Longitudinal Ends Research Articles

Assessment of shape memory alloy stent deployment in a stenosed artery

Purpose — Shape memory alloy (SMA) stents have been used increasingly for the treatment of complex arterial occlusions. There is an immediate need to quantify the mechanical performance of SMA stents to open occluded arteries. Methods — The stent crimping and expanding process was assessed through both numerical modeling and in-vitro studies. The implantation of a SMA stent in curved arteries with eccentric stenosis were simulated to evaluate the effect of artery curvature on arterial mechanics. Results — The crimping process stored a considerable amount of strain energy in the stent, which were then released through self-expansion until a balance between the stent and stenosed artery was achieved. The deployed SMA stent exhibited a dog-bone shape, where the longitudinal ends of the stent penetrated into the artery causing arterial stress concentrations. However, the maximum arterial stress was observed at the central portion of artery contacting the thin side of the plaque. Furthermore, stent-induced arterial mechanics were more pronounced in the curved artery than the straight artery. The maximum Von Mises stress in the curved artery with a curvature of 0.05 mm -1 was 37% larger than that found in the straight artery. The percentage of the intimal area at higher stress level (> 0.05 MPa) is 5.51% in the curved artery, compared to 1.76% in the straight artery. Conclusions — This work provided a fundamental understanding of the behavior of SMA stent and its impact on the vascular wall, and illuminated the possibilities for exploiting their potential to alleviate arterial injury.

Cardiac expression of skeletal muscle sodium channels increases longitudinal conduction velocity in the canine 1-week myocardial infarction

Skeletal muscle sodium channel (Nav1.4) expression in border zone myocardium increases action potential upstroke velocity in depolarized isolated tissue. Because resting membrane potential in the 1-week canine infarct is reduced, we hypothesized that conduction velocity (CV) is greater in Nav1.4 dogs compared with in control dogs. The purpose of this study was to measure CV in the infarct border zone border in dogs with and without Nav1.4 expression. Adenovirus was injected in the infarct border zone in 34 dogs. The adenovirus incorporated the Nav1.4- and a green fluorescent protein (GFP) gene (Nav1.4 group, n = 16) or only GFP (n = 18). After 1 week, upstroke velocity and CV were measured by sequential microelectrode recordings at 4 and 7 mM [K(+)] in superfused epicardial slabs. High-density in vivo epicardial activation mapping was performed in a subgroup (8 Nav1.4, 6 GFP) at three to four locations in the border zone. Microscopy and antibody staining confirmed GFP or Nav1.4 expression. Infarct sizes were similar between groups (30.6% +/- 3% of left ventricle mass, mean +/- standard error of the mean). Longitudinal CV was greater in Nav1.4 than in GFP sites (58.5 +/- 1.8 vs. 53.3 +/- 1.2 cm/s, 20 and 15 sites, respectively; P <.05). Transverse CV was not different between the groups. In tissue slabs, dV/dt(max) was higher and CV was greater in Nav1.4 than in control at 7 mM [K(+)] (P <.05). Immunohistochemical Nav1.4 staining was seen at the longitudinal ends of the myocytes. Nav1.4 channels in myocardium surviving 1 week infarction increases longitudinal but not transverse CV, consistent with the increased dV/dt(max) and with the cellular localization of Nav1.4.

A New Ejector for Highly Viscous Liquid Using Inertia of Beam Buckling Deformation

This paper describes a newly developed ejector that uses the inertia of beam buckling deformation, which can eject highly viscous liquids of over 30mPas at room temperature, to be used for fabrication of uniform spherical particles. The ejector is simply a beam consisting of a fluid path and a nozzle located at the approximate center in the longitudinal direction. By applying compression and rotation, the concave bend of the beam gradually changes its shape in the ejecting direction, starting from both longitudinal ends. When this change approaches the center, a sudden reversal buckling occurs and the droplet is separated from the meniscus by the force of the inertia. Adequate conditions for ejecting small droplets of highly viscous liquids were estimated both from the results of experiments and fluid simulations. Requisite inertia was lowered with ease by forming rear-side openings in the fluid path. The authors also demonstrated case examples with the use of an ejector that was experimentally created.

