Conjugacy invariant pseudo-norms, representability and RNA secondary structures

To a reasonable approximation, a secondary structures of RNA is determined by Watson-Crick pairing without pseudo-knots in such a way as to minimise the number of unpaired bases: We show that this minimal number is determined by the maximal conjugacy-invariant pseudo-norm on the free group on two generators subject to bounds on the generators. This allows us to construct lower bounds on the minimal number of unpaired bases by constructing conjugacy invariant pseudo-norms. We show that one such construction, based on isometric actions on metric spaces, gives a sharp lower bound. A major goal here is to formulate a purely mathematical question, based on considering orthogonal representations, which we believe is of some interest independent of its biological roots.

Potential of biomass energy for electricity generation in sub-Saharan Africa

The paper explores the biomass based power generation potential of Africa. Access to electricity in sub-Saharan Africa (SSA) is about 26% and falls to less than 1% in the rural areas. On the basis of the agricultural and forest produce of this region, the residues generated after processing are estimated for all the countries. The paper also addresses the use of gasification technology - an efficient thermo-chemical process for distributed power generation - either to replace fossil fuel in an existing diesel engine based power generation system or to generate electricity using a gas engine. This approach enables the implementation of electrification programs in the rural sector and gives access to grid quality power. This study estimates power generation potential at about 5000 MW and 10,000 MW by using 30% of residues generated during agro processing and 10% of forest residues from the wood processing industry, respectively. A power generation potential of 15000 MW could generate 100 terawatt-hours (TWh), about 15% of current generation in SSA. The paper also summarizes some of the experience in using the biomass gasification technology for power generation in Africa and India. The paper also highlights the techno economics and key barriers to promotion of biomass energy in sub-Saharan Africa. (C) 2011 International Energy Initiative. Published by Elsevier Inc. All rights reserved.

Influence of two photon absorption induced free carriers on coherent polariton and phonon generation in ZnTe crystals

Combination of femtosecond Kerr, two photon absorption, and impulsive stimulated Raman scattering (ISRS) experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in 〈110〉 cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two photon induced free carriers on the creation of both the polaritons and phonons is largest at 4 K where the free carrier lifetime is enhanced. The temperature dependant ISRS on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X).

Hydrogen generation fromammonia borane using nanocatalysts

The rapidly depleting petroleum feed stocks and increasing green house gas emissions around the world has necessitated a search for alternative renewable energy sources. Hydrogen with molecular weight of 2.016 g/mol and high chemical energy per mass equal to 142 MJ/kg has clearly emerged as an alternative to hydrocarbon fuels. Means for safe and cost effective storage are needed for widespread usage of hydrogen as a fuel.Chemical storage is the one of the safer ways to store hydrogen compared to compressed and liquefied hydrogen. It involves storing hydrogen in chemical bonds in molecules and materials where an on-board reaction is used to release hydrogen. Ammonia–borane, (AB,H3N·BH3) with a potential capacity of 19.6 wt% is considered a very promising solid state hydrogen storage material. It is thermally stable at ambient temperatures. There are two major routes for the generation of H2 from AB: catalytic hydrolysis/alcoholysis and catalytic thermal decomposition. There has been a flurry of research activity on the generation of H2 from AB recently. The present review deals with an overview of our efforts in developing cost-effective nanocatalysts for hydrogen generation from ammonia borane in protic solvents.

Efficacies of multivalent vs monovalent poly(ether imine) dendritic catalysts within a generation in multiple C-C bond forming reactions

Dendrimers are ideal platforms to study multivalent effects due to the presence of uniform end groups at their peripheries. This report concerns with a study of multivalent dendritic catalysts, both within and across dendrimer generations, and their effects to mediate C-C bond forming reactions on multivalent substrates that have two and three acrylate reactive sites. As many as fourteen multivalent dendritic catalysts were prepared using 0-3 generations of poly(propyl ether imine) dendrimers, incorporated with Pd(II) catalytic sites, both within and across the dendrimer generations. C-C Bond forming reactions of these substrates with iodobenzene, mediated by uniform concentration of the metal across all catalysts, showed formation of partially and fully functionalized cinnamates in varying ratios, depending on the extent of clustering of catalytic moieties at the peripheries of dendrimers within a dendrimer generation. In a given generation, higher clustering of catalytic moieties greatly assisted multiple C-C bond formations than presenting the same in lesser number. The studies demonstrate true benefits of clustering catalytic moieties within a dendrimer generation and the beneficial effects applicable to catalysis of substrates presenting more than one reactive center. (C) 2011 Elsevier B.V. All rights reserved.

