3,492 research outputs found
Shock accelerated vortex ring
The interaction of a shock wave with a spherical density inhomogeneity leads
to the development of a vortex ring through the impulsive deposition of
baroclinic vorticity. The present fluid dynamics videos display this phenomenon
and were experimentally investigated at the Wisconsin Shock Tube Laboratory's
(WiSTL) 9.2 m, downward firing shock tube. The tube has a square internal
cross-section (0.25 m x 0.25 m) with multiple fused silica windows for optical
access. The spherical soap bubble is generated by means of a pneumatically
retracted injector and released into free-fall 200 ms prior to initial shock
acceleration. The downward moving, M = 2.07 shock wave impulsively accelerates
the bubble and reflects off the tube end wall. The reflected shock wave
re-accelerates the bubble (reshock), which has now developed into a vortex
ring, depositing additional vorticity. In the absence of any flow disturbances,
the flow behind the reflected shock wave is stationary. As a result, any
observed motion of the vortex ring is due to circulation. The shocked vortex
ring is imaged at 12,500 fps with planar Mie scattering.Comment: For Gallery of Fluid Motion 200
Vibration Isolation Design for the Micro-X Rocket Payload
Micro-X is a NASA-funded, sounding rocket-borne X-ray imaging spectrometer
that will allow high precision measurements of velocity structure, ionization
state and elemental composition of extended astrophysical systems. One of the
biggest challenges in payload design is to maintain the temperature of the
detectors during launch. There are several vibration damping stages to prevent
energy transmission from the rocket skin to the detector stage, which causes
heating during launch. Each stage should be more rigid than the outer stages to
achieve vibrational isolation. We describe a major design effort to tune the
resonance frequencies of these vibration isolation stages to reduce heating
problems prior to the projected launch in the summer of 2014.Comment: 6 pages, 7 figures, LTD15 Conference Proceeding
Metabolic flexibility as a major predictor of spatial distribution in microbial communities
A better understand the ecology of microbes and their role in the global ecosystem could be achieved if traditional ecological theories can be applied to microbes. In ecology organisms are defined as specialists or generalists according to the breadth of their niche. Spatial distribution is often used as a proxy measure of niche breadth; generalists have broad niches and a wide spatial distribution and specialists a narrow niche and spatial distribution. Previous studies suggest that microbial distribution patterns are contrary to this idea; a microbial generalist genus (Desulfobulbus) has a limited spatial distribution while a specialist genus (Methanosaeta) has a cosmopolitan distribution. Therefore, we hypothesise that this counter-intuitive distribution within generalist and specialist microbial genera is a common microbial characteristic. Using molecular fingerprinting the distribution of four microbial genera, two generalists, Desulfobulbus and the methanogenic archaea Methanosarcina, and two specialists, Methanosaeta and the sulfate-reducing bacteria Desulfobacter were analysed in sediment samples from along a UK estuary. Detected genotypes of both generalist genera showed a distinct spatial distribution, significantly correlated with geographic distance between sites. Genotypes of both specialist genera showed no significant differential spatial distribution. These data support the hypothesis that the spatial distribution of specialist and generalist microbes does not match that seen with specialist and generalist large organisms. It may be that generalist microbes, while having a wider potential niche, are constrained, possibly by intrageneric competition, to exploit only a small part of that potential niche while specialists, with far fewer constraints to their niche, are more capable of filling their potential niche more effectively, perhaps by avoiding intrageneric competition. We suggest that these counter-intuitive distribution patterns may be a common feature of microbes in general and represent a distinct microbial principle in ecology, which is a real challenge if we are to develop a truly inclusive ecology
Roads in Rainforest: best practice guidelines for planning, design and management
These Guidelines were developed as a framework for understanding the primary ecological issues to be addressed in the planning, design and management of roads in rainforest environments. This manual has been created to assist in reducing the main impacts of roads, which are primarily:
⢠Habitat loss and fragmentation;
⢠Reduction in habitat quality;
⢠Edge effects;
⢠Reduced animal movements, resulting in restricted genetic flows and diminished survival rates in some species;
⢠Population reduction through road kill of wildlife species;
⢠Erosion, sedimentation and pollution;
⢠Impacts on scenic quality;
⢠Disturbance from vehicular noise, headlights and movement;
⢠Facilitation of the spread of exotic pests,
⢠weeds and diseases; and
⢠Direct mortality from road construction activities.