남해안 전기 백악기 진주층의 호성 퇴적층에서 산출된 Lockeia gigantus ichnosp. nov.

남해안의 경남 진도에 분포하는 전기 백악기 진주층의 호성 실트암에서 약 450여 개의 생흔 화석 Lockeia가 발견되었다. 이 생흔 화석들은 상당히 길쭉한 씨앗 모양이며, 대부분 길이가 60-70 mm, 폭이 15-20 mm이다. 그들은 특징적으로 날카로운 세로 고랑이 양쪽 가장자리에서 급하게 경사진 부분과 접하며, 주변부는 융기되어 있고, 세로 고랑의 양쪽 끝부분은 뽀족하다. 이 생흔 화석은 신종인 Lockeia gigantus ichnosp. nov.로 기재한다. Lockeia gigantus와 함께 드물게 발견되는 담수 이매패류인 Plicatounio는 이 휴식 생흔 화석의 가장 유력한 생성자로 판단된다. 이 신종 생흔화석은 현재까지 알려진 Lockeia 중에서 가장 크고 백악기 육성 퇴적층에서 세계적으로 처음 보고된 Lockeia이다. 이 화석은 또한 얕은 호수 환경의 생물 군집에서 살았던 생흔 화석 생성자 (이매패류인 Plicatounio)와 관련된 휴식 생흔화석의 특이한 예이다. About 450 specimens of Lockeia were discovered from the lacustrine siltstone of the Early Cretaceous Jinju Formation of Jin Island, southern coast of Korea. They are very elongated, seed-shaped Lockeia characterized by a large size, mostly 60-70 mm long and 15-20 mm wide. They are characteristically sharp longitudinal furrow bounded by steeply inclined both margins, elevated marginal rims and sharp pointed both longitudinal furrow ends. This trace fossil is herein described as Lockeia gigantus ichnosp. nov. Plicatounio, a freshwater bivalve which does not occur occurs occasionally within Lockeia gigantus is regarded as the most-likely producer of this resting trace fossil. This new trace fossil represents the largest Lockeia ever known and the first record of Lockeia from the Cretaceous non-marine deposits in the world. This fossil also represents an unusual example of resting trace fossil (Lockeia) associated with a possible producer (bivalve Plicatounio) lived in community in the shallow lacustrine environment.

Thermoelastic Analysis of Functionally Graded Cylinders Under Axial Loading

An analytical thermoelasticity solution for hollow finite-length cylinders made of functionally graded materials exposed to thermal loads, internal pressure and axial loadings is presented. For this purpose, the governing differential equations of equilibrium are obtained using the principle of minimum total potential energy. A first-order shear deformation shell theory, which accounts for the transverse shear strains and rotations, is considered for expressing displacement field. The governing differential equations are reduced to a set of linear algebraic equations using Fourier expansion series of the displacement field components in the axial coordinate. Subsequently, solution of the linear algebraic equations yields the thermoelastic response of the problem. The effects of inhomogeneity constant on behavior of the functionally graded cylinder are investigated. According to the results, stress and displacement components behave nonlinearly, especially for the regions near the longitudinal ends of the functionally graded cylinders.

Flux Distribution in Linear Permanent-Magnet Synchronous Machines Including Longitudinal End Effects

We investigated the longitudinal ends' influence on the flux distribution in a permanent-magnet linear synchronous machine with an analytic model and with numeric finite-element methods. We derived a general analytic expression, on closed form, from a linear reluctance model. The model reveals that the flux in a linear machine differs from that in a rotating machine in several aspects. The longitudinal ends introduce a pairwise coupled flux pattern, which will behave differently in circuits with odd or even numbers of magnets. In linear machines with an even number of magnets the pairwise coupled flux will spread throughout the whole machine, whereas in linear machines with an odd number of magnets it will be transformed into an equally distributed flux in the middle. The latter case will give rise to a nonsymmetric air gap flux distribution, where every second pole has larger flux. We confirmed the pairwise coupled flux and the nonsymmetric air gap distribution predicted by the analytic model by finite-element simulations. We noted additional effects when nonlinear behavior of the steel is taken into account. We conclude that saturation counteracts the pairwise coupled flux pattern at the longitudinal ends. Again, a nonsymmetric air gap flux distribution occurs as the pairwise coupled flux is transformed into an equally coupled flux. The pairwise coupling of the flux and the nonsymmetric air gap flux distribution give rise to a number of secondary effects, which we discuss.

