Browsing by Author "Dietrich, Marc"

Single crystalline BaTiO3 films have been grown by pulsed laser deposition on SrTiO3. Radioactive I I I in ions were implanted with energies of 60 and 400 keV, respectively. The lattice site of(111) In has been determined by emission channeling of conversion electrons emitted after the nuclear decay to Cd-111. Besides a large random fraction, 11(3)% of the events show that In substitutes Ti-sites directly after the implantation. The recovery of the lattice after the implantation has been monitored in the direct vicinity of the probes by perturbed angular correlation (PAC) spectroscopy in a wide temperature range. After annealing in air at a temperature of 1420 K for 10 min, PAC spectroscopy yields a unique electric field gradient at the site of the In-111(Cd-111)-probe with a quadrupole coupling constant of 28.7(5) MHz and a frequency distribution with a width of 4.2(2) MHz. The film starts to degrade at a temperature of 1520 K. Scanning electron microscopy and energy dispersive X-ray spectroscopy investigations have been used to monitor the degradation. (C) 2003 Elsevier B.V. All rights reserved.

Background: Tubulointerstitial fibrosis is an integral part of progressive renal disease. Human cortical fibroblasts are believed to be key effector cells in fibrogenesis. Thus, a reliable culture of these cells is necessary for studies of their pathophysiology. Methods: Cortical fibroblast culture from routine kidney biopsies were analyzed and the cells were characterized. Indirect immunofluorescence staining was done after the first passage for cytokeratin, vimentin, alpha -smooth muscle actin, CD 44, CD 54, CD 68, collagen types I, III, and HLA-DR. We then assessed the utility of the putative fibroblast markers CD 90, prolyl-4-hydroxylase (P4H) and F1b in simultaneous stainings of tubular epithelial cells. Results: During the study period, 49 biopsy cores were cultured and cortical fibroblasts could be successfully established in 21 cases (42.9%). There was no relation between the success rate of culture and the degree of interstitial fibrosis, but an association was seen with the time of completion of the first passage. There was a negative correlation between the extent of scarring and the percentage of cytokeratin positive cells (r=-0.66, p <0.001). All primary fibroblasts were negative for factor VIII, HLA-DR, CD 68, and cytokeratin. They expressed alpha -smooth muscle actin and collagen types I and III to variable degrees. There was a robust correlation between die percentage of alpha -smooth muscle actin positive cells and interstitial scarring but no such association with collagen type I or type III positive cells. The three putative fibroblast markers did not prove useful in differentiating between tubular epithelial cells; aid fibroblasts. However, since only fibroblasts stained positive for CD 90 and negative for cytokeratin, these two markers may suffice to distinguish fibroblasts from other renal cellular elements. Conclusions: Cortical renal fibroblasts can be easily cultured from kidney biopsy cores, though the success rate of pure cultures is below 50%. Staining for CD 90 and cytokeratin may suffice for initial characterization of these cells.

We report a detailed crystal field analysis of Pm3+ and Sm3+ as well as lattice location studies of Pm-147 and Nd-147 in 2H-aluminum nitride (w-AlN). The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of 60 keV. The decay chain of interest in this work is Nd-147 -> Pm-147 -> Sm-147 (stable). Lattice location studies applying the emission channeling technique were carried out using the beta(-) particles and conversion electrons emitted in the radioactive decay of Nd-147 -> Pm-147. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of 873 K as well as 1373 K. The main fraction of about 60% of both Pm-147 as well as Nd-147 atoms was located on substitutional Al sites in the AlN lattice; the remainder of the ions were located randomly within the AlN lattice. Following radioactive decay of Nd-147, the cathodoluminescence spectra of Pm3+ and Sm3+ were obtained between 500 nm and 1050 nm at sample temperatures between 12 K and 300 K. High-resolution emission spectra, representing intra-4f electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of Sm3+ (4f(5)) and Pm3+ (4f(4)) in cationic sites having C-3v symmetry in the AlN lattice. Using crystal-field splitting models, we obtained a rms deviation of 6 cm(-1) between 31 calculated-to-experimental energy (Stark) levels for Sm3+ in AlN. The results are similar to those reported for Sm3+ implanted into GaN. Using a set of crystal-field splitting parameters B-nm, for Pm3+ derived from the present Sm3+ analysis, we calculated the splitting for the F-5(1), I-5(4), and I-5(5) multiplet manifolds in Pm3+ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels F-4(5/2) (Sm3+) and F-5(1) (Pm3+).

The implantation sites of rare earth (RE) probes Ce-141 (t(1/2) = 32 d) and Gd-149 (t(1/2) = 9.28 d) in diamond have been investigated using the emission channeling (EC) technique. Parent isotopes Cs-141 and Dy-149 were implanted into type IIa diamond samples at an energy of 60 keV at the online isotope separator ISOLDE at CERN. Cs-141 decays through the chain Cs-141-Ba-141-La-141-Ce-141-Pr-141. EC measurements were made on the 102 keV conversion electrons emitted in the decay of Pr-141 to its ground state. The decay of Dy-149 follows the chain Dy-149-Tb-149-Gd-149-Eu-149-(149) Sm. EC measurements were made on the 101 keV electrons emitted in the decay of Eu-149. Two-dimensional channeling patterns of the conversion electrons were obtained along <110> and <111> axial directions by raster scans with a Si surface barrier detector. Comparison of the observed patterns with simulated spectra show that in diamond 45-50% of the RE atoms are located near substitutional sites, unlike the case in Si. (C) 2002 Elsevier Science B.V. All rights reserved.

