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1.
Jorge Segovia Chen Chen Ian C. Cloët Craig D. Roberts Sebastian M. Schmidt Shaolong Wan 《Few-Body Systems》2014,55(1):1-33
Predictions obtained with a confining, symmetry-preserving treatment of a vector ? vector contact interaction at leading-order in a widely used truncation of QCD’s Dyson–Schwinger equations are presented for Δ and Ω baryon elastic form factors and the γN → Δ transition form factors. This simple framework produces results that are practically indistinguishable from the best otherwise available, an outcome which highlights that the key to describing many features of baryons and unifying them with the properties of mesons is a veracious expression of dynamical chiral symmetry breaking in the hadron bound-state problem. The following specific results are of particular interest. The Δ elastic form factors are very sensitive to m Δ. Hence, given that the parameters which define extant simulations of lattice-regularised QCD produce Δ-resonance masses that are very large, the form factors obtained therewith are a poor guide to properties of the Δ(1232). Considering the Δ-baryon’s quadrupole moment, whilst all computations produce a negative value, the conflict between theoretical predictions entails that it is currently impossible to reach a sound conclusion on the nature of the Δ-baryon’s deformation in the infinite momentum frame. Results for analogous properties of the Ω baryon are less contentious. In connection with the N → Δ transition, the Ash-convention magnetic transition form factor falls faster than the neutron’s magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and Δ; and, furthermore, these quadrupole ratios do slowly approach their anticipated asymptotic limits. 相似文献
2.
Dr. Kimiaka C. Guérard Vincent Hamel Dr. Amandine Guérinot Cloé Bouchard‐Aubin Prof. Sylvain Canesi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18068-18071
A rapid route to 5,5‐ and 5,6‐ bicyclic systems is provided by an 1,3‐alkyl‐shift process mediated by a hypervalent iodine reagent on aromatics. The structures obtained contain several unsaturations with different behaviors and reactivities. Such diversity allows further elaborations for the rapid formation of compact systems present in a variety of natural products. The potential for further transformations has been demonstrated by performing a double Michael addition. This cyclization process is regio‐ and stereoselective due to the presence of a former benzylic substituent. Furthermore, an extension of this approach has been accomplished on indole derivatives. 相似文献
3.
A dressed-quark core contribution to nucleon electromagnetic form factors is calculated. It is defined by the solution of
a Poincaré covariant Faddeev equation in which dressed-quarks provide the elementary degree of freedom and correlations between
them are expressed via diquarks. The nucleon-photon vertex involves a single parameter; namely, a diquark charge radius. It
is argued to be commensurate with the pion’s charge radius. A comprehensive analysis and explanation of the form factors is
built upon this foundation. A particular feature of the study is a separation of form factor contributions into those from
different diagram types and correlation sectors, and subsequently a flavour separation for each of these. Amongst the extensive
body of results that one could highlight are: , owing to the presence of axial-vector quark-quark correlations; and for both the neutron and proton the ratio of Sachs
electric and magnetic form factors possesses a zero. 相似文献
4.
Cloé?Desmet Andrea?Valsesia Arianna?Oddo Giacomo?Ceccone Valentina?Spampinato Fran?ois?Rossi Pascal?ColpoEmail author 《Journal of nanoparticle research》2017,19(3):117
Characterisation of engineered nanomaterials (NMs) is of outmost importance for the assessment of the potential risks arising from their extensive use. NMs display indeed a large variety of physico-chemical properties that drastically affect their interaction with biological systems. Among them, hydrophobicity is an important property that is nevertheless only slightly covered by the current physico-chemical characterisation techniques. In this work, we developed a method for the direct characterisation of NM hydrophobicity. The determination of the nanomaterial hydrophobic character is carried out by the direct measurement of the affinity of the NMs for different collectors. Each collector is an engineered surface designed in order to present specific surface charge and hydrophobicity degrees. Being thus characterised by a combination of surface energy components, the collectors enable the NM immobilisation with surface coverage in relation to their hydrophobicity. The experimental results are explained by using the extended DLVO theory, which takes into account the hydrophobic forces acting between NMs and collectors. 相似文献
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6.
