Two-dimensional photonic band-gap structures as quasi-metals

By considering waves that propagate out of the transverse plane, we show that common high index materials (eg GaAs) with a 2D array of air holes can act in some ways like a 3D photonic band-gap structure. In particular, we describe a dielectric "quasi-metal" that reflects all propagating light incident from free space

Utilization of antenatal care among pregnant women of urban slums of Dhaka City, Bangladesh

Maternal health services have a potentially critical role in the improvement of reproductive health. The use of health services is related to the availability, quality and cost of the services, as well as to social structure, health beliefs and the personal characteristics of the users. Antenatal care (ANC) is an important determinant of high maternal mortality rate and one of the basic components of maternal care on which the life of mothers and babies depend. It is a key strategy for reducing maternal mortality, but millions of women in developing countries do not receive it. Extracting 3549 women from the 2006-2007 Urban Health Survey, this study assessed the utilization of antenatal care and its related factor in urban slums for pregnant women. A Cross-sectional survey was carried out large, medium and small urban squatter settlements of Dhaka City. Two hundred married women in the age range 15-49 years were interviewed. Socio-demographic characteristics of women who received and who did not receive antenatal care in their previous pregnancy were assessed by frequency distribution and bivariate analysis. Antenatal care used in any of the previous pregnancy among women under study was 861(64.3%). Education and ANC is significantly related suggesting that the higher the level of education the higher is the likelihood of receiving ANC during pregnancy because educated women are aware about the importance of ANC during pregnancy. There is a strong association between the income of the respondents and ANC received by the respondents. This study indicates that overall knowledge about antenatal care was found to be better among women who had utilized antenatal care as compared to women who did not receive antenatal care.. There is also a need to evaluate the services provided by government health facilities and to find out why women are not utilizing the government health services though these services are available at subsidized rate

Low power acousto-optic device in tapered single-mode fibre

We report a new acousto-optic device based on tapered single-mode fibre. Since the overlap between acoustic and optical waves is complete, very little acoustic power (less than 1 microwatt) is required

Low power all-fibre intensity modulator at 2.7MHz

A monolithic single-mode fibre acousto-optic amplitude modulator is reported. Nearly 100% modulation is achieved at a modulation frequency of 2.7MHz for an electrical drive power of 2mW

All fibre polariser using a null coupler

We report a new fibre polariser based on a twisted null taper coupler. The best extinction ratio observed so far is 15dB

3x3 all-fibre routing switch

An all-fibre acousto-optic switch has been constructed from a 3x3 null fused coupler. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB. The switch shares the advantages of an earlier 2x2 switch but with more fibre ports. and should permit the design of compound routing arrays with fewer switching elements per channel

All-fibre 3 x 3 acousto-optic switch

We report an all-fibre 3 x 3 acousto-optic switch. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB

40-MHz all-fiber acoustooptic frequency shifter

We report the development of a 40 MHz four-port all-fibre frequency shifter operating at a wavelength of 1.55 µm. The device has a high conversion efficiency, low drive power requirement and is manufactured from standard telecommunications fibre

Inter-Seasonal Time Series Imagery Enhances Classification Accuracy of Grazing Resource and Land Degradation Maps in a Savanna Ecosystem

<jats:p>In savannas, mapping grazing resources and indicators of land degradation is important for assessing ecosystem conditions and informing grazing and land management decisions. We investigated the effects of classifiers and used time series imagery—images acquired within and across seasons—on the accuracy of plant species maps. The study site was a grazed savanna in southern Kenya. We used Sentinel-2 multi-spectral imagery due to its high spatial (10–20 m) and temporal (five days) resolution with support vector machine (SVM) and random forest (RF) classifiers. The species mapped were important for grazing livestock and wildlife (three grass species), indicators of land degradation (one tree genus and one invasive shrub), and a fig tree species. The results show that increasing the number of images, including dry season imagery, results in improved classification accuracy regardless of the classifier (average increase in overall accuracy (OA) = 0.1632). SVM consistently outperformed RF, and the most accurate model and was SVM with a radial kernel using imagery from both wet and dry seasons (OA = 0.8217). Maps showed that seasonal grazing areas provide functionally different grazing opportunities and have different vegetation characteristics that are critical to a landscape’s ability to support large populations of both livestock and wildlife. This study highlights the potential of multi-spectral satellite imagery for species-level mapping of savannas.</jats:p&gt