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Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered1,2. Atomically thin two-dimensional semiconductors have great potential for realizing high-performance electronic devices1,3. However, owing to metal-induced gap states (MIGS)4–7, energy barriers at the metal–semiconductor interface—which fundamentally lead to high contact resistance and poor current-delivery capability—have constrained the improvement of two-dimensional semiconductor transistors so far2,8,9. Here we report ohmic contact between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where the MIGS are sufficiently suppressed and degenerate states in the TMD are spontaneously formed in contact with bismuth. Through this approach, we achieve zero Schottky barrier height, a contact resistance of 123 ohm micrometres and an on-state current density of 1,135 microamps per micrometre on monolayer MoS2; these two values are, to the best of our knowledge, the lowest and highest yet recorded, respectively. We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS2, WS2 and WSe2. Our reported contact resistances are a substantial improvement for two-dimensional semiconductors, and approach the quantum limit. This technology unveils the potential of high-performance monolayer transistors that are on par with state-of-the-art three-dimensional semiconductors, enabling further device downscaling and extending Moore’s law. Electric contacts of semimetallic bismuth on monolayer semiconductors are shown to suppress metal-induced gap states and thus have very low contact resistance and a zero Schottky barrier height.

High density sintered Sm(Fe0.8Co0.2)11Ti bulk magnets were successfully produced using a newly developed high pressure pressing fabrication method. The purity of the hard magnetic ThMn12 phase in the bulk magnet reached to higher than 97 wt.%. The phase transformation behavior from amorphous to ThMn12 phase during heat treatment was systematically investigated by transmission electron microscopy. The remanent magnetization and maximum energy product of a bulk magnet were 96.0 emu/g and 12.22 MGOe, respectively. To the best of our knowledge, the achieved maximum energy product is the highest among all the SmFe12-based bulk magnets reported.

Bladder outlet obstruction (BOO) due to benign prostatic hyperplasia (BPH) is the most common cause of lower urinary tract symptoms (LUTS) in older men. Although medical treatments can reduce BPH-related LUTS and even prevent invasive treatments, at least one in five men who complain of LUTS due to BPH will eventually need surgery. Of LUTS, storage symptoms persist in 20 to 40% of patients even after the obstruction is resolved. The present study aims to investigate the predisposing factors of the persistent storage symptoms after HoLEP in patients with BPH and their correlations to the recovery time of the symptoms. A total of 127 patients with complaints of storage symptoms and who underwent transurethral HoLEP surgery at Pusan National University Hospital from May 2014 to June 2017 were included in this study. Urodynamic studies were performed in all patients, and BOO was confirmed by urodynamic studies before HoLEP. All patients were asked to complete the IPSS (also known as the American Urological Association score) and the Overactive Bladder Symptom Score (OABSS) questionnaire to evaluate LUTS on the day before HoLEP and 3 months after HoLEP. Patients were divided into group I, which included patients with persistent storage symptoms after HoLEP, and group II, which included patients without storage symptoms after HoLEP. Of a total of 127 patients, 68 were included in group I, and the remaining 59 were included in group II. In the univariable analysis, group I showed statistically significantly older mean age, higher mean peak detrusor pressure during filling cystometry, and lower mean MCC than group II. Multivariate analysis of these three variables showed that only mean age and mean peak detrusor pressure during filling cystometry had statistically significant differences. In group I, 12 patients had storage symptoms until 12 months after surgery. When comparing these patients with the remaining 56 patients, only mean age showed statistically significant differences. Old age and high peak detrusor pressure during filling cystometry were the predictors of persistent storage symptoms after HoLEP. Furthermore, older patients were unlikely to recover storage symptoms until 12 months after operation.

Herein, nanoporous Al2O3, CeO2, TiO2, ZrO2, and SnO2 were used as the supports for Pd nanoparticles, and effects of surface characteristics on catalytic performances for dehydrogenation of 2-[(n-me...

Freestanding graphene on a trench has been fabricated extensively using a transfer process of chemical vapor deposition grown graphene. Here, we demonstrate that freestanding graphene can be grown directly on a trench without a transfer process. A shallow trench was made on a 6H–SiC(0001) wafer using a focused ion beam lithography. The shallow trench was heated to a high temperature under Ar atmosphere. The heat treatment made the shallow trench become deeper and wider. Subsequently, epitaxial graphene was floating on the trench, resulting in freestanding graphene, where underlying bulk SiC was self-etched after the growth of epitaxial graphene. The freestanding graphene on a trench was characterized using Raman spectroscopy and atomic force microscopy. Such freestanding graphene writing can be applied to semiconductor fabrication process of freestanding graphene devices without a transfer process.

In this study, the applicability of the composite model for assessing seawater intrusion and soil salinization in coastal aquifers due to climate change was investigated. In this approach, flow in the saturated zone of a coastal aquifer is simulated using a three-dimensional saturated–unsaturated transport model and flow in the unsaturated zone between the surface and groundwater level is simulated using a one-dimensional model in the vertical direction. Long-term sea-level predictions obtained using the representative concentration pathway (RCP) 4.5 and 8.5 scenarios were applied for computing the sea-level rise for 91 country-managed reclaimed areas in the Republic of Korea. Composite results were obtained and analyzed for seawater intrusion and soil salinization due to sea-level rise. In the results of groundwater and soil salinity in all 91 reclaimed land, the increasing rate of groundwater and soil salinity in the RCP 4.5 scenario was 13.5% and 10.4%, respectively. In the RCP 8.5 scenario, the increasing rate of groundwater and soil salinity was 14.1% and 11.1%, respectively. The groundwater level increased to 0.41 m in the RCP 4.5 scenario and 0.51 m in the RCP 8.5 scenario. The results for two representative reclaimed land areas in the Heungwang and Deokchon districts were examined in detail. The composite analysis revealed that widespread damage could be caused by sea-level rise in the reclaimed land and that seawater intrusion in many regions will accelerate groundwater salinization over time. Moreover, the reclaimed land areas were characterized in terms of watershed size, presence of ponds, water levels of the ponds, and pond locations. In reclaimed land located in small watersheds, the groundwater recharge area was smaller than in land located in larger watershed areas. Consequently, the seawater in small watersheds penetrated further inland. Ponds with water levels higher than the sea level effectively prevented seawater intrusion into groundwater. If the water level of a pond is similar to or lower than the sea level, it indicates that seawater has already penetrated a large part of the aquifer. The composite model developed in this study seems to be one of the simulation methods that can be applied when simulating saturated and unsaturated zone to a large number of sites. Also, the study results could be used to establish and implement a long-term comprehensive plan for water resources at the national level, considering seawater intrusion due to climate change and providing a basis for establishing countermeasures against future seawater intrusion.

