On a High-Fidelity Hierarchical Approach to Buckling Load Calculations

NASA Technical Reports Server (NTRS)

Arbocz, Johann; Starnes, James H.; Nemeth, Michael P.

2001-01-01

As a step towards developing a new design philosophy, one that moves away from the traditional empirical approach used today in design towards a science-based design technology approach, a recent test series of 5 composite shells carried out by Waters at NASA Langley Research Center is used. It is shown how the hierarchical approach to buckling load calculations proposed by Arbocz et al can be used to perform an approach often called "high fidelity analysis", where the uncertainties involved in a design are simulated by refined and accurate numerical methods. The Delft Interactive Shell DEsign COde (short, DISDECO) is employed for this hierarchical analysis to provide an accurate prediction of the critical buckling load of the given shell structure. This value is used later as a reference to establish the accuracy of the Level-3 buckling load predictions. As a final step in the hierarchical analysis approach, the critical buckling load and the estimated imperfection sensitivity of the shell are verified by conducting an analysis using a sufficiently refined finite element model with one of the current generation two-dimensional shell analysis codes with the advanced capabilities needed to represent both geometric and material nonlinearities.

A Method to Represent Heterogeneous Materials for Rapid Prototyping: The Matryoshka Approach

PubMed Central

Lei, Shuangyan; Frank, Matthew C.; Anderson, Donald D.; Brown, Thomas D.

2015-01-01

Purpose The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones. Design/methodology/approach Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are “stacked” inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone. Findings The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing. Originality/Value This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate. PMID:26120277

Modeling of thin-walled structures interacting with acoustic media as constrained two-dimensional continua

NASA Astrophysics Data System (ADS)

Rabinskiy, L. N.; Zhavoronok, S. I.

2018-04-01

The transient interaction of acoustic media and elastic shells is considered on the basis of the transition function approach. The three-dimensional hyperbolic initial boundary-value problem is reduced to a two-dimensional problem of shell theory with integral operators approximating the acoustic medium effect on the shell dynamics. The kernels of these integral operators are determined by the elementary solution of the problem of acoustic waves diffraction at a rigid obstacle with the same boundary shape as the wetted shell surface. The closed-form elementary solution for arbitrary convex obstacles can be obtained at the initial interaction stages on the background of the so-called “thin layer hypothesis”. Thus, the shell–wave interaction model defined by integro-differential dynamic equations with analytically determined kernels of integral operators becomes hence two-dimensional but nonlocal in time. On the other hand, the initial interaction stage results in localized dynamic loadings and consequently in complex strain and stress states that require higher-order shell theories. Here the modified theory of I.N.Vekua–A.A.Amosov-type is formulated in terms of analytical continuum dynamics. The shell model is constructed on a two-dimensional manifold within a set of field variables, Lagrangian density, and constraint equations following from the boundary conditions “shifted” from the shell faces to its base surface. Such an approach allows one to construct consistent low-order shell models within a unified formal hierarchy. The equations of the N th-order shell theory are singularly perturbed and contain second-order partial derivatives with respect to time and surface coordinates whereas the numerical integration of systems of first-order equations is more efficient. Such systems can be obtained as Hamilton–de Donder–Weyl-type equations for the Lagrangian dynamical system. The Hamiltonian formulation of the elementary N th-order shell theory is here briefly described.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brink, Adam Ray; Quinn, D. Dane

This paper describes the energy dissipation arising from microslip for an elastic shell incorporating shear and longitudinal deformation resting on a rough-rigid foundation. This phenomenon is investigated using finite element (FE) analysis and nonlinear geometrically exact shell theory. Both approaches illustrate the effect of shear within the shell and observe a reduction in the energy dissipated from microslip as compared to a similar system neglecting shear deformation. In particular, it is found that the shear deformation allows for load to be transmitted beyond the region of slip so that the entire interface contributes to the load carrying capability of themore » shell. The energy dissipation resulting from the shell model is shown to agree well with that arising from the FE model, and this representation can be used as a basis for reduced order models that capture the microslip phenomenon.« less

A Method to Represent Heterogeneous Materials for Rapid Prototyping: The Matryoshka Approach.

PubMed

Lei, Shuangyan; Frank, Matthew C; Anderson, Donald D; Brown, Thomas D

The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones. Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are "stacked" inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone. The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing. This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate.

Modeling of nonlinear viscous stress in encapsulating shells of lipid-coated contrast agent microbubbles

PubMed Central

Doinikov, Alexander A.; Haac, Jillian F.; Dayton, Paul A.

2009-01-01

A general theoretical approach to the development of zero-thickness encapsulation models for contrast microbubbles is proposed. The approach describes a procedure that allows one to recast available rheological laws from the bulk form to a surface form which is used in a modified Rayleigh-Plesset equation governing the radial dynamics of a contrast microbubble. By the use of the proposed procedure, the testing of different rheological laws for encapsulation can be carried out. Challenges of existing shell models for lipid-encapsulated microbubbles, such as the dependence of shell parameters on the initial bubble radius and the “compression-only” behavior, are discussed. Analysis of the rheological behavior of lipid encapsulation is made by using experimental radius-time curves for lipid-coated microbubbles with radii in the range 1.2 – 2.5 μm. The curves were acquired for a research phospholipid-coated contrast agent insonified with a 20-cycle, 3.0 MHz, 100 kPa acoustic pulse. The fitting of the experimental data by a model which treats the shell as a viscoelastic solid gives the values of the shell surface viscosity increasing from 0.30×10-8 kg/s to 2.63×10-8 kg/s for the range of bubble radii indicated above. The shell surface elastic modulus increases from 0.054 N/m to 0.37 N/m. It is proposed that this increase may be a result of the lipid coating possessing the properties of both a shear-thinning and a strain-softening material. We hypothesize that these complicated rheological properties do not allow the existing shell models to satisfactorily describe the dynamics of lipid encapsulation. In the existing shell models, the viscous and the elastic shell terms have the linear form which assumes that the viscous and the elastic stresses acting inside the lipid shell are proportional to the shell shear rate and the shell strain, respectively, with constant coefficients of proportionality. The analysis performed in the present paper suggests that a more general, nonlinear theory may be more appropriate. It is shown that the use of the nonlinear theory for shell viscosity allows one to model the “compression-only” behavior. As an example, the results of the simulation for a 2.03- μm-radius bubble insonified with a 6-cycle, 1.8 MHz, 100 kPa acoustic pulse are given. These parameters correspond to the acoustic conditions under which the “compression-only” behavior was observed by de Jong et al. [Ultrasound Med. Biol. 33 (2007) 653–656]. It is also shown that the use of the Cross law for the modeling of the shear-thinning behavior of shell viscosity reduces the variance of experimentally estimated values of the shell viscosity and its dependence on the initial bubble radius. PMID:18990417

Resonance frequencies of lipid-shelled microbubbles in the regime of nonlinear oscillations

PubMed Central

Doinikov, Alexander A.; Haac, Jillian F.; Dayton, Paul A.

2009-01-01

Knowledge of resonant frequencies of contrast microbubbles is important for the optimization of ultrasound contrast imaging and therapeutic techniques. To date, however, there are estimates of resonance frequencies of contrast microbubbles only for the regime of linear oscillation. The present paper proposes an approach for evaluating resonance frequencies of contrast agent microbubbles in the regime of nonlinear oscillation. The approach is based on the calculation of the time-averaged oscillation power of the radial bubble oscillation. The proposed procedure was verified for free bubbles in the frequency range 1–4 MHz and then applied to lipid-shelled microbubbles insonified with a single 20-cycle acoustic pulse at two values of the acoustic pressure amplitude, 100 kPa and 200 kPa, and at four frequencies: 1.5, 2.0, 2.5, and 3.0 MHz. It is shown that, as the acoustic pressure amplitude is increased, the resonance frequency of a lipid-shelled microbubble tends to decrease in comparison with its linear resonance frequency. Analysis of existing shell models reveals that models that treat the lipid shell as a linear viscoelastic solid appear may be challenged to provide the observed tendency in the behavior of the resonance frequency at increasing acoustic pressure. The conclusion is drawn that the further development of shell models could be improved by the consideration of nonlinear rheological laws. PMID:18977009

Static and free-vibration analyses of cracks in thin-shell structures based on an isogeometric-meshfree coupling approach

NASA Astrophysics Data System (ADS)

Nguyen-Thanh, Nhon; Li, Weidong; Zhou, Kun

2018-03-01

This paper develops a coupling approach which integrates the meshfree method and isogeometric analysis (IGA) for static and free-vibration analyses of cracks in thin-shell structures. In this approach, the domain surrounding the cracks is represented by the meshfree method while the rest domain is meshed by IGA. The present approach is capable of preserving geometry exactness and high continuity of IGA. The local refinement is achieved by adding the nodes along the background cells in the meshfree domain. Moreover, the equivalent domain integral technique for three-dimensional problems is derived from the additional Kirchhoff-Love theory to compute the J-integral for the thin-shell model. The proposed approach is able to address the problems involving through-the-thickness cracks without using additional rotational degrees of freedom, which facilitates the enrichment strategy for crack tips. The crack tip enrichment effects and the stress distribution and displacements around the crack tips are investigated. Free vibrations of cracks in thin shells are also analyzed. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the coupling approach.

Shear effects on energy dissipation from an elastic beam on a rigid foundation

DOE PAGES

Brink, Adam Ray; Quinn, D. Dane

2015-10-20

This paper describes the energy dissipation arising from microslip for an elastic shell incorporating shear and longitudinal deformation resting on a rough-rigid foundation. This phenomenon is investigated using finite element (FE) analysis and nonlinear geometrically exact shell theory. Both approaches illustrate the effect of shear within the shell and observe a reduction in the energy dissipated from microslip as compared to a similar system neglecting shear deformation. In particular, it is found that the shear deformation allows for load to be transmitted beyond the region of slip so that the entire interface contributes to the load carrying capability of themore » shell. The energy dissipation resulting from the shell model is shown to agree well with that arising from the FE model, and this representation can be used as a basis for reduced order models that capture the microslip phenomenon.« less

Structure models: From shell model to ab initio methods. A brief introduction to microscopic theories for exotic nuclei

NASA Astrophysics Data System (ADS)

Bacca, Sonia

2016-04-01

A brief review of models to describe nuclear structure and reactions properties is presented, starting from the historical shell model picture and encompassing modern ab initio approaches. A selection of recent theoretical results on observables for exotic light and medium-mass nuclei is shown. Emphasis is given to the comparison with experiment and to what can be learned about three-body forces and continuum properties.

Study of Shell Zone Formation in Lithographic and Anodizing Quality Aluminum Alloys: Experimental and Numerical Approach

NASA Astrophysics Data System (ADS)

Brochu, Christine; Larouche, André; Hark, Robert

Shell thickness is an important quality factor for lithographic and anodizing quality aluminum alloys. Increasing pressure is placed on casting plants to produce a thinner shell zone for these alloys. This study, based on plant trials and mathematical modelling highlights the most significant parameters influencing shell zone formation. Results obtained show the importance of metal temperature and distribution and mould metal level on shell zone formation. As an answer to specific plant problems, this study led to the development of improved metal distribution systems for DC casting of litho and anodizing quality alloys.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

NASA Astrophysics Data System (ADS)

Carrião, Marcus S.; Bakuzis, Andris F.

2016-04-01

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy. Electronic supplementary information (ESI) available: Unit cells per region calculation; core-shell Hamiltonian; magnetisation description functions; energy argument of Brillouin function; polydisperse models; details of experimental procedure; LRT versus core-shell model; model calculation software; and shell thickness study. See DOI: 10.1039/C5NR09093H

NASA Structural Analysis Report on the American Airlines Flight 587 Accident - Local Analysis of the Right Rear Lug

NASA Technical Reports Server (NTRS)

Raju, Ivatury S; Glaessgen, Edward H.; Mason, Brian H; Krishnamurthy, Thiagarajan; Davila, Carlos G

2005-01-01

A detailed finite element analysis of the right rear lug of the American Airlines Flight 587 - Airbus A300-600R was performed as part of the National Transportation Safety Board s failure investigation of the accident that occurred on November 12, 2001. The loads experienced by the right rear lug are evaluated using global models of the vertical tail, local models near the right rear lug, and a global-local analysis procedure. The right rear lug was analyzed using two modeling approaches. In the first approach, solid-shell type modeling is used, and in the second approach, layered-shell type modeling is used. The solid-shell and the layered-shell modeling approaches were used in progressive failure analyses (PFA) to determine the load, mode, and location of failure in the right rear lug under loading representative of an Airbus certification test conducted in 1985 (the 1985-certification test). Both analyses were in excellent agreement with each other on the predicted failure loads, failure mode, and location of failure. The solid-shell type modeling was then used to analyze both a subcomponent test conducted by Airbus in 2003 (the 2003-subcomponent test) and the accident condition. Excellent agreement was observed between the analyses and the observed failures in both cases. From the analyses conducted and presented in this paper, the following conclusions were drawn. The moment, Mx (moment about the fuselage longitudinal axis), has significant effect on the failure load of the lugs. Higher absolute values of Mx give lower failure loads. The predicted load, mode, and location of the failure of the 1985-certification test, 2003-subcomponent test, and the accident condition are in very good agreement. This agreement suggests that the 1985-certification and 2003- subcomponent tests represent the accident condition accurately. The failure mode of the right rear lug for the 1985-certification test, 2003-subcomponent test, and the accident load case is identified as a cleavage-type failure. For the accident case, the predicted failure load for the right rear lug from the PFA is greater than 1.98 times the limit load of the lugs. I.

Structural Analysis of the Right Rear Lug of American Airlines Flight 587

NASA Technical Reports Server (NTRS)

Raju, Ivatury S.; Glaessgen, Edward H.; Mason, Brian H.; Krishnamurthy, Thiagarajan; Davila, Carlos G.

2006-01-01

A detailed finite element analysis of the right rear lug of the American Airlines Flight 587 - Airbus A300-600R was performed as part of the National Transportation Safety Board s failure investigation of the accident that occurred on November 12, 2001. The loads experienced by the right rear lug are evaluated using global models of the vertical tail, local models near the right rear lug, and a global-local analysis procedure. The right rear lug was analyzed using two modeling approaches. In the first approach, solid-shell type modeling is used, and in the second approach, layered-shell type modeling is used. The solid-shell and the layered-shell modeling approaches were used in progressive failure analyses (PFA) to determine the load, mode, and location of failure in the right rear lug under loading representative of an Airbus certification test conducted in 1985 (the 1985-certification test). Both analyses were in excellent agreement with each other on the predicted failure loads, failure mode, and location of failure. The solid-shell type modeling was then used to analyze both a subcomponent test conducted by Airbus in 2003 (the 2003-subcomponent test) and the accident condition. Excellent agreement was observed between the analyses and the observed failures in both cases. The moment, Mx (moment about the fuselage longitudinal axis), has significant effect on the failure load of the lugs. Higher absolute values of Mx give lower failure loads. The predicted load, mode, and location of the failure of the 1985- certification test, 2003-subcomponent test, and the accident condition are in very good agreement. This agreement suggests that the 1985-certification and 2003-subcomponent tests represent the accident condition accurately. The failure mode of the right rear lug for the 1985-certification test, 2003-subcomponent test, and the accident load case is identified as a cleavage-type failure. For the accident case, the predicted failure load for the right rear lug from the PFA is greater than 1.98 times the limit load of the lugs.

Measurement of L-shell transitions in M-shell ions in the laboratory and identification in stellar coronae

DOE PAGES

Lepson, J. K.; Beiersdorfer, P.; Hell, N.; ...

2017-04-04

Based on laboratory data from the Lawrence Livermore EBIT-I electron beam ion trap and calculations using the relativistic multi-reference Møller-Plesset (MRMP) perturbation theory approach, we identify L-shell transitions of M-shell iron ions in emission spectra of the nearby stars Capella and Procyon. In conclusion, these lines are weaker than the well known, prominent lines from Fe XVII. However, they need to be taken into account when modeling the spectra, especially of cool stars.

Radiative Properties of Carriers in Cdse-Cds Core-Shell Heterostructured Nanocrystals of Various Geometries

NASA Astrophysics Data System (ADS)

Zhou, S.; Dong, L.; Popov, S.; Friberg, A. T.

2013-07-01

We report a model on core-shell heterostructured nanocrystals with CdSe as the core and CdS as the shell. The model is based on one-band Schrödinger equation. Three different geometries, nanodot, nanorod, and nanobone, are implemented. The carrier localization regimes with these structures are simulated, compared, and analyzed. Based on the electron and hole wave functions, the carrier overlap integral that has a great impact on stimulated emission is further investigated numerically by a novel approach. Furthermore, the relation between the nanocrystal size and electron-hole recombination energy is also examined.

The KATE shell: An implementation of model-based control, monitor and diagnosis

NASA Technical Reports Server (NTRS)

Cornell, Matthew

1987-01-01

The conventional control and monitor software currently used by the Space Center for Space Shuttle processing has many limitations such as high maintenance costs, limited diagnostic capabilities and simulation support. These limitations have caused the development of a knowledge based (or model based) shell to generically control and monitor electro-mechanical systems. The knowledge base describes the system's structure and function and is used by a software shell to do real time constraints checking, low level control of components, diagnosis of detected faults, sensor validation, automatic generation of schematic diagrams and automatic recovery from failures. This approach is more versatile and more powerful than the conventional hard coded approach and offers many advantages over it, although, for systems which require high speed reaction times or aren't well understood, knowledge based control and monitor systems may not be appropriate.

Large scale shell model study of nuclear spectroscopy in nuclei around 132Sn

NASA Astrophysics Data System (ADS)

Lo Iudice, N.; Bianco, D.; Andreozzi, F.; Porrino, A.; Knapp, F.

2012-10-01

The properties of low-lying 2+ states in chains of nuclei in the proximity of the magic number N=82 are investigated within a new shell model approach exploiting an iterative algorithm alternative to Lanczos. The calculation yields levels and transition strengths in overall good agreement with experiments. The comparative analysis of the E2 and M1 transitions supports, in many cases, the scheme provided by the interacting boson model.

Finite Element Analysis of Geodesically Stiffened Cylindrical Composite Shells Using a Layerwise Theory

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.

On the Development of Multi-Step Inverse FEM with Shell Model

NASA Astrophysics Data System (ADS)

Huang, Y.; Du, R.

2005-08-01

The inverse or one-step finite element approach is increasingly used in the sheet metal stamping industry to predict strain distribution and the initial blank shape in the preliminary design stage. Based on the existing theory, there are two types of method: one is based on the principle of virtual work and the other is based on the principle of extreme work. Much research has been conducted to improve the accuracy of simulation results. For example, based on the virtual work principle, Batoz et al. developed a new method using triangular DKT shell elements. In this new method, the bending and unbending effects are considered. Based on the principle of extreme work, Majlessi and et al. proposed the multi-step inverse approach with membrane elements and applied it to an axis-symmetric part. Lee and et al. presented an axis-symmetric shell element model to solve the similar problem. In this paper, a new multi-step inverse method is introduced with no limitation on the workpiece shape. It is a shell element model based on the virtual work principle. The new method is validated by means of comparing to the commercial software system (PAMSTAMP®). The comparison results indicate that the accuracy is good.

Deformation in Micro Roll Forming of Bipolar Plate

NASA Astrophysics Data System (ADS)

Zhang, P.; Pereira, M.; Rolfe, B.; Daniel, W.; Weiss, M.

2017-09-01

Micro roll forming is a new processing technology to produce bipolar plates for Proton Exchange Membrane Fuel Cells (PEMFC) from thin stainless steel foil. To gain a better understanding of the deformation of the material in this process, numerical studies are necessary before experimental implementation. In general, solid elements with several layers through the material thickness are required to analyse material thinning in processes where the deformation mode is that of bending combined with tension, but this results in high computational costs. This pure solid element approach is especially time-consuming when analysing roll forming processes which generally involves feeding a long strip through a number of successive roll stands. In an attempt to develop a more efficient modelling approach without sacrificing accuracy, two solutions are numerically analysed with ABAQUS/Explicit in this paper. In the first, a small patch of solid elements over the strip width and in the centre of the “pre-cut” sheet is coupled with shell elements while in the second approach pure shell elements are used to discretize the full sheet. In the first approach, the shell element enables accounting for the effect of material being held in the roll stands on material flow while solid elements can be applied to analyse material thinning in a small discrete area of the sheet. Experimental micro roll forming trials are performed to prove that the coupling of solid and shell elements can give acceptable model accuracy while using shell elements alone is shown to result in major deviations between numerical and experimental results.

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.

Ab initio description of p-shell hypernuclei.

PubMed

Wirth, Roland; Gazda, Daniel; Navrátil, Petr; Calci, Angelo; Langhammer, Joachim; Roth, Robert

2014-11-07

We present the first ab initio calculations for p-shell single-Λ hypernuclei. For the solution of the many-baryon problem, we develop two variants of the no-core shell model with explicit Λ and Σ(+),Σ(0),Σ(-) hyperons including Λ-Σ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent meson-exchange hyperon-nucleon interaction. We validate the approach for s-shell hypernuclei and apply it to p-shell hypernuclei, in particular to (Λ)(7)Li, (Λ)(9)Be, and (Λ)(13)C. We show that the chiral hyperon-nucleon interactions provide ground-state and excitation energies that generally agree with experiment within the cutoff dependence. At the same time we demonstrate that hypernuclear spectroscopy provides tight constraints on the hyperon-nucleon interactions.

Statistical mechanics of shell models for two-dimensional turbulence

NASA Astrophysics Data System (ADS)

Aurell, E.; Boffetta, G.; Crisanti, A.; Frick, P.; Paladin, G.; Vulpiani, A.

1994-12-01

We study shell models that conserve the analogs of energy and enstrophy and hence are designed to mimic fluid turbulence in two-dimensions (2D). The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager [Nuovo Cimento Suppl. 6, 279 (1949)], Hopf [J. Rat. Mech. Anal. 1, 87 (1952)], and Lee [Q. Appl. Math. 10, 69 (1952)]. In the presence of forcing and dissipation we observe a forward flux of enstrophy and a backward flux of energy. These fluxes can be understood as mean diffusive drifts from a source to two sinks in a system which is close to local equilibrium with Lagrange multipliers (``shell temperatures'') changing slowly with scale. This is clear evidence that the simplest shell models are not adequate to reproduce the main features of two-dimensional turbulence. The dimensional predictions on the power spectra from a supposed forward cascade of enstrophy and from one branch of the formal statistical equilibrium coincide in these shell models in contrast to the corresponding predictions for the Navier-Stokes and Euler equations in 2D. This coincidence has previously led to the mistaken conclusion that shell models exhibit a forward cascade of enstrophy. We also study the dynamical properties of the models and the growth of perturbations.

Shell-NASA Vibration-Based Damage Characterization

NASA Technical Reports Server (NTRS)

Rollins, John M.

2014-01-01

This article describes collaborative research between Shell International Exploration and Production (IE&P) scientists and ISAG personnel to investigate the feasibility of ultrasonic-based characterization of spacecraft tile damage for in-space inspection applications. The approach was proposed by Shell personnel in a Shell-NASA "speed-matching" session in early 2011 after ISAG personnel described challenges inherent in the inspection of MMOD damage deep within spacecraft thermal protection system (TPS) tiles. The approach leveraged Shell's relevant sensor and analytical expertise. The research addressed the difficulties associated with producing 3D models of MMOD damage cavities under the surface of a TPS tile, given that simple image-based sensing is constrained by line of sight through entry holes that have diameters considerably smaller than the underlying damage cavities. Damage cavity characterization is needed as part of a vehicle inspection and risk reduction capability for long-duration, human-flown space missions. It was hoped that cavity characterization could be accomplished through the use of ultrasonic techniques that allow for signal penetration through solid material.

Loop Variables in String Theory

NASA Astrophysics Data System (ADS)

Sathiapalan, B.

The loop variable approach is a proposal for a gauge-invariant generalization of the sigma-model renormalization group method of obtaining equations of motion in string theory. The basic guiding principle is space-time gauge invariance rather than world sheet properties. In essence it is a version of Wilson's exact renormalization group equation for the world sheet theory. It involves all the massive modes and is defined with a finite world sheet cutoff, which allows one to go off the mass-shell. On shell the tree amplitudes of string theory are reproduced. The equations are gauge-invariant off shell also. This paper is a self-contained discussion of the loop variable approach as well as its connection with the Wilsonian RG.

Semiclassical approaches to nuclear dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magner, A. G., E-mail: magner@kinr.kiev.ua; Gorpinchenko, D. V.; Bartel, J.

The extended Gutzwiller trajectory approach is presented for the semiclassical description of nuclear collective dynamics, in line with the main topics of the fruitful activity of V.G. Solovjov. Within the Fermi-liquid droplet model, the leptodermous effective surface approximation was applied to calculations of energies, sum rules, and transition densities for the neutron–proton asymmetry of the isovector giant-dipole resonance and found to be in good agreement with the experimental data. By using the Strutinsky shell correction method, the semiclassical collective transport coefficients, such as nuclear inertia, friction, stiffness, and moments of inertia, can be derived beyond the quantum perturbation approximation ofmore » the response function theory and the cranking model. The averaged particle-number dependences of the low-lying collective vibrational states are described in good agreement with the basic experimental data, mainly due to the enhancement of the collective inertia as compared to its irrotational flow value. Shell components of the moment of inertia are derived in terms of the periodic-orbit free-energy shell corrections. A good agreement between the semiclassical extended Thomas–Fermi moments of inertia with shell corrections and the quantum results is obtained for different nuclear deformations and particle numbers. Shell effects are shown to be exponentially dampted out with increasing temperature in all the transport coefficients.« less

Structure of Enceladus' Ice Shell

NASA Astrophysics Data System (ADS)

Hemingway, D.

2016-12-01

Constraining the internal structure of Enceladus is essential for understanding its evolution, its highly active south polar region, and its prospects for habitability. Of particular interest is the thickness of the icy shell, which has implications for the thermal structure, the effects of tidal stresses, and the conduits feeding the jets and plume. Since Enceladus' low order gravity field was first measured [1], several studies of shape and gravity have suggested the presence of an internal ocean beneath the icy shell [1-3]. These analyses, however, involve several assumptions and approximations and yield distinct shell thickness estimates (ranging from 18-60 km), only some of which are compatible with estimates from the measured physical librations (15-25 km [4,5]). Part of the challenge is that standard approaches to interior modeling (e.g., Radau-Darwin) are not well suited to Enceladus due to its fast rotation and relatively large non-hydrostatic topography [2,6]. Because of Enceladus' small radius, results are also sensitive to the details of the compensation model [7,8]. Here we apply an analytical compensation model that accommodates the spherical geometry in a manner that is distinct from previous studies, and employ a high fidelity numerical approach to modeling the hydrostatic equilibrium figure [6]. We show that the resulting shell thickness estimates are smaller than in previous models—in agreement with the libration observations—suggesting the possibility of an extremely thin ice crust at the south pole. While a range of mean shell thicknesses are permitted within the observational constraints, the amplitude of lateral shell thickness variations is well constrained. In particular, the shell is 10 km thicker at the north pole than at the south pole, potentially helping to explain the nature of the north-south polar asymmetry in endogenic activity. 1. Iess et al., Science. 344, 78-80 (2014). 2. McKinnon, Geophys. Res. Lett.42 (2015). 3. Cadek et al., Geophys. Res. Lett. (2016). 4. Thomas et al., Icarus. 264, 37-47 (2016). 5. Van Hoolst, Baland, Trinh, Icarus. 277, 311-318 (2016). 6. Tricarico, Astrophys. J. 782, 99 (2014). 7. Jeffreys, The Earth (Cambridge University Press, 6thed, 1976). 8. Turcotte, Willemann, Haxby, Norberry, J. Geophys. Res. 86, 3951-3959 (1981).

Understanding valence-shell electron-pair repulsion (VSEPR) theory using origami molecular models

NASA Astrophysics Data System (ADS)

Endah Saraswati, Teguh; Saputro, Sulistyo; Ramli, Murni; Praseptiangga, Danar; Khasanah, Nurul; Marwati, Sri

2017-01-01

Valence-shell electron-pair repulsion (VSEPR) theory is conventionally used to predict molecular geometry. However, it is difficult to explore the full implications of this theory by simply drawing chemical structures. Here, we introduce origami modelling as a more accessible approach for exploration of the VSEPR theory. Our technique is simple, readily accessible and inexpensive compared with other sophisticated methods such as computer simulation or commercial three-dimensional modelling kits. This method can be implemented in chemistry education at both the high school and university levels. We discuss the example of a simple molecular structure prediction for ammonia (NH3). Using the origami model, both molecular shape and the scientific justification can be visualized easily. This ‘hands-on’ approach to building molecules will help promote understanding of VSEPR theory.

Computational investigation of longitudinal diffusion, eddy dispersion, and trans-particle mass transfer in bulk, random packings of core-shell particles with varied shell thickness and shell diffusion coefficient.

PubMed

Daneyko, Anton; Hlushkou, Dzmitry; Baranau, Vasili; Khirevich, Siarhei; Seidel-Morgenstern, Andreas; Tallarek, Ulrich

2015-08-14

In recent years, chromatographic columns packed with core-shell particles have been widely used for efficient and fast separations at comparatively low operating pressure. However, the influence of the porous shell properties on the mass transfer kinetics in core-shell packings is still not fully understood. We report on results obtained with a modeling approach to simulate three-dimensional advective-diffusive transport in bulk random packings of monosized core-shell particles, covering a range of reduced mobile phase flow velocities from 0.5 up to 1000. The impact of the effective diffusivity of analyte molecules in the porous shell and the shell thickness on the resulting plate height was investigated. An extension of Giddings' theory of coupled eddy dispersion to account for retention of analyte molecules due to stagnant regions in porous shells with zero mobile phase flow velocity is presented. The plate height equation involving a modified eddy dispersion term excellently describes simulated data obtained for particle-packings with varied shell thickness and shell diffusion coefficient. It is confirmed that the model of trans-particle mass transfer resistance of core-shell particles by Kaczmarski and Guiochon [42] is applicable up to a constant factor. We analyze individual contributions to the plate height from different mass transfer mechanisms in dependence of the shell parameters. The simulations demonstrate that a reduction of plate height in packings of core-shell relative to fully porous particles arises mainly due to reduced trans-particle mass transfer resistance and transchannel eddy dispersion. Copyright © 2015 Elsevier B.V. All rights reserved.

Fabrication of core-shell micro/nanoparticles for programmable dual drug release by emulsion electrospraying

NASA Astrophysics Data System (ADS)

Wang, Yazhou; Zhang, Yiqiong; Wang, Bochu; Cao, Yang; Yu, Qingsong; Yin, Tieying

2013-06-01

The study aimed at constructing a novel drug delivery system for programmable multiple drug release controlled with core-shell structure. The core-shell structure consisted of chitosan nanoparticles as core and polyvinylpyrrolidone micro/nanocoating as shell to form core-shell micro/nanoparticles, which was fabricated by ionic gelation and emulsion electrospray methods. As model drug agents, Naproxen and rhodamine B were encapsulated in the core and shell regions, respectively. The core-shell micro/nanoparticles thus fabricated were characterized and confirmed by scanning electron microscope, transmission electron microscope, and fluorescence optical microscope. The core-shell micro/nanoparticles showed good release controllability through drug release experiment in vitro. It was noted that a programmable release pattern for dual drug agents was also achieved by adjusting their loading regions in the core-shell structures. The results indicate that emulsion electrospraying technology is a promising approach in fabrication of core-shell micro/nanoparticles for programmable dual drug release. Such a novel multi-drug delivery system has a potential application for the clinical treatment of cancer, tuberculosis, and tissue engineering.

Short-Range Correlated Magnetic Core-Shell CrO₂/Cr₂O₃ Nanorods: Experimental Observations and Theoretical Considerations.

PubMed

Gandhi, Ashish C; Li, Tai-Yue; Chan, Ting Shan; Wu, Sheng Yun

2018-05-09

With the evolution of synthesis and the critical characterization of core-shell nanostructures, short-range magnetic correlation is of prime interest in employing their properties to develop novel devices and widespread applications. In this regard, a novel approach of the magnetic core-shell saturated magnetization (CSSM) cylinder model solely based on the contribution of saturated magnetization in one-dimensional CrO₂/Cr₂O₃ core-shell nanorods (NRs) has been developed and applied for the determination of core-diameter and shell-thickness. The nanosized effect leads to a short-range magnetic correlation of ferromagnetic core-CrO₂ extracted from CSSM, which can be explained using finite size scaling method. The outcome of this study is important in terms of utilizing magnetic properties for the critical characterization of core-shell nanomagnetic materials.

Prediction of the vibroacoustic behavior of a submerged shell with non-axisymmetric internal substructures by a condensed transfer function method

NASA Astrophysics Data System (ADS)

Meyer, V.; Maxit, L.; Guyader, J.-L.; Leissing, T.

2016-01-01

The vibroacoustic behavior of axisymmetric stiffened shells immersed in water has been intensively studied in the past. On the contrary, little attention has been paid to the modeling of these shells coupled to non-axisymmetric internal frames. Indeed, breaking the axisymmetry couples the circumferential orders of the Fourier series and considerably increases the computational costs. In order to tackle this issue, we propose a sub-structuring approach called the Condensed Transfer Function (CTF) method that will allow assembling a model of axisymmetric stiffened shell with models of non-axisymmetric internal frames. The CTF method is developed in the general case of mechanical subsystems coupled along curves. A set of orthonormal functions called condensation functions, which depend on the curvilinear abscissa along the coupling line, is considered. This set is then used as a basis for approximating and decomposing the displacements and the applied forces at the line junctions. Thanks to the definition and calculation of condensed transfer functions for each uncoupled subsystem and by using the superposition principle for passive linear systems, the behavior of the coupled subsystems can be deduced. A plane plate is considered as a test case to study the convergence of the method with respect to the type and the number of condensation functions taken into account. The CTF method is then applied to couple a submerged non-periodically stiffened shell described using the Circumferential Admittance Approach (CAA) with internal substructures described by Finite Element Method (FEM). The influence of non-axisymmetric internal substructures can finally be studied and it is shown that it tends to increase the radiation efficiency of the shell and can modify the vibrational and acoustic energy distribution.

Silica-Coated Core-Shell Structured Polystyrene Nanospheres and Their Size-Dependent Mechanical Properties.

PubMed

Cao, Xu; Pan, Guoshun; Huang, Peng; Guo, Dan; Xie, Guoxin

2017-08-22

The core-shell structured PS/SiO 2 composite nanospheres were synthesized on the basis of a modified Stöber method. The mechanical properties of monodisperse nanospheres were characterized with nanoindentation on the basis of the atomic force microscopy (AFM). The surface morphologies of PS/SiO 2 composite nanospheres was scanned with the tapping mode of AFM, and the force-distance curves were measured with the contact mode of AFM. Different contact models were compared for the analyses of experimental data. The elastic moduli of PS/SiO 2 composite nanosphere (4-40 GPa) and PS nanosphere (∼3.4 GPa) were obtained with the Hertz and Johnson-Kendall-Roberts (JKR) models, respectively, and the JKR model was proven to be more appropriate for calculating the elastic modulus of PS/SiO 2 nanospheres. The elastic modulus of SiO 2 shell gradually approached a constant value (∼46 GPa) with the increase of SiO 2 shell thickness. A core-shell model was proposed for describing the relationship between PS/SiO 2 composite nanosphere's elastic modulus and shell thickness. The mechanical properties of the composite nanospheres were reasonably explained on the basis of the growth mechanism of PS/SiO 2 composite nanospheres, in particular the SiO 2 shell's formation process. Available research data of PS/SiO 2 composite nanospheres in this work can provide valuable guidance for their effective application in surface engineering, micro/nanomanufacturing, lubrication, and so on.

Analysis of shell-type structures subjected to time-dependent mechanical and thermal loading

NASA Technical Reports Server (NTRS)

Simitses, George J.

1990-01-01

The development of a general mathematical model and solution methodologies for analyzing structural response of thin, metallic shell-like structures under dynamic and/or static thermomechanical loads is examined. In the mathematical model, geometric as well as material-type of nonlinearities are considered. Traditional as well as novel approaches are reported and detailed applications are presented in the appendices. The emphasis for the mathematical model, the related solution schemes, and the applications, is on thermal viscoelastic and viscoplastic phenomena, which can predict creep and ratchetting.

Analysis of shell-type structures subjected to time-dependent mechanical and thermal loading

NASA Technical Reports Server (NTRS)

Simitses, G. J.

1991-01-01

This report deals with the development of a general mathematical model and solution methodology for analyzing the structural response of thin, metallic shell-like structures under dynamic and/or static thermomechanical loads. In the mathematical model, geometric as well as the material-type of nonlinearities are considered. Traditional as well as novel approaches are reported and detailed applications are presented in the appendices. The emphasis for the mathematical model, the related solution schemes, and the applications, is on thermal viscoelastic and viscoplastic phenomena, which can predict creep and ratchetting.

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.

Projected shell model study of odd-odd f-p-g shell proton-rich nuclei

NASA Astrophysics Data System (ADS)

Palit, R.; Sheikh, J. A.; Sun, Y.; Jain, H. C.

2003-01-01

A systematic study of two-quasiparticle bands of the proton-rich odd-odd nuclei in the mass A˜70 80 region is performed using the projected shell model approach. The study includes Br, Rb, and Y isotopes with N=Z+2 and Z+4. We describe the energy spectra and electromagnetic transition strengths in terms of the configuration mixing of the angular-momentum projected multi-quasiparticle states. Signature splitting and signature inversion in the rotational bands are discussed and are shown to be well described. A preliminary study of the odd-odd N=Z nucleus 74Rb, using the concept of spontaneous symmetry breaking is also presented.

Interplay between proton-neutron pairing and deformation in self-conjugated medium mass nuclei

NASA Astrophysics Data System (ADS)

Gambacurta, Danilo; Lacroix, Denis

2016-05-01

We employ a model combining self-consistent mean-field and shell model techniques to study the competition between particle-like and proton-neutron pairing correlations in fp-shell even-even self-conjugate nuclei. Deformation effects are realistically and microscopically described. The resulting approach can give a precise description of pairing correlations and eventually treat the coexistence of different condensate formed of pairs with different total spin/ isospin. The standard BCS calculations are systematically compared with approaches including correlation effects beyond the independent quasi-particle picture. The competition between proton-neutron correlations in the isoscalar and isovector channels is also analyzed, as well as their dependence on the deformation properties.

Spectroscopy of the odd-odd fp-shell nucleus {sup 52}Sc from secondary fragmentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gade, A.; Bazin, D.; Mueller, W.F.

2006-03-15

The odd-odd fp-shell nucleus {sup 52}Sc was investigated using in-beam {gamma}-ray spectroscopy following secondary fragmentation of a {sup 55}V and {sup 57}Cr cocktail beam. Aside from the known {gamma}-ray transition at 674(5) keV, a new decay at E{sub {gamma}}=212(3) keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of {sup 52}Sc irrespective of the choice of the effective interaction. In addition, the frequencymore » of spin values predicted by the shell model is successfully modeled by a spin distribution formulated in a statistical approach with an empirical, energy-independent spin-cutoff parameter.« less

Biological materials: a materials science approach.

PubMed

Meyers, Marc A; Chen, Po-Yu; Lopez, Maria I; Seki, Yasuaki; Lin, Albert Y M

2011-07-01

The approach used by Materials Science and Engineering is revealing new aspects in the structure and properties of biological materials. The integration of advanced characterization, mechanical testing, and modeling methods can rationalize heretofore unexplained aspects of these structures. As an illustration of the power of this methodology, we apply it to biomineralized shells, avian beaks and feathers, and fish scales. We also present a few selected bioinspired applications: Velcro, an Al2O3-PMMA composite inspired by the abalone shell, and synthetic attachment devices inspired by gecko. Copyright © 2010 Elsevier Ltd. All rights reserved.

Enhanced collectivity along the N = Z line: Lifetime measurements in 44Ti, 48Cr, and 52Fe

NASA Astrophysics Data System (ADS)

Arnswald, K.; Braunroth, T.; Seidlitz, M.; Coraggio, L.; Reiter, P.; Birkenbach, B.; Blazhev, A.; Dewald, A.; Fransen, C.; Fu, B.; Gargano, A.; Hess, H.; Hirsch, R.; Itaco, N.; Lenzi, S. M.; Lewandowski, L.; Litzinger, J.; Müller-Gatermann, C.; Queiser, M.; Rosiak, D.; Schneiders, D.; Siebeck, B.; Steinbach, T.; Vogt, A.; Wolf, K.; Zell, K. O.

2017-09-01

Lifetimes of the 21+ states in 44Ti, 48,50Cr, and 52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of 44Ti and 52Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N = Z nuclei compared to neighboring isotopes. The B (E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0 f 1 p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon-nucleon potential. The theoretical approaches underestimate the B (E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone 42Ca.

A statistical model for monitoring shell disease in inshore lobster fisheries: A case study in Long Island Sound

PubMed Central

Chen, Yong

2017-01-01

The expansion of shell disease is an emerging threat to the inshore lobster fisheries in the northeastern United States. The development of models to improve the efficiency and precision of existing monitoring programs is advocated as an important step in mitigating its harmful effects. The objective of this study is to construct a statistical model that could enhance the existing monitoring effort through (1) identification of potential disease-associated abiotic and biotic factors, and (2) estimation of spatial variation in disease prevalence in the lobster fishery. A delta-generalized additive modeling (GAM) approach was applied using bottom trawl survey data collected from 2001–2013 in Long Island Sound, a tidal estuary between New York and Connecticut states. Spatial distribution of shell disease prevalence was found to be strongly influenced by the interactive effects of latitude and longitude, possibly indicative of a geographic origin of shell disease. Bottom temperature, bottom salinity, and depth were also important factors affecting the spatial variability in shell disease prevalence. The delta-GAM projected high disease prevalence in non-surveyed locations. Additionally, a potential spatial discrepancy was found between modeled disease hotspots and survey-based gravity centers of disease prevalence. This study provides a modeling framework to enhance research, monitoring and management of emerging and continuing marine disease threats. PMID:28196150

Shell model description of heavy nuclei and abnormal collective motions

NASA Astrophysics Data System (ADS)

Qi, Chong

2018-05-01

In this contribution I present systematic calculations on the spectroscopy and electromagnetic transition properties of intermediate-mass and heavy nuclei around 100Sn and 208Pb. We employed the large-scale configuration interaction shell model approach with realistic interactions. Those nuclei are the longest isotopic chains that can be studied by the nuclear shell model. I will show that the yrast spectra of Te isotopes show a vibrational-like equally spaced pattern but the few known E2 transitions show rotational-like behaviour. These kinds of abnormal collective behaviors cannot be reproduced by standard collective models and provide excellent background to study the competition of single-particle and various collective degrees of freedom. Moreover, the calculated B(E2) values for neutron-deficient and heavier Te isotopes show contrasting different behaviours along the yrast line, which may be related to the enhanced neutron-proton correlation when approaching N=50. The deviations between theory and experiment concerning the energies and E2 transition properties of low-lying 0+ and 2+ excited states and isomeric states in those nuclei may provide a constraint on our understanding of nuclear deformation and intruder configuration in that region.

B(E2)↑ Measurements for Radioactive Neutron-Rich Ge Isotopes: Reaching the N=50 Closed Shell

NASA Astrophysics Data System (ADS)

Padilla-Rodal, E.; Galindo-Uribarri, A.; Baktash, C.; Batchelder, J. C.; Beene, J. R.; Bijker, R.; Brown, B. A.; Castaños, O.; Fuentes, B.; del Campo, J. Gomez; Hausladen, P. A.; Larochelle, Y.; Lisetskiy, A. F.; Mueller, P. E.; Radford, D. C.; Stracener, D. W.; Urrego, J. P.; Varner, R. L.; Yu, C.-H.

2005-03-01

The B(E2;0+1→2+1) values for the radioactive neutron-rich germanium isotopes 78,80Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction.

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE PAGES

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony; ...

2017-11-07

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherukara, Mathew J.; Sasikumar, Kiran; DiChiara, Anthony

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. Here in this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplaymore » of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.« less

Ultrafast Three-Dimensional Integrated Imaging of Strain in Core/Shell Semiconductor/Metal Nanostructures.

PubMed

Cherukara, Mathew J; Sasikumar, Kiran; DiChiara, Anthony; Leake, Steven J; Cha, Wonsuk; Dufresne, Eric M; Peterka, Tom; McNulty, Ian; Walko, Donald A; Wen, Haidan; Sankaranarayanan, Subramanian K R S; Harder, Ross J

2017-12-13

Visualizing the dynamical response of material heterointerfaces is increasingly important for the design of hybrid materials and structures with tailored properties for use in functional devices. In situ characterization of nanoscale heterointerfaces such as metal-semiconductor interfaces, which exhibit a complex interplay between lattice strain, electric potential, and heat transport at subnanosecond time scales, is particularly challenging. In this work, we use a laser pump/X-ray probe form of Bragg coherent diffraction imaging (BCDI) to visualize in three-dimension the deformation of the core of a model core/shell semiconductor-metal (ZnO/Ni) nanorod following laser heating of the shell. We observe a rich interplay of radial, axial, and shear deformation modes acting at different time scales that are induced by the strain from the Ni shell. We construct experimentally informed models by directly importing the reconstructed crystal from the ultrafast experiment into a thermo-electromechanical continuum model. The model elucidates the origin of the deformation modes observed experimentally. Our integrated imaging approach represents an invaluable tool to probe strain dynamics across mixed interfaces under operando conditions.

Neutrinoless double-β decay of 48Ca in the shell model: Closure versus nonclosure approximation

NASA Astrophysics Data System (ADS)

Sen'kov, R. A.; Horoi, M.

2013-12-01

Neutrinoless double-β decay (0νββ) is a unique process that could reveal physics beyond the Standard Model. Essential ingredients in the analysis of 0νββ rates are the associated nuclear matrix elements. Most of the approaches used to calculate these matrix elements rely on the closure approximation. Here we analyze the light neutrino-exchange matrix elements of 48Ca 0νββ decay and test the closure approximation in a shell-model approach. We calculate the 0νββ nuclear matrix elements for 48Ca using both the closure approximation and a nonclosure approach, and we estimate the uncertainties associated with the closure approximation. We demonstrate that the nonclosure approach has excellent convergence properties which allow us to avoid unmanageable computational cost. Combining the nonclosure and closure approaches we propose a new method of calculation for 0νββ decay rates which can be applied to the 0νββ decay rates of heavy nuclei, such as 76Ge or 82Se.

Computational modeling of Krypton gas puffs with tailored mass density profiles on Z

DOE PAGES

Jennings, Christopher A.; Ampleford, David J.; Lamppa, Derek C.; ...

2015-05-18

Large diameter multi-shell gas puffs rapidly imploded by high current (~20 MA, ~100 ns) on the Z generator of Sandia National Laboratories are able to produce high-intensity Krypton K-shell emission at ~13 keV. Efficiently radiating at these high photon energies is a significant challenge which requires the careful design and optimization of the gas distribution. To facilitate this, we hydrodynamically model the gas flow out of the nozzle and then model its implosion using a 3-dimensional resistive, radiative MHD code (GORGON). This approach enables us to iterate between modeling the implosion and gas flow from the nozzle to optimize radiativemore » output from this combined system. Furthermore, guided by our implosion calculations, we have designed gas profiles that help mitigate disruption from Magneto-Rayleigh–Taylor implosion instabilities, while preserving sufficient kinetic energy to thermalize to the high temperatures required for K-shell emission.« less

Efficacy of the SU(3) scheme for ab initio large-scale calculations beyond the lightest nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dytrych, T.; Maris, Pieter; Launey, K. D.

2016-06-09

We report on the computational characteristics of ab initio nuclear structure calculations in a symmetry-adapted no-core shell model (SA-NCSM) framework. We examine the computational complexity of the current implementation of the SA-NCSM approach, dubbed LSU3shell, by analyzing ab initio results for 6Li and 12C in large harmonic oscillator model spaces and SU(3)-selected subspaces. We demonstrate LSU3shell's strong-scaling properties achieved with highly-parallel methods for computing the many-body matrix elements. Results compare favorably with complete model space calculations and signi cant memory savings are achieved in physically important applications. In particular, a well-chosen symmetry-adapted basis a ords memory savings in calculations ofmore » states with a fixed total angular momentum in large model spaces while exactly preserving translational invariance.« less

Large Eddy Simulation of Transient Flow, Solidification, and Particle Transport Processes in Continuous-Casting Mold

NASA Astrophysics Data System (ADS)

Liu, Zhongqiu; Li, Linmin; Li, Baokuan; Jiang, Maofa

2014-07-01

The current study developed a coupled computational model to simulate the transient fluid flow, solidification, and particle transport processes in a slab continuous-casting mold. Transient flow of molten steel in the mold is calculated using the large eddy simulation. An enthalpy-porosity approach is used for the analysis of solidification processes. The transport of bubble and non-metallic inclusion inside the liquid pool is calculated using the Lagrangian approach based on the transient flow field. A criterion of particle entrapment in the solidified shell is developed using the user-defined functions of FLUENT software (ANSYS, Inc., Canonsburg, PA). The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern inside the liquid pool exhibits quite satisfactory agreement with the corresponding measurements. The predicted complex instantaneous velocity field is composed of various small recirculation zones and multiple vortices. The transport of particles inside the liquid pool and the entrapment of particles in the solidified shell are not symmetric. The Magnus force can reduce the entrapment ratio of particles in the solidified shell, especially for smaller particles, but the effect is not obvious. The Marangoni force can play an important role in controlling the motion of particles, which increases the entrapment ratio of particles in the solidified shell obviously.

The Effects of Sand Sediment Volume Heterogeneities on Sound Propagation and Scattering

DTIC Science & Technology

2011-09-01

previously developed at APL- UW for the study of high-frequency acoustics . These models include perturbation models applied to scattering from the...shell shapes (Figure 1). The acoustic modeling to this point has utilized Ivakin’s unified approach to volume and roughness scattering [3...sediments: A modeling approach and application to a shelly sand-mud environment,” in the Proceeding of the European Conference on Underwater Acoustics

Sound Transmission through Cylindrical Shell Structures Excited by Boundary Layer Pressure Fluctuations

NASA Technical Reports Server (NTRS)

Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

1996-01-01

This paper examines sound transmission into two concentric cylindrical sandwich shells subject to turbulent flow on the exterior surface of the outer shell. The interior of the shells is filled with fluid medium and there is an airgap between the shells in the annular space. The description of the pressure field is based on the cross-spectral density formulation of Corcos, Maestrello, and Efimtsov models of the turbulent boundary layer. The classical thin shell theory and the first-order shear deformation theory are applied for the inner and outer shells, respectively. Modal expansion and the Galerkin approach are used to obtain closed-form solutions for the shell displacements and the radiation and transmission pressures in the cavities including both the annular space and the interior. The average spectral density of the structural responses and the transmitted interior pressures are expressed explicitly in terms of the summation of the cross-spectral density of generalized force induced by the boundary layer turbulence. The effects of acoustic and hydrodynamic coincidences on the spectral density are observed. Numerical examples are presented to illustrate the method for both subsonic and supersonic flows.

Criteria for applicability of the impulse approach to collisions

NASA Astrophysics Data System (ADS)

Sharma, Ramesh D.; Bakshi, Pradip M.; Sindoni, Joseph M.

1990-06-01

Using an exact formulation of impulse approach (IA) to atom-diatom collisions, we assess its internal consistency. By comparing the cross sections in the forward and reverse directions for the vibrational-rotational inelastic processes, using the half-on-the-shell (post and prior) models of the two-body t matrix, we show that in both cases the IA leads to a violation of the semidetailed balance (SDB) condition for small scattering angles. An off-shell model for the two-body t matrix, which preserves SDB, is shown to have other serious shortcomings. The cross sections are studied quantitatively as a function of the relative translational energy and the mass of the incident particle, and criteria discussed for the applicability of IA.

Quantified Gamow shell model interaction for p s d -shell nuclei

NASA Astrophysics Data System (ADS)

Jaganathen, Y.; Betan, R. M. Id; Michel, N.; Nazarewicz, W.; Płoszajczak, M.

2017-11-01

Background: The structure of weakly bound and unbound nuclei close to particle drip lines is one of the major science drivers of nuclear physics. A comprehensive understanding of these systems goes beyond the traditional configuration interaction approach formulated in the Hilbert space of localized states (nuclear shell model) and requires an open quantum system description. The complex-energy Gamow shell model (GSM) provides such a framework as it is capable of describing resonant and nonresonant many-body states on equal footing. Purpose: To make reliable predictions, quality input is needed that allows for the full uncertainty quantification of theoretical results. In this study, we carry out the optimization of an effective GSM (one-body and two-body) interaction in the p s d f -shell-model space. The resulting interaction is expected to describe nuclei with 5 ≤A ≲12 at the p -s d -shell interface. Method: The one-body potential of the 4He core is modeled by a Woods-Saxon + spin-orbit + Coulomb potential, and the finite-range nucleon-nucleon interaction between the valence nucleons consists of central, spin-orbit, tensor, and Coulomb terms. The GSM is used to compute key fit observables. The χ2 optimization is performed using the Gauss-Newton algorithm augmented by the singular value decomposition technique. The resulting covariance matrix enables quantification of statistical errors within the linear regression approach. Results: The optimized one-body potential reproduces nucleon-4He scattering phase shifts up to an excitation energy of 20 MeV. The two-body interaction built on top of the optimized one-body field is adjusted to the bound and unbound ground-state binding energies and selected excited states of the helium, lithium, and beryllium isotopes up to A =9 . A very good agreement with experimental results was obtained for binding energies. First applications of the optimized interaction include predictions for two-nucleon correlation densities and excitation spectra of light nuclei with quantified uncertainties. Conclusion: The new interaction will enable comprehensive and fully quantified studies of structure and reactions aspects of nuclei from the p s d region of the nuclear chart.

Quantified Gamow shell model interaction for p s d -shell nuclei

DOE PAGES

Jaganathen, Y.; Betan, R. M. Id; Michel, N.; ...

2017-11-20

Background: The structure of weakly bound and unbound nuclei close to particle drip lines is one of the major science drivers of nuclear physics. A comprehensive understanding of these systems goes beyond the traditional configuration interaction approach formulated in the Hilbert space of localized states (nuclear shell model) and requires an open quantum system description. The complex-energy Gamow shell model (GSM) provides such a framework as it is capable of describing resonant and nonresonant many-body states on equal footing. Purpose: To make reliable predictions, quality input is needed that allows for the full uncertainty quantification of theoretical results. In thismore » study, we carry out the optimization of an effective GSM (one-body and two-body) interaction in the psdf-shell-model space. The resulting interaction is expected to describe nuclei with 5 ≤ A ≲ 12 at the p-sd-shell interface. Method: The one-body potential of the 4He core is modeled by a Woods-Saxon + spin-orbit + Coulomb potential, and the finite-range nucleon-nucleon interaction between the valence nucleons consists of central, spin-orbit, tensor, and Coulomb terms. The GSM is used to compute key fit observables. The χ 2 optimization is performed using the Gauss-Newton algorithm augmented by the singular value decomposition technique. The resulting covariance matrix enables quantification of statistical errors within the linear regression approach. Results: The optimized one-body potential reproduces nucleon- 4He scattering phase shifts up to an excitation energy of 20 MeV. The two-body interaction built on top of the optimized one-body field is adjusted to the bound and unbound ground-state binding energies and selected excited states of the helium, lithium, and beryllium isotopes up to A = 9 . A very good agreement with experimental results was obtained for binding energies. First applications of the optimized interaction include predictions for two-nucleon correlation densities and excitation spectra of light nuclei with quantified uncertainties. In conclusion: The new interaction will enable comprehensive and fully quantified studies of structure and reactions aspects of nuclei from the psd region of the nuclear chart.« less

Solar radiation stress in climbing snails: behavioural and intrinsic features define the Hsp70 level in natural populations of Xeropicta derbentina (Pulmonata).

PubMed

Di Lellis, Maddalena A; Seifan, Merav; Troschinski, Sandra; Mazzia, Christophe; Capowiez, Yvan; Triebskorn, Rita; Köhler, Heinz-R

2012-11-01

Ectotherms from sunny and hot environments need to cope with solar radiation. Mediterranean land snails of the superfamily Helicoidea feature a behavioural strategy to escape from solar radiation-induced excessive soil heating by climbing up vertical objects. The height of climbing, and also other parameters like shell colouration pattern, shell orientation, shell size, body mass, actual internal and shell surface temperature, and the interactions between those factors may be expected to modulate proteotoxic effects in snails exposed to solar radiation and, thus, their stress response. Focussing on natural populations of Xeropicta derbentina, we conducted a 'snapshot' field study using the individual Hsp70 level as a proxy for proteotoxic stress. In addition to correlation analyses, an IT-model selection approach based on Akaike's Information Criterion was applied to evaluate a set of models with respect to their explanatory power and to assess the relevance of each of the above-mentioned parameters for individual stress, by model averaging and parameter estimation. The analysis revealed particular importance of the individuals' shell size, height above ground, the shell colouration pattern and the interaction height × orientation. Our study showed that a distinct set of behavioural traits and intrinsic characters define the Hsp70 level and that environmental factors and individual features strongly interact.

Optimization of wall thickness and lay-up for the shell-like composite structure loaded by non-uniform pressure field

NASA Astrophysics Data System (ADS)

Shevtsov, S.; Zhilyaev, I.; Oganesyan, P.; Axenov, V.

2017-01-01

The glass/carbon fiber composites are widely used in the design of various aircraft and rotorcraft components such as fairings and cowlings, which have predominantly a shell-like geometry and are made of quasi-isotropic laminates. The main requirements to such the composite parts are the specified mechanical stiffness to withstand the non-uniform air pressure at the different flight conditions and reduce a level of noise caused by the airflow-induced vibrations at the constrained weight of the part. The main objective of present study is the optimization of wall thickness and lay-up of composite shell-like cowling. The present approach assumes conversion of the CAD model of the cowling surface to finite element (FE) representation, then its wind tunnel testing simulation at the different orientation of airflow to find the most stressed mode of flight. 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. A wall thickness of the shell had to change over its surface to minimize the objective at the constrained weight. We used a parameterization of the problem that assumes an initiation of auxiliary sphere with varied radius and coordinates of the center, which were the design variables. Curve that formed by the intersection of the shell with sphere defined boundary of area, which should be reinforced by local thickening the shell wall. To eliminate a local stress concentration this increment was defined as the smooth function defined on the shell surface. As a result of structural optimization we obtained the thickness of shell's wall distribution, which then was used to design the draping and lay-up of composite prepreg layers. The global strain energy in the optimized cowling was reduced in2.5 times at the weight growth up to 15%, whereas the eigenfrequencies at the 6 first natural vibration modes have been increased by 5-15%. The present approach and developed programming tools that demonstrated a good efficiency and stability at the acceptable computational costs can be used to optimize a wide range of shell-like structures made of quasi-isotropic laminates.

A robust approach for analysing dispersion of elastic waves in an orthotropic cylindrical shell

NASA Astrophysics Data System (ADS)

Kaplunov, J.; Nobili, A.

2017-08-01

Dispersion of elastic waves in a thin orthotropic cylindrical shell is considered, within the framework of classical 2D Kirchhoff-Love theory. In contrast to direct multi-parametric analysis of the lowest propagating modes, an alternative robust approach is proposed that simply requires evaluation of the evanescent modes (quasi-static edge effect), which, at leading order, do not depend on vibration frequency. A shortened dispersion relation for the propagating modes is then derived by polynomial division and its accuracy is numerically tested against the full Kirchhoff-Love dispersion relation. It is shown that the same shortened relation may be also obtained from a refined dynamic version of the semi-membrane theory for cylindrical shells. The presented results may be relevant for modelling various types of nanotubes which, according to the latest experimental findings, possess strong material anisotropy.

Burrowing behaviour of robotic bivalves with synthetic morphologies.

PubMed

Germann, D P; Carbajal, J P

2013-12-01

Several bivalve species burrow into sandy sediments to reach their living position. There are many hypotheses concerning the functional morphology of the bivalve shell for burrowing. Observational studies are limited and often qualitative and should be complemented by a synthetic approach mimicking the burrowing process using a robotic emulation. In this paper we present a simple mechatronic set-up to mimic the burrowing behaviour of bivalves. As environment we used water and quartz sand contained in a glass tank. Bivalve shells were mathematically modelled on the computer and then materialized using a 3D printer. The burrowing motion of the shells was induced by two external linear motors. Preliminary experiments did not expose any artefacts introduced to the burrowing process by the set-up. We tested effects of shell size, shape and surface sculpturing on the burrowing performance. Neither the typical bivalve shape nor surface sculpture did have a clear positive effect on burrowing depth in the performed experiments. We argue that the presented method is a valid and promising approach to investigate the functional morphology of bivalve shells and should be improved and extended in future studies. In contrast to the observation of living bivalves, our approach offers complete control over the parameters defining shell morphology and motion pattern. The technical set-up allows the systematic variation of all parameters to quantify their effects. The major drawback of the built set-up was that the reliability and significance of the results was limited by the lack of an optimal technique to standardize the sediment state before experiments.

Variational asymptotic modeling of composite dimensionally reducible structures

NASA Astrophysics Data System (ADS)

Yu, Wenbin

A general framework to construct accurate reduced models for composite dimensionally reducible structures (beams, plates and shells) was formulated based on two theoretical foundations: decomposition of the rotation tensor and the variational asymptotic method. Two engineering software systems, Variational Asymptotic Beam Sectional Analysis (VABS, new version) and Variational Asymptotic Plate and Shell Analysis (VAPAS), were developed. Several restrictions found in previous work on beam modeling were removed in the present effort. A general formulation of Timoshenko-like cross-sectional analysis was developed, through which the shear center coordinates and a consistent Vlasov model can be obtained. Recovery relations are given to recover the asymptotic approximations for the three-dimensional field variables. A new version of VABS has been developed, which is a much improved program in comparison to the old one. Numerous examples are given for validation. A Reissner-like model being as asymptotically correct as possible was obtained for composite plates and shells. After formulating the three-dimensional elasticity problem in intrinsic form, the variational asymptotic method was used to systematically reduce the dimensionality of the problem by taking advantage of the smallness of the thickness. The through-the-thickness analysis is solved by a one-dimensional finite element method to provide the stiffnesses as input for the two-dimensional nonlinear plate or shell analysis as well as recovery relations to approximately express the three-dimensional results. The known fact that there exists more than one theory that is asymptotically correct to a given order is adopted to cast the refined energy into a Reissner-like form. A two-dimensional nonlinear shell theory consistent with the present modeling process was developed. The engineering computer code VAPAS was developed and inserted into DYMORE to provide an efficient and accurate analysis of composite plates and shells. Numerical results are compared with the exact solutions, and the excellent agreement proves that one can use VAPAS to analyze composite plates and shells efficiently and accurately. In conclusion, rigorous modeling approaches were developed for composite beams, plates and shells within a general framework. No such consistent and general treatment is found in the literature. The associated computer programs VABS and VAPAS are envisioned to have many applications in industry.

