Cyclotron-resonant exciton transfer between the nearly free and strongly localized radiative states of a two-dimensional hole gas in a high magnetic field

Avoided crossing of the emission lines of a nearly free positive trion and a cyclotron replica of an exciton bound to an interface acceptor has been observed in the magneto-photoluminescence spectra of p-doped GaAs quantum wells. Identification of the localized state depended on the precise mapping of the anti-crossing pattern. The underlying coupling is caused by an exciton transfer combined with a resonant cyclotron excitation of an additional hole. The emission spectrum of the resulting magnetically tunable coherent state probes weak localization in the quantum well.Comment: 5 pages, 5 figure

Excitonic luminescence of the I2_2-intercalated HfS2_2

Photoluminescence from bulk HfS$_2$ grown by the chemical vapor transport (CVT) method is reported. A series of emission lines is apparent at low temperature in the energy range of 1.4 - 1.5 eV. Two groups of the observed excitonic transitions followed by their replicas involving acoustic and optical phonons are distinguished using classical intensity correlation analysis. The emission is attributed to the recombination of excitons bound to iodine (I$_2$) molecules intercalated between layers of HfS$_2$. The I$_2$ molecules are introduced to the crystal during the growth as halogen transport agents in the CVT growth process. Their presence in the crystal is confirmed by secondary ion mass spectroscopy.Comment: 5 pages, 6 figure

Unintentional high density p-type modulation doping of a GaAs/AlAs core-multi-shell nanowire

Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of considerable technological importance but remains a challenge due to the amphoteric behavior of the dopant atoms. Here we show that placing a narrow GaAs quantum well in the AlAs shell effectively getters residual carbon acceptors leading to an \emph{unintentional} p-type doping. Magneto-optical studies of such a GaAs/AlAs core multi-shell NW reveal quantum confined emission. Theoretical calculations of NW electronic structure confirm quantum confinement of carriers at the core/shell interface due to the presence of ionized carbon acceptors in the 1~nm GaAs layer in the shell. Micro-photoluminescence in high magnetic field shows a clear signature of avoided crossings of the $n=0$ Landau level emission line with the $n=2$ Landau level TO phonon replica. The coupling is caused by the resonant hole-phonon interaction, which points to a large 2D hole density in the structure.Comment: just published in Nano Letters (http://pubs.acs.org/doi/full/10.1021/nl500818k

Mutation increasing β-carotene concentrations does not adversely affect concentrations of essential mineral elements in pepper fruit

<div><p>Vitamin and mineral deficiencies are prevalent in human populations throughout the world. Vitamin A deficiency affects hundreds of millions of pre-school age children in low income countries. Fruits of pepper (<i>Capsicum annuum</i> L.) can be a major dietary source of precursors to Vitamin A biosynthesis, such as β-carotene. Recently, pepper breeding programs have introduced the orange-fruited (<i>of</i>) trait of the mutant variety Oranzheva kapiya, which is associated with high fruit β-carotene concentrations, to the mutant variety Albena. In this manuscript, concentrations of β-carotene and mineral elements (magnesium, phosphorus, sulphur, potassium, zinc, calcium, manganese, iron and copper) were compared in fruit from P31, a red-fruited genotype derived from the variety Albena, and M38, a genotype developed by transferring the orange-fruited mutation (<i>of</i>) into Albena. It was observed that fruit from M38 plants had greater β-carotene concentration at both commercial and botanical maturity (4.9 and 52.7 mg / kg fresh weight, respectively) than fruit from P31 plants (2.3 and 30.1 mg / kg fresh weight, respectively). The mutation producing high β-carotene concentrations in pepper fruits had no detrimental effect on the concentrations of mineral elements required for human nutrition.</p></div

Early Diagnosis of HIV Infection in Infants - One Caribbean and Six Sub-Saharan African Countries, 2011-2015.

Pediatric human immunodeficiency virus (HIV) infection remains an important public health issue in resource-limited settings. In 2015, 1.4 million children aged 50% decline. The most common challenges for access to testing for early infant diagnosis included difficulties in specimen transport, long turnaround time between specimen collection and receipt of results, and limitations in supply chain management. Further reductions in HIV mortality in children can be achieved through continued expansion and improvement of services for early infant diagnosis in PEPFAR-supported countries, including initiatives targeted to reach HIV-exposed infants, ensure access to programs for early infant diagnosis of HIV, and facilitate prompt linkage to treatment for children diagnosed with HIV infection

Photoluminescence Studies of Excitonic Complexes in Atomically Thin Mo(SySe1−y)2Mo(S_y Se_{1-y})_2 Alloys

