Controlling the polarisation correlation of photon pairs from a charge-tuneable quantum dot

Correlation between the rectilinear polarisations of the photons emitted from the biexciton decay in a single quantum dot is investigated in a device which allows the charge-state of the dot to be controlled. Optimising emission from the neutral exciton states maximises the operating efficiency of the biexciton decay. This is important for single dot applications such as a triggered source of entangled photons. As the bias on the device is reduced correlation between the two photons is found to fall dramatically as emission from the negatively charged exciton becomes significant. Lifetime measurements demonstrate that electronic spin-scattering is the likely cause.Comment: 3 figure

Inversion of exciton level splitting in quantum dots

The demonstration of degeneracy of exciton spin states is an important step toward the production of entangled photon pairs from the biexciton cascade. We measure the fine structure of exciton and biexciton states for a large number of single InAs quantum dots in a GaAs matrix; the energetic splitting of the horizontally and vertically polarized components of the exciton doublet is shown to decrease as the exciton confinement decreases, crucially passing through zero and changing sign. Thermal annealing is shown to reduce the exciton confinement, thereby increasing the number of dots with splitting close to zero

Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale

Exploring the understanding and experience of working memory in teaching professionals: A large-sample questionnaire study

Working memory (WM) underpins learning and is strongly associated with academic achievement. Children with poor WM need support in the classroom, but little is known about teachers’ understanding of WM. An online questionnaire (N = 1425) assessed educational professionals’ understanding of key concepts related to WM. Respondents generally showed some understanding, although most overestimated WM duration. There was also considerable variability in the signs identified as being associated with poor WM and possible strategies to assist such children. This demonstrates the need to provide teacher training about WM, and for collaboration between researchers and teachers in developing support materials

Can children prioritize more valuable information in working memory? An exploration into the effects of motivation and memory load

Recent research found no evidence that children aged 7-10 years are able to direct their attention to more valuable information in working memory. The current experiments examined whether children demonstrate this ability when the reward system used to motivate participants is engaging and age-appropriate. This was explored across different memory loads (3 vs 4 item arrays) and modes of presentation (sequential vs simultaneous). Younger (7-8 years) and older children (9-10 years) were shown three or four colored shapes and asked to recall the color of one probed item following a brief delay. Items were either presented sequentially (Experiment 1) or simultaneously (Experiment 2). Children completed a differential probe value condition, in which the first shape (Experiment 1) or the top-left shape (Experiment 2) was worth more ‘points’ than the other items, and an equal probe value condition, in which all shapes were equally valuable. Children were told they could use the points collected to play a specially-designed game at the end of the session, and that they would be given a prize if they collected enough points. When items were presented sequentially, significant probe value effects emerged, with children showing higher accuracy for the first item when this serial position was more valuable. This effect was consistent across age group and memory load. When items were encountered simultaneously, both groups showed probe value effects in the higher (4 item) memory load condition. This indicates that children can prioritize more valuable information in working memory when sufficiently motivated to do so

Black carbon as an additional indicator of the adverse health effects of airborne particles compared with PM10 and PM2.5.

Current air quality standards for particulate matter (PM) use the PM mass concentration [PM with aerodynamic diameters ≤ 10 μm (PM(10)) or ≤ 2.5 μm (PM(2.5))] as a metric. It has been suggested that particles from combustion sources are more relevant to human health than are particles from other sources, but the impact of policies directed at reducing PM from combustion processes is usually relatively small when effects are estimated for a reduction in the total mass concentration

Why does the probe value effect emerge in working memory? Examining the biased attentional refreshing account

People are able to prioritize more valuable information in working memory. The current study examined whether this value effect is due to the items of greater value being refreshed more than lower-value items during maintenance. To assess this possibility, we combined a probe value manipulation with a guided-refreshing procedure. Arrays of colored shapes were presented, and after a brief delay, participants reported the color of one randomly probed shape on a continuous color wheel. To manipulate probe value, one item was indicated as more valuable than the rest prior to encoding (i.e., worth more notional points), or all items were indicated as equally valuable. To guide refreshing, in some trials, two arrows were presented during maintenance, each arrow cueing the spatial location of one item. Participants were told to “think of” (i.e., refresh) the cued item. If value boosts are driven by attentional refreshing, cueing an item to be refreshed should enhance performance for items that are of low or equal value, but not items of high value, as these items would be refreshed regardless of the cue. This pattern of outcomes was observed, providing support for the hypothesis that attentional refreshing at least partially accounts for probe value effects in working memory