Dissertations / Theses on the topic 'Regrowth'
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Sidhu, Jatinder. "Pathogen regrowth in composted biosolids." Thesis, Sidhu, Jatinder (2000) Pathogen regrowth in composted biosolids. PhD thesis, Murdoch University, 2000. https://researchrepository.murdoch.edu.au/id/eprint/52513/.
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Composting is commonly used as an effective means of stabilising wastewater biosolids and reducing pathogen concentrations to very low levels. However, under certain conditions enteric bacteria such as Salmonella and E. coli can regrow in previously composted biosolids and compost based soil amendments. Regrowth of Salmonella in composted biosolids can pose a potential threat to public health.
Pathogen regrowth in composted biosolids is affected by a number of factors, such as moisture content, bio-available nutrients, temperature and indigenous microorganisms. However, assessment of the bio-safety of composted biosolids on the basis of these parameters is very difficult and unreliable. Moreover regrowth of
pathogens in composted biosolids is unpredictable. The main aim of this study was to find out whether regrowth of pathogens in composted biosolids could be prevented or controlled. To accomplish this goal, the effect of composting and storage on survival and regrowth of Salmonella typhimurium was investigated. The role of bio-available nutrients and indigenous microorganisms in suppression of Salmonella regrowth was investigated in detail.
The results of this study suggest that a full-scale windrow composting process carried out in accordance with recommended guidelines (ARMCANZ) is effective in reducing Salmonella concentrations to below detection limit. However, Salmonella regrowth in stored biosolids after 26 weeks, coinciding with a rainfall after a dry spell was observed. This suggests that Salmonella can survive the composting process in low numbers and regrowth can take place in the presence of favourable growth conditions.
A pathogen regrowth potential test using antibiotic-resistant S. typhimurium was developed to evaluate the pathogen regrowth potential of composted biosolids. The regrowth potential test was found to be a very useful tool for laboratory investigation. However, further validation of the pathogen regrowth potential test is required, prior to its routine use for monitoring composted biosolids.
The antagonistic activity of indigenous microorganisms was found to be the most significant factor in suppression of S. typhimuriwn growth in composted biosolids. Rapid growth of seeded S. typhimurium, with a maximum population density of more than 108 MPN g-1, was observed in sterilised biosolids. Conversely, growth of S.typhimurium was suppressed in non-sterilised compost with a maximum population density of less than 103 MPN g-1. The inactivation rate of Salmonella was also found to be significantly greater in non-sterilised compost as compared to sterilised compost. Maximum inhibition of Salmonella growth was observed in biosolids that had been composting for two weeks.
The specific growth rate of Salmonella was found to have a strong negative correlation (-0.85) with the maturity of the compost. However, a decline in bioavailable nutrients was not sufficient to prevent regrowth of Salmonella in composted biosolids stored for two years. The role of bio-available nutrients (age. of compost) was non significant (P<_ 0.05) as compared to the role of indigenous microorganisms in inhibition of Salmonella regrowth.
The antagonistic effect of indigenous microorganisms towards Salmonella declined with the storage of compost. A strong negative correlation (-0.85) between the Salmonella inactivation rate and age of compost was observed. Salmonella inactivation rate was also found to be seven times higher in biosolids composting for two weeks as compared to compost stored for two years. Consequently, it can be concluded that all composted biosolids had a Salmonella regrowth potential. However, the presence of biologically active indigenous microflora significantly reduced this regrowth potential. As a result of a decline in the antagonistic activity of indigenous microflora with storage, a longer Salmonella survival time could be expected in stored compost as compared to freshly composted biosolids. Consequently, long term storage of compost is not recommended as this may lead to an increased pathogen regrowth potential and longer survival time.
The dilution-plate procedure adopted in this study showed that bacterial concentrations in compost declined by two log10 during storage for two years, whereas population of actinomycetes and fungi increased during the same period. Indigenous bacteria and actinomycetes isolated from composted biosolids of different maturity were screened for their role in the suppression of Salmonella regrowth. Some of the indigenous bacteria were found to suppress Salmonella growth by one to two log10 when Salmonella was seeded into stationary phase culture of indigenous bacteria. None of the isolated indigenous microorganisms produced secondary metabolites active against Salmonella.
Somatic Salmonella (SS) phages were found to survive in composted biosolids for up to two years. Growth of Salmonella was suppressed by one to two log10 in the presence of SS phages. It is possible that Salmonella growth suppression in compost is due to an intense competition for limited nutrients in the presence of biologically active indigenous microorganisms, with some anti-Salmonella activity from SS phages.
The results of this study suggest that prevention of pathogen regrowth in composted biosolids is difficult due to the availability of nutrients and limited control over environmental factors which influence the antagonistic activity of indigenous microorganisms. However, regrowth of pathogens in composted biosolids can be prevented if a biologically active population of indigenous microorganisms is maintained. It is possible that by preventing rapid drying of compost during maturation biological activity of indigenous microorganisms can be maintained. Covering of compost piles during maturation can preserve moisture and the effect of preserving moisture on the antagonistic activity of indigenous microorganisms should be investigated. Research should be carried out further to identify the indigenous microorganisms which suppress Salmonella regrowth. Additional research work should also be carried out to determine the mechanism of growth suppression. Resolving this issue could provide a better understanding of the antagonistic effect of indigenous microflora towards pathogenic bacteria in composted biosolids.
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Johnson, D. W., S. E. Smith, and A. K. Dobrenz. "Improved Regrowth Salt Tolerance in Alfalfa." College of Agriculture, University of Arizona (Tucson, AZ), 1989. http://hdl.handle.net/10150/201009.
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Smith, Martin Peter. "Molecular beam epitaxial regrowth : technology and applications." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621068.
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Mazzoleni, Stefano. "Post-disturbance regrowth patterns in Mediterranean macchia." Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU546361.
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Traditionally, the southern botanists, facing much richer floras, dedicated their attention more to the disciplines of taxonomy and phytosociology. This created a detailed and extensive floristic knowledge on plant geographical distribution, poorly supported by an understanding of dynamic processes. This project was aimed to fill as much as possible of this lack of ecological approach in Mediterranean vegetation studies in Italy. The study area was located in the Campania region, southern Italy. The thesis programme was conceived as a series of investigations, starting with surveys and gradually narrowing down to specific experiments and analytical investigations. Site history is discussed as a key factor for the understanding of the regional variation of vegetation. Multivariate methods (Cluster Analysis, Principal Component Analysis) were used to analyse the vegetation composition data. They suggested that most observed changes of vegetation could reflect successional and degradation gradients rather than environmental differences. This view was supported by historical evidences of past-disturbance and dynamic processes, by study of ancient manuscripts, maps, paintings and photographs and by demographical data. The results of observations of both natural and experimental fires showed high ability to recover by vegetative sprouting and seed germination. Most fires were followed by 100&'37 survival with few exceptions in the case of the dry winter 1989 and of very hot fires. In these cases, Erica arborea was the most sensitive species. In contrast to fire, cutting depressed regrowth at one of the study sites located on most exposed and dry conditions. Recolonization after complete vegetation removal showed a different succession with an initial dominance of Dittrichia viscosa, later suppressed by Cistus spp. and Ampelodesmos mauritanicus. E.arborea did not recolonize after this kind of disturbance.
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Mann, Cindy Mary, of Western Sydney Hawkesbury University, and Faculty of Science and Technology. "Salmonella regrowth potential of two sewage sludge products." THESIS_FST_XXX_Mann_C.xml, 1997. http://handle.uws.edu.au:8081/1959.7/361.
