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Spectral Domain (spectral + domain)
Terms modified by Spectral Domain Selected AbstractsNew perspectives of optical coherrence tomography in diagnosis and follow-up of macular holesACTA OPHTHALMOLOGICA, Issue 2009SA KABANAROU Purpose To compare Time Domain (TD) with Spectral Domain (SD) OCT for imaging macular holes, identify retinal pathology and correlate anatomical morphology after surgical intervention for hole closure with visual outcome. Methods 34 eyes of 34 patients with idiopathic macular holes stage II- IV were included in this study. Comparative studies were performed with both SD OCT (Heidelberg, Germany) and TD OCT (Stratus) using standard scanning protocols of 6 radial 6-mm scans through the fovea. All patients underwent a standard three port- pars plana vitrectomy. Postoperatively, all patients were evaluated using both OCTs. ETDRS visual acuities were recorded pre- and post-operatively. Results In general TD and SD OCTs showed comparable images of macular holes. However, the boundary line between the inner and outer segments of the photoreceptors was better imaged with the SD OCT preoperatively and postoperatively. Poor visual acuity postoperatively was measured mainly in cases with morphological disruption in this boundary line despite hole closure. Conclusion SD OCT imaging enhances the visualization of retinal anatomy in macular holes relative to TD OCT. [source] Cardiac Dysrhythmia Associated with the Immediate Postictal State after Maximal Electroshock in Freely Moving RatEPILEPSIA, Issue 4 2002Olivier Darbin Summary: ,Purpose: Cardiac autonomic changes accompany complex partial seizures and generalized tonic,clonic seizures, and participate, at least partially, in the sudden and unexpected death in epilepsy (SUDEP). The analysis of the heart rate variability (HRV) is one of the simplest ways of providing insight into autonomic functions. The entropy quantifies the repetition of complex patterns in a signal and refers to systems randomness, regularity, and predictability. Clinical investigations have reported that entropy decreases in patients with a high risk of sudden cardiac death. The goal of this study was to evaluate the effects of the maximal electroshock (MES) on the entropy of HRV, monitored in the immediate postictal stage in the model of the freely moving rat. Methods: Entropy changes were correlated with the high and low frequencies of spectral analysis, which reflect the participation of the sympathetic and parasympathetic activities. Results: MES-induced arrhythmia is characterized by an HRV increase, an imbalance in favor of the parasympathetic activity, and a decrease in the entropy. Entropy decrease was restricted to the duration of the arrhythmia, suggesting that the postictal arrhythmia may be associated with a higher risk of lethal cardiac complications. Nevertheless, entropy changes did not correlate with spectral changes. Conclusions: The results suggest that the imbalance demonstrated in the spectral domain explains only partially the contribution of each autonomic system in the complexity of the heart rate during the postictal state. [source] Localized spectral analysis on the sphereGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005Mark A. Wieczorek SUMMARY It is often advantageous to investigate the relationship between two geophysical data sets in the spectral domain by calculating admittance and coherence functions. While there exist powerful Cartesian windowing techniques to estimate spatially localized (cross-)spectral properties, the inherent sphericity of planetary bodies sometimes necessitates an approach based in spherical coordinates. Direct localized spectral estimates on the sphere can be obtained by tapering, or multiplying the data by a suitable windowing function, and expanding the resultant field in spherical harmonics. The localization of a window in space and its spectral bandlimitation jointly determine the quality of the spatiospectral estimation. Two kinds of axisymmetric windows are here constructed that are ideally suited to this purpose: bandlimited functions that maximize their spatial energy within a cap of angular radius ,0, and spacelimited functions that maximize their spectral power within a spherical harmonic bandwidth L. Both concentration criteria yield an eigenvalue problem that is solved by an orthogonal family of data tapers, and the properties of these windows depend almost entirely upon the space,bandwidth product N0= (L+ 1) ,0/,. The first N0, 1 windows are near perfectly concentrated, and the best-concentrated window approaches a lower bound imposed by a spherical uncertainty principle. In order to make robust localized estimates of the admittance and coherence spectra between two fields on the sphere, we propose a method analogous to Cartesian multitaper spectral analysis that uses our optimally concentrated data tapers. We show that the expectation of localized (cross-)power spectra calculated using our data tapers is nearly unbiased for stochastic processes when the input spectrum is white and when averages are made over all possible realizations of the random variables. In physical situations, only one realization of such a process will be available, but in this case, a weighted average of the spectra obtained using multiple data tapers well approximates the expected spectrum. While developed primarily to solve problems in planetary science, our method has applications in all areas of science that investigate spatiospectral relationships between data fields defined on a sphere. [source] A forward-only recursion algorithm for MAP decoding of linear block codesINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2002Hans-Jürgen Zepernick Abstract The evolution of digital mobile communications along with the increase of integrated circuit complexity has resulted in frequent use of error control coding to protect information against transmission errors. Soft decision decoding offers better error performance compared to hard decision decoding but on the expense of decoding complexity. The maximum a posteriori (MAP) decoder is a decoding algorithm which processes soft information and aims at minimizing bit error probability. In this paper, a matrix approach is presented which analytically describes MAP decoding of linear block codes in an original domain and a corresponding spectral domain. The trellis-based decoding approach belongs to the class of forward-only recursion algorithms. It is applicable to high rate block codes with a moderate number of parity bits and allows a simple implementation in the spectral domain in terms of storage requirements and computational complexity. Especially, the required storage space can be significantly reduced compared to conventional BCJR-based decoding algorithms. Copyright © 2002 John Wiley & Sons, Ltd. [source] Improved myelin water quantification using spatially regularized non-negative least squares algorithmJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009Dosik Hwang PhD Abstract Purpose To improve the myelin water quantification in the brain in the presence of measurement noise and to increase the visibility of small focal lesions in myelin-water-fraction (MWF) maps. Materials and Methods A spatially regularized non-negative least squares (srNNLS) algorithm was developed for robust myelin water quantification in the brain. The regularization for the conventional NNLS algorithm was expanded into the spatial domain in addition to the spectral domain. Synthetic data simulations were performed to study the effectiveness of this new algorithm. Experimental free-induction-decay measurements were obtained using a multi-gradient-echo pulse sequence and MWF maps were estimated using the srNNLS algorithm. The results were compared with other conventional methods. Results A substantial decrease in MWF variability was observed in both simulations and experimental data when the srNNLS algorithm was applied. As a result, false lesions in the MWF maps disappeared and the visibility of small focal lesions improved greatly. On average, the contrast-to-noise ratio for focal lesions was improved by a factor of 2. Conclusion The MWF variability due to the measurement noise can be substantially reduced and the detection of small focal lesions can be improved by using the srNNLS algorithm. J. Magn. Reson. Imaging 2009;30:203,208. © 2009 Wiley-Liss, Inc. [source] Performance evaluation of Gunn oscillators for active mode-locking of erbium doped fiber ring lasersMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2008Deepa Venkitesh Abstract A cost-effective and rugged actively mode-locked erbium-doped fiber laser operated at GHz repetition rate is demonstrated with the use of a Gunn oscillator as the RF source for driving the optical modulator. The high power from the Gunn oscillator eliminates the need of an RF driver. The output of the laser in the time domain is processed numerically to predict its modal characteristics in the spectral domain. Experimental results regarding the evaluation of the Gunn oscillator for its suitability in active mode-locking, tunable operation of the laser in the C -band using a band pass filter as well as the results on the stability of the laser output in the time and frequency domain are presented. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2684,2688, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23778 [source] Infrared microstrip dipole antennas,FDTD predictions versus experimentMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2001Iulian Codreanu Abstract We report on the successful use of niobium microbolometers coupled to microstrip dipole antennas for the detection of midinfrared radiation. Measurements of the detector response versus antenna length performed at the 10.6 ,m wavelength allowed us to identify the first three current-wave resonances along the antenna arms. The detector response was also measured as a function of the radiation wavelength in the 9,11 ,m spectral domain. Excellent agreement between the experimental results and finite-difference time-domain (FDTD) predictions was obtained. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 381,383, 2001. [source] 2111: Adaptive optics imaging in hereditary macular diseasesACTA OPHTHALMOLOGICA, Issue 2010K NAKASHIMA Purpose This research aimed at exploring and characterizing differences in vivo between healthy and pathology retinas, hereditary macular diseases at the microscopic scale using a compact adaptive optics (AO) retinal camera and high resolution OCT. Methods Seven RP patients, Cone-rod dystrophies (3), Stargardt diseases (5), Occult macular dystrophies (4) and indeterminate macular dystrophies (4) had undergone en face retinal imaging by AO camera "rtx1" (Imagine Eyes, France). AO images were taken at the eccentricities from 0 deg to 6 deg temporal and nasal from fovea. Each patient was examined using high resolution spectral domain (SD)-OCT and infrared SLO (Spectralis OCT). Results Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. Conclusion Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. [source] The double vocal signature of crested penguins: is the identity coding system of rockhopper penguins Eudyptes chrysocome due to phylogeny or ecology?JOURNAL OF AVIAN BIOLOGY, Issue 5 2005Amanda Searby Parent-offspring recognition systems are used in bird colonies to avoid misdirected parental care. In penguins, where the risk of confusion is particularly high, recognition is achieved by acoustic signals that constitute highly efficient vocal signatures. Comparisons between species from the Pygoscelis and Aptenodytes genera have revealed interspecific differences on the encoding of information within the signatures which correlate with the presence/absence of nests in the colonies. However a recent study of individual recognition in macaroni penguins Eudyptes chrysolophus revealed diversity within nest-building species. This paper investigates whether the original and intermediate signature system found in macaroni penguins is shared by another species of Eudyptes, the rockhopper penguin E. chrysocome. Vocal signatures of rockhopper penguins were analysed and compared to macaroni penguins'. We used a methodology derived from the theory of information to determine which parameters of the call were likely to encode individual identity. Playbacks of modified calls in the field complemented the analyses, and parent-chick reunions were compared between the two species. Our results reveal a similar double signature system within the Eudyptes genus, which integrates information simultaneously from the temporal and spectral domains. This double encoding is made through the tempo given by the successive syllables of the call and the harmonic content of the call. While it confirms the hypothesis that signatures are simpler in nest-building species, this result reveals differences in the efficacies of signatures within this category. This suggests that other parameters such as the mean distance recognition should be considered to account for the differences in the encoding of the vocal signatures and in their resulting efficacies. [source] | |||||||||||||