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PENGUKURAN SUDUT KONTAK UNTUK MENGETAHUI POLARITAS CAIRAN SEBAGAI BAHAN MODUL PRAKTIKUM TEGANGAN PERMUKAAN
Full text linkTelah dilakukan penelitian untuk pengembangan alat pengukur sudut
kontak (goniometer) menjadi alat penentu polaritas larutan. Hasil penelitian ini
dapat digunakan sebagai metode dalam penentuan polaritas cairan melalui
praktikum tegangan permukaan pada tingkat sarjana. Pada penelitian ini dirakit
goniometer sederhana yang digunakan untuk pengambilan gambar tetesan cairan.
Cairan yang digunakan adalah n-heksana, aseton, etanol, propilen glikol, gliserol,
air, cairan etanol-air dengan rasio 1:3 dan 3:1, serta cairan aseton-etanol dengan
rasio 1:3 dan 3:1 kemudian diteteskan di atas plat polimer PTFE, PMMA, dan PVC.
Data yang diperoleh dari goniometer berupa gambar pemotretan cairan pada plat
polimer. Gambar yang diperoleh diproses dengan perangkat lunak ImageJ dan
tambahan plug-in Low-Bond Axisymmetric Drop Shape Analysis (LB-ADSA).
Hasil pemrosesan gambar merupakan besar sudut kontak yang terbentuk antara
cairan dan padatan polimer sesuai dengan skala polaritas Reichardt (ETN). Sudut
kontak terendah ditunjukkan oleh n-heksana (ETN = 0,09), yaitu 0,000° dan sudut
kontak tertinggi ditunjukkan oleh air (ETN = 1), yaitu 118,332° pada plat PTFE,
sedangkan pada plat PMMA berturut-turut n-heksana = 0,000°, air = 66,697°, dan
pada plat PVC n-heksana = 0,000°, air = 71,362°. Kurva skala polaritas terhadap
sudut kontak menunjukkan korelasi sigmoid dengan nilai R2 pada PTFE, PMMA,
dan PVC berturut-turut, yaitu 0,95511, 0,96579, dan 0,95469. Hasil menunjukkan
bahwa polaritas cairan dapat ditentukan dengan pengukuran sudut kontak pada
permukaan PTFE, PMMA, dan PVC
Evaluation of Syzygium myrtifolium leaves extract as an eco-friendly inhibitor for steel in reinforced concrete.
Full text linkReinforced concrete is a concrete mixture that is reinforced with steel to strengthen the concrete in a building construction. One of the problems with steel is corrosion which can damage the concrete structure. One way to inhibit the corrosion process is to inhibit the corrosion rate using organic/eco-friendly inhibitors. A potential eco-friendly inhibitor is Syzygium myrtifolium leaves. This study aims to determine the corrosion rate and inhibition efficiency in reinforcing steel (BjTP) 280. This research method begins with maceration of Syzygium myrtifolium leaves using 96% alcohol for 96 hours. Then BjTP 280 is immersed in concentrated extract with variations in immersing time of 0 hours, 24 hours, 72 hours, 120 hours, and 168 hours. Furthermore, BjTP 280 is used in K350 quality concrete structures. Calculation of corrosion rate using weight loss method based on ASTM G 31-72, corrosion testing based on ASTM C 876-91 by immersing concrete in 3.5% NaCl corrosive media solution and flowing 6 V DC current for 14 days. The corrosion rate (mm/year) in each variation of immersion in inhibitor decreased, respectively 875.95 (0 hours); 298.66 (24 hours); 99.55 (72 hours); 79.73 (120 hours); 42.66 (168 hours). Meanwhile, the inhibition efficiency value (%) increased successively, namely -% (0 hours); 65,9% (24 hours); 88,63% (72 hours); 90,93% (120 hours); 95,12% (168 hours). The results showed the best corrosion rate reduction of 42.66 mm/year with inhibition efficiency of 95,12% obtained at 168 hours of immersion
Antioxidant activity assay of Roselle (Hibiscus sabdariffa) seeds Ethanol extract with DPPH radical scavenging using UV-Vis Spectrophotometer
Full text linkHibiscus sabdariffa (Roselle) is known to have a strong antioxidant compound. Thus, the calyx becomes the most important area to research. Another part of this plant that was starting to be known for its benefits is rosella seeds. Roselle seeds are a source of fat-soluble antioxidants. The aim of this study was to investigate the antioxidant activity of Roselle Seed Ethanol Extract (RSEE) with the DPPH (1,1-Diphenyl-2 Picrylhidrazyl) radical scavenging method. This research begins by doing the extraction of Roselle seeds using ethanol (96%) as a solvent and then assessing the antioxidant activity (Radical Scavenging Activity/RSA) of