We present an automatization of Barnsley's manual algorithm for the solution of the inverse problem of iterated function systems (IFSs). The problem is to retrieve the number of mappings and the parameters of an I...
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We present an automatization of Barnsley's manual algorithm for the solution of the inverse problem of iterated function systems (IFSs). The problem is to retrieve the number of mappings and the parameters of an IFS from a digital binary image approximating the attractor induced by the IFS. Barnsley et al. described a way to manually solve the inverse problem by identifying the fragments, of which the collage is composed, and then computing the parameters of the mappings. The automatic algorithm searches through a finite set of points in the parameter space determining a set of affine mappings. The algorithm uses the collage theorem and the Hausdorff metric. The inverse problem of IFSs is related to image coding of binary images. If the number of mappings and the parameters of an IFS, with not too many mappings, could be obtained from a binary image, then this would give an efficient representation of the image. It is shown that the inverse problem solved by the automatic algorithm has a solution and some experiments show that the automatic algorithm is able to retrieve an IFS, including the number of mappings, from a digital binary image approximating the attractor induced by the IFS.
An automatic, adaptive, correlation-based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of...
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An automatic, adaptive, correlation-based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re-analyze waveforms manually or semi-automatically. We apply this technique to induced seismicity at the Soultz-sous-Forets geothermal site, France. The method is first applied to a small, previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking, visual, cross-correlation-based techniques. Relative centroid-adjusted hypocenters show a decrease in median mislocation from 31 to 7 m for preliminary and automatically adjusted picks, respectively, compared to the manual results. Narrow, intersecting joint features not observed in the preliminary hypocenter cloud, but revealed through manual repicking, are also recovered using the automatic method. We then address a larger catalogue of similar to7000 microearthquakes. After relocating the events using automatic repicks, the percentage of events clustering within 5 m of their nearest neighbor increases form 5 to 26% of the catalogue. Hypocenter relocations delineate narrow, linear features previously obscured within the seismic cloud, interpreted as faults or fractures which may correspond to fluid propagation paths, or to changes in stress as a result of elevated pore pressures. RMS travel-time residuals for the larger data set are reduced by only 0.2%;however, phase-pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations, which will affect location residuals. These pick biases are apparent on the adjusted, stacked waveforms and correcting them will be important prior to future velocity model refinements.
In this paper, we propose an automatic algorithm for estimating objects depth using f-k migration and velocity scanning method for the homogeneous medium. Experimental results show that the relative estimating error o...
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ISBN:
(纸本)078037536X
In this paper, we propose an automatic algorithm for estimating objects depth using f-k migration and velocity scanning method for the homogeneous medium. Experimental results show that the relative estimating error of depth is as low as 10%.
Background: Although prolonged duration of the signal-averaged (SA) P wave has been proposed as a noninvasive marker of atrial arrhythmias, clinical value of atrial SAECG is limited largely due to the difficulty with ...
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Background: Although prolonged duration of the signal-averaged (SA) P wave has been proposed as a noninvasive marker of atrial arrhythmias, clinical value of atrial SAECG is limited largely due to the difficulty with detection of the onset and offset of the high gain P wave. The aim of this study was to assess the reliability of automatic measurement of the atrial SAECG. Methods: Fifty-one healthy volunteers (30 men;32 ± 8 years) underwent a session of 3 atrial and 3 ventricular SAECG recordings. automatically detected onset and offset of SA QRS complex (QRS(tot)) and SA P wave (P(tot)) were subsequently corrected by two independent observers. For ventricular SAECG, three conventional time-domain parameters were calculated. For atrial SAECG, the following five parameters were measured: P(tot), root mean square voltages of the entire P(tot) (RMS-P) and of the terminal 40, 30, and 20 ms of P(tot). Relative errors of the different pairs of measurements were used to assess the interobserver and observer-computer variability. The Bland-Altman method was applied to express the agreement between measurements. Results: Although the mean interobserver relative errors were low for QRS(tot) and P(tot) (1.1% vs 1.5%), the observer-computer error was significantly higher for P(tot) than for QRS(tot) (1.7% vs 7.1%;P < 0.0001). For the voltage parameters, the lowest interobserver and observer-computer relative errors were found for RMS-P (6.6% vs 7.3%, P = ns). For RMS voltages of the terminal 40-20 ms of P(tot), relative errors exceeded 10%, but the interobserver error was significantly lower than the observer-computer error (P < 0.0001). Conclusion: automatic detection of the SA P-wave onset and offset is unreliable and the atrial SAECG requires manual correction. Given a good interobserver agreement, such a correction is unlikely to introduce any significant observer-dependent bias.
