Assessment of extreme and metocean conditions in the Maldives for OTEC applications

The Maldives is a group of tropical atolls, considered globally to be one of the most desirable holiday destinations. There is an urgent requirement to decrease their dependency on fossil fuels that are currently the main source of energy, and a number of renewable energy alternatives are being evaluated. Among these, due to the favorable oceanographic and bathymetric conditions, ocean thermal energy conversion (OTEC) systems represent a viable opportunity for clean and reliable power. However, the stresses the OTEC platform will need to endure during adverse environmental conditions are not well defined. The magnitude of these stresses will then have a direct influence on the design of the OTEC device. In order to overcome this uncertainty, this paper uses hindcast data sets from global weather and ocean models to assess the metocean conditions of the Maldives, with particular reference to extreme conditions. After selecting a suitable location for the deployment of the devices, return values calculated using the peaks‐over‐threshold (POT) methodology are estimated for wind, waves, and currents. The 100‐year return value for the significant wave height is found to be 4.5 m, with a joint occurrence of energy periods between 7.5 and 8.5 seconds, whereas the 100‐year return wind has a velocity of 17.8 m/s and the 100‐year return current of 1.9 m/s. The directionality of these extreme events is also considered, showing the southern and western sub‐quadrants as the prevailing sources, which provides essential information for positioning of the platform. Additional evaluations of tropical revolving storms (TRS) and variations in temperature and salinity patterns are also provided over a 1500‐m water column; temperature varies by approximately 24°C, and salinity by around 2 ppt, showing the suitability of OTEC platforms in the Maldives. This work is therefore of interest to offshore renewable energy stakeholders interested in developing a project in the Maldives or those conducting an analogous analysis in other locations.     

Silica removal from Mokai, New Zealand, geothermal brine by treatment with lime and a cationic precipitant

Preliminary experiments using two chemicals (CaO, a quicklime, and a cationic nitrogen-bearing precipitant, EC-004) to remove silica from geothermal brine were undertaken at the Mokai geothermal plant, New Zealand. The brine was mixed with the reagent (CaO or EC-004). The reaction was studied from the start of the experiment (NRT, 0 min, no retaining time) and after 15 min (15RT) at 90 °C. The concentration of silica in the brine was initially 954 mg/l, and decreased linearly with increasing reagent concentration. When CaO is added, the silica concentration at 15RT was 200 mg/l lower than at NRT and became almost zero on addition of 1.5 g/l. In contrast, when EC-004 is added, the total silica concentration nearly reaches the solubility of amorphous silica at 90 °C. In order to prevent silica scaling in Mokai brines cooled to 90 °C, the CaO and EC-004 added should be individually adjusted to 0.5 g/l and 80 mg/l, respectively.     

The effect of global cross flows on the flow field and local heat transfer performance of miniature centrifugal fans

Centrifugal fans are often integrated into thermal management solutions for a range of applications. Consequently, centrifugal fan designs can be subjected to varying environmental conditions, many of which can alter fan performance characteristics and ultimately influence the heat transfer performance of the cooling solution. Global cross flows are a commonly encountered practical operating condition, particularly in the cooling of electronics. Air-cooled electronic enclosures often incorporate miniature centrifugal fans to maintain reliable component operating temperatures at a local level, while larger system level fans are used to simultaneously control the ambient temperature within the enclosure. This type of operating condition has been investigated by introducing a uniform crossing air flow above a centrifugal fan inlet. Two scaled miniature centrifugal fan designs were selected to fundamentally assess the influence on local velocity field and heat transfer performance. This was achieved experimentally using Particle Image Velocimetry, and a combined infrared and heated-thin-foil technique developed for the accurate measurement of local heat transfer coefficients. the introduction of a crossing air flow above the fan inlet indirectly reduced both the local and global thermal performance of the centrifugal fan, and the resultant distorted inflow shifted the surface heat transfer distribution at the fan outlet from an axisymmetric to asymmetric profile. However, strategic positioning of components relative to a centrifugal fan can maintain the average component heat transfer coefficient at a similar level to a case without any cross flow. Results also indicate issues associated with the implementation of miniature centrifugal fan designs into crossing air flow environments, with reductions in thermal performance of over 30% observed.     

Equivalent circuit modeling of coupled resonator filters

Using the stacked crystal filter (SCF) concept, a coupled resonator filter (CRF) can be interpreted as a device in which 2 piezoresonators are stacked on top of each other in such a way that a certain degree of acoustic interaction occurs. The work presented in this paper reports a novel all-electrical model for the CRF. The model associates acoustical coupling with an equivalent electrical coupling between resonators. The resulting equivalent circuit makes it possible to apply classical filter synthesis techniques directly based on the coupling control between resonators. It complements with a synthesis approach the analysis approach of the Mason model.     

