Ellipsoidal Heads Research Articles

Novel Surface Structures Are Associated with the Adhesion of Actinobacillus actinomycetemcomitans to Collagen

Actinobacillus actinomycetemcomitans is a gram-negative, facultative, anaerobic bacterium that colonizes the human oral cavity and the upper respiratory tract. This bacterium is strongly associated with localized aggressive periodontitis and adult periodontitis and is the causative agent for other serious systemic infections. Recently, we have identified a protein, EmaA (extracellular matrix protein adhesin A), that mediates the adhesion of A. actinomycetemcomitans to collagen. The conserved sequence and predicted secondary structure suggest that EmaA is an orthologue of the Yersinia enterocolitica adhesin YadA. Electron microscopy examinations of A. actinomycetemcomitans have identified antenna-like protrusions associated with the surface of the bacterium. These structures are absent on emaA mutant strains and can be restored by transformation of the mutant strain with emaA in trans. The loss of these structures is associated with a decrease in the binding of this bacterium to collagen. The antenna-like structures are composed of a long rod that terminates in an ellipsoidal head region. The analysis of these structures using image processing techniques has provided an initial estimate of the overall dimensions, which suggests that the appendages are oligomeric structures formed by either three or four subunits. Together, the data suggest that emaA is required for the expression of novel appendages on the surface of A. actinomycetemcomitans that mediate the adhesion of the bacterium to collagen.

SEMEN COLLECTION IN RHINOCEROSES (RHINOCEROS UNICORNIS, DICEROS BICORNIS, CERATOTHERIUM SIMUM) BY ELECTROEJACULATION WITH A UNIQUELY DESIGNED PROBE

Electroejaculation in rhinoceroses has historically yielded inconsistent results, with the collection of high-quality, sperm-rich samples rare. The goal of this study was to develop a reliable method of electroejaculation in the rhinoceros by designing a rectal probe that appropriately fits the anatomy of this taxon and refining the procedure. A curved probe handle ending in an oblate, ellipsoid head was built using readily available supplies. A combination of rectal massage, penile massage, and electrical stimulation with a specially designed probe was employed in attempts to collect semen on 14 occasions from greater one-horned rhinoceroses (Rhinoceros unicornis; n = 4), black rhinoceroses (Diceros bicornis; n = 2) and a southern white rhinoceros (Ceratotherium simum; n = 1). During 13 of the 14 attempts, ejaculates were collected in multiple fractions. All but one of the ejaculates contained spermatozoa, and seven ejaculates contained good-quality fractions of semen (-60% sperm motility; > or =20 x 106 spermatozoa/ml) suitable for sperm banking and assisted reproduction procedures. Mean (+/-SEM) values for volume, pH, osmolality, and total sperm number for ejaculates containing good-quality fractions (98.2 +/-21.8 ml, 8.5+/-0.1, 290.4+/-6.7 mOsm, and 37.1+/-12.0 x 10(9), respectively) did not differ (P > 0.05) from those containing only poor-quality samples. Urine and/or erythrocyte contamination was not uncommon in fractions of both ejaculate types. Males producing good-quality samples ranged in age from 7 to 34 yr. None of the samples contained > or =75% morphologically normal spermatozoa. Electroejaculation with a uniquely designed probe consistently produced ejaculates in the rhinoceros. However, the production of high-quality samples continued to be challenging, occurring in only 50% of collection attempts. Regardless, the technology has progressed to a stage at which good-quality semen samples can be produced for sperm banking and assisted reproduction, and thereby can be integrated into intensive rhinoceros management strategies for the ultimate survival of this taxon.

Bicrystalline Hematite Nanowires

Bicrystalline nanowires of hematite (alpha-Fe(2)O(3)) have been successfully synthesized by the oxidation of pure iron. The product was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM in combination with focal series reconstruction, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy. The bicrystalline nanowires have diameters of 20-80 nm and lengths up to 20 microm. All of the investigated materials are found to be alpha-Fe(2)O(3) with a rhombohedral crystal structure. Investigations indicate that most of the bicrystalline nanowires are nanotwins with ellipsoidal heads. The orientation relationship between the nanotwins can be described as (110)(M)//(110)(T), [110](M)//[0](T). An energy-filtered TEM investigation indicates that the ellipsoidal head is iron-rich. The growth mechanism of such unique nanostructures is considered to be a solid-phase growth via surface and internal diffusions of molecules from base to tip.

