Coherent population trapping with polarization modulation

Coherent population trapping (CPT) is extensively studied for future vapor cell clocks of high frequency stability. In the constructive polarization modulation CPT scheme, a bichromatic laser field with polarization and phase synchronously modulated is applied on an atomic medium. A high contrast CPT signal is observed in this so-called double-modulation configuration, due to the fact that the atomic population does not leak to the extreme Zeeman states, and that the two CPT dark states, which are produced successively by the alternate polarizations, add constructively. Here we experimentally investigate CPT signal dynamics first in the usual configuration, a single circular polarization. The double-modulation scheme is then addressed in both cases: one pulse Rabi interaction and two pulses Ramsey interaction. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We show that a simple sevenlevel model explains the experimental observations. The double-modulation scheme yields a high contrast similar to the one of other high contrast configurations like push-pull optical pumping or crossed linear polarization scheme, with a setup allowing a higher compactness. The constructive polarization modulation is attractive for atomic clock, atomic magnetometer and high precision spectroscopy applications.Comment: 13 pages, 15 figures. To be published in Journ. Appl. Phys.(2016

Intraguild predation between lady beetles and lacewings: outcomes and consequences vary with focal prey and arena of interaction

Citation: Noppe, Christophe, J. P. Michaud, and Patrick De Clercq. 2012. “Intraguild Predation Between Lady Beetles and Lacewings: Outcomes and Consequences Vary With Focal Prey and Arena of Interaction.” Annals of the Entomological Society of America 105 (4): 562–71. https://doi.org/10.1603/AN11165.We examined reciprocal intraguild predation (IGP) and cannibalism among various combinations of Coleomegilla maculata DeGeer and Chrysoperla carnea Stephens larvae as they developed feeding on greenbugs, Schizaphis graminum Rondani, on sorghum plants in microcosms. Pairs of C. maculata larvae suppressed aphids better than pairs of C. carnea larvae or heterospecific larval pairs and yielded the highest rate of plant survival. IGP by C. carnea larvae occurred mostly in the first instar, whereas C. maculata larvae were more aggressive in later instars. Although C. carnea was the superior intraguild predator, winning 62.7% of contests in microcosms, this value increased to 88.9% when the experiment was repeated in petri dishes without plant material, regardless of whether greenbugs or eggs of Ephestia kuehniella Zeller were offered as focal prey. Provision in petri dishes of the sessile, higher quality prey (Ephestia) as opposed to greenbugs, improved the survival of solitary larvae and delayed cannibalism and IGP until later developmental stages in both species. Larvae of C. maculata that cannibalized took longer to develop and weighed less at pupation, independent of the arena or prey offered. Although larvae of C. carnea did not pay a cost for cannibalism or IGP in microcosms, there were some negative developmental effects of IGP in petri dishes, particularly on the Ephestia diet. These results illustrate how the plant, as a substrate, can mediate the strength of IGP interactions and how the relative suitability of the focal prey can influence both the timing and consequences of cannibalism and IGP

Predicting gully erosion susceptibility in South Africa by integrating literature directives with regional spatial data

Gully erosion has been identified as a severe land degradation process with environmental and socio-economic consequences. Identifying areas susceptible to gully erosion will aid in developing strategies to inhibit future degradation. Various approaches have been implemented to predict and map gully erosion susceptibility but are mostly restricted to small geographical extents because of process limitations. Here, we introduce a novel method that predicts gully erosion susceptibility on a regional/national scale (1.22 million km 2) by synthesising literature directives with a statistical approach. Findings from a literature review were used to extract physiographic properties associated with gully erosion that was conditioned to characterise susceptibility by using the Frequency Ratio model. The conditioned physiographic properties were aggregated by a weighted overlay procedure using an aggregation of controlling factors derived from the literature review as a weighting system. The gully susceptibility index (GSI) model was validated against a published gully inventory map (n = 163 019) and randomly generated 1-km 2 tessellation zones from which primary validation data were derived. Although uncertainties within the modelling procedure exist (e.g., gully site distribution, the spatial resolution of input data and determination of gully points), the validation shows that the GSI model is generally robust, identifying areas of contrasting susceptibilities. Furthermore, findings converge with other susceptibility metrics, which have been derived by different methodologies. Because empirical gully erosion research has been conducted worldwide, this model could be applied to regional-scale gully susceptibility modelling assessments (as a solitary method or combined with primary data) in other parts of the world. Additionally, the GSI model can be adopted to model environmental change scenarios.</p

