A flux-limiter method for dam-break flows over erodible sediment beds

Finite volume methods for dam-break flows over erodible sediment beds require a monotone numerical flux. In the present study we present a new flux-limiter scheme based on the Lax–Wendroff method coupled with a non-homogeneous Riemann solver and a flux limiter function. The non-homogeneous Riemann solver consists of a predictor stage for the discretization of gradient terms and a corrector stage for the treatment of source terms. The proposed method satisfy the conservation property such that the discretization of the flux gradients and the source terms are well-balanced in the numerical solution of suspended sediment models. The flux-limiter method provides accurate results avoiding numerical oscillations and numerical dissipation in the approximated solutions. Several standard test examples are considered to verify the performance and the accuracy of the proposed method.     

A tutorial on the deterministic Impulse Control Maximum Principle: Necessary and sufficient optimality conditions

This paper considers a class of optimal control problems that allows jumps in the state variable. We present the necessary optimality conditions of the Impulse Control Maximum Principle based on the current value formulation. By reviewing the existing impulse control models in the literature, we point out that meaningful problems do not satisfy the sufficiency conditions. In particular, such problems either have a concave cost function, contain a fixed cost, or have a control-state interaction, which have in common that they each violate the concavity hypotheses used in the sufficiency theorem. The implication is that the corresponding problem in principle has multiple solutions that satisfy the necessary optimality conditions. Moreover, we argue that problems with fixed cost do not satisfy the conditions under which the necessary optimality conditions can be applied. However, we design a transformation, which ensures that the application of the Impulse Control Maximum Principle still provides the optimal solution. Finally, we show for the first time that for some existing models in the literature no optimal solution exists.     

Fluorescent Studies of Salicylaldehyde and Other Related Carbonyl Compounds for the Selective and Sensitive Detection of Zinc(II) Ions in Aqueous Solution

Salicylaldehyde was found to have a high selectivity for zinc ions with simultaneous enhancement of fluorescence in aqueous buffer solution at optimum pH 8.5. The stoichiometry of the complex was determined to be 1:1 with a K(a) value of 3.4 × 10(4) M(-1) at 298 K. The fluorescence of the complex is not affected by common anions and Zn(2+) binds preferentially to salicylaldehyde in the presence of alkali, alkaline earth and heavy metal cations (Hg(2+), Cd(2+), Cr(3+) and Ni(2+)). This property is not observed with related phenolic compounds bearing a carbonyl group such as esters, amides, carboxylic acids and ketones.     

Fluorescence Characteristics and Inclusion of ICT Fluorescent Probe in Organized Assemblies

The inclusion behavior of an intramolecular charge transfer (ICT) fluorescent probe namely; 2-[3-(4-dimethylamino-phenyl)-allylidene]-tetralone (DMAPT) in organized assemblies of aqueous micellar, α- and β-cyclodextrins (CDs) and bovine serum albumin (BSA) pockets have been studied using steady-state absorption and fluorescence spectroscopy. The fluorescence characteristics (energy and intensity) of DMAPT are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement of the fluorescence intensity upon addition of different surfactants, confirming the solubilization of DMAPT in the hydrophobic micellar assembly. In addition, the fluorescence of DMAPT is more sensitive to the nature and concentration of the added CDs. In α- or β-CD solutions, the fluorescence intensity increases strongly (by 6 and 23 orders of magnitude, respectively). Upon encapsulation in the CD cavity, the molecular flexibility decreases due to the geometrical restrictions of the CD nanocavity which decreases the non radiative transition via the free rotation around the single and/or double bonds of the butadiene bridge. This was supported by finding that the fluorescence quantum yield of DMAPT increases with increasing the viscosity of the medium. The binding constants of DMAPT with micelles, α- and β-CD solutions have been calculated and were found to be highly dependent on the nature of the used surfactants or CDs. The thermodynamic parameters have been also determined and the difference in magnitude between the formed α- and β-CD-DMAPT inclusion complexes is discussed on the basis of the cavity size. Finally, the binding constant of DMAPT with bovine serum albumin was calculated, indicating the relative stability of the DMAPT-BSA complex. The energy transfer distance between BSA as a donor and DMAPT as an acceptor was obtained following the fluorescence quenching of BSA by DMAPT, via resonance mechanism as a quencher.     

Adaptive multi-resolution central-upwind schemes for systems of conservation laws

In this article, we develop an adaptive scheme for solving systems of hyperbolic conservation laws. In this scheme nonlinear shock and linear contact waves will be treated differently. The proposed scheme uses the Kurganov central-upwind scheme. Fourth-order non-oscillatory reconstruction is employed near shock only while the unlimited fifth-order reconstruction is used for smooth regions and linear contact waves. To distinguish between the smooth parts and discontinuities, we use an efficient adaptive multi-resolution technique. The advantages of the scheme are high resolution and computationally efficient since limiters are used only for shocks. Numerical experiments with one- and two-dimensional problems are presented which show the robustness of the proposed scheme.     

Raman Scattering at Resonant or Near-Resonant Conditions: A Generalized Short-Time Approximation

We investigate the dynamics of resonant Raman scattering in the course of the frequency de-tuning. The dephasing in the time domain makes the scattering fast when the photon energy is tuned from the absorption resonance. This makes frequency detuning to act as a cam-era shutter with a regulated scattering duration and provides a practical tool of controlling the scattering time in ordinary stationary measurements. The theory is applied to resonant Raman spectra of a couple of few-mode model systems and to trans-1,3,5-hexatriene and guanine-cytosine (G-C) Watson-Crick base pairs (DNA) molecules. Besides some particular physical effects, the regime of fast scattering leads to a simplification of the spectrum as well as to the scattering theory itself. Strong overtones appear in the Raman spectra when the photon frequency is tuned in the resonant region, while in the mode of fast scattering, the overtones are gradually quenched when the photon frequency is tuned more than one vibra-tional quantum below the first absorption resonance. The detuning from the resonant region thus leads to a strong purification of the Raman spectrum from the contamination by higher overtones and soft modes and purifies the spectrum also in terms of avoidance of dissociationand interfering fluorescence decay of the resonant state. This makes frequency detuning a very useful practical tool in the analysis of the resonant Raman spectra of complex systems and considerably improves the prospects for using the Raman effect for detection of foreign substances at ultra-low concentrations.     

The role of Co impurities and oxygen vacancies in the ferromagnetism of Co-doped SnO2: GGA and GGA+U studies

The electronic structure and ferromagnetic stability of Co-doped SnO₂ are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective U_Co transforms the ground state of Co-doped SnO₂ to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+U_Co calculations show that the pure substitutional Co defects in SnO₂ cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+U_Co show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of U_Co enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb U_O on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+U_Co calculations are not changed by the correction of band gap.     

Quark dynamics, thermal QCD, and the gravity dual

We perform a holographic renormalization of the supergravity action and compute the stress tensor of the dual gauge theory incorporating the logarithmic running of the gauge coupling. From the stress tensor we obtain the shear viscosity and the entropy of the medium at temperature T, and investigate the ratio η/s.