Copyright (c) 2008 Berkeley Electronic Press All rights reserved. http://www.bepress.com Recent documents in The Berkeley Electronic Press en-us Sun, 23 Nov 2008 02:11:46 PST 3600 http://www.bepress.com/cppm/vol3/iss1/51 http://www.bepress.com/cppm/vol3/iss1/51 Sat, 22 Nov 2008 00:34:21 PST The heat transfer cooling of a hot liquid in a stirred vessel has been studied experimentally with coolant flowing through a half-coil around the vessel. Correlations have been developed for the heat transfer coefficient of the half coil jacket. A mathematical model for the half coil jacket liquid temperature dynamics and its analytical solution is used to find the shell side temperature profile as a function of time. It is found that the model predictions are in satisfactory agreement with the experimental data and that the developed correlation is superior to previously published correlations for similar systems. Jayakumar Natesan Subramanian Heat transfer http://www.bepress.com/cppm/vol3/iss1/50 http://www.bepress.com/cppm/vol3/iss1/50 Sat, 22 Nov 2008 00:10:32 PST In the near future of chemical industry, communication between design, manufacturing, marketing and management should be centered on modeling and simulation, which could integrate the whole product and process development chains, process units and subdivisions of the company. Solutions to this topic often set aside one or more components from product, process and control models, hence, as a novel know-how, an information system methodology was developed. Its structure integrates models of these components with a process data warehouse where integration includes information, location, application and time integrity. It supports complex engineering tasks related to analysis of system performance, process optimization, operator training systems (OTS), decision support systems (DSS), reverse engineering or software sensors (soft-sensors). The case study in this article presents the application of the proposed methodology for product quality soft-sensor application by on-line melt index prediction of an operating polymerization technology. Balazs Balasko process optimization based on historical data based integrated process analysis http://www.bepress.com/ijfe/vol4/iss8/art6 http://www.bepress.com/ijfe/vol4/iss8/art6 Thu, 20 Nov 2008 19:42:09 PST The presence of common enterobacterial genes (wec E, F), the ubiquitous plant chloroplast gene of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL), maize intrinsic zein (Ze1) and recombinant cry1Ab genes in the gastrointestinal (GI) contents, peripheral blood mononuclear cells (PBMC) and visceral organs of mice and their progeny were examined by PCR. The wec E, F or rbcL were detected inconsistently in the PBMC, visceral organs, milk or liver of suckling mice, while Ze1 or cry1Ab were not detected. These results suggest that feed derived plant or enterobacterial DNAs were incompletely degraded in the GI tract, and part of them were absorbed into organs or milk as a source of transfer into suckling mice, but cry1Ab was not transferred. Detection of bacterial genes also suggested the influence of the immune system through stimulation of Toll-like receptor 9. Michiko Nakasuji Food Safety http://www.bepress.com/fhep/11/2/10 http://www.bepress.com/fhep/11/2/10 Wed, 19 Nov 2008 21:25:41 PST This paper contributes to the economics literature on nursing market shortages by putting forward two new models that suggest three new explanations for perceived nursing shortages. The first model focuses on hospitals hiring both permanent staff nurses and temporary contract nurses. It shows that hiring both classes of nurses can represent optimizing behavior, and that an interesting kind of perceived nursing shortage results from this dual hiring. The second model posits two classes of hospitals, ``premier" and ``funds-constrained," and generates two distinct kinds of nursing shortages: economic shortages, involving unfilled, budgeted positions, and ``noneconomic" professional standards shortages. We believe that the perceived existence of professional standards shortages may be a significant explanation for the widespread impression of persistent shortages. Mark C. Long Health Economics http://www.bepress.com/fhep/11/2/9 http://www.bepress.com/fhep/11/2/9 Wed, 19 Nov 2008 21:25:38 PST BACKGROUND: The utilization of a medicine, both before and after patent expiration, is one of the key determinants of its long-run value to society, as consumer and producer surplus accumulate as utilization occurs. However, while utilization during the years of patent protection is followed fairly closely, usage after that is generally not, as multiple manufacturers are usually involved in the production and sale of generic alternatives. Since utilization beyond patent expiration is poorly understood, we selected a random sample of 60 drugs and assessed their long-term, post-patent use during the period of generic competition.METHODS: At five-year intervals beginning with the year generic competition began (YGCB), we estimated the U.S. utilization of each drug (including all generic and branded formulations) based on the number of prescriptions dispensed as projected by the National Prescription Audit (1964 to 2006) conducted by IMS. These estimates were then compared to each medicine's baseline utilization, defined as the drug's usage during the last full year of patent protection - one year prior to the year generic competition began (YGCB-1). The absolute utilization levels were converted into relative utilization levels, whereby a measure of 1.0 indicates that utilization in that year was equal to utilization in the baseline year.RESULTS: Many drugs continued to be prescribed long after patent protection ended. Even after excluding one medicine that had unusually high utilization 15 to 30 years after generic competition began, relative utilization averaged between 0.64 and 0.99 for the 5-year intervals starting with YGCB+5 and ending with YGCB+30. This was true even though several of the medicines were available over-the-counter (OTC) during some of those years and we did not have data reflecting OTC utilization. After excluding those OTC years (to focus on medicines that had more complete data), relative utilization averaged between 0.88 and 1.15.CONCLUSION: Many medicines continue to be used far beyond their period of patent protection, somewhat countering the view that newer drugs quickly replace older ones. This extended, post-patent utilization can yield additional surplus for society that is over and above the surplus generated during the period of patent protection. Edward C. Mansley Health Policy http://www.bepress.com/fhep/11/2/8 http://www.bepress.com/fhep/11/2/8 Wed, 19 Nov 2008 13:47:18 PST This study examines the impact of state health insurance regulations on the price of high-deductible family and individual polices in the nongroup market. We use a unique and rich data set on actual insurance policies sold through a large Internet health insurance distributor to examine the impact of various regulations on policy prices, controlling for policy characteristics, demographic characteristics of the purchasers, and state-level demographics. We also use data from a single major insurance firm that provided offer prices for a family policy from a set of randomly selected zip codes. Both datasets suggest a strong statistical relationship between regulation and insurance prices. Amanda E. Kowalski Health Care Reform http://www.bepress.com/bis/vol3/iss2/art8 http://www.bepress.com/bis/vol3/iss2/art8 Wed, 19 Nov 2008 09:32:25 PST Borja Barragué http://www.bepress.com/bis/vol3/iss2/art7 http://www.bepress.com/bis/vol3/iss2/art7 Wed, 19 Nov 2008 09:32:23 PST Simon Eli Birnbaum http://www.bepress.com/bis/vol3/iss2/art6 http://www.bepress.com/bis/vol3/iss2/art6 Wed, 19 Nov 2008 09:32:18 PST A guaranteed income (GI) that replaces the welfare state is not currently on the political agenda, but it offers the possibility for a grand compromise that could attract a majority political coalition. Any large-scale GI cannot be economically feasible in addition to current welfare programmes. Financial constraints in both Western Europe and the United States require that the money for funding a GI comes from the existing Social Security budgets. Using conservative assumptions, the proposed GI is demonstrably superior to the current system in enabling the elderly to accumulate comfortable retirement incomes. Furthermore, the proposed GI effectively ends involuntary poverty, even assuming minimum-wage jobs and high unemployment. The work disincentive effects of the proposed GI are diminished by a high payback point that begins at US$25,000 of earned income. The proposed GI may be expected to bring about a substantial reduction in extramarital births, and to increase, to an uncertain extent, labour force participation among young males currently outside of the labour force. Charles Murray