Central Contact Research Articles

Medial Meniscus Posterior Root Tears Lead to Changes in Joint Contact Mechanics at Low Flexion Angles During Simulated Gait

Background: Previous biomechanical studies evaluating medial meniscus posterior root tears (MMPRTs) are limited to low loads applied at specified loading angles, which cannot capture the effects of MMPRTs during the multidirectional forces and moments placed across the knee during physiological activities. Purpose: To quantify the effects of MMPRTs on knee joint contact mechanics during simulated gait. Study Design: Controlled laboratory study. Methods: Six human cadaveric knees were mounted on a robotic simulator programmed to apply dynamic forces, moments, and flexion angles to mimic level walking. Twelve cycles of multidirectional and dynamic standard gait input waveforms, normalized to specimen-specific body weight, were applied to the following conditions: (1) native, intact meniscus and (2) MMPRT. Peak contact stress, contact area, and the position of the weighted center of contact across the medial tibial plateau throughout the stance phase of gait were quantified using an electronic sensor placed across the medial tibial plateau. The difference between the intact state and MMPRT condition was calculated for each metric, and then the means and 95% CIs were computed. Results: Despite heterogeneity in knee contact forces, MMPRTs significantly increased peak contact stress by a mean of 2 MPa across 20% to 37% of the simulated gait cycle and significantly decreased the contact area by a mean of 200 mm2 across 16% to 60% of the simulated gait cycle in comparison with the native state. There was no significant difference in the position of the weighted center of contact, in either the anterior-posterior or medial-lateral directions, after MMPRT. Conclusion: MMPRTs led to both a significant increase in peak contact stress and decreased contact areas for a portion of the simulated gait cycle ranging from 20% to 37% of gait, during which time the femur was flexed <15°. Clinical Relevance: Contact mechanics are significantly affected after MMPRTs during early to midstance and at knee flexion angles lower than demonstrated previously. These data provide further biomechanical justification for treating MMPRTs.

ACL transection results in a posterior shift and increased velocity of contact on the medial tibial plateau

Our objective was to quantify the effect of ACL transection on dynamic knee joint contact force distributions during simulated gait. Given the prevalence of medial compartment osteoarthritis in un-reconstructed ACL ruptured knees, we hypothesized that changes in contact mechanics after ACL transection would be most prevalent in the medial compartment. Twelve human cadaveric knees were tested using a dynamic knee gait simulator which was programmed to mimic a clinical Lachman exam and gait. An electronic pressure sensor was placed on the medial and lateral tibial plateaus under the menisci to quantify dynamic contact forces before and after ACL transection. Tibial translations and rotations, medial and lateral plateau peak contact stress, and position and velocity of the Weighted Center of Contact (WCoC) were computed. After ACL transection, the tibia translated more anteriorly in the Lachman examination and at heel strike during gait. Changes in contact mechanics across the medial tibial plateau during simulated gait were: an increase in the velocity of WCoC and a posterior shift in the WCoC, both of which occurred at heel strike; increased peak contact forces in the posterior-peripheral quadrant of the tibial plateau at 45% of the gait cycle; and an additional posterior shift in WCoC from 25 to 55% of the gait cycle. The only change in contact mechanics in the lateral plateau was a decrease in WCoC velocity in late stance. This data is suggested to further the study of biomechanical pathways (biomechanical biomarkers) in the relationship between altered knee contact mechanics and chondrocyte metabolic responses after ACL transection.

Transition from mixed stick-slip to gross-slip regime in fretting

Transition from mixed stick-slip to gross-slip regime of advanced materials namely Zircaloy-4/Inconel-600, Ti-6Al-4V/Inconel-600, and 9Cr-1Mo-steel/Ti-6Al-4V are explored. A wear map shows the influence of normal load and sliding amplitude on transition time. Extensive characterizations of worn surfaces captured the sequential changes of contact state (stick/slip) and associated chemical changes (material transfer and oxidation). Low cycle fatigue failure of plate creates deep inclined surface cracks (primary) and shallow subsurface cracks (secondary). Secondary crack breaks the adhesive junctions, transfers plate material to pin, and moves stick-slip boundary by unit distance towards the center of contact. Successive failures of plate with increasing time cause transition of regimes. Slight change of coefficient of friction and extensive wear debris are the external manifestations of transition.