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The disposal of sewage sludge is becoming an ever-increasing problem and a range of re-use options are being developed, with traditional composting and advanced alkaline stabilisation emerging as priority re-use alternatives in NSW. However, concerns have been raised regarding the dissemination of sludge related pathogens in the environment. Salmonella spp pose the greatest risk since they have the ability to proliferate in the absence of human and animal hosts. Composting processes eliminate salmonellae from sludge, but the opportunity for post-processing recontamination is considerable. This project examined the significance of post-processing recontamination of Salmonella broughton, introduced into composted sludge and N-Virosoil. In compost, inactivation rates of S. broughton showed an inverse relationship with simulated processing temperatures, with competitive exclusion by autocthonous compost flora thought to be the major mechanism of inhibition. S. broughton numbers were reduced to below the limits of detection after several weeks. S. broughton inactivation was also assessed in processed N-Virosoil and was found to be more immediate. It was concluded that both compost and N.Virosoil products have a low potential to support the regrowth of Salmonella spp.Master of Science (Hons)(Environmental Science)
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Mann, C. M. "Salmonella regrowth potential of two sewage sludge products /." View thesis View thesis, 1997. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030521.100917/index.html.
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Thesis (M.Sc. (Hons)) - University of Western Sydney, Hawkesbury."A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Hons.) (Environmental Science" --tp.
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Bailey, Philip. "Exploring remotely sensed shadow in Amazonian regrowth forests." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242720.
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Quierin, Marcus Alfred. "Gated resonant tunnelling diodes fabricated by MBE regrowth." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627241.
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Peters, Carrie Elizabeth. "Modification of interstitial fluid pressure in the murine carcinoma NT." Thesis, Brunel University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385182.
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Dantas, Mario. "Studies on succession in cleared areas of Amazonian rain forest." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253330.
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Gul-e-Hina, Ms. "Regrowth of bacterial pathogen indicators in electro- dewatered biosolids." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107904.
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Land application of biosolids from activated sludge wastewater treatment plant (WWTP) is an attractive disposal solution. However, to be land applied in the US and Canada, biosolids need to meet specific pathogen loads regulations at the time of land application (i.e., not immediately after treatment). This study examined bacterial regrowth potential after electro-dewatering of biosolids. During a 8-min typical electro-dewatering treatment performed in the laboratory or a control heat treatment, Escherichia coli and fecal coliform (FC) counts were reduced to below the detection limit. After treatment, the extent of E. coli and FC regrowth was assessed by incubating the biosolids in aerobic or anaerobic conditions. After aerobic incubation, FC and E. coli counts stabilized between 107-109 MPN/g-dry solids in all biosolids samples irrespective of treatments (electro-dewatering, heat-treatment and no treatment) despite different levels of pH and dryness. Total aerobic counts also stabilized between 107-109 CFU/g-dry solids after four days of incubation. Finally, stable FC and E. coli counts at the end of incubation of samples prepared by belt filter press during winter were 1 log lower than in samples prepared by centrifuge press during the summer. Although similar trends about the effects of dewatering processes were reported in the literature, it is not be possible to conclude because seasonal factors are confounded with process factors. After anaerobic incubation, E. coli and FC counts in electro-dewatered biosolids stabilized 1 log lower than their respective counts in heat-treated or not treated biosolids (107-108 vs 108-109 MPN/g-dry solids, respectively). This difference was not changed when electro-dewatering filtrate was added back into the electro-dewatered biosolids. At WWTP, biosolids are typically stored as large piles. It is therefore likely that a major portion of piles is anaerobic, and that storage (hence regrowth) takes place under anaerobic condition. This study suggests that the electro-dewatered biosolids would exhibit a lower level of regrowth than other biosolids. Microbial counts observed in this study would not allow land application of these biosolids after 7-day storage because the lowest counts observed for electro-dewatered biosolids under anaerobic conditions were just above the requirements for the US-EPA Class B (FC counts above106 MPN/g-dry solids). However, these results suggest that this technology could be improved such that biosolids could meet land application regulations even after extended storage periods.L'épandage de biosolides provenant des usines de traitement d'eaux usées par boues activées est une solution d'élimination intéressante. Toutefois, pour être épandues aux États-Unis et au Canada, les biosolides doivent répondre à des réglementations visant à limiter la quantité d'organismes pathogènes au moment de l'épandage (et non pas immédiatement après le traitement). Cette étude a examiné le potentiel de repousse bactérienne après électro-déshydratation des biosolides. Lors d'un traitement d'électro-déshydratation typique de 8 minutes effectué dans un laboratoire ou un traitement thermique de contrôle, le compte total d'Escherichia coli et de coliformes fécaux (CF) étaient en deca de la limite de détection. Après le traitement, l'étendue de la repousse de E. coli et de CF a été évaluée par incubation des biosolides dans des conditions aérobies ou anaérobies.Après une incubation aérobie, les comptes de CF et E. coli se sont stabilisés entre 107 à 109 NPP / g matières solides sèches dans tous les échantillons de biosolides, indépendamment des traitements (électro-déshydratation, traitement thermique et aucun traitement), malgré les différents niveaux de pH et de sécheresse. Les comptes aérobies totaux se sont également stabilisé entre 107 à 109 UFC / g de matières solides sèches, après quatre jours d'incubation. Enfin, le compte de FC et E. coli à la fin de l'incubation des échantillons préparés par des presses à filtres à bande au cours de l'hiver ont été 1 log inférieure à celle des échantillons préparés par des presses centrifugeuses pendant l'été. Bien que des tendances similaires sur les effets des procédés de déshydratation aient été rapportées dans la littérature, il n'est pas possible de conclure puisque les facteurs saisonniers sont confondus avec les facteurs de procédés. Après une incubation anaérobie, les comptes de E. coli et de CF dans les biosolides électro-déshydratées étaient 1 log inférieure aux compte respectif dans les biosolides traités thermiquement ou non traités (107-108 vs 108-109 NPP / g matières solides sèches, respectivement). Cette différence n'a pas été modifiée lorsque le filtrat d'électro-déshydratation a été rajouté dans le biosolides électro-déshydratées. A l'usine de traitement des eaux usées, les biosolides sont généralement stockés sous forme de monticule. Il est donc probable que la majeure partie des monticules soit anaérobie, et que le stockage (et donc la repousse) se déroule dans des conditions anaérobies. Cette étude suggère que les biosolides électro-déshydratées présentent un niveau inférieur de repousse des indicateurs pathogènes bactériens que d'autres biosolides. L'énumération microbienne observée dans cette étude ne permettrait pas l'épandage de ces biosolides après 7 jours d'entreposage, parce que même les énumérations les plus basses demeurent au-dessus des exigences pour le US-EPA classe B (FC > 106 NPP / g matières solides sèches). Toutefois, ces résultats suggèrent que cette technologie pourrait être améliorée de telle sorte que les biosolides peuvent respecter les règlements d'application sur les terres arables, même après des périodes d'entreposage étendues.
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Chen, Bosi. "Spectrum Regrowth for OFDM-based LTE and WIMAX Systems." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/601.
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An abstract of the thesis of Bosi Chen for the Master of Science in Electrical and Computer Engineering presented Aug 1st, 2012. Title: Spectrum Regrowth for OFDM-based LTE and WiMAX Systems. In OFDM-based (Orthogonal Frequency Dimension Multiplexing) LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access) Systems, one of the critical components is the RF power amplifier. With current technologies, RF power amplifiers are not perfectly linear. The nonlinearity of an RF power amplifier is one of the main concerns in RF power amplifier design. The nonlinearity control is described by the out-of-band power emission levels, and the nonlinearity of an RF power amplifier is usually described by IP3 (the third-order intercept point). However, there is need of a clear relationship or expression between the out-of-band power emission level and IP3 for LTE and WiMAX Systems, which helps the RF designers to choose components. This thesis presents the analysis of the nonlinear effect of an RF amplifier in LTE and WiMAX Systems, and the derivation of the expressions for the estimated out-of-band emission levels for LTE and WiMAX signals in terms of IP3 and the power level of the signal. The result will be helpful for RF engineers in the design and test of RF power amplifiers in LTE and WiMAX Systems.
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Boggess, Chadwick D. "Optimization of Growth Parameters for Algal Regrowth Potential Experiments." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1234.
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Water cost is one of the key deterrents in making algal biofuels a feasible alternative to traditional petroleum fuels. Research into recycling of algal media was conducted in a laboratory setting at the California Polytechnic State University in San Luis Obispo. A growth assay was created to allow for algal cultures, specifically Ward’s Chlorella sp., to proliferate in sealed culture vessels. Bold’s Basal Medium (BBM) was selected as the media due to its extensive use with freshwater algal strains. However, this medium can limit algal growth through nutrient limitation and it became necessary to augment the original recipe. 50mM of sodium bicarbonate was added to the media in order to buffer the purging of 100% CO2 into the culture vessel. The resultant pH of the CO2 saturated media was 6.25. The elemental? composition of Chlorella vulgaris was compared with the nutrient content of BBM to estimate possible nutrient limitations which could occur throughout growth (Oh Hama, 1988). From this analysis, the nitrogen and phosphorus concentration in BBM was augmented by a factor of three (BBM3N3P). Further, vitamins, specifically cyanocobalamin, thiamine HCL, and biotin, were incorporated after conducting a comparison growth study with BBM 3N3P. The average maximum specific growth rates for the normal BBM and for the vitamin-enhanced BBM were 0.689 +/- 0.0818 and 0.887 +/- 0.1901 (mean +/- std. deviation) per day, respectively. This difference was proved significant by a t-test with a p-value equal to 0.041. A standardized methodology for conducting a regrowth potential experiment was outlined by the research. One phase of this methodology included reintroduction of nutrients consumed during the first round of growth. Prior to continuing with this methodology the effect of supplementing trace metals and micronutrients into the culture was investigated. At a p-value of 0.0956, there was no significant difference between BBM 3N3P + vitamins and the same media with eight times the trace metal and micronutrient concentration. This allowed for up to seven rounds of regrowth with no inhibition caused from the restoration of these nutrients. A final regrowth was conducted on BBM 3N3P + vitamins + 50 mM bicarbonate. A significant difference existed between both the Round 1 and Round 2 cultures, as well as between the Round 2 cultures and their respective controls. This signified the possible release of allelochemicals by the Chlorella sp.. A preliminary investigation into the possible use of anaerobic digester effluent as a primary source of nutrients for algal cultures was also conducted. The digestate (diluted 50% v/v with a saline make-up) grew significantly faster than the controls (p-value<0.001). Further, after the introduction of trace metals and micronutrients the digestate columns outlived the control columns increasing the feasibility of using digestate to supplemental algal cultures.
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Elving, Josefine. "Pathogen inactivation and regrowth in organic waste during biological treatment /." SLU : Dept. of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, 2009. http://epsilon.slu.se/11652700.pdf.
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Selsby, Joshua. "Does heat treatment facilitate muscle regrowth following hind limb immobilization?" [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012042.
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Evans, R. J. "Electronic properties of molecular beam epitaxy structures prepared by regrowth." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598882.
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This dissertation is concerned with the fabrication and physics of Molecular Beam Epitaxy (MBE) regrown semiconductor devices. I use the term regrown to refer to a structure which has been fabricated by MBE growth over a surface which has been ex-situ patterned. The structures presented in this dissertation can be subdivided into two broad categories: the narrow facet channels and the patterned back-gates. The narrow facet channels form part of a new class of devices, where the amphoteric nature of silicon dopant in the AlGaAs lattice is used to create lateral confinement. Growth of a GaAs A1GaAs heterostructure over a (311)A substrate, which is etched to expose a narrow (100) facet, results in the formation of a narrow two dimensional electron gas (2DEG) on the facet which is interspersed between two, two dimensional hole gases (2DHGs). The transport characteristics of the narrow 2DEG can be modulated by applying voltage to the adjacent hole gases, i.e. biasing either or both of the two dimensional p-n junctions formed between the 2DEG and 2DHGs. The actual width of the electron channel was found to be considerably smaller that the lithographic facet width. Theoretical modelling showed that this was a result of the fabrication and growth of the sample and not the electro-statics of the system. The inverse structure of a narrow 2DHG interspersed between two 2DHGs was also fabricated. The transport through the narrow 2DHG could be modulated in a similar manner. The patterned back-gated structures are the simplest illustration of the fabrication technique and are discussed first in the dissertation. The patterned back-gate is formed as islands of n+ GaAs on an undoped GaAs substrate. Subsequently grown continuous layers are therefore guided in three dimensions over a wafer surface with regions of differing semiconductor compositions. This is a wafer scale fabrication technique, which completely dismisses the need for complicated lithography. The patterned back-gate was used to distinguish between the presence of an extended state formed between two 2DEGs and a second subband formed in one of the 2DEGs. The second subband was then used as a probe to characterise the regrowth interface. The series of back-gated long split gates showed quantisation plateaux illustrating the high quality of the samples fabricated using the regrowth technique.
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Ahmed, Ataf. "Regrowth applied to N-type modulation-doped Si/SiGe heterostructures." Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/275270.
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Conventional silicon/silicon-germanium (Si/SiGe) two dimensional electron gas (2DEG) heterostructures formed by modulation-doping, require a SiGe virtual substrate grown on a Si substrate. Active heterolayers are grown on this virtual substrate, usually in a single step process. This dissertation describes the growth of Si/SiGe wafers in a two stage process. The virtual substrate is removed from growth system and is cleaned ex-situ. The wafer is then returned to the growth chamber for the deposition of the active heterolayers, introducing a regrowth interface. The successful incorporation of this regrowth interface is shown along with an investigation into the effects of the interface on transport properties. A temperature gradient across the substrate heater, in the growth system that has been used, leads to a variation in the wafer structure. One useful consequence of this thermal gradient is that it is possible to use a single wafer to study the effect on the transport properties as a function of the Ge fraction, dopant concentration, quantum well depth and width. The introduction of arsine as an n-type dopant into the growth chamber results in all subsequent material being n-type due to surface segregation. An ex-situ ion implantation technique has been developed which can be used to form a modulation-doped region in an inverted Si/SiGe 2DEG. Forming a doped region ex-situ circumvents the need to introduce a dopant species into the growth system, preventing surface segregation. Low temperature measurements of devices fabricated using this technique are presented, showing that it is possible to form inverted Si/SiGe 2DEGs and that ex-situ ion implantation can be used to form dopant supply regions. This technique is subsequently developed to show selective area ex-situ ion implantation technique. The successful production of samples shows that selective doping in exact areas of a wafer during growth is feasible and this has important consequences in device production.
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Wang, Hong. "Critical factors controlling regrowth of opportunistic pathogens in premise plumbing." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19305.
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Opportunistic pathogens (e.g., Legionella pneumophila, Mycobacterium avium complex, Acanthamoeba polyphaga, Pseudomonas aeruginosa) residing in human-made water systems, particularly premise plumbing, are now the primary source of water-borne disease in developed countries. The prevention and control of opportunistic pathogens is a new challenge in premise plumbing due to the limited knowledge concerning the factors driving their occurrence and regrowth mechanisms, and also the complexity of premise plumbing conditions. The goal of this study is to identify key factors governing occurrence of opportunistic pathogens in drinking water distribution systems, particularly premise plumbing, via field investigations and lab-scale experiments. A molecular survey of three opportunistic pathogens (L. pneumophila, M. avium, P. aeruginosa), related groups (Legionella and mycobacteria) and two amoeba hosts (Acanthamoeba spp. and Hartmanella vermiformis) was performed in two real-word chloraminated drinking water distribution systems using quantitative polymerase chain reaction (q-PCR). A high occurrence of Legionella (" 69.0%) and mycobacteria (100%), lower occurrence of L. pneumophila (" 20%) and M. avium (" 33.3%), and rare detection of Pseudomonas aeruginosa (" 13.3%) was observed in both systems. Hartmanella vermiformis was more prevalent than Acanthamoeba. Three-minute flushing resulted in reduced gene copies of Legionella, mycobacteria, H. vermiformis and 16S rRNA genes (P<0.05) and distinct microbial community structure in postflushing water, implying strong regrowth potential of opportunistic pathogens in premise pluming.
In order to examine the influence of pipe material, disinfectant type, and water age on occurrence and persistence of the target microorganisms, triplicate simulated distribution systems (SDSs) comparing iron, cement and PVC pipe materials were fed either chlorinated or chloraminated tap water, and were sampled at water ages ranging from 1d to 5.7d. q-PCR quantification of target microorganisms in both biofilm and bulk water revealed that Legionella, mycobacteria, P. aeruginosa and both amoebas naturally colonized the six SDSs, but L. pneumophila and M. avium were not detected. Disinfectant type and dose have the strongest influence on the microbiota. Disinfectant decay was noted with water age, particularly in chloraminated SDSs (due to nitrification), generally resulting in increased microbial detection frequencies and densities with water age. Influence of pipe material became apparent at water ages corresponding to low disinfectant residual.
