The Resonate-and-fire Neuron: Time Dependent and Frequency Selective Neurons in Neural Networks

The means through which the nervous system perceives its environment is one of the most fascinating questions in contemporary science. Our endeavors to comprehend the principles of neural science provide an instance of how biological processes may inspire novel methods in mathematical modeling and engineering. The application ofmathematical models towards understanding neural signals and systems represents a vibrant field of research that has spanned over half a century. During this period, multiple approaches to neuronal modeling have been adopted, and each approach is adept at elucidating a specific aspect of nervous system function. Thus while bio-physical models have strived to comprehend the dynamics of actual physical processes occurring within a nerve cell, the phenomenological approach has conceived models that relate the ionic properties of nerve cells to transitions in neural activity. Further-more, the field of neural networks has endeavored to explore how distributed parallel processing systems may become capable of storing memory. Through this project, we strive to explore how some of the insights gained from biophysical neuronal modeling may be incorporated within the field of neural net-works. We specifically study the capabilities of a simple neural model, the Resonate-and-Fire (RAF) neuron, whose derivation is inspired by biophysical neural modeling. While reflecting further biological plausibility, the RAF neuron is also analytically tractable, and thus may be implemented within neural networks. In the following thesis, we provide a brief overview of the different approaches that have been adopted towards comprehending the properties of nerve cells, along with the framework under which our specific neuron model relates to the field of neuronal modeling. Subsequently, we explore some of the time-dependent neurocomputational capabilities of the RAF neuron, and we utilize the model to classify logic gates, and solve the classic XOR problem. Finally we explore how the resonate-and-fire neuron may be implemented within neural networks, and how such a network could be adapted through the temporal backpropagation algorithm

A study on the insertion characteristics of rectus muscles and its relation with the axial length of eye ball in cadaveric eyes from an eastern Indian population

The primary aim was to record measurements of relevant anatomy of recti muscle insertions in relation to limbus and with each other, and also to find whether these measurements vary with the axial length of the eyeball in an eastern Indian perspective. Eye balls ( n= 64, 20 female and 44 male) from Institutional eye bank were examined, within eight hours of death of the donor, under operating microscope by a single observer between May 2009 to April 2010.The mean distance from limbus to each rectus muscle at midpoint and at each end of insertion was measured by Castroviejo caliper. Additional parameters studied were length of each rectus muscle insertion (‘width’), distance between each rectus muscle insertion and measurement of axial length using 10 MHz ultrasonic A scan probe. Data collected was entered in Microsoft Office Excel 2007 and analysed by using statistical software SPSS 10. The frequency was calculated in percentages. Criteria for significance used in the study was at p<0.05. The mean age of the donors was 71years with a range of 26-86 years. Statistically significant difference (p<0.05) was found between male and female eyes regarding distance of limbus to midpoint point of only medial rectus muscle insertion. No statistically significant (p>0.05) difference was found between male and female eyes regarding length of line of rectus muscles insertion. No statistically significant correlation (p>0.05) was observed between the axial length and various measurements of rectus muscle insertion. Results of this study might help local strabismologists in revaluation of the spiral of Tilluax based on regional (Eastern Indian) perspective.Key words: Eye ball; Rectus muscles; Rectus muscle insertion; Axial length; Indian population

Bacteriological quality of water and diarrhoea among ethnic and non-ethnic communities of rural area of West Tripura, India

