1,354,970 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Scaling-Up Eutectic Freeze Crystallization
No full textA novel crystallization technology, Eutectic Freeze Crystallization (EFC) has been investigated and further developed in this thesis work. EFC operates around the eutectic temperature and composition of aqueous solutions and can be used for recovery of (valuable) dissolved salts (and/or or acids) and water from a wide variety of aqueous process streams. Using EFC, processes producing large quantities of saline solutions could be carried out in an ecologically and economically attractive way. An introduction and a brief summary of earlier work are given in Chapter 1. The experimental study on pilot scale Cooled Disc Column Crystallizer (CDCC-2) designed for continuous EFC operation is presented in Chapter 2. CDCC-2 was tested for an industrial MgSO4 stream and evaluated in terms of heat transfer, ice and salt sizes, production and growth rates. Application of conductivity and refractive index measurement techniques for inline concentration and supersaturation measurements of MgSO4 solution was studied in Chapter 3. Chapter 4 presents the CDCC-3 and Skid Mounted Unit, designed and constructed for 130 ton/year MgSO4.7H2O and water production capacities. MgSO4 salt crystal structure at eutectic conditions was studied and reported in Chapter 5. The MgSO4 crystal hydrate formed below approximately 0 oC was proven to be MgSO4.11H2O instead of the common reported MgSO4.12H2O. Crystal structure analysis and the molecular arrangement of these crystals were determined using single crystal X-ray diffraction. Raman spectroscopy was used for characterizing MgSO4.11H2O and for comparing the vibrational spectra with MgSO4.7H2O. Thermo gravimetric analysis confirmed the stochiometry of MgSO4.11H2O. Additionally the Miller indices of the major faces of MgSO4.11H2O crystals were defined. Chapter 6 covers the discovery of the natural occurrence of the MgSO4.11H2O new mineral -Meridianiite- as salt inclusions in sea ice from Saroma Lake-Japan and in Antarctic ice. In Chapter 7 nucleation and crystal growth of MgSO4 aqueous solution on a cooled surface were studied theoretically and experimentally. Coupled heat and mass flux equations from non-equilibrium thermodynamics (Onsager theory with reciprocal relations) were defined for crystal growth and the temperature jump at the interface of the growing crystal. Chapter 8 aims to describe the Cyclic Innovation Model (CIM) and to set a path for commercialization of the EFC technology.Mechanical Maritime and Materials Engineerin
Removal and Recovery of Phosphonate Antiscalants
No full textIn reverse osmosis (RO) desalination processes, the use of phosphonates prevents scaling, thus allowing for a higher product water recovery, which increases the efficiency of the process. However, a major concern associated with their use in RO desalination is the high cost and environmental impacts associated with the discharge of the waste brine or membrane concentrate containing phosphonates. Therefore, technologies are needed that can remove and recover phosphonate antiscalants from membrane concentrates. Chapters 2 to 5 of this thesis describe a process for the removal and recovery of phosphonate antiscalants by using adsorption technology. In Chapter 2 the phosphonate adsorption capacities of two commercially available anion exchange resins and activated carbon were compared to that of the cheap waste material iron-coated waste filtration sand (WFS). The results presented showed that, in contrast to the exchange resins, the equilibrium adsorption of nitrilotris(methylene phosphonic acid) (NTMP) on WFS is not suppressed at increasing ionic strength and is much less affected by the competitive anions carbonate and sulfate. The strong affinity of phosphonate with the iron oxy-hydroxide in the coating resulted in a relatively high adsorption capacity for NTMP of this waste material. Iron oxy-hydroxides perform very well in adsorbing phosphonates from membrane concentrates. Therefore, an iron oxy-hydroxide was selected that, in contrast with WFS, has a high purity and can be obtained commercially. Granular ferric hydroxide (GFH) was investigated as an adsorbent for NTMP in Chapter 3. Both the equilibrium and kinetics of NTMP adsorption on GFH were investigated. The adsorption kinetics were predicted fairly well with two models that considered either combined film-pore or combined film-surface diffusion as the main mechanisms for mass transport. It was demonstrated that phosphonate is preferentially adsorbed over sulfate by GFH and that the presence of calcium is beneficial for the adsorption process. Calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Spent GFH is reusable after