6,345 research outputs found
Ultrafast charge transfer coupled with lattice phonons in two-dimensional covalent organic frameworks
No full text© 2019, The Author(s). Covalent organic frameworks (COFs) have emerged as a promising light-harvesting module for artificial photosynthesis and photovoltaics. For efficient generation of free charge carriers, the donor–acceptor (D-A) conjugation has been adopted for two-dimensional (2D) COFs recently. In the 2D D-A COFs, photoexcitation would generate a polaron pair, which is a precursor to free charge carriers and has lower binding energy than an exciton. Although the character of the primary excitation species is a key factor in determining optoelectronic properties of a material, excited-state dynamics leading to the creation of a polaron pair have not been investigated yet. Here, we investigate the dynamics of photogenerated charge carriers in 2D D-A COFs by combining femtosecond optical spectroscopy and non-adiabatic molecular dynamics simulation. From this investigation, we elucidate that the polaron pair is formed through ultrafast intra-layer hole transfer coupled with coherent vibrations of the 2D lattice, suggesting a mechanism of phonon-assisted charge transfe
A finiteness theorem for positive definite almost n-regular quadratic forms
No full textA (positive definite integral) quadratic form is called almost n-regular if it represents almost all quadratic forms of rank n that are represented by its genus. For any integer n >= 2, it will be shown that there are only finitely many similarity classes of almost n-regular quadratic forms of rank n + 3.N
Molecular-level understanding of excited states of N-annulated rylene dye for dye-sensitized solar cells
No full text© 2020 American Chemical Society. In organic push-pull dyes for photovoltaics, it is important to understand the character of intramolecular charge transfer states. Accordingly, the dynamics of charge carriers in photosensitizers based on donor-acceptor structures have been widely studied. Recently, photosensitizers based on N-annulated rylene derivatives have been extensively utilized in organic solar cells due to their outstanding optical properties and considerable power conversion efficiencies, but the excited-state dynamics in those materials have not been investigated yet. Here, we explore the ultrafast dynamics of intramolecular charge transfer (ICT) occurring in the excited states of a diphenylamine N-annulated naphthalene dicarboximide derivative (DND) and present the photovoltaic performance of DND. By using steady-state absorption/emission spectroscopy, femtosecond broadband transient absorption spectroscopy, and DFT calculations, we found that the ICT dynamics of DND vary sensitively depending on the solvent polarity, and the ultrafast transition from the Franck- Condon state to the intramolecular charge transfer state is correlated to the solvation dynamics. This correlation underlines that the ultrafast ICT is strongly coupled with the solvation, accounting for the dependence of the ICT dynamics on the solvent polarity11sciescopu
Enhancement of Energy Transfer Efficiency with Structural Control of Multichromophore Light‐Harvesting Assembly
No full text© 2020 The Authors. Published by Wiley-VCH GmbH. Multichromophore systems (MCSs) are envisioned as building blocks of molecular optoelectronic devices. While it is important to understand the characteristics of energy transfer in MCSs, the effect of multiple donors on energy transfer has not been understood completely, mainly due to the lack of a platform to investigate such an effect systematically. Here, a systematic study on how the number of donors (n(D)) and interchromophore distances affect the efficiency of energy transfer (eta(FRET)) is presented. Specifically,eta(FRET)is calculated for a series of model MCSs using simulations, a series of multiporphyrin dendrimers with systematic variation ofn(D)and interdonor distances is synthesized, and eta(FRET)s of those dendrimers using transient absorption spectroscopy are measured. The simulations predict eta(FRET)in the multiporphyrin dendrimers well. In particular, it is found that eta(FRET)is enhanced by donor-to-donor energy transfer only when structural heterogeneity exists in an MCS, and the relationships between the eta(FRET)enhancement and the structural parameters of the MCS are revealed11sciescopu
