Combined High Power and High Frequency Operation of InGaAsP/InP Lasers at 1.3μm

A simultaneous operation of a semiconductor laser at high power and high speed was demonstrated in a buried crescent laser on a P-InP substrate. In a cavity length of 300μm, a maximum CW power of 130mW at room temperature was obtained in a junction-up mounting configuration. A 3dB bandwidth in excess of 12GHz at an output power of 52mW was observed

AlGaAs lasers with micro-cleaved mirrors suitable for monolithic integration

A technique has been developed for cleaving the mirrors of AlGaAs lasers without cleaving the substrate. Micro-cleaving involves cleaving a suspended heterostructure cantilever by ultrasonic vibrations. Lasers with microcleaved mirrors have threshold currents and quantum efficiencies identical to those of similar devices with conventionally cleaved mirrors

Damping of bulk excitations over an elongated BEC - the role of radial modes

We report the measurement of Beliaev damping of bulk excitations in cigar shaped Bose Einstein condensates of atomic vapor. By using post selection, excitation line shapes of the total population are compared with those of the undamped excitations. We find that the damping depends on the initial excitation energy of the decaying quasi particle, as well as on the excitation momentum. We model the condensate as an infinite cylinder and calculate the damping rates of the different radial modes. The derived damping rates are in good agreement with the experimentally measured ones. The damping rates strongly depend on the destructive interference between pathways for damping, due to the quantum many-body nature of both excitation and damping products.Comment: 5 pages, 4 figure

Spontaneous Symmetry Breaking through Mixing

We discuss a model, in which the negative mass square needed in the Higgs mechanism is generated by mixing with a heavy scalar. We have two scalar doublets in the standard model. Phenomenological properties of the heavy new scalar are discussed. The heavy scalar can be detected by the LHC.Comment: 4 page

A monolithically integrated optical repeater

A monolithically integrated optical repeater has been fabricated on a single-crystal semi-insulating GaAs substrate. The repeater consists of an optical detector, an electronic amplifier, and a double heterostructure crowding effect laser. The repeater makes use of three metal semiconductor field effect transistors, one of which is used as the optical detector. With light from an external GaAlAs laser incident on the detector, an overall optical power gain of 10 dB from both laser facets was obtained

Ultralow threshold graded-index separate-confinement heterostructure single quantum well (Al,Ga)As lasers

Broad area graded‐index separate‐confinement heterostructure single quantum well lasers grown by molecular‐beam epitaxy (MBE) with threshold current density as low as 93 A/cm^2 (520 μm long) have been fabricated. Buried lasers formed from similarly structured MBE material with liquid phase epitaxy regrowth had threshold currents at submilliampere levels when high reflectivity coatings were applied to the end facets. A cw threshold current of 0.55 mA was obtained for a laser with facet reflectivities of ∼80%, a cavity length of 120 μm, and an active region stripe width of 1 μm. These devices driven directly with logic level signals have switch‐on delays <50 ps without any current prebias. Such lasers permit fully on–off switching while at the same time obviating the need for bias monitoring and feedback control

Efficient design and evaluation of countermeasures against fault attacks using formal verification

This paper presents a formal verification framework and tool that evaluates the robustness of software countermeasures against fault-injection attacks. By modeling reference assembly code and its protected variant as automata, the framework can generate a set of equations for an SMT solver, the solutions of which represent possible attack paths. Using the tool we developed, we evaluated the robustness of state-of-the-art countermeasures against fault injection attacks. Based on insights gathered from this evaluation, we analyze any remaining weaknesses and propose applications of these countermeasures that are more robust

Microstructural Characterization of Precipitation Process in a Nickel-Alloy by Non-linear Ultrasonic

The nonlinear ultrasonic technique, using the amplitude ratio of higher harmonic frequencies and fundamental frequency, has been found to be strongly sensitive to the microstructure of bulk materials. It was reported earlier that in Al 2024 alloy the nonlinearity parameter increased with the generation of coherency precipitates. Similarly, Hurley et al reported that the nonlinear parameter linearly increases as a function of inhomogeneous strain due to the generation of a precipitate in low alloy steel. In contrast to these studies, in which researchers have studied ultrasonic nonlinearity in the context of single crystals and simple metals, we would like to study structural materials for the purpose of structural health monitoring. In order to characterize the material properties in facilities and during operation, one needs to understand the relation between the material degradation of structural materials and the features of the NDE parameters. Therefore, in the present study we attempted to assess the thermal degradation in one such structural material namely: Nimonic-263, nickel based precipitation hardenable alloy using the nonlinear technique. From the present study it was found that the response of the non-linear ultrasonic parameter b is faster and larger compared to the normal velocity measurements

Role of Chloride on the Fracture Behaviour of Micro‐alloyed Steel in E20 Simulated Fuel Ethanol Environment

The need to fully comprehend the potential of pipelines in fuel ethanol applications has necessitated this study. The influence of chloride in E20 on fracture toughness and tearing resistance of micro‐alloyed steel (MAS) was studied with three‐point bend specimens. Monotonic J‐integral tests were conducted with and without chloride. Results show a decrease in fracture toughness of MAS in the presence of chloride, and a concurrent increase in its ductile tearing resistance. Fractographic examinations showed that chloride in E20 promoted quasi‐cleavage fracture

Numerical modelling of dissipation energy of high tensile steel frames against cyclic earthquake excitations

The design of steel structures for ductile response requires (a) materialductility, (b) cross section and member ductility, and (c) structural ductility. Dissipating the earthquake input energy by means of plastic excursions has to be compatible with the plastic deformation capacity of the structure. This work concerns incremental approach of modeling for elastoplastic analysis of structural members subjected to harmonically varying severe earthquake loads and their parametric responses over a range of applied frequencies and amplitudes. Investigations have been carried out in respect of stable and reliable hysteretic energy dissipation mechanisms of high rise steel structures against typical time-history loading of four hypothetical frequencies. Eigen-buckling responses for high rise steel structures subjected to earthquake forces are derived using general purpose software (STAAD). Finally critical structural component is identified for the high rise steel structure for estimation of available in-elastic dissipation energy from material ductility against earthquake excitations. The novelty allows for a very useful generalized formulation for the basic analysis procedures adopted in non-linear material problems. All essential features of a non-linear finite element solution are described in relation to one dimensional model for elasto-plastic beam bending. Solutions techniques are programmed in FORTRAN 90 for Newton-Raphson iteration for non-linear finite element analysis to derive hysteretic energy dissipation of high rise steel structures