The Role of GABAergic Inhibition in Processing of lnteraural Time Difference in the Owl's Auditory System

The barn owl uses interaural time differences (ITDs) to localize the azimuthal position of sound. ITDs are processed by an anatomically distinct pathway in the brainstem. Neuronal selectivity for ITD is generated in the nucleus laminaris (NL) and conveyed to both the anterior portion of the ventral nucleus of the lateral lemniscus (VLVa) and the central (ICc) and external (ICx) nuclei of the inferior colliculus. With tonal stimuli, neurons in all regions are found to respond maximally not only to the real ITD, but also to ITDs that differ by integer multiples of the tonal period. This phenomenon, phase ambiguity, does not occur when ICx neurons are stimulated with noise. The main aim of this study was to determine the role of GABAergic inhibition in the processing of ITDs. Selectivity for ITD is similar in the NL and VLVa and improves in the ICc and ICx. Iontophoresis of bicuculline methiodide (BMI), a selective GABAA antagonist, decreased the ITD selectivity of ICc and ICx neurons, but did not affect that of VLVa neurons. Responses of VLVa and ICc neurons to unfavorable ITDs were below the monaural response levels. BMI raised both binaural responses to unfavorable ITDs and monaural responses, though the former remained smaller than the latter. During BMI application, ICx neurons showed phase ambiguity to noise stimuli and no longer responded to a unique ITD. BMI increased the response magnitude and changed the temporal discharge patterns in the VLVa, ICc, and ICx. Iontophoretically applied GABA exerted effects opposite to those of BMI, and the effects could be antagonized with simultaneous application of BMI. These results suggest that GABAergic inhibition (1) sharpens ITD selectivity in the ICc and ICx, (2) contributes to the elimination of phase ambiguity in the ICx, and (3) controls response magnitude and temporal characteristics in the VLVa, ICc, and ICx. Through these actions, GABAergic inhibition shapes the horizontal dimension of the auditory receptive fields

Experimental Studies on Free Vibrations of a long spanned Suspension Bridge

This paper presents the experimental results for static and dynamic characteristics of a suspension bridge with inclined hanger system comparing those with ordinary vertical hanger system by use of three spans suspension bridge model (3, 250+6, 500+3, 250). The discrepancy due to the inclination of hangers is studied by the model test on the natural frequencies, the frequency responses and the damping-amplitude relations for the above cases. The results indicate that the inclination of hanger system may increase the deflectional stiffness when the load acts asymmetrically and dynamically the damping effect in the free vibrations

Fundamental Studies on Earthquake Response of a Long Span Suspension Bridge

This paper deals theoretically with the earthquake response of a long span suspension bridge. An exact solution of this problem is seldom possible because of the complexity of the structure and the earthquake motions. For the convenience of the analysis a simplified structural system of the suspension bridge with finite degrees of freedom of motion is adopted, and the ground disturbances are assumed to be a simple shape. To simplify the problem, linearized deflection theory of suspension bridges is employed. Some parts of numerical calculation, natural frequencies and modes of the system, had been done on a high speed digital computer. On this investigation some response spectra are given, and the fundamental earthquake response characteristics of the suspension bridge are made clear

A Dynamical Consideration on Earthquake Damages of Bridge Piers : First Report

As was also noted from the results of the Fukui Earthquake of June 1948, it is now quite evident that the earthquake damage of the bridge substructure decisively affects the damage of the whole bridge, directly or indirectly, with almost no exception. In view of this fact, it is attempted in this paper to make a dynamical study from both theoretical and experimental points of view on the mechanism of earthquake damages of the bridge substructure and thereby contribute to the earthquake-proof design and construction of bridge piers

On the Experimental Stress Analysis of a Composite Box Girder Bridge

Experimental researches on composite box girders have been carried out on several bridges and test models and their structural behaviors are gradually becoming clear. The results of the measured stresses obtained at the Yamasu Bridge built in Kyoto in 1955 and the considerations of these results are described in this report. There is good agreement between the theoretical predictions and the actual behavior

On Galloping Oscillation of Square Prism in Two Dimensional Uniform Flow

In the connection of frequently used structural members of longspanned bridges, the aeroelastic characteristics of a square prism are investigated, based on the quasi-steady theory. The experimental results of the wind tunnel tests are compared with the theoretical characteristics, using the theory given by G. V. Parkinson. In this paper, some considerations on the critical wind velocity for galloping phenomenon of square prism are presented. Also, the qualitataive method to determine the induced amplitude is discussed

A Study on the Bandwidth Reduction of the Stiffness Matrix of a Framed Structure

How to give the numerical number for joints of a framed structure in order to reduce the bandwidth of its stiffness matrix, has been studied and a number of methods have been proposed already. Though the minimum bandwidth is wholly governed by the connectivity relationship between joints, only a few studies have taken that fact into the consideration. The connectivity relationship of a framed structure can be sufficiently shown by the use of a linear graph, which is composed of nodes and lines. Its characteristics can be understood by introducing the concept of graph theory. In this paper, the authors propose a graphical method to obtain the minimum bandwidth of tree structures. This is a kind of statically determinate system including no closed path, by the application of some definitions in graph theory. By use of the this sequential file method, all the nodal sequences are efficiently filed along the longest nodal sequence among the graph. The number of rows of filed nodal sequences present the bandwidth of the original structure

A Network-Topological Study on Statical Analysis of Rigid Framed Structures

For the numerical analysis of complex structures with high redundancy by use of the digital computer, there arise a number of difficulties to solve the problems on an account of the fact that the increase of the rank of matrice involved requires much storage and time to obtain numerical results. A network-topological formulation of structural analysis leads effective algorithm to solve these problems. The alternative derivation of Spiller's formula and a memory-saving algorithm is considered in this paper

A Theoretical Consideration on Helicoidal Girder

A theoretical consideration is given on an arbitrary supported helicoidal girder and an approximate method of analysis is presented, taking into an account the St. Venant's torsion in which the fundamental relationship between the sectional forces and deformations are obtained by use of the Reduction method