No description available.

Worm attacks have always been considered dangerous threats to the Internet since they can infect a large number of computers and consequently cause large-scale service disruptions and damage. Thus, research on modeling worm attacks, and defenses against them, have become vital to the field of computer and network security. This dissertation intends to systematically study two classes of countermeasures against worm attacks, known as traffic-based countermeasure and non-traffic based countermeasure. Traffic-based countermeasures are those whose means are limited to monitoring, collecting, and analyzing the traffic generated by worm attacks. Non-traffic based countermeasures do not have such limitations. For the traffic-based countermeasures, we first consider the worm attack that adopts feedback loop-control mechanisms which make its overall propagation traffic behavior similar to background non-worm traffic and circumvent the detection. We also develop a novel spectrumbased scheme to achieve highly effective detection performance against such attacks. We then consider worm attacks that perform probing traffic in a stealthy manner to obtain the location infrastructure of a defense system and introduce an information-theoretic based framework to obtain the limitations of such attacks and develop corresponding countermeasures. For the non-traffic based countermeasures, we first consider new unseen worm attacks and develop the countermeasure based on mining the dynamic signature of worm programs’ run-time execution. We then consider a generic worm attack that dynamically changes its propagation patterns and develops integrated countermeasures based on the attacker’s contradicted objectives. Lastly, we consider the real-world system setting with multiple incoming worm attacks that collaborate by sharing the history of their interactions with the defender and develop a generic countermeasure based on establishing the defender’s reputation of toughness in its repeated interactions with multiple incoming attackers to optimize the long-term defense performance. This dissertation research has broad impacts on Internet worm research since this work is fundamental, practical and extensible. Our developed framework can be used by researchers to understand key features of other forms of new worm attacks and develop countermeasures against them.

No description available.

No description available.

The primary purposes of the study were to describe and compare the skeletons of the three forms of Carphophis, evaluate a recent proposal to raise C. a. vermis to full species rank, and compare Carphophis to Calamaria, a genus of fossorial snakes found in Indo-Malayan forests.

Trichostrongylus tenuis is a nematode that lives in the caeca of wild red grouse. It causes disease in red grouse and can cause fluctuations in grouse pop ulations. The aim of the work described in this thesis was to study aspects of the ecology of the infective-stage larvae of T.tenuis, and also certain aspects of the pathology and immunology of red grouse and chickens infected with this nematode. The survival of the infective-stage larvae of T.tenuis was found to decrease as temperature increased, at temperatures between 0-30 C? and larvae were susceptible to freezing and desiccation. The lipid reserves of the infective-stage larvae declined as temperature increased and this decline was correlated to a decline in infectivity in the domestic chicken. The occurrence of infective-stage larvae on heather tips at caecal dropping sites was monitored on a moor; most larvae were found during the summer months but very few larvae were recovered in the winter. The number of larvae recovered from the heather showed a good correlation with the actual worm burdens recorded in young grouse when related to food intake. Examination of the heather leaflets by scanning electron microscopy showed that each leaflet consists of a leaf roll and the infective-stage larvae of T.tenuis migrate into the humid microenvironment' provided by these leaf rolls. Scanning electron microscopy showed that the adult nematodes burrowed into the mucosa as well as lying on its surface and that the caecal mucosa of heavily infected grouse became disrupted in areas of nematode activity. The caecal mucosa of lightly infected grouse exhibited little damage and the caecal mucosa of grouse treated with an anthelmintic and shot 5-6 months later was similar to that of lightly infected birds. Some of the nematodes from these treated birds were covered in rosette-shaped cells which have been tentatively identified as adherent lymphocytes. The cuticle of adult T.tenuis was superficially annulated but did not possess cuticular ridges, as described in some other trichostrongyle nematodes. Primary and challenge infections with T.tenuis were established in the domestic chicken and these reached patency but nematodes were expelled in blood-stained balls of mucus and all adult nematodes had been expelled from the birds 30 days after dosing with infective-stage. Following trickle doses of larvae, there was a rise and then a fall in nematode egg output but larvae administered later in the trickle infection appeared to fail to establish. Light and scanning electron microscopy showed haemorrhagic lesions and blood spots on the caecal mucosa of infected chickens and nematodes were found to burrow beneath mucus secreted on the mucosal surface. There were significant increases in the proportions of circulating leucocytes in infected chickens, but only on certain days of infection. No antibodies to T.tenuis were detected in the blood of infected chickens. There was a decrease in the length of the caeca of infected chickens during the period when the Ill nematodes were being expelled from the caeca. Nematode egg output continued to rise during an infection in young red grouse and there was no expulsion of nematodes from these infected birds. Infective-stage larvae that had been attenuated by cobalt 60 irradiation stimulated some degree of resistance to challenge infection in the domestic chicken but not in the red grouse. It was concluded that immunization with irradiated larvae would be of little use in the control of T.tenuis in red grouse.