Welcome Home: Exploring Housing Options for Adults with Developmental Disabilities in Maine

This poster describes various housing options offering varying levels of supports for adults living with developmental disabilities in Maine. It also provides information for housing options in other states.https://digitalcommons.library.umaine.edu/ccids_posters/1036/thumbnail.jp

Evaluating the effects of generalisation approaches and DEM resolution on the extraction of terrain indices in KwaZulu Natal, South Africa

Digital elevation model (DEM) data are elemental in deriving primary topographic attributes which serve as input variables to a variety of hydrologic and geomorphologic studies. There is however still varied consensus on the effect of DEM source and resolution on the application of these topographic attributes to landscape characterisation. While elevation data for South Africa are available from several major sources and resolutions: Shuttle Radar Topographic Mission (SRTM), Earth ENV and Stellenbosch University DEM (SUDEM). Limited research has been conducted in a local context comparing the extraction of terrain attributes to high resolution Digital Terrain Data (DTM) such as LiDAR (Light Detection and Ranging) that are becoming increasing available. However, the utility of LiDAR to topographic analyses presents its own challenges in terms of operational-relevant resolution, processing demands and limited spatial coverage. There is a need to quantify the impact that generalisation approaches have on simplifying detailed DEMs and to compare the accuracy and reliability of results between high resolution and coarse resolution data on the extraction of localized topographic variables. In this regional study, we analyse the accuracy on selected local terrain attributes: elevation, slope and topographic wetness index derived from DEMs from varying sources, at different spatial resolutions and using three generalisation algorithms, namely: mean cell aggregation, nearest neighbour and hydrological corrected topo-to-raster. We show that topographic variable extraction is highly dependent on DEM source and generalisation approach and while higher resolution DEMs may represent the “true“ surface more accurately, they do not necessarily offer the best results for all extracted variables. Our results highlight the caveats of selecting DEMs not “fit-for-purpose” for topographic analysis and offer a simple yet effective solution for reconciling the selection of DEMs based on neighbourhood size resolution prior to terrain analyses and topographic feature characterization