Ellipsoidal head model for fetal magnetoencephalography: forward and inverse solutions

Fetal magnetoencephalography (fMEG) is a non-invasive technique where measurements of the magnetic field outside the maternal abdomen are used to infer the source location and signals of the fetus' neural activity. There are a number of aspects related to fMEG modelling that must be addressed, such as the conductor volume, fetal position and orientation, gestation period, etc. We propose a solution to the forward problem of fMEG based on an ellipsoidal head geometry. This model has the advantage of highlighting special characteristics of the field that are inherent to the anisotropy of the human head, such as the spread and orientation of the field in relationship with the localization and position of the fetal head. Our forward solution is presented in the form of a kernel matrix that facilitates the solution of the inverse problem through decoupling of the dipole localization parameters from the source signals. Then, we use this model and the maximum likelihood technique to solve the inverse problem assuming the availability of measurements from multiple trials. The applicability and performance of our methods are illustrated through numerical examples based on a real 151-channel SQUID fMEG measurement system (SARA). SARA is an MEG system especially designed for fetal assessment and is currently used for heart and brain studies. Finally, since our model requires knowledge of the best-fitting ellipsoid's centre location and semiaxes lengths, we propose a method for estimating these parameters through a least-squares fit on anatomical information obtained from three-dimensional ultrasound images.

Synthesis and Microstructures of α-Fe2O3 Bicrystalline Nanowires

ABSTRACTNovel Fe2O3 nanowires have been successfully synthesized by a simple oxidation process of pure iron. The microstructure of the Fe2O3 nanowires have been systematically investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM). The investigated materials are found to be stoichiometric rhombohedral α-Fe2O3 with typical diameters of 20–80 nm and lengths up to 20 μm. In addition to known single crystal Fe2O3 nanowires, a great amount of novel bicrystalline nanowires were found with ellipsoidal heads. Investigations indicate that most of the bicrystalline nanowires are twins and their orientation relationship is obtained to be (−1, 1, 10)M//(−1, 1, 10)T, [110]M//[-1-10]T. High resolution TEM with numerical reconstruction of the electron exit wave was used to investigated the atomic structure of the micro-twins. Their growth mechanism is briefly discussed on the basis of solid phase growth process.

Optimal design of an ellipsoidal head of a pressure cylindrical vessel

AbstractThe subject of analysis is a stress concentration problem in a circular cylindrical vessel with ellipsoidal heads. The region of the junction of ellipsoidal and cylindrical shells is subject to stress concentration. Intensity of the concentration depends, first of all, on relative convexity of the ellipsoidal head, and the ratio of thicknesses of the shells. Based on the boundary disturbance theory the stress state in this cylindrical vessel was analytically described. Optimal ellipsoidal heads were determined on the grounds of three optimisation criteria.

Study on manufacture of container heads by two-step hydro-bulging of single-curvature polyhedron

Container heads are indispensable components of pressure vessels, which have a wide application in industry. The traditional method for manufacturing a large size container head is to form double-curvature petals and polar shell plates, then assemble and weld them into a container head, which needs large size dies and heavy presses. This paper presents a two-step hydro-bulging method for the manufacture of ellipsoidal container heads. The method involves formation of a single-curvature sector shell, which is assembled and welded into an enclosed tubular polyhedron, then the cylindrical and transition zones are formed through the primary hydro-bulging. Next, the polar zone is formed through the secondary hydro-bulging of the container head. Finally, the shell is cut to reveal the container heads. This paper also describes hydro-bulging experiments of a tubular polyhedron and an enclosed shell obtained from the tubular polyhedron. The results show that the two-step hydro-bulging technology of the single-curvature polyhedron can be used to manufacture large container heads without using large size dies and heavy presses.

Parametric study of reinforcement of pressure vessel head with offset nozzle

In this research, stress analysis of reinforced nozzle connections in ellipsoidal heads of pressure vessels was carried out using shell theory and the finite element method. Various reinforcement configurations such as integral reinforcement, torus transition and protruding nozzle were considered. A parametric study of the effects of reinforcements on the maximum stresses in the head–nozzle intersections under internal pressure loading was performed. The effects of the geometric parameters of the reinforcements are discussed.