Natural colonization of Legionella spp., Mycobacterium spp., Acanthamoeba spp., H. vermiformis and M. avium was also observed in biofilms from five annular reactors, which were used to investigate effects of prior granular activated carbon (GAC) biofiltration and disinfectant type (chlorine, chloramine) on opportunistic pathogens under premise plumbing conditions. GAC pre-treatment effectively reduced total organic carbon (TOC). In most cases, total bacteria and opportunistic pathogens were higher in undisinfected annular reactors, but the levels were not proportional to the level of GAC pre-treatment/TOC. Chlorine was more effective for controlling mycobacteria and Acanthamoeba, whereas chloramine was more effective for controlling Legionella. Both chlorine and chloramine effectively reduced M. avium and H. vermiformis numbers. Pyrosequencing of 16S rRNA genes in biofilms revealed a significant effect of GAC pre-treatment and disinfectant type on the microbial community structure.
Overall, the study provides insights to critical factors triggering proliferation of opportunistic pathogens in drinking water systems. Knowledge gained from this study can assist in formulating practical guidance for drinking water utilities and water consumers in terms of opportunistic pathogen prevention and control. "
Ph. D.
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spence, william h. "REGROWTH OF CHLORELLA SOROKINIANA ON RECYCLED MEDIA WITH REPLENISHED NUTRIENTS." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1644.
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Growth media recycling during algae cultivation is necessary to increase the efficiency and reduce the cost of biofuel production from algae feedstocks. Without recycling media, the cost of algae based biofuel production would be prohibitively high and large scale algae based biofuel production would not be economically viable. The ratio of media recycled to media wasted assumed for algae farms is generally calculated to maintain salt concentrations below growth inhibitory levels, ignoring the influence of secondary metabolites which might decrease productivity. Secondary metabolites, which include allelopathic or auto-inhibitory biological contaminants, might lead to the accumulation of growth-inhibiting compounds in recycled media used in algae production.
Chlorella sorokiniana (strain DOE1412) was a leading algae biofuel feedstock candidate and has not previously been evaluated for inhibitor production. To test the effects of water recycling on the growth of DOE1412, media was recycled through multiple rounds of algae cultivation. DOE1412 was grown in modified BG11 culture media until reaching the end of linear growth phase, at which point the biomass was removed, nutrients replenished to their initial concentrations, and the recycled culture media used for a subsequent round of growth. The culture media was recycled through five rounds of growth with cultures grown on recycled media compared to controls grown on freshly prepared growth media. Biomass density was monitored via optical density and the specific and productivity growth rates were used to quantify the extent of inhibition. Exploratory work was performed with the goal of identifying potential inhibitory substances produced by DOE1412 during cultivation. Samples of recycled media were analyzed for polyunsaturated fatty acids which have been demonstrated to be inhibitory. The carbohydrates content of used media was analyzed to assess the amount of organic materials shed by DOE1412 into recycled media during growth.
The log phase growth rate (day-1) of DOE1412 was inhibited by 3±2%, 8±1%, 10±2%, and 18.6±0.9% when grown in media recycled 1-4 times, respectively, with a 99% level of confidence that inhibition was observed in each round of regrowth. The productivity growth rate (OD750/day) of DOE1412 was not inhibited in media recycled 1-3 times. The productivity growth rate of DOE1412 was inhibited by 13±3% when grown in media recycled 4 times with a 99% level of confidence that inhibition was observed.
Zinc was found to accumulate in the recycled media to potentially toxic levels (>0.09 mg/L), therefore it is uncertain if the observed inhibition was due to an accumulation of inhibitory secondary metabolites or the accumulation of zinc.
Two inhibitory polyunsaturated acids, linoleic and linolenic acid, were identified in media recycled 4 times. The carbohydrate content of recycled media fluctuated between 8-10% of total fixed carbon in media recycled 1-3 times and increased to 18% in media recycled 4 times. However, changes observed in media recycled 4 times may have been due to improper storage of used media.
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Persson, Frank. "Biofilms in drinking water treatment : biofiltration, membrane fouling, and regrowth potential /." Go̊teborg [Sweden] : Dept. of Cell and Molecular Biology, Microbiology [Göteborg University], 2005. http://www.loc.gov/catdir/toc/fy0802/2006421401.html.
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Stordal, Britta Kristina. "Regrowth resistance in platinum-drug resistant small cell lung cancer cells." Bill Walsh Cancer Research Laboratories, Royal North Shore Hospital and The University of Sydney, 2007. http://hdl.handle.net/2123/2467.
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Doctor of Philosophy (PhD)The H69CIS200 cisplatin-resistant and H69OX400 oxaliplatin-resistant cell lines developed as part of this study, are novel models of low-level platinum resistance. These resistant cell lines do not have common mechanisms of platinum resistance such as increased expression of glutathione or decreased platinum accumulation. Rather, these cell lines have alterations in their cell cycle allowing them to proliferate rapidly post drug treatment in a process known as ‘regrowth resistance’. This alteration in cell cycle control has come at the expense of DNA repair capacity. The resistant cell lines show a decrease in nucleotide excision repair and homologous recombination repair, the reverse of what is normally associated with platinum resistance. The alterations in these DNA repair pathways help signal the G1/S checkpoint to allow the cell cycle to progress despite the presence of DNA damage. The decrease in DNA repair capacity has also contributed to the development of chromosomal alterations in the resistant cell lines. Similarities in chromosomal change between the two platinum resistant cell lines have been attributed to inherent vulnerabilities in the parental H69 cells rather than part of the mechanism of resistance. The H69CIS200 and H69OX400 resistant cells are cross-resistant to both cisplatin and oxaliplatin. This demonstrates that oxaliplatin does not have increased activity in low-level cisplatin-resistant cancer. Oxaliplatin resistance also developed more rapidly than cisplatin resistance suggesting that oxaliplatin may be less effective than cisplatin in the treatment of SCLC. The resistant cell lines have also become hypersensitive to taxol but show no alterations in the expression, polymerisation or morphology of tubulin. Rather, the PI3K/Akt/mTOR pathway is involved in both platinum resistance and taxol sensitivity as both are reversed with rapamycin treatment. mTOR is also phosphorylated in the resistant cell lines indicating that platinum resistance is associated with an increase in activity of this pathway. The mechanism of regrowth resistance in the platinum-resistant H69CIS200 and H69OX400 cells is a combination of activation of PI3K/Akt/mTOR signalling and alterations in control of the G1/S cell cycle checkpoint. However, more work remains to determine which factors in these pathways are governing this novel mechanism of platinum resistance.
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Ollos, Peter John. "Effects of drinking water biodegradability and disinfectant residual on bacterial regrowth." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0010/NQ32849.pdf.
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Lei, Hongchi. "GaAs-based distributed feedback lasers based on GaAs-InGaP regrowth technology." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18162/.