Dysplastic Patellofemoral Joints Lead to a Shift in Contact Forces: A 3D-Printed Cadaveric Model

Background: The distribution of contact forces across the dysplastic patellofemoral joint has not been adequately quantified because models cannot easily mimic the dysplasia of both the trochlea and the patella. Thus, the mechanical consequences of surgical treatments to correct dysplasia cannot be established. Purpose/Hypothesis: The objective of this study was to quantify the contact mechanics and kinematics of normal, mild, and severely dysplastic patellofemoral joints using synthetic mimics of the articulating surfaces on cadavers. We tested the hypothesis that severely dysplastic joints would result in significantly increased patellofemoral contact forces and abnormal kinematics. Study Design: Controlled laboratory study. Method: Patellofemoral dysplasia was simulated in 9 cadaveric knees by replacing the native patellar and trochlear surfaces with synthetic patellar and trochlear implants. For each knee, 3 synthetic surface geometries (normal, showing no signs of dysplasia; mild, exemplifying Dejour type A; and severe, exemplifying Dejour type B) were randomized for implantation and testing. Patellar kinematics and the sum of forces acting on the medial and lateral patellar facets were computed for each knee and for each condition at 10° increments from 0° to 70° of flexion. Results: A pronounced lateral shift in the weighted center of contact of the lateral facet occurred for severely dysplastic knees from 20° to 70° of flexion. Compared with normal geometries, lateral patellar facet forces exhibited a significant increase only with mild dysplasia from 50° to 70° of flexion and with severe dysplasia at 70° of flexion. No measurable differences in medial patellar facet mechanics or joint kinematics occurred. Conclusion: Our hypothesis was rejected: Severely dysplastic joints did not result in significantly increased patellofemoral contact forces and abnormal kinematics in our cadaveric simulation. Rather, severe dysplasia resulted in a pronounced lateral shift in contact forces across the lateral patellar facet, while changes in kinematics and the magnitude of contact forces were not significant. Clinical Relevance: Including dysplasia of both the patella and trochlea is required to fully capture the mechanics of this complex joint. The pronounced lateralization of contact force in severely dysplastic patellofemoral joints should be considered to avoid cartilage overload with surgical manipulation.

Gray Matter Sampling Differences Between Subdural Electrodes and Stereoelectroencephalography Electrodes.

Objective: Stereoelectroencephalography (SEEG) has seen a recent increase in popularity in North America; however, concerns regarding the spatial sampling capabilities of SEEG remain. We aimed to quantify and compare the spatial sampling of subdural electrode (SDE) and SEEG implants.Methods: Patients with drug-resistant epilepsy who underwent invasive monitoring were included in this retrospective case-control study. Ten SEEG cases were compared with ten matched SDE cases based on clinical presentation and pre-implantation hypothesis. To quantify gray matter sampling, MR and CT images were coregistered and a 2.5mm radius sphere was superimposed over the center of each electrode contact. The estimated recording volume of gray matter was defined as the cortical voxels within these spherical models. Paired t-tests were performed to compare volumes and locations of SDE and SEEG recording. A Ripley's K-function analysis was performed to quantify differences in spatial distributions.Results: The average recording volume of gray matter by each individual contact was similar between the two modalities. SEEG implants sampled an average of 20% more total gray matter, consisted of an average of 17% more electrode contacts, and had 77% more of their contacts covering gray matter within sulci. Insular coverage was only achieved with SEEG. SEEG implants generally consist of discrete areas of dense local coverage scattered across the brain; while SDE implants cover relatively contiguous areas with lower density recording.Significance: Average recording volumes per electrode contact are similar for SEEG and SDE, but SEEG may allow for greater overall volumes of recording as more electrodes can be routinely implanted. The primary difference lies in the location and distribution of gray matter than can be sampled. The selection between SEEG and SDE implantation depends on sampling needs of the invasive implant.

