Cell Separation in a Continuous Flow by Traveling Wave Dielectrophoresis

In this contribution we present a microfluidic chip for the continuous and label-free separation of cells. Strip electrodes produce a traveling electric field perpendicular to the pressure driven flow. Viable cells are deflected parallel to the field by traveling wave dielectrophoresis (twDEP) according to their volume and dielectric properties. With the present device we have successfully separated viable Saccharomyces cerevisiae and Jurkat T-cells from debris, non-viable cells and Lactobacillus casei

Temporal and spatial variations in the parasitoid complex of the horse chestnut leafminer during its invasion of Europe

The enemy release hypothesis posits that the initial success of invasive species depends on the scarcity and poor adaptation of native natural enemies such as predators and parasitoids. As for parasitoids, invading hosts are first attacked at low rates by a species-poor complex of mainly generalist species. Over the years, however, parasitoid richness may increase either because the invading host continuously encounters new parasitoid species during its spread (geographic spread-hypothesis) or because local parasitoids need different periods of time to adapt to the novel host (adjustment-hypothesis). Both scenarios should result in a continuous increase of parasitoid richness over time. In this study, we reconstructed the development of the hymenopteran parasitoid complex of the invasive leafminer Cameraria ohridella (Lepidoptera, Gracillariidae). Our results show that the overall parasitism rate increases as a function of host residence time as well as geographic and climatic factors, altogether reflecting the historic spread of C. ohridella. The same variables also explain the individual parasitism rates of several species in the parasitoid complex, but fail to explain the abundance of others. Evidence supporting the “geographic spread-hypothesis” was found in the parasitism pattern of Cirrospilus talitzkii (Hymenoptera, Eulophidae), while that of Pediobius saulius, another eulophid, indicated an increase of parasitism rates by behavioral, phenological or biological adjustments. Compared to fully integrated host-parasitoid associations, however, parasitism rates of C. ohridella are still very low. In addition, the parasitoid complex lacks specialists, provided that the species determined are valid and not complexes of cryptic (and presumably more specialized) species. Probably, the adjustment of specialist parasitoids requires more than a few decades, particularly to invaders which establish in ecological niches free of native hosts, thus eliminating any possibility of recruitment of pre-adapted parasitoids

Two- and three-dimensional coordination polymers from the reaction of bis- and tris(2-aminoethyl)amine with titanium and zirconium alkoxides

The reaction of bis(2-aminoethyl)amine with M(OiPr)4 (M = Ti, Zr) affords the chain-like coordination polymers [M2(OiPr)8-(H2NCH2CH2NHCH2 CH2NH2)]..., where only the NH2 groups of the amine are coordinated to the M2(OiPr)8 units. 2D NMR spectroscopy shows that the adducts dissoc. into the starting compds. when dissolved in CD2Cl2 but are slowly re-formed in soln. over a period of two weeks. Puckered layers of condensed six-membered rings of [Ti2(OiPr)8]3[N(CH2CH2NH2) 3]2 are formed when [Ti(OiPr)4] is treated with tris(2-aminoethyl)amine. The voids in the center of the rings are filled by non-coordinated Ti2(OiPr)8 guest mols. In contrast, chains of [Zr2(OiPr)8-(H2NCH2CH2NR'CH2 CH2NH2)] {R' = CH2CH2NH2[Zr2(OiPr)8-(HOiPr)]} are formed upon treatment of tris(2-aminoethyl)-amine with [Zr(OiPr)4]

