Effects of modulation defects on Hadamard transform time-of-flight mass spectrometry (HT-TOFMS)

In any Hadamard multiplexing technique, discrepancies between the intended and the applied encoding sequences may reduce the intensity of real spectral features and create discrete, artificial signals. In our implementation of Hadamard transform time-of-flight mass spectrometry (HT-TOFMS), the encoding sequence is applied to the ion beam by means of an interleaved comb of wires (Bradbury-Nielson gate), which shutters the ion beam on and off. By isolating and exaggerating individual skewing effects in simulating the HT-TOFMS process, we determined the nature of errors that arise from various defects. In particular, we find that the most damaging defects are: mismatched voltages between the wire sets and the acceleration voltage of the instrument, which cause positive and negative peaks throughout mass spectra; insufficient deflection voltage, which reduces the intensity of real peaks and causes negative peaks that are spread across the entire mass range; and voltage errors as the wire sets return from their deflection voltage to their transmission value, which yield significant reductions in peak intensities, create artificial peaks throughout mass spectra, and broaden real peaks by causing positive peaks to grow in the bins adjacent to them. Because the magnitude of the modulation defects grows as the applied modulation voltage is increased, Bradbury-Nielson gates with finer wire spacing, and hence stronger effective fields for a given applied voltage, were produced and installed. Operating at 10 to 15 V where errors in the electronics are essentially absent, the most finely spaced gate (100 microm) yielded signal-to-noise ratios that were more than two times higher than those achieved with more widely spaced gates. As an alternative method for minimizing skewing effects, HT-TOFMS data were post processed using an exact knowledge of the modulation defects. Nonbinary matrices that mimic the actual encoding process were built by measuring voltage versus time traces and then translating these traces to transmission versus time. Use of these matrices in the deconvolution step led to marked improvements in spectral resolution but require full knowledge of the encoding defects.     

Dyes of the triphenylmethane type as sensor materials for solvent vapours

Summary The formation of highly coloured trityl ions from substituted phthalides can be utilized for the detection of solvent vapours in the air down to nearly ten ppm. These optochemical sensor materials were optimized with respect to their sensitivity, stability, linearity of the response and exclusion of the humidity influence. For this purpose the 4,4,4-substituents at the aromatic rings of the dyes must yield an appropriate carbenium ion stability. Thus even small amounts of absorbed solvent vapours lead to the reduction of the dye concentration in the sensor layers. The largest sensitivity can be achieved by applying dyes with two — N(CH₃)₂ substituents or, instead of one dimethylamino group, the — OCH₃ group at the aryl rings. Further improvements to reduce the sensor response to moisture were possible by introducing into the phthalides large aromatic ring systems with a hydrophobic behaviour such as indolyl.

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Farbstoffe vom Triphenylmethan-Typus als Sensormaterial für LösungsmitteldÄmpfe

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Dedicated to Prof. Dr. Hans Hofmann on the occasion of his 60th birthday     

A STUDY OF THE PHOTODYNAMIC EFFICIENCIES OF SOME EYE LENS CONSTITUENTS

We have studied the photochemical quantum yields of singlet oxygen production (using the RNO bleaching method) and superoxide production (using the EPR-spin trapping method and the SOD-inhibitable ferricytochrome c reduction spectral assay) of kynurenine (Ky), N-formylkynurenine (NFK), 3-hydroxykynurenine (3HK), kynurenic acid (KUA), and the flavins, riboflavin (RF) and flavin mononucleotide (FMN). Such a study of the photodynamic efficiencies is important since these compounds appear endogenously in the eye. The singlet oxygen quantum yields of the flavins and KUA are high, while Ky and 3HK generate no detectable amounts of singlet oxygen. The superoxide quantum yields of the sensitizers are low compared to their singlet oxygen, and Ky and 3HK produce no detectable amounts of superoxide. The production of the superoxide radical is enhanced in the presence of electron donor molecules such as EDTA and NADH. These results suggest that the production of oxyradicals in the lens may be modulated by the presence of endogenous electron donor molecules such as the coenzymes NADH and NADPH, which are present in significant amounts in some lenses. They also suggest that Ky and 3HK, which are known to be present in aged lenses, might play a protective rather than a deleterious role in the eye.     

