2,361 research outputs found
On the performance of a nonlinear vibration isolator consisting of axially loaded curved beams
No full textA desirable characteristic for nonlinear vibration isolators is a high static stiffness and a low dynamic stiffness. A curved beam is a possible candidate for this role provided that the amplitude of vibration about the static equilibrium position is sufficiently small. However, for large amplitude oscillations, the nonlinear dynamics may have a detrimental effect. This paper considers the force transmissibility of a single degree-of-freedom system where the stiffness element is a curved, axially loaded beam. The transmitted force is calculated by numerical time domain integration of the equations of motion. The exact force-deflection relation for the beam is used for the spring. By comparison, a frequency domain solution is sought using the Harmonic Balance (HB) method in which the system is modelled as a Duffing oscillator. It is shown that the HB and time domain solutions are in close agreement for small amplitudes of excitation and both predict advantageous performance of the nonlinear isolator compared with its equivalent linear counterpart. However, significant discrepancies occur between the two solutions for large excitation since the beam can no longer be approximated by a linear and a cubic stiffness. It is also strongly asymmetric – soft in compression but stiff in extreme extension– which gives rise to an impulse in the transmitted force in each fundamental period. This numerical problem is alleviated by inserting a linear spring in series with the beam isolator with a modest compromise in isolation performance at the excitation frequency
Locating damage in waveguides from the phase of point frequency response measurements
No full textA method for detecting damage in uniform waveguide structures from two or more point frequency response functions (FRFs) is described. Attention is focussed on bending waves in beams although the method can in principle be applied to any waveguide structure. The input FRF is the superposition of directly injected waves and waves reflected from the damage and from other scattering regions in the structure. The phase of this FRF modulates with wavenumber, with the period of modulation in wavenumber space being related to the distances between the excitation point and scattering locations. The phase spectrum of the input FRF is found: the phase is determined, dispersive effects are removed by transforming from the frequency domain to the wavenumber domain, and the inverse Fourier transform from the wavenumber to the space domain found. Peaks in this phase spectrum indicate the distance to the scatterer. Two (or more) input FRFs can be used to determine the location of the scatterer unambiguously. Signal processing issues are discussed. Numerical results for a uniform beam with a breathing crack are given and experimental results for beams with a slot cut into them are presented. The approach lies in the middle ground between low frequency, modal methods and high frequency, ultrasonic methods. It allows one to interrogate a region of a structure rather than the complete structure and there is no requirement for a validated model of the structure in order to locate damage, apart from an estimate of the dispersion relation
Surveillance of adenoviruses and noroviruses in European recreational waters
No full textExposure to human pathogenic viruses in recreational waters has been shown to cause disease outbreaks. In the context of Article 14 of the revised European Bathing Waters Directive 2006/7/EC (rBWD, CEU, 2006) a Europe-wide surveillance study was carried out to determine the frequency of occurrence of two human enteric viruses in recreational waters. Adenoviruses were selected based on their near-universal shedding and environmental survival, and noroviruses (NoV) selected as being the most prevalent gastroenteritis agent worldwide. Concentration of marine and freshwater samples was done by adsorption/elution followed by molecular detection by (RT)-PCR. Out of 1410 samples, 553 (39.2%) were positive for one or more of the target viruses. Adenoviruses, detected in 36.4% of samples, were more prevalent than noroviruses (9.4%), with 3.5% GI and 6.2% GII, some samples being positive for both GI and GII. Of 513 human adenovirus-positive samples, 63 (12.3%) were also norovirus-positive, whereas 69 (7.7%) norovirus-positive samples were adenovirus-negative. More freshwater samples than marine water samples were virus-positive. Out of a small selection of samples tested for adenovirus infectivity, approximately one-quarter were positive. Sixty percent of 132 nested-PCR adenovirus-positive samples analysed by quantitative PCR gave a mean value of over 3000 genome copies per L of water. The simultaneous detection of infectious adenovirus and of adenovirus and NoV by (RT)PCR suggests that the presence of infectious viruses in recreational waters may constitute a public health risk upon exposure. These studies support the case for considering adenoviruses as an indicator of bathing water quality
‘Much of Sala, and but Little of Russia''A Journey Due North,' Household Words, and the Birth of a Special Correspondent
No full textWhen Dickens sent George Augustus Sala as a special correspondent to Russia just after the end of the Crimean War, he launched him in what was to become his best-known role as a journalist. Comprising twenty-two articles which appeared in weekly instalments from 4 October 1856 to 14 March 1857, Sala's essays are of interest not only for their representation of one of the significant geographical and cultural "others" of the mid-Victorian imagination, but for their distinctive style, which is vibrant and polyglot, eschewing political analysis and statistical information in favour of the flâneur's "gastronomy of the eye" – the vivid metropolitan travel writing so popular with mid-nineteenth-century readers
Determining potential for pollutant impacts in dynamic coastal waters: comparing morphological settings
No full textThe coastal focus and beach culture of Australia’s population in general, and the people of New South Wales in particular, mean that coastal systems are both highly prized and subjected to great pressures. The vast majority of the wastewater generated by the 7.3 million people of New South Wales is discharged directly to the ocean. The dispersion and fate of waterborne pollutants and their potential to impact coastal ecosystems are fundamentally determined by the dynamics of the coastal boundary layer (CBL). This turbulent interface between the coastline and the deep oceans is defined and classified for the first time in this thesis. Coastal morphologies and changes in the orientation of the coastline promote turbulence and strong gradients with extreme variability and heterogeneity over a broad range of scales. Conceptual models are presented to characterise New South Wales coastal boundary layer processes.
