AC conductivity analysis and dielectric relaxation behavior of (C6H20N3)BiBr6.H2O

The N‐(3‐ammoniumpropyl)‐1,3 diammoniumpropane hexabromobismuthate (III) monohydrate exhibits a structural phase transition at T = 330 °K, which has been characterized by differential scanning calorimetric. The alternating current electrical conductivity and the dielectric relaxation properties of the (C₆H₂₀N₃)BiBr₆.H₂O compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 100 Hz–1 MHz and 290–355 °K, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. The frequency dependent alternating current conductivity is well described by Jonscher's universal power law: σ(ω,T) = σ_DC(T) + A(T)ω^s(T). The nature of direct current conductivity variation suggests the Arrhenius type of electrical conductivity. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a non‐experiential decay function φ(t) = exp(?t/τ)^β. The variation of the value of these elements with temperatures confirmed the result detected by differential scanning calorimetry measurements. Thus, the near values of activation energies obtained from the impedance and modulus spectra confirm that the transport is through an ion hopping mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamic programming for stochastic target problems and geometric flows

Given a controlled stochastic process, the reachability set is the collection of all initial data from which the state process can be driven into a target set at a specified time. Differential properties of these sets are studied by the dynamic programming principle which is proved by the Jankov-von Neumann measurable selection theorem. This principle implies that the reachability sets satisfy a geometric partial differential equation, which is the analogue of the Hamilton-Jacobi-Bellman equation for this problem. By appropriately choosing the controlled process, this connection provides a stochastic representation for mean curvature type geometric flows. Another application is the super-replication problem in financial mathematics. Several applications in this direction are also discussed. Received October 24, 2000 / final version received July 24, 2001?Published online November 27, 2001     

Analysis of clustered tensegrity structures using a modified dynamic relaxation algorithm

Tensegrities are spatial, reticulated and lightweight structures that are increasingly investigated as structural solutions for active and deployable structures. Tensegrity systems are composed only of axially loaded elements and this provides opportunities for actuation and deployment through changing element lengths. In cable-based actuation strategies, the deficiency of having to control too many cable elements can be overcome by connecting several cables. However, clustering active cables significantly changes the mechanics of classical tensegrity structures. Challenges emerge for structural analysis, control and actuation. In this paper, a modified dynamic relaxation (DR) algorithm is presented for static analysis and form-finding. The method is extended to accommodate clustered tensegrity structures. The applicability of the modified DR to this type of structure is demonstrated. Furthermore, the performance of the proposed method is compared with that of a transient stiffness method. Results obtained from two numerical examples show that the values predicted by the DR method are in a good agreement with those generated by the transient stiffness method. Finally it is shown that the DR method scales up to larger structures more efficiently.     

Catalytic asymmetric hydrogenation of heterocyclic ketone-derived hydrazones, pronounced solvent effect on the inversion of configuration

An enantioselective hydrogenation of hydrazones derived from heterocyclic ketones was developed with up to 85% ee. The enantiomeric purity was enriched to >99% ee by crystallization from EtOAc in >80% yield. Optimization studies have revealed a notable solvent effect that resulted in inversion of enantioselectivity from 85% ee in MeOH to −27% ee in DCE. The hydrazone geometry and possible hydrogenation via endocyclic alkene were examined as possible factors for the inversion of enantioselectivity.     

Magnetic control of natural convection in the horizontal Bridgman configuration: symmetric and non-symmetric cross sections

This study deals with the electromagnetic damping of free-convective flows in cavities such as those used in the crystal growth horizontal Bridgman configuration. The cavities are filled with a dilute electrically conducting alloy and are subjected to a horizontal temperature gradient. The flow is steady and laminar under an external, vertical, transversal and uniform magnetic field. Several cross sections of the cavities were investigated and can either be centro-symmetric or not. The governing equations for such problems are two coupled partial differential equations, for the velocity and the induced magnetic fields, coupled with a third integral equation for mass conservation. A finite element method has been developed, and the numerical results for the variation of the velocity and the induced magnetic field in terms of the Hartmann number show a considerable decrease in convection intensity as the Hartmann number increases. Results also reveal the presence of the well-known Hartmann and parallel layers. For non-centro-symmetric sections, results show the way the flow reorganises into two cells as the Hartmann number increases.     

Valuation of power plants by utility indifference and numerical computation

This paper presents a real option valuation model of a power plant, which accounts for physical constraints and market incompleteness. Switching costs, minimum on-off times, ramp rates, or non-constant heat rates are important characteristics that can lead, if neglected, to overestimated values. The existence of non-hedgeable uncertainties is also a feature of energy markets that can impact assets value. We use the utility indifference approach to define the value of the physical asset. We derive the associated mixed optimal switching-control problem and provide a characterization of its solution by means of a coupled system of reflected Backward Stochastic Differential Equations (BSDE). We relate this system to a system of variational inequalities, and we provide a numerical comparative study by implementing BSDE simulation algorithms, and PDE finite differences schemes.     

Similarity to a contraction and hypercontractivity of composition operators

On the Hardy spaces with , we consider the composition operators induced by analytic self-maps of the open unit disc . First, we characterize those which are similar to contractions. Then, we give some necessary and sufficient conditions for them to be hypercontractive. Finally, we prove that, among those ones, only the zero-symbol composition operator sends into with a norm less than or equal to .

     

Assembly of long carbon nanotube bridges across transparent electrodes using novel thickness-controlled dielectrophoresis

The assembly of carbon nanotubes (CNTs) across planner electrodes using dielectrophoresis (DEP) is one of the standard methods used to fabricate CNT-based devices such as sensors. The medium drag velocity caused by electrokinetic phenomena such as electrothermal and electroosmotic might drive CNTs away from the deposition area. This problem becomes critical at large-scale electrode structures due to the high attenuation of the DEP force. Herein, we simulated and experimentally validated a novel DEP setup that uses a top glass cover to minimize the medium drag velocity. The simulation results showed that the drag velocity can be reduced by 2–3 orders of magnitude compared with the basic DEP setup. The simulation also showed that the optimum channel height to result in a significant drag velocity reduction was between 100 μm and 240 μm. We experimentally report, for the first time, the assembly and alignment of CNT bridges across indium tin oxide (ITO) electrodes with spacing up to 125 μm. We also derived an equation to optimize the CNT's concentration in suspensions based on the electrode gap width and channel height. The deposition of long CNTs across ITO electrodes has potential use in transparent electronics and microfluidic systems.     

Concise and Practical Asymmetric Synthesis of a Challenging Atropisomeric HIV Integrase Inhibitor

A practical and efficient synthesis of a complex chiral atropisomeric HIV integrase inhibitor has been accomplished. The combination of a copper‐catalyzed acylation along with the implementation of the BI‐DIME ligands for a ligand‐controlled Suzuki cross‐coupling and an unprecedented bis(trifluoromethane)sulfonamide‐catalyzed tert‐butylation renders the synthesis of this complex molecule robust, safe, and economical. Furthermore, the overall synthesis was conducted in an asymmetric and diastereoselective fashion with respect to the imbedded atropisomer.