IEEE Communications Surveys & Tutorials • 2nd Quarter 2006 2dvances in wireless communication and electronics have enabled the development of low-cost, lowpower, multifunctional sensor nodes. These tiny sensor nodes, consisting of sensing, data processing, and communication components, make it possible to deploy Wireless Sensor Networks (WSNs), which represent a significant improvement over traditional wired sensor networks. WSNs can greatly simplify system design and operation, as the environment being monitored does not require the communication or energy infrastructure associated with wired networks [1].WSNs are expected to be solutions to many applications, such as detecting and tracking the passage of troops and tanks on a battlefield, monitoring environmental pollutants, measuring traffic flows on roads, and tracking the location of personnel in a building. Many sensor networks have mission-critical tasks and thus require that security be considered [2,3]. Improper use of information or using forged information may cause unwanted information leakage and provide inaccurate results.While some aspects of WSNs are similar to traditional wireless ad hoc networks, important distinctions exist which greatly affect how security is achieved. The differences between sensor networks and ad hoc networks are [4]: • The number of sensor nodes in a sensor network can be several orders of magnitude higher than the nodes in an ad hoc network.• Sensor nodes are densely deployed.• Sensor nodes are prone to failures due to harsh environments and energy constraints.• The topology of a sensor network changes very frequently due to failures or mobility.• Sensor nodes are limited in computation, memory, and power resources.• Sensor nodes may not have global identification.These differences greatly affect how secure data-transfer schemes are implemented in WSNs. For example, the use of radio transmission, along with the constraints of small size, low cost, and limited energy, make WSNs more susceptible to denial-of-service attacks [5]. Advanced anti-jamming techniques such as frequency-hopping spread spectrum and physical tamper-proofing of nodes are generally impossible in a sensor network due to the requirements of greater design complexity and higher energy consumption [5]. Furthermore, the limited energy and processing power of nodes makes the use of public key cryptography nearly impossible. While the A YONG WANG, GARHAN ATTEBURY, AND BYRAV RAMAMURTHY UNIVERSITY OF NEBRASKA-LINCOLN ABSTRACTWireless Sensor Networks (WSNs) are used in many applications in military, ecological, and health-related areas. These applications often include the monitoring of sensitive information such as enemy movement on the battlefield or the location of personnel in a building. Security is therefore important in WSNs. However, WSNs suffer from many constraints, including low computation capability, small memory, limited energy resources, susceptibility to physical capture, and the use of insecure wireless communication channels. These constraints ...
The objective was to establish and evaluate a method for manufacture of custom trays for edentulous jaws using computer aided design and fused deposition modeling (FDM) technologies. A digital method for design the custom trays for edentulous jaws was established. The tissue surface data of ten standard mandibular edentulous plaster models, which was used to design the digital custom tray in a reverse engineering software, were obtained using a 3D scanner. The designed tray was printed by a 3D FDM printing device. Another ten hand-made custom trays were produced as control. The 3-dimentional surface data of models and custom trays was scanned to evaluate the accuracy of reserved impression space, while the difference between digitally made trays and hand-made trays were analyzed. The digitally made custom trays achieved a good matching with the mandibular model, showing higher accuracy than the hand-made ones. There was no significant difference of the reserved space between different models and its matched digitally made trays. With 3D scanning, CAD and FDM technology, an efficient method of custom tray production was established, which achieved a high reproducibility and accuracy.
Programmable hydrogels are defined as hydrogels that are able to change their properties and functions periodically, reversibly and/or sequentially on demand. They are different from those responsive hydrogels whose changes are passive or cannot be stopped or reversed once started and vice versa. The purpose of this review is to summarize major progress in developing programmable hydrogels from the viewpoints of principles, functions and biomedical applications. The principles are first introduced in three categories including biological, chemical and physical stimulation. With the stimulation, programmable hydrogels can undergo functional changes in dimension, mechanical support, cell attachment and molecular sequestration, which are introduced in the middle of this review. The last section is focused on the introduction and discussion of four biomedical applications including mechanistic studies in mechanobiology, tissue engineering, cell separation and protein delivery.
Performance evaluation is indispensable for a surgical simulator to become acceptable. A haptics-based dental simulator (iDental) has been developed and preliminary user evaluation on its first-generation prototype has been carried out to gain the knowledge. Based on detailed requirement analysis of Periodontics procedures, a combined evaluation method including qualitative and quantitative analysis was designed. Construct validity was used to compare the performance difference between two groups of participants (faculty members and dental graduate students). These participants were required to perform three periodontal examination and treatment procedures including periodontal pocket probing, calculus detection, and removal. From the evaluation results, we found that penetration between tool and teeth or cheek will greatly decrease the fidelity of the simulation, therefore, it is necessary to utilize 6-DOF haptic device with both force and torque feedback in dental simulator, and accordingly it is needed to extend point-based rendering to 6-DOF haptic rendering of multiregion contacts. Furthermore, several other key research topics that will enable haptic technology to be effective in a practical dental simulator were identified, including simulation of deformable body such as tongue and gingival, and simulation of occlusion of tongue and cheek on teeth, etc.
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