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Articles 91 - 103 of 103
Full-Text Articles in Engineering
Optimal Stimulus Electrode Dipole Orientation, Robert B. Szlavik, Hubert De Bruin
Optimal Stimulus Electrode Dipole Orientation, Robert B. Szlavik, Hubert De Bruin
Biomedical Engineering
The elicited M-Wave that results from the surface stimulation of the median nerve is highly dependent upon the geometric orientation of the stimulus electrode dipole. This phenomenon could make standardization of M-Wave measurements between tests performed on a single subject problematic. We present an experimental paradigm that illustrates this variability in terms of an estimate of the slope of the M-Wave peak potential versus stimulus current amplitude and the minimum stimulus current required to consistently elicit a minimal response. The design of an automated instrument for selecting the optimal stimulus electrode dipole orientation based on the electrode orientation experiment is …
The Effects Of Testing Methods On The Flexural Fatigue Life Of Human Cortical Bone, L. V. Griffin, J. C. Gibeling, R. B. Martin, V. A. Gibson, S. M. Stover
The Effects Of Testing Methods On The Flexural Fatigue Life Of Human Cortical Bone, L. V. Griffin, J. C. Gibeling, R. B. Martin, V. A. Gibson, S. M. Stover
Biomedical Engineering
A flexural model of four-point bending fatigue that has been experimentally validated for human cortical bone under load control was used to determine how load and displacement control testing affects the fatigue behavior of human cortical bone in three-point and symmetric four-point bending. Under load control, it was predicted that three-point bending produced no significant differences in fatigue life when compared to four-point bending. However, three-point bending produced less stiffness loss with increasing cycles than four-point bending. In four-point bending, displacement control was predicted to produce about one and a half orders of magnitude greater fatigue life when compared to …
Model Of Flexural Fatigue Damage Accumulation For Cortical Bone, L. V. Griffin, J. C. Gibeling, R. B. Martin, V. A. Gibson, S. M. Stover
Model Of Flexural Fatigue Damage Accumulation For Cortical Bone, L. V. Griffin, J. C. Gibeling, R. B. Martin, V. A. Gibson, S. M. Stover
Biomedical Engineering
Analytical models that predict modulus degradation in cortical bone subjected to uniaxial fatigue loading in tension and compression are presented. On the basis of experimental observations, damage was modeled as self-limiting for tension but not for compression. These mechanistic uniaxial damage models were then developed into a model for flexural fatigue of cortical bone based on laminated beam theory. The unknown coefficients in the uniaxial damage models were obtained by successfully fitting the resulting equations to uniaxial fatigue data from the literature on human cortical bone in tension and compression. Then, the predictions of the flexural model for the behavior …
Residual Strength Of Equine Bone Is Not Reduced By Intense Fatigue Loading: Implications For Stress Fracture, R. B. Martin, V. A. Gibson, S. M. Stover, J. C. Gibeling, L. V. Griffin
Residual Strength Of Equine Bone Is Not Reduced By Intense Fatigue Loading: Implications For Stress Fracture, R. B. Martin, V. A. Gibson, S. M. Stover, J. C. Gibeling, L. V. Griffin
Biomedical Engineering
Fatigue or stress fractures are an important clinical problem in humans as well as racehorses. An important question in this context is, when a bone experiences. fa!igue damage ~uring e~treme use, how much is it weakened compared to its original state? Since there are very ltmtted data on thts quesuon and stress fractures are common in racehorses, we sought to determine the effect of fatigue loading on the monotonic l:trength of equine cortical bone. Beams were machined from the dorsal, medial and lateral cortices of the third metacarpal bones of six thoroughbred racehorses. Beams from left and right bones were …
Simulating The Distribution Of Axon Size In Nerves, Robert B. Szlavik, Hubert De Bruin
Simulating The Distribution Of Axon Size In Nerves, Robert B. Szlavik, Hubert De Bruin
Biomedical Engineering
