140 research outputs found
Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots
Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong
tunnelling interactions that lead to the formation of hybridised states. We
report the results of investigations into single pairs of coupled QDs in the
presence of an electric field that is able to bring individual carrier levels
into resonance and to investigate the Stark shift properties of the excitons
present. Pronounced changes in the Stark shift behaviour of exciton features
are identified and attributed to the significant redistribution of the carrier
wavefunctions as resonance between two QDs is achieved. At low electric fields
coherent tunnelling between the two QD ground states is identified from the
change in sign of the permanent dipole moment and dramatic increase of the
electron polarisability, and at higher electric fields a distortion of the
Stark shift is attributed to a coherent tunnelling effect between the ground
state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure
Self-consistent Coulomb effects and charge distribution of quantum dot arrays
This paper considers the self-consistent Coulomb interaction within arrays of
self-assembled InAs quantum dots (QDs) which are embedded in a pn structure.
Strong emphasis is being put on the statistical occupation of the electronic QD
states which has to be solved self-consistently with the actual
three-dimensional potential distribution. A model which is based on a Green's
function formalism including screening effects is used to calculate the
interaction of QD carriers within an array of QDs, where screening due to the
inhomogeneous bulk charge distribution is taken into acount. We apply our model
to simulate capacitance-voltage (CV) characteristics of a pn structure with
embedded QDs. Different size distributions of QDs and ensembles of spatially
perodic and randomly distributed arrays of QDs are investigated.Comment: submitted to pr
Breast feeding in Australia: A comparative study of Aboriginal and non Aboriginal women
The superiority of breast feeding over bottle feeding is universally acknowledged, and its crucial contribution to infant health is accepted by health authorities. Australia in recognition of the importance of breast feeding to infant health, aims to increase the prevalence of breast feeding. Breast feeding provides benefits for all children, however the health advantage that is gained by breast feeding in comparison to artificial feeding is more apparent among disadvantaged groups. Aboriginal Australians are identified as one such disadvantaged group. This study compares the available literature regarding the prevalence of breast feeding in Aboriginal and non Aboriginal women. It is apparent that breast feeding prevalence differs, between population groups within Australia. Aboriginal children are less likely to have been breast fed than non Aboriginal children. The comparison, indicates that there are deficiencies in the research regarding breast feeding prevalence in both population groups. Many factors affect a woman's decision to breast feed, and the duration of her breast feeding. These factors include, socioeconomic status, age, marital status, educational attainment, occupation and smoking status. These factors are clearly associated with breast feeding in non Aboriginal women. For Aboriginal women, the factors influencing breast feeding are more complex. It is recommended therefore, that it is essential for future research to examine the attitudinal and socialdeterminants of infant feeding practices in Aboriginal women. This is necessary, if educational or interventional strategies are to be effective for this population
Prediction of crop coefficients from fraction of ground cover and height. Background and validation using ground and remote sensing data
ReviewThe current study aims at reviewing and providing advances on methods for estimating and applying crop coefficients
from observations of ground cover and vegetation height. The review first focuses on the relationships between single
Kc and basal Kcb and various parameters including the fraction of ground covered by the canopy (fc), the leaf area index
(LAI), the fraction of ground shaded by the canopy (fshad), the fraction of intercepted light (flight) and intercepted
photosynthetic active radiation (fIPAR). These relationships were first studied in the 1970âs, for annual crops, and later,
in the last decennia, for tree and vine perennials. Research has now provided a variety of methods to observe and
measure fc and height (h) using both ground and remote sensing tools, which has favored the further development of Kc
related functions. In the past, these relationships were not used predictively but to support the understanding of
dynamics of Kc and Kcb in relation to the processes of evapotranspiration or transpiration, inclusive of the role of soil
evaporation. Later, the approach proposed by Allen and Pereira (2009), the A&P approach, used fc and height (h) or LAI
data to define a crop density coefficient that was used to directly estimate Kc and Kcb values for a variety of annual and
perennial crops in both research and practice. It is opportune to review the A&P method in the context of a variety of
studies that have derived Kc and Kcb values from field measured data with simultaneously observed ground cover fc and
height. Applications used to test the approach include various tree and vine crops (olive, pear, and lemon orchards and
vineyards), vegetable crops (pea, onion and tomato crops), field crops (barley, wheat, maize, sunflower, canola, cotton
and soybean crops), as well as a grassland and a Bermudagrass pasture. Comparisons of Kcb values computed with the A
&P method produced regression coefficients close to 1.0 and coefficients of determinationâ„0.90, except for orchards.
Results indicate that the A&P approach can produce estimates of potential Kcb, using vegetation characteristics alone,
within reasonable or acceptable error, and are useful for refining Kcb for conditions of plant spacing, size and density
that differ from standard values. The comparisons provide parameters appropriate to applications for the tested crops.
In addition, the A&P approach was applied with remotely sensed fc data for a variety of crops in California using the
Satellite Irrigation Management Support (SIMS) framework. Daily SIMS crop ET (ETc-SIMS) produced Kcb values using
the FAO56 and A&P approaches. Combination of satellite derived fc and Kcb values with ETo data from Spatial CIMIS
(California Irrigation Management Information System) produced ET estimates that were compared with daily actual
crop ET derived from energy balance calculations from micrometeorological instrumentation (ETc EB).Results produced
coefficients of regression of 1.05 for field crops and 1.08 for woody crops, and R2 values of 0.81 and 0.91, respectively.
These values suggest that daily ETc-SIMS -based ET can be accurately estimated within reasonable error and that the A&P
approach is appropriate to support that estimation. It is likely that accuracy can be improved via progress in remote
sensing determination of fc. Tabulated Kcb results and calculation parameters are presented in a companion paper in this
Special Issueinfo:eu-repo/semantics/publishedVersio
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