Density functional approach to study structural properties and Electric Field Gradients in rare earth materials

We investigated the effect of spin polarization on the structural properties and gradient of electric field (EFG) on Sn, In, and Cd impurity in RSn$_3$ (R=Sm, Eu, Gd) and RIn$_3$ (R=Tm, Yb, Lu) compounds. The calculations were performed self-consistently using the scalar-relativistic full potential linearized augmented plane wave method. The local density approximations (LDA) and generalized gradient approximation without spin polarization (GGA) and with spin polarization (GGA+SP) to density functional theory were applied. In addition to that we performed some calculations within open core treatment (GGA+open core). It is clearly seen that GGA+SP is successful in predicting the larger lattice parameter and the dramatic drop of EFG for R=(Eu, Yb) relative to other rare earth compounds. This is an indication that spin splitting generated by spin polarization without any modification, is capable of treating properly the highly correlated f electrons in these systems.Comment: 14 Pages, 3 Figures, 5 Table

Pointwise estimates for the Bergman kernel of the weighted Fock space

We prove upper pointwise estimates for the Bergman kernel of the weighted Fock space of entire functions in $L^2(e^{-2\phi})$ where $\phi$ is a subharmonic function with $\Delta \phi$ a doubling measure. We derive estimates for the canonical solution operator to the inhomogeneous Cauchy-Riemann equation and we characterize the compactness of this operator in terms of $\Delta \phi$

Electronic Configuration of Yb Compounds

The total energy differences between divalent and trivalent configurations of Yb ions in a number of Yb compounds are studied. Two different band theoretical methods, which differ in the treatment of the localized f electrons, are used. The results show that in all Yb compounds the valence energy differences are equal to the energy needed to localize an f electron. These valence energy differences correlate with the number of f electrons hybridizing with the conduction bands in the trivalent configuration. For divalent YbS, the pressure induced f-electron delocalization implies an intermediate valency, as also indicated by experiment

High-pressure structural, elastic and electronic properties of the scintillator host material, KMgF_3

The high-pressure structural behaviour of the fluoroperovskite KMgF_3 is investigated by theory and experiment. Density functional calculations were performed within the local density approximation and the generalized gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. In situ high-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 40 GPa using synchrotron radiation. We find that the cubic Pm\bar{3}m crystal symmetry persists throughout the pressure range studied. The calculated ground state properties -- the equilibrium lattice constant, bulk modulus and elastic constants -- are in good agreement with experimental results. By analyzing the ratio between the bulk and shear modulii, we conclude that KMgF_3 is brittle in nature. Under ambient conditions, KMgF_3 is found to be an indirect gap insulator with the gap increasing under pressure.Comment: 4 figure

PENGARUH KOMPETENSI INVESTOR DAN OVERCONFIDENCE TERHADAP FREKUENSI PERDAGANGAN

Tujuan yang ingin dicapai dalam penelitian ini adalah untuk menguji pengaruh karakteristik demografi investor terhadap kompetensi investor dan menguji pengaruh kompetensi investor dan overconfidence terhadap frekuensi perdagangan. Penelitian ini merupakan hypothesis testing (pengujian hipotesis) dengan metode survei. Populasi dalam penelitian ini adalah Investor BEI. Sampel merupakan investor online dan investor langsung yang terdaftar di perusahaan sekuritas. Pengambilan sampel menggunakan dua metode yaitu: convenience samplinguntuk responden Online dan quota samplinguntuk responden langsung yang terdaftar di perusahaan sekuritas. Pengambilan sampel menggunakan dua cara karena tingkat respond rate responden terhadap kuesioner secara langsung rendah. Jadi untuk mendapatkan sejumlah responden yang memenuhi syarat minimal penulis menggunakan dua pengambilan sampel secara online dan secara langsung. Hasil pengujian menunjukkan hasil yang konsisten dengan penelitianpenelitian sebelumnya yang menemukan bahwa karakteristik demografi investor berpengaruh pada persepsi kompetensi investor, dimana investor dengan jenis kelamin laki-laki, usia muda, pendapatan yang tinggi, dan pendidikan yang tinggi akan menyebabkan investor merasa mempunyai kompetensi yang tinggi. Untuk persepsi kompetensi investor juga berpengaruh pada frekuensi perdagangan (trading). Dari hasil pengujian regresi linear menunjukkan bahwa ada pengaruh yang signifikan persepsi kompetensi investor pada frekuensi perdagangannya. Investor dengan persepsi kompetensi yang tinggi maka investor akan lebih sering melakukan aktivitas perdagangan (trading). Selanjutnya overconfidence mempengaruhi frekuensi perdagangan investor. Dari hasil pengujian regresi linear menunjukkan bahwa overconfidence berpengaruh signifikan terhadap frekuensi perdagangan. Investor dengan overconfidence yang tinggi maka akan sering melakukan perdagangan. Kata kunci: karakteristik demografi investor, kompetensi investor, overconfidence, frekuensi perdaganga

Advantageous grain boundaries in iron pnictide superconductors

High critical temperature superconductors have zero power consumption and could be used to produce ideal electric power lines. The principal obstacle in fabricating superconducting wires and tapes is grain boundaries-the misalignment of crystalline orientations at grain boundaries, which is unavoidable for polycrystals, largely deteriorates critical current density. Here, we report that High critical temperature iron pnictide superconductors have advantages over cuprates with respect to these grain boundary issues. The transport properties through well-defined bicrystal grain boundary junctions with various misorientation angles (thetaGB) were systematically investigated for cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (JcBGB) remained high (> 1 MA/cm2) and nearly constant up to a critical angle thetac of ~9o, which is substantially larger than the thetac of ~5o for YBCO. Even at thetaGB > thetac, the decay of JcBGB was much smaller than that of YBCO.Comment: to appear in Nature Communication

Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.National Science Foundation (U.S.)United States. Office of Naval Researc

Half-Metallic Graphene Nanoribbons

Electrical current can be completely spin polarized in a class of materials known as half-metals, as a result of the coexistence of metallic nature for electrons with one spin orientation and insulating for electrons with the other. Such asymmetric electronic states for the different spins have been predicted for some ferromagnetic metals - for example, the Heusler compounds- and were first observed in a manganese perovskite. In view of the potential for use of this property in realizing spin-based electronics, substantial efforts have been made to search for half-metallic materials. However, organic materials have hardly been investigated in this context even though carbon-based nanostructures hold significant promise for future electronic device. Here we predict half-metallicity in nanometre-scale graphene ribbons by using first-principles calculations. We show that this phenomenon is realizable if in-plane homogeneous electric fields are applied across the zigzag-shaped edges of the graphene nanoribbons, and that their magnetic property can be controlled by the external electric fields. The results are not only of scientific interests in the interplay between electric fields and electronic spin degree of freedom in solids but may also open a new path to explore spintronics at nanometre scale, based on graphene

Half-Metallic Ferrimagnetism in Mn_2VAl

We show that Mn_2VAl is a compound for which the generalized gradient approximation (GGA) to the exchange-correlation functional in density functional theory makes a qualitative change in predicted behavior compared to the usual local density approximation (LDA). Application of GGA leads to prediction of Mn_2VAl being a half-metallic ferrimagnet, with the minority channel being the conducting one. The electronic and magnetic structure is analyzed and contrasted with the isostructural enhanced semimetal Fe_2VAl.Comment: 5 pages, Latex, 6 postscript figures. Description and figures of the (minority) Fermi surfaces have been adde