Quadrupole collectivity beyond N = 50 in neutron- rich Se and Kr isotopes

NASA Astrophysics Data System (ADS)

Elman, Brandon; Gade, A.; Barofsky, D.; Bender, P. C.; Bowry, M.; Hjorth-Jensen, M.; Kemper, K. W.; Lipschutz, S.; Lunderberg, E.; Sachmpazidi, N.; Terpstra, N.; Walters, W. B.; Weisshaar, D.; Westerberg, A.; Williams, S. J.; Wimmer, K.

2017-09-01

We will present results on measuring the B (E 2 ;01+ ->2n+) strength for the neutron-rich 88,90Kr and 86Se isotopes from intermediate-energy Coulomb excitation. The electric quadrupole transition strengths to the first 2+ state complete, with considerably improved uncertainties, the evolution of quadrupole collectivity in the Kr and Se isotopes approaching N = 60 , for which 90Kr and 86Se had previously been the most uncertain. We also report significant excitation strength to several higher lying 2+ states in the krypton isotopes. The results confirm shell model calculations in the π (fpg) - ν (sdg) shell with only a minimally tuned shell model setup that is based on a nucleon-nucleon interaction derived from effective field theory with effective charges adjusted to 86Kr.

An Enriched Shell Finite Element for Progressive Damage Simulation in Composite Laminates

NASA Technical Reports Server (NTRS)

McElroy, Mark W.

2016-01-01

A formulation is presented for an enriched shell nite element capable of progressive damage simulation in composite laminates. The element uses a discrete adaptive splitting approach for damage representation that allows for a straightforward model creation procedure based on an initially low delity mesh. The enriched element is veri ed for Mode I, Mode II, and mixed Mode I/II delamination simulation using numerical benchmark data. Experimental validation is performed using test data from a delamination-migration experiment. Good correlation was found between the enriched shell element model results and the numerical and experimental data sets. The work presented in this paper is meant to serve as a rst milestone in the enriched element's development with an ultimate goal of simulating three-dimensional progressive damage processes in multidirectional laminates.

Reconstruction and analysis of hybrid composite shells using meshless methods

NASA Astrophysics Data System (ADS)

Bernardo, G. M. S.; Loja, M. A. R.

2017-06-01

The importance of focusing on the research of viable models to predict the behaviour of structures which may possess in some cases complex geometries is an issue that is growing in different scientific areas, ranging from the civil and mechanical engineering to the architecture or biomedical devices fields. In these cases, the research effort to find an efficient approach to fit laser scanning point clouds, to the desired surface, has been increasing, leading to the possibility of modelling as-built/as-is structures and components' features. However, combining the task of surface reconstruction and the implementation of a structural analysis model is not a trivial task. Although there are works focusing those different phases in separate, there is still an effective need to find approaches able to interconnect them in an efficient way. Therefore, achieving a representative geometric model able to be subsequently submitted to a structural analysis in a similar based platform is a fundamental step to establish an effective expeditious processing workflow. With the present work, one presents an integrated methodology based on the use of meshless approaches, to reconstruct shells described by points' clouds, and to subsequently predict their static behaviour. These methods are highly appropriate on dealing with unstructured points clouds, as they do not need to have any specific spatial or geometric requirement when implemented, depending only on the distance between the points. Details on the formulation, and a set of illustrative examples focusing the reconstruction of cylindrical and double-curvature shells, and its further analysis, are presented.

Control of the shell structural properties and cavity diameter of hollow magnesium fluoride particles.

PubMed

Nandiyanto, Asep Bayu Dani; Ogi, Takashi; Okuyama, Kikuo

2014-03-26

Control of the shell structural properties [i.e., thickness (8-25 nm) and morphology (dense and raspberry)] and cavity diameter (100-350 nm) of hollow particles was investigated experimentally, and the results were qualitatively explained based on the available theory. We found that the selective deposition size and formation of the shell component on the surface of a core template played important roles in controlling the structure of the resulting shell. To achieve the selective deposition size and formation of the shell component, various process parameters (i.e., reaction temperature and charge, size, and composition of the core template and shell components) were tested. Magnesium fluoride (MgF2) and polystyrene spheres were used as models for shell and core components, respectively. MgF2 was selected because, to the best of our knowledge, the current reported approaches to date were limited to synthesis of MgF2 in film and particle forms only. Therefore, understanding how to control the formation of MgF2 with various structures (both the thickness and morphology) is a prospective for advanced lens synthesis and applications.

Enhanced collectivity along the N = Z line: lifetime measurements in 44Ti, 48Cr, and 52Fe

NASA Astrophysics Data System (ADS)

Arnswald, K.; Reiter, P.; Coraggio, L.; Birkenbach, B.; Blazhev, A.; Braunroth, T.; Dewald, A.; Fransen, C.; Fu, B.; Gargano, A.; Hess, H.; Hirsch, R.; Itaco, N.; Lenzi, S. M.; Lewandowski, L.; Litzinger, J.; Müller-Gatermann, C.; Queiser, M.; Rosiak, D.; Schneiders, D.; Seidlitz, M.; Siebeck, B.; Steinbach, T.; Vogt, A.; Wolf, K.; Zell, K. O.

2018-02-01

Lifetimes of the {2}1+ states in 44Ti, 48,50Cr, and 52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of 44Ti and 52 Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N = Z nuclei compared to neighboring isotopes. The B(E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0f 1p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon-nucleon potential. The theoretical approaches underestimate the B(E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone 42 Ca. A detailed manuscript has meanwhile been published in Physics Letters B [1].

Adaptive resolution simulation of a biomolecule and its hydration shell: Structural and dynamical properties

NASA Astrophysics Data System (ADS)

Fogarty, Aoife C.; Potestio, Raffaello; Kremer, Kurt

2015-05-01

A fully atomistic modelling of many biophysical and biochemical processes at biologically relevant length- and time scales is beyond our reach with current computational resources, and one approach to overcome this difficulty is the use of multiscale simulation techniques. In such simulations, when system properties necessitate a boundary between resolutions that falls within the solvent region, one can use an approach such as the Adaptive Resolution Scheme (AdResS), in which solvent particles change their resolution on the fly during the simulation. Here, we apply the existing AdResS methodology to biomolecular systems, simulating a fully atomistic protein with an atomistic hydration shell, solvated in a coarse-grained particle reservoir and heat bath. Using as a test case an aqueous solution of the regulatory protein ubiquitin, we first confirm the validity of the AdResS approach for such systems, via an examination of protein and solvent structural and dynamical properties. We then demonstrate how, in addition to providing a computational speedup, such a multiscale AdResS approach can yield otherwise inaccessible physical insights into biomolecular function. We use our methodology to show that protein structure and dynamics can still be correctly modelled using only a few shells of atomistic water molecules. We also discuss aspects of the AdResS methodology peculiar to biomolecular simulations.

Vibration suppression of a piezo-equipped cylindrical shell in a broad-band frequency domain

NASA Astrophysics Data System (ADS)

Loghmani, Ali; Danesh, Mohammad; Kwak, Moon K.; Keshmiri, Mehdi

2017-12-01

This paper focuses on the dynamic modeling of a cylindrical shell equipped with piezoceramic sensors and actuators, as well as the design of a broad band multi-input and multi-output linear quadratic Gaussian controller for the suppression of vibrations. The optimal locations of actuators are derived by Genetic Algorithm (GA) to effectively control the specific structural modes of the cylinder. The dynamic model is derived based on the Sanders shell theory and the energy approach for both the cylinder and the piezoelectric transducers, all of which reflect the piezoelectric effect. The natural vibration characteristics of the cylindrical shell are investigated both theoretically and experimentally. The theoretical predictions are in good agreement with the experimental results. Then, the broad band multi-input and multi-output linear quadratic Gaussian controller was designed and applied to the test article. An active vibration control experiment is carried out on the cylindrical shell and the digital control system is used to implement the proposed control algorithm. The experimental results show that vibrations of the cylindrical shell can be suppressed by the piezoceramic sensors and actuators along with the proposed controller. The optimal location of the actuators makes the proposed control system more efficient than other configurations.

Fission properties of Po isotopes in different macroscopic-microscopic models

NASA Astrophysics Data System (ADS)

Bartel, J.; Pomorski, K.; Nerlo-Pomorska, B.; Schmitt, Ch

2015-11-01

Fission-barrier heights of nuclei in the Po isotopic chain are investigated in several macroscopic-microscopic models. Using the Yukawa-folded single-particle potential, the Lublin-Strasbourg drop (LSD) model, the Strutinsky shell-correction method to yield the shell corrections and the BCS theory for the pairing contributions, fission-barrier heights are calculated and found in quite good agreement with the experimental data. This turns out, however, to be only the case when the underlying macroscopic, liquid-drop (LD) type, theory is well chosen. Together with the LSD approach, different LD parametrizations proposed by Moretto et al are tested. Four deformation parameters describing respectively elongation, neck-formation, reflectional-asymmetric, and non-axiality of the nuclear shape thus defining the so called modified Funny Hills shape parametrization are used in the calculation. The present study clearly demonstrates that nuclear fission-barrier heights constitute a challenging and selective tool to discern between such different macroscopic approaches.

Free and Forced Vibrations of Thick-Walled Anisotropic Cylindrical Shells

NASA Astrophysics Data System (ADS)

Marchuk, A. V.; Gnedash, S. V.; Levkovskii, S. A.

2017-03-01

Two approaches to studying the free and forced axisymmetric vibrations of cylindrical shell are proposed. They are based on the three-dimensional theory of elasticity and division of the original cylindrical shell with concentric cross-sectional circles into several coaxial cylindrical shells. One approach uses linear polynomials to approximate functions defined in plan and across the thickness. The other approach also uses linear polynomials to approximate functions defined in plan, but their variation with thickness is described by the analytical solution of a system of differential equations. Both approaches have approximation and arithmetic errors. When determining the natural frequencies by the semi-analytical finite-element method in combination with the divide and conqure method, it is convenient to find the initial frequencies by the finite-element method. The behavior of the shell during free and forced vibrations is analyzed in the case where the loading area is half the shell thickness

The nuclear shell model toward the drip lines

NASA Astrophysics Data System (ADS)

Poves, A.; Caurier, E.; Nowacki, F.; Sieja, K.

2012-10-01

We describe the 'islands of inversion' that occur when approaching the neutron drip line around the magic numbers N=20, N=28 and N=40 in the framework of the interacting shell model in very large valence spaces. We explain these configuration inversions (and the associated shape transitions) as the result of the competition between the spherical mean field (monopole) that favors magicity and the correlations (multipole) that favor deformed intruder states. We also show that the N=20 and N=28 islands are in reality a single one, which for the magnesium isotopes is limited by N=18 and N=32.

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.

Systematics of first 2+ state g factors around mass 80

NASA Astrophysics Data System (ADS)

Mertzimekis, T. J.; Stuchbery, A. E.; Benczer-Koller, N.; Taylor, M. J.

2003-11-01

The systematics of the first 2+ state g factors in the mass 80 region are investigated in terms of an IBM-II analysis, a pairing-corrected geometrical model, and a shell-model approach. Subshell closure effects at N=38 and overall trends were examined using IBM-II. A large-space shell-model calculation was successful in describing the behavior for N=48 and N=50 nuclei, where single-particle features are prominent. A schematic truncated-space calculation was applied to the lighter isotopes. The variations of the effective boson g factors are discussed in connection with the role of F -spin breaking, and comparisons are made between the mass 80 and mass 180 regions.

Macro Scale Independently Homogenized Subcells for Modeling Braided Composites

NASA Technical Reports Server (NTRS)

Blinzler, Brina J.; Goldberg, Robert K.; Binienda, Wieslaw K.

2012-01-01

An analytical method has been developed to analyze the impact response of triaxially braided carbon fiber composites, including the penetration velocity and impact damage patterns. In the analytical model, the triaxial braid architecture is simulated by using four parallel shell elements, each of which is modeled as a laminated composite. Currently, each shell element is considered to be a smeared homogeneous material. The commercial transient dynamic finite element code LS-DYNA is used to conduct the simulations, and a continuum damage mechanics model internal to LS-DYNA is used as the material constitutive model. To determine the stiffness and strength properties required for the constitutive model, a top-down approach for determining the strength properties is merged with a bottom-up approach for determining the stiffness properties. The top-down portion uses global strengths obtained from macro-scale coupon level testing to characterize the material strengths for each subcell. The bottom-up portion uses micro-scale fiber and matrix stiffness properties to characterize the material stiffness for each subcell. Simulations of quasi-static coupon level tests for several representative composites are conducted along with impact simulations.

Numerical investigation of sound transmission through double wall cylinders with respect to active noise control

NASA Astrophysics Data System (ADS)

Coats, T. J.; Silcox, R. J.; Lester, H. C.

Market pressure for more fuel efficient air travel has led to increased use of turboprop and higher bypass turbofan engines. The low frequency components of propeller, jet and boundary layer noise are difficult to attenuate with conventional passive techniques. Weight and geometric restrictions for sound absorbing meterials limit the amount and type of treatment that may be applied. An active noise control (ANC) method is providing to be an attractive alternative. The approach taken in this paper uses a numerical finite/boundary element method (FEM/BEM) that may be easilty adapted to arbitrary geometries. A double walled cylinder is modeled using commercially available software. The outer shell is modeled as an aluminum cylinder, similar to that of aircraft skins. The inner shell is modeled as a composite material representative of a lightweight, stiff trim panel. Two different inner shell materials are used. The first is representative of current trim structure, the second a much stiffer composite. The primary source is generated by an exterior acoustic monopole. Control fields are generated using normal force inputs to the inner cylindrical shell. A linear least mean square (LMS) algorithm is used to determine amplitudes of control forces that minimize the interior acoustic field. Coupling of acoustic and structural modes and noise reductions are discussed for each of the inner shell materials.

Numerical investigation of sound transmission through double wall cylinders with respect to active noise control

NASA Technical Reports Server (NTRS)

Coats, T. J.; Silcox, R. J.; Lester, H. C.

1993-01-01

Market pressure for more fuel efficient air travel has led to increased use of turboprop and higher bypass turbofan engines. The low frequency components of propeller, jet and boundary layer noise are difficult to attenuate with conventional passive techniques. Weight and geometric restrictions for sound absorbing meterials limit the amount and type of treatment that may be applied. An active noise control (ANC) method is providing to be an attractive alternative. The approach taken in this paper uses a numerical finite/boundary element method (FEM/BEM) that may be easilty adapted to arbitrary geometries. A double walled cylinder is modeled using commercially available software. The outer shell is modeled as an aluminum cylinder, similar to that of aircraft skins. The inner shell is modeled as a composite material representative of a lightweight, stiff trim panel. Two different inner shell materials are used. The first is representative of current trim structure, the second a much stiffer composite. The primary source is generated by an exterior acoustic monopole. Control fields are generated using normal force inputs to the inner cylindrical shell. A linear least mean square (LMS) algorithm is used to determine amplitudes of control forces that minimize the interior acoustic field. Coupling of acoustic and structural modes and noise reductions are discussed for each of the inner shell materials.

Geometric Electron Models.

ERIC Educational Resources Information Center

Nika, G. Gerald; Parameswaran, R.

1997-01-01

Describes a visual approach for explaining the filling of electrons in the shells, subshells, and orbitals of the chemical elements. Enables students to apply the principles of atomic electron configuration while using manipulatives to model the building up of electron configurations as the atomic numbers of elements increase on the periodic…

[Individual growth modeling of the penshell Atrina maura (Bivalvia: Pinnidae) using a multi model inference approach].

PubMed

Aragón-Noriega, Eugenio Alberto

2013-09-01

Growth models of marine animals, for fisheries and/or aquaculture purposes, are based on the popular von Bertalanffy model. This tool is mostly used because its parameters are used to evaluate other fisheries models, such as yield per recruit; nevertheless, there are other alternatives (such as Gompertz, Logistic, Schnute) not yet used by fishery scientists, that may result useful depending on the studied species. The penshell Atrina maura, has been studied for fisheries or aquaculture supplies, but its individual growth has not yet been studied before. The aim of this study was to model the absolute growth of the penshell A. maura using length-age data. For this, five models were assessed to obtain growth parameters: von Bertalanffy, Gompertz, Logistic, Schnute case 1 and Schnute and Richards. The criterion used to select the best models was the Akaike information criterion, as well as the residual squared sum and R2 adjusted. To get the average asymptotic length, the multi model inference approach was used. According to Akaike information criteria, the Gompertz model better described the absolute growth of A. maura. Following the multi model inference approach the average asymptotic shell length was 218.9 mm (IC 212.3-225.5) of shell length. I concluded that the use of the multi model approach and the Akaike information criteria represented the most robust method for growth parameter estimation of A. maura and the von Bertalanffy growth model should not be selected a priori as the true model to obtain the absolute growth in bivalve mollusks like in the studied species in this paper.

Influence of particle size and shell thickness of core-shell packing materials on optimum experimental conditions in preparative chromatography.

PubMed

Horváth, Krisztián; Felinger, Attila

2015-08-14

The applicability of core-shell phases in preparative separations was studied by a modeling approach. The preparative separations were optimized for two compounds having bi-Langmuir isotherms. The differential mass balance equation of chromatography was solved by the Rouchon algorithm. The results show that as the size of the core increases, larger particles can be used in separations, resulting in higher applicable flow rates, shorter cycle times. Due to the decreasing volume of porous layer, the loadability of the column dropped significantly. As a result, the productivity and economy of the separation decreases. It is shown that if it is possible to optimize the size of stationary phase particles for the given separation task, the use of core-shell phases are not beneficial. The use of core-shell phases proved to be advantageous when the goal is to build preparative column for general purposes (e.g. for purification of different products) in small scale separations. Copyright © 2015 Elsevier B.V. All rights reserved.

Experimental investigation of mode I fracture for brittle tube-shaped particles

NASA Astrophysics Data System (ADS)

Stasiak, Marta; Combe, Gaël; Desrues, Jacques; Richefeu, Vincent; Villard, Pascal; Armand, Gilles; Zghondi, Jad

2017-06-01

We focus herein on the mechanical behavior of highly crushable grains. The object of our interest, named shell, is a hollow cylinder grain with ring cross-section, made of baked clay. The objective is to model the fragmentation of such shells, by means of discrete element (DE) approach. To this end, fracture modes I (opening fracture) and II (in-plane shear fracture) have to be investigated experimentally. This paper is essentially dedicated to mode I fracture. Therefore, a campaign of Brazilian-like compression tests, that result in crack opening, has been performed. The distribution of the occurrence of tensile strength is shown to obey a Weibull distribution for the studied shells, and Weibull's modulus was quantified. Finally, an estimate of the numerical/physical parameters required in a DE model (local strength), is proposed on the basis of the energy required to fracture through a given surface in mode I or II.

Fluid-structure interaction for nonlinear response of shells conveying pulsatile flow

NASA Astrophysics Data System (ADS)

Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

2016-06-01

Circular cylindrical shells with flexible boundary conditions conveying pulsatile flow and subjected to pulsatile pressure are investigated. The equations of motion are obtained based on the nonlinear Novozhilov shell theory via Lagrangian approach. The flow is set in motion by a pulsatile pressure gradient. The fluid is modeled as a Newtonian pulsatile flow and it is formulated using a hybrid model that contains the unsteady effects obtained from the linear potential flow theory and the pulsatile viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior. The case of shells containing quiescent fluid subjected to the action of a pulsatile transmural pressure is also addressed. Geometrically nonlinear vibration response to pulsatile flow and transmural pressure are here presented via frequency-response curves and time histories. The vibrations involving both a driven mode and a companion mode, which appear due to the axial symmetry, are also investigated. This theoretical framework represents a pioneering study that could be of great interest for biomedical applications. In particular, in the future, a more refined model of the one here presented will possibly be applied to reproduce the dynamic behavior of vascular prostheses used for repairing and replacing damaged and diseased thoracic aorta in cases of aneurysm, dissection or coarctation. For this purpose, a pulsatile time-dependent blood flow model is here considered by applying physiological waveforms of velocity and pressure during the heart beating period. This study provides, for the first time in literature, a fully coupled fluid-structure interaction model with deep insights in the nonlinear vibrations of circular cylindrical shells subjected to pulsatile pressure and pulsatile flow.

In-beam γ -ray spectroscopy of Mn 63

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baugher, T.; Gade, A.; Janssens, R. V. F.

2016-01-01

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number N = 40 have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions. Purpose: We report the observation of two new γ -ray transitions in 63 Mn , which establish the ( 9 / 2 - ) and ( 11 / 2 - ) levels on top of the previously known ( 7 / 2 - ) first-excited state. The lifetime for themore » ( 7 / 2 - ) and ( 9 / 2 - ) excited states were determined for the first time, while an upper limit could be established for the ( 11 / 2 - ) level. Method: Excited states in 63 Mn have been populated in inelastic scattering from a 9 Be target and in the fragmentation of 65 Fe . γ γ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened ( 7 / 2 - ) → 5 / 2 - , ( 9 / 2 - ) → ( 7 / 2 - ) , and ( 11 / 2 - ) → ( 9 / 2 - ) transitions was used to determine (limits for) the corresponding excited-state lifetimes. Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change. Conclusions: While the theoretical ( 7 / 2 - ) and ( 9 / 2 - ) excitation energies show little dependence on the model space, the calculated lifetime of the ( 7 / 2 - ) level and calculated energy of the ( 11 / 2 - ) level reveal the importance of including the neutron g 9 / 2 and d 5 / 2 orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data.« less

Comparison of nonmesonic hypernuclear decay rates computed in laboratory and center-of-mass coordinates

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Conti, C.; Barbero, C.; Galeão, A. P.

In this work we compute the one-nucleon-induced nonmesonic hypernuclear decay rates of {sub Λ}{sup 5}He, {sub Λ}{sup 12}C and {sub Λ}{sup 13}C using a formalism based on the independent particle shell model in terms of laboratory coordinates. To ascertain the correctness and precision of the method, these results are compared with those obtained using a formalism in terms of center-of-mass coordinates, which has been previously reported in the literature. The formalism in terms of laboratory coordinates will be useful in the shell-model approach to two-nucleon-induced transitions.

Magnetization of the Ising model on the Sierpinski pastry-shell

NASA Astrophysics Data System (ADS)

Chame, Anna; Branco, N. S.

1992-02-01

Using a real-space renormalization group approach, we calculate the approximate magnetization in the Ising model on the Sierpinski Pastry-shell. We consider, as an approximation, only two regions of the fractal: the internal surfaces, or walls (sites on the border of eliminated areas), with coupling constants JS, and the bulk (all other sites), with coupling constants Jv. We obtain the mean magnetization of the two regions as a function of temperature, for different values of α= JS/ JV and different geometric parameters b and l. Curves present a step-like behavior for some values of b and l, as well as different universality classes for the bulk transition.

Tidal deformability and I-Love-Q relations for gravastars with polytropic thin shells

NASA Astrophysics Data System (ADS)

Uchikata, Nami; Yoshida, Shijun; Pani, Paolo

2016-09-01

The moment of inertia, the spin-induced quadrupole moment, and the tidal Love number of neutron-star and quark-star models are related through some relations which depend only mildly on the stellar equation of state. These "I-Love-Q" relations have important implications for astrophysics and gravitational-wave astronomy. An interesting problem is whether similar relations hold for other compact objects and how they approach the black hole limit. To answer these questions, here we investigate the deformation properties of a large class of thin-shell gravastars, which are exotic compact objects that do not possess an event horizon nor a spacetime singularity. Working in a small-spin and small-tidal field expansion, we calculate the moment of inertia, the quadrupole moment, and the (quadrupolar electric) tidal Love number of gravastars with a polytropic thin shell. The I-Love-Q relations of a thin-shell gravastar are drastically different from those of an ordinary neutron star. The Love number and quadrupole moment for less compact models have the opposite sign relative to those of ordinary neutron stars, and the I-Love-Q relations continuously approach the black hole limit. We consider a variety of polytropic equations of state for the matter shell and find no universality in the I-Love-Q relations. However, we cannot deny the possibility that, similarly to the neutron-star case, an approximate universality might emerge for a limited class of equations of state. Finally, we discuss how a measurement of the tidal deformability from the gravitational-wave detection of a compact-binary inspiral can be used to constrain exotic compact objects like gravastars.

Nonlinear finite-element analysis of nanoindentation of viral capsids

NASA Astrophysics Data System (ADS)

Gibbons, Melissa M.; Klug, William S.

2007-03-01

Recent atomic force microscope (AFM) nanoindentation experiments measuring mechanical response of the protein shells of viruses have provided a quantitative description of their strength and elasticity. To better understand and interpret these measurements, and to elucidate the underlying mechanisms, this paper adopts a course-grained modeling approach within the framework of three-dimensional nonlinear continuum elasticity. Homogeneous, isotropic, elastic, thick-shell models are proposed for two capsids: the spherical cowpea chlorotic mottle virus (CCMV), and the ellipsocylindrical bacteriophage ϕ29 . As analyzed by the finite-element method, these models enable parametric characterization of the effects of AFM tip geometry, capsid dimensions, and capsid constitutive descriptions. The generally nonlinear force response of capsids to indentation is shown to be insensitive to constitutive particulars, and greatly influenced by geometric and kinematic details. Nonlinear stiffening and softening of the force response is dependent on the AFM tip dimensions and shell thickness. Fits of the models capture the roughly linear behavior observed in experimental measurements and result in estimates of Young’s moduli of ≈280-360MPa for CCMV and ≈4.5GPa for ϕ29 .

Alternating current dielectrophoresis of core-shell nanoparticles: Experiments and comparison with theory

NASA Astrophysics Data System (ADS)

Yang, Chungja

Nanoparticles are fascinating where physical and optical properties are related to size. Highly controllable synthesis methods and nanoparticle assembly are essential for highly innovative technological applications. Well-defined shaped and sized nanoparticles enable comparisons between experiments, theory and subsequent new models to explain experimentally observed phenomena. Among nanoparticles, nonhomogeneous core-shell nanoparticles (CSnp) have new properties that arise when varying the relative dimensions of the core and the shell. This CSnp structure enables various optical resonances, and engineered energy barriers, in addition to the high charge to surface ratio. Assembly of homogeneous nanoparticles into functional structures has become ubiquitous in biosensors (i.e. optical labeling), nanocoatings, and electrical circuits. Limited nonhomogenous nanoparticle assembly has only been explored. Many conventional nanoparticle assembly methods exist, but this work explores dielectrophoresis (DEP) as a new method. DEP is particle polarization via non-uniform electric fields while suspended in conductive fluids. Most prior DEP efforts involve microscale particles. Prior work on core-shell nanoparticle assemblies and separately, nanoparticle characterizations with dielectrophoresis and electrorotation, did not systematically explore particle size, dielectric properties (permittivity and electrical conductivity), shell thickness, particle concentration, medium conductivity, and frequency. This work is the first, to the best of our knowledge, to systematically examine these dielectrophoretic properties for core-shell nanoparticles. Further, we conduct a parametric fitting to traditional core-shell models. These biocompatible core-shell nanoparticles were studied to fill a knowledge gap in the DEP field. Experimental results (chapter 5) first examine medium conductivity, size and shell material dependencies of dielectrophoretic behaviors of spherical CSnp into 2D and 3D particle-assemblies. Chitosan (amino sugar) and poly-L-lysine (amino acid, PLL) CSnp shell materials were custom synthesized around a hollow (gas) core by utilizing a phospholipid micelle around a volatile fluid templating for the shell material; this approach proves to be novel and distinct from conventional core-shell models wherein a conductive core is coated with an insulative shell. Experiments were conducted within a 100 nl chamber housing 100 um wide Ti/Au quadrapole electrodes spaced 25 um apart. Frequencies from 100kHz to 80MHz at fixed local field of 5Vpp were tested with 10-5 and 10-3 S/m medium conductivities for 25 seconds. Dielectrophoretic responses of ~220 and 340(or ~400) nm chitosan or PLL CSnp were compiled as a function of medium conductivity, size and shell material. Experiments further examined shell thickness and particle concentration (chapter 6) dependencies on ~530 nm CSnp dielectrophoretic and electrorotational responses with ~30nm and ~80 nm shell thicknesses and at particle concentration count rates of 5000 +/- 500, 10000 +/- 500, and 15000 +/- 500 counts per second. Using similar experimental conditions, both dielectrophoretic and electrorotational CSnp responses were compiled versus frequency, shell thickness, and particle concentration. Knowledge gained from this study includes a unique resonance-like dielectrophoretic and electrorotational spectrum, which is significantly distinct from other cells and particles. CSnp dielectric properties were then calculated by parametrically fitting parameters to an existing core-shell model. The optimum conductivity and relative permittivity for the core and the shell are 1E-15 S/m, 1, 0.6 S/m, and 90, respectively. These properties can be exploited to rapidly assemble these unique core-shell particles for future structural color production in fabrics, vehicle, and wall painting.

Discovering Planetary Nebula Geometries: Explorations with a Hierarchy of Models

NASA Technical Reports Server (NTRS)

Huyser, Karen A.; Knuth, Kevin H.; Fischer, Bernd; Schumann, Johann; Granquist-Fraser, Domhnull; Hajian, Arsen R.

2004-01-01

Astronomical objects known as planetary nebulae (PNe) consist of a shell of gas expelled by an aging medium-sized star as it makes its transition from a red giant to a white dwarf. In many cases this gas shell can be approximately described as a prolate ellipsoid. Knowledge of the physics of ionization processes in this gaseous shell enables us to construct a model in three dimensions (3D) called the Ionization-Bounded Prolate Ellipsoidal Shell model (IBPES model). Using this model we can generate synthetic nebular images, which can be used in conjunction with Hubble Space Telescope (HST) images of actual PNe to perform Bayesian model estimation. Since the IBPES model is characterized by thirteen parameters, model estimation requires the search of a 13-dimensional parameter space. The 'curse of dimensionality,' compounded by a computationally intense forward problem, makes forward searches extremely time-consuming and frequently causes them to become trapped in local solutions. We find that both the speed and of the search can be improved by judiciously reducing the dimensionality of the search space. Our basic approach employs a hierarchy of models of increasing complexity that converges to the IBPES model. Earlier studies establish that a hierarchical sequence converges more quickly, and to a better solution, than a search relying only on the most complex model. Here we report results for a hierarchy of five models. The first three models treat the nebula as a 2D image, while the last two models explore its characteristics as a 3D object and enable us to characterize the physics of the nebula. This five-model hierarchy is applied to HST images of ellipsoidal PNe to estimate their geometric properties and gas density profiles.

AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity.

PubMed

Sarrazin, Baptiste; Tsapis, Nicolas; Mousnier, Ludivine; Taulier, Nicolas; Urbach, Wladimir; Guenoun, Patrick

2016-05-10

Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

PubMed

Carrião, Marcus S; Bakuzis, Andris F

2016-04-21

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.

Grain formation around carbon stars. 1: Stationary outflow models

NASA Technical Reports Server (NTRS)

Egan, Michael P.; Leung, Chun Ming

1995-01-01

Asymptotic giant branch (AGB) stars are known to be sites of dust formation and undergo significant mass loss. The outflow is believed to be driven by radiation pressure on grains and momentum coupling between the grains and gas. While the physics of shell dynamics and grain formation are closely coupled, most previous models of circumstellar shells have treated the problem separately. Studies of shell dynamics typically assume the existence of grains needed to drive the outflow, while most grain formation models assume a constant veolcity wind in which grains form. Furthermore, models of grain formation have relied primarily on classical nucleation theory instead of using a more realistic approach based on chemical kinetics. To model grain formation in carbon-rich AGB stars, we have coupled the kinetic equations governing small cluster growth to moment equations which determine the growth of large particles. Phenomenological models assuming stationary outflow are presented to demonstrate the differences between the classical nucleation approach and the kinetic equation method. It is found that classical nucleation theory predicts nucleation at a lower supersaturation ratio than is predicted by the kinetic equations, resulting in significant differences in grain properties. Coagulation of clusters larger than monomers is unimportant for grain formation in high mass-loss models but becomes more important to grain growth in low mass-loss situations. The properties of the dust grains are altered considerably if differential drift velocities are ignored in modeling grain formation. The effect of stellar temperature, stellar luminosity, and different outflow velocities are investigated. The models indicate that changing the stellar temperature while keeping the stellar luminosity constant has little effect on the physical parameters of the dust shell formed. Increasing the stellar luminosity while keeping the stellar temperature constant results in large differences in grain properties. For small outflow velocities, grains form at lower supersaturation ratios and close to the stellar photosphere, resulting in larger but fewer grains. The reverse is true when grains form under high outflow velocities, i.e., they form at higher supersaturation ratios, farther from the star, and are much smaller but at larger quantities.

On the Modeling of Shells in Multibody Dynamics

NASA Technical Reports Server (NTRS)

Bauchau, Olivier A.; Choi, Jou-Young; Bottasso, Carlo L.

2000-01-01

Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the, constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.

Simultaneous Thermoelectric and Optoelectronic Characterization of Individual Nanowires.

PubMed

Léonard, François; Song, Erdong; Li, Qiming; Swartzentruber, Brian; Martinez, Julio A; Wang, George T

2015-12-09

Semiconducting nanowires have been explored for a number of applications in optoelectronics such as photodetectors and solar cells. Currently, there is ample interest in identifying the mechanisms that lead to photoresponse in nanowires in order to improve and optimize performance. However, distinguishing among the different mechanisms, including photovoltaic, photothermoelectric, photoemission, bolometric, and photoconductive, is often difficult using purely optoelectronic measurements. In this work, we present an approach for performing combined and simultaneous thermoelectric and optoelectronic measurements on the same individual nanowire. We apply the approach to GaN/AlGaN core/shell and GaN/AlGaN/GaN core/shell/shell nanowires and demonstrate the photothermoelectric nature of the photocurrent observed at the electrical contacts at zero bias, for above- and below-bandgap illumination. Furthermore, the approach allows for the experimental determination of the temperature rise due to laser illumination, which is often obtained indirectly through modeling. We also show that under bias, both above- and below-bandgap illumination leads to a photoresponse in the channel with signatures of persistent photoconductivity due to photogating. Finally, we reveal the concomitant presence of photothermoelectric and photogating phenomena at the contacts in scanning photocurrent microscopy under bias by using their different temporal response. Our approach is applicable to a broad range of nanomaterials to elucidate their fundamental optoelectronic and thermoelectric properties.

Characterization and prediction of the backscattered form function of an immersed cylindrical shell using hybrid fuzzy clustering and bio-inspired algorithms.

PubMed

Agounad, Said; Aassif, El Houcein; Khandouch, Younes; Maze, Gérard; Décultot, Dominique

2018-02-01

The acoustic scattering of a plane wave by an elastic cylindrical shell is studied. A new approach is developed to predict the form function of an immersed cylindrical shell of the radius ratio b/a ('b' is the inner radius and 'a' is the outer radius). The prediction of the backscattered form function is investigated by a combined approach between fuzzy clustering algorithms and bio-inspired algorithms. Four famous fuzzy clustering algorithms: the fuzzy c-means (FCM), the Gustafson-Kessel algorithm (GK), the fuzzy c-regression model (FCRM) and the Gath-Geva algorithm (GG) are combined with particle swarm optimization and genetic algorithm. The symmetric and antisymmetric circumferential waves A, S 0 , A 1 , S 1 and S 2 are investigated in a reduced frequency (k 1 a) range extends over 0.1

PLGA-lecithin-PEG core-shell nanoparticles for controlled drug delivery.

PubMed

Chan, Juliana M; Zhang, Liangfang; Yuet, Kai P; Liao, Grace; Rhee, June-Wha; Langer, Robert; Farokhzad, Omid C

2009-03-01

Current approaches to encapsulate and deliver therapeutic compounds have focused on developing liposomal and biodegradable polymeric nanoparticles (NPs), resulting in clinically approved therapeutics such as Doxil/Caelyx and Genexol-PM, respectively. Our group recently reported the development of biodegradable core-shell NP systems that combined the beneficial properties of liposomal and polymeric NPs for controlled drug delivery. Herein we report the parameters that alter the biological and physicochemical characteristics, stability, drug release properties and cytotoxicity of these core-shell NPs. We further define scalable processes for the formulation of these NPs in a reproducible manner. These core-shell NPs consist of (i) a poly(D,L-lactide-co-glycolide) hydrophobic core, (ii) a soybean lecithin monolayer, and (iii) a poly(ethylene glycol) shell, and were synthesized by a modified nanoprecipitation method combined with self-assembly. Preparation of the NPs showed that various formulation parameters such as the lipid/polymer mass ratio and lipid/lipid-PEG molar ratio controlled NP physical stability and size. We encapsulated a model chemotherapy drug, docetaxel, in the NPs and showed that the amount of lipid coverage affected its drug release kinetics. Next, we demonstrated a potentially scalable process for the formulation, purification, and storage of NPs. Finally, we tested the cytotoxicity using MTT assays on two model human cell lines, HeLa and HepG2, and demonstrated the biocompatibility of these particles in vitro. Our data suggest that the PLGA-lecithin-PEG core-shell NPs may be a useful new controlled release drug delivery system.

Biomaterial shell bending with 3D-printed templates in vertical and alveolar ridge augmentation: a technical note.

PubMed

Draenert, Florian G; Gebhart, Florian; Mitov, Gergo; Neff, Andreas

2017-06-01

Alveolar ridge and vertical augmentations are challenging procedures in dental implantology. Even material blocks with an interconnecting porous system are never completely resorbed. Shell techniques combined with autologous bone chips are therefore the gold standard. Using biopolymers for these techniques is well documented. We applied three-dimensional (3-D) techniques to create an individualized bending model for the adjustment of a plane biopolymer membrane made of polylactide. Two cases with a vertical alveolar ridge defect in the maxilla were chosen. The cone beam computed tomography data were processed with a 3-D slicer and the Autodesk Meshmixer to generate data about the desired augmentation result. STL data were used to print a bending model. A 0.2-mm poly-D, L-lactic acid membrane (KLS Matin Inc., Tuttlingen, Germany) was bended accordingly and placed into the defect via a tunnel approach in both cases. A mesh graft of autologous bone chips and hydroxylapatite material was augmented beneath the shell, which was fixed with osteosynthesis screws. The operative procedure was fast and without peri- or postoperative complications or complaints. The panoramic x-ray showed correct fitting of the material in the location. Bone quality at the time of implant placement was type II, resulting in good primary stability. A custom-made 3-D model for bending confectioned biomaterial pieces is an appropriate method for individualized adjustment in shell techniques. The advantages over direct printing of the biomaterial shell and products on the market, such as the Xyoss shell (Reoss Inc., Germany), include cost-efficiency and avoidance of regulatory issues. Copyright © 2016 Elsevier Inc. All rights reserved.

Deformation of biological cells in the acoustic field of an oscillating bubble.

PubMed

Zinin, Pavel V; Allen, John S

2009-02-01

In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin, Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell's oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell's shell deforms due to a change in the shell area this oscillation depends on the surface area modulus K{A} , (c) the relative change in the area has a maximum at frequency f{K} approximately 1/2pi square root[K{A}(rhoa;{3})] , where a is the cell's radius and rho is its density. It was predicted that deformation of the cell wall at the frequency f{K} is high enough to rupture small bacteria such as E . coli in which the quality factor of natural vibrations is less than 1 (Q<1). For bacteria with high value quality factors (Q>1) , the area deformation has a strong peak near a resonance frequency f{K} however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers).

Deformation of biological cells in the acoustic field of an oscillating bubble

PubMed Central

Zinin, Pavel V.; Allen, John S.

2009-01-01

In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin et al., Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell’s oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell’s shell deforms due to a change in the shell area this oscillation depends on the surface area modulus KA, (c) the relative change in the area has a maximum at frequency fK∼12πKA/(ρa3), where a is the cell’s radius and ρ is its density. It was predicted that deformation of the cell wall at the frequency fK is high enough to rupture small bacteria such as E. coli in which the quality factor of natural vibrations is less than 1 (Q < 1). For bacteria with high value quality factors (Q > 1), the area deformation has a strong peak near a resonance frequency fK; however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers). PMID:19391781

Deformation of biological cells in the acoustic field of an oscillating bubble

NASA Astrophysics Data System (ADS)

Zinin, Pavel V.; Allen, John S., III

2009-02-01

In this work we develop a theoretical framework of the interaction of microbubbles with bacteria in the ultrasound field using a shell model of the bacteria, following an approach developed previously [P. V. Zinin , Phys. Rev. E 72, 61907 (2005)]. Within the shell model, the motion of the cell in an ultrasonic field is determined by the motion of three components: the internal viscous fluid, a thin elastic shell, and the surrounding viscous fluid. Several conclusions can be drawn from the modeling of sound interaction with a biological cell: (a) the characteristics of a cell’s oscillations in an ultrasonic field are determined both by the elastic properties of the shell the viscosities of all components of the system, (b) for dipole quadrupole oscillations the cell’s shell deforms due to a change in the shell area this oscillation depends on the surface area modulus KA , (c) the relative change in the area has a maximum at frequency fK˜(1)/(2π)KA/(ρa3) , where a is the cell’s radius and ρ is its density. It was predicted that deformation of the cell wall at the frequency fK is high enough to rupture small bacteria such as E . coli in which the quality factor of natural vibrations is less than 1 (Q<1) . For bacteria with high value quality factors (Q>1) , the area deformation has a strong peak near a resonance frequency fK ; however, the value of the deformation near the resonance frequency is not high enough to produce sufficient mechanical effect. The theoretical framework developed in this work can be extended for describing the deformation of a biological cell under any arbitrary, external periodic force including radiation forces unduced by acoustical (acoustical levitation) or optical waves (optical tweezers).

Perturbative dynamics of thin-shell wormholes beyond general relativity: An alternative approach

NASA Astrophysics Data System (ADS)

Rubín de Celis, Emilio; Tomasini, Cecilia; Simeone, Claudio

Recent studies relating the approximations for the equations-of-state for thin shells and their consequent perturbative evolution are extended to thin-shell wormholes in theories beyond general relativity and more than four spacetime dimensions. The assumption of equations-of-state of the same form for static and slowly evolving shells appears as a strong restriction excluding the possibility of oscillatory evolutions. Then the new results considerably differ from previous ones obtained within the usual linearized approach.

Modeling complicated rheological behaviors in encapsulating shells of lipid-coated microbubbles accounting for nonlinear changes of both shell viscosity and elasticity

NASA Astrophysics Data System (ADS)

Li, Qian; Matula, Thomas J.; Tu, Juan; Guo, Xiasheng; Zhang, Dong

2013-02-01

It has been accepted that the dynamic responses of ultrasound contrast agent (UCA) microbubbles will be significantly affected by the encapsulating shell properties (e.g., shell elasticity and viscosity). In this work, a new model is proposed to describe the complicated rheological behaviors in an encapsulating shell of UCA microbubbles by applying the nonlinear ‘Cross law’ to the shell viscous term in the Marmottant model. The proposed new model was verified by fitting the dynamic responses of UCAs measured with either a high-speed optical imaging system or a light scattering system. The comparison results between the measured radius-time curves and the numerical simulations demonstrate that the ‘compression-only’ behavior of UCAs can be successfully simulated with the new model. Then, the shell elastic and viscous coefficients of SonoVue microbubbles were evaluated based on the new model simulations, and compared to the results obtained from some existing UCA models. The results confirm the capability of the current model for reducing the dependence of bubble shell parameters on the initial bubble radius, which indicates that the current model might be more comprehensive to describe the complex rheological nature (e.g., ‘shear-thinning’ and ‘strain-softening’) in encapsulating shells of UCA microbubbles by taking into account the nonlinear changes of both shell elasticity and shell viscosity.

Modeling complicated rheological behaviors in encapsulating shells of lipid-coated microbubbles accounting for nonlinear changes of both shell viscosity and elasticity.

PubMed

Li, Qian; Matula, Thomas J; Tu, Juan; Guo, Xiasheng; Zhang, Dong

2013-02-21

It has been accepted that the dynamic responses of ultrasound contrast agent (UCA) microbubbles will be significantly affected by the encapsulating shell properties (e.g., shell elasticity and viscosity). In this work, a new model is proposed to describe the complicated rheological behaviors in an encapsulating shell of UCA microbubbles by applying the nonlinear 'Cross law' to the shell viscous term in the Marmottant model. The proposed new model was verified by fitting the dynamic responses of UCAs measured with either a high-speed optical imaging system or a light scattering system. The comparison results between the measured radius-time curves and the numerical simulations demonstrate that the 'compression-only' behavior of UCAs can be successfully simulated with the new model. Then, the shell elastic and viscous coefficients of SonoVue microbubbles were evaluated based on the new model simulations, and compared to the results obtained from some existing UCA models. The results confirm the capability of the current model for reducing the dependence of bubble shell parameters on the initial bubble radius, which indicates that the current model might be more comprehensive to describe the complex rheological nature (e.g., 'shear-thinning' and 'strain-softening') in encapsulating shells of UCA microbubbles by taking into account the nonlinear changes of both shell elasticity and shell viscosity.

A Qualitative Approach to the Evaluation of Expert Systems Shells.

ERIC Educational Resources Information Center

Slawson, Dean A.; And Others

This study explores an approach to the evaluation of expert system shells using case studies. The methodology and some of the results of an evaluation of the prototype development of an expert system using the shell "M1" are detailed, including a description of the participants and the project, the data collection process and materials,…

Enhancing absorption in coated semiconductor nanowire/nanorod core-shell arrays using active host matrices

NASA Astrophysics Data System (ADS)

Jule, Leta; Dejene, Francis; Roro, Kittessa

2016-12-01

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core-shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core-shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core-shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

SoftWAXS: a computational tool for modeling wide-angle X-ray solution scattering from biomolecules.

PubMed

Bardhan, Jaydeep; Park, Sanghyun; Makowski, Lee

2009-10-01

This paper describes a computational approach to estimating wide-angle X-ray solution scattering (WAXS) from proteins, which has been implemented in a computer program called SoftWAXS. The accuracy and efficiency of SoftWAXS are analyzed for analytically solvable model problems as well as for proteins. Key features of the approach include a numerical procedure for performing the required spherical averaging and explicit representation of the solute-solvent boundary and the surface of the hydration layer. These features allow the Fourier transform of the excluded volume and hydration layer to be computed directly and with high accuracy. This approach will allow future investigation of different treatments of the electron density in the hydration shell. Numerical results illustrate the differences between this approach to modeling the excluded volume and a widely used model that treats the excluded-volume function as a sum of Gaussians representing the individual atomic excluded volumes. Comparison of the results obtained here with those from explicit-solvent molecular dynamics clarifies shortcomings inherent to the representation of solvent as a time-averaged electron-density profile. In addition, an assessment is made of how the calculated scattering patterns depend on input parameters such as the solute-atom radii, the width of the hydration shell and the hydration-layer contrast. These results suggest that obtaining predictive calculations of high-resolution WAXS patterns may require sophisticated treatments of solvent.

META-GLARE: a shell for CIG systems.

PubMed

Bottrighi, Alessio; Rubrichi, Stefania; Terenziani, Paolo

2015-01-01

In the last twenty years, many different approaches to deal with Computer-Interpretable clinical Guidelines (CIGs) have been developed, each one proposing its own representation formalism (mostly based on the Task-Network Model) execution engine. We propose META-GLARE a shell for easily defining new CIG systems. Using META-GLARE, CIG system designers can easily define their own systems (basically by defining their representation language), with a minimal programming effort. META-GLARE is thus a flexible and powerful vehicle for research about CIGs, since it supports easy and fast prototyping of new CIG systems.

Characterization and Analysis of Triaxially Braided Polymer Composites under Static and Impact Loads

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.; Roberts, Gary D.; Blinzler, Brina J.; Kohlman, Lee W.; Binienda, Wieslaw K.

2012-01-01

In order to design impact resistant aerospace components made of triaxially-braided polymer matrix composite materials, a need exists to have reliable impact simulation methods and a detailed understanding of the material behavior. Traditional test methods and specimen designs have yielded unrealistic material property data due to material mechanisms such as edge damage. To overcome these deficiencies, various alternative testing geometries such as notched flat coupons have been examined to alleviate difficulties observed with standard test methods. The results from the coupon level tests have been used to characterize and validate a macro level finite element-based model which can be used to simulate the mechanical and impact response of the braided composites. In the analytical model, the triaxial braid unit cell is approximated by using four parallel laminated composites, each with a different fiber layup, which roughly simulates the braid architecture. In the analysis, each of these laminated composites is modeled as a shell element. Currently, each shell element is considered to be a smeared homogeneous material. Simplified micromechanics techniques and lamination theory are used to determine the equivalent stiffness properties of each shell element, and results from the coupon level tests on the braided composite are used to back out the strength properties of each shell element. Recent improvements to the model include the incorporation of strain rate effects into the model. Simulations of ballistic impact tests have been carried out to investigate and verify the analysis approach.

Multibody dynamic analysis using a rotation-free shell element with corotational frame

NASA Astrophysics Data System (ADS)

Shi, Jiabei; Liu, Zhuyong; Hong, Jiazhen

2018-03-01

Rotation-free shell formulation is a simple and effective method to model a shell with large deformation. Moreover, it can be compatible with the existing theories of finite element method. However, a rotation-free shell is seldom employed in multibody systems. Using a derivative of rigid body motion, an efficient nonlinear shell model is proposed based on the rotation-free shell element and corotational frame. The bending and membrane strains of the shell have been simplified by isolating deformational displacements from the detailed description of rigid body motion. The consistent stiffness matrix can be obtained easily in this form of shell model. To model the multibody system consisting of the presented shells, joint kinematic constraints including translational and rotational constraints are deduced in the context of geometric nonlinear rotation-free element. A simple node-to-surface contact discretization and penalty method are adopted for contacts between shells. A series of analyses for multibody system dynamics are presented to validate the proposed formulation. Furthermore, the deployment of a large scaled solar array is presented to verify the comprehensive performance of the nonlinear shell model.

Demonstration of high coupling efficiency to Al capsule in rugby hohlraum on NIF

NASA Astrophysics Data System (ADS)

Ping, Y.; Smalyuk, V.; Amendt, P.; Bennett, D.; Chen, H.; Dewald, E.; Goyon, C.; Graziani, F.; Johnson, S.; Khan, S.; Landen, O.; Nikroo, A.; Pino, J.; Ralph, J.; Seugling, R.; Strozzi, D.; Tipton, R.; Tommasini, R.; Wang, M.; Loomis, E.; Merritt, E.; Montgomery, D.

2017-10-01

A new design of the double-shell approach predicts a high coupling efficiency from the hohlraum to the capsule, with 700 kJ in the capsule instead of 200kJ in the conventional low-Z single-shell scheme, improving prospects of double-shell performance. A recent experiment on NIF has evaluated a first step toward this goal of energy coupling using 0.7x subscale Al capsule, Au rugby hohlraum and 1MJ drive. A shell velocity of 150 μm/ns was measured, DANTE peak temperature of 255 eV was measured, and shell kinetic energy of 36 kJ was inferred using a rocket model, all close to predictions and consistent with 330kJ of total energy coupled to the capsule. Data analysis and more results from subsequent experiments will be presented. In the next step, an additional 2x increase of total coupled energy up to 700 kJ is projected for full-scale 2-MJ drive in U Rugby hohlraum. This work was performed under DOE contract DE-AC52-07NA27344.

Users Manual AERCOARE Version 1.0

EPA Science Inventory

The work completed under this work assignment is a continuation of an evaluation report prepared by ENVIRON entitled “Evaluation of the COARE–AERMOD Alternative Modeling Approach for Simulation of Shell Exploratory Drilling Sources in the Beaufort and Chukchi Seas” dated Decembe...

Technical Note: Effect of explicit M and N-shell atomic transitions on a low-energy x-ray source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, Peter G. F., E-mail: peter.watson@mail.mcgill.ca; Seuntjens, Jan

Purpose: In EGSnrc, atomic transitions to and from the M and N-shells are treated in an average way by default. This approach is justified in which the energy difference between explicit and average M and N-shell binding energies is less than 1 keV, and for most applications can be considered negligible. However, for simulations of low energy x-ray sources on thin, high-Z targets, characteristic x-rays can make up a significant portion of the source spectra. As of release V4-2.4.0, EGSnrc has included an option to enable a more complete algorithm of all atomic transitions available in the EADL compilation. Inmore » this paper, the effect of M and N-shell averaging on the calculation of half-value layer (HVL) and relative depth dose (RDD) curve of a 50 kVp intraoperative x-ray tube with a thin gold target was investigated. Methods: A 50 kVp miniature x-ray source with a gold target (The INTRABEAM System, Carl Zeiss, Germany) was modeled with the EGSnrc user code cavity, both with and without M and N-shell averaging. From photon fluence spectra simulations, the source HVLs were determined analytically. The same source model was then used with egs-chamber to calculate RDD curves in water. Results: A 4% increase of HVL was reported when accounting for explicit M and N-shell transitions, and up to a 9% decrease in local relative dose for normalization at 3 mm depth in water. Conclusions: The EGSnrc default of using averaged M and N-shell binding energies has an observable effect on the HVL and RDD of a low energy x-ray source with high-Z target. For accurate modeling of this class of devices, explicit atomic transitions should be included.« less

Radiation from mixed multi-planar wire arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Safronova, A. S.; Kantsyrev, V. L.; Esaulov, A. A.

2014-03-15

The study of radiation from different wire materials in wire array Z-pinch plasma is a very challenging topic because it is almost impossible to separate different plasmas at the stagnation. A new approach is suggested based on planar wire array (PWA) loads to assess this problem. Multi-planar wire arrays are implemented that consist of few planes, each with the same number of wires and masses but from different wire materials, arranged in parallel rows. In particular, the experimental results obtained with triple PWAs (TPWAs) on the UNR Zebra generator are analyzed with Wire Ablation Dynamics Model, non-local thermodynamic equilibrium kineticmore » model, and 2D radiation magneto-hydrodynamic to illustrate this new approach. In TPWAs, two wire planes were from mid-atomic-number wire material and another plane was from alloyed Al, placed either in the middle or at the edge of the TPWA. Spatial and temporal properties of K-shell Al and L-shell Cu radiations were analyzed and compared from these two configurations of TPWAs. Advantages of the new approach are demonstrated and future work is discussed.« less

On demand manufacturing of patient-specific liquid capsules via co-ordinated 3D printing and liquid dispensing.

PubMed

Okwuosa, Tochukwu C; Soares, Cindy; Gollwitzer, Verena; Habashy, Rober; Timmins, Peter; Alhnan, Mohamed A

2018-06-15

A method for the production of liquid capsules with the potential of modifying drug dose and release is presented. For the first time, the co-ordinated use of fused deposition modelling (FDM), 3D printing and liquid dispensing to fabricate individualised dosage form on demand in a fully automated fashion has been demonstrated. Polymethacrylate shells (Eudragit EPO and RL) for immediate and extended release were fabricated using FDM 3D printing and simultaneously filled using a computer-controlled liquid dispenser loaded with model drug solution (theophylline) or suspension (dipyridamole). The impact of printing modes: simultaneous shell printing and filling (single-phase) or sequential 3D printing of shell bottom, filling and shell cap (multi-phase), nozzle size, syringe volume, and shell structure has been reported. The use of shell thickness of 1.6 mm, and concentric architecture allowed successful containment of liquid core whilst maintaining the release properties of the 3D printed liquid capsule. The linear relationship between the theoretical and the actual volumes from the dispenser reflected its potential for accurate dosing (R 2  = 0.9985). Modifying the shell thickness of Eudragit RL capsule allowed a controlled extended drug release without the need for formulation change. Owing to its low cost and versatility, this approach can be adapted to wide spectrum of liquid formulations such as small and large molecule solutions and obviate the need for compatibility with the high temperature of FDM 3D printing process. In a clinical setting, health care staff will be able to instantly manufacture in small volumes liquid capsules with individualised dose contents and release pattern in response to specific patient's needs. Copyright © 2018 Elsevier B.V. All rights reserved.

Long term stability of nanowire nanoelectronics in physiological environments.

PubMed

Zhou, Wei; Dai, Xiaochuan; Fu, Tian-Ming; Xie, Chong; Liu, Jia; Lieber, Charles M

2014-03-12

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease.

Long Term Stability of Nanowire Nanoelectronics in Physiological Environments

PubMed Central

2015-01-01

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease. PMID:24479700

On 3D inelastic analysis methods for hot section components

NASA Technical Reports Server (NTRS)

Mcknight, R. L.; Chen, P. C.; Dame, L. T.; Holt, R. V.; Huang, H.; Hartle, M.; Gellin, S.; Allen, D. H.; Haisler, W. E.

1986-01-01

Accomplishments are described for the 2-year program, to develop advanced 3-D inelastic structural stress analysis methods and solution strategies for more accurate and cost effective analysis of combustors, turbine blades and vanes. The approach was to develop a matrix of formulation elements and constitutive models. Three constitutive models were developed in conjunction with optimized iterating techniques, accelerators, and convergence criteria within a framework of dynamic time incrementing. Three formulations models were developed; an eight-noded mid-surface shell element, a nine-noded mid-surface shell element and a twenty-noded isoparametric solid element. A separate computer program was developed for each combination of constitutive model-formulation model. Each program provides a functional stand alone capability for performing cyclic nonlinear structural analysis. In addition, the analysis capabilities incorporated into each program can be abstracted in subroutine form for incorporation into other codes or to form new combinations.

The 3D inelastic analysis methods for hot section components

NASA Technical Reports Server (NTRS)

Mcknight, R. L.; Maffeo, R. J.; Tipton, M. T.; Weber, G.

1992-01-01

A two-year program to develop advanced 3D inelastic structural stress analysis methods and solution strategies for more accurate and cost effective analysis of combustors, turbine blades, and vanes is described. The approach was to develop a matrix of formulation elements and constitutive models. Three constitutive models were developed in conjunction with optimized iterating techniques, accelerators, and convergence criteria within a framework of dynamic time incrementing. Three formulation models were developed: an eight-noded midsurface shell element; a nine-noded midsurface shell element; and a twenty-noded isoparametric solid element. A separate computer program has been developed for each combination of constitutive model-formulation model. Each program provides a functional stand alone capability for performing cyclic nonlinear structural analysis. In addition, the analysis capabilities incorporated into each program can be abstracted in subroutine form for incorporation into other codes or to form new combinations.

Modeling Thermal Transport and Surface Deformation on Europa using Realistic Rheologies

NASA Astrophysics Data System (ADS)

Linneman, D.; Lavier, L.; Becker, T. W.; Soderlund, K. M.

2017-12-01

Most existing studies of Europa's icy shell model the ice as a Maxwell visco-elastic solid or viscous fluid. However, these approaches do not allow for modeling of localized deformation of the brittle part of the ice shell, which is important for understanding the satellite's evolution and unique geology. Here, we model the shell as a visco-elasto-plastic material, with a brittle Mohr-Coulomb elasto-plastic layer on top of a convective Maxwell viscoelastic layer, to investigate how thermal transport processes relate to the observed deformation and topography on Europa's surface. We use Fast Lagrangian Analysis of Continua (FLAC) code, which employs an explicit time-stepping algorithm to simulate deformation processes in Europa's icy shell. Heat transfer drives surface deformation within the icy shell through convection and tidal dissipation due to its elliptical orbit around Jupiter. We first analyze the visco-elastic behavior of a convecting ice layer and the parameters that govern this behavior. The regime of deformation depends on the magnitude of the stress (diffusion creep at low stresses, grain-size-sensitive creep at intermediate stresses, dislocation creep at high stresses), so we calculate effective viscosity each time step using the constitutive stress-strain equation and a combined flow law that accounts for all types of deformation. Tidal dissipation rate is calculated as a function of the temperature-dependent Maxwell relaxation time and the square of the second invariant of the strain rate averaged over each orbital period. After we initiate convection in the viscoelastic layer by instituting an initial temperature perturbation, we then add an elastoplastic layer on top of the convecting layer and analyze how the brittle ice reacts to stresses from below and any resulting topography. We also take into account shear heating along fractures in the brittle layer. We vary factors such as total shell thickness and minimum viscosity, as these parameters are not well constrained, and determine how this affects the thickness and deformation of the brittle layer.

Dynamic analysis of rotor flex-structure based on nonlinear anisotropic shell models

NASA Astrophysics Data System (ADS)

Bauchau, Olivier A.; Chiang, Wuying

1991-05-01

In this paper an anisotropic shallow shell model is developed that accommodates transverse shearing deformations and arbitrarily large displacements and rotations, but strains are assumed to remain small. Two kinematic models are developed, the first using two DOF to locate the direction of the normal to the shell's midplane, the second using three. The latter model allows for an automatic compatibility of the shell model with beam models. The shell model is validated by comparing its predictions with several benchmark problems. In actual helicopter rotor blade problems, the shell model of the flex structure is shown to give very different results shown compared to beam models. The lead-lag and torsion modes in particular are strongly affected, whereas flapping modes seem to be less affected.

The NASA Monographs on Shell Stability Design Recommendations: A Review and Suggested Improvements

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Starnes, James H., Jr.

1998-01-01

A summary of existing NASA design criteria monographs for the design of buckling-resistant thin-shell structures is presented. Subsequent improvements in the analysis for nonlinear shell response are reviewed, and current issues in shell stability analysis are discussed. Examples of nonlinear shell responses that are not included in the existing shell design monographs are presented, and an approach for including reliability based analysis procedures in the shell design process is discussed. Suggestions for conducting future shell experiments are presented, and proposed improvements to the NASA shell design criteria monographs are discussed.

The NASA Monographs on Shell Stability Design Recommendations: A Review and Suggested Improvements

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Starnes, James H., Jr.

1998-01-01

A summary of the existing NASA design criteria monographs for the design of buckling-resistant thin-shell structures is presented. Subsequent improvements in the analysis for nonlinear shell response are reviewed, and current issues in shell stability analysis are discussed. Examples of nonlinear shell responses that are not included in the existing shell design monographs are presented, and an approach for including reliability-based analysis procedures in the shell design process is discussed. Suggestions for conducting future shell experiments are presented, and proposed improvements to the NASA shell design criteria monographs are discussed.

Alloy and heterostructure architectures as promising tools for controlling electronic properties of semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Vaxenburg, Roman; Lifshitz, Efrat

2012-02-01

Tunability of energy levels and wavefunctions of carriers in colloidal quantum dots (CQDs) has a marked effect on numerous physical aspects, such as Coulomb interactions and charge separation, which in turn has a direct impact on the functioning of CQD-based opto-electronic devices. The electronic properties of CQDs are conventionally controlled by variation of their size. Here we demonstrate a theoretical approach to engineer the electronic properties of IV-VI CQDs by introducing an alloy composition in core and core/shell heterostructures, having the general chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), while maintaining a constant size. The theoretical model considered an effective mass anisotropy and smooth potential step at the core/shell interface. The model revealed the influence induced by variation of chemical composition and core-to-shell division on the band-gap energy, remote states’ density, internal charge separation, electron-hole Coulomb interaction, and optical transition oscillator strength.

