A two timescale stochastic approximation scheme for simulation-based parametric optimization

A two timescale stochastic approximation scheme which uses coupled iterations is used for simulation-based parametric optimization as an alternative to traditional "infinitesimal perturbation analysis" schemes, It avoids the aggregation of data present in many other schemes. Its convergence is analyzed, and a queueing example is presented.

New La2CuO4 derivatives La(2-2x)Sr(2x)Cu(1-x)M(x)O(4) (M=Ti, Mn, Fe, or Ru): A study of linear Cu-O-M electronic interaction in two dimensions

Oxides of the general formula La2-2xSr2xCu1-xII,M(x)(IV)O(4) (M = Ti, Mn, Fe, or Ru), crystallizing in the tetragonal K,NIF, structure, have been synthesized. For M=Ti, only the x=0,5 member could be prepared, while for M=Mn and Fe, the composition range is 0 Cu(III)-O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La2-2xSr2xCu1-xFexO4 for x less than or equal to 0.20 renders the samples metallic but not superconducting. (C) 1997 Academic Press.

Novel correlations in two dimensions: Two-body problem

We discuss a many-body Hamiltonian with two- and three-body interactions in two dimensions introduced recently by Murthy, Bhaduri and Sen. Apart from an analysis of some exact solutions in the many-body system, we analyse in detail the two-body problem which is completely solvable. We show that the solution of the two-body problem reduces to solving a known differential equation due to Heun. We show that the two-body spectrum becomes remarkably simple for large interaction strengths and the level structure resembles that of the Landau levels. We also clarify the 'ultraviolet' regularization which is needed to define an inverse-square potential properly and discuss its implications for our model.

Role of two consecutive alpha,beta-dehydrophenylalanines in peptide structure: Crystal and molecular structure of Boc-Leu-Delta Phe-Delta Phe-Ala-Phe-NHMe

An N-alpha-protected model pentapeptide containing two consecutive Delta Phe residues, Boc-Leu-Delta Phe-Delta Phe-Ala-Phe-NHMe, has been synthesized by solution methods and fully characterized. H-1-nmr studies provided evidence for the occurrence of a significant population of a conformer having three consecutive, intramolecularly II-bonded beta-bends in solution. The solid state structure has been determined by x-ray diffraction methods. The crystals grown from aqueous methanol are orthorhombic, space group P2(1)2(1)2(1),, a = 11.503(2), b = 16.554(2), c = 22.107(3) Angstrom, V = 4209(1) Angstrom,(3) and Z = 4. The x-ray data were collected on a CAD4 diffractometer using CuKalpha radiation (lambda = 1.5418 Angstrom). The structure was determined using direct methods and refined by full-matrix least-squares procedure. The R factor is 5.3%. The molecule is characterized by a right handed 3(10)-helical conformation ((phi) = -68.2 degrees (psi) = -26.3 degrees), which is made up of two consecutive type III beta-bends and one type I beta-bend. In the solid state the helical molecules are aligned head-to-tail, thus forming long rod like structures. A comparison with other peptide structures containing consecutive Delta Phe residues is also provided. The present study confirms that the -Delta Phe-Delta Phe-sequence can be accommodated in helical structures. (C) 1997 John Wiley & Sons, Inc.

The two-step positive temperature coefficient in resistance characteristics of n-(Ba,Pb)TiO3 ceramics created through inclusion of grain boundary modifier additives

Donor-doped n-(Ba,Pb)TiO3 polycrystalline ceramics exhibit distinctly two-step positive temperature coefficient of resistance (PTCR) characteristics when formulated with suitable combinations of B2O3 and Al2O3 as grain boundary modifiers by heterogeneous addition. B2O3 or Al2O3 when added singularly resulted in either steep or broad PTCR jumps respectively across the phase transition. The two-step PTCR is attributed to the activation of the acceptor states, created through B2O3 and Al2O3, for various temperature regimes above the Curie point (T-c). The changing pattern of trap states is evident from the presence of Ti4+-O--Al3+ type hole centres in the grain boundary layer regions, identified in the electron paramagnetic resonance (EPR) spectra. That charge redistribution occurs among the inter-band gap defect states on crossing the Curie temperature is substantiated by the temperature coefficient in the EPR results. Capacitance-voltage results clearly show that there is an increase in the density of trap states with the addition of B2O3 and Al2O3. The spread in energy values of these trap states is evident from the large change in barrier height (phi similar or equal to 0.25-0.6 eV) between 500 and 650 K.

