Search

Start Over Coverage 1-9 Format print

12. On invariant subspaces for polynomially bounded operators

Creator:
Liu, Junfeng
Format:
print, bez média, and svazek
Type:
model:article and TEXT
Subject:
matematika, mathematics, invariantní podprostory, polynomially bounded operator, invariant subspace, 13, and 51
Language:
English
Description:
We discuss the invariant subspace problem of polynomially bounded operators on a Banach space and obtain an invariant subspace theorem for polynomially bounded operators. At the same time, we state two open problems, which are relative propositions of this invariant subspace theorem. By means of the two relative propositions (if they are true), together with the result of this paper and the result of C. Ambrozie and V. Müller (2004) one can obtain an important conclusion that every polynomially bounded operator on a Banach space whose spectrum contains the unit circle has a nontrivial invariant closed subspace. This conclusion can generalize remarkably the famous result that every contraction on a Hilbert space whose spectrum contains the unit circle has a nontrivial invariant closed subspace (1988 and 1997)., Junfeng Liu., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

13. Pentastome assemblages of the Nile crocodile, Crocodylus niloticus Laurenti (Reptilia: Crocodylidae), in the Kruger National Park, South Africa

Creator:
Junker, Kerstin, Calitz, Frikkie, Govender, Danny, Boris Ronal'dovič Krasnov, and Boomker, Joop
Format:
print, počítač, and online zdroj
Type:
model:article and TEXT
Subject:
parazitologie, parasitology, Alofia, Leiperia, Sebekia, Pentastomida, abundance, prevalence, species richness, crocodilians, 2, and 59
Language:
English
Description:
Thirty-two specimens of the Nile crocodile, Crocodylus niloticus Laurenti (Reptilia: Crocodylidae), from the Kruger National Park, South Africa, and its vicinity were examined for pentastomid parasites during 1995 to 1999 and 2010 to 2011. Pentastomid parasites occurred throughout the year and were widespread in the study area with an overall prevalence of 97% and an overall mean abundance of 23.4 (0-81). Pentastome assemblages comprised six species in three sebekid genera: Alofia nilotici Riley et Huchzermeyer, 1995, A. simpsoni Riley, 1994, Leiperia cincinnalis Sambon, 1922, Sebekia cesarisi Giglioli in Sambon, 1922, S. minor (Wedl, 1861) and S. okavangoensis Riley et Huchzermeyer, 1995. The possible influence of host age, gender and geographic location (river system) on pentastome prevalence, abundance and species richness was investigated. Generally, neither host age, gender nor locality did affect infracommunities, likely because all hosts examined were adult or subadult and displayed comparable foraging behaviour, resulting in similar exposure pathways to fish intermediate hosts. Additionally, the longevity of pentastomids would contribute to accumulative infections as hosts mature. Structuring of pentastome assemblages was observed in as far as S. minor was the dominant species based on overall prevalence and abundance, followed by the equally common species S. cesarisi and L. cincinnalis. With an overall prevalence ranging from 34% to 41% and relatively low abundances, A. nilotici, A. simpsoni and S. okavangoensis form the rarer component of pentastome communities., Kerstin Junker, Frikkie Calitz, Danny Govender, Boris R. Krasnov, Joop Boomker., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

14. Scanning and transmission electron microscopy of the histopathological impact of Macrogyrodactylus clarii (Monogenea: Gyrodactylidae) on the gills of catfish, Clarias gariepinus

Creator:
El-Naggar, Mohammed Mohammed, Cable, Joanne, Zaky Arafa, Safaa, El-Abbassy, Samir Ahmed, and Kearn, Graham C
Format:
print, počítač, and online zdroj
Type:
model:article and TEXT
Subject:
histopatologie, nemoci ryb, histopathology, fish diseases, ultrastructure, aquatic health, monogeneans, 2, and 59
Language:
English
Description:
Scanning and transmission electron microscopy (TEM) were used to study the histopathological effects of the monogenean Macrogyrodactylus clarii Gussev, 1961 on the gills of the catfish Clarias gariepinus (Burchell). Suction generated during attachment created 'footprints' on host surfaces in which the host tissues were elevated above the general gill surface. 'Footprints' were bordered by four clefts caused by the muscular flaps on the anterior, lateral and posterior margins of the haptor. The hamuli points penetrate the gill tissue but no evidence was found for the insertion of the marginal hooklets. At the site of attachment, host cells adjacent to the lateral flaps often appeared compressed and widely spaced with large intercellular spaces. Desquamation of these surface epithelia was also apparent and some of the widely spaced epithelial cells had pseudopodium-like processes. Cells within the upper surface epithelial layer of the host were vacuolated and necrotic. Ruptured blood capillaries (blood spaces) in the secondary gill lamellae contained atypical compressed erythrocytes, agranular and granular leucocytes and evidence of haemorrhaging. Cells with fibrotic cytoplasm, putative phagocytes and host mucous cells were evidence of a host response at the site of parasite attachment. The possible role of these cells is discussed in relation to host resistance against infection., Mohammed Mohammed El-Naggar, Joanne Cable, Safaa Zaky Arafa, Samir Ahmed El-Abbassy, Graham C. Kearn., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

