1,720,962 research outputs found
Towards security and privacy for emerging wireless networks
No full textNovel network paradigms such as delay tolerant network (DTN), vehicular ad hoc network (VANET) have recently emerged to accommodate new wireless network application scenarios. DTN, designed to support networks characterized by intermittent connectivity and long delay, has been widely embraced for ad hoc applications in extreme environments such as battlefield, disaster area, rural area, etc. VANET allows vehicles travelling on the roads to exchange data that can improve traffic safety and convenience. Despite the advances in operational standardizations of DTN and VANET, security and privacy remain as major problems to their deployments in practice. This motivates the author to study and resolve the unaddressed security and privacy issues in DTN and VANET in this dissertation. First, the author proposes SNDW to detect and localize wormhole attack in DTN. Existing works rely on high connectivity or end-to-end path information which are not available in DTN. In SNDW, infrastructure nodes are deployed to monitor the number of neighbors in the areas assigned to them. Since the attacker forwards beacons from one location to another, the number of neighbors around the wormhole endpoint increases. An infrastructure node within the wormhole's transmission range can detect a significant increase of neighbor counts, despite the low density and connectivity in DTN. Upon detection, it can alert the neighborhood about the attack and further pinpoint the wormhole locations. Second, the author proposes SDBG to detect collusion blackhole and greyhole attacks in DTN. Existing works could handle the attacks launched by individuals but fail to detect adversaries that cooperate to cheat the defense system. In SDBG, encounter record (ER) is created by a node to record the list of messages it sends and receives in an encounter with another node. Upon encounter, nodes exchange their recent ERs so that they can evaluate one another's behavior. Forwarding ratio metrics are defined to capture the attacker's features such as receiving messages more than forwarding and forwarding messages mostly generated by themselves. A node calculates the forwarding ratio metrics of the peer from its ERs to detect the individual attacker. However, adversaries might avoid being detected by colluding with one another to forge ERs that promote their forwarding ratio metrics. Observing that fake ERs are created with higher frequency and higher numbers of sent messages than normal ERs, the author designs a robust algorithm that filters fake ERs and detects colluding attackers. Third, the author proposes FDER to detect flooding attack in DTN without imposing strict rate-limit policy like previous works. Instead, burst-limit policy, which allows nodes to generate burst traffic in a short period, is introduced to accommodate the nodes' on-demand transmissions. Each node also uses ERs to infer a peer's new message transmission rate over time and the number of forwarded replicas per message, thereby detecting if the peer exceeds the thresholds of messages or replicas. Burst-limit policy provides flexibility to nodes with high-demand traffic but may affect the delivery performance of other nodes with lower-demand traffic. To ensure the performance fairness, the author designs a forwarding policy, in which nodes sending out new messages at high rate will have lower forwarding priority in the network. Finally, the author attempts to address the trade-off between trust management and privacy in VANET. Existing works only focus on trust or privacy separately or have not provided a satisfactory solution to both issues. The author proposes a secure and flexible framework, including two components, ALRS and ATMS, to enable vehicles to manage privacy and trust respectively. ALRS supports vehicles to recognize either identities or trust levels of other vehicles despite them updating the pseudonyms to protect their privacy. The linkability information is kept confidential from external attackers and unauthorized internal nodes using encryption and private set intersection technique. Besides, the linkability can be revoked easily to prevent nodes from being traced by other internal nodes. ATMS is a context-aware trust management scheme for nodes to make more informative evaluation of the received data, using the entity trust enabled by ALRS.DOCTOR OF PHILOSOPHY (SCSE
Studies on Effects of Small-Amount Loading of Plasticizers on Poly(L-lactic acid) Crystallization
Get PDF京都工芸繊維大学博士（工学）Poly(L-lactic acid) (PLLA) is one of the most popularly utilized biobased polymer, as PLLA can be synthesized from renewable sources such as sugar, carbohydrate, etc. In recent several decades, scientists are interested in PLLA because of environment-friendly characteristics. However, there existing some big problems of PLLA, which are low crystallization rate and low crystallinity. In order to overcome such drawbacks, nucleation agents have been incorporated into PLLA. These are talc, clay, sodium salts, etc., playing its role in a solid state. On the contrary, it has been known that a special plasticizer (organic acid monoglyceride; OMG) can improve the crystallizability of PLLA. The results are significant because plasticizers are believed to delay crystallization of polymers by reducing the thermodynamical driving force of crystallization. Therefore, I intended to clarify the effects of plasticizers on the crystallization of PLLA in detail in this thesis. And finally, I propose a plausible mechanism to explain the role of plasticizer upon the crystallization of PLLA. In Chapter 1, I reported the experimental results of the effects of a plasticizer as an agent of improving crystallizability of PLLA. In Chapter 2, the effects of loading amount of plasticizers on improved crystallization of PLLA is carefully investigated by using a special plasticizer, OMG, and a general one, dioctyl phthalate. In order to identify the effect of the plasticizers, I conducted time-resolved small- and wide-angle X-ray scattering and differential scanning calorimetric measurements to follow, respectively, the isothermal and non-isothermal crystallization of PLLA/plasticizer specimens. Moreover, polarizing optical microscopic observation was conducted to evaluate the growth rate of a spherulite and the number of nuclei formed as a function of time. Finally, for understanding the role of plasticizer upon the crystallization of PLLA, a plausible model is proposed in Chapter 3. In the presence of the plasticizer molecules, the better folding of the PLLA chains was resulted, which has been experimentally confirmed by the fact that the surface free energy (σe) of the crystallites plane become lower. The free energy change upon the formation of a primary nucleus is then drawn as a function of the thickness of the primary nucleus using the values of σe (using the Hoffman - Lauritzen theory) and it was found that the energy barrier for the crystallization is decreased by the loading of plasticizers. This explains the enhancement of the crystallizability of PLLA in the presence of plasticizers
TCP proxy over Delay Tolerant Networks (DTN)
No full textThe emergence of challenged networks characterized by long end-to-end delay, non-continuous connectivity, high error rate and asymmetric data rate has motivated the research and standardization of DTN (Delay Tolerant Network) to improve the poor performance by TCP/IP protocol suite deployment in these networks. The objective of the project is to develop a proxy to enable TCP applications to run over DTN. The proxy design adapted the PEP’s (Performance Enhancing Proxy) approach of splitting network connection.
