196,511 research outputs found
Seasonal fluctuations of the fungusflora in mull and mor of an oak forest
No full textThis paper describes the fungusflora of three types of forest litter. The distribution of the fungi in space and time and their interrelationships with various aspects of the soil environment are considered. The work was part of a study of the mechanism of transformation of organic matter into soil humus. The information obtained is of importance in the Netherlands for two main reasons: 1. As a result ofthe rapidly increasing population, and the shift ofthe rural population to urban areas, valuable horticultural land, surrounding towns and cities, is constantly lost. Horticultural crops require soil with a good humus status. As this becomes unavailable, it must be created by proper soil supplementation and management. To this end, knowledge of the mechanism of the decomposition of organic material and the formation of good humus is desired. 2. As a result of the intensive use of soil for more profitable agricultural pursuits, only the poorer soils are available for forestry. This, combined with the long rotation period required in forestry, has decreased revenues, and it is clear that costs must be kept at a minimum. Fertilizers become uneconomical even on these poor soils. Consequently, more efficient use of the minerals present in the soil is a necessity. Minerals, accumulated in undecomposed litter, must be made available, and their loss by leaching must be prevented. Knorvledge of the mechanism of the decomposition of organic materials in soil is fundamental to attainment of these objectives
Advances in Protein Precipitation
No full textProteins are biological macromolecules, which are among the key components of all living organisms. Proteins are nowadays present in all fields of biotech industry, such as food and feed, synthetic and pharmaceutical industry. They are isolated from their natural sources or produced in different cell lines. Most important large-scale bioseparation techniques for proteins are precipitation, crystallization, membrane separations and chromatography. Food and feed proteins are usually recovered using low-resolution techniques such as membrane filtration and precipitation, whereas high-value proteins are recovered and purified by means of high-resolution techniques, such as crystallization and chromatography. Precipitation is a mature technique, which enables crude recovery of proteins from natural sources. Industrial scale precipitation is often associated with the consumption of large amounts of auxiliary materials, such as salts or organic solvents, and hence regarded as a burden for the environment. This thesis presents advances in protein precipitation based on a novel method, CO2-aided acidification. Precipitation based on carbon dioxide is an environmentally friendly technique, which relies on protein precipitation at its isoelectric point. The CO2-based acidification is used to develop a novel method for protein purification. It also forms a basis of a newly developed technique for active ingredient immobilization. Nowadays precipitation of food proteins is mainly performed using precipitants such as salts or organic solvents. As a consequence the precipitate needs to be treated to remove the precipitant and all process streams have to be additionally processed before the disposal. This puts an additional burden on the environment and the energy consumption. Chapter 2 presents a novel method for purification of glycinin from soy by using a single precipitant, CO2. The gaseous CO2 is used to acidify the solution containing a mixture of soy proteins, using the pressure as the control parameter. The subtle acidification enables selective precipitation of glycinin from the solution. The selective precipitation of glycinin is repeated several times to obtain a high grade of purity (98%). The protein is subsequently freeze–dried and a later re-solubilization indicates that the protein did not denature during the purification process. The purification process was successfully scaled up from a 50 mL to a 1 L vessel. The characteristic time analysis of the underlying mechanisms (precipitation, liquid mixing and mass transfer) showed that they remain unchanged with the scale-up. In addition, the characteristic time analysis reveals that the mass-transfer of the carbon dioxide from the gaseous to the liquid phase is the rate-limiting step. Bioseparation processes development traditionally relies on the empirical approach. Recently, however, a lot of attention has been devoted to the rational design of the bioseparation processes. For this approach protein characterization is a crucial step. One way to obtain valuable information about protein behavior is to measure thermodynamic properties of the protein solution. In Chapter 3 we present a study of thermodynamic properties of glycinin solutions as a function of pH. The osmotic second virial coefficient of glycinin solutions was measured by using static light scattering (SLS). Glycinin proved to be a cumbersome molecule for the SLS measurements, due to its size and pH-dependent solubility. We established a working window and successfully performed static and dynamic light scattering of glycinin solutions. The SLS measurements revealed that the second osmotic virial coefficient becomes highly negative with decreasing pH, which corresponds to the known property of glycinin to precipitate at its isoelectric point. The CLEA technology has been extensively developed in the past decades. It is based on a two-step approach: initial aggregation followed by cross-linking. The technique has been successfully used over years to immobilize different enzymes. In Chapter 4 we present a scouting study for using carbon dioxide as a precipitant in the initial aggregation step. The CO2-aided precipitation was tested for a number of enzymes using soy protein as a control. Under the conditions tested in the scouting study no aggregation in enzyme solutions was observed when subjected to the CO2-aided acidification. Theoretical considerations on the observed phenomena