Increased sensitivity and reproducibility through signal averaging in ranges near an instrumental limit of detection

Summary The application of a new multifunction low-cost signal averager which can be coupled to a variety of instruments is described. As examples such diverse fields as flameless atomic absorption spectroscopy of Tl traces and anodic stripping analysis of Cd in rock samples are investigated. In both cases the instrumental limit of detection can be significantly lowered through the improvement of the signal-to-noise ratio obtained after digital averaging. Even extremely fast signals can be handled, allowing a large number of repetitive scans within a relatively short amount of time. The signal-to-noise improvement is, within certain limits, proportional to n^1/2, where n is the number of repetitive measurements. The benefit of a special feature — subtraction of one signal-time curve from another — is demonstrated for the case of background correction. This low-priced averager is particularly valuable in all situations where fast signals are involved and no electronic damping of the amplifier can be tolerated; here it functions as an averaging transient recorder (or storage oscilloscope).

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Erhöhte Empfindlichkeit und Reproduzierbarkeit durch Signal-Mittelwertrechnung in Bereichen nahe einer instrumentellen NachweisgrenzeSpurenbestimmung von Thallium und Cadmium in Gesteinsproben

Zusammenfassung Es wird der Einsatz eines neuen multifunktionellen preiswerten Signal-Mittelwertrechners, der an eine Vielzahl von Geräten angeschlossen werden kann, beschrieben. Als Beispiele werden so unterschiedliche Einsatzbereiche wie die flammenlose Atomabsorptions-Spektroskopie von Tl-Spuren und die inverse Voltammetrie von Cd-Spuren in geochemischen Proben näher untersucht. In beiden Fällen kann eine instrumenteil bedingte Nachweisgrenze wegen des verbesserten Signal-Rausch-Verhältnisses durch die Mittelwertsbildung des digitalisierten Signals entscheidend gesenkt werden. Es können sogar extrem kurze Signale verarbeitet werden. Dies ermöglicht die Mitteilung über viele Wiederholungsläufe innerhalb einer relativ kurzen Zeit. Die Verbesserung des Signal-Rausch-Verhältnisses ist innerhalb gewisser Grenzen proportional zu n^1/2, mit n als Anzahl der Wiederholungsmessungen. Der Vorteil einer besonderen Möglichkeit — Subtraktion einer Signal-Zeit-Kurve von einer anderen — wird im Hinblick auf eine elegante Untergrundkompensation hin demonstriert. Dieser preiswerte Mittelwertsrechner ist besonders vorteilhaft in allen Fällen einsetzbar, wo schnelle Signale auftreten und daher keine elektronische Dämpfung des Verstärkers tolerierbar ist; in diesen Fällen funktioniert der Rechner wie ein mittelnder Transienten-Schreiber (oder Speicher-Oscillograph).

Dedicated to Prof. Dr. Fritz Umland on the occasion of his 60th birthday     

Photochemistry of the anthracene chromophore: novel isomerization of 1-(9-anthryl)-2-benzoylethylenes

Photoexcited cis-1-(9-anthryl)2-benzoylethylenes undergo a novel type of isomerization by skeletal rearrangement to give furano-annelated 5H-dibenzo[a,d]cycloheptenes.     

Cross sections for 197Au(n, γ)198Au and 115In(n, γ)116mIn in the neutron energy region 2.0–7.7 MeV

The cross sections for the reactions ¹⁹⁷Au(n, γ)¹⁹⁸Au and ¹¹⁵In(n, γ)^116mIn have been measured with the activation method in the neutron energy region 2.0–7.7 MeV. The influence of background neutrons on the results was studied in considerable detail. The main problems are caused by low-energy neutrons produced by charged-particle reactions in the target material and secondary neutrons from nonelastic reactions in the sample and surrounding materials.The measured capture cross sections are generally lower than previous results and the deviation tends to increase with increasing neutron energy. The data are also compared with calculations based on the compound-nucleus model and quite good agreement is obtained.     

Statistics of numerically generated turbulence

This paper considers numerically generated turbulence obtained by integrating the complete time-dependent three-dimensional Navier-Stokes equations. The simulated unidirectional turbulent flow, bounded by two parallel planes, is strongly inhomogeneous in the direction normal to the planes but homogeneous in the parallel directions. The resulting flow field, which is considered a numerical realization of fully developed turbulent channel flow, contains detailed information on spatial coherent flow structures as well as on the time-dependency and statistics of the three-dimensional velocity and pressure fields. Focussing here on the statistics of the numerically generated turbulence, second-moments and higher-moments are presented and compared with the most recent PTV and LDV laboratory measurements. It is concluded that direct numerical simulations are an invaluable approach to turbulence which complements field studies and laboratory investigations. Numerical experiments are now becoming a principal source of detailed and reliable information, which play a key role in the deepening of our understanding of turbulent flow phenomena.     

Synthesis of a new amino acid based cross-linker for preparation of substrate selective acrylic polymers

The synthesis of N,O-bisacryloyl-L-phenylalaninol is described as well as its application in the preparation of a L-phenylalanine ethyl ester selective acrylic polymer.     

Study of some silver-thiol complexes and polymers: Stoichiometry and optical effects

The silver complexes of various thiols of low molecular weight have been studied by amperometric and spectrophotometric titrations. Cysteine and cysteamine form complexes with silver containing up to 1.5 Ag⁺/—SH. The ligands participating in the binding of silver are the —SH and amino groups. Under some conditions it was found that 1:1 thiol-silver polymers were formed. These polymers probably have the general structure ? Ag? S(R)? Ag? S(R)? . Some of them were prepared in pure form and subjected to various studies. Molecular weight determinations of the cysteine-silver and glutathione-silver polymers yielded values of 4000–7000 daltons. Studies on the UV absorption characteristics revealed that all of the polymers showed some type of regular band pattern. The cysteamine-silver polymer is able to sensitize photographic emulsions.