1,330 research outputs found
Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 um
We present a detailed investigation into the optical characteristics of
individual InAs quantum dots (QDs) grown by metalorganic chemical vapor
deposition, with low temperature emission in the telecoms window around 1300
nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral,
positively charged, and negatively charged exciton and biexciton states.
Temperature-dependent measurements reveal dot-charging effects due to
differences in carrier diffusivity. We observe a pronounced linearly polarized
splitting of the neutral exciton and biexciton lines (~250 ueV) resulting from
asymmetry in the QD structure. This asymmetry also causes a mixing of the
excited trion states which is manifested in the fine structure and polarization
of the charged biexciton emission; from this data we obtain values for the
ratio between the anisotropic and isotropic electron-hole exchange energies of
(Delta1)/(Delta0)= 0.2--0.5. Magneto-PL spectroscopy has been used to
investigate the diamagnetic response and Zeeman splitting of the various
exciton complexes. We find a significant variation in g-factor between the
exciton, the positive biexciton, and the negative biexciton; this is also
attributed to anisotropy effects and the difference in lateral extent of the
electron and hole wavefunctions.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Dietary value for money? Investigating how the monetary value of diets in the National Diet and Nutrition Survey (NDNS) relate to dietary energy density
Estimating the monetary value of individualsâ diets allows investigation into how costs relate to dietary quality. A number of studies(1â2), including one in Scotland(3), have reported a strong negative relationship between diet costs and energy density. Most studies of this type neglect to address the issue of mathematical coupling, where energy is both the numerator in the energy density variable (kJ/g) and the denominator in energy-adjusted diet cost (e.g. E/10 MJ). As a result, the findings could be reflecting a mathematical relationship(4).
This study investigated how estimated diet costs of NDNS adults relate to dietary energy density using the âresidualsâ regressionmethod to account for energy. Diet diary information from 2008â2010 was matched to an in-house database of national average (2004) food prices (the DANTE cost database) to assign a cost to each food and non-alcoholic beverage consumed. Mean daily diet costs and costs per 10 MJ were calculated for each participant. Energy density (g/kJ) was derived from foods and milk.
The sample median diet cost was ÂŁ2.84 per day (IQR ÂŁ2.27, ÂŁ3.64), or ÂŁ4.05 per 10MJ (ÂŁ3.45, ÂŁ4.82). Values for energy density, food energy, and diet costs by quintiles of dietary energy density (1 = least energy dense) are presented in the table. Adjusted linear regression found a strong negative relationship: additional standard deviation above the diet cost expected for a given energy intake (the residual), there was an associated decrease in energy density of 0.46kJ/g (95% CI - 0.53, - 0.38, p<0.001).
This is the first time individual-level diet costs have been characterized for a representative British population. These diet costs represent the inherent value of the diet, and are not comparable to UK expenditure data. The analyses confirm a diet cost-energy density link that is not due to mathematical artefact, and suggest that those consuming more energy-dense diets are achieving more kilojoules for their money
Measuring diet in primary school children aged 8-11 years: validation of the Child and Diet Evaluation Tool (CADET) with an emphasis on fruit and vegetable intake.
Background/Objectives:The Child And Diet Evaluation Tool (CADET) is a 24-h food diary that measures the nutrition intake of children aged 3-7 years, with a focus on fruit and vegetable consumption. Until now CADET has not been used to measure nutrient intake of children aged 8-11 years. To ensure that newly assigned portion sizes for this older age group were valid, participants were asked to complete the CADET diary (the school and home food diary) concurrently with a 1-day weighed record. Subjects/Methods:A total of 67 children with a mean age of 9.3 years (s.d.: ± 1.4, 51% girls) participated in the study. Total fruit and vegetable intake in grams and other nutrients were extracted to compare the mean intakes from the CADET diary and Weighed record using t-tests and Pearson's r correlations. Bland-Altman analysis was also conducted to assess the agreement between the two methods. Results: Correlations comparing the CADET diary to the weighed record were high for fruit, vegetables and combined fruit and vegetables (r=0.7). The results from the Bland-Altman plots revealed a mean difference of 54âg (95% confidence interval: -88, 152) for combined fruit and vegetables intake. CADET is the only tool recommended by the National Obesity Observatory that has been validated in a UK population and provides nutrient level data on children's diets. Conclusions:The results from this study conclude that CADET can provide high-quality nutrient data suitable for evaluating intervention studies now for children aged 3-11 years with a focus on fruit and vegetable intake
Maternal iron status in early pregnancy and birth outcomes : insights from the Baby's Vascular health and Iron in Pregnancy study
