Location Of Peak Pressure Research Articles

Dynamic plantar loading index: Understanding the benefit of custom foot orthoses for painful pes cavus

The purpose of this study was to evaluate a new method showing how custom foot orthoses (CFO) improve dynamics of plantar loading. The method is based on the probability distribution of peak pressure time series and is quantified using the Regression Factor (RF). RF is a least square regression slope between the experimentally observed plantar pressure magnitude probability distribution and a modeled Gaussian shape. Plantar pressure data from a randomized controlled trial of 154 participants with painful Pes Cavus were retrospectively re-analyzed. The participants were randomized to an active treatment group given CFO or a control group given sham orthoses. The location of 2nd Peak pressure as a percentage of stance time (PLoc2) and its magnitude (PM2) was also calculated. In addition, plantar pressure data were collected on 23 healthy volunteers with normal foot alignment and no foot pain. Results demonstrated Pes Cavus had a significantly lower RF than healthy participants (0.30 v. 0.51; p<10−7). PM2 was reduced in both active and control groups. However, RF and the PLoc2 were only changed in the active group (p<0.005) without any significant change in the control group (p>0.5). This study suggests that painful Pes Cavus alters the shape of probability distribution of plantar loading during walking and CFO are an effective therapeutic solution that can significantly improve it. Further use of the RF index and 2nd peak pressure location as an outcome measure for treatment of foot and ankle deformities is suggested.

Wind pressures on multi-level flat roofs of medium-rise buildings

Since there is limited information on design of wind pressures on multi-level flat roofs from previous studies and in wind loading codes, a wind tunnel experiment was carried out on 1:67 scaled models of a series of medium-rise buildings. Using an assembled cubic plexiglass model and uniformly distributed pressure taps, multi-level flat roofs with different configurations were easily fabricated and pressures on the roofs measured. Mean and fluctuating, local peak and area-averaged pressure coefficients were mainly investigated and stochastic characteristics of wind pressures on multi-level flat roofs were determined. Parameters of step geometry such as the effects of step dimension and configuration were considered. The results showed no significant difference between minimum values of negative peak pressures on simple flat roofs and on multi-level flat roofs, while negative pressure distributions and maximum values of positive peak pressures on the low-roof of multi-level flat roofs were highly dependent on step parameters. A comparison with ASCE/SEI7-10 indicates that negative values with small tributary areas are larger than those in related contents in the code, while negative values in other zones and positive values agree closely with the code. Gaussian and negative-skewed non-Gaussian PDFs, as well as positive-skewed non-Gaussian ones, were measured for multi-level flat roofs.

Methodology for Use of a Neuroprosthetic to Reduce Plantar Pressure: Applications in Patients with Diabetic Foot Disease

Methodology for Use of a Neuroprosthetic to Reduce Plantar Pressure: Applications in Patients with Diabetic Foot Disease

Contact pressure on ACL hamstring grafts in the bone tunnel with interference screw fixation — Dynamic adaptation under load

IntroductionInterference screws used in fixation of anterior cruciate ligament (ACL) hamstring grafts create mechanical hold by forcing the graft into frictional contact with the bone tunnel. We analyzed the resultant graft–tunnel contact pressure using an in vitro model of human cadaver 8mm hamstring grafts. MethodsContact characteristics were assessed using both pressure sensitive films and a force sensor. Two screw sizes were investigated (8 and 9mm in an 8mm Sawbone tunnel), both with and without a bone wedge between graft and screw. Separately, time dependent relaxation of contact force was recorded over a one hour epoch and associated tendon water loss was measured. Pullout testing of 8mm tendon grafts from 8mm holes in Sawbone and porcine femora were performed after 1min and 1h. ResultsDuring screw insertion, measured peak pressures (>40MPa) exceeded the compressive failure stress of metaphyseal bone by more than an order of magnitude. Using a bone wedge between tendon and screw reduced local peak pressure by 85% but produced also inferior average contact pressure. In all approaches, initially achieved graft contact pressure rapidly decreased to approximately 25% within 30min. Pullout strength was significantly reduced after 1h in comparison to 1min in porcine bone as well as Sawbone. ConclusionViscoelastic adaptation of the tendon is severe and critically reduces effective graft–bone contact pressure. Consideration of this newly recognized effect may open new and improved approaches for tendon graft fixation.