Strengthening of Machinable Glass-Mica Composites

The effect of additives has been studied to improve the strength of machinable glass-mica ceramics. Titania, Y2O3-doped partially stabilized zirconia (Y-PSZ) and celsian (Ba1-xSrxAl2Si2O8, x=0, 0.1 and 0.2) powders (10 mass%) were mixed to the previously prepared glass-mica powder (content of F-flogopite: 45 vol%) by using a ball mill. The ball-mill grinding without additives improves the strength from 144 to 172 MPa through the size reduction of mica grains and the increase in sintered density. The addition of TiO2 and Y-PSZ is more effective to the microstructural refinement and the strengthening (190 MPa/TiO2, 220 MPa/Y-PSZ). Y-PSZ particles are segregated to the longitudinal ends of mica grains and suppress their longitudinal growth. It is expected that the Y-PSZ particles act as the reinforcements to the glass matrix to enhance the strength. The growth of titania particles under sintering results in the limited effect to structural refinement and the smaller strength than that for Y-PSZ-doped materials. The addition of celsians is further effective to the size reduction of mica grains and related densification to improve the strength (203-241 MPa) markedly. The celsian particles do not show their coarsening as well as Y-PSZ, and dissolve to the glass phase during sintering gradually. It is considered that the dissolution of celsians suppresses the growth of mica grains by changing the chemical composition of the glass phase. The increase of Young's modulus of the celsian-doped glass phase should also contribute to the strengthening.

Treatment planning dosimetric parameters for seed at short distances: Effects of air channels and neighboring seeds based on Monte Carlo study

The dose distributions around two different arrangements of a single radioactive 192Ir seed in water, (1) with air channels at the ends, and (2) surrounded by two nonactive ("dummy") seeds on both longitudinal ends, were calculated using MCNP4C Monte Carlo simulations at distances up to 1 cm. The contributions from beta particles and electrons emitted by 192Ir were included in the calculations. The effects of (a) the air channels at the seed ends and (b) the interference effect of the dummy seeds on the dose distribution were quantified and compared. It was found that the dummy seeds do not cause significant dose reduction for radial distances beyond 0.05 cm from the seed center. It is decided to report the dose rate values and the dosimetric parameters in TG43 format for a single seed with air channels for use in treatment planning computer systems. The dose rate constant (at 1 cm) of 192Ir seed, lambda, is 1.108 cGyU(-1) h(-1). The values of radial dose function, g(r), are within 1% from the TG43 recommended polynomial fit, except for distances within 0.08 cm. The anisotropy function, F(r, theta), attains large values near the seed ends and shallow angles (up to 8), as well as many values greater than 2 at the 20 degrees polar angle. Treatment planning systems involving intravascular brachytherapy do not compromise the accuracy for dosimetry of multiple seed trains by summing single seed values in water.

High-density cable and method therefor

A high-density cable of a type suitable for transmitting ultrasound signals from an ultrasonic probe to multiplexing circuitry during a medical ultrasound procedure is provided. The cable includes one or more flexible circuits arranged within a flexible sheath that surrounds and confines the flexible circuits. Each flexible circuit includes an elongate flexible substrate with oppositely-disposed surfaces and multiple conductors on at least one of these surfaces. The opposing longitudinal ends of the substrate define integral connectors for connecting with respective output connectors and/or electronic devices, such as an ultrasonic probe or multiplexing circuitry.

Autolysis during in vitro tracheary element differentiation: formation and location of the perforation.

