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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
In-situ Kinetics and X-ray Computed Microtomography Imaging Studies of Methane Hydrates in Host Sediments
No full textMethane hydrates naturally occur in abundance in permafrost and marine environments. Methane hydrates are ice-like inclusion compounds in which water molecules form a framework through hydrogen bonding and encapsulate methane molecules under conditions of low temperature and high pressure. In natural settings, the sediment-hydrate interaction governs the mechanical strength and other geophysical properties of formations containing methane hydrates. In this study, methane hydrate formation/dissociation kinetics was studied with methane/water (both pure water and seawater) hosted in consolidated Ottawa sand-cores at pressure-temperature (PT) conditions (P: 9.2 MPa; T: 4deg.C) mimicking sub-seafloor settings. The formation study was conducted by charging methane at different pore pressures followed by cooling. The hydrate formation was delayed with increasing pore pressure or consolidation of host sediment. The hydrate dissociation was achieved by incremental step-wise system depressurization during which time, gas output response, sediment cooling due to the reaction endothermicity and post-depressurization PT equilibrium were recorded. The dissociation events due to depressurization were short-lived. During depressurization, thermocouple monitoring showed that the temperature at the center of the core dropped more rapidly than at the middle radius and the boundary. Post-depressurization dissociation was thermally induced where sediments were allowed to warm up to a bath temperature. The post-depressurization PT equilibrium followed theoretical data for methane hydrates on the higher pressure side due to an excess pore pressure generated within confined core. The post-depressurization PT equilibrium was used to calculate the enthalpy of dissociation value as 59.45 kJ/mol. The gas output during depressurization was fit to estimate hydrate dissociation constant. A set of formation/decomposition runs was repeated with seawater. The formation kinetics of hydrates from seawater was found to be delayed with the degree of consolidation. The post-depressurization PT equilibrium values were utilized to calculate the enthalpy of dissociation of methane hydrates. The endothermic effect due to hydrate dissociation was recorded with the highest degree of cooling recorded at the center and the half-radius than that at the core boundary. The cooling responses during depressurization from three thermocouples placed at different lateral and radial positions within core were used as an indicative of presence of hydrates and their preferential dissociation positions. The post-depressurization dissociation was thermally induced, during which the sediments warmed up to the bath temperature. All post-depressurization pressure-temperature (PT) followed theoretical methane-seawater equilibrium on higher pressure side until all hydrates were dissociated. These post-depressurization PT equilibriums were used to estimate the enthalpy of dissociation of methane hydrates from seawater and a consolidated core as 54.774 kJ/mole. The microscopic visualization of time-resolved 3-dimensional (3-D) growth of individual tetrahydrofuran hydrates and methane hydrates formed within a porous media was performed using synchrotron X-ray computed microtomography. Tomographic data were acquired where ~1200 X-ray images were recorded while rotating the sample tube from 0-180deg. at the X2B beamline, National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL). Each tomogram was reconstructed for 2-dimensional cross-sectional images which were compiled to generate 3-D volume. The images of hydrate patches, formed from excess tetrahydrofuran and methane in aqueous solutions, show random nucleation and growth concomitant with grain movement but independent of container-wall effect. Away from grain surfaces, hydrate surface curvature was convex showing that liquid, not hydrate, was the wetting phase, similar to ice growth in porous media. The time-resolved 3-D images show methane hydrate as pore-filling that is well represented by a model reported by Dvorkin et al. (1999). The observed methane hydrate (sI) growth in porous media is similar to that observed for tetrahydrofuran hydrate (sII) reported previously in this study. The contact angle for the methane hydrate system was measured to be 154.25deg. from the CMT data. A combination of patchy and pore-filling microstructure properties could lead to sediment instability, in the event of methane release by hydrate decomposition.Advisor(s): Devinder Mahajan. Committee Member(s): Michael Dudley; Tadanori Koga; Rudy Rogers.Stony Brook University Libraries. SBU Graduate School in Department of Materials Science and Engineering. Lawrence Martin (Dean of Graduate School)
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
Performance Evaluation and Characterization of Metallic Bipolar Plates in a Proton Exchange Membrane (PEM) Fuel Cell
No full textBipolar plate and membrane electrode assembly (MEA) are the two most repeated components of a proton exchange membrane (PEM) fuel cell stack. Bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack. The bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cell, and constitute the backbone of a power stack. In addition, bipolar plates must have excellent corrosion resistance to withstand the highly corrosive environment inside the fuel cell, and they must maintain low interfacial contact resistance throughout the operation to achieve optimum power density output. Currently, commercial bipolar plates are made of graphite composites because of their relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite's manufacturability, permeability, and durability for shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. Since bipolar plates must possess the combined advantages of both metals and graphite composites in the fuel cell technology, various methods and techniques are being developed to combat metallic corrosion and eliminate the passive layer formed on the metal surface that causes unacceptable power reduction and possible fouling of the catalyst and the electrolyte. The main objective of this study was to explore the possibility of producing efficient, cost-effective and durable metallic bipolar plates that were capable of functioning in the highly corrosive fuel cell environment. Bulk materials such as Poco graphite, graphite composite, SS310, SS316, incoloy 800, titanium carbide and zirconium carbide were investigated as potential bipolar plate materials. In this