Root Mean Square Acceleration Research Articles

Gait analysis of patients with Parkinson's disease using a portable triaxial accelerometer

AbstractBackgroundGait disturbance is a major problem for Parkinson's disease patients.AimWe examined the nature of parkinsonian gait using a triaxial accelerometer, and elucidated differences as compared with healthy adults.MethodsA total of 16 patients with idiopathic Parkinson's disease, 14 healthy young adults and 10 healthy older adults took part in the study. The accelerometer was placed at the level of the L4 spinous process and the participants were instructed to walk along a 30‐m horizontal walkway. Gait speed and acceleration were analyzed on the middle 10 m. Acceleration data were obtained by using the root mean square of acceleration in three directions as the mean acceleration value.ResultsGait speed and mean acceleration had a high correlation in healthy young and older adults, but not in the Parkinson's disease patients. Gait speed in the Parkinson's disease patients was significantly slower than that in the healthy older adults (P < 0.05). Evaluations of each component of acceleration showed that the mediolateral component in the patients was significantly high as compared with that in the healthy older adults (P < 0.05), although the vertical and anteroposterior components were not different between the Parkinson's disease patients and healthy adults.ConclusionsGait speed in Parkinson's disease patients is significantly slower than that in healthy older adults. Furthermore, it is suggested that gait in Parkinson's disease patients swings in a more bilateral manner as compared with the gait in normal controls.

Stochastic shock response spectrum decomposition method based on probabilistic definitions of temporal peak acceleration, spectral energy, and phase lag distributions of mechanical impact pyrotechnic shock test data

Most of the times pyrotechnic shock design and test requirements for space systems are provided in Shock Response Spectrum (SRS) without the input time history. Since the SRS does not describe the input or the environment, a decomposition method is used to obtain the source time history. The main objective of this paper is to develop a decomposition method producing input time histories that can satisfy the SRS requirement based on the pyrotechnic shock test data measured from a mechanical impact test apparatus. At the heart of this decomposition method is the statistical representation of the pyrotechnic shock test data measured from the MIT Lincoln Laboratory (LL) designed Universal Pyrotechnic Shock Simulator (UPSS). Each pyrotechnic shock test data measured at the interface of a test unit has been analyzed to produce the temporal peak acceleration, Root Mean Square (RMS) acceleration, and the phase lag at each band center frequency. Maximum SRS of each filtered time history has been calculated to produce a relationship between the input and the response. Two new definitions are proposed as a result. The Peak Ratio (PR) is defined as the ratio between the maximum SRS and the temporal peak acceleration at each band center frequency. The ratio between the maximum SRS and the RMS acceleration is defined as the Energy Ratio (ER) at each band center frequency. Phase lag is estimated based on the time delay between the temporal peak acceleration at each band center frequency and the peak acceleration at the lowest band center frequency. This stochastic process has been applied to more than one hundred pyrotechnic shock test data to produce probabilistic definitions of the PR, ER, and the phase lag. The SRS is decomposed at each band center frequency using damped sinusoids with the PR and the decays obtained by matching the ER of the damped sinusoids to the ER of the test data. The final step in this stochastic SRS decomposition process is the Monte Carlo (MC) simulation. The MC simulation identifies combinations of the PR and decays that can meet the SRS requirement at each band center frequency. Decomposed input time histories are produced by summing the converged damped sinusoids with the MC simulation of the phase lag distribution.

A wireless accelerometer node for reliable and valid measurement of lumbar accelerations during treadmill running

This study investigated the reliability of a wireless accelerometer and its agreement with optical motion capture for the measurement of root mean square (RMS) acceleration during running. RMS acceleration provides a whole-body metric of movement mechanics and economy. Fifteen healthy college-age participants performed treadmill running for two 60-s trials at 2.22, 2.78, and 3.33 m/s and one trial of 150 s (five 30-s epochs) at 2.78 m/s. We assessed between-trial and within-trial reliability, and agreement in each axis between a trunk-mounted wireless accelerometer and a reflective marker on the accelerometer measured by optical motion capture. Intraclass correlations assessing between-trial repeatability were 0.89–0.97, depending on the axis, and intraclass correlations assessing within-trial repeatability were 0.99–1.00. Bland–Altman analyses assessing agreement indicated mean difference values between −0.03 and 0.03 g, depending on the axis. Anterio-posterior acceleration had the greatest limits of agreement (LOA) (±0.12 g) and vertical acceleration had the smallest LOA (±0.03 g). For measuring RMS acceleration of the trunk, this wireless accelerometer node provides repeatable and valid measurement compared with the standard laboratory method of optical motion capture.

