The piezoelectric cantilever with a tip mass (Mass-PC), as a conventional vibration energy harvester, usually works at its fundamental frequency matching ambient excitation. By attaching an oscillator to a piezoelectric cantilever (Osc-PC), a double-mode energy harvester is developed to harvest more power from two matched ambient driving frequencies. Meanwhile, it allows the first operating frequency of the Osc-PC to be adjusted to be very low with only a limited mass attached. A distributed-parameter model of this harvester and the explicit expressions of its operating frequencies are derived to analyze and design the Osc-PC. Numerical investigations reveal that a heaver oscillator placed near the clamped end of the piezoelectric cantilever has better performance at the given exciting frequencies. Following the specified design criteria, an Osc-PC whose operating frequencies match two given exciting frequencies was constructed for the purpose of experimental testing. The results show that, compared to that of a corresponding Mass-PC whose operating frequency matches the lower exciting frequency, the energy harvesting efficiency of the Osc-PC increases by almost four times at the first operating frequency, while the output power at the second operating frequency of the Osc-PC accounts for 68% of that of the Mass-PC.
The phase-shifting algorithms are essential for a Fizeau interferometer to reconstruct the topography of the optical element’s surface or wavefront. There are differences between different algorithms for reconstruction results, especially for the suppression of noise. To acquire a more accurate Instrument transfer function (ITF) which reflects the axial spatial frequency response of a Fizeau interferometer, the algorithm transfer function which represents the characteristics of the calculation process in spatial frequency was proposed. In this paper, numerical simulations calculated and analyzed several transfer functions of the well-known phase-shifting algorithms. Then, the ITFs of a step plate with a height of 118 nm were measured with different algorithms by experiments and the results were analyzed. The simulations and experimental results indicate that the phase-shifting algorithm has an effect on the ITF measurement but it is not a key factor affecting the ITF measurement.
In a beam-like structure, which acts as a vibration transmission path, transmitted energy can be effectively suppressed by employing an active force. The energy transmission control can also be achieved at a certain frequency band without external energy by attaching a mechanical system, which may be composed with piezoelectric transducers, on the beam. A mass-spring attachment is modeled to investigate the relationship between the mechanical impedance and the working frequency. Then, the relationship between the working bandwidth and circuit parameters of the piezoelectric transducer is developed to show the feasibility of adjusting the working bandwidth. A case study of a passive system called as dog-bone structure was carried out to show that control range can be expanded by changing the dimension of the system. In addition, the piezoelectric constant and capacity also determine the control performance.
Problem background
Early detection of acute ischemic stroke (AIS) may provide patients with benefits against harmful health and financial impacts. The use of non-contrast computed tomography images for early detect of the infarct remains controversial.
Materials & methods
Here, we used the UCATR algorithm to extract the pixel values of the infarct and the corresponding contralateral healthy area as the control surface in each NCCT slice for the whole brain. Magnetic resonance imaging results were used to verify both areas. We found significant pathological changes in the infarct compared with the corresponding contralateral healthy area in each NCCT slice.
Attained results
Our approach validated that NCCT can be used to detect the lesion area in the early stage of AIS.
Conclusions
With obvious advantages such as saving time and the ability to quantify the infarct volume, this approach could help more patients survive the fatal and irreversible pathological process of AIS and improve their quality of life after AIS treatment.
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