Various methods have been suggested to realize freestanding or suspended graphene, which is expected to exhibit the intrinsic properties of graphene. However, in previously reported methods, multiple-step processes have been applied to produce freestanding graphene on a substrate. Here, we demonstrate that quasifreestanding graphene on a substrate can be realized through a simple single-step process. In this experiment, self-etching of nano-scale SiC steps of 8° off-axis vicinal SiC contributed to the formation of quasifreestanding graphene on an Si-faced SiC wafer, which was confirmed using low-energy electron diffraction, Raman spectroscopy, scanning electron microscopy and two-probe resistance measurements. Such a single-step technique for the growth of quasifreestanding graphene could pave the way towards graphene-based silicon-carbide micro-electronics.

Corynebacterium glutamicum, an important industrial strain, has a relatively slower reproduction rate. To acquire a growth-boosted C. glutamicum, a descendant strain was isolated from a continuous culture after 600 generations. The isolated descendant C. glutamicum, JH41 strain, was able to double 58% faster (td=1.15 h) than the parental type strain (PT, td=1.82 h). To understand the factors boosting reproduction, the transcriptomes of JH41 and PT strains were compared. The mRNAs involved in respiration and TCA cycle were upregulated. The intracellular ATP of the JH41 strain was 50% greater than the PT strain. The upregulation of NCgl1610 operon (a putative dyp-type heme peroxidase, a putative copper chaperone, and a putative copper importer) that presumed to role in the assembly and redox control of cytochrome c oxidase was found in the JH41 transcriptome. Plasmid-driven expression of the operon enabled the PT strain to double 19% faster (td=1.82 h) than its control (td=2.17 h) with 14% greater activity of cytochrome c oxidase and 27% greater intracellular ATP under the oxidative stress conditions. Upregulations of genes those might enhance translation fitness were also found in the JH41 transcriptome. Plasmid-driven expressions of NCgl0171 (encoding a cold-shock protein) and NCgl2435 (encoding a putative peptidyl-tRNA hydrolase) enabled the PT to double 22% and 32% faster than its control, respectively (empty vector: td=1.93 h, CspA: td=1.58 h, and Pth: td=1.44 h). Based on the results, the factors boosting growth rate in C. gluctamicum were further discussed in the viewpoints of cellular energy state, oxidative stress management, and translation.

Physicochemical properties between colloidal engineered nanomaterials (ENMs) and aerosols released from consumer spray products were characterized. A dynamic light scattering (DLS), transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometer (ICP-MS) were used to evaluate the suspended ENMs in the products. Direct-reading instruments, TEM, and ICP-MS were used to characterize the properties of aerosolized ENMs. The aerosolized organic compounds with ENMs were assumed to be vaporized for a short time after spraying. The median diameter of ENMs in product solutions measured by DLS was about 200-350 nm, while individual particle was confirmed from 3 to 50 nm by TEM. The size of aerosolized ENMs was ranged from 7 to 44 nm, and their aggregates were about 100-1000 nm in near distance. Some inorganic substances including raw nanomaterials were also found in the aerosol. The particles released from the propellant sprays were identified in far distance, while they were not found in far distance when pump sprays were used. The number concentration from the propellant sprays increased up to 6000 particles/cm3 /g at near distance and dispersed to far distance, while the most of droplets emitted from pump sprays were settled down near sprayer's location. We found other metals besides labeled ENMs are included in each product and the characteristics of the particles are different when they are sprayed.

Since around the year 2000, hundreds of people in Korea have developed humidifier disinfectant-associated lung injury (HDLI). We collected all HD exposure-related information from the field investigations into the locations in which the 1199 registered patients had used HD. Among the people who registered, 38% (1st round = 214, 2nd = 73, 3rd = 166) were confirmed as HDLI patients. Children aged under eight years old made up the highest proportion of HDLI cases (N = 279, 62%), followed by pregnant women (N = 31, 7%). One hundred thirty-three (29%) of the confirmed HDLI patients died. Fifty-seven percent of HDLI patients (N = 259) developed HDLI after

Mathematical models with small numbers of parameters are useful for hydrological analyses and water resources planning as they are easier to prepare, use, and interpret compared to more complex models. Many simple model structures and simulation strategies have been developed, but there is still substantial room for improvement in the efficiency of daily rainfall-runoff modeling. This study proposes daily rainfall-runoff models that require only two to four parameters yet are capable of predicting peak discharge and baseflow. Parsimonious model structures were obtained using the hyperbolic tangent function and combining it with one subsurface layer and two parameters of a Tank model. The daily rainfall-runoff models proposed based on the Two-Parameter Hyperbolic Model (TPHM) and Tank model were applied to 41 watersheds throughout South Korea. Model accuracy was evaluated by comparing observed and simulated watershed streamflow and compared with that of a nine-parameter Tank model. The original TPHM and its variants yielded slightly better efficiency with a smaller number of parameters than the Tank model when reproducing high flows on a daily basis. The accuracy of low flow and flow duration curve predictions provided by the TPHM-based models was higher in watersheds with relatively large baseflow temporal variability. The results suggested that the TPHM-based structures be alternative parsimonious daily rainfall-runoff simulation models. This study demonstrates that daily high streamflow can be efficiently simulated using a two-parameter hydrological model, and daily baseflow simulation can be improved by adding two additional parameters to the model.

The Sm(Fe0.8Co0.2)11Ti were prepared by using arc-melting and melt spinning methods, and their crystallographic and magnetic properties were analyzed by using XRD, VSM, and Mossbauer spectrometer. From the refined XRD patterns, Sm(Fe0.8Co0.2)11Ti sample exhibited tetragonal structure with the space group I4/mmm and it was confirmed that Ti and Co atom were found to be located at 8i and 8f-site, respectively. The Mossbauer spectra of the samples were obtained at 295 K, and investigated the hyperfine interaction and site occupancy in Sm(Fe0.8Co0.2)11Ti sample. From the hysteresis curves up to 20 kOe at 295 K, the magnetization at 20 kOe (M20 kOe) and intrinsic coercivity (Hc) of the sample showed the highest values of M20 kOe = 107.43 emu/g and Hc = 2399.3 Oe, when annealed at 800 °C for 4 h.

