Mean-shape vector quantizer for ECG signal compression

A direct waveform mean-shape vector quantization (MSVQ) is proposed here as an alternative for electrocardiographic (ECG) signal compression. In this method, the mean values for short ECG signal segments are quantized as scalars and compression of the single-lead ECG by average beat substraction and residual differencing their waveshapes coded through a vector quantizer. An entropy encoder is applied to both, mean and vector codes, to further increase compression without degrading the quality of the reconstructed signals. In this paper, the fundamentals of MSVQ are discussed, along with various parameters specifications such as duration of signal segments, the wordlength of the mean-value quantization and the size of the vector codebook. The method is assessed through percent-residual-difference measures on reconstructed signals, whereas its computational complexity is analyzed considering its real-time implementation. As a result, MSVQ has been found to be an efficient compression method, leading to high compression ratios (CR's) while maintaining a low level of waveform distortion and, consequently, preserving the main clinically interesting features of the ECG signals. CR's in excess of 39 have been achieved, yielding low data rates of about 140 bps. This compression factor makes this technique especially attractive in the area of ambulatory monitoring.     

Liquefaction, Cyclic Mobility, and Failure of Silt

It is known that the mechanical properties of low-plasticity silt are similar to those of sand, and yet silts are frequently used as coastal reclamation materials in many cities and industrial areas and will thus be susceptible to liquefaction. Samples of a low-plasticity silt have been tested under monotonic and cyclic loading under isotropic and anisotropic stress conditions to characterize liquefaction, cyclic failure, and to develop an empirical model describing its cyclic strength. A sedimentation technique produced samples that had the highest susceptibility to liquefaction. Contractive behavior of monotonically loaded samples was triggered when the stress path reached an initial phase transformation (IPT) in both compression and extension tests. The samples became dilative after reaching a phase transformation (PT) point. The cyclic shear behavior of the silt samples prepared using the sedimentation method and consolidated at various initial sustained deviator stress ratios was examined in terms of two different failure criteria: a double amplitude axial strain εa,DA = 5% for reversal conditions; or axial plastic strain εa,P = 5% for nonreversal. For isotropically consolidated samples the initial phase transformation determined from undrained monotonic extension tests was the boundary between stable and contractive behavior. For anisotropically consolidated samples failure was defined by a bounding surface formed by undrained monotonic compression tests. An empirical model was developed relating the number of cycles to failure under conditions of both liquefaction and cyclic mobility to the initial anisotropic sustained deviator stress and cyclic deviator stress ratio.     

Diagnostic acceptability of FFT-based ECG data compression

There are three signal domains in which ECG data compression can be performed, namely time domain, frequency domain and parameter extraction. The present paper deals with the frequency domain method of compression using fast Fourier transform. The algorithm has been tested on the third set of the CSE database library. A performance evaluation has been made using two important parameters, namely compression ratio and percent root-mean-square difference besides visual comparison. Further, in order to know the clinical acceptable quality of the reconstructed signal peak, boundary and interval measurements were made both on the reconstructed and the original signal of the same record for comparison. The visual examination reveals that most of the noise in the original signal had been filtered out during the compression. This amounts to reduction of electromyographic noise to a considerable extent. The experimental observations show that a compression ratio of 8 is feasible while ensuring clinical acceptability.     

Acute pain and use of local anesthesia: tooth drilling and childbirth labor pain beliefs among Anglo-Americans, Chinese, and Scandinavians

Based on the premise that the QRS complex is also involved in reversible ischemia, we designed a computerized electrocardiographic method, that we have named Ventricular Ischemic Site Analysis (VISA). This method compares mean resting QRS to the QRS complex recorded during exercise or pharmacologic stress. The effect of ischemia on the electrical process of myocardial depolarization can be seen as a smaller slope in the QR and/or RS segment of the QRS signal, thus causing a local change in shape of the QRS. This method makes it possible to evaluate both the maximum entity of the change in shape and the time at which this occurs with reference to the beginning of the cycle. The VISA test was compared to SPECT and to the normal ECG stress test on a group of 53 patients who underwent a SPECT 99mTc-Sestamibi for suspected myocardial ischemia. Among the 39 patients confirmed as ischemic, the VISA test was positive in 37, while the ischemic alterations of the ST-T segment were observed in only 10 patients. According to this study, the sensitivity of the VISA test is comparable to the levels seen in SPECT. Moreover, this method demonstrates a trend towards localization of the ischemia in posterior or lateral sites when the shape change in localized in RS segment, and in anterior or infero-apical sites when the change is in QR segment. In addition to increasing sensitivity with respect to normal ECG stress tests, this method may also represent a new field of application for the ECG stress test, offering the possibility of localizing ischemic areas via simple computerized electrocardiography.     