The broad aims of this thesis are to investigate the coastal boundary layer processes that affect dispersal and advection of pollutants, and to develop conceptual models and tools to facilitate coastal management.
Remote sensed ocean colour and sea surface temperature observations define meso-scale CBL phenomena, and this study demonstrates their application to support management decisions in relation to marine algal (phytoplankton) blooms. However, considerable scope exists to improve regional algorithms to deliver better ocean colour products for the optically complex (Case 2) waters of the inner coastal boundary layer.
Past failures to consider the CBL (morphological) settings of pollutant discharges to coastal waters have led to inefficient pollutant discharge systems and potential environmental impacts. Two case studies, investigate the principal forcing mechanisms and demonstrate the importance of morphology in controlling the dispersion and retention times of pollutants.
The first case study is focused on Sydney coastal waters where pollutant loadings are greater in magnitude and different in character than elsewhere in New South Wales. Here population pressures generate large wastewater loadings but the distances to offshore discharge locations are large compared to the scale of coastal roughness (headlands and bays) and the water is deep, thus reducing the risk of local retention of pollutants and increasing the potential for rapid dilution. By considering simulations of near field effluent plume behaviour in relation to long term ambient nutrient patterns specific periods of the year and depth intervals have been identified when outfalls would have an increased opportunity to influence bloom development, especially the upper half of the water column during late summer. However, algal blooms appear to be principally driven by seasonal oceanic nutrient enrichment. The research presented in this thesis, together with companion research previously published by the author and routine ongoing monitoring, indicate the viability of disposal of the Sydney’s excess sewage effluent (after source control and re-use options have been exhausted) via existing deepwater outfalls.
In contrast, inner CBL settings with coastal irregularities (e.g. headlands and bays) have a greater propensity to trap pollutants. A new hydrodynamically relevant morphological classification of New South Wales bays, headlands and islands provides both broad context for case studies and guides preliminary assessments for other locations. This classification reveals a borderline propensity for flow separation and re-circulation in the lee of Corambirra Point which is the focus of the second case study off Coffs Harbour in northern NSW. Direct observations and 3D finite difference hydrodynamic (Eulerian) and particle tracking (Lagrangian) model simulations quantify transient re-circulation associated with local current accelerations and a persistent shear zone located in the wake to the south of Corambirra Point. The flux of ambient water across the prescribed outfall alignment increases eighteen fold, over a shear zone spanning a cross-shore distance of just 1.4km (from 1.6km to 3km offshore). In contrast, the potential for re-entrainment and trapping of effluent in transient re-circulation cells was demonstrated to be insignificant. The proposed location of the outfalls was 1.5km offshore whereas the greatest gain per unit extension of the proposed discharge point coincides with the centre of the shear zone located ~2km offshore.
These case studies illustrate specific coastal boundary layer effects and indicate how an understanding of the spatial and temporal scales of these effects can be used to target more specific assessments of potential pollutant impacts. Simple morphological risk assessment tools are also presented to identify factors and processes which limit the exposure of sensitive environments to high pollutant concentrations and loads. Eddy retention effects are generally not incorporated in existing near field models but potential re-entrainment effects in wake zones can be assessed through the eddy retention value, which is introduced in this thesis. Although the approach presented here is focused on New South Wales coastal waters, the framework serves as a basis for general application elsewhere, and as a foundation for further refinement for application to NSW coastal waters.
