Tight Mesh Research Articles

Use of the pipeline embolization device for the treatment of recurrent intracranial aneurysm after previous stent-assisted embolization

Aneurysmal subarachnoid haemorrhage remains an important cause of stroke mortality and morbidity. With the advance of endovascular treatment, increasingly more ruptured intracranial aneurysms are being treated with endovascular embolization. Endovascular treatment has a unique form of recurrence and complication, and the recurrence of intracranial aneurysm treated by stent-assisted embolization is a significant challenge. The pipeline embolization device (PED), a dedicated flow-modifying device, has been available in Hong Kong since September 2008. The PED (eV3, Irvine, CA, USA) is a woven wire mesh tube made of 25% platinum and 75% cobalt-nickel alloy; it is designed to provide 30–35% metal coverage of the inner surface of the target vessel with a pore size of 0.02–0.05 mm (approximately three times more than other commonly used intracranial stents). Here, we illustrate the PED treatment of a recurrent intracranial aneurysm after stent-assisted embolization. A 46-year-old man presented with the sudden onset of severe headache; computed tomography of his brain showed diffuse basal cistern subarachnoid haemorrhage. Computed tomographic angiography showed a left internal carotid artery aneurysm (5.4 mm height and 2.9 mm neck). He was treated with endovascular embolization, which was complicated with coil protrusion. Emergency stent (Neuroform3; Boston Scientific, Natick, MA, USA) deployment to avoid further coil dislodgement was undertaken and embolization continued to occlude the aneurysm. On 1-year follow-up angiography, the aneurysm had recurred with a wide neck (3.5 mm height, 3.8 mm neck). After discussing different treatment and management options, the patient decided to undergo treatment with the PED. He was given 75 mg clopidogrel and 160 mg aspirin daily for 5 days before the procedure. Under general anaesthesia and right femoral arterial puncture, a guiding catheter was inserted into the cavernous segment of his left internal carotid artery. A 3-F microcatheter was placed across the neck of the aneurysm under microguidewire guidance. The PED, mounted on a delivery wire and constrained within a sheath, was inserted into the rotating haemostatic valve and introduced into the hub of the microcatheter. Under heparinization, by pushing the delivery wire, the PED was advanced through the whole length of the microcatheter. The PED delivery wire was then held in place while the microcatheter retracted, supplemented by delivery wire rotation, to initiate deployment. Mainly through forward pressure on the delivery wire, the device was further deployed to create a tight mesh. Finally, the microcatheter was advanced to compress the proximal end of the PED, and the delivery wire was retracted. Check angiography showed aneurysm contrast stasis and layering within the dependent portion, forming an eclipse sign on the subtracted venous phase image. The patient did not experience new focal neurological deficit after the procedure. He was prescribed 75 mg clopidogrel and 160 mg aspirin daily for 3 months and 160 mg aspirin for another 3 months. On 3-month follow up angiography, the patent aneurysm sac had decreased in size. The aneurysm is expected to gradually thrombose after 6 to 12 months. In conclusion, the availability of the PED enhanced the set of tools available for the endovascular treatment of recurrent wide-necked intracranial aneurysm.

Tailored sizes of constrictive external vein meshes for coronary artery bypass surgery

External mesh constriction of vein grafts was shown to mitigate intimal hyperplasia by lowering circumferential wall stress and increasing fluid shear stress. As under-constriction leaves vein segments unsupported and thus prone to neointimal proliferation while over-constriction may cause wall folding optimal mesh sizing holds a key to clinical success. Diameter fluctuations and the occurrence of wall folding as a consequence of external constriction with knitted Nitinol meshes were assessed in saphenous vein grafts from 100 consecutive coronary artery bypass (CABG) patients. Subsequently, mesh dimensions were identified that resulted in the lowest number of mesh sizes for all patients either guaranteeing tight continual mesh contact along the entire graft length (stipulation A) or preventing wall folding (stipulation B). A mathematical data classification analysis and a statistical single-stage partitioning approach were independently applied alternatively prioritizing stipulation A or B. Although the risk of folding linearly increased when constriction exceeded 24.6% (Chi squared test p = 0.0004) the actual incidence of folding (8.6% of veins) as well as the degree of lumenal encroachment (6.2 ± 2.1%) were low. Folds were always single, narrow longitudinal formations (height: 23.3 ± 4.0% of inner diameter/base: 16.6 ± 18.1% of luminal circumference). Both analytical methods provided an optimum number of 4 mesh sizes beyond which no further advantage was seen. While the size ranges recommended by both methods assured continual tight mesh contact with the vein the narrower range suggested by the mathematical data classification analysis (3.0–3.7 mm) put 20.6 ± 12.5% of length in 69% of veins at risk of folding as opposed to 21.3 ± 25.9% being at risk in the wider size range (3.0–4.2 mm) suggested by the statistical partitioning approach. Four mesh sizes would provide uninterrupted mesh contact in 98% of vein grafts in CABG procedures with only 26% of their length being at risk of relatively mild wall folding.

