7,414 research outputs found
Collecting Data from Children Ages 9-13
Provides a summary of literature on common methods used to collect data, such as diaries, interviews, observational methods, and surveys. Analyzes age group-specific considerations, advantages, and drawbacks, with tips for improving data quality
The Value of Reunification in Germany: An Analysis of Changes in Life Satisfaction
We quantify the value of changes in life circumstances in Germany following reunification. To this end, we develop and implement a fixed-effect estimator for ordinal life satisfaction in the German Socio-Economic Panel. We find strong negative effects on life satisfaction from being recently fired, losing a spouse through either death or separation and time spent in hospital, whilst we find strong positive effects from income and marriage. Using a new casual decomposition technique, we find that East Germans experienced a continued improvement in life satisfaction after 1990 to which increased household incomes contributed around 12%. Most of the increase is explained by improved average circumstances, such as public services. For West Germans, we find virtually no change in satisfaction between 1991 and 1999.Life satisfaction, German Reunification, Random and Fixed-Effects Panel Models, Causal Decomposition
Oxide-apertured microcavity single-photon emitting diode
We have developed a microcavity single-photon source based on a single
quantum dot within a planar cavity in which wet-oxidation of a high-aluminium
content layer provides lateral confinement of both the photonic mode and the
injection current. Lateral confinement of the optical mode in optically pumped
structures produces a strong enhancement of the radiative decay rate. Using
microcavity structures with doped contact layers, we demonstrate a
single-photon emitting diode where current may be injected into a single dot
Observation of the Purcell effect in high-index-contrast micropillar
We have fabricated pillar microcavity samples with Bragg mirrors consisting
of alternate layers of GaAs and Aluminium Oxide. Compared to the more widely
studied GaAs/AlAs micropillars these mirrors can achieve higher reflectivities
with fewer layer repeats and reduce the mode volume. We have studied a number
of samples containing a low density of InGaAs/GaAs self assembled quantum dots
in a cavity and here report observation of a three fold enhancement in the
radiative lifetime of a quantum dot exciton state due to the Purcell effect
Quantum key distribution using a triggered quantum dot source emitting near 1.3 microns
We report the distribution of a cryptographic key, secure from photon number
splitting attacks, over 35 km of optical fiber using single photons from an
InAs quantum dot emitting ~1.3 microns in a pillar microcavity. Using below
GaAs-bandgap optical excitation, we demonstrate suppression of multiphoton
emission to 10% of the Poissonian level without detector dark count
subtraction. The source is incorporated into a phase encoded interferometric
scheme implementing the BB84 protocol for key distribution over standard
telecommunication optical fiber. We show a transmission distance advantage over
that possible with (length-optimized) uniform intensity weak coherent pulses at
1310 nm in the same system.Comment: 4 pages, 4 figure
Experimental position-time entanglement with degenerate single photons
We report an experiment in which two-photon interference occurs between
degenerate single photons that never meet. The two photons travel in opposite
directions through our fibre-optic interferometer and interference occurs when
the photons reach two different, spatially separated, 2-by-2 couplers at the
same time. We show that this experiment is analogous to the conventional
Franson-type entanglement experiment where the photons are entangled in
position and time. We measure wavefunction overlaps for the two photons as high
as 94 3%.Comment: Updated to published version, new fig. 4., corrected typo
Facet recovery and light emission from GaN/InGaN/GaN core-shell structures grown by metal organic vapour phase epitaxy on etched GaN nanorod arrays
The use of etched nanorods from a planar template as a growth scaffold for a highly regular GaN/InGaN/GaN core-shell structure is demonstrated. The recovery of m-plane non-polar facets from etched high-aspect-ratio GaN nanorods is studied with and without the introduction of a hydrogen silsesquioxane passivation layer at the bottom of the etched nanorod arrays. This layer successfully prevented c-plane growth between the nanorods, resulting in vertical nanorod sidewalls (∼89.8°) and a more regular height distribution than re-growth on unpassivated nanorods. The height variation on passivated nanorods is solely determined by the uniformity of nanorod diameter, which degrades with increased growth duration. Facet-dependent indium incorporation of GaN/InGaN/GaN core-shell layers regrown onto the etched nanorods is observed by high-resolution cathodoluminescence imaging. Sharp features corresponding to diffracted wave-guide modes in angle-resolved photoluminescence measurements are evidence of the uniformity of the full core-shell structure grown on ordered etched nanorods
Inter-seasonal population dynamics and pest status of Bemisia tabaci (Gennadius) biotype B in an Australian cropping system
Bemisia tabaci, biotype B, commonly known as the silverleaf whitefly (SLW) is an alien species that invaded Australia in the mid-90s. This paper reports on the invasion ecology of SLW and the factors that are likely to have contributed to the first outbreak of this major pest in an Australian cotton cropping system, population dynamics of SLW within whitefly-susceptible crop (cotton and cucurbit) and non-crop vegetation (sowthistle, Sonchus spp.) components of the cropping system were investigated over four consecutive growing seasons (September-June) 2001/02-2004/05 in the Emerald Irrigation Area (EIA) of Queensland, Australia. Based on fixed geo-referenced sampling sites, variation in spatial and temporal abundance of SLW within each system component was quantified to provide baseline data for the development of ecologically sustainable pest management strategies. Parasitism of large (3rd and 4th instars) SLW nymphs by native aphelinid wasps was quantified to determine the potential for natural control of SLW populations. Following the initial outbreak in 2001/02, SLW abundance declined and stabilised over the next three seasons. The population dynamics of SLW is characterised by inter-seasonal population cycling between the non-crop (weed) and cotton components of the EIA cropping system. Cotton was the largest sink for and source of SLW during the study period. Over-wintering populations dispersed from weed host plant sources to cotton in spring followed by a reverse dispersal in late summer and autumn to broad-leaved crops and weeds. A basic spatial source-sink analysis showed that SLW adult and nymph densities were higher in cotton fields that were closer to over-wintering weed sources throughout spring than in fields that were further away. Cucurbit fields were not significant sources of SLW and did not appear to contribute significantly to the regional population dynamics of the pest. Substantial parasitism of nymphal stages throughout the study period indicates that native parasitoid species and other natural enemies are important sources of SLW mortality in Australian cotton production systems. Weather conditions and use of broad-spectrum insecticides for pest control are implicated in the initial outbreak and on-going pest status of SLW in the region
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