1,721,010 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
Recommended from our members
The Development and Implementation of Interactive Virtual Laboratories
Full text linkThe Interactive Virtual Laboratories (IVLs) are a series of two-dimensional simulations designed to help students conceptually learn difficult concepts in thermodynamics. Three studies were performed to help elucidate how the IVLs affect student learning. In the first study, eight students were observed while completing one of the IVLs. The students were examined to see how they approached guided questions and used the molecular simulations to make sense of the abstract thermodynamics concepts. The IVLs did not force students to use a conceptual approach; however, students who did not use a conceptual approach were unable to fully answer the conceptual questions. In the second study, an IVL was implemented in a junior-level thermodynamics classroom of over 100 students. Student responses and feedback were examined. Of the students who responded, 58% were able to clearly show they understood the main conceptual question. In the third study, student perceptions on performance in the engineering classroom were examined. Almost 70% of students involved in the study said that they felt rote learning was in some way rewarded in engineering, possibly explaining why some students chose to use rote learning exclusively while completing the IVL.Keywords: Thermodynamics, Simulation, Conceptual, Education, Epistemolog
Recommended from our members
Electron spin resonance of ZnS:Mn thin films grown by halide transport chemical vapor deposition
No full textRecommended from our members
Fault probability and confidence interval estimation of random defects seen in integrated circuit processing
No full textVarious methods of estimating the fault probabilities based on defect data of random defects seen in integrated circuit manufacturing are examined. Estimates of fault probabilities based on defect data are less costly than those based on critical area analysis and are potentially more reliable because they are based on actual manufacturing data. Due to limited sample size, means of estimating the confidence interval associated with these estimates are also examined. Because the mathematical expressions associated with defect data-based estimates of the fault probabilities are not amenable to analytical means of obtaining confidence intervals, bootstrapping was employed. The results show that one method of estimating the fault probabilities based on defect data proposed previously is not applicable when using typical in-line data. Furthermore, the results indicate that under typical fab conditions, the assumption of a Poisson random defect distribution gives accurate fault probabilities. The yields as predicted by the fault probabilities estimated from the limited yield concept and kill ratio and those estimated from critical area simulation are shown to be comparable to actual yields observed in the fab. It is also shown that with in-line data, the FP estimated for a given inspection step is a weighted average of the fault probabilities of the defect mechanisms operating at that inspection step. Four bootstrapped based methods of confidence interval estimation for fault probabilities of random defects are examined. The study is based on computer simulation of randomly distributed defects with pre-assigned fault probabilities on dice and the resulting count of different categories of die. The results show that all four methods perform well when the number of fatal defects is reasonably high but deteriorate in performance as the number of fatal defects decrease. The results also show that the BCA (bias-corrected and accelerated) method is more likely to succeed with a smaller number of fatal defects. This success is attributed to its ability to account for change of the standard deviation of the sampling distribution of the FP estimates with the PP of the population, and to account for median bias in the sampling distribution
Recommended from our members
Modeling and simulation of CF₄/O₂ microwave plasma afterglows
Full text linkA gas phase kinetic model for the CF₄/O₂ microwave discharge plasma and afterglow of our laboratory has been developed. A reaction pathway identifying the major chemical reactions is proposed. The rate coefficients of the electron impact dissociation reactions are determined at three different plasma powers using both published electron molecule collision cross section data and plug flow analysis of data collected in our system. Agreement between calculated and experimental rate coefficients is better than 20%. Fluid simulations of a two-dimensional mathematical model were performed using computational fluid dynamics. It is found that the model reproduced qualitatively the general trends of the experimental data. The effects of plasma power, feed gas composition, residence time and pressure on the product distribution of the system are studied. CF₄ conversion increases with power and residence time. The variation of CF₄ conversion and carbon containing species
