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In recent years, the software production industry has experienced significant changes largely caused by extensive growth of globalisation, outsourcing, and competitive pressure. With these changes, risks in the software supply chain (SSC) have become a growing concern. Such risks include product tampering during development or delivery, potential compromises in quality and assurance due to software defects, production delays, and increased production costs. In this context, this study is aimed at evaluating the primary risks in the software supply chain using Bayesian belief networks combined with the analytic hierarchy process and noisy-OR (a generalisation of the logical OR) techniques to reduce the number of queries required of a given decision maker. A numerical example was presented to illustrate the application in which software suppliers were ranked according to their level of risk. The results indicated that, by using the proposed model, decision makers would be able to select a low-risk supplier by evaluating the probability of system failure caused by tampering or the introduction of defective code in the software. In addition, the proposed approach contributes to a better understanding of the risk main factors in an SSC and could be used to support managerial decision-making related to software products. [ABSTRACT FROM AUTHOR]

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The fundamental excited state decay processes relating to the 4I11/2 → 4I13/2 transition in singly Er3+-doped tellurite (TZNL) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 4I11/2 energy level at 970 nm and selective laser excitation of the 4I13/2 energy level at 1485 nm has established that energy transfer upconversion by way of a dipole-dipole interaction between two excited erbium ions in the 4I13/2 level populates the 4I11/2 upper laser level of the 3 μm transition. This upconversion has been analyzed for Er2O3 concentrations between 0.5 mol. % and 2.2 mol. %. The 4I13/2 and 4I11/2 energy levels emit luminescence with peaks located at 1532 nm and 2734 nm, respectively, with radiative decay efficiencies of 65% and 6.8% for the higher (2.2 mol. %) concentration sample. The low 2.7 μm emission efficiency is due to the non-radiative decay bridging the 4I11/2 → 4I13/2 transition and energy transfer to the OH- groups in the glass. Excited state absorption was observed to occur from the 4I13/2 and 4I11/2 levels with peak absorptions occurring at 1550 nm and 971 nm, respectively. The decay time of the 4I11/2 excited state decreased with an increase in the Er3+ concentration, which related to energy transfer to OH- ions that had a measured concentration of 6.6 × 1018 cm-3. Results from numerical simulations showed that a population inversion is reached at a threshold pumping intensity of ∼80 kW cm-2 for a cw laser pump at 976 nm if [Er3+] ≥ 1.2 × 1021 cm-3 (or [Er2O3] ≥ 2.65 mol. %) without OH- impurities being present. [ABSTRACT FROM AUTHOR]

In this work we present the spectroscopic properties of KY3F10 (KY3F) single crystals activated with thulium and co-doped with ytterbium and neodymium ions. The most important processes that lead to the thulium up-conversion emissions in the blue and ultraviolet regions were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the up-conversion process that populates 1G4 and 1D2 (Tm3+) excited states. Analysis of the energy-transfer processes dynamics using selective pulsed-laser excitations in Yb:Tm:Nd, Tm:Nd, and Tm:Yb KY3F crystals show that the energy transfer from Nd3+ to Yb3+ ions is the mechanism responsible for the enhancement of the blue up-conversion efficiency in the Yb:Tm:Nd:KY3F when compared with the Yb:Tm system. A study of the energy transfer processes in Yb:Tm:Nd:KY3F crystal showed that the 1G4 excited level is mainly populated by a sequence of two nonradiative energy transfers that starts well after the Nd3+ and Tm3+ excitation at 797 nm according to: Nd3+ (4F3/2) → Yb3+ (2F7/2) followed by Yb3+ (2F5/2) → Tm (3H4) → Tm3+ (1G4). Results of numerical simulation of the rate equations system showed that a population inversion for 483.1 nm laser emission line is attained for a pumping rate threshold of 98 s-1, which is equivalent to an intensity of 3.3 KW cm-2 for a continuous laser pumping at 797 nm for Yb(30 mol%):Tm(0.5 mol%):Nd(1 mol%):KY3F. Nevertheless, best Yb3+ concentration for the laser emission near 483.1 nm was estimated to be within 40 and 50 mol%. On the other hand, a population inversion was not observed for the case of 960 nm (Yb3+) pumping. [ABSTRACT FROM AUTHOR]

The primary excited state decay processes relating to the 6H13/2→6H15/2∼3 μm laser transition in singly Dy3+-doped fluoride (ZBLAN) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 6F9/2, 6H7/2 energy levels at 1125 nm and 6F11/2, 6H9/2 energy levels at 1358 nm established that the energy levels above the 6H11/2 level, excluding the 4F9/2 level, are entirely quenched by multiphonon emission in ZBLAN glass. The 6H11/2 and 6H13/2 energy levels emit luminescence with peaks at ∼1700 and ∼2880 nm, respectively, but at low quantum (luminescence) efficiencies. The quantum efficiency of the 6H11/2 level and 6H13/2 level is ∼9×10-5 and ∼1.3×10-2, respectively, for [Dy3+]=0.5 mol % based on calculations of the radiative lifetimes using the Judd–Ofelt theory. Excited state absorption (ESA) was detected by monitoring the rise time of the 1700 nm luminescence after tuning the probe wavelength across the spectral range from 1100 to 1400 nm. As a result of nonradiative decay of the higher excited states, ESA contributes to the heating of ∼3 μm fiber lasers based on Dy3+-doped fluoride glass. For [Dy3+] up to 4 mol %, we found no evidence of energy transfer processes between Dy3+ ions that influence the decay characteristics of the 6H11/2 and 6H13/2 energy levels. [ABSTRACT FROM AUTHOR]