regeneration with a sodium hydroxide solution, showing that NTMP can be recovered from the RO concentrate. In analogy with Chapter 3, the adsorption and desorption of NTMP from RO membrane concentrate on iron-coated waste filtration sand (WFS) has been investigated in Chapter 4. Equilibrium adsorption was described well with a Langmuir isotherm. Although the low cost and on-site availability of WFS is advantageous over GFH, the results revealed some drawbacks. WFS appeared to have a much lower adsorption capacity compared to GFH, which was related to the presence of impurities, the presence of manganese oxides, and aging of the ferrihydrite phase in the coating of WFS. The aim of Chapter 5 was to employ GFH in a packed bed adsorption column. The effective diffusivities and external film mass transfer coefficients estimated in Chapter 3 were used to predict the concentration of phosphonate in the effluent. Also, the regeneration of the saturated column with sodium hydroxide solution was investigated. In addition, it was investigated whether the regeneration solution containing the recovered phosphonate could be further concentrated by using a nano-filtration or a calcium-phosphonate precipitation step. The use of nano-filtration seemed to be more attractive. The first five chapters show that adsorptive removal of phosphonate antiscalants offers a viable way to improve RO concentrate treatment processes and enables the recovery of the phosphonate for reuse in the RO desalination process. Another way of tackling the unwanted discharge of phosphonates is minimizing their use. Smart sensors that predict the risk of scaling at an early stage can help to control the dosage of phosphonate antiscalants. This will allow for minimum usage of phosphonates without the risk of scaling. Chapters 6, 7, and 8 contribute to the development of such a sensor. Focus was on the development of the actuator part of the sensor that enhances crystal growth and precipitation by ultrasonic irradiation. In Chapter 6 the effect of ultrasonic irradiation on the crystallization of calcite was investigated. Seeded calcite growth experiments were conducted under constant composition conditions while the applied ultrasonic irradiation created cavitation bubbles throughout the suspension. In this way it was demonstrated that ultrasound enhances the crystallization rate of calcite substantially (i.e., 46 %), due to the ability of the generated cavitation bubbles altering the crystals’ habit and size. The increased surface area available for crystal growth resulted in enhancement of the observed crystallization rate. In Chapter 7, the cavitation phenomena that are responsible for the previously observed volumetric crystallization rate enhancement were visualized using high speed photography. Cavitation clusters cause attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation causes deagglomeration only. Cavitation inception on the surface gave the small crystals momentum. However, it was shown that breakage of accelerated crystals by interparticle collisions is unrealistic because, upon bubble collapse, they subsequently experienced a deceleration much stronger than expected from drag forces. These direct observations contradict the general assumption that interparticle collisions always play an important role in particle attrition by cavitation. Scanning electron microscopy pictures of irradiated calcite crystals showed deep circular indentations, possibly caused by shockwave induced jet impingement. Moreover, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures. The possibility of using ultrasound as a tool to enhance the demineralization of supersaturated calcium carbonate solutions (e.g., membrane concentrates) containing growth inhibitors was investigated in Chapter 8. The inhibiting effect of the phosphonate NTMP on crystal growth can be mitigated by ultrasonic irradiation. The results can be explained in part by breakage and attrition of poisoned crystals, resulting in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that ultrasound can also degrade NTMP. These observations confirm in part the hypothesis that ultrasound can be used as actuator. As an alternative to the removal of phosphonates or minimizing their use by smart sensoring techniques, phosphonates may also entirely be replaced by environmental friendly antiscalants, which is the subject of Chapter 9. The effectiveness of such an alternative, carboxymethyl inulin (CMI) biopolymers, in inhibiting calcium carbonate crystallization was compared to two phosphonate antiscalants. Compared to the phosphonates, the biopolymers exhibited a stronger inhibitory effect on the crystal growth of calcite. It was shown that the ability of the biopolymers to mitigate the spontaneous precipitation of calcium carbonate is controlled by their degree of carboxylation. The biopolymers can affect the crystal habit similar to the phosphonates, which suggests that their function as crystal growth inhibitor is comparable. These results demonstrate that CMI biopolymers are effective calcium carbonate crystallization inhibitors, indicating they can replace phosphonates as antiscalant. In Chapter 10, the results presented in this work are being discussed and, where possible, placed into perspective of future desalination developments.Process and EnergyMechanical, Maritime and Materials Engineerin
