Direct formulation of a 4-node hybrid shell element with rotational degrees of freedom
NASA Technical Reports Server (NTRS)
Aminpour, Mohammad A.
1990-01-01
A simple 4-node assumed-stress hybrid quadrilateral shell element with rotational or drilling degrees of freedom is formulated. The element formulation is based directly on a 4-node element. This direct formulation requires fewer computations than a similar element that is derived from an internal 8-node isoparametric element in which the midside degrees of freedom are eliminated in favor of rotational degree of freedom at the corner nodes. The formulation is based on the principle of minimum complementary energy. The membrane part of the element has 12 degrees of freedom including rotational degrees of freedom. The bending part of the element also has 12 degrees of freedom. The bending part of the quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields are assumed along the edges of the element. The element Cartesian-coordinate system is chosen such as to make the stress field invariant with respect to node numbering. The membrane part of the stress field is based on a 9-parameter equilibrating stress field, while the bending part is based on a 13-parameter equilibrating stress field. The element passes the patch test, is nearly insensitive to mesh distortion, does not lock, possesses the desirable invariance properties, has no spurious modes, and produces accurate and reliable results.
A 4-node assumed-stress hybrid shell element with rotational degrees of freedom
NASA Technical Reports Server (NTRS)
Aminpour, Mohammad A.
1990-01-01
An assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or drilling degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element. This process is accomplished by assuming quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields along the edges of the element. In addition, the degrees of freedom at midside nodes are approximated in terms of the degrees of freedom at corner nodes. During this process the rotational degrees of freedom at the corner nodes enter into the formulation of the element. The stress field are expressed in the element natural-coordinate system such that the element remains invariant with respect to node numbering.
An assumed-stress hybrid 4-node shell element with drilling degrees of freedom
NASA Technical Reports Server (NTRS)
Aminpour, M. A.
1992-01-01
An assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or 'drilling' degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element by expressing the midside displacement degrees of freedom in terms of displacement and rotational degrees of freedom at corner nodes. The element passes the patch test, is nearly insensitive to mesh distortion, does not 'lock', possesses the desirable invariance properties, has no hidden spurious modes, and for the majority of test cases used in this paper produces more accurate results than the other elements employed herein for comparison.
NASA Astrophysics Data System (ADS)
Wang, Zhen; Sun, Qin
2014-06-01
A new 4-node quadrilateral flat shell element is developed for geometrically nonlinear analyses of thin and moderately thick laminated shell structures. The flat shell element is constructed by combining a quadrilateral area coordinate method (QAC) based membrane element AGQ6-II, and a Timoshenko beam function (TBF) method based shear deformable plate bending element ARS-Q12. In order to model folded plates and connect with beam elements, the drilling stiffness is added to the element stiffness matrix based on the mixed variational principle. The transverse shear rigidity matrix, based on the first-order shear deformation theory (FSDT), for the laminated composite plate is evaluated using the transverse equilibrium conditions, while the shear correction factors are not needed. The conventional TBF methods are also modified to efficiently calculate the element stiffness for laminate. The new shell element is extended to large deflection and post-buckling analyses of isotropic and laminated composite shells based on the element independent corotational formulation. Numerical results show that the present shell element has an excellent numerical performance for the test examples, and is applicable to stiffened plates.
A 4-node Bilinear Isoparametric Element in Rockwell NASTRAN
NASA Technical Reports Server (NTRS)
Liao, C.; Allison, R. E.
1985-01-01
The development and evaluation of the Rockwell NASTRAN four node quadrilateral (QUAD4) element is presented. The element derivation utilizes bilinear isoparametric techniques both for membrane and bending characteristics. The QUAD4 element coordinate system, membrane properties, lumped mass matrix, and treatment of warping are based upon the COSMIC/NASTRAN QDMEMI element while the bending characteristics are based on a paper by T. J. R. Hughes. The effects of warping on the bending stiffness, consistent mass, and geometric stiffness are based upon a paper by R. H. MacNeal. Numerical integration is accomplished by Gaussian quadrature on a 2 x 2 grid. Practical user support features include variable element thickness, thermal analysis and layered composite material definitions.
NASA Technical Reports Server (NTRS)
Davila, Carlos G.; Camanho, Pedro P.; Turon, Albert
2007-01-01
A cohesive element for shell analysis is presented. The element can be used to simulate the initiation and growth of delaminations between stacked, non-coincident layers of shell elements. The procedure to construct the element accounts for the thickness offset by applying the kinematic relations of shell deformation to transform the stiffness and internal force of a zero-thickness cohesive element such that interfacial continuity between the layers is enforced. The procedure is demonstrated by simulating the response and failure of the Mixed Mode Bending test and a skin-stiffener debond specimen. In addition, it is shown that stacks of shell elements can be used to create effective models to predict the inplane and delamination failure modes of thick components. The results indicate that simple shell models can retain many of the necessary predictive attributes of much more complex 3D models while providing the computational efficiency that is necessary for design.
Finite element shell instability analysis
NASA Technical Reports Server (NTRS)
1975-01-01
Formulation procedures and the associated computer program for finite element thin shell instability analysis are discussed. Data cover: (1) formulation of basic element relationships, (2) construction of solution algorithms on both the conceptual and algorithmic levels, and (3) conduction of numerical analyses to verify the accuracy and efficiency of the theory and related programs therein are described.
Adaptive finite element strategies for shell structures
NASA Technical Reports Server (NTRS)
Stanley, G.; Levit, I.; Stehlin, B.; Hurlbut, B.
1992-01-01
The present paper extends existing finite element adaptive refinement (AR) techniques to shell structures, which have heretofore been neglected in the AR literature. Specific challenges in applying AR to shell structures include: (1) physical discontinuities (e.g., stiffener intersections); (2) boundary layers; (3) sensitivity to geometric imperfections; (4) the sensitivity of most shell elements to mesh distortion, constraint definition and/or thinness; and (5) intrinsic geometric nonlinearity. All of these challenges but (5) are addressed here.
Multi-element spherical shell generation
NASA Technical Reports Server (NTRS)
Morrison, Andrew D. (Inventor)
1990-01-01
A nozzle assembly in a multi-element spherical shell generation system includes first and second side-by-side spaced apart nozzles and a web portion extending between and connecting the nozzles. The first nozzle has an inner orifice adapted to discharge a first filler material and an outer annular orifice separated from and defined in concentric relation about the inner orifice and adapted to discharge a first shell material. The second nozzle has an inner orifice adapted to discharge a second filler material and an outer annular orifice separated from and defined in concentric relation about the inner orifice and adapted to discharge a second shell material. A multi-element spherical shell can be formed through employment of the nozzle assembly by merger with one another after discharge from the outer orifices of the nozzles of a pair of adjacent annular streams of liquid or molten shell wall material of different compositions and encapsulation by the mixed shell wall materials of a common encapsulated core fluids also simultaneously discharged by the inner orifices nozzles. On the other hand, the pair of encapsulating streams of shell wall material can be of the same materials which merge together and encapsulate core fluids of different compositions which will merge together after discharge from the nozzles.
Asymmetric quadrilateral shell elements for finite strains
NASA Astrophysics Data System (ADS)
Areias, P.; Dias-da-Costa, D.; Pires, E. B.; Van Goethem, N.
2013-07-01
Very good results in infinitesimal and finite strain analysis of shells are achieved by combining either the enhanced-metric technique or the selective-reduced integration for the in-plane shear energy and an assumed natural strain technique (ANS) in a non-symmetric Petrov-Galerkin arrangement which complies with the patch-test. A recovery of the original Wilson incompatible mode element is shown for the trial functions in the in-plane components. As a beneficial side-effect, Newton-Raphson convergence behavior for non-linear problems is improved with respect to symmetric formulations. Transverse-shear and in-plane patch tests are satisfied while distorted-mesh accuracy is higher than with symmetric formulations. Classical test functions with assumed-metric components are required for compatibility reasons. Verification tests are performed with advantageous comparisons being observed in all of them. Applications to large displacement elasticity and finite strain plasticity are shown with both low sensitivity to mesh distortion and (relatively) high accuracy. A equilibrium-consistent (and consistently linearized) updated-Lagrangian algorithm is proposed and tested. Concerning the time-step dependency, it was found that the consistent updated-Lagrangian algorithm is nearly time-step independent and can replace the multiplicative plasticity approach if only moderate elastic strains are present, as is the case of most metals.
Nonlinear Finite Element Analysis of Shells with Large Aspect Ratio
NASA Technical Reports Server (NTRS)
Chang, T. Y.; Sawamiphakdi, K.
1984-01-01
A higher order degenerated shell element with nine nodes was selected for large deformation and post-buckling analysis of thick or thin shells. Elastic-plastic material properties are also included. The post-buckling analysis algorithm is given. Using a square plate, it was demonstrated that the none-node element does not have shear locking effect even if its aspect ratio was increased to the order 10 to the 8th power. Two sample problems are given to illustrate the analysis capability of the shell element.
Summary compilation of shell element performance versus formulation.
Heinstein, Martin Wilhelm; Hales, Jason Dean; Breivik, Nicole L.; Key, Samuel W.
2011-07-01
This document compares the finite element shell formulations in the Sierra Solid Mechanics code. These are finite elements either currently in the Sierra simulation codes Presto and Adagio, or expected to be added to them in time. The list of elements are divided into traditional two-dimensional, plane stress shell finite elements, and three-dimensional solid finite elements that contain either modifications or additional terms designed to represent the bending stiffness expected to be found in shell formulations. These particular finite elements are formulated for finite deformation and inelastic material response, and, as such, are not based on some of the elegant formulations that can be found in an elastic, infinitesimal finite element setting. Each shell element is subjected to a series of 12 verification and validation test problems. The underlying purpose of the tests here is to identify the quality of both the spatially discrete finite element gradient operator and the spatially discrete finite element divergence operator. If the derivation of the finite element is proper, the discrete divergence operator is the transpose of the discrete gradient operator. An overall summary is provided from which one can rank, at least in an average sense, how well the individual formulations can be expected to perform in applications encountered year in and year out. A letter grade has been assigned albeit sometimes subjectively for each shell element and each test problem result. The number of A's, B's, C's, et cetera assigned have been totaled, and a grade point average (GPA) has been computed, based on a 4.0-system. These grades, combined with a comparison between the test problems and the application problem, can be used to guide an analyst to select the element with the best shell formulation.
Direct mapping of nuclear shell effects in the heaviest elements.
Minaya Ramirez, E; Ackermann, D; Blaum, K; Block, M; Droese, C; Düllmann, Ch E; Dworschak, M; Eibach, M; Eliseev, S; Haettner, E; Herfurth, F; Heßberger, F P; Hofmann, S; Ketelaer, J; Marx, G; Mazzocco, M; Nesterenko, D; Novikov, Yu N; Plaß, W R; Rodríguez, D; Scheidenberger, C; Schweikhard, L; Thirolf, P G; Weber, C
2012-09-01
Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.
Direct mapping of nuclear shell effects in the heaviest elements.
Minaya Ramirez, E; Ackermann, D; Blaum, K; Block, M; Droese, C; Düllmann, Ch E; Dworschak, M; Eibach, M; Eliseev, S; Haettner, E; Herfurth, F; Heßberger, F P; Hofmann, S; Ketelaer, J; Marx, G; Mazzocco, M; Nesterenko, D; Novikov, Yu N; Plaß, W R; Rodríguez, D; Scheidenberger, C; Schweikhard, L; Thirolf, P G; Weber, C
2012-09-01
Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152. PMID:22878498
Diagenetic changes in the elemental composition of unrecrystallized mollusk shells
Ragland, P.C.; Pilkey, O.H.; Blackwelder, B. W.
1979-01-01
The Mg, Sr, Mn, Fe, Na and K contents were determined for 230 apparently unrecrystallized mollusk shells (gastropods and bivalves) ranging in age from late Cretaceous to Holocene. Consistent differences between the Holocene and fossil shells with respect to concentrations of all these elements are attributed to postburial diagenetic changes. Fossil-Holocene shell comparisons are made on the intergeneric level, a more severe test of compositional differences than was previous work involved with few species. The observed differences re-emphasize the need for extreme caution in the use of the many geochemical tools which assume that no compositional changes have taken place prior to recrystallization of calcareous materials. ?? 1979.
A novel versatile multilayer hybrid stress solid-shell element
NASA Astrophysics Data System (ADS)
Rah, K.; Van Paepegem, W.; Degrieck, J.
2013-06-01
This paper presents a versatile multilayer locking free hybrid stress solid-shell element that can be readily employed for a wide range of geometrically linear elastic structural analyses, i.e. from shell-like isotropic structures to multilayer anisotropic composites. This solid-shell element has eight nodes with only displacement degrees of freedom and a few internal parameters that provide the locking free behavior and accurate interlaminar stress resolution through the element thickness. These elements can be stacked on top of each other to model multilayer structures, fulfilling the interlaminar stress continuity at the interlayer surfaces and zero traction conditions on the top and bottom surfaces of composite laminates. The element formulation is based on the modified form of the well-known Fraeijs de Veubeke-Hu-Washizu (FHW) multifield variational principle with enhanced assumed strains (EAS formulation) and assumed natural strains (ANS formulation) to alleviate the different types of locking phenomena in solid-shell elements. The distinct feature of the present formulation is its ability to accurately calculate the interlaminar stress field in multilayer structures, which is achieved by incorporating an assumed stress field in a standard EAS formulation based on the FHW principle. To assess the present formulation's accuracy, a variety of popular numerical benchmark examples related to element patch tests, convergence, mesh distortion, shell and laminated composite analyses are investigated and the results are compared with those available in the literature. This assessment reveals that the proposed solid-shell formulation provides very accurate results for a wide range of structural analyses.
A Shear Deformable Shell Element for Laminated Composites
NASA Technical Reports Server (NTRS)
Chao, W. C.; Reddy, J. N.
1984-01-01
A three-dimensional element based on the total Lagrangian description of the motion of a layered anisotropic composite medium is developed, validated, and used to analyze layered composite shells. The element contains the following features: geometric nonlinearity, dynamic (transient) behavior, and arbitrary lamination scheme and lamina properties. Numerical results of nonlinear bending, natural vibration, and transient response are presented to illustrate the capabilities of the element.
Shell Element Verification & Regression Problems for DYNA3D
Zywicz, E
2008-02-01
A series of quasi-static regression/verification problems were developed for the triangular and quadrilateral shell element formulations contained in Lawrence Livermore National Laboratory's explicit finite element program DYNA3D. Each regression problem imposes both displacement- and force-type boundary conditions to probe the five independent nodal degrees of freedom employed in the targeted formulation. When applicable, the finite element results are compared with small-strain linear-elastic closed-form reference solutions to verify select aspects of the formulations implementation. Although all problems in the suite depict the same geometry, material behavior, and loading conditions, each problem represents a unique combination of shell formulation, stabilization method, and integration rule. Collectively, the thirty-six new regression problems in the test suite cover nine different shell formulations, three hourglass stabilization methods, and three families of through-thickness integration rules.
NASA Technical Reports Server (NTRS)
Barut, A.; Madenci, Erdogan; Tessler, A.
1997-01-01
This study presents a transient nonlinear finite element analysis within the realm of a multi-body dynamics formulation for determining the dynamic response of a moderately thick laminated shell undergoing a rapid and large rotational motion and nonlinear elastic deformations. Nonlinear strain measure and rotation, as well as 'the transverse shear deformation, are explicitly included in the formulation in order to capture the proper motion-induced stiffness of the laminate. The equations of motion are derived from the virtual work principle. The analysis utilizes a shear deformable shallow shell element along with the co-rotational form of the updated Lagrangian formulation. The shallow shell element formulation is based on the Reissner-Mindlin and Marguerre theory.
An Enriched Shell Element for Delamination Simulation in Composite Laminates
NASA Technical Reports Server (NTRS)
McElroy, Mark
2015-01-01
A formulation is presented for an enriched shell finite element capable of delamination simulation in composite laminates. The element uses an adaptive splitting approach for damage characterization that allows for straightforward low-fidelity model creation and a numerically efficient solution. The Floating Node Method is used in conjunction with the Virtual Crack Closure Technique to predict delamination growth and represent it discretely at an arbitrary ply interface. The enriched element is verified for Mode I delamination simulation using numerical benchmark data. After determining important mesh configuration guidelines for the vicinity of the delamination front in the model, a good correlation was found between the enriched shell element model results and the benchmark data set.
Finite Element Transient Dynamic Analysis of Laminated Stiffened Shells
NASA Astrophysics Data System (ADS)
PRUSTY, B. GANGADHARA; SATSANGI, S. K.
2001-11-01
The present work describes the transient dynamic response of unstiffened/stiffened composite plates/shells using finite element method. Composite panels find wide applications in aerospace, marine and other engineering because of its high strength to weight ratios. These structures are often subjected to air-blast loading, underwater shock etc., which requires a thorough dynamic response analysis under such loading. A modified approach of shell and stiffener modelling is adopted here using an eight-noded isoparametric quadratic element for the shell and a three-noded curved stiffener element for the stiffeners on the concept of equal displacements at the shell-stiffener interface. The present formulation obviates the need for imposing the mesh line along the stiffeners; rather it accommodates the stiffeners elegantly anywhere placed arbitrarily inside the element with computational efficiency. Newmarks method for direct time integration has been adopted for the solution of the governing equation for undamped motion. The transient dynamic response of stiffened and unstiffened structures subjected to various kinds of time variant loading has been studied and the results are compared with the published ones.
A new SMA shell element based on the corotational formulation
NASA Astrophysics Data System (ADS)
Bisegna, P.; Caselli, F.; Marfia, S.; Sacco, E.
2014-11-01
Aim of this paper is to develop a new shape memory alloy (SMA) facet-shell finite element accounting for material and geometric nonlinearities. A corotational formulation is exploited, able to filter out large rigid-body motions from the element transformation. Accordingly, a geometrically linear core-element is employed, along with a SMA constitutive model formulated in the small strain framework. In particular, in accordance with the formulation of the classical thin shell theory, a plane-stress SMA model accounting for the pseudo-elastic as well as the shape memory effect is adopted. The time integration of the evolutive equation is performed developing a step-by-step backward-Euler numerical procedure. A highly efficient implementation of the corotational machinery is used, endowed with a fully consistent tangent stiffness. Applications are carried out for assessing the performances of the developed computational procedure and to investigate on some interesting engineering examples. The numerical results show the effectiveness of the proposed shell element, whose simplicity makes it attractive for the design of new advanced SMA-based devices undergoing significant configuration changes during their operation.
Structural optimization of thin shells using finite element method
NASA Technical Reports Server (NTRS)
Gotsis, Pascal K.
1992-01-01
The objective of the present work was the structural optimization of thin shell structures that are subjected to stress and displacement constraints. In order to accomplish this, the structural optimization computer program DESAP1 was modified and improved. In the static analysis part of the DESAP1 computer program the torsional spring elements, which are used to analyze thin, shallow shell structures, were eliminated by modifying the membrane stiffness matrix of the triangular elements in the local coordinate system and adding a fictitious rotational stiffness matrix. This simplified the DESAP1 program input, improved the accuracy of the analysis, and saved computation time. In the optimization part of the DESAP1 program the stress ratio formula, which redesigns the thickness of each finite element of the structure, was solved by an analytical method. This scheme replaced the iterative solution that was previously used in the DESAP1 program, thus increasing the accuracy and speed of the design. The modified program was used to design a thin, cylindrical shell structure with optimum weight, and the results are reported in this paper.
Nonlinear probabilistic finite element models of laminated composite shells
NASA Technical Reports Server (NTRS)
Engelstad, S. P.; Reddy, J. N.
1993-01-01
A probabilistic finite element analysis procedure for laminated composite shells has been developed. A total Lagrangian finite element formulation, employing a degenerated 3-D laminated composite shell with the full Green-Lagrange strains and first-order shear deformable kinematics, forms the modeling foundation. The first-order second-moment technique for probabilistic finite element analysis of random fields is employed and results are presented in the form of mean and variance of the structural response. The effects of material nonlinearity are included through the use of a rate-independent anisotropic plasticity formulation with the macroscopic point of view. Both ply-level and micromechanics-level random variables can be selected, the latter by means of the Aboudi micromechanics model. A number of sample problems are solved to verify the accuracy of the procedures developed and to quantify the variability of certain material type/structure combinations. Experimental data is compared in many cases, and the Monte Carlo simulation method is used to check the probabilistic results. In general, the procedure is quite effective in modeling the mean and variance response of the linear and nonlinear behavior of laminated composite shells.
Curved Thermopiezoelectric Shell Structures Modeled by Finite Element Analysis
NASA Technical Reports Server (NTRS)
Lee, Ho-Jun
2000-01-01
"Smart" structures composed of piezoelectric materials may significantly improve the performance of aeropropulsion systems through a variety of vibration, noise, and shape-control applications. The development of analytical models for piezoelectric smart structures is an ongoing, in-house activity at the NASA Glenn Research Center at Lewis Field focused toward the experimental characterization of these materials. Research efforts have been directed toward developing analytical models that account for the coupled mechanical, electrical, and thermal response of piezoelectric composite materials. Current work revolves around implementing thermal effects into a curvilinear-shell finite element code. This enhances capabilities to analyze curved structures and to account for coupling effects arising from thermal effects and the curved geometry. The current analytical model implements a unique mixed multi-field laminate theory to improve computational efficiency without sacrificing accuracy. The mechanics can model both the sensory and active behavior of piezoelectric composite shell structures. Finite element equations are being implemented for an eight-node curvilinear shell element, and numerical studies are being conducted to demonstrate capabilities to model the response of curved piezoelectric composite structures (see the figure).
Accuracy of the TRIA3 thick shell element
NASA Technical Reports Server (NTRS)
Case, William R.; Concha, Marco; Mcginnis, Mark
1992-01-01
The accuracy of the new TRIA3 thick shell element is assessed via comparison with a theoretical solution for thick homogeneous and honeycomb flat simply supported plates under the action of a uniform pressure load. The theoretical thick plate solution is based on the theory developed by Reissner and includes the effects of transverse shear flexibility which are not included in the thin plate solutions based on Kirchoff plate theory. In addition, the TRIA3 is assessed using a set of finite element test problems developed by the MacNeal-Schwendler Corp. (MSC). Comparison of the COSMIC TRIA3 element as well as those from MSC and Universal Analytics Inc. (UAI) for these problems is presented. The current COSMIC TRIA3 element is shown to have excellent comparison with both the theoretical solutions and also those from the two commercial versions of NASTRAN with which it is compared.
Accuracy of the QUAD4 thick shell element
NASA Technical Reports Server (NTRS)
Case, William R.; Bowles, Tiffany D.; Croft, Alicia K.; Mcginnis, Mark A.
1990-01-01
The accuracy of the relatively new QUAD4 thick shell element is assessed via comparison with a theoretical solution for thick homogeneous and honeycomb flat simply supported plates under the action of a uniform pressure load. The theoretical thick plate solution is based on the theory developed by Reissner and includes the effects of transverse shear flexibility which are not included in the thin plate solutions based on Kirchoff plate theory. In addition, the QUAD4 is assessed using a set of finite element test problems developed by the MacNeal-Schwendler Corp. (MSC). Comparison of the COSMIC QUAD4 element as well as those from MSC and Universal Analytics, Inc. (UAI) for these test problems is presented. The current COSMIC QUAD4 element is shown to have excellent comparison with both the theoretical solutions and also those from the two commercial versions of NASTRAN that it was compared to.
NASA Technical Reports Server (NTRS)
1976-01-01
The development of two new shell finite elements for applications to large deflection problems is considered. The elements in question are doubly curved and of triangular and quadrilateral planform. They are restricted to small strains of elastic materials, and can accommodate large rotations. The elements described, which are based on relatively simple linear elements, make use of a new displacement function approach specifically designed for strongly nonlinear problems. The displacement function development for nonlinear applications is based on certain beam element formulations, and the strain-displacement equations are of a shallow shell type. Additional terms were included in these equations in an attempt to avoid the large errors characteristic of shallow shell elements in certain types of problems. An incremental nonlinear solution procedure specifically adopted to the element formulation was developed. The solution procedure is of combined incremental and total Lagrangian type, and uses a new updating scheme. A computer program was written to evaluate the developed formulations. This program can accommodate small element groups in arbitrary arrangements. Two simple programs were successfully solved. The results indicate that this new type of element has definite promise and should be a fruitful area for further research.
A shell element for computing 3D eddy currents -- Applications to transformers
Guerin, C.; Tanneau, G.; Meunier, G.; Labie, P.; Ngnegueu, T.; Sacotte, M.
1995-05-01
A skin depth-independent shell element to model thin conducting sheets is described in a finite element context. This element takes into account the field variation through depth due to skin effect. The finite element formulation is first described, then boundary conditions at the edge of conducting shells and the possibility of describing non conducting line gaps and holes are discussed. Finally, a computation of an earthing transformer model with an aluminium shield modelled with shell elements is presented.
Finite element analysis of laminated plates and shells, volume 1
NASA Technical Reports Server (NTRS)
Seide, P.; Chang, P. N. H.
1978-01-01
The finite element method is used to investigate the static behavior of laminated composite flat plates and cylindrical shells. The analysis incorporates the effects of transverse shear deformation in each layer through the assumption that the normals to the undeformed layer midsurface remain straight but need not be normal to the mid-surface after deformation. A digital computer program was developed to perform the required computations. The program includes a very efficient equation solution code which permits the analysis of large size problems. The method is applied to the problem of stretching and bending of a perforated curved plate.
A shell finite element model of the pelvic floor muscles.
d'Aulignac, D; Martins, J A C; Pires, E B; Mascarenhas, T; Jorge, R M Natal
2005-10-01
The pelvic floor gives support to the organs in the abdominal cavity. Using the dataset made public in (Janda et al. J. Biomech. (2003) 36(6), pp. 749-757), we have reconstructed the geometry of one of the most important parts of the pelvic floor, the levator ani, using NURB surfaces. Once the surface is triangulated, the corresponding mesh is used in a finite element analysis with shell elements. Based on the 3D behavior of the muscle we have constructed a shell that takes into account the direction of the muscle fibers and the incompressibility of the tissue. The constitutive model for the isotropic strain energy and the passive strain energy stored in the fibers is adapted from Humphrey's model for cardiac muscles. To this the active behavior of the skeletal muscle is added. We present preliminary results of a simulation of the levator ani muscle under pressure and with active contraction. This research aims at helping simulate the damages to the pelvic floor that can occur after childbirth. PMID:16298856
A finite element approach for shells of revolution with a local deviation
NASA Technical Reports Server (NTRS)
Han, K. J.; Gould, P. L.
1982-01-01
A finite element model that is suitable for the static analysis of shells of revolution with arbitrary local deviations is presented. The model employs three types of elements: rotational, general, and transitional shell elements. The rotational shell elements are used in the region where the shell is axisymmetric. The general shell element are used in the local region of the deviation. The transitional shell elements connect these two distinctively different types of elements and make it possible to combine them in a single analysis. The form of the global stiffness matrix resulting when different forms of nodal degrees of freedom are combined is illustrated. The coupling of harmonic degrees of freedom due to the locally nonaxisymmetric geometry was studied. The use of a substructuring technique and separate partial harmonic analysis is recommended.
NASA Technical Reports Server (NTRS)
Gerhard, Craig Steven; Gurdal, Zafer; Kapania, Rakesh K.
1996-01-01
Layerwise finite element analyses of geodesically stiffened cylindrical shells are presented. The layerwise laminate theory of Reddy (LWTR) is developed and adapted to circular cylindrical shells. The Ritz variational method is used to develop an analytical approach for studying the buckling of simply supported geodesically stiffened shells with discrete stiffeners. This method utilizes a Lagrange multiplier technique to attach the stiffeners to the shell. The development of the layerwise shells couples a one-dimensional finite element through the thickness with a Navier solution that satisfies the boundary conditions. The buckling results from the Ritz discrete analytical method are compared with smeared buckling results and with NASA Testbed finite element results. The development of layerwise shell and beam finite elements is presented and these elements are used to perform the displacement field, stress, and first-ply failure analyses. The layerwise shell elements are used to model the shell skin and the layerwise beam elements are used to model the stiffeners. This arrangement allows the beam stiffeners to be assembled directly into the global stiffness matrix. A series of analytical studies are made to compare the response of geodesically stiffened shells as a function of loading, shell geometry, shell radii, shell laminate thickness, stiffener height, and geometric nonlinearity. Comparisons of the structural response of geodesically stiffened shells, axial and ring stiffened shells, and unstiffened shells are provided. In addition, interlaminar stress results near the stiffener intersection are presented. First-ply failure analyses for geodesically stiffened shells utilizing the Tsai-Wu failure criterion are presented for a few selected cases.
Quantifying Square Membrane Wrinkle Behavior Using MITC Shell Elements
NASA Technical Reports Server (NTRS)
Jacobson, Mindy B.; Iwasa, Takashi; Natori, M. C.
2004-01-01
For future membrane based structures, quantified predictions of membrane wrinkling behavior in terms of amplitude, angle and wavelength are needed to optimize the efficiency and integrity of such structures, as well as their associated control systems. For numerical analyses performed in the past, limitations on the accuracy of membrane distortion simulations have often been related to the assumptions made while using finite elements. Specifically, this work demonstrates that critical assumptions include: effects of gravity. supposed initial or boundary conditions, and the type of element used to model the membrane. In this work, a 0.2 square meter membrane is treated as a structural material with non-negligible bending stiffness. Mixed Interpolation of Tensorial Components (MTTC) shell elements are used to simulate wrinkling behavior due to a constant applied in-plane shear load. Membrane thickness, gravity effects, and initial imperfections with respect to flatness were varied in numerous nonlinear analysis cases. Significant findings include notable variations in wrinkle modes for thickness in the range of 50 microns to 1000 microns, which also depend on the presence of an applied gravity field. However, it is revealed that relationships between overall strain energy density for cases with differing initial conditions are independent of assumed initial con&tions. In addition, analysis results indicate that the relationship between amplitude scale (W/t) and structural scale (L/t) is linear in the presence of a gravity field.
Effective Simulation of Delamination in Aeronautical Structures Using Shells and Cohesive Elements
NASA Technical Reports Server (NTRS)
Davila, Carlos G.; Camanho, Pedro P.; Turon, Albert
2007-01-01
A cohesive element for shell analysis is presented. The element can be used to simulate the initiation and growth of delaminations between stacked, non-coincident layers of shell elements. The procedure to construct the element accounts for the thickness offset by applying the kinematic relations of shell deformation to transform the stiffness and internal force of a zero-thickness cohesive element such that interfacial continuity between the layers is enforced. The procedure is demonstrated by simulating the response and failure of the Mixed Mode Bending test and a skin-stiffener debond specimen. In addition, it is shown that stacks of shell elements can be used to create effective models to predict the inplane and delamination failure modes of thick components. The results indicate that simple shell models can retain many of the necessary predictive attributes of much more complex 3D models while providing the computational efficiency that is necessary for design.
Trace Element Uptake in Marine Bivalve Shells Constraints from Field- and Laboratory Studies
NASA Astrophysics Data System (ADS)
Klünder, M.; Hippler, D.; Witbaard, R.; Frei, D.; Immenhauser, A.
2006-12-01
There is an increasing interest in the use of the trace element signatures recorded in calcium carbonate skeletons of marine organisms as archives of past and present environmental conditions, such as temperature, salinity or nutrition level. Because of their global occurrence in the modern and ancient oceans, the trace element chemistry of bivalve shells might be used as a potential proxy for present and past environmental conditions. If the composition of bivalve shells, for instance, can be shown to represent the environment in which they lived, then shells can be used to investigate conditions in the lifetime of the animal. And as the shell material is sequentially deposited, an understanding of the internal shell structure will enable time- resolution of the analyses. Therefore, the trace element signature of bivalve shells may provide an important record of climate changes and global geochemical cycles. One of the difficulties of using the trace element signatures of bivalve shells as proxies for environmental conditions is that little is known about the mechanisms by which the trace elements are incorporated into the shells. There has been quite an amount of research into the use of bivalve shell chemistry as proxy for one or more environmental parameters, but there are relatively few datasets in which both bivalve shells and the water in which the animals lived have been analysed. It is as yet not clear to what extent the trace element incorporation into bivalve shells is governed by biological processes, like growth rate and metabolism of the animals, or by physical and crystal chemical parameters. An added difficulty is that the existing data do suggest that trace element uptake in bivalve shells may be species specific. Therefore, studies that investigate the relationships between the content of these elements in the shells and the ambient water and the possible incorporation mechanisms are needed if the potential that bivalve shells offer as
Addition of higher order plate and shell elements into NASTRAN computer program
NASA Technical Reports Server (NTRS)
Narayanaswami, R.; Goglia, G. L.
1976-01-01
Two higher order plate elements, the linear strain triangular membrane element and the quintic bending element, along with a shallow shell element, suitable for inclusion into the NASTRAN (NASA Structural Analysis) program are described. Additions to the NASTRAN Theoretical Manual, Users' Manual, Programmers' Manual and the NASTRAN Demonstration Problem Manual, for inclusion of these elements into the NASTRAN program are also presented.
NASA Technical Reports Server (NTRS)
Reddy, J. N.
1981-01-01
Finite element papers published in the open literature on the static bending and free vibration of layered, anisotropic, and composite plates and shells are reviewed. A literature review of large-deflection bending and large-amplitude free oscillations of layered composite plates and shells is also presented. Non-finite element literature is cited for continuity of the discussion.
Shell model nuclear matrix elements for competing mechanisms contributing to double beta decay
Horoi, Mihai
2013-12-30
Recent progress in the shell model approach to the nuclear matrix elements for the double beta decay process are presented. This includes nuclear matrix elements for competing mechanisms to neutrionless double beta decay, a comparison between closure and non-closure approximation for {sup 48}Ca, and an updated shell model analysis of nuclear matrix elements for the double beta decay of {sup 136}Xe.
NASTRAN implementation of an isoparametric doubly-curved quadrilateral shell element
NASA Technical Reports Server (NTRS)
Potvin, A. B.; Leick, R. D.
1978-01-01
A quadrilateral shell element, CQUAD4, was added to level 15.5 and subsequently to level 16.0 of NASTRAN. The element exhibited doubly curved surfaces and used biquadratic interpolation functions. Reduced integration techniques were used to improve the performance of the element in thin shell problems. The creation of several new bulk data items is discussed, along with a special module, GPNORM, to process SHLNORM bulk data cards. In addition to the theoretical basis for the element stiffness matrix, consistent mass and load matrices are presented. Several potential sources of degenerate behavior of the element were investigated. Guidelines for proper use of the element were suggested. Performance of the element on several widely published classical examples was demonstrated. The results showed a significant improvement over presently available NASTRAN shell elements for even the coarsest meshes. Potential applications to two classes of practical problems are discussed.
Takesue, R.K.; Bacon, C.R.; Thompson, J.K.
2008-01-01
A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carr?? et al. [Carr?? M., Bentaleb I
Comparison of symbolic and numerical integration methods for an assumed-stress hybrid shell element
NASA Technical Reports Server (NTRS)
Rengarajan, Govind; Knight, Norman F., Jr.; Aminpour, Mohammad A.
1993-01-01
Hybrid shell elements have long been regarded with reserve by the commercial finite element developers despite the high degree of reliability and accuracy associated with such formulations. The fundamental reason is the inherent higher computational cost of the hybrid approach as compared to the displacement-based formulations. However, a noteworthy factor in favor of hybrid elements is that numerical integration to generate element matrices can be entirely avoided by the use of symbolic integration. In this paper, the use of the symbolic computational approach is presented for an assumed-stress hybrid shell element with drilling degrees of freedom and the significant time savings achieved is demonstrated through an example.
Shear-flexible finite-element models of laminated composite plates and shells
NASA Technical Reports Server (NTRS)
Noor, A. K.; Mathers, M. D.
1975-01-01
Several finite-element models are applied to the linear static, stability, and vibration analysis of laminated composite plates and shells. The study is based on linear shallow-shell theory, with the effects of shear deformation, anisotropic material behavior, and bending-extensional coupling included. Both stiffness (displacement) and mixed finite-element models are considered. Discussion is focused on the effects of shear deformation and anisotropic material behavior on the accuracy and convergence of different finite-element models. Numerical studies are presented which show the effects of increasing the order of the approximating polynomials, adding internal degrees of freedom, and using derivatives of generalized displacements as nodal parameters.
Hybrid Semiloof elements for plates and shells based upon a modified Hu-Washizu principle
NASA Technical Reports Server (NTRS)
Pian, T. H. H.; Sumihara, K.
1984-01-01
Hybrid SemiLoof elements for plates and shells are developed based upon modified Hu-Washizu principle. In the new version of the assumed stress hybrid formulation the equilibrium equations are satisfied through the introduction of internal displacement parameters as Lagrange multipliers. The inversion of the resulting H-matrices is simplified particularly when the stresses are expressed in terms of natural coordinates. A 24-DOF triangular element and a 32-DOF quadrilateral element based on shallow shell theory are derived and evaluated.
RELATIONSHIP OF AMEBOCYTES AND TERRESTRIAL ELEMENTS TO ADULT SHELL DEPOSITION IN EASTERN OYSTERS
Fisher, William S. Submitted. Relationship of Amebocytes and Terrestrial Elements to Adult Shell Deposition in Eastern Oysters. J. Shellfish Res. 30 p. (ERL,GB 1197).
Freshwater runoff contains terrestrial elements from geological deposits that may be vital to eastern oys...
NASA Astrophysics Data System (ADS)
Duan, M.
2004-12-01
In this paper, a geometrically nonlinear hybrid/mixed curved quadrilateral shell element (HMSHEL4N) with four nodes is developed based on the modified Hellinger/Reissner variational principles. The performance of element is investigated and tested using some benchmark problems. A number of numerical examples of plate and shell nonlinear deflection problems are included. The results are compared with theoretical solutions and other numerical results. It is shown that HMSHEL4N does not possess spurious zero energy modes and any locking phenomenon, and is convergent and insensitive to the distorted mesh. A good agreement of the results with theoretical solutions, and better performance compared with displacement finite element method, are observed. It is seen that an efficient shell element based on stress and displacement field assumptions in solution and time is obtained.
Propagation of flexural and membrane waves with fluid loaded NASTRAN plate and shell elements
NASA Technical Reports Server (NTRS)
Kalinowski, A. J.; Wagner, C. A.
1983-01-01
Modeling of flexural and membrane type waves existing in various submerged (or in vacuo) plate and/or shell finite element models that are excited with steady state type harmonic loadings proportioned to e(i omega t) is discussed. Only thin walled plates and shells are treated wherein rotary inertia and shear correction factors are not included. More specifically, the issue of determining the shell or plate mesh size needed to represent the spatial distribution of the plate or shell response is of prime importance towards successfully representing the solution to the problem at hand. To this end, a procedure is presented for establishing guide lines for determining the mesh size based on a simple test model that can be used for a variety of plate and shell configurations such as, cylindrical shells with water loading, cylindrical shells in vacuo, plates with water loading, and plates in vacuo. The procedure for doing these four cases is given, with specific numerical examples present only for the cylindrical shell case.
Trace element ratios in bivalve shells as records of environmental conditions
NASA Astrophysics Data System (ADS)
Tynan, S.; Opdyke, B.; Welch, S.; Beavis, S.
2007-12-01
Stable isotope and trace element data from the carbonate of both marine and freshwater bivalves are proving to be useful tools in studies of palaeoclimate and environmental change. However, much of the work already done has shown that the trace element ratios in bivalve shells exhibit a complex relationship with the ambient environment and caution must be exercised when attempting to use them as environmental proxies. This work examines the feasibility of using the trace element ratios Mg/Ca, Sr/Ca, Ba/Ca and Mn/Ca of the shells of a number of different species of bivalves as records of the temperature and salinity of their ambient aquatic environment. The species analysed were the estuarine oysters Saccostrea glomerata, Ostrea angasi, and Crassostrea gigas, an estuarine mussel, Mytilus galloprovincialis, and the freshwater mussel Velesunio ambiguus. The estuarine shells were taken from monitoring experiments conducted over a period of 12 months at two different field sites. Freshwater shells were collected wild, from locations close to water monitoring stations. Preliminary results show distinct variations in the Mg/Ca of O. angasi shells with an apparent seasonal pattern. V. ambiguus shells show clear patterns in Mn/Ca, linked to environmental variations.
Free vibration of composite skewed cylindrical shell panel by finite element method
NASA Astrophysics Data System (ADS)
Haldar, Salil
2008-03-01
In this paper a composite triangular shallow shell element has been used for free vibration analysis of laminated composite skewed cylindrical shell panels. In the present element first-order shear deformation theory has been incorporated by taking transverse displacement and bending rotations as independent field variables. The interpolation function used to approximate transverse displacement is one order higher than for bending rotations. This has made the element free from locking in shear. Two types of mass lumping schemes have been recommended. In one of the mass lumping scheme the effect of rotary inertia has been incorporated in the element formulations. Free vibration of skewed composite cylindrical shell panels having different thickness to radius ratios ( h/R=0.01-0.2), length to radius ratios ( L/R), number of layers and fiber orientation angles have been analyzed following the shallow shell method. The results for few examples obtained in the present analysis have compared with the published results. Some new results of composite skewed cylindrical shell panels have been presented which are expected to be useful to future research in this direction.
Guerin, C.; Tanneau, G.; Meunier, G.; Brunotte, X.; Albertini, J.B.
1994-09-01
This paper deals with magnetostatic finite element formulations for modeling narrow gaps in an iron core, as well as thin iron shells. These special elements have been developed for gaps in transformers or motors. Nodal elements are used with magnetic scalar potentials as state variable. The principle and the formulations of the new finite elements are described. Three numerical examples are then presented so as to validate and verify the usefulness of the special elements in terms of reduction of number of unknowns and CPU time.
Average l-shell fluorescence yields for elements 56 <= Z <= 92
NASA Astrophysics Data System (ADS)
Singh, Surinder; Mehta, D.; Garg, R. R.; Kumar, Sudhir; Garg, M. L.; Singh, Nirmal; Mangal, P. C.; Hubbell, J. H.; Trehan, P. N.
1990-07-01
The average L-shell fluorescence yields, ¯gw L, have been evaluated for the elements with 56 ⩽ Z ⩽ 92 using our measured values of photon induced total L X-ray production cross-sections and Scofield's (1973) theoretical total L shell photo-ionisation cross-sections. These values are compared with the values tabulated by earlier workers and with theoretical values based on relativistic Hartree-Dirac-Slater (RHDS) calculations [Chen et al. Phys. Rev. A24 (1981) 177]. A good agreement is found with the values based on RHDS calculations for the elements 56 ⩽ Z ⩽ 92.
The importance of closed shell structures in the synthesis of super heavy elements
NASA Astrophysics Data System (ADS)
Hamilton, J. H.; Hofmann, S.; Oganessian, Y. T.
2015-02-01
The importance of shell closures and gaps in the single-particle energies for protons and neutrons on the stability of elements beyond Z = 100 will be described. Following the development of microscopic models with shell corrections, microscopic-macroscopic models predicted large gaps in the single-particle energy levels for protons and neutrons at Z = 102, 108 and N = 152, 162 for the same deformed shapes. Shell gaps for spherical shapes for N = 184 and Z = 114, 120 or 126 were also predicted to form an "Island of Stability" with very long half lives for fission and alpha decay. Cold fusion reactions involving beams of Ca to Zn and targets of stable 208Pb and 209Bi were pioneered at GSI and used to synthesize new elements for Z = 107 to 112 and in Japan a new isotope of 113. Hot fusion reactions between radioactive actinide targets and neutron-rich 48Ca beams were pioneered in JINR leading to the synthesis of new elements with Z = 113 to 118. Data on two neutron separation energies, spontaneous fission half lives and total half lives of super heavy elements showing the importance of reinforcement of the Z = 102, N = 152 and Z = 108, N = 162 single particle level gaps at the same deformation and Z = 114-126, N = 184 shell gaps in the synthesis of super heavy elements 107 to 118 are presented along with the latest results on their synthesis.
NASA Technical Reports Server (NTRS)
Saravanos, Dimitris A.
1996-01-01
Mechanics for the analysis of laminated composite shells with piezoelectric actuators and sensors are presented. A new mixed-field laminate theory for piezoelectric shells is formulated in curvilinear coordinates which combines single-layer assumptions for the displacements and a layerwise representation for the electric potential. The resultant coupled governing equations for curvilinear piezoelectric laminates are described. Structural mechanics are subsequently developed and an 8-node finite-element is formulated for the static and dynamic analysis of adaptive composite structures of general laminations containing piezoelectric layers. Evaluations of the method and comparisons with reported results are presented for laminated piezoelectric-composite plates, a closed cylindrical shell with a continuous piezoceramic layer and a laminated composite semi-circular cantilever shell with discrete cylindrical piezoelectric actuators and/or sensors.
A finite element study of the stability of spontaneous curling of thin shells
NASA Astrophysics Data System (ADS)
Han, Xiaomin; Guo, Qiaohang; Chu, Kevin; Trase, Ian; Hu, Nan; Chen, Zi
Thin shells are of great interest in engineering due to their ubiquity in nature. The mechanical instabilities of thin shells are a key factor in understanding many real world phenomena, such as the closure of a Venus flytrap or the curling of a dried leaf. Given the analytical theory that quantitatively described the stability of thin shells subject to surface stress, we are able to identify a dimensionless parameter that controls the stability of thin shells. Finite element analyses are employed to numerically examine the predictions. Bi-layer plates are fabricated where one layer is pre-stretched and has much smaller Young's modulus than the other layer to examine mechanical instability. By measuring the two principle curvatures on the plate, the onset of bifurcation can be determined. Different initial conditions and material properties are taken into account in the FEA, including initial curvature, Poisson's ratio, and the magnitude of surface stress. The numerical experiments agree well with the theory.
A Mixed Multi-Field Finite Element Formulation for Thermopiezoelectric Composite Shells
NASA Technical Reports Server (NTRS)
Lee, Ho-Jun; Saravanos, Dimitris A.
1999-01-01
Analytical formulations are presented which account for the coupled mechanical, electrical, and thermal response of piezoelectric composite shell structures. A new mixed multi-field laminate theory is developed which combines "single layer" assumptions for the displacements along with layerwise fields for the electric potential and temperature. This laminate theory is formulated using curvilinear coordinates and is based on the principles of linear thermopiezoelectricity. The mechanics have the inherent capability to explicitly model both the active and sensory responses of piezoelectric composite shells in thermal environment. Finite element equations are derived and implemented for an eight-noded shell element. Numerical studies are conducted to investigate both the sensory and active responses of piezoelectric composite shell structures subjected to thermal loads. Results for a cantilevered plate with an attached piezoelectric layer are com- pared with corresponding results from a commercial finite element code and a previously developed program. Additional studies are conducted on a cylindrical shell with an attached piezoelectric layer to demonstrate capabilities to achieve thermal shape control on curved piezoelectric structures.
A computer program for anisotropic shallow-shell finite elements using symbolic integration
NASA Technical Reports Server (NTRS)
Andersen, C. M.; Bowen, J. T.
1976-01-01
A FORTRAN computer program for anisotropic shallow-shell finite elements with variable curvature is described. A listing of the program is presented together with printed output for a sample case. Computation times and central memory requirements are given for several different elements. The program is based on a stiffness (displacement) finite-element model in which the fundamental unknowns consist of both the displacement and the rotation components of the reference surface of the shell. Two triangular and four quadrilateral elements are implemented in the program. The triangular elements have 6 or 10 nodes, and the quadrilateral elements have 4 or 8 nodes. Two of the quadrilateral elements have internal degrees of freedom associated with displacement modes which vanish along the edges of the elements (bubble modes). The triangular elements and the remaining two quadrilateral elements do not have bubble modes. The output from the program consists of arrays corresponding to the stiffness, the geometric stiffness, the consistent mass, and the consistent load matrices for individual elements. The integrals required for the generation of these arrays are evaluated by using symbolic (or analytic) integration in conjunction with certain group-theoretic techniques. The analytic expressions for the integrals are exact and were developed using the symbolic and algebraic manipulation language.
NASA Astrophysics Data System (ADS)
Yasin, M. Yaqoob; Kapuria, S.
2014-01-01
In this work, we present a new efficient four-node finite element for shallow multilayered piezoelectric shells, considering layerwise mechanics and electromechanical coupling. The laminate mechanics is based on the zigzag theory that has only seven kinematic degrees of freedom per node. The normal deformation of the piezoelectric layers under the electric field is accounted for without introducing any additional deflection variables. A consistent quadratic variation of the electric potential across the piezoelectric layers with the provision of satisfying the equipotential condition of electroded surfaces is adopted. The performance of the new element is demonstrated for the static response under mechanical and electric potential loads, and for free vibration response of smart shells under different boundary conditions. The predictions are found to be very close to the three dimensional piezoelasticity solutions for hybrid shells made of not only single-material composite substrates, but also sandwich substrates with a soft core for which the equivalent single layer (ESL) theories perform very badly.
NASA Technical Reports Server (NTRS)
Rankin, C. C.
1988-01-01
A consistent linearization is provided for the element-dependent corotational formulation, providing the proper first and second variation of the strain energy. As a result, the warping problem that has plagued flat elements has been overcome, with beneficial effects carried over to linear solutions. True Newton quadratic convergence has been restored to the Structural Analysis of General Shells (STAGS) code for conservative loading using the full corotational implementation. Some implications for general finite element analysis are discussed, including what effect the automatic frame invariance provided by this work might have on the development of new, improved elements.
Analytical Derivations of Single-Particle Matrix Elements in Nuclear Shell Model
NASA Astrophysics Data System (ADS)
Fatah, Aziz H.; Radhi, R. A.; Abdullah, Nzar R.
2016-07-01
We present analytical method to calculate single particle matrix elements used in atomic and nuclear physics. We show seven different formulas of matrix elements of the operator f(r)dr m where f(r) = rμ, rμ jJ(qr), V(r) corresponding to the Gaussian and the Yukawa potentials used in nuclear shell models and nuclear structure. In addition, we take into account a general integral formula of the matrix element
Titovich, Alexey S; Norris, Andrew N; Haberman, Michael R
2016-06-01
The use of cylindrical elastic shells as elements in acoustic metamaterial devices is demonstrated through simulations and underwater measurements of a cylindrical-to-plane wave lens. Transformation acoustics of a circular region to a square dictate that the effective density in the lens remain constant and equal to that of water. Piecewise approximation to the desired effective compressibility is achieved using a square array with elements based on the elastic shell metamaterial concept developed by Titovich and Norris [J. Acoust. Soc. Am. 136(4), 1601-1609 (2014)]. The sizes of the elements are chosen based on availability of shells, minimizing fabrication difficulties. The tested device is neutrally buoyant comprising 48 elements of nine different types of commercial shells made from aluminum, brass, copper, and polymers. Simulations indicate a broadband range in which the device acts as a cylindrical to plane wave lens. The experimental findings confirm the broadband quadropolar response from approximately 20 to 40 kHz, with positive gain of the radiation pattern in the four plane wave directions. PMID:27369162
Zhang, Shuai; Chen, Zhen; Fu, Yu-qiang; Gong, Hui-li; Guan, Hua-shi; Liu, Hong-bing
2015-11-01
A comparable study were carried out by determination of trace elements on five marine-derived shell traditional Chinese medicine (TCM) (Ostreae Concha, Haliotidis Concha, Margaritifera Concha, Meretricis Concha, and Arcae Concha), which were recorded in the Chinese Pharmacopoeia (2010 version). Seven trace elements in 51 batches of this type of shell TCM were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), combined with principal component analysis (PCA) methods. The content of element Se, which exhibited significant differences among different drugs, could be used as a key element to distinguish this type of drugs. Meanwhile, the contents of elements Co, Cu, Mo, and Ba in Haliotidis Concha, Co and As in Margaritifera Concha, Mo and As in Meretricis Concha, Mo, As, and Ba in Arcae Concha, and Zn in Meretricis Concha were relatively stable. In the PCA plot, Arcae Concha and Meretricis Concha could be efficiently distinguished from Ostreae Concha together with Haliotidis Concha, and Margaritifera Concha. The results also showed a correlation with their medicinal function. In conclusion, trace elements in marine-derived shell TCM could not be neglected for their quality control.
Zhang, Shuai; Chen, Zhen; Fu, Yu-qiang; Gong, Hui-li; Guan, Hua-shi; Liu, Hong-bing
2015-11-01
A comparable study were carried out by determination of trace elements on five marine-derived shell traditional Chinese medicine (TCM) (Ostreae Concha, Haliotidis Concha, Margaritifera Concha, Meretricis Concha, and Arcae Concha), which were recorded in the Chinese Pharmacopoeia (2010 version). Seven trace elements in 51 batches of this type of shell TCM were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), combined with principal component analysis (PCA) methods. The content of element Se, which exhibited significant differences among different drugs, could be used as a key element to distinguish this type of drugs. Meanwhile, the contents of elements Co, Cu, Mo, and Ba in Haliotidis Concha, Co and As in Margaritifera Concha, Mo and As in Meretricis Concha, Mo, As, and Ba in Arcae Concha, and Zn in Meretricis Concha were relatively stable. In the PCA plot, Arcae Concha and Meretricis Concha could be efficiently distinguished from Ostreae Concha together with Haliotidis Concha, and Margaritifera Concha. The results also showed a correlation with their medicinal function. In conclusion, trace elements in marine-derived shell TCM could not be neglected for their quality control. PMID:27071261
Rapid Parallel Calculation of shell Element Based On GPU
NASA Astrophysics Data System (ADS)
Wanga, Jian Hua; Lia, Guang Yao; Lib, Sheng; Li, Guang Yao
2010-06-01
Long computing time bottlenecked the application of finite element. In this paper, an effective method to speed up the FEM calculation by using the existing modern graphic processing unit and programmable colored rendering tool was put forward, which devised the representation of unit information in accordance with the features of GPU, converted all the unit calculation into film rendering process, solved the simulation work of all the unit calculation of the internal force, and overcame the shortcomings of lowly parallel level appeared ever before when it run in a single computer. Studies shown that this method could improve efficiency and shorten calculating hours greatly. The results of emulation calculation about the elasticity problem of large number cells in the sheet metal proved that using the GPU parallel simulation calculation was faster than using the CPU's. It is useful and efficient to solve the project problems in this way.
A solid-shell Cosserat point element ( SSCPE) for elastic thin structures at finite deformation
NASA Astrophysics Data System (ADS)
Jabareen, Mahmood; Mtanes, Eli
2016-07-01
The objective of this study is to develop a new solid-shell element using the Cosserat point theory for modeling thin elastic structures at finite deformations. The point-wise Green-Lagrange strain tensor is additively decomposed into homogeneous and inhomogeneous parts. Only the latter part of the strain tensor is modified by the assumed natural strain ANS concept to avoid both curvature-thickness locking and transverse shear locking. To the authors' knowledge, such modification has not been applied yet in the literature, and here it is referred to as the assumed natural inhomogeneous strain ANIS concept. Moreover, a new methodology for determining the constitutive coefficients of the strain energy function, which controls the inhomogeneous deformations, is proposed. The resulting coefficients ensure both accuracy, robustness, and elimination of all locking pathologies in the solid-shell Cosserat point element ( SSCPE). The performance of the developed SSCPE is verified and tested via various benchmark problems and compared to other solid, shell, and solid-shell elements. These examples demonstrate that the SSCPE is accurate, robust, stable, free of locking, and can be used for modeling thin structures at both small and finite deformations.
Developments in variational methods for high performance plate and shell elements
NASA Technical Reports Server (NTRS)
Felippa, Carlos A.; Militello, Carmelo
1991-01-01
High performance elements are simple finite elements constructed to deliver engineering accuracy with coarse arbitrary grids. This is part of a series on the variational foundations of high-performance elements, with emphasis on plate and shell elements constructed with the free formulation (FF) and assumed natural strain (ANS) methods. Parameterized variational principles are studied that provide a common foundation for the FF and ANS methods, as well as for a combination of both. From this unified formulation a variant of the ANS formulation, called the assumed natural deviatoric strain (ANDES) formulation, emerges as an important special case. The first ANDES element, a high-performance 9 degrees of freedom triangular Kirchhoff plate bending element, is briefly described to illustrate the use of the new formulation.
Average M shell fluorescence yields for elements with 70≤Z≤92
Kahoul, A.; Deghfel, B.; Aylikci, V.; Aylikci, N. K.; Nekkab, M.
2015-03-30
The theoretical, experimental and analytical methods for the calculation of average M-shell fluorescence yield (ω{sup ¯}{sub M}) of different elements are very important because of the large number of their applications in various areas of physical chemistry and medical research. In this paper, the bulk of the average M-shell fluorescence yield measurements reported in the literature, covering the period 1955 to 2005 are interpolated by using an analytical function to deduce the empirical average M-shell fluorescence yield in the atomic range of 70≤Z≤92. The results were compared with the theoretical and fitted values reported by other authors. Reasonable agreement was typically obtained between our result and other works.
NASA Astrophysics Data System (ADS)
Wanamaker, A. D.; Gillikin, D. P.
