Alternative methods for the reduction of evaporation: practical exercises for the science classroom

Across the world, freshwater is valued as the most critically important natural resource, as it is required to sustain the cycle of life. Evaporation is one of the primary environmental processes that can reduce the amount of quality water available for use in industrial, agricultural and household applications. The effect of evaporation becomes intensified especially during conditions of drought, particularly in traditionally arid and semi-arid regions, such as those seen in a number of countries over the past 10 years. In order to safeguard against the influence of droughts and to save water from being lost to the evaporative process, numerous water saving mechanisms have been developed and tested over the past century. Two of the most successful and widely used mechanisms have included floating hard covers and chemical film monolayers. This paper describes a laboratory based project developed for senior high school and first year university classes, which has been designed to introduce students to the concepts of evaporation, evaporation modelling and water loss mitigation. Specifically, these ideas are delivered by simulating the large-scale deployment of both monolayers and floating hard covers on a small water tank under numerous user defined atmospheric and hydrodynamic conditions, including varying surface wind speeds and underwater bubble plumes set to changing flow rates

Is the East Australian Current causing a marine ecological hot-spot and an important fisheries near Fraser Island, Australia?

The distributions of chlorophyll-a (Chl-a) blooms near the Fraser Island continental shelf along the east coast of Australia were analysed for the period 2002–2012. The blooms were found to exhibit two distinct quasi climatological patterns. The first pattern was a broad near-coast mid-shelf distribution that prevailed from about March to July each year. The second pattern was established due to re-occurring outer-shelf Chl-a blooms southeast of Fraser Island from about August to February. The outer-shelf Chl-a bloom concentration maxima appeared to be higher than those associated with the near coast pattern. Both distributions were found to be characterised by significant year-to-year variability in the number of total blooms, the length of blooms and the Chl-a bloom concentration maxima. The physical cause of the outer-shelf Chl-a concentration maxima was of particular interest, since this location overlaps with a region previously identified as a key eastern Australian marine ecological site and important fisheries. In this analysis, we found that the area also overlaps with a hot-spot in EAC-generated bottom layer stress, which appears to be the main driver of the 'Southeast Fraser Island Upwelling System'

Natural or Artificial? Habitat-Use by the Bull Shark, Carcharhinus leucas

BACKGROUND: Despite accelerated global population declines due to targeted and illegal fishing pressure for many top-level shark species, the impacts of coastal habitat modification have been largely overlooked. We present the first direct comparison of the use of natural versus artificial habitats for the bull shark, Carcharhinus leucas, an IUCN ‘Near-threatened’ species - one of the few truly euryhaline sharks that utilises natural rivers and estuaries as nursery grounds before migrating offshore as adults. Understanding the value of alternate artificial coastal habitats to the lifecycle of the bull shark is crucial for determining the impact of coastal development on this threatened but potentially dangerous species. METHODOLOGY/FINDINGS: We used longline surveys and long-term passive acoustic tracking of neonate and juvenile bull sharks to determine the ontogenetic value of natural and artificial habitats to bull sharks associated with the Nerang River and adjoining canals on the Gold Coast, Australia. Long-term movements of tagged sharks suggested a preference for the natural river over artificial habitat (canals). Neonates and juveniles spent the majority of their time in the upper tidal reaches of the Nerang River and undertook excursions into adjoining canals. Larger bull sharks ranged further and frequented the canals closer to the river mouth. CONCLUSIONS/SIGNIFICANCE: Our work suggests with increased destruction of natural habitats, artificial coastal habitat may become increasingly important to large juvenile bull sharks with associated risk of attack on humans. In this system, neonate and juvenile bull sharks utilised the natural and artificial habitats, but the latter was not the preferred habitat of neonates. The upper reaches of tidal rivers, often under significant modification pressure, serve as nursery sites for neonates. Analogous studies are needed in similar systems elsewhere to assess the spatial and temporal generality of this research