the extract, which is compared with the ascorbic acid standard at several concentrations (5-200 ppm). Antioxidant activity was assessed with DPPH Radical Scavenging using UV-Vis spectrophotometer and IC50 value parameters. The results of this study were the absorbance of DPPH from spectrophotometer at 517 nm was 0,824 (purple color). The absorbance of RSEE and ascorbic acid at 5 ppm to 200 ppm, respectively 0.523-0.124 and 0.594-0.112. The antioxidant activity (RSA) of the RSEE and ascorbic acid, respectively was 57.93% and 59.24%. The IC50 value of RSEE was 30.158 μg/ml and as comparison is ascorbic acid, the IC50 value was 26.948 μg/ml. Thus, the antioxidant activity of roselle seeds ethanol extract (RSEE) belongs to a very strong category (<50 μg /ml). This is due to the presence of several phenolic compounds and unsaturated fatty acid derivatives
EKSTRAKSI MINYAK ATSIRI DAUN ROSELLA (Hibiscus SabdaÃiffa L ) METODE WATER STEAM DESTILATION
Full text linkThe rosella plant has antioxidant and coloring compounds that are useful for coloring and aromatic various drinks. The research aimed to study the extraction of essential oils from rosella leaves through phytochemical screening and sensory testing of the oil results. The research method used extraction of essential oil using water steam distillation, color, aroma analysis using the hedonic method, and antioxidant activity using the DPPH method. Results showed the amount of essential oils in leaves is 0.0087% in 1 kg of dry material. Rosella Leaf Oil 25% like the yellow color, 75% like it, 0% dislike it, 30% like the aroma of the leaf essential oil, 70% like it, and 0% dislike it. The antioxidant activity in rosella leaves with concentrations (ppm): of 5, 10, 25, 50, 100, and 200 ppm (22,5; 29,7; 34,9; 42,13; 44,5; 51, 4)%. A comparison or control test using ascorbic acid with the same concentration as above showed a percentage of inhibition (37,53;44,16; 51,84; 61,19; 72,45; 88,22)%. The IC 50 value of ascorbic acid (as a control) is 26.94 ppm and the IC 50 of Rosella leaf extract is 171.27 ppm, which is classified as having weak antioxidant activity in the leaves. The GC-MS results showed essential oil consists cis-3 Hexenyl Acetate (11.50%), 3-Cyclohexene-1-methanol (4.97%), 2-Propenoic acid (2.65%), Linalool 3,7-oxide (2.15%), Methyl 4-methylhexanoate (1,54%), Butanoic acid (0.54 %), 3-Methylpent-3-en-2-ol (0.25%), 1-Hexen-3-ol (0,24%)
Antioxidant activity assay of Roselle (Hibiscus sabdariffa) seeds Ethanol extract with DPPH radical scavenging using UV-Vis Spectrophotometer
Full text linkHibiscus sabdariffa (Roselle) is known to have a strong antioxidant compound. Thus, the calyx becomes the most important area to research. Another part of this plant that was starting to be known for its benefits is rosella seeds. Roselle seeds are a source of fat-soluble antioxidants. The aim of this study was to investigate the antioxidant activity of Roselle Seed Ethanol Extract (RSEE) with the DPPH (1,1-Diphenyl-2 Picrylhidrazyl) radical scavenging method. This research begins by doing the extraction of Roselle seeds using ethanol (96%) as a solvent and then assessing the antioxidant activity (Radical Scavenging Activity/RSA) of the extract, which is compared with the ascorbic acid standard at several concentrations (5-200 ppm). Antioxidant activity was assessed with DPPH Radical Scavenging using UV-Vis spectrophotometer and IC50 value parameters. The results of this study were the absorbance of DPPH from spectrophotometer at 517 nm was 0,824 (purple color). The absorbance of RSEE and ascorbic acid at 5 ppm to 200 ppm, respectively 0.523-0.124 and 0.594-0.112. The antioxidant activity (RSA) of the RSEE and ascorbic acid, respectively was 57.93% and 59.24%. The IC50 value of RSEE was 30.158 μg/ml and as comparison is ascorbic acid, the IC50 value was 26.948 μg/ml. Thus, the antioxidant activity of roselle seeds ethanol extract (RSEE) belongs to a very strong category (<50 μg /ml). This is due to the presence of several phenolic compounds and unsaturated fatty acid derivatives
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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