共查询到20条相似文献,搜索用时 15 毫秒
1.
C. Corredor J. Diaz J. M. Diaz H. A. Farach C. P. Poole 《Applied magnetic resonance》1995,9(3):309-317
The electron spin resonance spectra fromGallus domesticus egg shells exhibit a strong free radical singlet, a spectrum due to Mn2+ ions in a calcite site, a low field line line atg≈30/7 due to Mn2+ in a rhombic site, and spectral lines arising from Fe3+ ions. Details of the ESR spectral lines did not correlate with fertile, non-fertile or color type egg-shell characteristics. 相似文献
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In data and image processing the role of optics is already well established. Due to inherent parallelism the optical systems run faster than its electronic counterparts. Optical nonlinear material can be used as a successful optical switch. The primary requirement for proper functioning of such nonlinear material based logic devices is a fixed intensity level of the optical signal against a specific logic state. In this communication, the authors propose a new concept to obtain a fixed intensity level of optical signal against a specific logic state for data processing. The scheme may extend a tremendous application not only to the area of all-optical computation, but also to optical communication process. 相似文献
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Surányi P Kiss P Ruzsics B Brott BC Simor T Elgavish GA 《Magnetic resonance imaging》2007,25(5):641-651
INTRODUCTION: Inhomogeneity of magnetic fields, both B(0) and B(1), has been a major challenge in magnetic resonance imaging (MRI). Field inhomogeneity leads to image artifacts and unreliability of signal intensity (SI) measurements. This work proposes and shows the feasibility of generating equilibrium signal intensity (SI(Eq)) maps that can be utilized either to speed up relaxation-rate measurement or to enhance image quality and relaxation-rate-based weighting in various applications. METHODS: A 1.5-T MRI scanner was used. In canines (n=4), myocardial infarction was induced, and 48 h after the administration of 0.05 mmol kg(-1) Gd(ABE-DTTA), a contrast agent with slow tissue kinetics, in vivo R(1) mapping was carried out using an inversion recovery (IR)-prepared, fast gradient-echo sequence with varying inversion times (TIs). To test the SI(Eq) mapping method without the confounding effects of motion and blood flow, we carried out ex vivo R(1) mapping after the administration of 0.2 mmol kg(-1) Gd(DTPA) using an IR-prepared, fast spin-echo sequence in another group of dogs (n=2). R(1,full) maps and SI(Eq) maps were generated from the data from both sequences by three-parameter nonlinear curve fitting of the SI versus TI dependence. R(1,full) maps served as the reference standard. Raw IR images were then divided by the SI(Eq) maps, yielding corrected SI maps (COSIMs). Additionally, R(1) values were calculated from each single-TI image separately, using the SI(Eq) value and a one-parameter curve-fitting procedure (R(1,single)). Voxelwise correlation analysis was carried out for the COSIMs and the R(1,single) maps, both versus the standard R(1,full) maps. Deviations of R(1,single) from R(1,full) were statistically evaluated. RESULTS: In vivo, COSIM versus R(1,full) showed significantly (P<.05) better correlation [correlation coefficient (CC)=0.95] than SI versus R(1,full) with a TI=700-800 ms, which is 200-300 ms longer than the tau(null) (500 ms) of viable myocardium. With such TIs, SI versus R(1,full) yielded CCs of 0.86-0.88. R(1,single) versus R(1,full) yielded a peak CC of 0.96 at TI=700-900 ms. Mean deviations of R(1,single) from R(1,full) were below 5% for TIs between 500 and 1000 ms. Ex vivo, where tau(null) was 300 ms, the advantage of correction with SI(Eq) was not in the improvement of linear correlation but more in the reduction of scatter. Peak CCs for SI versus R(1,full) and COSIM versus R(1,full) at TI=500 ms were 0.96 for both. The ex vivo CC for R(1,single) versus R(1,full) at TI=500 ms was 0.98. Mean deviations of R(1,single) from R(1,full) were below 5% for TIs between 400 and 700 ms. CONCLUSIONS: Once the corresponding SI(Eq) map is obtained from a control stack, R(1) can be obtained accurately, using only a single IR image and without the need for a stack of TI-varied images. This approach could be applied in various dynamic MRI studies where short measurement time, once the dynamics has started, is of essence. When using this method with IR-prepared T(1)-weighted images, it is essential that the single TI be chosen such that the longitudinal relaxation in all voxels of interest would have passed tau(null). SI(Eq) maps are also useful in eliminating confounders from MR images to allow obtaining SI values that reflect more faithfully the relaxation parameter (R(1)) sought. 相似文献
