• Applied Chemistry for Engineering
• /
• v.17 no.3
• /
• pp.235-242
• /
• 2006

Liquid phase alkylation of biphenyl (BP) was studied over large pore zeolites. Selective formation of the least bulky products, 4,4'-diisopropylbiphenyl (4,4'-DIPB) occurred only in the isopropylation of BP over some large pore molecular sieves. H-mordenites (MOR) gave the highest selectivity among them. The dealumination of MOR enhanced catalytic activity and the selectivity of 4,4'-DIPB because of the decrease of coke-deposition. Non-selective catalysis occurs on external acid sites over MOR with the low $SiO_2/Al_2O_3$ ratio because severe coke-deposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with reaction temperature. Selective formation of 4,4'-DIPB was observed at moderate temperatures such as $250^{\circ}C$, whereas the decrease of the selectivity of 4,4'-DIPB occurred at higher temperatures as $300^{\circ}C$. However, 4,4'-DIPB was almost exclusive isomer in the encapsulated DIPB isomers inside the pores even at high temperatures. These decreases of the selectivity of 4,4'-DIPB are due to the isomerization of 4,4'-DIPB on the external acid sites. Some 12-membered molecular sieves, such as SSZ-24, MAPO-5 (M:Mg, Zn, Si), SSZ-31, and ZSM-12, which have straight channels, gave 4,4'-DIPB with moderate to high selectivity; however; SSZ-55, SSZ-42, and MAPO-36 (M: Mg, Zn) gave lower selectivity because of cages in 12-membered one dimensional channels. Three dimensional H-Y and Beta zeolites also yield 4,4'-DIPB in low yield because of their wide circumstances for the isopropylation of BP. The increasing the size of alkylating agent enhanced the shape-selective alkylaiton even for the zeolites, such as UTD-1. The ethylation of BP to ethylbiphenyls (EBPs) and diethylbiphenyls (DEBPs) over MOR was non-selective. The ethylation of BP to EBPs was controlled kinetically. However, there was difference in reactivity of EBPs and DEBPs for their further ethylation. 4-EBP was ethylated preferentially among the isomers, although the formation of 4,4'-DEBP was less selective. The least bulky 4-EBP and 4,4'-DEBP have the highest reactivity among EBPs and DEBPs for the ethylation to polyethylbiphenyls (PEBPs). These results show that the environments of MOR pores are too loose for shape selective formation of the least bulky isomers, 4-EBP and 4,4'-DEBP in the ethylation of BP, and that MOR pores have enough space for the further ethylation of 4,4'-DEBP.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.8B
• /
• pp.699-706
• /
• 2008

This paper compares throughput performance of TCP and SCTP in a variety of network environments. For experiments, we construct a Linux-based testbed and consider a set of performance metrics such as MSS(Maximum Segment Size), transmission delay, and packet loss rate. In addition, we analyze the effect of SCTP multi-streaming on throughput. From the experimental results, we can see that SCTP provides throughput gain of approximately $20%{\sim}50%$ over TCP. This performance gain comes from the distinctive features of SCTP such as chunk bundling, initial congestion window of 2 MTU and SACK(Selective ACK) based error control. In the lossy networks, we can see that SCTP multi-streaming transmissions can effectively overcome the so-called HoLB(Head-of-Line Blocking) phenomenon of TCP.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.347-347
• /
• 2009

