T h e separation of protein mixtures by continuous annular chromatography (CAC) is studied in a preparative-scale apparatus. S-Sepharose, a strong-acid porous cation-exchange resin is used as the separation medium, and mixtures of albumin, hemoglobin, and cytochrome c are used as a model separation system. Equilibrium and mass-transfer parameters are developed for this system on the basis of fixed-bed chromatograph experiments. A mathematical model is then successfully used in conjunction with these parameters to simulate the performance of the CAC separations. The continuous separation performance of the annular apparatus is found to be essentially the same as the batchwise performance of an equivalent conventional chromatograph, making the unit attractive for preparative and process-scale applications where continuous throughput is desirable.Continuous annular chromatography (CAC) is a process concept that allows operation of chromatographic separations in a truly continuous, steady-state fashion. The process utilizes an annular sorbent bed, packed in the space between two concentric cylinders. When the system is operated as an isocratic chromatograph, the eluent is uniformly distributed at the top along the bed circumference, while the bed assembly is slowly rotated around its axis. The feed to be separated is continuously introduced a t the top of the bed at a point (or sector) that remains fixed in space. The chromatographic elution of the feed components coupled with the bed rotation causes the formation of individual helical component bands that extend to the bottom of the bed. Here the separated components are continuously recovered at different angular distances from the feed point. The early developmenta of the CAC technology have been reviewed by Carta and Byers (1989). Some significant advances have recently been made. Two improved operating modes, which are common in conventional chromatography, have been implemented: stepwise elution, which leads to gradient elution when multiple concentration steps are used, and displacement development. In addition some new applications of the technology have been investigated, including the separation of sugars (Howard et al., 1988; Byers et al., 1989Byers et al., , 1990, the separation of metal ion mixtures by stepwise elution (Carta et al. 1989), and the separation of mixtures of amino acids by displacement development . Both experimental and theoretical studies were carried out for these systems with CAC units ranging in scale from 10.2 to 45.1 cm in diameter and from 30 to 110 cm in depth. Various resins and sorbents were used with sizes varying from -30 to 400 pm in diameter.The general conclusion that can be drawn from these liquid chromatography studies is that, provided that hydrodynamic (axial) dispersion does not present a significant contribution to the broadening of chromatographic peaks, it is generally possible to specify conditions that permit continuous operation with the CAC while retaining the separation performance of an equivalent fixed-bed p...

Mathematical modeling of chromatographic operations has received considerable attention in the past. For systems where equilibrium and mass transfer processes are represented by linear relationships, analytic solutions of the models are possible in general. A comprehensive review of such solutions is given by Ruthven (1984).Solutions for the calculation of breakthrough curves have been obtained by taking into account external film mass transfer resistance (Anzelius, 1926), axial dispersion and intraparticle diffusion (Lapidus and Amundson, 1952;Rosen, 1952Rosen, , 1954, and combinations of axial dispersion with external film resistance and macropore/micropore diffusion within the sorbent particles (Kawazoe and Takeuchi, 1974;Rasmuson and Neretnieks, 1980;Rasmuson, 1982). These solutions often require the numerical evaluation of infinite integrals, for which special algorithms have been devised (Rasmuson and Neretnieks, 1981;Rasmuson, 1985). Chen and Hsu (1987) have recently introduced an algorithm based on the Fast-Fourier-Transform which simplifies and speeds up such integrations.The effects of particle-size distribution on chromatography have been addressed by several authors. Dougharty (1972) and Moharir et al. (1981) have treated linear chromatographic pulses with moment analyses, and Rasmuson (1985) has provided an analytic solution which permits the calculation of breakthrough curves with nonuniform particles from the numerical evaluation of an infinite integral. Rasmuson's solution includes the effects of particle shape, intraparticle diffusion, sorption kinetics, and external resistance.Recently, Carta (1988) has introduced an explicit analytic solution for chromatography with a time-periodic input concentration. This solution allows the direct computation of breakthrough curves and chromatographic peaks, and can be integrated to obtain the time-average effluent concentration in any desired "product cut." In this note we provide a generalization Correspondence concerning this paper should be addressed to G. Carta of this solution which is valid for an arbitrary particle-size distribution. Unlike previous treatments by other authors, the solution provided does not require the numerical evaluation of infinite integrals and is valid both for pulse and step changes in the feed concentration. Finally, the solution permits the prediction of the cyclic performance of periodic operations. Problem StatementConsidering a homogeneously packed bed, we define an arbitrary, normalized particle-size distribution function, f(R), in such a way thatf(R)dR is the volume fraction of particles with radius between R and R + dR. Pore diffusion is assumed to occur in these particles with an effective diffusion coefficient, D, .Axial dispersion and film mass transfer resistance are recognized as dependent on the particle-size distribution (Dougharty, 1972). Yet, this dependence is generally not available in terms of explicit relationships and is best handled with empirical coefficients. Intraparticle diffusion, on the other hand,...

Stress is a complex phenomenon that has significant effects on students which may disturb their physiological, psychological, and spiritual health and wellbeing. Nursing students have been identified to be at high risk for stress during their training. Stress can arise from new clinical experiences, academic load, and personal stressors (Jones & Johnston, 2006). This increase in stress can lead to the student's inability to assimilate and learn within the classroom and clinical settings. A review of the literature provided evidence that reported a positive relationship between guided imagery and a decrease in stress and anxiety. This evidence-based practice (EBP) project assessed whether a stress relief guided imagery intervention improved perceived stress in nursing students. The Stetler Model and the Neuman Systems Model were utilized as a foundational framework to guide this project. Fourth-semester sophomore nursing students from the Fundamentals of Nursing course were invited to participate in the project. Participant demographics were collected, and Cohen's Perceived Stress Scale (PSS) was administered to students prior to the intervention. The intervention included 20 min of a stress relief guided imagery audio CD by Belleruth Naparstek. At the completion of the 8-week period, the Cohen's PSS was re-administered, and students completed a post-intervention self-report survey of usefulness to evaluate project success. Paired samples t tests were performed on pre-and post-intervention PSS scores, which did not reveal a statistically significant difference (p = .239). Of 21 students, 13 had lower perceived levels of stress post intervention. The results of the post-intervention survey indicated that 18 of 21 students would utilize guided imagery in the future; 19 of 21 students would recommend guided imagery to family, friends, and patients; and 20 of 21 students found guided imagery helpful in reducing school-related stressors. Implications for future practice have been validated by the results of this EBP project. Based on the positive results of this study, the integration of guided imagery in undergraduate nursing curricula should be considered to reduce perceived stress among nursing students.