1,720,992 research outputs found
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
CORRELATION BETWEEN BULK DENSITY AND ELECTRICAL IMPEDANCE ON PODSOLIC SOIL: I. EXPERIMENT IN LABORATORY
Full text linkPercobaan tentang korelasi antara berat volume (BV) dan impedensi listrik (Z) dilaksanakan pada tanah Podsolik berlempung
di Kota Bengkulu yang diambil dari kedalaman 0 – 10 cm. Contoh tanah dikering anginkan, dihaluskan menjadi agregat
berukuran 0 – 2 mm, lalu dimasukkan ke dalam silinder (diameter dan tinggi masing-masing 8,20 cm) yang telah dilengkapi
dengan sepasang sensor. Nilai BV dan kadar air tanah diukur, arus listrik AC dengan frekuensi 5 kHz dialirkan melalui
contoh tanah, dan beda potensial yang terjadi di kedua sensor diukur dengan oscilloscope. Nilai beda potensial yang terukur
lalu dikonversi menjadi nilai impedensi Z. Tanah di dalam silinder kemudian dipadatkan kembali, nilai BV dan beda
potensial selanjutnya diukur seperti langkah sebelumnya. Langkah-langkah di atas diulangi untuk contoh tanah yang
memiliki kadar air yang berbeda, sehingga diperoleh berbagai nilai Z untuk kombinasi BV dan kadar air yang berbeda. Nilai
BV hasil pengukuran selanjutnya dikorelasikan dengan nilai Z, sementara kadar air dijadikan salah satu faktor yang
mempengaruhi keeratan hubungan dari kedua variabel tersebut. Berat volume memiliki korelasi yang sangat erat dengan Z (r
berkisar antara 0.81 dan 0.99) sementara bentuk hubungan tersebut mengikuti hukum eksponensial. Logaritma dari BV
menurun sebesar 0,002 sampai 0,2 Mg m-3 untuk setiap ohm peningkatan dari Z, tergantung pada kadar air tanah pada saat
pengukuran. Hasil penelitian menunjukkan bahwa nilai Z dapat digunakan untuk menduga nilai BV dan sifat-sifat lain yang
berhubungan dengannya.
Kata-kata kunci: Berat volume, impedensi listrik, kadar air
MONITORING KADAR AIR TANAH MELALUI PENGUKURAN SIFAT DIELEKTRIK PADA LAHAN JAGUNG
Full text linkThis research aims to monitor soil water content in the field through the measurement of the electrical impedance during the early period of corn growth in the dry season. Two levels of tillage and four types of mulch were arranged at a split plot design with three replications. Part of experiment plot was cultivated twice and the other part was not cultivated. Each main plot was then divided into four sub-plots of 3 x 4 m each of wich was applied with 100% imperata mulch, 80% imperata and 20% kerinyu mulch, 50% imperata and 50% kerinyu, or 100% kerinyu. Two sets of wire, where the lowest 10 cm part was not isolated, were inserted into 10 and 20 cm soil depth therefore they measured the electrical impedance at the 0-10 and 10-20 cm soil layers. The electrical impedance values were measured using the digital ohm-meter that produce the electrical current at frequency of 1 kHz. Results show that the measured electrical impedance values have a very high sensitivity to the fluctuation of soil water content in the field. When calibrated to the same soil, the values can be transformed into water content values. During the measurement period, the cultivated soil is consistently drier at the 0-10 depth and wetter at the 10-20 depth compared to the uncultivated soil. The combination of 50% imperata and 50% kerinyu mulch maintains higher soil water content uring the dry season compared to other combinations. The research suggests that monitoring of soil water content can be conducted directly in the field through the measurement of electrical impedance
Soil structure associated with cover crops and grass leys in degraded lowland soils of Delta
No full textRates of change of surface soil structure under different short-term cover crops
and grass leys were studied on lowland soils in the Fraser River delta, British Columbia,
Canada. The impact of cropping systems on soil structure was assessed under three
environments: (i) short term (<1 -yr) effects from overwinter cover crops, (ii) short term
(<3 -yr) effects associated with a grass ley reclamation program, and (iii) long term effects
associated with varying cultivated crop and grass rotations. In the overwinter study, fall
planted cover cropping treatments, including bare control, winter-killed spring barley, fall
rye, and annual ryegrass (for 1993-1994 only), were compared at separate sites in 1992-
1993 and 1993-1994 for their effects on soil physical properties. At the reclamation
study, two cropping practices - spring-sown barley underseeded with clover for winter
cover cropping and grass ley - were established in a subsurface drained site and an
adjacent poorly drained (no subsurface drainage) site. Measurements in the crop rotation
study were conducted on five adjacent fields with different cropping histories.