Investigations were carried out to determine the effect of ecological factors on the induction of diapause in the spruce budworm. Experimental rearings were conducted at elevations of 2500, 4200 and 4750 feet. The foliage of spruce, Douglas fir and alpine fir were used as hosts. Progeny of Ontario, two-year and one-year types reared under one-year and two-year life cycle conditions were used as experimental insects. A trend was observed in emergence from hibernation with the one-year type leading, followed by the two-year and finally the Ontario type. It was shown that the one-year type larvae may adopt the two-year habit. The main factor influencing this is a prolonged development period for the parents. The larvae reared at the higher elevations showed a greater proportion entering diapause. Food played a smaller role with spruce and Douglas fir being more favourable for diapause than alpine fir. The increased percentage of larvae in diapause in 1952 is attributed to a longer development period for their parents and to a sharp drop in temperature occurring about 12 days prior to diapause. The Ontario material may adopt the two-year habit. The factors contributing to this have not been clearly shown as the rearing results are inconclusive. There were no definite differences shown in the time for development among the three foods. The insects at the lowest station developed in approximately three weeks less time than at the highest. The difference between the upper stations was slight. The impracticability of converting a one-year life cycle population to a two-year cycle by forest management is noted. The diapause theories of Wigglesworth and Andrewartha are commented on. A possible course of evolution leading to the establishment of a two-year life cycle population is given. / Science, Faculty of / Zoology, Department of / Graduate

In the region of Lillooet, B.C. a small population of spruce budworm, Ohoristoneura fumiferana (Clem.), has maintained a relatively constant sub-epidemic level for several decades, feeding on Douglas fir, Pseudotsuga taxifolia (Poir.) Britt. No tree mortality has occurred. This population has been under observation for ten years, and it is apparent that an effective natural control complex is operating in the area. Spiders are prominent among the predators of insects in the region. Field observations revealed that many spiders captured both larvae and moths of the spruce budworm. A collection of arboreal spiders of the region was made and identified. Feeding tests were conducted with spiders to determine the budworm-feeding species. Both caged and free spiders were tested. Population samples were taken to determine the relative abundance of spider species in the area, and to discover any differences that may exist between spider populations in the infested forest and in the non-infested forest. Four families were found to comprise eighty percent of the arboreal spiders of the Lillooet district, and seventy percent consisted of only two families, the Thomisidae and the Salticidae. The Thomisids do not capture spruce budworm larvae, but may capture moths. The Salticids capture both larvae and moths. Families Argiopidae and Theridiidae occasionally capture larvae and frequently capture moths. No difference was demonstrated between spider populations in the infested forest and the non-infested forest. / Forestry, Faculty of / Graduate

M.Sc. / Imbrasia belina is a well-utilised natural resource in southern Africa. This resource can only be utilised sustainably after a thorough study of its ecology, breeding system and its genetic structures are assessed. The implementing of breeding programmes should be evaluated with well-defined management and conservation controls and regulations. The purpose of this study was to establish the amount of genetic variation and gene flow in two wild populations and the staggered generations of I. be/ina, and to determine which developmental stage should be used for further studies. Gene products of 41 protein-coding loci were analysed by horizontal starch gel electrophoresis. High levels of polymorphism (42% and 47%) and heterozygosity (0.182 to 0.21 0) were present in all groups. Results from initial studies indicated developmental constraints on the expression of several loci, namely CK, GPO and PEP-S. After further studies with larger sample sizes, it now appears that there are only allozyme and not isozyme differences between the individuals from the various developmental stages. The groups studied exhibit a large amount of variation within, but little differentiation and a large amount of gene flow between them. Results of the study indicate that the genetic diversity of I. be/ina populations is healthy. Thus, sustainable utilisation of the Messina Experimental farm (November/December) group is recommended due to the high heterozygosity and genetic variation in this population.

No description available.