Modeling and Optimization of Vehicle Suspension Employing a Nonlinear Fluid Inerter

An ideal inerter has been applied to various vibration engineering fields because of its superior vibration isolation performance. This paper proposes a new type of fluid inerter and analyzes the nonlinearities including friction and nonlinear damping force caused by the viscosity of fluid. The nonlinear model of fluid inerter is demonstrated by the experiments analysis. Furthermore, the full-car dynamic model involving the nonlinear fluid inerter is established. It has been detected that the performance of the vehicle suspension may be influenced by the nonlinearities of inerter. So, parameters of the suspension system including the spring stiffness and the damping coefficient are optimized by means of QGA (quantum genetic algorithm), which combines the genetic algorithm and quantum computing. Results indicate that, compared with the original nonlinear suspension system, the RMS (root-mean-square) of vertical body acceleration of optimized suspension has decreased by 9.0%, the RMS of pitch angular acceleration has decreased by 19.9%, and the RMS of roll angular acceleration has decreased by 9.6%.

Correlative Analysis of Hydraulic Bushing of Suspension Control Arm and Full Vehicle Ride Comfort

To analyze and compare the vehicle performance effects of hydraulic bushings with those of the traditional rubber bushings of double wishbone front suspensions, we test the static and dynamic properties of the hydraulic bushings of control arms. The mechanical model is built in ADAMS and is then used as the basis for establishing the full vehicle model. The random road surface spectra of different levels are built using the harmony superposition method. The ride comfort of the full vehicle with a control arm installed with hydraulic and rubber bushings is simulated on random and bump roads. The frequency spectrum characteristic and root mean square (RMS) of the vertical and longitudinal acceleration of the foot floor and seat rail are calculated via power spectrum estimation, and the handling stability of the full vehicle is then simulated. The effects of the change in hydraulic bushing stiffness on ride comfort are finally analyzed. The following results are obtained. (1) The effects of such change on vehicle handling are relatively small regardless of the type of bushing used. (2) The vehicle shows acceptable ride comfort on level A and level B roads but shows poor ride comfort on bump road when a hydraulic bushing is used. (3) Large hydraulic bushing stiffness increases the vertical acceleration RMS on level A, level B, and bump roads. However, the variety of RMS is extremely small on level D roads, the responses of the vertical and longitudinal acceleration curves are slow, and the time oscillation of the curves is relatively long on bump road.

Wireless Tri-Axial Trunk Accelerometry Detects Deviations in Dynamic Center of Mass Motion Due to Running-Induced Fatigue.

Small wireless trunk accelerometers have become a popular approach to unobtrusively quantify human locomotion and provide insights into both gait rehabilitation and sports performance. However, limited evidence exists as to which trunk accelerometry measures are suitable for the purpose of detecting movement compensations while running, and specifically in response to fatigue. The aim of this study was therefore to detect deviations in the dynamic center of mass (CoM) motion due to running-induced fatigue using tri-axial trunk accelerometry. Twenty runners aged 18–25 years completed an indoor treadmill running protocol to volitional exhaustion at speeds equivalent to their 3.2 km time trial performance. The following dependent measures were extracted from tri-axial trunk accelerations of 20 running steps before and after the treadmill fatigue protocol: the tri-axial ratio of acceleration root mean square (RMS) to the resultant vector RMS, step and stride regularity (autocorrelation procedure), and sample entropy. Running-induced fatigue increased mediolateral and anteroposterior ratios of acceleration RMS (p < .05), decreased the anteroposterior step regularity (p < .05), and increased the anteroposterior sample entropy (p < .05) of trunk accelerometry patterns. Our findings indicate that treadmill running-induced fatigue might reveal itself in a greater contribution of variability in horizontal plane trunk accelerations, with anteroposterior trunk accelerations that are less regular from step-to-step and are less predictable. It appears that trunk accelerometry parameters can be used to detect deviations in dynamic CoM motion induced by treadmill running fatigue, yet it is unknown how robust or generalizable these parameters are to outdoor running environments.

