Research Institutes

Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/840

Browse

Now showing 1 - 20 of 56

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning
(Ecological Society of America, 2012-06) Smith, Alain; Page, Bruce R.; Duffy, Kevin Jan; Slotow, Rob
Large trees, as keystone structures, are functionally important in savanna ecosystems, and low recruitment and slow growth makes their conservation important. Understanding factors influencing their distribution is essential for mitigation of excessive mortality, for example from management fires or large herbivores. We recorded the locations of large trees in Hluhluwe-Imfolozi Park (HiP) using GPS to record trees along 43 km of 10 m-wide transects. Maximum entropy modeling (MaxEnt) uses niche modeling to predict the distribution of a species from the probability of finding it within raster squares, based on environmental variables and recorded locations. MaxEnt is typically applied at a regional spatial scale, and here we assessed its usefulness when predicting the distribution of species at a small (local) scale. HiP has variable topography, heterogeneous soils, and a strong rainfall gradient, resulting in a wide variety of habitat types. We used locations of 179 Acacia nigrescens and 106 Sclerocarya birrea (large trees ≥ 5m), and raster environmental layers for: aspect, elevation, geology, annual rainfall, slope, soil and vegetation. A. nigrescens was largely restricted to the Imfolozi section, while S. birrea had a wider distribution across the reserve. Understanding the interaction of environmental variables dictating tree distribution may facilitate habitat restoration, and will assist planning decisions for persistence of large trees within reserves, including options to reduce fire frequency or herbivore impacts. Though the AUC (Area Under the Curve) values used to test model predictions were high for both species, the ground truthing test data showed that distribution for A. nigrescens was more accurate than that for S. birrea, highlighting the need for independent test data to assess model accuracy. We emphasize that MaxEnt can be used at finer spatial scales than those typically used for species occurrence, but models must be tested using spatially independent test data.
Heavy impact on seedlings by the impala suggests a central role in woodland dynamics
(Cambridge University Press, 2012-04-12) O'Kane, Christopher A. J.; Duffy, Kevin Jan; Page, Bruce R.; Macdonald, David W.
Research has increasingly established that mesoherbivores influence the regeneration of woody plants. However the relationship between mesoherbivore density and degree of impact, and the spatial component of this impact, has not been well established. Using a novel sampling design, we assessed in iMfolozi Park, South Africa, the impact of impala (Aepyceros melampus) across the full complement of woody species within the home range, evaluating its spatial component and relationship to impala density. We used four GPS collars, in separate breeding herds, and a GIS to detect zones of different density of impala in the landscape, thus defining a fine-grain browsing gradient. We assessed impact on woody recruits (≤ 0.5 m height) across this gradient by means of 1600 random 1 × 1-m quadrats. Densities of woody seedlings, and mean percentage of remaining canopy, were significantly less in areas of high impala density versus low-density areas. There was a significant correlation between increasing impala density and decreasing density of favoured woody recruits. We propose a hypothesis of impala-induced patch dynamics. It seems likely that the ubiquitous impala may create and sustain a shifting mosaic of patches, and thus function as a key determinant of landscape heterogeneity.
Stable isotope turnover and variability in tail hairs of captive and free-ranging African elephants (Loxodonta africana) reveal dietary niche differences within populations
(NRC Research Press, 2013) Codron, Jacqueline; Kirkman, Kevin; Duffy, Kevin Jan; Sponheimer, Matt; Lee-Thorp, Julia A.; Ganswindt, Andre; Clauss, Marcus; Codron, Daryl
Many herbivore species expand their dietary niche breadths by switching from browse-rich diets in dry seasons to grass-rich diets in rainy seasons, in response to phenological changes in plant availability and quality. We analyzed stable isotope series along tail hairs of captive and free-ranging African elephant (Loxodonta africana (Blumenbach, 1797)) to compare patterns of seasonal dietary variability across individuals. Results from elephants translocated from the wild into captivity, where their diets are semicontrolled, revealed tail hair growth rates of 0.34 mm/day, on average, and relatively rapid isotope turnover through the transition from wild into captivity. Sampling hairs at 10 mm increments thus archives dietary chronologies at a resolution suitable for tracking diet switches at seasonal, and even subseasonal, scales. Hairs of free-ranging elephants showed extensive carbon isotopic variability within individuals, consistent with seasonal switches between C3-browsing and C4-grazing. Similarly extensive, but asynchronous, shifts in nitrogen isotope ratios were also observed, suggesting an influence of factors other than seasonality. Across individuals, switching patterns differed across habitats, and across age classes, with older, larger animals including increasing amounts of C3 browse into their diets. These results demonstrate how stable isotope approaches characterize complex patterns of resource use in wildlife populations.