15. Structure of parasite communities in urban environments: the case of helminths in synanthropic rodents

Creator:
Hancke, Diego and Suárez, Olga Virginia
Format:
print, počítač, and online zdroj
Type:
model:article and TEXT
Subject:
urbanizace, ekologie, zoonózy, urbanization, ecology, zoonoses, parasites, infracommunity, component community, compound community, 2, and 59
Language:
English
Description:
Identifying patterns with sufficient predictive power is a constant challenge for ecologists to address ecological problems related to species conservation, pollution or infectious disease control. During the last years, the amounts of parasitological studies in this sense increased, but they are still scarce in urban environments. The main aim of this study was to investigate if the helminth communities of urban rodents are structured within host assembly (compound community) or they are a result of random events occurring at each individual host scale (infracommunity). A total of 203 rodents belonging to four species, Rattus rattus (Linnaeus), Rattus norvegicus (Berkenhout), Mus musculus Linnaeus and the native Oligoryzomys flavescens (Waterhouse) and captured in different landscape units of the City of Buenos Aires (industrial-residential neighbourhoods, shantytowns and parklands) were analysed. The results showed that infracommunities could be grouped according to composition and relative abundances and that they respond to the structure of the host community. Thus, the component communities defined in this study could be identified as subsets of the compound community (rodent assemblage) and infracommunities (each host) as random samples within each one. Quantitative differences among component communities were denoted by comparing the infection levels of helminths described as central species. Therefore, infracommunities of R. norvegicus and O. flavescens were the most predictable because of the high abundance of the nematodes Heterakis spumosa Schneider, 1866 and Nippostrongylus brasiliensis (Travassos, 1914), and Stilestrongylus flavescens (Sutton et Durette-Desset, 1991), respectively. Several mechanisms contribute to complexity of the structure of parasite communities, where specific parasites, definitive and intermediate hosts, and environmental and anthropogenic factors all play a role in the dynamics of the compound community., Diego Hancke, Olga Virginia Suárez., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

16. Temporal variation in infection levels and reproductive traits of the acanthocephalan Pseudoleptorhynchoides lamothei in the blue sea catfish Ariopsis guatemalensis (Günther, 1864)

Creator:
Carpio-Hernández, Dolores I, Violante-González, Juan, Monks, Scott, Rojas-Herrera, Agustín A, García-Ibáñez, Sergio, Toribio-Jiménez, Jeiri, and Castro-Mondragón, Himmer
Format:
print, počítač, and online zdroj
Type:
model:article and TEXT
Subject:
dynamika, sumec, dynamics, Silurus, Mexiko, Mexico, helminths, brackish water fish, Tres Palos Lagoon, 2, and 59
Language:
English
Description:
Current data on reproductive biology and population dynamics of the acanthocephalans are scarce mainly in regions from the tropical Pacific. An analysis was done to identify possible factors that influence variation in infection levels of the acanthocephalan Pseudoleptorhynchoides lamothei Salgado-Maldonado, 1976 in its final host, the blue sea catfish Ariopsis guatemalensis (Günther, 1864), and describe its main reproductive traits. A total of 1,094 A. guatemalensis were collected from Tres Palos Lagoon from August 2014 to December 2015. Prevalence of P. lamothei varied from 1.47% to 38.33%, and mean abundance from 0.03 to 4.44 helminths per examined host. In female P. lamothei relative fecundity increased with total length. Temporal variations in P. lamothei infection levels were attributed mainly to changes in host feeding and reproductive behaviour in response to local environmental factors as climatic season, and variations in water temperature., Dolores I. Carpio-Hernández, Juan Violante-González, Scott Monks, Agustín A. Rojas-Herrera, Sergio García-Ibáñez, Jeiri Toribio-Jiménez and Himmer Castro-Mondragón., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

17. Toxoplasmosis in Nigeria: the story so far (1950-2016): a review

Creator:
Ohiolei, John Asekhaen and Isaac, Clement
Format:
print, počítač, and online zdroj
Type:
model:article and TEXT
Subject:
toxoplazmóza, živočichové, životní prostředí, toxoplasmosis, animals, environment, Nigérie, Nigeria, Toxoplasma gondii, seroprevalence, humans, 2, and 59
Language:
English
Description:
Toxoplasmosis is caused by intracellular protozoan parasite, Toxoplasma gondii (Nicolle et Manceaux, 1908). Cats and other felids are the definitive hosts. It could be transmitted to man and animals by consumption of infected undercooked meat and contaminated food items including drinking water. Results of toxoplasmosis epidemiological surveys in animals and humans in South-West, North-West, North-East and North-Central Zones of Nigeria have been reported with greater impact on the health of pregnant women and HIV-infected individuals. Meanwhile, studies in states within the South-South and South-East Zones are relatively scanty or non-existent. Overall, the seroprevalence of human toxoplasmosis in Nigeria is estimated at 32% with the following reports for North-West (32%), North-East (22%), North-Central (24%) and South-West (37%). Information on the genetic diversity of isolates of T. gondii in humans and animals including the role of the environment in transmission and maintenance of the disease are highly needed., John Asekhaen Ohiolei, Clement Isaac., and Obsahuje bibliografii
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public