Low Loss,High NA Chalcogenide Glass Fibers for Broadband Mid‐Infrared Supercontinuum Generation

High‐purity Ge–As–Se and Ge–As–S chalcogenide glasses were prepared by modified physical and chemical purification techniques. Using the purified glasses, step‐index fibers with a small core (~5.5 μm) and large numerical aperture (~1.3) were fabricated. When a 13.5‐cm‐long fiber was pumped with 320 fs pulses at a repetition rate of 10.5 MHz at 4.1 μm, supercontinuum spanning from ~1.8 to ~9.8 μm with a dynamic range of ±10 dB and an average power of ~3 mW was generated.     

Measurement and exploration of individual beliefs about the consequences of building information modelling use

Information and communication technology (ICT) is becoming increasingly important in construction although the rate of adoption is considered slow and the industry faces specific implementation challenges. Mainstream information systems research has shown that individuals’ beliefs and expectations of the consequences of ICT use predict subsequent usage. We describe the development of scales to measure beliefs about the consequences of building information modelling (BIM) and their use in a survey of employees of a large construction contracting organization in the United Kingdom. Scales for performance expectancy, effort expectancy, social influence, facilitating conditions, compatibility, and attitude toward using technology were adapted from existing measures. In an analysis of responses from 762 construction employees the scales showed acceptable measurement properties. Expectations about the consequences of BIM use were broadly favourable although there is a need for more data for comparisons. The structure of the responses showed that expectations that BIM would enhance job performance were strongly related to expectations that BIM use was compatible with preferred and existing ways of working. Results also suggest that social influence is complex and may be multidimensional.     

High Brightness 2.2–12 μm Mid‐Infrared Supercontinuum Generation in a Nontoxic Chalcogenide Step‐Index Fiber

An environment friendly nonlinear chalcogenide glass fiber with a Ge‐Sb‐Se core and a Ge‐Se cladding is fabricated for bright broadband mid‐infrared (MIR) supercontinuum (SC) generation. The fabricated Ge‐Sb‐Se/Ge‐Se fiber with a core diameter of 6 μm shows zero group velocity dispersion at ~4.2 μm and ~7.3 μm. By pumping the fiber with a length of 11 cm at 4.485 μm with 330 fs pulses, we achieve a SC covering the 2.2–12 μm spectral range and with an output average power of ~17 mW. This bright broadband SC source is promising for high‐resolution MIR spectroscopy.     

Predicting Blast Waves from the Axial Direction of a Cylindrical Charge

Bare, cylindrical, explosive charges produce secondary shock waves in the direction of least presented area. Whilst the source of these shock waves was explored in the 1940’s, no attempt was made to predict them. This paper describes the detonation of bare, cylindrical charges of PE4 (RDX binder 88/12 %), mass 0.2 to 0.46 kg and with a length to diameter ratio of 4 to 1. High speed camera footage showed (i) the formation of the separate, primary, shock waves from the sides and ends of the charge, (ii) Mach reflection of these separate shock waves, giving rise to reflected, secondary shock waves, and (iii) the secondary shock waves catching and merging with the primary shock wave. In the axial direction, the secondary shock wave’s peak overpressure and impulse exceeded that of the primary shock wave for scaled distances, Z=R/M^1/3 ≥3.9 m kg^−1/3, where M is the mass in kg and R the distance from the charge in m. It was found possible to predict the primary peak overpressure, P, at all distances in the axial direction, for a constant length to diameter ratio, using P=3075 Z⁻³−1732 Z⁻²+305 Z⁻¹. Close in the primary peak overpressure is proportional to M/R³ in the axial direction. It was not possible to predict the secondary peak overpressure with the data obtained. The total impulse from both shock waves, I, in the axial direction can be predicted using I=746(M^2/3/R)³−708(M^2/3/R)²+306(M^2/3/R).     

Role of strain induced crystallization and oxidative crosslinking in fracture properties of rubbers

Tensile properties and crack propagation properties, especially critical strain energy release rate in mode I, G_IC, have been used to investigate fracture properties of elastomers and their relationships with microstructure. These investigations were mainly based on a series of comparisons: first, the behaviour of polychloroprene rubber (CR), undergoing stress hardening due to strain induced crystallization (SIC) and oxidative crosslinking (OCL) was compared with that of chlorinated polyethylene (CPE), which undergoes SIC but not OCL, and with a polyurethane based on hydroxyl terminated polybutadiene (PU) which undergoes OCL but not SIC. Comparisons were also made on CR between fracture behaviour at ambient temperature, where SIC occurs and at 100 °C where there is no SIC. Finally, oxidative crosslinking was used to vary in a continuous way the crosslink density in CR and PU, in order to evaluate the role of crosslinking in fracture behaviour.     

用于汽车的高亮LED照明

毋庸置疑,高亮LED将成为未来一代汽车的主要特征.这是由于LED相对于传统的白炽光照明方案,具备许多重要优势.同时,采用LED也可带动技术上,甚至汽车设计风格上的变化.但是,正如任何革新技术,LED在广泛运用于汽车照明前,仍有许多困难需要克服.     

