Fully Characterizing Axially Symmetric Szekeres Models with Three Data Sets
NASA Astrophysics Data System (ADS)
Célérier, Marie-Nöelle Mishra, Priti; Singh, Tejinder P.
2015-01-01
Inhomogeneous exact solutions of General Relativity with zero cosmological constant have been used in the literature to challenge the ΛCDM model. From one patch Lemaître-Tolman-Bondi (LTB) models to axially symmetric quasi-spherical Szekeres (QSS) Swiss-cheese models, some of them are able to reproduce to a good accuracy the cosmological data. It has been shown in the literature that a zero Λ LTB model with a central observer can be fully determined by two data sets. We demonstrate that an axially symmetric zero Λ QSS model with an observer located at the origin can be fully reconstructed from three data sets, number counts, luminosity distance and redshift drift. This is a first step towards a future demonstration involving five data sets and the most general Szekeres model.
Redshift drift in axially symmetric quasispherical Szekeres models
NASA Astrophysics Data System (ADS)
Mishra, Priti; Célérier, Marie-Noëlle; Singh, Tejinder P.
2012-10-01
Models of inhomogeneous universes constructed with exact solutions of Einstein’s general relativity have been proposed in the literature with the aim of reproducing the cosmological data without any need for a dark energy component. Besides large scale inhomogeneity models spherically symmetric around the observer, Swiss-cheese models have also been studied. Among them, Swiss cheeses where the inhomogeneous patches are modeled by different particular Szekeres solutions have been used for reproducing the apparent dimming of the type Ia supernovae. However, the problem of fitting such models to the type Ia supernovae data is completely degenerate and we need other constraints to fully characterize them. One of the tests which is known to be able to discriminate between different cosmological models is the redshift drift. This drift has already been calculated by different authors for Lemaître-Tolman-Bondi models. We compute it here for one particular axially symmetric quasispherical Szekeres Swiss cheese which has previously been shown to reproduce to a good accuracy the type Ia supernovae data, and we compare the results to the drift in the ΛCDM model and in some Lemaître-Tolman-Bondi models that can be found in the literature. We show that it is a good discriminator between them. Then, we discuss our model’s remaining degrees of freedom and propose a recipe to fully constrain them.
Axially symmetric multi-baryon solutions and their quantization in the chiral quark soliton model
NASA Astrophysics Data System (ADS)
Komori, S.; Sawado, N.; Shiiki, N.
2004-05-01
We study axially symmetric solutions with B=2-5 in the chiral quark soliton model. In the background of axially symmetric chiral fields, the quark eigenstates and profile functions of the chiral fields are computed self-consistently. The resultant quark bound spectrum are doubly degenerate due to the symmetry of the chiral field. Upon quantization, various observable spectra of the chiral solitons are obtained. Taking account of the Finkelstein-Rubinstein constraints, we show that the quantum numbers of our solitons coincide with the physical observations for B=2 and 4 while B=3 and 5 do not.
Axially Symmetric Cosmological Model with Bulk Stress in Saez-Ballester Theory of Gravitation
NASA Astrophysics Data System (ADS)
Mete, V. G.; Nimkar, A. S.; Elkar, V. D.
2016-01-01
An Axially symmetric non-static space time is considered in presence of bulk stress in scalar tensor theory formulated by Saez and Ballester (Phys. Lett. A113, 467 1985). For solving the field equations, relation between metric potential and shear velocity is proportional to scale expansion are used. Also various physical and geometrical properties of the model have been discussed.
Achromatic axially symmetric wave plate.
Wakayama, Toshitaka; Komaki, Kazuki; Otani, Yukitoshi; Yoshizawa, Toru
2012-12-31
An achromatic axially symmetric wave plate (AAS-WP) is proposed that is based on Fresnel reflections. The wave plate does not introduce spatial dispersion. It provides retardation in the wavelength domain with an axially symmetric azimuthal angle. The optical configuration, a numerical simulation, and the optical properties of the AAS-WP are described. It is composed of PMMA. A pair of them is manufactured on a lathe. In the numerical simulation, the achromatic angle is estimated and is used to design the devices. They generate an axially symmetric polarized beam. The birefringence distribution is measured in order to evaluate the AAS-WPs. PMID:23388751
Revised NASA axially symmetric ring model for coupled-cavity traveling-wave tubes
NASA Technical Reports Server (NTRS)
Wilson, Jeffrey D.
1987-01-01
A versatile large-signal, two-dimensional computer program is used by NASA to model coupled-cavity travelling-wave tubes (TWTs). In this model, the electron beam is divided into a series of disks, each of which is further divided into axially symmetric rings which can expand and contract. The trajectories of the electron rings and the radiofrequency (RF) fields are determined from the calculated axial and radial space-charge, RF, and magnetic forces as the rings pass through a sequence of cavities. By varying electrical and geometric properties of individual cavities, the model is capable of simulating severs, velocity tapers, and voltage jumps. The calculated electron ring trajectories can be used in designing magnetic focusing and multidepressed collectors. The details of using the program are presented, and results are compared with experimental data.
Kinetic models of two-dimensional plane and axially symmetric current sheets: Group theory approach
Vasko, I. Y.; Artemyev, A. V.; Popov, V. Y.; Malova, H. V.
2013-02-15
In this paper, we present new class of solutions of Grad-Shafranov-like (GS-like) equations, describing kinetic plane and axially symmetric 2D current sheets. We show that these equations admit symmetry groups only for Maxwellian and {kappa}-distributions of charged particles. The admissible symmetry groups are used to reduce GS-like equations to ordinary differential equations for invariant solutions. We derive asymptotes of invariant solutions, while invariant solutions are found analytically for the {kappa}-distribution with {kappa}=7/2. We discuss the difference of obtained solutions from equilibria widely used in other studies. We show that {kappa} regulates the decrease rate of plasma characteristics along the current sheet and determines the spatial distribution of magnetic field components. The presented class of plane and axially symmetric (disk-like) current sheets includes solutions with the inclined neutral plane.
Fluid-structure interaction in axially symmetric models of abdominal aortic aneurysms.
Fraser, K H; Li, M-X; Lee, W T; Easson, W J; Hoskins, P R
2009-02-01
Abdominal aortic aneurysm disease progression is probably influenced by tissue stresses and blood flow conditions and so accurate estimation of these will increase understanding of the disease and may lead to improved clinical practice. In this work the blood flow and tissue stresses in axially symmetric aneurysms are calculated using a complete fluid-structure interaction as a benchmark for calculating the error introduced by simpler calculations: rigid walled for the blood flow, homogeneous pressure for the tissue stress, as well as one-way-coupled interactions. The error in the peak von Mises stress in a homogeneous pressure calculation compared with a fluid-structure interaction calculation was less than 3.5 per cent for aneurysm diameters up to 7 cm. The error in the mean wall shear stress, in a rigid-walled calculation compared with a fluid-structure interaction calculation, varied from 30 per cent to 60 per cent with increasing aneurysm diameter. These results suggest that incorporation of the fluid-structure interaction is unnecessary for purely mechanical modelling, with the aim of evaluating the current rupture probability. However, for more complex biological modelling, perhaps with the aim of predicting the progress of the disease, where accurate estimation of the wall shear stress is essential, some form of fluid-structure interaction is necessary. PMID:19278197
Suspension model blood flow through an inclined tube with an axially non-symmetrical stenosis
NASA Astrophysics Data System (ADS)
Chakraborty, Uday Shankar; Biswas, Devajyoti; Paul, Moumita
2011-03-01
The flow of blood in an inclined artery with an axially non-symmetrical but radially symmetrical mild stenosis has been presented in this study. To account for the slip at stenotic wall, hematocrit and inclination of the artery, blood has been represented by a particle-fluid suspension. The expression for the flow characteristics, namely, the impedance (resistance to flow), the wall shear stress and the shear stress at the throat of the stenosis have been derived and represented graphically with respect to different flow parameters. The impedance increases with the hematocrit and stenosis size but decreases with slip at wall and angle of inclination of the artery. The shear stress at the maximum stenosis height increases with the inclination of the artery but possess the characteristics similar to that of impedance with respect to other parameters. As an application, theoretical values of effective viscosity computed with the help of the present analysis are compared with experimental results and found that they are in reasonable agreement for low hematocrit values in small blood carrying vessels.
Quasi-axially symmetric stellarators
Garabedian, Paul R.
1998-01-01
Confinement of a plasma for controlled thermonuclear fusion is studied numerically. Toroidal equilibria are considered, with an emphasis on the Modular Helias-like Heliac 2 (MHH2), which is a stellarator of low aspect ratio with just two field periods surrounded by 16 modular coils. The geometry is fully three-dimensional, but there is an axial symmetry of the magnetic structure that is calculated to give confinement competitive with that in circular tokamaks. Additional vertical and toroidal field coils, together with a current drive, provide the flexibility and the control of rotational transform necessary for a successful experiment. An MHH3 device with three field periods and comparable quasi-axial symmetry is presented, too, and because of reversed shear, its physical properties may be better. Variational analysis of equilibrium and stability is shown to give a more reliable prediction of performance for these stellarators than linearized or local theories that suffer from a failure of differentiability and convergence. PMID:9707544
Quasi-axially symmetric stellarators.
Garabedian, P R
1998-08-18
Confinement of a plasma for controlled thermonuclear fusion is studied numerically. Toroidal equilibria are considered, with an emphasis on the Modular Helias-like Heliac 2 (MHH2), which is a stellarator of low aspect ratio with just two field periods surrounded by 16 modular coils. The geometry is fully three-dimensional, but there is an axial symmetry of the magnetic structure that is calculated to give confinement competitive with that in circular tokamaks. Additional vertical and toroidal field coils, together with a current drive, provide the flexibility and the control of rotational transform necessary for a successful experiment. An MHH3 device with three field periods and comparable quasi-axial symmetry is presented, too, and because of reversed shear, its physical properties may be better. Variational analysis of equilibrium and stability is shown to give a more reliable prediction of performance for these stellarators than linearized or local theories that suffer from a failure of differentiability and convergence. PMID:9707544
Polarization converters based on axially symmetric twisted nematic liquid crystal.