The dilution effect caused by boundary-layer evolution over land has strong influences on air quality. Accurate and continuous measurements of the boundary-layer height over urban areas are therefore needed for complete air-quality assessments. Commercial ceilometers, in combination with reliable and simple methodologies, can be used to retrieve the mixed-layer height, and represent a means of obtaining information on vertical mixing and atmospheric structure above cities. Here, we evaluate various retrieval algorithms based on the gradient method against high-temporal-resolution radiosonde observations. Based on the results, we propose a simple algorithm by using the gradient method, the correction of background noise and the moving averages, with the minimum number of parameters that need to be adjusted to the local properties and the instrument itself. The algorithm is adjusted for Seoul, Korea, and improves the retrieval performance by reducing high-frequency noise. The algorithm is used to investigate the relationship between the evolution of the daytime mixed-layer height and air pollution under a two-layer mixing model where changes in concentration depend only on the urban boundary-layer growth and air entrainment from the free atmosphere. Using 2 months of ceilometer retrievals of mixed-layer height and air-quality data from across the city, we find strong negative correlations for primary emitted pollutants such as NO2, CO, SO2, and particulate matter smaller than 10 µm, and a modest positive correlation for O3. The results provide insight into the significant influence of urban boundary-layer evolution on Seoul’s air quality.

The isotropic nanoparticles (NPs) and anisotropic bulk samples of MnBi were prepared from Mn NPs by using zero-field and field-assisted reactive sintering, respectively. The MnBi NPs are irregular in shape with size d

Photodiodes composed of graphene and other two-dimensional materials are potential for high-sensitivity self-powered photodetectors, but the photovoltaic effect of graphene-based two-dimensional heterojunctions is often depressed and is, therefore, weaker than what it is expected. In this work, we have revealed that the loss of zero-bias photocurrent in the molybdenum disulfide (MoS2)/graphene photodiode originates from the interlayer coupling of photocarriers at the interface. By introducing atomically thin hexagonal boron nitride (h-BN) film into the MoS2/graphene interface, the interlayer carrier coupling at the MoS2/graphene interface under zero-bias is substantially blocked by the h-BN layer while the transport of photo-generated holes is realized through quantum tunneling. Therefore, the insertion of h-BN could increase the zero-bias photocurrent of the MoS2/graphene heterojunction for over three orders, and a high-sensitivity self-power vertical MoS2/h-BN/graphene van der Waals (vdW) heterostructure tunneling photodetector can be developed, which exhibits a high photo conversion efficiency (external quantum efficiency over 80%), improved photocurrent to dark current ratio (over 1000) and a corresponding high specific detectivity (5.9 × 1014 Jones for white-noise limited detectivity and 6.7 × 1010 Jones for the measured detectivity). This intriguing photovoltaic effect restoring has significant potential in practical applications of high-sensitivity graphene-based self-powered photodetection.

A high pixel density image sensor for the Short Wave Infrared (SWIR) range is presented. A PbS quantum dot (QD) photodiode array is monolithically integrated on a silicon custom readout IC. Imaging in VIS and SWIR is demonstrated using focal plane arrays with pixel pitch down to record 1.82 μm. Through-silicon vision and lens-free imaging (LFI) microscopy are shown as applications that can benefit from high resolution/small pixel dimensions. In the LFI demonstration, the captured hologram is computationally reconstructed to acquire SWIR microscopic images, resulting in a wavelength equivalent resolution LFI microscopy system. To our knowledge, this is the smallest pitch SWIR pixel ever reported and the first LFI system using a QD image sensor.

We previously reported a Corynebacterium glutamicum JH41 strain with a 58% faster growth rate through application of adaptive laboratory evolution. To verify that the fast-reproducing strain was useful as a host for recombinant protein expression, we introduced a plasmid responsible for the secretory production of a recombinant protein. The JH41 strain harboring the plasmid indeed produced the secretory recombinant protein at a 2.7-fold greater rate than its ancestral strain. To provide the reverse engineering targets responsible for boosting recombinant protein production and cell reproduction, we compared the genome sequence of the JH41 strain with its ancestral strain. Among the 15 genomic variations, a point mutation was confirmed in the 14 bases upstream of NCgl1959 (encoding a presumed siderophore-binding protein). This mutation allowed derepression of NCgl1959, thereby increasing iron consumption and ATP generation. A point mutation in the structural gene ramA (A239G), a LuxR-type global transcription regulator involved in central metabolism, allowed an increase in glucose consumption. Therefore, mutations to increase the iron and carbon consumption were concluded as being responsible for the enhanced production of recombinant protein and cell reproduction in the evolved host.

Rare-earth-free permanent magnets have attracted considerable attention due to their favorable properties and applicability for cost-effective, high-efficiency, and sustainable energy devices. However, the magnetic field annealing process, which enhances the performance of permanent magnets, needs to be optimized for different magnetic fields and phases. Therefore, we investigated the effect of composition on the crystallization of amorphous MnBi to the ferromagnetic low-temperature phase (LTP). The optimal compositions and conditions were applied to magnetic field annealing under 2.5 T for elemental Mg- and Sb/Mg pair-substituted MnBi. The optimum MnBi composition for the highest purity LTP was determined to be Mn56Bi44, and its maximum energy product, (BH)max, was 5.62 MGOe. The Mg-substituted MnBi exhibited enhanced squareness (Mr/Ms), coercivity (Hc), and (BH)max values up to 0.8, 9659 Oe, and 5.64 MGOe, respectively, whereas the same values for the Sb/Mg pair-substituted MnBi were 0.76, 7038 Oe, and 5.60 MGOe, respectively. The substitution effects were also investigated using first-principles calculations. The density of states and total magnetic moments of Mn16Bi15Mg and Mn16Bi15Sb were similar to those of pure Mn16Bi16. Conversely, the Sb-substituted MnBi resulted in a dramatic enhancement in the anisotropy constant (K) from a small negative value (&minus, 0.85 MJ/m3) to a large positive value (6.042 MJ/m3).

