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Sample records for spherical calcia stabilized

  1. Microwave technique applied to the hydrothermal synthesis and sintering of calcia stabilized zirconia nanoparticles

    NASA Astrophysics Data System (ADS)

    Rizzuti, Antonino; Corradi, Anna; Leonelli, Cristina; Rosa, Roberto; Pielaszek, Roman; Lojkowski, Witold

    2010-01-01

    This study is focused on the synthesis of zirconia nanopowders stabilized by 6%mol calcia prepared under hydrothermal conditions using microwave technology. Sodium hydroxide-based hydrolysis of zirconyl chloride solution containing calcium nitrate followed by microwave irradiation at the temperature of 220 °C for 30 min was sufficient to obtain white powders of crystalline calcia stabilized zirconia. By means of X-ray diffraction and transmission electron microscopy, it was shown that tetragonal zirconia nanocrystallites with a size of ca 7 nm and diameter/standard deviation ratio of 0.10 were formed. The effects of the [Ca2+] and [NaOH] as well as temperature and time of microwave irradiation on the density and specific surface area were evaluated. Sintering test of the tetragonal nanopowders at 1,300 °C in air was performed in a monomode microwave applicator. The sample was sintered to the density of 95% and the grain size, analyzed by field emission scanning electron microscopy, was in the range from 90 to 170 nm.

  2. Bulk and Interface Thermodynamics of Calcia-, and Yttria-doped Zirconia Ceramics: Nanograined Phase Stability

    NASA Astrophysics Data System (ADS)

    Drazin, John Walter

    while simultaneously collecting the energetic contribution of the adsorbing water vapor. With this data and apparatus, I have derived a 2nd order differential equation that relates the surface energy to the measured quantities such that I collected surfaces energies for over 35 specimens in the calcia-zirconia and yttria-zirconia systems for the first time. From the results, it was found that the monoclinic polymorph had the largest surface energy in the range of 1.9 - 2.1 ( J/m2) while the tetragonal surface energies were roughly 1.4 - 1.6 (J/m2), the cubic surface energies were roughly 0.8 - 1.0 (J/m2), and the amorphous surface energies were the smallest at roughly 0.7 - 0.8 (J/m 2). With the measured surface energy data, collected for the first time, we can create a nano-grain phase diagram similar to a bulk phase diagram that shows the stable polymorph as a function of dopant concentration and grain size using the bulk enthalpy data collected from high temperature oxide melt drop solution calorimetry. The phase diagrams show that pure zirconia will transform into tetragonal and cubic polymorphs from the monoclinic one at 7 and 5 nm respectively which confirms the experimental observations. The results are powerful predictive tools successfully applied in the nCZ and nYZ systems to a high degree of accuracy and adds a new development to conventional bulk phase diagrams. These diagrams should be the basis for nanotechnological efforts in nCZ and nYZ based systems, and suggest similar efforts are needed in other nano systems to pursue an in depth understanding and optimization of nanomaterials. After working on the theoretical aspects of phase stability, the focus of the research will shift to producing dense samples to measure observable quantities such as oxygen conduction and mechanical hardness. However, producing said samples with the nanocrystalline grain sizes has also been challenging as conventional sintering requires high temperatures which, as a consequence

  3. Stability of thick spherical shells

    NASA Astrophysics Data System (ADS)

    Liu, I.-Shih

    1995-06-01

    The pressure-radius relation of spherical rubber balloons has been derived and its stability behavior investigated before. In this work, we show that similar results remain valid for thick spherical shells of Mooney-Rivlin materials. In addition, we show that eversion of a spherical shell is possible for any incompressible isotropic materials if the shell is not too thick.

  4. PRODUCTION OF SLIP CAST CALCIA HOLLOWWARE

    DOEpatents

    Stoddard, S.D.; Nuckolls, D.E.; Cowan, R.E.

    1963-12-31

    A method for producing slip cast calcia hollow ware in which a dense calcia grain is suspended in isobutyl acetate or a mixture of tertiary amyl alcohol and o-xylene is presented. A minor amount of triethanolamine and oleic acid is added to the suspension vehicle as viscosity adjusting agents and the suspension is cast in a plaster mold, dried, and fired. (AEC)

  5. Stability of spherical converging shock wave

    SciTech Connect

    Murakami, M.; Sanz, J.; Iwamoto, Y.

    2015-07-15

    Based on Guderley's self-similar solution, stability of spherical converging shock wave is studied. A rigorous linear perturbation theory is developed, in which the growth rate of perturbation is given as a function of the spherical harmonic number ℓ and the specific heats ratio γ. Numerical calculation reveals the existence of a γ-dependent cut-off mode number ℓ{sub c}, such that all the eigenmode perturbations for ℓ > ℓ{sub c} are smeared out as the shock wave converges at the center. The analysis is applied to partially spherical geometries to give significant implication for different ignition schemes of inertial confinement fusion. Two-dimensional hydrodynamic simulations are performed to verify the theory.

  6. Stability of Spherical Vesicles in Electric Fields

    PubMed Central

    2010-01-01

    The stability of spherical vesicles in alternating (ac) electric fields is studied theoretically for asymmetric conductivity conditions across their membranes. The vesicle deformation is obtained from a balance between the curvature elastic energies and the work done by the Maxwell stresses. The present theory describes and clarifies the mechanisms for the four types of morphological transitions observed experimentally on vesicles exposed to ac fields in the frequency range from 500 to 2 × 107 Hz. The displacement currents across the membranes redirect the electric fields toward the membrane normal to accumulate electric charges by the Maxwell−Wagner mechanism. These accumulated electric charges provide the underlying molecular mechanism for the morphological transitions of vesicles as observed on the micrometer scale. PMID:20575588

  7. Propagation and stability of expanding spherical flames

    NASA Astrophysics Data System (ADS)

    Jomaas, Grunde

    High-fidelity experiments were conducted to determine the laminar flame speeds of various fuels, to define the transition boundaries of both cellular and spiral flame front instabilities that develop over the flame surface, and to determine the cellular flame acceleration constants for outwardly propagating spherical flames in a near-constant pressure environment up to 60 atmospheres. The flame front movement was monitored using schlieren cinematography and recorded with a high-speed digital camera. Experiments were conducted for a wide range of pressures and equivalence ratios to yield flame speed data for acetylene, ethylene, ethane, propylene, propane, dimethyl ether, and hydrogen/carbon monoxide in air. These data were post-processed in order to account for stretch effects, yielding laminar, unstretched flame speeds and Markstein lengths. The results were compared with existing chemical kinetics mechanisms and used to suggest improvements. The instant of transition to cellularity was experimentally determined for various fuels and fuel mixtures and subsequently interpreted on the basis of hydrodynamic and diffusional-thermal instabilities. Experimental results show that the transition Peclet number, Pec = Rc/ℓL, assumes an almost constant value for the near-equidiffusive acetylene and ethylene flames with wide ranges in the mixture stoichiometry, oxygen concentration, and pressure, where Rc is the flame radius at transition and ℓL the laminar flame thickness. However, for the non-equidiffusive hydrogen and propane flames, Pec respectively increases and decreases somewhat linearly with the mixture equivalence ratio. Evaluation of Pec using the theory of Bechtold and Matalon show complete qualitative agreement and satisfactory quantitative agreement, demonstrating the insensitivity of Pec to all system parameters for equidiffusive mixtures, and the dominance of the Markstein number, Ze(Le-1), in destabilization for non-equidiffusive mixtures, where Ze is the

  8. [Setting characteristics of calcia-bonded investments by hydration].

    PubMed

    Nishimura, F; Watari, F; Nomoto, S

    1989-07-01

    Calcium oxide (CaO) slurry mixed with water hardens and expands by hydration. The authors used this setting characteristic as a binder of zirconia-refractory investments. If a mixed slurry was placed in air, unreacted residual calcia powders absorbed water and reverted to calcium hydroxide (Ca (OH)2). This resulted in a large setting expansion that continued for several days. A carbon dioxide (CO2) gas atmosphere controlled this expansion of calcia. When mixed slurry was placed in a carbon dioxide gas atmosphere, calcium carbonate (CaCO3) was formed and prevented the further hydration of unreacted calcium oxide. Thus setting expansion values were controlled. The combined expansion of setting and thermal expansion, in CaO-CO2-bonded zirconia investments, was about 1.5-2.5%. On the whole, calcium oxide is expected to be a good binder for high temperature dental casting refractory.

  9. Stability of thin-shell wormholes with spherical symmetry

    SciTech Connect

    Eiroa, Ernesto F.

    2008-07-15

    In this article, the stability of a general class of spherically symmetric thin-shell wormholes is studied under perturbations preserving the symmetry. For this purpose, the equation of state at the throat is linearized around the static solutions. The formalism presented here is applied to dilaton wormholes, and it is found that there is a smaller range of possible stable configurations for them than in the case of Reissner-Nordstroem wormholes with the same charge.

  10. Spherical nuclei near the stability line and far from it

    NASA Astrophysics Data System (ADS)

    Isakov, V. I.

    2016-11-01

    Results of microscopic and semiphenomenological calculations of features of spherical nuclei lying near the stability line and far from it are presented. The reason why the nuclei being considered are spherical is that they are magic at least in one nucleon sort. The present analysis is performed for Z = 50 and Z = 28 isotopes and for N = 50 isotones, the region extending from neutron-rich to neutron-deficient nuclei being covered. The isotopic dependence of the mean-field spin-orbit nuclear potential is revealed; systematics of energies of levels and probabilities for electromagnetic transitions is examined; and root-mean-square radii of nuclei are calculated, along with the proton- and neutron-density distributions in them. Nuclei in the vicinity of closed shells are considered in detail, and the axial-vector weak coupling constant in nuclei is evaluated. A systematic comparison of the results of calculations with experimental data is performed.

  11. Spherical nuclei near the stability line and far from it

    SciTech Connect

    Isakov, V. I.

    2016-11-15

    Results of microscopic and semiphenomenological calculations of features of spherical nuclei lying near the stability line and far from it are presented. The reason why the nuclei being considered are spherical is that they are magic at least in one nucleon sort. The present analysis is performed for Z = 50 and Z = 28 isotopes and for N = 50 isotones, the region extending from neutron-rich to neutron-deficient nuclei being covered. The isotopic dependence of the mean-field spin–orbit nuclear potential is revealed; systematics of energies of levels and probabilities for electromagnetic transitions is examined; and root-mean-square radii of nuclei are calculated, along with the proton- and neutron-density distributions in them. Nuclei in the vicinity of closed shells are considered in detail, and the axial-vector weak coupling constant in nuclei is evaluated. A systematic comparison of the results of calculations with experimental data is performed.

  12. Spherical aberration standards and measurement system stability over time

    NASA Astrophysics Data System (ADS)

    Compertore, David; Ignatovich, Filipp; Marcus, Michael

    2015-10-01

    A Shack-Hartmann wave-front sensor system has been used to measure a set of plano-convex lenses at two different times, separated by almost 2 years. The plano-convex lenses were selected to cover a range of powers and apertures relevant to intraocular lenses, and were measured at two different orientations. The results demonstrate the high temporal stability of the measurement system, as well as of the glass standard. In addition, both times the effective focal lengths of the standards were measured using a NIST traceable nodal slide bench, and the center thicknesses were measured using low-coherence interferometer. The spherical aberration and the effective focal length results are analyzed for statistically significant changes. The results are also compared to the Zemax models of the standards.

  13. Kink stability of isothermal spherical self-similar flow revisited

    NASA Astrophysics Data System (ADS)

    Wang, Anzhong; Wu, Yumei

    2006-11-01

    The problem of kink stability of isothermal spherical self-similar flow in newtonian gravity is revisited. Using distribution theory we first develop a general formula of perturbations, linear or non-linear, which consists of three sets of differential equations, one in each side of the sonic line and the other along it. By solving the equations along the sonic line we find explicitly the spectrum, k, of the perturbations, whereby we obtain the stability criterion for the self-similar solutions. When the solutions are smoothly across the sonic line, our results reduce to those of Ori and Piran. To show such obtained perturbations can be matched to the ones in the regions outside the sonic line, we study the linear perturbations in the external region of the sonic line (the ones in the internal region are identically zero), by taking the solutions obtained along the line as the boundary conditions. After properly imposing other boundary conditions at spatial infinity, we are able to show that linear perturbations, satisfying all the boundary conditions, exist and do not impose any additional conditions on k. As a result, the complete treatment of perturbations in the whole spacetime does not alter the spectrum obtained by considering the perturbations only along the sonic line.

  14. Coating of calcia-doped ceria with amorphous silica shell by seeded polymerization technique

    SciTech Connect

    El-Toni, Ahmed Mohamed . E-mail: el-toni@mail.tagen.tohoku.ac.jp; Yin, Shu; Yabe, Shinryo; Sato, Tsugio

    2005-07-12

    Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products. However, its high catalytic ability for oxidation of organic materials makes it difficult to use as a sunscreen material. Therefore, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique in order to depress its oxidation catalytic ability. The catalytic ability as well as UV-shielding ability was investigated for coated particles.

  15. Effect of acoustic radiation on the stability of spherical bubble oscillations

    NASA Astrophysics Data System (ADS)

    Gumerov, Nail A.

    1998-07-01

    A recent analysis of the stability of spherical bubble oscillations shows that the high order shape modes are parametrically unstable with respect to small but finite perturbations [Z. C. Feng and L. G. Leal, J. Fluid Mech. 266, 209 (1994)]. Using a heuristic approach it is shown here that the acoustic radiation due to the liquid compressibility plays an important role in stabilization of the high frequency modes and overall stability of the bubble spherical shape.

  16. Stability and superluminality of spherical DBI Galileon solutions

    SciTech Connect

    Goon, Garrett L.; Hinterbichler, Kurt; Trodden, Mark

    2011-04-12

    We showed that, when considered as local modifications to gravity, such as in the solar system, there exists a region of parameter space in which spherically symmetric static solutions to a particular class of modified gravity theories exist and are stable.

  17. Stability and superluminality of spherical DBI Galileon solutions

    DOE PAGES

    Goon, Garrett L.; Hinterbichler, Kurt; Trodden, Mark

    2011-04-12

    We showed that, when considered as local modifications to gravity, such as in the solar system, there exists a region of parameter space in which spherically symmetric static solutions to a particular class of modified gravity theories exist and are stable.

  18. Cauchy horizon stability in a collapsing spherical dust cloud: I. Geometric optics approximation and spherically symmetric test fields

    NASA Astrophysics Data System (ADS)

    Ortiz, Néstor; Sarbach, Olivier

    2014-04-01

    A spherical dust cloud which is initially at rest and which has a monotonously decaying density profile collapses and forms a shell-focusing singularity. Provided the density profile is not too flat, meaning that its second radial derivative is negative at the centre, this singularity is visible to local, and sometimes even to global observers. According to the strong cosmic censorship conjecture, such naked singularities should be unstable under generic, non-spherical perturbations of the initial data or when more realistic matter models are considered. In an attempt to gain further insight into this stability issue, in this work we initiate the analysis of a simpler but related problem. We discuss the stability of test fields propagating in the vicinity of the Cauchy horizon associated to the naked central singularity. We first study the high-frequency limit and show that the fields undergo a blueshift as they approach the Cauchy horizon. However, in contrast to what occurs at inner horizons of black holes, we show that the blueshift is uniformly bounded along incoming and outgoing null rays. Motivated by this boundedness result, we take a step beyond the geometric optics approximation and consider the Cauchy evolution of spherically symmetric test scalar fields. We prove that under reasonable conditions on the initial data a suitable rescaled field can be continuously extended to the Cauchy horizon. In particular, this result implies that the physical field is everywhere finite on the Cauchy horizon away from the central singularity.

  19. Characterization and Stability of High Beta Spherical Flows

    NASA Astrophysics Data System (ADS)

    Siller, Robert; Mirnov, Vladimir; Forest, Cary

    2016-10-01

    The fluid response of a fully compressible, isothermal plasma in investigated in a spherical system with application to the Madison Plasma Dynamo Experiment (MPDX). Numerical results are found in a fully spectral code, solving separately for the equilibrium profile of a given drive, and the linear eigenmodes of the system. The example flows are driven by a large radial current drawn across a small axial field generating torque across the system. Numerical calculations show sample conditions near achievable conditions for exciting various instabilities, with the MRI and the dynamo instabilities of primary focus. DoE and NSF.

  20. Octupole response and stability of spherical shape in heavy nuclei

    NASA Astrophysics Data System (ADS)

    Abrosimov, V. I.; Davidovskaya, O. I.; Dellafiore, A.; Matera, F.

    2003-11-01

    The isoscalar octupole response of a heavy spherical nucleus is analyzed in a semiclassical model based on the linearized Vlasov equation. The octupole strength function is evaluated with different degrees of approximation. The zero-order fixed-surface response displays a remarkable concentration of strength in the 1ℏ ω and 3ℏ ω regions, in excellent agreement with the quantum single-particle response. The collective fixed-surface response reproduces both the high- and low-energy octupole resonances, but not the low-lying 3 - collective states, while the moving-surface response function gives a good qualitative description of all the main features of the octupole response in heavy nuclei. The role of triangular nucleon orbits, that have been related to a possible instability of the spherical shape with respect to octupole-type deformations, is discussed within this model. It is found that, rather than creating instability, the triangular trajectories are the only classical orbits contributing to the damping of low-energy octupole excitations.

  1. Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions

    NASA Astrophysics Data System (ADS)

    Kravchuk, Volodymyr P.; Rößler, Ulrich K.; Volkov, Oleksii M.; Sheka, Denis D.; van den Brink, Jeroen; Makarov, Denys; Fuchs, Hagen; Fangohr, Hans; Gaididei, Yuri

    2016-10-01

    Topologically stable structures include vortices in a wide variety of matter, skyrmions in ferro- and antiferromagnets, and hedgehog point defects in liquid crystals and ferromagnets. These are characterized by integer-valued topological quantum numbers. In this context, closed surfaces are a prominent subject of study as they form a link between fundamental mathematical theorems and real physical systems. Here we perform an analysis on the topology and stability of equilibrium magnetization states for a thin spherical shell with easy-axis anisotropy in normal directions. Skyrmion solutions are found for a range of parameters. These magnetic skyrmions on a spherical shell have two distinct differences compared to their planar counterpart: (i) they are topologically trivial and (ii) can be stabilized by curvature effects, even when Dzyaloshinskii-Moriya interactions are absent. Due to its specific topological nature a skyrmion on a spherical shell can be simply induced by a uniform external magnetic field.

  2. Ionic liquid-stabilized non-spherical gold nanofluids synthesized using a one-step method.

    PubMed

    Zhang, Hao; Cui, Hua; Yao, Shiwei; Zhang, Kelong; Tao, Haikun; Meng, Haibo

    2012-10-23

    Ionic liquid (IL)-stabilized non-spherical gold nanofluids have been synthesized by a one-step method in aqueous solution. The whole reaction proceeded in room temperature. In the presence of amino-functionalized ionic liquids, gold nanofluids with long-wave surface plasmon resonance (SPR) absorption (>600 nm) could be obtained by adopting tannic acid as the reductant. The specific SPR absorption was related to the non-spherical gold nanoparticles including gold triangle, decahedra, and icosahedra nanocrystals. All the nanocrystals were observed by transmission electron microscopy. It was deduced that the formation of non-spherical gold nanofluids was related to the hydroxyls in tannic acid while IL acted as the synthesis template.

  3. Ionic liquid-stabilized non-spherical gold nanofluids synthesized using a one-step method

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Cui, Hua; Yao, Shiwei; Zhang, Kelong; Tao, Haikun; Meng, Haibo

    2012-10-01

    Ionic liquid (IL)-stabilized non-spherical gold nanofluids have been synthesized by a one-step method in aqueous solution. The whole reaction proceeded in room temperature. In the presence of amino-functionalized ionic liquids, gold nanofluids with long-wave surface plasmon resonance (SPR) absorption (>600 nm) could be obtained by adopting tannic acid as the reductant. The specific SPR absorption was related to the non-spherical gold nanoparticles including gold triangle, decahedra, and icosahedra nanocrystals. All the nanocrystals were observed by transmission electron microscopy. It was deduced that the formation of non-spherical gold nanofluids was related to the hydroxyls in tannic acid while IL acted as the synthesis template.

  4. Ionic liquid-stabilized non-spherical gold nanofluids synthesized using a one-step method

    PubMed Central

    2012-01-01

    Ionic liquid (IL)-stabilized non-spherical gold nanofluids have been synthesized by a one-step method in aqueous solution. The whole reaction proceeded in room temperature. In the presence of amino-functionalized ionic liquids, gold nanofluids with long-wave surface plasmon resonance (SPR) absorption (>600 nm) could be obtained by adopting tannic acid as the reductant. The specific SPR absorption was related to the non-spherical gold nanoparticles including gold triangle, decahedra, and icosahedra nanocrystals. All the nanocrystals were observed by transmission electron microscopy. It was deduced that the formation of non-spherical gold nanofluids was related to the hydroxyls in tannic acid while IL acted as the synthesis template. PMID:23092303

  5. Stability of pear-shaped configurations bifurcated from a pressurized spherical balloon

    NASA Astrophysics Data System (ADS)

    Fu, Y. B.; Xie, Y. X.

    2014-08-01

    It is well-known that for most spherical rubber balloons the pressure versus volume curve associated with uniform inflation is N-shaped (the pressure increases rapidly to a maximum, falls to a minimum, and subsequently increases monotonically), and that somewhere along the descending branch of this curve the spherical shape may bifurcate into a pear shape through localized thinning near one of the poles. The bifurcation is associated with the (uniform) surface tension reaching a maximum. It is previously known that whenever a pear-shaped configuration becomes possible, it has lower energy than the co-existing spherical configuration, but the stability of the pear-shaped configuration itself is unknown. With the use of the energy stability criterion, it is shown in this paper that the pear-shaped configuration is unstable under pressure control, but stable under mass control. Our calculations are carried out using the Ogden material model as an example, but it is expected that the qualitative stability results should also be valid for other material models that predict a similar N-shaped behavior for uniform inflation.

  6. Curvature-driven stability of defects in nematic textures over spherical disks

    NASA Astrophysics Data System (ADS)

    Duan, Xiuqing; Yao, Zhenwei

    2017-06-01

    Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature-driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature-driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature-driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid-crystal textures in various applications.

  7. Beta-limiting instabilities and global mode stabilization in the National Spherical Torus Experiment

    SciTech Connect

    Sabbagh, S. A.; Peng, Yueng Kay Martin

    2003-01-01

    Research on the stability of spherical torus plasmas at and above the no-wall beta limit is being addressed on the National Spherical Torus Experiment @M. Ono et al., Nucl. Fusion 40, 557 ~2000!#, that has produced low aspect ratio plasmas, R/a;1.27 at plasma current exceeding 1.4 MA with high energy confinement (TauE/TauE ITER89P.2). Toroidal and normalized beta have exceeded 25% and 4.3, respectively, in q;7 plasmas. The beta limit is observed to increase and then saturate with increasing li . The stability factor bN /li has reached 6, limited by sudden beta collapses. Increased pressure peaking leads to a decrease in bN . Ideal stability analysis of equilibria reconstructed with EFIT @L. L. Lao et al., Nucl. Fusion 25, 1611 ~1985!# shows that the plasmas are at the no-wall beta limit for the n51 kink/ballooning mode. Low aspect ratio and high edge q theoretically alter the plasma stability and mode structure compared to standard tokamak configurations. Below the no-wall limit, stability calculations show the perturbed radial field is maximized near the center column and mode stability is not highly effected by a nearby conducting wall due to the short poloidal wavelength in this region. In contrast, as beta reaches and exceeds the no-wall limit, the mode becomes strongly ballooning with long poloidal wavelength at large major radius and is highly wall stabilized. In this way, wall stabilization is more effective at higher beta in low aspect ratio geometry. The resistive wall mode has been observed in plasmas exceeding the ideal no-wall beta limit and leads to rapid toroidal rotation damping across the plasma core.

  8. Criterion for the dynamical stability of a non-adiabatic spherical self-gravitating body

    NASA Astrophysics Data System (ADS)

    Stothers, Richard B.

    1999-04-01

    Why do stars and planets maintain their dynamical stability over cosmically long periods of time? The standard answer is that the first generalized adiabatic exponent of their material, Gamma_1, exceeds the value 4/3. Yet it has never been rigorously demonstrated (except for the simple one-zone model) that non-adiabatic effects do not modify this result at some level. Many authors, in fact, have suggested the probable need for a non-adiabatic correction to the square of the radial adiabatic eigenfrequency, sigma^2, which ostensibly governs dynamical stability in the more general case where Gamma_1 varies throughout a fully distributed self-gravitating spherical body. Here, a carefully controlled series of numerical experiments based on linear and non-linear hydrodynamical models of highly non-adiabatic spherically symmetric stellar envelopes (mimicking the envelopes of luminous blue variables) confirms, quite generally, that the purely adiabatic criterion sigma^2>0 does in fact determine dynamical stability. An accurate approximation to this criterion is further shown to be that the volumetric pressure-weighted average of Gamma_1 must exceed 4/3. These results, which concern only radial stability, verify the theoretical basis of the more sophisticated models for luminous blue variables that were constructed by the author and C.-w. Chin, but they do not support the objections to these models raised by W. Glatzel and M. Kiriakidis.

  9. Heaps of Shapes: Flow-Stabilized Solids with Non-Spherical Colloids

    NASA Astrophysics Data System (ADS)

    Lindauer, Scott; Shields, C. Wyatt, IV; Lopez, Gabriel P.; Daniels, Karen E.; Riehn, Robert

    Flow-stabilized solids are a class of fragile matter that are formed when a dense suspension of hard colloids is accumulated against a semipermeable barrier. We build a microfluidic device to confine Brownian particles in a quasi-2D channel; a controlled flow rate above a critical value forms flow-stabilized solids against the barrier. We extend prior work on submicron spherical particles, to particles of size 2-5 microns, and of various shapes: circular, rectangular, hexagonal, and triangular prisms. We perform experiments on these flow-stabilized solids to observe the angle of repose, packing fraction, and orientational order as a function of flow rate. We vary the flow rate quasi-statically in order to conduct the experiment at steady state. We find a critical flow rate below which no pile forms. In general, particles with less-circular shape form more stable heaps.

  10. Morphological stability criterion for a spherical crystallization front in a multicomponent system with chemical reactions

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.; Redkov, A. V.

    2014-12-01

    The morphological stability of a spherical crystal growing from a multicomponent medium due to the chemical reaction has been investigated. The approach used in this study is applicable to the case where the chemical compound forming the crystal does not exist in a gaseous (dissolved) form (for example, GaN). The investigation has been performed according to the classical scheme by the expansion of an infinitesimal deviation of the crystallization front from the initial shape into a series with the subsequent calculation of the time dependence of the coefficients of the expansion. It has been found that there is a similarity of the stability criteria for single-component and multicomponent crystals. In a multicomponent system, the single-component supersaturation analog determining the stability of a particle is the affinity of the chemical reaction. It has been shown that the morphological stability can also depend on the formation of other phases on the surface of the initial crystal, which is excluded in a single-component medium.

  11. Lignosulfonate-stabilized selenium nanoparticles and their deposition on spherical silica.

    PubMed

    Modrzejewska-Sikorska, Anna; Konował, Emilia; Klapiszewski, Łukasz; Nowaczyk, Grzegorz; Jurga, Stefan; Jesionowski, Teofil; Milczarek, Grzegorz

    2017-10-01

    We report a novel room-temperature synthesis of selenium nanoparticles, which for the first time uses lignosulfonate as a stabilizer. Various lignosulfonates obtained both from hardwood and softwood were tested. Selenium oxide was used as the precursor of zero-valent selenium. Three different reducers were tested - sodium borohydride, hydrazine and ascorbic acid - and the latter proved most effective in terms of the particle size and stability of the final colloid. The lignosulfonate-stabilized selenium nanoparticles had a negative zeta potential, dependent on pH, which for some lignosulfonates reached -50mV, indicating the excellent stability of the colloid. When spherical silica particles were introduced to the synthesis mixture, selenium nanoparticles were deposited on their surface. Additionally, star-like structures consisting of sharp selenium needles with silica cores were observed. After drying, the selenium-functionalized silica had a grey metallic hue. The method reported here is simple and cost-effective, and can be used for the preparation of large quantities of selenium colloids or the surface modification of other materials with selenium. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. Relevant parameter space and stability of spherical tokamaks with a plasma center column

    NASA Astrophysics Data System (ADS)

    Lampugnani, L. G.; Garcia-Martinez, P. L.; Farengo, R.

    2017-02-01

    A spherical tokamak (ST) with a plasma center column (PCC) can be formed inside a simply connected chamber via driven magnetic relaxation. From a practical perspective, the ST-PCC could overcome many difficulties associated with the material center column of the standard ST reactor design. Besides, the ST-PCC concept can be regarded as an advanced helicity injected device that would enable novel experiments on the key physics of magnetic relaxation and reconnection. This is because the concept includes not only a PCC but also a coaxial helicity injector (CHI). This combination implies an improved level of flexibility in the helicity injection scheme required for the formation and sustainment phases. In this work, the parameter space determining the magnetic structure of the ST-PCC equilibria is studied under the assumption of fully relaxed plasmas. In particular, it is shown that the effect of the external bias field of the PCC and the CHI essentially depends on a single parameter that measures the relative amount of flux of these two entities. The effect of plasma elongation on the safety factor profile and the stability to the tilt mode are also analyzed. In the first part of this work, the stability of the system is explained in terms of the minimum energy principle, and relevant stability maps are constructed. While this picture provides an adequate insight into the underlying physics of the instability, it does not include the stabilizing effect of line-tying at the electrodes. In the second part, a dynamical stability analysis of the ST-PCC configurations, including the effect of line-tying, is performed by numerically solving the magnetohydrodynamic equations. A significant stability enhancement is observed when the PCC contains more than the 70% of the total external bias flux, and the elongation is not higher than two.

  13. Stability of Schwarzschild-AdS for the Spherically Symmetric Einstein-Klein-Gordon System

    NASA Astrophysics Data System (ADS)

    Holzegel, Gustav; Smulevici, Jacques

    2013-01-01

    In this paper, we study the global behavior of solutions to the spherically symmetric coupled Einstein-Klein-Gordon (EKG) system in the presence of a negative cosmological constant. For the Klein-Gordon mass-squared satisfying a ≥ -1 (the Breitenlohner-Freedman bound being a > -9/8), we prove that the Schwarzschild-AdS spacetimes are asymptotically stable: Small perturbations of Schwarzschild-AdS initial data again lead to regular black holes, with the metric on the black hole exterior approaching, at an exponential rate, a Schwarzschild-AdS spacetime. The main difficulties in the proof arise from the lack of monotonicity for the Hawking mass and the asymptotically AdS boundary conditions, which render even (part of) the orbital stability intricate. These issues are resolved in a bootstrap argument on the black hole exterior, with the redshift effect and weighted Hardy inequalities playing the fundamental role in the analysis. Both integrated decay and pointwise decay estimates are obtained. As a corollary of our estimates on the Klein-Gordon field, one obtains in particular exponential decay in time of spherically-symmetric solutions to the linear Klein-Gordon equation on Schwarzschild-AdS.

  14. The confinement effect in spherical inhomogeneous quantum dots and stability of excitons

    NASA Astrophysics Data System (ADS)

    Benhaddou, F.; Zorkani, I.; Jorio, A.

    2017-06-01

    We investigate in this work the quantum confinement effect of exciton in spherical inhomogeneous quantum dots IQDs. The spherical core is enveloped by two shells. The inner shell is a semiconductor characterized by a small band-gap. The core and the outer shell are the same semiconductor characterized by a large band-gap. So there is a significant gap-offset creating a deep potential well where the excitons are localized and strongly confined. We have adopted the Ritz variational method to calculate numerically the excitonic ground state energy and its binding energy in the strong, moderate and low confinement regimes. The results show that the Ritz variational method is in good agreement with the perturbation method in strong confinement. There is a double confinement effect and dual control. The calculation checks the effective Rydberg R* at the asymptotic limit of bulk semiconductor when the thickness takes very large values. The excitonic binding energy increases, Thus giving the excitons a high stability even at ambient temperature. These nanosystems are promising in several applications: lighting, detection, biological labeling and quantum computing.

  15. The Effect of Viscosity on the Spherical Stability of Oscillating Gas Bubbles

    NASA Technical Reports Server (NTRS)

    Hao, Y.; Prosperetti, A.

    1999-01-01

    Gas bubbles driven in radial oscillations are subject to an instability of the spherical shape that is opposed by surface tension and viscosity. An exact linear formulation for the study of the phenomenon has been available for many years, but its complexity has discouraged a detailed investigation. With the recent theory of sonoluminescence of Lohse and co-workers, there has been a renewed interest in the problem and new data have become available. This paper presents a numerical method for the solution of the pertinent equations and compares the theory with these new data. The coupling of the strong nonlinearity of the bubble radial oscillations with the parametric mechanism of the surface instability results in a very complex structure for the stability boundary. Nevertheless, a good agreement between theory and data is found. A comparison with earlier approximate models is also made.

  16. Stability of an array of bottom-heavy, upswimming, spherical squirmers

    NASA Astrophysics Data System (ADS)

    Pedley, Timothy; Brumley, Douglas

    2011-11-01

    Numerical simulations by Ishikawa & Pedley (Phys Rev Lett. 100:088103,2008; IP) of identical, bottom-heavy, spherical squirmers swimming in a vertical planar monolayer reveal a configuration in which many equally-spaced spheres swim upwards in a hexagonal array. This occurs for sufficiently large values of the bottom-heaviness parameter G. Here we perform an instability analysis in which the forces and torques on individual spheres are calculated using lubrication theory for the gaps between neighbouring squirmers. The results show that stability is impossible in the absence of the repulsive force which IP introduced to save computer time whenever two squirmers were less than 0.00001 radii apart. When the force is present, there is a critical value of G above which stability is assured. An unexpected finding is the existence of another equilibrium configuration in which the spheres' orientations are not vertical and columns of spheres are not equally spaced; in this case, however, perturbation leads to limit-cycle oscillations, not to static stability. The above results are qualitatively unaffected if the monolayer is confined between vertical walls.

  17. Mechanical stability analysis on spherical sandwich sheet at low temperature loading conditions

    NASA Astrophysics Data System (ADS)

    Wang, Shanshuai; Li, Shuhui; Li, Zhimin

    2013-12-01

    The spherical sandwich sheet (S-S-S) is generally used in the aerospace industry, for example, the airplane, the rocket's fairing, the spacecraft and the satellite for the purpose of heat-insulation, weight-saving and dimension-reducing. The stability of the S-S-S is of general concern because of its particularly thin but large size. For some S-S-S used in fuel tank storing liquid oxygen of the rocket, it must be facing low temperature down to about -183 °C. Low temperature condition affects the stability of the S-S-S and then causes buckling of the structure. In this paper, a finite element (FE) model is established for evaluating the stability of the S-S-S via the sequential coupling mode. The material mechanical properties related to temperature are concerned in the FE model. The buckling modes and critical buckling loading are predicted accurately, since the FE model includes heat transfer simulating, thermal stress computing, buckling and post buckling process. It is found that the thermal stress generated from the low temperature loading reduces the critical buckling loading and changes the buckling modes of the S-S-S.

  18. Scale effect of spherical projectiles for stabilization of oblique detonation waves

    NASA Astrophysics Data System (ADS)

    Maeda, S.; Sumiya, S.; Kasahara, J.; Matsuo, A.

    2015-03-01

    Oblique detonation waves (ODWs) were stabilized by launching a spherical projectile with 1.2-1.4 times the Chapman-Jouguet (C-J) velocity into detonable mixtures at rest. We used smaller projectiles (3.18 mm diameter) than those (4.76 mm diameter) in our previous studies and investigated the effect of the projectile scale on the stabilization of ODWs. We carried out high time resolution schlieren visualization using a high-speed camera. The detonable mixtures used were stoichiometric oxygen mixtures with acetylene, ethylene or hydrogen. They were diluted with argon with a 50 % volumetric fraction, and a dilute mixture containing 75 % argon was also tested for the acetylene/oxygen mixture. Here, we discuss the detonation stability in terms of the curvature effect arising from the three-dimensional nature of a stabilized ODW around a projectile. The curvature effect attenuated the detonation wave to below its C-J velocity in the vicinity of the projectile before the wave velocity asymptotically reached the C-J velocity in the far field. Our previous study showed that the propagation limit of the curvature effect is responsible for the stabilizing criticality of detonation waves. By obtaining detailed distributions of the wave propagation velocity and radius of curvature at the stabilizing criticality, we showed that the radius of curvature at the local minimum point of the wave propagation velocity represents the critical radius of curvature required for curved self-sustained detonation. In this study, we focused on this critical mode of the stabilized ODW for a small projectile (3.18 mm diameter). Distributions of the wave velocity and radius of curvature were obtained in the critical mode of the stabilized ODW. We compare these distributions with those for a larger projectile (4.76 mm diameter) and discuss the stabilizing criticality. For the small projectile, the observed combustion regimes had qualitatively the same trend for the initial pressure of the mixture

  19. Magnetic Equilibrium and Stability Simulations of the National Spherical Torus Experiment Plasmas

    NASA Astrophysics Data System (ADS)

    Paoletti, F.; Sabbagh, S.; Garofalo, A.; Kaita, R.; Kaye, S.; Hatcher, R.; Lao, L.; Lazarus, E.; Turnbull, A.

    1997-11-01

    The numerical code EFIT(L. Lao, et al., Nucl. Fusion 25, 1611 (1985).) has been modified to accommodate the geometry of the National Spherical Torus Experiment (NSTX). Equilibrium solutions are calculated for both fixed and free boundary conditions to determine the operational space of NSTX plasmas. The p(ψ) and ff'(ψ) equilibrium profiles are chosen either generically or from time dependent experimentally produced profiles, measured in various operational regimes (L-mode, H-mode, etc.) of the DIII-D tokamak. Results supporting the design of the external magnetic diagnostics are shown. Particular attention is given to assess sufficient coverage of the diagnostic setup, since the main future use of the code will be for equilibrium reconstruction. The stability codes GATO(L. Bernard,Comput. Phys. Commun. 21, 377 (1981).) and PEST(R. Grimm, et al., Comput. Phys. Commun. 16, 253 (1976).) will be used, in conjunction with EFIT, to study the effects of configuration and location of the passive plates on the stability of the various equilibria.

  20. Gyrokinetic Stability Studies of the Microtearing Mode in the National Spherical Torus Experiment H-mode

    SciTech Connect

    Baumgaertel, J. A.; Redi, M. H.; Budny, R. V.; Rewoldt, G.; Dorland, W.

    2005-10-19

    Insight into plasma microturbulence and transport is being sought using linear simulations of drift waves on the National Spherical Torus Experiment (NSTX), following a study of drift wave modes on the Alcator C-Mod Tokamak. Microturbulence is likely generated by instabilities of drift waves, which cause transport of heat and particles. Understanding this transport is important because the containment of heat and particles is required for the achievement of practical nuclear fusion. Microtearing modes may cause high heat transport through high electron thermal conductivity. It is hoped that microtearing will be stable along with good electron transport in the proposed low collisionality International Thermonuclear Experimental Reactor (ITER). Stability of the microtearing mode is investigated for conditions at mid-radius in a high density NSTX high performance (H-mode) plasma, which is compared to the proposed ITER plasmas. The microtearing mode is driven by the electron temperature gradient, and believed to be mediated by ion collisions and magnetic shear. Calculations are based on input files produced by TRXPL following TRANSP (a time-dependent transport analysis code) analysis. The variability of unstable mode growth rates is examined as a function of ion and electron collisionalities using the parallel gyrokinetic computational code GS2. Results show the microtearing mode stability dependence for a range of plasma collisionalities. Computation verifies analytic predictions that higher collisionalities than in the NSTX experiment increase microtearing instability growth rates, but that the modes are stabilized at the highest values. There is a transition of the dominant mode in the collisionality scan to ion temperature gradient character at both high and low collisionalities. The calculations suggest that plasma electron thermal confinement may be greatly improved in the low-collisionality ITER.

  1. Linear stability of spherically symmetric and wormhole solutions supported by the sine-Gordon ghost scalar field

    SciTech Connect

    Dzhunushaliev, Vladimir; Folomeev, Vladimir; Singleton, Douglas; Myrzakulov, Ratbay

    2010-08-15

    In this paper we investigate wormhole and spherically symmetric solutions in four-dimensional gravity plus a matter source consisting of a ghost scalar field with a sine-Gordon potential. For the wormhole solutions we also include the possibility of electric and/or magnetic charges. For both types of solutions we perform a linear stability analysis and show that the wormhole solutions are stable and that when one turns on the electric and/or magnetic field the solution remains stable. The linear stability analysis of the spherically symmetric solutions indicates that they can be stable or unstable depending on one of the parameters of the system. This result for the spherically symmetric solution is nontrivial since a previous investigation of four-dimensional gravity plus a ghost scalar field with a {lambda}{phi}{sup 4} interaction found only unstable spherically symmetric solutions. Both the wormhole and spherically symmetric solutions presented here asymptotically go to anti-de Sitter space-time.

  2. Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks

    SciTech Connect

    Wang, Feng; Liu, J. Y.; Fu, G. Y.; Breslau, J. A.

    2013-10-15

    Extensive linear and nonlinear simulations have been carried out to investigate the energetic particle-driven fishbone instability in spherical tokamak plasmas with weakly reversed q profile and the q{sub min} slightly above unity. The global kinetic-MHD hybrid code M3D-K is used. Numerical results show that a fishbone instability is excited by energetic beam ions preferentially at higher q{sub min} values, consistent with the observed appearance of the fishbone before the “long-lived mode” in MAST and NSTX experiments. In contrast, at lower q{sub min} values, the fishbone tends to be stable. In this case, the beam ion effects are strongly stabilizing for the non-resonant kink mode. Nonlinear simulations show that the fishbone saturates with strong downward frequency chirping as well as radial flattening of the beam ion distribution. An (m, n) = (2, 1) magnetic island is found to be driven nonlinearly by the fishbone instability, which could provide a trigger for the (2, 1) neoclassical tearing mode sometimes observed after the fishbone instability in NSTX.

  3. Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Fu, G. Y.; Breslau, J. A.; Liu, J. Y.

    2013-10-01

    Extensive linear and nonlinear simulations have been carried out to investigate the energetic particle-driven fishbone instability in spherical tokamak plasmas with weakly reversed q profile and the qmin slightly above unity. The global kinetic-MHD hybrid code M3D-K is used. Numerical results show that a fishbone instability is excited by energetic beam ions preferentially at higher qmin values, consistent with the observed appearance of the fishbone before the "long-lived mode" in MAST and NSTX experiments. In contrast, at lower qmin values, the fishbone tends to be stable. In this case, the beam ion effects are strongly stabilizing for the non-resonant kink mode. Nonlinear simulations show that the fishbone saturates with strong downward frequency chirping as well as radial flattening of the beam ion distribution. An (m, n) = (2, 1) magnetic island is found to be driven nonlinearly by the fishbone instability, which could provide a trigger for the (2, 1) neoclassical tearing mode sometimes observed after the fishbone instability in NSTX.

  4. Stability of spherically symmetric, charged black holes and multipole moments for stationary systems

    NASA Astrophysics Data System (ADS)

    Gursel, Yekta

    This dissertation is written in two parts. Part I deals with the question of stability of a spherically symmetric, charged black hole against scalar, electromagnetic, and gravitational perturbations. It consists of two papers written in collaboration with Igor D. NoVikov, Vernon D. Sandberg and A. A. Starobinsky. In these papers we describe the dynamical evolution of these perturbations on the interior of a Reissner-Nordstrom black hole. The instability of the hole's Cauchy horizon is discussed in detail in terms of the energy densities of the test fields as measured by a freely falling observer approaching the Cauchy horizon. We conclude that the Cauchy horizon of the analytically extended Reissner-Nordstrom solution is highly unstable and not a physical feature of a realistic gravitational collapse. Part II of this dissertation addresses two problems closely connected with muitipole structure of stationary, asymptotically flat spacetimes. It consists of two papers written in collaboration with Kip S. Thorne despite the fact that his name does not appear on one of them. The first one (Paper III in this thesis) shows the equivalence of the moments defined by Kip S. Thorne and the moments defined by Robert Geroch and Richard Hansen. The second (Paper IV in this thesis) proves a conjecture by Kip S. Thorne: In the limit of "slow" motion, general relativistic gravity produces no changes whatsoever in the classical Euler equations of rigid body motion. We prove this conjecture by giving an algorithm for generating rigidly rotating solutions of Einstein's equations from nonrotating, static solutions.

  5. Flight Performance of a Spin-Stabilized 20-Inch-Diameter Solid-Propellant Spherical Rocket Motor

    NASA Technical Reports Server (NTRS)

    Levine, Jack; Martz, C. William; Swain, Robert L.; Swanson, Andrew G.

    1960-01-01

    A successful flight test of a spin-stabilized 20-inch-diameter solid-propellant rocket motor having a propellant mass fraction of 0.92 has been made. The motor was fired at altitude after being boosted by a three-stage test vehicle. Analysis of the data indicates that a total impulse of 44,243 pound-second with a propellant specific impulse of approximately 185 was achieved over a total action time of about 12 seconds. These results are shown to be in excellent agreement with data from ground static firing tests of these motors. The spherical rocket motor with an 11-pound payload attained a velocity of 15,620 feet per second (m = 16.7) with an incremental velocity increase for the spherical motor stage of 12,120 feet per second.

  6. Thermodynamic stability in elastic systems: Hard spheres embedded in a finite spherical elastic solid.

    PubMed

    Solano-Altamirano, J M; Goldman, Saul

    2015-12-01

    We determined the total system elastic Helmholtz free energy, under the constraints of constant temperature and volume, for systems comprised of one or more perfectly bonded hard spherical inclusions (i.e. "hard spheres") embedded in a finite spherical elastic solid. Dirichlet boundary conditions were applied both at the surface(s) of the hard spheres, and at the outer surface of the elastic solid. The boundary conditions at the surface of the spheres were used to describe the rigid displacements of the spheres, relative to their initial location(s) in the unstressed initial state. These displacements, together with the initial positions, provided the final shape of the strained elastic solid. The boundary conditions at the outer surface of the elastic medium were used to ensure constancy of the system volume. We determined the strain and stress tensors numerically, using a method that combines the Neuber-Papkovich spherical harmonic decomposition, the Schwartz alternating method, and Least-squares for determining the spherical harmonic expansion coefficients. The total system elastic Helmholtz free energy was determined by numerically integrating the elastic Helmholtz free energy density over the volume of the elastic solid, either by a quadrature, or a Monte Carlo method, or both. Depending on the initial position of the hard sphere(s) (or equivalently, the shape of the un-deformed stress-free elastic solid), and the displacements, either stationary or non-stationary Helmholtz free energy minima were found. The non-stationary minima, which involved the hard spheres nearly in contact with one another, corresponded to lower Helmholtz free energies, than did the stationary minima, for which the hard spheres were further away from one another.

  7. The Application of a Cylindrical-spherical Floating Ring Bearing as a Device to Control Stability of Turbogenerators

    NASA Technical Reports Server (NTRS)

    Leung, P. S.; Craighead, I. A.; Wilkinson, T. S.

    1991-01-01

    The development of a new device to control stability of turbogenerators is described. The device comprises a floating ring installed between the journal and bearing housing of a fluid film bearing. The journal and the inner surface of the ring are cylindrical while the outer surface of the ring and bearing surface are spherical providing axial location of the ring and self-alignment of the bearing. The employment of this device would lead to a consistent machine performance. System stability may be controlled by changing a number of bearing and floating ring parameters. This device also offers an additional advantage of having a very low frictional characteristic. A feasibility study was carried out to investigate the suitability of the new device to turbogenerator applications. Both theoretical analysis and experimental observations were carried out. Initial results suggest that the new floating ring device is a competitive alternative to other conventional arrangements.

  8. Hamiltonian structure of the Vlasov-Einstein system and the problem of stability for spherical relativistic star clusters

    SciTech Connect

    Kandrup, H.E. ); Morrison, P.J. )

    1993-07-01

    The Hamiltonian formulation of the Vlasov-Einstein system, which is appropriate for collisionless, self-gravitating systems, is presented. It is demonstrated explicitly in the context of a 3+1 splitting that, for spherically symmetric configurations, the Vlasov-Einstein system can be noncanonical Poisson bracket, with the Hamiltonian generating the evolution of the distribution function f (a noncanonical variable) being the conserved ADM mass-energy H[sub ADM]. This facilitates a geometric understanding of the evolution of f in an infinite-dimensional phase space, providing a natural interpretation of the constraints associated with conservation of phase space. This geometric interpretation also facilitates the derivation of improved criteria for linear stability by focusing on dynamically accessible perturbation [delta]f which satisfy all the constraints of phase space conservation. An explicit expression is derived for the energy [delta][sup (2)]H[sub ADM] associated with an arbitrary spherical phase space preserving perturbation of an arbitrary spherical equilibrium, and it is shown that the equilibrium must be linearly stable if [delta][sup (2)]H[sub ADM] is positive semi-definite. Insight into the Hamiltonian reformulation is provided by a description of general finite degree of freedom systems. Intuition derived from simple finite models clarifies several features of the Vlasov-Einstein system; for example, how, negative energy modes preclude necessary and sufficient conditions for stability and why, unlike the Newtonian case, the existence of negative energy perturbations for some static, isotropic equilibrium apparently signals the onset of a linear instability. An Appendix exhibits the construction of a completely covariant bracket which generates the Vlasov-Einstein system for arbitrary configurations in a form independent of any assumed 3+1 splitting. 87 refs.

  9. Stability of polar frosts in spherical bowl-shaped craters on the moon, Mercury, and Mars

    NASA Technical Reports Server (NTRS)

    Ingersoll, Andrew P.; Svitek, Tomas; Murray, Bruce C.

    1992-01-01

    A model of spherical bowl-shaped craters is described and applied to the moon, Mercury, and Mars. The maximum temperature of permanently shadowed areas are calculated using estimates of the depth/diameter ratios of typical lunar bowl-shaped craters and assuming a saturated surface in which the craters are completely overlapping. For Mars, two cases are considered: water frost in radiative equilibrium and subliming CO2 frost in vapor equilibrium. Energy budgets and temperatures are used to determine whether a craterlike depression loses mass faster or slower than a flat horizontal surface. This reveals qualitatively whether the frost surface becomes rougher or smoother as it sublimes.

  10. Uniformity of spherical shock wave dynamically stabilized by two successive laser profiles in direct-drive inertial confinement fusion implosions

    SciTech Connect

    Temporal, M.; Canaud, B.; Garbett, W. J.; Ramis, R.

    2015-10-15

    The implosion uniformity of a directly driven spherical inertial confinement fusion capsule is considered within the context of the Laser Mégajoule configuration. Two-dimensional (2D) hydrodynamic simulations have been performed assuming irradiation with two laser beam cones located at 49° and 131° with respect to the axis of symmetry. The laser energy deposition causes an inward shock wave whose surface is tracked in time, providing the time evolution of its non-uniformity. The illumination model has been used to optimize the laser intensity profiles used as input in the 2D hydro-calculations. It is found that a single stationary laser profile does not maintain a uniform shock front over time. To overcome this drawback, it is proposed to use two laser profiles acting successively in time, in order to dynamically stabilize the non-uniformity of the shock front.

  11. Stability of thermal boundary layers for convection in spherical shell : Application to the dynamics of Earth mantle.

    NASA Astrophysics Data System (ADS)

    Duchoiselle, L.; Deschamps, F.; Tackley, P. J.

    2009-04-01

    Improving the knowledge of convection into mantle of terrestrial planets required a better understanding of its physical and chemical state. Recently, with the help of massive computational resources, significant progresses were achieved in the numerical modeling of planetary mantles convection. Models with a high degree of complexity (including realistic viscosity laws, mixed mode of heating, spherical geometry, thermo-chemical convection, …) are now available. Among the parameters that recently became accessible, spherical geometry is a key ingredient because it affects the relative strength of the top and bottom thermal boundary layers. Despite these progresses, many details of planetary mantles convection remain unclear and so far, no model of Earth's mantle convection fits all available geophysical, geochemical, and geological constraints. Using STAGYY, which solve the usual conservative equations of mass, energy and momentum, we explored the on a yin-yang grid, we explored the influence of various parameters on convection in spherical geometry. First, we have performed several numerical experiments on varying important parameters including the Rayleigh number, the curvature (ratio between radius of the core and the planet one), the mode of heating (only from below or with an internal heating component), rheology (isoviscous or temperature dependence). In particular, we studied the evolution of the style of convection, average temperature, heat flux and critical Rayleigh number depending on these parameters. We have then built scaling laws between the parameters and observables, for instance between the Nusselt and Rayleigh number, and between the temperature and curvature factor. Our results suggest that extrapolations previously made from Cartesian models may not be valid in spherical geometry. In particular, the dependence of temperature on curvature differs significantly from that expected by Cartesian scaling laws. In addition, it also depends on the

  12. Development of new polysilsesquioxane spherical particles as stabilized active ingredients for sunscreens

    NASA Astrophysics Data System (ADS)

    Tolbert, Stephanie Helene

    Healthy skin is a sign of positive self-worth, attractiveness and vitality. Compromises to this are frequently caused by extended periods of recreation in the sun and in turn exposure to the harmful effects of UV radiation. To maintain strength and integrity, protection of the skin is paramount. This can be achieved by implementing skin-care products which contain sunscreen active ingredients that provide UV protection. Unfortunately, photo-degradation, toxicity, and photo-allergies limit the effectiveness of present day sunscreen ingredients. Currently, this is moderated by physically embedding within inert silica particles, but leaching of the active ingredient can occur, thereby negating protective efforts. Alternatively, this research details the preparation and investigation of bridged silsesquioxane analogues of commercial ingredients which can be chemically grafted to the silica matrix. Studies with bridged salicylate particles detail facile preparation, minimized leaching, and enhanced UV stability over physically encapsulated and pendant salicylate counterparts. In terms of UVB protective ability, the highest maintenance of sun protection factor (SPF) after extended UV exposure was achieved with bridged incorporation, and has been attributed to corollary UV stability. Additionally, bridged salicylate particles can be classified as broad-spectrum, and rate from moderate to good in terms of UVA protective ability. Particles incorporated with a bridged curcuminoid silsesquioxane were also prepared and displayed comparable results. As such, an attractive method for sunscreen isolation and stabilization has been developed to eliminate the problems associated with current sunscreens, all while maintaining the established UV absorbance profiles of the parent compound. To appreciate the technology utilized in this research, a thorough understanding of sol-gel science as it pertains to hybrid organic/silica particles, including methods of organic fragment

  13. Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

    SciTech Connect

    Ruiz Ruiz, J.; White, A. E.; Ren, Y.; Guttenfelder, W.; Kaye, S. M.; Leblanc, B. P.; Mazzucato, E.; Lee, K. C.; Domier, C. W.; Smith, D. R.; Yuh, H.

    2015-12-15

    Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which is shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.

  14. Critical stability of almost adiabatic convection in a rapidly rotating thick spherical shell

    SciTech Connect

    Starchenko, S. V.; Kotelnikova, M. S.

    2013-02-15

    In this work, the convection equations in the almost adiabatic approximation is studied for which the choice of physical parameters is primarily based on possible applications to the hydrodynamics of the deep interiors of the Earth and planets and moons of the terrestrial group. The initial system of partial differential equations (PDEs) was simplified to a single second-order ordinary differential equation for the pressure or vertical velocity component to investigate the linear stability of convection. The critical frequencies, modified Rayleigh numbers, and distributions of convection are obtained at various possible Prandtl numbers and in different thick fluid shells. An analytical WKB-type solution was obtained for the case when the inner radius of the shell is much smaller than the outer radius and convective sources are concentrated along the inner boundary.

  15. Spherical Monovalent Ions at Aqueous Liquid-Vapor Interfaces: Interfacial Stability and Induced Interface Fluctuations

    PubMed Central

    Ou, Shuching; Hu, Yuan; Patel, Sandeep; Wan, Hongbin

    2014-01-01

    Ion-specific interfacial behaviors of monovalent halides impact processes such as protein denaturation, interfacial stability, surface tension modulation, and as such, their molecular and thermodynamic underpinnings garner much attention. We use molecular dynamics simulations of monovalent anions in water to explore effects on distant interfaces. We observe long-ranged ion-induced perturbations of the aqueous environment as suggested by experiment and theory. Surface stable ions, characterized as such by minima in potentials of mean force computed using umbrella sampling MD simulations, induce larger interfacial fluctuations compared to non-surface active species, conferring more entropy approaching the interface. Smaller anions and cations show no interfacial potential of mean force minima. The difference is traced to hydration shell properties of the anions, and the coupling of these shells with distant solvent. The effects correlate with the positions of the anions in the Hofmeister series (acknowledging variations in force field ability to recapitulate essential underlying physics), suggesting how differences in induced, non-local perturbations of interfaces may be related to different specific-ion effects in dilute biophysical and nanomaterial systems. PMID:24032752

  16. Numerical studies on convective stability and flow pattern in three-dimensional spherical mantle of terrestrial planets

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takatoshi; Kameyama, Masanori; Ogawa, Masaki

    2016-09-01

    We explore thermal convection of a fluid with a temperature-dependent viscosity in a basally heated 3-D spherical shell using linear stability analyses and numerical experiments, while considering the application of our results to terrestrial planets. The inner to outer radius ratio of the shell f assumed in the linear stability analyses is in the range of 0.11-0.88. The critical Rayleigh number Rc for the onset of thermal convection decreases by two orders of magnitude as f increases from 0.11 to 0.88, when the viscosity depends sensitively on the temperature, as is the case for real mantle materials. Numerical simulations carried out in the range of f = 0.11-0.55 show that a thermal boundary layer (TBL) develops both along the surface and bottom boundaries to induce cold and hot plumes, respectively, when f is 0.33 or larger. However, for smaller f values, a TBL develops only on the bottom boundary. Convection occurs in the stagnant-lid regime where the root mean square velocity on the surface boundary is less than 1 per cent of its maximum at depth, when the ratio of the viscosity at the surface boundary to that at the bottom boundary exceeds a threshold that depends on f. The threshold decreases from 106.5 at f = 0.11 to 104 at f = 0.55. If the viscosity at the base of the convecting mantle is 1020-1021 Pa s, the Rayleigh number exceeds Rc for Mars, Venus and the Earth, but does not for the Moon and Mercury; convection is unlikely to occur in the latter planets unless the mantle viscosity is much lower than 1020 Pa s and/or the mantle contains a strong internal heat source.

  17. Electrostatic self-energy of a partially formed spherical shell in salt solution: application to stability of tethered and fluid shells as models for viruses and vesicles.

    PubMed

    Božič, Anže Lošdorfer; Šiber, Antonio; Podgornik, Rudolf

    2011-04-01

    We investigate the electrostatics of a partially formed, charged spherical shell in a salt solution. We solve the problem numerically at the Poisson-Boltzmann level and analytically in the Debye-Hückel regime. From the results on energetics of partially formed shells we examine the stability of tethered (crystalline) and fluid shells toward rupture. We delineate different regimes of stability, where, for fluid shells, we also include the effects of bending elasticity of the shells. Our analysis shows how charging of the shell induces its instability toward rupture but also provides insight regarding growth of charged shells.

  18. Hamiltonian structure of the Vlasov-Einstein system and the problem of stability for spherical relativistic star clusters

    SciTech Connect

    Kandrup, H.E. ); Morrison, P.J. . Inst. for Fusion Studies)

    1992-11-01

    The Hamiltonian formulation of the Vlasov-Einstein system, which is appropriate for collisionless, self-gravitating systems like clusters of stars that are so dense that gravity must be described by the Einstein equation, is presented. In particular, it is demonstrated explicitly in the context of a 3 + 1 splitting that, for spherically symmetric configurations, the Vlasov-Einstein system can be viewed as a Hamiltonian system, where the dynamics is generated by a noncanonical Poisson bracket, with the Hamiltonian generating the evolution of the distribution function f (a noncanonical variable) being the conserved ADM mass-energy H[sub ADM]. An explicit expression is derived for the energy [delta]([sup 2])H[sub ADM] associated with an arbitrary phase space preserving perturbation of an arbitrary spherical equilibrium, and it is shown that the equilibrium must be linearly stable if [delta]([sup 2])H[sub ADM] is positive semi-definite. Insight into the Hamiltonian reformulation is provided by a description of general finite degree of freedom systems.

  19. Hamiltonian structure of the Vlasov-Einstein system and the problem of stability for spherical relativistic star clusters

    SciTech Connect

    Kandrup, H.E.; Morrison, P.J.

    1992-11-01

    The Hamiltonian formulation of the Vlasov-Einstein system, which is appropriate for collisionless, self-gravitating systems like clusters of stars that are so dense that gravity must be described by the Einstein equation, is presented. In particular, it is demonstrated explicitly in the context of a 3 + 1 splitting that, for spherically symmetric configurations, the Vlasov-Einstein system can be viewed as a Hamiltonian system, where the dynamics is generated by a noncanonical Poisson bracket, with the Hamiltonian generating the evolution of the distribution function f (a noncanonical variable) being the conserved ADM mass-energy H{sub ADM}. An explicit expression is derived for the energy {delta}({sup 2})H{sub ADM} associated with an arbitrary phase space preserving perturbation of an arbitrary spherical equilibrium, and it is shown that the equilibrium must be linearly stable if {delta}({sup 2})H{sub ADM} is positive semi-definite. Insight into the Hamiltonian reformulation is provided by a description of general finite degree of freedom systems.

  20. Ordered Self-Assembly Mechanism of a Spherical Oncoprotein Oligomer Triggered by Zinc Removal and Stabilized by an Intrinsically Disordered Domain

    PubMed Central

    Smal, Clara; Alonso, Leonardo G.; Wetzler, Diana E.; Heer, Angeles; de Prat Gay, Gonzalo

    2012-01-01

    Background Self-assembly is a common theme in proteins of unrelated sequences or functions. The human papillomavirus E7 oncoprotein is an extended dimer with an intrinsically disordered domain, that can form large spherical oligomers. These are the major species in the cytosol of HPV transformed and cancerous cells. E7 binds to a large number of targets, some of which lead to cell transformation. Thus, the assembly process not only is of biological relevance, but represents a model system to investigate a widely distributed mechanism. Methodology/Principal Findings Using various techniques, we monitored changes in secondary, tertiary and quaternary structure in a time course manner. By applying a robust kinetic model developed by Zlotnik, we determined the slow formation of a monomeric “Z-nucleus” after zinc removal, followed by an elongation phase consisting of sequential second-order events whereby one monomer is added at a time. This elongation process takes place at a strikingly slow overall average rate of one monomer added every 28 seconds at 20 µM protein concentration, strongly suggesting either a rearrangement of the growing complex after binding of each monomer or the existence of a “conformation editing” mechanism through which the monomer binds and releases until the appropriate conformation is adopted. The oligomerization determinant lies within its small 5 kDa C-terminal globular domain and, remarkably, the E7 N-terminal intrinsically disordered domain stabilizes the oligomer, preventing an insoluble amyloid route. Conclusion We described a controlled ordered mechanism with features in common with soluble amyloid precursors, chaperones, and other spherical oligomers, thus sharing determining factors for symmetry, size and shape. In addition, such a controlled and discrete polymerization reaction provides a valuable tool for nanotechnological applications. Finally, its increased immunogenicity related to its supramolecular structure is the

  1. Preparation and properties of plate-like titanate (PLT)/calcia-doped ceria (CDC) composites by sol-gel coating method.

    PubMed

    Liu, Xiangwen; Liu, Jingxiao; Dong, Xiaoli; Yin, Shu; Sato, Tsugio

    2009-08-01

    In order to obtain UV-shielding materials with good comfort, higher safety and effective UV-shielding ability, lepidocrocite type plate-like titanate (K(0.8)Li(0.27)Ti(1.73)O(4), donated as: PLT)/calcia-doped ceria (donated as: CDC) composites were synthesized by a sol-gel method. After dissolving Ce(NO(3))(3).6H(2)O and Ca(NO(3))(2).4H(2)O into absolute ethanol at 40 degrees C, glacial acetic acid (HAc) and PLT particles dispersed into absolute ethanol were added. Then, the solution was heated at 60 degrees C to get gel-like substance. This gel was dried in a vacuum oven at 333 K for 5 h, and then, the product was collected and ground in an agate mortar followed by calcination at 1073 K for 2 h to form PLT/CDC composites. By optimization, 20 mass% of CDC was coated by one operation. PLT/CDC composites with higher CDC content were obtained by repeating the coating process. The morphology, catalytic activity for the oxidation of organic material, UV-shielding ability and dynamic friction coefficient of as-obtained PLT/CDC composites were characterized. As a result, broad-spectrum UV-shielding composite materials with good comfort and low oxidation catalytic activity were successfully synthesized.

  2. Spherical Camera

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Developed largely through a Small Business Innovation Research contract through Langley Research Center, Interactive Picture Corporation's IPIX technology provides spherical photography, a panoramic 360-degrees. NASA found the technology appropriate for use in guiding space robots, in the space shuttle and space station programs, as well as research in cryogenic wind tunnels and for remote docking of spacecraft. Images of any location are captured in their entirety in a 360-degree immersive digital representation. The viewer can navigate to any desired direction within the image. Several car manufacturers already use IPIX to give viewers a look at their latest line-up of automobiles. Another application is for non-invasive surgeries. By using OmniScope, surgeons can look more closely at various parts of an organ with medical viewing instruments now in use. Potential applications of IPIX technology include viewing of homes for sale, hotel accommodations, museum sites, news events, and sports stadiums.

  3. The effect of off-axis neutral beam injection on sawtooth stability in ASDEX Upgrade and Mega-Ampere Spherical Tokamak

    SciTech Connect

    Chapman, I. T.; de Bock, M. F.; Pinches, S. D.; Turnyanskiy, M. R.

    2009-07-15

    Sawtooth behavior has been investigated in plasmas heated with off-axis neutral beam injection in ASDEX Upgrade [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)] and the Mega-Ampere Spherical Tokamak (MAST) [A. Sykes et al., Nucl. Fusion 41, 1423 (2001)]. Provided that the fast ions are well confined, the sawtooth period is found to decrease as the neutral beam is injected further off-axis. Drift kinetic modeling of such discharges qualitatively shows that the passing fast ions born outside the q=1 rational surface can destabilize the n=1 internal kink mode, thought to be related to the sawtooth instability. This effect can be enhanced by optimizing the deposition of the off-axis beam energetic particle population with respect to the mode location.

  4. The effect of off-axis neutral beam injection on sawtooth stability in ASDEX Upgrade and Mega-Ampere Spherical Tokamak

    NASA Astrophysics Data System (ADS)

    Chapman, I. T.; de Bock, M. F.; Pinches, S. D.; Turnyanskiy, M. R.; Mast Team; Igochine, V. G.; Maraschek, M.; Tardini, G.; ASDEX Upgrade Team

    2009-07-01

    Sawtooth behavior has been investigated in plasmas heated with off-axis neutral beam injection in ASDEX Upgrade [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)] and the Mega-Ampere Spherical Tokamak (MAST) [A. Sykes et al., Nucl. Fusion 41, 1423 (2001)]. Provided that the fast ions are well confined, the sawtooth period is found to decrease as the neutral beam is injected further off-axis. Drift kinetic modeling of such discharges qualitatively shows that the passing fast ions born outside the q =1 rational surface can destabilize the n =1 internal kink mode, thought to be related to the sawtooth instability. This effect can be enhanced by optimizing the deposition of the off-axis beam energetic particle population with respect to the mode location.

  5. Equilibrium orientations of non-spherical and chemically anisotropic particles at liquid-liquid interfaces and the effect on emulsion stability.

    PubMed

    Ballard, Nicholas; Bon, Stefan A F

    2015-06-15

    The effective stabilization of emulsions by solid particles, a phenomenon known as Pickering stabilization, is well known to be highly dependent on the wettability and the adhesion energy of the stabilizer employed at the liquid-liquid interface. We present a user-friendly computational model that can be used to determine equilibrium orientations and the adhesion energy of colloidal particles at interfaces. The model determines the free energy profile of particle adsorption at liquid-liquid interfaces using a triangular tessellation scheme. We demonstrate the use of the model, using a variety of anisotropic particles and demonstrate its ability to predict and explain experimental observations of particle behaviour at interfaces. In particular, we show that the concept of hydrophilic lipophilic balance commonly applied to molecular surfactants is insufficient to explain the complexity of the activity of colloidal particles at interfaces. In addition, we show the importance of the knowledge of the free energy adsorption profile of single particles at interfaces and the impact on overall free energy of emulsification of packed ensembles of particles. The delicate balance between optimization of adhesion energy, adsorption dynamics and particle packing is shown to be of great importance in the formation of thermodynamically stable emulsions. In order to use the model, the code is implemented by freely available software that can be readily deployed on personal computers. Copyright © 2015 Elsevier Inc. All rights reserved.

  6. The spherical birdcage resonator

    NASA Astrophysics Data System (ADS)

    Harpen, Michael D.

    A description of the operation of a spherical resonator capable of producing a uniform magnetic induction throughout a spherical volume is presented. Simple closed-form expressions for the spectrum of resonant frequencies are derived for both the low-pass and the high-pass configuration of the resonator and are shown to compare favorably with observation in an experimental coil system. It is shown that the spherical resonator produces a uniform spherical field of view when used as a magnetic resonance imaging radiofrequency coil.

  7. Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles.

    PubMed

    Khalil, Kamal M S; Mahmoud, Hatem A; Ali, Tarek T

    2008-02-05

    Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (Stöber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.

  8. Analysis of the influence of synthetic paramaters on the structure and physico-chemical properties of non-spherical iron oxide nanocrystals and their biological stability and compatibility.

    PubMed

    Pardo, Alberto; Pujales, Rosa; Blanco, Mateo; Villar-Alvarez, Eva M; Barbosa, Silvia; Taboada, Pablo; Mosquera, Víctor

    2016-01-14

    In this work, we analyzed the effects of subtle changes in the synthetic conditions and synthetic parameters on the resulting size, shape, monodispersity, crystallinity and magnetic properties of iron oxide nanocrystals (IONCs) obtained through a modified one pot method for the production of mainly cubic-shaped nanoparticles (NPs). Cubic, octahedral and cuboctahedral shapes with different sizes and monodispersity could be obtained by slightly changing the stabilizer/precursor molar ratio, the precursor concentration, the reaction time and temperature and/or the heating rate. Their physical properties were evaluated using high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), selected-area electron diffraction (SAED) and a superconducting quantum interference (SQUID) device. It was found that monodisperse cubic nanocrystals from ca. 25 to 94 nm could be obtained either by changing the precursor concentration, the heating rate or the reaction time. These cubic nanocrystals were ferrimagnetic in the whole temperature rage analyzed, with saturation magnetization values even larger than those of bulk magnetite. In addition, slightly truncated octahedral NPs could be achieved at relatively large heating ramp rates, whereas cubooctahedral NPs were derived by simply increasing the stabilizer/precursor molar ratio. The saturation magnetization of both types of NPs was slightly lower than the cubic ones, but they were still ferrimagnetic in the whole temperature range analyzed. Moreover, transfer to aqueous solution was possible by a ligand exchange with dimercaptosuccinic acid (DMSA) providing, at the same time, chemical groups for additional functionalization if required. The DMSA-coated cubic IONCs were fairly stable in culture medium, allowing their internalization by different cell types. The NPs inside the cells were located in the cytoplasm and most of them showed a perinuclear distribution. Moreover, a great cytocompatibility in a

  9. Spherical neutron generator

    DOEpatents

    Leung, Ka-Ngo

    2006-11-21

    A spherical neutron generator is formed with a small spherical target and a spherical shell RF-driven plasma ion source surrounding the target. A deuterium (or deuterium and tritium) ion plasma is produced by RF excitation in the plasma ion source using an RF antenna. The plasma generation region is a spherical shell between an outer chamber and an inner extraction electrode. A spherical neutron generating target is at the center of the chamber and is biased negatively with respect to the extraction electrode which contains many holes. Ions passing through the holes in the extraction electrode are focused onto the target which produces neutrons by D-D or D-T reactions.

  10. Chemical Stability and Biological Properties of Plasma-Sprayed CaO-SiO2-ZrO2 Coatings

    NASA Astrophysics Data System (ADS)

    Liang, Ying; Xie, Youtao; Ji, Heng; Huang, Liping; Zheng, Xuebin

    2010-12-01

    In this work, calcia-stabilized zirconia powders were coated by silica derived from tetraethoxysilane (TEOS) hydrolysis. After calcining at 1400 °C, decalcification of calcia-stabilized zirconia by silica occurred and powders composed of Ca2SiO4, ZrO2, and CaZrO3 were prepared. We produced three kinds of powders with different Ca2SiO4 contents [20 wt.% (denoted as CZS2), 40 wt.% (denoted as CZS4), and 60 wt.% (denoted as CZS6)]. The obtained powders were sprayed onto Ti-6Al-4V substrates using atmospheric plasma spraying. The microstructure of the powders and coatings were analyzed. The dissolution rates of the coatings were assessed by monitoring the ions release and mass losses after immersion in Tris-HCl buffer solution. Results showed that the chemical stability of the coatings were significantly improved compared with pure calcium silicate coatings, and increased with the increase of Zr contents. The CZS4 coating showed not only good apatite-formation ability in simulated body fluid, but also well attachment and proliferation capability for the canine bone marrow stem cells. Results presented here indicate that plasma-sprayed CZS4 coating has medium dissolution rate and good biological properties, suggesting its potential use as bone implants.

  11. Wide scanning spherical antenna

    NASA Technical Reports Server (NTRS)

    Shen, Bing (Inventor); Stutzman, Warren L. (Inventor)

    1995-01-01

    A novel method for calculating the surface shapes for subreflectors in a suboptic assembly of a tri-reflector spherical antenna system is introduced, modeled from a generalization of Galindo-Israel's method of solving partial differential equations to correct for spherical aberration and provide uniform feed to aperture mapping. In a first embodiment, the suboptic assembly moves as a single unit to achieve scan while the main reflector remains stationary. A feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan thereby eliminating the need to oversize the main spherical reflector. In an alternate embodiment, both the main spherical reflector and the suboptic assembly are fixed. A flat mirror is used to create a virtual image of the suboptic assembly. Scan is achieved by rotating the mirror about the spherical center of the main reflector. The feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan.

  12. Large displacement spherical joint

    DOEpatents

    Bieg, Lothar F.; Benavides, Gilbert L.

    2002-01-01

    A new class of spherical joints has a very large accessible full cone angle, a property which is beneficial for a wide range of applications. Despite the large cone angles, these joints move freely without singularities.

  13. The Precessing Spherical Pendulum.

    ERIC Educational Resources Information Center

    Olsson, M. G.

    1978-01-01

    Explains how the spherical pendulum could be used to observe nonreentrant orbits, and shows, using theoretical analysis, that for small displacements the elliptical orbit will precess at a rate proportional to its area. (GA)

  14. Overview of spherical tokamak research in Japan

    NASA Astrophysics Data System (ADS)

    Takase, Y.; Ejiri, A.; Fujita, T.; Fukumoto, N.; Fukuyama, A.; Hanada, K.; Idei, H.; Nagata, M.; Ono, Y.; Tanaka, H.; Uchida, M.; Horiuchi, R.; Kamada, Y.; Kasahara, H.; Masuzaki, S.; Nagayama, Y.; Oishi, T.; Saito, K.; Takeiri, Y.; Tsuji-Iio, S.

    2017-10-01

    Nationally coordinated research on spherical tokamak is being conducted in Japan. Recent achievements include: (i) plasma current start-up and ramp-up without the use of the central solenoid by RF waves (in electron cyclotron and lower hybrid frequency ranges), (ii) plasma current start-up by AC Ohmic operation and by coaxial helicity injection, (iii) development of an advanced fuelling technique by compact toroid injection, (iv) ultra-long-pulse operation and particle control using a high temperature metal wall, (v) access to the ultra-high-β regime by high-power reconnection heating, and (vi) improvement of spherical tokamak plasma stability by externally applied helical field.

  15. Spherically Actuated Motor

    NASA Technical Reports Server (NTRS)

    Peeples, Steven

    2015-01-01

    A three degree of freedom (DOF) spherical actuator is proposed that will replace functions requiring three single DOF actuators in robotic manipulators providing space and weight savings while reducing the overall failure rate. Exploration satellites, Space Station payload manipulators, and rovers requiring pan, tilt, and rotate movements need an actuator for each function. Not only does each actuator introduce additional failure modes and require bulky mechanical gimbals, each contains many moving parts, decreasing mean time to failure. A conventional robotic manipulator is shown in figure 1. Spherical motors perform all three actuation functions, i.e., three DOF, with only one moving part. Given a standard three actuator system whose actuators have a given failure rate compared to a spherical motor with an equal failure rate, the three actuator system is three times as likely to fail over the latter. The Jet Propulsion Laboratory reliability studies of NASA robotic spacecraft have shown that mechanical hardware/mechanism failures are more frequent and more likely to significantly affect mission success than are electronic failures. Unfortunately, previously designed spherical motors have been unable to provide the performance needed by space missions. This inadequacy is also why they are unavailable commercially. An improved patentable spherically actuated motor (SAM) is proposed to provide the performance and versatility required by NASA missions.

  16. Spherical geodesic mesh generation

    SciTech Connect

    Fung, Jimmy; Kenamond, Mark Andrew; Burton, Donald E.; Shashkov, Mikhail Jurievich

    2015-02-27

    In ALE simulations with moving meshes, mesh topology has a direct influence on feature representation and code robustness. In three-dimensional simulations, modeling spherical volumes and features is particularly challenging for a hydrodynamics code. Calculations on traditional spherical meshes (such as spin meshes) often lead to errors and symmetry breaking. Although the underlying differencing scheme may be modified to rectify this, the differencing scheme may not be accessible. This work documents the use of spherical geodesic meshes to mitigate solution-mesh coupling. These meshes are generated notionally by connecting geodesic surface meshes to produce triangular-prismatic volume meshes. This mesh topology is fundamentally different from traditional mesh topologies and displays superior qualities such as topological symmetry. This work describes the geodesic mesh topology as well as motivating demonstrations with the FLAG hydrocode.

  17. Faraday instability of a spherical drop

    NASA Astrophysics Data System (ADS)

    Ebo Adou, A.; Tuckerman, Laurette; Shin, Seungwon; Chergui, Jalel; Juric, Damir

    2014-11-01

    A liquid drop subjected to an oscillatory radial force comprises a spherical version of the Faraday instability, with a subharmonic response which is half of the forcing frequency. The time-dependent shape of the drop and the velocity field in and around it are calculated using BLUE, a code based on a hybrid Front Tracking/Level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. We compare this shape with the spherical harmonic selected at onset, calculated by adapting the Floquet stability analysis of Kumar and Tuckerman to a spherical geometry. We interpret the shape in light of theoretical results by Busse, Matthews and others concerning pattern formation in the presence of O(3) symmetry.

  18. Spherical mirror mount

    NASA Technical Reports Server (NTRS)

    Meyer, Jay L. (Inventor); Messick, Glenn C. (Inventor); Nardell, Carl A. (Inventor); Hendlin, Martin J. (Inventor)

    2011-01-01

    A spherical mounting assembly for mounting an optical element allows for rotational motion of an optical surface of the optical element only. In that regard, an optical surface of the optical element does not translate in any of the three perpendicular translational axes. More importantly, the assembly provides adjustment that may be independently controlled for each of the three mutually perpendicular rotational axes.

  19. Recent Progress on Spherical Torus Research

    SciTech Connect

    Ono, Masayuki; Kaita, Robert

    2014-01-01

    The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ~ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ~ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of attractive fusion energy power source. Since the start of the two megaampere class ST facilities in 2000, National Spherical Torus Experiment (NSTX) in the US and Mega Ampere Spherical Tokamak (MAST) in UK, active ST research has been conducted worldwide. More than sixteen ST research facilities operating during this period have achieved remarkable advances in all of fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

  20. Statistical Mechanics of Thin Spherical Shells

    NASA Astrophysics Data System (ADS)

    Košmrlj, Andrej; Nelson, David R.

    2017-01-01

    We explore how thermal fluctuations affect the mechanics of thin amorphous spherical shells. In flat membranes with a shear modulus, thermal fluctuations increase the bending rigidity and reduce the in-plane elastic moduli in a scale-dependent fashion. This is still true for spherical shells. However, the additional coupling between the shell curvature, the local in-plane stretching modes, and the local out-of-plane undulations leads to novel phenomena. In spherical shells, thermal fluctuations produce a radius-dependent negative effective surface tension, equivalent to applying an inward external pressure. By adapting renormalization group calculations to allow for a spherical background curvature, we show that while small spherical shells are stable, sufficiently large shells are crushed by this thermally generated "pressure." Such shells can be stabilized by an outward osmotic pressure, but the effective shell size grows nonlinearly with increasing outward pressure, with the same universal power-law exponent that characterizes the response of fluctuating flat membranes to a uniform tension.

  1. Spherical colloidal photonic crystals.

    PubMed

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  2. Spherical coordinate descriptions of cylindrical and spherical Bessel beams.

    PubMed

    Poletti, M A

    2017-03-01

    This paper derives a generalized spherical harmonic description of Bessel beams. The spherical harmonic description of the well-known cylindrical Bessel beams is reviewed and a family of spherical Bessel beams are introduced which can provide a number of azimuthal phase variations for a single beam radial amplitude. The results are verified by numerical simulations.

  3. Spherical torus fusion reactor

    DOEpatents

    Peng, Yueng-Kay M.

    1989-01-01

    A fusion reactor is provided having a near spherical-shaped plasma with a modest central opening through which straight segments of toroidal field coils extend that carry electrical current for generating a toroidal magnet plasma confinement fields. By retaining only the indispensable components inboard of the plasma torus, principally the cooled toroidal field conductors and in some cases a vacuum containment vessel wall, the fusion reactor features an exceptionally small aspect ratio (typically about 1.5), a naturally elongated plasma cross section without extensive field shaping, requires low strength magnetic containment fields, small size and high beta. These features combine to produce a spherical torus plasma in a unique physics regime which permits compact fusion at low field and modest cost.

  4. Spherical torus fusion reactor

    DOEpatents

    Peng, Yueng-Kay M.

    1989-04-04

    A fusion reactor is provided having a near spherical-shaped plasma with a modest central opening through which straight segments of toroidal field coils extend that carry electrical current for generating a toroidal magnet plasma confinement fields. By retaining only the indispensable components inboard of the plasma torus, principally the cooled toroidal field conductors and in some cases a vacuum containment vessel wall, the fusion reactor features an exceptionally small aspect ratio (typically about 1.5), a naturally elongated plasma cross section without extensive field shaping, requires low strength magnetic containment fields, small size and high beta. These features combine to produce a spherical torus plasma in a unique physics regime which permits compact fusion at low field and modest cost.

  5. Sensational spherical shells

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Kendall, J. M., Jr.; Bahrami, P. A.; Wang, T. G.

    1986-01-01

    Fluid-dynamic and capillary forces can be used to form nearly perfect, very small spherical shells when a liquid that can solidify is passed through an annular die to form an annular jet. Gravity and certain properties of even the most ideal materials, however, can cause slight asymmetries. The primary objective of the present work is the control of this shell formation process in earth laboratories rather than space microgravity, through the development of facilities and methods that minimize the deleterious effects of gravity, aerodynamic drag, and uncontrolled cooling. The spherical shells thus produced can be used in insulation, recyclable filter materials, fire retardants, explosives, heat transport slurries, shock-absorbing armor, and solid rocket motors.

  6. Noncommuting spherical coordinates

    SciTech Connect

    Bander, Myron

    2004-10-15

    Restricting the states of a charged particle to the lowest Landau level introduces a noncommutativity between Cartesian coordinate operators. This idea is extended to the motion of a charged particle on a sphere in the presence of a magnetic monopole. Restricting the dynamics to the lowest energy level results in noncommutativity for angular variables and to a definition of a noncommuting spherical product. The values of the commutators of various angular variables are not arbitrary but are restricted by the discrete magnitude of the magnetic monopole charge. An algebra, isomorphic to angular momentum, appears. This algebra is used to define a spherical star product. Solutions are obtained for dynamics in the presence of additional angular dependent potentials.

  7. Hollow spherical shell manufacture

    DOEpatents

    O'Holleran, Thomas P.

    1991-01-01

    A process for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry.

  8. Sensational spherical shells

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Kendall, J. M., Jr.; Bahrami, P. A.; Wang, T. G.

    1986-01-01

    Fluid-dynamic and capillary forces can be used to form nearly perfect, very small spherical shells when a liquid that can solidify is passed through an annular die to form an annular jet. Gravity and certain properties of even the most ideal materials, however, can cause slight asymmetries. The primary objective of the present work is the control of this shell formation process in earth laboratories rather than space microgravity, through the development of facilities and methods that minimize the deleterious effects of gravity, aerodynamic drag, and uncontrolled cooling. The spherical shells thus produced can be used in insulation, recyclable filter materials, fire retardants, explosives, heat transport slurries, shock-absorbing armor, and solid rocket motors.

  9. Hollow spherical shell manufacture

    DOEpatents

    O'Holleran, T.P.

    1991-11-26

    A process is disclosed for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry. 3 figures.

  10. Spherical nitroguanidine process

    DOEpatents

    Sanchez, John A.; Roemer, Edward L.; Stretz, Lawrence A.

    1990-01-01

    A process of preparing spherical high bulk density nitroguanidine by dissing low bulk density nitroguanidine in N-methyl pyrrolidone at elevated temperatures and then cooling the solution to lower temperatures as a liquid characterized as a nonsolvent for the nitroguanidine is provided. The process is enhanced by inclusion in the solution of from about 1 ppm up to about 250 ppm of a metal salt such as nickel nitrate, zinc nitrate or chromium nitrate, preferably from about 20 to about 50 ppm.

  11. Formation and characterization of high surface area thermally stabilized titania/silica composite materials via hydrolysis of titanium(IV) tetra-isopropoxide in sols of spherical silica particles.

    PubMed

    Khalil, Kamal M S; Elsamahy, Ahmed A; Elanany, Mohamed S

    2002-05-15

    A direct synthetic route leading to titania particles dispersed on nonporous spherical silica particles has been investigated; 5, 10, and 20% (w/w) titania/silica sols mixtures were achieved via hydrolyzation of titanium tetra-isopropxide solution in the mother liquor of a freshly prepared sol of spherical silica particles (Stöber particles). Titania/silica materials were produced by subsequent drying and calcination of the xerogels so obtained for 3 h at 400 and 600 degrees C. The materials were investigated by means of thermal analyses (TGA and DSC), FT-IR, N(2) gas adsorption-desorption, powder X-ray diffraction (XRD), and transmission electron microscopy (TEM). In spite of the low surface area (13.1 m(2)/g) of the pure spherical silica particles calcined at 400 degrees C, high surface area and mesoporous texture titania/silica materials were obtained (e.g., S(BET) ca. 293 m(2)/g for the 10% titania/silica calcined at 400 degrees C). Moreover, the materials were shown to be amorphous toward XRD up to 600 degrees C, while reasonable surface areas were preserved. It has been concluded that dispersion of titania particles onto the surface of the nonporous spherical silica particles increase their roughness, therefore leading to composite materials of less firm packing and mesoporosity.

  12. Holographic Spherically Symmetric Metrics

    NASA Astrophysics Data System (ADS)

    Petri, Michael

    The holographic principle (HP) conjectures, that the maximum number of degrees of freedom of any realistic physical system is proportional to the system's boundary area. The HP has its roots in the study of black holes. It has recently been applied to cosmological solutions. In this article we apply the HP to spherically symmetric static space-times. We find that any regular spherically symmetric object saturating the HP is subject to tight constraints on the (interior) metric, energy-density, temperature and entropy-density. Whenever gravity can be described by a metric theory, gravity is macroscopically scale invariant and the laws of thermodynamics hold locally and globally, the (interior) metric of a regular holographic object is uniquely determined up to a constant factor and the interior matter-state must follow well defined scaling relations. When the metric theory of gravity is general relativity, the interior matter has an overall string equation of state (EOS) and a unique total energy-density. Thus the holographic metric derived in this article can serve as simple interior 4D realization of Mathur's string fuzzball proposal. Some properties of the holographic metric and its possible experimental verification are discussed. The geodesics of the holographic metric describe an isotropically expanding (or contracting) universe with a nearly homogeneous matter-distribution within the local Hubble volume. Due to the overall string EOS the active gravitational mass-density is zero, resulting in a coasting expansion with Ht = 1, which is compatible with the recent GRB-data.

  13. Recent progress on spherical torus research

    NASA Astrophysics Data System (ADS)

    Ono, Masayuki; Kaita, Robert

    2015-04-01

    The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ˜ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ˜ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

  14. Recent progress on spherical torus research

    SciTech Connect

    Ono, Masayuki; Kaita, Robert

    2015-04-15

    The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R{sub 0}/a) reduced to A ∼ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ∼ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

  15. Ribozyme-Spherical Nucleic Acids

    PubMed Central

    Hao, Liangliang; Kouri, Fotini M.; Briley, William E.; Stegh, Alexander H.; Mirkin, Chad A.

    2015-01-01

    Ribozymes are highly structured RNA sequences that can be tailored to recognize and cleave specific stretches of mRNA. Their current therapeutic efficacy remains low due to their large size and structural instability compared to shorter therapeutically relevant RNA such as small interfering RNA (siRNA) and microRNA (miRNA). Herein, a synthetic strategy that makes use of the spherical nucleic acid (SNA) architecture to stabilize ribozymes and transfect them into live cells is reported. The properties of this novel ribozyme SNA are characterized in the context of the targeted knockdown of O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair protein involved in chemotherapeutic resistance of solid tumors, foremost glioblastoma multiforme (GBM). Data showing the direct cleavage of full-length MGMT mRNA, knockdown of MGMT protein, and increased sensitization of GBM cells to therapy-mediated apoptosis, independent of transfection agents, provide compelling evidence for the promising properties of this new chemical architecture. PMID:26271335

  16. Spherical artifacts on ferrograms

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1976-01-01

    In the past, hollow spheres detected on ferrograms have been interpreted as being due to fretting, abrasion, cavitation erosion, and fatigue-related processes. Here it is reported that such spheres were found to result from the fact that a routine grinding operation on a steel plate was carried out about 20 feet away from the ferrograph. A similar grinding operation was performed on a piece of low carbon steel a few feet from the ferrograph, and after a few minutes of grinding, the resulting ferrogram contained thousands of particles of which more than 90% were spherical. Because of the widespread occurrence of ordinary grinding operations, it seems prudent that those utilizing the ferrograph be cognizant of this type of artifact.

  17. Spherical grating spectrometers

    NASA Astrophysics Data System (ADS)

    O'Donoghue, Darragh; Clemens, J. Christopher

    2014-07-01

    We describe designs for spectrometers employing convex dispersers. The Offner spectrometer was the first such instrument; it has almost exclusively been employed on satellite platforms, and has had little impact on ground-based instruments. We have learned how to fabricate curved Volume Phase Holographic (VPH) gratings and, in contrast to the planar gratings of traditional spectrometers, describe how such devices can be used in optical/infrared spectrometers designed specifically for curved diffraction gratings. Volume Phase Holographic gratings are highly efficient compared to conventional surface relief gratings; they have become the disperser of choice in optical / NIR spectrometers. The advantage of spectrometers with curved VPH dispersers is the very small number of optical elements used (the simplest comprising a grating and a spherical mirror), as well as illumination of mirrors off axis, resulting in greater efficiency and reduction in size. We describe a "Half Offner" spectrometer, an even simpler version of the Offner spectrometer. We present an entirely novel design, the Spherical Transmission Grating Spectrometer (STGS), and discuss exemplary applications, including a design for a double-beam spectrometer without any requirement for a dichroic. This paradigm change in spectrometer design offers an alternative to all-refractive astronomical spectrometer designs, using expensive, fragile lens elements fabricated from CaF2 or even more exotic materials. The unobscured mirror layout avoids a major drawback of the previous generation of catadioptric spectrometer designs. We describe laboratory measurements of the efficiency and image quality of a curved VPH grating in a STGS design, demonstrating, simultaneously, efficiency comparable to planar VPH gratings along with good image quality. The stage is now set for construction of a prototype instrument with impressive performance.

  18. Crystallization of calcia-gallia-silica glasses

    NASA Technical Reports Server (NTRS)

    Ray, C. S.; Day, D. E.

    1984-01-01

    A thermal image furance is presently used to study the critical cooling rate for glass formation, and the kinetics of crystallization, of the compositions 18.4CaO-(81.6-X)Ga2O3-XSiO2, where X = 3, 6, 9, and 13.8. Crystallization was studied nonisothermally, and the data were analyzed in light of the Avrami (1939) equation. Critical cooling rate and crystallization activation energy are both found to decrease with increasing silica content, and the results obtained by the present technique are noted to agree with those obtained on the basis of differential thermal analysis measurements.

  19. Double slotted socket spherical joint

    DOEpatents

    Bieg, Lothar F.; Benavides, Gilbert L.

    2001-05-22

    A new class of spherical joints is disclosed. These spherical joints are capable of extremely large angular displacements (full cone angles in excess of 270.degree.), while exhibiting no singularities or dead spots in their range of motion. These joints can improve or simplify a wide range of mechanical devices.

  20. Features of spherical torus plasmas

    SciTech Connect

    Peng, Y.K.M.; Strickler, D.J.

    1985-12-01

    The spherical torus is a very small aspect ratio (A < 2) confinement concept obtained by retaining only the indispensable components inboard to the plasma torus. MHD equilibrium calculations show that spherical torus plasmas with safety factor q > 2 are characterized by high toroidal beta (..beta../sub t/ > 0.2), low poloidal beta (..beta../sub p/ < 0.3), naturally large elongation (kappa greater than or equal to 2), large plasma current with I/sub p//(aB/sub t0/) up to about 7 MA/mT, strong paramagnetism (B/sub t//B/sub t0/ > 1.5), and strong plasma helicity (F comparable to THETA). A large near-omnigeneous region is seen at the large-major-radius, bad-curvature region of the plasma in comparison with the conventional tokamaks. These features combine to engender the spherical torus plasma in a unique physics regime which permits compact fusion at low field and modest cost. Because of its strong paramagnetism and helicity, the spherical torus plasma shares some of the desirable features of spheromak and reversed-field pinch (RFP) plasmas, but with tokamak-like confinement and safety factor q. The general class of spherical tori, which includes the spherical tokamak (q > 1), the spherical pinch (1 > q > O), and the spherical RFP (q < O), have magnetic field configurations unique in comparison with conventional tokamaks and RFPs. 22 refs., 12 figs.

  1. SPHERICAL SHOCK WAVES IN SOLIDS

    DTIC Science & Technology

    Contents: Introduction-Reasons for Studying Spherical Shock Waves, Physics of Cavity Expansion due to Explosive Impact, General Nature of Shock Waves...Governing Differential Equation of Self-Similar Motion; Application of the Theory of Self-Similar Motion to the Problem of Expansion of a Spherical

  2. Optimal mollifiers for spherical deconvolution

    NASA Astrophysics Data System (ADS)

    Hielscher, Ralf; Quellmalz, Michael

    2015-08-01

    This paper deals with the inversion of the spherical Funk-Radon transform, and, more generally, with the inversion of spherical convolution operators from the point of view of statistical inverse problems. This means we consider discrete data perturbed by white noise and aim at estimators with optimal mean square error for functions out of a Sobolev ball. To this end we analyze a specific class of estimators built upon the spherical hyperinterpolation operator, spherical designs and the mollifier approach. Eventually, we determine optimal mollifier functions with respect to the noise level, the number of data points and the smoothness of the original function. We complete this paper by providing a fast algorithm for the numerical computation of the estimator, which is based on the fast spherical Fourier transform, and by illustrating our theoretical results with numerical experiments.

  3. A spherical gas bearing for airborne application

    NASA Technical Reports Server (NTRS)

    Bouvier, A.; Schmertz, J. C.

    1974-01-01

    A spherical gas bearing is analyzed and tested for an airborne application. The externally pressurized bearing supports an inertially stabilized 36-in aperture, infrared telescope. The bearing provides the isolation of rotary motion from the aircraft and also serves as a seal between the aircraft cabin and cavity condition at 50,000 ft altitude. The accompanying temperature gradient of 135 F across the 16-in.-diam bearing created special design and manufacturing considerations. Test data on the static load under temperature and vacuum environment are presented in support of the analysis.

  4. Consider a spherical cow

    SciTech Connect

    Harte, J.

    1985-01-01

    Consider a Spherical Cow describes relatively simple mathematical methods for developing quantitative answers to often complex environmental problems. Early chapters provide systematic insights into problem solving and identifying mathematical tools and models that lead to back of the envelope answers. Subsequent chapters treat increasingly complex problems. Solutions are sought at different levels, e.g., informed guesses, quantitative solutions based on detailed analytical models, and ultimately, critical evaluation of the consequences of removing simplifying assumptions from the models. The vehicle employed is a collection of 44 challenging problems, with clearly worked out solutions, plus ample exercises. The book, though directed at environmentalists, should appeal to chemists. Many of the problems are rooted in chemistry, including acid rain, the CO/sub 2/ greenhouse effect, chemical contamination, and the disturbing of cyclical chemical balances. Readers feeling a civic responsibility to think and speak more clearly on environmental issues will find the essential modeling and quantitative approaches valuable assets beyond the help provided by the usual courses in science and mathematics. In fact, the techniques of problem solving have broad applicability beyond the specific environmental examples covered in this text.

  5. Immunomodulatory spherical nucleic acids.

    PubMed

    Radovic-Moreno, Aleksandar F; Chernyak, Natalia; Mader, Christopher C; Nallagatla, Subbarao; Kang, Richard S; Hao, Liangliang; Walker, David A; Halo, Tiffany L; Merkel, Timothy J; Rische, Clayton H; Anantatmula, Sagar; Burkhart, Merideth; Mirkin, Chad A; Gryaznov, Sergei M

    2015-03-31

    Immunomodulatory nucleic acids have extraordinary promise for treating disease, yet clinical progress has been limited by a lack of tools to safely increase activity in patients. Immunomodulatory nucleic acids act by agonizing or antagonizing endosomal toll-like receptors (TLR3, TLR7/8, and TLR9), proteins involved in innate immune signaling. Immunomodulatory spherical nucleic acids (SNAs) that stimulate (immunostimulatory, IS-SNA) or regulate (immunoregulatory, IR-SNA) immunity by engaging TLRs have been designed, synthesized, and characterized. Compared with free oligonucleotides, IS-SNAs exhibit up to 80-fold increases in potency, 700-fold higher antibody titers, 400-fold higher cellular responses to a model antigen, and improved treatment of mice with lymphomas. IR-SNAs exhibit up to eightfold increases in potency and 30% greater reduction in fibrosis score in mice with nonalcoholic steatohepatitis (NASH). Given the clinical potential of SNAs due to their potency, defined chemical nature, and good tolerability, SNAs are attractive new modalities for developing immunotherapies.

  6. Immunomodulatory spherical nucleic acids

    PubMed Central

    Radovic-Moreno, Aleksandar F.; Chernyak, Natalia; Mader, Christopher C.; Nallagatla, Subbarao; Kang, Richard S.; Hao, Liangliang; Walker, David A.; Halo, Tiffany L.; Merkel, Timothy J.; Rische, Clayton H.; Anantatmula, Sagar; Burkhart, Merideth; Mirkin, Chad A.; Gryaznov, Sergei M.

    2015-01-01

    Immunomodulatory nucleic acids have extraordinary promise for treating disease, yet clinical progress has been limited by a lack of tools to safely increase activity in patients. Immunomodulatory nucleic acids act by agonizing or antagonizing endosomal toll-like receptors (TLR3, TLR7/8, and TLR9), proteins involved in innate immune signaling. Immunomodulatory spherical nucleic acids (SNAs) that stimulate (immunostimulatory, IS-SNA) or regulate (immunoregulatory, IR-SNA) immunity by engaging TLRs have been designed, synthesized, and characterized. Compared with free oligonucleotides, IS-SNAs exhibit up to 80-fold increases in potency, 700-fold higher antibody titers, 400-fold higher cellular responses to a model antigen, and improved treatment of mice with lymphomas. IR-SNAs exhibit up to eightfold increases in potency and 30% greater reduction in fibrosis score in mice with nonalcoholic steatohepatitis (NASH). Given the clinical potential of SNAs due to their potency, defined chemical nature, and good tolerability, SNAs are attractive new modalities for developing immunotherapies. PMID:25775582

  7. A spherical electrostatic orrery

    NASA Astrophysics Data System (ADS)

    Smetana, Carole; Alexander, David; Robertson, Scott; Vilkaitis, Kim; Walch, Bob

    1996-11-01

    An electrostatic orrery for studying Keplerian orbits has been constructed in which one or more negatively charged hollow glass microparticles orbit a 9.5-mm-diam metal sphere at +8-kV potential in a vacuum. The device is similar to an earlier cylindrical orrery in which particles orbit a rod [Biewer et al., Am. J. Phys. 62(9), 821-827 (1994)]. Electrically biased cylinders covering the rod supporting the sphere give nearly spherical potential surfaces inside the trap. Additional electrodes at the boundary are used to reduce the perturbation of gravity and to prevent motion resulting in collisions with the supporting rod. Orbits last approximately 10 min or about 104 revolutions. The orbiters are illuminated with a slide projector and can be seen with the naked eye as well as videotaped. The trap has been used to observe orbital precession, interparticle collisions, and the effects of time-independent perturbations. This apparatus provides an opportunity for the study and demonstration of orbital motion in a laboratory.

  8. Spherical 3D isotropic wavelets

    NASA Astrophysics Data System (ADS)

    Lanusse, F.; Rassat, A.; Starck, J.-L.

    2012-04-01

    Context. Future cosmological surveys will provide 3D large scale structure maps with large sky coverage, for which a 3D spherical Fourier-Bessel (SFB) analysis in spherical coordinates is natural. Wavelets are particularly well-suited to the analysis and denoising of cosmological data, but a spherical 3D isotropic wavelet transform does not currently exist to analyse spherical 3D data. Aims: The aim of this paper is to present a new formalism for a spherical 3D isotropic wavelet, i.e. one based on the SFB decomposition of a 3D field and accompany the formalism with a public code to perform wavelet transforms. Methods: We describe a new 3D isotropic spherical wavelet decomposition based on the undecimated wavelet transform (UWT) described in Starck et al. (2006). We also present a new fast discrete spherical Fourier-Bessel transform (DSFBT) based on both a discrete Bessel transform and the HEALPIX angular pixelisation scheme. We test the 3D wavelet transform and as a toy-application, apply a denoising algorithm in wavelet space to the Virgo large box cosmological simulations and find we can successfully remove noise without much loss to the large scale structure. Results: We have described a new spherical 3D isotropic wavelet transform, ideally suited to analyse and denoise future 3D spherical cosmological surveys, which uses a novel DSFBT. We illustrate its potential use for denoising using a toy model. All the algorithms presented in this paper are available for download as a public code called MRS3D at http://jstarck.free.fr/mrs3d.html

  9. Convective flows of viscous fluid in spherical layers. Certain astrophysical applications

    NASA Technical Reports Server (NTRS)

    Yavorskaya, I. M.

    1980-01-01

    The convective stability of a viscous liquid in spherical layers is investigated taking into consideration rotation, the latitudinal temperature gradient, and shear flow. The results of calculating nonlinear convective motion in spherical layers are examined. A discussion is given of the applicability of the results obtained to studying convection in astrophysical objects.

  10. Unsteady Spherical Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind; Berhan, S.; Chernovsky, M.; Sacksteder, Kurt R.

    2001-01-01

    The absence of buoyancy-induced flows in microgravity (mu-g) and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between normal gravity (ng) and (mu-g) flames have been reported in experiments on candle flames, flame spread over solids, droplet combustion, and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment that changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation, that are often ignored in ng, become very important and sometimes even controlling. Furthermore, microgravity conditions considerably enhance flame radiation by: (i) the build-up of combustion products in the high-temperature reaction zone which increases the gas radiation, and (ii) longer residence times make conditions appropriate for substantial amounts of soot to form which is also responsible for radiative heat loss. Thus, it is anticipated that radiative heat loss may eventually extinguish the "weak" (low burning rate per unit flame area) mu-g diffusion flame. Yet, space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in mu-g will burn indefinitely. This may be because of the coupling between the fuel production rate and the flame via the heat-feedback mechanism for candle flames, flames over solids and fuel droplet flames. Thus, to focus only on the gas-phase phenomena leading to radiative extinction, aerodynamically stabilized gaseous diffusion flames are examined. This enables independent control of the fuel flow rate to help identify conditions under which radiative extinction occurs. Also, spherical geometry is chosen for the mu-g experiments and modeling because: (i) It reduces the complexity by making the problem one

  11. Milking the spherical cow - on aspherical dynamics in spherical coordinates

    NASA Astrophysics Data System (ADS)

    Pontzen, Andrew; Read, Justin I.; Teyssier, Romain; Governato, Fabio; Gualandris, Alessia; Roth, Nina; Devriendt, Julien

    2015-08-01

    Galaxies and the dark matter haloes that host them are not spherically symmetric, yet spherical symmetry is a helpful simplifying approximation for idealized calculations and analysis of observational data. The assumption leads to an exact conservation of angular momentum for every particle, making the dynamics unrealistic. But how much does that inaccuracy matter in practice for analyses of stellar distribution functions, collisionless relaxation, or dark matter core-creation? We provide a general answer to this question for a wide class of aspherical systems; specifically, we consider distribution functions that are `maximally stable', i.e. that do not evolve at first order when external potentials (which arise from baryons, large-scale tidal fields or infalling substructure) are applied. We show that a spherically symmetric analysis of such systems gives rise to the false conclusion that the density of particles in phase space is ergodic (a function of energy alone). Using this idea we are able to demonstrate that: (a) observational analyses that falsely assume spherical symmetry are made more accurate by imposing a strong prior preference for near-isotropic velocity dispersions in the centre of spheroids; (b) numerical simulations that use an idealized spherically symmetric setup can yield misleading results and should be avoided where possible; and (c) triaxial dark matter haloes (formed in collisionless cosmological simulations) nearly attain our maximally stable limit, but their evolution freezes out before reaching it.

  12. RAPID OPTIMAL SPH PARTICLE DISTRIBUTIONS IN SPHERICAL GEOMETRIES FOR CREATING ASTROPHYSICAL INITIAL CONDITIONS

    SciTech Connect

    Raskin, Cody; Owen, J. Michael

    2016-04-01

    Creating spherical initial conditions in smoothed particle hydrodynamics simulations that are spherically conformal is a difficult task. Here, we describe two algorithmic methods for evenly distributing points on surfaces that when paired can be used to build three-dimensional spherical objects with optimal equipartition of volume between particles, commensurate with an arbitrary radial density function. We demonstrate the efficacy of our method against stretched lattice arrangements on the metrics of hydrodynamic stability, spherical conformity, and the harmonic power distribution of gravitational settling oscillations. We further demonstrate how our method is highly optimized for simulating multi-material spheres, such as planets with core–mantle boundaries.

  13. Spherical harmonics in texture analysis

    NASA Astrophysics Data System (ADS)

    Schaeben, Helmut; van den Boogaart, K. Gerald

    2003-07-01

    The objective of this contribution is to emphasize the fundamental role of spherical harmonics in constructive approximation on the sphere in general and in texture analysis in particular. The specific purpose is to present some methods of texture analysis and pole-to-orientation probability density inversion in a unifying approach, i.e. to show that the classic harmonic method, the pole density component fit method initially introduced as a distinct alternative, and the spherical wavelet method for high-resolution texture analysis share a common mathematical basis provided by spherical harmonics. Since pole probability density functions and orientation probability density functions are probability density functions defined on the sphere Ω3⊂ R3 or hypersphere Ω4⊂ R4, respectively, they belong at least to the space of measurable and integrable functions L1( Ωd), d=3, 4, respectively. Therefore, first a basic and simplified method to derive real symmetrized spherical harmonics with the mathematical property of providing a representation of rotations or orientations, respectively, is presented. Then, standard orientation or pole probability density functions, respectively, are introduced by summation processes of harmonic series expansions of L1( Ωd) functions, thus avoiding resorting to intuition and heuristics. Eventually, it is shown how a rearrangement of the harmonics leads quite canonically to spherical wavelets, which provide a method for high-resolution texture analysis. This unified point of view clarifies how these methods, e.g. standard functions, apply to texture analysis of EBSD orientation measurements.

  14. Spherical demons: fast surface registration.

    PubMed

    Yeo, B T Thomas; Sabuncu, Mert; Vercauteren, Tom; Ayache, Nicholas; Fischl, Bruce; Golland, Polina

    2008-01-01

    We present the fast Spherical Demons algorithm for registering two spherical images. By exploiting spherical vector spline interpolation theory, we show that a large class of regularizers for the modified demons objective function can be efficiently implemented on the sphere using convolution. Based on the one parameter subgroups of diffeomorphisms, the resulting registration is diffeomorphic and fast - registration of two cortical mesh models with more than 100k nodes takes less than 5 minutes, comparable to the fastest surface registration algorithms. Moreover, the accuracy of our method compares favorably to the popular FreeSurfer registration algorithm. We validate the technique in two different settings: (1) parcellation in a set of in-vivo cortical surfaces and (2) Brodmann area localization in ex-vivo cortical surfaces.

  15. Spherical Demons: Fast Surface Registration

    PubMed Central

    Yeo, B.T. Thomas; Sabuncu, Mert; Vercauteren, Tom; Ayache, Nicholas; Fischl, Bruce; Golland, Polina

    2009-01-01

    We present the fast Spherical Demons algorithm for registering two spherical images. By exploiting spherical vector spline interpolation theory, we show that a large class of regularizers for the modified demons objective function can be efficiently implemented on the sphere using convolution. Based on the one parameter subgroups of diffeomorphisms, the resulting registration is diffeomorphic and fast – registration of two cortical mesh models with more than 100k nodes takes less than 5 minutes, comparable to the fastest surface registration algorithms. Moreover, the accuracy of our method compares favorably to the popular FreeSurfer registration algorithm. We validate the technique in two different settings: (1) parcellation in a set of in-vivo cortical surfaces and (2) Brodmann area localization in ex-vivo cortical surfaces. PMID:18979813

  16. Basketballs as spherical acoustic cavities

    NASA Astrophysics Data System (ADS)

    Russell, Daniel A.

    2010-06-01

    The sound field resulting from striking a basketball is found to be rich in frequency content, with over 50 partials in the frequency range of 0-12 kHz. The frequencies are found to closely match theoretical expectations for standing wave patterns inside a spherical cavity. Because of the degenerate nature of the mode shapes, explicit identification of the modes is not possible without internal investigation with a microphone probe. A basketball proves to be an interesting application of a boundary value problem involving spherical coordinates.

  17. Radiance calibration of spherical integrators

    NASA Technical Reports Server (NTRS)

    Mclean, James T.; Guenther, Bruce W.

    1989-01-01

    Techniques for improving the knowledge of the radiance of large area spherical and hemispherical integrating energy sources have been investigated. Such sources are used to calibrate numerous aircraft and spacecraft remote sensing instruments. Comparisons are made between using a standard source based calibration method and a quantum efficient detector (QED) based calibration method. The uncertainty involved in transferring the calibrated values of the point source standard lamp to the extended source is estimated to be 5 to 10 percent. The use of the QED allows an improvement in the uncertainty to 1 to 2 percent for the measurement of absolute radiance from a spherical integrator source.

  18. Nonlinear axisymmetric liquid currents in spherical annuli

    NASA Technical Reports Server (NTRS)

    Astafyeva, N. M.; Vvedenskaya, N. D.; Yavorskaya, I. M.

    1978-01-01

    A numerical analysis of non-linear axisymmetric viscous flows in spherical annuli of different gap sizes is presented. Only inner sphere was supposed to rotate at a constant angular velocity. The streamlines, lines of constant angular velocity, kinetic energy spectra, and spectra of velocity components are obtained. A total kinetic energy and torque needed to rotate the inner sphere are calculated as functions of Re for different gap sizes. In small-gap annulus nonuniqueness of steady solutions of Navier-Stokes equations is established and regions of different flow regime existences are found. Numerical solutions in a wide-gap annulus and experimental results are used in conclusions about flow stability in the considered range of Re. The comparison of experimental and numerical results shows close qualitative and quantitative agreement.

  19. Optofluidic encapsulation of crystalline colloidal arrays into spherical membrane.

    PubMed

    Kim, Shin-Hyun; Jeon, Seog-Jin; Yang, Seung-Man

    2008-05-07

    Double emulsion droplets encapsulating crystalline colloidal arrays (CCAs) with a narrow size distribution were produced using an optofluidic device. The shell phase of the double emulsion was a photocurable resin that was photopolymerized downstream of the fluidic channel within 1 s after drop generation. The present optofluidic synthesis scheme was very effective for fabricating highly monodisperse spherical CCAs that were made structurally stable by in situ photopolymerization of the encapsulating shells. The shell thickness and the number of core emulsion drops could be controlled by varying the flow rates of the three coflowing streams in the dripping regime. The spherical CCAs confined in the shell exhibited distinct diffraction patterns in the visible range, in contrast to conventional film-type CCAs. As a result of their structure, the spherical CCAs exhibited photonic band gaps for normal incident light independent of the position on the spherical surface. This property was induced by heterogeneous nucleation at the smooth wall of the spherical emulsion drop during crystallization into a face-centered cubic (fcc) structure. On the other hand, the solidified shells did not permit the penetration of ionic species, enabling the CCAs to maintain their structure in a continuous aqueous phase of high ionic strength for at least 1 month. In addition, the evaporation of water molecules inside the shell was slowed considerably when the core-shell microparticles were exposed to air: It took approximately 6 h for a suspension encapsulated in a thick shell to evaporate completely, which is approximately 1000 times longer than the evaporation time for water droplets with the same volume. Finally, the spherical CCAs additionally exhibited enhanced stability against external electric fields. The spherical geometry and high dielectric constant of the suspension contributed to reducing the electric field inside the shell, thereby inhibiting the electrophoretic movement of

  20. Euclidean, Spherical, and Hyperbolic Shadows

    ERIC Educational Resources Information Center

    Hoban, Ryan

    2013-01-01

    Many classical problems in elementary calculus use Euclidean geometry. This article takes such a problem and solves it in hyperbolic and in spherical geometry instead. The solution requires only the ability to compute distances and intersections of points in these geometries. The dramatically different results we obtain illustrate the effect…

  1. Euclidean, Spherical, and Hyperbolic Shadows

    ERIC Educational Resources Information Center

    Hoban, Ryan

    2013-01-01

    Many classical problems in elementary calculus use Euclidean geometry. This article takes such a problem and solves it in hyperbolic and in spherical geometry instead. The solution requires only the ability to compute distances and intersections of points in these geometries. The dramatically different results we obtain illustrate the effect…

  2. A Module in Spherical Trigonometry.

    ERIC Educational Resources Information Center

    Congleton, C. A.; Broome, L. E.

    1980-01-01

    This module, designed for use at the high school level as a four- to eight-hour topic, includes: the geometry of a sphere, the coordinate system used to describe points on the earth's surface, parallel and meridian sailing, and the solution of right spherical triangles. (Author/MK)

  3. Spherical-Bearing Analysis Program

    NASA Technical Reports Server (NTRS)

    Kleckner, R. J.

    1984-01-01

    Computer program SPHERBEAN, developed to predict thermomechanical performance characteristics of double-row spherical roller bearings over wide range of operating conditions. Analysis allows six degrees of freedom for each roller and three for each half of an optionally split cage. Program capabilities provide sufficient generality to allow detailed simulation of both high-speed and conventional bearing operation.

  4. Dispersion in Spherical Water Drops.

    ERIC Educational Resources Information Center

    Eliason, John C., Jr.

    1989-01-01

    Discusses a laboratory exercise simulating the paths of light rays through spherical water drops by applying principles of ray optics and geometry. Describes four parts: determining the output angles, computer simulation, explorations, model testing, and solutions. Provides a computer program and some diagrams. (YP)

  5. Dispersion in Spherical Water Drops.

    ERIC Educational Resources Information Center

    Eliason, John C., Jr.

    1989-01-01

    Discusses a laboratory exercise simulating the paths of light rays through spherical water drops by applying principles of ray optics and geometry. Describes four parts: determining the output angles, computer simulation, explorations, model testing, and solutions. Provides a computer program and some diagrams. (YP)

  6. A Module in Spherical Trigonometry.

    ERIC Educational Resources Information Center

    Congleton, C. A.; Broome, L. E.

    1980-01-01

    This module, designed for use at the high school level as a four- to eight-hour topic, includes: the geometry of a sphere, the coordinate system used to describe points on the earth's surface, parallel and meridian sailing, and the solution of right spherical triangles. (Author/MK)

  7. Dielectric analysis based on spherical-shell model for cationic and anionic spherical polyelectrolyte brushes

    NASA Astrophysics Data System (ADS)

    Guo, Xiaoxia; Zhao, Kongshuang

    2017-07-01

    We report here a dielectric study on cationic and anionic spherical polyelectrolyte brush (SPB) (consisting of a polystyrene (PS) core and poly (2-aminoethylmethacrylate hydrochloride (PAEMH) chains or poly (acrylic acid) (PAA) chains grafted onto the core) suspensions over a frequency range of 40 Hz-110 MHz. The relaxation behavior of the suspensions shows significant changes in the brush layer properties when changing the particle mass fraction or pH of the system. After eliminating the electrode polarization effect at a low frequency, two definite relaxations related to interfacial polarization, around 100 kHz and 10 MHz respectively, are observed. Based on a single layer spherical-shell model, we developed a curve-fitting procedure to analyze such dielectric spectra for soft particles, and then calculated the dielectric properties of the components of the SPBs (such as the permittivities and conductivities of the layer and solution phase), especially the layer thickness d s of the polyelectrolyte chain (PE) layer. We also found a larger confinement degree of counterions in the PAEMH brush due to the protonation of the amino group. Moreover, the repulsive force between the SPB particles is evaluated by using the d s combined with the relative theoretical formulas. We conclude that by raising (reducing) the acidity of the system, the stability of the PAEMH-SPB (PAA-SPB) suspension was improved. An increase in particle concentration can also improve the stability of these two dispersions.

  8. Buckling of spherical shells revisited

    NASA Astrophysics Data System (ADS)

    Hutchinson, John W.

    2016-11-01

    A study is presented of the post-buckling behaviour and imperfection sensitivity of complete spherical shells subject to uniform external pressure. The study builds on and extends the major contribution to spherical shell buckling by Koiter in the 1960s. Numerical results are presented for the axisymmetric large deflection behaviour of perfect spheres followed by an extensive analysis of the role axisymmetric imperfections play in reducing the buckling pressure. Several types of middle surface imperfections are considered including dimple-shaped undulations and sinusoidal-shaped equatorial undulations. Buckling occurs either as the attainment of a maximum pressure in the axisymmetric state or as a non-axisymmetric bifurcation from the axisymmetric state. Several new findings emerge: the abrupt mode localization that occurs immediately after the onset of buckling, the existence of an apparent lower limit to the buckling pressure for realistically large imperfections, and comparable reductions of the buckling pressure for dimple and sinusoidal equatorial imperfections.

  9. Orthogonality of spherical harmonic coefficients

    NASA Technical Reports Server (NTRS)

    Mcleod, M. G.

    1980-01-01

    Orthogonality relations are obtained for the spherical harmonic coefficients of functions defined on the surface of a sphere. Following a brief discussion of the orthogonality of Fourier series coefficients, consideration is given to the values averaged over all orientations of the coordinate system of the spherical harmonic coefficients of a function defined on the surface of a sphere that can be expressed in terms of Legendre polynomials for the special case where the function is the sum of two delta functions located at two different points on the sphere, and for the case of an essentially arbitrary function. It is noted that the orthogonality relations derived have found applications in statistical studies of the geomagnetic field.