Ko, Shih-Wei; Ting, Chi-Lun; Fuh, Andy Y-G; Lin, Tsung-Hsien
2010-02-15
An axially symmetric twisted nematic liquid crystal (ASTNLC) device, based on axially symmetric photoalignment, was demonstrated. Such an ASTNLC device can convert axial (azimuthal) to azimuthal (axial) polarization. The optical properties of the ASTNLC device are analyzed and found to agree with simulation results. The ASTNLC device with a specific device can be adopted as an arbitrary axial symmetric polarization converter or waveplate for axially, azimuthally or vertically polarized light. A design for converting linear polarized light to axially symmetric circular polarized light is also demonstrated. PMID:20389369
Zampolli, Mario; Tesei, Alessandra; Jensen, Finn B; Malm, Nils; Blottman, John B
2007-09-01
A frequency-domain finite-element (FE) technique for computing the radiation and scattering from axially symmetric fluid-loaded structures subject to a nonsymmetric forcing field is presented. The Berenger perfectly matched layer (PML), applied directly at the fluid-structure interface, makes it possible to emulate the Sommerfeld radiation condition using FE meshes of minimal size. For those cases where the acoustic field is computed over a band of frequencies, the meshing process is simplified by the use of a wavelength-dependent rescaling of the PML coordinates. Quantitative geometry discretization guidelines are obtained from a priori estimates of small-scale structural wavelengths, which dominate the acoustic field at low to mid frequencies. One particularly useful feature of the PML is that it can be applied across the interface between different fluids. This makes it possible to use the present tool to solve problems where the radiating or scattering objects are located inside a layered fluid medium. The proposed technique is verified by comparison with analytical solutions and with validated numerical models. The solutions presented show close agreement for a set of test problems ranging from scattering to underwater propagation. PMID:17927408
NASA Astrophysics Data System (ADS)
Cubarsi, Rafael
2014-07-01
Under a common potential, a finite mixture of ellipsoidal velocity distributions satisfying the Boltzmann collisionless equation provides a set of integrability conditions that may constrain the population kinematics. They are referred to as conditions of consistency and were discussed in a previous paper on mixtures of axisymmetric populations. As a corollary, these conditions are now extended to point-axial symmetry, that is, point symmetry around the rotation axis or bisymmetry, by determining which potentials are connected with a more flexible superposition of stellar populations. Under point-axial symmetry, the potential is still axisymmetric, but the velocity and mass distributions are not necessarily. A point-axial stellar system is, in a natural way, consistent with a flat velocity distribution of a disc population. Therefore, no additional integrability conditions are required to solve the Boltzmann collisionless equation for such a population. For other populations, if the potential is additively separable in cylindrical coordinates, the populations are not kinematically constrained, although under point-axial symmetry, the potential is reduced to the harmonic function, which, for the Galaxy, is proven to be non-realistic. In contrast, a non-separable potential provides additional conditions of consistency. When mean velocities for the populations are unconstrained, the potential becomes quasi-stationary, being a particular case of the axisymmetric model. Then, the radial and vertical mean velocities of the populations can differ and produce an apparent vertex deviation of the whole velocity distribution. However, single population velocity ellipsoids still have no vertex deviation in the Galactic plane and no tilt in their intersection with a meridional Galactic plane. If the thick disc and halo ellipsoids actually have non-vanishing tilt, as the surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data seem to show, the
Stationary axially symmetric solutions in Brans-Dicke theory
NASA Astrophysics Data System (ADS)
Kirezli, Pınar; Delice, Özgür
2015-11-01
Stationary, axially symmetric Brans-Dicke-Maxwell solutions are reexamined in the framework of the Brans-Dicke (BD) theory. We see that, employing a particular parametrization of the standard axially symmetric metric simplifies the procedure of obtaining the Ernst equations for axially symmetric electrovacuum spacetimes for this theory. This analysis also permits us to construct a two parameter extension in both Jordan and Einstein frames of an old solution generating technique frequently used to construct axially symmetric solutions for BD theory from a seed solution of general relativity. As applications of this technique, several known and new solutions are constructed including a general axially symmetric BD-Maxwell solution of Plebanski-Demianski with vanishing cosmological constant, i.e., the Kinnersley solution and general magnetized Kerr-Newman-type solutions. Some physical properties and the circular motion of test particles for a particular subclass of Kinnersley solution, i.e., a Kerr-Newman-NUT-type solution for BD theory, are also investigated in some detail.
STED microscopy based on axially symmetric polarized vortex beams
NASA Astrophysics Data System (ADS)
Zhehai, Zhou; Lianqing, Zhu
2016-03-01
A stimulated emission depletion (STED) microscopy scheme using axially symmetric polarized vortex beams is proposed based on unique focusing properties of such kinds of beams. The concept of axially symmetric polarized vortex beams is first introduced, and the basic principle about the scheme is described. Simulation results for several typical beams are then shown, including radially polarized vortex beams, azimuthally polarized vortex beams, and high-order axially symmetric polarized vortex beams. The results indicate that sharper doughnut spots and thus higher resolutions can be achieved, showing more flexibility than previous schemes based on flexible modulation of both phase and polarization for incident beams. Project supported by the National Natural Science Foundation of China (Grant Nos. 61108047 and 61475021), the Natural Science Foundation of Beijing, China (Grant No. 4152015), the Program for New Century Excellent Talents in Universities of China (Grant No. NCET-13-0667), and the Top Young Talents Support Program of Beijing, China (Grant No. CIT&TCD201404113).
Stationary axially symmetric relativistic thin discs with nonzero radial pressure
NASA Astrophysics Data System (ADS)
González, Guillermo A.; Gutiérrez-Piñeres, Antonio C.
2012-07-01
A detailed analysis of the surface energy-momentum (SEMT) tensor of stationary axially symmetric relativistic thin discs with nonzero radial pressure is presented. The physical content of the SEMT is analysed and expressions for the velocity vector, energy density, principal stresses and heat flow are obtained. We also present the counter-rotating model interpretation for these discs by considering the SEMT as the superposition of two counter-rotating perfect fluids. We analyse the possibility of counter-rotation along geodesics as well as counter-rotation with equal and opposite tangential velocities, and explicit expressions for the velocities are obtained in both the cases. By assuming a given choice for the counter-rotating velocities, explicit expressions for the energy densities and pressures of the counter-rotating fluids are then obtained. Some simple thin disc models obtained from the Kerr solution are also presented.
Axially symmetric shapes with minimum wave drag
NASA Technical Reports Server (NTRS)
Heaslet, Max A; Fuller, Franklyn B
1956-01-01
The external wave drag of bodies of revolution moving at supersonic speeds can be expressed either in terms of the geometry of the body, or in terms of the body-simulating axial source distribution. For purposes of deriving optimum bodies under various given conditions, it is found that the second of the methods mentioned is the more tractable. By use of a quasi-cylindrical theory, that is, the boundary conditions are applied on the surface of a cylinder rather than on the body itself, the variational problems of the optimum bodies having prescribed volume or caliber are solved. The streamline variations of cross-sectional area and drags of the bodies are exhibited, and some numerical results are given.
Electromagnetic fields in axial symmetric waveguides with variable cross section
Kheifets, S.
1980-02-15
A new class of separable variables is found which allows one to find an approximate analytical solution of the Maxwell equations for axial symmetric waveguides with slow (but not necessarily small) varying boundary surfaces. An example of the solution is given. Possible applications and limitations of this approach are discussed. 6 refs., 10 figs.
Perturbation approximation for orbits in axially symmetric funnels
NASA Astrophysics Data System (ADS)
Nauenberg, Michael
2014-11-01
A perturbation method that can be traced back to Isaac Newton is applied to obtain approximate analytic solutions for objects sliding in axially symmetric funnels in near circular orbits. Some experimental observations are presented for balls rolling in inverted cones with different opening angles, and in a funnel with a hyperbolic surface that approximately simulates the gravitational force.
Modifications to Axially Symmetric Simulations Using New DSMC (2007) Algorithms
NASA Technical Reports Server (NTRS)
Liechty, Derek S.
2008-01-01
Several modifications aimed at improving physical accuracy are proposed for solving axially symmetric problems building on the DSMC (2007) algorithms introduced by Bird. Originally developed to solve nonequilibrium, rarefied flows, the DSMC method is now regularly used to solve complex problems over a wide range of Knudsen numbers. These new algorithms include features such as nearest neighbor collisions excluding the previous collision partners, separate collision and sampling cells, automatically adaptive variable time steps, a modified no-time counter procedure for collisions, and discontinuous and event-driven physical processes. Axially symmetric solutions require radial weighting for the simulated molecules since the molecules near the axis represent fewer real molecules than those farther away from the axis due to the difference in volume of the cells. In the present methodology, these radial weighting factors are continuous, linear functions that vary with the radial position of each simulated molecule. It is shown that how one defines the number of tentative collisions greatly influences the mean collision time near the axis. The method by which the grid is treated for axially symmetric problems also plays an important role near the axis, especially for scalar pressure. A new method to treat how the molecules are traced through the grid is proposed to alleviate the decrease in scalar pressure at the axis near the surface. Also, a modification to the duplication buffer is proposed to vary the duplicated molecular velocities while retaining the molecular kinetic energy and axially symmetric nature of the problem.
Dain, Sergio; Ortiz, Omar E.
2009-07-15
We present numerical evidences for the validity of the inequality between the total mass and the total angular momentum for multiple axially symmetric (nonstationary) black holes. We use a parabolic heat flow to solve numerically the stationary axially symmetric Einstein equations. As a by-product of our method, we also give numerical evidences that there are no regular solutions of Einstein equations that describe two extreme, axially symmetric black holes in equilibrium.
Method of characteristics for three-dimensional axially symmetrical supersonic flows.
NASA Technical Reports Server (NTRS)
Sauer, R
1947-01-01
An approximation method for three-dimensional axially symmetrical supersonic flows is developed; it is based on the characteristics theory (represented partly graphically, partly analytically). Thereafter this method is applied to the construction of rotationally symmetrical nozzles. (author)
Axially symmetric dissipative fluids in the quasi-static approximation
NASA Astrophysics Data System (ADS)
Herrera, L.; di Prisco, A.; Ospino, J.; Carot, J.
2016-01-01
Using a framework based on the 1 + 3 formalism, we carry out a study on axially and reflection symmetric dissipative fluids, in the quasi-static regime. We first derive a set of invariantly defined “velocities”, which allow for an inambiguous definition of the quasi-static approximation. Next, we rewrite all the relevant equations in this approximation and extract all the possible, physically relevant, consequences ensuing the adoption of such an approximation. In particular, we show how the vorticity, the shear and the dissipative flux, may lead to situations where different kind of “velocities” change their sign within the fluid distribution with respect to their sign on the boundary surface. It is shown that states of gravitational radiation are not a priori incompatible with the quasi-static regime. However, any such state must last for an infinite period of time, thereby diminishing its physical relevance.
Three-dimensional equilibria in axially symmetric tokamaks.
Garabedian, Paul R
2006-12-19
The NSTAB and TRAN computer codes have been developed to study equilibrium, stability, and transport in fusion plasmas with three-dimensional (3D) geometry. The numerical method that is applied calculates islands in tokamaks like the Doublet III-D at General Atomic and the International Thermonuclear Experimental Reactor. When bifurcated 3D solutions are used in Monte Carlo computations of the energy confinement time, a realistic simulation of transport is obtained. The significance of finding many 3D magnetohydrodynamic equilibria in axially symmetric tokamaks needs attention because their cumulative effect may contribute to the prompt loss of alpha particles or to crashes and disruptions that are observed. The 3D theory predicts good performance for stellarators. PMID:17159158
Three-dimensional equilibria in axially symmetric tokamaks
Garabedian, Paul R.
2006-01-01
The NSTAB and TRAN computer codes have been developed to study equilibrium, stability, and transport in fusion plasmas with three-dimensional (3D) geometry. The numerical method that is applied calculates islands in tokamaks like the Doublet III-D at General Atomic and the International Thermonuclear Experimental Reactor. When bifurcated 3D solutions are used in Monte Carlo computations of the energy confinement time, a realistic simulation of transport is obtained. The significance of finding many 3D magnetohydrodynamic equilibria in axially symmetric tokamaks needs attention because their cumulative effect may contribute to the prompt loss of α particles or to crashes and disruptions that are observed. The 3D theory predicts good performance for stellarators. PMID:17159158
Neoclassical transport in quasi-axially symmetric stellarators
Mynick, H.E.
1997-04-01
The author presents a numerical and analytic assessment of the transport in two quasi-axially symmetric stellarators, including one variant of the MHH2 class of such devices, and a configuration they refer to as NHH2, closely related to MHH2. Monte Carlo simulation results are compared with expectations from established stellarator neoclassical theory, and with some empirical stellarator scalings, used as an estimate of the turbulent transport which might be expected. From the standpoint of transport, these may be viewed as either tokamaks with large ({delta} {approximately} 1%) but low-n ripple, or as stellarators with small ripple. For NHH2, numerical results are reasonably well explained by analytic neoclassical theory. MHH2 adheres less to assumptions made in most analytic theory, and its numerical results agree less well with theory than those for NHH2. However, for both, the non-axisymmetric contribution to the heat flux is comparable with the symmetric neoclassical contribution, and also falls into the range of the expected anomalous (turbulent) contribution. Thus, it appears effort to further optimize the thermal transport beyond the particular incarnations studied here would be of at most modest utility. However, the favorable thermal confinement relies heavily on the radial electric field. Thus, the present configurations will have a loss cone for trapped energetic ions, so that further optimization may be indicated for large devices of this type.
