An investigation of the myopia for future consequences theory of VMF patient behaviour on the Iowa Gambling Task: An abstract neural network simulation

Somatic marker theory proposes that body states act as a valence associated with potential choices based on prior outcomes; and thus aid decision-making. The main supporting evidence for this theory arose from clinical interviews of subjects with ventromedial prefrontal cortex (VMF) lesions and their performance on the Iowa Gambling Task (IGT). VMF patient behaviour has been described as myopia about future consequences. The aim of this paper is to investigate the implications of this description using an abstract simulation of the neural mechanisms that could underlie decision-making in this type of reinforcement learning task

Energy-rate based MAC protocol for wireless sensor networks and key pre-distribution schemes

Sensor networks are typically unattended because of their deployment in hazardous, hostile or remote environments. This makes the problem of conserving energy at individual sensor nodes challenging. S-MAC and PAMAS are two MAC protocols which periodically put nodes (selected at random) to sleep in order to achieve energy savings. Unlike these protocols, we propose an approach in which node duty cycles (i.e sleep and wake schedules) are based on their criticality. A distributed algorithm is used to find sets of winners and losers, who are then assigned appropriate slots in our TDMA based MAC protocol. We introduce the concept of energy-criticality of a sensor node as a function of energies and traffic rates. Our protocol makes more critical nodes sleep longer, thereby balancing the energy consumption. Security in sensor networks is more important than traditional networks as they are deployed in hostile environments and are more prone to capture. Trusted third party authentication schemes, public-key systems are not suitable owing to their high resource requirements. Key pre-distribution was introduced in to solve this problem. Our scheme achieves identical connectivity compared to the random key pre distribution using a less number of preloaded keys in each sensor node. Our proposed key pre-distribution scheme is based on assigning keys to sensors by placing them on a grid. This approach has been further modified to use multiple mappings of keys to nodes. In each mapping every node gets distinct set of keys which it shares with different nodes. The key assignment is done such that, there will be keys in common between nodes in different sub-grids. After randomly being deployed, the nodes discover common keys, authenticate and communicate securely. The analysis and simulation results show that this scheme is able to achieve better security compared to the random schemes

OPTIMIZATION OF DRILL DESIGN AND COOLANT SYSTEMS DURING DENTAL IMPLANT SURGERY

Dental implants are an effective alternative for the replacement of missing teeth. The success of the implant depends on how well a bone heals around the implant, a process known as osseointegration. However, excessive heat generated during the bone drilling will cause cell death and may prevent osseointegration of the implant, resulting in early failure. There are many factors which contribute to the heat generation during drilling. Experiments were carried out to investigate the affect of variable drilling factors on heat generation during drilling operation. Natural bone is not an ideal material for such research, as it varies widely in density and other parameters of interest.. It would be desirable to have a more uniform and consistent material to use in such studies. However, such a material must be similar to bone to allow the results to be extrapolated to the clinical situation. The current study describes and validates a model for use in such studies. Polymethylmethacrylate (PMMA) is the material chosen for our studies. A theoretical model was developed to study the effect of different drilling parameters on temperature rise during drilling operations. Comparison of observed results obtained from experiments was made with the results from theoretical study. Comparison of results for PMMA and human bone are also shown explaining how PMMA material can be substituted for human bone. The results suggest that the PMMA model is an acceptable surrogate for bone in such studies

Effect of Aging Time on Stiffness in Acid Catalyzed Silica Sol-Gels

The sol-gel method is employed in developing micro and nanoscale porous materials. This method produces highly customizable chemical structures, using a simple synthesis process. The potential of using such technology in synthesizing drug delivery mechanisms, bioceramics, and biocompatible polymers has resulted in the widespread use of the sol-gel process in biomedical applications. A sol-gel with a highly controlled pore structure can be loaded with a wide range of active ingredients for use as a controlled drug delivery mechanism. As such applications require high accuracy and precision, there is a need for quality control measures in large batch monolith synthesis to ensure adequate ingraining and active ingredient retention within the pore structure. This thesis characterized the mechanical properties of silica sols during an early development phase, called aging, to determine the conditions suitable for efficient active ingredient retention. The mechanical properties of an acid catalyzed silica sol-gel were studied at various aging times to determine whether retention of active ingredient within the pore structure changes as a result of changes in aging time and gel stiffness. There was a significant positive relationship between aging time up to 270 minutes after gelation and gel stiffness. However, the efficiency of active ingredient retention within the pore structure of a model compound, an organic pesticide, was not significantly correlated to stiffness in the aging time frame measured in this study. The change in stiffness over an aging time of 0 to 270 minutes after the gelation phase did not have a significant impact on the performance of this gel for retention of the representative model active ingredient application. Thus, the efficiency of active ingredient loading within the sol-gel pore structure is not altered by aging times within 4.5 hours after gelation and changes in the mechanical properties of increasing stiffness and decreasing hysteresis in that same timeframe