Background: Waterborne diseases are the major causes of health seeking by ethnic and non-ethnic communities of West Tripura district of India. Safe and wholesome water is a basic requirement for good health. Microbiological contamination of water is responsible for most of the waterborne diseases and diarrhoea is still a major killer of childhood.Methods: A community based cross-sectional study was conducted among 177 ethnic and non-ethnic households chosen by multi stage sampling from West Tripura District of North East India during June - July 2016 to assess the bacteriological quality of water and to find out its association with the occurrence of diarrhoea.Results: Among the ethnic and non-ethnic households shallow tube wells were the source for 52.18% and 62.35 %, deep tube wells for 19.56% and 29.41%, and pipe water for 20.65 % and 5.89 households respectively. Sanitary latrines ware used in 46.73% ethnic and 50.59% non-ethnic households. In both the group filtration was practiced by 85% and no purification by 1%. Covered vessels were used for storing water in 94.57% ethnic and 95.30% non-ethnic households. Source of water was mildly contaminated in 15% ethnic and 10% non-ethnic, moderate and heavy contaminations were 11% and 8% each respectively in both the groups. At the point of consumption moderate and heavy contaminations were 2% each in ethnic households. Mild and severe contaminations were 3% and 1% respectively in non-ethnic group. Diarrhoea was significantly more frequent among households consuming coliform contaminated water (p<0.05).Conclusions: Half of the study population was using insanitary latrine and one fifth were collecting water from contaminated sources. Hence provision of safe water and promotion of sanitary latrine is needed to prevent waterborne diseases in this community

Multisite Phosphorylation Modulates the T Cell Receptor ζ-Chain Potency but not the Switchlike Response

AbstractMultisite phosphorylation is ubiquitous in cellular signaling and is thought to provide signaling proteins with additional regulatory mechanisms. Indeed, mathematical models have revealed a large number of mechanisms by which multisite phosphorylation can produce switchlike responses. The T cell antigen receptor (TCR) is a multisubunit receptor on the surface of T cells that is a prototypical multisite substrate as it contains 20 sites that are distributed on 10 conserved immunoreceptor tyrosine-based activation motifs (ITAMs). The TCR ζ-chain is a homodimer subunit that contains six ITAMs (12 sites) and exhibits a number of properties that are predicted to be sufficient for a switchlike response. We have used cellular reconstitution to systematically study multisite phosphorylation of the TCR ζ-chain. We find that multisite phosphorylation proceeds by a nonsequential random mechanism, and find no evidence that multiple ITAMs modulate a switchlike response but do find that they alter receptor potency and maximum phosphorylation. Modulation of receptor potency can be explained by a reduction in molecular entropy of the disordered ζ-chain upon phosphorylation. We further find that the tyrosine kinase ZAP-70 increases receptor potency but does not modulate the switchlike response. In contrast to other multisite proteins, where phosphorylations act in strong concert to modulate protein function, we suggest that the multiple ITAMs on the TCR function mainly to amplify subsequent signaling

Systems model of T cell receptor proximal signaling reveals emergent ultrasensitivity

Receptor phosphorylation is thought to be tightly regulated because phosphorylated receptors initiate signaling cascades leading to cellular activation. The T cell antigen receptor (TCR) on the surface of T cells is phosphorylated by the kinase Lck and dephosphorylated by the phosphatase CD45 on multiple immunoreceptor tyrosine-based activation motifs (ITAMs). Intriguingly, Lck sequentially phosphorylates ITAMs and ZAP-70, a cytosolic kinase, binds to phosphorylated ITAMs with differential affinities. The purpose of multiple ITAMs, their sequential phosphorylation, and the differential ZAP-70 affinities are unknown. Here, we use a systems model to show that this signaling architecture produces emergent ultrasensitivity resulting in switch-like responses at the scale of individual TCRs. Importantly, this switch-like response is an emergent property, so that removal of multiple ITAMs, sequential phosphorylation, or differential affinities abolishes the switch. We propose that highly regulated TCR phosphorylation is achieved by an emergent switch-like response and use the systems model to design novel chimeric antigen receptors for therapy