Gapless excitations of axially symmetric vortices in systems with tensorial order parameter
Peterson, Adam J.; Shifman, Mikhail
2014-09-15
We extend the results of previous work on vortices in systems with tensorial order parameters. Specifically, we focus our attention on systems with a Ginzburg–Landau free energy with a global U(1){sub P}×SO(3){sub S}×SO(3){sub L} symmetry in the phase, spin and orbital degrees of freedom. We consider axially symmetric vortices appearing on the spin–orbit locked SO(3){sub S+L} vacuum. We determine the conditions required on the Ginzburg–Landau parameters to allow for an axially symmetric vortex with off diagonal elements in the order parameter to appear. The collective coordinates of the axial symmetric vortices are determined. These collective coordinates are then quantized using the time dependent Ginzburg–Landau free energy to determine the number of gapless modes propagating along the vortex.
An inverse problem design method for branched and unbranched axially symmetrical ducts
NASA Technical Reports Server (NTRS)
Nelson, C. D.; Yang, T.
1976-01-01
This paper concerns the potential flow design of axially symmetrical ducts of both circular and annular cross section with or without wall suction or blowing slots. The objective of the work was to develop a method by which such ducts could be designed with directly prescribed wall pressure variation. Previous axially symmetrical design methods applied only to circular cross sectional ducts and required that the pressure distribution be prescribed along the duct centerline and not along the duct wall. The present method uses an inverse problem approach which extends the method of Stanitz to the axially symmetrical case, and an approximation is used to account for the stagnation point in branched duct designs. Two examples of successful designs of diffusers with suction slots are presented.
NASA Technical Reports Server (NTRS)
Page, R. J.; Childs, M. E.
1974-01-01
An experimental investigation at Mach 4 of shock-induced turbulent boundary layer separation at the walls of axially symmetric flow passages is discussed, with particular emphasis placed on determining the shock strengths required for incipient separation. The shock waves were produced by interchangeable sting-mounted cones placed on the axes of the flow passages and aligned with the freestream flow. The interactions under study simulate those encountered in axially symmetric engine inlets of supersonic aircraft. Knowledges of the shock strengths required for boundary layer separation in inlets is important since for shocks of somewhat greater strength rather drastic alterations in the inlet flow field may occur.
NASA Technical Reports Server (NTRS)
Ye, Gang; Voigt, Gerd-Hannes
1989-01-01
A model is presented of an axially symmetric pole-on magnetosphere in MHD force balance, in which both plasma thermal pressure gradients and centrifugal force are taken into account. Assuming that planetary rotation leads to differentially rotating magnetotail field lines, the deformation of magnetotail field lines under the influence of both thermal plasma pressure and centrifugal forces was calculated. Analytic solutions to the Grad-Shafranov equation are presented, which include the centrifugal force term. It is shown that the nonrotational magnetosphere with hot thermal plasma leads to a field configuration without a toroidal B(phi) component and without field-aligned Birkeland currents. The other extreme, a rapidly rotating magnetosphere with cold plasma, leads to a configuration in which plasma must be confined within a thin disk in a plane where the radial magnetic field component B(r) vanishes locally.
Shearing and geodesic axially symmetric perfect fluids that do not produce gravitational radiation
NASA Astrophysics Data System (ADS)
Herrera, L.; Di Prisco, A.; Ospino, J.; Carot, J.
2015-01-01
Using a framework based on the 1 +3 formalism we carry out a study on axially and reflection symmetric perfect and geodesic fluids, looking for possible models of sources radiating gravitational waves. Therefore, the fluid should be necessarily shearing, for otherwise the magnetic part of the Weyl tensor vanishes, leading to a vanishing of the super-Poynting vector. However, for the family of perfect, geodesic fluids considered here, it appears that all possible cases reduce to conformally flat, shear-free, vorticity-free fluids, i.e., Friedman-Robertson-Walker. The super-Poynting vector vanishes and therefore no gravitational radiation is expected to be produced. The physical meaning of the obtained result is discussed.
Electromagnetic fields in an axial symmetric waveguide with variable cross section
Kheifets, S.
1980-07-01
A new class of separable variables is found which allows one to find an approximate analytical solution of the Maxwell equations for axial symmetric waveguides with slow (but not necessarily small) varying boundary surfaces. An example of the solution is given. Possible applications and limitations of this approach are discussed.
Axially symmetric loop phase-conjugation scheme with broadband longitudinally dispersed light beams
Odintsov, Vladimir I
2004-07-31
A loop phase-conjugation scheme based on an axially symmetric four-wave interaction of focused light beams is proposed. It is shown that, when a longitudinal dispersion is introduced into the light beams, this scheme allows a phase conjugation of spatially coherent broadband radiation. The region of coherent interaction of focused longitudinally dispersed light beams is estimated. (nonlinear optical phenomena)
Investigation of Flow in an Axially Symmetrical Heated Jet of Air
NASA Technical Reports Server (NTRS)
Corrsin, Stanley
1943-01-01
The work done under this contract falls essentially into two parts: the first part was the design and construction of the equipment and the running of preliminary tests on the 3-inch jet, carried out by Mr. Carl Thiele in 1940; the second part consisting in the measurement in the 1-inch jet flow in an axially symmetrical heated jet of air. (author)
Space charge field in a FEL with axially symmetric electron beam
Goncharov, I.A.; Belyavskiy, E.D.
1995-12-31
Nonlinear two-dimensional theory of the space charge of an axially symmetric electron beam propagating in combined right-hand polarized wiggler and uniform axial guide fields in a presence of high-frequency electromagnetic wave is presented. The well-known TE{sub 01} mode in a cylindrical waveguide for the model of radiation fields and paraxial approximation for the wiggler field are used. Space charge field components are written in the Lagrange coordinates by the twice averaged Green`s functions of two equally charged infinitely thin discs. For that {open_quotes}compensating charges{close_quotes} method is applied in which an electron ring model is substituted by one with two different radii and signs discs. On this approach the initial Green`s functions peculiarities are eliminated and all calculations are considerably simplified. Coefficients of a twice averaged Green`s function expansion into a Fourier series are obtained by use of corresponding expansion coefficients of longitudinal Green`s functions of equal radii discs and identical rings known from the one-dimensional theory of super HF devices taking into account electron bunches periodicity. This approach permit the space charge field components for an arbitrary stratified stream to be expressed in a simple and strict enough form. The expressions obtained can be employed in a nonlinear two-dimensional FEL theory in order to investigate beam dynamical defocusing and electrons failing on the waveguide walls in the high gain regime. This is especially important for FEL operation in mm and submm.
Electromagnetic torque and force in axially symmetric liquid-crystal droplets.
Jánossy, István
2008-10-15
Circularly polarized light exerts torque on birefringent objects. In the case of axially symmetric particles, however, the moment of radiation force balances the direct optical torque. This explains the observation that radial liquid-crystal droplets, in contrast to planar droplets, do not spin in circularly polarized light. The conclusion is in agreement with considerations based on the angular momentum conservation of light [Phys. Rev. Lett.96, 163905 (2006)]. PMID:18923626
NASA Astrophysics Data System (ADS)
Romano, Marcello
2010-04-01
A new method is introduced to control and analyze the rotational motion of an axially symmetric rigid-body spacecraft. In particular, this motion is seen as the combination of the rotation of a virtual sphere with respect to the inertial frame, and the rotation of the body, about its symmetry axis, with respect to this sphere. Two new exact solutions are introduced for the motion of axially symmetric rigid bodies subjected to a constant external torque in the following cases: (1) torque parallel to the angular momentum and (2) torque parallel to the vectorial component of the angular momentum on the plane perpendicular to the symmetry axis. By building upon these results, two rotational maneuvers are proposed for axially symmetric spacecraft: a detumbling maneuver and a nutation canceling maneuver. The two maneuvers are the minimum time maneuvers for spherically constrained maximum torque. These maneuvers are simple and elegant, as they reduce the control of the three degrees-of-freedom nonlinear rotational motion to a single degree-of-freedom linear problem. Furthermore, the complete (both for the dynamics and for the kinematics) and exact analytic solutions are found for the two maneuvers. An extended survey is reported in the introduction of the paper of the few cases where the rotation of a rigid body is fully reduced to an exact analytic solution in closed form.
Computation of the viscous supersonic flow over symmetrical and asymmetrical external axial corners
NASA Technical Reports Server (NTRS)
Kutler, P.; Pulliam, T. H.; Vigneron, Y. C.
1978-01-01
The primary objective of the reported investigation is the computational verification of the experimental results obtained by Salas and Daywitt (1978). Two existing computer codes were used to compute the supersonic flow field surrounding the external axial corner. For the inviscid and turbulent flow results, the unsteady, three-dimensional implicit code of Pulliam and Steger (1978) was used. For the laminar flow results, the unsteady two-dimensional explicit procedure of Vigneron et al. (1977) was employed. Inviscid solutions for a symmetric configuration with a rounded corner resulted in either single or triple surface crossflow stagnation point flows, depending on the corner radius. Numerical results obtained for the same symmetric configuration tested experimentally show the crossflow in the vicinity of the corner to be away from the corner and thus in agreement with the experimental oil flow results.
A cylindrical shell with an axial crack under skew-symmetric loading.
NASA Technical Reports Server (NTRS)
Yuceoglu, U.; Erdogan, F.
1973-01-01
The skew-symmetric problem for a cylindrical shell containing an axial crack is considered. It is assumed that the material has a special orthotropy - namely, that the shear modulus may be evaluated from the measured Young's moduli and Poisson ratios and is not an independent material constant. The problem is solved within the confines of an eighth-order linearized shallow shell theory. As numerical examples, the torsion of an isotropic cylinder and that of a specially orthotropic cylinder (titanium) are considered. The membrane and bending components of the stress intensity factor are calculated and are given as functions of a dimensionless shell parameter. In the torsion problem for the axially cracked cylinder the bending effects appear to be much more significant than that found for the circumferentially cracked cylindrical shell. Also, as the shell parameter increases, unlike the results found in the pressurized shell, the bending stresses around crack ends do not change sign.
Off-axis reflecting telescope with axially-symmetric optical property and its applications
NASA Astrophysics Data System (ADS)
Chang, Seunghyuk
2006-06-01
The basic concept and fundamental result of a recently developed geometric aberration theory for classical off-axis reflecting telescopes and imaging systems are presented. It is shown that a classical off-axis reflecting telescope can be designed to have practically axially-symmetric optical property by eliminating the dominant aberration (linear astigmatism) caused by the asymmetric geometry. A simple closed-form equation for elimination of linear astigmatism is presented. Also, to show how the developed aberration theory can be applied to current and future telescopes, several off-axis reflecting telescopes and imaging systems are designed and analyzed.
Axially symmetric polarization converter made of patterned liquid crystal quarter wave plate.
Fan, Fan; Du, Tao; Srivastava, Abhishek Kumar; Lu, Wang; Chigrinov, Vladimir; Kwok, Hoi Sing
2012-10-01
We present a method to fabricate a radially and azimuthally polarized light converter by deploying a patterned liquid crystal (LC) quarter-wave plates (QWP). The patterned QWP has been fabricated by providing the axially symmetric alignment to the LC layer by mean of photo-alignment. When the left handed circularly (LHC) or right handed circularly (RHC) polarized light passes through these patterned QWPs, the emergent light becomes radially or azimuthally polarized. Moreover, the proposed polarization converters are characterized by the fast response time, thus could find application in various fast photonic devices. PMID:23188267
The harmonic-map structure of the axially symmetric stationary Einstein equations
NASA Astrophysics Data System (ADS)
Whitman, Andrew P.; Stoeger, William R.
