OFDMA femtocells: a roadmap on interference avoidance - [topics in radio communications]

OFDMA femtocells have been pointed out by the industry as a good solution not only to overcome the indoor coverage problem but also to deal with the growth of traffic within macrocells. However, the deployment of a new femtocell layer may have an undesired impact on the performance of the macrocell layer. The allocation of spectrum resources and the avoidance of electromagnetic interference are some of the more urgent challenges that operators face before femtocells become widely deployed. In this article a coverage and interference analysis based on a realistic OFDMA macro/femtocell scenario is provided, as well as some guidelines on how the spectrum allocation and interference mitigation problems can be approached in these networks. Special attention is paid to the use of self-configuration and self-optimization techniques for the avoidance of interference.     

Phytoextraction of gold and copper from mine tailings with Helianthus annuus L. and Kalanchoe serrata L.

To examine the feasibility of gold phytoextraction, and the corresponding uptake of copper that is induced at the same time, field and laboratory scale experiments were carried out using mine tailings from the Magistral mine in Sinaloa State, Mexico. The locally available plant species Helianthus annuus L. (sunflower) and Kalanchoe serrata L. (magic tower) were used in this work, in combination with the chemical amendments: sodium cyanide (NaCN), ammonium thiocyanate (NH₄SCN), ammonium thiosulphate (NH₄)₂S₂O₃, and thiourea [SC (NH₂)₂] to promote gold uptake. The results show that for K. serrata, average copper concentrations were increased to above 4 mg/kg and gold concentrations to above 9 mg/kg in the dry matter of aerial tissues. For H. annuus average copper concentrations were increased to 118 mg/kg in roots, 141 mg/kg in stem and, 119 mg/kg in leaves while average gold concentrations were increased to 15 mg/kg in leaves, 16 mg/kg in roots and, 21 mg/kg in plant stems. Poor health of plants after treatment with chemicals to induce gold uptake could be a function of toxic concentrations of other trace elements such as copper in the plants. Our results confirm that phytoextraction technology can be used to recover precious metals from mine tailings, and that at the current market price for gold, this recovery may be economic. However, our results also highlight the differential response of plant species to copper and gold in the ground, and the importance of choosing the correct chemical to induce metal uptake.     

Surface adjustment of the IRAM 30 m radio telescope

The techniques used to set and stabilise the surface of the IRAM 30 m radio telescope to a final root mean square accuracy of about 50 mm are described. This involved both phase retrieval and phase coherent holography using a variety of radiation sources at several frequencies. A finite-element model was utilised in improving the temperature control system for the telescope structure. The factors influencing the ultimate surface accuracy are discussed.     

Constitutive and protein kinase C-regulated secretory cleavage of Alzheimer's beta-amyloid precursor protein: different control of early and late events by the proteasome

The physiological processing of the beta-amyloid precursor protein (betaAPP) by a protease called alpha-secretase gives rise to APP alpha, a C-terminally truncated fragment of betaAPP with known neurotrophic and cytoprotective properties. Several lines of evidence indicate that protein kinase C (PKC)-mediated events regulate this physiological pathway. We show here that the proteasome multicatalytic complex modulates the phorbol 12,13-dibutyrate-stimulated APP alpha secretion at several levels in human kidney 293 (HK293) cells. Two blocking agents of the proteasome, namely, Z-IE(Ot-Bu)A-leucinal and lactacystin, elicit a dual effect on PKC-regulated APP alpha secretion by metabolically labeled HK293 cells. Thus, short periods of preincubation (2-5 h) of the cells with the inhibitors trigger a drastic potentiation of APP alpha recovery, whereas long-term treatment of the cells (15-20 h) with the blocking agents leads to an overall decrease in the secretion of APP alpha. Such a dual effect was not observed on constitutive APP alpha secretion and intracellular formation generated by HK293 cells, which both only increase upon inhibitor treatments. Similar effects on the constitutive and PKC-regulated APP alpha secretion were observed with PC12 cells. Altogether, these data suggest distinct mechanisms underlying basal and PKC-regulated APP alpha production, indicating that this multicatalytic complex appears as a key contributor of the alpha-secretase pathway.