Low Temperature Magnetic Properties of the Double Exchange Model

We study the {\it ferromagnetic} (FM) Kondo lattice model in the strong coupling limit (double exchange (DE) model). The DE mechanism proposed by Zener to explain ferromagnetism has unexpected properties when there is more than one itinerant electron. We find that, in general, the many-body ground state of the DE model is {\it not} globally FM ordered (except for special filled-shell cases). Also, the low energy excitations of this model are distinct from spin wave excitations in usual Heisenberg ferromagnets, which will result in unusual dynamic magnetic properties.Comment: 5 pages, RevTeX, 5 Postscript figures include

A carbuncle cure for the Harten-Lax-van Leer contact (HLLC) scheme using a novel velocity-based sensor

AbstractA hybrid numerical flux scheme is proposed by adapting the carbuncle-free modified Harten-Lax-van Leer contact (HLLCM) scheme to smoothly revert to the Harten-Lax-van Leer contact (HLLC) scheme in regions of shear. This hybrid scheme, referred to as the HLLCT scheme, employs a novel, velocity-based shear sensor. In contrast to the non-local pressure-based shock sensors often used in carbuncle cures, the proposed shear sensor can be computed in a localized manner meaning that the HLLCT scheme can be easily introduced into existing codes without having to implement additional data structures. Through numerical experiments, it is shown that the HLLCT scheme is able to resolve shear layers accurately without succumbing to the shock instability.</jats:p

Some Insights into the Screech Tone of Under-Expanded Supersonic Jets Using Dynamic Mode Decomposition

Jet screech is an intense pure tone which has attracted decades of research interest due to its possible detrimental effect on engineering structures. Its modes and closure mechanisms have been investigated analytically, experimentally, and numerically; however, there are still outstanding questions regarding the generation and propagation of instabilities in the near-field region. Recent studies have identified that these instabilities travel inside the jet potential during the screech process to form the complete feedback loop. Using dynamic mode decomposition on a three-dimensional pressure near field from large-eddy simulation results, the present study examines the viability of modal decomposition to provide further insights into the screech mode and its associated characteristics, and investigates the effect of temperature mixing in jet screech. The results show that modal decomposition identifies the helical structure of screech mode. Furthermore, a method is proposed to reveal the temporal evolution of dynamic screech mode. It was found that the bulk behavior of the pressure field at screech frequency propagates backward toward the nozzle exit.Ministry of Education (MOE)The authors gratefully acknowledge the support provided for this study by the Singapore Ministry of Education AcRF Tier-2 Grant (Grant No. MOE2014-T2-1-002)

Persistent Current in the Ferromagnetic Kondo Lattice Model

In this paper, we study the zero temperature persistent current in a ferromagnetic Kondo lattice model in the strong coupling limit. In this model, there are spontaneous spin textures at some values of the external magnetic flux. These spin textures contribute a geometric flux, which can induce an additional spontaneous persistent current. Since this spin texture changes with the external magnetic flux, we find that there is an anomalous persistent current in some region of magnetic flux: near Phi/Phi_0=0 for an even number of electrons and Phi/Phi_0=1/2 for an odd number of electrons.Comment: 6 RevTeX pages, 10 figures include

Transport Properties of the One Dimensional Ferromagnetic Kondo Lattice Model : A Qualitative Approach to Oxide Manganites

The transport properties of the ferromagnetic Kondo lattice model in one dimension are studied via bosonization methods. The antiferromagnetic fluctuations, which normally appear because of the RKKY interactions, are explicitly taken into account as a direct exchange between the ``core'' spins. It is shown that in the paramagnetic regime with the local antiferromagnetic fluctuations, the resistivity decays exponentially as the temperature increases while in the ferromagnetic regime the system is an almost perfect conductor. %A non-perturbative description of localized spin polarons %in the paramagnetic region is obtained. The effect of a weak applied field is discussed to be reduced to the case of the ferromagnetic state leading to band splitting. The qualitative relevance of the results for the problem of the Oxide Manganites is emphasized.Comment: 4 pages, REVTe

Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides

A new mechanism is proposed to explain the colossal magnetoresistance and related phenomena. Moving electrons accompanied by Jahn-Teller phonon and spin-wave clouds may form composite polarons in ferromagnetic narrow-band manganites. The ground-state and finite-temperature properties of such composite polarons are studied in the present paper. By using a variational method, it is shown that the energy of the system at zero temperature decreases with the formation of composite polaron; the energy spectrum and effective mass of the composite polaron at finite temperature is found to be strongly renormalized by the temperature and the magnetic field. It is suggested that the composite polaron contribute significantly to the transport and the thermodynamic properties in ferromagnetic narrow-band metallic manganese oxides.Comment: Latex, no figur

Finite-Size Bosonization and Self-Consistent Harmonic Approximation

The self-consistent harmonic approximation is extended in order to account for the existence of Klein factors in bosonized Hamiltonians. This is important for the study of finite systems where Klein factors cannot be ignored a priori. As a test we apply the method to interacting spinless fermions with modulated hopping. We calculate the finite-size corrections to the energy gap and the Drude weight and compare our results with the exact solution for special values of the model parameters

Identification, cDNA cloning, and targeted deletion of p70, a novel, ubiquitously expressed SH3 domain-containing protein

In a screen for proteins that interact with Jak2, we identified a previously uncharacterized 70-kDa protein and cloned the corresponding cDNA. The predicated sequence indicates that p70 contains an SH3 domain and a C-terminal domain with similarities to the catalytic motif of phosphoglycerate mutase. p70 transcripts were found in all tissues examined. Similarly, when an antibody raised against a C-terminal peptide to analyze p70 protein expression was used, all murine tissues examined were found to express p70. To investigate the in vivo role of p70, we generated a p70-deficient mouse strain. Mice lacking p70 are viable, develop normally, and do not display any obvious abnormalities. No differences were detected in various hematological parameters, including bone marrow colony-forming ability, in response to cytokines that utilize Jak2. In addition, no impairment in B- and T-cell development and proliferative ability was detected

Dynamic similarity design method for an aero-engine dualrotor test rig

This paper presents a dynamic similarity design method to design a scale dynamic similarity model (DSM) for a dual-rotor test rig of an aero-engine. Such a test rig is usually used to investigate the major dynamic characteristics of the full-size model (FSM) and to reduce the testing cost and time for experiments on practical aero engine structures. Firstly, the dynamic equivalent model (DEM) of a dual-rotor system is modelled based on its FSM using parametric modelling, and the first 10 frequencies and mode shapes of the DEM are updated to agree with the FSM by modifying the geometrical shapes of the DEM. Then, the scaling laws for the relative parameters (such as geometry sizes of the rotors, stiffness of the supports, inherent properties) between the DEM and its scale DSM were derived from their equations of motion, and the scaling factors of the above-mentioned parameters are determined by the theory of dimensional analyses. After that, the corresponding parameters of the scale DSM of the dual-rotor test rig can be determined by using the scaling factors. In addition, the scale DSM is further updated by considering the coupling effect between the disks and shafts. Finally, critical speed and unbalance response analysis of the FSM and the updated scale DSM are performed to validate the proposed method