Minimization of stress concentration factor in cylindrical pressure vessels with ellipsoidal heads

The paper presents the problem of stress concentration in a cylindrical pressure vessel with ellipsoidal heads subject to internal pressure. At the line, where the ellipsoidal head is adjacent to the circular cylindrical shell, a shear force and bending moment occur, disturbing the membrane stress state in the vessel. The degree of stress concentration depends on the ratio of thicknesses of both the adjacent parts of the shells and on the relative convexity of the ellipsoidal head, with the range for radius-to-thickness ratio between 75 and 125. The stress concentration was analytically described and, afterwards, the effect of these values on the stress concentration ratio was numerically examined. Results of the analysis are shown on charts.

Development and calculation of an energy dependent normal brain tissue neutron RBE for evaluating neutron fields for BNCT.

In Boron Neutron Capture Therapy (BNCT) of malignant brain tumors, the energy dependence of a clinically relevant Relative Biological Effectiveness (RBE) for epithermal neutrons, RBE(En), is important in neutron field design. In the first half of this paper, we present the development of an expression for the energy dependent normal-tissue RBE, RBE(En). We then calculate a reasonable estimate for RBE(En) for adult brain tissue. In the second half of the paper, two separate RBE expressions are developed, one for the RBE of the neutrons that interact in tissue via the 14N(n,p)14C reaction, denoted RBE(N), and one for the RBE of the neutrons which interact in tissue via the 1H(n,n')1H reaction, denoted RBE(H). The absorbed-dose-averaged values of these expressions are calculated for the neutron flux spectrum in phantom for the Brookhaven Medical Research Reactor (BMRR) epithermal neutron beam. The calculated values, [RBE(norm)N] = 3.4 and [RBE(norm)H] = 3.2, are within 6% of being equal, and support the use of equal values for RBEN and RBE(H) by researchers at Brookhaven National Laboratory (BNL). Finally, values of [RBE(norm)N] and [RBE(norm)H], along with the absorbed-dose-averaged RBE for brain, [RBE(norm)b], were calculated as a function of depth along the centerline of an ellipsoidal head phantom using flux spectra calculated for our Accelerator-Based Neutron Source (ABNS). These values remained essentially constant with depth, supporting the use of constant values for RBE, as is done at BNL.

Fully stressed head of a pressure vessel

This work is devoted to a head of a vessel charged with internal uniform pressure. The analysis is aimed at finding a shape of the head that ensures its full charge with stresses. In a classical torispherical or ellipsoidal head the region of its joint with the cylindrical shell is loaded with shear force and bending moment as a result of the forced consistency of displacements of both parts of a vessel. The load causes high bending stresses in the area of the joint. Therefore, a shape of a head meridian is sought for which the shear force and the bending moment approach zero. Only membrane state stresses should occur in such a structure. The mathematical description is based on the theory of shells, taking account of boundary disturbances. The numerical solution determines the sought-after shape of the head and its minimal relative convexity.

Stresses in ellipsoidal pressure vessel heads with noncentral nozzle

The objective of this paper is further investigation of the shell intersection problem. The shell theory and finite element method are used for stress analysis of nozzle connections in ellipsoidal heads of the pressure vessels. Ellipsoidal heads having attached nozzles considerably displaced from the head axis are mainly considered. The features of the numerical procedure, structural modeling of nozzle-head shell intersections and SAIS special-purpose computer program are discussed. The results of stress analysis and parametric study of an ellipsoidal vessel head with a noncentral nozzle under internal pressure loading are presented.

Technical Basis for Code Cases on Design of Ellipsoidal and Torispherical Heads for ASME Section VIII Vessels

ASME Boiler and Pressure Vessel (B&PV) Code Committees have approved Code Cases 2260 and 2261 on the design of ellipsoidal and torispherical heads for Section VIII Division 1 and Division 2 vessels, respectively. Burst and low-cycle fatigue failure modes have been considered. A rationale is provided for including the foregoing referenced failure modes, and not including other failure modes such as dimensional changes, plastic collapse, knuckle yielding, etc. The basis for the specified design formulas to satisfy the burst and low-cycle fatigue criterion is discussed. The paper also discusses limitations and other requirements that have been imposed in the Code Cases. [S0094-9930(00)01401-3]

Optimal design of a horizontal circular tank with ellipsoidal heads

A horizontal circular tank, supported at both ends, is loaded by internal or external pressure. In the design process of such structures the proper choice of basic dimensions to ensure minimal mass may cause a problem. In this paper the optimal radii, lengths and wall thicknesses of a series of tanks of given capacity have been defined. The results of numerical analysis are presented in the form of diagrams.

