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Eingeladener Vortrag
- nein (138)
Several series of crown fluoro-chromo-ionophores covering a broad spectral range are investigated experimentally and compared to their theoretically studied dimethylamino (DMA) analogues. It is shown that the logarithm of the complex stability constants log KS for NaI and CaII ions do not correlate with the observed complexation-induced shift. Likewise, an unsatisfactory correlation is found between the local charge density on the amino nitrogen of the DMA dyes and log KS. However, using the charge of the whole dimethylamino group instead strongly improves this correlation. This can be understood by considering pyramidalization and hyperconjugation effects on the amino nitrogen. The observed correlation allows a novel approach to the design of fluoroionophores with optimized properties.
Syntheses and photophysical properties of a series of cation-sensitive polymethine and styryl dyes
(2000)
The syntheses and photophysical properties of 20 cation-sensitive fluoroionophores carrying the tetraoxa monoaza 15-crown-5 receptor are described and discussed. Whereas complexation induces only weak effects for the positively charged hemicyanine probes, the closely related styryl dyes show stronger changes in their photophysical properties upon cation binding in the analytically advantageous near-infrared (NIR) region. The strongest effects in both cation-induced spectral effects and complex stability constants are observed for the uncharged probes of styryl base-type, but these probes usually absorb and emit at shorter wavelengths in the UV/VIS region. For both styryl dyes and styryl bases, in some cases cation-induced fluorescence enhancement or quenching is found.
The photophysical properties of several newly synthesized 1-benzothiazole-3-(4-donor)-phenyl-substituted prop-2-en-1-ones (substituted chalcones) are studied as a function of solvent polarity, temperature, and metal ion by employing steady-state and time-resolved spectroscopy. To investigate the effect of bulkiness and donor strength of the anilino moiety on the spectroscopic properties of these dyes, the spectroscopic behavior of the 4-N-dimethylamino (DMA), the 4-N-tetraoxa-monoaza-15-crown-5 (A15C5), and the 4-N-tetrathia-monoaza-15-crown-5 (AT415C5) derivatives as well as the 3-julolidino (Jul) analogue is compared. Absorption and fluorescence measurements reveal that the strength of the intramolecular charge transfer (ICT) process increases on the order of AT415C5 < A15C5 ~ DMA < Jul. The slight but significant differences between the two crowned dyes are well-supported by the results of the X-ray structure analysis, where oxa aza and thia aza crowns show essentially different geometries. For both fluoroionophores, this variation of heteroatom substitution pattern of the receptor induces specific cation selectivities. The spectroscopic effects accompanying complexation and the different binding sites are studied by steady-state and time-resolved optical spectroscopy as well as NMR spectroscopy. Whereas the probe carrying a tetraoxa monoaza 15-crown-5 receptor shows cation-induced fluorescence enhancement in the presence of alkali and alkaline-earth metal ions, its tetrathia analogue binds selectively to HgII, AgI, and CuII in acetonitrile. Moreover, an increase in fluorescence is observed for the latter probe even upon coordination to the widely known fluorescence quencher HgII. Besides receptor complexation, chelate formation in the benzothiazole-carbonyl acceptor part of these intrinsic fluorescent probes is possible, leading to a chromoionophoric signaling behavior in the near-infrared (NIR).
Kémiai Adatbázisok
(2000)
The fundamental quantities in the depth sensing hardness test are force and displacement. The penetration depth used for the calculation of a certain hardness parameter (for instance HU, Eq. (1)) makes it necessary to determine the contact point. As shown in the paper, fitting of the forcedisplacement curve, F(h), by a second order polynomial and extrapolating to F=0 is not always the right way to achieve a sufficiently small uncertainty of depth. The feature of that procedure is analysed by a simple mathematical model. In dependence of the testing force, the scatter of the experimental data, and the required limit of depth uncertainty, a profound selection of the fitting range, the fitting function, and the extrapolation function should be done.