Characterization of silicon oxynitride films using ion beam analysis techniques

Heavy-ion elastic recoil detection analysis (HIERDA) is the ideal technique for quantitative analysis of silicon oxynitride films on silicon because of its unique ability to measure simultaneously all elements of interest (i.e., H, C, N, O and Si), thereby permitting key parameters such as the O/N-ratio to be determined in a single measurement. However, high-energy accelerators suitable for such HIERDA measurements are becoming much less readily available. Hence, the present paper investigates and calibrates an alternative IBA technique for simultaneous O, N and C analysis – namely, the use of (d,p) and (d,) nuclear reactions. Under optimum analysis conditions (850 keV deuterons and 150° detector angle), the Si background level sets a lower detection limit of 1×10¹⁶ nitrogen atoms/cm² and 3×10¹⁵ oxygen atoms/cm². H analysis is carried out separately, using low-energy ERDA and a 2 MeV ⁴He beam. Absolute cross-sections have been obtained for each of the (d,p) and (d,) groups. Comparison with data in the recent Handbook of Modern Ion Beam Materials Analysis shows reasonable agreement (10–15%) for the (d,p) reactions on oxygen and carbon. However, in the case of nitrogen, the measured cross-section values are 70% larger than the Handbook data. Several silicon oxynitride samples have been analyzed, first at UWO using 850 keV deuterons, and subsequently at ANU using HIERDA and a 200 MeV Au beam. The resulting O/N-ratios agree to within 10%. The relative importance of radiation damage effects is briefly discussed.     

Macroinvertebrate assemblages of littoral habitats in the Macquarie and Mersey rivers,Tasmania: Implications for the management of regulated rivers

Littoral habitats in large rivers are influenced to varying degrees by changes in discharge. Irrigation abstractions can increase the amount of habitat that would naturally be dewatered during low flow periods and therefore it is important to have some knowledge of the potential impact this may have on riverine macroinvertebrates. The macroinvertebrate assemblages of common littoral habitats in riffles, pools and runs in two reaches each of the Macquarie and Mersey Rivers, northern Tasmania, Australia were compared from samples collected during the low flow and irrigation season, between December 1991 and April 1992. The area under water of these habitats, riffle substrata, macrophyte beds and coarse woody debris, responded differently to changes in discharge. Within a reach, the same taxonomic groups often dominated the total number of macroinvertebrates for all habitats, but there were differences in the proportions contributed by these taxa to the different habitats. In general, taxa characteristic of slow-flowing or lentic habitats, such as ostracods and amphipods, were dominant in macrophyte beds in pools and runs, whereas taxa such as larval elmid beetles and hydropsychid caddisflies were dominant in riffles. A substantial component of the fauna from each habitat within a reach was unique to that habitat, but there was always a similar number of taxa common to all habitats. Classification and ordination grouped samples from both rivers firstly by habitat and secondly by month and reach. Total density and family richness of invertebrates differed by reach, habitat and month in both rivers, except for richness in the Mersey River where habitat was not significant. Differences in densities and numbers of invertebrate families among habitats were not consistent between reaches for each river. This study has highlighted the differences in macroinvertebrate assemblages of several littoral habitats in two lowland rivers in Tasmania. Differences in taxonomic composition, density and richness among habitats within reaches strongly imply the uniqueness of these habitats in terms of the invertebrate faunas that occupy them. We suggest that if maintenance of biotic diversity is an aim of instream flow management, water allocations that address low flows should place a high priority on the maintenance of a diversity of habitats.     

Observations of the preferential loss of major ions from melting snow and laboratory ice

Two types of laboratory experiments were undertaken to understand changes in the ionic composition of solutions from melting snows: (1) a set of field-laboratory experiments which involved partially melting recently collected snows and (2) experiments on the controlled melting of artificial ices of known composition. Sulphate and nitrate ions are preferentially lost with respect to chloride during the melting process so apparent elution sequence may be written SO₄²⁻ > NO₃⁻ > Cl⁻. Of the cations, sodium appears to be removed least readily giving an elution sequence Mg²⁺ = K⁺ > Na⁺. In the laboratory the differences in the efficiency of removal of ions from ice are small in the first stages of melting, but pronounced by the end of the melt. Sodium and chloride are expected to be proportionally enriched in residual leached snow packs. This is generally born out by field observations. The preferential loss of some ions is more evident in aged laboratory ice than in the freshly made ice. The changes in the ice and meltwater composition throughout the process of melting may be understood to arise from the mixing of two types of solutions: (i) an intergranular surficial brine with high solute concentration that occupies the ice grain boundaries and (ii) the meltwater from the ice grains.     

A coefficient of community loss to assess detrimental change in aquatic communities

Many techniques used to evaluate biological community data for effects of wastewater discharge do not discriminate between change and harmful change. A coefficient using the ratio of numbers of taxa lost between an unaffectd reference community and a pollution affected community, to the total number of taxa found in the affected community, provides a better evaluation of detrimental change. The value of the coefficient is determined by both the observed change in community richness as well as change in taxonomic similarity. The coefficient produces values from zero indicating no harmful change to infinity where there is complete loss of a community. Macroinvertebrate data suggests that values exceeding 0.8 are indicative of excessively harmful change in those communities.