Search

A novel model was recently proposed by Schulze-Forster et al. in [1] for unsupervised music source separation. This model allows to tackle some of the major shortcomings of existing source separation frameworks. Specifically, it eliminates the need for isolated sources during training, performs efficiently with limited data, and can handle homogeneous sources (such as singing voice). But, this model relies on an external multipitch estimator and incorporates an Ad hoc voice assignment procedure. In this paper, we propose to extend this framework and to build a fully differentiable model by integrating a multipitch estimator and a novel differentiable assignment module within the core model. We show the merits of our approach through a set of experiments, and we highlight in particular its potential for processing diverse and unseen data.

Solutions of the discrete Painlev\'e II hierarchy are shown to be in relation with a family of Toeplitz determinants describing certain quantities in multicritical random partitions models, for which the limiting behavior has been recently considered in the literature. Our proof is based on the Riemann-Hilbert approach for the orthogonal polynomials on the unit circle related to the Toeplitz determinants of interest. This technique allows us to construct a new Lax pair for the discrete Painlev\'e II hierarchy that is then mapped to the one introduced by Cresswell and Joshi.

Using Riemann-Hilbert methods, we establish a Tracy-Widom like formula for the generating function of the occupancy numbers of the Pearcey process. This formula is linked to a coupled vector differential equation of order three. We also obtain a non linear coupled heat equation. Combining these two equations we obtain a PDE for the logarithm of the the generating function of the Pearcey process., Comment: 18 pages, 3 figures

We extend Cellular Automata to time-varying discrete geometries. In other words we formalize, and prove theorems about, the intuitive idea of a discrete manifold which evolves in time, subject to two natural constraints: the evolution does not propagate information too fast; and it acts everywhere the same. For this purpose we develop a correspondence between complexes and labeled graphs. In particular we reformulate the properties that characterize discrete manifolds amongst complexes, solely in terms of graphs. In dimensions $n<4$, over bounded-star graphs, it is decidable whether a Cellular Automaton maps discrete manifolds into discrete manifolds., Comment: 19 pages, 10 figures

In NaNiO2, Ni3+ ions form a quasi two dimensional triangular lattice of S = 1=2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferro- magnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1-20 cm-1, in magnetic fields up to 14 T. The bulk of the results are interpreted in terms of a phenomenological model involving bi-axial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane. The direction of the easy plane is constrained by the collective Jahn-Teller distortion occurring in this material at 480 K.

In both spinel compounds GeCo$_2$O$_4$ and GeNi$_2$O$_4$ which order antiferromagnetically (at $T_N = 23.5 K$ and $T_{N_1} = 12.13 K$, $T_{N_2} = 11.46 K$) with different Curie Weiss temperatures ($T_{CW}$=80.5 K and -15 K), the usual magnetic frustration criterion $f=|T_{CW}|/T_N>>1$ is not fulfilled. Using neutron powder diffraction and magnetization measurements up to 55 T, both compounds are found with a close magnetic ground state at low temperature and a similar magnetic behavior (but with a different energy scale), even though spin anisotropy and first neighbor exchange interactions are quite different. This magnetic behavior can be understood when considering the main four magnetic exchange interactions. Frustration mechanisms are then enlightened., Comment: submitted to Phys.Rev.B (2006)

Thin films of Sm0.5Ca0.5MnO3 manganites with charge ordering (CO) properties and colossal magnetoresistance were synthesized by pulsed laser deposition technique on (100)-SrTiO3 and (100)-LaAlO3 substrates. We first compare the structural modifications as function of the substrate and film thickness. Secondly, measuring transport properties in magnetic fields up to 24T, we establish the temperature-field phase diagram describing the stability of the CO state and compare it to bulk material. We show that some structural modification induced by the substrate occurs and that the CO melting magnetic field is greatly reduced. Moreover, with the temperature decrease, no modification of the lattice parameters is observed. We then propose an explanation based on the quenching of the unit cell of the film that adopts the in-plane lattice parameters of the substrate and thus, prevents the complete growth of the CO state at low temperature., Comment: to be published in Journal of Applied Physics