This study aimed to quantify both chloromethylisothiazolinone (CMIT) and methylisothiazolinone (MIT) dissolved in different product brands and to characterize the exposure to these chemicals among humidifier disinfectant-associated lung injury (HDLI) patients. Both CMIT and MIT dissolved in different humidifier disinfectant (HD) products were quantified using gas chromatography&ndash, mass spectrometry. The inhalation level of CMIT and MIT was estimated based on HD-associated factors as reported by HDLI patients. A total of eleven HD products marketed until the end of 2011 were found to contain CMIT and/or MIT. The level of combined CMIT and/or MIT dissolved in these HD products ranged from 12 to 353 ppm. The level varied among HD products and the year of manufacture. The average inhalation levels were estimated to be 7.5, 4.1, and 3.2 &mu, g/m3 for the definite, probable, and possible groups, respectively. If probable and possible groups were collapsed together, the inhalation level of the collapsed group was significantly different from that of the definite group (p &lt, 0.001). All HDLI patients responded as having used HD not only while sleeping, but also as having a humidifier treated with HD within close proximity every day in insufficiently ventilated spaces. These HD use characteristics of patients may be directly/indirectly linked to the HDLI development.

Paddy fields play a critical role as storage for the retention of surface water in hydrological processes, but their water balance is complicated by irrigation and drainage management. Stud...

There is currently no governmental body in South Korea resembling the type of poison center (PC) recommended by the World Health Organization (WHO). All Organization for Economic Cooperation and Development (OECD) member countries except for South Korea maintain such a PC tasked with both preventing poisoning accidents and supporting the prompt treatment of poisoned patients. Such a PC could very possibly have allowed the country to more promptly recognize the widespread wave of humidifier disinfectant (HD) associated health effects, including fatal lung injury and death, that lasted started roughly in 2000 and continued through 2011. Despite this chemical poisoning tragedy, South Korea still lacks a surveillance system to monitor health effects caused by the use and consumption of materials that include products containing chemicals, foodborne pathogens, drugs, pesticides, etc. There have been no legal procedures for examining the potential risk of products or materials manufactured by industry. The reporting of national poisoning data or causes of poisoning, which is near ubiquitous in advanced countries with a PC, has not taken place We recommend that a PC should be established within the Korea Disease Control and Prevention Agency (KDCA). In addition, in order to perform surveillance of poisoning cases across the country, a certain number of regional PCs, including at large hospitals, will also be necessary.

Substantial mitigation of air pollutants emissions has been performed since 2013 around Beijing, and changes in the atmospheric characteristics have been expected over the downstream area of Beijing. In this study, both WRF-Chem simulation and on-site measurements were utilized for the Baengnyeong (island) supersite, one of the representative regional background sites located in the Yellow Sea, the entrance area of the long-range transport process in Korea. The changes in the chemical compositions of inorganic aerosols were examined for spring-time during the Chinese emission mitigation period from 2014 to 2016. The measured ratio of ionic species to PM2.5 at the Baengnyeong supersite showed changes in aerosol inorganic chemical compositions from sulfate in 2014 to nitrate in 2015–2016. The modeling results also showed that nitrate was low in 2014 and significantly increased in 2015 and 2016, and the acidic aerosol condition had also changed toward a more neutralized status in both the simulation and the observations. The WRF-Chem modeling study further indicated that the sulfur was not neutralized in 2014. However, in 2015 and 2016, SO2 was more sufficiently neutralized as sulfur emissions were substantially reduced in China, while at the same time nitrate had begun to increase in such a ‘SO2–poor’ condition in Beijing area in China, and thus approaching more enhanced neutralization over the Yellow Sea area. The causes of the higher nitrate based on the modeled characteristics of the ammonia-sulfate-nitrate aerosol formation in response to the SO2 emissions reduction in China are also discussed in this paper.

The use of humidifier disinfectant (HD) has been determined to be associated with lung injuries (HDLI) in Korea. Although HD brands containing polyhexamethylene guanidine (PHMG) oligomers have been found to cause more HDLI compared to brands containing other disinfectants, the physicochemical properties of PHMG have been poorly defined. We aimed to quantify the PHMG dissolved in HD brands, characterize the number-average (Mn) and weight-average (Mw) molecular masses, and identify the polymerization degree of PHMG. Analysis of the PHMG oligomers was performed using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF MS) operated in positive-ion reflectron mode. Eight brands of HD containing PHMG were identified. The PHMG concentrations in these brands ranged from 160 to 37,200 ppm (mean = 3100.9 ppm). Concentration was a significant variable among and within HD brands. The degree of PHMG oligomerization fell within the range of two to four. The averages of Mn and Mw were 517.2 g/mol (range: 422&ndash, 613 g/mol) and 537.3 g/mol (range: 441.0&ndash, 678.0 g/mol), respectively. Based on the average molecular weight and the degree of polymerization, the PHMG examined here could be regarded as oligomers, which may be associated with the highest proportion of HDLI being caused by PHMG.

We report three-pulse photodope-pump-probe measurements on photocarrier dynamics in semiconducting transition metal dichalcogenide monolayers of ${\mathrm{MoS}}_{2}$, ${\mathrm{WS}}_{2}$, ${\mathrm{MoSe}}_{2}$, and ${\mathrm{WSe}}_{2}$. The samples are fabricated by metal-organic chemical vapor deposition and mechanical exfoliation techniques and characterized by photoluminescence spectroscopy. In the time-resolved measurement, the samples are first photodoped by a prepulse, which injects background photocarriers of various densities. A pump pulse then injects photocarriers, whose dynamics is monitored by measuring a differential reflection of a time-delayed probe pulse. We found that the ultrafast decay component of the differential reflection signal, which has been widely reported before, shows minimal dependence on the background exciton density. This observation shows that a previously suggested carrier-trapping model cannot account for this component. The results thus further support an exciton-formation model that was previously proposed based on spectroscopic evidence.

