The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Surendra P Shah - One of the best experts on this subject based on the ideXlab platform.
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correlation among fresh State Behavior fiber dispersion and toughness properties of sfrcs
Journal of Materials in Civil Engineering, 2008Co-Authors: Liberato Ferrara, Y D Park, Surendra P ShahAbstract:Effective structural use of steel fiber-reinforced concrete (SFRC) relies on the assumption of uniform dispersion of fibers within the elements. Fiber dispersion related issues hence stand as a cutting edge research and technology development topic. The use of self-consolidating concrete (SCC), thanks to its rheological stability and self-placability, which leads to the elimination of compaction by vibration, may be helpful in guaranteeing a uniform dispersion of fibers. With reference to the latter, several techniques [e.g., based on alternate current impedance spectroscopy (AC-IS), microwave reflectometry etc.] have been developed in the last few years for its nondestructive monitoring. Investigation into the connections between fiber dispersion and the performance of the composite in the fresh and hardened State stand as the natural completion for a thorough assessment of the FRC properties, aimed at promoting its wider use for full load bearing structural applications. This paper presents the results of a research project aimed at the above said purpose. Based on a previously calibrated mix-design methodology, suitable specimens were cast with SFRC characterized by different performance in the fresh State (vibration-, self-, and segregation consolidating) and tested in four-point bending, in order to assess the connections among fresh State Behavior and fiber dispersion, herein investigated by means of AC-IS, and the performance in the hardened State. The results, highlighting this correlation, point out their importance for a design of the material composition “tailored” to the anticipated mechanical performance and to the specific structural application.
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fresh State Behavior fiber dispersion and hardened State properties of self compacting steel fiber reinforced concrete
Studi e ricerche - Politecnico di Milano. Scuola di specializzazione in costruzioni in cemento armato, 2007Co-Authors: Liberato Ferrara, Y D Park, Surendra P ShahAbstract:The results of a research project focusing on the correlation among fresh and hardened State properties and fiber dispersion in Self-Compacting Steel Fiber-Reinforced Concretes (SC-SFRC) are presented. Three SFRCs, containing 50 kg/m 3 hooked end fibers 35 mm long with an aspect ratio equal to 65, were designed, targeted to different levels of fresh State performance: vibrated, self-consolidating and a third one exhibiting segregation. Thin square plates (600x600x60 mm) were cast for each mix and the dispersion of fibers within them was investigated through Alternate Current Impedance Spectroscopy (AC-IS). Beams were cut from the plates and tested in 4-point bending and the mechanical performance in the hardened State was evaluated. The influence of fiber dispersion on the mechanical properties is discussed. The results highlight the connections existing among fresh State Behavior, fiber dispersion and mechanical properties of SFRC, pointing out their importance for a mix-design of a material "tailored" for the specific structural applications.
Prashant V Kamat - One of the best experts on this subject based on the ideXlab platform.
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thiolated gold nanoclusters for light energy conversion
ACS energy letters, 2018Co-Authors: Muhammad Abbas, Prashant V Kamat, Jin Ho BangAbstract:Few-atom gold nanoclusters (NCs) exhibit molecule-like properties due to a discrete electronic structure driven by the quantum confinement effect. Unlike plasmonic Au particles, these nonplasmonic particles of diameter less than 2 nm, commonly referred to as nanoclusters, possess a distinct excited-State Behavior that can offer a new opportunity to employ them as a photosensitizer. Their size-dependent excited-State Behavior enables establishing logical designing principles to build up efficient light energy conversion systems. The photodynamics of thiolated Au NCs and efforts to exploit the Au NCs in light energy conversion applications discussed in this Review show new opportunities to utilize them as photosensitizers. Current bottlenecks in implementing thiolated Au NCs in light conversion applications and new strategies and future directions to address these limitations are also discussed.
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size dependent excited State Behavior of glutathione capped gold clusters and their light harvesting capacity
Journal of the American Chemical Society, 2014Co-Authors: Kevin G Stamplecoskie, Prashant V KamatAbstract:Glutathione-protected gold clusters exhibit size-dependent excited State and electron transfer properties. Larger-size clusters (e.g., Au25GSH18) with core-metal atoms display rapid (<1 ps) as well as slower relaxation (∼200 ns) while homoleptic clusters (e.g., Au10–12GSH10–12) exhibit only slower relaxation. These decay components have been identified as metal–metal transition and ligand-to-metal charge transfer, respectively. The short lifetime relaxation component becomes less dominant as the size of the gold cluster decreases. The long-lived excited State and ability to participate in electron transfer are integral for these clusters to serve as light-harvesting antennae. A strong correlation between the ligand-to-metal charge-transfer excited State lifetime and photocatalytic activity was evidenced from the electron transfer to methyl viologen. The photoactivity of these metal clusters shows increasing photocatalytic reduction yield (0.05–0.14) with decreasing cluster size, Au25 < Au18 < Au15 < Au10–...
