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991.
Optical burst switching (OBS) is regarded as one of the most promising switching technologies for next generation optical
networks. However, the data burst contention problem is still unresolved thoroughly even though slotted OBS (SOBS) is studied
as a new paradigm reducing the blocking rate. In this article, we propose a tree-based slot allocation (TSA) algorithm for
loss-free SOBS networks, where the TSA algorithm originally avoids contention of the time-slots by reserving the time-slots
with different time-slot positions for the source nodes, respectively. In order to manage the time-slots efficiently, we also
propose an OBS superframe, which is a cyclic period and consists of multiple time-slots transmitted by the source nodes toward
the same incoming port of a destination node. In addition, we attempt to optimize multiplexing of the OBS superframes to reduce
wavelength consumption. On the other hand, when incoming traffic is beyond expectation, a source node may need more time-slots
to prevent packet loss because of buffer overflow. For reallocation of the time-slots, we propose a flow control scheme managing
some number of shared time-slots, where a control node adaptively allocates (or redeems) the time-slots to (or from) source
nodes by utilizing the shared time-slots based on fluctuating traffic condition. Simulation results show that the blocking
rate of the proposed TSA–OBS scheme is zero with acceptable queueing delay at moderate traffic offered loads. In addition,
multiplexing optimization simulated in the 14-node NSFNET achieves a 63% reduction of wavelength consumption. Moreover, the
proposed flow control scheme assisting the TSA algorithm maintains a target upper-bound of queueing delay at the source node,
so that packet loss caused by buffer overflow is prevented. 相似文献
992.
993.
994.
Cheol Soo Choi Pushpankur Ghoshal Malathi Srinivasan Sheene Kim Gary Cline Mulchand S. Patel 《Lipids》2010,45(11):987-995
The pyruvate dehydrogenase complex (PDC) plays a critical role in lipid synthesis and glucose homeostasis in the fed and fasting
states. The central role of the liver in the maintenance of glucose homeostasis has been established by studying changes in
key enzymes (including PDC) and the carbon-flux via several pathways under different metabolic states. In the present study
we have developed a murine model of liver-specific PDC deficiency using Cre-loxP technology to investigate its consequences
on lipid and carbohydrate metabolism. There was no incorporation of glucose-carbon into fatty acids by liver in vitro from
liver-specific Pdha1 knockout (L-PDHKO) male mice due to absence of hepatic PDC activity. Interestingly, there was a compensatory increase in
lipogenic capacity in epididymal adipose tissue from L-PDHKO mice. Both fat and lean body mass were significantly reduced
in L-PDHKO mice, which might be explained by an increase in total energy expenditure compared with wild-type littermate mice.
Furthermore, both liver and peripheral insulin sensitivities measured during a hyperinsulinemic-euglycemic clamp were improved
in L-PDHKO mice. The findings presented here demonstrate (i) the indispensable role of PDC for lipogenesis from glucose in
liver and (ii) specific adaptations in lipid and glucose metabolism in the liver and adipose tissue to compensate for loss
of PDC activity in liver only. 相似文献
995.
This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n‐hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
996.
Yiyoung Choi 《Polymer》2010,51(21):4713-4725
Supported hybrid catalysts using metallocenes and a nickel diimine catalyst were synthesized and used for ethylene slurry polymerization and ethylene/1-hexene copolymerization. Two types of metallocenes, together with a nickel diimine catalyst were supported onto SiO2 through chemical bonding, and a borate compound was physisorbed for the activation of the catalysts. These supported hybrid catalysts had high catalyst activities and made free-flowing polymer particles. The chemical composition distribution, molecular weight averages and distributions of resultant polymers were controlled by catalyst structure and polymerization conditions such as reaction temperature and the use of α-olefin. According to GPC-IR, 13C NMR and CEF characterization results of some polymers, more 1-hexene was incorporated in the high molecular weight region, short chain branches were generated by the chain walking mechanism in low molecular weight region. The morphologies of the resulting particles were investigated by SEM. 相似文献
997.
Hee Jung Kim Ji Eun Park Myung Gil Choi Sangdoo Ahn Suk-Kyu Chang 《Dyes and Pigments》2010,84(1):54-58
A novel, Hg2+-selective chemosensor was prepared via Mannich reaction of dichlorofluorescein with piperazinyl-coumarin moiety. The dichlorofluorescein–coumarin derivative exhibited well-defined Hg2+-selective chromogenic behavior, indicated by a green to pink colour change in solution, as well as fluorogenic signalling. Significant changes in fluorescence of the dichlorofluorescein subunit were analyzed in reference to the rather constant coumarin emission as an internal standard yielding Hg2+ selectivity. The Hg2+ selectivity of the chemosensor was not appreciably affected by the presence of common coexisting alkali, alkaline earth, and transition metal ions. The detection limit of the dichlorofluorescein–coumarin conjugate for the determination of Hg2+ ions was 4.3 × 10−6 mol L−1 and the conjugate dye could be used as a chemosensor for the analysis of Hg2+ ions in aqueous environments. 相似文献
998.
Dongho Seo Sangsun Park Yukwon Jeon Sung-Won Choi Yong-Gun Shul 《Korean Journal of Chemical Engineering》2010,27(1):104-109
The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up
and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition
is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration
with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off
cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ
and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode
interfacial structure, which is mainly attributed to the loss of cell performance. 相似文献
999.
Bokkyu Choi 《Electrochimica acta》2010,55(28):8771-6701
Fuel cell/battery (FCB) systems are promising power generation/energy storage systems because of their bi-functionality as fuel cells and as secondary batteries. We investigated the required charging after the discharged manganese dioxide (MnOOH) by oxygen gas under the rest condition and during the fuel cell operation mode using manganese dioxide as a positive electrode for the FCB system. Electrochemical characterization was performed using cyclic voltammetry and galvanostatic measurements. Additionally, changes in the crystal structure and the chemical functional groups during the electrode reactions were monitored by X-ray diffractometry and Fourier transform infrared spectroscopy. The results indicated that MnOOH formed via the electrochemical discharge of manganese dioxide (MnO2) and that the oxyhydroxide can be chemically transformed back to MnO2 with gaseous oxygen (O2). The recharged MnO2 can be used as the cathode in a fuel cell with an O2 supply and it can also be electrochemically discharged without an O2 supply. In addition, we confirmed that MnO2 does not convert to Mn3O4 during the charge/discharge cycles if the redox reaction is maintained within a restricted range where a homogeneous process exists between MnO2 and MnOOH. The results in this study suggest that the FCB system can be constructed using MnO2 as the positive electrode and a metal hydride (MH) as the negative electrode, which can be rapidly charged to more than 70% of the theoretical capacity within 10 min using pressurized H2 and electrochemically discharged, in an alkaline electrolyte. This system possesses a high-power generation efficiency, a high-energy density and a high load-following capability. 相似文献
1000.
Qiang Wang Ji Hyang Sohn So Ye Park Jin Seong Choi Joo Young Lee Jong Shik Chung 《Journal of Industrial and Engineering Chemistry》2010,16(1):68-73
Pure phase K4Zr5O12 is synthesized via solid state method in the present work. Various K/Zr ratios and temperatures are applied, and the synthesis process is investigated in detail by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Its catalytic activity for soot oxidation is studied by temperature programmed oxidation with different types of soot/catalyst contacts. It is revealed that K4Zr5O12 is very active in the presence of 2–10% O2 for both tight and loose contacts (Tp(tight) = 335 °C, Tp(ethanol) = 355 °C and Tp(shaking) = 370 °C). Thermal stability study shows that K4Zr5O12 is highly stable up to at least 900 °C. 相似文献