Search results for "transducer"
showing 10 items of 173 documents
Transthoracic three-dimensional echocardiographic volumetry of distorted left ventricles using rotational scanning
1997
The purpose of this study was to evaluate the relation of transthoracic three- and two-dimensional echocardiographic left ventricular volumetry to cineventriculographic volumetry. Twenty-five patients with distorted left ventricles were included in the study. To demonstrate the impact of acquiring data by rotational scanning, we performed three- and two-dimensional echocardiography in 36 latex ventricles with data acquisition in different areas of the ultrasound sectors. Interobserver and intraobserver variability were calculated to test for reproducibility. The three-dimensional imaging system consisted of a rotation motor device, a transthoracic 2.5 MHz transducer, a conventional ultrasou…
A comparison of the triceps surae and residual muscle moments at the ankle during cycling.
1991
The rigid linked system model and principles of inverse dynamics have been widely used to calculate residual muscle moments during various activities. EMG driven models and optimization algorithms have also been presented in the literature in efforts to estimate skeletal muscle forces and evaluate their possible contribution to the residual muscle moment. Additionally, skeletal muscle-tendon forces have been measured, directly, in both animals and humans. The purpose of this investigation was to calculate the moment produced by the triceps surae muscles and compare it to the residual muscle moment at the ankle during cycling at three power outputs (90, 180 and 270 W). Inferences were made r…
Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness
2013
Currently, photoplethysmography (PPG) is a frequently studied optical blood pulsation detection tech- nique among biophotonic and biomedical researchers due to the fact that it shows high potential for estimating the arterial stiffness (AS). The extraction of diagnostically useful information requires standardized measurement pro- cedure with good repeatability. However, the effects of a crucially important factor—the optimal contact pressure (CP) of the probe—are often ignored. Also, CP values are not reported to evaluate those effects. It is hypothesized that AS estimated from PPG pulse wave 2nd derivative parameter b∕a is strongly inconsistent when recorded at nonoptimal probe CP. Our pi…
Biomechanical Loading of Achilles Tendon During Normal Locomotion
1992
Direct in vivo Achilles tendon force measurements open up new possibilities for understanding the loading of the Achilles tendon during natural locomotion. This article describes how these human experiments can be performed. The results of these experiments imply that Achilles tendon forces are unexpectedly high in certain activities (e.g., hopping) and that the rates of loading rather than the absolute magnitudes of the recorded forces may be more relevant for clinical purposes as well as for the construction of artificial tendon materials.
A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop
2013
We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly bent fiber. The wavelength of the notches, distributed in a wavelength span from 1,400 to 1,700 nm, can be tuned by adjusting the diameter of the fiber loop and are sensitive to refractive index changes of the external medium. Sensitivities of 170 and 800 nm per refractive index unit for water solutions and for the refractive index interval 1.40-1.442, respectively, are demonstrated. We estimate a long range resolut…
Comparative analysis of acoustic emission signals generated by electrical discharges measured by the hydrophone and the wideband contact transducer
2005
The paper presents a comparative analysis of the acoustic emission (AE) pulses and signals generated by PDs. For this purpose the measurements of the acoustic emission signals generated by PDs were taken in the multipoint-plane system using a hydrophone placed directly in the area of discharge generation, and the AE pulses using a piezoelectric contact transducer which was on a side wall of a power transformer tub. Next, time runs and amplitude density spectra were drawn. Also the descriptors describing signals in the frequency domain were determined and the time-frequency analysis was carried out, which determined spectrograms for the energy density spectrum.
Highly Sensitive Detection of Naphthalene in Solvent Vapor Using a Functionalized PBG Refractive Index Sensor
2012
We report an optical refractive index sensor system based on a planar Bragg grating which is functionalized by substituted γ-cyclodextrin to determine low concentrations of naphthalene in solvent vapor. The sensor system exhibits a quasi-instantaneous shift of the Bragg wavelength and is therefore capable for online detection. The overall shift of the Bragg wavelength reveals a linear relationship to the analyte concentration with a gradient of 12.5 ± 1.5 pm/ppm. Due to the spectral resolution and repeatability of the interrogation system, this corresponds to acquisition steps of 80 ppb. Taking into account the experimentally detected signal noise a minimum detection limit of 0.48 ± 0.05 pp…
New n-type molecular semiconductor–doped insulator (MSDI) heterojunctions combining a triphenodioxazine (TPDO) and the lutetium bisphthalocyanine (Lu…
2018
International audience; Molecular semiconductor–doped insulator (MSDI) heterojunctions were designed using a new family of sublayers, namely triphenodioxazines (TPDO). The device obtained by combining the tetracyano triphenodioxazine bearing two triisopropylsilylethynyl moieties as a sublayer with the lutetium bisphthalocyanine (LuPc2) as a top layer showed a nonlinear current–voltage characteristic independent of the sign of the polarization, which is the signature of MSDI heterojunctions. Thus, a TPDO was used in a chemical sensor for the first time. Despite LuPc2 being the only material exposed to the atmosphere, the positive response of the device under ammonia revealed the key role pla…
Production and detection of atomic hexadecapole at Earth's magnetic field
2007
Anisotropy of atomic states is characterized by population differences and coherences between Zeeman sublevels. It can be efficiently created and probed via resonant interactions with light, the technique which is at the heart of modern atomic clocks and magnetometers. Recently, nonlinear magneto-optical techniques have been developed for selective production and detection of higher polarization moments, hexadecapole and hexacontatetrapole, in the ground states of the alkali atoms. Extension of these techniques into the range of geomagnetic fields is important for practical applications. This is because hexadecapole polarization corresponding to the $\Delta M=4$ Zeeman coherence, with maxim…
On the Design of Probe Signals in Wireless Acoustic Sensor Networks Self-Positioning Algorithms
2018
A wireless acoustic sensor network comprises a distributed group of devices equipped with audio transducers. Typically, these devices can interoperate with each other using wireless links and perform collaborative audio signal processing. Ranging and self-positioning of the network nodes are examples of tasks that can be carried out collaboratively using acoustic signals. However, the environmental conditions can distort the emitted signals and complicate the ranging process. In this context, the selection of proper acoustic signals can facilitate the attainment of this goal and improve the localization accuracy. This letter deals with the design and evaluation of acoustic probe signals all…