  10. Orthogonality of spherical harmonic coefficients

    NASA Technical Reports Server (NTRS)

    Mcleod, M. G.

    1980-01-01

    Orthogonality relations are obtained for the spherical harmonic coefficients of functions defined on the surface of a sphere. Following a brief discussion of the orthogonality of Fourier series coefficients, consideration is given to the values averaged over all orientations of the coordinate system of the spherical harmonic coefficients of a function defined on the surface of a sphere that can be expressed in terms of Legendre polynomials for the special case where the function is the sum of two delta functions located at two different points on the sphere, and for the case of an essentially arbitrary function. It is noted that the orthogonality relations derived have found applications in statistical studies of the geomagnetic field.

  11. Fresnel diffraction by spherical obstacles

    NASA Technical Reports Server (NTRS)

    Hovenac, Edward A.

    1989-01-01

    Lommel functions were used to solve the Fresnel-Kirchhoff diffraction integral for the case of a spherical obstacle. Comparisons were made between Fresnel diffraction theory and Mie scattering theory. Fresnel theory is then compared to experimental data. Experiment and theory typically deviated from one another by less than 10 percent. A unique experimental setup using mercury spheres suspended in a viscous fluid significantly reduced optical noise. The major source of error was due to the Gaussian-shaped laser beam.

  12. Contractions of affine spherical varieties

    SciTech Connect

    Arzhantsev, I V

    1999-08-31

    The language of filtrations and contractions is used to describe the class of G-varieties obtainable as the total spaces of the construction of contraction applied to affine spherical varieties, which is well-known in invariant theory. These varieties are local models for arbitrary affine G-varieties of complexity 1 with a one-dimensional categorical quotient. As examples, reductive algebraic semigroups and three-dimensional SL{sub 2}-varieties are considered.

  13. Sphericity Tests and Repeated Measures Data.

    ERIC Educational Resources Information Center

    Robey, Randall R.; Barcikowski, Robert S.

    The mixed model analysis of variance assumes a mathematical property known as sphericity. Several preliminary tests have been proposed to detect departures from the sphericity assumption. The logic of the preliminary testing procedure is to conduct the mixed model analysis of variance if the preliminary test suggests that the sphericity assumption…

  14. Compressible inviscid instability of rapidly expanding spherical material interfaces

    NASA Astrophysics Data System (ADS)

    Mankbadi, Mina R.; Balachandar, S.

    2012-03-01

    A high-order weighted essentially non-oscillatory scheme is employed to investigate the stability of a rapidly expanding material interface produced by a spherical shock tube. The flow structure is characterized by a forward moving primary shock, a backward moving secondary shock, and a spherical contact interface in-between. We consider herein the linear inviscid regime and focus on the development of the three-dimensional perturbations around the contact interface by solving a one-dimensional system of partial differential equations. Numerical simulations are performed to illustrate the effects of the contact interface's density discontinuity on the growth of the disturbances for various spherical wave numbers. In a spherical shock tube the instability is influenced by various mechanisms which include classical Rayleigh-Taylor (RT) effects, Bell-Plesset or geometry/curvature effects, the effects of impulsively accelerating the interface, and compressibility effects. Henceforth, the present instability will be referred to as non-classical RT instability to distinguish it from classical RT instability. For an extended intermediate time period, it can be shown that the small disturbances grow exponentially as in the classical RT instability. During this stage, the exponential growth rate increases with the spherical wave number, until it saturates for very large wave numbers due to the finite thickness limitation of the numerical representation of the contact interface. The results compare favorably with previous theoretical models; but indicate that in addition to compressibility, the space-time evolution of the contact interface's thickness plays a significant role. A parametric study is performed that varies the pressure and density ratios of the initial spherical container. The characteristics of the contact interface and the applicability of various instability theories is investigated for these regimes. Furthermore, varying the pressure and density ratios aids

  15. Spherical thin-shell wormholes and modified Chaplygin gas

    SciTech Connect

    Sharif, M.; Azam, M. E-mail: azammath@gmail.com

    2013-05-01

    The purpose of this paper is to construct spherical thin-shell wormhole solutions through cut and paste technique and investigate the stability of these solutions in the vicinity of modified Chaplygin gas. The Darmois-Israel formalism is used to formulate the stresses of the surface concentrating the exotic matter. We explore the stability of the wormhole solutions by using the standard potential method. We conclude that there exist more stable as well as unstable solutions than the previous study with generalized Chaplygin gas [19].

  16. Influence of dopant ion on localized relaxation of an oxygen vacancy in stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Ohta, M.; Wigmore, J. K.; Nobugai, K.; Miyasato, T.

    2002-05-01

    It is well known that stabilized zirconia exhibits long-range transport of oxygen ions which gives rise to diffusion relaxation of oxygen vacancies. The internal friction and the change in sound velocity in single-crystal calcia-stabilized zirconia (CSZ) doped with 12 mol % CaO were measured for longitudinal sound waves in the frequency range from 20 Hz to 700 Hz using a vibrating reed technique. In the temperature range from 300 K to 700 K, the relaxation strength exhibits strong anisotropy with respect to the directions of the k vectors. As the frequency increases the internal friction peak and the change in sound velocity shift toward high temperature, and the relaxation strength remains constant. The results show that a smaller number of oxygen vacancies contribute to diffusion relaxation than to localized relaxation, which is attributed to hopping of bound oxygen vacancies within the local structure. Comparison of the results with those reported previously for yttria-stabilized zirconia (YSZ) doped with 9.5 mol % Y2O3, suggests that oxygen vacancies are more strongly bound by the local structure in CSZ than in YSZ.

  17. A Spherical Aerial Terrestrial Robot

    NASA Astrophysics Data System (ADS)

    Dudley, Christopher J.

    This thesis focuses on the design of a novel, ultra-lightweight spherical aerial terrestrial robot (ATR). The ATR has the ability to fly through the air or roll on the ground, for applications that include search and rescue, mapping, surveillance, environmental sensing, and entertainment. The design centers around a micro-quadcopter encased in a lightweight spherical exoskeleton that can rotate about the quadcopter. The spherical exoskeleton offers agile ground locomotion while maintaining characteristics of a basic aerial robot in flying mode. A model of the system dynamics for both modes of locomotion is presented and utilized in simulations to generate potential trajectories for aerial and terrestrial locomotion. Details of the quadcopter and exoskeleton design and fabrication are discussed, including the robot's turning characteristic over ground and the spring-steel exoskeleton with carbon fiber axle. The capabilities of the ATR are experimentally tested and are in good agreement with model-simulated performance. An energy analysis is presented to validate the overall efficiency of the robot in both modes of locomotion. Experimentally-supported estimates show that the ATR can roll along the ground for over 12 minutes and cover the distance of 1.7 km, or it can fly for 4.82 minutes and travel 469 m, on a single 350 mAh battery. Compared to a traditional flying-only robot, the ATR traveling over the same distance in rolling mode is 2.63-times more efficient, and in flying mode the system is only 39 percent less efficient. Experimental results also demonstrate the ATR's transition from rolling to flying mode.

  18. Physics of Spherical Torus Plasmas

    SciTech Connect

    Peng, Yueng Kay Martin

    2000-01-01

    Broad and important progress in plasma tests, theory, new experiments, and future visions of the spherical torus (ST, or very low aspect ratio tokamaks) have recently emerged. These have substantially improved our understanding of the potential properties of the ST plasmas, since the preliminary calculation of the ST magnetohydrodynamic equilibria more than a decade ago. Exciting data have been obtained from concept exploration level ST experiments of modest capabilities (with major radii up to 35 cm), making important scientific contributions to toroidal confinement in general. The results have helped approval and construction of new and/or more powerful ST experiments, and stimulated an increasing number of theoretical calculations of interest to magnetic fusion energy. Utilizing the broad knowledge base from the successful tokamak and advanced tokamak research, a wide range of new ST physics features has been suggested. These properties of the ST plasma will be tested at the 1 MA level with major radius up to similar to 80 cm in the new proof of principle devices National Spherical Torus Experiment (NSTX, U.S.) [M. Peng , European Conf. Abst. 22C, 451 (1998); S. M. Kaye , Fusion Technol. 36, 16 (1999); M. Ono , "Exploration of Spherical Torus Physics in the NSTX Device," 17th IAEA Fusion Energy Conf., paper IAEA-CN-69/ICP/01 (R), Yokohama, Japan (1998)], Mega Ampere Spherical Tokamak (MAST, U.K.) [A. C. Darke , Fusion Technol. 1, 799 (1995); Q. W. Morris , Proc. Int. Workshop on ST (Ioffe Inst., St. Petersburg, 1997), Vol. 1, p. 290], and Globus-M (R.F.) [V. K. Gusev , European Conf. Abst. 22C, 576 (1998)], which have just started full experimental operation. New concept exploration experiments, such as Pegasus (University of Wisconsin) [R. Fonck and the PEGASUS Team, Bull. Am. Phys. Soc. 44, 267 (1999)], Helicity Injected Tokamak-II (HIT-II, University of Washington) [T. R. Jarboe , Phys. Plasmas 5, 1807 (1998)], and Current Drive Experiment-Upgrade (CDX

  19. Electronic switching spherical array antenna

    NASA Technical Reports Server (NTRS)

    Stockton, R.

    1978-01-01

    This work was conducted to demonstrate the performance levels attainable with an ESSA (Electronic Switching Spherical Array) antenna by designing and testing an engineering model. The antenna was designed to satisfy general spacecraft environmental requirements and built to provide electronically commandable beam pointing capability throughout a hemisphere. Constant gain and beam shape throughout large volumetric coverage regions are the principle characteristics. The model is intended to be a prototype of a standard communications and data handling antenna for user scientific spacecraft with the Tracking and Data Relay Satellite System (TDRSS). Some additional testing was conducted to determine the feasibility of an integrated TDRSS and GPS (Global Positioning System) antenna system.

  20. Spherically symmetric canonical quantum gravity

    NASA Astrophysics Data System (ADS)

    Brahma, Suddhasattwa

    2015-06-01

    Canonical quantization of spherically symmetric space-times is carried out, using real-valued densitized triads and extrinsic curvature components, with specific factor-ordering choices ensuring in an anomaly free quantum constraint algebra. Comparison with previous work [Nucl. Phys. B399, 211 (1993)] reveals that the resulting physical Hilbert space has the same form, although the basic canonical variables are different in the two approaches. As an extension, holonomy modifications from loop quantum gravity are shown to deform the Dirac space-time algebra, while going beyond "effective" calculations.

  1. Radiative transfer in spherical atmospheres

    NASA Astrophysics Data System (ADS)

    Kalkofen, W.; Wehrse, R.

    A method for defining spherical model atmospheres in radiative/convective and hydrostatic equilibrium is presented. A finite difference form is found for the transfer equation and a matrix operator is developed as the discrete space analog (in curvilinear coordinates) of a formal integral in plane geometry. Pressure is treated as a function of temperature. Flux conservation is maintained within the energy equation, although the correct luminosity transport must be assigned for any given level of the atmosphere. A perturbed integral operator is used in a complete linearization of the transfer and constraint equations. Finally, techniques for generating stable solutions in economical computer time are discussed.

  2. APPARATUS FOR GRINDING SPHERICAL BODIES

    DOEpatents

    Burch, R.F. Jr.

    1963-09-24

    A relatively inexpensive device is described for grinding rough ceramic bodies into accurate spherical shapes using a conventional drill press and a belt sander. A horizontal disk with an abrasive-surfaced recess in its lower face is mounted eccentrically on a vertical shaft which is forced downward against a stop by a spring. Bodies to be ground are placed in the recess and are subjected to the abrasive action of the belt sander as the disk is rotated by the drill press. (AEC)

  3. Microwave signal amplification and Pierce instability on radial electron flows in cylindrical and spherical diodes

    SciTech Connect

    Gnavi, G.; Gratton, F.T. )

    1994-11-01

    Linear space charge perturbations of focused electron beams flowing between cylindrical and spherical electrodes on convergent or divergent trajectories are studied, and the amplification of high-frequency signals when the flow is modulated at one electrode is computed. It is shown that divergent beams give the largest amplification effect. The instability of electron beams drifting through grounded grids (Pierce instability in cylindrical or spherical diodes) is also considered. The instability threshold occurs at higher critical currents when the curvature of the electrodes is large. Results for planar electrodes are recovered in the limit of zero curvature devices. Spherical configurations have better signal amplification and stability properties than similar planar or cylindrical systems.

  4. Spherical and tubule nanocarriers for sustained drug release

    PubMed Central

    Shutava, T.; Fakhrullin, R.; Lvov, Y.

    2014-01-01

    We discuss new trends in Layer-by-Layer (LbL) encapsulation of spherical and tubular cores of 50–150 nm diameter and loaded with drugs. This core size decrease (from few micrometers to a hundred of nanometers) for LbL encapsulation required development of sonication assistant non-washing technique and shell PEGylation to reach high colloidal stability of drug nanocarriers at 2–3 mg/mL concentration in isotonic buffers and serum. For 120–170 nm spherical LbL nanocapsules of low soluble anticancer drugs, polyelectrolyte shell thickness controls drug dissolution. As for nanotube carriers, we concentrated on natural halloysite clay nanotubes as cores for LbL encapsulation that allows high drug loading and sustains its release over tens and hundreds hours. Further drug release prolongation was reached with formation of the tube-end stoppers. PMID:25450068

  5. Archimedes' floating bodies on a spherical Earth

    NASA Astrophysics Data System (ADS)

    Rorres, Chris

    2016-01-01

    Archimedes was the first to systematically find the centers of gravity of various solid bodies and to apply this concept in determining stable configurations of floating bodies. In this paper, we discuss an error in a proof developed by Archimedes that involves determining whether a uniform, spherical cap will float stably with its base horizontal in a liquid on a spherical Earth. We present a simpler, corrected proof and discuss aspects of his proof regarding a spherical cap that is not uniform.

  6. Measuring Spherical Harmonic Coefficients on a Sphere

    SciTech Connect

    Pollaine, S; Haan, S W

    2003-05-16

    The eigenfunctions of Rayleigh-Taylor modes on a spherical capsule are the spherical harmonics Y{sub l,m} These can be measured by measuring the surface perturbations along great circles and fitting them to the first few modes by a procedure described in this article. For higher mode numbers, it is more convenient to average the Fourier power spectra along the great circles, and then transform them to spherical harmonic modes by an algorithm derived here.

  7. Numerical evolutions of spherical Proca stars

    NASA Astrophysics Data System (ADS)

    Sanchis-Gual, Nicolas; Herdeiro, Carlos; Radu, Eugen; Degollado, Juan Carlos; Font, José A.

    2017-05-01

    Vector boson stars, or Proca stars, have been recently obtained as fully nonlinear numerical solutions of the Einstein-(complex)-Proca system [1]. These are self-gravitating, everywhere nonsingular, horizonless Bose-Einstein condensates of a massive vector field, which resemble in many ways, but not all, their scalar cousins, the well-known (scalar) boson stars. In this paper we report fully nonlinear numerical evolutions of Proca stars, focusing on the spherically symmetric case, with the goal of assessing their stability and the end point of the evolution of the unstable stars. Previous results from linear perturbation theory indicate that the separation between stable and unstable configurations occurs at the solution with maximal ADM mass. Our simulations confirm this result. Evolving numerically unstable solutions, we find, depending on the sign of the binding energy of the solution and on the perturbation, three different outcomes: (i) migration to the stable branch, (ii) total dispersion of the scalar field, or (iii) collapse to a Schwarzschild black hole. In the latter case, a long-lived Proca field remnant—a Proca wig—composed by quasibound states, may be seen outside the horizon after its formation, with a lifetime that scales inversely with the Proca mass. We comment on the similarities/differences with the scalar case as well as with neutron stars.

  8. Nonlinear fishbone dynamics in spherical tokamaks

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Fu, G. Y.; Shen, Wei

    2017-01-01

    Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. The results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. A substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.

  9. Nonlinear fishbone dynamics in spherical tokamaks

    SciTech Connect

    Wang, Feng; Fu, G. Y.; Shen, Wei

    2016-11-22

    Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. Our results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. Furthermore, a substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Finally, our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.

  10. Nonlinear fishbone dynamics in spherical tokamaks

    SciTech Connect

    Wang, Feng; Fu, G.Y.; Shen, Wei

    2017-01-01

    Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. The results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. A substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.

  11. Nonlinear fishbone dynamics in spherical tokamaks

    DOE PAGES

    Wang, Feng; Fu, G. Y.; Shen, Wei

    2016-11-22

    Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. Our results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturatesmore » due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. Furthermore, a substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Finally, our analysis shows that trapped particles provide the main drive to the mode in the nonlinear regime.« less

  12. Spherical collapse in chameleon models

    SciTech Connect

    Brax, Ph.; Steer, D.A. E-mail: rosenfel@ift.unesp.br

    2010-08-01

    We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough initial size of the inhomogeneity the collapsing region possesses a thin shell that shields the modification of gravity induced by the chameleon field, recovering the standard gravity results. We analyse the behaviour of a collapsing shell in a cosmological setting in the presence of a thin shell and find that, in contrast to the usual case, the critical density for collapse in principle depends on the initial comoving size of the inhomogeneity.

  13. Nonadiabatic charged spherical gravitational collapse

    SciTech Connect

    Di Prisco, A.; Herrera, L.; Le Denmat, G.; MacCallum, M. A. H.; Santos, N. O.

    2007-09-15

    We present a complete set of the equations and matching conditions required for the description of physically meaningful charged, dissipative, spherically symmetric gravitational collapse with shear. Dissipation is described with both free-streaming and diffusion approximations. The effects of viscosity are also taken into account. The roles of different terms in the dynamical equation are analyzed in detail. The dynamical equation is coupled to a causal transport equation in the context of Israel-Stewart theory. The decrease of the inertial mass density of the fluid, by a factor which depends on its internal thermodynamic state, is reobtained, with the viscosity terms included. In accordance with the equivalence principle, the same decrease factor is obtained for the gravitational force term. The effect of the electric charge on the relation between the Weyl tensor and the inhomogeneity of the energy density is discussed.

  14. Libsharp - spherical harmonic transforms revisited

    NASA Astrophysics Data System (ADS)

    Reinecke, M.; Seljebotn, D. S.

    2013-06-01

    We present libsharp, a code library for spherical harmonic transforms (SHTs), which evolved from the libpsht library and addresses several of its shortcomings, such as adding MPI support for distributed memory systems and SHTs of fields with arbitrary spin, but also supporting new developments in CPU instruction sets like the Advanced Vector Extensions (AVX) or fused multiply-accumulate (FMA) instructions. The library is implemented in portable C99 and provides an interface that can be easily accessed from other programming languages such as C++, Fortran, Python, etc. Generally, libsharp's performance is at least on par with that of its predecessor; however, significant improvements were made to the algorithms for scalar SHTs, which are roughly twice as fast when using the same CPU capabilities. The library is available at http://sourceforge.net/projects/libsharp/ under the terms of the GNU General Public License.

  15. Wormhole dynamics in spherical symmetry

    SciTech Connect

    Hayward, Sean A.

    2009-06-15

    A dynamical theory of traversable wormholes is detailed in spherical symmetry. Generically a wormhole consists of a tunnel of trapped surfaces between two mouths, defined as temporal outer trapping horizons with opposite senses, in mutual causal contact. In static cases, the mouths coincide as the throat of a Morris-Thorne wormhole, with surface gravity providing an invariant measure of the radial curvature or ''flaring-out''. The null energy condition must be violated at a wormhole mouth. Zeroth, first, and second laws are derived for the mouths, as for black holes. Dynamic processes involving wormholes are reviewed, including enlargement or reduction, and interconversion with black holes. A new area of wormhole thermodynamics is suggested.

  16. Spherical Parameterization Balancing Angle and Area Distortions.

    PubMed

    Nadeem, Saad; Su, Zhengyu; Zeng, Wei; Kaufman, Arie; Gu, Xianfeng

    2017-06-01

    This work presents a novel framework for spherical mesh parameterization. An efficient angle-preserving spherical parameterization algorithm is introduced, which is based on dynamic Yamabe flow and the conformal welding method with solid theoretic foundation. An area-preserving spherical parameterization is also discussed, which is based on discrete optimal mass transport theory. Furthermore, a spherical parameterization algorithm, which is based on the polar decomposition method, balancing angle distortion and area distortion is presented. The algorithms are tested on 3D geometric data and the experiments demonstrate the efficiency and efficacy of the proposed methods.

  17. Maximum entropy spherical deconvolution for diffusion MRI.

    PubMed

    Alexander, Daniel C

    2005-01-01

    This paper proposes a maximum entropy method for spherical deconvolution. Spherical deconvolution arises in various inverse problems. This paper uses the method to reconstruct the distribution of microstructural fibre orientations from diffusion MRI measurements. Analysis shows that the PASMRI algorithm, one of the most accurate diffusion MRI reconstruction algorithms in the literature, is a special case of the maximum entropy spherical deconvolution. Experiments compare the new method to linear spherical deconvolution, used previously in diffusion MRI, and to the PASMRI algorithm. The new method compares favourably both in simulation and on standard brain-scan data.

  18. Physics Basis for a Spherical Torus Power Plant

    SciTech Connect

    C.E. Kessel; J. Menard; S.C. Jardin; T.K. Mau; et al

    1999-11-01

    The spherical torus, or low-aspect-ratio tokamak, is considered as the basis for a fusion power plant. A special class of wall-stabilized high-beta high-bootstrap fraction low-aspect-ratio tokamak equilibrium are analyzed with respect to MHD stability, bootstrap current and external current drive, poloidal field system requirements, power and particle exhaust and plasma operating regime. Overall systems optimization leads to a choice of aspect ratio A = 1:6, plasma elongation kappa = 3:4, and triangularity delta = 0:64. The design value for the plasma toroidal beta is 50%, corresponding to beta N = 7:4, which is 10% below the ideal stability limit. The bootstrap fraction of 99% greatly alleviates the current drive requirements, which are met by tangential neutral beam injection. The design is such that 45% of the thermal power is radiated in the plasma by Bremsstrahlung and trace Krypton, with Neon in the scrapeoff layer radiating the remainder.

  19. Fast calculation of computer-generated spherical hologram by spherical harmonic transform

    NASA Astrophysics Data System (ADS)

    Sando, Y.; Barada, D.; Jackin, B. J.; Yatagai, T.

    2017-05-01

    This paper presents a fast calculation method for spherical computer-generated hologram by using a spherical harmonic transform. A three-dimensional (3D) object defined in the 3D Cartesian coordinate system is numerically Fourier transformed with fast Fourier transforms (FFTs). Fourier components on the spherical surface of the radius 1/λ are extracted. The wavefronts on the spherical surface can be calculated from the single spherical Fourier components. This paper reveals the analytical diffraction integral between the spherical Fourier components and the wavefront on the spherical surface. This diffraction integral is expressed in the form of convolution integral on the sphere and can be calculated very fast based on the spherical harmonic transform. By the numerical simulation, the validity and the effectiveness of our proposal has been verified.

  20. Acoustic radiation force control: Pulsating spherical carriers.

    PubMed

    Rajabi, Majid; Mojahed, Alireza

    2017-06-13

    The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required

  1. Three-point spherical mirror mount

    DOEpatents

    Cutburth, R.W.

    1984-01-23

    A three-point spherical mirror mount for use with lasers is disclosed. The improved mirror mount is adapted to provide a pivot ring having an outer surface with at least three spaced apart mating points to engage an inner spherical surface of a support housing.

  2. Light-weight spherical submergence vessel

    NASA Technical Reports Server (NTRS)

    Baker, I.

    1974-01-01

    Design vessel with very low thickness-to-radius ratio to obtain low weight, and fabricate it with aid of precision tracer-lathe to limit and control imperfections in spherical shape. Vessel is thin-walled, spherical, monocoque shell constructed from hemispheres joined with sealed and bolted meridional flange.

  3. How Spherical Is a Cube (Gravitationally)?

    ERIC Educational Resources Information Center

    Sanny, Jeff; Smith, David

    2015-01-01

    An important concept that is presented in the discussion of Newton's law of universal gravitation is that the gravitational effect external to a spherically symmetric mass distribution is the same as if all of the mass of the distribution were concentrated at the center. By integrating over ring elements of a spherical shell, we show that the…

  4. Onthe static and spherically symmetric gravitational field

    NASA Astrophysics Data System (ADS)

    Gottlieb, Ioan; Maftei, Gheorghe; Mociutchi, Cleopatra

    Starting from a generalization of Einstein 's theory of gravitation, proposed by one of the authors (Cleopatra Mociutchi), the authors study a particular spherical symmetric case. Among other one obtain the compatibility conditions for the existence of the static and spherically symmetruic gravitational filed in the case of extended Einstein equation.

  5. How Spherical Is a Cube (Gravitationally)?

    ERIC Educational Resources Information Center

    Sanny, Jeff; Smith, David

    2015-01-01

    An important concept that is presented in the discussion of Newton's law of universal gravitation is that the gravitational effect external to a spherically symmetric mass distribution is the same as if all of the mass of the distribution were concentrated at the center. By integrating over ring elements of a spherical shell, we show that the…

  6. Three-point spherical mirror mount

    DOEpatents

    Cutburth, Ronald W.

    1990-01-01

    A three-point spherical mirror mount for use with lasers is disclosed. The improved mirror mount is adapted to provide a pivot ring having an outer surface with at least three spaced apart mating points to engage an inner spherical surface of a support housing.

  7. Spherical combustion clouds in explosions

    NASA Astrophysics Data System (ADS)

    Kuhl, A. L.; Bell, J. B.; Beckner, V. E.; Balakrishnan, K.; Aspden, A. J.

    2013-05-01

    This study explores the properties of spherical combustion clouds in explosions. Two cases are investigated: (1) detonation of a TNT charge and combustion of its detonation products with air, and (2) shock dispersion of aluminum powder and its combustion with air. The evolution of the blast wave and ensuing combustion cloud dynamics are studied via numerical simulations with our adaptive mesh refinement combustion code. The code solves the multi-phase conservation laws for a dilute heterogeneous continuum as formulated by Nigmatulin. Single-phase combustion (e.g., TNT with air) is modeled in the fast-chemistry limit. Two-phase combustion (e.g., Al powder with air) uses an induction time model based on Arrhenius fits to Boiko's shock tube data, along with an ignition temperature criterion based on fits to Gurevich's data, and an ignition probability model that accounts for multi-particle effects on cloud ignition. Equations of state are based on polynomial fits to thermodynamic calculations with the Cheetah code, assuming frozen reactants and equilibrium products. Adaptive mesh refinement is used to resolve thin reaction zones and capture the energy-bearing scales of turbulence on the computational mesh (ILES approach). Taking advantage of the symmetry of the problem, azimuthal averaging was used to extract the mean and rms fluctuations from the numerical solution, including: thermodynamic profiles, kinematic profiles, and reaction-zone profiles across the combustion cloud. Fuel consumption was limited to ˜ 60-70 %, due to the limited amount of air a spherical combustion cloud can entrain before the turbulent velocity field decays away. Turbulent kinetic energy spectra of the solution were found to have both rotational and dilatational components, due to compressibility effects. The dilatational component was typically about 1 % of the rotational component; both seemed to preserve their spectra as they decayed. Kinetic energy of the blast wave decayed due to the

  8. All spherically symmetric charged anisotropic solutions for compact stars

    NASA Astrophysics Data System (ADS)

    Maurya, S. K.; Gupta, Y. K.; Ray, Saibal

    2017-06-01

    In the present paper we develop an algorithm for all spherically symmetric anisotropic charged fluid distributions. Considering a new source function ν (r) we find a set of solutions which is physically well behaved and represents compact stellar models. A detailed study specifically shows that the models actually correspond to strange stars in terms of their mass and radius. In this connection we investigate several physical properties like energy conditions, stability, mass-radius ratio, electric charge content, anisotropic nature and surface redshift through graphical plots and mathematical calculations. All the features from these studies are in excellent agreement with the already available evidence in theory as well as observations.

  9. Bifurcations of rotating waves in rotating spherical shell convection.

    PubMed

    Feudel, F; Tuckerman, L S; Gellert, M; Seehafer, N

    2015-11-01

    The dynamics and bifurcations of convective waves in rotating and buoyancy-driven spherical Rayleigh-Bénard convection are investigated numerically. The solution branches that arise as rotating waves (RWs) are traced by means of path-following methods, by varying the Rayleigh number as a control parameter for different rotation rates. The dependence of the azimuthal drift frequency of the RWs on the Ekman and Rayleigh numbers is determined and discussed. The influence of the rotation rate on the generation and stability of secondary branches is demonstrated. Multistability is typical in the parameter range considered.

  10. Static spherically symmetric solutions in f(G) gravity

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Fatima, H. Ismat

    2016-05-01

    We investigate interior solutions for static spherically symmetric metric in the background of f(G) gravity. We use the technique of conformal Killing motions to solve the field equations with both isotropic and anisotropic matter distributions. These solutions are then used to obtain density, radial and tangential pressures for power-law f(G) model. For anisotropic case, we assume a linear equation-of-state and investigate solutions for the equation-of-state parameter ω = -1.5. We check physical validity of the solutions through energy conditions and also examine its stability. Finally, we study equilibrium configuration using Tolman-Oppenheimer-Volkoff equation.

  11. Sheet-like assemblies of spherical particles with point-symmetrical patches.

    PubMed

    Mani, Ethayaraja; Sanz, Eduardo; Roy, Soumyajit; Dijkstra, Marjolein; Groenewold, Jan; Kegel, Willem K

    2012-04-14

    We report a computational study on the spontaneous self-assembly of spherical particles into two-dimensional crystals. The experimental observation of such structures stabilized by spherical objects appeared paradoxical so far. We implement patchy interactions with the patches point-symmetrically (icosahedral and cubic) arranged on the surface of the particle. In these conditions, preference for self-assembly into sheet-like structures is observed. We explain our findings in terms of the inherent symmetry of the patches and the competition between binding energy and vibrational entropy. The simulation results explain why hollow spherical shells observed in some Keplerate-type polyoxometalates (POM) appear. Our results also provide an explanation for the experimentally observed layer-by-layer growth of apoferritin--a quasi-spherical protein.

  12. Dynamics of non-spherical colloidal particles near and at oil-water interfaces

    NASA Astrophysics Data System (ADS)

    Wang, Anna; Dimiduk, Thomas G.; Fung, Jerome; Chaudhary, Kundan; Lewis, Jennifer A.; Razavi, Sepideh; Kretzschmar, Ilona; Manoharan, Vinothan N.

    2014-03-01

    Whereas much is known about how spherical colloidal particles interact with and at oil-water interfaces, not much is known about their non-spherical counterparts. The rotation of non-spherically symmetric particles adds extra degrees of freedom to how such particles interact with each other and the interface, so to study their three-dimensional dynamics we must first be able to image the rotation which has so far only been possible in viscous fluids or for particles with large aspect ratios. Here we track both the three-dimensional translation and the rotation of non-spherical colloidal particles at high speeds using the discrete dipole approximation in conjunction with digital holographic microscopy. We study the dynamics of such particles at an oil-water interface to determine interactions and dynamics prior to or after attachment. We aim to connect these measurements to the formation and stability of Pickering emulsions.

  13. Wrinkling crystallography on spherical surfaces.

    PubMed

    Brojan, Miha; Terwagne, Denis; Lagrange, Romain; Reis, Pedro M

    2015-01-06

    We present the results of an experimental investigation on the crystallography of the dimpled patterns obtained through wrinkling of a curved elastic system. Our macroscopic samples comprise a thin hemispherical shell bound to an equally curved compliant substrate. Under compression, a crystalline pattern of dimples self-organizes on the surface of the shell. Stresses are relaxed by both out-of-surface buckling and the emergence of defects in the quasi-hexagonal pattern. Three-dimensional scanning is used to digitize the topography. Regarding the dimples as point-like packing units produces spherical Voronoi tessellations with cells that are polydisperse and distorted, away from their regular shapes. We analyze the structure of crystalline defects, as a function of system size. Disclinations are observed and, above a threshold value, dislocations proliferate rapidly with system size. Our samples exhibit striking similarities with other curved crystals of charged particles and colloids. Differences are also found and attributed to the far-from-equilibrium nature of our patterns due to the random and initially frozen material imperfections which act as nucleation points, the presence of a physical boundary which represents an additional source of stress, and the inability of dimples to rearrange during crystallization. Even if we do not have access to the exact form of the interdimple interaction, our experiments suggest a broader generality of previous results of curved crystallography and their robustness on the details of the interaction potential. Furthermore, our findings open the door to future studies on curved crystals far from equilibrium.

  14. Nanophotonics of isolated spherical particles

    NASA Astrophysics Data System (ADS)

    Geints, Yu. É.; Zemlyanov, A. A.; Panina, E. K.

    2010-09-01

    The problem of extreme focusing of an optical beam into the spatial region with wavelength dimensions is considered with the use of the special features of radiation interaction with isolated spherical particles. Results of numerical computations of the optical field intensity at the surface of silver particles of different radii upon exposure to laser radiation with different wavelengths are presented. It is demonstrated that the relative intensity of the plasmon optical field on the nanoparticle surface increases and the field focusing region decreases with increasing particle radius. Results of numerical computations illustrating the influence of the shell of composite nanoparticles comprising a dielectric core and a metal shell on the optical field intensity in the vicinity of the particle are presented. The problem of local optical foci of a transparent microparticle (photonic nanojets) is investigated. It is established that variation of the micron particle size, its optical properties, and laser radiation parameters allows the amplitude and spatial characteristics of the photonic nanojet region to be controlled efficiently.

  15. Study on Octahedral Spherical Hohlraum

    NASA Astrophysics Data System (ADS)

    Lan, Ke; Liu, Jie; Huo, Wenyi; Li, Zhichao; Yang, Dong; Li, Sanwei; Ren, Guoli; Chen, Yaohua; Jiang, Shaoen; He, Xian-Tu; Zhang, Weiyan

    2015-11-01

    In this talk, we report our recent study on octahedral spherical hohlraum which has six laser entrance holes (LEHs). First, our study shows that the octahedral hohlraums have robust high symmetry during the capsule implosion at hohlraum-to- capsule radius ratio larger than 3.7 and have potential superiority on low backscatter without supplementary technology. Second, we study the laser arrangement and constraints of the octahedral hohlraums and give their laser arrangement design for ignition facility. Third, we propose a novel octahedral hohlraum with LEH shields and cylindrical LEHs, in order to increase the laser coupling efficiency and improve the capsule symmetry and to mitigate the influence of the wall blowoff on laser transport. Fourth, we study the sensitivity of capsule symmetry inside the octahedral hohlraums to laser power balance, pointing accuracy, deviations from the optimal position and target fabrication accuracy, and compare the results with that of tradiational cylinders and rugby hohlraums. Finally, we present our recent experimental studies on the octahedral hohlraums on SGIII prototype laser facility.

  16. Osmotic buckling of spherical capsules.

    PubMed

    Knoche, Sebastian; Kierfeld, Jan

    2014-11-07

    We study the buckling of elastic spherical shells under osmotic pressure with the osmolyte concentration of the exterior solution as a control parameter. We compare our results for the bifurcation behavior with results for buckling under mechanical pressure control, that is, with an empty capsule interior. We find striking differences for the buckling states between osmotic and mechanical buckling. Mechanical pressure control always leads to fully collapsed states with opposite sides in contact, whereas uncollapsed states with a single finite dimple are generic for osmotic pressure control. For sufficiently large interior osmolyte concentrations, osmotic pressure control is qualitatively similar to buckling under volume control with the volume prescribed by the osmolyte concentrations inside and outside the shell. We present a quantitative theory which also captures the influence of shell elasticity on the relationship between osmotic pressure and volume. These findings are relevant for the control of buckled shapes in applications. We show how the osmolyte concentration can be used to control the volume of buckled shells. An accurate analytical formula is derived for the relationship between the osmotic pressure, the elastic moduli and the volume of buckled capsules. This also allows use of elastic capsules as osmotic pressure sensors or deduction of elastic properties and the internal osmolyte concentration from shape changes in response to osmotic pressure changes. We apply our findings to published experimental data on polyelectrolyte capsules.

  17. Chemical waves on spherical surfaces

    NASA Astrophysics Data System (ADS)

    Maselko, Jerzy; Showalter, Kenneth

    1989-06-01

    THE concentric-circular and spiral patterns exhibited by the Belousov-Zhabotinsky (BZ) reaction in thin films of solution are representative of spatiotemporal behaviour in a two-dimensional, planar excitable medium1-6. Here we report BZ chemical waves propagating on the two-dimensional surface of a sphere. A wave on the surface of a single cation-exchange bead, loaded with ferroin and bathed in BZ reaction mixture containing no catalyst, develops to form a rotating spiral. Unlike spiral waves in thin films of solution, which typically wind out to connect with a twin rotating in the opposite direction, these waves rotate from pole to pole in a single direction. The spiral winds outward from a meandering source at one pole, crosses the equator, and undergoes self-annihilation as it winds into itself at the other pole. This behaviour, which is not possible in a two-dimensional planar configuration, arises from qualitative (negative to positive) and quantitative changes in wavefront curvature as the wave traverses the spherical surface. These observations of a single spiral wave contrast with theoretical predictions7,8 of counter-rotating spirals in this geometry.

  18. Electrical properties of spherical syncytia.

    PubMed Central

    Eisenberg, R S; Barcilon, V; Mathias, R T

    1979-01-01

    Syncytial tissues consist of many cells whose intracellular spaces are electrically coupled one to another. Such tissues typically include narrow, tortuous extracellular space and often have specialized membranes at their outer surface. We derive differential equations to describe the potentials induced when a sinusoidal or steady current is applied to the intracellular space with a microelectrode. We derive solutions for spherical preparations with isotropic properties or with a particular anisotropy in effective extracellular and intracellular resistivities. Solutions are presented in an approximate form with a simple physical interpretation. The leading term in the intracellular potential describes an "isopotential" cell in which there is no spatial variation of intracellular potential. The leading term in the extracellular potential, and thus the potential across the inner membranes, varies with radial position, even at zero frequency. The next term of the potentials describes the direct effects of the point source of current and, for the parameters given here, acts as a series resistance producing a large local potential drop essentially independent of frequency. A lumped equivalent circuit describes the "low frequency" behavior of the syncytium, and a distributed circuit gives a reasonably accurate general description. Graphs of the spatial variation and frequency dependence of intracellular, extracellular, and transmembrane potential are given, the response to sinusoidal currents is used to calculate numerically the response to a step function of current. PMID:262383

  19. QED with a spherical mirror

    SciTech Connect

    Hetet, G.; Blatt, R.; Slodicka, L.; Hennrich, M.; Glaetzle, A.

    2010-12-15

    We investigate the quantum electrodynamic (QED) properties of an atomic electron close to the focus of a spherical mirror. We first show that the spontaneous emission and excited-state level shift of the atom can be fully suppressed with mirror-atom distances of many wavelengths. A three-dimensional theory predicts that the spectral density of vacuum fluctuations can indeed vanish within a volume {lambda}{sup 3} around the atom, with the use of a far-distant mirror covering only half of the atomic emission solid angle. The modification of these QED atomic properties is also computed as a function of the mirror size, and large effects are found for only moderate numerical apertures. We also evaluate the long-distance ground-state energy shift (Casimir-Polder shift) and find that it scales as ({lambda}/R){sup 2} at the focus of a hemispherical mirror of radius R, as opposed to the well-known ({lambda}/R){sup 4} scaling law for an atom at a distance R from an infinite plane mirror. Our results are relevant for investigations of QED effects as well as free-space coupling to single atoms using high-numerical-aperture lenses.

  20. Nematic textures in spherical shells

    NASA Astrophysics Data System (ADS)

    Vitelli, V.; Nelson, D. R.

    2006-08-01

    The equilibrium texture of nematic shells is studied as a function of their thickness. For ultrathin shells the ground state has four short (1)/(2) disclination lines but, as the thickness of the film increases, a three-dimensional escaped configuration composed of two pairs of half-hedgehogs becomes energetically favorable. We derive an exact solution for the nematic ground state in the one Frank constant approximation and study the stability of the corresponding texture against thermal fluctuations.

  1. Spherical gravitational collapse in N dimensions

    SciTech Connect

    Goswami, Rituparno; Joshi, Pankaj S.

    2007-10-15

    We investigate here spherically symmetric gravitational collapse in a space-time with an arbitrary number of dimensions and with a general type I matter field, which is a broad class that includes most of the physically reasonable matter forms. We show that given the initial data for matter in terms of the initial density and pressure profiles at an initial surface t=t{sub i} from which the collapse evolves, there exist the rest of the initial data functions and classes of solutions of Einstein equations which we construct here, such that the space-time evolution goes to a final state which is either a black hole or a naked singularity, depending on the nature of initial data and evolutions chosen, and subject to validity of the weak energy condition. The results are discussed and analyzed in the light of the cosmic censorship hypothesis in black hole physics. The formalism here combines the earlier results on gravitational collapse in four dimensions in a unified treatment. Also the earlier work is generalized to higher-dimensional space-times to allow a study of the effect of the number of dimensions on the possible final outcome of the collapse in terms of either a black hole or naked singularity. No restriction is adopted on the number of dimensions, and other limiting assumptions such as self-similarity of space-time are avoided, in order to keep the treatment general. Our methodology allows us to consider to an extent the genericity and stability aspects related to the occurrence of naked singularities in gravitational collapse.

  2. Oscillatory Extinction Of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Law, C. K.; Yoo, S. W.; Christianson, E. W.

    2003-01-01

    Since extinction has been observed in an oscillatory manner in Le greater than 1 premixed flames, it is not unreasonable to expect that extinction could occur in an unsteady manner for diffusion flames. Indeed, near-limit oscillations have been observed experimentally under microgravity conditions for both candle flames and droplet flames. Furthermore, the analysis of Cheatham and Matalon on the unsteady behavior of diffusion flames with heat loss, identified an oscillatory regime which could be triggered by either a sufficiently large Lewis number (even without heat loss) or an appreciable heat loss (even for Le=1). In light of these recent understanding, the present investigation aims to provide a well-controlled experiment that can unambiguously demonstrate the oscillation of diffusion flames near both the transport- and radiation-induced limits. That is, since candle and jet flames are stabilized through flame segments that are fundamentally premixed in nature, and since premixed flames are prone to oscillate, there is the possibility that the observed oscillation of these bulk diffusion flames could be triggered and sustained by the oscillation of the premixed flame segments. Concerning the observed oscillatory droplet extinction, it is well-known that gas-phase oscillation in heterogeneous burning can be induced by and is thereby coupled with condensed-phase unsteadiness. Consequently, a convincing experiment on diffusion flame oscillation must exclude any ingredients of premixed flames and other sources that may either oscillate themselves or promote the oscillation of the diffusion flame. The present experiment on burner-generated spherical flames with a constant reactant supply endeavored to accomplish this goal. The results are further compared with those from computational simulation for further understanding and quantification of the flame dynamics and extinction.

  3. Gravitational energy in spherical symmetry

    NASA Astrophysics Data System (ADS)

    Hayward, Sean A.

    1996-02-01

    Various properties of the Misner-Sharp spherically symmetric gravitational energy E are established or reviewed. In the Newtonian limit of a perfect fluid, E yields the Newtonian mass to leading order and the Newtonian kinetic and potential energy to the next order. For test particles, the corresponding Hájíček energy is conserved and has the behavior appropriate to energy in the Newtonian and special-relativistic limits. In the small-sphere limit, the leading term in E is the product of volume and the energy density of the matter. In vacuo, E reduces to the Schwarzschild energy. At null and spatial infinity, E reduces to the Bondi-Sachs and Arnowitt-Deser-Misner energies, respectively. The conserved Kodama current has charge E. A sphere is trapped if E>1/2r, marginal if E=1/2r, and untrapped if E<1/2r, where r is the areal radius. A central singularity is spatial and trapped if E>0, and temporal and untrapped if E<0. On an untrapped sphere, E is nondecreasing in any outgoing spatial or null direction, assuming the dominant energy condition. It follows that E>=0 on an untrapped spatial hypersurface with a regular center, and E>=1/2r0 on an untrapped spatial hypersurface bounded at the inward end by a marginal sphere of radius r0. All these inequalities extend to the asymptotic energies, recovering the Bondi-Sachs energy loss and the positivity of the asymptotic energies, as well as proving the conjectured Penrose inequality for black or white holes. Implications for the cosmic censorship hypothesis and for general definitions of gravitational energy are discussed.

  4. Wrinkling crystallography on spherical surfaces

    PubMed Central

    Brojan, Miha; Terwagne, Denis; Lagrange, Romain; Reis, Pedro M.

    2015-01-01

    We present the results of an experimental investigation on the crystallography of the dimpled patterns obtained through wrinkling of a curved elastic system. Our macroscopic samples comprise a thin hemispherical shell bound to an equally curved compliant substrate. Under compression, a crystalline pattern of dimples self-organizes on the surface of the shell. Stresses are relaxed by both out-of-surface buckling and the emergence of defects in the quasi-hexagonal pattern. Three-dimensional scanning is used to digitize the topography. Regarding the dimples as point-like packing units produces spherical Voronoi tessellations with cells that are polydisperse and distorted, away from their regular shapes. We analyze the structure of crystalline defects, as a function of system size. Disclinations are observed and, above a threshold value, dislocations proliferate rapidly with system size. Our samples exhibit striking similarities with other curved crystals of charged particles and colloids. Differences are also found and attributed to the far-from-equilibrium nature of our patterns due to the random and initially frozen material imperfections which act as nucleation points, the presence of a physical boundary which represents an additional source of stress, and the inability of dimples to rearrange during crystallization. Even if we do not have access to the exact form of the interdimple interaction, our experiments suggest a broader generality of previous results of curved crystallography and their robustness on the details of the interaction potential. Furthermore, our findings open the door to future studies on curved crystals far from equilibrium. PMID:25535355

  5. Spherical Shell Vortex Model For Compound Drops

    NASA Astrophysics Data System (ADS)

    Shusser, Michael; Weihs, Daniel

    2003-11-01

    A new generalization of the classical solution for inviscid incompressible flow with vorticity known as Hill's spherical vortex is presented here. The new solution includes a concentric sphere inside the spherical body produced by Hill's vortex. The internal sphere can be filled with a different fluid,with limiting cases of a spherical cavity, or solid sphere. This solution is applicable to coated pill and pellet manfacture.The present solution also includes internal swirling about the axis parallel to the direction of oncoming flow.

  6. Spherical bearing. [to reduce vibration effects

    NASA Technical Reports Server (NTRS)

    Myers, W. N.; Hein, L. A. (Inventor)

    1978-01-01

    A spherical bearing including an inner ball with an opening for receiving a shaft and a spherical outer surface is described. Features of the bearing include: (1) a circular outer race including a plurality of circumferentially spaced sections extending around the inner ball for snugly receiving the inner ball; and (2) a groove extending circumferentially around the race producing a thin wall portion which permits the opposed side portions to flex relative to the ball for maximizing the physical contact between the inner surface of the race and the spherical outer surface of the ball.

  7. The effects of spherical geometry on baroclinic instability

    NASA Technical Reports Server (NTRS)

    Moura, A. D.; Stone, P. H.

    1976-01-01

    A baroclinic stability analysis is performed for a simple family of zonal shear profiles over a sphere, using a two-layer, quasi-geostrophic model. The stability properties and the structure of the most unstable waves are qualitatively similar to those on a beta-plane. However, the spherical geometry plays a major role in locating some of the important features of the most unstable waves. In particular, the locations of the maximum wave amplitude, maximum eddy heat fluxes, and maximum convergence of the eddy angular momentum flux are all well correlated with the location of the maximum excess of the vertical shear over the minimum value necessary for local instability on a sphere. Consequently the eddy momentum flux tends to generate a mid-latitude jet even if there is no preexisting mid-latitude jet in the basic state zonal flow. These findings suggest some of the elements needed for parameterizing the meridional variations of baroclinic eddy fluxes accurately.

  8. The effects of spherical geometry on baroclinic instability

    NASA Technical Reports Server (NTRS)

    Moura, A. D.; Stone, P. H.

    1976-01-01

    A baroclinic stability analysis is performed for a simple family of zonal shear profiles over a sphere, using a two-layer, quasi-geostrophic model. The stability properties and the structure of the most unstable waves are qualitatively similar to those on a beta-plane. However, the spherical geometry plays a major role in locating some of the important features of the most unstable waves. In particular, the locations of the maximum wave amplitude, maximum eddy heat fluxes, and maximum convergence of the eddy angular momentum flux are all well correlated with the location of the maximum excess of the vertical shear over the minimum value necessary for local instability on a sphere. Consequently the eddy momentum flux tends to generate a mid-latitude jet even if there is no preexisting mid-latitude jet in the basic state zonal flow. These findings suggest some of the elements needed for parameterizing the meridional variations of baroclinic eddy fluxes accurately.

  9. Effect of Trapped Energetic Ions on MHD Activity in Spherical Tori

    SciTech Connect

    R.B. White; Ya.I. Kolesnichenko; V.V. Lutsenko; V.S. Marchenko

    2002-05-30

    It is shown that the increase of beta (the ratio of plasma pressure to the magnetic field pressure) may change the character of the influence of trapped energetic ions on MHD stability in spherical tori. Namely, the energetic ions, which stabilize MHD modes (such as the ideal-kink mode, collisionless tearing mode, and semi-collisional tearing mode) at low beta, have a destabilizing influence at high beta unless the radial distribution of the energetic ions is very peaked.

  10. The secondary buckling transition: wrinkling of buckled spherical shells.

    PubMed

    Knoche, Sebastian; Kierfeld, Jan

    2014-07-01

    We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an approximate analytic model due to Pogorelov. In the buckled shape, both approaches exhibit a locally compressive hoop stress in a region where experiments and simulations show the development of polygonal wrinkles, along the dimple edge. In a simplified model based on the stability equations of shallow shells, a critical value for the compressive hoop stress is derived, for which the compressed circumferential fibres will buckle out of their circular shape in order to release the compression. By applying this wrinkling criterion to the solutions of the axisymmetric models, we can calculate the critical volume for the secondary buckling transition. Using the Pogorelov approach, we also obtain an analytical expression for the critical volume at the secondary buckling transition: The critical volume difference scales linearly with the bending stiffness, whereas the critical volume reduction at the classical axisymmetric buckling transition scales with the square root of the bending stiffness. These results are confirmed by another stability analysis in the framework of Donnel, Mushtari and Vlasov (DMV) shell theory, and by numerical simulations available in the literature.

  11. Preparation and characterization of size controllable spherical silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Yang, Ai-ling; Li, Shun-pin; Wang, Yu-jin; Bao, Xi-chang; Yang, Ren-qiang

    2014-05-01

    By adjusting pH values of reactant system, the mass ratio of stabilizer/water and aging temperature, size controllable spherical silver nanoparticles (NPs) were synthesized. The properties of silver NPs are characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and ultraviolet visible (UV-VIS) absorption spectra. Within the pH values of 7.0-11.0, the aging temperature of 80 °C is better to improve silver NPs in shape to nearly sphere, concentrate size distribution and reduce aggregation than the aging temperature of 25 °C. The shape and dispersibility of silver NPs are the best when the pH of the reactant system is within 7.0-8.0. With pH of 7.5, aging at 80 °C, and stabilizer/water mass ratio of 1%, the spherical silver NPs with sizes of 50-70 nm were synthesized. The results are promising to be used to synthesize core/shell NPs when silver NPs are as core.

  12. The buckling of spherical liposomes.

    PubMed

    Pamplona, D C; Greenwood, J A; Calladine, C R

    2005-12-01

    In the classical "first approximation" theory of thin-shell structures, the constitutive relations for a generic shell element--i.e. the elastic relations between the bending moments and membrane stresses and the corresponding changes in curvature and strain, respectively-are written as if an element of the shell is flat, although in reality it is curved. In this theory it is believed that discrepancies on account of the use of "flat" constitutive relations will be negligible provided the ratio shell-radius/thickness is of sufficiently large order. In the study of drawing of narrow, cylindrical "tethers" from liposomes it has been known for many years that it is necessary to use instead a constitutive law which explicitly describes a curved element in order to make sense of the mechanics; and indeed such tethers are generally of "thick-walled" proportions. In this paper we show that the proper constitutive relations for a curved element must also be used in the study, by means of shell equations, of the buckling of initially spherical thin-walled giant liposomes under exterior pressure: these involve the inclusion of what we call the "Mkappa" terms, which are not present in the standard "first-approximation" theory. We obtain analytical expressions for both the bifurcation buckling pressure and the slope of the post-buckling path, in terms of the dimensions and elastic constants of the lipid bi-layer, and also the initial state of bending moment in the vesicle. We explain physically how the initial bending moment can affect the bifurcation pressure, whereas it cannot in "first-approximation" theory. We use these results to map the conditions under which the vesicle buckles into an oblate, as distinct from a prolate ("rugby-ball") shape. Some of our results were obtained long ago by the use of energy methods; but our aim here has been to identify precisely what is lacking in "first-approximation" theory in relation to liposomes, and so to put the "shell equations

  13. How Spherical Is a Cube (Gravitationally)?

    NASA Astrophysics Data System (ADS)

    Sanny, Jeff; Smith, David

    2015-02-01

    An important concept that is presented in the discussion of Newton's law of universal gravitation is that the gravitational effect external to a spherically symmetric mass distribution is the same as if all of the mass of the distribution were concentrated at the center.1,2 By integrating over ring elements of a spherical shell, we show that the gravitational force on a point mass outside the shell is the same as that of a particle with the same mass as the shell at its center. This derivation works for objects with spherical symmetry while depending on the fact that the gravitational force between two point masses varies inversely as the square of their separation.3 If these conditions are not met, then the problem becomes more difficult. In this paper, we remove the condition of spherical symmetry and examine the gravitational force between two uniform cubes.

  14. Sphericity determination using resonant ultrasound spectroscopy

    DOEpatents

    Dixon, Raymond D.; Migliori, Albert; Visscher, William M.

    1994-01-01

    A method is provided for grading production quantities of spherical objects, such as roller balls for bearings. A resonant ultrasound spectrum (RUS) is generated for each spherical object and a set of degenerate sphere-resonance frequencies is identified. From the degenerate sphere-resonance frequencies and known relationships between degenerate sphere-resonance frequencies and Poisson's ratio, a Poisson's ratio can be determined, along with a "best" spherical diameter, to form spherical parameters for the sphere. From the RUS, fine-structure resonant frequency spectra are identified for each degenerate sphere-resonance frequency previously selected. From each fine-structure spectrum and associated sphere parameter values an asphericity value is determined. The asphericity value can then be compared with predetermined values to provide a measure for accepting or rejecting the sphere.

  15. FY 2005 Miniature Spherical Retroreflectors Final Report

    SciTech Connect

    Anheier, Norman C.; Bernacki, Bruce E.; Johnson, Bradley R.; Riley, Brian J.; Sliger, William A.

    2005-12-01

    Research done by the Infrared Photonics team at Pacific Northwest National Laboratory (PNNL) is focused on developing miniature spherical retroreflectors using the unique optical and material properties of chalcogenide glass to reduce both performance limiting spherical and chromatic aberrations. The optimized optical performance will provide efficient signal retroreflection that enables a broad range of remote detection scenarios for mid-wave infrared (MWIR) and long-wave infrared (LWIR) sensing applications. Miniature spherical retroreflectors can be developed to aid in the detection of signatures of nuclear proliferation or other chemical vapor or radiation signatures. Miniature spherical retroreflectors are not only well suited to traditional bistatic LIDAR methods for chemical plume detection and identification, but could enable remote detection of difficult semi-volatile chemical materials or low level radiation sources.

  16. Sphericity determination using resonant ultrasound spectroscopy

    DOEpatents

    Dixon, R.D.; Migliori, A.; Visscher, W.M.

    1994-10-18

    A method is provided for grading production quantities of spherical objects, such as roller balls for bearings. A resonant ultrasound spectrum (RUS) is generated for each spherical object and a set of degenerate sphere-resonance frequencies is identified. From the degenerate sphere-resonance frequencies and known relationships between degenerate sphere-resonance frequencies and Poisson's ratio, a Poisson's ratio can be determined, along with a 'best' spherical diameter, to form spherical parameters for the sphere. From the RUS, fine-structure resonant frequency spectra are identified for each degenerate sphere-resonance frequency previously selected. From each fine-structure spectrum and associated sphere parameter values an asphericity value is determined. The asphericity value can then be compared with predetermined values to provide a measure for accepting or rejecting the sphere. 14 figs.

  17. Spherical operator classification for coronary artery extraction.

    PubMed

    Geng, Chen; Yang, Jian; Dai, Yakang; Liu, Zhaobang; Dong, Yuefang

    2014-01-01

    Computed tomography angiography (CTA) is a major noninvasive technology for imaging coronary artery disease, and effective and accurate vessel tracking method can help radiologists diagnose the disease more accurately. In this paper, a novel 3D vessel tracking method based on CTA data is presented. The method is comprised of preprocessing, a novel spherical operator, and hierarchical clustering, where the spherical operator consists of rays that are casted different directions in a spherical coordinate system. The vascular boundary is extracted by the spherical operator, and the tracking direction is also obtained by the hierarchical clustering. The method is evaluated with the Rotterdam Coronary Artery Algorithm Evaluation Framework. Results indicate that our method outperforms current state-of-the-art methods in terms of the overlap ratio on the vessel tracking of coronary arteries in CTA data.

  18. Feasibility study for the Spherical Torus Experiment

    SciTech Connect

    Lazarus, E.A.; Attenberger, S.E.; Baylor, L.R.; Borowski, S.K.; Brown, R.L.; Carreras, B.A.; Charlton, L.A.; Chipley, K.K.; Dalton, G.R.; Fowler, R.H.

    1985-10-01

    The design of the Spherical Torus Experiment (STX) is discussed. The physics of the plasma are given in a magnetohydrodynamic model. The structural aspects and instrumentation of the device are described. 19 refs., 103 figs. (WRF)

  19. FY 2006 Miniature Spherical Retroreflectors Final Report

    SciTech Connect

    Anheier, Norman C.; Bernacki, Bruce E.; Krishnaswami, Kannan

    2006-12-28

    Research done by the Infrared Photonics team at Pacific Northwest National Laboratory (PNNL) is focused on developing miniature spherical retroreflectors using the unique optical and material properties of chalcogenide glass to reduce both performance limiting spherical aberrations. The optimized optical performance will provide efficient signal retroreflection that enables a broad range of remote detection scenarios for mid-wave infrared (MWIR) and long-wave infrared (LWIR) sensing applications. Miniature spherical retroreflectors can be developed to aid in the detection of signatures of nuclear proliferation or other chemical vapor or radiation signatures. Miniature spherical retroreflectors are not only well suited to traditional LIDAR methods for chemical plume detection and identification, but could enable remote detection of difficult semi-volatile chemical materials or low level radiation sources.

  20. Observation of spherical ion-acoustic solitons

    SciTech Connect

    Nakamura, Y.; Ooyama, M.; Ogino, T.

    1980-11-10

    Spherically converging positive and negative ion-acoustic pulses are investigated experimentally. Their behavior agrees with computer simulations based on the fluid model of plasma. Large positive pulses are identified as solitons.

  1. PREPARATION OF SPHERICAL URANIUM DIOXIDE PARTICLES

    DOEpatents

    Levey, R.P. Jr.; Smith, A.E.

    1963-04-30

    This patent relates to the preparation of high-density, spherical UO/sub 2/ particles 80 to 150 microns in diameter. Sinterable UO/sub 2/ powder is wetted with 3 to 5 weight per cent water and tumbled for at least 48 hours. The resulting spherical particles are then sintered. The sintered particles are useful in dispersion-type fuel elements for nuclear reactors. (AEC)

  2. Localized waves with spherical harmonic symmetries

    NASA Astrophysics Data System (ADS)

    Mills, M. S.; Siviloglou, G. A.; Efremidis, N.; Graf, T.; Wright, E. M.; Moloney, J. V.; Christodoulides, D. N.

