Cross-fostering and Parent-offspring Responses in Cichlasoma citrinellum (Pisces, Cichlidae)

Previous studies of parent-young interactions in cichlid fish have established some of the details of such relations, but have raised, or left unanswered many questions. In particular, there are questions as to the recognition of parents and young by each other, and to what extent learning might be involved in such recognition. Based on observations of exchanges of parents between families of Cichlasoma citrinellum, we suggest that parents learn to recognize young during each parental cycle. They appear to have a moderately short term memory for recognition of young, and accept young corresponding to this memory. Parental fish accept conspecific fry younger than, or the same age, but not those older than their own. Successive presentations of young fry maintained parental behavior for much longer than normal. Changes in color pattern, and some aspects of parental behavior are described

An economic analysis of soil conservation policy for selected commercial farms in KwaZulu-Natal.

Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1995.Inherent in the erosion process is a high level of uncertainty. This is associated with the inability to accurately quantify and predict the consequences of prolonged erosion for agricultural production, or estimate the time period over which induced innovations will be able to compensate for it. Therefore, there are incentives to formulate strategies that will achieve tangible reductions in erosion. Data were collected through a postal survey conducted in October 1993, from the following five commercial farming regions: Dalton/Wartburg, Camperdown/Eston, Dundee, Estcourt, and Winterton. Soil conservation incentives are expected to differ according to enterprise types and site-specific circumstances, and stratifying according to these regions incorporates a diverse spectrum of agricultural systems. There were 480 potential survey respondents, and 159 (35 percent) usable questionnaires were returned. The response rate is relatively good for a postal survey, although results may be slightly biased in favour of farmers that are concerned or interested in soil conservation. Adoption of soil conservation measures is modelled as a multi-stage decision process, representing the following phases: awareness of the erosion problem, the perception that erosion is worth trying to resolve, farmers' technical and financial abilities to implement soil conservation measures required for their farms, and finally the actual adoption of conservation practices. A logistic regression analysis shows visible erosion impacts, knowledge of erosion's adverse implications for agricultural productivity, farmers' willingness to invest their own capital in conservation activities, predominantly crop farms, and sufficient financial resources, have significant positive impacts on adoption. The mean predicted probability score for the Technical Ability model is 0.54, illustrating farmers' lack of technical soil conservation skills to implement appropriate conservation measures is a major constraining factor within the adoption process. Variables influencing conservation effort, reflecting the extensiveness and effectiveness of soil conservation measures, are expected to differ from those affecting adoption, and effort is modelled separately using linear regression. Results support prior expectations indicating conservation effort depends mainly on the following financial characteristics: farmers' willingness to invest their own capital in conservation activities, debt fmancing, and on-farm financial and managerial benefits from implementing soil conservation activities. Farmers' perceptions regarding the monitoring and enforcement of soil conservation legislation are also analyzed using frequency tables. Although 65 percent of respondents believe that violations of Act 43/1983 will be discovered, only 20 percent perceive that transgressions will be both detected and subsequently prosecuted. This suggests the transactions costs related to enforcing prosecutions are high, and the possibility of being prosecuted is unlikely to encourage farmers to implement soil conservation activities. Agents (eg. Soil Conservation Committees and extension officers), and media (eg. extension service reports) play an invaluable role in promoting soil conservation. High transactions costs associated with enforcing legislation indicate it may be appropriate for the government to play an active part in research, and in providing information about erosion and soil conservation, to facilitate a better functioning land market. This is distinct from having a clear advantage over market forces in the use of this information. Cross-compliance programs, should perhaps be considered as short to medium-term strategies, to encourage farmers to implement soil conservation activities

