Flow-through electrodes. IV. Axial diffusion effects

The simple theory of flow-through electrodes was generalized by analysis of axial diffusion phenomena. The effect of axial diffusion coupled with forced convection on the electrochemical behaviour of flow-through electrodes was analyzed assuming laminar flow through a structurless medium (the analysis is thus applicable also to e.g. capillary bundle models with sufficiently small pores' radii). Diffusional effects involving both reactants and products were considered and the electrochemical kinetic equations allowed for both forward and backward reaction orders with respect to substrates and products. Axial ohmic effects were included.The effect of convection in the pre-electrode chamber was taken into account in establishing the boundary conditions at the electrode entrance. A system of differential equations and boundary conditions describing the model was formulated. The integration was carried out by means of Hamming's method with automatic step size adjustment. The effects of various parameters (flow-rate, exchange current density, conductivity of the electrolyte, etc.) were examined in terms of deviations from the simple model. The regions of large, negligible and small (within 10%) deviations were defined and interpreted.     

Auto-ignition of methane–air mixtures flowing along an array of thin catalytic plates

In this paper, the heterogeneous ignition of a methane–air mixture flowing along an infinite array of catalytic parallel plates has been studied by inclusion of gas expansion effects and the finite heat conduction on the plates. The system of equations considers the full compressible Navier–Stokes equations coupled with the energy equations of the plates. The gas expansion effects which arise from temperature changes have been considered. The heterogeneous kinetics considers the adsorption and desorption reactions for both reactants. The limits of large and small longitudinal thermal conductance of the plate material are analyzed and the critical conditions for ignition are obtained in closed form. The governing equations are solved numerically using finite differences. The results show that ignition is more easily produced as the longitudinal wall thermal conductance increases, and the effects of the gas expansion on the catalytic ignition process are rather small due to the large value of the activation energy of the desorption reaction of adsorbed oxygen atoms.     

Multi-objective sequence dependent setup times permutation flowshop: A new algorithm and a comprehensive study

The permutation flowshop scheduling problem has been thoroughly studied in recent decades, both from single objective as well as from multi-objective perspectives. To the best of our knowledge, little has been done regarding the multi-objective flowshop with Pareto approach when sequence dependent setup times are considered. As setup times and multi-criteria problems are important in industry, we must focus on this area. We propose a simple, yet powerful algorithm for the sequence dependent setup times flowshop problem with several criteria. The presented method is referred to as Restarted Iterated Pareto Greedy or RIPG and is compared against the best performing approaches from the relevant literature. Comprehensive computational and statistical analyses are carried out in order to demonstrate that the proposed RIPG method clearly outperforms all other algorithms and, as a consequence, it is a state-of-art method for this important and practical scheduling problem.     

Thermodynamic model for the analysis of calorimetric data of oligomeric proteins

The thermodynamic parameters for the process of protein unfolding can be obtained through differential scanning calorimetry. However, the unfolding process may not be a two-state one. Between the native and the unfolded state, there may be association or dissociation processes or the formation of an intermediate state. As a consequence of this, the precise interpretation of the calorimetric data should be done with a specific thermodynamic model. In this work, we present two general models for the unfolding process of an oligomeric protein: N n right harpoon over left harpoon nN right harpoon over left harpoon nD (model A) and N n right harpoon over left harpoon I n right harpoon over left harpoon nD (model B). In model A, the first step represents the dissociation of the oligomer into the monomeric native species, and the second step represents the denaturation process. In model B, the first step represents the conformational change of the oligomer, and the second step represents the dissociation of this species with the concomitant unfolding process. A canonical ensemble was employed to describe these systems, by considering that the total protein concentration remains constant. In the present work, we show and analyze the behavior of these systems in different conditions and how this analysis could help with the identification of the unfolding mechanism experimentally observed.     

Water Activity Regulates the Q(A)(-) to Q(B) electron transfer in photosynthetic reaction centers from Rhodobacter sphaeroides