Date of Acceptance: 16/03/2015 Acknowledgements N. A. A. was funded by a Wellcome Trust Research Training Fellowship (WT87789). H. J. M. and H. E. H. are supported by the Scottish Governmentâs Rural and Environment Science and Analytical Services. N. A. B. S. is supported by Cerebra. The authorsâ contributions are as follows: N. A. A. was responsible for organising the study conduct, data collection and database management, performed the statistical analysis, interpreted the results and drafted the paper. N. A. A., N. A. B. S., J. E. C., H. J. M. and D. C. G. contributed to the study concept and design, and interpretation of results. H. J. M. and H. E. H. analysed the laboratory samples. J. E. C. and D. C. G. provided advice on statistical strategy and analysis. All authors have fully participated in the reporting stage and have critically reviewed and approved the final draft of the paper. The authors declare no conflict of interestPeer reviewedPublisher PD
gem-Dibromocyclopropanes and enzymatically derived cis-1,2-dihydrocatechols as building blocks in alkaloid synthesis
The application of the title building blocks, the 6,6-dibromobicyclo[3.1.0]hexanes
and the cis-1,2-dihydrocatechols, to the total synthesis of crinine and lycorinine alkaloids is
described.We thank the Australian Research Council and the Institute of Advanced Studies for generous financial
support
Longitudinal photocurrent spectroscopy of a single GaAs/AlGaAs v-groove quantum wire
Modulation-doped GaAs v-groove quantum wires (QWRs) have been fabricated with
novel electrical contacts made to two-dimensional electron-gas (2DEG)
reservoirs. Here, we present longitudinal photocurrent (photoconductivity/PC)
spectroscopy measurements of a single QWR. We clearly observe conductance in
the ground-state one-dimensional subbands; in addition, a highly
temperature-dependent response is seen from other structures within the
v-groove. The latter phenomenon is attributed to the effects of structural
topography and localization on carrier relaxation. The results of
power-dependent PC measurements suggest that the QWR behaves as a series of
weakly interacting localized states, at low temperatures
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Picoliter-volume inkjet printing into planar microdevice reservoirs for low-waste, high-capacity drug loading.
Oral delivery of therapeutics is the preferred route for systemic drug administration due to ease of access and improved patient compliance. However, many therapeutics suffer from low oral bioavailability due to low pH and enzymatic conditions, poor cellular permeability, and low residence time. Microfabrication techniques have been used to create planar, asymmetric microdevices for oral drug delivery to address these limitations. The geometry of these microdevices facilitates prolonged drug exposure with unidirectional release of drug toward gastrointestinal epithelium. While these devices have significantly enhanced drug permeability in vitro and in vivo, loading drug into the micron-scale reservoirs of the devices in a low-waste, high-capacity manner remains challenging. Here, we use picoliter-volume inkjet printing to load topotecan and insulin into planar microdevices efficiently. Following a simple surface functionalization step, drug solution can be spotted into the microdevice reservoir. We show that relatively high capacities of both topotecan and insulin can be loaded into microdevices in a rapid, automated process with little to no drug waste
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Formative evaluation of the usability and acceptability of myfood24 among adolescents: a UK online dietary assessments tool
BackgroundMyfood24 is a new online 24 h dietary assessment tool developed for use among the UK population. Limited information is available on the usability and acceptability of such tools. Hence this study aims to determine the usability and acceptability of myfood24 among British adolescents (11-18y) before and after making the improvements.MethodsA total of 84 adolescents were involved in two stages. In stage-I (beta-version of myfood24), 14 adolescents were recruited, 7 of whom (group-1) were asked to enter standardized tasks in a testing room with screen capture software. The remaining 7-adolescents (group-2) were asked to report their previous food intake using myfood24 at home. All participants then completed a usability and acceptability questionnaire. Stage-II was carried out after making amendments to the live-version of myfood24 in which 70 adolescents were asked to enter their food intake for two days and then complete the same questionnaire. Thematic analysis was conducted of observer comments and open-ended questions.ResultsNavigation, presentation errors and failure to find functions were the main usability issues identified in the beta-version. Significant improvements were found in the usability and acceptability of most functions after implementing certain features like a spell checker, auto-fill option, and adding âmouse hoverâ to help with the use of some functions. Adolescentsâ perceptions of searching food items, selecting food portion sizes and making a list function were significantly improved in the live-version. The mean completion time of myfood24 reduced from 31 (SD?=?6) minutes in the beta-version to 16 (SD?=?5) minutes in the live-version. The mean system usability score (SUS) of myfood24 improved from 66/100 (95 % CI 60, 73) in the beta-version to 74/100 (95 % CI 71, 77) in the live-version, which is considered as âgoodâ. Of the adolescents in stage-II, 41 % preferred using myfood24 to the interviewer-administered 24 h recall because myfood24 was quicker, easier to use and provided the adolescents with privacy when reporting dietary intake.ConclusionConsidering adolescentsâ feedback has helped in improving the usability and acceptability of the final-version of myfood24. myfood24 appears to support adolescentsâ need in reporting their dietary intake, which may potentially improve the overall quality of adolescentsâ self-reported dietary information
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