Multisite phosphorylation in T cell receptor proximal signalling

T cell receptor proximal signalling represents a specific instance of a multisite phosphorylation system. Receptor phosphorylation is regulated by the opposing actions of the kinase LCK, and phosphatases such as CD45 and CD148. Particular phosphoforms recruit the kinase ZAP-70, which once bound, propagates downstream signalling. In this thesis we investigate the functional consequences of multiple phosphorylation sites on the dose-response profiles of receptor phosphorylation. We combine mathematical modelling with cellular reconstitution to assess the effect of multiple modification sites on the potency and sensitivity of receptor phosphorylation. We find that multiple sites enhance the potency of receptor phosphorylation, but do not alter the sensitivity of dose-response profiles. This correlation between the number of sites and response potency is consistent with a mechanism whereby phosphorylation mediates an enhancement in the enzymatic efficiencies of modification.</p

Effect of pyrophyllite on the mullitization in triaxial porcelain system

China clay (kaolin) was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 5% pyrophyllite as a replacement of china clay improved the fired strength by about 24% compared to that of the conventional body fired at 1300 degrees C. Percentage of mullite was found to increase in the fired specimens when kaolinite was progressively replaced by pyrophyllite. However, beyond 7.5% pyrophyllite addition, amorphous SiO(2) released from pyrophyllite dehydroxylate inhibited further recrystallization of mullite. There was very insignificant change in the phase compositions with mixes having pyrophyllite content higher than 7.5%. Entire phenomenon has been explained on the basis of structural reorganization of pyrophyllite during dehydroxylation. Presence of large amount of undissolved quartz of smaller size as well as isolated pores in the microstructures of specimens containing pyrophyllite more than 7.5% are assumed to hinder the propagation of crack and thereby improving the mechanical properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition. (C) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Chemisorption of yttrium nitrate on AlN particles

Homogenization of Y2O3 as a sintering additive in AIN green compact has been achieved by chemisorption of Y(NO3)(3) on AIN particles in isopropanol suspension. Substantial adsorption of Y(NO3)(3) equivalent to a Y2O3 content up to a maximum of 1.4 wt% of AIN has been observed. Electrokinetic mobility measurements of the coated particles and the adsorption studies show that the adsorption takes place in isopropanol suspension. SEM shows a good homogeneous distribution of Y2O3 in the green ceramic compacts, and no trace of secondary crystallization has been observed

Effect of pyrophyllite incorporation in porcelain composition on mechanical properties and microstructure

China clay (Kaolin) and quartz in the ratio of 1:2 was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 15% pyrophyllite as a replacement of a combination of china clay and quartz decreased the linear shrinkage by 5.03% while fired strength was improved by about 31.5% compared to that of the conventional body fired at 1300 degrees C. Incorporation of pyrophyllite beyond 15% resulted in early vitrification of porcelain composition, although in lower proportion the effect is not so significant. Percentage of mullite was found to increase in the fired specimens even when kaolinite was progressively replaced by pyrophyllite. However, beyond 22.5% pyrophyllite addition, there occurred large volume of glass formation. Presence of large volume of glassy phase as well as formation of large pores of various shapes resulted in deterioration in ceramic properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition. (C) 2009 Published by Elsevier Ltd and Techna Group S.r.l

Pyrophyllite as raw material for ceramic applications in the perspective of its pyro-chemical properties

General pyro-chemical properties of pyrophyllite were studied using one Indian variety as sample. In addition to normal routine analysis, thermal expansion, infrared spectroscopy, DTA, XRD and SEM studies were also employed to understand the pyro-chemical properties of the specimen at different temperatures. The results indicate that the specimen contains pyrophyllite as major phase with sericite, quartz and diaspore as minor phases. Unlike kaolinite, pyrophyllite contains low alumina and high silica which on heating mainly produces mullite and amorphous silica. Mullite crystallization from pyrophyllite is rather easy than that from kaolinite. The silica in turn yields large amount of viscous liquid at high temperature. It is suggested that pyrophyllite may be utilized in such compositions favourably where mullite is a desirable phase by partial replacement of china clay which is a viable alternative particularly in the background of depleting reserves of kaolinite and its continuous cost escalation. Additionally amorphous silica produced in the reaction system may acts as an in situ produced filler material that reduces the use of quartz in such system. (C) 2009 Published by Elsevier Ltd and Techna Group S.r.l