Continuum and three-nucleon force effects on Be 9 energy levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langhammer, Joachim; Navrátil, Petr; Quaglioni, Sofia

2015-02-05

In this paper, we extend the recently proposed ab initio no-core shell model with continuum to include three-nucleon (3N) interactions beyond the few-body domain. The extended approach allows for the assessment of effects of continuum degrees of freedom as well as of the 3N force in ab initio calculations of structure and reaction observables of p- and lower-sd-shell nuclei. As a first application we concentrate on energy levels of the 9Be system for which all excited states lie above the n- 8Be threshold. For all energy levels, the inclusion of the continuum significantly improves the agreement with experiment, which wasmore » an issue in standard no-core shell model calculations. Furthermore, we find the proper treatment of the continuum indispensable for reliable statements about the quality of the adopted 3N interaction from chiral effective field theory. Finally, in particular, we find the 1/2 + resonance energy, which is of astrophysical interest, in good agreement with experiment.« less

Two-dimensional membrane as elastic shell with proof on the folds revealed by three-dimensional atomic mapping

NASA Astrophysics Data System (ADS)

Zhao, Jiong; Deng, Qingming; Ly, Thuc Hue; Han, Gang Hee; Sandeep, Gorantla; Rümmeli, Mark H.

2015-11-01

The great application potential for two-dimensional (2D) membranes (MoS2, WSe2, graphene and so on) aroused much effort to understand their fundamental mechanical properties. The out-of-plane bending rigidity is the key factor that controls the membrane morphology under external fields. Herein we provide an easy method to reconstruct the 3D structures of the folded edges of these 2D membranes on the atomic scale, using high-resolution (S)TEM images. After quantitative comparison with continuum mechanics shell model, it is verified that the bending behaviour of the studied 2D materials can be well explained by the linear elastic shell model. And the bending rigidities can thus be derived by fitting with our experimental results. Recall almost only theoretical approaches can access the bending properties of these 2D membranes before, now a new experimental method to measure the bending rigidity of such flexible and atomic thick 2D membranes is proposed.

Method of forming cavitated objects of controlled dimension

DOEpatents

Anderson, Paul R.; Miller, Wayne J.

1982-01-01

A method of controllably varying the dimensions of cavitated objects such as hollow spherical shells wherein a precursor shell is heated to a temperature above the shell softening temperature in an ambient atmosphere wherein the ratio of gases which are permeable through the shell wall at that temperature to gases which are impermeable through the shell wall is substantially greater than the corresponding ratio for gases contained within the precursor shell. As the shell expands, the partial pressures of permeable gases internally and externally of the shell approach and achieve equilibrium, so that the final shell size depends solely upon the difference in impermeable gas partial pressures and shell surface tension.

Coordinated scheduling for dynamic real-time systems

NASA Technical Reports Server (NTRS)

Natarajan, Swaminathan; Zhao, Wei

1994-01-01

In this project, we addressed issues in coordinated scheduling for dynamic real-time systems. In particular, we concentrated on design and implementation of a new distributed real-time system called R-Shell. The design objective of R-Shell is to provide computing support for space programs that have large, complex, fault-tolerant distributed real-time applications. In R-shell, the approach is based on the concept of scheduling agents, which reside in the application run-time environment, and are customized to provide just those resource management functions which are needed by the specific application. With this approach, we avoid the need for a sophisticated OS which provides a variety of generalized functionality, while still not burdening application programmers with heavy responsibility for resource management. In this report, we discuss the R-Shell approach, summarize the achievement of the project, and describe a preliminary prototype of R-Shell system.

Design and Fabrication of a Ring-Stiffened Graphite-Epoxy Corrugated Cylindrical Shell

NASA Technical Reports Server (NTRS)

Johnson, R., Jr.

1978-01-01

Design and fabrication of supplement test panels that represent key portions of the cylinder are described, as are supporting tests of coupons, sample joints, and stiffening ring elements. The cylindrical shell is a ring-stiffened, open corrugation design that uses T300/5208 graphite-epoxy tape as the basic material for the shell wall and stiffening rings. The test cylinder is designed to withstand bending loads producing the relatively low maximum load intensity in the shell wall of 1,576 N/cm. The resulting shell wall weight, including stiffening rings and fasteners, is 0.0156 kg/m. The shell weight achieved in the graphite-epoxy cylinder represents a weight saving of approximately 23 percent, compared to a comparable aluminum shell. A unique fabrication approach was used in which the cylinder wall was built in three flat segments, which were then wrapped to the cylindrical shape. Such an approach, made possible by the flexibility of the thin corrugated wall in a radial direction, proved to be a simple approach to building the test cylinder. Based on tooling and fabrication methods in this program, the projected costs of a production run of 100 units are reported.

THREE-DIMENSIONAL MODELING OF THE DYNAMICS OF THERAPEUTIC ULTRASOUND CONTRAST AGENTS

PubMed Central

Hsiao, Chao-Tsung; Lu, Xiaozhen; Chahine, Georges

2010-01-01

A 3-D thick-shell contrast agent dynamics model was developed by coupling a finite volume Navier-Stokes solver and a potential boundary element method flow solver to simulate the dynamics of thick-shelled contrast agents subjected to pressure waves. The 3-D model was validated using a spherical thick-shell model validated by experimental observations. We then used this model to study shell break-up during nonspherical deformations resulting from multiple contrast agent interaction or the presence of a nearby solid wall. Our simulations indicate that the thick viscous shell resists the contrast agent from forming a re-entrant jet, as normally observed for an air bubble oscillating near a solid wall. Instead, the shell thickness varies significantly from location to location during the dynamics, and this could lead to shell break-up caused by local shell thinning and stretching. PMID:20950929

HIFiRE-5 Boundary Layer Transition and HIFiRE-1 Shock Boundary Layer Interaction

DTIC Science & Technology

2015-10-01

pressure calcium-fluoride window and a new wind tunnel model consisting of a steel forebody and a PEEK plastic shell. This model contained a large...wind tunnel data. These models were then applied to the supersonic 2 Approved for public release; distribution unlimited. ascent phase of the...the tuned RANS models predicted upstream influence well. These results lend confidence to the approach of calibrating RANS models with wind tunnel

Two aspects of black hole entropy in Lanczos-Lovelock models of gravity

NASA Astrophysics Data System (ADS)

Kolekar, Sanved; Kothawala, Dawood; Padmanabhan, T.

2012-03-01

We consider two specific approaches to evaluate the black hole entropy which are known to produce correct results in the case of Einstein’s theory and generalize them to Lanczos-Lovelock models. In the first approach (which could be called extrinsic), we use a procedure motivated by earlier work by Pretorius, Vollick, and Israel, and by Oppenheim, and evaluate the entropy of a configuration of densely packed gravitating shells on the verge of forming a black hole in Lanczos-Lovelock theories of gravity. We find that this matter entropy is not equal to (it is less than) Wald entropy, except in the case of Einstein theory, where they are equal. The matter entropy is proportional to the Wald entropy if we consider a specific mth-order Lanczos-Lovelock model, with the proportionality constant depending on the spacetime dimensions D and the order m of the Lanczos-Lovelock theory as (D-2m)/(D-2). Since the proportionality constant depends on m, the proportionality between matter entropy and Wald entropy breaks down when we consider a sum of Lanczos-Lovelock actions involving different m. In the second approach (which could be called intrinsic), we generalize a procedure, previously introduced by Padmanabhan in the context of general relativity, to study off-shell entropy of a class of metrics with horizon using a path integral method. We consider the Euclidean action of Lanczos-Lovelock models for a class of metrics off shell and interpret it as a partition function. We show that in the case of spherically symmetric metrics, one can interpret the Euclidean action as the free energy and read off both the entropy and energy of a black hole spacetime. Surprisingly enough, this leads to exactly the Wald entropy and the energy of the spacetime in Lanczos-Lovelock models obtained by other methods. We comment on possible implications of the result.

Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core-Shell Architecture.

PubMed

Felts, Ashley C; Slimani, Ahmed; Cain, John M; Andrus, Matthew J; Ahir, Akhil R; Abboud, Khalil A; Meisel, Mark W; Boukheddaden, Kamel; Talham, Daniel R

2018-05-02

The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb a Co b [Fe(CN) 6 ] c · mH 2 O (RbCoFe-PBA) as core with the isostructural K j Ni k [Cr(CN) 6 ] l · nH 2 O (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

Al{sub 2}O{sub 3} - TiO{sub 2}-A simple sol-gel strategy to the synthesis of low temperature sintered alumina-aluminium titanate composites through a core-shell approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayasankar, M.; Ananthakumar, S.; Mukundan, P.

A simple sol-gel based core-shell approach for the synthesis of alumina-aluminium titanate composite is reported. Alumina is the core and titania is the shell. The coating of titania has been performed in aqueous medium on alumina particle by means of heterocoagulation of titanyl chloride. Further heat treatment results in low temperature formation of aluminium titanate as well as low temperature sintering of alumina-aluminium titanate composites. The lowering of the reaction temperature can be attributed to the maximisation of the contact surface between the reactants due to the core-shell approach involving nanoparticles. The mechanism of formation of aluminium titanate and themore » observations on densification features in the present process are compared with that of mixture of oxides under identical conditions. The sintered alumina-aluminium titanate composite has an average grain size of 2 {mu}m. - Graphical abstract: The article presents a simple sol-gel process through core-shell approach to the synthesis of low temperature sintered alumina-aluminium titanate. The lowering of the reaction temperature can be attributed to the maximisation of the contact surface between the reactant due to the core-shell approach. This material showed the better microstructure control compared to the standard solid-state mixing route.« less

Singlet-paired coupled cluster theory for open shells

NASA Astrophysics Data System (ADS)

Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

2016-06-01

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

Accurate structure, thermodynamics and spectroscopy of medium-sized radicals by hybrid Coupled Cluster/Density Functional Theory approaches: the case of phenyl radical

PubMed Central

Barone, Vincenzo; Biczysko, Malgorzata; Bloino, Julien; Egidi, Franco; Puzzarini, Cristina

2015-01-01

The CCSD(T) model coupled with extrapolation to the complete basis-set limit and additive approaches represents the “golden standard” for the structural and spectroscopic characterization of building blocks of biomolecules and nanosystems. However, when open-shell systems are considered, additional problems related to both specific computational difficulties and the need of obtaining spin-dependent properties appear. In this contribution, we present a comprehensive study of the molecular structure and spectroscopic (IR, Raman, EPR) properties of the phenyl radical with the aim of validating an accurate computational protocol able to deal with conjugated open-shell species. We succeeded in obtaining reliable and accurate results, thus confirming and, partly, extending the available experimental data. The main issue to be pointed out is the need of going beyond the CCSD(T) level by including a full treatment of triple excitations in order to fulfil the accuracy requirements. On the other hand, the reliability of density functional theory in properly treating open-shell systems has been further confirmed. PMID:23802956

Experimental aspects of the adiabatic approach in estimating the effect of electron screening on alpha decay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karpeshin, F. F., E-mail: fkarpeshin@gmail.com; Trzhaskovskaya, M. B.

2015-12-15

Special features of the effect of the electron shell on alpha decay that have important experimental implications are studied within the adiabatic approach. The magnitude of the effect is about several tenths of a percent or smaller, depending on the transition energy and on the atomic number. A dominant role of inner shells is shown: more than 80% of the effect is saturated by 1s electrons. This circumstance plays a crucial role for experiments, making it possible to measure this small effect by a difference method in the same storage rings via a comparison of, for example, decay probabilities inmore » bare nuclei and heliumlike ions. The reasons behind the relative success and the applicability limits of the frozen-shell model, which has been used to calculate the effect in question for more than half a century, are analyzed. An interesting experiment aimed at studying charged alpha-particle states is proposed. This experiment will furnish unique information for testing our ideas of the interplay of nonadiabatic and adiabatic processes.« less

Predictor-based multivariable closed-loop system identification of the EXTRAP T2R reversed field pinch external plasma response

NASA Astrophysics Data System (ADS)

Olofsson, K. Erik J.; Brunsell, Per R.; Rojas, Cristian R.; Drake, James R.; Hjalmarsson, Håkan

2011-08-01

The usage of computationally feasible overparametrized and nonregularized system identification signal processing methods is assessed for automated determination of the full reversed-field pinch external plasma response spectrum for the experiment EXTRAP T2R. No assumptions on the geometry of eigenmodes are imposed. The attempted approach consists of high-order autoregressive exogenous estimation followed by Markov block coefficient construction and Hankel matrix singular value decomposition. It is seen that the obtained 'black-box' state-space models indeed can be compared with the commonplace ideal magnetohydrodynamics (MHD) resistive thin-shell model in cylindrical geometry. It is possible to directly map the most unstable autodetected empirical system pole to the corresponding theoretical resistive shell MHD eigenmode.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, R.D.; Bakshi, P.M.; Sindoni, J.M.

Using an exact formulation of impulse approach (IA) to atom-diatom collisions, we assess its internal consistency. By comparing the cross sections in the forward and reverse directions for the vibrational-rotational inelastic processes, using the half-on-the-shell (post and prior) models of the two-body {ital t} matrix, we show that in both cases the IA leads to a violation of the semidetailed balance (SDB) condition for small scattering angles. An off-shell model for the two-body {ital t} matrix, which preserves SDB, is shown to have other serious shortcomings. The cross sections are studied quantitatively as a function of the relative translational energymore » and the mass of the incident particle, and criteria discussed for the applicability of IA.« less

Simultaneous thermoelectric and optoelectronic characterization of individual nanowires

DOE PAGES

Leonard, Francois; Wang, George T.; Swartzentruber, Brian S.; ...

2015-11-03

Semiconducting nanowires have been explored for a number of applications in optoelectronics such as photodetectors and solar cells. Currently, there is ample interest in identifying the mechanisms that lead to photoresponse in nanowires in order to improve and optimize performance. However, distinguishing among the different mechanisms, including photovoltaic, photothermoelectric, photoemission, bolometric, and photoconductive, is often difficult using purely optoelectronic measurements. In this work, we present an approach for performing combined and simultaneous thermoelectric and optoelectronic measurements on the same individual nanowire. We apply the approach to GaN/AlGaN core/shell and GaN/AlGaN/GaN core/shell/shell nanowires and demonstrate the photothermoelectric nature of the photocurrentmore » observed at the electrical contacts at zero bias, for above- and below-bandgap illumination. Furthermore, the approach allows for the experimental determination of the temperature rise due to laser illumination, which is often obtained indirectly through modeling. We also show that under bias, both above- and below-bandgap illumination leads to a photoresponse in the channel with signatures of persistent photoconductivity due to photogating. Finally, we reveal the concomitant presence of photothermoelectric and photogating phenomena at the contacts in scanning photocurrent microscopy under bias by using their different temporal response. Furthermore, our approach is applicable to a broad range of nanomaterials to elucidate their fundamental optoelectronic and thermoelectric properties.« less

Discrete-Layer Piezoelectric Plate and Shell Models for Active Tip-Clearance Control

NASA Technical Reports Server (NTRS)

Heyliger, P. R.; Ramirez, G.; Pei, K. C.

1994-01-01

The objectives of this work were to develop computational tools for the analysis of active-sensory composite structures with added or embedded piezoelectric layers. The targeted application for this class of smart composite laminates and the analytical development is the accomplishment of active tip-clearance control in turbomachinery components. Two distinct theories and analytical models were developed and explored under this contract: (1) a discrete-layer plate theory and corresponding computational models, and (2) a three dimensional general discrete-layer element generated in curvilinear coordinates for modeling laminated composite piezoelectric shells. Both models were developed from the complete electromechanical constitutive relations of piezoelectric materials, and incorporate both displacements and potentials as state variables. This report describes the development and results of these models. The discrete-layer theories imply that the displacement field and electrostatic potential through-the-thickness of the laminate are described over an individual layer rather than as a smeared function over the thickness of the entire plate or shell thickness. This is especially crucial for composites with embedded piezoelectric layers, as the actuating and sensing elements within these layers are poorly represented by effective or smeared properties. Linear Lagrange interpolation polynomials were used to describe the through-thickness laminate behavior. Both analytic and finite element approximations were used in the plane or surface of the structure. In this context, theoretical developments are presented for the discrete-layer plate theory, the discrete-layer shell theory, and the formulation of an exact solution for simply-supported piezoelectric plates. Finally, evaluations and results from a number of separate examples are presented for the static and dynamic analysis of the plate geometry. Comparisons between the different approaches are provided when possible, and initial conclusions regarding the accuracy and limitations of these models are given.

A software architecture for automating operations processes

NASA Technical Reports Server (NTRS)

Miller, Kevin J.

1994-01-01

The Operations Engineering Lab (OEL) at JPL has developed a software architecture based on an integrated toolkit approach for simplifying and automating mission operations tasks. The toolkit approach is based on building adaptable, reusable graphical tools that are integrated through a combination of libraries, scripts, and system-level user interface shells. The graphical interface shells are designed to integrate and visually guide a user through the complex steps in an operations process. They provide a user with an integrated system-level picture of an overall process, defining the required inputs and possible output through interactive on-screen graphics. The OEL has developed the software for building these process-oriented graphical user interface (GUI) shells. The OEL Shell development system (OEL Shell) is an extension of JPL's Widget Creation Library (WCL). The OEL Shell system can be used to easily build user interfaces for running complex processes, applications with extensive command-line interfaces, and tool-integration tasks. The interface shells display a logical process flow using arrows and box graphics. They also allow a user to select which output products are desired and which input sources are needed, eliminating the need to know which program and its associated command-line parameters must be executed in each case. The shells have also proved valuable for use as operations training tools because of the OEL Shell hypertext help environment. The OEL toolkit approach is guided by several principles, including the use of ASCII text file interfaces with a multimission format, Perl scripts for mission-specific adaptation code, and programs that include a simple command-line interface for batch mode processing. Projects can adapt the interface shells by simple changes to the resources configuration file. This approach has allowed the development of sophisticated, automated software systems that are easy, cheap, and fast to build. This paper will discuss our toolkit approach and the OEL Shell interface builder in the context of a real operations process example. The paper will discuss the design and implementation of a Ulysses toolkit for generating the mission sequence of events. The Sequence of Events Generation (SEG) system provides an adaptable multimission toolkit for producing a time-ordered listing and timeline display of spacecraft commands, state changes, and required ground activities.

Nonclassical models of the theory of plates and shells

NASA Astrophysics Data System (ADS)

Annin, Boris D.; Volchkov, Yuri M.

2017-11-01

Publications dealing with the study of methods of reducing a three-dimensional problem of the elasticity theory to a two-dimensional problem of the theory of plates and shells are reviewed. Two approaches are considered: the use of kinematic and force hypotheses and expansion of solutions of the three-dimensional elasticity theory in terms of the complete system of functions. Papers where a three-dimensional problem is reduced to a two-dimensional problem with the use of several approximations of each of the unknown functions (stresses and displacements) by segments of the Legendre polynomials are also reviewed.

Analysis of repeated signals during shell fights in the hermit crab Pagurus bernhardus

PubMed Central

Briffa, M.; Elwood, R. W.; Dick, J. T. A.

1998-01-01

Shell exchanges between hermit crabs may occur after a period of shell rapping, when the initiating or attacking crab brings its shell rapidly and repeatedly into contact with the shell of the non-initiator or defender, in a series of bouts. There are two opposing models of hermit crab shell exchange and the function of shell rapping. The negotiation model views shell exchange as a mutualistic activity, in which the initiator supplies information about the quality of its shell via the fundamental frequency of the rapping sound. The aggression model views shell rapping as either detrimental to the defending crab, or as providing it with information about the initiator's ability or motivation to continue, or both. The negotiation model makes no predictions about the temporal pattern of rapping, but under the aggression model it would be expected that crabs that rapped more vigorously would be more likely to effect an exchange. Repeating the signal could be expected under either model. Crabs that achieve an exchange rap more vigorously, rapping is more persistent when a clear gain in shell quality may be achieved, and the vigour is greater when the relative resource-holding potential (or 'fighting ability') is high. These findings support the aggression model rather than the negotiation model. Contrary to the predictions of game theory, crabs that do not effect an exchange appear to signal that they are about to give up. The data suggest that rapping is performed repeatedly because the accumulation of all of the performances acts as a signal of stamina.

Efficacy of the SU(3) scheme for ab initio large-scale calculations beyond the lightest nuclei

DOE PAGES

Dytrych, T.; Maris, P.; Launey, K. D.; ...

2016-06-22

We report on the computational characteristics of ab initio nuclear structure calculations in a symmetry-adapted no-core shell model (SA-NCSM) framework. We examine the computational complexity of the current implementation of the SA-NCSM approach, dubbed LSU3shell, by analyzing ab initio results for 6Li and 12C in large harmonic oscillator model spaces and SU3-selected subspaces. We demonstrate LSU3shell’s strong-scaling properties achieved with highly-parallel methods for computing the many-body matrix elements. Results compare favorably with complete model space calculations and significant memory savings are achieved in physically important applications. In particular, a well-chosen symmetry-adapted basis affords memory savings in calculations of states withmore » a fixed total angular momentum in large model spaces while exactly preserving translational invariance.« less

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.

Reverse-Engineering Laboratory Astrophysics: Oxygen Inner-shell Absorption in the ISM

NASA Technical Reports Server (NTRS)

Garcia, J.; Gatuzz, E.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

2017-01-01

The modeling of X-ray spectra from photoionized astrophysical plasmas has been significantly improved due to recent advancements in the theoretical and numerical frameworks, as well as a consolidated and reliable atomic database of inner-shell transitions for all the relevant ions. We discuss these developments and the current state of X-ray spectral modeling in the context of oxygen cold absorption in the interstellar medium (ISM). Unconventionally, we use high-resolution astrophysical observations to accurately determine line positions, and adjust the theoretical models for a comprehensive interpretation of the observed X-ray spectra. This approach has brought to light standing discrepancies in the neutral oxygen absorption-line positions determined from observations and laboratory measurements. We give an overview of our current efforts to devise a definitive model of oxygen photoabsorption that can help to resolve the existing controversy regarding ISM atomic and molecular fractions.

Reverse-engineering laboratory astrophysics: Oxygen inner-shell absorption in the ISM

NASA Astrophysics Data System (ADS)

García, J.; Gatuzz, E.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

2017-03-01

The modeling of X-ray spectra from photoionized astrophysical plasmas has been significantly improved due to recent advancements in the theoretical and numerical frameworks, as well as a consolidated and reliable atomic database of inner-shell transitions for all the relevant ions. We discuss these developments and the current state of X-ray spectral modeling in the context of oxygen cold absorption in the interstellar medium (ISM). Unconventionally, we use high-resolution astrophysical observations to accurately determine line positions, and adjust the theoretical models for a comprehensive interpretation of the observed X-ray spectra. This approach has brought to light standing discrepancies in the neutral oxygen absorption-line positions determined from observations and laboratory measurements. We give an overview of our current efforts to devise a definitive model of oxygen photoabsorption that can help to resolve the existing controversy regarding ISM atomic and molecular fractions.

On the interplay of shell structure with low- and high-frequency mechanics of multifunctional magnetic microbubbles.

PubMed

Poehlmann, Melanie; Grishenkov, Dmitry; Kothapalli, Satya V V N; Härmark, Johan; Hebert, Hans; Philipp, Alexandra; Hoeller, Roland; Seuss, Maximilian; Kuttner, Christian; Margheritelli, Silvia; Paradossi, Gaio; Fery, Andreas

2014-01-07

Polymer-shelled magnetic microbubbles have great potential as hybrid contrast agents for ultrasound and magnetic resonance imaging. In this work, we studied US/MRI contrast agents based on air-filled poly(vinyl alcohol)-shelled microbubbles combined with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are integrated either physically or chemically into the polymeric shell of the microbubbles (MBs). As a result, two different designs of a hybrid contrast agent are obtained. With the physical approach, SPIONs are embedded inside the polymeric shell and with the chemical approach SPIONs are covalently linked to the shell surface. The structural design of hybrid probes is important, because it strongly determines the contrast agent's response in the considered imaging methods. In particular, we were interested how structural differences affect the shell's mechanical properties, which play a key role for the MBs' US imaging performance. Therefore, we thoroughly characterized the MBs' geometric features and investigated low-frequency mechanics by using atomic force microscopy (AFM) and high-frequency mechanics by using acoustic tests. Thus, we were able to quantify the impact of the used SPIONs integration method on the shell's elastic modulus, shear modulus and shear viscosity. In summary, the suggested approach contributes to an improved understanding of structure-property relations in US-active hybrid contrast agents and thus provides the basis for their sustainable development and optimization.

Error analysis and correction of discrete solutions from finite element codes

NASA Technical Reports Server (NTRS)

Thurston, G. A.; Stein, P. A.; Knight, N. F., Jr.; Reissner, J. E.

1984-01-01

Many structures are an assembly of individual shell components. Therefore, results for stresses and deflections from finite element solutions for each shell component should agree with the equations of shell theory. This paper examines the problem of applying shell theory to the error analysis and the correction of finite element results. The general approach to error analysis and correction is discussed first. Relaxation methods are suggested as one approach to correcting finite element results for all or parts of shell structures. Next, the problem of error analysis of plate structures is examined in more detail. The method of successive approximations is adapted to take discrete finite element solutions and to generate continuous approximate solutions for postbuckled plates. Preliminary numerical results are included.

A shell approach for fibrous reinforcement forming simulations

NASA Astrophysics Data System (ADS)

Liang, B.; Colmars, J.; Boisse, P.

2018-05-01

Because of the slippage between fibers, the basic assumptions of classical plate and shell theories are not verified by fiber reinforcement during a forming. However, simulations of reinforcement forming use shell finite elements when wrinkles development is important. A shell formulation is proposed for the forming simulations of continuous fiber reinforcements. The large tensile stiffness leads to the quasi inextensibility in the fiber directions. The fiber bending stiffness determines the curvature of the reinforcement. The calculation of tensile and bending virtual works are based on the precise geometry of the single fiber. Simulations and experiments are compared for different reinforcements. It is shown that the proposed fibrous shell approach not only correctly simulates the deflections but also the rotations of the through thickness material normals.

Large-scale configuration interaction description of the structure of nuclei around 100Sn and 208Pb

NASA Astrophysics Data System (ADS)

Qi, Chong

2016-08-01

In this contribution I would like to discuss briefly the recent developments of the nuclear configuration interaction shell model approach. As examples, we apply the model to calculate the structure and decay properties of low-lying states in neutron-deficient nuclei around 100Sn and 208Pb that are of great experimental and theoretical interests.

Yolk@Shell Nanoarchitectures with Bimetallic Nanocores-Synthesis and Electrocatalytic Applications.

PubMed

Guiet, Amandine; Unmüssig, Tobias; Göbel, Caren; Vainio, Ulla; Wollgarten, Markus; Driess, Matthias; Schlaad, Helmut; Polte, Jörg; Fischer, Anna

2016-10-10

In the present paper, we demonstrate a versatile approach for the one-pot synthesis of metal oxide yolk@shell nanostructures filled with bimetallic nanocores. This novel approach is based on the principles of hydrophobic nanoreactor soft-templating and is exemplified for the synthesis of various AgAu NP @tin-rich ITO (AgAu@ITO TR ) yolk@shell nanomaterials. Hydrophobic nanoreactor soft-templating thereby takes advantage of polystyrene-block-poly(4-vinylpiridine) inverse micelles as two-compartment nanoreactor template, in which the core and the shell of the micelles serve as metal and metal oxide precursor reservoir, respectively. The composition, size and number of AuAg bimetallic nanoparticles incorporated within the ITO TR yolk@shell can easily be tuned. The conductivity of the ITO TR shell and the bimetallic composition of the AuAg nanoparticles, the as-synthesized AuAg NP @ITO TR yolk@shell materials could be used as efficient electrocatalysts for electrochemical glucose oxidation with improved onset potential when compared to their gold counterpart.

Automatic determination of 3D orientations of fossilized oyster shells from a densely packed Miocene shell bed

NASA Astrophysics Data System (ADS)

Puttonen, Ana; Harzhauser, Mathias; Puttonen, Eetu; Mandic, Oleg; Székely, Balázs; Molnár, Gábor; Pfeifer, Norbert

2018-02-01

Shell beds represent a useful source of information on various physical processes that cause the depositional condition. We present an automated method to calculate the 3D orientations of a large number of elongate and platy objects (fossilized oyster shells) on a sedimentary bedding plane, developed to support the interpretation of possible depositional patterns, imbrications, or impact of local faults. The study focusses on more than 1900 fossil oyster shells exposed in a densely packed Miocene shell bed. 3D data were acquired by terrestrial laser scanning on an area of 459 m2 with a resolution of 1 mm. Bivalve shells were manually defined as 3D-point clouds of a digital surface model and stored in an ArcGIS database. An individual shell coordinate system (ISCS) was virtually embedded into each shell and its orientation was determined relative to the coordinate system of the entire, tectonically tilted shell bed. Orientation is described by the rotation angles roll, pitch, and yaw in a Cartesian coordinate system. This method allows an efficient measurement and analysis of the orientation of thousands of specimens and is a major advantage compared to the traditional 2D approach, which measures only the azimuth (yaw) angles. The resulting data can variously be utilized for taphonomic analyses and the reconstruction of prevailing hydrodynamic regimes and depositional environments. For the first time, the influence of possible post-sedimentary vertical displacements can be quantified with high accuracy. Here, the effect of nearby fault lines—present in the reef—was tested on strongly tilted oyster shells, but it was found out that the fault lines did not have a statistically significant effect on the large tilt angles. Aside from the high reproducibility, a further advantage of the method is its non-destructive nature, which is especially suitable for geoparks and protected sites such as the studied shell bed.

Resource Letter NSM-1: New insights into the nuclear shell model

DOE Office of Scientific and Technical Information (OSTI.GOV)

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. Whenmore » 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.« less

Plates and shells containing a surface crack under general loading conditions

NASA Technical Reports Server (NTRS)

Joseph, Paul F.; Erdogan, Fazil

1987-01-01

Various through and part-through crack problems in plates and shells are considered. The line-spring model of Rice and Levy is generalized to the skew-symmetric case to solve surface crack problems involving mixed-mode, coplanar crack growth. Compliance functions are introduced which are valid for crack depth to thickness ratios at least up to .95. This includes expressions for tension and bending as well as expressions for in-plane shear, out-of-plane shear, and twisting. Transverse shear deformation is taken into account in the plate and shell theories and this effect is shown to be important in comparing stress intensity factors obtained from the plate theory with three-dimensional solutions. Stress intensity factors for cylinders obtained by the line-spring model also compare well with three-dimensional solution. By using the line-spring approach, stress intensity factors can be obtained for the through crack and for part-through crack of any crack front shape, without recalculation integrals that take up the bulk of the computer time. Therefore, parameter studies involving crack length, crack depth, shell type, and shell curvature are made in some detail. The results will be useful in brittle fracture and in fatigue crack propagation studies. All problems considered are of the mixed boundary value type and are reducted to strongly singular integral equations which make use of the finite-part integrals of Hadamard. The equations are solved numerically in a manner that is very efficient.

Librations and tides of icy satellites: model comparison for Enceladus

NASA Astrophysics Data System (ADS)

Trinh, A.; Van Hoolst, T.; Baland, R. M.; Beuthe, M.; Rivoldini, A.; Dehant, V. M. A.

2015-12-01

The latest measurements of the librations of Enceladus suggest that it could have a global subsurface ocean or a non-hydrostatic core (Thomas et al. 2014). Further observations should constrain the properties of the ice shell, and similar insights are expected from future investigation of Europa and Ganymede.Detailed models of the librations and tides are therefore required to properly interpret these measurements in terms of interior structure. Here we compare the `classical', separate tide and libration models (where spherical symmetry is assumed to compute the tides, Van Hoolst et al. 2013) with our combined tide+libration model (Trinh et al. 2013), both extended to account for non-hydrostatic structure.Even with a global ocean, different mechanisms act to prevent Enceladus's shell from moving independently from the rest. Among those, pressure coupling across the flattened boundaries of the ocean requires special care if the shape is not fully relaxed. We discuss how it should be modelled in the classical approach to be consistent with the combined model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vakili, Hajar; Rahvar, Sohrab; Kroupa, Pavel, E-mail: vakili@physics.sharif.edu

Shell galaxies are understood to form through the collision of a dwarf galaxy with an elliptical galaxy. Shell structures and kinematics have been noted to be independent tools to measure the gravitational potential of the shell galaxies. We compare theoretically the formation of shells in Type I shell galaxies in different gravity theories in this work because this is so far missing in the literature. We include Newtonian plus dark halo gravity, and two non-Newtonian gravity models, MOG and MOND, in identical initial systems. We investigate the effect of dynamical friction, which by slowing down the dwarf galaxy in themore » dark halo models limits the range of shell radii to low values. Under the same initial conditions, shells appear on a shorter timescale and over a smaller range of distances in the presence of dark matter than in the corresponding non-Newtonian gravity models. If galaxies are embedded in a dark matter halo, then the merging time may be too rapid to allow multi-generation shell formation as required by observed systems because of the large dynamical friction effect. Starting from the same initial state, the observation of small bright shells in the dark halo model should be accompanied by large faint ones, while for the case of MOG, the next shell generation patterns iterate with a specific time delay. The first shell generation pattern shows a degeneracy with the age of the shells and in different theories, but the relative distance of the shells and the shell expansion velocity can break this degeneracy.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fogarty, Aoife C., E-mail: fogarty@mpip-mainz.mpg.de; Potestio, Raffaello, E-mail: potestio@mpip-mainz.mpg.de; Kremer, Kurt, E-mail: kremer@mpip-mainz.mpg.de

A fully atomistic modelling of many biophysical and biochemical processes at biologically relevant length- and time scales is beyond our reach with current computational resources, and one approach to overcome this difficulty is the use of multiscale simulation techniques. In such simulations, when system properties necessitate a boundary between resolutions that falls within the solvent region, one can use an approach such as the Adaptive Resolution Scheme (AdResS), in which solvent particles change their resolution on the fly during the simulation. Here, we apply the existing AdResS methodology to biomolecular systems, simulating a fully atomistic protein with an atomistic hydrationmore » shell, solvated in a coarse-grained particle reservoir and heat bath. Using as a test case an aqueous solution of the regulatory protein ubiquitin, we first confirm the validity of the AdResS approach for such systems, via an examination of protein and solvent structural and dynamical properties. We then demonstrate how, in addition to providing a computational speedup, such a multiscale AdResS approach can yield otherwise inaccessible physical insights into biomolecular function. We use our methodology to show that protein structure and dynamics can still be correctly modelled using only a few shells of atomistic water molecules. We also discuss aspects of the AdResS methodology peculiar to biomolecular simulations.« less

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.

Dynamic-thresholding level set: a novel computer-aided volumetry method for liver tumors in hepatic CT images

NASA Astrophysics Data System (ADS)

Cai, Wenli; Yoshida, Hiroyuki; Harris, Gordon J.

2007-03-01

Measurement of the volume of focal liver tumors, called liver tumor volumetry, is indispensable for assessing the growth of tumors and for monitoring the response of tumors to oncology treatments. Traditional edge models, such as the maximum gradient and zero-crossing methods, often fail to detect the accurate boundary of a fuzzy object such as a liver tumor. As a result, the computerized volumetry based on these edge models tends to differ from manual segmentation results performed by physicians. In this study, we developed a novel computerized volumetry method for fuzzy objects, called dynamic-thresholding level set (DT level set). An optimal threshold value computed from a histogram tends to shift, relative to the theoretical threshold value obtained from a normal distribution model, toward a smaller region in the histogram. We thus designed a mobile shell structure, called a propagating shell, which is a thick region encompassing the level set front. The optimal threshold calculated from the histogram of the shell drives the level set front toward the boundary of a liver tumor. When the volume ratio between the object and the background in the shell approaches one, the optimal threshold value best fits the theoretical threshold value and the shell stops propagating. Application of the DT level set to 26 hepatic CT cases with 63 biopsy-confirmed hepatocellular carcinomas (HCCs) and metastases showed that the computer measured volumes were highly correlated with those of tumors measured manually by physicians. Our preliminary results showed that DT level set was effective and accurate in estimating the volumes of liver tumors detected in hepatic CT images.

Photoionization cross section and binding energy of single dopant in hollow cylindrical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; El-Yadri, M.; Dujardin, F.; Restrepo, R. L.; Duque, C. A.

2017-02-01

In this study, we have investigated the confined donor impurity in a hollow cylindrical-shell quantum dot. The charges are assumed to be completely confined to the interior of the shell with rigid walls. Within the framework of the effective-mass approximation and by using a simple variational approach, we have computed the donor binding energy as a function of the shell sizes in order to study the behavior of the electron-impurity attraction for a very small thickness. Our results show that the binding energy of a donor impurity placed at the center of cylindrical core/shell dots depends strongly on the shell size. The binding energy increases when the shell-wideness becomes smaller and shows the same behavior as in a simple cylindrical quantum dot. A special case has been studied, which corresponds to the ratio between the inner and outer radii near to one (a/b → 1) for which our model gives a non-significant behavior of the impurity binding energy. This fact implies the existence of a critical value (a/b) for which the binding energy of the donor impurity tends to the limit value of 4 effective Rydbergs as in a 2D quantum well. We also analyse the photoionization cross section considering only the in-plane incident radiation polarization. We determine its behavior as a function of photon energy, shell size, and donor position. The measurement of photoionization in such systems would be of great interest to understand the optical properties of carriers in quantum dots.

The limits of hamiltonian structures in three-dimensional elasticity, shells, and rods

NASA Astrophysics Data System (ADS)

Ge, Z.; Kruse, H. P.; Marsden, J. E.

1996-01-01

This paper uses Hamiltonian structures to study the problem of the limit of three-dimensional (3D) elastic models to shell and rod models. In the case of shells, we show that the Hamiltonian structure for a three-dimensional elastic body converges, in a sense made precise, to that for a shell model described by a one-director Cosserat surface as the thickness goes to zero. We study limiting procedures that give rise to unconstrained as well as constrained Cosserat director models. The case of a rod is also considered and similar convergence results are established, with the limiting model being a geometrically exact director rod model (in the framework developed by Antman, Simo, and coworkers). The resulting model may or may not have constraints, depending on the nature of the constitutive relations and their behavior under the limiting procedure. The closeness of Hamiltonian structures is measured by the closeness of Poisson brackets on certain classes of functions, as well as the Hamiltonians. This provides one way of justifying the dynamic one-director model for shells. Another way of stating the convergence result is that there is an almost-Poisson embedding from the phase space of the shell to the phase space of the 3D elastic body, which implies that, in the sense of Hamiltonian structures, the dynamics of the elastic body is close to that of the shell. The constitutive equations of the 3D model and their behavior as the thickness tends to zero dictates whether the limiting 2D model is a constrained or an unconstrained director model. We apply our theory in the specific case of a 3D Saint Venant-Kirchhoff material and derive the corresponding limiting shell and rod theories. The limiting shell model is an interesting Kirchhoff-like shell model in which the stored energy function is explicitly derived in terms of the shell curvature. For rods, one gets (with an additional inextensibility constraint) a one-director Kirchhoff elastic rod model, which reduces to the well-known Euler elastica if one adds an additional single constraint that the director lines up with the Frenet frame.

Multiphysics modeling of the steel continuous casting process

NASA Astrophysics Data System (ADS)

Hibbeler, Lance C.

This work develops a macroscale, multiphysics model of the continuous casting of steel. The complete model accounts for the turbulent flow and nonuniform distribution of superheat in the molten steel, the elastic-viscoplastic thermal shrinkage of the solidifying shell, the heat transfer through the shell-mold interface with variable gap size, and the thermal distortion of the mold. These models are coupled together with carefully constructed boundary conditions with the aid of reduced-order models into a single tool to investigate behavior in the mold region, for practical applications such as predicting ideal tapers for a beam-blank mold. The thermal and mechanical behaviors of the mold are explored as part of the overall modeling effort, for funnel molds and for beam-blank molds. These models include high geometric detail and reveal temperature variations on the mold-shell interface that may be responsible for cracks in the shell. Specifically, the funnel mold has a column of mold bolts in the middle of the inside-curve region of the funnel that disturbs the uniformity of the hot face temperatures, which combined with the bending effect of the mold on the shell, can lead to longitudinal facial cracks. The shoulder region of the beam-blank mold shows a local hot spot that can be reduced with additional cooling in this region. The distorted shape of the funnel mold narrow face is validated with recent inclinometer measurements from an operating caster. The calculated hot face temperatures and distorted shapes of the mold are transferred into the multiphysics model of the solidifying shell. The boundary conditions for the first iteration of the multiphysics model come from reduced-order models of the process; one such model is derived in this work for mold heat transfer. The reduced-order model relies on the physics of the solution to the one-dimensional heat-conduction equation to maintain the relationships between inputs and outputs of the model. The geometric parameters in the model are calibrated such that the reduced-order model temperatures match a small, periodic subdomain of the mold. These parameters are demonstrated to be insensitive to the calibration conditions. The thermal behavior of the detailed, three-dimensional mold models used in this work can be approximated closely with a few arithmetic calculations after calibrating the reduced-order model of mold heat transfer. The example application of the model includes the effects of the molten steel jet on the solidification front and the ferrostatic pressure. The model is demonstrated to match measurements of mold heat removal and the thickness of a breakout shell all the way around the perimeter of the mold, and gives insight to the cause of breakouts in a beam-blank caster. This multiphysics modeling approach redefines the state of the art of process modeling for continuous casting, and can be~used in future work to explore the formation and prevention of defects and other practical issues. This work also explores the eigen-problem for an arbitrary 3x3 matrix. An explicit, algebraic formula for the eigenvectors is presented.

Effects of cluster-shell competition and BCS-like pairing in 12C

NASA Astrophysics Data System (ADS)

Matsuno, H.; Itagaki, N.

2017-12-01

The antisymmetrized quasi-cluster model (AQCM) was proposed to describe α-cluster and jj-coupling shell models on the same footing. In this model, the cluster-shell transition is characterized by two parameters, R representing the distance between α clusters and Λ describing the breaking of α clusters, and the contribution of the spin-orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with the α-cluster model wave function. Not only the closure configurations of the major shells but also the subclosure configurations of the jj-coupling shell model can be described starting with the α-cluster model wave functions; however, the particle-hole excitations of single particles have not been fully established yet. In this study we show that the framework of AQCM can be extended even to the states with the character of single-particle excitations. For ^{12}C, two-particle-two-hole (2p2h) excitations from the subclosure configuration of 0p_{3/2} corresponding to a BCS-like pairing are described, and these shell model states are coupled with the three α-cluster model wave functions. The correlation energy from the optimal configuration can be estimated not only in the cluster part but also in the shell model part. We try to pave the way to establish a generalized description of the nuclear structure.

Design of efficient stiffened shells of revolution

NASA Technical Reports Server (NTRS)

Majumder, D. K.; Thornton, W. A.

1976-01-01

A method to produce efficient piecewise uniform stiffened shells of revolution is presented. The approach uses a first order differential equation formulation for the shell prebuckling and buckling analyses and the necessary conditions for an optimum design are derived by a variational approach. A variety of local yielding and buckling constraints and the general buckling constraint are included in the design process. The local constraints are treated by means of an interior penalty function and the general buckling load is treated by means of an exterior penalty function. This allows the general buckling constraint to be included in the design process only when it is violated. The self-adjoint nature of the prebuckling and buckling formulations is used to reduce the computational effort. Results for four conical shells and one spherical shell are given.

Overcoming the fragility - X-ray computed micro-tomography elucidates brachiopod endoskeletons.

PubMed

Seidel, Ronald; Lüter, Carsten

2014-01-01

The calcareous shells of brachiopods offer a wealth of informative characters for taxonomic and phylogenetic investigations. In particular scanning electron microscopy (SEM) has been used for decades to visualise internal structures of the shell. However, to produce informative SEM data, brachiopod shells need to be opened after chemical removal of the soft tissue. This preparation occasionally damages the shell. Additionally, skeletal elements of taxonomic/systematic interest such as calcareous spicules which are loosely embedded in the lophophore and mantle connective tissue become disintegrated during the preparation process. Using a nondestructive micro-computed tomography (μCT) approach, the entire fragile endoskeleton of brachiopods is documented for the first time. New insights on the structure and position of tissue-bound skeletal elements (spicules) are given as add ons to existing descriptions of brachiopod shell anatomy, thereby enhancing the quality and quantity of informative characters needed for both taxonomic and phylogenetic studies. Here, we present five modern, articulated brachiopods (Rectocalathis schemmgregoryi n. gen., n. sp., Eucalathis sp., Gryphus vitreus, Liothyrella neozelanica and Terebratulina retusa) that were X-rayed using a Phoenix Nanotom XS 180 NF. We provide links to download 3D models of these species, and additional five species with spicules can be accessed in the Supplemental Material. In total, 17 brachiopod genera covering all modern articulated subgroups and 2 inarticulated genera were X-rayed for morphological analysis. Rectocalathis schemmgregoryi n. gen., n. sp. is fully described. Micro-CT is an excellent non-destructive tool for investigating calcified structures in the exo- and endoskeletons of brachiopods. With high quality images and interactive 3D models, this study provides a comprehensive description of the profound differences in shell anatomy, facilitates the detection of new delicate morphological characters of the endoskeleton and gives new insights into the body plan of modern brachiopods.

Theoretical Studies of Nanocluster Formation

DTIC Science & Technology

2016-05-26

background, technical approach 2. Core-shell nanoclusters (Mg/Cu, Si/Al, etc.) - energetic additives for propellants , explosives - gas generators...shell nanocluster synthesis Core-shell nanoclusters such as SiAln, NinAlm, Aln(CuO)m, etc. may be useful ingredients in propellants and explosives

He 3 ( α , γ ) Be 7 and H 3 ( α , γ ) Li 7 astrophysical S factors from the no-core shell model with continuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dohet-Eraly, Jeremy; Navratil, Petr; Quaglioni, Sofia

The 3He(α,γ) 7Be and 3H(α,γ) 7Li astrophysical S factors are calculated within the no-core shell model with continuum using a renormalized chiral nucleon–nucleon interaction. The 3He(α,γ) 7Be astrophysical S factors agree reasonably well with the experimental data while the 3H(α,γ) 7Li ones are overestimated. The seven-nucleon bound and resonance states and the α + 3He/ 3H elastic scattering are also studied and compared with experiment. Here, the low-lying resonance properties are rather well reproduced by our approach. At low energies, the s-wave phase shift, which is non-resonant, is overestimated.

Steady state model for the thermal regimes of shells of airships and hot air balloons

NASA Astrophysics Data System (ADS)

Luchev, Oleg A.

1992-10-01

A steady state model of the temperature regime of airships and hot air balloons shells is developed. The model includes three governing equations: the equation of the temperature field of airships or balloons shell, the integral equation for the radiative fluxes on the internal surface of the shell, and the integral equation for the natural convective heat exchange between the shell and the internal gas. In the model the following radiative fluxes on the shell external surface are considered: the direct and the earth reflected solar radiation, the diffuse solar radiation, the infrared radiation of the earth surface and that of the atmosphere. For the calculations of the infrared external radiation the model of the plane layer of the atmosphere is used. The convective heat transfer on the external surface of the shell is considered for the cases of the forced and the natural convection. To solve the mentioned set of the equations the numerical iterative procedure is developed. The model and the numerical procedure are used for the simulation study of the temperature fields of an airship shell under the forced and the natural convective heat transfer.

Gamow-Teller response in the configuration space of a density-functional-theory-rooted no-core configuration-interaction model

NASA Astrophysics Data System (ADS)

Konieczka, M.; Kortelainen, M.; Satuła, W.

2018-03-01

Background: The atomic nucleus is a unique laboratory in which to study fundamental aspects of the electroweak interaction. This includes a question concerning in medium renormalization of the axial-vector current, which still lacks satisfactory explanation. Study of spin-isospin or Gamow-Teller (GT) response may provide valuable information on both the quenching of the axial-vector coupling constant as well as on nuclear structure and nuclear astrophysics. Purpose: We have performed a seminal calculation of the GT response by using the no-core configuration-interaction approach rooted in multireference density functional theory (DFT-NCCI). The model treats properly isospin and rotational symmetries and can be applied to calculate both the nuclear spectra and transition rates in atomic nuclei, irrespectively of their mass and particle-number parity. Methods: The DFT-NCCI calculation proceeds as follows: First, one builds a configuration space by computing relevant, for a given physical problem, (multi)particle-(multi)hole Slater determinants. Next, one applies the isospin and angular-momentum projections and performs the isospin and K mixing in order to construct a model space composed of linearly dependent states of good angular momentum. Eventually, one mixes the projected states by solving the Hill-Wheeler-Griffin equation. Results: The method is applied to compute the GT strength distribution in selected N ≈Z nuclei including the p -shell 8Li and 8Be nuclei and the s d -shell well-deformed nucleus 24Mg. In order to demonstrate a flexibility of the approach we present also a calculation of the superallowed GT β decay in doubly-magic spherical 100Sn and the low-spin spectrum in 100In. Conclusions: It is demonstrated that the DFT-NCCI model is capable of capturing the GT response satisfactorily well by using a relatively small configuration space, exhausting simultaneously the GT sum rule. The model, due to its flexibility and broad range of applicability, may either serve as a complement or even as an alternative to other theoretical approaches, including the conventional nuclear shell model.

Modeling mantle convection in the spherical annulus

NASA Astrophysics Data System (ADS)

Hernlund, John W.; Tackley, Paul J.

2008-12-01

Most methods for modeling mantle convection in a two-dimensional (2D) circular annular domain suffer from innate shortcomings in their ability to capture several characteristics of the spherical shell geometry of planetary mantles. While methods such as rescaling the inner and outer radius to reduce anomalous effects in a 2D polar cylindrical coordinate system have been introduced and widely implemented, such fixes may have other drawbacks that adversely affect the outcome of some kinds of mantle convection studies. Here we propose a new approach that we term the "spherical annulus," which is a 2D slice that bisects the spherical shell and is quantitatively formulated at the equator of a spherical polar coordinate system after neglecting terms in the governing equations related to variations in latitude. Spherical scaling is retained in this approximation since the Jacobian function remains proportional to the square of the radius. We present example calculations to show that the behavior of convection in the spherical annulus compares favorably against calculations performed in other 2D annular domains when measured relative to those in a fully three-dimensional (3D) spherical shell.

Merging single-shot XFEL diffraction data from inorganic nanoparticles: a new approach to size and orientation determination

DOE PAGES

Li, Xuanxuan; Spence, John C. H.; Hogue, Brenda G.; ...

2017-09-22

X-ray free-electron lasers (XFELs) provide new opportunities for structure determination of biomolecules, viruses and nanomaterials. With unprecedented peak brilliance and ultra-short pulse duration, XFELs can tolerate higher X-ray doses by exploiting the femtosecond-scale exposure time, and can thus go beyond the resolution limits achieved with conventional X-ray diffraction imaging techniques. Using XFELs, it is possible to collect scattering information from single particles at high resolution, however particle heterogeneity and unknown orientations complicate data merging in three-dimensional space. Using the Linac Coherent Light Source (LCLS), synthetic inorganic nanocrystals with a core–shell architecture were used as a model system for proof-of-principle coherentmore » diffractive single-particle imaging experiments. To deal with the heterogeneity of the core–shell particles, new computational methods have been developed to extract the particle size and orientation from the scattering data to assist data merging. The size distribution agrees with that obtained by electron microscopy and the merged data support a model with a core–shell architecture.« less

Merging single-shot XFEL diffraction data from inorganic nanoparticles: a new approach to size and orientation determination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xuanxuan; Spence, John C. H.; Hogue, Brenda G.

X-ray free-electron lasers (XFELs) provide new opportunities for structure determination of biomolecules, viruses and nanomaterials. With unprecedented peak brilliance and ultra-short pulse duration, XFELs can tolerate higher X-ray doses by exploiting the femtosecond-scale exposure time, and can thus go beyond the resolution limits achieved with conventional X-ray diffraction imaging techniques. Using XFELs, it is possible to collect scattering information from single particles at high resolution, however particle heterogeneity and unknown orientations complicate data merging in three-dimensional space. Using the Linac Coherent Light Source (LCLS), synthetic inorganic nanocrystals with a core–shell architecture were used as a model system for proof-of-principle coherentmore » diffractive single-particle imaging experiments. To deal with the heterogeneity of the core–shell particles, new computational methods have been developed to extract the particle size and orientation from the scattering data to assist data merging. The size distribution agrees with that obtained by electron microscopy and the merged data support a model with a core–shell architecture.« less

Comparison of experimental and modeled absorption enhancement by black carbon (BC) cored polydisperse aerosols under hygroscopic conditions.

PubMed

Shamjad, P M; Tripathi, S N; Aggarwal, S G; Mishra, S K; Joshi, Manish; Khan, Arshad; Sapra, B K; Ram, Kirpa

2012-08-07

The quantification of the radiative impacts of light absorbing ambient black carbon (BC) particles strongly depends on accurate measurements of BC mass concentration and absorption coefficient (β(abs)). In this study, an experiment has been conducted to quantify the influence of hygroscopic growth of ambient particles on light absorption. Using the hygroscopic growth factor (i.e., Zdanovskii-Stokes-Robinson (ZSR) approach), a model has been developed to predict the chemical composition of particles based on measurements, and the absorption and scattering coefficients are derived using a core-shell assumption with light extinction estimates based on Mie theory. The estimated optical properties agree within 7% for absorption coefficient and 30% for scattering coefficient with that of measured values. The enhancement of absorption is found to vary according to the thickness of the shell and BC mass, with a maximum of 2.3 for a shell thickness of 18 nm for the particles. The findings of this study underline the importance of considering aerosol-mixing states while calculating their radiative forcing.

Oxygen isotopes of marine mollusc shells record Eocene elevation change in the Pyrenees

NASA Astrophysics Data System (ADS)

Huyghe, Damien; Mouthereau, Frédéric; Emmanuel, Laurent

2012-09-01

Constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate/tectonics retroactions. Here, we use oxygen stable-isotope record on oyster shells, preserved in marine foreland deposits, to examine the past elevation of the Pyrenees during the Eocene. Our approach is based on the comparison with the Paris basin, an intracratonic basin not influenced by orogenic growth. The finding of a shift of 1.5‰ between 49 and 41 Ma, indicating more negative δ18Oc in the south Pyrenean foreland, is interpreted to reflect the inflow of river water sourced from higher elevation in the Pyrenees. To test this and provide paleoelevation estimate, we adopt a morphologic-hydrological model accounting for the hypsometry of drainage basin. Our best fitting model shows that the Pyrenees rose up to 2000 m. This indicates that the Pyrenees reached high elevation in the Eocene, thus providing new critical constraints on their long-term orogenic development. δ18O of marine mollusc shells are proved potentially attractive for paleoelevation studies, especially for mountain belts where elevated continental surfaces have not been preserved.

Improvement of Progressive Damage Model to Predicting Crashworthy Composite Corrugated Plate

NASA Astrophysics Data System (ADS)

Ren, Yiru; Jiang, Hongyong; Ji, Wenyuan; Zhang, Hanyu; Xiang, Jinwu; Yuan, Fuh-Gwo

2018-02-01

To predict the crashworthy composite corrugated plate, different single and stacked shell models are evaluated and compared, and a stacked shell progressive damage model combined with continuum damage mechanics is proposed and investigated. To simulate and predict the failure behavior, both of the intra- and inter- laminar failure behavior are considered. The tiebreak contact method, 1D spot weld element and cohesive element are adopted in stacked shell model, and a surface-based cohesive behavior is used to capture delamination in the proposed model. The impact load and failure behavior of purposed and conventional progressive damage models are demonstrated. Results show that the single shell could simulate the impact load curve without the delamination simulation ability. The general stacked shell model could simulate the interlaminar failure behavior. The improved stacked shell model with continuum damage mechanics and cohesive element not only agree well with the impact load, but also capture the fiber, matrix debonding, and interlaminar failure of composite structure.

Testing the hydrodynamics and stability of ammonoids: empirical and simulation studies

NASA Astrophysics Data System (ADS)

White, Thomas; Astrop, Timothy; Ren, Qilong; Angioni, Stefano; Carley, Michael; Wills, Matthew

2016-04-01

The coiled shells of ammonoids have classically been modelled in theoretical morphospaces with just a few variables. As dynamic accretionary structures, their shells preserve developmental trajectory as well as adult morphology. In traversing mass extinction events, the morphospace occupation of ammonoids was repeatedly reduced, but the clade often recolonized much of this morphospace in the wake of each mass extinction. The gross morphology of ammonoid shells was therefore subject to high levels of homoplasy and convergence. However, it is unclear what precise functions the ammonoid shells may have been optimized for, neither is it known what determined the bounds of their morphospace given that not all geometrically possible forms were realized. We demonstrate that the actualized occupation of Raupian morphospace can be predicted from numerical modelling, given the dual requirements for stability and manoeuvrability, both while stationary within the water column and while swimming. We test these theoretical predictions in two ways: firstly using 3D printed models in waterflow tank experiments, and secondly using computational fluid dynamic (CFD) approaches. All concur that ammonoids were not especially efficient or impressive swimmers. Spherocone forms maximized stability at the expense of manoeuvrability, while platycone and oxycone morphologies were better adapted for more rapid directional change rather than stability. We speculate that the former were optimized for stability within the water column, while the latter were adapted for moving dynamically around obstructions close to the bottom or for predation-avoidance manoeuvres.

Structure of 8B from elastic and inelastic 7Be+p scattering

NASA Astrophysics Data System (ADS)

Mitchell, J. P.; Rogachev, G. V.; Johnson, E. D.; Baby, L. T.; Kemper, K. W.; Moro, A. M.; Peplowski, P.; Volya, A. S.; Wiedenhöver, I.

2013-05-01

Background: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics.Purpose: The resonant structure of 8B is studied in this work.Method: Excitation functions for elastic and inelastic 7Be+p scattering were measured using a 7Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions was performed.Results: New low-lying resonances at 1.9, 2.54, and 3.3 MeV in 8B are reported with spin-parity assignment 0+, 2+, and 1+, respectively. Comparison to the time-dependent continuum shell (TDCSM) model and ab initio no-core shell model/resonating-group method (NCSM/RGM) calculations is performed. This work is a more detailed analysis of the data first published as a Rapid Communication. J. P. Mitchell, G. V. Rogachev, E. D. Johnson, L. T. Baby, K. W. Kemper , [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.82.011601 82, 011601(R) (2010)].Conclusions: Identification of the 0+, 2+, 1+ states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of 8B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio no-core shell model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.

Theory of morphological transformation of viral capsid shell during the maturation process in the HK97 bacteriophage and similar viruses

NASA Astrophysics Data System (ADS)

Konevtsova, O. V.; Lorman, V. L.; Rochal, S. B.

2016-05-01

We consider the symmetry and physical origin of collective displacement modes playing a crucial role in the morphological transformation during the maturation of the HK97 bacteriophage and similar viruses. It is shown that the experimentally observed hexamer deformation and pentamer twist in the HK97 procapsid correspond to the simplest irreducible shear strain mode of a spherical shell. We also show that the icosahedral faceting of the bacteriophage capsid shell is driven by the simplest irreducible radial displacement field. The shear field has the rotational icosahedral symmetry group I while the radial field has the full icosahedral symmetry Ih. This difference makes their actions independent. The radial field sign discriminates between the icosahedral and the dodecahedral shapes of the faceted capsid shell, thus making the approach relevant not only for the HK97-like viruses but also for the parvovirus family. In the frame of the Landau-Ginzburg formalism we propose a simple phenomenological model valid for the first reversible step of the HK97 maturation process. The calculated phase diagram illustrates the discontinuous character of the virus shape transformation. The characteristics of the virus shell faceting and expansion obtained in the in vitro and in vivo experiments are related to the decrease in the capsid shell thickness and to the increase of the internal capsid pressure.

Influence of a finite number of baffles on shell-and-tube heat exchanger performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, R.K.; Pignotti, A.

1997-01-01

In single-phase shell-and-tube heat exchangers, thermal performance prediction is customarily accomplished with an idealization that the number of baffles used is very large and can be assumed to approach infinity. Under this idealization, the temperature change within each baffle compartment is very small in comparison with the total temperature change of the shell fluid through the heat exchanger. Thus the shell fluid can be considered as uniform (perfectly mixed) at every cross section (in a direction normal to the shell axis). It is with this model that the mean temperature difference correction factor is normally derived for single-phase exchangers. Inmore » reality, a finite number of baffles are used, and the condition stated above can be achieved only partially. In this article, a comprehensive review is made and new results are derived where needed to assess the influence of a finite number of baffles on heat transfer performance for 1-1, 1-2, and 1-N TEMA E, 1-2 TEMA J, and 1-2 TEMA G and H single-phase shell-and-tube exchangers. It is shown that the number of baffles required to achieve the performance within about 2% of an exchanger with an infinite number of baffles varies with the type of exchanger and the performance parameters. The new results are presented in tabular form.« less

Application of the Shell/3D Modeling Technique for the Analysis of Skin-Stiffener Debond Specimens

NASA Technical Reports Server (NTRS)

Krueger, Ronald; O'Brien, T. Kevin; Minguet, Pierre J.

2002-01-01

The application of a shell/3D modeling technique for the simulation of skin/stringer debond in a specimen subjected to three-point bending is 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/13D 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.

Experimental Demonstration of Underwater Acoustic Scattering Cancellation

PubMed Central

Rohde, Charles A.; Martin, Theodore P.; Guild, Matthew D.; Layman, Christopher N.; Naify, Christina J.; Nicholas, Michael; Thangawng, Abel L.; Calvo, David C.; Orris, Gregory J.

2015-01-01

We explore an acoustic scattering cancellation shell for buoyant hollow cylinders submersed in a water background. A thin, low-shear, elastic coating is used to cancel the monopole scattering from an air-filled, neutrally buoyant steel shell for all frequencies where the wavelength is larger than the object diameter. By design, the uncoated shell also has an effective density close to the aqueous background, independently canceling its dipole scattering. Due to the significantly reduced monopole and dipole scattering, the compliant coating results in a hollow cylindrical inclusion that is simultaneously impedance and sound speed matched to the water background. We demonstrate the proposed cancellation method with a specific case, using an array of hollow steel cylinders coated with thin silicone rubber shells. These experimental results are matched to finite element modeling predictions, confirming the scattering reduction. Additional calculations explore the optimization of the silicone coating properties. Using this approach, it is found that scattering cross-sections can be reduced by 20 dB for all wavelengths up to k0a = 0.85. PMID:26282067

Electronic transport properties of inner and outer shells in near ohmic-contacted double-walled carbon nanotube transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuchun; Zhou, Liyan; Zhao, Shangqian

2014-06-14

We investigate electronic transport properties of field-effect transistors based on double-walled carbon nanotubes, of which inner shells are metallic and outer shells are semiconducting. When both shells are turned on, electron-phonon scattering is found to be the dominant phenomenon. On the other hand, when outer semiconducting shells are turned off, a zero-bias anomaly emerges in the dependence of differential conductance on the bias voltage, which is characterized according to the Tomonaga-Luttinger liquid model describing tunneling into one-dimensional materials. We attribute these behaviors to different contact conditions for outer and inner shells of the double-walled carbon nanotubes. A simple model combiningmore » Luttinger liquid model for inner metallic shells and electron-phonon scattering in outer semiconducting shells is given here to explain our transport data at different temperatures.« less

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.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaganathen, Y.; Betan, R. M. Id; Michel, N.

