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排序方式: 共有222条查询结果,搜索用时 31 毫秒
101.
Qi Ye Henderson Mark Xu Ming Chen Jin Shi Peijun He Chunyang Skinner G. William 《Landscape Ecology》2004,19(4):375-388
We characterized and analyzed the dynamics of a rapidly expanding urban landscape of Beijing Municipality, based on the Hierarchical Regional Space (HRS) model. We focused on ecological processes such as flows of energy, materials and population between the urban core and its periphery, and how these processes co-evolved with urbanization. We treated the HRS as an alternative to the cellular automata (CA) approach to characterizing and modeling of landscape dynamics. With LANDSAT data, we showed that the urban area of Beijing expanded from 269 km2 to 901 km2 in the period from 1975 to 1997, an increase of 2.35 times in 22 years. Meanwhile, a number of secondary urban centers formed on areas that used to be sparsely populated around the city. These secondary centers quickly expanded and ultimately merged with each other and with the urban core. The changes in spatial pattern and organization were accompanied by evolution of urban functions and particularly the interactions between the urban core and its periphery. We demonstrated a dramatic increase in dependence of the urban core on the periphery as well as the cores influence on the periphery with a case analysis of the vegetable supply to Beijing. The tightening link between the city and its periphery reinforces the urbanization process and further drives the transformation of the regions landscape. We conclude that the HRS model is capable of characterizing the patterns and processes of complex and dynamic landscapes such as the case of Beijing, and this model has great potential for quantitative modeling of human dominated landscapes as well.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
102.
Nasal and frontal sinus mucosa of the adult dog contain numerous olfactory sensory neurons and ensheathing glia 总被引:4,自引:0,他引:4
Skinner AP Pachnicke S Lakatos A Franklin RJ Jeffery ND 《Research in veterinary science》2005,78(1):9-15
Olfactory glial cells have been the focus of much recent research interest because of their possible future use as cellular transplants in repair of spinal cord injury. Although olfactory glial cells can be collected from the olfactory bulb for in vitro culture, alternative sites would be preferable for safer surgical access. This study was designed to investigate the distribution of olfactory sensory neurons and olfactory glial cells within the canine peripheral olfactory system. Using immunohistochemistry and electron microscopy on perfused tissue we demonstrate that olfactory sensory neurons are found in both the caudal nasal and the frontal sinus epithelia. Olfactory ensheathing glia were found in the mucosa at both these sites implying that surgical access for harvesting cells for transplantation would be straightforward. 相似文献
103.
Carbon and phosphorus transformations during decomposition of pine forest floor with different phosphorus status 总被引:7,自引:0,他引:7
Summary Information on the mineralization of inorganic phosphate (Pi) from organically bound P (Po) during decomposition of forest floor and soil organic matter is vital for understanding P
supply in forest ecosystems. Carbon (C) and phosphorus (P) fluxes were determined for forest floor samples from three Pinus radiata plots which had received no P (Control), 62.5 kg P ha–1 (Low P) and 125 kg P ha–1 (High P) 20 years before sampling. The P concentration of the forest floor samples had increased with fertilizer application,
and the C:P ratio ranged between 585 and 1465. During a 9-week laboratory incubation 8.2–19.0% of the forest floor C was evolved
as CO2-C. The amount of CO2 evolved from the forest floor of the Control plot was more than twice the amounts from the Low P and High P plots. There
was little change in net P mineralization in the Control and Low P treatments throughout the incubation, but it increased
slightly for the High P samples, suggesting a critical forest floor C:P ratio of 550 for net P mineralization. Changes in
the 32P-specific activities of the Pi and microbial P pools during incubation, and concurrent changes in microbial-32P and 32Pi, indicated internal P cycling between these pools. The rate of internal P cycling varied with forest floor quality, and was
highest in the High P forest floor. The High P samples had microbial C:P ratios of 22 : 1 which remained constant during the
incubation, suggesting the microorganisms had adequate P levels.
Received: 2 July 1997 相似文献
104.
105.
Captive breeding of the white rhinoceros, Ceratotherium simum, and the Cape buffalo, Syncerus caffer
Skinner JD Dott HM Matthee A Hunt L 《The Onderstepoort journal of veterinary research》2006,73(3):237-239
Breeding records of 40 white rhinoceros and 155 Cape buffalo were analysed. Three rhinoceros cows bred in captivity, themselves conceived for the first time at 84, 87 and 95 months of age, respectively. Rhinoceros cows breed throughout the year. There is no evidence of a relationship between calving interval and month of birth. Calving intervals were normally distributed about the mean of 34 months and there were no significant differences between bulls, cows or sex of calf. There was no difference in the sex ratio of calves born to young cows nor older cows. The male:female ratio of the calves was 1:1. Younger cows did not have shorter birth intervals. Although captive Cape buffaloes breed throughout the year, there is a preponderance of births in midsummer. There was some evidence that larger cows produce heavier calves and that season of birth may influence birth weight. Male calves weighed 41.20 +/- 0.68 kg vs 39.00 +/- 0.73 kg (range 24-60 kg) for female calves but this difference was not significant. Calving intervals were normally distributed about the mean of 395 days and the male:female ratio of the calves was 1:1.2. 相似文献
106.
