Giga-Hertz Transverse Electromagnetic (GTEM) cell is a simpler and cheaper alternative to the full-scale anechoic chamber. It is an equipment of choice in a lot of partial discharge (PD) research, ...especially for antenna validation. According to a good practice the cell must be validated, or also known as calibrated, for its usability. The calibration term means validating the uniformity of electrical field produced at the point of measurement. This paper introduced a verification technique to be used to validate the integrity of input and response signals. This step is essential so that the reproducibility of the experiment is warranted and also to support the calibration analysis result. It was found that the input and response signals were reproducible and consistent. The calibration analysis on the existing bespoke GTEM showed that electric field uniformity at the prescribed area of testing complied with an established practice. Therefore, the GTEM cell can be used to conduct related experiment.
Electron avalanches in liquid argon mixtures Kim, J.G.; Dardin, S.M.; Kadel, R.W. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2004, Letnik:
534, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon (xe) in the high electric field (
>
7
MV/cm) near the point of a chemically etched needle in a ...point–plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure-dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure-independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure-dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure-independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 or 122
keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure-dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.
Partial discharges may occur in defective insulation systems of high voltage equipment, such as gas insulated substations and power transformers. These discharges generate electromagnetic waves that ...can be detected using ultrahigh frequency (UHF) sensors. UHF sensors must meet certain sensitivity criteria over a wide frequency range so as to be capable of detecting small discharges. Sensor frequency response is measured using a gigahertz transverse electromagnetic calibration system. Previous research has shown that finite-difference time-domain (FDTD) simulation of the calibration process can accurately model the response of the existing sensors. The work reported here demonstrates how a new sensor can be designed entirely using FDTD modeling. The proposed new partial discharge sensor has a physical construction that was selected to make it more robust, simple to manufacture, and convenient to install on metal-clad high-voltage apparatus. The internal structure of the UHF sensor was developed and optimized entirely within the FDTD software domain before the physical device was manufactured and tested. Simulated and experimental calibration results were found to be in agreement to within 10%. This finding validates the design methodology and optimization process. The approach described in this paper will help to streamline the design of UHF partial discharge sensors for specific applications in future.
Electron avalanching in liquid argon is being studied as a function of voltage, pressure, radiation intensity, and the concentrations of certain additives, especially xenon. The avalanches produced ...in an intense electric field at the tip of a tungsten needle are initiated by ionization from a movable americium (/sup 241/Am) gamma-ray source. Photons from xenon excimers are detected as photomultiplier signals in coincidence with the current pulse from the needle. In pure liquid argon, the avalanche behavior is erratic, but the addition of even a small amount of xenon (/spl les/100 ppm) stabilizes the performance. Similar attempts with neon (30%) as an additive to argon have been unsuccessful. Tests with higher energy gamma-rays (/sup 57/Co) yield spectra and other performance characteristics quite similar to those using the /sup 241/Am source. Two types of signal pulses are commonly observed: a set of pulses that are sensitive to ambient pressure and a set of somewhat smaller pulses that are not pressure dependent.
Previously, we showed how small admixtures of xenon (Xe) stabilize electron avalanches in liquid Argon (LAr). In the present work, we have measured the positive charge carrier mobility in LAr with ...small admixtures of Xe to be 6.4/spl times/10/sup -3/ cm/sup 2//Vs, in approximate agreement with the mobility measured in pure LAr and consistent with holes as charge carriers. We have measured the concentration of Xe actually dissolved in the liquid and compared the results with expectations based on the amount of Xe gas added to the LAr. We also have tested LAr doped with krypton to investigate the mechanism of avalanche stabilization.
To compare the corneal clarity measurement between penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK) in patients with keratoconus, using densitometry software for the ...Oculus Pentacam.
A retrospective comparative study was carried out at Manchester Royal Eye Hospital. Data were collected 12-18 months after corneal transplantation for keratoconus, including postoperative corneal densitometry, best corrected visual acuity (BCVA), central corneal thickness (CCT), and other relevant clinical details.
Analysis of 37 keratoconus eyes from 36 patients found there was a significantly higher corneal densitometry measurement after DALK than PK. This was predominantly in the posterior layer of the concentric zone 0-2 mm of the cornea (
=0.0004). A significant correlation was found between postoperative BCVA and corneal densitometry in DALK groups at full thickness (
=0.03). This correlation was seen in the central 0-2 mm (
=0.03) and posterior 0-2 mm (
=0.04) zones. In addition, within the DALK group, a correlation was found between central corneal thickness and densitometry at full thickness 2-6 mm (
=0.007), central 0-2 (
=0.04), central 2-6 mm (
=0.01), and at posterior 2-6 mm (
=0.01) zones.
This study showed that corneal densitometry measurement differs depending on the type of corneal transplantation used to treat keratoconus patients. Densitometry may have an important role to play in the final BCVA achieved by patients undergoing corneal transplantation for keratoconus. Analysis of Oculus Pentacam images provides an objective evaluation to monitor the cornea status after the surgery.
Objective: The purpose of this study was to analyse the effectiveness of resistance exercise in functional fitness in women with primary Sjögren's syndrome (pSS).