Commercial spray products are commonly used in daily life and airborne particles generated by these products may cause adverse health effects. Our study was aimed to characterize the behaviors of airborne particles from spray products and to determine the deposition loss rate. Four categories of spray products with highly frequent use - air fresheners, fabric deodorants, window cleaners, and a bathroom cleaner - were selected for the study. The products were applied in a cleanroom according to the instructions for use. Airborne particles (10–10,000 nm) were measured within the breathing zone of a user with a scanning mobility particle sizer and an optical particle spectrometer. Additionally, filter sampling was performed to examine the morphological characteristics of the particles using a field emission-scanning electron microscope (FE-SEM). The initial concentration and particle size distribution varied among different spray types and products. Two propellant-type air fresheners that we tested showed a high initial concentration of smaller sized particles. However, one of these and all hand-pressure type propellants showed a low initial concentration in all size ranges. We observed that particles in nucleation mode (10–31.6 nm) decreased and aggregated particles shifted to accumulation mode (100–1,000 nm) over time. The FS-SEM analysis confirmed the aggregation of nano-sized particles for all products. The deposition loss rates of various particle sizes depended on the initial concentration and distribution of particle sizes. For two air fresheners with high initial concentrations, the loss rate of small-sized particles was higher than that of the other products whereas the particle loss rate of large-sized particles was higher, regardless of initial concentration. The results of this study can give us useful information in the behaviors of airborne particles in the consumer spray products and resulting exposure assessment especially in the application to the exposure modeling of spray products.

This study applied ratio correction factor (RCF) optimization to calibrate the daily storage of agricultural reservoirs located in ungauged catchments that lack stream flow data. Using Run theory, we then assessed the impacts of climate change on the resilience of agricultural reservoir operations during reservoir drought conditions. First, we optimized the RCFs of inflow and outflow in three agricultural reservoirs in Korea using limited measurement data from 2008 to 2017, the results showed high performance regarding the simulation of daily reservoir storage. Second, we simulated daily storage volume in reservoirs from 2018 to 2099, using future climate change data, and analyzed the duration and intensity of reservoir drought conditions, which indicated that the storage capacity is under the critical value. Without calibration, the correlation between the simulated and measured reservoir water volumes was very low, but the correlation increased after calibration of the simulated water volumes. A linear relationship between the simulated and measured volumes was observed with a correlation coefficient value of 0.9, indicating that the simulated reservoir values after calibration closely match the measured values. In addition, the maximum intensity of reservoir drought in the Kicheon reservoir was determined to be 486,000 m3 before calibration but 506,000 m3 after calibration. The duration results showed that long-term reservoir drought conditions will be observed more often in the future owing to climate change, and this could be a negative factor affecting the resilience of reservoir operations.

Green chemistry-based non-isocyanate polyurethanes (NIPU) are synthesized and 3D-printed via rapid, projection photopolymerization into compliant mechanisms of 3D structure with spatially-localized material properties. Trimethylolpropane allyl ether–cyclic carbonate is used to couple the unique properties of two types of reaction chemistry: (1) primary diamine-cyclic carbonate ring-opening conjugation for supplanting conventional isocyanate-polyol reactions in creating urethane groups, with the additional advantage of enabling modular segment interchangeability within the diurethane prepolymers; and (2) thiol-ene (click) conjugation for non-telechelic, low monodispersity, quasi-crystalline-capable, and alternating step-growth co-photopolymerization. Fourier Transform Infrared Spectroscopy is used to monitor the functional group transformation in reactions, and to confirm these process-associated molecular products. The extent of how these processes utilize molecular tunability to affect material properties were investigated through measurement-based comparison of the various polymer compositions: frequency-related dynamic mechanical analysis, tension-related elastic-deformation mechanical analysis, and material swelling analysis. Stained murine myoblasts cultured on NIPU slabs were evaluated via fluorescent microscopy for “green-chemistry” affects on cytocompatibility and cell adhesion to assess potential biofouling resistance. 3D multi-material structures with micro-features were printed, thus demonstrating the capability to spatially pattern different NIPU materials in a controlled manner and build compliant mechanisms.

Harmful emissions including particulates, volatile organic compounds, and aldehydes are generated during three-dimensional (3D) printing. Ultrafine particles are particularly important due to their ability to penetrate deep into the lung. We modeled inhalation exposure by particle size during 3D printing. A total of six thermoplastic filaments were used for printing under manufacturer's recommended conditions, and particle emissions in the size range between 10 nm and 10 μm were measured. The inhalation exposure dose including inhaled and deposited doses was estimated using a mathematical model. For all materials, the number of particles between 10 nm and 1 μm accounted for a large proportion among the released particles, with nano-sized particles being the dominant size. More than 1.3 × 109 nano-sized particles/kgbw/g (95.3 ± 104.0 ng/kgbw/g) could be inhaled, and a considerable amount was deposited in respiratory regions. The total deposited dose in terms of particle number was 3.1 × 108 particles/kgbw/g (63.6% of the total inhaled dose), and most (41.3%) were deposited in the alveolar region. The total mass of particles deposited was 19.8 ± 16.6 ng/kgbw/g, with 10.1% of the total mass deposited in the alveolar region. Given our findings, the inhalation exposure level is mainly determined by printing conditions, particularly the filament type and manufacturer-recommended extruder temperature.

The ferromagnetic MnAl-C powders were prepared by using a one-step solid-state reaction method starting from Mn micro-/nano-particles and Al/C micropowders. The bulk MnAl-C with enhanced coercivity was prepared by high-pressure compaction of these MnAl-C powders. The grain size of the τ-phase was significantly reduced during high-pressure compaction, which may also result in a decomposition of the τ-MnAl. Carbon element stabilizes the τ-phase under both ambient and high pressures. The annealing temperature and time intervals are crucial for the preparation of high purity τ-phase samples. The MnAl-C with smaller particle size were produced from Mn nanoparticles. In comparison with the samples prepared from Mn micropowders, the product prepared from Mn nanoparticles shows lower purity, owing to the surface oxidation of the precursor nanoparticles. After high pressure compaction, the coercivities of the bulk MnAl and MnAl-C were increased from 0.05 T and 0.08 T to 0.39 T and 0.22 T, respectively. The room temperature magnetization of the MnAl-C sample at 4 T reached up to 95 Am2/kg.

