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At least 613 records · Page 34Linked to original sources
PubMed2004

Volar fixed-angle fixation of distal radius fractures: the DVR plate.

Volar fixed-angle fixation of distal radius fractures is a new method of treatment that provides the benefits of stable internal fixation without incurring the disadvantages of the dorsal approach. The DVR plate is a new fixation implant that was introduced specifically for the purpose of managing both dorsal and volar displaced fractures from the volar aspect. Experience gained applying volar fixed-angle fixation to clinically complex cases led to the description of a new surgical approach and to refinement in design of the implant. The need to reduce fractures with significant articular displacement and the need to debride dorsal organized hematoma or callus in old fractures led to the development of an extended form of the flexor carpi radialis approach that provides improved dorsal exposure by mobilizing the proximal radius out of the way and allows the use of the fracture plane for intrafocal exposure. The use of this implant in severely osteoporotic bone and in those fractures presenting severe articular fragmentation or displacement led to the improvement of its design. The plate's ability to stabilize the distal radius was optimized by taking full advantage of the principles of subchondral support and buttress fixation.

Journal Article↗
PubMed2001

Gyration radius of a circular polymer under a topological constraint with excluded volume.

It is nontrivial whether the average size of a ring polymer should become smaller or larger under a topological constraint. Making use of some knot invariants, we numerically evaluate the mean-square radius of gyration for ring polymers having a fixed knot type, where the ring polymers are given by self-avoiding polygons consisting of freely jointed hard cylinders. We obtain plots of the gyration radius versus the number of polygonal nodes for the trivial, trefoil, and figure-eight knots. We discuss possible asymptotic behaviors of the gyration radius under the topological constraint. In the asymptotic limit, the size of a ring polymer with a given knot is larger than that of no topological constraint when the polymer is thin, and the effective expansion becomes weak when the polymer is thick enough.

Journal Article↗
PubMed2002

Finite-size and asymptotic behaviors of the gyration radius of knotted cylindrical self-avoiding polygons.

Several nontrivial properties are shown for the mean-square radius of gyration R2(K) of ring polymers with a fixed knot type K. Through computer simulation, we discuss both finite size and asymptotic behaviors of the gyration radius under the topological constraint for self-avoiding polygons consisting of N cylindrical segments with radius r. We find that the average size of ring polymers with the knot K can be much larger than that of no topological constraint. The effective expansion due to the topological constraint depends strongly on the parameter r that is related to the excluded volume. The topological expansion is particularly significant for the small r case, where the simulation result is associated with that of random polygons with the knot K.

Journal Article↗
PubMed2004

Retardation of ice growth in glass capillaries: measurement of the critical capillary radius.

An experiment was designed to compare the freezing of an aqueous solution in glass microcapillaries and in thin films. The velocity dependence of the ice front propagation in glass capillaries with radii of 87.5 microm-1.5 microm was observed. A critical capillary radius r(0), corresponding to certain thermal conditions, was obtained, below which the ice growth inside the capillaries was retarded. This critical capillary radius is further related to lambda(0), the smallest wavelength used in the Mullins-Sekerka criterion for the instability analysis of bulk solidifications [Mullins and Sekerka, J. Appl. Phys. 35, 444 (1964)]. It was found that for the present hypothesis, r(0)=lambda(0)/4 gives good predictions. The relation between the propagation velocity (or cooling rate) and the critical radius (or pore size) is summarized in a chart for applications in capillary-porous media, such as in the freezing of biological tissues.

Journal Article↗
PubMed2005

Effect of the deformation radius on the evolution of vortex properties in geostrophic turbulence.

