Variational Calculations for 3^3He Impurities on 4^4He Droplets

Variational Monte Carlo method is used to calculate ground state properties of $^4$He droplets, containing 70, 112, 168, 240, 330, and 728 particles. The resulting particle and kinetic energy densities are used as an input in the Feynman-Lekner theory for $^3$He impurities. The kinetic energy density of $^4$He atoms and the energy of the $^3$He surface states are compared with the results of previous phenomenological calculations.Comment: 12 pages, in revtex 3.0, with 5 .ps figure

Density functional calculations for 4He droplets

A novel density functional, which accounts correctly for the equation of state, the static response function and the phonon-roton dispersion in bulk liquid helium, is used to predict static and dynamic properties of helium droplets. The static density profile is found to exhibit significant oscillations, which are accompanied by deviations of the evaporation energy from a liquid drop behaviour in the case of small droplets. The connection between such oscillations and the structure of the static response function in the liquid is explicitly discussed. The energy and the wave function of excited states are then calculated in the framework of time dependent density functional theory. The new functional, which contains backflow-like effects, is expected to yield quantitatively correct predictions for the excitation spectrum also in the roton wave-length range.Comment: 15 pages, REVTEX, 10 figures available upon request or at http://anubis.science.unitn.it/~dalfovo/papers/papers.htm

Structural and dynamical properties of superfluid helium: a density functional approach

We present a novel density functional for liquid 4He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superfluid helium in various geometries. The equilibrium properties of the free surface, droplets and films at zero temperature are calculated. Our predictions agree closely to the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity dependent interaction, which accounts for backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]

Evolution of the electronic structure with size in II-VI semiconductor nanocrystals

In order to provide a quantitatively accurate description of the band gap variation with sizes in various II-VI semiconductor nanocrystals, we make use of the recently reported tight-binding parametrization of the corresponding bulk systems. Using the same tight-binding scheme and parameters, we calculate the electronic structure of II-VI nanocrystals in real space with sizes ranging between 5 and 80 {\AA} in diameter. A comparison with available experimental results from the literature shows an excellent agreement over the entire range of sizes.Comment: 17 pages, 4 figures, accepted in Phys. Rev.

Stress-strain behaviour of unconfined and confined hybrid glass/steel fibre self-compacting concrete

An experimental study was conducted to investigate the effectiveness of transverse reinforcing bars of self-compacting concrete mix (PSCC) and hybrid glass fiber reinforced self-compacting concrete mix (HFRSCC) grade M 40 under monotonically increasing axial compression. was performed for cylinders enclosed in . The behavior of SCC cylinders surrounded by a circular ring and having different volume ratios and clearances was compared under axial compression. In this work, we present a mathematical model developed to predict the stress-strain behavior of SCC and FRSCC under constrained and unconstrained conditions and validate the model using experimental results. To develop SCC, Nan Su blending method based on filling rate 1.12 and 1.14, S/A ratio 0.50 and 0.57 is applied. The steel and glass fiber usage in the hybrid fiber reinforced SCC mixture is assumed to be 1% and 0.05% of the concrete volume respectively. M 40 grade plain self-compacting concrete mixes (PSCC) and hybrid glass/steel fiber reinforced self-compacting concrete mixes (HFRSCC) constrained to different volume ratios, stresses, strains, elastic moduli, plasticity ratios, ductility ratios, and unlimited strength ratios ) has been evaluated experimentally. The following conclusions can be drawn from the stress-strain diagram: 1) Maximum load-bearing capacity and strain at peak stress are higher for his HFRSCC than for PSCC. 2) The presence of steel and fiberglass increases the strength bearing capacity and allows it to withstand greater loads at peak loads. 3) If the containment is in the form of a lateral ring boundary, the effect of fibers is almost negligible. This clearly shows that HFRSCC has a stronger containment effect compared to his PSCC. The strength confinement factor is lower for HFRSCC, suggesting that HFRSCC offers a superior confinement factor compared with his PSCC

Shell structure in mixed 3He-4He droplets

Due to the immiscibility of 3He into 4He at very low temperatures, mixed helium droplets consist of a core of 4He atoms coated by a 3He layer whose thickness depends on the number of atoms of each isotope. When these numbers are such that the centrifugal kinetic energy of the 3He atoms is small and can be considered as a perturbation to the mean-field energy, a novel shell structure arises, with magic numbers different from these of pure 3He droplets. If the outermost shell is not completely filled, the valence atoms align their spins up to the maximum value allowed by the Pauli principle