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excited State Behavior of luminescent glutathione protected gold clusters
Journal of Physical Chemistry C, 2014Co-Authors: Kevin G Stamplecoskie, Yongsiou Chen, Prashant V KamatAbstract:The excited-State Behavior of luminescent gold clusters provides new insights in understanding their photocatalytic activity in the visible region. The excited State of glutathione-protected gold nanoclusters (AuGSH), which is characterized by the long-lived excited State (τ = 780 ns), arises from the ligand-to-metal type transition. These AuGSH clusters are in a partially oxidized State (Au(I)) and are readily reduced by chemical or electrochemical methods. Interestingly, a metal core transition with short-lived lifetime (τ < 3 ps) appears along with a longer lifetime in reduced AuGSH clusters. The role of the oxidation State of gold clusters in dictating the photocatalytic reduction of methyl viologen is discussed.
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realizing visible photoactivity of metal nanoparticles excited State Behavior and electron transfer properties of silver ag8 clusters
Journal of Physical Chemistry Letters, 2012Co-Authors: Weita Chen, Yungjung Hsu, Prashant V KamatAbstract:Silver nanoclusters complexed with dihydrolipoic acid (DHLA) exhibit molecular-like excited-State properties with well-defined absorption and emission features. The 1.8 nm diameter Ag nanoparticles capped with Ag8 clusters exhibit fluorescence maximum at 660 nm with a quantum yield of 0.07%. Although the excited State is relatively short-lived (τ 130 ps), it exhibits significant photochemical reactivity. By introducing MV(2+) as a probe, we have succeeded in elucidating the interfacial electron transfer dynamics of Ag nanoclusters. The formation of MV(+•) as the electron-transfer product with a rate constant of 2.74 × 10(10) s(-1) confirms the ability of these metal clusters to participate in the photocatalytic reduction process. Basic understanding of excited-State processes in fluorescent metal clusters paves the way toward the development of biological probes, sensors, and catalysts in energy conversion devices.
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triplet excited State Behavior of fullerenes pulse radiolysis and laser flash photolysis of fullerenes c60 and c70 in benzene
The Journal of Physical Chemistry, 1992Co-Authors: Nada M Dimitrijevic, Prashant V KamatAbstract:Both pulse radiolysis and laser flash photolysis techniques have been employed to characterize the triplet excited State Behavior of C 60 and C 70 in benzene at 296 K. Apart from the previously reported absorption in the visible, we were able to characterize its absorption in the UV region and determine the extinction coefficients in the visible region. Pulse radiolysis experiments give indirect confirmation for the spectral features of the triplet excited States
Don T. Tilley - One of the best experts on this subject based on the ideXlab platform.
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expanded helicenes a general synthetic strategy and remarkable supramolecular and solid State Behavior
Journal of the American Chemical Society, 2017Co-Authors: Gavin R Kiel, Patrick W. Smith, Daniel S. Levine, Sajan Patel, Don T. TilleyAbstract:A divergent synthetic strategy allowed access to several members of a new class of helicenes, the “expanded helicenes”, which are composed of alternating linearly and angularly fused rings. The strategy is based on a three-fold, partially intermolecular [2+2+n] (n = 1 or 2) cycloaddition with substrates containing three diyne units. Investigation of aggregation Behavior, both in solution and in the solid State, revealed that one of these compounds forms an unusual homochiral, π-stacked dimer via an equilibrium that is slow on the NMR time scale. The versatility of the method was harnessed to access a selenophene-annulated expanded helicene that, in contrast to its benzannulated analogue, exhibits long-range π-stacking in the solid State. The new helicenes possess low racemization barriers, as demonstrated by dynamic 1H NMR spectroscopy.