2014-12-01
The long-lived ocean quahog, Arctica islandica, is a fairly well developed and tested marine proxy archive, however, the utility of elemental ratios in A. islandica shell material as environmental proxies remains questionable. To further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization, A. islandica shells were grown at constant temperatures under two regimes during a 16-week period from March 27 to July 21, 2011. Seawater from the Darling Marine Center in Walpole, Maine was pumped into temperature and flow controlled tanks that were exposed to ambient food and salinity conditions. A total of 20 individual juvenile clams with an average shell height of 36 mm were stained with calcein (a commonly used biomarker) and cultured at 10.3 ± 0.3 °C for six weeks. After this, shell heights were measured and the clams were again stained with calcein and cultured at 15.0 ± 0.4 °C for an additional 9.5 weeks. The average shell growth during the first phase of the experiment was 2.4 mm with a linear extension rate of 0.40 mm/week. The average shell growth during the second phase of the experiment was 3.2 mm with an extension rate of 0.34 mm/week. Average salinity values were 30.2 ± 0.7 and 30.7 ±0.7 in the first and second phases of the experiment, respectively. Oxygen isotopes from the cultured seawater were collected throughout the experiment and provide the basis for establishing if shells grew in oxygen isotopic equilibrium. Elemental ratios (primarily Ba/Ca, Mg/Ca, Sr/Ca) in the aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), while stable oxygen and carbon isotope ratios were measured using continuous flow isotope ratio mass spectrometry. Continuous sampling within and across the temperature conditions (from 10 °C to 15 °C) coupled with the calcein markings provides the ability to place each sample into a precise temporal framework. The
Symmetry of Isoscalar Matrix Elements and Systematics in the sd and beginning of fp shells
NASA Astrophysics Data System (ADS)
Orce, J. N.; Petkov, P.; Velázquez, V.; McKay, C. J.; Lesher, S. R.; Choudry, S.; Mynk, M.; Linnemann, A.; Jolie, J.; von Brentano, P.; Werner, V.; Yates, S. W.; McEllistrem, M. T.
2006-03-01
A careful determination of the lifetime and measurement of the branching ratio for decay of the first 2T=1+ state in 42Sc has allowed an accurate experimental test of charge independence in the A = 42 isobaric triplet. A lifetime of 69(17) fs was measured at the University of Kentucky, while relative intensities for the 975 keV and 1586 keV transitions depopulating the first 2T=1+ state have been determined at the University of Cologne as 100(1) and 8(1), respectively. Both measurements give an isoscalar matrix element, M0, of 6.4(9) (W.u.)1/2. This result confirms charge independence for the A=42 isobaric triplet. Shell model calculations have been carried out for understanding the global trend of M0 values for A = 4n + 2 isobaric triplets ranging from A = 18 to A = 42. The 21 (T=1)+ → 01 (T=1)+ transition energies, reduced transition probabilities and M0 values are reproduced to a high degree of accuracy. The trend of M0 strength along the sd shell is interpreted in terms of the shell structure. Certain discrepancies arise at the extremes of the sd shell, for the A = 18 and A = 38 isobaric triplets, which might be explained in terms of the low valence space at the extremes of the sd shell.
NASA Technical Reports Server (NTRS)
Martin, C. Wayne; Breiner, David M.; Gupta, Kajal K. (Technical Monitor)
2004-01-01
Mathematical development and some computed results are presented for Mindlin plate and shell elements, suitable for analysis of laminated composite and sandwich structures. These elements use the conventional 3 (plate) or 5 (shell) nodal degrees of freedom, have no communicable mechanisms, have no spurious shear energy (no shear locking), have no spurious membrane energy (no membrane locking) and do not require arbitrary reduction of out-of-plane shear moduli or under-integration. Artificial out-of-plane rotational stiffnesses are added at the element level to avoid convergence problems or singularity due to flat spots in shells. This report discusses a 6-node curved triangular element and a 4-node quadrilateral element. Findings show that in regular rectangular meshes, the Martin-Breiner 6-node triangular curved shell (MB6) is approximately equivalent to the conventional 8-node quadrilateral with integration. The 4-node quadrilateral (MB4) has very good accuracy for a 4-node element, and may be preferred in vibration analysis because of narrower bandwidth. The mathematical developments used in these elements, those discussed in the seven appendices, have been applied to elements with 3, 4, 6, and 10 nodes and can be applied to other nodal configurations.
Critical time step for a bilinear laminated composite Mindlin shell element.
Hammerand, Daniel Carl
2004-06-01
The critical time step needed for explicit time integration of laminated shell finite element models is presented. Each layer is restricted to be orthotropic when viewed from a properly oriented material coordinate system. Mindlin shell theory is used in determining the laminated response that includes the effects of transverse shear. The effects of the membrane-bending coupling matrix from the laminate material model are included. Such a coupling matrix arises even in the case of non-symmetric lay-ups of differing isotropic layers. Single point integration is assumed to be used in determining a uniform strain response from the element. Using a technique based upon one from the literature, reduced eigenvalue problems are established to determine the remaining non-zero frequencies. It is shown that the eigenvalue problem arising from the inplane normal and shear stresses is decoupled from that arising from the transverse shear stresses. A verification example is presented where the exact and approximate results are compared.
NASA Astrophysics Data System (ADS)
Karmakar, Amit; Kishimoto, Kikuo
In this paper a finite element method is presented to study the effects of delamination on free vibration characteristics of graphite-epoxy composite pretwisted rotating shells. Lagrange’s equation of motion is used to derive the dynamic equilibrium equation and moderate rotational speeds are considered wherein the Coriolis effect is negligible. An eight noded isoparametric plate bending element is employed in the formulation incorporating rotary inertia and effects of transverse shear deformation based on Mindlin’s theory. To satisfy the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front, a multipoint constraint algorithm is incorporated which leads to unsymmetric stiffness matrices. Parametric studies are performed in respect of location of delamination, fibre orientation, rotational speed and twist angle on natural frequencies of cylindrical shallow shells. Numerical results obtained for symmetric and unsymmetric laminates are the first known non-dimensional frequencies for the analyses carried out here.
NASA Astrophysics Data System (ADS)
Sohn, Dongwoo; Im, Seyoung
2013-06-01
In this paper, novel finite elements that include an arbitrary number of additional nodes on each edge of a quadrilateral element are proposed to achieve compatible connection of neighboring nonmatching meshes in plate and shell analyses. The elements, termed variable-node plate elements, are based on two-dimensional variable-node elements with point interpolation and on the Mindlin-Reissner plate theory. Subsequently the flat shell elements, termed variable-node shell elements, are formulated by further extending the plate elements. To eliminate a transverse shear locking phenomenon, the assumed natural strain method is used for plate and shell analyses. Since the variable-node plate and shell elements allow an arbitrary number of additional nodes and overcome locking problems, they make it possible to connect two nonmatching meshes and to provide accurate solutions in local mesh refinement. In addition, the curvature and strain smoothing methods through smoothed integration are adopted to improve the element performance. Several numerical examples are presented to demonstrate the effectiveness of the elements in terms of the accuracy and efficiency of the analyses.
A 6-node co-rotational triangular elasto-plastic shell element
NASA Astrophysics Data System (ADS)
Li, Zhongxue; Xiang, Yu; Izzuddin, Bassam A.; Vu-Quoc, Loc; Zhuo, Xin; Zhang, Chuanjie
2015-05-01
A 6-node co-rotational triangular elasto-plastic shell element is developed. The local coordinate system of the element is defined by the vectors directing from one vertex to the other two vertices and their cross product. Based on such a co-rotational framework, the element rigid-body rotations are excluded in calculating the local nodal variables from the global nodal variables. The two smallest components of each nodal orientation vector are defined as rotational variables, resulting in the desired additive property for all nodal variables in a nonlinear incremental solution procedure. Different from other existing co-rotational finite element formulations, both the element tangent stiffness matrices in the local and in the global coordinate systems are symmetric owing to the commutativity of the nodal variables in calculating the second derivatives of the strain energy with respect to the local nodal variables and, through chain differentiation, with respect to the global nodal variables. For elasto-plastic analysis, the Maxwell-Huber-Hencky-von Mises yield criterion is employed together with the backward-Euler return-mapping method for the evaluation of the elasto-plastic stress state, where a consistent tangent modulus matrix is employed. To overcome locking problems, the assumed linear membrane strains and shear strains are obtained by using the line integration method proposed by MacNeal, and the assumed higher-order membrane strains are obtained by enforcing the stationarity of the mixed displacement-strain canonical functional, these assumed strains are then employed to replace the corresponding conforming strains. The reliability and convergence of the present 6-node triangular shell element formulation are verified through two elastic plate patch tests as well as two elastic and five elasto-plastic plate/shell problems undergoing large displacements and large rotations.
NASA Astrophysics Data System (ADS)
Kulikov, G. M.; Mamontov, A. A.; Plotnikova, S. V.; Mamontov, S. A.
2015-11-01
A hybrid-mixed ANS four-node shell element by using the sampling surfaces (SaS) technique is developed. The SaS formulation is based on choosing inside the nth layer In not equally spaced SaS parallel to the middle surface of the shell in order to introduce the displacements of these surfaces as basic shell variables. Such choice of unknowns with the consequent use of Lagrange polynomials of degree In - 1 in the thickness direction for each layer permits the presentation of the layered shell formulation in a very compact form. The SaS are located inside each layer at Chebyshev polynomial nodes that allows one to minimize uniformly the error due to the Lagrange interpolation. To implement the efficient analytical integration throughout the element, the enhanced ANS method is employed. The proposed hybrid-mixed four-node shell element is based on the Hu-Washizu variational equation and exhibits a superior performance in the case of coarse meshes. It could be useful for the 3D stress analysis of thick and thin doubly-curved shells since the SaS formulation gives the possibility to obtain numerical solutions with a prescribed accuracy, which asymptotically approach the exact solutions of elasticity as the number of SaS tends to infinity.
Multi-field variational formulations and related finite elements for piezoelectric shells
NASA Astrophysics Data System (ADS)
Lammering, Rolf; Mesecke-Rischmann, Simone
2003-12-01
Smart structures technology characterized by structurally integrated sensors and actuators has recently expanded significantly especially as regards lightweight constructions in aeronautics and robotics, e.g. to allow vibration suppression and noise attenuation. In order to be capable of solving these complex issues the finite element method as a well established design tool has to be extended. This paper focuses on shallow sandwich composite shell structures with thin piezoelectric patches bonded to the surfaces. For the proper design of plate and shell structures with integrated piezoelectric materials, various variational formulations and corresponding finite elements are presented. The starting point is the well known two-field variational formulation where the linear piezoelectric effect is taken into account so that the displacements and the electric potential serve as independent variables. Here, the mostly assumed linear variation of the electric potential through the thickness is assumed. Next, it is shown that a quadratic variation of the electric potential through the thickness can be deduced directly from the charge conservation condition. This quadratic variation of the electric potential in the thickness direction is compared with the linear gradient of the first two-field variational formulation. Moreover, in order to allow the implementation of alternative formulations of the constitutive equations by switching of the independent variables and nonlinear material behaviour, a three-field variational formulation is presented in analogy to the Hu-Washizu principle. Adopting this variational principle a hybrid finite element is derived where the dielectric displacement is formulated as an additional degree of freedom. This independent variable can be condensed on the element level and does not enter the system of equations. For the first time all these different variational formulations are developed for a Reissner-Mindlin shallow shell element
Ricardo, Fernando; Génio, Luciana; Costa Leal, Miguel; Albuquerque, Rui; Queiroga, Henrique; Rosa, Rui; Calado, Ricardo
2015-07-07
Determining seafood geographic origin is critical for controlling its quality and safeguarding the interest of consumers. Here, we use trace element fingerprinting (TEF) of bivalve shells to discriminate the geographic origin of specimens. Barium (Ba), manganese (Mn), magnesium (Mg), strontium (Sr) and lead (Pb) were quantified in cockle shells (Cerastoderma edule) captured with two fishing methods (by hand and by hand-raking) and from five adjacent fishing locations within an estuarine system (Ria de Aveiro, Portugal). Results suggest no differences in TEF of cockle shells captured by hand or by hand-raking, thus confirming that metal rakes do not act as a potential source of metal contamination that could somehow bias TEF results. In contrast, significant differences were recorded among locations for all trace elements analysed. A Canonical Analysis of Principal Coordinates (CAP) revealed that 92% of the samples could be successfully classified according to their fishing location using TEF. We show that TEF can be an accurate, fast and reliable method to determine the geographic origin of bivalves, even among locations separated less than 1 km apart within the same estuarine system. Nonetheless, follow up studies are needed to determine if TEF can reliably discriminate between bivalves originating from different ecosystems.
Ricardo, Fernando; Génio, Luciana; Costa Leal, Miguel; Albuquerque, Rui; Queiroga, Henrique; Rosa, Rui; Calado, Ricardo
2015-01-01
Determining seafood geographic origin is critical for controlling its quality and safeguarding the interest of consumers. Here, we use trace element fingerprinting (TEF) of bivalve shells to discriminate the geographic origin of specimens. Barium (Ba), manganese (Mn), magnesium (Mg), strontium (Sr) and lead (Pb) were quantified in cockle shells (Cerastoderma edule) captured with two fishing methods (by hand and by hand-raking) and from five adjacent fishing locations within an estuarine system (Ria de Aveiro, Portugal). Results suggest no differences in TEF of cockle shells captured by hand or by hand-raking, thus confirming that metal rakes do not act as a potential source of metal contamination that could somehow bias TEF results. In contrast, significant differences were recorded among locations for all trace elements analysed. A Canonical Analysis of Principal Coordinates (CAP) revealed that 92% of the samples could be successfully classified according to their fishing location using TEF. We show that TEF can be an accurate, fast and reliable method to determine the geographic origin of bivalves, even among locations separated less than 1 km apart within the same estuarine system. Nonetheless, follow up studies are needed to determine if TEF can reliably discriminate between bivalves originating from different ecosystems. PMID:26149418
Calculation of K-shell fluorescence yields for low-Z elements
Nekkab, M.; Kahoul, A.; Deghfel, B.; Aylikci, N. Küp; Aylikçi, V.
2015-03-30
The analytical methods based on X-ray fluorescence are advantageous for practical applications in a variety of fields including atomic physics, X-ray fluorescence surface chemical analysis and medical research and so the accurate fluorescence yields (ω{sub K}) are required for these applications. In this contribution we report a new parameters for calculation of K-shell fluorescence yields (ω{sub K}) of elements in the range of 11≤Z≤30. The experimental data are interpolated by using the famous analytical function (ω{sub k}/(1−ω{sub k})){sup 1/q} (were q=3, 3.5 and 4) vs Z to deduce the empirical K-shell fluorescence yields. A comparison is made between the results of the procedures followed here and those theoretical and other semi-empirical fluorescence yield values. Reasonable agreement was typically obtained between our result and other works.
SAPNEW: Parallel finite element code for thin shell structures on the Alliant FX/80
NASA Technical Reports Server (NTRS)
Kamat, Manohar P.; Watson, Brian C.
1992-01-01
The results of a research activity aimed at providing a finite element capability for analyzing turbo-machinery bladed-disk assemblies in a vector/parallel processing environment are summarized. Analysis of aircraft turbofan engines is very computationally intensive. The performance limit of modern day computers with a single processing unit was estimated at 3 billions of floating point operations per second (3 gigaflops). In view of this limit of a sequential unit, performance rates higher than 3 gigaflops can be achieved only through vectorization and/or parallelization as on Alliant FX/80. Accordingly, the efforts of this critically needed research were geared towards developing and evaluating parallel finite element methods for static and vibration analysis. A special purpose code, named with the acronym SAPNEW, performs static and eigen analysis of multi-degree-of-freedom blade models built-up from flat thin shell elements.
SAPNEW: Parallel finite element code for thin shell structures on the Alliant FX/80
NASA Astrophysics Data System (ADS)
Kamat, Manohar P.; Watson, Brian C.
1992-02-01
The results of a research activity aimed at providing a finite element capability for analyzing turbo-machinery bladed-disk assemblies in a vector/parallel processing environment are summarized. Analysis of aircraft turbofan engines is very computationally intensive. The performance limit of modern day computers with a single processing unit was estimated at 3 billions of floating point operations per second (3 gigaflops). In view of this limit of a sequential unit, performance rates higher than 3 gigaflops can be achieved only through vectorization and/or parallelization as on Alliant FX/80. Accordingly, the efforts of this critically needed research were geared towards developing and evaluating parallel finite element methods for static and vibration analysis. A special purpose code, named with the acronym SAPNEW, performs static and eigen analysis of multi-degree-of-freedom blade models built-up from flat thin shell elements.
NASA Astrophysics Data System (ADS)
Park, Hun
A comprehensive methodology to accurately predict the dynamic response of composite panels under blast wave pressure loading has been successfully developed for the first time. It includes the modeling of geometrically nonlinear dynamic effect, progressive failure and strain-rate effect on constitutive equation and strength. For dynamic analysis, a nonlinear solid shell element formulation is combined with the trapezoidal rule for numerical integration in time. The progressive damage incorporates the effect of the material failure, such as fiber failure, matrix cracking and fiber-matrix shearing failure on the stiffness and strength. Material degradation models based on the rule of mixtures are proposed for each failure mode. To implement the strain-rate effect on the constitutive equation of the material, a viscoplastic model is adopted. In this model, three material parameters are determined by conducting uniaxial tension tests on off-axis specimen. The effect of strain rates on material strength is implemented via the linear least square fit of the test data. A key ingredient of the analysis is a geometrically nonlinear solid shell element based on the assumed strain formulation to alleviate element locking. In this approach, the composite shell is treated as a three-dimensional solid. Accordingly, the change of shell thickness is allowed and the kinematics of deformation is described by six vector components at a point on the shell midsurface. The mass matrix always remains constant during the analysis. Example problems under static and dynamic loadings are solved to investigate the behavior of composite panels undergoing large deformation while experiencing material damage. The analysis results are compared with the test data available. Results of the numerical analysis show that the effect of the progressive failure and strain-rates on structural responses are considerable. For a composite plate under static pressure loadings, maximum displacement and
NASA Technical Reports Server (NTRS)
Lebiedzik, Catherine
1995-01-01
Development of design tools to furnish optimal acoustic environments for lightweight aircraft demands the ability to simulate the acoustic system on a workstation. In order to form an effective mathematical model of the phenomena at hand, we have begun by studying the propagation of acoustic waves inside closed spherical shells. Using a fully-coupled fluid-structure interaction model based upon variational principles, we have written a finite element analysis program and are in the process of examining several test cases. Future investigations are planned to increase model accuracy by incorporating non-linear and viscous effects.
Seltzer, M.D.; Berry, K.H.
2005-01-01
The outer keratin layer (scute) of desert tortoise shells consists of incrementally grown laminae in which various bioaccumulated trace elements are sequestered during scute deposition. Laser ablation ICP-MS examination of laminae in scutes of dead tortoises revealed patterns of trace elemental distribution from which the chronology of elemental uptake can be inferred. These patterns may be of pathologic significance in the case of elemental toxicants such as arsenic, which has been linked to both shell and respiratory diseases. Laser ablation transects, performed along the lateral surfaces of sectioned scutes, offered the most successful means of avoiding exogenous contamination that was present on the scute exterior. Semiquantitative determination of elemental concentrations was achieved using sulfur, a keratin matrix element, as an internal standard. The results presented here highlight the potential of laser ablation ICP-MS as a diagnostic tool for investigating toxic element uptake as it pertains to tortoise morbidity and mortality.
Seltzer, Michaeld; Berry, Kristinh
2005-03-01
The outer keratin layer (scute) of desert tortoise shells consists of incrementally grown laminae in which various bioaccumulated trace elements are sequestered during scute deposition. Laser ablation ICP-MS examination of laminae in scutes of dead tortoises revealed patterns of trace elemental distribution from which the chronology of elemental uptake can be inferred. These patterns may be of pathologic significance in the case of elemental toxicants such as arsenic, which has been linked to both shell and respiratory diseases. Laser ablation transects, performed along the lateral surfaces of sectioned scutes, offered the most successful means of avoiding exogenous contamination that was present on the scute exterior. Semiquantitative determination of elemental concentrations was achieved using sulfur, a keratin matrix element, as an internal standard. The results presented here highlight the potential of laser ablation ICP-MS as a diagnostic tool for investigating toxic element uptake as it pertains to tortoise morbidity and mortality.
Seltzer, Michaeld; Berry, Kristinh
2005-03-01
The outer keratin layer (scute) of desert tortoise shells consists of incrementally grown laminae in which various bioaccumulated trace elements are sequestered during scute deposition. Laser ablation ICP-MS examination of laminae in scutes of dead tortoises revealed patterns of trace elemental distribution from which the chronology of elemental uptake can be inferred. These patterns may be of pathologic significance in the case of elemental toxicants such as arsenic, which has been linked to both shell and respiratory diseases. Laser ablation transects, performed along the lateral surfaces of sectioned scutes, offered the most successful means of avoiding exogenous contamination that was present on the scute exterior. Semiquantitative determination of elemental concentrations was achieved using sulfur, a keratin matrix element, as an internal standard. The results presented here highlight the potential of laser ablation ICP-MS as a diagnostic tool for investigating toxic element uptake as it pertains to tortoise morbidity and mortality. PMID:15740773
NASA Astrophysics Data System (ADS)
Mii, H.; Lin, Y.; You, C.; Li, M.
2002-12-01
We have analyzed the isotope and element compositions of two modern and two Late Pleistocene Anadara granosa shells to quantitatively characterize the paleoenvironment in Szekou Formation, Hengchun, southern Taiwan. δ18O values of modern shells (-2.2+/-0.8 permil; mean+/-1σ ; N = 76) are in good agreement with those calculated values based on available seawater δ18O and temperature data, thus reach apparently isotopic equilibrium. Fossil shells, retaining the originally aragonitic mineralogy, indicate that these shells are not altered by diagenesis. Mean δ18O and δ13C values of the Lower Szekou Fm. (LSz) shell are respectively -0.6+/-0.7 permil (N = 82) and -3.6+/-0.7 permil. Average δ18O and δ13C values of the Upper Szekou Fm. (USz; 25 m above LSz) shell are -0.7+/-0.7 permil (N = 47) and -2.6+/-0.8 permil, respectively. Both LSz and USz show positive linear correlation between δ18O and δ13C values with different slope (intersect at δ18O= -5.4, δ13C= -6.8 permil). Therefore, samples from Szekou Fm. show significant fresh water-seawater mixing signals. Average δ18O value of fossil specimens is 1.5 permil greater than that of modern ones and is most likely due to global glaciation effect. Assuming the δ18O of seawater was 1.5 permil, the winter seawater temperature of studied area was about 24°C. The calculated temperature is comparable to that of modern seawater. With the seasonal temperature range of 5°C, the river water δ18O values were estimated between -6.4 and -7.5 permil. Average Mg/Ca, Sr/Ca, and Ba/Ca ratios are respectively 0.22+/-0.02 mmol/mol, 1.48+/-0.15 mmol/mol, and 24.64+/-5.01 μmol/mol for LSz (N=16) and 0.28+/-0.09 mmol/mol, 1.67+/-0.25 mmol/mol, and 11.57+/-3.14 μmol/mol for USz (N=24). Episodic minima of Mg/Ca ratios are generally coinciding to δ18O maxima. Thus, Mg/Ca ratio may be also varied as a function of temperature in the aragonitic shells. Metabolic activity of A. granosa should be the major factor controlling Sr
NASA Astrophysics Data System (ADS)
Sabri, Farhad; Lakis, Aouni A.
2010-03-01
In this study, aeroelastic analysis of a truncated conical shell subjected to the external supersonic airflow is carried out. The structural model is based on a combination of linear Sanders thin shell theory and the classic finite element method. Linearized first-order potential (piston) theory with the curvature correction term is coupled with the structural model to account for pressure loading. The influence of stress stiffening due to internal or external pressure and axial compression is also taken into account. The fluid-filled effect is considered as a velocity potential variable at each node of the shell elements at the fluid-structure interface in terms of nodal elastic displacements. Aeroelastic equations using the hybrid finite element formulation are derived and solved numerically. The results are validated using numerical and theoretical data available in the literature. The analysis is accomplished for conical shells of different boundary conditions and cone angles. In all cases the conical shell loses its stability through coupled-mode flutter. This proposed hybrid finite element method can be used efficiently for design and analysis of conical shells employed in high speed aircraft structures.
An assessment of finite-element modeling techniques for thick-solid/thin-shell joints analysis
NASA Technical Reports Server (NTRS)
Min, J. B.; Androlake, S. G.
1993-01-01
The subject of finite-element modeling has long been of critical importance to the practicing designer/analyst who is often faced with obtaining an accurate and cost-effective structural analysis of a particular design. Typically, these two goals are in conflict. The purpose is to discuss the topic of finite-element modeling for solid/shell connections (joints) which are significant for the practicing modeler. Several approaches are currently in use, but frequently various assumptions restrict their use. Such techniques currently used in practical applications were tested, especially to see which technique is the most ideally suited for the computer aided design (CAD) environment. Some basic thoughts regarding each technique are also discussed. As a consequence, some suggestions based on the results are given to lead reliable results in geometrically complex joints where the deformation and stress behavior are complicated.
Shell-model analysis of the 136Xe double beta decay nuclear matrix elements.
Horoi, M; Brown, B A
2013-05-31
Neutrinoless double beta decay, if observed, could distinguish whether the neutrino is a Dirac or a Majorana particle, and it could be used to determine the absolute scale of the neutrino masses. 136Xe is one of the most promising candidates for observing this rare event. However, until recently there were no positive results for the allowed and less rare two-neutrino double beta decay mode. The small nuclear matrix element associated with the long half-life represents a challenge for nuclear structure models used for its calculation. We report a new shell-model analysis of the two-neutrino double beta decay of 136Xe, which takes into account all relevant nuclear orbitals necessary to fully describe the associated Gamow-Teller strength. We further use the new model to analyze the main contributions to the neutrinoless double beta decay matrix element, and show that they are also diminished.
Mok, G.C.
1982-01-01
By comparisons with existing analytical and experimental results, it is shown that an approximate method can be used in the study of fluid mass coupling effects in the dynamic analysis of concentric circular cylindrical shells. In the approximate method, the fluid is represented by a mass matrix that is determined from a two-dimensional, small-amplitude, incompressible and inviscid fluid flow analysis, and the shell structures are modelled using axisymmetric shell finite elements for nonaxisymmetric deformations. An empirical relation is given to specify the condition under which the present method will be applicable. 18 refs.
Zorn, Gilad; Dave, Shivang R.; Gao, Xiaohu; Castner, David G.
2011-01-01
In the biological sciences the use of core-shell quantum dots (QDs) has gained wide usage, but analytical challenges still exist for characterizing the QD structure. The application of energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy (XPS) to bulk materials is relatively straightforward, however, for meaningful applications of surface science techniques to multilayer nanoparticles requires novel modifications and analysis methods. To experimentally characterize the elemental composition and distribution in CdSe/CdS/ZnS QDs, we first develop a XPS signal subtraction technique capable of separating the overlapped selenium 3s (core) and sulfur 2s (shell) peaks (both peaks have binding energies near 230eV) with higher precision than is typically reported in the nanoparticle literature. This method is valid for any nanoparticle containing selenium and sulfur. Then we apply a correction formula to the XPS data and determine that the 2 nm stoichiometric CdSe core is surrounded by 2 CdS layers and a stoichimetric ZnS monolayer. These findings and the multi-approach methodology represent a significant advancement in the detailed surface science study of multi-layer nanoparticles. In agreement with recent surprising findings, the time-of-flight secondary mass spectrometry measurements suggest that the surface sites of the QDs used in this study are primarily covered with a mixture of octadecylphosphonic acid and trioctylphophine oxide. PMID:21226467
Lotnyk, A
2014-01-01
Summary Magnetically anisotropic as well as magnetic core–shell nanoparticles (CS-NPs) with controllable properties are highly desirable in a broad range of applications. With this background, a setup for the synthesis of heterostructured magnetic core–shell nanoparticles, which relies on (optionally pulsed) DC plasma gas condensation has been developed. We demonstrate the synthesis of elemental nickel nanoparticles with highly tunable sizes and shapes and Ni@Cu CS-NPs with an average shell thickness of 10 nm as determined with scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements. An analytical model that relies on classical kinetic gas theory is used to describe the deposition of Cu shell atoms on top of existing Ni cores. Its predictive power and possible implications for the growth of heterostructured NP in gas condensation processes are discussed. PMID:24778973
Génio, Luciana; Simon, Klaus; Kiel, Steffen; Cunha, Marina R
2015-12-08
Geochemical markers are being increasingly applied to fundamental questions in population and community ecology in marine habitats because they allow inferences on individuals dispersal, but vital effects, small sample size and instrumental limitation are still challenging particularly in deep-sea studies. Here we use shells of the deep-sea bivalve Idas modiolaeformis to assess potential effects of sample storage, mineralogy, and valve orientation on LA-ICPMS measurements. Trace element concentrations of (24)Mg, (43)Ca, (88)Sr, (137)Ba, (208)Pb, and (238)U are not affected by the two most commonly used storage methods of biologic deep-sea samples (frozen at -20°C and fixed in 95% ethanol); thus combined analysis of differently preserved specimens is possible when the number of individuals is insufficient and distinct sample fixation is needed for multiple purposes. Valve orientation had a strong impact on quantification of trace elements in the calcitic but not in the aragonitic layer of adult shells. Hence, to enable comparisons between adult shells and entirely aragonitic embryonic shells, a reference map of site-specific signatures can potentially be generated using the aragonitic layer of the adult shells. Understanding ontogenetic changes and environmental effects in trace element incorporation is critical before geochemical fingerprinting can be used as a tool for larval dispersal studies in the deep-sea.
Génio, Luciana; Simon, Klaus; Kiel, Steffen; Cunha, Marina R.
2015-01-01
Geochemical markers are being increasingly applied to fundamental questions in population and community ecology in marine habitats because they allow inferences on individuals dispersal, but vital effects, small sample size and instrumental limitation are still challenging particularly in deep-sea studies. Here we use shells of the deep-sea bivalve Idas modiolaeformis to assess potential effects of sample storage, mineralogy, and valve orientation on LA-ICPMS measurements. Trace element concentrations of 24Mg, 43Ca, 88Sr, 137Ba, 208Pb, and 238U are not affected by the two most commonly used storage methods of biologic deep-sea samples (frozen at –20°C and fixed in 95% ethanol); thus combined analysis of differently preserved specimens is possible when the number of individuals is insufficient and distinct sample fixation is needed for multiple purposes. Valve orientation had a strong impact on quantification of trace elements in the calcitic but not in the aragonitic layer of adult shells. Hence, to enable comparisons between adult shells and entirely aragonitic embryonic shells, a reference map of site-specific signatures can potentially be generated using the aragonitic layer of the adult shells. Understanding ontogenetic changes and environmental effects in trace element incorporation is critical before geochemical fingerprinting can be used as a tool for larval dispersal studies in the deep-sea. PMID:26643064
NASA Astrophysics Data System (ADS)
Freitas, Pedro; Richardson, Christopher; Chenery, Simon; Butler, Paul; Reynolds, David; Gaspar, Miguel; Scourse, James
2015-04-01
The great potential of bivalve shells as a high-resolution geochemical proxy archive of environmental conditions at the time of growth has been known for several decades. The elemental composition of bivalve shells has been studied with the purpose of reconstructing environmental conditions: e.g. seawater temperature (Sr and Mg), primary productivity (Li, Mn, Mo and Ba), redox conditions (Mn and Mo), terrigenous inputs (Li) and pollution (Cu, Zn, Cd and Pb). However, the interpretation of such records remains extremely challenging and complex, with processes affecting element incorporation in the shell (e.g. crystal fabrics, organic matrix, shell formation mechanisms and physiological processes) and the influence of more than one environmental parameter affecting elemental composition of bivalve shells. Nevertheless, bivalve shells remain an underused source of information on environmental conditions, with the potential to record high-resolution (sub-weekly to annually), multi-centennial time series of geochemical proxy data. The relatively long-lived bivalve (>100 years) Glycymeris glycymeris occurs in coastal shelf seas of Europe and North West Africa and is a valid annually resolved sclerochronological archive for palaeonvironmental reconstructions. The temporal framework provided by absolute annually dated shell material makes Glycymeris glycymeris a valuable, albeit unexplored, resource for investigating sub-annually resolved geochemical proxies. We present a first evaluation on the potential of Ba, P and U, the latter two elements rarely studied in bivalves, in Glycymeris glycymeris shells to record variations in the environmental conditions, respectively primary productivity, dissolved inorganic phosphorus and carbonate ion concentration/pH. High-resolution (31 to 77 samples per year) profiles of elemental/Ca ratios (E/Ca) over four years of growth (2001 to 2004) were obtained by LA-ICP-MS on two shells (13 and 16 years old) live-collected in 2010 at 30 m
Static analysis of reinforced thin-walled plates and shells by means of finite element models
NASA Astrophysics Data System (ADS)
Carrera, E.; Zappino, E.; Cavallo, T.
2016-03-01
In this paper, variable kinematic one-dimensional (1D) structural models have been used to analyze thin-walled structures with longitudinal stiffeners and static loads. These theories have hierarchical features and are based on the Carrera Unified Formulation (CUF). CUF describes the displacement field of a slender structure as the product of two function expansions, one over the cross-sectional coordinates, Taylor (TE) or Lagrange (LE) expansions were used here, and one along the beam axis. The results obtained using the refined 1D models have been compared with those from classical finite element analyses that make use of plates/shells and solids elements. The performances of classical and refined structural models have been compared in terms of accuracy and computational costs. The results show that the use of the LE over the cross-section allows the strain/stress fields to be evaluated accurately for all the structural components. The comparisons with the results obtained using the classical models highlight how, the use of 1D refined models, allows the number of degrees of freedom (DOF) to be reduced, meanwhile, the accuracy of the results can be preserved.
Distributions of 15 elements on 58 absorbers from simulated Hanford Double-Shell Slurry Feed (DSSF)
Marsh, S.F.; Svitra, Z.V.; Bowen, S.M.
1994-11-01
As part of the Hanford Tank Waste Remediation System program at Los Alamos, we evaluated 58 commercially available or experimental absorber materials for their ability to remove hazardous components from high-level waste. These absorbers included cation and anion exchange resins, inorganic exchangers, composite absorbers, pillared layered materials, and a series of liquid extractants sorbed on porous support-beads. We tested these absorbers with a solution that simulates Hanford double-shell slurry feed (DSSF) (pH 14.0). To this simulant solution we added the appropriate radionuclides and used gamma spectrometry to measure fission products (Ce, Cs, Sr, Tc, and Y), actinides (U and Am), and matrix elements (Cr, Co, Fe, Mn, Ni, V, Zn, and Zr). For each of 870 element/absorber combinations, we measured distribution coefficients for dynamic contact periods of 30 min, 2 h, and 6 h to obtain information about sorption kinetics. On the basis of these 2610 measured distribution coefficients, we determined that many of the tested absorbers may be suitable for processing DSSF solutions.
NASA Technical Reports Server (NTRS)
Anderson, C. M.; Noor, A. K.
1975-01-01
Computerized symbolic integration was used in conjunction with group-theoretic techniques to obtain analytic expressions for the stiffness, geometric stiffness, consistent mass, and consistent load matrices of composite shallow shell structural elements. The elements are shear flexible and have variable curvature. A stiffness (displacement) formulation was used with the fundamental unknowns consisting of both the displacement and rotation components of the reference surface of the shell. The triangular elements have six and ten nodes; the quadrilateral elements have four and eight nodes and can have internal degrees of freedom associated with displacement modes which vanish along the edges of the element (bubble modes). The stiffness, geometric stiffness, consistent mass, and consistent load coefficients are expressed as linear combinations of integrals (over the element domain) whose integrands are products of shape functions and their derivatives. The evaluation of the elemental matrices is divided into two separate problems - determination of the coefficients in the linear combination and evaluation of the integrals. The integrals are performed symbolically by using the symbolic-and-algebraic-manipulation language MACSYMA. The efficiency of using symbolic integration in the element development is demonstrated by comparing the number of floating-point arithmetic operations required in this approach with those required by a commonly used numerical quadrature technique.
HAMMERAND,DANIEL C.; KAPANIA,RAKESH K.
2000-05-01
A triangular flat shell element for large deformation analysis of linear viscoelastic laminated composites is presented. Hygrothermorheologically simple materials are considered for which a change in the hygrothermal environment results in a horizontal shifting of the relaxation moduli curves on a log time scale, in addition to the usual hygrothermal loads. Recurrence relations are developed and implemented for the evaluation of the viscoelastic memory loads. The nonlinear deformation process is computed using an incremental/iterative approach with the Newton-Raphson Method used to find the incremental displacements in each step. The presented numerical examples consider the large deformation and stability of linear viscoelastic structures under deformation-independent mechanical loads, deformation-dependent pressure loads, and thermal loads. Unlike elastic structures that have a single critical load value associated with a given snapping of buckling instability phenomenon, viscoelastic structures will usually exhibit a particular instability for a range of applied loads over a range of critical times. Both creep buckling and snap-through examples are presented here. In some cases, viscoelastic results are also obtained using the quasielastic method in which load-history effects are ignored, and time-varying viscoelastic properties are simply used in a series of elastic problems. The presented numerical examples demonstrate the capability and accuracy of the formulation.
NASA Technical Reports Server (NTRS)
Graf, W.; Chang, T. Y.; Saleeb, A. F.
1986-01-01
Three-dimensional thick shell elements with 8, 16, and 18 nodes are formulated by using the hybrid/mixed method. In bending applications, these elements are free from locking effect and give improved stress predictions. Finite element equations are derived from the Hellinger-Reissner variational principle in which both the displacement and stress fields are approximated by independent interpolation functions. For the assumption of stress parameters, three guidelines are followed: (1) suppression of kinematic deformation modes, (2) invariant element property, and (3) the constraint index exhibited by the element, when applied to constrained-media problems, must be greater than or equal to one. Numerical results are presented to show the element's behavior characteristics regarding sensitivity to locking, distortion effect (patch tests), mesh convergence and the accuracy of stress evaluation.
The photosphere-corona Interface: enrichement of the corona in low FIP elements and helium shells
NASA Astrophysics Data System (ADS)
Bazin, C.; Koutchmy, S.; Lamy, P.; Veselovski, I.
2014-12-01
Slitless consecutive spectra were obtained during the contacts of the last total solar eclipses (2008, 2009, 2010, 2012, et 2013). They allowed to show that the overabundance of low First Ionisation Potential (FIP) elements (Fe II, Ti II, Ba II) in the corona comes from the low layers of the solar atmosphere, just near and above the temperature minimum region of the high photosphere. All spectra are recorded with a fast CCD/CMOS camera, with an equivalent radial resolution of 60 milliarcseconds, or 45 km in the solar atmosphere, above a solar edge not affected by the parasitic light like it is outside of total eclipse conditions. Many emission lines of low FIP elements appear in regions situated between 200 to 600 km above the solar limb defined by the true continuum measured between the lines. This continuum appears at these altitudes where the beta of the plasma is near 1. The He I 4713 Å and He II 4686 Å (Paschen alpha line) shells appear at the height of 800 km above the solar edge and higher. The light curve I = f(h) of each ion is located at a particuliar altitude in the solar atmosphere. The scale height corresponds to a density variation, which allows to evaluate the temperature thanks to the hydrostatic equilibrium assumption. Moreover, with ionised Titanium lines taken as markers, we show a similarity between the photosphere-corona interface and the prominence-corona interface. We discuss the role of the magnetic field and the ambipolar diffusion for supplying the corona in mass, without taking into account the role of spicules. The photo-ionisation of the helium lines by the EUV coronal lines is illustrated thanks to an extract of SDO/AIA coronal stacked image simultaneously obtained.
NASA Astrophysics Data System (ADS)
Börner, Nicole; De Baere, Bart; Francois, Roger; Frenzel, Peter; Schwalb, Antje
2014-05-01
Trace element analyses of ostracod shells are a vital tool for paleoenvironmental reconstructions from lake sediments (Börner et al., 2013). Conventional batch dissolution ICP-MS is the most common way for analyzing trace elements in ostracod shells. However, due to dissolution or secondary overgrowth the primary signal may be masked. Resulting variations in trace element composition have been identified to be in the order of a magnitude range. Therefore, the application of the newly developed flow-through technique will be assessed. The flow-through time-resolved analysis technique allows to chemically separate mineral phases of different solubility such as, in particular, original shell calcite from overgrowth calcite, and thus to correct the measurements for the biogenic signal. During a flow-through experiment, eluent is continuously pumped through a sample column, typically a filter in which the ostracod valves are loaded. The gradual dissolution of the substrate is controlled by a combination of eluent type, eluent temperature and eluent flow rate. The dissolved sample then flows directly to a mass spectrometer. The resulting data is a chromatogram, featuring different mineral phases dissolving as time progresses. Hence, the flow-through technique provides a detailed geochemical fingerprint of the substrate and therefore additional data relative to conventional methods. To calibrate this technique for the application to ostracods we use ostracod shells from Southern Tibetan Plateau lakes, which feature an alkaline environment but show highly diverse hydrochemistry. Cleaned as well as uncleaned ostracod shells show similarity in their trace element signals, allowing measurements without prior cleaning of the shells, and thus more time-efficient sample throughput. Measurements of unclean shells are corrected for the biogenic signal using an equation from Klinkhammer et al. (2004). Another advantage is that the measurements can be carried out on single ostracod
NASA Astrophysics Data System (ADS)
Mejdoubi, Abdelilah; Brosseau, Christian
2007-11-01
Herein, we report finite-element calculations of the effective (relative) permittivity of composite materials consisting of inclusions and inclusion arrays with a core-shell structure embedded in a surrounding host. The material making up the core of the two-dimensional structures, or cross sections of infinite three-dimensional objects (parallel, infinitely long, and identical cylinders) where the properties and characteristics are invariant along the perpendicular cross sectional plane, is assumed to have a negative real part of the permittivity, while the coating material (annular shell) is considered to be lossless. While strictly valid only in a dc situation, our analysis can be extended to treat electric fields that oscillate with time, provided that the wavelengths and attenuation lengths associated with the fields are much larger than the microstructure dimension in order that the homogeneous (effective-medium) representation of the composite structure makes sense. While one may identify features of the electrostatic resonance (ER) which are common to core-shell structures characterized by permittivities with real parts of opposite signs, it appears that the predicted ER positions are sensitive to the shell thickness and can be tuned through varying this geometric parameter. For example, we observe that the ER is broadened and shifted as the loss and the shell thickness are increased, respectively. We also argue that such core shell may also be valuable in controlling ER characteristics via polarization in an external electric field. In addition, by considering calculations of the electric field distribution, we find that the ER results in very strong and local-field enhancements into small parts of the shell perimeter. Our findings open up possibilities for the development of hybrid structures that could exploit the ER features for a particular application.
NASA Astrophysics Data System (ADS)
Nguyen-Van, H.; Mai-Duy, N.; Tran-Cong, T.
2008-06-01
This paper reports numerical analyses of free vibration of laminated composite plate/shell structures of various shapes, span-to-thickness ratios, boundary conditions and lay-up sequences. The method is based on a novel four-node quadrilateral element, namely MISQ20, within the framework of the first-order shear deformation theory (FSDT). The element is built by incorporating a strain smoothing method into the bilinear four-node quadrilateral finite element where the strain smoothing operation is based on mesh-free conforming nodal integration. The bending and membrane stiffness matrices are based on the boundaries of smoothing cells while the shear term is evaluated by 2×2 Gauss quadrature. Through several numerical examples, the capability, efficiency and simplicity of the element are demonstrated. Convergence studies and comparison with other existing solutions in the literature suggest that the present element is robust, computationally inexpensive and free of locking.
NASA Astrophysics Data System (ADS)
Fa, D.; Ferguson, J. E.; Atkinson, T. C.; Barton, R. N.; Ditchfield, P.; Finlayson, G.; Finlayson, J. C.; Henderson, G. M.
2007-12-01
Seasonal resolution climate records from mid and high latitudes would allow investigation of the role of seasonality in controlling mean climate on diverse timescales, and of the evolution of climate systems such as the North Atlantic Oscillation (NAO). But achieving such seasonal resolution is difficult for regions outside the growth range of surface corals. Marine mollusc shells provide a possible archive and contain growth increments varying in scale from tidal to annual. However, finding and dating sequences of marine mollusc shells spanning long periods of time is difficult due to sea-level change and the destructional nature of most coastal environments. In this study, we have made use of the habit of hominins on Gibraltar to collect molluscs for food over at least the last 120 kyr. In archaeological excavations of two caves (Gorham's and Vanguard Caves), mollusc shells were found, in habitation levels and in sediment blown into the caves. Existing 14C, OSL, and U-series chronologies provide a chronological framework for this suite of samples. The species found are predominantly Mytilus (mussels) or Patella (limpets). Gibraltar is an interesting location for paleoclimate reconstruction due to its proximity to the boundary of modern day climate belts but also due to its anthropological and archaeological importance. To gain a quantitative understanding of the local controls on stable isotopes and trace elements within Gibraltarian shells, we have initiated a water-sampling programme; emplaced a temperature and salinity logger near the sampling site; and marked live Patella and Mytilus with fluorescent dye to firmly establish growth rates and controls on chemical composition. We have also conducted stable-isotope and trace-element analysis of modern and fossil Patella and Mytilus shells by micromilling. Recent Patella and Mytilus shells show that the oxygen isotope composition of modern shells allow the accurate reconstruction of the full seasonal range in sea
Sorte, Cascade J. B.; Etter, Ron J.; Spackman, Robert; Boyle, Elizabeth E.; Hannigan, Robyn E.
2013-01-01
As the climate warms, species that cannot tolerate changing conditions will only persist if they undergo range shifts. Redistribution ability may be particularly variable for benthic marine species that disperse as pelagic larvae in ocean currents. The blue mussel, Mytilus edulis, has recently experienced a warming-related range contraction in the southeastern USA and may face limitations to northward range shifts within the Gulf of Maine where dominant coastal currents flow southward. Thus, blue mussels might be especially vulnerable to warming, and understanding dispersal patterns is crucial given the species' relatively long planktonic larval period (>1 month). To determine whether trace elemental “fingerprints” incorporated in mussel shells could be used to identify population sources (i.e. collection locations), we assessed the geographic variation in shell chemistry of blue mussels collected from seven populations between Cape Cod, Massachusetts and northern Maine. Across this ∼500 km of coastline, we were able to successfully predict population sources for over two-thirds of juvenile individuals, with almost 80% of juveniles classified within one site of their collection location and 97% correctly classified to region. These results indicate that significant differences in elemental signatures of mussel shells exist between open-coast sites separated by ∼50 km throughout the Gulf of Maine. Our findings suggest that elemental “fingerprinting” is a promising approach for predicting redistribution potential of the blue mussel, an ecologically and economically important species in the region. PMID:24244724
Chen, Bing; Peng, Dengfeng; Chen, Xian; Qiao, Xvsheng; Fan, Xianping; Wang, Feng
2015-10-19
Core-shell structured nanoparticles are increasingly used to host luminescent lanthanide ions but the structural integrity of these nanoparticles still lacks sufficient understanding. Herein, we present a new approach to detect the diffusion of dopant ions in core-shell nanostructures using luminescent lanthanide probes whose emission profile and luminescence lifetime are sensitive to the chemical environment. We show that dopant ions in solution-synthesized core-shell nanoparticles are firmly confined in the designed locations. However, annealing at certain temperatures (greater than circa 350 °C) promotes diffusion of the dopant ions and leads to degradation of the integrity of the nanoparticles. These insights into core-shell nanostructures should enhance our ability to understand and use lanthanide-doped luminescent nanoparticles.
Immel, Françoise; Broussard, Cédric; Catherinet, Bastien; Plasseraud, Laurent; Alcaraz, Gérard; Bundeleva, Irina; Marin, Frédéric
2016-01-01
The zebra mussel Dreissena polymorpha is a well-established invasive model organism. Although extensively used in environmental sciences, virtually nothing is known of the molecular process of its shell calcification. By describing the microstructure, geochemistry and biochemistry/proteomics of the shell, the present study aims at promoting this species as a model organism in biomineralization studies, in order to establish a bridge with ecotoxicology, while sketching evolutionary conclusions. The shell of D. polymorpha exhibits the classical crossed-lamellar/complex crossed lamellar combination found in several heterodont bivalves, in addition to an external thin layer, the characteristics of which differ from what was described in earlier publication. We show that the shell selectively concentrates some heavy metals, in particular uranium, which predisposes D. polymorpha to local bioremediation of this pollutant. We establish the biochemical signature of the shell matrix, demonstrating that it interacts with the in vitro precipitation of calcium carbonate and inhibits calcium carbonate crystal formation, but these two properties are not strongly expressed. This matrix, although overall weakly glycosylated, contains a set of putatively calcium-binding proteins and a set of acidic sulphated proteins. 2D-gels reveal more than fifty proteins, twenty of which we identify by MS-MS analysis. We tentatively link the shell protein profile of D. polymorpha and the peculiar recent evolution of this invasive species of Ponto-Caspian origin, which has spread all across Europe in the last three centuries. PMID:27213644
Broussard, Cédric; Catherinet, Bastien; Plasseraud, Laurent; Alcaraz, Gérard; Bundeleva, Irina; Marin, Frédéric
2016-01-01
The zebra mussel Dreissena polymorpha is a well-established invasive model organism. Although extensively used in environmental sciences, virtually nothing is known of the molecular process of its shell calcification. By describing the microstructure, geochemistry and biochemistry/proteomics of the shell, the present study aims at promoting this species as a model organism in biomineralization studies, in order to establish a bridge with ecotoxicology, while sketching evolutionary conclusions. The shell of D. polymorpha exhibits the classical crossed-lamellar/complex crossed lamellar combination found in several heterodont bivalves, in addition to an external thin layer, the characteristics of which differ from what was described in earlier publication. We show that the shell selectively concentrates some heavy metals, in particular uranium, which predisposes D. polymorpha to local bioremediation of this pollutant. We establish the biochemical signature of the shell matrix, demonstrating that it interacts with the in vitro precipitation of calcium carbonate and inhibits calcium carbonate crystal formation, but these two properties are not strongly expressed. This matrix, although overall weakly glycosylated, contains a set of putatively calcium-binding proteins and a set of acidic sulphated proteins. 2D-gels reveal more than fifty proteins, twenty of which we identify by MS-MS analysis. We tentatively link the shell protein profile of D. polymorpha and the peculiar recent evolution of this invasive species of Ponto-Caspian origin, which has spread all across Europe in the last three centuries. PMID:27213644
NASA Technical Reports Server (NTRS)
Rengarajan, Govind; Aminpour, Mohammad A.; Knight, Norman F., Jr.
1992-01-01
An improved four-node quadrilateral assumed-stress hybrid shell element with drilling degrees of freedom is presented. The formulation is based on Hellinger-Reissner variational principle and the shape functions are formulated directly for the four-node element. The element has 12 membrane degrees of freedom and 12 bending degrees of freedom. It has nine independent stress parameters to describe the membrane stress resultant field and 13 independent stress parameters to describe the moment and transverse shear stress resultant field. The formulation encompasses linear stress, linear buckling, and linear free vibration problems. The element is validated with standard tests cases and is shown to be robust. Numerical results are presented for linear stress, buckling, and free vibration analyses.
NASA Technical Reports Server (NTRS)
Krueger, Ronald; Minguet, Pierre J.; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
The debonding of a skin/stringer specimen subjected to tension was studied using three-dimensional volume element modeling and computational fracture mechanics. Mixed mode strain energy release rates were calculated from finite element results using the virtual crack closure technique. The simulations revealed an increase in total energy release rate in the immediate vicinity of the free edges of the specimen. Correlation of the computed mixed-mode strain energy release rates along the delamination front contour with a two-dimensional mixed-mode interlaminar fracture criterion suggested that in spite of peak total energy release rates at the free edge the delamination would not advance at the edges first. The qualitative prediction of the shape of the delamination front was confirmed by X-ray photographs of a specimen taken during testing. The good correlation between prediction based on analysis and experiment demonstrated the efficiency of a mixed-mode failure analysis for the investigation of skin/stiffener separation due to delamination in the adherents. The application of a shell/3D modeling technique for the simulation of skin/stringer debond in a specimen subjected to three-point bending is also demonstrated. The global structure was modeled with shell elements. A local three-dimensional model, extending to about three specimen thicknesses on either side of the delamination front was used to capture the details of the damaged section. Computed total strain energy release rates and mixed-mode ratios obtained from shell/3D simulations were in good agreement with results obtained from full solid models. The good correlations of the results demonstrated the effectiveness of the shell/3D modeling technique for the investigation of skin/stiffener separation due to delamination in the adherents.
Cho, Yong Beom; Yang, Shin Suk; Lee, Woo Yong; Song, Sang Yong; Kim, Seok-Hyung; Shin, Hee Jung; Yun, Seong Hyeon; Chun, Ho-Kyung
2010-06-01
This study was conducted to determine the clinical significance of neuroendocrine differentiation in cases of T3-T4 node-negative colorectal cancer. Eighty-nine patients diagnosed with T3-T4 node-negative colorectal cancer who underwent curative resection were enrolled. Tumors expressing neuroendocrine markers were classified as either low expression (
Element substitution by living organisms: the case of manganese in mollusc shell aragonite
NASA Astrophysics Data System (ADS)
Soldati, Analia L.; Jacob, Dorrit E.; Glatzel, Pieter; Swarbrick, Janine C.; Geck, Jochen
2016-03-01
Determining the manganese concentration in shells of freshwater bivalves provides a unique way to obtain information about climate and environmental changes during time-intervals that pre-date instrumental data records. This approach, however, relies on a thorough understanding of how manganese is incorporated into the shell material –a point that remained controversial so far. Here we clarify this issue, using state-of-the-art X-ray absorption and X-ray emission spectroscopy in combination with band structure calculations. We verify that in the shells of all studied species manganese is incorporated as high-spin Mn2+, i.e. manganese always has the same valence as calcium. More importantly, the unique chemical sensitivity of valence-to-core X-ray emission enables us to show that manganese is always coordinated by a CO3-octahedron. This, firstly, provides firm experimental evidence for manganese being primarily located in the inorganic carbonate. Secondly, it indicates that the structure of the aragonitic host is locally altered such that manganese attains an octahedral, calcitic coordination. This modification at the atomic level enables the bivalve to accommodate many orders of magnitude more manganese in its aragonitic shell than found in any non-biogenic aragonite. This outstanding feature is most likely facilitated through the non-classical crystallization pathway of bivalve shells.
Element substitution by living organisms: the case of manganese in mollusc shell aragonite
Soldati, Analia L.; Jacob, Dorrit E.; Glatzel, Pieter; Swarbrick, Janine C.; Geck, Jochen
2016-01-01
Determining the manganese concentration in shells of freshwater bivalves provides a unique way to obtain information about climate and environmental changes during time-intervals that pre-date instrumental data records. This approach, however, relies on a thorough understanding of how manganese is incorporated into the shell material –a point that remained controversial so far. Here we clarify this issue, using state-of-the-art X-ray absorption and X-ray emission spectroscopy in combination with band structure calculations. We verify that in the shells of all studied species manganese is incorporated as high-spin Mn2+, i.e. manganese always has the same valence as calcium. More importantly, the unique chemical sensitivity of valence-to-core X-ray emission enables us to show that manganese is always coordinated by a CO3-octahedron. This, firstly, provides firm experimental evidence for manganese being primarily located in the inorganic carbonate. Secondly, it indicates that the structure of the aragonitic host is locally altered such that manganese attains an octahedral, calcitic coordination. This modification at the atomic level enables the bivalve to accommodate many orders of magnitude more manganese in its aragonitic shell than found in any non-biogenic aragonite. This outstanding feature is most likely facilitated through the non-classical crystallization pathway of bivalve shells. PMID:26957325
NASA Astrophysics Data System (ADS)
Sobota, Paul; Dornisch, Wolfgang; Klinkel, Sven
2016-08-01
The present approach deals with the dynamical analysis of thin structures using an isogeometric Reissner-Mindlin shell formulation. Here, a consistent and a lumped mass matrix are employed for the implicit time integration method. The formulation allows for large displacements and finite rotations. The Rodrigues formula, which incorporates the axial vector is used for the rotational description. It necessitates an interpolation of the director vector in the current configuration. Two concept for the interpolation of the director vector are presented. They are denoted as continuous interpolation method and discrete interpolation method. The shell formulation is based on the assumption of zero stress in thickness direction. In the present formulation an interface to 3D nonlinear material laws is used. It leads to an iterative procedure at each integration point. Here, a J2 plasticity material law is implemented. The suitability of the developed shell formulation for natural frequency analysis is demonstrated in numerical examples. Transient problems undergoing large deformations in combination with nonlinear material behavior are analyzed. The effectiveness, robustness and superior accuracy of the two interpolation methods of the shell director vector are investigated and are compared to numerical reference solutions.
NASA Astrophysics Data System (ADS)
Kala, Zdeněk; Kala, Jiří
2012-09-01
The paper deals with the influence of correlation length, of Gauss random field, and of yield strength of a hotrolled I-beam under bending on the ultimate load carrying capacity limit state. Load carrying capacity is an output random quantity depending on input random imperfections. Latin Hypercube Sampling Method is used for sampling simulation. Load carrying capacity is computed by the programme ANSYS using shell finite elements and nonlinear computation methods. The nonlinear FEM computation model takes into consideration the effect of lateral-torsional buckling on the ultimate limit state.
NASA Astrophysics Data System (ADS)
McClintock, J. B.; Amsler, C. D.; Amsler, M. O.; Duquette, A.; Angus, R. A.; Hall-Spencer, J. M.; Milazzo, M.
2014-04-01
There is concern that the use of natural volcanic CO2 vents as analogs for studies of the impacts of ocean acidification on marine organisms are biased due to physiochemical influences other than seawater pH alone. One issue that has been raised is whether potentially harmful trace elements in sediments that are rendered more soluble and labile in low pH environments are made more bioavailable, and sequestered in the local flora and fauna at harmful levels. In order to evaluate this hypothesis, we analyzed the concentrations of trace elements in shells (an established proxy for tissues) of four species of gastropods (two limpets, a topshell and a whelk) collected from three sites in Levante Bay, Vulcano Island. Each sampling site increased in distance from the primary CO2 vent and thus represented low, moderate, and ambient seawater pH conditions. Concentrations of As, Cd, Co, Cr, Hg, Mo, Ni, Pb, and V measured in shells using ICP-OES were below detection thresholds for all four gastropod species at all three sites. However, there were measurable concentrations of Sr, Mn, and U in the shells of the limpets Patella caerulea, P. rustica, and the snail Osilinus turbinatus, and similarly, Sr, Mn, U, and also Zn in the shells of the whelk Hexaplex trunculus. Levels of these elements were within the ranges measured in gastropod shells in non-polluted environments, and with the exception of U in the shells of P. caerulea, where the concentration was significantly lower at the collecting site closest to the vent (low pH site), there were no site-specific spatial differences in concentrations for any of the trace elements in shells. Thus trace element enhancement in sediments in low-pH environments was not reflected in greater bioaccumulations of potentially harmful elements in the shells of common gastropods.