Background: The structure of weakly bound and unbound nuclei close to particle drip lines is one of the major science drivers of nuclear physics. A comprehensive understanding of these systems goes beyond the traditional configuration interaction approach formulated in the Hilbert space of localized states (nuclear shell model) and requires an open quantum system description. The complex-energy Gamow shell model (GSM) provides such a framework as it is capable of describing resonant and nonresonant many-body states on equal footing. Purpose: To make reliable predictions, quality input is needed that allows for the full uncertainty quantification of theoretical results. In thismore » study, we carry out the optimization of an effective GSM (one-body and two-body) interaction in the psdf-shell-model space. The resulting interaction is expected to describe nuclei with 5 ≤ A ≲ 12 at the p-sd-shell interface. Method: The one-body potential of the 4He core is modeled by a Woods-Saxon + spin-orbit + Coulomb potential, and the finite-range nucleon-nucleon interaction between the valence nucleons consists of central, spin-orbit, tensor, and Coulomb terms. The GSM is used to compute key fit observables. The χ 2 optimization is performed using the Gauss-Newton algorithm augmented by the singular value decomposition technique. The resulting covariance matrix enables quantification of statistical errors within the linear regression approach. Results: The optimized one-body potential reproduces nucleon- 4He scattering phase shifts up to an excitation energy of 20 MeV. The two-body interaction built on top of the optimized one-body field is adjusted to the bound and unbound ground-state binding energies and selected excited states of the helium, lithium, and beryllium isotopes up to A = 9 . A very good agreement with experimental results was obtained for binding energies. First applications of the optimized interaction include predictions for two-nucleon correlation densities and excitation spectra of light nuclei with quantified uncertainties. In conclusion: The new interaction will enable comprehensive and fully quantified studies of structure and reactions aspects of nuclei from the psd region of the nuclear chart.« less

Evaluation of different approaches to modeling the second-order ionospheric delay on GPS measurements

NASA Astrophysics Data System (ADS)

Garcia-Fernandez, M.; Desai, S. D.; Butala, M. D.; Komjathy, A.

2013-12-01

This work evaluates various approaches to compute the second order ionospheric correction (SOIC) to Global Positioning System (GPS) measurements. When estimating the reference frame using GPS, applying this correction is known to primarily affect the realization of the origin of the Earth's reference frame along the spin axis (Z coordinate). Therefore, the Z translation relative to the International Terrestrial Reference Frame 2008 is used as the metric to evaluate various published approaches to determining the slant total electron content (TEC) for the SOIC: getting the slant TEC from GPS measurements, and using the vertical total electron content (TEC) given by a Global Ionospheric Model (GIM) to transform it to slant TEC via a mapping function. All of these approaches agree to 1 mm if the ionospheric shell height needed in GIM-based approaches is set to 600 km. The commonly used shell height of 450 km introduces an offset of 1 to 2 mm. When the SOIC is not applied, the Z axis translation can be reasonably modeled with a ratio of +0.23 mm/TEC units of the daily median GIM vertical TEC. Also, precise point positioning (PPP) solutions (positions and clocks) determined with and without SOIC differ by less than 1 mm only if they are based upon GPS orbit and clock solutions that have consistently applied or not applied the correction, respectively. Otherwise, deviations of few millimeters in the north component of the PPP solutions can arise due to inconsistencies with the satellite orbit and clock products, and those deviations exhibit a dependency on solar cycle conditions.

Modelling the optical properties of aerosols in a chemical transport model

NASA Astrophysics Data System (ADS)

Andersson, E.; Kahnert, M.

2015-12-01

According to the IPCC fifth assessment report (2013), clouds and aerosols still contribute to the largest uncertainty when estimating and interpreting changes to the Earth's energy budget. Therefore, understanding the interaction between radiation and aerosols is both crucial for remote sensing observations and modelling the climate forcing arising from aerosols. Carbon particles are the largest contributor to the aerosol absorption of solar radiation, thereby enhancing the warming of the planet. Modelling the radiative properties of carbon particles is a hard task and involves many uncertainties arising from the difficulties of accounting for the morphologies and heterogeneous chemical composition of the particles. This study aims to compare two ways of modelling the optical properties of aerosols simulated by a chemical transport model. The first method models particle optical properties as homogeneous spheres and are externally mixed. This is a simple model that is particularly easy to use in data assimilation methods, since the optics model is linear. The second method involves a core-shell internal mixture of soot, where sulphate, nitrate, ammonia, organic carbon, sea salt, and water are contained in the shell. However, by contrast to previously used core-shell models, only part of the carbon is concentrated in the core, while the remaining part is homogeneously mixed with the shell. The chemical transport model (CTM) simulations are done regionally over Europe with the Multiple-scale Atmospheric Transport and CHemistry (MATCH) model, developed by the Swedish Meteorological and Hydrological Institute (SMHI). The MATCH model was run with both an aerosol dynamics module, called SALSA, and with a regular "bulk" approach, i.e., a mass transport model without aerosol dynamics. Two events from 2007 are used in the analysis, one with high (22/12-2007) and one with low (22/6-2007) levels of elemental carbon (EC) over Europe. The results of the study help to assess the significance of aerosol morphology for modelling radiative forcing and aerosol optical properties relevant to interpreting remote sensing observations. The uncertainties introduced by the optics model are gauged by comparing them to model uncertainties related to the inclusion or omission of aerosol dynamic processes.

Unexpected storm-time nightside plasmaspheric density enhancement at low L shell

NASA Astrophysics Data System (ADS)

Chu, X.; Bortnik, J.; Denton, R. E.; Yue, C.

2017-12-01

We have developed a three-dimensional dynamic electron density (DEN3D) model in the inner magnetosphere using a neural network approach. The DEN3D model can provide spatiotemporal distribution of the electron density at any location and time that spacecraft observations are not available. Given DEN3D's good performance in predicting the structure and dynamic evolution of the plasma density, the salient features of the DEN3D model can be used to gain further insight into the physics. For instance, the DEN3D models can be used to find unusual phenomena that are difficult to detect in observations or simulations. We report, for the first time, an unexpected plasmaspheric density increase at low L shell regions on the nightside during the main phase of a moderate storm during 12-16 October 2004, as opposed to the expected density decrease due to storm-time plasmaspheric erosion. The unexpected density increase is first discovered in the modeled electron density distribution using the DEN3D model, and then validated using in-situ density measurements obtained from the IMAGE satellite. The density increase was likely caused by increased earthward transverse field plasma transport due to enhanced nightside ExB drift, which coincided with enhanced solar wind electric field and substorm activity. This is consistent with the results of physics-based simulation SAMI3 model which show earthward enhanced plasma transport and electron density increase at low L shells during storm main phase.

Experimental analysis and numerical modeling of mollusk shells as a three dimensional integrated volume.

PubMed

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. Copyright © 2012 Elsevier Ltd. All rights reserved.

Multi-Scale Analyses of Three Dimensional Woven Composite 3D Shell With a Cut Out Circle

NASA Astrophysics Data System (ADS)

Nguyen, Duc Hai; Wang, Hu

2018-06-01

A composite material are made by combining two or more constituent materials to obtain the desired material properties of each product type. The matrix material which can be polymer and fiber is used as reinforcing material. Currently, the polymer matrix is widely used in many different fields with differently designed structures such as automotive structures and aviation, aerospace, marine, etc. because of their excellent mechanical properties; in addition, they possess the high level of hardness and durability together with a significant reduction in weight compared to traditional materials. However, during design process of structure, there will be many interruptions created for the purpose of assembling the structures together or for many other design purposes. Therefore, when this structure is subject to load-bearing, its failure occurs at these interruptions due to stress concentration. This paper proposes multi-scale modeling and optimization strategies in evaluation of the effectiveness of fiber orientation in an E-glass/Epoxy woven composite 3D shell with circular holes at the center investigated by FEA results. A multi-scale model approach was developed to predict the mechanical behavior of woven composite 3D shell with circular holes at the center with different designs of material and structural parameters. Based on the analysis result of laminae, we have found that the 3D shell with fiber direction of 450 shows the best stress and strain bearing capacity. Thus combining several layers of 450 fiber direction in a multi-layer composite 3D shell reduces the stresses concentrated on the cuts of the structures.

Scale-free models for the structure of business firm networks.

PubMed

Kitsak, Maksim; Riccaboni, Massimo; Havlin, Shlomo; Pammolli, Fabio; Stanley, H Eugene

2010-03-01

We study firm collaborations in the life sciences and the information and communication technology sectors. We propose an approach to characterize industrial leadership using k -shell decomposition, with top-ranking firms in terms of market value in higher k -shell layers. We find that the life sciences industry network consists of three distinct components: a "nucleus," which is a small well-connected subgraph, "tendrils," which are small subgraphs consisting of small degree nodes connected exclusively to the nucleus, and a "bulk body," which consists of the majority of nodes. Industrial leaders, i.e., the largest companies in terms of market value, are in the highest k -shells of both networks. The nucleus of the life sciences sector is very stable: once a firm enters the nucleus, it is likely to stay there for a long time. At the same time we do not observe the above three components in the information and communication technology sector. We also conduct a systematic study of these three components in random scale-free networks. Our results suggest that the sizes of the nucleus and the tendrils in scale-free networks decrease as the exponent of the power-law degree distribution lambda increases, and disappear for lambda>or=3 . We compare the k -shell structure of random scale-free model networks with two real-world business firm networks in the life sciences and in the information and communication technology sectors. We argue that the observed behavior of the k -shell structure in the two industries is consistent with the coexistence of both preferential and random agreements in the evolution of industrial networks.

An Automated Approach to Peanut dring with real-time monitoring of in-shell Kernel Moisture Content with a Microwave Sensor

USDA-ARS?s Scientific Manuscript database

Today’s peanut drying processes utilize decision support software based on modeling and require substantial human interaction for moisture sampling. These conditions increase the likelihood of peanuts being overdried or underdried. This research addresses the need for an automated controller with re...

Tailored Core Shell Cathode Powders for Solid Oxide Fuel Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swartz, Scott

2015-03-23

In this Phase I SBIR project, a “core-shell” composite cathode approach was evaluated for improving SOFC performance and reducing degradation of lanthanum strontium cobalt ferrite (LSCF) cathode materials, following previous successful demonstrations of infiltration approaches for achieving the same goals. The intent was to establish core-shell cathode powders that enabled high performance to be obtained with “drop-in” process capability for SOFC manufacturing (i.e., rather than adding an infiltration step to the SOFC manufacturing process). Milling, precipitation and hetero-coagulation methods were evaluated for making core-shell composite cathode powders comprised of coarse LSCF “core” particles and nanoscale “shell” particles of lanthanum strontiummore » manganite (LSM) or praseodymium strontium manganite (PSM). Precipitation and hetero-coagulation methods were successful for obtaining the targeted core-shell morphology, although perfect coverage of the LSCF core particles by the LSM and PSM particles was not obtained. Electrochemical characterization of core-shell cathode powders and conventional (baseline) cathode powders was performed via electrochemical impedance spectroscopy (EIS) half-cell measurements and single-cell SOFC testing. Reliable EIS testing methods were established, which enabled comparative area-specific resistance measurements to be obtained. A single-cell SOFC testing approach also was established that enabled cathode resistance to be separated from overall cell resistance, and for cathode degradation to be separated from overall cell degradation. The results of these EIS and SOFC tests conclusively determined that the core-shell cathode powders resulted in significant lowering of performance, compared to the baseline cathodes. Based on the results of this project, it was concluded that the core-shell cathode approach did not warrant further investigation.« less

Numerical Characterization of a Composite Bonded Wing-Box

NASA Technical Reports Server (NTRS)

Smeltzer, Stanley S., III; Lovejoy, Andrew E.; Satyanarayana, Arunkumar

2008-01-01

The development of composite wing structures has focused on the use of mechanical fasteners to join heavily-loaded areas, while bonded joints have been used only for select locations. The focus of this paper is the examination of the adhesive layer in a generic bonded wing box that represents a "fastenerless" or unitized structure in order to characterize the general behavior and failure mechanisms. A global/local approach was applied to study the response of the adhesive layer using a global shell model and a local shell/solid model. The wing box was analyzed under load to represent a high-g up-bending condition such that the strains in the composite sandwich face sheets are comparable to an expected design allowable. The global/local analysis indicates that at these wing load levels the strains in the adhesive layer are well within the adhesive's elastic region, such that yielding would not be expected in the adhesive layer. The global/local methodology appears to be a promising approach to evaluate the structural integrity of the adhesively bonded structures.

In vivo bioactivity of rhBMP-2 delivered with novel polyelectrolyte complexation shells assembled on an alginate microbead core template.

PubMed

Abbah, Sunny-Akogwu; Liu, Jing; Lam, Raymond W M; Goh, James C H; Wong, Hee-Kit

2012-09-10

Electrostatic interactions between polycations and polyanions are being explored to fabricate polyelectrolyte complexes (PEC) that could entrap and regulate the release of a wide range of biomolecules. Here, we report the in vivo application of PEC shells fabricated from three different polycations: poly-l-ornithine (PLO), poly-l-arginine (PLA) and DEAE-dextran (DEAE-D) to condense heparin on the surface of alginate microbeads and further control the delivery of recombinant human bone morphogenetic protein 2 (rhBMP-2) in spinal fusion application. We observed large differences in the behavior of PEC shells fabricated from the cationic polyamino acids (PLO and PLA) when compared to the cationic polysaccharide, DEAE-D. Whereas DEAE-D-based PEC shells eroded and released rhBMP-2 over 2 days in vitro, PLO- and PLA-based shells retained at least 60% of loaded rhBMP-2 after 3 weeks of incubation in phosphate-buffered saline. In vivo implantation in a rat model of posterolateral spinal fusion revealed robust bone formation in the PLO- and PLA-based PEC shell groups. This resulted in a significantly enhanced mechanical stability of the fused segments. However, bone induction and biomechanical stability of spine segments implanted with DEAE-D-based carriers were significantly inferior to both PLO- and PLA-based PEC shell groups (p<0.01). From these results, we conclude that PEC shells incorporating native heparin could be used for growth factor delivery in functional bone tissue engineering application and that PLA- and PLO-based complexes could represent superior options to DEAE-D for loading and in vivo delivery of bioactive BMP-2 in this approach. Copyright © 2012 Elsevier B.V. All rights reserved.

Static response of coated microbubbles compressed between rigid plates: Simulations and asymptotic analysis including elastic and adhesive forces

NASA Astrophysics Data System (ADS)

Lytra, A.; Pelekasis, N.

2018-03-01

The static response of coated microbubbles is investigated with a novel approach employed for modeling contact between a microbubble and the cantilever of an atomic force microscope. Elastic tensions and moments are described via appropriate constitutive laws. The encapsulated gas is assumed to undergo isothermal variations. Due to the hydrophilic nature of the cantilever, an ultrathin aqueous film is formed, which transfers the force onto the shell. An interaction potential describes the local pressure applied on the shell. The problem is solved in axisymmetric form with the finite element method. The response is governed by the dimensionless bending, k^ b=kb/(χ R02 ), pressure, P^ A=(PAR0 )/χ , and interaction potential, W ^ =w0/χ . Hard polymeric shells have negligible resistance to gas compression, while for the softer lipid shells gas compressibility is comparable with shell elasticity. As the external force increases, numerical simulations reveal that the force versus deformation (f vs d) curve of polymeric shells exhibits a transition from the linear O(d) (Reissner) regime, marked by flattened shapes around the contact region, to a non-linear O(d1/2) (Pogorelov) regime dominated by shapes exhibiting crater formation due to buckling. When lipid shells are tested, buckling is bypassed as the external force increases and flattened shapes prevail in an initially linear f vs d curve. Transition to a curved upwards regime is observed as the force increases, where gas compression and area dilatation form the dominant balance providing a nonlinear regime with an O(d3) dependence. Asymptotic analysis recovers the above patterns and facilitates estimation of the shell mechanical properties.

Multi-parameter optimization of piezoelectric actuators for multi-mode active vibration control of cylindrical shells

NASA Astrophysics Data System (ADS)

Hu, K. M.; Li, Hua

2018-07-01

A novel technique for the multi-parameter optimization of distributed piezoelectric actuators is presented in this paper. The proposed method is designed to improve the performance of multi-mode vibration control in cylindrical shells. The optimization parameters of actuator patch configuration include position, size, and tilt angle. The modal control force of tilted orthotropic piezoelectric actuators is derived and the multi-parameter cylindrical shell optimization model is established. The linear quadratic energy index is employed as the optimization criterion. A geometric constraint is proposed to prevent overlap between tilted actuators, which is plugged into a genetic algorithm to search the optimal configuration parameters. A simply-supported closed cylindrical shell with two actuators serves as a case study. The vibration control efficiencies of various parameter sets are evaluated via frequency response and transient response simulations. The results show that the linear quadratic energy indexes of position and size optimization decreased by 14.0% compared to position optimization; those of position and tilt angle optimization decreased by 16.8%; and those of position, size, and tilt angle optimization decreased by 25.9%. It indicates that, adding configuration optimization parameters is an efficient approach to improving the vibration control performance of piezoelectric actuators on shells.

Comparison of finite-difference schemes for analysis of shells of revolution. [stress and free vibration analysis

NASA Technical Reports Server (NTRS)

Noor, A. K.; Stephens, W. B.

1973-01-01

Several finite difference schemes are applied to the stress and free vibration analysis of homogeneous isotropic and layered orthotropic shells of revolution. The study is based on a form of the Sanders-Budiansky first-approximation linear shell theory modified such that the effects of shear deformation and rotary inertia are included. A Fourier approach is used in which all the shell stress resultants and displacements are expanded in a Fourier series in the circumferential direction, and the governing equations reduce to ordinary differential equations in the meridional direction. While primary attention is given to finite difference schemes used in conjunction with first order differential equation formulation, comparison is made with finite difference schemes used with other formulations. These finite difference discretization models are compared with respect to simplicity of application, convergence characteristics, and computational efficiency. Numerical studies are presented for the effects of variations in shell geometry and lamination parameters on the accuracy and convergence of the solutions obtained by the different finite difference schemes. On the basis of the present study it is shown that the mixed finite difference scheme based on the first order differential equation formulation and two interlacing grids for the different fundamental unknowns combines a number of advantages over other finite difference schemes previously reported in the literature.

Optimisation of warpage on thin shell plastic part using response surface methodology (RSM) and glowworm swarm optimisation (GSO)

NASA Astrophysics Data System (ADS)

Asyirah, B. N.; Shayfull, Z.; Nasir, S. M.; Fathullah, M.; Hazwan, M. H. M.

2017-09-01

In manufacturing a variety of parts, plastic injection moulding is widely use. The injection moulding process parameters have played important role that affects the product's quality and productivity. There are many approaches in minimising the warpage ans shrinkage such as artificial neural network, genetic algorithm, glowworm swarm optimisation and hybrid approaches are addressed. In this paper, a systematic methodology for determining a warpage and shrinkage in injection moulding process especially in thin shell plastic parts are presented. To identify the effects of the machining parameters on the warpage and shrinkage value, response surface methodology is applied. In thos study, a part of electronic night lamp are chosen as the model. Firstly, experimental design were used to determine the injection parameters on warpage for different thickness value. The software used to analyse the warpage is Autodesk Moldflow Insight (AMI) 2012.

Open source integrated modeling environment Delta Shell

NASA Astrophysics Data System (ADS)

Donchyts, G.; Baart, F.; Jagers, B.; van Putten, H.

2012-04-01

In the last decade, integrated modelling has become a very popular topic in environmental modelling since it helps solving problems, which is difficult to model using a single model. However, managing complexity of integrated models and minimizing time required for their setup remains a challenging task. The integrated modelling environment Delta Shell simplifies this task. The software components of Delta Shell are easy to reuse separately from each other as well as a part of integrated environment that can run in a command-line or a graphical user interface mode. The most components of the Delta Shell are developed using C# programming language and include libraries used to define, save and visualize various scientific data structures as well as coupled model configurations. Here we present two examples showing how Delta Shell simplifies process of setting up integrated models from the end user and developer perspectives. The first example shows coupling of a rainfall-runoff, a river flow and a run-time control models. The second example shows how coastal morphological database integrates with the coastal morphological model (XBeach) and a custom nourishment designer. Delta Shell is also available as open-source software released under LGPL license and accessible via http://oss.deltares.nl.

Gold/silver core-shell 20 nm nanoparticles extracted from citrate solution examined by XPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engelhard, Mark H.; Smith, Jordan N.; Baer, Donald R.

Silver nanoparticles of many types are widely used in consumer and medical products. The surface chemistry of particles and the coatings that form during synthesis or use in many types of media can significantly impact the behaviors of particles including dissolution, transformation and biological or environmental impact. Consequently it is useful to be able to extract information about the thickness of surface coatings and other attributes of nanoparticles produced in a variety of ways. It has been demonstrated that X-ray Photoelectron Spectroscopy (XPS) can be reliably used to determine the thickness of organic and other nanoparticles coatings and shells. However,more » care is required to produce reliable and consistent information. Here we report the XPS spectra from gold/silver core-shell nanoparticles of nominal size 20 nm removed from a citrate saturated solution after one and two washing cycles. The Simulation of Electron Spectra for Surface Analysis (SESSA) program had been used to model peak amplitudes to obtain information on citrate coatings that remain after washing and demonstrate the presence of the gold core. This data is provided so that others can compare use of SESSA or other modeling approaches to quantify the nature of coatings to those already published and to explore the impacts particle non-uniformities on XPS signals from core-shell nanoparticles.« less

Universal analytical scattering form factor for shell-, core-shell, or homogeneous particles with continuously variable density profile shape.

PubMed

Foster, Tobias

2011-09-01

A novel analytical and continuous density distribution function with a widely variable shape is reported and used to derive an analytical scattering form factor that allows us to universally describe the scattering from particles with the radial density profile of homogeneous spheres, shells, or core-shell particles. Composed by the sum of two Fermi-Dirac distribution functions, the shape of the density profile can be altered continuously from step-like via Gaussian-like or parabolic to asymptotically hyperbolic by varying a single "shape parameter", d. Using this density profile, the scattering form factor can be calculated numerically. An analytical form factor can be derived using an approximate expression for the original Fermi-Dirac distribution function. This approximation is accurate for sufficiently small rescaled shape parameters, d/R (R being the particle radius), up to values of d/R ≈ 0.1, and thus captures step-like, Gaussian-like, and parabolic as well as asymptotically hyperbolic profile shapes. It is expected that this form factor is particularly useful in a model-dependent analysis of small-angle scattering data since the applied continuous and analytical function for the particle density profile can be compared directly with the density profile extracted from the data by model-free approaches like the generalized inverse Fourier transform method. © 2011 American Chemical Society

Influence of corneal thickness on the intraocular pressure readings for Maklakoff's tonometer of different weight

NASA Astrophysics Data System (ADS)

Franus, D. V.

2018-05-01

Research is conducted into variation in the stress-strain state of the corneoscleral shell of the human eye under loading by a flat base stamp of varying weight. A three-dimensional finite-element model of the contact problem of loading of the corneoscleral shell in the ANSYS program package is presented. Cornea and sclera are modeled as conjugated transversely isotropic spherical shells. The cornea is modeled as a multilayer shell with variable thickness in which all modeled layers have their own individual elastic properties. The research deals with the numerical calculation of the diameter of the contact zone between the shell and the stamp. Values of correction coefficients for intraocular pressure are obtained depending on the thickness of the corneal shell in its center, allowing the true intraocular pressure to be determined more accurately.

Computational modeling of the effective Young's modulus values of fullerene molecules: a combined molecular dynamics simulation and continuum shell model.

PubMed

Ghavanloo, Esmaeal; Izadi, Razie; Nayebi, Ali

2018-02-28

Estimating the Young's modulus of a structure in the nanometer size range is a difficult task. The reliable determination of this parameter is, however, important in both basic and applied research. In this study, by combining molecular dynamics (MD) simulations and continuum shell theory, we designed a new approach to determining the Young's modulus values of different spherical fullerenes. The results indicate that the Young's modulus values of fullerene molecules decrease nonlinearly with increasing molecule size and understandably tend to the Young's modulus of an ideal flat graphene sheet at large molecular radii. To the best of our knowledge, this is first time that a combined atomistic-continuum method which can predict the Young's modulus values of fullerene molecules with high precision has been reported.

Intensification of delignification and subsequent hydrolysis for the fermentable sugar production from lignocellulosic biomass using ultrasonic irradiation.

PubMed

Subhedar, Preeti B; Ray, Pearl; Gogate, Parag R

2018-01-01

The present work deals with intensification of delignification and subsequent enzymatic hydrolysis of sustainable biomass such as groundnut shells, coconut coir and pistachio shells using ultrasound assisted approach so as to develop an economical approach for obtaining bioethanol. Process intensification, in the current context, is referred to as any improvements giving enhanced rates possibly with lower energy and chemical as well as enzyme requirement for delignification and hydrolysis respectively. Conventional processing for both delignification and enzymatic hydrolysis has also been investigated for establishing the degree of intensification. The obtained results for delignification of biomass established that for conventional alkaline treatment, the extent of delignification for the case of groundnut shells, coconut coir and pistachio shells were 41.8, 45.9 and 38% which increased to 71.1, 89.5 and 78.9% respectively giving almost 80-100% increase for the ultrasound assisted approach. Under optimized conditions, the conventional approach resulted in reducing sugar yields as 10.2, 12.1 and 8.1g/L for groundnut shells, coconut coir and pistachio shells respectively whereas for the case of ultrasound-assisted enzymatic hydrolysis, the obtained yields were 21.3, 23.9 and 18.4g/L in same order of biomass. The material samples were characterized by several characterization techniques for establishing the morphological changes obtained due to the use of ultrasound which were found to be favorable for enhanced delignification and hydrolysis for the ultrasound assisted approach. Overall, the results of this work establish the process intensification benefits due to the application of ultrasound for different sustainable biomass with mechanistic understanding based on the morphological analyses. Copyright © 2017 Elsevier B.V. All rights reserved.

Simulation of the stress computation in shells

NASA Technical Reports Server (NTRS)

Salama, M.; Utku, S.

1978-01-01

A self-teaching computer program is described, whereby the stresses in thin shells can be computed with good accuracy using the best fit approach. The program is designed for use in interactive game mode to allow the structural engineer to learn about (1) the major sources of difficulties and associated errors in the computation of stresses in thin shells, (2) possible ways to reduce the errors, and (3) trade-off between computational cost and accuracy. Included are derivation of the computational approach, program description, and several examples illustrating the program usage.

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.

Room temperature exchange bias in multiferroic BiFeO3 nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

NASA Astrophysics Data System (ADS)

Zhang, Chuang; Wang, Shou Yu; Liu, Wei Fang; Xu, Xun Ling; Li, Xiu; Zhang, Hong; Gao, Ju; Li, De Jun

2017-05-01

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO3 nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek's model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO3 nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.

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…

Geodynamic Modeling of Planetary Ice-Oceans: Evolution of Ice-Shell Thickness in Convecting Two-Phase Systems

NASA Astrophysics Data System (ADS)

Allu Peddinti, D.; McNamara, A. K.

2016-12-01

Along with the newly unveiled icy surface of Pluto, several icy planetary bodies show indications of an active surface perhaps underlain by liquid oceans of some size. This augments the interest to explore the evolution of an ice-ocean system and its surface implications. The geologically young surface of the Jovian moon Europa lends much speculation to variations in ice-shell thickness over time. Along with the observed surface features, it suggests the possibility of episodic convection and conduction within the ice-shell as it evolved. What factors would control the growth of the ice-shell as it forms? If and how would those factors determine the thickness of the ice-shell and consequently the heat transfer? Would parameters such as tidal heating or initial temperature affect how the ice-shell grows and to what significance? We perform numerical experiments using geodynamical models of the two-phase ice-water system to study the evolution of planetary ice-oceans such as that of Europa. The models evolve self-consistently from an initial liquid ocean as it cools with time. The effects of presence, absence and magnitude of tidal heating on ice-shell thickness are studied in different models. The vigor of convection changes as the ice-shell continues to thicken. Initial modeling results track changes in the growth rate of the ice-shell as the vigor of the convection changes. The magnitude and temporal location of the rate change varies with different properties of tidal heating and values of initial temperature. A comparative study of models is presented to demonstrate how as the ice-shell is forming, its growth rate and convection are affected by processes such as tidal heating.

Finite Rotation Analysis of Highly Thin and Flexible Structures

NASA Technical Reports Server (NTRS)

Clarke, Greg V.; Lee, Keejoo; Lee, Sung W.; Broduer, Stephen J. (Technical Monitor)

2001-01-01

Deployable space structures such as sunshields and solar sails are extremely thin and highly flexible with limited bending rigidity. For analytical investigation of their responses during deployment and operation in space, these structures can be modeled as thin shells. The present work examines the applicability of the solid shell element formulation to modeling of deployable space structures. The solid shell element formulation that models a shell as a three-dimensional solid is convenient in that no rotational parameters are needed for the description of kinematics of deformation. However, shell elements may suffer from element locking as the thickness becomes smaller unless special care is taken. It is shown that, when combined with the assumed strain formulation, the solid shell element formulation results in finite element models that are free of locking even for extremely thin structures. Accordingly, they can be used for analysis of highly flexible space structures undergoing geometrically nonlinear finite rotations.

Do climate variables and human density affect Achatina fulica (Bowditch) (Gastropoda: Pulmonata) shell length, total weight and condition factor?

PubMed

Albuquerque, F S; Peso-Aguiar, M C; Assunção-Albuquerque, M J T; Gálvez, L

2009-08-01

The length-weight relationship and condition factor have been broadly investigated in snails to obtain the index of physical condition of populations and evaluate habitat quality. Herein, our goal was to describe the best predictors that explain Achatina fulica biometrical parameters and well being in a recently introduced population. From November 2001 to November 2002, monthly snail samples were collected in Lauro de Freitas City, Bahia, Brazil. Shell length and total weight were measured in the laboratory and the potential curve and condition factor were calculated. Five environmental variables were considered: temperature range, mean temperature, humidity, precipitation and human density. Multiple regressions were used to generate models including multiple predictors, via model selection approach, and then ranked with AIC criteria. Partial regressions were used to obtain the separated coefficients of determination of climate and human density models. A total of 1.460 individuals were collected, presenting a shell length range between 4.8 to 102.5 mm (mean: 42.18 mm). The relationship between total length and total weight revealed that Achatina fulica presented a negative allometric growth. Simple regression indicated that humidity has a significant influence on A. fulica total length and weight. Temperature range was the main variable that influenced the condition factor. Multiple regressions showed that climatic and human variables explain a small proportion of the variance in shell length and total weight, but may explain up to 55.7% of the condition factor variance. Consequently, we believe that the well being and biometric parameters of A. fulica can be influenced by climatic and human density factors.

Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

PubMed

Zhou, Ling; Fu, Qiuyun; Xue, Fei; Tang, Xiahui; Zhou, Dongxiang; Tian, Yahui; Wang, Geng; Wang, Chaohong; Gou, Haibo; Xu, Lei

2017-11-22

Flexible nanocomposites composed of high dielectric constant fillers and polymer matrix have shown great potential for electrostatic capacitors and energy storage applications. To obtain the composited material with high dielectric constant and high breakdown strength, multi-interfacial composited particles, which composed of conductive cores and insulating shells and possessed the internal barrier layer capacitor (IBLC) effect, were adopted as fillers. Thus, Fe 3 O 4 @BaTiO 3 core-shell particles were prepared and loaded into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polymer matrix. As the mass fraction of core-shell fillers increased from 2.5 wt % to 30 wt %, the dielectric constant of the films increased, while the loss tangent remained at a low level (<0.05 at 1 kHz). Both high electric displacement and high electric breakdown strength were achieved in the films with 10 wt % core-shell fillers loaded. The maximum energy storage density of 7.018 J/cm 3 was measured at 2350 kV/cm, which shows significant enhancement than those of the pure P(VDF-HFP) films and analogous composited films with converse insulating-conductive core-shell fillers. A Maxwell-Wagner capacitor model was also adopted to interpret the efficiency of IBLC effects on the suppressed loss tangent and the superior breakdown strength. This work explored an effective approach to prepare dielectric nanocomposites for energy storage applications experimentally and theoretically.

Compressible Fluids Interacting with a Linear-Elastic Shell

NASA Astrophysics Data System (ADS)

Breit, Dominic; Schwarzacher, Sebastian

2018-05-01

We study the Navier-Stokes equations governing the motion of an isentropic compressible fluid in three dimensions interacting with a flexible shell of Koiter type. The latter one constitutes a moving part of the boundary of the physical domain. Its deformation is modeled by a linearized version of Koiter's elastic energy. We show the existence of weak solutions to the corresponding system of PDEs provided the adiabatic exponent satisfies {γ > 12/7} ({γ >1 } in two dimensions). The solution exists until the moving boundary approaches a self-intersection. This provides a compressible counterpart of the results in Lengeler and Růžičkaka (Arch Ration Mech Anal 211(1):205-255, 2014) on incompressible Navier-Stokes equations.

Numerical modeling of the 3D dynamics of ultrasound contrast agent microbubbles using the boundary integral method

NASA Astrophysics Data System (ADS)

Wang, Qianxi; Manmi, Kawa; Calvisi, Michael L.

2015-02-01

Ultrasound contrast agents (UCAs) are microbubbles stabilized with a shell typically of lipid, polymer, or protein and are emerging as a unique tool for noninvasive therapies ranging from gene delivery to tumor ablation. While various models have been developed to describe the spherical oscillations of contrast agents, the treatment of nonspherical behavior has received less attention. However, the nonspherical dynamics of contrast agents are thought to play an important role in therapeutic applications, for example, enhancing the uptake of therapeutic agents across cell membranes and tissue interfaces, and causing tissue ablation. In this paper, a model for nonspherical contrast agent dynamics based on the boundary integral method is described. The effects of the encapsulating shell are approximated by adapting Hoff's model for thin-shell, spherical contrast agents. A high-quality mesh of the bubble surface is maintained by implementing a hybrid approach of the Lagrangian method and elastic mesh technique. The numerical model agrees well with a modified Rayleigh-Plesset equation for encapsulated spherical bubbles. Numerical analyses of the dynamics of UCAs in an infinite liquid and near a rigid wall are performed in parameter regimes of clinical relevance. The oscillation amplitude and period decrease significantly due to the coating. A bubble jet forms when the amplitude of ultrasound is sufficiently large, as occurs for bubbles without a coating; however, the threshold amplitude required to incite jetting increases due to the coating. When a UCA is near a rigid boundary subject to acoustic forcing, the jet is directed towards the wall if the acoustic wave propagates perpendicular to the boundary. When the acoustic wave propagates parallel to the rigid boundary, the jet direction has components both along the wave direction and towards the boundary that depend mainly on the dimensionless standoff distance of the bubble from the boundary. In all cases, the jet directions for the coated and uncoated bubble are similar but the jet width and jet velocity are smaller for a coated bubble. The effects of shell thickness and shell viscosity are analyzed and determined to affect the bubble dynamics, including jet development.

Verification of Orthogrid Finite Element Modeling Techniques

NASA Technical Reports Server (NTRS)

Steeve, B. E.

1996-01-01

The stress analysis of orthogrid structures, specifically with I-beam sections, is regularly performed using finite elements. Various modeling techniques are often used to simplify the modeling process but still adequately capture the actual hardware behavior. The accuracy of such 'Oshort cutso' is sometimes in question. This report compares three modeling techniques to actual test results from a loaded orthogrid panel. The finite element models include a beam, shell, and mixed beam and shell element model. Results show that the shell element model performs the best, but that the simpler beam and beam and shell element models provide reasonable to conservative results for a stress analysis. When deflection and stiffness is critical, it is important to capture the effect of the orthogrid nodes in the model.

Preparation and characterization of SiO2-coated submicron-sized L10 Fe-Pt particles

NASA Astrophysics Data System (ADS)

Hayashi, Yoshiaki; Ogawa, Tomoyuki; Ishiyama, Kazushi

2018-05-01

The development of magnets with higher performance is attracting increasing interest. The optimization of their microstructure is essential to enhance their properties, and a microstructure comprising magnetically isolated hard magnetic grains of a single-domain size has been proposed as an ideal structure for enhancing the coercivity of magnets. To obtain magnets with an ideal structure, we consider the fabrication of magnets by an approach based on core/shell nanoparticles with a hard magnetic core and a non-magnetic shell. In this study, to obtain particles for our proposed approach, we attempted to fabricate L10 Fe-Pt/SiO2-core/shell particles with submicron-sized cores less than the critical single-domain size. The fabrication of such core/shell particles was confirmed from morphology observations and XRD analysis of the particles. Although the formation of more desirable core/shell particles with submicron-sized single-crystal cores in the single-domain size range was not achieved, the fabricated core/shell particles showed a high coercivity of 25 kOe.

An organized approach to the control of hazards to health at work.

PubMed

Molyneux, M K; Wilson, H G

1990-04-01

Shell U.K. has an approach which facilitates the implementation of its occupational hygiene programme in its many locations. The main elements of the system are Company Policy, Standards, Methods and Management. The Policy sets the scene and is rigorous in its aims. The new COSHH legislation has emphasized particular duties which have influenced the approach. The Company Occupational Health Guidelines [Guidelines on Health at Work for Shell in the U.K. Shell U.K. Ltd, London (1989)] set the standards for control of exposure, among other things, and the Company adopts appropriate methods to achieve them. Of particular note is the Company's COSHH Programme [Implementation of the Shell U.K. Policy on the Control of Substances Hazardous to Health. Shell U.K. Ltd, London (1989)] which applies to all hazards to health (including physical and biological agents) in the workplace. Its introduction has been given full corporate support and is in the process of implementation. Appropriate procedures have been introduced for assessments of risk and for work histories. Guidance has been given on competence, reflecting a philosphy based on a team approach using local resources to the full, supported by corporate resources as required. The awards of the British Examining and Registration Board in Occupational Hygiene (1987) are used as the professional standard. Because of difficulties in obtaining basic hazard data, an internal core hazard data system (CHADS) [Core Hazard Data System. Shell U.K Ltd, London (1989)] has been introduced. The whole programme is managed through Occupational Hygiene Focal Points (OHFP) which represent local activities but also participate in corporate strategy. Through them the multidisciplinary approach is promoted, working in conjunction with local and sector Medical Advisers. Work done by the central Occupational Hygiene Unit is recorded and the reports are used for time management and recovery of costs. In its entirety, the approach is being used successfully to implement a comprehensive occupational hygiene programme in a diversified and dispersed industrial organization.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adam, C.; Klimas, P.; Sanchez-Guillen, J.

For the baby Skyrme model with a specific potential, compacton solutions, i.e., configurations with a compact support and parabolic approach to the vacuum, are derived. Specifically, in the nontopological sector, we find spinning Q-balls and Q-shells, as well as peakons. Moreover, we obtain compact baby skyrmions with nontrivial topological charge. All these solutions may form stable multisoliton configurations provided they are sufficiently separated.

Final report SI 08-SI-004: Fusion application targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biener, J; Kucheyev, S O; Wang, M Y

2010-12-03

Complex target structures are necessary to take full advantage of the unique laboratory environment created by inertial confinement fusion experiments. For example, uses-of-ignition targets that contain a thin layer of a low density nanoporous material inside a spherical ablator shell allow placing dopants in direct contact with the DT fuel. The ideal foam for this application is a low-density hydrocarbon foam that is strong enough to survive wetting with cryogenic hydrogen, and low enough in density (density less than {approx}30 mg/cc) to not reduce the yield of the target. Here, we discuss the fabrication foam-lined uses-of-ignition targets, and the developmentmore » of low-density foams that can be used for this application. Much effort has been directed over the last 20 years toward the development of spherical foam targets for direct-drive and fast-ignition experiments. In these targets, the spherical foam shell is used to define the shape of the cryogenic DT fuel layer, or acts as a surrogate to simulate the cryogenic fuel layer. These targets are fabricated from relatively high-density aerogels (>100 mg/cc) and coated with a few micron thick permeation barrier. With exception of the above mentioned fast ignition targets, the wall of these targets is typically larger than 100 microns. In contrast, the fusion application targets for indirect-drive experiments on NIF will require a much thinner foam shell surrounded by a much thicker ablator shell. The design requirements for both types of targets are compared in Table 1. The foam shell targets for direct-drive experiments can be made in large quantities and with reasonably high yields using an encapsulation technique pioneered by Takagi et al. in the early 90's. In this approach, targets are made by first generating unsupported foam shells using a triple-orifice droplet generator, followed by coating the dried foam shells with a thin permeation barrier. However, this approach is difficult, if not impossible, to transfer to the lower density and thinner wall foam shells required for indirect-drive uses-of-ignition targets for NIF that then would have to be coated with an at least hundred-micron-thick ablator film. So far, the thinnest shells that have been fabricated using the triple-orifice-droplet generator technique had a wall thickness of {approx}20 microns, but despite of being made from a higher-density foam formulation, the shells were mechanically very sensitive, difficult to dry, and showed large deviations from roundness. We thus decided to explore a different approach based on using prefabricated thick-walled spherical ablator shells as templates for the thin-walled foam shell. As in the case of the above mentioned encapsulation technique, the foam is made by sol-gel chemistry. However, our approach removes much the requirements on the mechanical stability of the foam shell as the foam shell is never handled in its free-standing form, and promises superior ablator uniformity and surface roughness. As discussed below, the success of this approach depends strongly on the availability of suitable aerogel chemistries (ideally pure hydrocarbon (CH)-based systems) with suitable rheological properties (high viscosity and high modulus near the gel point) that produce low-density and mechanically strong foams.« less

Geometric screening of core/shell hydrogel microcapsules using a tapered microchannel with interdigitated electrodes.

PubMed

Niu, Ye; Qi, Lin; Zhang, Fen; Zhao, Yi

2018-07-30

Core/shell hydrogel microcapsules attract increasing research attention due to their potentials in tissue engineering, food engineering, and drug delivery. Current approaches for generating core/shell hydrogel microcapsules suffer from large geometric variations. Geometrically defective core/shell microcapsules need to be removed before further use. High-throughput geometric characterization of such core/shell microcapsules is therefore necessary. In this work, a continuous-flow device was developed to measure the geometric properties of microcapsules with a hydrogel shell and an aqueous core. The microcapsules were pumped through a tapered microchannel patterned with an array of interdigitated microelectrodes. The geometric parameters (the shell thickness and the diameter) were derived from the displacement profiles of the microcapsules. The results show that this approach can successfully distinguish all unencapsulated microparticles. The geometric properties of core/shell microcapsules can be determined with high accuracy. The efficacy of this method was demonstrated through a drug releasing experiment where the optimization of the electrospray process based on geometric screening can lead to controlled and extended drug releasing profiles. This method does not require high-speed optical systems, simplifying the system configuration and making it an indeed miniaturized device. The throughput of up to 584 microcapsules per minute was achieved. This study provides a powerful tool for screening core/shell hydrogel microcapsules and is expected to facilitate the applications of these microcapsules in various fields. Copyright © 2018 Elsevier B.V. All rights reserved.

Simulations of heart valves by thin shells with non-linear material properties

NASA Astrophysics Data System (ADS)

Borazjani, Iman; Asgharzadeh, Hafez; Hedayat, Mohammadali

2016-11-01

The primary function of a heart valve is to allow blood to flow in only one direction through the heart. Triangular thin-shell finite element formulation is implemented, which considers only translational degrees of freedom, in three-dimensional domain to simulate heart valves undergoing large deformations. The formulation is based on the nonlinear Kirchhoff thin-shell theory. The developed method is intensively validated against numerical and analytical benchmarks. This method is added to previously developed membrane method to obtain more realistic results since ignoring bending forces can results in unrealistic wrinkling of heart valves. A nonlinear Fung-type constitutive relation, based on experimentally measured biaxial loading tests, is used to model the material properties for response of the in-plane motion in heart valves. Furthermore, the experimentally measured liner constitutive relation is used to model the material properties to capture the flexural motion of heart valves. The Fluid structure interaction solver adopts a strongly coupled partitioned approach that is stabilized with under-relaxation and the Aitken acceleration technique. This work was supported by American Heart Association (AHA) Grant 13SDG17220022 and the Center of Computational Research (CCR) of University at Buffalo.

Structural Configuration Analysis of Crew Exploration Vehicle Concepts

NASA Technical Reports Server (NTRS)

Mukhopadhyay, V.

2006-01-01

Structural configuration modeling and finite element analysis of crew exploration vehicle (CEV) concepts are presented. In the structural configuration design approach, parametric solid models of the pressurized shell and tanks are developed. The CEV internal cabin pressure is same as in the International Space Station (ISS) to enable docking with the ISS without an intermediate airlock. Effects of this internal pressure load on the stress distribution, factor of safety, mass and deflections are investigated. Uniform 7 mm thick skin shell, 5 mm thick shell with ribs and frames, and isogrid skin construction options are investigated. From this limited study, the isogrid construction appears to provide most strength/mass ratio. Initial finite element analysis results on the service module tanks are also presented. These rapid finite element analyses, stress and factor of safety distribution results are presented as a part of lessons learned and to build up a structural mass estimation and sizing database for future technology support. This rapid structural analysis process may also facilitate better definition of the vehicles and components for rapid prototyping. However, these structural analysis results are highly conceptual and exploratory in nature and do not reflect current configuration designs being conducted at the program level by NASA and industry.

Modification of a Macromechanical Finite-Element Based Model for Impact Analysis of Triaxially-Braided Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.; Blinzler, Brina J.; Binienda, Wieslaw K.

2010-01-01

A macro level finite element-based model has been developed to simulate the mechanical and impact response of triaxially-braided polymer matrix composites. In the analytical model, the triaxial braid architecture is simulated by using four parallel shell elements, each of which is modeled as a laminated composite. For the current analytical approach, each shell element is considered to be a smeared homogeneous material. The commercial transient dynamic finite element code LS-DYNA is used to conduct the simulations, and a continuum damage mechanics model internal to LS-DYNA is used as the material constitutive model. The constitutive model requires stiffness and strength properties of an equivalent unidirectional composite. Simplified micromechanics methods are used to determine the equivalent stiffness properties, and results from coupon level tests on the braided composite are utilized to back out the required strength properties. Simulations of quasi-static coupon tests of several representative braided composites are conducted to demonstrate the correlation of the model. Impact simulations of a represented braided composites are conducted to demonstrate the capability of the model to predict the penetration velocity and damage patterns obtained experimentally.

Analysis of Composite Skin-Stiffener Debond Specimens Using a Shell/3D Modeling Technique and Submodeling

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.

Optical properties of light absorbing carbon aggregates mixed with sulfate: assessment of different model geometries for climate forcing calculations.

PubMed

Kahnert, Michael; Nousiainen, Timo; Lindqvist, Hannakaisa; Ebert, Martin

2012-04-23

Light scattering by light absorbing carbon (LAC) aggregates encapsulated into sulfate shells is computed by use of the discrete dipole method. Computations are performed for a UV, visible, and IR wavelength, different particle sizes, and volume fractions. Reference computations are compared to three classes of simplified model particles that have been proposed for climate modeling purposes. Neither model matches the reference results sufficiently well. Remarkably, more realistic core-shell geometries fall behind homogeneous mixture models. An extended model based on a core-shell-shell geometry is proposed and tested. Good agreement is found for total optical cross sections and the asymmetry parameter. © 2012 Optical Society of America

Isospin symmetry breaking and large-scale shell-model calculations with the Sakurai-Sugiura method

NASA Astrophysics Data System (ADS)

Mizusaki, Takahiro; Kaneko, Kazunari; Sun, Yang; Tazaki, Shigeru

2015-05-01

Recently isospin symmetry breaking for mass 60-70 region has been investigated based on large-scale shell-model calculations in terms of mirror energy differences (MED), Coulomb energy differences (CED) and triplet energy differences (TED). Behind these investigations, we have encountered a subtle problem in numerical calculations for odd-odd N = Z nuclei with large-scale shell-model calculations. Here we focus on how to solve this subtle problem by the Sakurai-Sugiura (SS) method, which has been recently proposed as a new diagonalization method and has been successfully applied to nuclear shell-model calculations.

Monte Carlo simulations of nematic and chiral nematic shells

NASA Astrophysics Data System (ADS)

Wand, Charlie R.; Bates, Martin A.

2015-01-01

We present a systematic Monte Carlo simulation study of thin nematic and cholesteric shells with planar anchoring using an off-lattice model. The results obtained using the simple model correspond with previously published results for lattice-based systems, with the number, type, and position of defects observed dependent on the shell thickness with four half-strength defects in a tetrahedral arrangement found in very thin shells and a pair of defects in a bipolar (boojum) configuration observed in thicker shells. A third intermediate defect configuration is occasionally observed for intermediate thickness shells, which is stabilized in noncentrosymmetric shells of nonuniform thickness. Chiral nematic (cholesteric) shells are investigated by including a chiral term in the potential. Decreasing the pitch of the chiral nematic leads to a twisted bipolar (chiral boojum) configuration with the director twist increasing from the inner to the outer surface.

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.

Scale-free models for the structure of business firm networks

NASA Astrophysics Data System (ADS)

Kitsak, Maksim; Riccaboni, Massimo; Havlin, Shlomo; Pammolli, Fabio; Stanley, H. Eugene

2010-03-01

We study firm collaborations in the life sciences and the information and communication technology sectors. We propose an approach to characterize industrial leadership using k -shell decomposition, with top-ranking firms in terms of market value in higher k -shell layers. We find that the life sciences industry network consists of three distinct components: a “nucleus,” which is a small well-connected subgraph, “tendrils,” which are small subgraphs consisting of small degree nodes connected exclusively to the nucleus, and a “bulk body,” which consists of the majority of nodes. Industrial leaders, i.e., the largest companies in terms of market value, are in the highest k -shells of both networks. The nucleus of the life sciences sector is very stable: once a firm enters the nucleus, it is likely to stay there for a long time. At the same time we do not observe the above three components in the information and communication technology sector. We also conduct a systematic study of these three components in random scale-free networks. Our results suggest that the sizes of the nucleus and the tendrils in scale-free networks decrease as the exponent of the power-law degree distribution λ increases, and disappear for λ≥3 . We compare the k -shell structure of random scale-free model networks with two real-world business firm networks in the life sciences and in the information and communication technology sectors. We argue that the observed behavior of the k -shell structure in the two industries is consistent with the coexistence of both preferential and random agreements in the evolution of industrial networks.

Thin Shell Model for NIF capsule stagnation studies

NASA Astrophysics Data System (ADS)

Hammer, J. H.; Buchoff, M.; Brandon, S.; Field, J. E.; Gaffney, J.; Kritcher, A.; Nora, R. C.; Peterson, J. L.; Spears, B.; Springer, P. T.

2015-11-01

We adapt the thin shell model of Ott et al. to asymmetric ICF capsule implosions on NIF. Through much of an implosion, the shell aspect ratio is large so the thin shell approximation is well satisfied. Asymmetric pressure drive is applied using an analytic form for ablation pressure as a function of the x-ray flux, as well as time-dependent 3D drive asymmetry from hohlraum calculations. Since deviations from a sphere are small through peak velocity, we linearize the equations, decompose them by spherical harmonics and solve ODE's for the coefficients. The model gives the shell position, velocity and areal mass variations at the time of peak velocity, near 250 microns radius. The variables are used to initialize 3D rad-hydro calculations with the HYDRA and ARES codes. At link time the cold fuel shell and ablator are each characterized by a density, adiabat and mass. The thickness, position and velocity of each point are taken from the thin shell model. The interior of the shell is filled with a uniform gas density and temperature consistent with the 3/2PV energy found from 1D rad-hydro calculations. 3D linked simulations compare favorably with integrated simulations of the entire implosion. Through generating synthetic diagnostic data, the model offers a method for quickly testing hypothetical sources of asymmetry and comparing with experiment. Prepared by LLNL under Contract DE-AC52-07NA27344.

HR Del REMNANT ANATOMY USING TWO-DIMENSIONAL SPECTRAL DATA AND THREE-DIMENSIONAL PHOTOIONIZATION SHELL MODELS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moraes, Manoel; Diaz, Marcos

2009-12-15

The HR Del nova remnant was observed with the IFU-GMOS at Gemini North. The spatially resolved spectral data cube was used in the kinematic, morphological, and abundance analysis of the ejecta. The line maps show a very clumpy shell with two main symmetric structures. The first one is the outer part of the shell seen in H{alpha}, which forms two rings projected in the sky plane. These ring structures correspond to a closed hourglass shape, first proposed by Harman and O'Brien. The equatorial emission enhancement is caused by the superimposed hourglass structures in the line of sight. The second structuremore » seen only in the [O III] and [N II] maps is located along the polar directions inside the hourglass structure. Abundance gradients between the polar caps and equatorial region were not found. However, the outer part of the shell seems to be less abundant in oxygen and nitrogen than the inner regions. Detailed 2.5-dimensional photoionization modeling of the three-dimensional shell was performed using the mass distribution inferred from the observations and the presence of mass clumps. The resulting model grids are used to constrain the physical properties of the shell as well as the central ionizing source. A sequence of three-dimensional clumpy models including a disk-shaped ionization source is able to reproduce the ionization gradients between polar and equatorial regions of the shell. Differences between shell axial ratios in different lines can also be explained by aspherical illumination. A total shell mass of 9 x 10{sup -4} M {sub sun} is derived from these models. We estimate that 50%-70% of the shell mass is contained in neutral clumps with density contrast up to a factor of 30.« less

3D tooth microwear texture analysis in fishes as a test of dietary hypotheses of durophagy

NASA Astrophysics Data System (ADS)

Purnell, Mark A.; Darras, Laurent P. G.

2016-03-01

An understanding of how extinct animals functioned underpins our understanding of past evolutionary events, including adaptive radiations, and the role of functional innovation and adaptation as drivers of both micro- and macroevolution. Yet analysis of function in extinct animals is fraught with difficulty. Hypotheses that interpret molariform teeth in fishes as evidence of durophagous (shell-crushing) diets provide a good example of the particular problems inherent in the methods of functional morphology. This is because the assumed close coupling of form and function upon which the approach is based is weakened by, among other things, behavioural flexibility and the absence of a clear one to one relationship between structures and functions. Here we show that ISO 25178-2 standard parameters for surface texture, derived from analysis of worn surfaces of molariform teeth of fishes, vary significantly between species that differ in the amount of hard-shelled prey they consume. Two populations of the Sheepshead Seabream (Archosargus probatocephalus) were studied. This fish is not a dietary specialist, and one of the populations is known to consume more vegetation and less hard-shelled prey than the other; this is reflected in significant differences in their microwear textures. The Archosargus populations differ significantly in their microwear from the specialist shell-crusher Anarhichas lupus (the Atlantic Wolffish). Multivariate analysis of these three groups of fishes lends further support to the relationship between diet and tooth microwear, and provides robust validation of the approach. Application of the multivariate models derived from microwear texture in Archosargus and Anarhichas to a third fish species—the cichlid Astatoreochromis alluaudi—successfully separates wild caught fish that ate hard-shelled prey from lab-raised fish that did not. This cross-taxon validation demonstrates that quantitative analysis of tooth microwear texture can differentiate between fishes with different diets even when they range widely in size, habitat, and in the structure of their trophic apparatus. The approach thus has great potential as an additional tool for dietary analysis in extant fishes, and for testing dietary hypotheses in ancient and extinct species.

A parallel finite element procedure for contact-impact problems using edge-based smooth triangular element and GPU

NASA Astrophysics Data System (ADS)

Cai, Yong; Cui, Xiangyang; Li, Guangyao; Liu, Wenyang

2018-04-01

The edge-smooth finite element method (ES-FEM) can improve the computational accuracy of triangular shell elements and the mesh partition efficiency of complex models. In this paper, an approach is developed to perform explicit finite element simulations of contact-impact problems with a graphical processing unit (GPU) using a special edge-smooth triangular shell element based on ES-FEM. Of critical importance for this problem is achieving finer-grained parallelism to enable efficient data loading and to minimize communication between the device and host. Four kinds of parallel strategies are then developed to efficiently solve these ES-FEM based shell element formulas, and various optimization methods are adopted to ensure aligned memory access. Special focus is dedicated to developing an approach for the parallel construction of edge systems. A parallel hierarchy-territory contact-searching algorithm (HITA) and a parallel penalty function calculation method are embedded in this parallel explicit algorithm. Finally, the program flow is well designed, and a GPU-based simulation system is developed, using Nvidia's CUDA. Several numerical examples are presented to illustrate the high quality of the results obtained with the proposed methods. In addition, the GPU-based parallel computation is shown to significantly reduce the computing time.

Disentangling the history of complex multi-phased shell beds based on the analysis of 3D point cloud data

NASA Astrophysics Data System (ADS)

Harzhauser, Mathias; Djuricic, Ana; Mandic, Oleg; Dorninger, Peter; Nothegger, Clemens; Székely, Balázs; Molnár, Gábor; Pfeifer, Norbert

2015-04-01

Shell beds are key features in sedimentary records throughout the Phanerozoic. The interplay between burial rates and population productivity is reflected in distinct degrees of shelliness. Consequently, shell beds may provide informations on various physical processes, which led to the accumulation and preservation of hard parts. Many shell beds pass through a complex history of formation being shaped by more than one factor. In shallow marine settings, the composition of shell beds is often strongly influenced by winnowing, reworking and transport. These processes may cause considerable time averaging and the accumulation of specimens, which have lived thousands of years apart. In the best case, the environment remained stable during that time span and the mixing does not mask the overall composition. A major obstacle for the interpretation of shell beds, however, is the amalgamation of shell beds of several depositional units in a single concentration, as typically for tempestites and tsunamites. Disentangling such mixed assemblages requires deep understanding of the ecological requirements of the taxa involved - which is achievable for geologically young shell beds with living relatives - and a statistic approach to quantify the contribution by the various death assemblages. Furthermore it requires understanding of sedimentary processes potentially involved into their formation. Here we present the first attempt to describe and decipher such a multi-phase shell-bed based on a high resolution digital surface model (1 mm) combined with ortho-photos with a resolution of 0.5 mm per pixel. Documenting the oyster reef requires precisely georeferenced data; owing to high redundancy of the point cloud an accuracy of a few mm was achieved. The shell accumulation covers an area of 400 m2 with thousands of specimens, which were excavated by a three months campaign at Stetten in Lower Austria. Formed in an Early Miocene estuary of the Paratethys Sea it is mainly composed of shells of the giant oyster Crassostrea gryphoides along with numerous other bivalves, gastropods and barnacles. More than 10.000 objects were outlined on the digital surface model and characterized in respect to taxonomy, convex up/down position, left/right shell, orientation, fragmentation and several other features. The outlines and attribute data were stored in a georeferenced ArcGIS database. Already the first analyses and visualizations of the obtained data-sets pointed out different degrees of taxon distribution, composition, and taphonomic grade allowing an identification of at least four discrete ecosystem/depositional phases now amalgamated in a single shell-bed. Based on examples from the present research the presentation will demonstrate enormous potential of high resolution terrestrial laser scanning in paleontology and sedimentology. Representing a pioneering study, lessons have been learned about the benefits as well as the limitations of its application for taphonomic studies. The project is supported by the Austrian Science Fund (FWF P 25883-N29).

Tidal deformation of Enceladus' ice shell with variable thickness and Maxwell rheology

NASA Astrophysics Data System (ADS)

Soucek, Ondrej; Behounkova, Marie; Cadek, Ondrej; Tobie, Gabriel; Choblet, Gael

2017-04-01

Tidal deformation of icy moons has been traditionally studied using the spectral approach which is very efficient for perfectly spherical bodies with radially dependent rheological structure. Measurements of Enceladus' topography (Nimmo et al., 2011) and low-degree gravity (Iess et al., 2014) indicate that the ice shell is significantly thinned in the southern hemisphere (Iess et al., 2014; McKinnon, 2015) and according to recent gravity, shape and libration inversion, it may be only a few kilometers thick at the south pole (Cadek et al., 2016). These variations may potentially have a significant effect on the amplitude and pattern of tidal deformation, stress and associated heating inside the shell, but cannot be straightforwardly incorporated into the existing spectral codes. In order to circumvent this difficulty and to quantify the effects of ice-shell thickness variations, we have developed a three-dimensional finite element code in the framework of FEniCS package (Alnaes et al., 2015). Using this numerical tool, we address the changes in tidally-induced deformation amplitude, stresses and tidal heating for structural models of Enceladus' ice shell of various complexity. Considering Maxwell viscoelastic rheology of the shell, we compare models with uniform thickness consistent with the libration data and with constant viscosity, synthetic models with analytically parameterized thinning in the south polar region and depth-dependent viscosity varying over several orders of magnitude, and finally, models with the shell topography and thickness based on the recent model of Cadek et al. (2016). We find that the thinning of the ice shell around the south pole may lead to amplification of the stress and displacement in this region region by a factor of up to 2 and 4, respectively, depending on the average ice shell thickness, the amplitude of thinning and the viscosity structure. Our results also suggest that lateral variations of ice thickness can induce significant anomalies of the surface heat flux and, together with other effects (e.g. Souček et al., 2016), may thus contribute to the hemispheric dichotomy observed on Enceladus. Alnaes, M. S., Blechta, J., Hake, J., Johansson, J., Kehlet, B., Logg, A., Richardson, C., Ring, J., Rognes, M. E.,Wells, G. N., 2015. The FEniCS Project Version 1.5. Archive of Numerical Software 3 (100), 9-23. Cadek, O., Tobie, G., van Hoolst, T., Masse, M., Choblet, G., Lefevre, A., Mitri, G., Baland, R.-M., Behounkova, M., Bourgeois, O., Trinh, A., 2016. Enceladus's internal ocean and ice shell constrained from Cassini gravity, shape, and libration data. Geophys. Res. Let. 46, 5653-5660. Iess, L., Stevenson, D. J., Parisi, M., Hemingway, D., Jacobson, R. A., Lunine, J. I., Nimmo, F., Armstrong, J. W., Asmar, S. W., Ducci, M., Tortora, P., Apr. 2014. The Gravity Field and Interior Structure of Enceladus. Science 344, 78-80. McKinnon, W. B., Apr. 2015. Effect of Enceladus's rapid synchronous spin on interpretation of Cassini gravity. Geophys. Res. Let. 42, 2137-2143. Nimmo, F., Bills, B. G., Thomas, P. C., 2011. Geophysical implications of the long-wavelength topography of the Saturnian satellites. J. Geophys. Res. 116 (E15), E11001. Soucek, O., Hron, J., Behounkova, M., Cadek, O., 2016. Effect of the tiger stripes on the deformation of Saturn's moon Enceladus. Geophys. Res. Let. 43, 7417-7423.

