Home About us Contact
|
Home About us Contact | ||
|
|
||
Phase Lead (phase + lead)
Selected AbstractsImproved PI controller with delayed or filtered integral modeAICHE JOURNAL, Issue 12 2002Jietae Lee Integral action is almost always included in process control systems to eliminate steady-state offset without uncertain process gain. The open-loop pole, however, at the origin of the integral term causes some problems such as integral windup. Various methods to solve these problems were studied. For better control performance and robustness, a filter was added to the integral term, which decouples the effective frequency ranges between the integral and proportional terms without degradation of the integral action. It produces a phase lead in a certain frequency range without having a derivative term, enhancing the control performances and stability robustness. Based on the internal model control method or the direct synthesis method, tuning rules for the proposed controller are given. [source] Fragmentation of star-forming clouds enriched with the first dustMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Raffaella Schneider ABSTRACT The thermal and fragmentation properties of star forming clouds have important consequences on the corresponding characteristic stellar mass. The initial composition of the gas within these clouds is a record of the nucleosynthetic products of previous stellar generations. In this paper, we present a model for the evolution of star forming clouds enriched by metals and dust from the first supernovae (SNe), resulting from the explosions of metal-free progenitors with masses in the range 12,30 M, and 140,260 M,. Using a self-consistent approach, we show that: (i) metals depleted on to dust grains play a fundamental role, enabling fragmentation to solar or subsolar mass scales already at metallicities Zcr= 10,6 Z,; (ii) even at metallicities as high as 10,2 Z,, metals diffused in the gas phase lead to fragment mass scales which are ,100 M,; (iii) C atoms are strongly depleted on to amorphous carbon grains and CO molecules so that C ii plays a minor role in gas cooling, leaving O i as the main gas-phase cooling agent in low-metallicity clouds. These conclusions hold independently of the assumed SN progenitors and suggest that the onset of low-mass star formation is conditioned to the presence of dust in the parent clouds. [source] Effect of morphology on barrier properties of poly(ethylene terephthalate),POLYMER ENGINEERING & SCIENCE, Issue 3 2005A.A. Natu The effects of morphology on the barrier properties of poly(ethylene terephthalate) (PET) have been investigated. Various levels of crystallinity can be developed in PET as a result of thermal exposure, orientation, and heat setting. The morphologies of the crystalline phase are affected by the conditions of their formation. As a result of morphological differences, samples with equivalent levels of crystallinity have been found to exhibit different oxygen barrier properties. These differences are most apparent at low and intermediate levels of crystallinity. For thermally crystallized systems, at the same crystalline content, increasing superstructure size in the crystalline phase leads to greater tortuosity for the permeant molecules, resulting in lower permeability. For stretched and heat set PET, transport properties can be correlated with birefringence as well as overall orientation, measured in terms of fraction of molecules in the trans or extended chain conformation. At high levels of crystallinity, where the spherulites become volume filling, permeation takes place primarily through the interlamellar regions of the crystalline phase and is controlled by level of crystallinity, independent of the mode of crystallization. The barrier properties of PET, before spherulitic impingement occurs, are governed by the size and number of spherulites as well as by the amorphous orientation present in non-crystalline regions. POLYM. ENG. SCI., 45:400,409, 2005. © 2005 Society of Plastics Engineers [source] Assessment of potential approaches to improve Eucalyptus globulus kraft pulping yieldJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2007A. S. Santiago Abstract The main goal of this work is to study the potential approaches to improve polysaccharides retention during Eucalyptus globulus kraft pulping. The addition of anthraquinone to kraft pulping leads to the highest pulp yield while the addition of urea promotes lower depolymerization of polysaccharides (higher pulp viscosity), but does not have a significant effect on yield. The early interruption of kraft cooking followed by oxygen delignification is a reliable approach to increase pulp yield, particularly when pulping is interrupted at the end of the faster and more selective kinetic regime (bulk phase). Yield loss during oxygen delignification is considerably lower than that incurred in the last phase of kraft pulping. Pulping with OH,/HS, charge profiling, carried out with liquor injection in three different phases leads to a yield increase. However, this increase results from a lower total alkali charge applied when profiling pulping is compared to standard pulping conditions, rather than to alkali profiling. Standard kraft pulping with different active alkali (AA) charges demonstrated that this operational variable is determinant for pulp yield and viscosity. Pulping experiences with lower AA (14%) resulted in a higher and almost constant pulp viscosity and in a higher pulp yield, assigned to improved retention of both cellulose and xylan. During the last stage of pulping, cellulose content decreases, this being mainly responsible for the decrease of pulp yield, while xylan content is almost constant, a feature attributed to the peculiar structure of this E. globulus's hemicellulose. Copyright © 2007 Society of Chemical Industry [source] | ||||||||||