Er-doped SiO2–Al2O3 thin films prepared by the sol–gel route

The synthesis of homogeneous and pure silica–alumina binary glasses doped with rare-earth (RE) ions such as Er³⁺ is currently a key challenge for the development of integrated optics devices such as lasers, optical amplifiers or waveguides. In this study Er³⁺-doped SiO₂–Al₂O₃ films were prepared by the sol–gel route. Aluminium sec-butoxide, Al(O-sec-C₄H₉)₃ (ASB), and tetraethoxysilane, Si(OC₂H₅)₄ (TEOS), were used as glass oxide precursors, whereas erbium was introduced as Er(NO₃)₃. The alumina content in the silica matrix was 10 at.%, while erbium doping ranged between 200 and 5000 ppm. The preparation of the starting sol–gel solution and the layer deposition by a dip-coating procedure were performed in dry-box under nitrogen atmosphere. The obtained films were subsequently annealed in air between 300 and 1000 °C. After treatment at 500 °C, layers 200 nm thick were obtained. The composition, microstructure and surface morphology of the films were investigated by X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), glancing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). Crack-free, transparent, high purity films were obtained, characterised by compositional and microstructural homogeneity.     

Time‐multiplexed tiled projection system with improved pixel and spatial resolution

We propose two methods to increase the pixel and spatial resolution of Digital Micromirror Devices (DMD)‐based projectors by utilizing the large bandwidth provided by their high pattern rates. By varying the intensity of the illumination for each binary pattern displayed on the DMD, the time required to display an 8‐bit grayscale image can be reduced by up to factor 32 compared to using constant illumination and binary pulse‐width modulation (BPWM). The high image rate projection is then spatially separated by either using a galvanometer scanner or sequentially illuminating the DMD from different directions, thus creating multiple independently addressable projections which are then tiled to form a larger, higher resolution image.     

Urban Social Media Demographics: An Exploration of Twitter Use in Major American Cities

This article explores intersections between place, race/ethnicity, and gender amongst American Twitter users and makes an argument that studying the intensity of tweets provides insights into how and why particular groups tweet. Given recent events in American political life such as the shooting in Ferguson, Missouri and the reactions by young, urban African Americans on Twitter, understanding the role of race, place, gender, and age is important. We observed the time between tweets of urban American Twitter users and explored whether the medium may be providing traditionally marginalized groups, such as young Black men, with potential avenues for mobilizing communication and access to resources.     

Multi-block Poisson grid generator for cascade simulations

High quality computational grids can greatly enhance the accuracy of turbine and compressor cascade simulations especially when time-dependent results are sought where vortical structures are convected through the computational domain. A technique for generating periodic structured grids for cascade simulations based on the Poisson equations is described. To allow for more complex geometries, the grid can be divided into individual zones or blocks. The grids are generated simultaneously in all blocks, assuring continuity of the grid lines and their slopes across the zonal boundaries. Simple geometric rules can be employed for enforcing orthogonality at block boundaries. The method results in grids with low grid distortion by allowing both, block boundaries and grid points on physical boundaries, to move freely. Results are presented for a linear turbine and a linear compressor cascade.     

The early host and material response of hydroxyapatite/β-tricalciumphosphate porous ceramics after implantation into the femur of rats

The early responses of host and hydroxyapatite/-tricalciumphosphate (HA-TCP) porous ceramic implants were studied using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) at 3, 7, 14, 21, and 28 days after implantation into the femur of rats. Micropores (<5 m) and macropores of the implant surface provided effective structures for anchoring of various tissue components. Mineralization started directly on the implant surface and was observed in macropores and micropores, suggesting bone-bonding by epitaxis. Bone-bonding was observed with and without an amorphous intervening interface layer. The composition of this layer and the mechanisms guiding its production are not yet fully understood. Extracellular matrix filled up the clefts between HA-TCP crystal grain clusters. These processes contributed to the mechanical stabilization of the interface. Slight changes of implant grain surface morphology were observed which were explained by leaching of impurities, such as TCP and/or by dissolution acting on single grains. Diameters of pores and HA-TCP grains did not change in a period up to 28 days, which seems to be related to the relatively short periods of insertion and the material properties. Leaching and degradation were observed and loose particles of implant origin were phagocytosed by macrophages and multinuclear giant cells which dominated at non-bonding interfaces.     

L-thiocitrulline. A stereospecific, heme-binding inhibitor of nitric-oxide synthases

Nitric-oxide synthase (NOS) catalyzes the oxidation of L-arginine to citrulline and nitric oxide (NO). The enzyme is inhibited by a variety of N omega-monosubstituted L-arginine analogs, and some of these compounds are useful in reversing pathologies associated with the overproduction of NO (e.g. the hypotension of septic shock). We report here that L-thiocitrulline (gamma-thioureido-L-norvaline) is a potent, stereospecific inhibitor of the constitutive brain and endothelial isoforms of NOS as well as the isoform induced in vascular smooth muscle cells by lipopolysaccharide and interferon-gamma. Steady state kinetic studies show L-thiocitrulline inhibition is competitive with L-arginine (Ki approximately 4-20% of KArgm), indicating that initial binding is as a substrate/product analog. In contrast to L-arginine and N omega-methyl-L-arginine, the prototypic NOS inhibitor, L-thiocitrulline binding elicits a "Type II" difference spectrum, indicating a high spin to low spin transition of the iron in the heme cofactor. This finding suggests that L-thiocitrulline is contributing the sixth ligand to heme iron, probably through the thioureido sulfur. Such interaction with heme iron neither stimulates nor inhibits the direct flavin-mediated cytochrome c reduction activity of the enzyme, but it does inhibit heme-dependent superoxide formation. In vivo, L-thiocitrulline is a potent pressor agent in both normal and endotoxemic rats, the latter finding suggesting utility in treating the hypotension of septic shock.     