Ferromagnetic τ-phase Mn54Al46C2.44 particles were synthesized, and its composites with commercial Sm2Fe17N3 and synthesized Fe65Co35 powders were fabricated. Smaller grain size than the single domain size of the Mn54Al46C2.44 without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the Mn54Al46C2.44 can be enhanced by magnetic exchange coupling with the hard magnetic Sm2Fe17N3 and soft magnetic Fe65Co35. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the Mn54Al46C2.44 based composites containing Sm2Fe17N3 and Fe65Co35 could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

Bulk MnAl-C magnets were prepared via high-pressure compaction of melt-spun ribbons. The e → τ phase transformation (PT) in the melt-spun MnAl and MnAlC ribbons occurs mainly via the massive mode, whereas the displacive mode is not prominent. The massive PT temperatures of the melt–spun MnAl and MnAlC ribbons were measured to be in the range 660–739 K and 700–758 K, respectively. The PT temperatures of the melt-spun MnAlC ribbons are lower than those of water–quenched MnAlC. The annealing process for producing τ-phase from e-phase was optimized based on the measured PT temperature range. As a result, no decomposition of the metastable e/τ-phase MnAl and MnAlC were observed during the optimized high temperature annealing. High-purity τ-phase MnAlC ribbons with high magnetization (122 Am2/kg at 8 T) and low coercivity (0.13 T) were obtained. The coercivity of the bulk MnAlC obtained by high-pressure compaction was significantly enhanced and reached 0.38 T partially due to the grain refinement of the sample during high-pressure deformation.

The low temperature phase Mn55Bi45-xGax (x = 0, 1, 3, 5, and 10) alloys were prepared by induction melting process with subsequent low temperature annealing. The effects of Ga-doping on the crystal structure and magnetic properties of the alloys were systematically studied. The room temperature coercivities of Mn55Bi45-xGax after ball milling increased from 1.43 T for x = 0 to 1.66 T for x = 5, while the saturation magnetization decreased from 60.7 Am2/kg (x = 0) to 45.1 Am2/kg (x = 5). The maximum energy product (BH)max of Mn55Bi44Ga powders reached 7.87 MGOe. The Curie temperature of the Mn55Bi45-xGax alloys increased from 633 K to 658 K with increasing Ga concentration in the range of 0 ≤ x ≤ 5.

The temperature for phase transformation of e → τ in Mn 54 Al 46 C x (hereafter denoted by MnAlC x , x = 0–5) alloys was systematically studied by using the traditional thermal analysis method and a more precise magnetic measurement method developed in this work. The effect of carbon content and cold-rolling on the magnetic properties of the MnAlC x alloys was studied. The onset temperature of massive growth of τ- from e-phase increases with increasing carbon content in MnAlC x . The carbon content has little effect on the onset temperature of displacive growth of e → τ but has substantial effect on the displacive growth rate at certain temperature. Pure τ-MnAlC x with varied x was obtained by annealing the e-phase at optimum temperatures determined by our method. The Curie temperature of the MnAlC x decreases significantly first and then increases slightly with increasing carbon content. The coercivity and the remanent magnetization of the as-prepared τ-MnAlC x increase with increasing x first and become stable at x > 3 and x > 4, respectively. A cold-rolling method was introduced in this work to enhance the magnetic properties of τ-MnAlC x . The coercivity and remanent magnetization of the τ-MnAl after cold-rolling were enhanced up to 4.3 times and 3.3 times, respectively. The coercivity of the cold-rolled τ-MnAlC x decreases with increasing x and becomes stable when x > 2. The remanent magnetization and saturation magnetization of the cold-rolled τ-MnAlC x vary little with x .

The authors report on the origin of the strain sensitivity for an organic C26H16N2 (heptazole) thinfilm and its application for the detection of tensile strain. From the electrical characterization on the thin-film transistor adopting a heptazole channel, heptazole film exhibits p-channel conduction with a relatively low value of field-effect mobility (0.05 cm2/Vs), suggesting a hopping conduction behavior via hole carriers. By analyzing the strain and temperature dependences of the electrical conductivity, we reveal that the electrical conduction for a heptazole thin-film is dominated by the variable range hopping process with quite a large energy separation (224.9 meV) between the localized states under a relatively long attenuation length (10.46 A). This indicates that a change in the inter-grain spacing that is much larger than the attenuation length is responsible for the reversible modification of electrical conductivity depending on strain for the heptazole film. By utilizing our heptazole thin-film both as a strain sensitive passive resistor and an active semiconducting channel layer, we can achieve a strain gauge device exhibiting reversible endurance for tensile strains up to 2.12%. Consequently, this study advances the understanding of the fundamental strain sensing mechanism in a heptazole thin-film toward finding a promise material with a strain gauge for applications as potential flexible devices and/or wearable electronics.

Hollow and microporous organic network bearing alkynone moieties was prepared via carbonylative Sonogashira coupling. The carbonyl groups in the network showed unusual chemical reactivities, compared with those of a model alkynone compound. The observed differences between the reactivities of alkynones in the molecule and in the network were analyzed based on the "network effect".

We report a facile method for the synthesis of large-area tungsten disulfide (WS2) films by means of chemical vapor deposition (CVD). To promote WS2 film growth, the precursor solution, which includes pre-reduced tungsten suboxides, is prepared by using hydrazine as the strong reducing agent and spin-coated onto the growth substrate. Growth is then carried out in a CVD chamber vaporized with dimethyl disulfide as the sulfur precursor. Although only WS2 flakes are grown with unreduced tungsten precursors under a hydrogen atmosphere, WS2 films are readily attained on pre-reduced tungsten suboxide substrates without the need for further reduction by hydrogen, which is noted to induce discontinuity of the grown film. The result presents the coverage of WS2 to be proportional to the amount of reduced tungsten suboxides, which is revealed by X-ray photoelectron spectroscopy. Furthermore, it is found that the multilayer WS2 flakes grow along the grain boundary, which allows the analysis of the grain size of WS2 ...

Monolayer MoS2, among many other transition metal dichalcogenides, holds great promise for future applications in nanoelectronics and optoelectronics due to its ultrathin nature, flexibility, sizable band gap, and unique spin-valley coupled physics. However, careful study of these properties at low temperature has been hindered by an inability to achieve low-temperature Ohmic contacts to monolayer MoS2, particularly at low carrier densities. In this work, we report a new contact scheme that utilizes cobalt (Co) with a monolayer of hexagonal boron nitride (h-BN) that has the following two functions: modifies the work function of Co and acts as a tunneling barrier. We measure a flat-band Schottky barrier of 16 meV, which makes thin tunnel barriers upon doping the channels, and thus achieve low-T contact resistance of 3 kΩ.μm at a carrier density of 5.3 × 1012/cm2. This further allows us to observe Shubnikov–de Haas oscillations in monolayer MoS2 at much lower carrier densities compared to previous work.

