Modeling the effects of density dependent emigration, weak Allee effects, and matrix hostility on patch-level population persistence

© 2020 the Author(s), licensee AIMS Press. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0) The relationship between conspecific density and the probability of emigrating from a patch can play an essential role in determining the population-dynamic consequences of an Allee effect. In this paper, we model a population that inside a patch is diffusing and growing according to a weak Allee effect per-capita growth rate, but the emigration probability is dependent on conspecific density. The habitat patch is one-dimensional and is surrounded by a tuneable hostile matrix. We consider five different forms of density dependent emigration (DDE) that have been noted in previous empirical studies. Our models predict that at the patch-level, DDE forms that have a positive slope will counteract Allee effects, whereas, DDE forms with a negative slope will enhance them. Also, DDE can have profound effects on the dynamics of a population, including producing very complicated population dynamics with multiple steady states whose density profile can be either symmetric or asymmetric about the center of the patch. Our results are obtained mathematically through the method of sub-super solutions, time map analysis, and numerical computations using Wolfram Mathematica

Small irrigation tanks as a source of malaria mosquito vectors: a study in north-central Sri Lanka

Watersheds / Tank irrigation / Rehabilitation / Malaria / Waterborne diseases / Disease vectors / Sri Lanka / Yan Oya

Treatment of colour industry wastewaters with concomitant bioelectricity production in a sequential stacked mono-chamber microbial fuel cells–aerobic system

The scalability of any microbial fuel cell (MFC)-based system is of vital importance if it is to be utilized for potential field applications. In this study, an integrated MFC–aerobic bioreactor system was investigated for its scalability with the purpose of treating a simulated dye wastewater and industrial wastewaters originated from textile dyebaths and leather tanning. The influent containing real wastewater was fed into the reactor in continuous mode at ambient temperature. Three MFC units were integrated to act in unison as a single module for wastewater treatment and a continuously stirred aerobic bioreactor operating downstream to the MFC module was installed in order to ensure more complete degradation of colouring agents found in the wastewater. Total colour removal in the final effluent exceeded 90% in all experiments where both synthetic (AO-7 containing) and real wastewater were used as the influent feed. The chemical oxygen demand reduction also exceeded 80% in all experiments under the same conditions. The MFC modules connected in parallel configuration allowed obtaining higher current densities than that can be obtained from a single MFC unit. The maximum current density of the MFC stack reached 1150 mA m−2 when connected in a parallel configuration. The outcome of this work implies that suitably up-scaled MFC–aerobic integrated bioprocesses could be used for colour industry wastewater treatment under industrially relevant conditions with possible prospects of bioelectricity generation

Incidence of some pathogenic organisms in cultured shrimp (penaeus monodon) collected from Chilaw

Samples offarm shrimp and pond water were collectedfrom Chi/aw. Totalbacterial counts of coliforms and Escherichia coli are reportedfor these samples.Pathogens Vibrio parahaemolyticus, and Salmonella along with qualitativemicroflora are also reported.The bacterial counts of water rangedfrom 5 x 102/gto 8.8 x 103/g whereasthat of shrimp rangedfrom 2.0 x IO"/g to 9.0 x lO'/g. E. coli. ranged from 3 toII/g for prawns 3/I00ml. to 49/I00ml. for pond water. Two shrimp sampleswere positive for v. parahaemolyticus bacterial counts, coliforms or E. colicounts did not show any correlation with water salinity, which rangedfrom 14-18ppt,Gram positive bacteria were predominant in shrimp and were representedby Micrococci (41.8%). Corynebacterium (19.3%) and Bacillus (14.2%).Common gram-negatives were Vibrios (19.2%) and Pseudomonas (5%)

Re-examining the Spatial Distribution of Fluoride in Groundwater of Sri Lanka: A Field Study at Nochchiyagama, Anuradhapura