social policy http://www.bepress.com/bis/vol3/iss2/art5 http://www.bepress.com/bis/vol3/iss2/art5 Wed, 19 Nov 2008 09:32:16 PST This article assesses Van Parijs's proposal for an unconditional universal basic income according to the Rawlsian criterion of stability--a criterion Van Parijs arguably shares. First, I examine a number of stability-generating features of conceptions of justice that pertain to their scope and content. Second, I evaluate these features relative to an unconditional versus a conditional scheme, and argue that they favour the latter. Third, I rebut four central objections to the core argument. Although the unconditional scheme may emerge as the winner, all things considered, introducing the factor of stability or sustainability nevertheless deepens our understanding of the nature and justifiability of the basic income proposal. Søren F. Midtgaard http://www.bepress.com/bis/vol3/iss2/art4 http://www.bepress.com/bis/vol3/iss2/art4 Wed, 19 Nov 2008 09:32:14 PST This article examines republican arguments for a basic income that turn on a right to exit the labour market. It gives criteria for the maintenance of republican freedom in markets, arguing that a right to exit or effective market power will guarantee republican freedom in markets. The article then considers whether a basic income is either sufficient or necessary to protect republican freedom both in labour markets and elsewhere. If a basic income is necessary to protect republican freedom in the labour market, I argue it is not sufficient to protect that freedom elsewhere. If citizens lack the means to maintain their republican freedom in the labour market, then there may be other spheres of life where they are vulnerable to subordination, whether or not they have a basic income. Some sociological evidence on cultural consumption patterns is presented. Robert Jubb Political theory http://www.bepress.com/bis/vol3/iss2/art3 http://www.bepress.com/bis/vol3/iss2/art3 Wed, 19 Nov 2008 09:32:12 PST The lottery question asks whether you would stop working, continue working in the same job or continue working in a different job if you won a sum of money large enough to allow you to live on it comfortably for the rest of your life without working. This literature review reports the results of 22 surveys carried out between 1955 and 2005 where this issue was raised in connection with basic income, and devotes specific attention to how the results have hitherto been analyzed. Used as a measure of employability, other dimensions of the lottery question, such as occupational discontent and satisfaction beyond economic necessity, have been largely overshadowed despite their prominence in the statistical material. The prevalence of non-financial employment commitment (NEC) has also been overestimated because of an analytical dichotomy between those who would continue working and those who would stop working completely if finances permitted. Suggestions for further studies include a clear distinction between non-financial commitment to current employment and to employment as such. Roland Paulsen sociology of work http://www.bepress.com/bis/vol3/iss2/art2 http://www.bepress.com/bis/vol3/iss2/art2 Wed, 19 Nov 2008 09:32:11 PST The Editors http://www.bepress.com/bis/vol3/iss2/art1 http://www.bepress.com/bis/vol3/iss2/art1 Wed, 19 Nov 2008 09:32:09 PST The Editors http://www.bepress.com/sagmb/vol7/iss1/art35 http://www.bepress.com/sagmb/vol7/iss1/art35 Tue, 18 Nov 2008 16:41:45 PST Recent biotechnology advances allow for multiple types of omics data, such as transcriptomic, proteomic or metabolomic data sets to be integrated. The problem of feature selection has been addressed several times in the context of classification, but needs to be handled in a specific manner when integrating data. In this study, we focus on the integration of two-block data that are measured on the same samples. Our goal is to combine integration and simultaneous variable selection of the two data sets in a one-step procedure using a Partial Least Squares regression (PLS) variant to facilitate the biologists' interpretation. A novel computational methodology called ``sparse PLS" is introduced for a predictive analysis to deal with these newly arisen problems. The sparsity of our approach is achieved with a Lasso penalization of the PLS loading vectors when computing the Singular Value Decomposition. Sparse PLS is shown to be effective and biologically meaningful. Comparisons with