Early experience of retrograde cerebral perfusion

Continuous records of arterial blood pressure can be obtained non-invasively with Finapres, even for periods of 24 hours. Increasingly, storage of such records is done digitally, requiring large disc capacities. It is therefore necessary to find methods to store blood pressure waveforms in compressed form. The method of selection of significant points known from ECG data compression is adapted. Points are selected as significant wherever the first derivative of the pressure wave changes sign. As a second stage recursive partitioning is used to select additional points such that the difference between the selected points, linearly interpolated, and the original curve remains below a maximum. This method is tested on finger arterial pressure waveform epochs of 60 s duration taken from 32 patients with a wide range of blood pressures and heart rates. An average compression factor of 4.6 (SD 1.0) is obtained when accepting a maximum difference of 3 mmHg. The root mean squared error is 1 mmHg averaged over the group of patient waveforms. Clinically relevant parameters such as systolic, diastolic and mean pressure are reproduced with an offset error of less than 0.5 (0.3) mmHg and scatter less than 0.6 (0.1) mmHg. It is concluded that a substantial compression factor can be achieved with a simple and computationally fast algorithm and little deterioration in waveform quality and pressure level accuracy.     

Identification of anovulation and transient luteal function using a urinary pregnanediol-3-glucuronide ratio algorithm

The sensitivity and specificity of a urinary pregnanediol-3-glucuronide (PdG) ratio algorithm to identify anovulatory cycles was studied prospectively in two independent populations of women. Urinary hormone data from the first group was used to develop the algorithm, and data from the second group was used for its validation. PdG ratios were calculated by a cycles method in which daily PdG concentrations indexed by creatinine (CR) from cycle day 11 onward were divided by a baseline PdG (average PdG/Cr concentration for cycle days 6-10). In the interval method, daily PdG/CR concentrations from day 1 onward were divided by baseline PdG (lowest 5-day average of PdG/CR values throughout the collection period). Evaluation of the first study population (n = 6) resulted in cycles with PdG ratios > or = 3 for > or = 3 consecutive days being classified as ovulatory; otherwise they were anovulatory. The sensitivity and specificity of the PdG ratio algorithm to identify anovulatory cycles in the second population were 75% and 89.5%, respectively, for all cycles (n = 88); 50% and 88.3% for first cycles (n = 40) using the cycles method; 75% and 92.2%, respectively, for all cycles (n = 89); and 50% and 94.1% for first cycles (n = 40) using the interval method. The "gold standard" for anovulation was weekly serum samples < or = 2 ng/ml progesterone. The sensitivity values for all cycles and for the first cycle using both methods were underestimated because of apparent misclassification of cycles using serum progesterone due to infrequent blood collection. Blood collection more than once a week would have greatly improved the sensitivity and modestly improved the specificity of the algorithm. The PdG ratio algorithm provides an efficient approach for screening urine samples collected in epidemiologic studies of reproductive health in women.     

干湿循环和含水率对尾砂压缩固结特性的影响研究

为辅助计算尾矿存积的沉降距离,指导放矿、尾矿子坝堆筑,提高尾矿坝的经济效益.研究干湿循环作用和含水率对湖南某金属尾矿库尾砂的压缩固结特性的影响.对含水率为10％、12％、14％、16％和18％的尾砂分别进行0～5次脱湿—吸湿—再脱湿试验,借助GZQ-1型全自动高压固结仪对试样开展了快速固结试验.研究结果表明:(1)相同...     

ECG processing techniques based on neural networks and bidirectional associative memories

Two ECG processing techniques are described for the classification of QRSs, PVCs and normal and ischaemic beats. The techniques use neural network (NN) technology in two ways. The first technique, uses nonlinear ECG mapping preprocessing and subsequently for classification uses a shrinking algorithm based on NNs. This technique is applied to the QRS/PVC problem with good result. The second technique is based on the Bidirectional Associative Memory (BAM) NN and is used to distinguish normal from ischaemic beats. In this technique the ECG beat is treated as a digitized image which is then transformed into a bipolar vector suitable for input in the BAM. The results show that this method, if properly calibrated, can result in a fast and reliable ischaemic beat detection algorithm.     