The lattice location of rare earths Tm in 3C- and 4H-SiC and Yb in 6H-SiC were studied using the emission channeling technique. Radioactive rare earth ions were implanted at the on-line isotope separator ISOLDE at CERN with an energy of 60 keV and fluences of 2 x 10(13) ions/cm(2). in order to determine the lattice location of the implanted impurities, angular dependent electron yields around certain axes were recorded with conversion electrons arising in the decay Tm-167-Er-167 (t(1/2) = 9.28 d) and Yb-169-Tm-169 (t(1/2) = 30.0 d). The effect of annealing on the normalized electron yields was studied up to 873 K for the 3C- and 4H-SiC samples and up to 1073 K for the 6H-SiC sample. In all cases the implanted rare earths are located on near substitutional silicon sites. (C) 2003 Elsevier B.V. All rights reserved.

The lattice sites of ion-implanted Li atoms in 6H-, 4H-, and 3C-SiC were studied. Radioactive Li-8 ions (t(1/2)=0.84 s) were implanted with 60 keV into the crystalline SiC samples, and the channeling and blocking effects of 1.6 MeV alpha particles emitted in the decay were measured to determine the Li lattice sites. The alpha emission channeling spectra measured along different crystallographic directions reveal that Li occupies mainly interstitial sites with tetrahedral symmetry, centered along the c-axis atom rows in the hexagonal lattices. In the cubic 3C-SiC structure, Li is located on tetrahedral interstitial sites as well. For 6H-SiC, the implantation temperature was varied between 200 and 823 K without observing significant changes in the emission channeling spectra. Thus, Li diffusion or Li defect interaction resulting in a lattice site change does not occur in this temperature regime. (C) 2002 American Institute of Physics.

We examine rest-frame ultraviolet spectra of 70 high-redshift quasars (z greater than or equal to 3.5) to study the chemical enrichment history of the gas closely related to the quasars and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-redshift quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z/Z(circle dot) similar or equal to 4-5 in the line-emitting gas. Assuming a timescale of tau(evol) similar or equal to 0.5-0.8 Gyr for the chemical enrichment of the gas, the first major star formation for quasars with z similar or equal to 4 should have started at a redshift of z(f) similar or equal to 6-8, corresponding to an age of the universe of several times 10(8) yr (H-0 = 65 km s(-1) Mpc(-1), Omega(M) = 0.3, Omega(Lambda) = 0.7). We note that this also appears to be the era of reionization of the universe. Finally, there is some evidence for a positive luminosity-metallicity relation in this high-redshift quasar sample.

We present the results of a long-term variability campaign of very broad-line AGNs with line widths broader than FWHM > 5000 km s(-1). The main goal of our investigation was to study whether the widths of the optical broad emission lines are correlated with the optical intensity variations on timescales of years. Our AGN sample consisted of 10 objects. We detected a significant correlation between optical continuum variability amplitudes and H beta emission line widths ( FWHM) and, to a lesser degree, between H beta line intensity variations and H beta equivalent widths. We add the spectroscopic data of variable AGNs from the literature to supplement our sample. The AGNs from other optical variability campaigns with different line-widths helped to improve the statistical significance of our very broad-line AGN sample. After including the data on 35 additional galaxies, the correlation between optical continuum variability amplitudes and H beta emission line widths becomes even more significant and the probability that this is a random correlation drops to 0.7 percent.

We present the final installment of an intensive 13 year study of variations of the optical continuum and broad Hbeta emission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 Hbeta measurements. The Hbeta variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, rproportional toL(ion)(1/2). Moreover, the apparently linear nature of the correlation between the Hbeta response time and the nonstellar optical continuum F-opt arises as a consequence of the changing shape of the continuum as it varies, specifically F(opt)proportional toF(UV)(0.56). .

We present results of a long-term optical variability campaign on the Seyfert 1 galaxy NGC 7603 over a period of nearly 20 years. The optical continuum and the Balmer and Helium lines varied by a factor of 5 to 10 in this broad-line Seyfert 1 galaxy. Furthermore, it is remarkable that the optical FeII line blends varied with the same amplitude as the H alpha and HeI lines. During the first half of the campaign (until 1990) there was a strong correlation between Balmer decrement variations, H beta intensity variations and emission line asymmetry. This behaviour changed afterwards when the H beta line intensity was higher than on average.

Deep BRIH-images as well as long-slit spectra takenwith the ESO-2.2m and VLT-telescopes of the QSO HE1013-2136(z = 0.785) are presented. They show the QSO apparently in the last phase of a similar to 1:3 merger. Two tidal tails extending 9" and 3.5" (68 and 26 kpc) and several condensations within 3.5" projected distance are clearly detected. The latter could be companion galaxies to the QSO or debris of a merger remnant. Due to the complexity of the system, the morphology of the host galaxy is not well constrained, however, the host galaxy seems to be as bright as 2-3 L . The I- and H-band images of HE 1013-2136 show remarkable differences, which are hard to asses. At present it cannot be ruled out that one of the merging galaxies formed a ring-like structure. The spectrum of the QSO shows it to be an extreme Fe II emitter, which is typical for IR-bright QSOs. At least one of the nearby condensations is most likely at the same redshift as the QSO, however, no signs of (post)starburst activity seen in many nearby interacting QSOs are detected. HE1013-2136 shows many similarities to the low-redshift (z = 0.29) intermediate QSO PG 1700+518 and could thus be a unique probe of the ULIRG-QSO connection at large look-back times. (c) 2006 Elsevier B.V. All rights reserved.