Specific Features of MuGFETs at High Temperatures over aWide Frequency Range

2012 ◽  
pp. 251-278
Keyword(s):  
High Temperatures ◽  
Frequency Range

scholarly journals A Study on the Dielectric Behaviour of Epoxy/Hafnium Oxide Nanopowder Composites

2011 ◽  
Vol 20 (5) ◽  
pp. 096369351102000 ◽  
Author(s):  
S.N. Georga
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
High Temperatures ◽  
High Frequency ◽  
Dielectric Response ◽  
Hafnium Oxide ◽  
Filler Concentration ◽  
High Frequency Range ◽  
Frequency Range ◽  
Low Frequencies

The dielectric response of 10 and 15phr epoxy/HfO2 nanocomposite systems has been studied in a wide frequency and temperature range. The experimental results show an enhancement of the dielectric permittivity with increasing filler concentration. The dielectric spectra reveal the presence of α-relaxation and a weak MWS effect. In the high frequency range the real part of the electrical conductivity obeys the Universal Dielectric Response (UDR), whereas at low frequencies and high temperatures DC conductivity is observed. VFT (Vogel-Fulcher-Tamann) parameters are calculated for all measured specimens.

Bridge method for studying the spectra of current fluctuations in tungsten filaments at the frequency range 1.5∙10–5–5∙10–1 Hz

2021 ◽  
pp. 18-25
Author(s):  
Yuriy A. Zakharov ◽  
Sergey S. Gots ◽  
Rauf Z. Bakhtizin
Keyword(s):  
Spectral Analysis ◽  
High Temperatures ◽  
Personal Computer ◽  
Low Frequency ◽  
Current Fluctuations ◽  
Frequency Range ◽  
Bridge Method ◽  
Measurement Results ◽  
Tungsten Filaments ◽  
Frequency Current

The problem of the absence of methods for measuring low-frequency fluctuation processes at high temperatures is considered. An original bridge method is proposed for measuring the spectra of low-frequency current fluctuations in tungsten filaments of electric lamps in a controlled temperature range of 300–2700 K. Application of the bridge measurement scheme allows us to reduce the influence of degradation processes in the filament and the power source's own noise on the measurement results by several orders of magnitude. Spectral analysis of low frequency current fluctuations is performed at the frequency range 1.5∙10–5–5∙10–1 Hz using an automated setup based on a personal computer under the control of specially developed software.

Characterisation and Validation of an Optical Pressure Sensor for Combustion Monitoring at Low Frequency

2021 ◽  
Author(s):  
Gianluca Nicchiotti ◽  
Stephane A. Page ◽  
Krzysztof Solinski ◽  
Lukas Andracher ◽  
Nina Paulitsch ◽  
...  
Keyword(s):  
High Temperatures ◽  
Low Frequency ◽  
Frequency Range ◽  
New Paradigm ◽  
Low Frequencies ◽  
Efficient Operation ◽  
Machine Performance ◽  
Novel Approach ◽  
Pressure Dynamics ◽  
Optical Pressure

Abstract This paper introduces a novel approach to monitor pressure dynamics in turbomachinery. This innovation is motivated by the need expressed by machine OEMs and end-users to detect and avoid combustion instabilities, as well as lean-blowout (LBO), in low emission combustion systems. Such situations are often characterised by a marked increase of pressure signals in low frequency range. The piezoelectric technology, conventionally used for pressure measurements, presents sensitivity and stability issues at high temperatures and low frequencies. Here a new paradigm for pressure sensing, based on optical interferometry, is characterised and validated. The interferometric sensing system is designed to provide a larger range of measurement frequencies with better performance, in the low frequency range (< 50Hz), while exposed to high temperatures. This unique feature allows the real-time observation of events, such as the specific behaviour of a low frequency flame dynamic, which is characteristic of an imminent LBO. This improved monitoring system will support an optimisation of the machine performance, leading to a safer, cleaner, more flexible and more cost-efficient operation for the end-user. The novel measurement system has been characterised under non-reactive and reactive conditions within the frame of a joint study between Meggitt SA, Combustion Bay One e.U. and FH Joanneum GmbH. The technology is first described, including the relevant hardware and software components of the measurement chain. The different experimental set-ups and conditions are also illustrated. The results of the test campaign and their subsequent analysis are then presented, supporting the expected advantages over piezoelectric technology. In conclusion, a possible strategy for the detection of LBO precursors based on low frequency data is proposed.

In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

1991 ◽  
Vol 49 ◽  
pp. 660-661
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
High Temperatures ◽  
Image Resolution ◽  
Atomic Processes ◽  
Crystal Surfaces ◽  
Beam Radiation ◽  
Surface Areas ◽  
Transmission Electron ◽  
Reflection Electron Microscopy ◽  
Gas Reactions

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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