Rhomboidal Cells Research Articles

Periodic rhomboidal cells for symmetry-preserving homogenization and isotropic metamaterials

In the design and analysis of composite materials based on periodic arrangements of sub-units it is of paramount importance to control the emergent material symmetry in relation to the elastic response. The target material symmetry plays also an important role in additive manufacturing. In numerous applications it would be useful to obtain effectively isotropic materials. While these typically emerge from a random microstructure, it is not obvious how to achieve isotropy with a periodic order. We prove that arrangements of inclusions based on a rhomboidal cell that generates the face-centered cubic lattice do in fact preserve any material symmetry of the constituents, so that spherical inclusions of isotropic materials in an isotropic matrix produce effectively isotropic composites.

A new moss species from northwestern China: Bryum glacierum (Bryaceae)

The form of the gemmae appears to be constant within Bryum species, and it is an important character for distinguishing among closely related species. In this study, we describe a new species of Bryum, B. glacierum Y.Y. Liu & Y.H. Wu, that was collected from Tianshan Mountain in China along with a description of its gemmae. This species is distinguished morphologically by (1) gemmiforfm to julaceous shoots; (2) broadly ovate leaves, strongly concave, with obtuse to acuminate apex, plane and undifferentiated leaf margins, rhombic to rhomboidal distal and medial cells; and (3) dark red-brown, obconic or ovate bulbils with peg-like leaf primordia, densely clustered in the leaf axils of sterile shoots. The new moss species is currently known from two localities in northwestern China. The species seems to prefer high altitudes, growing as a pioneer mainly on ground exposed by retreating glaciers. The principal distinctive characters that separate Bryum glacierum from similar species of Bryum and Pohlia are discussed. An identification key for bulbiferous species of Bryum in China is provided.

Numerical and Experimental Analysis of Labyrinth Seals with Rhomboidal Cells

The labyrinth seals are devices commonly used in turbomachinery to reduce hot gas leakages through engine clearances, which adversely affect the gas turbine performance. For this reason, in the last decades, many in-depth analyses and optimization studies were carried out on this topic using experimental, analytical and numerical approaches. In this work, an innovative rhomboidal pattern is presented, obtained through Computational Fluid Dynamics (CFD) simulations, which is more dissipative than commonly used honeycomb cells. The experiments, performed using a Test Article that reproduces a stage and the next stator of a real low-pressure turbine suitably scaled, allowed to validate the numerical results in a situation that closely approximates the real one of use. The results obtained show that the leakages flow fraction of the total mass flow rate that bypasses the blade, which is 29.4% using a honeycomb pattern, is reduced to 27% with rhomboidal cells. The experimental results also made it possible to verify that the new pattern also behaves well from a thermal point of view, giving rise to temperature differences with respect to the honeycomb of less than 1%.

The sphenoidal emissary foramen and the emissary vein: Anatomy and clinical relevance.

Although the sphenoidal emissary foramen (SEF) and its content are anatomically and clinically relevant, accurate description of them in the modern literature is lacking. This study aimed to examine and describe the SEF and its content (the sphenoidal emissary vein [SEV]). We analyzed 1,000 computed tomography (CT) images, 170 dry skulls, 50 formalin-fixed specimens, and three specimens (heads) following guidelines proposed by Dr. Albert L. Rhoton Jr. MD for latex injection. SEV morphology was determined by histological staining and electron microscopy. The SEF was observed in 46.8% of the CTs studied (25.4% bilateral and 21.4% unilateral), and 45.2% of the dry skulls (18.8% bilateral and 26.4% unilateral). In 9.5% of CTs and 21.1% of dry skulls there was a blind channel in the external surface of the cranial base; since there was no communication with the cranial cavity, it was not considered as the SEF. During the dissections, the SEF was found in seven individuals. In three of them, the SEV was an alternative route for venous drainage of the venous plexus of the foramen ovale. Its walls were composed of collagen fibers and its endothelium contained rhomboid cells resembling those commonly found in the superior sagittal sinus. The presence of the SEF and SEV can anatomically explain the spread of certain cranial base pathologies from or toward Meckel's cave or the cavernous sinus, and should be taken into account during procedures in the middle cranial fossa, percutaneous approaches, odontological procedures, and treatment of dural arteriovenous fistulas. Clin. Anat., 33:767-781, 2020. © 2019 Wiley Periodicals, Inc.