NASA Astrophysics Data System (ADS)
Swann, C. P.; Carriker, M. R.; Ewart, J. W.
1984-04-01
Although use of the shells of bivalves has been suggested for monitoring metals in natural waters, little is known of the relationship of environmental conditions and age of molluscs with the concentration and distribution of elements in the shells. This report covers technical aspects as well as some preliminary results for an experiment designed to provide information of the effects of these parameters. Using in-air and -helium PIXE, monthly analyses, covering a 7 month period, have been made on new shells of 10 young American oysters growing in each of three habitats: (I) filtered Atlantic seawater, fed cultured algae; (II) as for I with addition of silt from the Broadkill estuary; and (III) Broadkill estuary. Weekly analyses were also performed on particulates collected on 0.45 μm pore filters. After the 7 month period oysters were sacrificed, and soft tissues dried to constant weight and analyzed. Although definitive conclusions cannot be drawn until the study is completed, results demonstrate certain effects which suggest further experimentation.
NASA Astrophysics Data System (ADS)
Rollion-Bard, Claire; Saulnier, Ségolène; Vigier, Nathalie; Schumacher, Aimryc; Chaussidon, Marc; Lécuyer, Christophe
2016-04-01
Magnesium content in the ocean is ≈ 1290 ppm and is one of the most abundant elements. It is involved in the carbon cycle via the dissolution and precipitation of carbonates, especially Mg-rich carbonates as dolomites. The Mg/Ca ratio of the ocean is believed to have changed through time. The causes of these variations, i.e. hydrothermal activity change or enhanced precipitation of dolomite, could be constrained using the magnesium isotope composition (δ26Mg) of carbonates. Brachiopods, as marine environmental proxies, have the advantage to occur worldwide in a depth range from intertidal to abyssal, and have been found in the geological record since the Cambrian. Moreover, as their shell is in low-Mg calcite, they are quite resistant to diagenetic processes. Here we report δ26Mg, δ18O, δ13C values along with trace element contents of one modern brachiopod specimen (Terebratalia transversa) and one fossil specimen (Terebratula scillae, 2.3 Ma). We combined δ26Mg values with oxygen and carbon isotope compositions and trace element contents to look for possible shell geochemical heterogeneities in order to investigate the processes that control the Mg isotope composition of brachiopod shells. We also evaluate the potential of brachiopods as a proxy of past seawater δ26Mg values. The two investigated brachiopod shells present the same range of δ26Mg variation (up to 2 ‰)). This variation cannot be ascribed to changes in environmental parameters, i.e. temperature or pH. As previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the δ26Mg value of this layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends, combined to linear relationships between δ26Mg values and REE contents, are best
On the Assumed Natural Strain method to alleviate locking in solid-shell NURBS-based finite elements
NASA Astrophysics Data System (ADS)
Caseiro, J. F.; Valente, R. A. F.; Reali, A.; Kiendl, J.; Auricchio, F.; Alves de Sousa, R. J.
2014-06-01
In isogeometric analysis (IGA), the functions used to describe the CAD geometry (such as NURBS) are also employed, in an isoparametric fashion, for the approximation of the unknown fields, leading to an exact geometry representation. Since the introduction of IGA, it has been shown that the high regularity properties of the employed functions lead in many cases to superior accuracy per degree of freedom with respect to standard FEM. However, as in Lagrangian elements, NURBS-based formulations can be negatively affected by the appearance of non-physical phenomena that "lock" the solution when constrained problems are considered. In order to alleviate such locking behaviors, the Assumed Natural Strain (ANS) method proposed for Lagrangian formulations is extended to NURBS-based elements in the present work, within the context of solid-shell formulations. The performance of the proposed methodology is assessed by means of a set of numerical examples. The results allow to conclude that the employment of the ANS method to quadratic NURBS-based elements successfully alleviates non-physical phenomena such as shear and membrane locking, significantly improving the element performance.
Stress Recovery and Error Estimation for 3-D Shell Structures
NASA Technical Reports Server (NTRS)
Riggs, H. R.
2000-01-01
The C1-continuous stress fields obtained from finite element analyses are in general lower- order accurate than are the corresponding displacement fields. Much effort has focussed on increasing their accuracy and/or their continuity, both for improved stress prediction and especially error estimation. A previous project developed a penalized, discrete least squares variational procedure that increases the accuracy and continuity of the stress field. The variational problem is solved by a post-processing, 'finite-element-type' analysis to recover a smooth, more accurate, C1-continuous stress field given the 'raw' finite element stresses. This analysis has been named the SEA/PDLS. The recovered stress field can be used in a posteriori error estimators, such as the Zienkiewicz-Zhu error estimator or equilibrium error estimators. The procedure was well-developed for the two-dimensional (plane) case involving low-order finite elements. It has been demonstrated that, if optimal finite element stresses are used for the post-processing, the recovered stress field is globally superconvergent. Extension of this work to three dimensional solids is straightforward. Attachment: Stress recovery and error estimation for shell structure (abstract only). A 4-node, shear-deformable flat shell element developed via explicit Kirchhoff constraints (abstract only). A novel four-node quadrilateral smoothing element for stress enhancement and error estimation (abstract only).
Finite Element Vibration Analysis of Rectangular Membrane
NASA Astrophysics Data System (ADS)
Chen, S. H.; Lin, W. J.; Leung, A. Y. T.
2010-05-01
Some pre-tensioned 4-node rectangular elements and 8-node triangular elements are constructed for the free vibration analysis of membranes by finite element. The shape functions are given to derive the element stiffness and mass matrices in accordance with the minimum potential energy principle. Two typical examples show that the calculation by the 4-node rectangular element is very close to the theoretical solution, and 8-node rectangular element has higher accuracy than the 4-node rectangular element. For dense grid, the result is almost consistent with the theoretical solution.
Maker, B.N.
1995-04-14
This report provides a user`s manual for NIKE3D, a fully implicit three-dimensional finite element code for analyzing the finite strain static and dynamic response of inelastic solids, shells, and beams. Spatial discretization is achieved by the use of 8-node solid elements, 2-node truss and beam elements, and 4-node membrane and shell elements. Over twenty constitutive models are available for representing a wide range of elastic, plastic, viscous, and thermally dependent material behavior. Contact-impact algorithms permit gaps, frictional sliding, and mesh discontinuities along material interfaces. Several nonlinear solution strategies are available, including Full-, Modified-, and Quasi-Newton methods. The resulting system of simultaneous linear equations is either solved iteratively by an element-by-element method, or directly by a factorization method, for which case bandwidth minimization is optional. Data may be stored either in or out of core memory to allow for large analyses.
Elastic-plastic mixed-iterative finite element analysis: Implementation and performance assessment
NASA Technical Reports Server (NTRS)
Sutjahjo, Edhi; Chamis, Christos C.
1993-01-01
An elastic-plastic algorithm based on Von Mises and associative flow criteria is implemented in MHOST-a mixed iterative finite element analysis computer program developed by NASA Lewis Research Center. The performance of the resulting elastic-plastic mixed-iterative analysis is examined through a set of convergence studies. Membrane and bending behaviors of 4-node quadrilateral shell finite elements are tested for elastic-plastic performance. Generally, the membrane results are excellent, indicating the implementation of elastic-plastic mixed-iterative analysis is appropriate.
Pihosh, Yuriy; Turkevych, Ivan; Mawatari, Kazuma; Fukuda, Nobuko; Ohta, Ryoichi; Tosa, Masahiro; Shimamura, Kiyoshi; Villora, Encarnacion G; Kitamori, Takehiko
2014-08-01
We demonstrate a new approach to plasmonic enhanced photocatalytic water splitting by developing a novel core-shell Ti@TiO2 brush nanostructure where an elongated Ti nanorod forms a plasmonic core that concentrates light inside of a nanotubular anodic TiO2 shell. Following the ubiquitous element approach aimed at providing an enhanced device functionality without the usage of noble or rare earth elements, we utilized only inexpensive Ti to create a complex Ti@TiO2 nanostructure with an enhanced UV and Vis photocatalytic activity that emerges from the interplay between the surface plasmon resonance in the Ti core, Vis light absorption in the Ti-rich oxide layer at the Ti/TiO2 interface and UV light absorption in the nanotubular TiO2 shell. PMID:25030613
NASA Astrophysics Data System (ADS)
Zheng, Shijie; Wang, Xinwei; Chen, Wanji
2004-08-01
In the present paper, a novel refined hybrid piezoelectric element formulation is developed for mechanical analysis and active vibration control of laminated structures bonded to piezoelectric sensors and actuators. By invoking the electrical field potential equation, a 'quasi-decoupling' method for treating the coupling electromechanical effects is presented and a modified generalized variational principle with a weaker interelement continuity condition is proposed. On the basis of this functional, a general formulation for a refined hybrid piezoelectric element method is established by incorporating an orthogonal interpolation approach and enhanced assumed strain (EAS) modes. A linearly distributed transverse EAS in the thickness direction is adopted to overcome the thickness locking of solid shell elements. Compared with the conventional incompatible brick element approach, the present formulation is very reliable, more accurate, computationally efficient and can be used to model the response of thin plates and shell structures.
Neotectonics of Asia: Thin-shell finite-element models with faults
NASA Technical Reports Server (NTRS)
Kong, Xianghong; Bird, Peter
1994-01-01
As India pushed into and beneath the south margin of Asia in Cenozoic time, it added a great volume of crust, which may have been (1) emplaced locally beneath Tibet, (2) distributed as regional crustal thickening of Asia, (3) converted to mantle eclogite by high-pressure metamorphism, or (4) extruded eastward to increase the area of Asia. The amount of eastward extrusion is especially controversial: plane-stress computer models of finite strain in a continuum lithosphere show minimal escape, while laboratory and theoretical plane-strain models of finite strain in a faulted lithosphere show escape as the dominant mode. We suggest computing the present (or neo)tectonics by use of the known fault network and available data on fault activity, geodesy, and stress to select the best model. We apply a new thin-shell method which can represent a faulted lithosphere of realistic rheology on a sphere, and provided predictions of present velocities, fault slip rates, and stresses for various trial rheologies and boundary conditions. To minimize artificial boundaries, the models include all of Asia east of 40 deg E and span 100 deg on the globe. The primary unknowns are the friction coefficient of faults within Asia and the amounts of shear traction applied to Asia in the Himalayan and oceanic subduction zones at its margins. Data on Quaternary fault activity prove to be most useful in rating the models. Best results are obtained with a very low fault friction of 0.085. This major heterogeneity shows that unfaulted continum models cannot be expected to give accurate simulations of the orogeny. But, even with such weak faults, only a fraction of the internal deformation is expressed as fault slip; this means that rigid microplate models cannot represent the kinematics either. A universal feature of the better models is that eastern China and southeast Asia flow rapidly eastward with respect to Siberia. The rate of escape is very sensitive to the level of shear traction in the
M -shell x-ray production by 0. 6--4. 0-MeV protons in ten elements from hafnium to thorium
Pajek, M. ); Kobzev, A.P.; Sandrik, R.; Skrypnik, A.V. ); Ilkhamov, R.A.; Khusmurodov, S.H. ); Lapicki, G. )
1990-07-01
{ital M}-shell x-ray production cross sections for selected heavy elements, namely, {sub 72}Hf, {sub 73}Ta, {sub 74}W, {sub 75}Re, {sub 76}Os, {sub 77}Ir, {sub 78}Pt, {sub 79}Au, {sub 83}Bi, and {sub 90}Th, were measured for protons of energy 0.6--4.0 MeV. The experimental results are compared with the predictions of the first Born and semiclassical approximations for {ital M}-shell ionization; these data are also compared with the theory that accounts for the projectile's energy loss and Coulomb deflection as well as for the target's {ital M}-shell electron perturbed stationary state and relativistic nature (ECPSSR). Generally, fair agreement between the data and the ECPSSR theory is found. Some systematical discrepancies observed for the lightest elements (Hf, Ta, and W) are explained as possible ambiguities in the {ital M}-shell Coster-Kronig factors and fluorescence yields, which were used to convert theoretical {ital M}-subshell ionization cross sections to the total {ital M}-x-ray production cross sections. The experimental total {ital M}-shell ionization cross sections were obtained from measured {ital M}-x-ray cross sections using the proposed approximate average fluorescence yield {bar {omega}}{sub {ital M}} that relies on two fluorescence yields and the Coster-Kronig factor for {ital only} {ital M}{sub 4} and {ital M}{sub 5} subshells.
SINGLE-SHELL TANKS LEAK INTEGRITY ELEMENTS/SX FARM LEAK CAUSES AND LOCATIONS - 12127
VENETZ TJ; WASHENFELDER D; JOHNSON J; GIRARDOT C
2012-01-25
Washington River Protection Solutions, LLC (WRPS) developed an enhanced single-shell tank (SST) integrity project in 2009. An expert panel on SST integrity was created to provide recommendations supporting the development of the project. One primary recommendation was to expand the leak assessment reports (substitute report or LD-1) to include leak causes and locations. The recommendation has been included in the M-045-9IF Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) as one of four targets relating to SST leak integrity. The 241-SX Farm (SX Farm) tanks with leak losses were addressed on an individual tank basis as part of LD-1. Currently, 8 out of 23 SSTs that have been reported to having a liner leak are located in SX Farm. This percentage was the highest compared to other tank farms which is why SX Farm was analyzed first. The SX Farm is comprised of fifteen SSTs built 1953-1954. The tanks are arranged in rows of three tanks each, forming a cascade. Each of the SX Farm tanks has a nominal I-million-gal storage capacity. Of the fifteen tanks in SX Farm, an assessment reported leak losses for the following tanks: 241-SX-107, 241-SX-108, 241-SX-109, 241-SX-111, 241-SX-112, 241-SX-113, 241-SX-114 and 241-SX-115. The method used to identify leak location consisted of reviewing in-tank and ex-tank leak detection information. This provided the basic data identifying where and when the first leaks were detected. In-tank leak detection consisted of liquid level measurement that can be augmented with photographs which can provide an indication of the vertical leak location on the sidewall. Ex-tank leak detection for the leaking tanks consisted of soil radiation data from laterals and drywells near the tank. The in-tank and ex-tank leak detection can provide an indication of the possible leak location radially around and under the tank. Potential leak causes were determined using in-tank and ex-tank information that is not directly related to
Single-Shell Tanks Leak Integrity Elements/ SX Farm Leak Causes and Locations - 12127
Girardot, Crystal; Harlow, Don; Venetz, Theodore; Washenfelder, Dennis; Johnson, Jeremy
2012-07-01
Washington River Protection Solutions, LLC (WRPS) developed an enhanced single-shell tank (SST) integrity project in 2009. An expert panel on SST integrity was created to provide recommendations supporting the development of the project. One primary recommendation was to expand the leak assessment reports (substitute report or LD-1) to include leak causes and locations. The recommendation has been included in the M-045-91F Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) as one of four targets relating to SST leak integrity. The 241-SX Farm (SX Farm) tanks with leak losses were addressed on an individual tank basis as part of LD-1. Currently, 8 out of 23 SSTs that have been reported to having a liner leak are located in SX Farm. This percentage was the highest compared to other tank farms which is why SX Farm was analyzed first. The SX Farm is comprised of fifteen SSTs built 1953-1954. The tanks are arranged in rows of three tanks each, forming a cascade. Each of the SX Farm tanks has a nominal 1-million-gal storage capacity. Of the fifteen tanks in SX Farm, an assessment reported leak losses for the following tanks: 241-SX-107, 241-SX-108, 241-SX-109, 241-SX- 111, 241-SX-112, 241-SX-113, 241-SX-114 and 241-SX-115. The method used to identify leak location consisted of reviewing in-tank and ex-tank leak detection information. This provided the basic data identifying where and when the first leaks were detected. In-tank leak detection consisted of liquid level measurement that can be augmented with photographs which can provide an indication of the vertical leak location on the sidewall. Ex-tank leak detection for the leaking tanks consisted of soil radiation data from laterals and dry-wells near the tank. The in-tank and ex-tank leak detection can provide an indication of the possible leak location radially around and under the tank. Potential leak causes were determined using in-tank and ex-tank information that is not directly related to
Rao, D.; Swapna, M; Cesareo, R; Brunetti, A; Akatsuka, T; Yuasa, T; Takeda, T; Tromba, G; Gigante, G
2009-01-01
In this study, synchrotron-based micro-beam was utilized for elemental mapping of a small animal shell. A thin X-ray spot of the order of {approx}10 em was focused on the sample. With this spatial resolution and high flux throughput, the X-ray fluorescent intensities for Ca, Mn, Fe, Ni, Zn, Cr and Cu were measured using a liquid-nitrogen-cooled 13-element energy-dispersive HpGe detector. The sample is scanned in a estep-and-repeat' mode for fast elemental mapping and generated elemental maps at 8, 10 and 12 keV. All images are of 10 em resolution and the measurement time was 1 s per point. The accumulation of trace elements was investigated from the soft-tissue in small areas. Analysis of the small areas will be better suited to establish the physiology of metals in specific structures like small animal shell and the distribution of other trace elements.
Akman, Ferdi
2016-09-01
The K to Li (i=2,3), K to L, and K to M shell vacancy transfer probabilities for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er were determined at 59.54keV using a reflection geometry. The measurements were performed using an (241)Am annular radioactive source and a high resolution Si(Li) detector. The experimental results were compared with the theoretical values of Hartree-Slater and Hartree-Fock theories, semi-empirical and other available experimental results in the literature. Reasonable agreement is observed between the measured and theoretical results.
Merschel, Gila; Bau, Michael
2015-11-15
High-technology metals - such as the rare earth elements (REE) - have become emerging contaminants in the hydrosphere, yet little is known about their bioavailability. The Rhine River and the Weser River in Germany are two prime examples of rivers that are subjected to anthropogenic REE input. While both rivers carry significant loads of anthropogenic Gd, originating from contrast agents used for magnetic resonance imaging, the Rhine River also carries large amounts of anthropogenic La and lately Sm which are discharged into the river from an industrial point source. Here, we assess the bioavailability of these anthropogenic microcontaminants in these rivers by analyzing the aragonitic shells of the freshwater bivalve Corbicula fluminea. Concentrations of purely geogenic REE in shells of comparable size cover a wide range of about one order of magnitude between different sampling sites. At a given sampling site, geogenic REE concentrations depend on shell size, i.e. mussel age. Although both rivers show large positive Gd anomalies in their dissolved loads, no anomalous enrichment of Gd relative to the geogenic REE can be observed in any of the analyzed shells. This indicates that the speciations of geogenic and anthropogenic Gd in the river water differ from each other and that the geogenic, but not the anthropogenic Gd is incorporated into the shells. In contrast, all shells sampled at sites downstream of the industrial point source of anthropogenic La and Sm in the Rhine River show positive La and Sm anomalies, revealing that these anthropogenic REE are bioavailable. Only little is known about the effects of long-term exposure to dissolved REE and their general ecotoxicity, but considering that anthropogenic Gd and even La have already been identified in German tap water and that anthropogenic La and Sm are bioavailable, this should be monitored and investigated further.
Li, Yan; Yang, Jia-lin; Jiang, Yan
2012-03-28
With the extensive use of rare earth elements (REEs) in agriculture as fertilizer and feed additives, the concentration of REEs has increased in environmental and biological samples and finally impaired human health by food chain accumulation. The determination of trace REEs has gained considerable importance because of their toxicity and increasing occurrence. In this work, walnut shell has been used as the green adsorbent in online preconcentration and detection of REEs in food and agricultural products coupled with inductively coupled plasma mass spectrometry (ICP-MS). Because of the porous surface and abundant -COO(-) groups on the walnut shell surface, the walnut shell-packed microcolumn provides high adsorption efficiency and high tolerable capacity for coexisting ions. Under the optimized conditions, the adsorption efficiency of the walnut shell packed microcolumn was as high as 98.9% for 15 REEs, and the tolerable concentration ratios were between 2000 and 80,000,000 for 37 kinds of coexisting interfering ions. The enhancement factors achieved were 79-102 for 15 REEs with a sample loading volume of 4.7 mL. The detection limits were in the range of 2-34 pg g(-1). The relative standard deviation for 11 replicate preconcentrations of 2.5 ng L(-1) REEs solution ranged from 0.5 to 2.0%. The present method was successfully applied to selective determination of REEs in 4 environmental and biological certified reference materials and 18 locally collected food and agricultural products.
Optimum rotationally symmetric shells for flywheel rotors
Blake, Henry W.
2000-01-01
A flywheel rim support formed from two shell halves. Each of the shell halves has a disc connected to the central shaft. A first shell element connects to the disc at an interface. A second shell element connects to the first shell element. The second shell element has a plurality of meridional slits. A cylindrical shell element connects to the second shell element. The cylindrical shell element connects to the inner surface of the flywheel rim. A flywheel rim support having a disc connected an outer diameter of a shaft. Two optimally shaped shell elements connect to the optimally shaped disc at an interface. The interface defines a discontinuity in a meridional slope of said support. A cylindrical shell element connects to the two shell elements. The cylindrical shell element has an outer surface for connecting to the inner surface of the flywheel rim. A flywheel rim casing includes an annular shell connected to the central shaft. The annular shell connects to the flywheel rim. A composite shell surrounds the shaft, annular shell and flywheel rim.
Schwenke, David W
2015-04-14
In this work, we systematically derive the matrix elements of the nuclear rotation operators for open shell diatomic and polyatomic molecules in a parity adapted Hund's case (a) basis. Our expressions are valid for an arbitrary number of electrons and arbitrary electronic configurations. The common ad hoc sign changes of angular momentum operators are shown to be equivalent to a change in phase of basis functions. We show how to relate this basis to that required for scattering calculations. We also give the expressions for Einstein A coefficients for electric dipole, electric quadrupole, and magnetic dipole transitions.
Schwenke, David W.
2015-04-14
In this work, we systematically derive the matrix elements of the nuclear rotation operators for open shell diatomic and polyatomic molecules in a parity adapted Hund’s case (a) basis. Our expressions are valid for an arbitrary number of electrons and arbitrary electronic configurations. The common ad hoc sign changes of angular momentum operators are shown to be equivalent to a change in phase of basis functions. We show how to relate this basis to that required for scattering calculations. We also give the expressions for Einstein A coefficients for electric dipole, electric quadrupole, and magnetic dipole transitions.
Civitarese, Osvaldo; Suhonen, Jouni
2013-12-30
In this work we report on general properties of the nuclear matrix elements involved in the neutrinoless double β{sup −} decays (0νβ{sup −}β{sup −} decays) of several nuclei. A summary of the values of the NMEs calculated along the years by the Jyväskylä-La Plata collaboration is presented. These NMEs, calculated in the framework of the quasiparticle random phase approximation (QRPA), are compared with those of the other available calculations, like the Shell Model (ISM) and the interacting boson model (IBA-2)
Hoffman, E.L.; Ammerman, D.J.
1995-04-01
A series of tests investigating dynamic pulse buckling of a cylindrical shell under axial impact is compared to several 2D and 3D finite element simulations of the event. The purpose of the work is to investigate the performance of various analysis codes and element types on a problem which is applicable to radioactive material transport packages, and ultimately to develop a benchmark problem to qualify finite element analysis codes for the transport package design industry. Four axial impact tests were performed on 4 in-diameter, 8 in-long, 304 L stainless steel cylinders with a 3/16 in wall thickness. The cylinders were struck by a 597 lb mass with an impact velocity ranging from 42.2 to 45.1 ft/sec. During the impact event, a buckle formed at each end of the cylinder, and one of the two buckles became unstable and collapsed. The instability occurred at the top of the cylinder in three tests and at the bottom in one test. Numerical simulations of the test were performed using the following codes and element types: PRONTO2D with axisymmetric four-node quadrilaterals; PRONTO3D with both four-node shells and eight-node hexahedrons; and ABAQUS/Explicit with axisymmetric two-node shells and four-node quadrilaterals, and 3D four-node shells and eight-node hexahedrons. All of the calculations are compared to the tests with respect to deformed shape and impact load history. As in the tests, the location of the instability is not consistent in all of the calculations. However, the calculations show good agreement with impact load measurements with the exception of an initial load spike which is proven to be the dynamic response of the load cell to the impact. Finally, the PRONIT02D calculation is compared to the tests with respect to strain and acceleration histories. Accelerometer data exhibited good qualitative agreement with the calculations. The strain comparisons show that measurements are very sensitive to gage placement.
NASA Astrophysics Data System (ADS)
Roopnarine, P. D.; Anderson, L.; Roopnarine, D.; Gillikin, D. P.; Goodwin, D.
2010-12-01
Documenting the effects of modern stressors on coastal benthic marine communities requires a combination of baseline historical data and modern dynamic data. E.g., landfall of hydrocarbons from the 2010 Deepwater Horizon rig and well explosion in the Gulf of Mexico is impacting coastal areas long affected by natural seepage, as well as petroleum exploration and development. In Louisiana, exploration in coastal areas that began in the 1920s expanded greatly with the development of the first mobile drilling barge in 1933. In total nearly 50,000 wells have been drilled in the Gulf of Mexico since the 1930s. Given this historical context, we are assessing pathways and rates at which crude oil components from the 2010 spill are incorporated into northern Gulf of Mexico coastal food webs. Sclerochronological techniques are being used to unlock the high-resolution physical and chemical records preserved within mollusc shells. We are analyzing historical specimens collected from the late 19th through late 20th centuries, baseline specimens collected in May 2010 in Louisiana and Alabama before visible hydrocarbons were present, and specimens collected in August 2010 after hydrocarbons made landfall. We are examining changes in life history traits (growth rate, recruitment, mortality, reproduction) of the commercial oyster Crassostrea virginica, and other common, co-occurring molluscs that are primary and secondary consumers in Gulf of Mexico coastal food webs. The taxa include the marsh-dwelling gastropod Littoraria irrorata and mussel Geukensia demissa, and open-water species including the bivalves Ischadium recurvum and Tellina alternata. These consumers range from epifaunal, sessile, filter feeders; to infaunal, mobile, deposit feeders; to epifaunal, mobile, omnivorous grazers. In this way, multiple potential pathways into coastal food webs are being monitored. Because environmental perturbations of many scales are recorded by the accretionary growth of mollusc shells
Cho, Yong Beom; Lee, Woo Yong; Song, Sang Yong; Shin, Hee Jung; Yun, Seong Hyeon; Chun, Ho-Kyung
2007-11-01
Reversion-inducing cysteine-rich protein with Kazal motifs (RECK) is a novel membrane-anchored matrix metalloproteinase (MMP) inhibitor. RECK, MMP-2, and MMP-9 are believed to play crucial roles in tumor progression. This study was designed to examine the prognostic value of RECK, MMP-2, and MMP-9 in conjunction with other clinicopathologic factors in patients of T3-T4 node-negative colorectal cancer. RECK and MMP expression was observed using immunohistochemical analysis of the primary tumor from 89 patients with curatively resected T3-4 N0 colorectal cancer retrospectively. High RECK expression was observed in 51 cases, whereas expression was low in the other 38 cases. MMP-2 and MMP-9 expression was positive in cancer cells in 24 and 33 cases, respectively. RECK and MMP-2 expression was not significantly associated with any clinicopathologic factors. However, expression of MMP-9 was correlated with tumor location. A statistically significant inverse correlation was found between RECK and MMP-2 expression, and a statistically significant correlation was found between MMP-2 and MMP-9 expression. However, no association between RECK and MMP-9 expression was observed. Univariate analysis demonstrated that rectal tumor location, preoperative carcinoembryonic antigen more than 5 ng/mL, positive lymphatic invasion, less than 12 dissected lymph nodes, and positive MMP-9 expression were poor prognostic factors of disease-free survival. A multivariate analysis confirmed that enhanced MMP-9 expression was an independent and significant factor for prediction of a poor prognosis. In addition, positive lymphatic invasion and less than 12 dissected lymph nodes were significant negative prognostic factors. In conclusion, MMP-9 status represents a novel prognostic factor in evaluation of T3-T4 node-negative colorectal cancer.
NASA Technical Reports Server (NTRS)
Fallon, D. J.; Thornton, E. A.
1983-01-01
Documentation for the computer program FLUTTER is presented. The theory of aerodynamic instability with thermal prestress is discussed. Theoretical aspects of the finite element matrices required in the aerodynamic instability analysis are also discussed. General organization of the computer program is explained, and instructions are then presented for the execution of the program.
NASA Astrophysics Data System (ADS)
Kieniewicz, Johanna M.; Smith, Jennifer R.
2007-11-01
Authigenic calcite silts at Wadi Midauwara in Kharga Oasis, Egypt, indicate the prolonged presence of surface water during the Marine Isotope Stage 5e pluvial phase recognized across North Africa. Exposed over an area of ˜ 4.25 km 2, these silts record the ponding of water derived from springs along the Libyan Plateau escarpment and from surface drainage. The δ 18O values of these lacustrine carbonates (- 11.3‰ to - 8.0‰ PDB), are too high to reflect equilibrium precipitation with Nubian aquifer water or water of an exclusively Atlantic origin. Mg/Ca and Sr/Ca of the silts have a modest negative covariance with silt δ 18O values, suggesting that the water may have experienced the shortest residence time in local aquifers when the water δ 18O values were highest. Furthermore, intra-shell δ 18O, Sr/Ca, and Ba/Ca analyses of the freshwater gastropod Melanoides tuberculata are consistent with a perennially fresh water source, suggesting that strong evaporative effects expected in a monsoonal climate did not occur, or that dry season spring flow was of sufficient magnitude to mute the effects of evaporation. The input of a second, isotopically heavier water source to aquifers, possibly Indian Ocean monsoonal rain, could explain the observed trends in δ 18O and minor element ratios.
Imperfection Insensitive Thin Shells
NASA Astrophysics Data System (ADS)
Ning, Xin
with superior mass efficiency. An efficient computational method for the buckling analysis of corrugated and stiffened cylindrical shells subject to axial compression has been developed in this thesis. This method modifies the traditional Bloch wave method based on the stiffness matrix method of rotationally periodic structures. A highly efficient algorithm has been developed to implement the modified Bloch wave method. This method is applied in buckling analyses of a series of corrugated composite cylindrical shells and a large-scale orthogonally stiffened aluminum cylindrical shell. Numerical examples show that the modified Bloch wave method can achieve very high accuracy and require much less computational time than linear and nonlinear analyses of detailed full finite element models. This thesis presents parametric studies on a series of externally pressurized pseudo-spherical shells, i.e., polyhedral shells, including icosahedron, geodesic shells, and triambic icosahedra. Several optimization methods have been developed to further improve the performance of pseudo-spherical shells under external pressure. It has been shown that the buckling pressures of the shell designs obtained from the optimizations are much higher than the spherical shells and not sensitive to imperfections.
Geometrically nonlinear analysis of layered composite plates and shells
NASA Technical Reports Server (NTRS)
Chao, W. C.; Reddy, J. N.
1983-01-01
A degenerated three dimensional finite element, based on the incremental total Lagrangian formulation of a three dimensional layered anisotropic medium was developed. Its use in the geometrically nonlinear, static and dynamic, analysis of layered composite plates and shells is demonstrated. A two dimenisonal finite element based on the Sanders shell theory with the von Karman (nonlinear) strains was developed. It is shown that the deflections obtained by the 2D shell element deviate from those obtained by the more accurate 3D element for deep shells. The 3D degenerated element can be used to model general shells that are not necessarily doubly curved. The 3D degenerated element is computationally more demanding than the 2D shell theory element for a given problem. It is found that the 3D element is an efficient element for the analysis of layered composite plates and shells undergoing large displacements and transient motion.
NASA Astrophysics Data System (ADS)
Wisshak, Max; López Correa, Matthias; Gofas, Serge; Salas, Carmen; Taviani, Marco; Jakobsen, Joachim; Freiwald, André
2009-03-01
A conspicuous new deep-sea oyster, Neopycnodonte zibrowii sp. n., is described from the Azores Archipelago, where it thrives in 420 to >500 m water depth in high densities concealed underneath overhangs. The new species reaches a relatively large size, which may exceed 20 cm, and is characterised by a very unusual hinge line morphology, straight without a bulge of the resilium. It is compared to the extant Indo-Pacific Empressostrea kostini Huber and Lorenz, 2007 and to the cosmopolitan Neopycnodonte cochlear (Poli, 1791), which has a broadly sympatric distribution at shallower depths in the Azores and Bay of Biscay. Radiocarbon dating reveals that individuals reach an impressive lifespan of one to more than five centuries, placing them among the longest-lived molluscs known to date. They often grow on top of each other, forming stacks that resemble dish piles—an effective measure to optimise shell stability with minimal biomineralisation effort, but with the drawback of increased bioerosion ultimately leading to detachment. Three microstructure types are developed in N. zibrowii: (1) the cross-foliated, calcitic, dorsal to central endostracum and aragonitic ligostracum, (2) the porous vesicular structure of the calcitic ventral endostracum, and (3) the simple prismatic aragonitic myostracum. Foliated and vesicular shell portions show sub-millimetre-scale first-order increments delineated by conchiolin-rich growth breaks (interpreted as reproductive cyclicity), and less distinct second-order increments (interpreted as annual in nature). This pattern is clearly reflected by the elemental composition with the primary growth breaks lacking Ca and Sr but including Mg and S as organic matrix constituents. The second-order increments within the calcite are mirrored by moderately co-varying Mg/Ca and S/Ca fluctuations at stable Sr concentrations, reflecting varying proportions of organic matrix. Dorsal and central endostracum transects reveal a low inter-valve, but
M-shell ionization of heavy elements by 0.1-1.0 MeV/amu {sup 1,2}H and {sup 3,4}He ions
Pajek, M.; Banas, D.; Braziewicz, J.; Czarnota, M.; Bienkowski, A.; Jaskola, M.; Korman, A.; Trautmann, D.; Lapicki, G.
2006-01-15
The M-shell ionization in high-Z atoms by low-energy light {sub 1}{sup 1}H, {sub 1}{sup 2}H, {sub 2}{sup 3}He, and {sub 2}{sup 4}He ions have been studied systematically in the energy range 0.1-1.0 MeV/amu in order to verify the available theoretical approaches describing the M-shell ionization by charged particles in asymmetric collisions. The present low-energy data, combined with our earlier results reported for M-shell ionization by hydrogen and helium ions for higher energies, form a systematic experimental basis to test the theoretical predictions of M-shell ionization based on the plane-wave Born approximation (PWBA), the semiclassical approximation (SCA), and the binary-encounter approximation (BEA). In the PWBA based approaches the energy loss (E), Coulomb deflection (C), perturbed stationary state (PSS), and relativistic (R) effects were considered within the ECPSSR theory and its recent modification, called the ECUSAR theory, in which a description of the PSS effect was corrected to account for the united- and separated-atom (USA) electron binding energy limits. In the SCA calculations with relativistic wave functions the binding effect was included only in the limiting cases of separated-atom and united-atom limits. Possible contribution of the electron capture, multiple ionization, and recoil ionization to the M-shell vacancy production, which is dominated for light ions impact by direct single ionization process, are also discussed. The universal scaling of measured M-shell x-ray production and ionization cross sections was investigated in detail. Using the present data the isotopic effect has been studied by comparing the measured M-shell ionization cross-section ratios for equal-velocity hydrogen {sub 1}{sup 1}H and {sub 1}{sup 2}H as well as helium {sub 2}{sup 3}He and {sub 2}{sup 4}He isotopes. In addition, the ratios of measured ionization cross sections for {sub 1}{sup 2}H and {sub 2}{sup 4}He were used to investigate the role of the binding
2008-06-03
Provides the shell of a plugin based application environment that builds on MVC Framework to allow one to rapidly construct an application by using a collection of plugins. The MVC Shell is implemented in C# as a .NET 2.0 application that can then be used as a shell for building a plugin based application. The infrastructure allows for dynamically processing a specified collection of plugins in order to determine the functionality of the application, wheremore » all plugins operate within the context of the underlying MVC Framework environment.« less
McGillicuddy, Nicola; Nesterenko, Ekaterina P; Nesterenko, Pavel N; Stack, Elaine M; Omamogho, Jesse O; Glennon, Jeremy D; Paull, Brett
2013-12-20
Bare core-shell silica (1.7μm) has been modified with iminodiacetic acid functional groups via standard silane chemistry, forming a new N-hydroxyethyliminodiacetic acid (HEIDA) functionalised core-shell stationary phase. The column was applied in high-performance chelation ion chromatography and evaluated for the retention of alkaline earth, transition and heavy metal cations. The influence of nitric acid eluent concentration, addition of complexing agent dipicolinic acid, eluent pH and column temperature on the column performance was investigated. The efficiencies obtained for transition and heavy metal cations (and resultant separations) were comparable or better than those previously obtained for alternative fully porous silica based chelation stationary phases, and a similarly modified monolithic silica column, ranging from ∼15 to 56μm HETP. Increasing the ionic strength of the eluent with the addition of KNO3 (0.75M) and increasing the column temperature (70°C) facilitated the isocratic separation of a mixture of 14 lanthanides and yttrium in under 12min, with HETP averaging 18μm (7μm for Ce(III)).
NASA Technical Reports Server (NTRS)
Leissa, A. W.
1973-01-01
The vibrational characteristics and mechanical properties of shell structures are discussed. The subjects presented are: (1) fundamental equations of thin shell theory, (2) characteristics of thin circular cylindrical shells, (3) complicating effects in circular cylindrical shells, (4) noncircular cylindrical shell properties, (5) characteristics of spherical shells, and (6) solution of three-dimensional equations of motion for cylinders.
Building Atoms Shell by Shell.
ERIC Educational Resources Information Center
Sussman, Beverly
1993-01-01
Describes an atom-building activity where students construct three-dimensional models of atoms using a styrofoam ball as the nucleus and pom-poms, gum drops, minimarshmallows, or other small items of two different colors to represent protons and neutrons attached. Rings of various sizes with pom-poms attached represent electron shells and…
NASA Astrophysics Data System (ADS)
Roy, Kenneth I.; Kennedy, Robert G., III; Fields, David E.
2013-02-01
The traditional concept of terraforming assumes ready availability of candidate planets with acceptable qualities: orbiting a star in its "Goldilocks zone", liquid water, enough mass, years longer than days, magnetic field, etc. But even stipulating affordable interstellar travel, we still might never find a good candidate elsewhere. Whatever we found likely would require centuries of heavy terraforming, just as Mars or Venus would here. Our increasing appreciation of the ubiquity of life suggests that any terra nova would already possess it. We would then face the dilemma of introducing alien life forms (us, our microbes) into another living world. Instead, we propose a novel method to create habitable environments for humanity by enclosing airless, sterile, otherwise useless planets, moons, and even large asteroids within engineered shells, which avoids the conundrum. These shells are subject to two opposing internal stresses: compression due to the primary's gravity, and tension from atmospheric pressure contained inside. By careful design, these two cancel each other resulting in zero net shell stress. Beneath the shell an Earth-like environment could be created similar in almost all respects to that of Home, except for gravity, regardless of the distance to the sun or other star. Englobing a small planet, moon, or even a dwarf planet like Ceres, would require astronomical amounts of material (quadrillions of tons) and energy, plus a great deal of time. It would be a quantum leap in difficulty over building Dyson Dots or industrializing our solar system, perhaps comparable to a mission across interstellar space with a living crew within their lifetime. But when accomplished, these constructs would be complete (albeit small) worlds, not merely large habitats. They could be stable across historic timescales, possibly geologic. Each would contain a full, self-sustaining ecology, which might evolve in curious directions over time. This has interesting implications
Generic element processor (application to nonlinear analysis)
NASA Technical Reports Server (NTRS)
Stanley, Gary
1989-01-01
The focus here is on one aspect of the Computational Structural Mechanics (CSM) Testbed: finite element technology. The approach involves a Generic Element Processor: a command-driven, database-oriented software shell that facilitates introduction of new elements into the testbed. This shell features an element-independent corotational capability that upgrades linear elements to geometrically nonlinear analysis, and corrects the rigid-body errors that plague many contemporary plate and shell elements. Specific elements that have been implemented in the Testbed via this mechanism include the Assumed Natural-Coordinate Strain (ANS) shell elements, developed with Professor K. C. Park (University of Colorado, Boulder), a new class of curved hybrid shell elements, developed by Dr. David Kang of LPARL (formerly a student of Professor T. Pian), other shell and solid hybrid elements developed by NASA personnel, and recently a repackaged version of the workhorse shell element used in the traditional STAGS nonlinear shell analysis code. The presentation covers: (1) user and developer interfaces to the generic element processor, (2) an explanation of the built-in corotational option, (3) a description of some of the shell-elements currently implemented, and (4) application to sample nonlinear shell postbuckling problems.
NASA Astrophysics Data System (ADS)
Kiliclar, Yalin; Laurischkat, Roman; Vladimirov, Ivaylo N.; Reese, Stefanie
2011-08-01
The presented project deals with a robot based incremental sheet metal forming process, which is called roboforming and has been developed at the Chair of Production Systems. It is characterized by flexible shaping using a freely programmable path-synchronous movement of two industrial robots. The final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the part contour in lateral direction. However, the resulting geometries formed in roboforming deviate several millimeters from the reference geometry. This results from the compliance of the involved machine structures and the springback effects of the workpiece. The project aims to predict these deviations caused by resiliences and to carry out a compensative path planning based on this prediction. Therefore a planning tool is implemented which compensates the robots's compliance and the springback effects of the sheet metal. The forming process is simulated by means of a finite element analysis using a material model developed at the Institute of Applied Mechanics (IFAM). It is based on the multiplicative split of the deformation gradient in the context of hyperelasticity and combines nonlinear kinematic and isotropic hardening. Low-order finite elements used to simulate thin sheet structures, such as used for the experiments, have the major problem of locking, a nonphysical stiffening effect. For an efficient finite element analysis a special solid-shell finite element formulation based on reduced integration with hourglass stabilization has been developed. To circumvent different locking effects, the enhanced assumed strain (EAS) and the assumed natural strain (ANS) concepts are included in this formulation. Having such powerful tools available we obtain more accurate geometries.
NASA Astrophysics Data System (ADS)
Kim, Jae Woong; Jang, Beom Seon; Kang, Sung Wook
2014-06-01
I-core sandwich panel that has been used more widely is assembled using high power CO-laser welding. Kim et al. (2013) proposed a circular cone type heat source model for the T-joint laser welding between face plate and core. It can cover the negative defocus which is commonly adopted in T-joint laser welding to provide deeper penetration. In part I, a volumetric heat source model is proposed and it is verified thorough a comparison of melting zone on the cross section with experiment results. The proposed model can be used for heat transfer analysis and thermal elasto-plastic analysis to predict welding deformation that occurs during laser welding. In terms of computational time, since the thermal elasto-plastic analysis using 3D solid elements is quite time consuming, shell element model with multi-layers have been employed instead. However, the conventional layered approach is not appropriate for the application of heat load at T-Joint. This paper, Part II, suggests a new method to arrange different number of layers for face plate and core in order to impose heat load only to the face plate.
Fortescue, P.; Zumwalt, L.R.
1961-11-28
A fuel element was developed for a gas cooled nuclear reactor. The element is constructed in the form of a compacted fuel slug including carbides of fissionable material in some cases with a breeder material carbide and a moderator which slug is disposed in a canning jacket of relatively impermeable moderator material. Such canned fuel slugs are disposed in an elongated shell of moderator having greater gas permeability than the canning material wherefore application of reduced pressure to the space therebetween causes gas diffusing through the exterior shell to sweep fission products from the system. Integral fission product traps and/or exterior traps as well as a fission product monitoring system may be employed therewith. (AEC)
NASA Astrophysics Data System (ADS)
Palmeri, P.; Quinet, P.; Mendoza, C.; Bautista, M. A.; Witthoeft, M. C.; Kallman, T. R.
2016-05-01
Context. With the recent launching of the Hitomi X-ray space observatory, K lines and edges of chemical elements with low cosmic abundances, namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn, can be resolved and used to determine important properties of supernova remnants, galaxy clusters and accreting black holes and neutron stars. Aims: The second stage of the present ongoing project involves the computation of the accurate photoabsorption and photoionisation cross sections required to interpret the X-ray spectra of such trace elements. Methods: Depending on target complexity and computer tractability, ground-state cross sections are computed either with the close-coupling Breit-Pauli R-matrix method or with the autostructure atomic structure code in the isolated-resonance approximation. The intermediate-coupling scheme is used whenever possible. In order to determine a realistic K-edge behaviour for each species, both radiative and Auger dampings are taken into account, the latter being included in the R-matrix formalism by means of an optical potential. Results: Photoabsorption and total and partial photoionisation cross sections are reported for isoelectronic sequences with electron numbers 3 ≤ N ≤ 11. The Na sequence (N = 11) is used to estimate the contributions from configurations with a 2s hole (i.e. [2s]μ) and those containing 3d orbitals, which will be crucial when considering sequences with N > 11. Conclusions: It is found that the [2s]μ configurations must be included in the target representations of species with N ≥ 11 as they contribute significantly to the monotonic background of the cross section between the L and K edges. Configurations with 3d orbitals are important in rendering an accurate L edge, but they can be practically neglected in the K-edge region.
Structural Assessment of Advanced Composite Tow-Steered Shells
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey; Stanford, Bret K.; Hrinda, Glenn A.; Wang, Zhuosong; Martin, Robert a.; Kim, H. Alicia
2013-01-01
The structural performance of two advanced composite tow-steered shells, manufactured using a fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles vary continuously around the shell circumference from 10 degrees on the shell crown and keel, to 45 degrees on the shell sides. The two shells differ in that one shell has the full 24-tow course applied during each pass of the fiber placement system, while the second shell uses the fiber placement system s tow drop/add capability to achieve a more uniform shell wall thickness. The shells are tested in axial compression, and estimates of their prebuckling axial stiffnesses and bifurcation buckling loads are predicted using linear finite element analyses. These preliminary predictions compare well with the test results, with an average agreement of approximately 10 percent.
Stress analysis of filament wound open-ended composite shells
NASA Astrophysics Data System (ADS)
Gramoll, K. C.
1993-04-01
Membrane stresses and radial displacements for a filament wound, open-ended composite shell with internal pressure loading are developed. The shell is considered to be open at the crown as required by planar filament winding. The shell thickness and material properties vary along the meridian line due to the filament winding process. The membrane stress resultants are compared with finite elements using large deflection nonlinear anisotropic axisymmetric elements for an ellipsoidal shell. Finite elements show large bending stresses near the open edge for an ellipsoid, spheroid and netting shell. The ellipsoid and spheroid shells also show bending stresses throughout the dome structure. Radial deformations are also compared to finite element results for the three dome types.
Shell model Monte Carlo methods
Koonin, S.E.; Dean, D.J.
1996-10-01
We review quantum Monte Carlo methods for dealing with large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in fluctuating one-body fields; resultant path integral is evaluated stochastically. We first discuss the motivation, formalism, and implementation of such Shell Model Monte Carlo methods. There then follows a sampler of results and insights obtained from a number of applications. These include the ground state and thermal properties of pf-shell nuclei, thermal behavior of {gamma}-soft nuclei, and calculation of double beta-decay matrix elements. Finally, prospects for further progress in such calculations are discussed. 87 refs.
Ecology and shell chemistry of Loxoconcha matagordensis
Cronin, T. M.; Kamiya, T.; Dwyer, G.S.; Belkin, H.; Vann, C.D.; Schwede, S.; Wagner, R.
2005-01-01
Studies of the seasonal ecology and shell chemistry of the ostracode Loxoconcha matagordensis and related species of Loxoconcha from regions off eastern North America reveal that shell size and trace elemental (Mg/Ca ratio) composition are useful in paleothermometry using fossil populations. Seasonal sampling of populations from Chesapeake Bay, augmented by samples from Florida Bay, indicate that shell size is inversely proportional to water temperature and that Mg/Ca ratios are positively correlated with the water temperature in which the adult carapace was secreted. Microprobe analyses of sectioned valves reveal intra-shell variability in Mg/Ca ratios but this does not strongly influence the utility of whole shell Mg/Ca analyses for paleoclimate application.
The transuranium elements: From neptunium and plutonium to element 112
Hoffman, D.C. |
1996-07-26
Beginning in the 1930`s, both chemists and physicists became interested in synthesizing new artificial elements. The first transuranium element, Np, was synthesized in 1940. Over the past six decades, 20 transuranium elements have been produced. A review of the synthesis is given. The procedure of naming the heavy elements is also discussed. It appears feasible to produce elements 113 and 114. With the Berkeley Gas-filled Separator, it should be possible to reach the superheavy elements in the region of the spherical Z=114 shell, but with fewer neutrons than the N=184 spherical shell. 57 refs, 6 figs.
Hofmann, S.
1996-12-31
The new elements 110, 111, and 112 were synthesized and unambiguously identified in experiments at SHIP. Due to strong shell effects the dominant decay mode is not fission, but emission of alpha particles. Theoretical investigations predict that maximum shell effects should exist in nuclei near proton number 114 and neutron number 184. Measurements give hope that isotopes of element 114 close to the island of spherical Superheavy Elements could be produced by fusion reactions using {sup 118}Pb as target. systematic studies of the reaction cross-sections indicate that transfer of nucleons is the important process to initiate the fusion.
Accurate stress resultants equations for laminated composite deep thick shells
Qatu, M.S.
1995-11-01
This paper derives accurate equations for the normal and shear force as well as bending and twisting moment resultants for laminated composite deep, thick shells. The stress resultant equations for laminated composite thick shells are shown to be different from those of plates. This is due to the fact the stresses over the thickness of the shell have to be integrated on a trapezoidal-like shell element to obtain the stress resultants. Numerical results are obtained and showed that accurate stress resultants are needed for laminated composite deep thick shells, especially if the curvature is not spherical.
NASA Astrophysics Data System (ADS)
Hofmann, S.
The nuclear shell model predicts that the next doubly magic shell closure beyond 208Pb is at a proton number Z=114, 120, or 126 and at a neutron number N=172 or 184. The outstanding aim of experimental investigations is the exploration of this region of spherical `SuperHeavy Elements' (SHEs). Experimental methods have been developed which allowed for the identification of new elements at production rates of one atom per month. Using cold fusion reactions which are based on lead and bismuth targets, relatively neutron-deficient isotopes of the elements from 107 to 113 were synthesized at GSI in Darmstadt, Germany, and/or at RIKEN in Wako, Japan. In hot fusion reactions of 48Ca projectiles with actinide targets more neutron-rich isotopes of the elements from 112 to 116 and even 118 were produced at the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. Recently, part of these data which represent the first identification of nuclei located on the predicted island of SHEs were confirmed in two independent experiments. The decay data reveal that for the heaviest elements, the dominant decay mode is α emission rather than fission. Decay properties as well as reaction cross-sections are compared with results of theoretical studies. Finally, plans are presented for the further development of the experimental set-up and the application of new techniques. At a higher sensitivity, the detailed exploration of the region of spherical SHEs will be in the center of interest of future experimental work. New data will certainly challenge theoretical studies on the mechanism of the synthesis, on the nuclear decay properties, and on the chemical behavior of these heaviest atoms at the limit of stability.
ERIC Educational Resources Information Center
Etzold, Carol
1983-01-01
Discusses shell classification exercises. Through keying students advanced from the "I know what a shell looks like" stage to become involved in the classification process: observing, labeling, making decisions about categories, and identifying marine animals. (Author/JN)
NASA Astrophysics Data System (ADS)
Ponnurangam, A.; Bau, M.; Brenner, M.; Koschinsky, A.
2015-09-01
Mussel shells are potential bioarchives of proxies for changes of the physico-chemical conditions in the bivalve's habitat. One such proxy is the distribution of the Rare Earths and Yttrium (REY) in seawater, as REY speciation in seawater is sensitive to pH and temperature variations, due to the impact of these parameters on the activity of CO32- in seawater. We present a new protocol for sample preparation and determination of REY concentrations in bivalve shells, that includes sample treatment with NaOCl followed by REY separation and preconcentration. The data obtained was further used to calculate REY partition coefficients between shells of M. edulis and ambient seawater, and acquired results were then used in the investigation of the potential effects of pH and temperature on REY partitioning. Shells of M. edulis mussels from the North Sea show consistent shale-normalized ("SN") REY patterns that increase from the light REY to the middle REY and decrease from the middle REY to the heavy REY. Despite being different to the general seawater REYSN pattern, the shells still display distinct REY features of seawater such as a negative CeSN anomaly and small positive YSN and GdSN anomalies. Apparent partition coefficients for the REY between the shell and seawater (appDREYshell/seawater) are low and decrease strongly from the light REY (4.04 for La) to the heavy REY (0.34 for Lu). However, assuming that only the free REY3+ are incorporated into the shell, appDREY3+shell/seawater values are higher and rather similar for all REY (102.46 for La; 113.44 for Lu), but show a slight maximum at Tb (199.18). Although the impact of vital effects i.e. REY speciation in a mussel's extrapallial fluid from which the carbonate minerals precipitate, cannot be quantified yet, it appears that M. edulis shells are bioarchives of some REY features of seawater. We modelled the REYSN patterns of a hypothetical mussel shell at pH 8.2 and 7.6 and at temperatures of 25 and 5
Identification of material constants for a composite shell structure
Carne, T.G.; Martinez, D.R.
1987-01-01
A finite element model of a composite shell was created. The model includes uncertain orthotropic elastic constants. To identify these constants, a modal survey was performed on an actual shell. The resulting modal data along with the finite element model of the shell were used in a Bayes estimation algorithm. Values of the elastic constants were estimated which minimized the differences between the test results and the finite element predictions. The estimation procedure employed the concept of successive linearization to obtain an approximate solution to the original nonlinear estimation problem.
NASA Astrophysics Data System (ADS)
Ponnurangam, A.; Bau, M.; Brenner, M.; Koschinsky, A.
2016-02-01
Mussel shells are potential bioarchives of proxies for changes in the physicochemical conditions in the bivalve's habitat. One such proxy is the distribution of rare earths and yttrium (REY) in seawater, as REY speciation in seawater is sensitive to pH and temperature variations, due to the impact of these parameters on the activity of CO32- in seawater. We present a new protocol for sample preparation and determination of ultratrace concentrations of REY in bulk bivalve shells (comprised of calcite and aragonite) that includes sample treatment with NaOCl followed by REY separation and preconcentration. The data obtained were used to calculate REY partition coefficients between bulk bimineralic shells of Mytilus edulis (calcite aragonite mix) and ambient seawater, and the results acquired were then used to investigate the potential effects of pH and temperature on REY partitioning.Shells of Mytilus edulis mussels from the North Sea show consistent shale-normalized (SN) REY patterns that increase from the light REY to the middle REY and decrease from the middle REY to the heavy REY. Despite being different from the general seawater REYSN pattern, the shells still display distinct REY features of seawater, such as a negative CeSN anomaly and small positive YSN and GdSN anomalies. Apparent REY partition coefficients between shells and seawater (appDTot.REYshell/seawater) are low and decrease strongly from the light REY (4.04 for La) to the heavy REY (0.34 for Lu). However, assuming that only the free REY3+ are incorporated into the shell, modDFreeREY3+shell/seawater values are higher and comparatively similar for all REY (102.46 for La; 113.44 for Lu) but show a slight maximum at Tb (199.18). Although the impact of vital effects, such as REY speciation in a mussel's extrapallial fluid from which the carbonate minerals precipitate, cannot be quantified yet, it appears that M. edulis shells are bioarchives of some REY features of seawater.We modeled the REYSN patterns
Probabilistic Dynamic Buckling of Smart Composite Shells
NASA Technical Reports Server (NTRS)
Abumeri, Galib H.; Chamis, Christos C.
2003-01-01
A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right below the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10 percent at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.
Probabilistic Dynamic Buckling of Smart Composite Shells
NASA Technical Reports Server (NTRS)
Chamis, Christos C.; Abumeri, Galib H.
2007-01-01
A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of intraply hybrid composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right next to the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10% at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.
Damping control of 'smart' piezoelectric shell structures
NASA Astrophysics Data System (ADS)
Tzou, H. S.
Advanced 'smart' structures with self-sensation and control capabilities have attracted much attention in recent years. 'Smart' piezoelectric structures (conventional structures integrated with piezoelectric sensor and actuator elements) possessing self-monitoring and adaptive static and/or dynamic characteristics are very promising in many applications. This paper presents a study on 'smart' piezoelectric shell structures. A generic piezoelastic vibration theory for a thin piezoelectric shell continuum made of a hexagonal piezoelectric material is first derived. Piezoelastic system equation and electrostatic charge equation are formulated using Hamilton's principle and Kirchhoff-Love thin shell assumptions. Dynamic adaptivity, damping control, of a simply supported cylindrical shell structure is demonstrated in a case study. It shows that the system damping increases with the increase of feedback voltage for odd modes. The control scheme is ineffective for all even modes because of the symmetrical boundary conditions.
Trends in Ionization Energy of Transition-Metal Elements
ERIC Educational Resources Information Center
Matsumoto, Paul S.
2005-01-01
A rationale for the difference in the periodic trends in the ionization energy of the transition-metal elements versus the main-group elements is presented. The difference is that in the transition-metal elements, the electrons enter an inner-shell electron orbital, while in the main-group elements, the electrons enter an outer-shell electron…
Wheelock, C.W.; Baumeister, E.B.