Universal response spectrum procedure for predicting walking-induced floor vibration

Floor vibrations caused by people walking are an important serviceability problem both for human occupants and vibration-sensitive equipment. Present design methodologies available for prediction of vibration response due to footfall loading are complex and suffer from division between low and high frequency floors. In order to simplify the design process and to avoid the problem of floor classification, this paper presents a methodology for predicting vibration response metrics due to pedestrian footfalls for any floor type having natural frequency in the range 1–20Hz.Using a response spectrum approach, a database of 852 weight-normalised vertical ground reaction force (GRF) time histories recorded for more than 60 individuals walking on an instrumented treadmill was used to calculate response metrics. Chosen metrics were peak values of 1s peak root-mean-square (RMS) acceleration and peak envelope one-third octave velocities. These were evaluated by weight-normalising the GRFs and applying to unit-mass single degree of freedom oscillators having natural frequencies in the range 1–20Hz and damping ratios in the range 0.5–5%. Moreover, to account for effect of mode shape and duration of crossing (i.e. duration of dynamic loading), the recorded GRFs were applied for three most typical mode shapes and floor spans from 5m to 40m.The resulting peak values as functions of frequency i.e. spectra are condensed to statistical representations for chosen probability of being exceeded over a wide range of applications. RMS (acceleration) spectra show strong peaks corresponding to the first harmonic of pacing rate followed by clear minima at approximately 3.5Hz, a second much smaller peak corresponding to the second harmonic and a steady decline with increasing frequency beginning around 5Hz. One-third octave spectra show asymptotic trends with frequency, span and damping.A comprehensive validation exercise focusing on the acceleration RMS spectra was based on a representative range of floor samples for which modal properties had been identified and walking response studied during experimental campaigns of vibration serviceability evaluation. Due to the statistical approach an exact validation would not be possible, hence measured peak RMS values were matched to distributions for the equivalent idealised structure. In the vast majority of cases the measured values, intended to represent worst-case conditions, fitted the upper decile of the corresponding simulated spectra indicating consistency with the proposed approach.

Ride comfort optimization of a multi-axle heavy motorized wheel dump truck based on virtual and real prototype experiment integrated Kriging model

The optimization of hydro-pneumatic suspension parameters of a multi-axle heavy motorized wheel dump truck is carried out based on virtual and real prototype experiment integrated Kriging model in this article. The root mean square of vertical vibration acceleration, in the center of sprung mass, is assigned as the optimization objective. The constraints are the natural frequency, the working stroke, and the dynamic load of wheels. The suspension structure for the truck is the adjustable hydro-pneumatic suspension with ideal vehicle nonlinear characteristics, integrated with elastic and damping elements. Also, the hydraulic systems of two adjacent hydro-pneumatic suspension are interconnected. Considering the high complexity of the engineering model, a novel kind of meta-model called virtual and real prototype experiment integrated Kriging is proposed in this article. The interpolation principle and the construction of virtual and real prototype experiment integrated Kriging model were elucidated. Being different from traditional Kriging, virtual and real prototype experiment integrated Kriging combines the respective advantages of actual test and Computer Aided Engineering simulation. Based on the virtual and real prototype experiment integrated Kriging model, the optimization results, obtained by experimental verification, showed significant improvement in the ride comfort by 12.48% for front suspension and 11.79% for rear suspension. Compared with traditional Kriging, the optimization effect was improved by 3.05% and 3.38% respectively. Virtual and real prototype experiment integrated Kriging provides an effective way to approach the optimal solution for the optimization of high-complexity engineering problems.