Phenol degrading ability of Rhodococcus pyrinidivorans and Pseudomonas aeruginosa isolated from activated sludge plants in South Africa
(Taylor and Francis, 2013-03-13) Kumari, Sheena K.; Bux, Faizal; Chetty, Dereshen; Ramdhani, Nishani
Phenol, a common constituent in many industrial wastewaters is a major pollutant and has several adverse effects on the environment. The potential of various microorganisms to utilize phenol for their metabolic activity has been observed to be an effective means of remediating this toxic compound from the environment particularly wastewater. Five indigenous bacterial isolates (PD1-PD5) were obtained from phenol bearing industrial wastewater using the mineral salts medium. The isolates were further characterized based on their morphology, biochemical reactions and 16S rRNA phylogeny. The 16S rRNA sequence analysis using universal primers (27f/1492r) revealed that PD1, PD2, PD3 and PD4 were closely related to the actinomycete Rhodococcus pyrinidivorans (99%) and PD5 to Pseudomonas aeruginosa (99%). Growth kinetic patterns and phenol degradation abilities of the two representative isolates (PD1 and PD5) were also evaluated. Both the species were effective in utilizing phenol as the sole carbon source and could tolerate phenol concentrations of up to 500 to 600 mg/L. The ability of these isolates to utilize higher concentrations of phenol as their sole carbon source makes them potential candidates and better competitors in the bioremediation process.
Nutritional status and food intake data on children and adolescents in residential care facilities in Durban
(Health and Medical Publications Group (HMPG), 2013) Grobbelaar, Hendrina Helena; Oldewage-Theron, Wilna; Napier, Carin E.
Objective: The aim of this study was to examine growth indicators and dietary intake patterns of children aged 4-18 years residing in residential care facilities in Durban. Method: Thirty-three girls and 110 boys, aged 5-18 years, in three different children’s homes participated in the study. Anthropometric measurements included weight and height and were analysed using the World Health Organization’s AnthroPlus® version 1.0.2 statistical software. The seven-day-cycle menus were analysed for nutrient and energy intake using the FoodFinder® version 3 software programme. Daily nutrient intakes were reported as means and standard deviations, and comparisons were made with the dietary reference intakes for specific age groups. Average served portion sizes were established by plate waste studies and observation. Results: The results showed that stunting and overweight were prevalent in this group. 4.7% of the boys aged 4-8 years and 3.3% of the boys aged 14-18 years were severely stunted. 13.3% of the girls aged 9-13 years and 20% of the girls aged 14-18 years were stunted. The body mass index for age reported that a small number (6.7% of the girls aged 9-13 years and 3.3% of the boys aged 14-18 years) were wasted. The results also showed that 33.3% of the girls aged 4-8 years and 33.4% of the girls aged 9-13 years were at risk of being overweight. 26.7% of the girls aged 14-18 years were overweight (> + 2 standard deviations). Most of the children in the 4-8 age group (83.3% of the boys and 100% of the girls) fell in the normal range for weight for age, while only one boy was underweight. One hundred per cent or more of the dietary reference intakes for energy, protein, carbohydrate and most of the micronutrients were met, except for calcium and iodine. A low intake of vitamin C among older boys and girls was reported. None of the groups met the recommended fibre intake. Conclusion: The results indicated a need for the development and implementation of a comprehensive nutrition education programme for both child care workers and children.
