Tortuous Shape Research Articles

Adsorption of Phenol and Basic Dye on Carbon Nanotubes/Carbon Fabric Composites from Aqueous Solution

The liquid-phase adsorption of phenol and dye (basic violet 10) onto carbon nanotube (CNT)-activated carbon fabric (ACF) composites, prepared by a catalytic chemical vapor deposition (CCVD) approach, has been investigated. The CCVD technique enables the decoration of CNTs on microscaled ACFs, creating a hierarchy CNT-ACF composite. The as-grown nanotubes were found to have a tortuous shape and to be several micrometers in length. The deposition of CNTs efficiently shifts the micropore size distribution of ACFs to mesoporosity. The adsorption isotherms for phenol and BV10 on ACF and CNT-ACF adsorbents are well characterized by the Dubinin-Radushkevich and Langmuir models. The surface accessibility, the equilibrium rate constant, and the adsorption energy are significantly enhanced due to the deposition of CNTs, as analyzed by these models. Accordingly, the existence of CNTs on ACF adsorbent plays a positive role in facilitating pore accessibility to adsorbate and providing more adsorptive sites for the liquid-phase adsorption.

Composite Material of Concrete Meso-Failure Test

With static and dynamic load for the research background, this paper conducted a four-phase composite model for concrete damage test simulation of micro-mechanics. The two kinds of three-point bending beam load ware studied in case of failure process. The study found that the location of the main crack in the most disadvantaged section of beam shear in the vicinity. Crack is always along the aggregate and the mortar bond zone be extended. The main crack extension direction is always toward the load point. The main crack is showing a tortuous shape. Dynamic load and static load the stress - strain curve is basically similar shape, but basically the same as the starting point of the initial fracture. Stress wave in the sample after multiple visits, is the main reason leading to the breakdown of the sample. Dynamic load cases, the concrete elastic modulus higher than the static modulus of elasticity, numerical simulation results agree well with the experimental results.

Mechanical Buckling of Veins Under Internal Pressure

Venous tortuosity is associated with multiple disease states and is often thought to be a consequence of venous hypertension and chronic venous disease. However, the underlying mechanisms of vein tortuosity are unclear. We hypothesized that increased pressure causes vein buckling that leads to a tortuous appearance. The specific aim of this study was to determine the critical buckling pressure of veins. We determined the buckling pressure of porcine jugular veins and measured the mechanical properties of these veins. Our results showed that the veins buckle when the transmural pressure exceeds a critical pressure that is strongly related to the axial stretch ratio in the veins. The critical pressures of the eight veins tested were 14.2 +/- 5.4 and 26.4 +/- 9.0 mmHg at axial stretch ratio 1.5 and 1.7, respectively. In conclusion, veins buckle into a tortuous shape at high lumen pressures or reduced axial stretch ratios. Our results are useful in understanding the development of venous tortuosity associated with varicose veins, venous valvular insufficiency, diabetic retinopathy, and vein grafts.

008 Biomechanical design of the intracranial stent for the cerebral aneurysm treatment

Introduction: The mechanical characteristic required for an aneurysm stent is high longitudinal flexibility and low radial stiffness. Longitudinal flexibility is necessary to navigate the tortuous shape inherent to the intracranial...

Fabrication of 3D micro-cantilevers based on MBE-grown strained semiconductor layers

Strain-driven bending process proposed for the fabrication of small and precise cantilevers is reported. The process starts from the multi-layer structure grown by molecular beam epitaxy (MBE). The cantilevers consist of the two parts imitating the beam and the tip, each of which has different bending direction and radius. The shape determined by location of strained layer in multi-layer structure controlled with layer design and fabrication process including selective etching technique. We demonstrated cantilevers having a rolling up beam with 5 – 20 μ m length and a rolling down thinner tip with 3 μ m length. However the tips showed tortuous shape. The complex shape might originate from inhomogeneity dissolving of extra compounds generated in sacrifice layer etching process. Moreover, we measured resonant frequencies of the fabricated cantilevers by optical lever method. We obtained high resonant frequency of 2 MHz for the cantilever with 5 μ m length, 1 μ m width, and 100 nm thickness. This frequency seems suitable for video-rate scanning in dynamic mode atomic force microscopy (AFM). These results suggest that the strain-driven bending process is applicable to three-dimensional (3D) micro-cantilevers for video-rate scanning in dynamic AFM.

