Showing papers by "Fraunhofer Society published in 1992"

Coherent submillimeter-wave emission from charge oscillations in a double-well potential.

Abstract: We directly observe the electromagnetic radiation emitted by electrons coherently oscillating between the two wells of a semiconductor coupled-quantum-well structure. Using time-resolved coherent detection of the submillimeter-wave radiation from these spatial charge oscillations, we trace up to fourteen oscillations at 1.5 THz before phase relaxation destroys the coherence of the oscillating wave packet. In addition to the oscillatory electromagnetic signal, we also observe an instantaneous signal from electric-field-induced optical rectification in the semiconductor structure.

Increase in global atmospheric concentrations of mercury inferred from measurements over the Atlantic Ocean

Abstract: ANTHROPOGENIC processes, such as coal burning, waste incineration and ore refining, are believed to contribute to the emission of mercury into the atmosphere1–5. The atmospheric concentration of mercury should therefore have increased as a consequence of increases in anthropogenic emissions3. Indeed, analyses of dated soil6, peat bog7,8 and lake-sediment records8–13 indicate that the deposition of atmospheric mercury may have doubled since the beginning of the nineteenth century. But such an increase in atmospheric mercury concentrations has so far not been detected in ice-core records14,15 (perhaps because of problems with contamination), and is not consistent with most mercury budgets2,4,5,16,17, in which natural sources are thought to dominate. Here we present measurements of total gaseous mercury over the Atlantic Ocean for 1977–90, which show that atmospheric concentrations of mercury have in fact increased by 1.46 ±0.17% per year in the Northern Hemisphere, and by 1.17 ±0.16% per year in the Southern Hemisphere. These rates of increase are consistent with the results of the soil, peat bog and lake-sediment analyses, and lead us to suggest that anthropogenic, rather than natural, sources are at present more important in the mercury cycle.

A micro membrane pump with electrostatic actuation

Abstract: A bulk micromachined membrane pump with outer dimensions of 7 mm*7 mm*2 mm and electrostatic actuation is presented. The micropump consists of four silicon chips, which form two passive check valves, a pump membrane and a counterelectrode for electrostatic actuation. Direct electrostatic forces are used for the deflection of the pump membrane, which has an area of 4 mm*4 mm and a thickness of 25 mu m. The liquid to be pumped is not subjected to any electrical field. The separation between the movable membrane and the electrically isolated stator is 4 mu m. >

Intelligent decision support systems

Abstract: This paper explores the basic ingredients of intelligent decision support systems in partial contrast to approaches followed by expert systems.

Field studies on Norway spruce trees at high altitudes: II. Defence systems against oxidative stress in needles

Abstract: summary Antioxidants were characterized in needles from mature spruce trees [Picea abies (L.) Karst.] grown in a forest on the Wank mountain in the Bavarian Calcareous Alps at three altitudes (870 m, 1270 m, and 1700 m). The effect of elevation, season and needle age on the activities of superoxide dismutase, glutathione reductase, ascorbate peroxidase, and the content of ascorbate and glutathione was analyzed. Ascorbate peroxidase and superoxide dismutase activity were little affected by stress from higher altitudes. Superoxide dismutase activity decreased with increasing needle age at all three altitudes. Maximum levels of glutathione and glutathione reductase were found in needles from the highest altitude, but the increase was not linear with increasing elevation. At the middle altitude, levels of glutatione reductase and glutatione were as low as, or even lower than at the lowest site. The mean ascorbate content increased with increasing altitude by about 2 μmol g−1 fresh weight per site. The seasonal change of the ascorbate content in the needles was twofold higher at the upper than at the lower sampling site. These findings suggest that superoxide dismutase and ascorbate peroxidase activities were sufficient to cope with a higher production of toxic oxygen species which probably occurs at high altitudes, and that adaptation was necessary for the antioxidant substrates and their regeneration system.

Low latency time CORDIC algorithms

Abstract: Several methods for increasing the speed of the CORDIC algorithm are presented. First, an improved method which guarantees a constant scale factor when employing redundant addition schemes is developed. Then, an architecture with increased parallelism which considerably reduces the CORDIC latency time and the amount of hardware is described. >

Polarization dependence of heavy- and light-hole quantum beats

Abstract: Simultaneous excitation of heavy- and light-hole quantum-well excitons with linearly polarized ultrashort laser pulses results in oscillating four-wave-mixing and pump-probe signals. These are elliptically polarized, except for exactly parallel and perpendicular incident polarizations, for which they are also linearly polarized. In the latter case, the heavy- and light-hole components are in phase or out of phase, respectively.

