Influence of Bi and Mn on the green luminescence of ZnO ceramics

The effect of the addition of Bi and Mn on the photoluminescence from ZnO ceramics has been investigated. The effect of the presence of impurities on the green luminescence band can be compared to the effect of oxidizing treatments. A narrow green band has been observed in Mn‐doped samples

The origin of the red luminescence in Mg-doped GaN

Optically-detected magnetic resonance (ODMR) and positron annihilation spectroscopy (PAS) experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.Comment: 4 pages, 3 figure

Integrating DC fast/rapid chargers in low voltage distribution networks

The continued dependence on fossil fuel-based vehicles with high carbon emissions for road transport has grown rapidly over the last years. In response to the pressing needs to achieve electrification of the transport sector to facilitate a reduction on greenhouse and other dangerous emissions, ultra-low carbon emission electric vehicles (EVs) have been proposed. However, it is important to ensure that existing infrastructure is designed to meet the large uptake of EVs and their charging technologies. The long charging battery durations have led the EV manufacturers to develop faster charging technology, known as DC fast charging, to increase the overall customer comfort (i.e. reduced charging duration). Fast chargers provide hundreds of kW of power and, therefore, the installed capacity of distribution networks will constrain the success of e-mobility. The aim of this paper is to analyse the impacts of integrating 250 kW DC fast chargers on a real low voltage distribution network in Cardiff, Wales. PSCAD/EMTDC is used to examine the operating conditions of the network under maximum and variable consumer load profiles. Simulation cases show that the 250 kW charger can be integrated without affecting the stability of the network while maintaining acceptable voltage operation

Spillover of a hepatitis A outbreak among men who have sex with men (MSM) to the general population, the Netherlands, 2017.

Since 2015, outbreaks of hepatitis A among men who have sex with men (MSM) have been reported worldwide. To examine the impact of these MSM outbreaks in the Netherlands, we combined notification and epidemiological data with sequence analysis. Our results show the hazards of outbreaks within risk-groups spilling over into the largely susceptible general population. One third of the outbreak-related hepatitis A virus genotypes were detected in non-MSM cases

Estimation of Rwanda's power system inertia as input for long-term dynamic frequency response regulation planning

Changes in the quota between conventional generation and renewable energy sources constitute major challenges that the modern power systems have to encounter. Conventional power plants are replaced by renewable generation (e.g. wind turbines, photovoltaics) that contribute to the reduction of power system inertia. This may introduce frequency stability issues because frequency is affected by the amount of system inertia, along with the response of controllable frequency reserves and the amount of power imbalance. Therefore, the estimation and analysis of power system inertia and the frequency response assessment is essential to ensure power system stability and security. This paper proposes a novel method to estimates the inertia constant for three different periods in future, namely, 2025, 2035 and 2050 based on the produced future energy scenarios (FES) for Rwandan's power system. In addition, the paper evaluates the frequency response dynamics for each scenario. Results show that the highest progression in renewable energy resources penetration resulted to a larger reduction in the system inertia constant (from 7.2 in control area 1 to 3.83s in control area 3) and the largest frequency drop was observed during the high progression scenario in the year 2050 where the PV and imported power penetration was expected to reach more than 30% of the total installed capacity

Do Two Symmetry Breaking Transitions in Photosynthetic Light Harvesting Complexes Form One, Two or More Kibble Zurek Model Topological Defects?

Kibble and Zurek proposed that rapid symmetry breaking transitions in the hot, early universe could result in causally disconnected topological defects such as cosmic strings. This type of first order transition has analogues in certain second order transitions present in condensed matter such as liquid crystals, super fluids, and charge density waves in terms of flux tubes or vortices. Recently, we discovered that Rhodopseudomonas acidophilus photosynthetic light harvesting complex might have different types of coherent ground and excited states, suggesting that there are two different symmetry breaking transitions. The B 850 ground states comprise eight identical rings each containing 18 bacteriochlorophyll components, and each ring has undergone a Bose Einstein phase transition to a charge density wave that lowers the energy. The excited state coherence results from polariton formation from the non-crossing of bosons, here an extension of exciton theory. The result is short-lived quasi-particles with very low mass that can form an unusual BEC. We suggest the oriented, circular B 850 and enclosed singlet B 875 compounds create a new cavity structure with some attributes of a nano pillar. Since both the ground and excited states should contain solitons, we envisage three fast light pulse experiments could be able to map both the Kibble Zurek Model phase transitions and energy transfers as a function of light intensity and time in this complex at room temperature

Formation of oriented particles in an amorphous host: ZnS nanocrystals in silicon

Processes for incorporating randomly oriented crystalline precipitates in an amorphous host can be traced back to the 17th century when Cassius produced “gold ruby” glass. In this glass, octahedral colloidal precipitates of gold scatter light by the Mie process to produce a deep red color. In contrast to gold ruby glass, we describe a type of material in which the crystalline precipitates are crystallographically aligned in a coherent manner—even though they are dispersed in an amorphous matrix. Ion implantation and thermal processing are first used to form zinc sulfide nanocrystals that are coherently oriented with respect to a crystalline Si host. The Si is then amorphized by ion irradiation leaving the highly radiation-resistant ZnS precipitates in an aligned crystalline state. The process is anticipated to find applications in the creation of surfaces with unique optoelectronic properties. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69678/2/APPLAB-74-5-697-1.pd

Tortillas on the roaster: Central America’s maize–bean systems and the changing climate

Maize and beans are a vital component of human diets and culture in Central America. More than a million smallholder families grow these crops for subsistence, producing 70% of the maize and 100% of the beans consumed locally. Average yields are low, however – 1.5 t/ha for maize and 0.7 t/ha for beans – on the approximately 2.5 million hectares of land sown to these crops (40% of the total area harvested) in El Salvador, Guatemala, Honduras, and Nicaragua. In the years to come, a harsher climate together with soil degradation1, widespread poverty, and rural people’s limited access to services and infrastructure will pose challenging obstacles to production. By 2025, these pressures could result in total annual losses of maize and bean production in the four countries of around 350,000 t – with a gross production value of around US$120 million. To ward off this threat to the food security of some 100,000 households, effective adaptation strategies must be developed in collaboration with stakeholders in the maize and bean value chains. These strategies require strong public support and must draw on both scientific and community knowledge