Use of the method of particular solutions in nonlinear, two-point boundary-value problems. Part 1 - Uncontrolled systems

Nonlinear two-point boundary-value problem solution by combined techniques of quasilinearization and method of particular solution

Performance of a highly sensitive optical waveguide Mach-Zehnder interferometer immunosensor

We describe a highly sensitive sensor which uses the evanescent field of a reusable planar optical waveguide as the sensing element. The waveguide used is optimized to obtain a steep dependence of the propagation velocity on the refractive-index profile near the surface. The adsorption of a layer of proteins thus results in a phase change, which is measured interferometrically using a Mach-Zehnder interferometer set-up. The stability of the interferometer is such that phase changes = (1 × 10-2)2pi per hour can be measured. Immunoreactions have been monitored down to concentrations of 5 × 10-11 M of a 40 kDa protein

Transcoding of MPEG Bitstreams

This paper discusses the problem of transcoding as it may occur in, for instance, the following situation. Suppose a satellite transmits an MPEG-compressed video signal at say 9 Mbit/s. This signal must be relayed at a cable head end. However, since the cable capacity is only limited, the cable head end will want to relay this incoming signal at a lower bit-rate of, say, 5 Mbit/s. The problem is how to convert a compressed video signal of a given bit-rate into a compressed video signal of a lower bit-rate. The specific transcoding problem discussed in this paper is referred to as bit-rate conversion. Basically, a transcoder used for such a purpose will consist of a cascaded decoder and encoder. It is shown in the paper that the complexity of this combination can be significantly reduced. The paper also investigates the loss of picture quality that may be expected when a transcoder is in the transmission chain. The loss of quality as compared to that resulting in the case of transmission without a transcoder is studied by means of computations using simplified models of the transmission chains and by means of using computer simulations of the complete transmission chain. It will be shown that the presence of two quantizers, i.e. cascaded quantization, in the transmission chain is the main cause of extra losses, and it will be shown that the losses in terms of SNR will be some 0.5 ¿ 1.0 dB greater than in the case of a transmission chain without a transcoder

Generalization and performance improvement of a coherence multiplexing system

Usually a coherence multiplexing system uses delay-filters at the transmitter and receiver to perform the code. An extension to other filter types is described. Using a continuous source the signal-to-beat noise ratio is proportional to the square of the inverse of the number of simultaneous users. A further extension is made by using a pulsed source and by replacing the filters by banks of filters. Each element of each filter bank also comprizes a unique delay. In that case the SNR can be made proportional to the inverse of the number of users, so that more users can be handled simultaneously

Use of the method of particular solutions in nonlinear, two-point boundary-value problems. Part 2 - Controlled systems

Method of particular solutions used to solve two point boundary value problem for nonlinear controlled syste

Municipal Local Economic Development and the Multiplier effect: Piloting a Community Enterprise Identification Method in South Africa and Namibia

Local Economic Development (LED) is a contested concept in southern Africa, and has become synonymous with delivery of generic job-creation projects, often grant-dependent and unsustainable. Municipal LED has followed this pattern in South Africa since 1994, with little lasting success. Each local economy is unique, and has its own problems and opportunities. The ’Plugging the Leaks’ method recognizes that communities themselves know best how money enters and exits their area. By asking people to analyse their local economy as a 'leaky bucket', the method puts control back in the hands of local people, rather than external experts, and allows them to analyse their own local economy to identify gaps and opportunities for enterprise. By better networking and working collectively to improve their local economy, local communities are able to re-circulate cash internally. This circulation of cash is explained as the local multiplier effect in the workshops. A pilot process of running ‘Plugging the Leaks’ workshops in low income communities in South Africa and Namibia revealed that spending choices in these communities are severely limited in a context where there is no effective welfare state. Therefore, empowerment with this method came from the discovery of collective action and networking, rather than from individual spending choices. Local start-up business tends to be limited to survivalist and copy-cat one-person ventures, and are a last resort when formal employment is absent. In this context collective enterprise offers the necessary empowerment for people to attempt financially sustainable ventures that respond to a gap in the local economy. The pilot project is attempting to show that municipal LED staff can play the role of facilitator for initiating the enterprise-identification process and further mobilise state enterprise support agencies around the locus of LED, without crossing the line between facilitation and implementation of ’projects’

Development of an optical waveguide interferometric immunosensor

A Mach-Zehnder interferometer is presented, which uses the evanescent field of a planar optical waveguide as the sensing element. Changes in the refractive index profile occurring in the immediate vicinity of the waveguide surface cause the propagation velocity of the light passing through it to change. This is measured interferometrically. Adsorption processes of antibodies onto the waveguide surface as well as immunoreactions have been monitored. Concentrations of 2.5 × 10¿8 M (1 × 10-3 mg/ml) of the antigen HCG (molecular weight = 39 600) have been measured so far

Low loss, high contrast optical waveguides based on CMOS compatible LPCVD processing: technology and experimental results

A new class of integrated optical waveguide structures is presented, based on low cost CMOS compatible LPCVD processing. This technology allows for medium and high index contrast waveguides with very low channel attenuation. The geometry is basically formed by a rectangular cross-section silicon nitride (Si3N4) filled with and encapsulated by silicon dioxide (SiO2). The birefringence and minimal bend radius of the waveguide is completely controlled by the geometry of the waveguide layer structures. Experiments on typical geometries will be presented, showing excellent characteristics (channel attenuation ≤ 0.1 dB/cm, IL ≤ 1.5 dB, PDL ≤ 0.2 dB, Bg ≤ 1×10-4, bend radius « 1 mm)

Ring resonator-based Tunable Optical Delay Line in LPCVD Waveguide Technology

Optical circuits providing a time delay to signals modulated on optical carriers are considered important for optical communication systems and phased array antennas. A continuously tunable optical delay line is demonstrated in low-cost CMOS compatible LPCVD planar waveguide technology. The device consists of three cascaded ringresonator all-pass filters with fixed circumference of 2 cm (delay of 0.12 ns and FSR of 8.4 GHz). The measured group delay ranges from 0 ns up to 1.2 ns with a bandwidth of 500 MHz and delay ripple smaller than 1 ps, which is in accordance with the calculations