Augmenting fish health usingEmblica officinalisagainst triarylmethane dye induced blood toxicity inCyprinus carpio

Blood is a sensitive bioindicator of stress observed by organisms in response to toxicants. Erythrocytic morphological abnormalities serve as a reliable determinant of fish health. Malachite green, a multifunctional dye was assessed for toxicity in Cyprinus carpio. Dye-induced blood toxicity has been determined through biochemical and ultra structural endpoints at 15, 30 and 60 days in the fish. Further, an attempt has been made to combat the adverse effects of the toxicant through supplementation with Emblica officinalis. Electron microscopic study depicted erythrocytic remodelling in form of surface blebbing, lobopodial projections and shrinkage; appearance of crenate, acanthocytes, echinocytes, dacrocytes, spherocytes and rhomboidal cells. Hepatic marker enzymes showed significantly (p < 0.05) elevated levels of biomarker enzymes, alkaline phosphatase, serum glutamate oxaloacetate transaminase and serum glutamate pyruvate transaminase. Contrarily feeding with E. officinalis extract (1,000 mg/kg feed) significantly attenuated biochemical and morphological alterations, indicating the protective efficacy of E. officinalis. Both toxicity and attenuation observed were in exposure-dependent manner.

Localized patterns in crushed conical shells

We use experiments and numerical simulations to study the rapid buckling of thin-walled cones as they impact a solid surface at high velocities. The buildup of air pressure inside the cone localizes the deformations to the impacting interface with the solid surface, leading to the hierarchical formation of an ordered pattern of small rhomboidal cells. In contrast, when the inner air pressure is not allowed to develop, the ordered pattern is destabilized and the cone collapses in a highly disordered state on long length scales. Numerical simulations confirm that the transition between ordered and disordered crumpling is governed by the competition between the elastic deformation energy of the shells and the work required to pressurize the air. Our results show how dynamic stabilization via tensioning suppresses long wavelength subcritical instabilities in shells and leads to the localization and propagation of short wavelength patterns.

Phenotypic alteration of vascular smooth muscle cells as a sequence of mild hyper‐caloric intake in the absence of hyperglycemia: Potential modulation by antidiabetic drugs

Diabetic patients remain at a high risk of atherosclerotic cardiovascular disease in addition to hypertension and microvascular complications. A significant proportion of diabetic patients present with vascular abnormalities upon initial diagnosis implicating an early vascular insult in the course of development of diabetes. A contractile‐to‐synthetic vascular smooth muscle cell (VSMC) phenotypic switch is associated with different diseases including atherosclerosis, diabetes, hypertension, and cancer. In the present study, we examined whether early metabolic derangement in the course of diabetes development was associated with VSMC phenotypic alteration before hyperglycemia develops. For this purpose, we used a high‐calorie diet (HC) fed rat model with delayed development of hyperglycemia. Up to 12 weeks of feeding, neither increased serum glucose nor elevated mean arterial pressure was detected. Control and HC rats were sacrificed at 4, 8, and 12 weeks, and their aortae were dissected for isolation of primary VSMCs. VSMC morphology changed whereby the typical hill‐and‐valley culture pattern was gradually substituted by densely packed areas of rhomboid cells in explants for aortic tissues from HC rats. This changed appeared to be dependent on the duration of feeding. VSMC proliferation and migration increased in cultures derived from HC‐fed rats compared to controls at the same age and passage number. Moreover, VSMC contractile phenotype markers smooth muscle alpha actin and calponin gradually decreased in cells cultured from HC‐fed rats in a manner proportional to the feeding duration. In vitro, exposure to pioglitazone, but not metformin was associated with a reduction in VSMC proliferation in cells derived from HC‐fed rats. On the contrary, similar exposure to increased oleiate and palmitate concentrations in the culture medium resulted in an increased proliferation of VSMCs from control rats. Our results indicate that VSMC phenotype and function is potentially affected by the early metabolic derangement associated with the development of diabetes regardless of the blood glucose concentration. Studies to investigate the effect of chronic exposure of HC‐fed rats to metformin and pioglitazone on VSMC phenotype are underway.Support or Funding InformationSupported by AUB MPP fund #320148This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Taxonomic Revision of the Moss GenusLepidopilidium(Pilotrichaceae)1

