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This dissertation concerns investigations on two of the most important problems in establishing communication security in computer networks: (1) developing a model which precisely describes the mechanism that enforces the security policy and requirements for a secure network, and (2) designing a key management scheme for establishing a secure session for end-to-end encryption between a pair of communicants. The security mechanism attempts to ensure secure flow of information between entities assigned to different security classes in different computer systems attached to a computer communication network. The mechanism also controls the accesses to the network devices by the subjects (users and processes executed on behalf of the users). The communication security problem is formulated by using a mathematical model which precisely describes the security requirements for the network. The model integrates the notions of access control and information flow control to provide a Trusted Network Base (TNB) for the network. The demonstration of security of the network when the security mechanism is designed following the present model is given by using mathematical induction techniques. The problem of designing key management schemes for establishing end-to-end encrypted sessions between source-destination pairs when the source and the destination are on different networks interconnected via Gateways and intermediate networks is examined. In such an internet environment, the key management problem attains a high degree of complexity due to the differences in the key distribution mechanisms used in the constituent networks and the infeasibility of effecting extensive hardware and software changes to the existing networks. A hierarchical approach for key management is presented which utilizes the existing network specific protocols at the lower levels and protocols between Authentication Servers and/or Control Centers of different networks at the higher levels. Details of this approach are discussed for specific illustrative scenarios to demonstrate the implementational simplicity. A formal verification of the security of the resulting system is also conducted by an axiomatic procedure utilizing certain combinatory logic principles. This approach is general and can be used for verifying the security of any existing key management scheme.

published_or_final_version / Radioisotope / Master / Master of Philosophy

No description available.

Athletes wear mouthguards to decrease the risk of injuries. However, many athletes resist wearing mouthguards due to problems with speech and breathing during play. Breathing difficulties may suggest limitations with ventilation. The purpose of this study was to examine peak inspiratory and peak expiratory air flow at different ventilatory rates using various types of mouthguards and a no mouthguard condition. Mouthguards were fitted into a dental model and air was ventilated through the model at three flow rates (30, 45, 60 strokes·min-1) using 2 and 3 L syringes. Flows were recorded using a Medisoft Ergocard. Peak flows (L·s -1) were recorded for 10 strokes during each condition. At 180 L·min -1, only bimolar mouthguards impeded air flow compared to the no mouthguard condition. In addition, the Shock Doctor bimolar mouthguard experienced decreased peak values compared to several mouthguards. Results suggest that peak flow is lowered at high ventilation with bimolar mouthguards.

No description available.

The work contained in this thesis explores the economic issues of screening women, and the subsequent use of hormone replacement therapy (HRT), for the prevention of osteoporosis. The thesis is divided into five sections. In the first section the background to the problem is described as are the relevant economic evaluation techniques. In addition, the relevant economic literature is reviewed. The second section of the thesis, contains the results of research aimed at estimating the costs of population screening followed by treating the women at highest risk. The three chapters in this section address the following issues: estimating total screening costs; developing an economic definition of at risk status; and describing the HRT compliance rate after screening and its associated costs. In the third section the consequences of screening are examined. Hence, the osteoporosis risk profile of non attenders is described and the effects of HRT on women's quality of life is explored. Finally, this section is completed with a study looking at the predictive value of bone density screening. The fourth section is a synthesis of all the costs and consequences described in the preceding sections with relevant additional information from the literature. This section shows that screening perimenopausal women will be very expensive in terms of cost per quality adjusted life years (QALY) gained. In contrast, screening women and treating them when they are aged 70 appears to generate a relatively low cost per QALY. The final, fifth section, of the thesis describes outstanding research issues which need to be addressed before any screening programme is implemented.

There is no abstract available for this thesis.

In 1999, Indiana's General Assembly enacted law requiring every Indiana school"% corporation to designate a Safety Specialist. A training and certification program was established which required the designated Safety Specialist to attend six days of training in 1999-2000, and to attend subsequent annual training.In this study, a survey was conducted among the 294 Safety Specialists from the first group of trainees to determine the impact the Safety Specialist program has had in Indiana school corporations in such areas as school climate, student behavior, administrator/teacher behavior, safety awareness, and the implementation of "best practice" programs. Variables such as school size, location, occupation of the Safety Specialist, number of buildings in the corporation, and full-time vs. part-time status of the Safety Specialist, were considered. The survey return rate was 73%.Data were analyzed using ANOVA, Pearson correlation, and a t-test. ANOVA indicated that school size, location, and the occupation of the Safety Specialist were significant (F scores greater than 1.0) in determining changes in overall safety awareness and "best practice."School corporations with more than 2000 students showed greater safety awareness and implemented "best practice" programs more often than corporations with fewer than 2000 students; urban schools indicated higher levels of safety awareness and utilized "best practice" programs more often than suburban or rural schools; schools where the Safety Specialist is the superintendent, assistant superintendent, or "other" had "best practice" programs in place and had more safety awareness than schools where the Safety Specialist was the principal, assistant principal, or teacher.Pearson correlation testing indicated little correlation between the number of school buildings and any of the research topics. However, a positive correlation of .806 did exist between school climate and administrator/teacher behavior.The t-test revealed no differences in any category between part-time and full-time Safety Specialists; mean scores in each category were similar.A follow-up case study conducted in five schools of varying size and location revealed results similar to the survey: Safety Specialists in the majority of schools considered the training to have, been worthwhile, its overall impact positive, and their schools to be safer than ever before. / Department of Educational Leadership