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Laboratory Simulation (laboratory + simulation)
Selected AbstractsLaboratory simulation of impacts on aluminum foils of the Stardust spacecraft: Calibration of dust particle size from comet Wild-2METEORITICS & PLANETARY SCIENCE, Issue 2 2006A. T. Kearsley The ability of soft aluminum alloy to record hypervelocity impacts as bowl-shaped craters offers an opportunistic substrate for recognition of impacts by particles of a potentially wide size range. In contrast to impact surveys conducted on samples from low Earth orbit, the simple encounter geometry for Stardust and Wild-2, with a known and constant spacecraft-particle relative velocity and effective surface-perpendicular impact trajectories, permits closely comparable simulation in laboratory experiments. For a detailed calibration program, we have selected a suite of spherical glass projectiles of uniform density and hardness characteristics, with well-documented particle size range from 10 ,m to nearly 100 ,m. Light gas gun buckshot firings of these particles at approximately 6 km s,1 onto samples of the same foil as employed on Stardust have yielded large numbers of craters. Scanning electron microscopy of both projectiles and impact features has allowed construction of a calibration plot, showing a linear relationship between impacting particle size and impact crater diameter. The close match between our experimental conditions and the Stardust mission encounter parameters should provide another opportunity to measure particle size distributions and fluxes close to the nucleus of Wild-2, independent of the active impact detector instruments aboard the Stardust spacecraft. [source] Dynamic study of stacked packaging units by operational modal analysisPACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2010Carlos Bernad Abstract Laboratory simulation of transport vibration has been the object of many studies in recent years due to the financial implications of potential customer claims in respect of damage caused during product distribution and the need for tools for packaging optimization. Most of these works concentrate on the special nature of transport vibrations and how to reproduce them: Power Spectral Density (PSD) profiles related to road and truck characteristics, the non-stationary aspects of the environment, the non-Gaussian characteristics of the recorded vibrations and the best procedures for meaningful laboratory testing. In the present work, a different point of view is applied to the issue. The paper deals with the dynamics of different corrugated stacked packaging units by means of operational modal analysis and a 6 degrees of freedom multi-axis shaker table. The results show the already known non-linear behaviour of the paperboard containers and the natural frequencies and modes likely to appear in the packaging. The relevance of bending-like modes in relation to laboratory testing is discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Special series in MAPS for 2002: Laboratory simulations of circumstellar dust analogs: Expectations for comet nucleus encountersMETEORITICS & PLANETARY SCIENCE, Issue 1 2002Article first published online: 26 JAN 2010 [source] The role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment: findings of a laboratory simulationEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2005Tony Wells Abstract Long-term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate. Cubic rock samples (15 mm × 15 mm × 15 mm) were cut from larger rocks and subjected to time-compressed climatic conditions simulating the tropical wet season climate at the Ranger Uranium Mine in the Northern Territory, Australia. Fragmentation, moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying. To determine the impact of climatic variables, five climatic regimes were simulated, varying water application, temperature and drying. One of the climatic regimes reproduced observed temperature and moisture variability at the Ranger Uranium Mine, but over a compressed time scale. It is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades. While wetting and drying alone does produce changes to rock morphology, the incorporation of temperature variation further enhances weathering rates. Although little fragmentation occurred in experiments, significant changes to internal pore structure were observed, which could potentially enhance other weathering mechanisms. Moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching. Finally, experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy. The samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates. Copyright © 2005 John Wiley & Sons, Ltd. [source] The predatory impact of the freshwater invader Dikerogammarus villosus on native Gammarus pulex (Crustacea: Amphipoda); influences of differential microdistribution and food resourcesJOURNAL OF ZOOLOGY, Issue 1 2005Calum MacNeil Abstract Predation between invading and native species can produce patterns of exclusion and coexistence. Dikerogammarus villosus, a Ponto-Caspian amphipod species, has invaded many central European freshwaters in the past decade, replacing native Gammarus amphipod species. For instance, the arrival of D. villosus in Holland has been accompanied by the decline of Gammarus duebeni and G. tigrinus populations