Spherical perfect lens: Solutions of Maxwell's equations for spherical geometry
NASA Astrophysics Data System (ADS)
Anantha Ramakrishna, S.; Pendry, J. B.
2004-03-01
It has been recently proved that a slab of negative refractive index material acts as a perfect lens in that it makes accessible the subwavelength image information contained in the evanescent modes of a source. Here we elaborate on perfect lens solutions to spherical shells of negative refractive material where magnification of the near-field images becomes possible. The negative refractive materials then need to be spatially dispersive with ɛ(r)˜1/r and μ(r)˜1/r. We concentrate on lenslike solutions for the extreme near-field limit. Then the conditions for the TM and TE polarized modes become independent of μ and ɛ, respectively.
Circuital model for the spherical geodesic waveguide perfect drain
NASA Astrophysics Data System (ADS)
González, Juan C.; Grabovičkić, Dejan; Benítez, Pablo; Miñano, Juan C.
2012-08-01
The perfect drain for the Maxwell fish eye (MFE) is a non-magnetic dissipative region placed in the focal point to absorb all the incident radiation without reflection or scattering. The perfect drain was recently designed as a material with complex permittivity that depends on frequency. However, this material is only a theoretical material, so it cannot be used in practical devices. The perfect drain has been claimed as necessary for achieving super-resolution (Leonhardt 2009 New J. Phys. 11 093040), which has increased the interest in practical perfect drains suitable for manufacturing. Here, we present a practical perfect drain that is designed using a simple circuit (made of a resistance and a capacitor) connected to the coaxial line. Moreover, we analyze the super-resolution properties of a device equivalent to the MFE, known as a spherical geodesic waveguide, loaded with this perfect drain. The super-resolution analysis for this device is carried out using COMSOL Multiphysics. The results of simulations predict a super-resolution of up to λ/3000.
Spherically symmetric Einstein-aether perfect fluid models
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.
Perfect imaging analysis of the spherical geodesic waveguide
NASA Astrophysics Data System (ADS)
González, Juan C.; Benítez, Pablo; Miñano, Juan C.; Grabovičkić, Dejan
2012-12-01
Negative Refractive Lens (NRL) has shown that an optical system can produce images with details below the classic Abbe diffraction limit. This optical system transmits the electromagnetic fields, emitted by an object plane, towards an image plane producing the same field distribution in both planes. In particular, a Dirac delta electric field in the object plane is focused without diffraction limit to the Dirac delta electric field in the image plane. Two devices with positive refraction, the Maxwell Fish Eye lens (MFE) and the Spherical Geodesic Waveguide (SGW) have been claimed to break the diffraction limit using positive refraction with a different meaning. In these cases, it has been considered the power transmission from a point source to a point receptor, which falls drastically when the receptor is displaced from the focus by a distance much smaller than the wavelength. Although these systems can detect displacements up to λ/3000, they cannot be compared to the NRL, since the concept of image is different. The SGW deals only with point source and drain, while in the case of the NRL, there is an object and an image surface. Here, it is presented an analysis of the SGW with defined object and image surfaces (both are conical surfaces), similarly as in the case of the NRL. The results show that a Dirac delta electric field on the object surface produces an image below the diffraction limit on the image surface.
NASA Astrophysics Data System (ADS)
Yadav, R. B. S.; Prasad, U.
1993-05-01
The nonstatic conformally flat spherically symmetric perfect fluid distribution in Einstein-Cartan theory is considered, and the field equations and their general solution are obtained using Hehl's approach (1974). Particular attention is given to the solution in co-moving coordinates and the explicit expressions for pressure, density, expansion, rotation, and shear and nonzero components of flow vector.
Conformally flat static spherically symmetric perfect-fluid distribution in Einstein-Cartan theory
NASA Astrophysics Data System (ADS)
Kalyanshetti, S. B.; Waghmode, B. B.
1983-06-01
We consider the static, conformally flat spherically symmetric perfect-fluid distribution in Einstein-Cartan theory and obtain the field equations. These field equations are solved by adopting Hehl's approach with the assumption that the spins of the particles composing the fluid are all aligned in the radial direction only and the reality conditions are discussed.
Spherical gradient-index lenses as perfect imaging and maximum power transfer devices.
Gordon, J M
2000-08-01
Gradient-index lenses can be viewed from the perspectives of both imaging and nonimaging optics, that is, in terms of both image fidelity and achievable flux concentration. The simple class of gradient-index lenses with spherical symmetry, often referred to as modified Luneburg lenses, is revisited. An alternative derivation for established solutions is offered; the method of Fermat's strings and the principle of skewness conservation are invoked. Then these nominally perfect imaging devices are examined from the additional vantage point of power transfer, and the degree to which they realize the thermodynamic limit to flux concentration is determined. Finally, the spherical gradient-index lens of the fish eye is considered as a modified Luneburg lens optimized subject to material constraints. PMID:18349958
Weathering a Perfect Storm from Space
Love, Jeffrey J.
2016-01-01
Extreme space-weather events — intense solar and geomagnetic storms — have occurred in the past: most recently in 1859, 1921 and 1989. So scientists expect that, sooner or later, another extremely intense spaceweather event will strike Earth again. Such storms have the potential to cause widespread interference with and damage to technological systems. A National Academy of Sciences study projects that an extreme space-weather event could end up costing the American economy more than $1 trillion. The question now is whether or not we will take the actions needed to avoid such expensive consequences. Let’s assume that we do. Below is an imagined scenario of how, sometime in the future, an extreme space-weather event might play out.
Fabrication of Spherical Reflectors in Outer Space
NASA Technical Reports Server (NTRS)
Wang, Yu; Dooley, Jennifer; Dragovan, Mark; Serivens, Wally
2005-01-01
A process is proposed for fabrication of lightweight spherical reflectors in outer space for telescopes, radio antennas, and light collectors that would be operated there. The process would obviate the relatively massive substrates and frames needed to support such reflectors in normal Earth gravitation. According to the proposal, fabrication of a reflector would begin with blowing of a bubble to the specified reflector radius. Taking advantage of the outer-space vacuum as a suitable environment for evaporative deposition of metal, a metal-evaporation source would be turned on and moved around the bubble to deposit a reflective metal film over the specified reflector area to a thickness of several microns. Then the source would be moved and aimed to deposit more metal around the edge of the reflector area, increasing the thickness there to approximately equal to 100 micron to form a frame. Then the bubble would be deflated and peeled off the metal, leaving a thin-film spherical mirror having an integral frame. The mirror would then be mounted for use. The feasibility of this technology has been proved by fabricating a prototype at JPL. As shown in the figure, a 2-in. (.5-cm) diameter hemispherical prototype reflector was made from a polymer bubble coated with silver, forming a very smooth surface.
On imploding cylindrical and spherical shock waves in a perfect gas
NASA Astrophysics Data System (ADS)
Ponchaut, N. F.; Hornung, H. G.; Pullin, D. I.; Mouton, C. A.
2006-08-01
The problem of a cylindrically or spherically imploding and reflecting shock wave in a flow initially at rest is studied without the use of the strong-shock approximation. Dimensional arguments are first used to show that this flow admits a general solution where an infinitesimally weak shock from infinity strengthens as it converges towards the origin. For a perfect-gas equation of state, this solution depends only on the dimensionality of the flow and on the ratio of specific heats. The Guderley power-law result can then be interpreted as the leading-order, strong-shock approximation, valid near the origin at the implosion centre. We improve the Guderley solution by adding two further terms in the series expansion solution for both the incoming and the reflected shock waves. A series expansion, valid where the shock is still weak and very far from the origin, is also constructed. With an appropriate change of variables and using the exact shock-jump conditions, a numerical, characteristics-based solution is obtained describing the general shock motion from almost infinity to very close to the reflection point. Comparisons are made between the series expansions, the characteristics solution, and the results obtained using an Euler solver. These show that the addition of two terms to the Guderley solution significantly extends the range of validity of the strong-shock series expansion.
Nematic order on curved spherical spaces
NASA Astrophysics Data System (ADS)
Fernandez-Nieves, Alberto; Lopez-Leon, Teresa; Devaiah, Sharan; Pairam, Ekapop
2010-03-01
When nematic liquid crystals are confined to spherical shells, complex defect structures emerge. These structures are characterized by a varying number of point defects and disclination lines, depending on the elastic energy of the liquid crystal, the thickness of the shell, and the boundary conditions for the director at the confining spheres. Topology establishes restrictions that must be fulfilled, but it is the energy landscape that ultimately determines the final state of the system. By using double emulsion droplets, we can experimentally address this fascinating interplay between topology and energy. We find a wealth of defect structures in our shells and propose that the shell thickness inhomogeneity is the key parameter enabling the broad range of configurations we observe; these include long-time predicted configurations, as well as new structures and transitions between them that where never considered before. In addition, we hope to extend our studies to non-spherical surfaces, such as the torus and higher-genus surfaces. For this purpose, we have recently generated toroidal droplets and have studied their hydrodynamic stability. On these closed surfaces, the nature of the defect structure is expected to be qualitatively different from that of the spherical case.
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.
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.
Coherent States of Quantum Free Particle on the Spherical Space
NASA Astrophysics Data System (ADS)
Dehdashti, Shahram; Roknizadeh, Rasoul; Mahdifar, Ali; Chen, Hongsheng
2016-01-01
In this paper, we study the quantum free particle on the spherical space by applying da costa approach for quantum particle on the curved space. We obtain the discrete energy eigenvalues and associated normalized eigenfunctions of the free particle on the sphere. In addition, we introduce the Gazeau-Klauder coherent states of free particle on the sphere. Then, the Gaussian coherent states is defined, which is used to describe the localized particle on the spherical space. Finally, we study the relation between the f-deformed coherent states and Gazeau-Klauder ones for this system.
Spherically symmetric collapse of a perfect fluid in f(R) gravity
NASA Astrophysics Data System (ADS)
Chakrabarti, Soumya; Banerjee, Narayan
2016-05-01
The present work investigates the gravitational collapse of a perfect fluid in f ( R) gravity models. For a general f ( R) theory, it is shown analytically that a collapse is quite possible. The singularity formed as a result of the collapse is found to be a curvature singularity of shell focusing type. The possibility of the formation of an apparent horizon hiding the central singularity depends on the initial conditions.
A global conformal extension theorem for perfect fluid Bianchi space-times
Luebbe, Christian Tod, Paul
2008-12-15
A global extension theorem is established for isotropic singularities in polytropic perfect fluid Bianchi space-times. When an extension is possible, the limiting behaviour of the physical space-time near the singularity is analysed.
NASA Astrophysics Data System (ADS)
Guzatov, D. V.
2005-10-01
Expressions for the frequency shift of radiation of an atom located near a cluster of two perfectly conducting spherical nanoparticles are obtained within the framework of a classical model. The asymptotic expression is found for the radiation frequency shift of an atom located between spheres approaching each other.
Photoelectric sheath formation around small spherical objects in space
Misra, Shikha Sodha, M. S.; Mishra, S. K.
2015-04-15
The formation of a photoelectron sheath around positively charged small (∼cm) spherical objects roaming in near earth space due to the solar radiation (with continuous spectrum) and the solar wind plasma has been investigated. The sheath structure has been derived, taking into account anisotropic photoelectron flux with the Poisson equation, spherical geometry of the object, and half Fermi Dirac distribution of photoelectron velocities. Two cases, viz., when the object is illuminated by (i) isotropic or (ii) unidirectional (parallel beam) radiation, have been analyzed. The analysis predicts a spherically symmetric sheath in case of isotropic illumination, while a symmetry in sheath about a θ=π/4 is seen in case of parallel beam illumination; θ is the angle of incidence which is the angle made by the normal to a surface element with the direction of incidence of solar radiation. The radial and angular profiles of the electric potential and electron density in the photoelectron sheath have been evaluated and illustrated graphically; the dependence of the sheath structure on the solar wind plasma parameters, material properties of the spherical object, and its size have been discussed.
Variation of Space Radiation Exposure inside Spherical and Hemispherical Geometries
NASA Astrophysics Data System (ADS)
Lin, Zi-Wei; Baalla, Younes; Townsend, Lawrence
2008-10-01
We calculate the space radiation exposure to blood-forming organs everywhere inside a hemispherical dome that represents a lunar habitat. We derive the analytical path length distribution from any point inside a hemispherical or a spherical shell. Because the average path length increases with the distance from the center, the center of the hemispherical dome on the lunar surface has the largest radiation exposure while locations on the inner surface of the dome have the lowest exposure. This conclusion differs from an earlier study on a hemispherical dome but agrees with another earlier study on a spherical-shell shield. We also find that the reduction in the radiation exposure from the center to the inner edge of the dome can be as large as a factor of 3 or more for the radiation from solar particle events while being smaller for the radiation from galactic cosmic rays.
Horizons versus singularities in spherically symmetric space-times
Bronnikov, K. A.; Elizalde, E.; Odintsov, S. D.; Zaslavskii, O. B.
2008-09-15
We discuss different kinds of Killing horizons possible in static, spherically symmetric configurations and recently classified as 'usual', 'naked', and 'truly naked' ones depending on the near-horizon behavior of transverse tidal forces acting on an extended body. We obtain the necessary conditions for the metric to be extensible beyond a horizon in terms of an arbitrary radial coordinate and show that all truly naked horizons, as well as many of those previously characterized as naked and even usual ones, do not admit an extension and therefore must be considered as singularities. Some examples are given, showing which kinds of matter are able to create specific space-times with different kinds of horizons, including truly naked ones. Among them are fluids with negative pressure and scalar fields with a particular behavior of the potential. We also discuss horizons and singularities in Kantowski-Sachs spherically symmetric cosmologies and present horizon regularity conditions in terms of an arbitrary time coordinate and proper (synchronous) time. It turns out that horizons of orders 2 and higher occur in infinite proper times in the past or future, but one-way communication with regions beyond such horizons is still possible.
On projective invariants of spherically symmetric Finsler spaces in Rn
NASA Astrophysics Data System (ADS)
Sadeghzadeh, Nasrin; Hesamfar, Maedeh
2015-05-01
In this paper, we study projective invariants of spherically symmetric Finsler metrics in Rn. We find the necessary and sufficient conditions for the metrics to be Weyl, Douglas and generalized Douglas-Weyl (GDW) types. In particular, we find the necessary and sufficient condition for the metrics to be of scalar flag curvature. Also we show that two classes of GDW and Douglas spherically symmetric Finsler metrics coincide.
Planar electromagnetic wave scattering by a spherical inclusion embedded in a lossy half-space
NASA Astrophysics Data System (ADS)
Osharin, Alexander M.
1998-11-01
The solution of the plane electromagnetic wave scattering problem by a spherical inclusion embedded into half-space with dielectric losses is obtained. To treat the problem the translation-addition theorems for the basic vector solutions of the Maxwell's equations in spherical, cylindrical and rectangular coordinate systems together with the field series expansion techniques are used. Matching the boundary conditions for the tangential components of the electric and magnetic field at the two half-spaces interface and also at the sphere boundary allows to reduce the above mentioned problem to the infinite set of linear inhomogeneous equations. No restrictions on the half-space losses value as far as the size and complex permittivity of the spherical inclusion and its burial depth are implied. The results could be useful in sea foam-covered areas investigations and in diagnostics of the porous lossy materials.
Equilibrium points of the tilted perfect fluid Bianchi VIh state space
NASA Astrophysics Data System (ADS)
Apostolopoulos, Pantelis S.
2005-05-01
We present the full set of evolution equations for the spatially homogeneous cosmologies of type VIh filled with a tilted perfect fluid and we provide the corresponding equilibrium points of the resulting dynamical state space. It is found that only when the group parameter satisfies h > -1 a self-similar solution exists. In particular we show that for h > -{1/9} there exists a self-similar equilibrium point provided that γ ∈ ({2(3+sqrt{-h})/5+3sqrt{-h}},{3/2}) whereas for h < -{frac 19} the state parameter belongs to the interval γ ∈(1,{2(3+sqrt{-h})/5+3sqrt{-h}}). This family of new exact self-similar solutions belongs to the subclass nαα = 0 having non-zero vorticity. In both cases the equilibrium points have a six-dimensional stable manifold and may act as future attractors at least for the models satisfying nαα = 0. Also we give the exact form of the self-similar metrics in terms of the state and group parameter. As an illustrative example we provide the explicit form of the corresponding self-similar radiation model (γ = {frac 43}), parametrised by the group parameter h. Finally we show that there are no tilted self-similar models of type III and irrotational models of type VIh.
Affine spherical homogeneous spaces with good quotient by a maximal unipotent subgroup
Avdeev, Roman S
2012-11-30
For an affine spherical homogeneous space G/H of a connected semisimple algebraic group G, we consider the factorization morphism by the action on G/H of a maximal unipotent subgroup of G. We prove that this morphism is equidimensional if and only if the weight semigroup of G/H satisfies a simple condition. Bibliography: 16 titles.
NASA Technical Reports Server (NTRS)
Feinberg, Lee; Hagopian, John; Budinoff, Jason; Dean, Bruce; Howard, Joe
2005-01-01
This paper summarizes efforts underway at the Goddard Space Flight Center to demonstrate a new type of space telescope architecture that builds on the rigid, segmented telescope heritage of the James Webb Space Telescope but that solves several key challenges for future space telescopes. The architecture is based on a cost-effective segmented spherical primary mirror combined with a unique wavefront sensing and control system that allows for continuous phasing of the primary mirror. The segmented spherical primary allows for cost-effective 3-meter class (eg, Midex and Discovery) missions as well as enables 30-meter telescope solutions that can be manufactured in a reasonable amount of time and for a reasonable amount of money. The continuous wavefront sensing and control architecture enables missions in low-earth-orbit and missions that do not require expensive stable structures and thermal control systems. For the 30-meter class applications, the paper discusses considerations for assembling and testing the telescopes in space. The paper also summarizes the scientific and technological roadmap for the architecture and also gives an overview of technology development, design studies, and testbed activities underway to demonstrate it s feasibility.
NASA Technical Reports Server (NTRS)
Feinberg, Lee D.; Hagopian, John; Budinoff, Jason; Dean, Bruce; Howard, Joe
2004-01-01
This paper summarizes efforts underway at the Goddard Space Flight Center to demonstrate a new type of space telescope architecture that builds on the rigid segmented telescope heritage of the James Webb Space Telescope but that solves several key challenges for future space telescopes. The architecture is based on a cost-effective segmented spherical primary mirror combined with a unique wavefront sensing and control system that allows for continuous phasing of the primary mirror. The segmented spherical primary allows for cost-effective 3-meter class (e.g., Midex and Discovery) missions as well as enables 30-meter telescope solutions that can be manufactured in a reasonable amount of time and for a reasonable amount of money. The continuous wavefront sensing and control architecture enables missions in low-earth-orbit and missions that do not require expensive stable structures and thermal control systems. For the 30-meter class applications, the paper discusses considerations for assembling and testing the telescopes in space. The paper also summarizes the scientific and technological roadmap for the architecture and also gives an overview of technology development, design studies, and testbed activities underway to demonstrate its feasibility.
A new approach for the evaluation of the effective electrode spacing in spherical ion chambers
NASA Astrophysics Data System (ADS)
Maghraby, Ahmed M.; Shqair, Mohammed
2016-10-01
Proper determination of the effective electrode spacing (deff) of an ion chamber ensures proper determination of its collection efficiency either in continuous or in pulsed radiation in addition to the proper evaluation of the transit time. Boag's method for the determination of deff assumes the spherical shape of the internal electrode of the spherical ion chambers which is not always true, except for some cases, its common shape is cylindrical. Current work provides a new approach for the evaluation of the effective electrode spacing in spherical ion chambers considering the cylindrical shape of the internal electrode. Results indicated that deff values obtained through current work are less than those obtained using Boag's method by factors ranging from 12.1% to 26.9%. Current method also impacts the numerically evaluated collection efficiency (f) where values obtained differ by factors up to 3% at low potential (V) values while at high V values minor differences were noticed. Additionally, impacts on the evaluation of the transit time (τi) were obtained. It is concluded that approximating the internal electrode as a sphere may result in false values of deff, f, and τi.
Navier-Stokes structure of merged layer flow on the spherical nose of a space vehicle
NASA Technical Reports Server (NTRS)
Jain, A. C.; Woods, G. H.
1988-01-01
Hypersonic merged layer flow on the forepart of a spherical surface of a space vehicle has been investigated on the basis of the full steady-state Navier-Stokes equations using slip and temperature jump boundary conditions at the surface and free-stream conditions far from the surface. The shockwave-like structure was determined as part of the computations. Using an equivalent body concept, computations were carried out under conditions that the Aeroassist Flight Experiment (AFE) Vehicle would encounter at 15 and 20 seconds in its flight path. Emphasis was placed on understanding the basic nature of the flow structure under low density conditions. Particular attention was paid to the understanding of the structure of the outer shockwave-like region as the fluid expands around the sphere. Plots were drawn for flow profiles and surface characteristics to understand the role of dissipation processes in the merged layer of the spherical nose of the vehicle.
Design of spherical varied line-space gratings for a high-resolution EUV spectrometer
NASA Technical Reports Server (NTRS)
Harada, Tatsuo; Kita, Toshiaki; Bowyer, Stuart; Hurwitz, Mark
1991-01-01
A highly efficient EUV spectrograph is designed for high-resolution spectroscopic observation. The spectrograph is designed for point source astronomy in a 40-120 nm bandpass and is to be ORFEUS (Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer), scheduled for launch as the first payload of a German space platform Astro-SPAS (Astronomy Shuttle Pallet Satellite). The design uses spherical varied line-space (SVLS) grating to minimize astigmatism, coma, and spherical aberration. The effectiveness and practical feasibility of the design is proved by an SVLS grating for visible use. The image focusing properties of the SVLS grating for ORFEUS are compared to those with toroidal uniform line-space (TULS) design. The SVLS design is superior to the TULS, theoretically in resolution and image concentration, but also practically with not only fabrication ease. Four SVLS gratings with nominal groove densities of 6000, 4550, 3450, and 2616 gr./mm, and a 200 mm x 200 mm ruled area have been ruled using a numerically controlled ruling engine for use in ORFEUS.
A perfect liftoff of Space Shuttle Endeavour on mission STS-100
NASA Technical Reports Server (NTRS)
2001-01-01
KENNEDY SPACE CENTER, Fla. - Space Shuttle Endeavour races into space, springing forth from clouds of smoke and steam, on mission STS-100. Liftoff of the ninth flight to the International Space Station occurred at 2:40:42 p.m. EDT. The 11-day mission will deliver and integrate the Spacelab Logistics Pallet/Launch Deployment Assembly, which includes the Space Station Remote Manipulator System and the UHF Antenna. The mission includes two planned spacewalks for installation of the SSRMS on the Station. Also onboard is the Multi-Purpose Logistics Module Raffaello, carrying resupply stowage racks and resupply/return stowage platforms.
A perfect liftoff of Space Shuttle Endeavour on mission STS-100
NASA Technical Reports Server (NTRS)
2001-01-01
KENNEDY SPACE CENTER, Fla. - Space Shuttle Endeavour leaps from Launch Pad 39A amid billows of smoke and steam as it races into space on mission STS-100. Liftoff of Endeavour on the ninth flight to the International Space Station occurred at 2:40:42 p.m. EDT. The 11-day mission will deliver and integrate the Spacelab Logistics Pallet/Launch Deployment Assembly, which includes the Space Station Remote Manipulator System and the UHF Antenna. The mission includes two planned spacewalks for installation of the SSRMS on the Station. Also onboard is the Multi-Purpose Logistics Module Raffaello, carrying resupply stowage racks and resupply/return stowage platforms.
A perfect liftoff of Space Shuttle Endeavour on mission STS-100
NASA Technical Reports Server (NTRS)
2001-01-01
KENNEDY SPACE CENTER, Fla. - Flames from Space Shuttle Endeavour light up the clouds as the Shuttle races into space on mission STS-100. Liftoff of Endeavour on the ninth flight to the International Space Station occurred at 2:40:42 p.m. EDT. The 11- day mission will deliver and integrate the Spacelab Logistics Pallet/Launch Deployment Assembly, which includes the Space Station Remote Manipulator System and the UHF Antenna. The mission includes two planned spacewalks for installation of the SSRMS on the Station. Also onboard is the Multi-Purpose Logistics Module Raffaello, carrying resupply stowage racks and resupply/return stowage platforms.
Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion
NASA Technical Reports Server (NTRS)
Williams, Craig H.; Dudzinski, Leonard A.; Borowski, Stanley K.; Juhasz, Albert J.
2005-01-01
A conceptual vehicle design enabling fast, piloted outer solar system travel was created predicated on a small aspect ratio spherical torus nuclear fusion reactor. The initial requirements were satisfied by the vehicle concept, which could deliver a 172 mt crew payload from Earth to Jupiter rendezvous in 118 days, with an initial mass in low Earth orbit of 1,690 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including artificial gravity payload, central truss, nuclear fusion reactor, power conversion, magnetic nozzle, fast wave plasma heating, tankage, fuel pellet injector, startup/re-start fission reactor and battery bank, refrigeration, reaction control, communications, mission design, and space operations. Detailed fusion reactor design included analysis of plasma characteristics, power balance/utilization, first wall, toroidal field coils, heat transfer, and neutron/x-ray radiation. Technical comparisons are made between the vehicle concept and the interplanetary spacecraft depicted in the motion picture 2001: A Space Odyssey.
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.
STS-103 perfect night-time landing for Space Shuttle Discovery
NASA Technical Reports Server (NTRS)
1999-01-01
The orbiter Discovery looks like a blue ghost as it drops from the darkness onto lighted runway 33 at KSC's Shuttle Landing Facility. After traveling more than 3,267,000 miles on a successful eight-day mission to service the Hubble Space Telescope, the orbiter touches down at 7:00:47 p.m. EST. Aboard are Commander Curtis L. Brown Jr., Pilot Scott J. Kelly, and Mission Specialists Steven L. Smith, C. Michael Foale (Ph.D.), John M. Grunsfeld (Ph.D.), Claude Nicollier of Switzerland and Jean-Frangois Clervoy of France, who spent the Christmas holiday in space in order to accomplish their mission before the end of 1999. During the mission, Discovery's four space-walking astronauts, Smith, Foale, Grunsfeld and Nicollier, spent 24 hours and 33 minutes upgrading and refurbishing Hubble, making it more capable than ever to renew its observations of the universe. Mission objectives included replacing gyroscopes and an old computer, installing another solid state recorder, and replacing damaged insulation in the telescope. Hubble was released from the end of Discovery's robot arm on Christmas Day. This was the 96th flight in the Space Shuttle program and the 27th for the orbiter Discovery. The landing was the 20th consecutive Shuttle landing in Florida and the 13th night landing in Shuttle program history.
NASA Astrophysics Data System (ADS)
Guenneau, Sébastien; Ramakrishna, S. Anantha
2009-06-01
Newly discovered metamaterials have opened new vistas for better control of light via negative refraction, whereby light refracts in the "wrong" manner. These are dielectric and metallic composite materials structured at subwavelength lengthscales. Their building blocks consist of local resonators such as conducting thin bars and split rings driving the material parameters such as the dielectric permittivity and magnetic permeability to negative (complex) values. Combined together, these structural elements can bring about a (complex valued) negative effective refractive index for the Snell-Descartes law and result in negative refraction of radiation. Negative refractive index materials can support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as imaging with subwavelength image resolution through the Pendry-Veselago slab lens. Other geometries have also been investigated, such as cylindrical or spherical lenses that enable a magnification of images with subwavelength resolution. Superlenses of three-fold (equilateral triangle), four-fold (square) and six-fold (hexagonal) geometry allow for multiple images, respectively two, three, and five. Generalization to rectangular and triangular checkerboards consisting of alternating cells of positive and negative refractive index represents a very singular situation in which the density of modes diverges at the corners, with an infinity of images. Sine-cosecant anisotropic heterogeneous square and triangular checkerboards can be respectively mapped onto three-dimensional cubic and icosahedral corner lenses consisting of alternating positive and negative refractive regions. All such systems with corners between negative and positive refractive media display very singular behavior with the local density of states becoming infinitely large at the corner, in the limit of no dissipation. We investigate all of these, using the unifying viewpoint of transformation optics
NASA Astrophysics Data System (ADS)
Williams, Craig H.; Borowski, Stanley K.; Dudzinski, Leonard A.; Juhasz, Albert J.
1999-01-01
A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Initial requirements were for a human mission to Saturn with a>5% payload mass fraction and a one way trip time of less than one year. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 235 days, with an initial mass in low Earth orbit of 2,941 mt. Engineering conceptual design, analysis, and assessment was performed on all major systems including payload, central truss, nuclear reactor (including diverter and fuel injector), power conversion (including turbine, compressor, alternator, radiator, recuperator, and conditioning), magnetic nozzle, neutral beam injector, tankage, start/re-start reactor and battery, refrigeration, communications, reaction control, and in-space operations. Detailed assessment was done on reactor operations, including plasma characteristics, power balance, and component design.
NASA Technical Reports Server (NTRS)
Williams, Craig H.; Borowski, Stanley K.; Dudzinski, Leonard A.; Juhasz, Albert J.
1998-01-01
A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Initial requirements were for a human mission to Saturn with a greater than 5% payload mass fraction and a one way trip time of less than one year. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 235 days, with an initial mass in low Earth orbit of 2,941 mt. Engineering conceptual design, analysis, and assessment was performed on all ma or systems including payload, central truss, nuclear reactor (including divertor and fuel injector), power conversion (including turbine, compressor, alternator, radiator, recuperator, and conditioning), magnetic nozzle, neutral beam injector, tankage, start/re-start reactor and battery, refrigeration, communications, reaction control, and in-space operations. Detailed assessment was done on reactor operations, including plasma characteristics, power balance, power utilization, and component design.
Harding, E. C.; Ao, T.; Bailey, J. E.; Loisel, G.; Sinars, D. B.; Geissel, M.; Rochau, G. A.; Smith, I. C.
2015-04-15
The application of a space-resolving spectrometer to X-ray Thomson Scattering (XRTS) experiments has the potential to advance the study of warm dense matter. This has motivated the design of a spherical crystal spectrometer, which is a doubly focusing geometry with an overall high sensitivity and the capability of providing high-resolution, space-resolved spectra. A detailed analysis of the image fluence and crystal throughput in this geometry is carried out and analytical estimates of these quantities are presented. This analysis informed the design of a new spectrometer intended for future XRTS experiments on the Z-machine. The new spectrometer collects 6 keV x-rays with a spherically bent Ge (422) crystal and focuses the collected x-rays onto the Rowland circle. The spectrometer was built and then tested with a foam target. The resulting high-quality spectra prove that a spherical spectrometer is a viable diagnostic for XRTS experiments.
Harding, E C; Ao, T; Bailey, J E; Loisel, G; Sinars, D B; Geissel, M; Rochau, G A; Smith, I C
2015-04-01
The application of a space-resolving spectrometer to X-ray Thomson Scattering (XRTS) experiments has the potential to advance the study of warm dense matter. This has motivated the design of a spherical crystal spectrometer, which is a doubly focusing geometry with an overall high sensitivity and the capability of providing high-resolution, space-resolved spectra. A detailed analysis of the image fluence and crystal throughput in this geometry is carried out and analytical estimates of these quantities are presented. This analysis informed the design of a new spectrometer intended for future XRTS experiments on the Z-machine. The new spectrometer collects 6 keV x-rays with a spherically bent Ge (422) crystal and focuses the collected x-rays onto the Rowland circle. The spectrometer was built and then tested with a foam target. The resulting high-quality spectra prove that a spherical spectrometer is a viable diagnostic for XRTS experiments.
NASA Astrophysics Data System (ADS)
Harding, E. C.; Ao, T.; Bailey, J. E.; Loisel, G.; Sinars, D. B.; Geissel, M.; Rochau, G. A.; Smith, I. C.
2015-04-01
The application of a space-resolving spectrometer to X-ray Thomson Scattering (XRTS) experiments has the potential to advance the study of warm dense matter. This has motivated the design of a spherical crystal spectrometer, which is a doubly focusing geometry with an overall high sensitivity and the capability of providing high-resolution, space-resolved spectra. A detailed analysis of the image fluence and crystal throughput in this geometry is carried out and analytical estimates of these quantities are presented. This analysis informed the design of a new spectrometer intended for future XRTS experiments on the Z-machine. The new spectrometer collects 6 keV x-rays with a spherically bent Ge (422) crystal and focuses the collected x-rays onto the Rowland circle. The spectrometer was built and then tested with a foam target. The resulting high-quality spectra prove that a spherical spectrometer is a viable diagnostic for XRTS experiments.
NASA Astrophysics Data System (ADS)
Gauthier, Robert C.; Alzahrani, Mohammed A.; Jafari, Seyed Hamed
2015-02-01
The plane wave expansion (PWM) technique applied to Maxwell's wave equations provides researchers with a supply of information regarding the optical properties of dielectric structures. The technique is well suited for structures that display a linear periodicity. When the focus is directed towards optical resonators and structures that lack linear periodicity the eigen-process can easily exceed computational resources and time constraints. In the case of dielectric structures which display cylindrical or spherical symmetry, a coordinate system specific set of basis functions have been employed to cast Maxwell's wave equations into an eigen-matrix formulation from which the resonator states associated with the dielectric profile can be obtained. As for PWM, the inverse of the dielectric and field components are expanded in the basis functions (Fourier-Fourier-Bessel, FFB, in cylindrical and Fourier- Bessel-Legendre, BLF, in spherical) and orthogonality is employed to form the matrix expressions. The theoretical development details will be presented indicating how certain mathematical complications in the process have been overcome and how the eigen-matrix can be tuned to a specific mode type. The similarities and differences in PWM, FFB and BLF are presented. In the case of structures possessing axial cylindrical symmetry, the inclusion of the z axis component of propagation constant makes the technique applicable to photonic crystal fibers and other waveguide structures. Computational results will be presented for a number of different dielectric geometries including Bragg ring resonators, cylindrical space slot channel waveguides and bottle resonators. Steps to further enhance the computation process will be reported.
Bai, Mingsian R; Yao, Yueh Hua; Lai, Chang-Sheng; Lo, Yi-Yang
2016-03-01
In this paper, four delay-and-sum (DAS) beamformers formulated in the modal domain and the space domain for open and solid spherical apertures are examined through numerical simulations. The resulting beampatterns reveal that the mainlobe of the solid spherical DAS array is only slightly narrower than that of the open array, whereas the sidelobes of the modal domain array are more significant than those of the space domain array due to the discrete approximation of continuous spherical Fourier transformation. To verify the theory experimentally, a three-dimensionally printed spherical array on which 32 micro-electro-mechanical system microphones are mounted is utilized for localization and separation of sound sources. To overcome the basis mismatch problem in signal separation, source localization is first carried out using minimum variance distortionless response beamformer. Next, Tikhonov regularization (TIKR) and compressive sensing (CS) are employed to extract the source signal amplitudes. Simulations and experiments are conducted to validate the proposed spherical array system. Objective perceptual evaluation of speech quality test and a subjective listening test are undertaken in performance evaluation. The experimental results demonstrate better separation quality achieved by the CS approach than by the TIKR approach at the cost of computational complexity. PMID:27036243
Bai, Mingsian R; Yao, Yueh Hua; Lai, Chang-Sheng; Lo, Yi-Yang
2016-03-01
In this paper, four delay-and-sum (DAS) beamformers formulated in the modal domain and the space domain for open and solid spherical apertures are examined through numerical simulations. The resulting beampatterns reveal that the mainlobe of the solid spherical DAS array is only slightly narrower than that of the open array, whereas the sidelobes of the modal domain array are more significant than those of the space domain array due to the discrete approximation of continuous spherical Fourier transformation. To verify the theory experimentally, a three-dimensionally printed spherical array on which 32 micro-electro-mechanical system microphones are mounted is utilized for localization and separation of sound sources. To overcome the basis mismatch problem in signal separation, source localization is first carried out using minimum variance distortionless response beamformer. Next, Tikhonov regularization (TIKR) and compressive sensing (CS) are employed to extract the source signal amplitudes. Simulations and experiments are conducted to validate the proposed spherical array system. Objective perceptual evaluation of speech quality test and a subjective listening test are undertaken in performance evaluation. The experimental results demonstrate better separation quality achieved by the CS approach than by the TIKR approach at the cost of computational complexity.
Perfect imaging with geodesic waveguides
NASA Astrophysics Data System (ADS)
Miñano, Juan C.; Benítez, Pablo; González, Juan C.
2010-12-01
Transformation optics is used to prove that a spherical waveguide filled with an isotropic material with radial refractive index n=1/r has radially polarized modes (i.e. the electric field is only radial) with the same perfect focusing properties as the Maxwell fish-eye (MFE) lens. An approximate version of that device, comprising a thin waveguide with a homogeneous core, paves the way to experimentally attaining perfect imaging in the MFE lens.
ERIC Educational Resources Information Center
Adamsky, Carol; Morris, Joyce
A classroom language learning exercise, Pictionary Perfect, is described and documented. With this game, junior high school English-as-a-Second-Language (ESL) and bilingual students create illustrated dictionaries with a desktop publishing program and a computer. The students are introduced to computers and research skills while developing English…
Spherical space Bessel-Legendre-Fourier localized modes solver for electromagnetic waves.
Alzahrani, Mohammed A; Gauthier, Robert C
2015-10-01
Maxwell's vector wave equations are solved for dielectric configurations that match the symmetry of a spherical computational domain. The electric or magnetic field components and the inverse of the dielectric profile are series expansion defined using basis functions composed of the lowest order spherical Bessel function, polar angle single index dependant Legendre polynomials and azimuthal complex exponential (BLF). The series expressions and non-traditional form of the basis functions result in an eigenvalue matrix formulation of Maxwell's equations that are relatively compact and accurately solvable on a desktop PC. The BLF matrix returns the frequencies and field profiles for steady states modes. The key steps leading to the matrix populating expressions are provided. The validity of the numerical technique is confirmed by comparing the results of computations to those published using complementary techniques.
Shurshakov, Vyacheslav A.; Tolochek, Raisa V.; Kartsev, Ivan S.; Petrov, Vladislav M.; Nikolaev, Igor V.; Moskalyova, Svetlana I.; Lyagushin, Vladimir I.
2014-01-01
Space radiation is known to be key hazard of manned space mission. To estimate accurately radiation health risk detailed study of dose distribution inside human body by means of human phantom is conducted. In the space experiment MATROSHKA-R, the tissue-equivalent spherical phantom (32 kg mass, 35 cm diameter and 10 cm central spherical cave) made in Russia has been used on board the ISS for more than 8 years. Owing to the specially chosen phantom shape and size, the chord length distributions of the detector locations are attributed to self-shielding properties of the critical organs in a real human body. If compared with the anthropomorphic phantom Rando used inside and outside the ISS, the spherical phantom has lower mass, smaller size and requires less crew time for the detector installation/retrieval; its tissue-equivalent properties are closer to the standard human body tissue than the Rando-phantom material. Originally the spherical phantom was installed in the star board crew cabin of the ISS Service Module, then in the Piers-1, MIM-2 and MIM-1 modules of the ISS Russian segment, and finally in JAXA Kibo module. Total duration of the detector exposure is more than 1700 days in 8 sessions. In the first phase of the experiment with the spherical phantom, the dose measurements were realized with only passive detectors (thermoluminescent and solid-state track detectors). The detectors are placed inside the phantom along the axes of 20 containers and on the phantom outer surface in 32 pockets of the phantom jacket. After each session the passive detectors are returned to the ground. The results obtained show the dose difference on the phantom surface as much as a factor of 2, the highest dose being observed close to the outer wall of the compartment, and the lowest dose being in the opposite location along the phantom diameter. Maximum dose rate measured in the phantom is obviously due to the galactic cosmic ray (GCR) and Earth' radiation belt contribution on
NASA Astrophysics Data System (ADS)
Shurshakov, Vyacheslav; Akatov, Yu; Petrov, V.; Kartsev, I.; Polenov, Boris; Petrov, V.; Lyagushin, V.
In the space experiment MATROSHKA-R, the spherical tissue equivalent phantom (30 kg mass, 35 cm diameter and 10 cm central spherical cave) made in Russia has been installed in the star board crew cabin of the ISS Service Module. Due to the specially chosen phantom shape and size, the chord length distributions of the detector locations are attributed to self-shielding properties of the critical organs in a real human body. If compared with the anthropomorphic phantom Rando used inside and outside the ISS, the spherical phantom has lower mass, smaller size, and requires less crew time for the detector retrieval; its tissue-equivalent properties are closer to the standard human body tissue than the Rando-phantom material. In the first phase of the experiment the dose measurements were realized with only passive detectors (thermoluminescent and solid state track detectors). There were two experimental sessions with the spherical phantom in the crew cabin, (1) from Jan. 29, 2004 to Apr. 30, 2004 and (2) from Aug. 11, 2004 to Oct. 10, 2005. The detectors are placed inside the phantom along the axes of 20 containers and on the phantom outer surface in 32 pockets of the phantom jacket. The results obtained with the passive detectors returned to the ground after each session show the dose difference on the phantom surface as much as a factor of 2, the highest dose being observed close to the outer wall of the crew cabin, and the lowest dose being in the opposite location along the phantom diameter. Maximum dose rate measured in the phantom (0.31 mGy/day) is obviously due to the galactic cosmic ray (GCR) and Earth' radiation belt contribution on the ISS trajectory. Minimum dose rate (0.15 mGy/day) is caused mainly by the strongly penetrating GCR particles and is observed behind more than 5 g/cm2 tissue shielding. Critical organ doses, mean-tissue and effective doses of a crew member in the crew cabin are also estimated with the spherical phantom. The estimated effective
Strickler, D.J.; Peng, Y-K.M.; Borowski, S.K.; Selcow, E.C.; Miller, J.B.
