Ali Abbasi

Source Location Anonymity for Sensor Networks

Motivated by applications like sensor, peer to peer networks there has been growing interest in monitoring large scale distributed systems. In these applications, source location anonymity is an attractive and critical security property. Most of prior works assumed a weak adversary model where the adversary sees only local network traffic, but here we consider source anonymity against a global eavesdropper. Attaining location unobservability under global attacker is very difficult and expensive to achieve, because sensor networks are very limited in resources. In this work we propose a distributed algorithm to mix real event traffic with carefully chosen dummy traffic to hide the real event traffic pattern. We assume that we have fixed amount of resources to send dummy traffic and we try to share it among sensors so as to maximize the degree of anonymity of the system. Through simulation, we illustrate that the proposed technique is efficient in protecting location information from the eavesdropper.

Floating Thrombus in the Aortic Arch as an Origin of Simultaneous Peripheral Emboli

Abstract  Few cases of a floating thrombus in a normal aorta have been reported without other underlying reasons for the thrombus formation and its systemic embolic complications. We report a case in which a floating thrombus in the proximal aortic arch was detected after echocardiography and computed tomography angiography as an origin of upper extremities and ophthalmic embolism.

Hydatid cyst of the right ventricle in early pregnancy.

Although hydatic cyst disease rarely involves myocardium and endocardium, cardiac echinococcosis, a potentially life‐threatening condition, should be managed promptly. We report a case of right ventricle hydatid cyst detected after syncopal attack in a pregnant woman by using echocardiography.

The anatomy of superficial inferior epigastric artery flap

PURPOSE To describe the anatomical variations of superficial inferior epigastric artery (SIEA) flap as a muscle-sparing flap. METHODS A series of 40 dissections were performed on 20 preserved or fresh male cadavers. The site origin and drainage of vessels, caliber, length, and correlation between diameter and length of pedicle were identified. RESULTS The SIEA and SIEV were identified at inguinal ligament level in 38 (95%) and 40 (100%) dissections, respectively. The SIEA originated directly from a common femoral artery 22 (57.9%) or a common trunk with other arteries. The SIEA was found within 1 cm of the midpoint of the inguinal ligament in 33 of 38 cases. The meanSD length of SIEA was 3.041.73 (0.5-7) cm. The meanSD caliber of SIEA was 1.450.35 (0.7-2.1) mm. The length of SIEV ranged from 2.2 to 12 cm with a meanSD of 5.452.08 cm. The caliber of SIEV ranged from 1.6 to 4 mm with a meanSD of 2.140.45 mm. The length of SIEA correlated with caliber of arterial pedicle (p<0.001 and correlation coefficient = 0.517). CONCLUSION The inferior epigastric artery flap can be applied to microsurgical flap transfer, potentially in breast reconstruction, hemifacial atrophy, phalloplasty, or when extremely large amounts of skin coverage are required.

Effect of completion of cardiac rehabilitation on heart rate recovery.

To evaluate the effects of a cardiac rehabilitation program on heart rate recovery after percutaneous transluminal coronary angioplasty, a historical cohort study was performed on 436 patients of whom 285 were grouped on completion of 5, 10, or 24 training sessions. All 3 groups showed significant improvements in heart rate recovery, peak heart rate during treadmill testing, and end-training heart rate, from baseline to follow-up. Heart rate recovery on follow-up correlated significantly with the number of completed exercise sessions. The number of sessions, baseline ejection fraction, and age were independent predictors of mean post-training heart rate recovery. The cardiac rehabilitation program had a significant effect on peak heart rate and heart rate recovery, regardless of the underlying characteristics of the patients.

MOTE: Efficient monitoring of top-k set in sensor networks

Top-k monitoring is a noteworthy query that recently has been put into practice in wireless sensor networks (WSN). In top-k monitoring (i.e., an instance of continuous distributed monitoring), base station or coordinator continuously monitors k sensors with the highest (or lowest) values. Since the goal in such applications is to perform monitoring task while incurring minimum communication (data traffic) overhead, local constraints should be set at remote sites to filter unnecessary updates. Thereby, the novelty of this paper lies on the investigation of a method called MOTE where model-based optimization technique is utilized to set filters at remote sensors. In the proposed technique, the problem of optimal filter setting for maintaining top-k set is formulated as a variant of set cover which is an np-hard problem with well studied approximation methods. Simulation results demonstrate the validity of the proposed MOTE algorithm in improving the performance compared to other filter setting methods.

