Self-stabilized passive, harmonically mode-locked stretched-pulse erbium fiber ring laser

We have studied a passive, harmonically mode-locked stretched-pulse erbium fiber ring laser with net positive dispersion that is self-stabilized by gain depletion and electrostriction. Periodic pulses with supermode suppression of >75 dB and picosecond jitter are achieved. The pulses are compressible to 125 fs by external chirp compensation. The repetition rate is 220 MHz, and the average power is as high as 80 mW.     

Numerical sensitivity of trajectories across conformational energy hypersurfaces from geometry optimized molecular orbital calculations: AM1, MNDO,and MINDO/3

The monocyclic β-lactam [[4(S)-methyl-2-oxo-1-azetidinyl]thia]acetic acid was studied by the semiempirical molecular orbital methods AM1, MNDO, and MINDO/3. Using the reaction coordinate option in the program MOPAC on VAX and Cray X-MP computers, the potential energy curve was calculated for rotation of the C2-N1-S-C torsional angle in the conformationally flexible side chain while optimizing all other geometrical variables in the molecule. The trajectory taken during geometry optimization was found to be sensitive to the computer, the program version, the convergence criteria, and the degree of code optimization used in the calculation. In order to reduce the likelihood of spurious results, conformational or reaction energy hypersurfaces need to be calculated with the more precise SCF convergence and minimization criteria available in programs for MINDO/3, MNDO, and AM1 calculations. The nitrogen in the model β-lactam antibiotic is predicted to invert periodically as the dihedral angle to the exocyclic N-substituent sweeps through 360°.     

Über Reaktionen mit Betainen, 16. Mitt.: Über Betaine und ihre Beziehungen zu N-Yliden Kristallstruktur von Trimethylammoniumtrifluoracetylmethylid

Monatshefte für Chemie - Chemical Monthly - The crystal structure of1 was determined by X-ray structure analysis. Some further chemical reactions are presented which are in full accord with...     

The strains and the energy in thin elastic shells of arbitrary shape for arbitrary deformation

Zusammenfassung Im ersten Teil (I) werden Formeln entwickelt, welche die kinetische und potentielle Energie dünner Schalen beliebiger Form explizit als Funktion eines beliebigen Verschiebungsfeldes ausdrücken. Dies geschieht auf rein analytische Weise ohne Zuhilfenahme geometrischer Darstellungen einzelner Schalenelemente. Von besonderem Wert für viele Anwendungen ist es, dass vollständige Freiheit in der Wahl der Flächenkoordinaten besteht.Im zweiten Teil (II) wird zunächst die Anwendung der Theorie auf zwei bekannte Beispiele gezeigt: 1. Platte in schiefwinkligen Koordinaten, 2. zylindrische Schale. Als neues Beispiel wird 3. die schraubenflächige Schale eingehend behandelt. Für einen besonderen Einspannungsfall wird die Frequenz der Grundschwingung als Funktion der Verwindung angenähert numerisch berechnet.     

Einige Probleme im Zusammenhang mit der direkten Bestimmung der spezifischen Wärmen mittels Differential Scanning-Kalorimetrie

The relation between sample mass andDSC-amplitude was investigated under various experimental conditions for vitreous quartz, both as discs and powders. Contrary to other authors³ proportionality has been found up to the highest masses (75 mg) used. A statistical analysis of the data indicates that the accuracy of directC _p-measurements byDSC can be increased by determining the blank value by extrapolation of the amplitudes for several masses to zero mass instead of using the usual procedure, which involves a run with the empty pans. The overall error ofC _p due to instrument errors is estimated not to exceed 2%.