Analysis of auxiliary crowning in parallel gear shaving

Gear shaving is one of the most efficient and economical ways to finish gears roughed by gear hobbing or shaping. In parallel gear shaving process, the tooth profile of workgear can be longitudinally crowned by an auxiliary crowning mechanism that rocks the workgear with respect to a moving pivot. There are two independent motion parameters in parallel shaving, the tight rotational meshing between workgear and shaving cutter and the traverse motion of the workgear by moving pivot. A mathematical model for the tooth profile of workgear finished by the parallel shaving process is proposed to simulate the kinematical motion of parallel shaving process with the auxiliary crowning mechanism by two parameter meshing equations. The proposed mathematical model is verified by experiment and can be applied to calculate the crowning of the workgear from the machine setup of crowning mechanism.

Dynamic modeling and analysis of a spur planetary gear involving tooth wedging and bearing clearance nonlinearity

Abstract Tooth wedging, also known as tight mesh, occurs when a gear tooth comes into contact on the drive-side and back-side simultaneously. Tooth wedging risks bearing failures from elevated forces. This work studies the nonlinear tooth wedging behavior and its correlation with planet bearing forces by analyzing the dynamic response of an example planetary gear. This planetary gear is representative of a wind turbine geartrain. A two-dimensional lumped-parameter model is extended to include tooth separation, back-side contact, tooth wedging, and bearing clearances. The results show significant impact of tooth wedging on planet bearing forces for a wide range of operating speeds. To develop a physical understanding of the tooth wedging mechanism, connections between planet bearing forces and tooth forces are studied by investigating physical forces and displacements acting throughout the planetary gear. A method to predict tooth wedging based on geometric interactions is developed and verified. The major causes of tooth wedging relate directly to translational vibrations caused by gravity forces and the presence of clearance-type nonlinearities in the form of backlash and bearing clearance.

EFFECT OF TREATMENT OF STARCHY WATER ON QUALITY OF PASTA DURING CONTINUOUS COOKING

ABSTRACT Industrial continuous pasta cookers are filled with thousands of liters of cooking water. During the cooking process, the starch leaches from the cooked pasta. As the starch concentration increases, the cooked pasta becomes less firm and stickier. Starchy water must be constantly released to reduce the starch concentration. This requires addition of fresh makeup water and energy used to reheat it. The effects of presteaming freshly extruded pasta and posttreatment at high temperature and pressure of the starchy cooking water on the pasta cooking quality was tested. The posttreatment consisted of elevating the water temperature to 120C and the pressure to 1.0297 × 10 5 Pa. The viscosity of cooking water decreased from 1.039 × 10−5 m2/s to 7.280 × 10−6 m2/s as a result of the temperature degradation of amylose. Applying high pressure/temperature treatment to the cooking water, as well as straining it through a tight mesh screen, makes it possible to use the same cooking water for a longer period of time. This, in turn, reduces the wastewater produced in continuous cookers, without decreasing the quality of cooked pasta. This results in the conservation of the water and energy.

A novel bioartificial myocardial tissue and its prospective use in cardiac surgery.

Congenital heart defects such as atrial septal defect, ventricular septal defect, double outlet ventricles and the hypoplastic left heart syndrome as well as ischemic heart disease are associated with aplastic, defective or necrotic myocardial structures. In many of these instances patch closure, reconstruction of the defect or revascularization is required. We have developed a contractile bioartificial myocardial tissue, which offers new perspectives for various reconstructive surgical interventions, including congenital heart surgery. Neonatal rat cardiomyocytes were seeded in vitro in a commercially available collagen scaffold. Histological examination and ultrastructural evaluation were performed. Protein and mRNA analysis were carried out by two-dimensional electrophoresis and reverse transcription-polymerase chain reaction (RT-PCR). Force measurements of contractions from the spontaneously beating or the pharmacologically stimulated bioartificial myocardial patch were obtained. A solid matrix of 20 x 15 x 2 mm with spontaneous contractions resulted 36 h after cardiomyocyte seeding. Histology showed a tight mesh of collagen fibrils. Two-dimensional electrophoresis and RT-PCR revealed cardiotypical proteins (actin, tropomyosin, creatine kinase, ventricular light chain) and mRNA (myosin heavy chain, Connexin 43). The elasticity curve during passive stretch was similar to that of myocardium. Contractile force increased after topical administration of Ca(2+) and adrenaline. However, stretch led to the highest levels of contractile force. Our novel contractile bioartificial tissue can be engineered in vitro and may open novel avenues for myocardial tissue replacement in congenital and reconstructive heart surgery. From the current standpoint autologous or allogeneic cells would be preferred over xenogeneic sources.