1992-06-01
We systematically review the solutions of the vacuum Einstein equations for the axially symmetric stationary case which are harmonic maps. In particular, we show that the interesting part of the Kerr solution is a composition of a harmonic map intoH {1/2} with a totally geodesic map fromH {1/2} into SS(1,1). We also point out, relying on Sanchez' results, that there is an analogous structure for the Lorentz-domain cases involving cylindrical gravitational waves and colliding plane waves.
Carbon-13 and tin-119 relaxation studies of some axially symmetrical organotin compounds
NASA Astrophysics Data System (ADS)
Chapelle, S.; Granger, P.
We have studied a variety of axially symmetrical tin compounds by 119Sn and 13C NMR. Tin was observed at two field strengths and, except for Ph 3SnCl, T1 is field independent and governed mainly by spin-rotation. A chemical-shift anisotropy of 136 ppm is observed for 119Sn in Ph 3SnCl. Deverell's relationship provides a good estimate of the values of the spin-rotational constants and the theory of Woessner, Snowden, and Huntress leads to the values of the rotational diffusion constants.
NASA Technical Reports Server (NTRS)
Nelson, C. D., Jr.; Hudson, W. G.; Yang, T.
1974-01-01
This paper presents a procedure for the design and the performance prediction of axially symmetrical contoured wall diffusers employing suction boundary layer control. An inverse problem approach was used in the potential flow design of the diffuser wall contours. The experimentally observed flow characteristics and the stability of flows within the diffuser are also described. Guidelines for the design of low suction (less than 10 percent of the inlet flow) and thus high effectiveness contoured wall diffusers are also provided based on the results of the experimental program.
EBQ code: transport of space-charge beams in axially symmetric devices
Paul, A.C.
1982-11-01
Such general-purpose space charge codes as EGUN, BATES, WOLF, and TRANSPORT do not gracefully accommodate the simulation of relativistic space-charged beams propagating a long distance in axially symmetric devices where a high degree of cancellation has occurred between the self-magnetic and self-electric forces of the beam. The EBQ code was written specifically to follow high current beam particles where space charge is important in long distance flight in axially symmetric machines possessing external electric and magnetic field. EBQ simultaneously tracks all trajectories so as to allow procedures for charge deposition based on inter-ray separations. The orbits are treated in Cartesian geometry (position and momentum) with z as the independent variable. Poisson's equation is solved in cylindrical geometry on an orthogonal rectangular mesh. EBQ can also handle problems involving multiple ion species where the space charge from each must be included. Such problems arise in the design of ion sources where different charge and mass states are present.
NASA Technical Reports Server (NTRS)
Voigt, Gerd-Hannes
1986-01-01
Field-aligned Birkeland currents and the angle of the magnetic line twist were calculated for an axially symmetric pole-on magnetosphere (assumed to be in MHD equilibrium). The angle of the field line twist was shown to have a strong radial dependence on the axisymmetric magnetotail as well as on the ionospheric conductivity and the amount of thermal plasma contained in closed magnetotail flux tubes. The field line twist results from the planetary rotation, which leads to the development of a toroidal magnetic B-sub-phi component and to differentially rotating magnetic field lines. It was shown that the time development of the toroidal magnetic B-sub-phi component and the rotation frequency are related through an induction equation.
Absence of saturation for finite injected currents in axially symmetric cavity diode
NASA Astrophysics Data System (ADS)
Biswas, Debabrata; Kumar, Raghwendra; Puri, R. R.
2003-11-01
The Child-Langmuir law is investigated numerically using a fully electromagnetic particle-in-cell code for a closed axially symmetric diode. It is found that the average current transmitted to the anode (JTR) increases with the injected current (JIN) even after the formation of virtual cathode in both the nonrelativistic and relativistic cases. The increase is found to be a power law, JTR˜JIN1-β. In other words, the time averaged fraction f of electrons reaching the anode varies with the input current as, f˜JIN-β, where β<1. In contrast, for an infinite parallel plate diode, f˜JIN-1. The possibility of asymptotic saturation is also discussed.
NASA Astrophysics Data System (ADS)
Herrera, L.; Di Prisco, A.; Ibáñez, J.; Ospino, J.
2014-04-01
We carry out a general study on the collapse of axially (and reflection-)symmetric sources in the context of general relativity. All basic equations and concepts required to perform such a general study are deployed. These equations are written down for a general anisotropic dissipative fluid. The proposed approach allows for analytical studies as well as for numerical applications. A causal transport equation derived from the Israel-Stewart theory is applied, to discuss some thermodynamic aspects of the problem. A set of scalar functions (the structure scalars) derived from the orthogonal splitting of the Riemann tensor are calculated and their role in the dynamics of the source is clearly exhibited. The characterization of the gravitational radiation emitted by the source is discussed.
A combined finite element-boundary element formulation for solution of axially symmetric bodies
NASA Technical Reports Server (NTRS)
Collins, Jeffrey D.; Volakis, John L.
1991-01-01
A new method is presented for the computation of electromagnetic scattering from axially symmetric bodies. To allow the simulation of inhomogeneous cross sections, the method combines the finite element and boundary element techniques. Interior to a fictitious surface enclosing the scattering body, the finite element method is used which results in a sparce submatrix, whereas along the enclosure the Stratton-Chu integral equation is enforced. By choosing the fictitious enclosure to be a right circular cylinder, most of the resulting boundary integrals are convolutional and may therefore be evaluated via the FFT with which the system is iteratively solved. In view of the sparce matrix associated with the interior fields, this reduces the storage requirement of the entire system to O(N) making the method attractive for large scale computations. The details of the corresponding formulation and its numerical implementation are described.
Octupolar approximation for the excluded volume of axially symmetric convex bodies
NASA Astrophysics Data System (ADS)
Piastra, Marco; Virga, Epifanio G.
2013-09-01
We propose a simply computable formula for the excluded volume of convex, axially symmetric bodies, based on the classical Brunn-Minkoski theory for convex bodies, which is briefly outlined in an Appendix written in a modern mathematical language. This formula is applied to cones and spherocones, which are regularized cones; a shape-reconstruction algorithm is able to generate the region in space inaccessible to them and to compute their excluded volume, which is found to be in good agreement with our approximate analytical formula. Finally, for spherocones with an appropriately tuned amplitude, we predict the occurrence of a relative deep minimum of the excluded volume in a configuration lying between the parallel alignment (where the excluded volume is maximum) and the antiparallel alignment (where the excluded volume is minimum).
Charge-exchange QRPA with the Gogny Force for Axially-symmetric Deformed Nuclei
Martini, M.; Goriely, S.; Péru, S.
2014-06-15
In recent years fully consistent quasiparticle random-phase approximation (QRPA) calculations using finite range Gogny force have been performed to study electromagnetic excitations of several axially-symmetric deformed nuclei up to the {sup 238}U. Here we present the extension of this approach to the charge-exchange nuclear excitations (pnQRPA). In particular we focus on the Isobaric Analog and Gamow-Teller resonances. A comparison of the predicted GT strength distribution with existing experimental data is presented. The role of nuclear deformation is shown. Special attention is paid to β-decay half-lives calculations for which experimental data exist and for specific isotone chains of relevance for the r-process nucleosynthesis.
A Priori Bound on the Velocity in Axially Symmetric Navier-Stokes Equations
NASA Astrophysics Data System (ADS)
Lei, Zhen; Navas, Esteban A.; Zhang, Qi S.
2016-01-01
Let v be the velocity of Leray-Hopf solutions to the axially symmetric three-dimensional Navier-Stokes equations. Under suitable conditions for initial values, we prove the following a priori bound |v(x, t)| ≤ C |ln r|^{1/2}/r^2, qquad 0 < r ≤ 1/2, where r is the distance from x to the z axis, and C is a constant depending only on the initial value. This provides a pointwise upper bound (worst case scenario) for possible singularities, while the recent papers (Chiun-Chuan et al., Commun PDE 34(1-3):203-232, 2009; Koch et al., Acta Math 203(1):83-105, 2009) gave a lower bound. The gap is polynomial order 1 modulo a half log term.
Nonlinear resonance and envelope instability of intense beam in axial symmetric periodic channel
NASA Astrophysics Data System (ADS)
Li, Chao; Liu, Zhicong; Zhao, Yaliang; Qin, Qing
2016-03-01
When an intense charged particle beam propagates through a given periodic focusing channel, it will experience the phenomena of nonlinear resonance, collective instability or chaotic motion with different conditions. In this paper, the collective envelope instability mechanisms are studied for symmetric beam propagation in an axially symmetric periodic channel. The beam is characterized as collectively stable if there exists a stable fixed point (SFP) located at the matched beam condition (rm , 0) in (r ,pr) phase space. It is found that the well-known collective envelope instability is dynamically related to the period-two orbits bifurcation of the matched SFP, meanwhile the unique stable SFP turns into an unstable saddle-node, surrounded by 1/2 resonance islands. However, higher orders of resonance (l / n, n > 2) coming from period-n bifurcation will not lead to collective beam instability because a new SFP emerges immediately upon the bifurcation process. The orders of SFP bifurcation is numerically depicted by the envelope tune ν=ϕ/360, where ϕ is the eigenphase of the Poincar e ´ tangent map T(s) in one focusing period at SFP, as functions of depressed phase advance. With strong space charge, due to these resonances from SFP bifurcation could be overlapped, mismatched beam would even show chaotic motion. For specific parameters, regular orbits, resonance islands, chaotic regions formed by resonance overlapping are clearly depicted with frequency analysis and Lyapunov spectral exponents, a method that may prove useful when extended to higher phase-space dimensions.
NASA Astrophysics Data System (ADS)
Lin, C.-C.; Huang, T.-C.; Chu, C.-C.; Hsiao, Vincent K. S.
2016-07-01
We demonstrate an optically switchable half-wave plate (HWP) composed of a photoaligned and axially symmetric liquid crystal (ASLC) film containing two azobenzene derivatives, methyl red (MR) and 4-butyl-4‧-methoxyazobenzene (BMAB). MR is responsible for photoalignment, and BMAB is used for optical tuning and switching the state of polarization (SOP) of probe beam (633 nm He-Ne laser) passing through the MR/BMAB doped ASLC film. The photoaligned ASLC film is first fabricated using a line-shaped laser beam (532 nm) exposure applied on a rotating LC sample. The fabricated ASLC film can passively change the linearly polarized light. Under UV light exposure, the formation of cis-BMAB (bend-like shape) within the film disrupts the LC molecules, switches the LC orientation, and further changes the SOP of the probe beam. Under laser irradiation (532 nm), the formation of trans-BMAB (rod-like shape) reverts the LC orientation back and simultaneously generates cis-MR, helping anchor the LC in the previously photoaligned orientation. The photoaligned MR/BMAB-doped LC HWP can change the linear SOP under alternating UV and visible light exposure.
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.
1997-01-01
A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates that are subjected to linearly varying edge loads, uniform shear loads, or combinations of these loads is presented. The study focuses on the effects of the shape of linearly varying edge load distribution, plate orthotropy, and plate flexural anisotropy on plate buckling behavior. In addition, the study exmines the interaction of linearly varying edge loads and uniform shear loads with plate flexural anisotropy and orthotropy. Results obtained by using a special purpose nondimensional analysis that is well suited for parametric studies of clamped and simply supported plates are presented for [+/- theta](sub s), thin graphite-epoxy laminates that are representative of spacecraft structural components. Also, numerous generic buckling-design charts are presented for a wide range of nondimensional parameters that are applicable to a broad class of laminate constructions. These charts show explicitly the effects of flexural orthotropy and flexural anisotropy on plate buckling behavior for linearly varying edge loads, uniform shear loads, or combinations of these loads. The most important finding of the present study is that specially orthotropic and flexurally anisotropic plates that are subjected to an axial edge load distribution that is tension dominated can support shear loads that are larger in magnitude than the shear buckling load.
