Yu-Shun Wang

Impact of age on the injury pattern and survival of people with cervical cord injuries

Study design: A retrospective, follow-up study.Objectives: To differentiate the injury pattern and survival of people with cervical cord injuries with onset at different ages.Setting: Rehabilitation wards of a university hospital that is a tertiary referral center in Taipei, Taiwan.Methods: The records of acute and traumatic cervical cord injury patients hospitalized from 1989 to 1997 were reviewed. All subjects received comprehensive rehabilitation programs during hospitalization. Their survival status at the end of follow-up was studied.Results: Forty-seven of 109 (43.1%) people with cervical cord injuries were 50 years or older at onset. Older patients were more frequently injured by minor falls, resulting in more incomplete quadriplegia. They also showed fewer spinal fractures, and more demonstrated associated spondylosis and ossification of the posterior longitudinal ligament. Eleven (10.2%) subjects were deceased, found by a linkage to a death registration database at the end of follow-up. The significant predictor of survival status at follow-up was older age at injury using Cox proportional hazards model.Conclusion: Spinal cord injured patients had different injury patterns, demanding different preventative strategies. Those injured at older ages were at higher risk of mortality according to our study.Sponsorship: This study was supported in part by grants from the National Taiwan University Hospital (89S2005), Taipei, Taiwan.Spinal Cord (2001) 39, 375–380.

Maximization of Wireless Mesh Networks Survivability to Assure Service Continuity under Intelligent Attacks

Service continuity is a critical issue in wireless networks. Unfortunately, jamming attacks seriously threatens the continuity of wireless networks. The open nature of wireless mediums makes it vulnerable to any wireless capable devices. There are only few researches address the issue of how the service providers should deploy its topology or allocate its resources to minimize the impact of jamming attacks launched by malicious attackers. In this paper, a mathematical model formulating an attack-defense scenario of the problem is proposed. The results show when deploying defense resources, considering hops from core node is more useful than link degree. With the advantage of simulations, the concept of incomplete information can be taken into account which though raises the difficulty of the problem, but makes the problem closer to reality.

Effective Proactive and Reactive Defense Strategies against Malicious Attacks in a Virtualized Honeynet

Virtualization plays an important role in the recent trend of cloud computing. It allows the administrator to manage and allocate hardware resources flexibly. However, it also causes some security issues. This is a critical problem for service providers, who simultaneously strive to defend against malicious attackers while providing legitimate users with high quality service. In this paper, the attack-defense scenario is formulated as a mathematical model where the defender applies both proactive and reactive defense mechanisms against attackers with different attack strategies. In order to simulate real-world conditions, the attackers are assumed to have incomplete information and imperfect knowledge of the target network. This raises the difficulty of solving the model greatly, by turning the problem nondeterministic. After examining the experiment results, effective proactive and reactive defense strategies are proposed. This paper finds that a proactive defense strategy is suitable for dealing with aggressive attackers under “winner takes all” circumstances, while a reactive defense strategy works better in defending against less aggressive attackers under “fight to win or die” circumstances.

Maximization of Network Survivability under Malicious and Epidemic Attacks

Due to the Internets scalability and connectivity, enterprises and organizations increasingly rely upon it to provide services for customers. However, attackers intelligently attack enterprises and organizations through continuous vulnerability exploitation and advanced malware. Recently, assailants have applied the characteristics of fast propagation and epidemic attack infection to launch more deliberate attacks, by using obtained network topology information. This paper examines malicious and epidemic attacks, taking into account various defense mechanisms. Attackers are assumed to only have incomplete information regarding the target network, which raises the difficulty of solving this problem and renders the nature of the problem non-deterministic. Our purpose is to help defenders evaluate average network survivability when making defense-related decisions. This scenario is modeled as a mathematical formulation, and through our simulation results, meaningful and useful defense guidelines are proposed.

Modeling Synergy Effects Considering Both Positive and Negative Factors Between Participants

Modeling synergy effects to measure the effectiveness of collaboration is a meaningful and important issue. However, there are only few previous works quantifying collaborative effects. Further, previous models consider only positive effects regardless of potential disharmonious factors which are common in real world. In this paper, a mathematical formulation measuring synergy effects which takes both positive and negative effects into consideration is introduced. Implications and comparisons between proposed model and a wildly applied model, Cobb-Douglas function, are also proposed in simulation results.

