S. Radhakrishnan

Bio: S. Radhakrishnan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Medicine & Osteoporosis. The author has an hindex of 8, co-authored 16 publications receiving 248 citations.

Analysis of hand forces in health and disease during maximum isometric grasping of cylinders.

Abstract: An analysis of force distribution in the hand during maximum isometric grasping actions is reported in a detailed and accurate manner. A microcomputer-controlled instrument which measures all 12 phalangeal forces of fingers simultaneously, in a single attempt at squeezing a cylindrical object, is described. The study involved 20 normal subjects of different weights and age groups grasping tubes of 50 mm, 75 mm, 90 mm and 110 mm diameters. Normal grasp forces decreased significantly with the increase in tube diameter, with the force being concentrated more on the distal segments of the fingers on the proximal and middle segments. The mean percentage contributions of finger forces to total grip strength, from index to little fingers, were 31, 33, 22 and 14 per cent, respectively. The study was extended to cover leprotic and paralytic hands to assess their functional capabilities. In the case of leprosy subjects, the grip strength decreased with the severity of the disease and was only about 50 per cent of that of normal subjects. In hemiplegics, the grip strength was only about one-eighth of the normal values. The above assessment procedure provides baseline data which could serve as guidelines to a clinician in assessing the severity of the disease and observing the patient's recovery following the treatment. It would also be useful in the design of hand-operated controls and prosthetic arms.

Three-dimensional stress analysis for the mechanics of plantar ulcers in diabetic neuropathy.

Abstract: In diabetic neuropathic subjects, the hardness of foot sole soft tissue increases, and its thickness reduces, in different foot sole areas. Finite element analysis (FEA) of a three-dimensional two-arch model of the foot was performed to evaluate the effect of foot sole stresses on plantar ulcer development. Three sets of foot sole soft-tissue properties, i.e. isotropic (with control hardness value), diabetic isotropic (with higher hardness value) and anisotropic diabetic conditions, were simulated in the push-off phase, with decreasing foot sole soft-tissue thicknesses in the forefoot region, and the corresponding stresses were calculated. The results of the stress analyses for diabetic subject (anisotropic) foot models showed that, with non-uniformly increased hardness and decreased foot sole soft-tissue thickness, the normal and shear stresses at the foot sole increased (compared with control values) by 52.6% and 53.4%, respectively. Stress analyses also showed high ratios of gradients of normal and shear stresses of the order of 6.6 and 3.3 times the control values on the surface of the foot sole, and high relative values of stress gradients for normal and shear stresses of 6.25 and 4.35 times control values, respectively, between the foot sole surface and the adjacent inner layer of the foot sole, around a particular region of the foot sole with anisotropic properties. These ratios of high gradients and relative gradients of stresses due to changes in soft-tissue properties may be responsible for the development of plantar ulcers in diabetic neuropathic feet.

Importance of partitioning membranes of the brain and the influence of the neck in head injury modelling

Abstract: A head injury model consisting of the skull, the CSF, the brain and its partitioning membranes and the neck region is simulated by considering its near actual geometry. Three-dimensional finite-element analysis is carried out to investigate the influence of the partitioning membranes of the brain and the neck in head injury analysis through free-vibration analysis and transient analysis. In free-vibration analysis, the first five modal frequencies are calculated, and in transient analysis intracranial pressure and maximum shear stress in the brain are determined for a given occipital impact load.

Quantitative ultrasound technique for the assessment of osteoporosis and prediction of fracture risk

Abstract: Osteoporosis in men and women is increasingly recognised as an important health issue. Bone mineral density (BMD) and bone strength appears to be major determinants of osteoporotic fracture. Measurement of bone strength by ultrasound is found to be a competitive means of measuring osteoporotic fracture risk and provide additional information about bone's structure and composition. In the present work quantitative ultrasound assessment of osteoporosis is carried out in Indian men and women by measuring broadband ultrasound attenuation (BUA) and speed of sound (SOS) through calcaneum bone to provide a clinical measure called the stiffness index (SI). The SI is the sum of the scaled and normalised BUA and SOS values, which is a measure of bone strength and is sensitive to bone structure used to predict the risk of bone fracture due to osteoporosis. Measurement of SI is carried out in 283 men, 108 premenopausal and 85 postmenopausal women. SI results expressed as T-score and Z-score are used to assist the physicians in the diagnosis of osteoporosis. The presence of osteoporosis is defined as T-score lower than -2.5. Observation shows that osteoporosis is predominant in postmenopausal women population who are at greater risk of fracture compared to premenopausal women and men. The effect of age, weight, height and body mass index (BMI) on SI in men and women is analyzed. The SI has negative correlation with age and is found to be a significant factor in both men and women with a high percentage of bone mineral loss in early menopausal women. In univariate analysis body weight and BMI have moderate positive correlation with SI in men and women. Height seems to have no significant effect on SI. There is a rapid loss of bone mineral content leading sudden decrease in SI during the first five years after menopause and it continues to decrease at a lesser rate with increasing age.

