Novel synchronous DPSK optical regenerator based on a feed-forward based carrier extraction scheme

We experimentally demonstrate a novel synchronous 10.66Gbit/s DPSK OEO regenerator which uses a feed-forward carrier extraction scheme with an injection-locked laser to synchronize the regenerated signal wavelength to the incoming signal wavelength. After injection-locking, a low-cost DFB laser used at the regenerator exhibited the same linewidth characteristics as the narrow line-width transmitter laser. The phase regeneration properties of the regenerator were evaluated by emulating random Gaussian phase noise applied to the DPSK signal before the regenerator using a phase modulator driven by an arbitrary waveform generator. The overall performance was evaluated in terms of electrical eye-diagrams, BER measurements, and constellation diagrams.

Full-field feed-forward equalizer with adaptive system optimization

We numerically investigate the combination of full-field detection and feed-forward equalizer (FFE) for adaptive chromatic dispersion compensation up to 2160 km in a 10 Gbit/s on-off keyed optical transmission system. The technique, with respect to earlier reports, incorporates several important implementation modules, including the algorithm for adaptive equalization of the gain imbalance between the two receiver chains, compensation of phase misalignment of the asymmetric Mach-Zehnder interferometer, and simplified implementation of field calculation. We also show that in addition to enabling fast adaptation and simplification of field calculation, full-field FFE exhibits enhanced tolerance to the sampling phase misalignment and reduced sampling rate when compared to the full-field implementation using a dispersive transmission line.

The scope to improve the efficiency of solar-powered reverse osmosis

The aim of this paper is to identify and evaluate potential areas of technical improvement to solar-powered desalination systems that use reverse osmosis (RO). We compare ideal with real specific energy consumption (SEC) to pinpoint the causes of inefficiency. The ideal SEC is compared among different configurations including a batch system driven by a piston, and continuous systems with single or multiple stages with or without energy recovery in each case. For example, to desalinate 1 m3 of freshwater from normal seawater (osmotic pressure 27 bar) will require at least 0.94 kWh of solar energy; thus in a sunny coastal location, up to 1850 m3 of water per year per m2 (m3/m2) of land covered by solar collectors could theoretically be desalinated. For brackish water (osmotic pressure 3 bar), 11570 m3/m2 of fresh water could theoretically be obtained under the same conditions. These ideal values are compared with practically achieved values reported in the literature. The practical energy consumption is found to be typically 40-200 times higher depending on feed water composition, system configuration and energy recovery. For state-of-the-art systems, energy losses at the various steps in the conversion process are quantified and presented with the help of Sankey diagrams. Improvements that could reduce the losses are discussed. Consequently, recommendations for areas of R&D are highlighted with particular reference to emerging technologies. It is concluded that there is considerable scope to improve the efficiency of solar-powered RO system.

Molecular dynamics study of solvent transport in nanoscale osmosis

An ideal of osmotic equilibrium between an ideal solution and pure solvent separated by a semi-permeable membrane is studied numerically using the method of molecular dynamics. The osmotic flow is observed as the inflow of the solvent across the membrane from the dilute to the concentrated side. The validity of van't Hoff's law for osmotic pressure is confirmed over a wide range of concentrations. It is found that the law is established by a balance between non-uniform partial pressures of solute and solvent. Furthermore, the present model permits an understanding of the mechanism of the osmotic flow in the relaxation process as the liquids evolve from the initial state to the equilibrium state. We focus in particular on the interaction between solute and solvent. ©2008 The Physical Society of Japan.

A learning feed-forward current controller for linear reciprocating vapor compressors

Direct-drive linear reciprocating compressors offer numerous advantages over conventional counterparts which are usually driven by a rotary induction motor via a crank shaft. However, to ensure efficient and reliable operation under all conditions, it is essential that motor current of a linear compressor follows a sinusoidal current command with a frequency which matches the system resonant frequency. The design of a high-performance current controller for linear compressor drive presents a challenge since the system is highly nonlinear, and an effective solution must be low cost. In this paper, a learning feed-forward current controller for the linear compressors is proposed. It comprises a conventional feedback proportional-integral controller and a feed-forward B-spline neural network (BSNN). The feed-forward BSNN is trained online and in real time in order to minimize the current tracking error. Extensive simulation and experiment results with a prototype linear compressor show that the proposed current controller exhibits high steady state and transient performance. © 2009 IEEE.

Phase dependent forward three wave amplification in photorefractive BSO

The results of three wave mixing experiments in photorefractive Bi12SiO20 are presented. The results confirm theoretical predictions that amplification by three wave mixing is strongly dependent on the phase relationship between the three beams at the input to the medium.

Feed-forward neural networks and topographic mappings for exploratory data analysis

A recent novel approach to the visualisation and analysis of datasets, and one which is particularly applicable to those of a high dimension, is discussed in the context of real applications. A feed-forward neural network is utilised to effect a topographic, structure-preserving, dimension-reducing transformation of the data, with an additional facility to incorporate different degrees of associated subjective information. The properties of this transformation are illustrated on synthetic and real datasets, including the 1992 UK Research Assessment Exercise for funding in higher education. The method is compared and contrasted to established techniques for feature extraction, and related to topographic mappings, the Sammon projection and the statistical field of multidimensional scaling.

NITL : what the transport and logistics industry needs going forward

The transport industry - particularly in road transport - is under serious competitive pressure. Rising costs - evident but not limited to fuel and insurance - combined with a market place that has become more demanding in relation to price and service, has resulted in a situation where companies have had to seriously reassess the nature of their competitive advantage. The competitive strategies of companies in the sector are being reviewed in light of the effective commoditisation of transport as a direct result of the traditional strong emphasis on cost and price reductions.

Desalination of brackish water by a batch reverse osmosis desalink system for use with solar thermal energy

For remote, semi-arid areas, brackish groundwater (BW) desalination powered by solar energy may serve as the most technically and economically viable means to alleviate the water stresses. For such systems, high recovery ratio is desired because of the technical and economical difficulties of concentrate management. It has been demonstrated that the current, conventional solar reverse osmosis (RO) desalination can be improved by 40–200 times by eliminating unnecessary energy losses. In this work, a batch-RO system that can be powered by a thermal Rankine cycle has been developed. By directly recycling high pressure concentrates and by using a linkage connection to provide increasing feed pressures, the batch-RO has been shown to achieve a 70% saving in energy consumption compared to a continuous single-stage RO system. Theoretical investigations on the mass transfer phenomena, including dispersion and concentration polarization, have been carried out to complement and to guide experimental efforts. The performance evaluation of the batch-RO system, named DesaLink, has been based on extensive experimental tests performed upon it. Operating DesaLink using compressed air as power supply under laboratory conditions, a freshwater production of approximately 300 litres per day was recorded with a concentration of around 350 ppm, whilst the feed water had a concentration range of 2500–4500 ppm; the corresponding linkage efficiency was around 40%. In the computational aspect, simulation models have been developed and validated for each of the subsystems of DesaLink, upon which an integrated model has been realised for the whole system. The models, both the subsystem ones and the integrated one, have been demonstrated to predict accurately the system performance under specific operational conditions. A simulation case study has been performed using the developed model. Simulation results indicate that the system can be expected to achieve a water production of 200 m3 per year by using a widely available evacuated tube solar collector having an area of only 2 m2. This freshwater production would satisfy the drinking water needs of 163 habitants in the Rajasthan region, the area for which the case study was performed.