    2012-12-01

    We introduce a class of propagation invariant spatiotemporal optical wave packets with spherical harmonic symmetries in their field configurations. The evolution of these light orbitals is considered theoretically in anomalously dispersive media, and their spinning dynamics are analyzed in terms of their corresponding energy flows. Similarly, localized waves generated via spherical superposition from Archimedean and Platonic solids in k⃗-ω space are investigated in this work.

  3. On Nonlinear Functionals of Random Spherical Eigenfunctions

    NASA Astrophysics Data System (ADS)

    Marinucci, Domenico; Wigman, Igor

    2014-05-01

    We prove central limit theorems and Stein-like bounds for the asymptotic behaviour of nonlinear functionals of spherical Gaussian eigenfunctions. Our investigation combines asymptotic analysis of higher order moments for Legendre polynomials and, in addition, recent results on Malliavin calculus and total variation bounds for Gaussian subordinated fields. We discuss applications to geometric functionals like the defect and invariant statistics, e.g., polyspectra of isotropic spherical random fields. Both of these have relevance for applications, especially in an astrophysical environment.

  4. Spherical cows in dark matter indirect detection

    NASA Astrophysics Data System (ADS)

    Bernal, Nicolás; Necib, Lina; Slatyer, Tracy R.

    2016-12-01

    Dark matter (DM) halos have long been known to be triaxial, but in studies of possible annihilation and decay signals they are often treated as approximately spherical. In this work, we examine the asymmetry of potential indirect detection signals of DM annihilation and decay, exploiting the large statistics of the hydrodynamic simulation Illustris. We carefully investigate the effects of the baryons on the sphericity of annihilation and decay signals for both the case where the observer is at 8.5 kpc from the center of the halo (exemplified in the case of Milky Way-like halos), and for an observer situated well outside the halo. In the case of Galactic signals, we find that both annihilation and decay signals are expected to be quite symmetric, with axis ratios very different from 1 occurring rarely. In the case of extragalactic signals, while decay signals are still preferentially spherical, the axis ratio for annihilation signals has a much flatter distribution, with elongated profiles appearing frequently. Many of these elongated profiles are due to large subhalos and/or recent mergers. Comparing to gamma-ray emission from the Milky Way and X-ray maps of clusters, we find that the gamma-ray background appears less spherical/more elongated than the expected DM signal from the large majority of halos, and the Galactic gamma ray excess appears very spherical, while the X-ray data would be difficult to distinguish from a DM signal by elongation/sphericity measurements alone.

  5. Characterization of spherical Si by photoluminescence measurement

    NASA Astrophysics Data System (ADS)

    Nagai, Takehiko; Liu, Zhengxin; Masuda, Atsushi; Kondo, Michio

    2007-05-01

    Spherical silicon (Si) with a size of ˜1mm diameter was fabricated by the dropping method for the applications of spherical Si solar cells. In this research work, we characterized spherical Si by means of photoluminescence (PL) measurement at 4 and 18K. The horn-type spherical Si crystals, formed under large undercooled conditions without a seeding technique, showed D-band luminescence originating from dislocations, whereas intrinsic PL bands of Si were not observed. In contrast, for the tear-type spherical Si crystals, formed under shadow undercooling by a seeding technique with Si powder, the boron (B) bound and Si intrinsic phonon-assisted PL bands were clearly observed both at 4 and 18K. Moreover, the intensity ratio of B bound exciton band to Si intrinsic phonon-assisted PL band showed good correlation to the minority carrier lifetime measured with microwave photoconductance decay method. These experimental results suggested that the crystallinity of the tear-type spherical Si is significantly improved by the seeding technique compared with the horn-type ones, which contain a large amount of B-related defects.

  6. GRACE gravity solutions using a combination of spherical harmonics and surface density grids

    NASA Astrophysics Data System (ADS)

    Lemoine, Jean-Michel; Bourgogne, Stéphane; Biancale, Richard; Bruinsma, Sean

    2017-04-01

    CNES/GRGS has been committed for the last twelve years to computing spherical harmonics models of the Earth gravity field from the GRACE dataset. Due to the tradeoff that has to be found between spatial resolution and stability of the solutions, it is difficult with spherical harmonics to accurately model the strong but narrow signals like, for instance, the ocean-continent gravity contrast along the coastlines. In order to overcome this limitation, CNES/GRGS is exploring, after some other groups ( JPL, GSFC, GET…) but with a slightly different method, the possibility to use surface gravity grids in combination with spherical harmonics for the GRACE solutions. In our case the spherical harmonics model is used for the static part of the gravity field and the direct gravitational attraction of a surface regular grid for the time-varying part. Not ignoring the caveats on the interpretation of EWH or surface mascons raised by Chao (2016), we will present the results obtained from simulation studies and from the use of actual GRACE measurements. In particular a comparison between the "direct attraction" approach and the "energy integral" approach will be made and, in the first case, between a purely spherical harmonics solution and a "spherical harmonics + surface grid" solution.

  7. Summation by parts methods for spherical harmonic decompositions of the wave equation in any dimensions

    NASA Astrophysics Data System (ADS)

    Gundlach, Carsten; Martín-García, José M.; Garfinkle, David

    2013-07-01

    We investigate numerical methods for wave equations in n + 2 spacetime dimensions, written in spherical coordinates, decomposed in spherical harmonics on Sn, and finite-differenced in the remaining coordinates r and t. Such an approach is useful when the full physical problem has spherical symmetry, for perturbation theory about a spherical background, or in the presence of boundaries with spherical topology. The key numerical difficulty arises from lower order 1/r terms at the origin r = 0. As a toy model for this, we consider the flat space linear wave equation in the form \\dot{\\pi }=\\psi ^{\\prime }+p\\psi /r, \\dot{\\psi }=\\pi ^{\\prime }, where p = 2l + n and l is the leading spherical harmonic index. We propose a class of summation by parts (SBP) finite-differencing methods that conserve a discrete energy up to boundary terms, thus guaranteeing stability and convergence in the energy norm. We explicitly construct SBP schemes that are second- and fourth-order accurate at interior points and the symmetry boundary r = 0, and first- and second-order accurate at the outer boundary r = R.

  8. Preparation and Optical Properties of Spherical Inverse Opals by Liquid Phase Deposition Using Spherical Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Aoi, Y.; Tominaga, T.

    2013-03-01

    Titanium dioxide (TiO2) inverse opals in spherical shape were prepared by liquid phase deposition (LPD) using spherical colloidal crystals as templates. Spherical colloidal crystals were produced by ink-jet drying technique. Aqueous emulsion droplets that contain polystyrene latex particles were ejected into air and dried. Closely packed colloidal crystals with spherical shape were obtained. The obtained spherical colloidal crystals were used as templates for the LPD. The templates were dispersed in the deposition solution of the LPD, i.e. a mixed solution of ammonium hexafluorotitanate and boric acid and reacted for 4 h at 30 °C. After the LPD process, the interstitial spaces of the spherical colloidal crystals were completely filled with titanium oxide. Subsequent heat treatment resulted in removal of templates and spherical titanium dioxide inverse opals. The spherical shape of the template was retained. SEM observations indicated that the periodic ordered voids were surrounded by titanium dioxide. The optical reflectance spectra indicated that the optical properties of the spherical titanium dioxide inverse opals were due to Bragg diffractions from the ordered structure. Filling in the voids of the inverse opals with different solvents caused remarkable changes in the reflectance peak.

  9. Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface

    DOE PAGES

    Terrones, Guillermo; Carrara, Mark D.

    2015-05-01

    For a spherical interface of radius R separating two different homogeneous regions of incompressible viscous fluids under the action of a radially directed acceleration, we perform a linear stability analysis in terms of spherical surface harmonics Y n to derive the dispersion relation. The instability behavior is investigated by computing the growth rates and the most-unstable modes as a function of the spherical harmonic degree n. This general methodology is applicable to the entire parameter space spanned by the Atwood number, the viscosity ratio, and the dimensionless number B = (αRΡ²2/μ²²)¹/³ R (where αR, Ρ2 and μ2 are the localmore » radial acceleration at the interface, and the density and viscosity of the denser overlying fluid, respectively). While the mathematical formulation here is general, this paper focuses on instability that arises at a spherical viscous fluid/vacuum interface as there is a great deal to be learned from the effects of one-fluid viscosity and sphericity alone. To quantify and understand the effect that curvature and radial accelerationhave on the Rayleigh-Taylor instability, a comparison of the growth rates, under homologous driving conditions, between the planar and spherical interfaces is performed. The derived dispersion relation for the planar interface accounts for an underlying finite fluid region of thickness L and normal acceleration αR. Under certain conditions, the development of the most-unstable modes at a spherical interface can take place via the superposition of two adjacent spherical harmonics Yn and Yn+1. This bimodality in the evolution of disturbances in the linear regime does not have a counterpart in the planar configuration where the most-unstable modes are associated with a unique wave number.« less

  10. Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface

    SciTech Connect

    Terrones, Guillermo; Carrara, Mark D.

    2015-05-01

    For a spherical interface of radius R separating two different homogeneous regions of incompressible viscous fluids under the action of a radially directed acceleration, we perform a linear stability analysis in terms of spherical surface harmonics Y n to derive the dispersion relation. The instability behavior is investigated by computing the growth rates and the most-unstable modes as a function of the spherical harmonic degree n. This general methodology is applicable to the entire parameter space spanned by the Atwood number, the viscosity ratio, and the dimensionless number B = (αRΡ²2/μ²²/³ R (where αR, Ρ2 and μ2 are the local radial acceleration at the interface, and the density and viscosity of the denser overlying fluid, respectively). While the mathematical formulation here is general, this paper focuses on instability that arises at a spherical viscous fluid/vacuum interface as there is a great deal to be learned from the effects of one-fluid viscosity and sphericity alone. To quantify and understand the effect that curvature and radial accelerationhave on the Rayleigh-Taylor instability, a comparison of the growth rates, under homologous driving conditions, between the planar and spherical interfaces is performed. The derived dispersion relation for the planar interface accounts for an underlying finite fluid region of thickness L and normal acceleration αR. Under certain conditions, the development of the most-unstable modes at a spherical interface can take place via the superposition of two adjacent spherical harmonics Yn and Yn+1. This bimodality in the evolution of disturbances in the linear regime does not have a counterpart in the planar configuration where the most-unstable modes are associated with a unique wave number.

  11. Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface

    NASA Astrophysics Data System (ADS)

    Terrones, Guillermo; Carrara, Mark D.

    2015-05-01

    For a spherical interface of radius R separating two different homogeneous regions of incompressible viscous fluids under the action of a radially directed acceleration, we perform a linear stability analysis in terms of spherical surface harmonics Yn to derive the dispersion relation. The instability behavior is investigated by computing the growth rates and the most-unstable modes as a function of the spherical harmonic degree n. This general methodology is applicable to the entire parameter space spanned by the Atwood number, the viscosity ratio, and the dimensionless number B = ( a R ρ2 2 / μ2 2 ) 1 / 3 R (where aR, ρ2, and μ2 are the local radial acceleration at the interface, and the density and viscosity of the denser overlying fluid, respectively). While the mathematical formulation herein is general, this paper focuses on instability that arises at a spherical viscous fluid/vacuum interface as there is a great deal to be learned from the effects of one-fluid viscosity and sphericity alone. To quantify and understand the effect that curvature and radial acceleration have on the Rayleigh-Taylor instability, a comparison of the growth rates, under homologous driving conditions, between the planar and spherical interfaces is performed. The derived dispersion relation for the planar interface accounts for an underlying finite fluid region of thickness L and normal acceleration aR. Under certain conditions, the development of the most-unstable modes at a spherical interface can take place via the superposition of two adjacent spherical harmonics Yn and Yn+1. This bimodality in the evolution of disturbances in the linear regime does not have a counterpart in the planar configuration where the most-unstable modes are associated with a unique wave number.

  12. Progress Towards High Performance, Steady-state Spherical Torus

    SciTech Connect

    M. Ono; M.G. Bell; R.E. Bell; T. Bigelow; M. Bitter; W. Blanchard; J. Boedo; C. Bourdelle; C. Bush; W. Choe; J. Chrzanowski; D.S. Darrow; S.J. Diem; R. Doerner; P.C. Efthimion; J.R. Ferron; R.J. Fonck; E.D. Fredrickson; G.D. Garstka; D.A. Gates; T. Gray; L.R. Grisham; W. Heidbrink; K.W. Hill; D. Hoffman; T.R. Jarboe; D.W. Johnson; R. Kaita; S.M. Kaye; C. Kessel; J.H. Kim; M.W. Kissick; S. Kubota; H.W. Kugel; B.P. LeBlanc; K. Lee; S.G. Lee; B.T. Lewicki; S. Luckhardt; R. Maingi; R. Majeski; J. Manickam; R. Maqueda; T.K. Mau; E. Mazzucato; S.S. Medley; J. Menard; D. Mueller; B.A. Nelson; C. Neumeyer; N. Nishino; C.N. Ostrander; D. Pacella; F. Paoletti; H.K. Park; W. Park; S.F. Paul; Y.-K. M. Peng; C.K. Phillips; R. Pinsker; P.H. Probert; S. Ramakrishnan; R. Raman; M. Redi; A.L. Roquemore; A. Rosenberg; P.M. Ryan; S.A. Sabbagh; M. Schaffer; R.J. Schooff; R. Seraydarian; C.H. Skinner; A.C. Sontag; V. Soukhanovskii; J. Spaleta; T. Stevenson; D. Stutman; D.W. Swain; E. Synakowski; Y. Takase; X. Tang; G. Taylor; J. Timberlake; K.L. Tritz; E.A. Unterberg; A. Von Halle; J. Wilgen; M. Williams; J.R. Wilson; X. Xu; S.J. Zweben; R. Akers; R.E. Barry; P. Beiersdorfer; J.M. Bialek; B. Blagojevic; P.T. Bonoli; M.D. Carter; W. Davis; B. Deng; L. Dudek; J. Egedal; R. Ellis; M. Finkenthal; J. Foley; E. Fredd; A. Glasser; T. Gibney; M. Gilmore; R.J. Goldston; R.E. Hatcher; R.J. Hawryluk; W. Houlberg; R. Harvey; S.C. Jardin; J.C. Hosea; H. Ji; M. Kalish; J. Lowrance; L.L. Lao; F.M. Levinton; N.C. Luhmann; R. Marsala; D. Mastravito; M.M. Menon; O. Mitarai; M. Nagata; G. Oliaro; R. Parsells; T. Peebles; B. Peneflor; D. Piglowski; G.D. Porter; A.K. Ram; M. Rensink; G. Rewoldt; P. Roney; K. Shaing; S. Shiraiwa; P. Sichta; D. Stotler; B.C. Stratton; R. Vero; W.R. Wampler; G.A. Wurden

    2003-10-02

    Research on the Spherical Torus (or Spherical Tokamak) is being pursued to explore the scientific benefits of modifying the field line structure from that in more moderate aspect-ratio devices, such as the conventional tokamak. The Spherical Tours (ST) experiments are being conducted in various U.S. research facilities including the MA-class National Spherical Torus Experiment (NSTX) at Princeton, and three medium-size ST research facilities: Pegasus at University of Wisconsin, HIT-II at University of Washington, and CDX-U at Princeton. In the context of the fusion energy development path being formulated in the U.S., an ST-based Component Test Facility (CTF) and, ultimately a Demo device, are being discussed. For these, it is essential to develop high-performance, steady-state operational scenarios. The relevant scientific issues are energy confinement, MHD stability at high beta (B), noninductive sustainment, ohmic-solenoid-free start-up, and power and particle handling. In the confinement area, the NSTX experiments have shown that the confinement can be up to 50% better than the ITER-98-pby2 H-mode scaling, consistent with the requirements for an ST-based CTF and Demo. In NSTX, CTF-relevant average toroidal beta values bT of up to 35% with the near unity central betaT have been obtained. NSTX will be exploring advanced regimes where bT up to 40% can be sustained through active stabilization of resistive wall modes. To date, the most successful technique for noninductive sustainment in NSTX is the high beta-poloidal regime, where discharges with a high noninductive fraction ({approx}60% bootstrap current + neutral-beam-injected current drive) were sustained over the resistive skin time. Research on radio-frequency-based heating and current drive utilizing HHFW (High Harmonic Fast Wave) and EBW (Electron Bernstein Wave) is also pursued on NSTX, Pegasus, and CDX-U. For noninductive start-up, the Coaxial Helicity Injection (CHI), developed in HIT/HIT-II, has been

  13. Competitive interaction between two different spherical sinks

    NASA Astrophysics Data System (ADS)

    McDonald, Nyrée; Strieder, William

    2004-10-01

    Competitive interactions within diverse mixed populations of chemically active sites are prevalent throughout nature, science, and engineering. Their effects are readily seen in the distribution of dead and surviving aerobic cells within a thick biofilm and particle shape changes during the growth and coarsening of crystals. Even in the most dilute case, competition for a reactant requires at least two spheres/cells, and the solution of the two-spherical sink problem is of interest for several reasons. The solution accurately describes lower cell concentration behavior (108 cells/l), and like the Smoluchowski diffusion-reaction treatment for a single sphere, the analysis is extremely helpful in understanding the fundamental phenomena of the effect on the first spherical sink of the presence of a second different spherical sink. In addition these exact solutions are required for the systematic extension to higher density behavior by rigorous expansions in the spherical sink densities. The method of the twin spherical expansion is used with a formal matrix elimination scheme to generate an exact solution for two distinct spherical sinks of differing sizes and kinetics. The two sinks exist in a medium, which supplies a reactant to the sinks via Fickian diffusion. The two sinks compete for the same reactant with different first-order reactions occurring at the surface of each sink. Earlier work focused on two spherical sinks of the same size with identical surface reaction kinetics. This work has been advanced to allow for diversity in the theory of cellular or reactive sink competition. A number of interesting higher order interactive phenomena are observed in this paper when the different reactive sinks are in close proximity.

  14. Models of spherical shells as sources of Majumdar-Papapetrou type spacetimes

    NASA Astrophysics Data System (ADS)

    García-Reyes, Gonzalo

    2017-03-01

    By starting with a seed Newtonian potential-density pair we construct relativistic thick spherical shell models for a Majumdar-Papapetrou type conformastatic spacetime. As a simple example, we considerer a family of Plummer-Hernquist type relativistic spherical shells. As a second application, these structures are then used to model a system composite by a dust disk and a halo of matter. We study the equatorial circular motion of test particles around such configurations. Also the stability of the orbits is analyzed for radial perturbation using an extension of the Rayleigh criterion. The models considered satisfying all the energy conditions.

  15. Spherical Harmonic Analysis via Bayesian Inference

    NASA Astrophysics Data System (ADS)

    Muir, J. B.; Tkalcic, H.

    2014-12-01

    The real spherical harmonics form a compact, simple and commonly used set of basis functions for describing fields in tomographic inverse problems. It is therefore often useful to perform spherical harmonic analysis on data to represent it in the spherical harmonic parametrisation. Most existing algorithms, based on Fourier transforms, require that data be interpolated to a regular grid; this is not appropriate for the sparse, irregularly distributed data found in many geophysical applications. Instead, this work casts the problem of spherical harmonic analysis as an inverse problem, and applies the methods of Bayesian inference to overcome regularization problems in the inversion. This allows irregular data to be easily handled, and directly provides error estimates for the inverted spherical harmonic parameters. Synthetic tests have shown that this method easily handles relatively large amounts of added Gaussian noise. So far, this method has been applied to estimate the power in each harmonic degree for tomographic maps of the deep mantle based on PKP-PKIKP and PcP-P differential travel times, showing that they agree at global length scales despite local heterogeneity results being heavily influenced by data coverage. This potentially allows for simple heuristic arguments to constrain the global variation in core-mantle boundary topography based on the similarity between PKP and PcP derived tomographic maps.

  16. ELSA- The European Levitated Spherical Actruator

    NASA Astrophysics Data System (ADS)

    Ruiz, M.; Serin, J.; Telteu-Nedelcu, D.; De La Vallee Poussin, H.; Onillon, E.; Rossini, L.

    2014-08-01

    The reaction sphere is a magnetic bearing spherical actuator consisting of a permanent magnet spherical rotor that can be accelerated in any direction. It consists of an 8-pole permanent magnet spherical rotor that is magnetically levitated and can be accelerated about any axis by a 20-pole stator with electromagnets. The spherical actuator is proposed as a potential alternative to traditional momentum exchange devices such as reaction wheels (RWs) or control moment gyroscopes (CMGs). This new actuator provides several benefits such as reduced mass and power supply allocated to the attitude and navigation unit, performance gain, and improved reliability due to the absence of mechanical bearings. The paper presents the work done on the levitated spherical actuator and more precisely the electrical drive including its control unit and power parts. An elegant breadboard is currently being manufactured within the frame of an FP7 project. This project also comprises a feasibility study to show the feasibility of integrating such a system on a flight platform and to identify all the challenges to be solved in terms of technology or components to be developed.

  17. Tensor Spherical and Pseudo-Spherical Harmonics in Four-Dimensional Spaces

    NASA Astrophysics Data System (ADS)

    Tomita, K.

    1982-07-01

    Explicit expressions for tensor spherical harmonics on the 3 sphere in the four-dimensional Euclidean space are derived, and extended to derive those for pseudo-spherical harmonics. They are useful for the analyses of large-scale perturbations in the Friedmann universe models.

  18. A charged fusion product diagnostic for a spherical tokamak

    NASA Astrophysics Data System (ADS)

    Perez, Ramona Leticia Valenzuela

    Designs for future nuclear fusion power reactors rely on the ability to create a stable plasma (hot ionized gas of hydrogen isotopes) as a medium with which to sustain nuclear fusion reactions. My dissertation work involves designing, constructing, testing, installing, operating, and validating a new diagnostic for spherical tokamaks, a type of reactor test facility. Through detecting charged particles emitted from the plasma, this instrument can be used to study fusion reaction rates within the plasma and how they are affected by plasma perturbations. Quantitatively assessing nuclear fusion reaction rates at specific locations inside the plasma and as a function of time can provide valuable data that can be used to evaluate theory-based simulations related to energy transport and plasma stability. The Proton Detector (PD), installed in the Mega Amp Spherical Tokamak (MAST) at the Culham Centre for Fusion Energy (CCFE) in Abingdon, England, was the first instrument to experimentally detect 3 MeV Protons and 1 MeV Tritons created from deuterium- deuterium (hydrogen isotopes) nuclear fusion reactions inside a spherical tokamak's plasma. The PD consists of an array of particle detectors with a protective housing and the necessary signal conditioning electronics and readout. After several years of designing (which included simulations for detector orientations), fabricating, and testing the PD, it was installed in MAST and data were collected over a period of two months in the summer of 2013. Proton and triton rates as high as 200 kHz were measured and an initial radial profile of these fusion reaction rates inside the plasma was extracted. These results will be compared to a complementary instrument at MAST as well as theory-based simulations and form the knowledge basis for developing a larger future instrument. The design and performance of all instrument components (electrical, computational, mechanical), and subsequent data analysis methods and results are

  19. Static spherically symmetric wormholes with isotropic pressure

    NASA Astrophysics Data System (ADS)

    Cataldo, Mauricio; Liempi, Luis; Rodríguez, Pablo

    2016-06-01

    In this paper we study static spherically symmetric wormhole solutions sustained by matter sources with isotropic pressure. We show that such spherical wormholes do not exist in the framework of zero-tidal-force wormholes. On the other hand, it is shown that for the often used power-law shape function there are no spherically symmetric traversable wormholes sustained by sources with a linear equation of state p = ωρ for the isotropic pressure, independently of the form of the redshift function ϕ (r). We consider a solution obtained by Tolman at 1939 for describing static spheres of isotropic fluids, and show that it also may describe wormhole spacetimes with a power-law redshift function, which leads to a polynomial shape function, generalizing a power-law shape function, and inducing a solid angle deficit.

  20. The spherically symmetric Standard Model with gravity

    NASA Astrophysics Data System (ADS)

    Balasin, H.; Böhmer, C. G.; Grumiller, D.

    2005-08-01

    Spherical reduction of generic four-dimensional theories is revisited. Three different notions of "spherical symmetry" are defined. The following sectors are investigated: Einstein-Cartan theory, spinors, (non-)abelian gauge fields and scalar fields. In each sector a different formalism seems to be most convenient: the Cartan formulation of gravity works best in the purely gravitational sector, the Einstein formulation is convenient for the Yang-Mills sector and for reducing scalar fields, and the Newman-Penrose formalism seems to be the most transparent one in the fermionic sector. Combining them the spherically reduced Standard Model of particle physics together with the usually omitted gravity part can be presented as a two-dimensional (dilaton gravity) theory.

  1. Electromagnetic cloaking in higher order spherical cloaks

    NASA Astrophysics Data System (ADS)

    Sidhwa, H. H.; Aiyar, R. P. R. C.; Kulkarni, S. V.

    2017-06-01

    The inception of transformation optics has led to the realisation of the invisibility devices for various applications, one of which is spherical cloaking. In this paper, a formulation for a higher-order spherical cloak has been proposed to reduce its physical thickness significantly by introducing a nonlinear relation between the original and transformed coordinate systems and it has been verified using the ray tracing approach. Analysis has been carried out to observe the anomalies in the variation of refractive index for higher order cloaks indicating the presence of poles in the relevant equations. Furthermore, a higher-order spherical cloak with predefined values of the material characteristics on its inner and outer surfaces has been designed for practical application.

  2. Thermal Fluid Multiphysics Optimization of Spherical Tokamak

    SciTech Connect

    Lumsdaine, Arnold; Tipton, Joseph B; Peng, Yueng Kay Martin

    2012-01-01

    An experimental Fusion Nuclear Science Facility (FNSF) is required that will create the environment that simultaneously achieves high energy neutrons and high ion fluence necessary in order to bridge the gaps from ITER to the realization of a fusion nuclear power plant. One concept for achieving this is a high duty cycle spherical torus. This study will focus on thermal modeling of the spherical torus centerpost using computational fluid dynamics to effectively model the thermal transfer of the cooling fluid to the centerpost. The design of the fluid channels is optimized in order to minimize the temperature in the centerpost. Results indicate the feasibility of water cooling for a long-pulse spherical torus FNSF.

  3. Elastic properties of spherically anisotropic piezoelectric composites

    NASA Astrophysics Data System (ADS)

    Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming

    2010-09-01

    Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed.

  4. The ESSA solution. [Electronic Switching Spherical Array

    NASA Technical Reports Server (NTRS)

    Hockensmith, R. P.; Stockton, R.

    1977-01-01

    ESSA (Electronic Switching Spherical Array) is a fixed truncated spherical antenna with its elements over the complete surface, conceived to satisfy many future antenna system requirements. Constant gain and beam shape throughout large volumetric coverage regions are the principle characteristics. In the present paper, the two existing types of ESSA are discussed. ESSA I is a simple nonphase correcting aperture approach characterized by light weight, low dc power consumption, gain between +7 and +14 dB, and 90% spherical coverage. ESSA II is a phase corrected aperture which would have very low sidelobe levels and improved gain over ESSA I (12 to 22 dB), but would be heavier and require more dc power.

  5. Design and implementation of spherical ultrasonic motor.

    PubMed

    Mashimo, Tomoaki; Toyama, Shigeki; Ishida, Hiroshi

    2009-11-01

    We present a mechanical design and implementation of spherical ultrasonic motor (SUSM) that is an actuator with multiple rotational degrees of freedom (multi-DOF). The motor is constructed of 3 annular stators and a spherical rotor and is much smaller and simpler than conventional multi-DOF mechanisms such as gimbals using servomotors. We designed a novel SUSM using experimental data from a single annular stator and a finite element method. The SUSM using a spherical rotor of diameter 20 mm without any reduction gear has demonstrated advantages of high responsiveness, good accuracy, and high torque at low speed. The dynamic implementation of SUSM was consistent with the driving model of SUSM based on a friction drive.

  6. Background reduction of a spherical gaseous detector

    SciTech Connect

    Fard, Ali Dastgheibi; Loaiza, Pia; Piquemal, Fabrice; Giomataris, Ioannis; Gray, David; Gros, Michel; Magnier, Patrick; Navick, Xavier-François

    2015-08-17

    The Spherical gaseous detector (or Spherical Proportional Counter, SPC) is a novel type of detector. It consists of a large spherical volume filled with gas, using a single detection readout channel. The detector allows 100 % detection efficiency. SEDINE is a low background version of SPC installed at the Laboratoire Souterrain de Modane (LSM) underground laboratory (4800 m.w.e) looking for rare events at very low energy threshold, below 100 eV. This work presents the details on the chemical cleaning to reduce internal {sup 210}Pb surface contamination on the copper vessel and the external radon reduction achieved via circulation of pure air inside anti-radon tent. It will be also show the radon measurement of pure gases (Ar, N, Ne, etc) which are used in the underground laboratory for the low background experiments.

  7. Background reduction of a spherical gaseous detector

    NASA Astrophysics Data System (ADS)

    Fard, Ali Dastgheibi; Loaiza, Pia; Piquemal, Fabrice; Giomataris, Ioannis; Gray, David; Gros, Michel; Magnier, Patrick; Navick, Xavier-François; Savvidis, Ilias

    2015-08-01

    The Spherical gaseous detector (or Spherical Proportional Counter, SPC) is a novel type of detector. It consists of a large spherical volume filled with gas, using a single detection readout channel. The detector allows 100 % detection efficiency. SEDINE is a low background version of SPC installed at the Laboratoire Souterrain de Modane (LSM) underground laboratory (4800 m.w.e) looking for rare events at very low energy threshold, below 100 eV. This work presents the details on the chemical cleaning to reduce internal 210Pb surface contamination on the copper vessel and the external radon reduction achieved via circulation of pure air inside anti-radon tent. It will be also show the radon measurement of pure gases (Ar, N, Ne, etc) which are used in the underground laboratory for the low background experiments.

  8. Spherical aberration in electrically thin flat lenses.

    PubMed

    Ruphuy, Miguel; Ramahi, Omar M

    2016-08-01

    We analyze the spherical aberration of a new generation of lenses made of flat electrically thin inhomogeneous media. For such lenses, spherical aberration is analyzed quantitatively and qualitatively, and comparison is made to the classical gradient index rod. Both flat thin and thick lenses are made of gradient index materials, but the physical mechanisms and design equations are different. Using full-wave three-dimensional numerical simulation, we evaluate the spherical aberrations using the Maréchal criterion and show that the thin lens gives significantly better performance than the thick lens (rod). Additionally, based on ray tracing formulation, third-order analysis for longitudinal aberration and optical path difference are presented, showing strong overall performance of thin lenses in comparison to classical rod lenses.

  9. ELM Suppression through density profile modification with lithium wall coatings in the National Spherical Torus Experiment

    SciTech Connect

    Maingi, Rajesh; Osborne, T.; LeBlanc, B; Bell, R. E.; Manickam, J.; Snyder, P.; Menard, J.; Mansfield, D.K.; Kugel, H.; Kaita, R.; Gerhardt, S.P.; Sabbagh, S. A.; Kelly, F.A.

    2009-01-01

    Reduction or elimination of edge localized modes (ELMs) while maintaining high confinement is essential for future fusion devices, e.g. the ITER. An ELM-free regime was recently obtained in the National Spherical Torus Experiment, following lithium (li) evaporation onto the plasma facing components. Edge stability calculations indicate that the pre-li discharges were unstable to low-n peeling/ballooning modes, while broader pressure profiles stabilized the post-li discharges. Normalized energy confinement increased by 50% post-li, with no sign of ELMs up to the global stability limit.

  10. Glass formation and properties in the gallia-calcia system

    NASA Technical Reports Server (NTRS)

    Whichard, G.; Day, D. E.

    1984-01-01

    The critical cooling rate for glass formation was measured for five compositions in the Ga2O3-CaO system and varied from a low of (315 + or - 85) C/s for a eutectic melt containing 37.5 mol pct Ga2O3 to a high of (840 + or - 60) C/s for a melt containing 52 mol pct Ga2O3. The density and refractive index both increased with increasing Ga2O3 content, but the crystallization temperature and microhardness varied only slightly. The IR spectra of these glasses suggest that both GaO4 tetrahedra and GaO6 octahedra are present.

  11. Spherical aberrations of human astigmatic corneas.

    PubMed

    Zhao, Huawei; Dai, Guang-Ming; Chen, Li; Weeber, Henk A; Piers, Patricia A

    2011-11-01

    To evaluate whether the average spherical aberration of human astigmatic corneas is statistically equivalent to human nonastigmatic corneas. Spherical aberrations of 445 astigmatic corneas prior to laser vision correction were retrospectively investigated to determine Zernike coefficients for central corneal areas 6 mm in diameter using CTView (Sarver and Associates). Data were divided into groups according to cylinder power (0.01 to 0.25 diopters [D], 0.26 to 0.75 D, 0.76 to 1.06 D, 1.07 to 1.53 D, 1.54 to 2.00 D, and >2.00 D) and according to age by decade. Spherical aberrations were correlated with age and astigmatic power among groups and the entire population. Statistical analyses were conducted, and P<.05 was considered statistically significant. Mean patient age was 42.6±11 years. Astigmatic corneas had an average astigmatic power of 0.78±0.58 D and mean spherical aberration was 0.25±0.13 μm for the entire population and approximately the same (0.27 μm) for individual groups, ranging from 0.23 to 0.29 μm (P>.05 for all tested groups). Mean spherical aberration of astigmatic corneas was not correlated significantly with cylinder power or age (P>.05). Spherical aberrations are similar to those of nonastigmatic corneas, permitting the use of these additional data in the design of aspheric toric intra-ocular lenses. Copyright 2011, SLACK Incorporated.

  12. Toroidal membrane vesicles in spherical confinement

    NASA Astrophysics Data System (ADS)

    Bouzar, Lila; Menas, Ferhat; Müller, Martin Michael

    2015-09-01

    We investigate the morphology of a toroidal fluid membrane vesicle confined inside a spherical container. The equilibrium shapes are assembled in a geometrical phase diagram as a function of scaled area and reduced volume of the membrane. For small area the vesicle can adopt its free form. When increasing the area, the membrane cannot avoid contact and touches the confining sphere along a circular contact line, which extends to a zone of contact for higher area. The elastic energies of the equilibrium shapes are compared to those of their confined counterparts of spherical topology to predict under which conditions a topology change is favored energetically.

  13. Density Profile of Spherical Polymer Brushes

    NASA Astrophysics Data System (ADS)

    Förster, S.; Wenz, E.; Lindner, P.

    1996-07-01

    Small angle neutron scattering measurements were made on a series of block copolymer micelles that represent model systems for spherical polymer brushes. We find hyperbolic density profiles of the form r-α with values of α between 1.05 and 1.35. This as well as the scaling of the brush height with the aggregation number f are in agreement with the model proposed by Daoud and Cotton [J. Phys. (Paris) 43, 531 (1982)] for unswollen and swollen spherical polymer brushes.

  14. Toroidal membrane vesicles in spherical confinement.

    PubMed

    Bouzar, Lila; Menas, Ferhat; Müller, Martin Michael

    2015-09-01

    We investigate the morphology of a toroidal fluid membrane vesicle confined inside a spherical container. The equilibrium shapes are assembled in a geometrical phase diagram as a function of scaled area and reduced volume of the membrane. For small area the vesicle can adopt its free form. When increasing the area, the membrane cannot avoid contact and touches the confining sphere along a circular contact line, which extends to a zone of contact for higher area. The elastic energies of the equilibrium shapes are compared to those of their confined counterparts of spherical topology to predict under which conditions a topology change is favored energetically.

  15. Spherical harmonic analysis of steady photospheric flows

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    1987-01-01

    A technique is presented in which full disk Doppler velocity measurements are analyzed using spherical harmonic functions to determine the characteristics of the spectrum of spherical harmonic modes and the nature of steady photospheric flows. Synthetic data are constructed in order to test the technique. In spite of the mode mixing due to the lack of information about the motions on the backside of the sun, solar rotation and differential rotation can be accurately measured and monitored for secular changes, and meridional circulations with small amplitudes can be measured. Furthermore, limb shift measurements can be accurately obtained, and supergranules can be fully resolved and separated from giant cells by their spatial characteristics.

  16. The defect variance of random spherical harmonics

    NASA Astrophysics Data System (ADS)

    Marinucci, Domenico; Wigman, Igor

    2011-09-01

    The defect of a function f:M\\rightarrow {R} is defined as the difference between the measure of the positive and negative regions. In this paper, we begin the analysis of the distribution of defect of random Gaussian spherical harmonics. By an easy argument, the defect is non-trivial only for even degree and the expected value always vanishes. Our principal result is evaluating the defect variance, asymptotically in the high-frequency limit. As other geometric functionals of random eigenfunctions, the defect may be used as a tool to probe the statistical properties of spherical random fields, a topic of great interest for modern cosmological data analysis.

  17. A Spherical Electro Optic High Voltage Sensor

    DTIC Science & Technology

    1989-06-01

    electro - optic (EO) crystal is introduced for photonic measurement of pulsed high-voltage fields. A spherical shape is used in order to reduce electric field gradients in the vicinity of the sensor. The sensor is pure dielectric and is interrogated remotely using a laser. The sensor does not require the connection of any conducting components, which results in the highest electrical isolation. The spherical nature of the crystal coupled with the incident laser beam, and crossed polarizers (intensity modulation scheme). automatically produces interference figures. The

  18. Spherical target experiments at KMS Fusion

    SciTech Connect

    Slater, D.C.; Tarvin, J.A.; Charatis, G.; Rockett, P.D.; Shepard, C.L.; Johnson, R.R.; Larsen, J.T.; Fechner, W.; Berger, R.L.

    1982-01-01

    KMS Fusion is currently performing a set of spherical target experiments designed to evaluate the effectiveness of three techniques for achieving higher convergence implosions. They are: (1) cryogenically frozen fuel layers; (2) submicron wavelength laser light; and (3) temporally tailored pulse shapes. A second set of experiments provides information about energy transport by thermal and suprathermal electrons and uses multilayered targets as an integral component of the diagnostics. These results, in conjunction with existing laser-target coupling data, will provide a very comprehensive test of our understanding of laser plasma interaction, energy transport, and hydrodynamic response of small scale spherical laser fusion experiments.

  19. Design of artificial spherical superposition compound eye

    NASA Astrophysics Data System (ADS)

    Cao, Zhaolou; Zhai, Chunjie; Wang, Keyi

    2015-12-01

    In this research, design of artificial spherical superposition compound eye is presented. The imaging system consists of three layers of lens arrays. In each channel, two lenses are designed to control the angular magnification and a field lens is added to improve the image quality and extend the field of view. Aspherical surfaces are introduced to improve the image quality. Ray tracing results demonstrate that the light from the same object point is focused at the same imaging point through different channels. Therefore the system has much higher energy efficiency than conventional spherical apposition compound eye.

  20. Inflation in spherically symmetric inhomogeneous models

    SciTech Connect

    Stein-Schabes, J.A.

    1986-11-01

    Exact analytical solutions of Einstein's equations are found for a spherically symmetric inhomogeneous metric in the presence of a massless scalar field with a flat potential. The process of isotropization and homogenization is studied in detail. It is found that the time dependence of the metric becomes de Sitter for large times. Two cases are studied. The first deals with a homogeneous scalar field, while the second with a spherically symmetric inhomogeneous scalar field. In the former case the metric is of the Robertson-Walker form, while the latter is intrinsically inhomogeneous. 16 refs.

  1. Direct-illumination spherical-target experiments

    SciTech Connect

    Johnson, R.R.

    1982-01-01

    A set of spherical target experiments was designed to evaluate the effectiveness of three techniques for achieving higher convergence implosions. They are (1) cryogenically frozen fuel layers, (2) submicron wavelength laser light, and (3) temporally tailored pulse shapes. A second set of experiments provides information about energy transport by thermal and suprathermal electrons and uses multilayered targets as an integral component of the diagnostics. These results, in conjunction with existing laser-target coupling data, provide a more comprehensive test of our understanding of laser plasma interaction, energy transport, and hydrodynamic response of small scale spherical laser fusion experiments.

  2. Spherical quartz crystals investigated with synchrotron radiation

    SciTech Connect

    Pereira, N. R.; Macrander, A. T.; Hill, K. W.; Baronova, E. O.; George, K. M.; Kotick, J.

    2015-10-15

    The quality of x-ray spectra and images obtained from plasmas with spherically bent crystals depends in part on the crystal’s x-ray diffraction across the entire crystal surface. We employ the energy selectivity and high intensity of synchrotron radiation to examine typical spherical crystals from alpha-quartz for their diffraction quality, in a perpendicular geometry that is particularly convenient to examine sagittal focusing. The crystal’s local diffraction is not ideal: the most noticeable problems come from isolated regions that so far have failed to correlate with visible imperfections. Excluding diffraction from such problem spots has little effect on the focus beyond a decrease in background.

  3. Spherical collapse in quintessence models with zero speed of sound

    SciTech Connect

    Creminelli, Paolo; D'Amico, Guido; Noreña, Jorge; Senatore, Leonardo; Vernizzi, Filippo E-mail: norena@sissa.it E-mail: senatore@ias.edu

    2010-03-01

    We study the spherical collapse model in the presence of quintessence with negligible speed of sound. This case is particularly motivated for w < −1 as it is required by stability. As pressure gradients are negligible, quintessence follows dark matter during the collapse. The spherical overdensity behaves as a separate closed FLRW universe, so that its evolution can be studied exactly. We derive the critical overdensity for collapse and we use the extended Press-Schechter theory to study how the clustering of quintessence affects the dark matter mass function. The effect is dominated by the modification of the linear dark matter growth function. A larger effect occurs on the total mass function, which includes the quintessence overdensities. Indeed, here quintessence constitutes a third component of virialized objects, together with baryons and dark matter, and contributes to the total halo mass by a fraction ∼ (1+w)Ω{sub Q}/Ω{sub m}. This gives a distinctive modification of the total mass function at low redshift.

  4. Excitonic transitions in spherical inhomogeneous QD, new monocolor nanosource

    NASA Astrophysics Data System (ADS)

    Benhaddou, F.; Zorkani, I.; Jorio, A.; Feddi, E.

    2015-11-01

    We study in this investigation the excitonic transitions in new spherical nanosystems also called inhomogeneous quantum dots IQD. They are promising in many technological applications: photovoltaic, LED, QD Laser and quantum computing. The excitonic binding energy significantly increases; which gives them greater stability at room temperature. The well-semiconductors in these nanostructures become luminescent under dual control core-well, in a wide spectral range from near UV to near and medium infrared IR. These optical properties enriched the field of IQD which generally have a high quantum efficiency and high photostability. The IQD presented are made out off ZnSe/HgS/ZnSe; CdS/GaSb/CdS; ZnS/HgS/ZnS and CdS/InSb/CdS modeled by a spherical well with infinite potential. Our theoretical investigation shows that the high degree of confinement in the well retains the 1 se - 1 pe - 2 se (1 sh - 1 ph - 2 sh) order, guarantees excitonic transitions and isolates the ground state 1 se - 1 sh (E2se,h - E1pe,h can be exceed 6 eV). The strong confinement provided by the infinite barrier, reduces the population relaxation and limit the coupling between the well and the electrostatic environment. These results qualify the nanostructure as a monocolor source and a system of two levels.

  5. Divertor Heat Flux Mitigation in the National Spherical Torus Experiment

    SciTech Connect

    Soukhanovskii, V A; Maingi, R; Gates, D A; Menard, J E; Paul, S F; Raman, R; Roquemore, A L; Bell, M G; Bell, R E; Boedo, J A; Bush, C E; Kaita, R; Kugel, H W; LeBlanc, B P; Mueller, D

    2008-08-04

    Steady-state handling of divertor heat flux is a critical issue for both ITER and spherical torus-based devices with compact high power density divertors. Significant reduction of heat flux to the divertor plate has been achieved simultaneously with favorable core and pedestal confinement and stability properties in a highly-shaped lower single null configuration in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 2000] using high magnetic flux expansion at the divertor strike point and the radiative divertor technique. A partial detachment of the outer strike point was achieved with divertor deuterium injection leading to peak flux reduction from 4-6 MW m{sup -2} to 0.5-2 MW m{sup -2} in small-ELM 0.8-1.0 MA, 4-6 MW neutral beam injection-heated H-mode discharges. A self-consistent picture of outer strike point partial detachment was evident from divertor heat flux profiles and recombination, particle flux and neutral pressure measurements. Analytic scrape-off layer parallel transport models were used for interpretation of NSTX detachment experiments. The modeling showed that the observed peak heat flux reduction and detachment are possible with high radiated power and momentum loss fractions, achievable with divertor gas injection, and nearly impossible to achieve with main electron density, divertor neutral density or recombination increases alone.

  6. Simulation on the aggregation process of spherical particle confined in a spherical shell

    NASA Astrophysics Data System (ADS)

    Wang, J.; Xu, J. J.; Zhang, L.

    2016-04-01

    The aggregation process of spherical particles confined in a spherical shell was studied by using a diffusion-limited cluster-cluster aggregation (DLCA) model. The influence of geometrical confinement and wetting-like properties of the spherical shell walls on the particle concentration profile, aggregate structure and aggregation kinetics had been explored. The results show that there will be either depletion or absorption particles near the shell walls depending on the wall properties. It is observed that there are four different types of density distribution which can be realized by modifying the property of the inner or outer spherical shell wall. In addition, the aggregate structure will become more compact in the confined spherical shell comparing to bulk system with the same particle volume fraction. The analysis on the aggregation kinetics indicates that geometrical confinement will promote the aggregation process by reducing the invalid movement of the small aggregates and by constraining the movement of those large aggregates. Due to the concave geometrical characteristic of the outer wall of the spherical shell, its effects on the aggregating kinetics and the structure of the formed aggregates are more evident than those of the inner wall. This study will provide some instructive information of controlling the density distribution of low-density porous polymer hollow spherical shells and helps to predict gel structures developed in confined geometries.

  7. The Hadley and Rossby regimes in a spherical atmosphere

    NASA Technical Reports Server (NTRS)

    Feldstein, S. B.; Clark, J. H. E.

    1985-01-01

    The properties of the steady Hadley and Rossby regimes for a thermally forced rotating fluid on a sphere are studied. The two layer modified geostrophic model is employed which allows for thermal advection by the divergent wind and time dependent static stability. Heating processes are parameterized using the Newtonian approximation and Rayleigh friction is accounted for. The equations are transformed to spectral form using spherical harmonics and then truncated retaining a simple axisymmetric state and initial, one wave. A time independent Hadley circulation is obtained which is neutral to axisymmetric disturbances but unstable to wave like perturbations for intermediate values of the meridional temperature gradient, indicating the existence of both an upper and lower symmetric Hadley regime. An analytical solution for the steady Rossby circulation is determined for values of the meridional temperature gradient where the Hadley regime is unstable. Linear perturbation theory is used to show that within the steady Rossby regime two or more waves cannot exist simultaneously.

  8. Physics results from the National Spherical Torus Experiment

    SciTech Connect

    M.G. Bell

    2000-06-13

    The National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory is designed for studying toroidal plasma confinement at very low aspect-ratio, A=R/a = 0.85m/0.68m {approximately} 1.25, with cross-section elongation up to 2.2 and triangularity up to 0.5, for plasma currents up to 1 MA and vacuum toroidal magnetic fields up to 0.6 T on axis. Conducting plates are installed close to the plasma on the outboard side to stabilize kink modes. This should permit operation with toroidal-{beta} approaching 40%. The plasmas will be heated by up to 6 MW High-Harmonic Fast Waves (HHFW) at a frequency 30 MHz and by 5 MW of 80 keV deuterium Neutral Beam Injection. Inductive plasma startup can be supplemented by the process of Coaxial Helicity Injection (CHI).

  9. Modulational Instability of Cylindrical and Spherical NLS Equations. Statistical Approach

    SciTech Connect

    Grecu, A. T.; Grecu, D.; Visinescu, Anca; De Nicola, S.; Fedele, R.

    2010-01-21

    The modulational (Benjamin-Feir) instability for cylindrical and spherical NLS equations (c/s NLS equations) is studied using a statistical approach (SAMI). A kinetic equation for a two-point correlation function is written and analyzed using the Wigner-Moyal transform. The linear stability of the Fourier transform of the two-point correlation function is studied and an implicit integral form for the dispersion relation is found. This is solved for different expressions of the initial spectrum (delta-spectrum, Lorentzian, Gaussian), and in the case of a Lorentzian spectrum the total growth of the instability is calculated. The similarities and differences with the usual one-dimensional NLS equation are emphasized.

  10. Thin-shell wormholes: Linearization stability

    SciTech Connect

    Poisson, E.; Visser, M.

    1995-12-15

    The class of spherically symmetric thin-shell wormholes provides a particularly elegant collection of exemplars for the study of traversable Lorentzian wormholes. In the present paper we consider linearized (spherically symmetric) perturbations around some assumed static solution of the Einstein field equations. This permits us to relate stability issues to the (linearized) equation of state of the exotic matter which is located at the wormhole throat. {copyright} 1995 The American Physical Society.

  11. METHOD OF MAKING SPHERICAL ACTINIDE CARBIDE

    DOEpatents

    White, G.D.; O'Rourke, D.C.

    1962-12-25

    This patent describes a method of making uniform, spherical, nonpyrophoric UC. UO/sub 2/ and carbon are mixed in stoichiometric proportions and passed through a plasma flame of inert gas at 10,000 to 13,000 deg C. (AEC)

  12. Noncommutative spherically symmetric spacetimes at semiclassical order

    NASA Astrophysics Data System (ADS)

    Fritz, Christopher; Majid, Shahn

    2017-07-01

    Working within the recent formalism of Poisson-Riemannian geometry, we completely solve the case of generic spherically symmetric metric and spherically symmetric Poisson-bracket to find a unique answer for the quantum differential calculus, quantum metric and quantum Levi-Civita connection at semiclassical order O(λ) . Here λ is the deformation parameter, plausibly the Planck scale. We find that r, t, d r, d t are all forced to be central, i.e. undeformed at order λ, while for each value of r, t we are forced to have a fuzzy sphere of radius r with a unique differential calculus which is necessarily nonassociative at order λ2 . We give the spherically symmetric quantisation of the FLRW cosmology in detail and also recover a previous analysis for the Schwarzschild black hole, now showing that the quantum Ricci tensor for the latter vanishes at order λ. The quantum Laplace-Beltrami operator for spherically symmetric models turns out to be undeformed at order λ while more generally in Poisson-Riemannian geometry we show that it deforms to □f+λ2ωαβ(Ricγα-Sγα)(∇^βdf)γ+O(λ2) in terms of the classical Levi-Civita connection \\widehat\

  13. Plastic flow around rigid spherical inclusions

    NASA Technical Reports Server (NTRS)

    Ruoff, A. L.; Nelson, D. A., Jr.

    1974-01-01

    The extent of plastic flow in a spherical solid (assumed to be homogeneous and elastically and plastically isotropic), surrounding a concentric rigid sphere was calculated as a function of applied external pressure. The applied pressure necessary to cause plastic deformation throughout the solid was obtained.

  14. Spherical Model of Interests in Croatia

    ERIC Educational Resources Information Center

    Sverko, Iva

    2008-01-01

    In order to analyze the validity of spherical model of interests in Croatia, three Croatian samples of primary school students (N = 437), secondary school students (N = 540) and university students (N = 630) were administered a translated version of the Personal Globe Inventory (PGI, [Tracey, T.J.G. (2002). Personal Globe Inventory: Measurement of…

  15. A Generalization of the Spherical Inversion

    ERIC Educational Resources Information Center

    Ramírez, José L.; Rubiano, Gustavo N.

    2017-01-01

    In the present article, we introduce a generalization of the spherical inversion. In particular, we define an inversion with respect to an ellipsoid, and prove several properties of this new transformation. The inversion in an ellipsoid is the generalization of the elliptic inversion to the three-dimensional space. We also study the inverse images…

  16. Effective pair potentials for spherical nanoparticles

    NASA Astrophysics Data System (ADS)

    van Zon, Ramses

    2009-02-01

    An effective description for rigid spherical nanoparticles in a fluid of point particles is presented. The points inside the nanoparticles and the point particles are assumed to interact via spherically symmetric additive pair potentials, while the distribution of points inside the nanoparticles is taken to be spherically symmetric and smooth. The resulting effective pair interactions between a nanoparticle and a point particle, as well as between two nanoparticles, are then given by spherically symmetric potentials. If overlap between particles is allowed, as can occur for some forms of the pair potentials, the effective potential generally has non-analytic points. It is shown that for each effective potential the expressions for different overlapping cases can be written in terms of one analytic auxiliary potential. Even when only non-overlapping situations are possible, the auxiliary potentials facilitate the formulation of the effective potentials. Effective potentials for hollow nanoparticles (appropriate e.g. for buckyballs) are also considered and shown to be related to those for solid nanoparticles. For hollow nanoparticles overlap is more physical, since this covers the case of a smaller particle embedded in a larger, hollow nanoparticle. Finally, explicit expressions are given for the effective potentials derived from basic pair potentials of power law and exponential form, as well as from the commonly used London-van der Waals, Morse, Buckingham, and Lennard-Jones potentials. The applicability of the latter is demonstrated by comparison with an atomic description of nanoparticles with an internal face centered cubic structure.

  17. Spherical Model of Interests in Croatia

    ERIC Educational Resources Information Center

    Sverko, Iva

    2008-01-01

    In order to analyze the validity of spherical model of interests in Croatia, three Croatian samples of primary school students (N = 437), secondary school students (N = 540) and university students (N = 630) were administered a translated version of the Personal Globe Inventory (PGI, [Tracey, T.J.G. (2002). Personal Globe Inventory: Measurement of…

  18. Fast discharge in a spherical cavity

    SciTech Connect

    Antsiferov, P. S. Dorokhin, L. A.

    2014-04-15

    The work is devoted to the study of the plasma, created by a fast discharge in a spherical cavity. The discharge was driven by an inductive storage with plasma erosion opening switch (dI/dt ∼10{sup 12} A/s). The plasma was produced in a spherical cavity (alumina, 11 mm diameter). Xe, Ar, and He at the pressure 80 Pa were used as working gases. The time evolution of the spatial structure and of extreme ultraviolet (EUV) spectra of the discharge plasma was studied by means of micro channel plate detector. The discharges with Xe and Ar resulted in the stable appearance of the spherically shaped plasma with the diameter about 1–3 mm. The plasma emission in the EUV region lasts ∼500 ns. The EUV spectrum of Ar discharge at the moment of maximum of the electron temperature T{sub e} contains the lines of Ar X (ionization potential 478.7 eV), that indicates a value of T{sub e} in the range 50–100 eV. The mechanism of plasma appearance can be the cumulation of the convergent spherical shock wave, generated by fast heat deposition and magnetic pressure in working media near the inner surface of the discharge volume.

  19. A Generalization of the Spherical Inversion

    ERIC Educational Resources Information Center

    Ramírez, José L.; Rubiano, Gustavo N.

    2017-01-01

    In the present article, we introduce a generalization of the spherical inversion. In particular, we define an inversion with respect to an ellipsoid, and prove several properties of this new transformation. The inversion in an ellipsoid is the generalization of the elliptic inversion to the three-dimensional space. We also study the inverse images…

  20. Numerical relativity in spherical polar coordinates: Evolution calculations with the BSSN formulation

    NASA Astrophysics Data System (ADS)

    Baumgarte, Thomas W.; Montero, Pedro J.; Cordero-Carrión, Isabel; Müller, Ewald

    2013-02-01

    In the absence of symmetry assumptions most numerical relativity simulations adopt Cartesian coordinates. While Cartesian coordinates have some desirable properties, spherical polar coordinates appear better suited for certain applications, including gravitational collapse and supernova simulations. Development of numerical relativity codes in spherical polar coordinates has been hampered by the need to handle the coordinate singularities at the origin and on the axis, for example by careful regularization of the appropriate variables. Assuming spherical symmetry and adopting a covariant version of the Baumgarte-Shapiro-Shibata-Nakamura equations, Montero and Cordero-Carrión recently demonstrated that such a regularization is not necessary when a partially implicit Runge-Kutta method is used for the time evolution of the gravitational fields. Here we report on an implementation of the Baumgarte-Shapiro-Shibata-Nakamura equations in spherical polar coordinates without any symmetry assumptions. Using a partially implicit Runge-Kutta method we obtain stable simulations in three spatial dimensions without the need to regularize the origin or the axis. We perform and discuss a number of tests to assess the stability, accuracy and convergence of the code, namely weak gravitational waves, “hydro-without-hydro” evolutions of spherical and rotating relativistic stars in equilibrium, and single black holes.

  1. Analytical expression for a class of spherically symmetric solutions in Lorentz-breaking massive gravity

    NASA Astrophysics Data System (ADS)

    Li, Ping; Li, Xin-zhou; Xi, Ping

    2016-06-01

    We present a detailed study of the spherically symmetric solutions in Lorentz-breaking massive gravity. There is an undetermined function { F }(X,{w}1,{w}2,{w}3) in the action of Stückelberg fields {S}φ ={{{Λ }}}4\\int {{{d}}}4x\\sqrt{-g}{ F }, which should be resolved through physical means. In general relativity, the spherically symmetric solution to the Einstein equation is a benchmark and its massive deformation also plays a crucial role in Lorentz-breaking massive gravity. { F } will satisfy the constraint equation {T}01=0 from the spherically symmetric Einstein tensor {G}01=0, if we maintain that any reasonable physical theory should possess the spherically symmetric solutions. The Stückelberg field {φ }i is taken as a ‘hedgehog’ configuration {φ }i=φ (r){x}i/r, whose stability is guaranteed by the topological one. Under this ansätz, {T}01=0 is reduced to d{ F }=0. The functions { F } for d{ F }=0 form a commutative ring {R}{ F }. We obtain an expression of the solution to the functional differential equation with spherical symmetry if { F }\\in {R}{ F }. If { F }\\in {R}{ F } and \\partial { F }/\\partial X=0, the functions { F } form a subring {S}{ F }\\subset {R}{ F }. We show that the metric is Schwarzschild, Schwarzschild-AdS or Schwarzschild-dS if { F }\\in {S}{ F }. When { F }\\in {R}{ F } but { F }\

  2. A pseudospectral matrix method for time-dependent tensor fields on a spherical shell

    SciTech Connect

    Brügmann, Bernd

    2013-02-15

    We construct a pseudospectral method for the solution of time-dependent, non-linear partial differential equations on a three-dimensional spherical shell. The problem we address is the treatment of tensor fields on the sphere. As a test case we consider the evolution of a single black hole in numerical general relativity. A natural strategy would be the expansion in tensor spherical harmonics in spherical coordinates. Instead, we consider the simpler and potentially more efficient possibility of a double Fourier expansion on the sphere for tensors in Cartesian coordinates. As usual for the double Fourier method, we employ a filter to address time-step limitations and certain stability issues. We find that a tensor filter based on spin-weighted spherical harmonics is successful, while two simplified, non-spin-weighted filters do not lead to stable evolutions. The derivatives and the filter are implemented by matrix multiplication for efficiency. A key technical point is the construction of a matrix multiplication method for the spin-weighted spherical harmonic filter. As example for the efficient parallelization of the double Fourier, spin-weighted filter method we discuss an implementation on a GPU, which achieves a speed-up of up to a factor of 20 compared to a single core CPU implementation.