Abstract Lepidopilidium (Mull. Hal.) Broth. (Pilotrichaceae) consists of mainly epiphytic and epiphyllous, pleurocarpous mosses distributed in the tropical, subtropical, and south temperate regions of Central America, South America, Africa, southern India, and Sri Lanka. The genus is characterized by a moderately to strongly complanate habit; the presence of a moderately to well-developed stem hyalodermis; dimorphic dorsal, ventral, and lateral leaves; prominent double costae; smooth, hexagonal, rhomboidal, or fusiform leaf cells; smooth or papillose setae; collenchymatous exothecial cells; 2-celled stomata; massive annuli; a hookeriaceous-type peristome; and sparsely pilose or glabrous mitrate calyptrae. Six species are taxonomically accepted: L. brevisetum (Hampe) Broth., L. devexum (Mitt.) Broth., L. divaricatum (Dozy & Molk.) Broth., L. furcatum (Thwaites & Mitt.) Broth., L. isleanum (Besch.) Broth., and L. nitens (Hornsch.) Broth., with 19 names newly synonymized. Lepidopilum chenagonii Renauld & Car...

Regulation of S100A4 expression via the JAK2–STAT3 pathway in rhomboid-phenotype pulmonary arterial smooth muscle cells exposure to hypoxia

To investigate the effect of JAKs–STATs signal pathway on expression of S100A4 in pulmonary arterial smooth muscle cells (PASMCs), the action of S100A4 and hypoxia induced factor 1 (HIF-1) on the proliferation of hypoxic PASMCs.The results showed that S100A4 immunostaining was localized in the cytoplasm and nuclei of PASMCs exposure to hypoxia and it was predominantly expressed in rhomboid cells (R-SMCs). The mRNA and protein levels of S100A4 expression increased in PASMCs after hypoxic stimulus for 4, 8, 16h. The immunofluorescence intensity and protein levels of S100A4 were suppressed, and the number of R-SMCs was reduced, when pretreatment with HIF-1α siRNA, STAT3 siRNA, S100A4 siRNA, and S100A4 inhibitor NSC 95397. Pretreatment with HIF-1α siRNA and anti-IL-6 antibodies, the levels of phospho-JAK2, -STAT3, and S100A4 were decreased, while HIF-1α kept stable in hypoxic cells. Importantly, pretreatment with HIF-1α siRNA, anti-IL-6 antibodies, STAT3 siRNA, and S100A4 siRNA, significantly attenuated the proliferation of PASMCs exposure to hypoxia. These data demonstrate that S100A4 is predominantly expressed in hypoxic R-SMCs, and regulated by the activation of JAK2–STAT3 signal pathway, which is dependent on hypoxia-induced HIF-1α expression. These results suggest that JAK2–STAT3 and HIF-1α could serve as targets for the regulation of phenotype modulation of PASMCs during the process of pulmonary vessel lesions.

Morphological and physiological modifications of cyanobacteria in experimental cyanobacterium-actinomycete associations

Associations of cyanobacteria and actinomycetes were formed experimentally from the cyanobacterium Anabaena variabilis ATCC 29413 and the streptomycetes isolated from apogeotropic roots of sago plants. Based on their phenotypic properties and the 16S rRNA gene sequencing, the streptomycetes were identified as representatives of Streptomyces pluricolorescens (strains 1 and 2). Cyanobacteria developing in monoculture and in association with an actinomycete were essentially different in their morphological and physiological-biochemical characteristics. In associations, cyanobacteria showed a higher (by tens of times) nitrogen-fixing activity compared to the monoculture and the morphological modifications of which were not observed in the monoculture (increase in cell size, increase in the portion of heterocysts among vegetative cells, appearance of the forms of unbalanced growth of cyanobacteria as giant, disc-shaped, curved, and rhomboid cells). At extremely low humidity (aw 0.50), associated cyanobacterial cells remained viable, whereas in the monoculture, chlorophyll decomposition and cells death occurred. The methods of high-resolution (H1 600 MHz) nuclear magnetic resonance (NMR) and pulsed-gradient spin echo NMR revealed a fraction of mobile protons in lyophilized samples of the cyanobacterium-actinomycete association, which was evidence of the presence of free water. This fraction was not found in the lyophilized samples of cyanobacterial and streptomycete monocultures. The revealed differences can explain the survival of cyanobacterial cells in associations.

