Note on Coherent States and Adiabatic Connections, Curvatures

We give a possible generalization to the example in the paper of Zanardi and Rasetti (quant-ph/9904011). For this generalized one explicit forms of adiabatic connection, curvature and etc. are given.Comment: Latex file, 12 page

Interaction of substrate uridyl 3',5'-adenosine with ribonuclease A: a molecular dynamics study

A wealth of information available from x-ray crystallographic structures of enzyme-ligand complexes makes it possible to study interactions at the molecular level. However, further investigation is needed when i) the binding of the natural substrate must be characterized, because ligands in the stable enzyme-ligand complexes are generally inhibitors or the analogs of substrate and transition state, and when ii) ligand binding is in part poorly characterized. We have investigated these aspects in the binding of substrate uridyl 3',5'-adenosine (UpA) to ribonuclease A (RNase A). Based on the systematically docked RNase A-UpA complex resulting from our previous study, we have undertaken a molecular dynamics simulation of the complex with solvent molecules. The molecular dynamics trajectories of this complex are analyzed to provide structural explanations for varied experimental observations on the ligand binding at the B2 subsite of ribonuclease A. The present study suggests that B2 subsite stabilization can be effected by different active site groups, depending on the substrate conformation. Thus when adenosine ribose pucker is O4'-endo, Gln69 and Glu111 form hydrogen-bonding contacts with adenine base, and when it is C2'-endo, Asn71 is the only amino acid residue in direct contact with this base. The latter observation is in support of previous mutagenesis and kinetics studies. Possible roles for the solvent molecules in the binding subsites are described. Furthermore, the substrate conformation is also examined along the simulation pathway to see if any conformer has the properties of a transition state. This study has also helped us to recognize that small but concerted changes in the conformation of the substrate can result in substrate geometry favorable for 2',3' cyclization. The identified geometry is suitable for intraligand proton transfer between 2'-hydroxyl and phosphate oxygen atom. The possibility of intraligand proton transfer as suggested previously and the mode of transfer before the formation of cyclic intermediate during transphosphorylation are discussed

Invariants and chaos in the Volterra gyrostat without energy conservation

The model of the Volterra gyrostat (VG) has not only played an important role in rigid body dynamics but also served as the foundation of low-order models of many naturally occurring systems. It is well known that VG possesses two invariants, or constants of motion, corresponding to kinetic energy and squared angular momentum, giving oscillatory solutions to its equations of motion. Nine distinct subclasses of the VG have been identified, two of which the Euler gyroscope and Lorenz gyrostat are each known to have two constants. This paper provides a complete characterization of constants of motion of the VG and its subclasses, showing how these enjoy two constants of motion even when rendered in terms of a non-invertible transformation of parameters, leading to a transformed Volterra gyrostat (tVG). If the quadratic coefficients of the tVG sum to zero, as they do for the VG, the system conserves energy. In all of these cases, the flows preserve volume; however, physical models where the quadratic coefficients do not sum to zero are ubiquitous, and characterization of constants of motion and the resulting dynamics for this more general class of models with volume conservation but without energy conservation is lacking. We provide such a characterization for each of the subclasses. Those with three linear feedback terms have no constants of motion, and thereby admit rich dynamics including chaos. This gives rise to a broad class of three-dimensional volume conserving chaotic flows, arising naturally from model reduction techniques

Minimal chaotic models from the Volterra gyrostat

Low-order models obtained through Galerkin projection of several physically important systems (e.g., Rayleigh-B\'enard convection, mid-latitude quasi-geostrophic dynamics, and vorticity dynamics) appear in the form of coupled gyrostats. Forced dissipative chaos is an important phenomenon in these models, and this paper considers the minimal chaotic models, in the sense of having the fewest external forcing and linear dissipation terms, arising from an underlying gyrostat core. It is shown here that a critical distinction is whether the gyrostat core (without forcing or dissipation) conserves energy, depending on whether the sum of the quadratic coefficients is zero. The paper demonstrates that, for the energy-conserving case of the gyrostat core, the requirement of a characteristic pair of fixed points that repel the chaotic flow dictates placement of forcing and dissipation in the minimal chaotic models. In contrast, if the core does not conserve energy, the forcing can be arranged in additional ways for chaos to appear, especially for the cases where linear feedbacks render fewer invariants in the gyrostat core. In all cases, the linear mode must experience dissipation for chaos to arise. Thus, the Volterra gyrostat presents a clear example where the arrangement of fixed points circumscribes more complex dynamics

Superfluid-Insulator transition of ultracold atoms in an optical lattice in the presence of a synthetic magnetic field

We study the Mott insulator-superfluid transition of ultracold bosonic atoms in a two-dimensional square optical lattice in the presence of a synthetic magnetic field with p/q (p and q being co-prime integers) flux quanta passing through each lattice plaquette. We show that on approach to the transition from the Mott side, the momentum distribution of the bosons exhibits q precursor peaks within the first magnetic Brillouin zone. We also provide an effective theory for the transition and show that it involves q interacting boson fields. We construct, from a mean-field analysis of this effective theory, the superfluid ground states near the transition and compute, for q=2,3, both the gapped and the gapless collective modes of these states. We suggest experiments to test our theory.Comment: 4 pages, 4 figs; v

Formation and characterization of borohydride reduced electroless nickel deposits

The present work aims to study the formation of electroless Ni-B deposits and evaluation of their characteristic properties. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni-B deposits. The influence of variation in bath constituents as well as operating conditions on the plating rate, and, the nickel and boron content, of the resultant Ni-B deposits were studied. Selected deposits were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), evolved gas analysis (EGA), vibrating sample magnetometer (VSM) and transmission electron microscope (TEM), respectively, for assessing the phase content, phase transformation behaviour, liberation of hydrogen during crystallization, saturation magnetic moment and micro-structural features. The corrosion resistance of Ni-B deposits, in 3.5% sodium chloride solution, both in as-plated and heat-treated (450 ◦C/1 h) conditions, was also evaluated by potentiostatic polarization and electrochemical impedance studies. XRD patterns reveal that Ni-B deposits of the present study are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. DSC traces exhibit two exothermic peaks at 306 and 427 ◦C, corresponding to the phase transformation of amorphous Ni-B to crystalline nickel and Ni3B phases and the transformation of a higher phase compound to Ni3B and Ni2B, respectively. TEM microstructures and EGA strongly support the occurrence of phase transitions at 306 and 427 ◦C. Electroless Ni-B deposits demonstrate a moderate corrosion resistance in 3.5% sodium chloride solution. The extent of corrosion resistance offered by electroless Ni-B deposits is relatively less compared to electroless Ni-9 wt.% P deposit

Electroless Ni–P/Ni–B duplex coatings: preparation and evaluation of microhardness, wear and corrosion resistance

The present work deals with the formation of Ni–P/Ni–B duplex coatings by electroless plating process and evaluation of their hardness, wear resistance and corrosion resistance. The Ni–P/Ni–B duplex coatings were prepared using dual baths (acidic hypophosphite- and alkaline borohydride-reduced electroless nickel baths) with both Ni–P and Ni–B as inner layers and with varying single layer thickness. Scanning electron microscopy (SEM) was used to assess the duplex interface. The microhardness, wear resistance and corrosion resistance of electroless nickel duplex coatings were compared with electroless Ni–P and Ni–B coatings of similar thickness. The study reveals that the Ni–P and Ni–B coatings are amorphous in their as-plated condition and upon heat-treatment at 450 ◦C for 1 h, both Ni–P and Ni–B coatings crystallize and produce nickel, nickel phosphide and nickel borides in the respective coatings. All the three phases are formed when Ni–P/Ni–B and Ni–B/Ni–P duplex coatings are heat-treated at 450◦C for 1 h. The duplex coatings are uniform and the compatibility between the layers is good. The microhardness, wear resistance and corrosion resistance of the duplex coating is higher than Ni–P and Ni–B coatings of similar thickness. Among the two types of duplex coatings studied, hardness and wear resistance is higher for coatings having Ni–B coating as the outer layer whereas better corrosion resistance is offered by coatings having Ni–P coating as the outer layer

Electro- and electroless plated coatings for corrosion protection

This chapter presents an overview of the fundamental aspects of electro- and electroless deposition process, the mechanism of deposition, alloy deposition, etc. and the utility of these coatings for corrosion protection. Both electro- and electroless deposition techniques are simple, cost-effective and offer unique advantages for preparing deposits with desirable qualities. In electrodeposition, the plating rate, stability of the bath and the number of turnovers are very high but the resultant coatings lack uniformity on complex shapes and blind holes and they need a post-finishing treatment to achieve the desired performance. In electroless deposition, the plating rate, bath stability and the number of turnovers are relatively less but the resultant coatings are more uniform and do not require post-finishing treatment. Electroplated coatings offer corrosion protection to the substrate metals in three possible ways: (i) cathodic protection; (ii) barrier action; and (iii) environmental modification or control. The corrosion performance of electroplated coatings is influenced by a variety of factors, which include structure, crystallographic texture, grain size, porosity, impurities and triple junctions, interactions involving metallic underplates and cleanliness or freedom from processing contaminants. Electroless nickel does not perform as a sacrificial coating in the same way that electrodeposited Zn or Cd performs on steel substrate to provide protection against corrosion. It behaves as a true barrier coating, protecting the substrate by sealing it off from the corrosive environments. Consequently, the thickness of the deposit and the absence of porosity are of great importance. The electroless nickel coating shows superior corrosion resistance compared to electroplated nickel coatings. The most important factors that determine the corrosion resistance of electroless plated coatings are: substrate composition, structure and surface finish; pretreatment of the substrate to achieve a clean, uniform surface; adequate deposit thickness to meet the severity and time of exposure to the corrosive environment; the properties of the deposit (composition, porosity, internal stress etc.) which depends on pH, formulation and prolonged use (turnover) of the plating solution; post plating treatments of the coating such as passivation and annealing; and the aggressiveness of the corrosive environment condition. Electro- and electroless deposited ternary/quaternary alloy coatings, composite coatings, duplex coatings, graded coatings and multilayer coatings are some of the promising developments to achieve improved corrosion resistance

Cathodic electrosynthesis of alumina thin films and powders

The present work explores the utility of cathodic electrosynthesis methodology in the preparation of alumina thin films and powders

Electroless Ni–B coatings: preparation and evaluation of hardness and wear resistance

The present work aims to study the hardness and wear resistance of electroless Ni–B coatings. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni–B coatings. The structure, microhardness and wear resistance of electroless Ni–B coatings, both in as-plated and heat-treated conditions, were evaluated using X-ray diffraction (XRD), Leitz microhardness tester and a pin-on-disc wear test apparatus. XRD patterns reveal that electroless Ni–B coatings are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. The microhardness of the electroless Ni–B coatings increases with increase in heat-treatment temperature and exhibit two maxima in the hardness vs. heattreatment temperature curve. The specific wear rate increases with increase in applied load from 20 to 40 N and at all applied loads, the specific wear rate and coefficient of friction are less for heat-treated electroless Ni–B deposits compared to that obtained for as-plated ones. The wear process of electroless Ni–B coatings is governed by an adhesive wear mechanism