Existing scientific literature indicates that coastal boundary layer processes also shape the distributions of the biological species and communities. This further motivates the development of a process based understanding of coastal boundary layer dynamics as a fundamental platform to support environmental protection and biodiversity conservation initiatives
Conservation genetics of Pristis sawfishes in Australian waters
No full textNorthern Australia is believed to contain the last ‘viable’ populations of the critically endangered Freshwater Sawfish, Pristis microdon, Dwarf Sawfish, Pristis clavata, and Green Sawfish, Pristis zijsron, making these populations of global significance. Mitochondrial and microsatellite markers were used to investigate the population structure, levels of genetic diversity, and evolutionary history of each of these species in northern Australian waters. Pristis microdon, which utilizes freshwater rivers as juveniles and marine waters as adults, has high levels of mtDNA heterogeneity and no nDNA heterogeneity; indicating that this species has female philopatry coupled with male-biased dispersal in northern Australian waters. The conservation plans for this species should, therefore, place a high priority on the protection of females, pupping grounds, and nursery areas to minimize the risk of extirpation. Conservation plans also need to consider the likelihood that a decline in the abundance of this species in one location could have an effect on its abundance and genetic ‘health’ in other locations via male gene flow. In contrast, P. clavata and P. zijsron, which spend their entire lives in marine and/or estuarine waters, each have heterogeneity in the mtDNA and nDNA markers, suggesting that gene flow in both males and females is restricted at large spatial scales in northern Australian waters. Consequently, the risk of extirpation for each of these species is relatively high since a decline in abundance is unlikely to be replenished by immigration from other locations. Therefore, conservation plans for P. clavata and P. zijsron should place a high priority on the protection of males and females, as well as pupping grounds and nursery areas. Most of the assemblages of each of the Pristis species contained moderate and high levels of diversity in mtDNA and nDNA markers, respectively. This suggests that the prognosis for the short and medium-term survival of each of these species in Australian waters is relatively good, providing that measures are put in place to curb any further declines in abundance. However, the levels of mtDNA diversity in the assemblage of each of P. clavata and P. zijsron in the Gulf of Carpentaria were reduced and, therefore, these assemblages may warrant special conservation status. Finally, the evolutionary histories of the Pristis species in Australian waters have most likely played an important role in shaping the observed patterns of population structure and levels of genetic diversity, however, the relative influence of contemporary versus historic factors on the amount and distribution of genetic variation in each of these species remains somewhat unresolved
Investigating the influence of drone flight on the stability of cancer medicines.
No full textMonoclonal Antibodies (mAbs) are being used in the treatment of both malignant and non-malignant diseases and whilst highly effective, certain products have very short expiry times. Clinical deterioration and supply chain disruption can often lead to wastage and there is a need to reduce this by improving efficiency in logistics practices between manufacturing sites and administration locations. This study aimed to investigate the influence of drone flight on the stability of cancer medicines. Clinically expired, premanufactured monoclonal antibodies (mAbs) were investigated, contained inside instrumented Versapaks, and flown in a Skylift (Mugin) V50 vertical take-off and landing drone through seven phases of flight, (take-off, hover, transition, cruise, transition, hover, and landing). Storage specifications (2-8°C) were met, and any vibrations emanating from the drone and transmitted through the packaging during flight were monitored using accelerometers. Vibration occurred largely above 44 Hz which was consistent with rotor speeds during operation and was significantly greater in amplitude during transition than in forward flight or in hover. Bench experiments validated assurance practices, exploring the edge-of-quality failure by applying extremes of rotational vibration to the mAbs. Aggregation and fragmentation represented a loss of quality in the mAbs and would pose a risk to patient safety. No significant difference was identified in the aggregation and fragmentation of all flown mAbs samples, indicating structural integrity. Flown mAbs in their infusion bags had similar particle sizes compared to controls, (Bevacizumab 11.8±0.17 nm vs. 11.6±0.05 nm, Trastuzumab 11.2±0.05 nm vs. 11.3±0.13 nm, Rituximab 11.4±0.27 nm vs. 11.5±0.05 nm) and aggregate content (Bevacizumab 1.25±0.03% vs 1.32±0.02% p = 0.11, Trastuzumab 0.15±0.06% vs. 0.16±0.06% p = 0.75, Rituximab 0.11±0.02% vs. 0.11±0.01% p = 0.73). The quality of the three mAbs was assured, suggesting that the V50 drone did not induce sufficient levels of vibration to adversely affect their quality
Geolocators reveal migration and pre-breeding behaviour of the critically endangered Balearic Shearwater Puffinus mauretanicus
No full textUsing combined miniature archival light and salt-water immersion loggers, we characterise the year-round individual at-sea
movements of Europe’s only critically endangered seabird, the Balearic shearwater Puffinus mauretanicus, for the first time.
Focusing on the non-breeding period, we show that all of the 26 breeding birds tracked from their breeding site on
Mallorca in the Mediterranean Sea successfully made a 2–4 month migration into the Atlantic Ocean, where they utilised
well-defined core areas off Portuguese and French coasts. As well as identifying high-risk areas in the Atlantic, our results
confirm that breeding birds spend most of the year concentrated around productive waters of the Iberian shelf in the
western Mediterranean. Migration phenology appeared largely unrelated to the subsequent (distinctly synchronous)
breeding attempt, suggesting that any carry-over effects were compensated for during a long pre-laying period spent over
winter in the Mediterranean. Using the light and salt-water immersion data alone we were also able to characterise the
pattern of pre-laying visits to the colony in considerable detail, demonstrating that breeding pairs appear to coordinate
their over-day visits using a high frequency of night-time visits throughout the winter. Our study shows that geolocation
technology is a valuable tool for assessing the spatial distribution of risks to this critically endangered species, and also
provides a low-impact method for remotely observing the detailed behaviour of seabird species that may be sensitive to
disturbance from traditional study methods
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