Nanophotonic switch using ZnO nanorod double-quantum-well structures

The authors report on time-resolved near-field spectroscopy of ZnO/ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices. (C) 2007 American Institute of Physics.open116881sciescopu

Beyond malaria--causes of fever in outpatient Tanzanian children.

BACKGROUND: As the incidence of malaria diminishes, a better understanding of nonmalarial fever is important for effective management of illness in children. In this study, we explored the spectrum of causes of fever in African children. METHODS: We recruited children younger than 10 years of age with a temperature of 38°C or higher at two outpatient clinics--one rural and one urban--in Tanzania. Medical histories were obtained and clinical examinations conducted by means of systematic procedures. Blood and nasopharyngeal specimens were collected to perform rapid diagnostic tests, serologic tests, culture, and molecular tests for potential pathogens causing acute fever. Final diagnoses were determined with the use of algorithms and a set of prespecified criteria. RESULTS: Analyses of data derived from clinical presentation and from 25,743 laboratory investigations yielded 1232 diagnoses. Of 1005 children (22.6% of whom had multiple diagnoses), 62.2% had an acute respiratory infection; 5.0% of these infections were radiologically confirmed pneumonia. A systemic bacterial, viral, or parasitic infection other than malaria or typhoid fever was found in 13.3% of children, nasopharyngeal viral infection (without respiratory symptoms or signs) in 11.9%, malaria in 10.5%, gastroenteritis in 10.3%, urinary tract infection in 5.9%, typhoid fever in 3.7%, skin or mucosal infection in 1.5%, and meningitis in 0.2%. The cause of fever was undetermined in 3.2% of the children. A total of 70.5% of the children had viral disease, 22.0% had bacterial disease, and 10.9% had parasitic disease. CONCLUSIONS: These results provide a description of the numerous causes of fever in African children in two representative settings. Evidence of a viral process was found more commonly than evidence of a bacterial or parasitic process. (Funded by the Swiss National Science Foundation and others.)

Anharmonic scattering of longitudinal acoustic phonons : Herring processes in tetragonal TeO2 crystals

We calculate the anharmonic scattering rates of low-frequency longitudinal (L) acoustic phonons with thermally excited phonons via the Herring process L + ST→FT (with ST and FT the slow-transverse and fast-transverse phonons, respectively) in a tetragonal TeO2 crystal. For temperatures well below the Debye temperature, we find a scattering rate = A2T3 as predicted by Herring. An analytical expression is derived for the variation of the coefficient with propagation direction. A typical value of A is of the order of 10–22 s K–3. For propagation along the fourfold axis, i.e., the [001] direction, however, A = 0, indicating that in this direction L phonons are stable against the Herring processes. This is in contradiction to the recent experimental result reported by Damen et al. [Phys. Rev. B 59, 349 (1999)]. We show that the vanishing of the scattering rate in the [001] direction can be understood in terms of the physics of the Herring process

A reassessment of the epidemiology of Rice yellow mottle virus following recent advances in field and molecular studies

The available knowledge on the epidemiology of Rice yellow mottle virus (RYMV) is reassessed in the light of major advances in field and molecular studies of the disease it causes in rice. Previously undescribed means of transmission by mammals and through leaf contact have been discovered recently. Several agricultural practices, including the use of seedbed nurseries, have also contributed to a massive build-up of RYMV inoculum. Phytosanitation is now known to be critical to reduce disease incidence in rice. A new model of the ecology of RYMV in which man plays a central role has emerged. Furthermore, estimates of the evolutionary rate of change of RYMV provided a time-frame for its epidemiology, the first attempt for a plant virus. Earlier interpretations of the patterns of virus diversity which assumed a long-term evolution, and assigned a major role to adaptive events had to be discarded. In contrast, a wave-like model of dispersal of RYMV, which postulates its initial diversification in East Africa, followed by westward spread across the continent, was developed, refined and dated. The most salient - and largely unexpected - finding is that RYMV emerged recently and subsequently spread rapidly throughout Africa in the last two centuries, Diversification and Spread of RYMV has been concomitant with an extension of rice cultivation in Africa since the 19th century. This major agro-ecological change increased the encounters between primary hosts of RYMV and Cultivated rice. It also modified the landscape ecology in ways that facilitated virus spread