classical PLS are performed on a simulated data set and on real data sets. On one data set, a thorough biological interpretation of the obtained results is provided. We show that sparse PLS provides a valuable variable selection tool for highly dimensional data sets. Kim-Anh Lê Cao Computational Biology/Bioinformatics Microarrays Statistical Models http://www.bepress.com/bejeap/vol8/iss1/art46 http://www.bepress.com/bejeap/vol8/iss1/art46 Tue, 18 Nov 2008 12:47:11 PST Universal Pre-Kindergarten (Pre-K) programs differ from widely known and extensively evaluated programs like Head Start and Perry Preschool because access is open to all children of the appropriate age. To estimate the intent-to-treat effects of these programs on the long term educational achievement of children, I use a differences-in-differences framework and individual-level data from the National Assessment of Educational Progress. For disadvantaged children residing in small towns and rural areas, Universal Pre-K availability increases both reading and mathematics test scores at fourth grade as well as the probability of students being on-grade for their age. Increases in some measures of achievement also were seen among other groups, though the patterns were less uniform across outcome measures. The results correspond with other work showing children living in less densely populated areas are those most likely to enroll in preschool because of the program's availability. Maria D. Fitzpatrick I28 H24 H42 http://www.bepress.com/sagmb/vol7/iss1/art34 http://www.bepress.com/sagmb/vol7/iss1/art34 Tue, 18 Nov 2008 09:52:05 PST We address a potential shortcoming of three probabilistic models for detecting interspecific recombination in DNA sequence alignments: the multiple change-point model (MCP) of Suchard et al. (2003), the dual multiple change-point model (DMCP) of Minin et al. (2005), and the phylogenetic factorial hidden Markov model (PFHMM) of Husmeier (2005). These models are based on the Bayesian paradigm, which requires the solution of an integral over the space of branch lengths. To render this integration analytically tractable, all three models make the same assumption that the vectors of branch lengths of the phylogenetic tree are independent among sites. While this approximation reduces the computational complexity considerably, we show that it leads to the systematic prediction of spurious topology changes in the Felsenstein zone, that is, the area in the branch lengths configuration space where maximum parsimony consistently infers the wrong topology due to long-branch attraction. We apply two Bayesian hypothesis tests, based on an inter- and an intra-model approach to estimating the marginal likelihood. We then propose a revised model that addresses these shortcomings, and compare it with the aforementioned models on a set of synthetic DNA sequence alignments systematically generated around the Felsenstein zone. Dirk Husmeier Computational Biology/Bioinformatics Statistical Models http://www.bepress.com/ijcre/vol6/A100 http://www.bepress.com/ijcre/vol6/A100 Tue, 18 Nov 2008 06:11:37 PST Titanium dioxide was immobilized onto spherical activated carbon particles via the sol-gel coating method. The photo-catalyst, annealed at 500 °C, was found to posses the highest activity according to the results of a bench-scale test. The photocatalytic performance of the immobilized photocatalyst was studied in a three-phase fluidized bed photoreactor, with the use of phenol as the model pollutant. Effects of both liquid and air flow rates on the phenol degradation rate were examined. The experimental results showed that the increase of liquid and air flow rates may enhance the phenol degradation rate. However, very high liquid and air flow rates could lead to the decrease in the performance of the three-phase fluidized bed photoreactor. The results on the effect of initial phenol concentration on the degradation rate indicated that the photocatalytic reaction in the three-phase fluidized bed followed the first order kinetics and could be reasonably fitted by the Langmiur-Hinshelwood kinetics model. Compared to the three-phase fluidized bed in which air is introduced into the bed from the distributor, the liquid-solids fluidized bed in which oxygen is provided by injecting air into the freeboard region of the reactor showed a better phenol destruction performance and is thus preferred for photodegradation of water contaminants. Shuangshi Dong Fluidized bed