1,721,017 research outputs found
Erratum: "Spin" splitting in asymmetric double quantum wells: A mechanism for "spin"-dependent hole delocalization (Physical Review Letters (1993) 70, 13, (2051))
No full textProceedings of the13th International Conference on Modulated Semiconductor Structures (MSS-13)
No full textDamage modelling strategies for unidirectional laminates subjected to impact using CZM and orthotropic plasticity law
No full textIn the present paper, the crashworthiness of a thick unidirectional carbon fibre reinforced polymer is investigated. This material is manufactured via compression moulding process. A Low-Velocity Impact (LVI) test is implemented on a quasi-isotropic laminate for the experimental evaluation of the energy absorption due to impact, while the internal failure mechanism is detected using Computerized Tomography (CT). Two different Finite Element (FE) models are applied to model the damage onset and propagation: firstly, a shell-based model and, secondly, a solid-based model using Cohesive Zone Method (CZM). In the CZM, the analytical modelling of the cohesive element properties is adopted, and the critical force evaluated experimentally is related to the energy release rate of mode II, and to the equivalent elastic properties of the laminate. The strength and weakness of the proposed approach in mimicking the impact behaviour and the actual failure mechanism, are discussed, and validated versus numerical simulation. The models are in good agreement with the experimental results; in fact, the relative error of the maximum force is about 4 per cent, and it occurs in the shell-based model
A high-performance full-configuration-interaction study of Wigner crystallization in quantum dots
No full textWe study the transition between liquid and solid electron phases of a two-dimensional quantum dot by performing extensive full-configuration- interaction calculations. From the analysis of pair correlation functions we find evidence of localization for values of the dimensionless density parameter λ ≈ 4. © 2007 American Institute of Physics
Double photo-ionization of he near a polarizable surfaces
No full textWe calculate the differential cross section of the direct double photoionization of He physisorbed on apolarizable surface. By including the influence of the surface potential in the correlated two-electron final-statewave function, we show that the differential cross section carries detailed information on the electroniccorrelations at the surface. In particular, photoemission along opposite directions, which is prohibited in thefree space, is allowed if the surface potential is long ranged
Optimization of semiconductor quantum devices by evolutionary search
No full textA novel simulation strategy is proposed for searching for semiconductor quantum devices that are optimized with respect to required performances. Based on evolutionary programming, a technique that implements the paradigm of genetic algorithms in more-complex data structures than strings of bits, the proposed algorithm is able to deal with quantum devices with preset nontrivial constraints (e.g., transition energies, geometric requirements). Therefore our approach allows for automatic design, thus avoiding costly by-hand optimizations. We demonstrate the advantages of the proposed algorithm through a relevant and nontrivial application, the optimization of a second-harmonic-generation device working in resonance conditions
Stability and dynamical properties of a double-layer Wigner crystal in two dimensions
No full textWe investigate the zero-temperature phase diagram and melting transition of a two-dimensional Wigner crystal (WC) of classical Coulombic particles in a double-layer structure. In contrast with the single-layer WC, we find that five different crystalline phases are stable in different ranges of inter-layer distance/particle density. Phase boundaries consist of both continuous and discontinuous transitions. From the phonon frequencies of the system we evaluate the melting temperature of the WC. We suggest the possibility of structural phase transitions as a function of temperature
The Gecko® Approach to Friction: A Novel Teaching Learning Sequence
No full textWe here propose a novel teaching–learning sequence on tribology, based on the experimental investigation of Gecko® Nanoplast®, a bio-inspired micro-structured synthetic material with peculiar tribological properties. Measurements of static and dynamic friction show that Gecko® does not obey to Leonardo-Amontons’ law, thus providing a way to introduce the key concept of real—as opposed to nominal—contact area. As in ‘real’ material-science research, investigation of the Gecko® macroscopic behavior is combined with its structural determination, based on both optical microscopy observations and on diffraction measurements. The sequence has been tested on a group of honors high-school students with encouraging results
Strong exciton binding in hybrid GaAs-based nanostructures
No full textWe propose a new type of hybrid systems formed by conventional semi-conductor nanostructures with the addition of remote insulating layers, where electron-hole interaction is enhanced by combining quantum and dielectric confinement over different length scales. Due to the polarization charges induced by dielectric mismatch at the semiconductor/insulator interfaces, the exciton binding energy can be strongly enhanced. By a novel theoretical scheme, we show that, for realistic structures based on conventional III-V quantum wires, such remote dielectric confinement allows exciton binding at room temperature
- …