Coherent vortices in geostrophic turbulence grow in size and become fewer as they merge. It is shown that the deformation radius L(D) has no effect on the growth of the average vortex radius a as a grows from a L(D) to a>> L(D) . Its growth is algebraic, given by a proportional to t(xi/4) , where xi=0.72 . However, the deformation radius does have an effect on the decay of the number of vortices or vortex density rho, given by rho proportional to t(-xi) for a < > L(D) . Thus the decay of rho becomes slower once a has grown to a size comparable to that of L(D) . One scaling theory for the entire range from a<< L(D) to a>> L(D) is presented and verified by numerical experiments. A special method for quadruplicating the numerical domain when the vortices become too few is proposed, which keeps the computation inexpensive. This work generalizes and agrees with previous work, in which the two special cases a< > L(D) are independently investigated.

Journal Article↗
PubMed1998

Outer radius-wall thickness ratio, a postmortem quantitative histology in human coronary arteries.

Although the anatomy, histology and pathology of human coronary arteries have been studied extensively, little is known about the functional relationship between vessel radius and wall thickness. It is the purpose of this study to present detailed measurements and to describe this relationship covering the range from the feeding coronary artery to the arterioles. Human hearts of 10 adults less than 36 +/- 3 years old were investigated immediately postmortem. Ten cubic tissue blocks, measuring about 10 mm in length on each side, were dissected from the left ventricular wall. After fixation by immersion, 15-microm sections were prepared and outer and inner perimeters of 52 arterial segments were digitalized. Vessel radius and wall thickness were calculated and plotted to show their relationship over the whole range of vessel calibers. Outer vessel radii ranged from 100 to 3,000 microm and wall thickness from 80 to 800 microm. Plotting the outer vessel radius against the wall thickness, the data points were found to cluster around a straight line. A significant correlation between the two parameters was found (R2 = 0.79). This mathematical correlation and the good agreement of the presented results with data from other species indicate a common physiologic concept.

Adult↗
PubMed1992

Ultrafast computed tomography analysis of regional radius-to-wall thickness ratios in normal and volume-overloaded human left ventricle.

BACKGROUND: This study tested two hypotheses: 1) regional left ventricular radius-to-wall thickness ratios (R/T) are uniform in normal subjects, and 2) patients with left ventricular hypertrophy secondary to compensated volume overload normalize global and regional R/T. METHODS AND RESULTS: Ultrafast computed tomography was used to measure regional short-axis ventricular R/T in 11 normal subjects and 13 patients with compensated aortic insufficiency (AI) of moderate severity (regurgitant fraction, greater than or equal to 25%). Radius and wall thickness dimensions were calculated by two different methods. In method 1, the average radius and wall thickness were determined for each planimetric transaxial tomographic image. In method 2, the left ventricle was three-dimensionally reconstructed; then, new radii and wall thickness were recalculated as if all the images were acquired orthogonal to the endocardial surface at each tomographic level. In normals, the mean R/T ratio was 1.75 +/- 0.11 (SEM) with method 1 and 1.80 +/- 0.07 with method 2. The R/T ratios varied as a function of the relative apex-to-base position. R/T ratios at the basal four levels were relatively uniform, whereas R/T at the lower three tomographic levels were significantly less than those at the base (p less than 0.01). Patients with AI had a mean regurgitant fraction of 44 +/- 3.8% (range, 25-63%). The mean R/T ratio was 2.18 +/- 0.16 with method 1 and 2.55 +/- 0.18 with method 2. Similar to the pattern observed in normals, the regional R/T ratios at the lower three or four levels were significantly less than the basal R/T ratios (p less than 0.01). Regional comparison of the normal to the volume-overloaded ventricles demonstrated that R/T ratios in the AI patients were significantly greater at the upper five levels with method 1 and at all eight levels with method 2 (p less than 0.01-0.001, AI versus normal). CONCLUSIONS: These findings demonstrate that regional R/T ratios are heterogeneous in both normals and patients with left ventricular hypertrophy secondary to compensated aortic insufficiency. Furthermore, these findings challenge the accepted hypothesis that global and regional R/T ratios normalize in patients with compensated volume-overload hypertrophy.

Adult↗
PubMed2003

Radius margin bounds for support vector machines with the RBF kernel.

