Rate models are often used to study the behavior of large networks of spiking neurons. Here we propose a procedure to derive rate models which take into account the fluctuations of the input current and firing rate adaptation, two ubiquitous features in the central nervous system which have been previously overlooked in constructing rate models. The procedure is general and applies to any model of firing unit. As examples, we apply it to the leaky integrate-and-fire (IF) neuron, the leaky IF neuron with reversal potentials, and to the quadratic IF neuron. Two mechanisms of adaptation are considered, one due to an afterhyperpolarization current, the other to an adapting threshold for spike emission. The parameters of these simple models can be tuned to match experimental data obtained from neocortical pyramidal neurons. Finally, we show how the stationary model can be used to predict the time-varying activity of a large population of adapting neurons.

This paper proposes a novel learning-based approach to synthesize cursive handwriting of the user's personal handwriting style, by combining shape and physical models together. In the training process, some sample paragraphs written by the user are collected and these cursive handwriting samples are segmented into individual characters by using a two-level writer-independent segmentation algorithm. Samples for each letter are then aligned and trained using shape models. In the synthesis process, a delta log-normal model based conditional sampling algorithm is proposed to produce smooth and natural cursive handwriting of the user's style from models.

Abstract. The anatomical connectivity of the nervous system of the nematode Caenorhabditis elegans has been almost completely described, but determination of the neurophysiological basis of behavior in this system is just beginning. Here we used an optimization algorithm to search for patterns of connectivity sufficient to compute the sensorimotor transformation underlying C. elegans chemotaxis, a simple form of spatial orientation behavior in which turning probability is modulated by the rate of change of chemical concentration. Optimization produced differentiator networks capable of simulating chemotaxis. A surprising feature of these networks was inhibitory feedback connections on all neurons. Further analysis showed that feedback regulates the latency between sensory input and behavior. Common patterns of connectivity between the model and biological networks suggest new functions for previously identified connections in the C. elegans nervous system. Keywords: integration

Academic Dissertation to be presented with the assent of

Recently, a class of phenomena known as self-organized criticality (SOC) has been discovered. SOC is characterized by two properties: firstly, the system exhibits power law behavior typical of a critical state, with no characteristic time or length scales; and secondly, this state is approached naturally, without tuning any external parameters. Early studies explained SOC in terms of conserved quantities [1,2]. Then Bak et al. [3] suggested that the Game of Life, GL, a cellular automaton lacking any conserved quantities, also exhibited SOC. This sparked a debate as to whether GL truly is SOC; conflicting data suggested it was subcritical [4,5,6]. In this paper I explore both sides of the argument in an attempt to resolve the issue. By finding an explicit form for the scaling function the opposing arguments are reconciled and, with some slight reservations, GL is judged to be subcritical. The differences between the analysis herein and other studies is highlighted. I also introduce th...

This is to certify that I have examined this copy of a doctoral dissertation by

Abstract not found

This paper is on automated visual inspection of tablets that may, in contrast to manual tablet sorting, provide objective and reproducible tablet quality assurance. Visual inspection of the ever-increasing numbers of produced imprinted tablets, regulatory enforced for unambiguous identification of active ingredients and dosage strength of each tablet, is especially demanding. The problem becomes more tractable by incorporating some a priori knowledge of the imprint shape and/or appearance. For this purpose, we consider two alternative automated tablet defect detection methods. The geometrical method, incorporating geometrical a priori knowledge of the imprint shape, enables specific inspection of the imprinted and non-imprinted tablet surface, while the statistical method exploits statistical a priori knowledge of tablet surface appearance, derived from a training image database. The two methods were evaluated on a large tablet image database, consisting of 3445 images of four types of imprinted tablets, with and without typical production defects. A ‘gold standard ’ for testing the performances of the two inspection methods was established by manually classifying the tablets into good and five defective classes. The results, obtained by ROC (receiver operating characteristics) analysis, indicate that the statistical method yields better defect detection sensitivity and specificity than the geometrical method. Both presented image analysis methods are quite general and promising tools for automated visual inspection of imprinted pharmaceutical tablets.

The operational range of electrostatic MEMS parallel plate actuators can be extended beyond pull-in in the presence of an intermediate dielectric layer, which has a significant effect on the behavior of such actuators. Here, we study the behavior of cantilever beam electrostatic actuators beyond pull-in using a beam model along with a dielectric layer. The results from the simple beam model are validated with 3D simulations performed in CoventorWareTM. Three possible static configurations of the beam are identified over the operational voltage range. We call them floating, pinned and flat; the latter two are also called arc-type and S-type in the literature. We compute the voltage ranges over which the three configurations can exist and the points where transitions occur between these configurations. Voltage ranges are identified where bi-stable and tri-stable states exist. A classification of all possible transitions (pull-in and pull-out as well as transitions we term pull-down and pull-up) is presented based on the dielectric layer parameters. Dynamic stability analyses are presented for the floating and pinned configurations. For high dielectric layer thickness, discontinuous transitions between configurations disappear and the actuator has smooth predictable behavior, but at the expense of lower overall tunability. (Some figures in this article are in colour only in the electronic version) 1.

The most likely voltage path and large deviations approximations