photocatalysis http://www.bepress.com/ijcre/vol6/A99 http://www.bepress.com/ijcre/vol6/A99 Mon, 17 Nov 2008 19:01:47 PST The reduction of NO over coal-derived chars and the catalytic effect of Fe on NO-char reaction during char combustion were investigated in a drop-tube furnace in a temperature range of 1323-1523K. The catalytic characteristics of Fe in the NO-char reaction were studied in detail. The results show that iron (Fe) is an effective catalyst for the NO reduction by char derived from de-ashed coal at a high temperature, i.e., the chars with catalysts have high activity in the NO-char reaction. Furthermore, the stoichiometric ratio (SR) in the reaction zone has a significant influence on the catalytic activity of Fe-catalysts, which will be more effective in SR=0.7-0.9. The catalytic activity of Fe depends slightly on its loading amount, while the specific activity of the catalyst obviously decreased with the increasing of the Fe-loading amount. The effect of the temperatures used in the experiments on the NO reduction is small, which suggests the NO-char reaction mainly depends on the diffusion of reactants to char, the reactants' surface adsorption, and the desorption of products under high temperature. However, the effect of the temperature on NO reduction by metal-free char is much more important than that of NO reduction by Fe-loaded char. Bei-Jing Zhong http://www.bepress.com/ijeeps/vol9/iss5/art5 http://www.bepress.com/ijeeps/vol9/iss5/art5 Mon, 17 Nov 2008 16:50:45 PST A strategy is presented for the self-tuning of a voltage source converter (VSC) based Flexible AC Transmission Systems (FACTS) according to the prevailing system condition. L-index, which is a power system voltage stability status indicator, and its associated parameters are used to automatically regulate the modulation signal of the VSC. This will lead to a proportionate adjusting of the magnitude of the current injected into, or absorbed from, the interconnected load bus by the FACTS device. This regulating scheme will enhance seamless and optimal reactive power compensation by utilizing the dynamic operational nature of present day distressed power system networks. Results obtained using this method when applied to selected load buses of the IEEE 14 bus system under varying practical scenarios showed its capability to appropriately control FACTS devices operation to accommodate system changing conditions. It is hoped that the outcome of this work will provide efficient tools for the determination of power system status, ensure optimal utilization of the dynamic reactive power compensation devices and reduce system outages. Damian O. Dike Power System Reactive Compensation http://www.bepress.com/ijeeps/vol9/iss5/art4 http://www.bepress.com/ijeeps/vol9/iss5/art4 Mon, 17 Nov 2008 16:50:43 PST Control actions, and among others control Lyapunov functions based approaches, for improving the dynamic behaviour of electrical power systems are traditionally derived using a classical differential-algebraic model for the system, which neglects transmission networks dynamics. In the paper, an energy function which is based upon a completely differential model for power system description, is employed for deriving stabilising control actions for FACTS devices complemented with active power exchange capabilities, which have been proposed to provide additional improvements to power system dynamic behavior compared with reactive-only compensators. The use of the extended invariance principle is proposed to circumvent the difficulty arising from non-negative definite terms in the time derivative of the proposed energy function. The improvement of the dynamic behaviour achieved with the proposed strategy is proven by means of numerical applications. Antonio Griffo Power systems stability http://www.bepress.com/ijeeps/vol9/iss5/art3 http://www.bepress.com/ijeeps/vol9/iss5/art3 Mon, 17 Nov 2008 16:50:40 PST Power-stealing phenomena not only make the power industry suffer a tremendous economic loss, but also threaten the security and reliability of some rural electric networks in China.In this paper, an anti power-stealing monitoring system is developed, which contains a remote anti power-stealing terminal, a GPRS and Internet network, and a monitoring center. The anti power-stealing terminals are developed based on STPM01 and module GR47, which are installed in remote villages to detect power-stealing and measure power consumption. Power comparison methods