1961-09-01
A reactor fuel element utilizing fissionable fuel materials in plate form is described. This fuel element consists of bundles of fuel-bearing plates. The bundles are stacked inside of a tube which forms the shell of the fuel element. The plates each have longitudinal fins running parallel to the direction of coolant flow, and interspersed among and parallel to the fins are ribs which position the plates relative to each other and to the fuel element shell. The plate bundles are held together by thin bands or wires. The ex tended surface increases the heat transfer capabilities of a fuel element by a factor of 3 or more over those of a simple flat plate.
Shell model description of band structure in 48Cr
Vargas, Carlos E.; Velazquez, Victor M.
2007-02-12
The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements.
Fluctuating shells under pressure
Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.
2012-01-01
Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558
Comparative study of the shell development of hard- and soft-shelled turtles
Nagashima, Hiroshi; Shibata, Masahiro; Taniguchi, Mari; Ueno, Shintaro; Kamezaki, Naoki; Sato, Noboru
2014-01-01
The turtle shell provides a fascinating model for the investigation of the evolutionary modifications of developmental mechanisms. Different conclusions have been put forth for its development, and it is suggested that one of the causes of the disagreement could be the differences in the species of the turtles used – the differences between hard-shelled turtles and soft-shelled turtles. To elucidate the cause of the difference, we compared the turtle shell development in the two groups of turtle. In the dorsal shell development, these two turtle groups shared the gene expression profile that is required for formation, and shared similar spatial organization of the anatomical elements during development. Thus, both turtles formed the dorsal shell through a folding of the lateral body wall, and the Wnt signaling pathway appears to have been involved in the development. The ventral portion of the shell, on the other hand, contains massive dermal bones. Although expression of HNK-1 epitope has suggested that the trunk neural crest contributed to the dermal bones in the hard-shelled turtles, it was not expressed in the initial anlage of the skeletons in either of the types of turtle. Hence, no evidence was found that would support a neural crest origin. PMID:24754673
Comparative study of the shell development of hard- and soft-shelled turtles.
Nagashima, Hiroshi; Shibata, Masahiro; Taniguchi, Mari; Ueno, Shintaro; Kamezaki, Naoki; Sato, Noboru
2014-07-01
The turtle shell provides a fascinating model for the investigation of the evolutionary modifications of developmental mechanisms. Different conclusions have been put forth for its development, and it is suggested that one of the causes of the disagreement could be the differences in the species of the turtles used - the differences between hard-shelled turtles and soft-shelled turtles. To elucidate the cause of the difference, we compared the turtle shell development in the two groups of turtle. In the dorsal shell development, these two turtle groups shared the gene expression profile that is required for formation, and shared similar spatial organization of the anatomical elements during development. Thus, both turtles formed the dorsal shell through a folding of the lateral body wall, and the Wnt signaling pathway appears to have been involved in the development. The ventral portion of the shell, on the other hand, contains massive dermal bones. Although expression of HNK-1 epitope has suggested that the trunk neural crest contributed to the dermal bones in the hard-shelled turtles, it was not expressed in the initial anlage of the skeletons in either of the types of turtle. Hence, no evidence was found that would support a neural crest origin.
Lindl, J.D.; Bangerter, R.O.
1975-10-31
Multiple shell fusion targets for use with electron beam and ion beam implosion systems are described. The multiple shell targets are of the low-power type and use a separate relatively low Z, low density ablator at large radius for the outer shell, which reduces the focusing and power requirements of the implosion system while maintaining reasonable aspect ratios. The targets use a high Z, high density pusher shell placed at a much smaller radius in order to obtain an aspect ratio small enough to protect against fluid instability. Velocity multiplication between these shells further lowers the power requirements. Careful tuning of the power profile and intershell density results in a low entropy implosion which allows breakeven at low powers. For example, with ion beams as a power source, breakeven at 10-20 Terrawatts with 10 MeV alpha particles for imploding a multiple shell target can be accomplished.
Calculation of tubular joints as compound shells
NASA Astrophysics Data System (ADS)
Golovanov, A. I.
A scheme for joining isoparametric finite shell elements with a bend in the middle surface is described. A solution is presented for the problem of the stress-strain state of a T-joint loaded by internal pressure. A refined scheme is proposed for calculating structures of this kind with allowance for the stiffness of the welded joint.
Microstructural characacterization of shell components in the mollusc Physa sp.
de Paula, Silvia M; Silveira, Marina
2005-01-01
Shells of the freshwater, pulmonate snail Physa (Mollusca, Gasteropoda), ranging from 0.5 to 10 mm in length, were studied using scanning microscopy, x-ray analysis, and infrared spectroscopy. Results obtained suggest that the shell is composed of aragonite, which occurs in several distinct crystalline forms. A selective distribution of crystalline forms (hexagonal plates, prisms, rhombohedra, and spherulites) occurred along specific sites of the shell. A variable distribution of the forms was also detected in adult shells and in protoconchs of developing embryos. Qualitative elemental analysis, using an energy-dispersive spectrometer, corroborates the presence of calcium, phosphorus and sulphur ions.
Fast optimization of static axisymmetric shell structures
NASA Astrophysics Data System (ADS)
Jacoby, Jeffrey
An axisymmetric shell optimization procedure is developed which is a fast, user-friendly and practical tool for design use in disciplines including aerospace, mechanical and civil engineering. The shape and thickness of a shell can be optimized to minimize shell mass, mass/volume ratio or stress with constraints imposed on von Mises stress and local buckling. The procedure was created with the aid of the GENOPT optimization development system (Dr. D. Bushnell, Lockheed Missiles and Space Co) and uses the FAST1 shell analysis program (Prof. C. R. Steele, Stanford University) to perform the constraint analysis. The optimization method used is the modified method of feasible directions. The procedure is fast because exact analysis methods allow complex shells to be modelled with only a few large shell elements and still retain a sufficiently accurate solution. This is of particular advantage near shell boundaries and intersections which can have small regions of very detailed variation in the solution. Finite element methods would require many small elements to capture accurately this detail with a resulting increase in computation time and model complexity. Reducing the complexity of the model also reduces the size of the required input and contributes to the simplicity of the procedure. Optimization design variables are the radial and axial coordinates of nodes and the shape parameters and thicknesses of the elements. Thickness distribution within an element can be optimized by specifying the thickness at evenly spaced control points. Spline interpolation is used to provide a smooth thickness variation between the control points. An effective method is developed for reducing the number of required stress constraint equations. Various shells have been optimized and include models for comparison with published results. Shape, thickness and shape/thickness optimization has been performed on examples including a simple aerobrake, sphere-nozzle intersections, ring
Distributed neural signals on parabolic cylindrical shells
NASA Astrophysics Data System (ADS)
Hu, S. D.; Li, H.; Tzou, H. S.
2013-06-01
Parabolic cylindrical shells are commonly used as key components in communication antennas, space telescopes, solar collectors, etc. This study focuses on distributed modal neural sensing signals on a flexible simply-supported parabolic cylindrical shell panel. The parabolic cylindrical shell is fully laminated with a piezoelectric layer on its outer surface and the piezoelectric layer is segmented into infinitesimal elements (neurons) to investigate the microscopic distributed neural sensing signals. Since the dominant vibration component of the shell is usually the transverse oscillation, a new transverse mode shape function is defined. Two shell cases, i.e., the ratio of the meridian height to the half span distance of a parabola at 1:4 (shallow) and 1:1 (deep), are studied to reveal the curvature effect to the neural sensing signals. Studies suggest that the membrane signal component dominates for lower natural modes and the bending signal component dominates for higher natural modes. The meridional membrane and bending signal components are mostly concentrated on the high-curvature areas, while the longitudinal bending component is mostly concentrated on the relatively flat areas. The concentration behavior becomes more prominent as the parabolic cylindrical shell deepens, primarily resulting from the enhanced membrane effect due to the increased curvature.
Compressive behavior of a turtle's shell: experiment, modeling, and simulation.
Damiens, R; Rhee, H; Hwang, Y; Park, S J; Hammi, Y; Lim, H; Horstemeyer, M F
2012-02-01
The turtle's shell acts as a protective armor for the animal. By analyzing a turtle shell via finite element analysis, one can obtain the strength and stiffness attributes to help design man-made armor. As such, finite element analysis was performed on a Terrapene carolina box turtle shell. Experimental data from compression tests were generated to provide insight into the scute through-thickness behavior of the turtle shell. Three regimes can be classified in terms of constitutive modeling: linear elastic, perfectly inelastic, and densification regions, where hardening occurs. For each regime, we developed a model that comprises elasticity and densification theory for porous materials and obtained all the material parameters by correlating the model with experimental data. The different constitutive responses arise as the deformation proceeded through three distinctive layers of the turtle shell carapace. Overall, the phenomenological stress-strain behavior is similar to that of metallic foams. PMID:22301179
Shell Buckling Design Criteria Based on Manufacturing Imperfection Signatures
NASA Technical Reports Server (NTRS)
Hilburger, Mark W.; Nemeth, Michael P.; Starnes, James H., Jr.
2004-01-01
An analysis-based approach .for developing shell-buckling design criteria for laminated-composite cylindrical shells that accurately accounts for the effects of initial geometric imperfections is presented. With this approach, measured initial geometric imperfection data from six graphite-epoxy shells are used to determine a manufacturing-process-specific imperfection signature for these shells. This imperfection signature is then used as input into nonlinear finite-element analyses. The imperfection signature represents a "first-approximation" mean imperfection shape that is suitable for developing preliminary-design data. Comparisons of test data and analytical results obtained by using several different imperfection shapes are presented for selected shells. Overall, the results indicate that the analysis-based approach presented for developing reliable preliminary-design criteria has the potential to provide improved, less conservative buckling-load estimates, and to reduce the weight and cost of developing buckling-resistant shell structures.
Acoustic radiation from a shell with internal structures
NASA Technical Reports Server (NTRS)
El-Raheb, M.; Wagner, P.
1989-01-01
A method is developed to compute frequency response and acoustic radiation of a complex shell. The axisymmetric geometry of the shell includes cylindrical, conical, and spherical segments stiffened by discrete rings and bulkheads. The shell is coupled to internal masses and elastic frames. Shell segments are treated by transfer matrices. Rings, bulkheads, frames, and concentrated masses are treated by impedances at junctions of segments. The shell is coupled to an external acoustic fluid treated by Green's function and curved surface elements. A major issue facing the method's treatment of the fluid would be lack of existence or uniqueness encountered in the uncoupled, external acoustic problem at characteristic wavenumbers. By using a simple spherical shell, without internal structures, this potential hindrance is shown not to arise. A fuller application of the method awaits subsequent results.
NASA Astrophysics Data System (ADS)
Liu, Yan
2002-06-01
Some shells from both salt water and fresh water show the phenomenon of iridescence color. Pearls and mother-of-pearls also display this phenomenon. In the past, the cause of the iridescence color was attributed to interference. A scanning electron microscope (SEM) was used to study the surface structure of the shell of the mollusk Pinctada Margaritifera. There is a groove structure of reflection grating on the surface area in where the iridescence color appears. An optic experiment with a laser obtained a diffraction pattern produced by the reflection grating structure of the shell. The study led to a conclusion that the iridescence color of the shell is caused by diffraction. A SEM image of the shells of an abalone Haliotis Rufescens (red abalone) showed a statistically regularly arranged tile structure that serves as a two-dimensional grating. This grating structure causes the iridescence color of the shell of red abalone. The dominant color of the iridescence of shells is caused by the uneven grating efficiency in the visible wavelength range when a shell functions as a reflection grating. The wavelength of the dominant color should be at or near the wavelength of the maximum efficiency of the grating.
Static cylindrical matter shells
NASA Astrophysics Data System (ADS)
Arık, Metin; Delice, Özgür
2005-08-01
Static cylindrical shells composed of massive particles arising from matching of two different Levi-Civita space-times are studied for the shell satisfying either an isotropic or an anisotropic equation of state. We find that these solutions satisfy the energy conditions for certain ranges of the parameters.
NASA Astrophysics Data System (ADS)
Bentley, Ian
2016-03-01
The appearance and disappearance of nuclear shells and sub-shells has been at the forefront of recent nuclear theory and experimental efforts. This work extends a previously introduced method of structural analysis and applies it to protons in an attempt to provide a more complete understanding of shell structure in nuclei. Experimental observables including the mean square charge radius, as well as other spectroscopic and mass related quantities have been analyzed for shell structure features. A preliminary analysis using Nilsson coefficient fits of experimental quantities, such as odd mass spectra and B(E2) values, along isotopic chains will be discussed. The goal of this work is to provide a means of predicting shell structure far from stability. This work was supported by the National Science Foundation under Grants PHY1419765 and PHY0822648.
Environmental effects on shell microstructures of Cerastoderma edule
NASA Astrophysics Data System (ADS)
Milano, Stefania; Schöne, Bernd R.; Witbaard, Rob
2015-04-01
Bivalve shells serve as sensitive recorders of environmental conditions. However, reconstruction of a specific environmental parameter is still challenging. For example, variable shell growth rates simultaneously provide information on water temperature, food availability and food quality. Likewise, shell oxygen isotope values function as a dual proxy of water temperature and salinity (=oxygen isotope signature of the ambient water). Reconstruction of water temperature from δ18Oshell requires knowledge of δ18Oshell and vice versa. Unfortunately, the incorporation of trace elements in the shell is strongly controlled by biological effects and, hence, the element-to-calcium ratios of the shell are difficult to interpret in terms of environmental variables. Here, we studied if the structural properties (shell architecture, shell microstructures, fabrics) of the shell of the common cockle can function as an alternative proxy of environmental variables. Specimens of C. edule were collected alive from the intertidal zone of the North Sea. Temperature and salinity were monitored at the site where the shells lived on hourly basis for almost one year. Each portion of the shell was temporally contextualized with the tidally-deposited growth increments. Shell microstructures (composite prismatic structures) were analyzed under with a scanning electron microscope (SEM). The change of the size and shape of the mesocrystals was strongly correlated to water temperature during the growing season (May - Sep.). With rising temperatures, the size of mesocrystals increased and their morphology changed from rounded to elongated shape. Our findings suggest that shell microstructures of C. edule may serve a new, independent proxy for water temperature.
NASA Astrophysics Data System (ADS)
Klug, William S.; Bruinsma, Robijn F.; Michel, Jean-Philippe; Knobler, Charles M.; Ivanovska, Irena L.; Schmidt, Christoph F.; Wuite, Gijs J. L.
2006-12-01
We report a combined theoretical and experimental study of the structural failure of viral shells under mechanical stress. We find that discontinuities in the force-indentation curve associated with failure should appear when the so-called Föppl von Kármán (FvK) number exceeds a critical value. A nanoindentation study of a viral shell subject to a soft-mode instability, where the stiffness of the shell decreases with increasing pH, confirms the predicted onset of failure as a function of the FvK number.
Modeling of microencapsulated polymer shell solidification
Boone, T.; Cheung, L.; Nelson, D.; Soane, D.; Wilemski, G.; Cook, R.
1995-03-08
A finite element transport model has been developed and implemented to complement experimental efforts to improve the quality of ICF target shells produced via controlled-mass microencapsulation. The model provides an efficient means to explore the effect of processing variables on the dynamics of shell dimensions, concentricity, and phase behavior. Comparisons with experiments showed that the model successfully predicts the evolution of wall thinning and core/wall density differences. The model was used to efficiently explore and identify initial wall compositions and processing temperatures which resulted in concentricity improvements from 65 to 99%. The evolution of trace amounts of water entering into the shell wall was also tracked in the simulations. Comparisons with phase envelope estimations from modified UNIFAP calculations suggest that the water content trajectory approaches the two-phase region where vacuole formation via microphase separation may occur.
Mussel Shell Evaluation as Bioindicator For Heavy Metals
NASA Astrophysics Data System (ADS)
Andrello, Avacir Casanova; Lopes, Fábio; Galvão, Tiago Dutra
2010-05-01
Recently, in Brazil, it has appeared a new and unusual "plague" in lazer and commercial fishing. It is caused by the parasitic larval phase of certain native bivalve mollusks of fresh water known as "Naiades" and its involves the presence of big bivalve of fresh water, mainly Anodontites trapesialis, in the tanks and dams of the fish creation. These bivalve mollusks belong to the Unionoida Order, Mycetopodidae Family. The objective of the present work was to analyze the shells of these mollusks to verify the possibility of use as bioindicators for heavy metals in freshwater. The mollusks shells were collected in a commercial fishing at Londrina-PR. A qualitative analysis was made to determine the chemical composition of the shells and verify a possible correlation with existent heavy metals in the aquatic environment. In the inner part of the shells were identified the elements Ca, P, Fe, Mn and Sr and in the outer part were identified Ca, P, Fe, Mn, Sr and Cu. The Ca ratio of the outer part by inner part of the analyzed shells is around of 1, as expected, because Ca is the main compound of mollusks shells. The ratio of P, Fe, Mn, and Sr to the Ca were constant in all analyzed shells, being close to 0.015. The ratio Cu/Ca varied among the shells, showing that this mollusk is sensitive to concentration of this element in the aquatic environment.
Yong, Ee Hou; Nelson, David R; Mahadevan, L
2013-10-25
On microscopic scales, the crystallinity of flexible tethered or cross-linked membranes determines their mechanical response. We show that by controlling the type, number, and distribution of defects on a spherical elastic shell, it is possible to direct the morphology of these structures. Our numerical simulations show that by deflating a crystalline shell with defects, we can create elastic shell analogs of the classical platonic solids. These morphologies arise via a sharp buckling transition from the sphere which is strongly hysteretic in loading or unloading. We construct a minimal Landau theory for the transition using quadratic and cubic invariants of the spherical harmonic modes. Our approach suggests methods to engineer shape into soft spherical shells using a frozen defect topology.
Hollow spherical shell manufacture
O'Holleran, T.P.
1991-11-26
A process is disclosed for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry. 3 figures.
Hollow spherical shell manufacture
O'Holleran, Thomas P.
1991-01-01
A process for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry.
NASA Astrophysics Data System (ADS)
Currie, Malcolm J.
This cookbook describes the fundamentals of writing scripts using the UNIX C shell. It shows how to combine Starlink and private applications with shell commands and constructs to create powerful and time-saving tools for performing repetitive jobs, creating data-processing pipelines, and encapsulating useful recipes. The cookbook aims to give practical and reassuring examples to at least get you started without having to consult a UNIX manual. However, it does not offer a comprehensive description of C-shell syntax to prevent you from being overwhelmed or intimidated. The topics covered are: how to run a script, defining shell variables, prompting, arithmetic and string processing, passing information between Starlink applications, obtaining dataset attributes and FITS header information, processing multiple files and filename modification, command-line arguments and options, and loops. There is also a glossary.
Bearing capacity of shell strip footing on reinforced sand.
Azzam, W R; Nasr, A M
2015-09-01
In this paper, the ultimate load capacities of shell foundations on unreinforced and reinforced sand were determined by laboratory model tests. A series of loading tests were carried out on model shell footing with and without single layer of reinforcement. The tests were done for shell foundation at different shell embedment depth and subgrade density. The results were compared with those for flat foundations without reinforcement. The model test results were verified using finite element analysis using program PLAXIS. The experimental studies indicated that, the ultimate load capacity of shell footing on reinforced subgrade is higher than those on unreinforced cases and the load settlement curves were significantly modified. The shell foundation over reinforced subgrade can be considered a good method to increase the effective depth of the foundation and decrease the resulting settlement. Also the rupture surface of shell reinforced system was significantly deeper than both normal footing and shell footing without reinforcement. The numerical analysis helps in understanding the deformation behavior of the studied systems and identifies the failure surface of reinforced shell footing.
Bearing capacity of shell strip footing on reinforced sand.
Azzam, W R; Nasr, A M
2015-09-01
In this paper, the ultimate load capacities of shell foundations on unreinforced and reinforced sand were determined by laboratory model tests. A series of loading tests were carried out on model shell footing with and without single layer of reinforcement. The tests were done for shell foundation at different shell embedment depth and subgrade density. The results were compared with those for flat foundations without reinforcement. The model test results were verified using finite element analysis using program PLAXIS. The experimental studies indicated that, the ultimate load capacity of shell footing on reinforced subgrade is higher than those on unreinforced cases and the load settlement curves were significantly modified. The shell foundation over reinforced subgrade can be considered a good method to increase the effective depth of the foundation and decrease the resulting settlement. Also the rupture surface of shell reinforced system was significantly deeper than both normal footing and shell footing without reinforcement. The numerical analysis helps in understanding the deformation behavior of the studied systems and identifies the failure surface of reinforced shell footing. PMID:26425361
Bearing capacity of shell strip footing on reinforced sand
Azzam, W.R.; Nasr, A.M.
2014-01-01
In this paper, the ultimate load capacities of shell foundations on unreinforced and reinforced sand were determined by laboratory model tests. A series of loading tests were carried out on model shell footing with and without single layer of reinforcement. The tests were done for shell foundation at different shell embedment depth and subgrade density. The results were compared with those for flat foundations without reinforcement. The model test results were verified using finite element analysis using program PLAXIS. The experimental studies indicated that, the ultimate load capacity of shell footing on reinforced subgrade is higher than those on unreinforced cases and the load settlement curves were significantly modified. The shell foundation over reinforced subgrade can be considered a good method to increase the effective depth of the foundation and decrease the resulting settlement. Also the rupture surface of shell reinforced system was significantly deeper than both normal footing and shell footing without reinforcement. The numerical analysis helps in understanding the deformation behavior of the studied systems and identifies the failure surface of reinforced shell footing. PMID:26425361
ERIC Educational Resources Information Center
Sutley, Jane
2009-01-01
"Shells and Patterns" was a project the author felt would easily put smiles on the faces of her fifth-graders, and teach them about unity and the use of watercolor pencils as well. It was thrilling to see the excitement in her students as they made their line drawings of shells come to life. For the most part, they quickly got the hang of…
Sorokin, S. A.; Chaikovsky, S. A.
1997-05-05
Experiments on the double shell liner (DSL) implosions with and without an initial axial magnetic were performed on the SNOP-3 pulse generator (1.1 MA, 100 ns). In implosions of a DSL without an initial axial magnetic field, high radial compressions of the inner shell were observed, as in previous experiments with an initial axial magnetic field. Possible mechanisms for the formation of the initial azimuthal magnetic field are discussed.
Strontium and barium incorporation into freshwater bivalve shells
NASA Astrophysics Data System (ADS)
Zhao, Liqiang; Schöne, Bernd R.
2015-04-01
Despite strong vital control, trace elements of bivalve shells can potentially serve as proxies of environmental change. However, to reconstruct past environments with the geochemical properties of the shells and determine the degree to which the element levels are biologically influenced, it is essential to experimentally determine the relationship between environmental variables and the element composition of the shells. In particular, the trace element geochemistry of freshwater bivalve shells has so far received little attention. Here, we present a controlled laboratory experiment that aimed at providing a better understanding of the influence of changing environmental variables on the incorporation of trace elements into freshwater bivalve shells. Under controlled conditions, Asian clams Corbicula fluminea were reared for 5 weeks in three sets of experiments: (1) different water temperature (10, 16, and 22° C) and different food levels (an equally mixed Scenedesmu quadricanda and Chlorella vulgaris at rations of 0.4, 2, 4, and 8 × 104 cells ml-1 d-1); (2) different water temperature (10, 16, and 22° C) and different element levels (Sr, Ba); (3) five sediment types (sand, slightly muddy sand, muddy sand, slightly sandy mud and mud). In the first set of experiments, shell Sr/Ca showed a significantly negative correlation with temperature, where Sr/Ca decreased linearly by about 1.6 to 2.1% per 1° C, but responded far more weakly to food availability. On the other hand, temperature and food availability affected shell Ba/Ca ratios, which potentially confounds the interpretation of Ba/Ca variations. Moreover, shell Sr/Ca and Ba/Ca exhibited a clearly negative dependence on shells growth rate that varied significantly among combinations of temperature and food availability. In the second set of experiments, shell Sr/Ca and Ba/Ca were positively and linearly related to water Sr/Ca and Ba/Ca for all temperatures. However, significantly negative effects of
Slave finite elements: The temporal element approach to nonlinear analysis
NASA Technical Reports Server (NTRS)
Gellin, S.
1984-01-01
A formulation method for finite elements in space and time incorporating nonlinear geometric and material behavior is presented. The method uses interpolation polynomials for approximating the behavior of various quantities over the element domain, and only explicit integration over space and time. While applications are general, the plate and shell elements that are currently being programmed are appropriate to model turbine blades, vanes, and combustor liners.
Multi-Shell Hollow Nanogels with Responsive Shell Permeability
NASA Astrophysics Data System (ADS)
Schmid, Andreas J.; Dubbert, Janine; Rudov, Andrey A.; Pedersen, Jan Skov; Lindner, Peter; Karg, Matthias; Potemkin, Igor I.; Richtering, Walter
2016-03-01
We report on hollow shell-shell nanogels with two polymer shells that have different volume phase transition temperatures. By means of small angle neutron scattering (SANS) employing contrast variation and molecular dynamics (MD) simulations we show that hollow shell-shell nanocontainers are ideal systems for controlled drug delivery: The temperature responsive swelling of the inner shell controls the uptake and release, while the thermoresponsive swelling of the outer shell controls the size of the void and the colloidal stability. At temperatures between 32 °C < T < 42 °C, the hollow nanocontainers provide a significant void, which is even larger than the initial core size of the template, and they possess a high colloidal stability due to the steric stabilization of the swollen outer shell. Computer simulations showed, that temperature induced switching of the permeability of the inner shell allows for the encapsulation in and release of molecules from the cavity.
Multi-Shell Hollow Nanogels with Responsive Shell Permeability.
Schmid, Andreas J; Dubbert, Janine; Rudov, Andrey A; Pedersen, Jan Skov; Lindner, Peter; Karg, Matthias; Potemkin, Igor I; Richtering, Walter
2016-03-17
We report on hollow shell-shell nanogels with two polymer shells that have different volume phase transition temperatures. By means of small angle neutron scattering (SANS) employing contrast variation and molecular dynamics (MD) simulations we show that hollow shell-shell nanocontainers are ideal systems for controlled drug delivery: The temperature responsive swelling of the inner shell controls the uptake and release, while the thermoresponsive swelling of the outer shell controls the size of the void and the colloidal stability. At temperatures between 32 °C < T < 42 °C, the hollow nanocontainers provide a significant void, which is even larger than the initial core size of the template, and they possess a high colloidal stability due to the steric stabilization of the swollen outer shell. Computer simulations showed, that temperature induced switching of the permeability of the inner shell allows for the encapsulation in and release of molecules from the cavity.
Multi-Shell Hollow Nanogels with Responsive Shell Permeability
Schmid, Andreas J.; Dubbert, Janine; Rudov, Andrey A.; Pedersen, Jan Skov; Lindner, Peter; Karg, Matthias; Potemkin, Igor I.; Richtering, Walter
2016-01-01
We report on hollow shell-shell nanogels with two polymer shells that have different volume phase transition temperatures. By means of small angle neutron scattering (SANS) employing contrast variation and molecular dynamics (MD) simulations we show that hollow shell-shell nanocontainers are ideal systems for controlled drug delivery: The temperature responsive swelling of the inner shell controls the uptake and release, while the thermoresponsive swelling of the outer shell controls the size of the void and the colloidal stability. At temperatures between 32 °C < T < 42 °C, the hollow nanocontainers provide a significant void, which is even larger than the initial core size of the template, and they possess a high colloidal stability due to the steric stabilization of the swollen outer shell. Computer simulations showed, that temperature induced switching of the permeability of the inner shell allows for the encapsulation in and release of molecules from the cavity. PMID:26984478
Free vibration of laminated composite stiffened hyperbolic paraboloid shell panel with cutout
NASA Astrophysics Data System (ADS)
Sahoo, Sarmila
2016-08-01
Composite shell structures are extensively used in aerospace, civil, marine and other engineering applications. In practical civil engineering applications, the necessity of covering large column free open areas is often an issue and hyperbolic paraboloid shells are used as roofing units. Quite often, to save weight and also to provide a facility for inspection, cutouts are provided in shell panels. The paper considers free vibration characteristics of stiffened composite hyperbolic paraboloid shell panel with cutout in terms of natural frequency and mode shapes. A finite element code is developed for the purpose by combining an eight noded curved shell element with a three noded curved beam element. The size of the cutouts and their positions with respect to the shell centre are varied for different edge conditions to arrive at a set of inferences of practical engineering significances.
The adsorption of rare earth ions using carbonized polydopamine nano shells
Sun, Xiaoqi; Luo, Huimin; Mahurin, Shannon Mark; Dai, Sheng; Liu, Rui; Hou, Xisen; Dai, Sheng
2016-01-07
Herein we report the structure effects of nano carbon shells prepared by carbonized polydopamine for rare earth elements (REEs) adsorption for the first time. The solid carbon sphere, 60 nm carbon shell and 500 nm carbon shell were prepared and investigated for adsorption and desorption of REEs. The adsorption of carbon shells for REEs was found to be better than the solid carbon sphere. The effect of acidities on the adsorption and desorption properties was discussed in this study. The good adsorption performance of carbon shells can be attributed to their porous structure, large specific surface area, amine group andmore » carbonyl group of dopamine.« less
Lee, M.C.; Kendall, J.M.,JR.; Bahrami, P.A.; Wang, T.G.
1986-01-01
Fluid-dynamic and capillary forces can be used to form nearly perfect, very small spherical shells when a liquid that can solidify is passed through an annular die to form an annular jet. Gravity and certain properties of even the most ideal materials, however, can cause slight asymmetries. The primary objective of the present work is the control of this shell formation process in earth laboratories rather than space microgravity, through the development of facilities and methods that minimize the deleterious effects of gravity, aerodynamic drag, and uncontrolled cooling. The spherical shells thus produced can be used in insulation, recyclable filter materials, fire retardants, explosives, heat transport slurries, shock-absorbing armor, and solid rocket motors.
Hamza, Alex V.; Biener, Juergen; Wild, Christoph; Woerner, Eckhard
2016-11-01
A novel method for fabricating diamond shells is introduced. The fabrication of such shells is a multi-step process, which involves diamond chemical vapor deposition on predetermined mandrels followed by polishing, microfabrication of holes, and removal of the mandrel by an etch process. The resultant shells of the present invention can be configured with a surface roughness at the nanometer level (e.g., on the order of down to about 10 nm RMS) on a mm length scale, and exhibit excellent hardness/strength, and good transparency in the both the infra-red and visible. Specifically, a novel process is disclosed herein, which allows coating of spherical substrates with optical-quality diamond films or nanocrystalline diamond films.
Shell Biorefinery: Dream or Reality?
Chen, Xi; Yang, Huiying; Yan, Ning
2016-09-12
Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers.
Shell Biorefinery: Dream or Reality?
Chen, Xi; Yang, Huiying; Yan, Ning
2016-09-12
Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers. PMID:27484462
Oyster shell conveyor used to lift shells from the dock ...
Oyster shell conveyor used to lift shells from the dock into the receiving room housed in the 1965 concrete block addition. - J.C. Lore Oyster House, 14430 Solomons Island Road, Solomons, Calvert County, MD
Effects of Shell-Buckling Knockdown Factors in Large Cylindrical Shells
NASA Technical Reports Server (NTRS)
Hrinda, Glenn A.
2012-01-01
Shell-buckling knockdown factors (SBKF) have been used in large cylindrical shell structures to account for uncertainty in buckling loads. As the diameter of the cylinder increases, achieving the manufacturing tolerances becomes increasingly more difficult. Knockdown factors account for manufacturing imperfections in the shell geometry by decreasing the allowable buckling load of the cylinder. In this paper, large-diameter (33 ft) cylinders are investigated by using various SBKF's. An investigation that is based on finite-element analysis (FEA) is used to develop design sensitivity relationships. Different manufacturing imperfections are modeled into a perfect cylinder to investigate the effects of these imperfections on buckling. The analysis results may be applicable to large- diameter rockets, cylindrical tower structures, bulk storage tanks, and silos.
ERIC Educational Resources Information Center
Simpson, Andrew; Wu, Zoe
2002-01-01
Reconsiders development and licensing of agreement as a syntactic projection and argues for a productive developmental relation between agreement and the category of focus. Suggests that focus projections are initially selected by a variety of functional heads with real semantic content, then, over time decays into a simple concord shell. Upon…
ERIC Educational Resources Information Center
Matthews, Catherine
1992-01-01
Presents three inquiry-based lessons to develop the science process skills of observation, identification, and classification. Activities use whelk eggs and snail shells as the focus of the students' inquiries. Provides a list of 19 facts about whelks and snails. (MDH)
ERIC Educational Resources Information Center
Lutz, E. F.
1986-01-01
Shows how olefin isomerization and the exotic olefin metathesis reaction can be harnessed in industrial processes. Indicates that the Shell Higher Olefins Process makes use of organometallic catalysts to manufacture alpha-olefins and internal carbon-11 through carbon-14 alkenes in a flexible fashion that can be adjusted to market needs. (JN)
ERIC Educational Resources Information Center
Seier, Mark; Goedeken, Suzy
2005-01-01
In 2002 Shell Creek Watershed Improvement Group turned to the Newman Grove Public Schools' science department to help educate the public on water quality in the watershed and to establish a monitoring system that would be used to improve surface and groundwater quality in the creek's watershed. Nebraska Department of Environmental Quality provided…
BOWOOSS: bionic optimized wood shells with sustainability
NASA Astrophysics Data System (ADS)
Pohl, Göran
2011-04-01
In architecture, shell construction is used for the most efficient, large spatial structures. Until now the use of wood rather played a marginal role, implementing those examples of architecture, although this material offers manifold advantages, especially against the background of accelerating shortage of resources and increasing requirements concerning the energy balance. Regarding the implementation of shells, nature offers a wide range of suggestions. The focus of the examinations is on the shells of marine plankton, especially of diatoms, whose richness in species promises the discovery of entirely new construction principles. The project is targeting at transferring advantageous features of these organisms on industrial produced, modular wood shell structures. Currently a transfer of these structures in CAD - models is taking place, helping to perform stress analysis by computational methods. Micro as well as macro structures are the subject of diverse consideration, allowing to draw the necessary conclusions for an architectural design. The insights of these tests are the basis for the development of physical models on different scales, which are used to verify the different approaches. Another important aim which is promoted in the project is to enhance the competitiveness of timber construction. Downsizing of the prefabricated structural elements leads to considerable lower transportation costs as abnormal loads can be avoided as far as possible and means of transportation can be loaded with higher efficiency so that an important contribution to the sustainability in the field of architecture can also be made.
Stability of charged thin shells
Eiroa, Ernesto F.; Simeone, Claudio
2011-05-15
In this article we study the mechanical stability of spherically symmetric thin shells with charge, in Einstein-Maxwell and Einstein-Born-Infeld theories. We analyze linearized perturbations preserving the symmetry, for shells around vacuum and shells surrounding noncharged black holes.
Hierarchic plate and shell models based on p-extension
NASA Technical Reports Server (NTRS)
Szabo, Barna A.; Sahrmann, Glenn J.
1988-01-01
Formulations of finite element models for beams, arches, plates and shells based on the principle of virtual work was studied. The focus is on computer implementation of hierarchic sequences of finite element models suitable for numerical solution of a large variety of practical problems which may concurrently contain thin and thick plates and shells, stiffeners, and regions where three dimensional representation is required. The approximate solutions corresponding to the hierarchic sequence of models converge to the exact solution of the fully three dimensional model. The stopping criterion is based on: (1) estimation of the relative error in energy norm; (2) equilibrium tests, and (3) observation of the convergence of quantities of interest.
Nonlinear behavior of shells of revolution under cyclic loading.
NASA Technical Reports Server (NTRS)
Levine, H. S.; Armen, H., Jr.; Winter, R.; Pifko, A.
1973-01-01
A large deflection elastic-plastic analysis is presented applicable to orthotropic axisymmetric plates and shells of revolution subjected to monotonic and cyclic loading conditions. The analysis is based on the finite-element method. It employs a new higher order, fully compatible, doubly curved orthotropic shell-of-revolution element using cubic Hermitian expansions for both meridional and normal displacements. Both perfectly plastic and strain hardening behavior are considered. Strain hardening is incorporated through use of the Prager-Ziegler kinematic hardening theory, which predicts an ideal Bauschinger effect. Numerous sample problems involving monotonic and cyclic loading conditions are analyzed.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 7 Agriculture 2 2010-01-01 2010-01-01 false Split shell. 51.2002 Section 51.2002 Agriculture... Standards for Grades of Filberts in the Shell 1 Definitions § 51.2002 Split shell. Split shell means a shell... of the shell, measured in the direction of the crack....
Cai, Fei; Sutter, Markus; Bernstein, Susan L; Kinney, James N; Kerfeld, Cheryl A
2015-04-17
Bacterial microcompartments (BMCs) are self-assembling organelles composed entirely of protein. Depending on the enzymes they encapsulate, BMCs function in either inorganic carbon fixation (carboxysomes) or organic carbon utilization (metabolosomes). The hallmark feature of all BMCs is a selectively permeable shell formed by multiple paralogous proteins, each proposed to confer specific flux characteristics. Gene clusters encoding diverse BMCs are distributed broadly across bacterial phyla, providing a rich variety of building blocks with a predicted range of permeability properties. In theory, shell permeability can be engineered by modifying residues flanking the pores (symmetry axes) of hexameric shell proteins or by combining shell proteins from different types of BMCs into chimeric shells. We undertook both approaches to altering shell properties using the carboxysome as a model system. There are two types of carboxysomes, α and β. In both, the predominant shell protein(s) contain a single copy of the BMC domain (pfam00936), but they are significantly different in primary structure. Indeed, phylogenetic analysis shows that the two types of carboxysome shell proteins are more similar to their counterparts in metabolosomes than to each other. We solved high resolution crystal structures of the major shell proteins, CsoS1 and CcmK2, and the presumed minor shell protein CcmK4, representing both types of cyanobacterial carboxysomes and then tested the interchangeability. The in vivo study presented here confirms that both engineering pores to mimic those of other shell proteins and the construction of chimeric shells is feasible.
The computer in shell stability analysis
NASA Technical Reports Server (NTRS)
Almroth, B. O.; Starnes, J. H., Jr.
1975-01-01
Some examples in which the high-speed computer has been used to improve the static stability analysis capability for general shells are examined. The fundamental concepts of static stability are reviewed with emphasis on the differences between linear bifurcation buckling and nonlinear collapse. The analysis is limited to the stability of conservative systems. Three examples are considered. The problem of cylinders subjected to bending loads is used as an example to illustrate that a simple structure can have a sufficiently complicated nonlinear behavior to require a computer analysis for accurate results. An analysis of the problems involved in the modeling of stiffening elements in plate and shell structures illustrates the necessity that the analyst recognizes all important deformation modes. The stability analysis of the Skylab structure indicates the size of problems that can be solved with current state-of-the-art capability.
Chemistry of the superheavy elements.
Schädel, Matthias
2015-03-13
The quest for superheavy elements (SHEs) is driven by the desire to find and explore one of the extreme limits of existence of matter. These elements exist solely due to their nuclear shell stabilization. All 15 presently 'known' SHEs (11 are officially 'discovered' and named) up to element 118 are short-lived and are man-made atom-at-a-time in heavy ion induced nuclear reactions. They are identical to the transactinide elements located in the seventh period of the periodic table beginning with rutherfordium (element 104), dubnium (element 105) and seaborgium (element 106) in groups 4, 5 and 6, respectively. Their chemical properties are often surprising and unexpected from simple extrapolations. After hassium (element 108), chemistry has now reached copernicium (element 112) and flerovium (element 114). For the later ones, the focus is on questions of their metallic or possibly noble gas-like character originating from interplay of most pronounced relativistic effects and electron-shell effects. SHEs provide unique opportunities to get insights into the influence of strong relativistic effects on the atomic electrons and to probe 'relativistically' influenced chemical properties and the architecture of the periodic table at its farthest reach. In addition, they establish a test bench to challenge the validity and predictive power of modern fully relativistic quantum chemical models.
Chemistry of the superheavy elements.
Schädel, Matthias
2015-03-13
The quest for superheavy elements (SHEs) is driven by the desire to find and explore one of the extreme limits of existence of matter. These elements exist solely due to their nuclear shell stabilization. All 15 presently 'known' SHEs (11 are officially 'discovered' and named) up to element 118 are short-lived and are man-made atom-at-a-time in heavy ion induced nuclear reactions. They are identical to the transactinide elements located in the seventh period of the periodic table beginning with rutherfordium (element 104), dubnium (element 105) and seaborgium (element 106) in groups 4, 5 and 6, respectively. Their chemical properties are often surprising and unexpected from simple extrapolations. After hassium (element 108), chemistry has now reached copernicium (element 112) and flerovium (element 114). For the later ones, the focus is on questions of their metallic or possibly noble gas-like character originating from interplay of most pronounced relativistic effects and electron-shell effects. SHEs provide unique opportunities to get insights into the influence of strong relativistic effects on the atomic electrons and to probe 'relativistically' influenced chemical properties and the architecture of the periodic table at its farthest reach. In addition, they establish a test bench to challenge the validity and predictive power of modern fully relativistic quantum chemical models. PMID:25666065
Relativistic shell model calculations
NASA Astrophysics Data System (ADS)
Furnstahl, R. J.
1986-06-01
Shell model calculations are discussed in the context of a relativistic model of nuclear structure based on renormalizable quantum field theories of mesons and baryons (quantum hadrodynamics). The relativistic Hartree approximation to the full field theory, with parameters determined from bulk properties of nuclear matter, predicts a shell structure in finite nuclei. Particle-hole excitations in finite nuclei are described in an RPA calculation based on this QHD ground state. The particle-hole interaction is prescribed by the Hartree ground state, with no additional parameters. Meson retardation is neglected in deriving the RPA equations, but it is found to have negligible effects on low-lying states. The full Dirac matrix structure is maintained throughout the calculation; no nonrelativistic reductions are made. Despite sensitive cancellations in the ground state calculation, reasonable excitation spectra are obtained for light nuclei. The effects of including charged mesons, problems with heavy nuclei, and prospects for improved and extended calculations are discussed.
X-ray fluorescence microtomography of SiC shells
Ice, G.E.; Chung, J.S.; Nagedolfeizi, M.
1997-04-01
TRISCO coated fuel particles contain a small kernel of nuclear fuel encapsulated by alternating layers of C and SiC. The TRISCO coated fuel particle is used in an advanced fuel designed for passive containment of the radioactive isotopes. The SiC layer provides the primary barrier for radioactive elements in the kernel. The effectiveness of this barrier layer under adverse conditions is critical to containment. The authors have begun the study of SiC shells from TRISCO fuel. They are using the fluorescent microprobe beamline 10.3.1. The shells under evaluation include some which have been cycled through a simulated core melt-down. The C buffer layers and nuclear kernels of the coated fuel have been removed by laser drilling through the SiC and then exposing the particle to acid. Elements of interest include Ru, Sb, Cs, Ce and Eu. The radial distribution of these elements in the SiC shells can be attributed to diffusion of elements in the kernel during the melt-down. Other elements in the shells originate during the fabrication of the TRISCO particles.
Jung, J; Do, B C; Yang, Q D
2016-07-13
In this paper, a thermal-mechanical augmented finite-element method (TM-AFEM) has been proposed, implemented and validated for steady-state and transient, coupled thermal-mechanical analyses of complex materials with explicit consideration of arbitrary evolving cracks. The method permits the derivation of explicit, fully condensed thermal-mechanical equilibrium equations which are of mathematical exactness in the piece-wise linear sense. The method has been implemented with a 4-node quadrilateral two-dimensional (2D) element and a 4-node tetrahedron three-dimensional (3D) element. It has been demonstrated, through several numerical examples that the new TM-AFEM can provide significantly improved numerical accuracy and efficiency when dealing with crack propagation problems in 2D and 3D solids under coupled thermal-mechanical loading conditions. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'. PMID:27242303
New Tooling System for Forming Aluminum Beverage Can End Shell
NASA Astrophysics Data System (ADS)
Yamazaki, Koetsu; Otsuka, Takayasu; Han, Jing; Hasegawa, Takashi; Shirasawa, Taketo
2011-08-01
This paper proposes a new tooling system for forming shells of aluminum beverage can ends. At first, forming process of a conversional tooling system has been simulated using three-dimensional finite element models. Simulation results have been confirmed to be consistent with those of axisymmetric models, so simulations for further study have been performed using axisymmetric models to save computational time. A comparison shows that thinning of the shell formed by the proposed tooling system has been improved about 3.6%. Influences of the tool upmost surface profiles and tool initial positions in the new tooling system have been investigated and the design optimization method based on the numerical simulations has been then applied to search optimum design points, in order to minimize thinning subjected to the constraints of the geometrical dimensions of the shell. At last, the performance of the shell subjected to internal pressure has been confirmed to meet design requirements.
Nonlinear shell analyses of the space shuttle solid rocket boosters
NASA Technical Reports Server (NTRS)
Knight, Norman F., Jr.; Gillian, Ronnie E.; Nemeth, Michael P.
1989-01-01
A variety of structural analyses have been performed on the Solid Rocket Boosters (SRB's) to provide information that would contribute to the understanding of the failure which destroyed the Space Shuttle Challenger. This paper describes nonlinear shell analyses that were performed to characterize the behavior of an overall SRB structure and a segment of the SRB in the vicinity of the External Tank Attachment (ETA) ring. Shell finite element models were used that would accurately reflect the global load transfer in an SRB in a manner such that nonlinear shell collapse and ovalization could be assessed. The purpose of these analyses was to calculate the overall deflection and stress distributions for these SRB models when subjected to mechanical loads corresponding to critical times during the launch sequence. Static analyses of these SRB models were performed using a snapshot picture of the loads. Analytical results obtained using these models show no evidence of nonlinear shell collapse for the pre-liftoff loading cases considered.
Computer analysis of shells of revolution using asymptotic results
NASA Technical Reports Server (NTRS)
Steele, C. R.; Ranjan, G. V.; Goto, C.; Pulliam, T. H.
1979-01-01
It is suggested that asymptotic results for the behavior of thin shells can be incorporated in a general computer code for the analysis of a complex shell structure. The advantage when compared to existing finite difference or finite element codes is a substantial reduction in computational labor with the capability of working to a specified level of accuracy. A reduction in user preparation time and dependance on user judgment is also gained, since mesh spacing can be internally generated. The general theory is described in this paper, as well as the implementation in the computer code FAST 1 (Functional Algorithm for Shell Theory) for the analysis of the general axisymmetric shell structure with axisymmetric loading.
Finite element analysis of flexible, rotating blades
NASA Technical Reports Server (NTRS)
Mcgee, Oliver G.
1987-01-01
A reference guide that can be used when using the finite element method to approximate the static and dynamic behavior of flexible, rotating blades is given. Important parameters such as twist, sweep, camber, co-planar shell elements, centrifugal loads, and inertia properties are studied. Comparisons are made between NASTRAN elements through published benchmark tests. The main purpose is to summarize blade modeling strategies and to document capabilities and limitations (for flexible, rotating blades) of various NASTRAN elements.
Chou, Ju; Clement, Garret; Bursavich, Bradley; Elbers, Don; Cao, Baobao; Zhou, Weilie
2010-06-01
The aim of this study was the multi-elemental detection of toxic metals such as lead (Pb) in non-crushed oyster shells by using a portable X-ray fluorescence (XRF) spectrometer. A rapid, simultaneous multi-element analytical methodology for non-crushed oyster shells has been developed using a portable XRF which provides a quick, quantitative, non-destructive, and cost-effective mean for assessment of oyster shell contamination from Pb. Pb contamination in oyster shells was further confirmed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The results indicated that Pb is distributed in-homogeneously in contaminated shells. Oyster shells have a lamellar structure that could contribute to the high accumulation of Pb on oyster shells.
Non-linear dynamic analysis of anisotropic cylindrical shells
Lakis, A.A.; Selmane, A.; Toledano, A.
1996-12-01
A theory to predict the influence of geometric non-linearities on the natural frequencies of an empty anisotropic cylindrical shell is presented in this paper. It is a hybrid of finite element and classical thin shell theories. Sanders-Koiter non-linear and strain-displacement relations are used. Displacement functions are evaluated using linearized equations of motion. Modal coefficients are then obtained for these displacement functions. Expressions for the mass, linear and non-linear stiffness matrices are derived through the finite element method. The uncoupled equations are solved with the help of elliptic functions. The period and frequency variations are first determined as a function of shell amplitudes and then compared with the results in the literature.
Onset and Cessation of Thermal Convection within Titan's Ice Shell
NASA Astrophysics Data System (ADS)
Mitri, G.; Tobie, G.; Choblet, G.
2015-12-01
The onset of thermal convection within the outer ice shell of Titan is believed to be at the origin of methane outgassing on Titan (Tobie et al., 2006), a possible factor in Titan's resurfacing processes (Mitri et al., 2008), and to have a major role in the evolution and tectonic activity of this Saturnian icy satellite (Tobie et al., 2005; Mitri and Showman, 2008; Mitri et al., 2010). Recent measurements of the gravity field (Iess et al., 2010, 2012) and the modeling of the shape and topography (Zebker et al., 2009; Mitri et al., 2014) have recently improved our knowledge of the thermal state and structure of Titan's outer ice shell. Mitri et al. (2014) found that Titan's surface topography is consistent with an isostatically compensated ice shell of variable thickness, likely at the present in a thermally conductive state (see also Nimmo and Bills, 2010; Hemingway et al., 2013), overlying a relatively dense (~1200-1350 kg m-3) subsurface ocean. As Titan's ice shell is not currently experiencing thermal convection it is likely that the ice shell could have experienced during its history both the onset and the cessation of thermal convection; thermal convection could be present within the ice shell for limited times or in fact be episodic. We investigate the evolution of Titan's outer ice shell from the crystallization of the underlying ocean with a focus on the onset and cessation of thermal convection. To simulate convection in a growing ice shell, we numerically solve the thermal convection equations for a Newtonian rheology in a two dimensional Cartesian domain using finite element method, with a moving bottom boundary to ocean crystallization. We discuss how the crystallization process affects the onset of convection and in which conditions the cessation of thermal convection may occur. The geological consequences of the changes of the thermal state and structure of the outer ice shell will also be discussed.
Effects of alga polysaccharide capsule shells on in-vivo bioavailability and disintegration
NASA Astrophysics Data System (ADS)
Li, Ting; Guo, Shuju; Ma, Lin; Yuan, Yi; Han, Lijun
2012-01-01
Gelatin has been used in hard capsule shells for more than a century, and some shortcomings have appeared, such as high moisture content and risk of transmitting diseases of animal origin to people. Based on available studies regarding gelatin and vegetable shells, we developed a new type of algal polysaccharide capsule (APPC) shells. To test whether our products can replace commercial gelatin shells, we measured in-vivo plasma concentration of 12 selected volunteers with a model drug, ibuprofen, using high performance liquid chromatography (HPLC), by calculating the relative bioavailability of APPC and Qualicaps® referenced to gelatin capsules and assessing bioequivalence of the three types of shells, and calculated pharmacokinetic parameters with the software DAS 2.0 (China). The results show that APPC shells possess bioequivalence with Qualicaps® and gelatin shells. Moreover, the disintegration behavior of four types of shells (APPC, Vegcaps®, Qualicaps® and gelatin shells) with the content of lactose and radioactive element (99mTc) was observed via gamma-scintigraphic images. The bioavailability and gamma-scintigraphic studies showed that APPC was not statistically different from other vegetable and gelatin capsule shells with respect to in-vivo behavior. Hence, it can be concluded that APPCs are exchangeable with other vegetable and gelatin shells.
Effects of Imperfections on the Buckling Response of Compression-Loaded Composite Shells
NASA Technical Reports Server (NTRS)
Hilburger, Mark W.; Starnes, James H., Jr.
2000-01-01
The results of an experimental and numerical study of the effects of imperfections on the buckling response of unstiffened thin-walled composite cylindrical shells are presented. Results that identify the individual and combined effects of traditional initial geometric shell-wall imperfections and non-traditional shell-wall thickness variations, shell-end geometric imperfections and variations in loads applied to the ends of the shells on the shell buckling response are included. In addition, results illustrating the effects of manufacturing flaws in the form of gaps between adjacent pieces of graphite-epoxy tape in some of the laminate plies are presented in detail. The shells have been analyzed with a nonlinear finite-element analysis code that accurately accounts for these effects on the buckling and nonlinear responses of the shells. The numerical results indicate that traditional and nontraditional initial imperfections can cause a significant reduction in the buckling load of a compression-loaded composite shell. Furthermore, the results indicate that the imperfections couple in a nonlinear manner. The numerical results correlate well with the experimental results. The nonlinear analysis results are also compared to the results from a traditional linear bifurcation buckling analysis. The results suggest that the nonlinear analysis procedure can be used for determining accurate, high-fidelity design knockdown factors for shell buckling and collapse. The results can also be used to determine the effects of manufacturing tolerances on the buckling response of composite shells.
Flow-induced instabilities of shells of revolution with non-zero Gaussian curvatures conveying fluid
NASA Astrophysics Data System (ADS)
Chang, Gary Han; Modarres-Sadeghi, Yahya
2016-02-01
We study flow-induced instabilities of axis-symmetric shells of revolution with an arbitrary meridian and non-zero Gaussian curvatures. We consider a fluid-structure interaction (FSI) model based on an inviscid flow model and a thin shell theory. This FSI model is solved using a method that combines the Galerkin technique with the boundary element method (BEM). The present method is capable of investigating the dynamic behavior of doubly-curved shells in contact with flow without the need for an analytical solution of the perturbed flow potential. Shells of revolution with different values of non-zero Gaussian curvatures are investigated and their behavior is compared to shells with zero Gaussian curvature. It is found that the added mass natural frequencies of shells of revolution are larger than those of conical shells with the same inlet, outlet and length. Shells of revolution, with both positive and negative Gaussian curvatures, lose their instability by buckling, however, shells with negative Gaussian curvatures buckle at modes similar to those observed in uniform and conical shells, while shells with positive Gaussian curvatures buckle with localized deformations close to the area with higher local flow velocities.
3-D Finite Element Code Postprocessor
1996-07-15
TAURUS is an interactive post-processing application supporting visualization of finite element analysis results on unstructured grids. TAURUS provides the ability to display deformed geometries and contours or fringes of a large number of derived results on meshes consisting of beam, plate, shell, and solid type finite elements. Time history plotting is also available.
The structure of circumstellar shells
NASA Technical Reports Server (NTRS)
Fix, John D.
1993-01-01
This document provides a report on research activities carried out with the support of NASA grant NAG 5-1174, the Structure of Circumstellar Shells, funded under the Astrophysics Data Program. The research carried out with the support of this grant is a study of the properties of circumstellar dust shells for which spectra are available through IRAS low resolution spectrometry (LRS). This research consisted of the development and application of models of axisymmetric circumstellar shells and a preliminary survey of the applicability of neural nets for analysis of the IRAS LRS spectra of circumstellar dust shells.
Production and Identification of Transactinide Elements
NASA Astrophysics Data System (ADS)
Münzenberg, G.; Gupta, M.
Microscopic nuclear theories predict a region of superheavy elements (SHEs) at the next doubly magic shell closure above 208Pb. Early models locate the shell closure at Z = 114, more recent calculations place it at Z = 120. The closed neutron shell is located at N = 184. These predictions motivated the search for superheavy elements in nature and in the laboratory to explore the limits of the chart of nuclides toward its upper end. A new region of shell stabilization, centered at Z = 108 and N = 162 has been discovered. It interconnects the transuranium region and the superheavy elements. As of 2009, the heaviest element accepted by the Union of Pure and Applied Chemistry is Z = 112. The discovery of elements 113 to 116 and 118 has been reported. All of these elements have been created by the complete fusion of heavy ions. Production rates decrease to less than one atom per month for the heaviest species. Half-lives range down to below microseconds. The elements at the top of the nuclear chart have been discovered on the basis of single-atom decays after separation in-flight. The production and investigation of the transactinide elements with Z = 104 and beyond form the subject matter of this chapter. After a brief history of their discoveries and experimental methods, nuclear structure and the production of heavy elements will be discussed. The prospects for the synthesis and investigation of heavy elements using advanced technologies such as new high-current heavy-ion accelerators, radioactive beams, and ion traps will be outlined. The importance of closed nuclear shells for the existence and production of the heaviest elements will be addressed briefly.
Equations of nonlinear dynamics of elastic shells in cylindrical Eulerian coordinates
NASA Astrophysics Data System (ADS)
Zubov, L. M.
2016-05-01
The equations of dynamics of elastic shells subjected to large deformations are formulated. The Eulerian coordinates on a circular cylinder and time are accepted as independent variables, and one of the unknown functions is the distance from a point of the shell surface to the cylinder axis. The equations of dynamics of nonlinearly elastic shells in the Eulerian coordinates are convenient for exact formulation of the problem on the interaction of strongly deformable shells with moving fluids and gases. The equations obtained can be used for dynamic calculations of fluids and gases flowings in pipelines, blood vessels, hoses, and other nonlinearly deformable thin-walled tubular elements of constructions.
Fiber optic well monitoring for Shell`s North Sea field
1995-12-01
After eight years of development work, Alcatel Kabel Norge has reached an agreement with Shell U.K. Exploration and Production to install Alcatel`s first commercial Sub-Sea Fiber Optic Well Monitoring (FOWM) system in Shell`s Guillemot A-OP2 well on its completion in August 1996. The FOWM project was started in 1988 by Norske Shell and Alcatel. BP Norway joined the project in 1991, and additional support has been contributed by Norsk Hydro and the Norwegian Research Council. The first Alcatel FOWM system was installed in onshore gas Well 7 in NAM`s Sleen field in the Netherlands in October 1993. The final offshore test took place in late 1994, in BP Norway`s Well 2/1 A-32 in Gyda field, in the Norwegian North Sea. FOWM is a new type of permanently installed downhole monitoring system based on an optical sensor system integrating simple passive silicon resonator sensors with optical communication. The system tolerates high pressure and high temperatures (HPHT). Main elements that contribute to its high reliability are discussed.
