Quadrature Compensation in Wide-Band Double Balanced Modulators

It is shown that double balanced microwave mixers, operating over a wide band of frequencies at the RF input ports, have spurious outputs due to lack of quadrature in the RF hybrid section, which can be minimized by introducing phase compensation into the modulation ports.     

A method for very low fluence implantations using Rutherford scattering

A simple method for extremely low fluence ion implantation is described. It is based on implanting ions which are Rutherford backscattered (RBS) from a thin gold layer into the desired target. This method enables ion implantations to be carried out, as are needed to realize quantum centers on the atomic scale to serve as qubits and other nano sized devices. The required implantation fluences are orders of magnitude below the commonly-used current integration capabilities; hence control on the implanted fluence is usually complicated. The described method enables control on the implanted fluence even when extremely low. The dependence of the energy and fluence of scattered ions on the angle and scattering target thickness is analyzed by using SRIM simulations. These are verified for the case of N scattering implantation by direct counting in a surface barrier detector and for the case of Xe by counting the tracks that scattered and implanted Xe ions leaved in HOPG as viewed by scanning probe microscopy.     

Electron field emission from the 2D hole gas in hydrogen terminated,polycrystalline diamond

The results of field emission measurements from hydrogen and non-hydrogen terminated polycrystalline, B-doped and undoped diamond surfaces are reported. The field emission from the undoped polycrystalline diamond show different current density vs. electric field characteristics than field emission from hydrogen terminated polycrystalline B-doped diamond and from hydrogen terminated single crystal undoped diamond. These differences are attributed to differences in the conduction mechanisms, being bulk conductivity in B-doped diamond and surface conductivity in undoped hydrogen terminated single crystalline and polycrystalline diamond. In contrast to the hydrogen terminated single crystal undoped diamond case, where discrete jumps in the current density vs. electric field curves are observed [L. Gan, E. Baskin, C. Saguy and R. Kalish, Phys. Rev. Lett. 96, 196808 (2006).] the results for the undoped polycrystalline case follow the Fowler Nordheim formalism, reflecting the presence of an ensemble of 2D surface energy states due to the various angles between the crystallite surfaces and the electric field. The parameters extracted from the Fowler Nordheim representation of the data for hydrogen terminated B-doped and undoped polycrystalline diamond, yield a Fermi energy level near the surface region for of 0.34 eV below the valance band maximum for the undoped sample.     

Decision boundaries in one-dimensional categorization.

Decision-boundary theories of categorization are often difficult to distinguish from exemplar based theories of categorization. The authors developed a version of the decision-boundary theory, called the single-cutoff model, that can be distinguished from the exemplar theory. The authors present 2 experiments that test this decision-boundary model. The results of both experiments point strongly to the absence of single cutoffs in most participants, and no participant displayed use of the optimal boundary. The range of nonoptimal solutions shown by individual participants was accounted for by an exemplar-based adaptive-learning model. When combined with the results of previous research, this suggests that a comprehensive model of categorization must involve both rules and exemplars, and possibly other representations as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bainitic structures and thermomechanical treatments applied to steel

An investigation of the response of H11 steel to thermomechanical treatment involving transformation to bainites continues the search for methods to improve the mechanical properties of low-alloy steels.     

Thermal embrittlement of 18 Ni(350) maraging steel

The embrittlement of as-solutionized 18 Ni(350) Maraging steel was monitored as a function of heat treatment variables by means of Charpy impact tests. The processing parameters of interest were annealing temperatures in the range of 1900° to 2400°F, intermediate holding temperatures in the range of 1300° to 1800°F, and the quenching rate. The changes in fracture mode with heat treatment were characterized by replica and scanning electron microscopy. The severity of thermal embrittlement increases with decreasing cooling rate from the annealing treatment upon direct quenching to room temperature. Intermediate isothermal holding, particularly at 1500° to 1600°F, further accentuates the embrittlement. A large grain size is beneficial to the toughness when rapid direct quenches from the annealing range are imposed but is detrimental upon air cooling or intermediate holding. The major loss in toughness may be associated with the diffusion of interstitial impurity atoms (C+N) to the austenite grain boundaries during cooling or intermediate isothermal holding below 2000°F. An advanced stage of the embrittlement is characterized by the discrete precipitation of Ti(C,N) platelets on these boundaries. Thermal embrittlement is accompanied by change in fracture mode from transgranular dimpled rupture to intergranular quasi-cleavage.     

Design and fabrication of dispersion-shifted depressed-clad triangular-profile (DDT) single-mode fibre

A new depressed-clad triangular-index-profile single-mode fibre with dispersion minimum shifted to the 1.55 ?m region is investigated. Fibres with high cutoff wavelength (?1.1 ?m) and low dispersion slope (?0.052 ps/km nm2) at their minimum dispersion wavelength (?1.55 ?m) were fabricated. Results from 226.7 km of fibre show an average loss of 0.241 dB/km at 1.55 ?m and 0.232 dB/km at the loss minimum.