Determining acoustical directionality in an impedance tube using multiple fixed microphones

Acoustic impedance of a port or object is a valuable piece of knowledge describing how well sound is transmitted or reflected. The commonly used slotted-line method is labourious and time consuming, requiring manual movement to find the maxima and minima at each frequency. This paper outlines a technique to computationally determine the magnitude and phase of the constituent travelling waves from the standing plane sound wave measurements in an impedance tube. Measured magnitude and phase data from multiple fixed microphones carefully spaced along the length of the impedance tube is numerically fitted to incident and reflected wave models, which can then be used to calculate the complex acoustic impedance at each frequency of interest

A community programme to reduce salt intake and blood pressure in Ghana

Background In Africa hypertension is common and stroke is increasing. Detection, treatment and control of high blood pressure (BP) is limited. BP can be lowered by reducing salt intake. In Africa salt is added to the food by the consumer, as processed food is rare. A population-wide approach with programmes based on health education and promotion is thus possible. Methods We carried out a community-based cluster randomised trial of health promotion in 1,013 participants from 12 villages (628 women, 481 rural dwellers); mean age 55 years to reduce salt intake and BP. Average BP was 125/74 mmHg and urinary sodium (UNa) 101 mmol/day. A health promotion intervention was provided over 6 months to all villages. Assessments were made at 3 and 6 months. Primary end-points were urinary sodium excretion and BP levels. Results There was a significant positive relationship between salt intake and both systolic (2.17 mmHg [95% CI 0.44 to 3.91] per 50 mmol of UNa per day, p < 0.001) and diastolic BP (1.10 mmHg [0.08 to 1.94], p < 0.001) at baseline. At six months the intervention group showed a reduction in systolic (2.54 mmHg [-1.45 to 6.54]) and diastolic (3.95 mmHg [0.78 to 7.11], p = 0.015) BP when compared to control. There was no significant change in UNa. Smaller villages showed greater reductions in UNa than larger villages (p = 0.042). Irrespective of randomisation, there was a consistent and significant relationship between change in UNa and change in systolic BP, when adjusted for confounders. A difference in 24-hour UNa of 50 mmol was associated with a lower systolic BP of 2.12 mmHg (1.03 to 3.21) at 3 months and 1.34 mmHg (0.08 to 2.60) at 6 months (both p < 0.001). Conclusion In West Africa the lower the salt intake, the lower the BP. It would appear that a reduction in the average salt intake in the whole community may lead to a small but significant reduction in population systolic BP

Measuring the Values for Time

Most economic models for time allocation ignore constraints on what people can actually do with their time. Economists recently have emphasized the importance of considering prior consumption commitments that constrain behavior. This research develops a new model for time valuation that uses time commitments to distinguish consumers' choice margins and the different values of time these imply. The model is estimated using a new survey that elicits revealed and stated preference data on household time allocation. The empirical results support the framework and find an increasing marginal opportunity cost of time as longer time blocks are used.

Cascaded wavelength conversions using four-wave mixing in semiconductor optical amplifiers

Wavelength conversion in wavelength-division multiplexed (WDM) communication systems would provide significant network performance improvement. Optoelectronic, cross-gain saturation, and cross phase saturation wavelength converters are candidate technologies that have been well characterized, however, they are not “transparent” to either bit-rate or modulation format. Complete transparency is offered only by ultrafast wave mixing techniques-in the present case four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs)

Mechanical oscillation and cooling actuated by the optical gradient force

In this work we combine the large per-photon optical gradient force with the sensitive feedback of a high quality factor whispering-gallery microcavity. The cavity geometry, consisting of a pair of silica disks separated by a nanoscale gap, shows extremely strong dynamical backaction, powerful enough to excite giant coherent oscillations even under heavily damped conditions (mechanical Q=4). In vacuum, the threshold for regenerative mechanical oscillation is lowered to an optical input power of only 270-nanoWatts, or roughly 1000 stored cavity photons, and efficient cooling of the mechanical motion is obtained with a temperature compression factor of 13-dB for 4-microWatts of dropped optical input power.Comment: 29 pages, 8 figure

Why HITnet kiosks didn\u27t hit the mark for sexual health education of Western Australian Aboriginal youth

Objective: To assess the use, appropriateness of, and staff feedback on specific sexual health modules, which were installed on Heuristic Interactive Technology (HITnet) kiosks at Aboriginal Community Controlled Health Services (ACCHS). The HITnet kiosks were aimed at Aboriginal youth visiting these sites. Methods: Modules on the HITnet kiosks were assessed for (1) cultural appropriateness using Yunkaporta’s Aboriginal pedagogy framework and (2) compliance with the World Health Organization’s (WHO) advice on key elements for comprehensive sexual health education for young people. Data measuring kiosk use were obtained through HITnet kiosk activity reports. An online survey of ACCHS staff was used to qualitatively assess use of, and staff perceptions of, HITnet kiosks. Results: Kiosk modules were consistent with seven of the eight elements of Yunkaporta’s framework and all of the WHO recommendations. The most popular module generated 3,066 purposeful sessions and the least popular module generated 724 purposeful sessions across nine sites in 2012. While teenagers were the most frequent of the kiosk user groups (39.5% in 2012), the majority of users (56%) were not in the target group (i.e. elders 4%, adults 25%, children 27%). Key issues reported by ACCHS staff (n=11) included: lack of clarity regarding staff responsibility for overseeing kiosk functionality; kiosks attracting “inappropriate ages”; and “lack of privacy” based on kiosk location, screen visibility, and absence of headphones preventing discreet access. Conclusions: The modules were tailored to a young Aboriginal audience through technology thought to be appealing to this group. However, barriers to use of the kiosk included kiosk design features, location, and lack of clarity around responsibility for kiosk operation. Implications: Aboriginal youth need easy access to sexual health messages in a ‘safe’, non-judgmental space. Information and communication that is accessible via personal and mobile devices may be a better vehicle than public kiosks

Cross talk penalty in two-channel wavelength conversion by four-wave mixing in a strained semiconductor optical amplifier

A crucial function in wavelength-division multiplexed (WDM) all-optical networks is a wavelength converter. This function enhances wavelength routing options and improves network reconfigurability. Here we present a systematic study of the cross talk penalty as a function of the pump-to-signal power ratio for two 2.5-Gbit/s ASK channels separated by 1.5 nm

Wavelength conversion up to 18 nm at 10 Gb/s by four-wave mixing in a semiconductor optical amplifier

We characterize the conversion bandwidth of a four-wave mixing semiconductor optical amplifier wavelength converter. Conversion of 10-Gb/s signals with bit-error-rate (BER) performance of <10^-9 is demonstrated for wavelength down-shifts of up to 18 nm and upshifts of up to 10 nm

Wavelength conversion for WDM communication systems using four-wavemixing in semiconductor optical amplifiers

Four-wave mixing (FWM) in semiconductor optical amplifiers is an attractive mechanism for wavelength conversion in wavelength-division multiplexed (WDM) systems since it provides modulation format and bit rate transparency over wide tuning ranges. A series of systems experiments evaluating several aspects of the performance of these devices at bit rates of 2.5 and 10 Gb/s are presented. Included are single-channel conversion over 18 nm of shift at 10 Gb/s, multichannel conversion, and cascaded conversions. In addition time resolved spectral analysis of wavelength conversion is presented