Thermodynamic and Transport Properties of H<sub>2</sub>/H<sub>2</sub>O/NaB(OH)<sub>4</sub> Mixtures Using the Delft Force Field (DFF/B(OH)<sub>4</sub><sup>-</sup>)
No full textSodium borohydride (NaBH4) has a high hydrogen (H2 ) gravimetric capacity of 10.7 wt %. NaBH4 releases H2 through a hydrolysis reaction in which aqueous NaB(OH)4 is formed as a byproduct. NaB(OH)4 strongly influences the thermophysical properties of aqueous solutions (i.e., densities, viscosities, and electrical conductivities) and the hydrolysis reaction kinetics and conversion of NaBH4. Here, molecular dynamics (MD) simulations are performed to compute viscosities, electrical conductivities, and self-diffusivities of H2 , Na+, and B(OH)4- for a temperature and concentration range of 298-353 K and 0-5 mol NaB(OH)4/kg water, respectively. Continuous fractional component Monte Carlo (CFCMC) simulations are used to compute the solubilities of H2 and activities of water in aqueous NaB(OH)4 solutions for the same temperature and concentration range. A new force field is developed (Delft force field of B(OH)4-: DFF/B(OH)4-) in which B(OH)4- is modeled as a tetrahedral structure with a scaled charge of −0.85. The OH group in B(OH)4- is modeled as a single interaction site. This force field is based on TIP4P/2005 water and the Madrid-2019 Na+ force field. The MD simulations can accurately capture the densities and viscosities within 2.5% deviation from available experimental data at 298 K up to a concentration of 5 mol NaB(OH)4/kg water. The computed electrical conductivities deviate by ca. 10% from experimental data at 298 K for the same concentration range. Based on the molecular simulations results, engineering equations are developed for shear viscosities, self-diffusivities of H2, Na+, and B(OH)4-, and solubilities of H2, which can be used to design and model NaBH4 hydrolysis reactors.Engineering ThermodynamicsComplex Fluid ProcessingTeam Poulumi De
Oh Holly, The Fish is Dead
No full textFrom Kurt Vonnegut to Stephen King, many novelists use metanarrative techniques to insert fictional versions of themselves in the stories they tell. The function of deploying such techniques is often to draw attention to the liminal space between the fictional constructs inherent in the novel as a form, and the real world from which the constructs draw inspiration, and indeed, are read by an audience. For emerging writers working in short form narratives, however, the structural demands of the short story or flash fiction make the use of similar techniques problematic in the level of depth to which they can be deployed.\ud
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‘Oh Holly, the fish is dead’ is the fourth in a series of short stories that work to overcome the structural limitations of a succinct form by developing a fractured fictional version of the author over a number of pieces and published across a range of sites. The accumulative affect is a richer metanarrative textual arrangement that also allows for the individual short stories to function independently
Flight Dynamics Mission Support and Quality Assurance Process
No full textThis paper summarizes the method of the Computer Sciences Corporation Flight Dynamics Operation (FDO) quality assurance approach to support the National Aeronautics and Space Administration Goddard Space Flight Center Flight Dynamics Support Branch. Historically, a strong need has existed for developing systematic quality assurance using methods that account for the unique nature and environment of satellite Flight Dynamics mission support. Over the past few years FDO has developed and implemented proactive quality assurance processes applied to each of the six phases of the Flight Dynamics mission support life cycle: systems and operations concept, system requirements and specifications, software development support, operations planing and training, launch support, and on-orbit mission operations. Rather than performing quality assurance as a final step after work is completed, quality assurance has been built in as work progresses in the form of process assurance. Process assurance activities occur throughout the Flight Dynamics mission support life cycle. The FDO Product Assurance Office developed process checklists for prephase process reviews, mission team orientations, in-progress reviews, and end-of-phase audits. This paper will outline the evolving history of FDO quality assurance approaches, discuss the tailoring of Computer Science Corporations's process assurance cycle procedures, describe some of the quality assurance approaches that have been or are being developed, and present some of the successful results
Continuous Hamiltonian dynamics and area-preserving homeomorphism group of D2
No full textThe main purpose of this paper is to propose a scheme of a proof of the nonsimpleness of the group {\rm Homeo}^\Omega(D^2,\del D^2) of area preserving homeomorphisms of the 2-disc . We first establish the existence of Alexander isotopy in the category of Hamiltonian homeomorphisms. This reduces the question of extendability of the well-known Calabi homomorphism \Cal: {\rm Diff}^\Omega(D^1,\del D^2) \to \R to a homomorphism \overline \Cal: {\rm Hameo(}D^2,\del D^2) \to \R to that of the vanishing of the basic phase function , a Floer theoretic graph selector constructed in \cite{oh:jdg}, that is associated to the graph of the topological Hamiltonian loop and its normalized Hamiltonian on that is obtained via the natural embedding . Here {\rm Hameo(}D^2,\del D^2) is the group of Hamiltonian homeomorphisms introduced by M\"uller and the author \cite{oh:hameo1}. We then provide an evidence of this vanishing conjecture by proving the conjecture for the special class of \emph{weakly graphical} topological Hamiltonian loops on via a study of the associated Hamiton-Jacobi equation.1111Ysciescopuskc
Asarum chungbuensis B. U. Oh. Since 2005
No full textAsarum chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh (2005: 24) Basionym: Asiasarum sieboldii Miq. f. chungbuensis C.S. Yook & J.G. Kim (1996: 343) Type (neotype, designated here):— KOREA. Gyeonggi-do: Pocheon-si, Mt. Gwangdeoksan, 294 m, 38°04′51″N, 127°25′18″E, 27 April 2020, H. D.Jang & G. H. Nam 506 (KB! barcode NIBRVP774931)(Fig. 1). Notes: —Regarding the scientific name of this taxon, Yamaki (Feb. 1996) published the name of Asiasarum sieboldii (Miq.) F. Maek. var. versicolor (1996: 1), and Yook & Kim (Nov. 1996) published the name of Asiasarum sieboldii (Miq.) F. Maek. f. chungbuensis in the same year. Later, Lee & Lee (2000) republished it with a new combination name Asarum versicolor (Yamaki) Y.N. Lee (2000: 19). Oh et al. (2005) made a new combination name Asarum chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh. Since then, A. versicolor (Yamaki) Y.N. Lee has been accepted as the legitimate name, having priority (Yamaji et al. 2007, So & Kim 2008, Oh 2008, National Institute of Biological Resources 2011). In contrast, A. chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh has been treated as a superfluous name of A. versicolor. However, we detected problems regarding the scientific name A. versicolor (Yamaki) Y.N. Lee. Lee (2000) referred to the basionym as “ Asiasarum sieboldii Miq. var. versicolor Yamaki, J. Jap. Bot. 71: 1–10, 1995”; thus, the name has not been validly published because whole pages of the protologue have been cited. According to Article 41.5 of the ICN (Turland et al. 2018), a new combination name is not validly published unless its basionym is clearly indicated, and a full and direct reference is given to its author and place of valid publication, with page or plate reference and date on or after January 1, 1953. In addition, according to Article 11.2 of the ICN, although Asiasarum sieboldii var. versicolor Yamaki was published before A. sieboldii f. chungbuensis C.S. Yook & J.G. Kim, neither of these names have any priority outside the rank at which they were published. Consequently, A. versicolor (Yamaki) Y.N. Lee is unacceptable, and A. chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh is accepted as the legitimate name of this taxon.Published as part of Jang, Hyun-Do, Nam, Gi-Heum, Oh, Hyun-Kyung & Leem, Hyosun, 2021, Typification of the names Asarum chungbuensis and A. maculatum (Aristolochiaceae), pp. 295-299 in Phytotaxa 508 (3) on page 298, DOI: 10.11646/phytotaxa.508.3.5, http://zenodo.org/record/542599
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