Worldsheet instantons,torsion curves and non-perturbative superpotentials

As a first step towards computing instanton-generated superpotentials in heterotic standard model vacua, we determine the Gromov–Witten invariants for a Calabi–Yau threefold with fundamental group π₁(X)=Z₃×Z₃${\pi }_1(X)={\mathbb{Z}}_3\times {\mathbb{Z}}_3$. We find that the curves fall into homology classes in H₂(X,Z)=Z³⊕(Z₃⊕Z₃)$H_2(X,\mathbb{Z})={\mathbb{Z}}^3\oplus ({\mathbb{Z}}_3\oplus {\mathbb{Z}}_3)$. The unexpected appearance of the finite torsion subgroup in the homology group complicates our analysis. However, we succeed in computing the complete genus-0 prepotential. Expanding it as a power series, the number of instantons in any integral homology class can be read off. This is the first explicit calculation of the Gromov–Witten invariants of homology classes with torsion. We find that some curve classes contain only a single instanton. This ensures that the contribution to the superpotential from each such instanton cannot cancel.     

Fast separations with open tubular ion exchange capillary columns

Fused silica columns of 4.6 μm i.d. were coated with 3-sulfopropylsilane as a cation exchanger and 3-(2-aminoethyl-amino)-propylsilane as an anion exchanger. Fast separations of cations (< 25 seconds) and of anions (< 35 seconds) were obtained, using a potentiometric microelectrode as a detector. In proceeding towards smaller i.d.s, a mixture of alkali metal cations could be separated successfully in an uncoated fused silica capillary of 2.3 μm i.d. as a result of retention by the surface silanol groups at pH 9.4.     

Ger?t zur automatischen L?sungsherstellung

Zusammenfassung Ein Gerät wird beschrieben, das die vollautomatische Herstellung von Lösungen wählbarer Konzentrationen erlaubt. Hierbei wird eine elektrische Waage automatisch tariert, die Einwaage elektrisch analog umgerechnet und die erforderliche Lösungsmittelmenge über elektrische Teflonventile gravimetrisch zudosiert. Es lassen sich Genauigkeiten von besser als 1 erreichen.

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Device for the automatic preparation of solutions

A device is described for the fully automatic preparation of solutions of selectable concentrations. An electric balance is automatically tared, the weighed-in quantity is electrically converted (analog conversion) and the solvent quantity required is gravimetrically fed in by means of electrical Teflon valves. Accuracies better than 1 can be achieved.

     

Note on fundamental operations

A new type of generalization of fundamental calculating operations is attempted. Instead of generalizing the nature of the elements upon which operations are acting, the nature of the operations themselves is changed. By iterating the step which leads from addition to multiplication, new types of operations are generated. Some of these operations are discussed briefly.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Quantitative abdominal aortic flow measurements at controlled levels of ergometer exercise

Measuring the exercise-induced flow changes in the arteries of the body is a major challenge. The use of quantitative MR flow measurements for this purpose is hampered by movement artifacts and ECG triggering problems. To quantify exercise-induced flow changes in the abdominal aorta, we applied a fast hybrid phase contrast sequence with K-space segmentation and echo planar imaging readouts during a 12 heart beat, single breathhold post exercise scanning window after ergometer exercise in nine volunteers. Central k-space was acquired first. The changes in heart rate throughout the scanning window were quantified. The mean decrease in heart rate after six heart beats post exercise was less than 4% and less than 14% after 11 heart beats indicating that the exercise state was very well represented during the acquisition of central k-space. Abdominal aortic flow increased from 1.4+/-0.3 l/min at rest to 7.9+/-1.1 l/min at 131 watt. Retrograde flow reached a maximum value of 1.2 l/min at rest, and lasted 140 ms on average. Only for one out of the nine volunteers was there any retrograde flow present during exercise (at 33 watt and 65 watt exercise). It was concluded that retrograde flow patterns in the abdominal aorta associated with oscillating wall shear stresses and development of atherosclerosis disappeared with increasing levels of exercise. The feasibility of using fast quantitative phase contrast measurements during a post exercise scanning window to represent controlled exercise levels was demonstrated.     

Isolement et analyse structurale du collybolide,nouveau sesquiterpene extrait de Collybia maculata alb. et sch. ex fries (basidiomycetes)

From Collybia maculata Alb. et Sch. ex. Fries two sesquiterpenes of a new type have been isolated, collybolide 1 and isocollybolide 2, artefacts resulting from carboxylic acid precursors as yet not isolated. The structure of collybolide is established by correlation with that of isocollybolide, already known, and their reactivity has been studied. NMR spectra allow the conformational analysis of all products isolated.A series of lactones (β-, γ-, σ- and ?-lactones) in various solvents has been studied through ₁₃C NMR spectroscopy. The chemical shift of the carbonyl carbon appears characteristic of the type of lactone. The distinction is particularly clear between γ-lactones (+13·5 to +16 ppm/CS₂) and σ-lactones (+20 to +22 ppm).     

Etude par RMN de la Structure des Cyano-2 Alcoyl-2 Norbornenes-5

Interpretation of the NMR spectra of the isomeric 2-cyano-2-alkyl-5-norbornenes allowed the assignment of their respective structures. In the case of the 2-cyano-2-methyl-5-norbornene the structure assignment was confirmed by chemical synthesis (alkaline hydrolysis and iodo-lactonisation).