Application of Quasi Steady-State Model to Slow Mode Periodic Pulsation of the Liquid in Trickle Bed Reactors

Many published studies show the benefits of forced pulsation of the liquid flow rate in a trickle bed reactor, especially when mass transfer phenomena are rate controlling. Two types of periodic liquid pulsation, the slow and fast mode, are examined in the literature, depending on the period of the pulsation.

The aim of this work is to show that, when slow mode pulsation occurs, the quasi steady-state model can be applied. The model assumes that the mean conversion rate in pulsed mode is the weighted mean of the two steady conversion rates at the minimum and maximum liquid flow rates. In fact, the period of the liquid pulsation is long enough to allow the reactor to reach the quasi steady-state conditions at every level of the liquid flow rate. The validity of the model is checked with experimental data concerning α-methylstyrene hydrogenation to cumene.     

The Dynamics and Evolution of Industries

The empirical evidence, the major stylized facts, the currentexplanations and the relevant unanswered questions concerningthe dynamics and evolution of industrial structure are discussedin this paper. Three levels of analysis of the dynamics andevolution of industries are distinguished: specific dimensionsof industry dynamics, structural dynamics and structural evolution.The first level refers to the dynamics related to specific featuresof industrial structures such as industrial demography, firmgrowth and size distribution and persistence in asymmetric performanceat the firm level. The second refers to the dynamics over timeof structural variables: entry, exit, firm size and concentration,as well as product and process innovation. The third refersto a broader view of industrial structure and its evolutionover time: the emergence of new industries, the generation andtransformation of technologies and products within an industry,the development and change of capabilities, the changing boundariesof firms in terms of growth, vertical integration, diversification,the development of networks and the role played by institutions(such as the government, scientific institutions, financialinstitutions, suppliers and users).     

Rearrangement of Porous CaO Aggregates During Calcite Decomposition in Vacuum

High-resolution SEM photographs, N₂ adsorption isotherms, Hg porosimetry, and micrometer measurements were used to characterize CaO particle shapes and pore-size distributions that result when calcite crystals are decomposed in vacuum at 686°C. The surface area of the CaO produced from large calcite crystals is constant at 116.4 m²/g independent of the extent of reaction. The volume occupied by a CaO aggregate is 98±2% that of the original calcite crystal. The ∼54% total porosity is comprised of 42% pores of ∼5 nm cross section and 12% pores of ∼10 μ m cross section. The duplex pore structure is formed by a diffusionless repacking of CaO particles that initially form with a more uniform distribution of particles and pores.     

A CYBERNETIC APPROACH TO POPULATION DYNAMICS MODELING

Abstract

Some problems arising when modeling population dynamics by means of stochastic difference and differential equations are discussed. For a particular parametrization of logistic growth equations limit diffusion processes are constructed and interpreted in the light of the Ito-Stratonovich controversy. An indirect confirmation of the validity of May's conjecture on the persistence of a population in a randomly varying environment is also obtained. An extension of these results to a wider class of growth equations is finally provided.     

A discrete maximum principle for systems with pure delays†

This paper deals with necessary arid sufficient conditions for the optimization of nonlinear multivariate discrete systems containing pure delays in dynamics, in performance index, and in constraints. Using non-linear programming, it is shown that a discrete maximum principle similar to the one derived by Pearson and Sridhar (1966) is valid for a subclass of these problems, that is systems with linear dynamics, concave inequality constraints, and convex performance index. As an application, the optimal piceewise constant control with optimal non-uniform sampling of systems described by differential equations is derived.     

Dental-derived stem cells and biowaste biomaterials: What’s next in bone regenerative medicine applications

The human teeth and oral cavity harbor various populations of mesenchymal stem cells (MSCs), so calleddental-derived stem cells (D-dSCs) with self-renewing and multilineage differentiation capabilities. D-dSCs propertiesinvolves a strong paracrine component resulting from the high levels of bioactive molecules they secrete in responseto the local microenvironment. Altogether, this viewpoint develops a general picture of current innovative strategiesto employ D-dSCs combined with biomaterials and bioactive factors for regenerative medicine purposes, and offersinformation regarding the available scientific data and possible applications.     

Earthnet's coordination scheme for AVHRR data

Abstract

Earthnet's plan for a coordinated Advanced Very High Resolution Radiometer (AVHRR) data service in Europe, as outlined by Fusco and Muirhead (1987), is beginning to take'shape. Three High Resolution Picture Transmission (HRPT) stations are contributing to the data acquisition (providing coverage from West Africa to the Middle East and over the North Pole), the AVHRR catalogue is on-line and an autonomous workstation for AVHRR acquisition, processing and archiving to optical disc is in an advanced state of development.     

Technological Regimes and Sectoral Patterns of Innovative Activities

This paper focuses on the relationships between observed patternsof innovative activities within a sector and the related contextand underlying microeconomic processes that might account furthem. it claims that there are some invariant features (withrespect to relative prices and incentives mechanisms) of learningand knowledge accumulation that greatly affect the rare andstructure of innovative activity. These features are differentacross sectors. The paper proposes that the specific patternof innovative activity of a sector can be explained as the outcomeof different technological regimes that are implied by the natureof technology and knowledge. The notion of technological regimeprovides a synthetic representation of some of the most importanteconomic properties of technologies and of the characteristicsof the learning processes that are involved in innovative activities.     

ORGANIC ACIDS PROFILE IN TOMATO JUICE BY HPLC WITH UV DETECTION

A simple method was developed to determine 10 organic acids simultaneously in tomato products using reverse‐phase high performance liquid chromatography (HPLC) column with the diode array detector set at 210 nm. After centrifugation and filtration, the samples were passed through to an anion exchange resin and the organic acids were released using 0.1 N HCl. The chromatographic separation was achieved with isocratic analysis in a 20‐min run. The method was reliable and sensitive. The coefficient of determination of the standard calibration curve is 0.9925 ≤ r² ≤ 0.9999 and the limit of detection ranged from 0.08 to 6.00 mg/kg for trans‐aconitic acid and acetic acid, respectively. The limit of quantification ranged from 0.19 to 15.18 mg/kg for trans‐aconitic and acetic acid, respectively. To establish the efficiency of the anion resin the procedure was applied to a standard solution of a mixture of organic acids. The organic acids recovery ranged from 87.0% ± 1.9 for citramalic acid to 109.9% ± 5.2 for fumaric acid.