The project goal has been achieved as the TCP proxy developed can allow general TCP packets to be transmitted over DTN, in both normal condition of continuous connectivity and extreme condition of very long delay and disrupted connectivity. Other common TCP applications, namely HTTP and SSH have been successfully tested to function properly over DTN. The exception is FTP as its operation specification requires special handling by the proxy which cannot be supported by the general TCP proxy designed. This is thus a limitation of the developed TCP proxy.
The project outcome not only demonstrates the functionality and usability of DTN in wireless intermittent-connectivity networks but also successfully explores the possibility of using proxy to enable existing TCP applications to run in DTN environment.
For future work, the recommendations to improve the proxy performance and functionality include developing specialized proxy to handle FTP and designing the TCP proxy to be located within the realms of the router instead of the current implementation of having the TCP proxy being co-located within the same node as the TCP applications.Bachelor of Engineering (Computer Science
Applying E-learning at a Company for Training Staff : Vinpearl one member limited company
No full textThe main objective of the thesis was to research the feasibility of E-learning application at Vinpearl one member limited company through analyzing the company’s existing needs and then suggest and build the most appropriate E-learning method for the improvement of the staff’s skills. The research also aimed at inspiring E-learning values and its dominant features to the company’s staff and managers.
In order to acquire opinions and attitudes of employees and managers about the pros and cons of E-learning on staff training, qualitative research method was used in this thesis which comprised of two unstructured open-ended interviews: a group interview with five managers whose departments called for a new more appropriate training method and an interview with director of human resource manager who would determine whether E-learning is applied for training or not.
The result of the interviews yielded a lot of insights in which employees faithfully revealed their concerns of current training situation and their expectations of new training system that might generate outcomes and encourage a new learning culture within the company. However, as director of human resource department stated E-learning application seems to be a high risk-taking mission since it requires an extensive adaption from the company.
Concluded, the interviews succeeded in imparting E-learning’s potential to the managers as a precious candidate on a race of selecting the best training method. Through analysis and assortment, the research thrived on building the company a prospective E-learning model for the so-called “remarkable innovation” for employee training area in Vietnam generally
TCP proxy over Delay Tolerant Networks (DTN)
No full textThe emergence of challenged networks characterized by long end-to-end delay, non-continuous connectivity, high error rate and asymmetric data rate has motivated the research and standardization of DTN (Delay Tolerant Network) to improve the poor performance by TCP/IP protocol suite deployment in these networks. The objective of the project is to develop a proxy to enable TCP applications to run over DTN. The proxy design adapted the PEP’s (Performance Enhancing Proxy) approach of splitting network connection.
The project goal has been achieved as the TCP proxy developed can allow general TCP packets to be transmitted over DTN, in both normal condition of continuous connectivity and extreme condition of very long delay and disrupted connectivity. Other common TCP applications, namely HTTP and SSH have been successfully tested to function properly over DTN. The exception is FTP as its operation specification requires special handling by the proxy which cannot be supported by the general TCP proxy designed. This is thus a limitation of the developed TCP proxy.
The project outcome not only demonstrates the functionality and usability of DTN in wireless intermittent-connectivity networks but also successfully explores the possibility of using proxy to enable existing TCP applications to run in DTN environment.
For future work, the recommendations to improve the proxy performance and functionality include developing specialized proxy to handle FTP and designing the TCP proxy to be located within the realms of the router instead of the current implementation of having the TCP proxy being co-located within the same node as the TCP applications.Bachelor of Engineering (Computer Science
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