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This thesis describes the conceptualisation and realisation of GaAs-based self-aligned stripe (SAS) distributed feedback lasers (DFB) based on GaAs-InGaP regrowth technology, and its incorporation into the development of master oscillator power amplifier (MOPA) photonic integrated circuit (PIC). GaAs-based SAS DFB lasers operate via a single longitudinal mode and provide a robust, portable and low cost solution to enable a broad range of potential applications. Compared to other waveguides, e.g. ridge waveguide, SAS structures enable narrower active regions and demonstrate better characteristics with a lower sensitivity to temperature. In my designs, InGaP/GaAs buried gratings are formed utilising an Al-free grating sequence GaAs-InGaP-GaAs, whilst the SAS waveguides are realised via a stripe-etched n-doped InGaP optoelectronic confinement layer, where no AlGaAs is exposed during the fabrication process. Chapter 1 goes through the development of DFB lasers over almost 5 decades since its birth in 1970s, followed by discussion of the gap between present GaAs-based PIC technologies and their commercialisation. After, Chapter 2 introduces the experimental methodology involved in the research activities conducted: fundamental principles of DFB lasers and the 4-stage research process. The following 3 chapters describe the 3 main projects in this research. Chapter 3 begins with the design of 2×, 4× and 6× InGaAs QWs narrow ridge DFB lasers in, and then moved onto the conceptualisation and realisation of 2× and 4× InGaAs QWs SAS DFB lasers in Chapter 4. This SAS-DFB technology was then applied to the development of monolithically integrated 4× InGaAs QWs MOPA PIC in Chapter 5. In Chapter 6, I outline some future work to be conducted for further achievement. An optimised design of SAS-DFB-MOPA is first discussed. I then present some preparatory works for two other potential future directions: widely tunable GaAs-based sampled grating distributed Bragg reflector laser (SG-DBR) and high power ~1180nm In(Ga)As/GaAs DWELL (dot-in-a-well) SAS-DFB-MOPA.
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Schiffman, Paula M. "Carbon storage during the regrowth and conversion of Virginia Piedmont forests." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45731.
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Recent increases in atmospheric carbon dioxide caused by the combustion of fossil fuels and tropical deforestation may result in global warming. Carbon accumulation by regrowing temperate forests, in regions such as the southeastern United States, may have been extensive enough to counterbalance releases of carbon from the tropics. In the Virginia Piedmont, large amounts of carbon have accumulated in phytomass and detritus of loblolly pine (Pinus taeda) plantations and natural forests regrowing on post-agricultural fields. After 50 years, carbon in phytomass of old field plantations was 200,000 kg/ha, twice the amount accumulated by natural forests. Detrital carbon accumulations totaled over 100,000 kg/ha, but were dependent upon amounts of erosional loss prior to reforestation.
The forested land area in the southeastern United States has stabilized, and forest conversion is now the primary form of reforestation. Therefore, the region's ability to continue to store carbon has been questioned. Still, the phytomass of late-rotation converted plantations stored 200,000 kg carbon/ha, twice the amount of the natural forests they replaced. In addition, while the harvest of natural forests resulted in small reductions in detrital carbon, it was rapidly restored to over 100,000 kg/ha within 30 years.
Houghton et al. (1983) developed a series of models describing carbon dynamics during reforestation. My data show that patterns of carbon accumulation exhibited by regrowing loblolly pine plantations are different from their models. Therefore, modifications of the models are suggested to improve estimates of carbon storage in temperate forests.Master of Science
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Stordal, Britta. "Regrowth resistance in platinum-drug resistant small cell lung cancer cells." Connect to full text, 2006. http://hdl.handle.net/2123/2467.
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Thesis (Ph. D.)--University of Sydney, 2007.Title from title screen (viewed 10 June 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Discipline of Medicine, Faculty of Medicine. Degree awarded 2007; thesis submitted 2006. Includes bibliographical references. Also available in print form.
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Chapman, Rudy T., Katherine C. Burgess, Russ W. Brown, and Diego J. Rodriguez-Gil. "Axonal regrowth of olfactory sensory neurons after chemical ablation with methimazole." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/asrf/2018/schedule/17.
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The olfactory system is of great interest in research due to the olfactory epithelium’s regenerative capability and as a potential as a source of neural stem cells. The olfactory sensory neurons are constantly being replaced by the stem cells that lie at the base of the olfactory epithelium. These stem cells also remain intact after an injury to the epithelium and lead to the regeneration of the olfactory epithelium. We have developed a fate mapping technique to trace axonal regrowth from newly born olfactory sensory neurons using an inducible Cre-ERT2 model after chemical ablation by the drug methimazole. Our data shows that newly generated olfactory sensory neurons labeled 1 day after chemical ablation by injection of 4-HO-tamoxifen extend an axon that reaches the olfactory bulb and extend to the glomeruli in a timeline that is consistent with control mice that received 4-HO-tamoxifen but were injected with saline 1 day prior. In addition, we assessed the functional recovery of the olfactory epithelium by testing the ability of mice to find a hidden cookie after methimazole injection. Mice were tested at 3 and 14 days post methimazole. There was a severe impairment in the ability to find a hidden cookie at 3 days post methimazole. The mice tested at 14 days post methimazole showed an improvement in the ability to find the cookie but the latency to find the cookie was still significantly higher than controls. In conclusion, while we demonstrate that axons extend to the olfactory bulb and the glomeruli earlier than 14 days, our behavioral data suggest that there must be a critical number of axons that must reach each specific glomerulus to regain function of the olfactory system.
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Shorter, James Gordon. "Molecular mechanisms regulating Golgi architecture during the mammalian cell division cycle." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313395.
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Ga̧siorek, Stanisława. "Solid phase epitaxial regrowth of alkali ion irradiated [alpha]-quartz [alpha-quartz]." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970906064.
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Blakemore, Philip. "Optimisation of steam reconditioning for regrowth-ash and plantation-grown eucalypt species." University of Sydney, 2008. http://hdl.handle.net/2123/2343.
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Doctor of PhilosophySteam reconditioning to recover collapse, in mid to low density eucalypt species, has been known for over ninety years. The current industrial practices for steam reconditioning have largely been based on a few older studies, which were often poorly documented and based on very small sample sizes. On top of this, many local practices and ‘rules of thumb’ have developed over time, many of which have a questionable scientific basis. This thesis was undertaken to more rigorously investigate and fundamentally understand collapse recovery, and try to optimise its application. The most obvious variable that kiln operators have control over is the moisture content of the timber prior to steam reconditioning. Experiments were undertaken to generate a range of moisture gradients (ranging from minimal to more industrially realistic) to evaluate the effect of moisture content on collapse recovery. An optimal moisture content for the core of the boards was found to be between about 18–20%, although there was no statistical difference in recoveries between about 17–25% moisture content. Below 15% moisture content recovery dropped off severely and intra-ring internal checking closure was incomplete, while at 25% moisture content an increased level of normal shrinkage, due to the early removal of drying stresses, was the main drawback. Above a core moisture content of about 35% incomplete closure of intra-ring internal checks was again observed. There was little evidence of re-collapse occurring in these high moisture content samples. Previously established relationships between density and collapse and drying rate were again generally observed in these experiments. However, for the first time an effect of collapse in reducing the fitted drying diffusion coefficients was also observed. It was also observed that, provided the moisture content of the board was in the critical range, most of the collapse recovery was achieved in the time it took to get the core of the board up to the steaming temperature of close to 100°C. This suggests that for most thicknesses a conservative reconditioning period of two hours at temperature is all that is required. This recommended shortening of the reconditioning cycle could dramatically increase the throughput of timber through the steam reconditioning chambers. Alternatively, it could mean that where modern final drying kilns are being used, the reconditioning treatment could be carried out within the final drying kiln. A finite element model was developed to demonstrate the mechanism by which collapse recovery occurs. The theory tested was that the elastic component that stores the energy to restore the shape of the deformed cell is primarily found in the S1 and S3 layers. In contrast, the inelastic component is primarily found in the S2 layer. The model generated here provided limited support for this theory.
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左雨鵬 and Yu-pang Eric Cho. "Axonal regrowth and morphological plasticity of retinal ganglion cellsin the adult hamster." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1990. http://hub.hku.hk/bib/B31232188.
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Tokajian, Sima Toros. "Regrowth of bacteria and their genotypic identification in drinking water in Lebanon." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270989.
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Blakemore, Philip Alexander. "Optimisation of steam reconditioning for regrowth-ash and plantation-grown eucalypt species." Connect to full text, 2008. http://ses.library.usyd.edu.au/handle/2123/2343.
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Thesis (Ph. D.)--University of Sydney, 2008.Includes graphs and tables. Includes list of publications: p. iv. Title from title screen (viewed May 5, 2008). Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemical and Biomolecular Engineering. Includes bibliographical references. Also available in print form.
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Hsin, Yue-ming. "Improved HBT performance by base width reduction and selective extrinsic base regrowth /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9809137.
