Search results for "clusters"
showing 10 items of 1274 documents
Evidence of superatom electronic shells in ligand-stabilized aluminum clusters
2011
Ligand-stabilized aluminum clusters are investigated by density functional theory calculations. Analysis of Kohn-Sham molecular orbitals and projected density of states uncovers an electronic shell structure that adheres to the superatom complex model for ligand-stabilized aluminum clusters. In this current study, we explain how the superatom complex electron-counting rule is influenced by the electron-withdrawing ligand and a dopant atom in the metallic core. The results may guide the prediction of new stable ligand-stabilized (superatom) complexes, regardless of core and electron-withdrawing ligand composition.
Effects of Silver Doping on the Geometric and Electronic Structure and Optical Absorption Spectra of the Au_{25-n}Ag_{n}(SH)_{18}^{-} (n = 1, 2, 4, 6…
2012
The effect of silver doping of the Au25(SH)18– nanoparticle is studied by investigating Au25–nAgn(SH)18– (n = 1, 2, 4, 6, 8, 10, 12) systems using DFT. For n = 1, doping of the icosahedral shell of the metal core is energetically more favorable than doping of the metal–thiolate units or the center of the core. For n ≥ 2, only doping of the core surface is considered, and arrangements where the silver dopants are in close proximity tend to be slightly less favorable. However, energy differences are small, and all conformations are accessible under experimental conditions. Boltzmann-averaged excitation spectra for these systems show similar features to the undoped Au25(SH)18–. The main differ…
Laser resonant ionization of plutonium
1985
Resonance ionization mass spectrometry (RIMS) has been tested for the isotope-selective determination of trace amounts of plutonium. An atomic beam is formed by evaporating plutonium atoms from a rhenium-filament heated to 1800 °C. The radiation of a pulsed dye laser excites the atoms in a two-photon process (λ=595.2 nm) followed by photoionization of the excited atoms. Mass selectivity is obtained by use of a time-of-flight spectrometer. A resonant signal of239Pu was measured with 1013 atoms deposited on the filament.
Time-dependent density-functional theory in the projector augmented-wave method
2008
We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born–Oppenheimer potential surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear e…
Trumpler 14 and 16 in the Carina nebula
2017
We present the first extensive spectroscopic study of the global population in star clusters Trumpler 16, Trumpler 14, and Collinder 232 in the Carina nebula, using data from the Gaia-ESO Survey, down to solar-mass stars. In addition to the standard homogeneous survey data reduction, a special processing was applied here because of the bright nebulosity surrounding Carina stars. We find about 400 good candidate members ranging from OB types down to slightly subsolar masses. About 100 heavily reddened early-type Carina members found here were previously unrecognized or poorly classified, including two candidate O stars and several candidate Herbig Ae/Be stars. Their large brightness makes th…
Site-specific targeting of enterovirus capsid by functionalized monodisperse gold nanoclusters
2014
Development of precise protocols for accurate site-specific conjugation of monodisperse inorganic nanoparticles to biological material is one of the challenges in contemporary bionanoscience and nanomedicine. We report here a successful site-specific covalent conjugation of functionalized atomically monodisperse gold clusters with 1.5-nm metal cores to viral surfaces. Water-soluble Au102(para-mercaptobenzoic acid)44 clusters, functionalized by maleimide linkers to target cysteines of viral capsid proteins, were synthesized and conjugated to enteroviruses echovirus 1 and coxsackievirus B3. Quantitative analysis of transmission electron microscopy images and the known virus structures showed …
Evaluation of the perceived social impacts of the Formula E Grand Prix of Santiago de Chile David
2020
[Abstract] The aim of this study is to analyse residents' perception of the social impact of the Formula E Grand Prix of Santiago de Chile. A sample of 414 residents was collected through a questionnaire made up of 46 items regarding possible positive and negative impacts. Descriptive analysis, confirmatory factorial analysis and cluster analysis were performed. The results showed two groups with different perceptions of this sporting event: realistic (n=152) and favourable (n=162). Sociodemographic variables referring to education level, civil status, income level, location of the family residence and political orientation contribute to significantly differentiating the clusters. The varia…
How to boost clusters and regional change through cooperative social innovation
2020
The aim of this paper is to illustrate how social innovation is promoted and spread by cooperative clusters in order to develop regional change. This paper focuses on the main drivers of the spreading and exaptation processes of social innovation. The cooperative cluster model, the exaptation concept, the top-down approach, the meso-institutions concept and the meso-level perspective are used to capture the strategic approach of spreading social innovation. The study analyses two successful clusters: Mondragon, made up of industrial SMEs, and Anecoop, an agricultural cooperative group, both leading clusters in their respective region. Qualitative methodology is used to compare both case stu…
Reaching net zero energy at the neighbourhood scale: feasibility studies in the south of Italy
2020
Il concetto di “edificio a energia netta zero” è stato recentemente implementato in tutti i regolamenti dei paesi europei. Tuttavia, l’approccio dettato dall’Europa si concentra principalmente sulla scala dell’edificio singolo, tralasciando alcuni aspetti riguardanti ad esempio l’interazione di generazione e carico tra edifici e le interazioni energetiche tra edifici. L’obiettivo di questo studio consiste nell’applicazione della definizione di net zero energy building ad un gruppo di edifici ubicati nell’Italia meridionale e caratterizzati da una destinazione d’uso variegata. Lo status quo di una ventina di edifici è stato simulato in ambiente energy plus e sono state successivamente selezi…
Fluctuations of the Casimir-Polder force between an atom and a conducting wall
2007
We consider the quantum fluctuations of the Casimir-Polder force between a neutral atom and a perfectly conducting wall in the ground state of the system. In order to obtain the atom-wall force fluctuation we first define an operator directly associated to the force experienced by the atom considered as a polarizable body in an electromagnetic field, and we use a time-averaged force operator in order to avoid ultraviolet divergences appearing in the fluctuation of the force. This time-averaged force operator takes into account that any measurement involves a finite time. We also calculate the Casimir-Polder force fluctuation for an atom between two conducting walls. Experimental observabili…