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Wyświetlanie 1-15 z 19
Tytuł:
A method for probing the refractive index change in photorefractive crystals
Autorzy:
Fu, M.
Gao, C.
Wang, X.
Cui, Y.
Dai, S
Powiązania:
https://bibliotekanauki.pl/articles/174913.pdf
Data publikacji:
2013
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
Fourier transform profilometry
refractive index change
photorefractive effect
Opis:
A method for probing refractive index changes in photorefractive crystals using an interferometric technique and digital image processing was proposed. Based on equal thickness interference in LiNbO3 crystal and Fourier transform profilometry, we obtained phase value changes in interferograms induced by a photorefractive effect, and further calculated refractive index changes. The maximal values for extraordinary light (e-light) and ordinary light (o-light) are 6.6×10–4 and 1.2×10–4, respectively.
Źródło:
Optica Applicata; 2013, 43, 4; 731-737
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Improved method for phase wraps reduction in profilometry
Autorzy:
Du, G.
Wang, M.
Zhou, C.
Si, S.
Li, H.
Lei, Z.
Li, Y.
Powiązania:
https://bibliotekanauki.pl/articles/173793.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
phase unwrapping
zero-padding
Fourier transform
carrier-frequency
profilometry
Opis:
In order to completely eliminate, or greatly reduce the number of phase wraps in 2D wrapped phase map, Gdeisat and co-workers proposed an algorithm, which uses shifting the spectrum towards the origin. But the spectrum can be shifted only by an integer number, meaning that the phase wraps reduction is often not optimal. In addition, Gdeisat’s method will take much time to make the Fourier transform, inverse Fourier transform, select and shift the spectral components. In view of the above problems, we proposed an improved method for phase wraps elimination or reduction. First, the wrapped phase map is padded with zeros, the carrier frequency of the projected fringe is determined by high resolution, which can be used as the moving distance of the spectrum. And then realize frequency shift in spatial domain. So it not only can enable the spectrum to be shifted by a rational number when the carrier frequency is not an integer number, but also reduce the execution time. Finally, the experimental results demonstrated that the proposed method is feasible.
Źródło:
Optica Applicata; 2017, 47, 2; 295-306
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
High-security image encryption by multiplexing phase encoding in domains of dual optical transforms
Autorzy:
Li, Zhihui
Gao, Bin
Pan, Xiaoou
Li, Linlin
Wang, Chenxuan
Zuo, Weizhuo
Ji, Yu
Liu, Shutian
Liu, Zhengjun
Powiązania:
https://bibliotekanauki.pl/articles/27310099.pdf
Data publikacji:
2023
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
extended fractional Fourier transform
geometric operations
random phase encoding
Opis:
A novel optical image encryption is proposed based on multiplexing of the random phase encoding with shift and rotation operations in domains of two transforms, extended fractional Fourier transform (eFrFT) and Fresnel transform. The original image is subjected to eFrFT with the action of the random phase mask. The mask is shifted and rotated to enhance the security of this encryption method. The image obtained from eFrFT is entered into Fresnel diffraction by the use of the phase mask to obtain the final encrypted image. We plan for the phase keys to be multiplexed in order to decrease the amount of keys that need to be stored in an application. Here, the displacement, rotation angle, and wavelength in this system can be used as additional keys to improve the security and reliability of the encryption system. Numerical experiments are conducted to verify the effectiveness and security of the method. The findings demonstrate that the keys are sufficiently sensitive for high security.
Źródło:
Optica Applicata; 2023, 53, 3; 447--466
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental study of an anomalous hollow beam with orbital angular momentum
Autorzy:
Lu, Xingyuan
Zhao, Chengliang
Hoenders, Bernhard J.
Yang, Yuanjie
Cai, Yangjian
Powiązania:
https://bibliotekanauki.pl/articles/173518.pdf
Data publikacji:
2019
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
anomalous hollow beam
orbital angular momentum
focused intensity
Fourier transform
Opis:
Anomalous hollow beam has potential applications in the optical trapping and free space optical communications, etc. It is noted that, thus far, although a large number of studies have been carried out in this field, most of them are theoretical studies and only quite a few cases have experimental results. Here, we experimentally study the generating of anomalous hollow beam carrying orbital angular momentum, and measure its topological charge. We show that the number of dark rings in the Fourier transform of intensity patterns is equal to the topological charge. The experimental results agree well with the simulations.
