Phonon surface mapping of graphite: disentangling quasi--degenerate phonon dispersions

The two-dimensional mapping of the phonon dispersions around the $K$ point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at $K$. We observe an almost degeneracy of the three TO, LA and LO derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect opposite to that of the electronic band structure. We determined the electron--phonon coupling constant to be 166$\rm(eV/\AA)^2$ in excellent agreement to $GW$ calculations. These results are fundamental for understanding angle-resolved photoemission, double--resonance Raman and transport measurements of graphene based systems

Tight--binding description of the quasiparticle dispersion of graphite and few--layer graphene

A universal set of third--nearest neighbour tight--binding (TB) parameters is presented for calculation of the quasiparticle (QP) dispersion of $N$ stacked $sp^2$ graphene layers ($N=1... \infty$) with $AB$ stacking sequence. The QP bands are strongly renormalized by electron--electron interactions which results in a 20% increase of the nearest neighbour in--plane and out--of--plane TB parameters when compared to band structure from density functional theory. With the new set of TB parameters we determine the Fermi surface and evaluate exciton energies, charge carrier plasmon frequencies and the conductivities which are relevant for recent angle--resolved photoemission, optical, electron energy loss and transport measurements. A comparision of these quantitities to experiments yields an excellent agreement. Furthermore we discuss the transition from few layer graphene to graphite and a semimetal to metal transition in a TB framework.Comment: Corresponding author: A. Gr\"uneis Tel.: +49 351 4659 519 e--mail: [email protected]

Transport through open quantum dots: making semiclassics quantitative

We investigate electron transport through clean open quantum dots (quantum billiards). We present a semiclassical theory that allows to accurately reproduce quantum transport calculations. Quantitative agreement is reached for individual energy and magnetic field dependent elements of the scattering matrix. Two key ingredients are essential: (i) inclusion of pseudo-paths which have the topology of linked classical paths resulting from diffraction in addition to classical paths and (ii) a high-level approximation to diffractive scattering. Within this framework of the pseudo-path semiclassical approximation (PSCA), typical shortcomings of semiclassical theories such as violation of the anti-correlation between reflection and transmission and the overestimation of conductance fluctuations are overcome. Beyond its predictive capabilities the PSCA provides deeper insights into the quantum-to-classical crossover.Comment: 20 pages, 19 figure

DNA self-assembly-driven positioning of molecular components on nanopatterned surfaces.

We present a method for the specific, spatially targeted attachment of DNA molecules to lithographically patterned gold surfaces-demonstrated by bridging DNA strands across nanogap electrode structures. An alkanethiol self-assembled monolayer was employed as a molecular resist, which could be selectively removed via electrochemical desorption, allowing the binding of thiolated DNA anchoring oligonucleotides to each electrode. After introducing a bridging DNA molecule with single-stranded ends complementary to the electrode-tethered anchoring oligonucleotides, the positioning of the DNA molecule across the electrode gap, driven by self-assembly, occurred autonomously. This demonstrates control of molecule positioning with resolution limited only by the underlying patterned structure, does not require any alignment, is carried out entirely under biologically compatible conditions, and is scalable

The Leiodolide B Puzzle

Out of options? Even though a systematic approach was chosen, which led to a set of four diastereomeric macrolides modeled around the proposed structure of leiodolide B (see picture), the puzzle concerning the stereostructure of this cytotoxic metabolite derived from a deep-sea sponge still remains unsolved

The Formosalides: Structure Determination by Total Synthesis

Total synthesis allowed the constitution of the cytotoxic marine macrolides of the formosalide family to be confirmed and their previously unknown stereostructure to be assigned with confidence. The underlying blueprint was inherently modular to ensure that each conceivable isomer could be reached. This flexibility derived from the use of strictly catalyst controlled transformations to set the stereocenters, except for the anomeric position, which is under thermodynamic control; as an extra safety measure, all stereogenic centers were set prior to ring closure to preclude any interference of the conformation adopted by the macrolactone rings of the different diastereomers. Late‐stage macrocyclization by ring‐closing alkyne metathesis was followed by a platinum‐catalyzed transannular 6‐exo‐dig hydroalkoxylation/ketalization to craft the polycyclic frame. The side chain featuring a very labile unsaturation pattern was finally attached to the core by Stille coupling

Explant analysis and implant registries are both needed to further improve patient safety

In the early days of total joint replacement, implant fracture, material problems and wear presented major problems for the long-term success of the operation. Today, failures directly related to the implant comprise only 2–3% of the reasons for revision surgeries, which is a result of the material and design improvements in combination with the standardization of pre-clinical testing methods and the post-market surveillance required by the legal regulation. Arthroplasty registers are very effective tools to document the long-term clinical performance of implants and implantation techniques such as fixation methods in combination with patient characteristics. Revisions due to implant failure are initially not reflected by the registries due to their small number. Explant analysis including patient, clinical and imaging documentation is crucial to identify failure mechanisms early enough to prevent massive failures detectable in the registries. In the past, early reaction was not always successful, since explant analysis studies have either been performed late or the results did not trigger preventive measures until clinical failures affected a substantial number of patients. The identification of implant-related problems is only possible if all failures are reported and related to the number of implantations. A system that analyses all explants from revisions attributed to implant failure is mandatory to reduce failures, allowing improvement of risk assessment in the regulatory proces

An amphitropic cAMP-binding protein in yeast mitochondria

ABSTRACT: We describe the first example of a mitochondrial protein with a covalently attached phos-phatidylinositol moiety acting as a membrane anchor. The protein can be metabolically labeled with both stearic acid and inositol. The stearic acid label is removed by phospholipase D whereupon the protein with the retained inositol label is released from the membrane. This protein is a cAMP receptor of the yeast Saccharomyces cereuisiae and tightly associated with the inner mitochondrial membrane. However, it is converted into a soluble form during incubation of isolated mitochondria with Ca2+ and phospholipid (or lipid derivatives). This transition requires the action of a proteinaceous, N-ethylmaleimide-sensitive component of the intermembrane space and is accompanied by a decrease in the lipophilicity of the cAMP receptor. We propose that the component of the intermembrane space triggers the amphitropic behavior of the mitochondrial lipid-modified CAMP-binding protein through a phospholipase activity. Only in recent years specific fatty acids have been recog-nized to play important roles in the association of proteins with membranes. Both noncovalent and covalent interactions be-tween fatty acids and proteins have been reported. Among the latter are GTP-binding proteins (Molenaar et al., 1988)

Evaluation of detailed aromatic mechanisms (MCMv3 and MCMv3.1) against environmental chamber data

International audienceA high quality dataset on the photo-oxidation of benzene, toluene, p-xylene and 1,3,5-trimethylbenzene has been obtained from experiments in the European Photoreactor (EUPHORE), a large outdoor environmental reaction chamber. The experiments were designed to test sensitive features of detailed aromatic mechanisms, and the dataset has been used to evaluate the performance of the Master Chemical Mechanism Version 3 (MCMv3). An updated version (MCMv3.1) was constructed based on recent experimental data, and details of its development are described in a companion paper. The MCMv3.1 aromatic mechanisms have also been evaluated using the EUPHORE dataset. Significant deficiencies have been identified in the mechanisms, in particular: 1) an over-estimation of the ozone concentration, 2) an under-estimation of the NO oxidation rate, 3) an under-estimation of OH. The use of MCMv3.1 improves the model-measurement agreement in some areas but significant discrepancies remain