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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 27 (1989), S. 373-398 
    ISSN: 1432-1416
    Keywords: Acquired immunodeficiency syndrome (AIDS) ; Distributed delays ; Human immunodeficiency virus (HIV) ; Sexually transmitted diseases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In this study, we investigate systematically the role played by the reproductive number (the number of secondary infections generated by an infectious individual in a population of susceptibles) on single group populations models of the spread of HIV/AIDS. Our results for a single group model show that if R ⩽ 1, the disease will die out, and strongly suggest that if R 〉 1 the disease will persist regardless of initial conditions. Our extensive (but incomplete) mathematical analysis and the numerical simulations of various research groups support the conclusion that the reproductive number R is a global bifurcation parameter. The bifurcation that takes place as R is varied is a transcritical bifurcation; in other words, when R crosses 1 there is a global transfer of stability from the infection-free state to the endemic equilibrium, and vice versa. These results do not depend on the distribution of times spent in the infectious categories (the survivorship functions). Furthermore, by keeping all the key statistics fixed, we can compare two extremes: exponential survivorship versus piecewise constant survivorship (individuals remain infectious for a fixed length of time). By choosing some realistic parameters we can see (at least in these cases) that the reproductive numbers corresponding to these two extreme cases do not differ significantly whenever the two distributions have the same mean. At any rate a formula is provided that allows us to estimate the role played by the survivorship function (and hence the incubation period) in the global dynamics of HIV. These results support the conclusion that single population models of this type are robust and hence are good building blocks for the construction of multiple group models. Our understanding of the dynamics of HIV in the context of mathematical models for multiple groups is critical to our understanding of the dynamics of HIV in a highly heterogeneous population.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1335
    Keywords: Renal carcinoma ; metastasis ; pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The metastatic behaviour of renal cell carcinoma has been studied in a series of 687 necropsies. The observations were consistent with the concept of “metastatic inefficiency”, in that in 295 cases, including 25 with renal vein invasion, there were no detectable metastases. In the present series, renal vein involvement was not an important prognostic factor in stage 1 or 2 disease. In 73% of cases without lung metastases there were none in other sites, and in 84% of those with lung metastases there were others elsewhere, consistent with a metastatic “cascade” in which metastases first developed in the lungs and were later detected in other organs. However, the observations did not permit discrimination between anatomic cascades, in which other organs were seeded from metastasizing pulmonary metastases, and temporal cascades, in which the other were seeded at the same time as the lungs, but with fewer cancer cells. The patterns of arterial metastasis were consistent with the “seed-and-soil” hypothesis, and a novel index was developed to quantify differential organ “soils”. The contralateral kidney was not the best soil for metastases from renal carcinoma. Given the presence of lymph node metastasis, the probability of heamatogenous metastasis is 90%. However, in the absence of nodal metastasis, approximately half the cases had haematogenous metastasis.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Parasitology research 74 (1987), S. 69-72 
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Surface structures of the early third-stage larae were examined by scanning electron microscopy. There were hemispherical head-bulbs at the apical ends. These bulbs could be clearly distinguished from the bodies. The head-bulbs (52 × 29 Μm) had four transverse rows of sharp booklets. The number of booklets in each row was 37, 36, 38, and 43, posteriorly. The larvae possessed a pair of lateral lips in the head-bulb. Each of the lips had two labial papillae and an amphid between the papillae. Small unidentate cuticular spines were present along the entire length of larvae on their transverse striations. The number of these cuticular striations was 175–217. A pair of cervical papillae and an excretory pore were present on the anterior part of the body. Another pair of papillae was detected laterally on the posterior one-third of the body. The shape of the posterior body papillae resembled that of cervical papillae. The cuticular spines were absent around the anus.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Human evolution 4 (1989), S. 87-92 
    ISSN: 1824-310X
    Keywords: Biface ; China
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract More and more archaeological discoveries show that bifaces are not absent from China, South and East Asia. Bifaces played a very important role in early Paleolithic industries here. The tool assemblage of this industry is similar to those of biface cultures in Africa and Europe. These discoveries will increasingly fill and level up the ≪gap≫ between the cultures of the East and West.
    Type of Medium: Electronic Resource
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