1985-01-01
The Ignition Spherical Torus (IST) is a small aspect ratio device retaining only indispensable components along the major axis of a tokamak plasma, such as a cooled, normal conductor producing a toroidal magnetic field. The IST is expected to be a cost-effective approach to ignition by taking advantage of low field, large natural plasma elongation, high plasma current, high beta, and tokamak confinement. These result in compact, high-performance devices with relatively simple magnetic systems as compared with ignition tokamaks of larger aspect ratio. The plasma enhancement of the toroidal field on axis, or plasma paramagnetism, is significant in the IST. The use of this plasma-enhanced field in conventional tokamak beta and density limits leads to increased plasma pressure and performance and therefore smaller device size for a given ignition margin.
Generating perfect fluid spheres in general relativity
NASA Astrophysics Data System (ADS)
Boonserm, Petarpa; Visser, Matt; Weinfurtner, Silke
2005-06-01
Ever since Karl Schwarzschild’s 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star—a static spherically symmetric blob of fluid with position-independent density—the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres.
NASA Astrophysics Data System (ADS)
Pourmatin, Hossein; Dayal, Kaushik
2016-10-01
We consider the scattering of incident plane-wave electrons from a defect in a crystal modeled by the time-harmonic Schrödinger equation. While the defect potential is localized, the far-field potential is periodic, unlike standard free-space scattering problems. Previous work on the Schrödinger equation has been almost entirely in free-space conditions; a few works on crystals have been in one-dimension. We construct absorbing boundary conditions for this problem using perfectly matched layers in a tight-binding formulation. Using the example of a point defect in graphene, we examine the efficiency and convergence of the proposed absorbing boundary condition.
Highly Hybridizable Spherical Nucleic Acids by Tandem Glutathione Treatment and Polythymine Spacing.
Sun, Jing; Curry, Dennis; Yuan, Qipeng; Zhang, Xu; Liang, Hao
2016-05-18
Gold nanoparticle (AuNP)-templated spherical nucleic acids (SNAs) have been demonstrated as an important functional material in bionanotechnology. Fabrication of SNAs having high hybridization capacity to their complementary sequences is critical to ensure their applicability in areas such as antisense gene therapy and cellular sensing. The traditional salt-aging procedure is effective but tedious, requiring 1-3 days to complete. The rapid low-pH assisted protocol is efficient, but causes concerns related to nonspecific DNA adsorption to the AuNP core. To address these issues, we systematically compared the SNAs prepared by these two methods (salt-aging method and low-pH protocol). In terms of the number of complementary DNA that each SNA can bind and the average binding affinity of each thiolated DNA probe to its complementary strand, both methods yielded comparable hybridizability, although higher loading capacity was witnessed with SNAs made using the low-pH method. Additionally, it was found that nonspecific DNA binding could be eliminated almost completely by a simple glutathione (GSH) treatment of SNAs. Compared to conventional methods using toxic mercapto-hexanol or alkanethiols to remove nonspecific DNA adsorption, GSH is mild, cost-effective, and technically easy to use. In addition, GSH-passivated SNAs minimize the toxicity concerns related to AuNP-induced GSH depletion and therefore offer a more biocompatible alternative to previously reported SNAs. Moreover, rational design of probe sequences through inclusion of a polythymine spacer into the DNA sequences resulted in enhanced DNA loading capacity and stability against salt-induced aggregation. This work provides not only efficient and simple technical solutions to the issue of nonspecific DNA adsorption, but also new insights into the hybridizability of SNAs. PMID:27128167
Shen, Xiao; Hernandez-Pagan, Emil; Zhou, Wu; Puzyrev, Yevgeniy S.; Idrobo Tapia, Juan Carlos; Macdonald, Janet; Pennycook, Stephen J.; Pantelides, Sokrates T.
2014-11-14
The search for optimal thermoelectric materials aims for structures in which the crystalline order is disrupted to lower the thermal conductivity without degradation of the electron conductivity. Here we report the synthesis and characterization of ternary nanoparticles (two cations and one anion) that exhibit a new form of crystal-line order: an uninterrupted, perfect, global Bravais lattice, in which the two cations exhibit a wide array of distinct ordering patterns within the cation sublattice, form-ing interlaced domains and phases. Partitioning into domains and phases is not unique; the corresponding boundaries have no structural defects or strain and entail no energy cost. We call this form of crystalline order “interlaced crystals” and present the example of hexagonal-CuInS_{2}. Interlacing is possible in multi-cation tetrahedral-ly-bonded compound with an average of two electrons per bond. Interlacing has min-imal effect on electronic properties, but should strongly reduce phonon transport, making interlaced crystals attractive for thermoelectric applications.
Shen, Xiao; Hernandez-Pagan, Emil; Zhou, Wu; Puzyrev, Yevgeniy S.; Idrobo Tapia, Juan Carlos; Macdonald, Janet; Pennycook, Stephen J.; Pantelides, Sokrates T.
2014-11-14
The search for optimal thermoelectric materials aims for structures in which the crystalline order is disrupted to lower the thermal conductivity without degradation of the electron conductivity. Here we report the synthesis and characterization of ternary nanoparticles (two cations and one anion) that exhibit a new form of crystal-line order: an uninterrupted, perfect, global Bravais lattice, in which the two cations exhibit a wide array of distinct ordering patterns within the cation sublattice, form-ing interlaced domains and phases. Partitioning into domains and phases is not unique; the corresponding boundaries have no structural defects or strain and entail no energy cost.more » We call this form of crystalline order “interlaced crystals” and present the example of hexagonal-CuInS2. Interlacing is possible in multi-cation tetrahedral-ly-bonded compound with an average of two electrons per bond. Interlacing has min-imal effect on electronic properties, but should strongly reduce phonon transport, making interlaced crystals attractive for thermoelectric applications.« less
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.
Bidirectional slapper detonators in spherical explosion systems
NASA Astrophysics Data System (ADS)
Martinez, Ernest C.
1990-11-01
A bidirectional slapper detonator has been proven effective for producing a spherically expanding shock wave. Two bridge foils are used to propel flyers in opposite directions, thereby initiating two explosive pellets, each embedded in one hemisphere of a spherical system. This detonation system produces a nearly perfect spherically expanding detonation front.
NASA Astrophysics Data System (ADS)
Peldszus, Regina; Dalke, Hilary; Pretlove, Stephen; Welch, Chris
2014-01-01
In contemporary orbital missions, workloads are so high and varied that crew may rarely experience stretches of monotony. However, in historical long duration missions, occurrences of monotony were, indeed, reported anecdotally by crew. Of the effective countermeasures that appear to be at hand, many rely on visual or logistical proximity to the Earth, and are not feasible in the remote context of an extended deep space mission scenario. There, particularly in- and outbound cruising stages would be characterised by longer, comparably uneventful periods of low workload, coupled with confinement and unchanging vehicle surroundings. While the challenge of monotony has been pointed out as an exploration-related research area, it has received less explicit attention from a habitation design perspective than other human behaviour and performance issues. The paper addresses this gap through a literature review of the theory and application of design-based mitigation strategies. It outlines models of emergence of monotony, situates the phenomenon in a remote mission context as a problem of sensory, social and spatio-temporal isolation, and discusses proposed countermeasures related to habitability. The scope of the literature is extended to primary sources in the form of a qualitative review of six onboard diaries from orbital and simulator missions, highlighting a range of habitat-related design themes. These are translated into the autonomous deep space setting with the overall rationale of integrating affordances into onboard habitation systems and placing emphasis on reinforcing positive situational characteristics.
Zhou, Xiangrong; Hirano, Yasushi; Tachibana, Rie; Hara, Takeshi; Kido, Shoji; Fujita, Hiroshi
2013-01-01
Minimum description length (MDL) based group-wise registration was a state-of-the-art method to determine the corresponding points of 3D shapes for the construction of statistical shape models (SSMs). However, it suffered from the problem that determined corresponding points did not uniformly spread on original shapes, since corresponding points were obtained by uniformly sampling the aligned shape on the parameterized space of unit sphere. We proposed a particle-system based method to obtain adaptive sampling positions on the unit sphere to resolve this problem. Here, a set of particles was placed on the unit sphere to construct a particle system whose energy was related to the distortions of parameterized meshes. By minimizing this energy, each particle was moved on the unit sphere. When the system became steady, particles were treated as vertices to build a spherical mesh, which was then relaxed to slightly adjust vertices to obtain optimal sampling-positions. We used 47 cases of (left and right) lungs and 50 cases of livers, (left and right) kidneys, and spleens for evaluations. Experiments showed that the proposed method was able to resolve the problem of the original MDL method, and the proposed method performed better in the generalization and specificity tests. PMID:23861721
NASA Astrophysics Data System (ADS)
Williams, C. H.; Borowski, S. K.; Dudzinski, L. A.; Juhasz, A. J.
1999-11-01
A conceptual space vehicle concept to support NASA's 21^st century requirements was designed to enable human, multi-month travel throughout the outer solar system. The design was predicated on an ignited, spherical torus fusion reactor (R=2.5 m; a=1.25 m) burning spin polarized D^3He fuel and operating at high beta (30%). Peaked plasma temperature (50 keV) and number density (5×10^20 m-3) profiles were used. Engineering design was performed on all major vehicle systems including fusion reactor, fast wave plasma heating, power conversion, magnetic nozzle (for direct plasma propulsion), tankage and others, with emphasis on 1D fusion power balance, operation physics, first wall, toroidal field coils, and heat transfer. Two related proof-of-concept experiments at OSU, LANL, and PPPL are discussed. Results showed a 108 mt crew habitat payload could be delivered to Saturn rendezvous in 214 days using 6,145 MW of plasma jet power.
Magnetic fields of spherical compact stars in a braneworld
Ahmedov, B. J.; Fattoyev, F. J.
2008-08-15
We study the stellar magnetic field configuration in dependence on brane tension and present solutions of Maxwell equations in the external background space-time of a magnetized spherical star in a Randall-Sundrum II type braneworld. The star is modeled as a sphere consisting of perfect highly magnetized fluid with infinite conductivity and a frozen-in magnetic field. With respect to solutions for magnetic fields found in the Schwarzschild space-time, brane tension introduces enhancing corrections to the exterior magnetic field which could be relevant for the magnetic fields of magnetized compact objects as pulsars and magnetars and may provide observational evidence for the brane tension.
Challenging the standard perfect fluid paradigm
NASA Astrophysics Data System (ADS)
O'Brien, James
2015-04-01
We show that the standard perfect fluid paradigm is not necessarily a valid description of a curved space steady state gravitational source. Simply by virtue of not being flat, curved space geometries have to possess intrinsic length scales, and such length scales can affect the fluid structure.We show that for the specific case of a static, spherically symmetric geometry, the steady state energy-momentum tensor that ensues will in general be of the form Tμν =(ρ + p) UμUν + pgμν + qπμν where πμν is a symmetric, traceless rank two tensor which obeys Uμπμν = 0 . Such a qπμν type term is absent for an incoherently averaged steady state fluid in a spacetime where there are no intrinsic length scales, and in principle would thus be missed in a covariantizing of a flat spacetime Tμν. While it is reassuring that we find that in practice the effect of such qπμν type terms is small for weak gravity stars, for strong gravity systems their potential influence would need to be explored.
ERIC Educational Resources Information Center
Scott, Paul
2007-01-01
In "Just Perfect: Part 1," the author defined a perfect number N to be one for which the sum of the divisors d (1 less than or equal to d less than N) is N. He gave the first few perfect numbers, starting with those known by the early Greeks. In this article, the author provides an extended list of perfect numbers, with some comments about their…
Jakubowicz, J.; Adamek, G.; Pałka, K.; Andrzejewski, D.
2015-02-15
The paper describes the formation, morphology and mechanical properties of Ti void composites. The Ti void composites were made using 100 and 325 mesh Ti powder for solid scaffold formation. The spherical and polyhedral voids (pores) were formed using saccharose particles (table sugar) of different shapes. The Ti void composite morphology was investigated by microcomputed tomography and scanning electron microscopy. The Ti void composites of designed porosity of 50–70% were made. Compression test was applied for mechanical properties estimation. It has been found, that Ti void composites made from 100 mesh Ti and those having spherical pores have a higher strength and elastic modulus, i.e. for the designed porosity of 50% for 100 and 325 mesh Ti void composites, a compressive strength was 32.32 and 20.13 MPa, respectively. It has been shown that this is related to better sintering of the 100 mesh Ti powders compared with the 325 mesh Ti powders. A correlation between microcomputed tomography data and mechanical properties has also been shown. The Ti void composites, made with the use of saccharose as a space holder, described in this work should be a promising material for biomedical applications, where interconnected pores and good mechanical properties are required. - Highlights: • Ti scaffolds of the porosity of 50–70% were made. • Saccharose particles as space holder were applied. • The voids in the scaffolds were designed with spherical and polyhedral shape. • The scaffold structure was investigated by SEM and micro-CT. • Micro-CT data and mechanical properties of the Ti scaffold have been correlated.
Mass of Perfect Fluid Black Shells
NASA Astrophysics Data System (ADS)
Zloshchastiev, Konstantin G.
The spherically symmetric singular perfect fluid shells are considered when their radii are equal to the event horizon (the black shells). We study their observable masses, depending at least on the three parameters, viz. the square speed of sound in the shell, instantaneous radial velocity of the shell at a moment when it reaches the horizon, and integration constant related to surface mass density. We discuss the features of black shells depending on the equation of state.
ERIC Educational Resources Information Center
Landphair, Juliette
2007-01-01
What exactly is perfect? Students describe perfection as a combination of characteristics valued by their peer culture: intelligence, thin and fit physical appearance, social poise. As students chug through their daily lives--morning classes, organization meetings, club sports practice or the gym, dinner, another class, more meetings, library,…
Spherical Torus Center Stack Design
C. Neumeyer; P. Heitzenroeder; C. Kessel; M. Ono; M. Peng; J. Schmidt; R. Woolley; I. Zatz
2002-01-18
The low aspect ratio spherical torus (ST) configuration requires that the center stack design be optimized within a limited available space, using materials within their established allowables. This paper presents center stack design methods developed by the National Spherical Torus Experiment (NSTX) Project Team during the initial design of NSTX, and more recently for studies of a possible next-step ST (NSST) device.
Jia, Jiangang; Siddiq, Abdur R; Kennedy, Andrew R
2015-08-01
Porous Ti with open porosity in the range of 70-80% has been made using Ti powder and a particulate leaching technique using porous, spherical, NaCl beads. By incorporating the Ti powder into a pre-existing network of salt beads, by tapping followed by compaction, salt dissolution and "sintering", porous structures with uniform density, pore and strut sizes and a predictable level of connectivity have been produced, showing a significant improvement on the structures made by conventional powder mixing processes. Parts made using beads with sizes in the range of 0.5-1.0 mm show excellent promise as porous metals for medical devices, showing structures and porosities similar to those of commercial porous metals used in this sector, with inter-pore connections that are similar to trabecular bone. The elastic modulus (0.86 GPa) is lower than those for commercial porous metals and more closely matches that of trabecular bone and good compressive yield strength is retained (21 MPa). The ability to further tailor the structure, in terms of the density and the size of the pores and interconnections has also been demonstrated by immersion of the porous components in acid.
Jia, Jiangang; Siddiq, Abdur R; Kennedy, Andrew R
2015-08-01
Porous Ti with open porosity in the range of 70-80% has been made using Ti powder and a particulate leaching technique using porous, spherical, NaCl beads. By incorporating the Ti powder into a pre-existing network of salt beads, by tapping followed by compaction, salt dissolution and "sintering", porous structures with uniform density, pore and strut sizes and a predictable level of connectivity have been produced, showing a significant improvement on the structures made by conventional powder mixing processes. Parts made using beads with sizes in the range of 0.5-1.0 mm show excellent promise as porous metals for medical devices, showing structures and porosities similar to those of commercial porous metals used in this sector, with inter-pore connections that are similar to trabecular bone. The elastic modulus (0.86 GPa) is lower than those for commercial porous metals and more closely matches that of trabecular bone and good compressive yield strength is retained (21 MPa). The ability to further tailor the structure, in terms of the density and the size of the pores and interconnections has also been demonstrated by immersion of the porous components in acid. PMID:25957839
Electromagnetic Detection of a Perfect Invisibility Cloak
Zhang Baile; Wu, Bae-Ian
2009-12-11
A perfect invisibility cloak is commonly believed to be undetectable from electromagnetic (EM) detection because it is equivalent to a curved but empty EM space created from coordinate transformation. Based on the intrinsic asymmetry of coordinate transformation applied to motions of photons and charges, we propose a method to detect this curved EM space by shooting a fast-moving charged particle through it. A broadband radiation generated in this process makes a cloak visible. Our method is the only known EM mechanism so far to detect an ideal perfect cloak (curved EM space) within its working band.
NASA Astrophysics Data System (ADS)
Brunner, Raimund; Schmidtke, Gerhard; Konz, Werner; Nikutowski, Bernd
A new versatile instrument for space applications enables measurements of several space parameters by one sensor. The low-cost device consists of three isolated spheres, the metallic sphere (MS), a highly transparent Inner Grid (IG) and an Outer Grid (OG). Each one is being connected to sensitive floating electrometers. Simply by setting different potentials to the outer grid as well as to the sphere and varying the voltage to the inner grid, measurements of spectral solar EUV irradiance (15-200 nm), of local plasma parameters such as electron and ion densities, electron energies and temperatures as well as ion compositions. This detector does not require any (solar) pointing device. The primary goal is to study the impact of solar activity with space weather included as well as subsequent reactions of the ionospheric/thermospheric systems. It can be operated in LEO and MEO orbits, in the interplanetary medium and in the planetary ionospheres as well. On the other hand, monitoring the space environment can lead to a better understanding of its interaction with the spacecraft, i.e. charging of satellites. In principal the data can be used to study the propagation as well as post-analysis of such anomalies. We will present the sensor design and laboratory measurements to demonstrate the capability of SEPS for measuring EUV photon fluxes as well as plasma parameters in the energy range from 0 to +/- 70 eV. Measurements with a mock-up are performed in the IPM laboratory, at BESSY-PTB electron synchrotron in Berlin and at the ESA/ESTEC plasma chamber.
Perfect lens makes a perfect trap.
Lu, Zhaolin; Murakowski, Janusz; Schuetz, Christopher A; Shi, Shouyuan; Schneider, Garrett J; Samluk, Jesse P; Prather, Dennis W
2006-03-20
In this work, we present for the first time a new and realistic application of the "perfect lens", namely, electromagnetic traps (or tweezers). We combined two recently developed techniques, 3D negative refraction flat lenses (3DNRFLs) and optical tweezers, and experimentally demonstrated the very unique advantages of using 3DNRFLs for electromagnetic traps. Super-resolution and short focal distance of the flat lens result in a highly focused and strongly convergent beam, which is a key requirement for a stable and accurate electromagnetic trap. The translation symmetry of 3DNRFL provides translation-invariance for imaging, which allows an electromagnetic trap to be translated without moving the lens, and permits a trap array by using multiple sources with a single lens. Electromagnetic trapping was demonstrated using polystyrene particles in suspension, and subsequent to being trapped to a single point, they were then accurately manipulated over a large distance by simple movement of a 3DNRFL-imaged microwave monopole source.
NASA Technical Reports Server (NTRS)
Ferguson, R. E.; Patterson, T. D.; Moreno, M. R.
1975-01-01
A fixed beam array antenna approach is proposed to meet the omnidirectional receiving and transmitting requirements of LST (Large Space Telescope). The proposed method uses an antenna of known performance and scales the size and frequency to conform with the LST 1/5-th scale model. The simplification that the approach provides over switching antenna elements on board the LST or switching from the ground by frequency diversity makes it worthy of consideration against the factors of performance, cost, reliability, and operations complexity. For LST applications, the system capabilities, requirements, and margins are summarized. The areas to be covered by further investigations into the proposed LST antenna are noted.
Unidirectional perfect absorber
Jin, L.; Wang, P.; Song, Z.
2016-01-01
This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices. PMID:27615125
Unidirectional perfect absorber
NASA Astrophysics Data System (ADS)
Jin, L.; Wang, P.; Song, Z.
2016-09-01
This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices.
Unidirectional perfect absorber.
Jin, L; Wang, P; Song, Z
2016-01-01
This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices. PMID:27615125
Unidirectional perfect absorber.
Jin, L; Wang, P; Song, Z
2016-09-12
This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices.
NASA Astrophysics Data System (ADS)
Brunner, Raimund; Schmidtke, Gerhard; Konz, Werner; Pfeffer, Wilfried
A low-cost monitor to measure the EUV and plasma environment in space is presented. The device consists of three (or more) isolated spheres, a metallic sphere, one or more highly trans-parent Inner Grids and Outer Grids. Each one is being connected to a sensitive floating elec-trometer. By setting different potentials to the grids as well as to the sphere and varying one or more of their voltages, measurements of spectral solar EUV irradiance (15-200 nm), of local plasma parameters such as electron and ion densities, electron energies and temperatures as well as ion compositions and debris events can be derived from the current recordings. This detector does not require any (solar) pointing device. The primary goal is to study the impact of solar activity events (e.g. CMEs) as well as subsequent reactions of the ionospheric/thermospheric systems (including space weather occurences). The capability of SEPS for measuring EUV pho-ton fluxes as well as plasma parameters in the energy range from 0 to +/-70 eV is demonstrated by laboratory measurements as performed in the IPM laboratory, at BESSY-PTB electron syn-chrotron in Berlin and at ESA/ESTEC plasma chamber. Based on the laboratory recording of plasma recombination EUV emission the sensor is suitable to detect also auroral and airglow radiations. -The state of the art in the development of this device is reported.
NASA Astrophysics Data System (ADS)
Pendry, J. B.
2003-04-01
A slab of negatively refracting material is known to focus light and if 1 n = the focussing will be perfect, producing an image which is an exact replica of the object. Magnifying the image requires a new design concept in which the surface of the negatively refracting lens is curved. Here we show how a hollow cylinder of material can be designed to magnify an image but otherwise with the same perfection as the original lens. Curvature requires that ɛ and μ are now a function of position.
Electrodynamics of Perfect Conductors
NASA Astrophysics Data System (ADS)
Fiolhais, Miguel C. N.; Essén, Hanno
2013-05-01
The most general electrodynamic equations of a perfect conducting state are obtained using a variational principle in a classical framework, following an approach by Pierre-Gilles de Gennes. London equations are derived as the time-independent case of these equations, corresponding to the magnetostatic minimal energy state of the perfect conducting system. For further confirmation, the same equations are also derived in the classical limit of the Coleman-Weinberg model, the most successful quantum macroscopic theory of superconductivity. The magnetic field expulsion is, therefore, a direct consequence of zero resistivity and not an exclusive property of superconductors.
Near-perfect diffraction grating rhomb
Wantuck, Paul J.
1990-01-01
A near-perfect grating rhomb enables an output beam to be diffracted to an angle offset from the input beam. The correcting grating is tipped relative to the dispersing grating to provide the offset angle. The correcting grating is further provided with a groove spacing which differs from the dispersing grating groove space by an amount effective to substantially remove angular dispersion in the output beam. A near-perfect grating rhomb has the capability for selective placement in a FEL to suppress sideband instabilities arising from the FEL.
ERIC Educational Resources Information Center
Murray, Jeannette
2010-01-01
In a perfect world, all children should live at home with their family, play with the kids in their neighborhood, walk or ride the school bus to a community-based school--after affectionately kissing or hugging their parents goodbye. They should receive adequate classroom services and return home at 3 p.m. or thereabouts. They may even…
ERIC Educational Resources Information Center
Hinshaw, Craig
2005-01-01
For thousands of years, the three perfections--painting, poetry, and calligraphy--have been considered the mark of an enlightened person throughout Asian cultures. Fifth-grade students learned about these three hallmarks by studying three works from the Detroit Institute of Art's Asian collection: a nineteenth-century Japanese hand scroll, a…
ERIC Educational Resources Information Center
Russo, Ruth
1998-01-01
A chemistry teacher describes the elements of the ideal chemistry textbook. The perfect text is focused and helps students draw a coherent whole out of the myriad fragments of information and interpretation. The text would show chemistry as the central science necessary for understanding other sciences and would also root chemistry firmly in the…
ERIC Educational Resources Information Center
Bacon, David
2010-01-01
The United States today faces an economic crisis worse than any since the Great Depression of the 1930s. Nowhere is it sharper than in the nation's schools. Last year, California saw a perfect storm of protest in virtually every part of its education system. K-12 teachers built coalitions with parents and students to fight for their jobs and their…
ERIC Educational Resources Information Center
DiConsiglio, John
2012-01-01
Alumni relations and stewardship officers have the makings of a strong partnership. Alumni relations and stewardship can be a natural fit--a perfect match even--according to Mary Jo Chiara of St. Joseph's College (SJC) in New York. Both strive to cultivate long-term relationships with constituents and build increasing levels of engagement and…
Perfect lens makes a perfect trap
NASA Astrophysics Data System (ADS)
Lu, Zhaolin; Murakowski, Janusz; Schuetz, Christopher A.; Shi, Shouyuan; Schneider, Garrett J.; Samluk, Jesse P.; Prather, Dennis W.
2006-03-01
In this work, we present for the first time a new and realistic application of the “perfect lens”, namely, electromagnetic traps (or tweezers). We combined two recently developed techniques, 3D negative refraction flat lenses (3DNRFLs) and optical tweezers, and experimentally demonstrated the very unique advantages of using 3DNRFLs for electromagnetic traps. Super-resolution and short focal distance of the flat lens result in a highly focused and strongly convergent beam, which is a key requirement for a stable and accurate electromagnetic trap. The translation symmetry of 3DNRFL provides translation-invariance for imaging, which allows an electromagnetic trap to be translated without moving the lens, and permits a trap array by using multiple sources with a single lens. Electromagnetic trapping was demonstrated using polystyrene particles in suspension, and subsequent to being trapped to a single point, they were then accurately manipulated over a large distance by simple movement of a 3DNRFL-imaged microwave monopole source.
Perfect Quantum Cosmological Bounce
NASA Astrophysics Data System (ADS)
Gielen, Steffen; Turok, Neil
2016-07-01
We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a "perfect bounce", in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order. This picture provides a natural, unitary description of quantum mechanical evolution across a cosmological bounce. We provide evidence for a semiclassical description in which all fields pass "around" the cosmological singularity along complex classical paths.
Perfect Quantum Cosmological Bounce.
Gielen, Steffen; Turok, Neil
2016-07-01
We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a "perfect bounce", in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order. This picture provides a natural, unitary description of quantum mechanical evolution across a cosmological bounce. We provide evidence for a semiclassical description in which all fields pass "around" the cosmological singularity along complex classical paths. PMID:27447496
Perfect Quantum Cosmological Bounce.
Gielen, Steffen; Turok, Neil
2016-07-01
We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a "perfect bounce", in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order. This picture provides a natural, unitary description of quantum mechanical evolution across a cosmological bounce. We provide evidence for a semiclassical description in which all fields pass "around" the cosmological singularity along complex classical paths.
BNL
2016-07-12
Evidence to date suggests that gold-gold collisions the Relativistic Heavy Ion Collider at Brookhaven are indeed creating a new state of hot, dense matter, but one quite different and even more remarkable than had been predicted. Instead of behaving like a gas of free quarks and gluons, as was expected, the matter created in RHIC's heavy ion collisions appears to be more like a "perfect" liquid.
BNL
2008-08-12
Evidence to date suggests that gold-gold collisions the Relativistic Heavy Ion Collider at Brookhaven are indeed creating a new state of hot, dense matter, but one quite different and even more remarkable than had been predicted. Instead of behaving like a gas of free quarks and gluons, as was expected, the matter created in RHIC's heavy ion collisions appears to be more like a "perfect" liquid.
Livingston, J.P.
1959-01-27
A die is presented for pressing powdered materials into a hemispherical shape of uniforin density and wall thickness comprising a fcmale and male die element held in a stationary spaced relation with the space being equivalent to the wall thickness and defining the hemispherical shape, a pressing ring linearly moveable along the male die element, an inlet to fill the space with powdered materials, a guiding system for moving the pressing ring along the male die element so as to press the powdered material and a heating system for heating the male element so that the powdered material is heated while being pressed.
NASA Astrophysics Data System (ADS)
Georgiev, G. H.; Dinkova, C. L.
2013-10-01
Long spirals in the Euclidean plane have been introduced by A. Kurnosenko five years ago. Using a natural map of the shape sphere into the extended Gaussian plane we study spherical curves that are pre-images of plane long spirals. Loxodromes and spherical spiral antennas are typical examples of such spherical long spirals. The set of all planar spirals leaves invariant under an arbitrary similarity transformation. This set is divided in two disjoint classes by A. Kirnosenko. The first class is consist of the so-called short spirals which are widely used in geometric modeling. The second class of planar long spirals contains well-known logarithmic spiral and Archimedean spirals which have many applications in mathematics, astrophysics and industry. The notion of simplicial shape space is due to D. Kendall. The most popular simplicial shape space of order (2,3) is the set of equivalence classes of similar triangles in the plane. The sphere of radius 1/2 centered at the origin can be considered as a model of this quotient space, so-called the shape sphere. F. Bookstein and J. Lester showed that the one-point extension of the Euclidean plane, so-called the extended Gaussian plane, is another model of the same simplicial shape space. The present paper gives a description of long spirals on the shape sphere by the use a natural conformal mapping between two models. First, we examine long spirals in the extended Gaussian plane. After that, we describe some differential geometric properties of the shape sphere. Finally, we discuss parameterizations of long spirals on the shape sphere.
Spherical colloidal photonic crystals.
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
NASA Astrophysics Data System (ADS)
Nagamatsu, Aiko; Tolochek, Raisa; Shurshakov, Vyacheslav; Nikolaev, Igor; Tawara, Hiroko; Kitajo, Keiichi; Shimada, Ken
The measurement of radiation environmental parameters in space is essential to support radiation risk assessments for astronauts and establish a benchmark for space radiation models for present and future human space activities. Since Japanese Experiment Module ‘KIBO’ was attached to the International Space Station (ISS) in 2008, we have been performing continuous space radiation dosimetery using a PADLES (Passive Dosimeter for Life-Science Experiments in Space) consisting of CR-39 PNTDs (Plastic Nuclear track detectors) and TLD-MSOs (Mg2SiO4:Tb) for various space experiments onboard the ‘KIBO’ part of the ISS. The MATROSHKA-R experiments aims to verify of dose distributions in a human body during space flight. The phantom consists of tissue equivalent material covered by a poncho jacket with 32 pockets on the surface. 20 container rods with dosimeters can be struck into the spherical phantom. Its diameter is 370 mm and it is 32 kg in weight. The first experiment onboard the KIBO at Forward No.2 area (JPM1F2 Rack2) was conducted over 114 days from 21 May to 12 September 2012 (the installation schedule inside the phantom) on the way to solar cycle 24th upward curve. 16 PADLES packages were deployed into 16 poncho pockets on the surface of the spherical phantom. Another 12 PADLES packages were deployed inside 4 rods (3 packages per rod in the outer, middle and inner side). Area monitoring in the KIBO was conducted in the same period (Area PADLES series #8 from 15 May to 16 September, 2012). Absorbed doses were measured at 17 area monitoring points in the KIBO and 28 locations (16 packages in poncho pockets and 12 inside 4 rods) in the phantom. The maximum value measured with the PADLES in the poncho pockets on the surface of the spherical phantom facing the outer wall was 0.43 mGy/day and the minimum value measured with the PADLES in the poncho pockets on the surface of the spherical phantom facing the KIBO interior was 0.30 mGy/day. The maximum absorbed
Ultra-Perfect Sorting Scenarios
NASA Astrophysics Data System (ADS)
Ouangraoua, Aïda; Bergeron, Anne; Swenson, Krister M.
Perfection has been used as a criteria to select rearrangement scenarios since 2004. However, there is a fundamental bias towards extant species in the original definition: ancestral species are not bound to perfection. Here we develop a new theory of perfection that takes an egalitarian view of species, and apply it to the complex evolution of mammal chromosome X.
Goeke, R.; Farnsworth, A.V.; Neumann, C.C.; Sweatt, W.C.; Warren, M.E.; Weed, J.W.
1996-06-01
This report discusses a novel fabrication process to produce nearly perfect optics. The process utilizes vacuum deposition techniques to optimally modify polished optical substrate surfaces. The surface figure, i.e. contour of a polished optical element, is improved by differentially filling in the low spots on the surface using flux from a physical vapor deposition source through an appropriate mask. The process is expected to enable the manufacture of diffraction-limited optical systems for the UV, extreme UV, and soft X-ray spectral regions, which would have great impact on photolithography and astronomy. This same technique may also reduce the fabrication cost of visible region optics with aspheric surfaces.
Five dimensional spherically symmetric cosmological model in Brans-Dicke theory of gravitation
NASA Astrophysics Data System (ADS)
Rao, V. U. M.; Jaysudha, V.
2015-08-01
In this paper, we consider the spherically symmetric space-time in five dimensions in Brans-Dicke (Phys. Rev. 124:925, 1961) theory of gravitation in the presence of perfect fluid distribution. A determinate solution of the highly non-linear field equations is presented using (i) relation between metric potentials and (ii) an equation of state which represents disordered radiation in five dimensional universe. The solution obtained describes five dimensional radiating model in Brans-Dicke theory. Some physical and kinematical properties of the model are also discussed.
Perfect fluid tori orbiting Kehagias-Sfetsos naked singularities
NASA Astrophysics Data System (ADS)
Stuchlík, Z.; Pugliese, D.; Schee, J.; Kučáková, H.
2015-09-01
We construct perfect fluid tori in the field of the Kehagias-Sfetsos (K-S) naked singularities. These are spherically symmetric vacuum solutions of the modified Hořava quantum gravity, characterized by a dimensionless parameter ω M^2, combining the gravitational mass parameter M of the spacetime with the Hořava parameter ω reflecting the role of the quantum corrections. In dependence on the value of ω M^2, the K-S naked singularities demonstrate a variety of qualitatively different behavior of their circular geodesics that is fully reflected in the properties of the toroidal structures, demonstrating clear distinction to the properties of the torii in the Schwarzschild spacetimes. In all of the K-S naked singularity spacetimes the tori are located above an "antigravity" sphere where matter can stay in a stable equilibrium position, which is relevant for the stability of the orbiting fluid toroidal accretion structures. The signature of the K-S naked singularity is given by the properties of marginally stable tori orbiting with the uniform distribution of the specific angular momentum of the fluid, l= const. In the K-S naked singularity spacetimes with ω M^2 > 0.2811, doubled tori with the same l= const can exist; mass transfer between the outer torus and the inner one is possible under appropriate conditions, while only outflow to the outer space is allowed in complementary conditions. In the K-S spacetimes with ω M^2 < 0.2811, accretion from cusped perfect fluid tori is not possible due to the non-existence of unstable circular geodesics.
A proposed mechanism for the formation of spherical vivianite crystal aggregates in sediments
Zelibor, J.L.; Senftle, F.E.; Reinhardt, J.L.
1988-01-01
Vivianite [Fe3(PO4)2??8H2O] is often found in the form of nodules composed of spherical aggregates of crystals. Crystallization of vivianite in agar gels of various concentrations yield crystal aggregates (nodules) that have spherical morphology and a bimodal size distribution. The aggregates were formed under both biotic and abiotic conditions. When special redox cells fitted with electrodes were used, more perfect spherical structures were formed when the electrodes were shorted than when they were on open circuit. In nature, vivianite nodules generally are found in sediments or clays that are gelatinous, often caused by the presence of organic debris. A model consistent with experimental observations and based on the dynamics of gels is proposed to explain a possible origin of nodular vivianite. To maintain iron and phosphate concentrations in sedimentary pore spaces filled with gel-like organic debris, the electric field spanning the aerobic-anerobic zones in the upper sediments may be an important driving force in addition to diffusion. It is suggested that the combination of the gel medium in the pore spaces and the natural electric field in the upper sediments could be contributing causes to explain the spherical aggregates of vivianite crystals found in nature. ?? 1988.
Perfect and Near-Perfect Adaptation in Cell Signaling.
Ferrell, James E
2016-02-24
Adaptation is an important basic feature of cellular regulation. Previous theoretical work has identified three types of circuits-negative feedback loops, incoherent feedforward systems, and state-dependent inactivation systems-that can achieve perfect or near-perfect adaptation. Recent work has added another strategy, termed antithetic integral feedback, to the list of motifs capable of robust perfect adaptation. Here, we discuss the properties, limitations, and biological relevance of each of these circuits. PMID:27135159
Medical Practice Makes Perfect
NASA Technical Reports Server (NTRS)
1998-01-01
Cedaron Medical Inc., was founded in 1990 as a result of a NASA SBIR (Small Business Innovative Research) grant from Johnson Space Center to develop a Hand Testing and Exercise Unit for use in space. From that research came Dexter, a comprehensive workstation that creates a paperless environment for medical data management.
Three-point spherical mirror mount
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.
Three-point spherical mirror mount
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.
Structured metal film as a perfect absorber.
Xiong, Xiang; Jiang, Shang-Chi; Hu, Yu-Hui; Peng, Ru-Wen; Wang, Mu
2013-08-01
A new type of absorber, a four-tined fish-spear-like resonator (FFR), constructed by the two-photon polymerization process, is reported. An absorbance of more than 90% is experimentally realized and the resonance occurs in the space between the tines. Since a continuous layer of metallic thin film covers the structure, it is perfectly thermo- and electroconductive, which is the mostly desired feature for many applications. PMID:23661582
Electromagnetic detection of a perfect carpet cloak.
Shi, Xihang; Gao, Fei; Lin, Xiao; Zhang, Baile
2015-01-01
It has been shown that a spherical invisibility cloak originally proposed by Pendry et al. can be electromagnetically detected by shooting a charged particle through it, whose underlying mechanism stems from the asymmetry of transformation optics applied to motions of photons and charges [PRL 103, 243901 (2009)]. However, the conceptual three-dimensional invisibility cloak that exactly follows specifications of transformation optics is formidably difficult to implement, while the simplified cylindrical cloak that has been experimentally realized is inherently visible. On the other hand, the recent carpet cloak model has acquired remarkable experimental development, including a recently demonstrated full-parameter carpet cloak without any approximation in the required constitutive parameters. In this paper, we numerically investigate the electromagnetic radiation from a charged particle passing through a perfect carpet cloak and propose an experimentally verifiable model to demonstrate symmetry breaking of transformation optics. PMID:25997798
Electromagnetic Detection of a Perfect Carpet Cloak
Shi, Xihang; Gao, Fei; Lin, Xiao; Zhang, Baile
2015-01-01
It has been shown that a spherical invisibility cloak originally proposed by Pendry et al. can be electromagnetically detected by shooting a charged particle through it, whose underlying mechanism stems from the asymmetry of transformation optics applied to motions of photons and charges [PRL 103, 243901 (2009)]. However, the conceptual three-dimensional invisibility cloak that exactly follows specifications of transformation optics is formidably difficult to implement, while the simplified cylindrical cloak that has been experimentally realized is inherently visible. On the other hand, the recent carpet cloak model has acquired remarkable experimental development, including a recently demonstrated full-parameter carpet cloak without any approximation in the required constitutive parameters. In this paper, we numerically investigate the electromagnetic radiation from a charged particle passing through a perfect carpet cloak and propose an experimentally verifiable model to demonstrate symmetry breaking of transformation optics. PMID:25997798
An approach towards a perfect thermal diffuser
Vemuri, Krishna P.; Bandaru, Prabhakar R.
2016-01-01
A method for the most efficient removal of heat, through an anisotropic composite, is proposed. It is shown that a rational placement of constituent materials, in the radial and the azimuthal directions, at a given point in the composite yields a uniform temperature distribution in spherical diffusers. Such arrangement is accompanied by a very significant reduction of the source temperature, in principle, to infinitesimally above the ambient temperature and forms the basis for the design of a perfect thermal diffuser with maximal heat dissipation. Orders of magnitude enhanced performance, compared to that obtained through the use of a diffuser constituted from a single material with isotropic thermal conductivity has been observed and the analytical principles underlying the design were validated through extensive computational simulations. PMID:27404569
Electromagnetic Detection of a Perfect Carpet Cloak
NASA Astrophysics Data System (ADS)
Shi, Xihang; Gao, Fei; Lin, Xiao; Zhang, Baile
2015-05-01
It has been shown that a spherical invisibility cloak originally proposed by Pendry et al. can be electromagnetically detected by shooting a charged particle through it, whose underlying mechanism stems from the asymmetry of transformation optics applied to motions of photons and charges [PRL 103, 243901 (2009)]. However, the conceptual three-dimensional invisibility cloak that exactly follows specifications of transformation optics is formidably difficult to implement, while the simplified cylindrical cloak that has been experimentally realized is inherently visible. On the other hand, the recent carpet cloak model has acquired remarkable experimental development, including a recently demonstrated full-parameter carpet cloak without any approximation in the required constitutive parameters. In this paper, we numerically investigate the electromagnetic radiation from a charged particle passing through a perfect carpet cloak and propose an experimentally verifiable model to demonstrate symmetry breaking of transformation optics.
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.
