Interactions of L-serine at the active site of serine hydroxymethyltransferases: induction of thermal stability

Serine hydroxymethyltransferase (SHMT), EC 2.1.2.1, exhibits broad substrate and reaction specificity. In addition to cleaving many 3-hydroxyamino acids to glycine and an aldehyde, the enzyme also catalyzed the decarboxylation, transamination and racemization of several substrate analogues of amino acids. To elucidate the mechanism of interaction of substrates, especially L-serine with the enzyme, a comparative study of interaction of L-serine with the enzyme from sheep liver and Escherichia coli, was carried out. The heat stability of both the enzymes was enhanced in the presence of serine, although to different extents. Thermal denaturation monitored by spectral changes indicated an alteration in the apparent T, of sheep liver and E. coli SHMTs from 55 +/- 1 degrees C to 72 +/- 3 degrees C at 40 mM serine and from 67 +/- 1 degrees C to 72 +/- 1 degrees C at 20 mM serine, respectively. Using stopped flow spectrophotometry k values of (49 +/- 5)(.)10(-3) s(-1) and (69 +/- 7).10(-3) s(-1) for sheep liver and E. coli enzymes were determined at 50 mM serine. The binding of serine monitored by intrinsic fluorescence and sedimentation velocity measurements indicated that there was no generalized change in the structure of both proteins. However, visible CD measurements indicated a change in the asymmetric environment of pyridoxal 5'-phosphate at the active site upon binding of serine to both the enzymes. The formation of an external aldimine was accompanied by a change in the secondary structure of the enzymes monitored by far UV-CD spectra. Titration microcalorimetric studies in the presence of serine (8 mM) also demonstrated a single class of binding and the conformational changes accompanying the binding of serine to the enzyme resulted in a more compact structure leading to increased thermal stability of the enzyme.

Phase separation in critical and off-critical fluids: specific experimental behaviours at criticality

The phase separation in fluids close to a critical point can be observed in the form of either an interconnected pattern (critical case) or a disconnected pattern (off-critical case). These two regimes have been investigated in different ways. First, a sharp change in pattern is shown to occur very close to the critical point when the composition is varied. No crossover has been observed between the t1 behaviour (interconnected) and a t1/3 behaviour (disconnected), where t is time. This latter growth law, which occurs in the case of compact droplets, will be discussed. Second, it has been observed that a growing interconnected pattern leaves a signature in the form of small droplets. The origin of such a distribution will be discussed in terms of coalescence of domains. No distribution of this kind is observed in the off-critical case.

Robust/Optimal Temperature Profile Control of a High-Speed Aerospace Vehicle Using Neural Networks

An approximate dynamic programming (ADP)-based suboptimal neurocontroller to obtain desired temperature for a high-speed aerospace vehicle is synthesized in this paper. A I-D distributed parameter model of a fin is developed from basic thermal physics principles. "Snapshot" solutions of the dynamics are generated with a simple dynamic inversion-based feedback controller. Empirical basis functions are designed using the "proper orthogonal decomposition" (POD) technique and the snapshot solutions. A low-order nonlinear lumped parameter system to characterize the infinite dimensional system is obtained by carrying out a Galerkin projection. An ADP-based neurocontroller with a dual heuristic programming (DHP) formulation is obtained with a single-network-adaptive-critic (SNAC) controller for this approximate nonlinear model. Actual control in the original domain is calculated with the same POD basis functions through a reverse mapping. Further contribution of this paper includes development of an online robust neurocontroller to account for unmodeled dynamics and parametric uncertainties inherent in such a complex dynamic system. A neural network (NN) weight update rule that guarantees boundedness of the weights and relaxes the need for persistence of excitation (PE) condition is presented. Simulation studies show that in a fairly extensive but compact domain, any desired temperature profile can be achieved starting from any initial temperature profile. Therefore, the ADP and NN-based controllers appear to have the potential to become controller synthesis tools for nonlinear distributed parameter systems.

Two-mode quantum systems: Invariant classification of squeezing transformations and squeezed states

A general analysis of squeezing transformations for two-mode systems is given based on the four-dimensional real symplectic group Sp(4, R). Within the framework of the unitary (metaplectic) representation of this group, a distinction between compact photon-number-conserving and noncompact photon-number-nonconserving squeezing transformations is made. We exploit the U(2) invariant squeezing criterion to divide the set of all squeezing transformations into a two-parameter family of distinct equivalence classes with representative elements chosen for each class. Familiar two-mode squeezing transformations in the literature are recognized in our framework and seen to form a set of measure zero. Examples of squeezed coherent and thermal states are worked out. The need to extend the heterodyne detection scheme to encompass all of U(2) is emphasized, and known experimental situations where all U(2) elements can be reproduced are briefly described.