Role of N-methyl-2-pyrrolidone for preparation of Fe3O4@SiO2 controlled the shell thickness

NASA Astrophysics Data System (ADS)

Wee, Sung-Bok; Oh, Hyeon-Cheol; Kim, Tae-Gyun; An, Gye-Seok; Choi, Sung-Churl

2017-04-01

We developed a simple and novel approach for the synthesis of Fe3O4@SiO2 nanoparticles with controlled shell thickness, and studied the mechanism. The introduction of N-methyl-2-pyrrolidone (NMP) led to trapping of monomer nuclei in single shell and controlled the shell thickness. Fe3O4@SiO2 controlled the shell thickness, showing a high magnetization value (64.47 emu/g). Our results reveal the role and change in the chemical structure of NMP during the core-shell synthesis process. NMP decomposed to 4-aminobutanoic acid in alkaline condition and decreased the hydrolysis rate of the silica coating process.

Electronic, Optical, and Thermal Properties of Reduced-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Huang, Shouting

Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell N-Ws. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphene-like system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

Shell effects in a multinucleon transfer process

NASA Astrophysics Data System (ADS)

Zhu, Long; Wen, Pei-Wei; Lin, Cheng-Jian; Bao, Xiao-Jun; Su, Jun; Li, Cheng; Guo, Chen-Chen

2018-04-01

The shell effects in multinucleon transfer process are investigated in the systems 136Xe + 198Pt and 136Xe + 208Pb within the dinuclear system (DNS) model. The temperature dependence of shell corrections on potential energy surface is taken into account in the DNS model and remarkable improvement for description of experimental data is noticed. The reactions 136Xe + 186W and 150Nd + 186W are also studied. It is found that due to shell effects the projectile 150Nd is more promising for producing transtarget nuclei rather than 136Xe with neutron shell closure.

Dating High Arctic Holocene relative sea level changes using juvenile articulated marine shells in raised beaches

NASA Astrophysics Data System (ADS)

Long, Antony J.; Strzelecki, Mateusz C.; Lloyd, Jerry M.; Bryant, Charlotte L.

2012-08-01

High Arctic raised beaches provide evidence for changes in relative sea-level (RSL), sea-ice extent, storminess, and variations in sediment supply. In many High Arctic areas, driftwood and whale bone are usually the preferred targets for radiocarbon dating, with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level. Here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile, articulated specimens of Astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest. Radiocarbon dates from articulated valves of A. borealis from eight raised beaches from Billefjorden, Svalbard, provide a chronology for Holocene beach ridge formation and RSL change that compares favourably to the most precise records developed from elsewhere in Svalbard using driftwood or whale bone. We demonstrate the value of this new approach by comparing our record with previously published RSL data from eastern Svalbard to test different models of Late Weichselian ice load in this region. We find support for a major ice dome centred south and east of Kong Karls Land but no evidence for a significant ice dome located over easternmost Spitsbergen or southern Hinlopen Strait as proposed from recent marine geophysical survey. The approach is potentially applicable elsewhere in Svalbard and the High Arctic to address questions of RSL change and beach ridge chronology, and hence wider questions regarding palaeoclimate and ice load history.

Using a novel rigid-fluoride polymer to control the interfacial thickness of graphene and tailor the dielectric behavior of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) nanocomposites.

PubMed

Han, Xianghui; Chen, Sheng; Lv, Xuguang; Luo, Hang; Zhang, Dou; Bowen, Chris R

2018-01-24

Polymer nanocomposites based on conductive fillers for high performance dielectrics have attracted increasing attention in recent years. However, a number of physical issues are unclear, such as the effect of interfacial thickness on the dielectric properties of the polymer nanocomposites, which limits the enhancement of permittivity. In this research, two core-shell structured reduced graphene oxide (rGO)@rigid-fluoro-polymer conducting fillers with different shell thicknesses are prepared using a surface-initiated reversible-addition-fragmentation chain transfer polymerization method, which are denoted as rGO@PTFMS-1 with a thin shell and rGO@PTFMS-2 with a thick shell. A rigid liquid crystalline fluoride-polymer poly{5-bis[(4-trifluoro-methoxyphenyl)oxycarbonyl]styrene} (PTFMS) is chosen for the first time to tailor the shell thicknesses of rGO via tailoring the degree of polymerization. The effect of interfacial thickness on the dielectric behavior of the P(VDF-TrFE-CTFE) nanocomposites with rGO and modified rGO is studied in detail. The results demonstrate that the percolation threshold of the nanocomposites increased from 0.68 vol% to 1.69 vol% with an increase in shell thickness. Compared to the rGO@PTFMS-1/P(VDF-TrFE-CTFE) composites, the rGO@PTFMS-2/P(VDF-TrFE-CTFE) composites exhibited a higher breakdown strength and a lower dielectric constant, which can be interpreted by interfacial polarization and the micro-capacitor model, resulting from the insulating nature of the rigid-polymer shell and the change of rGO's morphology. The findings provide an innovative approach to tailor dielectric composites, and promote a deeper understanding of the influence of interfacial region thickness on the dielectric performance.

Spiral Form of the Human Cochlea Results from Spatial Constraints.

PubMed

Pietsch, M; Aguirre Dávila, L; Erfurt, P; Avci, E; Lenarz, T; Kral, A

2017-08-08

The human inner ear has an intricate spiral shape often compared to shells of mollusks, particularly to the nautilus shell. It has inspired many functional hearing theories. The reasons for this complex geometry remain unresolved. We digitized 138 human cochleae at microscopic resolution and observed an astonishing interindividual variability in the shape. A 3D analytical cochlear model was developed that fits the analyzed data with high precision. The cochlear geometry neither matched a proposed function, namely sound focusing similar to a whispering gallery, nor did it have the form of a nautilus. Instead, the innate cochlear blueprint and its actual ontogenetic variants were determined by spatial constraints and resulted from an efficient packing of the cochlear duct within the petrous bone. The analytical model predicts well the individual 3D cochlear geometry from few clinical measures and represents a clinical tool for an individualized approach to neurosensory restoration with cochlear implants.

The rotation and fracture history of Europa from modeling of tidal-tectonic processes

NASA Astrophysics Data System (ADS)

Rhoden, Alyssa Rose

Europa's surface displays a complex history of tectonic activity, much of which has been linked to tidal stress caused by Europa's eccentric orbit and possibly non-synchronous rotation of the ice shell. Cycloids are arcuate features thought to have formed in response to tidal normal stress while strike-slip motion along preexisting faults has been attributed to tidal shear stress. Tectonic features thus provide constraints on the rotational parameters that govern tidal stress, and can help us develop an understanding of the tidal-tectonic processes operating on ice covered ocean moons. In the first part of this work (Chapter 3), I test tidal models that include obliquity, fast precession, stress due to non-synchronous rotation (NSR), and physical libration by comparing how well each model reproduces observed cycloids. To do this, I have designed and implemented an automated parameter-searching algorithm that relies on a quantitative measure of fit quality to identify the best fits to observed cycloids. I apply statistical techniques to determine the tidal model best supported by the data and constrain the values of Europa's rotational parameters. Cycloids indicate a time-varying obliquity of about 1° and a physical libration in phase with the eccentricity libration, with amplitude >1°. To obtain good fits, cycloids must be translated in longitude, which implies non-synchronous rotation of the icy shell. However, stress from NSR is not well-supported, indicating that the rotation rate is slow enough that these stresses relax. I build upon the results of cycloid modeling in the second section by applying calculations of tidal stress that include obliquity to the formation of strike-slip faults. I predict the slip directions of faults with the standard formation model---tidal walking (Chapter 5)---and with a new mechanical model I have developed, called shell tectonics (Chapter 6). The shell tectonics model incorporates linear elasticity to determine slip and stress release on faults and uses a Coulomb failure criterion. Both of these models can be used to predict the direction of net displacement along faults. Until now, the tidal walking model has been the only model that reproduces the observed global pattern of strike-slip displacement; the shell tectonics model incorporates a more physical treatment of fault mechanics and reproduces this global pattern. Both models fit the regional patterns of observed strike-slip faults better when a small obliquity is incorporated into calculations of tidal stresses. Shell tectonics is also distinct from tidal walking in that it calculates the relative growth rates of displacements in addition to net slip direction. Examining these growth rates, I find that certain azimuths and locations develop offsets more quickly than others. Because faults with larger offsets are easier to identify, this may explain why observed faults cluster in azimuth in many regions. The growth rates also allow for a more sophisticated statistical comparison between the predictions and observations. Although the slip directions of >75% of faults are correctly predicted using shell tectonics and 1° of obliquity, a portion of these faults could be fit equally well with a random model. Examining these faults in more detail has revealed a region of Europa in which strike-slip faults likely formed through local extensional and compressional deformation rather than as a result of tidal shear stress. This approach enables a better understanding of the tectonic record, which has implications on Europa's rotation history.

Modelling studies in aqueous solution of lanthanide (III) chelates designed for nuclear magnetic resonance biomedical applications

NASA Astrophysics Data System (ADS)

Henriques, E. S.; Geraldes, C. F. G. C.; Ramos, M. J.

Molecular dynamics simulations and complementary modelling studies have been carried out for the [Gd(DOTA)·(H2O)]- and [Tm(DOTP)]5- chelates in aqueous media, to provide a better understanding of several structural and dynamical properties of these versatile nuclear magnetic resonance (NMR) probes, including coordination shells and corresponding water exchange mechanisms, and interactions of these complexes with alkali metal ions. This knowledge is of key importance in the areas of 1H relaxation and shift reagents for NMR applications in medical diagnosis. A new refinement of our own previously developed set of parameters for these Ln(III) chelates has been used, and is reported here. Calculations of water mean residence times suggest a reassessment of the characterization of the chelates' second coordination shell, one where the simple spherical distribution model is discarded in favour of a more detailed approach. Na+ probe interaction maps are in good agreement with the available site location predictions derived from 23Na NMR shifts.

Surface functionalization of magnetite nanoparticle: A new approach using condensation of alkoxysilanes

NASA Astrophysics Data System (ADS)

Rodriguez, A. F. R.; Costa, T. P.; Bini, R. A.; Faria, F. S. E. D. V.; Azevedo, R. B.; Jafelicci, M.; Coaquira, J. A. H.; Martínez, M. A. R.; Mantilla, J. C.; Marques, R. F. C.; Morais, P. C.

2017-09-01

In this study we report on successful production of two samples (BR15 and BR16) comprising magnetite (Fe3O4) nanoparticles ( 10 nm) surface-functionalized via hydrolysis and condensation of alkoxysilane agents, namely 3-aminopropyl-trimethoxisilane (APTS) and N-propyl-trimethoxisilane (NPTS). The as-produced samples were characterized using transmission electron microscopy (TEM), x-ray diffraction (XRD), magnetization measurements (5 K and 300 K hysteresis cycles and zero field-cooled/field-cooled measurements), and Mössbauer spectroscopy (77 and 297 K). The Mössbauer data supported the model picture of a core-shell magnetite-based system. This material system shows shell properties influenced by the surface-coating design, either APTS-coated (BR15) or APTS+NPTS-coated (sample BR16). Analyses of the Mössbauer spectra indicates that the APTS-coated sample presents Fe(III)-rich core and Fe(II)-rich shell with strong hyperfine field; whereas, the APTS+NPTS-coated sample leads to a mixture of two main nanostructures, one essentially surface-terminated with APTS whereas the other surface-terminated with NPTS, both presenting weak hyperfine fields compared with the single surface-coated sample. Magnetization measurements support the core-shell picture built from the analyses of the Mössbauer data. Our findings emphasize the capability of the Mössbauer spectroscopy in assessing subtle differences in surface-functionalized iron-based core-shell nanostructures.

Phase Behavior of Salt-Free Polyelectrolyte Gel-Surfactant Systems.

PubMed

Andersson, Martin; Hansson, Per

2017-06-22

Ionic surfactants tend to collapse the outer parts of polyelectrolyte gels, forming shells that can be used to encapsulate other species including protein and peptide drugs. In this paper, the aqueous phase behavior of covalently cross-linked polyacrylate networks containing sodium ions and dodecyltrimethylammonium ions as counterions is investigated by means of swelling isotherms, dye staining, small-angle X-ray scattering, and confocal Raman spectroscopy. The equilibrium state is approached by letting the networks absorb pure water. With an increasing fraction of surfactant ions, the state of the water-saturated gels is found to change from being swollen and monophasic, via multiphasic states, to collapsed and monophasic. The multiphasic gels have a swollen, micelle-lean core surrounded by a collapsed, micelle-rich shell, or a collapsed phase forming a spheroidal inner shell separating two micelle-lean parts. It is shown that the transition between monophasic and core-shell states can be induced by variation of the osmotic pressure and variation of the charge of the micelles by forming mixed micelles with the nonionic surfactant octaethyleneglycol monododecylether. The experimental data are compared with theoretical predictions of a model derived earlier. In the calculations, the collapsed shell is assumed to be homogeneous, an approximation introduced here and shown to be excellent for a wide range of compositions. The theoretical results highlight the electrostatic and hydrophobic driving forces behind phase separation.

A compact circumstellar shell as the source of high-velocity features in SN 2011fe

NASA Astrophysics Data System (ADS)

Mulligan, Brian W.; Wheeler, J. Craig

2018-05-01

High-velocity features (HVFs), especially of Ca II, are frequently seen in Type Ia supernova observed prior to B-band maximum (Bmax). These HVFs evolve in velocity from more than 25 000 km s-1, in the days after first light, to about 18 000 km s-1 near Bmax. To recreate the evolution of the Ca II near-infrared triplet (CaNIR) HVFs in SN 2011fe, we consider the interaction between a model Type Ia supernova and compact circumstellar shells with masses between 0.003 and 0.012 M⊙. We fit the observed CaNIR feature using synthetic spectra generated from the models using SYN++. The CaNIR feature is better explained by the supernova model interacting with a shell than the model without a shell, with a shell of mass 0.005 M⊙ tending to be better fitting than the other shells. The evolution of the optical depth of CaNIR suggests that the ionization state of calcium within the ejecta and shell is not constant. We discuss the method used to measure the observed velocity of CaNIR and other features and conclude that HVFs or other components can be falsely identified. We briefly discuss the possible origin of the shells and the implications for the progenitor system of the supernova.

Inner-shell radiation from wire array implosions on the Zebra generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouart, N. D.; Giuliani, J. L.; Dasgupta, A.

2014-03-15

Implosions of brass wire arrays on Zebra have produced L-shell radiation as well as inner-shell Kα and Kβ transitions. The L-shell radiation comes from ionization stages around the Ne-like charge state that is largely populated by a thermal electron energy distribution function, while the K-shell photons are a result of high-energy electrons ionizing or exciting an inner-shell (1s) electron from ionization stages around Ne-like. The K- and L-shell radiations were captured using two time-gated and two axially resolved time-integrated spectrometers. The electron beam was measured using a Faraday cup. A multi-zone non-local thermodynamic equilibrium pinch model with radiation transport ismore » used to model the x-ray emission from experiments for the purpose of obtaining plasma conditions. These plasma conditions are used to discuss some properties of the electron beam generated by runaway electrons. A simple model for runaway electrons is examined to produce the Kα radiation, but it is found to be insufficient.« less

Titanate-silica mesostructured nanocables: synthesis, structural analysis and biomedical applications

NASA Astrophysics Data System (ADS)

Su, Yonghua; Qiao, Shizhang; Yang, Huagui; Yang, Chen; Jin, Yonggang; Stahr, Frances; Sheng, Jiayu; Cheng, Lina; Ling, Changquan; Qing Lu, Gao

2010-02-01

1D hierarchical composite mesostructures of titanate and silica were synthesized via an interfacial surfactant templating approach. Such mesostructures have complex core-shell architectures consisting of single-crystalline H2Ti3O7 nanobelts inside the ordered mesoporous SiO2 shell, which are nontoxic and highly biocompatible. The overall diameter of as-prepared 1D hierarchical composite mesostructures is only approx. 34.2 nm with a length over 500 nm on average. A model to explain the formation mechanism of these mesostructures has been proposed; the negatively charged surface of H2Ti3O7 nanobelts controls the formation of the octadecyltrimethylammonium bromide (C18TAB) bilayer, which in turn regulates the cooperative self-assembly of silica and C18TAB complex micelles on the interface to produce a mesoporous silica shell. More importantly, the application of synthesized mesostructured nanocables as anticancer drug reservoirs has also been explored, which indicates that the membranes containing these mesoporous nanocables have a great potential to be used as transdermal drug delivery systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior formore » strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.« less

Semiclassical S-matrix for black holes

DOE PAGES

Bezrukov, Fedor; Levkov, Dmitry; Sibiryakov, Sergey

2015-12-01

In this study, we propose a semiclassical method to calculate S-matrix elements for two-stage gravitational transitions involving matter collapse into a black hole and evaporation of the latter. The method consistently incorporates back-reaction of the collapsing and emitted quanta on the metric. We illustrate the method in several toy models describing spherical self-gravitating shells in asymptotically flat and AdS space-times. We find that electrically neutral shells reflect via the above collapse-evaporation process with probability exp(–B), where B is the Bekenstein-Hawking entropy of the intermediate black hole. This is consistent with interpretation of exp(B) as the number of black hole states.more » The same expression for the probability is obtained in the case of charged shells if one takes into account instability of the Cauchy horizon of the intermediate Reissner-Nordström black hole. As a result, our semiclassical method opens a new systematic approach to the gravitational S-matrix in the non-perturbative regime.« less

A model for large amplitude oscillations of coated bubbles accounting for buckling and rupture

NASA Astrophysics Data System (ADS)

Marmottant, Philippe; van der Meer, Sander; Emmer, Marcia; Versluis, Michel; de Jong, Nico; Hilgenfeldt, Sascha; Lohse, Detlef

2005-12-01

We present a model applicable to ultrasound contrast agent bubbles that takes into account the physical properties of a lipid monolayer coating on a gas microbubble. Three parameters describe the properties of the shell: a buckling radius, the compressibility of the shell, and a break-up shell tension. The model presents an original non-linear behavior at large amplitude oscillations, termed compression-only, induced by the buckling of the lipid monolayer. This prediction is validated by experimental recordings with the high-speed camera Brandaris 128, operated at several millions of frames per second. The effect of aging, or the resultant of repeated acoustic pressure pulses on bubbles, is predicted by the model. It corrects a flaw in the shell elasticity term previously used in the dynamical equation for coated bubbles. The break-up is modeled by a critical shell tension above which gas is directly exposed to water.

Modeling Type IIn Supernovae: Understanding How Shock Development Effects Light Curves Properties

NASA Astrophysics Data System (ADS)

De La Rosa, Janie

2016-06-01

Type IIn supernovae are produced when massive stars experience dramatic mass loss phases caused by opacity edges or violent explosions. Violent mass ejections occur quite often just prior to the collapse of the star. If the final episode happens just before collapse, the outward ejecta is sufficiently dense to alter the supernova light-curve, both by absorbing the initial supernova light and producing emission when the supernova shock hits the ejecta. Initially, the ejecta is driven by shock progating through the interior of the star, and eventually expands through the circumstellar medium, forming a cold dense shell. As the shock wave approaches the shell, there is an increase in UV and optical radiation at the location of the shock breakout. We have developed a suite of simple semi-analytical models in order to understand the relationship between our observations and the properties of the expanding SN ejecta. When we compare Type IIn observations to a set of modeled SNe, we begin to see the influence of initial explosion conditions on early UV light curve properties such as peak luminosities and decay rate.The fast rise and decay corresponds to the models representing a photosphere moving through the envelope, while the modeled light curves with a slower rise and decay rate are powered by 56Ni decay. However, in both of these cases, models that matched the luminosity were unable to match the low radii from the blackbody models. The effect of shock heating as the supernova material blasts through the circumstellar material can drastically alter the temperature and position of the photosphere. The new set of models redefine the initial modeling conditions to incorporate an outer shell-like structure, and include late-time shock heating from shocks produced as the supernova ejecta travels through the inhomogeneous circumstellar medium.

I. Episodic volcanism of tidally heated satellites with application to Io. II. Polar wander of a synchronously rotating satellite with application to Europa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ojakangas, G.W.

1988-01-01

Two examples of planetary bodies that may have coupled thermal and dynamical evolutions are investigated. The work is presented in three individual papers. The first example is that of a tidally heated satellite in an orbital resonance, for which the tidal dissipation rate is a strongly increasing function of the internal temperature. For such a satellite, a feedback mechanism exists between the orbital and thermal energies, which may lead to periodic variations in tidal heating within the satellite and its orbital eccentricity. A simple model of this mechanisms is presented in the first paper and is applied specifically to Io.more » The second examples is that of an ice shell on Europa, which is decoupled from the silicate core by a layer of liquid water. In the second paper, the spatially varying thickness that such a shell would have in thermal equilibrium with tidal dissipation within it, surface solar insolation and heat flow from the core is calculation for reasonable rheological laws for ice. The contribution of these variations in ice thickness to Europa's inertia tensor is estimated, and the implications for nonsynchronous rotation of Europa are discussed. In the third paper, a detailed dynamical model is developed, which demonstrates that such a shell may exhibit large-scale polar wander as it approaches thermal equilibrium, because of the destabilizing effect of the variations in ice thickness on the inertia tensor of the shell.« less

Updating the Jovian Proton Radiation Environment - 2015

NASA Technical Reports Server (NTRS)

Garrett, Henry; Martinez-Sierra, Luz Maria; Evans, Robin

2015-01-01

Since publication in 1983 by N. Divine and H. Garrett, the Jet Propulsion Laboratory's plasma and radiation models have been the design standard for NASA's missions to Jupiter. These models consist of representations of the cold plasma and electrons, the warm and auroral electrons and protons, and the radiation environment (electron, proton, and heavy ions). To date, however, the high-energy proton model has been limited to an L-shell of 12. With the requirement to compute the effects of the high energy protons and other heavy ions on the proposed Europa mission, the extension of the high energy proton model from approximately 12 L-shell to approximately 50 L-shell has become necessary. In particular, a model of the proton environment over that range is required to estimate radiation effects on the solar arrays for the mission. This study describes both the steps taken to extend the original Divine proton model out to an approximately 50 L-shell and the resulting model developed to accomplish that goal. In addition to hydrogen, the oxygen, sulfur, and helium heavy ion environments have also been added between approximately 6 L-shell and approximately 50 L-shell. Finally, selected examples of the model's predictions are presented to illustrate the uses of the tool.

Controlled Formation of Radial Core-Shell Si/Metal Silicide Crystalline Heterostructures.

PubMed

Kosloff, Alon; Granot, Eran; Barkay, Zahava; Patolsky, Fernando

2018-01-10

The highly controlled formation of "radial" silicon/NiSi  core-shell nanowire heterostructures has been demonstrated for the first time. Here, we investigated the "radial" diffusion of nickel atoms into crystalline nanoscale silicon pillar 11 cores, followed by nickel silicide phase formation and the creation of a well-defined shell structure. The described approach is based on a two-step thermal process, which involves metal diffusion at low temperatures in the range of 200-400 °C, followed by a thermal curing step at a higher temperature of 400 °C. In-depth crystallographic analysis was performed by nanosectioning the resulting silicide-shelled silicon nanopillar heterostructures, giving us the ability to study in detail the newly formed silicide shells. Remarkably, it was observed that the resulting silicide shell thickness has a self-limiting behavior, and can be tightly controlled by the modulation of the initial diffusion-step temperature. In addition, electrical measurements of the core-shell structures revealed that the resulting shells can serve as an embedded conductive layer in future optoelectronic applications. This research provides a broad insight into the Ni silicide "radial" diffusion process at the nanoscale regime, and offers a simple approach to form thickness-controlled metal silicide shells in the range of 5-100 nm around semiconductor nanowire core structures, regardless the diameter of the nanowire cores. These high quality Si/NiSi core-shell nanowire structures will be applied in the near future as building blocks for the creation of utrathin highly conductive optically transparent top electrodes, over vertical nanopillars-based solar cell devices, which may subsequently lead to significant performance improvements of these devices in terms of charge collection and reduced recombination.

Effects of Combined Loads on the Nonlinear Response and Residual Strength of Damaged Stiffened Shells

NASA Technical Reports Server (NTRS)

Starnes, James H., Jr.; Rose, Cheryl A.; Rankin, Charles C.

1996-01-01

The results of an analytical study of the nonlinear response of stiffened fuselage shells with long cracks are presented. The shells are modeled with a hierarchical modeling strategy and analyzed with a nonlinear shell analysis code that maintains the shell in a nonlinear equilibrium state while the crack is grown. The analysis accurately accounts for global and local structural response phenomena. Results are presented for various combinations of internal pressure and mechanical loads, and the effects of crack orientation on the shell response are described. The effects of combined loading conditions and the effects of varying structural parameters on the stress-intensity factors associated with a crack are presented.

Flexible configuration-interaction shell-model many-body solver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Calvin W.; Ormand, W. Erich; McElvain, Kenneth S.

BIGSTICK Is a flexible configuration-Interaction open-source shell-model code for the many-fermion problem In a shell model (occupation representation) framework. BIGSTICK can generate energy spectra, static and transition one-body densities, and expectation values of scalar operators. Using the built-in Lanczos algorithm one can compute transition probabflity distributions and decompose wave functions into components defined by group theory.

The Vibration Analysis of Tube Bundles Induced by Fluid Elastic Excitation in Shell Side of Heat Exchanger

NASA Astrophysics Data System (ADS)

Bao, Minle; Wang, Lu; Li, Wenyao; Gao, Tianze

2017-09-01

Fluid elastic excitation in shell side of heat exchanger was deduced theoretically in this paper. Model foundation was completed by using Pro / Engineer software. The finite element model was constructed and imported into the FLUENT module. The flow field simulation adopted the dynamic mesh model, RNG k-ε model and no-slip boundary conditions. Analysing different positions vibration of tube bundles by selecting three regions in shell side of heat exchanger. The results show that heat exchanger tube bundles at the inlet of the shell side are more likely to be failure due to fluid induced vibration.

An improved understanding of the Alaska coastal current: The application of a bivalve growth-temperature model to reconstruct freshwater-influenced paleoenvironments

USGS Publications Warehouse

Hallmann, N.; Schone, B.R.; Irvine, G.V.; Burchell, M.; Cokelet, E.D.; Hilton, M.R.

2011-01-01

Shells of intertidal bivalve mollusks contain sub-seasonally to interannually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of ???1.3 ??C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with ??18Oshell values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4 ?? 1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 988-1447 cal yr BP was characterized by ???1-2 ??C colder and much drier (2-5 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 599-1014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 ??C temperature decrease during summers and 1-2 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growth-temperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time. ?? 2011 SEPM (Society for Sedimentary Geology).

An Efficient Analysis Methodology for Fluted-Core Composite Structures

NASA Technical Reports Server (NTRS)

Oremont, Leonard; Schultz, Marc R.

2012-01-01

The primary loading condition in launch-vehicle barrel sections is axial compression, and it is therefore important to understand the compression behavior of any structures, structural concepts, and materials considered in launch-vehicle designs. This understanding will necessarily come from a combination of test and analysis. However, certain potentially beneficial structures and structural concepts do not lend themselves to commonly used simplified analysis methods, and therefore innovative analysis methodologies must be developed if these structures and structural concepts are to be considered. This paper discusses such an analysis technique for the fluted-core sandwich composite structural concept. The presented technique is based on commercially available finite-element codes, and uses shell elements to capture behavior that would normally require solid elements to capture the detailed mechanical response of the structure. The shell thicknesses and offsets using this analysis technique are parameterized, and the parameters are adjusted through a heuristic procedure until this model matches the mechanical behavior of a more detailed shell-and-solid model. Additionally, the detailed shell-and-solid model can be strategically placed in a larger, global shell-only model to capture important local behavior. Comparisons between shell-only models, experiments, and more detailed shell-and-solid models show excellent agreement. The discussed analysis methodology, though only discussed in the context of fluted-core composites, is widely applicable to other concepts.

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.

Fragmentation of protostars dust shells at the Hayashi stage

NASA Astrophysics Data System (ADS)

Abdulmyanov, T. R.

2017-09-01

The aim of this study is to determine the density variations of a protostars dust shells at the Hayashi stage. The simplified model of the density wave perturbations are obtained on the base hydrodynamic equations. According to this model, the fragmentation of dust shells may occur at the stage of slow compression of protostar. Using the solution of the wave equation, the 3-D profiles of the density of the dust shell are defined.

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.

Cohesive Elements for Shells

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.

Specific pathways for the incorporation of dissolved barium and molybdenum into the bivalve shell: an isotopic tracer approach in the juvenile Great Scallop (Pecten maximus).

PubMed

Tabouret, Hélène; Pomerleau, Sébastien; Jolivet, Aurélie; Pécheyran, Christophe; Riso, Ricardo; Thébault, Julien; Chauvaud, Laurent; Amouroux, David

2012-07-01

Dissolved barium and molybdenum incorporation in the calcite shell was investigated in the Great Scallop Pecten maximus. Sixty six individuals were exposed for 16 days to two successive dissolved Ba and Mo concentrations accurately differentiated by two different isotopic enrichments (⁹⁷Mo, ⁹⁵Mo; ¹³⁵Ba, ¹³⁷Ba). Soft tissue and shell isotopic composition were determined respectively by quantitative ICP-MS (Inductively Coupled Plasma Mass Spectrometer) and laser ablation--ICP-MS. Results from Ba enrichment indicate the direct incorporation of dissolved Ba into the shell in proportion to the levels in the water in which they grew with a 6-8 day delay. The low spike contributions and the low partition coefficient (D(Mo) = 0.0049 ± 0.0013), show that neither the soft tissue nor the shell were significantly sensitive to Mo enrichment. These results eliminate direct Mo shell enrichment by the dissolved phase, and favour a trophic uptake that will be investigated using the successive isotopic enrichment approach developed in this study. Copyright © 2012 Elsevier Ltd. All rights reserved.

Acoustical contribution calculation and analysis of compressor shell based on acoustic transfer vector method

NASA Astrophysics Data System (ADS)

Chen, Xiaol; Guo, Bei; Tuo, Jinliang; Zhou, Ruixin; Lu, Yang

2017-08-01

Nowadays, people are paying more and more attention to the noise reduction of household refrigerator compressor. This paper established a sound field bounded by compressor shell and ISO3744 standard field points. The Acoustic Transfer Vector (ATV) in the sound field radiated by a refrigerator compressor shell were calculated which fits the test result preferably. Then the compressor shell surface is divided into several parts. Based on Acoustic Transfer Vector approach, the sound pressure contribution to the field points and the sound power contribution to the sound field of each part were calculated. To obtain the noise radiation in the sound field, the sound pressure cloud charts were analyzed, and the contribution curves in different frequency of each part were acquired. Meanwhile, the sound power contribution of each part in different frequency was analyzed, to ensure those parts where contributes larger sound power. Through the analysis of acoustic contribution, those parts where radiate larger noise on the compressor shell were determined. This paper provides a credible and effective approach on the structure optimal design of refrigerator compressor shell, which is meaningful in the noise and vibration reduction.

Development of hydrogel TentaGel shell-core beads for ultrahigh throughput solution-phase screening of encoded OBOC combinatorial small molecule libraries.

PubMed

Baek, Hyoung Gee; Liu, Ruiwu; Lam, Kit S

2009-01-01

The one-bead one-compound (OBOC) combinatorial library method enables the rapid generation and screening of millions of discrete chemical compounds on beads. Most of the OBOC screening methods require the library compounds to remain tethered to the bead during screening process. Methods have also been developed to release library compounds from immobilized beads for in situ solution phase or "lawn" assays. However, this latter approach, while extremely powerful, is severely limited by the lack of suitable solid supports for such assays. Here, we report on the development of a novel hydrogel TentaGel shell-core (HTSC) bead in which hydrogel is grafted onto the polystyrene-based TentaGel (TG) bead as an outer shell (5-80 mum thick) via free radical surface-initiated polymerization. This novel shell-core bilayer resin enables the preparation of encoded OBOC combinatorial small molecule libraries, such that the library compounds reside on the highly hydrophilic outer layer and the coding tags reside in the polystyrene-based TG core. Using fluorescein as a model small molecule compound, we have demonstrated that fluorescein molecules that have been linked covalently to the hydrogel shell via a disulfide bond could readily diffuse out of the hydrogel layer into the bead surrounding after reduction with dithiothreitol. In contrast, under identical condition, the released fluorescein molecules remained bound to unmodified TG bead. We have prepared an encoded OBOC small molecule library on the novel shell-core beads and demonstrated that the beads can be readily decoded.

Mathematical Modeling of Electrodynamics Near the Surface of Earth and Planetary Water Worlds

NASA Technical Reports Server (NTRS)

Tyler, Robert H.

2017-01-01

An interesting feature of planetary bodies with hydrospheres is the presence of an electrically conducting shell near the global surface. This conducting shell may typically lie between relatively insulating rock, ice, or atmosphere, creating a strong constraint on the flow of large-scale electric currents. All or parts of the shell may be in fluid motion relative to main components of the rotating planetary magnetic field (as well as the magnetic fields due to external bodies), creating motionally-induced electric currents that would not otherwise be present. As such, one may expect distinguishing features in the types of electrodynamic processes that occur, as well as an opportunity for imposing specialized mathematical methods that efficiently address this class of application. The purpose of this paper is to present and discuss such specialized methods. Specifically, thin-shell approximations for both the electrodynamics and fluid dynamics are combined to derive simplified mathematical formulations describing the behavior of these electric currents as well as their associated electric and magnetic fields. These simplified formulae allow analytical solutions featuring distinct aspects of the thin-shell electrodynamics in idealized cases. A highly efficient numerical method is also presented that is useful for calculations under inhomogeneous parameter distributions. Finally, the advantages as well as limitations in using this mathematical approach are evaluated. This evaluation is presented primarily for the generic case of bodies with water worlds or other thin spherical conducting shells. More specific discussion is given for the case of Earth, but also Europa and other satellites with suspected oceans.

Ethanol Gas Detection Using a Yolk-Shell (Core-Shell) α-Fe2O3 Nanospheres as Sensing Material.

PubMed

Wang, LiLi; Lou, Zheng; Deng, Jianan; Zhang, Rui; Zhang, Tong

2015-06-17

Three-dimensional (3D) nanostructures of α-Fe2O3 materials, including both hollow sphere-shaped and yolk-shell (core-shell)-shaped, have been successfully synthesized via an environmentally friendly hydrothermal approach. By expertly adjusting the reaction time, the solid, hollow, and yolk-shell shaped α-Fe2O3 can be selectively synthesized. Yolk-shell α-Fe2O3 nanospheres display outer diameters of 350 nm, and the interstitial hollow spaces layer is intimately sandwiched between the inner and outer shell of α-Fe2O3 nanostructures. The possible growth mechanism of the yolk-shell nanostructure is proposed. The results showed that the well-defined bilayer interface effectively enhanced the sensing performance of the α-Fe2O3 nanostructures (i.e., yolk-shell α-Fe2O3@α-Fe2O3), owing predominantly to the unique nanostructure, thus facilitated the transport rate and augmented the adsorption quantity of the target gas molecule under gas detection.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiOx core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M.; Lu, Ming-Chang; Chueh, Yu-Lun

2014-04-01

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants. Electronic supplementary information (ESI) available: Detailed experimental results are included for the following: SEM images of the HITEC molten salt with and without a mixture of Sn/SiOx core-shell NPs; statistical diameter distribution of pure Sn and Sn/SiOx core-shell NPs; the HAADF image and EDS linescan profile of a Sn/SiOx core-shell NP; XRD analysis for Sn NPs annealing at different heating temperatures; the XRD spectra of Sn/SiOx core-shell NPs before and after RTA for the shell protection test. See DOI: 10.1039/c3nr06810b

Single-particle and collective motion in unbound deformed 39Mg

NASA Astrophysics Data System (ADS)

Fossez, K.; Rotureau, J.; Michel, N.; Liu, Quan; Nazarewicz, W.

2016-11-01

Background: Deformed neutron-rich magnesium isotopes constitute a fascinating territory where the interplay between collective rotation and single-particle motion is strongly affected by the neutron continuum. The unbound f p -shell nucleus 39Mg is an ideal candidate to study this interplay. Purpose: In this work, we predict the properties of low-lying resonant states of 39Mg, using a suite of realistic theoretical approaches rooted in the open quantum system framework. Method: To describe the spectrum and decay modes of 39Mg we use the conventional shell model, Gamow shell model, resonating group method, density matrix renormalization group method, and the nonadiabatic particle-plus-rotor model formulated in the Berggren basis. Results: The unbound ground state of 39Mg is predicted to be either a Jπ=7/2 - state or a 3/2 - state. A narrow Jπ=7/2 - ground-state candidate exhibits a resonant structure reminiscent of that of its one-neutron halo neighbor 37Mg, which is dominated by the f7 /2 partial wave at short distances and a p3 /2 component at large distances. A Jπ=3/2 - ground-state candidate is favored by the large deformation of the system. It can be associated with the 1/2 -[321 ] Nilsson orbital dominated by the ℓ =1 wave; hence its predicted width is large. The excited Jπ=1/2 - and 5 /2- states are expected to be broad resonances, while the Jπ=9/2 - and 11/2 - members of the ground-state rotational band are predicted to have very small neutron decay widths. Conclusion: We demonstrate that the subtle interplay between deformation, shell structure, and continuum coupling can result in a variety of excitations in an unbound nucleus just outside the neutron drip line.

Shell shock at Queen Square: Lewis Yealland 100 years on

PubMed Central

Jones, Edgar; Lees, Andrew J.

2013-01-01

This article reviews the treatment of functional neurological symptoms during World War I by Lewis Yealland at the National Hospital for the Paralysed and Epileptic in London. Yealland was among the first doctors in Britain to incorporate electricity in the systematic treatment of shell shock. Our analysis is based on the original case records of his treatment of 196 soldiers with functional motor and sensory symptoms, functional seizures and somatoform disorders. Yealland’s treatment approach integrated peripheral and central electrical stimulation with a variety of other—psychological and physical—interventions. A combination of electrical stimulation of affected muscles with suggestion of imminent improvement was the hallmark of his approach. Although his reported success rates were high, Yealland conducted no formal follow-up. Many of the principles of his treatment, including the emphasis on suggestion, demonstration of preserved function and the communication of a physiological illness model, are encountered in current therapeutic approaches to functional motor and sensory symptoms. Yealland has been attacked for his use of electrical stimulation and harsh disciplinary procedures in popular and scientific literature during and after World War I. This criticism reflects changing views on patient autonomy and the social role of doctors and directly impacts on current debates on ethical justification of suggestive therapies. We argue that knowledge of the historical approaches to diagnosis and management of functional neurological syndromes can inform both aetiological models and treatment concepts for these challenging conditions. PMID:23384604

Polarization effects on spectra of spherical core/shell nanostructures: Perturbation theory against finite difference approach

NASA Astrophysics Data System (ADS)

Ibral, Asmaa; Zouitine, Asmaa; Assaid, El Mahdi; El Achouby, Hicham; Feddi, El Mustapha; Dujardin, Francis

2015-02-01

Poisson equation is solved analytically in the case of a point charge placed anywhere in a spherical core/shell nanostructure, immersed in aqueous or organic solution or embedded in semiconducting or insulating matrix. Conduction and valence band-edge alignments between core and shell are described by finite height barriers. Influence of polarization charges induced at the surfaces where two adjacent materials meet is taken into account. Original expressions of electrostatic potential created everywhere in the space by a source point charge are derived. Expressions of self-polarization potential describing the interaction of a point charge with its own image-charge are deduced. Contributions of double dielectric constant mismatch to electron and hole ground state energies as well as nanostructure effective gap are calculated via first order perturbation theory and also by finite difference approach. Dependencies of electron, hole and gap energies against core to shell radii ratio are determined in the case of ZnS/CdSe core/shell nanostructure immersed in water or in toluene. It appears that finite difference approach is more efficient than first order perturbation method and that the effect of polarization charge may in no case be neglected as its contribution can reach a significant proportion of the value of nanostructure gap.

Fabrication and Characterization of Novel Electrothermal Self-Healing Microcapsules with Graphene/Polymer Hybrid Shells for Bitumenious Material.

PubMed

Wang, Xinyu; Guo, Yandong; Su, Junfeng; Zhang, Xiaolong; Wang, Yingyuan; Tan, Yiqiu

2018-06-09

Self-healing bituminous material has been a hot research topic in self-healing materials, and this smart self-healing approach is a promising a revolution in pavement material technology. Bitumen has a self-healing naturality relating to temperature, healing time, and aging degree. To date, heat induction and microencapsulation rejuvenator are two feasible approaches, which have been put into real applications. However, both methods have disadvantages limiting their practical results and efficiency. It will be an ideal method combining the advantages and avoiding the disadvantages of the above two methods at the same time. The aim of this work was to synthesize and characterize electrothermal self-healing microcapsules containing bituminous rejuvenator with graphene/organic nanohybrid structure shells. The microcapsules owned electric conductivity capability because of the advent of graphene, and realized the self-healing through the two approaches of heat induction and rejuvenation. The microcapsule shells were fabricated using a strength hexamethoxymethylmelamine (HMMM) resin and graphene by two-step hybrid polymerization. Experimental tests were carried out to character the morphology, integrity, and shell structure. It was found that the electric charge balance determined the graphene/HMMM microstructure. The graphene content in shells could not be greatly increased under an electrostatic balance in emulsion. X-ray photoelectron spectroscopy (XPS), Energy dispersive spectrometer (EDS), Transmission electron microscope (TEM) and Atomic force microscopy (AFM) results indicated that the graphene had deposited on shells. TGA/DTG tests implied that the thermal decomposition temperature of microcapsules with graphene had increased to about 350 °C. The thermal conductivity of microcapsules had been sharply increased to about 8.0 W/m²·K with 2.0 wt % graphene in shells. At the same time, electrical resistivity of microcapsules/bitumen samples had a decrease with more graphene in bitumen.

Controlling flexible structures with second order actuator dynamics

NASA Technical Reports Server (NTRS)

Inman, Daniel J.; Umland, Jeffrey W.; Bellos, John

1989-01-01

The control of flexible structures for those systems with actuators that are modeled by second order dynamics is examined. Two modeling approaches are investigated. First a stability and performance analysis is performed using a low order finite dimensional model of the structure. Secondly, a continuum model of the flexible structure to be controlled, coupled with lumped parameter second order dynamic models of the actuators performing the control is used. This model is appropriate in the modeling of the control of a flexible panel by proof-mass actuators as well as other beam, plate and shell like structural numbers. The model is verified with experimental measurements.

Weak field equations and generalized FRW cosmology on the tangent Lorentz bundle

NASA Astrophysics Data System (ADS)

Triantafyllopoulos, A.; Stavrinos, P. C.

2018-04-01

We study field equations for a weak anisotropic model on the tangent Lorentz bundle TM of a spacetime manifold. A geometrical extension of general relativity (GR) is considered by introducing the concept of local anisotropy, i.e. a direct dependence of geometrical quantities on observer 4‑velocity. In this approach, we consider a metric on TM as the sum of an h-Riemannian metric structure and a weak anisotropic perturbation, field equations with extra terms are obtained for this model. As well, extended Raychaudhuri equations are studied in the framework of Finsler-like extensions. Canonical momentum and mass-shell equation are also generalized in relation to their GR counterparts. Quantization of the mass-shell equation leads to a generalization of the Klein–Gordon equation and dispersion relation for a scalar field. In this model the accelerated expansion of the universe can be attributed to the geometry itself. A cosmological bounce is modeled with the introduction of an anisotropic scalar field. Also, the electromagnetic field equations are directly incorporated in this framework.

Shell models of magnetohydrodynamic turbulence

NASA Astrophysics Data System (ADS)

Plunian, Franck; Stepanov, Rodion; Frick, Peter

2013-02-01

Shell models of hydrodynamic turbulence originated in the seventies. Their main aim was to describe the statistics of homogeneous and isotropic turbulence in spectral space, using a simple set of ordinary differential equations. In the eighties, shell models of magnetohydrodynamic (MHD) turbulence emerged based on the same principles as their hydrodynamic counter-part but also incorporating interactions between magnetic and velocity fields. In recent years, significant improvements have been made such as the inclusion of non-local interactions and appropriate definitions for helicities. Though shell models cannot account for the spatial complexity of MHD turbulence, their dynamics are not over simplified and do reflect those of real MHD turbulence including intermittency or chaotic reversals of large-scale modes. Furthermore, these models use realistic values for dimensionless parameters (high kinetic and magnetic Reynolds numbers, low or high magnetic Prandtl number) allowing extended inertial range and accurate dissipation rate. Using modern computers it is difficult to attain an inertial range of three decades with direct numerical simulations, whereas eight are possible using shell models. In this review we set up a general mathematical framework allowing the description of any MHD shell model. The variety of the latter, with their advantages and weaknesses, is introduced. Finally we consider a number of applications, dealing with free-decaying MHD turbulence, dynamo action, Alfvén waves and the Hall effect.

Interface engineered ferrite@ferroelectric core-shell nanostructures: A facile approach to impart superior magneto-electric coupling

NASA Astrophysics Data System (ADS)

Abraham, Ann Rose; Raneesh, B.; Das, Dipankar; Oluwafemi, Oluwatobi Samuel; Thomas, Sabu; Kalarikkal, Nandakumar

2018-04-01

The electric field control of magnetism in multiferroics is attractive for the realization of ultra-fast and miniaturized low power device applications like nonvolatile memories. Room temperature hybrid multiferroic heterostructures with core-shell (0-0) architecture (ferrite core and ferroelectric shell) were developed via a two-step method. High-Resolution Transmission Electron Microscopy (HRTEM) images confirm the core-shell structure. The temperature dependant magnetization measurements and Mossbauer spectra reveal superparamagnetic nature of the core-shell sample. The ferroelectric hysteresis loops reveal leaky nature of the samples. The results indicate the promising applications of the samples for magneto-electric memories and spintronics.

Refined hierarchical kinematics quasi-3D Ritz models for free vibration analysis of doubly curved FGM shells and sandwich shells with FGM core

NASA Astrophysics Data System (ADS)

Fazzolari, Fiorenzo A.; Carrera, Erasmo

2014-02-01

In this paper, the Ritz minimum energy method, based on the use of the Principle of Virtual Displacements (PVD), is combined with refined Equivalent Single Layer (ESL) and Zig Zag (ZZ) shell models hierarchically generated by exploiting the use of Carrera's Unified Formulation (CUF), in order to engender the Hierarchical Trigonometric Ritz Formulation (HTRF). The HTRF is then employed to carry out the free vibration analysis of doubly curved shallow and deep functionally graded material (FGM) shells. The PVD is further used in conjunction with the Gauss theorem to derive the governing differential equations and related natural boundary conditions. Donnell-Mushtari's shallow shell-type equations are given as a particular case. Doubly curved FGM shells and doubly curved sandwich shells made up of isotropic face sheets and FGM core are investigated. The proposed shell models are widely assessed by comparison with the literature results. Two benchmarks are provided and the effects of significant parameters such as stacking sequence, boundary conditions, length-to-thickness ratio, radius-to-length ratio and volume fraction index on the circular frequency parameters and modal displacements are discussed.

Two-nucleon high-spin states, the Bansal-French model and the crude shell model

NASA Astrophysics Data System (ADS)

Chan, Tsan Ung

1987-08-01

Recent data on two-nucleon stretched high-spin states agree well with the crude shell model predictions. For two-neutron high-spin states, the A and T linear dependence of B2n in the Bansal-French model can be deduced from the A and T linear dependence of Bn and the crude shell model. 7-2 states in some Zn and Ge even nuclei might be two-proton states. This hypothesis should be confirmed by two-proton transfer reaction.

Further Results in Bend-Buckling Analysis of Ring Stiffened Cylindrical Shells.

DTIC Science & Technology

1986-08-01

Submerged Shell Targets, NSWC TR 84-380, Dec 1984. 2. Moussouros, M., "Finite Element Modeling Techniques for Buckling Analysis of Cylindrical Shells...KCR, MBR , M0 , F0 , and I, R is the mean radius as given by R0 ) R0 - Mean radius of circular cylindrical shell (perfect shell or radius of

X-rays from Eta Carinae

NASA Technical Reports Server (NTRS)

Chlebowski, T.; Seward, F. D.; Swank, J.; Szymkowiak, A.

1984-01-01

X-ray observations of Eta Car obtained with the high-resolution imager and solid-state spectrometer of the Einstein observatory are reported and interpreted in terms of a two-shell model. A soft component with temperature 5 million K is located in the expanding outer shell, and the hard core component with temperature 80 million K is attributed to the interaction of a high-velocity stellar wind from the massive central object with the inner edge of a dust shell. Model calculations based on comparison with optical and IR data permit estimation of the mass of the outer shell (0.004 solar mass), the mass of the dust shell (3 solar mass), and the total shell expansion energy (less than 2 x 10 to the 49th ergs).

Perspectives on land snails - sampling strategies for isotopic analyses

NASA Astrophysics Data System (ADS)

Kwiecien, Ola; Kalinowski, Annika; Kamp, Jessica; Pellmann, Anna

2017-04-01

Since the seminal works of Goodfriend (1992), several substantial studies confirmed a relation between the isotopic composition of land snail shells (d18O, d13C) and environmental parameters like precipitation amount, moisture source, temperature and vegetation type. This relation, however, is not straightforward and site dependent. The choice of sampling strategy (discrete or bulk sampling) and cleaning procedure (several methods can be used, but comparison of their effects in an individual shell has yet not been achieved) further complicate the shell analysis. The advantage of using snail shells as environmental archive lies in the snails' limited mobility, and therefore an intrinsic aptitude of recording local and site-specific conditions. Also, snail shells are often found at dated archaeological sites. An obvious drawback is that shell assemblages rarely make up a continuous record, and a single shell is only a snapshot of the environmental setting at a given time. Shells from archaeological sites might represent a dietary component and cooking would presumably alter the isotopic signature of aragonite material. Consequently, a proper sampling strategy is of great importance and should be adjusted to the scientific question. Here, we compare and contrast different sampling approaches using modern shells collected in Morocco, Spain and Germany. The bulk shell approach (fine-ground material) yields information on mean environmental parameters within the life span of analyzed individuals. However, despite homogenization, replicate measurements of bulk shell material returned results with a variability greater than analytical precision (up to 2‰ for d18O, and up to 1‰ for d13C), calling for caution analyzing only single individuals. Horizontal high-resolution sampling (single drill holes along growth lines) provides insights into the amplitude of seasonal variability, while vertical high-resolution sampling (multiple drill holes along the same growth line) produces replicable results. This reproducibility enables not only sequential testing of isotopic changes in shells exposed to artificially elevated temperatures, but also systematic assessment of different cleaning methods. Goodfriend, 1992. The use of land snail shells in paleoenvironmental reconstruction, EPSL 11, 655-685

Radiocarbon dating late Quaternary loess deposits using small terrestrial gastropod shells

USGS Publications Warehouse

Pigati, Jeff S.; McGeehin, John P.; Muhs, Daniel R.; Bettis, E. Arthur

2013-01-01

Constraining the ages and mass accumulation rates of late Quaternary loess deposits is often difficult because of the paucity of organic material typically available for 14C dating and the inherent limitations of luminescence techniques. Radiocarbon dating of small terrestrial gastropod shells may provide an alternative to these methods as fossil shells are common in loess and contain ∼12% carbon by weight. Terrestrial gastropod assemblages in loess have been used extensively to reconstruct past environmental conditions but have been largely ignored for dating purposes. Here, we present the results of a multi-faceted approach to understanding the potential for using small terrestrial gastropod shells to date loess deposits in North America. First, we compare highly resolved 14C ages of well-preserved wood and gastropod shells (Succineidae) recovered from a Holocene loess section in Alaska. Radiocarbon ages derived from the shells are nearly identical to wood and plant macrofossil ages throughout the section, which suggests that the shells behaved as closed systems with respect to carbon for at least the last 10 ka (thousands of calibrated 14C years before present). Second, we apply 14C dating of gastropod shells to late Pleistocene loess deposits in the Great Plains using stratigraphy and independent chronologies for comparison. The new shell ages require less interpretation than humic acid radiocarbon ages that are commonly used in loess studies, provide additional stratigraphic coverage to previous dating efforts, and are in correct stratigraphic order more often than their luminescence counterparts. Third, we show that Succineidae shells recovered from historic loess in the Matanuska River Valley, Alaska captured the 20th century 14C bomb spike, which suggests that the shells can be used to date late Holocene and historic-aged loess. Finally, results from Nebraska and western Iowa suggest that, similar to other materials, shell ages approaching ∼40 ka should be viewed with caution as they may reflect trace amounts of contamination. In sum, our results show that small terrestrial gastropod shells, especially from the Succineidae family, provide reliable ages for late Quaternary loess deposits in North America.

Enhanced Photoelectrochemical Behavior of H-TiO2 Nanorods Hydrogenated by Controlled and Local Rapid Thermal Annealing

NASA Astrophysics Data System (ADS)

Wang, Xiaodan; Estradé, Sonia; Lin, Yuanjing; Yu, Feng; Lopez-Conesa, Lluis; Zhou, Hao; Gurram, Sanjeev Kumar; Peiró, Francesca; Fan, Zhiyong; Shen, Hao; Schaefer, Lothar; Braeuer, Guenter; Waag, Andreas

2017-05-01

Recently, colored H-doped TiO2 (H-TiO2) has demonstrated enhanced photoelectrochemical (PEC) performance due to its unique crystalline core—disordered shell nanostructures and consequent enhanced conduction behaviors between the core-shell homo-interfaces. Although various hydrogenation approaches to obtain H-TiO2 have been developed, such as high temperature hydrogen furnace tube annealing, high pressure hydrogen annealing, hydrogen-plasma assisted reaction, aluminum reduction and electrochemical reduction etc., there is still a lack of a hydrogenation approach in a controlled manner where all processing parameters (temperature, time and hydrogen flux) were precisely controlled in order to improve the PEC performance of H-TiO2 and understand the physical insight of enhanced PEC performance. Here, we report for the first time a controlled and local rapid thermal annealing (RTA) approach to prepare hydrogenated core-shell H-TiO2 nanorods grown on F:SnO2 (FTO) substrate in order to address the degradation issue of FTO in the typical TiO2 nanorods/FTO system observed in the conventional non-RTA treated approaches. Without the FTO degradation in the RTA approach, we systematically studied the intrinsic relationship between the annealing temperature, structural, optical, and photoelectrochemical properties in order to understand the role of the disordered shell on the improved photoelectrochemical behavior of H-TiO2 nanorods. Our investigation shows that the improvement of PEC performance could be attributed to (i) band gap narrowing from 3.0 to 2.9 eV; (ii) improved optical absorption in the visible range induced by the three-dimensional (3D) morphology and rough surface of the disordered shell; (iii) increased proper donor density; (iv) enhanced electron-hole separation and injection efficiency due to the formation of disordered shell after hydrogenation. The RTA approach developed here can be used as a suitable hydrogenation process for TiO2 nanorods/FTO system for important applications such as photocatalysis, hydrogen generation from water splitting and solar energy conversion.

Enhanced Photoelectrochemical Behavior of H-TiO2 Nanorods Hydrogenated by Controlled and Local Rapid Thermal Annealing.

PubMed

Wang, Xiaodan; Estradé, Sonia; Lin, Yuanjing; Yu, Feng; Lopez-Conesa, Lluis; Zhou, Hao; Gurram, Sanjeev Kumar; Peiró, Francesca; Fan, Zhiyong; Shen, Hao; Schaefer, Lothar; Braeuer, Guenter; Waag, Andreas

2017-12-01

Recently, colored H-doped TiO 2 (H-TiO 2 ) has demonstrated enhanced photoelectrochemical (PEC) performance due to its unique crystalline core-disordered shell nanostructures and consequent enhanced conduction behaviors between the core-shell homo-interfaces. Although various hydrogenation approaches to obtain H-TiO 2 have been developed, such as high temperature hydrogen furnace tube annealing, high pressure hydrogen annealing, hydrogen-plasma assisted reaction, aluminum reduction and electrochemical reduction etc., there is still a lack of a hydrogenation approach in a controlled manner where all processing parameters (temperature, time and hydrogen flux) were precisely controlled in order to improve the PEC performance of H-TiO 2 and understand the physical insight of enhanced PEC performance. Here, we report for the first time a controlled and local rapid thermal annealing (RTA) approach to prepare hydrogenated core-shell H-TiO 2 nanorods grown on F:SnO 2 (FTO) substrate in order to address the degradation issue of FTO in the typical TiO 2 nanorods/FTO system observed in the conventional non-RTA treated approaches. Without the FTO degradation in the RTA approach, we systematically studied the intrinsic relationship between the annealing temperature, structural, optical, and photoelectrochemical properties in order to understand the role of the disordered shell on the improved photoelectrochemical behavior of H-TiO 2 nanorods. Our investigation shows that the improvement of PEC performance could be attributed to (i) band gap narrowing from 3.0 to 2.9 eV; (ii) improved optical absorption in the visible range induced by the three-dimensional (3D) morphology and rough surface of the disordered shell; (iii) increased proper donor density; (iv) enhanced electron-hole separation and injection efficiency due to the formation of disordered shell after hydrogenation. The RTA approach developed here can be used as a suitable hydrogenation process for TiO 2 nanorods/FTO system for important applications such as photocatalysis, hydrogen generation from water splitting and solar energy conversion.

Influence of an asymmetric ring on the modeling of an orthogonally stiffened cylindrical shell

NASA Technical Reports Server (NTRS)

Rastogi, Naveen; Johnson, Eric R.

1994-01-01

Structural models are examined for the influence of a ring with an asymmetrical cross section on the linear elastic response of an orthogonally stiffened cylindrical shell subjected to internal pressure. The first structural model employs classical theory for the shell and stiffeners. The second model employs transverse shear deformation theories for the shell and stringer and classical theory for the ring. Closed-end pressure vessel effects are included. Interacting line load intensities are computed in the stiffener-to-skin joints for an example problem having the dimensions of the fuselage of a large transport aircraft. Classical structural theory is found to exaggerate the asymmetric response compared to the transverse shear deformation theory.

Cross-shell excitations in Si 31

DOE PAGES

Tai, P. -L.; Tabor, S. L.; Lubna, R. S.; ...

2017-07-28

The Si-31 nucleus was produced through the O-18(18O, an) fusion-evaporation reaction at E-lab = 24 MeV. Evaporated a particles from the reaction were detected and identified in the Microball detector array for channel selection. Multiple gamma-ray coincidence events were detected in Gammasphere. The energy and angle information for the alpha particles was used to determine the Si-31 recoil kinematics on an event-by-event basis for a more accurate Doppler correction. A total of 22 new states and 52 new gamma transitions were observed, including 14 from states above the neutron separation energy. The positive-parity states predicted by the shell-model calculations inmore » the sd model space agree well with experiment. The negative-parity states were compared with shell-model calculations in the psdpf model space with some variations in the N = 20 shell gap. The best agreement was found with a shell gap intermediate between that originally used for A approximate to 20 nuclei and that previously adapted for P-32,P-34. This variation suggests the need for a more universal cross-shell interaction.« less

Old and New Magic Numbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talmi, Igal

2008-11-11

The discovery of magic numbers led to the shell model. They indicated closure of major shells and are robust: proton magic numbers are rather independent of the occupation of neutron orbits and vice versa. Recently the magic property became less stringent and we hear a lot about the discovery of new magic numbers. These, however, indicate sub-shell closures and strongly depend on occupation numbers and hence, may be called quasi-magic numbers. Some of these have been known for many years and the mechanism for their appearance as well as disappearance, was well understood within the simple shell model. The situationmore » will be illustrated by a few examples which demonstrate the simple features of the shell model. Will this simplicity emerge from the complex computations of nuclear many-body theory?.« less

CdSe/AsS core-shell quantum dots: preparation and two-photon fluorescence.

PubMed

Wang, Junzhong; Lin, Ming; Yan, Yongli; Wang, Zhe; Ho, Paul C; Loh, Kian Ping

2009-08-19

Arsenic(II) sulfide (AsS)-coated CdSe core-shell nanocrystals can be prepared by a cluster-complex deposition approach under mild conditions. At 60 degrees C, growth of an AsS shell onto a CdSe nanocrystal can be realized through the crystallization of a cluster complex of AsS/butylamine in a mixed solvent of isopropanol/chloroform. The new, type I core-shell nanocrystal exhibits markedly enhanced one-photon fluorescence as well two-photon upconversion fluorescence. The nanocrystals can be used for infrared-excited upconversion cellular labeling.

Predictable Particle Engineering: Programming the Energy Level, Carrier Generation, and Conductivity of Core-Shell Particles.

PubMed

Yuan, Conghui; Wu, Tong; Mao, Jie; Chen, Ting; Li, Yuntong; Li, Min; Xu, Yiting; Zeng, Birong; Luo, Weiang; Yu, Lingke; Zheng, Gaofeng; Dai, Lizong

2018-06-20

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO 2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.

Low-energy nuclear spectroscopy in a microscopic multiphonon approach

NASA Astrophysics Data System (ADS)

Lo Iudice, N.; Ponomarev, V. Yu; Stoyanov, Ch; Sushkov, A. V.; Voronov, V. V.

2012-04-01

The low-lying spectra of heavy nuclei are investigated within the quasiparticle-phonon model. This microscopic approach goes beyond the quasiparticle random-phase approximation by treating a Hamiltonian of separable form in a microscopic multiphonon basis. It is therefore able to describe the anharmonic features of collective modes as well as the multiphonon states, whose experimental evidence is continuously growing. The method can be put in close correspondence with the proton-neutron interacting boson model. By associating the microscopic isoscalar and isovector quadrupole phonons with proton-neutron symmetric and mixed-symmetry quadrupole bosons, respectively, the microscopic states can be classified, just as in the algebraic model, according to their phonon content and their symmetry. In addition, these states disclose the nuclear properties which are to be ascribed to genuine shell effects, not included in the algebraic approach. Due to its flexibility, the method can be implemented numerically for systematic studies of spectroscopic properties throughout entire regions of vibrational nuclei. The spectra and multipole transition strengths so computed are in overall good agreement with the experimental data. By exploiting the correspondence of the method with the interacting boson model, it is possible to embed the microscopic states into this algebraic frame and, therefore, face the study of nuclei far from shell closures, not directly accessible to merely microscopic approaches. Here, it is shown how this task is accomplished through systematic investigations of magnetic dipole and, especially, electric dipole modes along paths moving from the vibrational to the transitional regions. The method is very well suited to the study of well-deformed nuclei. It provides reliable descriptions of low-lying magnetic as well as electric multipole modes of nuclei throughout the rare-earth and actinide regions. Attention is focused here on the low-lying 0+ states produced in large abundance in recent experiments. The analysis shows that the quasiparticle-phonon model accounts for the occurrence of so many 0+ levels and discloses their nature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nick Cannell; Adrian S. Sabau

The investment casting process allows the production of complex-shape parts and close dimensional tolerances. One of the most important phases in the investment casting process is the design of the pattern die. Pattern dies are used to create wax patterns by injecting wax into dies. The first part of the project involved preparation of reports on the state of the art at that time for all the areas under consideration (die-wax, wax-shell, and shell-alloy). The primary R&D focus during Phase I was on the wax material since the least was known about it. The main R&D accomplishments during this phasemore » were determination of procedures for obtaining the thermal conductivity and viscoelastic properties of an unfilled wax and validating those procedures. Phase II focused on die-wax and shell-alloy systems. A wax material model was developed based on results obtained during the previous R&D phase, and a die-wax model was successfully incorporated into and used in commercial computer programs. Current computer simulation programs have complementary features. A viscoelastic module was available in ABAQUS but unavailable in ProCAST, while the mold-filling module was available in ProCAST but unavailable in ABAQUS. Thus, the numerical simulation results were only in good qualitative agreement with experimental results, the predicted shrinkage factors being approximately 2.5 times larger than those measured. Significant progress was made, and results showed that the testing and modeling of wax material had great potential for industrial applications. Additional R&D focus was placed on one shell-alloy system. The fused-silica shell mold and A356 aluminum alloy were considered. The experimental part of the program was conducted at ORNL and commercial foundries, where wax patterns were injected, molds were invested, and alloys were poured. It was very important to obtain accurate temperature data from actual castings, and significant effort was made to obtain temperature profiles in the shell mold. A model for thermal radiation within the shell mold was developed, and the thermal model was successfully validated using ProCAST. Since the fused silica shells had the lowest thermal expansion properties in the industry, the dewaxing phase, including the coupling between wax-shell systems, was neglected. The prefiring of the empty shell mold was considered in the model, and the shell mold was limited to a pure elastic material. The alloy dimensions were obtained from numerical simulations only with coupled shell-alloy systems. The alloy dimensions were in excellent quantitative agreement with experimental data, validating the deformation module. For actual parts, however, the creep properties of the shell molds must also be obtained, modeled, and validated.« less

Applying a Qualitative Modeling Shell to Process Diagnosis: The Caster System.

