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At least 235 records · Page 13Linked to original sources
PubMed2000

Time-frequency analysis of myoelectric signals during dynamic contractions: a comparative study.

In this paper, we introduce the nonstationary signal analysis methods to analyze the myoelectric (ME) signals during dynamic contractions by estimating the time-dependent spectral moments. The time-frequency analysis methods including the short-time Fourier transform, the Wigner-Ville distribution, the Choi-Williams distribution, and the continuous wavelet transform were compared for estimation accuracy and precision on synthesized and real ME signals. It is found that the estimates provided by the continuous wavelet transform have better accuracy and precision than those obtained with the other time-frequency analysis methods on simulated data sets. In addition, ME signals from four subjects during three different tests (maximum static voluntary contraction, ramp contraction, and repeated isokinetic contractions) were also examined.

Action Potentials↗
PubMed1978

Control of Thylakoid Growth in Phaseolus vulgaris.

An attempt was made to answer whether the extent of thylakoid growth in Phaseolus vulgaris is controlled by a feedback inhibition mechanism, operating after insertion of all of the necessary components of the mature thylakoid, in the right amounts and ratio, or by parameters independent of the developmental stage of the membrane. This was done by following the growth of thylakoids, as monitored by the rate of chlorophyll accumulation and the rate of thylakoid protein synthesis, in etiolated plants exposed either directly to continuous light (transformation of prolamellar body to mature thylakoid) or first to periodic light and then to continuous light (transformation of prolamellar body to primary thylakoids and then to mature thylakoids). It was found that prolonged etiolation has no effect on the rate of thylakoid synthesis in continuous light. However, prolonged preexposure to periodic light diminishes drastically the rate of new thylakoid synthesis in continuous light. Since the thylakoids formed in the latter case are far from being complete, it seems that thylakoid growth can stop long before all of the necessary components are incorporated. Parameters independent of the developmental stage and composition of the membrane, therefore, seem to control membrane growth.

Journal Article↗
PubMed1992

[Echo-Doppler evaluation of the internal mammary artery bypass on the left coronary artery: a 4-year follow-up].

In this study ultrasonographic techniques are suggested to monitor internal mammary artery bypass graft on the anterior descending coronary artery. One hundred and fourty patients were studied using 3 different ultrasonographic methods: zero-crossing continuous wave Doppler, fast Fourier transform (FFT) continuous wave Doppler and high resolution echo-Doppler. The patients underwent the ultrasonographic examinations 3 times a year for 4 years. By means of FFT Doppler analysis and echo-Doppler it was possible to perform the study in 138 patients and by zero-crossing system in 127 patients. Ultrasonographic techniques showed pathologies of the graft in 17 (13%) patients: 15 with obstructive pathologies and 2 with haemodetournament of the second intercostal artery.

Adult↗
PubMed1979

Continuous lines of RSV-transformed embryo cells and peritoneal macrophages of Japanese quails.

Four continuous lines of RSV-transformed quail cells were established; QERC-31F and QERC-31N cells derived from quail embryo cells and PERP and PERY cells from adult quail peritoneal macrophages. Marked morphological difference was noted between QERC-31F and QERC-31N; the former showed fusiform shape and the latter nodular shape. Both PERP and PERY showed macrophage-like morphology with phagocytic capacity. All four cell lines contained gs antigen and gp 85. Production of transforming virus was found in QERC-31N, PERP and PERY. In spite of failure in production of transforming virus, EQRC-31F was demonstrated to produce C-type particles by electron microscopy and to contain tumor-specific surface antigen by in vivo immunization and in vitro microcytotoxicity tests.

Animals↗
PubMed1988

Dibutyryl cAMP inhibits expression of transformation-related properties in Kirsten murine sarcoma virus transformed Balb/c-3T3 cells despite continued presence of p21v-Ki-ras.