Background. This study assesses the feasibility of Tc-99m-labeled sestamibi electrocardiographic gated single-photon emission computed tomography (SPECT) with a short acquisition time (6.7 minutes, ''fast'...
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Background. This study assesses the feasibility of Tc-99m-labeled sestamibi electrocardiographic gated single-photon emission computed tomography (SPECT) with a short acquisition time (6.7 minutes, ''fast'' gated SPECT) for the evaluation of stress myocardial perfusion and poststress myocardial function. Simultaneous assessment of stress perfusion and poststress function is possible with standard gated SPECT acquisition (19.3 minutes) of stress-injected sestamibi. Sestamibi gated SPECT can be used to evaluate regional wall motion (PWM), thickening, and left ventricular ejection fraction (LVEF);the feasibility of fast gated SPECT has not been evaluated previously. Methods and Results. Fifty patients were studied who underwent treadmill exercise, sestamibi injection (25 to 30 mCi), and standard gated SPECT 15 minutes after exercise, immediately followed by fast gated SPECT. All patients underwent rest (TI)-T-201 SPECT before exercise testing. All studies were analyzed by semiquantitative visual scoring. Both standard and fast gated SPECT were read for stress perfusion and poststress wall motion and thickening, dividing the left ventricle into 20 segments, on a 5-point scale described previously. The measurement of LVEF used a previously described automatic algorithm. Average myocardial counts per pixel were 58 +/- 19 for standard gated SPECT and 13 +/- 4 for fast gated SPECT (p = 0.0001). Heart/lung ratio was 10.2 +/- 4.8 for regular gated SPECT and 10.3 +/- 5.7 for fast gated SPECT (difference not significant). Perfusion analysis showed exact agreement in 92% of the segments (kappa = 0.76;p < 0.01). Correlation between LVEFs measured from standard and fast gated SPECT was 0.94. Analysis of 998 segments (two segments were uninterpretable) showed exact agreement in 96% (kappa = 0.89;p < 0.001) for RWM and 94% (kappa = 0.83;p < 0.001) for thickening between standard and fast gated SPECT. In 225 segments with abnormal RWM and 189 segments with abnormal thickening by both
A personal computer-based technique was developed that reduces the extent of human efforts in obtaining data, like numerical density of profiles on area, describing the distribution of specific features of histologica...
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A personal computer-based technique was developed that reduces the extent of human efforts in obtaining data, like numerical density of profiles on area, describing the distribution of specific features of histological sections, e.g., density of synaptic profiles or of histochemical reaction products in specified tissue compartments. The procedure consists of (i) marking the objects to be counted, (ii) recording the borderlines of (reference) tissue domains of interest, and (iii) allocating the marked objects to the corresponding domains automatically. This automatic sorting of objects into defined tissue domains is achieved by an algorithm operating on two sets of coordinates: (i) coordinates of points that constitute the boundary of tissue domains (perimeter points) and (ii) coordinates of points marking the particular objects to be sorted. The principle of the sorting calculation is to construct 'segments' of the loop by lines parallel to the ordinate which pass through neighbouring perimeter points. The 'items' to be sorted are classified by the sign of marker flags allocated to each point depending on which side of the perimeter segment they are located. Segmentation and classification procedures are sequentially repeated along the entire perimeter of each domain specified by the operator which may result during the procedure in multiple changes of the sign of the flags. The internal or external location of each item finally is represented by the last sign of its flag. Objects, allocated to domains can be counted and processed further for numerical density determination.
Two automatic programs for solving linear Fredholm integral equations of the second kind are described and illustrated. It is assumed that the kernel function and solution are smooth and that they are given analytical...
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