DTIC Science & Technology

1986-03-01

Process Diagnosis: The Caster System by Timothy F. Thompson and William J. Clancey Department of Computer Science Stanford University Stanford, CA 94303...MODELING SHELL TO PROCESS DIAGNOSIS: THE CASTER SYSTEM 12 PERSONAL AUTHOR(S) TIMOTHY F. THOMPSON. WESTINGHOUSE R&D CENTER, WILLIAM CLANCEY, STANFORD...editions are obsolete. Applying a Qualitative Modeling Shell to Process Diagnosis: The Caster System by Timothy F. Thompson, Westinghouse R&D Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gronke, M.; Dijkstra, M., E-mail: maxbg@astro.uio.no

We perform Lyman- α (Ly α ) Monte-Carlo radiative transfer calculations on a suite of 2500 models of multiphase, outflowing media, which are characterized by 14 parameters. We focus on the Ly α spectra emerging from these media and investigate which properties are dominant in shaping the emerging Ly α profile. Multiphase models give rise to a wide variety of emerging spectra, including single-, double-, and triple-peaked spectra. We find that the dominant parameters in shaping the spectra include (i) the cloud covering factor, f {sub c} , which is in agreement with earlier studies, and (ii) the temperature andmore » number density of residual H i in the hot ionized medium. We attempt to reproduce spectra emerging from multiphase models with “shell models” which are commonly used to fit observed Ly α spectra, and investigate the connection between shell-model parameters and the physical parameters of the clumpy media. In shell models, the neutral hydrogen content of the shell is one of the key parameters controlling Ly α radiative transfer. Because Ly α spectra emerging from multiphase media depend much less on the neutral hydrogen content of the clumps, the shell-model parameters such as H i column density (but also shell velocity and dust content) are generally not well matched to the associated physical parameters of the clumpy media.« less

Ion acceleration in shell cylinders irradiated by a short intense laser pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, A.; ELI-ALPS, Szeged; Platonov, K.

The interaction of a short high intensity laser pulse with homo and heterogeneous shell cylinders has been analyzed using particle-in-cell simulations and analytical modeling. We show that the shell cylinder is proficient of accelerating and focusing ions in a narrow region. In the case of shell cylinder, the ion energy exceeds the ion energy for a flat target of the same thickness. The constructed model enables the evaluation of the ion energy and the number of ions in the focusing region.

Ballistic Simulation Method for Lithium Ion Batteries (BASIMLIB) Using Thick Shell Composites (TSC) in LS-DYNA

DTIC Science & Technology

2016-08-04

BAllistic SImulation Method for Lithium Ion Batteries (BASIMLIB) using Thick Shell Composites (TSC) in LS-DYNA Venkatesh Babu, Dr. Matt Castanier, Dr...Objective • Objective and focus of this work is to develop a – Robust simulation methodology to model lithium - ion based batteries in its module and full...unlimited  Lithium Ion Phosphate (LiFePO4) battery cell, module and pack was modeled in LS-DYNA using both Thin Shell Layer (TSL) and Thick Shell

Vibration Power Flow In A Constrained Layer Damping Cylindrical Shell

NASA Astrophysics Data System (ADS)

Wang, Yun; Zheng, Gangtie

2012-07-01

In this paper, the vibration power flow in a constrained layer damping (CLD) cylindrical shell using wave propagation approach is investigated. The dynamic equations of the shell are derived with the Hamilton principle in conjunction with the Donnell shell assumption. With these equations, the dynamic responses of the system under a line circumferential cosine harmonic exciting force is obtained by employing the Fourier transform and the residue theorem. The vibration power flows inputted to the system and transmitted along the shell axial direction are both studied. The results show that input power flow varies with driving frequency and circumferential mode order, and the constrained damping layer can obviously restrict the exciting force from inputting power flow into the base shell especially for a thicker viscoelastic layer, a thicker or stiffer constraining layer (CL), and a higher circumferential mode order, can rapidly attenuate the vibration power flow transmitted along the base shell axial direction.

Ultrasonic approach to the synthesis of HMX@TATB core-shell microparticles with improved mechanical sensitivity.

PubMed

Huang, Bing; Hao, Xiaofei; Zhang, Haobin; Yang, Zhijian; Ma, Zhigang; Li, Hongzhen; Nie, Fude; Huang, Hui

2014-07-01

To improve the safety of sensitive explosive HMX while maintaining explosion performance, a moderately powerful but insensitive explosive TATB was used to coat HMX microparticles via a facile ultrasonic method. By using Estane as surface modifier and nano-sized TATB as the shell layer, the HMX@TATB core-shell microparticles with a monodisperse size and compact shell structure were successfully constructed. Both scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of perfect core-shell structured composites. Based on a systematic and comparative study of the effect of experimental conditions, a possible formation mechanism of core-shell structure was proposed in detail. Moreover, the perfect core-shell HMX@TATB microparticles exhibited a unique thermal behavior and significantly improved mechanical sensitivity compared with that of the physical mixture. Copyright © 2014 Elsevier B.V. All rights reserved.

Ultra-high-performance core–shell structured Ru@Pt/C catalyst prepared by a facile pulse electrochemical deposition method

DOE PAGES

Chen, Dan; Li, Yuexia; Liao, Shijun; ...

2015-08-03

Core–shell structured catalysts, made by placing either a monolayer or a thin layer of a noble metal on relatively cheap core-metal nanoparticles, are fascinating and promising fuel cell catalysts due to their high utilization of noble metals. Here, we report our development of a core–shell structured catalyst, Ru@Pt/C, generated by a novel and facile pulse electrochemical deposition (PED) approach. We demonstrate that compared with a commercial Pt/C catalyst, this novel catalyst achieves over four times higher mass activity towards the anodic oxidation of methanol, and 3.6 times higher mass activity towards the cathodic reduction of oxygen. Importantly, we find thatmore » the intrinsic activity of Pt in this Ru@Pt/C catalyst is doubled due to the formation of the core–shell structure. The catalyst also shows superior stability: even after 2000 scans, it still retains up to 90% of the peak current. As a result, our findings demonstrate that this novel PED approach is a promising method for preparing high-performance core–shell catalysts for fuel cell applications.« less

Communication: Spin densities within a unitary group based spin-adapted open-shell coupled-cluster theory: Analytic evaluation of isotropic hyperfine-coupling constants for the combinatoric open-shell coupled-cluster scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Datta, Dipayan, E-mail: datta.dipayan@gmail.com; Gauss, Jürgen, E-mail: gauss@uni-mainz.de

We report analytical calculations of isotropic hyperfine-coupling constants in radicals using a spin-adapted open-shell coupled-cluster theory, namely, the unitary group based combinatoric open-shell coupled-cluster (COSCC) approach within the singles and doubles approximation. A scheme for the evaluation of the one-particle spin-density matrix required in these calculations is outlined within the spin-free formulation of the COSCC approach. In this scheme, the one-particle spin-density matrix for an open-shell state with spin S and M{sub S} = + S is expressed in terms of the one- and two-particle spin-free (charge) density matrices obtained from the Lagrangian formulation that is used for calculating themore » analytic first derivatives of the energy. Benchmark calculations are presented for NO, NCO, CH{sub 2}CN, and two conjugated π-radicals, viz., allyl and 1-pyrrolyl in order to demonstrate the performance of the proposed scheme.« less

A parameter-free variational coupling approach for trimmed isogeometric thin shells

NASA Astrophysics Data System (ADS)

Guo, Yujie; Ruess, Martin; Schillinger, Dominik

2017-04-01

The non-symmetric variant of Nitsche's method was recently applied successfully for variationally enforcing boundary and interface conditions in non-boundary-fitted discretizations. In contrast to its symmetric variant, it does not require stabilization terms and therefore does not depend on the appropriate estimation of stabilization parameters. In this paper, we further consolidate the non-symmetric Nitsche approach by establishing its application in isogeometric thin shell analysis, where variational coupling techniques are of particular interest for enforcing interface conditions along trimming curves. To this end, we extend its variational formulation within Kirchhoff-Love shell theory, combine it with the finite cell method, and apply the resulting framework to a range of representative shell problems based on trimmed NURBS surfaces. We demonstrate that the non-symmetric variant applied in this context is stable and can lead to the same accuracy in terms of displacements and stresses as its symmetric counterpart. Based on our numerical evidence, the non-symmetric Nitsche method is a viable parameter-free alternative to the symmetric variant in elastostatic shell analysis.

The Embryonic Transcriptome of the Red-Eared Slider Turtle (Trachemys scripta)

PubMed Central

Kaplinsky, Nicholas J.; Gilbert, Scott F.; Cebra-Thomas, Judith; Lilleväli, Kersti; Saare, Merly; Chang, Eric Y.; Edelman, Hannah E.; Frick, Melissa A.; Guan, Yin; Hammond, Rebecca M.; Hampilos, Nicholas H.; Opoku, David S. B.; Sariahmed, Karim; Sherman, Eric A.; Watson, Ray

2013-01-01

The bony shell of the turtle is an evolutionary novelty not found in any other group of animals, however, research into its formation has suggested that it has evolved through modification of conserved developmental mechanisms. Although these mechanisms have been extensively characterized in model organisms, the tools for characterizing them in non-model organisms such as turtles have been limited by a lack of genomic resources. We have used a next generation sequencing approach to generate and assemble a transcriptome from stage 14 and 17 Trachemys scripta embryos, stages during which important events in shell development are known to take place. The transcriptome consists of 231,876 sequences with an N50 of 1,166 bp. GO terms and EC codes were assigned to the 61,643 unique predicted proteins identified in the transcriptome sequences. All major GO categories and metabolic pathways are represented in the transcriptome. Transcriptome sequences were used to amplify several cDNA fragments designed for use as RNA in situ probes. One of these, BMP5, was hybridized to a T. scripta embryo and exhibits both conserved and novel expression patterns. The transcriptome sequences should be of broad use for understanding the evolution and development of the turtle shell and for annotating any future T. scripta genome sequences. PMID:23840449

Covalent immobilization of molecularly imprinted polymer nanoparticles using an epoxy silane.

PubMed

Kamra, Tripta; Chaudhary, Shilpi; Xu, Changgang; Johansson, Niclas; Montelius, Lars; Schnadt, Joachim; Ye, Lei

2015-05-01

Molecularly imprinted polymers (MIPs) can be used as antibody mimics to develop robust chemical sensors. One challenging problem in using MIPs for sensor development is the lack of reliable conjugation chemistry that allows MIPs to be fixed on transducer surface. In this work, we study the use of epoxy silane to immobilize MIP nanoparticles on model transducer surfaces without impairing the function of the immobilized nanoparticles. The MIP nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model transducer surface is functionalized with a self-assembled monolayer of epoxy silane, which reacts with the core-shell MIP particles to enable straightforward immobilization. The whole process is characterized by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show that the MIP particles are immobilized uniformly on surface. The photoelectron spectroscopy results further confirm the action of each functionalization step. The molecular selectivity of the MIP-functionalized surface is verified by radioligand binding analysis. The particle immobilization approach described here has a general applicability for constructing selective chemical sensors in different formats. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

Electro-mechanical analysis of composite and sandwich multilayered structures by shell elements with node-dependent kinematics

NASA Astrophysics Data System (ADS)

Carrera; Valvano; Kulikov

2018-01-01

In this work, a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed. The main idea of models coupling is developed by presenting the concept of nodal dependent kinematics where the same finite element can present at each node a different approximation of the main unknowns by setting a node-wise through-the-thickness approximation base. In a global/local approach scenario, the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states, and their electro-mechanical coupling present a complex distribution. Several numerical investigations are carried out to validate the accuracy and efficiency of the present shell element. An accurate representation of mechanical stresses and electric displacements in localized zones is possible with reduction of the computational costs if an accurate distribution of the higher-order kinematic capabilities is performed. On the contrary, the accuracy of the solution in terms of mechanical displacements and electric potential values depends on the global approximation over the whole structure. The efficacy of the present node-dependent variable kinematic models, thus, depends on the characteristics of the problem under consideration as well as on the required analysis type.

Nuclear structure for SNe r- and neutrino processes

NASA Astrophysics Data System (ADS)

Suzuki, Toshio

2014-09-01

SNe r- and neutrino-processes are investigated based on recent advances in the studies of spin responses in nuclei. New shell-model Hamiltonians, which can well describe spin responses in nuclei with proper tensor components, are used to make accurate evaluations of reaction cross sections and rates in astrophysical processes. Nucleosyntheses in SNe r- and ν -processes as well as rp-processes are discussed with these new reaction rates with improved accuracies. (1) Beta-decay rates for N = 126 isotones are evaluated by shell-model calculations, and new rates are applied to study r-process nucleosynthesis in SNe's around its third peak as well as beyond the peak region up to uranium. (2) ν -processes for light-element synthesis in core-collapse SNe are studied with a new shell-model Hamiltonian in p-shell, SFO. Effects of MSW ν -oscillations on the production yields of 7Li and 11B and sensitivity of the yield ratio on ν -oscillation parameters are discussed. ν -induced reactions on 16O are also studied. (3) A new shell-model Hamiltonian in pf-shell, GXPF1J, is used to evaluate e-capture rates in pf-shell nuclei at stellar environments. New e-capture rates are applied to study nucleosynthesis in type-Ia supernova explosions, rp-process and X-ray bursts.

Host susceptibility hypothesis for shell disease in American lobsters.

PubMed

Tlusty, Michael F; Smolowitz, Roxanna M; Halvorson, Harlyn O; DeVito, Simone E

2007-12-01

Epizootic shell disease (ESD) in American lobsters Homarus americanus is the bacterial degradation of the carapace resulting in extensive irregular, deep erosions. The disease is having a major impact on the health and mortality of some American lobster populations, and its effects are being transferred to the economics of the fishery. While the onset and progression of ESD in American lobsters is undoubtedly multifactorial, there is little understanding of the direct causality of this disease. The host susceptibility hypothesis developed here states that although numerous environmental and pathological factors may vary around a lobster, it is eventually the lobster's internal state that is permissive to or shields it from the final onset of the diseased state. To support the host susceptibility hypothesis, we conceptualized a model of shell disease onset and severity to allow further research on shell disease to progress from a structured model. The model states that shell disease onset will occur when the net cuticle degradation (bacterial degradation, decrease of host immune response to bacteria, natural wear, and resorption) is greater than the net deposition (growth, maintenance, and inflammatory response) of the shell. Furthermore, lesion severity depends on the extent to which cuticle degradation exceeds deposition. This model is consistent with natural observations of shell disease in American lobster.

In-Flight Aeroelastic Stability of the Thermal Protection System on the NASA HIAD, Part I: Linear Theory

NASA Technical Reports Server (NTRS)

Goldman, Benjamin D.; Dowell, Earl H.; Scott, Robert C.

2014-01-01

Conical shell theory and piston theory aerodynamics are used to study the aeroelastic stability of the thermal protection system (TPS) on the NASA Hypersonic Inflatable Aerodynamic Decelerator (HIAD). Structural models of the TPS consist of single or multiple orthotropic conical shell systems resting on several circumferential linear elastic supports. The shells in each model may have pinned (simply-supported) or elastically-supported edges. The Lagrangian is formulated in terms of the generalized coordinates for all displacements and the Rayleigh-Ritz method is used to derive the equations of motion. The natural modes of vibration and aeroelastic stability boundaries are found by calculating the eigenvalues and eigenvectors of a large coefficient matrix. When the in-flight configuration of the TPS is approximated as a single shell without elastic supports, asymmetric flutter in many circumferential waves is observed. When the elastic supports are included, the shell flutters symmetrically in zero circumferential waves. Structural damping is found to be important in this case. Aeroelastic models that consider the individual TPS layers as separate shells tend to flutter asymmetrically at high dynamic pressures relative to the single shell models. Several parameter studies also examine the effects of tension, orthotropicity, and elastic support stiffness.

Exploring the Physics of Unstable Nuclei

NASA Astrophysics Data System (ADS)

Volya, Alexander

In this presentation the Continuum Shell Model (CSM) approach is advertised as a powerful theoretical tool for studying physics of unstable nuclei. The approach is illustrated using 17O as an example, which is followed by a brief presentation of the general CSM formalism. The successes of the CSM are highlighted and references are provided throughout the text. As an example, the CSM is applied perturbatively to 20O allowing one to explore the effects of continuum on positions of weakly bound states and low-lying resonances, as well as to discern some effects of threshold discontinuity.

Planetary Ice-Oceans: Numerical Modeling Study of Ice-Shell Growth in Convecting Two-Phase Systems

NASA Astrophysics Data System (ADS)

Allu Peddinti, Divya; McNamara, Allen

2017-04-01

Several icy bodies in the Solar system such as the icy moons Europa and Enceladus exhibit signs of subsurface oceans underneath an ice-shell. For Europa, the geologically young surface, the presence of surface features and the aligned surface chemistry pose interesting questions about formation of the ice-shell and its interaction with the ocean below. This also ties in with its astrobiological potential and implications for similar ice-ocean systems elsewhere in the cosmos. The overall thickness of the H2O layer on Europa is estimated to be 100-150 km while the thickness of the ice-shell is debated. Additionally, Europa is subject to tidal heating due to interaction with Jupiter's immense gravity field. It is of interest to understand how the ice-shell thickness varies in the presence of tidal internal heating and the localization of heating in different regions of the ice-shell. Thus this study aims to determine the effect of tidal internal heating on the growth rate of the ice-shell over time. We perform geodynamic modeling of the ice-ocean system in order to understand how the ice-shell thickness changes with time. The convection code employs the ice Ih-water phase diagram in order to model the two-phase convecting ice-ocean system. All the models begin from an initial warm thick ocean that cools from the top. The numerical experiments analyze three cases: case 1 with no tidal internal heating in the system, case 2 with constant tidal internal heating in the ice and case 3 with viscosity-dependent tidal internal heating in the ice. We track the ice-shell thickness as a function of time as the system cools. Modeling results so far have identified that the shell growth rate changes substantially at a point in time that coincides with a change in the planform of ice-convection cells. Additionally, the velocity vs depth plots indicate a shift from a conduction dominant to a convection dominant ice regime. We compare the three different cases to provide a comprehensive understanding of the temporal variation in the ice-shell thickness due to the addition of heating in the ice.

Double-detonation Sub-Chandrasekhar Supernovae: Synthetic Observables for Minimum Helium Shell Mass Models

NASA Astrophysics Data System (ADS)

Kromer, M.; Sim, S. A.; Fink, M.; Röpke, F. K.; Seitenzahl, I. R.; Hillebrandt, W.

2010-08-01

In the double-detonation scenario for Type Ia supernovae, it is suggested that a detonation initiates in a shell of helium-rich material accreted from a companion star by a sub-Chandrasekhar-mass white dwarf. This shell detonation drives a shock front into the carbon-oxygen white dwarf that triggers a secondary detonation in the core. The core detonation results in a complete disruption of the white dwarf. Earlier studies concluded that this scenario has difficulties in accounting for the observed properties of Type Ia supernovae since the explosion ejecta are surrounded by the products of explosive helium burning in the shell. Recently, however, it was proposed that detonations might be possible for much less massive helium shells than previously assumed (Bildsten et al.). Moreover, it was shown that even detonations of these minimum helium shell masses robustly trigger detonations of the carbon-oxygen core (Fink et al.). Therefore, it is possible that the impact of the helium layer on observables is less than previously thought. Here, we present time-dependent multi-wavelength radiative transfer calculations for models with minimum helium shell mass and derive synthetic observables for both the optical and γ-ray spectral regions. These differ strongly from those found in earlier simulations of sub-Chandrasekhar-mass explosions in which more massive helium shells were considered. Our models predict light curves that cover both the range of brightnesses and the rise and decline times of observed Type Ia supernovae. However, their colors and spectra do not match the observations. In particular, their B - V colors are generally too red. We show that this discrepancy is mainly due to the composition of the burning products of the helium shell of the Fink et al. models which contain significant amounts of titanium and chromium. Using a toy model, we also show that the burning products of the helium shell depend crucially on its initial composition. This leads us to conclude that good agreement between sub-Chandrasekhar-mass explosions and observed Type Ia supernovae may still be feasible but further study of the shell properties is required.

Merging first principle structure studies and few-body reaction formalism

NASA Astrophysics Data System (ADS)

Crespo, R.; Cravo, E.; Arriaga, A.; Wiringa, R.; Deltuva, A.; Diego, R.

2018-02-01

Calculations for nucleon knockout from a 7Li beam due to the collision with a proton target at 400 MeV/u are shown based on ab initio Quantum Monte Carlo (QMC) and conventional shell-model nuclear structure approaches to describe the relative motion between the knockout particle and the heavy fragment of the projectile. Structure effects on the total cross section are shown.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cacciari, C.; Clementini, G.

Attention is given to the folowing topics: population I and II variable stars; LP variables, the sun, and mass determination; and predegenerate and degenerate variables. Particular papers are presented on alternative evolutionary approaches to the absolute magnitude of the RR Lyrae variables; the evolution of the Cepheid stars; nonradial pulsations in rapidly rotating Delta Scuti stars; dynamical models of dust shells around Mira variables; and pulsations of central stars of planetary nebulae.

Spherical silicon-shell photonic band gap structures fabricated by laser-assisted chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wang, H.; Yang, Z. Y.; Lu, Y. F.

2007-02-01

Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures.

A versatile cooperative template-directed coating method to construct uniform microporous carbon shells for multifunctional core-shell nanocomposites.

PubMed

Guan, Buyuan; Wang, Xue; Xiao, Yu; Liu, Yunling; Huo, Qisheng

2013-03-21

A very simple cooperative template-directed coating method is developed for the preparation of core-shell, hollow, and yolk-shell microporous carbon nanocomposites. Particularly, the cationic surfactant C16TMA(+)·Br(-) used in the coating procedure improves the core dispersion in the reaction media and serves as the soft template for mesostructured resorcinol-formaldehyde resin formation, which results in the uniform polymer and microporous carbon shell coating on most functional cores with different surface properties. The core diameter and the shell thickness of the nanocomposites can be precisely tailored. This approach is highly reproducible and scalable. Several grams of polymer and carbon nanocomposites can be easily prepared by a facile one-pot reaction. The Au@hydrophobic microporous carbon yolk-shell catalyst favors the reduction of more hydrophobic nitrobenzene than hydrophilic 4-nitrophenol by sodium borohydride, which makes this type of catalyst@carbon yolk-shell composites promising nanomaterials as selective catalysts for hydrophobic reactants.

Shell Tectonics: A Mechanical Model for Strike-slip Displacement on Europa

NASA Technical Reports Server (NTRS)

Rhoden, Alyssa Rose; Wurman, Gilead; Huff, Eric M.; Manga, Michael; Hurford, Terry A.

2012-01-01

We introduce a new mechanical model for producing tidally-driven strike-slip displacement along preexisting faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history.

Raman-Scattering Line Profiles of the Symbiotic Star AG Peg

NASA Astrophysics Data System (ADS)

Lee, Seong-Jae; Hyung, Siek

2017-06-01

The high dispersion Hα and Hβ line profiles of the Symbiotic star AG Peg consist of top double Gaussian and bottom components. We investigated the formation of the broad wings with Raman scattering mechanism. Adopting the same physical parameters from the photo-ionization study of Kim and Hyung (2008) for the white dwarf and the ionized gas shell, Monte Carlo simulations were carried out for a rotating accretion disk geometry of non-symmetrical latitude angles from -7° < θ < +7° to -16° < θ < +16°. The smaller latitude angle of the disk corresponds to the approaching side of the disk responsible for weak blue Gaussian profile, while the wider latitude angle corresponds to the other side of the disk responsible for the strong red Gaussian profile. We confirmed that the shell has the high gas density ˜ 109.85 cm-3 in the ionized zone of AG Peg derived in the previous photo-ionization model study. The simulation with various HI shell column densities (characterized by a thickness ΔD × gas number density nH) shows that the HI gas shell with a column density Hhi ≈ 3 - 5 × 1019 cm-2 fits the observed line profiles well. The estimated rotation speed of the accretion disk shell is in the range of 44 - 55 kms-1. We conclude that the kinematically incoherent structure involving the outflowing gas from the giant star caused an asymmetry of the disk and double Gaussian profiles found in AG Peg.

Two-nucleon high-spin states, the Bansal-French model and the crude shell model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chan, T.U.

Recent data on two-nucleon stretched high-spin states agree well with the crude shell model predictions. For two-neutron high-spin states, the A and T linear dependence of B/sub 2n/ in the Bansal-French model can be deduced from the A and T linear dependence of B/sub n/ and the crude shell model. 7/sub 2//sup -/ states in some Zn and Ge even nuclei might be two-proton states. This hypothesis should be confirmed by two-proton transfer reaction.

Effects of Drift-Shell Splitting by Chorus Waves on Radiation Belt Electrons

NASA Astrophysics Data System (ADS)

Chan, A. A.; Zheng, L.; O'Brien, T. P., III; Tu, W.; Cunningham, G.; Elkington, S. R.; Albert, J.

2015-12-01

Drift shell splitting in the radiation belts breaks all three adiabatic invariants of charged particle motion via pitch angle scattering, and produces new diffusion terms that fully populate the diffusion tensor in the Fokker-Planck equation. Based on the stochastic differential equation method, the Radbelt Electron Model (REM) simulation code allows us to solve such a fully three-dimensional Fokker-Planck equation, and to elucidate the sources and transport mechanisms behind the phase space density variations. REM has been used to perform simulations with an empirical initial phase space density followed by a seed electron injection, with a Tsyganenko 1989 magnetic field model, and with chorus wave and ULF wave diffusion models. Our simulation results show that adding drift shell splitting changes the phase space location of the source to smaller L shells, which typically reduces local electron energization (compared to neglecting drift-shell splitting effects). Simulation results with and without drift-shell splitting effects are compared with Van Allen Probe measurements.

Influences of external vs. core-shell mixing on aerosol optical properties at various relative humidities.

PubMed

Ramachandran, S; Srivastava, Rohit

2013-05-01

Aerosol optical properties of external and core-shell mixtures of aerosol species present in the atmosphere are calculated in this study for different relative humidities. Core-shell Mie calculations are performed using the values of radii, refractive indices and densities of aerosol species that act as core and shell, and the core-shell radius ratio. The single scattering albedo (SSA) is higher when the absorbing species (black carbon, BC) is the core, while for a sulfate core SSA does not vary significantly as the BC in the shell dominates the absorption. Absorption gets enhanced in core-shell mixing of absorbing and scattering aerosols when compared to their external mixture. Thus, SSA is significantly lower for a core-shell mixture than their external mixture. SSA is more sensitive to core-shell ratio than mode radius when BC is the core. The extinction coefficient, SSA and asymmetry parameter are higher for external mixing when compared to BC (core)-water soluble aerosol (shell), and water soluble aerosol (core)-BC (shell) mixtures in the relative humidity range of 0 to 90%. Spectral SSA exhibits the behaviour of the species which acts as a shell in core-shell mixing. The asymmetry parameter for an external mixture of water soluble aerosol and BC is higher than BC (core)-water soluble aerosol (shell) mixing and increases as function of relative humidity. The asymmetry parameter for the water soluble aerosol (core)-BC (shell) is independent of relative humidity as BC is hydrophobic. The asymmetry parameter of the core-shell mixture decreases when BC aerosols are involved in mixing, as the asymmetry parameter of BC is lower. Aerosol optical depth (AOD) of core-shell mixtures increases at a higher rate when the relative humidity exceeds 70% in continental clean and urban aerosol models, whereas AOD remains the same when the relative humidity exceeds 50% in maritime aerosol models. The SSA for continental aerosols varies for core-shell mixing of water soluble aerosol (core)-shell (BC) when compared to their external mixture, while the SSA for maritime aerosols does not vary significantly for different mixing scenarios because of the dominance of sea salt aerosols. Thus, these results confirm that aerosol mixing can modify the physical and optical characteristics of aerosols, which vary as a function of relative humidity. These calculations will be useful in parameterising the effect of core-shell vs. external mixing of aerosols in global climate models, and in the evaluation of aerosol radiative effects.

Buckling of Thin Cylindrical Shell Subject to Uniform External Pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forasassi, G.; Lo Frano, R.

2006-07-01

The buckling of cylindrical shells under uniform external pressure loading has been widely investigated. In general, when tubes are subjected to external pressure, collapse is initiated by yielding, but interaction with instability is significant, in that imperfections associated with fabrication of shells reduce the load bearing capacity by a significant amount even when thickness is considerable. A specific buckling analysis is used to predict collapse failure of long pressure vessels and pipelines when they are subjected to external over-pressure. The problem of buckling for variable load conditions is relevant for the optimisation of several Nuclear Power Plant applications as, formore » instance, the IRIS (International Reactor Innovative and Secure) LWR integrated Steam Generator (SG) tubes. In this paper, we consider in addition to the usual assumptions of thin shell, homogeneous and isotropic material, also the tube geometric imperfections and plastic deformations that may affect the limit load. When all those conditions are considered at present, a complete theoretical analysis was not founding the literature. At Pisa University a research activity is being carried out on the buckling of thin walled metal specimen, with reference to several geometries and two different stainless steel materials. A test equipment (with the necessary data acquisition facility), suitable for carrying out many test on this issue, as well as numerical models implemented on the MARC FEM code, were set up. In this report, the results of the performed analyses of critical pressure load determination with different numerical and experimental approaches are presented. The numerical results obtained are compared with the experimental results, for the same geometry and loading conditions, showing a good agreement between these two approaches. (authors)« less

A Leonard-Sanders-Budiansky-Koiter-Type Nonlinear Shell Theory with a Hierarchy of Transverse-Shearing Deformations

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.

2013-01-01

A detailed exposition on a refined nonlinear shell theory suitable for nonlinear buckling analyses of laminated-composite shell structures is presented. This shell theory includes the classical nonlinear shell theory attributed to Leonard, Sanders, Koiter, and Budiansky as an explicit proper subset. This approach is used in order to leverage the exisiting experience base and to make the theory attractive to industry. In addition, the formalism of general tensors is avoided in order to expose the details needed to fully understand and use the theory. The shell theory is based on "small" strains and "moderate" rotations, and no shell-thinness approximations are used. As a result, the strain-displacement relations are exact within the presumptions of "small" strains and "moderate" rotations. The effects of transverse-shearing deformations are included in the theory by using analyst-defined functions to describe the through-the-thickness distributions of transverse-shearing strains. Constitutive equations for laminated-composite shells are derived without using any shell-thinness approximations, and simplified forms and special cases are presented.

Imperfection sensitivity of pressured buckling of biopolymer spherical shells

NASA Astrophysics Data System (ADS)

Zhang, Lei; Ru, C. Q.

2016-06-01

Imperfection sensitivity is essential for mechanical behavior of biopolymer shells [such as ultrasound contrast agents (UCAs) and spherical viruses] characterized by high geometric heterogeneity. In this work, an imperfection sensitivity analysis is conducted based on a refined shell model recently developed for spherical biopolymer shells of high structural heterogeneity and thickness nonuniformity. The influence of related parameters (including the ratio of radius to average shell thickness, the ratio of transverse shear modulus to in-plane shear modulus, and the ratio of effective bending thickness to average shell thickness) on imperfection sensitivity is examined for pressured buckling. Our results show that the ratio of effective bending thickness to average shell thickness has a major effect on the imperfection sensitivity, while the effect of the ratio of transverse shear modulus to in-plane shear modulus is usually negligible. For example, with physically realistic parameters for typical imperfect spherical biopolymer shells, the present model predicts that actual maximum external pressure could be reduced to as low as 60% of that of a perfect UCA spherical shell or 55%-65% of that of a perfect spherical virus shell, respectively. The moderate imperfection sensitivity of spherical biopolymer shells with physically realistic imperfection is largely attributed to the fact that biopolymer shells are relatively thicker (defined by smaller radius-to-thickness ratio) and therefore practically realistic imperfection amplitude normalized by thickness is very small as compared to that of classical elastic thin shells which have much larger radius-to-thickness ratio.

Semi-analytical approach to estimate railroad tank car shell puncture

DOT National Transportation Integrated Search

2011-03-16

This paper describes the development of engineering-based equations to estimate the puncture resistance of railroad tank cars under a generalized shell or side impact scenario. Resistance to puncture is considered in terms of puncture velocity, which...

Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Aryya; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav

2015-07-14

Auger decay is an efficient ultrafast relaxation process of core-shell or inner-shell excited atom or molecule. Generally, it occurs in femto-second or even atto-second time domain. Direct measurement of lifetimes of Auger process of single ionized and double ionized inner-shell state of an atom or molecule is an extremely difficult task. In this paper, we have applied the highly correlated complex absorbing potential-equation-of-motion coupled cluster (CAP-EOMCC) approach which is a combination of CAP and EOMCC approach to calculate the lifetime of the states arising from 2p inner-shell ionization of an Ar atom and 3d inner-shell ionization of Kr atom. Wemore » have also calculated the lifetime of Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}D, Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}S, and Ar{sup 2+}(2p{sup −1}3s{sup −1}) {sup 1}P double ionized states. The predicted results are compared with the other theoretical results as well as experimental results available in the literature.« less

Viscoelastic damped response of cross-ply laminated shallow spherical shells subjected to various impulsive loads

NASA Astrophysics Data System (ADS)

Şahan, Mehmet Fatih

2017-11-01

In this paper, the viscoelastic damped response of cross-ply laminated shallow spherical shells is investigated numerically in a transformed Laplace space. In the proposed approach, the governing differential equations of cross-ply laminated shallow spherical shell are derived using the dynamic version of the principle of virtual displacements. Following this, the Laplace transform is employed in the transient analysis of viscoelastic laminated shell problem. Also, damping can be incorporated with ease in the transformed domain. The transformed time-independent equations in spatial coordinate are solved numerically by Gauss elimination. Numerical inverse transformation of the results into the real domain are operated by the modified Durbin transform method. Verification of the presented method is carried out by comparing the results with those obtained by the Newmark method and ANSYS finite element software. Furthermore, the developed solution approach is applied to problems with several impulsive loads. The novelty of the present study lies in the fact that a combination of the Navier method and Laplace transform is employed in the analysis of cross-ply laminated shallow spherical viscoelastic shells. The numerical sample results have proved that the presented method constitutes a highly accurate and efficient solution, which can be easily applied to the laminated viscoelastic shell problems.

Analysis of composite plates by using mechanics of structure genome and comparison with ANSYS

NASA Astrophysics Data System (ADS)

Zhao, Banghua

Motivated by a recently discovered concept, Structure Genome (SG) which is defined as the smallest mathematical building block of a structure, a new approach named Mechanics of Structure Genome (MSG) to model and analyze composite plates is introduced. MSG is implemented in a general-purpose code named SwiftComp(TM), which provides the constitutive models needed in structural analysis by homogenization and pointwise local fields by dehomogenization. To improve the user friendliness of SwiftComp(TM), a simple graphic user interface (GUI) based on ANSYS Mechanical APDL platform, called ANSYS-SwiftComp GUI is developed, which provides a convenient way to create some common SG models or arbitrary customized SG models in ANSYS and invoke SwiftComp(TM) to perform homogenization and dehomogenization. The global structural analysis can also be handled in ANSYS after homogenization, which could predict the global behavior and provide needed inputs for dehomogenization. To demonstrate the accuracy and efficiency of the MSG approach, several numerical cases are studied and compared using both MSG and ANSYS. In the ANSYS approach, 3D solid element models (ANSYS 3D approach) are used as reference models and the 2D shell element models created by ANSYS Composite PrepPost (ACP approach) are compared with the MSG approach. The results of the MSG approach agree well with the ANSYS 3D approach while being as efficient as the ACP approach. Therefore, the MSG approach provides an efficient and accurate new way to model composite plates.

Equation-of-motion coupled-cluster method for ionised states with spin-orbit coupling using open-shell reference wavefunction

NASA Astrophysics Data System (ADS)

Wang, Zhifan; Wang, Fan

2018-04-01

The equation-of-motion coupled-cluster method for ionised states at the singles and doubles level (EOM-IP-CCSD) with spin-orbit coupling (SOC) included in post-Hartree-Fock (HF) steps is extended to spatially non-degenerate open-shell systems such as high spin states of s1, p3, σ1 or π2 configuration in this work. Pseudopotentials are employed to treat relativistic effects and spin-unrestricted scalar relativistic HF determinant is adopted as reference in calculations. Symmetry is not exploited in the implementation since both time-reversal and spatial symmetry is broken due to SOC. IPs with the EOM-IP-CCSD approach are those from the 3Σ1- states for high spin state of π2 configuration, while the ground state is the 3Σ0- state. When removing an electron from the high spin state of p3 configuration, only the 3P2 state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s1 configuration, diatomic molecules with π2 configuration and SOC splitting of the ionised π1 state, as well as IPs of VA atoms with p3 configuration. Our results demonstrate that this approach can be applied to ionised states of spatially non-degenerate open-shell states containing heavy elements with reasonable accuracy.

Electronically cloaked nanoparticles

NASA Astrophysics Data System (ADS)

Shen, Wenqing

The concept of electronic cloaking is to design objects invisible to conduction electrons. The approach of electronic cloaking has been recently suggested to design invisible nanoparticle dopants with electronic scattering cross section smaller than 1% of the physical cross section (pi a2), and therefore to enhance the carrier mobility of bulk materials. The proposed nanoparticles have core-shell structures. The dopants are incorporated inside the core, while the shell layer serves both as a spacer to separate the charge carriers from their parent atoms and as a cloaking shell to minimize the scattering cross section of the electrons from the ionized nanoparticles. Thermoelectric materials are usually highly doped to have enough carrier density. Using invisible dopants could achieve larger thermoelectric power factors by enhancing the electronic mobility. Core-shell nanoparticles show an advantage over one-layer nanoparticles, which are proposed in three-dimensional modulation doping. However designing such nanoparticles is not easy as there are too many parameters to be considered. This thesis first shows an approach to design hollow nanoparticles by applying constrains on variables. In the second part, a simple mapping approach is introduced where one can identify possible core-shell particles by comparing the dimensionless parameters of chosen materials with provided maps. In both parts of this work, several designs with realistic materials were made and proven to achieve electronic cloaking. Improvement in the thermoelectric power factor compared to the traditional impurity doping method was demonstrated in several cases.

Dynamical systems for modeling evolution of the magnetic field of the Sun, stars and planets

NASA Astrophysics Data System (ADS)

Popova, E.

2016-12-01

The magnetic activity of the Sun, stars and planets are connected with a dynamo process based on the combined action of the differential rotation and the alpha-effect. Application of this concept allows us to get different types of solutions which can describe the magnetic activity of celestial bodies. We investigated the dynamo model with the meridional circulation by the low-mode approach. This approach is based on an assumption that the magnetic field can be described by non-linear dynamical systems with a relatively small number of parameters. Such non-linear dynamical systems are based on the equations of dynamo models. With this method dynamical systems have been built for media which contains the meridional flow and thickness of the spherical shell where dynamo process operates. It was shown the possibility of coexistence of quiasi-biennial oscillations, 22-year cycle, and grand minima of magnetic activity which is consistent with the observational data for the solar activity. We obtained different regimes (oscillations, vacillations, dynamo-bursts) depending on a value of the dynamo-number, the meridional circulation, and thickness of the spherical shell. We discuss features of these regimes and compare them with the observed features of the magnetic fields of the Sun, stars and Earth. We built theoretical paleomagnetic time scale and butterfly-diagrams for the helicity and toroidal magnetic field for different regimes.

Silica Nanoparticles for Intracellular Protein Delivery: a Novel Synthesis Approach Using Green Fluorescent Protein

NASA Astrophysics Data System (ADS)

Schmidt, Sarah; Tavernaro, Isabella; Cavelius, Christian; Weber, Eva; Kümper, Alexander; Schmitz, Carmen; Fleddermann, Jana; Kraegeloh, Annette

2017-09-01

In this study, a novel approach for preparation of green fluorescent protein (GFP)-doped silica nanoparticles with a narrow size distribution is presented. GFP was chosen as a model protein due to its autofluorescence. Protein-doped nanoparticles have a high application potential in the field of intracellular protein delivery. In addition, fluorescently labelled particles can be used for bioimaging. The size of these protein-doped nanoparticles was adjusted from 15 to 35 nm using a multistep synthesis process, comprising the particle core synthesis followed by shell regrowth steps. GFP was selectively incorporated into the silica matrix of either the core or the shell or both by a one-pot reaction. The obtained nanoparticles were characterised by determination of particle size, hydrodynamic diameter, ζ-potential, fluorescence and quantum yield. The measurements showed that the fluorescence of GFP was maintained during particle synthesis. Cellular uptake experiments demonstrated that the GFP-doped nanoparticles can be used as stable and effective fluorescent probes. The study reveals the potential of the chosen approach for incorporation of functional biological macromolecules into silica nanoparticles, which opens novel application fields like intracellular protein delivery.

Models of Uranium continuum radio emission

NASA Technical Reports Server (NTRS)

Romig, Joseph H.; Evans, David R.; Sawyer, Constance B.; Schweitzer, Andrea E.; Warwick, James W.

1987-01-01

Uranium continuum radio emission detected by the Voyager 2 Planetary Radio Astronomy experiment during the January 1986 encounter is considered. The continuum emissions comprised four components (equatorial emissions, anomaly emissions, strong nightside emissions, and weak nightside emissions) associated with different sources. The equatorial emissions appeared most prominently during the days before closest approach and extended from 40 kHz or below to about 120 kHz. The anomaly emissions were seen about 12 hours before closest approach and extended to about 250 kHz. The agreement found between Miranda's phase and strong radio emission at 20.4 kHz, just after closest approach, suggests intense dynamic activity on the Miranda L shell.

Ab initio calculation of one-nucleon halo states

NASA Astrophysics Data System (ADS)

Rodkin, D. M.; Tchuvil'sky, Yu M.

2018-02-01

We develop an approach to microscopic and ab initio description of clustered systems, states with halo nucleon and one-nucleon resonances. For these purposes a basis combining ordinary shell-model components and cluster-channel terms is built up. The transformation of clustered wave functions to the uniform Slater-determinant type is performed using the concept of cluster coefficients. The resulting basis of orthonormalized wave functions is used for calculating the eigenvalues and the eigenvectors of Hamiltonians built in the framework of ab initio approaches. Calculations of resonance and halo states of 5He, 9Be and 9B nuclei demonstrate that the approach is workable and labor-saving.

Slush Fund: The Multiphase Nature of Oceanic Ices and Its Role in Shaping Europa's Icy Shell

NASA Astrophysics Data System (ADS)

Buffo, J.; Schmidt, B. E.; Huber, C.

2017-12-01

The role of Europa's ice shell in mediating ocean-surface interaction, constraining potential habitability of the underlying hydrosphere, and dictating the surface morphology of the moon is discussed extensively in the literature, yet the dynamics and characteristics of the shell itself remain largely unconstrained. Some of the largest unknowns arise from underrepresented physics and varying a priori assumptions built into the current ice shell models. Here we modify and apply a validated one-dimensional reactive transport model designed to simulate the formation and evolution of terrestrial sea ice to the Europa environment. The top-down freezing of sea ice due to conductive heat loss to the atmosphere is akin to the formation of the Jovian moon's outer ice shell, albeit on a different temporal and spatial scale. Nevertheless, the microscale physics that govern the formation of sea ice on Earth (heterogenous solidification leading to brine pockets and channels, multiphase reactive transport phenomena, gravity drainage) likely operate in a similar manner at the ice-ocean interface of Europa, dictating the thermal, chemical, and mechanical properties of the ice shell. Simulations of the European ice-ocean interface at different stages during the ice shell's evolution are interpolated to produce vertical profiles of temperature, salinity, solid fraction, and eutectic points throughout the entire shell. Additionally, the model is coupled to the equilibrium chemistry package FREZCHEM to investigate the impact a diverse range of putative European ocean chemistries has on ice shell properties. This method removes the need for a priori assumptions of impurity entrainment rates and ice shell properties, thus providing a first principles constraint on the stratigraphic characteristics of a simulated European ice shell. These insights have the potential to improve existing estimates for the onset of solid state convection, melt lens formation due to eutectic melting, ice shell thickness, and ocean-surface interaction rates. Moreover, this work aims to shed light on the important role microscale physics plays in determining the macroscale properties of icy worlds by highlighting and adapting successful multiphase reactive transport sea ice models utilized in large scale Earth systems science simulations.

Nanolaminate Mirrors With "Piston" Figure-Control Actuators

NASA Technical Reports Server (NTRS)

Lowman, Andrew; Redding, David; Hickey, Gregory; Knight, Jennifer; Moynihan, Philip; Lih, Shyh0Shiuh; Barbee, Troy

2003-01-01

Efforts are under way to develop a special class of thin-shell curved mirrors for high-resolution imaging in visible and infrared light in a variety of terrestrial or extraterrestrial applications. These mirrors can have diameters of the order of a meter and include metallic film reflectors on nanolaminate substrates supported by multiple distributed piezoceramic gpiston h-type actuators for micron-level figure control. Whereas conventional glass mirrors of equivalent size and precision have areal mass densities between 50 and 150 kg/sq m, the nanolaminate mirrors, including not only the reflector/ shell portions but also the actuators and the backing structures needed to react the actuation forces, would have areal mass densities that may approach .5 kg/m2. Moreover, whereas fabrication of a conventional glass mirror of equivalent precision takes several years, the reflector/shell portion of a nanolaminate mirror can be fabricated in less than a week, and its actuation system can be fabricated in 1 to 2 months. The engineering of these mirrors involves a fusion of the technological heritage of multisegmented adaptive optics and deformable mirrors with more recent advances in metallic nanolaminates and in mathematical modeling of the deflections of thin, curved shells in response to displacements by multiple, distributed actuators. Because a nanolaminate shell is of the order of 10 times as strong as an otherwise identical shell made of a single, high-strength, non-nanolaminate metal suitable for mirror use, a nanolaminate mirror can be made very thin (typically between 100 and 150 m from the back of the nanolaminate substrate to the front reflecting surface). The thinness and strength of the nanolaminate are what make it possible to use distributed gpiston h-type actuators for surface figure control with minimal local concentrated distortion (called print-through in the art) at the actuation points.

A Novel Approach to Constrain the Mass Ratio of Minor Mergers in Elliptical Galaxies: Application to NGC 4889, the Brightest Cluster Galaxy in Coma

NASA Astrophysics Data System (ADS)

Gu, Meng; Ho, Luis C.; Peng, Chien Y.; Huang, Song

2013-08-01

Minor mergers are thought to be important for the buildup and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (MI ≈ -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of ~90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

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.

Discussion paper: The kink oscillations of the thin nonuniform coronal loops

NASA Astrophysics Data System (ADS)

Mikhalyaev, B. B.

2006-12-01

[1] MHD-oscillations of an inhomogeneous coronal loop consisting of a dense cord and a surrounding shell are investigated. Magnetic field in the cord is longitudinal and in the shell is azimuthal only. Usually the nonuniform field leads to the existence of resonance. However here we assume the resonance points non exist in the tube, i.e. the resonances are cutted. Our approach pursue a target - an investigation of an influence of the wave radiation on the tube oscillations. The resonant absorption of tube oscillation energy is eliminated. The same tube effectively radiate a magnetosonic waves into the environment and the Q-factor of the tube oscillations is small. The presented model can explain the fast damping of the coronal loop oscillations observed by the TRACE EUV channel.

Mass stability in classical Stueckelberg-Horwitz-Piron electrodynamics

NASA Astrophysics Data System (ADS)

Land, Martin

2017-05-01

It is well-known that the 5D gauge structure of Stueckelberg-Horwitz-Piron (SHP) electrodynamics permits the exchange of mass between particles and the electromagnetic fields induced by their motion, even at the classical level. This phenomenon presents two closely related problems: (1) Under what circumstances can real particles evolve sufficiently off-shell to account for mass changing phenomena such as flavor-changing neutrino interactions and low energy nuclear reactions? (2) What accounts for the stability of the measured masses of the known particles? To approach these questions, we first propose a toy model in which a particle evolving through a complex charged environment can acquire a significant mass shift for a short time. We then consider a classical self-interaction that tends to restore on-shell propagation.

A Small-Scale Comparison of Iceland Scallop Size Distributions Obtained from a Camera Based Autonomous Underwater Vehicle and Dredge Survey

PubMed Central

Singh, Warsha; Örnólfsdóttir, Erla B.; Stefansson, Gunnar

2014-01-01

An approach is developed to estimate size of Iceland scallop shells from AUV photos. A small-scale camera based AUV survey of Iceland scallops was conducted at a defined site off West Iceland. Prior to height estimation of the identified shells, the distortions introduced by the vehicle orientation and the camera lens were corrected. The average AUV pitch and roll was and deg that resulted in error in ground distance rendering these effects negligible. A quadratic polynomial model was identified for lens distortion correction. This model successfully predicted a theoretical grid from a frame photographed underwater, representing the inherent lens distortion. The predicted shell heights were scaled for the distance from the bottom at which the photos were taken. This approach was validated by height estimation of scallops of known sizes. An underestimation of approximately cm was seen, which could be attributed to pixel error, where each pixel represented cm. After correcting for this difference the estimated heights ranged from cm. A comparison of the height-distribution from a small-scale dredge survey carried out in the vicinity showed non-overlapping peaks in size distribution, with scallops of a broader size range visible in the AUV survey. Further investigations are necessary to evaluate any underlying bias and to validate how representative these surveys are of the true population. The low resolution images made identification of smaller scallops difficult. Overall, the observations of very few small scallops in both surveys could be attributed to low recruitment levels in the recent years due to the known scallop parasite outbreak in the region. PMID:25303243

A small-scale comparison of Iceland scallop size distributions obtained from a camera based autonomous underwater vehicle and dredge survey.

PubMed

Singh, Warsha; Örnólfsdóttir, Erla B; Stefansson, Gunnar

2014-01-01

An approach is developed to estimate size of Iceland scallop shells from AUV photos. A small-scale camera based AUV survey of Iceland scallops was conducted at a defined site off West Iceland. Prior to height estimation of the identified shells, the distortions introduced by the vehicle orientation and the camera lens were corrected. The average AUV pitch and roll was 1.3 and 2.3 deg that resulted in <2% error in ground distance rendering these effects negligible. A quadratic polynomial model was identified for lens distortion correction. This model successfully predicted a theoretical grid from a frame photographed underwater, representing the inherent lens distortion. The predicted shell heights were scaled for the distance from the bottom at which the photos were taken. This approach was validated by height estimation of scallops of known sizes. An underestimation of approximately 0.5 cm was seen, which could be attributed to pixel error, where each pixel represented 0.24 x 0.27 cm. After correcting for this difference the estimated heights ranged from 3.8-9.3 cm. A comparison of the height-distribution from a small-scale dredge survey carried out in the vicinity showed non-overlapping peaks in size distribution, with scallops of a broader size range visible in the AUV survey. Further investigations are necessary to evaluate any underlying bias and to validate how representative these surveys are of the true population. The low resolution images made identification of smaller scallops difficult. Overall, the observations of very few small scallops in both surveys could be attributed to low recruitment levels in the recent years due to the known scallop parasite outbreak in the region.

Calculation methods study on hot spot stress of new girder structure detail

NASA Astrophysics Data System (ADS)

Liao, Ping; Zhao, Renda; Jia, Yi; Wei, Xing

2017-10-01

To study modeling calculation methods of new girder structure detail's hot spot stress, based on surface extrapolation method among hot spot stress method, a few finite element analysis models of this welded detail were established by finite element software ANSYS. The influence of element type, mesh density, different local modeling methods of the weld toe and extrapolation methods was analyzed on hot spot stress calculation results at the toe of welds. The results show that the difference of the normal stress in the thickness direction and the surface direction among different models is larger when the distance from the weld toe is smaller. When the distance from the toe is greater than 0.5t, the normal stress of solid models, shell models with welds and non-weld shell models tends to be consistent along the surface direction. Therefore, it is recommended that the extrapolated point should be selected outside the 0.5t for new girder welded detail. According to the results of the calculation and analysis, shell models have good grid stability, and extrapolated hot spot stress of solid models is smaller than that of shell models. So it is suggested that formula 2 and solid45 should be carried out during the hot spot stress extrapolation calculation of this welded detail. For each finite element model under different shell modeling methods, the results calculated by formula 2 are smaller than those of the other two methods, and the results of shell models with welds are the largest. Under the same local mesh density, the extrapolated hot spot stress decreases gradually with the increase of the number of layers in the thickness direction of the main plate, and the variation range is within 7.5%.

Nonlinear Response and Residual Strength of Damaged Stiffened Shells Subjected to Combined Loads

NASA Technical Reports Server (NTRS)

Starnes, James H., Jr.; Britt, Vicki O.; Rose, Cheryl A.; Rankin, Charles C.

1996-01-01

The results of an analytical study of the nonlinear response of stiffened fuselage shells with long cracks are presented. The shells are modeled with a hierarchical modeling strategy and analyzed with a nonlinear shell analysis code that maintains the shell in a nonlinear equilibrium state while the crack is grown. The analysis accurately accounts for global and local structural response phenomena. Fuselage skins, frames stringers and failsafe straps are included in the models. Results are presented for various combinations of internal pressure and mechanical bending, vertical shear and torsion loads, and the effects of crack orientation and location on the shell response are described. These results indicate that the nonlinear interaction between the in-plane stress resultants and the out-of-plane displacements near a crack can significantly affect the structural response of the shell, and the stress-intensity factors associated with a crack that are used to predict residual strength. The effects of representative combined loading conditions on the stress-intensity factors associated with a crack are presented. The effects of varying structural parameters on the stress-intensity factors associated with a crack, and on self-similar and non-self-similar crack-growth are also presented.

A new electron density model of the plasmasphere for operational applications and services

NASA Astrophysics Data System (ADS)

Jakowski, Norbert; Hoque, Mohammed Mainul

2018-03-01

The Earth's plasmasphere contributes essentially to total electron content (TEC) measurements from ground or satellite platforms. Furthermore, as an integral part of space weather, associated plasmaspheric phenomena must be addressed in conjunction with ionosphere weather monitoring by operational space weather services. For supporting space weather services and mitigation of propagation errors in Global Navigation Satellite Systems (GNSS) applications we have developed the empirical Neustrelitz plasmasphere model (NPSM). The model consists of an upper L shell dependent part and a lower altitude dependent part, both described by specific exponential decays. Here the McIllwain parameter L defines the geomagnetic field lines in a centered dipole model for the geomagnetic field. The coefficients of the developed approaches are successfully fitted to numerous electron density data derived from dual frequency GPS measurements on-board the CHAMP satellite mission from 2000 to 2005. The data are utilized for fitting up to the L shell L = 3 because a previous validation has shown a good agreement with IMAGE/RPI measurements up to this value. Using the solar radio flux index F10.7 as the only external parameter, the operation of the model is robust, with 40 coefficients fast and sufficiently accurate to be used as a background model for estimating TEC or electron density profiles in near real time GNSS applications and services. In addition to this, the model approach is sensitive to ionospheric coupling resulting in anomalies such as the Nighttime Winter Anomaly and the related Mid-Summer Nighttime Anomaly and even shows a slight plasmasphere compression of the dayside plasmasphere due to solar wind pressure. Modelled electron density and TEC values agree with estimates reported in the literature in similar cases.

van der Waals three-body force shell model (VTSM) for the lattice dynamical studies of thallous bromide

NASA Astrophysics Data System (ADS)

Tiwari, Sarvesh K.; Pandey, L. K.; Shukla, Lal Ji; Upadhyaya, K. S.

2009-12-01

The van der Waals three-body force shell model (VTSM) has been developed by modifying the three-body force shell model (TSM) for the lattice dynamics of ionic crystals with cesium chloride (CsCl) structure. This new model incorporates van der Waals interactions along with long-range Coulomb interactions, three-body interactions and short-range second neighbour interactions in the framework of a rigid shell model (RSM). In the present paper, VTSM has been used to study the lattice dynamics of thallous bromide (TlBr), from which adequacy of VTSM has been established. A comparative study of the dynamical behaviour of TlBr has also been done between the present model and TSM, the model over which modification has been made to obtain the present model VTSM. Good agreement has been observed between the theoretical and experimental results, which give confidence that it is an appropriate model for the complete description of ionic crystals with CsCl structure.

Stress concentration in a cylindrical shell containing a circular hole.

NASA Technical Reports Server (NTRS)

Adams, N. J. I.

1971-01-01

The state of stress in a cylindrical shell containing a circular cutout was determined for axial tension, torsion, and internal pressure loading. The solution was obtained for the shallow shell equations by a variational method. The results were expressed in terms of a nondimensional curvature parameter which was a function of shell radius, shell thickness, and hole radius. The function chosen for the solution was such that when the radius of the cylindrical shell approaches infinity, the flat-plate solution was obtained. The results are compared with solutions obtained by more rigorous analytical methods, and with some experimental results. For small values of the curvature parameter, the agreement is good. For higher values of the curvature parameter, the present solutions indicate a limiting value of stress concentration, which is in contrast to previous results.

Gesellschaft fuer angewandte Mathematik und Mechanik, Scientific Annual Meeting, Universitaet Hannover, Hanover, Federal Republic of Germany, Apr. 8-12, 1990, Reports

NASA Astrophysics Data System (ADS)

Various papers on applied mathematics and mechanics are presented. Among the individual topics addressed are: dynamical systems with time-varying or unsteady structure, micromechanical modeling of creep rupture, forced vibrations of elastic sandwich plates with thick surface layers, postbuckling of a complete spherical shell under a line load, differential-geometric approach to the multibody system dynamics, stability of an oscillator with stochastic parametric excitation, identification strategies for crack-formation in rotors, identification of physical parameters of FEMs, impact model for elastic and partly plastic impacts on objects, varying delay and stability in dynamical systems. Also discussed are: parameter identification of a hybrid model for vibration analysis using the FEM, vibration behavior of a labyrinth seal with through-flow, similarities in the boundary layer of fiber composite materials, distortion parameter in shell theories, elastoplastic crack problem at finite strain, algorithm for computing effective stiffnesses of plates with periodic structure, plasticity of metal-matrix composites in a mixed stress-strain space formation, constitutive equations in directly formulated plate theories, microbuckling and homogenization for long fiber composites.

Aircraft system aft telescope cavity configuration study for Stratospheric Observatory for Infrared Astronomy (SOFIA), phase 2

NASA Technical Reports Server (NTRS)

1994-01-01

The SOFIA Aircraft System (AS) Phase 1 Study was a broad-based study which addressed itself to satisfying technical and programmatic requirements by drawing from existing technology and applying cost-efficient commercial approaches to the aircraft modification. In this SOFIA AS Phase 2 Study, five critical areas of the aircraft were selected for more detailed investigation: forward pressure bulkhead, aft bulkhead, 'free' shell to bulkhead interface, shell cut-out to bulkhead interface, and flooring. The in-depth investigation of these areas upon a finite element model (FEM), with a fine grid model in areas of particular interest, is discussed. The FEM code used is called 'STRAP' and was developed by the engineering firm, Rasmussen and Associates. STRAP is NASTRAN compatible to within 1%. The loads applied to the model were approximated from known 747 envelope conditions. The areas of investigation, and a section through the fuselage is shown. The thrust of this investigation was to develop the design concepts conceived under phase 1 to the point where detailed design could be undertaken with a high level of confidence.

SYMPLECTIC INVARIANTS AND FLOWERS' CLASSIFICATION OF SHELL MODEL STATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmers, K.

1961-01-01

Flowers has given a classification of shell model states in j-j coupling for a fixed number of nucleons in a shell with respect to a symplectic group. The relation between these classifications for the various nucleon numbers is studied and is found to be governed by another symplectic group, the transformations of which in general change the nucleon number. (auth)

Applicability of the Continuum-Shell Theories to the Mechanics of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Harik, V. M.; Gates, T. S.; Nemeth, M. P.

2002-01-01

Validity of the assumptions relating the applicability of continuum shell theories to the global mechanical behavior of carbon nanotubes is examined. The present study focuses on providing a basis that can be used to qualitatively assess the appropriateness of continuum-shell models for nanotubes. To address the effect of nanotube structure on their deformation, all nanotube geometries are divided into four major classes that require distinct models. Criteria for the applicability of continuum models are presented. The key parameters that control the buckling strains and deformation modes of these classes of nanotubes are determined. In an analogy with continuum mechanics, mechanical laws of geometric similitude are presented. A parametric map is constructed for a variety of nanotube geometries as a guide for the applicability of different models. The continuum assumptions made in representing a nanotube as a homogeneous thin shell are analyzed to identify possible limitations of applying shell theories and using their bifurcation-buckling equations at the nano-scale.

Projected shell model study on nuclei near the N = Z line

NASA Astrophysics Data System (ADS)

Sun, Y.

2003-04-01

Study of the N ≈ Z nuclei in the mass-80 region is not only interesting due to the existence of abundant nuclear-structure phenomena, but also important in understanding the nucleosynthesis in the rp-process. It is difficult to apply a conventional shell model due to the necessary involvement of the g 9/2 sub-shell. In this paper, the projected shell model is introduced to this study. Calculations are systematically performed for the collective levels as well as the quasi-particle excitations. It is demonstrated that calculations with this truncation scheme can achieve a comparable quality as the large-scale shell model diagonalizations for 48 Cr, but the present method can be applied to much heavier mass regions. While the known experimental data of the yrast bands in the N ≈ Z nuclei (from Se to Ru) are reasonably described, the present calculations predict the existence of high- K states, some of which lie low in energy under certain structure conditions.