Effective network defense strategies to maximize system survivability of wireless mesh networks under malicious and jamming attacks

Continuity of wireless networks is a critical issue for wireless networks. Unfortunately, there is a category of attacks that seriously threatens the continuity of wireless networks: the jamming attack. The open nature of wireless mediums makes them vulnerable to any wireless capable devices. However, there have not been any studies that address the issue of how the service providers should deploy its topology or allocate its resources to minimize the impact of jamming attacks launched by malicious attackers. In this paper, a mathematical model formulating an attack-defense scenario of the problem is proposed. The results show when deploying defense resources, considering hops from the core node is more useful than link degrees. With the advantage of simulations, the concept of incomplete information can be taken into account which, while increasing the difficulty of the problem, makes the problem closer to reality.

Effective Network Defense Strategies against Malicious Attacks with Various Defense Mechanisms under Quality of Service Constraints

How to apply timely and effective defense strategies against attackers while maximizing system survivability is a critical issue for a defender. This paper mathematically models attack and defense scenarios, using various defensive mechanisms during both the planning and defending stages and under quality of service constraints. This model incorporates high degrees of randomness, as attackers are assumed to have incomplete information. Given such non-deterministic problems, this paper identifies the appropriate time for applying defense in depth or resource concentration strategy.

Redundancy and Defense Resource Allocation Algorithms to Assure Service Continuity against Natural Disasters and Intelligent Attackers

In this paper, we discuss Redundancy Allocation Problem (RAP) in network environments. By efficiently combining redundancy with extra defense mechanisms, we attempt to ensure the continuity of a network service, and enhance its survivability against malicious attackers that utilize accumulated experience. We construct an attack/defense scenario, in which an attacker and a defender compete against each other, and formulate it as a two-phase nonlinear integer programming problem. We adopt a Lagrange an Relaxation-based solution approach to resolve the above problem, and further prove the efficacy of our approach by computer experiments. The result shows LR-Based attack algorithm is better than other strategies we compared. Further, no matter what kind of attack/defense cost function is adopted, the LR-Based allocation algorithm can always provide a much better defense capability than others.

A cyber-attack synergy model considering both positive and negative impacts from each attacker

An emerging attack strategy, collaborative attack, is considered the next generation type of attack. There are only a few models quantifying the synergy of a collaborating attack. Further, previous models consider only positive effects regardless of potential disharmonious factors which are common in the real world. Contributions of this work are summarized as follows: first, this paper introduces a mathematical formulation measuring synergy which takes both positive and negative effects into consideration. This model can not only be applied in measuring collaborative attack effectiveness, but also be used to describe the synergy in other teamwork scenarios. The scenario of an applicable cyber-warfare can take place in a wired network, wireless network, or sensor network. Secondly, a meaningful connection between contest success function and Cobb-Douglas function is proposed and integrated in a cyber-attack scenario. Both the contest intensity of the contest success function and the sum of exponents of Cobb-Douglas function reflect an environmental factor regarding whether it encourages investing or not. Lastly, comparisons between the proposed model and the Cobb-Douglas function are also presented with a subsequent discussion of implications. The behavior of the proposed model is closer to reality and less coupled to another exogenous variable, contest intensity.

Effective Network Defense Strategies to Assure Service Continuity Under Collaborative Attacks

Malicious attacks have become a major source of risk for service providers. In this paper, a network attack and defense scenario is modeled as a bi-level mathematical formulation where the commanders try to disrupt the services while the defender has to assure the service continuity. Since the high degree of complexity and non-deterministic characteristic, Monte Carlo simulations are applied to evaluate the average network survivability. As for the attack and defense scenario, an emerging type of attack, collaborative attack, is considered. The defender must apply appropriate strategies, which includes deploying various proactive and reactive defense mechanisms, under budget and predefined quality of service constraints to protect the system. The virtualization technology is also considered as the topology platform.