On Comparative Performance Testing of Prechamber and Open Chamber Laser Ignition

Laser ignition is a potential ignition technology to achieve reliable lean burn ignition in high brake mean effective pressure (BMEP) internal combustion engines. The technology has the potential to increase brake thermal efficiency and reduce exhaust emissions. This submission reports on engine testing of a Caterpillar G3516C stationary natural gas fueled engine with three types of ignition approaches: (i) nonfueled electric prechamber plug with electrodes at the base of the prechamber, (ii) nonfueled laser prechamber plug with laser spark in the middle of the prechamber, and (iii) open chamber plug with laser spark in the main chamber. In the second configuration, a stock nonfueled prechamber plug was modified to incorporate a sapphire window and a focusing lens to form a laser prechamber plug. A 1064 nm Q-switched Nd:YAG laser was used to create laser sparks. For these tests, a single cylinder of the engine was retrofitted with the laser plug while the remaining cylinders were run with conventional electric ignition system at baseline ignition timing of 24 deg before top dead center (BTDC). The performances of the three plugs were compared in terms of indicated mean effective pressures (IMEP), mass burn fraction duration and coefficient of variation (COV) of IMEP, and COV of peak pressure location. Test data show comparable performance between electric and laser prechamber plugs, albeit with a lower degree of variability in engine’s performance for electric prechamber plug compared to the laser prechamber plug. The open chamber plug exhibited poorer variability in engine performance. All results are discussed in the context of prechamber and engine fluid mechanics.

Effect of Tibial Tuberosity Advancement on the Contact Mechanics and the Alignment of the Patellofemoral and Femorotibial Joints

To evaluate the effect of tibial tuberosity advancement (TTA) on patellofemoral (PF) contact mechanics, and alignment of the PF and femorotibial (FT) joints in cranial cruciate ligament (CrCL)-deficient stifles of dogs. Ex vivo biomechanical study. Unpaired cadaveric hind limbs (n=9). Digital pressure sensors placed in the PF joint were used to measure contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 135°. The FT and PF poses were obtained using a 2-dimensional computer digitization technique. Each specimen was tested under normal, CrCL-deficient, and TTA-treated conditions. Data was normalized and analyzed, after testing for normality by Wilk-Shapiro, using 1 sample T-test, paired T-test, and ANOVA; P≤.05 was considered significant. Bonferroni's correction was used when needed. A significant cranioproximal tibial displacement and increase in patellar tilt were found in the CrCL-deficient joints. Both FT and PF alignments were restored after TTA. Contact areas and peak pressure did not vary between conditions. Peak pressure location displaced proximally from intact to CrCL-deficient condition and returned to normal after TTA. Total force measured in the CrCL-deficient stifle and TTA conditions were significantly lower than in the control. TTA restored the normal FT and PF alignment, and reduced the retropatellar force by about 20%.

TDC Offset Estimation from Motored Cylinder Pressure Data based on Heat Release Shaping

Finding the correct Top Dead Center (TDC) offset for an internal combustion engine is harder than it seems. This study introduces a novel method to find the TDC offset based on the simple assumption that the heat loss power through the combustion chamber walls is constant for motored cycles in a narrow Crank Angle interval around TDC. The proposed method uses nonlinear least squares optimization to find the combination of specific heat ratio and TDC offset that makes the heat loss power as constant as possible. An important subproblem is to determine the peak pressure location with high accuracy. Fitting a third order Fourier series to the motored cylinder pressure allows the pressure maximum to be estimated with a standard deviation of 0.005° Crank Angle (CA) and it can also be used instead of the measured pressure to reduce the uncertainty of the TDC estimate by approximately 50%. The standard deviation of a single-cycle TDC estimate is approximately 0.025° CA when using a crank resolution of 0.2° CA for the measurements. The bias of the TDC estimate is in the 0-0.02° CA range both when comparing to measurements with a TDC sensor and with simulated motored cycles. The method can be used both for calibration and on-board diagnostics purposes e.g. during cranking, fuel cut-off or engine switch-off. The third order Fourier series fit comes with a significant computational penalty but since it is only applied very intermittently this does not have to be a serious issue.

