Studies of response to earthquake ground motion

A study is made of the accuracy of electronic digital computer calculations of ground displacement and response spectra from strong-motion earthquake accelerograms. This involves an investigation of methods of the preparatory reduction of accelerograms into a form useful for the digital computation and of the accuracy of subsequent digital calculations. Various checks are made for both the ground displacement and response spectra results, and it is concluded that the main errors are those involved in digitizing the original record. Differences resulting from various investigators digitizing the same experimental record may become as large as 100% of the maximum computed ground displacements. The spread of the results of ground displacement calculations is greater than that of the response spectra calculations. Standardized methods of adjustment and calculation are recommended, to minimize such errors.

Studies are made of the spread of response spectral values about their mean. The distribution is investigated experimentally by Monte Carlo techniques using an electric analog system with white noise excitation, and histograms are presented indicating the dependence of the distribution on the damping and period of the structure. Approximate distributions are obtained analytically by confirming and extending existing results with accurate digital computer calculations. A comparison of the experimental and analytical approaches indicates good agreement for low damping values where the approximations are valid. A family of distribution curves to be used in conjunction with existing average spectra is presented. The combination of analog and digital computations used with Monte Carlo techniques is a promising approach to the statistical problems of earthquake engineering.

Methods of analysis of very small earthquake ground motion records obtained simultaneously at different sites are discussed. The advantages of Fourier spectrum analysis for certain types of studies and methods of calculation of Fourier spectra are presented. The digitizing and analysis of several earthquake records is described and checks are made of the dependence of results on digitizing procedure, earthquake duration and integration step length. Possible dangers of a direct ratio comparison of Fourier spectra curves are pointed out and the necessity for some type of smoothing procedure before comparison is established. A standard method of analysis for the study of comparative ground motion at different sites is recommended.

Specklegram in a grapefruit fiber and its response to external mechanical disturbance in a single-multiple-single mode fiber structure

Specklegram in multimode fiber has successfully been used as a sensor for detecting mechanical disturbance. Speckles in a multimode pure silica grapefruit fiber are observed and compared to that of a step-index multimode fiber, showing different features between them. The sensitivities to external disturbance of two kinds of fiber were measured, based on single-multiple-single mode (SMS) fiber structure. Experimental results show that the grapefruit fiber shows higher sensitivity than does the step-index multimode fiber. The transmission spectrum of the grapefruit fiber was measured as well, showing some oscillation features that are significantly different from that of a step-index multimode fiber. The experiments may provide suggestions to understand the mechanisms of light propagation in grapefruit fibers. (D 2008 Optical Society of America.

Dynamic response of hysteretic systems with application to a system containing limited slip

A general class of single degree of freedom systems possessing rate-independent hysteresis is defined. The hysteretic behavior in a system belonging to this class is depicted as a sequence of single-valued functions; at any given time, the current function is determined by some set of mathematical rules concerning the entire previous response of the system. Existence and uniqueness of solutions are established and boundedness of solutions is examined.

An asymptotic solution procedure is used to derive an approximation to the response of viscously damped systems with a small hysteretic nonlinearity and trigonometric excitation. Two properties of the hysteresis loops associated with any given system completely determine this approximation to the response: the area enclosed by each loop, and the average of the ascending and descending branches of each loop.

The approximation, supplemented by numerical calculations, is applied to investigate the steady-state response of a system with limited slip. Such features as disconnected response curves and jumps in response exist for a certain range of system parameters for any finite amount of slip.

To further understand the response of this system, solutions of the initial-value problem are examined. The boundedness of solutions is investigated first. Then the relationship between initial conditions and resulting steady-state solution is examined when multiple steady-state solutions exist. Using the approximate analysis and numerical calculations, it is found that significant regions of initial conditions in the initial condition plane lead to the different asymptotically stable steady-state solutions.

Microorganisms of the East African Great Lakes and their response to environmental changes

We have reviewed the phytoplankton composition and succession in the East African Great Lakes, their response to environmental changes, and the communities of microorganisms of the microbial food web. Recent studies in some great lakes, as well as progress in understanding phytoplankton succession and response to environmental factors, enable us to update knowledge of the phytoplankton ecology of these lakes. In particular, we present information indicating that phytoplankton composition in lakes Tanganyika and Kivu may reflect recent changes as a result of global warming or species introduction. We also stress the importance of microbes (at the base of the food web) in these systems and suggest that the microbial food web, which has been mostly overlooked until recently, may play a very large role in determining productivity and nutrient cycling in these large lakes.

Time response of optical switching properties of Sb thin films under focused laser pulses

The time response of optical switching properties of Sb thin films under focused laser pulses is investigated. The results show that the response course can be divided into onset, opening, and closing stages. Formulas for their lengths are given. The onset and opening times decrease with increasing pumping light power density. The closing time is about 150 ns. For optical memory, if the power density of the readout and recording lasers changes from 5 x 10(9) to 15 x 10(9) W/m(2), the onset time changes from 2.5 to 0.30 mus, and the opening time is on the nanosecond scale. (C) 2003 Society of Photo-Optical Instrumentation Engineers.