The Pinatubo eruption cloud observed by lidar at Garmisch‐Partenkirchen

Abstract: The spread of the stratospheric plume from the explosive eruption of the Philippine volcano Pinatubo in mid-June 1991 has been observed at Garmisch by lidar since July 1, 1991. The layered structure of the volcanic debris can be related to three transport phases to northern mid-latitudes. The aerosols centered at 15–17 km were transported to Garmisch in early July by the shortest possible route. The double layered aerosol structure observed in August coincided with the typical transport pattern at mid-latitudes in summer with westerlies below 20 km and easterlies above. After the change to the winter wind regime with westerlies throughout the altitude range of stratospheric aerosols, one large layer was observed sice the beginning of October, extending from the tropopause to about 28 km. This transport pattern and the layered structure of aerosols is similar to that which had been observed at the same lidar site after the El Chichon eruption in 1982.

Field studies on Norway spruce trees at high altitudes I. \Mineral, pigment and soluble protein contents of needles as affected by climate and pollution

Abstract: summary The present study was performed on mature Norway spruce trees (Picea abies L.) with needle losses in the range of 25–35 %. The trees were growing at three altitudes (870, 1270, and 1700 m above sea level) in a mountain forest in the Calcareous Alps of Bavaria. The objectives were to assess the role of climate and pollution in addition to nutrient disorders for damage to spruce trees. During the growing season the average temperature was up to 5 °C lower and the average ozone concentration was about twofold higher at the high altitude in comparison to the low altitude (13 and 18 °C, and 60 and 35 nl I−1 ozone, respectively); the average NOx and SO2 concentrations did not exceed 5 nl I−1. Foliar analysis of pollutants did not indicate critical levels of Pb, Cd, Cl, F and S. Biometrical parameters, foliar element composition, pigment and protein content of the needles were determined during four seasons. Average dry:fresh weight ratios, specific needle weights, projected needle areas, soluble protein and carotenoid contents were similar within the 20 % range for needles from all three altitudes. Foliar analysis of nutrients indicated a low nutrient status especially for nitrogen, and showed a phosphorus deficiency in needles from the three sites. The chlorophyll content of the needles decreased with increasing altitude. Since nutrient imbalances were greatest in needles from the lowest site, it was concluded that the greater damage to spruce trees and lower chlorophyll content of the needles at altitudes > 1000 m above sea level were not caused by nutrient disorders.

ALSYN: flexible rule-based layout synthesis for analog IC's

Abstract: ALSYN (Analog Layout SYNthesis), a tool that synthesizes layout from netlist-level descriptions for a broad range of analog integrated circuits, is presented. User-defined rules derive partitioning and other control information, based on parameters and topology of the circuit. Equivalent control information can also be set individually, e.g. supplied in the input netlist by preceding circuit synthesis or during interactive use of the synthesis system. This flexible concept enables designers to incorporate their own reusable knowledge into the synthesis process and to explore design space with the assistance of ALSYN. A flexible module generator environment and easy technology database access offer support for extending the library of parameterized layout primitives with variable shapes. Fast tools for constructive placement, using the MinCut/slicing tree approach, and for maze-style routing and postprocessing, offer various means of coping with the individual requirements of most analog applications. >

Linear and rotational magnetic micromotors fabricated using silicon technology

Abstract: Different types of sliding, rolling, or rotating micromotors with rare-earth-based permanent magnet rotors are presented. The magnets move synchronously with rotating or traveling magnetic fields generated by 25- mu m-thick gold current lines on silicon substrates. The magnets are guided in channels or openings in the silicon itself or in additional glass layers. For magnets with a typical dimension of 1 mm, forces and torques of 150 mu N and 100 nNm were achieved. Maximum velocities of 24 cm/s and 2000 r.p.m. have been measured. Magnetic clamping to the bottom confines the rotor to the system and allows motor operation at any tilt angle. The noncontact magnetic transmission of forces to drive a ferromagnetic fluid has been demonstrated. >

Long-distance Transport of Reduced Sulphur in Spruce (Picea abies L.)