Towards a general understanding of hydrothermal polymerization of polyimides

Hydrothermal polymerization (HTP) has been recently established as a novel route to synthesize polyimides of outstanding crystallinity. In this contribution, we lay out the basic theoretical and experimental framework for understanding the mechanistic underpinnings of this process. For this purpose, we hydrothermally synthesize two representative polyimides that are known to form amorphous polymers when synthesized classically. Hydrothermal polymerization, in contrast, yields unprecedented crystallinity after only two hours. The co-monomers diamine and dianhydride form monomer salts via acid–base reaction when brought in contact in water. We show that the physicochemical properties of the crystalline monomer salts (i.e. solubility, solid-state polymerization temperature) are important factors for the crystallinity and the morphology of the corresponding hydrothermally synthesized polyimide. We develop a mechanistic model of hydrothermal polymerization processes allowing us to relate the polymerization parameters (concentration, reaction temperature, reaction time) to the obtained polyimide crystallinity and morphology. By adjusting the parameters, the achieved crystallinity can be further increased and high morphological homogeneity can be obtained. We believe that the developed mechanistic picture is applicable for the hydrothermal polymerization of any polyimide.publishe

Mono-, Di-, and Trimetallic Methacrylate-substituted Metal Oxide Clusters Derived from Hafnium Butoxide

\u2002The methacrylate-substituted clusters Hf4O2(OMc)12, Hf6O4(OH)4(OMc)12(BuOH), Ti4Hf4O6(OBu)4(OMc)16, and Ti2Zr5HfO6(OMc)20 (OMc=methacrylate) were prepared by reacting Hf(OBu)4, or Hf(OBu)4/Ti(OBu)4 and Hf(OBu)4/Zr(OBu)4/Ti(OBu)4 mixtures, respectively, with methacrylic acid. All clusters were characterized by X-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temperature NMR studies revealed that the methacrylate ligands of Hf4O2(OMc)12 are highly dynamic even at 1280\ub0C

Segmental front line dynamics of randomly pinned ferroelastic domain walls

Dynamic mechanical analysis (DMA) measurements as a function of temperature, frequency, and dynamic force amplitude are used to perform a detailed study of the domain wall motion in LaAlO3. In previous DMA measurements Harrison et al. [Phys. Rev. B 69, 144101 (2004)] found evidence for dynamic phase transitions of ferroelastic domain walls in LaAlO3. In the present work we focus on the creep-to-relaxation region of domain wall motion using two complementary methods. We determine, in addition to dynamic susceptibility data, waiting time distributions of strain jerks during slowly increasing stress. These strain jerks, which result from self-similar avalanches close to the depinning threshold, follow a power-law behavior with an energy exponent ɛ=1.7±0.1. Also, the distribution of waiting times between events follows a power law N(tw)∝t−(n+1)w with an exponent n=0.9, which transforms to a power law of susceptibility S(ω)∝ω−n. The present dynamic susceptibility data can be well fitted with a power law, with the same exponent (n=0.9) up to a characteristic frequency ω≈ω∗, where a crossover from stochastic DW motion to the pinned regime is well described using the scaling function of Fedorenko et al

Hafnium Oxide Doped Mesostructured Silica Films

Hafnium oxide doped silica films with ordered mesostructures were produced with hafnium:silicon ratios between 1:60 and 1:6. A surfactant\u2013hafnium alkoxide complex was synthesized and used as a template in a sol\u2013gel dip-coating process. Face-centred orthorhombic, 2D centred rectangular and lamellar films were formed by evaporation-induced self-assembly (EISA). The influence of subsequent heat treatment was studied by GISAXS and TEM. The surface and in-depth molecular composition of the films was studied by XPS.(\ua9 Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007

Formation of organically surface-modified metal oxo clusters from carboxylic acids and metal alkoxides: a mechanistic study

The reaction of Zr(OR)4 (OR = OnBu, OnPr) with methacrylic acid was monitored by extended X-ray absorption fine structure (EXAFS), 1H and 13C NMR, HPLC, and Raman measurements. The study revealed that the initial dimeric zirconium alkoxides react rapidly with the carboxylic acid and form higher aggregated multinuclear compounds. EXAFS investigations showed that the structures of the resulting aggregates in solution depend on the carboxylic acid to alkoxide ratio. In addition, the reaction rates also differ depending on this ratio; while for a methacrylic acid to zirconium alkoxide ratio of 4 361 the reaction is slow, metal oxo clusters form rapidly with a 7 361 ratio. Methacrylic acid ester is simultaneously formed during the reaction, with concomitant production of water, required for the formation and condensation reactions in the cluster preparation