The ornithological diaries of Helmut Sick (1910 - 1991)

On the 10th of January 2010 Helmut Sick, the German-Brazilian explorer of neotropical birds would have had his 100th anniversary. He made his PhD under supervision of Erwin Stresemann in 1937 about the structure of bird feathers. 1939 he joined a three months expedition to Brazil but was so fascinated about the bird life that he stayed much longer and in 1952 he became citizen of Brazil. Helmut Sick was director at the National Museum Boa Vista and was professor for zoology an the State University in Rio. He became member of the Academia Brasileira de Ciências und honorary citizen of Rio de Janeiro. His probably most important book were the two volumes of „Ornitologia brasiliera, uma introduÇão“, which has been revised in 1993 in an English version “Birds in Brazil. A natural history“. Over 68 years Helmut Sick conducted an ornithological diary with very detailed, sometimes even artistic descriptions of his observations. His notes between 1923 and 1938 comprise 12 diary books with 80 pages each. The authors secured the material and looked through it. Here a short description of the contents is given. A publication list and more material are available online (see bottom of the text). Helmut Sick died in a traffic accident on 5th March 1991 in Rio de Janeiro

High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument

We present the results of N-band spectro-interferometric observations of the silicate carbon star IRAS08002-3803 with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). The observations were carried out using two unit telescopes (UT2 and UT3) with projected baseline lengths ranging from 39 to 47 m. Our observations of IRAS08002-3803 have spatially resolved the dusty environment of a silicate carbon star for the first time and revealed an unexpected wavelength dependence of the angular size in the N band: the uniform-disk diameter is found to be constant and ~36 mas (72 Rstar) between 8 and 10 micron, while it steeply increases longward of 10 micron to reach ~53 mas (106 Rstar) at 13 micron. Model calculations with our Monte Carlo radiative transfer code show that neither spherical shell models nor axisymmetric disk models consisting of silicate grains alone can simultaneously explain the observed wavelength dependence of the visibility and the spectral energy distribution (SED). We propose that the circumstellar environment of IRAS08002-3803 may consist of two grain species coexisting in the disk: silicate and a second grain species, for which we consider amorphous carbon, large silicate grains, and metallic iron grains. Comparison of the observed visibilities and SED with our models shows that such disk models can fairly -- though not entirely satisfactorily -- reproduce the observed SED and N-band visibilities. Our MIDI observations and the radiative transfer calculations lend support to the picture where oxygen-rich material around IRAS08002-3803 is stored in a circumbinary disk surrounding the carbon-rich primary star and its putative low-luminosity companion.Comment: 15 pages, 8 figures, accepted for publication in A&

Relativistic Transport Approach for Nucleus-Nucleus Collisions from SIS to SPS Energies

We formulate a covariant transport approach for high energy nucleus-nucleus collisions where the real part of the nucleon selfenergies is fitted to nuclear matter properties which are evaluated on the basis of a NJL-type Lagrangian for the quark degrees of freedom. The parameters of the quark-model Lagrangian are fixed by the Gell-Mann, Oakes and Renner relation, the pion- nucleon $\Sigma$-term, the nucleon energy as well as the nuclear binding energy at saturation density $\rho_0$. We find the resulting scalar and vector selfenergies for nucleons to be well in line with either Dirac-Brueckner computations for $\rho \leq 2 \rho_0$ or those from the phenomenological optical potential when accounting for a swelling of the nucleon at finite nuclear matter density. The meson-baryon interaction density is modelled to describe a decrease of the meson mass with baryon density. The imaginary part of the hadron selfenergies is determined by a string fragmentation model which accounts for the in-medium mass of hadrons in line with the 'chiral' dynamics employed. The applicability of the transport approach is demonstrated in comparison with experimental data from SIS to SPS energies. The enhancement of the K$^+/\pi^+$ ratio in A + A collisions compared to p + A reactions at AGS energies is reproduced within the 'chiral' dynamics. Furthermore, detailed predictions for the stopping in Pb + Pb collisions at 153 GeV/A are presented.Comment: 1 compressed uuencoded postscript file with 23 figures included, 45 page

Electron spin operation by electric fields: spin dynamics and spin injection

Spin-orbit interaction couples electron spins to electric fields and allows electrical monitoring of electron spins and electrical detection of spin dynamics. Competing mechanisms of spin-orbit interaction are compared, and optimal conditions for the electric operation of electrons spins in a quantum well by a gate voltage are established. Electric spin injection into semiconductors is discussed with a special emphasis on the injection into ballistic microstructures. Dramatic effect of a long range Coulomb interaction on transport phenomena in space-quantized low-dimensional conductors is discussed in conclusion.Comment: A plenary paper at the 11th Intern. Conf. on Narrow Gap Semiconductors (Buffalo, NY, June 2003). To be published in Physica

Novel strategies to target the survivin pathway in cancer – interference with nuclear export prevents the tumor promoting activites of survivin : meeting abstract

Survivin functions as an apoptosis inhibitor and a regulator of cell division during development and tumorigenesis. Since survivin is a highly relevant target for tumor therapy, we investigated whether interference with it’s dynamic cellular localization represents a novel strategy to inhibit survivin’s cancer promoting functions. We confirmed survivin overexpression in head and neck as well as in colorectal cancers and identified an evolutionary conserved Crm1-dependent nuclear export signal (NES) in survivin. Importantly, nuclear export was required for survivin mediated protection against chemo- and radiotherapy-induced apoptosis by securing efficient interference with cytoplasmic caspases. In dividing cells, the NES was required for tethering of survivin and of the survivin/Aurora-B kinase complex to the mitotic machinery, which was inevitable for proper cell division. The clinical relevance of our findings was supported by showing that preferential nuclear localization of survivin correlated with enhanced survival in a cohort of colorectal cancer patients. Targeting survivin’s nuclear export by the application of NES-specific antibodies promoted its nuclear accumulation and inhibited its cytoprotective function. We here show that nuclear export is essential for the tumor promoting activities of survivin and encourage the identification of chemical inhibitors to specifically interfere with survivin’s nuclear export as a novel class of anticancer therapeutics

Spin-orbit coupling and spin transport

Recent achievements in semiconductor spintronics are discussed. Special attention is paid to spin-orbit interaction, coupling of electron spins to external electric fields, and spin transport in media with spin-orbit coupling, including the mechanisms of spin-Hall effect. Importance of spin-transport parameters at spin-precession wave vector $k_{\rm so}$ is emphasized, and existence of an universal relation between spin currents and spin accumulation at the spatial scale of $\ell_{\rm so}\approx k_{\rm so}^{-1}$ is conjectured.Comment: Plenary paper at 16th International Conference on Electronic Properties of 2D Systems (Albuquerque, NM, July 10-15, 2005). Minor editorial changes, references updated. Accepted for Physica

Rashba interferometers: Spin-dependent single and two-electron interference

Quantum transport in semiconductor nanostructures can be described theoretically in terms of the propagation and scattering of electron probability waves. Within this approach, elements of a phase-coherent electric circuit play a role similar to quantum-optical devices that can be characterised by scattering matrices. Electronic analogues of well-know optical interferometers have been fabricated and used to study special features of charge carriers in solids. We present results from our theoretical investigation into the interplay between spin precession and quantum interference in an electronic Mach-Zehnder interferometer with spin-orbit coupling of the Rashba type. Intriguing spin-dependent transport effects occur, which can be the basis for novel spintronic devices such as a magnet-less spin-controlled field-effect transistor and a variety of single-qubit gates. Their functionality arises entirely from spin-dependent interference of each single input electron with itself. We have also studied two-electron interference effects for the spin-dependent Mach-Zehnder interferometer, obtaining analytical expressions for its two-fermion-state scattering matrix. Using this result, we consider ways to generate two-electron output states for which the Rashba spin-subband quantum number and the output-arm index are entangled. Combining spin-dependent interference in our proposed Mach-Zehnder interferometer with a projective charge measurement at the output enables entanglement generation. As our particular scheme involves tuneable spin precession, electric-field control of entanglement production can be achieved.Comment: 7 pages, 5 figures, Elsevier style, submitted to special issue of Solid State Communications, v2: replacement to rectify formatting problems, v3: minor changes + 3 references adde

Dissipation effects in spin-Hall transport of electrons and holes

We investigate the spin-Hall effect of both electrons and holes in semiconductors using the Kubo formula in the correct zero-frequency limit taking into account the finite momentum relaxation time of carriers in real semiconductors. This approach allows to analyze the range of validity of recent theoretical findings. In particular, the spin-Hall conductivity vanishes for vanishing spin-orbit coupling if the correct zero-frequency limit is performed.Comment: 5 pages, no figures, version to appear in Phys. Rev.

Anisotropic transport in the two-dimensional electron gas in the presence of spin-orbit coupling

In a two-dimensional electron gas as realized by a semiconductor quantum well, the presence of spin-orbit coupling of both the Rashba and Dresselhaus type leads to anisotropic dispersion relations and Fermi contours. We study the effect of this anisotropy on the electrical conductivity in the presence of fixed impurity scatterers. The conductivity also shows in general an anisotropy which can be tuned by varying the Rashba coefficient. This effect provides a method of detecting and investigating spin-orbit coupling by measuring spin-unpolarized electrical currents in the diffusive regime. Our approach is based on an exact solution of the two-dimensional Boltzmann equation and provides also a natural framework for investigating other transport effects including the anomalous Hall effect.Comment: 10 pages, 1 figure included. Discussion of experimental impact enlarged; error in calculation of conductivity contribution corrected (cf. Eq. (A14)), no changes in qualitative results and physical consequence