work, different alloys and compositions of chromium carbide coatings on aluminum and SS316 substrates were also tested for suitability in performing as PEM fuel cell bipolar plates. Interfacial contact resistance and accelerated corrosion resistance tests were carried out for various bulk materials and chromium carbide coatings. Results of the study showed that chromium carbide protective coatings had relatively low interfacial contact resistance and moderate corrosion resistance in comparison to other metals.Single fuel cells with 6.45cm2 and 50cm2 active areas were fabricated and tested for performance and lifetime durability using chromium carbide coated aluminum bipolar plates and graphite composite bipolar plates as a control reference. Polarization curves and power curves were recorded from these single cells under various load conditions. The results showed that coated aluminum bipolar plates had an advantage of anchoring the terminals directly into the plates resulting in higher power density of the fuel cell. This was due to the elimination of additional ICR to the power stack caused by the need for extra terminal plates. However, this study also revealed that direct terminal anchoring was efficient and useable only with metallic bipolar plates but was inapplicable to graphite composite plates due to the poor mechanical strength and brittleness of the graphite composite material. In addition, the 1000 hour lifetime testing of coated aluminum single cells conducted at 70øC cell temperature under cyclic loading condition showed minimal power degradation (<5%) due to metal corrosion. Surface characterization was also conducted on the bipolar plates and MEAs to identify possible chemical change to their surfaces during the fuel cell operation and the electrochemical reaction.The single cell performance evaluation was complemented by an extended study on the fuel cell stack level. For the latter, a ten-cell graphite composite stack with a 40 cm2 active area was fabricated and evaluated for the effect of humidity and operating temperature on the stack performance. Graphite plates were selected for this study to eliminate any possible metal corrosion. A finite element analysis (FEA) model of a bipolar plate was developed to evaluate the effect of air cooling system design parameters and different bipolar plate materials on maintaining the PEM power stack at a safe operating temperature of 80øC or less. In the final stage of this work, a three-cell metallic stack with a 50 cm2 active area and coated aluminum bipolar plates was fabricated based on the positive results that were obtained from earlier studies. The three-cell stack was successfully operated and tested for 750 hours at different temperatures and power densities. This laboratory testing coupled with characterization studies showed that small amounts of aluminum oxide were observed on the coating surface due to localized imperfections in the coating and a lack of protection in the uncoated areas, such as internal manifolds and mounting plates. However, the scanning electron microscopy (SEM) and the energy dispersive x-ray spectroscopy (EDX) showed that coating thickness, chemistry, and surface morphology remained consistent after 750 hours of operation.Advisor(s): Devinder Mahajan. Hazem Tawfik. Committee Member(s): Charles Fortmann; Mahmoud Abd Elhamid.Stony Brook University Libraries. SBU Graduate School in Department of Materials Science and Engineering. Lawrence Martin (Dean of Graduate School)
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
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
Asymmetric homogeneous hydrogenation of olefinic compounds using a rhodium catalyst with chiral phosphine ligands
No full textThe hydridorhodium(I)phosphine complex HRh(diop)₂ [(+)-diop = (+)-2,3,-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] has been studied for catalytic asymmetric hydrogenation of a number of olefinic substrates. Certain olefinic carboxylic acids have been reduced to products with up to about 60% enantiomeric excess. Some rate data show the importance of the degree of substitution at the olefinic bond in terms of steric effects and the -COOH function of the substrate also plays a role. Kinetic and spectrophotometry studies on the hydrogenation of itaconic acid in n-butanol-toluene (2:1) solutions are best interpreted in terms of a mechanism involving formation of a metal alkyl via coordination of the olefinic substrate, followed by reaction with H₂ to give saturated product and the starting catalyst complex. The actual catalyst is thought to be HRh(diop)(diop*) where diop* represents a monodentate diop with one dangling -CH₂PPh₂ moiety. The catalyst systems are somewhat complicated by the occurrence of a number of slower side-reactions, the extent of these varying from negligible for the more rapidly reducing substrates, to possibly of prime importance in the slow hydrogenations. The initial hydride catalyst, for example, is slowly decomposed to the cationic [Rh(diop)₂] complex by protons from the olefinic substrate. Under H₂ the cation reversibly forms a dihydride. The cation is also formed from a reaction that appears to involve an intermediate alkyl complex and the butanol.Science, Faculty ofChemistry, Department ofGraduat
Bis (ditertiaryphosphine) complexes of rhodium, and catalytic asymmetric hydrogenation
No full textRhodium(I)-bis(ditertiaryphosphine) complexes of the general formula
Rh(P⁀P)₂Cl[P⁀P = Ph₂P(Ch₂)n PPh₂, n = 1-4, and (+)-diop (diop = 2,3-0 isopropylidene 2,3-dihydroxy-1,4 bis(diphenylphosphino)butane] have been prepared by treating [Rh(Ccyclooctene)C₂Cℓ]₂ with the appropriate ditertiaryphosphine. The n=1, and n=4 and diop species are five-coordinate in the solid state and in non-polar solvents, while the n=2 and 3 species contain ionic chloride. The cationic complexes Rh(P⁀P)₂ +X- were prepared from the Rh(P⁀P)₂ Cℓ species by adding AgX[X=SbF₆,PF₆,BF₄] . Reaction of the chloro
complexes with borohydride has yielded the hydrides, H Rh(P⁀P)₂, for the
n=2 and 3 diphosphines, and for (+)-diop. ¹H and ³¹P nmr, as well as visible spectral data, are presented: a solvent-dependent deshielding of ortho protons of the phenyl groups is observed in some of the complexes, and the ligand CH₂ protons are coupled to the rhodium in the Rh(Ph PCI^PPh^^ cation; the P atom in this bis(diphenylphosphino) ligand shows an unusual highfield shift on coordination to rhodium. Preliminary kinetic data for catalytic hydrogenation of methylene succinic0 acid or itaconic acid (IA) show that the cationic and hydrido complexes are more active than the corresponding chloro complexes, and that activity generally increases with increasing chain length of the diphosphine.