Fluoride is well known for both beneficial and detrimental effects on human health. Fluorideimproves the dental health by preventing cavities. However, excessive amounts of fluoridelead to the development of dental and skeletal fluorosis. There is a narrow range betweenfluoride intake which is advantageous and those which begin to be damaging. Dentalfluorosis caused by fluoride rich drinking water is a common health issue in the dry climatezone of Sri Lanka. The spatial distribution of fluoride in groundwater in Sri Lanka has beenextensively studied and several fluoride distribution maps have been published to date.However, careful analysis of these maps reveal that the fluoride distribution presented insome geographical regions does not agree with each other. This study focused on examiningthe fluoride distribution in Nochchiyagama, Anuradhapura to re-evaluate its fluoridedistribution. During the study, approximately 200 water samples were collected from dug andtube wells, water reservoirs and canals. Fluoride concentration of the samples was determinedby the fluoride selective electrode method. Other physico-chemical properties of water suchas pH, conductivity, hardness etc. were determined by internationally accepted standardmethods. The average fluoride concentration in Nochchiyagama was 1.1±0.8 mg/l (n=202) inthe range 0.29 to 5.52 mg/l; however, many of the published maps state the fluoridedistribution in the Nochchiyagamaarea as 0.5 to 1.0 mg/l. A careful examination of thefluoride data reveals two distinct fluoride distribution patterns. The geographical areabetween the Puttlam-Anuradhapura highway (A12) and the Wilpaththu National Parkgenerally has a higher fluoride content with an average 1.2±1.0 mg/l (n=103) in the range0.31 to 5.52 mg/l. The area between Puttlam-Anuradhapura highway (A12) andThabuththegama-Anuradhapura highway (A28) has an average fluoride concentration of0.9±0.5 mg/l (n=99) in the range 0.29 to 2.53 mg/l. The first geographical area had abouteight fluoride hot spots (<2.5 mg/l) while other region had only two. One of the most visiblehydrological differences in these two regions is that the first region solely depends onrainwater for water requirements while the other one has a complex network of irrigationalcanals distributing water from the Kala Oya irrigational scheme

Preferred growth direction of III-V nanowires on differently oriented Si substrates

One of the nanowire (NW) characteristics is its preferred elongation direction. Here, we investigated the impact of Si substrate crystal orientation on the growth direction of GaAs NWs. We first studied the self-catalyzed GaAs NW growth on Si (111) and Si (001) substrates. SEM observations show GaAs NWs on Si (001) are grown along four directions without preference on one or some of them. This non-preferential NW growth on Si (001) is morphologically in contrast to the extensively reported vertical preferred GaAs NW growth on Si (111) substrates. We propose a model based on the initial condition of an ideal Ga droplet formation on Si substrates and the surface free energy calculation which takes into account the dangling bond surface density for different facets. This model provides further understanding of the different preferences in the growth of GaAs NWs along selected directions depending on the Si substrate orientation. To verify the prevalence of the model, NWs were grown on Si (311) substrates. The results are in good agreement with the three-dimensional mapping of surface free energy by our model. This general model can also be applied to predictions of NW preferred growth directions by the vapor-liquid-solid growth mode on other group IV and III–V substrates

Preferred growth direction of III-V nanowires on differently oriented Si substrates

One of the nanowire characteristics is its preferred elongation direction. Here, we investigated the impact of Si substrate crystal orientation on the growth direction of GaAs nanowires. We first studied the self-catalyzed GaAs nanowire growth on Si (111) and Si (001) substrates. SEM observations show GaAs nanowires on Si (001) are grown along four directions without preference on one or some of them. This non-preferential nanowire growth on Si (001) is morphologically in contrast to the extensively reported vertical preferred GaAs nanowire growth on Si (111) substrates. We propose a model based on the initial condition of an ideal Ga droplet formation on Si substrates and the surface free energy calculation which takes into account the dangling bond surface density for different facets. This model provides further understanding of the different preferences in the growth of GaAs nanowires along selected directions depending on the Si substrate orientation. To verify the prevalence of the model, nanowires were grown on Si (311) substrates. The results are in good agreement with the three-dimensional mapping of surface free energy by our model. This general model can also be applied to predictions of nanowire preferred growth directions by the vapor-liquid-solid growth mode on other group IV and III-V substrates

GaAsP nanowires containing intentional and self-forming quantum dots

Downloading of the abstract is permitted for personal use only. GaAsP nanowires (NWs) containing a range of different heterostructures are shown to be a highly promising system for the fabrication of efficient and novel ultra-small light emitters. NWs containing GaAs radial quantum wells (QWs) have emission with high thermal stability, due to both large electron and hole confinement potentials. A structure containing three QWs exhibits very low threshold lasing at low temperatures. Within the GaAsP central region of the same NW, the formation of quantum wires (QWRs) on three of the six vertices is observed, these QWRs are aligned parallel to the NW axis. The presence of twins causes a 180° rotation of the crystal about the growth axis, breaking the QWRs into short sections which may act as quantum dots (QDs). Optical studies of the NWs support the formation of optically active QWRs and QDs. In a second type of NW, during growth of the GaAsP NW core the introduction of a short GaAs section forms a QD. The inclusion of up to 50 QDs with high structural and optical quality is shown to be possible; indicating the potential for the fabrication of QD lasers. A structure with only one QD exhibits a single sharp emission line and behavior consistent with single exciton recombination. The addition of passivation layers, grown as a shell on the NW core, is shown to be essential in obtaining good optical properties. Our studies hence demonstrate that GaAsP-GaAs NWs containing heterostructures have significant potential for a range of novel light emitting applications