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471.
Keith Clay 《Researches on Population Ecology》1996,38(2):191-201
The interaction between two species often depends on the presence or absence of a third species. One widespread three-species
interaction involves fungal endophytes infecting grasses and the herbivores that feed upon them. The endophytes are allied
with the fungal family Clavicipitaceae and grow systemically in intercellular spaces in above-ground plant tissues including
seeds. Like relatedClaviceps species, the endophytes produce a variety of alkaloids that make the host plants toxic or distasteful to herbivores. A large
number of grass species are infected, especially cool-season grasses in temperate areas. Field and laboratory studies have
shown that herbivores avoid infected plants in choice trials and suffer increased mortality and decreased growth on infected
grasses in feeding experiments. Resistance to herbivores may provide a selective advantage to infected plants in competitive
interactions with noninfected plants. Recent studies have shown that differential herbivory can reverse competitive hierarchies
among plant species. Both endophyte-infected and noninfected tall fescue grass (Festuca arundinacea) are outcompeted by orchardgrass (Dactylis glomerata) in the absence of insect herbivory. However, when herbivores are present infected tall fescue outcompetes orchardgrass.
These results suggest that the frequency of infection in grass species and grassland communities will increase over time.
Several studies are reviewed illustrating increases in infection frequency within grass populations subject to herbivore pressure.
Endophytic fungi may be important regulators of plant-herbivore interactions and so indirectly affect the structure and dynamics
of plant communities. 相似文献
472.
Two parallel surveys were carried out based in the north-east of England and Cumbria: one ascertaining statutory social work services provided for child and adult survivors of sexual abuse, the other drawing upon the perceptions of adult survivors of child sexual abuse about existing and desirable forms of provision for adults and children. The surveys indicate the need for greater genuine partnership between service users and statutory agencies in the field of child sexual abuse, similar to that which is being pioneered in the field of adult care and disability. A community-orientated response to sexual abuse, centred on service-users, is required if one of the largest social problems facing us today is to be effectively challenged. 相似文献
473.
Keith Hitchins 《International social security review》1993,46(3):79-98
In Hungary for most of the nineteenth century mutual benefit societies played a key role in providing various social groups with aid in case of illness, accident, disability or death. The majority were linked to the burgeoning working-class movement and were voluntary associations whose members had no other recourse in times of adversity. Hungary was undergoing transformation in the nineteenth century. Changes in goods production and the craft guilds accelerated the establishment of workers'benefit societies, and so did the lack of a coherent system of social insurance in the new industrial order. They grew in tandem with the expansion of Hungary's economy and the return of constitutional government in 1867, and flourished from the 1870s to the decade preceding the First World War. Austria and Germany provided theoretical justifications and practical models. By the 1890s voluntary mutual benefit societies faced increasing competition from the State. As the economy and social structures evolved, successive governments sponsored their own insurance programmes. By the turn of the century, private companies were also offering life and accident insurance and the appeal of mutual benefit societies to both workers and the middle class diminished. Between the two world wars, they continued to serve a substantial segment of the population. 相似文献
474.
This study examined the mediating role of self-perceived health between perceived spirituality, religiosity, and life satisfaction
among a stratified, random sample of college students, while controlling for gender. Although both models displayed excellent
fit criteria, the perceived spirituality and life satisfaction model was fully mediated by self-perceived health χ2 (n=459, 4) = 1.64, p=0.80, CFI =0.99, TLI=0.99), and the perceived religiosity and life satisfaction model was partially mediated by self-perceived
health χ2 (n=459, 10) = 22.29, p=0.01 CFI = 0.99, TLI = 0.99). Both models were equal for men and women. Students who describe themselves as spiritual (or
religious) are likely to report greater self-perceived health and greater self-perceived health likely influences life satisfaction
for both men and women. Results preliminarily support the contention that life satisfaction is related to differing reported
health status, whether physical or mental, and that life satisfaction may be influenced by religiosity and spirituality engagement.
Implications for colleges and universities are discussed. 相似文献
475.
Given the high prevalence of tuberculosis (TB) and the mortality rate associated with the disease, numerous models, such as the Gammaitoni and Nucci (GN) model, were developed to model the risk of transmission. These models typically rely on a quanta generation rate as a measurement of infectivity. Since the quanta generation rate cannot be measured directly, the unique contribution of this work is to develop state estimators to estimate the quanta generation rate from available measurements. To estimate the quanta generation rate, the GN model is adapted into an augmented single-room GN model and a simplified two-room GN model. Both models are shown to be observable, i.e., it is theoretically possible to estimate the quanta generation rate given available measurements. Kalman filters are used to estimate the quanta generation rate. First, a continuous-time extended Kalman filter is used for both adapted models using a simulation and measurement sampling rate of 60 s. Accurate quanta generate rate estimates are achieved in both cases. A more realistic scenario is also considered with a measurement sampling rate of one day. For these estimates, a hybrid extended Kalman filter (HEKF) is used. Accurate quanta generation rate estimates are achieved for the more realistic scenario. Future work could potentially use the HEKFs, the adapted models, and real-time measurements in a control system feedback loop to reduce the transmission of TB in confined spaces such as hospitals. 相似文献
476.
This paper treats some of the important considerations in constructing an analytical model for the distribution of demand during lead time. It presents a formal model that can be developed along one of two lines. The first has order size and order intensity leading to a compound distribution of period demand, then period demand and lead time giving rise to a compound distribution of demand during lead time. The second has order intensity and lead time giving rise to a compound distribution of lead-time order intensity, then lead-time order intensity and order size leading to a compound distribution of demand during lead time. The paper also condenses the state of the art in a table and proposes some simple classification schemes that could help researchers extend that state of the art. 相似文献