Toeplitz Operators with Special Symbols on Segal-Bargmann Spaces

We study the boundedness of Toeplitz operators on Segal-Bargmann spaces in various contexts. Using Gutzmer's formula as the main tool we identify symbols for which the Toeplitz operators correspond to Fourier multipliers on the underlying groups. The spaces considered include Fock spaces, Hermite and twisted Bergman spaces and Segal-Bargmann spaces associated to Riemannian symmetric spaces of compact type.

Sputter deposited LiPON thin films from powder target as electrolyte for thin film battery applications

Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio frequency (rf) magnetron sputtering from Li3PO4 powder compact target. High deposition rates and ease of manufacturing powder target compared with conventional ceramic Li3PO4 targets offer flexibility in handling and reduce the cost associated. Rf power density varied from 1.7 Wcm(-2) to 3 Wcm(-2) and N-2 flow from 10 to 30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both triply, NE and doubly. Nd coordinated form. With increased presence of NE, ionic conductivity of LiPON was found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic conductivity of 1.1 x 10(-6) Scm(-1) for optimum rf power and N-2 flow conditions. (C) 2011 Elsevier B.V. All rights reserved.

Low-frequency variability and the galactic distribution of electron-density fluctuation

A sample of 96 compact flat-spectrum extragalactic sources, spread evenly over all galactic latitudes, has been studied at 327 MHz for variability over a time interval of about 15 yr. The variability shows a dependence on galactic latitude being less both at low and high latitudes and peaking around absolute value of b approximately 15-degrees. The latitude dependence is surprisingly similar in both the galactic centre and anticentre directions. Assuming various single and multi-component distributions for the ionized, irregular interstellar plasma, we have tried to generate the observed dependence using a semi-qualitative treatment of refractive interstellar scintillations. We find that it is difficult to fit our data with any single or double component cylindrical distribution. Our data suggests that the observed variability could be influenced by the spiral structure of our Galaxy.

Combustion synthesis and properties of the NASICON family of materials

The fine-particle NASICON family of materials, MZr2P3O12(where M = Na, K, ½Ca and ¼Zr) and NbZrP3O12, have been prepared by the combustion of aqueous heterogeneous mixtures of stoichiometric amounts of metal nitrate, zirconyl nitrate, niobium phosphate, diammonium hydrogen phosphate, ammonium perchlorate and carbohydrazide (CH) at 400 °C. The formation of NASICON materials was confirmed by powder X-ray diffraction (XRD), IR, solid-state (31P) NMR spectroscopy and thermal expansion coefficient measurements. The combustion-synthesized NASICON powders have an average agglomerate size of 9�13 µm with a specific surface area varying from 8 to 28 m2 g�1. The powders pelletized and sintered in the range 1100�1200 °C for 5 h achieved 95�97% theoretical density and showed fine-grain microstructure. The coefficient of thermal expansion of a sintered compact was measured up to 500 °C and ranged from �1.5 × 10�6°C�1 to 1.0 × 10�6°C�1 depending on the composition.

Seyfert Galaxies: Nuclear Radio Structure And Unification

A radio study of a carefully selected sample of 20 Seyfert galaxies that are matched in orientation-independent parameters, which are measures of intrinsic active galactic nucleus power and host galaxy properties, is presented to test the predictions of the unified scheme hypothesis. Our sample sources have core flux densities greater than 8 mJy at 5 GHz on arcsec scales due to the feasibility requirements. These simultaneous parsec-scale and kiloparsec-scale radio observations reveal (1) that Seyfert 1 and Seyfert 2 galaxies have an equal tendency to show compact radio structures on milliarcsecond scales, (2) the distributions of parsec-scale and kiloparsec-scale radio luminosities are similar for both Seyfert 1 and Seyfert 2 galaxies, (3) there is no evidence for relativistic beaming in Seyfert galaxies, (4) similar distributions of source spectral indices in spite of the fact that Seyferts show nuclear radio flux density variations, and (5) the distributions of the projected linear size for Seyfert 1 and Seyfert 2 galaxies are not significantly different as would be expected in the unified scheme. The latter could be mainly due to a relatively large spread in the intrinsic sizes. We also find that a starburst alone cannot power these radio sources. Finally, an analysis of the kiloparsec-scale radio properties of the CfA Seyfert galaxy sample shows results consistent with the predictions of the unified scheme.

The role of Compton and Raman scattering in the quasar continuum

There are three ways in which an electromagnetic wave can undergo scattering in a plasma: (i) when the scattering of radiation occurs by a single electron, it is called Compton Scattering (CS); (ii) if it occurs by a longitudinal electron plasma mode, it is called Stimulated Raman Scattering (SRS), and (iii) if it occurs by a highly damped electron plasma mode, it is called Stimulated Compton Scattering (SCS). The non-thermal continuum of quasars is believed to be produced through the combined action of synchrotron and inverse Compton processes, which are essentially single-particle processes. Here, we investigate the role of SRS and SCS in the generation of continuum radiation from these compact objects. It is shown as an example that the complete spectrum of 3C 273 can be reproduced by suitably combining SCS and SRS. The differential contributions of SCS and SRS under different values of the plasma parameters are also calculated.