(Dimethylamino)borylene and Related Complexes of Electron-Rich Metal Fragments: Generation of Nucleophile-Resistant Cations by Spontaneous Halide Ejection

Spontaneous halide ejection from a three-coordinate Lewis acid has been shown to offer a remarkable new route to cationic metal complexes featuring a linear, multiply bonded boron-donor Ligand. The exploitation of electron-rich [CpM(PR3)(2)] fragments within boryl systems of the type LnMB(hal)NR2 leads to the spontaneous formation in polar solvents of chemically robust borylene complexes, [LnM(BNR2)](+), with exceptionally low electrophilicity and short M-B bonds. This is reflected by M-B distances (ca. 1.80 angstrom for FeB systems) which are more akin to alkyl-/aryl-substituted borylene complexes and, perhaps most strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron center (Delta H = -7.4 kcal mol(-1), cf. -40.7 kcal mol(-1) for BCl3). Despite the strong pi electron release from the metal fragment implied by this suppressed reactivity and by such short M-B bonds, the barrier to rotation about the Fe=B bond in the unsymmetrical variant [CpFe(dmpe)(BN{C6H4OMe-4}Me)](+) is found to be very small (ca. 2.9 kcal mol(-1)). This apparent contradiction is rationalized by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2](+) fragment, which mean that the M-B pi interaction does not fall to zero even in the highest energy conformation.

Tar characterisation in new generation agro-residue gasifiers - Cyclone and downdraft open top twin air entry systems

This paper deals with the characterisation of tar from two configurations of bioresidue thermochemical conversion reactors designed for producer gas based power generation systems. The pulverised fuel reactor is a cyclone system (R1) and the solid bioresidue reactor (denoted R2) is an open top twin air entry system both at 75-90 kg/h capacity (to generate electricity similar to 100 kVA). The reactor, R2, has undergone rigorous test in a major Indo-Swiss programme for the tar quantity at various conditions. The former is a recent technology development. Tars collected from these systems by a standard tar collection apparatus at the laboratory at Indian Institute of Science have been analysed at the Royal Institute of Technology (KTH), Sweden. The results of these analyses show that these thermochemical conversion reactors behave differently from the earlier reactors reported in literature in so far as tar generation is concerned. The extent of tar in hot gas is about 700-800 ppm for R1 and 70-100 ppm for R2. The amounts of the major compounds - naphthalene and phenol-are much lower that what is generally understood to happen in the gasifiers in Europe. It is suggested that the longer residence times at high temperatures allowed for in these reactors is responsible for this behavior. It is concluded the new generation reactor concepts extensively tried out at lower power levels hold promise for high power atmospheric gasification systems for woody as well as pulverisable bioresidues.

Five-level inverter voltage-space phasor generation for an open-end winding induction motor drive

A topology for voltage-space phasor generation equivalent to a five-level inverter for an open-end winding induction motor is presented. The open-end winding induction motor is fed from both ends by two three-level inverters. The three-level inverters are realised by cascading two two-level inverters. This inverter scheme does not experience neutral-point fluctuations. Of the two three-level inverters only one will be switching at any instant in the lower speed ranges. In the multilevel carrier-based SPWM used for the proposed drive, a progressive discrete DC bias depending on the speed range is given to the reference wave to reduce the inverter switchings. The drive is implemented and tested with a 1 HP open-end winding induction motor and experimental results are presented.

A neural network based automatic generation control design through reinforcement learning

This paper presents the design and implementation of a learning controller for the Automatic Generation Control (AGC) in power systems based on a reinforcement learning (RL) framework. In contrast to the recent RL scheme for AGC proposed by us, the present method permits handling of power system variables such as Area Control Error (ACE) and deviations from scheduled frequency and tie-line flows as continuous variables. (In the earlier scheme, these variables have to be quantized into finitely many levels). The optimal control law is arrived at in the RL framework by making use of Q-learning strategy. Since the state variables are continuous, we propose the use of Radial Basis Function (RBF) neural networks to compute the Q-values for a given input state. Since, in this application we cannot provide training data appropriate for the standard supervised learning framework, a reinforcement learning algorithm is employed to train the RBF network. We also employ a novel exploration strategy, based on a Learning Automata algorithm,for generating training samples during Q-learning. The proposed scheme, in addition to being simple to implement, inherits all the attractive features of an RL scheme such as model independent design, flexibility in control objective specification, robustness etc. Two implementations of the proposed approach are presented. Through simulation studies the attractiveness of this approach is demonstrated.

Reinforcement learning controllers for automatic generation control in power systems having re-heat units with GRC and dead-band

A new automatic generation controller (AGC) design approach, adopting reinforcement learning (RL) techniques, was recently pro- posed [1]. In this paper we demonstrate the design and performance of controllers based on this RL approach for automatic generation control of systems consisting of units having complex dynamics—the reheat type of thermal units. For such systems, we also assess the capabilities of RL approach in handling realistic system features such as network changes, parameter variations, generation rate constraint (GRC), and governor deadband.