Application of radio-immunoassays to assess the fate of estrogen EDCs in full scale wastewater treatment plants
(Taylor and Francis, 2013) Bux, Faizal; Surujlal-Naicker, Swastika
Wastewater effluents have been documented as major contributors of hormone endocrine disrupting compounds (EDCs) in to the aquatic ecosystem. The need for rapid, simple and cost effective methods to detect these EDCs has increased. The use of Radio-immunoassays (RIA) were assessed to determine the fate of estradiol in a laboratory batch test and the three natural estrogens (estrone (E1), estradiol (E2) and estriol (E3)) in wastewater treatment plants (WWTPs) with different types of configurations. Precision of the RIAs were done using intra-assay and inter-assay validations. The E2 intra-assay variation was <8% and inter-assay variation was <11% for standards 1 to 6. E1 RIA showed less than 8% for both the intra-assay and inter-assay variations. E3 RIA showed extremely good variations with both the intra and inter-assay variations being below <8% for all standards. The lab scale investigation showed a 94% reduction in E2 after 5 h and after 10 h both E2 and E1 were no longer detected. The simple activated sludge process, the biological nutrient removal (BNR) activated sludge process and the oxidation pond had final effluent concentrations of 10.75, 5.96 and 25.48 pg E2/mL respectively; 20.80, 9.30 and 46.55 pg E1/mL, respectively, and 0.12, 0.07 and 0.17 ng E3/mL, respectively. Thus far findings indicated that the RIA can be employed as a rapid technique for detection of natural estrogens in water. Results indicate that these potential problematic hormone EDCs are still present in final wastewater effluents that are discharged in to South African aquatic sources.
Constructed wetlands : a future alternative wastewater treatment technology
(Academic Journals, 2013-07-17) Mthembu, M. S.; Odinga, C. A.; Swalaha, Feroz Mahomed; Bux, Faizal
Wastewater treatment will always pose problems if there are no new alternative technologies in place to replace the currently available technologies. More recently, it has been estimated that developing countries will run out of water by 2050. This is a course for concern not only to the communities but also a challenge to the scientist to find new ways of wastewater recycling. Water losses can be avoided the rough implementation of easy and inexpensive technologies for wastewater treatment. Environmental concerns over insufficiently performing septic systems and high expenses in the construction of sewer systems as well as their operations with centralized water purification systems have spurred investigation into the appropriateness of the use of wetland technology for wastewater treatment. Constructed wetland efficiency and potential application in wastewater treatment has been reported decades ago. However, the logistics and research for their commercial applications in wastewater treatment has not been documented in details. Research has shown that wetland systems can achieve high treatment efficiencies with regards to both organic and inorganic nutrients as well as pathogen removal if properly managed and efficiently utilized. This can have a profound effect in the management and conservation of our scarce and yet depleting water resources.
Effect of thermal pre-treatment on inoculum sludge to enhance bio-hydrogen production from alkali hydrolysed rice straw in a mesophilic anaerobic baffled reactor.
(Taylor & Francis, 2013) Bux, Faizal; Kumari, Sheena K.; Tawfik, Ahmed; El-berry, Haitham
The effect of thermal pre-treatment on inoculum sludge for continuous H2 production from alkali hydrolysed rice straw using anaerobic baffled reactor (ABR) was investigated. Two reactors, ABR1 and ABR2, were inoculated with untreated and thermally pre-treated sludge, respectively. Both reactors were operated in parallel at a constant hydraulic retention time of 20 h and organic loading rate ranged from 0.5 to 2.16 g COD/L d. The results obtained indicated that ABR2 achieved a better hydrogen conversion rate and hydrogen yield as compared with ABR1. The hydrogen conversion rates were 30% and 24%, while the hydrogen yields were 1.19 and 0.97 mol H2/mol glucose for ABR2 and ABR1, respectively. Similar trend was observed for chemical oxygen demand (COD) and carbohydrate removal, where ABR2 provided a removal efficiency of 53±2.3% for COD and 46±2% for carbohydrate. The microbial community analysis using 16S rRNA phylogeny revealed the presence of different species of bacteria, namely Clostridium, Prevotella, Paludibacter, Ensifer, and Petrimonas within the reactors. Volatile fatty acids generated from ABR1 and ABR2 were mainly in the form of acetate and butyrate and a relatively low fraction of propionate was detected in ABR1. Based on these results, thermal pre-treatment of inoculum sludge is preferable for hydrogen production from hydrolysed rice straw.
Synthesis, characterization and biological study of novel heterocyclic compounds
(2013) Patel, Nidhi; Bux, Faizal; Vyavahare, Lochan Vishwas; Singh, Arun
3-hydroxybenzofuran-2-carbohydrazide (2) undergoes facile condensation with aromatic aldehydes to afford the corresponding N-arylidene-3-hydroxybenzofuran-2-carbohydrazide (3a-e) in good yields. Cyclo condensation of compounds (3a-e) with chloro acetyl chloride yields N-(3-chloro-2-oxo-4-arylazetidin-1-yl)-3-hydroxybenzofuran-2-carboxamide (4a-e). The structures of these compounds were established on the basis of analytical and spectral data. The newly synthesized compounds were evaluated for their antibacterial and antifungal activities.
