Adsorption of Hexavalent Chromium on Chitosan Beads: Sorption Isotherms and Kinetics

Abstract

Chitosan is a biopolymer that is usually obtained in a flaked form, nonporous and partially soluble in acidic media. The low porosity of the polymer introduces diffusion constraints which are rate limiting. Modifying the structure of the chitosan is a way to improve the accessibility of the adsorption sites. In this study, the modifications were carried out by dissolving chitosan flakes in an acetic acid solution followed by precipitation in a sodium hydroxide solution to form gel beads. The study deals with the influence of several parameters (metal ion concentration, size of the beads, Chitosan conditioning) on metal ion diffusion. Both sorption isotherms and kinetics were taken into account. The use of this material allowed an adsorption capacity of 76 mg g^?1 to be obtained.     

HIGH-ORDER CONTRASTS FOR SELF-ADAPTIVE SOURCE SEPARATION

This paper is concerned with the problem of separating independent non-Gaussian sources. This is done by adaptively maximizing a contrast function based on fourth-order cumulants of the (mixed) obser$softhyphen;vations. The first cla ss of solutions involves a first stage where the signal vector is adaptively whitened. In order to implement in the second stage the proper separating task, new contrast functions are proposed, especially when all the source kurtosises have the same sign. These contrasts involve only self-cumulants of the outputs. The second class of solutions requires a single separating stage. However, the associated contrasts involve cross-cumulants in addition to self-cumulants. They essentially apply to correlated ve ctors with normalized powers (rather than to white vectors). The resulting adaptive one-stage and two-stage systems achieve satisfactory separation performance independently of the statistics of sources and of the kind of linear mixture.     

SIMULATION OF AN IMMOBILIZED ENZYME PARTICLE USING β-GALACTOSIDASE ADSORBED TO A PHENOL-FORMALDEHYDE RESIN

The mass transfer and kinetic properties of both soluble and immobilized β-galactosidase were investigated. A reversible enzyme kinetic model was found to best fit the soluble and immobilized enzymatic lactose hydrolysis. A finite difference model was used to simulate the steady state and unsteady state behavior of an immobilized enzyme particle. The performance of the catalyst in a stirred tank reactor was simulated by using the physical properties of the support with the kinetic model and varying the effective substrate diffusivity to fit the data. A sensitivity analysis was performed to evaluate the effect of particle size, diffusivity, external mass transfer coefficient and enzyme loading.     

Calorimetric Examination of Cut Fresh Pineapple Metabolism

Isothermal microcalorimetric analysis of cut fresh pineapple was used to examine metabolic events occurring in the fruit under different storage conditions. The results define conditions most suited for cut pineapple storage. The baseline heat production for pineapple tissue is quite low (0.2 μW per mg wet weight). During storage, heat producing metabolic reactions develop which cause spoilage of the fruit. The time course of heat production during storage is affected by changes in atmosphere and by chemical treatments. Effects of inhibitor and antibiotic additions indicate that most of the heat production associated with spoilage is related to the growth of microbial flora.     

Engineering Entrepreneurship: An Example of A Paradigm Shift in Engineering Education

This paper describes a course on technology‐based entrepreneurship. Brown University's Division of Engineering has created a two‐semester course sequence designed to introduce students to entrepreneurship through a unique merger of classroom learning and industry participation. The course is open to advanced undergraduates from all engineering disciplines, and emphasis is placed upon recruiting almost half of the student participants from outside of engineering in order to develop “team building” skills. Local “parent companies” provide seed ideas or concepts to student groups who use skills learned in the classroom (both in this course as well as other courses) to develop and refine the parent company's idea and turn it into a viable simulated spin‐off business or new start‐up. Managers from the parent companies serve in an evolving role over the two‐semester sequence beginning as a “board of directors” for the spin‐off and eventually evolving into a potential source of start‐up capital (or possibly a customer for the products of the company). The faculty carefully manage the student‐company interface. Deliverables at the end of the two‐semester sequence include a business plan and a prototype product.     

纳米技术涌动未来——极其微小的工艺，革命性的效应

技术引擎：碳纳米管 碳纳米管的强度远远超过钢铁，并且拥有极好的导热与导电性，正因如此，其未来的应用涉及面板广，从CPU到电池，再到散热片等。