Hydrostatic pressure influences morphology and expression of VE-cadherin of vascular endothelial cells

Bovine aortic endothelial cells (BAECs) were exposed to hydrostatic pressures of 50, 100, and 150 mmHg and changes in morphology and expression of vascular endothelial (VE)-cadherin were studied. After exposure to hydrostatic pressure, BAECs exhibited elongated and tortuous shape without predominant orientation, together with the development of centrally located, thick stress fibers. Pressured BAECs also exhibited a multilayered structure unlike those under control conditions and showed a significant increase in proliferation compared with control cells. Western blot analysis demonstrated that protein level of VE-cadherin were significantly lower under pressure conditions than under control conditions. Inhibition of VE-cadherin expression, using an antibody to VE-cadherin, induced the formation of numerous randomly distributed intercellular gaps, elongated and tortuous shapes, and multilayering. These responses were similar to those of pressured BAECs. The exposure of BAECs to hydrostatic pressure may therefore downregulate the expression of VE-cadherin, resulting in loss of contact inhibition followed by increased proliferation and formation of a multilayered structure.

X-ray microtomographic characterisation of pore evolution during homogenisation and rolling of Al–6Mg

The effect of homogenisation heat treatment and subsequent hot rolling on the evolution of porosity in a direct chill cast Al–6Mg (wt-%) alloy was studied. Porosity was quantified using conventional 2D optical metallography and X-ray microtomography (XMT) which allowed 3D imaging. Metallographic observations show an increase in maximum pore length during heat treatment and at the centre line during rolling. These observations together with the high temperatures might suggest a classical interpore Ostwald ripening mechanism is operative. However, XMT revealed that the pores have a highly tortuous shape, which when sectioned metallographically is not apparent and can lead to misinterpretation. X-ray microtomography observations proved that these tortuous 3D shapes spheroidised during homogenisation owing to localised coarsening of high curvatures within the complex, branching structure of each pore, termed intrapore coarsening. Accelerated centreline intrapore coarsening was observed during the initial rolling passes when relatively low reduction ratios were used. Finite element modelling was used to demonstrate that under the geometric rolling conditions employed the central region of the billet experienced a tensile rather than a compressive hydrostatic stress. This combined with deformation enhanced diffusion is proposed as the reason for the accelerated intrapore spheroidisation. X-ray microtomography was critical to revealing the true 3D pore shape and the mechanisms of pore coarsening, which could have been misinterpreted if only 2D metallography was used.

Multiscale modelling of solidification microstructures, including microsegregation and microporosity, in an Al–Si–Cu alloy

Phase transition phenomena in metallic alloys involve complex physical processes occurring over a wide range of temporal, spatial and energy scales. Multiscale modelling is a powerful methodology for understanding these complex systems. In this paper, a multiscale model of grain and pore formation is presented during solidification. At the microscale, a combined stochastic-deterministic approach based on the cellular automata method is used to solve multicomponent diffusion in a three-phase system (liquid, solid and gas), simulating the nucleation and growth of both grains and pores. The impingement of the growing pores upon the developing solid is also solved to predict the tortuous shape of the porosity, a critical factor for fatigue properties. The micromodel is coupled with a finite element method (FEM) solution of the macroscale heat transfer and fluid flow in industrial castings through the temperature and pressure fields. The result model was used to investigate the influence of local solidification time, hydrogen content, local metallostatic pressure and alloy composition upon the predicted grain structure and pore morphology. Comparison of the model predictions to both laboratory and industrial scale castings are presented.