Źródło:
Optica Applicata; 2019, 49, 2; 217-226
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Balance disturbances coefficient as a new value to assess ability to maintain balance on the basis of FFT curves
Autorzy:
Jurkojc, J.
Powiązania:
https://bibliotekanauki.pl/articles/307349.pdf
Data publikacji:
2018
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
równowaga
stabilografia
szybka transformacja Fouriera
balance
stabilography
fast Fourier transform
coefficient
Opis:
The aim of this study was to formulate a new balance disturbances coefficient enabling objective balance assessment on the basis of fast Fourier transform curves. The article presents the method of coefficient calculation and possible ways of its interpretation. Methods: 11 healthy participants took part in the experiment. There were four measurements: two in real environment with eyes open and eyes closed as well as two in virtual environment with scenery (surroundings) oscillating with frequency 0.7 Hz and 1.4 Hz. Scenery was displayed by means of the Oculus Rift system, whereas position of centre of pressure was measured with the use of Zebris FDM-S platform. Obtained centre of pressure positions were used to calculate fast Fourier transform, and then balance disturbances coefficient. Results: Comparisons of coefficient values obtained for the whole group and two selected participants were presented in order to explain how to interpret and use the coefficient. For better explanation of coefficient interpretation the most popular time domain stabilometric quantities and fast Fourier transform curves were presented as well. Conclusions: The balance disturbances coefficient makes it possible to quantitatively and objectively determine, on the basis of fast Fourier transform curves, the influence of the oscillating scenery on the tested person as well as show how the overall equilibrium of that person was disturbed.
Źródło:
Acta of Bioengineering and Biomechanics; 2018, 20, 1; 143-151
1509-409X
2450-6303
Pojawia się w:
Acta of Bioengineering and Biomechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance and stability analysis of series-cascaded, high-gain, interleaved boost converter for photovoltaic applications
Autorzy:
Prasanna Kumar, C.
Venugopal, N.
Powiązania:
https://bibliotekanauki.pl/articles/1193536.pdf
Data publikacji:
2018
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
series cascade
interleaved boost converter
high gain
stability
fast Fourier transform
Opis:
Interleaved boost converters (IBCs) are cascaded in parallel in most of the applications. This novel approach connects IBC in series cascade. The IBC has an optimal operating duty cycle of 0.5. Normally, photovoltaic source voltage is low because of space constraints. In order to boost the source voltage, a conventional boost converter is replaced with series-cascaded IBC in this paper. The single-stage IBC also boosts the voltage to twice the input voltage. In the proposed converter, output voltage is about four times the input voltage with the same 0.5 duty cycle. A mathematical model is developed and simulated for the proposed work in MATLAB/Simulink platform. The output of the proposed circuit is analysed through fast Fourier transform to know the harmonic content due to the switching. The system is tested for stability with signal-flow graph modelling. The proposed work is realised using hardware and tested to validate the model.
Źródło:
Power Electronics and Drives; 2018, 3, 38; 85-97
2451-0262
2543-4292
Pojawia się w:
Power Electronics and Drives
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analysis of Synchrophasor Estimatioo Errors
Autorzy:
Łukowicz, M.
Cygan, S.
Powiązania:
https://bibliotekanauki.pl/articles/410593.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
synchrophasor estimation
dynamic phasor
Fourier transform
Taylor Fourier series
phase locked loop
dynamic filter
Opis:
This papers discusses the analytical analysis of the syochrophasor estimation employed in electrical systems. Short time Fourier trsnsform with the phase locked loop and Taylor Fourier series are analyzed for signals relating to different states which may occor in real power systems. The object is the accurate phasor estimation regardless of the shape of input signal, what for some signal types is cumbersome. As a result of active and reactive power disturbance in a power system, the frequency deviation and amplitude fluctuations may appear in power system signals. As a consequences of short circuits or overvoltages signal changes occur. Ibis leads to unacceptable errors in short time Fourier transform resulting from Fourier transform properties. This paper presents character of occurring errors and their consequences individually for any signal deviation.
