Longitudinal vortices in a transitioning boundary layer

Naturally occurring spanwise variations of the streamwise velocity component, characteristic of longitudinal vortices embedded in a transitioning boundary layer were explored using hot-wire anemometers. A vibrating ribbon introduced stable or unstable Tollmien-Schlichting waves into the laminar boundary layer. These damped or growing disturbances always developed a strong three dimensional pattern even though no spanwise perturbations were artificially induced. Changing the radius of the leading edge and other modifications to the flat plate, wind tunnel and boundary layer did not alter the spanwise wavelength of the vortices

Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition

We investigate the dynamics of a large anisotropic spin whose easy-axis component is coupled to a bosonic bath with a spectral function J(\w)\propto \omega^s. Such a spin complex might be realized in a single-molecular magnet. Using the non-perturbative renormalization group, we calculate the line of quantum-phase transitions in the sub-ohmic regime ($s<1$). These quantum-phase transitions only occur for integer spin $J$. For half-integer $J$, the low temperature fixed-point is identical to the fixed-point of the spin-boson model without quantum-tunneling between the two levels. Short-time coherent oscillations in the spin decay prevail even into the localized phase in the sub-ohmic regime. The influence of the reorganization energy and the recurrence time on the decoherence in the absence of quantum-tunneling is discussed.Comment: 14 pages,7 figure

Ab initio study of a mechanically gated molecule: From weak to strong correlation

The electronic spectrum of a chemically contacted molecule in the junction of a scanning tunneling microscope can be modified by tip retraction. We analyze this effect by a combination of density functional, many-body perturbation and numerical renormalization group theory, taking into account both the non-locality and the dynamics of electronic correlation. Our findings, in particular the evolution from a broad quasiparticle resonance below to a narrow Kondo resonance at the Fermi energy, correspond to the experimental observations.Comment: 4 pages, 3 figure

A Numerical Renormalization Group approach to Green's Functions for Quantum Impurity Models

We present a novel technique for the calculation of dynamical correlation functions of quantum impurity systems in equilibrium with Wilson's numerical renormalization group. Our formulation is based on a complete basis set of the Wilson chain. In contrast to all previous methods, it does not suffer from overcounting of excitation. By construction, it always fulfills sum rules for spectral functions. Furthermore, it accurately reproduces local thermodynamic expectation values, such as occupancy and magnetization, obtained directly from the numerical renormalization group calculations.Comment: 13 pages, 7 figur

The young star cluster system of the Antennae galaxies

“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s10509-009-0103-xThe study of young star cluster (YSC) systems, preferentially in starburst and merging galaxies, has seen great interest in the recent past, as it provides important input to models of star formation. However, even some basic properties (such as the luminosity function; LF) of YSC systems are still being debated. Here, we study the photometric properties of the YSC system in the nearest major merger system, the Antennae galaxies. We find evidence for the existence of a statistically significant turnover in the LF.Peer reviewe

On the variation in crack-opening stresses at different locations in a three-dimensional body

Crack propagation and closure behavior of thin, and thick middle crack tension specimens under constant amplitude loading were investigated using a three dimensional elastic plastic finite element analysis of fatigue crack propagation and closure. In the thin specimens the crack front closed first on the exterior (free) surface and closed last in the interior during the unloading portion of cyclic loading; a load reduced displacement technique was used to determine crack opening stresses at specified locations in the plate from the displacements calculated after the seven cycle. All the locations were on the plate external surface and were located near the crack tip, behind the crack tip, at the centerline of the crack. With this technique, the opening stresses at the specified points were found to be 0.52, 0.42, and 0.39 times the maximum applied stress

Kondo effect by controlled cleavage of a single molecule contact

Conductance measurements of a molecular wire, contacted between an epitaxial molecule-metal bond and the tip of a scanning tunneling microscope, are reported. Controlled retraction of the tip gradually de-hybridizes the molecule from the metal substrate. This tunes the wire into the Kondo regime in which the renormalized molecular transport orbital serves as spin impurity at half filling and the Kondo resonance opens up an additional transport channel. Numerical renormalization group simulations suggest this type of behavior to be generic for a common class of metal molecule bonds. The results demonstrate a new approach to single-molecule experiments with atomic-scale contact control and prepare the way for the ab initio simulation of many-body transport through single-molecule junctions.Comment: Main text: 41 pages including references and captions, 9 figures. Supplementary information: 5 pages including 2 figures New experimental and theoretical data supporting initial claims are added. The paper has been reworked from the letter format into a longer versio

Climbing fiber regulation of spontaneous Purkinje cell activity and cerebellum-dependent blink responses

It has been known for a long time that GABAergic Purkinje cells in the cerebellar cortex, as well as their target neurons in the cerebellar nuclei, are spontaneously active. The cerebellar output will, therefore, depend on how input is integrated into this spontaneous activity. It has been shown that input from climbing fibers originating in the inferior olive controls the spontaneous activity in Purkinje cells. While blocking climbing fiber input to the Purkinje cells causes a dramatic increase in the firing rate, increased climbing fiber activity results in reduced Purkinje cell activity. However, the exact calibration of this regulation has not been examined systematically. Here we examine the relation between climbing fiber stimulation frequency and Purkinje cell activity in unanesthetized decerebrated ferrets. The results revealed a gradual suppression of Purkinje cell activity, starting at climbing fiber stimulation frequencies as low as 0.5 Hz. At 4 Hz, Purkinje cells were completely silenced. This effect lasted an average of 2 min after the stimulation rate was reduced to a lower level. We also examined the effect of sustained climbing fiber stimulation on overt behavior. Specifically, we analyzed conditioned blink responses, which are known to be dependent on the cerebellum, while stimulating the climbing fibers at different frequencies. In accordance with the neurophysiological data, the conditioned blink responses were suppressed at stimulation frequencies of =4 Hz

The genes that carcinogens act upon

No abstract available