are presented. In addition, a screening study of the classical organic precipitants for the manufacturing of CLEAs is described. The morphology and structure of the CLEA particles is evaluated. Immobilization of active ingredients has been widely explored for the past few decades. It is applied in food, cosmetic and pharmaceutical industry and relies on a stabile matrix to immobilize and protect an active ingredient. The purpose is to obtain prolonged activity and in some cases sustained release of the active ingredient. In Chapter 5 we present a novel method for active ingredient immobilization based on the CO2-aided co-precipitation with glycinin. Thanks to its property to precipitate easily at its isoelectric point, glycinin was used as a matrix for the active ingredient co-precipitation. The proof of principle was shown using the enzyme lipase, which is successfully co-precipitated into the glycinin matrix while retaining its activity. Importantly, the obtained co-precipitate was of food-grade quality, without organic precipitants or salts. This makes an obvious advantage in reduced post-processing and a broad range of application possibilities. In Chapter 6 a detailed characterization of the co-precipitate of glycinin and lipase is presented. The co-precipitate was tested for resolubilization and lipase activity at different pH conditions. The resolubility of the co-precipitate was shown to be equivalent to that of glycinin. The lipase activity was enhanced as compared to native lipase. In addition, lipase in the co-precipitate retained activity at otherwise harsh conditions, indicating the protective role of the glycinin matrix. The dissolution of the co-precipitate was successfully described by a model based on two mechanisms: disintegration of the particles into multimers and diffusion of the multimers into the liquid phase. The model fitted reasonably well the experimentally obtained data. Lipase activity in the liquid phase was observed even when the co-precipitate scarcely dissolved. This indicates that lipase can diffuse from the co-precipitate particles into the liquid phase.BiotechnologyApplied Science
Physical Aspects of Scraped Heat Exchanger Crystallizers: An Application in Eutectic Freeze Crystallization
No full textOne of the most important natural resources is fresh water. An unfortunate issue is however, the low availability and high demand of fresh water world-wide. From the total resources industry consumes about 20 % (1200 km3 yearly) [UN, 2007]. Industrial aqueous waste streams are therefore widely occurring, and their reuse becomes obligatory. For the recovery of water from dilute solutions multistage flash evaporation has been used for a long time. Reverse osmosis has proven to be a better alternative energy-wise, but is only a good option up to a solute concentration of about 5% above which the required pressure becomes too high. Conventional separation processes then become too expensive, and the residual often large waste streams are collected in ponds for further atmospheric drying or discharged in surface waters. For the treatment of more concentrated waste waters novel separation techniques therefore had to be developed where besides pure water, one or more pure inorganic or/and organic compounds were obtained, and where only a minor bleed stream remains for e.g. incineration or disposal. If indeed additionally one or more pure secondary raw materials can be produced for reuse or with a market value, such a separation process becomes economically feasible, and has a fair chance to be implemented. Eutectic Freeze Crystallization fits this requirement. In this crystallization process, that operates under eutectic conditions, pure ice and a second pure solid compound such as a salt or an acid, are simultaneously formed in case of a binary aqueous solution. For a more complex solution both pure ice and a mixture of compounds or in subsequent steps pure ice and one of the pure compounds are formed. Since ice floats to the top of the vessel and the other compound(s) present in the solution settle(s) to the bottom, the separation of the ice from the salts is facilitated. For the first prototypes of EFC crystallizers horizontal heat exchanger disks were used with holes to allow transportation of crystals through these holes during their segregation. EFC research continues to improve these designs and create new ones that minimize energy consumption by cutting energy losses to the environment, by increasing the heat fluxes by improved scraper designs, and recently by a radical change in heat exchanger geometry to improve the gravitational separation efficiency. This research focuses on physical phenomena that take place inside a common cooling crystallizer or inside a eutectic freeze crystallizer with a scraped heat exchanger surface with the aim to improve the scraper and the crystallizer design. One of the limiting factors for heat transfer in EFC processes is the formation of an insulating ice scale layer on the heat exchanger surface. In spite of the fact that scrapers are used to increase the heat transfer at the solution side, as well as to avoid the formation of an insulating ice scale layer, such scrapers are only effective in keeping the surface free from ice up to a certain temperature difference between the coolant and the solution. Earlier experiments have also demonstrated that for a horizontal heat exchanger surface that was evenly cooled underneath and evenly scraped at the top, scaling still preferentially starts at specific areas of the surface. Since ice scale formation at a certain spot on the heat exchanger surface is a consequence of the local temperature difference between the surface and the solution, this implies that the temperature at the surface differs locally. These variations in local temperatures are most likely induced by the flow field of the liquid insidethe crystallizer. In chapter 2 the temperature distribution across the horizontal heat exchanger surface at the bottom of the crystallizer was therefore measured by Liquid Crystal Thermometry and the local heat transfer distribution