Dynamics of Fractional Brownian Walks

We investigate the dynamics of polymers whose solution configurations are represented by fractional Brownian walks. The calculation of the two dynamical quantities considered here, the longest relaxation time tau(r) and the intrinsic viscosity [eta], is formulated in terms of Langevin equations and is carried out within the continuum approach developed in an earlier paper. Our results for tau(r) and [eta] reproduce known scaling relations and provide reasonable numerical estimates of scaling amplitudes. The possible relevance of the work to the study of globular proteins and other compact polymeric phases is discussed.

The Equations of Equilibrium in Orthogonal Curvilinear Reference Coordinates

Analytical solutions to problems in finite elasticity are most often derived using the semi-inverse approach along with the spatial form of the equations of motion involving the Cauchy stress tensor. This procedure is somewhat indirect since the spatial equations involve derivatives with respect to spatial coordinates while the unknown functions are in terms of material coordinates, thus necessitating the use of the chain rule. In this classroom note, we derive compact expressions for the components of the divergence, with respect to orthogonal material coordinates, of the first Piola-Kirchhoff stress tensor. The spatial coordinate system is also assumed to be an orthogonal curvilinear one, although, not necessarily of the same type as the material coordinate system. We show by means of some example applications how analytical solutions can be derived more directly using the derived results.

Improved preprocessing methods for modulo scheduling algorithms

Instruction scheduling with an automaton-based resource conflict model is well-established for normal scheduling. Such models have been generalized to software pipelining in the modulo-scheduling framework. One weakness with existing methods is that a distinct automaton must be constructed for each combination of a reservation table and initiation interval. In this work, we present a different approach to model conflicts. We construct one automaton for each reservation table which acts as a compact encoding of all the conflict automata for this table, which can be recovered for use in modulo-scheduling. The basic premise of the construction is to move away from the Proebsting-Fraser model of conflict automaton to the Muller model of automaton modelling issue sequences. The latter turns out to be useful and efficient in this situation. Having constructed this automaton, we show how to improve the estimate of resource constrained initiation interval. Such a bound is always better than the average-use estimate. We show that our bound is safe: it is always lower than the true initiation interval. This use of the automaton is orthogonal to its use in modulo-scheduling. Once we generate the required information during pre-processing, we can compute the lower bound for a program without any further reference to the automaton.

Influence of the roughness of aggregate surface on the interface bond strength

An experimental investigation on the bond strength of the interface between mortar and aggregate is reported. Composite compact specimens were used for applying Mode I and Mode 11 loading effects. The influence of the type of mortar and type of aggregate and its roughness on the bond strength of the interface has been studied. It has been observed that the bond strength of the interface in tension is significantly low, though the mortars exhibited higher strength. The highest tensile bond strength values have been observed with rough concrete surface with M-13 mortar. The bond strength of the interface in Mode I load depends on the type of aggregate surface and its roughness, and the type of mortar, The bond strength of the interface between mortar M-13 cast against rough concrete in direct tension seems to be about one third of the strength of the mortar. However, it is about 1/20th to 1/10th with the mortar M-12 in sandwiched composite specimens. The bond strength of the interface in shear (Mode IT) significantly increases as the roughness and the phase angle of the aggregate surface increase. The strength of mortar on the interface bond strength has been very significant. The sandwiched composite specimens show relatively low bond strength in Mode I loading. The behavior of the interface in both Mode I and Mode 11 loading effects has been brittle, indicating catastrophic failure. (C) 2002 Elsevier Science Ltd. All rights reserved.

The effect of powder processing on densification, microstructure and mechanical properties of hydroxyapatite

The influence of powder processing and sintering temperature on densification, microstructure and mechanical properties of hydroxyapatite (HAp) ceramics was studied. The as-dried, calcined and processed HAp powders were uniaxially compacted and sintered at various temperatures (1000-1400 degreesC) for 3 h. The as-dried and processed powders, attained 97% of theoretical density (TD) at 1100 degreesC) at higher sintering temperatures, the density of the as-dried powder compact was found to decrease. A uniform microstructure with fine grain size (2.3 pm) was observed for material obtained from processed powder, whereas exaggerated grain growth with closed pores were observed in as-dried and unprocessed powder compacts. The Vickers' hardness, fracture toughness and flexural strength of HAp were determined and a maximum value of 6.3 GPa and 0.88 MPam(1/2) and 60.3 MPa, respectively were obtained for processed compact. The processing of HAp has improved its densification, microstructure homogeneity and mechanical properties. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.