Picosecond-resolution fluorescence lifetime measuring system with a cw laser and a radio

A procedure for measurement of fluorescence lifetimes with picosecond time resolution is described. A cw laser beam is modulated with a standing-wave acousto-optic modulator. The modulated beam is split; one part serves as a reference beam, the other part excites the fluorescent sample. The sample flourescence and the reference beam, attenuated and delayed optically to be equal in amplitude and opposite in phase to the fluorescence, are incident onto a single photomultiplier tube. The thus achieved photodetector ac null is monitored either by an AM radio, whose intermediate-frequency signal is displayed on an oscilloscope, or by a spectrum analyzer. With 30-MHz light modulation and the radio, lifetimes could be determined with resolution better than 15 ps. With the spectrum anlyzer and 170-MHz light modulation frequency we have achieved 4-ps lifetime resolution. Correction for photomultiplier transit time versus incident wavelength is made.     

Enrichment of humic material with hydroxybenzene moieties intensifies its physiological effects on the nematode Caenorhabditis elegans

Dissolved humic substances are taken up by organisms and interact on various molecular and biochemical levels. In the nematode Caenorhabditis elegans, such material can promote longevity and increase its reproductive capacity; moreover, the worms tend to stay for longer in humic-enriched environments. Here, we tested the hypothesis that the chemical enrichment of humic substances with hydroxybenzene moieties intensifies these physiological effects. Based on the leonardite humic acid HuminFeed (HF), we followed a polycondensation reaction in which this natural humic substance and a dihydroxybenzene (hydroquinone or benzoquinone) served as reaction partners. Several analytical methods showed the formation of the corresponding copolymers. The chemical modification boosted the antioxidant properties of HF both in vitro and in vivo. Humic substances enriched with hydroxybenzene moieties caused a significantly increased tolerance to thermal stress in C. elegans and extended its lifespan. Exposed nematodes showed delayed linear growth and onset of reproduction and a stronger pumping activity of the pharynx. Thus, treated nematodes act younger than they really are. In this feature the modified HF replicated the biological impact of hydroquinone-homopolymers and various plant polyphenol monomers, thereby supporting the hydroxybenzene moieties of humic substances as major effective structures for the physiological effects observed in C. elegans.     

Is a vegan or a vegetarian diet associated with the microbiota composition in the gut? Results of a new cross-sectional study and systematic review

Abstract

It is assumed that diet influences the composition of gut microbiota, which in turn may affect human health status. This systematic review aimed to summarize associations of a vegan or vegetarian diet with the composition of microbiota. A literature search was conducted in PubMed and Embase for eligible human studies with vegan or vegetarian diets as an exposure and microbiota composition as an outcome in healthy adults. Furthermore, data from our cross-sectional study with vegan participants were included. Out of sixteen included studies, six investigated the association between gut microbiota composition in both vegans and in vegetarians, six in vegans and four studies in vegetarians compared to omnivores, respectively. Among 5 different phyla, 28 families, 96 genera and 177 species, Bacteroides, Bifidobacterium and Prevotella were the most reported genera, followed by the species Prevotella copri, Faecalibacterium prausnitzii and Escherichia coli in all diets. No consistent association between a vegan diet or vegetarian diet and microbiota composition compared to omnivores could be identified. Moreover, some studies revealed contradictory results. This result could be due to high microbial individuality, and/or differences in the applied approaches. Standardized methods with high taxonomical and functional resolutions are needed to clarify this issue.     

High cw power using an external cavity for spectral beam combining of diode laser-bar emission

In extension to known concepts of wavelength-multiplexing diode laser arrays, a new external cavity is presented. The setup simultaneously improves the beam quality of each single emitter of a standard 25 emitter broad-area stripe laser bar and spectrally superimposes the 25 beams into one. By using this external resonator in an "off-axis" arrangement, beam qualities of Mslow2<14 and Mfast2<3 with optical powers in excess of 10 W in cw operation are obtained.     

Electrospinning and Photocrosslinking of Highly Modified Fungal Chitosan

The main focus of this study is to elucidate and optimize the electrospinning process for highly modified fungal chitosan. An efficient one-step process for functionalization of chitosan with arylazide and other desired functional groups via amidation is used for synthesis. Critical electrospinning process parameters, namely, molecular weight, concentration, and ratio of chitosan and additive poly(ethylene oxide) as well as degree of substitution of chitosan are identified by systematic parameter variation following design-of-experiment guidelines. Their influence on the viscoelastic properties of spinning solutions is studied and attributed to changes in chain entanglements. These changes result in drastic shifts in the electrohydrodynamic jet behavior and the resulting fiber morphologies. When the viscosity is increased above a critical limit, complete cancellation of whipping instabilities is observed, resulting in a stable linear jet and highly aligned but partly coalescing microfibers. It is shown how this process conditions can be avoided and how the production of uniform and defect-free nanofibers from highly functional chitosan can be carried out. In addition, a new photocrosslinking method for generation of water and acid stable chitosan nanofiber meshes is established.     

Efficient iteration schemes for anisotropic hyperelasto‐plasticity

Numerical issues arising when integrating hyperelasto‐plastic constitutive equations with elastic anisotropy, stemming from anisotropic damage, and plastic anisotropy as represented by kinematic hardening are discussed. In particular, solution algorithms for the corresponding non‐linear system of equations due to implicit integration algorithms are addressed. It is shown that algorithms like staggered iteration and quasi‐Newton techniques are superior to a pure Newton technique when the cpu time is compared. However, the drawback of the staggered and the quasi‐Newton technique is that rather small time steps must be taken to ensure convergence, which can be of importance when applying complex constitutive models in a finite element programme. Copyright © 2005 John Wiley & Sons, Ltd.     

Proton beam writing of microstructures at the ion nanoprobe LIPSION

Proton beam writing (PBW) is a direct writing technique which allows the creation of three-dimensional structures with a high aspect ratio in the micrometer and nanometer range in photoresist materials without the use of templates. At the high-energy ion nanoprobe LIPSION of the University of Leipzig this technique was established recently. In this article the latest results concerning this topic are presented. PBW was successfully performed with the positive resist polymethyl methacrylate (PMMA) which is now used at LIPSION in addition to the negative resist SU-8. With the new data acquisition system MICRODAS being commissioned, a new scan program was developed and tested which is dedicated to the creation of arbitrarily shaped structures. Squares with dimensions down to 1.2 μm were created in SU-8 at LIPSION. Furthermore, Ni grids were produced by electroplating, using templates written in PMMA resist. In addition, first structures for studying the growing behavior of Bragg reflectors and the optical characterisation of ZnO nanowhiskers were produced by PBW.