Invariant meromorphic functions on Stein spaces

In this paper we develop fundamental tools and methods to study meromorphic functions in an equivariant setup. As our main result we construct quotients of Rosenlicht-type for Stein spaces acted upon holomorphically by complex-reductive Lie groups and their algebraic subgroups. In particular, we show that in this setup invariant meromorphic functions separate orbits in general position. Applications to almost homogeneous spaces and principal orbit types are given. Furthermore, we use the main result to investigate the relation between holomorphic and meromorphic invariants for reductive group actions. As one important step in our proof we obtain a weak equivariant analogue of Narasimhan's embedding theorem for Stein spaces.Comment: 20 pages, 1 figur

Computational Analysis of Composition-Structure-Property-Relationships in NZP-type Materials for Li-Ion Batteries

Compounds crystallizing in the structure of NaZr$_2$(PO$_4$)$_3$ (NZP) are considered as promising materials for solid state electrolytes in Li-ion batteries. Using density functional theory (DFT), a systematic computational screening of 18 NZP compounds, namely LiX$_2$(LO$_4$)$_3$ with X = Ti, V, Fe, Zr, Nb, Ru, Hf, Ta, Os, and L = P, Mn is performed with respect to their activation energies for vacancy-mediated Li migration. It is shown how the different ionic radii of the cationic substitutions influence structural characteristics such as the octahedron volumes around Li ions on the initial and transition state sites, which affect the activation energies (''composition-structure-property'' relationships). The prevalent assumption that structural bottlenecks formed by triangularly arranged oxygen atoms at a certain location along the migration path determine the energy barriers for Li migration is not supported by the DFT results. Instead, the ionic neighborhood of the migrating ion in the initial and in the transition state needs to be taken into account to relate the structure to the activation energies. This conclusion applies to Na containing NZP compounds as well.Comment: 26 pages, 9 figure

International Equity Flows and the Predictability of U.S. Stock Returns

We examined the link between international equity flows and U.S. stock returns. Based on the results of tests of in-sample and out-of-sample predictability of stock returns, we found evidence of a strong positive (negative) link between international equity flows and contemporaneous (one-month-ahead) stock returns. Our results also indicate that an investor, in real time, could have used information on the link between international equity flows and one-month-ahead stock returns to improve the performance of simple trading rules.International equity flows; predictability of stock returns; performance of trading rules; the United States

The VITEWRITE Model of Handwriting Production

This article describes the VITEWRITE model for generating handwriting movements. The model consists of a sequential controller, or motor program, that interacts with a trajectory generator to move a hand with redundant degrees of freedom. The neural trajectory generator is the Vector Integration to Endpoint (VITE) model for synchronous variable-speed control of multijoint movements. VITE properties enable a simple control strategy to generate complex handwritten script if the hand model contains redundant degrees of freedom. The controller launches transient directional commands to independent hand synergies at times when the hand begins to move, or when a velocity peak in the outflow command to a given synergy occurs. The VITE model translates these temporally disjoint synergy commands into smooth curvilinear trajectories among temporally overlapping synergetic movements. Each synergy exhibits a unimodal velocity profile during any stroke, generates letters that are invariant under speed and size rescaling, and enables effortless connection of letter shapes into words. Speed and size rescaling are achieved by scalar GO and GRO signals that express computationally simple volitional commands. Psychophysical data such as the isochrony principle, asymmetric velocity profiles, and the two-thirds power law relating movement curvature and velocity arise as emergent properties of model interactions.Office of Naval Research (N00014-92-J-1309); National Science Foundation (IRI-90-24877, IRI-87-16960); Air Force Office of Scientific Research (F49620-92-J-0225); Defense Advanced Research Projects Agency (AFOSR 90-0083

Near bottom sediment characterization offshore SW San Clemente Island

Normal incidence, 23.5 kHz seafloor acoustic backscatter data and bottom video were measured with the Deep Tow instrument package of the Scripps Institution of Oceanography in 100 meter water depth south of San Clemente Island, CA. The collected data were processed using an echo envelopesediment characterization method, to derive geoacoustic parameters such as particle mean grain size and the strength of the power law characterizing the roughness energy density spectrum of thesediment-water interface. Two regions, sand and silt, were selected based on available ground truth, perceived along-track sediment homogeneity, data quality and tow fish stability. Distinction between sand and fine grain sediments can be accomplished by creation of feature vectors comprised of mean grain size (MΦ) and interface roughness spectral strength (w2). Estimates for mean grain size and roughness spectral strength (MΦ, w2) were (1.5, 0.0095) for sand, and (6.7, 0.0033) for silt, where MΦ is expressed in PHI units, and w2 has units cm4. These results are consistent with local ground truth measurements and illustrate the potential of this sediment characterization method in survey mode