Workmen\u27s Compensation

Covers cases on horseplay during the course of employment

Recent Community Property Decisions

Covers cases on the character of federal savings bonds purchased with community funds and property acquired under installment purchase contracts

Signal diversity for laser-Doppler vibrometers with raw-signal combination

The intensity of the reflected measuring beam is greatly reduced for laser-Doppler vibrometer (LDV) measurements on rough surfaces since a considerable part of the light is scattered and cannot reach the photodetector (laser speckle effect). The low intensity of the reflected laser beam leads to a so-called signal dropout, which manifests as noise peaks in the demodulated velocity signal. In such cases, no light reaches the detector at a specific time and, therefore, no signal can be detected. Consequently, the overall quality of the signal decreases significantly. In the literature, first attempts and a practical implementation to reduce this effect by signal diversity can be found. In this article, a practical implementation with four measuring heads of a Multipoint Vibrometer (MPV) and an evaluation and optimization of an algorithm from the literature is presented. The limitations of the algorithm, which combines velocity signals, are shown by evaluating our measurements. We present a modified algorithm, which generates a combined detector signal from the raw signals of the individual channels, reducing the mean noise level in our measurement by more than 10 dB. By comparing the results of our new algorithm with the algorithms of the state-of-the-art, we can show an improvement of the noise reduction with our approach

Lateral resolution limit of laser Doppler vibrometer microscopes for the measurement of surface acoustic waves

The lateral or transverse resolution of single-point interferometers for vibration measurement is especially critical for microelectromechanical systems (MEMS) vibrating up to the gigahertz range. In this regime, the acoustic wavelengths are typically in the range of the size of the laser focus. Thus, a successful vibration measurement requires distinct knowledge about the lateral resolution limit and its dependencies with instrumentation parameters. In this paper, we derive an analytic approximation formula, which allows for estimation of the systematic measurement deviation of the vibration amplitude and, thus, a definition of the lateral resolution limit of single-point interferometers for vibration measurement. Further, a compensation and an optimum numerical aperture are proposed the reduce the measurement deviation. For this, the model includes a laser-interferometer microscope of Mach-Zehnder type with Gaussian laser beams considering the Gouy effect and wavefront curvature. As a measurement scenario, an unidirectional surface acoustic wave (SAW) is regarded. The theoretic findings have been validated in the experiment with a representative vibration measurement on a SAW filter at 433 MHz with our heterodyne laser-Doppler interferometer with offset-locked semiconductor lasers. The provided formulas help instrument designers and users to choose suitable instrument parameters, especially the numerical aperture of the utilized microscope objective

Educational access in south Africa: country analytic review

Meaningful access to education requires more than full enrolment; it requires high attendance rates, progression through grades with little or no repetition, and learning outcomes that confirm that basic skills are being mastered. This Review describes and explains patterns of access to schools in South Africa for children between the ages of 5 and 15 years. It outlines policy and legislation on access to education and provides a statistical analysis of learners enrolled in school, out-of-school children and learners vulnerable to exclusion. The quantitative data is supported by a review of research which explains the patterns of access and exclusion. The Review also analyses the way in which educational access is conceptualised, and identifies areas for future research

Model validation and prediction of photoacoustic tumor detection with LDV

Photoacoustic (PA) imaging enables the detection of tumors with ultrasound sensors. A laser Doppler vibrometer (LDV) measures sound waves without contact and may enable non-contact PA imaging (PAI). A successful acquisition with LDV of the PA-signals generated by a tumor irradiated by a pulsed laser depends on several factors: the metrological characteristics of the LDV, the characteristics of the laser pulse as well as the properties of the tumor and of the tissue. In this work, we prove with experiments on tissue-mimicking phantoms the validity of a simulation model based on prior work. We use the validated model to simulate the photoacoustic tumor detection with LDV. Subsequently, we estimate the photoacoustic tumor detection capabilities of a self-designed LDV with the validated model. We derive the limits for the minimal detectable size of tumors for a given depth in tissue. The smallest inclusion detected with our LDV-system on a tissue-mimicking phantom was a sphere with a radius of 200 μm at a depth of 14 mm. With our experimentally validated model, we have predicted the possibility to detect an inclusion in breast tissue with a radius up to approximately 300 μm at a depth of 22 mm

The persistence of gender inequality in Zimbabwe: factors that impede the advancement of women into leadership positions in primary schools

We investigated and analysed the factors that women teachers consider asbarriers to their advancement to headship positions in Zimbabwean primary schools. Specifically, we sought to identify the factors perceived by women school heads to be causes of persistent under-representation of women in school headship positions. Data were collected through structured face-to-face interviews and focus group discussions with 13 experienced women school heads. The findings revealed that although the majority of the women teachers in the study sample were qualified for promotion to school headship positions, they had not attempted to apply for them. The majority of the women teachers in the study sample were adequately qualified for promotion to school headship positions. Indeed, a large number of them either had a university degree or were pursuing degree studies and also had extensive experience. But most of themhad not attempted to apply for school headship and hence were still classteachers. Gender stereotypes were shown to be one of the major causes ofpersistent under-representation of women in primary school headship. Theinfluence of gender role stereotypes was found to manifest in the form of low self esteem; lack of confidence; women’s perception that their role in the family overrides all other roles; and lack of support from the home and the workplace

Signal diversity for the reduction of signal dropouts and speckle noise in a laser-Doppler extensometer

A recently demonstrated laser-Doppler extensometer is affected by signal dropouts caused by speckle noise, whereby the carrier-to-noise ratio (C/N) falls below the so-called frequency-modulation threshold. In this article, we present a new optical setup with polarization signal diversity for reducing speckle-induced dropouts dramatically. The probability of a signal dropout can be substantially reduced using weighted combination signals from different photodetectors collecting the scattered light at two orthogonal polarizations. Therefore, we prove in this paper that signal diversity enables a laser-Doppler extensometer for industrial applications. Furthermore, a theoretical model based on the speckle statistics for estimating the probability of signal dropout is introduced. The relationship between the occurrence of signal dropouts and the demodulation bandwidth is studied. The experimental results of the occurrence of dropouts highly match the theoretical estimated probability distribution. Finally, strain measurement demonstrates a significant reduction of speckle noise with the implemented technique