Adaptive Finite Element Analysis of the Anisotropic Biphasic Theory of Tissue-Equivalent Mechanics

Abstract

The nonlinear partial differential equations of the anisotropic biphasic theory of tissue-equivalent mechanics are solved with axial symmetry by an adaptive finite element system. The adaptive procedure operates within a method-of-lines framework using finite elements in space and backward difference software in time. Spatial meshes are automatically refined, coarsened, and relocated in response to error indications and material deformation. Problems with arbitrarily complex two-dimensional regions may be addressed. With meshes graded in high-error regions, the adaptive solutions have fewer degrees of freedom than solutions with comparable accuracy obtained on fixed quasi-uniform meshes. The adaptive software is used to address problems involving an isometric cell traction assay, where a cylindrical tissue equivalent is adhered at its end to fixed circular platens; a prototypical bioartificial artery; and a novel configuration that is intended as an initial step in a study to determine bioartificial arteries having optimal collagen and cell concentrations.     

Multiple effects of temperature,photoperiod and food quality on the performance of a pine sawfly

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DELIMITING SPAWNING AREAS OF WEAKFISH CYNOSCION REGALIS (FAMILY SCIAENIDAE) IN PAMLICO SOUND,NORTH CAROLINA USING PASSIVE HYDROACOUSTIC SURVEYS

ABSTRACT

Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong association (r = 0.78) between the log₁₀— transformed abundance of early-stage sciaenid-type eggs and maximum sound pressure levels, with the greatest numbers occurring at the inlet stations. These results suggest that passive hydroacoustic surveys can be used to delimit spawning areas for conservation and management purposes.     

Industrial microbiology of solar salt production

Solar salterns can be modeled as giant outdoor chemostats, much like a series of dams on a slow-moving river. Microorganisms and their products play an essential, but sometimes uncharacterized, role in salt production in these ponds, from seawater salinity up through NaCl saturation. They may physically affect the evaporation process and their by-products may chemically modify or bind with dissolved ions. Many solar salt facilities engage microbiologists to establish monitoring programs for analyses of nutrients, standing crop and associated biological variables in the ponds. Other solar salt companies engage microbiologists only when there are “crises” in the ponds that interfere with salt production. Journal of Industrial Microbiology & Biotechnology (2002) 28, 42–47 DOI: 10.1038/sj/jim/7000173 Received 20 May 2001/ Accepted in revised form 13 June 2001     

Population genetic structure, phylogeography and spawning philopatry in walleye (Stizostedion vitreum) from mitochondrial DNA control region sequences

Mitochondrial (mt) DNA control region sequences were used to test the genetic and phylogeographic structure of walleye Stizostedion vitreum populations at different geographical scales: among spawning sites, lake basins, lakes, and putative glacial refugia in the Great Lakes region. Sequencing 199 walleye revealed nucleotide substitutions and tandemly repeated sequences that varied in copy number, as well as in sequence composition, in 1200 bp of the mtDNA control region. Variable numbers of copies of an 11-bp tandem repeat showed no geographical patterning and were not used in further analyses. Substitutions in the other areas of the control region yielded 19 haplotypes, revealing phylogeographic structure and significant differences among glacial refugia, lakes, basins and some spawning sites. Differences among spawning populations were consistent with reduced gene flow, philopatry and possible natal homing. Analysis of spawning populations showed consistency of genotypic frequencies among years and between males and females, supporting philopatry in both sexes. The unglaciated plateau in southern Ohio, USA housed a very different haplotype that diverged prior to the Missouri, Mississippi and Atlantic glacial refugia types. Haplotypes from the three refugia colonized the Great Lakes after retreat of the Wisconsin glaciers, and their present distribution reflects the geography of their prior isolation and differential colonization. Populations that became associated with spawning localities appear to have diverged further due to philopatry, resulting in fine-scale phylogeographic structuring.     

ASSESSMENT OF IMPEDANCE MICROBIOLOGICAL METHOD FOR THE DETECTION OF ESCHERICHIA COLI IN FOODS

This study was conducted to determine the sensitivity and specificity of the impedance-based microbiological method for the detection of Escherichia coli in foods within 24 h of testing. A Malthus Microbiological Analyzer system (Malthus System V, Malthus Instruments Ltd., Bury, United Kingdom), and a modified Malthus Coliform Broth Medium (MCBM), and an incubation temperature of 44C were used. The sensitivity of the impedance method was determined by testing E. coli-negative food samples spiked with different concentrations of E. coli. The specificity of the method was determined by testing E. coli -negative food samples spiked with Klebsiella pneumoniae, Enterobacter cloacae and Pseudomonas aeruginosa. The test results were compared with those obtained by the Most Probable Number (MPN) method. Milk, milk products, raw and ready-to-eat meats, and vegetables were tested for the presence of E. coli by both methods. The sensitivity of the impedance method and the MPN method for the detection of foods containing 10¹ CFU/g was 100% and 84.4%, respectively. Both methods had a specificity of 100% for food samples spiked with 10¹ CFU/g E. coli. The specificity of the impedance and the MPN methods for the detection of E. coli in naturally contaminated milk and meat samples was 100% and 95.7% respectively. E. coli was detected in foods by the impedance method within 4–24 h of testing at a detection limit of 1 CFU/mL. These results demonstrate that the impedance method can be used as a rapid and sensitive method for the detection of E. coli in foods.     

Supercooling point plasticity during cold storage in the freeze‐tolerant sugarbeet root maggot Tetanops myopaeformis

Abstract The sugarbeet root maggot Tetanops myopaeformis (Röder) overwinters as a freeze‐tolerant third‐instar larva. Although most larvae are considered to overwinter for only 1 year, some may exhibit prolonged diapause in the field. In the laboratory, they can live for over 5 years using a combination of diapause and post‐diapause quiescence. In the present study, the cold survival strategies of these larvae during storage is investigated by measuring their supercooling points in combination with survival data. Supercooling points (SCPs) change significantly during storage, highlighted by a marked increase in the range of SCPs recorded, although the ability to tolerate freezing is not affected. Additionally, a freezing event ‘re‐focuses’ the SCPs of aged larvae to levels similar to those seen at diapause initiation. This change in SCPs is dependant not only on the initial freezing event, but also on the parameters of the incubation period between freezing events. Finally, the temperatures of larval overwintering microhabitats are monitored during the 2007–2008 boreal winter. The results indicate that, although overwintering larva are physiologically freeze‐tolerant, they may essentially be freeze avoidant during overwintering via microhabitat selection.     

Rapid and unexpected effects of piscivore introduction on trophic position and diet of perch (Perca flavescens) in lakes recovering from acidification and metal contamination

1. Yellow perch (Perca flavescens) are often the only surviving fish species in acidified lakes. We studied four lakes along a gradient of recovery from acidification and that had different food web complexities. All had abundant yellow perch, two had low piscivore abundance, one had a well‐established piscivore population and one was manipulated by introducing piscivorous smallmouth bass (Micropterus dolomieu). We hypothesised that there would be strong effects on perch abundance, behaviour and diet induced by the presence of piscivores. 2. In the manipulated lake, the bass reduced yellow perch abundance by 75% over a 2‐year period. Concomitantly, perch use of the pelagic habitat fell from 48 to 40%. 3. In contrast to findings from less disturbed systems, yellow perch in the littoral zone of the manipulated lake did not strongly shift from zooplankton to benthic food sources after the arrival of piscivores. Diet analysis using stable carbon isotopes revealed a strong continued reliance on zooplankton in all lakes, independent of the degree of piscivory. The failure to switch to benthos in the refuge area of the littoral zone is most likely related to the depauperate benthos communities in these formerly acidified lakes. 4. Yellow perch in lakes recovering from acidification face a considerable ecological challenge as the necessary switch to benthic diet is hindered by a low abundance of benthos. The arrival of piscivores in these recovering lakes imposes further restrictions on perch access to food items. We infer that future recovery of perch populations (and higher trophic levels) will have to be preceded by the re‐establishment of diverse benthic macroinvertebrate communities in these lakes.