Comparing Ground Motion Intensity, Root Mean Square of Acceleration and Time Duration from Four Definitions of Strong Motion

Variation of strong motion intensity, root mean square of ground acceleration and time-duration in seconds obtained from 83 accelerograms of 18 earthquakes with magnitudes between 5 to 7.7 were investigated considering four definitions of strong section of accelerograms given by Vanmarcke-Lai; Bolt, Trifunac-Brady and McCaan-Shah. Strong motion intensities were calculated for all definitions of strong duration. Even though, durations in seconds and root mean square of ground acceleration values resulted quite different among the four definitions of strong sections, both durations in seconds and root mean square of acceleration squared values tend to compensate each other to yield the same strong motion intensity for each definition used. Q-ratio as defined by Vanmarcke-Lai (Peak Ground Acceleration divided by root mean square of acceleration) was found not constant but instead it varied significantly for all strong motion definitions. Similarly, ratio of strong motion intensity over peak ground acceleration squared as defined by Vanmarcke-Lai holds linear for time durations less than 20-30 seconds for all definitions, afterwards it shows large dispersion. Finally, Vanmarcke-Lai time duration in seconds appears to increase from near field distance up to a certain medium distance after which it starts to decrease.

Predicting Falls in Older Adults

Accelerometers have been evaluated extensively regarding their ability to assess postural sway. Horizontal center of mass (COM) accelerations have been reported to be positively associated fall risk in older adult populations. In fact, we previously reported that an accelerometer-based balance assessment (ABA) was superior to select clinical measures at retrospectively discriminating fallers from non-fallers. PURPOSE: Understanding that a retrospective analysis of fall risk is inherently flawed, we aimed to prospectively evaluate the ABA. METHODS: Ninety-three independent community-living otherwise healthy older adults (age 86±6 years) were recruited from multiple facilities. For the baseline assessment, participants completed the ABA (8 static balance tasks), Timed Up-and-Go (TUG), Berg Balance Scale (BBS), and the Activities-Specific Balance Confidence (ABC) Scale. Participants were then called weekly for 12 months to evaluate falls after the baseline assessment. We then compared outcomes from the ABA and clinical assessments between participants who never fell, participants who fell once, and participants who fell two or more times during the follow-up period. RESULTS: During the 12-month follow-up, 22/93 (24%) of the participants fell once and 32/93 (34%) fell at least twice. The average root mean square of the horizontal COM accelerations across the 8 ABA static balance conditions for non-fallers, one time fallers, and multiple fallers (0.0126 ± 0.0049 g, 0.0122 ± 0.0030 g, and 0.0129 ± 0.0042 g, respectively) were statistically similar. Likewise, there were no significant differences between non-fallers, one time fallers, and multiple fallers with respect to the TUG (15.7 ± 12.0 s, 17.1 ± 10.2 s, and 12.8 ± 4.7 s, respectively), BBS (46.7 ± 7.4, 45.1 ± 10.1, and 47.3 ± 5.1, respectively), or the ABC Scale (69.6 ± 19.1, 68.0 ± 16.2, and 65.8 ± 18.1, respectively). CONCLUSIONS: In this 12-month prospective study, 58% of our study population fell at least once, but baseline performance on the ABA, TUG, BBS, and ABC Scale was not significantly associated with future single or multiple falls.

Effects of low light on the stability of the head and pelvis of the healthy elderly.

[Purpose] The purpose of this study was to evaluate the changes in body stability of the elderly while walking on even surface ground under low light. [Subjects] Ten young males and ten elderly males participated in this experiment. [Methods] Each subject walked along a 7 m walkway five times at their preferred walking speed under normal (>300 lux, NORM) and low light conditions (<5 lux, LOW). To compare the changes in body stability, the root mean square of acceleration (RMSacc) at the head and pelvis was used. [Results] The results show that the body stability of young adults showed a similar RMSacc in all directions at the head and pelvis between the normal and low light walking conditions. In contrast, the RMSacc in all directions at the head and pelvis during low light walking by elderly adults was significantly greater than that of normal light walking. [Conclusion] It was confirmed that, despite walking on even ground, low light condition affects the body stability of the elderly. To clearly evaluate the effect of low light with aging on gait pattern, further study will be necessary to perform additional experiments under various environmental conditions to investigate walking speed, multi-tasking, stairs, and uneven walkway performance.

