ABSTRACT
GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.
ABSTRACT
A series of chromatographic separations performed on the ethanol extracts of the peels of Citrus grandis has led to the characterization of forty compounds, including seventeen coumarins, eight flavonoids, two triterpenoids, four benzenoids, two steroids, one lignan, one amide, and five other compounds, respectively. The chemical structures of the purified constituents were identified on the basis of spectroscopic elucidation, including 1D- and 2D-NMR, UV, IR, and mass spectrometric analysis. Most of the isolated compounds were examined for their inhibition of superoxide anion generation and elastase release by human neutrophils. Among the isolates, isomeranzin (3), 17,18-dihydroxybergamottin (12), epoxybergamottin (13), rhoifolin (19), vitexicarpin (22) and 4-hydroxybenzaldehyde (29) displayed the most significant inhibition of superoxide anion generation and elastase release with IC50 values ranged from 0.54 to 7.57 µM, and 0.43 to 4.33 µM, respectively. In addition, 7-hydroxy-8-(2'-hydroxy-3'-methylbut-3'-enyl)coumarin (8) and 17,18-dihydroxybergamottin (12) also exhibited the protection of neurons against A-mediated neurotoxicity at 50 µM.
Subject(s)
Anti-Inflammatory Agents/pharmacology , Citrus/chemistry , Coumarins/pharmacology , Flavonoids/pharmacology , Neuroprotective Agents/pharmacology , Triterpenes/pharmacology , Amyloid beta-Peptides/antagonists & inhibitors , Amyloid beta-Peptides/toxicity , Animals , Anti-Inflammatory Agents/chemistry , Anti-Inflammatory Agents/isolation & purification , Cell Death/drug effects , Cerebral Cortex/cytology , Cerebral Cortex/drug effects , Complex Mixtures/chemistry , Coumarins/chemistry , Coumarins/isolation & purification , Flavonoids/chemistry , Flavonoids/isolation & purification , Fruit/chemistry , Humans , Leukocyte Elastase/antagonists & inhibitors , Leukocyte Elastase/metabolism , Lignans/chemistry , Lignans/isolation & purification , Lignans/pharmacology , Neurons/cytology , Neurons/drug effects , Neuroprotective Agents/chemistry , Neuroprotective Agents/isolation & purification , Neutrophils/cytology , Neutrophils/drug effects , Neutrophils/metabolism , Peptide Fragments/antagonists & inhibitors , Peptide Fragments/toxicity , Primary Cell Culture , Rats , Rats, Sprague-Dawley , Steroids/chemistry , Steroids/isolation & purification , Steroids/pharmacology , Superoxides/antagonists & inhibitors , Superoxides/chemistry , Triterpenes/chemistry , Triterpenes/isolation & purification , Waste ProductsABSTRACT
This study investigates the capacity of albumin-grafted biomaterials as tissue engineering scaffolds to regenerate cartilaginous components. Porcine knee chondrocytes were seeded and cultivated in porous ternary matrix consisting of polyethylene oxide, chitin, and chitosan with surface albumin. The results revealed that the quantity of albumin did not affect the viability of porcine knee chondrocytes in the constructs. However, a high grafting concentration of albumin favored the adhesion of porcine knee chondrocytes on the scaffolding pore surface. After cultivation over 4 weeks, an increase in the concentration of albumin enhanced the quantities of porcine knee chondrocytes, glycosaminoglycans, and collagen in the constructs. The histological staining of porcine knee chondrocytes showed an active chondrocytic growth in the albumin-grafted constructs. In addition, the safranin-O staining indicated that the surface albumin could stabilize the secretion of glycosaminoglycans. Moreover, the immunochemical staining against type II collagen exhibited a regular production of collagen by phenotypic porcine knee chondrocytes in the constructs. Albumin-grafted polyethylene oxide/chitin/chitosan scaffolds can be a promising biomimetic substrate in neocartilage formation.