Eine Mikromethode zur Stickstoffbestimmung

Zusammenfassung Die Bestimmung von Ammoniak- bzw. Aminostickstoff in trockenem organischen Material erfolgt durch Schmelze mit einem Gemisch von Natriumhydroxyd und krist. Natriumacetat in einer für diesen Zweck entwickelten Apparatur.An Hand von Modellsubstanzen wird gezeigt, daß Ammoniakstickstoffbestimmungen von Proteinen und Aminosäuregemischen durchgeführt werden können, ohne daß im Falle von Proteinen eine Hydrolyse notwendig ist. Damit ergibt sich die Möglichkeit der Durchführung von routinemäßigen Aminostickstoffbestimmungen. Der heterocyclisch im Indol-, Imidazol- und Chinolinring festgelegte Stickstoff wird nicht erfaßt, dagegen der Aminostickstoff der Aminosäuren, der Amino- und Amidstickstoff von Glutamin und Asparagin sowie der gesamte Stickstoff des Arginins und des Pyrrolidinringes.     

Passion for precision.

Optical frequency combs from mode-locked femtosecond lasers have revolutionized the art of counting the frequency of light. They can link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective.     

Bemerkung zur Eulerschen Gleichung

Ohne Zusammenfassung     

Synthesis and characterization of magnetic poly(glycidyl methacrylate) microspheres

Magnetic nanoparticles encapsulated in poly(glycidyl methacrylate) microspheres were prepared and their detailed structural and magnetic characteristics given. Iron oxide nanoparticles were obtained by chemical coprecipitation of Fe(II) and Fe(III) salts and stabilized with dextran, (carboxymethyl)dextran or tetramethylammonium hydroxide. The microspheres were prepared by emulsion or dispersion polymerization of glycidyl methacrylate in the presence of ferrofluid. The microspheres were uniform both in shape and usually also in size; their size distribution was narrow. All the magnetic parameters confirm superparamagnetic nature of the microspheres. Blocking temperature was not observed, suggesting the absence of magnetic interactions at low temperatures. This is most probably caused by complete encapsulation and the absence of agglomeration. Such microspheres can be used in biomedical applications.     

Coherence in microchip traps

We report the coherent manipulation of internal states of neutral atoms in a magnetic microchip trap. Coherence lifetimes exceeding 1 s are observed with atoms at distances of 5-130 microm from the microchip surface. The coherence lifetime in the chip trap is independent of atom-surface distance within our measurement accuracy and agrees well with the results of similar measurements in macroscopic magnetic traps. Because of the absence of surface-induced decoherence, a miniaturized atomic clock with a relative stability in the 10(-13) range can be realized. For applications in quantum information processing, we propose to use microwave near fields in the proximity of chip wires to create potentials that depend on the internal state of the atoms.     

Carrier envelope phase noise in stabilized amplifier systems

At present most laser systems for generating phase-stabilized high-energy pulses are chirped pulse amplifier systems that involve the selection and subsequent amplification of pulses from a phase-stabilized seed oscillator. We investigate the effect of the picking process on the carrier envelope phase stability and how the phase noise of the picked pulse sequence can be estimated from the phase noise properties of the seed oscillator. All noise components from the original pulse train above the picking frequency are aliased into the picked pulse train and therefore cannot be neglected.