Interference effects on local peak pressures between two buildings

Local peak pressure coefficients between two buildings were studied by using wind tunnel experiments for various locations, different height ratios of interfering building and wind directions. The measured local peak pressure coefficients were compared to those obtained previously from a study on an isolated building. This study also investigated interference effects for local peak pressures on a principal building with various configurations and different height ratios of an interfering building. The experimental results have been examined and presented from the viewpoint of cladding design. The results show that highest peak suctions on a principal building increased with increase in height ratios of the interfering building. The oblique configuration generated more severe peak suction than the tandem configuration. To examine the interference effects for local peak pressures in detail, interference factors for maximum positive and minimum negative peak pressures at each measurement point ( i, j) of the principal building for all wind directions are presented and discussed.

Neural networks and fuzzy logic-based spark advance control of SI engines

In SI engines, spark advance (SA) needs to be controlled to get Maximum Brake Torque (MBT) timing. Spark advance can be controlled either by open loop or by closed loop controller. The open loop controller requires extensive testing and calibration of engine, to develop look up tables. In closed loop controller, empirical rules relating variables deduced from cylinder pressure are used. One of such empirical rules is to fix location of peak pressure (LPP) at a desired value of the crank angle. In the present work, a combined neural network and fuzzy logic-based control scheme is designed for SA control to get MBT timing. The fuzzy logic controller is designed to maintain LPP of SI engine close to 16° ATDC. The controller works in conjunction with Recurrent Neural Network model for cylinder pressure identification. LPP is estimated from cylinder pressure curve reconstructed using neural network model and is used as feedback signal to fuzzy logic controller. The simulations have been carried out to test the performance of the combined neural network and fuzzy logic-based control strategy. The simulation results show that the proposed strategy can quite satisfactorily control LPP to its desired value.

Pressure distribution over the palm region during forward falls on the outstretched hands

Falls on the outstretched hands are the cause of over 90% of wrist fractures, yet little is known about bone loading during this event. We tested how the magnitude and distribution of pressure over the palm region during a forward fall is affected by foam padding (simulating a glove) and arm configuration, and by the faller’s body mass index (BMI) and thickness of soft tissues over the palm region. Thirteen young women with high ( n=7) or low ( n=6) BMI participated in a “torso release experiment” that simulated falling on both outstretched hands with the arm inclined either at 20° or 40° from the vertical. Trials were acquired with and without a 5 mm thick foam pad secured to the palm. Outcome variables were the magnitude and location of peak pressure ( d, θ) with respect to the scaphoid, total impact force, and integrated force applied to three concentric areas, including “danger zone” of 2.5 cm radius centered at the scaphoid. Soft tissue thickness over the palm was measured by ultrasound. The 5 mm foam pad reduced peak pressure, and peak force to the danger zone, by 83% and 13%, respectively. Peak pressure was 77% higher in high BMI when compared with low BMI participants. Soft tissue thickness over the palm correlated positively with distance ( d) ( R=0.79, p=0.001) and force applied outside the danger zone ( R=0.76, p=0.002), but did not correlate with BMI ( R=0.43, p=0.14). The location of peak pressure was shunted 4 mm further from the scaphoid at 20° than that of 40° falls ( d=25 mm (SD 8), θ=−9° (SD 17) in the 20° falls versus d=21 mm (SD 8), θ=−5° (SD 24) in the 40° falls). Peak force to the entire palm was 11% greater in 20° compared with 40° falls. These results indicate that even a 5 mm thick foam layer protects against wrist injury, by attenuating peak pressure over the palm during forward falls. Increased soft tissue thickness shunts force away from the scaphoid. However, soft tissue thickness is not predicted by BMI, and peak pressures are greater in high individuals than that of low BMI individuals. These results contribute to our understanding of the mechanics and prevention of wrist and hand injuries during falls.