Gas distribution and starbursts in shell galaxies
NASA Technical Reports Server (NTRS)
Weil, Melinda L.; Hernquist, Lars
1993-01-01
Detailed maps of most elliptical galaxies reveal that, whereas the greatest part of their luminous mass originates from a smooth distribution with a surface brightness approximated by a de Vaucouleurs law, a small percentage of their light is contributed by low surface brightness distortions termed 'fine structures'. The sharp-edged features called 'shells' are successfully reproduced by merger and infall models involving accretion from less massive companions. In this context, dwarf spheroidal and compact disk galaxies are likely progenitors of these stellar phenomena. However, it is probable that the sources of shell-forming material also contain significant amounts of gas. This component may play an important role in constraining the formation and evolution of shell galaxies. To investigate the effects of the gaseous component, numerical simulations were performed to study the tidal disruption of dwarf galaxies containing both gas and stars by more massive primaries, and the evolution of the ensuing debris. The calculations were performed with a hybrid N-body/hydrodynamics code. Collisionless matter is evolved using a conventional N-body technique and gas is treated using smoothed particle hydrodynamics in which self-gravitating fluid elements are represented as particles evolving according to Lagrangian hydrodynamic equations. An isothermal equation of state is employed so the gas remains at a temperature 104 K. Owing to the large mass ratio between the primary and companion, the primary is modeled as a rigid potential and the self-gravity of both galaxies is neglected.
Automated shell theory for rotating structures (ASTROS)
NASA Technical Reports Server (NTRS)
Foster, B. J.; Thomas, J. M.
1971-01-01
A computer program for analyzing axisymmetric shells with inertial forces caused by rotation about the shell axis is developed by revising the STARS II shell program. The basic capabilities of the STARS II shell program, such as the treatment of the branched shells, stiffened wall construction, and thermal gradients, are retained.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 7 Agriculture 2 2010-01-01 2010-01-01 false Shell. 51.2289 Section 51.2289 Agriculture Regulations... Standards for Shelled English Walnuts (Juglans Regia) Definitions § 51.2289 Shell. Shell means the outer shell and/or the woody partition from between the halves of the kernel, and any fragments of either....
Fracture mechanics analyses of partial crack closure in shell structures
NASA Astrophysics Data System (ADS)
Zhao, Jun
2007-12-01
This thesis presents the theoretical and finite element analyses of crack-face closure behavior in shells and its effect on the stress intensity factor under a bending load condition. Various shell geometries, such as spherical shell, cylindrical shell containing an axial crack, cylindrical shell containing a circumferential crack and shell with double curvatures, are all studied. In addition, the influence of material orthotropy on the crack closure effect in shells is also considered. The theoretical formulation is developed based on the shallow shell theory of Delale and Erdogan, incorporating the effect of crack-face closure at the compressive edges. The line-contact assumption, simulating the crack-face closure at the compressive edges, is employed so that the contact force at the closure edges is introduced, which can be translated to the mid-plane of the shell, accompanied by an additional distributed bending moment. The unknown contact force is computed by solving a mixed-boundary value problem iteratively, that is, along the crack length, either the normal displacement of the crack face at the compressive edges is equal to zero or the contact pressure is equal to zero. It is found that due to the curvature effects crack closure may not always occur on the entire length of the crack, depending on the direction of the bending load and the geometry of the shell. The crack-face closure influences significantly the magnitude of the stress intensity factors; it increases the membrane component but decreases the bending component. The maximum stress intensity factor is reduced by the crack-face closure. The significant influence of geometry and material orthotropy on rack closure behavior in shells is also predicted based on the analytical solutions. Three-dimensional FEA is performed to validate the theoretical solutions. It demonstrates that the crack face closure occurs actually over an area, not on a line, but the theoretical solutions of the stress intensity
Hi shells, supershells, shell-like objects, and ''worms''
Heiles, C.
1984-08-01
We present photographic representations of the combination of two Hi surveys, so as to eliminate the survey boundaries at Vertical BarbVertical Bar = 10/sup 0/. We also present high-contrast photographs for particular velocities to exhibit weak Hi features. All of these photographs were used to prepare a new list of Hi shells, supershells, and shell-like objects. We discuss the structure of three shell-like objects that are associated with high-velocity gas, and with gas at all velocities that is associated with radio continuum loops I, II, and III. We use spatial filtering to find wiggly gas filaments: ''worms'': crawling away from the galactic plane in the inner Galaxy. The ''worms'' are probably parts of shells that are open at the top; such shells should be good sources of hot gas for the galactic halo.
Stress and vibraton analyses of anisotropic shells of revolution
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.; Peters, Jeanne M.
1988-01-01
An efficient computational strategy is presented for reducing the cost of the stress and free vibration analyses of laminated anisotropic shells of revolution. The analytical formulation is based on a form of the Sanders-Budiansky shell theory including the effects of both the transverse shear deformation and the laminated anisotropic material response. The fundamental unknowns consist of the eight strain components, the eight stress resultants and the five generalized displacements of the shell. Each of the shell variables is expressed in terms of trigonometric functions (Fourier series) in the circumferential co-ordinate, and a three-field mixed finite element model is used for the discretization in the meridional direction. The shell response associated with a range of Fourier harmonics is approximated by a linear combination of a few global approximation vectors, which are generated at a particular value of the Fourier harmonic, within that range. The full equations of the finite element model are solved for only a single Fourier harmonic, and the response corresponding to the other Fourier harmonics is generated using a reduced system of equations with considerably fewer degrees of freedom.
Imperfection Insensitivity Analyses of Advanced Composite Tow-Steered Shells
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey; Farrokh, Babak; Stanford, Bret K.; Weaver, Paul M.
2016-01-01
Two advanced composite tow-steered shells, one with tow overlaps and another without overlaps, were previously designed, fabricated and tested in end compression, both without cutouts, and with small and large cutouts. In each case, good agreement was observed between experimental buckling loads and supporting linear bifurcation buckling analyses. However, previous buckling tests and analyses have shown historically poor correlation, perhaps due to the presence of geometric imperfections that serve as failure initiators. For the tow-steered shells, their circumferential variation in axial stiffness may have suppressed this sensitivity to imperfections, leading to the agreement noted between tests and analyses. To investigate this further, a numerical investigation was performed in this study using geometric imperfections measured from both shells. Finite element models of both shells were analyzed first without, and then, with measured imperfections that were then, superposed in different orientations around the shell longitudinal axis. Small variations in both the axial prebuckling stiffness and global buckling load were observed for the range of imperfections studied here, which suggests that the tow steering, and resulting circumferentially varying axial stiffness, may result in the test-analysis correlation observed for these shells.
Testing refined shell-model interactions in the s d shell: Coulomb excitation of 26Na
NASA Astrophysics Data System (ADS)
Siebeck, B.; Seidlitz, M.; Blazhev, A.; Reiter, P.; Altenkirch, R.; Bauer, C.; Butler, P. A.; de Witte, H.; Elseviers, J.; Gaffney, L. P.; Hess, H.; Huyse, M.; Kröll, T.; Lutter, R.; Pakarinen, J.; Pietralla, N.; Radeck, F.; Scheck, M.; Schneiders, D.; Sotty, C.; van Duppen, P.; Vermeulen, M.; Voulot, D.; Warr, N.; Wenander, F.; Miniball Collaboration; Rex-Isolde Collaboration
2015-01-01
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal s d interaction (USD) describing nuclei within the s d shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus 26Na with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive beam experiment with 26Na (T1 /2=1 ,07 s ) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with γ rays observed by the segmented MINIBALL array. Coulomb excitation cross sections of the beam have been obtained by normalization to the well known Coulomb excitation cross sections of the 104Pd target. Results: The observation of three γ -ray transitions in 26Na together with available spectroscopic data allows us to determine E 2 - and M 1 -transitional matrix elements. Results are compared to theoretical predictions. Conclusion: The improved theoretical description of 26Na could be validated. Remaining discrepancies between experimental data and theoretical predictions indicate the need for future experiments and possibly further theoretical improvements.
NASA Technical Reports Server (NTRS)
Rose, Cheryl A.; Young, Richard D.; Starnes, James H., Jr.
1999-01-01
Results of a geometrically nonlinear finite element parametric study to determine curvature correction factors or "bulging factors" that account for increased stresses due to curvature for longitudinal cracks in unstiffened pressurized cylindrical shells are presented. Geometric parameters varied in the study include the shell radius, the shell wall thickness, and the crack length. The major results are presented in graphs of the bulging factor as a function of the applied load and as a function of geometric parameters that include the shell radius, the shell thickness and the crack length. The computed bulging factors are compared with solutions based on linear shallow shell theory, and with semi-empirical solutions that approximately account for the nonlinear deformation in the vicinity of the crack. The effect of biaxial loads on the computed bulging factors is also discussed.
Biomineralisation in Mollusc shells
NASA Astrophysics Data System (ADS)
Dauphin, Y.; Cuif, J. P.; Salomé, M.; Williams, C. T.
2009-04-01
The main components of Mollusc shells are carbonate minerals: calcite and aragonite. ACC is present in larval stages. Calcite and aragonite can be secreted simultaneously by the mantle. Despite the small number of varieties, the arrangement of the mineral components is diverse, and dependant upon the taxonomy. They are also associated with organic components much more diverse, the diversity of which reflects the large taxonomic diversity. From TGA analyses, the organic content (water included) is high (>5% in some layers). The biomineralisation process is not a passive precipitation process, but is strongly controlled by the organism. The biological-genetic control is shown by the constancy of the arrangement of the layers, the mineralogy and the microstructure in a given species. Microstructural units (i.e. tablets, prisms etc.) have shapes that do not occur in non-biogenic counterparts. Nacreous tablets, for example, are flattened on their crystallographic c axis, which is normally the axis of maximum growth rate for non-biogenic aragonite. Morever, their inner structure is species-specific: the arrangements of nacreous tablets in Gastropoda - Cephalopoda, and in Bivalvia differ, and the inner arrangement of the nacreous tablets is different in ectocochlear and endocochlear Cephalopoda. The organic-mineral ratios also differ in the various layers of a shell. Differences in chemical composition also demonstrates the biological-genetic control: for example, aragonite has a low Sr content unknown in non-biogenic samples; two aragonitic layers in a shell have different Sr and Mg contents, S is higher in calcitic layers. Decalcification releases soluble (SOM) and insoluble (IOM) organic components. Insoluble components form the main part of the intercrystalline membranes, and contain proteins, polysaccharides and lipids. Soluble phases are present within the crystals and the intercrystalline membranes. These phases are composed of more or less glycosylated proteins
Foam shell cryogenic ICF target
Darling, Dale H.
1987-01-01
A uniform cryogenic layer of DT fuel is maintained in a fusion target having a low density, small pore size, low Z rigid foam shell saturated with liquid DT fuel. Capillary action prevents gravitational slumping of the fuel layer. The saturated shell may be cooled to produce a solid fuel layer.
Dynamic stability of periodic shells with moving loads
NASA Astrophysics Data System (ADS)
Ruzzene, M.; Baz, A.
2006-10-01
A moving load causes the radial displacements of an axi-symmetric shell to be several times higher than that produced by the static application of the same load. The travel velocity of the moving load affects the amplitude of the radial response and a critical velocity above which the shell response becomes unstable can be identified. A finite element model (FEM) is developed to analyze the dynamic response of axi-symmetric shells subjected to axially moving loads. The model accounts for the effect of periodically placing stiffening rings along the shell, on the dynamic response and stability characteristics of the shell. Shape functions obtained from the steady-state solution of the equation of motion for a uniform shell are utilized in the development of the FEM. The model is formulated in a reference frame moving with the load in order to enable study of the shell stability using wave propagation and attenuation criteria. Hence, the critical velocity can be identified as the minimum velocity allowing the propagation of applied perturbations. Such stability boundaries are conveniently identified through a transfer matrix formulation. The model is used to determine the critical velocities of the moving load for various arrangements and geometry of the stiffening rings. The obtained results indicate that stiffening the shell generally increases the critical velocity and generates a pattern of alternating stable and unstable regions. The presented analysis provides a viable means for designing a wide variety of stable dynamic systems operating with fast moving loads such as crane booms, robotic arms and gun barrels.
Dynamic stability of periodic shells with moving loads
NASA Astrophysics Data System (ADS)
Ruzzene, Massimo; Baz, Amr M.
2001-08-01
A moving load causes the radial displacements of an axi- symmetric shell to be several times higher than that produced by the static application of the same load. The travel velocity of the moving load affects the amplitude of the radial response and a critical velocity above which the shell response becomes unstable can be identified. A finite element model (FEM) is developed to analyze the dynamic response of axi-symmetric shells subjected to axially moving loads. The model accounts for the effect of periodically placing stiffening rings along the shell, on the dynamic response and stability characteristics of the shell. Shape functions obtained from the steady-state solution of the equation of motion for a uniform shell are utilized in the development of the FEM. The model is formulated in a reference frame moving with the load in order to enable studying the shell stability using wave propagation and attenuation criteria. Hence, the critical velocity can be identified as the minimum velocity allowing the propagation of applied perturbations. Such stability boundaries are conveniently identified through a transfer mis formulation. The model is used to determine the critical velocities of the moving load for various arrangements and geometry of the stiffening rings. The obtained results indicate that stiffening the shell generally increases the critical velocity and generates a pattern of alternating stable and unstable regions. The presented analysis provides a viable means for designing a wide variety of stable dynamic systems operating with fast moving loads such as crane booms, robotic arms and gun barrels.
NASA Technical Reports Server (NTRS)
Young, Richard D.; Rose, Cheryl A.; Starnes, James H., Jr.
2000-01-01
Results of a geometrically nonlinear finite element parametric study to determine curvature correction factors or bulging factors that account for increased stresses due to curvature for longitudinal and circumferential cracks in unstiffened pressurized cylindrical shells are presented. Geometric parameters varied in the study include the shell radius, the shell wall thickness, and the crack length. The major results are presented in the form of contour plots of the bulging factor as a function of two nondimensional parameters: the shell curvature parameter, lambda, which is a function of the shell geometry, Poisson's ratio, and the crack length; and a loading parameter, eta, which is a function of the shell geometry, material properties, and the applied internal pressure. These plots identify the ranges of the shell curvature and loading parameters for which the effects of geometric nonlinearity are significant. Simple empirical expressions for the bulging factor are then derived from the numerical results and shown to predict accurately the nonlinear response of shells with longitudinal and circumferential cracks. The numerical results are also compared with analytical solutions based on linear shallow shell theory for thin shells, and with some other semi-empirical solutions from the literature, and limitations on the use of these other expressions are suggested.
Design and Analysis of Tow-Steered Composite Shells Using Fiber Placement
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey
2008-01-01
In this study, a sub-scale advanced composite shell design is evaluated to determine its potential for use on a future aircraft fuselage. Two composite shells with the same nominal 8-ply [+/-45/+/-Theta](sub s) layup are evaluated, where Theta indicates a tow-steered ply. To build this shell, a fiber placement machine would be used to steer unidirectional prepreg tows as they are placed around the circumference of a 17-inch diameter right circular cylinder. The fiber orientation angle varies continuously from 10 degrees (with respect to the shell axis of revolution) at the crown, to 45 degrees on the side, and back to 10 degrees on the keel. All 24 tows are placed at each point on every fiber path in one structure designated as the shell with overlaps. The resulting pattern of tow overlaps causes the laminate thickness to vary between 8 and 16 plies. The second shell without tow overlaps uses the capability of the fiber placement machine to cut and add tows at any point along the fiber paths to fabricate a shell with a nearly uniform 8-ply laminate thickness. Issues encountered during the design and analysis of these shells are presented and discussed. Static stiffness and buckling loads of shells with tow-steered layups are compared with the performance of a baseline quasi-isotropic shell using both finite element analyses and classical strength of materials theory.
Design and Analysis of an X-Ray Mirror Assembly Using the Meta-Shell Approach
NASA Technical Reports Server (NTRS)
McClelland, Ryan S.; Bonafede, Joseph; Saha, Timo T.; Solly, Peter M.; Zhang, William W.
2016-01-01
Lightweight and high resolution optics are needed for future space-based x-ray telescopes to achieve advances in high-energy astrophysics. Past missions such as Chandra and XMM-Newton have achieved excellent angular resolution using a full shell mirror approach. Other missions such as Suzaku and NuSTAR have achieved lightweight mirrors using a segmented approach. This paper describes a new approach, called meta-shells, which combines the fabrication advantages of segmented optics with the alignment advantages of full shell optics. Meta-shells are built by layering overlapping mirror segments onto a central structural shell. The resulting optic has the stiffness and rotational symmetry of a full shell, but with an order of magnitude greater collecting area. Several meta-shells so constructed can be integrated into a large x-ray mirror assembly by proven methods used for Chandra and XMM-Newton. The mirror segments are mounted to the meta-shell using a novel four point semi-kinematic mount. The four point mount deterministically locates the segment in its most performance sensitive degrees of freedom. Extensive analysis has been performed to demonstrate the feasibility of the four point mount and meta-shell approach. A mathematical model of a meta-shell constructed with mirror segments bonded at four points and subject to launch loads has been developed to determine the optimal design parameters, namely bond size, mirror segment span, and number of layers per meta-shell. The parameters of an example 1.3 m diameter mirror assembly are given including the predicted effective area. To verify the mathematical model and support opto-mechanical analysis, a detailed finite element model of a meta-shell was created. Finite element analysis predicts low gravity distortion and low sensitivity to thermal gradients.
An Energy Decaying Scheme for Nonlinear Dynamics of Shells
NASA Technical Reports Server (NTRS)
Bottasso, Carlo L.; Bauchau, Olivier A.; Choi, Jou-Young; Bushnell, Dennis M. (Technical Monitor)
2000-01-01
A novel integration scheme for nonlinear dynamics of geometrically exact shells is developed based on the inextensible director assumption. The new algorithm is designed so as to imply the strict decay of the system total mechanical energy at each time step, and consequently unconditional stability is achieved in the nonlinear regime. Furthermore, the scheme features tunable high frequency numerical damping and it is therefore stiffly accurate. The method is tested for a finite element spatial formulation of shells based on mixed interpolations of strain tensorial components and on a two-parameter representation of director rotations. The robustness of the, scheme is illustrated with the help of numerical examples.
Single-shell tank retrieval program mission analysis report
Stokes, W.J.
1998-08-11
This Mission Analysis Report was prepared to provide the foundation for the Single-Shell Tank (SST) Retrieval Program, a new program responsible for waste removal for the SSTS. The SST Retrieval Program is integrated with other Tank Waste Remediation System activities that provide the management, technical, and operations elements associated with planning and execution of SST and SST Farm retrieval and closure. This Mission Analysis Report provides the basis and strategy for developing a program plan for SST retrieval. This Mission Analysis Report responds to a US Department of Energy request for an alternative single-shell tank retrieval approach (Taylor 1997).
Isogeometric shape optimisation of shell structures using multiresolution subdivision surfaces
NASA Astrophysics Data System (ADS)
Xiao, Xiao; Bandara, Kosala; Cirak, Fehmi
2016-08-01
We introduce the isogeometric shape optimisation of thin shell structures using subdivision surfaces. Both triangular Loop and quadrilateral Catmull-Clark subdivision schemes are considered for geometry modelling and finite element analysis. A gradient-based shape optimisation technique is implemented to minimise compliance, i.e. to maximise stiffness. Different control meshes describing the same surface are used for geometry representation, optimisation and finite element analysis. The finite element analysis is performed with subdivision basis functions corresponding to a sufficiently fine control mesh. During iterative shape optimisation the geometry is updated starting from the coarsest control mesh and proceeding to increasingly finer control meshes. The proposed approach is applied to three optimisation examples, namely a catenary, a roof over a rectangular domain, and free-form architectural shell roof. The influence of the geometry description and the used subdivision scheme on the obtained optimised curved geometries are investigated in detail.
Buckling and Damage Resistance of Transversely-Loaded Composite Shells
NASA Technical Reports Server (NTRS)
Wardle, Brian L.
1998-01-01
Experimental and numerical work was conducted to better understand composite shell response to transverse loadings which simulate damage-causing impact events. The quasi-static, centered, transverse loading response of laminated graphite/epoxy shells in a [+/-45(sub n)/O(sub n)](sub s) layup having geometric characteristics of a commercial fuselage are studied. The singly-curved composite shell structures are hinged along the straight circumferential edges and are either free or simply supported along the curved axial edges. Key components of the shell response are response instabilities due to limit-point and/or bifurcation buckling. Experimentally, deflection-controlled shell response is characterized via load-deflection data, deformation-shape evolutions, and the resulting damage state. Finite element models are used to study the kinematically nonlinear shell response, including bifurcation, limit-points, and postbuckling. A novel technique is developed for evaluating bifurcation from nonlinear prebuckling states utilizing asymmetric spatial discretization to introduce numerical perturbations. Advantages of the asymmetric meshing technique (AMT) over traditional techniques include efficiency, robustness, ease of application, and solution of the actual (not modified) problems. The AMT is validated by comparison to traditional numerical analysis of a benchmark problem and verified by comparison to experimental data. Applying the technique, bifurcation in a benchmark shell-buckling problem is correctly identified. Excellent agreement between the numerical and experimental results are obtained for a number of composite shells although predictive capability decreases for stiffer (thicker) specimens which is attributed to compliance of the test fixture. Restraining the axial edge (simple support) has the effect of creating a more complex response which involves unstable bifurcation, limit-point buckling, and dynamic collapse. Such shells were noted to bifurcate into
Glass shell manufacturing in space
NASA Technical Reports Server (NTRS)
Downs, R. L.; Ebner, M. A.; Nolen, R. L., Jr.
1981-01-01
Highly-uniform, hollow glass spheres (shells), which are used for inertial confinement fusion targets, were formed from metal-organic gel powder feedstock in a vertical furnace. As a result of the rapid pyrolysis caused by the furnace, the gel is transformed to a shell in five distinct stages: (a) surface closure of the porous gel; (b) generation of a closed-cell foam structure in the gel; (c) spheridization of the gel and further expansion of the foam; (d) coalescence of the closed-cell foam to a single-void shell; and (e) fining of the glass shell. The heat transfer from the furnace to the falling gel particle was modeled to determine the effective heating rate of the gel. The model predicts the temperature history for a particle as a function of mass, dimensions, specific heat, and absorptance as well as furnace temperature profile and thermal conductivity of the furnace gas. A model was developed that predicts the gravity-induced degradation of shell concentricity in falling molten shells as a function of shell characteristics and time.
Crack problems in cylindrical and spherical shells
NASA Technical Reports Server (NTRS)
Erdogan, F.
1976-01-01
Standard plate or shell theories were used as a starting point to study the fracture problems in thin-walled cylindrical and spherical shells, assuming that the plane of the crack is perpendicular to the surface of the sheet. Since recent studies have shown that local shell curvatures may have a rather considerable effect on the stress intensity factor, the crack problem was considered in conjunction with a shell rather than a plate theory. The material was assumed to be isotropic and homogeneous, so that approximate solutions may be obtained by approximating the local shell crack geometry with an ideal shell which has a solution, namely a spherical shell with a meridional crack, a cylindrical shell with a circumferential crack, or a cylindrical shell with an axial crack. A method of solution for the specially orthotropic shells containing a crack was described; symmetric and skew-symmetric problems are considered in cylindrical shells with an axial crack.
NASA Astrophysics Data System (ADS)
The Periodic Table of the elements will now have to be updated. An international team of researchers has added element 110 to the Earth's armory of elements. Though short-lived—of the order of microseconds, element 110 bottoms out the list as the heaviest known element on the planet. Scientists at the Heavy Ion Research Center in Darmstadt, Germany, made the 110-proton element by colliding a lead isotope with nickel atoms. The element, which is yet to be named, has an atomic mass of 269.
Layerwise Finite Elements for Smart Piezoceramic Composite Plates in Thermal Environments
NASA Technical Reports Server (NTRS)
Saravanos, Dimitris A.; Lee, Ho-Jun
1996-01-01
Analytical formulations are presented which account for the coupled mechanical, electrical, and thermal response of piezoelectric composite laminates and plate structures. A layerwise theory is formulated with the inherent capability to explicitly model the active and sensory response of piezoelectric composite plates having arbitrary laminate configurations in thermal environments. Finite element equations are derived and implemented for a bilinear 4-noded plate element. Application cases demonstrate the capability to manage thermally induced bending and twisting deformations in symmetric and antisymmetric composite plates with piezoelectric actuators, and show the corresponding electrical response of distributed piezoelectric sensors. Finally, the resultant stresses in the thermal piezoelectric composite laminates are investigated.
MicroShell Minimalist Shell for Xilinx Microprocessors
NASA Technical Reports Server (NTRS)
Werne, Thomas A.
2011-01-01
MicroShell is a lightweight shell environment for engineers and software developers working with embedded microprocessors in Xilinx FPGAs. (MicroShell has also been successfully ported to run on ARM Cortex-M1 microprocessors in Actel ProASIC3 FPGAs, but without project-integration support.) Micro Shell decreases the time spent performing initial tests of field-programmable gate array (FPGA) designs, simplifies running customizable one-time-only experiments, and provides a familiar-feeling command-line interface. The program comes with a collection of useful functions and enables the designer to add an unlimited number of custom commands, which are callable from the command-line. The commands are parameterizable (using the C-based command-line parameter idiom), so the designer can use one function to exercise hardware with different values. Also, since many hardware peripherals instantiated in FPGAs have reasonably simple register-mapped I/O interfaces, the engineer can edit and view hardware parameter settings at any time without stopping the processor. MicroShell comes with a set of support scripts that interface seamlessly with Xilinx's EDK tool. Adding an instance of MicroShell to a project is as simple as marking a check box in a library configuration dialog box and specifying a software project directory. The support scripts then examine the hardware design, build design-specific functions, conditionally include processor-specific functions, and complete the compilation process. For code-size constrained designs, most of the stock functionality can be excluded from the compiled library. When all of the configurable options are removed from the binary, MicroShell has an unoptimized memory footprint of about 4.8 kB and a size-optimized footprint of about 2.3 kB. Since MicroShell allows unfettered access to all processor-accessible memory locations, it is possible to perform live patching on a running system. This can be useful, for instance, if a bug is
Linear versus nonlinear theories for laminated composite plates and shells
Qatu, M.S.
1995-11-01
Linear and nonlinear shear-deformation theories for laminated composite plates and shells are discussed in this paper. The emphasis here is on the range of validity for each class of theories. The finite element method is used to determine the maximum stresses for a wide range of statically loaded plate and shell panels with various thickness ratios. This paper concludes that for the vast majority of composite materials and for moderately thick plates and shells, stresses normally reach the maximum allowable stress before nonlinear terms can become important. This has been demonstrated by showing that for the limiting case of shear deformation theories (in which the minimum span length (or radius) to thickness ratio is 20), the material usually fails before the maximum deflection reaches the magnitude of the thickness (where nonlinear terms start to become significant).
Passively Damped Laminated Piezoelectric Shell Structures with Integrated Electric Networks
NASA Technical Reports Server (NTRS)
Saravanos, Dimitris A.
1999-01-01
Multi-field mechanics are presented for curvilinear piezoelectric laminates interfaced with distributed passive electric components. The equations of motion for laminated piezoelectric shell structures with embedded passive electric networks are directly formulated and solved using a finite element methodology. The modal damping and frequencies of the piezoelectric shell are calculated from the poles of the system. Experimental and numerical results are presented for the modal damping and frequency of composite beams with a resistively shunted piezoceramic patch. The modal damping and frequency of plates, cylindrical shells and cylindrical composite blades with piezoelectric-resistor layers are predicted. Both analytical and experimental studies illustrate a unique dependence of modal damping and frequencies on the shunting resistance and show the effect of structural shape and curvature on piezoelectric damping.
Chemical effect on the K shell absorption parameters of some selected cerium compounds
NASA Astrophysics Data System (ADS)
Akman, F.; Kaçal, M. R.; Durak, R.
2016-08-01
In this study, the photoelectric cross section values of Ce, CeCl3.7H2O, Ce2(SO4)3, Ce(OH)4 and Ce2O3 samples were measured in the energy range from 31.82 keV up to 51.70 keV by adopting in narrow beam geometry. Using these photoelectric cross sections, the K shell photoelectric cross sections at the K-edge, the K shell absorption jump ratios and jump factors, the Davisson-Kirchner ratios and K shell oscillator strength values were estimated experimentally. The measured parameters were compared with the theoretical calculated values. It is observed that the K shell photoelectric cross section at the K-edge and K shell oscillator strength values of an element are affected by the chemical environment of material while the K shell absorption jump ratio, K shell absorption jump factor and Davisson-Kirchner ratio are not affected by the chemical environment of material for the present samples. To the best of our knowledge, the chemical effects on the Davisson-Kirchner ratio and K shell oscillator strength have not been discussed for any element by now.
Insulative laser shell coupler
Arnold, Phillip A.; Anderson, Andrew T.; Alger, Terry W.
1994-01-01
A segmented coaxial laser shell assembly having at least two water jacket sections, two pairs of interconnection half rings, a dialectric break ring, and a pair of threaded ring sections. Each water jacket section with an inner tubular section that defines an inner laser cavity with water paths adjacent to at least a portion of the exterior of the inner tubular section, and mating faces at the end of the water jacket section through which the inner laser cavity opens and which defines at least one water port therethrough in communication with the water jackets. The water paths also define in their external surface a circumferential notch set back from and in close proximity to the mating face. The dielectric break ring has selected thickness and is placed between, and in coaxial alignment with, the mating faces of two of the adjacent water jacket sections. The break ring also defines an inner laser cavity of the same size and shape as the inner laser cavity of the water jacket sections and at least one water passage through the break ring to communicate with at least one water port through the mating faces of the water jacket sections.
Insulative laser shell coupler
Arnold, P.A.; Anderson, A.T.; Alger, T.W.
1994-09-20
A segmented coaxial laser shell assembly having at least two water jacket sections, two pairs of interconnection half rings, a dielectric break ring, and a pair of threaded ring sections is disclosed. Each water jacket section with an inner tubular section that defines an inner laser cavity with water paths adjacent to at least a portion of the exterior of the inner tubular section, and mating faces at the end of the water jacket section through which the inner laser cavity opens and which defines at least one water port therethrough in communication with the water jackets. The water paths also define in their external surface a circumferential notch set back from and in close proximity to the mating face. The dielectric break ring has selected thickness and is placed between, and in coaxial alignment with, the mating faces of two of the adjacent water jacket sections. The break ring also defines an inner laser cavity of the same size and shape as the inner laser cavity of the water jacket sections and at least one water passage through the break ring to communicate with at least one water port through the mating faces of the water jacket sections. 4 figs.
Stellar Populations of Shell Galaxies
NASA Astrophysics Data System (ADS)
Carlsten, Scott; Zenteno, Alfredo
2016-01-01
We present a study of the inner (out to ˜1 effective radius) stellar populations in a sample of 9 shell galaxies. We derive stellar population parameters from long slit spectra by both analyzing the Lick indices of the galaxies and by fitting high resolution SSP model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. We find the presence of young stellar populations in several of the galaxies, implying recent star formation and allowing us to speculate on the age of the shells. Analyzing the metallicity gradients in our sample, we find an average metallicity gradient of -0.16±0.10 dex/decade in radius. Finally, we compare this with galaxy evolution models to try to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers in their past but it is unclear whether the shells formed from these events or from separate minor mergers.
Collapsing thin shells with rotation
NASA Astrophysics Data System (ADS)
Delsate, Térence; Rocha, Jorge V.; Santarelli, Raphael
2014-06-01
We construct exact solutions describing the motion of rotating thin shells in a fully backreacted five-dimensional rotating black hole spacetime. The radial equation of motion follows from the Darmois-Israel junction conditions, where both interior and exterior geometries are taken to be equal angular momenta Myers-Perry solutions. We show that rotation generates anisotropic pressures and momentum along the shell. Gravitational collapse scenarios including rotation are analyzed and a new class of stationary solutions is introduced. Energy conditions for the anisotropic matter shell are briefly discussed. We find that the weak energy condition is not violated for the collapse scenario where the shell starts at rest from infinity, nor for the new class of stationary solutions in anti-de Sitter. We further prove that the cosmic censorship conjecture is always satisfied in our setup.
7 CFR 996.19 - Shelled peanuts.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 8 2012-01-01 2012-01-01 false Shelled peanuts. 996.19 Section 996.19 Agriculture... STANDARDS FOR DOMESTIC AND IMPORTED PEANUTS MARKETED IN THE UNITED STATES Definitions § 996.19 Shelled peanuts. Shelled peanuts means the kernels or portions of kernels of peanuts after the shells are removed....
7 CFR 996.19 - Shelled peanuts.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 8 2014-01-01 2014-01-01 false Shelled peanuts. 996.19 Section 996.19 Agriculture... STANDARDS FOR DOMESTIC AND IMPORTED PEANUTS MARKETED IN THE UNITED STATES Definitions § 996.19 Shelled peanuts. Shelled peanuts means the kernels or portions of kernels of peanuts after the shells are removed....
7 CFR 996.19 - Shelled peanuts.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 8 2013-01-01 2013-01-01 false Shelled peanuts. 996.19 Section 996.19 Agriculture... STANDARDS FOR DOMESTIC AND IMPORTED PEANUTS MARKETED IN THE UNITED STATES Definitions § 996.19 Shelled peanuts. Shelled peanuts means the kernels or portions of kernels of peanuts after the shells are removed....
Structural Performance of Advanced Composite Tow-Steered Shells With Cutouts
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey; Turpin, Jason D.; Stanford, Bret K.; Martin, Robert A.
2014-01-01
The structural performance of two advanced composite tow-steered shells with cutouts, manufactured using an automated fiber placement system, is assessed using both experimental and analytical methods. The shells' fiber orientation angles vary continuously around their circumference from +/-10 degrees on the crown and keel, to +/-45 degrees on the sides. The raised surface features on one shell result from application of all 24 tows during each fiber placement system pass, while the second shell uses the system's tow drop/add capability to achieve a more uniform wall thickness. These unstiffened shells were previously tested in axial compression and buckled elastically. A single cutout, scaled to represent a passenger door on a commercial aircraft, is then machined into one side of each shell. The prebuckling axial stiffnesses and bifurcation buckling loads of the shells with cutouts are also computed using linear finite element structural analyses for initial comparisons with test data. When retested, large deflections were observed around the cutouts, but the shells carried an average of 92 percent of the axial stiffness, and 86 percent of the buckling loads, of the shells without cutouts. These relatively small reductions in performance demonstrate the potential for using tow steering to mitigate the adverse effects of typical design features on the overall structural performance.
Structural Characterization of Advanced Composite Tow-Steered Shells with Large Cutouts
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey; Turpin, Jason D.; Gardner, Nathaniel W.; Stanford, Bret K.; Martin, Robert A.
2015-01-01
The structural performance of two advanced composite tow-steered shells with large cutouts, manufactured using an automated fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles of the shells vary continuously around their circumference from +/- 10 degrees on the crown and keel, to +/- 45 degrees on the sides. The raised surface features on one shell result from application of all 24 tows during each fiber placement system pass, while the second shell uses the tow drop/add capability of the system to achieve a more uniform wall thickness. These unstiffened shells, both without and with small cutouts, were previously tested in axial compression and buckled elastically. In this study, a single unreinforced cutout, scaled to represent a cargo door on a commercial aircraft, is machined into one side of each shell. The prebuckling axial stiffnesses and bifurcation buckling loads of these shells with large cutouts are also computed using linear finite element structural analyses for preliminary comparisons with test data. During testing, large displacements are observed around the large cutouts, but the shells maintain an average of 91 percent of the axial stiffness, and also carry 85 percent of the buckling loads, when compared to the pristine shells without cutouts. These relatively small reductions indicate that there is great potential for using tow steering to mitigate the adverse effects of large cutouts on the overall structural performance.
Koto, Yusuke; Kano, Naoki; Wang, Yudan; Sakamoto, Nobuo; Imaizumi, Hiroshi
2010-01-01
Biosorption experiment from aqueous solutions containing known amount of rare earth elements (REEs) using pre-treated Buccinum tenuissimum shell was explored to evaluate the efficiency of shell biomass as sorbent for REEs. In this work, four kinds of sieved shell samples: (a) “Ground original sample”, (b) “Heat-treatment (480°C, 6 hours) sample”, (c) “Heat-treatment (950°C, 6 hours) sample” and (d) “Heat-treatment (950°C, 6 hours) and water added sample” were used. Furthermore, to confirm the characteristics of the shell biomass, the crystal structure, the surface morphology, and the specific surface area of these shell samples were determined. Consequently, the following matters have been mainly clarified. (1) The crystal structure of the shell biomass was transformed from aragonite (CaCO3) into calcite (CaCO3) phase by heat-treatment (480°C, 6 hours); then mainly transformed into calcium oxide (CaO) by heat-treatment (950°C, 6 hours), and calcium hydroxide (Ca(OH)2) by heat-treatment (950°C, 6 hours) and adding water. (2) The shell biomass showed excellent sorption capacity for lanthanides. (3) Adsorption isotherms using the shell biomass can be described by Langmuir and Freundlich isotherms satisfactorily for lanthanides except “heat-treatment (950°C, 6 hours) sample”. (4) Shell biomass (usually treated as waste material) can be an efficient sorbent for lanthanides in future. PMID:20981250
Koto, Yusuke; Kano, Naoki; Wang, Yudan; Sakamoto, Nobuo; Imaizumi, Hiroshi
2010-01-01
Biosorption experiment from aqueous solutions containing known amount of rare earth elements (REEs) using pre-treated Buccinum tenuissimum shell was explored to evaluate the efficiency of shell biomass as sorbent for REEs. In this work, four kinds of sieved shell samples: (a) "Ground original sample", (b) "Heat-treatment (480°C, 6 hours) sample", (c) "Heat-treatment (950°C, 6 hours) sample" and (d) "Heat-treatment (950°C, 6 hours) and water added sample" were used. Furthermore, to confirm the characteristics of the shell biomass, the crystal structure, the surface morphology, and the specific surface area of these shell samples were determined. Consequently, the following matters have been mainly clarified. (1) The crystal structure of the shell biomass was transformed from aragonite (CaCO(3)) into calcite (CaCO(3)) phase by heat-treatment (480°C, 6 hours); then mainly transformed into calcium oxide (CaO) by heat-treatment (950°C, 6 hours), and calcium hydroxide (Ca(OH)(2)) by heat-treatment (950°C, 6 hours) and adding water. (2) The shell biomass showed excellent sorption capacity for lanthanides. (3) Adsorption isotherms using the shell biomass can be described by Langmuir and Freundlich isotherms satisfactorily for lanthanides except "heat-treatment (950°C, 6 hours) sample". (4) Shell biomass (usually treated as waste material) can be an efficient sorbent for lanthanides in future.
Deformation of compound shells under action of internal shock wave loading
NASA Astrophysics Data System (ADS)
Chernobryvko, Marina; Kruszka, Leopold; Avramov, Konstantin
2015-09-01
The compound shells under the action of internal shock wave loading are considered. The compound shell consists of a thin cylindrical shell and two thin parabolic shells at the edges. The boundary conditions in the shells joints satisfy the equality of displacements. The internal shock wave loading is modelled as the surplus pressure surface. This pressure is a function of the shell coordinates and time. The strain rate deformation of compound shell takes place in both the elastic and in plastic stages. In the elastic stage the equations of the structure motions are obtained by the assumed-modes method, which uses the kinetic and potential energies of the cylindrical and two parabolic shells. The dynamic behaviour of compound shells is treated. In local plastic zones the 3-D thermo-elastic-plastic model is used. The deformations are described by nonlinear model. The stress tensor elements are determined using dynamic deformation theory. The deformation properties of materials are influenced by the strain rate behaviour, the influence of temperature parameters, and the elastic-plastic properties of materials. The dynamic yield point of materials and Pisarenko-Lebedev's criterion of destruction are used. The modified adaptive finite differences method of numerical analysis is suggested for those simulations. The accuracy of the numerical simulation is verified on each temporal step of calculation and in the case of large deformation gradients.
Marine bivalve geochemistry and shell ultrastructure from modern low pH environments
NASA Astrophysics Data System (ADS)
Hahn, S.; Rodolfo-Metalpa, R.; Griesshaber, E.; Schmahl, W. W.; Buhl, D.; Hall-Spencer, J. M.; Baggini, C.; Fehr, K. T.; Immenhauser, A.
2011-10-01
Bivalve shells can provide excellent archives of past environmental change but have not been used to interpret ocean acidification events. We investigated carbon, oxygen and trace element records from different shell layers in the mussels Mytilus galloprovincialis (from the Mediterranean) and M. edulis (from the Wadden Sea) combined with detailed investigations of the shell ultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy) were transplanted and grown in water with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the east coast of the island of Ischia. The shells of transplanted mussels were compared with M. edulis collected at pH ~8.2 from Sylt (German Wadden Sea). Most prominently, the shells recorded the shock of transplantation, both in their shell ultrastructure, textural and geochemical record. Shell calcite, precipitated subsequently under acidified seawater responded to the pH gradient by an in part disturbed ultrastructure. Geochemical data from all test sites show a strong metabolic effect that exceeds the influence of the low-pH environment. These field experiments showed that care is needed when interpreting potential ocean acidification signals because various parameters affect shell chemistry and ultrastructure. Besides metabolic processes, seawater pH, factors such as salinity, water temperature, food availability and population density all affect the biogenic carbonate shell archive.
A violin shell model: vibrational modes and acoustics.
Gough, Colin E
2015-03-01
A generic physical model for the vibro-acoustic modes of the violin is described treating the body shell as a shallow, thin-walled, guitar-shaped, box structure with doubly arched top and back plates. comsol finite element, shell structure, software is used to identify and understand the vibrational modes of a simply modeled violin. This identifies the relationship between the freely supported plate modes when coupled together by the ribs and the modes of the assembled body shell. Such coupling results in a relatively small number of eigenmodes or component shell modes, of which a single volume-changing breathing mode is shown to be responsible for almost all the sound radiated in the monopole signature mode regime below ∼1 kHz for the violin, whether directly or by excitation of the Helmholtz f-hole resonance. The computations describe the influence on such modes of material properties, arching, plate thickness, elastic anisotropy, f-holes cut into the top plate, the bass-bar, coupling to internal air modes, the rigid neck-fingerboard assembly, and, most importantly, the soundpost. Because the shell modes are largely determined by the symmetry of the guitar-shaped body, the model is applicable to all instruments of the violin family. PMID:25786935
A violin shell model: vibrational modes and acoustics.
Gough, Colin E
2015-03-01
A generic physical model for the vibro-acoustic modes of the violin is described treating the body shell as a shallow, thin-walled, guitar-shaped, box structure with doubly arched top and back plates. comsol finite element, shell structure, software is used to identify and understand the vibrational modes of a simply modeled violin. This identifies the relationship between the freely supported plate modes when coupled together by the ribs and the modes of the assembled body shell. Such coupling results in a relatively small number of eigenmodes or component shell modes, of which a single volume-changing breathing mode is shown to be responsible for almost all the sound radiated in the monopole signature mode regime below ∼1 kHz for the violin, whether directly or by excitation of the Helmholtz f-hole resonance. The computations describe the influence on such modes of material properties, arching, plate thickness, elastic anisotropy, f-holes cut into the top plate, the bass-bar, coupling to internal air modes, the rigid neck-fingerboard assembly, and, most importantly, the soundpost. Because the shell modes are largely determined by the symmetry of the guitar-shaped body, the model is applicable to all instruments of the violin family.
Mesoscale modeling of functional properties in core-shell nanoparticles
NASA Astrophysics Data System (ADS)
Mangeri, John; Heinonen, Olle; Karpeev, Dmitry; Nakhmanson, Serge
2015-03-01
Core-shell nanoparticle systems of Zn-ZnO and ZnO-TiO2 are studied computationally using the highly scalable MOOSE finite-element framework, developed at Idaho National Lab. The elastic anisotropic mismatch of the core and shell create an imprinting effect within the shell that produces a wide variation of strains. Due to this diversity of strains, the sharp band gap edges of the bulk semiconductor are observed to be ``thinned-out'' much like amorphous silicon. We show that a variety of factors, such as particle size, core-to-shell volume ratio, applied hydrostatic pressure, shell microstructure, as well as the effect of surface elasticity, can influence the distribution of optical band-gap values within the particle, which may prove useful within the field of photovoltaics. Part of the work by O.H. was supported by Award 70NANB14H012 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Material Design.
A Shell/3D Modeling Technique for the Analysis of Delaminated Composite Laminates
NASA Technical Reports Server (NTRS)
Krueger, Ronald; OBrien, T. Kevin
2000-01-01
A shell/3D modeling technique was developed for which a local solid finite element model is used only in the immediate vicinity of the delamination front. The goal was to combine the accuracy of the full three-dimensional solution with the computational efficiency of a shell finite element model. Multi-point constraints provided a kinematically compatible interface between the local 3D model and the global structural model which has been meshed with shell finite elements. Double Cantilever Beam, End Notched Flexure, and Single Leg Bending specimens were analyzed first using full 3D finite element models to obtain reference solutions. Mixed mode strain energy release rate distributions were computed using the virtual crack closure technique. The analyses were repeated using the shell/3D technique to study the feasibility for pure mode I, mode II and mixed mode I/II cases. Specimens with a unidirectional layup and with a multidirectional layup were simulated. For a local 3D model, extending to a minimum of about three specimen thicknesses on either side of the delamination front, the results were in good agreement with mixed mode strain energy release rates obtained from computations where the entire specimen had been modeled with solid elements. For large built-up composite structures the shell/3D modeling technique offers a great potential for reducing the model size, since only a relatively small section in the vicinity of the delamination front needs to be modeled with solid elements.
Slowly rotating thin shell gravastars
NASA Astrophysics Data System (ADS)
Uchikata, Nami; Yoshida, Shijun
2016-01-01
We construct the solutions of slowly rotating gravastars with a thin shell. In the zero-rotation limit, we consider the gravastar composed of a de Sitter core, a thin shell, and Schwarzschild exterior spacetime. The rotational effects are treated as small axisymmetric and stationary perturbations. The perturbed internal and external spacetimes are matched with a uniformly rotating thin shell. We assume that the angular velocity of the thin shell, Ω, is much smaller than the Keplerian frequency of the nonrotating gravastar, {{{Ω }}}{{k}}. The solutions within an accuracy up to the second order of {{Ω }}/{{{Ω }}}{{k}} are obtained. The thin shell matter is assumed to be described by a perfect fluid and to satisfy the dominant energy condition in the zero-rotation limit. In this study, we assume that the equation of state for perturbations is the same as that of the unperturbed solution. The spherically symmetric component of the energy density perturbations, δ {σ }0, is assumed to vanish independently of the rotation rate. Based on these assumptions, we obtain many numerical solutions and investigate properties of the rotational corrections to the structure of the thin shell gravastar.
A hybrid-stress element based on Hamilton principle
NASA Astrophysics Data System (ADS)
Cen, Song; Zhang, Tao; Li, Chen-Feng; Fu, Xiang-Rong; Long, Yu-Qiu
2010-08-01
A novel hybrid-stress finite element method is proposed for constructing simple 4-node quadrilateral plane elements, and the new element is denoted as HH4-3 β here. Firstly, the theoretical basis of the traditional hybrid-stress elements, i.e., the Hellinger-Reissner variational principle, is replaced by the Hamilton variational principle, in which the number of the stress variables is reduced from 3 to 2. Secondly, three stress parameters and corresponding trial functions are introduced into the system equations. Thirdly, the displacement fields of the conventional bilinear isoparametric element are employed in the new models. Finally, from the stationary condition, the stress parameters can be expressed in terms of the displacement parameters, and thus the new element stiffness matrices can be obtained. Since the required number of stress variables in the Hamilton variational principle is less than that in the Hellinger-Reissner variational principle, and no additional incompatible displacement modes are considered, the new hybrid-stress element is simpler than the traditional ones. Furthermore, in order to improve the accuracy of the stress solutions, two enhanced post-processing schemes are also proposed for element HH4-3 β. Numerical examples show that the proposed model exhibits great improvements in both displacement and stress solutions, implying that the proposed technique is an effective way for developing simple finite element models with high performance.
Comparison of aragonitic molluscan shell proteins.
Furuhashi, Takeshi; Miksik, Ivan; Smrz, Miloslav; Germann, Bettina; Nebija, Dashnor; Lachmann, Bodo; Noe, Christian
2010-02-01
Acidic macromolecules, as a nucleation factor for mollusc shell formation, are a major focus of research. It remains unclear, however, whether acidic macromolecules are present only in calcified shell organic matrices, and which acidic macromolecules are crucial for the nucleation process by binding to chitin as structural components. To clarify these questions, we applied 2D gel electrophoresis and amino acid analysis to soluble shell organic matrices from nacre shell, non-nacre aragonitic shell and non-calcified squid shells. The 2D gel electrophoresis results showed that the acidity of soluble proteins differs even between nacre shells, and some nacre (Haliotis gigantea) showed a basic protein migration pattern. Non-calcified shells also contained some moderately acidic proteins. The results did not support the correlation between the acidity of soluble shell proteins and shell structure.
Parameter identification of material constants in a composite shell structure
Martinez, D.R.; Carne, T.G.
1988-01-01
One of the basic requirements in engineering analysis is the development of a mathematical model describing the system. Frequently, comparisons with test data are used as a measurement of the adequacy of the model. An attempt is typically made to update or improve the model to provide a test-verified analysis tool. System identification provides a systematic procedure for accomplishing this task. The terms system identification, parameter estimation, and model correlation all refer to techniques that use test information to update or verify mathematical models. The goal of system identification is to improve the correlation of model predictions with measured test data, and produce accurate, predictive models. For nonmetallic structures the modeling task is often difficult due to uncertainties in the elastic constants. In this work a parameter identification procedure was used to determine the elastic constants of a cylindrical, graphite epoxy composite shell. A finite element model of the shell was created, which included uncertain orthotropic elastic constants. A modal survey test was then performed on the shell. The resulting modal data, along with the finite element model of the shell, were used in a Bayes estimation algorithm. This permitted the use of covariance matrices to weight the confidence in the initial parameter values as well as confidence in the measured test data. The estimation procedure also employed the concept of successive linearization to obtain an approximate solution to the original nonlinear estimation problem. 17 refs., 7 figs.
Mass of Perfect Fluid Black Shells
NASA Astrophysics Data System (ADS)
Zloshchastiev, Konstantin G.
The spherically symmetric singular perfect fluid shells are considered when their radii are equal to the event horizon (the black shells). We study their observable masses, depending at least on the three parameters, viz. the square speed of sound in the shell, instantaneous radial velocity of the shell at a moment when it reaches the horizon, and integration constant related to surface mass density. We discuss the features of black shells depending on the equation of state.
NASA Astrophysics Data System (ADS)
Gates, Jacklyn
2013-04-01
In 1966 Myers and Swiatecki predicted a new closed shell, centered at an element with Z=126 and A=310. In this region, now referred to as the ``Island of Stability,'' shell-effects were predicted to stabilize elements with Z 114-126 against fission, leading to predicted half-lives of years or longer and the predicted existence of so-called ``superheavy'' nuclei. By comparison, the heaviest known element at that time was rutherfordium (Rf), with Z=104 and a half-life of about one minute. Some of the theoretical calculations even predicted half-lives longer than the age of the universe, suggesting that these superheavy elements may even exist in nature. Later predictions suggested that nuclides in the Island of Stability might be produced at rates more characteristic of element with Z<=100. Initial experiments were unsuccessful in discovering superheavy nuclei in nature or at particle accelerators, leading to a concerted effort by experimentalists and theoreticians to i) improve the theoretical predictions ii) develop techniques to improve the sensitivity of experiments and iii) to progressively extend the known elements towards this region. Over the next five decades, fourteen new elements with Z>=105 and more than a hundred isotopes were discovered. Experimental sensitivies were increased by six orders of magnitude. Within the last decade, six new elements and more than fifty new isotopes with Z>=112 have been discovered. These most recent discoveries have begun to approach the edges of the Island of Stability. The nuclei exhibit longer lifetimes and higher production rates than those found in some of the lighter elements. This presentation will discuss the advances that have led us to the shores of the Island of Stability and where the field goes from here.
Measurement of K Shell Photoelectric Cross Sections at a K Edge--A Laboratory Experiment
ERIC Educational Resources Information Center
Nayak, S. V.; Badiger, N. M.
2007-01-01
We describe in this paper a new method for measuring the K shell photoelectric cross sections of high-Z elemental targets at a K absorption edge. In this method the external bremsstrahlung (EB) photons produced in the Ni target foil by beta particles from a weak[superscript 90]Sr-[superscript 90]Y beta source are passed through an elemental target…
NASA Astrophysics Data System (ADS)
Helser, Terry L.
2003-04-01
This puzzle uses the symbols of 39 elements to spell the names of 25 animals found in zoos. Underlined spaces and the names of the elements serve as clues. To solve the puzzle, students must find the symbols that correspond to the elemental names and rearrange them into the animals' names.
Chemical characterization of element 112.
Eichler, R; Aksenov, N V; Belozerov, A V; Bozhikov, G A; Chepigin, V I; Dmitriev, S N; Dressler, R; Gäggeler, H W; Gorshkov, V A; Haenssler, F; Itkis, M G; Laube, A; Lebedev, V Ya; Malyshev, O N; Oganessian, Yu Ts; Petrushkin, O V; Piguet, D; Rasmussen, P; Shishkin, S V; Shutov, A V; Svirikhin, A I; Tereshatov, E E; Vostokin, G K; Wegrzecki, M; Yeremin, A V
2007-05-01
The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of (283)112 through the alpha decay of the short-lived (287)114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of (283)112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.
Chemical characterization of element 112.
Eichler, R; Aksenov, N V; Belozerov, A V; Bozhikov, G A; Chepigin, V I; Dmitriev, S N; Dressler, R; Gäggeler, H W; Gorshkov, V A; Haenssler, F; Itkis, M G; Laube, A; Lebedev, V Ya; Malyshev, O N; Oganessian, Yu Ts; Petrushkin, O V; Piguet, D; Rasmussen, P; Shishkin, S V; Shutov, A V; Svirikhin, A I; Tereshatov, E E; Vostokin, G K; Wegrzecki, M; Yeremin, A V
2007-05-01
The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of (283)112 through the alpha decay of the short-lived (287)114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of (283)112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides. PMID:17476264
Shell Model Nuclear Level Densities using the Methods of Statistical Spectroscopy
NASA Astrophysics Data System (ADS)
Karampagia, Sofia; Sen'kov, Roman; Zelevinsky, Vladimir; Brown, Alex B.
2016-03-01
An algorithm has been developed for the calculation of spin- and parity-dependent nuclear level densities, based on a two-body shell-model Hamiltonian. Instead of diagonalizing the full shell-model Hamiltonian, the algorithm uses methods of statistical spectroscopy in order to derive nuclear level densities. This method allows one to calculate the exact level densities (coinciding with the shell model densities) very fast and for model spaces that the shell model cannot reach. In this work we study the evolution of the level density under variation of specific matrix elements of the shell-model Hamiltonian. We also study the impact on the calculated level density as a result the expansion of single-particle model space. As an application of the method, whenever it is possible and experimental information exists, we make a comparison of the nuclear level densities calculated within our method with experimental level densities. Supported by the NSF Grant PHY-1404442.
NASA Astrophysics Data System (ADS)
Mangeri, John; Heinonen, Olle; Karpeyev, Dmitry; Nakhmanson, Serge
2015-07-01
Core-shell nanoparticle systems of Zn-ZnO and ZnO -TiO2 are studied computationally using finite-element methods. The inclusion of a surface free energy and the elastic mismatch of the core and shell create an imprinting effect within the shell structure that produces a wide variation of strains. Due to this diversity of strains, the sharp, direct, band-gap edges of the bulk semiconductor are observed to be broadened. We show that a variety of factors, such as particle size, core-to-shell volume ratio, applied hydrostatic pressure, shell microstructure, as well as the effect of elastic anisotropy, can influence the distribution of optical band-gap values throughout the particle.
A simple low temperature synthesis route for ZnO-MgO core-shell nanowires.
Plank, N O V; Snaith, H J; Ducati, C; Bendall, J S; Schmidt-Mende, L; Welland, M E
2008-11-19
We report a hydrothermal synthesis method for MgO shell coatings directly onto the surface of ZnO nanowire arrays. The entire process can be carried out below 100 °C. The MgO shells are produced by the addition of 10 mM magnesium nitrate with 0.2 M sodium hydroxide in water, resulting in a shell thickness of up to 8 nm, verified by high resolution transmission electron microscopy. The viability of the MgO layer as a functional element of optoelectronic devices was tested on solid-state organic hole-transporter based dye-sensitized solar cells. Incorporation of the MgO shell into the solar cell resulted in substantive efficiency improvements of over 400% in comparison to the pristine ZnO nanowire based photovoltaics, indicating that electrons can efficiently tunnel through the 'insulating' MgO shell.
Overview of Hanford Single Shell Tank (SST) Structural Integrity
Rast, Richard S.; Washenfelder, Dennis J.; Johnson, Jeremy M.
