Structural Influence of the Ligand Geometry on Construction of Coordination Polymers Formed from Silver(I) Chloride Ribbons and Bipodal Nitrogen Donor Ligands

An assembly of adducts of silver nitrate and KCl and bipodal nitrogen donor ligands, 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)ethylene (tbpe) or 1,2-bis(4-pyridyl)ethane (bpe), at room temperature affords new supramolecular coordination polymers (SCP), [AgCl·bpy] (1), [(AgCl)₂·tbpe] (2) and [(AgCl)₃·(bpe)₂] (3). X-ray single crystal analyses reveal that 1–3 have 3D-supramolecular networks composed of different types of infinite 1D-ribbons of ladder, 1, and staircase, 2 and 3, structures formed from fused minicyle {Ag₂(μ₃-Cl)₂} motifs, which are bridged by the nitrogen donor ligands to form 2D-layers. The 2D-layers are interconnected by extensive hydrogen bonds and π–π stacking thereby creating 3D-networks. The products are also characterized by IR and electronic absorption spectra. SCP 1–3 display strong fluorescence in the solid state at room temperature.     

Modeling of ion transport reactor for oxy‐fuel combustion

This paper aims at investigating the performance of a cylindrical ion transport reactor designed for oxy‐fuel combustion. The cylindrical reactor walls are made of dense, nonporous, mixed‐conducting ceramic membranes that only allow oxygen permeation from the outside air into the combustion chamber. The sweep gas (CO₂ and CH₄) enters the reactor from one side and mixes with the oxygen permeate, and the products are discharged from the other side. The process of oxygen permeation through the reactor walls is influenced by the flow condition and composition of air at the feed side (inlet air side) and the gas mixture at the permeate side (sweep gas side). The modeling of the flow process is based on the numerical solution of the conservation equations of mass, momentum, energy, and species in the axisymmetric flow domain. The membrane is modeled as a selective layer in which the oxygen permeation depends on the prevailing temperatures as well as the oxygen partial pressure at both sides of the membrane. The CFD calculations were carried out using fluent 12.1 (ANSYS, Inc., Canonsburg, PA, USA), whereas the mass transfer of oxygen through the membrane is modeled by a set of user defined functions. The model results were validated against previous experimental data, and the comparison showed a good agreement. The study focused on the effect of oxygen partial pressure and temperature on the resulting combustion zones inside the reactor for the two cases of co‐current and counter‐current flow regimes. The results indicated that the oxygen to fuel mass ratio increases as the percentage of CO₂ increases in the inflow sweep gas for both co‐current and counter‐current flows. The obtained sweep mixture ratio (CO₂/CH₄) of 24 is found within the stoichiometric limit over most of the reactor length in the co‐current configuration, whereas the sweep mixture ratio of 15.67 is found in the counter‐current configuration owing to the high O₂ permeation. Copyright © 2012 John Wiley & Sons, Ltd.     

Comments on the security of Chen’s authenticated encryption scheme

Chen (Computers and Electrical Engineering, vol. 30, 2004) illustrated that Tseng et al.’s authenticated encryption schemes, with message linkages for message flows, do not achieve their claimed integrity and authenticity properties. Furthermore, Chen presented some modified schemes to repair these flaws. In this paper, we show that the modified schemes proposed by Chen are not secure. In particular, we present an attack that allows a dishonest referee, in case of a dispute, to decrypt all the future and past authenticated ciphertext between the contended parties. We also present a simple fix to prevent this attack.     

Elastic stability analysis of loosely fitted thin liners – A proposed simplified procedure and evaluation of existing solutions

The paper reports the results of an extensive numerical simulation to estimate the elastic buckling pressure and the corresponding thrust and bending moment induced in loosely fitted thin liners. The study is conducted numerically using a two-dimensional (2D) non-linear finite element model that accounts for the effects of large deformations on the stability of loosely fitted liners. The finite element results together with a non-linear multi-variant regression analysis are used to develop simplified non-dimensional formulae that provide the critical pressure, thrust and bending moments, at buckling, based on the liner’s geometry and material properties.In addition, several other analytical and numerical solutions for the same problem are revisited and critically reviewed. For comparison purposes, two of such methods are extended to allow for the calculation of the thrust and bending moment developed at the most heavily stressed point in the loosely fitted liners at the onset of buckling. In general, the comparison reveals the appropriateness of the proposed regression models in predicting the critical pressure and the associated thrust and bending moment induced in imperfect loosely fitted liners. Developed formulae provide designers with a simple and reliable means for ensuring stability and safety of such special type of structures.     