Transformation of a laterally diverging boundary layer flow to a two-dimensional boundary layer flow

Laterally diverging boundary layer flow over a plate is shown to be reducible to a two-dimensional flow by modelling the diverging streamlines by a source flow.

Absolute Entropy and Energy of Carbon Dioxide Using the Two-Phase Thermodynamic Model

The two-phase thermodynamic (2PT) model is used to determine the absolute entropy and energy of carbon dioxide over a wide range of conditions from molecular dynamics trajectories. The 2PT method determines the thermodynamic properties by applying the proper statistical mechanical partition function to the normal modes of a fluid. The vibrational density of state (DoS), obtained from the Fourier transform of the velocity autocorrelation function, converges quickly, allowing the free energy, entropy, and other thermodynamic properties to be determined from short 20-ps MD trajectories. The anharmonic effects in the vibrations are accounted for by the broadening of the normal modes into bands from sampling the velocities over the trajectory. The low frequency diffusive modes, which lead to finite DoS at zero frequency, are accounted for by considering the DoS as a superposition of gas-phase and solid-phase components (two phases). The analytical decomposition of the DoS allows for an evaluation of properties contributed by different types of molecular motions. We show that this 2PT analysis leads to accurate predictions of entropy and energy of CO2 over a wide range of conditions (from the triple point to the critical point of both the vapor and the liquid phases along the saturation line). This allows the equation of state of CO2 to be determined, which is limited only by the accuracy of the force field. We also validated that the 2PT entropy agrees with that determined from thermodynamic integration, but 2PT requires only a fraction of the time. A complication for CO2 is that its equilibrium configuration is linear, which would have only two rotational modes, but during the dynamics it is never exactly linear, so that there is a third mode from rotational about the axis. In this work, we show how to treat such linear molecules in the 2PT framework.

Nonlinear dynamics and chaotic motions in feedback-controlled two- and three-degree-of-freedom robots

The dynamics of a feedback-controlled rigid robot is most commonly described by a set of nonlinear ordinary differential equations. In this paper we analyze these equations, representing the feedback-controlled motion of two- and three-degrees-of-freedom rigid robots with revolute (R) and prismatic (P) joints in the absence of compliance, friction, and potential energy, for the possibility of chaotic motions. We first study the unforced or inertial motions of the robots, and show that when the Gaussian or Riemannian curvature of the configuration space of a robot is negative, the robot equations can exhibit chaos. If the curvature is zero or positive, then the robot equations cannot exhibit chaos. We show that among the two-degrees-of-freedom robots, the PP and the PR robot have zero Gaussian curvature while the RP and RR robots have negative Gaussian curvatures. For the three-degrees-of-freedom robots, we analyze the two well-known RRP and RRR configurations of the Stanford arm and the PUMA manipulator respectively, and derive the conditions for negative curvature and possible chaotic motions. The criteria of negative curvature cannot be used for the forced or feedback-controlled motions. For the forced motion, we resort to the well-known numerical techniques and compute chaos maps, Poincare maps, and bifurcation diagrams. Numerical results are presented for the two-degrees-of-freedom RP and RR robots, and we show that these robot equations can exhibit chaos for low controller gains and for large underestimated models. From the bifurcation diagrams, the route to chaos appears to be through period doubling.

Post-seizure EEG fractal dimension of first ECT predicts antidepressant response at two weeks

Background: Duration of seizure by itself is an insufficient criterion for a therapeutically adequate seizure in ECT. Therefore, measures of seizure EEG other than its duration need to be explored as indices of seizure adequacy and predictors of treatment response. We measured the EEG seizure using a geometrical method-fractal dimension (FD) and examined if this measure predicted remission. Methods: Data from an efficacy study on melancholic depressives (n = 40) is used for the present exploration. They received thrice or once weekly ECTs, each schedule at two energy levels - high or low energy level. FD was computed for early-, mid- and post-seizure phases of the ictal EEG. Average of the two channels was used for analysis. Results: Two-thirds of the patients (n = 25) were remitted at the end of 2 weeks. As expected, a significantly higher proportion of patients receiving thrice weekly ECT remitted than in patients receiving once weekly ECT. Smaller post-seizure FD at first ECT is the only variable which predicted remission status after six ECTs. within the once weekly ECT group too, smaller post-seizure FD was associated with remission status. Conclusions: Post-seizure FD is proposed as a novel measure of seizure adequacy and predictor of treatment response. Clinical implications: Seizure measures at first ECT may guide selection of ECT schedule to optimize ECT. Limitations: The study examined short term antidepressant effects only. The results may not be generalized to medication-resistant depressives. (C) 1999 Elsevier Science B.V. All rights reserved.