Perfect imaging with positive refraction
NASA Astrophysics Data System (ADS)
Leonhardt, Ulf; Tyc, Tomáš; Danner, Aaron
2010-10-01
We present several refractive index profiles for perfect imaging with positive refraction other than Maxwell's fish eye. Numerical simulations show that these profiles may transfer images with, in principle, unlimited resolution. Such profiles could overcome the fundamental limitations of perfect imaging with negative refraction and find practical applications in nanolithography.
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.
Relativistic spherical plasma waves
NASA Astrophysics Data System (ADS)
Bulanov, S. S.; Maksimchuk, A.; Schroeder, C. B.; Zhidkov, A. G.; Esarey, E.; Leemans, W. P.
2012-02-01
Tightly focused laser pulses that diverge or converge in underdense plasma can generate wake waves, having local structures that are spherical waves. Here we study theoretically and numerically relativistic spherical wake waves and their properties, including wave breaking.
Miller, David A B
2006-12-11
We show in principle how to cloak a region of space to make its contents classically invisible or transparent to waves. The method uses sensors and active sources near the surface of the region, and could operate over broad bandwidths. A general expression is given for calculating the necessary sources, and explicit, fully causal simulations are shown for scalar waves. Vulnerability to broad-band probing is discussed, and any active scheme should detectable by a quantum probe, regardless of bandwidth. PMID:19529679
NASA Astrophysics Data System (ADS)
2008-05-01
ESO celebrates 10 years since First Light of the VLT Today marks the 10th anniversary since First Light with ESO's Very Large Telescope (VLT), the most advanced optical telescope in the world. Since then, the VLT has evolved into a unique suite of four 8.2-m Unit Telescopes (UTs) equipped with no fewer than 13 state-of-the-art instruments, and four 1.8-m moveable Auxiliary Telescopes (ATs). The telescopes can work individually, and they can also be linked together in groups of two or three to form a giant 'interferometer' (VLTI), allowing astronomers to see details corresponding to those from a much larger telescope. Green Flash at Paranal ESO PR Photo 16a/08 The VLT 10th anniversary poster "The Very Large Telescope array is a flagship facility for astronomy, a perfect science machine of which Europe can be very proud," says Tim de Zeeuw, ESO's Director General. "We have built the most advanced ground-based optical observatory in the world, thanks to the combination of a long-term adequately-funded instrument and technology development plan with an approach where most of the instruments were built in collaboration with institutions in the member states, with in-kind contributions in labour compensated by guaranteed observing time." Sitting atop the 2600m high Paranal Mountain in the Chilean Atacama Desert, the VLT's design, suite of instruments, and operating principles set the standard for ground-based astronomy. It provides the European scientific community with a telescope array with collecting power significantly greater than any other facilities available at present, offering imaging and spectroscopy capabilities at visible and infrared wavelengths. Blue Flash at Paranal ESO PR Photo 16b/08 A Universe of Discoveries The first scientifically useful images, marking the official 'First Light' of the VLT, were obtained on the night of 25 to 26 May 1998, with a test camera attached to "Antu", Unit Telescope number 1. They were officially presented to the press on
Miloch, W. J.; Pecseli, H. L.; Trulsen, J.; Vladimirov, S. V.
2008-09-07
The parameter dependence of the ion focus behind perfectly conducting or alternatively perfectly insulating spherical grains for different electron to ion temperature ratios is studied. For elongated, insulating dust grains we study the potential and plasma density wakes in drifting plasma for rods or plates of different lengths and different inclination angles. These two characteristics (i.e., the rod length and the inclination angle are important for the exact charge distribution on the surface and the wake pattern. For this case we discuss also the interaction potential between two elongated grains in a flowing plasma.Our simulations are carried out in two spatial dimensions by a Particle-in-Cell code, treating ions and electrons as individual particles. These studies can be relevant for finite size dust grains suspended in a plasma sheath or larger objects in space, e.g., meteoroids.
Solute drag on perfect and extended dislocations
NASA Astrophysics Data System (ADS)
Sills, R. B.; Cai, W.
2016-04-01
The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.
A perfect launch viewed across Banana Creek
NASA Technical Reports Server (NTRS)
2000-01-01
Billows of smoke and steam surround Space Shuttle Discovery as it lifts off from Launch Pad 39A on mission STS-92 to the International Space Station. The perfect on-time liftoff occurred at 7:17 p.m. EDT, sending a crew of seven on the 100th launch in the history of the Shuttle program. Discovery carries a payload that includes the Integrated Truss Structure Z-1, first of 10 trusses that will form the backbone of the Space Station, and the third Pressurized Mating Adapter that will provide a Shuttle docking port for solar array installation on the sixth Station flight and Lab installation on the seventh Station flight. Discovery's landing is expected Oct. 22 at 2:10 p.m. EDT.
A perfect launch viewed across Banana Creek
NASA Technical Reports Server (NTRS)
2000-01-01
Space Shuttle Discovery seems to burst forth from a pillow of smoke as it lifts off from Launch Pad 39A on mission STS-92 to the International Space Station. The brilliant light from the solid rocket booster flames is reflected in nearby water. The perfect on-time liftoff occurred at 7:17 p.m. EDT, sending a crew of seven on the 100th launch in the history of the Shuttle program. Discovery carries a payload that includes the Integrated Truss Structure Z-1, first of 10 trusses that will form the backbone of the Space Station, and the third Pressurized Mating Adapter that will provide a Shuttle docking port for solar array installation on the sixth Station flight and Lab installation on the seventh Station flight. Discovery's landing is expected Oct. 22 at 2:10 p.m. EDT.
Filtering with perfectly correlated measurement noise.
NASA Technical Reports Server (NTRS)
Reasenberg, R.
1972-01-01
Examination of (radar) Doppler data which are formed by mi1ing the returning microwave signal with a replica of the transmitted signal, counting the cycles of the beat, and sampling the counter at evenly spaced intervals t sub i. It is shown that the amount of information which can be extracted from a set of data may be larger if the associated noise is perfectly correlated than if it is white, and that the use of the white noise assumption in the filter may result in the loss of some of this information.
Beam expander telescope design utilizing fast spherical primaries.
Southwell, W H
1979-04-15
An exact geometrical ray analysis has been used to derive the profiles for telescope secondaries that perfectly recollimate beams incident on fast concave spherical mirrors. Both Cassegrainian and Gregorian configurations are possible. The high magnification designs tend to redistribute the energy profile and may be used, for example, to make Gaussian beams more uniform. PMID:20208915
Beam expander telescope design utilizing fast spherical primaries.
Southwell, W H
1979-04-15
An exact geometrical ray analysis has been used to derive the profiles for telescope secondaries that perfectly recollimate beams incident on fast concave spherical mirrors. Both Cassegrainian and Gregorian configurations are possible. The high magnification designs tend to redistribute the energy profile and may be used, for example, to make Gaussian beams more uniform.
All static spherically symmetric anisotropic solutions of Einstein's equations
Herrera, L.; Di Prisco, A.; Ospino, J.
2008-01-15
An algorithm recently presented by Lake to obtain all static spherically symmetric perfect fluid solutions is extended to the case of locally anisotropic fluids (principal stresses unequal). As expected, the new formalism requires the knowledge of two functions (instead of one) to generate all possible solutions. To illustrate the method some known cases are recovered.
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.
Dynamics of microparticles trapped in a perfect vortex beam.
Chen, Mingzhou; Mazilu, Michael; Arita, Yoshihiko; Wright, Ewan M; Dholakia, Kishan
2013-11-15
We analyze microparticle dynamics within a "perfect" vortex beam. In contrast to other vortex fields, for any given integer value of the topological charge, a "perfect" vortex beam has the same annular intensity profile with fixed radius of peak intensity. For a given topological charge, the field possesses a well-defined orbital angular momentum density at each point in space, invariant with respect to azimuthal position. We experimentally create a perfect vortex and correct the field in situ, to trap and set in motion trapped microscopic particles. For a given topological charge, a single trapped particle exhibits the same local angular velocity moving in such a field independent of its azimuthal position. We also investigate particle dynamics in "perfect" vortex beams of fractional topological charge. This light field may be applied for novel studies in optical trapping of particles, atoms, and quantum gases.
Extreme super-resolution using the spherical geodesic waveguide
NASA Astrophysics Data System (ADS)
Miñano, Juan Carlos; González, Juan Carlos; Benítez, Pablo; Grabovičkić, Dejan
2012-06-01
Leonhardt demonstrated (2009) that the 2D Maxwell Fish Eye lens (MFE) can focus perfectly 2D Helmholtz waves of arbitrary frequency, i.e., it can transport perfectly an outward (monopole) 2D Helmholtz wave field, generated by a point source, towards a "perfect point drain" located at the corresponding image point. Moreover, a prototype with λ/5 super-resolution (SR) property for one microwave frequency has been manufactured and tested (Ma et al, 2010). Although this prototype has been loaded with an impedance different from the "perfect point drain", it has shown super-resolution property. However, neither software simulations nor experimental measurements for a broad band of frequencies have yet been reported. Here we present steady state simulations for two cases, using perfect drain as suggested by Leonhardt and without perfect drain as in the prototype. All the simulations have been done using a device equivalent to the MFE, called the Spherical Geodesic Waveguide (SGW). The results show the super-resolution up to λ/3000, for the system loaded with the perfect drain, and up to λ /500 for a not perfect load. In both cases super-resolution only happens for discrete number of frequencies. Out of these frequencies, the SGW does not show super-resolution in the analysis carried out.
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.
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.
ERIC Educational Resources Information Center
Asher, Sandy
1995-01-01
Presents a script for a 1-act play about a 17-year-old girl whose mother neglects her and her alcoholic absentee father. Relates how the protagonist, Tara, becomes pregnant by a classmate who she barely knows, and plans to leave home to raise her child alone after graduating high school. (PA)
Design of spherical symmetric gradient index lenses
NASA Astrophysics Data System (ADS)
Miñano, Juan C.; Grabovičkić, Dejan; Benítez, Pablo; González, Juan C.; Santamaría, Asunción
2012-10-01
Spherical symmetric refractive index distributions also known as Gradient Index lenses such as the Maxwell-Fish-Eye (MFE), the Luneburg or the Eaton lenses have always played an important role in Optics. The recent development of the technique called Transformation Optics has renewed the interest in these gradient index lenses. For instance, Perfect Imaging within the Wave Optics framework has recently been proved using the MFE distribution. We review here the design problem of these lenses, classify them in two groups (Luneburg moveable-limits and fixed-limits type), and establish a new design techniques for each type of problem.
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.
Will a perfect model agree with perfect observations? The impact of spatial sampling
NASA Astrophysics Data System (ADS)
Schutgens, Nick A. J.; Gryspeerdt, Edward; Weigum, Natalie; Tsyro, Svetlana; Goto, Daisuke; Schulz, Michael; Stier, Philip
2016-05-01
The spatial resolution of global climate models with interactive aerosol and the observations used to evaluate them is very different. Current models use grid spacings of ˜ 200 km, while satellite observations of aerosol use so-called pixels of ˜ 10 km. Ground site or airborne observations relate to even smaller spatial scales. We study the errors incurred due to different resolutions by aggregating high-resolution simulations (10 km grid spacing) over either the large areas of global model grid boxes ("perfect" model data) or small areas corresponding to the pixels of satellite measurements or the field of view of ground sites ("perfect" observations). Our analysis suggests that instantaneous root-mean-square (RMS) differences of perfect observations from perfect global models can easily amount to 30-160 %, for a range of observables like AOT (aerosol optical thickness), extinction, black carbon mass concentrations, PM2.5, number densities and CCN (cloud condensation nuclei). These differences, due entirely to different spatial sampling of models and observations, are often larger than measurement errors in real observations. Temporal averaging over a month of data reduces these differences more strongly for some observables (e.g. a threefold reduction for AOT), than for others (e.g. a twofold reduction for surface black carbon concentrations), but significant RMS differences remain (10-75 %). Note that this study ignores the issue of temporal sampling of real observations, which is likely to affect our present monthly error estimates. We examine several other strategies (e.g. spatial aggregation of observations, interpolation of model data) for reducing these differences and show their effectiveness. Finally, we examine consequences for the use of flight campaign data in global model evaluation and show that significant biases may be introduced depending on the flight strategy used.
NASA Astrophysics Data System (ADS)
Tomassetti, Giuseppe; Cohen, Tal; Abeyaratne, Rohan
2016-11-01
Taking the cue from experiments on actin growth on spherical beads, we formulate and solve a model problem describing the accretion of an incompressible elastic solid on a rigid sphere due to attachment of diffusing free particles. One of the peculiar characteristics of this problem is that accretion takes place on the interior surface that separates the body from its support rather than on its exterior surface, and hence is responsible for stress accumulation. Simultaneously, ablation takes place at the outer surface where material is removed from the body. As the body grows, mechanical effects associated with the build-up of stress and strain energy slow down accretion and promote ablation. Eventually, the system reaches a point where internal accretion is balanced by external ablation. The present study is concerned with this stationary regime called "treadmilling". The principal ingredients of our model are: a nonstandard choice of the reference configuration, which allows us to cope with the continually evolving material structure; and a driving force and a kinetic law for accretion/ablation that involves the difference in chemical potential, strain energy and the radial stress. By combining these ingredients we arrive at an algebraic system which governs the stationary treadmilling state. We establish the conditions under which this system has a solution and we show that this solution is unique. Moreover, by an asymptotic analysis we show that for small beads the thickness of the solid is proportional to the radius of the support and is strongly affected by the stiffness of the solid, whereas for large beads the stiffness of the solid is essentially irrelevant, the thickness being proportional to a characteristic length that depends on the parameters that govern diffusion and accretion kinetics.
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.
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.
Effective perfect fluids in cosmology
Ballesteros, Guillermo; Bellazzini, Brando E-mail: brando.bellazzini@pd.infn.it
2013-04-01
We describe the cosmological dynamics of perfect fluids within the framework of effective field theories. The effective action is a derivative expansion whose terms are selected by the symmetry requirements on the relevant long-distance degrees of freedom, which are identified with comoving coordinates. The perfect fluid is defined by requiring invariance of the action under internal volume-preserving diffeomorphisms and general covariance. At lowest order in derivatives, the dynamics is encoded in a single function of the entropy density that characterizes the properties of the fluid, such as the equation of state and the speed of sound. This framework allows a neat simultaneous description of fluid and metric perturbations. Longitudinal fluid perturbations are closely related to the adiabatic modes, while the transverse modes mix with vector metric perturbations as a consequence of vorticity conservation. This formalism features a large flexibility which can be of practical use for higher order perturbation theory and cosmological parameter estimation.
Large displacement spherical joint
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.
Algorithmic Construction of Exact Solutions for Neutral Static Perfect Fluid Spheres
NASA Astrophysics Data System (ADS)
Hansraj, Sudan; Krupanandan, Daniel
2013-07-01
Although it ranks amongst the oldest of problems in classical general relativity, the challenge of finding new exact solutions for spherically symmetric perfect fluid spacetimes is still ongoing because of a paucity of solutions which exhibit the necessary qualitative features compatible with observational evidence. The problem amounts to solving a system of three partial differential equations in four variables, which means that any one of four geometric or dynamical quantities must be specified at the outset and the others should follow by integration. The condition of pressure isotropy yields a differential equation that may be interpreted as second-order in one of the space variables or also as first-order Ricatti type in the other space variable. This second option has been fruitful in allowing us to construct an algorithm to generate a complete solution to the Einstein field equations once a geometric variable is specified ab initio. We then demonstrate the construction of previously unreported solutions and examine these for physical plausibility as candidates to represent real matter. In particular we demand positive definiteness of pressure, density as well as a subluminal sound speed. Additionally, we require the existence of a hypersurface of vanishing pressure to identify a radius for the closed distribution of fluid. Finally, we examine the energy conditions. We exhibit models which display all of these elementary physical requirements.
NASA Astrophysics Data System (ADS)
Schulz-Weiling, Markus; Sadeghi, Hossein; Hung, Jachin; Grant, Edward
2016-10-01
This paper offers a toolbox for characterizing the initial conditions and predicting the evolution of the ultracold plasma that forms after resonant laser preparation of a Rydberg gas entrained in a differentially pumped supersonic molecular beam. The conditions afforded by a skimmed free-jet expansion combined with the geometry of laser excitation, determines the phase-space volume of the excited gas. A hydrodynamic shell model, that accounts for the ellipsoidal spatial distribution of this excitation volume in concert with the deforming effects of dissociative recombination, serves to simulate the ambipolar expansion of this molecular ultracold plasma.
Casimir interactions of an object inside a spherical metal shell
Zaheer, Saad; Rahi, Sahand Jamal; Emig, Thorsten; Jaffe, Robert L.
2010-03-15
We investigate the electromagnetic Casimir interactions of an object contained within an otherwise empty, perfectly conducting spherical shell. For a small object we present analytical calculations of the force, which is directed away from the center of the cavity, and the torque, which tends to align the object opposite to the preferred alignment outside the cavity. For a perfectly conducting sphere as the interior object, we compute the corrections to the proximity force approximation (PFA) numerically. In both cases the results for the interior configuration match smoothly onto those for the corresponding exterior configuration.
Optimizing imperfect cloaks to perfection.
Cai, Liang-Wu
2012-10-01
Transformation optics has been an essential tool for designing cloaking devices for electromagnetic and acoustic waves. All these designs have one requirement in common: material singularity. At the interface between the cloak and the cloaked region, some material properties have to approach infinity, while some others approach zero. This paper attempts to answer a central question in physically realizing such cloaks: is material singularity a requirement for perfect cloaking? This paper demonstrates that, through optimization, perfect cloaking can be achieved using a layered cloak construction without material singularity. Two examples are used for this demonstration. In one example, the initial design is based on the Cummer-Schurig prescription for acoustic cloaking that requires mass-anisotropic material. Another example uses the two isotropic layers to achieve the equivalent mass-anisotropy for each anisotropic layer. During the optimization processes, only material properties of cloaks' constituent layers are adjusted while the geometries remain unchanged. In both examples, the normalized total scattering cross section can be reduced to 0.002 (0.2%) or lower in numerical computations. The capabilities and other characteristics of the optimization in other tasks such as cloaking penetrable objects and isolating strong resonance in such objects are also explored. PMID:23039559
Spherical geodesic mesh generation
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.
Will a perfect global model agree with perfect observations?
NASA Astrophysics Data System (ADS)
Schutgens, N.; Gryspeerdt, E.; Tsyro, S.; Weigum, N.; Partridge, D.; Goto, D.; Schulz, M.; Stier, P.
2015-12-01
Global aerosol models and observations differ strongly in their spatio-temporal sampling. Model results are typical of large gridboxes (200 by 200 km), while observations are made over much smaller areas (e.g. 10 by 10 km for MODIS, even smaller for ground sites). Model results are always available in contrast to observations that are intermittent due to orbital constraints, retrieval limitations and instrument failure/maintenance. These twin issues of temporal sampling and spatial aggregation are relevant for any observation, be it remotely sensed, or in-situ. We ask this question: will a perfect model agree with perfect observations? The short answer is: unlikely. Using two different modelling frame-works (year-long global model runs collocated with actual observations and month-long high resolution regional models runs) we show that significant errors can be introduced in a model to observation comparison due to different spatio-temporal sampling. These sampling errors are typically larger than observational errors and are of comparable size as true model errors. While the temporal sampling issue can be dealt with by properly resampling model data to observation times, the spatial aggregation issue introduces noise into the comparison. We propose and evaluate several strategies for mitigating this noise. The most succesfull strategy is further temporal averaging of the data. However, this seems to have a less benefical effect on surface in-situ observations than on remotely sensed column-integrated measurements. For instance, monthly averaged black carbon mass concentrations measured at ground sites still allow significant (~ 30%) noise into the comparison. Furthermore, flight campaign data, by its nature, are not open to long-term (monthly, yearly) averaging and allow sampling errors of 50% or more in black carbon mass concentrations. Other observables (AOT, extinction profiles, number densities, PM2.5, CCN) will also be discussed.
Naked singularities in self-similar spherical gravitational collapse
Ori, A.; Piran, T.
1987-11-09
We present general-relativistic solutions of self-similar spherical collapse of an adiabatic perfect fluid. We show that if the equation of state is soft enough (GAMMA-1<<1), a naked singularity forms. The singularity resembles the shell-focusing naked singularities that arise in dust collapse. This solution increases significantly the range of matter fields that should be ruled out in order that the cosmic-censorship hypothesis will hold.
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.
Retroreflector spherical satellite
NASA Astrophysics Data System (ADS)
Akentyev, A. S.; Vasiliev, V. P.; Sadovnikov, M. A.; Sokolov, A. L.; Shargorodskiy, V. D.
2015-10-01
Specific features of spherical retroreflector arrays for high-precision laser ranging are considered, and errors in distance measurements are analyzed. A version of a glass retroreflector satellite with a submillimeter "target error" is proposed. Its corner cube reflectors are located in depressions to reduce the working angular aperture, and their faces have a dielectric interference coating.
Revisiting perfect fluid dark matter: Observational constraints from our galaxy
NASA Astrophysics Data System (ADS)
Potapov, Alexander A.; Garipova, Guzel M.; Nandi, Kamal K.
2016-02-01
We revisit certain features of an assumed spherically symmetric perfect fluid dark matter halo in the light of the observed data of our galaxy, the Milky Way (MW). The idea is to apply the Faber-Visser approach of combined observations of rotation curves and lensing to a first post-Newtonian approximation to "measure" the equation of state ω (r) of the perfect fluid galactic halo. However, for the model considered here, no constraints from lensing are used as it will be sufficient to consider only the rotation curve observations. The lensing mass together with other masses will be just computed using recent data. Since the halo has attractive gravity, we shall impose the constraint that ω (r) ≥ 0 for r ≤RMW, where RMW ˜ 200 kpc is the adopted halo radius of our galaxy. The observed circular velocity ℓ (= 2 vc2 / c02) from the flat rotation curve and a crucial adjustable parameter D appearing in the perfect fluid solution then yield different numerical ranges of ω (r). It is demonstrated that the computed observables such as the rotation curve mass, the lens mass, the post-Newtonian mass of our galaxy compare well with the recent mass data. We also calculate the Faber-Visser χ-factor, which is a measure of pressure content in the dark matter. Our analysis indicates that a range 0 ≤ ω (r) ≤ 2.8 ×10-7 for the perfect fluid dark matter can reasonably describe the attractive galactic halo. This is a strong constraint indicating a dust-like CDM halo (ω ˜ 0) supported also by CMB constraints.
Perfect fluid and scalar field in the Reissner-Nordstroem metric
Babichev, E. O.; Dokuchaev, V. I. Eroshenko, Yu. N.
2011-05-15
We describe the spherically symmetric steady-state accretion of perfect fluid in the Reissner-Nordstroem metric. We present analytic solutions for accretion of a fluid with linear equations of state and of the Chaplygin gas. We also show that under reasonable physical conditions, there is no steady-state accretion of a perfect fluid onto a Reissner-Nordstroem naked singularity. Instead, a static atmosphere of fluid is formed. We discuss a possibility of violation of the third law of black hole thermodynamics for a phantom fluid accretion.
Conformal and traversable wormholes with monopole and perfect fluid in f(R)-gravity
NASA Astrophysics Data System (ADS)
Taşer, Doǧukan; Doǧru, Melis Ulu
2016-10-01
We investigate spherically symmetric spacetime filled with global monopole and perfect fluid in f(R)-gravity. We consider field equations of f(R)-gravity in order to understand the global monopole and the perfect fluid curve to the spacetime. It has taken advantages of conformal symmetry properties of the spacetime to solve these equations. The obtained solutions are improved in case of phantom energy. It is shown that obtained f(R) function is consistent with well-known models of the modified gravity. Also, it is examined whether the obtained solutions support a traversable wormhole geometry. Obtained results of the solutions have been concluded.
Zonal spherical aberration correction utilizing axial electrodes
NASA Astrophysics Data System (ADS)
Chao, Liang C.
2005-01-01
Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents because it results in large tails on the current density distribution. Merwe has shown that for coaxial lenses, negative spherical aberration can be found for rays pass through zonal regions. Merwe"s calculation is valid only for periodic or quasi-periodic lenses and requires a constant axial potential distribution. We have calculated zonal focusing properties of lenses with axial electrodes using nine-point finite difference method and direct ray tracing. Our calculation results indicate that an axial electrode protruding partially into the lens can correct the spherical aberration. When a three-element electrostatic lens is operated at deceleration mode, the introduction of an axial electrode creates zonal regions where the spherical aberration is negative. At deceleration mode, the induced surface charges on the axial electrode have an opposite sign relative to the primary beam. This is in agreement with our previous findings on the study of the correction of spherical aberration utilizing space charges. Same phenomenon was found when an axial electrode is used in conjunction with a cathode lens.
Quantum Perfect-Fluid Kaluza-Klein Cosmology
NASA Astrophysics Data System (ADS)
Huang, Wung-Hong; Wang, I.-Chin
The perfect-fluid cosmology in the (1+d+D)-dimensional Kaluza-Klein space-times for an arbitrary barotropic equation of state p = (γ-1)ρ is quantized by using the Schutz's variational formalism. We make efforts in the mathematics to solve the problems in two cases. In the first case of the stiff fluid γ = 2 we exactly solve the Wheeler-DeWitt equation when the d space is flat. After the superposition of the solutions the wave-packet function is obtained exactly. We analyze the Bohmian trajectories of the final-stage wave-packet functions and show that the scale functions of the flat d spaces and the compact D spaces will eventually evolve into the nonzero finite values. In the second case of γ≈2, we use the approximated wave function in the Wheeler-DeWitt equation to find the analytic forms of the final-stage wave-packet functions. After analyzing the Bohmian trajectories we show that the flat d spaces will be expanding forever while the scale function of the contracting D spaces would not become zero within finite time. Our investigations indicate that the quantum effect in the quantum perfect-fluid cosmology could prevent the extra compact D spaces in the Kaluza-Klein theory from collapsing into a singularity or that the "crack-of-doom" singularity of the extra compact dimensions is made to occur at t = ∞.
Hollow spherical shell manufacture
O'Holleran, T.P.
1991-11-26
A process is disclosed for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry. 3 figures.
Hollow spherical shell manufacture
O'Holleran, Thomas P.
1991-01-01
A process for making a hollow spherical shell of silicate glass composition in which an aqueous suspension of silicate glass particles and an immiscible liquid blowing agent is placed within the hollow spherical cavity of a porous mold. The mold is spun to reduce effective gravity to zero and to center the blowing agent, while being heated so as to vaporize the immiscible liquid and urge the water carrier of the aqueous suspension to migrate into the body of the mold, leaving a green shell compact deposited around the mold cavity. The green shell compact is then removed from the cavity, and is sintered for a time and a temperature sufficient to form a silicate glass shell of substantially homogeneous composition and uniform geometry.
Spherical torus fusion reactor
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.
Spherical torus fusion reactor
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.
Spherical torus experiment (STX)
McManamy, T.J.; Lazarus, E.A.
1985-01-01
The principal engineering features of the proposed Spherical Torus Experiment (STX) are described. Design is dominated by the small bore available for the ohmic heating (OH) solenoid and structural considerations for a situation in which B/sub p/ is approximately equal to B/sub t/. Unique features of a spherical torus plasma include large elongations without shaping fields; an exceptionally high ratio of plasma current to toroidal field, giving the potential for stability at very high beta; strong paramagnetism; and a variety of configurations, ranging from tokamak (q/sub a/) to revised-field pinch (RFP) (q/sub a/ < 1). Access to this regime requires aspect ratios less than 2. A feasibility study has been done for a beam-heated device with A = 1.67, R0 = 0.45, and K = 2. 3 refs., 9 figs.
Optical design of zero-power Hubble Space Telescope wave-front correctors for null testing.
Hannan, P G; Davila, P; Wood, H J
1993-04-01
The optical design of the second-generation wide-field/planetary-camera instrument for the Hubble Space Telescope has been modified to compensate for the spherical aberration of the optical telescope assembly (OTA) by introduction of undercorrected spherical aberration into the wave front. This instrument can be tested in a simple manner to ensure that its aberration contribution has the proper sign and magnitude. We present designs for a near-zero power doublet lens that can be used to generate a spherically aberrated wave front that is similar to the OTA wave front. When this lens is used in combination with the instrument, a near-perfect or nulled wave front should be produced, resulting in a high-quality point image on axis. We also present lens designs for a similar test that can be performed on the OTA simulators now being built to verify the other second-generation instruments.
Optical design of zero-power Hubble Space Telescope wave-front correctors for null testing
NASA Technical Reports Server (NTRS)
Hannan, Paul G.; Davila, Pam; Wood, H. J.
1993-01-01
The optical design of the second-generation wide-field/planetary-camera instrument for the Hubble Space Telescope has been modified to compensate for the spherical aberration of the optical telescope assembly (OTA) by introduction of undercorrected spherical aberration into the wave front. This instrument can be tested in a simple manner to ensure that its aberration contribution has the proper sign and magnitude. We present designs for a near-zero power doublet lens that can be used to generate a spherically aberrated wave front that is similar to the OTA wave front. When this lens is used in combination with the instrument, a near-perfect or nulled wave front should be produced, resulting in a high-quality point image on axis. We also present lens designs for a similar test that can be performed on the OTA simulators now being built to verify the other second-generation instruments.
Spherical nitroguanidine process
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.
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.
Turnable perfect absorption at infrared frequencies by a Graphene-hBN Hyper Crystal.
Wu, Jipeng; Jiang, Leyong; Guo, Jun; Dai, Xiaoyu; Xiang, Yuanjiang; Wen, Shuangchun
2016-07-25
In this article, we have theoretically demonstrated that the perfect absorption at infrared frequencies can be achieved and controlled by using a graphene-hexagonal Boron Nitride (hBN) hyper crystal. hBN, the latest natural hyperbolic material, can be regarded as an excellent substrate to form a hyper crystal with graphene. Although the perfect absorption by a half-space of hBN crystal can be achieved due to its high optical anisotropy, but the perfect absorption can only appear at certain fixed wavenumber and incidence angle. By introducing a graphene-hBN hyper crystal, we can get perfect absorption at different wavenumbers and incidence angles by varying the Fermi energy level of graphene sheets via electrostatic biasing. We show that the perfect absorption can be realized at different Fermi energies for TM waves. PMID:27464161
Spherical polytropic balls cannot mimic black holes
NASA Astrophysics Data System (ADS)
Saida, Hiromi; Fujisawa, Atsuhito; Yoo, Chul-Moon; Nambu, Yasusada
2016-04-01
The so-called black hole shadow is a dark region which is expected to appear in a fine image of optical observation of black holes. It is essentially an absorption cross section of the black hole, and the boundary of shadow is determined by unstable circular orbits of photons (UCOP). If there exists a compact object possessing UCOP but no black hole horizon, it can provide us with the same shadow image as black holes, and detection of a shadow image cannot be direct evidence of black hole existence. This paper examines whether or not such compact objects can exist under some suitable conditions. We investigate thoroughly the static spherical polytropic ball of perfect fluid with single polytrope index, and then investigate a representative example of a piecewise polytropic ball. Our result is that the spherical polytropic ball which we have investigated cannot possess UCOP, if the speed of sound at the center is subluminal (slower than light). This means that, if the polytrope treated in this paper is a good model of stellar matter in compact objects, the detection of a shadow image can be regarded as good evidence of black hole existence. As a by-product, we have found the upper bound of the mass-to-radius ratio of a polytropic ball with single index, M_{ast }/R_{ast } < 0.281, under the condition of subluminal sound speed.
Measuring Shell Resonances of Spherical Acoustic Resonators
NASA Astrophysics Data System (ADS)
Truong, D.; Sparasci, F.; Foltête, E.; Ouisse, M.; Pitre, L.
2011-01-01
Coupling between the gas and shell is a concern in the experiment used at LNE-CNAM to determine the Boltzmann constant k B by an acoustic method. As the walls of real resonators are not perfectly rigid, some perturbations occur in the frequency range of the acoustic resonances measured within helium gas contained in the cavity. As a contribution for a better understanding of this phenomenon, an experiment to measure the shell modes of the spherical resonators is in use in this laboratory. A work in progress to assess these modes using a hammer blow method together with modal analysis is reported here. The study is carried out with an air-filled, copper-walled, half-liter quasi-spherical resonator in the frequency range from 1 Hz to 20 kHz. Results show that the shell modes expand into multiple resonances of similar modal shape, including the "breathing" mode. The observations reported in other studies of shell perturbations at other frequencies than the breathing frequency are confirmed.
NASA Astrophysics Data System (ADS)
Chen, Menglin L. N.; Jiang, Li Jun; Sha, Wei E. I.
2016-02-01
Orbital angular momentum (OAM) is a promising degree of freedom for fundamental studies in electromagnetics and quantum mechanics. The unlimited state space of OAM shows a great potential to enhance channel capacities of classical and quantum communications. By exploring the Pancharatnam-Berry phase concept and engineering anisotropic scatterers in a metasurface with spatially varying orientations, a plane wave with zero OAM can be converted to a vortex beam carrying nonzero OAM. In this paper, we proposed two types of novel perfect electric conductor-perfect magnetic conductor anisotropic metasurfaces. One is composed of azimuthally continuous loops and the other is constructed by azimuthally discontinuous dipole scatterers. Both types of metasurfaces are mounted on a mushroom-type high impedance surface. Compared to previous metasurface designs for generating OAM, the proposed ones achieve nearly perfect conversion efficiency. In view of the eliminated vertical component of electric field, the continuous metasurface shows very smooth phase pattern at the near-field region, which cannot be achieved by convectional metasurfaces composed of discrete scatterers. On the other hand, the metasurface with discrete dipole scatterers shows a great flexibility to generate OAM with arbitrary topological charges. Our work is fundamentally and practically important to high-performance OAM generation.
Characterization of two-qubit perfect entanglers
Rezakhani, A.T.
2004-11-01
Here we consider perfect entanglers from another perspective. It is shown that there are some special perfect entanglers which can maximally entangle a full product basis. We explicitly construct a one-parameter family of such entanglers together with the proper product basis that they maximally entangle. This special family of perfect entanglers contains some well-known operators such as controlled-NOT (CNOT) and double-CNOT, but not {radical}(SWAP). In addition, it is shown that all perfect entanglers with entangling power equal to the maximal value (2/9) are also special perfect entanglers. It is proved that the one-parameter family is the only possible set of special perfect entanglers. Also we provide an analytic way to implement any arbitrary two-qubit gate, given a proper special perfect entangler supplemented with single-qubit gates. Such gates are shown to provide a minimum universal gate construction in that just two of them are necessary and sufficient in implementation of a generic two-qubit gate.
Computation of Thermally Perfect Compressible Flow Properties
NASA Technical Reports Server (NTRS)
Witte, David W.; Tatum, Kenneth E.; Williams, S. Blake
1996-01-01
A set of compressible flow relations for a thermally perfect, calorically imperfect gas are derived for a value of c(sub p) (specific heat at constant pressure) expressed as a polynomial function of temperature and developed into a computer program, referred to as the Thermally Perfect Gas (TPG) code. The code is available free from the NASA Langley Software Server at URL http://www.larc.nasa.gov/LSS. The code produces tables of compressible flow properties similar to those found in NACA Report 1135. Unlike the NACA Report 1135 tables which are valid only in the calorically perfect temperature regime the TPG code results are also valid in the thermally perfect, calorically imperfect temperature regime, giving the TPG code a considerably larger range of temperature application. Accuracy of the TPG code in the calorically perfect and in the thermally perfect, calorically imperfect temperature regimes are verified by comparisons with the methods of NACA Report 1135. The advantages of the TPG code compared to the thermally perfect, calorically imperfect method of NACA Report 1135 are its applicability to any type of gas (monatomic, diatomic, triatomic, or polyatomic) or any specified mixture of gases, ease-of-use, and tabulated results.
PERFECTLY MATCHED LAYERS FOR ELASTIC WAVES IN CYLINDRICAL AND SPHERICAL COORDINATES. (R825225)
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...
A quantum reduction to spherical symmetry in loop quantum gravity
NASA Astrophysics Data System (ADS)
Bodendorfer, N.; Lewandowski, J.; Świeżewski, J.
2015-07-01
Based on a recent purely geometric construction of observables for the spatial diffeomorphism constraint, we propose two distinct quantum reductions to spherical symmetry within full 3 + 1-dimensional loop quantum gravity. The construction of observables corresponds to using the radial gauge for the spatial metric and allows to identify rotations around a central observer as unitary transformations in the quantum theory. Group averaging over these rotations yields our first proposal for spherical symmetry. Hamiltonians of the full theory with angle-independent lapse preserve this spherically symmetric subsector of the full Hilbert space. A second proposal consists in implementing the vanishing of a certain vector field in spherical symmetry as a constraint on the full Hilbert space, leading to a close analogue of diffeomorphisms invariant states. While this second set of spherically symmetric states does not allow for using the full Hamiltonian, it is naturally suited to implement the spherically symmetric midisuperspace Hamiltonian, as an operator in the full theory, on it. Due to the canonical structure of the reduced variables, the holonomy-flux algebra behaves effectively as a one parameter family of 2 + 1-dimensional algebras along the radial coordinate, leading to a diagonal non-vanishing volume operator on 3-valent vertices. The quantum dynamics thus becomes tractable, including scenarios like spherically symmetric dust collapse.
Classical universes are perfectly predictable!
NASA Astrophysics Data System (ADS)
Schmidt, Jan Hendrik
I argue that in a classical universe, all the events that ever happen are encoded in each of the universe's parts. This conflicts with a statement which is widely believed to lie at the basis of relativity theory: that the events in a space-time region R determine only the events in R's domain of dependence but not those in other space-time regions. I show how, from this understanding, a new prediction method (which I call the 'Smoothness Method') can be obtained which allows us to predict future events on the basis of local observational data. Like traditional prediction methods, this method makes use of so-called ' ceteris paribus clauses', i.e. assumptions about the unobserved parts of the universe. However, these assumptions are used in a way which enables us to predict the behaviour of open systems with arbitrary accuracy, regardless of the influence of their environment-which has not been achieved by traditional methods. In a sequel to this paper (Schmidt, 1998), I will prove the Uniqueness and Predictability Theorems on which the Smoothness Method is based, and comment in more detail on its mathematical properties.
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.
Robustness of oscillatory α2 dynamos in spherical wedges
NASA Astrophysics Data System (ADS)
Cole, E.; Brandenburg, A.; Käpylä, P. J.; Käpylä, M. J.
2016-10-01
Context. Large-scale dynamo simulations are sometimes confined to spherical wedge geometries by imposing artificial boundary conditions at high latitudes. This may lead to spatio-temporal behaviours that are not representative of those in full spherical shells. Aims: We study the connection between spherical wedge and full spherical shell geometries using simple mean-field dynamos. Methods: We solve the equations for one-dimensional time-dependent α2 and α2Ω mean-field dynamos with only latitudinal extent to examine the effects of varying the polar angle θ0 between the latitudinal boundaries and the poles in spherical coordinates. Results: In the case of constant α and ηt profiles, we find oscillatory solutions only with the commonly used perfect conductor boundary condition in a wedge geometry, while for full spheres all boundary conditions produce stationary solutions, indicating that perfect conductor conditions lead to unphysical solutions in such a wedge setup. To search for configurations in which this problem can be alleviated we choose a profile of the turbulent magnetic diffusivity that decreases toward the poles, corresponding to high conductivity there. Oscillatory solutions are now achieved with models extending to the poles, but the magnetic field is strongly concentrated near the poles and the oscillation period is very long. By changing both the turbulent magnetic diffusivity and α profiles so that both effects are more concentrated toward the equator, we see oscillatory dynamos with equatorward drift, shorter cycles, and magnetic fields distributed over a wider range of latitudes. Those profiles thus remove the sensitive and unphysical dependence on θ0. When introducing radial shear, we again see oscillatory dynamos, and the direction of drift follows the Parker-Yoshimura rule. Conclusions: A reduced α effect near the poles with a turbulent diffusivity concentrated toward the equator yields oscillatory dynamos with equatorward migration and
Developments in Coherent Perfect Polarization Rotation
NASA Astrophysics Data System (ADS)
Crescimanno, Michael; Andrews, James; Zhou, Chaunhong; Baker, Michael
2015-05-01
Coherent Perfect Polarization Rotation (CPR) is a useful technique akin to Coherent Perfect Absorption (CPA, also known as the anti-laser) but that results in very high efficiency optical mode conversion. We describe the analysis of recent experimental data from our CPR testbed, the use of CPR in miniaturizing optical isolators and CPR phenomena in non-linear optics. Work supported by the N.S.F. under Grant No. ECCS-1360725.
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.
NASA Astrophysics Data System (ADS)
Lehtola, Susi; Parkhill, John; Head-Gordon, Martin
2016-10-01
Novel implementations based on dense tensor storage are presented for the singlet-reference perfect quadruples (PQ) [J. A. Parkhill et al., J. Chem. Phys. 130, 084101 (2009)] and perfect hextuples (PH) [J. A. Parkhill and M. Head-Gordon, J. Chem. Phys. 133, 024103 (2010)] models. The methods are obtained as block decompositions of conventional coupled-cluster theory that are exact for four electrons in four orbitals (PQ) and six electrons in six orbitals (PH), but that can also be applied to much larger systems. PQ and PH have storage requirements that scale as the square, and as the cube of the number of active electrons, respectively, and exhibit quartic scaling of the computational effort for large systems. Applications of the new implementations are presented for full-valence calculations on linear polyenes (CnHn+2), which highlight the excellent computational scaling of the present implementations that can routinely handle active spaces of hundreds of electrons. The accuracy of the models is studied in the π space of the polyenes, in hydrogen chains (H50), and in the π space of polyacene molecules. In all cases, the results compare favorably to density matrix renormalization group values. With the novel implementation of PQ, active spaces of 140 electrons in 140 orbitals can be solved in a matter of minutes on a single core workstation, and the relatively low polynomial scaling means that very large systems are also accessible using parallel computing.
Double slotted socket spherical joint
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.
Features of spherical torus plasmas
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.
Non-diffracting speckles of a perfect vortex beam
NASA Astrophysics Data System (ADS)
Gangi Reddy, Salla; P, Chithrabhanu; Vaity, Pravin; Aadhi, A.; Prabhakar, Shashi; Singh, R. P.
2016-05-01
We generate perfect optical vortex (POV) beams, whose intensity distribution is independent of the order, and scatter them through a rough surface. We show that the size of produced speckles is independent of the order of the POV and their Fourier transform gives the random non-diffracting fields. The invariant size of speckles over the free space propagation verifies their non-diffracting or non-diverging nature. The size of speckles can be easily controlled by changing the axicon parameter, used to generate the Bessel-Gauss beams whose Fourier transform provides the POV. These results may be useful in applications of POV for authentication in cryptography.
Hawking radiation from a spherical loop quantum gravity black hole
NASA Astrophysics Data System (ADS)
Gambini, Rodolfo; Pullin, Jorge
2014-06-01
We introduce quantum field theory on quantum space-times techniques to characterize the quantum vacua as a first step toward studying black hole evaporation in spherical symmetry in loop quantum gravity and compute the Hawking radiation. We use as quantum space-time the recently introduced exact solution of the quantum Einstein equations in vacuum with spherical symmetry and consider a spherically symmetric test scalar field propagating on it. The use of loop quantum gravity techniques in the background space-time naturally regularizes the matter content, solving one of the main obstacles to back-reaction calculations in more traditional treatments. The discreteness of area leads to modifications of the quantum vacua, eliminating the trans-Planckian modes close to the horizon, which in turn eliminates all singularities from physical quantities, like the expectation value of the stress-energy tensor. Apart from this, the Boulware, Hartle-Hawking and Unruh vacua differ little from the treatment on a classical space-time. The asymptotic modes near scri are reproduced very well. We show that the Hawking radiation can be computed, leading to an expression similar to the conventional one but with a high frequency cutoff. Since many of the conclusions concern asymptotic behavior, where the spherical mode of the field behaves in a similar way as higher multipole modes do, the results can be readily generalized to non spherically symmetric fields.
Immunomodulatory spherical nucleic acids.
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.
Buckling of spherical capsules.
Knoche, Sebastian; Kierfeld, Jan
2011-10-01
We investigate buckling of soft elastic capsules under negative pressure or for reduced capsule volume. Based on nonlinear shell theory and the assumption of a hyperelastic capsule membrane, shape equations for axisymmetric and initially spherical capsules are derived and solved numerically. A rich bifurcation behavior is found, which is presented in terms of bifurcation diagrams. The energetically preferred stable configuration is deduced from a least-energy principle both for prescribed volume and prescribed pressure. We find that buckled shapes are energetically favorable already at smaller negative pressures and larger critical volumes than predicted by the classical buckling instability. By preventing self-intersection for strongly reduced volume, we obtain a complete picture of the buckling process and can follow the shape from the initial undeformed state through the buckling instability into the fully collapsed state. Interestingly, the sequences of bifurcations and stable capsule shapes differ for prescribed volume and prescribed pressure. In the buckled state, we find a relation between curvatures at the indentation rim and the bending modulus, which can be used to determine elastic moduli from experimental shape analysis. PMID:22181297
Immunomodulatory spherical nucleic acids
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
Size-controlled growth of spherical nanoparticles of Y-doped BaZrO3 perovskite
NASA Astrophysics Data System (ADS)
Srinivas Reddy, G.; Bauri, Ranjit
2016-04-01
Yttrium-doped BaZrO3 (BZY) was processed by a simple yet effective chemical synthesis route that yielded perfectly spherical particles. The particle size was found to decrease with increasing molar concentration of cations in the solution. Thus, the process offered a great ease of controlling the particle size as well. The close control over morphology and size can provide an opportunity of tuning the properties of such particles. The average particle size as obtained from high-resolution scanning electron microscopy (HR-SEM) was 243, 206, 149, and 79 nm at 0.2, 0.5, 0.8, and 1 M concentration, respectively. At a processing temperature of 60 °C, the undesirable phases, BaCO3 and Zr1-xYxO2, were present along with BZY even after calcination at 600 °C, and it took a very long processing time (160 min) for complete phase formation. The BZY phase formed within 45 min at a reaction temperature of 90 °C and yielded phase pure powders on calcination at the same temperature (600 °C). The d-spacing (2.98 Å) obtained from the lattice fringes in high-resolution transmission electron microscopy (HR-TEM) confirmed the cubic perovskite phase of BaZrO3. The average crystallite size calculated from XRD analysis coupled with the TEM observations revealed that each spherical particle consists of only few crystallites.
S2HAT: Scalable Spherical Harmonic Transform Library
NASA Astrophysics Data System (ADS)
Stompor, Radek
2011-10-01
Many problems in astronomy and astrophysics require a computation of the spherical harmonic transforms. This is in particular the case whenever data to be analyzed are distributed over the sphere or a set of corresponding mock data sets has to be generated. In many of those contexts, rapidly improving resolutions of both the data and simulations puts increasingly bigger emphasis on our ability to calculate the transforms quickly and reliably. The scalable spherical harmonic transform library S2HAT consists of a set of flexible, massively parallel, and scalable routines for calculating diverse (scalar, spin-weighted, etc) spherical harmonic transforms for a class of isolatitude sky grids or pixelizations. The library routines implement the standard algorithm with the complexity of O(n^3/2), where n is a number of pixels/grid points on the sphere, however, owing to their efficient parallelization and advanced numerical implementation, they achieve very competitive performance and near perfect scalability. S2HAT is written in Fortran 90 with a C interface. This software is a derivative of the spherical harmonic transforms included in the HEALPix package and is based on both serial and MPI routines of its version 2.01, however, since version 2.5 this software is fully autonomous of HEALPix and can be compiled and run without the HEALPix library.
Perfect-fluid cosmologies with extra dimensions
NASA Astrophysics Data System (ADS)
Gleiser, Reinaldo J.; Diaz, Mario C.
1988-06-01
We give an analysis of the solutions of the n-dimensional vacuum Einstein equations with a metric in the form of a direct sum of a Friedmann-Robertson-Walker (FRW) metric and a Kasner-type Euclidean metric. The solutions are interpreted as four-dimensional perfect-fluid cosmological FRW models, using the simple ansatz proposed by Ibán~ez and Verdaguer. We first obtain the general solution for flat models. These are perfect-fluid solutions that can be made compatible with contraction of all the extra dimensions. The general compatibility of the field equations is then discussed. It is found that for n>5 both open and closed models admit a range of perfect-fluid solutions whose qualitative behavior is analyzed.
Quadratic quantum cosmology with Schutz' perfect fluid
NASA Astrophysics Data System (ADS)
Vakili, Babak
2010-01-01
We study the classical and quantum models of a Friedmann-Robertson-Walker (FRW) cosmology, coupled to a perfect fluid, in the context of the f(R) gravity. Using Schutz' representation for the perfect fluid, we show that, under a particular gauge choice, it may lead to the identification of a time parameter for the corresponding dynamical system. Moreover, this formalism gives rise to a Schrödinger-Wheeler-DeWitt (SWD) equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the wavefunction of the universe. In the case of f(R) = R2 (pure quadratic model), for some particular choices of the perfect fluid source, exact solutions to the SWD equation can be obtained and the corresponding results are compared to the usual f(R) = R model.
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.
Spherical Model for Turbulence
NASA Astrophysics Data System (ADS)
Mou, Chung-Yu.
A new set of models for homogeneous, isotropic turbulence is considered in which the Navier-Stokes equations for incompressible fluid flow are generalized to a set of N coupled equations in N velocity fields. It is argued that in order to be useful these models must embody a new group of symmetries, and a general formalism is laid out for their construction. The work is motivated by similar techniques that have had extraordinary success in improving the theoretical understanding of equilibrium phase transitions in condensed matter systems. The key result is that these models simplify when N is large. The so-called spherical limit, N to infty, can be solved exactly, yielding a closed pair of nonlinear integral equations for the response and correlation functions. These equations, known as Kraichnan's Direct Interaction Approximation (DIA) equations, are, for the first time, solved fully in the scale-invariant turbulent regime, and the implications of these solutions for real turbulence (N = 1) are discussed. In particular, it is argued that previously applied renormalization group techniques, based on an expansion in the exponent, y, that characterizes the driving spectrum, are incorrect, and that the Kolmogorov exponent zeta has a nontrivial dependence on N, with zeta(N toinfty) = {3over2}. This value is remarkably close to the experimental result, zeta~{5over3}, which must therefore result from higher order corrections in powers of {1over N}. Prospects for calculating these corrections are briefly discussed: though daunting, such a calculations would, for the first time, provide a controlled perturbation expansion for the Kolmogorov, and other, exponents. Our techniques may also be applied to other nonequilibrium dynamical problems, such as the KPZ equation for interface growth, and perhaps to turbulence in nonlinear wave systems.
Spherical model for turbulence
NASA Astrophysics Data System (ADS)
Mou, Chung-Yu
A new set of models for homogeneous, isotropic turbulence is considered in which the Navier-Stokes equations for incompressible fluid flow are generalized to a set of N coupled equations in N velocity fields. It is argued that in order to be useful these models must embody a new group of symmetries, and a general formalism is laid out for their construction. The work is motivated by similar techniques that have had extraordinary success in improving the theoretical understanding of equilibrium phase transitions in condensed matter systems. The key result is that these models simplify when N is large. The so-called spherical limit, N approaches infinity, can be solved exactly, yielding a closed pair of nonlinear integral equations for the response and correlation functions. These equations, known as Kraichnan's Direct Interaction Approximation (DIA) equations, are, for the first time, solved fully in the scale-invariant turbulent regime, and the implications of these solutions for real turbulence (N = 1) are discussed. In particular, it is argued that previously applied renormalization group techniques, based on an expansion in the exponent, y, that characterizes the driving spectrum, are incorrect, and that the Kolmogorov exponent zeta has a nontrivial dependence on N, with zeta(N approaches infinity) = 3/2. This value is remarkably close to the experimental result, zeta approximately equals 5/3, which must therefore result from higher order corrections in powers of 1/N. Prospects for calculating these corrections are briefly discussed: though daunting, such a calculation would, for the first time, provide a controlled perturbation expansion for the Kolmogorov, and other exponents. Our techniques may also be applied to other nonequilibrium dynamical problems, such as the KPZ equation for interface growth, and perhaps to turbulence in nonlinear wave systems.
NASA Astrophysics Data System (ADS)
Shabbir, Ghulam; Mahomed, F. M.; Qureshi, M. A.
2016-11-01
A study of proper projective symmetry in the most general form of non-static spherically symmetric space-time is given using direct integration and algebraic techniques. In this study, we show that when the above space-time admits proper projective symmetry it becomes a very special class of static spherically symmetric space-times.
Antenna system providing a spherical radiation pattern
NASA Technical Reports Server (NTRS)
Sickles, II, Louis (Inventor)
1993-01-01
An antenna system provides a substantially spherical radiation pattern about a structure located above ground level, by locating the individual radiation pattern of each of a plurality of individual antennae, each positioned to have a radiation pattern covering only a portion of the desired sphere, and then applying all antenna signals, during either transmission or reception time intervals, through space-diversity and/or time-diversity apparatus, to cause the patterns of all of the antennae to combine into the desired substantially-spherical pattern. The antennae may have substantially hemispherical patterns, with each antenna of a pair thereof being directed in a direction generally opposite to the other antenna of that pair. Time domain multiple access (TDMA) operation of a master system station, with transmission in different time slots for different portions of the coverage sphere, and selection of the strongest received signal from among all of the plurality N of signals simultaneously received by the plurality N of antennae, can provide the desired spherical radiation pattern in both the transmission and reception modes of operation.
Selective coherent perfect absorption in metamaterials
Nie, Guangyu; Shi, Quanchao; Zhu, Zheng; Shi, Jinhui
2014-11-17
We show multi-band coherent perfect absorption (CPA) in simple bilayered asymmetrically split ring metamaterials. The selectivity of absorption can be accomplished by separately excited electric and magnetic modes in a standing wave formed by two coherent counterpropagating beams. In particular, each CPA can be completely switched on/off by the phase of a second coherent wave. We propose a practical scheme for realizing multi-band coherent perfect absorption of 100% that is allowed to work from microwave to optical frequency.
Generation of perfect vectorial vortex beams.
Li, Peng; Zhang, Yi; Liu, Sheng; Ma, Chaojie; Han, Lei; Cheng, Huachao; Zhao, Jianlin
2016-05-15
We propose the concept of perfect vectorial vortex beams (VVBs), which not merely have intensity profile independent of the polarization order and the topological charge of spiral phase, but also have stable intensity profile and state of polarization (SoP) upon propagation. Utilizing a Sagnac interferometer, we approximately generate perfect VVBs with locally linear and elliptical polarizations, and demonstrate that such beams can keep their intensity profile and SoP at a certain propagation distance. These proposed VVBs can be expanded to encode information and quantum cryptography, as well as to enrich the conversion of spin and orbital angular momenta. PMID:27176963
Nearly perfect valley filter in silicene.
Zhang, Qingtian; Chan, K S; Long, Mengqiu
2016-02-10
We demonstrate theoretically how a perfect valley filter can be obtained in silicene under the effects of a ferromagnetic stripe and an electric field perpendicular to silicene. A ferromagnetic stripe or an electric field alone can not generate any valley polarization in silicene, but a combination of them can make a perfect valley filter. Two configurations, one with magnetization of the ferromagnetic stripe being perpendicular to the silicene plane and one being parallel to the current direction, are considered. Our proposed device is useful for the realization of a valley beam filter in the development of valleytronic devices.
Testing spherical evolution for modelling void abundances
NASA Astrophysics Data System (ADS)
Achitouv, Ixandra; Neyrinck, Mark; Paranjape, Aseem
2015-08-01
We compare analytical predictions of void volume functions to those measured from N-body simulations, detecting voids with the ZOBOV void finder. We push to very small, non-linear voids, below few Mpc radius, by considering the unsampled dark matter density field. We also study the case where voids are identified using haloes. We develop analytical formula for the void abundance of both the excursion set approach and the peaks formalism. These formulas are valid for random walks smoothed with a top-hat filter in real space, with a large class of realistic barrier models. We test the extent to which the spherical evolution approximation, which forms the basis of the analytical predictions, models the highly aspherical voids that occur in the cosmic web, and are found by a watershed-based algorithm such as ZOBOV. We show that the volume function returned by ZOBOV is quite sensitive to the choice of treatment of subvoids, a fact that has not been appreciated previously. For reasonable choices of subvoid exclusion, we find that the Lagrangian density δv of the ZOBOV voids - which is predicted to be a constant δv ≈ -2.7 in the spherical evolution model - is different from the predicted value, showing substantial scatter and scale dependence. This result applies to voids identified at z = 0 with effective radius between 1 and 10 h-1 Mpc. Our analytical approximations are flexible enough to give a good description of the resulting volume function; however, this happens for choices of parameter values that are different from those suggested by the spherical evolution assumption. We conclude that analytical models for voids must move away from the spherical approximation in order to be applied successfully to observations, and we discuss some possible ways forward.
Weak-field limit of Kaluza-Klein models with spherical compactification: Experimental constraints
NASA Astrophysics Data System (ADS)
Chopovsky, Alexey; Eingorn, Maxim; Zhuk, Alexander
2012-03-01
We investigate the classical gravitational tests for the six-dimensional Kaluza-Klein model with spherical (of a radius a) compactification of the internal space. The model contains also a bare multidimensional cosmological constant Λ6. The matter, which corresponds to this ansatz, can be simulated by a perfect fluid with the vacuum equation of state in the external space and an arbitrary equation of state with the parameter ω1 in the internal space. For example, ω1=1 and ω1=2 correspond to the monopole two-forms and the Casimir effect, respectively. In the particular case Λ6=0, the parameter ω1 is also absent: ω1=0. In the weak-field approximation, we perturb the background ansatz by a pointlike mass. We demonstrate that in the case ω1>0 the perturbed metric coefficients have the Yukawa-type corrections with respect to the usual Newtonian gravitational potential. The inverse square law experiments restrict the parameters of the model: a/ω1≲6×10-3cm. Therefore, in the Solar System the parameterized post-Newtonian parameter γ is equal to 1 with very high accuracy. Thus, our model satisfies the gravitational experiments (the deflection of light and the time delay of radar echoes) at the same level of accuracy as general relativity. We demonstrate also that our background matter provides the stable compactification of the internal space in the case ω1>0. However, if ω1=0, then the parameterized post-Newtonian parameter γ=1/3, which strongly contradicts the observations.
Directional Spherical Cherenkov Detector
NASA Technical Reports Server (NTRS)
Wrbanek, John D.; Fralick, Gustave C.; Wrbanek, Susan Y.
2010-01-01
A proposed radiation-detecting apparatus would provide information on the kinetic energies, directions, and electric charges of highly energetic incident subatomic particles. The apparatus was originally intended for use in measuring properties of cosmic rays in outer space, but could also be adapted to terrestrial uses -- for example, radiation dosimetry aboard high-altitude aircraft and in proton radiation therapy for treatment of tumors.
Spherical stellarator with plasma current
NASA Astrophysics Data System (ADS)
Moroz, Paul E.
1996-08-01
Recently proposed novel concept of a spherical stellarator (P. E. Moroz, ``Spherical stellarator configuration,'' to appear in Phys. Rev. Lett) is enhanced by adding the plasma current to the otherwise pure stellarator system. The coil configuration of this ultra low aspect ratio system differs from that of a spherical tokamak by inclination of external parts of the toroidal field coils. It is shown that the configuration considered possesses many attractive properties, including: wide flexibility of operating regimes, compact design and coil simplicity, good access to the plasma, closed vacuum flux surfaces with large enclosed volume, significant external rotational transform, strong magnetic well, and a high plasma β [β(0) in excess of 30%] equilibrium. It is shown that the bootstrap effect in a spherical stellarator, in principle, can supply the full plasma current required for the high-β equilibrium.
Toroidal equilibria in spherical coordinates
Tsui, K. H.
2008-11-15
The standard Grad-Shafranov equation for axisymmetric toroidal plasma equilibrium is customary expressed in cylindrical coordinates with toroidal contours, and through which benchmark equilibria are solved. An alternative approach to cast the Grad-Shafranov equation in spherical coordinates is presented. This equation, in spherical coordinates, is examined for toroidal solutions to describe low {beta} Solovev and high {beta} plasma equilibria in terms of elementary functions.
Consistent Comparisons between Monopoly and Perfect Competition.
ERIC Educational Resources Information Center
Skeath, Susan E.; And Others
1992-01-01
Identifies inconsistencies in treatments of the perfect competition, monopoly welfare comparison in textbooks for economics instruction. Argues for explanation of how experiments are being conducted and explicit identification of all underlying assumptions. Suggests straightforward analysis of the social cost of monopoly based on a comparison…
Life, Liberty, and the Pursuit of Perfection.
ERIC Educational Resources Information Center
Hess, Lisa Lawmaster
1994-01-01
Perfectionists are accustomed to success and afraid of failure, have feelings of worth inextricably tied to the products they produce, impose a great deal of pressure on themselves, and may actually learn perfectionism from their parents. Counseling can help perfectionists realize that excellence is achievable but perfection is not. (JDD)
Children Prefer Certain Individuals over Perfect Duplicates
ERIC Educational Resources Information Center
Hood, Bruce M.; Bloom, Paul.
2008-01-01
Adults value certain unique individuals--such as artwork, sentimental possessions, and memorabilia--more than perfect duplicates. Here we explore the origins of this bias in young children, by using a conjurer's illusion where we appear to produce identical copies of real-world objects. In Study 1, young children were less likely to accept an…
Perfect Day: A Meditation about Teaching
ERIC Educational Resources Information Center
Valadez, Gilbert
2004-01-01
When asked by a student in a seminar recently if he could remember a perfect day teaching elementary school, the author writes memories of one he distinctly remembers because he gained new insight into teaching on that particular day. After returning to work following the devastating loss of a younger 19 year-old brother in a car crash, he resumed…
Mechanical Energy Changes in Perfectly Inelastic Collisions
ERIC Educational Resources Information Center
Mungan, Carl E.
2013-01-01
Suppose a block of mass "m"[subscript 1] traveling at speed "v"[subscript 1] makes a one-dimensional perfectly inelastic collision with another block of mass "m"[subscript 2]. What else does one need to know to calculate the fraction of the mechanical energy that is dissipated in the collision? (Contains 1 figure.)
A Reappraisal of the Nobody's Perfect Program
ERIC Educational Resources Information Center
Kennett, Deborah J.; Chislett, Gail; Olver, Ashley L. S.
2012-01-01
Nobody's Perfect Program (NP), involving 46 participants, was conducted from the spring of 2007 to the fall of 2009 in Peterborough, Canada. Prior to the program, parents completed demographic information, along with self-report measures assessing learned resourcefulness, the types of interactions with their children, parent resourcefulness,…
Maple Explorations, Perfect Numbers, and Mersenne Primes
ERIC Educational Resources Information Center
Ghusayni, B.
2005-01-01
Some examples from different areas of mathematics are explored to give a working knowledge of the computer algebra system Maple. Perfect numbers and Mersenne primes, which have fascinated people for a very long time and continue to do so, are studied using Maple and some questions are posed that still await answers.
Casimir energy for a double spherical shell: A global mode sum approach
NASA Astrophysics Data System (ADS)
Miltão, M. S. R.
2008-09-01
In this work we study the configuration of two perfectly conducting spherical shells. This is a problem of basic importance to make possible development of experimental apparatuses that they make possible to measure the spherical Casimir effect, an open subject. We apply the mode sum method via cutoff exponential function regularization with two independent parameters: one to regularize the infinite order sum of the Bessel functions; other, to regularize the integral that becomes related, due to the argument theorem, with the infinite zero sum of the Bessel functions. We obtain a general expression of the Casimir energy as a quadrature sum. We investigate two immediate limit cases as a consistency test of the expression obtained: that of a spherical shell and that of two parallel plates. In the approximation of a thin spherical shell we obtain an expression that allows to relate our result with that of the proximity-force approximation, supplying a correction to this result.
Stability analysis of self-similar behaviors in perfect fluid gravitational collapse
Mitsuda, Eiji; Tomimatsu, Akira
2006-06-15
Stability of self-similar solutions for gravitational collapse is an important problem to be investigated from the perspectives of their nature as an attractor, critical phenomena, and instability of a naked singularity. In this paper we study spherically symmetric non-self-similar perturbations of matter and metrics in spherically symmetric self-similar backgrounds. The collapsing matter is assumed to be a perfect fluid with the equation of state P={alpha}{rho}. We construct a single wave equation governing the perturbations, which makes their time evolution in arbitrary self-similar backgrounds analytically tractable. Further we propose an analytical application of this master wave equation to the stability problem by means of the normal mode analysis for the perturbations having the time dependence given by exp(i{omega}log vertical t vertical bar), and present some sufficient conditions for the absence of nonoscillatory unstable normal modes with purely imaginary {omega}.
Spherically symmetric conformal gravity and ''gravitational bubbles''
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.
3DHZETRN: Shielded ICRU spherical phantom
NASA Astrophysics Data System (ADS)
Wilson, John W.; Slaba, Tony C.; Badavi, Francis F.; Reddell, Brandon D.; Bahadori, Amir A.
2015-01-01
A computationally efficient 3DHZETRN code capable of simulating High (H) Charge (Z) and Energy (HZE) and light ions (including neutrons) under space-like boundary conditions with enhanced neutron and light ion propagation was recently developed for a simple homogeneous shield object. Monte Carlo benchmarks were used to verify the methodology in slab and spherical geometry, and the 3D corrections were shown to provide significant improvement over the straight-ahead approximation in some cases. In the present report, the new algorithms with well-defined convergence criteria are extended to inhomogeneous media within a shielded tissue slab and a shielded tissue sphere and tested against Monte Carlo simulation to verify the solution methods. The 3D corrections are again found to more accurately describe the neutron and light ion fluence spectra as compared to the straight-ahead approximation. These computationally efficient methods provide a basis for software capable of space shield analysis and optimization.
Spherical tensor analysis of nuclear magnetic resonance signals.
van Beek, Jacco D; Carravetta, Marina; Antonioli, Gian Carlo; Levitt, Malcolm H
2005-06-22
In a nuclear magnetic-resonance (NMR) experiment, the spin density operator may be regarded as a superposition of irreducible spherical tensor operators. Each of these spin operators evolves during the NMR experiment and may give rise to an NMR signal at a later time. The NMR signal at the end of a pulse sequence may, therefore, be regarded as a superposition of spherical components, each derived from a different spherical tensor operator. We describe an experimental method, called spherical tensor analysis (STA), which allows the complete resolution of the NMR signal into its individual spherical components. The method is demonstrated on a powder of a (13)C-labeled amino acid, exposed to a pulse sequence generating a double-quantum effective Hamiltonian. The propagation of spin order through the space of spherical tensor operators is revealed by the STA procedure, both in static and rotating solids. Possible applications of STA to the NMR of liquids, liquid crystals, and solids are discussed. PMID:16035785
Spherical-wave expansions of piston-radiator fields.
Wittmann, R C; Yaghjian, A D
1991-09-01
Simple spherical-wave expansions of the continuous-wave fields of a circular piston radiator in a rigid baffle are derived. These expansions are valid throughout the illuminated half-space and are useful for efficient numerical computation in the near-field region. Multipole coefficients are given by closed-form expressions which can be evaluated recursively.
Stability and superluminality of spherical DBI Galileon solutions
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.
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
Perfect drain for the Maxwell fish eye lens
NASA Astrophysics Data System (ADS)
González, Juan C.; Benítez, Pablo; Miñano, Juan C.
2011-02-01
Perfect imaging of electromagnetic waves using the Maxwell fish eye (MFE) requires a new concept: a point called the perfect drain that we shall call the perfect point drain. From the mathematical point of view, a perfect point drain is just like an ideal point source, except that it drains power from the electromagnetic field instead of generating it. We introduce here the perfect drain for the MFE as a dissipative region of non-zero size that completely drains the power from the point source. To accomplish this goal, the region must have a precise complex permittivity that depends on its size as well as on the frequency. The perfect point drain is obtained when the diameter of the perfect drain tends to zero. This interpretation of the perfect point drain is connected well with common concepts of electromagnetic theory, opening up both modeling in computer simulations and experimental verification of setups containing a perfect point drain.
Structured Metal Film as Perfect Absorber
NASA Astrophysics Data System (ADS)
Xiong, Xiang; Jiang, Shang-Chi; Peng, Ru-Wen; Wang, Mu
2014-03-01
With standing U-shaped resonators, fish-spear-like resonator has been designed for the first time as the building block to assemble perfect absorbers. The samples have been fabricated with two-photon polymerization process and FTIR measurement results support the effectiveness of the perfect absorber design. In such a structure the polarization-dependent resonance occurs between the tines of the spears instead of the conventional design where the resonance occurs between the metallic layers separated by a dielectric interlayer. The incident light neither transmits nor reflects back which results in unit absorbance. The power of light is trapped between the tines of spears and finally be absorbed. The whole structure is covered with a continuous metallic layer with good thermo-conductance, which provides an excellent approach to deal with heat dissipation, is enlightening in exploring metamaterial absorbers.
Basics of perfect communication through quantum networks
Kay, Alastair
2011-08-15
Perfect transfer of a quantum state through a one-dimensional chain is now well understood, allowing one not only to decide whether a fixed Hamiltonian achieves perfect transfer but to design a suitable one. We are particularly interested in being able to design, or understand the limitations imposed upon, Hamiltonians subject to various naturally arising constraints such as a limited coupling topology with low connectivity (specified by a graph) and type of interaction. In this paper, we characterize the necessary and sufficient conditions for transfer through a network and describe some natural consequences such as the impossibility of routing between many different recipients for a large class of Hamiltonians and the limitations on transfer rate. We also consider some of the trade-offs that arise in uniformly coupled networks (both Heisenberg and XX models) between transfer distance and the size of the network as a consequence of the derived conditions.
The Erythrocyte Ghost Is a Perfect Osmometer
Kwant, W. O.; Seeman, Philip
1970-01-01
The osmotic swelling of intact erythrocytes in hypotonic solutions was measured using microhematocrit tubes, Van Allen tubes, and a calibrated Coulter counter. In agreement with earlier workers the intact cells did not behave as perfect osmometers, the cells swelling less than predicted by the Boyle-van't Hoff law. Erythrocyte ghosts were prepared from fresh intact erythrocytes by one-step hemolysis in 0.25% NaCl at an extremely dilute concentration of cells and the membranes were sealed at 37°. The ghosts were mixed with NaCl solutions of different osmolarities and the MCV (mean cell volume) of the shrunken cells immediately monitored by a calibrated Coulter counter. It was found that the MCV values of the shrunken ghosts were accurately predicted by the Boyle-van't Hoff law. These results indicate that these erythrocyte ghosts behaved as perfect osmometers. PMID:5413078
Does negative refraction make a perfect lens?
NASA Astrophysics Data System (ADS)
Ramm, A. G.
2008-10-01
A discussion of a question, studied earlier by Veselago in 1967 and by Pendry in 2000, is given. The question is: can a slab of the material with negative refraction make a perfect lens? Pendry's conclusion was: yes, it can. Our conclusion is: no, in practice it cannot, because of the fluctuations of the refraction coefficient of the slab. Resolution ability of linear isoplanatic optical instruments is discussed.
Comment on 'Perfect imaging without negative refraction'
NASA Astrophysics Data System (ADS)
Blaikie, R. J.
2010-05-01
The prediction of 'perfect' imaging without negative refraction for Maxwell's fish-eye lens (Leonhardt U 2009 New J. Phys. 11 093040) is a consequence of imposing an active localized 'drain' at the image point rather than being a general property of the lens. This work then becomes analogous to other work using time-reversal symmetry and/or structured antennae to achieve super-resolution, which can be applied to many types of imaging system beyond the fish-eye lens.
The perfect machine. Building the Palomar telescope.
NASA Astrophysics Data System (ADS)
Florence, R.
The author's chronicle of the conception of the great 200-inch Palomar telescope is an inspiring account of the birth of big science and of America at its can-do apex. Countless scientists, engineers, administrators, and workmen - from Edwin Hubble, John D. Rockefeller, Elihu Root, and Andrew Carnegie, to unemployed laborers - come alive in this story of two decades of effort to create "the perfect machine".
Taming electromagnetic metamaterials for isotropic perfect absorbers
NASA Astrophysics Data System (ADS)
Anh, Doan Tung; Viet, Do Thanh; Trang, Pham Thi; Thang, Nguyen Manh; Quy, Ho Quang; Hieu, Nguyen Van; Lam, Vu Dinh; Tung, Nguyen Thanh
2015-07-01
Conventional metamaterial absorbers, which consist of a dielectric spacer sandwiched between metamaterial resonators and a metallic ground plane, have been inherently anisotropic. In this paper, we present an alternative approach for isotropic perfect absorbers using symmetric metamaterial structures. We show that by systematically manipulating the electrically and magnetically induced losses, one can achieve a desired absorption without breaking the structural homogeneity. Finite integration simulations and standard retrieval method are performed to elaborate on our idea.
Optimal Feedback Controlled Assembly of Perfect Crystals.
Tang, Xun; Rupp, Bradley; Yang, Yuguang; Edwards, Tara D; Grover, Martha A; Bevan, Michael A
2016-07-26
Perfectly ordered states are targets in diverse molecular to microscale systems involving, for example, atomic clusters, protein folding, protein crystallization, nanoparticle superlattices, and colloidal crystals. However, there is no obvious approach to control the assembly of perfectly ordered global free energy minimum structures; near-equilibrium assembly is impractically slow, and faster out-of-equilibrium processes generally terminate in defective states. Here, we demonstrate the rapid and robust assembly of perfect crystals by navigating kinetic bottlenecks using closed-loop control of electric field mediated crystallization of colloidal particles. An optimal policy is computed with dynamic programming using a reaction coordinate based dynamic model. By tracking real-time stochastic particle configurations and adjusting applied fields via feedback, the evolution of unassembled particles is guided through polycrystalline states into single domain crystals. This approach to controlling the assembly of a target structure is based on general principles that make it applicable to a broad range of processes from nano- to microscales (where tuning a global thermodynamic variable yields temporal control over thermal sampling of different states via their relative free energies).
A note on perfect scalar fields
NASA Astrophysics Data System (ADS)
Unnikrishnan, Sanil; Sriramkumar, L.
2010-05-01
We derive a condition on the Lagrangian density describing a generic, single, noncanonical scalar field, by demanding that the intrinsic, nonadiabatic pressure perturbation associated with the scalar field vanishes identically. Based on the analogy with perfect fluids, we refer to such fields as perfect scalar fields. It is common knowledge that models that depend only on the kinetic energy of the scalar field (often referred to as pure kinetic models) possess no nonadiabatic pressure perturbation. While we are able to construct models that seemingly depend on the scalar field and also do not contain any nonadiabatic pressure perturbation, we find that all such models that we construct allow a redefinition of the field under which they reduce to pure kinetic models. We show that, if a perfect scalar field drives inflation, then, in such situations, the first slow roll parameter will always be a monotonically decreasing function of time. We point out that this behavior implies that these scalar fields cannot lead to features in the inflationary, scalar perturbation spectrum.
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.
Coherent perfect absorption in one-sided reflectionless media
Wu, Jin-Hui; Artoni, M.; La Rocca, G. C.
2016-01-01
In optical experiments one-sided reflectionless (ORL) and coherent perfect absorption (CPA) are unusual scattering properties yet fascinating for their fundamental aspects and for their practical interest. Although these two concepts have so far remained separated from each other, we prove that the two phenomena are indeed strictly connected. We show that a CPA–ORL connection exists between pairs of points lying along lines close to each other in the 3D space-parameters of a realistic lossy atomic photonic crystal. The connection is expected to be a generic feature of wave scattering in non-Hermitian optical media encompassing, as a particular case, wave scattering in parity-time (PT) symmetric media. PMID:27759020
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…
Trapped surfaces in spherical stars
Bizon, P.; Malec, E.; O'Murchadha, N.
1988-09-05
We give necessary and sufficient conditions for the existence of trapped surfaces in spherically symmetric spacetimes. These conditions show that the formation of trapped surfaces depends on both the degree of concentration and the average flow of the matter. The result can be considered as a partial validation of the cosmic-censorship hypothesis.
Multi-element spherical shell generation
NASA Technical Reports Server (NTRS)
Morrison, Andrew D. (Inventor)
1990-01-01
A nozzle assembly in a multi-element spherical shell generation system includes first and second side-by-side spaced apart nozzles and a web portion extending between and connecting the nozzles. The first nozzle has an inner orifice adapted to discharge a first filler material and an outer annular orifice separated from and defined in concentric relation about the inner orifice and adapted to discharge a first shell material. The second nozzle has an inner orifice adapted to discharge a second filler material and an outer annular orifice separated from and defined in concentric relation about the inner orifice and adapted to discharge a second shell material. A multi-element spherical shell can be formed through employment of the nozzle assembly by merger with one another after discharge from the outer orifices of the nozzles of a pair of adjacent annular streams of liquid or molten shell wall material of different compositions and encapsulation by the mixed shell wall materials of a common encapsulated core fluids also simultaneously discharged by the inner orifices nozzles. On the other hand, the pair of encapsulating streams of shell wall material can be of the same materials which merge together and encapsulate core fluids of different compositions which will merge together after discharge from the nozzles.
On the perfect hexagonal packing of rods
NASA Astrophysics Data System (ADS)
Starostin, E. L.
2006-04-01
In most cases the hexagonal packing of fibrous structures or rods extremizes the energy of interaction between strands. If the strands are not straight, then it is still possible to form a perfect hexatic bundle. Conditions under which the perfect hexagonal packing of curved tubular structures may exist are formulated. Particular attention is given to closed or cycled arrangements of the rods like in the DNA toroids and spools. The closure or return constraints of the bundle result in an allowable group of automorphisms of the cross-sectional hexagonal lattice. The structure of this group is explored. Examples of open helical-like and closed toroidal-like bundles are presented. An expression for the elastic energy of a perfectly packed bundle of thin elastic rods is derived. The energy accounts for both the bending and torsional stiffnesses of the rods. It is shown that equilibria of the bundle correspond to solutions of a variational problem formulated for the curve representing the axis of the bundle. The functional involves a function of the squared curvature under the constraints on the total torsion and the length. The Euler-Lagrange equations are obtained in terms of curvature and torsion and due to the existence of the first integrals the problem is reduced to the quadrature. The three-dimensional shape of the bundle may be readily reconstructed by integration of the Ilyukhin-type equations in special cylindrical coordinates. The results are of universal nature and are applicable to various fibrous structures, in particular, to intramolecular liquid crystals formed by DNA condensed in toroids or packed inside the viral capsids. International Workshop on Biopolymers: Thermodynamics, Kinetics and Mechanics of DNA, RNA and Proteins, 30.05.2005-3.06.2005, The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy.
Four-wave interference and perfect blaze.
Güther, R
2012-10-01
The recently calculated high diffraction efficiencies for TE- and TM-polarized light (perfect blaze) for echelette gratings are explained by four-wave interference, which is formed as a double periodical pattern in the cross section of the grating plane. The blazed grating profile should match this interference pattern for a single reference light wavelength. The recently published data are the special case of a general design. The prognoses of the model are connected with large grating constants in comparison with the light wavelength, where short grating constants need comparison with numerical methods.
Spatial delocalization and perfect tunneling of matter waves: electron perfect lens.
Silveirinha, Mário G; Engheta, Nader
2013-05-24
It is theoretically demonstrated that electron states in semiconductors or graphene can be perfectly transmitted through a complementary material with dual properties, independent of the angle of incidence. It is shown that such complementary material may also provide a strong spatial delocalization of bounded electronic states, changing dramatically the confinement of the wave function, and acting effectively as a lens for the probability wave. The results are the electron analogue of a perfect lens for electromagnetic waves proposed in an earlier work. PMID:23745877
Spherical navigator registration using harmonic analysis for prospective motion correction.
Wyatt, C L; Ari, N; Kraft, R A
2005-01-01
Spherical navigators are an attractive approach to motion compensation in Magnetic Resonance Imaging. Because they can be acquired quickly, spherical navigators have the potential to measure and correct for rigid motion during image acquisition (prospectively as opposed to retrospectively). A limiting factor to prospective use of navigators is the time required to estimate the motion parameters. This estimation problem can be separated into a rotational and translational component. Recovery of the rotational motion can be cast as a registration of functions defined on a sphere. Previous methods for solving this registration problem are based on optimization strategies that are iterative and require k-space interpolation. Such approaches have undesirable convergence behavior for prospective use since the estimation complexity depends on both the number of samples and the amount of rotation. We propose and demonstrate an efficient algorithm for recovery of rotational motion using spherical navigators. We decompose the navigator magnitude using the spherical harmonic transform. In this framework, rigid rotations can be recovered from an over-constrained system of equations, leading to a computationally efficient algorithm for prospective motion compensation. The resulting algorithm is compared to existing approaches in simulated and actual navigator data. These results show that the spherical harmonic based estimation algorithm is significantly faster than existing methods and so is suited for prospective motion correction.
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.
X-ray absorption in perfect crystals
Zimmerman, J.D.
1984-08-01
Attenuation coefficients for germanium, silicon and HOPG were measured for the fundamental, second and third harmonic wavelengths of the tungsten L1, L..cap alpha../sub 1/, L..beta../sub 1/, and L..gamma.., excitation lines. The relation between the atomic scattering factor and the photoelectric contribution to the attenuation coefficient is discussed. Also, theoretical calculations of these are discussed along with theoretical calculations for the coherent and incoherent processes. Following this, the unique apparatus on which the experiment was performed along with some general experimental techniques which were used are described. This is proceeded by the results and discussion of the data obtained for the perfect crystals and HOPG. Also, experimental attenuation coefficients for HOPG are presented for different temperatures. Within the conclusions, the results of the data are summarized and differences in obtaining attenuation coefficients for the perfect crystals and HOPG are discussed. In the final chapter, recommendations are given for further studies to determine characteristics of the change of the linear attenuation coefficient in the regime of the thick crystal or small scattering angle. (WHK)
Metamaterial perfect absorber based hot electron photodetection.
Li, Wei; Valentine, Jason
2014-06-11
While the nonradiative decay of surface plasmons was once thought to be only a parasitic process that limits the performance of plasmonic devices, it has recently been shown that it can be harnessed in the form of hot electrons for use in photocatalysis, photovoltaics, and photodetectors. Unfortunately, the quantum efficiency of hot electron devices remains low due to poor electron injection and in some cases low optical absorption. Here, we demonstrate how metamaterial perfect absorbers can be used to achieve near-unity optical absorption using ultrathin plasmonic nanostructures with thicknesses of 15 nm, smaller than the hot electron diffusion length. By integrating the metamaterial with a silicon substrate, we experimentally demonstrate a broadband and omnidirectional hot electron photodetector with a photoresponsivity that is among the highest yet reported. We also show how the spectral bandwidth and polarization-sensitivity can be manipulated through engineering the geometry of the metamaterial unit cell. These perfect absorber photodetectors could open a pathway for enhancing hot electron based photovoltaic, sensing, and photocatalysis systems. PMID:24837991
Comparison of elliptical and spherical mirrors for the grasshopper monochromators at SSRL
Waldhauer, A. P.