A comparative study on the starting methods of three phasewound-rotor induction motors. I

This paper presents a comparative study on the starting performance of three phase wound-rotor induction motors under different methods of starting. These methods are online direct starting, variable rotor resistance starting and double feed starting. In the double feed starting, the rotor winding is connected in parallel with the stator winding across the supply for a predetermined short period. By this connection, the motor produces an extremely high starting torque. For carrying out the investigations sought, a rigorous state space mathematical model has been developed and simulated. The effect of torsional dynamics has been taken into considerations     

Überblick über die Entwicklung der Wasserstoff-Schmelzreduktion am Lehrstuhl für Metallurgie

Zusammenfassung  Die Entwicklung der Wasserstoff-Schmelzreduktion ist schon seit mehr als drei Jahrzehnten ein Forschungsschwerpunkt am Lehrstuhl für Metallurgie. Im vorliegenden Artikel werden die Laboreinrichtungen und Versuche zur Wasserstoff-Schmelzreduktion beschrieben. überlegungen zu einer alternativen Stahlerzeugungsroute auf Basis einer Wasserstoff-Plasma-Schmelzreduktion werden dargelegt und eine SWOT-Analyse durchgeführt.

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Survey about the Development of Hydrogen Smelting Reduction at the Chair of Metallurgy

Summary  Development of hydrogen smelting reduction is an object of research for more than three decades on the Chair of Metallurgy. This paper focuses on laboratory facilities and experiments for the investigation of hydrogen smelting reduction at the Chair of Metallurgy. – Considerations for an alternative steelmaking route based on hydrogen plasma smelting reduction are made and a SWOT analysis is presented.

     

Atmospheric methane: Its contribution to global warming

Methane, a significant atmospheric trace-gas, controls numerous chemical processes and species in the troposphere and stratosphere. Its concentration in the Earth's atmosphere has been increasing at a rate of about 1% per year during the last century, and reached 1·72 ppmv in 1990. Methane is a strong greenhouse gas with significantly adverse environmental impacts. On a molecule-for-molecule basis, it is more than 20 times as potent a greenhouse gas as carbon dioxide. The contribution of methane to global warming between 1880 and 1980 has been estimated to be about 15%, with an increasing share, 18%, during the 1980s. In this paper methods for estimating the change in atmospheric concentration of methane, and for predicting its global-warming effect, are described. Influences of some of the suggested emission-control policies are also discussed. Methane concentration in the atmosphere might reach a value of more than 4 ppmv by the end of the next century with no control policies implemented. This could produce an unavoidable long-term mean rise in the surface temperature of the Earth of more than 0·5°C.     

Field-oriented vector control of synchronous motors with additional field winding

This paper presents a new method to control a synchronous motor in such a way to resemble the characteristics of a DC motor. The method suggests including a second field winding to the rotor of a voltage-source-inverter-fed synchronous motor. The angular frequency of the inverter is made equal to the angular rotor speed, (of a self-controlled synchronous motor drive). The added field winding is in space quadrature to the main field winding and is properly excited in such a way as to diminish the direct axis component of the stator current at every load conditions. The motor is controlled to operate with zero power angle from the inverter side and zero direct axis current from the rotor excitation side. Therefore, it operates with minimum stator current and with unity power factor. The addition of the second field winding will not complicate the design because it is just a control winding. This winding may be made with smaller wire cross-section and a larger number of turns. The control on this winding is not complicated and it can be easily created. The synchronous motor along with the added field and the required control loops are simulated and tested extensively. The test results show excellent motor performance in motoring and regenerating modes of operation.