NF-κB–Dependent Plasticity of the Epithelial to Mesenchymal Transition Induced by Von Hippel-Lindau Inactivation in Renal Cell Carcinomas

The critical downstream signaling consequences contributing to renal cancer as a result of loss of the tumor suppressor gene von Hippel-Lindau (VHL) have yet to be fully elucidated. Here, we report that VHL loss results in an epithelial to mesenchymal transition (EMT). In studies of paired isogenic cell lines, VHL silencing increased the levels of N-cadherin and vimentin and reduced the levels of E-cadherin relative to the parental VHL(+) cell line, which displayed the opposite profile. VHL(+) cells grew as clusters of cuboidal and rhomboid cells, whereas VHL-silenced cells took on an elongated, fibroblastoid morphology associated with a more highly invasive character in Matrigel chamber assays. Based on earlier evidence that VHL loss can activate NF-kappaB, a known mediator of EMT, we tested whether NF-kappaB contributed to VHL-mediated effects on EMT. On pharmacologic or molecular inhibition of NF-kappaB, VHL-silenced cells regained expression of E-cadherin, lost expression of N-cadherin, and reversed their highly invasive phenotype. Introducing a pVHL-resistant hypoxia-inducible factor 1alpha (HIF1alpha) mutant (HIFalpha(M)) into VHL(+) cells heightened NF-kappaB activity, phenocopying EMT effects produced by VHL silencing. Conversely, inhibiting the heightened NF-kappaB activity in this setting reversed the EMT phenotype. Taken together, these results suggest that VHL loss induces an EMT that is largely dependent on HIFalpha-induced NF-kappaB. Our findings rationalize targeting the NF-kappaB pathway as a therapeutic strategy to treat renal tumors characterized by biallelic VHL inactivation.

Sustained hypoxia leads to the emergence of cells with enhanced growth, migratory, and promitogenic potentials within the distal pulmonary artery wall

All forms of chronic pulmonary hypertension (PH) are characterized by structural remodeling of the pulmonary artery (PA) media, a process previously attributed solely to changes in the phenotype of resident smooth muscle cells (SMC). However, recent experimental evidence in both systemic and pulmonary circulations suggests that other cell types, including circulating and local progenitors, contribute significantly to this process. The goal of this study was to determine if hypoxia-induced remodeling of distal PA (dPA) media involves the emergence of cells with phenotypic and functional characteristics distinct from those of resident dPA SMC and fibroblasts. In vivo, in contrast to the phenotypically uniform SMC composition of dPA media in control calves, the remodeled dPA media of neonatal calves with severe hypoxia-induced PH comprised cells exhibiting a distinct phenotype, including the expression of hematopoetic (CD45), leukocytic/monocytic (CD11b, CD14), progenitor (cKit), and motility-associated (S100A4) cell markers. Consistent with these in vivo observations, primary cell cultures isolated from dPA media of hypertensive calves yielded not only differentiated SMC, but also smaller, morphologically rhomboidal (thus termed here "R") cells that transiently expressed CD11b, constitutively expressed the mesenchymal cell marker type I procollagen, expressed high mRNA levels of progenitor cell markers cKit, CD34, CD73, as well as for inflammatory mediators, IL-6 and MCP-1, and, with time in culture, gained expression of a myofibroblast marker, alpha-SM-actin. R cells exhibited highly augmented proliferative, migratory, invasive, and potent promitogenic capabilities, which were due, at least in part, to the production of PDGFs, SDF-1/CXCL12, and S100A4. These data suggest that the cellular mechanisms of dPA remodeling include the emergence of cells with phenotypic and functional characteristics markedly distinct from those of resident dPA cells.

Characterization of cell motility in single heart valve interstitial cells in vitro.

Valve interstitial cells (VIC) are the most prevalent cells in the heart valve, regulating to a large extent the normal biology of the valve and its pathobiological response to disease. In the process of valve tissue repair by VICs, single cell motility is likely to be important, as it is in wound repair by most mesenchymal type cells. We designed in vitro experiments using low density monolayer cultures to study the association of morphology and motility in single VICs which expressed alpha-smooth muscle actin. We observed that the morphology of single VICs can be categorized into six types which are reminiscent of the shape of VICs seen in vivo during valve repair. Of these morphologies, round, rhomboid, tailed and spindled shaped VICs were the most common. VICs did change their morphology over time. Rhomboid cells could become tailed or spindle-shaped and vice versa. Using time-lapse imaging and immunofluorescent microscopy, we showed that VIC morphologies reflect differences in cell motility and cell-matrix interactions. Tailed and spindle-shaped VICs were the predominant motile types and were associated with few extracellular fibronectin fibrils and less focal adhesions, as demonstrated by vinculin staining. Round and rhomboid shaped VICs were less motile and were associated with prominent vinculin and extracellular fibronectin fibrils. We found that cell mitosis is an important determinant of VIC migration. Many of the motile VICs were associated with mitosis as the daughter cells separated by migrating as tailed and spindle shaped cells. Thus cell morphology is an important determinant of VIC motility.

