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Results for “Curvature”

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At least 19 recordsLinked to original sources

PubMed1988

Piezoelectric polymer curvature sensor for measurement of regional curvature radius of LV wall.

To evaluate regional myocardial function, we developed a curvature sensor for direct and instantaneous measurement of the regional curvature radius of the LV wall. The sensor is a bimorph of two sheets of thin piezoelectric polymer film. The relation between output voltage of the sensor and the reciprocal of the known curvature radius has been shown to be linear. In anesthetized dogs, we inserted the curvature sensor into the subepimyocardium with a specially designed introducer. Special care was taken to insert it parallel to the epicardial surface. Circumferential regional curvature radius, which is defined as the reciprocal of regional curvature, showed the same phasic changes as the short-axis diameter under control conditions. Under regional ischemia caused by transient occlusion of the coronary artery, amplitude of the phasic change in regional curvature radius decreased, whereas that of the short-axis diameter did not change or slightly increased. Phasic changes in regional curvature radius cannot be estimated from short-axis diameter during regional ischemia. We calculated regional wall tension from the directly measured regional curvature radius and LV pressure and found that tension-length loop clearly differentiates between regional myocardial function under control and ischemic conditions. We have concluded that our newly developed curvature sensor is accurate, that its practical use is feasible, and that measurement of the regional curvature radius of the LV wall provides detailed and accurate information on regional shape and function of the left ventricle.

Animals↗

PubMed1989

Visual perception of surface curvature: psychophysics of curvature detection induced by motion parallax.

The continuous approach to optic-flow processing shows that the curvature of a moving surface is related to a second spatial derivative of the velocity field, the spin variation (Droulez & Cornilleau-Pérès, 1989). With this approach as a theoretical framework, visual sensitivity to the curvature of a cylinder in motion was measured using a task of discrimination between cylindrical and planar patches. The results confirm the predictions suggested by the theory: (1) Sensitivity to curvature was always greater when the cylinder axis and the frontal translation were parallel than when they were orthogonal. The ratio of curvature detection thresholds in the two cases was between 1.3 and 2.5; the value predicted from the spin variation theory is about 2. (2) Sensitivity to curvature increased strongly with the velocity of the motion but was only weakly affected by its amplitude and the duration of viewing for the range of values used in our experiments.

Adult↗

PubMed1999

Mathematical modelling of morphogenesis in fungi: a key role for curvature compensation ('autotropism') in the local curvature distribution model.

The assumption that the mushroom stem has the ability to undergo autonomic straightening enables a mathematical model to be written that accurately mimics the gravitropic reaction of the stems of Coprinus cinereus. The straightening mechanism is called curvature compensation here, but is equivalent to the 'autotropism' that often accompanies the gravitropic reactions of axial organs in plants. In the consequently revised local curvature distribution model, local bending rate is determined by the difference between the 'bending signal' (generated by gravitropic signal perception systems) and the 'straightening signal' (proportional to the local curvature at the given point). The model describes gravitropic stem bending in the standard assay with great accuracy but has the virtue of operating well outside the experimental data set used in its derivation. It is shown, for example, that the mathematical model can be fitted to the gravitropic reactions of stems treated with metabolic inhibitors by a change of parameters that parallel the independently derived physiological interpretation of inhibitor action. The revised local curvature distribution model promises to be a predictive tool in the further analysis of gravitropism in mushrooms.

Calcimycin↗

PubMed1985

[The sagittal curvature of spine in idiopathic scoliosis--its morphological features and the correlation among sagittal and frontal curvatures and rotation of apical vertebra].

The change in sagittal curvature especially in thoracic kyphosis of idiopathic scoliosis patients, was analyzed and discussed. Those patients who had scoliotic deformity with typical vertebral rotation only in thoracic spine (ST group), showed significant decrease compared to normal person in thoracic kyphosis, but no difference in lumbar lordosis. Those suffering from scoliotic deformities with typical vertebral rotation in thoracic and lumbar spine showed a significant decrease in thoracic kyphosis and an increase in lumbar lordosis. However those changes in sagittal curvature were not found in FT group patients, who had scoliotic deformity without vertebral rotation. In conclusion, it is not the frontal curvature but the vertebral rotation which influenced the sagittal curvature of spine in patients with idiopathic scoliosis.

Adolescent↗

PubMed1980

Correction of 3 types of congenital curvatures of the penis, including the first reported case of dorsal curvature.

Herein is described treatment of 3 patients with different types of congenital penile curvature. The first reported case of correction of congenital dorsal curvature was accomplished by longitudinal closure of transverse incisions in the dorsal tunica albuginea, thus lengthening the concave dorsal aspect of the penis. The use of preoperative, intraoperative and postoperative photographs is advocated as well as the use of injected heparinized saline for penile turgidity to assess the severity of the curvature. The operation has yielded excellent results, and is safe and simple to perform. A familial predilection was noted in 2 patients.

Adult↗

PubMed1996

On measuring curvature and electrical diffusion coefficients in anisotropic myocardium: comments on "effects of bipolar point and line simulation in anisotropic rabbit epicardium: assessment of the critical radius of curvature for longitudinal block".