Źródło:
Present Problems of Power System Control; 2017, 8; 5-22
2084-2201
Pojawia się w:
Present Problems of Power System Control
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Spectral and Wavelet Analysis of Stator Current to Detect Angular Misalignment in PMSM Drive Systems
Autorzy:
Pietrzak, Przemysław
Wolkiewicz, Marcin
Powiązania:
https://bibliotekanauki.pl/articles/1956007.pdf
Data publikacji:
2021
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
fault diagnosis
permanent magnet synchronous motor
angular misalignment
fast Fourier transform
discrete wavelet transform
Opis:
This paper deals with the selected methods of detecting angular misalignment in drive systems with a permanent magnet synchronous motor (PMSM), which are based on the analysis of the stator phase current signal, as well as their experimental verification and comparison. The proposed and compared methods are spectral analysis and wavelet analysis of the stator current, stator current envelope, stator current space vector module. Furthermore, the influence of power supply frequency and load torque on the performance of the proposed diagnostic methods is also discussed. The experimental tests were carried out for an undamaged motor and for two levels of angular misalignment. The article discusses the question of exactly what damage symptoms can be extracted from each of the methods. In the case of spectral analyses, it is demonstrated which multiplicities of the failure frequency are the most sensitive to misalignment and the least sensitive to changes in motor operating condition, which may be considered novel in the case of drive systems with permanent magnet motors. It is also proven that discrete wavelet transform (DWT) of the envelope and monitoring of the value of the relevant components allows the detection of misalignment with the availability of measuring current only in one phase in various motor operating conditions.
Źródło:
Power Electronics and Drives; 2021, 6, 41; 42-60
2451-0262
2543-4292
Pojawia się w:
Power Electronics and Drives
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
One shot profilometry using iterative two-step temporal phase-unwrapping
Autorzy:
Du, G.
Wang, M.
Zhou, C.
Si, S.
Li, H.
Lei, Z.
Li, Y.
Powiązania:
https://bibliotekanauki.pl/articles/173912.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
phase unwrapping
composite fringe pattern
Fourier transform
two-step temporal phase-unwrapping
Opis:
This paper reviews two techniques that have been recently published for three-dimensional profilometry and proposes one shot profilometry using iterative two-step temporal phase-unwrapping by combining the composite fringe projection and the iterative two-step temporal phase unwrapping algorithm. In temporal phase unwrapping, many images with different frequency fringe pattern are needed to project, which would take much time. In order to solve this problem, Ochoa proposed a phase unwrapping algorithm based on phase partitions using a composite fringe. However, we found that the fringe order determined through the construction of phase partitions tended to be imprecise. Recently, we proposed an iterative two-step temporal phase unwrapping algorithm, which can achieve high sensitivity and high precision shape measurement. But it needs multiple frames of fringe images which would take much time. In order to take into account both the speed and accuracy of three-dimensional shape measurement, we get a new, and more accurate unwrapping method based on a composite fringe pattern by combining these two techniques. This method not only retains the speed advantage of Ochoa’s algorithm, but also greatly improves its measurement accuracy. Finally, the experimental evaluation is conducted to prove the validity of the proposed method.
Źródło:
Optica Applicata; 2017, 47, 1; 97-110
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spectral analysis for tilted fiber Bragg gratings in the corrosion detection for concrete structure
Autorzy:
Kwong, Kok Zee
Udos, Waldo
Lim, Kok-Sing
Lee, Foo Wei
Tan, Chee Ghuan
Samion, Muhamad Zharif
Ahmad, Harith
Powiązania:
https://bibliotekanauki.pl/articles/2172827.pdf
Data publikacji:
2022
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
tilted fibre Bragg grating
optical spectral analysis
Fourier transform
corrosion
steel bar
Opis:
An effective corrosion monitoring technique is sought after by the engineers for assessing the steel bar corrosion at the early stage for the maintenance and repair works, especially in the corrosive environments, such as coastal and marine. In this work, tilted fiber Bragg grating (TFBG) with the optical sensor is employed in corrosion monitoring of a reinforced concrete structure. Taking advantage of the high sensitivity of TFBG cladding resonance wavelengths to the change in the surrounding medium, the sensor is mounted on the steel bar that is embedded in a concreted block during an accelerated corrosion process. The acquired transmission spectrum of the TFBG during the procedure is digitally processed using Fourier Transform to produce an index that is sensitive to the generated corrosion product surrounding the TFBG sensor. This eases the analysis of the sophisticated TFBG transmission spectra. The generated index can be used as an indicator (indicator J ) for the corrosion process of the embedded steel bar in the concrete structure. This indicator J can act as an indicator to describe the corrosion activity and corrosion level at a specific point of the steel bar in concrete structures.