We studied the effects of simultaneous treatment with 0.1 mM N6, O2'-dibutyryl cAMP (dbcAMP) and 1 mM theophylline on several transformation-specific properties and on levels of the Kirsten murine sarcoma virus (Ki-MSV) transforming gene product p21v-Ki-ras, in a Ki-MSV-transformed mouse cell line (Balb/c-3T3, clone A31; KA31). The rate of logarithmic growth, cell motility, and final saturation density were reduced in dbcAMP-treated KA31 cultures. Capabilities for anchorage-independent growth were reduced in treated cells, to levels similar to those observed for the untransformed parental A31 cell line. Treatment with dbcAMP had no observable effect on the binding of 125I-labeled epidermal growth factor and did not alter fluorescence staining patterns for actin microfilaments and fibronectin which, although characteristic of normal cells, were also present in KA31 cells. Changes induced by dbcAMP were readily reversible, except for loss of anchorage-independent growth. However, this property was also reversible, provided removal of dbcAMP occurred 48 h prior to inoculation into soft agar medium. Immunoprecipitation with a monoclonal antibody directed against the protein p21v-Ki-ras (Y13-259) revealed the continued presence of this protein in dbcAMP-treated KA31 cells. We, therefore, conclude that cAMP mediates the inhibition of growth-related transformation-specific properties either by acting at steps subsequent to the expression of p21v-Ki-ras or on a pathway independent of p21ras function.

Actins↗
PubMed2005

Discovery of gradient pattern in dominant frequency maps during fibrillation: implication of rotor drift and epicardial conduction velocity changes.

Dominant frequency (DF) maps for mapping epicardial activations of ventricular fibrillation (VF) have been studied mainly using fast Fourier transform (FFT). Small and discrete DF domains exhibited in these DF maps have undermined the hypothesis of mother rotor for VF maintenance. We applied continuous Fourier transform (CFT) to generate high-precision DF maps and studied characteristics of these high-precision DF maps. Optical epicardial activations were recorded in isolated rabbit hearts (n=10). Continuous Fourier transform of 1-second segments was performed in VF (n=188) and ventricular tachycardia (n=189) at 0.1 Hz precisions. Banded gradient patterns of gradual change in DF values were observed in 136 of 188 VF segments, but not in ventricular tachycardia. These gradients were not observed when FFT was used. Gradients were observed along the conduction path of reentrant-like waves with decreasing DF values along the path. Spectra in the gradients did not exhibit bimodal spectra as is usually observed in traditional DF domain boundaries. Time-space plots revealed clear association between gradient pattern and epicardial conduction velocity changes. Prior simulation studies predicted a gradient in activation rate during rotor drift. This gradient pattern has been observed for the first time experimentally by only using CFT, but not FFT. High-precision DF videos indicated the existence of gradient movement from one spatial location to another, smoothly instead of randomly disappearing from one location and appearing in another. The discovery of associated pseudoconduction velocity changes, and gradient patterns might suggest that dominant rotor (mother rotor) drifting plays a maintenance role only detectable by CFT and not FFT.

Animals↗
PubMed2005

Resolution enhancement of composite spectra using wavelet-based derivative spectrometry.

An approach based on the using of the continuous wavelet transform (CWT) in derivative spectrometry (DS) is considered. Within the framework of the approach we develop a numerical differentiation algorithm with continuous wavelets for improving resolution of composite spectra. The wavelet-based derivative spectrometry (WDS) method results in best contrast in differential curves compared to the conventional derivative spectrometry method. A main advantage is that, as opposed to DS, WDS gives stable estimations of derivative in the wavelet domain without using the regularization. A wavelet shape and the information redundancy are of the greatest importance when the continuous wavelet transform is used. As an appropriate wavelet we offer to utilize the nth derivative of a component with a priori known shape. The energy distribution into scales allows one to determine a unique wavelet projection and in that way to avoid the information redundancy. A comparative study of WDS and DS with the statistical regularization method (SRM) is made; in particular, limits of applicability of these are given. Examples of the application of both DS and WDS for improving resolution of synthetic composite bands and real-world composite ones coming from molecular spectroscopy are given.

Algorithms↗
PubMed2003

Scanning probe microscopy with landmark referenced control for direct biological investigations.

We report the successful use of continuous wavelet transforms applied to atomic force microscope data sets for landmark recognition of biological features. The data sets were images of mixed red and white blood cells. Contrast enhancement followed by continuous wavelet transform of the data was used to successfully distinguish erythrocytes from neutrophil and monocyte leukocytes within the mixed cell images. All of the above are spherical objects between 6 and 8 microns in diameter, which demonstrates the ability to sort similar biological objects into distinct classes. The implications for development of on-line scanning probe recognition microscopy are discussed.