Transition metal dichalcogenides show new emergent properties at monolayer thickness, notably strong Coulomb and electron-phonon interactions enable new insight into physics of many body effects. Here, we report photoluminescence and reflectivity contrast measurements of excitons (X) and trions (T) and the Raman spectra of phonons in monolayers of $Mo(S_ySe_{1-y})_2$ alloys with sulfur mole content from y=0 up to y=1. Binary MoSe₂ and ternary $Mo(S_ySe_{2-y})$ alloys exhibit contrasting behavior in the temperature evolution of excitons and trions photoluminescence intensity from T=7-295 K. In MoSe₂ a trion dominates photoluminescence spectra at low temperatures but exciton dominates photoluminescence at higher temperature. In contrast, in ternary $Mo(S_ySe_{1-y})_2$ alloys and MoS₂ trions dominate photoluminescence spectra at all measured temperatures, with the trion to exciton photoluminescence intensity ratio increasing with sulfur content. We attribute the strong increase of the trion photoluminescence intensity in $Mo(S_ySe_{1-y})_2$ monolayers with increase of sulfur mole content to the significant increase of the two-dimensional electron gas concentration and also to the strong exciton-trion coupling mediated by an optical phonon. We also demonstrate that increasing sulfur content in $Mo(S_ySe_{1-y})_2$ alloys stabilizes total photoluminescence intensity at high temperature

Zawartosc niektorych mikroelementow w szpinaku nowozelandzkim w warunkach zroznicowanego nawozenia azotem

W trzyletnim doświadczeniu polowym badano wpływ nawożenia azotem w dawkach 100, 150, 200 kg N·ha⁻¹ na zawartość, miedzi, cynku i manganu w liściach i łodygach szpinaku nowozelandzkiego. Saletrę amonową stosowano w trzech terminach: jedną trzecią dawki przed sadzeniem rozsady, natomiast dwie pozostałe po pierwszym i drugim zbiorze. Z przeprowadzonych badań wynika, że wzrastające nawożenie azotem w największym stopniu wpłynęło na podwyższenie poziomu manganu w roślinie. Liście szpinaku nowozelandzkiego charakteryzowały się większą koncentracją cynku i manganu a mniejszą miedzi, aniżeli łodygi. Ponadto zawartość wszystkich pierwiastków w liściach i łodygach szpinaku była uzależniona od terminu zbioru i lat badań.In a three year field experiment the effect of applied nitrogen fertilization at rates of 100, 150, 200 kg N·ha⁻¹ on the content of copper, zinc and manganese in leaves and stems of New Zealand spinach was studied. Every dose of nitrogen used as ammonium nitrate was applied in 3 terms: one third before planting, and other two third’s after first and second harvest. The study showed that increasing doses of nitrogen affected the content of manganese in tested plants. The leaves of New Zealand spinach contained more zinc and manganese and less copper than the stems. Moreover, the contents of all tested elements in both, leaves and stems of New Zealand spinach, depended on term of harvest and year of experiment

Wplyw przedsiewnego traktowania nasion na zawartosc wybranych mikroelementow w szpinaku nowozelandzkim [Tetragonia expansa Murr.]

W pracy określono wpływ przedsiewnego traktowania nasion (zamrażanie i moczenie w 0,01% roztworze Gibrescolu) na zmiany zawartości wybranych mikroelementów (Mn, Cu, Zn i Fe) w liściach i łodygach pozbawionych liści szpinaku nowozelandzkiego. Stwierdzono, iż przedsiewne traktowanie nasion wpłynęło istotnie na zmniejszenie zawartości wszystkich badanych mikroelementów w plonie szpinaku nowozelandzkiego. Porównując analizowane części roślin wykazano istotnie więcej manganu, cynku i żelaza w liściach, a miedzi w łodygach szpinaku nowozelandzkiego.The effect of pre-sowing treatment of seeds (freezing and wetting in 0.01% solution of Gibrescol) on the changes of some microelement contents (Mn, Cu, Zn, Fe) in leaves and stalks (without leaves) of New Zealand spinach was investigated. It was proved that pre-sowing treatment of seeds significantly influenced decreasing of all analyzed microelement content in the yield of New Zealand spinach. Comparison of tested plant parts showed significantly higher amounts of manganese, zinc and iron in the leaves, while copper in the stalks of New Zealand spinach

The perspectives of pre-frail and frail older people on being advised about exercise: a qualitative study

Advance Access publication 14 November 2017Background. Exercise is considered to be the most effective strategy to treat, prevent and delay frailty, a prevalent geriatric syndrome observed in clinical practice. Encouraging frail older people to take up exercise is crucial in the management of this condition. The study aimed to explore pre-frail and frail older peoples’ perspectives in relation to being advised about exercise and their perceptions of the general practitioners’ (GPs) role in promoting exercise for older people. Methods. Semi-structured interviews were conducted with 12 community-dwelling older (median age 83 years) participants screened pre-frail or frail using the FRAIL Screen. Their attitudes towards exercise, the advice received, their access to relevant information and their perceptions of the GP’s role in promoting exercise were explored. Thematic analysis was conducted to analyse data. Results. The majority of participants had a positive attitude towards exercise, and many participants indicated a preference for being advised firstly by their GPs and then other healthcare professionals. Participants living in the community reported difficulties in accessing information on exercise and indicated that local governments and GP practices should promote exercise for older people more actively. Participants living in retirement villages, however, reported having access to relevant information and being encouraged to participate in exercise. Conclusion. This research identified a gap in current practice, demonstrating that GPs, healthcare providers and local governments should promote exercise for older people more actively. Convincing health professionals to encourage regular exercise among their older patients would provide an opportunity to avoid and manage frailty in this population.Agathe Daria Jadczak, Joanne Dollard, Neha Mahajan and Renuka Visvanatha