The electrical excitation threshold of a nerve axon is dependent upon the physical properties of the axon membrane as well as the axon diameter. Histological studies have confirmed that peripheral afferent muscle nerves have a characteristic distribution of axon diameters. We approximate a probability density function for this distribution that consists of the summation of several Gaussian functions. A transformation technique is then applied for the random generation of the nerve axon diameters from uniformly distributed random numbers. For the example presented, the resultant distribution of peripheral afferent muscle nerve axon diameters conforms approximately to the characteristic distribution that has …
Pulsed Transient Tissue Conductivity Measurement, Robert B. Szlavik, Hubert De Bruin
Pulsed Transient Tissue Conductivity Measurement, Robert B. Szlavik, Hubert De Bruin
Biomedical Engineering
The authors present an alternative technique for obtaining tissue conductivity as a function of frequency. Pulsed transient tissue impedance measurement differs significantly from other commonly used swept frequency techniques in that the conductivity of a tissue sample can be obtained from a voltage transient response to a current pulse. By obtaining the conductivity across a band of frequencies from a transient measurement, the necessity for direct conductivity measurements at each frequency point is eliminated. Calibration and verification of the technique was carried out by measuring the impedance magnitude and phase of simple RC circuit combinations. The authors present conductivity measurements …
Spice Compatible Equivalent Circuit Models Of Skeletal Muscle Tissue, Robert B. Szlavik, Hubert De Bruin
Spice Compatible Equivalent Circuit Models Of Skeletal Muscle Tissue, Robert B. Szlavik, Hubert De Bruin
Biomedical Engineering
The authors present equivalent circuit models of skeletal muscle tissue for the directions parallel and transverse to the fiber. The parallel model is based on a distributed parameter equivalent circuit approach where the tissue between the electrodes is divided into small segments, each of which is represented by an equivalent circuit. Parameters for the equivalent circuits me calculated from the electrical characteristics of the tissue components and their physical arrangement. The authors compare the conductivity frequency response of the equivalent circuit modelling approach to other models presented in the literature. The advantage to the authors' equivalent circuit approach is that …
Calcium Buffering Is Required To Maintain Bone Stiffness In Saline Solution, M. B. Gustafson, R. B. Martin, V. Gibson, D. H. Storms, S. M. Stover, J. Gibeling, L. Griffin
Calcium Buffering Is Required To Maintain Bone Stiffness In Saline Solution, M. B. Gustafson, R. B. Martin, V. Gibson, D. H. Storms, S. M. Stover, J. Gibeling, L. Griffin
Biomedical Engineering
This work determined whether mineral dissolution due to prolonged testing or storage of bone s~'imens in normal salint: would alter Lheir elastic modulus. In one experiment, small pieces of equine third metacarpal bone were soaked in normal saline supplemented with varying amounts of CaCI1. Changing Ca ion concentrations in the bath were monitored and the equilibrium concentration was determined. In a second experiment, the elastic moduli of twenty 4 x 10 x 100 mm equine third metacarpal beams were determined non-destructively in four-point bending. Half the beams were then soaked for 10 days in normal saline, and the other half …
In Vitro Fatigue Behavior Of The Equine Third Metacarpus: Remodeling And Microcrack Damage Analysis, R.B. Martin, V.A. Gibson, S.M. Stover, J.C. Gibeling, L.V. Griffin
In Vitro Fatigue Behavior Of The Equine Third Metacarpus: Remodeling And Microcrack Damage Analysis, R.B. Martin, V.A. Gibson, S.M. Stover, J.C. Gibeling, L.V. Griffin
Biomedical Engineering