Biodiesel production potential of wastewater microalgae chlorella SP. under photoautotrophic and heterotrophic growth conditions
(BAAR, 2012-10) Viswanath, Buddolla; Bux, Faizal
In the present study, a microalgae (Chlorella sp.) isolated from wastewater pond has been studied in both photoautotrophic and heterotrophic growth conditions in bioreactor to evaluate the cell growth rate and lipid content for biodiesel production. Maximum amount of biomass was recovered from the bioreactor of Chlorella sp. grown under heterotrophic growth conditions with 8.90 gL-1 compared to photoautotrophic growth conditions, which was almost 3.6, fold lesser than the former. Heterotrophic growth of Chlorella sp. resulted in the accumulation of high lipid content in cells compared autotrophic growth by enhancing lipid production by 4.4 fold. The results suggested that heterotrophic growth of microalgae is an efficient method for the production of biomass and high lipid content in the cells, which can reduce the cost of microalgal biomass production and microalgal oil production. The quality of the oil produced from the cells of heterotrophic growth is also superior compared the oil from photoautotrophic growth.
Child and youth care workers: Profile, nutrition knowledge and food safety and hygiene practices
(AOSIS OpenJournals, 2014-08-06) Grobbelaar, Hendrina Helena; Napier, Carin E.
Background: Facilities concerned with children ‘in need of care’ should not only be considered as a last resort for a child’s care, but also as an intervention that requires more than addressing a child’s basic physical needs. The nutritional needs of children are particularly important to consider as they are a fundamental part of the care provided. Objectives: The purpose of this descriptive quantitative study was to investigate the profile, nutrition knowledge, food safety and hygiene practices of child and youth care workers (CCWs) in residential care settings in order to guide the development of a food preparation and nutrition manual. Method: The residential care settings included in this study were three that were selected randomly in Durban. CCWs (N = 40) employed permanently or part-time were included. Convenience purposive sampling of the CCWs was undertaken. A structured self-administered questionnaire, developed and tested for this purpose, was used to gather information on the profile, nutrition knowledge, food safety and hygiene practices. The data were analysed for descriptive statistics (means and frequencies). Results: The majority of CCWs were women aged 18−34 years. Very few had completed a relevant tertiary qualification. The results indicated that the respondents’ knowledge was fair on general nutrition guidelines, but there were areas of concern. Specifically, knowledge on recommended fruit and vegetable intake, correct serving sizes and importance of a variety in the diet were lacking. Some knowledge about food safety and hygiene practices was demonstrated, but not in totality. Conclusion: The overall findings supported the development of a comprehensive food preparation and nutrition manual for child residential care facilities.
Comparative assessment of the bacterial communities associated with Aedes aegypti larvae and water from domestic water storage containers
(Parasites and Vectors, 2014) Dada, Nsa; Jumas-Bilak, Estelle; Manguin, Sylvie; Seidu, Razak; Stenström, Thor-Axel; Overgaard, Hans J.
Background: Domestic water storage containers constitute major Aedes aegypti breeding sites. We present for the first time a comparative analysis of the bacterial communities associated with Ae. aegypti larvae and water from domestic water containers. Methods: The 16S rRNA-temporal temperature gradient gel electrophoresis (TTGE) was used to identify and compare bacterial communities in fourth-instar Ae. aegypti larvae and water from larvae positive and negative domestic containers in a rural village in northeastern Thailand. Water samples were cultured for enteric bacteria in addition to TTGE. Sequences obtained from TTGE and bacterial cultures were clustered into operational taxonomic units (OTUs) for analyses. Results: Significantly lower OTU abundance was found in fourth-instar Ae. aegypti larvae compared to mosquito positive water samples. There was no significant difference in OTU abundance between larvae and mosquito negative water samples or between mosquito positive and negative water samples. Larval samples had significantly different OTU diversity compared to mosquito positive and negative water samples, with no significant difference between mosquito positive and negative water samples. The TTGE identified 24 bacterial taxa, belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and TM7 (candidate phylum). Seven of these taxa were identified in larval samples, 16 in mosquito positive and 13 in mosquito negative water samples. Only two taxa, belonging to the phyla Firmicutes and Actinobacteria, were common to both larvae and water samples. Bacilli was the most abundant bacterial class identified from Ae. aegypti larvae, Gammaproteobacteria from mosquito positive water samples, and Flavobacteria from mosquito negative water samples. Enteric bacteria belonging to the class Gammaproteobacteria were sparsely represented in TTGE, but were isolated from both mosquito positive and negative water samples by selective culture. Conclusions: Few bacteria from water samples were identified in fourth-instar Ae. aegypti larvae, suggesting that established larval bacteria, most likely acquired at earlier stages of development, control the larval microbiota. Further studies at all larval stages are needed to fully understand the dynamics involved. Isolation of enteric bacteria from water samples supports earlier outcomes of E. coli contamination in Ae. aegypti infested domestic containers, suggesting the need to further explore the role of enteric bacteria in Ae. aegypti infestation.