We report a simple wireless power charging (WPC) antenna system (50 mm $\times40$ mm $\times0.1$ mm) for use in simulating power transfer efficiency ( $\eta $ ) with and without ferrite and a metallic object (battery case), thereby identifying suitable magnetic parameters and ferrite sheet thickness. The simulation results suggest that magnetic loss tangent (tan $\delta _{\mu }$ ) and permeability ( $\mu '$ ) need to be less than 0.05 and higher than 125 at 13.56 MHz, respectively, to achieve at least 75% of the transfer efficiency ( $\eta _{\mathrm {max}}$ ) of the WPC antenna without ferrite and the metallic object. Accordingly, we have fabricated Ni x Zn0.85– x Cu0.15Fe2O4 (x = 0.32 – 0.38) spinel ferrites using a one-step sintering process and obtained relatively high $\mu '$ of 169 and low tan $\delta _{\mu }$ of 0.1 with a nickel (Ni) concentration of 0.38. This magnetic loss is still too high to achieve 75% of the $\eta _{\mathrm {max}}$ value. In order to further reduce the magnetic loss, a two-step sintering process was used. The two-step sintered Ni0.38Zn0.47Cu0.15Fe2O4 shows $\mu '$ of 132 and a tan $\delta _{\mu }$ of 0.03 at 13.56 MHz, respectively. Therefore, this ferrite meets criteria identified by the transfer efficiency simulation and is a good candidate for 13.56-MHz wireless power transfer charging antenna system. In addition, our designed WPC system is capable of evaluating other magnetic materials that are suitable for WPC antenna applications.

We evaluated the spatial-temporal dispersion of airborne nanomaterials during the use of spray consumer products and estimated the level of consumer inhalation exposure. A total of eight spray products including five propellant and three pump types were selected to evaluate the dispersion of airborne nanoparticles across time and space in a cleanroom which could control the background particles. Four products were advertised to contain silver and one contained titanium nanoparticles, while three products were specified no ENM but as being manufactured through the use of nanotechnology. We used direct-reading instruments with a thermodesorber unit to measure the particles (number, mass, surface area), as well as filter sampling to examine physicochemical characteristics. Sampling was conducted simultaneously at each location (1 m, near-field; 2, 3 m, far-field) by distance from the source. We estimated the inhaled doses at the breathing zone, and the doses deposited in each part of the respiratory tract using the experimental data and mathematical models. Nanoparticles released from the propellant sprays persisted in the air and dispersed over a large distance due to their small size (1466-5565 particles/cm

We report on the synthesis of large-area molybdenum disulfide (MoS2) film on an insulating substrate by means of chemical vapor deposition. A single mixture of molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (C2H6S2) was utilized as an organic liquid precursor for the synthesis of MoS2 film. Carbon impurities stemming from the dissociation of the organic precursor are effectively removed by water oxidation, and hydrogen gas, which is a by-product of the oxidation of carbon impurities, inhibits the formation of molybdenum oxides. The use of a liquid precursor assisted with water oxidation ensures high reproducibility and full-coverage of MoS2 film for large area, which is not typically achieved with solid precursors such as molybdenum oxide and sulfur powder. We believe that our approach will advance the synthesis of transition metal dichalcogenides.

Solar renewable energy (SRE) applications are substantial in eradicating the rising global energy shortages and reversing the approaching environmental apocalypse. Hence, effective solar irradiance forecasting models are crucial in utilizing SRE efficiently. This paper introduces a partially amended hybrid model (PAHM) by the implementation of a new algorithm. The algorithm innovatively utilizes bi-directional gated unit (Bi-GRU), autoregressive integrated moving average (ARIMA) and naive decomposition models to predict solar irradiance in 5-min and 60-min intervals. Meanwhile, the models’ generalizability strengths would be tested under an 11-fold cross-validation and are further classified according to their computational costs. The dataset consists of 32 months’ solar irradiance and weather conditions records. A fundamental result of this study was that the single models (Bi-GRU and ARIMA) outperformed the hybrid models (PAHM, classical hybrid model) in the 5-min predictions, negating the assumptions that hybrid models oust single models in every time interval. PAHM provided the highest accuracy level in the 60-min predictions and improved the accuracy levels of the classical hybrid model by 5%, on average. The single models were rigorous under the 11-fold cross-validation, performing well with different datasets; although the computational efficiency of the Bi-GRU model was, by far, the best among the models.

International audience; The formation of nanopores under electron irradiation is an ideal process to quantify chemical bonds in 2D materials. Nowadays, High Resolution Transmission Electron Microscopy (HRTEM) allows investigating such nucleation and growth phenomena with incomparable spatial and temporal resolution. Moreover, theoretical calculations are usually exploited to confirm characteristic features of these atomic-scale observations. Nevertheless, the full understanding of the ejection mechanisms of atoms requires studying in details the interplay between the very dynamic edge structure of expanding nanopores and the displacement energy of edge atoms (E D). Here, the dynamics of triangular nanopores in hexagonal boron nitride (h-BN) under various electron dose rates was followed by aberration-corrected HRTEM with high 2 temporal resolution to provide new in situ insights into their growth processes. We notably reveal that the ejection of atomic pairs is an elemental mechanisms that considerably speeds up the expansion of nanopores. Atomic-scale calculations were exploited to quantify the structure-dependent E D of all the ejected edge atoms. They revealed strong variations of this threshold energy during the growth processes. This quantitative study reconciles theoretical and experimental measurements of the ejection rate of atoms in h-BN under electron irradiation which is essential for nanopore engineering in this atomically-thin membrane.

