Richard G. Absher

Genealogies of clones of diploid fibroblasts: Cinemicrophotographic observations of cell division patterns in relation to population age☆

Direct assessment of cell division patterns of human diploid fibroblasts (WI-38) has been achieved using techniques of time-lapse cinemicrophotography. Pedigrees of progeny cells in clones from middle and late passage WI-38 cultures are presented. The passage 28 clone exhibited a division pattern that was highly synchronous through four generations and had an average interdivision time that increased linearly from the second through sixth generations. Division was essentially logarithmic through the fourth generation. The passage 53 clone was much more variable in interdivision time, less synchronous, and less motile than the passage 28 clone. While there is considerable overlap in the interdivision times of cells of the passage 28 and 53 clones, the late passage cells generally exhibit more variation in interdivision times. The average population doubling time was 16.8 h in thepassage 28 clone and 32.0 h in the passage 53 clone.

Clonal variation and aging of diploid fibroblasts: Cinematographic studies of cell pedigrees☆

Abstract Time-lapse cinematographic (TLC) analysis of clones of human diploid fibroblasts indicate heterogeneity in clonal division behaviour. Variations are noted in interdivision time, clone size and generations per clone. Correlation coefficients for interdivision times of sister pairs are high in young clones and generally low in aged clones. A consistent division pattern at all population doubling levels is one of low average interdivision time for early and late generations of a clone and high average interdivision time for the middle range of generations of a clone. The clonal division patterns observed experimentally have been duplicated in computer simulated pedigrees. The computer model is based on an oscillating system which allows for flux of regulator substances. The critical concentrations of regulator substances determine the clonal division pattern for a given progenitor cell.

Time-Lapse Cinemicrophotographic Studies of Cell Division Patterns of Human Diploid Fibroblasts (WI-38) during their in Vitro Lifespan

Genealogies of human diploid embryonic lung fibroblasts, WI-38 were prepare from analysis of filmed sequences of clones at passages 20, 28 and 53. The results indicate heterogeneity in cell division patterns, interdivision time and migration activity. The relationship of the cell division patterns to age of culture is difficult to assess at this time because of the heterogeneity of the clones, however, the late passage culture appeared to be more variable in terms of sister-sister, and mother-daughter relationships. The passage 28 culture was representative of a highly proliferating clone, exhibiting short interdivision times and a synchronous division pattern. The passage 20 and 53 clones exhibited longer interdivision times and less synchronous division pattern than the passage 28 clone. A gradual lengthening of average interdivision time with successive generations has been observed in all genealogies regardless of passage level of the donor culture. A portion of daughter cells in the fifth and sixth generation exhibited lower interdivision time than the mother cell. The effects of nutrients, space, and mitotic inhibitors or stimulators on interdivision time of the cells within the clones is discussed.

Spectral estimation based on the Wigner-Ville representation

Several classical techniques to estimate the component frequencies in a multicomponent signal are based on Fourier-like transformations. The frequency estimates obtained from their spectral peaks are affected by the window length and phase, thus presenting a large variance even in the absence of noise. Analytic signal based spectral estimators present no phase dependence for mono-component signals but, contrary to previous claims, they are not phase invariant for multicomponent signals, and perform worse than their real signal counterparts in high noise. The analysis of Wigner-Ville (WVD) spectra of continuous and discrete signals with time-limited windows demonstrates a better frequency concentration and less phase dependence than real or analytic signal Fourier spectra. The WVD presents accurate frequency estimates for multicomponent stationary signals, where crossterm interference is attenuated by smoothing the WVD in time (SWVD). It also has an excellent performance in the presence of noise, making it a good alternative to classical spectral estimation approaches. Furthermore, it is especially appropriate for the case of nonstationary multicomponent signals due to the good WVD temporal resolution, thus representing a superior spectral estimation technique suitable for the analysis of a variety of physical processes.

Mathematical models and computer simulations of proliferation of human diploid fibroblast clones.

