Electronic and structural properties of biazulene,terazulene, and polyazulene isomers

Facile graph theoretical MO solutions are demonstrated. The dihedral angles between the azulene units at the bridging bond in biazulenes were determined by MM2 calculations. Polyazulenes are predicted to be conductive only via the polaron mechanism. Polaron conduction in 1,3‐ and 2,6‐polyazulene is qualitatively predicted to be more facile than in 4,8‐ and 5,7‐polyazulene. Copyright © 2007 John Wiley & Sons, Ltd.     

Nuclear power plant optimal control by successive linear programming

An attempt to find optimal controls for an extremely load-following nuclear power plant during large load pick-ups is reported in this paper. The choice of the numerical method to solve this highly constrained dynamic optimization problem is discussed. The results reported demonstrate the efficacy of the successive linear programming method in tackling this problem without recourse to model linearization.The first author wishes to express his gratitude for many helpful discussions with Prof. S. L. Mehndiratta, Indian Institute of Technology, Bombay and Mr. B. F. Chamany, Bhabha Atomic Research Centre, Bombay, India.     

CASM—The Right Environment for Simulation

The modeller approaching discrete-event simulation has expected and received a high degree of computer support. The processing power simply to run a model and analyse the results would, of course, be taken for granted, but support has gone far beyond this in promoting the easier and speedier construction of models through specialized program structures, languages and lately program generators. Computer graphics capabilities of mini- and microcomputers have been exploited to secure a readier acceptance of simulation models and results. These support facilities constitute the computer environment within which the fortunate modeller works at present. What more could be expected?The work of an L.S.E. group of researchers is guided by a picture of an ideal environment for simulation modelling. We shall describe this picture and illustrate the progress made towards its implementation. Our principal intention is to promote discussion amongst simulation practitioners about their own ‘ideal’ of a computer support environment and the nature of deficiencies in the current systems.     

Almost locatedness in uniform spaces

A weak form of the constructively important notion of locatedness is lifted from the context of a metric space to that of a uniform space. Certain fundamental results about almost located and totally bounded sets are then proved.     

Baire*1, Baire 1 and Zahorski properties of higher order derivatives

Summary It is proved that if f is continuous and the approximate symmetric d.l.V.P. derivatives D_a^n-2f of f of order n-2 exist in (a,b) then under a certain smoothness type condition on f, D_a^n-2f is in Baire*1. Also Zahorski property and Denjoy property for the ordinary symmetric d.l.V.P. derivative Dⁿf are established under certain suitable conditions.     

Uncertainty principles on two step nilpotent Lie groups

We extend an uncertainty principle due to Cowling and Price to two step nilpotent Lie groups, which generalizes a classical theorem of Hardy. We also prove an analogue of Heisenberg inequality on two step nilpotent Lie groups.     

Optical and structural characterization of nickel selenide nanoparticles synthesized by simple methods

A series of nickel selenide (NiSe₂, NiSe and Ni₃Se₄) nanoparticles have been synthesized by three different methods, i.e. the single-source precursor (method 1), the thermolysis of trioctylphosphine selenide (TOPSe) and nickel chloride in hexadecylamine (method 2) as well as the reaction of nickel chloride and selenium using sodium borohydride as a reducing agent in methanol and in water (method 3). The optical properties of nickel selenide synthesized from all the methods showed good nanometric characteristics with an observed blue-shift in absorption band-edge from bulk nickel selenide. The structural characteristics varied with the methods employed, with method 1 producing 10 nm spherical NiSe₂ particles, method 2 star-shaped NiSe particles, while method 3 produced hexagonal NiSe nanoparticles in methanol and rod-shaped Ni₃Se₄ particles in water.     

Characterization of aging-induced microstructural changes in M250 maraging steel using magnetic parameters

The best combinations of mechanical properties (yield stress and fracture toughness) of M250 maraging steel is obtained through short-term thermal aging (3–10 h) at 755 K. This is attributed to the microstructure containing precipitation of intermetallic phases in austenite-free low-carbon martensite matrix. Over-aged microstructure, containing reverted austenite degrades the mechanical properties drastically. Hence, it necessitates identification of a suitable non-destructive evaluation (NDE) technique for detecting any reverted austenite unambiguously during aging. The influence of aging on microstructure, room temperature hardness and non-destructive magnetic parameters such as coercivity (H_c), saturation magnetization (M_s) and magnetic Barkhausen emission (MBE) RMS peak voltage is studied in order to derive correlations between these parameters in aged M250 maraging steel. Hardness was found to increase with precipitation of intermetallics during initial aging and decrease at longer durations due to austenite reversion. Among the different magnetic parameters studied, MBE RMS peak voltage was found to be very sensitive to austenite reversion (non-magnetic phase) as they decreased drastically up on initiation of austenite reversion. Hence, this parameter can be effectively utilized to detect and quantify the reverted austenite in maraging steel specimen. The present study clearly indicates that the combination of MBE RMS peak voltage and hardness can be used for unambiguous characterization of microstructural features of technological and practical importance (3–10 h of aging duration at 755 K) in M250 grade maraging steel.