Distributed base station activation for energy-efficient operation of cellular networks

Dynamic base station activation (DBA) has recently emerged as a viable solution for reducing energy consumption in cellular networks. While most of the works on this topic focused on centralized decision making algorithms, in this paper we investigate distributive solutions. These solutions are particularly desirable due to importance of self-organization and self-optimization in future cellular networks. The goal of DBA is to achieve an optimal trade-off between network operators revenue and operational cost while guaranteeing coverage for network users. The problem is posed as a network utility maximization aiming to find the optimal activation schedule of each base station. Using Lagrangian duality, the problem is decomposed into smaller subproblems, where each subproblem is solved locally at its associated base station. Controlled message passing among base stations ensures convergence to the global optimal solution. Moreover, this general solution is further extended to capture the combinatorial nature of DBA. Finally, numerical results are provided to demonstrate the behavior of our solution in terms of utility and cost trade-off and convergence in some example network scenarios.

A distributed clustering algorithm for fault-tolerant event region detection in wireless sensor networks

Wireless sensor networks which are envisioned to consist of many simple processing, storage, sensing, and communication capabilities are believed to open the doors to a plethora of new applications. Efficient robust data aggregation is a key feature in information processing in wireless sensor environments, especially in the presence of faulty sensor nodes which arise due to harsh environments or manufacturing reasons. These conditions highly affect the quality of gathering data in different locations and times. In this paper we propose a distributed localized method for detecting regions that are susceptible to message loss above a given threshold, and then based on this method we suggest an algorithm for clustering nodes in that region which proportionally adapts based on message loss. Simulation experiments confirm the validity of the proposed algorithm with a high degree of accuracy.

Flooding-Assisted Threshold Assignment for Aggregate Monitoring in Sensor Networks

The research community has witnessed a large interest in monitoring large scale distributed systems. In these applications typically we wish to monitor a global system condition which is defined as a function of local network elements parameters. In this paper, we address Aggregate Threshold Queries in sensor networks, which are used to detect when an aggregate value of all sensor measurements crosses a predetermined threshold. The major constraint in designing monitoring applications is reducing the amount of communication burden which is the dominant factor of energy drain in wireless sensor networks. In this study, we address the aggregate threshold monitoring problem by proposing a distributed algorithm to set local thresholds on each sensor node so as to minimize the probability of global polling. We adopt the FPTAS optimization formulation of the problem [2] and propose a distributed algorithm as the solution to the problem. Simulation results demonstrate the validity of the proposed distributed algorithm in attaining very close performance as the centralized schema.

Cost-aware monitoring of network-wide aggregates in wireless sensor networks

Abstract Motivated by applications of wireless sensor networks, there have been growing interests in monitoring large scale distributed systems. In these applications, we usually wish to monitor global system conditions defined as a function of network measurements. In this paper, we study optimal strategies for reactive monitoring to be employed for monitoring network-wide aggregates of sensor nodes’ measurements. Our primary concern in adopting such a monitoring mechanism is to reduce the communication cost which is the dominant factor of energy drain in wireless sensor networks. To adapt the structure of monitoring mechanism to the statistics of nodes’ measurements, we devise a simple yet efficient algorithm that is appropriate for a class of distribution functions. Towards this, we consider a sigmoid approximation of the CDF of the underlying event and cast the underlying design problem as a convex optimization problem. This allows us to propose an algorithm to set monitoring parameters in accordance to the statistics of the events measured by spatially scattered sensor nodes. Through simulation experiments, we illustrate that the proposed algorithm, referred to as SATA, can significantly reduce the communication overhead of the monitoring mechanism in sensor networks. Our results show that compared to heuristic methods, the cost of monitoring mechanism can be reduced significantly.