In the Li1-xNaxNiO2 solid solutions three different single phase regions exist: for x > 0.9, forx = 0.7 and for x < 0.3. Although the intermediate compound does not show the cooperative Jahn-Teller transition of NaNiO2, its magnetic properties remain very similar with, in particular, the low temperature 3D magnetic ordering. Therefore, the strong coupling between orbital and spindegrees of freedom, characteristic of other oxides like perovskites, and usually invoked to explainthe absence of both long-range orbital and magnetic ordering in LiNiO2, seems not to take placein these layered compounds with 90-degree bonds. We also discuss the relevance of the O crystal fieldsplitting induced by the trigonal distortion, in generating AFM Ni-Ni in-plane interactions.

Compressed Pr0.5Ca0.5MnO3 films (250nm) deposited on LaAlO3 have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic., Comment: to be published in EPJB

We have investigated the magnetic-field-induced phase transition of charge-ordered (CO) Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ thin films, deposited onto (100)-oriented LaAlO$_3$ and (100)-oriented SrTiO$_3$ substrates using the pulsed laser deposition technique, by measuring the transport properties with magnetic fields up to 22T. The transition to a metallic state is observed on both substrates by application of a critical magnetic field ($H_C>10T$ at 60K). The value of the field required to destroy the charge-ordered insulating state, lower than the bulk compound, depends on both the substrate and the thickness of the film. The difference of the critical magnetic field between the films and the bulk material is explained by the difference of in-plane parameters at low temperature (below the CO transition). Finally, these results confirm that the robustness of the CO state, depends mainly on the stress induced by the difference in the thermal dilatations between the film and the substrate., Comment: 10 pages, 6 figures. To be published in Phys. Rev. B

Susceptibility, high-field magnetization and submillimeter wave electron spin resonance measurements of layered quasi-stoichiometric Li1-xNi1+xO2 are reported and compared to isomorphic NaNiO2. A new mechanism of magnetic frustration induced by the excess Ni ions always present in the Li layers is proposed. We finally comment on the possible realization of an orbital liquid state in this controversial compound., Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, Rapid Comm

The role played by the Nd ions in the magnetic properties of Nd0.5Ca0.5MnO3 and Nd0.7Ca0.3MnO3 is studied using static magnetization, neutron diffraction and high frequency (9.4-475GHz) Electron Spin Resonance. We show that the Nd ions are weakly coupled to the Mn ions via ferromagnetic exchange and are responsible for the peculiar ferromagnetic resonance observed in the FM phase of both compounds (ground state below 120K for x=0.3, high field state for x=0.5). We then use ESR to look for magnetic phase separation in the low field, CO phase of Nd0.5Ca0.5MnO3. We show that there is no trace of the FM phase imbedded in the CO phase, contrary to what is observed in La0.5Ca0.5MnO3 or Pr0.5Sr0.5MnO3., Comment: to be published in phys.Rev.B as a Rapid Comm

In the manganite Nd0.5Ca0.5MnO3, charge ordering occurs at much higher temperature than the antiferromagnetic order (TCO=250K,TN=160K). The magnetic behavior of the phase TN

The magnetic phase diagram of $La_{1-\delta}MnO_{3}$ powdered samples have been studied as a function of $\delta $ in the low doping range. $La_{0.97}MnO_{3}$ has a canted magnetic structure at low temperature $(\theta \simeq 130\QTR{group}{{}^{\circ}})$. Above $T_{C}=118K$, it becomes a paramagnet with a huge effective magnetic moment, $\mu_{eff}=6.0\mu_{B}$, reflecting the presence of magnetoelastic polarons which are not affected by the magnetic field (up to 20T) nor the temperature $(1.2T_{C}