Cumulatively, these impacts threaten the biodiversity and integrity of ecosystem processes throughout Queenslandâs tropical forests. It is therefore imperative that current and future road infrastructure be designed with consideration of these factors within the context of the natural environment.
This document provides a set of principles and supporting guidelines for implementing best practice planning, design and management for ecologically sustainable roads within rainforests
throughout Queensland. The intention of these Guidelines is to describe the particular aspects
of rainforest environments that are unique and thus require particular consideration when
designing and constructing roads in these habitats.
Therefore, these Guidelines were specifically developed to:
⢠Inform planners, engineers and managers about the key ecological elements (Principles) to consider when building roads in rainforest environments;
⢠Identify the most important issues to consider when planning, designing and implementing plans for road infrastructure so that the impacts to the primary ecological elements of rainforests are minimised. Each major issue is clarified within its own âGuidelineâ; and
⢠Provide a set of steps and checklists within each Guideline to ensure that the core Principles are maintained throughout the different phases of planning, design and construction
Tensile Properties of AM Maraging steel
Additively Manufactured (AM) materials have great potential for producing graded materials, embedded structures and near net complex shapes. AM maraging steel properties have been compared with wrought maraging steel. The comparison featured interrupted tensile tests over a range of temperatures and strain rates. In addition a specially designed Tensile Split Hopkinson Pressure Bar (TSHPB) has been built to test very high strength metals at high strain rates. The results showed that the AM maraging steel was much more ductile than expected and exhibited significant necking under all conditions tested. All the samples exhibited ductile fracture. Although not as ductile as the wrought material, the AM material could be cost effective through economies of scale for complex components. The microstructure contained inclusions which derived from either the powder or the AM process and thus there is significant potential to improve these materials further. A modified Armstrong-Zerilli model was also constructed for these materials and shown to predict the raw experimental data within experimental error using DYNA3D simulations.</jats:p
Host-Derived Artificial MicroRNA as an Alternative Method to Improve Soybean Resistance to Soybean Cyst Nematode
Citation: Tian, B., Li, J. R., Oakley, T. R., Todd, T. C., & Trick, H. N. (2016). Host-Derived Artificial MicroRNA as an Alternative Method to Improve Soybean Resistance to Soybean Cyst Nematode. Genes, 7(12), 13. doi:10.3390/genes7120122Citation: Tian, B., . . . & Trick, H. (2016). Host-Derived Artificial MicroRNA as an Alternative Method to Improve Soybean Resistance to Soybean Cyst Nematode. Genes, 7(12), 13.
https://doi.org/10.3390/genes7120122The soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pests limiting soybean production worldwide. Novel approaches to managing this pest have focused on gene silencing of target nematode sequences using RNA interference (RNAi). With the discovery of endogenous microRNAs as a mode of gene regulation in plants, artificial microRNA (amiRNA) methods have become an alternative method for gene silencing, with the advantage that they can lead to more specific silencing of target genes than traditional RNAi vectors. To explore the application of amiRNAs for improving soybean resistance to SCN, three nematode genes (designated as J15, J20, and J23) were targeted using amiRNA vectors. The transgenic soybean hairy roots, transformed independently with these three amiRNA vectors, showed significant reductions in SCN population densities in bioassays. Expression of the targeted genes within SCN eggs were downregulated in populations feeding on transgenic hairy roots. Our results provide evidence that host-derived amiRNA methods have great potential to improve soybean resistance to SCN. This approach should also limit undesirable phenotypes associated with off-target effects, which is an important consideration for commercialization of transgenic crops
Copyright and cultural work: an exploration
This article first discusses the contemporary debate on cultural âcreativityâ and the economy. Second, it considers the current state of UK copyright law and how it relates to cultural work. Third, based on empirical research on British dancers and musicians, an analysis of precarious cultural work is presented. A major focus is how those who follow their art by way of âportfolioâ work handle their rights in ways that diverge significantly from the current simplistic assumptions of law and cultural policy. Our conclusions underline the distance between present top-down conceptions of what drives production in the cultural field and the actual practice of dancers and musicians