NASA Astrophysics Data System (ADS)
Roque, Kristine Faith J.; Tapang, Giovanni A.; Saloma, Caesar A.
2015-07-01
We present the parametric investigation of the axial trapping forces generated by the interaction of an ellipsoidal dielectric and a focused, randomly polarized Gaussian beam in the geometrical optics regime. We show that particle elongation along the optical axis results to a more unstable axial trap compared to that of a reference sphere due to the more positive axial forces for positive axial displacements. Decreasing the refractive index difference between the particle and the surrounding medium (Δn = 0.09) decreases the magnitude of the axial force for positive particle displacements; and for a narrow range of axial displacements an axial trap can be achieved. Increasing the beam wavelength increases the magnitude of the axial force and for 1060 nm an axial trap can be achieved.
Modelling non-symmetric collagen fibre dispersion in arterial walls
Holzapfel, Gerhard A.; Niestrawska, Justyna A.; Ogden, Ray W.; Reinisch, Andreas J.; Schriefl, Andreas J.
2015-01-01
New experimental results on collagen fibre dispersion in human arterial layers have shown that the dispersion in the tangential plane is more significant than that out of plane. A rotationally symmetric dispersion model is not able to capture this distinction. For this reason, we introduce a new non-symmetric dispersion model, based on the bivariate von Mises distribution, which is used to construct a new structure tensor. The latter is incorporated in a strain-energy function that accommodates both the mechanical and structural features of the material, extending our rotationally symmetric dispersion model (Gasser et al. 2006 J. R. Soc. Interface 3, 15–35. (doi:10.1098/rsif.2005.0073)). We provide specific ranges for the dispersion parameters and show how previous models can be deduced as special cases. We also provide explicit expressions for the stress and elasticity tensors in the Lagrangian description that are needed for a finite-element implementation. Material and structural parameters were obtained by fitting predictions of the model to experimental data obtained from human abdominal aortic adventitia. In a finite-element example, we analyse the influence of the fibre dispersion on the homogeneous biaxial mechanical response of aortic strips, and in a final example the non-homogeneous stress distribution is obtained for circumferential and axial strips under fixed extension. It has recently become apparent that this more general model is needed for describing the mechanical behaviour of a variety of fibrous tissues. PMID:25878125
Axial Symmetric Solutions to Einstein's Field Equations for Deformed Neutron Stars
NASA Astrophysics Data System (ADS)
Zubairi, Omair; Weber, Fridolin
2016-03-01
Traditional models of neutron stars are constructed under of assumption that they are perfect spheres. This is not correct, however, if the matter inside of neutron stars is described by an non-isotropic model for the equation of state. Examples of such stars are magnetars and neutron stars that would contain color-superconducting quark matter. In this work, we derive the stellar structure equations which describe the properties of non-isotropic neutron stars. The equations are solved numerically in two dimensions. We calculate stellar properties such as masses and radii along with pressure and density profiles and investigate any changes from conventional spherically symmetric neutron stars. This work was supported through the National Science Foundation under Grants PHYS-1411708 and DUE-1259951. Additional computing resources were provided by the CSRC at SDSU and the Department of Sciences at Wentworth Institute of Technology.
Flow Separation Ahead of a Blunt Axially Symmetric Body at Mach Numbers 1.76 to 2.10
NASA Technical Reports Server (NTRS)
Moeckel, W E
1951-01-01
The pressure distribution and drag were determined for a spherical-nosed axially symmetric body with thin projecting rods at Mach numbers of 1.76, 1.93, and 2.10. The upstream projection distance of the rods was varied over a wide range to study changes in the character of the flow separation and to determine the variation of drag and pressure distribution with tip projection. Drag coefficients between 0.18 and 0.30 were obtained for most tip projections at each Mach number.
NASA Technical Reports Server (NTRS)
Warsi, Z. U. A.; Weed, R. A.; Thompson, J. F.
1980-01-01
A formulation of the complete Navier-Stokes problem for a viscous hypersonic flow in general curvilinear coordinates is presented. This formulation is applicable to both the axially symmetric and three dimensional flows past bodies of revolution. The equations for the case of zero angle of attack were solved past a circular cylinder with hemispherical caps by point SOR finite difference approximation. The free stream Mach number and the Reynolds number for the test case are respectively 22.04 and 168883. The whole algorithm is presented in detail along with the preliminary results for pressure, temperature, density and velocity distributions along the stagnation line.
Modelling larval transport in a axial convergence front
NASA Astrophysics Data System (ADS)
Robins, P.
2010-12-01
Marine larvae exhibit different vertical swimming behaviours, synchronised by factors such as tidal currents and daylight, in order to aid retention near the parent populations and hence promote production, avoid predation, or to stimulate digestion. This paper explores two types of larval migration in an estuarine axial convergent front which is an important circulatory mechanism in many coastal regions where larvae are concentrated. A parallelised, three-dimensional, ocean model was applied to an idealised estuarine channel which was parameterised from observations of an axial convergent front which occurs in the Conwy Estuary, U.K. (Nunes and Simpson, 1985). The model successfully simulates the bilateral cross-sectional recirculation of an axial convergent front, which has been attributed to lateral density gradients established by the interaction of the lateral shear of the longitudinal currents with the axial salinity gradients. On the flood tide, there is surface axial convergence whereas on the ebb tide, there is (weaker) surface divergence. Further simulations with increased/decreased tidal velocities and with stronger/weaker axial salinity gradients are planned so that the effects of a changing climate on the secondary flow can be understood. Three-dimensional Lagrangian Particle Tracking Models (PTMs) have been developed which use the simulated velocity fields to track larvae in the estuarine channel. The PTMs take into account the vertical migrations of two shellfish species that are commonly found in the Conwy Estuary: (i) tidal migration of the common shore crab (Carcinus maenas) and (ii), diel (daily) migration of the Great scallop (Pecten maximus). These migration behaviours are perhaps the most widespread amongst shellfish larvae and have been compared with passive (drifting) particles in order to assess their relative importance in terms of larval transport. Preliminary results suggest that the net along-estuary dispersal over a typical larval
NASA Astrophysics Data System (ADS)
Nam-Il, Kim; Moon-Young, Kim
2005-06-01
An improved numerical method to exactly evaluate the dynamic element stiffness matrix is proposed for the spatially coupled free vibration analysis of non-symmetric thin-walled curved beams subjected to uniform axial force. For this purpose, firstly equations of motion, boundary conditions and force-deformation relations are rigorously derived from the total potential energy for a curved beam element. Next systems of linear algebraic equations with non-symmetric matrices are constructed by introducing 14 displacement parameters and transforming the fourth-order simultaneous differential equations into the first-order simultaneous equations. And then explicit expressions for displacement parameters are numerically evaluated via eigensolutions and the exact 14×14 element stiffness matrix is determined using force-deformation relations. In order to demonstrate the validity and the accuracy of this study, the spatially coupled natural frequencies of non-symmetric thin-walled curved beams subjected to uniform compressive and tensile forces are evaluated and compared with analytical and finite element solutions using Hermitian curved beam elements or ABAQUS's shell element. In addition, some results by the parametric study are reported.
Scaling model for symmetric star polymers
NASA Astrophysics Data System (ADS)
Ramachandran, Ram; Rai, Durgesh K.; Beaucage, Gregory
2010-03-01
Neutron scattering data from symmetric star polymers with six poly (urethane-ether) arms, chemically bonded to a C-60 molecule are fitted using a new scaling model and scattering function. The new scaling function can describe both good solvent and theta solvent conditions as well as resolve deviations in chain conformation due to steric interactions between star arms. The scaling model quantifies the distinction between invariant topological features for this star polymer and chain tortuosity which changes with goodness of solvent and steric interaction. Beaucage G, Phys. Rev. E 70 031401 (2004).; Ramachandran R, et al. Macromolecules 41 9802-9806 (2008).; Ramachandran R, et al. Macromolecules, 42 4746-4750 (2009); Rai DK et al. Europhys. Lett., (Submitted 10/2009).
NASA Astrophysics Data System (ADS)
Romano, Marcello
2008-08-01
New exact analytic solutions are introduced for the rotational motion of a rigid body having two equal principal moments of inertia and subjected to an external torque which is constant in magnitude. In particular, the solutions are obtained for the following cases: (1) Torque parallel to the symmetry axis and arbitrary initial angular velocity; (2) Torque perpendicular to the symmetry axis and such that the torque is rotating at a constant rate about the symmetry axis, and arbitrary initial angular velocity; (3) Torque and initial angular velocity perpendicular to the symmetry axis, with the torque being fixed with the body. In addition to the solutions for these three forced cases, an original solution is introduced for the case of torque-free motion, which is simpler than the classical solution as regards its derivation and uses the rotation matrix in order to describe the body orientation. This paper builds upon the recently discovered exact solution for the motion of a rigid body with a spherical ellipsoid of inertia. In particular, by following Hestenes’ theory, the rotational motion of an axially symmetric rigid body is seen at any instant in time as the combination of the motion of a “virtual” spherical body with respect to the inertial frame and the motion of the axially symmetric body with respect to this “virtual” body. The kinematic solutions are presented in terms of the rotation matrix. The newly found exact analytic solutions are valid for any motion time length and rotation amplitude. The present paper adds further elements to the small set of special cases for which an exact solution of the rotational motion of a rigid body exists.
Global Aspects of Charged Particle Motion in Axially Symmetric Multipole Magnetic Fields
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2003-01-01
The motion of a single charged particle in the space outside of a compact region of steady currents is investigated. The charged particle is assumed to produce negligible electromagnetic radiation, so that its energy is conserved. The source of the magnetic field is represented as a point multipole. After a general description, attention is focused on magnetic fields with axial symmetry. Lagrangian dynamical theory is utilized to identify constants of the motion as well as the equations of motion themselves. The qualitative method of Stonner is used to examine charged particle motion in axisymmetric multipole fields of all orders. Although the equations of motion generally have no analytical solutions and must be integrated numerically to produce a specific orbit, a topological examination of dynamics is possible, and can be used, d la Stonner, to completely describe the global aspects of the motion of a single charged particle in a space with an axisymmetric multipole magnetic field.
NASA Technical Reports Server (NTRS)
Hood, L. L.
1987-01-01
Saturn's main rings exist within a zone of negligible magnetospheric losses and surface alteration effects, substantially due to the solid-body absorption of inwardly diffusing magnetospheric particles. This process is presently shown to be especially efficient in the inner magnetosphere of Saturn, due to the near-axial symmetry of the planetary magnetic field relative to the equatorial rotation plane; under the assumption of comparable diffusion rates, the inward magnetospheric particle transport is far more inhibited in the inner Saturnian magnetosphere than in the same regions of Jupiter and Uranus, even when only rings of comparable widths and depths are considered. In light of this, ring particle surface exposure to the ion fluxes of the radiation belt remains a prepossessing rationale for low Uranian ring albedos.
Hood, L.L.
1987-07-01
Saturn's main rings exist within a zone of negligible magnetospheric losses and surface alteration effects, substantially due to the solid-body absorption of inwardly diffusing magnetospheric particles. This process is presently shown to be especially efficient in the inner magnetosphere of Saturn, due to the near-axial symmetry of the planetary magnetic field relative to the equatorial rotation plane; under the assumption of comparable diffusion rates, the inward magnetospheric particle transport is far more inhibited in the inner Saturnian magnetosphere than in the same regions of Jupiter and Uranus, even when only rings of comparable widths and depths are considered. In light of this, ring particle surface exposure to the ion fluxes of the radiation belt remains a prepossessing rationale for low Uranian ring albedos. 86 references.
