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Contraction of the ciliary muscle during marked accommodation causes the leading edge of the retina to advance as much as 0.5 centimeter. Near the posterior pole of the eye, the upward and downward extensional strains on the retina should be reasonably balanced. In the horizontal meridian an asymmetry is introduced because of the nasal location of the optic nerve head. Observers were asked to bisect the space between two parallel lines while fixating a movable line lying near the midpoint of the two lines. The test was conducted with the target far from and near the subject, in the horizontal and vertical meridians, and was repeated with accommodation paralyzed by a cycloplegic agent. Marked accommodation induced significant spatial distortions in the horizontal meridian. The effect is largely retinal. 相似文献
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Streptococcus agalactiae Multilocus sequence type 261 is associated with mortalities in the emerging Ghanaian tilapia industry
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Jeffery W. Bentley Jorge Andrade-Piedra Paul Demo Beloved Dzomeku Kim Jacobsen Enoch Kikulwe 《Journal of Crop Improvement》2018,32(5):599-621
Vegetatively propagated crop (VPC) seed tends to remain true to varietal type but is bulky, often carries disease, and is slow to produce. So VPC seed needs to be handled differently than that of other crops, e.g., it tends to be sourced locally, often must be fresh, and it is less often sold on the market. Hence, a framework was adapted to describe and support interventions in such seed systems. The framework was used with 13 case studies to understand VPC seed systems for roots, tubers, and bananas, including differing roles and sometimes conflicting goals of stakeholders, and to identify potential coordination breakdowns when actors fail to develop a shared understanding and vision. In this article, we review those case studies. The framework is a critical tool to (a) document VPC seed systems and build evidence; (b) diagnose and treat coordination breakdown and (c) guide decision-makers and donors on the design of more sustainable seed system interventions for VPCs. The framework can be used to analyze past interventions and will be useful for planning future VPC seed programs. 相似文献
5.
Daniel Adjei‐Boateng Michael Kojo Essel Nelson Wheatson Agbo 《Aquaculture Research》2012,43(10):1480-1486
This study was conducted to assess the optimum clam size and substratum type for the culture of Galatea paradoxa. The experiment was conducted over a 90‐day period at the Volta Estuary, Ghana. Three size classes of G. paradoxa categorized as small (27.6 ± 0.4 mm), medium (36.8 ± 0.4 mm) and large (50.0 ± 0.6 mm), were used to ascertain the effect of a sandy and muddy substratum on growth performance and survival. Growth increased from the small‐sized clams to the large‐sized clams at 2.54, 3.03 and 3.43 g, respectively, over the experimental period. Growth was higher (P < 0.05) in the muddy substratum (3.58 g) compared with sandy (2.41 g). Similarly, the specific growth rate increased from 0.99% day?1 in the small‐sized clams to 1.36% day?1 in the large‐sized clams. Survival rates were significantly higher (99.4%) for the large‐sized clams compared with the medium (78.8%) and the small‐size clams (74.1%). There was significant interaction between the size class and the substratum type with a trend towards increasing survival rate from the small to the large size clams in both substrata. The survival rate was lower in the muddy substratum (71.4%) compared with the sandy substratum (96.7%). The yield was significantly higher in the muddy (2.01 kg m?2 90 day?1) compared with sandy substratum (1.87 kg m?2 90 day?1). The results of this study indicate that the culture of small‐sized clams is best practiced on sandy substratum due to their elevated survival rates, whereas the muddy substratum appears most suitable for the culture of larger clams (>40 mm) because of their relatively higher survivorship and better growth performance. 相似文献
6.