In vivo articular contact pattern of a total wrist arthroplasty design

Total wrist arthroplasty (TWA) designs suffer from relatively high complication rates when compared to other arthroplasties. Understanding the contact pattern of hip and knee replacement has improved their design and function; however, the in vivo contact pattern of TWA has not yet been examined and is thus the aim of this study. We hypothesized that the center of contact (CoC) is located at the geometric centers of the carpal component and radial component in the neutral posture and that the CoC moves along the principal arcs of curvature throughout primary anatomical motions. Wrist motion and implant kinematics of six patients with the Freedom® total wrist implant were studied during various tasks using biplanar videoradiography. The location of the CoC of the components was investigated by calculating distance fields between the articular surfaces. We found the CoC at the neutral posture was not at the geometric centers but was located 3.5 mm radially on the carpal component and 1.2 mm ulnarly on the radial component. From extension to flexion, the CoC moved 10.8 mm from dorsal to volar side on the carpal component (p < 0.0001) and 7.2 mm from volar to dorsal on the radial component (p = 0.0009). From radial to ulnar deviation, the CoC moved 12.4 mm from radial to ulnar on the carpal component (p < 0.0001), and 5.6 mm from ulnar to radial on the radial component (p = 0.009). The findings of this study may eventually improve TWA success by advancing future designs through a more accurate understating of their kinematic performance in vivo.

The effect of lateral extra-articular tenodesis on in vivo cartilage contact in combined anterior cruciate ligament reconstruction.

Lateral extra-articular tenodesis (LET) may confer improved rotational stability after anterior cruciate ligament reconstruction (ACLR). Little is known about how LET affects in vivo cartilage contact after ACLR. The aim of this study was to investigate the effect of LET in combination with ACLR (ACLR + LET) on in vivo cartilage contact kinematics compared to isolated ACLR (ACLR) during downhill running. It was hypothesised that cartilage contact area in the lateral compartment would be larger in ACLR + LET compared with ACLR, and that the anterior-posterior (A-P) position of the contact center on the lateral tibia would be more anterior after ACLR + LET than after ACLR. Twenty patients were randomly assigned into ACLR + LET or ACLR during surgery (ClinicalTrials.gov:NCT02913404). At 6months and 12months after surgery, participants were imaged during downhill running using biplane radiography. Tibiofemoral motion was tracked using a validated registration process. Patient-specific cartilage models, obtained from 3T MRI, were registered to track bone models and used to calculate the dynamic cartilage contact area and center of cartilage contact in both the medial and lateral tibiofemoral compartments, respectively. The side-to-side differences (SSD) were compared between groups using a Mann-Whitney U test. At 6months after surgery, the SSD in A-P cartilage contact center in ACLR + LET (3.9 ± 2.6mm, 4.4 ± 3.1mm) was larger than in ACLR (1.2 ± 1.6mm, 1.5 ± 2.0mm) at 10% and 20% of the gait cycle, respectively (p < 0.01, p < 0.05). There was no difference in the SSD in cartilage contact center at 12months after surgery. There was no difference in SSD of cartilage contact area in the medial and lateral compartments at both 6 and 12months after surgery. There were no adverse events during the trial. LET in combination with ACLR may affect the cartilage contact center during downhill running in the early post-operation phase, but this effect is lost in the longer term. This suggests that healing and neuromuscular adaptation occur over time and may also indicate a dampening of the effect of LET over time. (337 /350 words) LEVEL OF EVIDENCE: Level II.

Forward bias degradation and thermal simulations of vertical geometry β-Ga2O3 Schottky rectifiers

Vertical geometry β-Ga2O3 Schottky rectifiers of various sizes were deliberately stressed at a high forward current density level until a sudden decrease of reverse bias breakdown voltage was observed. The diodes were fabricated on an Sn-doped (n = 3.6 × 1018 cm−3) (001) β-Ga2O3 single crystal substrate with a 10 μm epilayer grown by halide vapor phase epitaxy with a carrier concentration of 3.5 × 1016 cm−3. The forward bias stressing caused reverse breakdown degradation and thermally induced failure on both the Ni/Au Schottky contact and the epitaxial layer due to the low thermal conductivity of Ga2O3. The resulting temperature distributions at forward bias under different current conditions were simulated using 3D finite element analysis. The temperature profile at the surface during the rectifier turn-on period shows a strong dependence with crystalline orientation, evidenced by infrared camera measurements. The maximum junction temperature rise occurs at the center of the metal contact and is in the range of 270–350 °C.