Border of Notch activity establishes a boundary between the two dorsal appendage tube cell types

Boundaries establish and maintain separate populations of cells critical for organ formation. We show that Notch signaling establishes the boundary between two types of post-mitotic epithelial cells, the Rhomboid- and the Broad-positive cells. These cells will undergo morphogenetic movements to generate the two sides of a simple organ, the dorsal appendage tube of the Drosophila egg chamber. The boundary forms due to a difference in Notch levels in adjacent cells. The Notch expression pattern mimics the boundary; Notch levels are high in Rhomboid cells and low in Broad cells. Notch − mutant clones generate an ectopic boundary: ectopic Rhomboid cells arise in Notch + cells adjacent to the Notch − mutant cells but not further away from the clonal border. Pangolin, a component of the Wingless pathway, is required for Broad expression and for rhomboid repression. We further show that Broad represses rhomboid cell autonomously. Our data provide a foundation for understanding how a single row of Rhomboid cells arises adjacent to the Broad cells in the dorsal appendage primordia. Generating a boundary by the Notch pathway might constitute an evolutionarily conserved first step during organ formation in many tissues.

The identity of Isothecium marocanum Thér. & Meyl.

Within a larger study of the genus Isothecium, a search for type material of Isothecium marocanum Ther. & Meyl. was performed. This taxon was described from Morocco in 1932 (Theriot & Meylan, 1932), but has not been further reported or revised. Type material was not found during a general search for all available Moroccan bryophyte material in Paris (PC; R. M. Ros and M. J. Cano, pers. comm.), where I. Theriot's original herbarium is located, but we traced an isotype in J. Braun-Blanquet's herbarium with the help of J. Mathez in Montpellier (MPU) and B. Toussaint in Bailleul (BAIL). Braun-Blanquet's bryophyte herbarium will soon be moved from BAIL to MPU, where the rest of his herbarium is already housed. The isotype is mixed with Homalothecium sericeum (Hedw.) Schimp., which was also noted on the envelope of the type, and a small piece of Orthotrichum lyellii Hook. & Taylor. Originally, Theriot had written an unpublished herbarium name on the specimen, but it undoubtedly belongs to the species we today call Scorpiurium deflexifolium (Solms) M.Fleisch. & Loeske. The type of I. marocanum agrees completely with the latter in leaf shape and areolation. The leaves are ovate, strongly narrowed towards their insertion, and gradually narrowed towards a broadly acute apex. The single costa ends shortly below the leaf apex, and the margin is recurved in its lower part and plane and denticulate or strongly so above. The marginal cells are similar to those further in, whereas in Isothecium the marginal cells are frequently shorter than the lamina cells closer to the costa. The median leaf lamina cells are 15-4065-9 mm and smooth, and the rectangular, quadrate or rhomboidal alar cells form a triangular or ovate, indistinctly delimited unistratose group that extends up along leaf margin 20-30% of the leaf length. In Isothecium the alar cells are usually partly bistratose near the leaf insertion, strongly incrassate, opaque and form indistinct, yellowish to brownish auricles. All the material of Isothecium marocanum is sterile, and sporophytes have not been described (Theriot & Meylan, 1932). While the holotype could potentially exist in Meylan's herbarium in Lausanne (LAU), we do not lectotypify the name, but make the following synonymy:

Theory of the Orthogonal Dimer Heisenberg Spin Model for SrCu2(BO3)2

AbstractFor Abstract see ChemInform Abstract in Full Text.