Vibrational spectra and structure of cis- and trans-1,2- dimethoxyethylenes

The vapor, liquid and CCl₄ solution infrared spectra of cis- and trans-1,2-dimethoxyethylene were recorded in the region 250–4000 cm^?1. The laser-Raman spectra were obtained in the liquid state only. The vibrational spectra show that at least two rotational isomers exist for each molecule. Further, the spectra indicate that for both the cis- and trans molecules, one of the rotational isomers has at least one planar conformer. Some vibrational assignments are made for the observed infrared and Raman bands of the cis- and trans- 1,2-dimethoxyethylenes.     

Gefügedarstellung von Sphärolithen unter Anwendung der Ionenätzung

Zusammenfassung Es wird an einigen Beispielen gezeigt, da? Gefügeeinzelheiten in Hochpolymeren durch Anwendung der Ionen?tzung in ein Oberfl?chenrelief überführt werden k?nnen. Die Methode ist daher gleicherma?en geeignet für lichtmikroskopische Untersuchungen mit dem Interferenzkontrast-Verfahren wie für elektronenmikroskopische Untersuchungen mittels Oberfl?chenabdruck-Technik. Gefügebilder von Sph?rolithen in Polypropylen und Poly?thylen lassen sich zwanglos deuten, wenn man ein vonKeller vorgeschlagenes Kristallisationsmodell zugrunde legt.

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Summary It is shown, with examples, that through the use of ion etching, the structure of high polymers can be transformed into a surface relief. The method is applicable to interference-contrast light microscopy, and to electron-microscopy, using replica techniques. Spherulites in polypropylene and polyethylene are easily interpreted, if one bases the interpretation onKellers suggested crystallisation model.

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Frl.Meurer und FrauPudritz danken wir für die Durchführung der elektronen- und lichtmikroskopischen Untersuchungen.     

A blood vessel exposed to ultrasound: a mathematical simulation of the temperature field

In this article we present a mathematical simulation of the temperature field in and around a blood vessel when it is sonicated by a focused ultrasound beam. A simplified geometry is considered: a cylindrical blood vessel is embedded in tissue parallel to a flat skin surface. The ultrasound transducer is placed on the skin above the blood vessel, perpendicular to the skin surface. The 3D geometry of the problem is simplified by transformation, which maps the domain into a parallelepiped. A computational algorithm and computer program were developed. The simulation provides the conditions for successful occlusion of a blood vessel and demonstrates the significant role of the blood flow rate on the temperature difference between the vessel wall and the surrounding tissue. Comparing the predictions with published experimental data tested the validity of the method.     

Ultrashort-laser-pulse measurement using swept beams

We demonstrate a frequency-resolved optical gating (FROG) device that uses a sweepshot geometry that combines the advantages of multishot and single-shot pulse-measurement devices, has only one moving part, a galvanometer, and requires no computer control. Like a multishot device, it focuses the beam to a small spot (rather than a line focus) and has a high intensity in the nonlinear medium. Like single-shot devices, it makes measurements quickly, generating an entire FROG trace on a single camera screen (rather than requiring many camera downloads).     

Short-Chain Branching in Polyethylene and Poly(vinyl Chloride) Using Pyrolysis Hydrogenation Gas Chromatography and 13C Nuclear Magnetic Resonance Analysis

This study compares the use of pyrolysis hydrogenation gas chromatography (PHGC) and ¹³C Fourier transform nuclear magnetic resonance (FTNMR) methods for the analysis of reference polyethylene (PE) samples, ethylene-α-olefin copolymers, and specially prepared poly(vinyl chloride) (PVC) samples which were reduced to their PE skeletal structures. The nature and relative quantities of the short branches along the polymer chains were determined using both techniques. Improved high-resolution PHGC data, obtained with a fused silica capillary separation column, gave results which were in satisfactory agreement with the ¹³C FTNMR data. This approach confirms that detailed microstructural information can be obtained with these methods by using carefully controlled experimental conditions and appropriate reference systems.