EXPERIMENTAL RESEARCH OF CONTACT INTERACTION OF RADIAL HYDROTRANSMISSION’S BALL ROLLER WITH PROFILED BACKGROUND

Experimental research of the interaction of the radial hydrotransmission’s ball roller with a treadmill were carried out using the contact marks method , oriented on the technology, using sensitive to the contact pressure of the films. The research results of contact interaction of the ball piston of the radial hydrotransmission with its stator ring (with a treadmill of complex transverse profile) clearly indicate the validity of numerically determined tendencies in the pattern of the contact pressure distribution when changing the shape of the track and the properties of the intermediate layer. At the same time, convergence is observed as the form of contact areas and distribution of contact pressure, as well as the nature of their perturbation when changing certain factors. When the radius of the cross-section of the treadmill changes from a value less than the radius of the piston, to a greater extent, there is a gradual transition from two drop-like contact spots to one dumbbell, and then to an elliptic one. The contact pressure at the same time changes its distribution, reducing the maximum at the periphery and gradually changing the maximum position at the central. At the same time, at the geometric center of the possible contact, the contact pressure is initially zero (with increasing critical force), and then it increases, gaining a local minimum, and eventually it reaches the global maximum (for certain parameters of the geometric form and level of loading).

Lateral Meniscal Graft Transplantation: Effect of Fixation Method on Joint Contact Mechanics During Simulated Gait

Background: Controversy exists regarding the optimal bony fixation technique for lateral meniscal allografts. Purpose/Hypothesis: The objective was to quantify knee joint contact mechanics across the lateral plateau for keyhole and bone plug meniscal allograft transplant fixation techniques throughout simulated gait. It was hypothesized that both methods of fixation would improve contact mechanics relative to the meniscectomized condition, while keyhole fixation would restore the distribution of contact stress closer to that of the intact knee. Study Design: Controlled laboratory study. Methods: Six human cadaveric knees were mounted on a multidirectional dynamic simulator and subjected to the following conditions: (1) native intact meniscus, (2) keyhole fixation of the native meniscus, (3) bone plug fixation of the native meniscus, and (4) meniscectomy. Contact area, peak contact stress, and the distribution of stress across the tibial plateau were computed at 14% and 45% of the gait cycle, at which axial forces are at their highest. Translation of the weighted center of contact stress throughout simulated gait was computed. Results: Both bony fixation techniques improved contact mechanics relative to the meniscectomized condition. The keyhole technique was not significantly different from the intact condition for the following metrics: contact area, peak contact stress, distribution of force between the meniscal footprint and cartilage-to-cartilage contact, and the position of the weighted center of contact. In contrast, bone plug fixation resulted in a significant decrease of 21% to 28% in contact area at 14% and 45% of the simulated gait cycle, a significant increase in peak contact stresses of 34% at 45% of the gait cycle, and a shift in the weighted center of contact, which increased forces in the cartilage-to-cartilage contact area at 45% of the gait cycle. Conclusion: While both keyhole and bone plug fixation methods improved lateral compartment contact mechanics relative to the meniscectomized knee, keyhole fixation restored contact mechanics closer to that of the intact knee. Clinical Relevance: Method of meniscal fixation is under the direct control of the surgeon. From a biomechanics perspective, keyhole fixation is advocated for its ability to mimic intact knee joint contact mechanics.

Analysis of Contact Position for Subthalamic Nucleus Deep Brain Stimulation-Induced Hyperhidrosis.