  3. Aspheric versus Spherical Posterior Chamber Intraocular Lenses

    PubMed Central

    Jafarinasab, Mohammad-Reza; Feizi, Sepehr; Baghi, Ahmad-Reza; Ziaie, Hossein; Yaseri, Mehdi

    2010-01-01

    Purpose To compare spherical aberration and contrast sensitivity function following implantation of four different foldable posterior chamber intraocular lenses (IOLs), namely Sensar, Akreos AO, Tecnis, and AcrySof IQ. Methods In this randomized clinical trial, 68 eyes of 68 patients with senile cataracts underwent phacoemulsification and IOL implantation with Sensar (n=17), Akreos AO (n=17), Tecnis (n=17), or AcrySof IQ (n=17). Uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), spherical aberration and contrast sensitivity function (CSF) were compared among the study groups, 3 months after surgery. Results There was no significant difference between the study groups in terms of age (P = 0.21). Mean postoperative BSCVA with Sensar, Akreos AO, Tecnis, and AcrySof IQ was 0.15±0.10, 0.12±0.9, 0.08±0.08, and 0.08±0.07 logMAR, respectively (P=0.08). Spherical aberration measured over a 4 mm pupil was significantly higher with Sensar and Akreos AO than the two other IOLs. The difference between Tecnis and AcrySof IQ was significantly in favor of the former IOL. Over a 6 mm pupil, spherical aberrations were comparable with Sensar and Akreos AO, furthermore spherical aberration was also comparable among eyes implanted with Akreos AO, AcrySof IQ, and Tecnis. Sensar yielded significantly inferior results as compared to Acrysof IQ and Tecnis. CSF with Sensar was inferior to the three aspheric IOLs at the majority of spatial frequencies. Tecnis yielded significantly better mesopic CSF at 1.5 and 3 cycles per degree spatial frequencies. Conclusion Tecnis and AcrySof IQ provided significantly better visual function as compared to Sensar and Akreos AO, especially with smaller pupil size. However, this difference diminished with increasing pupil size. PMID:22737364

  4. Axi-symmetric patterns of active polar filaments on spherical and composite surfaces

    NASA Astrophysics Data System (ADS)

    Srivastava, Pragya; Rao, Madan

    2014-03-01

    Experiments performed on Fission Yeast cells of cylindrical and spherical shapes, rod-shaped bacteria and reconstituted cylindrical liposomes suggest the influence of cell geometry on patterning of cortical actin. A theoretical model based on active hydrodynamic description of cortical actin that includes curvature-orientation coupling predicts spontaneous formation of acto-myosin rings, cables and nodes on cylindrical and spherical geometries [P. Srivastava et al, PRL 110, 168104(2013)]. Stability and dynamics of these patterns is also affected by the cellular shape and has been observed in experiments performed on Fission Yeast cells of spherical shape. Motivated by this, we study the stability and dynamics of axi-symmetric patterns of active polar filaments on the surfaces of spherical, saddle shaped and conical geometry and classify the stable steady state patterns on these surfaces. Based on the analysis of the fluorescence images of Myosin-II during ring slippage we propose a simple mechanical model for ring-sliding based on force balance and make quantitative comparison with the experiments performed on Fission Yeast cells. NSF Grant DMR-1004789 and Syracuse Soft Matter Program.

  5. Progress Towards High-Performance, Steady-State Spherical Torus

    SciTech Connect

    Lawrence Livermore National Laboratory

    2004-01-04

    Research on the spherical torus (or spherical tokamak) (ST) is being pursued to explore the scientific benefits of modifying the field line structure from that in more moderate aspect ratio devices, such as the conventional tokamak. The ST experiments are being conducted in various US research facilities including the MA-class National Spherical Torus Experiment (NSTX) at Princeton, and three medium sized ST research facilities: PEGASUS at University of Wisconsin, HIT-II at University of Washington, and CDX-U at Princeton. In the context of the fusion energy development path being formulated in the US, an ST-based Component Test Facility (CTF) and, ultimately a Demo device, are being discussed. For these, it is essential to develop high performance, steady-state operational scenarios. The relevant scientific issues are energy confinement, MHD stability at high beta ({beta}), non-inductive sustainment, Ohmic-solenoid-free start-up, and power and particle handling. In the confinement area, the NSTX experiments have shown that the confinement can be up to 50% better than the ITER-98-pby2 H-mode scaling, consistent with the requirements for an ST-based CTF and Demo. In NSTX, CTF-relevant average toroidal beta values {beta}{sub T} of up to 35% with a near unity central {beta}{sub T} have been obtained. NSTX will be exploring advanced regimes where {beta}{sub T} up to 40% can be sustained through active stabilization of resistive wall modes. To date, the most successful technique for non-inductive sustainment in NSTX is the high beta poloidal regime, where discharges with a high non-inductive fraction ({approx}60% bootstrap current+NBI current drive) were sustained over the resistive skin time. Research on radio-frequency (RF) based heating and current drive utilizing high harmonic fastwave and electron Bernstein wave is also pursued on NSTX, PEGASUS, and CDX-U. For non-inductive start-up, the coaxial helicity injection, developed in HIT/HIT-II, has been adopted on NSTX

  6. Compressible instability of rapidly expanding spherical material interfaces

    NASA Astrophysics Data System (ADS)

    Mankbadi, Mina Reda

    The focus herein is on the instability of a material interface formed during an abrupt release of concentrated energy as in detonative combustion, explosive dispersals, and inertial-confinement fusion. These applications are modeled as a spherical shock-tube in which high-pressure gas initially contained in a small spherical shell is suddenly released. A forward-moving shock and an inward-moving secondary shock are formed, and between them a material interface develops that separates high-density fluid from the low-density one. The wrinkling of this interface controls mixing and energy release. The interface's stability is studied with and without the inclusion of metalized particulates. A numerical scheme is developed to discretize the full nonlinear equations of the base flow, and the 3D linearized perturbed flow equations. Linearization is followed by spherical harmonic decomposition of the disturbances, thereby reducing the 3D computational domain to one-dimensional radial domain. The 3D physical nature of the disturbances is maintained throughout the procedure. An extended Roe-Pike scheme coupled with a WENO scheme is developed to capture the discontinuities and accurately predict the disturbances. In Chapter 2, the contact interface's stability is analyzed in the inviscid single-phase. The disturbances grow exponentially and the growth rate is insensitive to the radial initial-disturbance profile. For wave numbers less than 100, the results are in accordance with previous theories but clarify that compressibility reduces the growth rate. Unlike the classical RTI, the growth rate reaches saturation at high wavenumbers. The parametric studies show that for specific ratios of initial pressure and temperature, the instability can be eliminated altogether. Chapter 3 discusses the full effects of viscosity and thermal diffusivity. Although Prandtl number effects are minimal, viscous effects dampen the high-wave numbers. For a given Reynolds number there is a peak

  7. Occurrence of spherical ceramic debris in indentation and sliding contact

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    Indenting experiments were conducted with the silicon carbide (0001) surface in contact with a spherical diamond indenter in air. Sliding friction experiments were also conducted with silicon carbide in contact with iron and iron-based binary alloys at room temperature and 800 C. Fracture pits with a spherical particle and spherical wear debris were observed as a result of indenting and sliding. Spherical debris may be produced by a mechanism that involves a spherical-shaped fracture along the circular or spherical stress trajectories under the inelastic deformation zone.

  8. Ambiguity of the critical load for spherical shells with shear damageability of the material

    NASA Astrophysics Data System (ADS)

    Babich, D. V.; Dorodnykh, T. I.

    2016-06-01

    The structural-probabilistic approach to the modeling of combined crack formation and material deformation processes is used to develop a technique for solving bifurcation stability problems for thin-walled structural members made of damageable materials under single and repeated loadings. The example of a uniformly compressed spherical shell is used to show that, under repeated loading, thin-walled structural members made of shear damageable materials can lose stability under loads smaller than the upper critical loads. The ambiguity of the critical loads for various damage accumulation processes in the material of thin-walled structures depends on the level and character of loading. This phenomenon can be one possible cause of the experimental data spread and the discrepancy between theoretical and experimental results used to determine the critical loads for spherical and cylindrical shells.

  9. Do spherical tokamaks have a thermonuclear future?

    NASA Astrophysics Data System (ADS)

    Mirnov, S. V.

    2012-12-01

    This work has been initiated by the publication of a review by B.V.Kuteev et al., "Intense Fusion Neutron Sources" [Plasma Physics Reports 36, 281 (2010)]. It is stated that the key thesis of the above review that a spherical tokamak can be recommended for research neutron sources and for demonstration hybrid systems as an alternative to expensive "classical" tokamaks of the JET and ITER type is inconsistent. The analysis of the experimental material obtained during the last 10 years in the course of studies on the existing spherical tokamaks shows that the TIN-ST fusion neutron source spherical tokamak proposed by the authors of the review and intended, according to the authors' opinion, to replace "monsters" in view of its table-top dimensions (2 m3) and laboratory-level energetics cannot be transformed into any noticeable stationary megawatt-power neutron source competing with the existing classical tokamaks (in particular, with JET with its quasi-steady DT fusion power at a level of 5 MW). Namely, the maximum plasma current in the proposed tokamak will be not 3 MA, as the authors suppose erroneously, but, according to the present-day practice of spherical tokamaks, within 0.6-0.7 MA, which will lead to a reduction on the neutron flux by two to three orders of magnitude from the expected 5 MW. The possibility of the maintenance of the stationary process itself even in such a "weakened" spherical tokamak is very doubtful. The experience of the largest existing devices of this type (such as NSTX and MAST) has shown that they are incapable of operating even in a quasi-steady operating mode, because the discharge in them is spontaneously interrupted about 1 s after the beginning of the current pulse, although its expected duration is of up to 5 s. The nature of this phenomenon is the subject of further study of the physics of spherical tokamaks. This work deals with a critical analysis of the available experimental data concerning such tokamaks and a discussion of

  10. Attributes of color represented by a spherical model

    NASA Astrophysics Data System (ADS)

    Chen, Tieling; Ma, Jun; Deng, Zhongmin

    2013-10-01

    The paper introduces a spherical coordinate system-based color model and studies the color change in the model. A circular cone with a spherical top tightly circumscribing the RGB color cube is equipped with a properly rotated spherical coordinate system. Similar to the commonly used color models with a hue component such as the HSV model, the spherical model specifies color by describing the color attributes recognized by human vision, using the components of the spherical coordinate system. The formulas of conversions between the spherical model and the RGB color model are provided, which are mathematically simpler and more intuitively understandable than those for commonly used models with a hue component. Most importantly, color changes are perceptually smoother in the spherical model. Comparisons between the spherical model and the HSV model on color changes are made in the paper.

  11. Preparation and Evaluation of Two Apatites with Spherical Nanocrystal Morphology.

    PubMed

    Zhang, Yali; Li, Qihong; Li, Xiaojie; Li, Yong; Wang, Chunhui; Zhao, Yantao; Song, Yingliang; Liu, Yanpu

    2016-03-01

    Spherical nanocrystal of apatite has been proved to be beneficial for osteoblast growth. Two apatites with spherical nanocrystal morphology were prepared in this study by chemical wet method and further sintering process. SEM exhibited that both apatites had spherical nanocrystal morphology. The crystal morphology and size was approaching to each other. XRD showed the apatites separately were hydroxyapatite and tricalcium phosphate phases. The cellular biocompatibility was evaluated by osteoblasts for these two spherical nanocrstal apatites. The MTT result indicated a higher cell proliferation rate for spherical tricalcium phosphate group. The ALP activity assay also strongly favored the tricalcium phosphate group. RT-PCR results indicated that Collagen I had a higher transcription level on the spherical tricalcium phosphate group. SEM results showed robust cell growth on the materials. It was concluded that the spherical nanophase tricalcium phosphate was superior to the cellular biocompatibility of spherical nanophase hydroxyapatite and the results were helpful in the manufacture of more suitable tissue engineering scaffolds.

  12. Colloidal cholesteric liquid crystal in spherical confinement

    PubMed Central

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  13. Elastic dipole response of spherical nuclei

    SciTech Connect

    Bastrukov, S.I.

    1992-10-01

    Within the framework of the nuclear fluid-dynamics the isoscalar dipole response of spherical nuclei is studied. Two kinds of elastic-like transverse oscillations of incompressible nucleus are found to be result in E1, T = 0 and M1, T = 0 spin-independent resonances. The isoscalar electric mode is accompanied by excitation in the nucleus volume of the torus-like current structure, known in the continuum theory as a poloidal dipole or spherical vortex of Hill. The dipole magnetic resonance belongs to the excitation of axially symmetric differential rotations. These motions are described by the toroidal dipole field harmonic in time. The estimates of energies and PWBA-computed form-factors for these modes are presented. 28 refs., 3 figs.

  14. Imaging with Spherically Bent Crystals or Reflectors

    SciTech Connect

    Bitter, M; Hill, K W; Scott, S; Ince-Cushman, A; Reinke, M; Podpaly, Y; Rice, J E; Beiersdorfer, P

    2010-06-01

    This paper consists of two parts: Part I describes the working principle of a recently developed x-ray imaging crystal spectrometer, where the astigmatism of spherically bent crystals is being used with advantage to record spatially resolved spectra of highly charged ions for Doppler measurements of the ion-temperature and toroidal plasmarotation- velocity profiles in tokamak plasmas. This type of spectrometer was thoroughly tested on NSTX and Alcator C-Mod, and its concept was recently adopted for the design of the ITER crystal spectrometers. Part II describes imaging schemes, where the astigmatism has been eliminated by the use of matched pairs of spherically bent crystals or reflectors. These imaging schemes are applicable over a wide range of the electromagnetic radiation, which includes microwaves, visible light, EUV radiation, and x-rays. Potential applications with EUV radiation and x-rays are the diagnosis of laserproduced plasmas, imaging of biological samples with synchrotron radiation, and lithography.

  15. Spherical harmonics and integration in superspace

    NASA Astrophysics Data System (ADS)

    DeBie, H.; Sommen, F.

    2007-06-01

    In this paper, the classical theory of spherical harmonics in {\\bb R}^m is extended to superspace using techniques from Clifford analysis. After defining a super-Laplace operator and studying some basic properties of polynomial null-solutions of this operator, a new type of integration over the supersphere is introduced by exploiting the formal equivalence with an old result of Pizzetti. This integral is then used to prove orthogonality of spherical harmonics of different degree, Green-like theorems and also an extension of the important Funk-Hecke theorem to superspace. Finally, this integration over the supersphere is used to define an integral over the whole superspace, and it is proven that this is equivalent with the Berezin integral, thus providing a more sound definition of the Berezin integral.

  16. Mach reflection of spherical detonation waves

    SciTech Connect

    Hull, L.M.

    1993-07-01

    When two detonation waves collide, the shape of the wave front at their intersection can be used to categorize the flow as regular or irregular reflection. In the case of regular reflection, the intersection of the waves forms a cusp. In the case of irregular reflection, the cusp is replaced by a leading shock locus that bridges the incident waves. Many workers have studied irregular or Mach reflection of detonation waves, but most of the their experimental work has focused on the interaction of plane detonation waves. Reflection of spherical detonation waves has received less attention. This study also differs from previous work in that the focus is to measure the relationship between the detonation velocity and the local wave curvatue for irregular reflection of spherical detonation waves. Two explosives with different detonation properties, PBX 9501 and PBX 9502, are compared.

  17. Disordered spherical bead packs are anisotropic

    NASA Astrophysics Data System (ADS)

    Schröder-Turk, G. E.; Mickel, W.; Schröter, M.; Delaney, G. W.; Saadatfar, M.; Senden, T. J.; Mecke, K.; Aste, T.

    2010-05-01

    Investigating how tightly objects pack space is a long-standing problem, with relevance for many disciplines from discrete mathematics to the theory of glasses. Here we report on the fundamental yet so far overlooked geometric property that disordered mono-disperse spherical bead packs have significant local structural anisotropy manifest in the shape of the free space associated with each bead. Jammed disordered packings from several types of experiments and simulations reveal very similar values of the cell anisotropy, showing a linear decrease with packing fraction. Strong deviations from this trend are observed for unjammed configurations and for partially crystalline packings above 64%. These findings suggest an inherent geometrical reason why, in disordered packings, anisotropic shapes can fill space more efficiently than spheres, and have implications for packing effects in non-spherical liquid crystals, foams and structural glasses.

  18. Testing the spherical evolution of cosmic voids

    NASA Astrophysics Data System (ADS)

    Demchenko, Vasiliy; Cai, Yan-Chuan; Heymans, Catherine; Peacock, John A.

    2016-11-01

    We study the spherical evolution model for voids in ΛCDM, where the evolution of voids is governed by dark energy at an earlier time than that for the whole universe or in overdensities. We show that the presence of dark energy suppresses the growth of peculiar velocities, causing void shell-crossing to occur at progressively later epochs as ΩΛ increases. We apply the spherical model to evolve the initial conditions of N-body simulated voids and compare the resulting final void profiles. We find that the model is successful in tracking the evolution of voids with radii greater than 30 h-1 Mpc, implying that void profiles could be used to constrain dark energy. We find that the initial peculiar velocities of voids play a significant role in shaping their evolution. Excluding the peculiar velocity in the evolution model delays the time of shell crossing.

  19. Quality metric for spherical panoramic video

    NASA Astrophysics Data System (ADS)

    Zakharchenko, Vladyslav; Choi, Kwang Pyo; Park, Jeong Hoon

    2016-09-01

    Virtual reality (VR)/ augmented reality (AR) applications allow users to view artificial content of a surrounding space simulating presence effect with a help of special applications or devices. Synthetic contents production is well known process form computer graphics domain and pipeline has been already fixed in the industry. However emerging multimedia formats for immersive entertainment applications such as free-viewpoint television (FTV) or spherical panoramic video require different approaches in content management and quality assessment. The international standardization on FTV has been promoted by MPEG. This paper is dedicated to discussion of immersive media distribution format and quality estimation process. Accuracy and reliability of the proposed objective quality estimation method had been verified with spherical panoramic images demonstrating good correlation results with subjective quality estimation held by a group of experts.

  20. Spherical silicon micromirrors bent by anodic bonding.

    PubMed

    Wu, Tong; Yamasaki, Takahiro; Hokari, Ryohei; Hane, Kazuhiro

    2011-06-06

    We propose here a novel and stable method for fabricating spherical micromirror by bonding a flat freestanding single-crystal-silicon (SCS) membrane with a fulcrum on a glass substrate. Smooth convex spherical surface is achieved inside the fulcrum by the bending moment generated in the circumference of the SCS membrane. The surface profiles fit well with parabolic curves within 36nm RMS error indicating a good optical performance. By modifying the diameter of the fulcrum, we also demonstrate that it is possible to fabricate micromirrors with a wide range of focal length (0.4mm-1.6mm). The fabricated micromirrors are also used as the mold for replication of micro polymeric lenses. The surface profiles of the micromirrors are transferred to the polymeric replica with a high accuracy.

  1. Flow past a porous approximate spherical shell

    NASA Astrophysics Data System (ADS)

    Srinivasacharya, D.

    2007-07-01

    In this paper, the creeping flow of an incompressible viscous liquid past a porous approximate spherical shell is considered. The flow in the free fluid region outside the shell and in the cavity region of the shell is governed by the Navier Stokes equation. The flow within the porous annulus region of the shell is governed by Darcy’s Law. The boundary conditions used at the interface are continuity of the normal velocity, continuity of the pressure and Beavers and Joseph slip condition. An exact solution for the problem is obtained. An expression for the drag on the porous approximate spherical shell is obtained. The drag experienced by the shell is evaluated numerically for several values of the parameters governing the flow.

  2. Clusters of polyhedra in spherical confinement

    NASA Astrophysics Data System (ADS)

    Teich, Erin; van Anders, Greg; Klotsa, Daphne; Dshemuchadse, Julia; Glotzer, Sharon

    Dense particle packing in a confining volume is a rich, largely unexplored problem, with applications in blood clotting, plasmonics, industrial packaging and transport, colloidal molecule design, and information storage. We report simulation results for dense clusters of the Platonic solids in spherical confinement, for up to N = 60 constituent particles. We discuss similarities between clusters in terms of symmetry, a connection to spherical codes, and generally the interplay between isotropic geometrical confinement and anisotropic particle shape. Our results showcase the structural diversity and experimental utility of families of solutions to the problem of packing in confinement. E.T. acknowledges support by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1256260.

  3. Spontaneous spherical symmetry breaking in atomic confinement

    NASA Astrophysics Data System (ADS)

    Sveshnikov, Konstantin; Tolokonnikov, Andrey

    2017-07-01

    The effect of spontaneous breaking of initial SO(3) symmetry is shown to be possible for an H-like atom in the ground state, when it is confined in a spherical box under general boundary conditions of "not going out" through the box surface (i.e. third kind or Robin's ones), for a wide range of physically reasonable values of system parameters. The most novel and nontrivial result, which has not been reported previously, is that such an effect takes place not only for attractive, but also for repulsive interactions of atomic electrons with the cavity environment. Moreover, in the limit of a large box size R ≫ aB the regime of an atom, soaring over a plane with boundary condition of "not going out", is reproduced, rather than a spherically symmetric configuration, which would be expected on the basis of the initial SO(3) symmetry of the problem.

  4. A Simple Weighing Method for Spherical Cells.

    PubMed

    Zhao, Qili; Shirinzadeh, Bijan; Cui, Maosheng; Sun, Mingzhu; Zhao, Xin

    2015-08-01

    This article presents a simple weighing method for spherical cells to avoid the high cost of correlated devices in traditional cell-weighing methods. In this method, the constant falling speeds of the spherical objects in liquid are derived to estimate their masses online. Using this method, the detected density of one type of microbead is highly in accordance with the known value. This method is proved to be capable of detecting tiny variations of the cell mass (at least within 1% of the cell mass). Finally, the proposed method is applied in nuclear transplantation operations, and, for the first time, the proper amount of the removed cytoplasm in porcine enucleation is estimated. The proposed method is able to weigh cells with a success rate of 92% at an average speed of 22 s/cell, and it can be performed on traditional microoperation systems, which makes it easily applicable in biological applications. © 2015 Society for Laboratory Automation and Screening.

  5. Crack problems in cylindrical and spherical shells

    NASA Technical Reports Server (NTRS)

    Erdogan, F.

    1976-01-01

    Standard plate or shell theories were used as a starting point to study the fracture problems in thin-walled cylindrical and spherical shells, assuming that the plane of the crack is perpendicular to the surface of the sheet. Since recent studies have shown that local shell curvatures may have a rather considerable effect on the stress intensity factor, the crack problem was considered in conjunction with a shell rather than a plate theory. The material was assumed to be isotropic and homogeneous, so that approximate solutions may be obtained by approximating the local shell crack geometry with an ideal shell which has a solution, namely a spherical shell with a meridional crack, a cylindrical shell with a circumferential crack, or a cylindrical shell with an axial crack. A method of solution for the specially orthotropic shells containing a crack was described; symmetric and skew-symmetric problems are considered in cylindrical shells with an axial crack.

  6. Colloidal cholesteric liquid crystal in spherical confinement

    NASA Astrophysics Data System (ADS)

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-08-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter.

  7. Nonlinear axisymmetric flexural vibration of spherical shells

    NASA Technical Reports Server (NTRS)

    Kunieda, H.

    1972-01-01

    Axisymmetric responses are presented of a nonshallow thin-walled spherical shell on the basis of nonlinear bending theory. An ordinary differential equation with nonlinearity of quadratic as well as cubic terms associated with variable time is derived. The derivation is based on the assumption that the deflection mode is the sum of four Legendre polynomials, and the Galerkin procedure is applied. The equation is solved by asymptotic expansion, and a first approximate solution is adopted. Unstable regions of this solution are discussed.

  8. Survival probability for open spherical billiards

    NASA Astrophysics Data System (ADS)

    Dettmann, Carl P.; Rahman, Mohammed R.

    2014-12-01

    We study the survival probability for long times in an open spherical billiard, extending previous work on the circular billiard. We provide details of calculations regarding two billiard configurations, specifically a sphere with a circular hole and a sphere with a square hole. The constant terms of the long-time survival probability expansions have been derived analytically. Terms that vanish in the long time limit are investigated analytically and numerically, leading to connections with the Riemann hypothesis.

  9. Survival probability for open spherical billiards.

    PubMed

    Dettmann, Carl P; Rahman, Mohammed R

    2014-12-01

    We study the survival probability for long times in an open spherical billiard, extending previous work on the circular billiard. We provide details of calculations regarding two billiard configurations, specifically a sphere with a circular hole and a sphere with a square hole. The constant terms of the long-time survival probability expansions have been derived analytically. Terms that vanish in the long time limit are investigated analytically and numerically, leading to connections with the Riemann hypothesis.

  10. Interpolating Spherical Harmonics for Computing Antenna Patterns

    DTIC Science & Technology

    2011-07-01

    and Antenna Patterns 1 2 Short-Wire Antennas 3 3 Spherical Harmonic Expansions 10 4 Adaptive Spline Interpolation ( ASI ) 14 5 Testing the ASI Algorithm...frequency band is possible. This report offers a simple adaptive spline interpolation ( ASI ) algorithm to benchmark more sophisticated pattern...θ, φ) and their expansions. Sec- tion 4 uses one of the antenna patterns to develop the ASI algorithm and the error bounds. Section 5 tests the ASI

  11. Wave equation on spherically symmetric Lorentzian metrics

    SciTech Connect

    Bokhari, Ashfaque H.; Al-Dweik, Ahmad Y.; Zaman, F. D.; Kara, A. H.; Karim, M.

    2011-06-15

    Wave equation on a general spherically symmetric spacetime metric is constructed. Noether symmetries of the equation in terms of explicit functions of {theta} and {phi} are derived subject to certain differential constraints. By restricting the metric to flat Friedman case the Noether symmetries of the wave equation are presented. Invertible transformations are constructed from a specific subalgebra of these Noether symmetries to convert the wave equation with variable coefficients to the one with constant coefficients.

  12. Spherical Cancer Models in Tumor Biology1

    PubMed Central

    Weiswald, Louis-Bastien; Bellet, Dominique; Dangles-Marie, Virginie

    2015-01-01

    Three-dimensional (3D) in vitro models have been used in cancer research as an intermediate model between in vitro cancer cell line cultures and in vivo tumor. Spherical cancer models represent major 3D in vitro models that have been described over the past 4 decades. These models have gained popularity in cancer stem cell research using tumorospheres. Thus, it is crucial to define and clarify the different spherical cancer models thus far described. Here, we focus on in vitro multicellular spheres used in cancer research. All these spherelike structures are characterized by their well-rounded shape, the presence of cancer cells, and their capacity to be maintained as free-floating cultures. We propose a rational classification of the four most commonly used spherical cancer models in cancer research based on culture methods for obtaining them and on subsequent differences in sphere biology: the multicellular tumor spheroid model, first described in the early 70s and obtained by culture of cancer cell lines under nonadherent conditions; tumorospheres, a model of cancer stem cell expansion established in a serum-free medium supplemented with growth factors; tissue-derived tumor spheres and organotypic multicellular spheroids, obtained by tumor tissue mechanical dissociation and cutting. In addition, we describe their applications to and interest in cancer research; in particular, we describe their contribution to chemoresistance, radioresistance, tumorigenicity, and invasion and migration studies. Although these models share a common 3D conformation, each displays its own intrinsic properties. Therefore, the most relevant spherical cancer model must be carefully selected, as a function of the study aim and cancer type. PMID:25622895

  13. Two particle system in spherically confined plasma environment

    NASA Astrophysics Data System (ADS)

    Munjal, Dipti; Sen, K. D.; Prasad, Vinod

    2017-03-01

    Energy eigenvalues of Harmonium atom are reported for the first time under spherically confined Debye and spherically confined exponentially cosine screened coulomb potential. Energy of different states of Harmonium is analyzed as a function of confinement radius and Debye screening length. Comparison of radial matrix elements of Harmonium atom under spherically confined Debye and spherically confined exponentially cosine screened coulomb potential is done. Interesting results are obtained.

  14. Quantum corrected spherical collapse: A phenomenological framework

    SciTech Connect

    Ziprick, Jonathan; Kunstatter, Gabor

    2010-08-15

    A phenomenological framework is presented for incorporating quantum gravity motivated corrections into the dynamics of spherically symmetric collapse. The effective equations are derived from a variational principle that guarantees energy conservation and the existence of a Birkhoff theorem. The gravitational potential can be chosen as a function of the areal radius to yield specific nonsingular static spherically symmetric solutions that generically have two horizons. For a specific choice of potential, the effective stress energy tensor violates only the dominant energy condition. The violations are maximum near the inner horizon and die off rapidly. A numerical study of the quantum corrected collapse of a spherically symmetric scalar field in this case reveals that the modified gravitational potential prevents the formation of a central singularity and ultimately yields a static, mostly vacuum, spacetime with two horizons. The matter 'piles up' on the inner horizon giving rise to mass inflation at late times. The Cauchy horizon is transformed into a null, weak singularity, but in contrast to Einstein gravity, the absence of a central singularity renders this null singularity stable.

  15. Spherically symmetric thick branes cosmological evolution

    NASA Astrophysics Data System (ADS)

    Bernardini, A. E.; Cavalcanti, R. T.; da Rocha, Roldão

    2015-01-01

    Spherically symmetric time-dependent solutions for the 5D system of a scalar field canonically coupled to gravity are obtained and identified as an extension of recent results obtained by Ahmed et al. (JHEP 1404:061. arXiv:1312.3576 [hep-th], 2014). The corresponding cosmology of models with regularized branes generated by such a 5D scalar field scenario is also investigated. It has been shown that the anisotropic evolution of the warp factor and consequently the Hubble like parameter are both driven by the radial coordinate on the brane, which leads to an emergent thick brane-world scenario with spherically symmetric time dependent warp factor. Meanwhile, the separability of variables depending on fifth dimension, , which is exhibited by the equations of motion, allows one to recover the extra dimensional profiles obtained in Ahmed et al. (2014), namely the extra dimensional part of the scale (warp) factor and the scalar field dependence on . Therefore, our results are mainly concerned with the time dependence of a spherically symmetric warp factor. Besides evincing possibilities for obtaining asymmetric stable brane-world scenarios, the extra dimensional profiles here obtained can also be reduced to those ones investigated in Ahmed et al. (2014).

  16. LHCD Scenarios for Spherical Tokamak Plasmas

    SciTech Connect

    Takase, Y.; Ejiri, A.; Oosako, T.; Bonoli, P. T.; Wright, J. C.

    2007-09-28

    Noninductive plasma current start-up and sustainment are crucial issues for spherical tokamak reactors and other applications such as component test facility. It is widely recognized that the lower hybrid wave (the slow wave), which is most efficient in driving current, is not accessible to the core of a fully developed spherical tokamak plasma with very high dielectric constant. However, it may be useful in the initial plasma current ramp-up phase while the density is still low, where it is not practical to use other methods of noninductive current drive. Such a possibility is investigated theoretically for planned experiments on the TST-2 spherical tokamak at the University of Tokyo. The transmitters previously used for FWCD experiments on JFT-2M (200 MHz) are being prepared for this experiment. The combline antenna used for JFT-2M has been modified for use in TST-2. This antenna will be used to excite a unidirectional fast wave traveling in the toroidal direction with a toroidal mode number of 12 (corresponding to an initial parallel index of refraction of about 5). The fast wave can mode convert to the lower hybrid wave and drive current under some conditions. Examination of the dispersion relation indicates that there may be a suitable regime at relatively high field (0.3 T) and low density (<1x10{sup 19} m{sup -3})

  17. Growing an actin gel on spherical surfaces.

    PubMed Central

    Noireaux, V; Golsteyn, R M; Friederich, E; Prost, J; Antony, C; Louvard, D; Sykes, C

    2000-01-01

    Inspired by the motility of the bacteria Listeria monocytogenes, we have experimentally studied the growth of an actin gel around spherical beads grafted with ActA, a protein known to be the promoter of bacteria movement. On ActA-grafted beads F-actin is formed in a spherical manner, whereas on the bacteria a "comet-like" tail of F-actin is produced. We show experimentally that the stationary thickness of the gel depends on the radius of the beads. Moreover, the actin gel is not formed if the ActA surface density is too low. To interpret our results, we propose a theoretical model to explain how the mechanical stress (due to spherical geometry) limits the growth of the actin gel. Our model also takes into account treadmilling of actin. We deduce from our work that the force exerted by the actin gel on the bacteria is of the order of 10 pN. Finally, we estimate from our theoretical model possible conditions for developing actin comet tails. PMID:10692348

  18. Earth Sphericity Effects on Subduction Morphology

    NASA Astrophysics Data System (ADS)

    Morra, G.; Chatelain, P.; Tackley, P.; Koumoutsakos, P.

    2007-12-01

    We present here the first application in Geodynamics of a Multipole accelerated Boundary Element Method (FMM- BEM) for Stokes Flow. The approach offers the advantage of a reduced number of computational elements and linear scaling with the problem size. We show that this numerical mehod can be fruitfully applied to the simulation of several geodynamic systems at the planetary scale in spheical coordinates and we suggest a general appraoch for modeling combined mantle convection and plate tectonics. The potentialities of the approach are shown investigating the effect played by Earth sphericity on the subduction of a very wide oceanic lithosphere , comparing the morphology of the subducted lithosphere in a spherical and in flat setting. The results show a striking difference between the two models: while the slab on a "flat Earth" shows slight undulation, the same subducting plate on a spherical Earth-like setting presents a distinct folding below the trench far from the edges, with wavelength of (1000km-2000km) as Pacific trenches.

  19. Design Considerations for RNA Spherical Nucleic Acids (SNAs).

    PubMed

    Barnaby, Stacey N; Perelman, Grant A; Kohlstedt, Kevin L; Chinen, Alyssa B; Schatz, George C; Mirkin, Chad A

    2016-09-21

    Ribonucleic acids (RNAs) are key components in many cellular processes such as cell division, differentiation, growth, aging, and death. RNA spherical nucleic acids (RNA-SNAs), which consist of dense shells of double-stranded RNA on nanoparticle surfaces, are powerful and promising therapeutic modalities because they confer advantages over linear RNA such as high cellular uptake and enhanced stability. Due to their three-dimensional shell of oligonucleotides, SNAs, in comparison to linear nucleic acids, interact with the biological environment in unique ways. Herein, the modularity of the RNA-SNA is used to systematically study structure-function relationships in order to understand how the oligonucleotide shell affects interactions with a specific type of biological environment, namely, one that contains serum nucleases. We use a combination of experiment and theory to determine the key architectural properties (i.e., sequence, density, spacer moiety, and backfill molecule) that affect how RNA-SNAs interact with serum nucleases. These data establish a set of design parameters for SNA architectures that are optimized in terms of stability.

  20. Design Considerations for RNA Spherical Nucleic Acids (SNAs)

    PubMed Central

    2016-01-01

    Ribonucleic acids (RNAs) are key components in many cellular processes such as cell division, differentiation, growth, aging, and death. RNA spherical nucleic acids (RNA-SNAs), which consist of dense shells of double-stranded RNA on nanoparticle surfaces, are powerful and promising therapeutic modalities because they confer advantages over linear RNA such as high cellular uptake and enhanced stability. Due to their three-dimensional shell of oligonucleotides, SNAs, in comparison to linear nucleic acids, interact with the biological environment in unique ways. Herein, the modularity of the RNA-SNA is used to systematically study structure–function relationships in order to understand how the oligonucleotide shell affects interactions with a specific type of biological environment, namely, one that contains serum nucleases. We use a combination of experiment and theory to determine the key architectural properties (i.e., sequence, density, spacer moiety, and backfill molecule) that affect how RNA-SNAs interact with serum nucleases. These data establish a set of design parameters for SNA architectures that are optimized in terms of stability. PMID:27523252

  1. Spherical Joint Piston and Connecting Rod Developed

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Under an interagency agreement with the Department of Energy, the NASA Lewis Research Center manages a Heavy-Duty Diesel Engine Technology (HDET) research program. The overall program objectives are to reduce fuel consumption through increased engine efficiency, reduce engine exhaust emissions, and provide options for the use of alternative fuels. The program is administered with a balance of research contracts, university research grants, and focused in-house research. The Cummins Engine Company participates in the HDET program under a cost-sharing research contract. Cummins is researching and developing in-cylinder component technologies for heavy-duty diesel engines. An objective of the Cummins research is to develop technologies for a low-emissions, 55-percent thermal efficiency (LE-55) engine. The best current-production engines in this class achieve about 46-percent thermal efficiency. Federal emissions regulations are driving this technology. Regulations for heavy duty diesel engines were tightened in 1994, more demanding emissions regulations are scheduled for 1998, and another step is planned for 2002. The LE-55 engine emissions goal is set at half of the 1998 regulation level and is consistent with plans for 2002 emissions regulations. LE-55 engine design requirements to meet the efficiency target dictate a need to operate at higher peak cylinder pressures. A key technology being developed and evaluated under the Cummins Engine Company LE-55 engine concept is the spherical joint piston and connecting rod. Unlike conventional piston and connecting rod arrangements which are joined by a pin forming a hinged joint, the spherical joint piston and connecting rod use a ball-and-socket joint. The ball-and-socket arrangement enables the piston to have an axisymmetric design allowing rotation within the cylinder. The potential benefits of piston symmetry and rotation are reduced scuffing, improved piston ring sealing, improved lubrication, mechanical and thermal

  2. Gravity inversion in spherical coordinates using tesseroids

    NASA Astrophysics Data System (ADS)

    Uieda, Leonardo; Barbosa, Valeria C. F.

    2014-05-01

    Satellite observations of the gravity field have provided geophysicists with exceptionally dense and uniform coverage of data over vast areas. This enables regional or global scale high resolution geophysical investigations. Techniques like forward modeling and inversion of gravity anomalies are routinely used to investigate large geologic structures, such as large igneous provinces, suture zones, intracratonic basins, and the Moho. Accurately modeling such large structures requires taking the sphericity of the Earth into account. A reasonable approximation is to assume a spherical Earth and use spherical coordinates. In recent years, efforts have been made to advance forward modeling in spherical coordinates using tesseroids, particularly with respect to speed and accuracy. Conversely, traditional space domain inverse modeling methods have not yet been adapted to use spherical coordinates and tesseroids. In the literature there are a range of inversion methods that have been developed for Cartesian coordinates and right rectangular prisms. These include methods for estimating the relief of an interface, like the Moho or the basement of a sedimentary basin. Another category includes methods to estimate the density distribution in a medium. The latter apply many algorithms to solve the inverse problem, ranging from analytic solutions to random search methods as well as systematic search methods. We present an adaptation for tesseroids of the systematic search method of "planting anomalous densities". This method can be used to estimate the geometry of geologic structures. As prior information, it requires knowledge of the approximate densities and positions of the structures. The main advantage of this method is its computational efficiency, requiring little computer memory and processing time. We demonstrate the shortcomings and capabilities of this approach using applications to synthetic and field data. Performing the inversion of gravity and gravity gradient

  3. Facile room-temperature solution-phase synthesis of a spherical covalent organic framework for high-resolution chromatographic separation.

    PubMed

    Yang, Cheng-Xiong; Liu, Chang; Cao, Yi-Meng; Yan, Xiu-Ping

    2015-08-07

    A simple and facile room-temperature solution-phase synthesis was developed to fabricate a spherical covalent organic framework with large surface area, good solvent stability and high thermostability for high-resolution chromatographic separation of diverse important industrial analytes including alkanes, cyclohexane and benzene, α-pinene and β-pinene, and alcohols with high column efficiency and good precision.

  4. Shape evolution of a core-shell spherical particle under hydrostatic pressure.

    PubMed

    Colin, Jérôme

    2012-03-01

    The morphological evolution by surface diffusion of a core-shell spherical particle has been investigated theoretically under hydrostatic pressure when the shear modulii of the core and shell are different. A linear stability analysis has demonstrated that depending on the pressure, shear modulii, and radii of both phases, the free surface of the composite particle may be unstable with respect to a shape perturbation. A stability diagram finally emphasizes that the roughness development is favored in the case of a hard shell with a soft core.

  5. Scattering of a Spherical Wave by a Thin Hard Strip

    NASA Astrophysics Data System (ADS)

    Ouis, D.

    1999-02-01

    This paper is concerned with a theoretical solution to the problem of scattering of a spherical wave by a strip. The strip is infinitely thin, infinite in length and of width 2a. The problem is first brought into the wave space through a spatial Fourier transform of the wave equation and of the boundary conditions on the strip. The Fourier transform is taken with respect to the co-ordinate axis parallel to the edges of the strip. Using the boundary conditions on the strip leads to an integral equation of the first kind, the unknown of which is the discontinuous potential jump across the strip. This latter is expanded into some suitable functions and the coefficients of the series expansion are thereafter determined from an infinite system of equations. The system's matrix is found to be mainly diagonal and tests on the stability of the numerical calculations suggest the significant number of equations in the system be limited to approximatelyka+5, withkbeing the wavenumber. Finally, after solving the system of equations and going back to the scattered field, the expression of this latter is made from an infinite series over some infinite double integrals whose approximate evaluation is made with the help of the two-dimensional stationary phase method. This treatment corresponds to the far field case. A further consideration of the right side of the system of equations leads to an improved value of the scattered field. Comparisons are made to an approximated prediction of the scattered field by using the Biot and Tolstoy exact theory of diffraction of a spherical wave by a hard wedge. The implementation of this approach to the strip requires the further consideration of the multiple diffraction between its edges for improving the calculated value of the scattered field. Some numerical examples are treated with discussions on their results.

  6. Biodistribution and toxicity of spherical aluminum oxide nanoparticles.

    PubMed

    Park, Eun-Jung; Lee, Gwang-Hee; Yoon, Cheolho; Jeong, Uiseok; Kim, Younghun; Cho, Myung-Haing; Kim, Dong-Wan

    2016-03-01

    With the rapid development of the nano-industry, concerns about their potential adverse health effects have been raised. Thus, ranking accurately their toxicity and prioritizing for in vivo testing through in vitro toxicity test is needed. In this study, we used three types of synthesized aluminum oxide nanoparticles (AlONPs): γ-aluminum oxide hydroxide nanoparticles (γ-AlOHNPs), γ- and α-AlONPs. All three AlONPs were spherical, and the surface area was the greatest for γ-AlONPs, followed by the α-AlONPs and γ-AlOHNPs. In mice, γ-AlOHNPs accumulated the most 24 h after a single oral dose. Additionally, the decreased number of white blood cells (WBC), the increased ratio of neutrophils and the enhanced secretion of interleukin (IL)-8 were observed in the blood of mice dosed with γ-AlOHNPs (10 mg kg(-1)). We also compared their toxicity using four different in vitro test methods using six cell lines, which were derived from their potential target organs, BEAS-2B (lung), Chang (liver), HACAT (skin), H9C2 (heart), T98G (brain) and HEK-293 (kidney). The results showed γ-AlOHNPs induced the greatest toxicity. Moreover, separation of particles was observed in a transmission electron microscope (TEM) image of cells treated with γ-AlOHNPs, but not γ-AlONPs or α-AlONPs. In conclusion, our results suggest that the accumulation and toxicity of AlONPs are stronger in γ-AlOHNPs compared with γ-AlONPs and α-AlONPs owing their low stability within biological system, and the presence of hydroxyl group may be an important factor in determining the distribution and toxicity of spherical AlONPs.

  7. Cauchy-perturbative matching reexamined: Tests in spherical symmetry

    SciTech Connect

    Zink, Burkhard; Pazos, Enrique; Diener, Peter; Tiglio, Manuel

    2006-04-15

    During the last few years progress has been made on several fronts making it possible to revisit Cauchy-perturbative matching (CPM) in numerical relativity in a more robust and accurate way. This paper is the first in a series where we plan to analyze CPM in the light of these new results. One of the new developments is an understanding of how to impose constraint-preserving boundary conditions (CPBC); though most of the related research has been driven by outer boundaries, one can use them for matching interface boundaries as well. Another front is related to numerically stable evolutions using multiple patches, which in the context of CPM allows the matching to be performed on a spherical surface, thus avoiding interpolations between Cartesian and spherical grids. One way of achieving stability for such schemes of arbitrary high order is through the use of penalty techniques and discrete derivatives satisfying summation by parts (SBP). Recently, new, very efficient and high-order accurate derivatives satisfying SBP and associated dissipation operators have been constructed. Here we start by testing all these techniques applied to CPM in a setting that is simple enough to study all the ingredients in great detail: Einstein's equations in spherical symmetry, describing a black hole coupled to a massless scalar field. We show that with the techniques described above, the errors introduced by Cauchy-perturbative matching are very small, and that very long-term and accurate CPM evolutions can be achieved. Our tests include the accretion and ring-down phase of a Schwarzschild black hole with CPM, where we find that the discrete evolution introduces, with a low spatial resolution of {delta}r=M/10, an error of 0.3% after an evolution time of 1,000,000M. For a black hole of solar mass, this corresponds to approximately 5s, and is therefore at the lower end of timescales discussed e.g. in the collapsar model of gamma-ray burst engines.

  8. The influence of the magnetic field on the heat transfer rate in rotating spherical shells

    NASA Astrophysics Data System (ADS)

    Cabello, Ares; Avila, Ruben

    2016-11-01

    Studies of the relationship between natural convection and magnetic field generation in spherical annular geometries with rotation are essential to understand the internal dynamics of the terrestrial planets. In such studies it is important to calculate and analyze the heat transfer rate at the inner and the outer spheres that confine the spherical gap. Previous investigations indicate that the magnetic field has a stabilizing effect on the onset of the natural convection, reduces the intensity of convection and modifies the flow patterns. However so far it is still unclear how the magnetic field change the heat transfer rate behaviour. We investigate the heat transfer rate (Nu) in a rotating spherical gap with a self gravity field varying linearly with radius, and its relation with the intensity of the magnetic field induced by the geodynamo effect. The Boussinesq fluid equations are solved by using a spectral element method (SEM). To avoid the singularity at the poles, the cubed-sphere algorithm is used to generate the spherical mesh. Several cases are simulated in which the Rayleigh number, the magnetic Reynolds number and the Taylor number are the variable parameters. The flow patterns, the temperature distribution and the Nusselt numbers at both spheres are calculated. Special thanks to DGAPA-UNAM Project PAPIIT IN11731, sponsor of this investigation.

  9. Spherical crystallization: A technique use to reform solubility and flow property of active pharmaceutical ingredients

    PubMed Central

    Chatterjee, Arindam; Gupta, Madan Mohan; Srivastava, Birendra

    2017-01-01

    Tablets have been choice of manufacturers over the years due to their comparatively low cost of manufacturing, packaging, shipping, and ease of administration; also have better stability and can be considered virtually tamper proof. A major challenge in formulation development of the tablets extends from lower solubility of the active agent to the elaborated manufacturing procedures for obtaining a compressible granular material. Moreover, the validation and documentation increases, as the numbers of steps increases for an industrially acceptable granulation process. Spherical crystallization (SC) is a promising technique, which encompass the crystallization, agglomeration, and spheronization phenomenon in a single step. Initially, two methods, spherical agglomeration, and emulsion solvent diffusion, were suggested to get a desired result. Later on, the introduction of modified methods such as crystallo-co-agglomeration, ammonia diffusion system, and neutralization techniques overcame the limitations of the older techniques. Under controlled conditions such as solvent composition, mixing rate and temperature, spherical dense agglomerates cluster from particles. Application of the SC technique includes production of compacted spherical particles of drug having improved uniformity in shape and size of particles, good bulk density, better flow properties as well as better solubility so SC when used on commercial scale will bring down the production costs of pharmaceutical tablet and will increase revenue for the pharmaceutical industries in the competitive market. This review summarizes the technologies available for SC and also suggests the parameters for evaluation of a viable product. PMID:28405573

  10. Optimization of hot melt extrusion parameters for sphericity and hardness of polymeric face-cut pellets.

    PubMed

    Alshetaili, Abdullah S; Almutairy, Bjad K; Alshahrani, Saad M; Ashour, Eman A; Tiwari, Roshan V; Alshehri, Sultan M; Feng, Xin; Alsulays, Bader B; Majumdar, Soumyajit; Langley, Nigel; Kolter, Karl; Gryczke, Andreas; Martin, Scott T; Repka, Michael A

    2016-11-01

    The aim of this study was to formulate face-cut, melt-extruded pellets, and to optimize hot melt process parameters to obtain maximized sphericity and hardness by utilizing Soluplus(®) as a polymeric carrier and carbamazepine (CBZ) as a model drug. Thermal gravimetric analysis (TGA) was used to detect thermal stability of CBZ. The Box-Behnken design for response surface methodology was developed using three factors, processing temperature ( °C), feeding rate (%), and screw speed (rpm), which resulted in 17 experimental runs. The influence of these factors on pellet sphericity and mechanical characteristics was assessed and evaluated for each experimental run. Pellets with optimal sphericity and mechanical properties were chosen for further characterization. This included differential scanning calorimetry, drug release, hardness friability index (HFI), flowability, bulk density, tapped density, Carr's index, and fourier transform infrared radiation (FTIR) spectroscopy. TGA data showed no drug degradation upon heating to 190 °C. Hot melt extrusion processing conditions were found to have a significant effect on the pellet shape and hardness profile. Pellets with maximum sphericity and hardness exhibited no crystalline peak after extrusion. The rate of drug release was affected mainly by pellet size, where smaller pellets released the drug faster. All optimized formulations were found to be of superior hardness and not friable. The flow properties of optimized pellets were excellent with high bulk and tapped density.

  11. Axisymmetric flow near a spherical obstacle placed in a spherical cavity

    NASA Astrophysics Data System (ADS)

    Milleret, M.; Bellet, D.; Ly, D. P.

    1981-10-01

    An attempt to model the waves near a prosthetic spherical cardiac Starr valve placed in the aorta is presented. The laminar flow is considered incompressible and Newtonian, and of fixed form. Volumetric forces are neglected, and equations for stationary flow are written, considering stagnation flow at the wall, the axial symmetry of the problem, and the hydrodynamic conditions upstream and downstream from the singularity. The calculations were made by using a finite element method. The numerical results were compared with experimental results obtained from laser velocimetry of liquid flow (vaseline) in a transparent tank with a spherical obstacle. A good match was found for Re in the range 5-100.

  12. Deterministic phase retrieval employing spherical illumination

    NASA Astrophysics Data System (ADS)

    Martínez-Carranza, J.; Falaggis, K.; Kozacki, T.

    2015-05-01

    Deterministic Phase Retrieval techniques (DPRTs) employ a series of paraxial beam intensities in order to recover the phase of a complex field. These paraxial intensities are usually generated in systems that employ plane-wave illumination. This type of illumination allows a direct processing of the captured intensities with DPRTs for recovering the phase. Furthermore, it has been shown that intensities for DPRTs can be acquired from systems that use spherical illumination as well. However, this type of illumination presents a major setback for DPRTs: the captured intensities change their size for each position of the detector on the propagation axis. In order to apply the DPRTs, reescalation of the captured intensities has to be applied. This condition can increase the error sensitivity of the final phase result if it is not carried out properly. In this work, we introduce a novel system based on a Phase Light Modulator (PLM) for capturing the intensities when employing spherical illumination. The proposed optical system enables us to capture the diffraction pattern of under, in, and over-focus intensities. The employment of the PLM allows capturing the corresponding intensities without displacing the detector. Moreover, with the proposed optical system we can control accurately the magnification of the captured intensities. Thus, the stack of captured intensities can be used in DPRTs, overcoming the problems related with the resizing of the images. In order to prove our claims, the corresponding numerical experiments will be carried out. These simulations will show that the retrieved phases with spherical illumination are accurate and can be compared with those that employ plane wave illumination. We demonstrate that with the employment of the PLM, the proposed optical system has several advantages as: the optical system is compact, the beam size on the detector plane is controlled accurately, and the errors coming from mechanical motion can be suppressed easily.

  13. Automated semi-spherical irradiance meter

    NASA Astrophysics Data System (ADS)

    Tecpoyotl-Torres, M.; Vera-Dimas, J. G.; Escobedo-Alatorre, J.; Cabello-Ruiz, R.; Varona, J.

    2011-09-01

    In this semi-spherical meter, a single detector is used to realize all measurements, which is located on the extreme of a rectangular ring (assumed as joined two mobile branches in order to compensate the weights), describing half-meridians from 0° up to 170°. The illumination source under test is located at the center of the mobile support, which can rotate 360° horizontally. The two combined movements allow us to obtain a semi-spherical geometry. The number of measurement points is determined by the two step-motors located under the mobile support of the luminary and on one of the two fixed arms, which support the mobile rectangular ring, respectively. The mechanical arrangement has the enough rigidity to support the precision required for the acquisition stage, based on a dsPIC. The main advantages of this arrange are: Its low costs (using recyclable materials only such as "electronic waste"), a reliable detection based on a single photo-detector, with an integrated amplification stage, and the mechanical design. The received power by the detector is useful to obtain the irradiance profile of the lighting sources under test. The semi-spherical geometry of the meter makes it useful for the analysis of directive and non directive sources, in accordance with the angle described by the mobile ring. In this work, special attention is given to LED lamps due to its impact in several sceneries of the daily life. A comparison between the irradiance patterns of two LED lamps is also given.

  14. Spherical transceivers for ultrafast optical wireless communications

    NASA Astrophysics Data System (ADS)

    Jin, Xian; Hristovski, Blago A.; Collier, Christopher M.; Geoffroy-Gagnon, Simon; Born, Brandon; Holzman, Jonathan F.

    2016-02-01

    Optical wireless communications (OWC) offers the potential for high-speed and mobile operation in indoor networks. Such OWC systems often employ a fixed transmitter grid and mobile transceivers, with the mobile transceivers carrying out bi-directional communication via active downlinks (ideally with high-speed signal detection) and passive uplinks (ideally with broad angular retroreflection and high-speed modulation). It can be challenging to integrate all of these bidirectional communication capabilities within the mobile transceivers, however, as there is a simultaneous desire for compact packaging. With this in mind, the work presented here introduces a new form of transceiver for bi-directional OWC systems. The transceiver incorporates radial photoconductive switches (for high-speed signal detection) and a spherical retro-modulator (for broad angular retroreflection and high-speed all-optical modulation). All-optical retromodulation are investigated by way of theoretical models and experimental testing, for spherical retro-modulators comprised of three glasses, N-BK7, N-LASF9, and S-LAH79, having differing levels of refraction and nonlinearity. It is found that the spherical retro-modulator comprised of S-LAH79, with a refractive index of n ≍ 2 and a Kerr nonlinear index of n2 ≍ (1.8 ± 0.1) × 10-15 cm2/W, yields both broad angular retroreflection (over a solid angle of 2π steradians) and ultrafast modulation (over a duration of 120 fs). Such transceivers can become important elements for all-optical implementations in future bi-directional OWC systems.

  15. Vacuum energy of a spherical plasma shell

    NASA Astrophysics Data System (ADS)

    Bordag, M.; Khusnutdinov, N.

    2008-04-01

    We consider the vacuum energy of the electromagnetic field interacting with a spherical plasma shell together with a model for the classical motion of the shell. We calculate the heat kernel coefficients, especially that for the TM mode, and carry out the renormalization by redefining the parameters of the classical model. It turns out that this is possible and results in a model which, in the limit of the plasma shell becoming an ideal conductor, reproduces the vacuum energy found by Boyer in 1968.

  16. Inversion of band patterns in spherical tumblers.

    PubMed

    Chen, Pengfei; Lochman, Bryan J; Ottino, Julio M; Lueptow, Richard M

    2009-04-10

    Bidisperse granular mixtures in spherical tumblers segregate into three bands: one at each pole and one at the equator. For low fill levels, large particles are at the equator; for high fill levels, the opposite occurs. Segregation is robust, though the transition depends on fill level, particle size, and rotational speed. Discrete element method simulations reproduce surface patterns and reveal internal structures. Particle trajectories show that small particles flow farther toward the poles than large particles in the upstream portion of the flowing layer for low fill levels leading to a band of small particles at each pole. The opposite occurs for high fill levels, though more slowly.

  17. Numerical investigations of gaseous spherical diffusion flames

    NASA Astrophysics Data System (ADS)

    Lecoustre, Vivien R.

    Spherical diffusion flames have several unique characteristics that make them attractive from experimental and theoretical perspectives. They can be modeled with one spatial dimension, which frees computational resources for detailed chemistry, transport, and radiative loss models. This dissertation is a numerical study of two classes of spherical diffusion flames: hydrogen micro-diffusion flames, emphasizing kinetic extinction, and ethylene diffusion flames, emphasizing sooting limits. The flames were modeled using a one-dimensional, time-accurate diffusion flame code with detailed chemistry and transport. Radiative losses from products were modeled using a detailed absorption/emission statistical narrow band model and the discrete ordinates method. During this work the code has been enhanced by the implementation of a soot formation/oxidation model using the method of moments. Hydrogen micro-diffusion flames were studied experimentally and numerically. The experiments involved gas jets of hydrogen. At their quenching limits, these flames had heat release rates of 0.46 and 0.25 W in air and in oxygen, respectively. These are the weakest flames ever observed. The modeling results confirmed the quenching limits and revealed high rates of reactant leakage near the limits. The effects of the burner size and mass flow rate were predicted to have a significant impact on the flame chemistry and species distribution profiles, favoring kinetic extinction. Spherical ethylene diffusion flames at their sooting limits were also examined. Seventeen normal and inverse spherical flames were considered. Initially sooty, these flames were experimentally observed to reach their sooting limits 2 s after ignition. Structure of the flames at 2 s was considered, with an emphasis on the relationships among local temperature, carbon to oxygen atom ratio (C/O), and scalar dissipation rate. A critical C/O ratio was identified, along with two different sooting limit regimes. Diffusion flames

  18. Zeeman transitions in spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Yakar, Y.; ćakır, B.; Yılmazer, F.; Özmen, A.

    2017-02-01

    In this study, the effects of external magnetic field on the energy states of a spherical quantum dot with infinite potential barrier have been investigated by using Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method. Linear Zeeman states and Zeeman transition energies are calculated as a function of dot radius and magnetic field strength. We also carry out the effect of external magnetic field on the ground state binding energy. The results show that the impurity energy states, binding energy and Zeeman transition energies are strongly affected by magnetic field strength and dot radius.

  19. Polymer and spherical nanoparticle diffusion in nanocomposites

    NASA Astrophysics Data System (ADS)

    Karatrantos, Argyrios; Composto, Russell J.; Winey, Karen I.; Clarke, Nigel

    2017-05-01

    Nanoparticle and polymer dynamics in nanocomposites containing spherical nanoparticles were investigated by means of molecular dynamics simulations. We show that the polymer diffusivity decreases with nanoparticle loading due to an increase of the interfacial area created by nanoparticles, in the polymer matrix. We show that small sized nanoparticles can diffuse much faster than that predicted from the Stokes-Einstein relation in the dilute regime. We show that the nanoparticle diffusivity decreases at higher nanoparticle loading due to nanoparticle-polymer interface. Increase of the nanoparticle radius slows the nanoparticle diffusion.

  20. Diffusion of spherical particles in microcavities.

    PubMed

    Imperio, A; Padding, J T; Briels, W J

    2011-04-21

    The diffusive motion of a colloidal particle trapped inside a small cavity filled with fluid is reduced by hydrodynamic interactions with the confining walls. In this work, we study these wall effects on a spherical particle entrapped in a closed cylinder. We calculate the diffusion coefficient along the radial, azimuthal, and axial direction for different particle positions. At all locations the diffusion is smaller than in a bulk fluid and it becomes anisotropic near the container's walls. We present a simple model which reasonably well describes the simulation results for the given dimensions of the cylinder, which are taken from the recent experimental work.

  1. Spherical Panoramas for Astrophysical Data Visualization

    NASA Astrophysics Data System (ADS)

    Kent, Brian R.

    2017-05-01

    Data immersion has advantages in astrophysical visualization. Complex multi-dimensional data and phase spaces can be explored in a seamless and interactive viewing environment. Putting the user in the data is a first step toward immersive data analysis. We present a technique for creating 360° spherical panoramas with astrophysical data. The three-dimensional software package Blender and the Google Spatial Media module are used together to immerse users in data exploration. Several examples employing these methods exhibit how the technique works using different types of astronomical data.

  2. Half-spherical shell deep drawing

    NASA Astrophysics Data System (ADS)

    Nepershin, Rostislav I.; Prusakov, Maksim A.

    2017-07-01

    Computer numerical simulation of non-steady thin-walled half-spherical shell deep drawing is presented. Initial elastic stage of clamped thin workpiece bending followed by the elastic-plastic and rigid-plastic Mises membrane stages with work hardening and wall thickness variation are considered. Tresca yield criterion is used in the region of material biaxial tension. Plastic unload effect induced by non-homogeneous work hardening along the shell generator is included in simulation procedure with the result of good correlation of predicted and experimental drawing force versus punch displacement relation for commercial stainless sheet steel.