2013-11-14
To improve the understanding of the single-shell tanks (SSTs) integrity, Washington River Protection Solutions, LLC (WRPS), the USDOE Hanford Site tank contractor, developed an enhanced Single-Shell Tank Integrity Project (SSTIP) in 2009. An expert panel on SST integrity, consisting of various subject matters experts in industry and academia, was created to provide recommendations supporting the development of the project. This panel developed 33 recommendations in four main areas of interest: structural integrity, liner degradation, leak integrity and prevention, and mitigation of contamination migration, Seventeen of these recommendations were used to develop the basis for the M-45-10-1 Change Package for the Hanford Federal Agreement and Compliance Order, which is also known as the Tri-Party Agreement. The structural integrity of the tanks is a key element in completing the cleanup mission at the Hanford Site. There are eight primary recommendations related to the structural integrity of Hanford Single-Shell Tanks. Six recommendations are being implemented through current and planned activities. The structural integrity of the Hanford is being evaluated through analysis, monitoring, inspection, materials testing, and construction document review. Structural evaluation in the form of analysis is performed using modern finite element models generated in ANSYS. The analyses consider in-situ, thermal, operating loads and natural phenomena such as earthquakes. Structural analysis of 108 of 149 Hanford Single-Shell Tanks has concluded that the tanks are structurally sound and meet current industry standards. Analysis of the remaining Hanford Single-Shell Tanks is scheduled for FY2014. Hanford Single-Shell Tanks are monitored through a dome deflection program. The program looks for deflections of the tank dome greater than 1/4 inch. No such deflections have been recorded. The tanks are also subjected to visual inspection. Digital cameras record the interior surface of
Computational procedures for postbuckling of composite shells
NASA Technical Reports Server (NTRS)
Stanley, G. M.; Felippa, Carlos A.
1989-01-01
A recently developed finite-element capability for general nonlinear shell analysis, featuring the use of three-dimensional constitutive equations within an efficient resultant-oriented framework, is employed to simulate the postbuckling response of an axially compressed composite cylindrical panel with a circular cutout. The problem is a generic example of modern composite aircraft components for which postbuckling strength (i.e., fail-safety) is desired in the presence of local discontinuities such as holes and cracked stiffeners. While the computational software does a reasonable job of predicting both the buckling load and the qualitative aspects of postbuckling (compared both with experiment and another code) there are some discrepancies due to: (1) uncertainties in the nominal layer material properties, (2) structural sensitivity to initial imperfections, and (3) the neglect of dynamic and local material delamination effects in the numerical model. Corresponding refinements are suggested for the realistic continuation of this type of analysis.
Torrefaction of pomaces and nut shells.
Chiou, Bor-Sen; Valenzuela-Medina, Diana; Bilbao-Sainz, Cristina; Klamczynski, Artur K; Avena-Bustillos, Roberto J; Milczarek, Rebecca R; Du, Wen-Xian; Glenn, Greg M; Orts, William J
2015-02-01
Apple, grape, olive, and tomato pomaces as well as almond and walnut shells were torrefied at different temperatures and times in a muffle furnace. The fiber content and thermal stability of the raw byproducts were examined and the moisture and ash contents, elemental composition, and gross calorific values of the raw and torrefied samples were characterized. Response surface methodology and a central composite design were used to examine the effects of temperature and time on mass and energy yields of the torrefied byproducts. Raw apple pomace had the highest hemicellulose content, whereas raw grape pomace had the highest lignin content. Raw tomato pomace had the highest gross calorific value because of its high carbon content. Temperature had a larger effect on mass and energy yields than time. Grape pomace generally had the highest mass and energy yields. Also, energy yields of the byproducts could be predicted from mass loss values.
Torrefaction of pomaces and nut shells.
Chiou, Bor-Sen; Valenzuela-Medina, Diana; Bilbao-Sainz, Cristina; Klamczynski, Artur K; Avena-Bustillos, Roberto J; Milczarek, Rebecca R; Du, Wen-Xian; Glenn, Greg M; Orts, William J
2015-02-01
Apple, grape, olive, and tomato pomaces as well as almond and walnut shells were torrefied at different temperatures and times in a muffle furnace. The fiber content and thermal stability of the raw byproducts were examined and the moisture and ash contents, elemental composition, and gross calorific values of the raw and torrefied samples were characterized. Response surface methodology and a central composite design were used to examine the effects of temperature and time on mass and energy yields of the torrefied byproducts. Raw apple pomace had the highest hemicellulose content, whereas raw grape pomace had the highest lignin content. Raw tomato pomace had the highest gross calorific value because of its high carbon content. Temperature had a larger effect on mass and energy yields than time. Grape pomace generally had the highest mass and energy yields. Also, energy yields of the byproducts could be predicted from mass loss values. PMID:25479394
Buckling of Cracked Laminated Composite Cylindrical Shells Subjected to Combined Loading
NASA Astrophysics Data System (ADS)
Allahbakhsh, Hamidreza; Shariati, Mahmoud
2013-10-01
A series of finite element analysis on the cracked composite cylindrical shells under combined loading is carried out to study the effect of loading condition, crack size and orientation on the buckling behavior of laminated composite cylindrical shells. The interaction buckling curves of cracked laminated composite cylinders subject to different combinations of axial compression, bending, internal pressure and external pressure are obtained, using the finite element method. Results show that the internal pressure increases the critical buckling load of the CFRP cylindrical shells and bending and external pressure decrease it. Numerical analysis show that axial crack has the most detrimental effect on the buckling load of a cylindrical shell and results show that for lower values of the axial compressive load and higher values of the external pressure, the buckling is usually in the global mode and for higher values of axial compressive load and lower levels of external pressure the buckling mode is mostly in the local mode.
Tearing resistance of a thin shell against projectile penetration: Material property effects
Trinh, K.V.
1994-01-01
This report presents results from a series of finite element analyses performed to study material effects on the tearing resistance of a thin shell subjected to projectile penetration. These analyses simulated a round, slender projectile impacting the top center of a metallic cylindrical shell at high speed. We varied eight selected shell material properties systematically using an L18 matrix (design of experiment technique). From the results, we determined effects of the eight properties on the minimum projectile velocity required to penetrate the shell. The material properties examined here included: yield strength, hardening and recovery characteristics, heat coefficient, initial porosity, and damage exponent (a void growth parameter). The DYNA2D finite element code along with the Sandia plasticity/damage model for ductile metals were used in the analyses.
Assessing open-system behavior of 14C in terrestrial gastropod shells
Rech, J.A.; Pigati, J.S.; Lehmann, S.B.; McGimpsey, C.N.; Grimley, D.A.; Nekola, J.C.
2011-01-01
In order to assess open-system behavior of radiocarbon in fossil gastropod shells, we measured the 14C activity on 10 aliquots of shell material recovered from Illinoian (~190-130 ka) and pre-Illinoian (~800 ka) loess and lacustrine deposits in the Midwestern USA. Eight of the 10 aliquots yielded measurable 14C activities that ranged from 0.25 to 0.53 percent modern carbon (pMC), corresponding to apparent 14C ages between 48.2 and 42.1 ka. This small level of open-system behavior is common in many materials that are used for 14C dating (e.g. charcoal), and typically sets the upper practical limit of the technique. Two aliquots of gastropod shells from the Illinoian-aged Petersburg Silt (Petersburg Section) in central Illinois, USA, however, yielded elevated 14C activities of 1.26 and 1.71 pMC, which correspond to apparent 14C ages of 35.1 and 32.7 ka. Together, these results suggest that while many fossil gastropods shells may not suffer from major (>1%) open-system problems, this is not always the case. We then examined the mineralogy, trace element chemistry, and physical characteristics of a suite of fossil and modern gastropod shells to identify the source of contamination in the Petersburg shells and assess the effectiveness of these screening techniques at identifying samples suitable for 14C dating. Mineralogical (XRD) and trace element analyses were inconclusive, which suggests that these techniques are not suitable for assessing open-system behavior in terrestrial gastropod shells. Analysis with scanning electron microscopy (SEM), however, identified secondary mineralization (calcium carbonate) primarily within the inner whorls of the Petersburg shells. This indicates that SEM examination, or possibly standard microscope examination, of the interior of gastropod shells should be used when selecting fossil gastropod shells for 14C dating. ?? 2011 by the Arizona Board of Regents on behalf of the University of Arizona.
Assessing open-system behavior of 14C in terrestrial gastropod shells
Rech, Jason A.; Pigati, Jeffrey S.; Lehmann, Sophie B.; McGimpsey, Chelsea N.; Grimley, David A.; Nekola, Jeffrey C.
2011-01-01
In order to assess open-system behavior of radiocarbon in fossil gastropod shells, we measured the 14C activity on 10 aliquots of shell material recovered from Illinoian (~190-130 ka) and pre-Illinoian (~800 ka) loess and lacustrine deposits in the Midwestern USA. Eight of the 10 aliquots yielded measurable 14C activities that ranged from 0.25 to 0.53 percent modern carbon (pMC), corresponding to apparent 14C ages between 48.2 and 42.1 ka. This small level of open-system behavior is common in many materials that are used for 14C dating (e.g. charcoal), and typically sets the upper practical limit of the technique. Two aliquots of gastropod shells from the Illinoian-aged Petersburg Silt (Petersburg Section) in central Illinois, USA, however, yielded elevated 14C activities of 1.26 and 1.71 pMC, which correspond to apparent 14C ages of 35.1 and 32.7 ka. Together, these results suggest that while many fossil gastropods shells may not suffer from major (>1%) open-system problems, this is not always the case. We then examined the mineralogy, trace element chemistry, and physical characteristics of a suite of fossil and modern gastropod shells to identify the source of contamination in the Petersburg shells and assess the effectiveness of these screening techniques at identifying samples suitable for 14C dating. Mineralogical (XRD) and trace element analyses were inconclusive, which suggests that these techniques are not suitable for assessing open-system behavior in terrestrial gastropod shells. Analysis with scanning electron microscopy (SEM), however, identified secondary mineralization (calcium carbonate) primarily within the inner whorls of the Petersburg shells. This indicates that SEM examination, or possibly standard microscope examination, of the interior of gastropod shells should be used when selecting fossil gastropod shells for 14C dating.
Foam shell project: Progress report
Overturf, G.; Reibold, B.; Cook, B.; Schroen-Carey, D.
1994-03-25
The authors report on their work to produce a foam shell target for two possible applications: (1) as liquid-layered cryogenic target on Omega Upgrade, and (2) as a back-up design for the NIF. This target consists of a roughly 1 mm diameter and 100 {mu}m thick spherical low-density foam shell surrounding a central void. The foam will be slightly overfilled with liquid D{sub 2} or DT, the overfilled excess being symmetrically distributed on the inside of the shell and supported by thermal gradient techniques. The outside of the foam is overcoated with full density polymer which must be topologically smooth. The technology for manufacturing this style of foam shell involves microencapsulation techniques and has been developed by the Japanese at ILE. Their goal is to determine whether this technology can be successfully adapted to meet US ICF objectives. To this end a program of foam shell development has been initiated at LLNL in collaboration with both the General Atomics DOE Target Fabrication Contract Corporation and the Target Fabrication Group at LLE.
Identification of material constants for a composite shell structure
Carne, T.G.; Martinez, D.R.
1987-03-01
One of the basic requirements of an engineering analysis is the development of an adequate mathematical model describing the system. Frequently, comparisons with test data are used as a measure of the model's adequacy, or the test data are directly used to update or modify the model. For nonmetallic structures, the modeling task is often more difficult due to uncertainties in the elastic constants. System identification provides a methodology for systematically updating the mathematical model for improved correlation with test data. In this work a finite element model of a composite shell was created. The model includes uncertain orthotropic elastic constants. To identify these constants, a modal survey was performed on an actual shell. The resulting modal data along with the finite element model of the shell were used in a Bayes estimation algorithm. Values of the elastic constants were estimated which minimized the differences between the test results and the finite element predictions. The estimation procedure employed the concept of successive linearization to obtain an approximate solution to the original nonlinear estimation problem.
Simple formulas for strain-energy release rates with higher order and singular finite elements
NASA Technical Reports Server (NTRS)
Raju, I. S.
1986-01-01
A general finite element procedure for obtaining strain-energy release rates for crack growth in isotropic materials is presented. The procedure is applicable to two-dimensional finite element analyses and uses the virtual crack-closure method. The procedure was applied to non-singular 4-noded (linear), 8-noded (parabolic), and 12-noded (cubic) elements and to quarter-point and cubic singularity elements. Simple formulas for strain-energy release rates were obtained with this procedure for both non-singular and singularity elements. The formulas were evaluated by applying them to two mode I and two mixed mode problems. Comparisons with results from the literature for these problems showed that the formulas give accurate strain-energy release rates.
Calculation of strain-energy release rates with higher order and singular finite elements
NASA Technical Reports Server (NTRS)
Raju, I. S.
1987-01-01
A general finite element procedure for obtaining strain-energy release rates for crack growth in isotropic materials is presented. The procedure is applicable to two-dimensional finite element analyses and uses the virtual crack-closure method. The procedure was applied to nonsingular 4-noded (linear), 8-noded (parabolic), and 12-noded (cubic) elements and to quarter-point and cubic singularity elements. Simple formulas for strain-energy release rates were obtained with this procedure for both nonsingular and singularity elements. The formulas were evaluated by applying them to two mode I and two mixed mode problems. Comparisons with results from the literature for these problems showed that the formulas give accurate strain-energy release rates.
Dominant thermogravimetric signatures of lignin in cashew shell as compared to cashew shell cake.
Gangil, Sandip
2014-03-01
Dominant thermogravimetric signatures related to lignin were observed in cashew shell as compared to these signatures in cashew shell cake. The phenomenon of weakening of lignin from cashew shell to cashew shell cake was explained on the basis of changes in the activation energies. The pertinent temperature regimes responsible for the release of different constituents of both the bio-materials were identified and compared. The activation energies of cashew shell and cashew shell cake were compared using Kissinger-Akahira-Sunose method. Thermogravimetric profiling of cashew shell and cashew shell cake indicated that these were different kinds of bio-materials.
Laminated Thin Shell Structures Subjected to Free Vibration in a Hygrothermal Environment
NASA Technical Reports Server (NTRS)
Gotsis, Pascal K.; Guptill, James D.
1994-01-01
Parametric studies were performed to assess the effects of various parameters on the free-vibration behavior (natural frequencies) of (+/- theta)(sub 2) angle-ply, fiber composite, thin shell structures in a hygrothermal environment. Knowledge of the natural frequencies of structures is important in considering their response to various kinds of excitation, especially when structures and force systems are complex and when excitations are not periodic. The three dimensional, finite element structural analysis computer code CSTEM was used in the Cray YMP computer environment. The fiber composite shell was assumed to be cylindrical and made from T300 graphite fibers embedded in an intermediate-modulus, high-strength matrix. The following parameters were investigated: the length and the laminate thickness of the shell, the fiber orientation, the fiber volume fraction, the temperature profile through the thickness of the laminate, and laminates with different ply thicknesses. The results indicate that the fiber orientation and the length of the laminated shell had significant effects on the natural frequencies. The fiber volume fraction, the laminate thickness, and the temperature profile through the shell thickness had weak effects on the natural frequencies. Finally, the laminates with different ply thicknesses had an insignificant influence on the behavior of the vibrated laminated shell. Also, a single through-the-thickness, eight-node, three dimensional composite finite element analysis appears to be sufficient for investigating the free-vibration behavior of thin, composite, angle-ply shell structures.
Advanced solid elements for sheet metal forming simulation
NASA Astrophysics Data System (ADS)
Mataix, Vicente; Rossi, Riccardo; Oñate, Eugenio; Flores, Fernando G.
2016-08-01
The solid-shells are an attractive kind of element for the simulation of forming processes, due to the fact that any kind of generic 3D constitutive law can be employed without any additional hypothesis. The present work consists in the improvement of a triangular prism solid-shell originally developed by Flores[2, 3]. The solid-shell can be used in the analysis of thin/thick shell, undergoing large deformations. The element is formulated in total Lagrangian formulation, and employs the neighbour (adjacent) elements to perform a local patch to enrich the displacement field. In the original formulation a modified right Cauchy-Green deformation tensor (C) is obtained; in the present work a modified deformation gradient (F) is obtained, which allows to generalise the methodology and allows to employ the Pull-Back and Push-Forwards operations. The element is based in three modifications: (a) a classical assumed strain approach for transverse shear strains (b) an assumed strain approach for the in-plane components using information from neighbour elements and (c) an averaging of the volumetric strain over the element. The objective is to use this type of elements for the simulation of shells avoiding transverse shear locking, improving the membrane behaviour of the in-plane triangle and to handle quasi-incompressible materials or materials with isochoric plastic flow.
Chemical Analysis Of Beryllium Shells
Gunther, J; Cook, R
2005-11-17
There is a need to understand the level of high-Z impurities in Beryllium shells prepared by sputter coating. The Ignition Point Design Requirements state the following: ''Except for allowed ingredients, as listed in the ablator composition entries, the ablator material in all layers shall contain sufficiently low impurity levels that the sum over all impurities of atom fraction*Z{sup 2} shall be less than or equal to 0.2''. This is a tight specification that requires careful materials analysis. Early in the first quarter of FY06, we undertook a study of Be shell impurities via ICP-MS{sup 2} and determined that the impurity levels in the sputtered shells are very close to the specification.
Buckling analysis of laminated thin shells in a hot environment
NASA Technical Reports Server (NTRS)
Gotsis, Pascal K.; Guptil, James D.
1993-01-01
Results are presented of parametric studies to assess the effects of various parameters on the buckling behavior of angle-ply, laminated thin shells in a hot environment. These results were obtained by using a three-dimensional finite element analysis. An angle-ply, laminated thin shell with fiber orientation of (theta/-theta)(sub 2) was subjected to compressive mechanical loads. The laminated thin shell had a cylindrical geometry. The laminate contained T300 graphite fibers embedded in an intermediate-modulus, high-strength (IMHS) matrix. The fiber volume fraction was 55 percent and the moisture content was 2 percent. The residual stresses induced into the laminate structure during the curing were taken into account. Parametric studies were performed to examine the effect on the critical buckling load of the following parameters: cylinder length and thickness, internal hydrostatic pressure, different ply thicknesses, different temperature profiles through the thickness of the structure, and different lay up configurations and fiber volume fractions. In conjunction with these parameters the ply orientation was varied from 0 deg to 90 deg. Seven ply angles were examined: 0 deg, 15 deg, 30 deg, 45 deg, 60 deg, 75 deg, and 90 deg. The results show that the ply angle theta and the laminate thickness had significant effects on the critical buckling load. The fiber volume fraction, the fiber orientations, and the internal hydrostatic pressure had important effects on the critical buckling load. The cylinder length had a moderate influence on the buckling load. The thin shell with (theta/-theta)(sub 2) or (theta/-theta)(sub s) angle-ply laminate had better buckling-load performance than the thin shell with (theta)(sub 4) angle-ply laminate. The temperature profiles through the laminate thickness and various laminates with the different ply thicknesses has insignificant effects on the buckling behavior of the thin shells.
Shell may expand detergent alcohols
1996-10-23
Shell Chemical is studying plans to expand detergent alcohols capacity in the US, CW has learned. The company is considering adding capacity for about 80 million lbs/year. If the project is approved, it would be implemented at the company`s Geismar, LA site. Shell will make a final decision on whether to proceed with the project within six months. It has been rumored to be considering a capacity addition as a result of tightening supply of natural and synthetic detergent alcohols.
DOE R&D Accomplishments Database
Mayer, M. G.
1948-02-01
It has been suggested in the past that special numbers of neutrons or protons in the nucleus form a particularly stable configuration.{sup1} The complete evidence for this has never been summarized, nor is it generally recognized how convincing this evidence is. That 20 neutrons or protons (Ca{sup40}) form a closed shell is predicted by the Hartree model. A number of calculations support this fact.{sup2} These considerations will not be repeated here. In this paper, the experimental facts indicating a particular stability of shells of 50 and 82 protons and of 50, 82, and 126 neutrons will be listed.
Analysis of Thick Sandwich Shells with Embedded Ceramic Tiles
NASA Technical Reports Server (NTRS)
Davila, Carlos G.; Smith, C.; Lumban-Tobing, F.
1996-01-01
The Composite Armored Vehicle (CAV) is an advanced technology demonstrator of an all-composite ground combat vehicle. The CAV upper hull is made of a tough light-weight S2-glass/epoxy laminate with embedded ceramic tiles that serve as armor. The tiles are bonded to a rubber mat with a carefully selected, highly viscoelastic adhesive. The integration of armor and structure offers an efficient combination of ballistic protection and structural performance. The analysis of this anisotropic construction, with its inherent discontinuous and periodic nature, however, poses several challenges. The present paper describes a shell-based 'element-layering' technique that properly accounts for these effects and for the concentrated transverse shear flexibility in the rubber mat. One of the most important advantages of the element-layering technique over advanced higher-order elements is that it is based on conventional elements. This advantage allows the models to be portable to other structural analysis codes, a prerequisite in a program that involves the computational facilities of several manufacturers and government laboratories. The element-layering technique was implemented into an auto-layering program that automatically transforms a conventional shell model into a multi-layered model. The effects of tile layer homogenization, tile placement patterns, and tile gap size on the analysis results are described.
NASA Astrophysics Data System (ADS)
Constans, E. W.; Koopmann, G. H.; Belegundu, A. D.
1998-10-01
A numerical design tool is presented for minimizing radiated sound power from a vibrating shell structure using a material tailoring approach. A finite element method using shell elements is used to predict the vibration response of the shell. The sound power generated by the shell under a harmonic force input is computed with a lumped parameter/wave superposition method. A simulated annealing algorithm is used to find optimal point mass distributions for minimum sound power. It is shown that optimal designs are achieved through converting certain mode shapes of the shell into “weak radiators”, i.e., modes with low net volume velocities. Close agreement is found between predicted noise levels and experimental measurements, thus providing initial validation of the method as an effective means of finding optimal structural designs for minimum sound power.
NASA Astrophysics Data System (ADS)
Rohmer, Marie-Madeleine; Demuynck, Jean; Bénard, Marc; Wiest, Roland; Bachmann, Christian; Henriet, Charles; Ernenwein, René
1990-08-01
This series of three papers presents a program system for ab initio molecular orbital calculations on vector and parallel computers. Part II is devoted to SCF iterations on closed-shell and open-shell configurations starting from a file of two-electron integrals on the basis of contracted Gaussians (CGTOs). In a preliminary step, the two-electron integrals ( pq‖ rs) are reordered according to increasing values of index pq = p( p-1)/2+ q. Then, in the first SCF iteration step, a file of semi-ordered P supermatrix elements (or P and Q supermatrix elements in the open-shell case) is generated from the file of semi-ordered integrals. This file is processed at each iteration step in an efficient vector loop to generate the electron repulsion matrix. Convergence is automatically controlled through level-shifting techniques. The most time-consuming parts are the integral sorting and the generation of the P supermatrix, which are carried out only once. Subsequent SCF iteration steps respectively require 0.9 s and 1.7 s for the process of 10 7 supermatrix elements by the closed-shell and the open-shell programs on a CRAY-2 processor.
Finite Element Modeling of the Buckling Response of Sandwich Panels
NASA Technical Reports Server (NTRS)
Rose, Cheryl A.; Moore, David F.; Knight, Norman F., Jr.; Rankin, Charles C.
2002-01-01
A comparative study of different modeling approaches for predicting sandwich panel buckling response is described. The study considers sandwich panels with anisotropic face sheets and a very thick core. Results from conventional analytical solutions for sandwich panel overall buckling and face-sheet-wrinkling type modes are compared with solutions obtained using different finite element modeling approaches. Finite element solutions are obtained using layered shell element models, with and without transverse shear flexibility, layered shell/solid element models, with shell elements for the face sheets and solid elements for the core, and sandwich models using a recently developed specialty sandwich element. Convergence characteristics of the shell/solid and sandwich element modeling approaches with respect to in-plane and through-the-thickness discretization, are demonstrated. Results of the study indicate that the specialty sandwich element provides an accurate and effective modeling approach for predicting both overall and localized sandwich panel buckling response. Furthermore, results indicate that anisotropy of the face sheets, along with the ratio of principle elastic moduli, affect the buckling response and these effects may not be represented accurately by analytical solutions. Modeling recommendations are also provided.
Tonneson, L.C.
1997-01-01
Trace elements used in nutritional supplements and vitamins are discussed in the article. Relevant studies are briefly cited regarding the health effects of selenium, chromium, germanium, silicon, zinc, magnesium, silver, manganese, ruthenium, lithium, and vanadium. The toxicity and food sources are listed for some of the elements. A brief summary is also provided of the nutritional supplements market.
Method and apparatus for an inflatable shell
NASA Technical Reports Server (NTRS)
Johnson, Christopher J. (Inventor)
2012-01-01
A method of assembling an inflatable shell of a structure comprises folding a plurality of shell sections about a set of fold lines and integrating the plurality of shell sections together with one another to form the shell. In another embodiment, an inflatable shell comprises a plurality of shell sections, each shell section having two pairs of fold lines for folding into stowage comprising a first gore section having a plurality of first gore panels layered and collectively folded about at a first set of fold lines. Each layer of the first gore panels and second gore panels are configured such that, once the first gore panel and second gore panel are attached to one another at the respective side edges of each panel, the lines of attachment forming a second set of fold lines for the shell section. A system and method for fabricating gore panels is also disclosed.
Modal interaction in laminated stiffened plates and shells
NASA Astrophysics Data System (ADS)
Zeggane, Madjid
A buckled shell element model is developed for the analysis of nonlinear modal interaction of local and overall instabilities of axially compressed laminated thin walled stiffened structures. The new element, contains within itself all the essential local modes liable to be triggered in the interaction and the associated second order fields. Amplitude modulation in the form of "slowly varying" functions is employed to describe the variation of amplitude of local buckles as they come under the influence of overall bending of the structure. The buckled element is formulated using h-p version type polynomials in two dimensions. First the local buckling and the associated postbuckling response of a substructure are studied using a first order shear deformation theory (SDT) based on an asymptotic approach. The efficiency and accuracy of the SDT is highlighted by comparing the results to those computed by the classical (Kirchoff) theory (CPT). The effects of shear deformation and imperfection-sensitivity are discussed. Brief parametric studies which investigate the influence of level of shell curvature, stockiness of the stiffener and material properties are presented. Second, a locally buckled shell element, in which the first and second order fields are embedded, is presented to investigate the effect of local-overall modal interaction. This model can be used to analyze panels, subjected to axial compression which can be designed for service in their locally postbuckled states. The interaction of two local modes and the overall mode is then studied. In certain cases, for example in doubly symmetric columns, a second local mode is triggered in the interaction and this is accounted for by treating the problem as the interaction of overall with two local modes. Examples of box columns, I-section columns, and sandwich plates and shells are studied. Various bench mark computations testify to the accuracy and efficiency of the present algorithm, whether when compared to
Shell structures for biogas plants
Sasse, L.
1982-01-01
The shell structures designed for biogas plants of the fixed-dome type by the Bremen Overseas Research and Development Association are described. Biogas digesters of the design described have been successfully tested in Rwanda and India without structural or contractural problems.
Shell Games: Uncovering Periodic Properties.
ERIC Educational Resources Information Center
Lamb, William G.
1983-01-01
Describes activities (demonstrations/experiments) used to introduce history of periodic properties--without electrons, orbitals, filling shells, or any conception of atoms beyond Dalton's model. Activities supplement first chapter in a currently available chemistry text. Indicates potential danger of experiments if proper safety precautions are…
Notes on static cylindrical shells
NASA Astrophysics Data System (ADS)
Bicák, J.; Zofka, M.
2002-07-01
Static cylindrical shells made of various types of matter are studied as sources of the vacuum Levi-Civita metrics. Their internal physical properties are related to the two essential parameters of the metrics outside. The total mass per unit length of the cylinders is always less than ¼. The results are illustrated by a number of figures.
Surface-imprinted core-shell nanoparticles for sorbent assays.
Lu, Chun-Hua; Zhou, Wen-Hui; Han, Bing; Yang, Huang-Hao; Chen, Xi; Wang, Xiao-Ru
2007-07-15
In this paper, we present a general protocol for the making of surface-imprinted core-shell nanoparticles via surface reversible addition-fragmentation chain-transfer (RAFT) polymerization using RAFT agent functionalized model silica nanoparticles as the chain-transfer agent. In this protocol, trichloro(4-chloromethylphenyl)silane was immobilized on the surface of SiO2 nanoparticles, forming chloromethylphenyl functionalized silica (silica-Cl). RAFT agent functionalized silica was subsequently produced by substitute reaction of silica-Cl with PhC(S)SMgBr. The grafting copolymerization of 4-vinylpyridine and ethylene glycol dimethacrylate using surface RAFT polymerization and in the presence of 2,4-dichlorophenoxyacetic acid as the template led to the formation of surface-imprinted core-shell nanoparticles. The resulting surface-imprinted core-shell nanoparticles bind the original template 2,4-D with an appreciable selectivity over structurally related compounds. The potential use of the surface-imprinted core-shell nanoparticles as the recognition element in the competitive fluorescent binding assay for 2,4-D was also demonstrated. PMID:17563116
Optimal design of geodesically stiffened composite cylindrical shells
NASA Technical Reports Server (NTRS)
Gendron, G.; Guerdal, Z.
1992-01-01
An optimization system based on the finite element code Computations Structural Mechanics (CSM) Testbed and the optimization program, Automated Design Synthesis (ADS), is described. The optimization system can be used to obtain minimum-weight designs of composite stiffened structures. Ply thickness, ply orientations, and stiffener heights can be used as design variables. Buckling, displacement, and material failure constraints can be imposed on the design. The system is used to conduct a design study of geodesically stiffened shells. For comparison purposes, optimal designs of unstiffened shells and shells stiffened by rings and stingers are also obtained. Trends in the design of geodesically stiffened shells are identified. An approach to include local stress concentrations during the design optimization process is then presented. The method is based on a global/local analysis technique. It employs spline interpolation functions to determine displacements and rotations from a global model which are used as 'boundary conditions' for the local model. The organization of the strategy in the context of an optimization process is described. The method is validated with an example.
Use of the Bethe Equation for Inner-Shell Ionization by Electron Impact
Powell, Cedric J.; Llovet, Xavier; Salvat, Francesc
2016-01-01
We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, with L3-subshell ionization cross sections for Xe, and with M-shell ionization cross sections for three elements. The validity or otherwise of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used. PMID:27546903
Kaçal, Mustafa Recep; Han, Ibrahim; Akman, Ferdi
2014-10-29
Energy dispersive X-ray fluorescence technique (EDXRF) has been employed for measuring K-shell absorption jump factors and jump ratios for Ti, Cr, Fe, Co, Ni and Cu elements. The jump factors and jump ratios for these elements were determined by measuring K shell fluorescence parameters such as the Kα X-ray production cross-sections, K shell fluorescence yields, Kβ-to-Kα X-rays intensity ratios, total atomic absorption cross sections and mass attenuation coefficients. The measurements were performed using a Cd-109 radioactive point source and an Si(Li) detector in direct excitation and transmission experimental geometry. The measured values for jump factors and jump ratios were compared with theoretically calculated and the ones available in the literature. PMID:25464198
Recent advances in shell theory. [application of asymptotic approach to thin walled shells
NASA Technical Reports Server (NTRS)
Simmonds, J. G.
1976-01-01
The results reviewed are divided into two categories: those that relate two-dimensional shell theory to three-dimensional elasticity theory and those concerned with shell theory per se. In the second category results for general elastic systems that carry over, by specialization or analogy, to shells and results that are unique to shell theory itself are considered.
7 CFR 983.29 - Shelled pistachios.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 7 Agriculture 8 2010-01-01 2010-01-01 false Shelled pistachios. 983.29 Section 983.29 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE PISTACHIOS GROWN IN CALIFORNIA, ARIZONA, AND NEW MEXICO Definitions § 983.29 Shelled pistachios. Shelled pistachios means...
7 CFR 984.10 - Shelled walnuts.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 8 2012-01-01 2012-01-01 false Shelled walnuts. 984.10 Section 984.10 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE WALNUTS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 984.10 Shelled walnuts. Shelled walnuts means walnut kernels after...
7 CFR 984.10 - Shelled walnuts.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 7 Agriculture 8 2011-01-01 2011-01-01 false Shelled walnuts. 984.10 Section 984.10 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE WALNUTS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 984.10 Shelled walnuts. Shelled walnuts means walnut kernels after...
7 CFR 984.10 - Shelled walnuts.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 8 2014-01-01 2014-01-01 false Shelled walnuts. 984.10 Section 984.10 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE WALNUTS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 984.10 Shelled walnuts. Shelled walnuts means walnut kernels after...
7 CFR 984.10 - Shelled walnuts.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 7 Agriculture 8 2010-01-01 2010-01-01 false Shelled walnuts. 984.10 Section 984.10 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE WALNUTS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 984.10 Shelled walnuts. Shelled walnuts means walnut kernels after...
7 CFR 984.10 - Shelled walnuts.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 8 2013-01-01 2013-01-01 false Shelled walnuts. 984.10 Section 984.10 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE WALNUTS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 984.10 Shelled walnuts. Shelled walnuts means walnut kernels after...
21 CFR 886.3800 - Scleral shell.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Scleral shell. 886.3800 Section 886.3800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3800 Scleral shell. (a) Identification. A scleral shell is...
7 CFR 981.6 - Shelled almonds.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 7 Agriculture 8 2010-01-01 2010-01-01 false Shelled almonds. 981.6 Section 981.6 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE ALMONDS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 981.6 Shelled almonds. Shelled almonds mean raw or roasted almonds...
7 CFR 981.6 - Shelled almonds.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 8 2013-01-01 2013-01-01 false Shelled almonds. 981.6 Section 981.6 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE ALMONDS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 981.6 Shelled almonds. Shelled almonds mean raw or roasted almonds...
7 CFR 981.6 - Shelled almonds.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 8 2012-01-01 2012-01-01 false Shelled almonds. 981.6 Section 981.6 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE ALMONDS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 981.6 Shelled almonds. Shelled almonds mean raw or roasted almonds...
7 CFR 981.6 - Shelled almonds.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 8 2014-01-01 2014-01-01 false Shelled almonds. 981.6 Section 981.6 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE ALMONDS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 981.6 Shelled almonds. Shelled almonds mean raw or roasted almonds...
7 CFR 981.6 - Shelled almonds.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 7 Agriculture 8 2011-01-01 2011-01-01 false Shelled almonds. 981.6 Section 981.6 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE ALMONDS GROWN IN CALIFORNIA Order Regulating Handling Definitions § 981.6 Shelled almonds. Shelled almonds mean raw or roasted almonds...
Developments in Cylindrical Shell Stability Analysis
NASA Technical Reports Server (NTRS)
Knight, Norman F., Jr.; Starnes, James H., Jr.
1998-01-01
Today high-performance computing systems and new analytical and numerical techniques enable engineers to explore the use of advanced materials for shell design. This paper reviews some of the historical developments of shell buckling analysis and design. The paper concludes by identifying key research directions for reliable and robust methods development in shell stability analysis and design.
7 CFR 983.29 - Shelled pistachios.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 8 2012-01-01 2012-01-01 false Shelled pistachios. 983.29 Section 983.29 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE PISTACHIOS GROWN IN CALIFORNIA, ARIZONA, AND NEW MEXICO Definitions § 983.29 Shelled pistachios. Shelled pistachios means...
7 CFR 983.29 - Shelled pistachios.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 8 2013-01-01 2013-01-01 false Shelled pistachios. 983.29 Section 983.29 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE PISTACHIOS GROWN IN CALIFORNIA, ARIZONA, AND NEW MEXICO Definitions § 983.29 Shelled pistachios. Shelled pistachios means...
7 CFR 983.29 - Shelled pistachios.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 7 Agriculture 8 2011-01-01 2011-01-01 false Shelled pistachios. 983.29 Section 983.29 Agriculture... and Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE PISTACHIOS GROWN IN CALIFORNIA, ARIZONA, AND NEW MEXICO Definitions § 983.29 Shelled pistachios. Shelled pistachios means...
7 CFR 983.29 - Shelled pistachios.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 8 2014-01-01 2014-01-01 false Shelled pistachios. 983.29 Section 983.29 Agriculture... AND ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE PISTACHIOS GROWN IN CALIFORNIA, ARIZONA, AND NEW MEXICO Definitions § 983.29 Shelled pistachios. Shelled pistachios means...
Multilayer Active Shell Mirrors
NASA Astrophysics Data System (ADS)
Steeves, John
This thesis presents a novel active mirror technology based on carbon fiber composites and replication manufacturing processes. Multiple additional layers are implemented into the structure in order to provide the reflective layer, actuation capabilities and electrode routing. The mirror is thin, lightweight, and has large actuation capabilities. These features, along with the associated manufacturing processes, represent a significant change in design compared to traditional optics. Structural redundancy in the form of added material or support structures is replaced by thin, unsupported lightweight substrates with large actuation capabilities. Several studies motivated by the desire to improve as-manufactured figure quality are performed. Firstly, imperfections in thin CFRP laminates and their effect on post-cure shape errors are studied. Numerical models are developed and compared to experimental measurements on flat laminates. Techniques to mitigate figure errors for thicker laminates are also identified. A method of properly integrating the reflective facesheet onto the front surface of the CFRP substrate is also presented. Finally, the effect of bonding multiple initially flat active plates to the backside of a curved CFRP substrate is studied. Figure deformations along with local surface defects are predicted and characterized experimentally. By understanding the mechanics behind these processes, significant improvements to the overall figure quality have been made. Studies related to the actuation response of the mirror are also performed. The active properties of two materials are characterized and compared. Optimal active layer thicknesses for thin surface-parallel schemes are determined. Finite element simulations are used to make predictions on shape correction capabilities, demonstrating high correctabiliity and stroke over low-order modes. The effect of actuator saturation is studied and shown to significantly degrade shape correction performance. The
Parameter identification of material constants in a composite shell structure
NASA Technical Reports Server (NTRS)
Martinez, David R.; Carne, Thomas G.
1988-01-01
One of the basic requirements in engineering analysis is the development of a mathematical model describing the system. Frequently comparisons with test data are used as a measurement of the adequacy of the model. An attempt is typically made to update or improve the model to provide a test verified analysis tool. System identification provides a systematic procedure for accomplishing this task. The terms system identification, parameter estimation, and model correlation all refer to techniques that use test information to update or verify mathematical models. The goal of system identification is to improve the correlation of model predictions with measured test data, and produce accurate, predictive models. For nonmetallic structures the modeling task is often difficult due to uncertainties in the elastic constants. A finite element model of the shell was created, which included uncertain orthotropic elastic constants. A modal survey test was then performed on the shell. The resulting modal data, along with the finite element model of the shell, were used in a Bayes estimation algorithm. This permitted the use of covariance matrices to weight the confidence in the initial parameter values as well as confidence in the measured test data. The estimation procedure also employed the concept of successive linearization to obtain an approximate solution to the original nonlinear estimation problem.
The Magellania venosa Biomineralizing Proteome: A Window into Brachiopod Shell Evolution.
Jackson, Daniel J; Mann, Karlheinz; Häussermann, Vreni; Schilhabel, Markus B; Lüter, Carsten; Griesshaber, Erika; Schmahl, Wolfgang; Wörheide, Gert
2015-04-24
Brachiopods are a lineage of invertebrates well known for the breadth and depth of their fossil record. Although the quality of this fossil record attracts the attention of paleontologists, geochemists, and paleoclimatologists, modern day brachiopods are also of interest to evolutionary biologists due to their potential to address a variety of questions ranging from developmental biology to biomineralization. The brachiopod shell is a composite material primarily composed of either calcite or calcium phosphate in close association with proteins and polysaccharides which give these composite structures their material properties. The information content of these biomolecules, sequestered within the shell during its construction, has the potential to inform hypotheses focused on describing how brachiopod shell formation evolved. Here, using high throughput proteomic approaches and next generation sequencing, we have surveyed and characterized the first shell-proteome and shell-forming transcriptome of any brachiopod, the South American Magellania venosa (Rhynchonelliformea: Terebratulida). We find that the seven most abundant proteins present in the shell are unique to M. venosa, but that these proteins display biochemical features found in other metazoan biomineralization proteins. We can also detect some M. venosa proteins that display significant sequence similarity to other metazoan biomineralization proteins, suggesting that some elements of the brachiopod shell-forming proteome are deeply evolutionarily conserved. We also employed a variety of preparation methods to isolate shell proteins and find that in comparison to the shells of other spiralian invertebrates (such as mollusks) the shell ultrastructure of M. venosa may explain the effects these preparation strategies have on our results.
The Magellania venosa Biomineralizing Proteome: A Window into Brachiopod Shell Evolution
Jackson, Daniel J.; Mann, Karlheinz; Häussermann, Vreni; Schilhabel, Markus B.; Lüter, Carsten; Griesshaber, Erika; Schmahl, Wolfgang; Wörheide, Gert
2015-01-01
Brachiopods are a lineage of invertebrates well known for the breadth and depth of their fossil record. Although the quality of this fossil record attracts the attention of paleontologists, geochemists, and paleoclimatologists, modern day brachiopods are also of interest to evolutionary biologists due to their potential to address a variety of questions ranging from developmental biology to biomineralization. The brachiopod shell is a composite material primarily composed of either calcite or calcium phosphate in close association with proteins and polysaccharides which give these composite structures their material properties. The information content of these biomolecules, sequestered within the shell during its construction, has the potential to inform hypotheses focused on describing how brachiopod shell formation evolved. Here, using high throughput proteomic approaches and next generation sequencing, we have surveyed and characterized the first shell-proteome and shell-forming transcriptome of any brachiopod, the South American Magellania venosa (Rhynchonelliformea: Terebratulida). We find that the seven most abundant proteins present in the shell are unique to M. venosa, but that these proteins display biochemical features found in other metazoan biomineralization proteins. We can also detect some M. venosa proteins that display significant sequence similarity to other metazoan biomineralization proteins, suggesting that some elements of the brachiopod shell-forming proteome are deeply evolutionarily conserved. We also employed a variety of preparation methods to isolate shell proteins and find that in comparison to the shells of other spiralian invertebrates (such as mollusks) the shell ultrastructure of M. venosa may explain the effects these preparation strategies have on our results. PMID:25912046
Analytic formula for quadrupole-quadrupole matrix elements
NASA Astrophysics Data System (ADS)
Rosensteel, G.
1990-12-01
An analytic formula is reported for general matrix elements of the microscopic quadrupole-quadrupole operator in the U(3)-boson approximation. The complete infinite-dimensional basis of A-fermion wave functions is compatible with the harmonic-oscillator shell model and consists of np-nh configurations, with spurious center-of-mass excitations removed, which are symmetry adapted to the Elliott U(3) and symplectic Sp(3,R) models. The formula expresses the general Q2.Q2 matrix element with respect to this complete orthonormal basis as a Racah SU(3) U coefficient times a closed-shell matrix element. An oscillator closed-shell matrix element of Q2.Q2 is a square root of a rational function of the integer quantum numbers of the U(3) basis.
Shell Model Depiction of Isospin Mixing in sd Shell
Lam, Yi Hua; Smirnova, Nadya A.; Caurier, Etienne
2011-11-30
We constructed a new empirical isospin-symmetry breaking (ISB) Hamiltonian in the sd(1s{sub 1/2}, 0d{sub 5/2} and 0d{sub 3/2}) shell-model space. In this contribution, we present its application to two important case studies: (i){beta}-delayed proton emission from {sup 22}Al and (ii) isospin-mixing correction to superallowed 0{sup +}{yields}0{sup +}{beta}-decay ft-values.
ERIC Educational Resources Information Center
Tsang, Chin Fu
1975-01-01
Discusses the possibility of creating elements with an atomic number of around 114. Describes the underlying physics responsible for the limited extent of the periodic table and enumerates problems that must be overcome in creating a superheavy nucleus. (GS)
ERIC Educational Resources Information Center
Daniel, Esther Gnanamalar Sarojini; Saat, Rohaida Mohd.
2001-01-01
Introduces a learning module integrating three disciplines--physics, chemistry, and biology--and based on four elements: carbon, oxygen, hydrogen, and silicon. Includes atomic model and silicon-based life activities. (YDS)
On chaotic behavior of gravitating stellar shells.
Barkov, M V; Bisnovatyi-Kogan, G S; Neishtadt, A I; Belinski, V A
2005-03-01
Motion of two gravitating spherical stellar shells around a massive central body is considered. Each shell consists of point particles with the same specific angular momenta and energies. In the case when one can neglect the influence of gravitation of one ("light") shell onto another ("heavy") shell ("restricted problem") the structure of the phase space is described. The scaling laws for the measure of the domain of chaotic motion and for the minimal energy of the light shell sufficient for its escape to infinity are obtained. PMID:15836258
K-shell transitions in L-shell ions with the EBIT calorimeter spectrometer
NASA Astrophysics Data System (ADS)
Hell, Natalie; Brown, G. V.; Wilms, J.; Beiersdorfer, P.; Kelley, R. L.; Kilbourne, C. A.; Porter, F. S.
2015-08-01
With the large improvement in effective area of Astro-H's micro-calorimeter soft X-ray spectrometer (SXS) over grating spectrometers, high-resolution X-ray spectroscopy with good signal to noise will become more commonly available, also for faint and extended sources. This will result in a range of spectral lines being resolved for the first time in celestial sources, especially in the Fe region. However, a large number of X-ray line energies in the atomic databases are known to a lesser accuracy than that expected for Astro-H/SXS, or have no known uncertainty at all. To benchmark the available calculations, we have therefore started to measure reference energies of K-shell transition in L-shell ions for astrophysically relevant elements in the range 11 ≤ Z ≤ 28 (Na to Ni), using the Lawrence Livermore National Laboratory's EBIT-I electron beam ion trap coupled with the NASA/GSFC EBIT calorimeter spectrometer (ECS). The ECS has a resolution of ~5eV, i.e., similar to Astro-H/SXS and Chandra/HETG. A comparison to crystal spectra of lower charge states of sulfur with ~0.6eV resolution shows that the analysis of spectra taken at ECS resolution allows us to determine the transition energies of the strongest components.Work at LLNL was performed under the auspices of DOE under contract DE-AC52-07NA27344 and supported by NASA's APRA program.
Shell growth and environmental control of methanophyllic Thyasirid bivalves from Svalbard cold seeps
NASA Astrophysics Data System (ADS)
Carroll, Michael; Åström, Emmelie; Ambrose, William; Locke, William; Oliver, Graham; Hong, Wei-Li; Carroll, JoLynn
2016-04-01
The analysis of molluscan shell material (sclerochronology) can provide information about an organism's age, growth history, and environmental conditions during its lifetime. Bivalve molluscs are common members of hydrothermal vents and methane cold seeps communities where, supported by chemosynthetic symbionts, they can reach high density and biomass. But little is known about methane-associated bivalve populations inhabiting high-Arctic cold seeps, and sclerochronological analysis of methane-influenced bivalves is rare. We measured growth rates and elemental and isotopic shell signatures in a newly discovered species of bivalve (Thyasiridae) from cold seeps at 350-390m depth southwest of Svalbard. First discovered in 2014, recently described shells of Thyasira capitanea sp.nov. were found at 2 independent seep systems in Storfjordrenna. Mean shell carbon isotopic ratios from inorganic δ13C (mean = -4.8‰) and organic δ13C (mean = -26.9‰) fractions clearly indicate a methane influenced habitat and food source for these organisms. Shell mineral ratios (Li/Ca, Mg/Ca, Mn/Ca, Fe/Ca, Sr/Ca, Ba/Ca, Pb/Ca) sampled along the axis of growth with laser-ablated ICP-MS exhibit variability through time and between sites, suggesting that concentrations of these elements that may be affected by methane emissions. The mineralogical data also elucidates the internal pattern of shell deposition and growth checks, and combined with the isotopic and growth rate data, enables us to interpret the temporal history of methane release from these locations.
NASA Astrophysics Data System (ADS)
Zheng, Ling; Zhang, Dongdong; Wang, Yi
2011-02-01
In this paper, the application of active constrained layer damping (ACLD) treatments is extended to the vibration control of cylindrical shells. The governing equation of motion of cylindrical shells partially treated with ACLD treatments is derived on the basis of the constitutive equations of elastic, piezoelectric and visco-elastic materials and an energy approach. The damping of a visco-elastic layer is modeled by the complex modulus formula. A finite element model is developed to describe and predict the vibration characteristics of cylindrical shells partially treated with ACLD treatments. A closed-loop control system based on proportional and derivative feedback of the sensor voltage generated by the piezo-sensor of the ACLD patches is established. The dynamic behaviors of cylindrical shells with ACLD treatments such as natural frequencies, loss factors and responses in the frequency domain are further investigated. The effects of several key parameters such as control gains, location and coverage of ACLD treatments on vibration suppression of cylindrical shells are also discussed. The numerical results indicate the validity of the finite element model and the control strategy approach. The potential of ACLD treatments in controlling vibration and sound radiation of cylindrical shells used as major critical structures such as cabins of aircraft, hulls of submarines and bodies of rockets and missiles is thus demonstrated.
Smart composite shell structures with shape memory alloy wires and thin foils
NASA Astrophysics Data System (ADS)
Kim, Jung-Taek; Kim, Cheol; Lee, Sang-Ryong
2005-02-01
Shape memory alloys (SMAs) find many applications in smart composite structural systems as the active components. Their ability to provide a high force and large displacement makes them an excellent candidate for an actuator for controlling the shape of smart structures. In this paper, using a macroscopic model that captures the thermo-mechanical behaviors and the two-way shape memory effect (TWSME) of SMAs smart morphing polymeric composite shell structures like shape-changeable UAV wings is demonstrated and analyzed numerically and experimentally when subjected to various kinds of pressure loads. The controllable shapes of the morphing shells to that thin SMA strip actuator are attached are investigated depending on various phase transformation temperatures. SMA strips start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the shell structures to deform three dimensionally. The behaviors of composite shells attached with SMA strip actuators are analyzed using the finite element methods and 3-D constitutive equations of SMAs. Several morphing composite shell structures are fabricated and their experimental shape changes depending on temperatures are compared to the numerical results. That two results show good correlations indicates the finite element analysis and 3-D constitutive equations are accurate enough to utilize them for the design of smart composite shell structures for various applications.
Multi-proxies Approach of Climatic Records In Terrestrial Mollusks Shells
NASA Astrophysics Data System (ADS)
Labonne, M.; Rousseau, D. D.; Ben Othman, D.; Luck, J. M.; Metref, S.
Fossil land snails shells constitute a valuable source of information for the study of Quaternary deposits as they are commonly preserved in many regions and notably in loess sequences. The use of stable isotope composition of the carbonate in the shells was previously applied to reconstruct past climate or environnements but the technic was not widely exploited and compared with other proxies from the same sequence. In this study, we have analysed stables isotopes, trace elements and Sr isotopes from both shells of land snails Vertigo modesta and the sediment from the Eustis upper Pleistocene loess sequence (Nebraska, USA). This serie developed during the last glaciation and records the last deglaciation between 18,000 and 12,000 B.P. years. We compare the paleoclimatic information obtained by different proxies, such as mag- netic susceptibility, temperature and moisture estimated by land snails assemblage with geochemical data measured on land snails shells in order to validate the climatic information obtained with this proxy. Our study demonstrates that shell carbonate reflects environmental conditions estimated by other proxies. Carbon and oxygen iso- topes show cyclic variations (millenial cycles) along the profile which correlate with stratigraphic units and could be link with the retreat of the Laurentide ice sheet. Trace element and Sr isotopes in the shells indicate various origins for the eolian dusts in the two main loess units along the sequence.
NASA Astrophysics Data System (ADS)
Chowdhury, Puja B.; Mitra, Anirban; Sahoo, Sarmila
2016-01-01
A review of literature reveals that bending analysis of laminated composite stiffened hypar shells with cutout have not received due attention. Being a doubly ruled surface, a skewed hypar shell fulfils aesthetic as well as ease of casting requirements. Further, this shell allows entry of north light making it suitable as civil engineering roofing units. Hypar shell with cutout subjected to uniformly distributed load exhibits improved performances with stiffeners. Hence relative performances of antisymmetric angle-ply laminated composite stiffened hypar shells in terms of displacements and stress resultants are studied in this paper under static loading. A curved quadratic isoparametric eight noded element and three noded beam elements are used to model the shell surface and the stiffeners respectively. Results obtained from the present study are compared with established ones to check the correctness of the present approach. A number of additional problems of antisymmetric angle-ply laminated composite stiffened hypar shells are solved for various fibre orientations, number of layers and boundary conditions. Results are interpreted from practical application standpoints and findings important for a designer to decide on the shell combination among a number of possible options are highlighted.
Pressure Shell Approach to Integrated Environmental Protection
NASA Technical Reports Server (NTRS)
Kennedy, Kriss J.
2011-01-01
The next generation of exploration mission human systems will require environmental protection such as radiation protection that is effective and efficient. In order to continue human exploration, habitat systems will require special shells to protect astronauts from hostile environments. The Pressure Shell Approach to integrated environmental (radiation) protection is a multi-layer shell that can be used for multifunctional environmental protection. Self-healing, self-repairing nano technologies and sensors are incorporated into the shell. This shell consists of multiple layers that can be tailored for specific environmental protection needs. Mainly, this innovation focuses on protecting crew from exposure to micrometeorites, thermal, solar flares, and galactic cosmic ray (GCR) radiation. The Pressure Shell Approach consists of a micrometeoroid and secondary ejecta protection layer; a thin, composite shell placed in between two layers that is non-structural; an open cavity layer that can be filled with water, regolith, or polyethylene foam; a thicker composite shell that is a structural load bearing that is placed between two layers; and a bladder coating on the interior composite shell. This multi-layer shell creates an effective radiation protection system. Most of its layers can be designed with the materials necessary for specific environments. In situ materials such as water or regolith can be added to the shell design for supplemental radiation protection.
High-temperature ceramic heat exchanger element for a solar thermal receiver
NASA Technical Reports Server (NTRS)
Strumpf, H. J.; Kotchick, D. M.; Coombs, M. G.
1982-01-01
A study has been completed on the development of a high-temperature ceramic heat exchanger element to be integrated into a solar reciver producing heated air. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The ceramic shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is fabricated by an innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. Fabrication of a one-half scale demonstrator ceramic receiver has been completed.
Numerical treatment of a geometrically nonlinear planar Cosserat shell model
NASA Astrophysics Data System (ADS)
Sander, Oliver; Neff, Patrizio; Bîrsan, Mircea
2016-05-01
We present a new way to discretize a geometrically nonlinear elastic planar Cosserat shell. The kinematical model is similar to the general six-parameter resultant shell model with drilling rotations. The discretization uses geodesic finite elements (GFEs), which leads to an objective discrete model which naturally allows arbitrarily large rotations. GFEs of any approximation order can be constructed. The resulting algebraic problem is a minimization problem posed on a nonlinear finite-dimensional Riemannian manifold. We solve this problem using a Riemannian trust-region method, which is a generalization of Newton's method that converges globally without intermediate loading steps. We present the continuous model and the discretization, discuss the properties of the discrete model, and show several numerical examples, including wrinkling of thin elastic sheets in shear.
Shell evolution beyond N =40 : 69,71,73Cu
NASA Astrophysics Data System (ADS)
Sahin, E.; Doncel, M.; Sieja, K.; de Angelis, G.; Gadea, A.; Quintana, B.; Görgen, A.; Modamio, V.; Mengoni, D.; Valiente-Dobón, J. J.; John, P. R.; Albers, M.; Bazzacco, D.; Benzoni, G.; Birkenbach, B.; Cederwall, B.; Clément, E.; Curien, D.; Corradi, L.; Désesquelles, P.; Dewald, A.; Didierjean, F.; Duchêne, G.; Eberth, J.; Erduran, M. N.; Farnea, E.; Fioretto, E.; de France, G.; Fransen, C.; Gernhäuser, R.; Gottardo, A.; Hackstein, M.; Hagen, T.; Hernández-Prieto, A.; Hess, H.; Hüyük, T.; Jungclaus, A.; Klupp, S.; Korten, W.; Kusoglu, A.; Lenzi, S. M.; Ljungvall, J.; Louchart, C.; Lunardi, S.; Menegazzo, R.; Michelagnoli, C.; Mijatović, T.; Million, B.; Molini, P.; Montagnoli, G.; Montanari, D.; Möller, O.; Napoli, D. R.; Obertelli, A.; Orlandi, R.; Pollarolo, G.; Pullia, A.; Recchia, F.; Reiter, P.; Rosso, D.; Rother, W.; Salsac, M.-D.; Scarlassara, F.; Schlarb, M.; Siem, S.; Singh, Pushpendra P.; Söderström, P.-A.; Stefanini, A. M.; Stézowski, O.; Sulignano, B.; Szilner, S.; Theisen, Ch.; Ur, C. A.; Yalcinkaya, M.
2015-03-01
The level structure of the neutron-rich 69Cu ,71Cu , and 73Cu isotopes has been investigated by means of multinucleon transfer reactions. The experiment was performed at Laboratori Nazionali di Legnaro using the AGATA Demonstrator array coupled to the PRISMA magnetic spectrometer. Lifetimes of excited states in Cu nuclei were measured with the recoil-distance Doppler-shift method. The resulting electromagnetic matrix elements for transitions from excited states in 69,71,73Cu nuclei are used to assess the collective or single-particle character of these states. The results are compared with predictions of large-scale shell-model calculations, giving further insight into the evolution of the proton p f shell as neutrons fill the 1 g9 /2 orbital.
Buckliballs: Buckling-Induced Pattern Transformation of Structured Elastic Shells
NASA Astrophysics Data System (ADS)
Bertoldi, Katia; Shim, Jongmin; Perdigou, Claude J.; Chen, Elizabeth R.; Reis, Pedro M.
2012-02-01
We present a class of continuum shell structures, the buckliball, which, undergo a structural transformation induced by buckling under pressure loading. The geometry of the buckliball comprises a spherical shell patterned with a regular array of circular voids. Moreover, we show that the buckling-induced pattern transformation is possible only with five specific hole arrangements. These voids are covered with a thin membrane, thereby making the ball air tight. Beyond a critical internal pressure, the thin ligaments between the voids buckle leading to a cooperative buckling cascade of the skeleton of the ball. Both precision desktop-scale experiments and finite element simulations are used to explore the underlying mechanics in detail and proof of concept of the proposed structures. We find excellent qualitative and quantitative agreement between experiments and simulations. This pattern transformation induced by a mechanical instability opens the possibility for reversible encapsulation, over a wide range of length scales.
