Static and dynamic analyses of mountain bikes and their riders

Mountain biking is a globally popular sport, in which the rider uses a mountain bike to ride on off-road terrain. A mountain bike has either a front suspension system only or a full-suspension system to decrease the external vibration resulting from the terrain irregularities and to increase riding comfort. Despite the added comfort of full-suspension of mountain bikes, there are some disadvantages because the chain-suspension interaction and bobbing effect absorb some of the rider's pedalling power and lead to the reduction of pedalling efficiency. In this study, a technique for evaluating the pedalling efficiency of a bike rider in seated cycling by using engineering mechanics is developed. This method is also found to be useful for determining the correct crank angle for the beginning of the downstroke and that of the upstroke during each pedalling cycle. Next, five mathematical models of rider-bike systems are developed in Simulink and SimMechanics, including one hard-tail (HT) bike, and four full-suspension (FS) bikes [single pivot, four-bar-linkage horst link, four-bar-linkage faux bar, and virtual pivot point (VPP)]. In each of the five rider-bike systems, a PID controller is applied on the rider's elbow to prevent his upper body from falling down due to gravity. A pedalling controller is also developed in Simulink, which is based on the previous theory for evaluating the rider's pedalling efficiency written in Matlab. Another PID controller is used for the pedalling control by sensing the real-time moving speed and applying a suitable pedalling force to achieve a desired speed. The dynamic responses for each of the five rider-bike systems moving on a flat road surface (without bumps) and rough terrain (with bumps) are investigated. The values determined include the pedalling force, pedalling torque and power, forward velocity, contact forces of front and rear wheels, compressions of front suspension (front fork) and rear suspension (rear shock absorber), sprocket distance, chain tension force, and vertical accelerations of handlebar and seats. The numerical results reveal that, while moving on flat road surface, the pedalling efficiency of hard-tail bike is highest, and the bobbing effect of the VPP bike is most serious. However, while moving on rough terrain, the riding conditions for each of the four full-suspension bikes are more stable than the hard-tail bike

Effect on Spasticity After Performance of Dynamic-Repeated-Passive Ankle Joint Motion Exercise in Chronic Stroke Patients

Spasticity associated with abnormal muscle tone is a common motor disorder following stroke, and the spastic ankle may affect ambulatory function. The purpose of this study was to investigate the short-term effect of dynamic-repeated-passive ankle movements with weight loading on ambulatory function and spastic hypertonia of chronic stroke patients. In this study, 12 chronic stroke patients with ankle spasticity and inefficient ambulatory ability were enrolled. Stretching of the plantar-flexors of the ankle in the standing position for 15 minutes was performed passively by a constant-speed and electrically powered device. The following evaluations were done before and immediately after the dynamic-repeated-passive ankle movements. Spastic hypertonia was assessed by the Modified Ashworth Scale (MAS; range, 0–4), Achilles tendon reflexes test (DTR; range, 0–4), and ankle clonus (range, 0–5). Improvement in ambulatory ability was determined by the timed up-and-go test (TUG), the 10-minute walking test, and cadence (steps/minute). In addition, subjective experience of the influence of ankle spasticity on ambulation was scored by visual analog scale (VAS). Subjective satisfaction with the therapeutic effect of spasticity reduction was evaluated by a five-point questionnaire (1 = very poor, 2 = poor, 3 = acceptable, 4 = good, 5 = very good). By comparison of the results before and after intervention, these 12 chronic stroke patients presented significant reduction in MAS and VAS for ankle spasticity, the time for TUG and 10-minute walking speed (p < 0.01). The cadence also increased significantly (p < 0.05). In addition, subjective satisfaction with the short-term therapeutic effect was mainly good (ranging from acceptable to very good). In conclusion, 15 minutes of dynamic-repeated-passive ankle joint motion exercise with weight loading in the standing position by this simple constant-speed machine is effective in reducing ankle spasticity and improving ambulatory ability

Low Polarization Voltage and High Sensitivity CMOS Condenser Microphone Using Stress Relaxation Design

AbstractIn this paper, a CMOS condenser microphone with high sensitivity and low polarization voltage was designed, simulated and fabricated. Due to CMOS process temperature variant and lattice defects, the poly-membrane would be invoked normal stress and gradient stress. These two residual stresses would deform the membrane and increase the membrane's rigidity. For these concerns, an interlace slots design is utilized to reduce the normal stress up to 90%, and the annealing process is applied to decrease the gradient stress. The acoustical sensitivity was increased considerably to -45dBV at 2.7V bias voltage, and, the noise level is -85dBV at 1KHz

Note on a Single-Machine Scheduling Problem with Sum of Processing Times Based Learning and Ready Times

In the recent 20 years, scheduling with learning effect has received considerable attention. However, considering the learning effect along with release time is limited. In light of these observations, in this paper, we investigate a single-machine problem with sum of processing times based learning and ready times where the objective is to minimize the makespan. For solving this problem, we build a branch-and-bound algorithm and a heuristic algorithm for the optimal solution and near-optimal solution, respectively. The computational experiments indicate that the branch-and-bound algorithm can perform well the problem instances up to 24 jobs in terms of CPU time and node numbers, and the average error percentage of the proposed heuristic algorithm is less than 0.5%

High Genetic Stability of Dengue Virus Propagated in MRC-5 Cells as Compared to the Virus Propagated in Vero Cells

This work investigated the replication kinetics of the four dengue virus serotypes (DEN-1 to DEN-4), including dengue virus type 4 (DEN-4) recovered from an infectious cDNA clone, in Vero cells and in MRC-5 cells grown on Cytodex 1 microcarriers. DEN-1 strain Hawaii, DEN-2 strain NGC, DEN-3 strain H-87, and DEN-4 strain H-241 , and DEN-4 strain 814669 derived from cloned DNA, were used to infect Vero cells and MRC-5 cells grown in serum-free or serum-containing microcarrier cultures. Serum-free and serum-containing cultures were found to yield comparable titers of these viruses. The cloned DNA-derived DEN-4 started genetically more homogeneous was used to investigate the genetic stability of the virus propagated in Vero cells and MRC-5 cells. Sequence analysis revealed that the DEN-4 propagated in MRC-5 cells maintained a high genetic stability, compared to the virus propagated in Vero cells. Amino acid substitutions of Gly104Cys and Phe108Ile were detected at 70%, 60%, respectively, in the envelope (E) protein of DEN-4 propagated in Vero cells, whereas a single mutation of Glu345Lys was detected at 50% in E of the virus propagated in MRC-5 cells. Sequencing of multiple clones of three separate DNA fragments spanning 40% of the genome also indicated that DEN-4 propagated in Vero cells contained a higher number of mutations than the virus growing in MRC-5 cells. Although Vero cells yielded a peak virus titer approximately 1 to 17 folds higher than MRC-5 cells, cloned DEN-4 from MRC-5 cells maintained a greater stability than the virus from Vero cells. Serum-free microcarrier cultures of MRC-5 cells offer a potentially valuable system for the large-scale production of live-attenuated DEN vaccines