Effects of plasma sheet properties on storm‐time ring current

Using an electrically self‐consistent kinetic ring current model, we investigate how different conditions of plasma sheet distribution affect the ring current properties. Results include comparative studies in (1) varying the radial distance of the plasma sheet boundary; (2) varying local time distribution of the source population; (3) varying the source spectra, with #2 as our main focus. Our results show that a source that is farther away from Earth leads to a stronger ring current than a source that is closer to the Earth. Local time distribution of the source plays an important role in determining both the radial and azimuthal (local time) location of the ring current peak pressure. We found that postmidnight source locations generally lead to a stronger ring current. This finding is in agreement with Lavraud et al. (2008). However, our results do not exhibit any simple dependence of the local time distribution of the peak ring current (within the lower energy range) on the local time distribution of the source, as suggested by Lavraud et al. (2008). Instead, the local time distribution of source populations has to compete with the dynamically updated self‐consistent electric field (through the coupling to the ionosphere) in controlling the ring current intensity and peak location. Our results also show that different source spectra lead to different (though the difference may not be very significant) ring current intensities and that low‐energy plasma in the kiloelectron volt range at the boundary constitutes a dominant source population to the ring current. In addition, we found that the radial location of source population is also important to ring current development.

On the effect of aortic root geometry on the coronary entry-flow after a bileaflet mechanical heart valve implant: a numerical study

The simultaneous replacement of a diseased aortic valve, aortic root and ascending aorta with a prosthesis is known as Bentall procedure (Bentall and De Bono in Thorax 23:338, 1968). This is a nowadays standard surgical approach in which the Valsalva sinuses of the aortic root are sacrificed and the coronary arteries are reconnected directly to the graft. The important function of the natural sinuses in the presence of the natural valve is well established; however, very little information is available about whether or not their presence can affect the functioning of a prosthetic bi-leaflet valve and the coronary flow. In the present work, we study the effect of the aortic root geometry on the blood flow through such devices, focusing the attention on the coronary entry-flow. Three root geometries have been considered, two mimicking the prostheses used in practice by surgeons (a straight tube, and the more recent tube with a circular pseudo-sinus), and a third maintaining the natural shape with three sinuses, obtained by Reul et al. (J Biomech 23:181-191, 1990) by averaging numerous angiographies of the aortic root in healthy patients. Direct numerical simulations of the flow inside the three prostheses, assumed as undeformable, under physiological pulsatile inflow conditions are presented. The dynamics of the valvular leaflets is obtained by a fully-coupled fluid-structure-interaction approach and the coronary perfusion is reproduced by modulating in time an equivalent porosity, an thus the resistance, of the coronary channels. The results indicate that the sinuses do not significantly influence the coronary entry flow, in agreement with the in vivo observations of De Paulis et al. (Eur J Cardio-thorac Surg 26:66-72, 2004). Nevertheless, the peak pressure at the joints of the coronary arteries is smaller in the natu- ral-like aortic root geometry. The latter also produces a further beneficial effect of a reduction in the leaflets' angular velocity at the closure onto the valvular ring. These phenomena, if confirmed in more realistic clinical conditions, suggest that the use of a prothesis with physiologic sinuses would potentially reduce the local pressure peak, with the associated risk of post-operative bleeding and pseudo-aneurysm formation. It would also reduce the haemolysis effects caused by the red blood cells squashing between impacting solid artificial surfaces.

Effect of Transection of the Caudal Menisco‐Tibial Ligament on Medial Femorotibial Contact Mechanics

To evaluate the effect of transection of the medial caudal menisco-tibial ligament on contact mechanics in a canine cadaveric model of cranial cruciate ligament (CCL) rupture and tibial plateau leveling osteotomy (TPLO). Ex vivo biomechanical study. Unpaired pelvic limbs (n=8) from 28-35 kg dogs. Cadaveric pelvic limbs with CCL-deficient stifles stabilized with TPLO were axially loaded using a material testing machine with 30% body weight and a stifle angle of 135 degrees. Medial compartment femorotibial contact force and area, peak and mean contact pressure, and peak pressure location were measured with pressure sensors. A paired t-test was used for comparison; P<.05 was considered significant. Transection of the caudal menisco-tibial ligament resulted in a significant decrease in contact area, from 145 +/- 24 to 71 +/- 25 mm(2) (P<.001) and a significant increase in peak pressure magnitude from 2.9 +/- 0.4 to 4.1 +/- 0.5 MPa (P<.001). Transection of the caudal menisco-tibial ligament caused a significant increase in load in the caudal portion of the medial compartment (P<.001). Our results suggest that transecting the caudal menisco-tibial ligament eliminates the load bearing function of the medial meniscus and results in significant changes in medial femorotibial contact mechanics. The abnormal cartilage contact stresses after transection of the caudal menisco-tibial ligament may have a negative impact on the cartilage homeostasis and predispose to further degeneration of the medial compartment after TPLO.

Dynamic Contact Mechanics of the Medial Meniscus as a Function of Radial Tear, Repair, and Partial Meniscectomy

The menisci are integral to normal knee function. The purpose of this study was to measure the contact pressures transmitted to the medial tibial plateau under physiological loads as a function of the percentage of the meniscus involved by the radial tear or repair. Our hypotheses were that (1) there is a threshold size of radial tears above which contact mechanics are adversely affected, and (2) partial meniscectomy results in increased contact pressure compared with that found after meniscal repair. A knee simulator was used to apply physiological multidirectional dynamic gait loads across human cadaver knees. A sensor inserted below the medial meniscus recorded contact pressures in association with (1) an intact meniscus, (2) a radial tear involving 30% of the meniscal rim width, (3) a radial tear involving 60% of the width, (4) a radial tear involving 90% of the width, (5) an inside-out repair with horizontal mattress sutures, and (6) a partial meniscectomy. The effects of these different types of meniscal manipulation on the magnitude and location of the peak contact pressure were assessed at 14% and 45% of the gait cycle. The peak tibial contact pressure in the intact knees was 6 +/- 0.5 MPa and 7.4 +/- 0.6 MPa at 14% and 45% of the gait cycle, respectively. The magnitude and location of the peak contact pressure were not affected by radial tears involving up to 60% of the meniscal rim width. Radial tears involving 90% resulted in a posterocentral shift in peak-pressure location manifested by an increase in pressure in that quadrant of 1.3 +/- 0.5 MPa at 14% of the gait cycle relative to the intact condition. Inside-out mattress suture repair of a 90% tear did not restore the location of the pressure peak to that of the intact knee. Partial meniscectomy led to a further increase in contact pressure in the posterocentral quadrant of 1.4 +/- 0.7 MPa at 14% of the gait cycle. Large radial tears of the medial meniscus are not functionally equivalent to meniscectomies; the residual meniscus continues to provide some load transmission and distribution functions across the joint.

Effect of Cranial Cruciate Ligament Deficiency, Tibial Plateau Leveling Osteotomy, and Tibial Tuberosity Advancement on Contact Mechanics and Alignment of the Stifle in Flexion