The effects of nonphysical carrier velocities in high-gradient single event track simulations

This paper deals with two modeling issues imposed by low-energy ion track structures. In most PISCES-like semiconductor charge transport simulation codes, the diffusion velocity, as predicted by Fick's Law, exceeds thermal velocity at high-gradient regions of the low-energy ion initial track structure. Our numerical study results indicate this nonphysical diffusion velocity effect does not affect the fidelity of the track temporal evolution; thus, it plays no part in a macroscopic charge collection device level simulation. In addition, the analysis on the temporal evolution of the narrow track structures provides an efficient gridding scheme to eliminate the need of computationally expensive tight mesh to describe the initial narrow tracks of low-energy ions.

Anatomie du goût philosophique

An anatomy of philosophical taste Philosophical reflection is usually thought of as being free of social or empirical determination. Studying the research practices of students enrolled in Master or Doctor of Philosophy programs shows that, on the contrary, their reflection is highly dependent on the teaching program. The study also reveals that the space of philosophy subjects is very hierarchical and that this hierarchy corresponds to the ranking of the students treating the subjects. Philosophical reflection then is no freer than any other practice from the tight mesh of determinations that binds all human activities.

Energetic cost of web construction and its effect on web relocation in the web-building spider Agelena limbata.

Although spider webs may be effective in trapping prey, they require energy for construction. The design of webs varies in complexity from species to species. I assume that the energetic cost of web construction is significantly different among web types or species. This cost may constrain foraging tactics, particularly web relocation, because web relocation also requires energy to make a new web. To clarify the effect of the cost of web construction on web relocation, the energy cost of web construction and the rate of web relocation were estimated for the spider Agelena limbata. This spider constructs a sheet-funnel web consisting of a tight mesh of silk threads. This web was costly in terms of the energy needed for construction, which ranged from 9 to 19 times the daily maintenance energy. The daily rate of web relocation was below 1%, indicating high web-site tenacity. Relocation rates of species which built different types of web were compared in relation to cost of web construction. Orbweavers, which produce less costly webs than sheet-funnel weavers, relocate webs more frequently. Sheetweavers, which make webs of intermediate cost, appear to relocate webs more frequently than sheetfunnel weavers but less frequently than orbweavers. These results suggest that the energy cost of web construction is important in determining the frequency of web relocation.

Geosat data give wind speed and wave height

The Navy has released Geosat radar cross section and significant wave height data from the 18‐month Geodetic Mission for use by the general public. These data, when combined with data from the Exact Repeat Mission, comprise the most dense global wind speed and wave height data set ever archived. The accuracy of the data when compared with NDBC buoys has been shown [Dobson et al., 1987] to be +/− 1.7 m/s for wind speed and +/− 0.5 m for wave height.The Geosat altimeter orbits the Earth at an altitude of 800 km and, during the Geodetic Mission, laid down a ground track which precessed about 100 km every 3 days forming a tight mesh over 72 days which was repeated for three consecutive 72‐day periods. The primary mission of the instrument was to measure the marine geoid, but it also measured radar cross section (RCS) and significant wave height (SWH). RCS is the return signal backscattered from the ocean surface and is proportional to wind speed. SWH is obtained from the slope of radar‐returned pulse. Data are available at a one per second rate with complete global coverage.

A technique for the detection of robot joint gear tightness

AbstractA new technique for the examination of gear tightness in robot joint drive systems is presented. A single robot joint is subjected to random excitation while the rest of the joints are constrained. The corresponding link motion is monitored by two accelerometers mounted on the link. The transfer function of the translational component of link acceleration is then obtained. From the half peak magnitude bandwidth of the first resonant frequency it is possible to determine whether the joint gears under testing have a tight or loose meshing. Tests were performed on the wrist rotation joint of an industrial robot in two steady state positions with the end effector loaded and unloaded.