What are the ideal characteristics of a venous stent?

Historically, the stents used in the venous system were not dedicated scaffolds. They were largely adapted arterial stents. An essential feature of a venous stent is compliance, in order to adapt its crosssectional area to the vein. It should also be crush resistant, corrosion resistant and fatigue resistant. The material should be radiopaque, for follow-up. Another characteristic of the ideal venous stent is flexibility, to adapt its shape to the vein, not vice versa. The scaffold should be uncovered too, in order to avoid the occlusion of collaterals. The ideal venous stent should not migrate, so it is necessary a large diameter and a long length. The radial force is important to prevent migration. However, current stents derived from arterial use display high radial force, which could affect the patency of the thin venous wall. Alternatively, if the stent has an anchor point, that permits a passive anchoring, the radial force required to avoid migration will be lower. Dedicated venous stents were not available until very recently. Furthermore, there is a preclinical study about a new compliant nitinol stent, denominated Petalo CVS. Out of the commonest causes of large veins obstruction, dedicated venous stent could also treat other diseases described more recently, such as the jugular variant of the Eagle syndrome, JEDI syndrome and jugular lesions of the chronic cerebrospinal venous insufficiency that result unfavorable for angioplasty according to Giaquinta classification.

DETERMINATION OF THE FUNCTION OF THE ROD’S CROSS-SECTIONAL AREA USING VIBRATION EIGENFREQUENCIES

The paper presents solutions to the direct and inverse problems on longitudinal vibrations of a rod with a variable cross-sectional area. The law of variation of the cross-sectional area is modeled as an exponential function of a polynomial of degree n . The method for reconstructing this function is based on representing the fundamental system of solutions of the direct problem in the form of a Maclaurin series in the variables x and λ. Examples of solutions for various section functions and various boundary conditions are given. It is shown that to recover n unknown coefficients of a polynomial, n eigenvalues are required, and the solution is dual. An unambiguous solution was obtained only for the case of elastic fixation at one of the rod’s ends. The numerical estimation of the method error was made using input data noise. It is shown that the error in finding the variable crosssectional area is less than 1% with the error in the eigenvalues of longitudinal vibrations not exceeding 0.0001.

Nerve ultrasound in the assessment of cross-sectional area in healthy children

Introduction. Nerve ultrasound continues to progress due to improved technical equipment and knowledge, but so far not enough research has been done to determine the normative values of the cross-sectional area in children, and the obtained results differ between laboratories and researchers.Aim of the study. To determine the normative values of peripheral nerves» cross-sectional area in children 5–18 years old.Materials and methods. High resolution nerve ultrasound of brachial plexus, median, ulnar, radial, femoral, sciatic, tibial and peroneal nerves was performed in 30 children in real time. Nerve trunks were visualized throughout the limb from both sides. The cross-sectional area of the nerves was measured by a manual tracing method with the rounding of the hypoechogenic contours of the nerve trunk. Nerves’ crosssectional area was measured at distal and proximal sites. The obtained data were statistically processed using Excel and Statistica 10.Results. No bilateral cross-sectional area’s differences were found in children. Boys had significantly thicker nerves compared to girls, older age group (13–17 years old) compared to younger ones. There was a significant correlation between cross-sectional area of the median nerve at the level of the wrist, sciatic nerve and children’ height and weight.Conclusions. The normal values of cross-sectional area in children can be used in the practical work of a neurologists, neurophysiologists and ultrasound technicians.

Ventilation of molds for die casting

This paper describes the factors that affect gas content in castings during pressure molding. The possibility of removing air and gases from the cavity of the mold through the ventilation channels in the process of filling it with liquid metal is considered. It is shown that the previously used assumption about the outflow of gases from the mold as through a hole in a thin wall is not correct. The calculations, taking into account the friction factor in narrow ventilation ducts, showed that the required crosssectional area of the ventilation ducts increases 4–6 times with a depth of 0,12 mm. If the obtained value of the cross-sectional area of the ventilation ducts is not possible to realize, at a given depth, it is proposed to use an accompanying vacuum to solve the problem.

Evaluation of the Carrying Capacity of Rectangular Steel-Concrete Columns

Experimental studies of rectangular steel-concrete columns under centric compression with random eccentricity were conducted. The stress-strain state and the carrying capacity exhaustion have been assessed. The regression dependence is proposed to determine the maximum carrying capacity of such columns. The mathematical model takes into account the combined influence of the physical and geometric characteristics of the columns, such as their length, crosssectional area, casing thickness, prism strength of concrete, yield strength of steel, modulus of elasticity of both steel and concrete. The correspondence of the obtained model to the experimental data, as well as the significance of the regression parameters are confirmed by the Fisher and Student criteria.