Combined experimental/analytical modeling of shell/payload structures
Martinez, D.R.; Miller, A.K.; Carne, T.G.
1985-12-01
This study evaluates the accuracy of computed modal frequencies obtained from a combined experimental/analytical model of a shell/payload structure. A component mode synthesis technique was used which incorporated free modes and residual effects. The total structure is physically divided into the two subsystems which are connected through stiff joints. The payload was tested to obtain its free-free modes, while a finite element model of the shell was analyzed to obtain its modal description. Both the translational and rotational components of the experimental mode shapes at the payload interface were used in the coupling. Sensitivity studies were also performed to determine the effect of neglecting the residual terms of the payload. Results from a previous study of a combined experimental/analytical model for a beam structure are also given. The beam structure was used to examine the basic procedures and difficulties in experimentally measuring, and analytically accounting for the rotational and residual quantities.
Turbine blade with spar and shell
Davies, Daniel O.; Peterson, Ross H.
2012-04-24
A turbine blade with a spar and shell construction in which the spar and the shell are both secured within two platform halves. The spar and the shell each include outward extending ledges on the bottom ends that fit within grooves formed on the inner sides of the platform halves to secure the spar and the shell against radial movement when the two platform halves are joined. The shell is also secured to the spar by hooks extending from the shell that slide into grooves formed on the outer surface of the spar. The hooks form a serpentine flow cooling passage between the shell and the spar. The spar includes cooling holes on the lower end in the leading edge region to discharge cooling air supplied through the platform root and into the leading edge cooling channel.
Indentation of Ellipsoidal and Cylindrical Elastic Shells
NASA Astrophysics Data System (ADS)
Vella, Dominic; Ajdari, Amin; Vaziri, Ashkan; Boudaoud, Arezki
2012-10-01
Thin shells are found in nature at scales ranging from viruses to hens’ eggs; the stiffness of such shells is essential for their function. We present the results of numerical simulations and theoretical analyses for the indentation of ellipsoidal and cylindrical elastic shells, considering both pressurized and unpressurized shells. We provide a theoretical foundation for the experimental findings of Lazarus et al. [following paper, Phys. Rev. Lett. 109, 144301 (2012)PRLTAO0031-9007] and for previous work inferring the turgor pressure of bacteria from measurements of their indentation stiffness; we also identify a new regime at large indentation. We show that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth. Our results reveal how geometry rules the rigidity of shells.
NASA Technical Reports Server (NTRS)
Young, Richard D.; Rose, Cheryl A.; Starnes, James H., Jr.
2000-01-01
Results of a geometrically nonlinear finite element parametric study to determine curvature correction factors or bulging factors that account for increased crack-tip stresses due to curvature for longitudinal and circumferential cracks in unstiffened cylindrical shells subjected to combined loads are presented. Nondimensional parameters varied in the study include the shell curvature parameter, l , which is a function of the shell radius, the shell wall thickness, and the crack length; a pressure loading parameter, h , which is a function of the shell geometry, material properties and the applied internal pressure; and a biaxial loading parameter, c , which is the ratio of the farfield axial stress to the farfield circumferential stress. The major results are presented in the form of contour plots of the bulging factor as a function of these three nondimensional parameters. These plots identify the ranges of the shell curvature and loading parameters for which the effects of geometric nonlinearity are significant, and show the effect of the biaxial loads on the value of the bulging factor. Simple empirical expressions for the bulging factor are then derived from the numerical results and are shown to predict accurately the nonlinear response of shells with longitudinal and circumferential cracks.
Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study.
Bazalova-Carter, Magdalena; Ahmad, Moiz; Xing, Lei; Fahrig, Rebecca
2015-10-01
Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at [Formula: see text] with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies.
Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study.
Bazalova-Carter, Magdalena; Ahmad, Moiz; Xing, Lei; Fahrig, Rebecca
2015-10-01
Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at [Formula: see text] with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies. PMID:26839910
Hypersonic vibrations of Ag@SiO2 (cubic core)-shell nanospheres.
Sun, Jing Ya; Wang, Zhi Kui; Lim, Hock Siah; Ng, Ser Choon; Kuok, Meng Hau; Tran, Toan Trong; Lu, Xianmao
2010-12-28
The intriguing optical and catalytic properties of metal-silica core-shell nanoparticles, inherited from their plasmonic metallic cores together with the rich surface chemistry and increased stability offered by their silica shells, have enabled a wide variety of applications. In this work, we investigate the confined vibrational modes of a series of monodisperse Ag@SiO(2) (cubic core)-shell nanospheres synthesized using a modified Stöber sol-gel method. The particle-size dependence of their mode frequencies has been mapped by Brillouin light scattering, a powerful tool for probing hypersonic vibrations. Unlike the larger particles, the observed spheroidal-like mode frequencies of the smaller ones do not scale with inverse diameter. Interestingly, the onset of the deviation from this linearity occurs at a smaller particle size for higher-energy modes than for lower-energy ones. Finite element simulations show that the mode displacement profiles of the Ag@SiO(2) core-shells closely resemble those of a homogeneous SiO(2) sphere. Simulations have also been performed to ascertain the effects that the core shape and the relative hardness of the core and shell materials have on the vibrations of the core-shell as a whole. As the vibrational modes of a particle have a bearing on its thermal and mechanical properties, the findings would be of value in designing core-shell nanostructures with customized thermal and mechanical characteristics.
Resource Letter NSM-1: New insights into the nuclear shell model
Dean, David Jarvis; Hamilton, J. H.
2011-01-01
This Resource Letter provides a guide to the literature on the spherical shell model as applied to nuclei. The nuclear shell model describes the structure of nuclei starting with a nuclear core developed by the classical neutron and proton magic numbers N,Z=2,8,20,28,50,82, 126, where gaps occur in the single-particle energies as a shell is filled, and the interactions of valence nucleons that reside beyond that core. Various modern extensions of this model for spherical nuclei are likewise described. Significant extensions of the nuclear shell model include new magic numbers for spherical nuclei and now for deformed nuclei as well. When both protons and neutrons have shell gaps at the same spherical or deformed shapes, they can reinforce each other to give added stability to that shape and lead to new magic numbers. The vanishings of the classical spherical shell model energy gaps and magic numbers in new neutron-rich nuclei are described. Spherical and deformed shell gaps are seen to be critical for the existence of elements with Z > 100.
Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study
Bazalova-Carter, Magdalena; Ahmad, Moiz; Xing, Lei; Fahrig, Rebecca
2015-01-01
Abstract. Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at ±120 deg with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies. PMID:26839910
Faghih Shojaei, M; Mohammadi, V; Rajabi, H; Darvizeh, A
2012-12-01
In this paper, a new numerical technique is presented to accurately model the geometrical and mechanical features of mollusk shells as a three dimensional (3D) integrated volume. For this purpose, the Newton method is used to solve the nonlinear equations of shell surfaces. The points of intersection on the shell surface are identified and the extra interior parts are removed. Meshing process is accomplished with respect to the coordinate of each point of intersection. The final 3D generated mesh models perfectly describe the spatial configuration of the mollusk shells. Moreover, the computational model perfectly matches with the actual interior geometry of the shells as well as their exterior architecture. The direct generation technique is employed to generate a 3D finite element (FE) model in ANSYS 11. X-ray images are taken to show the close similarity of the interior geometry of the models and the actual samples. A scanning electron microscope (SEM) is used to provide information on the microstructure of the shells. In addition, a set of compression tests were performed on gastropod shell specimens to obtain their ultimate compressive strength. A close agreement between experimental data and the relevant numerical results is demonstrated. PMID:23137621
On Hybrid and mixed finite element methods
NASA Technical Reports Server (NTRS)
Pian, T. H. H.
1981-01-01
Three versions of the assumed stress hybrid model in finite element methods and the corresponding variational principles for the formulation are presented. Examples of rank deficiency for stiffness matrices by the hybrid stress model are given and their corresponding kinematic deformation modes are identified. A discussion of the derivation of general semi-Loof elements for plates and shells by the hybrid stress method is given. It is shown that the equilibrium model by Fraeijs de Veubeke can be derived by the approach of the hybrid stress model as a special case of semi-Loof elements.
Shell Evolutions and Nuclear Forces
NASA Astrophysics Data System (ADS)
Sorlin, O.
2014-03-01
During the last 30 years, and more specifically during the last 10 years, many experiments have been carried out worldwide using different techniques to study the shell evolution of nuclei far from stability. What seemed not conceivable some decades ago became rather common: all known magic numbers that are present in the valley of stability disappear far from stability and are replaced by new ones at the drip line. By gathering selected experimental results, beautifully consistent pictures emerge, that very likely take root in the properties of the nuclear forces.The present manuscript describes some of these discoveries and proposes an intuitive understanding of these shell evolutions derived from observations. Extrapolations to yet unstudied regions, as where the explosive r-process nucleosynthesis occurs, are proposed. Some remaining challenges and puzzling questions are also addressed.
Glass shell manufacturing in space
NASA Technical Reports Server (NTRS)
Nolen, R. L.; Downs, R. L.; Ebner, M. A.
1982-01-01
Highly-uniform, hollow glass spheres, which are used for inertial-confinement fusion targets, are formed from metal-organic gel powder feedstock in a drop-tower furnace. The modelling of this gel-to-sphere transformation has consisted of three phases: gel thermochemistry, furnance-to-gel heat transfer, and gravity-driven degradation of the concentricity of the molten shell. The heat transfer from the furnace to the free-falling gel particle was modelled with forced convection. The gel mass, dimensions, and specific heat as well as furnace temperature profile and furnace gas conductivity, were controlled variables. This model has been experimentally verified. In the third phase, a mathematical model was developed to describe the gravity-driven degradation of concentricity in molten glass shells.
Density Measurements of Be Shells
Cook, R C
2005-02-15
The purpose of this memo is to lay out the uncertainties associated with the measurement of density of Be ablators by the weigh and volume method. I am counting on the readers to point out any faulty assumptions about the techniques or uncertainties associated with them. Based on the analysis presented below we should expect that 30 {micro}m thick shells will have an uncertainty in the measured density of about 2% of the value, coming more or less equally from the mass and volume measurement. The uncertainty is roughly inversely proportional to the coating thickness, thus a 60 {micro}m walled shell would result in a 1% uncertainty in the density.
The shell coal gasification process
Koenders, L.O.M.; Zuideveld, P.O.
1995-12-01
Future Integrated Coal Gasification Combined Cycle (ICGCC) power plants will have superior environmental performance and efficiency. The Shell Coal Gasification Process (SCGP) is a clean coal technology, which can convert a wide range of coals into clean syngas for high efficiency electricity generation in an ICGCC plant. SCGP flexibility has been demonstrated for high-rank bituminous coals to low rank lignites and petroleum coke, and the process is well suited for combined cycle power generation, resulting in efficiencies of 42 to 46% (LHV), depending on choice of coal and gas turbine efficiency. In the Netherlands, a 250 MWe coal gasification combined cycle plant based on Shell technology has been built by Demkolec, a development partnership of the Dutch Electricity Generating Board (N.V. Sep). The construction of the unit was completed end 1993 and is now followed by start-up and a 3 year demonstration period, after that the plant will be part of the Dutch electricity generating system.
Premature detonation problem. [Artillery shells
Pimbley, G.H.; Marshall, E.F.
1980-05-01
Determining how cavities or voids in the explosive loads of artillery shells cause in-bore premature detonations is important to military authorities. Though answers continue to be elusive, in detailing recent studies of the problem at LASL, some traditional approaches were examined and a new direction of investigation is suggested. The aquarium experiment and the pipe test were devised at LASL to model the events taking place in a base gap, or in an internal cavity, in the load of an accelerating artillery shell. Numerical simulation was used to assess the data from these experiments. Both the experimental and the numerical simulation phases of the project are described. The commonly accepted gas compression, thermal ignition mechanism is not consistent with the results of this study. The dominant mechanism or mechanisms have not been identified.
A Shell/3D Modeling Technique for Delaminations in Composite Laminates
NASA Technical Reports Server (NTRS)
Krueger, Ronald
1999-01-01
A shell/3D modeling technique was developed for which a local solid finite element model is used only in the immediate vicinity of the delamination front. The goal was to combine the accuracy of the full three-dimensional solution with the computational efficiency of a plate or shell finite element model. Multi-point constraints provide a kinematically compatible interface between the local 3D model and the global structural model which has been meshed with plate or shell finite elements. For simple double cantilever beam (DCB), end notched flexure (ENF), and single leg bending (SLB) specimens, mixed mode energy release rate distributions were computed across the width from nonlinear finite element analyses using the virtual crack closure technique. The analyses served to test the accuracy of the shell/3D technique for the pure mode I case (DCB), mode II case (ENF) and a mixed mode I/II case (SLB). Specimens with a unidirectional layup where the delamination is located between two 0 plies, as well as a multidirectional layup where the delamination is located between two non-zero degree plies, were simulated. For a local 3D model extending to a minimum of about three specimen thicknesses in front of and behind the delamination front, the results were in good agreement with mixed mode strain energy release rates obtained from computations where the entire specimen had been modeled with solid elements. For large built-up composite structures modeled with plate elements, the shell/3D modeling technique offers a great potential, since only a relatively small section in the vicinity of the delamination front needs to be modeled with solid elements.
Shell Models of Superfluid Turbulence
NASA Astrophysics Data System (ADS)
Wacks, Daniel H.; Barenghi, Carlo F.
2011-12-01
Superfluid helium consists of two inter-penetrating fluids, a viscous normal fluid and an inviscid superfluid, coupled by a mutual friction. We develop a two-fluid shell model to study superfluid turbulence and investigate the energy spectra and the balance of fluxes between the two fluids in a steady state. At sufficiently low temperatures a 'bottle-neck' develops at high wavenumbers suggesting the need for a further dissipative effect, such as the Kelvin wave cascade.
Cross Sections for Inner-Shell Ionization by Electron Impact
Llovet, Xavier; Powell, Cedric J.; Salvat, Francesc; Jablonski, Aleksander
2014-03-15
An analysis is presented of measured and calculated cross sections for inner-shell ionization by electron impact. We describe the essentials of classical and semiclassical models and of quantum approximations for computing ionization cross sections. The emphasis is on the recent formulation of the distorted-wave Born approximation by Bote and Salvat [Phys. Rev. A 77, 042701 (2008)] that has been used to generate an extensive database of cross sections for the ionization of the K shell and the L and M subshells of all elements from hydrogen to einsteinium (Z = 1 to Z = 99) by electrons and positrons with kinetic energies up to 1 GeV. We describe a systematic method for evaluating cross sections for emission of x rays and Auger electrons based on atomic transition probabilities from the Evaluated Atomic Data Library of Perkins et al. [Lawrence Livermore National Laboratory, UCRL-ID-50400, 1991]. We made an extensive comparison of measured K-shell, L-subshell, and M-subshell ionization cross sections and of Lα x-ray production cross sections with the corresponding calculated cross sections. We identified elements for which there were at least three (for K shells) or two (for L and M subshells) mutually consistent sets of cross-section measurements and for which the cross sections varied with energy as expected by theory. The overall average root-mean-square deviation between the measured and calculated cross sections was 10.9% and the overall average deviation was −2.5%. This degree of agreement between measured and calculated ionization and x-ray production cross sections was considered to be very satisfactory given the difficulties of these measurements.
Kim, Heung Soo; Sohn, Jung Woo; Jeon, Juncheol; Choi, Seung-Bok
2013-01-01
In this work, active vibration control of an underwater cylindrical shell structure was investigated, to suppress structural vibration and structure-borne noise in water. Finite element modeling of the submerged cylindrical shell structure was developed, and experimentally evaluated. Modal reduction was conducted to obtain the reduced system equation for the active feedback control algorithm. Three Macro Fiber Composites (MFCs) were used as actuators and sensors. One MFC was used as an exciter. The optimum control algorithm was designed based on the reduced system equations. The active control performance was then evaluated using the lab scale underwater cylindrical shell structure. Structural vibration and structure-borne noise of the underwater cylindrical shell structure were reduced significantly by activating the optimal controller associated with the MFC actuators. The results provide that active vibration control of the underwater structure is a useful means to reduce structure-borne noise in water. PMID:23389344
Use of extracts from oyster shell and soil for cultivation of Spirulina maxima.
Jung, Joo-Young; Kim, Sunmin; Lee, Hansol; Kim, Kyochan; Kim, Woong; Park, Min S; Kwon, Jong-Hee; Yang, Ji-Won
2014-12-01
Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima.
Synthesis and characterization of Zn 3P 2/ZnS core/shell nanowires
NASA Astrophysics Data System (ADS)
Sun, T.; Wu, P. C.; Guo, Z. D.; Dai, Y.; Meng, H.; Fang, X. L.; Shi, Z. J.; Dai, L.; Qin, G. G.
2011-05-01
Fully-surrounded Zn3P2/ZnS core/shell nanowires (NWs) were synthesized for the first time via a two-step method: a catalyst free chemical vapor deposition followed by a low-pressure vulcanization process. Field emission scanning electron microscopy, high-resolution transmission electron microscopy, and high-angle angular dark field scanning transmission electron microscopy were used to characterize the morphologies, crystal structure, and element composition of the core/shell NWs. The band structure analysis demonstrates that the Zn3P2/ZnS core-shell NW type-II heterostructures have bright potential in photovoltaic nanodevice applications. The core/shell NW growth method used here can be extended to other material system.
Use of extracts from oyster shell and soil for cultivation of Spirulina maxima.
Jung, Joo-Young; Kim, Sunmin; Lee, Hansol; Kim, Kyochan; Kim, Woong; Park, Min S; Kwon, Jong-Hee; Yang, Ji-Won
2014-12-01
Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima. PMID:24871274
Numerical modelling of the stability of loaded shells of revolution containing fluid flows
NASA Astrophysics Data System (ADS)
Bochkarev, S. A.; Matveenko, V. P.
2008-03-01
A mixed finite-element algorithm is proposed to study the dynamic behavior of loaded shells of revolution containing a stationary or moving compressible fluid. The behavior of the fluid is described by potential theory, whose equations are reduced to integral form using the Galerkin method. The dynamics of the shell is analyzed with the use of the variational principle of possible displacements, which includes the linearized Bernoulli equation for calculating the hydrodynamic pressure exerted on the shell by the fluid. The solution of the problem reduces to the calculation and analysis of the eigenvalues of the coupled system of equations. As an example, the effect of hydrostatic pressure on the dynamic behavior of shells of revolution containing a moving fluid is studied under various boundary conditions.
Yu, Kuang; Carter, Emily A
2014-03-28
The density functional theory (DFT)+U method is an efficient and effective way to calculate the ground-state properties of strongly correlated transition metal compounds, with the effective U parameters typically determined empirically. Two ab initio methods have been developed to compute the U parameter based on either constrained DFT (CDFT) or unrestricted Hartree-Fock (UHF) theory. Previous studies have demonstrated the success of both methods in typical open-shell materials such as FeO and NiO. In this Communication we report numerical instability issues that arise for the CDFT method when applied to closed-shell transition metals, by using ZnO and Cu2O as examples. By contrast, the UHF method behaves much more robustly for both closed- and open-shell materials, making it more suitable for treating closed-shell transition metals, as well as main group elements. PMID:24697417
NASA Astrophysics Data System (ADS)
Yu, Kuang; Carter, Emily A.
2014-03-01
The density functional theory (DFT)+U method is an efficient and effective way to calculate the ground-state properties of strongly correlated transition metal compounds, with the effective U parameters typically determined empirically. Two ab initio methods have been developed to compute the U parameter based on either constrained DFT (CDFT) or unrestricted Hartree-Fock (UHF) theory. Previous studies have demonstrated the success of both methods in typical open-shell materials such as FeO and NiO. In this Communication we report numerical instability issues that arise for the CDFT method when applied to closed-shell transition metals, by using ZnO and Cu2O as examples. By contrast, the UHF method behaves much more robustly for both closed- and open-shell materials, making it more suitable for treating closed-shell transition metals, as well as main group elements.
Effect of Ice-Shell Thickness Variations on the Tidal Deformation of Enceladus
NASA Astrophysics Data System (ADS)
Choblet, G.; Cadek, O.; Behounkova, M.; Tobie, G.; Kozubek, T.
2015-12-01
Recent analysis of Enceladus's gravity and topography has suggested that the thickness of the ice shell significantly varies laterally - from 30-40 km in the south polar region to 60 km elsewhere. These variations may influence the activity of the geysers and increase the tidal heat production in regions where the ice shell is thinned. Using a model including a regional or global subsurface ocean and Maxwell viscoelasticity, we investigate the impact of these variations on the tidal deformation of the moon and its heat production. For that purpose, we use different numerical approaches - finite elements, local application of 1d spectral method, and a generalized spectral method. Results obtained with these three approaches for various models of ice-shell thickness variations are presented and compared. Implications of a reduced ice shell thickness for the south polar terrain activity are discussed.
Atomic inner-shell transitions
NASA Technical Reports Server (NTRS)
Crasemann, B.; Chen, M. H.; Mark, H.
1984-01-01
Atomic inner-shell processes have quite different characteristics, in several important aspects, from processes in the optical regime. Energies are large, e.g., the 1s binding energy reaches 100 keV at Z = 87; relativistic and quantum-electrodynamic effects therefore are strong. Radiationless transitions vastly dominate over photon emission in most cases. Isolated inner-shell vacancies have pronounced single-particle character, with correlations generally contributing only approximately 1 eV to the 1s and 2p binding energies; the structure of such systems is thus well tractable by independent-particle self-consistent-field atomic models. For systems containing multiple deep inner-shell vacancies, or for highly stripped ions, the importance of relativistic intermediate coupling and configuration interaction becomes pronounced. Cancellation of the Coulomb interaction can lead to strong manifestations of the Breit interaction in such phenomena as multiplet splitting and hypersatellite X-ray shifts. Unique opportunities arise for the test of theory.
Modal analysis of a shell-payload structure using test data
Carne, T.G.; Martinez, D.R.; Tucker, M.D.; Lauffer, J.P.
1985-01-01
This study evaluates the accuracy of computed modal frequencies obtained from a combined experimental/analytical model for a shell-payload structure. The total structure is physically divided into two subsystems, the shell and the internal payload, which are connected through a stiff joint. The payload was tested to obtain its free modes, while a finite element model of the shell was analyzed to obtain its modal description. A component mode synthesis technique was investigated which incorporates free modes and residual flexibility. The experimental modal data base for the payload was directly coupled with the finite element modal model of the shell to create an experimental/analytical model of the total structure. Both the translational and rotational elements of the payload mode shapes at the interface were measured and used in the coupling. The modal frequencies, computed using the combined experimental/analytical model, were then compared to those from a modal test of the entire structure. The sensitivity of the combined model to the residual flexibilities was also determined. Finally, recommended procedures for developing combined experimental/analytical models of shell-payload structures are given.
Benchmarking the QUAD4/TRIA3 element
NASA Astrophysics Data System (ADS)
Pitrof, Stephen M.; Venkayya, Vipperla B.
1993-09-01
The QUAD4 and TRIA3 elements are the primary plate/shell elements in NASTRAN. These elements enable the user to analyze thin plate/shell structures for membrane, bending and shear phenomena. They are also very new elements in the NASTRAN library. These elements are extremely versatile and constitute a substantially enhanced analysis capability in NASTRAN. However, with the versatility comes the burden of understanding a myriad of modeling implications and their effect on accuracy and analysis quality. The validity of many aspects of these elements were established through a series of benchmark problem results and comparison with those available in the literature and obtained from other programs like MSC/NASTRAN and CSAR/NASTRAN. Never-the-less such a comparison is never complete because of the new and creative use of these elements in complex modeling situations. One of the important features of QUAD4 and TRIA3 elements is the offset capability which allows the midsurface of the plate to be noncoincident with the surface of the grid points. None of the previous elements, with the exception of bar (beam), has this capability. The offset capability played a crucial role in the design of QUAD4 and TRIA3 elements. It allowed modeling layered composites, laminated plates and sandwich plates with the metal and composite face sheets. Even though the basic implementation of the offset capability is found to be sound in the previous applications, there is some uncertainty in relatively simple applications. The main purpose of this paper is to test the integrity of the offset capability and provide guidelines for its effective use. For the purpose of simplicity, references in this paper to the QUAD4 element will also include the TRIA3 element.
Benchmarking the QUAD4/TRIA3 element
NASA Technical Reports Server (NTRS)
Pitrof, Stephen M.; Venkayya, Vipperla B.
1993-01-01
The QUAD4 and TRIA3 elements are the primary plate/shell elements in NASTRAN. These elements enable the user to analyze thin plate/shell structures for membrane, bending and shear phenomena. They are also very new elements in the NASTRAN library. These elements are extremely versatile and constitute a substantially enhanced analysis capability in NASTRAN. However, with the versatility comes the burden of understanding a myriad of modeling implications and their effect on accuracy and analysis quality. The validity of many aspects of these elements were established through a series of benchmark problem results and comparison with those available in the literature and obtained from other programs like MSC/NASTRAN and CSAR/NASTRAN. Never-the-less such a comparison is never complete because of the new and creative use of these elements in complex modeling situations. One of the important features of QUAD4 and TRIA3 elements is the offset capability which allows the midsurface of the plate to be noncoincident with the surface of the grid points. None of the previous elements, with the exception of bar (beam), has this capability. The offset capability played a crucial role in the design of QUAD4 and TRIA3 elements. It allowed modeling layered composites, laminated plates and sandwich plates with the metal and composite face sheets. Even though the basic implementation of the offset capability is found to be sound in the previous applications, there is some uncertainty in relatively simple applications. The main purpose of this paper is to test the integrity of the offset capability and provide guidelines for its effective use. For the purpose of simplicity, references in this paper to the QUAD4 element will also include the TRIA3 element.
Contribution of inner shell Compton ionization to the X-ray fluorescence line intensity
NASA Astrophysics Data System (ADS)
Fernández, Jorge E.; Scot, Viviana; Di Giulio, Eugenio
2016-10-01
The Compton effect is a potential ionization mechanism of atoms. It produces vacancies in inner shells that are filled with the same mechanism of atomic relaxation as the one following photo-absorption. This contribution to X-ray fluorescence emission is frequently neglected because the total Compton cross-section is apparently much lower than the photoelectric one at useful X-ray energies. However, a more careful analysis suggests that is necessary to consider single shell cross sections (instead of total cross sections) as a function of energy. In this article these Compton cross sections are computed for the shells K, L1-L3 and M1-M5 in the framework of the impulse approximation. By comparing the Compton and the photoelectric cross-section for each shell it is then possible to determine the extent of the Compton correction to the intensity of the corresponding characteristic lines. It is shown that for the K shell the correction becomes relevant for excitation energies which are too high to be influent in X-ray spectrometry. In contrast, for L and M shells the Compton contribution is relevant for medium-Z elements and medium energies. To illustrate the different grades of relevance of the correction, for each ionized shell, the energies for which the Compton contribution reaches the extent levels of 1, 5, 10, 20, 50 and 100% of the photoelectric one are determined for all the elements with Z = 11-92. For practical applications it is provided a simple formula and fitting coefficients to compute average correction levels for the shells considered.
Moini, Mehdi; O'Halloran, Aoife; Peters, Alan M; France, Christine A M; Vicenzi, Edward P; DeWitt, Tamsen G; Langan, Esther; Walsh, Tim; Speakman, Robert J
2014-01-01
Irregular shell formation and black lines on the outside of live chambered nautilus shells have been observed in all adult specimens at aquariums and zoos soon after the organisms enter aquaria. Black lines have also been observed in wild animals at sites of broken shell, but continued growth from that point returns to a normal, smooth structure. In contrast, rough irregular deposition of shell continues throughout residence in aquaria. The composition and reasons for deposition of the black material and mitigation of this irregular shell formation is the subject of the current study. A variety of analytical techniques were used, including stable isotope mass spectrometry (SI-MS), inductively coupled plasma mass spectrometry (ICP-MS), micro x-ray fluorescence (µXRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) based X-ray microanalysis. Results indicate that the black material contains excess amounts of copper, zinc, and bromine which are unrelated to the Nautilus diet. The combination of these elements and proteins plays an important role in shell formation, growth, and strengthening. Further study will be needed to compare the proteomics of the shell under aquaria versus natural wild environments. The question remains as to whether the occurrence of the black lines indicates normal healing followed by growth irregularities that are caused by stress from chemical or environmental conditions. In this paper we begin to address this question by examining elemental and isotopic differences of Nautilus diet and salt water. The atomic composition and light stable isotopic ratios of the Nautilus shell formed in aquaria verses wild conditions are presented.
Moini, Mehdi; O'Halloran, Aoife; Peters, Alan M; France, Christine A M; Vicenzi, Edward P; DeWitt, Tamsen G; Langan, Esther; Walsh, Tim; Speakman, Robert J
2014-01-01
Irregular shell formation and black lines on the outside of live chambered nautilus shells have been observed in all adult specimens at aquariums and zoos soon after the organisms enter aquaria. Black lines have also been observed in wild animals at sites of broken shell, but continued growth from that point returns to a normal, smooth structure. In contrast, rough irregular deposition of shell continues throughout residence in aquaria. The composition and reasons for deposition of the black material and mitigation of this irregular shell formation is the subject of the current study. A variety of analytical techniques were used, including stable isotope mass spectrometry (SI-MS), inductively coupled plasma mass spectrometry (ICP-MS), micro x-ray fluorescence (µXRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) based X-ray microanalysis. Results indicate that the black material contains excess amounts of copper, zinc, and bromine which are unrelated to the Nautilus diet. The combination of these elements and proteins plays an important role in shell formation, growth, and strengthening. Further study will be needed to compare the proteomics of the shell under aquaria versus natural wild environments. The question remains as to whether the occurrence of the black lines indicates normal healing followed by growth irregularities that are caused by stress from chemical or environmental conditions. In this paper we begin to address this question by examining elemental and isotopic differences of Nautilus diet and salt water. The atomic composition and light stable isotopic ratios of the Nautilus shell formed in aquaria verses wild conditions are presented. PMID:24797217
Bean, R.W.
1963-11-19
A ceramic fuel element for a nuclear reactor that has improved structural stability as well as improved cooling and fission product retention characteristics is presented. The fuel element includes a plurality of stacked hollow ceramic moderator blocks arranged along a tubular raetallic shroud that encloses a series of axially apertured moderator cylinders spaced inwardly of the shroud. A plurality of ceramic nuclear fuel rods are arranged in the annular space between the shroud and cylinders of moderator and appropriate support means and means for directing gas coolant through the annular space are also provided. (AEC)
Rigid shells enhance survival of gekkotan eggs.
Andrews, Robin M
2015-11-01
The majority of lizards and snakes produce permeable parchment-shelled eggs that require high moisture conditions for successful embryonic development. One clade of gekkotan lizards is an exception; females produce relatively impermeable rigid-shelled eggs that normally incubate successfully under low moisture conditions. I tested the hypothesis that the rigid-shell increases egg survival during incubation, but only under low moisture conditions. To test this hypothesis, I incubated rigid-shelled eggs of Chondrodactylus turneri under low and under high moisture conditions. Eggs were incubated with parchment-shelled eggs of Eublepharis macularius to insure that incubation conditions were suitable for parchment-shelled eggs. Chondrodactylus turneri eggs had very high survival (>90%) when they were incubated under low moisture conditions. In contrast, eggs incubated under high moisture conditions had low survival overall, and lower survival than those of the parchment-shelled eggs of E. macularius. Mortality of C. turneri and E. macularius eggs incubated under high moisture conditions was the result of fungal infection, a common source of egg mortality for squamates under laboratory and field conditions. These observations document high survival of rigid-shelled eggs under low moisture conditions because eggs escape from fungal infection. Highly mineralized rigid shells also make egg survival independent of moisture availability and may also provide protection from small invertebrates in nature. Enhanced egg survival could thus compensate for the low reproductive output of gekkotans that produce rigid-shelled eggs.
Shape-tunable core-shell microparticles.
Klein, Matthias K; Saenger, Nicolai R; Schuetter, Stefan; Pfleiderer, Patrick; Zumbusch, Andreas
2014-10-28
Colloidal polymer particles are an important class of materials finding use in both everyday and basic research applications. Tailoring their composition, shape, and functionality is of key importance. In this article, we describe a new class of shape-tunable core-shell microparticles. They are composed of a cross-linked polystyrene (PS) core and a poly(methyl methacrylate) (PMMA) shell of varying thickness. In the first step, we prepared highly cross-linked PS cores, which are subsequently transferred into a nonpolar dispersant. They serve as the seed dispersion for a nonaqueous dispersion polymerization to generate the PMMA shell. The shape of the particles can subsequently be manipulated. After the shell growth stage, the spherical PS/PMMA core-shell colloids exhibit an uneven and wrinkled surface. An additional tempering procedure allows for smoothing the surface of the core-shell colloids. This results in polymer core-shell particles with a perfectly spherical shape. In addition to this thermal smoothing of the PMMA shell, we generated a selection of shape-anisotropic core-shell particles using a thermomechanical stretching procedure. Because of the unique constitution, we can selectively interrogate molecular vibrations in the PS core or the PMMA shell of the colloids using nonlinear optical microscopy techniques. This is of great interest because no photobleaching occurs, such that the particles can be tracked in real space over long times.
On axisymmetric/diamond-like mode transitions in axially compressed core-shell cylinders
NASA Astrophysics Data System (ADS)
Xu, Fan; Potier-Ferry, Michel
2016-09-01
Recent interests in curvature- and stress-induced pattern formation and pattern selection motivate the present study. Surface morphological wrinkling of a cylindrical shell supported by a soft core subjected to axial compression is investigated based on a nonlinear 3D finite element model. The post-buckling behavior of core-shell cylinders beyond the first bifurcation often leads to complicated responses with surface mode transitions. The proposed finite element framework allows predicting and tracing these bifurcation portraits from a quantitative standpoint. The occurrence and evolution of 3D instability modes including sinusoidally deformed axisymmetric patterns and non-axisymmetric diamond-like modes will be highlighted according to critical dimensionless parameters. Besides, the phase diagram obtained from dimensional analyses and numerical results could be used to guide the design of core-shell cylindrical systems to achieve the desired instability patterns.
Material and Geometric Nonlinear Analysis of Functionally Graded Plate-Shell Type Structures
NASA Astrophysics Data System (ADS)
Moita, J. S.; Araújo, A. L.; Mota Soares, C. M.; Mota Soares, C. A.; Herskovits, J.
2016-08-01
A nonlinear formulation for general Functionally Graded Material plate-shell type structures is presented. The formulation accounts for geometric and material nonlinear behaviour of these structures. Using the Newton-Raphson incremental-iterative method, the incremental equilibrium path is obtained, and in case of snap-through occurrence the automatic arc-length method is used. This simple and fast element model is a non-conforming triangular flat plate/shell element with 24 degrees of freedom for the generalized displacements. It is benchmarked in the solution of some illustrative plate- shell examples and the results are presented and discussed with numerical alternative models. Benchmark tests with material and geometrically nonlinear behaviour are also proposed.
Stable Tearing and Buckling Responses of Unstiffened Aluminum Shells with Long Cracks
NASA Technical Reports Server (NTRS)
Starnes, James H., Jr.; Rose, Cheryl A.
1998-01-01
The results of an analytical and experimental study of the nonlinear response of thin, unstiffened, aluminum cylindrical shells with a long longitudinal crack are presented. The shells are analyzed with a nonlinear shell analysis code that accurately accounts for global and local structural response phenomena. Results are presented for internal pressure and for axial compression loads. The effect of initial crack length on the initiation of stable crack growth and unstable crack growth in typical shells subjected to internal pressure loads is predicted using geometrically nonlinear elastic-plastic finite element analyses and the crack-tip-opening angle (CTOA) fracture criterion. The results of these analyses and of the experiments indicate that the pressure required to initiate stable crack growth and unstable crack growth in a shell subjected to internal pressure loads decreases as the initial crack length increases. The effects of crack length on the prebuckling, buckling and postbuckling responses of typical shells subjected to axial compression loads are also described. For this loading condition, the crack length was not allowed to increase as the load was increased. The results of the analyses and of the experiments indicate that the initial buckling load and collapse load for a shell subjected to axial compression loads decrease as the initial crack length increases. Initial buckling causes general instability or collapse of a shell for shorter initial crack lengths. Initial buckling is a stable local response mode for longer initial crack lengths. This stable local buckling response is followed by a stable postbuckling response, which is followed by general or overall instability of the shell.
Stable Tearing and Buckling Responses of Unstiffened Aluminum Shells with Long Cracks
NASA Technical Reports Server (NTRS)
Starnes, James H., Jr.; Rose, Cheryl A.
1999-01-01
The results of an analytical and experimental study of the nonlinear response of thin, unstiffened, aluminum cylindrical shells with a long longitudinal crack are presented. The shells are analyzed with a nonlinear shell analysis code that accurately accounts for global and local structural response phenomena. Results are presented for internal pressure and for axial compression loads. The effect of initial crack length on the initiation of stable crack growth and unstable crack growth in typical shells subjected to internal pressure loads is predicted using geometrically nonlinear elastic-plastic finite element analyses and the crack-tip-opening angle (CTOA) fracture criterion. The results of these analyses and of the experiments indicate that the pressure required to initiate stable crack growth and unstable crack growth in a shell subjected to internal pressure loads decreases as the initial crack length increases. The effects of crack length on the prebuckling, buckling and postbuckling responses of typical shells subjected to axial compression loads are also described. For this loading condition, the crack length was not allowed to increase as the load was increased. The results of the analyses and of the experiments indicate that the initial buckling load and collapse load for a shell subjected to axial compression loads decrease as the initial crack length increases. Initial buckling causes general instability or collapse of a shell for shorter initial crack lengths. Initial buckling is a stable local response mode for longer initial crack lengths. This stable local buckling response is followed by a stable postbuckling response, which is followed by general or overall instability of the shell.
The Role of the Icy Shell in the Thermal Evolution of Ceres
NASA Astrophysics Data System (ADS)
King, S. D.
2015-12-01
Ceres shape and crater morphology are consistent with a layer of low-density material that appears to be more dense and viscous than pure water ice, over an even more dense and viscous core. In order to understand the evolution of Ceres, we conduct a series of numerical experiments designed to understand the evolution of temperature and flow within a spherical body with a soft outer shell over a nearly rigid core using 3D spherical code CitcomS. In these experiments the sphere is heated from within using chondritic abundances of radiogenic elements. We study the impact of surface temperature, outer shell thickness, as well as the density and rheology of the softer outer shell and stiffer core on the thermal and dynamical evolution of the interior of the body, including both the soft shell and stiff core. For the outer shells with a thickness less than 10% of the radius of the body and a surface temperature at or below 90 K, the entire body remains in a conductive state and the temperature of the soft outer shell never exceeds the melting temperature of pure water ice throughout the history of the solar system. However for a range of outer shell thickness and surface temperatures, we find that within the first Gyr of evolution a degree-1 (i.e. single hemisphere) mode of convection encompassing both the stiff core and soft outer shell overtakes shorter-wavelength convective flow occurring in the softer outer shell. When this happens the body dramatically cools over a time interval of less than 100 Myrs and the internal temperature remains asymmetric throughout the subsequent evolution of the body.
ERIC Educational Resources Information Center
Herald, Christine
2001-01-01
Describes a research assignment for 8th grade students on the elements of the periodic table. Students use web-based resources and a chemistry handbook to gather information, construct concept maps, and present the findings to the full class using the mode of their choice: a humorous story, a slideshow or gameboard, a brochure, a song, or skit.…
Integrated Risk Information System (IRIS)
Mercury , elemental ; CASRN 7439 - 97 - 6 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinoge
Error estimation and adaptive mesh refinement for parallel analysis of shell structures
NASA Technical Reports Server (NTRS)
Keating, Scott C.; Felippa, Carlos A.; Park, K. C.
1994-01-01
The formulation and application of element-level, element-independent error indicators is investigated. This research culminates in the development of an error indicator formulation which is derived based on the projection of element deformation onto the intrinsic element displacement modes. The qualifier 'element-level' means that no information from adjacent elements is used for error estimation. This property is ideally suited for obtaining error values and driving adaptive mesh refinements on parallel computers where access to neighboring elements residing on different processors may incur significant overhead. In addition such estimators are insensitive to the presence of physical interfaces and junctures. An error indicator qualifies as 'element-independent' when only visible quantities such as element stiffness and nodal displacements are used to quantify error. Error evaluation at the element level and element independence for the error indicator are highly desired properties for computing error in production-level finite element codes. Four element-level error indicators have been constructed. Two of the indicators are based on variational formulation of the element stiffness and are element-dependent. Their derivations are retained for developmental purposes. The second two indicators mimic and exceed the first two in performance but require no special formulation of the element stiffness mesh refinement which we demonstrate for two dimensional plane stress problems. The parallelizing of substructures and adaptive mesh refinement is discussed and the final error indicator using two-dimensional plane-stress and three-dimensional shell problems is demonstrated.
Error estimation and adaptive mesh refinement for parallel analysis of shell structures
NASA Astrophysics Data System (ADS)
Keating, Scott C.; Felippa, Carlos A.; Park, K. C.
1994-11-01
The formulation and application of element-level, element-independent error indicators is investigated. This research culminates in the development of an error indicator formulation which is derived based on the projection of element deformation onto the intrinsic element displacement modes. The qualifier 'element-level' means that no information from adjacent elements is used for error estimation. This property is ideally suited for obtaining error values and driving adaptive mesh refinements on parallel computers where access to neighboring elements residing on different processors may incur significant overhead. In addition such estimators are insensitive to the presence of physical interfaces and junctures. An error indicator qualifies as 'element-independent' when only visible quantities such as element stiffness and nodal displacements are used to quantify error. Error evaluation at the element level and element independence for the error indicator are highly desired properties for computing error in production-level finite element codes. Four element-level error indicators have been constructed. Two of the indicators are based on variational formulation of the element stiffness and are element-dependent. Their derivations are retained for developmental purposes. The second two indicators mimic and exceed the first two in performance but require no special formulation of the element stiffness mesh refinement which we demonstrate for two dimensional plane stress problems. The parallelizing of substructures and adaptive mesh refinement is discussed and the final error indicator using two-dimensional plane-stress and three-dimensional shell problems is demonstrated.
Methode des elements finis hybride appliquee aux vibrations des coques spheriques
NASA Astrophysics Data System (ADS)
Menaa, Mohamed
The analysis of spherical shells filled with fluid and subjected to supersonic flow has been the subject of few research. Most of these studies treat the dynamic behaviour of empty shells. Few works have investigated spherical shells filled with fluid or subjected to supersonic flutter. In this thesis, we propose to develop a model to analyse the vibratory behaviour of both empty spherical shells and partially filled with fluid. This model is also applicable to study of the dynamic stability of spherical shells subjected to supersonic flow. The model developed is a combination of finite element method, thin shell theory, potential fluid theory and aerodynamic fluid theory. Different parameters are considered here in this study. In the first part of this study, free vibration analysis of spherical shell is carried out. The structural model is based on a combination of thin shell theory and the classical finite element method. Free vibration equations using the hybrid finite element formulation are derived and solved numerically. The results are validated using numerical and theoretical data available in the literature. The analysis is accomplished for spherical shells of different geometries, boundary conditions and radius to thickness ratios. This proposed hybrid finite element method can be used efficiently for design and analysis of spherical shells employed in high speed aircraft structures. In the second part of the present study, a hybrid finite element method is applied to investigate the free vibration of spherical shell filled with fluid. The structural model is based on a combination of thin shell theory and the classical finite element method. It is assumed that the fluid is incompressible and has no free-surface effect. Fluid is considered as a velocity potential variable at each node of the shell element where its motion is expressed in terms of nodal elastic displacement at the fluid-structure interface. Numerical simulation is done and vibration
Analysis of toughening mechanisms in the Strombus gigas shell.
DiPette, Scott; Ural, Ani; Santhanam, Sridhar
2015-08-01
A finite element analysis of the fracture mechanisms in the Strombus gigas conch shell is presented in this work. The S. gigas shell has a complex microarchitecture that consists of three main macroscopic layers of calcium carbonate: the inner, middle, and outer layers. Each layer is composed of lamellae of calcium carbonate, held together by a cohesive organic protein. As a result of this elaborate architecture, the S. gigas shell exhibits a much greater damage tolerance than the calcium carbonate by itself, with a work of fracture reported to be three magnitudes of order greater. The two main energy dissipating factors that contribute to this are multiple, parallel cracking along first-order interfaces in the inner and outer layers and crack bridging through the second-order interfaces of the middle layer. Finite element analysis was conducted to simulate and replicate flexural strength and work-of-fracture results obtained in the literature for both dry and wet physical bend test specimens. Several parameters were varied including protein strength and fracture toughness, initial protein damage, and the relative heights of macroscopic layers in order to create a model that predicted published, experimental results. The simulations indicate that having some initially weakened protein interfaces is key to matching the parallel cracking in the inner layer of the physical specimens. The wet models exhibit significantly higher work of fracture compared to the dry specimens in large part due to a crack growth resistance behavior in the middle layer, which was successfully modeled. The parametric studies that have been performed on the finite element models provide guidelines for manufacturing the ideal S. gigas-inspired, biomimetic composite.
Analysis of toughening mechanisms in the Strombus gigas shell.
DiPette, Scott; Ural, Ani; Santhanam, Sridhar
2015-08-01
A finite element analysis of the fracture mechanisms in the Strombus gigas conch shell is presented in this work. The S. gigas shell has a complex microarchitecture that consists of three main macroscopic layers of calcium carbonate: the inner, middle, and outer layers. Each layer is composed of lamellae of calcium carbonate, held together by a cohesive organic protein. As a result of this elaborate architecture, the S. gigas shell exhibits a much greater damage tolerance than the calcium carbonate by itself, with a work of fracture reported to be three magnitudes of order greater. The two main energy dissipating factors that contribute to this are multiple, parallel cracking along first-order interfaces in the inner and outer layers and crack bridging through the second-order interfaces of the middle layer. Finite element analysis was conducted to simulate and replicate flexural strength and work-of-fracture results obtained in the literature for both dry and wet physical bend test specimens. Several parameters were varied including protein strength and fracture toughness, initial protein damage, and the relative heights of macroscopic layers in order to create a model that predicted published, experimental results. The simulations indicate that having some initially weakened protein interfaces is key to matching the parallel cracking in the inner layer of the physical specimens. The wet models exhibit significantly higher work of fracture compared to the dry specimens in large part due to a crack growth resistance behavior in the middle layer, which was successfully modeled. The parametric studies that have been performed on the finite element models provide guidelines for manufacturing the ideal S. gigas-inspired, biomimetic composite. PMID:25955562
Cracked shells under skew-symmetric loading
NASA Technical Reports Server (NTRS)
Lelale, F.
1982-01-01
A shell containing a through crack in one of the principal planes of curvature and under general skew-symmetric loading is considered. By employing a Reissner type shell theory which takes into account the effect of transverse shear strains, all boundary conditions on the crack surfaces are satisfied separately. Consequently, unlike those obtained from the classical shell theory, the angular distributions of the stress components around the crack tips are shown to be identical to the distributions obtained from the plane and antiplane elasticity solutions. Extensive results are given for axially and circumferentially cracked cylindrical shells, spherical shells, and toroidal shells under uniform inplane shearing, out of plane shearing, and torsion. The effect of orthotropy on the results is also studied.
Thermal stresses in thick laminated composite shells
NASA Technical Reports Server (NTRS)
Yuan, F. G.
1993-01-01
The paper provides an analytical formulation to investigate the thermomechanical behavior of thick composite shells subjected to a temperature distribution which varies arbitrarily in the radial direction. For illustrative purposes, shells under uniform temperature change are presented. It is found that thermal twist would occur even for symmetric laminated shells. Under uniform temperature rise, results for off-axis graphite/epoxy shells show that extensional-shear coupling can cause tensile radial stress throughout the shell and tensile hoop stress in the inner region. Laminated graphite/epoxy shells can exhibit negative effective thermal expansion coefficients in the longitudinal and transverse directions. Finally, the stacking sequence has a strong influence on the thermal stress distributions.
Mussel Shell Impaction in the Esophagus
Kim, Sunmin; Kim, Hyung Hun; Jang, Gook Hwan; Song, Jun Young
2013-01-01
Mussels are commonly used in cooking around the world. The mussel shell breaks more easily than other shells, and the edge of the broken mussel shell is sharp. Impaction can ultimately cause erosion, perforation and fistula. Aside from these complications, the pain can be very intense. Therefore, it is essential to verify and remove the shell as soon as possible. In this report we describe the process of diagnosing and treating mussel shell impaction in the esophagus. Physicians can overlook this unusual foreign body impaction due to lack of experience. When physicians encounter a patient with severe chest pain after a meal with mussels, mussel shell impaction should be considered when diagnosing and treating the patient. PMID:23569440
Flow past a porous approximate spherical shell
NASA Astrophysics Data System (ADS)
Srinivasacharya, D.
2007-07-01
In this paper, the creeping flow of an incompressible viscous liquid past a porous approximate spherical shell is considered. The flow in the free fluid region outside the shell and in the cavity region of the shell is governed by the Navier Stokes equation. The flow within the porous annulus region of the shell is governed by Darcy’s Law. The boundary conditions used at the interface are continuity of the normal velocity, continuity of the pressure and Beavers and Joseph slip condition. An exact solution for the problem is obtained. An expression for the drag on the porous approximate spherical shell is obtained. The drag experienced by the shell is evaluated numerically for several values of the parameters governing the flow.
NASA Astrophysics Data System (ADS)
Ding, Xiaohong; Ji, Xuerong; Ma, Man; Hou, Jianyun
2013-11-01
The application of the adaptive growth method is limited because several key techniques during the design process need manual intervention of designers. Key techniques of the method including the ground structure construction and seed selection are studied, so as to make it possible to improve the effectiveness and applicability of the adaptive growth method in stiffener layout design optimization of plates and shells. Three schemes of ground structures, which are comprised by different shell elements and beam elements, are proposed. It is found that the main stiffener layouts resulted from different ground structures are almost the same, but the ground structure comprised by 8-nodes shell elements and both 3-nodes and 2-nodes beam elements can result in clearest stiffener layout, and has good adaptability and low computational cost. An automatic seed selection approach is proposed, which is based on such selection rules that the seeds should be positioned on where the structural strain energy is great for the minimum compliance problem, and satisfy the dispersancy requirement. The adaptive growth method with the suggested key techniques is integrated into an ANSYS-based program, which provides a design tool for the stiffener layout design optimization of plates and shells. Typical design examples, including plate and shell structures to achieve minimum compliance and maximum bulking stability are illustrated. In addition, as a practical mechanical structural design example, the stiffener layout of an inlet structure for a large-scale electrostatic precipitator is also demonstrated. The design results show that the adaptive growth method integrated with the suggested key techniques can effectively and flexibly deal with stiffener layout design problem for plates and shells with complex geometrical shape and loading conditions to achieve various design objectives, thus it provides a new solution method for engineering structural topology design optimization.
Development of Nanolaminate Thin Shell Mirrors
Hickey, G S; Lih, S S; Barbee, T
2002-08-09
The space science community has identified a need for ultra-light weight, large aperture optical systems that are capable of producing high-resolution images of low contrast. Current mirror technologies are limited due either to not being scalable to larger sizes at reasonable masses, or to lack of surface finish, dimensional stability in a space environment or long fabrication times. This paper will discuss the development of thin-shell, nano-laminate mirror substrates that are capable of being electro-actively figured. This technology has the potential to substantially reduce the cost of space based optics by allowing replication of ultra-lightweight primary mirrors from a master precision tool. Precision master tools have been shown to be used multiple times with repeatable surface quality results with less than one week fabrication times for the primary optical mirror substrate. Current development has developed a series of 0.25 and 0.5 meter spherical nanolaminate mirrors that are less than 0.5 kg/m{sup 2} areal density before electroactive components are mounted, and a target of less than 2.0 kg/m with control elements. This paper will provide an overview of nanolaminate materials for optical mirrors, modeling of their behavior under figure control and experiments conducted to validate precision control.
Shell boosts recovery at Kernridge
Moore, S.
1984-01-01
Since acquiring the Kernridge property in December 1979, Shell Oil Co. has drilled more than 1,800 wells and steadily increased production from 42,000 to 89,000 b/d of oil. Currently, the Kernridge Production Division of Shell California Production Inc. (SCPI), a newly formed subsidiary of Shell Oil Co., is operator for the property. The property covers approximately 35,000 mostly contiguous net acres, with production concentrated mainly on about 5,500 net acres. SCPI's four major fields in the area are the North and South Belridge, Lost Hills, and Antelope Hills. Most of the production comes from the North and South Belridge fields, which were previously held by the Belridge Oil Co. Productive horizons in the fields are the Tulare, Diatomite, Brown Shale, Antelope Shale, 64 Zone, and Agua sand. The Tulare and Diatomite are the two major reservoirs SCPI is developing. The Tulare, encountered between 400 and 1,300 ft, is made up of fine- to coarse-grained, unconsolidated sands with interbedded shales and silt stones and contains 13 /sup 0/ API oil. Using steam drive as the main recovery method, SCPI estimates an ultimate recovery from the Tulare formation of about 60% of the original 1 billion barrels in place. The Diatomite horizon, found between 800 and 3,500 ft and containing light, 28 /sup 0/ API oil, has high porosity (more than 60%), low permeability (less than 1 md), and natural fractures. Because of the Diatomite's low permeability, fracture stimulation is being used to increase well productivity. SCPI anticipates that approximately 5% of the almost 2 billion barrels of oil originally in place will be recovered by primary production.
Double-shell tank waste transfer facilities integrity assessment plan
Hundal, T.S.
1998-09-30
This document presents the integrity assessment plan for the existing double-shell tank waste transfer facilities system in the 200 East and 200 West Areas of Hanford Site. This plan identifies and proposes the integrity assessment elements and techniques to be performed for each facility. The integrity assessments of existing tank systems that stores or treats dangerous waste is required to be performed to be in compliance with the Washington State Department of Ecology Dangerous Waste Regulations, Washington Administrative Code WAC-173-303-640 requirements.
Structural design criteria for filament-wound composite shells
NASA Technical Reports Server (NTRS)
Hahn, H. T.; Jensen, D. W.; Claus, S. J.; Pai, S. P.; Hipp, P. A.
1994-01-01
Advanced composite cylinders, manufactured by filament winding, provide a cost effective solution to many present structural applications; however, the compressive performance of filament-wound cylinders is lower than comparable shells fabricated from unidirectional tape. The objective of this study was to determine the cause of this reduction in thin filament-wound cylinders by relating the manufacturing procedures to the quality of the cylinder and to its compressive performance. The experiments on cylinder buckling were complemented by eigenvalue buckling analysis using a detailed geometric model in a finite element analysis. The applicability of classical buckling analyses was also investigated as a design tool.
Scattering of low-energy neutrinos on atomic shells
Babič, Andrej; Šimkovic, Fedor
2015-10-28
We present a derivation of the total cross section for inelastic scattering of low-energy solar neutrinos and reactor antineutrinos on bound electrons, resulting in a transition of the electron to an excited state. The atomic-shell structure of various chemical elements is treated in terms of a nonrelativistic approximation. We estimate the interaction rates for modern neutrino detectors, in particular the Borexino and GEMMA experiments. We establish that in these experiments the effect can be safely neglected, but it could be accessible to future large-volume neutrino detectors with low energy threshold.
NASA Technical Reports Server (NTRS)
Mindle, W. L.; Torvik, P. J.
1986-01-01
The natural frequencies and associated mode shapes for three thick open cantilevered cylindrical shells were determined both numerically and experimentally. The shells ranged in size from moderately to very thick with length to thickness ratios of 16, 8 and 5.6, the independent dimension being the shell thickness. The shell geometry is characterized by a circumferential angle of the 142 degrees and a ratio of length to inner radii arc length near 1.0. The finite element analysis was performed using NASTRAN's (COSMIC) triangular plate bending element CTRIA2, which includes membrane effects. The experimental results were obtained through holographic interferometry which enables one to determine the resonant frequencies as well as mode shapes from photographs of time-averaged holograms.
Utilization of porous carbons derived from coconut shell and wood in natural rubber
Technology Transfer Automated Retrieval System (TEKTRAN)
The porous carbons derived from cellulose are renewable and environmentally friendly. Coconut shell and wood derived porous carbons were characterized with elemental analysis, ash content, x-ray diffraction, infrared absorbance, particle size, surface area, and pore volume. The results were compared...
Boson shells harboring charged black holes
Kleihaus, Burkhard; Kunz, Jutta; Laemmerzahl, Claus; List, Meike
2010-11-15
We consider boson shells in scalar electrodynamics coupled to Einstein gravity. The interior of the shells can be empty space, or harbor a black hole or a naked singularity. We analyze the properties of these types of solutions and determine their domains of existence. We investigate the energy conditions and present mass formulae for the composite black hole-boson shell systems. We demonstrate that these types of solutions violate black hole uniqueness.
Characterization of Russian ballistic furnace shells
Fearon, E
1999-02-18
The authors received another batch of polystyrene ballistic furnace shells on December 4, 1998. Assigned the batch number of LSC012, it consisted of three cassettes containing 36 shells in each cassette. A group of 27 of the shells were selected for characterization that ranged in diameter from 1880 to 1780 {micro}m. There were two shells with a diameter above 1900 {micro}m, but they were too fragile and did not survive initial handling. For characterization, they examined the shells through a stereo microscope, measured diameter and sphericity on RACI, and weighed a subset of the 27 shells that did not have large particles or polymer shards adhered to the outside in order to calculate wall thickness. They then selected the cleanest and most spherical shells for Sphere Mapping. This batch of shells has about the same physical appearance as the one they documented August 26, 1998. There were some shells with polymer shards adhered to the outside, a few large vacuoles or large particle embedded in the polymer wall, and some with a scattering of small black particles on the outside. There were no swirls in the shell walls. As mentioned in the previous report, each shell is measured with the RACI system in three orthogonal views. They now have new analysis software on RACI that returns the mode two amplitude of the sphere radius vs. angle of rotation around the edge of the shadowgram of the shell. From this they report the maximum radius out-of-round, the largest of the three different orientations.
