Optimized in-phase and opposed-phase MR imaging for accurate detection of small fat or water fractions: theoretical considerations and experimental application in emulsions

Object  

To optimize strategies and measurement parameters for quantification of small fat and water fractions (<10%) in mixtures of both components by 4-point in-phase and opposed-phase gradient-echo imaging and to compare theoretical results with in-vitro experiments using emulsions.     

Optical dilatometry for the control of microstructure development during sintering

An optical method for the in situ measurement of sintering shrinkage has been developed. It relies on a simple and robust CCD camera technique and is applicable up to high temperatures (2000 °C) and heating rates (10 K/min) in industrial furnace atmospheres. A resolution of less than 1 μm for a sample diameter of 10 mm has been achieved using a special geometrical arrangement and a smart image analysis algorithm. Systematic errors are small (<0.1%) and can be corrected by an additional measurement. A high reproducibility of shrinkage measurement has been observed in various sintering experiments. The optical dilatometer is very flexible: it has been used also for an accurate temperature calibration and for wetting experiments and it can be adjusted to different furnace types. Received: 17 May 2000 / Reviewed and accepted: 26 June 2000     

Study on surface and mechanical fiber characteristics and their effect on the adhesion properties to a polycarbonate matrix tuned by anodic carbon fiber oxidation

Polyacrylonitrile (PAN) based high strength carbon fibers were anodically oxidized using the galvanostatic mode in alkaline electrolyte solutions to influence the chemical surface composition. The change of chemical and physical properties was investigated using scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDX) and contact angle as well as zeta (ζ)-potential measurements.

An initially improved wettability for polar liquids, particularly water, was observed for oxidized carbon fibers. This result was confirmed by ζ-potential measurements. The chemical state of the oxygen containing surface groups changes during anodic oxidation in K₂CO₃/KOH due to further oxidation of C–OH and C=O groups to COOH groups. Therefore the surface acidity increases, which leads to a shift of the isoelectric point to lower pH values and increases the negative ζ_plateau value. The ζ–pH as well as the ζ–concentration dependence show the same tendency. During anodic oxidation of carbon fibers in KNO₃/KOH electrolyte solution beside ‘normal’ (like C–OH, C=O and COOH) surface oxides also carboxylate groups (COO⁻K⁺) were formed at the fiber surface in contrast to an oxidation in K₂CO₃/KOH which introduces ‘normal' surface oxides. No influence could be observed of such an anodic oxidation on the single fiber tensile strength. Contact angle measurements of polycarbonate melt droplets onto single carbon fibers show no dependence of the surface composition. The interfacial shear strength, measured using the microdroplet pull-off test were compared with the thermodynamic work of adhesion. The calculated as well as the measured adhesion show the same absence of any influence of fiber treatment.     

Impact of DICER1 and DROSHA on the Angiogenic Capacity of Human Endothelial Cells

RNAi-mediated knockdown of DICER1 and DROSHA, enzymes critically involved in miRNA biogenesis, has been postulated to affect the homeostasis and the angiogenic capacity of human endothelial cells. To re-evaluate this issue, we reduced the expression of DICER1 or DROSHA by RNAi-mediated knockdown and subsequently investigated the effect of these interventions on the angiogenic capacity of human umbilical vein endothelial cells (HUVEC) in vitro (proliferation, migration, tube formation, endothelial cell spheroid sprouting) and in a HUVEC xenograft assay in immune incompetent NSG^TM mice in vivo. In contrast to previous reports, neither knockdown of DICER1 nor knockdown of DROSHA profoundly affected migration or tube formation of HUVEC or the angiogenic capacity of HUVEC in vivo. Furthermore, knockdown of DICER1 and the combined knockdown of DICER1 and DROSHA tended to increase VEGF-induced BrdU incorporation and induced angiogenic sprouting from HUVEC spheroids. Consistent with these observations, global proteomic analyses showed that knockdown of DICER1 or DROSHA only moderately altered HUVEC protein expression profiles but additively reduced, for example, expression of the angiogenesis inhibitor thrombospondin-1. In conclusion, global reduction of miRNA biogenesis by knockdown of DICER1 or DROSHA does not inhibit the angiogenic capacity of HUVEC. Further studies are therefore needed to elucidate the influence of these enzymes in the context of human endothelial cell-related angiogenesis.     