Non-invasive assessment of magnitude and dispersion of atrial cycle length during chronic atrial fibrillation in man

AIMS: Atrial fibrillation cycle lengths can be assessed from right precordial ECG leads and the unipolar oesophageal ECG using a non-invasive method called Frequency Analysis of Fibrillatory ECG. The purpose of this report is to present the results from application of this method in a large group of patients with long-term atrial fibrillation and to examine the differences between patients with 'coarse' and 'fine' atrial fibrillation. METHODS AND RESULTS: Simultaneous 15 min recordings from V1, V2 and an oesophageal lead at a position behind the posterior atrium were obtained in 28 patients, aged 41 to 78 years, with long-term (> 1 month) atrial fibrillation. In each lead, using the time averaging technique, the QRST complexes were suppressed. Thereafter, the frequency distribution of the residual ECG was estimated by means of Fast Fourier Transform. In the 3-12 Hz range of each lead, the dominant atrial cycle length, the power maximum and the spectral width were calculated. In 26 patients (93%), frequency spectra in the 3-12 Hz range could be obtained. The dominant atrial cycle length ranged from 120 to 175 ms, mean 150+/-16 (SD) ms in V1, and from 120 to 190 ms, mean 150+/-16 in an oesophageal lead (ns). The absolute difference in the dominant atrial cycle length between V1 and the oesophageal lead was 10.4+/-7.7 ms. There was no significant difference in the dominant atrial cycle length in V1 between patients with coarse and fine atrial fibrillation. The power maximum in V1 was significantly greater in patients with coarse compared to fine atrial fibrillation (P=0.01). The spectral widths ranged from 10 to 55 ms and demonstrated significantly higher mean values in lead V2 compared to V1 (P=0.001). Compared to V1, the mean values tended to be smaller in the oesophageal lead (P=0.05). CONCLUSIONS: Using the Frequency Analysis of Fibrillatory ECG method, the dominant atrial cycle length, power maximum and spectral width can be estimated from the frequency spectra in the majority of patients with atrial fibrillation. Spatial dispersion of the dominant atrial cycle length occurs in some patients and may be an important proarrhythmic marker. The distinction between coarse and fine atrial fibrillation cannot be used as a marker of the atrial cycle length.     

Structures appearing in roughened steel surfaces obtained by self-dewetting with electron beams

Heating and fast cooling of steel surfaces by means of a pulsed electron gun gives rise to peculiar structures characterized by a roughened surface due to spinodal self-dewetting and an intermediate region described as a heat-affected zone. In this work, numerical simulations of the heating of a steel surface by means of a pulsed electron gun are performed and contrasted with the experiments. The predictions of the depth of the melt pool and time elapsed above critical temperatures are used to interpret the experimental results. The combination of micrographs, cross sections, and numerical simulations allowed us to conclude that the instabilities giving rise to the dewetting structure are not related to vapor ejection. It is also concluded that the onset of the instability is a very fast process (on the order of at most a few microseconds), yielding a dewetting process that evolves in the entire melted pool, and that the spatial pattern scales with time elapsed above the melting temperature and the pool depth. The heat-affected zone (intermediate region) can now be understood to be where a solid-solid transformation occurs.     

Model based optimisation of highly automated industrial batch annealing operation

Abstract

Modern batch annealing operations are highly automated facilities, equipped with online sensors, model based control and a production management system to archive material, process and quality parameters. In these operations, efficient models and algorithms are used to allocate the resources, schedule the operation and design process cycles of individual stacks. The present work endeavours to enhance the productivity of a highly automated batch annealing facility, operating well above its rated capacity. This was achieved by intelligent analysis of production data and a critical assessment of the prevalent thermal model used for designing the process cycle of the individual stack. Two major limitations, namely, the inability to capture non-isothermal kinetics and the stiff radial conductivity model, of the prevalent thermal model were identified. These limitations were eliminated by designing process cycles with an integrated process model, where phase transformation kinetics is incorporated. Implementation of these process cycles has enhanced the productivity of the batch annealing operation by 7–9%. These benefits have been validated through rigorous laboratory experiments and plant trials.     