Aggregate stability, bulk density and aeration porosity did not differ among
overwinter cover cropping practices at the 1992-1993 site. A lack of differences in this
study was probably due to low above-ground crop biomass when compared to the 1993-
1994 winter cover cropping site. In contrast, overwinter cover crops in the 1993-1994
study had higher aggregate stability, aeration porosity and water infiltration, and lower
bulk density and penetration resistance when compared to bare soil. Improved aggregate
stability with cover crops in the 1993-1994 study was related to increased organic carbon
in the soil, while increased aeration porosity and water infiltration were strongly correlated
with higher earthworm populations under cover crops. When the 1993-1994 field was
cultivated in spring, winter cropped soils had better structure than did soils left bare over
winter. Overall, the greatest structural improvements were observed under annual
ryegrass, followed by fall rye and winter-killed spring barley.
After three years of grass ley program at the Reclamation Site, grass consistently
had higher surface aggregate stability when compared to a combination of summer cash
plus winter clover cover cropping. Improved aggregate stability with grass was
significantly correlated with increased soil organic carbon content. Compared to the initial
values measured in spring 1991, grass increased aggregate stability, expressed as mean
weight diameter, by 0.4 to 0.7 mm and increased organic carbon content by 5 g kg⁻¹.
Water infiltration under grass also increased following improved aggregate stability. The
effects of cropping regimes on other soil structural characteristics varied with subsurface
drainage conditions. Integration of cash and clover cover cropping maintained low bulk
density and penetration resistance and high aeration porosity in the spring on the field with
subsurface drainage. In the poorly drained field, however, bulk density was lower and
aeration porosity was higher in the grass ley than in the cash-clover cover crop regime.
Soil profiles also dried more quickly in winter and early spring under grass ley when
subsurface drainage was not available. Earthworms migrated out into the field from their
source at the ditch verges at a rate of about 15 m yr ⁻¹ under all cropping and drainage
regimes.
The period that land has been under grass or cultivated crops can be used to
predict changes in selected properties of the soil at any given time. In the crop rotation
study, the period of cultivated crops since grass was strongly correlated with organic
carbon level in the soil. Organic carbon decreased significantly in the order of 2-yr grass
(0-yr cultivation) = 1-yr cultivation > 5-yr cultivation = 8-yr cultivation > 11-yr
cultivation. When soil water content at sampling was taken into consideration, previous
cropping history was correlated with aggregate stability.
Most structural characteristics observed in overwinter cover cropping and grass
ley studies were significantly influenced by the time of sampling. Aggregate stability
decreased from fall to spring, then increased again over summer and fall. The seasonal
variation in aggregate stability was attributed primarily to soil water content at the time of
sampling. Aeration porosity and water infiltration also decreased, while bulk density and
penetration resistance increased during fall-to-spring months. The seasonal variation in
structural characteristics was much more pronounced in the least stable soils, such as bare
and continued cash-winter cover cropping conditions, than in the more stable cover
cropped and grass ley soils.Land and Food Systems, Faculty ofGraduat
PENINGKATAN KUALITAS LAHAN BEKAS TAMBANG MELALUI REVEGETASI DAN KESESUAIANNYA SEBAGAI LAHAN PERTANIAN TANAMAN PANGAN
No full textPenelitian bertujuan untuk mengevaluasi peningkatan beberapa variabel kualitas tanah pada lahan bekas tambang batubara pasca reklamasi dan kesesuaiannya untuk dimanfaatkan menjadi lahan pertanian. Contoh tanah utuh dan terganggu diambil dari lahan bekas tambang PT. Bukit Asam (Persero) Tbk., Tanjung Enim, Sumatera Selatan yang telah direvegetasi masing-masing pada kedalaman 0-10 dan 0-20 cm. Pengambilan contoh tanah dilakukan di lokasi yang sama pada tahun 2006 dan 2010 ketika vegetasi berumur 8 dan 12 tahun. Contoh tanah utuh digunakan untuk analisis sifat-sifat fisik sedangkan contoh tanah terganggu untuk analisis sifat-sifat kimia tanah. Data fisik dan kimia tanah dianalisis secara deskriptif, lalu dibandingkan dengan interval nilai yang sesuai untuk pertumbuhan tanaman pangan. Hasil penelitian menunjukkan bahwa semua variabel fisik tanah (tekstur, berat volume, porositas total, kadar air dan resistensi penetrasi) dan variabel kimia tanah (pH, karbon organik, unsur hara, kation dapat ditukar, dan kapasitas tukar kation) telah meningkat ke level yang sesuai untuk tanaman pangan setelah direklamasi selama 12 tahun. Beberapa variabel kualitas tanah untuk tanaman pangan meningkat dari kategori sangat rendah menjadi rendah ketika umur vegetasi reklamasi bertambah dari 8 menjadi 12 tahun. Tindakan pengelolaan lahan bekas tambang yang harus dilakukan apabila digunakan untuk pertanian adalah pengolahan tanah, pengapuran dan pemupukan terutama fosfor
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