A Sparse and Spike‐Timing‐Based Adaptive Photoencoder for Augmenting Machine Vision for Spiking Neural Networks

Abstract: The representation of external stimuli in the form of action potentials or spikes constitutes the basis of energy efficient neural computation that emerging spiking neural networks (SNNs) aspire to imitate. With recent evidence suggesting that information in the brain is more often represented by explicit firing times of the neurons rather than mean firing rates, it is imperative to develop novel hardware that can accelerate sparse and spike‐timing‐based encoding. Here a medium‐scale integrated circuit composed of two cascaded three‐stage inverters and one XOR logic gate fabricated using a total of 21 memtransistors based on photosensitive 2D monolayer MoS2 for spike‐timing‐based encoding of visual information, is introduced. It is shown that different illumination intensities can be encoded into sparse spiking with time‐to‐first‐spike representing the illumination information, that is, higher intensities invoke earlier spikes and vice versa. In addition, non‐volatile and analog programmability in the photoencoder is exploited for adaptive photoencoding that allows expedited spiking under scotopic (low‐light) and deferred spiking under photopic (bright‐light) conditions, respectively. Finally, low energy expenditure of less than 1 µJ by the 2D‐memtransistor‐based photoencoder highlights the benefits of in‐sensor and bioinspired design that can be transformative for the acceleration of SNNs.

Computational biology of the heart , edited by Alexander V. Panfilov and Arun V. Holden. Pp. 416. £70. 1997. ISBN 0 471 96020 9 (John Wiley & Sons).

Abstract: Partial table of contents: Modelling Cardiac Excitation and Excitability (M. Boyett, et al.). Modelling Propagation in Excitable Media (A. Holden & A. Panfilov). Rotors, Fibrillation and Dimensionality (A. Winfree). A Mathematical Model of Cardiac Anatomy (P. Hunter, et al.). Finite Element Methods for Modelling Impulse Propagation in the Heart (J. Rogers, et al.). The Effects of Geometry and Fibre Orientation on Propagation and Extracellular Potentials in Myocardium (J. Keener & A. Panfilov). Forward and Inverse Problems in Electrocardiography (A. van Oosterom). Computational Electromechanics of the Heart (P. Hunter, et al.). Index.

Influence of FE model variability in predicting brain motion and intracranial pressure changes in head impact simulations

Abstract: In order to create a useful computational tool that will aid in the understanding and perhaps prevention of head injury, it is important to know the quantitative influence of the constitutive properties, geometry and model formulations of the intracranial contents upon the mechanics of a head impact event. The University College Dublin Brain Trauma Model (UCDBTM) [1] has been refined and validated against a series of cadaver tests and the influence of different model formulations has been investigated. In total six different model configurations were constructed: (i) the baseline model, (ii) a refined baseline model which explicitly differentiates between grey and white neural tissue, (iii) a model with three elements through the thickness of the cerebrospinal fluid (CSF) layer, (iv) a model simulating a sliding boundary, (v) a projection mesh model (which also distinguishes between neural tissue) and (vi) a morphed model. These models have been compared against cadaver tests of Trosseille [2] an...

Morphogenetic fields in embryogenesis, regeneration, and cancer: non-local control of complex patterning.

Abstract: Establishment of shape during embryonic development, and the maintenance of shape against injury or tumorigenesis, requires constant coordination of cell behaviors toward the patterning needs of the host organism. Molecular cell biology and genetics have made great strides in understanding the mechanisms that regulate cell function. However, generalized rational control of shape is still largely beyond our current capabilities. Significant instructive signals function at long range to provide positional information and other cues to regulate organism-wide systems properties like anatomical polarity and size control. Is complex morphogenesis best understood as the emergent property of local cell interactions, or as the outcome of a computational process that is guided by a physically encoded map or template of the final goal state? Here I review recent data and molecular mechanisms relevant to morphogenetic fields: large-scale systems of physical properties that have been proposed to store patterning information during embryogenesis, regenerative repair, and cancer suppression that ultimately controls anatomy. Placing special emphasis on the role of endogenous bioelectric signals as an important component of the morphogenetic field, I speculate on novel approaches for the computational modeling and control of these fields with applications to synthetic biology, regenerative medicine, and evolutionary developmental biology.