Model highlights likely long-term inﬂuences of mesobrowsers versus those of elephants on woodland dynamics
(Wiley Online Library, 2014-06) O'Kane, Christopher A. J.; Duffy, Kevin Jan; Page, Bruce R.; Macdonald, David W.
The potential long-term inﬂuences of mesobrowsers versus those of savannah elephants on woodland dynamics have not been explored. This may be a critical omission especially in southern African savannahs, where efforts to preserve existing woodlands are typically directed at elephant man-agement. We describe a simple browse–browser model, parameterized from an extensive review of the literature and our own data, including quantitative assessment of impala impact, from the study site, iMfolozi Park, South Africa. As there is a paucity of species-speciﬁc demographic data on savannah woody species, we modelled, in a novel approach, functional groups of plant species typical of Acacia wood-lands. Outputs suggest that over the long term (100 years), low-to-moderate densities of impala will have a similar impact on woodland structure, in terms of density of adult trees, as low-to-moderate densities of elephant. Further, the outputs highlight the apparently strong synergistic effect impala and elephant impacts combined have on woodland dynamics, suggesting that reduction or removal of either impala or elephant will radically reduce long-term destruc-tion of savannah woodlands. Recorded changes in adult tree numbers in iMfolozi broadly supported the model’s outputs.
Microbiological water quality along Vaal Gamagara’s potable water distribution system
(Business Perspectives, 2015) Mokhosi, Agnes; Dzwairo, Bloodless
Safe drinking water is essential to all life forms. Thus analysis for microbiological parameters is critical as this assists in declaring the fitness of potable water for human consumption, among other sustainable and “green uses”. The aim of this paper is to investigate the microbiological quality of potable water along Vaal Gamagara Water Treatment Plant’s (VGWTP) distribution system. A total of 10 samples were collected weekly along the system. The samples were col-lected from January to December 2013 in order to analyze for Escherichia coli (E.coli), total coliforms (TC) and Hete-rotrophic plate counts (HPC). The results showed that only 0.1% and 0.4% of samples analyzed were positive for E. coli and total coliforms, respectively. However, HPC results showed that 40% of the samples analyzed from June to December 2013 had higher counts than the recommended standard limit. The chlorine residual showed an increase from June to December 2013. An assessment of the results indicated that the integrity of the system was compromised for the research period. Water quality failures in a distribution system are unacceptable because they threaten human health and sometimes result in loss of life. Thus the assessment called for an urgent need to boost chlorine residual especially at points further away from the treatment plant. This was envisaged to provide a safety net for microbial compliance while the system was critically and continuously monitored, and further investigations were performed. Studies on chlorine decay were recommended as a priority in order to optimize disinfection and maintain good quality drinking water throughout the system.
Time correlation functions for non-Hermitian quantum systems
(American Physical Society, 2015-06-09) Sergi, Alessandro; Zloshchastiev, Konstantin G.
We introduce a formalism for time-dependent correlation functions for systems whose evolutions are governed by non-Hermitian Hamiltonians of general type. It turns out that one can define two different types of time correlation functions. Both these definitions seem to be physically consistent while becoming equivalent only in certain cases. Moreover, when autocorrelation functions are considered, one can introduce another function defined as the relative difference between the two definitions. We conjecture that such a function can be used to assess the positive semidefiniteness of the density operator without computing its eigenvalues. We illustrate these points by studying analytically a number of models with two energy levels.