  3. Space Radiation Detector with Spherical Geometry

    NASA Technical Reports Server (NTRS)

    Wrbanek, John D. (Inventor); Fralick, Gustave C. (Inventor); Wrbanek, Susan Y. (Inventor)

    2011-01-01

    A particle detector is provided, the particle detector including a spherical Cherenkov detector, and at least one pair of detector stacks. In an embodiment of the invention, the Cherenkov detector includes a sphere of ultraviolet transparent material, coated by an ultraviolet reflecting material that has at least one open port. The Cherenkov detector further includes at least one photodetector configured to detect ultraviolet light emitted from a particle within the sphere. In an embodiment of the invention, each detector stack includes one or more detectors configured to detect a particle traversing the sphere.

  4. Space Radiation Detector with Spherical Geometry

    NASA Technical Reports Server (NTRS)

    Wrbanek, John D. (Inventor); Fralick, Gustave C. (Inventor); Wrbanek, Susan Y. (Inventor)

    2012-01-01

    A particle detector is provided, the particle detector including a spherical Cherenkov detector, and at least one pair of detector stacks. In an embodiment of the invention, the Cherenkov detector includes a sphere of ultraviolet transparent material, coated by an ultraviolet reflecting material that has at least one open port. The Cherenkov detector further includes at least one photodetector configured to detect ultraviolet light emitted from a particle within the sphere. In an embodiment of the invention, each detector stack includes one or more detectors configured to detect a particle traversing the sphere.

  5. Stress analysis of spherical-mirror panels

    SciTech Connect

    Parks, V J; Sanford, R J

    1982-04-01

    An experimental analysis is reported of the stresses that occur in elastically deformed, spherically curved glass mirrors for solar energy applications. Bending and membrance stresses generated in forming the glass and the effects of springback are analyzed. In addition, thermal stresses caused by focusing the sun's rays on a small region of the mirrors are analyzed. Methods used in the analysis included the use of grids, photoelasticity, and strain gages. Results of the analysis are compared with a theoretical analysis performed by Shelltech Associates in a parallel effort.

  6. Static spherical metrics: a geometrical approach

    NASA Astrophysics Data System (ADS)

    Tiwari, A. K.; Maharaj, S. D.; Narain, R.

    2017-08-01

    There exist several solution generating algorithms for static spherically symmetric metrics. Here we use the geometrical approach of Lie point symmetries to solve the condition of pressure isotropy by finding the associated five-dimensional Lie algebra of symmetry generators. For the non-Abelian subalgebras the underlying equation is solved to obtain a general solution. Contained within this class are vacuum models, constant density models, metrics with linear equations of state and the Buchdahl representation of the polytrope with index five. For a different particular symmetry generator the condition of pressure isotropy is transformed to a Riccati equation which admits particular solutions.

  7. Stability of phantom wormholes

    SciTech Connect

    Lobo, Francisco S.N.

    2005-06-15

    It has recently been shown that traversable wormholes may be supported by phantom energy. In this work phantom wormhole geometries are modeled by matching an interior traversable wormhole solution, governed by the equation of state p={omega}{rho} with {omega}<-1, to an exterior vacuum spacetime at a finite junction interface. The stability analysis of these phantom wormholes to linearized spherically symmetric perturbations about static equilibrium solutions is carried out. A master equation dictating the stability regions is deduced, and by separating the cases of a positive and a negative surface energy density, it is found that the respective stable equilibrium configurations may be increased by strategically varying the wormhole throat radius. The first model considered, in the absence of a thin shell, is that of an asymptotically flat phantom wormhole spacetime. The second model constructed is that of an isotropic pressure phantom wormhole, which is of particular interest, as the notion of phantom energy is that of a spatially homogeneous cosmic fluid, although it may be extended to inhomogeneous spherically symmetric spacetimes.

  8. Bidispersed Sphere Packing on Spherical Surfaces

    NASA Astrophysics Data System (ADS)

    Atherton, Timothy; Mascioli, Andrew; Burke, Christopher

    Packing problems on spherical surfaces have a long history, originating in the classic Thompson problem of finding the ground state configuration of charges on a sphere. Such packings contain a minimal number of defects needed to accommodate the curvature; this is predictable using the Gauss-Bonnet theorem from knowledge of the topology of the surface and the local symmetry of the ordering. Famously, the packing of spherical particles on a sphere contains a 'scar' transition, where additional defects over those required by topology appear above a certain critical number of particles and self-organize into chains or scars. In this work, we study the packing of bidispersed packings on a sphere, and hence determine the interaction of bidispersity and curvature. The resultant configurations are nearly crystalline for low values of bidispersity and retain scar-like structures; these rapidly become disordered for intermediate values and approach a so-called Appollonian limit at the point where smaller particles can be entirely accommodated within the voids left by the larger particles. We connect our results with studies of bidispersed packings in the bulk and on flat surfaces from the literature on glassy systems and jamming. Supported by a Cottrell Award from the Research Corporation for Science Advancement.

  9. Saltation of Non-Spherical Sand Particles

    PubMed Central

    Wang, Zhengshi; Ren, Shan; Huang, Ning

    2014-01-01

    Saltation is an important geological process and the primary source of atmospheric mineral dust aerosols. Unfortunately, no studies to date have been able to precisely reproduce the saltation process because of the simplified theoretical models used. For example, sand particles in most of the existing wind sand movement models are considered to be spherical, the effects of the sand shape on the structure of the wind sand flow are rarely studied, and the effect of mid-air collision is usually neglected. In fact, sand grains are rarely round in natural environments. In this paper, we first analyzed the drag coefficients, drag forces, and starting friction wind speeds of sand grains with different shapes in the saltation process, then established a sand saltation model that considers the coupling effect between wind and the sand grains, the effect of the mid-air collision of sand grains, and the effect of the sand grain shape. Based on this model, the saltation process and sand transport rate of non-spherical sand particles were simulated. The results show that the sand shape has a significant impact on the saltation process; for the same wind speed, the sand transport rates varied for different shapes of sand grains by as much as several-fold. Therefore, sand shape is one of the important factors affecting wind-sand movement. PMID:25170614

  10. Spherical primary optical telescope (SPOT) segments

    NASA Astrophysics Data System (ADS)

    Hall, Christopher; Hagopian, John; DeMarco, Michael

    2012-09-01

    The spherical primary optical telescope (SPOT) project is an internal research and development program at NASA Goddard Space Flight Center. The goals of the program are to develop a robust and cost effective way to manufacture spherical mirror segments and demonstrate a new wavefront sensing approach for continuous phasing across the segmented primary. This paper focuses on the fabrication of the mirror segments. Significant cost savings were achieved through the design, since it allowed the mirror segments to be cast rather than machined from a glass blank. Casting was followed by conventional figuring at Goddard Space Flight Center. After polishing, the mirror segments were mounted to their composite assemblies. QED Technologies used magnetorheological finishing (MRF®) for the final figuring. The MRF process polished the mirrors while they were mounted to their composite assemblies. Each assembly included several magnetic invar plugs that extended to within an inch of the face of the mirror. As part of this project, the interaction between the MRF magnetic field and invar plugs was evaluated. By properly selecting the polishing conditions, MRF was able to significantly improve the figure of the mounted segments. The final MRF figuring demonstrates that mirrors, in the mounted configuration, can be polished and tested to specification. There are significant process capability advantes due to polishing and testing the optics in their final, end-use assembled state.

  11. Spherically symmetric conformal gravity and ``gravitational bubbles''

    NASA Astrophysics Data System (ADS)

    Berezin, V. A.; Dokuchaev, V. I.; Eroshenko, Yu. N.

    2016-01-01

    The general structure of the spherically symmetric solutions in the Weyl conformal gravity is described. The corresponding Bach equations are derived for the special type of metrics, which can be considered as the representative of the general class. The complete set of the pure vacuum solutions is found. It consists of two classes. The first one contains the solutions with constant two-dimensional curvature scalar of our specific metrics, and the representatives are the famous Robertson-Walker metrics. One of them we called the ``gravitational bubbles'', which is compact and with zero Weyl tensor. Thus, we obtained the pure vacuum curved space-times (without any material sources, including the cosmological constant) what is absolutely impossible in General Relativity. Such a phenomenon makes it easier to create the universe from ``nothing''. The second class consists of the solutions with varying curvature scalar. We found its representative as the one-parameter family. It appears that it can be conformally covered by the thee-parameter Mannheim-Kazanas solution. We also investigated the general structure of the energy-momentum tensor in the spherical conformal gravity and constructed the vectorial equation that reveals clearly some features of non-vacuum solutions. Two of them are explicitly written, namely, the metrics à la Vaidya, and the electrovacuum space-time metrics.

  12. Clusters of polyhedra in spherical confinement

    PubMed Central

    Teich, Erin G.; van Anders, Greg; Klotsa, Daphne; Dshemuchadse, Julia; Glotzer, Sharon C.

    2016-01-01

    Dense particle packing in a confining volume remains a rich, largely unexplored problem, despite applications in blood clotting, plasmonics, industrial packaging and transport, colloidal molecule design, and information storage. Here, we report densest found clusters of the Platonic solids in spherical confinement, for up to N=60 constituent polyhedral particles. We examine the interplay between anisotropic particle shape and isotropic 3D confinement. Densest clusters exhibit a wide variety of symmetry point groups and form in up to three layers at higher N. For many N values, icosahedra and dodecahedra form clusters that resemble sphere clusters. These common structures are layers of optimal spherical codes in most cases, a surprising fact given the significant faceting of the icosahedron and dodecahedron. We also investigate cluster density as a function of N for each particle shape. We find that, in contrast to what happens in bulk, polyhedra often pack less densely than spheres. We also find especially dense clusters at so-called magic numbers of constituent particles. Our results showcase the structural diversity and experimental utility of families of solutions to the packing in confinement problem. PMID:26811458

  13. Clusters of polyhedra in spherical confinement.

    PubMed

    Teich, Erin G; van Anders, Greg; Klotsa, Daphne; Dshemuchadse, Julia; Glotzer, Sharon C

    2016-02-09

    Dense particle packing in a confining volume remains a rich, largely unexplored problem, despite applications in blood clotting, plasmonics, industrial packaging and transport, colloidal molecule design, and information storage. Here, we report densest found clusters of the Platonic solids in spherical confinement, for up to [Formula: see text] constituent polyhedral particles. We examine the interplay between anisotropic particle shape and isotropic 3D confinement. Densest clusters exhibit a wide variety of symmetry point groups and form in up to three layers at higher N. For many N values, icosahedra and dodecahedra form clusters that resemble sphere clusters. These common structures are layers of optimal spherical codes in most cases, a surprising fact given the significant faceting of the icosahedron and dodecahedron. We also investigate cluster density as a function of N for each particle shape. We find that, in contrast to what happens in bulk, polyhedra often pack less densely than spheres. We also find especially dense clusters at so-called magic numbers of constituent particles. Our results showcase the structural diversity and experimental utility of families of solutions to the packing in confinement problem.

  14. Close packing of rods on spherical surfaces

    NASA Astrophysics Data System (ADS)

    Smallenburg, Frank; Löwen, Hartmut

    2016-04-01

    We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry of the closest-packed configuration as a function of the aspect ratio L/D, where L is the cylinder length and D the diameter of the rods. We find a rich variety of cluster structures. For larger clusters, we find that the best-packed configurations up to around 100 particles are highly dependent on the exact number of particles and aspect ratio. For even larger clusters, we find largely disordered clusters for very short rods (L/D = 0.25), while slightly longer rods (L/D = 0.5 or 1) prefer a global baseball-like geometry of smectic-like domains, similar to the behavior of large-scale nematic shells. Intriguingly, we observe that when compared to their optimal flat-plane packing, short rods adapt to the spherical geometry more efficiently than both spheres and longer rods. Our results provide predictions for experimentally realizable systems of colloidal rods trapped at the interface of emulsion droplets.

  15. Variational extensions of the mean spherical approximation

    NASA Astrophysics Data System (ADS)

    Blum, L.; Ubriaco, M.

    2000-04-01

    In a previous work we have proposed a method to study complex systems with objects of arbitrary size. For certain specific forms of the atomic and molecular interactions, surprisingly simple and accurate theories (The Variational Mean Spherical Scaling Approximation, VMSSA) [(Velazquez, Blum J. Chem. Phys. 110 (1990) 10 931; Blum, Velazquez, J. Quantum Chem. (Theochem), in press)] can be obtained. The basic idea is that if the interactions can be expressed in a rapidly converging sum of (complex) exponentials, then the Ornstein-Zernike equation (OZ) has an analytical solution. This analytical solution is used to construct a robust interpolation scheme, the variation mean spherical scaling approximation (VMSSA). The Helmholtz excess free energy Δ A=Δ E- TΔ S is then written as a function of a scaling matrix Γ. Both the excess energy Δ E( Γ) and the excess entropy Δ S( Γ) will be functionals of Γ. In previous work of this series the form of this functional was found for the two- (Blum, Herrera, Mol. Phys. 96 (1999) 821) and three-exponential closures of the OZ equation (Blum, J. Stat. Phys., submitted for publication). In this paper we extend this to M Yukawas, a complete basis set: We obtain a solution for the one-component case and give a closed-form expression for the MSA excess entropy, which is also the VMSSA entropy.

  16. Understanding pop-ins in spherical nanoindentation

    DOE PAGES

    Pathak, Siddhartha; Riesterer, Jessica L.; Kalidindi, Surya R.; ...

    2014-10-24

    In this study, pop-ins, or sudden displacement-bursts at constant load in a nanoindentation test, are typically attributed to the difficulty of setting up potent dislocation sources in the very small indentation zones in these experiments. Such displacement (and strain) bursts would intuitively indicate a sharp drop in stress during the pop-in event itself. However, spherical indentation stress-strain curves routinely exhibit a high and stable indentation stress value during the pop-in, and the indentation stresses decrease only after a further finite amount of additional indentation displacement has been applied. In order to understand this discrepancy, we utilize a combination of interruptedmore » spherical indentation tests along with depth profiling of the residual indentation surfaces using in-situ atomic force microscopy (AFM) to study pop-ins. The AFM surface profile maps show that there is an asymmetric profile change over a limited region around the indentation contact area for a single pop-in; the asymmetry disappears upon further loading beyond the pop-in. A plausible sequence of physical processes (related to metal plasticity) occurring underneath the indenter during and immediately after the occurrence of the pop-in is proposed to explain these observations.« less

  17. Understanding pop-ins in spherical nanoindentation

    SciTech Connect

    Pathak, Siddhartha; Riesterer, Jessica L.; Kalidindi, Surya R.; Michler, Johann

    2014-10-24

    In this study, pop-ins, or sudden displacement-bursts at constant load in a nanoindentation test, are typically attributed to the difficulty of setting up potent dislocation sources in the very small indentation zones in these experiments. Such displacement (and strain) bursts would intuitively indicate a sharp drop in stress during the pop-in event itself. However, spherical indentation stress-strain curves routinely exhibit a high and stable indentation stress value during the pop-in, and the indentation stresses decrease only after a further finite amount of additional indentation displacement has been applied. In order to understand this discrepancy, we utilize a combination of interrupted spherical indentation tests along with depth profiling of the residual indentation surfaces using in-situ atomic force microscopy (AFM) to study pop-ins. The AFM surface profile maps show that there is an asymmetric profile change over a limited region around the indentation contact area for a single pop-in; the asymmetry disappears upon further loading beyond the pop-in. A plausible sequence of physical processes (related to metal plasticity) occurring underneath the indenter during and immediately after the occurrence of the pop-in is proposed to explain these observations.

  18. Ultrarelativistic bound states in the spherical well

    NASA Astrophysics Data System (ADS)

    Żaba, Mariusz; Garbaczewski, Piotr

    2016-07-01

    We address an eigenvalue problem for the ultrarelativistic (Cauchy) operator (-Δ)1/2, whose action is restricted to functions that vanish beyond the interior of a unit sphere in three spatial dimensions. We provide high accuracy spectral data for lowest eigenvalues and eigenfunctions of this infinite spherical well problem. Our focus is on radial and orbital shapes of eigenfunctions. The spectrum consists of an ordered set of strictly positive eigenvalues which naturally splits into non-overlapping, orbitally labelled E(k,l) series. For each orbital label l = 0, 1, 2, …, the label k = 1, 2, … enumerates consecutive lth series eigenvalues. Each of them is 2l + 1-degenerate. The l = 0 eigenvalues series E(k,0) are identical with the set of even labeled eigenvalues for the d = 1 Cauchy well: E(k,0)(d = 3) = E2k(d = 1). Likewise, the eigenfunctions ψ(k,0)(d = 3) and ψ2k(d = 1) show affinity. We have identified the generic functional form of eigenfunctions of the spherical well which appear to be composed of a product of a solid harmonic and of a suitable purely radial function. The method to evaluate (approximately) the latter has been found to follow the universal pattern which effectively allows to skip all, sometimes involved, intermediate calculations (those were in usage, while computing the eigenvalues for l ≤ 3).

  19. Light gradients in spherical photosynthetic vesicles.

    PubMed

    Paillotin, G; Leibl, W; Gapiński, J; Breton, J; Dobek, A

    1998-07-01

    Light-gradient photovoltage measurements were performed on EDTA-treated thylakoids and on osmotically swollen thylakoids (blebs), both of spherical symmetry but of different sizes. In the case of EDTA vesicles, a negative polarity (due to the normal light gradient) was observed in the blue range of the absorption spectrum, and a positive polarity, corresponding to an inverse light gradient, was observed at lambda = 530 and lambda = 682 nm. The sign of the photovoltage polarity measured in large blebs (swollen thylakoids) is the same as that obtained for whole chloroplasts, although differences in the amplitudes are observed. An approach based on the use of polar coordinates was adapted for a theoretical description of these membrane systems of spherical symmetry. The light intensity distribution and the photovoltage in such systems were calculated. Fits to the photovoltage amplitudes, measured as a function of light wavelength, made it possible to derive the values of the dielectric constant of the protein, epsilons = 3, and the refractive index of the photosynthetic membrane for light propagating perpendicular and parallel to the membrane surface, nt = 1.42 and nn = 1.60, respectively. The latter two values determine the birefringence of the biological membrane, Deltan = nn - nt = 0.18.

  20. Spherically symmetric conformal gravity and ''gravitational bubbles''

    SciTech Connect

    Berezin, V.A.; Dokuchaev, V.I.; Eroshenko, Yu.N. E-mail: dokuchaev@inr.ac.ru

    2016-01-01

    The general structure of the spherically symmetric solutions in the Weyl conformal gravity is described. The corresponding Bach equations are derived for the special type of metrics, which can be considered as the representative of the general class. The complete set of the pure vacuum solutions is found. It consists of two classes. The first one contains the solutions with constant two-dimensional curvature scalar of our specific metrics, and the representatives are the famous Robertson-Walker metrics. One of them we called the ''gravitational bubbles'', which is compact and with zero Weyl tensor. Thus, we obtained the pure vacuum curved space-times (without any material sources, including the cosmological constant) what is absolutely impossible in General Relativity. Such a phenomenon makes it easier to create the universe from ''nothing''. The second class consists of the solutions with varying curvature scalar. We found its representative as the one-parameter family. It appears that it can be conformally covered by the thee-parameter Mannheim-Kazanas solution. We also investigated the general structure of the energy-momentum tensor in the spherical conformal gravity and constructed the vectorial equation that reveals clearly some features of non-vacuum solutions. Two of them are explicitly written, namely, the metrics à la Vaidya, and the electrovacuum space-time metrics.

  1. Rayleigh scattering of a spherical sound wave.

    PubMed

    Godin, Oleg A

    2013-02-01

    Acoustic Green's functions for a homogeneous medium with an embedded spherical obstacle arise in analyses of scattering by objects on or near an interface, radiation by finite sources, sound attenuation in and scattering from clouds of suspended particles, etc. An exact solution of the problem of diffraction of a monochromatic spherical sound wave on a sphere is given by an infinite series involving products of Bessel functions and Legendre polynomials. In this paper, a simple, closed-form solution is obtained for scattering by a sphere with a radius that is small compared to the wavelength. Soft, hard, impedance, and fluid obstacles are considered. The solution is valid for arbitrary positions of the source and receiver relative to the scatterer. Low-frequency scattering is shown to be rather sensitive to boundary conditions on the surface of the obstacle. Low-frequency asymptotics of the scattered acoustic field are extended to transient incident waves. The asymptotic expansions admit an intuitive interpretation in terms of image sources and reduce to classical results in appropriate limiting cases.

  2. Understanding pop-ins in spherical nanoindentation

    SciTech Connect

    Pathak, Siddhartha E-mail: siddharthapathak@gmail.com; Riesterer, Jessica L.; Michler, Johann; Kalidindi, Surya R.

    2014-10-20

    Pop-ins, or sudden displacement-bursts at constant load in a nanoindentation test, are typically attributed to the difficulty of setting up potent dislocation sources in the very small indentation zones in these experiments. Such displacement (and strain) bursts would intuitively indicate a sharp drop in stress during the pop-in event itself. However, spherical indentation stress-strain curves routinely exhibit a high and stable indentation stress value during the pop-in, and the indentation stresses decrease only after a further finite amount of additional indentation displacement has been applied. In order to understand this discrepancy, we utilize a combination of interrupted spherical indentation tests along with depth profiling of the residual indentation surfaces using in-situ atomic force microscopy (AFM) to study pop-ins. The AFM surface profile maps show that there is an asymmetric profile change over a limited region around the indentation contact area for a single pop-in; the asymmetry disappears upon further loading beyond the pop-in. A plausible sequence of physical processes (related to metal plasticity) occurring underneath the indenter during and immediately after the occurrence of the pop-in is proposed to explain these observations.

  3. Central MONDian spike in spherically symmetric systems

    NASA Astrophysics Data System (ADS)

    Hernandez, X.

    2017-08-01

    Under a MONDian view, astrophysical systems are expected to follow Newtonian dynamics whenever the local acceleration is above the critical a0 = 1.2 × 10-10 m s-2, and enter a modified regime for accelerations below this critical value. Indeed, the dark matter phenomenology on galactic and subgalactic scales appears always, and only, at low accelerations. It is standard to find the a < a0 regime towards the low density outskirts of astronomical systems, where under a Newtonian interpretation, dark matter becomes conspicuous. Thus, it is standard to find, and to think, of the dense central regions of observed systems as purely Newtonian. However, under spherical symmetry in the MONDian as in the Newtonian case, the local acceleration will tend to zero as one approaches the very centre of a mass distribution. It is clear that for spherically symmetric systems, an inner a < a0 region will necessarily appear interior to a critical radius, which will depend on the details of the density profile in question. Here, we calculate analytically such a critical radius for a constant-density core, and numerically for a cored isothermal profile. Under a Newtonian interpretation, such a central MONDian region will be interpreted as extra mass, analogous to the controversial black holes sometimes inferred to lie at the centres of globular clusters, despite an absence of nuclear activity detected to date. We calculate this effect and give predictions for the 'central black hole' mass to be expected under Newtonian interpretations of low density Galactic globular clusters.

  4. Relativistic radiative transfer in relativistic spherical flows

    NASA Astrophysics Data System (ADS)

    Fukue, Jun

    2017-02-01

    Relativistic radiative transfer in relativistic spherical flows is numerically examined under the fully special relativistic treatment. We first derive relativistic formal solutions for the relativistic radiative transfer equation in relativistic spherical flows. We then iteratively solve the relativistic radiative transfer equation, using an impact parameter method/tangent ray method, and obtain specific intensities in the inertial and comoving frames, as well as moment quantities, and the Eddington factor. We consider several cases; a scattering wind with a luminous central core, an isothermal wind without a core, a scattering accretion on to a luminous core, and an adiabatic accretion on to a dark core. In the typical wind case with a luminous core, the emergent intensity is enhanced at the center due to the Doppler boost, while it reduces at the outskirts due to the transverse Doppler effect. In contrast to the plane-parallel case, the behavior of the Eddington factor is rather complicated in each case, since the Eddington factor depends on the optical depth, the flow velocity, and other parameters.

  5. Conservative interpolation between general spherical meshes

    NASA Astrophysics Data System (ADS)

    Kritsikis, Evaggelos; Aechtner, Matthias; Meurdesoif, Yann; Dubos, Thomas

    2017-01-01

    An efficient, local, explicit, second-order, conservative interpolation algorithm between spherical meshes is presented. The cells composing the source and target meshes may be either spherical polygons or latitude-longitude quadrilaterals. Second-order accuracy is obtained by piece-wise linear finite-volume reconstruction over the source mesh. Global conservation is achieved through the introduction of a supermesh, whose cells are all possible intersections of source and target cells. Areas and intersections are computed exactly to yield a geometrically exact method. The main efficiency bottleneck caused by the construction of the supermesh is overcome by adopting tree-based data structures and algorithms, from which the mesh connectivity can also be deduced efficiently.The theoretical second-order accuracy is verified using a smooth test function and pairs of meshes commonly used for atmospheric modelling. Experiments confirm that the most expensive operations, especially the supermesh construction, have O(NlogN) computational cost. The method presented is meant to be incorporated in pre- or post-processing atmospheric modelling pipelines, or directly into models for flexible input/output. It could also serve as a basis for conservative coupling between model components, e.g., atmosphere and ocean.

  6. Spherical Rayleigh-Taylor Growth of Three-Dimensional Broadband Perturbations on OMEGA

    SciTech Connect

    Smalyuk, V.A.; Hu, S.X.; Hager, J.D.; Delettrez, J.A.; Meyerhofer, D.D.; Sangster, T.C.; Shvarts, D.

    2009-11-10

    Spherical Rayleigh–Taylor (RT) growth experiments of three-dimensional (3D) broadband nonuniformities were conducted in the acceleration phase of spherical implosions on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The targets consisted of 20- and 24-um-thick plastic spherical shells having diagnostic openings for backlighter x rays to image shell modulations. Experiments were conducted with square laser pulses at a low drive intensity of ~2 x 10^14 W/cm^2, high drive intensity of ~1 x 10^15 W/cm^2, and a shaped pulse consisting of a low-intensity foot and high-intensity drive part (peak intensity of ~1 x 10^15 W/cm^2). In low-intensity experiments, large RT growth was measured, resulting in shells being broken up by 3D modulations at the end of the drive. In the high-intensity experiments, no RT growth of the 3D modulations was detected. In the shaped-pulse experiments, perturbations grew during the low-intensity part of the drive and were stabilized later during the high-intensity part of the drive. The measured RT growth stabilization with the high-intensity drive was similar to previous observations in planar geometry [V. A. Smalyuk et al., Phys. Rev. Lett. 101, 025002 (2008)].

  7. Microstability in a ``MAST-like'' high confinement mode spherical tokamak equilibrium

    NASA Astrophysics Data System (ADS)

    Applegate, D. J.; Roach, C. M.; Cowley, S. C.; Dorland, W. D.; Joiner, N.; Akers, R. J.; Conway, N. J.; Field, A. R.; Patel, A.; Valovic, M.; Walsh, M. J.

    2004-11-01

    Gyrokinetic microstability analyses, with and without electromagnetic effects, are presented for a spherical tokamak plasma equilibrium closely resembling that from a high confinement mode (H mode) discharge in the mega-ampere spherical tokamak (MAST) [A. Sykes et al., Nucl. Fusion 41, 1423 (2001)]. Electrostatic ion temperature gradient driven modes (ITG modes) were found to be unstable on all surfaces, though they are likely to be substantially stabilized by equilibrium E×B flow shear. Electron temperature gradient driven modes (ETG modes) have stronger growth rates that substantially exceed the equilibrium flow shearing rates. Mixing length arguments suggest that ITG modes would give rise to significant transport if they are not stabilized by sheared flows, and predict weak transport from ETG turbulence. Significant plasma flows have been neglected in this first analysis, and are probably important in the delicate balance between ITG growth rates and flow shear, and in the formation of internal transport barriers on MAST. Electromagnetic effects are found to be important even in this low β discharge, especially for longer length-scale modes with k⊥ρispherical tokamak equilibria.

  8. Characterizing student mathematics teachers' levels of understanding in spherical geometry

    NASA Astrophysics Data System (ADS)

    Guven, Bulent; Baki, Adnan

    2010-12-01

    This article presents an exploratory study aimed at the identification of students' levels of understanding in spherical geometry as van Hiele did for Euclidean geometry. To do this, we developed and implemented a spherical geometry course for student mathematics teachers. Six structured, task-based interviews were held with eight student mathematics teachers at particular times through the course to determine the spherical geometry learning levels. After identifying the properties of spherical geometry levels, we developed Understandings in Spherical Geometry Test to test whether or not the levels form hierarchy, and 58 student mathematics teachers took the test. The outcomes seemed to support our theoretical perspective that there are some understanding levels in spherical geometry that progress through a hierarchical order as van Hiele levels in Euclidean geometry.

  9. Recent Progress on Spherical Torus Research and Implications for Fusion Energy Development Path

    NASA Astrophysics Data System (ADS)

    Ono, Masayuki

    2014-10-01

    The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A =R0 / a) reduced to A near 1.5, well below the normal tokamak operating range of A equal to 2.5 or greater. As the aspect ratio is reduced, the ideal tokamak beta (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural plasma elongation which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to the longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment (NSTX) in the US and Mega Ampere Spherical Tokamak (MAST) in the UK, active ST research has been conducted worldwide. More than sixteen ST research facilities operating during this period have achieved remarkable advances in all areas of fusion research, including fundamental fusion energy science as well as technological innovation. These results suggest exciting future prospects for ST research in both the near and longer term. The talk will summarize the key physics results from worldwide ST experiments, and describe ST community plans to provide the database for FNSF design while improving predictive capabilities for ITER and beyond. This work supported by DoE Contract No. DE-AC02-09CH11466.

  10. Energetic particles in spherical tokamak plasmas

    NASA Astrophysics Data System (ADS)

    McClements, K. G.; Fredrickson, E. D.

    2017-05-01

    Spherical tokamaks (STs) typically have lower magnetic fields than conventional tokamaks, but similar mass densities. Suprathermal ions with relatively modest energies, in particular beam-injected ions, consequently have speeds close to or exceeding the Alfvén velocity, and can therefore excite a range of Alfvénic instabilities which could be driven by (and affect the behaviour of) fusion α-particles in a burning plasma. STs heated with neutral beams, including the small tight aspect ratio tokamak (START), the mega amp spherical tokamak (MAST), the national spherical torus experiment (NSTX) and Globus-M, have thus provided an opportunity to study toroidal Alfvén eigenmodes (TAEs), together with higher frequency global Alfvén eigenmodes (GAEs) and compressional Alfvén eigenmodes (CAEs), which could affect beam current drive and channel fast ion energy into bulk ions in future devices. In NSTX GAEs were correlated with a degradation of core electron energy confinement. In MAST pulses with reduced magnetic field, CAEs were excited across a wide range of frequencies, extending to the ion cyclotron range, but were suppressed when hydrogen was introduced to the deuterium plasma, apparently due to mode conversion at ion-ion hybrid resonances. At lower frequencies fishbone instabilities caused fast particle redistribution in some MAST and NSTX pulses, but this could be avoided by moving the neutral beam line away from the magnetic axis or by operating the plasma at either high density or elevated safety factor. Fast ion redistribution has been observed during GAE avalanches on NSTX, while in both NSTX and MAST fast ions were transported by saturated kink modes, sawtooth crashes, resonant magnetic perturbations and TAEs. The energy dependence of fast ion redistribution due to both sawteeth and TAEs has been studied in Globus-M. High energy charged fusion products are unconfined in present-day STs, but have been shown in MAST to provide a useful diagnostic of beam ion

  11. Energetic particles in spherical tokamak plasmas

    DOE PAGES

    McClements, K. G.; Fredrickson, E. D.

    2017-03-21

    Spherical tokamaks (STs) typically have lower magnetic fields than conventional tokamaks, but similar mass densities. Suprathermal ions with relatively modest energies, in particular beam-injected ions, consequently have speeds close to or exceeding the Alfvén velocity, and can therefore excite a range of Alfvénic instabilities which could be driven by (and affect the behaviour of) fusion α-particles in a burning plasma. STs heated with neutral beams, including the small tight aspect ratio tokamak (START), the mega amp spherical tokamak (MAST), the national spherical torus experiment (NSTX) and Globus-M, have thus provided an opportunity to study toroidal Alfvén eigenmodes (TAEs), together withmore » higher frequency global Alfvén eigenmodes (GAEs) and compressional Alfvén eigenmodes (CAEs), which could affect beam current drive and channel fast ion energy into bulk ions in future devices. In NSTX GAEs were correlated with a degradation of core electron energy confinement. In MAST pulses with reduced magnetic field, CAEs were excited across a wide range of frequencies, extending to the ion cyclotron range, but were suppressed when hydrogen was introduced to the deuterium plasma, apparently due to mode conversion at ion–ion hybrid resonances. At lower frequencies fishbone instabilities caused fast particle redistribution in some MAST and NSTX pulses, but this could be avoided by moving the neutral beam line away from the magnetic axis or by operating the plasma at either high density or elevated safety factor. Fast ion redistribution has been observed during GAE avalanches on NSTX, while in both NSTX and MAST fast ions were transported by saturated kink modes, sawtooth crashes, resonant magnetic perturbations and TAEs. The energy dependence of fast ion redistribution due to both sawteeth and TAEs has been studied in Globus-M. High energy charged fusion products are unconfined in present-day STs, but have been shown in MAST to provide a useful diagnostic of

  12. Bending stresses in spherically hollow ball bearing and fatigue experiments

    NASA Technical Reports Server (NTRS)

    Nypan, L. J.; Coe, H. H.; Parker, R. J.

    1975-01-01

    Spherically hollow balls of 21.7, 50.0, and 56.5 percent mass reduction were operated in ball bearings and in a five-ball fatigue tester with differing outcomes. Available theoretical and experimental treatments of stresses in spherically hollow balls are reviewed and compared. Bending stresses are estimated for these spherically hollow balls to better understand the differences in ball bearing and fatigue test experience.

  13. Spherical solitons in Earth’S mesosphere plasma

    SciTech Connect

    Annou, K.; Annou, R.

    2016-01-15

    Soliton formation in Earth’s mesosphere plasma is described. Nonlinear acoustic waves in plasmas with two-temperature ions and a variable dust charge where transverse perturbation is dealt with are studied in bounded spherical geometry. Using the perturbation method, a spherical Kadomtsev–Petviashvili equation that describes dust acoustic waves is derived. It is found that the parameters taken into account have significant effects on the properties of nonlinear waves in spherical geometry.

  14. Temperature Chaos in Some Spherical Mixed p-Spin Models

    NASA Astrophysics Data System (ADS)

    Chen, Wei-Kuo; Panchenko, Dmitry

    2017-03-01

    We give two types of examples of the spherical mixed even- p-spin models for which chaos in temperature holds. These complement some known results for the spherical pure p-spin models and for models with Ising spins. For example, in contrast to a recent result of Subag who showed absence of chaos in temperature in the spherical pure p-spin models for p≥3, we show that even a smaller order perturbation induces temperature chaos.

  15. Crystal growth of drug materials by spherical crystallization

    NASA Astrophysics Data System (ADS)

    Szabó-Révész, P.; Hasznos-Nezdei, M.; Farkas, B.; Göcző, H.; Pintye-Hódi, K.; Erős, I.

    2002-04-01

    One of the crystal growth processes is the production of crystal agglomerates by spherical crystallization. Agglomerates of drug materials were developed by means of non-typical (magnesium aspartate) and typical (acetylsalicylic acid) spherical crystallization techniques. The growth of particle size and the spherical form of the agglomerates resulted in formation of products with good bulk density, flow, compactibility and cohesivity properties. The crystal agglomerates were developed for direct capsule-filling and tablet-making.

  16. GENERAL: Non-Spherical Gravitational Collapse of Strange Quark Matter

    NASA Astrophysics Data System (ADS)

    S, Zade S.; D, Patil K.; N, Mulkalwar P.

    2008-05-01

    We study the non-spherical gravitational collapse of the strange quark null fluid. The interesting feature which emerges is that the non-spherical collapse of charged strange quark matter leads to a naked singularity whereas the gravitational collapse of neutral quark matter proceeds to form a black hole. We extend the earlier work of Harko and Cheng [Phys. Lett. A 266 (2000) 249] to the non-spherical case.

  17. Spherical Cryogenic Hydrogen Tank Preliminary Design Trade Studies

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Bednarcyk, Brett A.; Collier, Craig S.; Yarrington, Phillip W.

    2007-01-01

    A structural analysis, sizing optimization, and weight prediction study was performed by Collier Research Corporation and NASA Glenn on a spherical cryogenic hydrogen tank. The tank consisted of an inner and outer wall separated by a vacuum for thermal insulation purposes. HyperSizer (Collier Research and Development Corporation), a commercial automated structural analysis and sizing software package was used to design the lightest feasible tank for a given overall size and thermomechanical loading environment. Weight trade studies were completed for different panel concepts and metallic and composite material systems. Extensive failure analyses were performed for each combination of dimensional variables, materials, and layups to establish the structural integrity of tank designs. Detailed stress and strain fields were computed from operational temperature changes and pressure loads. The inner tank wall is sized by the resulting biaxial tensile stresses which cause it to be strength driven, and leads to an optimum panel concept that need not be stiffened. Conversely, the outer tank wall is sized by a biaxial compressive stress field, induced by the pressure differential between atmospheric pressure and the vacuum between the tanks, thereby causing the design to be stability driven and thus stiffened to prevent buckling. Induced thermal stresses become a major sizing driver when a composite or hybrid composite/metallic material systems are used for the inner tank wall for purposes such as liners to contain the fuel and reduce hydrogen permeation.

  18. Spherically symmetric Einstein-aether perfect fluid models

    SciTech Connect

    Coley, Alan A.; Latta, Joey; Leon, Genly; Sandin, Patrik E-mail: genly.leon@ucv.cl E-mail: lattaj@mathstat.dal.ca

    2015-12-01

    We investigate spherically symmetric cosmological models in Einstein-aether theory with a tilted (non-comoving) perfect fluid source. We use a 1+3 frame formalism and adopt the comoving aether gauge to derive the evolution equations, which form a well-posed system of first order partial differential equations in two variables. We then introduce normalized variables. The formalism is particularly well-suited for numerical computations and the study of the qualitative properties of the models, which are also solutions of Horava gravity. We study the local stability of the equilibrium points of the resulting dynamical system corresponding to physically realistic inhomogeneous cosmological models and astrophysical objects with values for the parameters which are consistent with current constraints. In particular, we consider dust models in (β−) normalized variables and derive a reduced (closed) evolution system and we obtain the general evolution equations for the spatially homogeneous Kantowski-Sachs models using appropriate bounded normalized variables. We then analyse these models, with special emphasis on the future asymptotic behaviour for different values of the parameters. Finally, we investigate static models for a mixture of a (necessarily non-tilted) perfect fluid with a barotropic equations of state and a scalar field.

  19. Fabrication and cytocompatibility of spherical magnesium ammonium phosphate granules.

    PubMed

    Christel, Theresa; Geffers, Martha; Klammert, Uwe; Nies, Berthold; Höß, Andreas; Groll, Jürgen; Kübler, Alexander C; Gbureck, Uwe

    2014-09-01

    Magnesium phosphate compounds, as for example struvite (MgNH4PO4·6H2O), have comparable characteristics to calcium phosphate bone substitutes, but degrade faster under physiological conditions. In the present work, we used a struvite forming calcium doped magnesium phosphate cement with the formulation Ca0.75Mg2.25(PO4)2 and an ammonium phosphate containing aqueous solution to produce round-shaped granules. For the fabrication of spherical granules, the cement paste was dispersed in a lipophilic liquid and stabilized by surfactants. The granules were characterized with respect to morphology, size distribution, phase composition, compressive strength, biocompatibility and solubility. In general, it was seen that small granules can hardly be produced by means of emulsification, when the raw material is a hydraulic paste, because long setting times promote coalescence of initially small unhardened cement droplets. Here, this problem was solved by using an aqueous solution containing both the secondary (NH4)2HPO4 and primary ammonium phosphates NH4H2PO4 to accelerate the setting reaction. This resulted in granules with 97 wt.% having a size in the range between 200 and 1,000 μm. The novel solution composition doubled the compressive strength of the cement to 37 ± 5 MPa without affecting either the conversion to struvite or the cytocompatibility using human fetal osteoblasts.

  20. Spherical crystals in dusty plasmas - Simulation and theory

    NASA Astrophysics Data System (ADS)

    Bonitz, M.; Henning, C.; Golubnychiy, V.; Baumgartner, H.; Ludwig, P.; Arp, O.; Block, D.; Piel, A.; Melzer, A.; Kraeft, W. D.

    2006-10-01

    Coulomb crystals in spherically symmetric traps have been found in trapped cold ions and, recently, in dusty plasmas at room temperature [1] allowing for precision measurements, including individual particle positions and trajectories. Thus, for the first time, strong correlation phenomena can be studied directly on the microscopic level which allows for detailed comparisons with theoretical results and computer simulations. We present molecular dynamics and Monte Carlo simulations of Coulomb crystals in the range from 10 to 10,000 particles which agree very well with the measurements [3]. The results include the ground state shell configurations and symmetry properties [2,3], the crystal stability and melting behavior. Finally, a thermodynamic theory is developed and compared to simpler models, such as shell models [4]. [1] O. Arp, D. Block, A. Piel, and A. Melzer, Phys. Rev. Lett. 93, 165004 (2004). [2] P. Ludwig, S. Kosse, and M. Bonitz, Phys. Rev. E 71, 046403 (2005). [3] M. Bonitz, D. Block, O. Arp, V. Golubnychiy, H. Baumgartner, P. Ludwig, A. Piel, and A. Filinov, Phys. Rev. Lett. 96, 075001 (2006). [4] C. Henning et al., submitted for publication.

  1. Nonadiabatic charged spherical evolution in the postquasistatic approximation

    SciTech Connect

    Rosales, L.; Barreto, W.; Peralta, C.; Rodriguez-Mueller, B.

    2010-10-15

    We apply the postquasistatic approximation, an iterative method for the evolution of self-gravitating spheres of matter, to study the evolution of dissipative and electrically charged distributions in general relativity. The numerical implementation of our approach leads to a solver which is globally second-order convergent. We evolve nonadiabatic distributions assuming an equation of state that accounts for the anisotropy induced by the electric charge. Dissipation is described by streaming-out or diffusion approximations. We match the interior solution, in noncomoving coordinates, with the Vaidya-Reissner-Nordstroem exterior solution. Two models are considered: (i) a Schwarzschild-like shell in the diffusion limit; and (ii) a Schwarzschild-like interior in the free-streaming limit. These toy models tell us something about the nature of the dissipative and electrically charged collapse. Diffusion stabilizes the gravitational collapse producing a spherical shell whose contraction is halted in a short characteristic hydrodynamic time. The streaming-out radiation provides a more efficient mechanism for emission of energy, redistributing the electric charge on the whole sphere, while the distribution collapses indefinitely with a longer hydrodynamic time scale.

  2. Statistical mechanics of the spherical hierarchical model with random fields

    NASA Astrophysics Data System (ADS)

    Metz, Fernando L.; Rocchi, Jacopo; Urbani, Pierfrancesco

    2014-09-01

    We study analytically the equilibrium properties of the spherical hierarchical model in the presence of random fields. The expression for the critical line separating a paramagnetic from a ferromagnetic phase is derived. The critical exponents characterising this phase transition are computed analytically and compared with those of the corresponding D-dimensional short-range model, leading to conclude that the usual mapping between one dimensional long-range models and D-dimensional short-range models holds exactly for this system, in contrast to models with Ising spins. Moreover, the critical exponents of the pure model and those of the random field model satisfy a relationship that mimics the dimensional reduction rule. The absence of a spin-glass phase is strongly supported by the local stability analysis of the replica symmetric saddle-point as well as by an independent computation of the free-energy using a renormalization-like approach. This latter result enlarges the class of random field models for which the spin-glass phase has been recently ruled out.

  3. Strike Point Control for the National Spherical Torus Experiment (NSTX)

    SciTech Connect

    Kolemen, E.; Gates, D. A.; Rowley, C. W.; Kasdin, N. J.; Kallman, J.; Gerhardt, S.; Soukhanovskii, V.; Mueller, D.

    2010-07-09

    This paper presents the first control algorithm for the inner and outer strike point position for a Spherical Torus (ST) fusion experiment and the performance analysis of the controller. A liquid lithium divertor (LLD) will be installed on NSTX which is believed to provide better pumping than lithium coatings on carbon PFCs. The shape of the plasma dictates the pumping rate of the lithium by channeling the plasma to LLD, where strike point location is the most important shape parameter. Simulations show that the density reduction depends on the proximity of strike point to LLD. Experiments were performed to study the dynamics of the strike point, design a new controller to change the location of the strike point to desired location and stabilize it. The most effective PF coils in changing inner and outer strike points were identified using equilibrium code. The PF coil inputs were changed in a step fashion between various set points and the step response of the strike point position was obtained. From the analysis of the step responses, PID controllers for the strike points were obtained and the controller was tuned experimentally for better performance. The strike controller was extended to include the outer-strike point on the inner plate to accommodate the desired low outer-strike points for the experiment with the aim of achieving "snowflake" divertor configuration in NSTX.

  4. Electron Bernstein Wave Research on the National Spherical Torus Experiment

    SciTech Connect

    G. Taylor; A. Bers; T.S. Bigelow; M.D. Carter; J.B. Caughman; J. Decker; S. Diem; P.C. Efthimion; N.M. Ershov; E. Fredd; R.W. Harvey; J. Hosea; F. Jaeger; J. Preinhaelter; A.K. Ram; D.A. Rasmussen; A.P. Smirnov; J.B. Wilgen; J.R. Wilson

    2005-04-21

    Off-axis electron Bernstein wave current drive (EBWCD) may be critical for sustaining noninductive high-beta National Spherical Torus Experiment (NSTX) plasmas. Numerical modeling results predict that the {approx}100 kA of off-axis current needed to stabilize a solenoid-free high-beta NSTX plasma could be generated via Ohkawa current drive with 3 MW of 28 GHz EBW power. In addition, synergy between EBWCD and bootstrap current may result in a 10% enhancement in current-drive efficiency with 4 MW of EBW power. Recent dual-polarization EBW radiometry measurements on NSTX confirm that efficient coupling to EBWs can be readily accomplished by launching elliptically polarized electromagnetic waves oblique to the confining magnetic field, in agreement with numerical modeling. Plans are being developed for implementing a 1 MW, 28 GHz proof-of-principle EBWCD system on NSTX to test the EBW coupling, heating and current-drive physics at high radio-frequency power densities.

  5. Modelling of Spherical Gas Bubble Oscillations and Sonoluminescence

    NASA Technical Reports Server (NTRS)

    Prosperetti, A.; Hao, Y.

    1999-01-01

    The discovery of single-bubble sonoluminescence has led to a renewed interest in the forced radial oscillations of gas bubbles. Many of the more recent studies devoted to this topic have used several simplifications in the modelling, and in particular in accounting for liquid compressibility and thermal processes in the bubble. In this paper the significance of these simplifications is explored by contrasting the results of Lohse and co-workers with those of a more detailed model. It is found that, even though there may be little apparent difference between the radius-versus time behaviour of the bubble as predicted by the two models, quantities such as the spherical stability boundary and the threshold for rectified diffusion are affected in a quantitatively significant way. These effects are a manifestation of the subtle dependence upon dissipative processes of the phase of radial motion with respect to the driving sound field. The parameter space region, where according to the theory of Lohse and co-workers, sonoluminescence should be observable, is recalculated with the new model and is found to be enlarged with respect to the earlier estimate. The dependence of this parameter region on sound frequency is also illustrated.

  6. Magneto-hydro-dynamic limits in spherical tokamaks

    NASA Astrophysics Data System (ADS)

    Hender, T. C.; Allfrey, S. J.; Akers, R.; Appel, L. C.; Bevir, M. K.; Buttery, R. J.; Gryaznevich, M.; Jenkins, I.; Kwon, O. J.; McClements, K. G.; Martin, R.; Medvedev, S.; Nightingale, M. P. S.; Ribeiro, C.; Roach, C. M.; Robinson, D. C.; Sharapov, S. E.; Sykes, A.; Villard, L.; Walsh, M. J.

    1999-05-01

    The operational limits observed in spherical tokamaks, notably the small tight aspect ratio tokamak (START) device [A. Sykes et al., Nucl. Fusion 32, 694 (1992)], are consistent with those found in conventional aspect ratio tokamaks. In particular the highest β achieved (˜40%) is consistent with an ideal magneto-hydro-dynamic (MHD) Troyon type limit, the upper limit on density is well described by the Greenwald density (πa2n¯e/Ip˜1) and the normalized current (Ip/aBt) is limited such that q95≳2. Stability calculations indicate scope for increasing both normalized β and normalized current beyond the values so far achieved, although wall stabilization is generally needed for low-n modes. In double null configurations current terminating disruptions occur at each of the operational boundaries, though the current quench tends to be slow at the density limit and disruptions at high β may be due to the low q. In early limiter START discharges, before the divertor coils were installed, disruptions rarely occurred. Instead internal reconnection events which have all the characteristics of a disruption except the current quench occurred. These various disruptive behaviors are explained in terms of a model in which helicity is conserved during the disruption. Due to the low toroidal field beam ions in START, and α particles in a ST power plant, are super-Alfvénic. This gives the possibility for toroidal Alfvén eigenmodes (TAEs) to occur and such modes are frequently observed in START neutral beam injection (NBI) discharges, but seem to be benign. The features of these observed TAEs are shown to be in agreement with MHD calculations.

  7. Characteristic Matrices for Spherical Shell Photonic Systems

    NASA Technical Reports Server (NTRS)

    Fuller, Kirk A.; Smith, David D.

    2004-01-01

    We establish a parallel between the transfer matrix used in the study of plane-parallel photonic structures and the matrix characterizing transfer of partial waves in concentric spheres. We derive explicit expressions for the elements of the transfer matrix for concentric spherical layers, and from those expressions derive the scattering coefficients of a multilayered sphere. The transfer matrices are 4x4 block diagonal with only four independent elements. Matrix elements for the case of TM waves are related to those for the case of TE waves through simple interchange and multiplicative constants. In analogy with plane parallel layers, the transfer matrix for concentric multilayers is simply the product of the transfer matrices of the individual layers.

  8. Microtearing modes in spherical and conventional tokamaks

    NASA Astrophysics Data System (ADS)

    Moradi, S.; Pusztai, I.; Guttenfelder, W.; Fülöp, T.; Mollén, A.

    2013-06-01

    The onset and characteristics of microtearing modes (MTM) in the core of spherical (NSTX) and conventional tokamaks (ASDEX Upgrade and JET) are studied through local linear gyrokinetic simulations with GYRO (Candy and Belli 2011 General Atomics Report GA-A26818). For experimentally relevant core plasma parameters in the NSTX and ASDEX Upgrade tokamaks, in agreement with previous works, we find MTMs as the dominant linear instability. Also, for JET-like core parameters considered in our study an MTM is found as the most unstable mode. In all of these plasmas, finite collisionality is needed for MTMs to become unstable and the electron temperature gradient is found to be the fundamental drive. However, a significant difference is observed in the dependence of the linear growth rate of MTMs on electron temperature gradient. While it varies weakly and non-monotonically in JET and ASDEX Upgrade plasmas, in NSTX it increases with the electron temperature gradient.

  9. Theoretical Study of a Spherical Plasma Focus

    NASA Astrophysics Data System (ADS)

    Ay, Yasar

    A theoretical model is developed for two concentric electrodes spherical plasma focus device in order to investigate the plasma sheath dynamics, radiative emission, and the ion properties. The work focuses on the model development of the plasma sheath dynamics and its validation, followed by studying of the radiation effects and the beam-ion properties in such unique geometry as a pulsed source for neutrons, soft and hard x-rays, and electron and ion beams. Chapter 1 is an introduction on fusion systems including plasma focus. Chapter 2 is an extensive literature survey on plasma focus modeling and experiments including the various radiations and their mechanism. Chapter 3 details modeling and validation of the plasma sheath dynamics model with comparison between hydrogen, deuterium, tritium and deuterium-tritium mixture for the production of pulsed neutrons. Chapter 4 is a study of the radiative phase, in which neutron yield is investigated, as well as the predicted beam-ion properties. Chapter 5 summarizes and discusses the results. Chapter 6 provides concluding remarks and proposed future works. The phases of the developed model are the rundown phase I, rundown phase II, the reflected phase and a radiative phase. The rundown phase I starts immediately after the completion of the gas breakdown and ends when the current sheath reaches the equator point of the spherical shape. Then immediately followed by rundown phase II to start and it ends when the shock front hits the axis, which is the beginning of the reflected shock phase. Reflected shock front moves towards the incoming current sheath and meets it which is both the end of the reflected shock phase and the beginning of the radiative phase. After the reflected shock front and the current sheath meet, the current sheath continues to move radially inward by compressing the produced plasma column until it reaches the axis. Since the discharge current contains important information about the plasma dynamic

  10. Dynamic stiffness model of spherical parallel robots

    NASA Astrophysics Data System (ADS)

    Cammarata, Alessandro; Caliò, Ivo; D`Urso, Domenico; Greco, Annalisa; Lacagnina, Michele; Fichera, Gabriele

    2016-12-01

    A novel approach to study the elastodynamics of Spherical Parallel Robots is described through an exact dynamic model. Timoshenko arches are used to simulate flexible curved links while the base and mobile platforms are modelled as rigid bodies. Spatial joints are inherently included into the model without Lagrangian multipliers. At first, the equivalent dynamic stiffness matrix of each leg, made up of curved links joined by spatial joints, is derived; then these matrices are assembled to obtain the Global Dynamic Stiffness Matrix of the robot at a given pose. Actuator stiffness is also included into the model to verify its influence on vibrations and modes. The latter are found by applying the Wittrick-Williams algorithm. Finally, numerical simulations and direct comparison to commercial FE results are used to validate the proposed model.

  11. Refraction by a spherical nematic bubble

    NASA Astrophysics Data System (ADS)

    Sherman, Richard David

    1989-08-01

    A formalism is developed to study refraction by a spherical nematic bubble. It is applicable to bubbles that are larger than light wavelengths, but smaller than the dimensions for excitation of director-fluctuation-induced scattering. The technique yields a nonlinear differential equation and an associated integral which govern the trajectory of a ray inside a nematic region for an arbitrary director configuration. Explicit solutions are provided for five simple interior arrangements-isotropic, onion skin, radial star, horizontal (bottle brush), and vertical. It is then demonstrated that for extraordinary-ordinary refractive-index difference small compared to either, interfacial refraction at the bubble surface is the dominant contribution; deviations from a rectilinear path are small. When ranked in terms of decreasing scattering effectiveness, the sequence is horizontal, onion, isotropic, radial, and vertical if the light is linearly polarized and coupling optimally to the extraordinary index component; for unpolarized incoherent light the order becomes isotropic, horizontal, onion, radial, and vertical.

  12. Tracking a maneuvering target in spherical coordinates

    NASA Astrophysics Data System (ADS)

    Douglas, Andrew P.; Blanchard, Jeffrey A.; Grabbe, Michael T.

    2003-08-01

    This paper presents an Extended Kalman Filter for tracking a maneuvering target, where the kinematics of a typical target aircraft maneuver have been incorporated into the filter state equations. Such a formulation allows the target's motion to be accurately determined through estimation of heading and lateral acceleration. This is an improvement over the the typical approach of modeling target motion with acceleration terms represented by random processes, such as that used in the Singer model. In the following pages, a three-dimensional target maneuver model is formulated in conjunction with the kinematic equations of a sensor tracking a target in spherical coordinates. Three degree-of-freedom simulation results of the proposed filter, simplified for planar target maneuvers, are compared to a filter modeling target motion with the Singer model.

  13. A note on reflection of spherical waves

    NASA Astrophysics Data System (ADS)

    Taraldsen, Gunnar

    2005-06-01

    In 1909 Sommerfeld gave an exact solution for the reflection of a spherical wave from a plane surface in terms of an oscillatory integral and also presented an asymptotic solution for the case where both source and receiver are at the boundary. Weyl (1919) presented an alternative solution and also an asymptotic solution for the case where the source is at the boundary. It is known that the general case is solved if a general solution for the case where the source is at the boundary is known. Here it is demonstrated that it is sufficient to have the general solution for the case where both source and receiver are at the boundary. This is mainly of theoretical interest, but may have practical applications. As an example it is demonstrated that Sommerfeld's approximate solution gives Ingard's (1951) approximate solution which is valid for arbitrary source and receiver heights. .

  14. Indentation of pressurized viscoplastic polymer spherical shells

    NASA Astrophysics Data System (ADS)

    Tvergaard, V.; Needleman, A.

    2016-08-01

    The indentation response of polymer spherical shells is investigated. Finite deformation analyses are carried out with the polymer characterized as a viscoelastic/viscoplastic solid. Both pressurized and unpressurized shells are considered. Attention is restricted to axisymmetric deformations with a conical indenter. The response is analyzed for various values of the shell thickness to radius ratio and various values of the internal pressure. Two sets of material parameters are considered: one set having network stiffening at a moderate strain and the other having no network stiffening until very large strains are attained. The transition from an indentation type mode of deformation to a structural mode of deformation involving bending that occurs as the indentation depth increases is studied. The results show the effects of shell thickness, internal pressure and polymer constitutive characterization on this transition and on the deformation modes in each of these regimes.

  15. A Fast Spherical Filter with Uniform Resolution

    NASA Astrophysics Data System (ADS)

    Jakob-Chien, Rüdiger; Alpert, Bradley K.

    1997-09-01

    This paper introduces a fast algorithm for obtaining a uniform resolution representation of a function known at a latitude-longitude grid on the surface of a sphere, equivalent to a triangular, isotropic truncation of the spherical harmonic coefficients for the function. The proposedspectral truncation method,which is based on the fast multipole method and the fast Fourier transform, projects the function to a space with uniform resolution while avoiding surface harmonic transformations. The method requiresO(N2logN) operations forO(N2) grid points, as opposed toO(N3) operations for the standard spectral transform method, providing a reduced-complexity spectral method obviating the pole problem in the integration of time-dependent partial differential equations on the sphere. The filter's performance is demonstrated with numerical examples.

  16. Saltation movement of large spherical particles

    NASA Astrophysics Data System (ADS)

    Chara, Z.; Dolansky, J.; Kysela, B.

    2017-07-01

    The paper presents experimental and numerical investigations of the saltation motion of a large spherical particle in an open channel. The channel bottom was roughed by one layer of glass rods of diameter 6 mm. The plastic spheres of diameter 25.7 mm and density 1160 kgm-3 were fed into the water channel and theirs positions were viewed by a digital camera. Two light sheets were placed above and under the channel, so the flow was simultaneously lighted from the top and the bottom. Only particles centers of which moved through the light sheets were recorded. Using a 2D PIV method the trajectories of the spheres and the velocity maps of the channel flow were analyzed. The Lattice-Boldzmann Method (LBM) was used to simulate the particle motion.

  17. Electronically Steerable Spherical Array capabilities and interfaces

    NASA Technical Reports Server (NTRS)

    Taylor, T. H., Jr.

    1982-01-01

    The development of the Electronically Steerable Spherical Array (ESSA) was started in 1975. ESSA provides the inertialess antenna needed by user satellites for communication over their large coverage angles towards the Tracking Data Relay Satellite System (TDRSS). The performance of ESSA over large coverage angles is better than the performance provided by phased arrays. The primary difference between the two antenna types is the method of beam forming. The ESSA steers a beam by illuminating a set of elements which point in the desired direction. This set of elements is illuminated by a simple multipole switch called a switching power divider (SPD). Attention is given to details regarding the difference in performance between ESSA and phased arrays, the ESSA block diagram, the performance improvement achieved by phase compensation, power requirements, the four operating modes, multibeam operation, and the data interface.

  18. Advances in spherical neutron polarimetry with Cryopad

    NASA Astrophysics Data System (ADS)

    Lelièvre-Berna, E.; Bourgeat-Lami, E.; Fouilloux, P.; Geffray, B.; Gibert, Y.; Kakurai, K.; Kernavanois, N.; Longuet, B.; Mantegezza, F.; Nakamura, M.; Pujol, S.; Regnault, L.-P.; Tasset, F.; Takeda, M.; Thomas, M.; Tonon, X.

