Scientific Award 2003

SciencenewsBMW AG

Scientific Award 2003     

Photonic crystal waveguide-mode orthogonality conditions and computation of intrinsic waveguide losses

We simulate the propagation of light in a W1 planar photonic crystal waveguide with the three-dimensional finite-difference time-domain method and apply an inner product against previously calculated mode profiles to the simulated field cross sections. We show that this inner product satisfies mode orthogonality for both photonic crystal waveguides and segmented waveguides and use the obtained data to evaluate waveguide losses.     

ATP-independent contractile proteins from plants

Emerging technologies are creating increasing interest in smart materials that may serve as actuators in micro- and nanodevices. Mechanically active polymers currently studied include a variety of materials. ATP-driven motor proteins, the actuators of living cells, possess promising characteristics, but their dependence on strictly defined chemical environments can be disadvantagous. Natural proteins that deform reversibly by entropic mechanisms might serve as models for artificial contractile polypeptides with useful functionality, but they are rare. Protein bodies from sieve elements of higher plants provide a novel example. sieve elements form microfluidics systems for pressure-driven transport of photo-assimilates throughout the plant. Unique protein bodies in the sieve elements of legumes act as cellular stopcocks, by undergoing a Ca2+-dependent conformational switch in which they plug the sieve element. In living cells, this reaction is probably controlled by Ca2+-transporters in the cell membrane. Here we report the rapid, reversible, anisotropic and ATP-independent contractility in these protein bodies in vitro. Considering the unique biological function of the legume 'crystalloid' protein bodies and their contractile properties, we suggest to give them the distinctive name forisome ('gate-body'; from the Latin foris, the wing of a gate).     

Mechanical properties and surface defects of boron fibres prepared in a closed CVD system

The tensile strength of boron fibres, prepared on a tungsten wire substrate suspended in a closed CVD system, has been investigated. The influence of strain-rate, gauge length, and fibre diameter on the tensile fracture stress of the fibres has been evaluated and compared to fracture stress data of fibres produced in continuous CVD processes. Moreover, the E-modulus of the prepared fibres has been measured. Finally the surface defects of the fibres have been examined and classified into fracture stress depressive surface defects and non-fracture stress depressive surface defects.     

Optimization with respect to covariance sequence parameters

A general problem involving optimization of a covariance sequence is considered in the paper. One difficulty with this class of problems is to ensure that the covariance sequence is nonnegative definite (in other words, realizable). It is suggested that this difficulty can be overcome by reformulating the optimization problem in terms of the partial autocorrelation coefficients (PAC). One need only constrain these coefficients to lie in the range (−1, 1) to guarantee that the corresponding covariance sequence is nonnegative definite. The synthesis of a signal realizing the optimizing covariance sequence is also discussed. Special emphasis is given to the case when some of the PACs are either +1 or −1.     

Self-collimation in planar photonic crystals

We analyze, in three dimensions, the dispersion properties of dielectric slabs perforated with two-dimensional photonic crystals (PCs) of square symmetry. The band diagrams are calculated for all k-vectors in the first Brillouin zone, and not only along the characteristic high-symmetry directions. We have analyzed the equal-frequency contours of the first two bands, and we found that the square lattice planar photonic crystal is a good candidate for the self-collimation of light beams. We map out the group velocities for the second band of a square lattice planar PC and show that the group velocity is the highest in the region of maximum self-collimation. Such a self-collimated beam is predicted to show beating patterns due to the specific shape of the equal-frequency contours. A geometrical transformation maps the region of the first and second photonic bands where self-collimation takes place one onto the other and gives additional insights on the structural similarities of self-collimation in those two bands.     

