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K-space trajectory calibration for improved precision of quantitative ultrashort echo time imaging
Latta, P.; Starčuk jr., Zenon; Gruwel, M.; Tomanek, B.
2017 - English
Ultrashort echo time imaging (UTE) is often the method of choice for measurement of short-lived T2 signals from biological tissues. The UTE acquisition is based on radial or spiral sampling schemes which, in general, are sensitive to small discrepancies between prescribed and actual trajectories. Such errors are usually observed as image quality degradation, visible as ghosting or intensity variation. This is even more serious for quantitative applications when intensity variation can cause serious bias in the estimation of measured parameters such as proton density (PD). Here we investigate such behavior of UTE acquisition and demonstrate that proper calibration of the gradient channels could minimize these type of the errors. Phantom experiments proved the efficiency of the application trajectory calibration approach.
Keywords:
ultrashort Echo Time (UTE); K-space Trajectory Calibration; proton Density
Available at various institutes of the ASCR
K-space trajectory calibration for improved precision of quantitative ultrashort echo time imaging
Ultrashort echo time imaging (UTE) is often the method of choice for measurement of short-lived T2 signals from biological tissues. The UTE acquisition is based on radial or spiral sampling schemes ...
Effect of thermal radiation on low temperature measurement for various types of temperature sensor installations
Urban, Pavel; Hanzelka, Pavel; Králík, Tomáš; Vlček, Ivan; Srnka, Aleš
2017 - English
We investigated an effect of thermal radiation (300 K) on precision of low temperature measurement of a sample holder (or sample) in an UHV SEM/SPM microscope working at range down to 20 K for various ways of temperature sensor mounting. We designed a special copper casing for installation of Lake Shore\ntemperature sensors (CernoxTM and Si diodes) encapsulated in SD packages. The sensor body is attached direct to the casing using indium solder. The current leads pertaining to the sensor are thermally anchored but electrically insulated from the casing. Quality of sensors installation in the casing was tested for various ways of mounting on a cooled plate. Insufficient thermal anchoring of electrical wires and thermal shielding were imitated. Comparative measurement was also performed with sensors in SD package mounted without\ncasing. The experiments proved that our special design of temperature sensors casing is adequate for intended application of temperature measurement of sample holder in UHV SEM/SPM microscope. In contrary, measurement precision of unprotected sensors was absolutely unsuitable.
Keywords:
low temperature; temperature sensor; thermal radiation
Available at various institutes of the ASCR
Effect of thermal radiation on low temperature measurement for various types of temperature sensor installations
We investigated an effect of thermal radiation (300 K) on precision of low temperature measurement of a sample holder (or sample) in an UHV SEM/SPM microscope working at range down to 20 K for various ...
Phyllotactic Model Linking Nano and Macro World
Horáček, Miroslav; Meluzín, Petr; Krátký, Stanislav; Urbánek, Michal; Bok, Jan; Kolařík, Vladimír
2017 - English
Recently, the arrangement of diffraction primitives according to a phyllotactic model was presented. This arrangement was used to benchmarking purposes of the e-beam writer nano patterning. The phyllotactic arrangement has several interesting properties. One of them is related with the coherence between the nanoor microscopic domain of individual optical primitives and the properties of visually perceived images crated by these structures in the macro domain. This paper presents theoretical analysis of the phyllotactic arrangement in the referred context. Different approaches enabling the creation of diffractive optically variable images are proposed. The practical part of the presented work deals with the nano patterning of such structures using two different types of the e-beam pattern generators. One of them is a system with a variable shaped beam of electrons, while the other one is a system with a Gaussian-shaped beam. E-beam writing strategies and the use of inherent spiral patterns for exposure ordering and partitioning are also discussed.
Keywords:
nano patterning; spiral grating structure; phyllotactic pattern; e-beam writer
Available at various institutes of the ASCR
Phyllotactic Model Linking Nano and Macro World
Recently, the arrangement of diffraction primitives according to a phyllotactic model was presented. This arrangement was used to benchmarking purposes of the e-beam writer nano patterning. The ...
