Controlled synthesis of cell-laden microgels by radical-free gelation in droplet microfluidics

Micrometer-sized hydrogel particles that contain living cells can be fabricated with exquisite control through the use of droplet-based microfluidics and bioinert polymers such as polyethyleneglycol (PEG) and hyperbranched polyglycerol (hPG). However, in existing techniques, the microgel gelation is often achieved through harmful reactions with free radicals. This is detrimental for the viability of the encapsulated cells. To overcome this limitation, we present a technique that combines droplet microfluidic templating with bio-orthogonal thiol-ene click reactions to fabricate monodisperse, cell-laden microgel particles. The gelation of these microgels is achieved via the nucleophilic Michael addition of dithiolated PEG macro-cross-linkers to acrylated hPG building blocks and does not require any initiator. We systematically vary the microgel properties through the use of PEG linkers with different molecular weights along with different concentrations of macromonomers to investigate the influence of these parameters on the viability and proliferation of encapsulated yeast cells. We also demonstrate the encapsulation of mammalian cells including fibroblasts and lymphoblasts.     

ArtTAX - a new mobile spectrometer for energy-dispersive micro X-ray fluorescence spectrometry on art and archaeological objects

A newly developed spectrometer for energy-dispersive micro X-ray fluorescence spectrometry has been designed for the demands of archaeometry. ArtTAX combines the advantages of non-destructive and sensitive multi-elemental analysis at sub-mm resolution with the possibility of working outside the laboratory. The spectrometer consists of an air-cooled, low-power molybdenum tube, new generation polycapillary X-ray optics, a silicon drift detector without the need for liquid-nitrogen cooling, a CCD camera, and three light diodes for sample positioning. The motor-driven measurement head is fixed on a x,y,z-flexible tripod support which can be assembled and dismantled within minutes. The spot size of the primary X-ray beam was determined to be 94 microm for the Cu(Kalpha) energy, the detection limits are in a range of a few tens of microg g(-1) for the medium energy-range in glass. Additional open helium purging in the excitation and detection paths enables the determination of elements down to sodium, thus avoiding vacuum conditions or a size-limiting sample chamber. A selection of qualitative and quantitative results on pigment, metal, glass, and enamel analyses are presented to show the potential of ArtTAX in the field of art and archaeology.     

Energy functionals for microstructured multi-phase materials

For describing the influence of multi-phase materials with microstructure on different length scales as well as the evolution of phase changes under thermomechanical loading, an energetic model is developed. Relying on the incremental formulation of the energetic model, a new solution procedure for the coupled thermomechanical problem is proposed. This model can be applied to describe e.g. the macroscopic response of carbon fibre reinforced carbon. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved lasing properties of the HêN 2 + system at 391 nm and 428 nm by H2 admixture

The He/N₂ system lasing on the N ₂ ⁺ (B)N ₂ ⁺ (X, 0) transition at 391 nm and on the N ₂ ⁺ (B)N ₂ ⁺ (X, 1) transition at 428 nm was investigated by e-beam excitation. By adding H₂ the lower laser state is efficiently quenched, which leads to a drastic improvement of the laser properties. A kinetic model is proposed which accounts for the experimental results. For a laser amplifier operated at 5 bar total efficiencies of 0.6% and 0.7% are predicted for the 391 nm and the 428 nm transitions respectively.     

Surface modification by intense proton irradiation

In the present paper the mixing of thin metal layers on silicon or copper substrates induced by HIPIB (High Intensituy Pulsed Ion Beams) was investigated using a device which delivers mainly protons with a maximum ion energy of E ₀=250 keV, a pulse length of =50 ns, and an energy density per pulse of 3 J/cm². The temperature distribution in the samples which was evaluated by solving the one-dimensional heat-flow equation indicates that 1 m layers are heated well above the melting point. The samples were analysed by RBS (Rutherford Backscattering Spectrometry), SNMS (Sputtered Neutral Mass Spectrometry), X-ray diffraction and a microprobe. If the surface tension of the molten layer is larger than the one of the substrate, the layer material is splashed off. Chromium layers on copper are completely mixed after irradiation by a few shots and a considerable hardening of the surface is observed.     

VUV-transitions in ionic rare-gas alkali molecules

Mixtures of rare-gases (Rg) and alkali vapors (A) were excited by helium and argon ions. VUV transitions observed between 131.1 nm and 189.9 nm were ascribed to the decay of (RgA)⁺ ions where Rg=Kr, Xe and A=Cs, Rb, K, Na, Li. In the (ArA)⁺ systems (A=Rb, K, Na, Li) transitions appeared between 114.1 nm and 124.7 nm. Since the final state is only weakly bound, the (RgA)⁺ ions seem to be promising candidates for storage media of VUV lasers.     

Calculation of vertical ionization potentials by configuration interaction

The ionization potentials of H₂O, N₂, C₂H₂, and HCN were calculated by frozen-orbital configuration interaction using doouble-zeta and double-zeta plus polarization functions basis sets. The results are compared to the observed values and to those from Rayleigh—Schrödinger perturbation theory. The effects of higher excitations are estimated and discussed.