Alkoxo-bridged binuclear copper(II) complexes as nodes in constructing extended structures

Three new compounds exhibiting extended structures have been obtained by using alkoxo-bridged binuclear copper(II) complexes as nodes, and bis(4-pyridyl) derivatives as spacers: [Cu 2(H 2tea) 2(bpe)](ClO 4) 2·(bpe)·H 2O ( 1), [Cu 2(Hdea) 2(4,4′-bipy)](ClO 4) 2 ( 2), and [Cu 2(ap) 2(4,4′-bipy) 2](ClO 4) 3·(4,4′-bipy)·(H 2ap)·(H 2O) ( 3) (H 3tea=triethanolamine, H 2dea=diethanolamine, Hap=aminopropanol; bpe= trans-1,2-bis(4-pyridyl)ethylene, 4,4′-bipy=4,4′-bipyridine). The structure of 1 consists of infinite chains resulted by connecting the bis(alkoxo)-bridged unsymmetrical [Cu 2(H 2tea) 2] 2+ nodes with bis(4-pyridyl)ethylene rods. The Cu⋯Cu separations are of 2.924 and 13.402 Å in an alternate mode. The noncoordinated bpe molecules bind the parallel coordination polymer chains, spread along b axis, through intermolecular H-bonds, resulting in a double zigzag ladder network. In crystal 2, the 4,4′-bipy molecules connect centrosymmetric [Cu 2(Hdea) 2] 2+ nodes, resulting in infinite chains. The parallel chains are disposed in planes which are parallel to the ab crystallographic plane. The chains directions, [110] or [1−10], alternate in adjacent planes. The stereochemistry of the copper(II) ion is distorted square-pyramidal. The alternate Cu⋯Cu distances within the chain are: 2.9880(5) and 11.0310(5) Å. Compound 3 is a two-dimensional coordination polymer. There are two crystallographically independent centrosymmetric [Cu 2(ap) 2] cores. The distances between the alkoxo-bridged copper atoms within the nodes are: 3.071(2) and 3.036(2) Å. Each node is connected through four 4,4′-bipy bridges to four other nodes, resulting in a two-dimensional layer with rhombic meshes. The dimensions of the rhomboidal cells are 12.31 and 13.36 Å, with an angle between the edges of 83.4°. The uncoordinated 4,4′-bipy and water molecules, the H 2pa + (monoprotonated aminopropanol species) and perchlorate ions are interconnected through hydrogen bonds resulting in infinite chains. These hydrogen-bonded polymers fill the channels resulted through the stacking of the 2-D layers.

Axisymmetric deformation of shells of revolution made of fiber-reinforced elastomeric layers

The study of the deformation of shells of fiber-reinforced elastomers is based on a structural approach in which the elastomeric matrix and reinforcement are considered separately, without reduction of the composite to a medium having continuously changing characteristics. The concept underlying this approach was first explained in [1], where a momentless model of deformation was used as the basis for describing a method of designing a rubber shell with a reticular reinforcement and no binder. In [2], calculations were performed for certain shells of revolution made of an elastomer and reinforced along the middle surface using fibers with little or no tensility. The effect of the reinforcement was accounted for by a method employed to analyze momentless shells. Line~-r relations from the theory of elasticity were used in [3] to construct a momentless model of the deformation of a shell with a reticular reinforcement with allowance for the effect of the binder. In [4], a method was presented for solving momentless problems of the deformation of multilayered shells of revolution. Here, the mechanical properties of the reinforcing fibers and binders were described with the use of nonlinear elastic relations. The well-known models of deformation do not consider the moment character of the stress state of composite shells made of elastomeric layers. They are suitable for the design of very thin axisymmetric shells, in which the stress state is of a membrane (momentless) character. Here, we construct a structural model that describes the axisymmetric deformation of moment shells of revolution composed of elastomeric layers unidirectionally reinforced with fibers. The method is based on an iterative procedure for the design of shells of this type and employs the hypothesis of a compressible normal element. In accordance with this hypothesis, a normal element of the shell remains straight and normal to the plane of reference during deformation, undergoing elongations that vary through the thickness of each layer. The volume occupied by the reinforcing fibers is assumed to be small compared to the volume occupied by the binder. In accordance with the smallness of the relative volume of the reinforcement, the cross section of the fibers is assumed to be infinitely small. We will use an iterative method to determine the parameters of the deformed shell at each point of discretization of the given boundary-value problem. 1. We will examine a thin composite shell of N elastomeric layers unldirectionally reinforced with fibers. We will assume that the fibers are crossed (arranged antisymmetrically) in any two adjacent layers to form a reinforcing grid with rhomboid cells. The fibers may be arranged in the meridional direction in one layer and in the circumferential direction in the next layer. Some of the layers have no reinforcing material and are purely elastomeric. The thicknesses of the layers is assumed to be constant or to change smoothly in the meridional direction. We take the internal bounding surface of the shell as the plane of reference (the base coordinate plane). We refer this plane to an orthogonal coordinate system established by the lines of principal curvature. The transverse coordinate z is reckoned along an outer normal to the initial reference plane. As the running meridional coordinate, we take the length t of the generatrix of the coordinate surface from a point on the bounding contour to the current point. We will use the following notation: h is the total thickness of the shell; h k is the thickness of the k-th layer; z k and Zk+ 1 are values of the coordinate z for the lower and upper surfaces bounding the k-th layer; k 1 and k 2 are the principal curvatures of the coordinate surface of the shell; r is the distance from a point on the coordinate surface to the x axis (symmetry axis) of the shell; 0 is the angle between the normal to the coordinate surface and the symmetry axis; vkf is the frequency of fibers in the k-th layer; c~kf is the angle of inclination of the k-th layer fibers to the meridian. Quantities pertaining to the reinforcing

