Spectrum collapse, narrow linewidth, and Bogatov effect in diode lasers locked to high-Q optical microresonators.

We present a novel method allowing high-power single-frequency emission with sub-kHz linewidth from a compact multi-frequency diode laser locked to high-Q optical microresonator. Using high-Q MgF2microresonator and multi-frequency diode laser operating at 1535 nm with the output power of 100 mW and an emission spectrum consisting of approximately 50 lines with MHz linewidth, we observed a spectrum collapse to a single line or several lines with a sub-kHz linewidth and output power power of 50 mW. The Bogatov effect predicted more than 30 years ago was observed and studied in the spectrum of the locked laser. For analysis of the considered effect, original theoretical model taking into account self-injection locking effect, mode competition and Bogatov asymmetric mode interaction was developed and numerical modeling was performed. All numerical results are in a good agreement with our experimental data. Accurate analytical estimations for the parameters critical for the considered effect were obtained. The proposed method may be applied for different types of diode lasers operating in different spectral ranges.

Role of plantar fascia in the load bearing capacity of the human foot.

Plantar fascia release is an accepted and widely used surgical way to reduce heel pain, however its effect of the load bearing characteristics of the foot is not well studied. A simple biomechanical model is developed here to analyze load bearing mechanism of the foot during the stance phase of the gait cycle. Quasilinearization is used for the system identification, and all model's parameters are determined from the in vivo tests. The model is used to compare the load bearing mechanism of different pathological situations. The results of the study suggest that the plantar fascia carries as much as 14% of the total load on the foot. Its surgical release decreases dynamic loading on the ankle by only 10%. It is also found that the lowering of the arch degenerates the load bearing capacity of the foot. Thus, the plantar fascia plays an important part in the load bearing by the foot and its surgical release should be carefully considered.

Biomechanics of stair walking and jumping.

Physical activities such as stair walking and jumping result in increased dynamic loading on the human musculoskeletal system. Use of light weight, externally attached accelerometers allows for in-vivo monitoring of the shock waves invading the human musculoskeletal system during those activities. Shock waves were measured in four subjects performing stair walking up and down, jumping in place and jumping off a fixed elevation. The results obtained show that walking down a staircase induced shock waves with amplitude of 130% of that observed in walking up stairs and 250% of the shock waves experienced in level gait. The jumping test revealed levels of the shock waves nearly eight times higher than that in level walking. It was also shown that the shock waves invading the human musculoskeletal system may be generated not only by the heel strike, but also by the metatarsal strike. To moderate the risk of degenerative joint disorders four types of viscoelastic insoles were utilized to reduce the impact generated shock waves. The insoles investigated were able to reduce the amplitude of the shock wave by between 9% and 41% depending on the insole type and particular physical activity. The insoles were more effective in the reduction of the heel strike impacts than in the reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping trials than in the stair walking studies. The insoles were ranked in three groups on the basis of their shock absorbing capacity.

Shock absorption of meniscectomized and painful knees: a comparative in vivo study.

The principles of a noninvasive measurement of the shock absorbing capacity of the knee are presented. Accelerometry, which has been proven to be a useful tool for noninvasive measurements in biomechanical investigation, was employed for quantitative evaluation of the knee's shock absorbing capacity by registration of bone vibrations resulting from the gait. Results of the experiments show that both patients with painful knee and patients after meniscectomy suffer from insufficient shock absorbing capacity of the knee. It was found that the shock absorbing capacity of a normal knee is about 20% higher than that of a pathological one. The results indicate that while meniscectomy may reduce pain, instability, swelling, etc. in an injured knee, it cannot improve its reduced shock absorbing capacity, which eventually will lead to development of degenerative osteoarthritis. It seems that the pain syndrome is a biological reaction to severe repetitive overloading of the knee. Noninvasive in vivo determination of the knee's shock absorbing properties may be useful as an additional clinical technique to reveal a knee's pathology. It may lead to early discovery of knee insufficiency, so that preventive steps can be taken to delay or reverse the process of degeneration.

Low back pain: conservative treatment with artificial shock absorbers.

A new method of conservative treatment for low back pain (LBP) was studied by follow-up investigation of 382 patients during the last five years. The attempt to reduce repetitive impulsive intervertebral impact in the troublesome S1-L5-4 area by significant improvement of the foot's attenuational capacity through artificial viscoelastic shock absorbing was prompted by the authors' work on decreased capability of LBP spines to attenuate axially propagated walking stresses. Viscoelastic shoe inserts were used in addition to light flexible shoes as artificial shock absorbing devices. Maximal amplitudes of bone oscillation during walking were reduced by about 40% by the viscoelastic inserts. Rapid and surprisingly significant improvement of pain syndrome and patient mobility occurred in about 80% of the patients. The accelerographic patterns recorded on a sacrum of patient with LBP were unusual for a healthy subject; they usually disappeared after treatment in LBP cases. Results suggested that poor walking impact attenuation was a true cause for prolonging intervertebral structures overstrain and consequent degeneration. It seemed logical that as spine damage could be explained primarily by prolonged impulsive overstrain, treatment must include viscoelastic inserts which increase foot shock absorbing capacity and help cushion the spine.

Measurement of the impulsive bone motion by skin-mounted accelerometers.

A measurement system was designed to investigate longitudinal wave propagation through the lower extremity generated from foot strikes. The principal goal of the design was to eliminate measurement time lag and amplitude reduction, such that the acceleration measured by Skin Mounted Accelerometer--SMA is equal to the actual acceleration of the bone measured by Bone Mounted Accelerometer--BMA. For accurate dynamic measurement, it is important that the gain and phase of the measurement system are as close as possible to a constant and zero, respectively, for the frequency range being covered. An in vitro experiment was carried out to simultaneously measure skin and bone accelerations. The obtained information was used for identification of a linear spring/damper model representing the interface between the BMA and the SMA. The present work showed that the SMA overestimated the BMA by 12 percent in the signals between 15-30 Hz.