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Increased efficiency of dye sensitized solar cells through the localization of light
No full textThe effects of tuning and scattering on the enhancement of conventional nanocrystalline TiO 2 dye sensitized solar cells were investigated when coupled to an inverse opal photonic crystal or disordered macroporous TiO 2 film. Multiple scattering events and localization between the nanocrystalline TiO 2 film and the coupled films have led to an increase in the molar absorption to the red edge of the stop band for the Ruthenium535 dye as compared to a standard Gratzel cell. This enhancement has shown an improvement ≤ 26percent over conventional DSSC. Both Bragg diffraction and diffuse scattering events were attributed to this efficiency enhancement. The effect of introducing scattering centers, tuning the bilayer structure, and novel cell designs were presented. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8-22-26-2004)
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REVERSIBLE INTERCALATI0N OF GRAPHITE BY FLUORINE AND RELATED SYNTHETIC AND THERMODYNAMIC STUDIES
Get PDFGoing 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
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THE FLUORIDE ION AFFINITIES OF GeF4 AND BF3 FROM THERMODYNAMIC AND STRUCTURAL DATA FOR (SF3) 2GeF6, ClO2GeF5 AND C102BF4
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Electron transfer reactions in microporous solids
Get PDFWe have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation
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Electron transfer reactions in microporous solids
Get PDFBasic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H[sub 2] and I[sub 3][sup [minus]], or H[sub 2] and O[sub 2)] from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies
Increasing the conversion efficiency of dye-sensitized TiO 2 photoelectrochemical cells by coupling to photonic crystals
No full textThe mechanism of enhancing the light harvesting efficiency of dye-sensitized TiO 2 solar cells by coupling TiO 2 inverse opals or disordered scattering layers to conventional nanocrystalline TiO 2 films has been investigated. Monochromatic incident photon-to-current conversion efficiency (IPCE) at dye-sensitized TiO 2 inverse opals of varying stop band wavelengths and at disordered titania films was compared to the IPCE at bilayers of these structures coupled to nanocrystalline TiO 2 films and to the IPCE at nanocrystalline TiO 2 electrodes. The results showed that the bilayer architecture, rather than enhanced light harvesting within the inverse opal structures, is responsible for the bulk of the gain in IPCE. Several mechanisms of light interaction in these structures, including localization of heavy photons near the edges of a photonic gap, Bragg diffraction in the periodic lattice, and multiple scattering events at disordered regions in the photonic crystal or at disordered films, lead ultimately to enhanced backscattering. This largely accounts for the enhanced light conversion efficiency in the red spectral range (600-750 nm), where the sensitizer is a poor absorber. © 2005 American Chemical Society.Albada M. P. V., 1985, PHYS REV LETT, V55, P2692, DOI 10.1103-PhysRevLett.55.2692; ANDERSON PW, 1958, PHYS REV, V109, P1494; Barbe CJ, 1997, J AM CERAM SOC, V80, P3157; CARLSON RJ, 1984, APPL SPECTROSC, V38, P297, DOI 10.1366-0003702844555548; DOWLING JP, 1994, J APPL PHYS, V75, P1896, DOI 10.1063-1.356336; DOWLING JP, 1994, J MOD OPTIC, V41, P345, DOI 10.1080-09500349414550371; Ferber J, 1998, SOL ENERG MAT SOL C, V54, P265, DOI 10.1016-S0927-0248(98)00078-6; FLAUGH PL, 1984, APPL SPECTROSC, V38, P847, DOI 10.1366-0003702844554693; GARCIA N, 1991, PHYS REV LETT, V66, P1850, DOI 10.1103-PhysRevLett.66.1850; Huang SY, 1997, J PHYS CHEM B, V101, P2576, DOI 10.1021-jp962377q; Jiang P, 1999, CHEM MATER, V11, P2132, DOI 10.1021-cm990080+; JOHN S, 1984, PHYS REV LETT, V53, P2169, DOI 10.1103-PhysRevLett.53.2169; JOHN S, 1987, PHYS REV LETT, V58, P2486, DOI 10.1103-PhysRevLett.58.2486; Kalyanasundaram K., 1998, COORDINATION CHEM RE, V77, P347; Kang MG, 2003, SOL ENERG MAT SOL C, V75, P475, DOI 10.1016-S0927-0248(02)00202-7; Kishimoto H, 1998, J MATER CHEM, V8, P2019, DOI 10.1039-a801499j; Koenderink AF, 2000, PHYS LETT A, V268, P104; NAZEERUDDIN MK, 1993, J AM CHEM SOC, V115, P6382, DOI 10.1021-ja00067a063; Nishimura S, 2002, APPL PHYS LETT, V81, P4532, DOI 10.1063-1.1524693; Nishimura S, 2003, J AM CHEM SOC, V125, P6306, DOI 10.1021-ja034650p; OREGAN B, 1991, NATURE, V353, P737, DOI 10.1038-353737a0; Park NG, 2000, J PHYS CHEM B, V104, P8989, DOI 10.1021-jp994365l; Rothenberger G, 1999, SOL ENERG MAT SOL C, V58, P321, DOI 10.1016-S0927-0248(99)00015-X; SCALORA M, 1994, PHYS REV LETT, V73, P1368, DOI 10.1103-PhysRevLett.73.1368; Schlichthorl G, 1997, J PHYS CHEM B, V101, P8141, DOI 10.1021-jp9714126; Schuurmans FJP, 1999, PHYS REV LETT, V83, P2183, DOI 10.1103-PhysRevLett.83.2183; SOUKOULIS CM, 1989, PHYS REV LETT, V62, P575, DOI 10.1103-PhysRevLett.62.575; Stanley A., 1995, AUST J CHEM, V48, P1294; Stoytchev M, 1997, PHYS REV B, V55, pR8617; Tachibana Y, 2002, CHEM MATER, V14, P2527, DOI 10.1021-cm011563s; Tocci MD, 1996, PHYS REV A, V53, P2799, DOI 10.1103-PhysRevA.53.2799; Usami A, 1999, SOL ENERG MAT SOL C, V59, P163, DOI 10.1016-S0927-0248(99)00068-9; Usami A, 1997, CHEM PHYS LETT, V277, P105, DOI 10.1016-S0009-2614(97)00878-6; VANDERMARK MB, 1988, PHYS REV B, V37, P3575, DOI 10.1103-PhysRevB.37.3575; Vlasov YA, 1999, PHYS REV E, V60, P1030, DOI 10.1103-PhysRevE.60.1030; Wang W, 2001, J AM CHEM SOC, V123, P12528, DOI 10.1021-ja011262j; Wiersma DS, 1997, NATURE, V390, P671; WOLF PE, 1985, PHYS REV LETT, V55, P2696, DOI 10.1103-PhysRevLett.55.269618018718
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
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