Endothelial cell heterogeneity in experimentally-induced rabbit atherosclerosis. Demonstration of multinucleated giant endothelial cells by scanning electron microscopy and cell culture.

We investigated the aortic endothelial cells of cholesterol-fed rabbits, using scanning electron microscopy and a cell culture technique. Rabbits were given a 1% cholesterol diet intermittently for up to 40 weeks. In these animals, the area of endothelial cells was increased and the cells showed polymorphism in relation to the progression of atherosclerosis. In animals fed the cholesterol diet for 12, 28 and 40 weeks, the average area of the endothelial cells was 436 +/- 15, 762 +/- 153, and 836 +/- 165 microns2, respectively. In the cholesterol-fed 40-week group, in particular, giant endothelial cells, measuring more than 1200 microns2, accounted for 14% of the population. In animals fed a standard diet there was no significant difference in endothelial cell morphology between control 0-week and control 40-week groups; in both, the luminal surface of the thoracic aorta formed a homogeneous sheet covered by small rhomboidal endothelial cells, the area of most being less than 400 microns2. Primary cultured endothelial cells harvested from those control groups were mononuclear typical small cells with a centrally located nucleus; the proportion of binucleated cells was less than 2% and no multinucleated giant cells with three or more nuclei were detected. Endothelial cells from the cholesterol-fed groups, however, contained larger numbers of binucleated cells, with the number increasing in proportion to the duration of cholesterol feeding. The major distinguishing feature of the endothelial cells in the cholesterol-fed groups was the presence of multinucleated giant cells with three or more nuclei; these accounted for 2.3% and 3.3% of the total cell population in the cholesterol-fed 28- and 40-week groups, respectively. No bromodeoxyuridine uptake was found in the nuclei of the cultured multinucleated giant cells. Heterogeneity of endothelial cells, with the concomitant appearance of multinucleated giant cells, emerges with the progression of diet-induced atherosclerosis. The morphological alterations of endothelial cells observed in the present study intimately reflect changes in their function associated with the progression of atherosclerotic lesions.

Tantalum Balloon-expandable Stent: In Vivo Swine Studies

The authors describe the experimental use of a balloon-expandable tantalum vascular stent in normal and atherosclerotic microswine. Thirty-one stents (15 iliac, 13 aorta, two femoral, one renal) were placed in 11 animals. Stents were placed in both normal and stenotic atherosclerotic arteries. The animals were killed and the stents explanted 2-32 weeks after placement. Arteriography was performed just prior to death in all cases. All stents were patent arteriographically and on gross inspection. Histopathologic study showed a thin, smooth, endothelial-lined neointima over the segments with stents. This covering had a mean thickness of 2.9 x 10(-5) mm and appeared maximally developed 2-5 weeks after stent placement. The stent design incorporates the following engineering and clinical considerations: minimal profile and surface area and maximal expansion ratio, hoop strength, flexibility, fluoroscopic visibility, biocompatibility, and ease of placement. When compressed and mounted on the balloon catheter, the stent is flexible. This allows it to be easily maneuvered through tortuous or diseased vessels. On expansion, the stent becomes a semirigid tubular structure composed of multiple rhomboid cells. Stents with an expanded diameter of less than 11 mm can be introduced through a 7-F vascular sheath. Initial results suggest that this stent successfully incorporates a number of theoretically desirable features for a vascular prosthesis, and it may offer some advantages over previously described devices.