In der vorliegenden Arbeit wird die sicherheitstechnische Eigenschaft "Entzündlichkeit" von
Gasen und Gasgemischen vorgestellt. Die Definitionen und Prüfverfahren in den
unterschiedlichen technischen Rechtsbereichen werden erläutert. Zur Klassifizierung von
Gasgemischen in kleineren Mengen ist sowohl im europäischen Gefahrstoff-, als auch im
Gefahrgutrecht ein Rechenverfahren nach ISO 10156, Nr. 4.6, zulässig. Für die Anwendung
des Rechenverfahrens benötigt man Stoffkenngrößen (Tci, Kk), die im Anhang zur ISO 10156
für einige Stoffe aufgelistet sind. Im Rahmen einer Forschungskooperation wurden im
europäischen Kernforschungszentrum (CERN) in Genf, an der Uni-GH Paderborn und in der
BAM Explosionsbereiche von Dreistoffsystemen (Brenngas, Inertgas, Luft) nach DIN 51649
bestimmt, aus denen sich Tci- sowie KK-Werte berechnen lassen. Die so mit einheitlichen
Apparaturen und Prüfverfahren ermittelten Werte weichen z.T. erheblich von den Angaben
der ISO 10156 ab. Im letzten Abschnitt dieser Arbeit werden Druck- und Temperatureinfluss
auf die Entzündlichkeit diskutiert.
Chemie
(2000)
Four ISO/IEC-test charts have been defined in ISO/IEC 15775 (1999) to specify image reproduction of
colour copiers. Corresponding test charts have been defined in DIN 33866-1 to 5 (in print) to specify
image reproduction of colour copiers, printers, scanners and monitors. All colours of all test charts are
defined in CIELAB coordinates. In applications the devices including software are used for test chart
input and output in the three different combinations "analog - analog" (copiers), "digital - analog"
(printers, monitors) and "analog - digital" (scanners, Photo-CD-systems).
This paper uses mainly ISO/IEC-test colours of a 16 step grey scale (defined by olv*-coordinates
according to the standard) in the original scene to calibrate the variable (photographic and Photo-CD)
analog-digital process. The relative digital olv*-input data and the digital olv*'-output data are used to
get approximately the same digital output (image file) independent of exposure (e. g. between -1 stop
under to +2 stop over exposure for slide or negative film) and other variables, e. g. the digitizing Photo-
CD-process. This "direct" colour management method adds a new method compared to the ICC colour
management method which fails to handle variable processes and can not manage the variable data of
original scenes taken by the photographic process.
The committees ISO/IEC JTC1/SC28 and DIN-NI-28 "Information technology, Office equipment" have
worked together to develop the International Standard ISO/IEC 15775. The new national standards
DIN 33866-1 to 5 (in print, drafts May to Nov. 1999) and the International Standard ISO/IEC 15775
are based on equivalent colour series. Both use the same colour series both in digital and analog test
charts and approximately the same layout.
New colorimetric technologies of Germany and Japan have been used to produce the four DIN- and
ISO/IEC-test charts in offset printing (3600 dpi) which are in application for colour devices now.
The different productions will be shown, e. g. in halftone and continuous tone and in reflectance and
transmittance mode. Some problems of measurement (e. g. fluorencent photographic material) and the
accuracy of production is important for applications.
A flat area lamp which is shown at the conference has the chromaticity of D65. With transparent ISO/IEC-test chart material on top this equipment defines a reference monitor for comparison with display
output. For additional information see the URL: www.ps.bam.de
The International Standard series ISO/IEC 15775
and DIS ISO/IEC 19839-1 to 4 for specifying
image reproduction properties of colour reproduction
processes analog-analog (copiers), analog-digital
(scanners) and digital-analog (printers, monitors)
seem to overlap with the International Standard
series IEC 61966-X for scanners, printers and
displays. But there are fundamental differences. In
the ISO/IEC standards the coding of colours is
based on reflective colours (defined for standard
offset printing) and in the IEC series on luminous
colours (defined for television).
Members of the standard groups ISO/IEC JTC1/
SC28 and IEC TC100 TA2 which developed the
above standards try at the moment to define
extended colour spaces (wide gamut colour spaces)
compatible with the present spaces of the standards
ISO/IEC 15775:1999-12 and IEC 61966-2-1:1999-
10.The extended spaces should match the
requirements of both the users and the industry for
the different applications. Important advantages and
disadvantages of both solutions based on coding of
reflective and luminous colours are presented.
Four ISO/IEC-test charts in different modes (halftone
and continuous tone, in reflectance and
transmittance mode) have been defined in ISO/IEC
15775 and ISO/IEC DIS 19839-1 to 4 to
specify image reproduction properties of colour
copiers, printers, scanners and monitors.
Corresponding test charts have been defined in DIN
33866-1 to 5.
All colours of all test charts are defined in CIELAB
coordinates. Main colour series are equally spaced
in CIELAB colour space both in lightness L* and
chroma C*. Up to now there are productions of DIN
and JBMA (Japan Business Machine Makers
Association) according to ISO/IEC 15775 which can
be used for all applications.
Methodical aspects of soil sampling regarding the requirements of the federal soil protection act
(2000)
Verschiedene Labor- und Freilandstudien zeigen, dass Antrodia vaillantii ein Braunfäuleerreger ist, der chemisch geschütztes Holz (gemäss den Anforderungen der Gefährdungsklasse 4) stark abbauen kann. Hierbei spielt die erhöhte Oxalsäureproduktion des Pilzes und die daraus resultierende Kupferoxalatausfällung im Holz die entscheidende Rolle. Das Kupfer wird auf diese Weise für den Pilz weitgehend unschädlich gemacht und andere Holzschutzmittelbestandteile wie z.B. Chrom- und Arsenverbindungen verlieren ihre Fixierung im Holz und werden wasserlöslich. Dies führt zu Frühausfällen von chemisch geschütztem Holz im Erdkontakt innerhalb weniger Jahre. Laboruntersuchungen haben gezeigt, dass der Holzabbau durch A. vaillantii bei hoher Wasserverfügbarkeit außerhalb des Holzes angeregt werden kann. Das hohe Feuchtigkeitsbedürfnis des Pilzes ist möglicherweise die Ursache für den Befall von Holz in bis zu 1,2 m Bodentiefe. Neben der hohen Bodenfeuchte gibt es Anhaltspunkte für weitere Parameter, die zur positiven Selektion von A. vaillantii und damit seiner stellenweise starken Ausbreitung führen. Diese sind hohe Toleranz gegenüber bereits vorhandenen niedrigen pH-Werten im Boden, das aktive Einstellen niedriger pH-Werte im Boden durch Säureabgabe und die Festlegung von Kuper als Kupferoxalat.
Das Streckennetz der Deutschen Bahn wird mit Hilfe eines Schienenprüfzuges ständig auf betriebsbedingte Schädigungen überwacht. Bisher wurde hier ausschließlich das Ultraschallprüfverfahren eingesetzt. In Ergänzung dazu könnte die Wirbelstromprüfung für den Nachweis und die Bewertung spezieller Oberflächenrisse - sog. Head Checks - erfolgreich und wirtschaftlich sinnvoll eingesetzt werden. Über Laboruntersuchungen, die die grundsätzliche Eignung dieser Prüftechnik zeigten, wurde bereits berichtet. Der nächste Entwicklungsschritt besteht in der praktischen Erprobung unter realen Einsatzbedingungen. Hierbei stellen die hohen Prüfgeschwindigkeiten von bis zu 28 m/s (entsprechend 100 km/h Fahrgeschwindigkeit des Prüfzuges) eine besondere Herausforderung dar. Es gibt zahlreiche Probleme zu bewältigen. Diese betreffen beispielsweise die Sondenführung, die Signalfilterung, die Datenerfassung und die Unterdrückung von Störeinflüssen. Über erste Erfahrungen wird berichtet.