Sound-structure interaction analysis of an infinite-long cylindrical shell submerged in a quarter water domain and subject to a line-distributed harmonic excitation

NASA Astrophysics Data System (ADS)

Guo, Wenjie; Li, Tianyun; Zhu, Xiang; Miao, Yuyue

2018-05-01

The sound-structure coupling problem of a cylindrical shell submerged in a quarter water domain is studied. A semi-analytical method based on the double wave reflection method and the Graf's addition theorem is proposed to solve the vibration and acoustic radiation of an infinite cylindrical shell excited by an axially uniform harmonic line force, in which the acoustic boundary conditions consist of a free surface and a vertical rigid surface. The influences of the complex acoustic boundary conditions on the vibration and acoustic radiation of the cylindrical shell are discussed. It is found that the complex acoustic boundary has crucial influence on the vibration of the cylindrical shell when the cylindrical shell approaches the boundary, and the influence tends to vanish when the distances between the cylindrical shell and the boundaries exceed certain values. However, the influence of the complex acoustic boundary on the far-field sound pressure of the cylindrical shell cannot be ignored. The far-field acoustic directivity of the cylindrical shell varies with the distances between the cylindrical shell and the boundaries, besides the driving frequency. The work provides more understanding on the vibration and acoustic radiation behaviors of cylindrical shells with complex acoustic boundary conditions.

Thermodynamic Theory of Spherically Trapped Coulomb Clusters

NASA Astrophysics Data System (ADS)

Wrighton, Jeffrey; Dufty, James; Bonitz, Michael; K"{A}Hlert, Hanno

2009-11-01

The radial density profile of a finite number of identical charged particles confined in a harmonic trap is computed over a wide ranges of temperatures (Coulomb coupling) and particle numbers. At low temperatures these systems form a Coulomb crystal with spherical shell structure which has been observed in ultracold trapped ions and in dusty plasmas. The shell structure is readily reproduced in simulations. However, analytical theories which used a mean field approachfootnotetext[1]C. Henning et al., Phys. Rev. E 74, 056403 (2006) or a local density approximationfootnotetext[2]C. Henning et al., Phys. Rev. E 76, 036404 (2007) have, so far, only been able to reproduce the average density profile. Here we present an approach to Coulomb correlations based on the hypernetted chain approximation with additional bridge diagrams. It is demonstrated that this model reproduces the correct shell structure within a few percent and provides the basis for a thermodynamic theory of Coulomb clusters in the strongly coupled fluid state.footnotetext[3]J. Wrighton, J.W. Dufty, H. K"ahlert and M. Bonitz, J. Phys. A 42, 214052 (2009) and Phys. Rev. E (2009) (to be submitted)

Facile one-step synthesis of Ag@Fe3O4 core-shell nanospheres for reproducible SERS substrates

NASA Astrophysics Data System (ADS)

Sun, Lijuan; He, Jiang; An, Songsong; Zhang, Junwei; Ren, Dong

2013-08-01

A facile approach has been developed to synthesize Ag@Fe3O4 core-shell nanospheres, in which the Ag nanoparticle core was well wrapped by a permeable Fe3O4 shell. An in situ reduction of AgNO3 and Fe(NO3)3 was the basis of this one-step method with ethylene glycol as the reducing agent. The as-obtained Ag@Fe3O4 nanospheres were a highly efficient surface-enhanced Raman scattering (SERS) substrate; high reproducibility, stability, and reusability were obtained by employing 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as the Raman probe molecules. It was revealed that the SERS signals of 4-ATP and R6G on the Ag@Fe3O4 nanospheres were much stronger than those on the pure Ag nanoparticles, demonstrating that the magnetic enrichment procedures can improve SERS detection sensitivity efficiently. A highly efficient and recyclable SERS substrate was produced by the new model system that has potential applications in chemical and biomolecular assays.

Sensitivity of Double-Shell Ignition Capsules to Asymmetric Drive

NASA Astrophysics Data System (ADS)

Tregillis, I. L.; Magelssen, G. R.; Delamater, N. D.; Gunderson, M. A.; Hoffman, N. M.

2007-11-01

Double-shell (DS) targets [1] present an alternative approach to ignition via the cryogenic single-shell point design [2]. Although these targets present unique fabrication challenges, they embody many attractive features, including non-cryogenic fielding and low threshold temperatures (˜4 keV) for volume ignition [3-4]. We have used 2D radiation-hydrodynamic modeling to survey the behavior of DS targets under asymmetric temperature drive in rugby vacuum hohlraums. The yield is robust against deviations from symmetric illumination, varying smoothly as a function of the imposed P2 and P4 amplitudes. Ignition occurs even when 10% or more of the drive is contained in Legendre P2 or P4 components, with yield reductions on the order of 50% for the most extreme cases investigated here. [1] P. Amendt et al., Phys. of Plasmas 9, 2221 (2002) [2] D. A. Callahan et al., Phys. of Plasmas 13, 56307 (2005) [3] P. Amendt et al., Phys. Rev. Lett. 94, 65004 (2005) [4] W. S. Varnum et al., Phys. Rev. Lett. 84, 5153 (2000)

Kinetic Boltzmann approach adapted for modeling highly ionized matter created by x-ray irradiation of a solid.

PubMed

Ziaja, Beata; Saxena, Vikrant; Son, Sang-Kil; Medvedev, Nikita; Barbrel, Benjamin; Woloncewicz, Bianca; Stransky, Michal

2016-05-01

We report on the kinetic Boltzmann approach adapted for simulations of highly ionized matter created from a solid by its x-ray irradiation. X rays can excite inner-shell electrons, which leads to the creation of deeply lying core holes. Their relaxation, especially in heavier elements, can take complicated paths, leading to a large number of active configurations. Their number can be so large that solving the set of respective evolution equations becomes computationally inefficient and another modeling approach should be used instead. To circumvent this complexity, the commonly used continuum models employ a superconfiguration scheme. Here, we propose an alternative approach which still uses "true" atomic configurations but limits their number by restricting the sample relaxation to the predominant relaxation paths. We test its reliability, performing respective calculations for a bulk material consisting of light atoms and comparing the results with a full calculation including all relaxation paths. Prospective application for heavy elements is discussed.

Egg production forecasting: Determining efficient modeling approaches.

PubMed

Ahmad, H A

2011-12-01

Several mathematical or statistical and artificial intelligence models were developed to compare egg production forecasts in commercial layers. Initial data for these models were collected from a comparative layer trial on commercial strains conducted at the Poultry Research Farms, Auburn University. Simulated data were produced to represent new scenarios by using means and SD of egg production of the 22 commercial strains. From the simulated data, random examples were generated for neural network training and testing for the weekly egg production prediction from wk 22 to 36. Three neural network architectures-back-propagation-3, Ward-5, and the general regression neural network-were compared for their efficiency to forecast egg production, along with other traditional models. The general regression neural network gave the best-fitting line, which almost overlapped with the commercial egg production data, with an R(2) of 0.71. The general regression neural network-predicted curve was compared with original egg production data, the average curves of white-shelled and brown-shelled strains, linear regression predictions, and the Gompertz nonlinear model. The general regression neural network was superior in all these comparisons and may be the model of choice if the initial overprediction is managed efficiently. In general, neural network models are efficient, are easy to use, require fewer data, and are practical under farm management conditions to forecast egg production.

Transient Response of Shells of Revolution by Direct Integration and Modal Superposition Methods

NASA Technical Reports Server (NTRS)

Stephens, W. B.; Adelman, H. M.

1974-01-01

The results of an analytical effort to obtain and evaluate transient response data for a cylindrical and a conical shell by use of two different approaches: direct integration and modal superposition are described. The inclusion of nonlinear terms is more important than the inclusion of secondary linear effects (transverse shear deformation and rotary inertia) although there are thin-shell structures where these secondary effects are important. The advantages of the direct integration approach are that geometric nonlinear and secondary effects are easy to include and high-frequency response may be calculated. In comparison to the modal superposition technique the computer storage requirements are smaller. The advantages of the modal superposition approach are that the solution is independent of the previous time history and that once the modal data are obtained, the response for repeated cases may be efficiently computed. Also, any admissible set of initial conditions can be applied.

Free Vibrations of Nonthin Elliptic Cylindrical Shells of Variable Thickness

NASA Astrophysics Data System (ADS)

Grigorenko, A. Ya.; Efimova, T. L.; Korotkikh, Yu. A.

2017-11-01

The problem of the free vibrations of nonthin elliptic cylindrical shells of variable thickness under various boundary conditions is solved using the refined Timoshenko-Mindlin theory. To solve the problem, an effective numerical approach based on the spline-approximation and discrete-orthogonalization methods is used. The effect of the cross-sectional shape, thickness variation law, material properties, and boundary conditions on the natural frequency spectrum of the shells is analyzed.

7Be(p,gamma)8B S-factor from Ab Initio Wave Functions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Navratil, P; Bertulani, C A; Caurier, E

2006-10-12

There has been a significant progress in ab initio approaches to the structure of light nuclei. Starting from realistic two- and three-nucleon interactions the ab initio no-core shell model (NCSM) predicts low-lying levels in p-shell nuclei. It is a challenging task to extend ab initio methods to describe nuclear reactions. We present here a brief overview of the first steps taken toward nuclear reaction applications. In particular, we discuss our calculation of the {sup 7}Be(p,{gamma}){sup 8}B S-factor. We also present our first results of the {sup 3}He({alpha},{gamma}){sup 7}Be S-factor and of the S-factor of the mirror reaction {sup 3}H({alpha},{gamma}){sup 7}Li.more » The {sup 7}Be(p,{gamma}){sup 8}B and {sup 3}He({alpha},{gamma}){sup 7}Be reactions correspond to the most important uncertainties in solar model predictions of neutrino fluxes.« less

7Li(d,p)8Li transfer reaction in the NCSM/RGM approach

NASA Astrophysics Data System (ADS)

Raimondi, F.; Hupin, G.; Navrátil, P.; Quaglioni, S.

2018-03-01

Recently, we applied an ab initio method, the no-core shell model combined with the resonating group method, to the transfer reactions with light p-shell nuclei as targets and deuteron as the projectile. In particular, we studied the elastic scattering of deuterium on 7Li and the 7Li(d,p)8Li transfer reaction starting from a realistic two-nucleon interaction. In this contribution, we review of our main results on the 7Li(d,p)8Li transfer reaction, and we extend the study of the relevant reaction channels, by showing the dominant resonant phase shifts of the scattering matrix. We assess also the impact of the polarization effects of the deuteron below the breakup on the positive-parity resonant states in the reaction. For this purpose, we perform an analysis of the convergence trend of the phase and eigenphase shifts, with respect to the number of deuteron pseudostates included in the model space.

Pulsational stabilities of a star in thermal imbalance - Comparison between the methods

NASA Technical Reports Server (NTRS)

Vemury, S. K.

1978-01-01

The stability coefficients for quasi-adiabatic pulsations for a model in thermal imbalance are evaluated using the dynamical energy (DE) approach, the total (kinetic plus potential) energy (TE) approach, and the small amplitude (SA) approaches. From a comparison among the methods, it is found that there can exist two distinct stability coefficients under conditions of thermal imbalance as pointed out by Demaret. It is shown that both the TE approaches lead to one stability coefficient, while both the SA approaches lead to another coefficient. The coefficient obtained through the energy approaches is identified as the one which determines the stability of the velocity amplitudes. For a prenova model with a thin hydrogen-burning shell in thermal imbalance, several radial modes are found to be unstable both for radial displacements and for velocity amplitudes. However, a new kind of pulsational instability also appears, viz., while the radial displacements are unstable, the velocity amplitudes may be stabilized through the thermal imbalance terms.

Core excitations across the neutron shell gap in 207Tl

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, E.; Podolyák, Zs.; Grawe, H.

2015-05-05

The single closed-neutron-shell, one proton–hole nucleus 207Tl was populated in deep-inelastic collisions of a 208Pb beam with a 208Pb target. The yrast and near-yrast level scheme has been established up to high excitation energy, comprising an octupole phonon state and a large number of core excited states. Based on shell-model calculations, all observed single core excitations were established to arise from the breaking of the N=126 neutron core. While the shell-model calculations correctly predict the ordering of these states, their energies are compressed at high spins. It is concluded that this compression is an intrinsic feature of shell-model calculations usingmore » two-body matrix elements developed for the description of two-body states, and that multiple core excitations need to be considered in order to accurately calculate the energy spacings of the predominantly three-quasiparticle states.« less

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.

Graphitic carbon nitride nanosheet@metal-organic framework core-shell nanoparticles for photo-chemo combination therapy

NASA Astrophysics Data System (ADS)

Chen, Rui; Zhang, Jinfeng; Wang, Yu; Chen, Xianfeng; Zapien, J. Antonio; Lee, Chun-Sing

2015-10-01

Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process.Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04436g

Tunable plasmon resonance and enhanced second harmonic generation and upconverted fluorescence of hemispheric-like silver core/shell islands

NASA Astrophysics Data System (ADS)

Ding, Si-Jing; Nan, Fan; Yang, Da-Jie; Zhong, Yu-Ting; Hao, Zhong-Hua; Wang, Qu-Quan

2015-09-01

We investigate tunable plasmon resonance and enhanced second harmonic generation (SHG) and up-converted fluorescence (UCF) of the hemispheric-like silver core/shell islands. The Ag, Ag/Ag2O, and Ag/Ag2O/Ag island films are prepared by using a sputtering technique. The SHG and UCF of the Ag/Ag2O/Ag core/shell islands near the percolating regime is enhanced 2.34 and 3.94 times compared to the sum of two individual counterparts of Ag/Ag2O core/shell and Ag shell islands. The ratio of SHG intensity induced by p- and s-polarization is 0.86 for the initial Ag islands and increase to 1.61 for the Ag/Ag2O/Ag core/shell samples. The tunable intensity ratio of SHG to UCF of the Ag islands treated by thermal and laser annealing processes is also observed. The physical mechanism of the enhanced SHG and UCF in the Ag/Ag2O/Ag core/shell islands is discussed. Our observations provide a new approach to fabricate plasmon-enhanced optical nonlinear nanodevices with tunable SHG and UCF.We investigate tunable plasmon resonance and enhanced second harmonic generation (SHG) and up-converted fluorescence (UCF) of the hemispheric-like silver core/shell islands. The Ag, Ag/Ag2O, and Ag/Ag2O/Ag island films are prepared by using a sputtering technique. The SHG and UCF of the Ag/Ag2O/Ag core/shell islands near the percolating regime is enhanced 2.34 and 3.94 times compared to the sum of two individual counterparts of Ag/Ag2O core/shell and Ag shell islands. The ratio of SHG intensity induced by p- and s-polarization is 0.86 for the initial Ag islands and increase to 1.61 for the Ag/Ag2O/Ag core/shell samples. The tunable intensity ratio of SHG to UCF of the Ag islands treated by thermal and laser annealing processes is also observed. The physical mechanism of the enhanced SHG and UCF in the Ag/Ag2O/Ag core/shell islands is discussed. Our observations provide a new approach to fabricate plasmon-enhanced optical nonlinear nanodevices with tunable SHG and UCF. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03627e

Comparison of performance of shell-and-tube heat exchangers with conventional segmental baffles and continuous helical baffle

NASA Astrophysics Data System (ADS)

Ahmed, Asif; Ferdous, Imam Ul.; Saha, Sumon

2017-06-01

In the present study, three-dimensional numerical simulation of two shell-and-tube heat exchangers (STHXs) with conventional segmental baffles (STHXsSB) and continuous helical baffle (STHXsHB) is carried out and a comparative study is performed based on the simulation results. Both of the STHXs contain 37 tubes inside a 500 mm long and 200 mm diameter shell and mass flow rate of shell-side fluid is varied from 0.5 kg/s to 2 kg/s. At first, physical and mathematical models are developed and numerically simulated using finite element method (FEM). For the validation of the computational model, shell-side average nusselt number (Nus) is calculated from the simulation results and compared with the available experimental results. The comparative study shows that STHXsHB has 72-127% higher heat transfer coefficient per unit pressure drop compared to the conventional STHXsSB for the same shell-side mass flow rate. Moreover, STHXsHB has 59-63% lower shell-side pressure drop than STHXsSB.

Cenosphere formation from heavy fuel oil: a numerical analysis accounting for the balance between porous shells and internal pressure

NASA Astrophysics Data System (ADS)

Reddy, Vanteru M.; Rahman, Mustafa M.; Gandi, Appala N.; Elbaz, Ayman M.; Schrecengost, Robert A.; Roberts, William L.

2016-01-01

Heavy fuel oil (HFO) as a fuel in industrial and power generation plants ensures the availability of energy at economy. Coke and cenosphere emissions from HFO combustion need to be controlled by particulate control equipment such as electrostatic precipitators, and collection effectiveness is impacted by the properties of these particulates. The cenosphere formation is a function of HFO composition, which varies depending on the source of the HFO. Numerical modelling of the cenosphere formation mechanism presented in this paper is an economical method of characterising cenosphere formation potential for HFO in comparison to experimental analysis of individual HFO samples, leading to better control and collection. In the present work, a novel numerical model is developed for understanding the global cenosphere formation mechanism. The critical diameter of the cenosphere is modelled based on the balance between two pressures developed in an HFO droplet. First is the pressure (Prpf) developed at the interface of the liquid surface and the inner surface of the accumulated coke due to the flow restriction of volatile components from the interior of the droplet. Second is the pressure due to the outer shell strength (PrC) gained from van der Walls energy of the coke layers and surface energy. In this present study it is considered that when PrC ≥ Prpf the outer shell starts to harden. The internal motion in the shell layer ceases and the outer diameter (DSOut) of the shell is then fixed. The entire process of cenosphere formation in this study is analysed in three phases: regression, shell formation and hardening, and post shell hardening. Variations in pressures during shell formation are analysed. Shell (cenosphere) dimensions are evaluated at the completion of droplet evaporation. The rate of fuel evaporation, rate of coke formation and coke accumulation are analysed. The model predicts shell outer diameters of 650, 860 and 1040 µm, and inner diameters are 360, 410 and 430 µm respectively, for 700, 900 and 1100 µm HFO droplets. The present numerical model is validated with experimental results available from the literature. Total variation between computational and experimental results is in the range of 3-7%.

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.

Prediction for a Four-Neutron Resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shirokov, A. M.; Papadimitriou, G.; Mazur, A. I.

Here, we utilize various ab initio approaches to search for a low-lying resonance in the four-neutron (4n) system using the JISP16 realistic NN interaction. Our most accurate prediction is obtained using a J-matrix extension of the no-core shell model and suggests a 4n resonant state at an energy near E r = 0.8 MeV with a width of approximately Γ = 1.4 MeV.

Prediction for a Four-Neutron Resonance

DOE PAGES

Shirokov, A. M.; Papadimitriou, G.; Mazur, A. I.; ...

2016-10-28

Here, we utilize various ab initio approaches to search for a low-lying resonance in the four-neutron (4n) system using the JISP16 realistic NN interaction. Our most accurate prediction is obtained using a J-matrix extension of the no-core shell model and suggests a 4n resonant state at an energy near E r = 0.8 MeV with a width of approximately Γ = 1.4 MeV.

SPY: A new scission point model based on microscopic ingredients to predict fission fragments properties

NASA Astrophysics Data System (ADS)

Lemaître, J.-F.; Dubray, N.; Hilaire, S.; Panebianco, S.; Sida, J.-L.

2013-12-01

Our purpose is to determine fission fragments characteristics in a framework of a scission point model named SPY for Scission Point Yields. This approach can be considered as a theoretical laboratory to study fission mechanism since it gives access to the correlation between the fragments properties and their nuclear structure, such as shell correction, pairing, collective degrees of freedom, odd-even effects. Which ones are dominant in final state? What is the impact of compound nucleus structure? The SPY model consists in a statistical description of the fission process at the scission point where fragments are completely formed and well separated with fixed properties. The most important property of the model relies on the nuclear structure of the fragments which is derived from full quantum microscopic calculations. This approach allows computing the fission final state of extremely exotic nuclei which are inaccessible by most of the fission model available on the market.

One-pot synthesis of iniferter-bound polystyrene core nanoparticles for the controlled grafting of multilayer shells

NASA Astrophysics Data System (ADS)

Marchyk, Nataliya; Maximilien, Jacqueline; Beyazit, Selim; Haupt, Karsten; Sum Bui, Bernadette Tse

2014-02-01

A novel approach using one-pot synthesis for the production of uniform, iniferter-bound polystyrene core nanoparticles of size 30-40 nm is described. Conventional oil-in-water emulsion polymerisation of styrene and divinylbenzene, combining a hybrid initiation system (thermal and UV), triggered sequentially, was employed to form the surface-bound thiocarbamate iniferters in situ. The iniferter cores were then used as seeds for re-initiating further polymerisation by UV irradiation to produce water-compatible core-shell nanoparticles. Grafting of various shell-types is demonstrated: linear polymers of poly(N-isopropylacrylamide) brushes, crosslinked polymers bearing different surface charges and molecularly imprinted polymers. The shell thickness was readily tuned by varying the monomers' concentration and polymerisation time. Our method is straightforward and in addition, gives access to the preparation of fluorescent seeds and the possibility of grafting nanosized multiple shells. The core-shell nanoparticles were fully characterised by dynamic light scattering, transmission electron microscopy, Fourier transform infrared spectroscopy and microelemental analysis.A novel approach using one-pot synthesis for the production of uniform, iniferter-bound polystyrene core nanoparticles of size 30-40 nm is described. Conventional oil-in-water emulsion polymerisation of styrene and divinylbenzene, combining a hybrid initiation system (thermal and UV), triggered sequentially, was employed to form the surface-bound thiocarbamate iniferters in situ. The iniferter cores were then used as seeds for re-initiating further polymerisation by UV irradiation to produce water-compatible core-shell nanoparticles. Grafting of various shell-types is demonstrated: linear polymers of poly(N-isopropylacrylamide) brushes, crosslinked polymers bearing different surface charges and molecularly imprinted polymers. The shell thickness was readily tuned by varying the monomers' concentration and polymerisation time. Our method is straightforward and in addition, gives access to the preparation of fluorescent seeds and the possibility of grafting nanosized multiple shells. The core-shell nanoparticles were fully characterised by dynamic light scattering, transmission electron microscopy, Fourier transform infrared spectroscopy and microelemental analysis. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05295h

All (4,1): Sigma models with (4 , q) off-shell supersymmetry

NASA Astrophysics Data System (ADS)

Hull, Chris; Lindström, Ulf

2017-03-01

Off-shell (4 , q) supermultiplets in 2-dimensions are constructed for q = 1 , 2 , 4. These are used to construct sigma models whose target spaces are hyperkähler with torsion. The off-shell supersymmetry implies the three complex structures are simultaneously integrable and allows us to construct actions using extended superspace and projective superspace, giving an explicit construction of the target space geometries.

Modeling and optimization by particle swarm embedded neural network for adsorption of zinc (II) by palm kernel shell based activated carbon from aqueous environment.

PubMed

Karri, Rama Rao; Sahu, J N

2018-01-15

Zn (II) is one the common pollutant among heavy metals found in industrial effluents. Removal of pollutant from industrial effluents can be accomplished by various techniques, out of which adsorption was found to be an efficient method. Applications of adsorption limits itself due to high cost of adsorbent. In this regard, a low cost adsorbent produced from palm oil kernel shell based agricultural waste is examined for its efficiency to remove Zn (II) from waste water and aqueous solution. The influence of independent process variables like initial concentration, pH, residence time, activated carbon (AC) dosage and process temperature on the removal of Zn (II) by palm kernel shell based AC from batch adsorption process are studied systematically. Based on the design of experimental matrix, 50 experimental runs are performed with each process variable in the experimental range. The optimal values of process variables to achieve maximum removal efficiency is studied using response surface methodology (RSM) and artificial neural network (ANN) approaches. A quadratic model, which consists of first order and second order degree regressive model is developed using the analysis of variance and RSM - CCD framework. The particle swarm optimization which is a meta-heuristic optimization is embedded on the ANN architecture to optimize the search space of neural network. The optimized trained neural network well depicts the testing data and validation data with R 2 equal to 0.9106 and 0.9279 respectively. The outcomes indicates that the superiority of ANN-PSO based model predictions over the quadratic model predictions provided by RSM. Copyright © 2017 Elsevier Ltd. All rights reserved.

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles.

PubMed

Zhang, Jun; Liu, Xianghong; Wang, Liwei; Yang, Taili; Guo, Xianzhi; Wu, Shihua; Wang, Shurong; Zhang, Shoumin

2011-05-06

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.

An Aeroelastic Evaluation of the Flexible Thermal Protection System for an Inatable Aerodynamic Decelerator

NASA Astrophysics Data System (ADS)

Goldman, Benjamin D.

The purpose of this dissertation is to study the aeroelastic stability of a proposed flexible thermal protection system (FTPS) for the NASA Hypersonic Inflatable Aerodynamic Decelerator (HIAD). A flat, square FTPS coupon exhibits violent oscillations during experimental aerothermal testing in NASA's 8 Foot High Temperature Tunnel, leading to catastrophic failure. The behavior of the structural response suggested that aeroelastic flutter may be the primary instability mechanism, prompting further experimental investigation and theoretical model development. Using Von Karman's plate theory for the panel-like structure and piston theory aerodynamics, a set of aeroelastic models were developed and limit cycle oscillations (LCOs) were calculated at the tunnel flow conditions. Similarities in frequency content of the theoretical and experimental responses indicated that the observed FTPS oscillations were likely aeroelastic in nature, specifically LCO/flutter. While the coupon models can be used for comparison with tunnel tests, they cannot predict accurately the aeroelastic behavior of the FTPS in atmospheric flight. This is because the geometry of the flight vehicle is no longer a flat plate, but rather (approximately) a conical shell. In the second phase of this work, linearized Donnell conical shell theory and piston theory aerodynamics are used to calculate natural modes of vibration and flutter dynamic pressures for various structural models composed of one or more conical shells resting on several circumferential elastic supports. When the flight vehicle is approximated as a single conical shell without elastic supports, asymmetric flutter in many circumferential waves is observed. When the elastic supports are included, the shell flutters symmetrically in zero circumferential waves. Structural damping is found to be important in this case, as "hump-mode" flutter is possible. Aeroelastic models that consider the individual FTPS layers as separate shells exhibit asymmetric flutter at high dynamic pressures relative to the single shell models. Parameter studies also examine the effects of tension, shear modulus reduction, and elastic support stiffness. Limitations of a linear structural model and piston theory aerodynamics prompted a more elaborate evaluation of the flight configuration. Using nonlinear Donnell conical shell theory for the FTPS structure, the pressure buckling and aeroelastic limit cycle oscillations were studied for a single elastically-supported conical shell. While piston theory was used initially, a time-dependent correction factor was derived using transform methods and potential flow theory to calculate more accurately the low Mach number supersonic flow. Three conical shell geometries were considered: a 3-meter diameter 70° shell, a 3.7-meter 70° shell, and a 6-meter diameter 70° shell. The 6-meter configuration was loaded statically and the results were compared with an experimental load test of a 6-meter HIAD vehicle. Though agreement between theoretical and experimental strains was poor, circumferential wrinkling phenomena observed during the experiments was captured by the theory and axial deformations were qualitatively similar in shape. With piston theory aerodynamics, the nonlinear flutter dynamic pressures of the 3-meter configuration were in agreement with the values calculated using linear theory, and the limit cycle amplitudes were generally on the order of the shell thickness. Pre-buckling pressure loads and the aerodynamic pressure correction factor were studied for all geometries, and these effects resulted in significantly lower flutter boundaries compared with piston theory alone. In the final phase of this work, the existing linear and nonlinear FTPS shell models were coupled with NASA's FUN3D Reynolds Averaged Navier Stokes CFD code, allowing for the most physically realistic flight predictions. For the linear shell structural model, the elastically-supported shell natural modes were mapped to a CFD grid of a 6-meter HIAD vehicle, and a linear structural dynamics solver internal to the CFD code was used to compute the aeroelastic response. Aerodynamic parameters for a proposed HIAD re-entry trajectory were obtained, and aeroelastic solutions were calculated at three points in the trajectory: Mach 1, Mach 2, and Mach 11 (peak dynamic pressure). No flutter was found at any of these conditions using the linear method, though oscillations (of uncertain origin) on the order of the shell thickness may be possible in the transonic regime. For the nonlinear shell structural model, a set of assumed sinusoidal modes were mapped to the CFD grid, and the linear structural dynamics equations were replaced by a nonlinear ODE solver for the conical shell equations. Successful calculation and restart of the nonlinear dynamic aeroelastic solutions was demonstrated. Preliminary results indicated that dynamic instabilities may be possible at Mach 1 and 2, with a completely stable solution at Mach 11, though further study is needed. A major benefit of this implementation is that the coefficients and mode shapes for the nonlinear conical shell may be replaced with those of other types of structures, greatly expanding the aeroelastic capabilities of FUN3D.

A Complete Structural Inventory of the Mycobacterial Microcompartment Shell Proteins Constrains Models of Global Architecture and Transport*

PubMed Central

Mallette, Evan

2017-01-01

Bacterial microcompartments are bacterial analogs of eukaryotic organelles in that they spatially segregate aspects of cellular metabolism, but they do so by building not a lipid membrane but a thin polyhedral protein shell. Although multiple shell protein structures are known for several microcompartment types, additional uncharacterized components complicate systematic investigations of shell architecture. We report here the structures of all four proteins proposed to form the shell of an uncharacterized microcompartment designated the Rhodococcus and Mycobacterium microcompartment (RMM), which, along with crystal interactions and docking studies, suggests possible models for the particle's vertex and edge organization. MSM0272 is a typical hexameric β-sandwich shell protein thought to form the bulk of the facet. MSM0273 is a pentameric β-barrel shell protein that likely plugs the vertex of the particle. MSM0271 is an unusual double-ringed bacterial microcompartment shell protein whose rings are organized in an offset position relative to all known related proteins. MSM0275 is related to MSM0271 but self-organizes as linear strips that may line the facet edge; here, the presence of a novel extendable loop may help ameliorate poor packing geometry of the rigid main particle at the angled edges. In contrast to previously characterized homologs, both of these proteins show closed pores at both ends. This suggests a model where key interactions at the vertex and edges are mediated at the inner layer of the shell by MSM0271 (encircling MSM0273) and MSM0275, and the facet is built from MSM0272 hexamers tiling in the outer layer of the shell. PMID:27927988

A Complete Structural Inventory of the Mycobacterial Microcompartment Shell Proteins Constrains Models of Global Architecture and Transport.

PubMed

Mallette, Evan; Kimber, Matthew S

2017-01-27

Bacterial microcompartments are bacterial analogs of eukaryotic organelles in that they spatially segregate aspects of cellular metabolism, but they do so by building not a lipid membrane but a thin polyhedral protein shell. Although multiple shell protein structures are known for several microcompartment types, additional uncharacterized components complicate systematic investigations of shell architecture. We report here the structures of all four proteins proposed to form the shell of an uncharacterized microcompartment designated the Rhodococcus and Mycobacterium microcompartment (RMM), which, along with crystal interactions and docking studies, suggests possible models for the particle's vertex and edge organization. MSM0272 is a typical hexameric β-sandwich shell protein thought to form the bulk of the facet. MSM0273 is a pentameric β-barrel shell protein that likely plugs the vertex of the particle. MSM0271 is an unusual double-ringed bacterial microcompartment shell protein whose rings are organized in an offset position relative to all known related proteins. MSM0275 is related to MSM0271 but self-organizes as linear strips that may line the facet edge; here, the presence of a novel extendable loop may help ameliorate poor packing geometry of the rigid main particle at the angled edges. In contrast to previously characterized homologs, both of these proteins show closed pores at both ends. This suggests a model where key interactions at the vertex and edges are mediated at the inner layer of the shell by MSM0271 (encircling MSM0273) and MSM0275, and the facet is built from MSM0272 hexamers tiling in the outer layer of the shell. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Modeling the Electrostatics of Hollow Shell Suspensions: Ion Distribution, Pair Interactions, and Many-Body Effects.

PubMed

Hallez, Yannick; Meireles, Martine

2016-10-11

Electrostatic interactions play a key role in hollow shell suspensions as they determine their structure, stability, thermodynamics, and rheology and also the loading capacity of small charged species for nanoreservoir applications. In this work, fast, reliable modeling strategies aimed at predicting the electrostatics of hollow shells for one, two, and many colloids are proposed and validated. The electrostatic potential inside and outside a hollow shell with a finite thickness and a specific permittivity is determined analytically in the Debye-Hückel (DH) limit. An expression for the interaction potential between two such hollow shells is then derived and validated numerically. It follows a classical Yukawa form with an effective charge depending on the shell geometry, permittivity, and inner and outer surface charge densities. The predictions of the Ornstein-Zernike (OZ) equation with this pair potential to determine equations of state are then evaluated by comparison to results obtained with a Brownian dynamics algorithm coupled to the resolution of the linearized Poisson-Boltzmann and Laplace equations (PB-BD simulations). The OZ equation based on the DLVO-like potential performs very well in the dilute regime as expected, but also quite well, and more surprisingly, in the concentrated regime in which full spheres exhibit significant many-body effects. These effects are shown to vanish for shells with small thickness and high permittivity. For highly charged hollow shells, we propose and validate a charge renormalization procedure. Finally, using PB-BD simulations, we show that the cell model predicts the ion distribution inside and outside hollow shells accurately in both electrostatically dilute and concentrated suspensions. We then determine the shell loading capacity as a function of salt concentration, volume fraction, and surface charge density for nanoreservoir applications such as drug delivery, sensing, or smart coatings.

Modeling and simulation in biomedicine.

PubMed Central

Aarts, J.; Möller, D.; van Wijk van Brievingh, R.

1991-01-01

A group of researchers and educators in The Netherlands, Germany and Czechoslovakia have developed and adapted mathematical computer models of phenomena in the field of physiology and biomedicine for use in higher education. The models are graphical and highly interactive, and are all written in TurboPascal or the mathematical simulation language PSI. An educational shell has been developed to launch the models. The shell allows students to interact with the models and teachers to edit the models, to add new models and to monitor the achievements of the students. The models and the shell have been implemented on a MS-DOS personal computer. This paper describes the features of the modeling package and presents the modeling and simulation of the heart muscle as an example. PMID:1807745

Facile synthesis of hierarchical Co3O4@MnO2 core-shell arrays on Ni foam for asymmetric supercapacitors

NASA Astrophysics Data System (ADS)

Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Wen, Zhiyu; Liu, Qing

2014-04-01

Hierarchical Co3O4@MnO2 core-shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core-shell arrays on Ni foam have exhibited a high specific capacitance (560 F g-1 at a current density of 0.2 A g-1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg-1 and a maximum power density of 158 kW kg-1. The rational design of the unique core-shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.

Performance analysis of the node shell on a container door based on ANSYS

NASA Astrophysics Data System (ADS)

Li, Qingzhou; Zhou, Yi; Hu, Changqing; Cheng, Jiamin; Zeng, Xiaochen

2018-01-01

The structure of thenode shell on a container door was designed and analyzed in this study. The model of the shell was developed with ANSYS. The grids of the model were divided based on the Hex dominant method, and the stress distribution and the temperature distribution of the shell were calculated based on FEA (Finite Element Analysis) method. The analysis results indicated thatthe location of the concave upward side has the highest stress which also lower than the strength limit of the material. The temperature of the magnet installation location was highest, therefore the glue for fixing the magnet must has high temperature resistance. The results provide the basis for the further optimization of the shell.

http://www.nasa.gov/image-feature/goddard/hubble-spots-the-layers-of-ngc-3923

NASA Image and Video Library

2015-05-15

The glowing object in this Hubble Space Telescope image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra. NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers. Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centers approach, they initially oscillate about a common center, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed. NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image, and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed. Credit: ESA/Hubble & NASA

On sound transmission into a stiffened cylindrical shell with rings and stringers treated as discrete elements

NASA Technical Reports Server (NTRS)

Koval, L. R.

1980-01-01

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the transmission of an oblique plane sound wave into a finite cylindrical shell stiffened by stringers and ring frames. The rings and stringers are modeled as discrete structural elements. The numerical case studied was typical of a narrow-bodied jet transport fuselage. The numerical results show that the ring-frequency dip in the transmission loss curve that is present for a monocoque shell is still present in the case of a stiffened shell. The ring frequency effect is a result of the cylindrical geometry of the shell. Below the ring frequency, stiffening does not appear to have any significant effect on transmission loss, but above the ring frequency, stiffeners can enhance the transmission loss of a cylindrical shell.

Microbubble Sizing and Shell Characterization Using Flow Cytometry

PubMed Central

Tu, Juan; Swalwell, Jarred E.; Giraud, David; Cui, Weicheng; Chen, Weizhong; Matula, Thomas J.

2015-01-01

Experiments were performed to size, count, and obtain shell parameters for individual ultrasound contrast microbubbles using a modified flow cytometer. Light scattering was modeled using Mie theory, and applied to calibration beads to calibrate the system. The size distribution and population were measured directly from the flow cytometer. The shell parameters (shear modulus and shear viscosity) were quantified at different acoustic pressures (from 95 to 333 kPa) by fitting microbubble response data to a bubble dynamics model. The size distribution of the contrast agent microbubbles is consistent with manufacturer specifications. The shell shear viscosity increases with increasing equilibrium microbubble size, and decreases with increasing shear rate. The observed trends are independent of driving pressure amplitude. The shell elasticity does not vary with microbubble size. The results suggest that a modified flow cytometer can be an effective tool to characterize the physical properties of microbubbles, including size distribution, population, and shell parameters. PMID:21622051

Effect of Mesoscale and Multiscale Modeling on the Performance of Kevlar Woven Fabric Subjected to Ballistic Impact: A Numerical Study

NASA Astrophysics Data System (ADS)

Jia, Xin; Huang, Zhengxiang; Zu, Xudong; Gu, Xiaohui; Xiao, Qiangqiang

2013-12-01

In this study, an optimal finite element model of Kevlar woven fabric that is more computational efficient compared with existing models was developed to simulate ballistic impact onto fabric. Kevlar woven fabric was modeled to yarn level architecture by using the hybrid elements analysis (HEA), which uses solid elements in modeling the yarns at the impact region and uses shell elements in modeling the yarns away from the impact region. Three HEA configurations were constructed, in which the solid element region was set as about one, two, and three times that of the projectile's diameter with impact velocities of 30 m/s (non-perforation case) and 200 m/s (perforation case) to determine the optimal ratio between the solid element region and the shell element region. To further reduce computational time and to maintain the necessary accuracy, three multiscale models were presented also. These multiscale models combine the local region with the yarn level architecture by using the HEA approach and the global region with homogenous level architecture. The effect of the varying ratios of the local and global area on the ballistic performance of fabric was discussed. The deformation and damage mechanisms of fabric were analyzed and compared among numerical models. Simulation results indicate that the multiscale model based on HEA accurately reproduces the baseline results and obviously decreases computational time.

Multi-shell model of ion-induced nucleic acid condensation

NASA Astrophysics Data System (ADS)

Tolokh, Igor S.; Drozdetski, Aleksander V.; Pollack, Lois; Baker, Nathan A.; Onufriev, Alexey V.

2016-04-01

We present a semi-quantitative model of condensation of short nucleic acid (NA) duplexes induced by trivalent cobalt(iii) hexammine (CoHex) ions. The model is based on partitioning of bound counterion distribution around single NA duplex into "external" and "internal" ion binding shells distinguished by the proximity to duplex helical axis. In the aggregated phase the shells overlap, which leads to significantly increased attraction of CoHex ions in these overlaps with the neighboring duplexes. The duplex aggregation free energy is decomposed into attractive and repulsive components in such a way that they can be represented by simple analytical expressions with parameters derived from molecular dynamic simulations and numerical solutions of Poisson equation. The attractive term depends on the fractions of bound ions in the overlapping shells and affinity of CoHex to the "external" shell of nearly neutralized duplex. The repulsive components of the free energy are duplex configurational entropy loss upon the aggregation and the electrostatic repulsion of the duplexes that remains after neutralization by bound CoHex ions. The estimates of the aggregation free energy are consistent with the experimental range of NA duplex condensation propensities, including the unusually poor condensation of RNA structures and subtle sequence effects upon DNA condensation. The model predicts that, in contrast to DNA, RNA duplexes may condense into tighter packed aggregates with a higher degree of duplex neutralization. An appreciable CoHex mediated RNA-RNA attraction requires closer inter-duplex separation to engage CoHex ions (bound mostly in the "internal" shell of RNA) into short-range attractive interactions. The model also predicts that longer NA fragments will condense more readily than shorter ones. The ability of this model to explain experimentally observed trends in NA condensation lends support to proposed NA condensation picture based on the multivalent "ion binding shells."

Synthesis of hollow silica spheres with hierarchical shell structure by the dual action of liquid indium microbeads in vapor-liquid-solid growth.

PubMed

Wang, Jian-Tao; Wang, Hui; Ou, Xue-Mei; Lee, Chun-Sing; Zhang, Xiao-Hong

2011-07-05

Geometry-based adhesion arising from hierarchical surface structure enables microspheres to adhere to cells strongly, which is essential for inorganic microcapsules that function as drug delivery or diagnostic imaging agents. However, constructing a hierarchical structure on the outer shell of the products via the current microcapsule synthesis method is difficult. This work presents a novel approach to fabricating hollow microspheres with a hierarchical shell structure through the vapor-liquid-solid (VLS) process in which liquid indium droplets act as both templates for the formation of silica capsules and catalysts for the growth of hierarchical shell structure. This hierarchical shell structure offers the hollow microsphere an enhanced geometry-based adhesion. The results provide a facile method for fabricating hollow spheres and enriching their function through tailoring the geometry of their outer shells. © 2011 American Chemical Society

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

DOE PAGES

Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; ...

2015-10-04

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe 3O 4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly,more » our study offers a general approach to enhance Pd catalysis in acid for ORB.« less

Improved scaling laws for stage inert mass of space propulsion systems. Volume 2: System modeling and weight data

NASA Technical Reports Server (NTRS)

1971-01-01

Technical models and analytical approaches used to develop the weight data for vehicle system concepts using advanced technology are reported. Weight data are supplied for the following major system elements: engine, pressurization, propellant containers, structural shells and secondary structure, and environmental protection shields for the meteoroid and thermal design requirements. Scaling laws, improved and a simplified set, are developed from the system weight data. The laws consider the implications of the major design parameters and mission requirements on the stage inert mass.

Quasi-static axisymmetric eversion hemispherical domes made of elastomers

NASA Astrophysics Data System (ADS)

Kabrits, Sergey A.; Kolpak, Eugeny P.

2016-06-01

The paper considers numerical solution for the problem of quasi-static axisymmetric eversion of a spherical shell (hemisphere) under action of external pressure. Results based on the general nonlinear theory of shells made of elastomers, proposed by K. F. Chernykh. It is used two models of shells based on the hypotheses of the Kirchhoff and Timoshenko, modified K.F. Chernykh for the case of hyperelastic rubber-like material. The article presents diagrams of equilibrium states of eversion hemispheres for both models as well as the shape of the shell at different points in the diagram.

Nonlinear analysis of damaged stiffened fuselage shells subjected to combined loads

NASA Technical Reports Server (NTRS)

Starnes, James H., Jr.; Britt, Vicki O.; Young, Richard D.; Rankin, Charles C.; Shore, Charles P.; Bains, Jane C.

1994-01-01

The results of an analytical study of the nonlinear response of stiffened fuselage shells with long cracks are presented. The shells are modeled with a hierarchical modeling strategy that accounts for global and local response phenomena accurately. Results are presented for internal pressure and mechanical bending loads. The effects of crack location and orientation on shell response are described. The effects of mechanical fasteners on the response of a lap joint and the effects of elastic and elastic-plastic material properties on the buckling response of tension-loaded flat panels with cracks are also addressed.

Kinematic Methods of Designing Free Form Shells

NASA Astrophysics Data System (ADS)

Korotkiy, V. A.; Khmarova, L. I.

2017-11-01

The geometrical shell model is formed in light of the set requirements expressed through surface parameters. The shell is modelled using the kinematic method according to which the shell is formed as a continuous one-parameter set of curves. The authors offer a kinematic method based on the use of second-order curves with a variable eccentricity as a form-making element. Additional guiding ruled surfaces are used to control the designed surface form. The authors made a software application enabling to plot a second-order curve specified by a random set of five coplanar points and tangents.

Unified approach to the entropy of an extremal rotating BTZ black hole: Thin shells and horizon limits

NASA Astrophysics Data System (ADS)

Lemos, José P. S.; Minamitsuji, Masato; Zaslavskii, Oleg B.

2017-10-01

Using a thin shell, the first law of thermodynamics, and a unified approach, we study the thermodymanics and find the entropy of a (2 +1 )-dimensional extremal rotating Bañados-Teitelbom-Zanelli (BTZ) black hole. The shell in (2 +1 ) dimensions, i.e., a ring, is taken to be circularly symmetric and rotating, with the inner region being a ground state of the anti-de Sitter spacetime and the outer region being the rotating BTZ spacetime. The extremal BTZ rotating black hole can be obtained in three different ways depending on the way the shell approaches its own gravitational or horizon radius. These ways are explicitly worked out. The resulting three cases give that the BTZ black hole entropy is either the Bekenstein-Hawking entropy, S =A/+ 4 G , or an arbitrary function of A+, S =S (A+) , where A+=2 π r+ is the area, i.e., the perimeter, of the event horizon in (2 +1 ) dimensions. We speculate that the entropy of an extremal black hole should obey 0 ≤S (A+)≤A/+ 4 G . We also show that the contributions from the various thermodynamic quantities, namely, the mass, the circular velocity, and the temperature, for the entropy in all three cases are distinct. This study complements the previous studies in thin shell thermodynamics and entropy for BTZ black holes. It also corroborates the results found for a (3 +1 )-dimensional extremal electrically charged Reissner-Nordström black hole.

Influence of the shell thickness and charge distribution on the effective interaction between two like-charged hollow spheres.

PubMed

Angelescu, Daniel G; Caragheorgheopol, Dan

2015-10-14

The mean-force and the potential of the mean force between two like-charged spherical shells were investigated in the salt-free limit using the primitive model and Monte Carlo simulations. Apart from an angular homogeneous distribution, a discrete charge distribution where point charges localized on the shell outer surface followed an icosahedral arrangement was considered. The electrostatic coupling of the model system was altered by the presence of mono-, trivalent counterions or small dendrimers, each one bearing a net charge of 9 e. We analyzed in detail how the shell thickness and the radial and angular distribution of the shell charges influenced the effective interaction between the shells. We found a sequence of the potential of the mean force similar to the like-charged filled spheres, ranging from long-range purely repulsive to short-range purely attractive as the electrostatic coupling increased. Both types of potentials were attenuated and an attractive-to-repulsive transition occurred in the presence of trivalent counterions as a result of (i) thinning the shell or (ii) shifting the shell charge from the outer towards the inner surface. The potential of the mean force became more attractive with the icosahedrally symmetric charge model, and additionally, at least one shell tended to line up with 5-fold symmetry axis along the longest axis of the simulation box at the maximum attraction. The results provided a basic framework of understanding the non-specific electrostatic origin of the agglomeration and long-range assembly of the viral nanoparticles.

Efficacy of antimicrobials extracted from organic pecan shell for inhibiting the growth of Listeria spp.

PubMed

Babu, Dinesh; Crandall, Philip G; Johnson, Casey L; O'Bryan, Corliss A; Ricke, Steven C

2013-12-01

Growers and processors of USDA certified organic foods are in need of suitable organic antimicrobials. The purpose of the research reported here was to develop and test natural antimicrobials derived from an all-natural by-product, organic pecan shells. Unroasted and roasted organic pecan shells were subjected to solvent free extraction to produce antimicrobials that were tested against Listeria spp. and L. monocytogenes serotypes to determine the minimum inhibitory concentrations (MIC) of antimicrobials. The effectiveness of pecan shell extracts were further tested using a poultry skin model system and the growth inhibition of the Listeria cells adhered onto the skin model were quantified. The solvent free extracts of pecan shells inhibited Listeria strains at MICs as low as 0.38%. The antimicrobial effectiveness tests on a poultry skin model exhibited nearly a 2 log reduction of the inoculated cocktail mix of Listeria strains when extracts of pecan shell powder were used. The extracts also produced greater than a 4 log reduction of the indigenous spoilage bacteria on the chicken skin. Thus, the pecan shell extracts may prove to be very effective alternative antimicrobials against food pathogens and supplement the demand for effective natural antimicrobials for use in organic meat processing. © 2013 Institute of Food Technologists®

Mapping analysis and planning system for the John F. Kennedy Space Center

NASA Technical Reports Server (NTRS)

Hall, C. R.; Barkaszi, M. J.; Provancha, M. J.; Reddick, N. A.; Hinkle, C. R.; Engel, B. A.; Summerfield, B. R.

1994-01-01

Environmental management, impact assessment, research and monitoring are multidisciplinary activities which are ideally suited to incorporate a multi-media approach to environmental problem solving. Geographic information systems (GIS), simulation models, neural networks and expert-system software are some of the advancing technologies being used for data management, query, analysis and display. At the 140,000 acre John F. Kennedy Space Center, the Advanced Software Technology group has been supporting development and implementation of a program that integrates these and other rapidly evolving hardware and software capabilities into a comprehensive Mapping, Analysis and Planning System (MAPS) based in a workstation/local are network environment. An expert-system shell is being developed to link the various databases to guide users through the numerous stages of a facility siting and environmental assessment. The expert-system shell approach is appealing for its ease of data access by management-level decision makers while maintaining the involvement of the data specialists. This, as well as increased efficiency and accuracy in data analysis and report preparation, can benefit any organization involved in natural resources management.

Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1982-01-01

The line-spring model developed by Rice and Levy (1972) is used to obtain an approximate solution for a cylindrical shell containing a part-through surface crack. A Reissner type theory is used to account for the effects of the transverse shear deformations, and the stress intensity factor at the deepest penetration point of the crack is tabulated for bending and membrane loading by varying three-dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided, and qualitatively the line-spring model gives the expected results in comparison with elasticity solutions.

A modified two-layer iteration via a boundary point approach to generalized multivalued pseudomonotone mixed variational inequalities.

PubMed

Saddeek, Ali Mohamed

2017-01-01

Most mathematical models arising in stationary filtration processes as well as in the theory of soft shells can be described by single-valued or generalized multivalued pseudomonotone mixed variational inequalities with proper convex nondifferentiable functionals. Therefore, for finding the minimum norm solution of such inequalities, the current paper attempts to introduce a modified two-layer iteration via a boundary point approach and to prove its strong convergence. The results here improve and extend the corresponding recent results announced by Badriev, Zadvornov and Saddeek (Differ. Equ. 37:934-942, 2001).

Atomic-level simulation of ferroelectricity in perovskite solid solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepliarsky, M.; Instituto de Fisica Rosario, CONICET-UNR, Rosario,; Phillpot, S. R.

2000-06-26

Building on the insights gained from electronic-structure calculations and from experience obtained with an earlier atomic-level method, we developed an atomic-level simulation approach based on the traditional Buckingham potential with shell model which correctly reproduces the ferroelectric phase behavior and dielectric and piezoelectric properties of KNbO{sub 3}. This approach now enables the simulation of solid solutions and defected systems; we illustrate this capability by elucidating the ferroelectric properties of a KTa{sub 0.5}Nb{sub 0.5}O{sub 3} random solid solution. (c) 2000 American Institute of Physics.

Comparison of Mediterranean Pteropod Shell Biometrics and Ultrastructure from Historical (1910 and 1921) and Present Day (2012) Samples Provides Baseline for Monitoring Effects of Global Change.

PubMed

Howes, Ella L; Eagle, Robert A; Gattuso, Jean-Pierre; Bijma, Jelle

2017-01-01

Anthropogenic carbon perturbation has caused decreases in seawater pH and increases in global temperatures since the start of the 20th century. The subsequent lowering of the saturation state of CaCO3 may make the secretion of skeletons more problematic for marine calcifiers. As organisms that precipitate thin aragonite shells, thecosome pteropods have been identified as being particularly vulnerable to climate change effects. Coupled with their global distribution, this makes them ideal for use as sentinel organisms. Recent studies have highlighted shell dissolution as a potential indicator of ocean acidification; however, this metric is not applicable for monitoring pH changes in supersaturated basins. In this study, the novel approach of high resolution computed tomography (CT) scanning was used to produce quantitative 3-dimensional renderings pteropod shells to assess the potential of using this method to monitor small changes in shell biometrics that may be driven by climate change drivers. An ontogenetic analysis of the shells of Cavolinia inflexa and Styliola subula collected from the Mediterranean was used to identify suitable monitoring metrics. Modern samples were then compared to historical samples of the same species, collected during the Mediterranean leg of the Thor (1910) and Dana (1921) cruises to assess whether any empirical differences could be detected. Shell densities were calculated and scanning electron microscopy was used to compare the aragonite crystal morphology. pH for the collection years was hind-cast using temperature and salinity time series with atmospheric CO2 concentrations from ice core data. Historical samples of S. subula were thicker than S. subula shells of the same size from 2012 and C. inflexa shells collected in 1910 were significantly denser than those from 2012. These results provide a baseline for future work to develop monitoring techniques for climate change in the oceans using the novel approach of high-resolution CT scanning.

Comparison of Mediterranean Pteropod Shell Biometrics and Ultrastructure from Historical (1910 and 1921) and Present Day (2012) Samples Provides Baseline for Monitoring Effects of Global Change

PubMed Central

Gattuso, Jean-Pierre; Bijma, Jelle

2017-01-01

Anthropogenic carbon perturbation has caused decreases in seawater pH and increases in global temperatures since the start of the 20th century. The subsequent lowering of the saturation state of CaCO3 may make the secretion of skeletons more problematic for marine calcifiers. As organisms that precipitate thin aragonite shells, thecosome pteropods have been identified as being particularly vulnerable to climate change effects. Coupled with their global distribution, this makes them ideal for use as sentinel organisms. Recent studies have highlighted shell dissolution as a potential indicator of ocean acidification; however, this metric is not applicable for monitoring pH changes in supersaturated basins. In this study, the novel approach of high resolution computed tomography (CT) scanning was used to produce quantitative 3-dimensional renderings pteropod shells to assess the potential of using this method to monitor small changes in shell biometrics that may be driven by climate change drivers. An ontogenetic analysis of the shells of Cavolinia inflexa and Styliola subula collected from the Mediterranean was used to identify suitable monitoring metrics. Modern samples were then compared to historical samples of the same species, collected during the Mediterranean leg of the Thor (1910) and Dana (1921) cruises to assess whether any empirical differences could be detected. Shell densities were calculated and scanning electron microscopy was used to compare the aragonite crystal morphology. pH for the collection years was hind-cast using temperature and salinity time series with atmospheric CO2 concentrations from ice core data. Historical samples of S. subula were thicker than S. subula shells of the same size from 2012 and C. inflexa shells collected in 1910 were significantly denser than those from 2012. These results provide a baseline for future work to develop monitoring techniques for climate change in the oceans using the novel approach of high-resolution CT scanning. PMID:28125590

All (4,0): Sigma models with (4,0) off-shell supersymmetry

NASA Astrophysics Data System (ADS)

Hull, Chris; Lindström, Ulf

2017-08-01

Off-shell (4, 0) supermultiplets in 2-dimensions are formulated. These are used to construct sigma models whose target spaces are vector bundles over manifolds that are hyperkähler with torsion. The off-shell supersymmetry implies that the complex structures are simultaneously integrable and allows us to write actions using extended superspace and projective superspace, giving an explicit construction of the target space geometries.

LQR Control of Shell Vibrations Via Piezoceramic Actuators

NASA Technical Reports Server (NTRS)

delRosario, R. C. H.; Smith, R. C.

1997-01-01

A model-based Linear Quadratic Regulator (LQR) method for controlling vibrations in cylindrical shells is presented. Surface-mounted piezo-ceramic patches are employed as actuators which leads to unbounded control input operators. Modified Donnell-Mushtari shell equations incorporating strong or Kelvin-Voigt damping are used to model the system. The model is then abstractly formulated in terms of sesquilinear forms. This provides a framework amenable for proving model well-posedness and convergence of LQR gains using analytic semigroup results combined with LQR theory for unbounded input operators. Finally, numerical examples demonstrating the effectiveness of the method are presented.

Nuclear physics: Macroscopic aspects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swiatecki, W.J.

1993-12-01

A systematic macroscopic, leptodermous approach to nuclear statics and dynamics is described, based formally on the assumptions {h_bar} {yields} 0 and b/R << 1, where b is the surface diffuseness and R the nuclear radius. The resulting static model of shell-corrected nuclear binding energies and deformabilities is accurate to better than 1 part in a thousand and yields a firm determination of the principal properties of the nuclear fluid. As regards dynamics, the above approach suggests that nuclear shape evolutions will often be dominated by dissipation, but quantitative comparisons with experimental data are more difficult than in the case ofmore » statics. In its simplest liquid drop version the model exhibits interesting formal connections to the classic astronomical problem of rotating gravitating masses.« less

Global Curvature Buckling and Snapping of Spherical Shells.

NASA Astrophysics Data System (ADS)

Pezzulla, Matteo; Stoop, Norbert; Steranka, Mark; Bade, Abdikhalaq; Trejo, Miguel; Holmes, Douglas

A spherical shell under external pressure will eventually buckle locally through the development of a dimple. However, when a free spherical shell is subject to variations in natural curvature, it will either buckle globally or snap towards a buckled configuration. We study the similarities and differences between pressure and curvature instabilities in spherical shells. We show how the critical buckling natural curvature is largely independent of the thinness and half-angle of the shell, while the critical snapping natural curvature grows linearly with the half-angle. As a result, we demonstrate how a critical half-angle, depending only on the thinness of the shell, sets the threshold between two different kinds of snapping: as a rule of thumb, shallow shells snap into everted shells, while deep shells snap into buckled shells. As the developed models are purely geometrical, the results are applicable to a large variety of stimuli and scales. NSF CAREER CMMI-1454153.

Plume Activity and Tidal Deformation on Enceladus Influenced by Faults and Variable Ice Shell Thickness

NASA Astrophysics Data System (ADS)

Běhounková, Marie; Souček, Ondřej; Hron, Jaroslav; Čadek, Ondřej

2017-09-01

We investigated the effect of variations in ice shell thickness and of the tiger stripe fractures crossing Enceladus' south polar terrain on the moon's tidal deformation by performing finite element calculations in three-dimensional geometry. The combination of thinning in the polar region and the presence of faults has a synergistic effect that leads to an increase of both the displacement and stress in the south polar terrain by an order of magnitude compared to that of the traditional model with a uniform shell thickness and without faults. Assuming a simplified conductive heat transfer and neglecting the heat sources below the ice shell, we computed the global heat budget of the ice shell. For the inelastic properties of the shell described by a Maxwell viscoelastic model, we show that unrealistically low average viscosity of the order of 10^{13} Pa s is necessary for preserving the volume of the ocean, suggesting the important role of the heat sources in the deep interior. Similarly, low viscosity is required to predict the observed delay of the plume activity, which hints at other delaying mechanisms than just the viscoelasticity of the ice shell. The presence of faults results in large spatial and temporal heterogeneity of geysering activity compared to the traditional models without faults. Our model contributes to understanding the physical mechanisms that control the fault activity, and it provides potentially useful information for future missions that will sample the plume for evidence of life.

Self-assembly of core-shell structure PtO2@Pt nanodots and their formation evolution

NASA Astrophysics Data System (ADS)

Yang, Weijia; Liu, Junjie; Liu, Mingquan; Zhao, Zhicheng; Song, Yapeng; Tang, Xiufeng; Luo, Jianyi; Zeng, Qingguang; He, Xin

2018-05-01

Core-shell structure PtO2@Pt nanodots have been self-assembly by vacuum sputtering and high temperature annealing. First, Pt thin films with a small amount of PtO2 are grown on the sapphire substrates by vacuum sputtering. And then high temperature annealing on the thin films is carried out at 800 °C for 2 min to form Pt nanodots. During the cooling process, the atmosphere is deployed to supplant the nitrogen. Finally, even distributed core-shell structure PtO2@Pt nanodots with a diameter from 100 to 300 nm are achieved. Furthermore, the formation evolution of core-shell structure PtO2@Pt nanodots is also proposed. This work open up a new approach for fabricating core-shell structure nanodots.

Probing the pre-PN Mass Loss Histories in the PPN Dust Shells

NASA Astrophysics Data System (ADS)

Ueta, T.

2001-12-01

Proto-planetary nebulae (PPNs) are immediate progenitors of planetary nebulae (PNs) rapidly evolving over a relatively short time scale. Unlike the full-fledged PNs, the circumstellar dust shells of PPNs have neither been photo-ionized nor been swept up by fast winds. Since the PPN shells retain pristine fossil records of mass loss histories of these stars during the pre-PN phases, these dust shells provide ideal astronomical laboratories in which to investigate the origin of complex PN structures that we observe. We have conducted imaging surveys of the PPN shells in mid-infrared and optical wavelengths, probing the dust distribution directly via mid-infrared thermal dust emission arising from the shells and indirectly via dust-scattered stellar optical emission passing through the shells. From these surveys, we have found that (1) the PPN shells are intrinsically axisymmetric due to equatorially-enhanced superwind mass loss that occurred immediately before the beginning of the PPN phase, and (2) the variable degree of equatorial enhancement in the shells, which is probably related to the progenitor mass, has resulted in different optical depths and morphologies. To characterize the PPN shell geometries, we have developed and employed a 2.5 dimensional radiative transfer code that treats dust absorption, reemission, and an/isotropic scattering in any axisymmetric system illuminated by a central energy source. In the code, the dust optical properties are derived from the laboratory-measured refractive index using Mie theory allowing a distribution of sizes for each species in each composition layer in the shell. Our numerical analysis would be able to de-project and recover 3-D geometrical quantities, such as the pole-to-equator density ratio, from the observational data. These model calculations would provide constraining parameters for hydrodynamical models intended to generate equatorial enhancements during dust mass loss as well as initial parameters for magneto-hydrodynamical models aimed to reproduce highly complex PN morphologies.

Detecting and Classifying Human Touches in a Social Robot Through Acoustic Sensing and Machine Learning

PubMed Central

Alonso-Martín, Fernando; Gamboa-Montero, Juan José; Castillo, José Carlos; Castro-González, Álvaro; Salichs, Miguel Ángel

2017-01-01

An important aspect in Human–Robot Interaction is responding to different kinds of touch stimuli. To date, several technologies have been explored to determine how a touch is perceived by a social robot, usually placing a large number of sensors throughout the robot’s shell. In this work, we introduce a novel approach, where the audio acquired from contact microphones located in the robot’s shell is processed using machine learning techniques to distinguish between different types of touches. The system is able to determine when the robot is touched (touch detection), and to ascertain the kind of touch performed among a set of possibilities: stroke, tap, slap, and tickle (touch classification). This proposal is cost-effective since just a few microphones are able to cover the whole robot’s shell since a single microphone is enough to cover each solid part of the robot. Besides, it is easy to install and configure as it just requires a contact surface to attach the microphone to the robot’s shell and plug it into the robot’s computer. Results show the high accuracy scores in touch gesture recognition. The testing phase revealed that Logistic Model Trees achieved the best performance, with an F-score of 0.81. The dataset was built with information from 25 participants performing a total of 1981 touch gestures. PMID:28509865

Toward new benchmark adsorbents: preparation and characterization of activated carbon from argan nut shell for bisphenol A removal.