Early-Warning Method of Train Running Safety of a High-Speed Railway Bridge Based on Transverse Vibration Monitoring

Making use of long-term transverse vibration monitoring data of DaShengGuan Bridge, the early-warning method of train running safety of the high-speed railway bridge is established by adopting principal component analysis (PCA) method. Firstly, the root mean square (RMS) of the transverse acceleration of the main girder is used as the monitoring parameter for the train running safety. The correlation model between the RMS values measured from different positions is further adopted as the evaluating model for the train running safety. Finally, the effects of the environmental changes on the evaluating model are eliminated using the PCA method and the warning index for the train running safety is further constructed. The analysis results show that the correlation between the RMS values of the accelerations from different measuring positions on the main girder can be analyzed by a quadratic polynomial fitting model. The PCA method can effectively remove the environmental effects on the quadratic polynomial fitting model. The proposed warning method provides a good capability for detecting the abnormal changes of the measured transverse accelerations and hence it is suitable for early-warning of the train running safety.

Role of visual input in the control of dynamic balance: variability and instability of gait in treadmill walking while blindfolded

While vision obviously plays an essential role in orienting and obstacle avoidance, its role in the regulation of dynamic balance is not yet fully understood. The objective of this study was to assess dynamic stability while blindfolded, under optimal conditions that minimized the fear of falling. The hypothesis was that visual deprivation could be compensated for by using other sensory strategies to stabilize gait. One hundred healthy adults (aged 20-69 years) participated in the study. They were previously accustomed to blindfolded treadmill walking wearing a safety harness. Their preferred walking speeds (PWS) were assessed with eyes open (PWSEO) and with eyes closed (blindfolded, PWSEC). Three five-minute tests were performed: (A) normal walking at PWSEO, (B) blindfolded walking at PWSEC, and (C) normal walking at PWSEC. Trunk acceleration was measured with a lightweight inertial sensor. Dynamic stability was assessed by using (1) acceleration root mean square (RMS), which estimates the variability of the signal, and hence, the smoothness of the trunk movement and (2) local dynamic stability (LDS), which reflects the efficiency of the motor control to stabilize the trunk. Although walking at PWSEC with eyes open (comparing conditions A and C) had a slight impact on gait stability (relative difference: RMS +4 %, LDS -5 %), no destabilizing effect of visual deprivation (B vs. C, RMS -4 %, LDS -1 %) was observed. Therefore, it is concluded that when reassuring conditions are offered to individuals while walking, they are able to adopt alternative sensory strategies to control dynamic equilibrium without the help of vision.

Measurement and analysis of truck vibration levels as a function of packages locations in truck bed and suspension

During transport, due to vibration fruits and vegetables could be damaged. The vibration levels that transfer to fruits and vegetables may depend not only on vehicle characteristics (speed and suspension) and the road characteristics but also on the position of boxes packed in truck bed. The purpose of this research was to determine and analyze the vibration that occurs during truck transport as a function of box position and fruit position within the truck bed. For this purpose, two commercial trucks were used (with leaf-spring suspension and air-ride suspension). Test controllable factors includes: height positions of the container column (Bottom, Middle and Up), position of the container along the truck-bed (front axle and rear axle) and depth of fruit inside the container (Down and Top). The obtained values of the power spectral density were used to survey the effect of container positions on fruit vibration. RMS values were also obtained for different positions. The results showed that the power spectral density (PSD) was dependent on the position along the floor of the trucks. Higher vibration levels were recorded for fruits on top of the column. As the fruit height within a box increased, the vibration levels increased. ANOVA test results indicated that the considered factors significantly affected PSD values (Average PSD in the range of 0.1–5Hz and peak PSD) and root mean square of acceleration (P<0.05).