    2005-02-01

    Within the frame of the ILL millennium programme, the European ENPI network and the ILL-ASRC/JAERI Memorandum of Understanding, a third-generation Cryopad has been developed and built in three copies. The aim of this collaboration is to open new fields of investigation on the D3/ILL diffractometer, the IN22/CEA and TAS-1/JAERI three-axis spectrometers: complex antiferromagnetic structures, precision determination of antiferromagnetic distributions, magnetic-lattice excitations spectra, search for the neutron electric dipole moment, etc. We present the progress performed with the new-generation devices and show how easy and reliable it is today to carry out spherical neutron polarimetry measurements with Cryopad.

  19. Collective excitations of spherical semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Moradi, Afshin

    2016-10-01

    In this article, we study the dispersion properties of bulk and surface electrostatic oscillations of a spherical quantum electron-hole semiconductor plasma as a simple model of a semiconductor nanoparticle. We derive general dispersion relation for both bulk and surface modes, using quantum hydrodynamic theory (including the electrons and holes quantum recoil effects, quantum statistical pressures of the plasma species, as well as exchange and correlation effects) in conjunction with Poisson’s equation and appropriate boundary conditions. We show that for the arbitrary value of angular quantum number {\\ell }≥slant 1 there are only two surface plasmon modes, but two infinite series of bulk modes for {\\ell }≥slant 0 that owe their existence to the curvature of the interface. We use the typical values of GaAs semiconductor to compute the bulk and surface mode frequencies for different value of {\\ell }.

  20. Spark Plasma Sintering of Titanium Spherical Particles

    NASA Astrophysics Data System (ADS)

    Abedi, Mohammad; Moskovskikh, Dmitry O.; Rogachev, Alexander S.; Mukasyan, Alexander S.

    2016-10-01

    The densification kinetics for sintering of titanium spherical particles under two different experimental schemes, i.e., current-assisted and current-insulated were investigated. It was shown that measurable densification rate differences between the two schemes are recognized only for the preheating stage. For current-assisted experiments, consolidation starts at lower temperatures than for current-insulated samples. Also at high heating rates, the change of sample porosity all through the preheating stage is higher for current-assisted conditions, while at relatively low heating rates ( i.e., less than 100 K/min) they are comparable. All through the isothermal sintering stage, at a temperature of 1073 K (800 °C), the shrinkage rates are comparable for both experimental schemes within the measurement accuracy. The explanation of the observed effects within the framework of conventional sintering theory is also provided.

  1. Electronic Switching Spherical Array (ESSA) antenna systems

    NASA Technical Reports Server (NTRS)

    Hockensmith, R. P.

    1984-01-01

    ESSA (Electronic Switching Spherical Array) is an antenna system conceived, developed and qualified for linking satellite data transmissions with NASA's tracking and data relay satellites (TDRSS) and tracking and data acquisition satellites (TDAS). ESSA functions in the S band frequency region, cover 2 pi or more steradians with directional gain and operates in multiple selectable modes. ESSA operates in concert with the NASA's TDRS standard transponder in the retrodirective mode or independently in directional beam, program track and special modes. Organizations and projects to the ESSA applications for NASA's space use are introduced. Coverage gain, weight power and implementation and other performance information for satisfying a wide range of data rate requirements are included.

  2. Aerodynamic properties of spherical balloon wind sensors.

    NASA Technical Reports Server (NTRS)

    Fichtl, G. H.; Demandel, R. E.; Krivo, S. J.

    1972-01-01

    A first-order theory of the fluctuating lift and drag coefficients associated with the aerodynamically induced motions of rising and falling spherical wind sensors is developed. The equations of motion of a sensor are perturbed about an equilibrium state in which the buoyancy force balances the mean vertical drag force. It is shown that, to within first order in perturbation quantities, the aerodynamic lift force is confined to the horizontal, and the fluctuating drag force associated with fluctuations in the drag coefficient acts along the vertical. The perturbation equations are transformed with Fourier-Stieltjes integrals. The resulting equations lead to relationships between the power spectra of the aerodynamically induced velocity components and the spectra of the fluctuating lift and drag coefficients.

  3. Differential Light Scattering from Spherical Mammalian Cells

    PubMed Central

    Brunsting, Albert; Mullaney, Paul F.

    1974-01-01

    The differential scattered light intensity patterns of spherical mammalian cells were measured with a new photometer which uses high-speed film as the light detector. The scattering objects, interphase and mitotic Chinese hamster ovary cells and HeLa cells, were modeled as (a) a coated sphere, accounting for nucleus and cytoplasm, and (b) a homogeneous sphere when no cellular nucleus was present. The refractive indices and size distribution of the cells were measured for an accurate comparison of the theoretical model with the light-scattering measurements. The light scattered beyond the forward direction is found to contain information about internal cellular morphology, provided the size distribution of the cells is not too broad. ImagesFIGURE 1 PMID:4134589

  4. Effects of coating spherical iron oxide nanoparticles

    SciTech Connect

    Milosevic, Irena; Motte, Laurence; Aoun, Bachir; Li, Tao; Ren, Yang; Sun, Chengjun; Saboungi, Marie-Louise

    2017-01-01

    We investigate the effect of several coatings applied in biomedical applications to iron oxide nanoparticles on the size, structure and composition of the particles. The four structural techniques employed - TEM, DLS, VSM, SAXS and EXAFS - show no significant effects of the coatings on the spherical shape of the bare nanoparticles, the average sizes or the local order around the Fe atoms. The NPs coated with hydroxylmethylene bisphosphonate or catechol have a lower proportion of magnetite than the bare and citrated ones, raising the question whether the former are responsible for increasing the valence state of the oxide on the NP surfaces and lowering the overall proportion of magnetite in the particles. VSM measurements show that these two coatings lead to a slightly higher saturation magnetization than the citrate. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazu and Dr. Federica Migliardo.

  5. Angular momentum in cluster Spherical Collapse Model

    NASA Astrophysics Data System (ADS)

    Cupani, Guido; Mezzetti, Marino; Mardirossian, Fabio

    2011-11-01

    Our new formulation of the Spherical Collapse Model (SCM-L) takes into account the presence of angular momentum associated with the motion of galaxy groups infalling towards the centre of galaxy clusters. The angular momentum is responsible for an additional term in the dynamical equation which is useful to describe the evolution of the clusters in the non-equilibrium region which is investigated in the present paper. Our SCM-L can be used to predict the profiles of several strategic dynamical quantities as the radial and tangential velocities of member galaxies, and the total cluster mass. A good understanding of the non-equilibrium region is important since it is the natural scenario where the infall in galaxy clusters and the accretion phenomena present in these objects can be studied. Our results corroborate previous estimates and are in very good agreement with the analysis of recent observations and of simulated clusters.

  6. Preparing spherical lignin from rice husk.

    PubMed

    Zhang, Hongxi; Zhao, Xu; Ding, Xuefeng; Lei, Hong; Wang, Zichen

    2013-08-01

    Lignin is one of the important branched amorphous polymers, which generally has the irregular and fractal morphology. The preparation of regular sphere of lignin needs long steps and special conditions. In this study, the regular sphere of lignin can be simply prepared from rice husk (RH) under certain conditions. Namely, RH is mixed with 35% ethanol aqueous solution in the proportion of 1:10 (g:mL), non-isothermally heated to 493 K and kept for 5 h. After filtration and air-drying at room temperature, the regular lignin sphere with the diameter of 100-400 nm is obtained. The regular sphere of lignin has the potential utilization in fields such as reactive functional materials, photo sensing materials and surface active materials in cosmetics. The mechanism of formation of the regular spherical lignin is proposed and discussed in this paper.

  7. Characteristic Matrices for Spherical Shell Photonic Systems

    NASA Technical Reports Server (NTRS)

    Fuller, Kirk A.; Smith, David D.

    2004-01-01

    We establish a parallel between the transfer matrix used in the study of plane-parallel photonic structures and the matrix characterizing transfer of partial waves in concentric spheres. We derive explicit expressions for the elements of the transfer matrix for concentric spherical layers, and from those expressions derive the scattering coefficients of a multilayered sphere. The transfer matrices are 4x4 block diagonal with only four independent elements. Matrix elements for the case of TM waves are related to those for the case of TE waves through simple interchange and multiplicative constants. In analogy with plane parallel layers, the transfer matrix for concentric multilayers is simply the product of the transfer matrices of the individual layers.

  8. Spherical boson stars as black hole mimickers

    SciTech Connect

    Guzman, F. S.; Rueda-Becerril, J. M.

    2009-10-15

    We present spherically symmetric boson stars as black hole mimickers based on the power spectrum of a simple accretion disk model. The free parameters of the boson star are the mass of the boson and the fourth-order self-interaction coefficient in the scalar field potential. We show that even if the mass of the boson is the only free parameter, it is possible to find a configuration that mimics the power spectrum of the disk due to a black hole of the same mass. We also show that for each value of the self-interaction a single boson star configuration can mimic a black hole at very different astrophysical scales in terms of the mass of the object and the accretion rate. In order to show that it is possible to distinguish one of our mimickers from a black hole, we also study the deflection of light.

  9. Geometric inequalities in spherically symmetric spacetimes

    NASA Astrophysics Data System (ADS)

    Csukás, Károly Z.

    2017-07-01

    In geometric inequalities ADM mass plays more fundamental role than the concept of quasi-local mass. This paper is to demonstrate that using the quasi-local mass some new insights can be acquired. In spherically symmetric spacetimes the Misner-Sharp mass and the concept of the Kodama vector field provides an ideal setting to the investigations of geometric inequalities. We applying the proposed new techniques to investigate the spacetimes containing black hole or cosmological horizons but we shall also apply them in context of normal bodies. Most of the previous investigations applied only the quasi-local charges and the area. Our main point is to include the quasi-local mass in the corresponding geometrical inequalities. This way we recover some known relations but new inequalities are also derived.

  10. Preparation of Spherical Granules of Octacalcium Phosphate for Medical Application

    NASA Astrophysics Data System (ADS)

    Ito, Natsuko; Kamitakahara, Masanobu; Ioku, Koji

    2012-06-01

    Octacalcium phosphate (OCP) is regarded as a precursor of hydroxyapatite (HA) which is an inorganic constituent of human bones and teeth. OCP is also becoming regarded as one of the important biomaterials. Despite some studies on OCP as biomedical materials, there are few methods for shape forming of OCP. The objective of this study is preparing spherical granules of OCP. The spherical granular shape has an advantage for handling. The spherical granules can achieve easy injection into the defect site by a catheter. In the present study, preparation of spherical granules of OCP from α-tricalcium phosphate (α-TCP) was attempted. The starting material of α-TCP powder was dispersed in the gelatin solution. The resultant slurry was added into vegetable oil, and then the spherical granules of α-TCP/gelatin were formed by the surface tension of the slurry and the shearing force of stirring. By calcining the obtained α-TCP/gelatin granules, the spherical granules with α-TCP single phase were obtained. These spherical granules of α-TCP were immersed in the acetic acid buffer solution whose temperature and pH were controlled. The calcium phosphate spherical granules containing OCP were obtained. The shorter treatment time was favorable for preparing spherical granules containing more OCP.

  11. Foliation dependence of black hole apparent horizons in spherical symmetry

    NASA Astrophysics Data System (ADS)

    Faraoni, Valerio; Ellis, George F. R.; Firouzjaee, Javad T.; Helou, Alexis; Musco, Ilia

    2017-01-01

    Numerical studies of gravitational collapse to black holes make use of apparent horizons, which are intrinsically foliation dependent. We expose the problem and discuss possible solutions using the Hawking-Hayward quasilocal mass. In spherical symmetry, we present a physically sensible approach to the problem by restricting to spherically symmetric spacetime slicings. In spherical symmetry, the apparent horizons enjoy a restricted gauge independence in any spherically symmetric foliation, but physical quantities associated with them, such as surface gravity and temperature, are fully gauge dependent. The widely used comoving and Kodama foliations, which are of particular interest, are discussed in detail as examples.

  12. Compact expressions for spherically averaged position and momentum densities

    NASA Astrophysics Data System (ADS)

    Crittenden, Deborah L.; Bernard, Yves A.

    2009-08-01

    Compact expressions for spherically averaged position and momentum density integrals are given in terms of spherical Bessel functions (jn) and modified spherical Bessel functions (in), respectively. All integrals required for ab initio calculations involving s, p, d, and f-type Gaussian functions are tabulated, highlighting a neat isomorphism between position and momentum space formulae. Spherically averaged position and momentum densities are calculated for a set of molecules comprising the ten-electron isoelectronic series (Ne-CH4) and the eighteen-electron series (Ar-SiH4, F2-C2H6).

  13. Circle of least confusion of a spherical reflector.

    PubMed

    Hosken, Robert W

    2007-06-01

    A simple, tractable equation is provided for determining the size and location of the circle of least confusion of a concave spherical reflector. This method is exact for the object at infinity and with wave effects neglected. Designers of large radius Arecibo-like telescopes, both radio and optical, with symmetrical, spherical primaries should find the method useful. The mathematical results are valid for apertures with an angle of incidence up to 45 degrees. Comparisons of the location of the disk of least confusion with longitudinal spherical aberration and the radius of the disk with transverse spherical aberration are presented.

  14. Adaptive optics simulation of intraocular lenses with modified spherical aberration.

    PubMed

    Piers, Patricia A; Fernandez, Enrique J; Manzanera, Silvestre; Norrby, Sverker; Artal, Pablo

    2004-12-01

    Adaptive optics systems can be used to investigate the potential visual benefit associated with correcting ocular wave-front aberration. In this study, adaptive optics techniques were used to evaluate the potential advantages and disadvantages associated with intraocular lenses (IOLs) with modified spherical aberration profiles. An adaptive optics vision simulator was constructed that allows psychophysical tests to be performed while viewing targets through any desired ocular wave-front profile. With this simulator, the subjective visual performance of four subjects was assessed by letter acuity and contrast sensitivity (at 3, 6, and 15 cyc/deg) for two different values of induced spherical aberration. The values of spherical aberration were chosen to reproduce two conditions: the average amount measured in pseudophakic patients with implanted IOLs having spherical surfaces and the complete correction of the individual's spherical aberration. Visual performance was assessed in both white and green light, at best focus and for defocus of +/-0.5 and +/-1.0 D. There was an average improvement in visual acuity associated with the correction of spherical aberration of 10% and 38% measured in white and green light, respectively. Similarly, average contrast sensitivity measurements improved 32% and 57% in white and green light. When spherical aberration was corrected, visual performance was as good as or better than for the normal spherical aberration case for defocus as large as +/-1 D. Correcting ocular spherical aberration improves spatial vision in the best-focus position without compromising the subjective tolerance to defocus.

  15. Explosive fragmentation of liquids in spherical geometry

    NASA Astrophysics Data System (ADS)

    Milne, A.; Longbottom, A.; Frost, D. L.; Loiseau, J.; Goroshin, S.; Petel, O.

    2016-07-01

    Rapid acceleration of a spherical shell of liquid following central detonation of a high explosive causes the liquid to form fine jets that are similar in appearance to the particle jets that are formed during explosive dispersal of a packed layer of solid particles. Of particular interest is determining the dependence of the scale of the jet-like structures on the physical parameters of the system, including the fluid properties (e.g., density, viscosity, and surface tension) and the ratio of the mass of the liquid to that of the explosive. The present paper presents computational results from a multi-material hydrocode describing the dynamics of the explosive dispersal process. The computations are used to track the overall features of the early stages of dispersal of the liquid layer, including the wave dynamics, and motion of the spall and accretion layers. The results are compared with new experimental results of spherical charges surrounded by a variety of different fluids, including water, glycerol, ethanol, and vegetable oil, which together encompass a significant range of fluid properties. The results show that the number of jet structures is not sensitive to the fluid properties, but primarily dependent on the mass ratio. Above a certain mass ratio of liquid fill-to-explosive burster (F / B), the number of jets is approximately constant and consistent with an empirical model based on the maximum thickness of the accretion layer. For small values of F / B, the number of liquid jets is reduced, in contrast with explosive powder dispersal, where small F / B yields a larger number of particle jets. A hypothetical explanation of these features based on the nucleation of cavitation is explored numerically.

  16. Explosive fragmentation of liquids in spherical geometry

    NASA Astrophysics Data System (ADS)

    Milne, A.; Longbottom, A.; Frost, D. L.; Loiseau, J.; Goroshin, S.; Petel, O.

    2017-05-01

    Rapid acceleration of a spherical shell of liquid following central detonation of a high explosive causes the liquid to form fine jets that are similar in appearance to the particle jets that are formed during explosive dispersal of a packed layer of solid particles. Of particular interest is determining the dependence of the scale of the jet-like structures on the physical parameters of the system, including the fluid properties (e.g., density, viscosity, and surface tension) and the ratio of the mass of the liquid to that of the explosive. The present paper presents computational results from a multi-material hydrocode describing the dynamics of the explosive dispersal process. The computations are used to track the overall features of the early stages of dispersal of the liquid layer, including the wave dynamics, and motion of the spall and accretion layers. The results are compared with new experimental results of spherical charges surrounded by a variety of different fluids, including water, glycerol, ethanol, and vegetable oil, which together encompass a significant range of fluid properties. The results show that the number of jet structures is not sensitive to the fluid properties, but primarily dependent on the mass ratio. Above a certain mass ratio of liquid fill-to-explosive burster ( F / B), the number of jets is approximately constant and consistent with an empirical model based on the maximum thickness of the accretion layer. For small values of F / B, the number of liquid jets is reduced, in contrast with explosive powder dispersal, where small F / B yields a larger number of particle jets. A hypothetical explanation of these features based on the nucleation of cavitation is explored numerically.

  17. Dynamical systems and spherically symmetric cosmological models

    NASA Astrophysics Data System (ADS)

    He, Yanjing

    2006-06-01

    In this thesis we present a study of the timelike self-similar spherically symmetric cosmological models with two scalar fields with exponential potentials. We first define precisely the timelike self-similar spherically symmetric (TSS) spacetimes. We write the TSS metric in a conformally isometric form in a coordinate system adapted to the geometry of the spacetime manifold. In this coordinate system, both the metric functions of the TSS spacetimes and the potential functions of the scalar fields can be simplified to four undetermined functions of a single coordinate. As a result, the Einstein field equations reduce to an autonomous system of first-order ODEs and polynomial constraints in terms of these undetermined functions. By introducing new bounded variables as well as a new independent variable and solving the constraints, we are able to apply the theory of dynamical systems to study the properties of the TSS solutions. By finding invariant sets and associated monotonic functions, by applying the LaSalle Invariance Principle and the Monotonicity Principle, by applying the [straight phi] t -connected property of a limit set, and using other theorems, we prove that all of the TSS trajectories are heteroclinic trajectories. In addition, we conduct numerical simulations to confirm and support the qualitative analysis. We obtain all possible types of TSS solutions, by analyzing the qualitative behavior of the original system of ODES from those of the reduced one. We obtain asymptotic expressions for the TSS solutions (e.g., the asymptotic expressions for the metric functions, the source functions and the Ricci scalar). In particular, self-similar flat Friedmann-Robertson-Walker spacetimes are examined in order to obtain insights into the issues related to the null surface in general TSS spacetimes in these coordinates. A discussion of the divergence of the spacetime Ricci scalar and the possible extension of the TSS solutions across the null boundary is presented

  18. Spherical microwave confinement and ball lightning

    NASA Astrophysics Data System (ADS)

    Robinson, William Richard

    This dissertation presents the results of research done on unconventional energy technologies from 1995 to 2009. The present civilization depends on an infrastructure that was constructed and is maintained almost entirely using concentrated fuels and ores, both of which will run out. Diffuse renewable energy sources rely on this same infrastructure, and hence face the same limitations. I first examined sonoluminescence directed toward fusion, but demonstrated theoretically that this is impossible. I next studied Low Energy Nuclear Reactions and developed methods for improving results, although these have not been implemented. In 2000, I began Spherical Microwave Confinement (SMC), which confines and heats plasma with microwaves in a spherical chamber. The reactor was designed and built to provide the data needed to investigate the possibility of achieving fusion conditions with microwave confinement. A second objective was to attempt to create ball lightning (BL). The reactor featured 20 magnetrons, which were driven by a capacitor bank and operated in a 0.2 s pulse mode at 2.45 GHz. These provided 20 kW to an icosahedral array of 20 antennas. Video of plasmas led to a redesign of the antennas to provide better coupling of the microwaves to the plasma. A second improvement was a grid at the base of the antennas, which provided corona electrons and an electric field to aid quick formation of plasmas. Although fusion conditions were never achieved and ball lightning not observed, experience gained from operating this basic, affordable system has been incorporated in a more sophisticated reactor design intended for future research. This would use magnets that were originally planned. The cusp geometry of the magnetic fields is suitable for electron cyclotron resonance in the same type of closed surface that in existing reactors has generated high-temperature plasmas. Should ball lightning be created, it could be a practical power source with nearly ideal

  19. Stability mechanisms of oscillating vapor bubbles in acoustic fields.

    PubMed

    Zhang, Yuning; Gao, Yuhang; Du, Xiaoze

    2018-01-01

    Vapor bubble instability could enhance the sonochemical activities and accelerate the reaction rate. In the present paper, vapor bubble instability in acoustic fields is investigated through combining both the spherical and stiffness stabilities within a wide range of parameter zone (consisting of bubble radius, acoustic frequency and pressure amplitude) in order to determine the stability states of vapor bubbles. The status of bubble oscillations are divided into four zones in terms of their stability characteristics. Influences of several paramount parameters on the bubble stability are demonstrated in detail. Different orders of spherical instability are quantitatively given together with cases in high-frequency and low-frequency limits. The practical applications of the present work are twofold: identification of the parameter zones with rapid sonochemical reactions; validity of the spherical bubble assumption for simplification of the numerical studies. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. National Spherical Torus Experiment (NSTX) Torus Design, Fabrication and Assembly

    SciTech Connect

    C. Neumeyer; G. Barnes; J.H. Chrzanowski; P. Heitzenroeder; et al

    1999-11-01

    The National Spherical Torus Experiment (NSTX) is a low aspect ratio spherical torus (ST) located at Princeton Plasma Physics Laboratory (PPPL). Fabrication, assembly, and initial power tests were completed in February of 1999. The majority of the design and construction efforts were constructed on the Torus system components. The Torus system includes the centerstack assembly, external Poloidal and Toroidal coil systems, vacuum vessel, torus support structure and plasma facing components (PFC's). NSTX's low aspect ratio required that the centerstack be made with the smallest radius possible. This, and the need to bake NSTXs carbon-carbon composite plasma facing components at 350 degrees C, was major drivers in the design of NSTX. The Centerstack Assembly consists of the inner legs of the Toroidal Field (TF) windings, the Ohmic Heating (OH) solenoid and its associated tension cylinder, three inner Poloidal Field (PF) coils, thermal insulation, diagnostics and an Inconel casing which forms the inner wall of the vacuum vessel boundary. It took approximately nine months to complete the assembly of the Centerstack. The tight radial clearances and the extreme length of the major components added complexity to the assembly of the Centerstack components. The vacuum vessel was constructed of 304-stainless steel and required approximately seven months to complete and deliver to the Test Cell. Several of the issues associated with the construction of the vacuum vessel were control of dimensional stability following welding and controlling the permeability of the welds. A great deal of time and effort was devoted to defining the correct weld process and material selection to meet our design requirements. The PFCs will be baked out at 350 degrees C while the vessel is maintained at 150 degrees C. This required care in designing the supports so they can accommodate the high electromagnetic loads resulting from plasma disruptions and the resulting relative thermal expansions

  1. Thermophoresis of spherical and non-spherical particles: a review of theories and experiments.

    PubMed

    Zheng, F

    2002-03-29

    Thermophoresis is an important mechanism of micro-particle transport due to a temperature gradient in the surrounding medium and has found numerous applications, especially in the field of aerosol technology. Extensive studies, both theoretical and experimental, have been done to understand the nature of this phenomenon. However, it is clear that a lot more of work needs to be done before we can predict thermophoresis accurately for any given gas-particle system as well as particle shape and orientation in any flow regime. This paper reviews the existing theories and data in two major categories, for spherical particles and for non-spherical particles, as well as the various techniques in making thermophoresis measurements. The current state of development for thermophoresis studies is that for spheres the theories and experimental data agree with each other fairly well but for non-spherical particles in the transition regime the theories are yet to be developed and experimental data showing the effect of particle shape are much needed in all Knudsen number range. The best techniques of thermophoretic force measurements involve the use of electrodynamic balances to work on single micro-particles and the use of microgravity to minimize the effect of convection. A combination of the above two has not been attempted and should provide the most accurate data.

  2. BSSN equations in spherical coordinates without regularization: Vacuum and nonvacuum spherically symmetric spacetimes

    NASA Astrophysics Data System (ADS)

    Montero, Pedro J.; Cordero-Carrión, Isabel

    2012-06-01

    Brown [Phys. Rev. DPRVDAQ1550-7998 79, 104029 (2009)] has recently introduced a covariant formulation of the BSSN equations which is well suited for curvilinear coordinate systems. This is particularly desirable as many astrophysical phenomena are symmetric with respect to the rotation axis or are such that curvilinear coordinates adapt better to their geometry. However, the singularities associated with such coordinate systems are known to lead to numerical instabilities unless special care is taken (e.g., regularization at the origin). Cordero-Carrión will present a rigorous derivation of partially implicit Runge-Kutta methods in forthcoming papers, with the aim of treating numerically the stiff source terms in wavelike equations that may appear as a result of the choice of the coordinate system. We have developed a numerical code solving the BSSN equations in spherical symmetry and the general relativistic hydrodynamic equations written in flux-conservative form. A key feature of the code is that it uses a second-order partially implicit Runge-Kutta method to integrate the evolution equations. We perform and discuss a number of tests to assess the accuracy and expected convergence of the code—namely a pure gauge wave, the evolution of a single black hole, the evolution of a spherical relativistic star in equilibrium, and the gravitational collapse of a spherical relativistic star leading to the formation of a black hole. We obtain stable evolutions of regular spacetimes without the need for any regularization algorithm at the origin.

  3. Vibration modes of spherical shells and containment vessels.

    SciTech Connect

    Duffey, T. A.; Romero, C. D.

    2001-01-01

    Spherical pressure vessels are used to fully contain the effects of high explosions. In this paper, the vibrations of a spherical containment vessel undergoing elastic response are investigated. Vibration modes of containment vessels are of particular interest, as it is the superposition and interaction of different modes of response with closely spaced frequencies that has been reported to be the mechanism of 'strain growth'. First, the modal frequencies of a spherical shell for both axisymmetric and nonaxisymmetric response modes are discussed, based on a sequence of papers that have appeared in the open literature. Analytical predictions are then compared with numerical simulations using ABAQUS. It is found that the numerical simulations accurately predict both the axisymmetric and nonaxisymmetric modal frequencies for the complete spherical shell. Next, numerical simulations of modal frequencies for the more complex spherical containment vessel (with nozzles) are compared with the spherical shell results. Numerical simulations for the spherical containment vessel reveal that frequencies are somewhat similar to the complete spherical shell. Limited comparisons with experimentally recorded frequencies for participating modes of vessel dynamic response during high explosive containment testing are presented as well.

  4. Characterizing Student Mathematics Teachers' Levels of Understanding in Spherical Geometry

    ERIC Educational Resources Information Center

    Guven, Bulent; Baki, Adnan

    2010-01-01

    This article presents an exploratory study aimed at the identification of students' levels of understanding in spherical geometry as van Hiele did for Euclidean geometry. To do this, we developed and implemented a spherical geometry course for student mathematics teachers. Six structured, "task-based interviews" were held with eight student…

  5. No-scalar-hair theorem for spherically symmetric reflecting stars

    NASA Astrophysics Data System (ADS)

    Hod, Shahar

    2016-11-01

    It is proved that spherically symmetric compact reflecting objects cannot support static bound-state configurations made of scalar fields whose self-interaction potential V (ψ2) is a monotonically increasing function of its argument. Our theorem rules out, in particular, the existence of massive scalar hair outside the surface of a spherically symmetric compact reflecting star.

  6. Convergence rate of spherical harmonic expansions of smooth functions

    NASA Astrophysics Data System (ADS)

    Dai, Feng; Wang, Kunyang

    2008-12-01

    We extend a well-known result of Bonami and Clerc on the almost everywhere (a.e.) convergence of Cesàro means of spherical harmonic expansions. For smooth functions measured in terms of [phi]-derivatives on the unit sphere, we obtained the sharp a.e. convergence rate of Cesàro means of their spherical harmonic expansions.

  7. Sextupole system for the correction of spherical aberration

    DOEpatents

    Crewe, A.V.; Kopf, D.A.

    In an electron beam device in which an electron beam is developed and then focused by a lens to a particular spot, there is provided a means for eliminating spherical aberration. A sextupole electromagnetic lens is positioned between two focusing lenses. The interaction of the sextupole with the beam compensates for spherical aberration. (GHT)

  8. Systematic Calibration for a Backpacked Spherical Photogrammetry Imaging System

    NASA Astrophysics Data System (ADS)

    Rau, J. Y.; Su, B. W.; Hsiao, K. W.; Jhan, J. P.

    2016-06-01

    A spherical camera can observe the environment for almost 720 degrees' field of view in one shoot, which is useful for augmented reality, environment documentation, or mobile mapping applications. This paper aims to develop a spherical photogrammetry imaging system for the purpose of 3D measurement through a backpacked mobile mapping system (MMS). The used equipment contains a Ladybug-5 spherical camera, a tactical grade positioning and orientation system (POS), i.e. SPAN-CPT, and an odometer, etc. This research aims to directly apply photogrammetric space intersection technique for 3D mapping from a spherical image stereo-pair. For this purpose, several systematic calibration procedures are required, including lens distortion calibration, relative orientation calibration, boresight calibration for direct georeferencing, and spherical image calibration. The lens distortion is serious on the ladybug-5 camera's original 6 images. Meanwhile, for spherical image mosaicking from these original 6 images, we propose the use of their relative orientation and correct their lens distortion at the same time. However, the constructed spherical image still contains systematic error, which will reduce the 3D measurement accuracy. Later for direct georeferencing purpose, we need to establish a ground control field for boresight/lever-arm calibration. Then, we can apply the calibrated parameters to obtain the exterior orientation parameters (EOPs) of all spherical images. In the end, the 3D positioning accuracy after space intersection will be evaluated, including EOPs obtained by structure from motion method.

  9. Method for preparing spherical thermoplastic particles of uniform size

    DOEpatents

    Day, J.R.

    1975-11-17

    Spherical particles of thermoplastic material of virtually uniform roundness and diameter are prepared by cutting monofilaments of a selected diameter into rod-like segments of a selected uniform length which are then heated in a viscous liquid to effect the formation of the spherical particles.

  10. Decay rates of spherical and deformed proton emitters

    SciTech Connect

    Davids, C. N.; Esbensen, H.

    1999-11-23

    Using Green's function techniques, the authors derive expressions for the width of a proton decaying state in spherical and deformed nuclei. The authors show that the proton decay widths calculated by the exact expressions of Maglione et al. are equivalent to the distorted wave expressions of Bugrov et al., and that of {angstrom} berg et al. in the spherical case.

  11. Improvements in the spherical collapse model and dark energy cosmologies

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.

    In the present paper, we study how the effects of deviations from spherical symmetry of a system, produced by angular momentum, and shear stress, influence typical parameters of the spherical collapse model, like the linear density threshold for collapse of the non-relativistic component (δ c) and its virial overdensity (Δ V). The study is performed in the framework of the Einstein-de Sitter and Λ CDM models, and assuming that the vacuum component is not clustering within the homogeneous non-spherical overdensities. We start from the standard spherical top hat model (SCM) which does not take account the non-spherical effects, and we add to this model the shear term and angular momentum term, which are finally expressed in terms of the density contrast, δ . We find that the non-spherical terms change the non-linear evolution of the system and that the collapse stops ``naturally" at the virial radius, differently from the standard spherical collapse model. Moreover, shear and rotation gives rise to higher values of the linear overdensity parameter and different values of Δ V with respect to the standard spherical collapse model.

  12. Characterizing Student Mathematics Teachers' Levels of Understanding in Spherical Geometry

    ERIC Educational Resources Information Center

    Guven, Bulent; Baki, Adnan

    2010-01-01

    This article presents an exploratory study aimed at the identification of students' levels of understanding in spherical geometry as van Hiele did for Euclidean geometry. To do this, we developed and implemented a spherical geometry course for student mathematics teachers. Six structured, "task-based interviews" were held with eight student…

  13. Spatial symmetry breaking in rapidly rotating convective spherical shells

    NASA Technical Reports Server (NTRS)

    Zhang, Keke; Schubert, Gerald

    1995-01-01

    Many problems in geophysical and astrophysical convection systems are characterized by fast rotation and spherical shell geometry. The combined effects of Coriolis forces and spherical shell geometry produce a unique spatial symmetry for the convection pattern in a rapidly rotating spherical shell. In this paper, we first discuss the general spatial symmetries for rotating spherical shell convection. A special model, a spherical shell heated from below, is then used to illustrate how and when the spatial symmetries are broken. Symmetry breaking occurs via a sequence of spatial transitions from the primary conducting state to the complex multiple-layered columnar structure. It is argued that, because of the dominant effects of rotation, the sequence of spatial transitions identified from this particular model is likely to be generally valid. Applications of the spatial symmetry breaking to planetary convection problems are also discussed.

  14. Vibrations of moderately thick shallow spherical shells at large amplitudes

    NASA Astrophysics Data System (ADS)

    Sathyamoorthy, M.

    1994-04-01

    A shallow shell theory is presented for the geometrically nonlinear analysis of moderately thick isotropic spherical shells. Effects of transverse shear deformation and rotatory inertia are included in the governing equations of motion by means of tracing constants. When these effects are ignored, the governing equations readily reduce to those applicable for thin shallow spherical shells. Solutions to the system of thick shell equations are obtained by means of Galerkin's method and the numerical Runge-Kutta procedure. Numerical results are presented for certain cases of shallow spherical shells considering different geometric shell parameters. Transverse shear and rotatory inertia effects are found to be important in linear as well as nonlinear responses of shallow spherical shells. The nonlinear frequency-amplitude behavior is of the softening type for shallow spherical shells and of the hardening type for circular plates. Frequency ratios are lower at any given amplitude when the effects of transverse shear and rotatory inertia are included in the analysis.

  15. Fast Particle Destabilization of Toroidicity Induced Alfven Eigenmodes in National Spherical Torus Experiment

    SciTech Connect

    C.Z. Cheng; G.Y. Fu; M.V. Gorelenkova; N.N. Gorelenkov; R. White; S. Kaye

    1999-12-10

    Toroidicity induced Alfven Eigenmode (TAE) stability in National Spherical Torus Experiment (NSTX) is analyzed using the improved NOVA-K code, which includes finite orbit width and Larmor radius effects and is able to predicts the saturation amplitude for the mode using the quasilinear theory. Broad spectrum of unstable global TAEs with different toroidal mode numbers is predicted. Due to the strong poloidal field and the presence of the magnetic well in NSTX better particle confinement in the presence of TAEs in comparison with tokamaks is illustrated making use of the ORBIT code.

  16. Autoionization resonance states of two-electron atomic systems with finite spherical confinement

    SciTech Connect

    Chakraborty, Sumana; Ho, Y. K.

    2011-09-15

    We investigate the lowest-lying S-wave resonant states of two-electron atoms confined by a spherical quantum cavity under the framework of the stabilization method. Hylleraas-type wave functions (basis length N = 444) taking the correlation effects between all the charged particles into account are used in the present paper. The finite oscillator potential is used to represent the confinement potential. We present the resonant parameters (energies and widths) of the quantum-confined two-electron atoms with different depths and various ranges of the potentials.

  17. Comparison of Numerical Schemes for Solving a Spherical Particle Diffusion Equation

    NASA Astrophysics Data System (ADS)

    Fong, Fred K.; Mulkey, Lee A.

    1990-05-01

    A new robust iterative numerical scheme was developed for a nonlinear diffusive model which described sorption dynamics in spherical particle suspensions. The numerical scheme had been applied to finite difference and finite element models which showed rapid convergence and stability under wide ranges of partition coefficients. Comparisons were made with explicit finite difference and orthogonal collocation methods. The diffusive model assumes complete mixing in the bulk aqueous solution and considers intraaggregate transport within the suspended particles. The effect of particle size distribution of suspensions was also included in the model. Sorption was described using both linear and nonlinear isotherms.

  18. Spherical grating based x-ray Talbot interferometry.

    PubMed

    Cong, Wenxiang; Xi, Yan; Wang, Ge

    2015-11-01

    Grating interferometry is a state-of-the-art x-ray imaging approach, which can acquire information on x-ray attenuation, phase shift, and small-angle scattering simultaneously. Phase-contrast imaging and dark-field imaging are very sensitive to microstructural variation and offers superior contrast resolution for biological soft tissues. However, a common x-ray tube is a point-like source. As a result, the popular planar grating imaging configuration seriously restricts the flux of photons and decreases the visibility of signals, yielding a limited field of view. The purpose of this study is to extend the planar x-ray grating imaging theory and methods to a spherical grating scheme for a wider range of preclinical and clinical applications. A spherical grating matches the wave front of a point x-ray source very well, allowing the perpendicular incidence of x-rays on the grating to achieve a higher visibility over a larger field of view than the planer grating counterpart. A theoretical analysis of the Talbot effect for spherical grating imaging is proposed to establish a basic foundation for x-ray spherical gratings interferometry. An efficient method of spherical grating imaging is also presented to extract attenuation, differential phase, and dark-field images in the x-ray spherical grating interferometer. Talbot self-imaging with spherical gratings is analyzed based on the Rayleigh-Sommerfeld diffraction formula, featuring a periodic angular distribution in a polar coordinate system. The Talbot distance is derived to reveal the Talbot self-imaging pattern. Numerical simulation results show the self-imaging phenomenon of a spherical grating interferometer, which is in agreement with the theoretical prediction. X-ray Talbot interferometry with spherical gratings has a significant practical promise. Relative to planar grating imaging, spherical grating based x-ray Talbot interferometry has a larger field of view and improves both signal visibility and dose

  19. Scroll waves in spherical shell geometries.

    PubMed

    Chavez, Francisco; Kapral, Raymond; Rousseau, Guillaume; Glass, Leon

    2001-12-01

    The evolution of scroll waves in excitable media with spherical shell geometries is studied as a function of shell thickness and outer radius. The motion of scroll wave filaments that are the locii of phaseless points in the medium and organize the wave pattern is investigated. When the inner radius is sufficiently large the filaments remain attached to both the inner and outer surfaces. The minimum size of the sphere that supports spiral waves and the maximum number of spiral waves that can be sustained on a sphere of given size are determined for both regular and random initial distributions. When the inner radius is too small to support spiral waves the filaments detach from the inner surface and form a curved filament connecting the two spiral tips in the surface. In certain parameter domains the filament is an arc of a circle that shrinks with constant shape. For parameter values close to the meandering border, the filament grows and collisions with the sphere walls lead to turbulent filament dynamics. (c) 2001 American Institute of Physics.

  20. Spherical gravitational curvature boundary-value problem

    NASA Astrophysics Data System (ADS)

    Šprlák, Michal; Novák, Pavel

    2016-08-01

    Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.

  1. The Spherical Tokamak MEDUSA for Costa Rica

    NASA Astrophysics Data System (ADS)

    Ribeiro, Celso; Vargas, Ivan; Guadamuz, Saul; Mora, Jaime; Ansejo, Jose; Zamora, Esteban; Herrera, Julio; Chaves, Esteban; Romero, Carlos

    2012-10-01

    The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R<0.14m, a<0.10m, BT<0.5T, Ip<40kA, 3ms pulse)[1] is in a process of donation to Costa Rica Institute of Technology. The main objective of MEDUSA is to train students in plasma physics /technical related issues which will help all tasks of the very low aspect ratio stellarator SCR-1(A≡R/>=3.6, under design[2]) and also the ongoing activities in low temperature plasmas. Courses in plasma physics at undergraduate and post-graduate joint programme levels are regularly conducted. The scientific programme is intend to clarify several issues in relevant physics for conventional and mainly STs, including transport, heating and current drive via Alfv'en wave, and natural divertor STs with ergodic magnetic limiter[3,4]. [1] G.D.Garstka, PhD thesis, University of Wisconsin at Madison, 1997 [2] L.Barillas et al., Proc. 19^th Int. Conf. Nucl. Eng., Japan, 2011 [3] C.Ribeiro et al., IEEJ Trans. Electrical and Electronic Eng., 2012(accepted) [4] C.Ribeiro et al., Proc. 39^th EPS Conf. Contr. Fusion and Plasma Phys., Sweden, 2012

  2. Drop impact on spherical soft surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Simeng; Bertola, Volfango

    2017-08-01

    The impact of water drops on spherical soft surfaces is investigated experimentally through high-speed imaging. The effect of a convex compliant surface on the dynamics of impacting drops is relevant to various applications, such as 3D ink-jet printing, where drops of fresh material impact on partially cured soft substrates with arbitrary shape. Several quantities which characterize the morphology of impacting drops are measured through image-processing, including the maximum and minimum spreading angles, length of the wetted curve, and dynamic contact angle. In particular, the dynamic contact angle is measured using a novel digital image-processing scheme based on a goniometric mask, which does not require edge fitting. It is shown that the surface with a higher curvature enhances the retraction of the spreading drop; this effect may be due to the difference of energy dissipation induced by the curvature of the surface. In addition, the impact parameters (elastic modulus, diameter ratio, and Weber number) are observed to significantly affect the dynamic contact angle during impact. A quantitative estimation of the deformation energy shows that it is significantly smaller than viscous dissipation.

  3. Spherical nanoindentation stress–strain curves

    SciTech Connect

    Pathak, Siddhartha; Kalidindi, Surya R.

    2015-03-24

    Although indentation experiments have long been used to measure the hardness and Young's modulus, the utility of this technique in analyzing the complete elastic–plastic response of materials under contact loading has only been realized in the past few years – mostly due to recent advances in testing equipment and analysis protocols. This paper provides a timely review of the recent progress made in this respect in extracting meaningful indentation stress–strain curves from the raw datasets measured in instrumented spherical nanoindentation experiments. These indentation stress–strain curves have produced highly reliable estimates of the indentation modulus and the indentation yield strength in the sample, as well as certain aspects of their post-yield behavior, and have been critically validated through numerical simulations using finite element models as well as direct in situ scanning electron microscopy (SEM) measurements on micro-pillars. Much of this recent progress was made possible through the introduction of a new measure of indentation strain and the development of new protocols to locate the effective zero-point of initial contact between the indenter and the sample in the measured datasets. As a result, this has led to an important key advance in this field where it is now possible to reliably identify and analyze the initial loading segment in the indentation experiments.

  4. Perforation of woven fabric by spherical projectiles

    SciTech Connect

    Shim, V.P.W.; Tan, V.B.C.; Tay, T.E.

    1995-12-31

    Rectangular specimens of Twaron{reg_sign} fabric, clamped on two opposite sides, are subjected to impact perforation by 9.5 mm diameter spherical steel projectiles at speeds ranging from 140 m/s to 420 m/s. This plain woven fabric, comprising PPTA (poly-paraphenylene terepthalamide) fibers, is commonly employed in flexible an-nor applications. Its perforation response is examined in terms of residual velocity, energy absorbed and resulting deformation patterns. The existence of a critical or transition impact velocity, beyond which there is a significant reduction in energy absorbed by perforation, is observed. Differences in creasing and deformation induced in specimens are also demarcated by this transition impact velocity. Effects of difference in boundary conditions (clamped and free) on yarn breakage are also noted. A numerical model, based on an initially orthogonal network of pin-jointed bars interconnected at nodes, is formulated to simulate the fabric. Fiber yam mechanical properties are represented via a three-element spring-dashpot model which encapsulates viscoelastic behavior and fiber failure. Numerical results exhibit good correlation with experimental observations in terms of prediction of threshold perforation velocity, energy absorbed, occurrence of a transition critical velocity and fabric deformation characteristics.

  5. Spherical-wave effects in photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Sagurton, M.; Bullock, E. L.; Saiki, R.; Kaduwela, A.; Brundle, C. R.; Fadley, C. S.; Rehr, J. J.

    1986-02-01

    The influence of spherical-wave (SW) effects on the analysis of photoelectron diffraction (PD) data is considered by comparing full SW single-scattering calculations with similar calculations based upon the plane-wave (PW) approximation and a new approximation for including SW effects (SW(1)) due to Rehr, Albers, Natoli, and Stern, as well as with experimental data involving both scanned-energy and scanned-angle measurements. In general, SW effects are found to be much more important in forward scattering and to explain prior empirical adjustments of PW x-ray PD scattering amplitudes at higher energies of >~500 eV. The more easily used SW(1) approximation is also seen to allow very well for SW effects. Not all PD data are expected to be equally sensitive to SW corrections. For example, scanned-energy data for S/Ni(001) emphasizing backscattering events are about equally well described by the PW and SW models, whereas higher-energy azimuthal-scan data for O/Ni(001) in which forward scattering is dominant require SW corrections to describe some, but not all, directions of emission quantitatively.

  6. Spherical nanoindentation stress–strain curves

    DOE PAGES

    Pathak, Siddhartha; Kalidindi, Surya R.

    2015-03-24

    Although indentation experiments have long been used to measure the hardness and Young's modulus, the utility of this technique in analyzing the complete elastic–plastic response of materials under contact loading has only been realized in the past few years – mostly due to recent advances in testing equipment and analysis protocols. This paper provides a timely review of the recent progress made in this respect in extracting meaningful indentation stress–strain curves from the raw datasets measured in instrumented spherical nanoindentation experiments. These indentation stress–strain curves have produced highly reliable estimates of the indentation modulus and the indentation yield strength inmore » the sample, as well as certain aspects of their post-yield behavior, and have been critically validated through numerical simulations using finite element models as well as direct in situ scanning electron microscopy (SEM) measurements on micro-pillars. Much of this recent progress was made possible through the introduction of a new measure of indentation strain and the development of new protocols to locate the effective zero-point of initial contact between the indenter and the sample in the measured datasets. As a result, this has led to an important key advance in this field where it is now possible to reliably identify and analyze the initial loading segment in the indentation experiments.« less

  7. Gravothermal catastrophe in anisotropic spherical systems

    NASA Astrophysics Data System (ADS)

    Magliocchetti, Manuela; Pucacco, Giuseppe; Vesperini, Enrico

    1998-11-01

    In this paper we investigate the gravothermal instability of spherical stellar systems endowed with a radially anisotropic velocity distribution. We focus our attention on the effects of anisotropy on the conditions for the onset of instability and in particular we study the dependence of the spatial structure of critical models on the amount of anisotropy present in a system. The investigation has been carried out by the method of linear series which has already been used in the past to study the gravothermal instability of isotropic systems._ We consider models described by King, Wilson and Woolley-Dickens distribution functions. In the case of King and Woolley-Dickens models, our results show that, for quite a wide range of the amount of anisotropy in the system, the critical value of the concentration of the system (defined as the ratio of the tidal to the King core radius of the system) is approximately constant and equal to the corresponding value for isotropic systems. Only for very anisotropic systems does the critical value of the concentration start to change and it decreases significantly as the anisotropy increases and penetrates the inner parts of the system. For Wilson models the decrease of the concentration of critical models is preceded by an intermediate regime in which critical concentration increases, reaches a maximum and then starts to decrease. The critical value of the central potential always decreases as the anisotropy increases.

  8. Gravitaxis in Spherical Janus Swimming Devices

    PubMed Central

    2013-01-01

    In this work, we show that the asymmetrical distribution of mass at the surface of catalytic Janus swimmers results in the devices preferentially propelling themselves upward in a gravitational field. We demonstrate the existence of this gravitaxis phenomenon by observing the trajectories of fueled Janus swimmers, which generate thrust along a vector pointing away from their metallically coated half. We report that as the size of the spherical swimmer increases, the propulsive trajectories are no longer isotropic with respect to gravity, and they start to show a pronounced tendency to move in an upward direction. We suggest that this effect is due to the platinum caps asymmetric mass exerting an increasing influence on the azimuthal angle of the Janus sphere with size, biasing its orientation toward a configuration where the heavier propulsion generating surface faces down. This argument is supported by the good agreement we find between the experimentally observed azimuthal angle distribution for the Janus swimmers and predictions made by simple Boltzmann statistics. This gravitaxis phenomenon provides a mechanism to autonomously control and direct the motion of catalytic swimming devices and so enable a route to make autonomous transport devices and develop new separation, sensing, and controlled release applications. PMID:24134682

  9. The Spherical Tokamak MEDUSA for Mexico

    NASA Astrophysics Data System (ADS)

    Ribeiro, C.; Salvador, M.; Gonzalez, J.; Munoz, O.; Tapia, A.; Arredondo, V.; Chavez, R.; Nieto, A.; Gonzalez, J.; Garza, A.; Estrada, I.; Jasso, E.; Acosta, C.; Briones, C.; Cavazos, G.; Martinez, J.; Morones, J.; Almaguer, J.; Fonck, R.

    2011-10-01

    The former spherical tokamak MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R < 0.14m, a < 0.10m, BT < 0.5T, Ip < 40kA, 3ms pulse) is currently being recomissioned at the Universidad Autónoma de Nuevo León, Mexico, as part of an agreement between the Faculties of Mech.-Elect. Eng. and Phy. Sci.-Maths. The main objective for having MEDUSA is to train students in plasma physics & technical related issues, aiming a full design of a medium size device (e.g. Tokamak-T). Details of technical modifications and a preliminary scientific programme will be presented. MEDUSA-MX will also benefit any developments in the existing Mexican Fusion Network. Strong liaison within national and international plasma physics communities is expected. New activities on plasma & engineering modeling are expected to be developed in parallel by using the existing facilities such as a multi-platform computer (Silicon Graphics Altix XE250, 128G RAM, 3.7TB HD, 2.7GHz, quad-core processor), ancillary graph system (NVIDIA Quadro FE 2000/1GB GDDR-5 PCI X16 128, 3.2GHz), and COMSOL Multiphysics-Solid Works programs.

  10. Plasmonic and silicon spherical nanoparticle antireflective coatings.

    PubMed

    Baryshnikova, K V; Petrov, M I; Babicheva, V E; Belov, P A

    2016-03-01

    Over the last decade, plasmonic antireflecting nanostructures have been extensively studied to be utilized in various optical and optoelectronic systems such as lenses, solar cells, photodetectors, and others. The growing interest to all-dielectric photonics as an alternative optical technology along with plasmonics motivates us to compare antireflective properties of plasmonic and all-dielectric nanoparticle coatings based on silver and crystalline silicon respectively. Our simulation results for spherical nanoparticles array on top of amorphous silicon show that both silicon and silver coatings demonstrate strong antireflective properties in the visible spectral range. For the first time, we show that zero reflectance from the structure with silicon coatings originates from the destructive interference of electric- and magnetic-dipole responses of nanoparticle array with the wave reflected from the substrate, and we refer to this reflection suppression as substrate-mediated Kerker effect. We theoretically compare the silicon and silver coating effectiveness for the thin-film photovoltaic applications. Silver nanoparticles can be more efficient, enabling up to 30% increase of the overall absorbance in semiconductor layer. Nevertheless, silicon coatings allow up to 64% absorbance increase in the narrow band spectral range because of the substrate-mediated Kerker effect, and band position can be effectively tuned by varying the nanoparticles sizes.

  11. Signatures of Spherical Compactifications at the LHC

    SciTech Connect

    Davoudiasl, Hooman; Rizzo, Thomas G.

    2007-02-12

    TeV-scale extra dimensions may play an important role in electroweak or supersymmetry breaking. We examine the phenomenology of such dimensions, compactified on a sphere S{sup n}, n {ge} 2, and show that they possess distinct features and signatures. For example, unlike flat toroidal manifolds, spheres do not trivially allow fermion massless modes. Acceptable phenomenology then generically leads to ''non-universal'' extra dimensions with ''pole-localized'' 4-d fermions; the bosonic fields can be in the bulk. Due to spherical symmetry, some Kaluza-Klein (KK) modes of bulk gauge fields are either stable or extremely long-lived, depending on the graviton KK spectrum. Using precision electroweak data, we constrain the lightest gauge field KK modes to lie above {approx_equal} 4 TeV. We show that some of these KK resonances are within the reach of the LHC in several different production channels. The models we study can be uniquely identified by their collider signatures.

  12. Plasmonic and silicon spherical nanoparticle antireflective coatings

    PubMed Central

    Baryshnikova, K. V.; Petrov, M. I.; Babicheva, V. E.; Belov, P. A.

    2016-01-01

    Over the last decade, plasmonic antireflecting nanostructures have been extensively studied to be utilized in various optical and optoelectronic systems such as lenses, solar cells, photodetectors, and others. The growing interest to all-dielectric photonics as an alternative optical technology along with plasmonics motivates us to compare antireflective properties of plasmonic and all-dielectric nanoparticle coatings based on silver and crystalline silicon respectively. Our simulation results for spherical nanoparticles array on top of amorphous silicon show that both silicon and silver coatings demonstrate strong antireflective properties in the visible spectral range. For the first time, we show that zero reflectance from the structure with silicon coatings originates from the destructive interference of electric- and magnetic-dipole responses of nanoparticle array with the wave reflected from the substrate, and we refer to this reflection suppression as substrate-mediated Kerker effect. We theoretically compare the silicon and silver coating effectiveness for the thin-film photovoltaic applications. Silver nanoparticles can be more efficient, enabling up to 30% increase of the overall absorbance in semiconductor layer. Nevertheless, silicon coatings allow up to 64% absorbance increase in the narrow band spectral range because of the substrate-mediated Kerker effect, and band position can be effectively tuned by varying the nanoparticles sizes. PMID:26926602

  13. Spherical aberration and the sign of defocus.

    PubMed

    Thibos, Larry N; Bradley, Arthur; Liu, Tao; López-Gil, Norberto

    2013-11-01

    Visual sensing of the sign of defocus is important not only for the rapid control of accommodation but also for regulating the slower long-term growth of the eye. We examined the possibility that ocular spherical aberration (SA) elicits a sign of defocus by optical modeling of image formation using the principles of physical optics. Retinal image contrast, as measured by the area under the visually weighted modulation-transfer function, depends on both the magnitude and the sign of defocus relative to the sign of the SA. Image contrast is greater for hyperopic blur than for myopic blur when SA is positive and vice versa when SA is negative. When coupled with Wallman's hypothesis that retinal activity caused by image contrast inhibits eye growth, these results provide a testable hypothesis to account for myopia progression. For example, we suggest that hyperopic blur is a risk factor for myopia progression only when the eye has a negative SA because that is the combination leading to relatively low contrast in the defocused retinal image. Because the likelihood of a negative SA increases with accommodation, avoiding long hours of near work in the presence of accommodative lag may help prevent the onset and progression of myopia.

  14. Plasmonic and silicon spherical nanoparticle antireflective coatings

    NASA Astrophysics Data System (ADS)

    Baryshnikova, K. V.; Petrov, M. I.; Babicheva, V. E.; Belov, P. A.

    2016-03-01

    Over the last decade, plasmonic antireflecting nanostructures have been extensively studied to be utilized in various optical and optoelectronic systems such as lenses, solar cells, photodetectors, and others. The growing interest to all-dielectric photonics as an alternative optical technology along with plasmonics motivates us to compare antireflective properties of plasmonic and all-dielectric nanoparticle coatings based on silver and crystalline silicon respectively. Our simulation results for spherical nanoparticles array on top of amorphous silicon show that both silicon and silver coatings demonstrate strong antireflective properties in the visible spectral range. For the first time, we show that zero reflectance from the structure with silicon coatings originates from the destructive interference of electric- and magnetic-dipole responses of nanoparticle array with the wave reflected from the substrate, and we refer to this reflection suppression as substrate-mediated Kerker effect. We theoretically compare the silicon and silver coating effectiveness for the thin-film photovoltaic applications. Silver nanoparticles can be more efficient, enabling up to 30% increase of the overall absorbance in semiconductor layer. Nevertheless, silicon coatings allow up to 64% absorbance increase in the narrow band spectral range because of the substrate-mediated Kerker effect, and band position can be effectively tuned by varying the nanoparticles sizes.

  15. Spherically Symmetric Solutions of Light Galileon

    NASA Astrophysics Data System (ADS)

    Momeni, D.; Houndjo, M. J. S.; Güdekli, E.; Rodrigues, M. E.; Alvarenga, F. G.; Myrzakulov, R.

    2016-02-01

    We have been studied the model of light Galileon with translational shift symmetry ϕ → ϕ + c. The matter Lagrangian is presented in the form {L}_{φ }= -η (partial φ )2+β G^{μ ν }partial _{μ }φ partial _{ν }φ . We have been addressed two issues: the first is that, we have been proven that, this type of Galileons belong to the modified matter-curvature models of gravity in type of f(R,R^{μ ν }T_{μ ν }m). Secondly, we have been investigated exact solution for spherically symmetric geometries in this model. We have been found an exact solution with singularity at r = 0 in null coordinates. We have been proven that the solution has also a non-divergence current vector norm. This solution can be considered as an special solution which has been investigated in literature before, in which the Galileon's field is non-static (time dependence). Our scalar-shift symmetrized Galileon has the simple form of ϕ = t, which it is remembered by us dilaton field.

  16. Spherical tokamaks with plasma centre-post

    NASA Astrophysics Data System (ADS)

    Ribeiro, Celso

    2013-10-01

    The metal centre-post (MCP) in tokamaks is a structure which carries the total toroidal field current and also houses the Ohmic heating solenoid in conventional or low aspect ratio (Spherical)(ST) tokamaks. The MCP and solenoid are critical components for producing the toroidal field and for the limited Ohmic flux in STs. Constraints for a ST reactor related to these limitations lead to a minimum plasma aspect ratio of 1.4 which reduces the benefit of operation at higher betas in a more compact ST reactor. Replacing the MCP is of great interest for reactor-based ST studies since the device is simplified, compactness increased, and maintenance reduced. An experiment to show the feasibility of using a plasma centre-post (PCP) is being currently under construction and involves a high level of complexity. A preliminary study of a very simple PCP, which is ECR(Electron Cyclotron Resonance)-assisted and which includes an innovative fuelling system based on pellet injection, has recently been reported. This is highly suitable for an ultra-low aspect ratio tokamak (ULART) device. Advances on this PCP ECR-assisted concept within a ULART and the associated fuelling system are presented here, and will include the field topology for the PCP ECR-assisted scheme, pellet ablation modeling, and a possible global equilibrium simulation. VIE-ITCR, IAEA-CRP contr.17592, National Instruments-Costa Rica.

  17. Bounce-free spherical hydrodynamic implosion

    NASA Astrophysics Data System (ADS)

    Kagan, Grigory; Tang, Xian-Zhu; Hsu, Scott C.; Awe, Thomas J.

    2011-10-01

    In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. A solution family realizing such a regime has been explicitly found. This regime found is most naturally applied and would be of most benefit to plasma liner driven magneto-inertial fusion (MIF). That is, this version of inertial confinement relies on maintaining the compressed hot spot within the thermonuclear burning condition for as long as possible, rather than on initiating the burn wave. Consequently, in MIF it is the best-case scenario that the fuel target persists in the state of maximum compression after reaching stagnation. Also, the plasma liner driven MIF provides substantial freedom in shaping the profiles of the imploding flow (i.e. liner) pressure, density and fluid velocity. By comparing the fuel disassembly time against that of a stationary imploding flow case, we find that shaping this flow appropriately is likely to increase the dwell time and fusion gain by a factor of four or more. Moreover, in this newly found regime the shocked region of the liner is at rest. That is, the kinetic energy of the original liner is entirely converted into internal energy. Hence, our result supports the idea of using the deuterium-tritium in the inner parts of the liner or the so-called ``after-burner,'' which upon becoming shocked will also burn, thus further increasing the gain. The work is supported by LANL LDRD.

  18. Shear & Compression Plasma Viscosity In Spherical ICF

    NASA Astrophysics Data System (ADS)

    Morse, Richard

    2003-10-01

    In (1) the exceptional viscosity of DT plasmas (Braginskii) was estimated to reduce by orders of magnitude growth rates of the most threatening m=0 modes in liner implosions of cylindrical Z-pinch plasmas that reach a thermonuclear T=10keV. Here in spherical B=0 implosions shear viscosity is estimated, by numerical(2)(implicit in t) & analytic(Chandrasekhar) methods, to reduce similarly the growth of R-T modes in DT plasmas reaching 10keV, where μ ˜5.E4 poise, or higher T. Surface plasma interactions with the confining pusher shell(3) & Knudsen(large mfp) limitation of the viscous effects are discussed. Compression viscosity(Zel'dovich) adds noticeably to irreversible heating(reduced to quadratures) in such systems, esp. with final T>10keV &/or implosion velocities >10E7cm/s. Here double implosions, as suggested in (4), can increase significantly entropy production prior to final implosion &, consequently, heating efficiency. (1)Bull. APS 44-7 Nov99 BP189 (2)McCrory et. al. Nuc.Sci.. 64,163(77) & references (3)Montierth et al., PFB 4(4) Ap92 & references (4)Two Stage Heating Of Theta Pinches, Freidberg & Morse, Proc. '71 Garching Conf. On High β Plasmas

  19. Radiative Transfer in a Scattering Spherical Atmosphere

    NASA Astrophysics Data System (ADS)

    Hong, S. S.; Park, Y.-S.; Kwon, S. M.; Park, C.; Weinberg, J. L.

    2002-03-01

    We have written a code called QDM_sca, which numerically solves the problem of radiative transfer in an anisotropically scattering, spherical atmosphere. First we formulate the problem as a second order differential equation of a quasi-diffusion type. We then apply a three-point finite differencing to the resulting differential equation and transform it to a tri-diagonal system of simultaneous linear equations. After boundary conditions are implemented in the tri-diagonal system, the QDM_sca radiative code fixes the field of specific intensity at every point in the atmosphere. As an application example, we used the code to calculate the brightness of atmospheric diffuse light(ADL) as a function of zenith distance, which plays a pivotal role in reducing the zodiacal light brightness from night sky observations. On the basis of this ADL calculation, frequent uses of effective extinction optical depth have been fully justified in correcting the atmospheric extinction for such extended sources as zodiacal light, integrated starlight and diffuse galactic light. The code will be available on request.

  20. Natural melting within a spherical shell

    NASA Technical Reports Server (NTRS)

    Bahrami, Parviz A.

    1990-01-01

    Fundamental heat transfer experiments were performed on the melting of a phase change medium in a spherical shell. Free expansion of the medium into a void space within the sphere was permitted. A step function temperature jump on the outer shell wall was imposed and the timewise evolution of the melting process and the position of the solid-liquid interface was photographically recorded. Numerical integration of the interface position data yielded information about the melted mass and the energy of melting. It was found that the rate of melting and the heat transfer were significantly affected by the movement of the solid medium to the base of the sphere due to gravity. The energy transfer associated with melting was substantially higher than that predicted by the conduction model. Furthermore, the radio of the measured values of sensible energy in the liquid melt to the energy of melting were nearly proportional to the Stefan number. The experimental results are in agreement with a theory set forth in an earlier paper.

  1. Maximum mass of a barotropic spherical star

    NASA Astrophysics Data System (ADS)

    Fujisawa, Atsuhito; Saida, Hiromi; Yoo, Chul-Moon; Nambu, Yasusada

    2015-11-01

    The ratio of total mass {m}* to the surface radius {r}* of a spherical perfect fluid ball has an upper bound, {{Gm}}*/({c}2{r}*)≤slant {B}. Buchdahl (1959 Phys. Rev. 116 1027) obtained the value {{B}}{{Buch}}=4/9 under the assumptions that the object has a nonincreasing mass density in the outward direction and a barotropic equation of state. Barraco and Hamity (2002 Phys. Rev. D 65 124028) decreased Buchdahl's bound to a lower value, {{B}}{{BaHa}} = 3/8 (<4/9), by adding the dominant energy condition to Buchdahl's assumptions. In this paper, we further decrease Barraco-Hamity's bound to {{B}}{{new}}≃ 0.3636403 (<3/8) by adding the subluminal (slower than light) condition of sound speed. In our analysis we numerically solve the Tolman-Oppenheimer-Volkoff equations, and the mass-to-radius ratio is maximized by variation of mass, radius and pressure inside the fluid ball as functions of mass density.

  2. Chirped femtosecond pulse scattering by spherical particles

    NASA Astrophysics Data System (ADS)

    Kim, Dal-Woo; Xiao, Gang-Yao; Lee, Tong-Nyong

    1996-05-01

    Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g( tau ) = exp[- pi (1 + ib) tau 2], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength ( lambda 0 = 0.5 mu m) and pulse-filling coefficient (l0 = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the only on the amount of chirp (|b|), regardless of upchirp (b greater than 0) or downchirp (b less than 0).

  3. Scaling relationships and physics for mixed heating convection in planetary interiors: Isoviscous spherical shells

    NASA Astrophysics Data System (ADS)

    Weller, Matthew B.; Lenardic, Adrian; Moore, William B.

    2016-10-01

    We use a suite of 3-D numerical experiments to test and expand 2-D planar isoviscous scaling relationships of Moore (2008) for mixed heating convection in spherical geometry mantles over a range of Rayleigh numbers (Ra). The internal temperature scaling of Moore (2008), when modified to account for spherical geometry, matches our experimental results to a high degree of fit. The heat flux through the boundary layers scale as a linear combination of internal (Q) and basal heating, and the modified theory predictions match our experimental results. Our results indicate that boundary layer thickness and surface heat flux are not controlled by a local boundary layer stability condition (in agreement with the results of Moore (2008)) and are instead strongly influenced by boundary layer interactions. Subadiabatic mantle temperature gradients, in spherical 3-D, are well described by a vertical velocity scaling based on discrete drips as opposed to a scaling based on coherent sinking sheets, which was found to describe 2-D planar results. Root-mean-square (RMS) velocities are asymptotic for both low Q and high Q, with a region of rapid adjustment between asymptotes for moderate Q. RMS velocities are highest in the low Q asymptote and decrease as internal heating is applied. The scaling laws derived by Moore (2008), and extended here, are robust and highlight the importance of differing boundary layer processes acting over variable Q and moderate Ra.

  4. Spherical indentation method for determining the constitutive parameters of hyperelastic soft materials.

    PubMed

    Zhang, Man-Gong; Cao, Yan-Ping; Li, Guo-Yang; Feng, Xi-Qiao

    2014-01-01

    A comprehensive study on the spherical indentation of hyperelastic soft materials is carried out through combined theoretical, computational, and experimental efforts. Four widely used hyperelastic constitutive models are studied, including neo-Hookean, Mooney-Rivlin, Fung, and Arruda-Boyce models. Through dimensional analysis and finite element simulations, we establish the explicit relations between the indentation loads at given indentation depths and the constitutive parameters of materials. Based on the obtained results, the applicability of Hertzian solution to the measurement of the initial shear modulus of hyperelastic materials is examined. Furthermore, from the viewpoint of inverse problems, the possibility to measure some other properties of a hyperelastic material using spherical indentation tests, e.g., locking stretch, is addressed by considering the existence, uniqueness, and stability of the solution. Experiments have been performed on polydimethylsiloxane to validate the conclusions drawn from our theoretical analysis. The results reported in this study should help identify the extent to which the mechanical properties of hyperelastic materials could be measured from spherical indentation tests.

  5. Application of Vector Spherical Harmonics and Kernel Regression to the Computations of OMM Parameters

    NASA Astrophysics Data System (ADS)

    Marco, F. J.; Martínez, M. J.; López, J. A.

    2015-04-01

    The high quality of Hipparcos data in position, proper motion, and parallax has allowed for studies about stellar kinematics with the aim of achieving a better physical understanding of our galaxy, based on accurate calculus of the Ogorodnikov-Milne model (OMM) parameters. The use of discrete least squares is the most common adjustment method, but it may lead to errors mainly because of the inhomogeneous spatial distribution of the data. We present an example of the instability of this method using the case of a function given by a linear combination of Legendre polynomials. These polynomials are basic in the use of vector spherical harmonics, which have been used to compute the OMM parameters by several authors, such as Makarov & Murphy, Mignard & Klioner, and Vityazev & Tsvetkov. To overcome the former problem, we propose the use of a mixed method (see Marco et al.) that includes the extension of the functions of residuals to any point on the celestial sphere. The goal is to be able to work with continuous variables in the calculation of the coefficients of the vector spherical harmonic developments with stability and efficiency. We apply this mixed procedure to the study of the kinematics of the stars in our Galaxy, employing the Hipparcos velocity field data to obtain the OMM parameters. Previously, we tested the method by perturbing the Vectorial Spherical Harmonics model as well as the velocity vector field.

  6. Short-Scale Turbulent Fluctuations Driven by the Electron-Temperature Gradient in the National Spherical Torus Experiment

    SciTech Connect

    Mazzucato, E.; Smith, D. R.; Bell, R. E.; Kaye, S.; Davis, W.; Hosea, J.; LeBlanc, B; Wilson, J. R.; Ryan, Philip Michael; Domier, C. W.; Luhmann, N. C.; Yuh, H.; Lee, W.; Park, H.

    2008-01-01

    Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers k?e 0:1 0:4, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.

  7. SURFACE CHEMICAL EFFECTS ON COLLOID STABILITY AND TRANSPORT THROUGH NATURAL POROUS MEDIA

    EPA Science Inventory

    Surface chemical effects on colloidal stability and transport through porous media were investigated using laboratory column techniques. Approximately 100 nm diameter, spherical, iron oxide particles were synthesized as the mobile colloidal phase. The column packing material was ...

  8. SURFACE CHEMICAL EFFECTS ON COLLOID STABILITY AND TRANSPORT THROUGH NATURAL POROUS MEDIA

    EPA Science Inventory

    Surface chemical effects on colloidal stability and transport through porous media were investigated using laboratory column techniques. Approximately 100 nm diameter, spherical, iron oxide particles were synthesized as the mobile colloidal phase. The column packing material was ...

  9. Contributions of Spherical Harmonics to Magnetic and Gravitational Fields

    NASA Technical Reports Server (NTRS)

    Roithmayr, Carlos M.

    2004-01-01

    Gravitational forces are of cardinal importance in the dynamics of spacecraft; magnetic attractions sometime play a significant role also, as was the case with the Long Duration Exposure Facility, and as is now true for the first segment of Space Station Freedom. Both satellites depend on gravitational moment and a device known as a magnetic damper to stabilize their orientation. Magnetic fields are mathematically similar to gravitational fields in one important respect: each can be regarded as a gradient of a potential function that, in turn, can be described as an infinite series of spherical harmonics. Consequently, the two fields can be computed, in part, with quantities that need only be evaluated once, resulting in a savings of time when both fields are needed. The objective of this material is to present magnetic field and gravitational force expressions, and point out the terms that belong to both this is accomplished in Section 1 and 2. Section 3 contains the deductive reasoning with which one obtains the expressions of interest. Finally, examples in Section 4 show these equations can be used to reproduce others that arise in connection with special cases such as the magnetic field produced by a tilted dipole, and gravitational force exerted by an oblate spheroid. The mathematics are discussed in the context of terrestrial fields; however, by substituting appropriate constants, the results can be made applicable to fields belonging to other celestial bodies. The expressions presented here share the characteristics of algorithms set forth for computing gravitational force. In particular, computation is performed speedily by means of recursion formulae, and the expressions do not suffer from the shortcoming of a singularity when evaluated at points that lie on the polar axis.

  10. Modeling of Spherical Torus Plasmas for Liquid Lithium Wall Experiments

    SciTech Connect

    R. Kaita; S. Jardin; B. Jones; C. Kessel; R. Majeski; J. Spaleta; R. Woolley; L. Zakharo; B. Nelson; M. Ulrickson

    2002-01-29

    Liquid metal walls have the potential to solve first-wall problems for fusion reactors, such as heat load and erosion of dry walls, neutron damage and activation, and tritium inventory and breeding. In the near term, such walls can serve as the basis for schemes to stabilize magnetohydrodynamic (MHD) modes. Furthermore, the low recycling characteristics of lithium walls can be used for particle control. Liquid lithium experiments have already begun in the Current Drive eXperiment-Upgrade (CDX-U). Plasmas limited with a toroidally localized limiter have been investigated, and experiments with a fully toroidal lithium limiter are in progress. A liquid surface module (LSM) has been proposed for the National Spherical Torus Experiment (NSTX). In this larger ST, plasma currents are in excess of 1 MA and a typical discharge radius is about 68 cm. The primary motivation for the LSM is particle control, and options for mounting it on the horizontal midplane or in the divertor region are under consideration. A key consideration is the magnitude of the eddy currents at the location of a liquid lithium surface. During plasma start up and disruptions, the force due to such currents and the magnetic field can force a conducting liquid off of the surface behind it. The Tokamak Simulation Code (TSC) has been used to estimate the magnitude of this effect. This program is a two dimensional, time dependent, free boundary simulation code that solves the MHD equations for an axisymmetric toroidal plasma. From calculations that match actual ST equilibria, the eddy current densities can be determined at the locations of the liquid lithium. Initial results have shown that the effects could be significant, and ways of explicitly treating toroidally local structures are under investigation.

  11. Time evolution of entropy for spherical self-gravitating systems

    NASA Astrophysics Data System (ADS)

    Sui, Ning; He, Ping

    In this work, we investigate the dynamical evolution of spherical self-gravitating systems under their own gravity with N-body simulations. For this purpose, we study the evolution of the generalized virialization relations, and particularly focus on the time evolution of the coarse-grained entropy of dark matter halos under various perturbations. First, we construct six single perturbation models under four initial conditions to mimic typical disturbances that a realistic gravitating system may encounter. With the simulation results, we show the time evolution of the entropy for the six perturbation models. In all these models, at first the entropy increases rapidly for a short period of time, slowly evolves for a longer period of time and then remains nearly unchanged in the subsequent evolution. The main dynamical mechanisms behind these evolutions should be violent relaxation and phase mixing. However, under repeated perturbations to the system, the evolution of entropy of self-gravitating systems manifests complete differences from that of the usual thermodynamical systems. We see that the entropy of the end states of every single perturbation, according to different repeated perturbation modes, either decreases or increases. We argue that the increasing or decreasing of the end-state entropy should be the reflection of the complexity of the thermodynamical states of self-gravitating systems. These conclusions are independent of the initial conditions. Besides, we demonstrate that the generalized virialization relations can reveal whether or not, or in which radius interval, the collisionless Boltzmann equation is suitable for description of a self-gravitating system, and can be used as good stability criteria of the system.

  12. Bed of polydisperse viscous spherical drops under thermocapillary effects

    NASA Astrophysics Data System (ADS)

    Sharanya, V.; Raja Sekhar, G. P.; Rohde, Christian

    2016-08-01

    Viscous flow past an ensemble of polydisperse spherical drops is investigated under thermocapillary effects. We assume that the collection of spherical drops behaves as a porous media and estimates the hydrodynamic interactions analytically via the so- called cell model that is defined around a specific representative particle. In this method, the hydrodynamic interactions are assumed to be accounted by suitable boundary conditions on a fictitious fluid envelope surrounding the representative particle. The force calculated on this representative particle will then be extended to a bed of spherical drops visualized as a Darcy porous bed. Thus, the "effective bed permeability" of such a porous bed will be computed as a function of various parameters and then will be compared with Carman-Kozeny relation. We use cell model approach to a packed bed of spherical drops of uniform size (monodisperse spherical drops) and then extend the work for a packed bed of polydisperse spherical drops, for a specific parameters. Our results show a good agreement with the Carman-Kozeny relation for the case of monodisperse spherical drops. The prediction of overall bed permeability using our present model agrees well with the Carman-Kozeny relation when the packing size distribution is narrow, whereas a small deviation can be noted when the size distribution becomes broader.

  13. Spherical warm shield design for infrared imaging systems

    NASA Astrophysics Data System (ADS)

    Tian, Qijie; Chang, Songtao; He, Fengyun; Li, Zhou; Qiao, Yanfeng

    2017-09-01

    The F-number matching is the primary means to suppress stray radiation for infrared imaging systems. However, it is difficult to achieve exact F-number matching, owing to the restriction from detectors, or multiple F-number design. Hence, an additional shield is required to block the certain thermal radiation. Typical shield is called flat warm shield, which is flat and operates at room temperature. For flat warm shield, it cannot suppress stray radiation while achieving F-number matching. To overcome the restriction, a spherical reflective warm shield is required. First of all, the detailed theory of spherical warm shield design is developed on basis of the principle that stray radiation cannot directly reach the infrared focal plane array. According to the theory developed above, a polished spherical warm shield, whose radius is 18 mm, is designed to match an F/2 infrared detector with an F/4 infrared imaging system. Then, the performance and alignment errors of the designed spherical warm shield are analyzed by simulation. Finally, a contrast experiment between the designed spherical warm shield and two differently processed flat warm shields is performed in a chamber with controllable inside temperatures. The experimental results indicate that the designed spherical warm shield cannot only achieve F-number matching but suppress stray radiation sufficiently. Besides, it is demonstrated that the theory of spherical warm shield design developed in this paper is valid and can be employed by arbitrary infrared imaging systems.

  14. Wave Amplitude Dependent Engineering Model of Propellant Slosh in Spherical Tanks

    NASA Technical Reports Server (NTRS)

    Brodnick, Jacob; Westra, Douglas G.; Eberhart, Chad J.; Yang, Hong Q.; West, Jeffrey S.

    2016-01-01

    Liquid propellant slosh is often a concern for the controllability of flight vehicles. Anti-slosh devices are traditionally included in propellant tank designs to limit the amount of sloshing allowed during flight. These devices and any necessary supports can be quite heavy to meet various structural requirements. Some of the burden on anti-slosh devices can be relieved by exploiting the nonlinear behavior of slosh waves in bare smooth wall tanks. A nonlinear regime slosh model for bare spherical tanks was developed through a joint analytical and experimental effort by NASA/MSFC. The developed slosh model accounts for the large damping inherent in nonlinear slosh waves which is more accurate and drives conservatism from vehicle stability analyses that use traditional bare tank slosh models. A more accurate slosh model will result in more realistic predicted slosh forces during flight reducing or removing the need for active controls during a maneuver or baffles in the tank design. Lower control gains and smaller or fewer tank baffles can reduce cost and system complexity while increasing vehicle performance. Both Computational Fluid Dynamics (CFD) simulation and slosh testing of three different spherical tank geometries were performed to develop the proposed slosh model. Several important findings were made during this effort in addition to determining the parameters to the nonlinear regime slosh model. The linear regime slosh damping trend for spherical tanks reported in NASA SP-106 was shown to be inaccurate for certain regions of a tank. Additionally, transition to the nonlinear regime for spherical tanks was only found to occur at very large wave amplitudes in the lower hemisphere and was a strong function of the propellant fill level in the upper hemisphere. The nonlinear regime damping trend was also found to be a function of the propellant fill level.

  15. Time reversal for a single spherical scatterer.

    PubMed

    Chambers, D H; Gautesen, A K

    2001-06-01

    We show that the time reversal operator for a planar time reversal mirror (TRM) can have up to four distinct eigenvalues with a small spherical acoustic scatterer. Each eigenstate represents a resonance between the TRM and an induced scattering moment of the sphere. Their amplitude distributions on the TRM are orthogonal superpositions of the radiation patterns from a monopole and up to three orthogonal dipoles. The induced monopole moment is associated with the compressibility contrast between the sphere and the medium, while the dipole moments are associated with density contrast. The number of eigenstates is related to the number of orthogonal orientations of each induced multipole. For hard spheres (glass, metals) the contribution of the monopole moment to the eigenvalues is much greater than that of the dipole moments, leading to a single dominant eigenvalue. The other eigenvalues are much smaller, making it unlikely multiple eigenvalues could have been observed in previous experiments using hard materials. However, for soft materials such as wood, plastic, or air bubbles the eigenvalues are comparable in magnitude and should be observable. The presence of multiple eigenstates breaks the one-to-one correspondence between eigenstates and distinguishable scatterers discussed previously by Prada and Fink [Wave Motion 20, 151-163 (1994)]. However, eigenfunctions from separate scatterers would have different phases for their eigenfunctions, potentially restoring the ability to distinguish separate scatterers. Since relative magnitudes of the eigenvalues for a single scatterer are governed by the ratio of the compressibility contrast to the density contrast, measurement of the eigenvalue spectrum would provide information on the composition of the scatterer.

  16. HFE and Spherical Cryostats MC Study

    SciTech Connect

    Brodsky, Jason P.

    2016-09-26

    The copper vessel containing the nEXO TPC is surrounded by a buffer of HFE, a liquid refrigerant with very low levels of radioactive element contamination. The HFE is contained within the cryostat’s inner vessel, which is in turn inside the outer vessel. While some HFE may be necessary for stable cooling of nEXO, it is possible that using substantially more than necessary for thermal reasons will help reduce backgrounds originating in the cryostats. Using a larger amount of HFE is accomplished by making the cryostat vessels larger. By itself, increasing the cryostat size somewhat increases the background rate, as the thickness of the cryostat wall must increase at larger sizes. However, the additional space inside the cryostat will be filled with HFE which can absorb gamma rays headed for the TPC. As a result, increasing the HFE reduces the number of backgrounds reaching the TPC. The aim of this study was to determine the relationship between HFE thickness and background rate. Ultimately, this work should support choosing a cryostat and HFE size that satisfies nEXO’s background budget. I have attempted to account for every consequence of changing the cryostat size, although naturally this remains a work in progress until a final design is achieved. At the moment, the scope of the study includes only the spherical cryostat design. This study concludes that increasing cryostat size reduces backgrounds, reaching neglible backgrounds originating from the cryostat at the largest sizes. It also shows that backgrounds originating from the inherent radioactivity of the HFE plateau quickly, so may be considered essentially fixed at any quantity of HFE.

  17. Experimental investigation of reshocked spherical gas interfaces

    NASA Astrophysics Data System (ADS)

    Si, Ting; Zhai, Zhigang; Yang, Jiming; Luo, Xisheng

    2012-05-01

    The evolution of a spherical gas interface under reshock conditions is experimentally studied using the high-speed schlieren photography with high time resolutions. A number of experimental sets of helium or SF6 bubble surrounded by air for seven different end wall distances have been performed. Distinct flow structures are observed due to the additional vorticity and wave configuration caused by the reshock. In the air/helium case, the deformation of the reshocked bubble is dependent on the development of the penetrating air jet along the symmetry axis of the bubble. In general, two separate vortex rings can be observed, i.e., one develops slowly, and the other approaches and eventually impinges on the shock tube end wall. In the air/SF6 case, two SF6 jets moving in opposite directions are generated and the oscillation of the interface is observed for small end wall distances, while small scale vortex morphologies on the gas interface are found for large end wall distances. The physical mechanisms of the baroclinic vorticity generation and the pressure perturbation are highlighted in the interface evolution process. Based on the sequence of the schlieren images obtained during a single run for each case, the x-t diagrams of the shock and reshock interacting with the helium or SF6 bubble are plotted and the velocities estimated in linear stages are compared with those calculated from one-dimensional gas dynamics. The changes with time in the characteristic bubble sizes including the interface length, height, and vortex diameter are also measured.

  18. FY 2007 Miniature Spherical Retroreflectors Final Report

    SciTech Connect

    Anheier, Norman C.; Bernacki, Bruce E.; Krishnaswami, Kannan

    2008-02-20

    Miniature spherical retroreflectors, less than 8 millimeters in diameter, are currently being developed to enhance remote optical detection of nuclear proliferation activities. These retroreflecting spheres resemble small, sand-colored marbles that have the unique optical property of providing a strong reflection directly back to the source (i.e., retroreflecting) when illuminated with a laser. The addition of specific coatings, sensitive to specific chemicals or radioactive decay in the environment, can be applied to the surface of these retroreflectors to provide remote detection of nuclear proliferation activities. The presence of radioactive decay (e.g., alpha, gamma, neutron) or specific chemicals in the environment (e.g., TBP, acids) will change the optical properties of the spheres in a predictable fashion, thus indicating the presence or absence of the target materials. One possible scenario might employ an airborne infrared laser system (e.g., quantum-cascade lasers) to illuminate a section of ground littered with these retroreflective spheres. Depending on the coating and the presence of a specific chemical or radioisotope in the environment, the return signal would be modified in some predictable fashion because of fluorescence, frequency shifting, intensity attenuation/enhancement, or change in polarization. Research conducted in FY 2007 focused on developing novel optical fabrication processes and exploiting the unique material properties of chalcogenide infrared-transparent glass (germanium-arsenic-sulfur-tellurium compounds) to produce highly efficient retroreflectors. Pacific Northwest National Laboratory’s approach provides comparable performance to the ideal graded index sphere concept, developed by R. K. Luneburg in 1944 (Luneburg 1944), while greatly reducing the complexity in fabrication by utilizing chalcogenide glass materials and compression-molding processes.

  19. Wide-field aberration corrector for spherical gossamer primary mirrors

    NASA Astrophysics Data System (ADS)

    Beach, David A.

    2000-10-01

    If gossamer primary mirrors were to be constructed in a spherical form, it would be possible to arrange a simple null- test in situ. However, spherical mirrors would require correction of the large amount of spherical aberration created in pupils that generally will be greater than 2 m diameter. The design requirement is for diffraction-limited performance over a useful angular field. The otherwise excellent wide- field design solutions of the classical Schmidt and Maksutov are inapplicable in gossamer structures because of the mass and size penalty of large refractive components. However, it is possible for this mode of correction to be achieved near the prime focus by means of pupil transfer optics that minify the large entrance pupil down to more acceptable dimensions. A problem with these solutions is constraint of field coverage due to pupil aberrations created by the large spherical aberration of the primary mirror. This leads the designer towards slower primaries and the penalty of larger, heavier structures. A solution is presented here for spherical primaries with speeds up to f/4. This is based on the 'KiwiStar' principle presented here in 1997, in which a large spherical catoptric is combined by pupil-transfer with a smaller spherical catadioptric to give well corrected wide field images of high speed. This system is well suited to correction at the prime focus of large spherical mirrors, and has only one relatively small weak aspheric surface to provide zonal correction, all other surfaces being spherical. An example is presented of a 4 m diameter, f/2.5 system that is diffraction-limited over the whole of a 0.25 degree field (43 mm diameter), for a bandpass of 486 - 850 nm.

  20. Spherical interferometry for the characterization of precision spheres

    NASA Astrophysics Data System (ADS)

    Nicolaus, R. A.; Bartl, G.

    2016-09-01

    Interferometry with spherical wavefronts is usually used for characterizing precise optics. A special spherical interferometer was set up to measure the volume of high precision spheres used for the new definition of the SI unit kilogram, for which a fundamental constant, such as Planck’s constant h or Avogadro’s constant N A, was to be determined. Furthermore with this type of interferometer and with a special evaluating algorithm, absolute form deviations of spheres can be determined. With this knowledge, a sphere can be processed further to reach unrivaled small sphericity deviations.

  1. A spherical dc servo motor with three degrees of freedom

    NASA Astrophysics Data System (ADS)

    Kaneko, K.; Yamada, I.; Itao, K.

    1989-09-01

    A spherical dc servo motor with three degrees of freedom is proposed. First, the process of generating three-dimensional torque is analyzed to obtain the torque constant matrix. The matrix elements are shown to vary with rotor inclination, and winding currents are shown to interfere with each other. Then, the dynamics of the spherical motor are investigated theoretically and experimentally, considering torque interference, gyro moment and gravity. Finally, the trajectory of the prototype motor is shown in order to clarify its abilities. This new spherical motor is expected to produce a smaller, a lighter mechanism, since no gears or linkages are needed.

  2. On the Propagation and Interaction of Spherical Blast Waves

    NASA Technical Reports Server (NTRS)

    Kandula, Max; Freeman, Robert

    2007-01-01

    The characteristics and the scaling laws of isolated spherical blast waves have been briefly reviewed. Both self-similar solutions and numerical solutions of isolated blast waves are discussed. Blast profiles in the near-field (strong shock region) and the far-field (weak shock region) are examined. Particular attention is directed at the blast overpressure and shock propagating speed. Consideration is also given to the interaction of spherical blast waves. Test data for the propagation and interaction of spherical blast waves emanating from explosives placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure.

  3. Testing General Relativity with Spherical Resonant Mass Detectors

    NASA Astrophysics Data System (ADS)

    Sylvester, Alex J.

    2015-08-01

    Gravitational waves in f(R) gravity excite monopole and m = 0+/-2 quadrupole resonance modes of a spherical detector. This document reviews the basic ideas of general relativity and gravitational waves, and then applies those concepts to an f( R) gravitational wave. The acoustic response of a GW incident with a spherical detector is reviewed in detail, and the absorption cross section for an f(R) GW impinging on the spherical detector is calculated. Minimum detectable scalar wave amplitudes are explored for the Mario Schenberg detector. The mass of the scalar mode affects its detectability.

  4. Spherical mirror grazing incidence x-ray optics

    NASA Technical Reports Server (NTRS)

    Cash, Jr., Webster C. (Inventor)

    1997-01-01

    An optical system for x-rays combines at least two spherical or near spherical mirrors for each dimension in grazing incidence orientation to provide the functions of a lens in the x-ray region. To focus x-ray radiation in both the X and the Y dimensions, one of the mirrors focusses the X dimension, a second mirror focusses the Y direction, a third mirror corrects the X dimension by removing comatic aberration and a fourth mirror corrects the Y dimension. Spherical aberration may also be removed for an even better focus. The order of the mirrors is unimportant.

  5. Non-Spherical Microcapsules for Increased Core Content Volume Delivery

    NASA Technical Reports Server (NTRS)

    Oliva-Buisson, Yvette J.

    2014-01-01

    The goal of this project was to advance microencapsulation from the standard spherical microcapsule to a non-spherical, high-aspect ratio (HAR), elongated microcapsule. This was to be accomplished by developing reproducible methods of synthesizing or fabricating robust, non-spherical, HAR microcapsules. An additional goal of this project was to develop the techniques to the point where scale-up of these methods could be examined. Additionally, this project investigated ways to apply the microencapsulation techniques developed as part of this project to self-healing formulations.

  6. Determination of the Magnetic Moment with Spherical Measurements and Spherical Harmonics Modelling

    NASA Astrophysics Data System (ADS)

    Dumond, O.; Bergé, R.

    2012-05-01

    The magnetic moment of space equipment is a needed input for spacecraft magnetic budgeting. In general, a maximum value is also specified. Most of the time, due to the complexity of the equipment, the accurate determination of this magnetic global dipole moment is not possible by analysis. The magnetic sources that compose an equipment can be numerous and of various natures (actuators, current loops in circuits and wires, components, etc.). An experimental determination of the magnetic moment is then necessary. The basic method of the "6 faces" is not adapted for complex equipment (i.e. composed of several elementary dipoles). Intespace and CNES have experimented in the CNES magnetic test facility a method of determination of the magnetic moment using spherical measurements and spherical harmonics modelling. This method has been validated with simulation results and measurements on an assembly of 3 magnets. This paper will also compare the results obtained with other methods of magnetic moment determination. Another advantage of this method is to allow the measurement close to the equipment and then extrapolate the field at another higher distance.

  7. Analytical solution of the simplified spherical harmonics equations in spherical turbid media

    NASA Astrophysics Data System (ADS)

    Edjlali, Ehsan; Bérubé-Lauzière, Yves

    2016-10-01

    We present for the first time an analytical solution for the simplified spherical harmonics equations (so-called SPN equations) in the case of a steady-state isotropic point source inside a spherical homogeneous absorbing and scattering medium. The SPN equations provide a reliable approximation to the radiative transfer equation for describing light transport inside turbid media. The SPN equations consist of a set of coupled partial differential equations and the eigen method is used to obtain a set of decoupled equations, each resembling the heat equation in the Laplace domain. The equations are solved for the realistic partial reflection boundary conditions accounting for the difference in refractive indices between the turbid medium and its environment (air) as occurs in practical cases of interest in biomedical optics. Specifically, we provide the complete solution methodology for the SP3, which is readily applicable to higher orders as well, and also give results for the SP5. This computationally easy to obtain solution is investigated for different optical properties of the turbid medium. For validation, the solution is also compared to the analytical solution of the diffusion equation and to gold standard Monte Carlo simulation results. The SP3 and SP5 analytical solutions prove to be in good agreement with the Monte Carlo results. This work provides an additional tool for validating numerical solutions of the SPN equations for curved geometries.

  8. Next-Step Spherical Torus Experiment and Spherical Torus Strategy in the Fusion Energy Development Path

    SciTech Connect

    M. Ono; M. Peng; C. Kessel; C. Neumeyer; J. Schmidt; J. Chrzanowski; D. Darrow; L. Grisham; P. Heitzenroeder; T. Jarboe; C. Jun; S. Kaye; J. Menard; R. Raman; T. Stevenson; M. Viola; J. Wilson; R. Woolley; I. Zatz

    2003-10-27

    A spherical torus (ST) fusion energy development path which is complementary to proposed tokamak burning plasma experiments such as ITER is described. The ST strategy focuses on a compact Component Test Facility (CTF) and higher performance advanced regimes leading to more attractive DEMO and Power Plant scale reactors. To provide the physics basis for the CTF an intermediate step needs to be taken which we refer to as the ''Next Step Spherical Torus'' (NSST) device and examine in some detail herein. NSST is a ''performance extension'' (PE) stage ST with the plasma current of 5-10 MA, R = 1.5 m, and Beta(sub)T less than or equal to 2.7 T with flexible physics capability. The mission of NSST is to: (1) provide a sufficient physics basis for the design of CTF, (2) explore advanced operating scenarios with high bootstrap current fraction/high performance regimes, which can then be utilized by CTF, DEMO, and Power Plants, and (3) contribute to the general plasma/fusion science of high beta toroidal plasmas. The NSST facility is designed to utilize the Tokamak Fusion Test Reactor (or similar) site to minimize the cost and time required for the design and construction.

  9. Spherical nanocrystalline cellulose (NCC) from oil palm empty fruit bunch pulp via ultrasound assisted hydrolysis.

    PubMed

    Zianor Azrina, Z A; Beg, M Dalour H; Rosli, M Y; Ramli, Ridzuan; Junadi, Norhafzan; Alam, A K M Moshiul

    2017-04-15

    Nanocrystalline cellulose (NCC) was isolated from oil palm empty fruit bunch pulp (EFBP) using ultrasound assisted acid hydrolysis. The obtained NCC was analysed using FESEM, XRD, FTIR, and TGA, and compared with raw empty fruit bunch fibre (REFB), empty fruit bunch pulp (EFBP), and treated empty fruit bunch pulp (TEFBP). Based on FESEM analysis, it was found that NCC has a spherical shaped after acid hydrolysis with the assistance of ultrasound. This situation was different compared to previous studies that obtained rod-like shaped of NCC. Furthermore, the crystallinity of NCC is higher compared to REFB and EFBP. According to thermal stability, the NCC obtained shows remarkable sign of high thermal stability compared to REFB and EFBP. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Correction of Spherical Aberration in Grazing-Incidence X-ray Optics by Combination of Spherical-Concave Mirrors

    SciTech Connect

    Suzuki, Y.; Takeuchi, A.

    2011-09-09

    In grazing-incidence total-reflection mirror optics for x-rays, spherical aberrations and coma are the most serious aberrations for microfocusing and microimaging. High-resolution imaging is believed to be possible only when an aspherical mirror system is used. However, the spherical aberrations of a spherical-concave mirror in a grazing-incidence condition can be eliminated by sequential reflection of spherical mirrors of similar shapes. A sub-micrometer one-dimensional focusing is easily achieved by the spherical-aberration-corrected tandem-spherical mirror optics. By configuring four spherical mirrors in an analogy of the crossed mirror optics (Kirkpatrick-Baez optics), it is possible to achieve sub-micrometer focused beam size in the hard x-ray region. Preliminary experiments on x-ray microfocusing have been carried out at beamline 20XU of SPring-8, and a 0.5 {mu}mx0.4 {mu}m beam size was achieved at 8 keV.

  11. Design and implementation of a personal mobility of single spherical drive

    NASA Astrophysics Data System (ADS)

    Hoshino, Tasuku; Yazawa, Miki; Naganuma, Ryota; Takada, Kotaro

    2016-09-01

    This paper deals with a personal electric vehicle driven by a single spherical wheel. Using an appropriate feedback control, this driving strategy realizes dynamic stability in all directions and the vehicle can always be kept upright on the road surface of variety of slopes. It also enables immediate mobility to all directions, unlike personal vehicles of two- wheel type. The spherical wheel is driven by omnidirectional wheels as usual; however, since the number and location of wheels have huge effect on the driving performance, the authors firstly analyze kinematics of omnidirectional wheels and sphere and derive new configuration to achieve maximum power. Based on the kinematic analysis, the equation of motion of the vehicle is derived via Lagrangian formulation. The full dynamic model including kinematic constraints is then derived. Using the full model, a stabilizing controller for driving is designed based on partial feedback linearization technique. The vehicle is constructed and tested with a human driver. The proposed configuration of omnidirectional wheels, the controller design model and the control scheme are examined in practice. Results of the experiments, including going over uphill road and uneven ground, show much better driving performance than authors’ previous prototype of the similar.

  12. Photonic nanojet shaping of dielectric non-spherical microparticles

    NASA Astrophysics Data System (ADS)

    Liu, Cheng-Yang

    2014-11-01

    The photonic nanojet shaping effect in the dielectric non-spherical microparticles is reported. The specific spatial electromagnetic field is studied by using finite-difference time-domain calculation which constitutes the so-called photonic nanojet. The dielectric non-spherical microparticle is truncated by the cutting thickness. The latitudinal and longitudinal dimensions of the photonic nanojet and its peak intensity depending on the variation of cutting thickness are numerically researched. The shape dependence of the photonic nanojet in the non-spherical microparticles has been investigated by quality criterion. The practical results are drawn concerning the possible procedures to gain the control over the properties of photonic nanojet in the non-spherical microparticles. The shaping mechanism has a significant impact on the use of photonic nanojet to distinguish nanoscale specimens.

  13. FY 2008 Miniature Spherical Retroreflectors – Final Report

    SciTech Connect

    Anheier, Norman C.; Bernacki, Bruce E.; Klymyshyn, Nicholas A.; Krishnaswami, Kannan; Rodriguez, Carmen P.

    2009-02-01

    Through the duration of the NNSA Office of Nuclear Nonproliferation Research and Development (NA-22) Miniature Spherical Retroreflectors lifecycle project, our research team focused on developing solutions to the fabrication bottleneck that has inhibited development and deployment of wide-angle optically interrogated chemical and radiological remote sensing technology. Our team advanced the concept of step-index clad retroreflectors to approximate an optimized, but yet unrealized spherical gradient index design. An intensive numerical simulation effort was undertaken that resulted in optimized step-index optical designs for mid-infrared applications. Geometric optics ray trace modeling was performed to better understand the geometrical dependencies of the miniature spherical retroreflector application. We adopted and advanced the concept of optical cross section, a metric that provides relative performance comparisons between different retroreflector designs and our cross-section analysis demonstrated that our step-index design provided 90% of the range capacity of the ideal spherical index design.

  14. Orbital decay of satellite galaxies in spherical systems

    NASA Astrophysics Data System (ADS)

    Weinberg, M. D.

    1986-01-01

    The orbital-decay rate of a dwarf satellite moving in a spherical parent galaxy is considered on the basis of a theory of dynamical friction applicable to spherical systems, in which the orbits are determined exactly in a given spherical potential U(r). The spherical theory avoids the drag-force divergence that exists in Chandrasekhar's theory (CT), and the results may be regarded as determining the logarithimic factor appearing in CT. For a dwarf galaxy modeled by a Plummer law with a core radius gamma(rs) moving in a circular orbit in a singular isothermal sphere at radius rs, the logarithmic factor is ln Lambda = ln (0.75/gamma), corresponding to p-max = 1.2(rs). The response density of the sphere to the satellite (the satellite wake) is computed and compared with the wake in the infinite homogeneous case.

  15. Evaluating Descent and Ascent Trajectories Near Non-Spherical Bodies

    NASA Technical Reports Server (NTRS)

    Werner, Robert A.

    2010-01-01

    Spacecraft landing on small bodies pass through regions where conventional gravitation formulations using exterior spherical harmonics are inaccurate. An investigation shows that a formulation using interior solid spherical harmonics might be satisfactory. Interior spherical harmonic expansions are usable inside an imaginary, empty sphere. For this application, such a sphere could be positioned in empty space above the intended landing site and rotating with the body. When the spacecraft is inside this sphere, the interior harmonic expansion would be used instead of the conventional, exterior harmonic expansion. Coefficients can be determined by a least-squares fit to gravitation measurements synthesized from conventional formulations. Due to their unfamiliarity, recurrences for interior, as well as exterior, expansions are derived. Hotine's technique for partial derivatives of exterior spherical harmonics is extended to interior harmonics.

  16. Complete Vector Spherical Harmonic Expansion for Maxwell's Equations

    ERIC Educational Resources Information Center

    Lambert, R. H.

    1978-01-01

    Conventional expansions of solutions to Maxwell's equations in vector spherical harmonics apply only outside the sources. The complete solution, applying both inside and outside the sources, is given here. Harmonic time dependence is assumed. (Author/GA)

  17. Spherical shock in the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Kuramitsu, Y.; Matsukiyo, S.; Isayama, S.; Harada, D.; Oyama, T.; Fujino, R.; Sakawa, Y.; Morita, T.; Yamaura, Y.; Ishikawa, T.; Moritaka, T.; Sano, T.; Tomita, K.; Shimoda, R.; Sato, Y.; Uchino, K.; Pelka, A.; Crowston, R.; Woolsey, N.; Gregori, G.; Koenig, M.; Yuan, D. W.; Yin, C. L.; Li, Y. T.; Zhang, K.; Zhong, J. Y.; Wang, F. L.; Ohnishi, N.; Nagamine, K.; Yoneda, H.; Takabe, H.

    2016-03-01

    We investigate spherical collisionless shocks in the presence of an external magnetic field. Spherical collisionless shocks are common resultant of interactions between a expanding plasma and a surrounding plasma, such as the solar wind, stellar winds, and supernova remnants. Anisotropies often observed in shock propagations and their emissions, and it is widely believed a magnetic field plays a major role. Since the local observations of magnetic fields in astrophysical plasmas are not accessible, laboratory experiments provide unique capability to investigate such phenomena. We model the spherical shocks in the universe by irradiating a solid spherical target surrounded by a plasma in the presence of a magnetic field. We present preliminary results obtained by shadowgraphy.

  18. Spherical loudspeaker array for local active control of sound.

    PubMed

    Rafaely, Boaz

    2009-05-01

    Active control of sound has been employed to reduce noise levels around listeners' head using destructive interference from noise-canceling sound sources. Recently, spherical loudspeaker arrays have been studied as multiple-channel sound sources, capable of generating sound fields with high complexity. In this paper, the potential use of a spherical loudspeaker array for local active control of sound is investigated. A theoretical analysis of the primary and secondary sound fields around a spherical sound source reveals that the natural quiet zones for the spherical source have a shell-shape. Using numerical optimization, quiet zones with other shapes are designed, showing potential for quiet zones with extents that are significantly larger than the well-known limit of a tenth of a wavelength for monopole sources. The paper presents several simulation examples showing quiet zones in various configurations.

  19. Electron Optics for Biologists: Physical Origins of Spherical Aberrations

    ERIC Educational Resources Information Center

    Geissler, Peter; Zadunaisky, Jose

    1974-01-01

    Reports on the physical origins of spherical aberrations in axially symmetric electrostatic lenses to convey the essentials of electon optics to those who must think critically about the resolution of the electron microscope. (GS)

  20. Vector Operators and Spherical Harmonics in Quantum Mechanics.

    ERIC Educational Resources Information Center

    Andrews, M.

    1979-01-01

    Shows that the basic properties of spherical harmonics follow in a simple and elegant way from the commutation relations for angular momentum operators and the commutation relations between these operators and arbitrary vector operators. (Author/HM)

  1. Optical design of systems with off-axis spherical mirrors

    NASA Astrophysics Data System (ADS)

    Malacara-Hernández, Daniel; Gomez-Vieyra, Armando

    2011-09-01

    The astigmatism in reflective imaging systems can be eliminated by a proper configuration. However, the spherical and coma are the main residual aberrations in third order theory, but the behavior of all aberrations is not yet fully The main aberration of classical off-axis reflecting systems is primary astigmatism. The astigmatism in off-axis spherical understood. Expressions for the wavefront aberrations in an off-axis spherical mirror are presented. These formulas are derived from the optical path difference between an ellipsoid and a sphere, assuming a relatively small pupil and a small angle of incidence as it will be described with detail. Using the principle of the optical path difference, we developed the mathematical expressions that describe the third order wavefront aberrations in a two spherical mirror system when the object is finite.

  2. A spherical catadioptric telescope system based on Cooke corrector group

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Kang, Yusi; Liu, Weiqi

    2009-08-01

    To obtain a number of advantages in fabrication, testing and alignment, many designs in which spherical mirrors replace classical Cassegrain-form aspheric mirrors are present in the literature. However, spherical mirrors suffer from substantial spherical aberration and thereby require some form of corrector group. But in this case, the question encountered is that of making the basic optical configuration more complex. In this paper, a new design based on Cooke corrector group is presented for eliminating spherical aberration, which is believed to provide higher performance with less complexity than previous approaches. Besides, the cost and fabrication period will be extremely decreased. The telescope system using corrector group here can achieve good optical performance with f# of 10, full field of 0.5°, obscuration of 1/3 and MTF (Modulation Transfer Function) of 0.48 corresponding to 50@lp/mm.

  3. Spherical robot of combined type: Dynamics and control

    NASA Astrophysics Data System (ADS)

    Kilin, Alexander A.; Pivovarova, Elena N.; Ivanova, Tatyana B.

    2015-11-01

    This paper is concerned with free and controlled motions of a spherical robot of combined type moving by displacing the center of mass and by changing the internal gyrostatic momentum. Equations of motion for the nonholonomic model are obtained and their first integrals are found. Fixed points of the reduced system are found in the absence of control actions. It is shown that they correspond to the motion of the spherical robot in a straight line and in a circle. A control algorithm for the motion of the spherical robot along an arbitrary trajectory is presented. A set of elementary maneuvers (gaits) is obtained which allow one to transfer the spherical robot from any initial point to any end point.

  4. Complete Vector Spherical Harmonic Expansion for Maxwell's Equations

    ERIC Educational Resources Information Center

    Lambert, R. H.

    1978-01-01

    Conventional expansions of solutions to Maxwell's equations in vector spherical harmonics apply only outside the sources. The complete solution, applying both inside and outside the sources, is given here. Harmonic time dependence is assumed. (Author/GA)

  5. Fabrication of stainless steel spherical anodes for use with boat-mounted boom electroshocker

    USGS Publications Warehouse

    Martinez, Patrick J.; Tiffan, Kenneth F.

    1992-01-01

    A frugal method of fabricating spherical anodes from stainless steel mixing bowls is presented. We believe that the purported mechanical disadvantages of using spherical electrodes are largely unfounded.

  6. Diffraction in time of particles released from spherical traps

    SciTech Connect

    Godoy, Salvador

    2003-01-01

    We extend the theory of diffraction in time to particles with angular momentum. We consider the problem of the sudden release of a particle which initially was inside a spherical trap. The particle's free time evolution is described by spherical waves, which have amplitudes diffracted in time. The time-dependent density pattern is, for high or low energies, one of Fresnel or Fraunhofer diffraction by a single slit respectively.

  7. Microfluidic conformal coating of non-spherical magnetic particles

    PubMed Central

    Moon, Byeong-Ui; Hakimi, Navid; Hwang, Dae Kun; Tsai, Scott S. H.

    2014-01-01

    We present the conformal coating of non-spherical magnetic particles in a co-laminar flow microfluidic system. Whereas in the previous reports spherical particles had been coated with thin films that formed spheres around the particles; in this article, we show the coating of non-spherical particles with coating layers that are approximately uniform in thickness. The novelty of our work is that while liquid-liquid interfacial tension tends to minimize the surface area of interfaces—for example, to form spherical droplets that encapsulate spherical particles—in our experiments, the thin film that coats non-spherical particles has a non-minimal interfacial area. We first make bullet-shaped magnetic microparticles using a stop-flow lithography method that was previously demonstrated. We then suspend the bullet-shaped microparticles in an aqueous solution and flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the particles reach the interface between the immiscible fluids. We observe that upon crossing the oil-water interface, the microparticles become coated by a thin film of the aqueous fluid. When we increase the two-fluid interfacial tension by reducing surfactant concentration, we observe that the particles become trapped at the interface, and we use this observation to extract an approximate magnetic susceptibility of the manufactured non-spherical microparticles. Finally, using fluorescence imaging, we confirm the uniformity of the thin film coating along the entire curved surface of the bullet-shaped particles. To the best of our knowledge, this is the first demonstration of conformal coating of non-spherical particles using microfluidics. PMID:25332731

  8. Method to produce large, uniform hollow spherical shells

    DOEpatents

    Hendricks, Charles D.

    1985-01-01

    Large, uniform hollow spherical shells are produced by forming uniform size drops of heat decomposable or vaporizable material, evaporating the drops to form dried particles, coating the dried particles with a layer of shell forming material, and heating the composite particles to melt the outer layer and decompose or vaporize the inner particle to form an expanding inner gas bubble which expands the outer layer. By cycling the temperature and pressure on the hollow shells, spherical shells with uniform walls are produced.

  9. The effect of spherical convergence on the dynamics of instabilities

    SciTech Connect

    Chapyak, E.J.; Godwin, R.P.

    1997-11-01

    The authors extend previous work on instability growth in spherically converging layered fluid systems by characterizing linearized perturbation dynamics on the collapse of a spherical gas cavity surrounded by an incompressible fluid. They also investigate energy damping mechanisms related to fluid compressibility. Numerical examples are presented where water at STP initially surrounds a gas cavity filled with low pressure air. This work is of interest to the weapons community.

  10. Comparison of large aperture telescopes with parabolic and spherical primaries

    NASA Technical Reports Server (NTRS)

    Korsch, D.

    1986-01-01

    Quasi-Cassegrain-type four-mirror telescopes are compared to conventional two-mirror Cassegrain telescopes for use as high performance, very large aperture space telescopes. Spherical and parabolic primaries with continuous as well as segmented surfaces are considered. Imaging characteristics and misalignment sensitivities serve as the principal criteria of comparison. The evaluation shows that parabolic primaries yield superior wide-field performance, whereas spherical primaries hold distinct advantages regarding manufacturability and regarding certain alignment aspects in the case of segmentation.

  11. Towards AN Easier Orientation for Spherical Photogrammetry

    NASA Astrophysics Data System (ADS)

    Fangi, G.

    2015-02-01

    For architectural metric documentation, Spherical Photogrammetry (SP) has demonstrated its validity and efficiency in many projects already. The speed of surveying is high, the accuracy and completeness of the plotting are satisfactory. However, there are still many problems to be solved. The weakest point is the orientation procedure, which is rather difficult to perform, in the sense that only very experienced people can run it, and few people only make use of it. The old orientation steps are 1) model formation (limited to binocular panoramas couples); 2) link of all the models in a block adjustment with independent model triangulation; 3) block bundle adjustment with 4 parameters/pano (3 coord.+1 orientation bearing); 4) block bundle adjustment with 6 parameters/pano, say the previous 4 + 2 correction angles around the horizontal axes. The panoramas must be spherical and quasi-horizontal. In order to make easier the orientation, enabling more people to use SP, an improved approach has been set up. It consists in the combination of any possible model formed either by three and two panoramas. The trinocular vision, say the combination of three different panoramas to form a unique model, has the advantage to be much more robust in comparison to binocular vision in the sense that the trinocular model is likely to be more error-free than any of the three composing binocular models. It contains less model deformation, the model coordinates are validated by the mutual comparison of the three intersecting binocular models. In addition, the number of possible trinocular models is normally much larger than the one of binocular models. The steps for a semi-automatic orientation of a block of panoramas proceed as follows: - Form any possible trinocular models by combination of the panoramas; - in case that no trinocular model has been formed, form any possible binocular model; - run a block adjustment with the algorithm of independent model, to link together the models in

  12. Sphericity estimation bias for repeated measures designs in simulation studies.

    PubMed

    Bono, Roser; Arnau, Jaume; Blanca, María J; Alarcón, Rafael

    2016-12-01

    In this study, we explored the accuracy of sphericity estimation and analyzed how the sphericity of covariance matrices may be affected when the latter are derived from simulated data. We analyzed the consequences that normal and nonnormal data generated from an unstructured population covariance matrix-with low (ε = .57) and high (ε = .75) sphericity-can have on the sphericity of the matrix that is fitted to these data. To this end, data were generated for four types of distributions (normal, slightly skewed, moderately skewed, and severely skewed or log-normal), four sample sizes (very small, small, medium, and large), and four values of the within-subjects factor (K = 4, 6, 8, and 10). Normal data were generated using the Cholesky decomposition of the correlation matrix, whereas the Vale-Maurelli method was used to generate nonnormal data. The results indicate the extent to which sphericity is altered by recalculating the covariance matrix on the basis of simulated data. We concluded that bias is greater with spherical covariance matrices, nonnormal distributions, and small sample sizes, and that it increases in line with the value of K. An interaction was also observed between sample size and K: With very small samples, the observed bias was greater as the value of K increased.

  13. 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.

  14. Imperfection sensitivity of pressured buckling of biopolymer spherical shells.

    PubMed

    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.

  15. Studying 3D Spherical Shell Convection using ASPECT

    NASA Astrophysics Data System (ADS)

    Euen, G.; King, S. D.; Liu, S.

    2016-12-01

    Modeling convection in spherical geometries is crucial to gain an understanding of planet-scale mantle processes. However, modeling 3D spherical shells is computationally challenging. Few studies have been done using full 3D spherical shells. Here I present test cases for modeling 3D spherical shells using ASPECT. These cases are based on previous work using CitcomS done by Zhong et al., 2008. The cases were run on the BlueRidge and NewRiver clusters at ARC at Virginia Tech. Cases were run using varying numbers of processors and 2-5 global mesh refinements. Each added refinement increases the number of cells by a factor of 8. Two global refinements corresponds to 6,144 cells, three refinements have 49,152 cells, four refinements have 393,216 cells, and five refinements have 3,145,728 cells. To make these results comparable to Zhong et al., 2008 all adaptive mesh refinement was turned off. Cases ran very sporadically at first, with three major error types emerging. However, after ASPECT version 1.5.0 was released and the latest version was cloned from Github and built July 10 th -15 th , 2016, the cases ran with no errors. It should be noted that 2D spherical cases ran with no errors throughout the testing. ASPECT results matched well with the Zhong et al., 2008 results. We will present results varying the refinement and number of processors to demonstrate scaling and efficiency of the code for spherical problems.

  16. Broken Ergodicity in MHD Turbulence in a Spherical Domain

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.; wang, Yifan

    2011-01-01

    Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.

  17. Optical design study for NASA's spherical primary optical telescope (SPOT)

    NASA Astrophysics Data System (ADS)

    Howard, Joseph M.

    2004-10-01

    Several of NASA's future space telescopes project teams have chosen or are considering segmented primary mirrors as a part of their architecture. The James Webb Space Telescope (JWST) design employs a 6.5-meter conic primary mirror constructed of 18 hexagonal segments, where each hex is one of three off-axis surface profiles corresponding to its radial distance to the parent mirror axis. Other future mission concepts such as SAFIR (Single Aperture Far-Infra Red) and SUVO (Space Ultra Violet Optical telescope) are considering even larger segmented primary mirrors. The goal of the Spherical Primary Optical Telescope (SPOT) project discussed in this paper is to investigate the option of a spherical primary mirror for such future large aperture NASA missions. Ground-based telescopes such as the Hobby-Eberly have realized this design option, and the current baseline design for ESO's OWL project incorporates a 100-meter segmented spherical primary mirror. While the benefits of fabricating large numbers of identical spherical surface segments are obvious, the optical design for the telescope becomes more complex in order to correct the significant aberration resulting from a spherical primary surface. This paper briefly surveys design approaches of spherical primary telescopes. Image based performance comparisons are made, and examples are presented.

  18. Effects of Non-Sphericity on Mineral Dust Modeling

    NASA Technical Reports Server (NTRS)

    Ginoux, Paul; Torres, O.

    2003-01-01

    The dependency of non-sphericity on gravitational settling of mineral dust particles is parameterized for prolate ellipsoids and Reynolds number lower than 2. The settling speed is numerically solved from the momentum equation as a function of particle diameter and aspect ratio. The reduction of settling speed due to non-sphericity is included in the GO-CART model to simulate dust size distribution for April 2001. Two numerical schemes for solving sedimentation are compared. For particles of diameter greater than 5 micron the simulated size distribution is sensitive to the numerical sedimentation scheme. Changing the particle shape from spherical to non-spherical with lambda=2, makes little difference to the simulated surface concentration and size distribution except at the periphery of the dust sources. However, when very elongated particles (lambda=5) are simulated the differences between non-spherical and spherical particles are significant. With limited in-situ measurements reporting most frequent lambda around 1.5, the overall effects on global modeling is rather negligible and the essential benefit is to relax the CFL condition of Eulerian settling schemes.

  19. Wavefronts, caustics, and ronchigrams of a spherical wave reflected by a spherical mirror.

    PubMed

    Castro-Ramos, Jorge; Marciano-Melchor, Magdalena; Marcelino-Aranda, Mariana; Román-Hernández, Edwin; Santiago-Santiago, José Guadalupe; Silva-Ortigoza, Gilberto; Silva-Ortigoza, Ramón; Suárez-Xique, Román; Zárate-Paz, José Miguel

    2013-02-01

    The aim of the present work is twofold: first we obtain analytical expressions for both the wavefronts and the caustic associated with the light rays reflected by a spherical mirror after being emitted by a point light source located at an arbitrary position in free space, and second, we describe, in detail, the structure of the ronchigrams when the grating or Ronchi ruling is placed at different relative positions to the caustic region and the point light source is located on and off the optical axis. We find that, in general, the caustic has two branches: one is a segment of a line, and the other is a two-dimensional surface. The wavefronts, at the caustic region, have self intersections and singularities. The ronchigrams exhibit closed-loop fringes when the grating is placed at the caustic region.

  20. Blazar emission modeling: going beyond spherical cows

    NASA Astrophysics Data System (ADS)

    Giannios, Dimitrios

    emission: efficient dissipation, extended particle distributions, and rough equipartition between particles and magnetic field in the emitting region. In addition, we have shown that quasi-spherical plasmoids (or magnetic islands) filled with high-energy particles and magnetic fields are a self-consistent by-product of the reconnection process, and their properties make them excellent candidates for the blobs usually invoked in blazar emission modeling. Despite this recent progress, many questions remain to be addressed: What is the composition of blazar jets and how does it relate to the observed spectra? What is the statistics of flares produced by reconnection? What is the link between the large-scale jet structure and the emitting regions? This proposal plans to address these questions and ultimately develop a self-consistent model for the blazar emission, which can be easily extended to other relativistic astrophysical outflows, including gamma-ray bursts and pulsar wind nebulae. We propose to perform a suite of two- and three-dimensional PIC simulations of reconnection with parameters relevant for blazar jets. We describe a robust method - already demonstrated in our recent papers - to extrapolate the results from the microscopic plasma scales of PIC simulations to the macroscopic scales of blazar emission. This method will determine from first principles the particle distribution, magnetic field strength, geometry and size of the emitting regions. We plan to complement this study with large-scale models of the jet structure, to pin down the location and size of the dissipation region and to better determine the amount of dissipated energy. With this information and the extensive radiative transfer experience of Co-I Petropoulou, we will be able to calculate lightcurves, polarization patterns and spectra as well as predict the UHECR acceleration and neutrino emission associated to reconnection events in blazars.