Finite element analysis for buckling of pressure vessels with ellipsoidal head

In this paper, a finite element analysis is performed for buckling of the pressure vessels with ellipsoidal head subjected to uniform pressure. According to the characteristic of deformation of the pressure vessel, it is divided into some identical substructures. The degrees of freedom (DOFs) of joint nodes between the neighboring substructures are classified as master and slave ones. The stress and strain distributions of the whole structure are obtained by solving the static equations for only one substructure by introducing the displacement constraints between master and slave DOFs. The complex constraint method has been used to get the buckling load and mode for the whole structure by solving the eigenvalue problem for only one substructure without introducing any additional approximation. Some numerical examples have been given to illustrate the high efficiency and validity of this method.

Optimal design of a horizontal circular tank with ellipsoidal heads

Optimal design of a horizontal circular tank with ellipsoidal heads

A comparative structural characterization of two cellobiohydrolases from Trichoderma reesei: a high resolution electron microscopy study

The molecular structure of two homogeneously purified cellobiohydrolases from Trichoderma reesei has been studied employing high resolution transmission electron microscopy (TEM) and digital image processing. By combining low dose TEM, a 3% (w/v) solution of methylamine tungstate as the negative staining agent, and digital image processing, it has been possible to view intact molecular architectures of cellobiohydrolases from Trichoderma reesei. Cellobiohydrolase I (CBH I) and Cellobiohydrolase II (CBH II) have ellipsoidal heads and long, extended helical tails. CBH I is composed of a head with an average diameter of 4.5 ± 0.5 nm. The average length of CBH I is 15.1 ±1.3 nm. CBH II's head has an average diameter of 4.4 ± 0.3 nm. The average length of CBH I is 13.4 ± 2.6 nm. Overall, the structure of the digitally enhanced TEM images of these two glycosyl hydrolases correlated reasonably well with the reported models based on small angle X-ray scattering (SAXS), X-ray crystallography, and nuclear magnetic resonance imaging studies, thereby establishing the reliability of high resolution TEM studies in a novel way. The linker regions (LRs) of the two CBHs have been visualized. The LRs of both enzymes are probably helical in nature, suggesting an extended peptide sequence that lacks secondary structure due to the absence of amino acid/amino acid interactions in this region. A possible structural and functional role of O-glycosylation affiliated with these linker regions is discussed on the basis of combining the TEM observations with known biochemical data.

Discontinuity stresses in orthotropic pressure vessels

Expressions for stresses and displacements in orthotropic cylindrical, ellipsoidal, toroidal and conical shells are derived. Discontinuity stresses in orthotropic cylindrical pressure vessels connected to flat, ellipsoidal, and toriconical heads are determined. Stress intensification factors are also calculated. In some cases, the variation of stress intensification factors with moduli ratio and aspect ratio is also investigated.

Experimental research and finite-element simulation of plates hydrobulging in pairs

In this paper, the new hydrobulging technology is described for manufacturing giant ellipsoidal tank heads which could only be made through press and welding before. First, the head is divided into skirt and center parts; the skirt part is formed through traditional technology, while the center part is formed through hydrobulging. Then these two parts are welded together and if the shape and dimensions of the center part after hydrobulging are those of the required ellipsoidal head, then a whole ellipsoidal head is produced. The experiment was performed by hydrobulging plates in pairs under different boundary conditions to form the centre part of an ellipsoidal head. The deformations of the experimental work were measured and calculated and were compared with those of a standard ellipsoidal curvature which were nearest to the experimental curvatures. Finally numerical simulation of the hydrobulging plates in pairs under stiff boundary conditions was done using FEM.

Stress analysis of approximately ellipsoidal cold-spun tri-arc tank head and parameter optimization

It is well known that the thickness of a tank head is determined by its maximum stress and the stress of a traditional cold spun head is 1·7883 times that of a standard one. In order to reduce the maximum stress of the traditional cold spun head in which the generatrix is composed of two arcs, the authors have invented a new kind of generatrix which was composed of three arcs (tri-arc). By optimizing the parameters of the three arcs, it was found that the maximum stress of an approximately ellipsoidal head with this kind of generatrix is only 1·0959 times of that of a standard one. Therefore, its bearing capacity is greatly increased compared with the traditional one. This kind of approximately ellipsoidal head can also be formed through traditional cold spinning. The paper gives the volume difference of an approximately ellipsoidal tri-arc head and a standard ellipsoidal one.