Effectiveness of catalytic archipelagos—II: Random arrays of random islands

Voronoi polygons are used to simulate a random distribution of irregularly shaped catalytic islands. Finite element mathematics is used to determine the catalytic effectiveness of the islands when adsorbed reactants diffuse and disappear by a first order reaction at their boundaries. It is found that the catalytic effectiveness of the islands at any fractional coverage can be estimated reasonably accurately either from asymptotic formulae, valid for certain values of diffusion, adsorption, and reaction constants, or from the equivalent annulus approximation found earlier to be accurate for certain regular arrays of regular islands. The equivalent annulus approximation allows analytic prediction of the catalytic effectiveness for any set of parameter conditions given only the fraction area ratio Γ/Ω. Both of these quantities of which can be determined directly from a photomicrog of a representative sample.     

ON THE CONCEPT OF THE STEADY STATE IN CHEMICAL REACTOR ANALYSIS

The inlet and outlet streams of a chemical reactor may reach a steady state before the internal distributions of concentration, etc. have come to the steady state. Such a steady state, in which the reactor is viewed only as a system with certain inputs and outputs, may be called the black-box steady state (BBSS). The existence of a BBSS does not always imply that of a true SS, and the BBSS may be attained in a finite time even though the SS is only attained asymptotically. Indeed under some circumstances the BBSS can be achieved immediately upon start-up. Provided that the internal transients are not catastrophic, the practical, or operator's, concept of a steady state is really that of a BBSS.     

Effectiveness of catalytic archipelagos—I Regular arrays of regular islands

The interplay of the adsorption and desorption of reactants onto a catalytically active surface and their diffusion in that surface is an important process in catalysis. A surface with regularly distributed circular or rectangular catalyst islands in a plane has been investigated here under the assumption that the adsorbed reactant diffuses to the boundaries of the islands and disappears there by a first-order reaction. With the aid of the finite element method, effectiveness factors of the model systems have been calculated in terms of two dimensionless parameters ψ and μ, one measuring the ratio of the adsorption and desorption rates to that of surface diffusion and the other the rate of reaction to the rate of surface diffusion. It is found that the effectiveness factor for arrays whose symmetry elements are not too elongate can be approximated closely by that of an equivalent annulus whose inner and outer radii are calculated in terms of the geometrical parameters of the various systems. The equivalent annulus approximation is fairly accurate for these arrays in the parameter range 0.01 ?ψ, μ?10. Furthermore, outside this parameter range, asymptotic formulas are given which are accurate for all systems considered.     

Nop5p is a small nucleolar ribonucleoprotein component required for pre-18 S rRNA processing in yeast

We have identified a novel nucleolar protein, Nop5p, that is essential for growth in Saccharomyces cerevisiae. Monoclonal antibodies B47 and 37C12 recognize Nop5p, which has a predicted size of 57 kDa and possesses a KKX repeat motif at its carboxyl terminus. Truncations that removed the KKX motif were functional and localized to the nucleolus, but conferred slow growth at 37 degreesC. Nop5p shows significant sequence homology with yeast Sik1p/Nop56p, and putative homologues in archaebacteria, plants, and human. Depletion of Nop5p in a GAL-NOP5 strain lengthened the doubling time about 5-fold, and selectively reduced steady-state levels of 40 S ribosomal subunits and 18 S rRNA relative to levels of free 60 S subunits and 25 S rRNA. Northern blotting and primer extension analyses showed that Nop5p depletion impairs processing of 35 S pre-rRNA at the A0 and A2 cleavage sites. Nop5p is associated with the small nucleolar RNAs U3, snR13, U14, and U18. Depletion of Nop5p caused the nucleolar protein Nop1p (yeast fibrillarin) to be localized to the nucleus and cytosol. Also, 37C12 co-immunoprecipitated Nop1p. These results suggest that Nop5p functions with Nop1p in the execution of early pre-rRNA processing steps that lead to formation of 18 S rRNA.     

Assessing Disclosure Risk and Data Utility Trade-off in Transaction Data Anonymization

Organizations and businesses, including financial institutions and healthcare providers, are increasingly collecting and disseminating information about individuals in the form of transactions. A transaction associates an individual with a set of items, each representing a potentially confidential activity, such as the purchase of a stock or the diagnosis of a disease. Thus, transaction data need to be shared in a way that preserves individuals'' privacy, while remaining useful in intended tasks. While algorithms for anonymizing transaction data have been developed, the issue of how to achieve a "desired" balance between disclosure risk and data utility has not been investigated. In this paper, we assess the balance offered by popular algorithms using the R-U confidentiality map. Our analysis and experiments shed light on how the joint impact on disclosure risk and data utility can be examined, which allows the production of high-quality anonymization solutions.     

BN-C Hybrid Nanoribbons as Gas Sensors

The effects of carbon monoxide (CO) and ammonia (NH₃) molecules adsorption on the various composites of boron nitride and graphene BN-C hybrid nanoribbons are investigated using the non-equilibrium Green’s function (NEGF) technique based on density functional theory (DFT). The effects of adsorption with possible random configurations on the average of the density of states (DOS), transmission coefficient, and the current–voltage (I–V) characteristics are calculated. The results indicate that, by embedding armchair graphene nanoribbon (AGNR) with boron nitride nanoribbon (BNNR), the various electronic properties can be observed after gas molecule adsorption. The electronic structure and gap of hybrids system is modified due to gas adsorption, and the systems act like the n-type semiconductor by NH₃ molecule adsorption. The hybrid structures due to their tunable band gap are better candidates for gas detecting compared to the pristine BNNRs and AGNRs.     

Parameter and state estimation of the activated sludge process-I. Model development

A new approach is introduced for combined state and parameter estimation, named Linearized Maximum Likelihood (LML). The LML method is motivated by the uncertain and nonlinear activated sludge dynamics. In this article, the theoretical background leading to the development of the LML method is presented, along with the resulting numerical algorithm. In a companion article (Kabouris and Georgakakos, 1996) the LML method is applied to the parameter and state estimation of a nitrifying activated sludge process, modelled by the IAWPRC Activated Sludge Model 1.     

Parameter and state estimation of the activated sludge process-II. Applications

In a companion article (Kabouris and Georgakakos, 1996) the Linearized Maximum Likelihood (LML) method for the simultaneous estimation of activated sludge process states and parameters from noisy process measurements is presented. The present article describes the application of the LML method to the identification of a nitrifying activated sludge process, modelled by the IAWPRC Activated Sludge Model 1. It is concluded that identification of nine of the model parameters from process measurements is only possible when a sequential estimation scheme is applied and only influential measurements are considered.