Tracheary elements differentiated from isolated Zinnia: mesophyll cells were observed at various times of culture under a scanning electron microscope. Perforation occurred on the primary wall at one of the longitudinal ends in single tracheary elements. In double tracheary elements, which both of two cells derived from a single cell differentiated into, the pore opened on the primary walls both at the junction of the two tracheary elements and at a longitudinal end of one of the two tracheary elements. These results suggest not only that a single tracheary element has its own program to form a perforation at one end without being affected by neighboring cells, but also that isolated cells indeed hold some traces of polarity and cell-cell communication.

Myofibrillogenesis and formation of cell contacts mediate the localization of N‐RAP in cultured chick cardiomyocytes

The expression of N-RAP was investigated in immuofluorescently stained embryonic chick cardiomyocyte cultures. After 1 day in culture, the cardiomyocytes were spherical and N-RAP, titin, α-actinin, and vinculin were all diffusely distributed. As the cardiomyocytes spread and formed myofibrils and cell contacts, N-RAP became localized to distinct areas in the cells. During myofibrillogenesis, N-RAP was found concentrated in premyofibrils. As the premyofibrils transformed into bundles of mature myofibrils, N-RAP became concentrated at the longitundal ends of the cells, and was not found in the mature sarcomeres. At sites of cell-cell contacts, N-RAP was localized to the cell junction even in cells without any significant myofibril formation. As the cell-cell contacts became more extensive and formed structures resembling the intercalated disks found in hearts, N-RAP became even more specifically concentrated at these junctions. The results show that myofibrillogenesis and cell contact formation can each independently target N-RAP to the longitudinal ends of cardiomyocytes. Cell Motil. Cytoskeleton 47:63–76, 2000. Published 2000 Wiley-Liss, Inc.

Myofibrillogenesis and formation of cell contacts mediate the localization of N-RAP in cultured chick cardiomyocytes.

The expression of N-RAP was investigated in immuofluorescently stained embryonic chick cardiomyocyte cultures. After 1 day in culture, the cardiomyocytes were spherical and N-RAP, titin, alpha-actinin, and vinculin were all diffusely distributed. As the cardiomyocytes spread and formed myofibrils and cell contacts, N-RAP became localized to distinct areas in the cells. During myofibrillogenesis, N-RAP was found concentrated in premyofibrils. As the premyofibrils transformed into bundles of mature myofibrils, N-RAP became concentrated at the longitundal ends of the cells, and was not found in the mature sarcomeres. At sites of cell-cell contacts, N-RAP was localized to the cell junction even in cells without any significant myofibril formation. As the cell-cell contacts became more extensive and formed structures resembling the intercalated disks found in hearts, N-RAP became even more specifically concentrated at these junctions. The results show that myofibrillogenesis and cell contact formation can each independently target N-RAP to the longitudinal ends of cardiomyocytes.

Effects of steady electric fields on human retinal pigment epithelial cell orientation and migration in culture.

Low-level, steady electric fields of 6-10 volts/cm stimulated directional orientation and translocation of cultured human retinal pigment epithelial cells. The orientative movements (galvanotropism) consisted of somatic elongation of the cells into spindle shapes, followed by pivotal alignment orthogonal to the field. The anodal edges of the cells underwent retraction of their plasmalemmal extensions, while the cathode edges and the longitudinal ends developed lamellipodia and ruffled membranes. These tropic movements were followed by a translocational movement (galvanotaxis) of the cells towards the cathode. Staining of these migrating cells for actin showed the accumulation of stress fibers at the leading (cathodal) edge, as well as at the longitudinal ends of the elongated somata. These results suggest that endogenous, biologically-generated electric fields (eg., injury currents) may play a role in the guidance and migration of retinal pigment epithelial cells after retinal injury.

