Spatially resolved characterization of InGaAs/GaAs quantum dot structures by scanning spreading resistance microscopy

Cross-sectional scanning spreading resistance microscopy (SSRM) is used to investigate stacked InGaAs/GaAs quantum dot(QD)structures with different doping schemes. Spatially resolved imaging of the QDs by SSRM is demonstrated. The SSRM contrast obtained for the QD layers is found to depend on doping in the structure. In the undoped structures both QD-layers and QDs within the layers could be resolved, while in the dopedstructures the QD layers appear more or less uniformly broadened. The origin of the SSRM contrast in the QD layer in the different samples is discussed and correlated with doping schemes.T. Hakkarainen, O. Douhéret, and S. Anand would like to acknowledge the Swedish Research Council VR for fi- nancial support and the Kurt-Alice Wallenberg KAW foundation for financing the microscope. L. Fu, H. H. Tan, and C. Jagadish would like to acknowledge the Australian Research Council ARC for financial support and Australian National Fabrication Facility ANFF for access to the facilities

Ferroelectric properties of (1 − x)Bi(Zn1/2Ti1/2)O3–xPbZrO3 ceramics

The (1 − x)Bi(Zn1/2Ti1/2)O3–xPbZrO3 solid solution ceramics were prepared by using solid-state reaction method, and their ferroelectric properties were investigated. It was found that the perovskite structure is stable for compositions with x ≥ 0.900. Within this composition range, the crystal structure of the solid solution preserves the orthorhombic symmetry of PbZrO3 (PZ). The Curie point of the ceramics was found to decrease with increasing Bi(Zn1/2Ti1/2)O3 (BZT) content. The intermediate ferroelectric phase of PZ was stabilized by BZT addition and exists within a much wider temperature range in the solid solution

The morphotropic phase boundary and electrical properties of (1 − x)Pb(Zn1/2W1/2)O3–xPb(Zr0.5Ti0.5)O3 ceramics

Ceramics in the solid solution of (1 − x)Pb(Zn1/2W1/2)O3–xPb(Zr0.5Ti0.5)O3 system, with x = 0.80, 0.85, 0.90, and 0.95, were synthesized with the solid-state reaction technique. The perovskite phase formation in the sintered ceramics was analyzed with X-ray diffraction. It shows that the rhombohedral and the tetragonal phases coexist in the ceramic with x = 0.90, indicating the morphotropic phase boundary (MPB) within this pseudo-binary system. Dielectric and ferroelectric properties measurements indicate that the transition temperature decreases while the remanent polarization increases with the addition of Pb(Zn1/2W1/2)O3. In the composition of x = 0.85 which is close to the MPB in the rhombohedral side, a high piezoelectric property with d 33 = 222 pC/N was observed

Push Tests on Innovative Shear Connector for Composite Beam with Cold-formed Steel Section

In this study, experimental tests were conducted to investigate the ductility and strength capacity of new shear connector. Push test specimens were prepared and tested according to EN1994-1-1 standard. The push test specimen consists of two cold-formed steel lipped channel sections oriented back-to-back to form an I-section beam, transverse metal deck and normal concrete slabs grade C25/30. Angle brackets were obtained from the same section of the beam and fastened to the web of steel beam to provide the shear connection. Two shear connectors were tested namely; “SC1” and “SC2” shear connectors. Both shear connectors showed a ductile behavior and had satisfied the ductility requirements of EN1994-1-1 standard. It was concluded that the ductile behavior of shear connectors could enhance the design of composite beam

Entangling two distant nanocavities via a waveguide

In this paper, we investigate the generation of continuous variable entanglement between two spatially-separate nanocavities mediated by a coupled resonator optical waveguide in photonic crystals. By solving the exact dynamics of the cavity system coupled to the waveguide, the entanglement and purity of the two-mode cavity state are discussed in detail for the initially separated squeezing inputs. It is found that the stable and pure entangled state of the two distant nanocavities can be achieved with the requirement of only a weak cavity-waveguide coupling when the cavities are resonant with the band center of the waveguide. The strong couplings between the cavities and the waveguide lead to the entanglement sudden death and sudden birth. When the frequencies of the cavities lie outside the band of the waveguide, the waveguide-induced cross frequency shift between the cavities can optimize the achievable entanglement. It is also shown that the entanglement can be easily manipulated through the changes of the cavity frequencies within the waveguide band.Comment: 8 pages, 8 figure

A novel algorithm for DC analysis of piecewise-linear circuits: popcorn

Cataloged from PDF version of article.A fast and convergent iteration method for piecewise-linear analysis of nonlinear resistive circuits is presented. Most of the existing algorithms are applicable only to a limited class of circuits. In general, they are either not convergent or too slow for large circuits. The new algorithm presented in the paper is much more efficient than the existing ones and can be applied to any piecewise-linear circuit. It is based on the piecewise-linear version of the Newton-Raphson algorithm. As opposed to the Newton-Raphson method, the new algorithm is globally convergent from an arbitrary starting point. It is simple to understand and it can be easily programmed. Some numerical examples are given in order to demonstrate the effectiveness of the proposed algorithm in terms of the amount of computation

Vitrification of an intermediate level Magnox sludge waste

A novel iron containing alkali alkaline earth borosilicate glass has been developed that can vitrify up to 30 wt% (dry weight) of a Magnox sludge waste in a homogeneous wasteform at a melting temperature of 1200C. Ce was used as a simulant of the actinide content in the waste. The waste was spiked with 0.5wt% of Cs2O of which 90% was retained in the glass. 60% of the Cl was also retained. Mg content limited the waste loading as loadings in excess of 30wt% led to the formation of forsterite and in some cases CeO2 and MgFe2O4 based spinels. PCT leach testing of the glasses for periods up to 180 days indicated the formation of an amorphous magnesium (alumino-)silicate hydrated layer on the glass surface together with barium rich crystalline precipitates. No Ce was detected in the leachate

Three fermions in a box at the unitary limit: universality in a lattice model

We consider three fermions with two spin components interacting on a lattice model with an infinite scattering length. Low lying eigenenergies in a cubic box with periodic boundary conditions, and for a zero total momentum, are calculated numerically for decreasing values of the lattice period. The results are compared to the predictions of the zero range Bethe-Peierls model in continuous space, where the interaction is replaced by contact conditions. The numerical computation, combined with analytical arguments, shows the absence of negative energy solution, and a rapid convergence of the lattice model towards the Bethe-Peierls model for a vanishing lattice period. This establishes for this system the universality of the zero interaction range limit.Comment: 6 page

Open questions in the study of population III star formation

The first stars were key drivers of early cosmic evolution. We review the main physical elements of the current consensus view, positing that the first stars were predominantly very massive. We continue with a discussion of important open questions that confront the standard model. Among them are uncertainties in the atomic and molecular physics of the hydrogen and helium gas, the multiplicity of stars that form in minihalos, and the possible existence of two separate modes of metal-free star formation.Comment: 15 pages, 2 figures. To appear in the conference proceedings for IAU Symposium 255: Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxie