Schottky diodes for analogue phase shifters in GaAs MMICs

A simple Schottky diode structure, which is easily implemented in a foundry gallium arsenide (GaAs) process, is described. This structure occupies very much less area than the usual technique of realising Schottky diodes, using standard FET structures. Two variations of the diode have been characterized and modeled using a standard equivalent circuit. This has been used to design a simple analogue phase shifter based on a loaded-line configuration. The phase shifter was manufactured using a standard foundry process and has shown excellent results in terms of phase shift linearity with tuning voltage, combined with low insertion loss, over the range 2-8 GHz     

Filters: QoS support mechanisms for multipeer communications

The nature of distributed multimedia applications is such that they require multipeer communication support mechanisms. The multimedia traffic needs to be delivered to end-systems, networks, and end-users in a form that they can handle while satisfying the constraints imposed by the multimedia application. Quality-of-service (QoS) mechanisms that can ensure full quality media playout at high-performance workstations, while at the same time providing appropriately filtered lower quality media for playout at other end-systems, are required. Existing multicast support mechanisms are deficient for this purpose, in a heterogeneous environment, because they work on a common denominator premise where the quality delivered depends on the least capable link or node involved in the multicast session. This paper begins by discussing video compression; it proposes and analyzes the use of filtering mechanisms as means of supporting disparate receiver capabilities and QoS requirements. The paper describes the implementation of a number of filtering mechanisms and highlights the communications architecture within which these mechanisms are built. This architecture constitutes a specific network topology and a new protocol family developed within a UNIX-like operating system     

Quadrupole moment measurement of the highly deformed πg 9/2⊗νh 11/2 band in 130Pr

The quadrupole moment for the πg _9/2⊗νh _11/2 band in the ^130>Pr nucleus has been measured using the Doppler-shift attenuation method. A centroid shift analysis was carried out and a value of Q₀=6.1±0.4 eb, corresponding to an axial prolate deformation of β₂=0.35(3), has been determined. This is the first direct experimental confirmation of the deformation-driving character of the πg _9/2 orbital in an odd-odd nucleus in the A≃135 superdeformed region. Received: 23 April 1998     

A power-scaling strategy for longitudinally diode-pumped Tm:YLF lasers

We describe a power-scaling strategy for longitudinally diode-pumped Tm:YLF lasers based on optimisation of the thulium doping level and the gain geometry. Carefully designed laser experiments at lower powers are shown to allow a simple means for accurately predicting the thermal loading and hence the power-scaling properties of this system, including the effects of ground-state depletion, cross relaxation and energy-transfer upconversion. An optimised doping level of 2 at. % and a slab geometry are shown experimentally to allow scaling of a single gain unit to output powers of ∼70 W, limited by the available pump power, and a strategy for scaling well beyond 100-W output is discussed. PACS 42.55.-f; 42.55.Xi; 42.60.By     

Single-mode direct-ultraviolet-written channel waveguide laser in neodymium-doped silica on silicon

A waveguide laser with a neodymium-doped silica core is fabricated on a silicon substrate by a combination of flame hydrolysis deposition, solution doping, and direct UV writing. The neodymium-ion concentration is estimated to be approximately 8000 parts in 10(5). The propagation loss around 1.05 microns is < 0.8 dB/cm. Lasing in the range 1048-1056 nm and 1356 +/- 1 nm is observed. A slope efficiency of 33% for a high-reflectivity output coupler and a threshold of 4 mW of absorbed power for a 25% output coupler are measured for the 4F3/2-->4I11/2 transition.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Ion-exchanged tapered-waveguide laser in neodymium-doped BK7 glass

We report what is to our knowledge the first operation of a planar dielectric tapered-waveguide laser. The waveguide laser is fabricated by potassium-ion exchange in Nd(3+) -doped BK7 glass and consists of a single-mode channel waveguide of a few micrometers' width followed by a linear taper up to a broad region with a width of ~180microm . A slope efficiency of 42% is found both in the tapers and in standard channel waveguides fabricated upon the same substrate, indicating that the tapers and the channels have similar internal losses; hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be nearly diffraction limited.     

Education for the engineering mission

Engineering involves such a wide range of human endeavor that it demands diversity and innovation in the preparation of its practitioners. Engineering effort can be divided into three major categories: engineering technology, engineering practice, and engineering science. The qualifications of individuals whose activities would fall into each of these mutually interdependent categories are examined, as are the problems involved in training these individuals.