An important approach for efficient support vector machine (SVM) model selection is to use differentiable bounds of the leave-one-out (loo) error. Past efforts focused on finding tight bounds of loo (e.g., radius margin bounds, span bounds). However, their practical viability is still not very satisfactory. Duan, Keerthi, and Poo (2003) showed that radius margin bound gives good prediction for L2-SVM, one of the cases we look at. In this letter, through analyses about why this bound performs well for L2-SVM, we show that finding a bound whose minima are in a region with small loo values may be more important than its tightness. Based on this principle, we propose modified radius margin bounds for L1-SVM (the other case) where the original bound is applicable only to the hard-margin case. Our modification for L1-SVM achieves comparable performance to L2-SVM. To study whether L1- or L2-SVM should be used, we analyze other properties, such as their differentiability, number of support vectors, and number of free support vectors. In this aspect, L1-SVM possesses the advantage of having fewer support vectors. Their implementations are also different, so we discuss related issues in detail.

Artificial Intelligence↗
PubMed1976

Comparison of the acceleration and velocity of shortening of the ventricular radius. Their potential applicability of noninvasive measurements of ventricular performance.

The maximal rate and maximal acceleration of shortening of the radius of the minor axis of the ventricle were correlated with various indices of ventricular performance in 20 patients with angina. The maximal acceleration of shortening showed a closer correlation with the ejection fraction, rate of change of flow, and ejection rate of change of power than did the maximal rate of shortening. It also distinguished more sharply between patients with normal and abnormal values of these indices, showing no overlap of values. The maximal rate of shortening showed a less distinct separation. These observations suggest that the acceleration of shortening of the ventricular radius reflects ventricular performance more closely than does the rate of shortening of the radius. These results are relevant in regard to potential applications of these indices by noninvasive techniques, particularly echocardiography.

Angiocardiography↗
PubMedDate not supplied

On the p-norm joint spectral radius.

The p-norm joint spectral radius is defined by a bounded collection of square matrices with complex entries and of the same size. In the present paper the author investigates the p-norm joint spectral radius for integers. The method introduced in this paper yields some basic formulas for these spectral radii. The approach used in this paper provides a simple proof of Berger-Wang's relation concerning the infinity -norm joint spectral radius.

Mathematics↗
PubMed1997

Measurements of axial length and radius of corneal curvature in the rabbit eye.

The axial length of the eye, the radius of the anterior corneal surface, and the diameter of the cornea were measured on 40 eyes of 20 New Zealand White rabbits. The ultrasonographic measurements of the axial length of the eye showed a mean value of 15.12 +/- 0.51 mm (15.33 +/- 0.50 mm in males, 14.96 +/- 0.46 mm in females). The mean corneal radius was 7.26 +/- 0.26 mm (7.18 +/- 0.9 mm in males, 7.32 +/- 0.33 mm in females); the mean value of the difference in corneal curvature between two principle meridians was 0.21 +/- 0.12 mm; and the mean horizontal and vertical diameters of the cornea were 13.41 +/- 0.34 mm and 13.02 +/- 0.30 mm, respectively. Although the diameter of the cornea of rabbits was bigger than that of humans (average, horizontal 11.75 mm, vertical 10.55 mm), the axial length of the eye was 0.7 times that of humans (23-24 mm), and the radius of corneal curvature was relatively smaller than that in humans (7.7-7.8 mm).

Animals↗
PubMed1999

Biomechanical evaluation of fixation of intra-articular fractures of the distal part of the radius in cadavera: Kirschner wires compared with calcium-phosphate bone cement.