Objectives To analyze the hyperhidrosis neural network structure induced by subthalamic nucleus (STN) - deep brain stimulation (DBS). Materials and Methods Patients with Parkinson's disease treated with STN-DBS in Changhai Hospital between July 1, 2015, and December 1, 2016, were analyzed retrospectively. Using records of side effects of the intraoperative macrostimulation test, patients with skin sweats were selected as the sweating group. Based on the number of cases in the sweating group, the same number of patients was randomly selected from other STN-DBS patients without sweating to form the control group. The study standardized electrode position with Lead-DBS software to Montreal Neurological Institute (MNI) standard stereotactic space to compare the differences in three-dimensional coordinates of activated contacts between groups. Results Of 355 patients, 11 patients had sweats during intraoperative macrostimulation tests. There was no significant difference in the preoperative baseline information and the postoperative UPDRS-III improvement rate (Med-off, IPG-on) between groups. Contacts inducing sweat were more medial (X-axis) (11.02 ± 0.69 mm vs 11.98 ± 0.84 mm, P=0.00057) and more upward (Z-axis) (−7.15 ± 1.06 mm VS −7.98 ± 1.21 mm, P=0.032) than those of the control group. The straight-line distance between the center of the sweat contact and the nearest voxel of the red nucleus was closer than that of the control group (2.72 ± 0.65 mm VS 3.76 ± 0.85 mm, P=0.00012). Conclusions STN-DBS-induced sweat indicated that the contact was at superior medial of STN.

A theorem of target points for the ground reaction force in a planar serial-linked walking limb

An important energy expense in the legged locomotion of both animals and robots is the mechanical antagonism between muscles/actuators, which is the positive mechanical work of some muscles opposed by the simultaneous negative work of the others. One known way to minimize the mechanical antagonism is the proper employment of the redundant degrees of freedom of the limb. Here, I present and analyze a generalized model of a planar serial-linked limb composed of any number of segments and conclude that the minimization of the inter-actuator antagonism requires fixation of all the joint angles except the two defined by simple geometric considerations. So, regardless of the number of joints, the limb should optimally act as a two-joint system. Which of the redundant joints to fix or move depends on the instantaneous position of the joints relative to the vertical line through the center of the foot contact with the ground. Subsequently, for the first time, I pose and solve the following problem: how to eliminate the inter-actuator antagonism by the adjustment of the horizontal component of the ground reaction force. The solution is that, during the contact phase, the ground reaction force vector should be redirected so as to maintain alignment with the limb joints in the order in which they attain the smallest angular deflection from the vertical line through the foot. As the joints pass the vertical line through the point of limb contact with the ground one by one, abrupt changes of the horizontal ground force component from positive to negative should occur. Mammals cannot follow this algorithm exactly due to muscular actuator limitations and they tend to align the ground reaction force with some compromise target point above the hip or scapula. The suggested principles of the optimal choice of redundant degrees of freedom and direction of the ground reaction force can be implemented in robotics to achieve a lower cost of transport than is known for animals.

Modeling Current Sources for Neural Stimulation in COMSOL.

Background: Computational modeling provides an important toolset for designing and analyzing neural stimulation devices to treat neurological disorders and diseases. Modeling enables efficient exploration of large parameter spaces, where preclinical and clinical studies would be infeasible. Current commercial finite element method software packages enable straightforward calculation of the potential distributions, but it is not always clear how to implement boundary conditions to appropriately represent metal stimulating electrodes. By quantifying the effects of different electrode representations on activation thresholds for model axons, we provide recommendations for accurate and efficient modeling of neural stimulating electrodes.Methods: We quantified the effects of different representations of current sources for neural stimulation in COMSOL Multiphysics for monopolar, bipolar, and multipolar electrode designs.Results: We recommend modeling each electrode contact as a thin platinum domain, modeling the electrode substrate with the conductivity of silicone, and either using a point current source in the center of each electrode contact or using a boundary current source. Alternatively, to avoid possible numerical instabilities associated with a large range of conductivity values (i.e., platinum and silicone) and to eliminate the small mesh elements required for thin electrode contacts, the electrode substrate can be assigned the conductivity of platinum by using insulating boundaries between the substrate and surrounding medium, and within the substrate to isolate the contacts from each other. When modeling more than one contact, we recommend using superposition by solving the model once for each contact, leaving inactive contacts floating, and superposing the resulting potentials. We computed comparable errors in activation thresholds across the different implementations in a simplified model (electrode in a homogeneous, isotropic medium), and in realistic models of rat spinal cord stimulation (SCS) and human deep brain stimulation, indicating that the recommended approaches are applicable to different stimulation targets.

Sliding enhances fluid and solute transport into buried articular cartilage contacts.