In this work, we present the spectroscopic properties of LiYF4 (YLF) single crystals activated by high doping of erbium ions. The most important processes that lead to the up-conversion erbium emissions in the infrared region were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the up-conversion processes that populate the 4S3/2 excited state. A study of the energy transfer up-conversion (ETU) processes in Er:YLF showed that an ETU rate can be obtained from the 4I11/2 (ETU1) and 4S3/2 (ETU2) up-conversion luminescence transient analysis, i.e., from best fittings of the acceptor state luminescence. An analysis of the ETU rate dependence on the wavelength and intensity of pulsed laser excitations allowed us to obtain the ETU rate constants from the lower (4I13/2) and upper (4I11/2) laser levels to use them in the numerical solutions of the rate equation system for the Er-doped YLF crystal (15 mol %) pumped [continuous wave (cw)] at 972 nm. As a result, we found that the 4I11/2→4I13/2 laser emission (or small signal gain) shows a temporal profile intensity, which passes through a maximum at around 820 μs before getting the steady state regime. It was demonstrated that the ETU2 process (from the 4I11/2 level) is the mechanism responsible for the laser gain profile observed. The results of the numerical simulation of the rate equation system showed that the highest population inversion density of 8.5×1019 cm-3 for Er3+ (or a small signal gain of 2.54 cm-1) is obtained for 15 mol % of erbium in the YLF crystal when it is pumped by a cw laser at 972 nm using a pump intensity of 5.4 kW cm-2 (or a pumping rate of 300 s-1) for the laser transition near 2.75 μm. It was seen also that a pumping rate of 300 s-1 maximizes the population inversion in the cw pump regime. A simulation using a square wave pump with a pumping time of 1 ms showed a population inversion increasing by a factor of 1.31 with respect to the population inversion obtained in the continuous pump simulation. [ABSTRACT FROM AUTHOR]

In this work we present the spectroscopic properties of LiYF4 (YLF) single crystals activated with thulium and codoped with ytterbium and neodymium ions. The most important processes that lead to the thulium upconversion emissions in the blue region were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the upconversion process that populates 1G4(Tm3+) excited state. Analysis of the energy transfer processes dynamics using selective pulsed laser excitations in Yb:Tm:Nd, Tm:Nd, and Tm:Yb YLF crystals shows that the energy transfer from Nd3+ to Yb3+ ions is the mechanism responsible for the enhancement in the blue upconversion efficiency in the Yb:Tm:Nd:YLF when compared with the Yb:Tm system. A study of the energy transfer processes in YLF:Yb:Tm:Nd crystal showed that the 1G4 excited level is mainly populated by a sequence of two nonradiative energy transfers that start well after the Nd3+ and Tm3+ excitations at 797 nm according to Nd3+(4F3/2)→Yb3+(2F7/2), followed by Yb3+(2F5/2)→Tm(3H4)→Tm3+(1G4) . Results of numerical simulation of the rate equations system showed that a population inversion for 481.4 nm laser emission line is attained for a pumping rate threshold of 26 s-1, which is equivalent to an intensity of 880 W cm-2 for a continuous laser pumping at 797 nm. On the other hand, a population inversion was not observed for the case of 960 nm (Yb3+) pumping. [ABSTRACT FROM AUTHOR]

The primary excited state absorption processes relating to the 5I6→5I7 3 μm laser transition in singly Ho3+-doped fluoride glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 and 5I7 energy levels established the occurrence of two excited state absorption transitions from these energy levels that compete with previously described energy transfer upconversion processes. The 5I7→5I4 excited state absorption transition has peak cross sections at 1216 nm (σesa=2.8×10-21 cm2), 1174 nm (σesa=1×10-21 cm2), and 1134 nm (σesa=7.4×10-22 cm2) which have a strong overlap with the 5I8→5I6 ground state absorption. On the other hand, it was established that the excited state absorption transition 5I6→5S2 had a weak overlap with ground state absorption. Using numerical solution of the rate equations, we show that Ho3+-doped fluoride fiber lasers employing pumping at 1100 nm rely on excited state absorption from the lowest excited state of Ho3+ to maintain a population inversion and that energy transfer upconversion processes compete detrimentally with the excited state absorption processes in concentrated Ho3+-doped fluoride glass. [ABSTRACT FROM AUTHOR]

The deactivation of the two lowest excited states of Ho3+ was investigated in Ho3+ singly doped and Ho3+, Pr3+-codoped fluoride (ZBLAN) glasses. We establish that 0.1–0.3 mol % Pr3+ can efficiently deactivate the first excited (5I7) state of Ho3+ while causing a small reduction of ∼40% of the initial population of the second excited (5I6) state. The net effect introduced by the Pr3+ ion deactivation of the Ho3+ ion is the fast recovery of the ground state of Ho3+. The Burshstein model parameters relevant to the Ho3+→Pr3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532 nm excitations of singly Ho3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650 nm excitation of Ho3+-doped and Ho3+, Pr3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the 5I6 and the 5I7 excited states of Ho3+ was calculated to examine the beneficial effects on the gain associated with Pr3+ codoping. [ABSTRACT FROM AUTHOR]

Copyright of Acta Scientiarum: Technology is the property of Universidade Estadual de Maringa and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)