결정질 태양전지의 공정에 있어서 호모지니어스(homogeneous)한 구조보다 향상된 변환효율을 얻기 위해 선택적 도핑 방법에 관한 연구가 활발하다. 선택적 도핑 방법이란 에미터(emitter) 층을 $n^{++}$ 영역과 $n^+$ 영역으로 나누어 향상된 전류밀도와 개방전압을 얻기 위한 방법이다. 본 연구에서 제시된 RIE 에치-백 구조는 다수의 선택적 도핑 방법 중 하나이다. 기존의 에치-백 구조는 전면 전극 형성 후 RIE 공정을 수행하기 때문에 전면 전극이 손상되고 RIE 데미지(damage)가 발생되는 문제점이 있었다. 그러나 본 연구에서 제시된 구조는 기존의 에치-백 구조와 달리 RIE 에칭 후 발생된 데미지를 제거하는 추가적인 공정인 질산 패시베이션(nitric acid passivation)이 수행되었다. 또한 본 연구에서 새롭게 제시된 블라킹 마스크 페이스트(blocking mask paste)는 기존의 에치-백 구조에서 발생된 전극 손상 문제를 해결해 주고 있다. 이러한 결과로 호모지니어스 구조보다 향상된 전류밀도 (35.77 mA/$cm^2$), 개방전압 (625 mV), FF (78.01%), 변환효율 (17.43%)를 얻었다.

• Journal of Communications and Networks
• /
• v.12 no.3
• /
• pp.275-284
• /
• 2010

The current multihome-aware protocols (like stream control transmission protocol (SCTP) or parallel TCP for concurrent multipath data transfer (CMT) are not designed for high-capacity and large-latency networks; they often have performance problems transferring large data files over shared long-distance wide area networks. It has been shown that SCTP-CMT is more sensitive to receive buffer (rbuf) constraints, and this rbuf-blocking problem causes considerable throughput loss when multiple paths are used simultaneously. In this research paper, we demonstrate the weakness of SCTP-CMT rbuf constraints, and we then identify that rbuf-blocking problem in SCTP multihoming is mostly due to its loss-based nature for detecting network congestion. We present a simulation-based performance comparison of FAST TCP versus SCTP in high-speed networks for solving a number of throughput issues. This work proposes an end-to-end transport layer protocol (i.e., FAST TCP multihoming as a reliable, delaybased, multihome-aware, and selective ACK-based transport protocol), which can transfer data between a multihomed source and destination hosts through multiple paths simultaneously. Through extensive ns-2 simulations, we show that FAST TCP multihoming achieves the desired goals under a variety of network conditions. The experimental results and survey presented in this research also provide an insight on design decisions for the future high-speed multihomed transport layer protocols.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.12A
• /
• pp.975-982
• /
• 2003

A connection admission control scheme is proposed that can seamlessly support QoS in face of handoff in mobile packet networks. The proposed scheme is based on the adaptive time-selective bandwidth reservation with the reduced signaling and computational overhead. The reservation parameters are adjusted dynamically to cope with user mobility. Throughout the computer simulations, the performance of the proposed scheme is evaluated. As a result, it is shown that the proposed scheme reduces handoff call blocking probability remarkably, while other parameters (new call blocking probability and bandwidth utilization efficiency) are slightly deteriorated.

• Molecules and Cells
• /
• v.26 no.1
• /
• pp.48-52
• /
• 2008

We here demonstrate an anti-inflammatory action of raloxifene, a selective estrogen receptor modulator, in lipopolysaccharide (LPS)-induced murine macrophage RAW264.7 cells. Treatment with raloxifene at micromolar concentrations suppressed the production of nitric oxide (NO) by down-regulating expression of the inducible nitric oxide synthase (iNOS) gene in LPS-activated cells. The decreased expression of iNOS and subsequent reduction of NO were due to inhibition of nuclear translocation of transcription factor NF-${\kappa}B$. These effects were significantly inhibited by exposure to the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY294002, or by expression of a dominant negative mutant of PI 3-kinase. In addition, pretreatment with raloxifene reduced LPS-induced Akt phosphorylation as well as NF-${\kappa}B$ DNA binding activity and NF-${\kappa}B$-dependent reporter gene activity. Thus our findings indicate that raloxifene exerts its anti-inflammatory action in LPS-stimulated macrophages by blocking the PI 3-kinase-Akt-NF-${\kappa}B$ signaling cascade, and eventually reduces expression of pro-inflammatory genes such as iNOS.

