One Dimensional Kondo Lattice Model Studied by the Density Matrix Renormalization Group Method

Recent developments of the theoretical investigations on the one-dimensional Kondo lattice model by using the density matrix renormalization group (DMRG) method are discussed in this review. Short summaries are given for the zero-temperature DMRG, the finite-temperature DMRG, and also its application to dynamic quantities. Away from half-filling, the paramagnetic metallic state is shown to be a Tomonaga-Luttinger liquid with the large Fermi surface. For the large Fermi surface its size is determined by the sum of the densities of the conduction electrons and the localized spins. The correlation exponent K_rho of this metallic phase is smaller than 1/2. At half-filling the ground state is insulating. Excitation gaps are different depending on channels, the spin gap, the charge gap and the quasiparticle gap. Temperature dependence of the spin and charge susceptibilities and specific heat are discussed. Particularly interesting is the temperature dependence of various excitation spectra, which show unusual properties of the Kondo insulators.Comment: 18 pages, 23 Postscript figures, REVTe

A 16S rDNA-Based Quantitative Assay for Monitoring \u3ci\u3eLactobacillus Plantarum\u3c/i\u3e in Silage

Ensilage of herbaceous biomass can be enhanced by applying pre-selected fermentative bacteria, however insufficient is known about the population dynamics of such starter cultures under a range of ensiling conditions. Classical methods for species-specific quantification of bacteria are labour intensive. An alternative approach is the detection of bacteria based on molecular markers for species-specific regions within their genomic DNA (e.g. the 16S rDNA sequence). In this study, a quantitative marker assay using the real-time PCR technique (Q-PCR) is described for Lactobacillus plantarum, a bacterium often used for silage starter cultures

Quantum Fluctuations in the Chirped Pendulum

An anharmonic oscillator when driven with a fast, frequency chirped voltage pulse can oscillate with either small or large amplitude depending on whether the drive voltage is below or above a critical value-a well studied classical phenomenon known as autoresonance. Using a 6 GHz superconducting resonator embedded with a Josephson tunnel junction, we have studied for the first time the role of noise in this non-equilibrium system and find that the width of the threshold for capture into autoresonance decreases as the square root of T, and saturates below 150 mK due to zero point motion of the oscillator. This unique scaling results from the non-equilibrium excitation where fluctuations, both quantum and classical, only determine the initial oscillator motion and not its subsequent dynamics. We have investigated this paradigm in an electrical circuit but our findings are applicable to all out of equilibrium nonlinear oscillators.Comment: 5 pages, 4 figure

Probing Stellar Dynamics in Galactic Nuclei

Electromagnetic observations over the last 15 years have yielded a growing appreciation for the importance of supermassive black holes (SMBH) to the evolution of galaxies, and for the intricacies of dynamical interactions in our own Galactic center. Here we show that future low-frequency gravitational wave observations, alone or in combination with electromagnetic data, will open up unique windows to these processes. In particular, gravitational wave detections in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to unprecedented precision and will provide clues to the properties of the otherwise undetectable stellar remnants expected to populate the centers of galaxies. Such observations are therefore keys to understanding the interplay between SMBHs and their environments.Comment: 8 pages, Science white paper for the Astro2010 Decadal Surve