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对用X射线CCD作测量设备的在线针孔相机信号强度进行了估计。利用激光原型装置柱腔能谱曲线、PI-SX1300型号X射线CCD的量子效率曲线分别对在CCD加Be滤片和加不同材料的平面镜两种情况下的针孔相机成像获得的X射线信号在CCD上的信号强度计数进行了估算,结果表明:厚度不大于200 μm的Be滤片只能将信号强度的计数降低一个量级;3°入射的金平面镜,5°入射的镍、碳平面镜和硅平面镜虽然也可将信号强度计数降低一个量级,但这两种衰减方法得到的强度计数超过了CCD的饱和计数值。计算了不同厚度的Be滤片结合平面镜的针孔相机对信号强度计数的衰减情况,结果表明:Be的厚度在20~40 μm时,平面镜选择3°入射的金平面镜或者5°入射的镍平面镜,两者结合可以较好地衰减信号。 相似文献
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对用X射线CCD作测量设备的在线针孔相机信号强度进行了估计。利用激光原型装置柱腔能谱曲线、PI-SX1300型号X射线CCD的量子效率曲线分别对在CCD加Be滤片和加不同材料的平面镜两种情况下的针孔相机成像获得的X射线信号在CCD上的信号强度计数进行了估算,结果表明:厚度不大于200 μm的Be滤片只能将信号强度的计数降低一个量级;3°入射的金平面镜,5°入射的镍、碳平面镜和硅平面镜虽然也可将信号强度计数降低一个量级,但这两种衰减方法得到的强度计数超过了CCD的饱和计数值。计算了不同厚度的Be滤片结合平面镜的针孔相机对信号强度计数的衰减情况,结果表明:Be的厚度在20~40 μm时,平面镜选择3°入射的金平面镜或者5°入射的镍平面镜,两者结合可以较好地衰减信号。 相似文献
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Shin Toyoda Fumihiro Sato Hirotsugu Nishido Masahiro Kayama Jun-Ichiro Ishibashi 《Radiation measurements》2012,47(9):900-902
The alpha effectiveness was investigated for an ESR signal due to in barite by comparing the dose responses of the signal for gamma irradiation and for He ion implantation with an energy of 4 MeV. The value was obtained to be 0.043 ± 0.018 for samples from Morocco and to be 0.0089 ± 0.0006 for Kanehira Mine. The dose response for He ion implantation for the latter sample better fits to a correlation line but the signal shape changes with gamma ray dose, indicating contribution from an unknown radiation sensitive signal, while the former sample shows the same signal shapes. A value of 0.043 ± 0.018 is adopted as the alpha effectiveness of signal in barite, which is used for ESR dating of submarine hydrothermal activity. 相似文献
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Hélène Tissoux Pierre Voinchet Fréderic Lacquement François Prognon Davinia Moreno Christophe Falguères Jean-Jacques Bahain Shin Toyoda 《Radiation measurements》2012,47(9):894-899
Electron Spin Resonance (ESR) can be used as a method to estimate the age of sediment deposition using the paramagnetic centre related to aluminium impurities in quartz. This so-called Al-centre can be partially optically bleached and its signal intensity decreases in relation to time exposure to solar light, until it reaches a plateau value corresponding to a residual signal. This signal can be attributed to “Deep Aluminium Traps” (DAT) which cannot be reset by an exposure to sunlight. In this study, we have investigated the behaviour of the DAT signal in samples from different origins and ages. The intensity of the DAT signal has been isolated from the total aluminium signal by the exposure of different quartz samples to simulated solar light. We observed that the DAT intensities were sample dependant and therefore it should be determined for each sample. Moreover, DAT intensities of Pleistocene volcanic quartz increase with gamma laboratory irradiation, whereas DAT intensities of sedimentary quartz do not vary with added artificial doses. This suggests that DAT in quartz extracted from sediments must be inherited from the primary source of the quartz, and were saturated at the time of sedimentation. We thereby validate the ESR dating of quartz sediment protocol used so far. 相似文献
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We propose a calibration method for spatial distribution of photosensitivity of matrix radiation receivers. It is based on
measurements of time-stable distributions of the light beam intensity at several different combinations of mutual positions
of the beam and the radiation receiver. The scheme of the experiment was developed to realize this method, and the inverse
problem of reconstruction of the spatial distribution of photosensitivity from the measurement results was solved. Numerical
simulation of the experiment was used to study the features of the calibration algorithm. The spatial distributions of light
sensitivity of the matrices, which work on the principles of charge-coupled device operation, were calibrated in an experiment. 相似文献
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A nonlinear dynamics method for signal identification 总被引:4,自引:0,他引:4
Carroll TL 《Chaos (Woodbury, N.Y.)》2007,17(2):023109
When a radio frequency signal is radiated by a transmitter, the properties of the transmitter itself affect the properties of the signal. These transmitter-induced changes are known as unintentional modulation, to differentiate them from intentional modulation used to add information to the signal. The unintentional modulation can be used to identify which transmitter produced a signal. This paper shows how phase space analysis based on nonlinear dynamics ideas can be used to determine which of several amplifiers produced a signal. 相似文献
