Evolution of the electronic structure across the filling-control and bandwidth-control metal-insulator transitions in pyrochlore-type Ru oxides

We have performed photoemission and soft x-ray absorption studies of pyrochlore-type Ru oxides, namely, the filling-control system Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ and the bandwidth-control system Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$, which show insulator-to-metal transition with increasing Ca and Bi concentration, respectively. Core levels and the O 2$p$ valence band in Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ show almost the same amount of monotonous upward energy shifts with Ca concentration, which indicates that the chemical potential is shifted downward due to hole doping. The Ru 4$d$ band in Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ is also shifted toward the Fermi level ($E_F$) with hole doping and the density of states (DOS) at $E_F$ increases. The core levels in Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$, on the other hand, do not show clear energy shifts except for the Ru 3$d$ core level, whose line shape change also reflects the increase of metallic screening with Bi concentration. We observe pronounced spectral weight transfer from the incoherent to the coherent parts of the Ru 4d $t_{2g}$ band with Bi concentration, which is expected for a bandwidth-control Mott-Hubbard system. The increase of the DOS at $E_F$ is more abrupt in the bandwidth-control Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$ than in the filling-control Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$, in accordance with a recent theoretical prediction. Effects of charge transfer between the Bi 6$sp$ band and the Ru 4$d$ band are also discussed.Comment: 11 pages, 6 figure

Non linearly induced self waveguiding structure in dye doped nematic liquid crystals confined in capillaries

We report on experiments dealing with the propagation of a collimated laser beam in a dye doped nematic confined in a capillary of optical fiber size. The nematic is aligned in a such a way that the source beam is self focused. The behavior of the beam - focusing, multifocus regime, filamentation and undulation - already observed in larger cylindrical geometry and pure nematic is shown here to be reproduced in the dye doped medium, at much lower powers. Another feature is reported here: a stable regime looking like a waveguide appears in certain conditions, in which the beam to propagate in a narrow tube. This regime is simply modeled in terms of saturated reorientation of the nematic

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

Publicación con muchos autores, entre ellos la investigadora de la Universidad de Sevilla: Cano Megías, PilarDIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-Ip steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-Ip beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate βN in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.US Department of Energy - Office of Science - Office of Fusion Energy Sciences DE-FC02- 04ER54698 y DE-AC52-07NA2734

Importance of the V 3d-O 2p hybridization in the Mott-Hubbard material V2O3

We studied the changes in the electronic structure of V2O3 using a cluster model. The calculations included fluctuations from the coherent band in the metallic phase, and non-local Mott-Hubbard fluctuations in the insulating phase. The incoherent structure is mostly related to the usual ligand screening channel (3d2L). The coherent peak in the metallic phase corresponds to coherent band fluctuations (3d2C). The non-local screened state in the insulating phase (3d2D) appears at higher energies, opening the band gap. The photon energy dependence of the spectra is mostly due to the relative V 3d and O 2p cross sections. The present model reproduces also the observed changes in the V 1s core-level spectra. The above results suggest that the Mott-Hubbard transition in V2O3 requires a multi-band model.Comment: 4 pages, 4 figure

Optical response of metallic and insulating VO2 calculated with the LDA approach

We calculated the optical response of metallic and insulating VO2 using the LDA approach. The band structure calculation was based in the full-potential linear-muffin-tin method. The imaginary part of the dielectric function e2(w) is related to the different optical transitions. The Drude tail in the calculation of the metallic phase corresponds to intra-band d-d transitions. The calculation in the insulating phase is characterized by the transitions to the d||* band. The low frequency features, 0.0-5.0 eV, correspond to V 3d-V 3d transitions, whereas the high frequency structures, 5.0-12 eV, are related to O 2p-V 3d transitions. The calculation helps to explain the imaginary part of the dielectric function e2(w), as well as the electron-energy-loss and reflectance spectra. The results reproduce not only the energy position and relative intensity of the features in the spectra, but also the main changes across the metal-insulator transition and the polarization dependence. The main difference is a shift of about 0.6 eV in the calculation of the insulating phase. This discrepancy arises because the LDA calculation underestimates the value of the band gap

Computerized Ultrasonic Testing System (CUTS) for in-process thickness determination