Aerosol nucleation over oceans and the role of galactic cosmic rays

International audienceWe investigate formation of sulfate aerosol in the marine troposphere from neutral and charged nucleation of H2SO4 and H2O. A box model of neutral and charged aerosol processes is run on a grid covering the oceans. Input data are taken from a model of galactic cosmic rays in the atmosphere, and from global chemistry and transport models. We find a weak aerosol production over the tropical oceans in the lower and middle troposphere, and a stronger production at higher latitudes, most notably downwind of industrial regions. The highest aerosol production, however, occurs in the upper troposphere, in particular in the tropics. This finding supports the proposition by which non-sea salt marine boundary layer aerosol in tropical regions does not form in situ, but nucleates in the upper troposphere from convectively lifted and cloud processed boundary layer air rich in aerosol precursor gases, from where it descends in subsiding air masses compensating convection. Convection of boundary layer air also appears to drive the formation of condensation nuclei in the tropical upper troposphere which maintains the stratospheric aerosol layer in the absence of volcanic activity. Neutral nucleation contributes only marginally to aerosol production in our simulations. This highlights the importance of charged binary and of ternary nucleation involving ammonia for aerosol formation. In clean marine regions however, ammonia concentrations seem too low to support ternary nucleation, making binary nucleation from ions a likely pathway for sulfate aerosol formation. On the other hand, our analysis indicates that the variation of ionization by galactic cosmic rays over the decadal solar cycle does not entail a response in aerosol production and cloud cover via the second indirect aerosol effect that would explain observed variations in global cloud cover. We estimate that the variation in radiative forcing resulting from a response of clouds to the change in galactic cosmic ray ionization and subsequent aerosol production over the decadal solar cycle is smaller than the concurrent variation of total solar irradiance

Tailored fuel injection within a Mach 12 shape transitioning scramjet

Three-dimensional computational fluid dynamic simulations were performed for the Mach 12 Rectangular-to-Elliptical Shape-Transitioning scramjet. Present injector arrangements at the combustor entrance displayed low jet penetration, resulting in a oxygen-based combustion efficiency of 84.9%. It is proposed to convert three cowl-side injectors into one larger injector located further upstream. To support this, injector configurations were investigated computationally, taking injectors optimised for penetration at lower Mach numbers, and evaluating their performance at higher Mach number flight conditions. It was determined that reduced performance of these optimised injectors was encountered at scramjet flight conditions above their design point, with circular injectors at equal or greater injection angles displaying greater penetration and mixing capabilities

The SED of Low-Luminosity AGNs at high-spatial resolution

The inner structure of AGNs is expected to change below a certain luminosity limit. The big blue bump, footprint of the accretion disk, is absent for the majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol < 10^42 erg/s. However, the study of LLAGN is a complex task due to the contribution of the host galaxy, which light swamps these faint nuclei. This is specially critical in the IR range, at the maximum of the torus emission, due to the contribution of the old stellar population and/or dust in the nuclear region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear emission for some of the nearest LLAGNs in the Southern Hemisphere. These data were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays (Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy distribution (SED) for each AGN with a consistent spatial resolution (< 0.5") across the whole spectral range. From the individual SEDs, we construct an average SED for LLAGNs sampled in all the wavebands mentioned before. Compared with previous multiwavelength studies of LLAGNs, this work covers the mid-IR and NIR ranges with high-spatial resolution data. The LLAGNs in the sample present a large diversity in terms of SED shapes. Some of them are very well described by a self-absorbed synchrotron (e.g. NGC 1052), while some other present a thermal-like bump at ~1 micron (NGC 4594). All of them are significantly different when compared with bright Seyferts and quasars, suggesting that the inner structure of AGNs (i.e. the torus and the accretion disk) suffers intrinsic changes at low luminosities.Comment: 8 pages, 5 figures. To appear in the proceedings of "Astrophysics at High Angular Resolution" (AHAR 2011

Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling

We study the influence of the lattice structure, the Jahn-Teller effect and the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb). The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60 (bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases) the value Uc of the Coulomb integral at which the metal-insulator transition occurs. There is an important partial cancellation between the Jahn-Teller effect and the Hund's rule coupling.Comment: 4 pages, RevTeX, 3 eps figure, additional material available at http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene

High-resolution scanning force microscopy of gold nanoclusters on the KBr (001) surface

In this study we use a combination of dynamic scanning force microscopy experiments and first-principles simulations to study the imaging process of gold nanoclusters adsorbed on the (001) surface of KBr. In previous experiments atomic resolution was readily obtained on the KBr substrate. However, it was not possible to resolve atoms within the clusters themselves. This correlates with imaging simulations we present here using several different probable tip models: measurable contrast was readily achieved on the KBr surface and on the gold (001) surface, but simulations on the clusters demonstrated poor contrast for all tips. We further consider the role of cluster charging in the tip-surface interaction, and the role that surface defects play in the properties of adsorbed clusters.Peer reviewe