Abstract A mathematical model based on the simple concept of an oscillatory mechanism for regulation of cellular proliferation has been developed that describes the growth of clones of human diploid fibroblasts in vitro. Lineages of these cells have been obtained from time-lapse cinematographic sequences of proliferating clones. Computer simulations based upon the oscillator model have generated genealogies that behave as the experimentally-derived genealogies.

System Identification and Feedback Control of an Aerosol Production Process

A method for determining the relationship between the input (generator output rate) and output (chamber aerosol concentration) of an aerosol generating system is discussed. This relationship is modeled in terms of discrete transfer functions that separate the input that results from the physical aspects of the generating system from the input that is a result of the noise inherent to the process. A computer-aided design (CAD) software package was used to estimate these transfer functions and simulate the response of the modeled system to step-changes in generator output rate. The estimated transfer functions were then used to design a feedback control system that incorporated a proportional-integral-derivative (PID) control algorithm. This algorithm effectively established new concentration levels after step-changes in generator output rate of various magnitudes were made.

Parametric modeling of the Wigner half-kernel and its application to spectral estimation

Abstract Parametric spectral estimation methods provide high frequency resolution and allow a compact representation. The Wigner-Ville distribution (WVD), on the other hand, presents high frequency concentration and temporal resolution, but produces spectral crossterms and abundant data. WVD autoregressive (AR) modeling combines the advantages of both techniques. Using the analytic signal to compute the WVD kernel cancels negative frequency crossterms and provides a low-order complex predictor, half the size of real AR models. Crossterms and potential kernel symmetry problems are avoided by modeling the Smoothed WVD (SWVD) half-kernel. The developed representation is analyzed and compared to real and analytic AR spectral estimators. It is shown that the SWVD half-kernel AR covariance poles produce precise frequency estimates for monocomponent signals, independent of data length and phase, just like real and analytic AR estimators, but with the advantage of excellent performance in noise. These properties are verified experimentally and extended to multicomponent signals in noise, showing that while the analytic AR estimator performs slightly better than its real counterpart, the SWVD half-kernel results in a frequency estimation error reduction of around two orders of magnitude.

CAN UNDERGRADUATE TEST ENGINEERING EDUCATION BE "FASTER, BETTER, SOONER?"

I endorse the point of view that test engineers (1) design, develop, and implement the methodologies, processes, and strategies as well as the software, hardware, and personnel systems required to economically accomplish error detection, location, and removal and (2) they evaluate test results relative to theoretical, and application performance. Thus, test engineers operate at every stage of the product life-cycle and make a significant contribution to product quality

Segmentation and classification of nasal phonemes based on their time-frequency representation

Time-frequency analysis of speech provides detailed information which may be used for the study of its production mechanisms and for recognition purposes. The smoothed Wigner-Ville distribution can be used as an effective speech analysis tool when a high temporal resolution is required. Smoothing demands a careful balance between resolution and suppression of interferences in the distribution while taking into account the characteristics of the speech signal. The resulting representation is applied to analyze nasal phonemes and transitions in continuous speech and shown to unveil important transitory features not revealed by the spectrogram and to result in accurate segmentation and discrimination of their place of articulation.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A modulation model for the vowel sound /i/ in human speech

An approach has been developed that models a nonstationary speech signal with very low error on a pitch period by pitch period basis using an AM–FM model. The speech signal is first separated into two independent signals, a low‐frequency signal and a high‐frequency signal. AM and FM signals are extracted from the high‐frequency signal through the use of two nonlinear operators, the integral operator and the overmodulation detection algorithm. Model parameters are determined by a combination of direct Fourier series computation and parameter optimization using the correlation error measure and the Marquardt–Levenberg algorithm. This technique was applied to speech produced in various gas concentrations of air and helium in order to determine whether model parameters are directly related to the velocity of sound ratio. It was found that the amplitudes of the harmonics of the low‐frequency signal were emphasized with the increase of the velocity of sound ratio. The standard deviation of the carrier frequency...