MODELING OF COMPETITIVE ADSORPTION OF NITROGEN SPECIES IN HYDRODESULFURIZATION

Previously, we developed a simple, one-parameter model reproducing the observed inhibiting effect of nitrogen species in the hydrodesulfurization (HDS) of hindered sulfur heterocycles. The model owes its simplicity to some nontrivial assumptions. Here we develop a full model by relaxing these assumptions, which gives a more quantitative picture of how sulfur, nitrogen, and catalyst surface interact on many widely disparate time scales. Computational results build a strong case for the accuracy of the previous one-parameter theory. As such, the theory should be applicable to reaction systems in which catalyst poisoning is driven by nonequilibrium adsorption. Some of the complexities and subtleties in modeling the competitive adsorption effects in distillate HDS are discussed, giving special attention to the design of robust catalyst-deactivation-compensation operating strategies.     

Stochastic design sensitivity in structural dynamics

A method to analyse stochastic design sensitivity for problems of structural dynamics is presented. A combination of the adjoint variable approach and the second order perturbation method is used in the finite element context. An alternative form of the constraint functional that holds for all times is introduced to consider the time response of dynamic sensitivity. The terminal problem of the adjoint system is solved using equivalent homogeneous equations exicited by initial velocities. The numerical procedures are shown to be much more efficient when based on the fold superposition technique: the generalized co-ordinates are normalized and the correlated random variables are transformed to uncorrelated variables, whereas the secularities are eliminated by the fast Fourier transform of complex valued sequences. Numerical algorithms have been worked out and proved to be accurate and efficient; they can be readily adapted to fit into the existing finite element codes whose element derivative matrices can be explicitly generated. A number of numerical results for the deterministic and stochastic sensitivity analysis of beams and shells illustrates the paper.     

The role of ion and solvent transport during the redox process of conducting polymers

The understanding of the redox behavior of conducting polymers is essential for a successful application of these so-called synthetic metals as functional coatings. The redox process involves the exchange of ions and solvent molecules. This so called doping/dedoping process involves changes of the mechanical and the electronic structure of the polymer. This paper discusses investigations at poly(3,4-ethylenedioxythiophene (PEDOT) and poly(pyrrole) (Ppy) by the electrochemical quartz crystal microbalance (EQCM) technique and electrochemical impedance spectroscopy (EIS). In the case of PEDOT a determination of the anion and the solvent fluxes was possible, and it was found that most anions replace solvent molecules upon their incorporation. The doping/dedoping mechanism of Ppy is more complicated. Here, the first redox cycles are characterized by a complex interplay of cation, anion and solvent fluxes with irreversible changes of the polymer structure. However, in combination with EIS new insights of the ion and solvent exchange and its influence on the electronic properties can be achieved.     

Incremental finite element sensitivity analysis for non-linear mechanics applications

Finite element formulations for structural sensitivity analysis of non-linear systems with fixed overall shape are discussed. Both the direct differentiation and adjoint variable methods are employed. The resulting sensitivity algorithms are consistent with time integration scheme adopted for solving equilibrium problem. Effectiveness and computational aspects of the procedures are discussed and compared. Numerical algorithms are shown to be readily implemented in existing finite element codes. Large-scale examples illustrate the paper.     

Immunophenotypic analysis of peripheral blood mononuclear cells undergoing in vitro apoptosis after isolation from human immunodeficiency virus-infected children

Lymphocytes of human immunodeficiency virus (HIV)-infected individuals undergo accelerated apoptosis in vitro, but the subsets of cells affected have not been clearly defined. This study examined the relationship between lymphocyte phenotype and apoptotic cell death in HIV-infected children by flow cytometry. Direct examination of the phenotype of apoptotic lymphocytes was accomplished using a combination of surface antigen labeling performed simultaneously with the Tdt mediated Utp nick end-labeling (TUNEL) assay. In comparison to live cells, apoptotic lymphocytes displayed an overrepresentation of CD45RO and HLA-DR expressing cells, while CD28 and CD95 expressing cells were underrepresented. Lymphocytes expressing CD4, CD8, and CD38 were equally represented in apoptotic and live populations. When percent lymphocyte apoptosis follow- ing culture was examined independently with lymphocyte subsets in fresh blood, apoptosis was negatively correlated with the percentage of CD4 cells, but not with specific CD4 T-cell subsets. Although not correlated with the percentage of total CD8 cells, apoptosis was positively correlated with specific CD8 T-cell subsets expressing CD45RO and CD95 and negatively correlated for CD8 T cells expressing CD45RA. These results provide direct evidence that a population of activated lymphocytes with the memory phenotype lacking the costimulatory molecule CD28 are especially prone to undergo apoptosis. The findings related to CD95 expression in fresh and apoptotic cells implicate Fas-dependent and Fas-independent pathways of apoptosis in HIV disease in children.     

