Pulse energy scaling to 5 microJ from a femtosecond thin disk laser

We report an increase in pulse energy to 5.1 microJ obtained directly from a femtosecond diode-pumped Yb:YAG thin disk laser without external amplification. Stable passive mode locking was obtained with a semiconductor saturable absorber mirror (SESAM). The laser delivers 63 W of average output power in a nearly diffraction-limited beam (M2=1.1) at a center wavelength of 1030 nm. The pulse repetition rate is 12.3 MHz, and the pulses have a duration of 800 fs, which results in a peak power of 5.6 MW. The laser was operated in a box flooded with helium because the nonlinearity of air was found to be a limiting factor for the stability of the pulse formation at increasing pulse energies.     

SideLink: automated side-chain assignment of biopolymers from NMR data by relative-hypothesis-prioritization-based simulated logic

Previously we published the development of AutoLink, a program to assign the backbone resonances of macromolecules. The primary limitation of this program has proven to be its inability to directly recognize spectral data, relying on the user to define peak positions in its input. Here, we introduce a new program for the assignment of side-chain resonances. Like AutoLink, this new program, called SideLink, uses Relative Hypothesis Prioritization to emulate "human" logic. To address the higher complexity of side-chain assignment problems, the RHP algorithm has itself been advanced, making it capable of processing almost any combinatorial logic problem. Additionally, SideLink directly examines spectral data, overcoming the need and limitations of prior data interpretation by users.     

Degree bounds for linear discrepancy of interval orders and disconnected posets

Let $P$ be a poset in which each point is incomparable to at most $\Delta$ others. Tanenbaum, Trenk, and Fishburn asked in a 2001 paper if the linear discrepancy of such a poset is bounded above by $?(3\Delta ?1)/2?$. This paper answers their question in the affirmative for two classes of posets. The first class is the interval orders, which are shown to have linear discrepancy at most $\Delta$, with equality precisely for interval orders containing an antichain of size $\Delta +1$. The stronger bound is tight even for interval orders of width 2. The second class of posets considered is the disconnected posets, which have linear discrepancy at most $?(3\Delta ?1)/2?$. This paper also contains lemmas on the role of critical pairs in linear discrepancy as well as a theorem establishing that every poset contains a point whose removal decreases the linear discrepancy by at most 1.     

On the (non)vanishing of some “derived” categories of curved dg algebras

Since curved dg algebras, and modules over them, have differentials whose square is not zero, these objects have no cohomology, and there is no classical derived category. For different purposes, different notions of “derived” categories have been introduced in the literature. In this article, we show that for some concrete curved dg algebras, these derived categories vanish. This happens for example for the initial curved dg algebra whose module category is the category of precomplexes, and for certain deformations of dg algebras.     

Promoter Activation in Δhfq Mutants as an Efficient Tool for Specialized Metabolite Production Enabling Direct Bioactivity Testing

Natural products (NPs) from microorganisms have been important sources for discovering new therapeutic and chemical entities. While their corresponding biosynthetic gene clusters (BGCs) can be easily identified by gene‐sequence‐similarity‐based bioinformatics strategies, the actual access to these NPs for structure elucidation and bioactivity testing remains difficult. Deletion of the gene encoding the RNA chaperone, Hfq, results in strains losing the production of most NPs. By exchanging the native promoter of a desired BGC against an inducible promoter in Δhfq mutants, almost exclusive production of the corresponding NP from the targeted BGC in Photorhabdus, Xenorhabdus and Pseudomonas was observed including the production of several new NPs derived from previously uncharacterized non‐ribosomal peptide synthetases (NRPS). This easyPACId approach (easy Promoter Activated Compound Identification) facilitates NP identification due to low interference from other NPs. Moreover, it allows direct bioactivity testing of supernatants containing secreted NPs, without laborious purification.     

Complex-mass renormalization in chiral effective field theory

We consider a low-energy effective field theory of vector mesons and Goldstone bosons using the complex-mass renormalization. As an application we calculate the mass and the width of the ρ meson.     

