Genotoxicants: monitoring of occupational genotoxicants     

Perera FP 《Science (New York, N.Y.)》1986,234(4774):372-373

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Modelling land cover transitions: A solution to the problem of spatial dependence in data   总被引：1，自引：1，他引：1  

Weaver  Kevin  Perera  Ajith H. 《Landscape Ecology》2004,19(3):273-289

Raster-based spatial land cover transition models (LCTMs) are widely used in landscape ecology. However, many LCTMs do not account for spatial dependence of the input data, which may artificially fragment the output spatial configuration. We demonstrate the consequences of ignoring spatial dependence, thus assigning probabilities randomly in space, using a simple LCTM. We ran the model from four different initial conditions with distinct spatial configurations and results indicated that, after 20 simulation steps, all of them converged towards the spatial configuration of the random data set. From an ecological perspective this is a serious problem because ecological data often exhibit distinct spatial configuration related to ecological processes. As a solution, we propose an approach (region approach) that accounts for spatial dependence of LCTM input data. Underlying spatial dependence was used to apply spatial bias to probability assignment within the model. As a case study we applied a region approach to a Vegetation Transition Model (VTM); a semi-Markovian model that simulates forest succession. The VTM was applied to approximately 500,000 ha of boreal forest in Ontario, at 1 ha pixel resolution. When the stochastic transition algorithms were applied without accounting for spatial dependence, spatial configuration of the output data became progressively more fragmented. When the VTM was applied using the region approach to account for spatial dependence output fragmentation was reduced. Accounting for spatial dependence in transition models will create more reliable output for analyzing spatial patterns and relating those patterns to ecological processes.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   

Emulating natural landscape disturbance in forest management – an introduction   总被引：1，自引：0，他引：1  

Crow  Thomas R.  Perera  Ajith H. 《Landscape Ecology》2004,19(3):231-233

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Erratum     

Xianghua Xu  Xincai Chen  Jiyan Shi  Yingxu Chen  Weixiang Wu  A. Perera 《Journal of plant nutrition》2013,36(2)

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Studying genetic relationships among coconut varieties/populations using microsatellite markers     

L. Perera  J.R. Russell  J. Provan  W. Powell 《Euphytica》2003,132(1):121-128

The extent of genetic diversity and the genetic relationships among 94 coconut varieties/populations (51 Talls and 43 Dwarfs) representing the entire geographic range of cultivation/distribution of the coconut was assessed using 12 pairs of coconut micro satellite primers. A high level of genetic diversity was observed in the collection with the mean gene diversity of 0.647±0.139, with that of the mean gene diversity of Talls 0.703±0.125 and 0.374±0.204 of Dwarfs. A phenetic tree based on D_AD genetic distances clustered all the 94 varieties/populations into two main groups, with one group composed of all the Talls from southeast Asia, the Pacific, west coast of Panama, and all Dwarfs and the other of all Talls from south Asia, Africa, and the Indian Ocean coast of Thailand. The allele distribution of Dwarfs highlighted a unique position of Dwarf palms from the Philippines exhibiting as much variation as that in the Tall group. The grouping of all Dwarfs representing the entire geographic distribution of the crop with Talls from southeast Asia and the Pacific and the allele distribution between the Tall and Dwarf suggest that the Dwarfs originated from the Tall forms and that too from the Talls of southeast Asia and the Pacific. Talls from Pacific Islands recorded the highest level of genetic diversity (0.6±0.26) with the highest number of alleles (51) among all the regions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Fertility in buffaloes after oestrus synchronisation with cloprostenol and fixed time insemination.     

N Pathiraja  A S Abeyratne  B M Perera  V Buvanendran 《The Veterinary record》1979,104(13):279-281

Fifty-seven cycling buffalo cows of the river type were treated with two doses of 0.5 mg cloprostenol intramuscularly given 11 days apart. Each animal was inseminated twice at 72 and 96 hours after the second injection of cloprostenol. The first service conception rate diagnosed by rectal palpation at 90 days was 38.6 per cent. At the time of insemination the cervix was easily penetrable on both days in only 39 (68.4 per cent) of the animals. They were inseminated at or beyond the internal cervical os, while the others were inseminated in the cervical canal. There was a marked difference in conception rate between those receiving deep inseminations (48.7 per cent) and the others (16.7 per cent). In relation to the interval from calving to insemination the conception rates for those which had calved 60 to 90, 90 to 120 and 120 to 150 days earlier were 16.6, 36.4 and 55.5 per cent respectively. The use of cloprostenol treatment and fixed-time insemination is a useful method of overcoming the problem of oestrus detection in buffaloes. Acceptable levels of fertility can be obtained in those animals which have a sufficiently relaxed cervix to permit semen deposition at the internal os, provided the interval from calving to insemination is more than 90 days.  相似文献   

Effect of Supplementation of a Basal Diet of Maize Stover with Erythrina variegata,Gliricidia sepium or Leucaena leucocephala on Feed Intake and Digestibility by Goats     

