1,720,974 research outputs found
BMS flux algebra in celestial holography
Get PDFAbstract Starting from gravity in asymptotically flat spacetime, the BMS momentum fluxes are constructed. These are non-local expressions of the solution space living on the celestial Riemann surface. They transform in the coadjoint representation of the extended BMS group and correspond to Virasoro primaries under the action of bulk superrotations. The relation between the BMS momentum fluxes and celestial CFT operators is then established: the supermomentum flux is related to the supertranslation operator and the super angular momentum flux is linked to the stress-energy tensor of the celestial CFT. The transformation under the action of asymptotic symmetries and the OPEs of the celestial CFT currents are deduced from the BMS flux algebra
Chiroptical Signatures of Planar and Central Chirality in [2]Paracyclo[2](5,8)quinolinophane Derivatives
No full textElectronic and vibrational circular dichroism (ECD and VCD) spectra and specific optical rotation measurements at the sodium D-line (OR) have been taken for thirteen chiral [2]-paracyclo[2](5,8)quinolinophane derivatives and calculated by density functional theory. Besides the planar chirality from the paracyclophane moiety in all molecules, some of the investigated compounds also exhibit central chirality due to an
asymmetric carbon atom in the side-chain bound at C-2 of the heterocyclic ring. Characteristic bands for each type ofchirality were clearly identified in the VCD spectra in the CH-stretching and mid-IR regions, allowing assignment of absolute and relative configurations. ECD was found to be sensitive mostly, if not exclusively, to planar chirality, whereas OR was also very sensitive to central chirality. Configurational assignment of the different diastereomers by the
present method provided results that are in agreement with those inferred from NOE-NMR experiments
Circular Dichroism Spectra (350-185 nm) of a New Series of 4-Substituted [2.2] Paracyclophanes: a Quantitative Analysis within the De Voe Polarizability Model
No full textThe CD spectra of a new series of 4-substituted [2.2]paracyclophanes 1b- e have been measured down to 185 nm. Polarizability calculations within the DeVoe model satisfactorily reproduce the CD features over all the spectral range. In addition, the analysis of the complete CD spectrum allowed a phenomenological interpretation of the dependence of the sign of [α](D) on the nature of the substituents, at least for X=F, OH, I
Loop-corrected subleading soft theorem and the celestial stress tensor
No full textWe demonstrate that the one-loop exact subleading soft graviton theorem automatically follows from conservation of the BMS charges, provided that the hard and soft fluxes separately represent the extended BMS algebra at null infinity. This confirms that superrotations are genuine symmetries of the gravitational S-matrix beyond the semiclassical regime. In contrast with a previous proposal, the celestial stress tensor accounting for the one-loop corrections follows from the gravitational phase space analysis and does not require the addition of divergent counterterms. Moreover, we show that the symplectic form on the radiative phase space factorises into hard and soft sectors, and that the resulting canonical generators precisely coincide with the correct BMS fluxes
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
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
Electronic and Vibrational Circular Dichroism Spectra of Chiral 4-X-[2.2]paracyclophanes with X containing Fluorine Atoms
No full textThe absorption IR and vibrational circular dichroism (VCD) spectra of both enantiomers of 4-X-
[2.2]paracyclophanes (X ) F, CH2F, COCF3) have been recorded in the mid-IR and CH stretching regions.
The electronic CD (ECD) spectra have been collected as well. VCD spectra in the two IR regions, 900-1700
cm-1 and 2700-3200 cm-1, have been compared with the corresponding DFT calculated spectra. The absolute
configuration assignment was confirmed as previously determined. We have shown that, to various extents,
the VCD and ECD spectra bear some information on the relative mobility of the two phenyl rings and on the
existence of different conformers for the X group. It has been observed that X ) F and X ) CH2F groups
do not change the conformational and electronic properties of the parent X ) H and X ) CH3 molecules.
The X ) COCF3 group brings in a large perturbation to the [2.2]paracyclophanes, and the role of fluorine is
less important than that of oxygen
Effects of association colloids on elimination from 1,2-dihalo-1,2-diphenylethanes. The role of surfactant structure
No full textRates of E2 elimination of D,L-1,2dichloro-1,2-diphenylethane (1) and the analogous dibromide (2) were measured in aqueous cetyltrimethylammonium chloride and hydroxide (CTACl and CTAOH), cetyltripropylammonium
hydroxide (CTPAOH), didodecyldimethylammonium chloride and hydroxide (DDDACl and DDDAOH),and N,N-dimethyl-N-(2-hydroxyethyl)-n-hexadecylammonium hydroxide (DOH,OH). Micelles or other association colloids of these surfactants increase rates in solutions that contain OH-, and DOH,-OH is much more effective than the nonfunctional surfactants. Variations of first-order rate constants, kobs, with [surfactant] or [OH-] are fitted by a pseudophase model with water and micelles as distinct reaction media, to give second-order rate constants in the latter. These rate constants are in the sequence DOH,OH > CTPAOH = DDDACl > DDDAOH = CTAOH = CTACl. Micelles favor reactions of 2 over 1,
relative to reactivities in water, due to differences in amphiphilic interactions with the leaving halide ions
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