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Signal intensities of longitudinally detected ESR (LODESR) of 1,1-diphenyl-2-picrylhydrazyl powder were precisely measured
at 250 to 950 MHz under a constant magnetic field microwave that was applied using a single-turn coil. The LODESR signal intensity
was reduced linearly due to smaller Zeeman splitting. Because the noise level was constant, the sensitivity of LODESR was
approximately proportional to the resonant frequency. As far as we know, this study represents the first attempt to measure
precisely the relationship between the signal intensities and resonant frequencies of ESR in an experimental condition. 相似文献
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V. I. Nazaruk 《The European Physical Journal A - Hadrons and Nuclei》2009,39(2):249-253
The intermediate-state interaction and the structure of amplitudes of complicated processes in the medium (decays, reactions
and the n
transitions) are studied. It is proposed to use the branching ratio of channels of the free-space hadron-nucleon interaction
as a test in the construction and verification of the models. The corresponding formulas for the processes in the medium are
obtained. The connection between the particle self-energy and amplitudes of subprocesses is analyzed as well. 相似文献
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An analytical quasi-exact method for calculating eigenvibrations of thin circular cylindrical shells
A method for calculating the eigenfrequencies and corresponding deformation modes of a thin circular cylindrical shell is presented, based on analytical solutions of Flügge's shell theory equations. The partial differential equations are transformed into algebraic equations which can be solved with high accuracy. Consequently, the results can be considered as quasi-exact. Results of calculations are presented for a shell stiffened at both circular edges. Such boundary conditions are typical of the core barrel of a pressurized water reactor, for instance. Most of the calculated deformation modes show strong gradients of the displacements close to the boundaries. 相似文献
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We have developed a new numerical ray-tracing approach for LIDAR signal power function computation, in which the light round-trip propagation is analyzed by geometrical optics and a simple experiment is employed to acquire the laser intensity distribution. It is relatively more accurate and flexible than previous methods. We emphatically discuss the relationship between the inclined angle and the dynamic range of detector output signal in biaxial LIDAR system. Results indicate that an appropriate negative angle can compress the signal dynamic range. This technique has been successfully proved by comparison with real measurements. 相似文献
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It has previously been observed that during isometric dorsiflexion exercise, the time course of T2-weighted signal intensity (SI) changes is spatially heterogeneous. The purpose of this study was to test the hypothesis that this spatial heterogeneity would increase at higher contraction intensities. Eight subjects performed 90-s isometric dorsiflexion contractions at 30% and 60% of maximum voluntary contraction (MVC) while T2-weighted (repetition time/echo time=4000/35 ms) images were acquired. SI was measured before, during and after the contractions in regions of interest (ROIs) in the extensor digitorum longus (EDL) muscle and the deep and superficial compartments of the tibialis anterior (D-TA and S-TA, respectively). For all ROIs at 30% MVC, SI changes were similar. The maximum postcontraction SI was greater than the SI during exercise. At 60% MVC, SI changes during contraction were greater in the S-TA than in the D-TA and EDL. For the EDL and D-TA, the maximum postcontraction SI was greater than those during exercise. For the S-TA, the maximum postcontraction change was greater than the changes at t=8, 20 and 56 s but not the end-exercise value. We conclude that spatial heterogeneity increases during more intense dorsiflexion contractions, possibly reflecting regional differences in perfusion or neural activation of the muscle. 相似文献
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P.J. Jennings 《Surface science》1974,41(1):67-76
A perturbation series method for obtaining LEED intensities from the transfer matrix method is reported. This approach is based on simple physical considerations and is adaptable to a variety of surface structures. The intensities obtained from this approximation are of comparable accuracy with those obtained by the complete procedure but the computation times are considerably reduced. The method holds promise for intensity calculations on crystals with surface layers of adsorbed atoms. 相似文献