Intersubband spin-orbit coupling and spin splitting in symmetric quantum wells

In semiconductors with inversion asymmetry, spin-orbit coupling gives rise to the well-known Dresselhaus and Rashba effects. If one considers quantum wells with two or more conduction subbands, an additional, intersubband-induced spin-orbit term appears whose strength is comparable to the Rashba coupling, and which remains finite for symmetric structures. We show that the conduction band spin splitting due to this intersubband spin-orbit coupling term is negligible for typical III-V quantum wells.     

Correlation of the thermal stability and the decomposition kinetics of six different vegetal fibers

The thermal degradation behavior of six different vegetal fibers was studied using thermogravimetry under nitrogen atmosphere at four different heating rates (5, 10, 20 and 40 °C min^?1). The degradation models Kissinger, Friedman and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy and the frequency factor of these fibers. Furthermore, the solid state degradation mechanisms were determined using Criado’s method. Additionally, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy were analyzed to corroborate the obtained results. The results indicated that the apparent calculated activation energies can be more closely related to the exponential dependence of the rate of heterogeneous reactions than to the, necessary “energy”, which is commonly used. The Criado’s master curves indicated two different degradation mechanisms for the fibers: diffusion followed by random nucleation. The results also indicated that the crystallinity index as calculated by X-ray diffraction and determinated by FTIR does not necessarily represent higher thermal stability as noted by the thermogravimetric analysis curves. The thermal behavior and the degradation mechanism did not show to be influenced by the lignocellulosic components of the fibers, exception for buriti and sisal. This behavior was attributed to higher extractive content.     

The effect of post-consumer PET particles on the performance of flexible polyurethane foams

In this work, the use of post-consumer PET (polyethylene terephthalate), PET_pc, as reinforcement filler in flexible polyurethane foams was studied, with the aim of finding alternatives for the recycling of polymer packaging. Density, number of cells per linear centimeter, tensile resistance, strain at break and tear resistance of standard foams were compared to those of foams with PET_pc in the formulation, using 1.5 parts per hundred of polyol of PET_pc (granulometric range 0–297 μm). The produced foams were sectioned into top, mid-top, mid-bottom and bottom layers. Tensile resistance, strain at break and tear resistance of the reinforced foam surpassed those of the standard foam for all layers. The number of cells was constant but density increased towards the base of the block. In addition, the filled foams yielded better wear, compression set and compression resistance than the standard foam, whereas no significant variation in morphology (cell shape) was found.     

Conformational heterogeneity of the point defects in silica: The lifetime of the phosphorescence band at 2.7 eV

We have measured the excitation and emission energy dependence of the lifetimes of the 2.7 eV photoluminescence band associated to oxygen deficient centers in silica glasses. The non-exponential behavior of this time decay is consistent with intrinsic conformational heterogeneity of these point defects in the amorphous matrix. Accordingly, we have analyzed the data in terms of a radiative rates distribution. Moreover, both surface and bulk typologies of these point defects have been studied. The mean value of the lifetime distribution of the surface defects increases from 12 to 15 ms varying the excitation energy from 4.6 to 5.2 eV, and it increases from 14 to 15 ms in the emission energy interval between 2.6 and 3.0 eV. As well similar variations of the lifetime are observed for interior defects, when measured at different excitation and emission energies. We can also estimate the width of the lifetime distribution of this ensemble of point defects in silica glass.     

Heuristic algorithms for the multi-depot ring-star problem

In this paper, we consider the problem of designing urban optical networks. In particular, given a set of telephone exchanges, we must design a collection of ring-stars, where each ring-star is a cycle composed of a telephone exchange, some customers, some transition points used to save routing costs and customers not on the cycle connected to the cycle by a single edge. The ring topology is chosen in many fiber optic communication networks since it allows to prevent the loss of connection due to a single edge or even a single node failure. The objective is to minimize the total cost of the optical network which is mainly due to the excavation costs. We call this problem Multi-Depot Ring-Star Problem (MDRSP) and we formulate it as an optimization problem in Graph Theory. We present lower bounds and heuristic algorithms for the MDRSP. Computational results on randomly generated instances and real-life datasets are also presented.     

Entanglement in Finite Quantum Systems Under Twisted Boundary Conditions

In a recent publication, we have discussed the effects of boundary conditions in finite quantum systems and their connection with symmetries. Focusing on the one-dimensional Hubbard Hamiltonian under twisted boundary conditions, we have shown that properties, such as the ground-state and gap energies, converge faster to the thermodynamical limit (\(L \rightarrow \infty \)) if a special torsion Θ^? is adjusted to ensure particle-hole symmetry. Complementary to the previous research, the present paper extends our analysis to a key quantity for understanding correlations in many-body systems: the entanglement. Specifically, we investigate the average single-site entanglement 〈S_j〉 as a function of the coupling U/t in Hubbard chains with up to L =?8 sites and further examine the dependence of the per-site ground-state ??₀ on the torsion Θ in different coupling regimes. We discuss the scaling of ??₀ and 〈S_j〉 under Θ^? and analyze their convergence to Bethe Ansatz solution of the infinite Hubbard Hamiltonian. Additionally, we describe the exact diagonalization procedure used in our numerical calculations and show analytical calculations for the case study of a trimer.     

Separation of variables for integrable spin–boson models

We formulate the functional Bethe ansatz for bosonic (infinite dimensional) representations of the Yang–Baxter algebra. The main deviation from the standard approach consists in a half infinite Sklyanin lattice made of the eigenvalues of the operator zeros of the Bethe annihilation operator. By a separation of variables, functional TQ-equations are obtained for this half infinite lattice. They provide valuable information about the spectrum of a given Hamiltonian model. We apply this procedure to integrable spin–boson models subject to both twisted and open boundary conditions. In the case of general twisted and certain open boundary conditions polynomial solutions to these TQ-equations are found and we compute the spectrum of both the full transfer matrix and its quasi-classical limit. For generic open boundaries we present a two-parameter family of Bethe equations, derived from TQ-equations that are compatible with polynomial solutions for Q. A connection of these parameters to the boundary fields is still missing.     

One-nucleon transfer reactions induced by 32S on 34S AT Einc = 90.0 and 97.09 MeV

The one-proton and one-neutron transfer reactions in the interaction of ³⁴S with incident ³²S were studied in the 0–3.5 MeV excitation energy range of the exit nuclei. The experimental set-up (kinematic identification technique, implanted targets, etc.) has allowed an angular resolution of 0.2°, a mass resolution of 1.5% and a Q-value resolution of 0.35 MeV.Comparison with DWBA computations using an analytical approximation for the radial integral, with insertion of suitable recoil corrections, demonstrates the absorptive direct mechanisms of the reactions, even when double excitation of residual nuclei is present. The extracted values for the products of spectroscopic factors are in very good agreement with the known values and they are confirmed by EFR-DWBA computations. The selectivities of the reaction receive about the same contributions from the nuclear structure as from the specific reaction mechanism.     

Diode laser slit-jet spectra and analysis of the ν14 fundamental of 1-chloro-1,1-difluoroethane (HCFC-142b)

High resolution infrared spectra (0.001 cm⁻¹ FWHM) have been measured for mixtures of 1-chloro-1,1-difluoroethane in Ne, expanded in a supersonic planar jet. The ν₁₄ fundamental has been analyzed for both isotopic species, and .