Estimating the efficient price from the order flow: a Brownian Cox process approach

At the ultra high frequency level, the notion of price of an asset is very ambiguous. Indeed, many different prices can be defined (last traded price, best bid price, mid price,...). Thus, in practice, market participants face the problem of choosing a price when implementing their strategies. In this work, we propose a notion of efficient price which seems relevant in practice. Furthermore, we provide a statistical methodology enabling to estimate this price form the order flow

The nanoscale phase separation in hole-doped manganites

A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge-orbital order of the system. We show in the present article that rather than the macroscopic phase separation, an homogeneous short-ranged charge-orbital order accompanied by a spin glass state occurs, as an intrinsic result of the uniformity of the random potential perturbation induced by the solid solution of the cations on the $A$-sites of the structure of these materials. Hence the phase separation does occur, but in a more subtle and interesting nanoscopic form, here referred as ``homogeneous''. Remarkably, this ``nanoscale phase separation'' alone is able to bring forth the colossal magnetoresistance in the perovskite manganites, and is potentially relevant to a wide variety of other magnetic and/or electrical properties of manganites, as well as many other transition metal oxides, in bulk or thin film form as we exemplify throughout the article.Comment: jpsj2 TeX style (J. Phys. Soc. Jpn); 18 pages, 7 figure

Bandwidth-disorder phase diagram of half doped layered manganites

Phase diagrams in the plane of $r_A$ (the average ionic radius, related to one-electron bandwidth $W$) and $\sigma^2$ (the ionic radius variance, measuring the quenched disorder), or ``bandwidth-disorder phase diagrams'', have been established for perovskite manganites, with three-dimensional (3$D$) Mn-O network. Here we establish the intrinsic bandwidth-disorder phase diagram of half-doped layered manganites with the two-dimensional (2$D$) Mn-O network, examining in detail the ``mother state'' of the colossal magnetoresistance (CMR) phenomenon in crystals without ferromagnetic instability. The consequences of the reduced dimensionality, from 3$D$ to 2$D$, on the order-disorder phenomena in the charge-orbital sectors are also highlighted.Comment: REVTeX 4 style; 5 pages, 4 figure

Large-eddy simulation of the flow in a lid-driven cubical cavity

Large-eddy simulations of the turbulent flow in a lid-driven cubical cavity have been carried out at a Reynolds number of 12000 using spectral element methods. Two distinct subgrid-scales models, namely a dynamic Smagorinsky model and a dynamic mixed model, have been both implemented and used to perform long-lasting simulations required by the relevant time scales of the flow. All filtering levels make use of explicit filters applied in the physical space (on an element-by-element approach) and spectral (modal) spaces. The two subgrid-scales models are validated and compared to available experimental and numerical reference results, showing very good agreement. Specific features of lid-driven cavity flow in the turbulent regime, such as inhomogeneity of turbulence, turbulence production near the downstream corner eddy, small-scales localization and helical properties are investigated and discussed in the large-eddy simulation framework. Time histories of quantities such as the total energy, total turbulent kinetic energy or helicity exhibit different evolutions but only after a relatively long transient period. However, the average values remain extremely close

Eu0.5_{0.5}Sr1.5_{1.5}MnO4_4: a three-dimensional XY spin glass

The frequency, temperature, and dc-bias dependence of the ac-susceptibility of a high quality single crystal of the Eu$_{0.5}$Sr$_{1.5}$MnO$_4$ layered manganite is investigated. Eu$_{0.5}$Sr$_{1.5}$MnO$_4$ behaves like a XY spin glass with a strong basal anisotropy. Dynamical and static scalings reveal a three-dimensional phase transition near $T_g$ = 18 K, and yield critical exponent values between those of Heisenberg- and Ising-like systems, albeit slightly closer to the Ising case. Interestingly, as in the latter system, the here observed rejuvenation effects are rather weak. The origin and nature of the low temperature XY spin glass state is discussed.Comment: REVTeX 4 style; 5 pages, 4 figure

Semirelativistic potential model for low-lying three-gluon glueballs

The three-gluon glueball states are studied with the generalization of a semirelativistic potential model giving good results for two-gluon glueballs. The Hamiltonian depends only on 3 parameters fixed on two-gluon glueball spectra: the strong coupling constant, the string tension, and a gluon size which removes singularities in the potential. The Casimir scaling determines the structure of the confinement. Low-lying $J^{PC}$ states are computed and compared with recent lattice calculations. A good agreement is found for $1^{--}$ and $3^{--}$ states, but our model predicts a $2^{--}$ state much higher in energy than the lattice result. The $0^{-+}$ mass is also computed.Comment: 2 figure

The few-body problem in terms of correlated gaussians

In their textbook, Suzuki and Varga [Y. Suzuki and K. Varga, {\em Stochastic Variational Approach to Quantum-Mechanical Few-Body Problems} (Springer, Berlin, 1998)] present the stochastic variational method in a very exhaustive way. In this framework, the so-called correlated gaussian bases are often employed. General formulae for the matrix elements of various operators can be found in the textbook. However the Fourier transform of correlated gaussians and their application to the management of a relativistic kinetic energy operator are missing and cannot be found in the literature. In this paper we present these interesting formulae. We give also a derivation for new formulations concerning central potentials; the corresponding formulae are more efficient numerically than those presented in the textbook.Comment: 10 page

WIYN Open Cluster Study. XXXVIII. Stellar Radial Velocities in the Young Open Cluster M35 (NGC 2168)

We present 5201 radial-velocity measurements of 1144 stars, as part of an ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN 3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude range of 13.0<V<16.5 (1.6 - 0.8 Msun) and extends spatially to a radius of 30 arcminutes (7 pc in projection at a distance of 805 pc or 4 core radii). Due to its youth, M35 provides a sample of late-type stars with a range of rotation periods. Therefore, we analyze the radial-velocity measurement precision as a function of the projected rotational velocity. For narrow-lined stars (v sin i < 10 km/s), the radial velocities have a precision of 0.5 km/s, which degrades to 1.0 km/s for stars with v sin i = 50 km/s. The radial-velocity distribution shows a well-defined cluster peak with a central velocity of -8.16 +/- 0.05 km/s, permitting a clean separation of the cluster and field stars. For stars with >=3 measurements, we derive radial-velocity membership probabilities and identify radial-velocity variables, finding 360 cluster members, 55 of which show significant radial- velocity variability. Using these cluster members, we construct a color-magnitude diagram for our stellar sample cleaned of field star contamination. We also compare the spatial distribution of the single and binary cluster members, finding no evidence for mass segregation in our stellar sample. Accounting for measurement precision, we place an upper limit on the radial-velocity dispersion of the cluster of 0.81 +/- 0.08 km/s. After correcting for undetected binaries, we derive a true radial-velocity dispersion of 0.65 +/- 0.10 km/s.Comment: accepted for publication in A