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Population Present (population + present)
Selected AbstractsMicrobial Community Dynamics of a Continuous Mesophilic Anaerobic Biogas Digester Fed with Sugar Beet SilageENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2008B. Demirel Abstract The aim of the study was to investigate the long-term fermentation of an extremely sour substrate without any addition of manure. In the future, the limitation of manure and therefore the anaerobic digestion of silage with a very low buffering capacity will be an increasing general bottleneck for energy production from renewable biomass. During the mesophilic anaerobic digestion of sugar beet silage (without top and leaves) as the sole substrate (without any addition of manure), which had an extreme low pH of around 3.3, the highest specific gas production rate (spec. GPR) of 0.72,L/g volatile solids (VS),d was achieved at a hydraulic retention time (HRT) of 25,days compared to an organic loading rate (OLR) of 3.97,g VS/L,d at a pH of around 6.80. The methane (CH4) content of the digester ranged between 58 and 67,%, with an average of 63,%. The use of a new charge of substrate (a new harvest of the same substrate) with higher phosphate content improved the performance of the biogas digester significantly. The change of the substrate charge also seemed to affect the methanogenic population dynamics positively, thus improving the reactor performance. Using a new substrate charge, a further decrease in the HRT from 25 to 15,days did not influence the digester performance and did not seem to affect the structure of the methanogenic population significantly. However, a decrease in the HRT affected the size of the methanogenic population adversely. The lower spec. GPR of 0.54,L/g,VS,d attained on day,15 of the HRT could be attributed to a lower size of methanogenic population present in the anaerobic digester during this stage of the process. Furthermore, since sugar beet silage is a relatively poor substrate, in terms of the buffering capacity and the availability of nutrients, an external supply of buffering agents and nutrients is a prerequisite for a safe and stable digester operation. [source] Enumeration of Escherichia coli O157 in cattle faeces using most probable number technique and automated immunomagnetic separationLETTERS IN APPLIED MICROBIOLOGY, Issue 1 2004N. Fegan Abstract Aims:, To determine the numbers of Escherichia coli O157 present in the faeces of naturally infected cattle. Methods and Results:, A combination of the most probable number (MPN) technique and automated immunomagnetic separation (AIMS) was used to enumerate E. coli O157 in cattle faeces from both pasture-fed and grain-fed animals. A total of 22 E. coli O157 positive faecal samples were enumerated for E. coli O157 (10 from pasture-fed and 12 from grain-fed animals). The numbers of E. coli O157 in cattle faeces varied from undetectable (<3 MPN g,1 of faeces) to 2·4 × 104 MPN g,1. There was no significant difference (P = 0·06) between the numbers of E. coli O157 in pasture-fed or grain-fed cattle faeces, although the geometric mean (antilog of the mean of log10 transformed MPN values) was higher in grain-fed (130 MPN g,1) than in pasture-fed (13 MPN g,1). Conclusions:, Although the number of samples tested is small, the results indicate that E. coli O157 make up a small proportion of the total E. coli population present in cattle faeces. Significance and Impact of the Study:, Information on the numbers of E. coli O157 present in cattle will assist in developing more robust quantitative risk assessments and formulating intervention strategies. [source] Origin of ,-cells in regenerating pancreasBIOESSAYS, Issue 7 2008Kathy E. O'Neill The origin of insulin-expressing ,-cells in the adult mammalian pancreas is controversial. During normal tissue turnover and following injury, ,-cells may be replaced by duplication of existing ,-cells.1 However, an alternative source of ,-cells has recently been proposed based on neogenesis from a Ngn3-positive population present in regenerating pancreatic ducts.2 The appearance of ,-cells from Ngn3-positive progenitors is reminiscent of normal pancreas development, and Ngn3 -expressing cells isolated from regenerating pancreas can generate the full repertoire of endocrine phenotypes. The isolation and characterisation of the equivalent human progenitors may represent a significant step forward in the hunt for a cure for diabetes. BioEssays 30:617,620, 2008. © 2008 Wiley Periodicals, Inc. [source] Dynamics of an age-structured population drawn from a random numbers tableAUSTRAL ECOLOGY, Issue 4 2000Bertram G. Murray JR Abstract I constructed age-structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two-digit number following 00 or 01 ending one cohort's life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long-term growth rate (r) , 0. The populations' birth rates and growth rates and the females' per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age-structured populations can persist for long periods of time with long-term growth rates of zero in the absence of negative-feedback loops between a population's present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density-dependent regulation hypotheses. Thus, a long-term growth rate of zero found in natural populations need not indicate that a population's numbers are regulated by density-dependent factors. [source] Dynamics of an age-structured population drawn from a random numbers tableAUSTRAL ECOLOGY, Issue 4 2000BERTRAM G. MURRAY JR Abstract I constructed age-structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two-digit number following 00 or 01 ending one cohort's life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long-term growth rate (r) , 0. The populations' birth rates and growth rates and the females' per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age-structured populations can persist for long periods of time with long-term growth rates of zero in the absence of negative-feedback loops between a population's present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density-dependent regulation hypotheses. Thus, a long-term growth rate of zero found in natural populations need not indicate that a population's numbers are regulated by density-dependent factors. [source] | ||||||||||