Effects of electric fields on cytoskeleton of corneal stromal fibroblasts

Low-level, steady electric fields (6-10 volts/cm) stimulated cultured corneal stromal fibroblasts to undergo directional orientation and translocation. The orientative movements (galvanotropism) consisted of somatic elongation of the cells into spindle shapes along an imaginary axis perpendicular to the field; the cathodal edge of the cell underwent retraction, while the anodal edge and the longitudinal ends developed ruffled membranes and lamellipodia. The translocational movements (galvanotaxis) consisted of directed migration of the cells towards the anode. While most actin-containing stress fibers became aligned along the long axes of the elongated fibroblasts (with distal ends of the stress fibers terminating at the longitudinal extremes of the cells), some were aligned towards the anodal direction (with distal terminations inside ruffled membranes and lamellipodia on the leading anodal edge of cells). The distal ends of stress fibers were associated with discrete foci of vinculin, ie, focal indicators of cell-to-substrate adhesion; these foci were abundant at the longitudinal ends and at the anodal edge of the elongated cells. The observed cytoskeletal changes are consistent with an active, rather than passive, directed migration of stromal fibroblasts in response to constant electric fields.

4751464 Cavity resonator with improved magnetic field uniformity for high frequency operation and reduced dielectric heating in NMR imaging devices

A cavity resonator suitable for use in a high-speed nuclear magnetic resonance (NMR) imaging device comprises a plurality of transmission lines aligned parallel to a common axis and magnetically coupled to produce an essentially uniform dipole magnetic field perpendicular to the axis. The transmission lines are two conductor lines, with the first conductors being arranged inwardly of a second conductor common to all lines. The common conductor is symmetrically arranged about the axis of the resonator and constitutes a shield to contain the magnetic field within the cavity. The plurality of transmission lines are conductively isolated from each other but spaced in sufficiently close proximity to each to provide for strong mutual magnetic coupling amongst all transmission lines. A single inductive coupling loop may be provided for driving the resonator with a linearly polarized magnetic field and for receiving NMR information from the resonator. The use of a pair of inductive coupling loops spaced 90° about the resonator axis provides a circularly polarized magnetic field within the resonator when the loops are driven in electrical phase quadrature. Two inductive coupling loops for each imaging mode may be provided to eleminate undesirable modes and hence distortion in the NMR image. The common conductor and the longitudinal ends of the resonator are provided with slits designed to allow the changing high-speed gradient magnetic fields to fill the imaging volume fast enough to accomplish high-speed imaging.

Modeling of elongated fine ferromagnetic particles

This paper presents some results of a numerical micromagnetic calculation for ferromagnetic fine particles. Two basic shapes are discussed: elongated parallelopipeds and parallelopipeds with pointed ends. The variation of coercivity, switching field, and reversal modes with particle size, orientation, and material parameters are discussed. Equilibrium magnetization structures suggest that particles may have remanent states that are substantially nonuniform. The flipping mode, in which the magnetization reversal starts from the longitudinal ends of the particles, is found to be the energetically favorable switching mechanism. Small particles are switched by the quasi-coherent flipping mode, while large particles are reversed by the quasi-curling flipping mode. The angular dependence of the coercive and switching fields for three particle sizes is found to agree qualitatively with classical results, but both fields are quantitatively smaller. The nucleation field is compared with the Stoner–Wohlfarth model as well as with the curling mode, and is found to be about half of their value.

The electroacoustic description of an underwater magnetohydrodynamic transducer

The Lorentz law, electromagnetic force in a conducting‐dielectric, compressible, fluid medium, is investigated as a source of underwater acoustic radiation. The transducer system investigated consists of a duct which confines a conducting‐dielectric fluid medium. A time‐steady magnetic field and mutually orthogonal time‐varying current density are established across the transverse dimensions of the duct. The system radiates from the longitudinal ends of the duct in a dipole, two‐point array mariner. The electroacoustic system equations in two port form, theoretical and experimental projector sensitivity, and pressure field directivity patterns will be discussed. [Work supported by ONR.]

Cell-matrix interrelation and cell-to-cell connection in the secretory ameloblast layer of kitten teeth.