Design and performance of a SAW ladder-type filter at 3.15 GHzusing SAW mass-production technology [wireless LANs]

To meet the increasing demand for high-performance filters in gigahertz radio-communication systems, we have improved the design techniques and fabrication processes for surface-acoustic wave (SAW) devices. The standard optical projection printing technique based on i-line lithography used for mass-production was optimized, thus attaining a linewidth of 0.3 μm. As a first SAW device prototype, we designed and fabricated a ladder-type bandpass filter from LiTaO₃ substrates, at 3.15 GHz having a 3 dB-bandwidth of 128 MHz and a minimum insertion loss of 1.7 dB     

Dielectric relaxation of polar aromatics in unoriented and oriented linear low‐density polyethylene

The dielectric behavior of some polar aromatics dissolved in nonpolar unoriented and stretched linear low‐density polyethylene was investigated within the temperature region between 150 and 350 K. The measurements were carried out in the frequency range 1 kHz to 10 MHz. The maximum temperatures and the half widths of the loss tangent peaks depend upon the shape and the polar structure of guest molecules. Stretching the samples induced a shift of the loss tangent to higher temperatures, decreased the height, and increased the width of tan δ peak. The activation energy is also influenced by the type of guest molecules and orientation of polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1278–1282, 2001     

Grafted carbon fibers and their physico‐chemical properties. Part II. Grafting of liquid crystalline methacrylic monomers onto carbon fibers and the influence of an applied voltage to the carbon fiber embedded in a liquid crystalline matrix

Results of grafting reactions of a liquid crystalline (lc) monomer onto carbon fiber surfaces are presented and compared with results of noncovalently bonded lc polymer, which is proved reproducible by scanning electron microscopy. Electro‐optical investigations under a polarizing microscope hints of the possibility of changing lc polymer and lc low molecular mass matrix molecules properties by applying a certain voltage to the carbon fibers. Wetting and electrokinetic measurements were performed and correlated with grafting reaction parameters. Those investigations revealed a nearly complete coverage of the carbon fiber surfaces by lc polymers. These measurements are suitable to characterize carbon fibers modified by grafted or coated polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1893–1904, 1999     

MS-Based Screening of 5-Substituted Nipecotic Acid Derived Hydrazone Libraries as Ligands of the GABA Transporter 1

A screening of compound libraries based on nipecotic acid derivatives with lipophilic residues attached to the scarcely explored 5-position of the core structure was used for the search of new inhibitors of the γ-aminobutyric acid (GABA) transporter 1 (mGAT1). The generated compound libraries, which were based on hydrazone chemistry commonly used in dynamic combinatorial chemistry but rendered pseudostatic, were screened for their binding affinities toward mGAT1 by means of MS Binding Assays. With nipecotic acid derived hydrazone rac- 16 h [rac-(3R,5S)-{5-[(E)-2-{[5-(2-phenylethynyl)thiophen-2-yl]methylidene}hydrazin-1-yl]piperidine-3-carboxylic acid}-sodium chloride (1/2)], one hit was found and evaluated displaying sub-micromolar potency (pK_i=6.62±0.04) and a noncompetitive interaction mode at mGAT1. By bearing a 5-(2-phenylethynyl)thiophen-2-yl residue attached to the 5-position of nipecotic acid via a three-atom spacer, compound rac- 16 h contains a structural moiety so far unprecedented for these kinds of bioactive molecules, and complements novel 5-substituted nipecotic acid derived ligands of mGAT1 revealed in a recently published screening campaign. This new class of ligands, with an inhibition mode distinct from that of benchmark mGAT1 inhibitors, could serve as research tools for investigations of mGAT1-mediated GABA transport.