BACKGROUND: The purpose of this study was to compare the biomechanical efficacy of an injectable calcium-phosphate bone cement (Skeletal Repair System [SRS]) with that of Kirschner wires for the fixation of intraarticular fractures of the distal part of the radius. METHODS: Colles fractures (AO pattern, C2.1) were produced in ten pairs of fresh-frozen human cadaveric radii. One radius from each pair was randomly chosen for stabilization with SRS bone cement. These ten radii were treated with open incision, impaction of loose cancellous bone with use of a Freer elevator, and placement of the SRS bone cement by injection. In the ten control specimens, the fracture was stabilized with use of two horizontal and two oblique Kirschner wires. The specimens were cyclically loaded to a peak load of 200 newtons for 2000 cycles to evaluate the amount of settling, or radial shortening, under conditions simulating postoperative loading with the limb in a cast. Each specimen then was loaded to failure to determine its ultimate strength. RESULTS: The amount of radial shortening was highly variable among the specimens, but it was consistently higher in the Kirschner-wire constructs than in the bone fixed with SRS bone cement within each pair of radii. The range of shortening for all twenty specimens was 0.18 to 4.51 millimeters. The average amount of shortening in the SRS constructs was 50 percent of that in the Kirschner-wire constructs (0.51+/-0.34 compared with 1.01+/-1.23 millimeters; p = 0.015). With the numbers available, no significant difference in ultimate strength was detected between the two fixation groups. CONCLUSIONS: This study showed that fixation of an intra-articular fracture of the distal part of a cadaveric radius with biocompatible calcium-phosphate bone cement produced results that were biomechanically comparable with those produced by fixation with Kirschner wires. However, the constructs that were fixed with calcium-phosphate bone cement demonstrated less shortening under simulated cyclic load-bearing.

Biomechanical Phenomena↗
PubMed1990

The relationship between changes in tumour volume, tumour cell density and parenchymal cord radius in a human melanoma xenograft exposed to single dose irradiation.

A human melanoma xenograft, in which the viable tumour tissue formed cylindrical cuffs around blood vessels, was irradiated with single doses of 7.5 Gy and 15.0 Gy respectively. The nuclear density, the frequency of giant cells and the mean parenchymal cord radius were measured and compared to the tumour growth response. After 7.5 Gy, the growth rate was only slightly reduced and there were no significant changes in the nuclear density or the mean parenchymal cord radius. After 15.0 Gy the mean parenchymal cord radius decreased the first week. This coincided with swelling of endothelial cell nuclei and reduced density of functional capillary-like vessels. Although the number of tumour cells declined, the tumour volume increased the first days after irradiation with 15.0 Gy since the cell density was reduced.

Animals↗
PubMed2005

Effect of statin on restenosis after radius stent implantation in patients with acute coronary syndrome.

Despite reports that statin treatment reduces the rate of coronary restenosis with a balloon expandable stent, there is no evidence that statins affect the incidence of restenosis with a self-expanding Radius stent. Ninety-five patients with acute coronary syndrome who had been implanted with a Radius stent were classified into two groups: those with hyperlipidemia and initial statin treatment (statin group, n = 38) and those without statin treatment (comparative group, n = 57). At six months after stent implantation, the rate of coronary restenosis was significantly lower in the statin group (10.5%) than control group (28.1%) (p = 0.033), while there were no differences in morphology, maximal inflation pressure or stent size between the two groups. Interestingly, there was no difference in the serum lipid profile between the two groups at the 6-month follow-up, although the statin group had a significantly lower rate of restenosis. In conclusion, initial statin therapy reduced the rate of coronary restenosis even when a Radius stent was implanted.

Acute Disease↗
PubMed2001

A radius of curvature-based approach to cervical spine vertebra image analysis.

Radiologists interpret the normality of vertebras within cervical spine x-rays for determining the presence of osteoporosis. Features relating to vertebra fracture such as contrasting anterior and posterior heights are used in the vertebra normality assessment. Vertebra distortion along the anterior boundary can be used as an indicator of vertebra normality. As the vertebra becomes less normal in appearance, the vertebra boundary increasingly deviates from the general rectangular shape. This research introduces a radius of curvature-based approach to quantify the distortion in vertebra boundary shape for anterior osteophytes classification of vertebras within cervical spine x-ray images. An adaptive histogram analysis technique is used to enhance the vertebras within cervical spine x-ray images to facilitate vertebra feature extraction. A least squares technique is used for calculating the radii of curvature along the vertebra boundary. Radius of curvature and gray-level based features are computed using the anterior boundary point position with the minimum radius of curvature as the reference. A total of 118 cervical spine vertebras are used for training and testing various classifiers including a standard back propagation neural network, K-Means algorithm, quadratic discriminant classifier and LVQ3. The results from those classifiers are reported for recognizing vertebras as normal or abnormal.