distribution falls into two regimes. In the oxygen rich regime (below 25 mole % CF₄ in the feed), CO₂ is found to be the major product of CF₄ decomposition; homogeneous recombination reactions between atomic oxygen and the free radicals are found to be the dominant mechanism in the afterglow region resulting in high CF₄ conversions. Homogeneous reactions convert CO to CO₂. In the CF₄ rich regime (above 50 mole % CF₄), COF₂ is found to be the major product of CF₄ decomposition. Recombination reactions of CF₃ with atomic fluorine dominate in the afterglow region and limit conversion. Lowering pressures result in increased conversion of CF₄ and increased concentration of the carbon containing species
Recommended from our members
Plasma-induced modification of films containing polytetrafluoroethylene (PTFE)
Full text linkPolymer samples of polytetrafluoroethylene (PTFE) and a PTFE-glass weave (RF- 35P) are exposed to low pressure, non-equilibrium glow discharge plasmas for enhanced wettability as measured by static contact angles. Plasma treatments are performed in two parallel plate RF plasma systems, a downstream microwave plasma and a barrel etcher using feed gases composed of H₂, N₂, Ar, He, and 0₂. Surface analysis of the topography and chemical composition of treated samples is performed by atomic force microscopy (AFM), attenuated total reflection infrared (ATR-IR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF SIMS). Optical emission spectroscopy is used to correlate wettability to reactive species in the plasma, and plasma parameters to species emission. In the parallel plate plasma systems, the contact angle can change from approximately 95° to 5° with treatment while treatments in the downstream and barrel etcher systems do not result in a contact angle change. The difference in plasma performance is attributed to ion bombardment. Plasmas composed of 20 to 80% H₂O in (H₂ + N₂) give the best wettability improvement. Plasma exposure significantly reduces the surface fluorine content followed by incorporation of nitrogen, oxygen and hydrogen, apparently as amino, hydroxyl and carbonyl functional groups with evidence of an amide. The incorporation of oxygen likely originates through peroxy radicals subsequent to plasma exposure. It is proposed that using a higher applied power creates a more reactive surface. A larger percentage of H₂ in the plasma tends to passivate the surface, leading to a smaller wettability improvement which is correlated to the atomic hydrogen concentration in the plasma. The addition of He or Ar into the H₂/N₂ plasma tends to dilute or weaken the plasma effect on wettability. To a much greater extent, the addition of oxygen also decreases the wettability. This latter effect is attributed to etching reactions which result in a more hydrophobic surface. An etch rate of approximately 0.2 μ/min is observed, and this is the first report of PTFE etching with 0₂/H₂/N₂. The distance between the parallel plate electrodes (gap) is a significant factor for the wettability of treated polymers, while power, pressure and flow rate are not. The optimal storage conditions to retain the wettability of H₂/N₂ plasma-treated RF-35P are low pressure and low temperature. The following model of PTFE surface modification is proposed. Ion bombardment creates reactive sites that initiate surface reactions. Reactive species from the H₂/N₂ plasma modify the surface through incorporation of amino, hydroxyl and carbonyl surface groups. These new groups increase the polymer wettability. Atomic hydrogen in the mixture is required to improve the wettability, but too high of a concentration will passivate the surface and lessen the wettability improvement. If oxygen is present, the modified surface is etched away leaving a refreshed, more hydrophobic surface
Recommended from our members
Process optimization and electrical characterization of ZnS:Mn electroluminescent phosphors deposited by halide transport chemical vapor deposition
Full text linkProcess development of halide transport chemical vapor deposited (HTCVD) ZnS:Mn thin film has been studied. To this end, electrical characterization of HTCVD ZnS:Mn electroluminescent devices has been used. Process optimization focused on a simple design of experiment (DOE) with brightness as the major response. Deposition parameters such as HCl and H₂S gas flow rates, ZnS and Mn source temperatures and substrate temperature were studied. A substrate temperature of 550°C gives the brightest devices. ZnS source temperature and H₂S gas flow rate are insignificant parameters according to the statistical analysis. However HCl gas flow rate and Mn source temperature show strong interaction. It is proposed that the incorporation of Cl into the ZnS:Mn film causes the interaction. A Cl defect is also consistent with anomalous electrical behavior observed in the devices. Cl defects are thought to precipitate at the grain boundaries of the initial growth interface, then diffuse (or migrate) along the grain boundaries and possibly into the bulk crystal. This defect will easily form negative charge leading to asymmetric space charge in the bulk of the phosphor. Since the defects are believed to originate from the nucleation of Cl at high grain boundary density, one potential solution is to remove the Cl source as the grains begin to grow and only later expose the film to Cl. While film growth without HCl present at the beginning of deposition leads to brighter films, it is a sub-optimal solution. Part of the ZnS host does not have luminescent centers. It is believed other processing solutions need to be realized to make the HTCVD system viable
- …