A Computerized Ultrasonic Testing System (CUTS) was developed to measure, in real-time, the rate of deposition and thickness of chromium plated on the inside of thick steel tubes. The measurements are made from the outside of the tubes with the ultrasonic pulse-echo technique. The resolution of the system is 2.5 micron. (0.0001 in.) and the accuracy is better than 10 micron (0.0004 in.). The thickness is measured using six transducers mounted at different locations on the tube. In addition, two transducers are mounted on two reference standards, thereby allowing the system to be continuously calibrated. The tube temperature varies during the process, thus the input from eight thermocouples, located at the measurement sites, is used to calculate and compensate for the change in return time of the ultrasonic echo due to the temperature dependence of the sound velocity. CUTS is applicable to any commercial process where real-time change of thickness of a sample has to be known, with the advantage of facilitating increased efficiency and of improving process control

Compensation temperatures and exchange bias in La1.5Ca0.5CoIrO6

We report on the study of magnetic properties of the La1.5Ca0.5CoIrO6 double perovskite. Via ac magnetic susceptibility we have observed evidence of weak ferromagnetism and reentrant spin glass behavior on an antiferromagnetic matrix. Regarding the magnetic behavior as a function of temperature, we have found that the material displays up to three inversions of its magnetization, depending on the appropriate choice of the applied magnetic field. At low temperature the material exhibit exchange bias effect when it is cooled in the presence of a magnetic field. Also, our results indicate that this effect may be observed even when the system is cooled at zero field. Supported by other measurements and also by electronic structure calculations, we discuss the magnetic reversals and spontaneous exchange bias effect in terms of magnetic phase separation and magnetic frustration of Ir4+ ions located between the antiferromagnetically coupled Co ions.Comment: 10 pages, 8 figures and supplemental materia

Epigenetics in Canine Mammary Tumors: Upregulation of miR-18a and miR-18b Oncogenes Is Associated with Decreased ERS1 Target mRNA Expression and ERα Immunoexpression in Highly Proliferating Carcinomas

The expression of miRNAs is one of the main epigenetic mechanisms responsible for the regulation of gene expression in mammals, and in cancer, miRNAs participate by regulating the expression of protein-coding cancer-associated genes. In canine mammary tumors (CMTs), the ESR1 gene encodes for ERa, and represents a major target gene for miR-18a and miR-18b, previously found to be overexpressed in mammary carcinomas. A loss in ERa expression in CMTs is commonly associated with poor prognosis, and it is noteworthy that the downregulation of the ESR1 would appear to be more epigenetic than genetic in nature. In this study, the expression of ESR1 mRNA in formalin-fixed, paraffin-embedded (FFPE) canine mammary tumors (CMTs) was evaluated and compared with the expression levels of miR18a and miR18b, both assessed via RT-qPCR. Furthermore, the possible correlation between the miRNA expression data and the immunohistochemical prognostic factors (ERa immunoexpression; Ki67 proliferative index) was explored. A total of twenty-six FFPE mammary samples were used, including 22 CMTs (7 benign; 15 malignant) and four control samples (three normal mammary glands and one case of lobular hyperplasia). The obtained results demonstrate that miR-18a and miR-18b are upregulated in malignant CMTs, negatively correlating with the expression of target ESR1 mRNA. Of note, the upregulation of miRNAs strictly reflects the progressive loss of ERa immunoexpression and increased tumor cell proliferation as measured using the Ki67 index. The results suggest a central role of miR-18a and miR-18b in the pathophysiology of canine mammary tumors as potential epigenetic mechanisms involved in ERa downregulation. Moreover, as miRNA expression reflects ERa protein status and a high proliferative index, miR-18a and miR-18b may represent promising biomarkers with prognostic value. More detailed investigations on a larger number of cases are needed to better understand the influence of these miRNAs in canine mammary tumors

Congenital Oral Squamous Cell Carcinoma in a Suckling Piglet

A 3-week-old suckling piglet spontaneously died after septicemic colibacillosis. At postmortem examination, bulging and ulcerated lesions were seen, affecting the oral mucosa on the inner surface of the lower lip. After histopathological investigation, the diagnosis of congenital oral squamous cell carcinoma was made. To the best of our knowledge, this is the first case of congenital oral squamous cell carcinoma ever described. A relationship has been shown or suggested between papillomavirus infection and oral squamous cell carcinoma in humans and animals. However, next-generation sequencing study did not demonstrate any papillomavirus sequences in the case reported herein