Spectral functions of isolated Ce adatoms on paramagnetic surfaces

We report photoemission experiments revealing the full valence electron spectral function of Ce adatoms on Ag(111), W(110) and Rh(111) surfaces. A transfer of Ce 4f spectral weight from the ionization peak towards the Fermi level is demonstrated upon changing the substrate from Ag(111) to Rh(111). In the intermediate case of Ce on W(110) the ionization peak is found to be split. This evolution of the spectra is explained by means of first-principles theory which clearly demonstrates that a reliable understanding of magnetic adatoms on metal surfaces requires simultaneous low and high energy spectroscopic information.Comment: 4 pages, 3 figure

Correlated Electrons Step-by-Step: Itinerant-to-Localized Transition of Fe Impurities in Free-Electron Metal Hosts

High-resolution photoemission spectroscopy and realistic ab-initio calculations have been employed to analyze the onset and progression of d-sp hybridization in Fe impurities deposited on alkali metal films. The interplay between delocalization, mediated by the free-electron environment, and Coulomb interaction among d-electrons gives rise to complex electronic configurations. The multiplet structure of a single Fe atom evolves and gradually dissolves into a quasiparticle peak near the Fermi level with increasing the host electron density. The effective multi-orbital impurity problem within the exact diagonalization scheme describes the whole range of hybridizations.Comment: 10 pages, 4 figure

In-vacuo adaptive beam element for vibration control

This paper proposes a novel in-vacuo adaptive beam element for vibration control, which, in this study, is employed as an adaptive tuneable vibration absorber. The element is formed by a composite beam with a core of structured fabrics wrapped in a deflated plastic bag skin. The fabrics consist of 3D-printed chain mails of hollowed truss-like particles. A base post is connected at the middle section of the composite beam, such that its flexural vibration is controlled by a flapping fundamental natural mode whose natural frequency can be varied by changing the vacuum level in the bag. The dynamics of this arrangement replicates that of a suspended mass-spring-damper system and, thus, can be suitably used as a tuneable vibration absorber. The study considers in-vacuo composite beams with one or two overlapping chain mails made with cubic, spherical-octahedral, octahedral hollowed truss-like particles. To start with, the dynamic response of these structures is analysed with respect to dynamic stiffness frequency response functions measured with a six-point bending setup. The dynamic response of the centrally pinned in-vacuo adaptive beam element is then investigated considering the vibration transmissibility and base impedance frequency response functions. Finally, the tuning features and vibration control effects of the adaptive beam element are assessed by fitting it at the free termination of a clamped beam in order to control the resonant response of a target flexural mode. Overall, the experimental results have shown that the fundamental natural frequency of the proposed in-vacuo adaptive beam element can be swiftly lifted or lowered by modulating the vacuum level in the bag encasing the structured fabrics. Indicatively, the working centre frequency of the resulting absorber depends on the number of strips piled in the vacuum bag, which defines the thickness, and thus the reference bending stiffness, of the in-vacuo composite beam. Also, the working frequency bandwidth of the in-vacuo adaptive beam element mostly depends on the geometry, the material and the finishing of the chain mail particles. In fact, these properties infer on the number, the type (between convex or non-convex surfaces), the area and the friction coefficient of the contacts that develop between neighbouring particles of the mails and thus determine the range of bending stiffness that can be achieved by a given vacuum range in the deflated bag

Design of a tuned vbration absorber (TVA) for applications in transport engineering

The control of the response to tonal excitations or to broadband stochastic disturbances of a stiffened cylinder is investigated through the use of a Tuned Vibrating Absorber (TVA). In particular, the study considered both a purely passive device (Mechanical) and a semi-active one with shunt circuit (Electro-Mechanical) to evaluate the efficiencies and differences

Localized Magnetic States of Fe, Co, and Ni Impurities on Alkali Metal Films

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) have been used to study transition metal impurities on K and Na films. The multiplet structure of the XAS spectra indicates that Fe, Co, and Ni have localized atomic ground states with predominantly d7, d8, and d9 character, respectively. XMCD shows that the localized impurity states possess large, atomiclike, magnetic orbital moments that are progressively quenched as clusters are formed. Ni impurities on Na films are found to be nonmagnetic, with a strongly increased d10 character of the impurity state. The results show that the high magnetic moments of transition metals in alkali hosts originate from electron localization

3D sound radiation reconstruction from camera measurements

In general, the measurement of the sound radiation field by machinery and partitions requires time-consuming tests, which should be carried out in specially dedicated anechoic/reverberant facilities with calibrated sensors and complex acquisition and post processing equipment. This article introduces a two-step method for the identification from optical measurements of the free-field sound radiation generated by flexural vibrations of closed shells. In the first step, the flexural vibration of the shell is reconstructed with a frequency domain triangulation technique based on short multi-view video acquisitions made with a single high-resolution, high-speed camera. In the second step, the free-field sound radiation is derived from a discretized boundary integral formulation. The study is focused on the identification of the sound radiation from the flexural vibration of a baffled cylinder model structure. The vibration and sound fields reconstructed from the camera measurements are validated against direct measurements taken with a laser scanner vibrometer and a microphone array, respectively. Overall, this research demonstrates that optical methods based on camera measurements can be suitably employed to produce fast and accurate full-field measurements of sound radiation of closed shells (without the need for a dedicated measurement environment, e.g. reverberant, anechoic chambers)

Development and Applications of a Virtual Hybrid Platform for Multiscale Analysis of Advanced Structures of Aircraft (DEVISU)

This paper outlines the main findings of the project “DEvelopment and applications of a VIrtual hybrid platform for multiscale analysis of advanced StructUres of aircraft” (DEVISU), which deals with failure of composite structures and noise/vibration reduction, along with investigation of new materials for aerospace applications

A cryogenic solid-state reaction at the interface between Ti and the Bi2Se3topological insulator

peer reviewedUnderstanding the chemical processes at the interface between a metal and topological insulator (TI) is important when it comes to designing devices that exploit the peculiar topological surface states or studying the properties of TI heterostructures. In this paper we show that the interface between Ti and Bi2Se3 is unstable at RT and results in the formation of interfacial phases of titanium selenides and metallic Bi. The reaction has shown significant kinetics already at cryogenic temperatures, which is very surprising for a solid-state redox reaction. This can be explained with the possibility of electrons in the topological surface states playing a role in enhancing the Bi2Se3 surface reactivity due to the electron-bath effect. For the Ti coverage above 40 nm, the interfacial processes cause compressive stress that triggers the morphological change (buckling) of the deposited film. The observed interface reaction, with all of its consequences, has to be considered not only in the design of devices, where the Ti adhesion layer is often used for contacts, but also for possible engineering of 2D TI heterostructures

Ordered vacancy network induced by the growth of epitaxial graphene on Pt(111)

We have studied large areas of (v3×v3)R30° graphene commensurate with a Pt(111) substrate. A combination of experimental techniques with ab initio density functional theory indicates that this structure is related to a reconstruction at the Pt surface, consisting of an ordered vacancy network formed in the outermost Pt layer and a graphene layer covalently bound to the Pt substrate. The formation of this reconstruction is enhanced if low temperatures and polycyclic aromatic hydrocarbons are used as molecular precursors for epitaxial growth of the graphene layers