Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor

Discontinuous changes of the lattice parameters at the Mott metal-insulator transition are detected by high-resolution dilatometry on deuterated crystals of the layered organic conductor $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The uniaxial expansivities uncover a striking and unexpected anisotropy, notably a zero-effect along the in-plane c-axis along which the electronic interactions are relatively strong. A huge thermal expansion anomaly is observed near the end-point of the first-order transition line enabling to explore the critical behavior with very high sensitivity. The analysis yields critical fluctuations with an exponent $\tilde{\alpha} \simeq$ 0.8 $\pm$ 0.15 at odds with the novel criticality recently proposed for these materials [Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an intricate role of the lattice degrees of freedom in the Mott transition for the present materials.Comment: 4 pages, 4 figure

The evolution of faint AGN between z~1 and z~5 from the COMBO-17 survey

We present a determination of the optical/UV AGN luminosity function and its evolution, based on a large sample of faint (R<24) QSOs identified in the COMBO-17 survey. Using multi-band photometry in 17 filters within 350nm < lambda_obs < 930nm, we could simultaneously determine photometric redshifts with an accuracy of sigma_z<0.03 and obtain spectral energy distributions. The redshift range covered by the sample is 1.2<z<4.8, which implies that even at z~3, the sample reaches below luminosities corresponding to M_B = -23, conventionally employed to distinguish between Seyfert galaxies and quasars. We clearly detect a broad plateau-like maximum of quasar activity around z~2 and map out the smooth turnover between z~1 and z~4. The shape of the LF is characterised by some mild curvature, but no sharp `break' is present within the range of luminosities covered. Using only the COMBO-17 data, the evolving LF can be adequately described by either a pure density evolution (PDE) or a pure luminosity evolution (PLE) model. However, the absence of a strong L*-like feature in the shape of the LF inhibits a robust distinction between these modes. We present a robust estimate for the integrated UV luminosity generation by AGN as a function of redshift. We find that the LF continues to rise even at the lowest luminosities probed by our survey, but that the slope is sufficiently shallow that the contribution of low-luminosity AGN to the UV luminosity density is negligible. Although our sample reaches much fainter flux levels than previous data sets, our results on space densities and LF slopes are completely consistent with extrapolations from recent major surveys such as SDSS and 2QZ.Comment: 17 pages, 14 figures, Astronomy & Astrophysics, in print, revised versio

Tunnel Spectroscopy of a Proximity Josephson Junction

We present tunnel spectroscopy experiments on the proximity effect in lateral superconductor-normal metal-superconductor (SNS) Josephson junctions. Our weak link is embedded into a superconducting (S) ring allowing phase biasing of the Josephson junction by an external magnetic field. We explore the temperature and phase dependence of both the induced mini-gap and the modification of the density of states in the normal (N) metal. Our results agree with a model based on the quasiclassical theory in the diffusive limit. The device presents an advanced version of the superconducting quantum interference proximity transistor (SQUIPT), now reaching flux sensitivities of 3 nA$/\Phi_0$ where $\Phi_0$ is the flux quantum.Comment: 5 pages, 4 figure

Physical properties of the Schur complement of local covariance matrices

General properties of global covariance matrices representing bipartite Gaussian states can be decomposed into properties of local covariance matrices and their Schur complements. We demonstrate that given a bipartite Gaussian state $\rho_{12}$ described by a $4\times 4$ covariance matrix \textbf{V}, the Schur complement of a local covariance submatrix $\textbf{V}_1$ of it can be interpreted as a new covariance matrix representing a Gaussian operator of party 1 conditioned to local parity measurements on party 2. The connection with a partial parity measurement over a bipartite quantum state and the determination of the reduced Wigner function is given and an operational process of parity measurement is developed. Generalization of this procedure to a $n$-partite Gaussian state is given and it is demonstrated that the $n-1$ system state conditioned to a partial parity projection is given by a covariance matrix such as its $2 \times 2$ block elements are Schur complements of special local matrices.Comment: 10 pages. Replaced with final published versio

Numerical energy absorption study of composite tubes for axial impact loadings

This paper focuses on the numerical energy absorption behaviour of pultruded composite tubes under an axial impact loading case. The circular and square cross sectional glass-polyester composite tubes are considered for the study. In order to capture the typical failure modes such as delaminations, lamina bending, axial cracks and fibre fracturing, a new innovative approach was used using multiple shell elements, cohesive elements and pre-defined seams. To predict the correct peak crush load and the corresponding energy absorption, the importance of the numerical modelling of multiple delaminations and triggering are discussed. Two types of triggering were chosen for the study (45⁰ deg chamfering around the edges and a tulip pattern with an included angle between the edges of 60⁰). Finally, the results of this numerical investigation are compared with experimental data. The commercially available finite element code ABAQUS V6.7-3 Explicit was used for this study

Non-standard quantum so(3,2) and its contractions

A full (triangular) quantum deformation of so(3,2) is presented by considering this algebra as the conformal algebra of the 2+1 dimensional Minkowskian spacetime. Non-relativistic contractions are analysed and used to obtain quantum Hopf structures for the conformal algebras of the 2+1 Galilean and Carroll spacetimes. Relations between the latter and the null-plane quantum Poincar\'e algebra are studied.Comment: 9 pages, LaTe

Universality of transport properties of ultra-thin oxide films

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlOx-Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultra-thin barriers formed by diffusive oxidation of the Al surface. In the superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance comparing with conventional tunnel junctions originates from a universal bimodal distribution of transparencies across the Al-oxide barrier proposed earlier by Schep and Bauer. We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation.Comment: revised text and a new figur

SN2002kg -- the brightening of LBV V37 in NGC 2403

SN2002kg is a type IIn supernova, detected in October 2002 in the nearby spiral galaxy NGC 2403. We show that the position of SN2002kg agrees within the errors with the position of the LBV V37. Ground based and HST ACS images however show that V37 is still present after the SN2002kg event. We compiled a lightcurve of V37 which underlines the variablity of the object, and shows that SN2002kg was the brightening of V37 and not a supernova. The recent brightening is not a giant eruption, but more likely part of an S Dor phase. V37 shows strong Halpha +[NII] emission in recent images and in the SN2002kg spectrum, which we interprete as the signature of the presence of an LBV nebula. A historic spectrum lacks emission, which may hint that we are witnessing the formation of an LBV nebula.Comment: 4 pages, 5 figures, accepted in A&A Letter, paper with images in full resolution at http://www.astro.ruhr-uni-bochum.de/kweis/publications.htm

Unbounded-Error Classical and Quantum Communication Complexity

Since the seminal work of Paturi and Simon \cite[FOCS'84 & JCSS'86]{PS86}, the unbounded-error classical communication complexity of a Boolean function has been studied based on the arrangement of points and hyperplanes. Recently, \cite[ICALP'07]{INRY07} found that the unbounded-error {\em quantum} communication complexity in the {\em one-way communication} model can also be investigated using the arrangement, and showed that it is exactly (without a difference of even one qubit) half of the classical one-way communication complexity. In this paper, we extend the arrangement argument to the {\em two-way} and {\em simultaneous message passing} (SMP) models. As a result, we show similarly tight bounds of the unbounded-error two-way/one-way/SMP quantum/classical communication complexities for {\em any} partial/total Boolean function, implying that all of them are equivalent up to a multiplicative constant of four. Moreover, the arrangement argument is also used to show that the gap between {\em weakly} unbounded-error quantum and classical communication complexities is at most a factor of three.Comment: 11 pages. To appear at Proc. ISAAC 200