Epi-off-lenticule-on corneal collagen cross-linking in thin keratoconic corneas.

PURPOSE: To evaluate the safety and efficacy of corneal collagen cross-linking (CXL) performed on overlaying a corneal lenticule to thin recipient corneas of progressive keratoconus (KC) patients. METHODS: In this study were enrolled eyes of patients affected by progressive KC with a minimum corneal thickness less than 400 µm, after overlaying a lenticule of human corneal stroma prepared with the femtosecond laser. The lenticules used were 100 µm thick and of 8.5 mm diameter in all the cases. Both the host cornea and the lenticules were subjected to epithelial debridement. CXL was carried out according to the standard protocol. Visual acuity, refraction, slit-lamp examination, endothelial cell density, pachymetry and keratometry, anterior segment tomography (AS-OCT) and confocal microscopy were evaluated preoperatively and at 1, 3, 6 and 12 months postoperatively. RESULTS: CXL was performed in 10 eyes of 8 patients (main age 23), corneal thickness range 379-414 µm, mean 387.6 µm. One patient was lost at follow-up. In all other cases, visual acuity and the endothelial cell density remained stable over a 12-month follow-up. Preoperative mean K1 and mean K2 were 46.91 ± 1.9 and 50.75 ± 2.93, respectively, and at 12 months mean K1 was 47.36 ± 2.66 and mean K2 50.53 ± 3.35. The AS-OCT clearly showed a demarcation line in all patients at 1, 3 (mean depth 283 µm and 267 µm, respectively) and in some cases at 6 months. Reduced keratocyte density and stromal oedema were observed immediately up to 1 month after treatment, while a slight subepithelial haze was present at 1-month and completely disappeared by 6 months. CONCLUSION: This new technique seems to offer a therapeutic opportunity for young patients suffering from progressive KC with very thin corneas, in which the standard treatment is not indicate, and delay or avoid the need for a corneal transplant.

Proof-of-principle demonstration of a virtual flow meter-based transducer for gaseous helium monitoring in particle accelerator cryogenics.

A transducer based on a virtual flow meter is proposed for monitoring helium distribution and consumption in cryogenic systems for particle accelerators. The virtual flow meter allows technical and economical constraints, preventing installation of physical instruments in all the needed measurement points, to be overcome. Virtual flow meter performance for the alternative models of Samson [ http://www.samson.de (2015)] and Sereg-Schlumberger [ http://www.slb.com/ (2015)] is compared with the standard IEC 60534-2-1 [Industrial-process control valves-Part 2-1: Flow capacity-sizing equations for fluid flow under installed conditions (2011), https://webstore.iec.ch/publication/2461], for a large temperature range, for both gaseous and liquid helium phases, and for different pressure drops. Then, the calibration function of the transducer is derived. Finally, the experimental validation for the helium gaseous state on the test station for superconducting magnets in the laboratory SM18 [Pirotte et al., AIP Conf. Proc. 1573, 187 (2014)] at CERN is reported.

Metrological analysis of a virtual flowmeter-based transducer for cryogenic helium.

The metrological performance of a virtual flowmeter-based transducer for monitoring helium under cryogenic conditions is assessed. At this aim, an uncertainty model of the transducer, mainly based on a valve model, exploiting finite-element approach, and a virtual flowmeter model, based on the Sereg-Schlumberger method, are presented. The models are validated experimentally on a case study for helium monitoring in cryogenic systems at the European Organization for Nuclear Research (CERN). The impact of uncertainty sources on the transducer metrological performance is assessed by a sensitivity analysis, based on statistical experiment design and analysis of variance. In this way, the uncertainty sources most influencing metrological performance of the transducer are singled out over the input range as a whole, at varying operating and setting conditions. This analysis turns out to be important for CERN cryogenics operation because the metrological design of the transducer is validated, and its components and working conditions with critical specifications for future improvements are identified.

Analysis of vacuum ultraviolet electronic spectra of Ce3+ and Pr3+ ions in Ca9Lu(PO4)7: crystal-field calculations and simulation of optical spectra.

The 4f-5d excitation and emission spectra of Ce(3+) and Pr(3+) ions in Ca9Lu(PO4)7 as recently reported (2012 J. Phys.: Condens. Matter 24 385502) were further analyzed and simulated by employing the effective Hamiltonian model for the 4f(N) and 4f(N-1)5d electronic configurations of impurity lanthanide ions and the exchange charge model of crystal-field theory. The multi-site effect on the 4f-5d transition spectra was explicitly discussed from the points of view of the local structure and site occupation ratios of lanthanide ions in Ca9Lu(PO4)7. An excellent agreement between the predicted and measured spectra confirms the validity of the performed calculations. Based on these energy level and intensity calculation results, the radiative lifetimes of the 5d-4f emissions of Ce(3+) and Pr(3+) ions have been modeled to show nearly independent temperature trends. Comparison with the measured lifetimes suggests the nonradiative relaxation process in this host is probably related to the intrinsic defect states. In addition to the studies of the 4f-5d transitions, a general theoretical scheme to calculate the lowest 4f-6s transition energy of the Ce(3+) ion was proposed for the first time on the basis of the ligand polarization model. The predicted 6s energy position of the Ce(3+) ion in Ca9Lu(PO4)7 is solid evidence corroborating our previous spectroscopic assignment.

Interconfigurational 5d → 4f luminescence of Ce3+ and Pr3+ in Ca9Lu(PO4)7.

Ca(9)Lu(PO(4))(7):Ce (3+) and Ca (9)Lu (PO (4))(7):Pr (3+) polycrystalline materials were synthesized by solid state reaction at high temperature. The materials were characterized by powder x-ray diffraction (XRPD). The luminescence spectroscopy and the excited state dynamics of these compounds were investigated upon excitation with UV/VUV synchrotron radiation. Both materials showed efficient and fast 5d-4f emission upon direct VUV excitation into the 5d levels but only Ca(9)Lu(PO(4))(7):Ce (3+) revealed luminescence upon excitation across the bandgap. The decay kinetics of the 5d-4f emission upon VUV intra-center excitation is characterized by a decay time of 29 ns for Ce (3+) and 17 ns for Pr (3+) with no significant build-up after the excitation pulse. For the both compounds, no significant temperature dependence of the 5d-4f emission lifetime was observed within the range 8-300 K.

Nanocrystalline lanthanide-doped Lu3Ga5O12 garnets: interesting materials for light-emitting devices.

Nanocrystalline Lu(3)Ga(5)O(12), with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol-gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr(3+), Eu(3+), Gd(3+), Ho(3+), Er(3+) and Tm(3+) dopants, while room temperature excited luminescence spectra and emission decay curves of Eu(3+)-, Tm(3+)- and Ho(3+)-doped Lu(3)Ga(5)O(12) nanocrystals have been measured and are discussed. The Eu(3+) emission spectrum shows typical bands due to 5D(0)-->7F(J) (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu(3)Ga(5)O(12) materials show better luminescence intensities compared to Y(2)O(3), Gd(3)Ga(5)O(12) and Y(3)Al(5)O(12) nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm(3+)- and Ho(3+)-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions.