Biomedical subjects

Kamran Iqbal

Publications and source records attributed to Kamran Iqbal.

5 recordsLinked to original sources

PubMed2006

Interspeaker variation in habitual speaking rate: additional evidence.

PURPOSE: The purpose of the present study was to test the hypothesis that talkers previously classified by Y.-C. Tsao and G. Weismer (1997) as habitually fast versus habitually slow would show differences in the way they manipulated articulation rate across the rate continuum. METHOD: Thirty talkers previously classified by Tsao and Weismer (1997) as having habitually slow (n = 15; 7 males, 8 females) and habitually fast (n = 15; 8 males, 7 females) articulation rates produced a single sentence at 7 different rates, using a magnitude production paradigm. Hence, the participants were not randomly assigned to conditions. RESULTS: Quadratic regression functions relating measured to intended articulation rates were all statistically significant, and most important, there were significant differences between the slow and fast groups in the y intercepts of the functions, for both males and females. CONCLUSIONS: This study provides a constructive replication of Tsao and Weismer (1997), showing a difference between slow and fast talkers with a new set of speech materials and in a new task. The findings appear to be consistent with a biological basis for intertalker rate differences.

Female↗

PubMed2006

The effect of intertalker speech rate variation on acoustic vowel space.

The present study aimed to examine the size of the acoustic vowel space in talkers who had previously been identified as having slow and fast habitual speaking rates [Tsao, Y.-C. and Weismer, G. (1997) J. Speech Lang. Hear. Res. 40, 858-866]. Within talkers, it is fairly well known that faster speaking rates result in a compression of the vowel space relative to that measured for slower rates, so the current study was completed to determine if the same differences in the size of the vowel space occur across talkers who differ significantly in their habitual speaking rates. Results indicated that there was no difference in the average size of the vowel space for slow vs fast talkers, and no relationship across talkers between vowel duration and formant frequencies. One difference between the slow and fast talkers was in intertalker variability of the vowel spaces, which was clearly greater for the slow talkers, for both speaker sexes. Results are discussed relative to theories of speech production and vowel normalization in speech perception.

Adolescent↗

PubMed2005

PID controller tuning for the first-order-plus-dead-time process model via Hermite-Biehler theorem.

This paper discusses PID stabilization of a first-order-plus-dead-time (FOPDT) process model using the stability framework of the Hermite-Biehler theorem. The FOPDT model approximates many processes in the chemical and petroleum industries. Using a PID controller and first-order Padé approximation for the transport delay, the Hermite-Biehler theorem allows one to analytically study the stability of the closed-loop system. We derive necessary and sufficient conditions for stability and develop an algorithm for selection of stabilizing feedback gains. The results are given in terms of stability bounds that are functions of plant parameters. Sensitivity and disturbance rejection characteristics of the proposed PID controller are studied. The results are compared with established tuning methods such as Ziegler-Nichols, Cohen-Coon, and internal model control.

Journal Article↗

PubMed2004

Biodynamic modeling and simulation of multistage cell mutations.

The aim of this study is to present a mathematical computer simulation model for multistage carcinogenesis. The population genetic model is developed based on the reaction diffusion, logistic behavior, and Hollings Type II interactions between normal, benign, and premalignant cells. The simple form of the Fisher-Haldane-Wright equation of the genetic model of tumor suppressor gene and oncogenes is used to describe this type of interaction. Through computer simulation, we observe the behavior, stability, and traveling wave solution of the premalignant stage mutation as well as its survival under natural selection pressure. As a simple case of this model, the interaction between normal and tumor cells with one or two stages of mutations is analyzed.

Cell Transformation, Neoplastic↗

PubMed2004

Stabilizing PID controllers for a single-link biomechanical model with position, velocity, and force feedback.

In this paper we address the problem of PID stabilization of a single-link inverted pendulum-based biomechanical model with force feedback, two levels of position and velocity feedback, and with delays in all the feedback loops. The novelty of the proposed model lies in its physiological relevance, whereby both small and medium latency sensory feedbacks from muscle spindle (MS), and force feedback from Golgi tendon organ (GTO) are included in the formulation. The biomechanical model also includes active and passive viscoelastic feedback from Hill-type muscle model and a second-order low-pass function for muscle activation. The central nervous system (CNS) regulation of postural movement is represented by a proportional-integral-derivative (PID) controller. Padé approximation of delay terms is employed to arrive at an overall rational transfer function of the biomechanical model. The Hermite-Biehler theorem is then used to derive stability results, leading to the existence of stabilizing PID controllers. An algorithm for selection of stabilizing feedback gains is developed using the linear matrix inequality (LMI) approach.

Adaptation, Physiological↗