Deployment technique that takes advantage of the characteristics of Enterprise VRD2: an in vitro study

BackgroundEnterprise VRD, a stent frequently used to assist coil embolization of cerebral aneurysms, has been upgraded to reduce the risk of incomplete stent apposition (ISA), a known risk factor for thromboembolic complications.ObjectiveTo compare the performances of Enterprise VRD and Enterprise VRD2 in curved vessels, and to investigate a deployment method that takes advantage of the features of Enterprise VRD2 to achieve better vessel wall apposition.Materials and methodsA silicone vascular model connected to a temperature-adjustable perfusion circuit was used. First, Enterprise VRD and Enterprise VRD2 were deployed under fluoroscopy and then ISA was evaluated as the stent cross-sectional area ratio at the curved segment of the vessel. For the measurements, each stent was deployed in vessels with different angles of curvature. Second, the incidence of ISA after insertion of Enterprise VRD2 by the ‘pushing over outer curve technique’, in which stents are deployed along the outer curve of vessels with continuous wire advancement, was compared with ‘Heller's push and pull technique’.ResultsFor all stents, the cross-sectional area ratio decreased with acute curvature of the vessel. Comparisons of the two stents showed that Enterprise VRD2 was better than Enterprise VRD in maintaining a greater cross-sectional area ratio in curved vessels. In addition, kinking with an acute curvature was also minimized with Enterprise VRD2. Furthermore, ISA was reduced using our technique with Enterprise VRD2.ConclusionsEnterprise VRD2 is superior to Enterprise VRD in reducing ISA in curved vessels and can alter ISA according to the deployment technique used.

A New Approach to Modeling Static Hysteresis of Piezostack Actuator

This paper proposes a new recursive based polynomial approach for modeling a hysteresis of a piezostack actuator. The formulation is based on two main curves of hysteresis that are identified experimentally. In the proposed model, an adjusting function that relates the outer curve and its next minor is given. Its coefficients are obtained from the boundary conditions and experiment. From this adjusting function, a recursive-based polynomial formula for the cases of monotonic increasing and decreasing of input excitation are developed to predict the hysteresis. To evaluate the accuracy of the proposed new model, experiments with two different waveforms are carried out.

The Effect of Wellbore Curvature on Tubular Buckling and Lockup

This paper studies tubular buckling in curved wellbores (such as the build section of horizontal wells) and its effect on tubular “lockup” in horizontal or extended-reach wells. New buckling load equations are derived to properly predict tubular sinusoidal and helical buckling in such wellbores. The results show that the buckling loads to initiate sinusoidal and helical buckling of tubulars in curved wellbores are usually much larger than those in straight wellbores. This is because the curved wellbore tends to hold the axially compressed tubular against the outer-curve side of the wellbore. The tubular becomes less easy to buckle until higher axial compressive loads are applied. Less tubular lockup risk is then predicted for tubulars in horizontal or extended-reach wells by using the new buckling load equations. The new buckling loads in curved wellbores agree with those in straight wellbores when wellbore curvature approaches zero. Small-scale laboratory experiments also confirmed these theoretically derived buckling loads.

I.—Note on the Discovery of Bos Primigenius in the Lower Boulder-clay of Scotland

It Will interest some of your readers to hear that remains of Bos primigenius have recently been obtained from the true till or lower Boulder-clay of Scotland. The specimens hitherto found appear to have come either from the fine Glacial brick-clays, which are posterior in date to the larger portion of our Boulder-clay, or from deposits of still later age. A few days ago I heard that the navvies employed in making the new “Crofthead and Kilmarnock Extension Railway” had come upon what was described to me as a “wounderful big bull's head.” I lost no time in visiting the locality, and saw the fossil in the possession of Mr. John Strain, C.E., who allowed me to examine it, and was afterwards kind enough to accompany me to the railway cutting in order to point out the exact spot from which the relic was taken. The skull is in rather an imperfect state, and only one of the horn-cores remains, the other having been broken off near the base. The perfect core measures 31 inches in length along the outer curve, and gives at its base a circumferences of 14 inches. The breadth of the forehead between the horns is 10 inches. From the character of the flat forehead, from the origin of the cores, and from the direction and curvature of the remaining one, there can be no doubt that the skull is that of Bos primigenius.