Ocular and Extraocular Expression of Opsins in the Rhopalium of Tripedalia cystophora (Cnidaria: Cubozoa)
A growing body of work on the neuroethology of cubozoans is based largely on the capabilities of the photoreceptive tissues, and it is important to determine the molecular basis of their light sensitivity. The cubozoans rely on 24 special purpose eyes to extract specific information from a complex visual scene to guide their behavior in the habitat. The lens eyes are the most studied photoreceptive structures, and the phototransduction in the photoreceptor cells is based on light sensitive opsin molecules. Opsins are photosensitive transmembrane proteins associated with photoreceptors in eyes, and the amino acid sequence of the opsins determines the spectral properties of the photoreceptors. Here we show that two distinct opsins (Tripedalia cystophora-lens eye expressed opsin and Tripedalia cystophora-neuropil expressed opsin, or Tc-leo and Tc-neo) are expressed in the Tripedalia cystophora rhopalium. Quantitative PCR determined the level of expression of the two opsins, and we found Tc-leo to have a higher amount of expression than Tc-neo. In situ hybridization located Tc-leo expression in the retinal photoreceptors of the lens eyes where the opsin is involved in image formation. Tc-neo is expressed in a confined part of the neuropil and is probably involved in extraocular light sensation, presumably in relation to diurnal activity
Catch analysis of shrimp Palaemon serratus (Pennant) taken by different mesh sizes
Five mesh sizes were used to sample shrimp Palaemon serratus at depths of less than 30 m in Bantry Bay, southwest Ireland from June 1996 to March 1997. All of the meshes, with the exception of the smallest (2.5 mm) were made up of polyethylene and they were distributed over a gang of 20 Chinesehat-ended creels which were fished on fourteen occasions throughout the period which overlapped with the commercial fishing season. Some 5,000 shrimp were captured and the size distribution of the total catch per month reflected the growth of the species so it is supposed that the population was representatively sampled throughout. Selection was calculated using the alternate hauls method. Shrimps did not enter the pots in any numbers below the length of 50 mm (total length) and mesh selection could not he demonstrated at a mesh size of 5.2 mm. Thereafter, as the mesh sizes were ascended, selectivity became more significant. It was however weak; Lc values ranged between 58-75 mm for females and 71-88 mm total lengths for males for mesh sizes of 7.5 - 13.5 mm. These lengths coincide with the centre of the length frequency distribution of shrimp. As the mesh size increased, the ratio of females to males rose, but the numbers per haul declined abruptly in the 13.5 mm mesh.Funder: Marine Institut
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Research and theory for nursing and midwifery: Rethinking the nature of evidence
Background and Rationale: The rise in the principles of evidence-based medicine in the 1990s heralded a re-emerging orthodoxy in research methodologies. The view of the randomised controlled trial (RCT) as a âgold standardâ for evaluation of medical interventions has extended recently to evaluation of organisational forms and reforms and of change in complex systemsâwithin health care and in other human services. Relatively little attention has been given to the epistemological assumptions underlying such a hierarchy of research evidence.
Aims and Methods: Case studies from research in maternity care are used in this article to describe problems and limitations encountered in using RCTs to evaluate some recent policy-driven and consumer-oriented developments. These are discussed in relation to theory of knowledge and the epistemological assumptions, or paradigms, underpinning health services research. The aim in this discussion is not to advocate, or to reject, particular approaches to research but to advocate a more open and critical engagement with questions about the nature of evidence.
Findings and Discussion: Experimental approaches are of considerable value in investigating deterministic and probabilistic cause and effect relationships, and in testing often well-established but unevaluated technologies. However, little attention has been paid to contextual and cultural factors in the effects of interventions, in the culturally constructed nature of research questions themselves, or of the data on which much research is based. More complex, and less linear, approaches to methodology are needed to address these issues. A simple hierarchical approach does not represent the complexity of evidence well and should move toward a more cyclical view of knowledge development
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