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Expanded Helicenes: A General Synthetic Strategy and Remarkable Supramolecular and Solid-State Behavior
2017Co-Authors: Gavin R. Kiel, Sajan C. Patel, Patrick W. Smith, Daniel S. Levine, Don T. TilleyAbstract:A divergent synthetic strategy allowed access to several members of a new class of helicenes, the “expanded helicenes”, which are composed of alternating linearly and angularly fused rings. The strategy is based on a three-fold, partially intermolecular [2+2+n] (n = 1 or 2) cycloaddition with substrates containing three diyne units. Investigation of aggregation Behavior, both in solution and in the solid State, revealed that one of these compounds forms an unusual homochiral, π-stacked dimer via an equilibrium that is slow on the NMR time scale. The versatility of the method was harnessed to access a selenophene-annulated expanded helicene that, in contrast to its benzannulated analogue, exhibits long-range π-stacking in the solid State. The new helicenes possess low racemization barriers, as demonstrated by dynamic 1H NMR spectroscopy
Roberto Improta - One of the best experts on this subject based on the ideXlab platform.
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influence of base stacking on excited State Behavior of polyadenine in water based on time dependent density functional calculations
Proceedings of the National Academy of Sciences of the United States of America, 2007Co-Authors: Fabrizio Santoro, Vincenzo Barone, Roberto ImprotaAbstract:A thorough study of the excited-State properties of the stacked dimers and trimers of 9-methyladenine in B-DNA conformation has been performed in aqueous solution by using time-dependent density functional calculations and the solvent polarizable continuum model, and results were compared with experimental results on polyadenine oligomers. The effect of base stacking on the absorption and emission spectra is fully reproduced by our calculations. Although light absorption leads to a State (SB) delocalized over several nucleobases, excited-State geometry optimization indicates that SB subsequently evolves into a State in which the excitation is localized on a single base. Analysis of the excited-State potential energy surfaces shows that SB can easily decay into the lowest energy excited State, SCT, which is a dark excimer produced by intermonomer charge transfer between two stacked bases. The subpicosecond features of the time-resolved experiments are interpreted in terms of ultrafast decay from SB. After localization, two easy, radiationless decay channels are indeed open for SB: (i) ground-State recovery, according to the same mechanisms proposed for isolated adenine and/or (ii) decay to SCT. Our calculations suggest that the slowest part of the excited-State dynamics detected experimentally involves the SCT State.
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singlet excited State Behavior of uracil and thymine in aqueous solution a combined experimental and computational study of 11 uracil derivatives
Journal of the American Chemical Society, 2006Co-Authors: Thomas Gustavsson, Vincenzo Barone, Akos Banyasz, Elodie Lazzarotto, Dimitra Markovitsi, Giovanni Scalmani, Michael J Frisch, Roberto ImprotaAbstract:The excited-State properties of uracil, thymine, and nine other derivatives of uracil have been studied by steady-State and time-resolved spectroscopy. The excited-State lifetimes were measured using femtosecond fluorescence upconversion in the UV. The absorption and emission spectra of five representative compounds have been computed at the TD−DFT level, using the PBE0 exchange-correlation functional for ground- and excited-State geometry optimization and the Polarizable Continuum Model (PCM) to simulate the aqueous solution. The calculated spectra are in good agreement with the experimental ones. Experiments show that the excited-State lifetimes of all the compounds examined are dominated by an ultrafast (<100 fs) component. Only 5-substituted compounds show more complex Behavior than uracil, exhibiting longer excited-State lifetimes and biexponential fluorescence decays. The S0/S1 conical intersection, located at CASSCF (8/8) level, is indeed characterized by pyramidalization and out of plane motion of...
John S Duffield - One of the best experts on this subject based on the ideXlab platform.
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political culture and State Behavior why germany confounds neorealism
International Organization, 1999Co-Authors: John S DuffieldAbstract:During the past decade, a growing number of scholars have turned to cultural approaches to account for the foreign and security policies of States. Surprisingly, however, these scholars have devoted little attention to the concept that boasts the most venerable tradition in the field of political science, that of political culture, as a possible source of State Behavior. This neglect is unjustified. Like other cultural variables, political culture promises to explain phenomena that are enigmatic from the perspective of leading noncultural theories, such as neorealism. Yet it applies to a broader range of cases than do the many alternative cultural concepts, such as strategic culture and organizational culture, that have been employed. I begin by describing an important puzzle in the international relations literature that suggests the need to consider culture as a variable: the failure of neorealism to predict German security policy after unification. I then assess the various cultural approaches used in recent years to explain State Behavior. After noting the similarities in these approaches, I discuss the important differences that mark them and identify the reasons for the greater utility of political culture. Finally, I illustrate the explanatory power of the political culture approach by applying it to the case of German security policy since 1990.
