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The World Public Library Physics Collection contains 263 conversations regarding the nature of physics.

 
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The Equilibrium of a Buckled Plate Acted by the Forces N and by th...

Physics Literature

Excerpt: The equilibrium of a buckled plate acted by the forces +/-N and by a load q having the same magnitude but a contrary sense with respect to the load presented in Fig.F4 (b). In order to use the previous results, it is necessary to find when the mechanical state of stress / strain corresponding to the presence of the lateral forces is identical to the mechanical state of stress / strain corresponding to an unknown vertical load p=p(x) (Fig.F4b). The equilibrium co...

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Finite Plates

Physics Literature

Excerpt: In the case of the finite plates, the boundary conditions on the contour of the plate are essential ones in order to obtain the values of the integration constants. Some particular, most common cases will analysed in detail. As a consequence, a previous examination of the mean values Eijand ?ij, i, j=1,2,3. it is necessary.

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The Spherical Shell and the Model. Bernoullis Hypothesis. Displace...

Physics Literature

Excerpt: A spherical elastic, homogeneous shell having the elastic moduli equal to ?,? is considered and the usual spherical coordinate system (r,?,?) is used. However, some of the derived results are also valid in the case of a more general, non-elastic spherical shell. In the initial state, the homogeneous density is denoted by ?0 and the median spherical surface of the shell has the equation ...

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Elements of Rheology : Introduction.

Physics Literature

Excerpt: Especially for geological processes at a large time scale and great values of the stress, the internal friction of the material cannot be ignored. Consequently, the HOOKE?s law has to be replaced by assuming different constitutive equations (models). Their expressions are mainly depending on the time scale of the geophysical process to be modelled. In relation to seismic or seismological applications, for example, short periods and short stresses are required (u...

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The Accretion Wedge and the Model

Physics Literature

Excerpt: Consider a 2-D prismatic body having a triangular vertical section (Fig.I1), in the presence of gravity. The wedge rests on a rigid basement having the slope equal to ?0. Both the compressional force acting on the left side of the wedge and the friction to the basement cause thickening of the incompressible material and the development of a topographical slope equal to à. It is assumed that the material is into a state of plastic yielding according to the VON MI...

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General References

Physics Literature

Excerpt: Aki, K., Richards, P.G., 1980. Quantitative Seismology, Freeman And Co., New York // Backus, G., Continuum Mechanics, Samizdat Press // Bayly, B., 1992, Mechanics In Structural Geology, Springer - Verlag, N.Y. // Filonenco-Borodici, M.M., 1952, Theory Of Elasticity, Ed. Tehnica, Bucharest // Ivan, M., 1996, Seismology (In Romanian), V.I, Ed. Universitatii Bucuresti // Ivan, M., 1997a. A Finite Element Algorithm For Computing The Flexure Of The Crustal, In Press,...

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Chapter 3 Neural Decoding

Physics Literature

Excerpt: Encoding and Decoding. In chapters 1 and 2, we considered the problem of predicting neural responses to known stimuli. The nervous system faces the reverse problem, determining what is going on in the real world from neuronal spiking patterns. It is interesting to attempt such computations ourselves, using the responses of one or more neurons to identify a particular stimulus or to extract the value of a stimulus parameter. We will assess the accuracy with which...

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Chapter 1 Neural Encoding I : Firing Rates and Spike Statistics

Physics Literature

Introduction: Neurons are remarkable among the cells of the body in their ability to propagate signals rapidly over large distances. They do this by generating characteristic electrical pulses called action potentials, or more simply spikes, that can travel down nerve fibers. Neurons represent and transmit information by firing sequences of spikes in various temporal patterns. The study of neural coding, which is the subject of the first four chapters of this book, invol...

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Chapter 2 Neural Encoding II : Reverse Correlation and Visual Rece...

Physics Literature

Introduction: The spike-triggered average stimulus introduced in chapter 1 is a standard way of characterizing the selectivity of a neuron. In this chapter, we show how spike-triggered averages and reverse-correlation techniques can be used to construct estimates of firing rates evoked by arbitrary time-dependent stimuli. Firing rates calculated directly from reverse correlation functions provide only a linear estimate of the response of a neuron, but we also present in ...