Andersson, P. Andersson-Sunden, E.; Sjöstrand, H.; Jacobsson-Svärd, S.
2014-08-01
In nuclear boiling water reactor cores, the distribution of water and steam (void) is essential for both safety and efficiency reasons. In order to enhance predictive capabilities, void distribution assessment is performed in two-phase test-loops under reactor-relevant conditions. This article proposes the novel technique of fast-neutron tomography using a portable deuterium-tritium neutron generator to determine the time-averaged void distribution in these loops. Fast neutrons have the advantage of high transmission through the metallic structures and pipes typically concealing a thermal-hydraulic test loop, while still being fairly sensitive to the water/void content. However, commercially available fast-neutron generators also have the disadvantage of a relatively low yield and fast-neutron detection also suffers from relatively low detection efficiency. Fortunately, some loops are axially symmetric, a property which can be exploited to reduce the amount of data needed for tomographic measurement, thus limiting the interrogation time needed. In this article, three axially symmetric test objects depicting a thermal-hydraulic test loop have been examined; steel pipes with outer diameter 24 mm, thickness 1.5 mm, and with three different distributions of the plastic material POM inside the pipes. Data recorded with the FANTOM fast-neutron tomography instrument have been used to perform tomographic reconstructions to assess their radial material distribution. Here, a dedicated tomographic algorithm that exploits the symmetry of these objects has been applied, which is described in the paper. Results are demonstrated in 20 rixel (radial pixel) reconstructions of the interior constitution and 2D visualization of the pipe interior is demonstrated. The local POM attenuation coefficients in the rixels were measured with errors (RMS) of 0.025, 0.020, and 0.022 cm{sup −1}, solid POM attenuation coefficient. The accuracy and precision is high enough to provide a useful
NASA Astrophysics Data System (ADS)
Andersson, P.; Andersson-Sunden, E.; Sjöstrand, H.; Jacobsson-Svärd, S.
2014-08-01
In nuclear boiling water reactor cores, the distribution of water and steam (void) is essential for both safety and efficiency reasons. In order to enhance predictive capabilities, void distribution assessment is performed in two-phase test-loops under reactor-relevant conditions. This article proposes the novel technique of fast-neutron tomography using a portable deuterium-tritium neutron generator to determine the time-averaged void distribution in these loops. Fast neutrons have the advantage of high transmission through the metallic structures and pipes typically concealing a thermal-hydraulic test loop, while still being fairly sensitive to the water/void content. However, commercially available fast-neutron generators also have the disadvantage of a relatively low yield and fast-neutron detection also suffers from relatively low detection efficiency. Fortunately, some loops are axially symmetric, a property which can be exploited to reduce the amount of data needed for tomographic measurement, thus limiting the interrogation time needed. In this article, three axially symmetric test objects depicting a thermal-hydraulic test loop have been examined; steel pipes with outer diameter 24 mm, thickness 1.5 mm, and with three different distributions of the plastic material POM inside the pipes. Data recorded with the FANTOM fast-neutron tomography instrument have been used to perform tomographic reconstructions to assess their radial material distribution. Here, a dedicated tomographic algorithm that exploits the symmetry of these objects has been applied, which is described in the paper. Results are demonstrated in 20 rixel (radial pixel) reconstructions of the interior constitution and 2D visualization of the pipe interior is demonstrated. The local POM attenuation coefficients in the rixels were measured with errors (RMS) of 0.025, 0.020, and 0.022 cm-1, solid POM attenuation coefficient. The accuracy and precision is high enough to provide a useful indication
Andersson, P; Andersson-Sunden, E; Sjöstrand, H; Jacobsson-Svärd, S
2014-08-01
In nuclear boiling water reactor cores, the distribution of water and steam (void) is essential for both safety and efficiency reasons. In order to enhance predictive capabilities, void distribution assessment is performed in two-phase test-loops under reactor-relevant conditions. This article proposes the novel technique of fast-neutron tomography using a portable deuterium-tritium neutron generator to determine the time-averaged void distribution in these loops. Fast neutrons have the advantage of high transmission through the metallic structures and pipes typically concealing a thermal-hydraulic test loop, while still being fairly sensitive to the water/void content. However, commercially available fast-neutron generators also have the disadvantage of a relatively low yield and fast-neutron detection also suffers from relatively low detection efficiency. Fortunately, some loops are axially symmetric, a property which can be exploited to reduce the amount of data needed for tomographic measurement, thus limiting the interrogation time needed. In this article, three axially symmetric test objects depicting a thermal-hydraulic test loop have been examined; steel pipes with outer diameter 24 mm, thickness 1.5 mm, and with three different distributions of the plastic material POM inside the pipes. Data recorded with the FANTOM fast-neutron tomography instrument have been used to perform tomographic reconstructions to assess their radial material distribution. Here, a dedicated tomographic algorithm that exploits the symmetry of these objects has been applied, which is described in the paper. Results are demonstrated in 20 rixel (radial pixel) reconstructions of the interior constitution and 2D visualization of the pipe interior is demonstrated. The local POM attenuation coefficients in the rixels were measured with errors (RMS) of 0.025, 0.020, and 0.022 cm(-1), solid POM attenuation coefficient. The accuracy and precision is high enough to provide a useful
Staudhammer, Karl P.
2004-01-01
The Mach stem region in an axial symmetric shock implosion has generally been avoided in the dynamic consolidation of powders for a number of reasons. The prime reason being that the convergence of the shock waves in the cylindrical axis produce enormous pressures and concomitant temperatures that have melted tungsten. This shock wave convergence consequently results in a discontinuity in the hydro-code calculations. Dynamic deformation experiments on gold plated 304L stainless steel powders were undertaken. These experiments utilized pressures of 0.08 to 1.0 Mbar and contained a symmetric radial melt region along the central axis of the sample holder. To understand the role of deformation in a porous material, the pressure, and temperature as well as the deformation heat and associated defects must be accounted for. When the added heat of consolidation deformation exceeds the melt temperature of the 304 powders, a melt zone results that can consume large regions of the compact while still under the high-pressure pulse. As the shock wave traverses the sample and is removed in a momentum trap, its pressure/temperature are quenched. It is within this region that very high diffusion/alloying occurs and has been observed in the gold plated powders. Anomalous increases of gold diffusion into 304 stainless steel have been observed via optical microscopy, scanning electron microscopy and EDAX measurements. Values exceeding 1200 m/sec have been measured and correlated to the powder sizes, size distribution and packing density, concomitant with sample container strains ranging from 2.0% to 26%.
Höhne, Christian; Prager, Jens; Gravenkamp, Hauke
2015-12-01
In this paper, a method to determine the complex dispersion relations of axially symmetric guided waves in cylindrical structures is presented as an alternative to the currently established numerical procedures. The method is based on a spectral decomposition into eigenfunctions of the Laplace operator on the cross-section of the waveguide. This translates the calculation of real or complex wave numbers at a given frequency into solving an eigenvalue problem. Cylindrical rods and plates are treated as the asymptotic cases of cylindrical structures and used to generalize the method to the case of hollow cylinders. The presented method is superior to direct root-finding algorithms in the sense that no initial guess values are needed to determine the complex wave numbers and that neither starting at low frequencies nor subsequent mode tracking is required. The results obtained with this method are shown to be reasonably close to those calculated by other means and an estimate for the achievable accuracy is given. PMID:26126952
A non-thermal axially symmetric radio wake towards the Galactic centre
NASA Technical Reports Server (NTRS)
Yusef-Zadeh, Farhad; Bally, John
1987-01-01
A highly unusual radio source lying within 1 deg of the Galactic center has been discovered whose 'cometary' morphology suggests that it is a wake produced by a radio source moving supersonically with respect to the ambient interstellar medium. Maps of the source are shown, and its characteristics are discussed. Two possible models which might explain the wake are suggested.
NASA Astrophysics Data System (ADS)
Rusanov, Andrey; Rusanov, Roman; Lampart, Piotr
2015-10-01
The paper describes an algorithm for the design of axial and radial-axial type turbines. The algorithm is based on using mathematical models of various levels of complexity - from 1D to 3D. Flow path geometry is described by means of analytical methods of profiling using a limited number of parameters. 3D turbulent flow model is realised in the program complex IPMFlow, developed based on the earlier codes FlowER and FlowER-U. Examples of developed or modernized turbines for differentpurpose power machines are presented. They are: an expansion turbine, ORC turbine and cogeneration mediumpressure turbine.
Numerical relativity for D dimensional axially symmetric space-times: Formalism and code tests
NASA Astrophysics Data System (ADS)
Zilhão, Miguel; Witek, Helvi; Sperhake, Ulrich; Cardoso, Vitor; Gualtieri, Leonardo; Herdeiro, Carlos; Nerozzi, Andrea
2010-04-01
The numerical evolution of Einstein’s field equations in a generic background has the potential to answer a variety of important questions in physics: from applications to the gauge-gravity duality, to modeling black hole production in TeV gravity scenarios, to analysis of the stability of exact solutions, and to tests of cosmic censorship. In order to investigate these questions, we extend numerical relativity to more general space-times than those investigated hitherto, by developing a framework to study the numerical evolution of D dimensional vacuum space-times with an SO(D-2) isometry group for D≥5, or SO(D-3) for D≥6. Performing a dimensional reduction on a (D-4) sphere, the D dimensional vacuum Einstein equations are rewritten as a 3+1 dimensional system with source terms, and presented in the Baumgarte, Shapiro, Shibata, and Nakamura formulation. This allows the use of existing 3+1 dimensional numerical codes with small adaptations. Brill-Lindquist initial data are constructed in D dimensions and a procedure to match them to our 3+1 dimensional evolution equations is given. We have implemented our framework by adapting the Lean code and perform a variety of simulations of nonspinning black hole space-times. Specifically, we present a modified moving puncture gauge, which facilitates long-term stable simulations in D=5. We further demonstrate the internal consistency of the code by studying convergence and comparing numerical versus analytic results in the case of geodesic slicing for D=5, 6.
NASA Astrophysics Data System (ADS)
Albin, Michael; de, William; Horrocks, W., Jr.; Liotta, Frank J.
1982-01-01
The Eu(III) complex of the octadentate macrocyclic ligand, 1,4,7,10-tetraazacyclododecane-N,N',N'',N''' -tetraacetate, DOTA, has been examined by luminescence excitation, emission, and lifetime spectroscopy using pulsed dye laser techniques. The results confirm the expected axially symmetric nature of the major component in solution and reveal that 1.2 ± 0.4 water molecules arc coordinatcd to the Eu(III) ion in the complex.
The modelling of symmetric airfoil vortex generators
NASA Technical Reports Server (NTRS)
Reichert, B. A.; Wendt, B. J.
1996-01-01
An experimental study is conducted to determine the dependence of vortex generator geometry and impinging flow conditions on shed vortex circulation and crossplane peak vorticity for one type of vortex generator. The vortex generator is a symmetric airfoil having a NACA 0012 cross-sectional profile. The geometry and flow parameters varied include angle-of-attack alfa, chordlength c, span h, and Mach number M. The vortex generators are mounted either in isolation or in a symmetric counter-rotating array configuration on the inside surface of a straight pipe. The turbulent boundary layer thickness to pipe radius ratio is delta/R = 0. 17. Circulation and peak vorticity data are derived from crossplane velocity measurements conducted at or about 1 chord downstream of the vortex generator trailing edge. Shed vortex circulation is observed to be proportional to M, alfa, and h/delta. With these parameters held constant, circulation is observed to fall off in monotonic fashion with increasing airfoil aspect ratio AR. Shed vortex peak vorticity is also observed to be proportional to M, alfa, and h/delta. Unlike circulation, however, peak vorticity is observed to increase with increasing aspect ratio, reaching a peak value at AR approx. 2.0 before falling off.