Measurements of stratospheric aerosols with a combined elastic-Raman-backscatter lidar

Improvements made to the NASA Goddard Space Flight Center Stratospheric Ozone Lidar system have extended its atmospheric-aerosol-measuring capabilities. The methods by which aerosol-scattering ratio, aerosol backscatter, and aerosol extinction are simultaneously derived from lidar data are reported, and results obtained during several intercomparison campaigns at worldwide locations are shown. The results track the evolution of the Mt. Pinatubo aerosol cloud from 1991 to 1994 and report wavelength-dependence information for aerosol backscatter between 308 and 351 nm. Two analysis techniques, a more common inversion method and a combined elastic-Raman-backscatter approach, are also compared.     

Simulation of the S2 state multiline electron paramagnetic resonance signal of photosystem II: a multifrequency approach

The S2 state electron paramagnetic resonance (EPR) multiline signal of Photosystem II has been simulated at Q-band (35 Ghz), X-band (9 GHz) and S-band (4 GHz) frequencies. The model used for the simulation assumes that the signal arises from an essentially magnetically isolated MnIII-MnIV dimer, with a ground state electronic spin ST = 1/2. The spectra are generated from exact numerical solution of a general spin Hamiltonian containing anisotropic hyperfine and quadrupolar interactions at both Mn nuclei. The features that distinguish the multiline from the EPR spectra of model manganese dimer complexes (additional width of the spectrum (195 mT), additional peaks (22), internal "superhyperfine" structure) are plausibly explained assuming an unusual ligand geometry at both Mn nuclei, giving rise to normally forbidden transitions from quadrupole interactions as well as hyperfine anisotropy. The fitted parameters indicate that the hyperfine and quadrupole interactions arise from Mn ions in low symmetry environments, corresponding approximately to the removal of one ligand from an octahedral geometry in both cases. For a quadrupole interaction of the magnitude indicated here to be present, the MnIII ion must be 5-coordinate and the MnIV 5-coordinate or possibly have a sixth, weakly bound ligand. The hyperfine parameters indicate a quasi-axial anisotropy at MnIII, which while consistent with Jahn-Teller distortion as expected for a d4 ion, corresponds here to the unpaired spin being in the ligand deficient, z direction of the molecular reference axis. The fitted parameters for MnIV are very unusual, showing a high degree of anisotropy not expected in a d3 ion. This degree of anisotropy could be qualitatively accounted for by a histidine ligand providing pi backbonding into the metal dxy orbital, together with a weakly bound or absent ligand in the x direction.     

The "first generation" of endovascular stent-grafts for patients with aneurysms of the descending thoracic aorta

OBJECTIVE: Our goal was to determine whether endovascular stent-grafting is feasible and effective for patients with aneurysms of the descending thoracic aorta. METHODS: Starting in July 1992, we conducted a prospective, uncontrolled clinical trial in 103 patients (mean age 69 years [range 34-89 years]) who underwent endovascular treatment of aneurysms of the descending thoracic aorta using a custom-fabricated, self-expanding stent-graft device. Follow-up was 100% complete and averaged 22 months. Sixty-two patients (60%) were judged not to be reasonable candidates for a conventional "open" surgical procedure. RESULTS: Complete thrombosis of the aneurysm was ultimately achieved in 86 (83%) patients. The early mortality rate was 9% +/- 3% (+/- 70% CL). Multivariable analysis revealed that myocardial infarction or stroke was linked with a higher likelihood of early death (P = .001). Early serious complications included paraplegia in 3% +/- 2% and stroke in 7% +/- 3%. Actuarial survival estimates at 1 year and 2 years were 81% +/- 4% and 73% +/- 5% (+/- 1 SE), respectively; being judged not to be a surgical candidate portended a higher probability of death (P = .003). According to the intent-to-treat principle, "treatment failure" (including all late sudden unexplained deaths) occurred in 38 patients; 53% +/- 10% of patients were free from treatment failure at 3.7 years. Stent-graft related complications occurred commonly and were linked with several anatomic, technical, and patient-related risk factors. CONCLUSIONS: This 5-year clinical trial involving use of a "first generation" device indicates that endovascular stent-grafting of descending thoracic aortic aneurysms is feasible with acceptable medium-term results. More refined, commercially developed devices available today offer less traumatic and more precise stent-graft deployment; these major technical advantages, coupled with important lessons we have learned over time and better patient selection, should be associated with more salutary clinical results in the future.