To assess contact mechanics and 3-dimensional (3-D) joint alignment in cranial cruciate ligament (CCL)-deficient stifles before and after tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA) with the stifle in 90 degrees of flexion. In vitro biomechanical study. Cadaveric pelvic limb pairs (n=8) from dogs weighing 28-35 kg. Contralateral limbs were assigned to receive TPLO or TTA. Digital pressure sensors were used to measure femorotibial contact area, peak and mean contact pressure, and peak pressure location with the limb under a load of 30% body weight and stifle flexion angle of 90 degrees . 3-D poses were obtained using a Microscribe digitizer. Specimens were tested under normal, CCL deficient, and treatment conditions. Significant disturbances in alignment were not observed after CCL transection, although medial contact area was 10% smaller than normal (P=.003). There were no significant differences in contact mechanics or alignment between normal and TTA conditions; TPLO induced 6 degrees varus angulation (P<.001), 26% decrease in lateral peak pressure (P=.027), and 18% increase in medial mean pressure (P=.008) when compared with normal. Cranial tibial subluxation is nominal in CCL-deficient stifles loaded in flexion. Stifle alignment and contact mechanics are not altered by TTA, whereas TPLO causes mild varus and a subsequent increase in medial compartment loading. Cranial tibial subluxation of CCL-deficient stifles may not occur during postures that load the stifle in flexion. The significance of minor changes in loading patterns after TPLO is unknown.

Steady and unsteady flow within an axisymmetric tube dilatation

The flow field in an axisymmetric tube dilatation is studied employing a 2D PIV system and the commercial numerical code FLUENT. Experiment and numerical predictions are in good agreement providing similar trends and the same flow topology. For the steady case and for Re varying in the range 100–700, the recirculation zone length increases with Re, the flow reattachment line being displaced towards the exit of the model. Upstream of this line and a small distance from it, negative velocity maximizes close to the wall as well as the wall shear stress (in absolute value). Downstream of this region, the wall pressure peaks and wall shear takes a local maximum at the model exit. In the rest part of the cavity both wall shear and pressure do not practically vary due to separated flow. The axial velocity on the longitudinal axis of the model does not change streamwise for higher Re (Re = 690), resembling the near field of a jet, entraining fluid from the cavity region. In the unsteady case the flow rate is sinusoidal, the Womersley number is 3.3 and peak Re = 272. During early acceleration, a vortex ring is formed at the proximal part of the cavity and two stagnation points appear on the longitudinal axis of the model approaching each other as time progresses, eventually disappearing when the majority of the fluid particles changes direction. The velocity profile at the exit is most of the cycle blunt compared to the parabolic type profile at the model entrance. In contrast to the steady case, the pressure variation does not exhibit a local peak within the cavity rather varying in a smooth way. Conversely, wall shear stress shows high peaks at the distal end of the dilatation being proportional to the time dependent flow rate. The reattachment line travels along the wall, as well as the local pressure peak which is always located downstream of it. Massless particles released at various locations and time instants within a cycle are not trapped in the recirculation zone, being exposed to varying shear stress values.

Dynamics of Intracarpal Tunnel Pressure in Patients With Carpal Tunnel Syndrome

To measure pressure within the carpal tunnel (intracarpal tunnel pressures) in patients with carpal tunnel syndrome and determine the effect of quantified active hand use on both the magnitude and location of peak pressures, before and after division of the transverse carpal ligament. We measured intracarpal tunnel pressures intraoperatively in 12 patients with carpal tunnel syndrome at 5 standardized locations based on the distance between each patient's proximal pisiform and hook of hamate (HH) before endoscopic division of the ligament, using a semiconductor gauge pressure sensor inserted from proximal to distal into the tunnel under fluoroscopic control. At each location, pressure was recorded with fingers extended, fingers flexed, and 50% maximum grip using a grip dynamometer. Additional hand use activities, including maximum key and pulp pinch using a pinch dynamometer, 25% maximum grip, and maximum grip, were performed by a subset of these patients. After ligament division, we measured pressures during the same hand activities at a single location, HH. We analyzed the effect of hand activity, measurement location, and ligament division using repeated measures analysis of variance. Compared with fingers extended (mean pressure, 56 mm Hg), all pinch and grip activities caused significant increases in pressure at HH, with a mean peak pressure of 1151 mm Hg during maximum grip. After endoscopic release, pressures decreased significantly at HH for all hand activities. In patients with carpal tunnel syndrome, intracarpal tunnel pressures during active hand use are substantially greater than previously reported. Peak pressures occur at the HH, where the tunnel is most constricted and the median nerve is most compressed in carpal tunnel syndrome. Therapeutic IV.