A novel serum protein similar to C1q, produced exclusively in adipocytes

We describe a novel 30-kDa secretory protein, Acrp30 (adipocyte complement-related protein of 30 kDa), that is made exclusively in adipocytes and whose mRNA is induced over 100-fold during adipocyte differentiation. Acrp30 is structurally similar to complement factor C1q and to a hibernation-specific protein isolated from the plasma of Siberian chipmunks; it forms large homo-oligomers that undergo a series of post-translational modifications. Like adipsin, secretion of Acrp30 is enhanced by insulin, and Acrp30 is an abundant serum protein. Acrp30 may be a factor that participates in the delicately balanced system of energy homeostasis involving food intake and carbohydrate and lipid catabolism. Our experiments also further corroborate the existence of an insulin-regulated secretory pathway in adipocytes.     

Stratified oxide scale growth on two Cr-Ni steels oxidized in high-pressure steam at 800°C

A commercial 18% Cr-11% Ni steel and a laboratory-made 21% Cr-11% Ni alloy have been oxidized in steam at 50 atm pressure and with approximately 0.2 ppm O₂ at 800°C for 50–1000 hr. The oxide scales have been studied by optical microscopy, replica electron microscopy, x-ray, and selected-area-electron diffraction and microprobe analysis. The diffusion processes have been studied by gold markers and autoradiography by means of the reaction¹⁸O (p, n)¹⁸F. On both materials internal oxidation in combination with external scale formation is observed. The interface between the external scale and the inner internally oxidized scale coincides very closely with the original metal surface. The oxide phases present have been identified. The scale is of fairly even thickness on the 21% Cr-11% Ni alloy and grows by a cubic rate law. The scale on the commercial steel is of very irregular thickness; areas with protective Cr-oxide alternate with areas of the above-mentioned structure, so-called nodules. The zones of internal oxidation in the nodules are frequently intersected by bands of compact oxide. The growth mechanism of the nodules is discussed in terms of the theory for internal oxidation. The reason for the beneficial effect of increased Ni content with constant Cr content is discussed briefly.     

Application of 2D-fluorescence spectroscopy for on-line monitoring of pseudoenantiomeric transformations in supercritical carbon dioxide systems

2D-Fluorescence spectroscopy has been shown to be effective for the on-line monitoring of spectroscopic detectable substrates L-phenylalanine-7-amido-4-methylcoumarine (L-PheAMC) and D-phenylalanine-7-amido-4-trifluoromethylcoumarine (D-PheAFC) in supercritical carbon dioxide. Earlier investigations with the coumarine substrates in watery and organic phases showed their potential for on-line enantiomeric evaluations of enzymatic reactions in different reaction media. The solubility of the different substrates and their fluorescence maximums were investigated in SCCO2. The sole hydrolyzations of L-PheAMC and D-PheAFC with alpha-chymotrypsin and the esterase from porcine liver were tracked on-line in the supercritical medium; however, different solubility characteristics of the methyl- and trifluoromethyl-substituted coumarins influence the simultaneous detection of the L- and D-substrate within the applied high-pressure reactor system.     

Integrated portable genetic analysis microsystem for pathogen/infectious disease detection

An integrated portable genetic analysis microsystem including PCR amplification and capillary electrophoretic (CE) analysis coupled with a compact instrument for electrical control and laser-excited fluorescence detection has been developed. The microdevice contains microfabricated heaters, temperature sensors, and membrane valves to provide controlled sample positioning and immobilization in 200-nL PCR chambers. The instrument incorporates a solid-state laser and confocal fluorescence detection optics, electronics for sensing and powering the PCR reactor, and high-voltage power supplies for conducting CE separations. The fluorescein-labeled PCR products are amplified and electrophoretically analyzed in a gel-filled microchannel in <10 min. We demonstrate the utility of this instrument by performing pathogen detection and genotyping directly from whole Escherichia coli and Staphylococcus aureus cells. The E. coli detection assay consists of a triplex PCR amplification targeting genes that encode 16S ribosomal RNA, the fliC flagellar antigen, and the sltI shigatoxin. Serial dilution demonstrates a limit of detection of 2-3 bacterial cells. The S. aureus assay uses a femA marker to identify cells as S. aureus and a mecA marker to probe for methicillin resistance. This integrated portable genomic analysis microsystem demonstrates the feasibility of performing rapid high-quality detection of pathogens and their antimicrobial drug resistance.