We present the first Dyson–Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the
masses of meson and baryon ground- and excited-states within a single framework. At the core of our analysis is a symmetry-preserving
treatment of a vector–vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degree-of
freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in
modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of
baryon structure; e.g., relationships between the nucleon and Δ masses and those of the dressed-quark and diquark correlations
they contain. 相似文献
7.
I. C. Cloët G. Eichmann V. V. Flambaum C. D. Roberts M. S. Bhagwat A. Höll 《Few-Body Systems》2008,42(1-4):91-113
A calculation of the current quark-mass dependence of nucleon static electromagnetic properties is necessary in order to use observational data as a means to place constraints on the variation of Nature’s fundamental parameters. A Poincaré-covariant Faddeev equation, which describes baryons as composites of confined quarks and nonpointlike diquarks, is used to calculate this dependence. The results indicate that, like observables dependent on the nucleons’ magnetic moments, quantities sensitive to their magnetic and charge radii, such as the energy levels and transition frequencies in hydrogen and deuterium, might also provide a tool with which to place limits on the allowed variation in Nature’s constants. 相似文献
8.
Jorge Segovia Ian C. Cloët Craig D. Roberts Sebastian M. Schmidt 《Few-Body Systems》2014,55(12):1185-1222
We present a unified study of nucleon and \({\Delta}\) elastic and transition form factors, and compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a symmetry-preserving treatment of a vector \({\otimes}\) vector contact-interaction. The comparison emphasises that experiments are sensitive to the momentum dependence of the running couplings and masses in the strong interaction sector of the Standard Model and highlights that the key to describing hadron properties is a veracious expression of dynamical chiral symmetry breaking in the bound-state problem. Amongst the results we describe, the following are of particular interest: \({G_{E}^{p}(Q^{2})/G_{M}^{p}(Q^{2})}\) possesses a zero at Q 2 = 9.5 GeV2; any change in the interaction which shifts a zero in the proton ratio to larger Q 2 relocates a zero in \({G_{E}^{n}(Q^{2})/G_M^{n}(Q^{2})}\) to smaller Q 2; there is likely a value of momentum transfer above which \({G_{E}^{n} > G_{E}^{p}}\) ; and the presence of strong diquark correlations within the nucleon is sufficient to understand empirical extractions of the flavour-separated form factors. Regarding the \({\Delta(1232)}\) -baryon, we find that, inter alia: the electric monopole form factor exhibits a zero; the electric quadrupole form factor is negative, large in magnitude, and sensitive to the nature and strength of correlations in the \({\Delta(1232)}\) Faddeev amplitude; and the magnetic octupole form factor is negative so long as rest-frame P- and D-wave correlations are included. In connection with the \({N \to \Delta}\) transition, the momentum-dependence of the magnetic transition form factor, \({G_{M}^{*}}\) , matches that of \({G_{M}^{n}}\) once the momentum transfer is high enough to pierce the meson-cloud; and the electric quadrupole ratio is a keen measure of diquark and orbital angular momentum correlations, the zero in which is obscured by meson-cloud effects on the domain currently accessible to experiment. Importantly, within each framework, identical propagators and vertices are sufficient to describe all properties discussed herein. Our analysis and predictions should therefore serve as motivation for measurement of elastic and transition form factors involving the nucleon and its resonances at high photon virtualities using modern electron-beam facilities. 相似文献
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10.
Dr. Angel T. Garcia-Esparza Dr. Tatsuya Shinagawa Dr. Samy Ould-Chikh Muhammad Qureshi Dr. Xuyuan Peng Dr. Nini Wei Dr. Dalaver H. Anjum Dr. Alain Clo Dr. Tsu-Chien Weng Dr. Dennis Nordlund Dr. Dimosthenis Sokaras Prof. Jun Kubota Prof. Kazunari Domen Prof. Kazuhiro Takanabe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(21):5874-5878
For overall water-splitting systems, it is essential to establish O2-insensitive cathodes that allow cogeneration of H2 and O2. An acid-tolerant electrocatalyst is described, which employs a Mo-coating on a metal surface to achieve selective H2 evolution in the presence of O2. In operando X-ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O2 gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoOx/Pt/SrTiO3 with inhibited water formation from H2 and O2, which is the prevailing back reaction on the bare Pt/SrTiO3 photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis. 相似文献