Effect of hip protectors, falling angle and body mass index on pressure distribution over the hip during simulated falls

Background We examined how a soft shell hip protector affects the magnitude and distribution of force to the hip during simulated falls, and how the protective effect depends on the fall direction and the amount of soft tissue padding over the hip. Methods Fourteen young women with either high or low body mass index participated in a “pelvis release experiment” that simulated falls resulting in either lateral, anterolateral or posterolateral impact to the pelvis with/without a soft shell hip protector. Outcome variables were the magnitude and location of peak pressure ( d, theta) with respect to the greater trochanter, total impact force, and percent force applied to four defined hip regions. Findings The soft shell hip protector reduced peak pressure by 70%. The effect was two times greater in low than high body mass index individuals. The protector shunted the peak pressure distally along the shaft of the femur ( d = 52 mm (SD 22), theta = −21° (SD 49) in the unpadded trials versus d = 81 mm (SD 23), theta = −10° (SD 35) in the padded trials). Peak force averaged 12% greater in posterolateral and 17% lower in anterolateral than lateral falls. Interpretation Our results indicate that the hip protector we tested had a much stronger protective benefit for low than high body mass index individuals. Next generation protectors might be developed for improved shunting of pressure away from the femur, improved protection during posterolateral falls, and greater force attenuation for low body mass index individuals.

A Neural Network Implementation of Peak Pressure Position Control by Ionization Current Feedback

This paper describes a neural-network (NN)-based scheme for the control of a cylinder peak pressure position (PPP)—also known as the location of peak pressure (LPP)—by spark timing in a gasoline internal combustion engine. The scheme uses the ionization current to act as a virtual sensor, which is subsequently used for PPP control. A NN is trained offline on principal-component analysis data to predict the cylinder peak pressure position under dynamically varying engine load, speed, and spark advance (SA) settings. Experimental results demonstrate that the PPP prediction by the NN correlates well with those measured from in-cylinder pressure sensors across transients of load, SA, and engine speeds. The dynamic training data allow rapid model identification across the identified engine range, as opposed to just fixed operating points. A linear robust constrained-variance controller, which is a robustified form of the minimum variance controller, is used to regulate the PPP by SA control action, using the NN as a PPP sensor. The control scheme is validated by experimental implementation on a port fuel-injected four-cylinder 1.6 l gasoline internal combustion engine.

Effect of Tibial Plateau Leveling Osteotomy on Femorotibial Contact Mechanics and Stifle Kinematics

To evaluate the effects of tibial plateau leveling osteotomy (TPLO) on femorotibial contact mechanics and 3-dimensional (3D) kinematics in cranial cruciate ligament (CrCL)-deficient stifles of dogs. In vitro biomechanical study. Unpaired pelvic limbs from 8 dogs, weighing 28-35 kg. Digital pressure sensors placed subjacent to the menisci were used to measure femorotibial contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 135 degrees. Three-dimensional static poses of the stifle were obtained using a Microscribe digitizing arm. Each specimen was tested under normal, CrCL-deficient, and TPLO-treated conditions. Repeated measures analysis of variance with a Tukey post hoc test (P<.05) was used for statistical comparison. Significant disturbances to all measured contact mechanical variables were evident after CrCL transection, which corresponded to marked cranial tibial subluxation and increased internal tibial rotation in the CrCL-deficient stifle. No significant differences in 3D femorotibial alignment were observed between normal and TPLO-treated stifles; however, femorotibial contact area remained significantly smaller and peak contact pressures in both medial and lateral stifle compartments were positioned more caudally on the tibial plateau, when compared with normal. Whereas TPLO eliminates craniocaudal stifle instability during simulated weight bearing, the procedure fails to concurrently restore femorotibial contact mechanics to normal. Progression of stifle osteoarthritis in dogs treated with TPLO may be partly the result of abnormal stifle contact mechanics induced by altering the orientation of the proximal tibial articulating surface.