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Utsumi, Shunsuke. "Ecological consequences of herbivore-induced plant regrowth for arthropod communities on willows." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136925.
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Williams, Tyson. "Competitive exclusion as a means to reduce Escherichia coli regrowth in digested sludge." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9221.
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In recent years, it has been reported that numbers of Escherichia coli increase significantly following centrifugation of sludge during the treatment process. E. coli is used as an indicator of the microbiological quality of sludge-derived products destined for agricultural recycling and of the efficacy of the sludge treatment processes. The re-growth phenomenon is of concern because of the potential for additional treatment requirement / higher disposal costs and loss of consumer confidence associated with a compliance failure. It is hypothesised that a competitive exclusion treatment could be the solution wherein the digestate be exposed to a ‘probiotic’ or defined mixture of micro-organisms, to effectively out compete or eliminate any resident E. coli remaining following treatment. The competitive exclusion principle as a treatment method has already seen application in various industrial sectors, the most well-known being the poultry industry. In experiments it was determined that an antimicrobial producing organism would be most likely to succeed. From the candidates screened, Lactobacillus reuteri proved the most promising. L. reuteri is a known producer of reuterin in the presence of glycerol and organic acids as a part of its normal metabolic activity. In sludge derived nutrient broth in the presence of glycerol and low pH, L. reuteri addition resulted in a reduction of E. coli to undetectable levels. In sludge cake under the same conditions, L. reuteri was less successful. However the addition of glycerol and L. reuteri to sludge cake restricted E. coli growth to a 2 log increase from the initial concentration of E. coli recorded following pasteurisation (an average of around 1x102 cfu/gDs), in comparison in the positive control a 4 log increase was recorded. From this result the sludge cake could be defined as conventionally treated. It can be concluded that competitive exclusion and L. reuteri show promise as a treatment for reducing E. coli re-growth in sludge cake
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Cho, Yu-pang Eric. "Axonal regrowth and morphological plasticity of retinal ganglion cells in the adult hamster /." [Hong Kong : University of Hong Kong], 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12922882.
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Gard, Kevin. "Autocorrelation analysis of spectral regrowth generated by nonlinear circuits in wireless communication systems /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3112869.
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Williams, David Mervyl. "All-semiconductor photonic crystal surface emitting lasers at 980 nm through epitaxial regrowth." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5470/.
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The purpose of this thesis is to outline the novel method of epitaxial regrowth for fabrication of photonic crystal surface emitting lasers (PCSELs). Waveguide modelling is conducted to demonstrate that strong coupling to the photonic crystal occurs, and that a decent mode overlap with the active region is simultaneously achieved in an optimised structure. Details of the regrowth process and the various fabrication techniques involved are discussed. Characterisation of devices indicates that emission from these all-semiconductor structures is comparable to void based PCSELs.
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Angulo, Barrios Carlos. "Gallium arsenide based buried heterostructure laser diodes with aluminium-free semi-insulating materials regrowth." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3305.
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Semiconductor lasers based on gallium arsenide and relatedmaterials are widely used in applications such as opticalcommunication systems, sensing, compact disc players, distancemeasurement, etc. The performance of these lasers can beimproved using a buried heterostructure offering lateralcarrier and optical confinement. In particular, if theconfinement (burying) layer is implemented by epitaxialregrowth of an appropriate aluminium-free semi-insulating (SI)material, passivation of etched surfaces, reduced tendency tooxidation, low capacitance and integration feasibility areadditional advantages.
The major impediment in the fabrication of GaAs/AlGaAsburied-heterostructure lasers is the spontaneous oxidation ofaluminium on the etched walls of the structure. Al-oxide actsas a mask and makes the regrowth process extremely challenging.In this work, a HCl gas-basedin-situcleaning technique is employed successfully toremove Al-oxide prior to regrowth of SI-GaInP:Fe and SI-GaAs:Fearound Al-containing laser mesas by Hydride Vapour PhaseEpitaxy. Excellent regrowth interfaces, without voids, areobtained, even around AlAs layers. Consequences of usinginadequate cleaning treatments are also presented. Regrowthmorphology aspects are discussed in terms of different growthmechanisms.
Time-resolved photoluminescence characterisation indicates auniform Fe trap distribution throughout the regrown GaInP:Fe.Scanning capacitance microscopy measurements demonstrate thesemi-insulating nature of the regrown GaInP:Fe layer. Thepresence of EL2 defects in regrown GaAs:Fe makes more difficultthe interpretation of the characterisation results in the nearvicinity of the laser mesa.
GaAs/AlGaAs buried-heterostructure lasers, both in-planelasers and vertical-cavity surface-emitting lasers, withGaInP:Fe as burying layer are demonstrated for the first time.The lasers exhibit good performance demonstrating thatSI-GaInP:Fe is an appropriate material to be used for thispurpose and the suitability of our cleaning and regrowth methodfor the fabrication of this type of semiconductor lasers.Device characterisation indicates negligible leakage currentalong the etched mesa sidewalls confirming a smooth regrowthinterface. Nevertheless, experimental and simulation resultsreveal that a significant part of the injected current is lostas leakage through the burying material. This is attributed todouble carrier injection into the SI-GaInP:Fe layer.Simulations also predict that the function of GaInP:Fe ascurrent blocking layer should be markedly improved in the caseof GaAs-based longer wavelength lasers.
Keywords:semiconductor lasers, in-plane lasers, VCSELs,GaAs, GaInP, semi-insulating materials, hydride vapour phaseepitaxy, regrowth, buried heterostructure, leakage current,simulation.
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Van, der Heyden Francois. "Effects of defoliation on regrowth and carbon budgets of three semi-arid Karoo shrubs." Doctoral thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/14355.
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Includes bibliographies.Plant regrowth, nonstructural carbohydrate utilization patterns, photosynthesis and the partitioning of photosynthetic products in response to foliage removal were studied for the following karoo shrubs: Osteospermum sinuatum, a dwarf deciduous shrub with fleshy leaves, Pteronia pallens, a dwarf evergreen shrub with sclerophyllous leaves and Ruschia spinosa, a dwarf evergreen shrub with succulent leaves. Defoliation adversely affected both vegetative growth and reproductive output for periods up to 26 weeks following foliage removal. A gradient of increasing regrowth capacity with decreasing defoliation intensity and frequency was observed in all species. In terms of biomass production, defoliation was the least detrimental to the deciduous shrub, O. sinuatum, and the evergreen shrub, P. pallens, and the most injurious to the succulent shrub, R. spinosa. All species regrew better during spring and autumn, and no regrowth was recorded in the moderate (40%) or intensely (80%) defoliated plants during summer and winter over the 6-week monitoring periods. Spatial patterns of carbohydrate accumulation were the same for all species, with most of the total nonstructural carbohydrates (TNC) being stored in the twigs and stems. Karoo shrubs can be divided into two distinct groups based on the primary nonstructural polysaccharides accumulated in their plant parts. The Asteraceous plants, O. sinuatum and P. pallens, accumulate predominantly fructans. In contrast, the succulent species, R. spinosa, accumulate starch and fructans in equal proportions. Differences among species in terms of seasonal changes in TNC levels of undefoliated plants reflect the extent to which different species are dependent on stored carbohydrates or photosynthesis for normal vegetative growth processes. Repeated defoliations at a moderate frequency (26-week interval) resulted in the elevation of TNC concentrations of O. sinuatum and P. pallens. In contrast, defoliations at heavy or at leniant frequencies caused decreases in TNC concentrations in all plant parts of Ruschia spinosa. Restoration of plant storage TNC levels in excess of undefoliated plant TNC levels occurred prior to complete vegetative regrowth in the two Asteraceous shrubs which suggests that some factor(s) other than the carbon resource was limiting vegetative regrowth in karoo shrubs. Analyses of short-term changes (2-weekly) in TNC levels in response to defoliation demonstrated the elevation in TNC concentrations of Pteronia pallens plant parts only during the periods when no regrowth was recorded. This phenomenon illustrates that on a short-terms basis, regrowth and over-replenishment of reserves represent two alternate responses to defoliation. However, during periods when regrowth was recorded for P. pallens (autumn and spring), and during all seasons of the year for O. sinuatum and R. spinosa, depressions in TNC concentrations were observed in most plant parts up to six weeks following defoliation. This illustrates the large dependence these shrubs have on stored carbohydrates following defoliation. Defoliation had no effect on the photosynthetic rates of karoo shrubs for at least 11 days following defoliation. Foliage removal resulted in the redistribution of photoassimilates in all plant species. These changes in the allocation of newly produced photosynthates appear to be associated largely with the replenishment of carbohydrate reserves following the initial TNC utilization caused by foliage removal. Comparison of TNC utilization patterns, following defoliation of O. sinuatum in the dark (no photosynthesis) and in the light resolved the question of the relative importance of reserve carbohydrates and photosynthates following defoliation. Reserve carbohydrates were used only for the first 2 weeks following defoliation for respiratory functions while photoassimilates were used for the production of new foliage. The magnitude of nonstructural carbohydrate utilization in the absence of photosynthesis emphasized the importance of continuing photosynthesis to the survival of defoliated karoo shrubs. The differences among species in terms of the timing and the extent of changes (elevations or decreases) in TNC levels in response to defoliation are interpreted as being the result of alterations in plant chemistry which in turn are governed by species specific physiological adaptations to environmental constraints. Rangeland management guidelines are recommended within the framework of the observed short-term and long-term defoliation effects on karoo shrub plant production.
