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  • 1
    Keywords: Germany ; LINES ; COMPLEX ; COMPLEXES ; FLOW ; PARTICLES ; LINE ; PROBES ; SURFACE ; SOLIDS ; IMPLEMENTATION ; RE ; SIZE ; CHARGE ; USA ; physics ; GEOMETRY ; CONTACT ; INSTRUMENTS ; PIPELINES ; ELECTRIFICATION ; FLOWS
    Abstract: In this study examples for a noncontact procedure that allow the description of instant electric charging of moving microparticles that contact dielectric surfaces, for instance, of a flow hose are presented. The described principle is based on the measurement of induced currents in grounded metal wire probes, as moving particles pass close to the probe. The feasibility of the approach was tested with laser printer toner particles of a given size for different basic particle flow and charging conditions. An analytic description for the induced currents was developed and compared to observed effects in order to interpret the results qualitatively. The implementation of the presented procedure can be applied to transparent and nontransparent particle containers and flow lines of complex geometry which can be composed from the presented basic flow stream configurations. (C) 2007 American Institute of Physics
    Type of Publication: Journal article published
    PubMed ID: 17672797
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  • 2
    Keywords: COMBINATION ; Germany ; ENZYMES ; ACCURACY ; RESOLUTION ; MARKER ; FIELD ; FREQUENCIES ; MOLECULE ; MARKERS ; ELECTROPHORESIS ; KINETICS ; sensitivity ; TRACKING ; SINGLE ; microfluidics ; USA ; adsorption ; POSITION ; PARTICLE ; biological techniques ; electrokinetic effects ; laser cooling ; osmosis ; radiation pressure
    Abstract: We describe a combination of microelectrophoresis and laser-trap methodology to accurately measure the electric force acting on a charged microsphere which is trapped in an optical tweezer. This field/trap apparatus allows measuring of the zeta potential with submillivolt accuracy and high temporal resolution. The combination with stop-flow techniques in principle provides a mean to observe adsorption or enzyme kinetics with single molecule sensitivity. We show that it is possible to accurately profile the position and frequency dependent hydrodynamic and electro-osmotic flow inside a microchannel structure of dimensions typically used in microfluidic applications without the need of fluorescent markers. We found good agreement to the theory of electrophoretic flow when retardation effects for rapidly alternating electric fields are included
    Type of Publication: Journal article published
    PubMed ID: 19655953
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  • 3
    Keywords: IN-VIVO ; TIME ; DESIGN ; fluorescence correlation spectroscopy
    Abstract: We introduce a new multiple-tau hardware correlator design for computing fluorescence correlation functions (CFs) in real time. Use of hardware resources is minimized by scheduling the computation of different segments of the CFs on a single correlator block. Simultaneous calculation of two multiple-tau autocorrelation (ACFs) and two cross-correlation functions (CCFs) is implemented in LabVIEW on a National Instruments field programmable gate array (FPGA) card with a minimal sampling time of 400 ns. Raw data are stored with a time resolution of 50 ns. The design can be easily adapted to other FPGA cards and extended to more inputs.
    Type of Publication: Journal article published
    PubMed ID: 22559587
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  • 4
    Keywords: Germany ; ALGORITHM ; SYSTEM ; RESOLUTION ; QUALITY ; ACID ; PARTICLES ; VECTOR ; ARRAYS ; NUMBER ; SURFACE ; AMINO-ACIDS ; CALIBRATION ; PATTERN ; PHASE ; SIZE ; amino acids ; PEPTIDE ARRAYS ; COMBINATORIAL SYNTHESIS ; AREA ; MICROCHIP ; Microparticle deposition
    Abstract: Image processing and pattern analysis can evaluate the deposition quality of triboelectrically charged microparticles on charged surfaces. The image processing method presented in this paper aims at controlling the quality of peptide arrays generated by particle based solid phase Merrifield combinatorial peptide synthesis. Incorrectly deposited particles are detected before the amino acids therein are coupled to the growing peptide. The calibration of the image acquisition is performed in a supervised training step in which all parameters of the quality analyzing algorithm are learnt given one representative image. Then, the correct deposition pattern is determined by a linear support vector machine. Knowing the pattern, contaminated areas can be detected by comparing the pattern with the actual deposition. Taking into account the resolution of the image acquisition system and its magnification factor, the number and size of contaminating particles can be calculated out of the number of connected foreground pixels. (C) 2010 American Institute of Physics. [doi :10.1063/1.3456986]
    Type of Publication: Journal article published
    PubMed ID: 20687727
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  • 5
    Keywords: Germany ; SYSTEM ; EFFICIENCY ; QUALITY ; AIR ; FLOW ; PARTICLES ; ARRAYS ; ADHESION ; LAYER ; IMPLEMENTATION ; RE ; PATTERN ; ARRAY ; CHIP ; TECHNOLOGY ; USA ; CIRCULATION ; CONTACT ; detachment ; SURFACES
    Abstract: We examined the high precision deposition of toner and polymer microparticles with a typical size of similar to 10 mu m on electrode arrays with electrodes of 100 mu m and below using custom-made microelectronic chips. Selective desorption of redundant particles was employed to obtain a given particle pattern from preadsorbed particle layers. Microparticle desorption was regulated by dielectrophoretic attracting forces generated by individual pixel electrodes, tangential detaching forces of an air flow, and adhesion forces on the microchip surface. A theoretical consideration of the acting forces showed that without pixel voltage, the tangential force applied for particle detachment exceeded the particle adhesion force. When the pixel voltage was switched on, however, the sum of attracting forces was larger than the tangential detaching force, which was crucial for desorption efficiency. In our experiments, appropriately large dielectrophoretic forces were achieved by applying high voltages of up to 100 V on the pixel electrodes. In addition, electrode geometries on the chip's surface as well as particle size influenced the desorption quality. We further demonstrated the compatibility of this procedure to complementary metal oxide semiconductor chip technology, which should allow for an easy technical implementation with respect to high-resolution microparticle deposition. (C) 2008 American Institute of Physics
    Type of Publication: Journal article published
    PubMed ID: 18377044
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the synchronization of two commercial picosecond Ti:sapphire lasers with unprecedented low temporal jitter between the pulse trains. Pulse jitter is reduced from a few picoseconds to 20 fs with a stability of several hours. The technology enabling the tight pulse synchronization is reviewed in this article. We demonstrate the usefulness of the synchronization scheme by applying the technique to coherent anti-Stokes Raman scattering (CARS) microscopy. It is shown that CARS images can be acquired with a significant improvement in signal-to-noise ratio. This level of performance brings the fluctuations of the CARS signal down to the fundamental photon shot-noise limit. We present detailed statistical analysis of the pulse jitter and CARS noise along with enhanced CARS vibrational images of polymer beads. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2928-2936 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Increasing the imaging speed of tapping mode atomic force microscopy (AFM) has important practical and scientific applications. The scan speed of tapping-mode AFMs is limited by the speed of the feedback loop that maintains a constant tapping amplitude. This article seeks to illuminate these limits to scanning speed. The limits to the feedback loop are: (1) slow transient response of probe; (2) instability limitations of high-quality factor (Q) systems; (3) feedback actuator bandwidth; (4) error signal saturation; and the (5) rms-to-dc converter. The article will also suggest solutions to mitigate these limitations. These limitations can be addressed through integrating a faster feedback actuator as well as active control of the dynamics of the cantilever. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2958-2962 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A newly designed conical spot profile analyzing low-energy electron diffraction (LEED) allows optimized access to the sample up to an angle of 45° with respect to the surface plane. This allows in vivo LEED measurements during deposition or adsorption. The electron optics of the electrostatic deflection unit and the newly designed entrance lens were simulated and optimized using an electron-beam ray-tracing algorithm. Different sample distances can be accommodated by adjusting the deflection voltage between the front and rear section. A new "real-image" SPA-LEED operation mode is presented allowing simple control of the instrument and accurate electron-beam positioning on the sample. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2900-2905 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It is shown that self-heating of electrolytic capacitors causes the output current of a capacitor bank to increase with successive shots even though the charge voltage is held constant. Self heating of only 10 °C can cause a near tripling in the gas output of the gas puffing valves commonly used in spheromak research. By using metallized polypropylene film capacitors instead of electrolytic capacitors the reproducibility is substantially improved (the shot-to-shot variation in gas output is reduced to be 〈0.5%). © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2890-2899 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Aperture, pin-hole and collimator detection systems are often used in plasma diagnostics, for example, in soft x-ray detection and bolometer systems. In this article the simultaneous optimization of viewing-beam overlap and light yield is considered in multi-channel aperture and collimator systems for two-dimensional (2D) tomography. This article briefly highlights the relation between beamwidth overlap and spatial aliasing in tomography, and how aliasing can be avoided in theory and in practice. Three-dimensional (3D) single-channel aperture and collimator systems can be approximated by a combination of two planar systems if the aperture is rectangular. Three ways to optimize beamwidth overlap and light yield for planar aperture and collimator systems are considered in detail: overlap of the angular étendue at the full width at half maximum (FWHM), overlap of the geometric function at the FWHM a certain distance from the aperture, and arbitrary overlap for a given maximum beamwidth. The combination of 2D effects from all three optimization methods were used in the design of 3D apertures for a new multi-channel bolometer camera on the Joint European Torus tokamak. The resulting apertures are complex, but the new camera has several advantages over previous cameras. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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