1,720,986 research outputs found
PERFORMANCE EVALUATION OF CEMENT MORTAR AND CONCRETE WITH INCORPORATED MICRO FILLERS OBTAINED BY COLLISION MILLING IN DISINTEGRATOR
Get PDFThe Effect of Alkaline Material Particle Size on Adjustment Ability of Buffer Capacity
Get PDFThe pH control in biotechnological processes like anaerobic digestion is one of the key factors to ensure high efficiency in the biogas production process. The decrease of pH level in the digestion process occurs due to the rapid acid formation during metabolic processes of bacteria which leads to the inhibition of the methane producing bacteria; therefore further digestion process is limited. The efficiency of anaerobic digestion reactor decreases dramatically if the pH level falls under pH 6.6. This problem is common for single-stage continuous digesters with a high organic solid content; therefore the active pH controlling method is commonly used. By creating inorganic alkaline material, the passive pH controlling system could be created. Soluble alkalis are enclosed in the matrix of material during the activation process thus providing slow leaching of free alkalis from the material structure in water medium and ensuring pH increase. In this research a porous alkaline composite material was developed as a pH controlling agent for the biogas production. Two mixture compositions with a different Si/Al and Si/Na ratio were created. The effect of particle size of the material was investigated in order to provide different leaching rates for the described material. Granular material with particle fractions 1/2 mm, 2/4 mm and 4/8 mm and a cubical specimen with dimensions 20×20×20 mm were tested. The pH level of water medium increased up to pH 11.6 during the first day and final pH value decreased to 7.8 after 20-day leaching. Alkali leaching can be increased by 19-32% changing the mixture composition by adding glass powder to the alkaline material. The particle size factor was negligible for leaching rate of alkaline material due to the high porosity of material. Research results show that this composite material has a potential to be applied in pH control for biotechnological purposes.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7325</p
Compressive Strength of Cement Mortar Affected by Sand Microfiller Obtained with Collision Milling in Disintegrator
No full textThe Effect of Porous Alkali Activated Material Composition on Buffer Capacity in Bioreactors
No full textWith demand for primary energy continuously growing, search for renewable and efficient energy sources has been high on agenda of our society. One of the most promising energy sources is biogas technology. Residues coming from dairy industry and milk processing could be used in biogas production; however, low efficiency and high cost impede wide application of such technology. One of the main problems is management and conversion of organic residues through the anaerobic digestion process which is characterized by acidic environment due to the low whey pH (<6) whereas additional pH control system is required. Low buffering capacity of whey is responsible for the rapid acidification in biological treatments; therefore alkali activated material is a promising solution of this problem. Alkali activated material is formed using SiO2 and Al2O3 rich materials under highly alkaline solution. After material structure forming process is completed, free alkalis remain in the structure of materials which are available for leaching and could provide buffer capacity potential. In this research porous alkali activated material was investigated. Highly porous material structure ensures gradual leaching of alkalis during time which is important in biogas digestion process. Research of mixture composition and SiO2/Na2O and SiO2/Al2O ratio was studied to test the buffer capacity potential of alkali activated material. This research has proved that by changing molar ratio of components it is possible to obtain a material with different buffer capacity, and this novel material was seen to have considerable potential for using it in processes where buffer capacity and pH control is vitally important
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Properties of Foamed Lightweight High-Performance Phosphogypsum-Based Ternary System Binder
No full textThe potential of phosphogypsum (PG) as secondary raw material in construction industry is high if compared to other raw materials from the point of view of availability, total energy consumption, and CO2 emissions created during material processing. This work investigates a green hydraulic ternary system binder based on waste phosphogypsum (PG) for the development of sustainable high-performance construction materials. Moreover, a simple, reproducible, and low-cost manufacture is followed by reaching PG utilization up to 50 wt.% of the binder. Commercial gypsum plaster was used for comparison. High-performance binder was obtained and on a basis of it foamed lightweight material was developed. Low water-binder ratio mixture compositions were prepared. Binder paste, mortar, and foamed binder were used for sample preparation. Chemical, mineralogical composition and performance of the binder were evaluated. Results indicate that the used waste may be successfully employed to produce high-performance binder pastes and even mortars with a compression strength up to 90 MPa. With the use of foaming agent, lightweight (370–700 kg/m3) foam concrete was produced with a thermal conductivity from 0.086 to 0.153 W/mK. Water tightness (softening coefficient) of such foamed material was 0.5–0.64. Proposed approach represents a viable solution to reduce the environmental footprint associated with waste disposal
Environmental Benefit of Alternative Binders in Construction Industry: Life Cycle Assessment
No full textCarbon dioxide (CO2) emissions associated with Portland cement (PC) production is ranked as the highest among the construction materials and it is estimated that 8% of the worlds CO2 discharges is due to PC production. As an average, the production of PC clinker including calcination process generates 0.81 kg of carbon dioxide per one kg of cement. Hence, new approaches which limit the negative environmental impacts of cement production and are aimed at the development of advanced methodologies are introduced. Implementation of lower energy consumption materials in production, which could moderately substitute PC in binders, can be addressed as one of the probable methods in mitigating environmental risks. Therefore, alternative binders fit into the most promising solutions. Present research investigates the environmental impact of the building sector, if an alternative to PC binder is used. Life cycle assessment (LCA) was used in this research to assess the environmental impact of the alternative ternary gypsum-PC-pozzolan binder in the production of mortar, and the environmental benefits were calculated and compared to traditional cement-based building materials. Phosphogypsum was considered as a secondary raw material, as in the current approach it is collected in open stacks bringing environmental concerns. SimaPro LCA software with the Ecoinvent database was used for most of the calculation processes. Results indicate that with alternative binders up to 30% of energy can be saved and 57 wt.% of CO2 emissions can be reduced, bringing positive impact on the construction industries contribution to the environment
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