Expansion and Collapse in the Cosmic Web

We study the kinematics of the gaseous cosmic web at high redshift with Lyman alpha forest absorption in multiple QSO sightlines. Using a simple analytic model and a cosmological hydrodynamic simulation we constrain the underlying three-dimensional distribution of velocities from the observed line-of-sight distribution of velocity shear across the plane of the sky. The distribution is found to be in good agreement with the intergalactic medium (IGM) undergoing large scale motions dominated by the Hubble flow. Modeling the Lyman alpha clouds analytically and with a hydrodynamics simulation, the average expansion velocity of the gaseous structures causing the Lyman alpha forest in the lower redshift (z = 2) sample appears about 20 percent lower than the local Hubble expansion velocity. We interpret this as tentative evidence for some clouds undergoing gravitational collapse. However, the distribution of velocities is highly skewed, and the majority of clouds at redshifts from 2 to 3.8 expand typically about 5 - 20 percent faster than the Hubble flow. This behavior is explained if most absorbers in the column density range typically detectable are expanding filaments that stretch and drain into more massive nodes. We find no evidence for the observed distribution of velocity shear being significantly influenced by processes other than Hubble expansion and gravitational instability, like galactic winds. To avoid overly disturbing the IGM, winds may be old and/or limp by the time we observe them in the Lyman alpha forest, or they may occupy only an insignificant volume fraction of the IGM. (abridged)Comment: 63 pages, 26 figures, AAS Latex; ApJ, in pres

Transition from single to multi-walled carbon nanotubes grown by inductively coupled plasma enhanced chemical vapor deposition

In this work a simple and up-scalable technique for creating arrays of high purity carbon nanotubes via plasma enhanced chemical vapor deposition is demonstrated. Inductively coupled plasma enhanced chemical vapor deposition was used with methane and argon mixtures to grow arrays in a repeatable and controllable way. Changing the growth conditions such as temperature and growth time led to a transition between single and multi-walled carbon nanotubes and was investigated. This transition from single to multi-walled carbon nanotubes is attributed to a decrease in catalytic activity with time due to amorphous carbon deposition combined with a higher susceptibility of single-walled nanotubes to plasma etching. Patterning of these arrays was achieved by physical masking during the iron catalyst deposition process. The low growth pressure of 100 mTorr and lack of reducing gas such as ammonia or hydrogen or alumina supporting layer further show this to be a simple yet versatile procedure. These arrays were then characterized using scanning electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy. It was also observed that at high temperature (550 °C) single-walled nanotube growth was preferential while lower temperatures (450 °C) produced mainly multi-walled arrays

The Effects of Air Pollution Particles on Clearance Mechanisms Within the Lung

The effects of inhaled aIr pollution particles on lung clearance mechanisms is an important factor in understanding how the mammalian lung deals with such pollutants and, as such, how exposure to these pollutants can be regulated. The nanoparticle(diameter S lOOnm) and transition metal components of PMIO (particulate matter with a diameter less than lO~m) have been implicated as playing major roles in the impairment of alveolar macrophage function and the subsequent retention of particles in the respiratory system. The aim of this study was to investigate the effects of components of PMIO on macrophage functions both directly, by examining macrophage phagocytosis and migration, and indirectly, by studying peripheral factors affecting macrophagefunction such as recruitment by type II cells and complement based mechanisms.We hypothesised that the alveolar epithelial type II cell line would release leukocyte chemoattractants in response to particle exposure and that this could be measured by use of a macrophage migration assay. A sub-toxic dose (125 ~g/ml)of surrogate air pollutionparticles (fine and nanoparticle carbon black and titanium dioxide) was established by measuring LOH release from a murine alveolar macrophage cell line (1774.2) and an alveolar epithelial type II cell line (L-2) in response to particle exposure. Optimisation ofa chemotaxis assay and measurement of macrophage migration towards conditioned medium obtained from the particle-exposed type II cells was conducted and it was determined that carbon black nanoparticles induced type II cells to secrete a chemoattractant that resulted in significant increases in macrophage migration compared to the negative control. This was in contrast to other particle types tested in this study which did not induce any increases in macrophage migration.It was also hypothesised that complement proteins could be involved in macrophage recruitment to sites of particle deposition and, as such, the migration of macrophages towards particle exposed blood serum was examined in vitro. Foetal bovine serum (FBS) was exposed to fine and nanoparticle caroon black and titanium dioxide (l-Smg/ml) for 2 hours. It was found, in accord with the previous study involving type II cells, that carbon black nanoparticles could activate the generation of chemotactic factors in serum that could subsequently induce significant increases (