Study on moving principle of colonoscopic robot

The moving principle of a colonoscopic robot is presented in this paper. The robot mainly consists of soft mobile mechanism for earthworm locomotion and turning mechanism based on shape memory effect. The soft mobile mechanism contacts colon wall with air-in inflatable balloons, so the robot has better soft and non-invasive properties. The turning mechanism can be actively bent by shape memory alloy components. It ensures the robot to adapt to the tortuous shape of colon. Therefore, the colonoscopic robot has good safety, lower working strength of surgeon and higher efficiency of colonooscopy.

The transduodenal rendezvous: a new approach to deeply cannulate the main pancreatic duct

Deep cannulation of the main pancreatic duct (MPD) may be particularly difficult in chronic pancreatitis. This is often related to the presence of an obstacle (stone or stricture) or to the tortuous shape of the duct. We describe a new approach (advisable only in unusual, highly selected cases) to deeply cannulate the MPD through the papilla and to perform a standard, “over-the-wire” sphincterotomy. The MPD is punctured through the duodenal wall and a guidewire is passed in an anterograde fashion through the papilla into the duodenal lumen.

Spatial organization of patch and matrix compartments in the rat striatum

The visualization of mu opiate receptors by [ 3H]naloxone binding was used to determine precisely the spatial organization of the patch compartment in the rat striatum and its reproducibility in different animals. Three-dimensional reconstruction of the patch network was made using maps of autoradiographic data obtained from successive coronal, sagittal or horizontal sections. The extreme rostral pole of the striatum (A 11) was characterized by a large patch territory exhibiting complex and tortuous fields with several extensions. In the intermediate part of the structure (A 9.0–10.0), about 20 serial parallel continuous patch channels running in a mediolateral axis, obliquely oriented and displaying in some cases connecting branches, could be observed. However, no channels could be distinguished in the rostrocaudal direction. More caudally, patches were rare and of small size. In addition, the laterocaudal region of the striatum was almost exclusively represented by a large matrix field. Finally, a fine discontinuous band of [ 3H]naloxone binding was seen in all sections, bordering and limiting the dorsolateral part of the striatum. The topographical and spatial distribution of the patch compartment was similar in all animals investigated. However, due to the tortuous shape and the labyrinthine organization of the patches, the precise degree of reproducibility from one animal to another could not be established. Nevertheless, the prominent patch compartment observed in the rostral pole of the striatum, the patch channels, oriented in the mediolateral axis as well as the large laterocaudal matrix field were observed in all cases. These results were compared with previous data obtained in the cat in which patch (striosome) channels oriented along a rostrocaudal axis are also observed.

A quantitative approach to the effects of surface topography on tunnelling current between two large rough metal bodies

A convenient method is proposed to deal with the effects of some large-scale surface roughness when calculating the tunnelling current between two macroscopic rough metal bodies-for instance the two members of an electrical 'quasi-contact'. Surface topography is introduced through the distribution of local distances between electrodes, which describes both their nominal shape and their local roughness. Even for surfaces as simple as a plane, cylinder or sphere, this distribution is quite intricate and exhibits a highly tortuous shape. A few periodic roughness models, and a more realistic approach by means of fractals, are successively considered. In any case, the authors prove that only the beginning of the distance distribution is essential from the viewpoint of the tunneling current. A computed example allows one to assess quantitatively how the local topography may change drastically any prediction concerning the value of the current. Comparison between some reliable sphere/plane experimental results and the corresponding theoretical predictions proves to be very good and attests to the relevance of the proposed method.

Brucella canis infection in a 17-month-old child successfully treated with moxalactam

complications of meningitis. Occlusion of the supraclinoid portion of the internal carotid artery may be related to its tortuous shape, slow turbulent blood flow, and to its location at the base of the brain, where exudate in meningitis is most prominent. A repeat arteriogram was not considered justified in our patient because of the clinical improvement. His persisting neurologic deficit implies that he sustained a significant cerebral infarct. The striking unilateral CT appearance of H. influenzae meningitis seen in this patient has not been described. The presence of this finding on CT should suggest the likelihood of ipsilateral internal carotid artery occlusion. In this clinical situation, specific treatment of cerebral edema may be indicated. Thanks to D. C. Harwood-Nash and W. J. Logan for their assistance and to Jodi Stoyak for typing the manuscript. REFERENCES

On the extensive contact between veins and arteries in the human ovarian pedicle.

