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Event Timing Device Providing Subpicosecond Precision
Pánek, Petr; Kodet, J.; Procházka, I.
2013 - anglický
We are reporting on the latest experimental results achieved with an event timing device using a surface acoustic wave filter as a time interpolator. During the tests of the first version of the device, the noise of the filter excitation was identified as the dominant source of the measurement error. Therefore a new concept of the excitation with very low level of the noise energy was designed. This new solution led to considerable improvement of the device performance. It results from the experimental measurements that the single shot precision is repeatedly lower than 500 fs RMS when time marks generated synchronously with the time base are measured. When asynchronous time marks are split into two event timers and the resulting time difference is measured, the single shot precision is below 700 fs RMS per channel. In this case the measurement is affected not only by random errors, but also by non-linearity of the time interpolation. The temperature dependence is below 0.1 ps/K. Operating the device in a common laboratory environment without temperature stabilization, the stability TDEV better than 3 fs has been routinely achieved for range of averaging intervals from 10 s to several hours
Klíčová slova:
surface acoustic wave filter; time interpolation; event timing
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Event Timing Device Providing Subpicosecond Precision
We are reporting on the latest experimental results achieved with an event timing device using a surface acoustic wave filter as a time interpolator. During the tests of the first version of the ...
VLBI receiver chain monitoring
Michálek, V.; Kodet, J.; Schreiber, U.; Ploetz, Ch.; Procházka, I.; Pánek, Petr
2013 - anglický
he most demanding goal of the Global Geodetic Observing System initiative is the definition of station positions to an accuracy of 1mm and the corresponding velocities to 0.1 mm/year. The main remaining sources of error are caused by systematics, leading to intra- and inter- technique biases. In this work, we have focused on Very Long Base Interferometry (VLBI) and phase calibration generator currently in operation. This unit is injecting calibration tones into the detection chain through an input coupler located near the input of the antenna. The tones propagate further through entire detection chain and are recorded with the observed signal. Then they are extracted in post processing. These tones are generated out of an atomic frequency standard. The supplied frequency is significantly influenced by temperature and mechanical changes since usually a long cable is employed to bring the frequency to the calibration unit. To monitor the electrical length of the cable, calibration with a picosecond precision is essential. We have redesigned a phase calibration unit so that it enables the implementation of the Two Way Time Transfer (TWTT) method on single coaxial cable using two event timers to monitor the electrical length of the critical cable. Such a system has been installed in parallel to the unit currently in operation. The comparison of the TWTT method with previous measurement method is presented
Klíčová slova:
Frequency standards; Calibration; Two-way time transfers
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
VLBI receiver chain monitoring
he most demanding goal of the Global Geodetic Observing System initiative is the definition of station positions to an accuracy of 1mm and the corresponding velocities to 0.1 mm/year. The main ...
Single Photons Optical TwoWay Time Transfer Providing Picosecond Accuracy
Procházka, I.; Blažej, J.; Kodet, J.; Pánek, Petr
2013 - anglický
We are reporting on a new approach to an optical two-way time transfer based on signals of individual photons. This approach enables to reach extreme timing stabilities and minimal systematic errors using existing electro-optic technologies. In our indoor experiment we have achieved sub-picosecond precison and 3 ps accuracy of a two-way time transfer via free space optical channel. The entire system is compact and simple. It is a perspective technique for space application, where it might provide picosecond accuracies over space distances
Klíčová slova:
two-way time transfer; photon counting; picosecond stability
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Single Photons Optical TwoWay Time Transfer Providing Picosecond Accuracy
We are reporting on a new approach to an optical two-way time transfer based on signals of individual photons. This approach enables to reach extreme timing stabilities and minimal systematic errors ...
Time and Frequency Transfer Using Satellite Based Augmentation System GAGAN
Pánek, Petr; Kuna, Alexander
2013 - anglický
Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits signals both in L1 and L5 frequency channels. We used the GAGAN signals for an experimental common-view time transfer between IPE Prague and PTB Braunschweig which is a distance of 370 km and we also tested the time transfer properties using a single clock common-view. The L1 and ionosphere-free code measurements have markedly lower accuracy compared to a GPS common-view because of rather narrow bandwidth of the SBAS signal in L1 frequency channel. L5 code measurement provides much better precision. It results from the single clock common-view that the observed fluctuations can be described as white noise with standard deviations of 6 ns, 1.3 ns and 14 ns for L1, L5 and ionosphere-free combination. The results obtained from the carrier phase measurements are promising. The single clock common-view precision was approximately 30 ps RMS even for the ionosphere-free combination.
Klíčová slova:
Frequency channels; Navigation functions; GAGAN
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Time and Frequency Transfer Using Satellite Based Augmentation System GAGAN
Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits ...