Probing the limits of steric constraints in the oligomerization of copper(I) complexes: structures of two sterically congested oligomers

Oligomeric copper(I) clusters are formed by the insertion reaction of copper(I) aryloxides into heterocumulenes. The effect of varying the steric demands of the heterocumulene and the aryloxy group on the nuclearity of the oligomers formed has been probed. Reactions with copper(I)2-methoxyphenoxide and copper(I)2-methylphenoxide with PhNCS result in the formation of hexameric complexes hexakis[N-phenylimino(aryloxy)methanethiolato copper(I)] 3 and 4 respectively. Single crystal X-ray data confirmed the structure of 3. Similar insertion reactions of CS2 with the copper(I) aryloxides formed by 2,6-di-tert-butyl-4-methylphenol and 2,6-dimethylphenol result in oligomeric copper(I) complexes 7 and 8 having the (aryloxy)thioxanthate ligand. Complex 7 was confirmed to be a tetramer from single crystal X-ray crystallography. Reactions carried out with 2-mercaptopyrimidine, which has ligating properties similar to N-alkylimino(aryloxy)methanethiolate, result in the formation of an insoluble polymeric complex 11. The fluorescence spectra of oligomeric complexes are helpful in determining their nuclearity. Ir has been shown that a decrease in the steric requirements of either the heterocumulene or aryloxy parts of the ligand can compensate for steric constraints acid facilitate oligomerization. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthesis of two designed hairpin peptides on a newly developed 1,6-hexanediol diacrylate (HDODA)-crosslinked polystyrene resin

Synthesis of two designed hairpin peptides on 1,6-hexanediol diacrylate crosslinked polystyrene support using the standard solid phase methodology is described. Both the peptides are obtained in high yield and purity. The new polymeric system is an ideal support for the synthesis of hairpin peptides, which is a very difficult task by the solid phase method.

The onset of oscillatory Marangoni convection in a two-layer system of conducting fluid in the presence of a uniform magnetic field

A combination of numerical and analytical techniques is used to analyse the effect of magnetic field and encapsulated layer on the onset of oscillatory Marangoni instability in a two layer system. Oscillatory Marangoni instability is possible for a deformed free surface only when the system is heated from above. It is observed that the existence of a second layer has a positive effect on Marangoni overstability with magnetic field whereas it has an opposite effect without magnetic field.

Total peroxidase activity and peroxidase isoforms as modified by salt stress in two cultivars of fox-tail millet with differential salt tolerance

The effect of NaCl on total peroxidase activity, induction of isoperoxidases and lipid peroxidation in 5-day-old seedlings of two contrasting genotypes of Setaria italica L. (Prasad, a salt tolerant cultivar and Lepakshi, a salt susceptible cultivar), was studied. Total peroxidase activity increased under NaCl salinity and the degree of elevation in the activity was salt concentration dependent. Nevertheless, a greater activity was recorded in the tolerant cultivar (cv Prasad) compared to the susceptible (cv Lepakshi) one in all days of sampling. Further, the pattern of isoperoxidases was modified during stress conditions as evident from the electrophoregrams. Although, five acidic isoforms were detected in both cultivars, differences were found between the cultivars. Furthermore, it was observed that acidic isoperoxidases were strongly expressed and an acidic isoperoxidase, A(3p) (27 kDa) is specifically found in the tolerant cultivar (cv Prasad) under NaCl stress. This isoform was partially purified and found to be thermostable with pr 5.5 and the optimum pH 7.4. A close correlation exists between the rate of lipid peroxidation in terms of malonaldehyde (MDA) content and total peroxidase activity per gram fresh weight with salt tolerance of the two cultivars. The tolerant cultivar (cv Prasad) had low MDA content and high total peroxidase activity than the susceptible variety (cv Lepakshi) during salinity stress. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.

Two dimensional weak pseudomanifolds on seven vertices

In this article we have explicitly determined all the 2-dimensional weak pseudomanifolds on 7 vertices. We have proved that there are (up to isomorphism) 13 such weak pseudomanifolds. The geometric carriers of them are 6 topological spaces, three of which are not manifolds.

Two regiospecific alternative strategies in the synthesis of (-)-valeranone

Two regiospecific modifications have been developed in the synthesis of valeranone. The first one is based on the regiospecific protection of a diol and the second is based on the Wittig reaction of a hemiacetal.