The human ovarian arteries and their anatomical relation to the utero-ovarian venous plexus were studied in surgical specimens using roentgen angiography and corrosion casts. The arteries were in close contact with the veins, had a tortuous shape and sometimes a helical folding of inner layers of the wall. The results obtained are similar to the findings in a number of animal species and may represent the morphological basis for a counter-current exchange mechanism.

Diffusion of molecules on biological membranes of nonplanar form. A theoretical study

Lateral mobility of molecules on cell membranes has been recently studied by fluorescence photobleaching recovery (FPR) techniques. The interpretation of these results in terms of diffusion along the membranes is based on the assumption that the surface is planar, although biological membranes may have blebs and microvilli. To study the effect of nonplanarity on the diffusion rate, the diffusion equation along curved surfaces was derived and was solved numerically for a "wavy" surface of the form A cos kx cos ky. Calculations show that for k = 10 pi micrometer-1 and a bleached spot of 1 micrometer in diameter, the time dependence of the intensity of fluorescence in the bleached spot depends on A at A less than 0.5 micrometer, while at higher values of A (a and 2 micrometer) the dependence is weak. If one calculates diffusion coefficients from FPR measurements and assumes that the membrane is planar, the resulting diffusion coefficient is not less than about half of the real one. Because of the tortuous shape of the spot boundary, increasing the microvilli length from 0.5 micrometer to 1 or 2 micrometer does not change the diffusion rates. These considerations are valid for times when the diffusion is dominated by molecules that were initially located close to the spot boundary.

Leishmania in phlebotomid sandflies III. The ultrastructure of Leishmania mexicana amazonensis in the midgut and pharynx of Lutzomyia longipalpis

The fine structure of the promastigotes of Leishmania mexicana amazonensis in the midgut, cardia, oesophageal valve and pharynx of the sandfly Lutzomyia longipalpis is described. Differences were found between the nectomonad and the haptomonad promastigotes. There were fewer subpellicular microtubules in the nectomonads than in the fatter haptomonads; the mitochondrion of nectomonads was a single straight longitudinal ramus while that of haptomonads had a tortuous shape; the kinetoplast and nucleus lay closer together in the haptomonads which also had fewer free ribosomes and lipid containing bodies than the nectomonads; the nucleus was spherical in haptomonads but elongate in nectomonads. The reservoir region in the nectomonads was notably voluminous and the surface was modified for pinocytotic uptake of material through coated vesicles, and also for exocytosis. In both haptomonads and nectomonads, a contractile vacuole was present adjacent to the reservoir; flagellar-parasite desmosomes formed a collar anchoring the flagellum as it emerged from the reservoir; four reservoir-associated microtubules ran parallel to the flagellar reservoir; the basal body, axoneme and paraxial rod were similar in structure to those of other trypanosomatids. Apparently intracellular promastigotes were found in the midgut cells. Preliminary studies of pharyngeal forms showed that they were attached by hemidesmosomes to the cuticular pharynx. These forms were not typical promastigotes but had an opisthomastigote-like configuration with the reservoir running past the nucleus. Differences in the ultrastructure of Leishmania in the sandfly and in culture are discussed, and it is concluded that cultural forms should not be considered identical to those in the vector.

Life-History ofCycas circinalis L.—Part IV

Embryogeny and seed germination stages have been studied. Two types of proembryo have been recorded. The suspensor is long and assumes a tortuous shape in its final position in the endosperm. Very small portion of the proembryo is used for the formation of the embryo proper, greater portion is being used for the formation of suspensor and the haustorial tissue. The embryo grows at first towards the centre of the endosperm, when it reaches almost the bottom of the endosperm, it begins its growth towards the micropyle. During this growth, the different parts of the embryo-coleorhiza, cotyledons and plumule are organised.