The importance of inversion disorder in the visible light induced persistent luminescence in Cr3+^{3+} doped AB2_2O4_4 (A = Zn or Mg and B = Ga or Al)

Cr$^{3+}$ doped spinel compounds AB$_2$O$_4$ with A=Zn, Mg and B=Ga, Al exhibit a long near infrared persistent luminescence when excited with UV or X-rays. In addition, persistent luminescence of ZnGa$_2$O$_4$ and to a lesser extent MgGa$_2$O$_4$, can also be induced by visible light excitation via $^4$A$_2$ $\rightarrow$ $^4$T$_2$ transition of Cr$^{3+}$, which makes these compounds suitable as biomarkers for in vivo optical imaging of small animals. We correlate this peculiar optical property with the presence of antisite defects, which are present in ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. By using X-ray absorption fine structure (XAFS) spectroscopy, associated with electron paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown that an increase in antisite defects concentration results in a decrease in the Cr-O bond length and the octahedral crystal field energy. A part of the defects are in the close environment of Cr$^{3+}$ ions, as shown by the increasing strain broadening of EPR and XAFS peaks observed upon increasing antisite disorder. It appears that ZnAl$_2$O$_4$, which exhibits the largest crystal field splitting of Cr$^{3+}$ and the smallest antisite disorder, does not show considerable persistent luminescence upon visible light excitation as compared to ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. These results highlight the importance of Cr$^{3+}$ ions with neighboring antisite defects in the mechanism of persistent luminescence exhibited by Cr$^{3+}$ doped AB$_2$O$_4$ spinel compounds.Comment: 10 pages + supplementary (available on request

Who benefits from a job change: The dwarfs or the giants?

Empirical studies have shown that voluntary job-to-job changes have a positive effect on wage mobility. In this paper, we suggest that the impact of a job change on wage growth depends on the position in the wage distribution. Using panel data from the UK and Germany, we investigate the effect of employer changes and within-firm job changes on year-to-year wage mobility. We show that a change of employer results into a wage increase for the low-paid workers but not for the high-paid workers. Within-firm job changes produce, on average, moderate wage gains for the low-paid workers in the UK, but have no effect in Germany. Results on 3-year wage mobility are shown to be very similar to the results on year-to-year wage growth.low pay ; high pay ; job mobility ; wage mobility

Joint-rollout of FTTH and smart city fiber networks as a way to reduce rollout cost

Making cities smarter is the future. By bringing more technology into existing city infrastructure, smart city applications can arise. Whether these applications track devices e.g. public lightning, environmental measurements e.g. temperature or air quality, or analyze video streams e.g. for people density, it is expected that these will require a (near-) real time data connection. Upcoming 5G networks will be able to handle large amounts of connections at high speeds and low latencies and will therefor outperform current technologies such as 4G and low-power wide-area networks. In order to do so, these 5G networks fall back to numerous fiber connected small cells for up & downlink to the Internet. In this publication, we are looking into the additional fiber equipment and deployment cost to connect the required smart city network infrastructure, taking into account a Fiber-to-the-Home (FTTH) network is already available or will be installed as part of the smart city network rollout. More concretely, we are proposing a methodology comparing an anticipated and incremental planning approach for a number of different extensions upon the FTTH-network: connecting all electrical cabinets, connecting public lightning, and the connection of 5G using small cells. From this, we want to learn how much the total rollout cost can be reduced using a future-oriented smart city approach taking into account all future extensions, compared to an incremental short-time planning only planning additional fiber when required. In the meantime, we want to show the additional cost of creating a smart city network is limited when it is being combined with a FTTH rollout. Results of the proposed methodology and use case will be modeled planning and design software Comsof Fiber and will be published in a future work

La faune ichtyologique des bassins du Mono et du lac Togo (Togo)

D'une façon générale le climat du Togo peut se diviser en deux régimes principaux : un régime subéquatorial au Sud et un régime tropical au Nord. Le Mono qui coule du Nord au Sud subit l'influence combinée de ces deux climats. Son régime hydrologique est du type tropical de transition, c'est-à-dire qu'il n'y a qu'une crue mais plus durable que celle des rivières de la région sahélo-soudanienne. Au total, 50 espèces ont été recensées dans le Mono grâce à divers moyens d'échantillonnage. Cela est assez loin de la capacité théorique qui est estimée à 60-61 si l'on considère l'ensemble du bassin versant mais se situe près de la capacité théorique calculée (52-53) sur une base ne prenant en compte que la partie du Mono toujours en eau, le cours supérieur étant asséché environ six mois de l'année. Le régime alimentaire de 20 espèces a été étudié, il ne diffère pas de ce qui est habituellement observé dans les autres rivières d'Afrique de l'Ouest. Certaines espèces ont une période de reproduction limitée durant la saison des hautes eaux, d'autres n'ont pas de saison de frai particulière. La fécondité observée sur neuf espèces est de l'ordre de celle constatée chez les mêmes espèces d'Afrique occidentale. (Résumé d'auteur

Doped coupled frustrated spin-1/2 chains with four-spin exchange

The role of various magnetic inter-chain couplings is investigated by numerical methods in doped frustrated quantum spin chains. A non-magnetic dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The formation of a local magnetic moment is analyzed in term of soliton confinement. A four-spin coupling which might originate from cyclic exchange is shown to produce such a confinement in contrast to transverse magnetic exchange. Dopants on different chains experience an effective space-extended non-frustrating pairwise spin interaction.Comment: Few modifications and references added. Submitted to PR

Tetramerisation of a frustrated spin-1/2 chain

We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to adiabatic phonons with a general form of magnetoelastic coupling. For large enough frustration and lattice coupling a new tetramerised phase with three different bond lengths is found. We argue that the zig-zag spin-1/2 chain LiV$_2$O$_5$ might be a good candidate to observe such a phase