1,721,175 research outputs found
On fair window control for TCP with ECN using congestion level
No full textThe current congestion control mechanism for TCP with EGN suffers from the oscillation of the window size and the unfair sharing of network resources. These problems are caused by the insufficient information about the congestion level of a network and the different round trip time (RTT) among the connections respectively. In this paper, we propose a new window control algorithm for TCP with ECN to avoid the oscillation of the window size and to achieve the fairness among the connections
Unraveling the functional interaction structure of a biomolecular network through alternate perturbation of initial conditions
No full textVarious approaches attempting to infer the functional interaction structure of a hidden biontolecular network from experimental time-series measurements have been developed; however, due to both experimental limitations and methodological complexities, a large majority of these approaches have been unsuccessful. In particular, with respect to the elucidation of such networks, there are (i) a dimensionality problem: too many network nodes with too few available sampling points, (ii) a computational complexity problem: exponential complexity if a priori information is unavailable for regulatory nodes, and (iii) an experimental measurement problem: no guidelines for an appropriate experimental design for distinguishing direct and indirect influences among network nodes. Here, we sought to develop a new methodology capable of identifying the correct functional interaction structure with only a few sampling points through relatively simple computations. We also attempted to provide guidelines for an experimental design capable of supporting this methodology by taking proper measurements of the direct influences among the network nodes. In the present study, we considered an experiment where measurements were taken at two sampling time points with alternate perturbation (upregulation or down-regulation) of initial conditions while keeping the same initial conditions for unperturbed network nodes, and propose a new method of identifying the functional interaction structure from such measurements. The proposed method is able to avoid the dimensionality problem caused by the practically limited number of sampling time points, and does not suffer from the computational complexity problem, as it only uses a simple algebra based on the Mean Value Theorem (see Supplementary mathematical descriptions) without any other complicated computation. In addition, we provide a detailed guideline for an experimental design that can take proper measurements of the direct influences among the network nodes through perturbation of initial conditions. The proposed method is particularly useM for cases investigating the local interaction structure around a specific network node of interest. An example,-based on simulated data, is provided to illustrate the proposed method. (c) 2007 Elsevier B.V. All rights reserved
Nonlinear soil parameter effects on dynamic embedment of offshore pipeline on soft clay
Full text linkIn this paper, the effects of nonlinear soft clay on dynamic embedment of offshore pzpeline were investigated Seabed embedment by pipe-soil interactions has impacts on the structural boundary conditions for various subsea structures such as pipeline, riser, pile, and many other systems. A number of studies have been performed to estimate real soil behavior, but their estimation of seabed embedment has not been fully identified and there are still many uncertainties. In this regards, comparison of embedment between field survey and existing empirical models has been performed to identify uncertainties and investigate the effect of nonlinear soil parameter on dynamic embedment. From the comparison, it is found that the dynamic embedment with installation effects based on nonlinear soil model have an influence on seabed embedment. Therefore, the pipe embedment under dynamic condition by nonlinear parameters of soil models was investigated by Dynamic Embedment Factor (DEF) concept, which is defined as the ratio of the dynamic and static embedment of pipeline, in order to overcome the gap between field embedment and currently used empirical and numerical formula. Although DEF through various researches is suggested, its range is too wide and it does not consider dynamic laying effect. It is difficult to find critical parameters that are affecting to the embedment result. Therefore, the study on dynamic embedment factor by soft clay parameters of nonlinear soil model was conducted and the sensitivity analyses about parameters of nonlinear soil model were performed as well. The tendency on dynamic embedment factor was found by conducting numerical analyses. using OrcaFlex software. It is found that DEF was influenced by shear strength gradient than other factors. The obtained results will be useful to understand the pipe embedment on soft clay seabed for applying offshore pipeline designs such as on-bottom stability and five span analyses.open1156sciescopuskc
Effects of FIS protein on rnpB transcription in Escherichia coli
No full textFactor for inversion stimulation (FIS), the Escherichia coli protein, is a positive regulator of the transcription of genes that encode stable RNA species, such as rRNA and tRNA. Transcription of the rnpB gene encoding M1 RNA, the catalytic subunit of E. coli RNase P, rapidly declines under stringent conditions, as does that of other stable RNAs. There are multiple putative FIS binding sites upstream of the rnpB promoter. We tested whether FIS binds to these sites, and if so, how it affects rnpB transcription. In vitro binding assays revealed specific binding of FIS to multiple sites in the rnpB promoter region. Interestingly, FIS bound not only to the upstream region of the promoter, but also to the region from +4 to +18. FIS activated rnpB transcription in vitro, but the level of activation was much lower than that of the rrnB promoter for rRNA. We also examined the effects of FIS on rnpB transcription in vivo using isogenic fis(+) and fis(-) strains. rnpB transcription was higher in the fis(-) than the fis(+) cells during the transitions from lag to exponential phase, and from exponential to stationary phase.Korea Research
Foundation Gran
Inference of transcriptional regulatory networks based on initial mRNA expression profiles and DNA-binding motifs
No full textCharacteristics of Pt/SrTiO3/Pb(Zr-0.52, Ti-0.48)O-3/SrTiO3/Si ferroelectric gate oxide structure
No full textPt/SrTiO3/Pb(Zr-0.52, Ti-0.48)O-3/SrTiO3/Si (MIFIS) ferroelectric gate oxide structures were prepared by an r.f, sputtering method for application of non-destructive read out ferroelectric RAM (NDRO-FRAM) devices. In the MIFIS structure, a SrTiO3 (STO) film was used as a buffer layer to prevent the interaction between the Pb(Zr-0.52, Ti-0.48)O-3 (PZT) film and the Si substrate and also between the PZT film and the Pt top electrode. In the PZT/Si structure, a serious inter-diffusion of Pb into Si substrate was observed by Auger electron spectrometry (AES). However, STO/PZT/STO/Si structures had a perfect perovskite phase and a flat interface of PZT/STO/Si without the inter-diffusion of Pb into the Si substrate. When Pt/STO/PZT/STO/Si structures were post-annealed at 400 degrees C for 30 min after depositing the Pt top electrodes, the leakage current of MIFIS structure was improved to about 10(-8) A/cm(2). The property of the memory window of MIFIS structures was improved due to a low leakage current. When Pt/STO(25 nm)/PZT(160 nm)/STO(25 nm)/Si structures were annealed at 600 degrees C for 1 h and post-annealed at 400 degrees C for 30 min, the maximum value of the memory window was about 2 V at the applied voltage of 7 V. The memory window was increased as increasing the thickness of PZT film since a higher voltage was applied to the thicker PZT film. (C) 1999 Elsevier Science S.A. All rights reserved
Why have serine/threonine/tyrosine kinases been evolutionarily selected in eukaryotic signaling cascades?
No full textThe signal transduction systems of eukaryotes are different from those of prokaryotes with respect to their structures and mechanisms. The main signal transduction system of prokaryotes called the two-component system (TCS) is a one-step phosphorelay system composed of a histidine kinase (HK) while the central signal transduction system of eukaryotes called the mitogen-activated protein kinase (MAPK) cascade system (MCS)is a multi-step phosphorelay system composed of serine/threonine/tyrosine kinases (SrYKs). The two signal transduction systems are also different in their transphosphorylation mechanisms. HK in the TCS transfers its own phosphate group to the response regulator protein while STYKs in the MCS phosphorylate other proteins using ATP. We were intrigued by the different dynamics resulting from such differences and wondered why STYKs instead of HKs have been evolutionarily selected in eukaryotic signaling cascades. In this paper, we compared the dynamical characteristics of two mathematical models which reflect such differences between the TO and the MCS, and found that STYKs are more appropriate for cascade structures in eukaryotic signal transduction than HK with respect to the duration and settling time of response signals. (C) 2008 Elsevier Ltd. All rights reserved
Fatigue performance of deepwater SCR under short-term VIV considering various S-N curves
No full textIn this study, a method for fatigue performance estimation of deepwater steel catenary riser (SCR) under short-term vortex-induced vibration was investigated for selected S-N curves. General tendency between S-N curve capacity and fatigue performance was analysed. SCRs are generally used to transport produced oil and gas or to export separated oil and gas, and are exposed to various environmental loads in terms of current, wave, wind and others. Current is closely related with VIV and it affects fatigue life of riser structures significantly. In this regards, the process of appropriate S-N curve selection was performed in the initial design stage based on the scale of fabrication-related initial imperfections such as welding, hot spot, crack, stress concentration factor, and others. To draw the general tendency, the effects of stress concentration factor (SCF), S-N curve type, current profile, and three different sizes of SCRs were considered, and the relationship between S-N curve capacity and short-term VIV fatigue performance of SCR was derived. In case of S-N curve selection, DNV (2012) guideline was adopted and four different current profiles of the Gulf of Mexico (normal condition and Hurricane condition) and Brazil (Amazon basin and Campos basin) were considered. The obtained results will be useful to select the S-N curve for deepwater SCRs and also to understand the relationship between S-N curve capacity and short-term VIV fatigue performance of deepwater SCRs.국내111Nsciescopu
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