Mixed Solvent Reactive Recrystallization of Sodium Carbonate
No full textInvestigation of the reactive recrystallization of trona (sodium sesquicarbonate) and sodium bicarbonate to sodium carbonate (soda) in a mixed solvent led to the design of several alternative, less energy consumptive, economically very attractive process routes for the production of soda from all principal sodium carbonate sources. The kinetics of the recrystallization as well as of the superimposed chemical reaction, the decomposition of the bicarbonate ion, have been measured, a thermodynamic model for the prediction of the transition temperatures for hydrate recrystallization is presented and the different occurring recrystallization mechanisms are explained in detail. In addition, several inline purification processes for the recycle of the mixed solvent have been investigated: electrodialysis, ion exchange and reactive extraction. The formed soda of mixed solvent reactive recrystallization was also found to possess higher chemical purity, higher mechanical stability and lower bulk density than commercially available soda (dense soda ash).Design, Engineering and Productio
Effect of Ultrasound on Calcium Carbonate Crystallization
No full textScaling comprises the formation of hard mineral deposits on process or membrane equipment and calcium carbonate is the most common scaling salt. Especially in reverse osmosis (RO) membrane systems, scale formation has always been a serious limitation, causing flux decline, membrane degradation, loss of production and elevated operating costs. In this work a novel concept is proposed for the prediction of scale formation tendency. By enhancing the crystallization (kinetics) locally and monitoring the process itself, scaling can be predicted accurately before it occurs in the bulk solution. This will result in better scaling risk assessment, improving chemical dosage (preventing overdosing) and prevent the necessity of cleaning or membrane replacement. Ultrasound is selected as possible method for crystallization enhancement. Consequently, the topic of this research is the effect of ultrasound on crystallization of calcium carbonate.BiotechnologyApplied Science
A new technology for the reduction of particulate matter from diesel engines in ships
No full textIn this thesis the focus is on the particulate matter reduction of ships, as ships contribute significantly to the particulate matter concentration in ambient air. Because the fuel of sea ships contains a lot of ash, the emitted particulate matter will also contain a lot of ash. In car and truck applications the soot filters are cleaned by burning the particulate matter off of the filter. However, ash will not be burned off and accumulates in the filter. In the case of high-ash loads, like sea ships, a soot filter is not applicable, because the filters cannot be cleaned properly. The goal of the research was to develop a technology to reduce particulate matter that is fuel insensitive. In this thesis such a technology is described, tested and simulated for high-ash applications. The patented technology is based on coating particulate matter with water, and subsequently capturing by an electrostatic precipitator (ESP). In the present experimental set-up this was a two-stage ESP, which has a robust construction and a reduced risk of physical contact between the electrodes at different potential. The water-coated particles will flow off the collection plates, therefore allowing continuous operation of the ESP. The water stream needs to be cleaned before it is discharged in the surface waters. The required cleaning technology, however, is similar to the cleaning technologies used in sea water scrubbers. It is proven that the technology is capable of removing 80% of particulate matter, including the fraction of particulate matter smaller than 1 micrometer in (mobility) diameter. It was found that the new technology was rather insensitive to particle size and is thus very suitable to remove sub-micron particles.Mechanical Maritime and Materials Engineerin
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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