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The resistive switching phenomenon in MgO-based tunnel junctions is attributed to the effect of charged defects inside the barrier. The presence of electron traps in the MgO barrier, which can be filled and emptied, locally modifies the conductance of the barrier and leads to the resistive switching effects. A double-well model for trapped electrons in MgO is introduced to theoretically describe this phenomenon. Including the statistical distribution of potential barrier heights for these traps leads to a power-law dependence of the resistance as a function of time, under a constant bias voltage. This model also predicts a power-law relation of the hysteresis as a function of the voltage sweep frequency. Experimental transport results strongly support this model and in particular confirm the expected power laws dependencies of resistance. They moreover indicate that the exponent of these power laws varies with temperature as theoretically predicted. [ABSTRACT FROM AUTHOR]

Magnetic properties of Cr2O3 epitaxial clusters inserted in an Fe/MgO/Fe tunnel barrier are revealed by their tunnel magnetoresistance signature. The cluster assembly has been shown in a previous work to behave as a superparamagnet when a magnetic field was applied in the plane of the tunnel junction. We here demonstrate that an external large out-of plane electric field (in the order of 0.5 GV/m) favors in-plane magnetization orientation. This is due to an electric-field-induced magnetic anisotropy along the normal to the plane, corresponding to large anisotropy fields reaching up to 2 T. The assembly of clusters is thus strictly speaking not superparamagnetic and its magnetization cannot be exactly described by a Langevin law. This is attributed either to a strain-induced enhanced magnetoelectric effect or to a voltage-induced change of the magnetic anisotropy at interfaces with MgO. [ABSTRACT FROM AUTHOR]

The article presents the Tower and Glass Marbles problem, which is considered as a good vehicle for studying algorithmic reasoning at various levels of mathematical problems. It explores the one- and two-marble cases, which determine which floor from a building will the marble breaks as it is dropped. Also included is the Catseye Marble company which uses the same process of dropping marbles from various levels of its story office tower.

The article reports the case of a patient who had recurrent dislocation after a total hip replacement, in which the orientation of the acetabular component was suboptimal and had been unsuccessfully treated initially with a large femoral head. The case study shows that, when dislocation is associated with malposition of the acetabular component, treatment to stabilize the hip by polyethylene exchange alone may be insufficient, and effective treatment may require correction of the position of the acetabular component. Thus, the use of a large femoral head should not supplant the need for proper orientation of the acetabular component. The use of a larger femoral head and polyethylene cup in revision surgery for patients with a malpositioned acetabular component is not recommended.

The metal-insulator transition and the original magnetic phase that appear in vanadium oxide nanoclusters epitaxially embedded in an MgO matrix are studied via electron transport, magneto-resistance, and X-ray circular dichroism measurements. The metal-insulator transition temperature is observed to be in the range of 1.5–27 K. We observe, from 0.3 K to at least 125 K, a superparamagnetic behavior, whereas vanadium oxide, in its bulk phase, is reported to be anti-ferromagnetic (AF) at low temperatures. This striking feature is consistent with either ferromagnetic spin pairing or spin canting in the AF spin order along the 1D vanadium ion chains of the Magnéli phase or for the VO2(A)-like phase. Finally, the observed magneto-resistive effect, which reached up to 8% at low temperatures, indicates ferromagnetic behavior for some of the nanoparticles. This enables their integration in spintronic devices that could be combined with metal-insulator switching and magneto-resistive effects. [ABSTRACT FROM AUTHOR]

We study electron transport in an assembly of epitaxial Cr2O3 nanoparticles embedded in a MgO tunnel barrier: an unusual variation in the Coulomb blockade charging energy is observed as a function of the size of the clusters. In striking contrast to the expected increase in charging energy when decreasing the cluster size, an almost constant behavior is observed. We argue here that the spontaneous superparaelectric moment carried by the cluster core is the origin of this unusual behavior since it drives the dielectric constant in this cluster assembly. This phenomenon could be exploited to fabricate devices with single valued Coulomb blockade energy despite a statistical dispersion in the cluster size. [ABSTRACT FROM AUTHOR]

The near-field Coulomb interactionbetween a nanoemitter and a graphene monolayer results in strong Förster-typeresonant energy transfer and subsequent fluorescence quenching. Here,we investigate the distance dependence of the energy transfer ratefrom individual, (i) zero-dimensional CdSe/CdS nanocrystals and (ii)two-dimensional CdSe/CdS/ZnS nanoplatelets to a graphene monolayer.For increasing distances d, the energy transfer ratefrom individual nanocrystals to graphene decays as 1/d4. In contrast, the distance dependence of the energytransfer rate from a two-dimensional nanoplatelet to graphene deviatesfrom a simple power law but is well described by a theoretical model,which considers a thermal distribution of free excitons in a two-dimensionalquantum well. Our results show that accurate distance measurementscan be performed at the single particle level using graphene-basedmolecular rulers and that energy transfer allows probing dimensionalityeffects at the nanoscale. [ABSTRACT FROM AUTHOR]

Epitaxial growth of electrodes and tunnel barriers on graphene is one of the main technological bottlenecks for graphene spintronics. In this paper, we demonstrate that MgO(111) epitaxial tunnel barriers, one of the prime candidates for spintronic application, can be grown by molecular beam epitaxy on epitaxial graphene on SiC(0001). Ferromagnetic metals (Fe, Co, Fe20Ni80) were epitaxially grown on top of the MgO barrier, thus leading to monocrystalline electrodes on graphene. Structural and magnetic characterizations were performed on these ferromagnetic metals after annealing and dewetting: they form clusters with a 100 nm typical lateral width, which are mostly magnetic monodomains in the case of Fe. This epitaxial stack opens the way to graphene spintronic devices taking benefits from a coherent tunnelling current through the epitaxial MgO/graphene stack. [ABSTRACT FROM AUTHOR]

Abstract: Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is increasingly used as a bearing material in total hip replacements. Cross-linking of UHMWPE has been shown to increase wear resistance but decrease its fracture resistance. We analyzed the clinical fracture failure of four cross-linked UHMWPE total hip replacement components of four different designs via microscopic observation of the fracture surfaces, and found that in all cases fractures initiated at stress concentrations in an unsupported region of the component (termed the elevated rim). Finite element analyses (FEA) of each individual implant design were then conducted. Results from this analysis demonstrated that the predicted magnitude and orientation of maximum principal stress due to mechanical loading of the elevated rim was sufficient to propagate initiated fatigue cracks in each case. FEA also predicted that cracks may arrest after some amount of growth due to a steep stress gradient near the initiation site. Further, while anatomical positioning of the implant and material properties affect the risk of fracture, we examined whether these failures are strongly related to the notched elevated rim design feature that is common to the four failed cases presented here. We believe that cross-linked UHMWPE remains an excellent bearing material for total hip replacements but that designs employing this material should mitigate stress concentrations or other design features that increase the risk of fracture. [Copyright &y& Elsevier]