2,750 research outputs found
Improving the Classical Geophone Sensor Element by Digital Correction
Geophones are highly sensitive motion transducers that have been used by seismologists and geophysicists for decades. The conventional geophone's ratio of cost to performance, including noise, linearity and dynamic range is unmatched by advanced modern accelerometers. However, the problem of this sensor is that it measures velocity, and that the linear frequency range is limited to frequencies above the natural frequency, typically at 4-12 Hz. It is shown in this paper how the sensor signal can be digitally linearized 2 decades below the natural frequency obtaining a sensor that allows the user to measure displacement, velocity or acceleration with high sensitivity and large dynamic range
Strength training to contraction failure increases voluntary activation of the quadriceps muscle shortly after total knee arthroplasty:a cross-sectional study
OBJECTIVE: The objective of this study was to investigate voluntary activation of the quadriceps muscle during one set of knee extensions performed until contraction failure in patients shortly after total knee arthroplasty. DESIGN: This was a cross-sectional study of 24 patients with total knee arthroplasty. One set of knee extensions was performed until contraction failure, using a predetermined 10 repetition maximum loading. In the operated leg, electromyographic (EMG) activity of the lateral and medial vastus, semitendinosus, and biceps femoris muscles was recorded during the set. Muscle activity (%EMGmax) and median power frequency of the EMG power spectrum were calculated for each repetition decile (10%–100% contraction failure). RESULTS: Muscle activity increased significantly over contractions from a mean of 90.0 and 93.6 %EMGmax (lateral vastus and medial vastus, respectively) at 10% contraction failure to 99.3 and 105.5 %EMGmax at 100% contraction failure (P = 0.009 and 0.004). Median power frequency decreased significantly over contractions from a mean of 66.8 and 64.2 Hz (lateral vastus and medial vastus, respectively) at 10% contraction failure to 59.9 and 60.1 Hz at 100% contraction failure (P = 0.0006 and 0.0187). CONCLUSION: In patients shortly after total knee arthroplasty, 10 repetition maximum–loaded knee extensions performed in one set until contraction failure increases voluntary activation of the quadriceps muscle during the set. CLINICAL TRIALS: Gov-identifier: NCT01713140 to the abstract to increase trial transparency
Squeezed vacuum states from a whispering gallery mode resonator
Squeezed vacuum states enable optical measurements below the quantum limit
and hence are a valuable resource for applications in quantum metrology and
also quantum communication. However, most available sources require high pump
powers in the milliwatt range and large setups, which hinders real world
applications. Furthermore, degenerate operation of such systems presents a
challenge. Here, we use a compact crystalline whispering gallery mode resonator
made of lithium niobate as a degenerate parametric oscillator. We demonstrate
about 1.4 dB noise reduction below the shot noise level for only 300
of pump power in degenerate single mode operation. Furthermore,
we report a record pump threshold as low as 1.35 . Our results
show that the whispering gallery based approach presents a promising platform
for a compact and efficient source for nonclassical light.Comment: 2019 Optical Society of America. Users may use, reuse,
and build upon the article, or use the article for text or data mining, so
long as such uses are for non-commercial purposes and appropriate attribution
is maintained. All other rights are reserve
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