National Institute Of Materials Physics - Romania
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articles found
2041. Spontaneous collective coherence in driven dissipative cavity arrays
Authors:
Ruiz-Rivas, J; del Valle, E; Gies, C; Gartner, P; Hartmann, MJ
Published: SEP 4 2014, PHYSICAL REVIEW A, 90, DOI: 10.1103/PhysRevA.90.033808
We study an array of dissipative tunnel-coupled cavities, each interacting with an incoherently pumped two-level emitter. For cavities in the lasing regime, we find correlations between the light fields of distant cavities, despite the dissipation and the incoherent nature of the pumping mechanism. These correlations decay faster than any power of the distance for arrays in any dimension but become increasingly long ranged with increasing photon tunneling between adjacent cavities. The interaction-dominated and the tunneling-dominated regimes show markedly different scaling of the correlation length which always remains finite due to the finite photon trapping time. We propose a series of observables to characterize the spontaneous buildup of collective coherence in the system.
2042. Organic/inorganic-doped aromatic derivative crystals: Growth and properties
Authors:
Stanculescu, F; Ionita, I; Stanculescu, A
Published: SEP 1 2014, JOURNAL OF CRYSTAL GROWTH, 401, 220, DOI: 10.1016/j.jcrysgro.2014.01.056
Results of a comparative study on the growth from melt by the Bridgman-Slockbarger method of metadinitrobenzene (m-DNB) and benzil (Bz) crystals in the same experimental set-up and the same experimental conditions are presented. The incorporation of an inorganic (iodine) dopant in m-DNB was analyzed in the given experimental conditions from the point of view of the solid-liquid interlace stability. The limits for a stable growth and the conditions that favor the generation of morphological instability are emphasized. These limits for m-DNB are compatible with those previously determined for Bz, and therefore, even for a high gradient concentration at the growth interface, it is possible to grow mDNB and Bz crystals in the same experimental conditions characterized by a high AT and t', The optical properties were investigated in relation with the dopant incorporation in the crystal in the mentioned experimental conditions. Effects of the dopant (m-DNB/iodine in Bz and iodine in m-ONES) on the optical band gap and optical non-linear properties of the crystals are discussed. (C) 2014 Elsevier B.V. All rights reserved
2043. Evaluation of pristine and Eu2O3-added MgB2 ceramics for medical applications: hardness, corrosion resistance, cytotoxicity and antibacterial activity
Authors:
Batalu, D; Stanciuc, AM; Moldovan, L; Aldica, G; Badica, P
Published: SEP 1 2014, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 42, 361, DOI: 10.1016/j.msec.2014.05.046
Nano- or micropowders of Eu2O3 were added to MgB2, resulting in a composition of (MgB2)(0.975)(EuO1.5)(0.025). Pristine and doped samples were prepared using spark plasma sintering and tested for (i) Vickers hardness, (ii) pH evolution in phosphate-buffered saline solution, (iii) corrosion resistance (Tafel polarization curves), (iv) cytotoxicity (in vitro tests), and (v) antibacterial activity. Eu2O3 addition influenced the investigated properties. Solutions of MgB2-based samples show a relatively high saturation pH of 8.5. This value is lower than that of solutions incubated with Mg or other Mg-based biodegradable alloys reported in the literature. MgB2-based samples have lower electro-corrosion rates than Mg. Their Vickers hardness is 6.8-10.2 GPa, and these values are higher than those of biodegradable Mg-based alloys. MgB2 has low in vitro biocompatibility, good antibacterial activity against Escherichia coli, and mild activity against Staphylococcus aureus. Our results suggest that MgB2-based materials deserve attention in biomedical applications, such as implants or sterile medical instruments. (C) 2014 Elsevier B.V. All rights reserved.
2044. Significant enhancement of the critical current density for cubic BN addition into ex situ spark plasma sintered MgB2
Authors:
Badica, P; Aldica, G; Burdusel, M; Popa, S; Negrea, RF; Enculescu, M; Pasuk, I; Miu, L
Published: SEP 2014, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 27, DOI: 10.1088/0953-2048/27/9/095013
High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN)(x), x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature T-c = 38.8 K. The variation of the critical current density J(c) with the external magnetic field H for h-BN added sample is almost overlapping the J(c)(H) dependence for the pristine MgB2 sample. On the other hand, J(c) for the samples added with c-BN is larger at high magnetic fields, while the decrease of J(c) at low H is very small. At T = 20 K, a J(c) of 10(2) A cm(-2) is determined for the sample with x(c-BN) = 0.005 at H = 58 kOe, and for the sample with x(c-BN) = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.
2045. Simultaneous Laser-Induced Reduction and Nitrogen Doping of Graphene Oxide in Titanium Oxide/Graphene Oxide Composites
Authors:
Gyorgy, E; del Pino, AP; Logofatu, C; Cazan, C; Duta, A
Published: SEP 2014, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 97, 2724, DOI: 10.1111/jace.13013
Titanium oxide/graphene oxide nanocomposite thin films were grown by ultraviolet (UV) matrix-assisted pulsed laser evaporation (MAPLE) technique in controlled oxygen or nitrogen atmospheres. The effect of graphene oxide addition and laser-induced reduction as well as nitrogen doping on the wetting behavior and photoactive properties of titanium oxide thin films was investigated. Hydrophobic to hydrophilic conversion of titanium oxide films takes place progressively as the relative amount of graphene oxide in the MAPLE composite target increases. Nitrogen doping leads to further decrease of the static contact angle of the composite films. The photoactive properties of the synthesized materials were investigated through the evolution of contact angle under UV light irradiation. Wetting properties of both TiO2 and TiO2/GO nanocomposite thin films improved upon exposure to UV light.
2048. BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array
Authors:
Secu, CE; Matei, E; Secu, M; Damian, V
Published: SEP 2014, RADIATION MEASUREMENTS, 68, 41, DOI: 10.1016/j.radmeas.2014.07.001
Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient Xray phosphor the material might be used as X-ray micro-imaging detector. (C) 2014 Elsevier Ltd. All rights reserved.
2049. Abnormal anti-Stokes Raman scattering and coherent backscattering as manifestation of Anderson localization of light in nonlinear mesoscopic materials
Authors:
Smaranda, I; Mihut, L; Baibarac, M; Baltog, I; Lefrant, S
Published: SEP 2014, OPTICAL ENGINEERING, 53, DOI: 10.1117/1.OE.53.9.097109
We demonstrate that under continuous single-beam excitation, one can generate an abnormal antiStokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering. The effect has been observed in mesoscopic materials, which possess intrinsically nonlinear properties [lithium niobate (LiNbO3), bismuth germanium oxide (Bi12GeO20; BGO), bismuth silicon oxide (Bi12GeO20; BSO)], which have a nonzero electric susceptibility of the third order, chi((3)) not equal 0. Corroborated Raman and coherent backscattering studies demonstrate that the occurrence of both effects is conditioned by the existence of a mesoscopic morphology of the sample, which is able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, both AASRE and coherent backscattering effects are because of the Anderson localization of the light. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
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