and electricity energy comparison methods are used to confirm power-stealing. Information from anti power-stealing terminals is sent to the monitoring center through GPRS and the Internet.The monitoring system now is in operation in the Qingtongxia rural electric network, and results indicate that it is an effective way to discover power-stealing events using different power-stealing methods. Qichang Duan http://www.bepress.com/ijeeps/vol9/iss5/art2 http://www.bepress.com/ijeeps/vol9/iss5/art2 Mon, 17 Nov 2008 16:50:37 PST In this paper, a probabilistic method is proposed to analyze the very short-term steady-state performance of an unbalanced distribution electrical system characterized by the presence of wind farms. This method, which can take into account the uncertainties of loads and wind productions, is based on a Monte Carlo simulation procedure applied to the non-linear three-phase load flow equations, including wind farm models. Bayesian time series models are used to predict the next hour's wind speed probability density functions, making possible a predictive evaluation of the very short-term system steady-state behavior. Numerical applications are presented and discussed with reference to the three-phase unbalanced IEEE 34-bus test distribution system in the presence of wind farms connected at different busbars. Antonio Bracale distibuted generation distribution systems power system analysis http://www.bepress.com/ijeeps/vol9/iss5/art1 http://www.bepress.com/ijeeps/vol9/iss5/art1 Mon, 17 Nov 2008 16:50:34 PST In this paper, a new class of autotransformer-based full-wave AC-DC converters is designed, modeled and simulated to feed non-isolated DC varying loads. The proposed AC-DC converters are suitable in applications such as drives, field winding supply of large alternators, electromagnet power supplies and battery charging where isolation is not essentially required. It is considered an alternative to the popular bridge configuration that has two diodes in the path of load current. Bhim Singh AC-DC converter http://www.bepress.com/ev/vol5/iss7/art6 http://www.bepress.com/ev/vol5/iss7/art6 Mon, 17 Nov 2008 15:25:02 PST What is the likely future return on stocks, following recent market declines? Christopher Carroll consults the wisdom of Benjamin Graham, John Campbell and Robert Shiller for an answer. Christopher D. Carroll G10 http://www.bepress.com/ijfe/vol4/iss8/art5 http://www.bepress.com/ijfe/vol4/iss8/art5 Mon, 17 Nov 2008 03:03:42 PST Plums, which have a high water content level, are highly perishable and it is necessary to find alternatives to minimize product deterioration. Osmotic dehydration is one of these effective alternatives. Besides water removal from the product, the process also promotes solid gain due to high concentration of solute. In this study, the effect of different osmotic agents (sugar and sugar-glycerol) was reported. The Magee model could satisfactorily describe the solid gain and water loss during osmosis. Drying was conducted at 45, 55 and 65°C. Osmotic dehydration followed by air drying reduces the drying period. Osmotic dehydration resulted in a decrease in total convective dehydration time. The osmotic dehydration in sugar and sugar-glycerol solution reduced approximately 240 and 120 minutes as compared to the osmo-convective dehydration time of lye-treated plums at 65°C. The drying rate curves contained no constant rate period and showed a linear falling rate throughout the drying process. B. B. Ibitwar Food Engineering http://www.bepress.com/ijfe/vol4/iss8/art4 http://www.bepress.com/ijfe/vol4/iss8/art4 Mon, 17 Nov 2008 03:03:19 PST In this paper, two acetylcholinesterase (AChE) immobilization methods on the surface of a glassy carbon electrode (GCE) were compared. AChE-employed homogenate from chicken brain was home-made in the laboratory. The immobilization methods employed a cross-linking method with glutaraldehyde as a cross-linking agent, bovine serum albumin (BSA) as a protectant, and sol-gel method with tetraethoxysilane (TEOS). AChE was immobilized on chitosan membranes by these two immobilization methods. Then the enzyme membrane was fixed on the surface of GCE to prepare an AChE-GCE amperometric biosensor for the detection of organophosphorus pesticide. Measuring the activity of immobilization AChE by the oxidation current of thiocholine (TCh), produced by hydrolysis of the acetylthiocholine iodide (ATChI) substrate, the results showed that the activity of