335 research outputs found
Superconductivity in La1-xCexOBiSSe: carrier doping by mixed valence of Ce ions
We report the effects of Ce substitution on structural, electronic, and
magnetic properties of layered bismuth-chalcogenide La1-xCexOBiSSe (x = 0-0.9),
which are newly obtained in this study. Metallic conductivity was observed for
x > 0.1 because of electron carriers induced by mixed valence of Ce ions, as
revealed by bond valence sum calculation and magnetization measurements. Zero
resistivity and clear diamagnetic susceptibility were obtained for x = 0.2-0.6,
indicating the emergence of bulk superconductivity in these compounds.
Dome-shaped superconductivity phase diagram with the highest transition
temperature (Tc) of 3.1 K, which is slightly lower than that of F-doped
LaOBiSSe (Tc = 3.7 K), was established. The present study clearly shows that
the mixed valence of Ce ions can be utilized as an alternative approach for
electron-doping in layered bismuth-chalcogenides to induce superconductivity
Strategyproof matching with regional minimum and maximum quotas
This paper considers matching problems with individual/regional minimum/maximum quotas. Although such quotas are relevant in many real-world settings, there is a lack of strategyproof mechanisms that take such quotas into account. We first show that without any restrictions on the regional structure, checking the existence of a feasible matching that satisfies all quotas is NP-complete. Then, assuming that regions have a hierarchical structure (i.e., a tree), we show that checking the existence of a feasible matching can be done in time linear in the number of regions. We develop two strategyproof matching mechanisms based on the Deferred Acceptance mechanism (DA), which we call Priority List based Deferred Acceptance with Regional minimum and maximum Quotas (PLDA-RQ) and Round-robin Selection Deferred Acceptance with Regional minimum and maximum Quotas (RSDA-RQ). When regional quotas are imposed, a stable matching may no longer exist since fairness and nonwastefulness, which compose stability, are incompatible. We show that both mechanisms are fair. As a result, they are inevitably wasteful. We show that the two mechanisms satisfy different versions of nonwastefulness respectively; each is weaker than the original nonwastefulness. Moreover, we compare our mechanisms with an artificial cap mechanism via simulation experiments, which illustrate that they have a clear advantage in terms of nonwastefulness and student welfare
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