An integrated decision support tool for airlines schedule recovery during irregular operations

This paper presents a decision support tool for airlines schedule recovery during irregular operations. The tool provides airlines control centers with the capability to develop a proactive schedule recovery plan that integrates all flight resources. A rolling horizon modeling framework, which integrates a schedule simulation model and a resource assignment optimization model, is adopted for this tool. The schedule simulation model projects the list of disrupted flights in the system as function of the severity of anticipated disruptions. The optimization model examines possible resource swapping and flight re-quoting to generate an efficient schedule recovery plan that minimizes flight delays and cancellations. A detailed example that illustrates the application of the tool to recover the schedule of a major US air-carrier during a hypothetical ground delay program scenario is presented. The results of several experiments that illustrates overall model performance in terms of solution quality and computation experience are also given.     

Emission yields and the standard model in glow discharge optical emission spectroscopy: Links to the underlying physics and analytical interpretation of the experimental data

The so-called standard model is a semi-empirical, physically based model describing the signal response in the glow discharge optical emission spectroscopy. Its assumptions, implications and limitations are reviewed, including links to the underlying fundamental physics. Its implementation and practical use as a calibration model in analytical applications is described, including the determination of its key parameters, the emission yields. Some data processing techniques based on the standard model are reviewed, including the multi-element calibration fitting and the signal decomposition in complex spectra. It is shown how the emission yields can be used to collect information about the glow discharge excitation.     

Nematic-isotropic phase behaviours of polydisperse polymer/liquid crystal systems: Applicability of continuous thermodynamics

Phase behaviours of polydisperse polystyrene (PS)/nematic liquid crystals (LCs) P-ethoxy-benzylidene-p-n-butylaniline (EBBA) are investigated by thermo-optical analysis (TOA) technique. In this study, to describe nematic-isotropic transition of the polydisperse PS/EBBA systems, a continuous distribution function to obtain the composition of polydisperse polymers is considered precisely. We apply these molar mass distributions to the extended Flory–Huggins model. The proposed semi-empirical model gives a remarkable agreement with experimental data for the model systems.     

At-edge minima in elastic photon scattering amplitudes for dilute aqueous ions

Elastic photon scattering and absorption in the vicinity of core atomic orbital energies give rise to resonances in the elastic photon scattering cross-section. Of interest is whether a dilute-ion aqueous system provides an environment suitable for testing independent particle approximation (IPA) predictions. Predictions of the energy of these resonances have been determined for a Dirac–Slater exchange potential with a Latter tail. At BM28 (ESRF), tuneable X-rays were obtained at eV resolution using a 1 1 1 Si monochromator. From target systems including Cu²⁺ and Zn²⁺, the X-rays were scattered through high angle from an aqueous medium contained in a thin Perspex cell provided with 8 μm kaplan windows. An energy resolution of ∼500 eV from the HPGe detector was adequate to separate the elastic scattering signal from K_α radiation but not from Compton or K_β contributions. The Compton contribution from the medium was removed assuming validity of the relativistic impulse approximation. The contribution due to K_β fluorescence and the resonant X-ray Raman scattering process were handled by assuming the branching ratio for K_α and K_β contributions to be constant and to be accurately described by fluorescent yields measured above edge. At ionic concentrations ranging from 0.01 to 0.1 mol/l, resonance structures accord with predictions of elastic scattering cross-sections calculated within IPA. Amplitudes calculated using modified form-factors and anomalous scatter factors computed from a Dirac–Slater exchange potential were convolved with a Lorentzian of several eV (FWHM).     

Bifunctional copper modified graphitic carbon nitride catalysts for efficient tetracycline removal: Synergy of adsorption and photocatalytic degradation

In order to efficiently remove tetracycline in wastewater through the synergistic effect of adsorption and photocatalytic degradation, a series of novel composite materials (Cu doped g-C₃N₄) were synthesized by two-pot hydrothermal method. It was found that the composite materials with optimized ratio (Cu/CN-1) displayed outstanding adsorption and photocatalytic performance as compared with pure g-C₃N₄ photocatalyst. The removal efficiency of tetracycline (TC, 50 mg/L) reached almost 99% within 30 min by Cu/CN-1 through the synergy of adsorption and photocatalysis under visible-light irradiation, which was the highest removal efficiency ever reported. The adsorption kinetics and isotherms of TC on the Cu/CN-1 were well fitted with the pseudo-second-order kinetic model and Langmuir model, respectively. Moreover, it was confirmed that the main effective reactive groups were O₂⁻ and h⁺ in photocatalytic process. The Cu/CN-1 exhibited high stability and excellent reusability after five cycle experiments. Finally, the mechanism of synergy between Cu and g-C₃N₄ was proposed: on the one hand, the decoration of Cu particles significantly increased the adsorption sites of Cu/CN-1 to tetracycline, on the other hand, the modification of Cu particles effectively inhibits charge recombination and broadens the visible light absorption range of the photocatalyst.This study provided a promising photocatalyst to be used for TC removal in the actual wastewater.     