Solutes and interstitial water are naturally transported from cartilage by load-induced interstitial fluid pressures. Fluid and solute recovery during joint articulation have been primarily attributed to passive diffusion and mechanical 'pumping' from dynamic loading. This paper tests if the sliding action of articulation is a significant and independent driver of fluid and solute transport in cartilage. The large osteochondral samples utilized in the present study preserve the convergent wedges necessary for physiological hydrodynamics. Following static load-induced fluid exudation and prior to sliding, a fluorescent solute (AlexaFluor 633) was added to the lubricant bath. In situ confocal microscopy was used to quantify the transport of solute from the bath into the buried stationary contact area (SCA) during sliding. Following static exudation, significant reductions in friction and strain during sliding at 60mm/s were accompanied by significant solute transport into the inaccessible center of the buried contact; no such transport was detected for the 0- or 1mm/s sliding conditions. The results suggest that external hydrodynamic pressures from sliding induced advective flows that carried solutes from the bath toward the center of contact. These results provide the first direct evidence that the action of sliding is a significant contributor to fluid and solute recovery by cartilage. Furthermore, they indicate that the sliding-induced transport of solutes into the buried interface was orders of magnitude greater than that attributable to diffusion alone, a result with critical implications for disease prevention and tissue engineering.

Deep Brain Stimulation of the Dentato-Rubro-Thalamic Tract: Outcomes of Direct Targeting for Tremor

Targeting the dentato-rubro-thalamic tract (DRTt) has been suggested to be efficacious in deep brain stimulation (DBS) for tremor suppression, both in case reports and post-hoc analyses. This prospective observational study sought to analyze outcomes after directly targeting the DRTt in tremor patients. 20 consecutively enrolled intention tremor patients obtained pre-operative MRI with diffusion tensor (dTi) sequences. Mean baseline tremor amplitude based on The Essential Tremor Rating Assessment Scale was recorded. The DRTt was drawn for each individual on StealthViz software (Medtronic) using the dentate nucleus as the seed region and the ipsilateral pre-central gyrus as the end region and then directly targeted during surgery. Intraoperative testing confirmed successful tremor control. Post-operative analysis of electrode position relative to the DRTt was performed, as was post-operative assessment of tremor improvement. The mean age of patients was 66.8 years; mean duration of tremor was 16 years. Mean voltage for the L electrode = 3.4 V; R = 2.6 V. Mean distance from the center of the active electrode contact to the DRTt was 0.9 mm on the L, and 0.8 mm on the R. Improvement in arm tremor amplitude from baseline after DBS was significant (P < 0.001). Direct targeting of the DRTt in DBS is an effective strategy for tremor suppression. Accounting for hardware, software, and model limitations, depiction of the DRTt allows for placement of electrode contacts directly within the fiber tract for modulation despite any anatomical variation, which reproducibly resulted in good tremor control.

Clinical Outcome of Patients with Deep Brain Stimulation of the Centromedian Thalamic Nucleus for Refractory Epilepsy and Location of the Active Contacts

Objectives: To investigate the clinical outcome of patients treated with chronic deep brain stimulation (DBS) of the centromedian nucleus (CM) for refractory epilepsy and to determine the location of active contacts. Methods: The outcome of CM stimulation was evaluated as percent seizure reduction compared to the baseline 3 months. To establish the location of active contacts, 27 leads were studied in 14 patients with refractory epilepsy. An analysis was conducted to reveal whether any coordinates of the center of the active contacts predicted percent seizure reduction. Results: With an average follow-up of 18.2 ± 5.6 months, the mean percent seizure reduction (n = 14) was 68 ± 22.4% (25-100%). Eleven of the 14 patients (78.6%) achieved >50% improvement in seizure frequency. Specifically, all 4 patients (100%) with generalized epilepsy (Lennox-Gastaut syndrome) and 7 of 10 patients (70%) with multilobar epilepsy showed >50% reduction in seizure frequency. The mean coordinates of the center of the active contact were located in the superior part of the anterior ventrolateral CM. The calculated coordinates of laterality from midline (x), anterior-posterior (y) and height (z) from the posterior commissure did not correlate with seizure outcome measured by percent seizure reduction. However, the locations of active contacts used during chronic CM stimulation in multilobar epilepsy were identified more dorsal to those used in generalized epilepsy. Conclusions: Chronic CM stimulation is a safe and effective means in the treatment of refractory epilepsy.