NASA Technical Reports Server (NTRS)
Bilharz, Herbert; Hoelder, Ernst
1947-01-01
The present report concerns a method of computing the velocity and pressure distributions on bodies of revolution in axially symmetrical flow in the subsonic range. The differential equation for the velocity potential Phi of a compressible fluid motion is linearized tn the conventional manner, and then put in the form Delta(Phi) = 0 by affine transformation. The quantity Phi represents the velocity potential of a fictitious incompressible flow, for which a constant superposition of sources by sections is secured by a method patterned after von Karman which must comply with the boundary condition delta(phi)/delta(n) = 0 at the originally specified contour. This requirement yields for the "pseudo-stream function" psi a differential equation which must be fulfilled for as many points on the contour as source lengths are assumed. In this manner, the problem of defining the still unknown source intensities is reduced to the solution of an inhomogeneous equation system. The pressure distribution is then determined with the aid of Bernoulli's equation and adiabatic equation of state. Lastly, the pressure distributions in compressible and incompressible medium are compared on a model problem.
A Model for Axial Magnetic Bearings Including Eddy Currents
NASA Technical Reports Server (NTRS)
Kucera, Ladislav; Ahrens, Markus
1996-01-01
This paper presents an analytical method of modelling eddy currents inside axial bearings. The problem is solved by dividing an axial bearing into elementary geometric forms, solving the Maxwell equations for these simplified geometries, defining boundary conditions and combining the geometries. The final result is an analytical solution for the flux, from which the impedance and the force of an axial bearing can be derived. Several impedance measurements have shown that the analytical solution can fit the measured data with a precision of approximately 5%.
A nonspherically symmetric model for the peculiar A star Alpha-2
NASA Technical Reports Server (NTRS)
Bohm-Vitense, Erika; Van Dyk, Schuyler D.
1987-01-01
Observations show that in the optical region the peculiar A star Alpha-2 CVn has a flatter energy distribution during maximum light than during minimum light. This indicates that during maximum light a lower-temperature region, but necessarily larger surface area, than during minimum light is seen. This suggests a nonspherically symmetric star, which is oblate with respect to the magnetic axis and which is cooler at the magnetic poles than at the magnetic equator. The light variations of such nonspherically symmetric oblique rotator models have been studied. It is found that, for an oblate ellipsoid with an axial ratio of 0.92 and a temperature difference of about 1000 K between the poles and the equator, the overall variations of the optical and the ultraviolet energy distributions can be well understood.
Wakayama, Toshitaka Yonemura, Motoki; Oikawa, Hiroki; Sasanuma, Atsushi; Arai, Goki; Fujii, Yusuke; Dinh, Thanh-Hung; Otani, Yukitoshi; Higashiguchi, Takeshi; Sakaue, Kazuyuki; Washio, Masakazu; Miura, Taisuke; Takahashi, Akihiko; Nakamura, Daisuke; Okada, Tatsuo
2015-08-24
We demonstrated the generation of the intense radially polarized mid-infrared optical vortex at a wavelength of 10.6 μm by use of a passive axially symmetric zinc selenide (ZnSe) waveplate with high energy pulse throughput. The phase of the radially polarized optical vortex with the degree of polarization of 0.95 was spirally distributed in regard to the angle. The converted laser beam energy of about 2.6 mJ per pulse was obtained at the input pulse energy of 4.9 mJ, corresponding to the energy conversion efficiency of 56%.
NASA Technical Reports Server (NTRS)
Anderson, E. C.; Moss, J. N.
1975-01-01
The viscous shock layer equations applicable to hypersonic laminar, transitional, and turbulent flows of a perfect gas over two-dimensional plane or axially symmetric blunt bodies are presented. The equations are solved by means of an implicit finite difference scheme, and the results are compared with a turbulent boundary layer analysis. The agreement between the two solution procedures is satisfactory for the region of flow where streamline swallowing effects are negligible. For the downstream regions, where streamline swallowing effects are present, the expected differences in the two solution procedures are evident.
NASA Astrophysics Data System (ADS)
Pimshtein, V. G.
2016-07-01
The shadow visualization method is applied to study the process of loss of stability of the mixing layer of a subsonic axially symmetric turbulent jet under longitudinal internal action of saw-tooth sound waves of finite amplitude. Such action leads to the formation of a system of ring vortices in the mixing layer at the frequency of its intrinsic instability. The interaction of the vortices can be accompanied by sound emission. A similar phenomenon is also observed in turbulent jets for small supercritical pressure fluctuations on a nozzle.
Exactly solvable PT -symmetric models in two dimensions
NASA Astrophysics Data System (ADS)
Agarwal, Kaustubh S.; Pathak, Rajeev K.; Joglekar, Yogesh N.
2015-11-01
Non-Hermitian, PT -symmetric Hamiltonians, experimentally realized in optical systems, accurately model the properties of open, bosonic systems with balanced, spatially separated gain and loss. We present a family of exactly solvable, two-dimensional, PT potentials for a non-relativistic particle confined in a circular geometry. We show that the PT -symmetry threshold can be tuned by introducing a second gain-loss potential or its Hermitian counterpart. Our results explicitly demonstrate that PT breaking in two dimensions has a rich phase diagram, with multiple re-entrant PT -symmetric phases.
Radiative seesaw in left-right symmetric model
Gu Peihong; Sarkar, Utpal
2008-10-01
There are some radiative origins for the neutrino masses in the conventional left-right symmetric models with the usual bidoublet and triplet Higgs scalars. These radiative contributions could dominate over the tree-level seesaw and could explain the observed neutrino masses.
Alton, Gerald D.
1996-01-01
An electron cyclotron resonance (ECR) ion source includes a primary mirror coil disposed coaxially around a vacuum vessel in which a plasma is induced and introducing a solenoidal ECR-producing field throughout the length of the vacuum vessel. Radial plasma confinement is provided by a multi-cusp, multi-polar permanent magnet array disposed azimuthally around the vessel and within the primary mirror coil. Axial confinement is provided either by multi-cusp permanent magnets at the opposite axial ends of the vessel, or by secondary mirror coils disposed on opposite sides of the primary coil.
NASA Technical Reports Server (NTRS)
McAlister, K. W.; Huang, S. S.; Abrego, A. I.
2001-01-01
A model rotor was mounted horizontally in the settling chamber of a wind tunnel to obtain performance and wake structure data under low climb conditions. The immediate wake of the rotor was carefully surveyed using 3-component particle image velocimetry to define the velocity and vortical content of the flow, and used in a subsequent study to validate a theory for the separate determination of induced and profile drag. Measurements were obtained for two collective pitch angles intended to render a predominately induced drag state and another with a marked increase in profile drag. A majority of the azimuthally directed vorticity in the wake was found to be concentrated in the tip vortices. However, adjacent layers of inboard vorticity with opposite sense were clearly present. At low collective, the close proximity of the tip vortex from the previous blade caused the wake from the most recent blade passage to be distorted. The deficit velocity component that was directed along the azimuth of the rotor blade was never more that 15 percent of the rotor tip speed, and except for the region of the tip vortex, appeared to have totally disappeared form the wake left by the previous blade.
Target space pseudoduality in supersymmetric sigma models on symmetric spaces
NASA Astrophysics Data System (ADS)
Sarisaman, Mustafa
We discuss the target space pseudoduality in supersymmetric sigma models on symmetric spaces. We first consider the case where sigma models based on real compact connected Lie groups of the same dimensionality and give examples using three dimensional models on target spaces. We show explicit construction of nonlocal conserved currents on the pseudodual manifold. We then switch the Lie group valued pseudoduality equations to Lie algebra valued ones, which leads to an infinite number of pseudoduality equations. We obtain an infinite number of conserved currents on the tangent bundle of the pseudo-dual manifold. Since pseudoduality imposes the condition that sigma models pseudodual to each other are based on symmetric spaces with opposite curvatures (i.e. dual symmetric spaces), we investigate pseudoduality transformation on the symmetric space sigma models in the third chapter. We see that there can be mixing of decomposed spaces with each other, which leads to mixings of the following expressions. We obtain the pseudodual conserved currents which are viewed as the orthonormal frame on the pullback bundle of the tangent space of G˜ which is the Lie group on which the pseudodual model based. Hence we obtain the mixing forms of curvature relations and one loop renormalization group beta function by means of these currents. In chapter four, we generalize the classical construction of pseudoduality transformation to supersymmetric case. We perform this both by component expansion method on manifold M and by orthonormal coframe method on manifold SO( M). The component method produces the result that pseudoduality transformation is not invertible at all points and occurs from all points on one manifold to only one point where riemann normal coordinates valid on the second manifold. Torsion of the sigma model on M must vanish while it is nonvanishing on M˜, and curvatures of the manifolds must be constant and the same because of anticommuting grassmann numbers. We obtain
Petrova, T; Benova, E; Petrov, G; Zhelyazkov, I
1999-07-01
A model for description of the axial structure of a surface-wave-produced and -sustained plasma based on numerical calculation of a complete set of electrodynamic and kinetic equations is presented. The model includes a self-consistent solution to the electron Boltzmann equation, a set of particle balance equations for electrons, excited atoms, atomic and molecular ions, as well as Maxwell's equations with appropriate boundary conditions. A gas thermal balance equation is used to predict the neutral gas temperature self-consistently. Precise calculations of discharge characteristics of an argon plasma column sustained by an azimuthally symmetric surface wave at low and intermediate gas pressures have been performed. A comparison with available experimental data is done in order to test the validity of the model. PMID:11969832
The symmetric orbifold of {N}=2 minimal models
NASA Astrophysics Data System (ADS)
Gaberdiel, Matthias R.; Kelm, Maximilian
2016-07-01
cThe large level limit of the {N}=2 minimal models that appear in the duality with the {N}=2 supersymmetric higher spin theory on AdS3 is shown to be a natural subsector of a certain symmetric orbifold theory. We study the relevant decompositions in both the untwisted and the twisted sector, and analyse the structure of the higher spin representations in the twisted sector in some detail. These results should help to identify the string background of which the higher spin theory is expected to describe the leading Regge trajectory in the tensionless limit.
A Symmetrized Basis for Transitions in the Heisenberg Model
NASA Astrophysics Data System (ADS)
Haydock, Roger; Nex, C. M. M.
2013-03-01
The spin-S Heisenberg model has 2S+1 states on each site, for which there are (2S+1)2 possible transitions between these states. For N sites there are (2S+1)N states and (2S+1)2N transitions between states. This rapid increase in the number of transitions with sites appears to limit calculations to just a few sites. However for transitions induced by spin-spin interactions, we construct a symmetrized basis which only grows as 2N-3, making possible computations for much larger systems. Supported by the Richmond F. Snyder Fund.
Spectra of sigma models on semi-symmetric spaces
NASA Astrophysics Data System (ADS)
Cagnazzo, Alessandra; Schomerus, Volker; Tlapak, Vaclav
2016-05-01
Sigma models on semi-symmetric spaces provide the central building block for string theories on AdS backgrounds. Under certain conditions on the global supersymmetry group they can be made one-loop conformal by adding an appropriate fermionic Wess-Zumino term. We determine the full one-loop dilation operator of the theory. It involves an interesting new XXZ-like interaction term. Eigenvalues of our dilation operator, i.e. the one-loop anomalous dimensions, are computed for a few examples.