PubMed

Zbair, Mohamed; Ainassaari, Kaisu; Drif, Asmaa; Ojala, Satu; Bottlinger, Michael; Pirilä, Minna; Keiski, Riitta L; Bensitel, Mohammed; Brahmi, Rachid

2018-01-01

The use of argan nut shell as a precursor for producing activated carbon was investigated in this work. Two activated carbons AC-HP and AC-Na were prepared from argan nut shell by chemical activation method using phosphoric acid (H 3 PO 4 ) and sodium hydroxide (NaOH), respectively. Textural, morphological, and surface chemistry characteristics were studied by nitrogen physisorption, TGA, SEM, TXRF, FTIR, XRD, and by determining the pH PZC of the AC-HP. The adsorption experiments revealed that AC-HP was more efficient in adsorption of BPA due to high specific surface area (1372 m 2 /g) compared to AC-Na (798 m 2 /g). The obtained adsorption data of BPA on AC-HP correlated well with the pseudo-second-order model and the Langmuir isotherm (Qmax = 1250 mg/g at 293 K). The thermodynamic parameters (ΔG° < 0, ΔH° < 0, and ΔS° < 0) indicate that adsorption of BPA on AC-HP was spontaneous and exothermic in nature. The regeneration of AC-HP showed excellent results after 5 cycles (95-93%). This work does not only provide a potential way to use argan nut shell but also represents a sustainable approach to synthesize AC-HP, which might be an ideal material for various applications (energy storage, catalysis, and environmental remediation).

Simultaneous immobilization of glucose oxidase on the surface and cavity of hollow gold nanospheres as labels for highly sensitive electrochemical immunoassay of tumor marker.

PubMed

Song, Zhongju; Yuan, Ruo; Chai, Yaqin; Jiang, Wen; Su, Huilan; Che, Xin; Ran, Xiaoqi

2011-01-15

A novel tracer, glucose oxidase (GOD)-functionalized hollow gold nanospheres encapsulating glucose oxidase (Au(shell)@GOD), was designed to label the ferrocenemonocarboxylic-grafted secondary antibodies (Fc@Ab(2)) for highly sensitive detection of tumor marker using carboxyl group functionalized multiwall carbon nanotubes as platform. Initially, Au(shell)@GOD was synthesized specially by reverse micelle approach, and then the labeling of antibody and the preparation of GOD-functionalized Au(shell)@GOD were performed by one-pot assembly of Fc@Ab(2) and GOD on the surface of Au(shell)@GOD. The ferrocene used to label antibodies acted as a mediator of electron transfer between GOD and electrode surface. The high-content glucose oxidase in the tracer (on the surface and in the cavity) could significantly amplify the amperometric signal for sandwich-type immunoassay. Using carcinoembryonic antigen (CEA) as model analyte, the designed tracer showed linear range from 0.02 to 5.0 ng mL(-1) with the detection limit down to 6.7 pg mL(-1). The assay results of serum samples with the proposed method were in an acceptable agreement with the reference values. The new protocol showed acceptable stability and reproducibility, high sensitivity, and good precision, which could provide a promising potential for clinical screening and diagnosis of tumor disease. Copyright © 2010 Elsevier B.V. All rights reserved.

Detecting and Classifying Human Touches in a Social Robot Through Acoustic Sensing and Machine Learning.

PubMed

Alonso-Martín, Fernando; Gamboa-Montero, Juan José; Castillo, José Carlos; Castro-González, Álvaro; Salichs, Miguel Ángel

2017-05-16

An important aspect in Human-Robot Interaction is responding to different kinds of touch stimuli. To date, several technologies have been explored to determine how a touch is perceived by a social robot, usually placing a large number of sensors throughout the robot's shell. In this work, we introduce a novel approach, where the audio acquired from contact microphones located in the robot's shell is processed using machine learning techniques to distinguish between different types of touches. The system is able to determine when the robot is touched (touch detection), and to ascertain the kind of touch performed among a set of possibilities: stroke , tap , slap , and tickle (touch classification). This proposal is cost-effective since just a few microphones are able to cover the whole robot's shell since a single microphone is enough to cover each solid part of the robot. Besides, it is easy to install and configure as it just requires a contact surface to attach the microphone to the robot's shell and plug it into the robot's computer. Results show the high accuracy scores in touch gesture recognition. The testing phase revealed that Logistic Model Trees achieved the best performance, with an F -score of 0.81. The dataset was built with information from 25 participants performing a total of 1981 touch gestures.

A systematic study of superheavy nuclei for Z = 114 and beyond using the relativistic mean field approach

NASA Astrophysics Data System (ADS)

Patra, S. K.; Wu, Cheng-Li; Praharaj, C. R.; Gupta, Raj K.

1999-05-01

We have studied the structural properties of even-even, neutron deficient, Z = 114-126, superheavy nuclei in the mass region A ˜ 270-320, using an axially deformed relativistic mean field model. The calculations are performed with three parameter sets (NL1, TM1 and NL-SH), in order to see the dependence of the structural properties on the force used. The calculated ground state shapes are found to be parameter dependent. For some parameter sets, many of the nuclei are degenerate in their ground state configuration. Special attention is given to the investigation of the magic structures (spherical shell closures) in the superheavy region. We find that some known magic numbers are absent and new closed shells are predicted. Large shell gaps appear at Z = 80, 92, (114), 120 and 138, N = 138, (164), (172), 184, (198), (228) and 258, irrespective of the parameter sets used. The numbers in parenthesis are those which correspond to relatively smaller gaps. The existence of new magic numbers in the valley of superheavy elements is discussed. It is suggested that nuclei around Z = 114 and N = 164 ˜ 172 could be considered as candidates for the next search of superheavy nuclei. The existence of superheavy islands around Z = 120 and N = 172 or N = 184 double shell closure is also discussed.

Core-shell titanium dioxide-titanium nitride nanotube arrays with near-infrared plasmon resonances

NASA Astrophysics Data System (ADS)

Farsinezhad, Samira; Shanavas, Thariq; Mahdi, Najia; Askar, Abdelrahman M.; Kar, Piyush; Sharma, Himani; Shankar, Karthik

2018-04-01

Titanium nitride (TiN) is a ceramic with high electrical conductivity which in nanoparticle form, exhibits localized surface plasmon resonances (LSPRs) in the visible region of the solar spectrum. The ceramic nature of TiN coupled with its dielectric loss factor being comparable to that of gold, render it attractive for CMOS polarizers, refractory plasmonics, surface-enhanced Raman scattering and a whole host of sensing applications. We report core-shell TiO2-TiN nanotube arrays exhibiting LSPR peaks in the range 775-830 nm achieved by a simple, solution-based, low cost, large area-compatible fabrication route that does not involve laser-writing or lithography. Self-organized, highly ordered TiO2 nanotube arrays were grown by electrochemical anodization of Ti thin films on fluorine-doped tin oxide-coated glass substrates and then conformally coated with a thin layer of TiN using atomic layer deposition. The effects of varying the TiN layer thickness and thermal annealing on the LSPR profiles were also investigated. Modeling the TiO2-TiN core-shell nanotube structure using two different approaches, one employing effective medium approximations coupled with Fresnel coefficients, resulted in calculated optical spectra that closely matched the experimentally measured spectra. Modeling provided the insight that the observed near-infrared resonance was not collective in nature, and was mainly attributable to the longitudinal resonance of annular nanotube-like TiN particles redshifted due to the presence of the higher permittivity TiO2 matrix. The resulting TiO2-TiN core-shell nanotube structures also function as visible light responsive photocatalysts, as evidenced by their photoelectrochemical water-splitting performance under light emitting diode illumination using 400, 430 and 500 nm photons.

Ab initio treatment of fully open-shell medium-mass nuclei with the IM-SRG

NASA Astrophysics Data System (ADS)

Stroberg, Ragnar; Calci, Angelo; Holt, Jason; Navratil, Petr; Bogner, Scott; Hergert, Heiko; Roth, Robert; Schwenk, Achim

2016-09-01

The in-medium similarity renormalization group (IM-SRG) is a recently-developed theoretical many-body framework which - like the coupled cluster and the self-consistent Green's function approaches - allows for the treatment of medium-mass nuclei using interactions fit at the few-body level. I will give a brief overview of how the IM-SRG may be used to decouple a shell-model type valence space. I will then describe a recent development for the approximate treatment of residual 3N forces in the valence space which extends the reach of IM-SRG to essentially all medium-mass nuclei, and I will present some selected results spanning isotopic chains from beryllium (Z=4) to nickel (Z=28). Finally, I will discuss the consistent treatment of transition operators, highlighting the potential for future applications in electroweak physics.

The equation-of-motion coupled cluster method for triple electron attached states

NASA Astrophysics Data System (ADS)

Musiał, Monika; Olszówka, Marta; Lyakh, Dmitry I.; Bartlett, Rodney J.

2012-11-01

The initial implementation of the triple electron attachment (TEA) equation-of-motion (EOM) coupled cluster (CC) method is presented, aiming at the description of electronic states with three open shell electrons outside a suitably chosen closed shell vacuum. In particular, such an approach can be used for describing dissociation of chemical bonds predominantly formed by three valence electrons, for example, in LiC and NaC molecules. Both ground and excited states are considered while rigorously maintaining the correct spin value. The preliminary results show a correct asymptotic behavior of the dissociation curves. At the same time, we emphasize that a chemically accurate description will require an extension of the minimal TEA-EOM-CC model introduced here, analogous to those already used in the double ionization potential and double electron attachment methods.

A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J., E-mail: s.duan@163.com; Huang, X. B., E-mail: s.duan@163.com; Cai, H. C., E-mail: s.duan@163.com

Analyzing and modeling K-shell spectra emitted by low-to moderate-atomic number plasma is a useful and effective way to retrieve temperature density of z-pinch plasmas. In this paper, a non-LTE population kinetic model for quick analysis of K-shell spectra was proposed. The model contains ionization stages from bare nucleus to neutral atoms and includes all the important atomic processes. In the present form of the model, the plasma is assumed to be both optically thin and homogeneous with constant temperature and density, and only steady-state situation is considered. According to the detailed calculations for aluminum plasmas, contours of ratios of certainmore » K-shell lines in electron temperature and density plane as well as typical synthesized spectra were presented and discussed. The usefulness of the model is demonstrated by analyzing the spectrum from a neon gas-puff Z-pinch experiment performed on a 1 MA pulsed-power accelerator.« less

Plume Activity and Tidal Deformation on Enceladus Influenced by Faults and Variable Ice Shell Thickness

PubMed Central

Souček, Ondřej; Hron, Jaroslav; Čadek, Ondřej

2017-01-01

Abstract We investigated the effect of variations in ice shell thickness and of the tiger stripe fractures crossing Enceladus' south polar terrain on the moon's tidal deformation by performing finite element calculations in three-dimensional geometry. The combination of thinning in the polar region and the presence of faults has a synergistic effect that leads to an increase of both the displacement and stress in the south polar terrain by an order of magnitude compared to that of the traditional model with a uniform shell thickness and without faults. Assuming a simplified conductive heat transfer and neglecting the heat sources below the ice shell, we computed the global heat budget of the ice shell. For the inelastic properties of the shell described by a Maxwell viscoelastic model, we show that unrealistically low average viscosity of the order of 1013 Pa s is necessary for preserving the volume of the ocean, suggesting the important role of the heat sources in the deep interior. Similarly, low viscosity is required to predict the observed delay of the plume activity, which hints at other delaying mechanisms than just the viscoelasticity of the ice shell. The presence of faults results in large spatial and temporal heterogeneity of geysering activity compared to the traditional models without faults. Our model contributes to understanding the physical mechanisms that control the fault activity, and it provides potentially useful information for future missions that will sample the plume for evidence of life. Key Words: Enceladus—Tidal deformation—Faults—Variable ice shell thickness—Tidal heating—Plume activity and timing. Astrobiology 17, 941–954. PMID:28816521

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation

NASA Technical Reports Server (NTRS)

Lipatov, A. S.; Cooper, J F.; Paterson, W. R.; Sittler, E. C., Jr.; Hartle, R. E.; Simpson, David G.

2013-01-01

The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with Oþ þ and Sþ þ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).

Buckling Imperfection Sensitivity of Axially Compressed Orthotropic Cylinders

NASA Technical Reports Server (NTRS)

Schultz, Marc R.; Nemeth, Michael P.

2010-01-01

Structural stability is a major consideration in the design of lightweight shell structures. However, the theoretical predictions of geometrically perfect structures often considerably over predict the buckling loads of inherently imperfect real structures. It is reasonably well understood how the shell geometry affects the imperfection sensitivity of axially compressed cylindrical shells; however, the effects of shell anisotropy on the imperfection sensitivity is less well understood. In the present paper, the development of an analytical model for assessing the imperfection sensitivity of axially compressed orthotropic cylinders is discussed. Results from the analytical model for four shell designs are compared with those from a general-purpose finite-element code, and good qualitative agreement is found. Reasons for discrepancies are discussed, and potential design implications of this line of research are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murph, S.

This study describes a simple two-step approach to coat gold nanorods with a silica/titania shell. Gold nanorods with an aspect ratio of 2.5 (L = 48 {+-} 2 and d = 19 {+-} 1) are synthesized by a silver-seed mediated growth approach according to our previously reported procedure (Hunyadi Murph ACS Symposium Series, Volume 1064, Chapter 8, 2011, 127-163 and reference herein). Gold nanorods are grown on pre-formed gold nano-seeds in the presence of surfactant, cetyltrimethylammonium bromide (CTAB), and a small amount of silver ions. A bifunctional linker molecule which has a thiol group at one end and a silanemore » group at the other is used to derivatize gold nanorods. The silane group is subsequently reacted with both sodium silicate and titanium isopropoxide to a silica/titania shell around the gold nanorods. By fine tuning the reaction conditions, the silica/titania shell thickness can be controlled from {approx}5 to {approx}40nm. The resulting nanomaterials are stable, amenable to scale up and can be isolated without core aggregation or decomposition. These new materials have been characterized by scanning electron microscopy, energy dispersive X-ray analysis, UV-Vis spectroscopy and dynamic light scattering analysis. Photocatalytic activity of Au-silica/titania nanomaterials under visible and UV illumination is measured via degradation of a model dye, methyl orange (MO) under visible and UV illumination. The results indicate a 3 fold improvement in the photocatalytic decomposition rate of MO under visible illumination vs. UV illumination.« less

Magnetic solid-phase extraction of phthalate esters (PAEs) in apparel textile by core-shell structured Fe3O4@silica@triblock-copolymer magnetic microspheres.

PubMed

Xu, Mei; Liu, Minhua; Sun, Meirong; Chen, Kun; Cao, Xiujun; Hu, Yaoming

2016-04-01

In this paper, novel core-shell structured magnetic Fe3O4/silica nanocomposites with triblock-copolymer grafted on their surface (Fe3O4@SiO2@MDN) were successfully fabricated by combining a sol-gel method with a seeded aqueous-phase radical copolymerization approach. Owing to the excellent characteristics of the strong magnetic responsivity, outstanding hydrophilicity and abundant π-electron system, the obtained core-shell structured microspheres showed great potential as a magnetic solid phase extraction (MSPE) adsorbent. Several kinds of phthalate esters (PAEs) were selected as model analytes to systematically evaluate the applicability of adsorbents for extraction followed by gas chromatography-mass spectrometry (GC-MS) analyses. Various parameters, including adsorbents amounts, adsorption time, species of eluent, and desorption time were optimized. Under the optimized conditions, Validation experiments such as recovery, reproducibility, and limit of detection were carried on and showed satisfactory results. The analysis method showed excellent linearity with a wide range of 0.2-10mg/kg (R(2)>0.9974) and low limits of detection (LOD) of 0.02-0.09 mg/kg (S/N=3). Ultimately, the novel magnetic adsorbents were successfully employed to detect the PAEs in apparel textile samples. And the results indicated that this novel approach brought forward in the present work offered an attractive alternative for rapid, efficient and sensitive MSPE for PAEs compounds. Copyright © 2015 Elsevier B.V. All rights reserved.

Modeling Viral Capsid Assembly

PubMed Central

2014-01-01

I present a review of the theoretical and computational methodologies that have been used to model the assembly of viral capsids. I discuss the capabilities and limitations of approaches ranging from equilibrium continuum theories to molecular dynamics simulations, and I give an overview of some of the important conclusions about virus assembly that have resulted from these modeling efforts. Topics include the assembly of empty viral shells, assembly around single-stranded nucleic acids to form viral particles, and assembly around synthetic polymers or charged nanoparticles for nanotechnology or biomedical applications. I present some examples in which modeling efforts have promoted experimental breakthroughs, as well as directions in which the connection between modeling and experiment can be strengthened. PMID:25663722

Chaotic and regular instantons in helical shell models of turbulence

NASA Astrophysics Data System (ADS)

De Pietro, Massimo; Mailybaev, Alexei A.; Biferale, Luca

2017-03-01

Shell models of turbulence have a finite-time blowup in the inviscid limit, i.e., the enstrophy diverges while the single-shell velocities stay finite. The signature of this blowup is represented by self-similar instantonic structures traveling coherently through the inertial range. These solutions might influence the energy transfer and the anomalous scaling properties empirically observed for the forced and viscous models. In this paper we present a study of the instantonic solutions for a set of four shell models of turbulence based on the exact decomposition of the Navier-Stokes equations in helical eigenstates. We find that depending on the helical structure of each model, instantons are chaotic or regular. Some instantonic solutions tend to recover mirror symmetry for scales small enough. Models that have anomalous scaling develop regular nonchaotic instantons. Conversely, models that have nonanomalous scaling in the stationary regime are those that have chaotic instantons. The direction of the energy carried by each single instanton tends to coincide with the direction of the energy cascade in the stationary regime. Finally, we find that whenever the small-scale stationary statistics is intermittent, the instanton is less steep than the dimensional Kolmogorov scaling, independently of whether or not it is chaotic. Our findings further support the idea that instantons might be crucial to describe some aspects of the multiscale anomalous statistics of shell models.

ControlShell - A real-time software framework

NASA Technical Reports Server (NTRS)

Schneider, Stanley A.; Ullman, Marc A.; Chen, Vincent W.

1991-01-01

ControlShell is designed to enable modular design and impplementation of real-time software. It is an object-oriented tool-set for real-time software system programming. It provides a series of execution and data interchange mechansims that form a framework for building real-time applications. These mechanisms allow a component-based approach to real-time software generation and mangement. By defining a set of interface specifications for intermodule interaction, ControlShell provides a common platform that is the basis for real-time code development and exchange.

Determination of the temperature field of shell structures

NASA Astrophysics Data System (ADS)

Rodionov, N. G.

1986-10-01

A stationary heat conduction problem is formulated for the case of shell structures, such as those found in gas-turbine and jet engines. A two-dimensional elliptic differential equation of stationary heat conduction is obtained which allows, in an approximate manner, for temperature changes along a third variable, i.e., the shell thickness. The two-dimensional problem is reduced to a series of one-dimensional problems which are then solved using efficient difference schemes. The approach proposed here is illustrated by a specific example.

Thickness Constraints on the Icy Shells of the Galilean Satellites from a Comparison of Crater Shapes

NASA Technical Reports Server (NTRS)

Schenk, Paul M.

2002-01-01

A thin outer ice shell on Jupiter's large moon Europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean. The thickness of the outer ice shell is poorly constrained, however, with model-dependent estimates ranging from a few kilometers of depths of impact craters on Europa, Ganymede and Callisto that reveal two anomalous transitions in crater shape with diameter. The first transition is probably related to temperature-dependent ductility of the crust at shallow depths (7-8 km on Europa). The second transition is attributed to the influence of subsurface oceans on all three satellites, which constrains Europa's icy shell to be at least 19 km thick. The icy lithospheres of Ganymede and Callisto are equally ice-rich, but Europa's icy shell has a thermal structure about 0.25-0.5 times the thickness of Ganymede's or Callisto's shells, depending on epoch. The appearances of the craters on Europa are inconsistent with thin-ice-shell models and indicate that exchange of oceanic and surface material could be difficult.

Separative analyses of a chromatographic column packed with a core-shell adsorbent for lithium isotope separation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugiyama, T.; Sugura, K.; Enokida, Y.

2015-03-15

Lithium-6 is used as a blanket material for sufficient tritium production in DT fueled fusion reactors. A core-shell type adsorbent was proposed for lithium isotope separation by chromatography. The mass transfer model in a chromatographic column consisted of 4 steps, such as convection and dispersion in the column, transfer through liquid films, intra-particle diffusion and and adsorption or desorption at the local adsorption sites. A model was developed and concentration profiles and time variation in the column were numerically simulated. It became clear that core-shell type adsorbents with thin porous shell were saturated rapidly relatively to fully porous one andmore » established a sharp edge of adsorption band. This is very important feature because lithium isotope separation requires long-distance development of adsorption band. The values of HETP (Height Equivalent of a Theoretical Plate) for core-shell adsorbent packed column were estimated by statistical moments of the step response curve. The value of HETP decreased with the thickness of the porous shell. A core-shell type adsorbent is, then, useful for lithium isotope separation. (authors)« less

Simulations of polymorphic icosahedral shells assembling around many cargo molecules

NASA Astrophysics Data System (ADS)

Mohajerani, Farzaneh; Perlmutter, Jason; Hagan, Michael

Bacterial microcompartments (BMCs) are large icosahedral shells that sequester the enzymes and reactants responsible for particular metabolic pathways in bacteria. Although different BMCs vary in size and encapsulate different cargoes, they are constructed from similar pentameric and hexameric shell proteins. Despite recent groundbreaking experiments which visualized the formation of individual BMCs, the detailed assembly pathways and the factors which control shell size remain unclear. In this talk, we describe theoretical and computational models that describe the dynamical encapsulation of hundreds of cargo molecules by self-assembling icosahedral shells. We present phase diagrams and analysis of dynamical simulation trajectories showing how the thermodynamics, assembly pathways, and emergent structures depend on the interactions among shell proteins and cargo molecules. Our model suggests a mechanism for controlling insertion of the 12 pentamers required for a closed shell topology, and the relationship between assembly pathway and BMC size polydispersity. In addition to elucidating how native BMCs assemble,our results establish principles for reengineering BMCs or viral capsids as customizable nanoreactors that can assemble around a programmable set of enzymes and reactants. Supported by NIH R01GM108021 and Brandeis MRSEC DMR-1420382.

A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances.

PubMed

Kuai, Long; Geng, Baoyou; Wang, Shaozhen; Sang, Yan

2012-07-23

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Habitat Demonstration Unit (HDU) Pressurized Excursion Module (PEM) Systems Integration Strategy

NASA Technical Reports Server (NTRS)

Gill, Tracy; Merbitz, Jerad; Kennedy, Kriss; Tri, Terry; Toups, Larry; Howe, A. Scott

2011-01-01

The Habitat Demonstration Unit (HDU) project team constructed an analog prototype lunar surface laboratory called the Pressurized Excursion Module (PEM). The prototype unit subsystems were integrated in a short amount of time, utilizing a rapid prototyping approach that brought together over 20 habitation-related technologies from a variety of NASA centers. This paper describes the system integration strategies and lessons learned, that allowed the PEM to be brought from paper design to working field prototype using a multi-center team. The system integration process was based on a rapid prototyping approach. Tailored design review and test and integration processes facilitated that approach. The use of collaboration tools including electronic tools as well as documentation enabled a geographically distributed team take a paper concept to an operational prototype in approximately one year. One of the major tools used in the integration strategy was a coordinated effort to accurately model all the subsystems using computer aided design (CAD), so conflicts were identified before physical components came together. A deliberate effort was made following the deployment of the HDU PEM for field operations to collect lessons learned to facilitate process improvement and inform the design of future flight or analog versions of habitat systems. Significant items within those lessons learned were limitations with the CAD integration approach and the impact of shell design on flexibility of placing systems within the HDU shell.

Model uncertainties of local-thermodynamic-equilibrium K-shell spectroscopy

NASA Astrophysics Data System (ADS)

Nagayama, T.; Bailey, J. E.; Mancini, R. C.; Iglesias, C. A.; Hansen, S. B.; Blancard, C.; Chung, H. K.; Colgan, J.; Cosse, Ph.; Faussurier, G.; Florido, R.; Fontes, C. J.; Gilleron, F.; Golovkin, I. E.; Kilcrease, D. P.; Loisel, G.; MacFarlane, J. J.; Pain, J.-C.; Rochau, G. A.; Sherrill, M. E.; Lee, R. W.

2016-09-01

Local-thermodynamic-equilibrium (LTE) K-shell spectroscopy is a common tool to diagnose electron density, ne, and electron temperature, Te, of high-energy-density (HED) plasmas. Knowing the accuracy of such diagnostics is important to provide quantitative conclusions of many HED-plasma research efforts. For example, Fe opacities were recently measured at multiple conditions at the Sandia National Laboratories Z machine (Bailey et al., 2015), showing significant disagreement with modeled opacities. Since the plasma conditions were measured using K-shell spectroscopy of tracer Mg (Nagayama et al., 2014), one concern is the accuracy of the inferred Fe conditions. In this article, we investigate the K-shell spectroscopy model uncertainties by analyzing the Mg spectra computed with 11 different models at the same conditions. We find that the inferred conditions differ by ±20-30% in ne and ±2-4% in Te depending on the choice of spectral model. Also, we find that half of the Te uncertainty comes from ne uncertainty. To refine the accuracy of the K-shell spectroscopy, it is important to scrutinize and experimentally validate line-shape theory. We investigate the impact of the inferred ne and Te model uncertainty on the Fe opacity measurements. Its impact is small and does not explain the reported discrepancies.

Ni-NiO core-shell inverse opal electrodes for supercapacitors.

PubMed

Kim, Jae-Hun; Kang, Soon Hyung; Zhu, Kai; Kim, Jin Young; Neale, Nathan R; Frank, Arthur J

2011-05-14

A general template-assisted electrochemical approach was used to synthesize three-dimensional ordered Ni core-NiO shell inverse opals (IOs) as electrodes for supercapacitors. The Ni-NiO IO electrodes displayed pseudo-capacitor behavior, good rate capability and cycling performance. © The Royal Society of Chemistry 2011

Retrospective environmental biomonitoring - Mussel Watch expanded

NASA Astrophysics Data System (ADS)

Schöne, Bernd R.; Krause, Richard A.

2016-09-01

Monitoring bioavailable contaminants and determining baseline conditions in aquatic environments has become an important aspect of ecology and ecotoxicology. Since the mid-1970s and the initiation of the Mussel Watch program, this has been successfully accomplished with bivalve mollusks. These (mostly) sessile organisms reliably and proportionately record changes of a range of organic and inorganic pollutants occurring in the water, food or sediment. The great majority of studies have measured the concentration of pollutants in soft tissues and, to a much lesser extent, in whole shells or fractions thereof. Both approaches come with several drawbacks. Neither soft tissues nor whole shells can resolve temporal changes of the pollution history, except through the analysis of multiple specimens collected at different times. Soft tissues and shell fractions provide time-averaged data spanning months or years, and whole shells time-averaged data over the entire lifespan of the animal. Even with regular sampling of multiple specimens over long intervals of time, the resulting chronology may not faithfully resolve short-term changes of water quality. Compounding the problem, whole shell averages tend to be non-arithmetic and non-linear, because shell growth rate varies through seasons and lifetime, and different shell layers often vary ultrastructurally and can thus be chemically different from each other. Mussel Watch could greatly benefit from the potential of bivalve shells in providing high-resolution, temporally aligned archives of environmental variability. So far, only circa a dozen studies have demonstrated that the sclerochronological approach - i.e., combined growth pattern and high-resolution chemical analyses - can provide sub-seasonally to annually resolved time-series documenting the history of pollution over centuries and even millennia. On the other hand, the sclerochronological community has failed to fully appreciate that the formation of the shell and its chemical composition is controlled by the soft parts and that a robust interpretation of the shell record requires a detailed understanding of bivalve physiology, behavior and ecology. This review attempts to bring together the Mussel Watch and sclerochronology communities and lay the foundation of a new subdiscipline of the Mussel Watch: retrospective environmental biomonitoring. For this purpose, we provide an overview of seminal work from both fields and outline potential future research directions.

Shell-model predictions for Lambda Lambda hypernuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gal, A.; Millener, D.

2011-06-02

It is shown how the recent shell-model determination of {Lambda}N spin-dependent interaction terms in {Lambda} hypernuclei allows for a reliable deduction of {Lambda}{Lambda} separation energies in {Lambda}{Lambda} hypernuclei across the nuclear p shell. Comparison is made with the available data, highlighting {sub {Lambda}{Lambda}}{sup 11}Be and {sub {Lambda}{Lambda}}{sup 12}Be which have been suggested as possible candidates for the KEK-E373 HIDA event.

Adaptation from restricted geometries: the shell inclination of terrestrial gastropods.

PubMed

Okajima, Ryoko; Chiba, Satoshi

2013-02-01

The adaptations that occur for support and protection can be studied with regard to the optimal structure that balances these objectives with any imposed constraints. The shell inclination of terrestrial gastropods is an appropriate model to address this problem. In this study, we examined how gastropods improve shell angles to well-balanced ones from geometrically constrained shapes. Our geometric analysis and physical analysis showed that constantly coiled shells are constrained from adopting a well-balanced angle; the shell angle of such basic shells tends to increase as the spire index (shell height/width) increases, although the optimum angle for stability is 90° for flat shells and 0° for tall shells. Furthermore, we estimated the influences of the geometric rule and the functional demands on actual shells by measuring the shell angles of both resting and active snails. We found that terrestrial gastropods have shell angles that are suited for balance. The growth lines of the shells indicated that this adaptation depends on the deflection of the last whorl: the apertures of flat shells are deflected downward, whereas those of tall shells are deflected upward. Our observations of active snails demonstrated that the animals hold their shells at better balanced angles than inactive snails. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

Large enhanced dielectric permittivity in polyaniline passivated core-shell nano magnetic iron oxide by plasma polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joy, Lija K.; Sooraj, V.; Sethulakshmi, N.

2014-03-24

Commercial samples of Magnetite with size ranging from 25–30 nm were coated with polyaniline by using radio frequency plasma polymerization to achieve a core shell structure of magnetic nanoparticle (core)–Polyaniline (shell). High resolution transmission electron microscopy images confirm the core shell architecture of polyaniline coated iron oxide. The dielectric properties of the material were studied before and after plasma treatment. The polymer coated magnetite particles exhibited a large dielectric permittivity with respect to uncoated samples. The dielectric behavior was modeled using a Maxwell–Wagner capacitor model. A plausible mechanism for the enhancement of dielectric permittivity is proposed.

Porogranular materials composed of elastic Helmholtz resonators for acoustic wave absorption.

PubMed

Griffiths, Stéphane; Nennig, Benoit; Job, Stéphane

2017-01-01

A theoretical and experimental study of the acoustic absorption of granular porous media made of non-cohesive piles of spherical shells is presented. These shells are either rigid or elastic, possibly drilled with a neck (Helmholtz resonators), and either porous or impervious. A description is given of acoustic propagation through these media using the effective medium models proposed by Johnson (rigid particles) and Boutin (rigid Helmholtz resonators), which are extended to the configurations studied in this work. A solution is given for the local equation of elasticity of a shell coupled to the viscous flow of air through the neck and the micropores. The models and the simulations are compared to absorption spectra measured in reflection in an impedance tube. The effective medium models and the measurements show excellent agreement for configurations made of rigid particles and rigid Helmholtz resonators that induce an additional peak of absorption at low frequency. A shift of the Helmholtz resonance toward low frequencies, due to the softness of the shells is revealed by the experiments for elastic shells made of soft elastomer and is well reproduced by the simulations. It is shown that microporous shells enhance and broaden acoustic absorption compared to stiff or elastic resonators.

Vibration characteristics of 1/8-scale dynamic models of the space-shuttle solid-rocket boosters

NASA Technical Reports Server (NTRS)

Leadbetter, S. A.; Stephens, W.; Sewall, J. L.; Majka, J. W.; Barret, J. R.

1976-01-01

Vibration tests and analyses of six 1/8 scale models of the space shuttle solid rocket boosters are reported. Natural vibration frequencies and mode shapes were obtained for these aluminum shell models having internal solid fuel configurations corresponding to launch, midburn (maximum dynamic pressure), and near endburn (burnout) flight conditions. Test results for longitudinal, torsional, bending, and shell vibration frequencies are compared with analytical predictions derived from thin shell theory and from finite element plate and beam theory. The lowest analytical longitudinal, torsional, bending, and shell vibration frequencies were within + or - 10 percent of experimental values. The effects of damping and asymmetric end skirts on natural vibration frequency were also considered. The analytical frequencies of an idealized full scale space shuttle solid rocket boosted structure are computed with and without internal pressure and are compared with the 1/8 scale model results.

Modeling deformation and chaining of flexible shells in a nematic solvent with finite elements on an adaptive moving mesh

NASA Astrophysics Data System (ADS)

DeBenedictis, Andrew; Atherton, Timothy J.; Rodarte, Andrea L.; Hirst, Linda S.

2018-03-01

A micrometer-scale elastic shell immersed in a nematic liquid crystal may be deformed by the host if the cost of deformation is comparable to the cost of elastic deformation of the nematic. Moreover, such inclusions interact and form chains due to quadrupolar distortions induced in the host. A continuum theory model using finite elements is developed for this system, using mesh regularization and dynamic refinement to ensure quality of the numerical representation even for large deformations. From this model, we determine the influence of the shell elasticity, nematic elasticity, and anchoring condition on the shape of the shell and hence extract parameter values from an experimental realization. Extending the model to multibody interactions, we predict the alignment angle of the chain with respect to the host nematic as a function of aspect ratio, which is found to be in excellent agreement with experiments.

Ab initio results for intermediate-mass, open-shell nuclei

NASA Astrophysics Data System (ADS)

Baker, Robert B.; Dytrych, Tomas; Launey, Kristina D.; Draayer, Jerry P.

2017-01-01

A theoretical understanding of nuclei in the intermediate-mass region is vital to astrophysical models, especially for nucleosynthesis. Here, we employ the ab initio symmetry-adapted no-core shell model (SA-NCSM) in an effort to push first-principle calculations across the sd-shell region. The ab initio SA-NCSM's advantages come from its ability to control the growth of model spaces by including only physically relevant subspaces, which allows us to explore ultra-large model spaces beyond the reach of other methods. We report on calculations for 19Ne and 20Ne up through 13 harmonic oscillator shells using realistic interactions and discuss the underlying structure as well as implications for various astrophysical reactions. This work was supported by the U.S. NSF (OCI-0904874 and ACI -1516338) and the U.S. DOE (DE-SC0005248), and also benefitted from the Blue Waters sustained-petascale computing project and high performance computing resources provided by LSU.

Shell shock, trauma, and the First World War: the making of a diagnosis and its histories.

PubMed

Loughran, Tracey

2012-01-01

During the First World War, thousands of soldiers were treated for "shell shock," a condition which encompassed a range of physical and psychological symptoms. Shell shock has most often been located within a "genealogy of trauma," and identified as an important marker in the gradual recognition of the psychological afflictions caused by combat. In recent years, shell shock has increasingly been viewed as a powerful emblem of the suffering of war. This article, which focuses on Britain, extends scholarly analyses which question characterizations of shell shock as an early form of post-traumatic stress disorder. It also considers some of the methodological problems raised by recasting shell shock as a wartime medical construction rather than an essentially timeless manifestation of trauma. It argues that shell shock must be analyzed as a diagnosis shaped by a specific set of contemporary concerns, knowledges, and practices. Such an analysis challenges accepted understandings of what shell shock "meant" in the First World War, and also offers new perspectives on the role of shell shock in shaping the emergence of psychology and psychiatry in the early part of the twentieth century. The article also considers what relation, if any, might exist between intellectual and other histories, literary approaches, and perceptions of trauma as timeless and unchanging.

Controlling risks of P water pollution by sorption on soils, pyritic material, granitic material, and different by-products: effects of pH and incubation time.

PubMed

Romar-Gasalla, Aurora; Nóvoa-Muñoz, Juan Carlos; Arias-Estévez, Manuel; Fernández-Sanjurjo, María J; Álvarez-Rodríguez, Esperanza; Núñez-Delgado, Avelino

2018-05-13

Batch experiments were used to test P sorbent potential of soil samples, pyritic and granitic materials, mussel shell, mussel shell ash, sawdust, and slate waste fines for different pH and incubation times. Maximum P sorption varied in a wide range of pH: < 4 for pyritic material, 4-6 for forest soil, > 5 for slate fines, > 6 for shell ash, and pH 6-8 for mussel shell. P sorption was rapid (< 24 h) for forest soil, shell ash, pyritic material, and fine shell. On the opposite side, it was clearly slower for vineyard soil, granitic material, slate fines, pine sawdust, and coarse shell, with increased P sorption even 1 month later. For any incubation time, P sorption was > 90% in shell ash, whereas forest soil, pyritic material, and fine shell showed sorption rates approaching 100% within 24 h of incubation. These results could be useful to manage and/or recycle the sorbents tested when focusing on P immobilization or removal, in circumstances where pH changes and where contact time may vary from hours to days, thus aiding to diminish P pollution and subsequent eutrophication risks, promoting conservation and sustainability.

LA-ICP-MS-derived U-concentrations and microstructural domains within biogenic aragonite of Arctica islandica shell.

PubMed

Helama, Samuli; Heikkilä, Pasi; Rinne, Katja; Nielsen, Jan Kresten; Nielsen, Jesper Kresten

2015-05-01

Understanding of the uranium uptake processes (both in vivo and post-mortem) into the skeletal structures of marine calcifiers is a subject of multi-disciplinary interest. U-concentration changes within the molluscan shell may serve as a paleoceanographic proxy of the pH history. A proxy of this type is needed to track the effects of fossil fuel emissions to ocean acidification. Moreover, attaining reliable U-series dates using shell materials would be a geochronological breakthrough. Picturing the high-resolution changes of U-concentrations in shell profiles is now possible by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Here, we analyzed in situ U-concentration variations in sub-fossilized shells of ocean quahog (Arctica islandica), a commonly studied bivalve species in Quaternary geoscience, using LA-ICP-MS. Microstructural details of the shell profiles were achieved by the scanning electron microscopy (SEM). Comparison of the shell aragonite microstructure with the changes in U-concentration revealed that uranium of possibly secondary origin is concentrated into the porous granular layers of the shell. Our results reinforce the hypothesis that U-concentration variations can be linked with microstructural differences within the shell. A combination of LA-ICP-MS and SEM analyses is recommended as an interesting approach for understanding the U-concentration variations in similar materials.

Synthesis of Multicolor Core/Shell NaLuF4:Yb3+/Ln3+@CaF2 Upconversion Nanocrystals

PubMed Central

Li, Hui; Hao, Shuwei; Yang, Chunhui; Chen, Guanying

2017-01-01

The ability to synthesize high-quality hierarchical core/shell nanocrystals from an efficient host lattice is important to realize efficacious photon upconversion for applications ranging from bioimaging to solar cells. Here, we describe a strategy to fabricate multicolor core @ shell α-NaLuF4:Yb3+/Ln3+@CaF2 (Ln = Er, Ho, Tm) upconversion nanocrystals (UCNCs) based on the newly established host lattice of sodium lutetium fluoride (NaLuF4). We exploited the liquid-solid-solution method to synthesize the NaLuF4 core of pure cubic phase and the thermal decomposition approach to expitaxially grow the calcium fluoride (CaF2) shell onto the core UCNCs, yielding cubic core/shell nanocrystals with a size of 15.6 ± 1.2 nm (the core ~9 ± 0.9 nm, the shell ~3.3 ± 0.3 nm). We showed that those core/shell UCNCs could emit activator-defined multicolor emissions up to about 772 times more efficient than the core nanocrystals due to effective suppression of surface-related quenching effects. Our results provide a new paradigm on heterogeneous core/shell structure for enhanced multicolor upconversion photoluminescence from colloidal nanocrystals. PMID:28336867

Nanocrystalline p-hydroxyacetanilide (paracetamol) and gold core-shell structure as a model drug deliverable organic-inorganic hybrid nanostructure

NASA Astrophysics Data System (ADS)

Das, Subhojit; Paul, Anumita; Chattopadhyay, Arun

2013-09-01

We report on the generation of core-shell nanoparticles (NPs) having an organic nanocrystal (NC) core coated with an inorganic metallic shell, being dispersed in aqueous medium. First, NCs of p-hydroxyacetanilide (pHA)--known also as paracetamol--were generated in an aqueous medium. Transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) evidenced the formation of pHA NCs and of their crystalline nature. The NCs were then coated with Au to form pHA@Au core-shell NPs, where the thickness of the Au shell was on the order of nanometers. The formation of Au nanoshell--surrounding pHA NC--was confirmed from its surface plasmon resonance (SPR) band in the UV/Vis spectrum and by TEM measurements. Further, on treatment of the core-shell particles with a solution comprising NaCl and HCl (pH < 3), the Au shell could be dissolved, subsequently releasing pHA molecules. The dissolution of Au shell was marked by a gradual diminishing of its SPR band, while the release of pHA molecules in the solution was confirmed from TEM and FTIR studies. The findings suggest that the core-shell NP could be hypothesized to be a model for encapsulating drug molecules, in their crystalline forms, for slow as well as targeted release.We report on the generation of core-shell nanoparticles (NPs) having an organic nanocrystal (NC) core coated with an inorganic metallic shell, being dispersed in aqueous medium. First, NCs of p-hydroxyacetanilide (pHA)--known also as paracetamol--were generated in an aqueous medium. Transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) evidenced the formation of pHA NCs and of their crystalline nature. The NCs were then coated with Au to form pHA@Au core-shell NPs, where the thickness of the Au shell was on the order of nanometers. The formation of Au nanoshell--surrounding pHA NC--was confirmed from its surface plasmon resonance (SPR) band in the UV/Vis spectrum and by TEM measurements. Further, on treatment of the core-shell particles with a solution comprising NaCl and HCl (pH < 3), the Au shell could be dissolved, subsequently releasing pHA molecules. The dissolution of Au shell was marked by a gradual diminishing of its SPR band, while the release of pHA molecules in the solution was confirmed from TEM and FTIR studies. The findings suggest that the core-shell NP could be hypothesized to be a model for encapsulating drug molecules, in their crystalline forms, for slow as well as targeted release. Electronic supplementary information (ESI) available: See DOI: 10.1039/c3nr03566b

Preparation and Characterization of WS2@SiO2 and WS2@PANI Core-Shell Nanocomposites

PubMed Central

Sade, Hagit

2018-01-01

Two tungsten disulfide (WS2)-based core-shell nanocomposites were fabricated using readily available reagents and simple procedures. The surface was pre-treated with a surfactant couple in a layer-by-layer approach, enabling good dispersion of the WS2 nanostructures in aqueous media and providing a template for the polymerization of a silica (SiO2) shell. After a Stöber-like reaction, a conformal silica coating was achieved. Inspired by the resulting nanocomposite, a second one was prepared by reacting the surfactant-modified WS2 nanostructures with aniline and an oxidizing agent in an aqueous medium. Here too, a conformal coating of polyaniline (PANI) was obtained, giving a WS2@PANI nanocomposite. Both nanocomposites were analyzed by electron microscopy, energy dispersive X-ray spectroscopy (EDS) and FTIR, verifying the core-shell structure and the character of shells. The silica shell was amorphous and mesoporous and the surface area of the composite increases with shell thickness. Polyaniline shells slightly differ in their morphologies dependent on the acid used in the polymerization process and are amorphous like the silica shell. Electron paramagnetic resonance (EPR) spectroscopy of the WS2@PANI nanocomposite showed variation between bulk PANI and the PANI shell. These two nanocomposites have great potential to expand the use of transition metals dichalcogenides (TMDCs) for new applications in different fields. PMID:29534426

Realistic Gamow shell model for resonance and continuum in atomic nuclei

NASA Astrophysics Data System (ADS)

Xu, F. R.; Sun, Z. H.; Wu, Q.; Hu, B. S.; Dai, S. J.

2018-02-01

The Gamow shell model can describe resonance and continuum for atomic nuclei. The model is established in the complex-moment (complex-k) plane of the Berggren coordinates in which bound, resonant and continuum states are treated on equal footing self-consistently. In the present work, the realistic nuclear force, CD Bonn, has been used. We have developed the full \\hat{Q}-box folded-diagram method to derive the realistic effective interaction in the model space which is nondegenerate and contains resonance and continuum channels. The CD-Bonn potential is renormalized using the V low-k method. With choosing 16O as the inert core, we have applied the Gamow shell model to oxygen isotopes.

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.

Low energy dipole strength from large scale shell model calculations

NASA Astrophysics Data System (ADS)

Sieja, Kamila

2017-09-01

Low energy enhancement of radiative strength functions has been deduced from experiments in several mass regions of nuclei. Such an enhancement is believed to impact the calculated neutron capture rates which are crucial input for reaction rates of astrophysical interest. Recently, shell model calculations have been performed to explain the upbend of the γ-strength as due to the M1 transitions between close-lying states in the quasi-continuum in Fe and Mo nuclei. Beyond mean-↓eld calculations in Mo suggested, however, a non-negligible role of electric dipole in the low energy enhancement. So far, no calculations of both dipole components within the same theoretical framework have been presented in this context. In this work we present newly developed large scale shell model appraoch that allows to treat on the same footing natural and non-natural parity states. The calculations are performed in a large sd - pf - gds model space, allowing for 1p{1h excitations on the top of the full pf-shell con↓guration mixing. We restrict the discussion to the magnetic part of the dipole strength, however, we calculate for the ↓rst time the magnetic dipole strength between states built of excitations going beyond the classical shell model spaces. Our results corroborate previous ↓ndings for the M1 enhancement for the natural parity states while we observe no enhancement for the 1p{1h contributions. We also discuss in more detail the e↑ects of con↓guration mixing limitations on the enhancement coming out from shell model calculations.

Effect of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal solar cells

NASA Astrophysics Data System (ADS)

Sahin, Mehmet

2018-05-01

In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p–n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy () of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same . The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same , become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.

Effectively-truncated large-scale shell-model calculations and nuclei around 100Sn

NASA Astrophysics Data System (ADS)

Gargano, A.; Coraggio, L.; Itaco, N.

2017-09-01

This paper presents a short overview of a procedure we have recently introduced, dubbed the double-step truncation method, which is aimed to reduce the computational complexity of large-scale shell-model calculations. Within this procedure, one starts with a realistic shell-model Hamiltonian defined in a large model space, and then, by analyzing the effective single particle energies of this Hamiltonian as a function of the number of valence protons and/or neutrons, reduced model spaces are identified containing only the single-particle orbitals relevant to the description of the spectroscopic properties of a certain class of nuclei. As a final step, new effective shell-model Hamiltonians defined within the reduced model spaces are derived by way of a unitary transformation of the original large-scale Hamiltonian. A detailed account of this transformation is given and the merit of the double-step truncation method is illustrated by discussing few selected results for 96Mo, described as four protons and four neutrons outside 88Sr. Some new preliminary results for light odd-tin isotopes from A = 101 to 107 are also reported.

Synthesis and optical properties of core-multi-shell CdSe/CdS/ZnS quantum dots: Surface modifications

NASA Astrophysics Data System (ADS)

Ratnesh, R. K.; Mehata, Mohan Singh

2017-02-01

We report two port synthesis of CdSe/CdS/ZnS core-multi-shell quantum dots (Q-dots) and their structural properties. The multi-shell structures of Q-dots were developed by using successive ionic layer adsorption and reaction (SILAR) technique. The obtained Q-dots show high crystallinity with the step-wise adjustment of lattice parameters in the radial direction. The size of the core and core-shell Q-dots estimated by transmission electron microscopy images and absorption spectra is about 3.4 and 5.3 nm, respectively. The water soluble Q-dots (scheme-1) were prepared by using ligand exchange method, and the effect of pH was discussed regarding the variation of quantum yield (QY). The decrease of a lifetime of core-multi-shell Q-dots with respect to core CdSe indicates that the shell growth may be tuned by the lifetimes. Thus, the study clearly demonstrates that the core-shell approach can be used to substantially improve the optical properties of Q-dots desired for various applications.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source.

PubMed

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-10

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source

NASA Astrophysics Data System (ADS)

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-01

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH3)2)3. The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

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.

Morphomechanics and Developmental Constraints in the Evolution of Ammonites Shell Form.

PubMed

Erlich, Alexander; Moulton, Derek E; Goriely, Alain; Chirat, Regis

2016-11-01

The idea that physical processes involved in biological development underlie morphogenetic rules and channel morphological evolution has been central to the rise of evolutionary developmental biology. Here, we explore this idea in the context of seashell morphogenesis. We show that a morphomechanical model predicts the effects of variations in shell shape on the ornamental pattern in ammonites, a now extinct group of cephalopods with external chambered shell. Our model shows that several seemingly unrelated characteristics of synchronous, ontogenetic, intraspecific, and evolutionary variations in ornamental patterns among various ammonite species may all be understood from the fact that the mechanical forces underlying the oscillatory behavior of the shell secreting system scale with the cross-sectional curvature of the shell aperture. This simple morphogenetic rule, emerging from biophysical interactions during shell formation, introduced a non-random component in the production of phenotypic variation and channeled the morphological evolution of ammonites over millions of years. As such, it provides a paradigm for the concept of "developmental constraints." © 2016 Wiley Periodicals, Inc.

Sound transmission through double cylindrical shells lined with porous material under turbulent boundary layer excitation

NASA Astrophysics Data System (ADS)

Zhou, Jie; Bhaskar, Atul; Zhang, Xin

2015-11-01

This paper investigates sound transmission through double-walled cylindrical shell lined with poroelastic material in the core, excited by pressure fluctuations due to the exterior turbulent boundary layer (TBL). Biot's model is used to describe the sound wave propagating in the porous material. Three types of constructions, bonded-bonded, bonded-unbonded and unbonded-unbonded, are considered in this study. The power spectral density (PSD) of the inner shell kinetic energy is predicted for two turbulent boundary layer models, different air gap depths and three types of polyimide foams, respectively. The peaks of the inner shell kinetic energy due to shell resonance, hydrodynamic coincidence and acoustic coincidence are discussed. The results show that if the frequency band over the ring frequency is of interest, an air gap, even if very thin, should exist between the two elastic shells for better sound insulation. And if small density foam has a high flow resistance, a superior sound insulation can still be maintained.

Shell Model Far From Stability: Island of Inversion Mergers

NASA Astrophysics Data System (ADS)

Nowacki, F.; Poves, A.

2018-02-01

In this study we propose a common mechanism for the disappearance of shell closures far from stabilty. With the use of Large Scale Shell Model calculations (SM-CI), we predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons, which represents a come-back of the the harmonic oscillator shells in the very neutron rich regime. Our calculations preserve the doubly magic nature of the ground state of 78Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability. This new Island of Inversion (IoI) adds to the four well documented ones at N=8, 20, 28 and 40.

A contact algorithm for shell problems via Delaunay-based meshing of the contact domain

NASA Astrophysics Data System (ADS)

Kamran, K.; Rossi, R.; Oñate, E.

2013-07-01

The simulation of the contact within shells, with all of its different facets, represents still an open challenge in Computational Mechanics. Despite the effort spent in the development of techniques for the simulation of general contact problems, an all-seasons algorithm applicable to complex shell contact problems is yet to be developed. This work focuses on the solution of the contact between thin shells by using a technique derived from the particle finite element method together with a rotation-free shell triangle. The key concept is to define a discretization of the contact domain (CD) by constructing a finite element mesh of four-noded tetrahedra that describes the potential contact volume. The problem is completed by using an assumed-strain approach to define an elastic contact strain over the CD.

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.

Three-dimensional flat shell-to-shell coupling: numerical challenges

NASA Astrophysics Data System (ADS)

Guo, Kuo; Haikal, Ghadir

2017-11-01

The node-to-surface formulation is widely used in contact simulations with finite elements because it is relatively easy to implement using different types of element discretizations. This approach, however, has a number of well-known drawbacks, including locking due to over-constraint when this formulation is used as a twopass method. Most studies on the node-to-surface contact formulation, however, have been conducted using solid elements and little has been done to investigate the effectiveness of this approach for beam or shell elements. In this paper we show that locking can also be observed with the node-to-surface contact formulation when applied to plate and flat shell elements even with a singlepass implementation with distinct master/slave designations, which is the standard solution to locking with solid elements. In our study, we use the quadrilateral four node flat shell element for thin (Kirchhoff-Love) plate and thick (Reissner-Mindlin) plate theory, both in their standard forms and with improved formulations such as the linked interpolation [1] and the Discrete Kirchhoff [2] elements for thick and thin plates, respectively. The Lagrange multiplier method is used to enforce the node-to-surface constraints for all elements. The results show clear locking when compared to those obtained using a conforming mesh configuration.

Carrier relaxation mechanisms in self-assembled (In,Ga)As/GaAs quantum dots: Efficient P→S Auger relaxation of electrons

NASA Astrophysics Data System (ADS)

Narvaez, Gustavo A.; Bester, Gabriel; Zunger, Alex

2006-08-01

We calculate the P -shell-to- S -shell decay lifetime τ(P→S) of electrons in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole scattering within an atomistic pseudopotential-based approach. We find that this relaxation mechanism leads to fast decay of τ(P→S)˜1-7ps for dots of different sizes. Our calculated Auger-type P -shell-to- S -shell decay lifetimes τ(P→S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as both electrons and holes are present there is no need for an alternative polaron mechanism.

Spectrophotometry of the shell around AG Carinae

NASA Technical Reports Server (NTRS)

Mitra, P. Mila; Dufour, Reginald J.

1990-01-01

Spatially-resolved long-slit spectrophotometry are presented for two regions of the shell nebula around the P-Cygni variable star AG Carinae. The spectra cover the 3700-6800 A wavelength range. Emission-line diagnostics are used to derive extinction, electron temperatures, and densities for various positions in the nebula. The chemical abundances and ionization structure are calculated and compared with other types of planetary nebulae and shells around other luminous stars. It is found that the N/O and N/S ratios of Ag Car are high compared to solar neighborhood ISM values. The O/H depletion found for the AG Car shell approaches that found in the condensations of the Eta Car system.

Dynamic model of open shell structures buried in poroelastic soils

NASA Astrophysics Data System (ADS)

Bordón, J. D. R.; Aznárez, J. J.; Maeso, O.

2017-08-01

This paper is concerned with a three-dimensional time harmonic model of open shell structures buried in poroelastic soils. It combines the dual boundary element method (DBEM) for treating the soil and shell finite elements for modelling the structure, leading to a simple and efficient representation of buried open shell structures. A new fully regularised hypersingular boundary integral equation (HBIE) has been developed to this aim, which is then used to build the pair of dual BIEs necessary to formulate the DBEM for Biot poroelasticity. The new regularised HBIE is validated against a problem with analytical solution. The model is used in a wave diffraction problem in order to show its effectiveness. It offers excellent agreement for length to thickness ratios greater than 10, and relatively coarse meshes. The model is also applied to the calculation of impedances of bucket foundations. It is found that all impedances except the torsional one depend considerably on hydraulic conductivity within the typical frequency range of interest of offshore wind turbines.

Large-scale shell-model study of the Sn isotopes

NASA Astrophysics Data System (ADS)

Osnes, Eivind; Engeland, Torgeir; Hjorth-Jensen, Morten

2015-05-01

We summarize the results of an extensive study of the structure of the Sn isotopes using a large shell-model space and effective interactions evaluated from realistic two-nucleon potentials. For a fuller account, see ref. [1].

Hohlraum-driven mid-Z (SiO2) double-shell implosions on the omega laser facility and their scaling to NIF.

PubMed

Robey, H F; Amendt, P A; Milovich, J L; Park, H-S; Hamza, A V; Bono, M J

2009-10-02

High-convergence, hohlraum-driven implosions of double-shell capsules using mid-Z (SiO2) inner shells have been performed on the OMEGA laser facility [T. R. Boehly, Opt. Commun. 133, 495 (1997)]. These experiments provide an essential extension of the results of previous low-Z (CH) double-shell implosions [P. A. Amendt, Phys. Rev. Lett. 94, 065004 (2005)] to materials of higher density and atomic number. Analytic modeling, supported by highly resolved 2D numerical simulations, is used to account for the yield degradation due to interfacial atomic mixing. This extended experimental database from OMEGA enables a validation of the mix model, and provides a means for quantitatively assessing the prospects for high-Z double-shell implosions on the National Ignition Facility [Paisner, Laser Focus World 30, 75 (1994)].

Space-Time Fluid-Structure Interaction Computation of Flapping-Wing Aerodynamics

DTIC Science & Technology

2013-12-01

SST-VMST." The structural mechanics computations are based on the Kirchhoff -Love shell model. We use a sequential coupling technique, which is...mechanics computations are based on the Kirchhoff -Love shell model. We use a sequential coupling technique, which is ap- plicable to some classes of FSI...we use the ST-VMS method in combination with the ST-SUPS method. The structural mechanics computations are mostly based on the Kirchhoff –Love shell

A mixed helium-oxygen shell in some core-collapse supernova progenitors

NASA Astrophysics Data System (ADS)

Gofman, Roni Anna; Gilkis, Avishai; Soker, Noam

2018-04-01

We evolve models of rotating massive stars up to the stage of iron core collapse using the MESA code and find a shell with a mixed composition of primarily helium and oxygen in some cases. In the parameter space of initial masses of 13-40M⊙ and initial rotation velocities of 0-450 kms-1 that we investigate, we find a mixed helium-oxygen (He-O) shell with a significant total He-O mass and with a helium to oxygen mass ratio in the range of 0.5-2 only for a small fraction of the models. While the shell formation due to mixing is instigated by rotation, the pre-collapse rotation rate is not very high. The fraction of models with a shell of He-O composition required for an energetic collapse-induced thermonuclear explosion is small, as is the fraction of models with high specific angular momentum, which can aid the thermonuclear explosion by retarding the collapse. Our results suggest that the collapse-induced thermonuclear explosion mechanism that was revisited recently can account for at most a small fraction of core-collapse supernovae. The presence of such a mixed He-O shell still might have some implications for core-collapse supernovae, such as some nucleosynthesis processes when jets are present, or might result in peculiar sub-luminous core-collapse supernovae.

A mixed helium-oxygen shell in some core-collapse supernova progenitors

NASA Astrophysics Data System (ADS)

Gofman, Roni Anna; Gilkis, Avishai; Soker, Noam

2018-07-01

We evolve models of rotating massive stars up to the stage of iron core collapse using the MESA code and find a shell with a mixed composition of primarily helium and oxygen in some cases. In the parameter space of initial masses of 13-40 M⊙ and initial rotation velocities of 0-450 km s-1 that we investigate, we find a mixed helium-oxygen (He-O) shell with a significant total He-O mass and with a helium to oxygen mass ratio in the range of 0.5-2 only for a small fraction of the models. While the shell formation due to mixing is instigated by rotation, the pre-collapse rotation rate is not very high. The fraction of models with a shell of He-O composition required for an energetic collapse-induced thermonuclear explosion is small, as is the fraction of models with high specific angular momentum, which can aid the thermonuclear explosion by retarding the collapse. Our results suggest that the collapse-induced thermonuclear explosion mechanism that was revisited recently can account for at most a small fraction of core-collapse supernovae. The presence of such a mixed He-O shell still might have some implications for core-collapse supernovae, such as some nucleosynthesis processes when jets are present, or might result in peculiar sub-luminous core-collapse supernovae.

Rotational Splittings of Acoustic Modes in an Experimental Model of a Planetary Core

NASA Astrophysics Data System (ADS)

Adams, M. M.; Stone, D.; Lathrop, D. P.

2014-12-01

Planetary zonal flows can be probed in principle using the tools of helioseismology. We explore this technique using laboratory experiments where the measurement of zonal flows is also of geophysical relevance. The experiments are carried out in a device with a geometry similar to that of Earth's core. It consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter inner sphere. Air between the inner sphere and outer shell is used as the working fluid. A turbulent shear flow is driven in the air by independently rotating the inner sphere and outer shell. Acoustic modes are excited in the vessel with a speaker, and microphones are used to measure the rotational splittings of these modes. The radial profile of azimuthal velocities is inferred from these splittings, in an approach analogous to that used in helioseismology to determine solar velocity profiles. By varying the inner and outer rotation rates, different turbulent states can be investigated. Comparison is made to previous experimental investigations of turbulent spherical Couette flow. These experiments also serve as a test of this diagnostic, which may be used in the future in liquid sodium experiments, providing information on zonal flows in hydromagnetic experiments.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiO(x) core-shell nanoparticles.

PubMed

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M; Lu, Ming-Chang; Chueh, Yu-Lun

2014-05-07

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiO(x) core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiO(x) core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiO(x) core-shell NPs during cyclic heating processes. The latent heat of ∼29 J g(-1) for Sn/SiO(x) core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g(-1) K(-1) for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiO(x) core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.

Dyson shells: a retrospective

NASA Astrophysics Data System (ADS)

Bradbury, Robert J.

2001-08-01

More than 40 years have passed since Freeman Dyson suggested that advanced technological civilizations are likely to dismantle planets in their solar systems to harvest all of the energy their stars wastefully radiate into space. Clearly this was an idea that was ahead of its time. Since that time, dozens of SETI searches have been conducted and almost all of them have focused their attention on stars which by definition cannot be the advanced civilizations that Dyson envisioned. I will review the data that created the confusion between Dyson spheres and Dyson shells. The sources that disprove Dyson spheres while still allowing Dyson shells will be discussed. The use of outmoded ideas that have biased the few searches for Dyson Shells that have occurred will be pointed out. An update of the concept of Dyson shells to include our current knowledge of biotechnology, nanotechnology and computer science will be explored. Finally, an approach to setting limits on the abundance of Dyson shells in our galaxy using existing optical astronomical data and future optical satellites will be proposed.

Defects in Nematic Shells: A Γ-Convergence Discrete-to-Continuum Approach

NASA Astrophysics Data System (ADS)

Canevari, Giacomo; Segatti, Antonio

2018-07-01

In this paper we rigorously investigate the emergence of defects on Nematic Shells with a genus different from one. This phenomenon is related to a non-trivial interplay between the topology of the shell and the alignment of the director field. To this end, we consider a discrete XY system on the shell M, described by a tangent vector field with unit norm sitting at the vertices of a triangulation of the shell. Defects emerge when we let the mesh size of the triangulation go to zero, namely in the discrete-to-continuum limit. In this paper we investigate the discrete-to-continuum limit in terms of Γ-convergence in two different asymptotic regimes. The first scaling promotes the appearance of a finite number of defects whose charges are in accordance with the topology of shell M, via the Poincaré-Hopf Theorem. The second scaling produces the so called Renormalized Energy that governs the equilibrium of the configurations with defects.