within invaded systems. This study examined what may happen when D. villosus eventually encounters native Dutch populations of Gammarus pulex, and how factors such as microhabitat and food resource availability could contribute to a future species replacement or coexistence. A laboratory simulation of a lake/pooled area of river indicated that G. pulex and D. villosus differed in distribution within the same habitat, and showed that although the distribution of the native differed in the presence of the invader, the presence of the native had no effect on the distribution of the invader. Gammarus pulex suffered severe intraguild predation (IGP) from D. villosus in mixed species treatments with no reciprocal predation of D. villosus by G. pulex. This IGP occurred regardless of whether no alternative food resource was available (91% of the G. pulex population eliminated after 7 days), or alternative foods/prey were available to excess, such as leaf material (85%), chironomids (77%) or fish food flakes (74%). We conclude that although differential microdistribution of the two species could promote coexistence, the presence of alternative foods/prey resources, merely slow the rate of IGP and replacement of the native by the invader. Our study joins one of an increasing number emphasizing the potential damaging impacts of D. villosus on native communities. [source] On the influence of trigger level in distribution vibration surveysPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2009Vincent Rouillard Abstract This paper follows on from recently published research that examined the effects of recording parameters on the outcomes of distribution vibration surveys. Whereas the previous research focused on the effects of the sampling period at which sub-records of the process are captured, this paper deals with another often-used recording parameter, namely, the vibration level trigger. The paper describes the development of a software tool that was designed specifically to study the influence of various sampling parameters on continuously recorded vibration data. This software tool was used to undertake a thorough statistical analysis on a vibration record set consisting of continuously sampled data measured from a wide variety of vehicle types and routes. The paper shows that the outcomes of vibration surveys are very sensitive to the trigger level and can produce highly distorted results by introducing a bias that nearly always overestimates the overall vibration levels. This is reflected in estimates of common descriptors of random vibration processes such as the average power spectral density (PSD), the peak-hold PSD and the overall root-mean-square values. The main outcome of this analysis is the formulation of a correction method based on relationships between the true mean and peak-hold PSDs and estimates from sampled data. The effect and significance of the proposed correction procedure is demonstrated, especially in the context of laboratory simulation of distribution vibrations. The paper concludes by making specific recommendations for configuring high-capacity field data recorders and applying correction strategies to ensure that vibration surveys yield statistically sound results. Copyright © 2009 John Wiley & Sons, Ltd. [source] Solifluction processes on permafrost and non-permafrost slopes: results of a large-scale laboratory simulationPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2008Charles Harris Abstract We present results of full-scale physical modelling of solifluction in two thermally defined environments: (a) seasonal frost penetration but no permafrost, and (b) a seasonally thawed active layer above cold permafrost. Modelling was undertaken at the Laboratoire M2C, Université de Caen-Basse Normandie, Centre National de la Recherche Scientifique, France. Two geometrically similar slope models were constructed using natural frost-susceptible test soil. In Model 1 water was supplied via a basal sand layer during freezing. In Model 2 the basal sand layer contained refrigerated copper tubing that maintained a permafrost table. Soil freezing was from the top down in Model 1 (one-sided freezing) but from the top down and bottom up (two-sided freezing) in Model 2. Thawing occurred from the top down as a result of positive air temperatures. Ice segregation in Model 1 decreased with depth, but in Model 2, simulated rainfall led to summer frost heave associated with ice segregation at the permafrost table, and subsequent two-sided freezing increased basal ice contents further. Thaw consolidation in Model 1 decreased with depth, but in Model 2 was greatest in the ice-rich basal layer. Soil shear strain occurred during thaw consolidation and was accompanied by raised pore water pressures. Displacement profiles showed decreasing movement rates with depth in Model 1 (one-sided freezing) but ,plug-like' displacements of the active layer over a shearing basal zone in Model 2 (two-sided active layer freezing). Volumetric transport rates were approximately 2.8 times higher for a given rate of surface movement in the permafrost model compared with the non-permafrost model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Involutions resulting from annual freeze,thaw cycles: a laboratory simulation based on observations in northeastern JapanPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2007Yoshiko Ogino Abstract A pilot laboratory experiment using a reversed two-layer soil model simulated small-scale involutions formed in a seasonal frost environment during the last glacial period. At the modelled site, the interface between the upper aeolian sandy loam and the lower volcanic pumice constitutes small-scale involutions that display upward-extending tapered projections and downward-extending round hollows. Two scale-reduced laboratory models were subjected to three accelerated annual freeze,thaw cycles with monitoring of frost heave, soil temperature, moisture and pressure. Ice segregation near the layer interface induces upheaving of coarse pumice grains on freezing and earlier settlement of mobilised loam on thawing, resulting in deformation of the interface. A reconstructed 3-D interface displays mounds and depressions with a diameter of 15,20,cm and a height increasing with freeze, thaw alternations. The experimental results imply that the repetition of differential heave and soft-loam settlement promotes decimetre-scale involutions in near-saturated soils subject to deep seasonal frost penetration. Copyright © 2007 John Wiley & Sons, Ltd. [source] WARNING DISPLAYS IN SPINY ANIMALS: ONE (MORE) EVOLUTIONARY ROUTE TO APOSEMATISMEVOLUTION, Issue 12 2005Michael P. Speed Abstract To date, theoretical or laboratory simulations of aposematic evolution in prey animals have focused narrowly on internally stored chemical defense as the source of unprofitability and ignore aposematic advertisement of physical defenses such as spines (and defensive hairs, claws, etc.). This has occurred even though aposematism in spiny animals has been recognized since the 19th century. In this paper we present the first detailed theoretical consideration of aposematism in spiny animals, focusing on questions of initial evolution, costs of display, and coevolution of displays with defenses. Using an individual-based evolutionary model, we found that spines (or similar physical defenses) can easily evolve without aposematism, but when spines do evolve, aposematic displays can also easily evolve if they help to make the prey animal distinctive and if they draw attention to the physical threat. When aposematic displays evolve, they cause reduced investment in costly spines, so that, in addition to signaling unprofitability, aposematic display may enhance the cost-effectiveness of antipredator defenses (one exception to this conclusion is if the display is itself as costly as the defense). For animals with stinging spines, combining physical and chemical defense, the evolution of aposematic display may lead to reduced investment in the toxin compared to the spine. This occurs because spines act as both secondary (repellent) defenses and as primary defenses (their own visible, honest advertisement), whereas internally stored toxins only (generally) act as repellent secondary defenses. We argue that conspicuous aposematism in spines functions as an attention-getting mechanism, whereas conspicuous aposematic display in purely toxic animals may be explained by signal reliability arguments. Finally, one (more) route by which aposematism may initially evolve is by spiny rather than purely chemically defended species, spreading to species with other forms of secondary defense as the signal becomes common. [source] Pathogen safety of manufacturing processes for biological products: special emphasis on KOGENATE® BayerHAEMOPHILIA, Issue 2002D. C. Lee Summary., Manufacturers of human therapeutic proteins derived from biological sources continuously strive to improve the pathogen safety profiles of these products. Efforts to improve pathogen safety margins for these biological products are directed towards several areas within the manufacturing processes including: (a) sourcing and screening of raw materials (b) determining the potential for manufacturing processes to reduce pathogen titres, and (c) incorporating methods designed specifically to remove or inactivate contaminating pathogens. Methods that could potentially reduce pathogen titres are a major focus for many manufacturers. In general, these methods are grouped into two categories, pathogen clearance and pathogen inactivation. Assessments are performed on small-scale, laboratory simulations of the manufacturing process of interest that are spiked with a known amount of a selected pathogen. These studies provide estimates of the potential for a process step to remove or inactivate a particular pathogen. There are several pathogen clearance/inactivation methods that are inherent in manufacturing processes, however, some methods are intentionally incorporated into manufacturing for the sole purpose of reducing putative pathogen titres. Not only are well-known pathogens such as viruses targeted, but also suspected pathogens such as those associated with the transmissible spongiform encephalopathies (TSEs). The production processes for the isolation of several biological products, including recombinant KOGENATE® Bayer (Kogenate®FS), have been evaluated for the ability to reduce pathogen titres and/or have been designed to incorporate methods for reducing potential pathogen safety risks. Several processing steps with the potential to reduce pathogen titres have been identified. [source] | ||||||||||