Die Betriebsüberwachung der Radscheiben von Schienenfahrzeugen kann besonders wirt-schaftlich durchgeführt werden, wenn die Prüfung im eingebauten Zustand erfolgen kann. Hierzu kann z. B. eine Oberflächenprüfung nach dem Wirbelstromverfahren eingesetzt werden. Als Optimierungskriterien für die Sondenkonstruktion werden eine sehr hohe Prüfempfindlichkeit gegenüber kleinen Rissfehlern und eine gute Handhabbarkeit bei erschwerter Zugänglichkeit der Prüffläche gefordert. Hierzu wurde eine neuartige Wirbel-stromprüfsonde entwickelt. Die Besonderheit besteht darin, dass der Nachweis von sehr kurzen Rissen bei einer gleichzeitig großen Sensorspurbreite möglich ist. Der Zeitaufwand für die Radscheibenprüfung wird damit gegenüber dem bisherigen Stand der Technik um 2/3 reduziert.
Two fluorescent dyes were incorporated into sol-gel derived SiO2 matrices. The dye was added to SiO2 precursors of different degrees of pre-condensation and the spectroscopic properties of the immobilized dye were measured at various aging and drying stages of the resulting gels. The significant influence of the processing parameters on the spectroscopic properties is manifested in the relative intensity of a second red shifted emission band (550560 nm), which was observed besides the typical coumarin emission band (495 nm). The appearance of this long wavelength emission might be attributed to dye aggregation or to other reactions with the ambient matrix forced by micro porosity phenomena.
Overlayers of SiO2 (nominally 4, 6 and 8 nm thick) on silicon, prepared by thermal oxidation, were investigated using x-ray photoelectron spectroscopy (XPS). The thickness of these overlayers was obtained from a measurement of the photoelectron intensities originating from the substrate and the oxide overlayer by applying an appropriate quantitative model. The uncertainty budget of that thickness measurement method is given. The relative combined standard uncertainty of the method was found to be 15%. The effective attenuation lengths or the corresponding electron inelastic mean free paths are of considerable importance for both the estimated values of overlayer thickness and combined standard uncertainties. The XPS results were compared with ellipsometry data.
Chemical, morphological and accumulation phenomena in ultrashort-pulse laser ablation of TiN in air
(2000)
Ultrashort-pulse laser ablation (F=130 fs, 5=800 nm, repetition rate 2-20 Hz) of titanium nitride was investigated for laser fluences between 0.3 and 4.5 J/cm2 using the direct focusing technique in air. The influence of the laser pulse number and the peak fluence was investigated by means of several surface analytical techniques (optical microscopy, dynamic friction atomic force microscopy, scanning Auger electron microscopy and small-spot electron spectroscopy for chemical analysis). The correlation of the results about optical, physical and chemical properties of the irradiated areas allows us to propose a simple oxidation model, which explains different observed phenomena associated with surface damage such as mound formation and crater widening and clarifies the incubation behavior reported earlier for this material.
In recent years eure monitoring with ultrasonic methods became more important. An on-line measurement System for industrial applications is presented in this paper. It operates in through-transmission and the measured parameters are the sound velocity and the attenuation of the sound wave. An objective of this paper is to establish the ränge of possible applications for an ultrasonic eure monitoring System.
The stability of microstructure and the microhardness of a NiCoCrAlY alloy was studied after thermal treatment at high temperatures and subsequent quenching into ice water. The alloy revealed mainly two ordered phases, a gamma' phase with L12 lattice structure and a beta phase with B2 structure. The gamma' phase is shown to become unstable in the temperature range between 1073 K and 1373 K where it undergoes an order-disorder phase transformation. The low transformation temperature compared to pure Ni3Al is ascribed to deviations from the Ni3Al stoichiometry and to the additional alloying elements Co and Cr. The gamma'-gamma order-disorder transformation is shown to be attended by a decrease in microhardness of about 30 %.