1989-07-01
A comparison of the performance of a spherical and elliptical mirror in the grasshopper monochromator is presented. The problem was studied by ray tracing and then tested using visible (/lambda/=633 nm) laser light. Calculations using ideal optics yield an improvement in flux by a factor of up to 2.7, while tests with visible light show an increase by a factor of 5 because the old spherical mirror is compared to a new, perfect elliptical one. The FWHM of the measured focus is 90 /mu/m with a spherical mirror, and 25 /mu/m with an elliptical one. Elliptical mirrors have been acquired and are now being installed in the two grasshoppers at SSRL.
Comparison of elliptical and spherical mirrors for the grasshopper monochromators at SSRL
NASA Astrophysics Data System (ADS)
Waldhauer, A. P.
1989-07-01
A comparison of the performance of a spherical and elliptical mirror in the grasshopper monochromator is presented. The problem was studied by ray tracing and then tested using visible (λ=633 nm) laser light. Calculations using ideal optics yield an improvement in flux by a factor of up to 2.7, while tests with visible light show an increase by a factor of 5 because the old spherical mirror is compared to a new, perfect elliptical one. The FWHM of the measured focus is 90 μm with a spherical mirror, and 25 μm with an elliptical one. Elliptical mirrors have been acquired and are now being installed in the two grasshoppers at SSRL.
Costa, Andreu F; Yen, Yi-Fen; Drangova, Maria
2010-02-01
Subject motion remains a challenging problem to overcome in clinical and research applications of magnetic resonance imaging (MRI). Subject motion degrades the quality of MR images and the integrity of experimental data. A promising method to correct for subject motion in MRI is the spherical navigator (SNAV) echo. Spherical navigators acquire k-space data on the surface of a sphere in order to measure three-dimensional (3D) rigid-body motion. Analysis begins by registering the magnitude of two SNAVs to determine the 3D rotation between them. Several different methods to register SNAV data exist, each with specific capabilities and limitations. In this study, we assessed the accuracy, precision and computational requirements of measuring rotations about all three coordinate axes by correlating the spherical harmonic expansions of SNAV data. We compare the results of this technique to previous SNAV studies and show that, although computationally expensive, the spherical harmonic technique is a highly accurate, precise and robust method to register SNAVs and detect 3D rotations in MRI. A key advantage to the spherical harmonic technique is the ability to optimize the accuracy, precision, processing time and memory requirements by adjusting parameters used in the registration. While present developments are aimed at improving the programming efficiency and memory handling of the algorithm, this registration technique is currently well suited for retrospective motion correction applications, such as removing motion-related image artifacts and aligning slices within a high-resolution 3D volume.
ERIC Educational Resources Information Center
Ozier, Lance
2011-01-01
Pressure for students to produce writing perfection in the classroom often eclipses the emphasis placed on the need for students to practice writing. Occasions for students to choose, challenge, and reflect--to actually risk risking--are too often absent from conversations among students and teachers in countless English classrooms. Tom Romano…
CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS
Slany, P.; Kovar, J.; Stuchlik, Z.; Karas, V.
2013-03-01
A Newtonian model of non-conductive, charged, perfect fluid tori orbiting in combined spherical gravitational and dipolar magnetic fields is presented and stationary, axisymmetric toroidal structures are analyzed. Matter in such tori exhibits a purely circulatory motion and the resulting convection carries charges into permanent rotation around the symmetry axis. As a main result, we demonstrate the possible existence of off-equatorial charged tori and equatorial tori with cusps that also enable outflows of matter from the torus in the Newtonian regime. These phenomena qualitatively represent a new consequence of the interplay between gravity and electromagnetism. From an astrophysical point of view, our investigation can provide insight into processes that determine the vertical structure of dusty tori surrounding accretion disks.
Space Shuttle Endeavour launch
NASA Technical Reports Server (NTRS)
1992-01-01
A smooth countdown culminated in a picture-perfect launch as the Space Shuttle Endeavour (STS-47) climbed skyward atop a ladder of billowing smoke. Primary payload for the plarned seven-day flight was Spacelab-J science laboratory. The second flight of Endeavour marks a number of historic firsts: the first space flight of an African-American woman, the first Japanese citizen to fly on a Space Shuttle, and the first married couple to fly in space.
Perfect anti-reflection from first principles
NASA Astrophysics Data System (ADS)
Kim, Kyoung-Ho; Q-Han Park
2013-01-01
Reducing unwanted reflections through impedance matching, called anti-reflection, has long been an important challenge in optics and electrical engineering. Beyond trial and error optimization, however, a systematic way to realize anti-reflection is still absent. Here, we report the discovery of an analytic solution to this long standing problem. For electromagnetic waves, we find the graded permittivity and permeability that completely remove any given impedance mismatch. We demonstrate that perfect broadband anti-reflection is possible when a dispersive, graded refractive index medium is used for the impedance-matching layer. We also present a design rule for the ultra-thin anti-reflection coating which we confirm experimentally by showing the anti-reflection behavior of an exemplary λ/25-thick coating made of metamaterials. This work opens a new path to anti-reflection applications in optoelectronic device, transmission line and stealth technologies.
Towards creating the perfect electronic prescription.
Dhavle, Ajit A; Rupp, Michael T
2015-04-01
Significant strides have been made in electronic (e)-prescribing standards and software applications that have further fueled the adoption and use of e-prescribing. However, for e-prescribing to realize its full potential for improving the safety, effectiveness, and efficiency of prescription drug delivery, important work remains to be carried out. This perspective describes the ultimate goal of all e-prescribing stakeholders including prescribers and dispensing pharmacists: a clear, complete, and unambiguous e-prescription order that can be seamlessly received, processed, and fulfilled at the dispensing pharmacy without the need for additional clarification from the prescriber. We discuss the challenges to creating the perfect e-prescription by focusing on selected data segments and data fields that are available in the new e-prescription transaction as defined in the NCPDP SCRIPT Standard and suggest steps that could be taken to move the industry closer to achieving this vision. PMID:25038197
Perfect crystals grown from imperfect interfaces.
Falub, Claudiu V; Meduňa, Mojmír; Chrastina, Daniel; Isa, Fabio; Marzegalli, Anna; Kreiliger, Thomas; Taboada, Alfonso G; Isella, Giovanni; Miglio, Leo; Dommann, Alex; von Känel, Hans
2013-01-01
The fabrication of advanced devices increasingly requires materials with different properties to be combined in the form of monolithic heterostructures. In practice this means growing epitaxial semiconductor layers on substrates often greatly differing in lattice parameters and thermal expansion coefficients. With increasing layer thickness the relaxation of misfit and thermal strains may cause dislocations, substrate bowing and even layer cracking. Minimizing these drawbacks is therefore essential for heterostructures based on thick layers to be of any use for device fabrication. Here we prove by scanning X-ray nanodiffraction that mismatched Ge crystals epitaxially grown on deeply patterned Si substrates evolve into perfect structures away from the heavily dislocated interface. We show that relaxing thermal and misfit strains result just in lattice bending and tiny crystal tilts. We may thus expect a new concept in which continuous layers are replaced by quasi-continuous crystal arrays to lead to dramatically improved physical properties.
The Quest for the Perfect Scattering Experiment
NASA Astrophysics Data System (ADS)
Gay, T. J.
2001-04-01
Atomic collisions can be viewed as laboratories for the study of applied quantum mechanics. Electron-atom scattering is perhaps the most investigated quantum mechanical process in physics, but not the best understood. Indeed, the simplest example of this process, electron-hydrogen scattering, has only succumbed to comprehensive solution in the last two years. One of the Holy Grails of electron-atom scattering is the "perfect" experiment, in which all of the quantum mechanical scattering amplitudes are determined completely. This goal, first articulated by Bederson in 1969 [1], has led to increasingly sophisticated and intricate experiments. A history of these experiments will be presented, and their impact on the field evaluated. [1] B.Bederson, Comments At. Mol. Phys. 1, 41 (1969).
Recent Results from RHIC: The Perfect Liquid
Westfall, Gary
2006-07-19
In the past two years we have witnessed a leap forward in the understanding high temperature, high density, and strongly interacting matter produced in ultra-relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Combining measurements of Au+Au, d+Au, and p+p collisions at energies up to 200 GeV per nucleon pair in the center of mass frame, the four RHIC experimental groups, STAR, PHENIX, PHOBOS, and BRAHMS, have produced impressive experimental evidence for the existence of a new form of matter. In this Colloquium, I will present an overview of recent experimental results from RHIC including evidence for thermalization, hydrodynamic behavior of a perfect fluid, the partonic origin of flow, and jet suppression. These measurements point to the observation of a hot, dense, strongly interacting matter produced in central Au+Au collisions at the highest available energies.
LensPerfect Analysis of Abell 1689
NASA Astrophysics Data System (ADS)
Coe, Dan A.
2007-12-01
I present the first massmap to perfectly reproduce the position of every gravitationally-lensed multiply-imaged galaxy detected to date in ACS images of Abell 1689. This massmap was obtained using a powerful new technique made possible by a recent advance in the field of Mathematics. It is the highest resolution assumption-free Dark Matter massmap to date, with the resolution being limited only by the number of multiple images detected. We detect 8 new multiple image systems and identify multiple knots in individual galaxies to constrain a grand total of 168 knots within 135 multiple images of 42 galaxies. No assumptions are made about mass tracing light, and yet the brightest visible structures in A1689 are reproduced in our massmap, a few with intriguing positional offsets. Our massmap probes radii smaller than that resolvable in current Dark Matter simulations of galaxy clusters. And at these radii, we observe slight deviations from the NFW and Sersic profiles which describe simulated Dark Matter halos so well. While we have demonstrated that our method is able to recover a known input massmap (to limited resolution), further tests are necessary to determine the uncertainties of our mass profile and positions of massive subclumps. I compile the latest weak lensing data from ACS, Subaru, and CFHT, and attempt to fit a single profile, either NFW or Sersic, to both the observed weak and strong lensing. I confirm the finding of most previous authors, that no single profile fits extremely well to both simultaneously. Slight deviations are revealed, with the best fits slightly over-predicting the mass profile at both large and small radius. Our easy-to-use software, called LensPerfect, will be made available soon. This research was supported by the European Commission Marie Curie International Reintegration Grant 017288-BPZ and the PNAYA grant AYA2005-09413-C02.
Local Existence of Solutions of Self Gravitating Relativistic Perfect Fluids
NASA Astrophysics Data System (ADS)
Brauer, Uwe; Karp, Lavi
2014-01-01
This paper deals with the evolution of the Einstein gravitational fields which are coupled to a perfect fluid. We consider the Einstein-Euler system in asymptotically flat spacestimes and therefore use the condition that the energy density might vanish or tend to zero at infinity, and that the pressure is a fractional power of the energy density. In this setting we prove local in time existence, uniqueness and well-posedness of classical solutions. The zero order term of our system contains an expression which might not be a C ∞ function and therefore causes an additional technical difficulty. In order to achieve our goals we use a certain type of weighted Sobolev space of fractional order. In Brauer and Karp (J Diff Eqs 251:1428-1446, 2011) we constructed an initial data set for these of systems in the same type of weighted Sobolev spaces. We obtain the same lower bound for the regularity as Hughes et al. (Arch Ratl Mech Anal 63(3):273-294, 1977) got for the vacuum Einstein equations. However, due to the presence of an equation of state with fractional power, the regularity is bounded from above.
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
Spherical gravitational collapse in N dimensions
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.
Spherical gravitational collapse in N dimensions
NASA Astrophysics Data System (ADS)
Goswami, Rituparno; Joshi, Pankaj S.
2007-10-01
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=ti 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.
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.
Feedback as the source of imperfection in lossy perfect lenses
NASA Astrophysics Data System (ADS)
Rosenblatt, Gilad; Bartal, Guy; Orenstein, Meir
2016-02-01
The major barrier to realizing a perfect lens with left-handed materials is perceived to be their intrinsic loss. Here we show that only specific designs of perfect lenses are limited by loss—those in which material loss is translated to internal feedback. The asymptotically uniform transmission required for perfect lensing is hindered by such feedback, which generates resonances that lead to a spatial cutoff in the lens transmission. Moreover, uniform transmission and its resonant deterioration stem from completely separate classes of modal excitations. A perfect lens made of lossy left-handed materials is therefore not forbidden in principle. Pursuing perfect lens designs that avoid internal feedback offers a path towards realization of practical perfect lenses.
Advanced control of a flexible spherical wrist
NASA Astrophysics Data System (ADS)
Gorgenyi, Louis Alexander
1993-07-01
A flexible spherical wrist, susceptible to nonlinear torsional vibrations, was developed which utilizes controllers to provide position control and vibration rejection. The issue of robust performance and stability for this robot wrist is examined while adhearing to practical implementation limits. System identification techniques are used to obtain linear models of the dynamic equations of motion. These models contain physical information such as friction and cable drag, and several different parametric forms are presented. Asymptotic stability of the wrist under proportional derivative control is proven using a linearized set of dynamical equations. Experimental results show only stability rather than asymptotic stability due to friction and unmodeled dynamics. In addition, poor robustness of this control methodology is demonstrated when the orientation and payload are varied. One- and two-parameter Hardy space controllers are designed to address the robustness and implementation issues. Variations in wrist orientation and payload are modeled as multiplicative uncertainties. Simulation and experimental results are presented and compared to those of a tracking controller. The Hardy space controllers are shown to have superior robustness properties but poorer performance.
Physics of Spherical Torus Plasmas
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
APPARATUS FOR GRINDING SPHERICAL BODIES
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)
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.
Dynamics of particles and defects on spherical crystals
NASA Astrophysics Data System (ADS)
Guerra, Rodrigo; Kelleher, Colm; Chaikin, Paul
Repulsive particles confined to two dimensions can form nearly perfect crystals that melt via the well-know Kosterlitz-Thouless two-step process. By contrast, when identical particles are confined to the surface of a sphere, the curvature and topology of the surface distorts the crystal lattice and forces it to accommodate point-like disclinations and chains of dislocations. Extensive numerical and theoretical investigation has shown that these extended scars are intrinsic to the ground-state-energy configuration of these packings, as they relieve some of the stress induced by the curvature of the surface. Nevertheless, the effect of these defects on the kinetics and phase behavior of spherical crystals is not at all well understood. Here we present results of computer simulations and experiments that suggest that these scars facilitate the motion of particles close to them and fundamentally alter the nature of the mobility and liquid-to-solid transition of packings of particles confined to spherical surfaces.
Wake control with permeable multilayer structures: The spherical symmetry case.
Bowen, Patrick T; Smith, David R; Urzhumov, Yaroslav A
2015-12-01
We explore the possibility of controlling the wake and drag of a spherical object independently of each other, using radial distributions of permeability in the Brinkman-Stokes formalism. By discretizing a graded-permeability shell into discrete, macroscopically homogeneous layers, we are able to sample the entire functional space of spherically-symmetric permeabilities and observe quick convergence to a certain manifold in the wake-drag coordinates. Monte Carlo samplings with 10^{4}-10^{5} points have become possible thanks to our new algorithm, which is based on exact analytical solutions for the Stokes flow through an arbitrary multilayer porous sphere. The algorithm is not restricted to the Brinkman-Stokes equation and can be modified to account for other types of scattering problems for spherically-symmetric systems with arbitrary radial complexity. Our main practical finding for Stokes flow is that it is possible to reduce a certain measure of wake of a spherical object without any energy penalty and without active (power-consuming) force generation. PMID:26764826
Acoustic source localization in mixed field using spherical microphone arrays
NASA Astrophysics Data System (ADS)
Huang, Qinghua; Wang, Tong
2014-12-01
Spherical microphone arrays have been used for source localization in three-dimensional space recently. In this paper, a two-stage algorithm is developed to localize mixed far-field and near-field acoustic sources in free-field environment. In the first stage, an array signal model is constructed in the spherical harmonics domain. The recurrent relation of spherical harmonics is independent of far-field and near-field mode strengths. Therefore, it is used to develop spherical estimating signal parameter via rotational invariance technique (ESPRIT)-like approach to estimate directions of arrival (DOAs) for both far-field and near-field sources. In the second stage, based on the estimated DOAs, simple one-dimensional MUSIC spectrum is exploited to distinguish far-field and near-field sources and estimate the ranges of near-field sources. The proposed algorithm can avoid multidimensional search and parameter pairing. Simulation results demonstrate the good performance for localizing far-field sources, or near-field ones, or mixed field sources.
Wake control with permeable multilayer structures: The spherical symmetry case.
Bowen, Patrick T; Smith, David R; Urzhumov, Yaroslav A
2015-12-01
We explore the possibility of controlling the wake and drag of a spherical object independently of each other, using radial distributions of permeability in the Brinkman-Stokes formalism. By discretizing a graded-permeability shell into discrete, macroscopically homogeneous layers, we are able to sample the entire functional space of spherically-symmetric permeabilities and observe quick convergence to a certain manifold in the wake-drag coordinates. Monte Carlo samplings with 10^{4}-10^{5} points have become possible thanks to our new algorithm, which is based on exact analytical solutions for the Stokes flow through an arbitrary multilayer porous sphere. The algorithm is not restricted to the Brinkman-Stokes equation and can be modified to account for other types of scattering problems for spherically-symmetric systems with arbitrary radial complexity. Our main practical finding for Stokes flow is that it is possible to reduce a certain measure of wake of a spherical object without any energy penalty and without active (power-consuming) force generation.
Perfect terahertz absorber using fishnet based metafilm
Azad, Abul Kalam; Shchegolkov, Dmitry Yu; Chen, Houtong; Taylor, Antoinette; Smirnova, E I; O' Hara, John F
2009-01-01
We present a perfect terahertz (THz) absorber working for a broad-angle of incidence. The two fold symmetry of rectangular fishnet structure allows either complete absorption or mirror like reflection depending on the polarization of incident the THz beam. Metamaterials enable the ability to control the electromagnetic wave in a unique fashion by designing the permittivity or permeability of composite materials with desired values. Although the initial idea of metamaterials was to obtain a negative index medium, however, the evolution of metamaterials (MMs) offers a variety of practically applicable devices for controlling electromagnetic wave such as tunable filters, modulators, phase shifters, compact antenna, absorbers, etc. Terahertz regime, a crucial domain of the electromagnetic wave, is suffering from the scarcity of the efficient devices and might take the advantage of metamaterials. Here, we demonstrate design, fabrication, and characterization of a terahertz absorber based on a simple fishnet metallic film separated from a ground mirror plane by a dielectric spacer. Such absorbers are in particular important for bolometric terahertz detectors, high sensitivity imaging, and terahertz anechoic chambers. Recently, split-ring-resonators (SRR) have been employed for metamaterial-based absorbers at microwave and THz frequencies. The experimental demonstration reveals that such absorbers have absorptivity close to unity at resonance frequencies. However, the downside of these designs is that they all employ resonators of rather complicated shape with many fine parts and so they are not easy to fabricate and are sensitive to distortions.
Practice makes two hemispheres almost perfect.
Cherbuin, Nicolas; Brinkman, Cobie
2005-08-01
Some tasks produce a performance advantage for conditions that require the processing of stimuli in two visual fields compared to conditions where single hemifield processing is sufficient. This advantage, however, disappears with practice. Although no definitive evidence yet exists, there are several possible mechanisms that might lead to improved performance of within- compared to across-hemisphere processing with practice. These include a shift from a more demanding, algorithmic strategy to a less demanding memory-retrieval strategy (e.g., [G. Logan, Toward an instance theory of automatisation. Psych. Rev. 95 (1988) 492-527]), as discussed by Weissman and Compton [D.H. Weissman, R.J. Compton, Practice makes a hemisphere perfect: the advantage of interhemispheric recruitment is eliminated with practice. Laterality, 8 (4) (2003) 361-375], and/or a more generalised practice effect [K. Kirsner, C. Speelman, Skill acquisition and repetition priming: one principle, many processes? J. Exp. Psychol., Learn. Mem. Cogn., 22 (1996) 563-575]. Contrary to Weissman and Compton findings, our results suggest that although single-hemisphere performance improves with practice, bi-hemispheric performance also improves substantially. Furthermore, these effects do not appear to be due to a shift in strategy but rather due to a general practice effect.
Measuring Spherical Harmonic Coefficients on a Sphere
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.
MUSCLE: MUltiscale Spherical-ColLapse Evolution
NASA Astrophysics Data System (ADS)
Neyrinck, Mark C.
2016-05-01
MUSCLE (MUltiscale Spherical ColLapse Evolution) produces low-redshift approximate N-body realizations accurate to few-Megaparsec scales. It applies a spherical-collapse prescription on multiple Gaussian-smoothed scales. It achieves higher accuracy than perturbative schemes (Zel'dovich and second-order Lagrangian perturbation theory - 2LPT), and by including the void-in-cloud process (voids in large-scale collapsing regions), solves problems with a single-scale spherical-collapse scheme.
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.
Perfect Parenting: The Dictionary of 1,000 Parenting Tips.
ERIC Educational Resources Information Center
Pantley, Elizabeth
Using a dictionary format, this book addresses many of the issues faced by parents. Following an introduction that defines "perfect parenting" and lists nine "perfect parenting keys," topics are arranged alphabetically. Under each topic, a situation is stated, thoughts about the situation are offered, and solutions are suggested. Topics include…
Backscattering from a Gaussian distributed, perfectly conducting, rough surface
NASA Technical Reports Server (NTRS)
Brown, G. S.
1977-01-01
The problem of scattering by random surfaces possessing many scales of roughness is analyzed. The approach is applicable to bistatic scattering from dielectric surfaces, however, this specific analysis is restricted to backscattering from a perfectly conducting surface in order to more clearly illustrate the method. The surface is assumed to be Gaussian distributed so that the surface height can be split into large and small scale components, relative to the electromagnetic wavelength. A first order perturbation approach is employed wherein the scattering solution for the large scale structure is perturbed by the small scale diffraction effects. The scattering from the large scale structure is treated via geometrical optics techniques. The effect of the large scale surface structure is shown to be equivalent to a convolution in k-space of the height spectrum with the following: the shadowing function, a polarization and surface slope dependent function, and a Gaussian factor resulting from the unperturbed geometrical optics solution. This solution provides a continuous transition between the near normal incidence geometrical optics and wide angle Bragg scattering results.
Wormhole dynamics in spherical symmetry
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.
Nonadiabatic charged spherical gravitational collapse
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.
A multiband perfect absorber based on hyperbolic metamaterials.
Sreekanth, Kandammathe Valiyaveedu; ElKabbash, Mohamed; Alapan, Yunus; Rashed, Alireza R; Gurkan, Umut A; Strangi, Giuseppe
2016-01-01
In recent years, considerable research efforts have been focused on near-perfect and perfect light absorption using metamaterials spanning frequency ranges from microwaves to visible frequencies. This relatively young field is currently facing many challenges that hampers its possible practical applications. In this paper, we present grating coupled-hyperbolic metamaterials (GC-HMM) as multiband perfect absorber that can offer extremely high flexibility in engineering the properties of electromagnetic absorption. The fabricated GC-HMMs exhibit several highly desirable features for technological applications such as polarization independence, wide angle range, broad- and narrow- band modes, multiband perfect and near perfect absorption in the visible to near-IR and mid-IR spectral range. In addition, we report a direct application of the presented system as an absorption based plasmonic sensor with a record figure of merit for this class of sensors. PMID:27188789
A multiband perfect absorber based on hyperbolic metamaterials
Sreekanth, Kandammathe Valiyaveedu; ElKabbash, Mohamed; Alapan, Yunus; Rashed, Alireza R.; Gurkan, Umut A.; Strangi, Giuseppe
2016-01-01
In recent years, considerable research efforts have been focused on near-perfect and perfect light absorption using metamaterials spanning frequency ranges from microwaves to visible frequencies. This relatively young field is currently facing many challenges that hampers its possible practical applications. In this paper, we present grating coupled-hyperbolic metamaterials (GC-HMM) as multiband perfect absorber that can offer extremely high flexibility in engineering the properties of electromagnetic absorption. The fabricated GC-HMMs exhibit several highly desirable features for technological applications such as polarization independence, wide angle range, broad- and narrow- band modes, multiband perfect and near perfect absorption in the visible to near-IR and mid-IR spectral range. In addition, we report a direct application of the presented system as an absorption based plasmonic sensor with a record figure of merit for this class of sensors. PMID:27188789
A multiband perfect absorber based on hyperbolic metamaterials.
Sreekanth, Kandammathe Valiyaveedu; ElKabbash, Mohamed; Alapan, Yunus; Rashed, Alireza R; Gurkan, Umut A; Strangi, Giuseppe
2016-05-18
In recent years, considerable research efforts have been focused on near-perfect and perfect light absorption using metamaterials spanning frequency ranges from microwaves to visible frequencies. This relatively young field is currently facing many challenges that hampers its possible practical applications. In this paper, we present grating coupled-hyperbolic metamaterials (GC-HMM) as multiband perfect absorber that can offer extremely high flexibility in engineering the properties of electromagnetic absorption. The fabricated GC-HMMs exhibit several highly desirable features for technological applications such as polarization independence, wide angle range, broad- and narrow- band modes, multiband perfect and near perfect absorption in the visible to near-IR and mid-IR spectral range. In addition, we report a direct application of the presented system as an absorption based plasmonic sensor with a record figure of merit for this class of sensors.
"Whose perfection is it anyway?": a virtuous consideration of enhancement.
Keenan, James F
1999-08-01
Discussions of genetic enhancements often imply deep suspicions about human desires to manipulate or enhance the course of our future. These unspoken assumptions about the arrogance of the quest for perfection are at odds with the normally hopeful resonancy we find in contemporary theology. The author argues that these fears, suspicions and accusations are misplaced. The problem lies not with the question of whether we should pursue perfection, but rather what perfection we are pursuing. The author argues that perfection, properly understood, has an enormously positive function in the Roman Catholic tradition. The author examines three sources: the Scriptures, the scholastic tradition, and ascetical theology. He examines contemporary criticisms of perfectionism and suggests that an adequate virtue theory keeps us from engaging perfectionism as such. The author then shows how a positive, responsible view of perfection is an asset to our discussion on enhancement technology.
A multiband perfect absorber based on hyperbolic metamaterials
NASA Astrophysics Data System (ADS)
Sreekanth, Kandammathe Valiyaveedu; Elkabbash, Mohamed; Alapan, Yunus; Rashed, Alireza R.; Gurkan, Umut A.; Strangi, Giuseppe
2016-05-01
In recent years, considerable research efforts have been focused on near-perfect and perfect light absorption using metamaterials spanning frequency ranges from microwaves to visible frequencies. This relatively young field is currently facing many challenges that hampers its possible practical applications. In this paper, we present grating coupled-hyperbolic metamaterials (GC-HMM) as multiband perfect absorber that can offer extremely high flexibility in engineering the properties of electromagnetic absorption. The fabricated GC-HMMs exhibit several highly desirable features for technological applications such as polarization independence, wide angle range, broad- and narrow- band modes, multiband perfect and near perfect absorption in the visible to near-IR and mid-IR spectral range. In addition, we report a direct application of the presented system as an absorption based plasmonic sensor with a record figure of merit for this class of sensors.
Perfect crystal propagator for physical optics simulations with Synchrotron Radiation Workshop
NASA Astrophysics Data System (ADS)
Sutter, John P.; Chubar, Oleg; Suvorov, Alexey
2014-09-01
Until now, a treatment of dynamical diffraction from perfect crystals has been missing in the "Synchrotron Radiation Workshop" (SRW) wavefront propagation computer code despite the widespread use of crystals on X-ray synchrotron beamlines. Now a special "Propagator" module for calculating dynamical diffraction from a perfect crystal in the Bragg case has been written in C++, integrated into the SRW C/C++ library and made available for simulations using the Python interface of SRW. The propagator performs local processing of the frequency-domain electric field in the angular representation. A 2-D Fast Fourier Transform is used for changing the field representation from/to the coordinate representation before and after applying the crystal propagator. This ensures seamless integration of the new propagator with the existing functionalities of the SRW package, allows compatibility with existing propagators for other optical elements, and enables the simulation of complex beamlines transporting partially coherent X-rays. The code has been benchmarked by comparison with predictions made by plane-wave and spherical-wave dynamical diffraction theory. Test simulations for a selection of X-ray synchrotron beamlines are also shown.
Pair distribution function and structure factor of spherical particles
Howell, Rafael C.; Proffen, Thomas; Conradson, Steven D.
2006-03-01
The availability of neutron spallation-source instruments that provide total scattering powder diffraction has led to an increased application of real-space structure analysis using the pair distribution function. Currently, the analytical treatment of finite size effects within pair distribution refinement procedures is limited. To that end, an envelope function is derived which transforms the pair distribution function of an infinite solid into that of a spherical particle with the same crystal structure. Distributions of particle sizes are then considered, and the associated envelope function is used to predict the particle size distribution of an experimental sample of gold nanoparticles from its pair distribution function alone. Finally, complementing the wealth of existing diffraction analysis, the peak broadening for the structure factor of spherical particles, expressed as a convolution derived from the envelope functions, is calculated exactly for all particle size distributions considered, and peak maxima, offsets, and asymmetries are discussed.
Analyzing correlation functions with tesseral and Cartesian spherical harmonics
Danielewicz, Pawel; Pratt, Scott
2007-03-15
The dependence of interparticle correlations on the orientation of particle relative momentum can yield unique information on the space-time features of emission in reactions with multiparticle final states. In the present paper, the benefits of a representation and analysis of the three-dimensional correlation information in terms of surface spherical harmonics is presented. The harmonics include the standard complex tesseral harmonics and the real Cartesian harmonics. Mathematical properties of the lesser known Cartesian harmonics are illuminated. The physical content of different angular harmonic components in a correlation is described. The resolving power of different final-state effects with regard to determining angular features of emission regions is investigated. The considered final-state effects include identity interference, strong interactions, and Coulomb interactions. The correlation analysis in terms of spherical harmonics is illustrated with the cases of Gaussian and blast-wave sources for proton-charged meson and baryon-baryon pairs.
NASA Technical Reports Server (NTRS)
Richmond, J. H.
1974-01-01
A computer program is presented for a thin-wire antenna over a perfect ground plane. The analysis is performed in the frequency domain, and the exterior medium is free space. The antenna may have finite conductivity and lumped loads. The output data includes the current distribution, impedance, radiation efficiency, and gain. The program uses sinusoidal bases and Galerkin's method.
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.
Instability of spherically imploding shock waves
Chen, H.; Hilko, B.; Zhang, L.; Panarella, E.
1995-12-31
The importance of spherically imploding shock waves has increased recently due to their particular applications in inertial confinement fusion (ICF) and the Spherical Pinch (SP). In particular, the stability of spherically imploding shock waves plays a critical role in the ultimate success of ICF and SP. The instability of spherically imploding shock waves is now systematically investigated. The basic state is Guderley and Landau`s unsteady self-similar solution of the implosion of a spherical shock wave. The stability analysis is conducted by combining Chandresakhar`s approach to the stability of spherical flames together. The governing equations for disturbances are derived and they use the condition that perturbed gas flow is potential. The three dimensional perturbation velocity profile and a shock front perturbation are solved by using the kinematic and dynamic boundary conditions in the shock front. The time-dependent amplitudes of the perturbations are obtained by solving the system of ordinary differential equations. This enables them to study the time history of the spherically imploding shock wave subject to perturbations. The relative amplification and decay of the amplitudes of perturbations decides the stability/instability of the spherical imploding shock waves. Preliminary results are presented.
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.
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…
Laser Interferometer Space Antenna (LISA) Far Field Phase Patterns
NASA Technical Reports Server (NTRS)
Waluschka, Eugene; Obenschain, Arthur F. (Technical Monitor)
2000-01-01
The Laser Interferometer Space Antenna (LISA) consists of three spacecraft in orbit about the sun. The orbits are chosen such that the three spacecraft are always at (roughly) the vertices of a equilateral triangle with 5 million kilometer leg lengths. Even though the distances between the three spacecraft are 5 million kilometers, the expected phase shifts between any two beams, due to a gravitational wave, only correspond to a distance change of about 10 pico meters, which is about 10(exp -5) waves for a laser wavelength of 1064 nm. To obtain the best signal-to-noise ratio, noise sources such as changes in the apparent distances due to pointing jitter must be controlled carefully. This is the main reason for determining the far-field phase patterns of a LISA type telescope. Because of torque on the LISA spacecraft and other disturbances, continuous adjustments to the pointing of the telescopes are required. These pointing adjustments will be a "jitter" source. If the transmitted wave is perfectly spherical then rotations (Jitter) about its geometric center will not produce any effect at the receiving spacecraft. However, if the outgoing wave is not perfectly spherical, then pointing jitter will produce a phase variation at the receiving spacecraft. The following sections describe the "brute force" computational approach used to determine the scalar wave front as a function of exit pupil (Zernike) aberrations and to show the results (mostly graphically) of the computations. This approach is straightforward and produces believable phase variations to sub-pico meter accuracy over distances on the order of 5 million kilometers. As such this analyzes the far field phase sensitivity to exit pupil aberrations.
Computer code for determination of thermally perfect gas properties
NASA Technical Reports Server (NTRS)
Witte, David W.; Tatum, Kenneth E.
1994-01-01
A set of one-dimensional compressible flow relations for a thermally perfect, calorically imperfect gas is derived for the specific heat c(sub p), expressed as a polynomial function of temperature, and developed into the thermally perfect gas (TPG) computer code. The code produces tables of compressible flow properties similar to those of NACA Rep. 1135. Unlike the tables of NACA Rep. 1135 which are valid only in the calorically perfect temperature regime, the TPG code results are also valid in the thermally perfect calorically imperfect temperature regime which considerably extends the range of temperature application. Accuracy of the TPG code in the calorically perfect temperature regime is verified by comparisons with the tables of NACA Rep. 1135. In the thermally perfect, calorically imperfect temperature regime, the TPG code is validated by comparisons with results obtained from the method of NACA Rep. 1135 for calculating the thermally perfect calorically imperfect compressible flow properties. The temperature limits for application of the TPG code are also examined. The advantage of the TPG code is its applicability to any type of gas (monatomic, diatomic, triatomic, or polyatomic) or any specified mixture thereof, whereas the method of NACA Rep. 1135 is restricted to only diatomic gases.
NASA Technical Reports Server (NTRS)
Podhorodeski, R. P.; Fenton, R. G.; Goldenberg, A. A.
1989-01-01
Using a method based upon resolving joint velocities using reciprocal screw quantities, compact analytical expressions are generated for the inverse solution of the joint rates of a seven revolute (spherical-revolute-spherical) manipulator. The method uses a sequential decomposition of screw coordinates to identify reciprocal screw quantities used in the resolution of a particular joint rate solution, and also to identify a Jacobian null-space basis used for the direct solution of optimal joint rates. The results of the screw decomposition are used to study special configurations of the manipulator, generating expressions for the inverse velocity solution for all non-singular configurations of the manipulator, and identifying singular configurations and their characteristics. Two functions are therefore served: a new general method for the solution of the inverse velocity problem is presented; and complete analytical expressions are derived for the resolution of the joint rates of a seven degree of freedom manipulator useful for telerobotic and industrial robotic application.
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
Stability of imploding spherical shock waves
NASA Astrophysics Data System (ADS)
Chen, H. B.; Zhang, L.; Panarella, E.
1995-12-01
The stability of spherically imploding shock waves is systematically investigated in this letter. The basic state is Guderley and Landau's unsteady self-similar solution of the implosion of a spherical shock wave. The stability analysis is conducted by combining Chandrasekhar's approach to the stability of a viscous liquid drop with Zel'dovich's approach to the stability of spherical flames. The time-dependent amplitudes of the perturbations are obtained analytically by using perturbation method. The relative amplification and decay of the amplitudes of perturbations decides the stability/instability of the spherical imploding shock waves. It is found that the growth rate of perturbations is not in exponential form and near the collapse phase of the shocks, the spherically imploding shock waves are relatively stable.
Stability of imploding spherical shock waves
Chen, H.B.; Zhang, L.; Panarella, E.
1995-12-01
The stability of spherically imploding shock waves is systematically investigated in this letter. The basic state is Guderley and Landau`s unsteady self-similar solution of the implosion of a spherical shock wave. The stability analysis is conducted by combining Chandrasekhar`s approach to the stability of a viscous liquid drop with Zel`dovich`s approach to the stability of spherical flames. The time-dependent amplitudes of the perturbations are obtained analytically by using perturbation method. The relative amplification and decay of the amplitudes of perturbations are obtained analytically by using perturbation method. The relative amplification and decay of the amplitudes of perturbations decides the stability/instability of the spherical imploding shock waves. It is found that the growth rate of perturbations is not in exponential form and near the collapse phase of the shocks, the spherically imploding shock waves are relatively stable. 14 refs., 1 fig.
Protein-Precipitant-Specific Criteria for the Impact of Reduced Gravity on Crystal Perfection
NASA Technical Reports Server (NTRS)
Vekilov, Peter G.; Witherow, W. (Technical Monitor)
2003-01-01
The objective of this research is to provide quantitative criteria for the impact of reduced or enhanced convective transport on protein crystal perfection. Our earlier work strongly suggests that the magnitude of (lattice defect-inducing) fluctuations in the crystallization rate of proteins arise from the coupling of bulk transport and nonlinear interface kinetics. Hence, we surmised that, depending on the relative weight of bulk transport and interface kinetics in the control of the crystallization process on Earth, these fluctuations can either increase or decrease under reduced gravity conditions. The sign and magnitude of these changes depend on the specific protein-precipitant system. As a consequence, space environments can be either beneficial or detrimental for achieving structural perfection in protein crystals. The task objectives consist in systematic investigations of this hypothesis.
Perfect metamaterial absorbers with polarization angle independency in X-band waveguide
NASA Astrophysics Data System (ADS)
Sabah, Cumali
2016-04-01
The design and characterization of perfect metamaterial absorbers (MAs) based on simple configurations including square- and triangle-shapes, which operate in X-band frequency region are numerically and experimentally investigated. The proposed MAs provide perfect absorption with the polarization angle independency. In X-band waveguide, the absorption rates are 99.69% and 99.97% at the resonance frequencies of 10.57 GHz and 10.93 GHz for the square- and triangle-shaped MAs, respectively. In addition, the same configurations are numerically tested under free space boundary conditions to compare and discuss the obtained results. The suggested MAs enable myriad potential application areas for security and stealth technologies in X-band including wireless communication.
Near-Perfect Adaptation in the E. coli Chemotaxis Signal Transduction Network
NASA Astrophysics Data System (ADS)
Yang, Yang; Setayeshgar, Sima
2007-03-01
Biochemical reaction networks constitute the computing language of the cell, from converting external stimuli into appropriate intracellular signals to regulating gene expression. Precise adaptation is an important property of many signaling networks, allowing compensation for continued stimulation without saturation. Furthermore, a common feature of intracellular reaction networks is the ability to operate in a noisy environment where concentrations of key components, such as signaling molecules and enzymes controlling reaction rates are typically small and therefore fluctuations in their numbers are significant. In the context of the well- characterized E. coli chemotaxis signal transduction network, we present a new computational scheme that explores surfaces in the space of total protein concentrations and reaction rates on which (near-)perfect adaptation holds. The resulting dependencies between parameters provide conditions for (near-)perfect adaptation as well as ranges of numerical values for parameters not reliably known from experiments. We generalize the applicability of this scheme to other signaling networks.
Fast calculation of spherical computer generated hologram using spherical wave spectrum method.
Jackin, Boaz Jessie; Yatagai, Toyohiko
2013-01-14
A fast calculation method for computer generation of spherical holograms in proposed. This method is based on wave propagation defined in spectral domain and in spherical coordinates. The spherical wave spectrum and transfer function were derived from boundary value solutions to the scalar wave equation. It is a spectral propagation formula analogous to angular spectrum formula in cartesian coordinates. A numerical method to evaluate the derived formula is suggested, which uses only N(logN)2 operations for calculations on N sampling points. Simulation results are presented to verify the correctness of the proposed method. A spherical hologram for a spherical object was generated and reconstructed successfully using the proposed method.
Metamaterial perfect absorber based on artificial dielectric "atoms".
Liu, Xiaoming; Bi, Ke; Li, Bo; Zhao, Qian; Zhou, Ji
2016-09-01
In this work, we numerically designed and then experimentally verified a metamaterial perfect absorber based on artificial dielectric "atoms". This metamaterial absorber is composed of dielectric ceramic material (SrTiO_{3}) "atoms" embedded in a background matrix on a metal plate. The dielectric "atoms" couple strongly to the incident electric and magnetic fields at the Mie resonance mode, leading to the narrow perfect absorption band with simulated and experimental absorptivities of 99% and 98.5% at 8.96 GHz, respectively. The designed metamaterial perfect absorber is polarization insensitive and can operate in wide angle incidence.
Nearly Perfect Fluidity in a High Temperature Superconductor
Rameau, J. D.; Reber, T. J.; Yang, H. -B.; Akhanjee, S.; Gu, G. D.; Johnson, P. D.; Campbell, S.
2014-10-13
Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η/s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature Tc.