We report an experimental study on charge transfer properties of mixed-dimensional heterostructures formed by zero-dimensional PbS quantum dots and two-dimensional transition metal dichalcogenides. Monolayers of ${\mathrm{MoSe}}_{2}$ and ${\mathrm{MoS}}_{2}$ were fabricated by mechanical exfoliation and chemical vapor deposition techniques, respectively. PbS quantum dots with diameters of 2.3 and 5 nm were synthesized by a hot-injection method and characterized by optical absorption spectroscopy and ultraviolet photoemission spectroscopy. The quantum dots were deposited on the ${\mathrm{MoS}}_{2}$ and ${\mathrm{MoSe}}_{2}$ monolayers to form heterostructures. Photoluminescence and transient absorption measurements were performed on the heterostructures as well as individual materials to reveal their photocarrier dynamics. We found that the holes excited in ${\mathrm{MoSe}}_{2}$ can efficiently transfer to both 2.3- and 5-nm PbS quantum dots, while electrons in these quantum dots cannot transfer to ${\mathrm{MoSe}}_{2}$. Similar charge transfer properties were observed between ${\mathrm{MoS}}_{2}$ and the 5-nm PbS quantum dots, while no charge transfer was observed between ${\mathrm{MoS}}_{2}$ and the 2.3-nm quantum dots. These results provide useful information for understanding the physical mechanism of charge transfer in mixed-dimensional heterostructures and for developing PbS quantum-dot-based mixed-dimensional materials.

Ultrafine particles and other hazardous materials are emitted during 3D printing, but the effect of temperature on such particles has not been studied systematically. The aim of this study was to evaluate the effect of temperature on the emission rate of particulate matter during fused deposition modeling (FDM) three-dimensional (3D) printing using different filament types. The number concentration of particles was measured with direct-reading instruments in an exposure chamber at various temperatures while using four filament materials during 3D printing. The temperature was increased from 185 to 290°C in 15°C increments, while incorporating the manufacturer-recommended operating conditions. The emission rate increased gradually as the temperature increased for all filament types, and temperature was the key factor affecting the emission rate after filament type. For all filaments, at the lowest operating temperature, the emission rate was 107 -109 particles/min, whereas the emission rate at the highest temperature was about 1011 particles/min, that is, 100-10 000 times higher than the emission rate at the lowest temperature. To reduce particle emissions from 3D printing, we recommend printing at the lowest temperature possible or using low-emission materials.

We have calculated electronic structures of Mn4C using first-principles calculations based on density functional theory (DFT) within the Perdew Burke Ernzerhof-generalized gradient approximation (PBE-GGA). The calculated band structures and density of states (DOS) indicate that stability of cubic perovskite-type crystal structured Mn4C is originated from p-d hybridization between Mnb and C and d-d hybridization between Mna and Mnb sublattices. The mean field approximation (MFA) resulted in the Neel temperature (TN) of 879 K which is in close agreement with experimental TN. The temperature dependence of magnetic moments of Mna and Mnb sublattices were also calculated using the Brillouin function to investigate the origin of unusual linearly increasing magnetization below 400 K. It was found that the increasing magnetization is originated from strong mutual interdependence of more or less linearly decreasing magnetic moment of Mna and stationary magnetic moment of Mnb below 400 K.

In the semiconductor etch process, as the critical dimension (CD) decreases and the difficulty of the process control increases, in-situ and real-time etch profile monitoring becomes important. It leads to the development of virtual metrology (VM) technology, one of the measurement and inspection (MI) technology that predicts the etch profile during the process. Recently, VM to predict the etch depth using plasma information (PI) variables and the etch process data based on the statistical regression method had been developed and demonstrated high performance. In this study, VM using PI variables, named PI-VM, was extended to monitor the etch profile and investigated the role of PI variables and features of PI-VM. PI variables are obtained through analysis on optical emission spectrum data. The features in PI-VM are investigated in terms of plasma physics and etch kinetics. The PI-VM is developed to monitor the etch depth, bowing CD, etch depth times bowing CD (rectangular model), and etch area model (non-rectangular model). PI-VM for etch depth and bowing CD showed high prediction accuracy of R-square value (R2) 0.8 or higher. The rectangular and non-rectangular etch area model PI-VM showed prediction accuracy R2 of 0.78 and 0.49, respectively. The first trial of virtual metrology to monitor the etch profile will contribute to the development of the etch profile control technology.

Two dimensional (2D) p-MoTe2 channel-based nonvolatile memory transistors with ferroelectric P(VDF-TrFE) polymer has been studied using a bottom-gate device architecture, which is introduced to dramatically reduce both of the switching and drain voltages to minimum 8 V and 10 mV, respectively. In fact, most of 2D-channel ferroelectric FETs with the same P(VDF-TrFE) polymer have used top-gate architectures, utilizing high switching pulse voltages over 20–25 V due to the existence of dead layer, which is unavoidably formed at the interface between P(VDF-TrFE) and thermal-deposited Al top gate. Key effects to realize such a low 8–13 V switching thus originate from the bottom-gate architecture. On the one hand, keys to obtain the low operation/drain voltage come from anneal-free Ohmic contact which is obtained using H2O2 solution. Thanks to the low operation voltages of 10 mV, consuming power in the nonvolatile FETs can be minimized to ~a few pW for OFF/Erase state and ~a few hundred pW for ON/Program although it eventually becomes ~nW and ~30 nW for OFF and ON states in a practical circuit operation to switch organic light emitting diodes. Our approaches of bottom-gate architecture and H2O2 contact nicely work even for transparent nonvolatile memory FET.

Workers in the semiconductor fabrication process may be exposed to higher levels of hazardous materials, such as arsenic, during preventive maintenance (PM) tasks than during the regular operation of the fabrication process. This study investigates the exposure to arsenic and other metals during PM tasks in the ion implantation process. Airborne arsenic samples and bulk samples were obtained during various ion implanter PM tasks in a semiconductor fabrication factory. The arithmetic mean (AM) and standard deviation (SD) of airborne arsenic in personal samples were 0.64 µg m–3 ± 0.92 µg m–3 (n = 9), and the highest level was 2.39 µg m–3 during medium-current ion implanter PM tasks. For area samples, the AM and SD were 0.42 µg m–3 ± 0.69 µg m–3 (n = 5) and the highest level was 1.79 µg m–3 during medium-current ion implanter PM tasks. Arsenic was also found in the bulk samples of debris produced during PM tasks. Other metals (Ag, Al, Cu, Pb, Cr, Sn, Mn, Ti, Fe, and W) were found, but at low levels, prompting few health concerns compared with those of arsenic. This study found that PM workers were exposed to airborne arsenic levels that differed significantly according to the type of ion implanter used.