The molecular-level relationship between the properties of liquid water molecules and orientational order

The relationship between the orientational (tetrahedral) order (q) of an individual liquid water molecule and its various properties such as Voronoi volume, potential energy, kinetic energy, and nearest neighbors was thoroughly examined using molecular dynamics simulations of TIP5P model at 278, 298, and 318 K. By constructing Voronoi polyhedra (VP), we found that the average volume of water molecules classified according to q decreased monotonically as q increased, while the surface of VP increased in the range of high q. Kinetic energy was almost invariant but potential energy decreased monotonously as q increased. The volumes of molecules having a very large q increased as temperature decreased, implying a possible density maximum phenomena. Using time correlation functions, it was shown that total energy rather than potential energy was a more significant factor in the determination of the orientational order. With varying temperature, the relation between the properties of central molecules and those of nearest neighbor molecules were investigated. It required a very systematic cooperative motion to obtain LDL (low-density liquid) formed by ordering. It was supposed that density maximum phenomena should be accomplished by the growth of LDL and HDL (high-density liquid) of low quality with a consistent population of HDL and a drop of LDL of high quality as temperature lowered.     

Poly(vinyl alcohol) multilayer mixed matrix membranes for the dehydration of ethanol–water mixture

We have developed multilayer mixed matrix membranes (MMMMs) consisting of a selective mixed matrix membrane (MMM) top layer, a porous poly(acrylonitrile-co-methyl acrylate) [poly(AN-co-MA)] intermediate layer and a polyphenylene sulfide (PPS) nonwoven fabrics substrate. The selective MMM layer was formed by incorporating KA zeolite in poly(vinyl alcohol) (PVA) matrix followed by the cross-linking reaction of PVA with fumaric acid. The fumaric acid induced cross-linking reactions were confirmed by Fourier-transformation infrared (FTIR), and their effects on PVA thermal stability and glass transition temperature were characterized by thermolgravimetric analysis (TGA) and differential scanning calorimetry (DSC). The separation performance of the newly developed MMMMs was investigated in terms of permeance and selectivity (as well as flux and separation factor) with respect to zeolite content, feed temperature and composition for the ethanol–water separation by pervaporation. It is found that the separation performance of the MMMM is superior to that of multilayer homogenous membranes (MHM) containing no zeolite. For example, the MMMM with 20 wt.% KA zeolite loading exhibits a much higher selectivity than that of MHM (1279 versus 511) at 60 °C if the feed is a mixture of 80/20 (wt.%) ethanol/water. In addition, the activation energy of the water permeation is significantly reduced from 16.22 to 10.12 kJ/mol after adding of KA zeolite into the PVA matrix, indicating that water molecules require a much less energy to transport through the MMMM because the presence of hydrophilic channels in the framework of zeolite. The excellent pervaporation performance of the MMMM is also resulted from the good contact between zeolite-incorporated and polymer matrix cross-linked by fumaric acid.     

PARALLEL ANALYSIS OF COMBINED FINITE／DISCRETE ELEMENT SYSTEMS ON PC CLUSTER

A computational strategy is presented for the nonlinear dynamic analysis of largescale combined finite/discrete element systems on a PC cluster. In this strategy, a dual-level domain decomposition scheme is adopted to implement the dynamic domain decomposition. The domain decomposition approach perfectly matches the requirement of reducing the memory size per processor of the calculation. To treat the contact between boundary elements in neighbouring subdomains, the elements in a subdomain are classified into internal, nterfacial and external elements. In this way, all the contact detect algorithms developed for a sequential computation could be adopted directly in the parallel computation. Numerical examples show that this implementation is suitable for simulating large-scale problems. Two typical numerical examples are given to demonstrate the parallel efficiency and scalability on a PC cluster. The project supported by the National Natural Science Foundation of China (10372114) and the Engineering and Physical Sciences Research Council (EPSRC) of UK (GR/R21219)