Linear Segmented Arc-Shaped Piezoelectric Branch Beam Energy Harvester for Ultra-Low Frequency Vibrations

Piezoelectric energy harvesting systems have been drawing the attention of the research community over recent years due to their potential for recharging/replacing batteries embedded in low-power-consuming smart electronic devices and wireless sensor networks. However, conventional linear piezoelectric energy harvesters (PEH) are often not a viable solution in such advanced practices, as they suffer from a narrow operating bandwidth, having a single resonance peak present in the frequency spectrum and very low voltage generation, which limits their ability to function as a standalone energy harvester. Generally, the most common PEH is the conventional cantilever beam harvester (CBH) attached with a piezoelectric patch and a proof mass. This study investigated a novel multimode harvester design named the arc-shaped branch beam harvester (ASBBH), which combined the concepts of the curved beam and branch beam to improve the energy-harvesting capability of PEH in ultra-low-frequency applications, in particular, human motion. The key objectives of the study were to broaden the operating bandwidth and enhance the harvester’s effectiveness in terms of voltage and power generation. The ASBBH was first studied using the finite element method (FEM) to understand the operating bandwidth of the harvester. Then, the ASBBH was experimentally assessed using a mechanical shaker and real-life human motion as excitation sources. It was found that ASBBH achieved six natural frequencies within the ultra-low frequency range (<10 Hz), in comparison with only one natural frequency achieved by CBH within the same frequency range. The proposed design significantly broadened the operating bandwidth, favouring ultra-low-frequency-based human motion applications. In addition, the proposed harvester achieved an average output power of 427 μW at its first resonance frequency under 0.5 g acceleration. The overall results of the study demonstrated that the ASBBH design can achieve a broader operating bandwidth and significantly higher effectiveness, in comparison with CBH

Remote sensing of water waves: wave flume experiments on regular and irregular waves

Laser scanning technology is a form of remote sensing which has shown, in feasibility studies, that a water surface can be measured rapidly and accurately without in-situ sensors. The adoption of a terrestrial laser scanner (TLS) for wave measurements is an innovative use of state-of-the-art technology usually employed for surveying and high precision surface modelling. An experimental setup for the measurement of waves in a wave flume is detailed and the results of remote sensing of wave parameters are described. The experiment conducted involves a unique method for measuring wave parameters such as wave height, wave period and wavelength. The experiments function as a source of reliable laboratory controlled data, however it also provides a platform for the development of laser scanning technology for field measurements.Griffith Sciences, Griffith School of EngineeringFull Tex

Estudo comparativo de três mecanismos de redução de evaporação de reservatórios

O uso de tecnologias para redução da evaporação de reservatórios pode ajudar regiões áridas e semiáridas a superar a escassez hídrica. Alguns mecanismos, como filmes monomoleculares e estruturas flutuantes, podem apresentar efeitos negativos nos ambientes aquáticos e na qualidade da água. Este trabalho investigou a eficácia de três mecanismos de redução de evaporação que possuem alto desempenho ambiental: coberturas suspensas, destratificadores e quebra-ventos. A análise foi conduzida com o modelo DYRESM em um reservatório localizado no sudeste do estado de Queensland, Austrália. O modelo foi primeiramente calibrado e validado para o reservatório em estudo. Em seguida, as condições de contorno foram alteradas para refletir os efeitos dos mecanismos de redução de evaporação no comportamento térmico do reservatório. O método mais eficaz foi o uso de coberturas suspensas, que reduziu em 88% a evaporação. O uso de quebra-ventos reduziu em 27% a evaporação, e o uso de destratificadores não teve efeito significativo na redução da evaporação. Para cada um dos mecanismos estudados, uma análise compreensiva dos seus efeitos na temperatura da água e nas taxas de evaporação foi efetuada, inferindo sobre os potenciais resultados do uso destes mecanismos em reservatórios de outras condições climáticas