Artificial Intelligence↗
PubMed2004

[One family investigation and pathogeny research on ectrodactyly, absence of radius side part palm and split foot malformation].

OBJECTIVE: The paper is a study on the clinical symptoms and pathogeny of ectrodactyly and absence of radius side part palm and split foot malformation of some patients in one family. METHODS: Based on the patient family investigation,a normal control group and a patient group were established. Then, polymerase chain reaction technique was used for DNA sequencing and analysis of the two groups for their exons 5-8 gene group DNA of P63 gene. RESULTS: The medical examination found that the patients' upper bilateral limbs are short of thumbs, forefingers and middle fingers, and have radius side part palm and double lower limbs foot clefts malformation. The pathogeny research revealed that the PCR expansion pieces of the exons 5-8 of P63 are 284 bp, 259 bp, 245 bp and 259 bp respectively, and the size of the expansion piece of the patients was the same as that of the normal people group. However, a respective comparison between the DNA serial of the expansion piece of the patient and that of the normal people group and that of the P63 gene in the human gene bank showed that mutation occurs at the number 665 base pair of exon 5 of P63, namely a mutation from G to A. CONCLUSION: The ectrodactyly, absence of radius side part palm and split foot malformation are caused by the mutation of base pair at number 665 of the exon 5 of P63.

Exons↗
PubMed1986

Membrane pores in hypotonically dialyzed sheep erythrocytes remain open after three weeks of storage: entrapment of different stokes radius probes, [14C]sucrose and [3H]inulin.

Sheep carrier erythrocytes were prepared from dialyzed cells stored for 3 weeks. The initial pore size in freshly dialyzed cells exceeds the Stokes radius of that for hemoglobin. Hypotonically dialyzed erythrocytes are then very stable in a porous state. Two probes of different Stokes radius were used to determine the relative size of the pores. Sheep erythrocytes entrap inulin to a greater extent than sucrose, a much smaller molecule. With storage, a greater fraction of dialyzed cells become impermeable to inulin than to sucrose indicative of pore size greater than 5.2 less than 20 A. Since hemoglobin content did not change relative to storage, the pore size was less than the Stokes radius of hemoglobin. Pores generated by controlled hypotonic dialysis are unlike the single rupture pore found in erythrocyte ghosts.

Animals↗
PubMedDate not supplied

Shape and radius of posterior corneal surface.

BACKGROUND: The posterior corneal surface is often ignored in predictive models concerned with refractive surgery. In previous studies, the radius of this surface has been measured in a variety of ways, primarily over a large chord diameter of the surface, with the common assumption that the surface is spherical. The asphericity of this surface has not been adequately addressed in the past. METHODS: An algorithm is derived for the calculation of posterior corneal surface apical radius and using characteristics of the anterior corneal surface and topographic corneal thickness variation. Anterior corneal asphericity was measured using a commercially available photoelectric keratoscope. Using a marked soft contact lens, a simple method of locating noncentral corneal sites is described as an aid to ultrasonic pachometry. RESULTS: In a group of 20 normal subjects ranging in age from 19 to 23 years, the average posterior corneal surface apical radius and asphericity (p) was 5.80 mm (SD = +/- 0.42) and 0.64 (SD = 0.37) for the vertical meridian, and 5.82 mm (SD = +/- 0.40) and 0.52 (SD = 0.30) for the horizontal meridian. Average central corneal thickness was 533 mu (SD = +/- 19). CONCLUSIONS: The average asphericity values are below 1, hence the posterior corneal surface is described as a flattening ellipse. The rate of flattening of this surface is greater than the rate of flattening along the averaged anterior corneal surface.

Adult↗