Construction and measurement of the pre-series twin aperture resistive quadrupole magnet for the LHC beam cleaning insertions

CERN's Large Hadron Collider (LHC) requires 48 twin aperture resistive quadrupoles in the beam cleaning insertions. Canada is contributing these magnets to CERN in the framework of the TRIUMF-LHC collaboration contracts. A pre-series magnet was produced by Canadian industry and delivered in March 2001. This magnet incorporates important design changes that resulted from experience with a prototype magnet. The construction of this pre-series magnet and the measurements made at ALSTOM and at CERN are reported. A comparison is made between high precision pole distance measurements and the magnetic measurements performed with a rotating coil mole. Conclusions for series production and possibilities for multipole corrections are outlined.     

Modelling of electrostatic gate operations in the Kane solid state quantum computer

The nuclear spin quantum computer proposed by Kane [Nature 393 (1998) 133] exploits as a qubit array ³¹P dopants embedded within a silicon matrix. Single-qubit operations are controlled by the application of electrostatic potentials via a set of metallic ‘A’ gates, situated above the donors, on the silicon surface, that tune the resonance frequency of individual nuclear spins, and a globally applied RF magnetic field that flips spins at resonance. Coupling between qubits is controlled by the application of potentials via a set of ‘J’ gates, between the donors, that induce an electron-mediated coupling between nuclear spins. We report the results of the study of the electric field and potential profiles arising within the Kane device from typical gate operations. The extent to which a single nuclear spin can be tuned independently of its neighbours, by operation of an associated A-gate, is examined and key design parameters in the Kane architecture are addressed. Implications for current fabrication strategies involving the implantation of ³¹P atoms are discussed. Solution of the Poisson equation has been carried out by simulation using a TCAD modelling package (Integrated Systems Engineering AG).     

Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings

Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80/spl deg/C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5/spl deg/C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in/sup 2/) of axial compression on the fiber at -40/spl deg/C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75/spl deg/C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in/sup 2/) was observed at the lowest temperature.     

Optimized carry lookahead adders with direct feeding

This paper describes improvements to the parallel prefix adder designs and optimization algorithms of Chan, Oklobdzija, Schlag, Thomborson and Wei. Our “direct feeding” (DF) adder design avoids large signal fanouts along critical adder paths. Our “random pruning” heuristic limits the time and space required to find near-optimal DF adders, so that the search process runs in a few minutes on a Sun-4 workstation. Our improved carry lookahead adders are well suited for static CMOS implementation; our improvements may be applied to other parallel prefix CMOS circuits. Simulations with Mentor Graphics' Lsim indicate that our best DIP adders are 12% to 20% faster than the carry lookahead adders presented by Chan et al.     

Low standby power state storage for sub-130-nm technologies

Handheld and other battery-powered ICs require process scaling to increase functional integration and reduce active power consumption. Scaling also increases leakage current components to the point where standby power is frequently a limiting design factor. A scheme combining low-leakage thick-gate shadow latches and high-performance transistors is presented that decouples performance from standby power in sub-130-nm technologies. Circuit design and operation, including pulse-clocked latches, use of dynamic circuits, and inclusion of scan is presented. The approach is validated by experimental results on a 90-nm process.     

Tussle in cyberspace: defining tomorrow's Internet

The architecture of the Internet is based on a number of principles, including the self-describing datagram packet, the end-to-end arguments, diversity in technology and global addressing. As the Internet has moved from a research curiosity to a recognized component of mainstream society, new requirements have emerged that suggest new design principles, and perhaps suggest that we revisit some old ones. This paper explores one important reality that surrounds the Internet today: different stakeholders that are part of the Internet milieu have interests that may be adverse to each other, and these parties each vie to favor their particular interests. We call this process "the tussle". Our position is that accommodating this tussle is crucial to the evolution of the network's technical architecture. We discuss some examples of tussle, and offer some technical design principles that take it into account.     

Chemical natures and distributions of metal impurities in multicrystalline silicon materials

We present a comprehensive summary of our observations of metal‐rich particles in multicrystalline silicon (mc‐Si) solar cell materials from multiple vendors, including directionally‐solidified ingot‐grown, sheet, and ribbon, as well as multicrystalline float zone materials contaminated during growth. In each material, the elemental nature, chemical states, and distributions of metal‐rich particles are assessed by synchrotron‐based analytical x‐ray microprobe techniques. Certain universal physical principles appear to govern the behavior of metals in nearly all materials: (a) Two types of metal‐rich particles can be observed (metal silicide nanoprecipitates and metal‐rich inclusions up to tens of microns in size, frequently oxidized), (b) spatial distributions of individual elements strongly depend on their solubility and diffusivity, and (c) strong interactions exist between metals and certain types of structural defects. Differences in the distribution and elemental nature of metal contamination between different mc‐Si materials can largely be explained by variations in crystal growth parameters, structural defect types, and contamination sources. Copyright © 2006 John Wiley & Sons, Ltd.     

Ultra-wideband hybrid-mode feeds

A modified dielectric cone-loaded horn is described that maintains excellent return loss and pattern symmetry over a bandwidth ratio greater than 30:1. The mechanisms responsible for the extremely broadband operation and its application as a feed horn for a reflector antenna are discussed     

Bayesian Multi-Object Filtering With Amplitude Feature Likelihood for Unknown Object SNR

In many tracking scenarios, the amplitude of target returns are stronger than those coming from false alarms. This information can be used to improve the multiple-target state estimation by obtaining more accurate target and false-alarm likelihoods. Target amplitude feature is well known to improve data association in conventional tracking filters, such as probabilistic data association and multiple hypothesis tracking, and results in better tracking performance of low signal-to-noise ratio (SNR) targets. The advantage of using the target amplitude approach is that targets can be identified earlier through the enhanced discrimination between target and false alarms. One of the limitations of this approach is that it is usually assumed that the SNR of the target is known. We show that the reliable estimation of the SNR requires a significant number of measurements, and so we propose an alternative approach for situations where the SNR is unknown. We illustrate this approach in the context of multiple targets for different SNRs in the framework of finite set statistics (FISST). Furthermore, we illustrate how this can be incorporated into approximate multiple-object filters derived from FISST, including probability hypothesis density (PHD) and cardinalized PHD (CPHD) filters. We present simulation results for Gaussian mixture implementations of the filters that demonstrate a significant improvement in performance over just using location measurements.