35,949 research outputs found
Coordinated resource allocation scheme in the forward link of sectorized CDMA systems
No full textWe propose a coordinated resource allocation (CRA) scheme that can he used to allocate high data-rate users in sectorized cells. This scheme is useful for allocating high data-rate users at cell boundaries. In order to analyze the performance of the proposed scheme. we make an interference model for a sectorized CDMA system and suggest the system load measurement of the forward link. Based on this system load measurement, data throughput for the CD-MA system under perfect and imperfect power control is then analyzed. Numerical results show that throughput is significantly increased when the CRA scheme is used.
Fair queueing algorithm using channel status information in an integrated CDMA system
No full textA Fair Queueing Algorithm is proposed for data services in an integrated voice/data CDMA system. We introduce short-term and long-term fairness concepts to allocate data users fairly. Using these concepts, we propose a Weighted Fair Queueing with Status Control (WFQS) in the consideration of a Generalized Processor Sharing (GPS) fluid-flow model. This proposed scheme allocates resources using channel status information. The throughput and delay of data users could be improved when this scheme is applied to wireless channels.
Wireless packet scheduling in an integrated CDMA system using channel status information
No full textA fair queueing algorithm is proposed for data services in an integrated voice/data code-division multiple access (CDMA) system. After delay-sensitive voice users are allocated first, residual resources are allocated to data users according to the throughput maximization strategy. In order to fairly allocate data users, we use power resource concept which considers the BER and the rate requirement of data users, and apply weighted fair queueing (WFQ) to CDMA systems with consideration of a generalized processor sharing fluid-flow model. In order to implement this fair resource allocation scheme, a virtual clock for short-term fairness and a credit table method for long-term fairness are used. Based on these concepts, we propose weighted fair queueing with state control. This scheme allocates resources in the consideration of each channel state. When this scheme is applied to wireless channels, the throughput and delay of data services are shown. Numerical results show that the throughput of each data user has the same characteristics under wireless channel conditions. The throughput of data users can also be increased compared with a conventional WFQ scheme because available resources for data users in bad state are used by other users in good state. (C) 2004 Elsevier B.V. All rights reserved.
The Anti-Inflammatory Actions of Lcy-2-Cho, a Carbazole Analogue, in Vascular Smooth Muscle Cells
No full textLCY-2-CHO has anti-infl amm atory actions on macrophages. To understand its therapeutic implication in atherosclerosis, we examined its effects on the expressions of antiinflammatory and inflammatory proteins in cultured rat aortic vascular smooth muscle cells (VSMC). LCY-2-CHO is able to induce heme oxygenase-1 (HO-1) protein expression through a transcriptional action. The HO-1 inducting effect of LCY-2-CHO was inhibited by SB203580, N (G)-nitro-L- arginine methylester (L-NAME), and wortmannin, but was not affected by U0126 or SP600125. In accordance LCY-2 -CHO increased protein phosphorylation of p38, Akt, and eNOS. Nrf 2 is a transcription factor essential for HO-1 gene induction and we showed that LCY-2-CHO is able to cause Nrf2 nuclear translocation and this action depends on p38, Akt and eNOS. in addition to induce anti-inflammatory HO-1 , LCY- 2-CHO reduced interleukin-lp (IL-1 beta)-induced inflammatory mediators, inducible nitric oxide synthase ( iNOS), cyclooxygenase-2 (COX- 2), growth-related oncogene protein-alpha (GRO-alpha), and interleukin-8 ( IL-8). Inhibitory effect on IL-lp-mediated NF-KB activation was evidenced by the diminishment of I kappa B kinase (IKK) phosphorylation and I kappa B alpha degradation. In contrast , IL-1 beta-mediated ERK and JNK activations were not changed by LCY-2-CHO, while p38 activation by IL-1 beta and LCY-2-CHO displayed the nonadditivity. Taken together, given the overall anti-inflammatory properties of LCY-2-CHO in VSMC, in terms to induce HO-1 gene expression and inhibit inflammatory gene expression, these results highlight the therapeutic potential of LCY-2-CHO in atherosclerosis. (C) 2007 Elsevier Inc. All rights reserved
Pb cation induced low-temperature crystallization of (Ba center dot Pb) hexa-ferrite thin films
No full textWe have studied the low-temperature crystallization of (Ba•Pb) hexa-ferrite thin films using real time synchrotron X-ray scattering, anomalous X-ray scattering, and vibrating sample magnetometer. The crystallization temperature of amorphous (Ba•Pb) hexa-ferrite film (300-Å-thick, ∼530°C) was much lower than that of amorphous Ba hexa-ferrite film, ∼750°C. The crystalline (Ba•Pb) hexa-ferrite phase was formed by solid phase transformation of the interfacial crystalline Fe3O 4 phase through the diffusion of Ba or Pb cations. The low crystallization temperature of the (Ba•Pb) hexa-ferrite phase was due to the lower diffusion activation barrier of Pb cations than that of Ba cations. The small grain size (∼40 nm in diamter) and comparable magnetic properties (Ms : 337 emu/cm3, iHc : 1.60 kOe) of the crystallized (Ba•Pb) hexa-ferrite film also demonstrate its potential possibility for high-density recording media. © Springer Science + Business Media, LLC 2006.1
EGR장착 스파크점화 LPG엔진의 성능 및 배기 특성
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2001.2, [ 89 p. ]Exhaust Gas Recirculation (EGR) system has been used to reduce NOx emissions, to improve fuel economy and to suppress knock since it offers the benefits of charge dilution. However, the occurrence of excessive cyclic variation with high EGR rates, brings about an undesirable combustion instability within the engine cylinder resulting in the deterioration of both engine performance and emissions. Therefore, in order to avoid the reduction of thermal efficiency and to improve fuel economy, the optimum EGR rate should be derived effectively as a function of the operating conditions.
An experimental study was conducted to investigate the effects of EGR variables on performance and emission characteristics in a 2-liter 4-cylinder spark-ignition LPG fuelled engine. It also studied the effects of EGR on the reduction of thermal loading at exhaust manifold because the reduced gas temperature is desirable for the reliability of an engine in light of both thermal efficiency and material issue of exhaust manifold.
The steady-state test showed that the brake thermal efficiency increased and the brake specific fuel consumption decreased with the increase of EGR rate in hot EGR and with the decrease of EGR temperature in case of cooled EGR, while the stable combustion was maintained. The increase of EGR rate or the decrease of EGR temperature results in the reduction of emission even in the increase of HC emission. Furthermore, decreasing EGR temperature by 180℃ enabled the reduction of exhaust gas temperature by 15℃ in cooled EGR test at 1600rpm / 370kPa BMEP operation, and consequently the reduction of thermal load at exhaust.한국과학기술원 : 기계공학전공
Miniaturization of dipole antenna based on complex meta-material substrate and its application to MIMO system
No full textThis paper introduces a miniaturized antenna structure with a complex substrate, which is composed with CER-10 and meta-material. This complex substrate influences to the impedance value of antenna system, then this can make the antenna size reduction. The proposed antenna structure reduces the conventional antenna size by 66.7 % with respect to pure meta-material substrate reduction rate of 40 %. The proposed antenna provides 130 MHz bandwidth with the center frequency 1.8 GHz, and the total radiation efficiency of proposed antenna structure is 48.37 %. The S-parameter characteristic variation for some parameters, such as the dipole length, distance between 2 dipoles and the height of meta-material has been analyzed. For the detailed analysis of proposed antenna, the equivalent circuit model has been proposed, and has been verified by checking the S-parameter variation according to the variation of important parameters. For the effect of miniaturization on the MIMO environment, the channel capacity comparison in terms of the integration and mutual coupling have been analyzed. With the proposed antenna, the increase of integration and reduction of mutual coupling results in the increase of channel capacity
Weighted fair queueing for data service in a multimedia CDMA system
No full textVehicular Technology Conference Fall 2000. IEEE VTS Fall VTC2000. 52nd Vehicular Technology Conference (24-28 Sept. 2000 : Boston, MA, USA
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