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Exercises

Physics Literature

Excerpt: Generate spike sequences with a constant firing rate r0 using a Poisson spike generator. Then, add a refractory period to the model by allowing the firing rate r(t) to depend on time. Initially, r(t) = r0. After every spike, set r(t) to zero. Allow it to recover exponentially back to r0 by setting r(t + t) = r0 + (r(t) ? r0) exp(? t/çref) after every simulation time step t in which no spike occurs. The constant çref controls the refractory recovery rate. Initial...

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Chapter 4 Information Theory

Physics Literature

Excerpt: Entropy and Mutual Information. Neural encoding and decoding focus on the question: ?What does the response of a neuron tell us about a stimulus.? In this chapter we consider a related but different question: ?How much does the neural response tell us about a stimulus.? The techniques of information theory allow us to answer this question in a quantitative manner. Furthermore, we can use them to ask what forms of neural response are optimal for conveying informa...

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Mathematical Appendix

Physics Literature

Excerpt: The book assumes a familiarity with basic methods of linear algebra, differential equations, and probability theory, as covered in standard texts. This chapter describes the notation we use and briefly sketches highlights of various techniques. The references provide further information.

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Model Neurons I: Neuroelectronics

Physics Literature

Introduction: A great deal is known about the biophysical mechanisms responsible for generating neuronal activity, and these provide a basis for constructing neuron models. Such models range from highly detailed descriptions involving thousands of coupled differential equations to greatly simplified caricatures useful for studying large interconnected networks. In this chapter, we discuss the basic electrical properties of neurons and the mathematical models by which the...

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Chapter 6 Model Neurons II : Conductances and Morphology

Physics Literature

Excerpt: Levels of Neuron Modeling. In modeling neurons, we must deal with two types of complexity; the intricate interplay of active conductances that makes neuronal dynamics so rich and interesting, and the elaborate morphology that allows neurons to receive and integrate inputs from so many other neurons. The first part of this chapter extends the material presented in chapter 5, by examining single-compartment models with a wider variety of voltage-dependent conducta...

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Chapter 7 Network Models

Physics Literature

Introduction: Extensive synaptic connectivity is a hallmark of neural circuitry. For example, neurons in the mammalian neocortex each receive thousands of synaptic inputs. Network models allow us to explore the computational potential of such connectivity, using both analysis and simulations. As illustrations, we study in this chapter how networks can perform the following tasks: coordinate transformations needed in visually guided reaching, selective amplification leadi...

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Plasticity and Learning

Physics Literature

Introduction: Activity-dependent synaptic plasticity is widely believed to be the basic phenomenon underlying learning and memory, and it is also thought to play a crucial role in the development of neural circuits. To understand the functional and behavioral significance of synaptic plasticity, we must study how experience and training modify synapses, and how these modifications change patterns of neuronal firing to affect behavior. Experimental work has revealed ways ...

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References

Physics Literature

Excerpt: Abbott, LF (1994) Decoding neuronal firing and modeling neural networks. Quarterly Review of Biophysics 27:291-331. // Abbott, LF, Varela, JA, Sen, K & Nelson, SB (1997) Synaptic depression and cortical gain control. Science 275:220-224. // Adelson EH, Bergen JR (1985) Spatiotemporal energy models for the perception of motion. Journal of the Optical Society of America A2:284-299. // Ahmed, B, Anderson, JC, Douglas, RJ, Martin, KAC & Whitterage, D (1998) Estimate...

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Classical Conditioning and Reinforcement Learning

Physics Literature

Introduction: The ability of animals to learn to take appropriate actions in response to particular stimuli on the basis of associated rewards or punishments is a focus of behavioral psychology. The field is traditionally separated into classical (or Pavlovian) and instrumental (or operant) conditioning. In classical and instrumental conditioning classical conditioning, the reinforcers (i.e. the rewards or punishments) are delivered independently of any actions taken by ...

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Representational Learning

Physics Literature

Introduction: The response selectivities of individual neurons, and the way they are distributed across neuronal populations, define how sensory information is represented by neural activity in a particular brain region. Sensory information is typically represented in multiple regions, the visual system being a prime example, with the nature of the representation shifting progressively along the sensory pathway. In previous chapters, we discuss how such representations c...

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Theory and Operation of Direct-Current Machinery

By: Cyril M. Jansky

Physics Literature

Excerpt: In his instructional work the author has to deal with students of limited mathematical training. To meet the needs of this work this text has been prepared. Although it was thought inadvisable to omit mathematics entirely, only the more elementary principles used are, and these merely to make clearer the quantitative relations of the physical quantities involved in the theory of direct-current machines ...

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