Slow light structures in dye-doped polymer waveguides

We present a simple and consistent technique for fabricating slow light structures in dye-doped polymer waveguides using the process of irreversible photobleaching. The slow light structures are moiré gratings. The gratings are holographically written into channel waveguides photobleached in side-chained PMMA/DR1 films. The films are annealed during the photobleaching process in order to remove stresses in the films generated during the photobleaching process. These stresses have been observed to cause distortion and cracking of the film surface. The slowing factor for the moiré gratings is calculated from the reflectance spectrum of the waveguides using the Hilbert transform. Moiré gratings with slowing factors between 1.6 and 2.6 are demonstrated.     

A dynamic model for solder and the problem of accelerated life testing

Solder joint reliability under thermal cycling is a key problem in electronic packaging. Accelerated life testing (few cycles, larger temperature excursions) is often a practical necessity in predicting fatigue life in field environments (many cycles, smaller temperature excursions). Complex solder behavior with marked temperature dwell and cycle time influence at slower frequencies makes this a difficult problem. A dynamic model is presented which couples the effect of instability of coarsened grain shear band evolution in microstructure with the change in macroscopic constitutive behavior. Key features of the model include effects of shear band thickness compared with total solder joint thickness, pertinent to small scale design, and frictional resistance at slow deformation rates. Model correlation with test data is discussed and applied to the accelerated life test design.     

Molecular cloning and sequencing of a chitin synthase gene (CHS2) of Paracoccidioides brasiliensis

The nucleotide sequence of a chitin synthase gene (CHS2) of the dimorphic fungal human pathogen Paracoccidioides brasiliensis has been determined. The deduced amino acid sequence of Chs2p consists of 1043 residues and is highly homologous to other class II fungal chitin synthases. Computational structural analyses suggest very high similarity to other fungal chitin synthases with a highly variable region at the cytosolic amino-terminal region which may be related to its possible zymogenic nature, and the putative catalytic region close to seven membrane-spanning regions at the carboxyl terminus. The nucleotide sequence of CHS2 and its flanking regions has been submitted to GenBank under Accession Number Y09231. © 1998 John Wiley & Sons, Ltd.     

Calibration control of robot vertical assembly

Calibration methods that apply relative techniques to map robot inaccuracy increase robot flexibility by allowing for greater use and application of off-line path planning techniques. To successfully implement the off-line techniques described in this article, methods have been integrated for off-line tool control frame (TCF) calibration, data base integration, and on-line robot inaccuracy correction. The TCF calibration methods presented in this article successfully determine the TCF origin of the end-effectors and sensors attached to the robot distal link to within the robot repeatability. When the methods were applied to a SEIKO DTRAN RT-3000 robot, the TCP origins were statically predicted correct to within 0.025mm (0.001 in.). On-line methods determine robot inaccuracy by mapping robot configurations relative to operational parts or to spatial templates, in contrast to the contemporary global mapping approaches. For the Seiko robot the resulting inaccuracy distributions permit simple error correction equations to be applied, improving robot positioning accuracy to less than ±0.1 mm in locally large regions and to within the repeatability of the robot ±0.025 mm) in smaller regions. This represents an order-of-magnitude decrease in robot inaccuracy.     

Climate co-benefits of green building standards: water,waste and transportation

This paper quantifies the greenhouse gas (GHG) emissions co-benefits associated with water, waste and transportation usage in certified green commercial office buildings in California. The study compares the measured values of water, waste and transportation usage self-reported by office buildings certified under the Leadership in Energy and Environmental Design rating system for Existing Building Operations and Maintenance (LEED EBOM) to baseline values of conventional California office buildings. The green buildings in the LEED EBOM dataset produced 50% less GHGs due to water consumption than baseline buildings, 48% less due to solid waste management, and 5% less due to transportation. If applied to the entire California office building stock, performance typical of the certified green buildings would save 730,038?MgCO₂e/yr (metric tonnes) from transportation, 87,601?MgCO₂e/yr from water, and 45,280?MgCO₂e/yr from waste, for a total potential savings of about 862,920?MgCO₂e/yr relative to conventional construction. In addition, buildings earning additional credits for specified performance thresholds for water and waste in the LEED EBOM code attained performance levels even higher than required by the code provisions, suggesting that such code provisions in other contexts may help incentivize larger GHG emissions reductions than anticipated. Specific recommendations are made for building standards and certification schemes.     

世界公共交通简讯

匈牙利;意大利;