was calculated, while the fluid velocity inside the crystallizer was directly visualized by Stereoscopic PIV measurements. Liquid Crystal Thermometry revealed that the temperature on the heat exchanger surface was not uniformly distributed with temperature differences larger than 4 oC. Such differences are sufficient to explain the local variation in scaling tendency. Experimental results showed that in the middle of the scraped heat exchanger area the heat transfer is larger than around the shaft and close to the crystallizer wall. A strong secondary fluid flow in this crystallizer geometry was shown by stereoscopic PIV measurements. This flow pattern in the crystallizer is undoubtedly related to the differences in local heat flux, but the local heat fluxes could not directly be explained without a more detailed knowledge of the flow field close to the HE surface in the scraper region. For more detailed information on the flow pattern between the scrapers and thus more closely to the HE surface we had to rely on computational flow simulations, because this region was not accessible for PIV measurements. The turbulent flow in the total scraped HE crystallizer was therefore computationally resolved by Large Eddy Simulations using a Lattice Boltzmann scheme as reported in chapter 3. The simulations were validated by comparison with the PIV measurements performed previously. The LES results could explain the radial local heat transfer distribution along the HE surface. The local heat flux is higher in the middle region of the HE surface between the shaft and the outer wall because the fluid descends directly from the bulk, and its residence time near the HE surface is low. The lower local heat flux coefficient around the shaft is because the fluid is largely in solid body rotation. Close to the outside wall, a worse situation for heat flux is provoked by a static vortex that brings the fluid into a segregated area. These fluid flow results explain the local heat flux distribution measured by the TLC experiments. The shape of the scraper has a large impact on the turbulent fluid flow and related behavior of the scraped off ice particles in the direct vicinity of the HE surface. For a well-designed scraper the ice particles have to be transported up by the flow into the solution, and should not be redirected to the surface. In chapter 4 the liquid flow is visualized by dye injection and the particles are monitored directly for two types of commonly used scraper geometries. In conjunction with this experimental work direct numerical simulations of the two phase (solid-liquid) flow system were done. The particle-flow simulations used Lattice-Boltzmann discretization to solve the Navier-Stokes equations, and a Lagrangian approach to particle tracking. The simulation results were in qualitative agreement with the experimental visualizations of the same system, and provided good insight in the behaviour of the particles and the fluid flow induced by the two scraper geometries. Only drag and gravity forces acting on the particles were taken into account. Furthermore particles collided elastically with the HE surface and the walls defining the moving scraper. Our numerical approach without particle-particle collisions provided satisfactory results for the streamlined scraper because this shape did not accumulate the particles during its scraper action. For the vertically oriented scraper this simulation approach failed due to the build up of particles as could be observed from the visualisation experiments. It was therefore considered to be essential to include particle-particle collisions in order to predict accumulation of particles. When this was implemented the simulations were in agreement with the results of the visualization experiments. This type of simulations demonstrates that scrapers can be primarily designed based on numerical predictions. In chapter 5 a novel laboratory scale scraped cooled wall crystallizer with 130 liter capacity, two internal vertical cylindrical heat exchangers, and a total heat transfer area of 2.94 m2.m-3 crystallizer volume was designed. This crystallizer was tested for the recovery of Na2CO3.10H2O and ice from an industrial aqueous sodium carbonate/sodium bicarbonate solution. Compared with earlier designs this new design showed a high improvement in gravitational separation and ice scaling removal, and high heat transfer fluxes were achieved between the heat exchanger and the solution up to 10.5 kW.m-2. A cone installed in the top section effectively directed the ice crystals towards the outlet. The total solid content in the crystallizer was up to 36 wt% under steady state conditions, with average crystal sizes for ice of 100-200 mm and 50-120 mm for Na2CO3.10H2O. Impurities present in the solution, most likely the molybdate ions changed the habit of the Na2CO3.10H2O crystals from pseudo hexagonal for a pure system to lozenges. In Chapter 6 the performance was tested of a scaled up version of the new type of crystallizer with two heat exchanger modules stacked on top of each other. This crystallizer was directly connected to a continuous carbonate/bicarbonate containing blow-down stream in an industrial plant. The EFC process was effectively operated at a heat transfer of 5 kWm-2 without any ice scaling. Sodium carbonate decahydrate and pure ice were continuously produced at -3.8 oC by operating within the metastable zone width of bicarbonate. The crystals showed good filterability with a molybdenum content below 1 ppm. At -4.0 °C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product. Because of the necessity of an accurate phase diagram for the process described in chapter 6, the eutectic solubility lines of the ternary system NaHCO3-Na2CO3-H2O were determined experimentally and calculated with the extended UNIQUAC model in chapter 7. The extended UNIQUAC model describes the experimental data quite well. A special crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution. Anhydrous NaHCO3 and Na2CO3.10H2O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. The anhydrous NaHCO3 crystals were needle