Study of laser wobbling welding process through the radiation of plasma plume
Mrňa, Libor; Horník, Petr; Jedlička, Petr; Pavelka, Jan
2017 - English
During laser welding with wobbling to the vector of the welding speed adds trivial movement of the beam in the shape of a circle or other shapes. Therefore, the laser beam moves with much higher current speeds than during normal welding. The melting of material on the leading edge of the keyhole occurs periodically. This fact is reflected in the character of the radiation of plasma plume over the keyhole. Experiments were conducted in which it was obtained spectrum of plasma plume radiation by using autocorrelation function for different parameters of circular wobbling (circle diameter, frequency) and for different materials. In the spectra are found the higher harmonic frequency of wobbling. The results were also compared with the radiation of the plasma plume during pulsed laser welding where the laser beam also periodically melts the leading edge.
Keywords:
laser welding; wobbling; process monitoring
Available at various institutes of the ASCR
Study of laser wobbling welding process through the radiation of plasma plume
During laser welding with wobbling to the vector of the welding speed adds trivial movement of the beam in the shape of a circle or other shapes. Therefore, the laser beam moves with much higher ...
Babinet principle for plasmonic antennas: complementarity and differences
Horák, M.; Křápek, V.; Hrtoň, M.; Metelka, O.; Šamořil, T.; Stöger-Pollach, M.; Paták, Aleš; Šikola, T.
2017 - English
Plasmonics deals mainly with surface plasmon polaritons (SPP), which are collective oscillations of free electrons at metal-dielectric interfaces connected with the local electromagnetic field. When SPP are spatially restricted to a metallic nanoparticle, we talk about localized surface plasmons (LSP). LSP resonances can be characterized with an excellent spectral and spatial resolution by electron energy loss spectroscopy (EELS) and cathodoluminescence. Both techniques utilize an electron beam that interacts with the metallic nanoparticle and excites the LSP resonances. EELS measures the energy transferred from electrons to the LSP and cathodoluminescence deals with the light which the LSP emit during their decay. Babinet principle, originating in the wave theory of light and analysis of diffraction, relates the optical response of apertures in thin films and their complementary particle analogues. According to the Babinet principle, LSP in complementary particles and apertures have identical resonance energies and their near fields are closely linked: the electric field distribution of a specific in-plane polarization for an aperture corresponds to the magnetic field distribution of a perpendicular polarization for a particle.
Keywords:
Babinet principle; complementarity; plasmonic antennas; cathodoluminescence; EELS
Available at various institutes of the ASCR
Babinet principle for plasmonic antennas: complementarity and differences
Plasmonics deals mainly with surface plasmon polaritons (SPP), which are collective oscillations of free electrons at metal-dielectric interfaces connected with the local electromagnetic field. When ...
Phase and group refractive indices of air calculation by fitting\nof phase difference measured using a combination of laser and\nlow-coherence interferometry
Pikálek, Tomáš; Šarbort, Martin; Číp, Ondřej; Pham, Minh Tuan; Lešundák, Adam; Pravdová, Lenka; Buchta, Zdeněk
2017 - English
The air refractive index is an important parameter in interferometric length measurements, since it substantially\naffects the measurement accuracy. We present a refractive index of air measurement method based on monitoring\nthe phase difference between the ambient air and vacuum inside a permanently evacuated double-spaced cell. The cell is placed in one arm of the Michelson interferometer equipped with two light sources—red LED and HeNe laser, while the low-coherence and laser interference signals are measured separately. Both phase and group refractive indices of air can be calculated from the measured signals. The method was experimentally verified by\ncomparing the obtained refractive index values with two different techniques.
Keywords:
air refractive index; laser interferometry; low-coherence interferometry
Available at various institutes of the ASCR
Phase and group refractive indices of air calculation by fitting\nof phase difference measured using a combination of laser and\nlow-coherence interferometry
The air refractive index is an important parameter in interferometric length measurements, since it substantially\naffects the measurement accuracy. We present a refractive index of air measurement ...
Efficient implementation of Stockwell Transform for real-time embedded processing of physiologic signals
Holmes, D.; Pinto, S.C.; Felton, Ch.; Smítal, L.; Leinveber, P.; Jurák, Pavel; Gilbert, B.; Haider, C.
2017 - English
Physiologic monitoring enables scientists and physicians to study both normal and pathologic signals of the body. While wearable technologies are available today, many of these technologies are limited to data collection only. Embedded processors have minimal computational capabilities. We propose an efficient implementation of the Stockwell Transform which can enable real-time time-frequency analysis of biological signals in a microcontroller. The method is built upon the fact that the Stockwell Transform can be implemented as a compact filter bank with pre-computed filter taps. Additionally, due to the long tails of the gaussian windowing function, low amplitude filter taps can be removed. The method was implemented on a TI MSP430 processor. Simulated ECG data was fed into the processor to demonstrate performance and evaluate computational efficiency.
Keywords:
time-frequency analysis; biomedical monitoring; electrocardiography; real-time systems
Available at various institutes of the ASCR
Efficient implementation of Stockwell Transform for real-time embedded processing of physiologic signals
Physiologic monitoring enables scientists and physicians to study both normal and pathologic signals of the body. While wearable technologies are available today, many of these technologies are ...
Lift-off technology for thick metallic microstructures
Krátký, Stanislav; Horáček, Miroslav; Meluzín, Petr; Kolařík, Vladimír; Matějka, Milan; Oulehla, Jindřich; Pesic, Z.
2017 - English
This paper deals with a method enabling the preparation of thick metallic microstructures on metal substrates. Such metallic microstructures can be used as a resolution samples to characterize various microanalysis techniques, such as X-ray fluorescence (XRF) or X-ray photoelectron spectroscopy (XPS). Moreover, the\npatterned samples could be used as anodes to characterize focusing properties of X-ray tubes for micro CT systems. Considering that the standard lift-off technique is designated for structures with the thickness of several hundred nanometers at most, we had to modify lift-off technique to be possible to use it for preparation of very thick metal layers (several microns) with spatial resolution of a few microns. The mask with the desired pattern for UV exposure was prepared by e-beam lithography. SU-8 photoresist was used for a lift-off because of its aspect ratio ability, process purity and high resistance to heating. We used a thin layer of PMMA under the SU-8 masking layer to guarantee the photoresist would lift-off correctly. Thick aluminum layer was deposited by thermal evaporation. The dependence of metal layer thickness as a function of required exposed\nline width was determined. The final lift-off process was carried out in acetone ultrasonic bath. Generally, this technology can be used for the evaporate deposition of various materials with several microns thick layer in\nmicron resolution.
Keywords:
lift-off technique; SU-8 photoresist; e-beam lithography; thick layer evaporation
Available at various institutes of the ASCR
Lift-off technology for thick metallic microstructures
This paper deals with a method enabling the preparation of thick metallic microstructures on metal substrates. Such metallic microstructures can be used as a resolution samples to characterize various ...
Possibilites of using the Erichsen test for determination of forming limit diagram and its utilization for hydroforming
Řiháček, J.; Mrňa, Libor; Peterková, E.; Dvořák, M.
2017 - English
Forming limit diagrams (FLD) are used to determine process limitations in sheet metal forming, i.e. as a level of formability assisting in the estimation of stamping characteristics. This paper deals with the experimental determination of a forming limit curve (FLC) using the Erichsen test. In this case, FLC of an austenitic stainless\nsteel X5CrNi18-10 is obtained by performing the Erichsen test with different shapes of specimens. Furthermore, utilization of FLD for evaluation of a hydroforming process is shown in the second part of the paper.
Keywords:
Erichsen test; formability; hydroforming; FLD
Available at various institutes of the ASCR
Possibilites of using the Erichsen test for determination of forming limit diagram and its utilization for hydroforming
Forming limit diagrams (FLD) are used to determine process limitations in sheet metal forming, i.e. as a level of formability assisting in the estimation of stamping characteristics. This paper deals ...
Structural Colors of Self-Similar Nano Patterns
Meluzín, Petr; Horáček, Miroslav; Krátký, Stanislav; Kolařík, Vladimír
2017 - English
E-beam lithography is a flexible technology for various diffraction gratings origination. The e-beam patterning typically allows for the creation of optical diffraction gratings in the first diffraction order. However, the very high resolution enables also the patterning of structures providing the zero-order diffraction. Recently, we presented a work on the structural colors of metallic layers covering both regular-line structures and CGH (computer generated hologram) structures. This work presents a study dealing with zero-order diffraction structures with self-similar properties. The practical part of the work is focused on two aspects: design parameters and technological issues. Variations in design parameters include the tone of the structure (positive or negative),\nthe density of filling, the filling factor, and the depth of the structures. The achieved gamut of colors may by primarily extended by the proper selection of metal deposition technology and its parameters, and further by the proper selection of the metal and the thickness of its layer, these are the technological issues.
Keywords:
e-beam writer; nano patterning; self similarity; diffraction grating
Available at various institutes of the ASCR
Structural Colors of Self-Similar Nano Patterns
E-beam lithography is a flexible technology for various diffraction gratings origination. The e-beam patterning typically allows for the creation of optical diffraction gratings in the first ...
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