Źródło:
Optica Applicata; 2022, 52, 3; 429--439
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Image encryption algorithm based on rear-mounted phase mask and random decomposition
Autorzy:
Yadav, Shivani
Singh, Hukum
Powiązania:
https://bibliotekanauki.pl/articles/2086758.pdf
Data publikacji:
2022
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
fractional Fourier transform
random decomposition
rear-mounted phase mask
SVD
singular value decomposition
Opis:
To escalate the image encryption a new method has been devised which includes double random phase encoding (DRPE) using rear phase masking and random decomposition (RD) technique stranded on fractional Fourier transform. Here, asymmetric cryptographic system is developed in fractional Fourier transform (FrFT) mode using two random phase masks (RPM) and a rear mounted phase mask. In the projected scheme a colored image is decomposed into R, G and B channels. The amplitude of each channel is normalized, phase encoded and modulated using RPM. The modulated R, G and B channels of the colored image are individually transformed using FrFT to produce corresponding encrypted image. The proposed scheme is authorized on grayscale image also. The norm behind the development of the suggested scheme has been elaborated by carrying out cryptanalysis on system based on the RD. The method helps in escalations of the protection of double random phase encoding by cumulating the key length and the parameter amount, so that it vigorously can be used against various attacks. The forte of the suggested cryptographic system was verified using simulations with MATLAB 7.9.0 (R2008a). The efficiency of the suggested scheme includes the analysis using singular value decomposition (SVD), histogram and correlation coefficient.
Źródło:
Optica Applicata; 2022, 52, 2; 195--212
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Deflectometry for phase retrieval using a composite fringe
Autorzy:
Liu, T.
Zhou, C.
Liu, Y
Si, S
Lei, Z.
Powiązania:
https://bibliotekanauki.pl/articles/173892.pdf
Data publikacji:
2014
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
wavefront measurement
fringe analysis
phase retrieval
fast Fourier transform (FFT)
multifrequency heterodyne principle
Opis:
An improved deflectometry for wavefront measurement using a composite fringe is proposed to reduce the projection fringes and improve the accuracy. The single composite fringe contains four fringes in different directions. It goes through the tested objects and then is captured by a CCD camera. Two high frequency orthogonal fringe patterns and two single period orthogonal fringe patterns can be obtained from the composite fringe by fast Fourier transform. The unwrapping of the wrapped phase of the high frequency fringe is accomplished by the corresponding single period fringe using a heterodyne method. The wavefront is reconstructed by the integration of partial derivatives. Using only one fringe, the proposed method is more applicable to dynamic wavefront measurement. The experimental results demonstrate that the proposed method can retrieve the complex wavefronts more accurately.
Źródło:
Optica Applicata; 2014, 44, 3; 451-461
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Identification of the parameters of multi-mass direct drive system
Autorzy:
Łuczak, D.
Powiązania:
https://bibliotekanauki.pl/articles/1811899.pdf
Data publikacji:
2012
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
identification of the mechanical
resonance frequencies
spectral analysis
Fourier transform
chirp signal
sine signal
Opis:
This paper presents methods for the identification of mechanical resonance of multi mass direct drive system. Methods have been applied in the field of digital signal processing. Was used spectral analysis to identify the mechanical resonance frequencies of direct drive with elastic connection. Discussed methods of identification have been verified by simulation and real system. Two different input signal was presented: sine and chirp wave. Both input signals gave good result for determine mechanical resonance frequencies, however sine wave with variable frequency determined only for the number of frequency corresponding to the input signal frequency gave better result for determine mechanical antyresonance frequencies.
Źródło:
Prace Naukowe Instytutu Maszyn, Napędów i Pomiarów Elektrycznych Politechniki Wrocławskiej. Studia i Materiały; 2012, 66, 32; 62-66
1733-0718
Pojawia się w:
Prace Naukowe Instytutu Maszyn, Napędów i Pomiarów Elektrycznych Politechniki Wrocławskiej. Studia i Materiały
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Immobilization of rambutan (Nephelium lappaceum) peel as a sorbent for Basic Fuchsin removal
Autorzy:
Lee, H.-J.
Ong, S.-T.
Powiązania:
https://bibliotekanauki.pl/articles/207651.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
fuchsin
Fourier transform infrared spectrophotometry
FTIR
Nephelium lappaceum
fuksyna
spektroskopia w podczerwieni z transformatą Fouriera
Opis:
The potential of rambutan (Nephelium lappaceum) peel as a low-cost adsorbent in an immobilized condition to remove Basic Fuchsin from aqueous solution was studied. The effect of initial dye concentration, contact time, pH and adsorbent dosage for the dye removal was studied at room temperature (26±2 °C). Infrared spectrum of rambutan peel indicates the presence of C–O, –OH and C=C functional groups. The adsorption rate was found to be high at the first 30 min and the process reached equilibrium after 3 h with more than 80% of dye being removed. The uptake of Basic Fuchsin was more promising at pH slightly above 7. The study of sorption model and kinetic model showed that the adsorption of Basic Fuchsin on rambutan peel conformed to the Freundlich isotherm and pseudo-second order kinetics with a high correlation coefficient, R,sup>2 > 0.98. This indicates the Basic Fuchsin adsorbs chemically on the heterogeneous surface of rambutan peel. The maximum adsorption capacity determined from the Langmuir isotherm was 108.696 mg/g. It seems that rambutan peel has the potential to substitute activated carbon as an alternative low-cost adsorbent in the treatment of the dye effluent.
Źródło:
Environment Protection Engineering; 2017, 43, 1; 169-181
0324-8828
Pojawia się w:
Environment Protection Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Changes of albumin secondary structure after palmitic acid binding : FT-IR spectroscopic study
Autorzy:
Oleszko, A
Hartwich, J.
Gąsior-Głogowska, M.
Olsztyńska-Janus, S.
Powiązania:
https://bibliotekanauki.pl/articles/307332.pdf
Data publikacji:
2018
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
kwas palmitynowy
albumina
spektrometria FTIR
palmitic acid
albumin
Fourier transform infrared spectroscopy
protein secondary structure
Opis:
Purpose: Albumin is an universal transport protein. Plasma pool of free fatty acids arising from triglyceride hydrolysis, critical in energy metabolism and etiology of metabolic disorders is transported by albumin. According to various studies albumin has from seven to nine binding sites with diverse affinity to long chain fatty acids. X-ray diffraction crystallography measurements have provided data only for pure human serum albumin or albumin with fully saturated binding sites. These results have shown that amount of -helices is higher after fatty acids binding. Molecular mechanics simulations suggest that binding of fatty acids in two high-affinity sites leads to major conformational changes in albumin structure. The aim of this research was to investigate albumin secondary structure upon gradually increasing fatty acids to protein mole ratio. Methods: Fourier transform infrared spectroscopy was applied to study changes of bovine serum albumin (as an analogue of human serum albumin) -helical structures after binding palmitic acid in a range of 0–20 palmitic acid: albumin molar ratios representing pure protein, partial, full saturation and excess binding sites capacity. Results: Amount of -helices was increasing along with the amount of palmitic acid: bovine serum albumin molar ratio and reached maximum value around 2 mol/mol. Conclusions: Our studies confirmed molecular mechanics simulations and crystallographic studies. Palmitic acid binding in two high-affinity sites leads to major structural changes, filling another sites only slightly influenced bovine serum albumin secondary structure. The systematic study of fatty acids and albumin interactions, using an experimental model mimicking metabolic disorders, may results in new tools for personalized nanopharmacotherapy.
Źródło:
Acta of Bioengineering and Biomechanics; 2018, 20, 1; 59-64
1509-409X
2450-6303
Pojawia się w:
Acta of Bioengineering and Biomechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 19

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