Ten multipurpose tree species were planted both in monoculture and intercropped withArachis hypogea (groundnut) in a randomized complete block with three replications. The vigrou, biomass, nutrient content, and coppicing percentage of the trees were evaluated. Intercropping with groundnuts during the establishment phase did not affect subsequent growth and development of the species.Acacia mangium, Acacia auriculiformis, Cassia siamea, Calliandra calothyrsus andParaserianthes falcataria established well, when compared toGliricidia sepium, Leucaena leucocephala, Dialum guineense, Dubocia macrocarpa andMilicia excelsa. A. mangium, A. auriculiformis, C. calothyrsus, C. siamea andP. falcataria produced the highest leaf (4 to 20 t ha–1) and wood (12 to 37 t ha–1) biomass yield (primary growth) at one to three years after planting. Coppicing percentage ofA. mangium A. auriculiformis andP. falcataria were relatively low (35 to 50%).C. calothyrsus andC. siamea showed the highest coppicing percentage (95 to 100%) and produced the greatest coppice biomass (9 to 13 t ha–1). Total nitrogen and organic matter percentage of soils from under the stands of these two species were also significantly higher than that of the rest. The two species may thus be considered for use in agroforestry technologies for soil improvement on acid soils, which are typical of the moist tropics. 相似文献
7.
Aduli Enoch Othniel MALAU-ADULI Gideon Shaibu BAWA Kayode JOEL 《Animal Science Journal》2003,74(3):239-242
Egg production and layer bird mortality data obtained from five different private farms in Zaria within the subhumid zone of Nigeria, over a 6‐year period (1994–1999) were subjected to least squares analysis to determine the effects of age, season and year. It was demonstrated that age had a highly significant influence (P < 0.01) on egg production in that birds falling within the age group 30–39 weeks produced the highest number of eggs (3255 ± 109), while birds over 100 weeks of age produced the lowest number of eggs (1206 ± 412). Similarly, seasonal variation in egg production was also significant (P < 0.05); the highest egg production (2926 ± 90) was obtained during the early dry season, and the lowest (2423 ± 95) during the late wet season. Mortality was generally low (0.0–0.9%) and not significantly different from 20 to 49 weeks of age (P > 0.05). However, from 50 to 100 weeks of age, highly significant differences (P < 0.01) in mortality were observed, with the 90–100 weeks age group recording the highest mortality of 15.7 ± 1.3%. Furthermore, yearly variations in egg production and mortality were highly significant (P < 0.01) with 1999 producing the most eggs (4410 ± 102) and recording the lowest mortality (1.4%). It was concluded that due to the significant seasonal, age and yearly variations, data on egg production and mortality need to be adjusted for these effects to enable unbiased comparison between and within farms. Furthermore, farmers can make adequate feeding preparations commensurate with each season for optimal egg production. 相似文献
8.
Marney E. Isaac Eric O. Adjei Roland N. Issaka Vic R. Timmer 《Agroforestry Systems》2011,81(2):147-155
Shade tolerant species response to nutrient additions and light regulation by canopy trees in perennial agroforestry systems
has been well documented. However, accelerated early growth, particularly in cocoa-shade systems, may be offset by competition
for limited resources on nutrient poor sites. To date, few agroforestry management strategies focus on nutrient manipulation
of the shade tree component or strategies for precision nutrient application. Our research objective was to diagnose interactions
between nutrient supplied shade trees intercropped with cocoa. We established greenhouse trials in Kwadaso, Ghana cultivating
Terminalia superba seedlings with four fertility treatment levels: conventional rate (current practices) under linear additions, and half, full
and double conventional rate under exponential additions (steady-state nutrition) to determine maximal growth and nutrient
uptake. After 4 months of additions in the nursery, pre-fertilized T. superba seedlings were then out-planted into field trials with cocoa seedlings. After 4 months of intercropping, cocoa associated
with half rate exponentially supplied T. superba had significantly larger leaf area, greater leaf number, and higher nutrition (N and P uptake) than cocoa associated with
full rate conventionally supplied T. superba. This may be attributed to (1) more favorable light conditions under these taller shade seedlings and (2) the internal use
of nutrients associated with exponentially supplied T. superba seedlings, which lowered stress on native soil resources. The latter is corroborated with our findings on soil fertility
status. This strategy focused on reducing fertilizer inputs and developing precise plant nutrition technology for on-farm
use. Our findings suggest that shade seedlings under steady state nutrition can mitigate early growth competition in the field. 相似文献
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