Competitiveness of Inexperienced and Experienced Contractors in Bidding

This paper tests the assertion that experienced contractors are more competitive than inexperienced contractors by measuring the effect of experience on bidding competitiveness for building contracts procured by a regular client. Contractors are grouped into experienced and inexperienced contractors, and two levels of contractors’ experience are identified: (1) bidding experience only and (2) bidding plus construction experience. Results of two-sample t tests show that experienced contractors are more competitive than inexperienced contractors. Contractors’ competitiveness in respect of school contracts and other contracts are further compared in evaluating the relationship between the project type and experience effect. Experienced contractors are, on average, more competitive in competing for school contracts. It emerges that the factor of project type familiarity amplifies the experience effect. A comparison of experienced contractors’ competitiveness in bidding for (1) new building works and (2) alteration and extension works shows that the effect of experience would be more significant when contract works packages are highly standardized.     

Static and Dynamic Spins in Superconducting La2−x Sr x CuO4: The Risø Years

One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La_2?xSr_xCuO₄, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx.     

Electronic Transport in Ultrathin Gold Films on Si(111)

The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 ? 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 ? 300 K. With decreasing film thickness, i.e. decreasing sheet conductance G_s, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by G_s ∝ exp[?(T ₀ /T) ⁿ] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction. PACS numbers: 68.37.-d, 68.55.-a, 73.50.-h, 73.25.+i, 81.15.-z     

高频微型脉冲管制冷机的实用化研究

脉冲管制冷机经过多年的发展，性能不断改善，目前已开始进入实用化阶段。高频微型脉冲管制冷机结构紧凑，应用方便，并且主要工作在需求量较大的液氮温区，因此将首先得到一定规模的应用。介绍了作者针对脉冲管制冷机在红外和超导方面的应用所作的实用化工作，讨论了尚待解决的问题。     

Phase and amplitude comparison between experiment and calculation of ultrabroad-band pulses generated in a taper fiber

Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered.     

A Family of Far‐Infrared‐Transmitting Glasses in the Ga–Ge–Te System for Space Applications

Conditions of formation of bulk tellurium chalcogenide glasses, containing 70–80 at % Te associated to Ga and Ge are described. The characteristic temperatures are measured: the glass‐transition temperature, T_g, is situated in the range 140–185 °C and the difference T_x – T_g, where T_x is the onset crystallization temperature, is in the range 76–113 °C. Moreover, the optical transmission window is exceptional, ranging from 1.99 μm in the bandgap up to 28 μm in the phonon region. Developed within the framework of requirements for the Darwin mission (a search for and study of extrasolar planets), feasibility of infrared optical fibers formed from these glasses is studied. Drawing experiments are conducted with the glass Ga₂‐Ge₃Te₁₅, which possesses the maximum T_x – T_g, and a first optical fiber is presented.     

Der PC in zehn Jahren und seine Auswirkungen auf die Gesellschaft

In this article it is argued that in ten years’ time personal computers as we know them now won’t exist anymore — all their functions will by then be integrated in mobiles which will be our steady companions. As such, mobiles will change our lives to an enormous extent. Technology as well as consequences will be discussed in this paper.     

Using magnetic coupling to eliminate right half-plane zeros in boost converters

A dynamic analysis of the boost converter with an output filter reveals that magnetic coupling between inductors allows transfer of the zeros to the left half-plane of the control-to-output transfer function. Similar results requiring smaller magnetic components are obtained by combining magnetic coupling with damping of the output filter. The analysis is based on the application of the Routh-Hurtwitz's criterion to the numerator of the transfer function in order to derive the design conditions for the converter parameters. A design example illustrates the procedure, and experimental results verify the theoretical predictions. The application of these techniques will allow the design of high efficiency voltage boost-based regulators with dynamic behavior similar to buck-derived structures.     

Ideally selective diisocyanate building blocks: New perspectives for dendrimers and coating binders

Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial ones like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanate-functional coating resins. Without any increase in polydispersity, a hydroxyl-functional polyester can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings.