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Phase Shift (phase + shift)
Kinds of Phase Shift Selected AbstractsDevelopmental Alcohol Exposure Alters Light-Induced Phase Shifts of the Circadian Activity Rhythm in RatsALCOHOLISM, Issue 7 2004Yuhua Z. Farnell Background: Developmental alcohol (EtOH) exposure produces long-term changes in the photic regulation of rat circadian behavior. Because entrainment of circadian rhythms to 24-hr light/dark cycles is mediated by phase shifting or resetting the clock mechanism, we examined whether developmental EtOH exposure also alters the phase-shifting effects of light pulses on the rat activity rhythm. Methods: Artificially reared Sprague-Dawley rat pups were exposed to EtOH (4.5 g/kg/day) or an isocaloric milk formula (gastrostomy control; GC) on postnatal days 4 to 9. At 2 months of age, rats from the EtOH, GC, and suckle control groups were housed individually, and wheel-running behavior was continuously recorded first in a 12-hr light/12-hr dark photoperiod for 10 to 14 days and thereafter in constant darkness (DD). Once the activity rhythm was observed to stably free-run in DD for at least 14 days, animals were exposed to a 15-min light pulse at either 2 or 10 hr after the onset of activity [i.e., circadian time (CT) 14 or 22, respectively], because light exposure at these times induces maximal phase delays or advances of the rat activity rhythm. Results: EtOH-treated rats were distinguished by robust increases in their phase-shifting responses to light. In the suckle control and GC groups, light pulses shifted the activity rhythm as expected, inducing phase delays of approximately 2 hr at CT 14 and advances of similar amplitude at CT 22. In contrast, the same light stimulus produced phase delays at CT 14 and advances at CT 22 of longer than 3 hr in EtOH-treated rats. The mean phase delay at CT 14 and advance at CT 22 in EtOH rats were significantly greater (p < 0.05) than the light-induced shifts observed in control animals. Conclusions: The data indicate that developmental EtOH exposure alters the phase-shifting responses of the rat activity rhythm to light. This finding, coupled with changes in the circadian period and light/dark entrainment observed in EtOH-treated rats, suggests that developmental EtOH exposure may permanently alter the clock mechanism in the suprachiasmatic nucleus and its regulation of circadian behavior. [source] Altered interaction between cardiac vagal influence and delta sleep EEG suggests an altered neuroplasticity in patients suffering from major depressive disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 3 2010F. Jurysta Jurysta F, Kempenaers C, Lancini J, Lanquart J-P, van de Borne P, Linkowski P. Altered interaction between cardiac vagal influence and delta sleep EEG suggests an altered neuroplasticity in patients suffering from major depressive disorder. Objective:, Major depressive disorder (MDD), which is associated with altered neuroplasticity and increased relative cardiac sympathic activity, enhances the risk of cardiovascular pathologies. Interaction between cardiac sympatho-vagal indexes and delta sleep power is probably altered in MDD. Method:, Sleep characteristics and cardiac sympatho-vagal indexes of 10 depressive patients were compared to 10 control men across the first three non-rapid eye movement (NREM),REM cycles. Interaction between normalized high frequency (HF) and delta power bands was studied using coherence analysis. Results:, Patients showed increased sleep latency, stage 1 and wake durations. No differences in heart rate variabilities were observed: Total power, HF and RR-interval decreased from NREM to REM sleep and wakefulness in both groups. Gain value was lower in patients while coherence and phase shift were similar between groups. Modifications in HF appear 8 min before modifications in delta. Conclusion:, Major depressive disorder is related to an altered link between cardiac vagal influence and delta sleep, suggesting disorders in cardiovascular controls and an altered neuroplasticity. [source] The relationship between melatonin and cortisol rhythms: clinical implications of melatonin therapyDRUG DEVELOPMENT RESEARCH, Issue 3 2005N. Zisapel Abstract Disturbances in circadian rhythm have been linked to chronic diseases such as insomnia, hypertension, diabetes, and depression. Here we review recent studies on the age-related changes in cortisol and melatonin rhythms and then present descriptive statistics on our preliminary findings on the rectification of the cortisol rhythms by melatonin therapy in elderly patients with insomnia. In adults, the melatonin onset typically occurs during low cortisol secretion. Administration of exogenous melatonin around dusk will shift the phase of the human circadian clock to earlier hours (advance phase shift) leading to phase advances in circadian rhythms (e.g., sleep, endogenous melatonin, cortisol). With aging, the production of melatonin declines and is shifted to later hours while the production of cortisol increases and its peak occurs earlier in the night. In a randomized placebo-controlled crossover study with 8 patients with insomnia aged 55 years and older, a group characterized by low and delayed melatonin production, administration of prolonged-release melatonin in the evening was able to rectify the early onset cortisol production. This delay in nocturnal cortisol onset may explain in part the improvement in sleep quality in elderly patients with insomnia, in schizophrenics, and in depressed patients. Support of circadian pacemaker function by melatonin may provide a new strategy in the treatment of disorders related to impairments in the internal temporal order. The clinical benefit from a decrease in cortisol during the early part of the night may lie beyond the improvement of sleep into a better control of blood pressure, metabolism, and mood. Drug Dev. Res. 65:119,125, 2005. © 2005 Wiley-Liss, Inc. [source] Neural correlates of binaural masking level difference in the inferior colliculus of the barn owl (Tyto alba)EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2010Ali Asadollahi Abstract Humans and animals are able to detect signals in noisy environments. Detection improves when the noise and the signal have different interaural phase relationships. The resulting improvement in detection threshold is called the binaural masking level difference. We investigated neural mechanisms underlying the release from masking in the inferior colliculus of barn owls in low-frequency and high-frequency neurons. A tone (signal) was presented either with the same interaural time difference as the noise (masker) or at a 180° phase shift as compared with the interaural time difference of the noise. The changes in firing rates induced by the addition of a signal of increasing level while masker level was kept constant was well predicted by the relative responses to the masker and signal alone. In many cases, the response at the highest signal levels was dominated by the response to the signal alone, in spite of a significant response to the masker at low signal levels, suggesting the presence of occlusion. Detection thresholds and binaural masking level differences were widely distributed. The amount of release from masking increased with increasing masker level. Narrowly tuned neurons in the central nucleus of the inferior colliculus had detection thresholds that were lower than or similar to those of broadly tuned neurons in the external nucleus of the inferior colliculus. Broadly tuned neurons exhibited higher masking level differences than narrowband neurons. These data suggest that detection has different spectral requirements from localization. [source] An improved force-restore method for soil temperature predictionEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008Z. Gao Summary The force-restore method originally developed to enable soil temperature predictions assumes that soil is uniform with depth (i.e. the vertical gradient of thermal diffusivity is zero in soil) and that thermal conduction is the only heat transfer mechanism necessary for prediction of soil temperature. These assumptions hamper the applicability of the force-restore method to many natural soil conditions. The main objective of this study is to revise the force-restore method by extending it to include the possibility of soil heterogeneity with depth (i.e. non-zero vertical gradient of thermal diffusivity in soil) and to include the possible occurrence of convective heat transfer as well as conductive heat transfer in soil. Soil temperatures calculated by the current and the revised force-restore methods for a shallow soil layer were compared with measured soil temperatures at a bare soil site in the China Loess Plateau from 22 to 26 July 2005. Results showed that the revised method improved on the current force-restore method, which overestimated either the diurnal amplitude or the phase shift for the shallow soil layer. These results indicate that the revised force-restore method is more applicable than the current force-restore method for predicting soil temperatures in naturally occurring non-uniform soil. The revised force-restore method has potential application within many land-atmosphere numerical models. [source] Circannual control of the life cycle in the Varied Carpet Beetle Anthrenus verbasciFUNCTIONAL ECOLOGY, Issue 4 2003T. Nisimura Summary 1Anthrenus verbasci shows a circannual pupation rhythm, and a transfer from long-day to short-day conditions caused a phase shift. Short-day conditions produced synchronous pupation, and the critical day-length was between 13 and 14 h, which corresponded to the natural day-length in September. 2A decrease in temperature does not seem to act as a zeitgeber under natural conditions, because a change from 25 to 20 °C caused no or little phase shift. 3Under conditions of natural photoperiod and temperature, larvae pupated synchronously in April, although under natural day-length at 20 °C larvae pupated in February. Therefore, a decrease in day-length crossing the critical value in September probably shifts the phase of the circannual rhythm so that the gate to pupation opens in February, and probably low temperatures in winter suppress pupation until April. 4Newly hatching larvae transferred outdoors pupated successfully only when transferred between late April and mid-September, although larvae transferred after mid-July developed into smaller pupae than those transferred earlier. Therefore, synchronous pupation and emergence in spring are needed to allow larvae of the next generation to grow sufficiently before winter. [source] A correlation-based misfit criterion for wave-equation traveltime tomographyGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010T. Van Leeuwen SUMMARY Wave-equation traveltime tomography tries to obtain a subsurface velocity model from seismic data, either passive or active, that explains their traveltimes. A key step is the extraction of traveltime differences, or relative phase shifts, between observed and modelled finite-frequency waveforms. A standard approach involves a correlation of the observed and measured waveforms. When the amplitude spectra of the waveforms are identical, the maximum of the correlation is indicative of the relative phase shift. When the amplitude spectra are not identical, however, this argument is no longer valid. We propose an alternative criterion to measure the relative phase shift. This misfit criterion is a weighted norm of the correlation and is less sensitive to differences in the amplitude spectra. For practical application it is important to use a sensitivity kernel that is consistent with the way the misfit is measured. We derive this sensitivity kernel and show how it differs from the standard banana,doughnut sensitivity kernel. We illustrate the approach on a cross-well data set. [source] Diffusion through time-dependent mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000M. Holschneider Summary In this theoretical paper we show how to solve a time-dependent diffusion equation by means of a perturbation series. This technique is applied to the case of diffusion of a liquid through a time-dependent porous matrix. We compute to first order the phase and amplitude relations between the small deformation of the transporting matrix and the corresponding variation of the saturation at the surface. In particular we show that, for a large frequency range, there is a constant phase shift of ,/2 between the matrix and the surface saturation variations. Since the conductivity is to first approximation proportional to the saturation at the surface, this might explain the observed phase relations observed in an experiment in a cave near Abaratsubo (Japan). [source] Depth imaging in anisotropic media by symmetric non-stationary phase shiftGEOPHYSICAL PROSPECTING, Issue 3 2002Robert J. Ferguson ABSTRACT We present a new depth-imaging method for seismic data in heterogeneous anisotropic media. This recursive explicit method uses a non-stationary extrapolation operator to allow lateral velocity variation, and it uses the relationship between phase angle and the spectral coordinates of seismic data to allow velocity variation with phase angle. A qualitative comparison of migration impulse responses suggests that, for an equivalent cost, the symmetric non-stationary phase-shift (SNPS) operator is superior to the phase-shift plus interpolation (PSPI) operator, for very large depth intervals. To demonstrate the potential of the new method, seismic data from a physical model acquired over a transversely isotropic medium are imaged using a shot-record migration based on the SNPS operator. [source] Coral bleaching, reef fish community phase shifts and the resilience of coral reefsGLOBAL CHANGE BIOLOGY, Issue 9 2006DAVID R. BELLWOOD Abstract The 1998 global coral bleaching event was the largest recorded historical disturbance of coral reefs and resulted in extensive habitat loss. Annual censuses of reef fish community structure over a 12-year period spanning the bleaching event revealed a marked phase shift from a prebleach to postbleach assemblage. Surprisingly, we found that the bleaching event had no detectable effect on the abundance, diversity or species richness of a local cryptobenthic reef fish community. Furthermore, there is no evidence of regeneration even after 5,35 generations of these short-lived species. These results have significant implications for our understanding of the response of coral reef ecosystems to global warming and highlight the importance of selecting appropriate criteria for evaluating reef resilience. [source] Theta reset produces optimal conditions for long-term potentiationHIPPOCAMPUS, Issue 6 2004Holly McCartney Abstract Connections among theta rhythm, long-term potentiation (LTP) and memory in hippocampus are suggested by previous research, but definitive links are yet to be established. We investigated the hypothesis that resetting of local hippocampal theta to relevant stimuli in a working memory task produces optimal conditions for induction of LTP. The timings of the peak and trough of the first wave of reset theta were determined in initial sessions and used to time stimulation (4 pulses, 200 Hz) during subsequent performance. Stimulation on the peak of stimulus-reset theta produced LTP while stimulation on the trough did not. These results suggest that a memory-relevant stimulus produces a phase shift of ongoing theta rhythm that induces optimal conditions for the stimulus to undergo potentiation. © 2004 Wiley-Liss, Inc. [source] The zone of vegetation influence on baseflow revealed by diel patterns of streamflow and vegetation water use in a headwater basinHYDROLOGICAL PROCESSES, Issue 8 2002Barbara J. Bond Water use by vegetation can be closely linked to streamflow patterns on a variety of time scales. However, many of the details of these linkages are poorly understood. We compared diel (24 h) patterns of transpirational water use with streamflow patterns in a small headwater basin that displays a marked diel variation during summer months. The study site was in western Oregon. Our objectives were to: (1) determine the phase shift, i.e. the time lag between maximum transpiration and minimum streamflow, and the strength of the correlation at that time lag; (2) determine the amount of streamflow that is ,missing' during each diel cycle (i.e. the difference between base flow, defined by the daily maxima, and actual flow) and use it to estimate the zone, or area, of vegetation that influences daily streamflow patterns; (3) test and refine a conceptual model of how the coupling between vegetation water use and streamflow changes over the period of summer drought in this basin. We found that vegetation water use in the summer is coupled to streamflow over time scales of 4 to 8 h, and water-use-related fluctuations accounted for 1 to 6% of summer base flow. Direct evaporation from the channel was an order of magnitude less than the diel streamflow decrease. Transpiration within only 0·1 to 0·3% of the basin area accounted for the diel variation in streamflow. As the basin drained further through the summer, the coupling between vegetation and streamflow was diminished and occurred at longer time scales, and the zone of vegetation influence became smaller. This pattern is in accordance with our conceptual model, which attributes the summer decline in the strength of the vegetation,streamflow coupling to the increasing depth of plant-available water in the soil profile. Although this study is preliminary, we believe it is an important first step in describing better the coupling of vegetation water use to streamflow. Copyright © 2002 John Wiley & Sons, Ltd. [source] Magnetic and Electrical Characterizations of Half-Metallic Fe3O4 Nanowires,ADVANCED MATERIALS, Issue 17 2007M.-T. Chang The magnetic properties of magnetite (Fe3O4) nanowires are investigated by means of electron holography, which deduces the magnetic information from the phase shift of electrons. The magnetic flux is parallel to the longitudinal axis of the nanowires (see figure). Observations on the magnetization distribution reveal the possibility of regulating the spin current with the half-metallic nanowires, owing to the controlled magnetization distribution in the 1D form. [source] Changes in the sub-decadal covariability between Northern Hemisphere snow cover and the general circulation of the atmosphereINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2004Kazuyuki Saito Abstract Details of the sub-decadal covariability relationship between continental snow cover extent anomalies and the dominant mode of atmospheric variability, referred to as the Arctic oscillation (AO) or North Atlantic oscillation (NAO), for the period 1971,2001 are explored. On the seasonal time scale, the winter AO is found to be significantly correlated with the preceding autumn Eurasian snow cover (SNCEUR) throughout the period observed. Consistent with this finding, SNCEUR variability led the AO variability on the sub-decadal time scale in the early half of the record. However, starting in the mid 1980s, the AO and SNCEUR vary in phase. Analyses of the seasonal relationship and persistence of snow and atmospheric variables illustrate a phase shift in the sub-decadal variability between the AO and SNCEUR due to the loss of autumn,winter SNCEUR autocorrelation replaced by a significant winter,spring persistence and the emergence of a concurrent SNCEUR,AO connection in winter and spring. Similar analysis shows that the sub-decadal NAO variation is mostly described by the fluctuation in summer North American snow cover. Copyright © 2004 Royal Meteorological Society [source] Composite Material for Simultaneous and Contactless Luminescent Sensing and Imaging of Oxygen and Carbon Dioxide,ADVANCED MATERIALS, Issue 12 2006M. Borisov "Seeing" oxygen and carbon dioxide: A sensor material is described that enables simultaneous imaging and monitoring of carbon dioxide and oxygen (see figure). It relies on the measurement of the phase shift of the luminescence decay time of a material composed of microbead-contained indicators (with well-separated excitation and emission wavelengths) and polymers with excellent permeation selectivities as well as favorable optical and adhesive properties. [source] Molecular imaging in small animals,roles for micro-CTJOURNAL OF CELLULAR BIOCHEMISTRY, Issue S39 2002Erik L. Ritman Abstract X-ray micro-CT is currently used primarily to generate 3D images of micro-architecture (and the function that can be deduced from it) and the regional distribution of administered radiopaque indicators, within intact rodent organs or biopsies from large animals and humans. Current use of X-ray micro-CT can be extended in three ways to increase the quantitative imaging of molecular transport and accumulation within such specimens. (1) By use of heavy elements, other than the usual iodine, attached to molecules of interest or to surrogates for those molecules. The accumulation of the indicator in the physiological compartments, and the transport to and from such compartments, can be quantitated from the imaged spatial distribution of these contrast agents. (2) The high spatial resolution of conventional X-ray attenuation-based CT images can be used to improve the quantitative nature of radionuclide-based tomographic images (SPECT & PET) by providing correction for attenuation of the emitted gamma rays and the accurate delineation of physiological spaces known to selectively accumulate those indicators. Similarly, other imaging modalities which also localize functions in 2D images (such as histological sections subsequently obtained from the same specimen), can provide a synergistic combination with CT-based 3D microstructure. (3) By increasing the sensitivity and specificity of X-ray CT image contrast by use of methods such as: K-edge subtraction imaging, X-ray fluorescence imaging, imaging of the various types of scattered X-ray and the consequences of the change in the speed of X-rays through different tissues, such as refraction and phase shift. These other methods of X-ray imaging can increase contrast by more than an order of magnitude over that due to conventionally-used attenuation of X-ray. To fully exploit their potentials, much development of radiopaque indicators, scanner hardware and image reconstruction and analysis software will be needed. J. Cell. Biochem. Suppl. 39: 116,124, 2002. © 2002 Wiley-Liss, Inc. [source] The correlation between blood oxygenation level-dependent signal strength and latencyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2005Karsten Müller PhD Abstract Purpose To investigate the relationship between signal strength and latency of the blood oxygenation level-dependent (BOLD) signal. Materials and Methods Several correlation analyses were performed on data obtained in a functional magnetic resonance imaging (fMRI) experiment, where subjects were presented with a simple visual stimulus. The BOLD signal strength was correlated with both the phase shift of the spectral density matrix and time-to-peak calculated from trial-averaged time courses. Correlation coefficients were calculated for visual stimuli of 2, 6, and 15 seconds in duration. Results Analyzing all functional runs for the same subject separately, i.e., including for each run all significantly activated voxels, we observed that correlations between phase shift and signal strength, as well as between time-to-peak and signal strength, decreased with increasing stimulus length. However, when analyses were restricted to voxels found activated in all functional runs, we observed similar correlations between BOLD signal strength and latency in all runs, independent of the length of stimulation. This result was again obtained for both latency measures: the spectral density phase shift and time-to-peak. Conclusion For both latency measures, phase shift and time-to-peak, a high correlation between BOLD signal strength and latency was observed. We have shown that this correlation is independent of the length of visual stimulation. Thus, the correlation between BOLD signal strength and latency seems to be an inherent property of the BOLD response that is independent of the length of stimulation and can be observed using different methods for determining signal latency. J. Magn. Reson. Imaging 2005;21:489,494. © 2005 Wiley-Liss, Inc. [source] Investigating the stimulus-dependent temporal dynamics of the BOLD signal using spectral methodsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2003Karsten Müller PhD Abstract Purpose To compare several spectral parameters using different durations of visual hemifield stimulation in order to explore the different temporal behavior of the blood oxygenation-level dependent (BOLD) signal in various brain regions. Materials and Methods Spectral methods were applied to three different groups of subjects with visual stimulation lasting 6, 12, and 30 seconds. Furthermore, diffusion weighting was applied in an interleaved way. The core of the data processing was the computation of the spectral density matrix using the multidimensional weighted covariance estimate. Spectral parameters of coherence and phase shift were computed. Results The correlation between signal changes and phase shifts was dependent on the duration of the visual stimulation. The shorter the duration of visual stimulation, the stronger the correlation between percentage signal change and phase shift. Conclusion The experiments with short and long stimuli differed mainly in the distribution of the activated voxels in the plane of percentage signal change and phase shift. It was revealed that the height of the signal change depends on the phase shift, whereas the diffusion weighting has no influence. J. Magn. Reson. Imaging 2003;17:375,382. © 2003 Wiley-Liss, Inc. [source] Effect of MT1 melatonin receptor deletion on melatonin-mediated phase shift of circadian rhythms in the C57BL/6 mouseJOURNAL OF PINEAL RESEARCH, Issue 2 2005M. L. Dubocovich Abstract:, In the mouse suprachiasmatic nucleus (SCN), melatonin activates MT1 and MT2 G-protein coupled receptors, which are involved primarily in inhibition of neuronal firing and phase shift of circadian rhythms. This study investigated the ability of melatonin to phase shift circadian rhythms in wild type (WT) and MT1 melatonin receptor knockout (KO) C57BL/6 mice. In WT mice, melatonin (90 ,g/mouse, s.c.) administered at circadian time 10 (CT10; CT12 onset of activity) significantly phase advanced the onset of the circadian activity rhythm (0.60 ± 0.09 hr, n = 41) when compared with vehicle treated controls (,0.02 ± 0.07 hr, n = 28) (P < 0.001). In contrast, C57 MT1KO mice treated with melatonin did not phase shift circadian activity rhythms (,0.10 ± 0.12 hr, n = 42) when compared with vehicle treated mice (,0.12 ± 0.07 hr, n = 43). Similarly, in the C57 MT1KO mouse melatonin did not accelerate re-entrainment to a new dark onset after an abrupt advance of the dark cycle. In contrast, melatonin (3 and 10 pm) significantly phase advanced circadian rhythm of neuronal firing in SCN brain slices independent of genotype with an identical maximal shift at 10 pm (C57 WT: 3.61 ± 0.38 hr, n = 3; C57 MT1KO: 3.45 ± 0.11 hr, n = 4). Taken together, these results suggest that melatonin-mediated phase advances of circadian rhythms of neuronal firing in the SCN in vitro may involve activation of the MT2 receptor while in vivo activation of the MT1 and possibly the MT2 receptor may be necessary for the expression of melatonin-mediated phase shifts of overt circadian activity rhythms. [source] Optically controlled adaptive mirrorLASER PHYSICS LETTERS, Issue 11 2004F. Reinert Abstract We report on an adaptive mirror system that allows generating thermo-optically controlled wavefront corrections. The influence of the wavefront is based on the thermal dependence of the refractive index in a thin active layer. The thermal pattern in the active layer is generated by irradiation with a diode laser emitting at 805 nm. The active layer consists of a diluted aqueous solution of NdCl3. A Michelson interferometer is used to measure the wavefront distortions. A phase shift of 6, with a lateral resolution of better than 1 mm and a temporal rise/fall time of a few seconds can be achieved with an absorbed power of only 150 mW at an intensity of about 10 W/cm2. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Fast spin-echo triple-echo dixon (fTED) technique for efficient T2 -weighted water and fat imaging,MAGNETIC RESONANCE IN MEDICINE, Issue 1 2007Jingfei Ma Abstract Previously published fast spin-echo (FSE) implementations of a Dixon method for water and fat separation all require multiple scans and thus a relatively long scan time. Further, the minimum echo spacing (esp), a time critical for FSE image quality and scan efficiency, often needs to be increased in order to bring about the required phase shift between the water and fat signals. This work proposes and implements a novel FSE triple-echo Dixon (fTED) technique that can address these limitations. In the new technique, three raw images are acquired in a single FSE scan by replacing each frequency-encoding gradient in a conventional FSE with three consecutive gradients of alternating polarity. The timing of the three gradients is adjusted by selecting an appropriate receiver bandwidth (RBW) so that the water and fat signals for the three corresponding echoes have a relative phase shift of ,180°, 0°, and 180°, respectively. A fully automated postprocessing algorithm is then used to generate separate water-only and fat-only images for each slice. The technique was implemented with and without parallel imaging. We demonstrate that the new fTED technique enables both uniform water/fat separation and fast scanning with uncompromised scan parameters, including applications such as T2 -weighted separate water and fat imaging of the abdomen during breath-holding. Magn Reson Med 58:103,109, 2007. © 2007 Wiley-Liss, Inc. [source] Diffusion measurements free of motion artifacts using intermolecular dipole-dipole interactionsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2004Scott D. Kennedy Abstract Diffusion encoding, or diffusion weighting, is commonly achieved by applying a pair of balanced pulsed-field gradients during spin evolution. An alternative way to obtain diffusion measurements is to select dipolar correlation distances using the distant dipolar field (DDF) in systems with abundant spin density, such as water in tissues. Diffusion weighting using this effect is unique in that the refocusing "gradient" is carried within the sample, and thus the macroscopic motion of the sample is not expected to interfere with signal formation. The experiments presented here demonstrate that in moving phantoms, the phase shift of the signal due to linear motion is minimal in diffusion-weighted (DW) DDF measurements, and that motion artifacts in images of moving phantoms and the abdomen of live mice are small compared to standard pulsed-field-gradient methods. The technique may facilitate the use of DWI in typically motion-prone regions such as the abdomen, lungs, and heart. Magn Reson Med 52:1,6, 2004. © 2004 Wiley-Liss, Inc. [source] Soliton solutions of the Toda hierarchy on quasi-periodic backgrounds revisitedMATHEMATISCHE NACHRICHTEN, Issue 4 2009Iryna Egorova Abstract We investigate soliton solutions of the Toda hierarchy on a quasi-periodic finite-gap background by means of the double commutation method and the inverse scattering transform. In particular, we compute the phase shift caused by a soliton on a quasi-periodic finite-gap background. Furthermore, we consider short range perturbations via scattering theory. We give a full description of the effect of the double commutation method on the scattering data and establish the inverse scattering transform in this setting (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Imaging of cochlear tissue with a grating interferometer and hard X-raysMICROSCOPY RESEARCH AND TECHNIQUE, Issue 12 2009Claus-Peter Richter Abstract This article addresses an important current development in medical and biological imaging: the possibility of imaging soft tissue at resolutions in the micron range using hard X-rays. Challenging environments, including the cochlea, require the imaging of soft tissue structure surrounded by bone. We demonstrate that cochlear soft tissue structures can be imaged with hard X-ray phase contrast. Furthermore, we show that only a thin slice of the tissue is required to introduce a large phase shift. It is likely that the phase contrast image of the soft tissue structures is sufficient to image the structures even if surrounded by bone. For the present set of experiments, structures with low-absorption contrast have been visualized using in-line phase contrast imaging and a grating interferometer. The experiments have been performed at the Advanced Photon Source at Argonne National Laboratories, a third generation source of synchrotron radiation. The source provides highly coherent X-ray radiation with high-photon flux (>1012 photons/s) at high-photon energies (5,70 keV). Radiographic and light microscopy images of the gerbil cochlear slice samples were compared. It has been determined that a 20-,m thick tissue slice induces a phase shift between 1/3, and 2/3,. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Novel design of multiplexed sensors using a dual FBGs schemeMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2010S. Nafisah Abstract We propose a new system of the multiplexed sensors using a series of fiber Bragg gratings (FBGs), where the gratings separation lengths, Bragg wavelength, dip length, and birefringence can be configured as the sensing information. The transmission spectrum of a dual fiber Bragg gratings has been derived. Value of separation length between two FBGs, dL, is varied from 0.5 to 5.5 cm. The dip of separation length affects the transmission spectrum, which is indicated by the numbers of minimum dip values. Results show that the increasing in the separation length (dip length) between two FBGs leads to the formation of phase shift and increases the number of minimum transmission dip. For the dual FBGs to be used as a Fabry-Perot interferometer, it must have the smallest possible separation length. The multiplexed sensing application of more than two physical parameters can be operated by using such effects, for instance, strain, temperature, and gas sensor is plausible, while the self calibration between them is also available. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1218,1221, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25106 [source] Environmentally stable nonlinear optical polarization switching by using a nonreciprocal all-optical circuitMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2009Naoto Kishi Abstract We proposed and demonstrated a stable nonlinear optical polarization self-switching based on nonreciprocal nonlinear phase shift induced by self-phase modulation in optical fiber. The polarization self-switching was achieved at input power levels of around 10 mW in a nonreciprocal circuit using Faraday rotator mirrors. This nonlinear polarization switching is quite stable against polarization fluctuation caused by environmental perturbation. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2056,2059, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24548 [source] Metamaterial transmission lines with tunable phase and characteristic impedance based on complementary split ring resonatorsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2009Adolfo Vélez Abstract In this article, resonant-type tunable metamaterial transmission lines with independent control over the electrical parameters of the line, that is, the electrical length and characteristic impedance, are presented for the first time. Tuning is achieved by loading a host microstrip line with varactor-loaded complementary split ring resonators (VLCSRRs) and varactor diodes. By locating the varactor diodes in series configuration with the line, outside the region occupied by the VLCSRRs, it is possible to control the characteristic impedance and the electrical length (phase shift), over a wide band. As an illustrative example, a tunable 35 ,/90° line functional between 0.4 and 0.8 GHz (which represents more than 65% tuning range), is presented and applied to the design of a transmission line power divider. The device is small and it exhibits reasonable performance. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1966,1970, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24480 [source] Modified principle of distributed ferroelectric phase shifter considering the influence of interconnecting linesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2008An Yu Abstract The deviation between theoretic values and real data of distributed ferroelectric phase shifter is investigated by simulating an ideal model and analyzing an equivalent circuit. The deviation is shown to come from the parasitic inductance of interconnecting lines between loaded capacitors and center strip of CPW, which reduces the Bragg frequency, increases the insertion loss and phase shift. By introducing an effective capacitance to consider the effect of interconnecting lines, a modified principle is presented, which forecasts performances better. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 748,751, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23212 [source] Design of a UWB planar 180° hybrid exploiting microstrip-slot transitionsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2007A. M. Abbosh Abstract The article describes the design of a planar 180° hybrid with an ultra wideband (UWB) performance. The device employs two substrates with a common ground plane and various microstrip-slot transitions to achieve in-phase and out-of-phase signal division over an ultra wide frequency range. At the initial stage, simple design guidelines are used but the final dimensions are determined using a full-wave analysis and design software package. The simulated and measured results of the proposed device reveal a well balanced power split accompanied by a very good approximation of ideal 180° and 0° differential phase shift across the band 3.1 to more than 11 GHz. Also low insertion losses, good return loss at all of the four ports, high isolation between the input ports and fine isolation between output ports are noted across this frequency band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1343,1346, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22472 [source] Circularly polarized broadband high-efficiency active integrated antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2006S. Gao Abstract This letter presents a circularly polarized (CP) broadband high-efficiency active integrated antenna, where the broadband CP antenna is integrated directly with a broadband high-efficiency class-E power amplifier (PA). To achieve CP operation, a series feed using an L-shaped microstrip feed line below the ground plane is used to provide a 90° phase shift between crossed slots. The antenna serves both functions of a broadband CP radiator and a broadband harmonics-termination load network for the class-E PA. Measures results demonstrate both broadband CP radiation and high efficiency. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2145,2148, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21940 [source] | ||||||||||||||||||||||||||||