Rare Events,Escape Rates and Quasistationarity: Some Exact Formulae

We present a common framework to study decay and exchanges rates in a wide class of dynamical systems. Several applications, ranging from the metric theory of continuos fractions and the Shannon capacity of constrained systems to the decay rate of metastable states, are given. It is a pleasure to thank L. Bunimovich for calling our attention to formula (1.1) in the special case of the doubling map, and V. Baladi and M. Demers for discussions on this formula. We are indebted to the ESI where, during the Workshop on Hyperbolic Dynamical Systems with Singularities (2008), this work was started. L.C. thanks the ENS, Paris, where he was invited during part of this work. Also we like to thank the Institut Henri Poincare–Centre Emile Borel where, during the trimester Mécanique statistique, probabilités et systèmes de particules (2008), this work was finished. Finally, G.K. acknowledges the support by the DFG grant KE 514/7-1, and L.C. by the MIUR grant PRIN 2007B3RBEY.     

A Main‐Chain de Vries Smectic Liquid Crystal Polymer Prepared by Hoveyda–Grubbs Catalyst Initiated Acyclic Diene Metathesis Polymerization

A main‐chain liquid crystalline polymer has been obtained by applying a Hoveyda–Grubbs 2nd generation catalyst in acyclic diene metathesis polymerization (ADMET) of a monomer containing on one end a terminal dimethylvinylsilyl group and at the other end a terminal C C double bond. This material showed an interesting Iso‐de Vries SmA* – SmC* – Glass phase transition with a very small layer shrinkage on progressing from the SmA* phase into the SmC* phase. Will this material present a helical structure along the fiber axis in the SmC* temperature range? Several physical characterization methods including XRD, optical observation, and microtome technique have been used to investigate the internal structural organization in this liquid crystalline fiber.

     

Growth of the magnetic semiconductor Fe2? x Ti x O3± δ thin films by pulsed laser deposition

The understanding and control of the ilmenite–hematite solid solutions (Fe_2−x Ti _x O_3±δ or IH) thin film structure and properties are crucial for spintronics applications. Good quality films of Fe_2−x Ti _x O_3±δ on Al₂O₃(0001) substrates were obtained by pulsed laser deposition. For the studied compositions (x=1, 0.7, 0.5) in a wide oxygen pressure range all the films were epitaxial, with flat interfaces, and without secondary phases. Unconventional lattice strain relaxation with the increase of in-plane lattice parameter above its relaxed bulk value was observed for different film compositions, oxygen pressures, substrate temperatures, and film growth rates. This phenomenon is most likely explained by the buckling of a few first film monolayers because of a significant compressive stress induced on the film by the sapphire substrate. The IH thin films with x=0.7 and 0.5 exhibited the properties of a room temperature magnetic semiconductor. The resistivity changed over three orders of magnitude in the studied pressure range, thus clearly demonstrating the important role of oxygen stoichiometry in the creation of carriers.     

Cryopreservation for plant genebanks - a matter between high expectations and cautious reservation

Cryopreservation is the best method of storing germplasm efficiently and safely, particularly for the maintenance of vegetatively propagated material. In IPK cryopreservation is used for potato, garlic, mint and yam. IPK collaborates with other cryobanks and research groups (ECPGR, COST, EURALLIVEG) and finds considerable differences in the adoption of cryopreservation between crops and their host institutes, depending on crop, local and historical circumstances. A better understanding of the long-term benefits of cryopreservation and its further integration into general genebank management is therefore needed. Recommended approaches include: comparative validation of methods between different laboratories, detailed comparisons of crop-based methods, economical analyses, efficient integration strategies of cryobanks by genebanks; including safe duplication of cryopreserved resources for the limitation of risk of loss Importantly, there has been recent progress in the development of quality management systems. Cryopreservation is, however, characterized by high expectations. Therefore, to ensure its sustainable and practicable use, basic knowledge of storage protocols must be combined with increased awareness of the rationales required to validate, implement and apply cryobanking technologies in working genebanks.