NASA Astrophysics Data System (ADS)
Karpeshin, F. F.
2002-11-01
Main principles of the resonance effect arising in the electron shells in interaction of the nuclei with electromagnetic radiation are analyzed and presented in the historical aspect. Principles of NEET are considered from a more general position, as compared to how this is usually presented. Characteristic features of NEET and its reverse, TEEN, as internal conversion processes are analyzed, and ways are offered of inducing them by laser radiation. The ambivalent role of the Pauli exclusion principles in NEET and TEEN processes is investigated.
Martin-Moruno, Prado; Visser, Matt; Garcia, Nadiezhda Montelongo; Lobo, Francisco S.N. E-mail: nmontelongo@fis.cinvestav.mx E-mail: matt.visser@msor.vuw.ac.nz
2012-03-01
We construct generic spherically symmetric thin-shell gravastars by using the cut-and-paste procedure. We take considerable effort to make the analysis as general and unified as practicable; investigating both the internal physics of the transition layer and its interaction with 'external forces' arising due to interactions between the transition layer and the bulk spacetime. Furthermore, we discuss both the dynamic and static situations. In particular, we consider 'bounded excursion' dynamical configurations, and probe the stability of static configurations. For gravastars there is always a particularly compelling configuration in which the surface energy density is zero, while surface tension is nonzero.
Celestial mechanics of planet shells
NASA Astrophysics Data System (ADS)
Barkin, Yu V.; Vilke, V. G.
2004-06-01
The motion of a planet consisting of an external shell (mantle) and a core (rigid body), which are connected by a visco-elastic layer and mutually gravitationally interact with each other and with an external celestial body (considered as a material point), is studied (Barkin, 1999, 2002a,b; Vilke, 2004). Relative motions of the core and mantle are studied on the assumption that the centres of mass of the planet and external body move on unperturbed Keplerian orbits around the general centre of mass of the system. The core and mantle of the planet have axial symmetry and have different principal moments of inertia. The differential action of the external body on the core and mantle cause the periodic relative displacements of their centres of mass and their relative turns. An approximate solution of the problem was obtained on the basis of the linearization, averaging and small-parameter methods. The obtained analytical results are applied to the study of the possible relative displacements of the core and mantle of the Earth under the gravitational action of the Moon. For the suggested two-body Earth model and in the simple case of a circular (model) lunar orbit the new phenomenon of periodic translatory-rotary oscillations of the core with a fortnightly period the mantle was observed. The more remarkable phenomenon is the cyclic rotation with the same period (13.7 days) of the core relative to the mantle with a ‘large’ amplitude of 152 m (at the core surface).The results obtained confirm the general concept described by Barkin (1999, 2002a,b) that induced relative shell oscillations can control and dictate the cyclic and secular processes of energization of the planets and satellites in definite rhythms and on different time scales.The results obtained mean that giant moments and forces produce energy which causes in particular deformations of the viscoelastic layer between planet shells. This process is realized with different intensities on different time
Fish, Jennifer F; Stayton, Charles T
2014-04-01
Turtles experience numerous modifications in the morphological, physiological, and mechanical characteristics of their shells through ontogeny. Although a general picture is available of the nature of these modifications, few quantitative studies have been conducted on changes in turtle shell shape through ontogeny, and none on changes in strength or rigidity. This study investigates the morphological and mechanical changes that juvenile Trachemys scripta elegans undergo as they increase in size. Morphology and shell rigidity were quantified in a sample of 36 alcohol-preserved juvenile Trachemys scripta elegans. Morphometric information was used to create finite element models of all specimens. These models were used to assess the mechanical behavior of the shells under various loading conditions. Overall, we find that turtles experience complementary changes in size, shape, deformability, and relative strength as they grow. As turtles age their shells become larger, more elongate, relatively flatter, and more rigid. These changes are associated with decreases in relative (size independent) strength, even though the shells of larger turtles are stronger in an absolute sense. Decreased deformability is primarily due to changes in the size of the animals. Residual variation in deformability cannot be explained by changes in shell shape. This variation is more likely due to changes in the degree of connectedness of the skeletal elements in the turtle's shells, along with changes in the thickness and degree of mineralization of shell bone. We suggest that the mechanical implications of shell size, shape, and deformability may have a large impact on survivorship and development in members of this species as they mature. PMID:24301373
Single Shell Tank (SST) Retrieval Sequence & Double Shell Tank (DST) Space Evaluation
HOHL, T.M.
2001-09-20
This document describes the baseline single-shell tank (SST) waste retrieval sequence for the River Protection Project updated for Fiscal Year 2002. The double-shell tank (DST) space evaluation presents projected DST needs for Hanford for additional DSTs.
Single Shell Tank (SST) Retrieval Sequence and Double Shell Tank (DST) Space Evaluation
KIRCH, N.W.
2003-09-23
This document describes the baseline single-shell tank (SST) waste retrieval sequence for the River Protection Project updated for Fiscal Year 2002. The double-shell tank (DST) space evaluation presents projected DST needs for Hanford for additional DSTs.
Single Shell Tank (SST) Retrieval Sequence & Double Shell Tank (DST) Space Evaluation
STRODE, J.N.
2002-09-23
This document describes the baseline single-shell tank (SST) waste retrieval sequence for the River Protection Project updated for Fiscal Year 2002. The double-shell tank (DST) space evaluation presents projected DST needs for Hanford for additional DSTs.
Radiocarbon Dating: Fictitious Results with Mollusk Shells.
Keith, M L; Anderson, G M
1963-08-16
Evidence is presented to show that modern mollusk shells from rivers can have anomalous radiocarbon ages, owing mainly to incorporation of inactive (carbon-14-deficient) carbon from humus, probably through the food web, as well as by the pathway of carbon dioxide from humus decay. The resultant effect, in addition to the variable contributions of atmospheric carbon dioxide, fermentative carbon dioxide from bottom muds, and, locally, of carbonate carbon from dissolving limestones, makes the initial carbon-14-activity of ancient fresh-water shell indeterminate, but within limits. Consequent errors of shell radiocarbon dates may be as large as several thousand years for river shells.
Shell appraising deepwater discovery off Philippines
Scherer, M. ); Lambers, E.J.T.; Steffens, G.S. )
1993-05-10
Shell International Petroleum Co. Ltd. negotiated a farmout in 1990 from Occidental International Exploration and Production Co. for Block SC-38 in the South China Sea off Palawan, Philippines, following Oxy's discovery of gas in 1989 in a Miocene Nido limestone buildup. Under the terms of the farmout agreement, Shell became operator with a 50% share. Following the disappointing well North Iloc 1, Shell was successful in finding oil and gas in Malampaya 1. Water 700-1,000 m deep, remoteness, and adverse weather conditions have imposed major challenges for offshore operations. The paper describes the tectonic setting; the Nido limestone play; the Malampaya discovery; and Shell's appraisal studies.
Thin-shell instability in collisionless plasma.
Dieckmann, M E; Ahmed, H; Doria, D; Sarri, G; Walder, R; Folini, D; Bret, A; Ynnerman, A; Borghesi, M
2015-09-01
Thin-shell instability is one process which can generate entangled structures in astrophysical plasma on collisional (fluid) scales. It is driven by a spatially varying imbalance between the ram pressure of the inflowing upstream plasma and the downstream's thermal pressure at a nonplanar shock. Here we show by means of a particle-in-cell simulation that an analog process can destabilize a thin shell formed by two interpenetrating, unmagnetized, and collisionless plasma clouds. The amplitude of the shell's spatial modulation grows and saturates after about ten inverse proton plasma frequencies, when the shell consists of connected piecewise linear patches.
Design optimization of a torpedo shell structure
NASA Astrophysics Data System (ADS)
Yu, De-Hai; Song, Bao-Wei; Li, Jia-Wang; Yang, Shi-Xing
2008-03-01
An optimized methodology to design a more robust torpedo shell is proposed. The method has taken into account reliability requirements and controllable and uncontrollable factors such as geometry, load, material properties, manufacturing processes, installation, etc. as well as human and environmental factors. The result is a more realistic shell design. Our reliability optimization design model was developed based on sensitivity analysis. Details of the design model are given in this paper. An example of a torpedo shell design based on this model is given and demonstrates that the method produces designs that are more effective and reliable than traditional torpedo shell designs. This method can be used for other torpedo system designs.
Material with core-shell structure
Luhrs, Claudia; Richard, Monique N.; Dehne, Aaron; Phillips, Jonathan; Stamm, Kimber L.; Fanson, Paul T.
2011-11-15
Disclosed is a material having a composite particle, the composite particle including an outer shell and a core. The core is made from a lithium alloying material and the outer shell has an inner volume that is greater in size than the core of the lithium alloying material. In some instances, the outer mean diameter of the outer shell is less than 500 nanometers and the core occupies between 5 and 99% of the inner volume. In addition, the outer shell can have an average wall thickness of less than 100 nanometers.
Fracture Mitigation Strategies in Gastropod Shells
NASA Astrophysics Data System (ADS)
Salinas, Christopher; Kisailus, David
2013-04-01
For hundreds of millions of years, gastropods have been evolving, modifying their external calcified shells for defense against shell-breaking and drilling predators. They have evolved primarily to use two different aragonitic microstructures: the evolutionary older Nacre (mother of pearl) structure and the more recently developed crossed-lamellar structure. By using both of these structures, gastropods are able to produce shells that are significantly tougher then geologic aragonite. However, the crossed-lamellar structure allows for a wider variety of shell morphologies, ensuring its increasing presence since the Mesozoic Marine Revolution more than 200 million years ago.
S-cones in thin shells under indentation
NASA Astrophysics Data System (ADS)
Nasto, Alice; Ajdari, Amin; Lazarus, Arnaud; Vaziri, Ashkan; Reis, Pedro
2012-02-01
We perform a hybrid experimental and numerical investigation of the localization of deformation in indented thin spherical elastic shells. Past the initial linear response, an inverted cap develops as a Pogorelov circular ridge. For further indentation, this ridge looses axis-symmetry and sharp points of localized curvature form. We refer to these localized objects as s-cones (for shell-cones), in contrast with their developable cousins in plates (d-cones). We quantify the effect of systematically varying the indenter's radius of curvature (from point to plate load) on the formation and evolution of s-cones. In our precision desktop-scale experiments we use rapid prototyped elastomeric shells and rigid indenters of various shape. The mechanical response is measured through load-displacement compression tests and the deformation process is further characterized through digital imaging. In parallel, the experimental results are contrasted against nonlinear Finite Element simulations. Merging these two complementary approaches allows us to gain further physical insight towards rationalizing this geometrically nonlinear process.
Non-Deterministic Dynamic Instability of Composite Shells
NASA Technical Reports Server (NTRS)
Chamis, Christos C.; Abumeri, Galib H.
2004-01-01
A computationally effective method is described to evaluate the non-deterministic dynamic instability (probabilistic dynamic buckling) of thin composite shells. The method is a judicious combination of available computer codes for finite element, composite mechanics, and probabilistic structural analysis. The solution method is incrementally updated Lagrangian. It is illustrated by applying it to thin composite cylindrical shell subjected to dynamic loads. Both deterministic and probabilistic buckling loads are evaluated to demonstrate the effectiveness of the method. A universal plot is obtained for the specific shell that can be used to approximate buckling loads for different load rates and different probability levels. Results from this plot show that the faster the rate, the higher the buckling load and the shorter the time. The lower the probability, the lower is the buckling load for a specific time. Probabilistic sensitivity results show that the ply thickness, the fiber volume ratio and the fiber longitudinal modulus, dynamic load and loading rate are the dominant uncertainties, in that order.
Buckling-induced encapsulation of structured elastic shells under pressure
Shim, Jongmin; Perdigou, Claude; Chen, Elizabeth R.; Bertoldi, Katia; Reis, Pedro M.
2012-01-01
We introduce a class of continuum shell structures, the Buckliball, which undergoes a structural transformation induced by buckling under pressure loading. The geometry of the Buckliball comprises a spherical shell patterned with a regular array of circular voids. In order for the pattern transformation to be induced by buckling, the possible number and arrangement of these voids are found to be restricted to five specific configurations. Below a critical internal pressure, the narrow ligaments between the voids buckle, leading to a cooperative buckling cascade of the skeleton of the ball. This ligament buckling leads to closure of the voids and a reduction of the total volume of the shell by up to 54%, while remaining spherical, thereby opening the possibility of encapsulation. We use a combination of precision desktop-scale experiments, finite element simulations, and scaling analyses to explore the underlying mechanics of these foldable structures, finding excellent qualitative and quantitative agreement. Given that this folding mechanism is induced by a mechanical instability, our Buckliball opens the possibility for reversible encapsulation, over a wide range of length scales. PMID:22451901
The free vibration of plates, shallow shells and solids
NASA Astrophysics Data System (ADS)
Young, Philippe Georges
1993-07-01
The Ritz approach is used to study the free structural vibration problem of a wide class of plates, shallow shells, and solids. The boundaries and/or internal supports of the systems are considered and described by polynomials in Cartesian coordinates. The geometric boundary conditions at these boundaries or supports are enforced by including in a simple polynomial trial series the polynomial equation describing the position of the support raised to the appropriate power. For plates and shallow shells, in some instances, the displacement field is discretized into several domains or elements, and continuity conditions along the connecting boundaries are enforced using a penalty method approach. Complicating effects such as point masses, stepped geometry, cutouts, and internal point supports are also considered. The natural frequencies and mode shapes of isotropic rectangular plates are obtained, then isotropic and orthotropic plates of more general form are considered. The approach is extended to shallow shells of differing shapes and curvatures, as well as complicating effects. The approach is finally applied to studying free vibration of a class of solids including a sphere, cylinders, a cone, and a prismatic solid of more general cross-section.
Shell bone histology indicates terrestrial palaeoecology of basal turtles
Scheyer, Torsten M; Sander, P.Martin
2007-01-01
The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to the lifestyle of modern snapping turtles. Lately, this view was questioned based on limb bone proportions, and a terrestrial palaeoecology was suggested for the turtle stem. Here, we present independent shell bone microstructural evidence for a terrestrial habitat of the oldest and basal most well-known turtles, i.e. the Upper Triassic Proterochersis robusta and Proganochelys quenstedti. Comparison of their shell bone histology with that of extant turtles preferring either aquatic habitats or terrestrial habitats clearly reveals congruence with terrestrial turtle taxa. Similarities in the shell bones of these turtles are a diploe structure with well-developed external and internal cortices, weak vascularization of the compact bone layers and a dense nature of the interior cancellous bone with overall short trabeculae. On the other hand, ‘aquatic’ turtles tend to reduce cortical bone layers, while increasing overall vascularization of the bone tissue. In contrast to the study of limb bone proportions, the present study is independent from the uncommon preservation of appendicular skeletal elements in fossil turtles, enabling the palaeoecological study of a much broader range of incompletely known turtle taxa in the fossil record. PMID:17519193
Shell bone histology indicates terrestrial palaeoecology of basal turtles.
Scheyer, Torsten M; Sander, P Martin
2007-08-01
The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to the lifestyle of modern snapping turtles. Lately, this view was questioned based on limb bone proportions, and a terrestrial palaeoecology was suggested for the turtle stem. Here, we present independent shell bone microstructural evidence for a terrestrial habitat of the oldest and basal most well-known turtles, i.e. the Upper Triassic Proterochersis robusta and Proganochelys quenstedti. Comparison of their shell bone histology with that of extant turtles preferring either aquatic habitats or terrestrial habitats clearly reveals congruence with terrestrial turtle taxa. Similarities in the shell bones of these turtles are a diploe structure with well-developed external and internal cortices, weak vascularization of the compact bone layers and a dense nature of the interior cancellous bone with overall short trabeculae. On the other hand, 'aquatic' turtles tend to reduce cortical bone layers, while increasing overall vascularization of the bone tissue. In contrast to the study of limb bone proportions, the present study is independent from the uncommon preservation of appendicular skeletal elements in fossil turtles, enabling the palaeoecological study of a much broader range of incompletely known turtle taxa in the fossil record. PMID:17519193
A New Axi-Symmetric Element for Thin Walled Structures
NASA Astrophysics Data System (ADS)
Cardoso, Rui P. R.; Yoon, Jeong Whan; Dick, Robert E.
2010-06-01
A new axi-symmetric finite element for sheet metal forming applications is presented in this work. It uses the solid-shell element's concept with only a single element layer and multiple integration points along the thickness direction. The cross section of the element is composed of four nodes with two degrees of freedom each. The proposed formulation overcomes major locking pathologies including transverse shear locking, Poisson's locking and volumetric locking. Some examples are shown to demonstrate the performance and accuracy of the proposed element with special focus on the numerical simulations for the beverage can industry.
NASA Technical Reports Server (NTRS)
Ramsey, J. W., Jr.
1975-01-01
The effect on stresses in a cylindrical shell with a circular penetration subject to internal pressure was investigated in thin, shallow linearly, elastic cylindrical shells. Results provide numerical predictions of peak stress concentration factors around nonreinforced and reinforced penetrations in pressurized cylindrical shells. Analytical results were correlated with published formulas, as well as theoretical and experimental results. An accuracy study was made of the finite element program for each of the configurations considered important in pressure vessel technology. A formula is developed to predict the peak stress concentration factor for analysis and/or design in conjunction with the ASME Boiler and Pressure Vessel Code.
Cross-surface interface element for coupling built-up structural subdomains
NASA Technical Reports Server (NTRS)
Davila, C. G.; Ransom, J. B.; Aminpour, M. A.
1994-01-01
A new finite element for coupling built-up shell substructures is presented. The present work extends the hybrid variational formulation of the interface element developed by Aminpour and Ransom to permit coupling between two intersecting substructures. Designed for the assembly of independently built-up finite element models, this technique provides a level of modeling flexibility previously unavailable.
Lead behavior in abalone shell
NASA Astrophysics Data System (ADS)
Hirao, Yoshimitsu; Matsumoto, Akikazu; Yamakawa, Hiroshi; Maeda, Masaru; Kimura, Kan
1994-08-01
In order to gain information about the behavior of heavy metals in biological assimilation processes in a marine food chain and to investigate the possibility that lead pollution in a marine environment can be estimated by measurement of a small number of key materials from such a food chain, muscle and shell were analyzed from abalone ( Haliotis) from a shallow water locality in a Japanese coastal region. Lead concentrations in muscle were about 26 ppb for abalone of approximately 3 years old and decreased systematically with increasing age of animals sampled, to about 3.3 ppb for a specimen approximately 8 years old. Lead concentrations in shell material gradually decreased also, from 150 ppb to 82 ppb in the oldest specimen. The decrease of concentration in tissues with increasing age indicates that a mechanism for exclusion of lead during tissue growth becomes more efficient with age. Along the food chain in which abalone is the final stage, lead was enriched at the first stage, from seawater to algae, by a factor of 100. Lead was diminished at all subsequent stages of the chain. Tissue of artificially cultured abalone had four times higher lead values compared to abalone grown in natural conditions, and this appears to reflect the fact that lead concentration was three times higher in seawater in the cultured environment.
Transitional nuclei near shell closures
Mukherjee, G.
2014-08-14
High spin states in Bismuth and Thallium nuclei near the Z = 82 shell closure and Cesium nuclei near the N = 82 shell closure in A = 190 and A = 130 regions, respectively, have been experimentally investigated using heavy-ion fusion evaporation reaction and by detecting the gamma rays using the Indian National Gamma Array (INGA). Interesting shape properties in these transitional nuclei have been observed. The results were compared with the neighboring nuclei in these two regions. The total Routhian surface (TRS) calculations have been performed for a better understanding of the observed properties. In mass region A = 190, a change in shape from spherical to deformed has been observd around neutron number N = 112 for the Bi (Z = 83) isotopes with proton number above the magic gap Z = 82, whereas, the shape of Tl (Z = 81) isotopes with proton number below the magic gap Z = 82 remains stable as a function of neutron number. An important transition from aplanar to planar configuration of angular momentum vectors leading to the occurance of nuclar chirality and magnetic rotation, respectively, has been proposed for the unique parity πh{sub 11/2}⊗νh{sub 11/2} configuration in Cs isotopes in the mass region A ∼ 130 around neutron number N = 79. These results are in commensurate with the TRS calculations.
Lead behavior in abalone shell
Hirao, Yoshimitsu; Matsumoto, Akikazu; Kimura, Kan ); Yamakawa, Hiroshi; Maeda, Masaru )
1994-08-01
In order to gain information about the behavior of heavy metals in biological assimilation processes in a marine food chain and to investigate the possibility that lead pollution in a marine environment can be estimated by measurement of a small number of key materials from such a food chain, muscle and shell were analyzed from abalone (Haliotis) from a shallow water locality in a Japanese coastal region. Lead concentrations in muscle were about 26 ppb for abalone approximately 3 years old and decreased systematically with increasing age of animals sampled, to about 3.3 ppb for a specimen approximately 8 years old. Lead concentrations in shell material gradually decreased also, from 150 ppb to 82 ppb in the oldest specimen. The decrease of concentration in tissues with increasing age indicates that a mechanism for exclusion of lead during tissue growth becomes more efficient with age. Along the food chain in which abalone is the final stage, lead was enriched at the first stage, from seawater to algae, by a factor of 100. Lead was diminished at all subsequent stages of the chain. Tissue of artificially cultured abalone had four times higher lead values compared to abalone grown in natural conditions, and this appears to reflect the fact that lead concentration was three times higher in seawater in the cultured environment.
Properties of Shell-Model Wavefunctions at High Excitation Energies
NASA Astrophysics Data System (ADS)
Frazier, Njema Jioni
Within the framework of the nuclear shell model with a realistic residual hamiltonian one can obtain the exact solution of the many-body problem. This makes it possible to study the interrelation between regular and chaotic features of dynamics in a generic many-body system with strong interaction. As an important application, we analyse the fragmentation of simple configurations as a function of excitation energy and interaction strength and examine the transition strengths induced by simple operators as a function of excitation energy. The analysis is performed for two systems; that of 12 valence particles in the sd-shell, or 28Si, and that of 8 valence particles in the sd-shell, or 24Mg. For the system of 12 valence particles in the sd-shell, we examine the fragmentation of shell-model basis states. For the system of 8 valence nucleons in the sd-shell, we examine the fragmentation associated with single-nucleon transfer and Gamow-Teller transitions. For the fragmentation of basis states, we use our statistics to establish the generic shape of the strength function distribution in the region of strong mixing. For the realistic interaction, the strength function distribution is close to Gaussian in the central part of the energy spectra. The width of the distribution is larger than predicted by Fermi's golden rule (4). We then take this one step further and examine the strength distributions associated with the one-nucleon transfer operator, aλ†, and the Gamow-Teller (GT) operator, Σλλ'(σμ τ±) λλ'aλ†a λ'. The spectroscopic factor, which is proportional to the square of the matrix element for the aλ† operator, is the simplest quantity used in predicting experimental observables. In our discussion of Gamow-Teller transitions, we examine both the GT strength function distribution and the values of total strength B(GT). For all the cases we examine, we take advantage of the reliability of our model for low-lying levels and our statistics to explore
A triangular element based on generalized potential energy concepts
NASA Technical Reports Server (NTRS)
Thomas, G. R.; Gallagher, R. H.
1976-01-01
Stiffness equations are formulated for a doubly-curved triangular thin shell finite element. The strain energy component of the potential energy is first expressed in terms of displacements and displacement gradients with the aid of consistent deep shell strain-displacement equations. The element in-plane and normal displacement fields are approximated by complete cubic polynomials. These functions do not satisfy the interelement displacement admissibility conditions. Satisfaction is forced by the imposition of constraint conditions on the interelement boundaries; the constraints represent the modification of the potential energy. Some numerical results for a pinched cylinder, a cylindrical sphere, and a pinched sphere are examined.
Leach, David; Bergendahl, Peter Allen; Waldo, Stuart Forrest; Smith, Robert Leroy; Phelps, Robert Kim
2001-01-01
A turbine includes upper and lower inner shell sections mounting the nozzles and shrouds and which inner shell is supported by pins secured to a surrounding outer shell. To disassemble the turbine for access to the inner shell sections and rotor, an alignment fixture is secured to the lower outer shell section and has pins engaging the inner shell section. To disassemble the turbine, the inner shell weight is transferred to the lower outer shell section via the alignment fixture and cradle pins. Roller assemblies are inserted through access openings vacated by support pins to permit rotation of the lower inner shell section out of and into the lower outer shell section during disassembly and assembly. The alignment fixture includes adjusting rods for adjusting the inner shell axially, vertically, laterally and about a lateral axis. A roller over-cage is provided to rotate the inner shell and a dummy shell to facilitate assembly and disassembly in the field.
BV photometry of five shell galaxies
NASA Astrophysics Data System (ADS)
Pierfederici, F.; Rampazzo, R.
2004-06-01
Current views consider shell structures as bona fide signatures of a recent minor/major merging event though also weak interaction models (WIM) could produce long lasting shells on host galaxies possessing a stellar thick disc. We present a B V band photometric study of a sample of 5 shell galaxies belonging to the Malin & Carter (1983) compilation. The structural properties and colors of the galaxies, as well as the colors of their shells are examined in detail. We did not find signatures of the presence of double nuclei. NGC 7585 is the only E galaxy in the sample and has a moderately boxy structure. The other galaxies have either a discy structure or are mixed E/S0 type galaxies. NGC 474 is a true lenticular. NGC 6776 shows a diffuse asymmetric outer structure and a system of tails of the the same color of the galaxy body; but not clear shells. In general, the color of the shells in our sample is similar or slightly redder than that of the host galaxy, whose color, in turn, is typical of the early-type morphological class. One of the outer shells of NGC 474 is significantly bluer than the body of the galaxy. Since NGC 474 appears to be interacting with NGC 470, the color of this one shell could be explained as result of a recent acquisition of material through tidal interaction. The WIM hypothesis could explain both the red and the blue shells of NGC 474, this latter acquired from the fly-by of the nearby companion NGC 470, but the lack of the constancy of shell surface brightness as a ratio of the underlying galaxy brightness argues against WIM. We speculate about evidence, which also comes from different observations, that suggests a merging/accretion origin of the shells. Based on observations obtained at the Observatoire de Haute Provence, CNRS, Saint Michel l'Observatoire, France and ESO, La Silla, Chile
Synthesis of zirconium tungstate-zirconia core-shell composite particles
Khazeni, Nasser; Mavis, Bora; Guenduez, Guengoer; Colak, Uner
2011-11-15
Highlights: {yields} ZrW{sub 2}O{sub 8}-ZrO{sub 2} core-shell particles to offer solutions for sintering problems. {yields} Core synthesis by a precursor based on tungstic acid and zirconium acetate. {yields} Shell phase by urea hydrolysis in the presence of zirconium ions. {yields} [Urea]/[ZrOCl{sub 2}] ratio controls the rate of shell precursor precipitation. -- Abstract: In this work, ZrW{sub 2}O{sub 8}-ZrO{sub 2} core-shell composite particles were synthesized. ZrW{sub 2}O{sub 8} that was used in the core is a material with negative coefficient of thermal expansion, and it was synthesized from a high-pH precursor based on use of tungstic acid and zirconium acetate. Shell layer was composed of ZrO{sub 2} nanocrystallites and precipitated from an aqueous solution by urea hydrolysis. While volume of the shell was effectively controlled by the initial zirconium ion concentration in the solutions, the rate of precipitation was a function of the ratio of initial concentrations of urea to zirconium ions. It is hypothesized that isolation of the ZrW{sub 2}O{sub 8} within a layer of ZrO{sub 2}, will be a key element in solving problems associated with reactivity of ZrW{sub 2}O{sub 8} towards other components in sintering of ceramic-ceramic composites with tuned or zero thermal expansion coefficient.
The origin and loss of periodic patterning in the turtle shell.
Moustakas-Verho, Jacqueline E; Zimm, Roland; Cebra-Thomas, Judith; Lempiäinen, Netta K; Kallonen, Aki; Mitchell, Katherine L; Hämäläinen, Keijo; Salazar-Ciudad, Isaac; Jernvall, Jukka; Gilbert, Scott F
2014-08-01
The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a soft-shelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell.
Coherently Strained Si-SixGe1-x Core-Shell Nanowire Heterostructures.
Dillen, David C; Wen, Feng; Kim, Kyounghwan; Tutuc, Emanuel
2016-01-13
Coherently strained Si-SixGe1-x core-shell nanowire heterostructures are expected to possess a positive shell-to-core conduction band offset, allowing for quantum confinement of electrons in the Si core. We report the growth of epitaxial, coherently strained Si-SixGe1-x core-shell heterostructures through the vapor-liquid-solid mechanism for the Si core, followed in situ by the epitaxial SixGe1-x shell growth using ultrahigh vacuum chemical vapor deposition. The Raman spectra of individual nanowires reveal peaks associated with the Si-Si optical phonon mode in the Si core and the Si-Si, Si-Ge, and Ge-Ge vibrational modes of the SixGe1-x shell. The core Si-Si mode displays a clear red-shift compared to unstrained, bare Si nanowires thanks to the lattice mismatch-induced tensile strain, in agreement with calculated values using a finite-element continuum elasticity model combined with lattice dynamic theory. N-type field-effect transistors using Si-SixGe1-x core-shell nanowires as channel are demonstrated.
Free Vibration of Fiber Composite Thin Shells in a Hot Environment
NASA Technical Reports Server (NTRS)
Gotsis, Pascal K.; Guptill, James D.
1995-01-01
Results are presented of parametric studies to assess the effects of various parameters on the free vibration behavior (natural frequencies) of (plus or minus theta)2, angle-ply fiber composite thin shells in a hot environment. These results were obtained by using a three-dimensional finite element structural analysis computer code. The fiber composite shell is assumed to be cylindrical and made from T-300 graphite fibers embedded in an intermediate-modulus high-strength matrix (IMHS). The residual stresses induced into the laminated structure during curing are taken into account. The following parameters are investigated: the length and the thickness of the shell, the fiber orientations, the fiber volume fraction, the temperature profile through the thickness of the laminate and the different ply thicknesses. Results obtained indicate that: the fiber orientations and the length of the laminated shell had significant effect on the natural frequencies. The fiber volume fraction, the laminate thickness and the temperature profile through the shell thickness had a weak effect on the natural frequencies. Finally, the laminates with different ply thicknesses had insignificant influence on the behavior of the vibrated laminated shell.
NASA Astrophysics Data System (ADS)
Cai, Zhao-zhen; Zhu, Miao-yong
2014-03-01
By employing a two-dimensional transient thermo-mechanical coupled finite element model for simulating shell heat transfer behaviors within a slab continuous casting mold, we predicted the evolution of shell deformation and the thermal behaviors, including the mold flux film dynamical distribution, the air gap formation, as well as the shell temperature field and the growth of carbon steel solidification, in a 2120 mm × 266 mm slab continuous casting mold. The results show that the shell server deformation occurs in the off-corners in the middle and lower parts of the mold and thus causes the thick mold flux film and air gap to distribute primarily in the regions of 0-140 mm and 0-124 mm and 0-18 mm and 0-10 mm, respectively, from the corners of the wide and narrow faces of the shell under typical casting conditions. As a result, the hot spots, which result from the thick mold flux film filling the shell/mold gap, form in the regions of 20-100 mm from the corners of the wide and narrow faces of the shell and tend to expand as the shell moves downward.
NASA Astrophysics Data System (ADS)
Hahn, S.; Rodolfo-Metalpa, R.; Griesshaber, E.; Schmahl, W. W.; Buhl, D.; Hall-Spencer, J. M.; Baggini, C.; Fehr, K. T.; Immenhauser, A.
2012-05-01
Bivalve shells can provide excellent archives of past environmental change but have not been used to interpret ocean acidification events. We investigated carbon, oxygen and trace element records from different shell layers in the mussels Mytilus galloprovincialis combined with detailed investigations of the shell ultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy) were transplanted and grown in water with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the east coast of the island. Most prominently, the shells recorded the shock of transplantation, both in their shell ultrastructure, textural and geochemical record. Shell calcite, precipitated subsequently under acidified seawater responded to the pH gradient by an in part disturbed ultrastructure. Geochemical data from all test sites show a strong metabolic effect that exceeds the influence of the low-pH environment. These field experiments showed that care is needed when interpreting potential ocean acidification signals because various parameters affect shell chemistry and ultrastructure. Besides metabolic processes, seawater pH, factors such as salinity, water temperature, food availability and population density all affect the biogenic carbonate shell archive.
The ultimate step towards a tailored engineering of core@shell and core@shell@shell nanoparticles.
Llamosa, D; Ruano, M; Martínez, L; Mayoral, A; Roman, E; García-Hernández, M; Huttel, Y
2014-11-21
Complex core@shell and core@shell@shell nanoparticles are systems that combine the functionalities of the inner core and outer shell materials together with new physico-chemical properties originated by their low (nano) dimensionality. Such nanoparticles are of prime importance in the fast growing field of nanotechnology as building blocks for more sophisticated systems and a plethora of applications. Here, it is shown that although conceptually simple a modified gas aggregation approach allows the one-step generation of well-controlled complex nanoparticles. In particular, it is demonstrated that the atoms of the core and the shell of the nanoparticles can be easily inverted, avoiding intrinsic constraints of chemical methods.
Material Distribution Optimization for the Shell Aircraft Composite Structure
NASA Astrophysics Data System (ADS)
Shevtsov, S.; Zhilyaev, I.; Oganesyan, P.; Axenov, V.
2016-09-01
One of the main goal in aircraft structures designing isweight decreasing and stiffness increasing. Composite structures recently became popular in aircraft because of their mechanical properties and wide range of optimization possibilities.Weight distribution and lay-up are keys to creating lightweight stiff strictures. In this paperwe discuss optimization of specific structure that undergoes the non-uniform air pressure at the different flight conditions and reduce a level of noise caused by the airflowinduced vibrations at the constrained weight of the part. Initial model was created with CAD tool Siemens NX, finite element analysis and post processing were performed with COMSOL Multiphysicsr and MATLABr. Numerical solutions of the Reynolds averaged Navier-Stokes (RANS) equations supplemented by k-w turbulence model provide the spatial distributions of air pressure applied to the shell surface. At the formulation of optimization problem the global strain energy calculated within the optimized shell was assumed as the objective. Wall thickness has been changed using parametric approach by an initiation of auxiliary sphere with varied radius and coordinates of the center, which were the design variables. To avoid a local stress concentration, wall thickness increment was defined as smooth function on the shell surface dependent of auxiliary sphere position and size. Our study consists of multiple steps: CAD/CAE transformation of the model, determining wind pressure for different flow angles, optimizing wall thickness distribution for specific flow angles, designing a lay-up for optimal material distribution. The studied structure was improved in terms of maximum and average strain energy at the constrained expense ofweight growth. Developed methods and tools can be applied to wide range of shell-like structures made of multilayered quasi-isotropic laminates.
A viscoplastic model of expanding cylindrical shells subjected to internal explosive detonations
Martineau, R.L.
1998-04-01
Magnetic flux compression generators rely on the expansion of thin ductile shells to generate magnetic fields. These thin shells are filled with high explosives, which when detonated, cause the shell to expand to over 200% strain at strain-rates on the order of 10{sup 4} s{sup {minus}1}. Experimental data indicate the development and growth of multiple plastic instabilities which appear in a quasi-periodic pattern on the surfaces of the shells. These quasi-periodic instabilities are connected by localized zones of intense shear that are oriented approximately 45{degree} from the outward radial direction. The quasi-periodic instabilities continue to develop and eventually become through-cracks, causing the shell to fragment. A viscoplastic constitutive model is formulated to model the high strain-rate expansion and provide insight into the development of plastic instabilities. The formulation of the viscoplastic constitutive model includes the effects of shock heating and damage in the form of microvoid nucleation, growth, and coalescence in the expanding shell. This model uses the Johnson-Cook strength model with the Mie-Grueneisen equation of state and a modified Gurson yield surface. The constitutive model includes the modifications proposed by Tvergaard and the plastic strain controlled nucleation introduced by Neeleman. The constitutive model is implemented as a user material subroutine into ABAQUS/Explicit, which is a commercially available nonlinear explicit dynamic finite element program. A cylindrical shell is modeled using both axisymmetric and plane strain elements. Two experiments were conducted involving plane wave detonated, explosively filled, copper cylinders. Instability, displacement, and velocity data were recorded using a fast framing camera and a Fabry-Perot interferometer. Good agreement is shown between the numerical results and experimental data. An additional explosively bulged cylinder experiment was also performed and a photomicrograph of
Kang, Jie; Li, Yuan; Chen, Yingnan; Wang, Ailing; Yue, Bin; Qu, Yanrong; Zhao, Yongliang; Chu, Haibin
2015-11-15
Highlights: • Ag@SiO{sub 2} nanoparticles of different silica shell thicknesses were prepared via the Stöber process. • Sm and Dy complexes with benzoate, 1,10-phenanthroline and 2,2′-bipyridine were synthesized. • The complex-doped Ag@SiO{sub 2} composites show stronger luminescent intensities than pure complexes. • The luminescent intensities of the composites strongly depend on the SiO{sub 2} shell thickness. - Abstract: Three kinds of almost spherical core–shell Ag@SiO{sub 2} nanoparticles of different silica shell thicknesses (10, 25 and 80 nm) were prepared via the Stöber process. The Ag core nanoparticles were prepared by reducing silver nitrate with sodium citrate. The size, morphology and structure of core–shell Ag@SiO{sub 2} nanoparticles were characterized by transmission electron microscopy. Subsequently, eight kinds of lanthanide complexes with benzoate, 1,10-phenanthroline and 2,2′-bipyridine were synthesized. The composition of the lanthanide complexes was characterized by elemental analysis, IR and UV spectra. Finally, lanthanide complexes were attached to the surface of Ag@SiO{sub 2} nanoparticles to form lanthanide-complex-doped Ag@SiO{sub 2} nanocomposites. The results show that the complex-doped Ag@SiO{sub 2} nanocomposites display much stronger luminescence intensities than the lanthanide complexes. Furthermore, the luminescence intensities of the lanthanide-complex-doped Ag@SiO{sub 2} nanocomposites with SiO{sub 2} shell thickness of 25 nm are stronger than those of the nanocomposites with SiO{sub 2} shell thickness of 10 and 80 nm.
Howard, R.C.; Bokros, J.C.
1962-03-01
A fueled matrlx eontnwinlng uncomblned carbon is deslgned for use in graphlte-moderated gas-cooled reactors designed for operatlon at temperatures (about 1500 deg F) at which conventional metallic cladding would ordlnarily undergo undesired carburization or physical degeneratlon. - The invention comprlses, broadly a fuel body containlng uncombined earbon, clad with a nickel alloy contalning over about 28 percent by' weight copper in the preferred embodlment. Thls element ls supporirted in the passageways in close tolerance with the walls of unclad graphite moderator materlal. (AEC)
Isothermal Circumstellar Dust Shell Model for Teaching
ERIC Educational Resources Information Center
Robinson, G.; Towers, I. N.; Jovanoski, Z.
2009-01-01
We introduce a model of radiative transfer in circumstellar dust shells. By assuming that the shell is both isothermal and its thickness is small compared to its radius, the model is simple enough for students to grasp and yet still provides a quantitative description of the relevant physical features. The isothermal model can be used in a…
A Geometric Theory of Nonlinear Morphoelastic Shells
NASA Astrophysics Data System (ADS)
Sadik, Souhayl; Angoshtari, Arzhang; Goriely, Alain; Yavari, Arash
2016-08-01
Many thin three-dimensional elastic bodies can be reduced to elastic shells: two-dimensional elastic bodies whose reference shape is not necessarily flat. More generally, morphoelastic shells are elastic shells that can remodel and grow in time. These idealized objects are suitable models for many physical, engineering, and biological systems. Here, we formulate a general geometric theory of nonlinear morphoelastic shells that describes both the evolution of the body shape, viewed as an orientable surface, as well as its intrinsic material properties such as its reference curvatures. In this geometric theory, bulk growth is modeled using an evolving referential configuration for the shell, the so-called material manifold. Geometric quantities attached to the surface, such as the first and second fundamental forms, are obtained from the metric of the three-dimensional body and its evolution. The governing dynamical equations for the body are obtained from variational consideration by assuming that both fundamental forms on the material manifold are dynamical variables in a Lagrangian field theory. In the case where growth can be modeled by a Rayleigh potential, we also obtain the governing equations for growth in the form of kinetic equations coupling the evolution of the first and the second fundamental forms with the state of stress of the shell. We apply these ideas to obtain stress-free growth fields of a planar sheet, the time evolution of a morphoelastic circular cylindrical shell subject to time-dependent internal pressure, and the residual stress of a morphoelastic planar circular shell.
An egg shell-like retroperitoneal pseudocyst.
Li, Zhao-Lun; Li, Hong-Liang; Chen, Hai-Weng; Gan, Wei-Ming
2011-09-01
Retroperitoneal pseudocysts are rare entities. Egg shell-like calcified retroperitoneal pseudocyst is rarer. We report a 75-year-old woman with an egg shell-like calcified retroperitoneal pseudocyst. Subsequently, the calcified pseudocyst was dissected and excised completely through laparoscopy via a retroperitoneal approach.
A Well-Defined Bipolar Outflow Shell
NASA Astrophysics Data System (ADS)
Xie, Taoling; Goldsmith, Paul F.; Patel, Nimesh
1992-12-01
A well-defined "eggplant-shaped" thin shell is revealed in the Mon R2 central core region by CO and (13) CO J=1-0 maps obtained with QUARRY. This thin shell outlines the extended blue lobe of the massive bipolar outflow. The projected length and width of the shell are about 5.7 pc and 2.5 pc respectively, and the averaged projected thickness of the shell is ~ 0.3 pc. The shape of this shell can be satisfactorily accounted for quantitatively in terms of limb-brightening within the framework of the Shu et al shell model with radially directed wind, although the model seems to be oversimplified with respect to the complexity that our data reveal. The outflow shell's symmetry axis is estimated to be inclined by ~ 70(deg) with respect to the line of sight. We suggest that the coincident blue- and red-shifted emission and the bending of the red-shifted lobe are the result of the red-shifted shell being compressed, rather than having a second bipolar outflow aligned roughly perpendicular to the axis of the first bipolar outflow.
The wavefunction of a gravitating shell
Dokuchaev, V. I. Chernov, S. V.
2010-10-15
We have calculated a discrete spectrum and found an exact analytical solution in the form of Meixner polynomials for the wavefunction of a thin gravitating shell in the Reissner-Nordstroem geometry. We show that there is no extreme state in the quantum spectrum of the gravitating shell, as in the case of an extreme black hole.
Thick-shell nanocrystal quantum dots
Hollingsworth, Jennifer A.; Chen, Yongfen; Klimov, Victor I.; Htoon, Han; Vela, Javier
2011-05-03
Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.
Biomineral repair of abalone shell apertures.
Cusack, Maggie; Guo, Dujiao; Chung, Peter; Kamenos, Nicholas A
2013-08-01
The shell of the gastropod mollusc, abalone, is comprised of nacre with an outer prismatic layer that is composed of either calcite or aragonite or both, depending on the species. A striking characteristic of the abalone shell is the row of apertures along the dorsal margin. As the organism and shell grow, new apertures are formed and the preceding ones are filled in. Detailed investigations, using electron backscatter diffraction, of the infill in three species of abalone: Haliotis asinina, Haliotis gigantea and Haliotis rufescens reveals that, like the shell, the infill is composed mainly of nacre with an outer prismatic layer. The infill prismatic layer has identical mineralogy as the original shell prismatic layer. In H. asinina and H. gigantea, the prismatic layer of the shell and infill are made of aragonite while in H. rufescens both are composed of calcite. Abalone builds the infill material with the same high level of biological control, replicating the structure, mineralogy and crystallographic orientation as for the shell. The infill of abalone apertures presents us with insight into what is, effectively, shell repair.
Megranate-like nanoreactor with multiple cores and an acidic mesoporous shell for a cascade reaction
NASA Astrophysics Data System (ADS)
Wang, Xue; Guan, Buyuan; He, Yapeng; An, Dong; Zhang, Ye; Cao, Yu; Li, Xiang; Liu, Yunling; Huo, Qisheng
2015-02-01
Megranate-like nanoparticles possess a unique structure that is composed of multiple cores and shells, which is different from simple yolk-shell nanoparticles. Megranate-like nanoparticles can combine the properties of each component and be used as nanoreactors. This study describes the preparation of bifunctional megranate-like nanoreactors, consisting of multiple metal cores and thiol modified mesoporous SiO2 shells. Different metal nanoparticles (Pd, Pt, Au) can be incorporated into the structure as cores, and the thiol group in the shells can be oxidized to acidic -SO3H. The megranate-like nanoparticles show good bifunctional catalytic properties and recyclability in a cascade catalytic reaction for the desired benzimidazole derivative. Moreover, the individual components of the megranate-like nanoparticles also show good catalytic activities in the hydrogenation reduction of nitro-aromatics and the deprotection reaction of benzaldehyde dimethyl acetal.Megranate-like nanoparticles possess a unique structure that is composed of multiple cores and shells, which is different from simple yolk-shell nanoparticles. Megranate-like nanoparticles can combine the properties of each component and be used as nanoreactors. This study describes the preparation of bifunctional megranate-like nanoreactors, consisting of multiple metal cores and thiol modified mesoporous SiO2 shells. Different metal nanoparticles (Pd, Pt, Au) can be incorporated into the structure as cores, and the thiol group in the shells can be oxidized to acidic -SO3H. The megranate-like nanoparticles show good bifunctional catalytic properties and recyclability in a cascade catalytic reaction for the desired benzimidazole derivative. Moreover, the individual components of the megranate-like nanoparticles also show good catalytic activities in the hydrogenation reduction of nitro-aromatics and the deprotection reaction of benzaldehyde dimethyl acetal. Electronic supplementary information (ESI) available
The Vega particulate shell - Comets or asteroids?
NASA Technical Reports Server (NTRS)
Weissman, P. R.
1984-01-01
The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega. At the mean distance and temperature of the shell, the expected condensation products from a protostellar nebula would be dominated by frozen volatiles, in particular water ice. It is not possible to discriminate between dirty ice and silicate materials in the Vega shell on the basis of the IRAS data. The Vega shell is probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system. A possible hot inner shell around Vega may be an asteroid-like belt of material a few astronomical units from the star.
Variability in shell models of GRBs
Sumner, M.C.; Fenimore, E.E.
1997-09-01
Many cosmological models of gamma-ray bursts (GRBs) assume that a single relativistic shell carries kinetic energy away from the source and later converts it into gamma rays, perhaps by interactions with the interstellar medium or by internal shocks within the shell. Although such models are able to reproduce general trends in GRB time histories, it is difficult to reproduce the high degree of variability often seen in GRBs. The authors investigate methods of achieving this variability using a simplified external shock model. Since the model emphasizes geometric and statistical considerations, rather than the detailed physics of the shell, it is applicable to any theory that relies on relativistic shells. They find that the variability in GRBs gives strong clues to the efficiency with which the shell converts its kinetic energy into gamma rays.
Semiclassical shell structure in rotating Fermi systems
Magner, A. G.; Sitdikov, A. S.; Khamzin, A. A.; Bartel, J.
2010-06-15
The collective moment of inertia is derived analytically within the cranking model for any rotational frequency of the harmonic-oscillator potential well and at a finite temperature. Semiclassical shell-structure components of the collective moment of inertia are obtained for any potential by using the periodic-orbit theory. We found semiclassically their relation to the free-energy shell corrections through the shell-structure components of the rigid-body moment of inertia of the statistically equilibrium rotation in terms of short periodic orbits. The shell effects in the moment of inertia exponentially disappear with increasing temperature. For the case of the harmonic-oscillator potential, one observes a perfect agreement of the semiclassical and quantum shell-structure components of the free energy and the moment of inertia for several critical bifurcation deformations and several temperatures.
Engineered Magnetic Core-Shell Structures.
Alavi Nikje, Mir Mohammad; Vakili, Maryam
2015-01-01
In recent years, engineered magnetic core-shell structures are playing an important role in the wide range of various applications. These magnetic core-shell structures have attracted considerable attention because of their unique properties and various applications. Also, the synthesis of engineered magnetic core-shell structures has attracted practical interest because of potential applications in areas such as ferrofluids, medical imaging, drug targeting and delivery, cancer therapy, separations, and catalysis. So far a large number of engineered magnetic core-shell structures have been successfully synthesized. This review article focuses on the recent progress in synthesis and characterization of engineered magnetic core-shell structures. Also, this review gives a brief description of the various application of these structures. It is hoped that this review will play some small part in helping future developments in important field. PMID:26377655
The protein shells of bacterial microcompartment organelles
Yeates, Todd O.; Thompson, Michael C.; Bobik, Thomas A.
2011-01-01
SUMMARY Details are emerging on the structure and function of a remarkable class of capsid-like protein assemblies that serve as simple metabolic organelles in many bacteria. These bacterial microcompartments consist of a few thousand shell proteins, which encapsulate two or more sequentially acting enzymes in order to enhance or sequester certain metabolic pathways, particularly those involving toxic or volatile intermediates. Genomic data indicate that bacterial microcompartment shell proteins are present in a wide range of bacterial species, where they encapsulate varied reactions. Crystal structures of numerous shell proteins from distinct types of microcompartments have provided keys for understanding how the shells are assembled and how they conduct molecular transport into and out of microcompartments. The structural data emphasize a high level of mechanistic sophistication in the protein shell, and point the way for further studies on this fascinating but poorly appreciated class of subcellular structures. PMID:21315581
Thermal equilibrium in Europa's ice shell
NASA Astrophysics Data System (ADS)
Moore, William B.
2006-01-01
Models of tidal-convective equilibrium for Europa's ice shell are computed using a laboratory-derived composite flow law for ice. Volume diffusion creep is found to dominate the flow law at equilibrium, and thus the thickness of the shell is strongly dependent on the poorly known grain size of the ice. This grain size is, however, constrained to be less than a few millimeters if equilibrium is achieved at the current eccentricity. Europa's ice shell cannot be thinner than about 16 km in equilibrium at present, since tidal dissipation cannot generate enough heat in such a thin shell to balance the heat transport. No conductive equilibria are found; this is likely due to the fact that most of a conductive shell must be cold if temperature gradients are to be large enough to carry the heat. A minimum eccentricity of about 0.0025 (about 1/4 the present value) below which there are no equilibria is also found.
The vega particulate shell: comets or asteroids?
Weissman, P R
1984-06-01
The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega. At the mean distance and temperature of the shell, the expected condensation products from a protostellar nebula would be dominated by frozen volatiles, in particular water ice. It is not possible to discriminate between dirty ice and silicate materials in the Vega shell on the basis of the IRAS data. The Vega shell is probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system. A possible hot inner shell around Vega may be an asteroid-like belt of material a few astronomical units from the star. PMID:17731997
Shell-model phenomenology of low-momentum interactions
Schwenk, Achim; Zuker, Andres P.
2006-12-15
The first detailed comparison of the low-momentum interaction V{sub lowk} with G matrices is presented. We use overlaps to measure quantitatively the similarity of shell-model matrix elements for different cutoffs and oscillator frequencies. Over a wide range, all sets of V{sub lowk} matrix elements can be approximately obtained from a universal set by a simple scaling. In an oscillator mean-field approach, V{sub lowk} reproduces satisfactorily many features of the single-particle and single-hole spectra on closed-shell nuclei, in particular through remarkably good splittings between spin-orbit partners on top of harmonic oscillator closures. The main deficiencies of pure two-nucleon interactions are associated with binding energies and with the failure to ensure magicity for the extruder-intruder closures. Here, calculations including three-nucleon interactions are most needed. V{sub lowk} makes it possible to define directly a meaningful unperturbed monopole Hamiltonian, for which the inclusion of three-nucleon forces is tractable.
Electroformation of uranium hemispherical shells
Marshall, S.L.; Redey, L.; Vandegrift, G.F.; Vissers, D.R.
1989-11-01
This effort was directed at developing an electrochemical process for forming uniform and dendrite-free deposits of uranium from molten salts. This process is to be used for the electroformation of free-standing hemispherical shells of uranium for nuclear applications. Electrodeposition of uranium onto a substrate was accomplished with a fused chloride mixture containing 42 wt% UCl{sub 3} and a fused chloride-fluoride mixture containing 4 wt % UF{sub 4}. Under pulsed potential control at 504{degree}C, the chloride-fluoride mixture yielded the widest range of plating conditions for which dendrites could be avoided. Bipolar current pulse plating with both electrolytes gave good results, and successful application of this technique to a large tubular cathode has been demonstrated. 24 refs., 10 figs.
Shell model calculation for Te and Sn isotopes in the vicinity of {sup 100}Sn
Yakhelef, A.; Bouldjedri, A.
2012-06-27
New Shell Model calculations for even-even isotopes {sup 104-108}Sn and {sup 106,108}Te, in the vicinity of {sup 100}Sn have been performed. The calculations have been carried out using the windows version of NuShell-MSU. The two body matrix elements TBMEs of the effective interaction between valence nucleons are obtained from the renormalized two body effective interaction based on G-matrix derived from the CD-bonn nucleon-nucleon potential. The single particle energies of the proton and neutron valence spaces orbitals are defined from the available spectra of lightest odd isotopes of Sb and Sn respectively.
Static internal pressure capacity of Hanford Single-Shell Waste Tanks
Julyk, L.J.
1994-07-19
Underground single-shell waste storage tanks located at the Hanford Site in Richland, Washington, generate gaseous mixtures that could be ignited, challenging the structural integrity of the tanks. The structural capacity of the single-shell tanks to internal pressure is estimated through nonlinear finite-element structural analyses of the reinforced concrete tank. To determine their internal pressure capacity, designs for both the million-gallon and the half-million-gallon tank are evaluated on the basis of gross structural instability.
Shell middle distillate hydrogenation process
Lucien, J.P.; Berg, J.P. van den; Hooijdonk, H.M.J.H. van; Thielemans, G.L.B.; Germaine, G.; Gjers, M.
1994-12-31
The strive towards cleaner environment has lead to low sulfur specifications for middle distillate fuels. In addition compositional specifications are presently debated. Thus, to meet future emissions standards regarding, specifically, particulates emissions, the motor industry calls for improved automotive gasoil quality. Although automotive gasoil quality affects emissions from diesel engines it is considered less influential than engine design and maintenance. Sulfur, density and cetane number are the fuel properties having the greatest influence on diesel engine emissions although also aromatics and endpoint specifications have been defined in environmentally adopted government initiatives. This paper reviews the options which are available to tackle these new requirements. The high severity single stage concept (using conventional mixed sulfides catalysts) will be discussed in its potential to meet more severe product requirements as well as in terms of its limitations, especially at the point of aromatics saturation and cetaine upgrading. Furthermore, it is shown that the option of severe hydrotreating followed by hydrogenation with conventional noble metal catalysts is preferred if deep aromatics saturation is aimed at. However, this conventional two stage concept has limitations with respect to heaviness and sulfur and nitrogen content of feedstocks. The new Shell Middle Distillate Hydrogenation (SMDH) technology, applying a (semi) two stage approach based on the Shell developed hydrogenation catalyst is presented. The SMDH process will be discussed in its potential to break the limitations of the conventional options. The new catalyst is crucial in this process and allows a highly integrated mode of operation. A number of applications of this novel process will be discussed.
Postbuckling characteristics of angle-ply laminated truncated circular conical shells
NASA Astrophysics Data System (ADS)
Patel, B. P.; Singh, S.; Nath, Y.
2008-09-01
The postbuckling characteristics of the angle-ply laminated composite conical shells subjected to the torsion, the external pressure, the axial compression, and the thermal loading considering uniform temperature change are studied using the semi-analytical finite element approach. The finite element formulation is based on the first-order shear deformation theory and the field consistency principle. The variations in the stiffness coefficients along the meridional direction due to the changes in the ply-angle and the ply-thickness of the filament wound conical shells are incorporated in the finite element formulation. The nonlinear governing equations are solved using the Newton-Raphson iteration procedure coupled with the displacement control method to trace the prebuckling followed by the postbuckling equilibrium path. The presence of asymmetric perturbation in the form of a small magnitude load spatially proportional to the linear buckling mode shape is considered to initiate the bifurcation of the shell deformation. The influence of semi-cone angle, ply-angle and number of circumferential waves on the prebuckling/postbuckling response of the anti-symmetric angle-ply laminated circular conical shells is investigated.
NASA Technical Reports Server (NTRS)
OBrien, T. Kevin (Technical Monitor); Krueger, Ronald; Minguet, Pierre J.
2004-01-01
The application of a shell/3D modeling technique for the simulation of skin/stringer debond in a specimen subjected to tension and three-point bending was studied. The global structure was modeled with shell elements. A local three-dimensional model, extending to about three specimen thicknesses on either side of the delamination front was used to model the details of the damaged section. Computed total strain energy release rates and mixed-mode ratios obtained from shell/3D simulations were in good agreement with results obtained from full solid models. The good correlation of the results demonstrated the effectiveness of the shell/3D modeling technique for the investigation of skin/stiffener separation due to delamination in the adherents. In addition, the application of the submodeling technique for the simulation of skin/stringer debond was also studied. Global models made of shell elements and solid elements were studied. Solid elements were used for local submodels, which extended between three and six specimen thicknesses on either side of the delamination front to model the details of the damaged section. Computed total strain energy release rates and mixed-mode ratios obtained from the simulations using the submodeling technique were not in agreement with results obtained from full solid models.