High throughput optical readout of dense arrays of nanomechanical systems for sensing applications

We present an instrument based on the scanning of a laser beam and the measurement of the reflected beam deflection that enables the readout of arrays of nanomechanical systems without limitation in the geometry of the sample, with high sensitivity and a spatial resolution of few micrometers. The measurement of nanoscale deformations on surfaces of cm(2) is performed automatically, with minimal need of user intervention for optical alignment. To exploit the capability of the instrument for high throughput biological and chemical sensing, we have designed and fabricated a two-dimensional array of 128 cantilevers. As a proof of concept, we measure the nanometer-scale bending of the 128 cantilevers, previously coated with a thin gold layer, induced by the adsorption and self-assembly on the gold surface of several self-assembled monolayers. The instrument is able to provide the static and dynamic responses of cantilevers with subnanometer resolution and at a rate of up to ten cantilevers per second. The instrumentation and the fabricated chip enable applications for the analysis of complex biological systems and for artificial olfaction.     

Lumped parameter modeling and analysis of hybrid magnet engine valve actuator

The hybrid magnet engine valve actuator (HMEVA) composed of two types of magnets (permanent magnet and electromagnet) and two balanced springs is a promising tool for implementing innovative engine management strategies for variable valve timing. Finite Element Method (FEM), a favored actuator design tool due to its high accuracy, was utilized to analyze the electromagnetic actuator, but it consumes a lot of time especially in computation iterations for optimization. Accordingly, the magnetic equivalent circuit analysis can be an alternative tool to FEM because of its computation iteration capability with fair accuracy. In this paper, an equivalent magnetic circuit model of an HMEVA is developed considering the reluctances, external magnetic forces and so on, and the simulation results are presented. In addition, the result of lumped parameter analysis (LA) is compared with those obtained from finite element analysis for verification.     

A novel nonlinear observer‐based LQ control system design for wind energy conversion systems with single measurement

The issue of tracking the optimal power for wind energy conversion systems (WECSs) via regulating the rotor speed of the generator is taken into account in this study. Additionally, a novel polynomial observer is proposed for estimating not only aerodynamic torque in WECSs but also d‐axis and electromagnetic torque. Therefore, in this new approach, only the rotor speed of the generator is required to be measured instead of measuring all state variables. With the new observer form, the aerodynamic torque does not need to satisfy any constraints, which are mandatory in the previous methods. It should be noted that this methodology has not been investigated for the WECSs in any previous papers. To design a complete control system, a linear optimal control method cooperated with the polynomial observer is employed to track the optimal trajectory of a generator. Moreover, in this paper, the permanent magnet synchronous generator is used. In addition, on the basis of the Lyapunov theory and sum‐of‐square (SOS) technique, the conditions for observer synthesis are derived in the main theorems. Finally, the simulation results are provided to prove the effectiveness and merit of the proposed method.     

Comparative study of methods for producing gum arabic powder and the impact of DIC treatment (instant controlled pressure drop) on the properties of the product

In this study, gum arabic powder was produced according to four methods by inserting a restructuring stage by DIC treatment (instant controlled pressure drop) in the classic process of grinding and spray drying. Properties of the final product were compared, and the results show that DIC treatment enables to control and improve the properties of the powder. The DIC treatment can cause a controlled increase in the tapped bulk density, filling rate, compressibility, porosity; and a reduction in interstitial air volume and the loose bulk density. It also facilitated the subsequent grinding and intensified the drying kinetics. The impacts of pressure and DIC treatment time were examined. Pressure was the strongest factor influencing the properties of the gum arabic powder. Selecting an optimal pressure and treatment time plays a decisive role in controlling the properties of powders.