The rhodium-bis(diop) complexes efficiently catalyze the asymmetric hydrogenation of a number of prochiral substrates, optical purities of >90% being obtained in the hydrogenation of N-acylaminoacrylic acids. Steric factors at the olefinic bond, and coordination of the -NHCOR group through the "^C=0 moiety, seem important in determining the hydrogenation rates. The rates are slower in the more strongly coordinating DMA compared to n-butanol-toluene mixtures. The solvent medium has little effect on the
+degree of asymmetric induction, when using thre Rh[(+)-diop]2^ or HRh[(+)-diop]2 complexes, but reversal of product configuration is observed when using the Rh[(+)-diop]^Cl complex in DMA or in n-butanol-toluene mixtures. An unusual increase in optical purity of the product with increasing temperature has been observed in the hydrogenation of IA.
Detailed kinetic and spectroscopic studies on the hydrogenation of IA catalyzed by HRh[(+)-diop] are explained in terms of a mechanism involving the formation of a metal alkyl via coordination of the olefinic substrate, followed by reaction with H2 to yield the saturated product (S.P.) and regenerated catalyst (equations [l]-[3]). A monodentate diop(diop*) is invoked:
HRh(diop)2 _ HRh(diop)(diop*) [1]
HRh(diop) (diop*) + olefin k Rh(diop) (diop*) (alkyl) [2]
Rh(diop)(diop*)(alkyl) + > HRh(diop)(diop*) + S.P. [3]
The initial hydride catalyst is slowly decomposed by protons of the acidic substrate to give Rh(diop)2+. To avoid this complication, a mechanistic study was carried out on the HRh(diop)2"Styrene-H2 system, which was found to proceed via the same mechanism as outlined in equations [l]-[3],
A mechanistic study on the Rh(diop)2+BF^ -catalyzed hydrogenation of IA shows that the reaction proceeds mainly via the 'hydride' route:
Rh(diop)2+ + H2 ^ Rh(diop)2H2+ [4]
Rh(diop)2H2+ + IA v=^Rb(diop) (diop*) (H)2(IA)+ [5]
Rh(diop) (diop*) (H)2(IA)+ > Rh(diop)2+ + S.P. [6]
A complete inhibition of the hydrogenation by small amounts of added diop(diop:Rh>0.2) is tentatively attributed to formation of an inactive polymeric species:
nRh(diop)2H2+ + diop > [Rh(diop)(diop*)H2+]n [7]
The forward step of Reaction [4] was studied in detail in the absence of olefinic substrate. Spectroscopic and kinetic data are best explained in terms of dihydride formation via the consecutive reactions outlined in equation [8]:
Rh(diop)„+ s . •> Rh(diop)(diop*)S+ ——• Rh(diop) (diop*) (H) „S+
[8]
Rh(diop)2H2+
The dehydrogenation reaction was also studied.
The reactions of [Rh(P~P)2]A complexes (A=C£,BF4) with C0,C>2,H2 and
HC&(g) yield several new complexes. Thus the [Rh(P P)2XY] BF^ complexes
rs rs r\
(P P = dpm,dpp;XY=CO, P P=dpm,dpe,dpp;XY=02, P P=dpp, (+)-diop: XY=H2, and
rs
P P=dpm,dpe,dpp;XY=HC&) were isolated and characterized. The solution
31
structures were determined using especially variable temperature P nmr spectroscopy. The formally six-coordinate rhodium(III) dioxygen and the dihydrido complexes were assigned cis geometries, whereas the HC£ complexes were more fluxional and cis geometries could only be assigned with certainty to the dpp complex; for dpm and dpe complexes, the limiting spectra could not be achieved even at -60°C. For the five-coordinate rhodium(I) CO complexes, the dpp complex has been assigned a TBP structure but the dpm complex is fluxional even at -60°C.
Some stopped-flow kinetic data are presented for the addition of CO, 02, and B.^ to the Rh(P P>2 complexes. For the dpp system, the rate increased in the order CO>H2>02, although the reactions are not simple 1:1 single step additions, solvated species probably playing an important role (cf. equation [8]).Science, Faculty ofChemistry, Department ofGraduat
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