Notion of "curvature" and "propagation perpendicular to the activation front" inherited from electrophysiological theory of isotropic reaction-diffusion media do not apply directly to experimental data taken in uniformly anisotropic myocardium. They apply directly only after the concept of "curvature" is normalized and propagation is made to look perpendicular to activation fronts by rescaling distances to achieve isotropy. Without rescaling, the curvature-dependence of longitudinal propagation speed turns out counter-intuitively to measure transverse intercellular electrical coupling.

Action Potentials↗

PubMed1990

Wall extensibility and gravitropic curvature of sunflower hypocotyls: correlation between timing of curvature and changes in extensibility.

Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates could be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower (Helianthus annuus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.

Cell Division↗

PubMed2002

Simultaneous determination of curvature, plane of curvature, and temperature by use of a miniaturized sensing head based on fiber Bragg gratings.

We present what we believe to be a novel miniaturized sensor configuration based on fiber Bragg gratings for simultaneous measurement of curvature and temperature in smart structures and composite materials. Because of the particular geometry of the sensing head, it is possible not only to measure the radius of curvature but also to determine the plane of curvature. We arrange three Bragg gratings in the vertices of the smallest equilateral triangle that can be defined by the cross sections of the fibers. The set is then inserted into a glue-filled capillary stainless-steel tube to provide both suitable protection for the Bragg sensors and rotational symmetry to the sensing head. This tube also ensures isolation from axial strain, allowing for the additional determination of temperature. The proposed sensing head is particularly well suited for applications in smart structures because it can be embedded along any layer of a composite material (including the neutral line) without special concern for the relative orientation of the Bragg gratings and the composite layers. We can also use this sensing configuration to implement more-sophisticated sensors dedicated, for example, to the measurement of multiaxial acceleration or flow and temperature.

Journal Article↗

PubMed2006

Bayesian algorithms for PET image reconstruction with mean curvature and Gauss curvature diffusion regularizations.

The basic mathematical problem behind PET is an inverse problem. Due to the inherent ill-posedness of this inverse problem, the reconstructed images will have noise and edge artifacts. A roughness penalty is often imposed on the solution to control noise and stabilize the solution, but the difficulty is to avoid the smoothing of edges. In this paper, we propose two new types of Bayesian one-step-late reconstruction approaches which utilize two different prior regularizations: the mean curvature (MC) diffusion function and the Gauss curvature (GC) diffusion function. As they have been studied in image processing for removing noise, these two prior regularizations encourage preserving the edge while the reconstructed images are smoothed. Moreover, the GC constraint can preserve smaller structures which cannot be preserved by MC. The simulation results show that the proposed algorithms outperform the quadratic function and total variation approaches in terms of preserving the edges during emission reconstruction.

Algorithms↗

PubMed1995

Study of the lumbar curvature with various factors of pelvic inclination. Change of radiographic lumbar curvature according to hip joint flexion.

The objective of this study was to investigate the influence of the hip flexion upon parameters that are indicators of spinal mobility. These parameters include intervertebral disc angle and lumbar curvature by measurement of the radiography in twenty eight healthy men. The state of knowledge of how these parameters relate to lumbar mobility have resolved. The results of the parameters showed negligible changes in relation to the mobility of lumbar spine according to angle of hip flexion except at L4-L5 intervertebral disc angle and lumbar curvature (p < 0.05). This results of study confirms that hip joint movement therapy can be applied to these norms in patient management in supine position of for the stable spinal injuries in the upper lumbar region during early phase.

Adult↗

PubMedDate not supplied

[Congenital penile curvature (chordee without hypospadias): surgical treatment for correction of penile curvature and/or buccal mucosal graft urethroplasty].

Presented are the cases of 19 boys with ventral penile curvature without hypospadias. The cases were categorised into three groups according to the severity of the anomaly. In group I were 7 boys with ventral penile curvature affecting the shortening of the frenulum with skin tethering. The anomaly was corrected by fraenulotomy and, in 4 boys, by ventral "V" and "Y" penile skinplasty with excellent cosmetic results. In group II were 10 boys with an evident chordee. In 4 boys, the chordee was of type III according to Devin-Horton. A chordectomy was done with a "V" and "Y" skinplasty with very good result. The remaining 6 cases were chordee type II according to D-H. The same treatment was undertaken here, but with an additional Nesbit's dorsal tunica albuginea plication in 4 boys and a 50% success (3 of 6). In group III were 5 boys, 3 previously failed chordectomy from group II and 2 with "skin urethra" type chordee I according to D-H. All boys in this group were treated for urethroplasty with autologous buccal mucosal graft. Good results were obtained in 3 of 5 (60%). Successful outcome was achieved in both cases with "skin urethra" not previously treated. The results of our urethroplasty with buccal mucosa agree with those in literature. In the treatment of chordee without hypospadias, where it was necessary to reconstruct the urethra there was a constant problem of the shortage of local tissue, so we believe that buccal mucosa is a good choice.

Child, Preschool↗

PubMed1974