Improvement of the Shape Memory Effect in Fe‐based Alloys by Training

Shape recovery in iron‐based shape memory alloys is known to be incomplete. Thermomechanical cycling or training is recognized to improve the shape memory effect. In the present work, different aspects of training are studied: the number of cycles, the amount of deformation and the annealing temperature. As the number of cycles increases, the ? martensite plates become thinner and within the different grains they tend to align in the same direction. Still, different variants are present. XRD measurements showed a strong increase in the ? martensite volume from cycle 1 to cycle 2 and a slight decrease for further cycles. There exists an optimum deformation for obtaining stress induced ? martensite which is reversibly transformable to austenite during annealing. When the amount of deformation is too low, the fraction of stress induced ? martensite is very low, therefore, the shape memory effect is small. If the deformation is too large, slip may occur and different ? martensite variants are formed, which hinders the reverse ?→γ transformation. The recovery annealing temperature is critical for obtaining a good shape memory, especially during training. The recovery annealing temperature of 400°C is too low for completing the reverse transformation; annealing at 600°C is most commonly used.     

Interpretation of pooling experiments using the Markov chain Monte Carlo method

This paper describes an effective method for extracting as much information as possible from pooling experiments for library screening. Pools are collections of clones, and screening a pool with a probe determines whether any of these clones are positive for the probe. The results of the pool screenings are interpreted, or decoded, to infer which clones are candidates to be positive. These candidate positives are subjected to confirmatory testing. Decoding the pool screening results is complicated by the presence of errors, which typically lead to ambiguities in the inference of positive clones. However, in many applications there are reasonable models for the prior distributions for positives and for errors, and Bayes inference is the preferred method for ranking candidate positives. Because of the combinatoric complexity of the Bayes formulation, we implemented a decoding algorithm using a Markov chain Monte Carlo method. The algorithm was used in screening a library with 1298 clones using 47 pools. We corroborated the posterior probabilities for positives with results from confirmatory screening. We also simulated the screening of a 10-fold coverage library of 33,000 clones using 253 pools. The use of our algorithm, effective under conditions where combinatorial decoding techniques are imprudent, allows the use of fewer pools and also introduces needed robustness.     

A wavelet transform-based ECG compression method guaranteeing desired signal quality

This paper presents a new electrocardiogram (ECG) compression method based or orthonormal wavelet transform and an adaptive quantization strategy, by which a predetermined percent root mean square difference (PRD) can be guaranteed with high compression ratio and low implementation complexity.     

AZTDIS--a two-phase real-time ECG data compressor

An ECG sampled at a rate of 360 samples s-1 or more produces a large amount of redundant data that are difficult to store and transmit; we therefore need a process to represent the signals with clinically acceptable fidelity and with as small a number of code bits as possible. In this paper, a real-time ECG data-compression algorithm, AZTDIS, is presented. AZTDIS is an efficient algorithm which locates significant samples and at the same time encodes linear segments between them by using linear interpolation. The significant samples selected include, but are not limited to, the samples that have significant displacement from the encoded signal such that the allowed maximal error is limited to a constant epsilon, which is specified by the user. The way that AZTDIS computes the displacement of a sample from the encoded signal guarantees that the high activity regions are more accurately coded. The results from AZTDIS are compared with those from the well-known data-compression algorithm, AZTEC, which is also a real-time algorithm. It is found that under the same bit rate, a considerable improvement of root-mean-square error (RMSerr) can be achieved by employing the proposed AZTDIS algorithm. An average value of RMSerr of 9.715 can be achieved even at an average bit rate of 0.543 bits per sample by employing AZTDIS. By tuning the allowed maximal error of AZTDIS such that it has similar bit rate to AZTEC, the average value of RMSerr achieved by AZTDIS is 5.554 while the average value of RMSerr achieved by AZTEC under the same bit rate is 19.368.     

Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels

Theoretical and experimental investigations were carried out to determine the effect of process parameters on weld metal microstructures of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions. The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions investigated, the observed fusion zone structure ranged from duplex austenite (γ)+ferrite (δ) to fully austenitic or fully ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur. There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on the basis of the thermal cycles. The present investigation clearly demonstrated the potential of the computational model to provide detailed information regarding the heat transfer conditions experienced during welding.     