• Korean Journal of Materials Research
• /
• v.19 no.5
• /
• pp.240-244
• /
• 2009

Simple and high efficiency green phosphorescent devices using an intermixed double host of 4, 4', 4"-tris(N-carbazolyl) triphenylamine [TCTA], 1, 3, 5-tris (N-phenylbenzimiazole-2-yl) benzene [TPBI], phosphorescent dye of tris(2-phenylpyridine)iridium(III) [$Ir(ppy)_3$], and selective doping in the TPBI region were fabricated, and their electro luminescent characteristics were evaluated. In the device fabrication, layers of $70{\AA}$-TCTA/$90{\AA}$-$TCTA_[0.5}TPBI_{0.5}$/$90{\AA}$-TPBI doped with $Ir(ppy)_3$ of 8% and an undoped layer of $50{\AA}$-TPBI were successively deposited to form an emission region, and SFC137 [proprietary electron transporting material] with three different thicknesses of $300{\AA}$, $500{\AA}$, and $700{\AA}$ were used as an electron transport layer. The device with $500{\AA}$-SFC137 showed the luminance of $48,300\;cd/m^2$ at an applied voltage of 10 V, and a maximum current efficiency of 57 cd/A under a luminance of $230\;cd/m^2$. The peak wavelength in the electroluminescent spectral and color coordinates on the Commission Internationale de I'Eclairage [CIE] chart were 512 nm and (0.31, 0.62), respectively.

• Journal of Broadcast Engineering
• /
• v.25 no.6
• /
• pp.845-853
• /
• 2020

In this paper, we propose a method for classifying environmental sound for selective noise cancellation in industrial sites. Noise in industrial sites causes hearing loss in workers, and researches on noise cancellation have been widely conducted. However, the conventional methods have a problem of blocking all sounds and cannot provide the optimal operation per noise type because of common cancellation method for all types of noise. In order to perform selective noise cancellation, therefore, we propose a method for environmental sound classification based on deep learning. The proposed method uses new sets of acoustic features consisting of temporal and statistical properties of Mel-spectrogram, which can overcome the limitation of Mel-spectrogram features, and uses convolutional neural network as a classifier. We apply the proposed method to five-class sound classification with three noise classes and two non-noise classes. We confirm that the proposed method provides improved classification accuracy by 6.6% point, compared with that using conventional Mel-spectrogram features.

• Proceedings of the Korean Society of Applied Pharmacology
• /
• 1996.04a
• /
• pp.191-191
• /
• 1996

BQ-123, a selective $ET_{A}$ receptor antagonist, reverses various responses induced by Endothelin-1 and it has been reported that BQ-123 ameliorates the cerebrovascular constriction, hypertension, and decrease of blood flow. Previously, we announced that the level of Endothelin-2 increase in the brain and spinal cord of EAE-induced lewis rat and showed the origin of ET-1 is activated macrophages. Intracisternal injection of $ET_{A}$ receptor antagonist, BQ-123(10nmol) was done for visualizing the role of endothelin-1 on the pathogenesis of EAE. BQ-123 apparently blocked the severity of clinical score of EAE and decreased the histologically observed inflammatory region. The blocking effect on the progression of EAE model following BQ-123, suggests that BQ-123 is a physiological antagonist in terms of development of the sign of multiple sclerosis.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.8
• /
• pp.84-90
• /
• 2010

In focused ion beam (FIB) fabrication processes the ion beam intensity with Gaussian profile has a drawback for high resolution machining. In this paper, the fabrication method to modify the beam profile at substrate using silt mask is proposed to increase the machining resolution at high current. Slit mask is utilized to block the part of beam and transmit only high intensity portion. A nano manipulator is utilized to handle the silt mask. Geometrical analysis on fabricated profile through silt mask was conducted. By utilizing proposed method, improvement of machining resolution was achieved.