7,422 research outputs found
NEW TOTAL CARRIER PHASE ESTIMATOR IN FULLY PHASE-MODULATED SIGNALS
No full textThe open-loop phase estimator (OLPE) has been used to recover the carrier phase for burst mode communications. However, OLPE is not optimal in the presence of frequency offset. The authors propose a new carrier phase estimator in a feedforward form to restore the total carrier phase, including the carrier phase offset and/or the carrier frequency offset. The proposed estimator has significantly less complex hardware compared with the maximum likelihood estimator (MLE) in practical implementations
Heterogeneous PdAg alloy catalyst for selective methylation of aromatic amines with formic acid under an additive-free and solvothermal one-pot condition
Full text linkThe methylation of amines for the synthesis of methylamines and dimethylamines as platform chemicals has been attempted mostly by homogeneous catalysts with acid additives. However, there are scarcely any reports on heterogeneous catalytic methylation reactions except for a routine approach under high temperature and high pressure of CO2 and H-2 gases for extended reaction times. Here we report a heterogeneously catalyzed selective methylation of aromatic amines using reactive and nontoxic formic acid as the only source for the construction of methyl groups, under ambient pressure in an additive-free one-pot reaction condition. Equal proportions of Pd and Ag in the PdAg/Fe3O4/N-rGO catalyst deliver highly selective amine methylation without aromatic ring hydrogenation, as the strained Pd in the alloy is combined with the graphene-derived support, preventing nanoparticle agglomeration and the action of magnetite as a promoter. Both N-methylation and N, N-dimethylation of various substituted aromatic amines were performed with complete conversion and excellent 90-97% selectivity by controlling the reaction times in the range of 10-24 h at 140 degrees C without unwanted aromatic ring hydrogenation. Furthermore, the developed bimetallic catalyst provided high yields (88-91%) of methylation with CO2+H-2 gas under high pressure, which are as good as the results of homogenous catalysts with an acid additive. To the best of our knowledge, our use of this environmentally friendly methodology is the first time that this durable heterogeneous catalyst has readily performed highly selective methylation at ambient pressure, which is attractive for industrial applications.1193Ysciescopu
Influence of down-regulation of caspase-3 by siRNAs on sodium-butyrate-induced apoptotic cell death of Chinese hamster ovary cells producing thrombopoietin
No full textSodium butyrate (NaBu) can enhance the expression of foreign protein of recombinant Chinese hamster ovary (rCHO) cells, but it can also inhibit cell growth and induce cellular apoptosis. Thus, the beneficial effect of using a higher concentration of NaBu on foreign protein expression in rCHO cells is compromised by its growth inhibitory and cytotoxic effects. To overcome this cytotoxic effect of NaBu, an expression vector of small interfering RNAs (siRNAs) targeting against caspase-3, a kev effector component in apoptosis, was constructed and transfected into rCHO cells producing human thrombopoietin (hTPO). Using this siRNA strategy, rCHO cells (F21 cells) expressing a low level of caspase-3 proenzyme determined by RT-PCR and Western blot analysis were established. Under the condition of 1-5 mM NaBu addition at the exponential growth phase, down-regulation of caspase-3 in F21 cells could not effectively inhibit NaBu-induced apoptotic cell death. This NaBu-induced apoptotic cell death occurred because F21 cells appeared to compensate for the lack of caspase-3 by increasing the active caspase-7 level. These results suggest that the intracellular caspase's interconnectivity should be taken into consideration for the successful inhibition of apoptosis of rCHO cells. (c) 2005 Elsevier Inc. All rights reserved
Sloshing Behaviors of Rectangular and Cylindrical Liquid Tanks Subjected to Harmonic and Seismic Excitations
No full textPerformance analysis of mixed voice/data services in a microcell-based PCS network
No full textIn this paper, we present several traffic handling schemes For improving the QoSs (quality-of-services) in a microcell based PCS (personal communication services) network. Traffic handling schemes are devised for the efficient use of the limited radio resources with the increasing number of users and multimedia traffic. Both mathematical analysis and computer simulations are carried out for the performance evaluation in terms of the blocking probability of new call, the forced termination probability of handoff voice and data and the average delay of data. Analytical models by bivariate Markov processes are provided. It reveals that a finite queueing scheme for handoff delay sensitive data guarantees QoS metrics, such as the blocking probability of new voice and data and forced termination probability of handoff voice and data, as well as the efficient use of radio resources. The optimal number of reserved channels for handoff delay sensitive data and the optimal number of reserved channels for handoff traffic (in reserved channel scheme) are investigated and obtained. Dynamically controlled reserved channel schemes turn out to provide no significant performance improvement
Optical measurements of gas temperatures in atmospheric pressure RF cold plasmas
No full textRotational temperatures can be estimated directly from the ratios between peaks in the ultra violet (UV) band of OH molecular spectra. With a relatively poor spectral resolution of approximately 0.4 nm, ratios between two broad band peaks near 308 and 309 nm are identified to be sensitive to the gas temperatures in the range of 350 similar to 1000 K. In cold radio frequency (RF) generated atmospheric plasmas, rotational temperatures of molecules are measured to be in a relatively low temperature range of 400similar to700 K. These temperatures are confirmed to be in good agreement with gas temperatures measured by thermocouples. This simple emission spectroscopy can be used to monitor gas temperatures in cold atmospheric plasmas without any expensive spectrometer. (C) 2003 Elsevier Science B.V. All rights reserved.This work was supported by grant No. R01-2000-
00254 fromthe Korea Science and Engineering
Foundation
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