Publications by authors named "Sang-Tae Lee"

Forests are significant carbon reservoirs, with approximately one-third of this carbon stored in the soil. Forest thinning, a prevalent management technique, is designed to enhance timber production, preserve biodiversity, and maintain ecosystem functions. Through its influence on biotic and abiotic factors, thinning can profoundly alter soil carbon storage.

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Our investigation focused on assessing the influence of the metamorphic buffer in metamorphic high-electron-mobility transistors (MHEMT) that were grown on GaAs substrates. While an MHEMT exhibited elevated off-state current levels, its direct current (DC) and radio frequency (RF) traits were found to be comparable to those of InP-based lattice-matched high-electron-mobility transistors (LM-HEMTs). However, the Pulsed I-V measurement results confirmed the presence of the fast transient charging effect, leading to a more substantial degradation in drain current observed in MHEMT.

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Increasing research interests have been paid to understand the factors controlling soil nitrogen (N) stocks under diverse environmental conditions and forest thinning regimes. This study investigated soil N stocks across 13 temperate forests, each of which received three thinning intensities (unthinned control, 15-30 %, and 30-50 % basal area removals) under varying pre-treatment conditions (altitude, slope, soil pH, soil moisture, stand age, stand density, diameter at breast height, and tree height). The total N stored in the forest floor (L, F, and H layers) and mineral soils (0-10, 10-20, and 20-30 cm) was determined 1, 4, and 7 years after thinning.

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Soil organic carbon (SOC) is a primary regulator of the forest-climate feedback. However, its indicative capability for the soil CH sink is poorly understood due to the incomplete knowledge of the underlying mechanisms. Therefore, SOC is not explicitly included in the current model estimation of the global forest CH sink.

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Forest soil harbors diverse microbial communities with decisive roles in ecosystem processes. Vegetation shift from needleleaf to broadleaf species is occurring across the globe due to climate change and anthropogenic activities, potentially change forest soil microbial communities and C cycle. However, our knowledge on the impact of such vegetation shift on soil microbial community and activities, and its consequences on forest soil C dynamics are still not well established.

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Microbial biomass and enzyme activity are essential for ecosystem function in managed forests; however, uncertainty remains because microbial biomass and enzymatic responses to thinning highly differ with case studies. This study addressed the drivers for the site-specific responses of microbial biomass and enzyme activity to thinning. Study sites included two oak and three larch forests; each had un-thinned control, intermediate thinning (15-23% basal area reduction), and heavy thinning treatments (30-44% basal area reduction).

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Objectives: To identify risk factors and clinical outcomes in patients with bacteremia due to extended-spectrum beta-lactamase (ESBL) or carbapenemase-producing Escherichia coli, as well as to determine the prevalence and genetic background of such isolates.

Methods: Case control study was performed with patients with E. coli bacteremia between January 2008 and May 2013 (n = 115) at a tertiary university hospital in Japan.

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We report a case of rat-bite fever in a 94-year-old woman with Streptobacillus notomytis infection. We established an epidemiologic link between exposure to rats and human infection by performing nested PCRs that detected S. notomytis in the intraoral swab specimens obtained from rats captured in the patient's house.

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In this paper we account for the physics behind the exciton peak shift in GaN nanorods (NRs) due to hydrogenation. GaN NRs were selectively grown on a patterned Ti/Si(111) substrate using plasma-assisted molecular beam epitaxy, and the effect of hydrogenation on their optical properties was investigated in detail using low-temperature photoluminescence measurements. Due to hydrogenation, the emissions corresponding to the donor-acceptor pair and yellow luminescence in GaN NRs were strongly suppressed, while the emission corresponding to the neutral to donor bound exciton (DX) exhibited red-shift.

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A 70-year-old woman was admitted to our hospital with malaise, bilateral leg edema, and oliguria. She had a history of advanced uterine cancer. Bilateral double-J catheters were inserted because growth of intra-abdominal metastases led to bilateral ureteral stricture and hydronephrosis.

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An 82-year-old man with percutaneous nephrostomy presented to our Hospital with dysuria for one day. The patient's percutaneous nephrostomy tube was exchanged, with about 20 mL of creamy purulent urine being collected. Direct smear of the urine specimen showed polymorphonuclear leukocytes and small Gram-negative bacilli, some of which had undergone phagocytosis.

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3D surface profiling and high resolution imaging were performed to refine the Florin rings and epicuticular wax crystals of Pinus koraiensis needles. Needles were collected from four-year-old seedlings and air-dried for surface observations. Field emission scanning electron microscopy revealed that stomata were found on the abaxial (lower) surface of needles.

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It is found that the surface migration and nucleation behaviors of InSb quantum dots on AlSb/Si substrates, formed by molecular beam epitaxy in Stranski-Krastanov (SK) growth mode, are dependent on the substrate temperature. At relatively high temperatures above 430 degrees C, quantum dots are migrated and preferentially assembled onto the surface steps of high defect AlSb layers grown on Si substrates, while they are uniformly distributed on the surface at lower temperatures below 400 degrees C. It is also found that quantum dots located on the defect sites lead to effective termination of the propagation of micro-twin-induced structural defects into overlying layers, resulting in the low defect material grown on a largely mismatched substrate.

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The optical and electrochemical properties of the ruthenium phthalocyanine complexes [[(t-Bu)4Pc]Ru(4-Rpy)2], where R = NO2, Me, NH2, and NMe2, are reported. The electron density at the macrocycle may be adjusted using the axial ligand substituents, which have varying electron-donating/withdrawing strengths. Electrochemical data show that the axial pyridine ligand substituents exert significant influence over the phthalocyanine ring-based redox processes.

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This study is based on previous information regarding asymmetric activation in the prefrontal cortex by film-induced affects, as well as the inverse proportionality of prefrontal cortex activity to power in the alpha band of EEG. To search for a specific EEG band where the asymmetric activation in the prefrontal cortex by sound-induced affects is mainly reflected, we measured 32 college students' EEGs; 11 bands ranged from 6.5 to 35.

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To investigate the changes of cortico-cortical connectivity during odor stimulation of subjects classified by occupation, the mutual information content of EEGs was examined for general workers, perfume salespersons and professional perfume researchers. Analysis of the averaged-cross mutual information content (A-CMI) from the EEGs revealed that among the professional perfume researchers changes in the A-CMI values during odor stimulation were more apparent in the frontal region of the brain, while for the general workers and perfume salespersons such changes were more conspicuous in the overall posterior temporal, parietal and frontal regions. These results indicate that the brains of professional perfume researchers respond to odors mainly in the frontal region, reflecting the function of the orbitofrontal cortex (OFC) due to the occupational requirement of these subjects to discriminate or identify odors.

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