Transgenic sterility in Populus: expression properties of the poplar PTLF, Agrobacterium NOS and two minimal 35S promoters in vegetative tissues 总被引:2,自引:0,他引:2
Transgenic sterility is a desirable trait for containment of many kinds of transgenes and exotic species. Genetically engineered floral sterility can be imparted by expression of a cytotoxin under the control of a predominantly floral-tissue-specific promoter. However, many otherwise desirable floral promoters impart substantial non-floral expression, which can impair plant health or make it impossible to regenerate transgenic plants. We are therefore developing a floral sterility system that is capable of attenuating undesired background vegetative expression. As a first step towards this goal, we compared the vegetative expression properties of the promoter of the poplar (Populus trichocarpa Torr. & Gray) homolog of the floral homeotic gene LEAFY (PTLF), which could be used to impart male and female flower sterility, to that of three candidate attenuator-gene promoters: the cauliflower mosaic virus (CaMV) 35S basal promoter, the CaMV 35S basal promoter fused to the TMV omega element and the nopaline synthase (NOS) promoter. The promoters were evaluated via promoter::GUS gene fusions in a transgenic poplar hybrid (Populus tremula L. x P. alba L.) by both histochemical and fluorometric GUS assays. In leaves, the NOS promoter conveyed the highest activity and had a mean expression level 5-fold higher than PTLF, whereas the CaMV 35S basal promoter fused to the omega element and the CaMV 35S basal promoter alone directed mean expression levels that were 0.5x and 0.35x that of PTLF, respectively. Differential expression in shoots, leaves, stems and roots was observed only for the NOS and PTLF promoters. Strongest expression was observed in roots for the NOS promoter, whereas the PTLF promoter directed highest expression in shoots. The NOS promoter appears best suited to counteract vegetative expression of a cytotoxin driven by the PTLF promoter where 1:1 toxin:attenuator expression is required. 相似文献
107.
Newton M Fitzgerald S Rose RR Adams PW Tesch SD Sessions J Atzet T Powers RF Skinner C 《Science (New York, N.Y.)》2006,313(5787):615; author reply 615
Based on limited sampling 2 years after the 2002 Biscuit Fire in Oregon, Donato et al. (Brevia, 20 January 2006, p. 352) concluded that postfire logging reduced seedling regeneration by 71%. Analysis of the study methodology and raw data suggest that this estimate is statistically flawed and misleading and says nothing about the impacts of more prompt postfire harvest. 相似文献
108.
RA McKenzie AM Carmichael ML Schibrowski SA Duigan JA Gibson JD Taylor 《Australian veterinary journal》2009,87(1-2):27-32
Polioencephalomalacia was diagnosed histologically in cattle from two herds on the Darling Downs, Queensland, during July–August 2007. In the first incident, 8 of 20 18-month-old Aberdeen Angus steers died while grazing pastures comprising 60% Sisymbrium irio (London rocket) and 40% Capsella bursapastoris (shepherd's purse). In the second incident, 2 of 150 mixed-breed adult cattle died, and another was successfully treated with thiamine, while grazing a pasture comprising almost 100% Raphanus raphanistrum (wild radish). Affected cattle were either found dead or comatose or were seen apparently blind and head-pressing in some cases. For both incidents, plant and water assays were used to calculate the total dietary sulfur content in dry matter as 0.62% and 1.01% respectively, both exceeding the recommended 0.5% for cattle eating more than 40% forage. Blood and tissue assays for lead were negative in both cases. No access to thiaminase, concentrated sodium ion or extrinsic hydrogen sulfide sources were identified in either incident. Below-median late summer and autumn rainfall followed by above-median unseasonal winter rainfall promoted weed growth at the expense of wholesome pasture species before these incidents. 相似文献
109.
110.
Kessler JD Kahle KT Sun T Meerbrey KL Schlabach MR Schmitt EM Skinner SO Xu Q Li MZ Hartman ZC Rao M Yu P Dominguez-Vidana R Liang AC Solimini NL Bernardi RJ Yu B Hsu T Golding I Luo J Osborne CK Creighton CJ Hilsenbeck SG Schiff R Shaw CA Elledge SJ Westbrook TF 《Science (New York, N.Y.)》2012,335(6066):348-353