ブレーキ性能解明に対する 1DCAE の可能性

With the electrification of the automobile, requests to the measures of brake noise and drag has been increasing more and more. In the future, it will be need to consider measures from the functional design which is more upstream stage in order to respond to the required accuracy. In the stage of functional design, firstly, it is important to elucidate the fundamental mechanisms and it needs model which can be represent the mechanisms. In this paper, we reproduced the theoretical model of brake squeal by using a physical model based on 1DCAE which is one of the effective method in the functional design. Then, we considered about the two possibility to deal with more complex phenomenon by extending the reproduced model. One is effect of the pressure dependence of the pad rigidity. As a result, we showed that even if the system is in a stable state in the initial state, depending on conditions, the system changes in an unstable state. Another is consideration of multiple mode. We reduced the degree of freedom of cantilever FEM model and disc FEM model by using a reduction technique of FEM model and applied them to physics model. As a result, we showed the unstable mode changes by the combination of eigenvalue of cantilever and disc. Finally, we verified the friction point position δ0 by creating a FEM model of disc brake. We were able to confirm that the center of contact of pad and disk deviates from the center of the shape.

Use of quantitative tremor evaluation to enhance target selection during deep brain stimulation surgery for essential tremor

Abstract Deep brain stimulation (DBS), an effective surgical treatment for Essential Tremor (ET), requires test stimulations in the thalamus to find the optimum site for permanent electrode implantation. During these test stimulations, the changes in tremor are only visually evaluated. This, along with other parameters, increases the subjectivity when comparing the efficacy of different thalamic nuclei. We developed a method to quantitatively evaluate tremor during the test stimulations of DBS surgery and applied to 6 ET patients undergoing this treatment. From the quantitative data collected, we identified effective stimulation amplitudes for every test stimulation position and compared it with the ones identified visually during the surgery. We also classified the data based on the thalamic nuclei in which the center of the stimulating contact was present during test stimulations. Results indicate that, to achieve the same reduction in tremor, on average, the stimulation amplitude identified by our method was 0.6 mA lower than those identified by visual evaluation. The comparison of the different thalamic nuclei showed that stimulations in the Ventro-oral and the Intermediolateral nuclei of the thalamus result in higher reduction in tremor for similar stimulation amplitudes as the frequently targeted Ventrointermediate nucleus. We conclude that our quantitative tremor evaluation method is more sensitive than the widely used visual evaluation. Using such quantitative methods will aid in identifying the optimum target structure for patients undergoing DBS.

Current Injection from a Novel Narrow Contact into a Two-Dimensional Electron Gas under a High Magnetic Field

The average positions of carrier injection from electrical contacts into a two-dimensional electron gas were measured using a GaAs/AlGaAs heterostructure sample with a novel narrow contact. At zero magnetic field, carrier injection occurred near the center of the narrow contact. The position of carrier injection oscillated as a function of 1/B above 0.5 T and was at the corner of the sample in the quantum Hall effect regime. The experimental results were substantially accounted for by requiring that the Joule heating generated in the sample be minimized.

In vitro wear simulation on the RandomPOD wear testing system as a screening method for bearing materials intended for total knee arthroplasty

The 16-station RandomPOD wear test system, previously validated for prosthetic hip wear, was used in the simulation of knee wear mechanisms with a ball-on-flat test configuration. This consisted of a CoCr pin with a ground and polished spherical bearing surface (radius 28mm) against a conventional, gamma-sterilized UHMWPE disk in serum lubrication. The biaxial motion, consisting of x and y translations, and the load was non-cyclic. Relative to the disk, the center of contact wandered within a circle of 10mm diameter, and the average sliding velocity was 15.5mm/s (ranging from 0 to 31mm/s). The load varied non-cyclically between 0 and 142N (average 73N). In the 60-day test with 16 similar wear couples, moderate adhesive wear, the principal wear mechanism of a well-functioning prosthetic knee, dominated. This showed as a burnished, circular wear mark (diameter 13.2mm, area 137mm2). The wear factor was 2.04±0.03×10−6mm3/Nm (mean±95 percent confidence limit). For the first time a truly multidirectional, realistic and uniform, large capacity pin-on-disk simulation of knee wear mechanisms was implemented.