Effects of chronic flexed wrist posture on the elasticity and crosssectional area of the median nerve at the carpal tunnel among chronic stroke patients

Aim: To investigate the effects of chronic flexed wrist posture following spasticity on the elasticity and cross-sectional area (CSA) of the median nerve at the carpal tunnel among chronic stroke patients.Material and method: This prospective study included 24 consecutive patients (mean age, 56.5±11.56 years) with unilateral wrist spasticity following a stroke in a chronic phase. The CSA of the median nerve was measured by ultrasound (US). The elasticity was measured by Virtual Touch tissue imaging quantification (VTIQ; Siemens, Erlangen, Germany). SWV and CSA of the median nerves of the affected and unaffected sides for each patient were compared. The correlations between duration of time since the stroke, SWV and CSA of the median nerve were assessed. The interobserver agreement was assessed.Results: The CSA of the median nerve at the affected side was significantly lower than that of the unaffected side (p = 0.03). The SWV of the median nerve at the affected side was significantly higher than that on the unaffected side (p < 0.001). The interobserver agreement was excellent for both CSA and SWV measurements. There was a negatively fair correlation between CSA at the affected side and duration of time since stroke (r = -0.58, p < 0.05). The SWV of the median nerve at the affected side was not correlated with the duration of time since stroke (r ≤ 0.3, p ≥ 0.05).Conclusions: These results suggest that chronic flexed wrist posture may cause atrophy of the median nerve due to chronic compression after stroke and increase in the stiffness of the median nerve.

Thermal Diffusion Performance of a Diffuser by various Guide Vanes configurations

The use of vane-less diffuser with large diffusion angle has shown a setback in the diffusion process of high temperature working fluids. The hot gas flow was characterized as a jet-like flow. This paper presents problem, encountered practically, using a vane-less diffuser with large diffusion angle and how the problem is solved by CFD simulation. The investigated thermal diffuser has a length of 0.3 m, an inlet to outlet crosssectional area ratio of 1:25 and diffusion angle of 115.44o. To resolve the jet-like flow problem and poor distribution of the flow temperature at the diffuser outlet, the study suggested the use of guide-vanes into the diffuser. The study employed CFD simulation by ANSYS-FLUENT software to analyze the flow and thermal process in the diffuser. Three different shapes of guide vanes; block-shaped, oval-shaped and airfoil-shaped were considered in this study and at different vanes diffusion angles, as well as vane-less case, which was adopted as the bench mark case. The simulation results of the velocity, temperature and pressure at the diffuser outlet were compared for all cases. It was found that the guide vanes with symmetrical airfoil profile provided the best performance with most uniform distribution at the outlet of the diffuser. Also, the airfoil-shaped guide vanes resulted in lower pressure losses compared to the block-shaped and oval-shaped guide vanes. According to the analysis results, the diffuser was redesigned to improve the diffusion and temperature distribution across the diffuser outlet.

Productivity of apricot cultivars of medium late and late maturity in the Belgrade area

Characteristics of productivity and growth (yield per tree, trunk crosssectional area, yield efficiency and fruit weight) were studied in 30 apricot cultivars of medium late and late maturity in the Belgrade area during the six-year period (2009?2014). The cultivar ?Hungarian Best? was used as a control for comparison. The period of study was divided into initial bearing (trees aged three to four years) and full bearing (trees aged five to eight years). Significant differences in yield between cultivars and years were found. An average yield in the period of initial bearing ranged from 0.6 to 6.4 kg per tree, and in the period of full bearing from 4.5 to 18.4 kg per tree. Compared to the control cultivar, significantly higher yield was obtained in 11 cultivars. Adverse weather conditions resulted in a significant reduction in yield in two out of six years of study. Cumulative yield efficiency varied from 0.10 to 0.85 kg/cm2 and in 13 cultivars it was significantly higher compared to the control cultivar. Fruit weight ranged from 26.6 to 81.1 g. Compared to the control, fruit weight was significantly higher in nine cultivars, and significantly lower in ten cultivars. On the basis of high yield and large fruit size, introduced cultivars ?Roxana?, ?Mary de Cenad? and ?Silvercot? as well as domestic cultivars ?Novosadska Rodna?, ?NS-4? and ?NS-6? can be recommended for growing in the Belgrade area.