydrolysis, with 29.46 g/L of total fermentable sugar after 96 h. Optical microscopy showed that dilute acid pretreatment significantly changed cell wall structure, and broken and crushed cell walls could be clearly seen during pretreatment. Based on confocal Raman peak intensity, the ratio of lignin/cellulose [I(1600)/I(900)] was low for oxalic acid-pretreated biomass compared to sulfuric acid-pretreated biomass.

K-doped TiO2 nanowire networks were prepared by the corrosion reaction of Ti nanoparticles in an alkaline (potassium hydroxide: KOH) solution. The prepared nanostructures were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD) and photoluminescence (PL) spectra. Their sunlight-driven photocatalytic activity was also investigated with differently charged dye molecules, such as methylene blue, rhodamine B and methyl orange. The adsorption of the dye molecules on the photocatalyst surface would play a critical role in their selective photodegradation under sunlight illumination.

Graphene-based electrodes typically form a compact uniaxially oriented stacked structure during electrode preparation due to the highly anisotropic morphology. This leads to limited diffusion paths for the insertion of Li or Na when used as electrodes in rechargeable batteries. Here, we demonstrate that self-standing electrodes formed of randomly folded and/or crumpled graphene nanosheets can be obtained via a simple modified reduction process, and that the crumpled structure can significantly increase the power capability of graphene-based anodes of sodium-ion batteries. These electrodes can deliver a power density of approximately 20,000 W kg−1, which surpasses the Li storage capability of conventional graphene paper electrodes. Moreover, the specific capacity was stably maintained without a binder, conductive agent, or substrate for more than 500 charge/discharge cycles and 1000 cycles of repeated bending.

A seismic isolation system installed in a nuclear power plant will respond to the load caused by an earthquake. As a result, a larger displacement may occur in the presence of the system, compared to its absence. This increased displacement may involve higher seismic risks for some facilities. Probabilistic seismic fragility analysis is conducted to assess the seismic safety of the major elements and systems of a nuclear power plant that may be at increased seismic risk. The installation of piping systems that connect seismic-isolated and general structures may involve increased seismic risks because they are expected to have a large displacement. For the reliable analysis of the seismic fragility of piping systems, the failure modes and criteria that can represent actual failure must be defined. Therefore, in this study, the ultimate state of the elbow, the vulnerable part of piping systems, was defined as leakage, and an in-plane cyclic loading test was conducted. Moreover, an attempt was made to quantify the failure criteria for a 3-inch carbon steel pipe elbow using a damage index, which was based on the dissipated energy that used the moment-deformation angle relationship.

Graphene-based nanosheets (GNS) have been studied for use in electrochemical energy storage devices. A deeper understanding about the system is required for achieving enhanced power output and high energy storage. The effects of sulfur doping on the electrochemical properties of GNS are studied for their use as an anode material in lithium-ion batteries. Sulfur doping in GNS contributes to the high specific capacity by providing more lithium storage sites due to Faradaic reactions. In addition, superior rate performance of sulfur-doped GNS (S-GNS) is achieved through the improved electrical conductivity of S-GNS (1743 S m−1), which is two orders of magnitude higher than that of GNS (32 S m−1). In addition, good cyclic stability of S-GNS is maintained even after 500 cycles at a high current density of 1488 mA g−1 (4 C).

The energy-storage capacity of reduced graphene oxide (rGO) is investigated in this study. The rGO used here was prepared by thermal annealing under a nitrogen atmosphere at various temperatures (300, 400, 500 and 600 °C). We measured high-pressure H 2 isotherms at 77 K and the electrochemical performance of four rGO samples as anode materials in Li-ion batteries (LIBs). A maximum H 2 storage capacity of ∼5.0 wt% and a reversible charge/discharge capacity of 1220 mAh/g at a current density of 30 mA/g were achieved with rGO annealed at 400 °C with a pore size of approximately 6.7 A. Thus, an optimal pore size exists for hydrogen and lithium storage, which is similar to the optimum interlayer distance (6.5 A) of graphene oxide for hydrogen storage applications.