Fluorescence Studies of Melanin by Stepwise Two-Photon Femtosecond Laser Excitation

Fluorescence of synthetic melanin in the solvents H₂O, KOH, ethylene glycol monomethyl ether, and dimethyl sulfoxide has been excited by two-photon absorption at 800 nm, using 120-fs pulses with photon flux densities of 10²⁷ cm^–2.S^–1. Compared to the one-photon (400-nm)-induced fluorescence of melanin, the overall spectral shape is red-shifted and shows a strong environment sensitivity. The decay of the two-photon-induced fluorescence (TPF) of melanin is three-exponential, with a shortest main component of about 200 ps. The results of the TPF studies in line with the unique light absorption property of melanin of a monotonously decreasing absorption spectrum between the near UV-region and the near infrared region indicate that the TPF is realized via stepwise absorption of two 800-nm photons. In comparison to the simultaneous absorption of two photons, the stepwise process needs lower photon flux densities to get a sufficient population of the fluorescent level. This stepwise process offers new possibilities of selective excitation of melanin in skin tissue in a spectral region where there is no overlap with any absorption of another fluorescent tissue component. The first results with different samples of excised human skin tissue (healthy, nevus cell nevi, malignant melanoma) suggest that fluorescence excited in this way yields information on malignant transformation.     

The “AURAS” system for computer-aided autoradiogram evaluation

A compound device for autoradiogram evaluation is described which consists of a modified Zeiss rapid photometer and a Densitron system with a scanner for picture digitization and a microcomputer as processing unit. The mode of operation of the compound device is illustrated by some examples.     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.     

Experimental study on the aging process of the LR 115 cellulose nitrate radon detector

An experimental determination of the aging process of cellulose nitrate detector material was based on the examination of special properties of the LR 115 solid state nuclear track detectors (SSNTDs) of various ages up to 18 years. The examined relevant parameters are the bulk etching rate v_b and the track etching rate v_t. These parameters are responsible for the appearance, the size and the registration efficiency of tracks of -particles from radon gas in the detector. To find a correlation between these material parameters and the detector sensitivity an experimental calibration of indoor room and outdoor soil detector devices based on LR 115 took place at the Umweltforschungszentrum Leipzig-Halle (Germany). To avoid routine calibration work in external radon exposure facilities a correction of the age dependent calibration factors with the material parameters measured in one's own laboratory was targeted. In this study a general age dependence, however, was not found. The following statements for practical applications can be made. (i) the bulk etching rate v_b for detectors of the same batch has a depth dependence and this dependence is constant over 2 years (LR 115 September 1994). (ii) detectors of different batches older than 5 years and stored at room temperature show an odd v_b behaviour when v_b is used for describing track shapes. (iii) the calibration factor of detectors of different batches that were stored at about +4°C is constant over 5 years (LR 115 September 1994 and February 1999, Table 2).

The conclusion is that LR 115 detectors not older than 5 years and stored in a refrigerator at about +4°C should be preferred for radon measurements. Furthermore these detectors should be recalibrated every year and the microscope work of this calibrations should be performed by the same person who performs the measurements.

In addition, a phenomenon related to fundamental track formation mechanisms was found, that the time straggling of the time t_through when vertical tracks penetrate the 12 μm thick detector layer is independent of the age of the detectors and the energy of the -particle at the detector surface.     

Zur Erweiterung des abbildbaren Objektumfangs bei Aufuahmen mit γ-Strahlung

Vier verschiedene Chemische Verstärker werden hinsichtlich ihrer Eignung zur Erweiterung des Objektumfangs, der Verbesserung der Detailerkennbarkeit und der zu erzielenden Verkürzung der Belichtungszeit untersucht. Zur Materialprüfung ist das Verfahren nur für spezielle Fälle anwendbar.     

On Quantitative Autoradiography of Semiconductor Basic Material

It will be described methods of the quantitative evaluation of elements interesting in semiconductor technology and their distribution in silicon using autoradiographic techniques. The local concentration of the element phosphorus in dependence of their local distribution is determined with silver halide films. As standard samples silicon disks phosphorus diffused are used.

The distribution of the element boron and their local concentration is determined on the way of neutron induced autoradiography (NIAR). In this technique boron implanted or diffused silicon disks are used as standard samples. Different possibilities of the quantitative evaluation of autoradiograms will be considered and compared.     

Bestimmung von Diffusionskoeffizientcn an Autoradiogrammen mit Hilfe von Schwärzungsmomenten

Zur experimentellen Bestimmung des Diffusionskoeffizienten in Festkörpermaterialien werden sehr häufig autoradiographische Verfahren in der Radionuklid-Tracertechnik angewendet. Bedingt durch die autoradiographische Abbildung ist es im allgemeinen nicht möglich, den Diffusionskoeffizienten direkt aus dem Schwārzungsverlauf des Autoradiogramms abzulesen.

Aus diesem Grunde wurde ein mathematisches Verfahren entwickelt, das den Diffusionskoeffizienten in Abhängigkeit von Schwärzungsmomenten liefert, die nach einer bestimmten Vorschrift zu bilden sind. Die Lösung der autoradiographischen Abbildungsgleichung konnte dabei umgangen werden.

Das Verfahren wird an einem typischen Beispiel erläutert.     

Polyhalite and its analogous triple salts

Polyhalite (K₂SO₄ · MgSO₄ · 2CaSO₄ · 2H₂O) and analogue triple salts, where Mg²⁺ is substituted by Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺, have been synthesized. The salts were characterized by thermal analysis, Raman spectroscopy and X-ray powder diffraction. Diffraction patterns and Raman spectra resemble those of natural polyhalite, except K₂SO₄ · CuSO₄ · 2CaSO₄ · 2H₂O. The latter corresponds to the mineral leightonite, which is structurally different. For polyhalite analogues the cell parameters of the triclinic unit cell have been determined from the powder diffraction patterns. The length of the unit cell vectors varies regularly with the ionic radius of the substituted ion M ²⁺ and is explained by changes in the extension of the coordination octahedron of M ²⁺. Thereby increasing distances of the coordinated water molecules at M ²⁺ parallel with decreasing dehydration temperatures of the corresponding polyhalite. Correspondence: Daniela Freyer, Institut für Anorganische Chemie, TU Bergakademie Freiberg, 09599 Freiberg, Germany.