LOW SUPERSATURATION OVERGROWTH OF NANOPOROUS GaAs SUBSTRATES
Nohavica, Dušan; Grym, Jan; Gladkov, Petar; Hamplová, Marie
2012 - anglický
Oriented pore networks in GaAs were created by electrochemical dissolution. Low supersaturation overgrowth of the porous substrates by InxGa1-xAs (x<4%) was realized by Liquid Phase Epitaxy (LPE)
Klíčová slova:
Porous III-V semiconductors; Electrochemical etching; Pores conversion
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
LOW SUPERSATURATION OVERGROWTH OF NANOPOROUS GaAs SUBSTRATES
Oriented pore networks in GaAs were created by electrochemical dissolution. Low supersaturation overgrowth of the porous substrates by InxGa1-xAs (x<4%) was realized by Liquid Phase Epitaxy (LPE)
Development of bragg fibers for transfer of laser radiation at
Matějec, Vlastimil; Kašík, Ivan; Podrazký, Ondřej; Aubrecht, Jan; Frank, M.; Jelínek, M.; Kubeček, V.
2012 - anglický
Klíčová slova:
optical fiber sensor; photocatalysis; toluene
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Development of bragg fibers for transfer of laser radiation at
LAYERS OF METALS NANOPARTICLES ON VARIOUS SEMICONDUCTORS FOR HYDROGEN DETECTION
Černohorský, Ondřej; Žďánský, Karel; Yatskiv, Roman; Grym, Jan
2012 - anglický
Metal nanoparticles have many interesting properties which is given by their space restriction. Their large active surface is very well exploited during catalysis. Pd and Pt are metals know for their ability to dissociate molecular hydrogen on single atoms. We prepared Schottky diodes on semiconductors InP, GaN, GaAs, and InGaAs to obtain hydrogen sensor. Method of preparation such diodes is electrophoretic deposition of Pd or Pt nanoparticles from their colloid solution onto semiconductor substrate. Over the layer of nanoparticles, porous metal contact was prepared. Hydrogen molecules are dissociated on these metal nanoparticles and single atom which settles on the interface between metal and semiconductor and they increase or decrease Schottky barrier height. By this method we can measure from 1 ppm H2 in the air, where the current change is over one order of magnitude
Klíčová slova:
Schottky barrier; binary semiconductors; metal nanoparticles
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
LAYERS OF METALS NANOPARTICLES ON VARIOUS SEMICONDUCTORS FOR HYDROGEN DETECTION
Metal nanoparticles have many interesting properties which is given by their space restriction. Their large active surface is very well exploited during catalysis. Pd and Pt are metals know for their ...
Preparation and characterizatiobn of layers of Au, Pd and Rh nanoparticles deposited on n-InP substrates
Kostejn, M.; Žďánský, Karel; Piksová, K.; Zavadil, Jiří
2011 - anglický
Colloids of Au, Pd and Rh nanoparticles (NPs) were prepared in reverse micelles and surface plasmon absorption bands were identified. Layers of metal NPs were deposited on InP substrates by electrophoretic deposition and imaged by SEM. Low-temperature photoluminescence spectrum of InP was found to be enhanced mainly by Au NPs. Sensitivity to hydrogen of Schottky barriers prepared by dropping colloidal graphite onto the surface of InP partly covered with Pd NPs was measured by current change in 100 ppm H2/N2.
Klíčová slova:
semiconductor devices; nanostructures; sensors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Preparation and characterizatiobn of layers of Au, Pd and Rh nanoparticles deposited on n-InP substrates
Colloids of Au, Pd and Rh nanoparticles (NPs) were prepared in reverse micelles and surface plasmon absorption bands were identified. Layers of metal NPs were deposited on InP substrates by ...
Graphite Schottky barriers on n-InP and n-GaN with deposited Pd, Pt or bimetallic Pd/Pt nanoparticles for H2 sensing
Žďánský, Karel; Muller, M.; Černohorský, Ondřej; Yatskiv, Roman
2011 - anglický
High Schottky barriers have been achieved by applying colloidal graphite on n-type InP and on n-type GaN semiconductor crystal wafers. The barrier heights were shown to be close to Schottky-Mott limit ad thermionic emission theory. Porous properties of the graphite Schottky contacts were demonstrated by scanning electron microscopy.
Klíčová slova:
semiconductor devices; nanostructures; sensors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Graphite Schottky barriers on n-InP and n-GaN with deposited Pd, Pt or bimetallic Pd/Pt nanoparticles for H2 sensing
High Schottky barriers have been achieved by applying colloidal graphite on n-type InP and on n-type GaN semiconductor crystal wafers. The barrier heights were shown to be close to Schottky-Mott limit ...
Subspace Methods in Linear DS - CDMA Detection
Šimša, Jan
2011 - anglický
Application of signal subspace methods in linear mean square error (MSE) detectors of direct sequence CDMA signals. Focusing on the cross-spectral (CS) method, its origin and a relation to multistage Wiener filter (MWF) is shown. This filter results from splitting of correlation matrix
Klíčová slova:
spread spectrum; multiuser detectors; subspace methods
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Subspace Methods in Linear DS - CDMA Detection
Application of signal subspace methods in linear mean square error (MSE) detectors of direct sequence CDMA signals. Focusing on the cross-spectral (CS) method, its origin and a relation to multistage ...
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