Abstract: Individual needles of 4-year-old spruce trees (Picea abies L.) were exposed to 35 S-GSH via the cut surface of the needle tip for 2-3 h at different times during the growing season. From the previous year's source needle, 35 S-GSH was exported into the twig and translocated predominantly towards the twig apex

Error analysis of tomographic filters. I: Theory

Abstract: The technique of computerized tomography is being studied extensively by engineers, physicists and mathematicians to improve the quality of reconstructed images. Certain error estimates are available for the errors occuring in various tomographic algorithms under the assumption that the object cross-section possesses band-limited projection data. It is known, however, that the cross-section function has a finite support, and hence cannot be band-limited. A Sobolev space analysis has already been reported involving certain error estimates for predicting the inherent error in the convolution backprojection algorithm. The present study is an attempt towards developing a simplified two-dimensional Cartesian formula for predicting the comparative performance of the Fourier filters used in the convolution algorithm. This simplified approach involves the Laplacian of the object function and the second-order (Fourier space) derivatives of the filter functions.

The Effects Of New Technologies On Employment

Abstract: This paper is a contribution to the analysis of the relationship between technical change, economic development and employment. It forms part of a larger study of technical change and employment in Germany, encompassing a macroeconomic model of income circulation, a disaggregated econometric model of the sectoral differences of the effects of new technologies, and an input-output analysis of the direct and indirect effects of technological change. The present paper concentrates on examining the relationships between users and producers, the intersectoral technology flow matrix, and its links with the disaggregated demand model for analysing the influence of different technology variables on labour demand.

Segmentation of defects in textile fabric

Abstract: For fast inspection of defects in textile fabric the complexity of calculations has to be reduced, in order to limit the system costs. Additionally algorithms which are suitable for migration into hardware have to be chosen. Therefore in the paper a segmentation algorithm using first order statistics is applied. Preprocessing includes a logarithmic greyscale transformation to obtain insensitivity to illumination changes. Afterwards texture features are extracted by a set of linear filters, which consider local neighbourhood relations. The filtered images are evaluated by histograms being calculated on a window grid. Finally the histograms are classified by a perceptron net trained by backpropagation. An interactive teach-in program is provided to adapt the system to different kinds of textile fabric and appearances of defects. >

Efficient high-speed direct modulation in p-doped In/sub 0.35/Ga/sub 0.65/As/GaAs multiquantum well lasers

Abstract: The authors demonstrate p-type modulation-doped strainedlayer In0.35 Ga0.65As/GaAs multiquantum well lasers which achieve a 3dB direct modulation bandwidth of 20 GHz at a low CW drive current of 50mA in a simple 3 × 200 μm2 mesa structure. For the same device dimensions, a modulation bandwidth of 30 GHz was measured at a CW drive current of 114mA. This is the highest direct modulation bandwidth reported for any semiconductor laser.

Effects of glucocorticoids on the TPA-induced monocytic differentiation

Abstract: The human monocytic cell line U937 was used as a model system to investigate the effects of glucocorticoids on monocytic differentiation. Upon incu- bation with the phorbol ester 12-O-tetradecanoylphorbol- 13-acetate (TPA) (5 x 1OM) for 48 to 72 h, the imma- ture U93 7 cells ceased to proliferate and became morpho- logically and functionally macrophage-like. Preincuba- tion of the cells with glucocorticoids (dexamethasone and prednisolone, 1Oand 106 M) but not progesterone (106 M) had marked effects: The cells remained in suspension and developed very little cell-cell interaction. This cor- related with decreased expression of the surface molecules ICAM-1 and CD18 as determined by fluorescence- activated cell sorter analysis. The TPA-induced ability of the cells to release lysozyme or to generate reactive oxy- gen radicals (determined as reduction of nitroblue tetrazolium) was markedly reduced. The induction of cy- clooxygenase activity and thus the ability to release prostanoids was almost completely abolished. Inhibition of prostanoid synthesis was also observed when the glucocorticoids were administered 24 or 48 h after TPA. The primary step of TPA induction, the activation and translocation of protein kinase C, however, was not affected by glucocorticoids as determined by activity measurements and Western blot analysis. There was no change in the subsequent TPA-induced induction of c- fos. The down-regulation of the differentiation-related oncogenes c-myc and c-myb was the same in cells treated with TPA in the presence or absence of glucocorticoids. Furthermore, no significant effect of glucocorticoids on the TPA-induced growth arrest was observed. Glucocorti- coids thus interfere with TPA-induced functions, which are typical for activated macrophages; however, they do not impair the differentiation process and concomitant growth inhibition. J. Lcukoc. Biol. 52: 173-182; 1992.

Synthesis and substituent distribution of Na-cellulose sulfates via O-trimethylsilyl cellulose as intermediate

Abstract: Sulphation of cellulose was performed in an homogeneous aprotic system with SO3 or CISO3H, resp., via O-trimethylsilyl celluloses as reactive intermediates. Na-cellulose sulphates completely soluble in water and showing small chain degradation could be obtained at DSs≥ 0.25. The DSs in the range between 0.2 and 2.5 as well as the distribution of the sulphate half-ester groups within the AGU were regulated via the DSsi at one hand, the type and amount of sulphating agent at the other. Sulphation was performed either with the isolated and redissolved trimethylsilyl cellulose in N,N-dimethylformamide or tetrahydrofurane, or starting with an activated cellulose suspension, by achieving silylation and subsequent sulphation in one system of reaction. Obviously, the silyl group acts as a reactive group in subsequent sulphation, and the sites previously silylated are preferentially sulphated in the subsequent step of reaction, and the DSs is limited by the degree of silylation (DSsi) previously obtained. The homogeneous sulphation of trimethysilyl cellulose indicates a reactivity of silyl ether groups in the order of C-6 > C-2 ≫ C-3. Unter Verwendung von O-Trimethylsilylcellulose als reaktivem Zwischenprodukt wurde die homogene Sulfatierung von Cellulose mit SO3 bzw. CISO3H untersucht. Sulfatierungsgrad (DSs) und Substituentenverteilung im Anhydroglucosering liesen sich im DSs-Bereich zwischen 0,2 und 2,5 uber den DS an Silylethergruppen einerseits, die Art und Einsatzmenge des Sulfatierungsmittels andererseits steuern, wobei wasserlosliche, wenig abgebaute Cellulosesulfate ab DSs ≥ 0,25 erhalten werden. Die Sulfatierung erfolgte sowohl nach Isolierung und Wiederauflosung der O-Trimethylsilylcellulose, als auch, ausgehend von einer Suspension aktivierter Cellulose, durch Silylierung und nachfolgende Sulfatierung im gleichen Reaktionssystem. Offensichtlich wirkt die Silylethergruppe als reaktive Gruppe bei der nachfolgenden Sulfatierung, indem die vorher silylierten Positionen im Anhydroglucosering bevorzugt sulfatiert werden und der erreichbare DSs durch den vorher eingestellten Silylierungsgrad begrenzt wird. Bei der Homogensulfatierung von Trimethylsilylcellulosen wurde eine Reaktivitatsabstufung der Silylgruppen in den verschiedenen Positionen entsprechend C-6 > C-2 ≫ C-3 beobachtet.

Design and characterization of high performance 60 GHz pseudomorphic MODFET LNAs in CPW-technology based on accurate S-parameter and noise models

Abstract: An accurate database for active and passive MMIC components valid up to millimeter-wave frequencies has been established. The CAE models for the transistors and the passive CPW-components; which include the coplanar T-junction, are derived from on-wafer S-parameter measurements up to 63 GHz. For noise modeling of the MODFETs up to millimeter-wave frequencies, an approach based on the temperature noise model reported by M.W. Pospiezalski (1989) has been used. The parameter T/sub d/, which is required for the temperature model, is extracted from on-wafer noise parameter measurements up to 18 GHz. Using this database, the authors have designed and fabricated low-noise V-band two-stage amplifiers, using pseudomorphic MODFETs on a GaAs substrate, which have a performance of 10.5-dB gain and 5.2-dB noise figure at 58.5 GHz. Very good agreement between simulated and measured MMIC gain and noise performance is achieved up to V-band. >

Smart CMOS capacitive pressure transducer with on-chip calibration capability

Abstract: A capacitive pressure sensor with CMOS switched-capacitor circuitry for on-chip signal conditioning is introduced. It features differential generation and treatment of pressure-induced capacitance changes to suppress various parasitic effects. A digital calibration capability is provided for sensitivity adjustment and for temperature compensation. The fabrication of the transducer is largely congruent with a standard n-well CMOS process. The paper explains the function of the circuitry and its implications for the sensor design and presents experimental results obtained in testing the various components of the transducer as well as the overall sensor system.