The dynamic properties of single olivocochlear efferent neurones in the guinea pig cochlea were examined using sinusoidally amplitude modulated (AM) pure tones. The neural discharge, when displayed as a cyclic histogr...
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The dynamic properties of single olivocochlear efferent neurones in the guinea pig cochlea were examined using sinusoidally amplitude modulated (AM) pure tones. The neural discharge, when displayed as a cyclic histogram, clearly followed the rapid fluctuations in the continuous input sound. modulation transfer functions (MTFs) were constructed and in most cases showed a peak in the modulation response (MR) at a modulation frequency (MF) of 100 Hz. At this frequency a gain of as much as 12 dB was evident relative to the 30% modulated input signal. In 24% of neurones however, a large MR was present even at low MFs. This plurality of MTFs may be the result of recorded neurones emanating from a variety of cell bodies of origin Efferent group delays (mean of 8.2 .+-. 1.0 ms) were shorter and more tightly distributed than the minimum onset latency measurements (mean of 24.3 .+-. 12.5) made on the same neurones. It seems evident that a post-synaptic potential build is required from the onset of a stimulus to the first spike discharge. This may occur within a single afferent-interneurone(s)-efferent reflex arc. Among a variety of alternative explanations, the observation is consistent with the notion that the olivocochlear neurones receive facilitatory input from higher centres, which is suppressed under barbiturate anaesthesia. Continuous AM signals may allow post-synaptic build up and eliminate the dependence on this higher input and hence yield a short group delay.
PurposeThis study aimed to assess the optical quality of myopic and presbyopic IPCLs with different additional powers, and to investigate the effects of pupil size on the optical quality of these IPCLs using an in-vit...
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PurposeThis study aimed to assess the optical quality of myopic and presbyopic IPCLs with different additional powers, and to investigate the effects of pupil size on the optical quality of these IPCLs using an in-vitro modulation transfer function (MTF) measurement *** scatter functions (LSFs) were recorded using the OPAL Vector system and an eye phantom consisting of wet cells filled with a balanced salt solution. A myopic IPCL or a presbyopic IPCL was placed in the posterior chamber of this model. The MTF was calculated from the LSF using the fast Fourier transform techniques. The effective apertures were set at 2.0 to 5.0 mm in 1.0 mm *** in-focus MTF values of the myopic IPCL and presbyopic IPCL with additional powers of + 2.0 and + 4.0 diopters at 100 cycles/mm for an effective aperture of 3.0 mm were 43%, 27%, and 24%, respectively. The in-focus MTF value of both myopic and presbyopic IPCLs was the highest when the effective aperture was set at 3.0 mm, and it gradually worsened when the effective aperture became larger than 3.0 mm at 20, 60, and 100 cycles/*** myopic and presbyopic IPCLs provided excellent MTF values, but the additional power profile can deteriorate optical performance in presbyopic IPCL-implanted eyes, even with a low additional power. Pupil size can influence visual quality in IPCL-implanted eyes for both myopia and presbyopia. What is known:center dot Implantable phakic contact lens (IPCL) has been reported to be effective for the treatment of both myopia and presbyopia, with a noticeable advantage in reducing the patients' cost *** dot The optical properties of IPCL have not yet been thoroughly investigated, neither for myopic IPCLs nor for presbyopic *** is new:center dot The MTF of presbyopic IPCL was slightly lower than that of myopic IPCL even with a low additional *** dot The MTF values of both myopic and presbyopic IPCLs were the highest for a 3.0 mm-pupil size,
The performance of the infrared scanning radiometer (IRSR) is strongly stressed in convective heat transfer applications where high spatial frequencies in the signal that describes the thermal image are present. The n...
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The performance of the infrared scanning radiometer (IRSR) is strongly stressed in convective heat transfer applications where high spatial frequencies in the signal that describes the thermal image are present. The need to characterize more deeply the system spatial resolution has led to the formulation of a cascade model for the evaluation of the actual modulation transfer function of a sampled IR imaging system. The model can yield both the aliasing band and the averaged modulation response for a general sampling subsystem. For a line scan imaging system, which is the case of a typical IRSR, a rule of thumb that states whether the combined sampling-imaging system is either imaging-dependent or sampling-dependent is proposed. The model is tested by comparing it with other noncascade models as well as by ad hoc measurements performed on a commercial digitized IRSR.
A theoretically based calculation of the modulation transfer function is performed for phosphor screens excited by x-rays. It is assumed that the screens are of compact material so that scattering of the light generat...
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A theoretically based calculation of the modulation transfer function is performed for phosphor screens excited by x-rays. It is assumed that the screens are of compact material so that scattering of the light generated can be neglected. The absorption of both x-rays and light in the phosphor material is taken into account.
Objectives: The aim was to investigate the possibility of evaluating the modulation transfer function (MTF) of cone beam CT (CBCT) for dental use using the oversampling method. Methods: The CBCT apparatus (3D Accuitom...