AChE-employed sol-gel method with TEOS was higher than the cross-linking method with glutaraldehyde. Biosensor sensitivity and reproducibility were statistically evaluated for the different immobilization methods and the most suitable immobilization procedure was selected. Xia Sun Comparative Study on Immobilization Methods of Acetylcholinesterase in Detection of Organophosphorus Pesticide Residues http://www.bepress.com/ijfe/vol4/iss8/art3 http://www.bepress.com/ijfe/vol4/iss8/art3 Mon, 17 Nov 2008 03:03:05 PST Studies were conducted to find the effects of coagulation temperatures on yield and quality of tofu coagulated with calcium sulfate. Instrumental Textural Analyzer was used to measure the textural properties such as hardness, cohesiveness, adhesiveness, springiness and chewiness of tofu. It was found that hardness, cohesiveness, adhesiveness, springiness, chewiness and yield increase with coagulation temperature. The developed regression equations can be used for predicting these properties in the experimental range satisfactorily. Sujata S. Mhatre Dairy and Food Engineering http://www.bepress.com/ijfe/vol4/iss8/art2 http://www.bepress.com/ijfe/vol4/iss8/art2 Mon, 17 Nov 2008 03:02:43 PST Soaking characteristics of white rice grain in water are studied at 25, 40, 60, 70 and 80 °C. The kinetics of mass transfer are modeled using a linear driving force (LDF) approximation with constant diffusivity, which is capable of predicting the moisture ratio profile with time. This approximation is a relatively new approach in food engineering applications for systems in which the rate of mass transfer is controlled by intra-particle diffusion and nonlinear adsorption through porous adsorbent. The mass transfer is also modeled through Fick's law for unsteady-state diffusion using finite difference (FD) method, and compared with the LDF model. In general, the moisture uptake curves calculated with this new approximation compare favorably with the finite difference solution obtained in spherical coordinates, producing results of similar accuracy. Both the methods give a good agreement with the experimental data. The values of the effective diffusion coefficients are between 7.33×10-11 m2/s and 1.43×10-10 m2/s for a temperature of 25 and 80 °C respectively. Although gelatinization of starch is observed at a higher temperature which influences the increase in moisture content, the moisture uptake curves calculated with this new approximation compare favorably with the numerical solution of the non-linear diffusion equation. As such, it can be safely used to predict the unsteady-state moisture absorption kinetics of a rice grain, for the temperature range investigated. Abhishek Dutta Diffusion Food Engineering Computational methods http://www.bepress.com/ijfe/vol4/iss8/art1 http://www.bepress.com/ijfe/vol4/iss8/art1 Mon, 17 Nov 2008 03:02:26 PST The air-drying kinetics of plum tomato pieces pre-treated with different osmotic solutions were investigated. Four pre-treatment solutions (comprised of salt, sugar and/or calcium lactate), three sample geometries (halves, quarters and eighths) and two air-drying temperatures (55 and 65°C) were studied. In general, the rate of drying over time appeared to fit an exponential curve (R2 values between 0.74 and 0.99). A closer look at the data indicated that the rate of drying appeared to follow two separate falling rate periods. The change from one falling rate period to another was observed for samples at a transition moisture ratio of ~ 0.2, for all geometries and temperatures. Thus, modeling the process was improved by including the two falling rate periods. The drying constant (K) for the two falling rate periods ranged between 0.05 to 0.3 h-1. Moisture diffusivity values ranged from 2.5 x 10-9 to 9 x 10-9 m2 s-1 and were relatively constant during the first falling rate period. During the second falling rate period, the diffusivity increased as the moisture ratio decreased, though this change was less pronounced as the sample size decreased from halves to eighths. The untreated samples had lower diffusivities than those with osmotic pre-treatment but there were no differences amongst the various pre-treatment solutions. In general, moisture diffusivities showed a dependence on the sample size, as the larger tomato samples had higher values of diffusivity. The greater diffusivity seen in the larger samples may be due to the collapse of cell walls in the skin. Marianne S. Brooks dehydration