Leaf area changes and transpiration in vineyards under salt stress

Thesis (M.Sc. Agric.) -- University of Stellenbosch, 1999.ENGLISH SUMMARY: Irrigation of vines with saline water has long been a problem in the Western Cape region. Research in this respect financed by the Water Research Commission was done on vines to test the effect of 6 levels of irrigation water quality on production. The experiment consisted of two sites namely one at the Robertson experimental farm of the ARC outside of Robertson and the other on the Nietvoorbij experimental farm outside Stellenbosch. Each site had 6 treatments replicated 4 times. The treatments consisted of water with electrical conductivities of -40, 75, 150, 250, 350, 500 mS/m. The saline water was produced and controlled by a computerised injection system that injected a high concentration stock solution into the irrigation system. The stock solution consisted ofNaCI and CaCl2 mixed to a Na:Ca ratio. Description of the canopy surface and structure per plant is essential to the formulation and description of plant reaction resulting from plant-environmental interaction. This study looked at measurement techniques to non-destructively describe and quantify the reaction of canopies to different saline treatments. Measurement techniques consisted of physical destructive and non-destructive light interception techniques with special reference to the use of the Sunfleck Ceptometer and Dcor C2000 Plant Canopy Analyser. Destructive measurements were only done to calibrate the non-destructive techniques. The Dynamax Heat Balance Sap Flow Meter was used to measure differences in sap flow rate between plants from different treatments. The measured transpiration was compared with weather station derived evapotranspiration as well as the sodium absorption ratio of the different soils. It was found that leaf area indices do show treatment effects very clearly. It was also found that by the time treatment effects were visible, leaf damage was already irreversible. The method clearly highlights treatment effects but cannot be used in a production environment to help prevent leaf damage as a management tool. Sap flow measurement was done to show that sap flow is more sensitive and that differences do occur before leaf damage is visible. Sap flow measurements can therefore be used with greater success as a management and a research tool. A good calibration exercise to determine leaf area indices non-destructively led to the ability of producing reliable transpiration and evapotranspiration data.AFRIKAANSE OPSOMMING: Besproeiing van wingerd met brakwater is reeds 'n wesenlike probleem in die WesKaap Provinsie. Navorsing was deur die Waternavorsingskomrnissie geloods waar wingerd met ses grade van brakwater besproei was om brakwater se invloed op plantprestasie te meet. Die proef was tweeledig van aard met 'n perseel buite Robertson op die NIWW -proefplaas en 'n tweede op die Nietvoorbij proefplaas buite Stellenbosch. Daar was 6 brakwater behandelings nl., -40, 75, 150, 250, 350, 500 mSm-1 met 4 herhalings van elk. Die waterkwaliteit was beheer vanaf In inspuitstelsel gekoppel aan In hoe konsentrasie voorraad oplossing. Die voorraad oplossing het bestaan uit NaCl en CaCl2 gemeng in 'n Na:Ca verhouding. Beskrywing van die blaredak en blaredakstruktuur van 'n gewas is essensieel t.o.v. formulering en beskrywing van plantreaksie a.g. v. plant-omgewing interaksies. Daar was met hierdie studie gekyk na metingstegnieke om die blaredak deur niedestruktiewe metodes te beskryf en dus plantreaksie op verskillende brakwaterbehandelings te kwantifiseer. Metingstegnieke het bestaan uit fisiese destruktiewe metings en ligonderskeppings tegnieke waaronder die Sunfleck Ceptometer en Dcor C2000 Plant Canopy Analizer tel. Destruktiewe metings was slegs gedoen ter kalibrering van die nie-destruktiewe metodes. Die Dynamax Heat Balance Sapflow Meter was gebruik vir sapvloeimetings, om die verskille in transpirasie tussen behandelings waar te neem. Die gemete transpirasie was vergelyk met weerstasie afgeleide evapotranspirasie en ook met die natrium absorpsie verhouding van die verskillende gronde. Daar was gevind dat blaar oppervlakindekse wel duidelik behandelingsverskille uitwys. Daar is ook gevind dat teen die tyd dat verskille sigbaar is, daar reeds onomkeerbare skade aan die blare is. Blaar oppervlakindekse het dus wei gehelp om die behandelingsverskille uit te wys maar dit kan nie gebruik word in 'n produksie omgewing om blaarskade te help voorkom deur dit as 'n bestuurshulpmiddel aan te wend nie. Daarvoor was sapvloei metings gedoen om aan te toon dat verskille in sapvloei reeds bestaan voor blaarskade sigbaar is. Sapvloei metings sou dus met groter sukses aangewend kan word as 'n bestuurshulpmiddel en ook as navorsingshulpmiddel. 'n Goeie kalibreringsoefening om blaaroppervlak indekse akkuraat te bepaal m.b.v niedestruktiewe metodes, het gehelp om transpirasie en evapotranspirasie baie akkuraat te benader.Maste

Mechanical energy in toddler gait - A trade-off between economy and stability?

Mechanical energy expenditure was investigated in children who are just learning to walk and compared with adult mechanical energy expenditure during walking. First, we determined whether the inverted pendulum (IP) mechanism of energy exchange was present in toddlers. It seems that new walkers partially make use of this energy saving mechanism, but it is less efficient than in adults. The reduced recovery values (R=40% at optimal speeds in toddlers compared to 70% in adults) can be explained by their low self-selected walking speed in combination with their tossing gait (large vertical oscillations of the body) and by the observation that during as much as 25–50% of the gait cycle kinetic and potential energy are oscillating in-phase. The second step was to calculate positive external mechanical work (Wext). Since the IP mechanism is less efficient in toddlers, more mass-specific positive work has to be performed to lift and accelerate the centre of mass than in adults walking at the same speed, even when differences in body size are taken into account. The amount of positive internal work (Wint,k) necessary to move the body segments relative to the centre of mass was the third parameter we calculated. In toddlers Wint,k is largely determined by the kinetic energy of the lower limb. Compared to adults, toddlers have to perform less mass-specific work per unit distance to accelerate the body segments since the upper body is kept relatively stiff during walking and there is no arm swing. Apart from work performed on the centre of mass and work performed to move the body segments relative to the centre of mass, when walking some work is also performed during double contact as both legs are pushing against each other. Two methods were used to calculate this amount of work, both leading to the same conclusions. Mass-specific work during double contact is small in toddlers compared to adults because of their low walking speed. Finally the total amount of mechanical work performed in toddlers was compared to the work production observed in adults. Wext seems to be the major determinant for total mechanical energy expenditure. At intermediate froude numbers work production is comparable between adults and toddlers, but at low and high froude numbers Wtot increases due to the steep increases in Wext. Despite the fact that mechanical work requirements in toddler gait are underestimated if work during double contact is not taken into account, it is not a major determinant of the energy cost of walking