shaped with lengths between 5 and 10 ?m, that were agglomerated into particles of about 100 ?m to 300 ?m, while the Na2CO3.10H2O were hexagonally shaped with sizes between 100 and 500 ?m. Chapter 8 focuses at the interface between a scale layer that grows upon a cooling surface and the solution. Scale formation on heat exchangers is not only happening in EFC processes or for ice, but is frequently encountered in many cooling crystallization processes. Crystallization is mostly an exothermic process. According to irreversible thermodynamics, the heat released during crystallization at the interface is distributed to both the liquid and solid phases which are in contact with the interface also for isothermal conditions. The excess entropy production rate for heat and mass transport into, out of and across the interface was used to define the fluxes and forces of the system. The method describes the interface as a separate (two-dimensional) phase in local equilibrium. Coupled heat and mass flux equations from non-equilibrium thermodynamics were defined for crystal growth and the temperature jump at the interface of the growing crystal. For theoretical and experimental simplicity the growth of MgSO4·7H2O on a cold surface was taken as an example. For a growth rate of 2.33×10-3 mol.m-2.s-1, around 20-30% of the heat of crystallization is calculated to be transferred back into the liquid side. The interface resistivity to mass transfer is 1.26×103 J.m2.s.K-1.mol-2, while the interface resistivity to heat transfer is 2.1×10-7 m2.K-1.W-1.Process and EnergyMechanical, Maritime and Materials Engineerin
Process and equipment development for textile dyeing in supercritical carbon dioxide
No full textThe large-scale water pollution by the textile dyeing industry is a global environmental problem. The ever more stringent regulations on wastewater also make it an economical problem. In the last two decades therefore, research has been done on an environmentally benign technology, using supercritical carbon dioxide (scCO2) as a dye solvent, rather than water. The applicability of the technology is limited at this moment by two factors. Firstly, there is not enough knowledge on reactive and non-reactive dyeing. Secondly, because the process operates at conditions of typically 120C and 300 bar, high-pressure equipment is needed which results in high investment costs that stand in the way of industrial implementation. In this work, the supercritical dyeing process was investigated experimentally regarding both reactive and non-reactive dyeing and also new equipment was designed to minimize the equipment and process costs.Design, Engineering and Productio
Textile Dry Cleaning Using Carbon Dioxide: Process, Apparatus and Mechanical Action
No full textFabrics that are sensitive to water, may wrinkle or shrink when washed in regular washing machines and are usually cleaned by professional dry cleaners. Dry cleaning is a process of removing soils from substrate, in this case textile, using a non-aqueous solvent. The most common solvent in conventional dry cleaning is perchloroethylene (PER). Despite its satisfactory cleaning performance, PER has several drawbacks. One approach is to develop an alternative solvent for PER. CO2 is chosen in this study because it has several advantages compared to the other alternative solvents. The main objective of this study is to improve the cleaning performance of CO2 dry cleaning for particulate soils, firstly by studying and solving the redeposition problem, secondly by enhancing the amount of mechanical action applied to the fabric. Another objective of this thesis is to achieve more insight in the cleaning process since little information is available regarding the textile movement inside the rotating drum in the CO2 medium. This has been studied with an endoscopic camera in the 25 L CO2 dry cleaning machine. Experiments with an observation cell equipped with a mechanical actuator were performed to apply well defined forces on the textile, and use these results to perform a quantitative analysis of the mechanical forces. Based on the results of the above, an ideal CO2 dry cleaning machine and process has been designed. This is a combination of best practices, new insights obtained from the results of this study and the best available technologies. The performance and the investment costs of CO2 dry cleaning are not yet comparable with the conventional solvents or the other alternative solvents. However, we believe that CO2 is the only real green solvent for textile dry cleaning and our studies have shown that it has a high potential to replace PER in the future. The economy evaluation also showed that the operating costs for dry-cleaning using CO2 are comparable to the costs using PER.BiotechnologyApplied Science
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
The ideal solution
No full textA smart use of high-pressure carbon dioxide may make a special class of eco-friendly solvents known as ionic liquids much more attractive to the fine chemical industry. Researcher Dr. Maaike Kroon has demonstrated that, on paper at least, the savings can be astronomical.Applied Science
Cleaning power that's new as well as "green": Cleaning clothes using liquefied gas and solid amides
No full textWhenever you take your clothes to the dry-cleaners they usually come back as good as new, but always with that peculiar smell. Up to now the business of dry-cleaning has been associated with health hazards because of the potentially toxic and environmentally harmful solvents, the most commonly used one being perchloroethylene. Chemical engineer Maaike van Roosmalen has optimised a method for cleaning fabrics using liquid carbon dioxide. The process uses an amide derived from an amino acid to act as the cleansing agent. The results are already very close to those of conventional drycleaning methods, which may soon become obsolete, as the new system replaces the perchloroethylene with CO2, thereby minimizing the impact on the environment
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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