Perfect function transfer in two and three dimensions without initialization
Wu Lianao; Byrd, Mark; Wang, Z. D.; Shao Bin
2010-11-15
We find analytic models that can perfectly transfer, without state initialization or remote collaboration, arbitrary functions in two- and three-dimensional interacting bosonic and fermionic networks. This provides for the possible experimental implementation of state transfer through bosonic or fermionic atoms trapped in optical lattices. A significant finding is that the state of a spin qubit can be perfectly transferred through a fermionic system. Families of Hamiltonians are described that are related to the linear models and that enable the perfect transfer of arbitrary functions. Furthermore, we propose methods for eliminating certain types of errors.
Ultra-broadband perfect cross polarization conversion metasurface
NASA Astrophysics Data System (ADS)
Dong, Guoxiang; Shi, Hongyu; Xia, Song; Zhang, Anxue; Xu, Zhuo; Wei, Xiaoyong
2016-04-01
We propose a metasurface with multiple plasmon resonances that achieves an ultra-broadband perfect cross polarization conversion. The metasurface is composed of an array of unit resonators, three plasmon resonances are excited in the unit resonator, which leads to an ultra-broadband perfect cross polarization conversion. The cross polarization conversion efficiency is higher than 99%, and the bandwidth of the converter is 53.7% of the central wavelength. Both numerical and experimental results were used to validate the ultra-broadband perfect cross polarization converter presented here.
Nearly Perfect Fluidity in a High Temperature Superconductor
Rameau, J. D.; Reber, T. J.; Yang, H. -B.; Akhanjee, S.; Gu, G. D.; Johnson, P. D.; Campbell, S.
2014-10-13
Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η/s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature T_{c}.
Metamaterial perfect absorber based on artificial dielectric "atoms".
Liu, Xiaoming; Bi, Ke; Li, Bo; Zhao, Qian; Zhou, Ji
2016-09-01
In this work, we numerically designed and then experimentally verified a metamaterial perfect absorber based on artificial dielectric "atoms". This metamaterial absorber is composed of dielectric ceramic material (SrTiO_{3}) "atoms" embedded in a background matrix on a metal plate. The dielectric "atoms" couple strongly to the incident electric and magnetic fields at the Mie resonance mode, leading to the narrow perfect absorption band with simulated and experimental absorptivities of 99% and 98.5% at 8.96 GHz, respectively. The designed metamaterial perfect absorber is polarization insensitive and can operate in wide angle incidence. PMID:27607650
Globally optimal rotation alignment of spherical surfaces with associated scalar values
NASA Astrophysics Data System (ADS)
Pan, Rongjiang; Skala, Vaclav; Müller, Rolf
2013-09-01
We propose a new approach to global optimization algorithm based on controlled random search techniques for rotational alignment of spherical surfaces with associated scalar values. To reduce the distortion in correspondence and increase efficiency, the spherical surface is first re-sampled using a geodesic sphere. The rotation in space is represented using the modified Rodrigues parameters. Correspondence between two spherical surfaces is implemented in the parametric domain. We applied the methods to the alignment of beam patterns computed from the outer ear shapes of bats. The proposed method is compared with other approaches such as principal component analysis (PCA), exhaustive search in the discrete space of rotations defined by Euler angles and direct search using uniform samples over the special orthogonal group of rotations in 3D space. Experimental results demonstrate that the rotation alignment obtained using the proposed algorithm has a high degree of precision and gives the best results among the four approaches. [Figure not available: see fulltext.
Spherical accretion and AGN feedback
NASA Astrophysics Data System (ADS)
Nulsen, Paul
2014-06-01
For a supermassive black hole accreting from a hot, quasi-spherical atmosphere, it is almost inevitable that the fluid approximation fails inside some point within the Bondi radius, but well outside the black hole event horizon. Within the region where the particle mean free paths exceed the radius, the flow must be modeled in terms of the Fokker-Planck equation. In the absence of magnetic fields, it is analogous to the "loss cone" problem for consumption of stars by a black hole. The accretion rate is suppressed well below the Bondi accretion rate and a significant power must be conveyed outward for the flow to proceed. This situation is complicated significantly by the presence of a magnetic field, but I will argue that the main outcomes are similar. I will also argue that the power emerging from such a flow, although generally far too little to suppress cooling on large scales, is an important ingredient of the AGN feedback cycle on scales comparable to the Bondi radius.
Generalized spherical and simplicial coordinates
NASA Astrophysics Data System (ADS)
Richter, Wolf-Dieter
2007-12-01
Elementary trigonometric quantities are defined in l2,p analogously to that in l2,2, the sine and cosine functions are generalized for each p>0 as functions sinp and cosp such that they satisfy the basic equation cosp([phi])p+sinp([phi])p=1. The p-generalized radius coordinate of a point [xi][set membership, variant]Rn is defined for each p>0 as . On combining these quantities, ln,p-spherical coordinates are defined. It is shown that these coordinates are nearly related to ln,p-simplicial coordinates. The Jacobians of these generalized coordinate transformations are derived. Applications and interpretations from analysis deal especially with the definition of a generalized surface content on ln,p-spheres which is nearly related to a modified co-area formula and an extension of Cavalieri's and Torricelli's indivisibeln method, and with differential equations. Applications from probability theory deal especially with a geometric interpretation of the uniform probability distribution on the ln,p-sphere and with the derivation of certain generalized statistical distributions.
Plasma Effects in Spherical Implosions
NASA Astrophysics Data System (ADS)
Bellei, Claudio; Amendt, Peter; Wilks, Scott
2011-10-01
A remarkable self-similar solution to the problem of a spherically converging shock was published by Guderley in 1942. Being applicable to an ideal gas, this solution neglects viscosity, thermal conduction and radiation losses and presents singularities when the shock reaches the origin. Radiation hydrodynamic codes include the effects of non-ideality (with artificial viscosity in place of real viscosity), ensuring that the solution is well-behaved at all times. However during an ICF implosion, separation of the electron and ion species occurs at the shock front. For the high Mach number (M > 10) incoming (coalesced) shock that is typical of ICF scenarios, the width of the plasma shock front is comparable to the ion-ion mean-free-path λii ~ 1 μ m and much larger than the shock front width in an unionized gas at the same density (~10-2 μ m). Ahead of the plasma shock front, electrons pre-heat the inner gas over distances λei ~(mi /me) 1 / 2λii ~ 70 μ m. This decreases the strength of the incoming shock and lowers the temperature behind the rebound shock, a phenomenon analogous to the non-ideal gas effects found in hydro-codes. Prepared by LLNL under Contract DE-AC52-07NA27344.
Ribozyme-Spherical Nucleic Acids
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
Osmotic buckling of spherical capsules.
Knoche, Sebastian; Kierfeld, Jan
2014-11-01
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. PMID:25209240
Vectorial spherical-harmonics representation of an inhomogeneous elliptically polarized plane wave.
Frezza, F; Mangini, F
2015-07-01
In this paper, a generalization of the vectorial spherical-harmonics expansion of an inhomogeneous elliptically polarized plane wave is presented. The solution has been achieved using the Legendre functions generalized via hypergeometric and gamma functions, shifting the difficulty to the determination of only expansion coefficients. In order to validate the presented method, a Matlab code has been implemented. To compare the results a Mie scattering by a sphere is considered, then a truncation criterion for the numerical evaluation of the series is proposed, and the Mie scattering coefficients by perfectly conducting and dielectric spheres excited by an inhomogeneous elliptically polarized plane wave are shown. PMID:26367169
Vectorial spherical-harmonics representation of an inhomogeneous elliptically polarized plane wave.
Frezza, F; Mangini, F
2015-07-01
In this paper, a generalization of the vectorial spherical-harmonics expansion of an inhomogeneous elliptically polarized plane wave is presented. The solution has been achieved using the Legendre functions generalized via hypergeometric and gamma functions, shifting the difficulty to the determination of only expansion coefficients. In order to validate the presented method, a Matlab code has been implemented. To compare the results a Mie scattering by a sphere is considered, then a truncation criterion for the numerical evaluation of the series is proposed, and the Mie scattering coefficients by perfectly conducting and dielectric spheres excited by an inhomogeneous elliptically polarized plane wave are shown.
Static spherically symmetric Kerr-Schild metrics and implications for the classical double copy
NASA Astrophysics Data System (ADS)
Ridgway, Alexander K.; Wise, Mark B.
2016-08-01
We discuss the physical interpretation of stress-energy tensors that source static spherically symmetric Kerr-Schild metrics. We find that the sources of such metrics with no curvature singularities or horizons do not simultaneously satisfy the weak and strong energy conditions. Sensible stress-energy tensors usually satisfy both of them. Under most circumstances, these sources are not perfect fluids and contain shear stresses. We show that for these systems the classical double copy associates the electric charge density to the Komar energy density. In addition, we demonstrate that the stress-energy tensors are determined by the electric charge density and their conservation equations.
Novel approach to a perfect lens
NASA Astrophysics Data System (ADS)
Klimov, V. V.
2009-05-01
Within the framework of an exact analytical solution of Maxwell equations in a space domain, it is shown that optical scheme based on a slab with negative refractive index ( n = -1) (Veselago lens or Pendry lens) does not possess focusing properties in the usual sense. In fact, the energy in such systems does not go from object to its “image,” but from object and its “image” to an intersection point inside a metamaterial layer, or vice versa. A possibility of applying this phenomenon to a creation of entangled states of two atoms is discussed.
Perfect imaging with positive refraction in three dimensions
Leonhardt, Ulf; Philbin, Thomas G.
2010-01-15
Maxwell's fish eye has been known to be a perfect lens within the validity range of ray optics since 1854. Solving Maxwell's equations, we show that the fish-eye lens in three dimensions has unlimited resolution for electromagnetic waves.
New exact perfect fluid solutions of Einstein's equations. II
NASA Astrophysics Data System (ADS)
Uggla, Claes; Rosquist, Kjell
1990-12-01
A family of new spatially homogeneous Bianchi type VIh perfect fluid solutions of the Einstein equations is presented. The fluid flow is orthogonal to the spatially homogeneous hypersurfaces, and the pressure is proportional to the energy density.
Senseless demolition in progress, showing destruction of perfectly decent and ...
Senseless demolition in progress, showing destruction of perfectly decent and recyclable mill building. Problem exacerbated by high value of scrap iron. - Phoenix Iron Company, Rolling Mill, North of French Creek, west of Fairview Avenue, Phoenixville, Chester County, PA
Perfection and the Bomb: Nuclear Weapons, Teleology, and Motives.
ERIC Educational Resources Information Center
Brummett, Barry
1989-01-01
Uses Kenneth Burke's theory of perfection to explore the vocabularies of nuclear weapons in United States public discourse and how "the Bomb" as a God term has gained imbalanced ascendancy in centers of power. (MS)
Perfect state transfer without state initialization and remote collaboration
Markiewicz, Marcin; Wiesniak, Marcin
2009-05-15
We present a perfect state transfer protocol via a qubit chain with the evolution governed by the xx Hamiltonian. In contrast to the recent protocol announced in Phys. Rev. Lett. 101, 230502 (2008), our method does not demand any remote-cooperated initialization and sending classical information about measurement outcomes. We achieve the perfect state transfer only with the assumption of access to two spins at each end of the chain, while the initial state of the whole chain is irrelevant.
Jackson-type inequalities for spherical neural networks with doubling weights.
Lin, Shaobo; Zeng, Jinshan; Xu, Lin; Xu, Zongben
2015-03-01
Recently, the spherical data processing has emerged in many applications and attracted a lot of attention. Among all the methods for dealing with the spherical data, the spherical neural networks (SNNs) method has been recognized as a very efficient tool due to SNNs possess both good approximation capability and spacial localization property. For better localized approximant, weighted approximation should be considered since different areas of the sphere may play different roles in the approximation process. In this paper, using the minimal Riesz energy points and the spherical cap average operator, we first construct a class of well-localized SNNs with a bounded sigmoidal activation function, and then study their approximation capabilities. More specifically, we establish a Jackson-type error estimate for the weighted SNNs approximation in the metric of L(p) space for the well developed doubling weights.
Physics of Spherical Torus Plasmas
NASA Astrophysics Data System (ADS)
Peng, Y.-K. M.
1999-11-01
Broad and important progress in plasma tests, theory, new experiments, and future visions of the Spherical Torus (ST, or Very Low Aspect Ratio Tokamak) have emerged recently. These have substantially improved our understanding of the potential properties of the ST plasmas, since the preliminary calculation of the ST MHD equilibria more than a decade ago [Peng and Strickler, Nucl. Fusion 26 (1986) 576.]. Exciting data have been obtained from Concept Exploration-level ST experiments of modest capabilities (with major radii up to 35 cm). These include START (U.K.), HIT-I and II (University of Washington), CDX-U (PPPL), HIST and TS-3 (Japan), etc., and made important scientific contributions to toroidal confinement in general. These results have helped approval 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 (AT) research, a wide range of new ST physics features have been suggested. These properties of the ST plasma will be tested at the 1-MA level (with major radii up to 80 cm) in the new Proof-of-Principle devices NSTX (U.S.), MAST (U.K.), and Globus-M (R.F.), which are scheduled to resume experiments before this APS meeting. New Concept Exploration tests such as Pegasus (University of Wisconsin) and others in Japan present additional opportunities for progress. This tutorial paper will summarize our understanding and projections of the physics of the ST plasmas, the investigation of which will hopefully bring new excitement and enthusiasm for fusion energy sciences research in the U.S. and the world. the address below:
Wrinkling crystallography on spherical surfaces
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
Geometrodynamics in a spherically symmetric, static crossflow of null dust
Horvath, Zsolt; Kovacs, Zoltan; Gergely, Laszlo A.
2006-10-15
The spherically symmetric, static space-time generated by a crossflow of noninteracting radiation streams, treated in the geometrical optics limit (null dust), is equivalent to an anisotropic fluid forming a radiation atmosphere of a star. This reference fluid provides a preferred/internal time, which is employed as a canonical coordinate. Among the advantages we encounter a new Hamiltonian constraint, which becomes linear in the momentum conjugate to the internal time (therefore yielding a functional Schroedinger equation after quantization), and a strongly commuting algebra of the new constraints.
NASA Technical Reports Server (NTRS)
1997-01-01
Session WA1 includes short reports concerning: (1) Medical and Physiological Studies During 438-Day Space Flights: (2) Human Performance During a 14 Month Space Mission: (3) Homeostasis in Long-Term Microgravity Conditions; (4) Strategy of Preservation of Health of Cosmonauts in Prolonged and Superprolonged Space Flights; (5) Rehabilitation of Cosmonauts Health Following Long-Term Space Missions; and (6) Perfect Cosmonauts: Some Features of Bio-Portrait.
Compression dynamics of quasi-spherical wire arrays with different linear mass profiles
NASA Astrophysics Data System (ADS)
Mitrofanov, K. N.; Aleksandrov, V. V.; Gritsuk, A. N.; Grabovski, E. V.; Frolov, I. N.; Laukhin, Ya. N.; Oleinik, G. M.; Ol'khovskaya, O. G.
2016-09-01
Results of experimental studies of the implosion of quasi-spherical wire (or metalized fiber) arrays are presented. The goal of the experiments was to achieve synchronous three-dimensional compression of the plasma produced in different regions of a quasi-spherical array into its geometrical center. To search for optimal synchronization conditions, quasi-spherical arrays with different initial profiles of the linear mass were used. The following dependences of the linear mass on the poloidal angle were used: m l (θ) ∝ sin-1θ and m l (θ) ∝ sin-2θ. The compression dynamics of such arrays was compared with that of quasi-spherical arrays without linear mass profiling, m l (θ) = const. To verify the experimental data, the spatiotemporal dynamics of plasma compression in quasi-spherical arrays was studied using various diagnostics. The experiments on three-dimensional implosion of quasi-spherical arrays made it possible to study how the frozen-in magnetic field of the discharge current penetrates into the array. By measuring the magnetic field in the plasma of a quasi-spherical array, information is obtained on the processes of plasma production and formation of plasma flows from the wire/fiber regions with and without an additionally deposited mass. It is found that penetration of the magnetic flux depends on the initial linear mass profile m l (θ) of the quasi-spherical array. From space-resolved spectral measurements and frame imaging of plasma X-ray emission, information is obtained on the dimensions and shape of the X-ray source formed during the implosion of a quasi-spherical array. The intensity of this source is estimated and compared with that of the Z-pinch formed during the implosion of a cylindrical array.
Avni, Amir; Ahrens, Jens; Geier, Matthias; Spors, Sascha; Wierstorf, Hagen; Rafaely, Boaz
2013-05-01
The area of sound field synthesis has significantly advanced in the past decade, facilitated by the development of high-quality sound-field capturing and re-synthesis systems. Spherical microphone arrays are among the most recently developed systems for sound field capturing, enabling processing and analysis of three-dimensional sound fields in the spherical harmonics domain. In spite of these developments, a clear relation between sound fields recorded by spherical microphone arrays and their perception with a re-synthesis system has not yet been established, although some relation to scalar measures of spatial perception was recently presented. This paper presents an experimental study of spatial sound perception with the use of a spherical microphone array for sound recording and headphone-based binaural sound synthesis. Sound field analysis and processing is performed in the spherical harmonics domain with the use of head-related transfer functions and simulated enclosed sound fields. The effect of several factors, such as spherical harmonics order, frequency bandwidth, and spatial sampling, are investigated by applying the repertory grid technique to the results of the experiment, forming a clearer relation between sound-field capture with a spherical microphone array and its perception using binaural synthesis regarding space, frequency, and additional artifacts. The experimental study clearly shows that a source will be perceived more spatially sharp and more externalized when represented by a binaural stimuli reconstructed with a higher spherical harmonics order. This effect is apparent from low spherical harmonics orders. Spatial aliasing, as a result of sound field capturing with a finite number of microphones, introduces unpleasant artifacts which increased with the degree of aliasing error.
How should spin-weighted spherical functions be defined?
NASA Astrophysics Data System (ADS)
Boyle, Michael
2016-09-01
Spin-weighted spherical functions provide a useful tool for analyzing tensor-valued functions on the sphere. A tensor field can be decomposed into complex-valued functions by taking contractions with tangent vectors on the sphere and the normal to the sphere. These component functions are usually presented as functions on the sphere itself, but this requires an implicit choice of distinguished tangent vectors with which to contract. Thus, we may more accurately say that spin-weighted spherical functions are functions of both a point on the sphere and a choice of frame in the tangent space at that point. The distinction becomes extremely important when transforming the coordinates in which these functions are expressed, because the implicit choice of frame will also transform. Here, it is proposed that spin-weighted spherical functions should be treated as functions on the spin or rotation groups, which simultaneously tracks the point on the sphere and the choice of tangent frame by rotating elements of an orthonormal basis. In practice, the functions simply take a quaternion argument and produce a complex value. This approach more cleanly reflects the geometry involved, and allows for a more elegant description of the behavior of spin-weighted functions. In this form, the spin-weighted spherical harmonics have simple expressions as elements of the Wigner 𝔇 representations, and transformations under rotation are simple. Two variants of the angular-momentum operator are defined directly in terms of the spin group; one is the standard angular-momentum operator L, while the other is shown to be related to the spin-raising operator ð.
Microphase separations of the fluids with spherically symmetric competing interactions.
Kim, Soon-Chul; Suh, Soong-Hyuck; Seong, Baek-Seok
2012-09-21
A density functional perturbation theory has been developed for studying the phase behaviors of a competing system in the spherical pores. The pore size as well as the intensity of competing interactions exerts a strong influence on the vapor-liquid, vapor-cluster, and cluster-liquid transitions of a competing system. The microdomain spacing (D) of the cluster is commensurate with the periodicity of modulation in the particle density distributions of a competing system in a spherical pore with the pore radius (R). For the cluster phase, we find that the multi-vaporlike void is formed depending on the periodicity of modulation by finite-size artifacts. For R < D, the competing system only shows the vapor-liquid transition at a high amplitude. For R > D, the vapor-cluster and cluster-liquid transitions are found at a high amplitude, whereas at a low amplitude, the cluster-liquid transition only occurs. The competing system exhibits two tricritical points, which are joined to one another by the line of second-order transitions at the low and high densities. A comparison with the result of a slit pore shows that (i) the tricritical points in a spherical pore, which has the highest symmetry, occur at a low amplitude compared with that of a slit pore because of the geometrical properties of the pores, and that (ii) the slit pore relatively shows the wide vapor-cluster and cluster-liquid coexistence regions compared with that of a spherical pore: the geometrical symmetry of a pore results in a weaker tendency for phase separation. PMID:22998277
Compound catadioptric telescopes with all spherical surfaces.
Sigler, R D
1978-05-15
Catadioptric, all spherical Cassegrainian and Gregorian telescopes with one and two full aperture corrector lenses are investigated. Appropriate closed form third-order aberration equations are presented, and a variety of aplanatic and anastigmatic solutions are indicated. PMID:20198015
FY 2005 Miniature Spherical Retroreflectors Final Report
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.
Sphericity determination using resonant ultrasound spectroscopy
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.
Sphericity determination using resonant ultrasound spectroscopy
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.
FY 2006 Miniature Spherical Retroreflectors Final Report
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.
Vacuum static non-spherical GR equations
NASA Astrophysics Data System (ADS)
Karbanovski, V. V.; Beloushko, K. E.; Markov, V. N.; Kairov, T. V.; Melehina, O. V.
2015-11-01
The vacuum static non-spherical equations are considered. The new solutions, which not contain in class of the Schwarzschild-like metrics and also its generalization are obtain. The perspectives for further investigations are discussed.
Feasibility study for the Spherical Torus Experiment
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)
Compound catadioptric telescopes with all spherical surfaces.
Sigler, R D
1978-05-15
Catadioptric, all spherical Cassegrainian and Gregorian telescopes with one and two full aperture corrector lenses are investigated. Appropriate closed form third-order aberration equations are presented, and a variety of aplanatic and anastigmatic solutions are indicated.
Scientists Track 'Perfect Storm' on Mars
NASA Technical Reports Server (NTRS)
2001-01-01
Two dramatically different faces of our Red Planet neighbor appear in these comparison images showing how a global dust storm engulfed Mars with the onset of Martian spring in the Southern Hemisphere. When NASA's Hubble Space Telescope imaged Mars in June, the seeds of the storm were caught brewing in the giant Hellas Basin (oval at 4 o'clock position on disk) and in another storm at the northern polar cap.
When Hubble photographed Mars in early September, the storm had already been raging across the planet for nearly two months obscuring all surface features. The fine airborne dust blocks a significant amount of sunlight from reaching the Martian surface. Because the airborne dust is absorbing this sunlight, it heats the upper atmosphere. Seasonal global Mars dust storms have been observed from telescopes for over a century, but this is the biggest storm ever seen in the past several decades.
Mars looks gibbous in the right photograph because it is 26 million miles farther from Earth than in the left photo (though the pictures have been scaled to the same angular size), and our viewing angle has changed. The left picture was taken when Mars was near its closest approach to Earth for 2001 (an event called opposition); at that point the disk of Mars was fully illuminated as seen from Earth because Mars was exactly opposite the Sun.
Both images are in natural color, taken with Hubble's Wide Field Planetary Camera 2.
PREPARATION OF SPHERICAL URANIUM DIOXIDE PARTICLES
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)
Exact spherical solutions in Einsteinian gravitostatics
NASA Astrophysics Data System (ADS)
Ionescu-Pallas, Nicolae
The author found a new solution of the Einstein's field equations with nonvanishing cosmological constant, corresponding to a Spherical source of Radius R. The solution imply 2 Poisson-type equations and the solution is expressed in terms of the total energy of the Spherical source. Outside the source the found solution acquires the known form. The author establishes a direct connection between Einstein's gravitostatics and Newtonian one.
Sudhahar, S.; Zahid, I. MD; Kumar, M. Krishna; Kumar, R. Mohan
2015-06-24
Piperidinium p-hydroxybenzoate (PPHB) crystal was grown by slow evaporation method. Single crystal X-ray diffraction studies confirm that PPHB crystallizes in monoclinic crystal system with noncentrosymmetric space group Cc. The crystalline perfection of the grown crystal was evaluated by using high resolution X-ray diffractometry. UV-Visible transmission and birefringence studies were employed on the grown PPHB crystal. The laser induced damage threshold value was estimated using Nd:YAG laser. Thermal behavior of PPHB crystal has been investigated by TG-DTA analyses. Etching studies have been performed to assess the growth pattern of PPHB crystal.
Competitive interaction between two different spherical sinks.
McDonald, Nyrée; Strieder, William
2004-10-22
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 (10(8) 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. (c) 2004 American Institute of Physics.
Imprints of spherical nontrivial topologies on the cosmic microwave background.
Niarchou, Anastasia; Jaffe, Andrew
2007-08-24
The apparent low power in the cosmic microwave background (CMB) temperature anisotropy power spectrum derived from the Wilkinson Microwave Anisotropy Probe motivated us to consider the possibility of a nontrivial topology. We focus on simple spherical multiconnected manifolds and discuss their implications for the CMB in terms of the power spectrum, maps, and the correlation matrix. We perform a Bayesian model comparison against the fiducial best-fit cold dark matter model with a cosmological constant based both on the power spectrum and the correlation matrix to assess their statistical significance. We find that the first-year power spectrum shows a slight preference for the truncated cube space, but the three-year data show no evidence for any of these spaces.
Complexified spherical waves and their sources. A review
NASA Astrophysics Data System (ADS)
Tagirdzhanov, A. M.; Kiselev, A. P.
2015-08-01
Spherical waves in which one of the coordinates of a source point is complexified are considered. Interest in such exact solutions of the wave equation known as "complex source wave fields," is stipulated by their Gaussian localization, both in the time-harmonic regime and in the nonstationary case, under a proper choice of the wave form. Since a correct description of the square root occurring in the solution requires the choice of a branch cut, the solution has a jump in the physical space and thus satisfies an equation with a certain source. We study such sources in the physical space for various choices of a branch of the root for the time-harmonic and nonstationary cases. From this point of view, Izmest'ev—Deschamps Gaussian beams, Gaussian wave packets, solutions presented by Felsen and Heyman, Sheppard and Saghafi, Saari, as well as X-waves, are examined.
Reflectarray Demonstrated to Transform Spherical Waves into Plane Waves
NASA Technical Reports Server (NTRS)
Zaman, Afrosz J.
1998-01-01
The development of low-cost, high-efficiency array antennas has been the research focus of NASA Lewis Research Center's Communications Technology Division for the past 15 years. One area of current interest is reflectarray development. Reflectarrays have generally been used to replace reflector antennas. In this capacity, different configurations (such as prime focus and offset) and various applications (such as dual frequency and scanning) have been demonstrated with great success. One potential application that has not been explored previously is the use of reflectarrays to compensate for phase errors in space-power-combining applications, such as a space-fed lens and power-combining amplifiers. Recently, we experimentally investigated the feasibility of using a reflectarray as an alternative to a dielectric lens for such applications. The experiment involved transforming the spherical waves from an orthomode horn to plane waves at the horn aperture. The reflectarray consists of square patches terminated in open stubs to provide the necessary phase compensation.
Zhang, Yihui; Yang, Yongying; Li, Chen; Wu, Fan; Chai, Huiting; Yan, Kai; Zhou, Lin; Li, Yang; Liu, Dong; Bai, Jian; Shen, Yibing
2016-08-10
In the field of automatic optical inspection, it is imperative to measure the defects on spherical optical surfaces. So a novel spherical surface defect evaluation system is established in this paper to evaluate defects on optical spheres. In order to ensure the microscopic scattering dark-field imaging of optical spheres with different surface shape and radius of curvature, illumination with variable aperture angle is employed. In addition, the scanning path of subapertures along the parallels and meridians is planned to detect the large optical spheres. Since analysis shows that the spherical defect information could be lost in the optical imaging, the three-dimensional correction based on a pin-hole model is proposed to recover the actual spherical defects from the captured two-dimensional images. Given the difficulty of subaperture stitching and defect feature extraction in three-dimensional (3D) space after the correction, the 3D subapertures are transformed into a plane to be spliced through geometric projection. Then, methods of the surface integral and calibration are applied to quantitatively evaluate the spherical defects. Furthermore, the 3D panorama of defect distribution on the spherical optical components can be displayed through the inverse projective reconstruction. Finally, the evaluation results are compared with the OLYMPUS microscope, testifying to the micrometer resolution, and the detection error is less than 5%. PMID:27534456
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.
Experimental perfect state transfer of an entangled photonic qubit
NASA Astrophysics Data System (ADS)
Chapman, Robert J.; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-04-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems.
Experimental perfect state transfer of an entangled photonic qubit.
Chapman, Robert J; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-04-18
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems.
Experimental perfect state transfer of an entangled photonic qubit.
Chapman, Robert J; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-01-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems. PMID:27088483
Large-Scale All-Dielectric Metamaterial Perfect Reflectors
Moitra, Parikshit; Slovick, Brian A.; li, Wei; Kravchencko, Ivan I.; Briggs, Dayrl P.; Krishnamurthy, S.; Valentine, Jason
2015-05-08
All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. In this paper, we take advantage of the low absorption loss as well as the simple unit cell geometry to demonstrate large-scale (centimeter-sized) all-dielectric metamaterial perfect reflectors made from silicon cylinder resonators. These perfect reflectors, operating in the telecommunications band, were fabricated using self-assembly based nanosphere lithography. In spite of the disorder originating from the self-assembly process, the average reflectance of the metamaterial perfect reflectors is 99.7% at 1530 nm, surpassing the reflectance of metallic mirrors. Moreover, the spectral separation of the electric and magnetic resonances can be chosen to achieve the required reflection bandwidth while maintaining a high tolerance to disorder. Finally, the scalability of this design could lead to new avenues of manipulating light for low-loss and large-area photonic applications.
Large-Scale All-Dielectric Metamaterial Perfect Reflectors
Moitra, Parikshit; Slovick, Brian A.; li, Wei; Kravchencko, Ivan I.; Briggs, Dayrl P.; Krishnamurthy, S.; Valentine, Jason
2015-05-08
All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. In this paper, we take advantage of the low absorption loss as well as the simple unit cell geometry to demonstrate large-scale (centimeter-sized) all-dielectric metamaterial perfect reflectors made from silicon cylinder resonators. These perfect reflectors, operating in the telecommunications band, were fabricated using self-assembly based nanosphere lithography. In spite of the disorder originating from the self-assembly process, the average reflectance of the metamaterial perfect reflectors is 99.7% at 1530 nm, surpassing the reflectance of metallic mirrors. Moreover, the spectral separation of the electric and magnetic resonances canmore » be chosen to achieve the required reflection bandwidth while maintaining a high tolerance to disorder. Finally, the scalability of this design could lead to new avenues of manipulating light for low-loss and large-area photonic applications.« less
Experimental perfect state transfer of an entangled photonic qubit
Chapman, Robert J.; Santandrea, Matteo; Huang, Zixin; Corrielli, Giacomo; Crespi, Andrea; Yung, Man-Hong; Osellame, Roberto; Peruzzo, Alberto
2016-01-01
The transfer of data is a fundamental task in information systems. Microprocessors contain dedicated data buses that transmit bits across different locations and implement sophisticated routing protocols. Transferring quantum information with high fidelity is a challenging task, due to the intrinsic fragility of quantum states. Here we report on the implementation of the perfect state transfer protocol applied to a photonic qubit entangled with another qubit at a different location. On a single device we perform three routing procedures on entangled states, preserving the encoded quantum state with an average fidelity of 97.1%, measuring in the coincidence basis. Our protocol extends the regular perfect state transfer by maintaining quantum information encoded in the polarization state of the photonic qubit. Our results demonstrate the key principle of perfect state transfer, opening a route towards data transfer for quantum computing systems. PMID:27088483
Technology in Spherical Geometry Investigations: Reflections on Spontaneous Use and Motivation
ERIC Educational Resources Information Center
Sinclair, Margaret
2010-01-01
Students in a graduate geometry class used items such as paper, ribbon, plastic spheres, cardboard tubes, and markers to carry out investigations in spherical geometry. The hands-on activities helped students develop a new appreciation of geometry as a study of shape and space; however, the difficulty of subduing wayward elastics and drawing lines…
A relaxation method for minimizing a smooth function on a generalized spherical segment
NASA Astrophysics Data System (ADS)
Dulliev, A. M.
2014-02-01
The minimization of a smooth functional on a generalized spherical segment of a finite-dimensional Euclidean space is examined. A relaxation method that involves successive projections of the antigradient onto auxiliary sets of a simpler structure is proposed. It is shown that, under certain natural assumptions, this method converges to a stationary point.
Spherical Coordinate Systems for Streamlining Suited Mobility Analysis
NASA Technical Reports Server (NTRS)
Benson, Elizabeth; Cowley, Matthew; Harvill, Lauren; Rajulu. Sudhakar
2015-01-01
demonstrated that a spherical coordinate system is helpful in describing and visualizing the motion of a space suit. The system is particularly useful in describing the motion of the shoulder, where multiple degrees of freedom can lead to very complex motion paths.
Mono-disperse spherical Cu-Zn powder fabricated via the low wettability of liquid/solid interface
NASA Astrophysics Data System (ADS)
Lei, Chenglong; Huang, Haifu; Cheng, Zhenzhi; Tang, Shaolong; Du, Youwei
2015-12-01
Spherical Cu-Zn alloy powders were fabricated by combining the surface tension of a molten metal with the de-wetting of a metal droplet on a graphite surface. The effect that the gas pressure had on the surface morphology and composition was studied. The Zn concentration can be maintained at 20.18 wt.%, 15.5 wt.% and 12.08 wt.% using 0.22 MPa, 0.10 MPa, and 0.04 MPa, respectively, from a commercially available Cu-38 wt.%Zn raw material. The gas pressure was adjusted to control the surface volatility of Zn without affecting the spherical morphology, and higher gas pressure yielded less volatile Zn. The Cu-Zn alloy powders were perfectly spherical, even at a negative pressure of 0.04 MPa. The spherical Cu-Zn alloy particles hardly changed and were fully dense up to Cu-50 wt.%Zn, which allowed high-quality spherical Cu-Zn alloy powders to potentially serve a large composition range.
Cosmological perturbations of a perfect fluid and noncommutative variables
De Felice, Antonio; Gerard, Jean-Marc; Suyama, Teruaki
2010-03-15
We describe the linear cosmological perturbations of a perfect fluid at the level of an action, providing thus an alternative to the standard approach based only on the equations of motion. This action is suited not only to perfect fluids with a barotropic equation of state, but also to those for which the pressure depends on two thermodynamical variables. By quantizing the system we find that (1) some perturbation fields exhibit a noncommutativity quite analogous to the one observed for a charged particle moving in a strong magnetic field, (2) local curvature and pressure perturbations cannot be measured simultaneously, (3) ghosts appear if the null energy condition is violated.
Dual band metamaterial perfect absorber based on artificial dielectric "molecules".
Liu, Xiaoming; Lan, Chuwen; Li, Bo; Zhao, Qian; Zhou, Ji
2016-01-01
Dual band metamaterial perfect absorbers with two absorption bands are highly desirable because of their potential application areas such as detectors, transceiver system, and spectroscopic imagers. However, most of these dual band metamaterial absorbers proposed were based on resonances of metal patterns. Here, we numerically and experimentally demonstrate a dual band metamaterial perfect absorber composed of artificial dielectric "molecules" with high symmetry. The artificial dielectric "molecule" consists of four "atoms" of two different sizes corresponding to two absorption bands with near unity absorptivity. Numerical and experimental absorptivity verify that the dual-band metamaterial absorber is polarization insensitive and can operate in wide-angle incidence. PMID:27406699
Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface
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
Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface
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 = (α_{R}Ρ²_{2}/μ²_{²})¹^{/}³ R (where α_{R}, Ρ_{2} and μ_{2} 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 α_{R}. 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 Y_{n} and Y_{n+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.
Recent Progress on Spherical Torus Research
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.
Discontinuous Galerkin finite element method applied to the 1-D spherical neutron transport equation
Machorro, Eric . E-mail: machorro@amath.washington.edu
2007-04-10
Discontinuous Galerkin finite element methods are used to estimate solutions to the non-scattering 1-D spherical neutron transport equation. Various trial and test spaces are compared in the context of a few sample problems whose exact solution is known. Certain trial spaces avoid unphysical behaviors that seem to plague other methods. Comparisons with diamond differencing and simple corner-balancing are presented to highlight these improvements.
Current collection by a spherical high voltage probe: Electron trapping and collective processes
NASA Technical Reports Server (NTRS)
Palmadesso, Peter J.
1990-01-01
The author summarizes the results of theoretical studies of the interaction of an uninsulated, spherical, high voltage (10's of KV positive) probe with the ionospheric environment. The focus of this effort was the phenomenon of electron trapping and its implications for breakdown processes (collisional regime) and the current-voltage relationship governing current collection (collisionless regime) in space-based pulsed power systems with high voltage components exposed to space, e.g., the SPEAR I experiment.
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.
Stability of spherical converging shock wave
NASA Astrophysics Data System (ADS)
Murakami, M.; Sanz, J.; Iwamoto, Y.
2015-07-01
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 ℓc, such that all the eigenmode perturbations for ℓ > ℓc 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.
Thermal Fluid Multiphysics Optimization of Spherical Tokamak
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.
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.
Design and implementation of spherical ultrasonic motor.
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.
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.
Background reduction of a spherical gaseous detector
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.
A spherical Taylor-Couette dynamo
NASA Astrophysics Data System (ADS)
Marcotte, Florence; Gissinger, Christophe
2016-04-01
We present a new scenario for magnetic field amplification in the planetary interiors where an electrically conducting fluid is confined in a differentially rotating, spherical shell (spherical Couette flow) with thin aspect-ratio. When the angular momentum sufficiently decreases outwards, a primary hydrodynamic instability is widely known to develop in the equatorial region, characterized by pairs of counter-rotating, axisymmetric toroidal vortices (Taylor vortices) similar to those observed in cylindrical Couette flow. We characterize the subcritical dynamo bifurcation due to this spherical Taylor-Couette flow and study its evolution as the flow successively breaks into wavy and turbulent Taylor vortices for increasing Reynolds number. We show that the critical magnetic Reynolds number seems to reach a constant value as the Reynolds number is gradually increased. The role of global rotation on the dynamo threshold and the implications for planetary interiors are finally discussed.
A quadrilateralized spherical cube Earth data base
NASA Technical Reports Server (NTRS)
Chan, F. K.
1980-01-01
A quadrilateralized spherical cube was constructed to form the basis for the rapid storage and retrieval of high resolution data obtained of the Earth's surface. The structure of this data base was derived from a spherical cube, which was obtained by radially projecting a cube onto its circumscribing sphere. An appropriate set of curvilinear coordinates were chosen such that the resolution cells on the spherical cube were of equal area and were also of essentially the same shape. The main properties of the Earth data base were that the indexing scheme was binary and telescopic in nature, the resolution cells were strung together in a two dimensional manner, the cell addresses were easily computed, and the conversion from geographic to data base coordinates was comparatively simple. It was concluded that this data base structure was perhaps the most viable one for handling remotely sensed data obtained by satellites.
Spherical aberration in electrically thin flat lenses.
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. PMID:27505651
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.
Stability of spherical converging shock wave
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.
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.
A spherical collapse solution with neutrino outflow
Glass, E.N. )
1990-08-01
A three-parameter family of solutions of Einstein's field equations is given that represents a collapsing perfect fluid with outgoing neutrino flux. Solutions with naked'' singularities are exhibited. They can be forbidden by requiring pressure less than or equal to the density as a condition of cosmic censorship.
The Effects of Non-Sphericity in Diagnosis of Solar and Stellar Atmospheres
NASA Astrophysics Data System (ADS)
Pecker, Jean-Claude
1996-12-01
Between the interplanetary medium, filled by winds, magnetic structures, etc., and the interior of stars, opaque, and dominated heavily by the gravitational spherical field, the stellar atmosphere is a place where the true physical equilibrium, on the inside, sufficiently described by the parameters L, M, R, and the chemical composition X, Y, Z, is progressively changing into a situation far for equilibrium, which needs many more parameters to be properly described. The assumption that the equilibrium situation was dominating in the atmosphere has been generally accepted during the first half of this century. Since 1950 or so, we progressively learnt that the thermodynamical equilibrium (TE), and even the ‘local’ thermodynamical equilibrium (LTE), are far from being actually in existence, that the radiative equilibrium (RE) is not actually perfect, convection, diffusion, magnetism, dissipation processes... playing a non-negligible part in the energy transport, that the hydrostatic equilibrium (HE) is only an approximation, as the convection and the magnetism are affecting the atmospheric layers, that neither the sphericity of atmospheric layers (plane-parallel hypothesis: PP) is achieved, nor the homogeneity of stellar iso-τ layers. During the 1950s and following decades, we began to suspect these difficulties and their consequences. In this paper, we turn towards a new consequence of the last-mentioned effect: the influence of non-sphericity and inhomogeneity upon the stellar (and solar perhaps) abundances of elements.
Toroidal membrane vesicles in spherical confinement.
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.
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.
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.
Mass transport in annular spherical system
NASA Astrophysics Data System (ADS)
Bauer, Helmut F.
The mass transport between two concentric spheres with inlet and outlet at the poles was determined for ideal liquid flow (plug flow) and laminar flow for constant concentration at the spherical walls and constant concentration at the inlet. Velocity distribution and local concentration profiles were determined analytically for various widths of the annular spherical conduit and various diffusive flow parameters. It is found that with the increase of this parameter, the decay becomes quite rapid and that the same effect occurs for increasing diameter ratio of the spheres. This configuration may possibly be used as a basic element of an artificial kidney.