Aregheore EM  Perera D 《Tropical animal health and production》2004,36(2):175-189

Two 4 x 4 Latin square design experiments were carried out. In experiment 1, four mature Anglo-Nubian x Fiji local goats, pre-experimental body weight 25.0 +/- 0.6 kg, 22-24 months old, were used to study the effect of supplementation of a basal diet of maize stover with Erythrina variegata (EV), Gliricidia sepium (GS) and Leucaena leucocephala (LL) on dry matter intake (DMI) and nutrient digestibility. Maize stover treated with urea was used as a control diet. E. variegata was higher in crude protein content than LL or GS. The DMI of the urea treated stover diet was significantly lower (p < 0.05) than that of the diets of untreated stover supplemented with forage legumes. The DMI was significantly lower (p < 0.05) in the GS diet than in the EV or LL diets. Significant (p < 0.05) differences existed between the urea-treated stover and the diets of stover supplemented with forage legumes in the digestibility of dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), organic matter (OM) and energy. In experiment 2, four mature goats, pre-experimental body weight 27.0 +/- 0.3 kg, 24-28 months old, were used to measure their response when the urea-treated maize stover and the maize stover and forage legume diets were sprayed with molasses. The intake of the urea-treated stover diet sprayed with molasses was significantly lower (p < 0.05) that that of the maize stover/forage legume diets sprayed with molasses. The DMI of the diets improved with the addition of molasses. The DMI among the goats offered the maize stover/forage legume diets + molasses did not differ significantly. (p > 0.05). Statistically significant (p < 0.05) differences were obtained in this second study between the urea-treated stover and the stover supplemented with forage legumes in the digestibility of DM, CP, NDF, OM and energy. The stover supplemented with forage legumes had a higher (p < 0.05) nutrient digestibility. The present studies demonstrated that the use of forage legumes as protein supplements improved the feed quality of maize stover in the diets of mature goats. It is suggested that molasses should be sprayed on fresh leaves of Gliricicia sepium and other forage legumes that are initially rejected, in order to improve acceptance and DMI when fed to ruminant animals in confinement or in a cut-and-carry system of production.  相似文献   

Seroprevalence of Sarcosystis spp. in cattle and buffaloes from the wet and dry zones of Sri Lanka: a preliminary study     

Kalubowila DG  Udagama-Randeniya PV  Perera NA  Rajapakse RP 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2004,51(2):89-93

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of antibodies to Sarcosystis infection in cattle and buffaloes. Crude antigens derived from cystozoites of Sarcosystis cruzi and antibodies from the sera of naturally infected cattle and buffaloes were used. The assay was validated by determination of the specificity, sensitivity and negative and positive predictive values. Using ELISA, a sero-epidemiological survey for sarcosystosis was carried out in cattle (n = 215) and buffaloes (n = 123) from the wet and dry zones of Sri Lanka. The prevalence of infection in cattle was 69.3%. Prevalence of the infection collectively in both cattle and buffaloes in the dry zone was significantly higher (P < 0.001) than that in the wet zone. The number of sero-positive cattle and buffaloes in the dry zone was significantly higher than that in the wet zone (P < 0.05). Buffaloes in the dry and wet zones showed a greater prevalence of infection (P < 0.05) than cattle.  相似文献   

The effect of metabolic stress disinfection and disinfestation (MSDD) on ‘Hass’ avocado fruit physiology and mortality of longtailed mealybug (Pseudococcus longispinus)     

F. Zulhendri  L.E. JamiesonC.O. Perera  R.M. McDonaldP.G. Connolly  S.Y. QuekA.B. Woolf 《Postharvest Biology and Technology》2012,64(1):138-145

Metabolic stress disinfection and disinfestation (MSDD) is a potential quarantine treatment in which a combination of cycles of rapid decompression and compression are followed by exposure to ethanol vapour under decompression. The response of ‘Hass’ avocado (Persea americana Mill., cv. Hass) to MSDD treatment for control of longtailed mealybug (Pseudococcus longispinus) was investigated. The best treatment for the most resistant life stage (2nd/3rd instars) was 90-min MSDD treatment with 371 mg L⁻¹ ethanol. Early and late season ‘Hass’ avocados were subjected to MSDD treatments (with 371 mg L⁻¹ ethanol), or in air (control). Following the treatments, early season fruit were ripened at 20 °C and 25 °C. Half of the late season fruit were ripened at either 20 °C or 25 °C, and the remainder were stored at 5.5 °C for 6 weeks, then ripened at 20 °C. There were no significant difference in quality and rot incidence between non-treated controls and MSDD-treated fruit. The main disorders found were stem-end and body rots, vascular browning and flesh greying for the stored fruit. There were also no significant differences in fruit respiration rate or ethylene production. Thus, MSDD was shown to be a potentially ‘soft’ disinfestation treatment for surface pests of avocado.  相似文献   

Exercise-induced pulmonary haemorrhage in Thoroughbred racehorses: a longitudinal study     

E. J. Crispe  C. J. Secombe  D. I. Perera  A. A. Manderson  B. A. Turlach  G. D. Lester 《Equine veterinary journal》2019,51(1):45-51

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