Fibre to the home – infrastructure deployment issues

To date the use of optical fibre in the access network has typically only proved cost effective for supplying the high-bandwidthdemands of large corporate companies. For new and established network operators, however, the increasing demand forbandwidth to deliver bearer, interactive and bundled services to business and residential customers is requiring them to seriouslyconsider the high volume roll-out of optical-fibre-based systems. Network operators therefore face some major decisions, notonly in terms of the type of fibre transmission systems to deploy, but also on how to install a cost-effective network of fibrecables, ducting and joints to connect to the customers they wish to serve. Installing fibre in the ground represents a majorcommitment and a long term investment. Network operators can typically expected the fibre infrastructure to equate to at least60% of the cost of the overall access transmission system. Planning and building such networks involves major investment at theoutset, and, in todays highly competitive markets, operators are faced with the added complications of uncertain take-up ofservices by customers and the likelihood of high customer churn.This paper focuses on fibre to the home (FTTH) and the deployment options and challenges for the physical fibre infrastructure.The key difference associated with connecting optical fibre to residential properties instead of business properties is not technicalbut commercial. There is typically a much smaller potential revenue from a residential property than from a business property.This leads to a need for cost optimisation of both the transmission system and the fibre infrastructure. This paper examines thefibre infrastructure issues that need to be considered for an FTTH deployment and describes the fibre access network modellingactivities carried out by BTexact's Broadband Network Engineering unit. The aim of this modelling is both to automate theplanning of, and to optimise the costs of deploying, access networks based on real geographical and demographic data.     

Optical dating of palaeochannel deposits in the Riverine Plain,southeastern Australia: testing the reliability of existing thermoluminescence dates

We present the first quartz optically stimulated luminescence (OSL) ages for palaeochannel sediments from the Riverine Plain in southeastern Australia. For young fluvial sediments, we agree with the notion that analysis of the leading edge of a dose distribution curve provides an objective method for determining the OSL age. For a modern flood deposit (less than 200 years old), the OSL ages estimated using the leading edge method (250 +/- 50 years) and by using the lowest 5% of the measured dose in single aliquots (230 +/- 50 years) agree within experimental errors. For older sediments, we suggest that the mean estimate of the dose distribution is likely to provide a reliable estimate of the OSL age. The luminescence ages suggest that the Coleambally and Kerarbury palaeochannel systems were active between 105 and 80 ky and 55 and 35 thousand years ago; the Yanco palaeochannel system could have been active as recently as 9000 years ago.     

A simple method for visualizing the differences between related receptor sites

Pastor and Cruciani [J. Med. Chem. 38 (1995) 4637] and Kastenholz et al. [J. Med. Chem. 43 (2000) 3033] pioneered methods for comparing related receptors, with the ultimate goal of designing selective ligands. Such methods start with a reasonable superposition of high-resolution three-dimensional (3D) structures of the receptors. Next, molecular field maps are calculated for each receptor. Then the maps are analyzed to determine which map features are correlated with a particular subset of receptors. We present a method FLOGTV, based on the trend vector paradigm [J. Chem. Inf. Comput. Sci. 25 (1985) 64] to perform the analysis. This is mathematically simpler than the GRID/CPCA method of Kastenholz et al. and allows for the simultaneous comparison of many receptor structures. Also, the trend vector paradigm provides a method of selecting isopotential contours that are well above "noise". We demonstrate the method on four examples: HIV proteases versus two-domain acid proteases, thrombin versus trypsin and factor Xa, bacterial dihydrofolate reductases (DHFRs) versus vertebrate DHFRs, and P38 versus ERK protein kinases.     

Relationship between comfort and back posture and mobility in sitting-posture

The objective of this work is to analyze the causes of lumbar discomfort while sitting on a chair, by analyzing the relationship of lumbar curvature, pelvic inclination and their mobilities with discomfort. An experiment has been performed with healthy subjects, in which comfort, postural and mobility parameters have been measured. Their relationship has been analyzed with multivariate analysis. Factorial analysis has been used to represent all the correlated variables measured. Logistic regression and discriminant analyses have been used to classify discomfort/absence of discomfort. The results show that great changes of posture are a good indicator of discomfort, and that lordotic postures with forward leaned pelvis and low mobility are the principal causes of the increase of discomfort.     

Videothoracoscopic surgery

Although thoracoscopy has been used for diagnostic and minor therapeutic procedures for many years, there have been few reports of its use in performing major intrathoracic procedures which have traditionally required formal thoracotomy. We report our initial experience in this field. Fifty patients (M:F = 1.63:1, mean +/- SD age = 41.8 +/- 20.4 years, range = 14-80) underwent 54 endoscopic intrathoracic operations. The procedures carried out included wedge excision of solid pulmonary mass (10), pleurectomy (25), lung biopsy (14), and miscellaneous procedures (5). Under general anaesthesia a laparoscope attached to a video monitor was introduced into the chest. One or two additional stab incisions were made as needed for the introduction of standard surgical or endoscopic instruments and staplers. There were no deaths. One patient developed a second pneumothorax 7 days after endoscopic pleurectomy, necessitating open pleurodesis. All patients were discharged home between 2 and 11 days after surgery (mean +/- SD = 3.8 +/- 2.0 days). Endoscopic thoracic surgery is a safe and useful technique for certain cases. It merits further investigation and assessment.     

Mutational specificity of the syn 1,2-dihydrodiol 3,4-epoxide of 5-methylchrysene

The mutational specificity of the syn dihydrodiol epoxide of 5-methylchrysene in the supF gene of the pSP189 vector was examined. Transversion mutations at GC pairs predominated with G --> T and G --> C changes accounting for 42 and 21% of total base change mutations. The types of mutations found reflect the previously determined chemical preference of this reactive species for reaction with deoxyguanosine residues in DNA.     

Thermal effects on the microstructure and mechanical properties of ion implanted ceramics

The effects of varying the substrate temperature on the implantation-induced structures and surface mechanical properties of single crystal sapphire and MgO have been investigated for a range of 300 keV implanted ions. As the implantation temperature is lowered, the dose at which amorphization occurs is reduced and thus, for the same doses, more amorphous material is produced at lower temperatures. Quantitative modelling shows that the activation energy for annealing of the amorphous material during implantation is very much lower than might be expected for post-implantation thermal annealing of the same material. Also, as the implantation temperature increases there is a small amount of damage annealing in the damaged-but-crystalline material.Both the microhardness and implantation-induced stresses depend critically on the presence of amorphous material since this is relatively soft and can support only small stresses. However, while the hardness behaviour in the damaged-but-crystalline material is dominated by radiation hardening, the substitutionality, ionic misfit and charge state of the implanted ions have also been found to contribute to the further solid solution component of the hardening produced by ion implantation. These effects are also observed to be temperature dependent. Crazing of the implanted layers has also been reappraised. It has been established that the formation and configuration of crazes is a sensitive function of implantation temperature, and it is now proposed that crazes form in response to the stresses generated as a result of the thermal expansion mismatch between the amorphous layer and the substrate.     

The initiation and growth of fatigue cracks in a titanium aluminide alloy

The micromechanics of small, naturally initiated fatigue cracks and large through-thickness fatigue cracks have been studied in the titanium aluminide alloy Super Alpha 2. The microstructure investigated had equal volume fractions ofα ₂ and Β phases. Crack growth rates were higher than through α-Β titanium alloys. Initiation of small cracks was found always to occur in theα ₂ phase, and small cracks grew belowΔK _th, the minimum cyclic stress intensity required for growth of large fatigue cracks. A method previously proposed for reconciling the growth rates of large and small cracks is applied to these results.