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O'Connor, Erin E. "Post-fire Vegetative Regrowth Associated with Mature Tree Stands and Topography on Sofa Mountain." Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1432908700.
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Gold, Warren G. "The Effects of the Spatial Pattern of Defoliation on Regrowth of a Tussock Grass." DigitalCommons@USU, 1988. https://digitalcommons.usu.edu/etd/6458.
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The influence of the spatial pattern of foliage removal on regrowth was investigated in the field with a tussock grass, Agropyron desertorum. Tussocks were hand clipped in different spatial patterns that represented extremes of defoliation patterns which could be inflicted by natural herbivores. All defoliated tussocks exhibited increases in specific growth rates following clipping in mid-May. When foliage was removed from the upper portion of the canopy (younger foliage), regrowth rates and season-long aboveground biomass production were less than if the same amount of foliage was removed from low in the canopy (older foliage). The spatial pattern of defoliation also influenced tussock regrowth in a late-May clipping experiment, but differences in the effects of the clipping patterns were associated with the removal of apical meristems rather than with the age or location of foliage removed.
Changes in tussock carbon dioxide and water vapor exchange that were associated with changes in growth following mid-May clipping were explored. All clipped tussocks showed increases in integrated daytime carbon dioxide uptake per unit foliage area after defoliation. Differences among treatments in the response of net daytime carbon gain during the first 24 hours after clipping corresponded well with differences in tussock regrowth over a 14-day period following clipping. Increased carbon gain of clipped tussocks was associated with increases in tussock water vapor conductance and intercellular carbon dioxide concentration, and decreases in the ratio of carbon dioxide uptake to water vapor loss.
Differences among treatments in daytime carbon gain and regrowth were paralleled by the response of instantaneous rates of light-saturated net photosynthesis for entire tussocks. Defoliation increased the proportion of foliage directly illuminated within the tussock at solar noon. Changes in the fraction of sunlit foliage and the relative amounts of different-aged foliage in tussock canopies were correlated with the responses of light-saturated photosynthesis. Thus, the effects of the spatial pattern of foliage removal on canopy light microclimate and the age of remaining foliage had important implications for carbon gain and regrowth of tussocks following mid-May defoliation.
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Huhta, A. P. (Ari-Pekka). "Restorative mowing on semi-natural grasslands: community-level changes and species-level responses." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:9514259947.
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Abstract
This thesis operates at two levels of ecological research, describing the effects of withdrawal and
re-introduction of management on grasslands. The aim of the community-level survey was to explore the effects of
abandonment, mowing and grazing on semi-natural meadows in northern Finland. At the species level, the aim was to
evaluate the responses of three monocarpic meadow species to various degrees of simulated grazing under natural growth
conditions.
The community-level studies suggest that strongly competitive grass species with rapid vegetative
growth, especially those forming tussocks, are able to retain or increase their cover in abandoned meadows. However,
most species are able to persist in a meadow for a long time after abandonment, even when a group of immigrants arrive.
This leads to a temporary increase in species diversity, and it may therefore be used as an indicator of ongoing
succession. Nevertheless, abandonment is harmful for the rare archaeophytic species in the long run. Late mowing does
not have extensive short-term impacts on grass-dominated semi-natural meadows. Therefore, it is neither an efficient nor
a substitutional way of management when the goal is to restore a formerly grazed pasture. Mowing executed early in the
season may, however, be a more appropriate way of inducing changes in species composition and enhancing species
richness.
According to the results of the species-level studies, Erysimum strictum and
Rhinanthus minor tolerate well minor apical damage, while more severe damage has a detrimental
impact on the performance of both species. The observed differences in regrowth responses between the two species are
presumably due to their different habitat requirements in relation to competition. The species-level experiment with two
late-flowering populations of field gentian Gentianella campestris ssp.
campestris revealed that the southern, Swedish population that has been regularly grazed and mown
overcompensated for the intermediate (50%) damage level, whereas the northern, Finnish field gentians growing in
unmanaged habitats showed at best partial or full compensation. Regular grazing and mowing have presumably favoured
grazing-tolerant plant species, i.e. species with a good regrowth capacity.
Herbivory reshapes grassland plant communities in two ways: directly by affecting the survival and
reproductive success of individual plants and indirectly by changing the competitive environment. Tall and competitive
perennial species suffer relatively more from damage than true grassland species, i.e. small herbs and grasses, which
are better able to tolerate regular tissue losses and respond to damage within the ongoing growing season. As a result,
certain species benefit from grazing and mowing in the sense that they may gain more through competitive relaxation than
they lose in defoliation.
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Giannakis, Stefanos. "Solar disinfection of secondary effluent and the subsequent bacterial regrowth : considerations, limitations and environmental perspectives." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/283981.
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The present Thesis deals with the solar disinfection of synthetic secondary effluent under laboratory controlled conditions, focusing on the post-irradiation bacterial regrowth. The influence of various internal and external factors and their effect on solar disinfection, as well as bacterial regrowth kinetics are the subject under question. With the aid of a common fecal indicator microorganism, the effects of light intensity, temperature, initial bacterial concentration, light energy (wavelength), manner of delivery (continuous-intermittent) were investigated. Also, the post-treatment events, such as dark repair, photoreactivation and the survival in natural water matrices were assessed, along with the use of technical means (flow photoreactors with recirculation) and advanced oxidation processes (photo-Fenton and sonication) for regrowth risk minimization. The findings provided valuable output, conclusions on the suitability of solar irradiation as a secondary wastewater disinfection technique, indicating the limitations of its applicability, the considerations on the treatment specifications and its environmental perspectives.Η παρούσα Διδακτορική Διατριβή πραγματεύεται την απολύμανση δευτεροβάθμια επεξεργασμένων τεχνητών λυμάτων υπό ελεγχόμενες συνθήκες, μελετώντας το φαινόμενο της επανανάπτυξης / επανεμφάνισης των μικροοργανισμών μετά την ακτινοβολία των λυμάτων. Αντικείμενό της είναι η μελέτη της επίδρασης μιας ευρείας γκάμας ενδογενών και εξωγενών παραγόντων τόσο κατά την διαδικασία της απολύμανσης, όσο και στην κινητική του βακτηριακού πληθυσμού. Με τη χρήση κοινών οργανισμών δεικτών κοπρανώδους μόλυνσης, μελετήθηκε η επίδραση του αρχικού βακτηριακού πληθυσμού, η ένταση και το μήκος κύματος της ακτινοβολίας, η θερμοκρασία απολύμανσης και ο τρόπος παροχής του φωτός (συνεχής-ασυνεχής) κατά την διαδικασία. Μελετήθηκαν ακόμα τα φαινόμενα που λαμβάνουν χώρα μετά την ακτινοβολία, όπως το φαινόμενο της επανανάπτυξης του βακτηριακού πληθυσμού στο σκοτάδι, η φωτο-επιδιόρθωση και η επιβίωση των μικροοργανισμών σε φυσικά νερά μετά την ακτινοβολία. Διερευνήθηκε τέλος η δυνατότητα χρήσης αντιδραστήρων συνεχούς ροής με επανακυκλοφορία και ο συνδυασμός εφαρμογής προχωρημένων μεθόδων οξείδωσης (αντιδραστήριο photo-Fenton) με υπερήχους, στοχεύοντας στην ελαχιστοποίηση της πιθανότητας επανανάπτυξης των μικροοργανισμών. Τα αποτελέσματα κατέδειξαν ενδεδειγμένες πρακτικές εφαρμογής, συμπεράσματα για την καταλληλότητα της ηλιακής ακτινοβολίας ως μεθόδου απολύμανσης δευτεροβάθμια επεξεργασμένων λυμάτων, προβληματισμούς όσον αφορά τις τεχνικές λεπτομέρειες και περιβαλλοντικές ανησυχίες.