We report on the effects of water activity and surrounding viscosity on electron transfer reactions taking place within a membrane protein: the reaction center (RC) from the photosynthetic bacterium Rhodobacter sphaeroides. We measured the kinetics of charge recombination between the primary photoxidized donor (P(+)) and the reduced quinone acceptors. Water activity (aW) and viscosity (eta) have been tuned by changing the concentration of cosolutes (trehalose, sucrose, glucose, and glycerol) and the temperature. The temperature dependence of the rate of charge recombination between the reduced primary quinone, Q(A)(-), and P(+) was found to be unaffected by the presence of cosolutes. At variance, the kinetics of charge recombination between the reduced secondary quinone (Q(B)(-)) and P(+) was found to be severely influenced by the presence of cosolutes and by the temperature. Results collected over a wide eta-range (2 orders of magnitude) demonstrate that the rate of P(+)Q(B)(-) recombination is uncorrelated to the solution viscosity. The kinetics of P(+)Q(B)(-) recombination depends on the P(+)Q(A)(-)Q(B) <--> P(+)Q(A)Q(B)(-) equilibrium constant. Accordingly, the dependence of the interquinone electron transfer equilibrium constant on T and aW has been explained by assuming that the transfer of one electron from Q(A)(-) to Q(B) is associated with the release of about three water molecules by the RC. This implies that the interquinone electron transfer involves at least two RC substates differing in the stoichiometry of interacting water molecules.     

Assortment optimization under a multinomial logit model with position bias and social influence

Motivated by applications in retail, online advertising, and cultural markets, this paper studies the problem of finding an optimal assortment and positioning of products subject to a capacity constraint in a setting where consumers preferences can be modeled as a discrete choice under a multinomial logit model that captures the intrinsic product appeal, position biases, and social influence. For the static problem, we prove that the optimal assortment and positioning can be found in polynomial time. This is despite the fact that adding a product to the assortment may increase the probability of selecting the no-choice option, a phenomenon not observed in almost all models studied in the literature. We then consider the dynamics of such a market, where consumers are influenced by the aggregate past purchases. In this dynamic setting, we provide a small example to show that the natural and often used policy known as popularity ranking, that ranks products in decreasing order of the number of purchases, can reduce the expected profit as times goes by. We then prove that a greedy policy that applies the static optimal assortment and positioning at each period, always benefits from the popularity signal and outperforms any policy where consumers cannot observe the number of past purchases (in expectation).     

Geometric Entities Voting Schemes in the Conformal Geometric Algebra Framework

Traditional methods for geometric entities resort to the Hough transform and tensor voting schemes for detect lines and circles. In this work, the authors extend these approaches using representations in terms of k-vectors of the Conformal Geometric Algebra. Of interest is the detection of lines and circles in images, and planes, circles, and spheres in the 3-D visual space; for that, we use the randomized Hough transform, and by means of k-blades we code such geometric entities. Motivated by tensor voting, we have generalized this approach for any kind of geometric entities or geometric flags formulating the perceptual saliency function involving k-vectors. The experiments using real images show the performance of the algorithms.     

Dual biosensor immunoassay-directed identification of fluoroquinolones in chicken muscle by liquid chromatography electrospray time-of-flight mass spectrometry

Fluoroquinolones (FQs) are synthetic antibiotics of broad-spectrum antibacterial activity widely used to treat infections in farmed fish, turkeys, pigs, calves and poultry. Monitoring these substances residues is therefore regulated by law. For the detection of FQs, we studied the feasibility of coupling the simultaneous screening of several FQs, using a dual surface plasmon resonance (SPR) biosensor immunoassay (BIA), in parallel, with an analytical chemical methodology for their identification. Six FQs were simultaneously screened at or below their maximum residue level (MRL) in chicken muscle using a multi-FQ BIA for norfloxacin, ciprofloxacin, enrofloxacin, difloxacin and sarafloxacin, and a specific BIA for flumequine. The two BIAs were serially coupled in a multi-channel SPR biosensor featuring a dual BIA in a competitive inhibition format. The samples non-compliant during the screening with the dual BIA were further concentrated and fractionated with gradient liquid chromatography (LC). The effluent was splitted toward two 96-well fraction collectors resulting in two identical 96-well plates. One was re-screened with the dual BIA to identify the immunoactive fractions and direct the identification efforts toward the relevant fractions in the second well-plate with high resolution LC-electrospray time-of-flight mass spectrometry (ESI-TOFMS). The system not only allows the possibility to screen and identify known FQs, but also to discover unknown chemicals of similar structure which show activity in the dual BIA.     

Fast-atom bombardment mass spectrometry of brassinosteroid analogs

Positive ion fast-atom bombardment mass spectra of brassinosteroid analogs have been systematically obtained for the first time. The spectra of six brassinosteroid analogs and their corresponding 22S,23S isomers included the protonated molecule in medium to high relative intensity. The fragmentation pattern is dominated by side chain cleavage. There is a marked preferential loss of acetic acid from the [M + H]⁺ ion of 5α-hydrogen-3β-acetylated derivatives compared to the 5α-hydroxy-3β-acetylated analogs.