1,720,994 research outputs found
Mandelik Asit ve Propan-1,2,3-Trikarboksilik Asitin Kalsiyum Oksalat Monohidrat Kristalizasyonuna Etkisi
No full textThe effects of mandelic and propane-1,2,3-tricarboxylic acids as additives on calcium oxalate monohydrate (COM) crystals were investi-gated in this study. The physicochemical properties of the COM crystals prepared with and without these additives were characterized us-ing X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta po-tential analysis. The XRD and SEM results showed that the crystals prepared in pure medium were monohydrates and consisted primarily of hexagonal crystals, respectively. The additives mandelic acid and propane-1,2,3-tricarboxylic acid in the crystallization media signifi-cantly changed the size and morphology of the COM crystals, the effects of which were more pronounced with higher concentrations of the additives. The results of FTIR suggested that both carboxylic acids were adsorbed onto the surface of the COM crystals. The zeta po-tential analysis showed a negative charge on the surface of the COM crystals in the mandelic acid medium, while the surface became more positive in the medium containing increasing concentrations of propane-1,2,3-tricarboxylic acid. In addition, an analysis was conducted to evaluate the thermal characteristics of the COM crystals prepared with and without the additives. The data obtained were used to calculate the kinetic parameters, such as the activation energy and pre-exponential factor, using the Coats-Redfern method. The calculated activation energies for stages I, II, and III in pure medium were 98.76, 270.69, 258.55 kJ/mol, respectively, which were lower than that of COM crys-tals prepared in the two media containing the additives
THE PHYSICOCHEMICAL CHARACTERIZATION AND KINETIC PARAMETER_x000D_ ASSESSMENT OF HYDROXYAPATITE CRYSTALS
No full textThe crystallization of hydroxyapatite (HAP) was analyzed in a batch system in pure medium and in the presence of butyricacid as an additive. The experiments were conducted at different additive concentrations and the influences of the additive wereinvestigated. Firstly, the crystals obtained were characterized by X-ray diffraction, Brunauer–Emmett–Teller, transmissionelectron microscopy, zeta potential measurement, Fourier transform infrared spectroscopy, and thermogravimetric analysis.The structure, surface areas, morphology, surface potential charges, functional groups and thermal decomposition behavior ofthe crystals were determined. In the next step, thermal decomposition kinetic profiles were modeled using the distributedactivation energy model (DAEM), Flynn-Wall-Ozawa (FWO) and Friedman models. All the models used provided accuratefits of the TGA data with acceptably high values. The value for the crystals obtained from the butyric acid containingmedium was about 589 kJ/mol higher than that found for the crystals from the pure medium (538 kJ/mol). According to theresults of the characterization and kinetic analysis, butyric acid could be employed as an additive for the production of HAPcrystals with the desired quality and physical properties
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
Effects of polyelectrolytes on the hardness of borax decahydrate crystals
No full textThe hardness of borax decahydrate crystals was measured using cationicpolyelectrolytes of FO4115, FO4400 and FO4990 with anionic polyelectrolytesof AN923, AN930 and AN999 as an additive. The measurements were carriedout in the indentation load range of 10 g to 30 g. It was determined that theVickers hardness (HV) decreased with increasing applied load, showing thatthe borax decahydrate crystals exhibited an indentation size effect. Vickersmicrohardness measurements revealed that pure borax decahydrate crystals hada brittle structure, yet the crystals obtained in additive media were categorizedas a soft material. The proportional specimen resistance model was applied todetermine the load-independent microhardness. The crystal hardness of boraxdecahydrate was found to change depending on the type and concentration ofpolyelectrolyte used. In addition to the mechanical properties, the thermal andphysical characteristics of borax decahydrate crystals were investigated bythermogravimetric and Fourier transform infrared spectroscopy analysis. Thecharacterization results confirmed that the polyelectrolytes were adsorbed on thecrystal’s surface
Box–Behnken experimental design for zinc borate Zn2_x000D_ B6_x000D_ O11·7H2_x000D_ O
No full textThe present study investigated the effect of the operating conditions on thecrystallization of zinc borate. For zinc borate crystallization, sodium tetraboratedecahydrate and zinc sulfate heptahydrate were used as reactants. In thefirst part of the study, the crystals were characterized by X-ray diffractionspectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), lightmicroscopy, and particle size and thermogravimetric analysis. The resultsshow that the obtained crystals were in the form of Zn2B6O11·7H2O, and theoperating conditions had a significant effect on the size, morphology, andfiltration characteristics of the zinc borate crystals. In the second part ofthe study, Box–Behnken design (BBD) with response surface methodology(RSM) was employed to determine the optimal operating conditions for zincborate crystallization. The effects of stirring rate, temperature, and reactantfeed rate on the average particle size were investigated. The results show thatthe data sufficiently fit the second-order polynomial model. The crystallizationconditions, including stirring rate, temperature, and reactant feed rate, werestudied at 400–500 rpm, 45–85 ºC, and 300–900 mL/h, respectively. Theminimum particle size (3.3 µm) was obtained at a stirring rate of 450 rpm, atemperature of 85 ºC, and a reactant feed rate of 300 mL/h
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
INVESTIGATION OF THERMAL BEHAVIOUR OF TOBACCO FARM WASTE BY TGA-FTIR-MS
No full textBu çalı ş mada, tütün tarla atığ ı için termal bozundurma iş lemi termogravimetrik analiz (TGA) cihazı ile 20 ° C baş langıç sıcaklığ ı ndan 1000 ° Cye kadar 5, 10, 15 ve 20 ° C /dk ıs ı tma hı zları nda ve azot atmosferi altında gerçekleş tirilmiş tir. TGAdan elde edilen eğ riler ve veriler yardı m ı yla, tütün tarla atı ğ ı için Coats-Redfern yöntemi kullanı larak, aktivasyon enerjisi, reaksiyon mertebesi ve frekans faktörü belirlenmiş tir. Yapılan çalı ş mada, termogravimetrik analiz cihazı yla birleş tirilmiş Fourier Transform Infrared Spektroskopisi ve Kütle Spektroskopisi (TGA-FTIR-MS) kullanı larak, hammaddenin bozunması sı rası nda açığ a çıkan gazlar tespit edilmiş tir. Tütün tarla atı ğ ı n ı n pirolizi sırasında açığ a çıkan baş l ı ca ürünlerin, metan, amonyak, su, hidrojen siyanür, formaldehit, karbon dioksit ve propanal olduğ u belirlenmiş tir.In the present study, thermal degradation process of tobacco farm waste was examined by means of a thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTA) under nitrogen atmosphere at different heating rates of 5, 10, 15 and 20  C /min from 20  C to 1000 C. Using TGA data, the kinetic parameters, such as activation energy, pre-exponential factor and reaction order were determined by applying the Coats-Redfern (CR) method. In this study, by means of Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectrometer and Mass Spectrometer (TGA-FTIR-MS), gases evolved during the degradation of the sample were analyzed sensitively and at real time. Furthermore, the main gas products released during the pyrolysis of tobacco farm waste were determined as methane, amonia, water, hydrogen cyanide and formaldehyde, carbondioxide and propanal
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