Aquesta tesi tracta de la desinfecció d’un efluent secundari sintètic mitjançant llum solar en condicions controlades de laboratori, centrant-se en el recreixement dels bacteris després de la irradiació. La influencia de diversos factors interns i externs i el seu efecte en la desinfecció solar, així com la cinètica del recreixement bacterià són els temes estudiats. Amb l’ajuda d’un microorganisme indicador comú de contaminació fecal, es van investigar els efectes de la intensitat de la llum, de la temperatura, de la concentració inicial de bacteris, de l’energia lluminosa (longitud d’ona) i de la seva forma d’aplicació (contínua o intermitent). També es van estudiar els esdeveniments del posttractament, com son la reparació en foscor, la fotoreactivació i la supervivència en matrius naturals, així com l’ús de recursos tècnics (fotoreactors amb recirculació) i processos avançats d’oxidació (photo-Fenton i sonicació) per minimitzar el risc de recreixement. Els resultats obtinguts han permès formular conclusions valuoses sobre la idoneïtat d’utilitzar la radiació solar com a tècnica secundaria de desinfecció d’aigües residuals, indicant les limitacions de la seva aplicació, les consideracions sobre les especificacions del tractament i les seves perspectives ambientals.
En la presente Tesis doctoral se estudia la desinfección solar de un efluente secundario sintético en condiciones controladas de laboratorio, centrándose en el recrecimiento bacteriano después del tratamiento de irradiación. La influencia de diversos factores tanto internos como externos y sus efectos sobre la desinfección solar, así como el recrecimiento bacteriano son el tema principal de esta investigación. Empleando un microorganismo indicador fecal común, se investigaron los efectos de la intensidad de la luz, la temperatura, la concentración bacteriana inicial, la energía de la luz (longitud de onda) y la forma de suministro (continua-intermitente). Asimismo, se evaluaron los eventos posteriores al tratamiento, tales como la reparación oscura, la fotorreactivación y la supervivencia en matrices acuosas naturales, así como el uso de medios técnicos (fotorreactores de flujo con recirculación) y procesos de oxidación avanzada (foto-Fenton y sonicación) para mitigar el riesgo de recrecimiento. Los hallazgos proporcionaron valiosos resultados, conclusiones referentes a las aplicaciones prácticas, conclusiones sobre la adecuación de la irradiación solar como técnica de desinfección de aguas residuales secundarias, con indicaciones a las limitaciones de su aplicabilidad, consideraciones sobre las especificaciones del tratamiento y sus perspectivas ambientales
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Hsieh, Men-Chi Ravigururajan T. S. "Plaque behavior characteristics and regrowth of plaque in diseased arteries tissue during post-cryoplasty processes." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2006/t058.pdf.
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Thesis (M.S.)--Wichita State University, College of Engineering."May 2006." Title from PDF title page (viewed on October 31, 2006). Thesis adviser: T. S. Ravigururajan. Includes bibliographic references (leaves 89-95).
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Dutta, Partha Schneegurt Mark A. "Plaque behavior characteristics and regrowth of plaque in diseased arteries tissue during post-cryoplasty processes." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2006/t059.pdf.
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Thesis (M.S.)--Wichita State University, Dept. of Biological Sciences."May 2006." Title from PDF title page (viewed on October 31, 2006). Thesis adviser: Mark Schneegurt. Includes bibliographic references (leaves 41-58).
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Jarrar, Ahmed Ali. "Comparison of an essential oil mouth rinse and chlorhexidine on 4-day interproximal plaque regrowth." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1346_1210745930.
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Dental plaque is the most important etiological factor of periodontal diseases. Mechanical plaque control is the most effective way in preventing periodontal diseases. Chemical plaque control methods (such as mouthrinses) have been recommended to be used because of some drawbacks in the mechanical methods in some areas of the dentition (such as interproximal areas). But are these mouthrinses really effective in those areas? The aim of this study was to compare the effectiveness of Essential Oils mouthrinse (Listerine) on plaque formation in interproximal areas with Chlorhexidine and Sterile water.
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Dore, David William Biological Earth & Environmental Sciences (BEES) UNSW. "Application of simple physiological growth models to coastal eucalypt regrowth forests in New South Wales." Awarded by:University of New South Wales. Biological, Earth and Environmental Sciences (BEES), 2006. http://handle.unsw.edu.au/1959.4/26200.
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This thesis explores issues relating to the application of physiological-process models (???process models???) of forest growth to mixed species, mixed age forests, in particular the coastal blackbutt forests of New South Wales. Using a dataset provided by State Forests of New South Wales (Carter 1994 unpubl.) a numeric description of the forest was developed and stand-level parameters of interest were derived, in particular the plot by plot stemwood volume growth from 1975 to 1999. The amounts of harvested volume, volume that died and volume that grew into the measurement population were identified separately, and several different means of accounting for volume change over time were investigated. A method for quantifying the impact of harvesting and other silvicultural practices on the growth of the forest was developed and programs were written to convert the stand-level summary of the harvest impact into a semi-random selection of trees that would be ???harvested??? from the database under the set of silvicultural assumptions (Dore et al. 1999). A number of process models were investigated and reviewed before selecting one particular model, SUSTAIN (Dewar 1997) for adaption to these forests. This model is a relatively simple process model with a small number of input parameters. The model was adapted so that it could be used to compare the SUSTAIN estimate of growth with the growth of an individual stand of trees in the Kendall Forest Management Area, between Wauchope and Taree on the mid-north coast of NSW. To improve the accuracy of the prediction of growth by SUSTAIN, a method of re-setting the state of the stand to the actual condition at the time of remeasurement was developed. In addition, the SUSTAIN model was extended to enable two separate levels of canopy to be described and grown separately. Ultimately the model was only partially successful in mirroring the growth predicted by the empirical data. Its partial success is attributed primarily to the difficulties associated with correctly determining the allocation parameters used by the model to assign net photosynthate to the roots, foliage and stemwood. The nature of the change in allocation parameters when the forest stand is disturbed by harvest or fire needs further investigation.
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Probst, Thomas Adam. "HARVEST FREQUENCY AND CULTIVAR EFFECTS ON YIELD, QUALITY, AND REGROWTH RATE AMONG NEW ALFALFA CULTIVARS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/527.
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Alfalfa (Medicago sativa L.) is the most important forage crop in the United States and consistently produces high yields and quality, but harvest frequency is the most significant factor for maximizing forage yield and quality. The objective of this research was to determine forage yield, quality, and regrowth rate among new alfalfa cultivars under four different harvest frequencies. Some of these cultivars have been marketed as having rapid rates of regrowth after cutting to maximize the number of harvests per year. Five cultivars were placed under four harvest frequencies of 25, 30, 35, and 40 days in a split-plot design. There was a significant yield and regrowth rate effect across cultivars and harvest frequencies, but little forage quality effect during the two years of this research. These results confirm previous findings that a 35-d harvest frequency is optimal for forage yield, quality, and stand persistence.
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Borgan, Nawal Sunna'. "Microbial regrowth of water supplies in Amman distribution system and house-hold water storage tanks." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245733.
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