To investigate the cell-matrix interrelation and the structure and permeability of the junctional complexes of secretory ameloblasts, molar tooth germs from kittens were examined by means of scanning electron microscopy, routine thin sections and freeze-fracture replication. Scanning electron microscopy showed remarkably dissolved growth fronts of enamel in materials that had been fixed with glutaraldehyde and then subjected to EDTA perfusion for 10 min. By the action of EDTA, intercrystallite spaces in rod and interrod enamel were prominently widened, and their longitudinal ends of crystallites displayed irregular and extremely sparse structures. In enamel rods surrounded entirely by interrod enamel, and in enamel rods of the typical key hole shape with successive interrod enamel participation, the most striking dissolution of crystallites occurred at the boundaries between rod and interrod enamel, where broad expanses of rod-sheath spaces were observed. In thin sections, the Tomes processes of secretory ameloblasts occupying the above rods were rectangular or variations of a rectangular shape, respectively; and interameloblast spaces opened to the enamel growth fronts, which corresponded to the junction between rod and interrod enamel. In enamel rods standing in regular rows and showing the typical arcade shape, the centers of the rods were drastically dissolved and exhibited single and deep slits, whereas the boundaries between rod and interrod enamel showed no wide furrows. The Tomes processes occupying such arcade-shaped rods were typically triangular, and the interameloblast space always joined the type-1 face of process, which is responsible for enamel rod formation. Secretory ameloblast possessed two sets of junctional complexes at the proximal and distal ends of the cell body. The distal one was situated proximally to the Tomes process. Freeze-fracture replication demonstrated the functional structures of these junctions: the proximal junction was fascia occludens, and the distal one incomplete zonula occludens with many free-ending tight junctional strands and interstrand spaces or a less developed irregular junction.

Myofiber damage accompanying intramuscular parasitism by Sarcocystis muris

Myofiber degeneration which results from Sarcocystis infection exhibits a number of fine structural features suggestive of other myopathies and several welldefined fine structural features not characteristic of other myopathies. Some of these fine structural features are similar to those observed in intramuscular infections of Trichinella spiralis, another muscle parasite. Major alterations of the myofibrillar contractile apparatus occur at the periphery of the membrane bound parasitophorous vacuole which include splitting and fragmentation of the myofibrils at the longitudinal ends of the parasitophorous vacuole and Z line dissolution at the radial periphery. Membranous structural elements including mitochondria, sarcoplasmic reticulum and T system components become disarrayed as the myofibrils degenerate. Some minor hypertrophy of the sarcoplasmic reticulum occurs in conjunction with initial fragmentation of the myofibrils but no major dilation or hypertrophy has been observed. There is a distinctive membranous organization of the interface of the parasitophorous vacuole. The presence of pycnotic and fragmenting nuclei, sarcolemmal invaginations with accompanying fibrous connective tissue invasion and large areas of undifferentiated cytoplasm suggest the ultimate necrosis and destruction of infected myofibers. The similarity between morphological features of myofibrillar degeneration accompanying intramuscular Sarcocystis muris infections and those associated with a variety of myopathies resulting from other causes suggests that a common mechanism of muscle response to damage might result in the observed structural degeneration.

On the distribution of tree growth stresses ? Part I: An anisotropic plane strain theory

Growth stress distributions in trees are derived using the hypothesis that longitudinal and circumferential growth strains are continuously induced at the periphery of the growing stem. An axisymmetric plane deformation model serves as a basis for the cylindrically orthotropic analysis. By accounting for the influence on the total stress distribution of the strains in each new growth increment, a self-equilibriating distribution of growth stresses develops in the stem. In regions away from the central core of the stem, a simple closed form solution of the general anisotropic problem is given. The growth stress results of Kubler can be recovered from the present results by assuming isotropy in the cross section of the stem and avoiding the central region near the pith. The transition point where the peripheral longitudinal tension zone ends is shown to remain essentially unchanged in the more general theory from that given by Kubler. However, the point where the compression circumferential stress zone ends is shown to be a function of the ratio of the modulii in the radial and circumferential directions whereas in Kublers' theory it was independent of the elastic constants. Detailed results are given for the development of growth stresses as the stem grows and comparisons with the earlier theory noted.