We studied remodeling and microcrack damage in specimens of Thoroughbred racehorse third metacarpal bone that had been subjected to monotonic or fatigue failure. We asked three questions. What effects does mechanical loading have on histologically observable microcrack damage? Are there regional variations in remodeling of the equine cannon bone, and do these variations correlate with mechanical properties? To what extent are remodeling and microcrack damage age-dependent? Machined beams from the medial, lateral, and dorsal cortices were loaded to fracture in four-point bending monotonically, or cyclically at a load initially producing 10,000 microstrain. Specimens were then bulk-stained in basic fuchsin, and …
Osteonal Structure In The Equine Third Metacarpus, R. B. Martin, V. A. Gibson, S. M. Stover, J. C. Gibeling, L. V. Griffin
Osteonal Structure In The Equine Third Metacarpus, R. B. Martin, V. A. Gibson, S. M. Stover, J. C. Gibeling, L. V. Griffin
Biomedical Engineering
In studying the flexural fatigue properties of the equine third metacarpal (cannon) bone, we previously found that the dorsal region was weaker monotonically, but more fatigue resistant, than the lateral region. Fatigue resistance was associated with fracture surfaces which demonstrated that secondary osteons had “pulled out” of the surrounding matrix; this never happened in lateral specimens. We therefore became interested in the osteonal structure of this bone, and began to study its birefringence patterns in circularly polarized light. We found that the predominant type of secondary osteon was one in which only the outermost few lamellae were circumferential, with the …
Armature Position Sensor For A Relay, G. Stephen Perreira, Richard L. Kutin, Lanny V. Griffin
Armature Position Sensor For A Relay, G. Stephen Perreira, Richard L. Kutin, Lanny V. Griffin
Biomedical Engineering
A sensor for use with high-power solenoid-actuated relays, and for detecting and signalling relay armature position and hence the actuation state of the relay. The sensor is external to a sealed chamber in which the relay contacts and armature system are positioned, and includes a permanent magnet, the flux path of which includes the relay armature and base. Armature movement to close the relay alters the flux path to operate a reed switch adjacent the magnet, and the condition of the reed switch signals the unactuated or actuated state of the relay.
Artifactual Nonlinearity Due To Wear Grooves An Friction In Four-Point Bending Experiments Of Cortical Bone, L. V. Griffin, J. C. Gibeling, V. A. Gibson, R B. Martin, S. M. Stover
Artifactual Nonlinearity Due To Wear Grooves An Friction In Four-Point Bending Experiments Of Cortical Bone, L. V. Griffin, J. C. Gibeling, V. A. Gibson, R B. Martin, S. M. Stover
Biomedical Engineering
Experiments and analyses were performed to determine th e cause of a nonlinear force-deflection response observed in four-point flexural fatigue of beams ofcortical bone machined from the mid-diaphysis of the equine third metacarpus. Observable grooves which formed on the beam surface at supports and load noses were found to be the primary cause of the nonlinearity. An additional geometric nonlinearity at large deflections revealed by finite element modeling may be minimized by using the smallest diameter supports and load noses recommended in ASTM 790. However, frictional constraint of the beams at the load noses and supports can occur at low …
Fatigue Behavior Of The Equine Third Metacarpus: Mechanical Property Analysis, V.A. Gibson, S.M. Stover, R.B. Martin, J.C. Gibeling, N. H. Willits, M.B. Gustafson, L.V. Griffin
Fatigue Behavior Of The Equine Third Metacarpus: Mechanical Property Analysis, V.A. Gibson, S.M. Stover, R.B. Martin, J.C. Gibeling, N. H. Willits, M.B. Gustafson, L.V. Griffin
Biomedical Engineering
This is the first in a series of experiments to study the fatigue properties of equine cannon (third metacarpal) bone specimens from Throughbred racehorses. Monotonic and fatigue tests to failure were performed in four-point bending on diaphyseal specimens in a 37°C saline bath to answer three initial questions. (a) Will a linear variable differential transducer yield the same elastic modulus as strain gauges? (b) Will fatigue results depend on whether the periosteal or endosteal side of the beam is in tension? (c) Are there regional variations in the monotonic and fatigue properties of the cannon bone midshaft? Eighteen left-right pairs …