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Zhen H.L.,CAS Shanghai Institute of Technical Physics | Zhen H.L.,Leibniz Institute for Solid State and Materials Research | Huang G.S.,Fudan University | Kiravittaya S.,Leibniz Institute for Solid State and Materials Research | And 9 more authors.
Applied Physics Letters | Year: 2013

Pre-stressed multi-layer nanomembranes are rolled-up into a microtube in order to tune the strain applied to the contained coupled GaAs quantum wells. Additional GaAs/AlAs adjusting layers were deposited on the top of the nanomembrane to alter the thickness/stiffness of the to-be-rolled nanomembrane. In this way, microtubes with an adjustable diameter and strain are possible from a single initial grown sample. The internal strain state in the microtube affects the energy levels of the quantum wells and their coupling, which can be probed sensitively by photoluminescence. We measure different strain relaxation in rolled-up nanomembranes which we explain using a gradual change of the longitudinal relaxation as the distance of the nanomembrane from the etching front varies. © 2013 American Institute of Physics. Source

The successful results presented in the literature about the FSW aluminum-steel joints, ignore the appearance and formation of defects at the joint as reference points for evaluation. It also increases the controversy about the presence of intermetallic compounds of the type FexAly, and the lack of information about its origin. The objective of this study is to determine appropriate parameters for obtaining free defects aluminum-steel joints and their relation to the formation of deleterious phases during the FSW. Consolidated welded joints were obtained and determined the microstructure in aluminum alloy 6063-T5 and AISI SAE 1020 welds joints. It was used a tungsten carbide tool (WC-14Co) at rotation and weld speeds of 300 rpm and 150 mm. min-1, with tool offset of+0.5, +1.0and +1.5 mm. The results highlight the importance of heat input in the Al-steel welding surface appearance and penetration depth. The microstructural analysis reveals the formation of seven regions in the weld, highlighting the thermo-mechanically affected zone on the steel, a band of ultra fine grains offerrite and the absence of intermetallic compounds in the Al-steel interface. Source

Quintana K.J.,University of Santiago de Cali | Quintana K.J.,Autonomous University of Occidente | Falla R.,Autonomous University of Occidente | Franco F.,University of Santiago de Cali | And 2 more authors.
Revista Latinoamericana de Metalurgia y Materiales | Year: 2013

This article studies the mechanical behavior of Friction Stir Spot Welds, FSSW, in AA6063-T5 aluminum sheets, conducted on a universal milling machine and in a special machine for this welding technique. The microstructure analysis of the welded joints, allowed the correlation between the micro structural changes, caused by the thermal effects and the plastic deformation of the welding process, with the mechanical properties found in the welds. Additionally, the static behavior of the FSSW joints together with rivets was compared. The results showed that the tensile behavior of the welded joints exceeds in 100 % that of the riveted joints, showing an interfacial fracture type of failure. The values of microhardness in the heat affected zone are comparable with those of the base metal and show a drastic reduction in the thermo-mechanically affected zone that facilitates the fault condition under static load. Micro structural analysis shows a grain refinement of 90 % in the stirred zone related to the base metal, explaining the higher microhardness values in this zone. It was found a small increase in the mechanical behavior of welds made in the standard machine compared to those in the universal milling machine assigned to the better control of process parameters. © 2013 Universidad Simón Bolívar. Source

De Oliveira L.F.,Brazilian Synchrotron Light Laboratory (LNLS) | Bouchmella K.,Brazilian Synchrotron Light Laboratory (LNLS) | Goncalves K.D.A.,Laboratorio Nacional Of Biocieincias Lnbio | Bettini J.,Laboratorio Nacional Of Nanotecnologia Lnnano | And 2 more authors.
Langmuir | Year: 2016

The selective action of drugs in tumor cells is a major problem in cancer therapy. Most chemotherapy drugs act nonspecifically and damage both cancer and healthy cells causing various side effects. In this study, the preparation of a selective drug delivery system, which is able to act as a carrier for hydrophobic and anticancer drugs is reported. Amino-functionalized silica nanoparticles loaded with curcumin were successfully synthesized via sol-gel approach and duly characterized. Thereafter, the targeting ligand, folate, was covalently attached to amino groups of nanoparticle surface through amide bond formation. The cytotoxic effect of nanoparticles on prostate cancer cells line was evaluated and compared to normal cells line (prostate epithelial cell). Cytotoxicity experiments demonstrated that folate-functionalized nanoparticles were significantly cytotoxic to tumor cells, whereas normal cells were much less affected by the presence of these structures. © 2016 American Chemical Society. Source

Angelova T.,University of Valencia | Shtinkov N.,University of Ottawa | Ivanov T.,Sofia University | Donchev V.,Sofia University | And 5 more authors.
Applied Physics Letters | Year: 2012

Rolled-up semiconductor tubes of various diameters made of alternating In 0.215Ga 0.785As/GaAs layers have been investigated by means of Raman scattering. The optical and acoustic phonon modes of individual tubes have been studied and compared with the characteristics of the surrounding material. After tube formation, the frequency of the phonon modes shifts with respect to the as-grown material and disorder activated modes are observed. The frequency shifts are related to the residual strain in the tubes through the deformation potential approximation. Good agreement with atomistic valence force field simulations and x-ray micro-diffraction measurements is found. By comparison with x-ray data, a Raman strain constant K 0.65 is proposed for In 0.215Ga 0.785As. In the low frequency range, acoustic mode doublets are observed on the tubes that are absent in the surrounding material. They show clear evidence of the formation of periodic superlattices after the rolling-up process, and give insight into the quality of their interfaces. © 2012 American Institute of Physics. Source

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