Spherical quartz crystals investigated with synchrotron radiation
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.
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.
Guan, Jianguo; Li, Wei; Wang, Wei; Fu, Zhengyi
2011-09-26
A general boundary mapping method is proposed to enable the designing of various transformation devices with arbitrary shapes by reducing the traditional space-to-space mapping to boundary-to-boundary mapping. The method also makes the designing of complex-shaped transformation devices more feasible and flexible. Using the boundary mapping method, an arbitrarily shaped perfect electric conductor (PEC) reshaping device, which is called a "PEC reshaper," is demonstrated to visually reshape a PEC with an arbitrary shape to another arbitrary one. Unlike the previously reported simple PEC reshaping devices, the arbitrarily shaped PEC reshaper designed here does not need to share a common domain. Moreover, the flexibilities of the boundary mapping method are expected to inspire some novel PEC reshapers with attractive new functionalities.
Overemphasis on Perfectly Competitive Markets in Microeconomics Principles Textbooks
ERIC Educational Resources Information Center
Hill, Roderick; Myatt, Anthony
2007-01-01
Microeconomic principles courses focus on perfectly competitive markets far more than other market structures. The authors examine five possible reasons for this but find none of them sufficiently compelling. They conclude that textbook authors should place more emphasis on how economists select appropriate models and test models' predictions…
America's Perfect Storm: Three Forces Changing Our Nation's Future
ERIC Educational Resources Information Center
Kirsch, Irwin; Braun, Henry; Yamamoto, Kentaro; Sum, Andrew
2007-01-01
The authors offer the image of our nation as a nautical convoy. Some boats are large, well built, and able to ride out the heaviest of turbulent seas. Others are smaller, but still quite sturdy, and able to survive. Many however, are fragile, meagerly equipped, and easily capsized in rough waters. This convoy is in the midst of a perfect storm…
Unity and Duality in Barack Obama's "A More Perfect Union"
ERIC Educational Resources Information Center
Terrill, Robert E.
2009-01-01
Faced with a racialized political crisis that threatened to derail his campaign to become the first African American president of the United States, Barack Obama delivered a speech on race titled "A More Perfect Union." He begins by portraying himself as an embodiment of double consciousness, but then invites his audience to share his doubled…
Animal infection models and ethics -- the perfect infection model.
Zak, Oto; O'Reilly, Terence
1993-05-01
Experimental infection models have long been recognized as an essential part of testing anti-infective therapies. A perfect animal model would be a model that satisfied not only scientific criteria, but ethical criteria as well. In the design and execution of such experiments, scientific and ethical considerations are not mutually exclusive, but should be convergent and therefore result in the optimal model.
Perfect control of reflection and refraction using spatially dispersive metasurfaces
NASA Astrophysics Data System (ADS)
Asadchy, V. S.; Albooyeh, M.; Tcvetkova, S. N.; Díaz-Rubio, A.; Ra'di, Y.; Tretyakov, S. A.
2016-08-01
Nonuniform metasurfaces (electrically thin composite layers) can be used for shaping refracted and reflected electromagnetic waves. However, known design approaches based on the generalized refraction and reflection laws do not allow realization of perfectly performing devices: there are always some parasitic reflections into undesired directions. In this paper we introduce and discuss a general approach to the synthesis of metasurfaces for full control of transmitted and reflected plane waves and show that perfect performance can be realized. The method is based on the use of an equivalent impedance matrix model which connects the tangential field components at the two sides on the metasurface. With this approach we are able to understand what physical properties of the metasurface are needed in order to perfectly realize the desired response. Furthermore, we determine the required polarizabilities of the metasurface unit cells and discuss suitable cell structures. It appears that only spatially dispersive metasurfaces allow realization of perfect refraction and reflection of incident plane waves into arbitrary directions. In particular, ideal refraction is possible only if the metasurface is bianisotropic (weak spatial dispersion), and ideal reflection without polarization transformation requires spatial dispersion with a specific, strongly nonlocal response to the fields.
Inhomogeneous generalizations of Bianchi type VIh models with perfect fluid
NASA Astrophysics Data System (ADS)
Roy, S. R.; Prasad, A.
1991-07-01
Inhomogeneous universes admitting an Abelian G2 of isometry and filled with perfect fluid have been derived. These contain as special cases exact homogeneous universes of Bianchi type VIh. Many of these universes asymptotically tend to homogeneous Bianchi VIh universes. The models have been discussed for their physical and kinematical behaviors.
Designing the Perfect Plant: Activities to Investigate Plant Ecology
ERIC Educational Resources Information Center
Lehnhoff, Erik; Woolbaugh, Walt; Rew, Lisa
2008-01-01
Plant ecology is an important subject that often receives little attention in middle school, as more time during science classes is devoted to plant biology. Therefore, the authors have developed a series of activities, including a card game--Designing the Perfect Plant--to introduce student's to plant ecology and the ecological trade offs…
Perfect Power Prototype for Illinois Institute of Technology
Shahidehpour, Mohammad
2014-09-30
Starting in October 2008, Illinois Institute of Technology (IIT), in collaboration with over 20 participating members, led an extensive effort to develop, demonstrate, promote, and commercialize a microgrid system and offer supporting technologies that will achieve Perfect Power at the main campus of IIT. A Perfect Power system, as defined by the Galvin Electricity Initiative (GEI), is a system that cannot fail to meet the electric needs of the individual end-user. The Principle Investigator of this Perfect Power project was Dr. Mohammad Shahidehpour, Director of the Robert W. Galvin Center for Electricity Innovation at IIT. There were six overall objectives of the Perfect Power project: (1) Demonstrate the higher reliability introduced by the microgrid system at IIT; (2) Demonstrate the economics of microgrid operations; (3) Allow for a decrease of fifty percent (50%) of grid electricity load; (4) Create a permanent twenty percent (20%) decrease in peak load from 2007 level; (5) Defer planned substation through load reduction; (6) Offer a distribution system design that can be replicated in urban communities.
Computation of Thermally Perfect Properties of Oblique Shock Waves
NASA Technical Reports Server (NTRS)
Tatum, Kenneth E.
1996-01-01
A set of compressible flow relations describing flow properties across oblique shock waves, derived for a thermally perfect, calorically imperfect gas, is applied within the existing thermally perfect gas (TPG) computer code. The relations are based upon a value of cp expressed as a polynomial function of temperature. The updated code produces tables of compressible flow properties of oblique shock waves, as well as the original properties of normal shock waves and basic isentropic flow, in a format similar to the tables for normal shock waves found in NACA Rep. 1135. The code results are validated in both the calorically perfect and the calorically imperfect, thermally perfect temperature regimes through comparisons with the theoretical methods of NACA Rep. 1135, and with a state-of-the-art computational fluid dynamics code. The advantages of the TPG code for oblique shock wave calculations, as well as for the properties of isentropic flow and normal shock waves, are its ease of use, and its applicability to any type of gas (monatomic, diatomic, triatomic, polyatomic, or any specified mixture thereof).
The Meaning of the Perfective Aspect in Russian.
ERIC Educational Resources Information Center
Ferrell, James
1951-01-01
Descriptions of the perfective aspect in Russian taken from Miklosich, Saxmatov, Peskovsky, Fortunatov, and Karcevskij serve as background reading to the author's discussion of the problem. He explores three basic questions: (1) Is aspect a Russian problem in grammar or lexicography; (2) What is the nature of the correlation between the perfective…
The Perfect Storm—Genetic Engineering, Science, and Ethics
NASA Astrophysics Data System (ADS)
Rollin, Bernard E.
2012-07-01
Uncertainty about ethics has been a major factor in societal rejection of biotechnology. Six factors help create a societal "perfect storm" regarding ethics and biotechnology: Social demand for ethical discussion; societal scientific illiteracy; poor social understanding of ethics; a "Gresham's Law for Ethics;" Scientific Ideology; vested interests dominating ethical discussion. How this can be remedied is discussed.
The Perfect Storm--Genetic Engineering, Science, and Ethics
ERIC Educational Resources Information Center
Rollin, Bernard E.
2014-01-01
Uncertainty about ethics has been a major factor in societal rejection of biotechnology. Six factors help create a societal "perfect storm" regarding ethics and biotechnology: Social demand for ethical discussion; societal scientific illiteracy; poor social understanding of ethics; a "Gresham's Law for Ethics;" Scientific…
Computation of Thermally Perfect Oblique Shock Wave Properties
NASA Technical Reports Server (NTRS)
Tatum, Kenneth E.
1997-01-01
A set of compressible flow relations describing flow properties across oblique shock waves, derived for a thermally perfect, calorically imperfect gas, is applied within the existing thermally perfect gas (TPG) computer code. The relations are based upon the specific heat expressed as a polynomial function of temperature. The updated code produces tables of compressible flow properties of oblique shock waves, as well as the original properties of normal shock waves and basic isentropic flow, in a format similar to the tables for normal shock waves found in NACA Rep. 1135. The code results are validated in both the calorically perfect and the calorically imperfect, thermally perfect temperature regimes through comparisons with the theoretical methods of NACA Rep. 1135. The advantages of the TPG code for oblique shock wave calculations, as well as for the properties of isentropic flow and normal shock waves, are its ease of use and its applicability to any type of gas (monatomic, diatomic, triatomic, polyatomic, or any specified mixture thereof).
C. Neumeyer; H.M. Fan; J. Chrzanowski; P. Heitzenroeder; and the NSTX Team
1999-10-01
NSTX is one of the largest of a new class of magnetic plasma research devices known as spherical toroids (STs). The plasma in a ST is characterized by its almost spherical shape with a slender cylindrical region through its vertical axis. The so-called ''center stack'' is located in this region. It contains magnetic windings for confining the plasma, induce the plasma current, and shape the plasma. This paper will describe the engineering challenges of designing the center stack magnets to meet their operational requirements within this constrained space.
Eccentricity in Images of Circular and Spherical Targets and its Impact to 3D Object Reconstruction
NASA Astrophysics Data System (ADS)
Luhmann, T.
2014-06-01
This paper discusses a feature of projective geometry which causes eccentricity in the image measurement of circular and spherical targets. While it is commonly known that flat circular targets can have a significant displacement of the elliptical image centre with respect to the true imaged circle centre, it can also be shown that the a similar effect exists for spherical targets. Both types of targets are imaged with an elliptical contour. As a result, if measurement methods based on ellipses are used to detect the target (e.g. best-fit ellipses), the calculated ellipse centre does not correspond to the desired target centre in 3D space. This paper firstly discusses the use and measurement of circular and spherical targets. It then describes the geometrical projection model in order to demonstrate the eccentricity in image space. Based on numerical simulations, the eccentricity in the image is further quantified and investigated. Finally, the resulting effect in 3D space is estimated for stereo and multi-image intersections. It can be stated that the eccentricity is larger than usually assumed, and must be compensated for high-accuracy applications. Spherical targets do not show better results than circular targets. The paper is an updated version of Luhmann (2014) new experimental investigations on the effect of length measurement errors.
Toroidal configurations of perfect fluid in the Reissner-Nordström-(anti-)de Sitter spacetimes
Kucáková, Hana; Slaný, Petr; Stuchlík, Zdenĕk E-mail: petr.slany@fpf.slu.cz
2011-01-01
Influence of cosmological constant on toroidal fluid configurations around charged spherically symmetric black holes and naked singularities is demostrated by study of perfect-fluid tori with uniform distribution of specific angular momentum orbiting in the Reissner-Nordström-(anti-)de Sitter spacetimes. Toroidal configurations are allowed only in the spacetimes admitting existence of stable circular geodesics. Configurations with marginally closed equipotential (equipressure) surfaces crossing itself in a cusp allow accretion (through the inner cusp) and/or excretion (through the outer cusp) of matter from the toroidal configuration. Detailed classification of the Reissner-Nordström-(anti-)de Sitter spacetimes according to properties of the marginally stable tori is given. It is demonstrated that in the Reissner-Nordström-de Sitter naked-singularity spacetimes an interesting phenomenon of doubled tori can exist enabling exchange of matter between two tori in both inward and outward directions. In naked-singularity spacetimes the accretion onto the central singularity is impossible due to existence of a potential barrier.
The matter in the Big-Bang model is dust and not any arbitrary perfect fluid!
NASA Astrophysics Data System (ADS)
Mitra, Abhas
2011-05-01
We consider a spherically symmetric general relativistic perfect fluid in its comoving frame. It is found that, by integrating the local energy momentum conservation equation, a general form of g 00 can be obtained. During this study, we get a cue that an adiabatically evolving uniform density isolated sphere having ρ( r, t)= ρ 0( t), should comprise "dust" having p 0( t)=0; as recently suggested by Durgapal and Fuloria (J. Mod. Phys. 1:143, 2010) In fact, we offer here an independent proof to this effect. But much more importantly, we find that for the homogeneous and isotropic Friedmann-Robertson-Walker (FRW) metric having p( r, t)= p 0( t) and ρ( r, t)= ρ 0( t), g_{00} = e^{-2p0/(p0 +ρ0)}. But in general relativity (GR), one can choose an arbitrary t→ t ∗= f( t) without any loss of generality, and thus set g 00( t ∗)=1. And since pressure is a scalar, this implies that p 0( t ∗)= p 0( t)=0 in the Big-Bang model based on the FRW metric. This result gets confirmed by the fact the homogeneous dust metric having p( r, t)= p 0( t)=0 and ρ( r, t)= ρ 0( t) and the FRW metric are exactly identical. In other words, both the cases correspond to the same Einstein tensor Gab because they intrinsically have the same energy momentum tensor Tab=operatorname {diag}[ρ0(t), 0,0, 0].
Charged perfect fluid tori in strong central gravitational and dipolar magnetic fields
NASA Astrophysics Data System (ADS)
Kovář, Jiří; Slaný, Petr; Cremaschini, Claudio; Stuchlík, Zdeněk; Karas, Vladimír; Trova, Audrey
2016-06-01
We study electrically charged perfect fluid toroidal structures encircling a spherically symmetric gravitating object with Schwarzschild spacetime geometry and endowed with a dipole magnetic field. The work represents a direct continuation of our previous general-relativistic studies of electrically charged fluid in the approximation of zero conductivity, which formed tori around a Reissner-Nordström black hole or a Schwarzschild black hole equipped with a test electric charge and immersed in an asymptotically uniform magnetic field. After a general introduction of the zero-conductivity charged fluid model, we discuss a variety of possible topologies of the toroidal fluid configurations. Along with the charged equatorial tori forming interesting coupled configurations, we demonstrate the existence of the off-equatorial tori, for which the dipole type of magnetic field seems to be necessary. We focus on orbiting structures with constant specific angular momentum and on those in permanent rigid rotation. We stress that the general analytical treatment developed in our previous works is enriched here by the integrated form of the pressure equations. To put our work into an astrophysical context, we identify the central object with an idealization of a nonrotating magnetic neutron star. Constraining ranges of its parameters and also parameters of the circling fluid, we discuss a possible relevance of the studied toroidal structures, presenting along with their topology also pressure, density, temperature and charge profiles.
Properties of a polaron confined in a spherical quantum dot
NASA Astrophysics Data System (ADS)
Melnikov, Dmitriy V.
A Frohlich Hamiltonian describing the electron-phonon interaction in a spherical quantum dot embedded in another polar material is derived, taking into account interactions with both bulk longitudinal optical and surface optical phonons. The Hamiltonian is appropriate to the general case of a finite confining potential originating from a bandgap mismatch between the materials of the dot and the surrounding matrix. This Hamiltonian is then applied to treat the electron-phonon interaction in the adiabatic approximation for various quantum dot systems. It was found that, as the radius of the dot decreases, the magnitude of the electron-phonon interaction energy first increases, passes through a maximum, and then gradually decreases to the value appropriate to the situation where the electron is weakly localized inside the dot. For most dot radii the polaron properties are described well by a model assuming perfect electron confinement. Based on this result, the problem of the bound polaron confined perfectly in the quantum dot was investigated within the adiabatic and all-coupling variational approaches. The polaron properties have been studied performing both analytical and numerical calculations for various radii of the quantum dot and for different impurity positions inside the dot. Within the adiabatic approximation, it was found that the magnitude of the electron-phonon interaction increases as the radius decreases for any impurity position. It was also shown that the input from the electron-surface-phonon interaction to the total polaron energy is much larger than was found earlier for the free polaron confined in the dot. As a function of the impurity position, the electron-surface-phonon interaction energy increases as the impurity is shifted towards the surface, reaches its maximum when the impurity is positioned inside the dot and then decreases as the impurity moved close to surface. The all-coupling approach gave rise to the following results: for any
Tittl, Andreas; Harats, Moshe G; Walter, Ramon; Yin, Xinghui; Schäferling, Martin; Liu, Na; Rapaport, Ronen; Giessen, Harald
2014-10-28
Plasmonic devices with absorbance close to unity have emerged as essential building blocks for a multitude of technological applications ranging from trace gas detection to infrared imaging. A crucial requirement for such elements is the angle independence of the absorptive performance. In this work, we develop theoretically and verify experimentally a quantitative model for the angular behavior of plasmonic perfect absorber structures based on an optical impedance matching picture. To achieve this, we utilize a simple and elegant k-space measurement technique to record quantitative angle-resolved reflectance measurements on various perfect absorber structures. Particularly, this method allows quantitative reflectance measurements on samples where only small areas have been nanostructured, for example, by electron-beam lithography. Combining these results with extensive numerical modeling, we find that matching of both the real and imaginary parts of the optical impedance is crucial to obtain perfect absorption over a large angular range. Furthermore, we successfully apply our model to the angular dispersion of perfect absorber geometries with disordered plasmonic elements as a favorable alternative to current array-based designs. PMID:25251075
METHOD OF MAKING SPHERICAL ACTINIDE CARBIDE
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)
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…
Supersymmetric extension of the quantum spherical model
NASA Astrophysics Data System (ADS)
Gomes, Pedro R. S.; Bienzobaz, P. F.; Gomes, M.
2012-06-01
In this work, we present a supersymmetric extension of the quantum spherical model, both in components and also in the superspace formalisms. We find the solution for short- and long-range interactions through the imaginary time formalism path integral approach. The existence of critical points (classical and quantum) is analyzed and the corresponding critical dimensions are determined.
Programmable shape transformation of elastic spherical domes.
Abdullah, Arif M; Braun, Paul V; Hsia, K Jimmy
2016-07-20
We investigate mismatch strain driven programmable shape transformation of spherical domes and report the effects of different geometric and structural characteristics on dome behavior in response to applied mismatch strain. We envision a bilayer dome design where the differential swelling of the inner layer with respect to the passive outer layer in response to changes in dome surroundings (such as the introduction of an organic solvent) introduces mismatch strain within the bilayer system and causes dome shape transformation. Finite element analysis reveals that, in addition to snap-through, spherical domes undergo bifurcation buckling and eventually gradual bending to morph into cylinders with increasing mismatch strain. Besides demonstrating how the snap-through energy barrier depends on the spherical dome shape, our analysis identifies three distinct groups of dome geometries based on their mismatch strain-transformed configuration relationships. Our experiments with polymer-based elastic bilayer domes that exhibit differential swelling in organic solvents qualitatively confirm the finite element predictions. We establish that, in addition to externally applied stimuli (mismatch strain), bilayer spherical dome morphing can be tuned and hence programmed through its geometry and structural characteristics. Incorporation of an elastic instability mechanism such as snap-through within the framework of stimuli-responsive functional devices can improve their response time which is otherwise controlled by diffusion. Hence, our proposed design guidelines can be used to realize deployable, multi-functional, reconfigurable, and therefore, adaptive structures responsive to a diverse set of stimuli across multiple length scales.
Spherical fields as nonparaxial accelerating waves.
Alonso, Miguel A; Bandres, Miguel A
2012-12-15
We introduce nonparaxial spatially accelerating waves whose two-dimensional transverse profiles propagate along semicircular trajectories while approximately preserving their shape. We derive these waves by considering imaginary displacements on spherical fields, leading to simple closed-form expressions. The structure of these waves also allows the closed-form description of pulses.
Spherical torus, compact fusion at low field
Peng, Y.K.M.
1985-02-01
A spherical torus is obtained by retaining only the indispensable components on the inboard side of a tokamak plasma, such as a cooled, normal conductor that carries current to produce a toroidal magnetic field. The resulting device features an exceptionally small aspect ratio (ranging from below 2 to about 1.3), a naturally elongated D-shaped plasma cross section, and ramp-up of the plasma current primarily by noninductive means. As a result of the favorable dependence of the tokamak plasma behavior to decreasing aspect ratio, a spherical torus is projected to have small size, high beta, and modest field. Assuming Mirnov confinement scaling, an ignition spherical torus at a field of 2 T features a major radius of 1.5 m, a minor radius of 1.0 m, a plasma current of 14 MA, comparable toroidal and poloidal field coil currents, an average beta of 24%, and a fusion power of 50 MW. At 2 T, a Q = 1 spherical torus will have a major radius of 0.8 m, a minor radius of 0.5 m, and a fusion power of a few megawatts.
Fast discharge in a spherical cavity
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.
Analytic Modeling of Neural Tissue: I. A Spherical Bidomain.
Schwartz, Benjamin L; Chauhan, Munish; Sadleir, Rosalind J
2016-12-01
Presented here is a model of neural tissue in a conductive medium stimulated by externally injected currents. The tissue is described as a conductively isotropic bidomain, i.e. comprised of intra and extracellular regions that occupy the same space, as well as the membrane that divides them, and the injection currents are described as a pair of source and sink points. The problem is solved in three spatial dimensions and defined in spherical coordinates [Formula: see text]. The system of coupled partial differential equations is solved by recasting the problem to be in terms of the membrane and a monodomain, interpreted as a weighted average of the intra and extracellular domains. The membrane and monodomain are defined by the scalar Helmholtz and Laplace equations, respectively, which are both separable in spherical coordinates. Product solutions are thus assumed and given through certain transcendental functions. From these electrical potentials, analytic expressions for current density are derived and from those fields the magnetic flux density is calculated. Numerical examples are considered wherein the interstitial conductivity is varied, as well as the limiting case of the problem simplifying to two dimensions due to azimuthal independence. Finally, future modeling work is discussed. PMID:27613652
New second derivative theories of gravity for spherically symmetric spacetimes
NASA Astrophysics Data System (ADS)
Tibrewala, Rakesh
2015-06-01
We present new second derivative, generally covariant theories of gravity for spherically symmetric spacetimes (the general covariance is in the t-r plane) belonging to the class where the spherically symmetric Einstein-Hilbert theory is modified by the presence of {{g}θ θ } dependent functions. In 3+1 dimensional vacuum spacetimes there is a three-fold infinity of freedom in constructing such theories, as revealed by the presence of three arbitrary {{g}θ θ } dependent functions in the Hamiltonian (matter Hamiltonian also has the corresponding freedom). This result is not a contradiction to the theorem of Hojman et al [1], which is applicable to the full theory, whereas the above conclusion is for the symmetry reduced sector of the theory (which has a much reduced phase space). In the full theory where there are no special symmetries, the result of Hojman et al will continue to hold. In the process we also show that theories where the constraint algebra is deformed by the presence of {{g}θ θ } dependent functions—as is the case in the presence of inverse triad corrections in loop quantum gravity—can always be brought to the form where they obey the standard (undeformed) constraint algebra by performing a suitable canonical transformation. We prove that theories obtained after performing canonical transformation are inequivalent to the symmetry reduced general relativity and that the resulting theories fall within the purview of the theories mentioned above.
Recent progress on spherical torus research
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.
NASA Astrophysics Data System (ADS)
Takeuchi, Hiroshi; Kuniyoshi, Masaya; Daishido, Tsuneaki; Asuma, Kuniyuki; Matsumura, Nobuo; Takefuji, Kazuhiro; Niinuma, Kotaro; Ichikawa, Hajime; Okubo, Riki; Sawano, Akihiro; Yoshimura, Naoya; Fujii, Fumiyuki; Mizuno, Keiju; Akamine, Yukinori
2005-10-01
The Nasu Radio Interferometer, consisting of eight equally spaced, 20-m diameter fixed spherical antennas, was developed for the purpose of surveying unknown variable radio sources at 1.4GHz. An asymmetrical Gregorian sub-reflector was designed and installed on each antenna for the purpose of correcting aberrations caused by the spherical reflector. The total collecting area is 2512m2 and the field-of-view of each antenna is 0.°6 × 0.°6. In survey observations a spatial-fast Fourier-transform (FFT)-type multi-beam system will be used. We report on the design of spherical reflectors and a digital back-end system, the basic principle of spatial-FFT image forming, and a result of interferometric observations with an FPGA-based digital correlator.
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.
Quasi-spherical Approach (III): Treatment of the Earth's Center
NASA Astrophysics Data System (ADS)
Toyokuni, G.; Takenaka, H.; Wang, Y.; Kennett, B. L.
2006-12-01
We have worked to construct an accurate and efficient method for seismic waveform modeling for a laterally heterogeneous global earth. In the field of global seismology, the axisymmetric modeling which assumes structures to be axisymmetric about the axis through the source and solves the elastodynamic equation in spherical coordinates, has been an efficient modeling method. Although it can correctly model the geometrical spreading effects in 3D with computational resources comparable to 2D modeling, the conventional axisymmetric modeling cannot treat asymmetric (realistic) structures with respect to the source axis. In order to overcome this problem, the quasi-spherical finite-difference method (FDM) has been developed (Toyokuni et al., AGU Fall Meeting, 2004; Toyokuni et al., GRL, 2005). This method can model seismic wave propagation in a 2D slice of a global earth model with an arbitrary lateral heterogeneity, with a similar computation time and storage as for 2D modeling. We then implemented an arbitrary moment tensor sources into the quasi-spherical FDM scheme (Toyokuni et al., WPGM, 2006). However, these schemes could not treat the center of the earth due to the singularity at this point. This time, we extend the quasi-spherical FDM to be able to model seismic wave propagation through the earth's center. To achieve this, we introduce a discontinuous grid (Aoi &Fujiwara, BSSA, 1999) in the lateral direction, while we use non-uniform grid in the radial direction. For discontinuous change of the lateral grid spacing, the grid in the deeper region is set to have three times coarser interval than in the upper region. Wavefields from the deeper layer are passed to the upper layer through the fourth-order Lagrange interpolation. Then wavefields at the earth's center are evaluated also using Lagrange interpolation from the values around the center. In this presentation, we show some numerical examples to demonstrate the validity and feasibility of our method. In
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. PMID:26701708
NASA Astrophysics Data System (ADS)
Qu, Yegao; Hua, Hongxing; Meng, Guang
2015-10-01
A semi-analytical method is developed to predict the vibration and acoustic responses of submerged coupled spherical-cylindrical-spherical shells stiffened by circumferential rings and longitudinal stringers. The structural model of the coupled stiffened shell is formulated using a modified variational method combined with a multi-segment partitioning technique, whereas a spectral Kirchhoff-Helmholtz integral formulation is employed to model the exterior fluid. The stiffened rings and stringers, which may be few or many in number, non-uniform or uniform in size, and non-uniformly or uniformly spaced, are treated as discrete elements. The displacement and sound pressure variables are expanded in the form of a double mixed series using Fourier series and Chebyshev orthogonal polynomials. This provides a flexible way for the present method to account for the individual contributions of circumferential wave modes to the vibration and acoustic responses of coupled stiffened shells in an analytical manner. The application of the method is illustrated with several numerical examples, and comparisons are made with available solutions obtained from the coupled finite element/boundary element method. The contributions of different circumferential wave modes to the vibration responses, sound power and the directivity of radiated sound pressure for coupled shells bounded by light or heavy fluid are examined. Effects of the rings and stringers on the vibration and acoustic responses of the coupled shells are investigated.
NASA Astrophysics Data System (ADS)
Kang, Songgao; Lu, Kaichang; Zhu, Yafei
1991-12-01
The relationship between aberration and the aberration coefficient is the basic formulation in the field of aberration theory. The Seidel's formulations can only be used in the case of low performance (small aperture and small field), so that a set of correct relations between spherical aberration (SA) and spherical aberration coefficient (SAC) must be derived for the application of large aperture and small viewing field.
Magnetic field analysis of novel spherical actuators with three-dimensional pole arrays
NASA Astrophysics Data System (ADS)
Yan, Liang; Liang, Fengqi; Jiao, Zongxia; Wang, Tianyi
2016-06-01
Spherical actuator is an electric device that can achieve multiple degree-of-freedom rotary motions in a single joint. Permanent magnet array is a key factor that influences the output performance of electromagnetic spherical actuators. In this paper, a novel three-dimensional (3D) pole array is proposed to improve the system flux density and thus the output performance. Analysis of magnetic field distribution is extremely important for spherical actuators with 3D magnet arrays. Thus, the investigation of magnetic field is conducted in analytical, numerical, and experimental ways. The general solution of magnetic scalar potential in 3D space is formulated analytically based on Laplace's equations and spherical harmonics, and then specific solutions of the magnetic scalar potential and magnetic flux density are obtained by using boundary conditions. Numerical computation is utilized to validate the analytical model and to facilitate the observation of the magnetic field variation. A research prototype and a testing platform of magnetic field have been developed for experimental study. The testing platform can move the probe to any position around the spherical actuator and measure the flux density automatically. Experiments are conducted to obtain the flux distribution. Both numerical and experimental results validate the analytical model well.
Magnetic field analysis of novel spherical actuators with three-dimensional pole arrays.
Yan, Liang; Liang, Fengqi; Jiao, Zongxia; Wang, Tianyi
2016-06-01
Spherical actuator is an electric device that can achieve multiple degree-of-freedom rotary motions in a single joint. Permanent magnet array is a key factor that influences the output performance of electromagnetic spherical actuators. In this paper, a novel three-dimensional (3D) pole array is proposed to improve the system flux density and thus the output performance. Analysis of magnetic field distribution is extremely important for spherical actuators with 3D magnet arrays. Thus, the investigation of magnetic field is conducted in analytical, numerical, and experimental ways. The general solution of magnetic scalar potential in 3D space is formulated analytically based on Laplace's equations and spherical harmonics, and then specific solutions of the magnetic scalar potential and magnetic flux density are obtained by using boundary conditions. Numerical computation is utilized to validate the analytical model and to facilitate the observation of the magnetic field variation. A research prototype and a testing platform of magnetic field have been developed for experimental study. The testing platform can move the probe to any position around the spherical actuator and measure the flux density automatically. Experiments are conducted to obtain the flux distribution. Both numerical and experimental results validate the analytical model well. PMID:27370488
Dynamics of non-minimally coupled perfect fluids
NASA Astrophysics Data System (ADS)
Bettoni, Dario; Liberati, Stefano
2015-08-01
We present a general formulation of the theory for a non-minimally coupled perfect fluid in which both conformal and disformal couplings are present. We discuss how such non-minimal coupling is compatible with the assumptions of a perfect fluid and derive both the Einstein and the fluid equations for such model. We found that, while the Euler equation is significantly modified with the introduction of an extra force related to the local gradients of the curvature, the continuity equation is unaltered, thus allowing for the definition of conserved quantities along the fluid flow. As an application to cosmology and astrophysics we compute the effects of the non-minimal coupling on a Friedmann-Lemaȋtre-Robertson-Walker metric at both background and linear perturbation level and on the Newtonian limit of our theory.
Holographic perfect shuffle permutation element for a miniaturized switching network
NASA Astrophysics Data System (ADS)
Kobolla, H.; Schmidt, J.; Gluch, E.; Schwider, J.
1995-06-01
A holographic perfect shuffle element with 80 channels for a miniaturized switching network is reported. An array of vertical-cavity, surface-emitting lasers is used as a transmitter. The whole permutation is carried out totally in glass. The 80 channels are permuted within a rectangle with a volume of 3 mm \\times 4 mm \\times 2 mm. Four planes of stacked volume holograms recorded in dichromated gelatin form this perfect shuffle element with an angular spectrum between 7 deg and 35 deg. Changes in the wavelength of the diode lasers to Delta lambda = +/-10 nm can be compensated with this setup. The overall efficiency per channel lies between 40% and 60%. When Fresnel reflections and absorption are taken into account, a transmission per hologram between 78% and 90% is achieved.
Gravitational arcs as a perturbation of the perfect ring
NASA Astrophysics Data System (ADS)
Alard, C.
2007-11-01
The image of a point situated at the centre of a circularly symmetric potential is a perfect circle. The perturbative effect of non-symmetrical potential terms is to displace and break the perfect circle. These two effects, displacement and breaking, are directly related to the Taylor expansion of the perturbation at first order on the circle. The numerical accuracy of this perturbative approach is tested in the case of an elliptical potential with a core radius. The contour of the images and the caustic lines are well reproduced by the perturbative approach. These results suggest that the modelling of arcs, and in particular that of tangential arcs, may be simplified by using a general perturbative representation for points located on the circle. This linear perturbative approach is accurate when the gradient of the circular potential is almost linear; this constraint is satisfied when the potential is nearly isothermal.
Nonlocal memory effects allow perfect teleportation with mixed states.
Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki
2014-01-01
One of the most striking consequences of quantum physics is quantum teleportation - the possibility to transfer quantum states over arbitrary distances. Since its theoretical introduction, teleportation has been demonstrated experimentally up to the distance of 143 km. In the original proposal two parties share a maximally entangled quantum state acting as a resource for the teleportation task. If, however, the state is influenced by decoherence, perfect teleportation can no longer be accomplished. Therefore, one of the current major challenges in accomplishing teleportation over long distances is to overcome the limitations imposed by decoherence and the subsequent mixedness of the resource state. Here we show that, in the presence of nonlocal memory effects, perfect quantum teleportation can be achieved even with mixed photon polarisation states. Our results imply that memory effects can be exploited in harnessing noisy quantum systems for quantum communication and that non-Markovianity is a resource for quantum information tasks. PMID:24714695
Tunable enhanced optical absorption of graphene using plasmonic perfect absorbers
Cai, Yijun; Zhu, Jinfeng; Liu, Qing Huo
2015-01-26
Enhancement and manipulation of light absorption in graphene is a significant issue for applications of graphene-based optoelectronic devices. In order to achieve this purpose in the visible region, we demonstrate a design of a graphene optical absorber inspired by metal-dielectric-metal metamaterial for perfect absorption of electromagnetic waves. The optical absorbance ratios of single and three atomic layer graphene are enhanced up to 37.5% and 64.8%, respectively. The graphene absorber shows polarization-dependence and tolerates a wide range of incident angles. Furthermore, the peak position and bandwidth of graphene absorption spectra are tunable in a wide wavelength range through a specific structural configuration. These results imply that graphene in combination with plasmonic perfect absorbers have a promising potential for developing advanced nanophotonic devices.
Metamaterial perfect absorber using the magnetic resonance of dielectric inclusions
NASA Astrophysics Data System (ADS)
Dung, Nguyen Van; Tung, Bui Son; Khuyen, Bui Xuan; Yoo, Young Joon; Lee, YoungPak; Rhee, Joo Yull; Lam, Vu Dinh
2016-04-01
In this report, we introduce a stable metamaterial perfect absorber at GHz frequency based on a novel design of a Mie-type resonance. A single perfect absorption peak is achieved at 9.54 GHz, and the influence of the structural parameters on the absorption behavior is studied; the results were consistent with dielectric-resonator theory. The absorption is demonstrated to be polarizationinsensitive; furthermore, the absorber structure can work for a wide incident angle without any change in the resonance peak. Our absorber structure can also control 47% of the resonance peak's position by changing the temperature of the dielectric layer. Our absorber structure can also be applied as an electromagnetic-wave absorber for wide-incident-angle, thermally-controllable devices.
Theory of patch-antenna metamaterial perfect absorbers
NASA Astrophysics Data System (ADS)
Bowen, Patrick T.; Baron, Alexandre; Smith, David R.
2016-06-01
A metasurface that absorbs waves from all directions of incidence can be achieved if the surface impedance is made to vary as a function of incidence angle in a specific manner. Here we show that a periodic array of planar nanoparticles coupled to a metal film can act as an absorbing metasurface with an angle-dependent impedance. Through a semi-analytical calculation based on coupled-mode theory, we find the perfect absorbing condition is equivalent to balancing the Ohmic and radiative losses of the nanoparticles at normal incidence. Absorption over a wide range of incidence angles can then be obtained by tailoring the scattered far-field pattern of the individual planar nanoparticles such that their radiative losses remain constant. The theory provides a means of understanding the behavior of perfect absorbing structures that have been observed experimentally or numerically, reconciling previously published theories and enabling the optimization of absorbing surfaces.
Comment on `Stationary perfect fluid solutions with differential rotation'
NASA Astrophysics Data System (ADS)
Mars, Marc; Senovilla, José M. M.
2008-10-01
We vindicate our results in Mars and Senovilla (Phys Rev D 54, 6166 6180, 1996), which have been recently put in doubt or misunderstood in García and Ulloa (Gen Rel Grav 39, 1639 1650, 2007). In particular, we maintain that there indeed exist axially symmetric differentially rotating perfect-fluid solutions satisfying all energy conditions within the family of solutions presented in Senovilla (Class Quant Grav 9, L167 L169, 1992). We remark that the existence of an axis of symmetry can never be “re-interpreted” as the existence of a Killing horizon, and vice versa. We prove that such horizons are simply impossible for the perfect fluids within the family, and that regular axes of symmetry (or curvature singularities) are the only possibilities. Other inaccuracies or misunderstandings appeared in García and Ulloa (Gen Rel Grav 39, 1639 1650, 2007) are clarified.
Tunable enhanced optical absorption of graphene using plasmonic perfect absorbers
NASA Astrophysics Data System (ADS)
Cai, Yijun; Zhu, Jinfeng; Liu, Qing Huo
2015-01-01
Enhancement and manipulation of light absorption in graphene is a significant issue for applications of graphene-based optoelectronic devices. In order to achieve this purpose in the visible region, we demonstrate a design of a graphene optical absorber inspired by metal-dielectric-metal metamaterial for perfect absorption of electromagnetic waves. The optical absorbance ratios of single and three atomic layer graphene are enhanced up to 37.5% and 64.8%, respectively. The graphene absorber shows polarization-dependence and tolerates a wide range of incident angles. Furthermore, the peak position and bandwidth of graphene absorption spectra are tunable in a wide wavelength range through a specific structural configuration. These results imply that graphene in combination with plasmonic perfect absorbers have a promising potential for developing advanced nanophotonic devices.
Perfect fluids in the Einstein-Cartan theory
NASA Technical Reports Server (NTRS)
Ray, J. R.; Smalley, L. J.
1982-01-01
It is pointed out that whereas most of the discussion of the Einstein-Cartan (EC) theory involves the relationship between gravitation and elementary particles, it is possible that the theory, if correct, may be important in certain extreme astrophysical and cosmological problems. The latter would include something like the collapse of a spinning star or an early universe with spin. A set of equations that describe a macroscopic perfect fluid in the EC theory is derived and examined. The equations are derived starting from the fundamental variational principle for a perfect fluid in general relativity. A brief review of the study by Ray (1972) is included, and the results for the EC theory are presented.
Nonlocal memory effects allow perfect teleportation with mixed states
Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki
2014-01-01
One of the most striking consequences of quantum physics is quantum teleportation – the possibility to transfer quantum states over arbitrary distances. Since its theoretical introduction, teleportation has been demonstrated experimentally up to the distance of 143 km. In the original proposal two parties share a maximally entangled quantum state acting as a resource for the teleportation task. If, however, the state is influenced by decoherence, perfect teleportation can no longer be accomplished. Therefore, one of the current major challenges in accomplishing teleportation over long distances is to overcome the limitations imposed by decoherence and the subsequent mixedness of the resource state. Here we show that, in the presence of nonlocal memory effects, perfect quantum teleportation can be achieved even with mixed photon polarisation states. Our results imply that memory effects can be exploited in harnessing noisy quantum systems for quantum communication and that non-Markovianity is a resource for quantum information tasks. PMID:24714695
Thermodynamics of perfect fluids from scalar field theory
NASA Astrophysics Data System (ADS)
Ballesteros, Guillermo; Comelli, Denis; Pilo, Luigi
2016-07-01
The low-energy dynamics of relativistic continuous media is given by a shift-symmetric effective theory of four scalar fields. These scalars describe the embedding in spacetime of the medium and play the role of Stückelberg fields for spontaneously broken spatial and time translations. Perfect fluids are selected imposing a stronger symmetry group or reducing the field content to a single scalar. We explore the relation between the field theory description of perfect fluids to thermodynamics. By drawing the correspondence between the allowed operators at leading order in derivatives and the thermodynamic variables, we find that a complete thermodynamic picture requires the four Stückelberg fields. We show that thermodynamic stability plus the null-energy condition imply dynamical stability. We also argue that a consistent thermodynamic interpretation is not possible if any of the shift symmetries is explicitly broken.
Nonlocal memory effects allow perfect teleportation with mixed states.
Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki
2014-01-01
One of the most striking consequences of quantum physics is quantum teleportation - the possibility to transfer quantum states over arbitrary distances. Since its theoretical introduction, teleportation has been demonstrated experimentally up to the distance of 143 km. In the original proposal two parties share a maximally entangled quantum state acting as a resource for the teleportation task. If, however, the state is influenced by decoherence, perfect teleportation can no longer be accomplished. Therefore, one of the current major challenges in accomplishing teleportation over long distances is to overcome the limitations imposed by decoherence and the subsequent mixedness of the resource state. Here we show that, in the presence of nonlocal memory effects, perfect quantum teleportation can be achieved even with mixed photon polarisation states. Our results imply that memory effects can be exploited in harnessing noisy quantum systems for quantum communication and that non-Markovianity is a resource for quantum information tasks.
