1,374 research outputs found
Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud
A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud
For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud
Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
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[1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud
[2] A. Giesen, H. HĂĽgel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud
[3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. SolĂ©, J. GavaldĂ , M. AguilĂł, F. GĂĽell, J. Massons, T. Kirilov, F. DĂaz, Appl. Phys. B 74, 185 (2002).\ud
[4] M.C. Pujol, M.A. Bursukova, F. GĂĽell, X. Mateos, R. SolĂ©, J. GavaldĂ , M. AguilĂł, J. Massons, F. DĂaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud
[5] M.C. Pujol, X. Mateos, R. SolĂ©, J. Massons, J. GavaldĂ , F. DĂaz, M. AguilĂł, Mater. Sci. Forum 378-381, 710 (2001).\ud
[6] D. Ehrentraut, M. Pollnau, S. KĂĽck, Appl. Phys. B 75, 59 (2002)
Neural network interpolation of the magnetic field for the LISA Pathfinder Diagnostics Subsystem
LISA Pathfinder is a science and technology demonstrator of the European
Space Agency within the framework of its LISA mission, which aims to be the
first space-borne gravitational wave observatory. The payload of LISA
Pathfinder is the so-called LISA Technology Package, which is designed to
measure relative accelerations between two test masses in nominal free fall.
Its disturbances are monitored and dealt by the diagnostics subsystem. This
subsystem consists of several modules, and one of these is the magnetic
diagnostics system, which includes a set of four tri-axial fluxgate
magnetometers, intended to measure with high precision the magnetic field at
the positions of the test masses. However, since the magnetometers are located
far from the positions of the test masses, the magnetic field at their
positions must be interpolated. It has been recently shown that because there
are not enough magnetic channels, classical interpolation methods fail to
derive reliable measurements at the positions of the test masses, while neural
network interpolation can provide the required measurements at the desired
accuracy. In this paper we expand these studies and we assess the reliability
and robustness of the neural network interpolation scheme for variations of the
locations and possible offsets of the magnetometers, as well as for changes in
environmental conditions. We find that neural networks are robust enough to
derive accurate measurements of the magnetic field at the positions of the test
masses in most circumstances
MTBVAC vaccine is safe, immunogenic and confers protective efficacy against Mycobacterium tuberculosis in newborn mice
Development of novel more efficient preventive vaccines against tuberculosis (TB) is crucial to achieve TB eradication by 2050, one of the Millennium Development Goals (MDG) for the current century. MTBVAC is the first and only live attenuated vaccine based on a human isolate of Mycobacterium tuberculosis developed as BCG-replacement strategy in newborns that has entered first-in-human adult clinical trials. In this work, we characterize the safety, immunogenicity and protective efficacy of MTBVAC in a model of newborn C57/BL6 mice. Our data clearly indicate that MTBVAC is safe for newborn mice, and does not affect animal growth or organ development. In addition, MTBVAC-vaccinated mice at birth showed enhanced immunogenicity and better protection against M. tuberculosis challenge in comparison with BCG
Parameter estimation in LISA Pathfinder operational exercises
The LISA Pathfinder data analysis team has been developing in the last years
the infrastructure and methods required to run the mission during flight
operations. These are gathered in the LTPDA toolbox, an object oriented MATLAB
toolbox that allows all the data analysis functionalities for the mission,
while storing the history of all operations performed to the data, thus easing
traceability and reproducibility of the analysis. The parameter estimation
methods in the toolbox have been applied recently to data sets generated with
the OSE (Off-line Simulations Environment), a detailed LISA Pathfinder
non-linear simulator that will serve as a reference simulator during mission
operations. These operational exercises aim at testing the on-orbit experiments
in a realistic environment in terms of software and time constraints. These