Effects of Jatropha biodiesel on the performance, emissions, and combustion of a converted common-rail diesel engine

An experimental investigation into the effects of Jatropha biodiesel fuels on the engine performance, emissions, and combustion characteristics of a single-cylinder high-pressure common-rail diesel engine was performed under six different load operations (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 MPa). The test fuels included a conventional diesel fuel and three different blends of Jatropha biodiesel fuel (JB10, JB30, and JB50). The results revealed that the biodiesel blended fuels had a significant influence on the brake specific fuel consumption (BSFC) at all of the engine load conditions examined. In general, the use of Jatropha biodiesel blends resulted in a reduction in brake specific nitrogen oxide (BSNOx), brake specific carbon monoxide (BSCO), and smoke emissions, regardless of the load conditions. A large reduction of 20.2% in BSNOx emissions and 69.5% in smoke opacity were found for the engine when it was fuelled with the biodiesel blends. In terms of the engine combustion characteristics, a slightly shorter ignition delay (ID) and faster combustion duration were found to occur with the use of biodiesel blends under all loading operations. It was revealed that the peak apparent heat release rate (AHRR) for biodiesel blends is lower during low load operation; the AHRR was found to be comparable to that of baseline diesel during high-load operation. Finally, the vibration results demonstrated that the largest reduction, 11.3%, in the root mean square (RMS) of acceleration in comparison with the baseline diesel was obtained with JB50 at an engine load of 0.5 MPa.

Quantification of postural stability in older adults using mobile technology.

Traditional biomechanical systems used to capture kinematic data have shown that declines in postural stability are frequently present in older adults and neurological populations. Recent advances in processor speed and measuring capabilities of on-board electronics within mobile devices present an opportunity to gather kinematic data and apply biomechanical analyses to potentially quantify postural stability. The aim of this project was to determine if the kinematic data gathered using a mobile device were of sufficient quantity and quality to characterize postural stability in older adults. Twelve healthy older adults completed six different balance conditions under altered surface, stance and vision. Simultaneous kinematic measurements were gathered from a three-dimensional motion analysis system and iPad during balance conditions. Correlation between the two systems was significant across balance conditions and outcome measures: peak-to-peak (r = 0.70-0.99), normalized path length (r = 0.64-0.98), root mean square (r = 0.73-0.99) of linear acceleration, 95 % volume (r = 0.96-0.99) of linear and angular acceleration and total power across different frequencies (r = 0.79-0.92). The mean absolute percentage error metric, used to evaluate time-series measurements point-by-point, indicated that when measuring linear and angular acceleration, the iPad tracked the motion analysis system with average error between 6 and 10 % of motion analysis measurements across all balance conditions. Collectively, similar accuracy with the iPad compared to motion capture suggests the sensors provide sufficient accuracy and quality for the quantification of postural stability in older adults. The objectivity, portability, and ease of use of this device make it ideal for use in clinical environments, which often lack biomechanical systems.

Kinematic characteristics of gait in middle-aged adults during level walking.

Middle-aged people have shown a high fall incidence and degeneration in gait stability, while few studies concern that. This study aimed to assess the kinematic characteristics of gait in middle-aged people compared with younger and older ones during level walking, and to find sensitive indicators to characterize degenerated gait stability in middle-aged people. 13 middle-aged (mean age=52.1 years), with 13 older (mean age=74.8 years) and 13 young (mean age=23.3 years) healthy adults participated in this study. We assessed following gait parameters of the subjects during their level walking: 1) temporal-spatial gait parameters: normalized gait velocity, stride length, step length and their variability; 2) gait stability parameters: acceleration root mean square (RMS) of COM and its variability; and instantaneous COM-COP inclination angles. Compared with young and older subjects, middle-aged adults showed no significant difference in temporal-spatial gait parameters and their stride-to-stride variability (P>0.050); Compared with young subjects, middle-aged adults showed a significant higher value in medial-lateral (ML) direction of acceleration RMS of COM (P=0.038) and its stride-to-stride variability (P=0.030), as well as in COM-COP inclination angle (P=0.003). There was no significant difference in the above two parameters of gait stability between middle-aged and older subjects (P>0.050). Results illustrated that middle-aged subjects showed similar degenerated pattern in gait stability as the older ones in ML direction. Gait stability parameters, including ML acceleration of COM and its variability, as well as ML COM-COP inclination angle may help to characterize this degenerated gait stability. It's necessary for us to develop early interventions for middle-aged adults to prevent falls during walking.

Movement strategies for maintaining standing balance during arm tracking in people with multiple sclerosis.

The purpose of this study was to quantify hip and ankle movement strategies during a standing arm tracking task in people with multiple sclerosis (MS). Full-body kinematics and kinetics were assessed with motion analysis cameras and force plates in nine MS and nine age-matched control subjects. While standing, participants used their dominant hand to track a target moving around a large horizontal or vertical figure eight on a screen in front of them. The target moved at constant speed, or linearly increasing speeds, with a frequency between 0.05 Hz and 0.35 Hz. Hip and ankle moments and angles during tracking were calculated from kinematic and kinetic measurements. Ratios of peak-to-peak (PP) hip/ankle moments (kinetics) and angles (kinematics) were calculated to determine the strategies of the hips and ankles used to maintain balance during arm movements. Center of mass (CoM) root mean square (RMS) acceleration was calculated as a measure of overall balance performance. The MS group produced larger PP hip/ankle moments at all speeds compared with the control group (P < 0.05). The CoM RMS acceleration increased with tracking speed for both groups but was not significantly different between groups. Additionally, the ratios of hip to ankle moments were highly correlated with the Berg Balance Scale during horizontal steady-speed tracking in MS. These results suggest that people with MS increase the use of the hip during standing arm tracking compared with age-matched control subjects. This adapted strategy might allow people with MS to achieve balance performance similar to control subjects, possibly increasing the importance of the hip in maintaining balance during voluntary movements.

Analysis for Ride Comfort Evaluation of Passenger Car Traveling on Roads with Generalized Road Profiles and Conventional Speeds

To investigate how the conventional speeds to affect passenger cars ride comfort under a kind of road surface profiles, in multibody dynamics software (ADAMS/Car), a vehicle model was built based on the characteristic parameters of a passenger car. According to the relevant test regulations of ride comfort, the building methods of road surface profiles were discussed. Furthermore, a dynamics simulation analysis of the car was realized by ADAMS/Car and the acceleration-time histories of the seat surfaces X/Y/Z-axis under three conventional driving-speeds were acquired. A special MATLAB program was compiled to calculate the total weighted Root Mean Square (RMS) value by calling the above histories. According to the GB/T 4970-1996, a road test of a passenger car was carried out in the random road surface which equivalent to B level. The car was driven to get the values of total weighted acceleration RMS under three conventional driving-speeds. By comparing the road test result with simulation, the result indicated that the changing trend of total weighted RMS value is consistent as the driving-speed changes, and the ride comfort will decrease when the driving-speed increase. At the same time, it shows that the consistency of the simulation and road test is better.

An investigation of the engine performance, emissions and combustion characteristics of coconut biodiesel in a high-pressure common-rail diesel engine

An experimental investigation on engine performance, emissions, combustion and vibration characteristics with coconut biodiesel fuels was conducted in a high-pressure common-rail diesel engine under five different load operations (0.17, 0.34, 0.52, 0.69 and 0.86 MPa). The test fuels included a conventional diesel fuel and four different fuel blends of coconut biodiesel (B10, B20, B30 and B50). The results showed that biodiesel blended fuels have significant influences on the BSFC (brake specific fuel consumption) and BSEC (brake specific energy consumption) at all engine loads. In general, the use of coconut biodiesel blends resulted in a reduction of BSCO (brake specific carbon monoxide) and smoke emissions regardless of the load conditions. A large reduction of 52.4% in smoke opacity was found at engine load of 0.86 MPa engine load with B50. For combustion characteristics, a slightly shorter ignition delay and longer combustion duration were found with the use of biodiesel blends under all loading operations. It was found that generally the biodiesel blends produced lower peak heat release rate than baseline diesel. The vibration results showed that the largest reduction of 13.7% in RMS (root mean square) of acceleration was obtained with B50 at engine load of 0.86 MPa with respect to the baseline diesel.