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Objectives: The aim was to investigate the possibility of evaluating the modulation transfer function (MTF) of cone beam CT (CBCT) for dental use using the oversampling method. Methods: The CBCT apparatus (3D Accuitomo) with an image intensifier was used with a 100 mu m tungsten wire placed inside the scanner at a slight angle to the plane perpendicular to the plane of interest and scanned. 200 contiguous reconstructed images were used to obtain the oversampling line-spread function (LSF). The MTF curve was obtained by computing the Fourier transformation from the oversampled LSF. Line pair tests were also performed using Catphan (R). Results: The oversampling method provided smooth and reproducible MTF Curves. The MTF Curves revealed that the spatial resolution in the Z-axis direction was significantly higher than that in the axial direction. This result was also confirmed by the line pair test. Conclusions: MTF analysis was performed successfully using the oversampling method. In addition, this Study clarified that the 3D Accuitomo had high spatial resolution, especially in the 7-axis direction. Dentomaxillofacial Radiology (2010) 39, 28-32. doi: 10.1259/dmfr/27069629
PURPOSE: To determine whether the improvement in intermediate vision after bilateral implantation of an aspheric multifocal intraocular lens (IOL) with a +3.00 diopter (D) addition (add) occurs at the expense of optic...
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PURPOSE: To determine whether the improvement in intermediate vision after bilateral implantation of an aspheric multifocal intraocular lens (IOL) with a +3.00 diopter (D) addition (add) occurs at the expense of optical quality compared with the previous model with a +4.00 D add. SETTING: Department of Ophthalmology, University of Sao Paulo, Sao Paulo, Brazil. DESIGN: Prospective randomized double-masked comparative clinical trial. METHODS: One year after bilateral implantation of Acrysof Restor SN6AD1 +3.00 D IOLs or Acrysof Restor SN6AD3 +4.00 D IOLs, optical quality was evaluated by analyzing the in vivo modulation transfer function (MTF) and point-spread function (expressed as Strehl ratio). The Strehl ratio and MTF curve with a 4.0 pupil and a 6.0 mm pupil were measured by dynamic retinoscopy aberrometry. The uncorrected and corrected distance visual acuities at 4 m, uncorrected and distance-corrected near visual acuities at 40 cm, and uncorrected and distance-corrected intermediate visual acuities at 50 cm, 60 cm, and 70 cm were measured. RESULTS: Both IOL groups comprised 40 eyes of 20 patients. One year postoperatively, there were no statistically significant between-group differences in the MTF or Strehl ratio with either pupil size. There were no statistically significant between-group differences in distance or near visual acuity. Intermediate visual acuity was significantly better in the +3.00 D IOL group. CONCLUSION: Results indicate that the improvement in intermediate vision in eyes with the aspheric multifocal +3.00 D add IOL occurred without decreasing optical quality over that with the previous version IOL with a +4.00 D add.
Many random media such as clouds and fog are often inhomogeneously distributed and often have a layered structure. This paper presents the effects of such inhomogeneities on the image transmission in terms of the modu...
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Many random media such as clouds and fog are often inhomogeneously distributed and often have a layered structure. This paper presents the effects of such inhomogeneities on the image transmission in terms of the modulation transfer function (MTF). We derive an expression of the MTF for a layered inhomogeneous medium using the small-angle approximation which is valid for size parameters of >10 and optical distances of <5. We obtain numerical results and compare them with experimental data for different particle sizes and concentrations showing good agreement. We also explain the shower curtain effect using the expression for the MTF.
modulation-transfer-function (MTF) measurement often involves the use of three- and four-bar resolution targets. In the conversion of three- and four-bar image data to MTF, biased results can occur when we use series-...
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modulation-transfer-function (MTF) measurement often involves the use of three- and four-bar resolution targets. In the conversion of three- and four-bar image data to MTF, biased results can occur when we use series-expansion techniques appropriate for square-wave targets of infinite extent. For systems where the image data are digitally recorded, a convenient and accurate conversion of bar-target data to MTF can be performed using a Fourier-domain method.
In blazed diffractive optics produced by the diamond turning process, the finite size of the tool determines the decrease in diffraction efficiency of the desired order. Diffracted light of other orders degrades the i...
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In blazed diffractive optics produced by the diamond turning process, the finite size of the tool determines the decrease in diffraction efficiency of the desired order. Diffracted light of other orders degrades the image quality. To analyze the influence of the tool, we evaluate diffraction efficiency and phase of periodic gratings based on the electromagnetic theory and calculate modulation transfer function using a linear system approach.
Segmented windows will degrade the modulation transfer function of high-acuity sensors unless the optical thicknesses of the individual panes are carefully matched.
Segmented windows will degrade the modulation transfer function of high-acuity sensors unless the optical thicknesses of the individual panes are carefully matched.
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