simulations, so called operational exercises, are the last verification step
before translating these experiments into tele-command sequences for the
spacecraft, producing therefore very relevant datasets to test our data
analysis methods. In this contribution we report the results obtained with
three different parameter estimation methods during one of these operational
exercises.Comment: 10 pages, 3 figures, prepared for the Proceedings of the 9th Edoardo
Amaldi Conference on Gravitational Waves, JPC
Hyperfine structure and homogeneous broadening in Pr3+: KY(WO4)(2)
As part of a search for suitable materials for coherent quantum operations, relaxation times and hyperfine structure of the D-1(2)(1)-H-3(4)(1) transition in Pr3+:KY(WO4)(2) (0.29 at. %) at 4 K have been obtained using photon-echo and spectral hole burning techniques. The homogeneous linewidth and the effect of excitation-induced dephasing were measured using two-pulse photon-echo techniques. Linewidths of 23.4+/-1.0 and 17.6+/-0.9 kHz were obtained in the absence and presence of an external magnetic field of about 9 mT. The radiative lifetime (T-1) of the D-1(2) state was measured to be 43+/-2 mus using time-resolved laser-induced fluorescence and three-pulse photon-echo measurements. The transmission hole spectra were measured and directly yielded the quadrupole level splitting in the D-1(2) (3.77+/-0.03 and 4.58+/-0.04 MHz) and H-3(4) (17.1+/-0.1 and 33.2+/-0.3 MHz) states. The spectral hole lifetime due to population redistribution between the ground-state nuclear levels was also determined to be 70+/-10 ms. A strong dipole-dipole interaction observed in this crystal opens for potential applications in quantum computing schemes for performing quantum logic operations, but the short dephasing time makes it less useful in data storage applications
Liquid-phase epitaxy and optical investigation of stoichiometric KYb(WO<sub>4</sub>)<sub>2</sub> thin layers
Pinctada imbricata radiata in the Balearic Archipelago
The presence of Pinctada imbricata radiata (rayed pearl oyster) was explored in the Bay of Palma (Balearic Archipelago, NW Mediterranean Sea) by means of Rapid Assessment Surveys (RAS). Forty-three specimens were found in rocky substrates from recreational marinas and neighbouring natural habitats, including Cabrera National Park. Average hinge length was 26.8 ± 13.3 mm and average shell
height was 28.6 ± 16.2 mm; a maximum size of 55.6 × 55.9 mm was measured. The main occurrence of the exotic oyster in marinas, and also far away in Cabrera, points to maritime transport as the primary introduction vector; whereas records in the adjacent natural habitats suggest secondary spread by natural dispersal has occurred. Considering the populations of P. imbricata radiata documented in the
Balearic Archipelago, the bivalve seems to be well established in the area. The study explores the potential of RAS as early detection tools for invasive species along the coastline, and recommends further assessment on the ecological impact of P. imbricata radiata in marine protected areas.En prens
Liquid phase epitaxy and optical investigation of KYb(WO<sub>4</sub>)<sub>2</sub> thin layers
Heart Rate Variability Analysis Guided by Respiration in Major Depressive Disorder
In this study a Heart Rate Variability (HRV) analysis guided by respiration to evaluate different patterns of Autonomic Nervous System (ANS) in response to a cognitive stressor between Major Depressive Disorder (MDD) and control (CT) subjects is presented. Cardiorespiratory Time Frequency Coherence (TFC) reveals the local coupling of HRV and respiration signal which is essential and usually not included in estimation of ANS measures derived by HRV. Parasympathetic activity of ANS is measured as the power at the frequencies where TFC between HRV and respiration is significant, whereas sympathetic dominance is measured as the normalized power in the low frequency band [0.04,0.15] Hz of HRV excluding the power of those frequencies related to respiration. Results showed significantly lower (p <; 0.05) sympathetic dominance in MDD with respect to CT subjects during stress, suggesting that ANS reactivity as response to stress stimuli is lower in MDD patients. The study of ANS reactivity to a stressor may serve as a biomarker useful for the early diagnosis and monitoring of MDD patients
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