The acceptor strength of the boron-dipyrromethene chromophore in directly linked donoracceptor compounds can be tuned by substituents in such a way that a fast excited state charge transfer takes place even for the comparatively weak benzo crown electron donor. This leads to strong fluorescence quenching. Upon binding of cations (Na+ and K+) to the benzo crown receptor, the donor properties of the latter are further reduced, partly suppressing charge transfer. Large fluorescence enhancement factors and cation-selective fluorescence decay times result which are the basis for improved analytical application of these dyes as highly sensitive fluorescent probes.
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
The excitation energy transfer (EET) of a bichromophoric cross-shaped molecule was investigated by stationary polarized fluorescence spectroscopy in the solid state. For this purpose 2,2[prime],7,7[prime]-tetrakis(biphenyl-4-yl)-9,9[prime]-spirobifluorene was embedded in a polymeric bisphenol-A-polycarbonate (PC) matrix. The dependence of the fluorescence on concentration and wavelength was determined. The role of the intermolecular and intramolecular EET is dealt with separately and discussed by means of the degree of polarization. The intermolecular excitation energy transfer is described in terms of a Förster transfer mechanism. The intramolecular transfer is prevented for the zero-point vibrational levels by the molecular cross-shaped structure, but is found for a wide range of wavelength, presumably based on vibrationally excited states.
Drucksondierungen, teufengenaue Probenahme und Präparation MKW-kontaminierter Lockersedimente
(2000)
Using a rail-inspection train, the Deutsche Bahn's system of railroads is continuously checked for traffic-induced defects. Until now, only ultrasonic inspection was used. In addition, eddy-current inspection could successfully and efficiently be used to detect and evaluate certain surface cracks - so-called head checks. There have already been reports about laboratory tests which proved the general suitability of this test method [1,2]. The next step - described here - consisted of practical trials under real-life conditions. A test system which is able to fulfil the strict requirements (test speeds of up to 100 km/h, complex probe guidance, suppression of electrical and mechanical interference, recording of data, filtering and evaluation of data) was developed. As part of the rail-inspection train and as a manual system, this inspection system was successfully tested on the Deutsche Bahn's system of railroads under real-life conditions.
Ermittlung der Messunsicherheit in der organisch-chemischen Analytik - ein Beispiel aus der Praxis
(2000)
Fundamentals of Tribotesting
(2000)
Tribology is an experiment-oriented branch of a complex, interdisciplinary science, in which testing plays a major role in the solution of technical problems, in the field as well as in the development of tribomaterials. Various test methods are used for this purpose, and the results are sensitive to the choice of test method and test conditions.
In this paper, the effects of test parameters on friction and wear results are considered, some selected results of model tests with different types of materials are presented, and guidelines are derived, that help improve the reliability and level of confidence of tribological tests performed in laboratories.
Photo- and thermo-oxidative stability of aromatic spiro-linked bichromophoric cross-shaped molecules
(2000)
An extensive investigation of the photostability and the thermo-oxidative stability is presented for 2,2,7,7-tetrakis(biphenyl-4-yl)-9,9-spirobifluorene and 2,2,4,4,7,7-hexakis(biphenyl-4-yl)-9,9-spirobifluorene. Both compounds are conjugated fully aromatic systems that are being discussed as active functional materials for a variety of advanced applications. The effect of atmosphere, sample thickness and preparation procedure on photo-oxidative degradation are investigated in detail by absorption and fluorescence spectroscopy. Distinct mechanisms are described in terms of relevant parameters such as the quantum yields of the photo-oxidation and the fluorescence. No oxidative degradation could be detected under nitrogen. In ambient air a strong decrease of the fluorescence performance is found due to effective quenching by defective chromophores. Chemiluminescence investigations were performed to characterise the thermo-oxidative behaviour in the temperature region between 300 and 450 K. It becomes clear that even a stable chemical structure such as the investigated aromatic system does not guarantee sufficient photostability with regard to light emitting properties.
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