Computability of Countable Subshifts in One Dimension

We investigate the computability of countable subshifts in one dimension, and their members. Subshifts of Cantor?CBendixson rank two contain only eventually periodic elements. Any rank two subshift in 2^? is decidable. Subshifts of rank three may contain members of arbitrary Turing degree. In contrast, effectively closed ( $\Pi^{0}_{1}$ ) subshifts of rank three contain only computable elements, but $\Pi^{0}_{1}$ subshifts of rank four may contain members of arbitrary $\Delta^{0}_{2}$ degree. There is no subshift of rank ??+1.     

Triiodide PVC membrane electrodes based on charge-transfer complexes

Three new electrodes were prepared by incorporating two different charge-transfer complexes and amino crown ether into plasticized PVC membranes. The electrodes showed Nernstian response to triiodide ion over the activity range from 1.0 x 10(-5) to 1.0 x 10(-1) mol x L(-1) with detection limits at approximately 1.0 x 10(-6) mol x L(-1). The resulting electrodes have fast response times (20-30 s) and good stabilities (4 months) and can be used over a wide pH range of 2.5-9.0. The proposed electrodes exhibit anti-Hofmeister behavior with excellent selectivity toward triiodide ion against a wide range of common interferences. Comparative study suggests that amino (aza) crown ether alone or in the form of a charge-transfer complex with iodine, as an ionophore in a PVC liquid membrane, is sensitive to triiodide ion. The electrodes were used as indicator electrodes in potentiometric titration of triiodide ion against thiosulfate ion.     

Improving thermal performance of the roof enclosure of heavy construction buildings

High heat flux through the enclosures of heavy building constructions during summer and winter seasons is of great concern with respect to energy-related economics and environmental issues. This paper demonstrates the importance of quantitative evaluation of enclosure design and proves the potential for substantial energy savings by minor alterations of conventional roof designs. These modifications include adding insulation layer(s), removing construction details and obstructing fluid flow within the attic cavity by partial or full vertical partition within the cavity. The CFD approach adopted for this purpose is based on a numerical study of steady, conjugate natural convection in the cavity of an attic of heavy construction buildings. Because of the flow characteristics, laminar and turbulent models were employed for summer and winter day boundary conditions, respectively. Steady state results based on the finite-volume method were obtained for Rayleigh number in the range 10⁸–10¹⁰. Representative results illustrating the effects of the proposed design modifications on the local and total Nusselt numbers at the indoor surfaces are presented and discussed for summer and winter day boundary conditions. The results show that considerable energy saving may be achieved via relatively simple design changes. It is also shown that adding an insulation layer does not necessarily translate into energy conservation, and that eliminating a minor design detail might have significant rewards in terms of energy savings.     

AGA (Asset Governance Assessment) for analyzing affect of subsidy on MC (Marginal Cost) in electricity distribution sector

Nowadays subsidy payments on electrical energy have to be managed and controlled to prevent any side effect particularly in developing countries. Effects of some external factors on Energy consumption and electricity distribution indices are analyzed in this paper. External factors are classified into three categories of social behavior, governance and urban planning. MC (Marginal Cost) of electricity in distribution is considered as the main index to be analyzed. Also, ANN (Artificial Neural Network) is applied to simulate effect of the mentioned factors on MC of distribution sector. Numerical investigation on the indices for a sample DISCO (Distribution Company) in Iran is made, results indicate that the more subsidies are allocated to consumers the more MC is increased. AGA (Asset Governance Assessment), which is proposed as a kind of governance decision, could improve the performance efficiency and avoid lose of activities done by DISCOs through subsidy management.     

Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Morphological engineering of carbon-based materials: in the quest of efficient catalysts for overall water splitting

This work attempts to optimize the catalytic activity of the carbon-based materials by engineering their morphological structure. Several flake-like quantum dots with different shapes such as triangulene, elliptical, rhomboid, and square, as well as hydrocarbons having sunflower, kekulene, and snow-like structures, are considered and their electrocatalytic activities toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are theoretically evaluated. The activity analysis indicates that the OER overpotentials for the examined carbon materials vary in the range between 0.56 and 1.22 V. Benefiting from the improved electronic properties due to the proper morphology, remarkable catalytic activity was achieved for the snow-like morphology affording overpotentials of 0.56 V for OER and ?0.05 V for HER. In addition to snow-like, other morphologies such as triangulene and square can effectively promote acidic hydrogen evolution via Volmer-Heyrovsky mechanism. On contrary, the high values of free energies for H₂O dissociation step reveal that, under the alkaline condition, the examined carbon materials cannot be considered as efficient HER catalysts.