Recovery of data from perfectly twinned virus crystals revisited
Ginn, Helen Mary; Stuart, David Ian
2016-01-01
Perfect merohedral twinning of crystals is not uncommon and complicates structural analysis. An iterative method for the deconvolution of data from perfectly merohedrally twinned crystals in the presence of noncrystallographic symmetry (NCS) has been reimplemented. It is shown that the method recovers the data effectively using test data, and an independent metric of success, based on special classes of reflections that are unaffected by the twin operator, is now provided. The method was applied to a real problem with fivefold NCS and rather poor-quality diffraction data, and it was found that even in these circumstances the method appears to recover most of the information. The software has been made available in a form that can be applied to other crystal systems. PMID:27303802
Perfect conformal invisible device with feasible refractive indexes
NASA Astrophysics Data System (ADS)
Xu, Lin; Chen, Huanyang; Tyc, Tomáš; Xie, Yangbo; Cummer, Steven A.
2016-01-01
Optical conformal mapping has been used to construct several isotropic devices with novel functionalities. In particular, a conformal cloak could confer omnidirectional invisibility. However, the maximum values of the refractive indexes needed for current designs are too large to implement, even in microwave experiments. Furthermore, most devices designed so far have had imperfect impedance matching and therefore incomplete invisibility functionalities. Here we describe a perfect conformal invisible device with full impedance matching everywhere. The maximum value of refractive index required by our device is just about five, which is feasible for microwave and terahertz experiments using current metamaterial techniques. To construct the device, we use a logarithmic conformal mapping and a Mikaelian lens. Our results should enable a conformal invisible device with almost perfect invisibility to be made soon.
Perfectly matched layers for Maxwell's equations in second order formulation
Sjogreen, B; Petersson, A
2004-07-26
We consider the two-dimensional Maxwell's equations in domains external to perfectly conducting objects of complex shape. The equations are discretized using a node-centered finite-difference scheme on a Cartesian grid and the boundary condition are discretized to second order accuracy employing an embedded technique which does not suffer from a ''small-cell'' time-step restriction in the explicit time-integration method. The computational domain is truncated by a perfectly matched layer (PML). We derive estimates for both the error due to reflections at the outer boundary of the PML, and due to discretizing the continuous PML equations. Using these estimates, we show how the parameters of the PML can be chosen to make the discrete solution of the PML equations converge to the solution of Maxwell's equations on the unbounded domain, as the grid size goes to zero. Several numerical examples are given.
NASA Astrophysics Data System (ADS)
Greenberg, J. Mayo; van de Bult, C. E. P. M.; Allamandola, Louis J.
The chemical and physical properties of ice grains in interstellar space have been studied in the laboratory and theoretically modeled to compare with astronomical spectra between 2700 and 3700/cm. The observed polarization of starlight in this region clearly indicates that elongated particles are involved. Absorption characteristics for various shaped grains whose radii vary from approximately 0.1 to 1.0 micrometer, containing either pure amorphous H20 or amorphous mixtures of H20 with NH3, have been calculated with the aim of narrowing the range of acceptable grain parameters. By comparing the band shapes for spherical, spheroidal, and cylindrical grains with astronomical spectra we show that elongated particles whose radii are approximately equal to 0.15 micrometer produce an acceptable match and that both spherical and elongated particles whose radii are greater than or equal to 0.5 micrometer are definitely not consistent with observations. Details of the band shape are shown to depend on particle size, shape, and composition. Similar profiles can be produced by using different combinations of particle shape and composition. For example, the NH3 signature at 2.97 micrometer, which is prominent in a spherical grain, is greatly suppressed when in an elongated grain. This is exactly equivalent to reducing the concentration of NH3 in a spherical grain. A morphological grain model is used to explain the large variations in the observed strength of the 3.07 micrometer ice band from one region of space to another.
Thermodynamics of spherically symmetric spacetimes in loop quantum gravity
NASA Astrophysics Data System (ADS)
Mäkelä, Jarmo
2015-06-01
The choice of the area operator in loop quantum gravity is by no means unique. In addition to the area operator commonly used in loop quantum gravity there is also an area operator introduced by Krasnov in 1998, which gives uniformly spaced area spectra for the horizons of spacetime. Using Krasnov's area operator we consider the thermodynamics of spherically symmetric spacetimes equipped with horizons in loop quantum gravity. Among other things, our approach implies, in a pretty simple manner, that every horizon of spacetime emits thermal radiation and possesses entropy which, in the natural units, is one-quarter of its area. When applied to the de Sitter spacetime loop quantum gravity provides an explanation both to the presence and the smallness of the cosmological constant.
Static spherically symmetric wormholes in f( R, T) gravity
NASA Astrophysics Data System (ADS)
Zubair, M.; Waheed, Saira; Ahmad, Yasir
2016-08-01
In this work, we explore wormhole solutions in f( R, T) theory of gravity, where R is the scalar curvature and T is the trace of stress-energy tensor of matter. To investigate this, we consider a static spherically symmetric geometry with matter contents as anisotropic, isotropic, and barotropic fluids in three separate cases. By taking into account the Starobinsky f( R) model, we analyze the behavior of energy conditions for these different kinds of fluids. It is shown that the wormhole solutions can be constructed without exotic matter in few regions of space-time. We also give the graphical illustration of the results obtained and discuss the equilibrium picture for the anisotropic case only. It is concluded that the wormhole solutions with anisotropic matter are realistic and stable in this theory of gravity.
Critical collapse in the spherically symmetric Einstein-Vlasov model
NASA Astrophysics Data System (ADS)
Akbarian, Arman; Choptuik, Matthew W.
2014-11-01
We solve the coupled Einstein-Vlasov system in spherical symmetry using direct numerical integration of the Vlasov equation in phase space. Focusing on the case of massless particles we study critical phenomena in the model, finding strong evidence for generic type I behavior at the black hole threshold that parallels what has previously been observed in the massive sector. For differing families of initial data we find distinct critical solutions, so there is no universality of the critical configuration itself. However we find indications of at least a weak universality in the lifetime scaling exponent, which is yet to be understood. Additionally, we clarify the role that angular momentum plays in the critical behavior in the massless case.
Comment on ``Perfect imaging with positive refraction in three dimensions''
NASA Astrophysics Data System (ADS)
Merlin, R.
2010-11-01
Leonhardt and Philbin [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.81.011804 81, 011804(R) (2010)] have recently constructed a mathematical proof that the Maxwell's fish-eye lens provides perfect imaging of electromagnetic waves without negative refraction. In this comment, we argue that the unlimited resolution is an artifact of having introduced an unphysical drain at the position of the geometrical image. The correct solution gives focusing consistent with the standard diffraction limit.
Comment on ''Perfect imaging with positive refraction in three dimensions''
Merlin, R.
2010-11-15
Leonhardt and Philbin [Phys. Rev. A 81, 011804(R) (2010)] have recently constructed a mathematical proof that the Maxwell's fish-eye lens provides perfect imaging of electromagnetic waves without negative refraction. In this comment, we argue that the unlimited resolution is an artifact of having introduced an unphysical drain at the position of the geometrical image. The correct solution gives focusing consistent with the standard diffraction limit.
Covariant diagonalization of the perfect fluid stress-energy tensor
NASA Astrophysics Data System (ADS)
Garat, Alcides
2015-02-01
We introduce new tetrads that manifestly and covariantly diagonalize the stress-energy tensor for a perfect fluid with vorticity at every spacetime point. This new tetrad can be applied to introduce simplification in the analysis of astrophysical relativistic problems where vorticity is present through the Carter-Lichnerowicz equation. We also discuss the origin of inertia in this special case from the standpoint of our new local tetrads.
Adaptive Perfectly Matched Layer for Wood's anomalies in diffraction gratings.
Vial, Benjamin; Zolla, Frédéric; Nicolet, André; Commandré, Mireille; Tisserand, Stéphane
2012-12-17
We propose an Adaptive Perfectly Matched Layer (APML) to be used in diffraction grating modeling. With a properly tailored co-ordinate stretching depending both on the incident field and on grating parameters, the APML may efficiently absorb diffracted orders near grazing angles (the so-called Wood's anomalies). The new design is implemented in a finite element method (FEM) scheme and applied on a numerical example of a dielectric slit grating. Its performances are compared with classical PML with constant stretching coefficient.
The Perfect Family: Decision Making in Biparental Care
Akçay, Erol; Roughgarden, Joan
2009-01-01
Background Previous theoretical work on parental decisions in biparental care has emphasized the role of the conflict between evolutionary interests of parents in these decisions. A prominent prediction from this work is that parents should compensate for decreases in each other's effort, but only partially so. However, experimental tests that manipulate parents and measure their responses fail to confirm this prediction. At the same time, the process of parental decision making has remained unexplored theoretically. We develop a model to address the discrepancy between experiments and the theoretical prediction, and explore how assuming different decision making processes changes the prediction from the theory. Model Description We assume that parents make decisions in behavioral time. They have a fixed time budget, and allocate it between two parental tasks: provisioning the offspring and defending the nest. The proximate determinant of the allocation decisions are parents' behavioral objectives. We assume both parents aim to maximize the offspring production from the nest. Experimental manipulations change the shape of the nest production function. We consider two different scenarios for how parents make decisions: one where parents communicate with each other and act together (the perfect family), and one where they do not communicate, and act independently (the almost perfect family). Conclusions/Significance The perfect family model is able to generate all the types of responses seen in experimental studies. The kind of response predicted depends on the nest production function, i.e. how parents' allocations affect offspring production, and the type of experimental manipulation. In particular, we find that complementarity of parents' allocations promotes matching responses. In contrast, the relative responses do not depend on the type of manipulation in the almost perfect family model. These results highlight the importance of the interaction between nest
Perfect focusing of scalar wave fields in three dimensions.
Benítez, Pablo; Miñano, Juan C; González, Juan C
2010-04-12
A method to design isotropic inhomogeneous refractive index distribution is presented, in which the scalar wave field solutions propagate exactly on an eikonal function (i.e., remaining constant on the Geometrical Optics wavefronts). This method is applied to the design of "dipole lenses", which perfectly focus a scalar wave field emitted from a point source onto a point absorber, in both two and three dimensions. Also, the Maxwell fish-eye lens in two and three dimensions is analysed.
Perfect-fluid sources for the Levi-Civita metric
NASA Astrophysics Data System (ADS)
Ali, Ramadan M.
2007-08-01
Cylindrically symmetric perfect fluid solutions are derived for the Levi-Civita metric. The pressure P is finite. The matter density is greater than the stresses in the material. The solutions are inside cylinders of bounded radius at which the pressure vanishes. The range of σ, for which the sources have been matched to the Levi-Civeta metric is ∞> σ>0. The solutions are regular and satisfy energy conditions
Perfect teleportation and superdense coding with W states
Agrawal, Pankaj; Pati, Arun
2006-12-15
True tripartite entanglement of the state of a system of three qubits can be classified on the basis of stochastic local operations and classical communications. Such states can be classified into two categories: GHZ states and W states. It is known that GHZ states can be used for teleportation and superdense coding, but the prototype W state cannot be. However, we show that there is a class of W states that can be used for perfect teleportation and superdense coding.
Characterization of quantum circulant networks having perfect state transfer
NASA Astrophysics Data System (ADS)
Bašić, Milan
2013-01-01
In this paper we answer the question of when circulant quantum spin networks with nearest-neighbor couplings can give perfect state transfer. The network is described by a circulant graph G, which is characterized by its circulant adjacency matrix A. Formally, we say that there exists a perfect state transfer (PST) between vertices {a,bin V(G)} if | F( τ) ab | = 1, for some positive real number τ, where F( t) = exp(i At). Saxena et al. (Int J Quantum Inf 5:417-430, 2007) proved that | F( τ) aa | = 1 for some {ain V(G)} and {tauin {R}^+} if and only if all eigenvalues of G are integer (that is, the graph is integral). The integral circulant graph ICG n ( D) has the vertex set Z n = {0, 1, 2, . . . , n - 1} and vertices a and b are adjacent if {gcd(a-b,n)in D} , where {D subseteq {d : d mid n, 1 ≤ d < n}} . These graphs are highly symmetric and have important applications in chemical graph theory. We show that ICG n ( D) has PST if and only if {nin 4{N}} and {D=widetilde{D_3} \\cup D_2\\cup 2D_2\\cup 4D_2|cup {n/2^a}} , where {widetilde{D_3}={din D | n/din 8{N}}, D_2= {din D | n/din 8{N}+4}{setminus}{n/4}} and {ain{1,2}} . We have thus answered the question of complete characterization of perfect state transfer in integral circulant graphs raised in Angeles-Canul et al. (Quantum Inf Comput 10(3&4):0325-0342, 2010). Furthermore, we also calculate perfect quantum communication distance (distance between vertices where PST occurs) and describe the spectra of integral circulant graphs having PST. We conclude by giving a closed form expression calculating the number of integral circulant graphs of a given order having PST.
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
Practical multi-featured perfect absorber utilizing high conductivity silicon
NASA Astrophysics Data System (ADS)
Gok, Abdullah; Yilmaz, Mehmet; Bıyıklı, Necmi; Topallı, Kağan; Okyay, Ali K.
2016-03-01
We designed all-silicon, multi-featured band-selective perfect absorbing surfaces based on CMOS compatible processes. The center wavelength of the band-selective absorber can be varied between 2 and 22 μm while a bandwidth as high as 2.5 μm is demonstrated. We used a silicon-on-insulator (SOI) wafer which consists of n-type silicon (Si) device layer, silicon dioxide (SiO2) as buried oxide layer, and n-type Si handle layer. The center wavelength and bandwidth can be tuned by adjusting the conductivity of the Si device and handle layers as well as the thicknesses of the device and buried oxide layers. We demonstrate proof-of-concept absorber surfaces experimentally. Such absorber surfaces are easy to microfabricate because the absorbers do not require elaborate microfabrication steps such as patterning. Due to the structural simplicity, low-cost fabrication, wide spectrum range of operation, and band properties of the perfect absorber, the proposed multi-featured perfect absorber surfaces are promising for many applications. These include sensing devices, surface enhanced infrared absorption applications, solar cells, meta-materials, frequency selective sensors and modulators.
Preparation and Evaluation of Two Apatites with Spherical Nanocrystal Morphology.
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.
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.
Semiautomated inspection of superfinished spherical surfaces
Klingsporn, P.E.
1980-01-01
Lapping and polishing techniques are used at Bendix Kansas City to fabricate superfinished spherical metal surfaces. A laser-light reflection method has been developed for semiautomated inspection of the surfaces. The reflected and diffracted light intensity distributions from the spherical surface are measured with an array of photodetectors interfaced with a data sampler and a minicomputer programmed to distinguish between pits and scratches. For automated measurement, standard deviations for scratch width and depth are 3 and 0.3 ..mu..m (120 and 12 ..mu..in.), respectively, and for pit diameter and depth are 5.8 and 0.9 ..mu..m (230 and 36 ..mu..in.), respectively. A laser interferometric displacement measuring system interfaced with the computer is used for automated measurement of surface waviness.
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.
Colloidal cholesteric liquid crystal in spherical confinement.
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
Limiting Temperatures of Spherical Shock Wave Implosion.
Liverts, Michael; Apazidis, Nicholas
2016-01-01
Spherical shock wave implosion in argon is studied both theoretically and experimentally. It is shown that as the strength of the converging shock increases the nonideal gas effects become dominant and govern the evolution of thermal and transport gas properties limiting the shock acceleration, lowering the gas adiabatic index and the achievable energy density at the focus. Accounting for multiple-level ionization, excitation, Coulomb interaction and radiation effects, the limiting equilibrium temperatures to be achieved during the shock implosion are estimated. Focal temperatures of the order of 30 000 K are measured in experiments where converging spherical shock waves are created using a conventional gas-dynamic shock tube facility. PMID:26799021
Colloidal cholesteric liquid crystal in spherical confinement
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
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.
Spherical Target Temperature by Extended CFAST Calculation
Ma, C W
2009-05-05
The purpose of this calculation is to evaluate the temperature at the surface of a spherical target made of polyethylene during a room fire. The current calculation is separated into 2 steps: (1) CFAST code calculation--Calculate the air temperature; radiation flux to the target from the fire, surrounding air, and walls; convection flux; and target temperature. (2) Extended model calculation--Calculate the temperature of the target sphere taking into account the density, heat capacity, heat conductivity, and the spherical geometry of the target by solving the coupled finite difference equations. The second step calculation utilizes the air temperature and radiation flux determined by the CFAST code calculation in the first step.
Testing the spherical evolution of cosmic voids
NASA Astrophysics Data System (ADS)
Demchenko, Vasiliy; Cai, Yan-Chuan; Heymans, Catherine; Peacock, John A.
2016-08-01
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-1Mpc, 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.
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.
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.
Imaging with Spherically Bent Crystals or Reflectors
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.
Spherical self-organizing map using efficient indexed geodesic data structure.
Wu, Yingxin; Takatsuka, Masahiro
2006-01-01
The two-dimensional (2D) Self-Organizing Map (SOM) has a well-known "border effect". Several spherical SOMs which use lattices of the tessellated icosahedron have been proposed to solve this problem. However, existing data structures for such SOMs are either not space efficient or are time consuming when searching the neighborhood. We introduce a 2D rectangular grid data structure to store the icosahedron-based geodesic dome. Vertices relationships are maintained by their positions in the data structure rather than by immediate neighbor pointers or an adjacency list. Increasing the number of neurons can be done efficiently because the overhead caused by pointer updates is reduced. Experiments show that the spherical SOM using our data structure, called a GeoSOM, runs with comparable speed to the conventional 2D SOM. The GeoSOM also reduces data distortion due to removal of the boundaries. Furthermore, we developed an interface to project the GeoSOM onto the 2D plane using a cartographic approach, which gives users a global view of the spherical data map. Users can change the center of the 2D data map interactively. In the end, we compare the GeoSOM to the other spherical SOMs by space complexity and time complexity. PMID:16787738
Precursory singularities in spherical gravitational collapse
NASA Astrophysics Data System (ADS)
Lake, Kayll
1992-05-01
General conditions are developed for the formation of naked precursory ('shell-focusing') singularities in spherical gravitational collapse. These singularities owe their nakedness to the fact that the gravitational potential fails to be single valued prior to the onset of a true gravitational singularity. It is argued that they do not violate the spirit of cosmic censorship. Rather, they may well be an essentially generic feature of relativistic gravitational collapse.
Thermal deformations of a glass spherical satellite
NASA Astrophysics Data System (ADS)
Vasiliev, V. P.; Nenadovich, V. D.; Murashkin, V. V.; Sokolov, A. L.
2016-09-01
The effect of the kind of the reflecting coating of a glass spherical satellite on thermal deformations caused by the solar irradiation is considered. Two types of coating deposited on one of the hemispheres are considered: aluminum with a protective layer of bakelite varnish and interference dielectric coating for two orientations of the satellite orbit. Structures of a multilayer dielectric coating and technologies of its deposition are described.
Fast ion orbits in spherical tokamaks
Solano, E.R.
1995-07-20
In a spherical tokamak, the 1/R variation of the toroidal field is extreme, and for a given value of the safety factor a relatively low average toroidal field can be used, together with large plasma current and large plasma minor radius and elongation. The poloidal and toroidal fields are then of similar size. In consequence, the orbits of fast ions depart considerably from the guiding center orbits because of gyromotion in the small magnetic fields in the low field side.
Selfsimilar Spherical Compression Waves in Gas Dynamics
NASA Astrophysics Data System (ADS)
Meyer-ter-Vehn, J.; Schalk, C.
1982-08-01
A synopsis of different selfsimilar spherical compression waves is given pointing out their fundamental importance for the gas dynamics of inertial confinement fusion. Strong blast waves, various forms of isentropic compression waves, imploding shock waves and the solution for non-isentropic collapsing hollow spheres are included. A classification is given in terms of six singular points which characterise the different solutions and the relations between them. The presentation closely follows Guderley's original work on imploding shock waves
Selfsimilar spherical compression waves in gas dynamics
NASA Astrophysics Data System (ADS)
Meyer-Ter-Vehn, J.; Schalk, C.
1982-05-01
A synopsis of different selfsimilar spherical compression waves is given pointing out their fundamental importance for the gas dynamics of inertial confinement fusion. Strong blast waves, various forms of isentropic collapsing hollow spheres are included. A classification is given in terms of six singular points which characterize the different solutions and the relations between them. The presentation closely follows Guderley's original work on imploding shock waves.
Wave equation on spherically symmetric Lorentzian metrics
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.
Spherical Cancer Models in Tumor Biology1
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
Spherical cloaking with homogeneous isotropic multilayered structures
NASA Astrophysics Data System (ADS)
Qiu, Cheng-Wei; Hu, Li; Xu, Xiaofei; Feng, Yijun
2009-04-01
We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers.
Spherical cloaking with homogeneous isotropic multilayered structures.
Qiu, Cheng-Wei; Hu, Li; Xu, Xiaofei; Feng, Yijun
2009-04-01
We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. PMID:19518392
Modeling of thermal processes in spherical area
NASA Astrophysics Data System (ADS)
Demyanchenko, O.; Lyashenko, V.
2016-10-01
In this paper a mathematical model of the temperature field in spherical area with complex conditions of heat exchange with the environment is considered. The solution of the nonlinear initial boundary value problem is reduced to the solution of the nonlinear integral equation of Fredholm type respect to spatial coordinates and Volterra with the kernel in the form of the Green's function on the time coordinate.
On Recurrence Formulae of Solid Spherical Monogenics
Bock, S.; Guerlebeck, K.
2008-09-01
We construct a new orthonormal basis of solid spherical monogenics in L{sub 2}. The important property of the basis polynomials is that the hypercomplex derivative as well as the primitive yield (up to a factor) again a basis function of the same system. Besides we refine a decomposition theorem for monogenic functions. With these properties the polynomial system provides a powerful tool to analyze orthogonal series expansions.
Numerical simulation of spherical plasma focus diode
NASA Astrophysics Data System (ADS)
Jiang, W.; Masugata, K.; Yatsui, K.
1995-06-01
A self-magnetically insulated, three-dimensionally-focused ion-beam diode, spherical plasma focus diode (SPFD), is studied by numerical simulation using a two-dimensional, electromagnetic, relativistic particle-in-cell computer code. The calculated results of the diode impedance, the ion-current efficiency, and the focusing characteristics of the ion beam are presented. These results, except the data of the ion-beam current, are in good agreement with the experimental results.
Buden, D.
1990-10-01
Nuclear technology offers many advantages in an expanded solar system space exploration program. These cover a range of possible applications such as power for spacecraft, lunar and planetary surfaces, and electric propulsion; rocket propulsion for lunar and Mars vehicles; space radiation protection; water and sewage treatment; space mining; process heat; medical isotopes; and self-luminous systems. In addition, space offers opportunities to perform scientific research and develop systems that can solve problems here on Earth. These might include fusion and antimatter research, using the Moon as a source of helium-3 fusion fuel, and manufacturing perfect fusion targets. In addition, nuclear technologies can be used to reduce risk and costs of the Space Exploration Initiative. 1 fig.
Quantum corrected spherical collapse: A phenomenological framework
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.
RF experiments on spherical torus plasmas
Majeski, R.; Menard, J.; Batchelor, D.; Bigelow, T.; Carter, M. D.; Finkenthal, M.; Jaeger, E. F.; Jones, B.; Kaita, R.; Mau, T. K.
1999-09-20
Experimental operations are about to begin on the next generation of spherical torus (ST) devices-the National Spherical Torus eXperiment (NSTX) in the U.S. and the Mega-Amp Spherical Torus (MAST) in the U.K. The application of RF heating and current drive to these high beta, compact confinement devices is a challenging problem. The initial focus for NSTX had been on the High Harmonic Fast Wave (HHFW) regime. Although modeling of HHFW heating and current drive has been performed at ORNL, UCSD, MIT, and PPPL, there are few experiments in this frequency range. In conventional tokamaks, the DIII-D experiments at the 5{sup th}-7{sup th} cyclotron harmonic are the closest approach to the HHFW regime. In an ST, the only RF heating experiments to date have been performed at the 15{sup th} harmonic on the Current Drive eXperiment-Upgrade (CDX-U) at PPPL. General features of HHFW heating and current drive and the degree to which experimental confirmation of these features is available will be discussed. (c) 1999 American Institute of Physics.
Next Step Spherical Torus Design Studies
C. Neumeyer; P. Heitzenroeder; C. Kessel; M. Ono; M. Peng; J. Schmidt; R. Woolley; I. Zatz
2002-11-08
Studies are underway to identify and characterize a design point for a Next Step Spherical Torus (NSST) experiment. This would be a ''Proof of Performance'' device which would follow and build upon the successes of the National Spherical Torus Experiment (NSTX) a ''Proof of Principle'' device which has operated at PPPL since 1999. With the Decontamination and Decommissioning (D&D) of the Tokamak Fusion Test Reactor (TFTR) nearly completed, the TFTR test cell and facility will soon be available for a device such as NSST. By utilizing the TFTR test cell, NSST can be constructed for a relatively low cost on a short time scale. In addition, while furthering spherical torus (ST) research, this device could achieve modest fusion power gain for short-pulse lengths, a significant step toward future large burning plasma devices now under discussion in the fusion community. The selected design point is Q=2 at HH=1.4, P subscript ''fusion''=60 MW, 5 second pulse, with R subscript ''0''=1.5 m, A=1.6, I subscript ''p''=10vMA, B subscript ''t''=2.6 T, CS flux=16 weber. Most of the research would be conducted in D-D, with a limited D-T campaign during the last years of the program.
Batdorf parameter for the spherical shells tectonics
NASA Astrophysics Data System (ADS)
Kikuchi, Kazuhei; Nagahama, Hiroyuki
2015-04-01
The buckling phenomena of the subducting lithosphere due to the sphericity of the earth has been studied as spherical shell tectonics which happen the megaquake along the boundary of subducting lithosphere. The earthquake scale is decided by slab length or arc length. However, a relationship between slab length and the normalized hydrostatic pressure along the bottom circumferential edge of a hemispherical shell has not been clear yet. So, by using the data set of the geometrical parameters for subducting lithosphere andBuckingham's Pi-theorem, we found out a new linear relationship between Batdorf parameter Z = L2(l - v2)0.5/(Rh) for the measurement of the slab length L and the normalized hydrostatic pressure along the bottom circumferential edge of a hemispherical shell Q = qRL2/(π2D), where D = Eh3/[12(1 - v2)] with E = modulus of elasticity of lithosphere, R is Earth radius, q is the hydrostatic pressure along the bottom circumferential edge of a hemispherical shell, and h is the thickness of subducting lithosphere. In the engineering sciences, a similar relationship between Batdorf parameter for the panel length and normalized hydrostatic pressure was proposed for the buckling of partially liquid-filled circular cylindrical shells under hydrostatic pressure. Moreover, by previous researches, the slab length is approximately proportional to the arc length or the lithosphere thickness related to lithosphere age. Therefore, the Batdorf parameter for subducting lithosphere is an important parameter for the spherical shells tectonics.
Scaling Relationships for Spherical Polymer Brushes Revisited.
Chen, Guang; Li, Hao; Das, Siddhartha
2016-06-16
In this short paper, we revisit the scaling relationships for spherical polymer brushes (SPBs), i.e., polymer brushes grafted to rigid, spherical particles. Considering that the brushes can be described to be encased in a series of hypothetical spherical blobs, we identify significant physical discrepancies in the model of Daoud and Cotton (Journal of Physics, 1982), which is considered to be the state of the art in scaling modeling of SPBs. We establish that the "brush" configuration of the polymer molecules forming the SPBs is possible only if the swelling ratio (which is the ratio of the end-to-end length of the blob-encased polymer segment to the corresponding coil-like polymer segment) is always less than unity-a notion that has been erroneously overlooked in the model of Daoud and Cotton. We also provide new scaling arguments that (a) establish this swelling (or more appropriately shrinking) ratio as a constant (less than unity) for the case of "good" solvent, (b) recover the scaling predictions for blob dimension and monomer number and monomer concentration distributions within the blob, and
Kawakami, Hayato; Mitsuda, Eiji; Nambu, Yasusada; Tomimatsu, Akira
2009-07-15
In considering the gravitational collapse of matter, it is an important problem to clarify what kind of conditions leads to the formation of naked singularity. For this purpose, we apply the 1+3 orthonormal frame formalism introduced by Uggla et al. to the spherically symmetric gravitational collapse of a perfect fluid. This formalism allows us to construct an autonomous system of evolution and constraint equations for scale-invariant dynamical variables normalized by the volume expansion rate of the timelike orthonormal frame vector. We investigate the asymptotic evolution of such dynamical variables towards the formation of a central singularity and present a conjecture that the steep spatial gradient for the normalized density function is a characteristic of the naked singularity formation.
Characterisation of metachronal waves on the surface of the spherical colonial alga Volvox carteri
NASA Astrophysics Data System (ADS)
Brumley, Douglas; Polin, Marco; Morez, Constant; Goldstein, Raymond; Pedley, Timothy
2012-02-01
Volvox carteri is a spherical colonial alga, consisting of thousands of biflagellate cells. The somatic cells embedded on the surface of the colony beat their flagella in a coordinated fashion, producing a net fluid motion. Using high-speed imaging and particle image velocimetry (PIV) we have been able to accurately analyse the time-dependent flow fields around such colonies. The somatic cells on the colony surface may beat their flagella in a perfectly synchronised fashion, or may exhibit metachronal waves travelling on the surface. We analyse the dependence of this synchronisation on fundamental parameters in the system such as colony radius, characterise the speed and wavelength of the observed metachronal waves, and investigate possible models to account for the exhibited behaviour.
Spherically symmetric cosmological spacetimes with dust and radiation — numerical implementation
Lim, Woei Chet; Regis, Marco; Clarkson, Chris E-mail: regis@to.infn.it
2013-10-01
We present new numerical cosmological solutions of the Einstein Field Equations. The spacetime is spherically symmetric with a source of dust and radiation approximated as a perfect fluid. The dust and radiation are necessarily non-comoving due to the inhomogeneity of the spacetime. Such a model can be used to investigate non-linear general relativistic effects present during decoupling or big-bang nucleosynthesis, as well as for investigating void models of dark energy with isocurvature degrees of freedom. We describe the full evolution of the spacetime as well as the redshift and luminosity distance for a central observer. After demonstrating accuracy of the code, we consider a few example models, and demonstrate the sensitivity of the late time model to the degree of inhomogeneity of the initial radiation contrast.
Spherical finite rate of innovation theory for the recovery of fiber orientations.
Deslauriers-Gauthier, Samuel; Marziliano, Pina
2012-01-01
In this paper, we investigate the reconstruction of a signal defined as the sum of K orientations from samples taken with a kernel defined on the 3D rotation group. A potential application is the recovery of fiber orientations in diffusion magnetic resonance imaging. We propose an exact reconstruction algorithm based on the finite rate of innovation theory that makes use of the spherical harmonics representation of the signal. The number of measurements needed for perfect recovery, which may be as low as 3K, depends only on the number of orientations and the bandwidth of the kernel used. Furthermore, the angular resolution of our method does not depend on the number of available measurements. We illustrate the performance of the algorithm using several simulations.
Laser-assisted production of spherical TiO2 nanoparticles in water.
Boutinguiza, M; Rodríguez-González, B; del Val, J; Comesaña, R; Lusquiños, F; Pou, J
2011-05-13
TiO(2) nanoparticles with controllable average diameter have been obtained by laser ablation in water. A monomode ytterbium doped fiber laser (YDFL) was used to ablate a metallic titanium target placed in deionized water. The resulting colloidal solutions were subjected to laser radiation to study the resizing effect. The crystalline phases, morphology and optical properties of the obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray energy dispersive spectroscopy (EDS) and UV-vis absorption spectroscopy. The colloidal suspensions produced consisting of titanium dioxide crystalline nanoparticles show almost perfect spherical shape with diameters ranging from 3 to 40 nm. The nanoparticles are polycrystalline and exhibit anatase as well as rutile phases. PMID:21430320
Laser-assisted production of spherical TiO2 nanoparticles in water.
Boutinguiza, M; Rodríguez-González, B; del Val, J; Comesaña, R; Lusquiños, F; Pou, J
2011-05-13
TiO(2) nanoparticles with controllable average diameter have been obtained by laser ablation in water. A monomode ytterbium doped fiber laser (YDFL) was used to ablate a metallic titanium target placed in deionized water. The resulting colloidal solutions were subjected to laser radiation to study the resizing effect. The crystalline phases, morphology and optical properties of the obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray energy dispersive spectroscopy (EDS) and UV-vis absorption spectroscopy. The colloidal suspensions produced consisting of titanium dioxide crystalline nanoparticles show almost perfect spherical shape with diameters ranging from 3 to 40 nm. The nanoparticles are polycrystalline and exhibit anatase as well as rutile phases.
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
Murugan, G. Senthil Ramasamy, P.
2014-04-24
Polar organic nonlinear optical material, L-tartaric acid single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallized in monoclinic system with space group P2{sub 1}. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal quality is good and free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. Piezoelectric d{sub 33} co-efficient for the crystal has been examined and its value is 47 pC/N. The ferroelectric behaviour of the crystal was analyzed by polarization-electric field hysteresis loop measurement.
Economic analysis of crystal growth in space
NASA Technical Reports Server (NTRS)
Ulrich, D. R.; Chung, A. M.; Yan, C. S.; Mccreight, L. R.
1972-01-01
Many advanced electronic technologies and devices for the 1980's are based on sophisticated compound single crystals, i.e. ceramic oxides and compound semiconductors. Space processing of these electronic crystals with maximum perfection, purity, and size is suggested. No ecomonic or technical justification was found for the growth of silicon single crystals for solid state electronic devices in space.
Static spherically symmetric solutions in mimetic gravity: rotation curves and wormholes
NASA Astrophysics Data System (ADS)
Myrzakulov, Ratbay; Sebastiani, Lorenzo; Vagnozzi, Sunny; Zerbini, Sergio
2016-06-01
In this work, we analyse static spherically symmetric solutions in the framework of mimetic gravity, an extension of general relativity where the conformal degree of freedom of gravity is isolated in a covariant fashion. Here we extend previous works by considering, in addition, a potential for the mimetic field. An appropriate choice of such a potential allows for the reconstruction of a number of interesting cosmological and astrophysical scenarios. We explicitly show how to reconstruct such a potential for a general static spherically symmetric space-time. A number of applications and scenarios are then explored, among which are traversable wormholes. Finally, we analytically reconstruct potentials, which leads to solutions to the equations of motion featuring polynomial corrections to the Schwarzschild space-time. Accurate choices for such corrections could provide an explanation for the inferred flat rotation curves of spiral galaxies within the mimetic gravity framework, without the need for particle dark matter.
Aggerwal, Neel; Menon, Prema; Rao, Katragadda Lakshmi Narasimha; Sodhi, Kushaljit S.; Kakkar, Nandita
2015-01-01
Aims: The aim was to compare biliary amylase, common channel, and gall bladder/liver histopathology between spherical and fusiform choledochal cysts. Materials and Methods: Children undergoing cyst excision with Roux-en-Y hepatico-jejunostomy over a 17 months period were prospectively studied. The common channel was assessed by three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP). Results: Among 22 patients (spherical = 10, fusiform = 12), there was a higher incidence of spherical cysts in infants (5/7-71.4%) and fusiform cysts in older children (10/15-66.7%) (P = 0.09). Common channel identified in 14 (64%) cases was long (>10 mm) in 5 (38.2%) (one spherical, four fusiform [P = 0.5]) with associated high biliary amylase levels (>500 IU/L) in four (one spherical, three fusiform) (P = 0.05). Exact point of junction of common bile duct with pancreatic duct was visible with coronal half-Fourier-acquisition single-shot turbo spin-echo and 3D sampling perfection with application with optimize contrast using different flip angle evolution sequence using a reformatted plane of axis, particularly coronal, and coronal oblique orientation. Biliary amylase was raised (>100 IU/L) in 4 (40%) in the spherical group, compared to 8 (67%) in the fusiform group. Mean biliary amylase was similar in gallbladder and cyst in spherical but higher in gallbladder in fusiform cysts. Mean biliary amylase was <500 IU/L in 85.7% infants. Five out of 7 infants had liver fibrosis or cirrhosis on histopathology (P = 0.05). There were no dysplastic changes in the gallbladder epithelium. Conclusion: Three-dimensional MRCP delineated the common channel in two-third cases especially in coronal and coronal oblique orientation. The long common channel may have an etiological role in fusiform cysts. Spherical cysts, especially in infants, have a higher incidence of obstructive cholangiopathy. PMID:26166983
Asymmetric perfectly matched layer for the absorption of waves
Vay, Jean-Luc
2002-02-10
The Perfectly Matched Layer (PML) has become a standard for comparison in the techniques that have been developed to close the system of Maxwell equations (more generally wave equations) when simulating an open system. The original Berenger PML formulation relies on a split version of Maxwell equations with numerical electric and magnetic conductivities. They present here an extension of this formulation which introduces counterparts of the electric and magnetic conductivities affecting the term which is spatially differentiated in the equations. they phase velocity along each direction is also multiplied by an additional coefficient. They show that, under certain constraints on the additional numerical coefficients, this ''medium'' does not generate any reflection at any angle and any frequency and is then a Perfectly Matched Layer. Technically it is a super-set of Berenger's PML to which it reduces for a specific set of parameters and like it, it is anisotropic. However, unlike the PML, it introduces some asymmetry in the absorption rate and is therefore labeled an APML for Asymmetric Perfectly Matched Layer. They present here the numerical considerations that have led them to introduce such a medium as well as its theory. Several finite-different numerical implementations are derived (in one, two and three dimensions) and the performance of the APML is contrasted with that of the PML in one and two dimensions. Using plane wave analysis, they show that the APML implementations lead to higher absorption rates than the considered PML implementations. Although they have considered in this paper the finite-different discretization of Maxwell-like equations only, the APML system of equations may be used with other discretization schemes, such as finite-elements, and may be applied to other equations, for applications beyond electromagnetics.
Perfect electromagnetic absorption at one-atom-thick scale
Li, Sucheng; Duan, Qian; Li, Shuo; Yin, Qiang; Lu, Weixin; Li, Liang; Hou, Bo; Gu, Bangming; Wen, Weijia
2015-11-02
We experimentally demonstrate that perfect electromagnetic absorption can be realized in the one-atom thick graphene. Employing coherent illumination in the waveguide system, the absorbance of the unpatterned graphene monolayer is observed to be greater than 94% over the microwave X-band, 7–13 GHz, and to achieve a full absorption, >99% in experiment, at ∼8.3 GHz. In addition, the absorption characteristic manifests equivalently a wide range of incident angle. The experimental results agree very well with the theoretical calculations. Our work accomplishes the broadband, wide-angle, high-performance absorption in the thinnest material with simple configuration.
Probabilistically Perfect Cloning of Two Pure States: Geometric Approach
NASA Astrophysics Data System (ADS)
Yerokhin, V.; Shehu, A.; Feldman, E.; Bagan, E.; Bergou, J. A.
2016-05-01
We solve the long-standing problem of making n perfect clones from m copies of one of two known pure states with minimum failure probability in the general case where the known states have arbitrary a priori probabilities. The solution emerges from a geometric formulation of the problem. This formulation reveals that cloning converges to state discrimination followed by state preparation as the number of clones goes to infinity. The convergence exhibits a phenomenon analogous to a second-order symmetry-breaking phase transition.
Integrated optical modulators and switches using coherent perfect loss.
Grote, Richard R; Driscoll, Jeffrey B; Osgood, Richard M
2013-08-15
We propose a new type of amplitude modulator for integrated optics based on phase-controllable coherent perfect loss (CPL) from a resonant cavity. Temporal coupled-mode theory is employed to derive a simple set of equations that describe the device operation, and finite-difference time-domain simulations are used to verify these equations. Two examples of CPL modulators are described with this formalism: a ring resonator and a 1D photonic crystal cavity. We show that internal resonator loss, and thus critical coupling, are not strict requirements for CPL operation. These devices are simple to design and can act as compact switches and modulators for integrated optics. PMID:24104632
Seeking perfection: a Kantian look at human genetic engineering.
Gunderson, Martin
2007-01-01
It is tempting to argue that Kantian moral philosophy justifies prohibiting both human germ-line genetic engineering and non-therapeutic genetic engineering because they fail to respect human dignity. There are, however, good reasons for resisting this temptation. In fact, Kant's moral philosophy provides reasons that support genetic engineering-even germ-line and non-therapeutic. This is true of Kant's imperfect duties to seek one's own perfection and the happiness of others. It is also true of the categorical imperative. Kant's moral philosophy does, however, provide limits to justifiable genetic engineering. PMID:17516148
Seeking perfection: a Kantian look at human genetic engineering.
Gunderson, Martin
2007-01-01
It is tempting to argue that Kantian moral philosophy justifies prohibiting both human germ-line genetic engineering and non-therapeutic genetic engineering because they fail to respect human dignity. There are, however, good reasons for resisting this temptation. In fact, Kant's moral philosophy provides reasons that support genetic engineering-even germ-line and non-therapeutic. This is true of Kant's imperfect duties to seek one's own perfection and the happiness of others. It is also true of the categorical imperative. Kant's moral philosophy does, however, provide limits to justifiable genetic engineering.
Non-adiabatic perturbations in multi-component perfect fluids
Koshelev, N.A.
2011-04-01
The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.