Spheroidization cycles for medium carbon steels

An investigation has been made of spheroidization of medium carbon steels used in the bolt industry. Two process cycles were considered. One was the intercritical cycle, widely used in industry, in which the steel was heated above the lower critical, A1, temperature for approximately 2 hours; then cooled below it; and held for various periods to allow the austenite to transform and carbides to spheroidize. The other process was a subcritical cycle, which involved heating to below the A1 for various times. Wire samples of two steels were studied: AISI 1541, which is high in manganese and considered difficult to spheroidize, and AISI 4037, which is considered easier to spheroidize and is used extensively in industrial applications. Both cycles produced similar drops in hardness. However, 1 hour of the subcritical cycle yielded greater ductility than 32 hours of the intercritical process, as measured by tensile tests. Results of a new flare test designed to evaluate formability also indicated much faster spheroidization in the subcritical cycle. The level of spheroidization was defined in this study to be the percentage of carbide particles with aspect ratios less than 3. In 30 minutes, the subcritical cycle produced the same percentage of particles with an aspect ratio of less than 3 as produced by the intercritical cycle in 32 hours. The fast spheroidization in the subcritical process is attributed to the fine pearlite generated by the current practice of rapid cooling off the hot mill. This advantage is lost in the intercritical process as the original pearlite is dissolved above the A1 temperature.     

Mutagenesis of the genes encoding subunits A, C, H, I, J and K of the plastid NAD(P)H-plastoquinone-oxidoreductase in tobacco by polyethylene glycol-mediated plastome transformation

Plastids contain a NAD(P)H-plastoquinone-oxidoreductase (NDH complex) which is homologous to the eubacterial and mitochondrial NADH-ubiquinone-oxidoreductase (complex I), but the metabolic function of the enzyme is unknown. The enzyme consists of at least eleven subunits (A-K), which are all encoded on the plastid chromosome. We have mutagenized ndhC and ndhJ by insertion, and ndhK and ndhA-I by deletion and insertion, of a cassette which carried a spectinomycin resistance gene as a marker. The transformation was carried out by the polyethylene glycol-mediated plastid transformation method. Southern analysis revealed that even after repeated regeneration cycles each of the four different types of transformants had retained 1-5% of wild-type gene copies. This suggests that complete deletion of ndh genes is not compatible with viability. The transformants displayed two characteristic phenotypes: (i) they lack the rapid rise in chlorophyll fluorescence in the dark after illumination with actinic light for 5 min; in the wild-type this dark-rise reflects a transient reduction of the plastoquinone pool by reduction equivalents generated in the stroma; and (ii) transformants with defects in the ndhC-K-J operon accumulate starch, indicating inefficient oxidation of glucose via glycolysis and the oxidative pentose phosphate pathway. Both observations support the theory of chlororespiration, which postulates that the NDH complex acts as a valve to remove excess reduction equivalents in the chloroplast.     

Tongue flicking in agamid lizards: morphology, kinematics, and muscle activity patterns

We wanted to examine whether a relation between foraging strategy, morphology, the mechanics of tongue protrusion, and prey chemical detection and discrimination exists in agamid lizards. Tongue-flick behavior was observed in two species of this family: Uromastix acanthinurus and Plocederma stellio. Potential prey chemical discrimination by means of tongue flicking was examined by using applicator tests. Tongue flicks were subsequently recorded by high-speed video in combination with the electrical activity of a number of jaw and hyolingual muscles. The kinematics of jaws and tongue and the muscle activity patterns were quantified. To investigate if the observed differences in tongue-flick behavior (mainly in the frequency of use) are translated into corresponding differences in tongue morphology, the tongues of both species were examined by light and scanning electron microscopy. The species differed mainly in the surface morphology of the foretongue and in the abundance and distribution of taste buds on the tongue and oral cavity. These differences can be related to behavioural observations; whereas U. acanthinurus readily uses tongue flicks to detect and discriminate between food items, P. stellio does not. However, differences in tongue-flick mechanics (kinematics, electromyograms) between both species were minor. Based on the data gathered in this study and from previously published data, an evolutionary transformation series leading to the complex tongue-flick cycles as observed in snakes is proposed. The required morphological and mechanical changes that accompany such an evolutionary sequence are discussed.