Method: This is a randomized ...controlled clinical trial with 51 volunteers: 26 allocated to the exercise group (GEX) and 25 to the control group. The GEX underwent a supervised resistance-training programme for 16 weeks, with two sessions per week. The outcomes measured were: functional capacity (FC), by the Fullerton Functional Fitness Test; Daily Motor Activity Index (DMAI), evaluated by an actigraph; disease activity, by the ESSDAI; and quality of life, by the 36-item Short Form Health Survey (SF-36). The evaluations were performed by a blind evaluator at baseline (TØ) and after 16 weeks (T16wk).
Results: In the GEX, all FC parameters demonstrated improvement, except for the upper limb flexibility test (p = 0.866): upper and lower limb strength, flexibility, aerobic capacity, and agility (all p < 0.01). A similar situation occurred in the SF-36, where all domains demonstrated improvement except for the emotional aspect (p = 0.710): FC, physical aspects limitation, general health status, vitality, social aspects, and mental health (all p < 0.01). The DMAI (p = 0.2) and EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) (p = 0.284) did not change. No significant improvement was observed in the control group.
Conclusion: The supervised resistance exercise programme did not worsen the DMAI or disease activity, demonstrating the safety of the intervention, and was effective in improving FC and quality of life in women with pSS.
Registry identifier (clinical trials.gov): NCT03130062.
Corneal characteristics are unique to each eye and can vary among different levels of refractive errors. However, minimal data are available in the literature on corneal characteristics in myopic ...Malay school children including the difference between the low myopic group and the moderate myopic group. Therefore, this study aims to determine the corneal characteristics of myopic Malay school children and their associations with axial length.
A total of eighty-four data samples were extracted from forty-two myopic Malay school children. Measurements of the central corneal thickness (CCT), corneal curvature, corneal diameter, and axial length were measured using Lenstar LS900, a non-contact optical biometer. Data were later stratified by the spherical equivalent refraction (SER) into a low myopic group and a moderate myopic group, and paired
-test were employed to determine the differences in the corneal characteristics between these two groups. Univariate and multivariate linear regressions were performed to identify factors that are significantly associated with axial length.
There was no significant difference in the CCT, corneal curvature and corneal diameter between the low myopic group and the moderate myopic group (t
=0.015,
=0.99), (t
=-0.802,
=0.43) and (t
=-0.575,
=0.57), respectively. Pearson univariate correlation analysis found that axial length significantly correlated with corneal curvature (r=-0.765,
<0.001) and corneal diameter (r=0.614,
<0.001) but no significant correlation found with CCT (r=0.046,
=0.68). Multiple regression analysis showed that axial length was significantly associated with a flatter corneal curvature (
<0.001), older age (
<0.001) and larger corneal diameter (
=0.02).
This study reported the corneal characteristics in myopic Malay school children and its associations with axial length. Results of this study can serve as a reference value for the myopic Malay schoolchild population.
Myopia control lenses have been shown to modify visual function; however, it is arguable if these changes are short-term or long-term. We investigated the changes in accommodative behaviour and ...binocular vision functions of Malay myopic children who participated in a myopia control trial utilising spectacle lenses (n = 40). This article presents baseline accommodation and binocular vision measurements. The mean (± SD) age, spherical equivalent measured by cycloplegic autorefraction, and axial length (AL) for the right eyes were 10.00 ± 1.47 years, -3.02 ± 1.20 D, and 24.42 ± 0.93 mm, respectively. All participants had good distance and near visual acuities with high-contrast charts (100%), which were significantly better than low-contrast charts (10%) (
< 0.001). The mean (± SD) accommodative lag at baseline was 1.14 ± 0.35 D, while monocular and binocular accommodative amplitudes were 15.35 ± 2.07 D and 16.82 ± 2.27 D, respectively. Malay schoolchildren in this study were more esophoric at near compared to distance, with an accommodative-convergence over accommodation (AC/A) ratio of 5.64 ± 0.66 ∆/D. A higher degree of myopia was found to be associated with a longer AL (
= -0.49,
< 0.05) and higher esophoria at near (
= -0.46,
< 0.05). These baseline measures are consistent with data from other studies showing that myopic children have a high accommodative lag, an elevated AC/A ratio, a longer AL, and are more esophoric at near. The measures reported herein will serve as a basis for examining changes that occur within 12 months of wearing myopia control spectacle lenses.
Previous research has shown that some viscosity modifier additives are able to adsorb from oil solution on to metal surfaces to produce thick, viscous boundary films. These films enhance lubricant ...film formation in slow-speed and high temperature conditions and thus produce a significant reduction in friction. This article describes a systematic study of this phenomenon, which makes use of the versatile nature of polymethacrylate (PMA) chemistry. Dispersant polymethacrylates with a range of different functionalities, molecular weights, and architectures have been synthesized using controlled radical polymerization techniques. The influence of each of these features on boundary film formation and friction has been explored using optical interferometry and friction versus speed measurement. From the results, guidelines have been developed for designing PMAs having optimal boundary lubricating and, thus, friction-reducing properties.
Review led by Selda Gunsel
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