Algorithms↗
PubMedDate not supplied

Application of the wavelet method for the simultaneous quantitative determination of benazepril and hydrochlorothiazide in their mixtures.

The discrete and continuous wavelet transforms were applied to the overlapping signal analysis of the ratio data signal for simultaneous quantitative determination of the title subject compounds in samples. The ratio spectra data of the binary mixtures containing benazepril (BE) and hydrochlorothiazide (HCT) were transferred as data vectors into the wavelet domain. Signal compression, followed by a 1-dimension continuous wavelet transform (CWT), was used to obtain coincident transformed signals for pure BE and HCT and their mixtures. The coincident transformed amplitudes corresponding to both maximum and minimum points allowed construction of calibration graphs for each compound in the binary mixture. The validity of CWT calibrations was tested by analyzing synthetic mixtures of the investigated compounds, and successful results were obtained. All calculations were performed within EXCEL, C++, and MATLAB6.5 softwares. The obtained results indicated that our approach was flexible and applicable for the binary mixture analysis.

Algorithms↗
PubMed2001

Wavelet-based edge detection in ultrasound images.

We introduce a new wavelet-based method for edge detection in ultrasound (US) images. Each beam that is analyzed is first transformed into the wavelet domain using the continuous wavelet transform (CWT). Because the CWT preserves both scale and time information, it is possible to separate the signal into a number of scales. The edge is localized by first determining the scale at which the power spectrum, based on the wavelet transform, has its maximum value. Next, at this scale we find the position of the peak for the squared CWT. This method does not depend on any threshold, after the range of scales have been determined. We suggest a range of scales for US images in general. Sample edge detections are demonstrated in US images of straight and jagged edges of simple structures submerged in water bath, and of an abdominal aorta aneurysm phantom.

Algorithms↗
PubMed1983

Improved lymphocyte transformation in vitro of patients on continuous ambulatory peritoneal dialysis.

In vitro lymphoblastic transformation and sensitivity to methylprednisolone (MP) was studied in lymphocyte cultures obtained from patients on continuous ambulatory peritoneal dialysis (CAPD), on haemodialysis (HD) and control subjects. The PHA and Con A responses of peripheral blood lymphocytes (PBL) and T cells were identical in CAPD and control cultures, and in both significantly higher than in HD cultures (p less than 0.05). Both PBL and T cells from CAPD and control cultures were more resistant to the suppressive effects of MP than those from HD cultures. There was no relation between the duration of the dialysis period and the lymphocyte mitogen response in HD patients. Enhanced in vitro cell transformation and resistance to steroids during CAPD treatment may reflect an improved form of dialysis of importance for the general immune defence of the uraemic patient.

Adult↗
PubMed1987

Development of three-dimensional form perception.

In three experiments with infants and one with adults we explored the generality, limitations, and informational bases of early form perception. In the infant studies we used a habituation-of-looking-time procedure and the method of Kellman (1984), in which responses to three-dimensional (3-D) form were isolated by habituating 16-week-old subjects to a single object in two different axes of rotation in depth, and testing afterward for dishabituation to the same object and to a different object in a novel axis of rotation. In Experiment 1, continuous optical transformations given by moving 16-week-old observers around a stationary 3-D object specified 3-D form to infants. In Experiment 2 we found no evidence of 3-D form perception from multiple, stationary, binocular views of objects by 16- and 24-week-olds. Experiment 3A indicated that perspective transformations of the bounding contours of an object, apart from surface information, can specify form at 16 weeks. Experiment 3B provided a methodological check, showing that adult subjects could neither perceive 3-D forms from the static views of the objects in Experiment 3A nor match views of either object across different rotations by proximal stimulus similarities. The results identify continuous perspective transformations, given by object or observer movement, as the informational bases of early 3-D form perception. Detecting form in stationary views appears to be a later developmental acquisition.

Adult↗
PubMed2006

Blastula wall invagination examined on the basis of shape behavior of vesicular objects with laminar envelopes.

A complete description of the blastula shape transformations which occur in the process of gastrulation involves the mechanics of the blastula wall. It is inferred that the mechanical properties of this wall can, to a first approximation, be described in terms of elastic deformational modes which are equivalent to those of simple vesicular systems such as phospholipid vesicles and red blood cells. For membranes composed of an arbitrary number of aligned, laterally unconnected thin layers, these are area expansivity and local and non-local bending. Stable shapes of vesicular objects with laminar envelopes are defined as shapes which correspond to the minimum of the system elastic energy. The shape behavior of these objects is briefly reported. The criterion for the stability of the spherical shape of a vesicular object is derived. In particular we analyze the shape transition from a sphere to an invaginated gastrula. Conditions are demonstrated under which this shape transition can occur through a series of continuous shape transformations. A possible example of such a shape transformation is given. The blastula wall of the sea urchin is modeled as a closed laminar membranous system with three layers, the monocellular epithelial sheet and the extracellular apical lamina and hyaline layers. Experimentally measured elastic constants of some of these layers are shown to be in accord with the restrictions on their values imposed by the requirement for continuous shape transformations.

Animals↗
PubMed2000

Wavelet analysis and time-frequency distributions of the body surface ECG before and after angioplasty.

In a pilot study, electrocardiographic (ECG) recordings of patients with left and right coronary stenosis taken before and after angioplasty were analyzed using the continuous wavelet transform. Time-frequency distributions were obtained for different leads in order to examine the dynamics of the QRS-spectrum and establish features specific of ischemia in the time-frequency domain. We found relevant changes in the mid-frequency range, reflecting the ECG's response to percutaneous transluminal coronary angioplasty (PTCA). The changes appeared in ECG leads close to ischemic zones of the myocardium. Time-frequency distributions of the ECG during the QRS may thus become another electrocardiographic indicator of ischemia, alternative to ST-level in standard ECG or body surface mapping. The paper demonstrates the ability of the continuous wavelet transform to detect short lasting events of low amplitude superimposed on large signal deflections.

Angioplasty, Balloon, Coronary↗
PubMed2005

Stopped-flow Fourier transform infrared spectroscopy allows continuous monitoring of azide reduction, carbon monoxide inhibition, and ATP hydrolysis by nitrogenase.

Stopped-flow FTIR spectroscopy was used to monitor continuously the pre-steady- and steady-state phases of azide reduction by nitrogenase and the accompanying hydrolysis of ATP. This was characterized by a ca. 1.3 s lag phase that is explained by the number of Fe protein cycles required to effect the reductions of azide to N(2) + NH(3), N(2)H(4) + NH(3), or 3NH(3). Extrapolation of the steady-state time course for azide reduction to zero time showed that one azide binds within 200 ms to each FeMo cofactor. Inhibition of azide reduction by CO was established at times <400 ms, which was faster than the appearance of the first observable IR band assigned to CO (1904 cm(-)(1) detectable at ca. 1 s with maximum amplitude at ca. 7 s). IR bands associated with the rapidly formed (<400 ms) CO species that inhibits azide reduction were not observed over the range 1700-2100 cm(-)(1). This suggests either that the CO is initially bridging two or more Fe atoms or that a rapid reduction of CO to a formyl state occurs by insertion into a metal-hydride bond. The frequencies and time courses for the appearance and loss of the CO bands under hi- and lo-CO conditions were essentially unaffected by the presence of 20 mM azide, consistent with CO being a noncompetitive inhibitor of azide reduction and with azide and CO binding to different sites on the FeMo cofactor.

Adenosine Diphosphate↗
PubMed1995

The size and continuity of DNA segments integrated in Bacillus transformation.

We investigated the size and continuity of DNA segments integrated in Bacillus subtilis transformation. We transformed B. subtilis strain 1A2 toward rifampicin resistance (coded by rpoB) with genomic DNA and with a PCR-amplified 3.4-kb segment of the rpoB gene from several donors. Restriction analysis showed that smaller lengths of donor DNA integrated into the chromosome with transformation by PCR-amplified DNA than by genomic DNA. Nevertheless, integration of very short segments (< 2 kb) from large, genomic donor molecules was not a rare event. With PCR-amplified segments as donor DNA, smaller fragments were integrated when there was greater sequence divergence between donor and recipient. There was a large stochastic component to the pattern of recombination. We detected discontinuity in the integration of donor segments within the rpoB gene, probably due to multiple integration events involving a single donor molecule. The transfer of adaptations across Bacillus species may be facilitated by the small sizes of DNA segments integrated in transformation.

Bacillus subtilis↗