A probabilistic assessment of the contribution of wastewater-irrigated lettuce to Escherichia coli O157:H7 infection risk and disease burden in Kumasi, Ghana
(IWA Publishing, 2015-03) Seidu, Razak; Abubakari, Amina; Amoah, Isaac Dennis; Heistad, Arve; Stenström, Thor-Axel; Larbi, John A.; Abaidoo, Robert Clement
Wastewater use for vegetable production is widespread across the cities of many developing countries. Studies on the microbial health risks associated with the practice have largely depended on faecal indicator organisms with potential underestimation or overestimation of the microbial health risks and disease burdens. This study assessed the Escherichia coli O157:H7 infection risk and diarrhoeal disease burden measured in disability-adjusted life years (DALYs) associated with the consumption of wastewater-irrigated lettuce in Kumasi, Ghana using data on E. coli O157:H7 in ready-to-harvest, wastewater-irrigated lettuce. Two exposure scenarios – best case and worst case – associated with a single consumption of wastewater-irrigated lettuce were assessed. The assessment revealed wastewater-irrigated lettuce is contributing to the transmission of E. coli O157:H7 in Kumasi, Ghana. The mean E. coli O157:H7 infection risk and DALYs in the wet and dry seasons, irrespective of the exposure scenario, were above the World Health Organization tolerable daily infection risk of 2.7 × 10−7 per person per day and 10−6 DALYs per person per year. It is recommended that legislation with clear monitoring indicators and penalties is implemented to ensure that farmers and food sellers fully implement risk mitigating measures.
Quantum entropy of systems described by non-Hermitian Hamiltonians
(IOP Science, 2016-03-02) Sergi, Alessandro; Zloshchastiev, Konstantin G.
We study the quantum entropy of systems that are described by general non-Hermitian Hamiltonians, including those which can model the effects of sinks or sources. We generalize the von Neumann entropy to the non-Hermitian case and find that one needs both the normalized and non-normalized density operators in order to properly describe irreversible processes. It turns out that such a generalization monitors the onset of disorder in quantum dissipative systems. We give arguments for why one can consider the generalized entropy as the informational entropy describing the flow of information between the system and the bath. We illustrate the theory by explicitly studying few simple models, including tunneling systems with two energy levels and non-Hermitian detuning.
Non-Hermitian Hamiltonian Approach for Electromagnetic Wave Propagation and Dissipation tn Dielectric Media
(IEEE, 2016-06) Zloshchastiev, Konstantin G.
Using the formal analogy between a certain class of Maxwell equations and the Schrdinger equation, we derive the effective Hamiltonian operator that governs the propagation of electromagnetic (EM) wave modes inside nonconducting linear media, which include a large range of nanophotonic and plasmonic waveguides. It turns out that this Hamiltonian is essentially non-Hermitian, and thus requires a special treatment. We formulate the density operator approach for dynamical systems with non-Hermitian Hamiltonians, and derive a master equation that describes the statistical ensembles of EM wave modes. The method provides a theoretical instrument which can be used when designing the next generation of quantum EM devices for sensitive and non-invasive measurements.
Quantum-statistical approach to electromagnetic wave propagation and dissipation inside dielectric media and nanophotonic and plasmonic waveguides
(American Physical Society, 2016) Zloshchastiev, Konstantin G.
Quantum-statistical effects occur during the propagation of electromagnetic (EM) waves inside the dielectric media or metamaterials, which include a large class of nanophotonic and plasmonic waveguides with dissipation and noise. Exploiting the formal analogy between the Schr¨odinger equation and the Maxwell equations for dielectric linear media, we rigorously derive the effective Hamiltonian operatorwhich describes such propagation. This operator turns out to be essentially non-Hermitian in general, and pseudo-Hermitian in some special cases. Using the density operator approach for general non-Hermitian Hamiltonians, we derive a master equation that describes the statistical ensembles of EM wave modes. The method also describes the quantum dissipative and decoherence processes which happen during the wave’s propagation, and, among other things, it reveals the conditions that are necessary to control the energy and information loss inside the above-mentioned materials.
Identifying stability conditions and Hopf bifurcations in a consumer resource model using a consumption threshold
(Elsevier, 2016) Duffy, Kevin Jan; Collins, Obiora Cornelius
The existence, or not, of cyclic dynamics is one of the pivotal aspects of ecological populations. This work considers a consumer resource model found in ecology that can describe both cyclic and non-cyclic dynamics depending on parameter conditions. A threshold consumption number C0 is introduced, similar to the basic reproduction in epidemiological models. It is shown that consumer survival requires C0 > 1 and that a Hopf bifurcation occurs at , where is defined here and is greater than 1. This result is discussed with an example and extensions to other more complicated models.