4,137 research outputs found
The importance of inversion disorder in the visible light induced persistent luminescence in Cr doped ABO (A = Zn or Mg and B = Ga or Al)
Cr doped spinel compounds ABO 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 ZnGaO and to a lesser
extent MgGaO, can also be induced by visible light excitation via
A T transition of Cr, 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 ZnGaO and MgGaO. 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 ions, as shown by the increasing
strain broadening of EPR and XAFS peaks observed upon increasing antisite
disorder. It appears that ZnAlO, which exhibits the largest crystal
field splitting of Cr and the smallest antisite disorder, does not show
considerable persistent luminescence upon visible light excitation as compared
to ZnGaO and MgGaO. These results highlight the importance of
Cr ions with neighboring antisite defects in the mechanism of persistent
luminescence exhibited by Cr doped ABO 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 gĂ©nĂ©rale le climat du Togo peut se diviser en deux rĂ©gimes principaux : un rĂ©gime subĂ©quatorial au Sud et un rĂ©gime tropical au Nord. Le Mono qui coule du Nord au Sud subit l'influence combinĂ©e de ces deux climats. Son rĂ©gime hydrologique est du type tropical de transition, c'est-Ă -dire qu'il n'y a qu'une crue mais plus durable que celle des riviĂšres de la rĂ©gion sahĂ©lo-soudanienne. Au total, 50 espĂšces ont Ă©tĂ© recensĂ©es dans le Mono grĂące Ă divers moyens d'Ă©chantillonnage. Cela est assez loin de la capacitĂ© thĂ©orique qui est estimĂ©e Ă 60-61 si l'on considĂšre l'ensemble du bassin versant mais se situe prĂšs de la capacitĂ© thĂ©orique calculĂ©e (52-53) sur une base ne prenant en compte que la partie du Mono toujours en eau, le cours supĂ©rieur Ă©tant assĂ©chĂ© environ six mois de l'annĂ©e. Le rĂ©gime alimentaire de 20 espĂšces a Ă©tĂ© Ă©tudiĂ©, il ne diffĂšre pas de ce qui est habituellement observĂ© dans les autres riviĂšres d'Afrique de l'Ouest. Certaines espĂšces ont une pĂ©riode de reproduction limitĂ©e durant la saison des hautes eaux, d'autres n'ont pas de saison de frai particuliĂšre. La fĂ©conditĂ© observĂ©e sur neuf espĂšces est de l'ordre de celle constatĂ©e chez les mĂȘmes espĂšces d'Afrique occidentale. (RĂ©sumĂ© 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
LiVO might be a good candidate to observe such a phase
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