Ramanujan's identities for eta-functions

Research partially supported by National Science Foundation grant DMS-8820680     

Photon emission from adsorbed C60 molecules with sub-nanometer lateral resolution

We present the first experimental demonstration of spatially resolved photon emission of individual molecules on a surface. A scanning tunneling microscope (STM) was used as a local electron source to excite photon emission from hexagonal arrays of C₆₀ molecules on Au(110) surfaces. Specifically, we show that in maps of photon emission intensities, C₆₀ fullerenes appear as arrays of individual light emitters 4 Å in diameter and separated by 10 Å. Comparison with simultaneously recorded STM images reveals, that most intense emission is detected when the STM tip is centered above a molecule. The results demonstrate the highest spatial resolution of light emission to date using a scanning probe technique.     

Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.     

High performance flow flame atomic absorption spectrometry for interference-free trace determination

In High Performance Flow Atomic Spectrometry (HPF-AS), the aerosol is generated by injecting the sample solution into the gas mixing chamber with the aid of an HPLC pump (Hydraulic High Pressure Nebulization, HHPN, working pressure about 200 bar). Using an additional analytical HPLC column, between sample injection valve and nebulization nozzle, the elements under investigation can be separated from interfering elemental traces or major components (High Performance/Pressure Flow System, HPF). The elements to be determined and the interfering substances reach the flame at different times. This means, for example, that traces of Mg in solutions containing aluminum can be determined without interference. Compared to pneumatic nebulization, there is a 20 fold increase in the detection power when determining calcium in a saturated NaCl solution. HPF-AS is a rapid and sensitive method which allows separation of the calcium from the matrix with subsequent determination in less than 90 s.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Multielementanreicherung von Elementspuren aus Reinstaluminium durch Membranfiltration der APDTC-Komplexe

Zusammenfassung Es wird ein Verfahren zur Multielementanreicherung (Bi, Cd, Co, Fe, In, Ni, Pb, Tl und Zn) aus Aluminium beschrieben, bei dem als Trennschritt lediglich eine Membranfiltration der mit Ammoniumpyrrolidindithiocarbamidat ausgef?llten Spuren vorgenommen wird. Bei Reinstaluminium mu? mit einer Cu²⁺-Tr?gerf?llung im Mikrogrammbereich gearbeitet werden, um eine quantitative Abtrennung der Spuren zu erzielen. Bei technischen Qualit?ten kann wegen der hohen Eigenverunreinigungen auf den Tr?gerzusatz verzichtet werden. Man erh?lt ein nahezu matrixfreies Spurenkonzentrat, aus dem die Elemente mit der Flammen-AAS (Injektionsmethode) bestimmt werden. Die mit dieser Methode erreichbaren Nachweisgrenzen (3s-Werte) liegen je nach Element zwischen 0,004 und 0,1 μg/g.

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Multielement preconcentration of traces of elements from high-purity aluminium by membrane filtration of the APDTC complexes

Summary A procedure for preconcentration of traces of Bi, Cd, Co, Fe, In, Ni, Pb, Tl, and Zn from pure aluminium is described. For the separation the traces are precipitated with ammonium pyrrolidinedithiocarbamidate and then filtered through a membrane filter. For the analysis of high-purity aluminium it is necessary to precipitate Cu²⁺ in microgram amounts as a collector, to attain a quantitative separation of the traces. For analysis of technical aluminium no collector is required because of the high content of traces in this material. In this way an almost matrix-free trace concentrate is obtained, in which the elements will be determined by flame atomic-absorption (injection method). The detection limits differ between 0.004 and 0.1 μg/g, according to the individual elements.