Active Inference for Binary Symmetric Hidden Markov Models
NASA Astrophysics Data System (ADS)
Allahverdyan, Armen E.; Galstyan, Aram
2015-10-01
We consider active maximum a posteriori (MAP) inference problem for hidden Markov models (HMM), where, given an initial MAP estimate of the hidden sequence, we select to label certain states in the sequence to improve the estimation accuracy of the remaining states. We focus on the binary symmetric HMM, and employ its known mapping to 1d Ising model in random fields. From the statistical physics viewpoint, the active MAP inference problem reduces to analyzing the ground state of the 1d Ising model under modified external fields. We develop an analytical approach and obtain a closed form solution that relates the expected error reduction to model parameters under the specified active inference scheme. We then use this solution to determine most optimal active inference scheme in terms of error reduction, and examine the relation of those schemes to heuristic principles of uncertainty reduction and solution unicity.
Mixed dark matter in left-right symmetric models
NASA Astrophysics Data System (ADS)
Berlin, Asher; Fox, Patrick J.; Hooper, Dan; Mohlabeng, Gopolang
2016-06-01
Motivated by the recently reported diboson and dijet excesses in Run 1 data at ATLAS and CMS, we explore models of mixed dark matter in left-right symmetric theories. In this study, we calculate the relic abundance and the elastic scattering cross section with nuclei for a number of dark matter candidates that appear within the fermionic multiplets of left-right symmetric models. In contrast to the case of pure multiplets, WIMP-nucleon scattering proceeds at tree-level, and hence the projected reach of future direct detection experiments such as LUX-ZEPLIN and XENON1T will cover large regions of parameter space for TeV-scale thermal dark matter. Decays of the heavy charged W' boson to particles in the dark sector can potentially shift the right-handed gauge coupling to larger values when fixed to the rate of the Run 1 excesses, moving towards the theoretically attractive scenario, gR = gL. This region of parameter space may be probed by future collider searches for new Higgs bosons or electroweak fermions.
Mixed dark matter in left-right symmetric models
Berlin, Asher; Fox, Patrick J.; Hooper, Dan; Mohlabeng, Gopolang
2016-06-08
Motivated by the recently reported diboson and dijet excesses in Run 1 data at ATLAS and CMS, we explore models of mixed dark matter in left-right symmetric theories. In this study, we calculate the relic abundance and the elastic scattering cross section with nuclei for a number of dark matter candidates that appear within the fermionic multiplets of left-right symmetric models. In contrast to the case of pure multiplets, WIMP-nucleon scattering proceeds at tree-level, and hence the projected reach of future direct detection experiments such as LUX-ZEPLIN and XENON1T will cover large regions of parameter space for TeV-scale thermal darkmore » matter. Decays of the heavy charged W(') boson to particles in the dark sector can potentially shift the right-handed gauge coupling to larger values when fixed to the rate of the Run 1 excesses, moving towards the theoretically attractive scenario, gR = gL. Furthermore, this region of parameter space may be probed by future collider searches for new Higgs bosons or electroweak fermions.« less
Left-right symmetric model with SU(2)-triplet fermions
Gu Peihong
2011-11-01
We consider an SU(3){sub c} x SU(2){sub L} x SU(2){sub R} x U(1){sub B-L} left-right symmetric model with three Higgs scalars including an SU(2){sub L} doublet, an SU(2){sub R} doublet and an SU(2){sub L} x SU(2){sub R} bidoublet. In addition to usual SU(2)-doublet fermions, our model contains SU(2)-triplet fermions with Majorana masses. The neutral components of the left-handed triplets can contribute a canonical seesaw while the neutral components of the right-handed triplets associated with the right-handed neutrinos can contribute a double/inverse-type seesaw. Our model can be embedded into an SO(10) grand unification theory where the triplets belong to the 45=(1,3,1,0)+(1,1,3,0)+... representations.
Heterotic free fermionic and symmetric toroidal orbifold models
NASA Astrophysics Data System (ADS)
Athanasopoulos, P.; Faraggi, A. E.; Nibbelink, S. Groot; Mehta, V. M.
2016-04-01
Free fermionic models and symmetric heterotic toroidal orbifolds both constitute exact backgrounds that can be used effectively for phenomenological explorations within string theory. Even though it is widely believed that for Z_2× Z_2 orbifolds the two descriptions should be equivalent, a detailed dictionary between both formulations is still lacking. This paper aims to fill this gap: we give a detailed account of how the input data of both descriptions can be related to each other. In particular, we show that the generalized GSO phases of the free fermionic model correspond to generalized torsion phases used in orbifold model building. We illustrate our translation methods by providing free fermionic realizations for all Z_2× Z_2 orbifold geometries in six dimensions.
Modeling the aeroacoustics of axial fans from CFD calculations
NASA Astrophysics Data System (ADS)
Salesky, Alexandre; Hennemand, Vincent; Kouidri, Smaine; Berthelot, Yves
2002-11-01
The main source of aeroacoustic noise in axial fans is the distribution of the fluctuating, unsteady, aerodynamic forces on the blades. Numerical simulations were carried out with the CFD code (NUMECA), first with steady flow conditions to validate the aerolic performances (pressure drop as a function of flow rate) of the simulated six-bladed axial fans. Simulations were then made with unsteady flows to compute the fluctuating force distributions on the blades. The turbulence was modeled either with the Baldwin-Lomax model or with the K-epsilon model (extended wall function). The numerical results were satisfactory both in terms of numerical convergence and in terms of the physical characteristic of the forces acting on the blades. The numerical results were then coupled into an in-house aeroacoustics code that computes the farfield radiated noise spectrum and directivity, based on the Ffowcs-Williams Hawkings formulation, or alternatively, on the simpler Lowson model. Results compared favorably with data obtained under nonanechoic conditions, based upon ISO 5801 and ISO 5136 standards.
HTS axial flux induction motor with analytic and FEA modeling
NASA Astrophysics Data System (ADS)
Li, S.; Fan, Y.; Fang, J.; Qin, W.; Lv, G.; Li, J. H.
2013-11-01
This paper presents a high-temperature superconductor (HTS) axial-flux induction motor, which can output levitation force and torque simultaneously. In order to analyze the character of the force, analytic method and finite element method are adopted to model the motor. To make sure the HTS can carry sufficiently large current and work well, the magnetic field distribution in HTS coil is calculated. An effective method to improve the critical current of HTS coil is presented. Then, AC losses in HTS windings in the motor are estimated and tested.
Finite difference seismic modeling of axial magma chambers
Swift, S.A.; Dougherty, M.E.; Stephen, R.A. )
1990-11-01
The authors tested the feasibility of using finite difference methods to model seismic propagation at {approximately}10 Hx through a two-dimensional representation of an axial magma chamber with a thin, liquid lid. This technique produces time series of displacement or pressure at seafloor receivers to mimic a seismic refraction experiment and snapshots of P and S energy propagation. The results indicate that the implementation is stable for models with sharp velocity contrasts and complex geometries. The authors observe a high-energy, downward-traveling shear phase, observable only with borehole receivers, that would be useful in studying the nature and shape of magma chambers. The ability of finite difference methods to model high-order wave phenomena makes this method ideal for testing velocity models of spreading axes and for planning near-axis drilling of the East Pacific Rise in order to optimize the benefits from shear wave imaging of sub-axis structure.
New mixing angles in the left-right symmetric model
NASA Astrophysics Data System (ADS)
Kokado, Akira; Saito, Takesi
2015-12-01
In the left-right symmetric model neutral gauge fields are characterized by three mixing angles θ12,θ23,θ13 between three gauge fields Bμ,WLμ 3,WRμ 3, which produce mass eigenstates Aμ,Zμ,Zμ', when G =S U (2 )L×S U (2 )R×U (1 )B-L×D is spontaneously broken down until U (1 )em . We find a new mixing angle θ', which corresponds to the Weinberg angle θW in the standard model with the S U (2 )L×U (1 )Y gauge symmetry, from these mixing angles. It is then shown that any mixing angle θi j can be expressed by ɛ and θ', where ɛ =gL/gR is a ratio of running left-right gauge coupling strengths. We observe that light gauge bosons are described by θ' only, whereas heavy gauge bosons are described by two parameters ɛ and θ'.
A left-right symmetric flavor symmetry model
NASA Astrophysics Data System (ADS)
Rodejohann, Werner; Xu, Xun-Jie
2016-03-01
We discuss flavor symmetries in left-right symmetric theories. We show that such frameworks are a different environment for flavor symmetry model building compared to the usually considered cases. This does not only concern the need to obey the enlarged gauge structure, but also more subtle issues with respect to residual symmetries. Furthermore, if the discrete left-right symmetry is charge conjugation, potential inconsistencies between the flavor and charge conjugation symmetries should be taken care of. In our predictive model based on A_4 we analyze the correlations between the smallest neutrino mass, the atmospheric mixing angle and the Dirac CP phase, the latter prefers to lie around maximal values. There is no lepton flavor violation from the Higgs bi-doublet.
Spherically symmetric Einstein-aether perfect fluid models
NASA Astrophysics Data System (ADS)
Coley, Alan A.; Leon, Genly; Sandin, Patrik; Latta, Joey
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.
Left-right symmetric heterotic-string derived models
Cleaver, Gerald B.; Faraggi, Alon E.; Savage, Christopher
2001-03-15
Recently it was demonstrated that free fermionic heterotic strings can produce models with solely the minimal supersymmetric standard model states in the low energy spectrum. This unprecedented result provides further strong evidence for the possibility that the true string vacuum shares some of the properties of the free fermionic models. Past free fermionic models have focused on several possible unbroken observable SO(10) subgroups at the string scale, which include the flipped SU(5) (FSU5), the Pati-Salam (PS) string models, and the string standard-like models (SLM). We extend this study to include the case in which the SO(10) symmetry is broken to the left-right symmetric (LRS) gauge group, SO(10){yields}SU(3){sub C}xU(1){sub B-L}xSU(2){sub L}xSU(2){sub R}. We present several models of this type and discuss their phenomenological features. The most striking new outcome of the LRS string models, in contrast with the case of the FSU5, the PS, and the SLM string models, is that they can produce effective field theories that are free of Abelian anomalies. We discuss the distinction between the two types of free fermionic models which result in the presence, or absence, of an anomalous U(1). As a counterexample we also present a LRS model that does contain an anomalous U(1). Additionally, we discuss how in string models the standard model spectrum may arise from the three 16 representations of SO(10), while the weak hypercharge does not have the canonical SO(10) embedding.
Cardiac electrophysiology numerical models using symmetric multiprocessing (SMP).
Petsios, Stefanos Konstantinos D; Fotiadis, Dimitrios I
2009-01-01
Multi-dimensional electrophysiological models have been introduced to investigate electrical propagation in tissue level, based on cell-dynamics models. The models include a set of non-linear differential equations which describe the dynamics of cell and tissue excitation. However, as models evolve, it is inevitable that proper and powerful tools need to be introduced in order to reproduce the detailed and thus computationally intensive simulations. To build such tools, several computational methodologies need to be adopted regarding efficiency and reliability. On the other hand improvements apply to the hardware too. State of the art computers, even personal computers, tend to make use of multiple core Central Processing Units. Unfortunately the aforementioned methodologies follow sequential logic, resulting to low efficiency of the working platform. In this work we present the performance bottleneck in symmetric multiprocessing (SMP) for simulations of propagation phenomena in cardiac tissue electrophysiological models. We demonstrate the scalability and efficacy of the different methodologies used in the discretisation scheme and message passing in SMP. PMID:19965052
Modeling shrouded stator cavity flows in axial-flow compressors
Wellborn, S.R.; Tolchinsky, I.; Okiishi, T.H.
2000-01-01
Experiments and computational analyses were completed to understand the nature of shrouded stator cavity flows. From this understanding, a one-dimensional model of the flow through shrouded stator cavities was developed. This model estimates the leakage mass flow, temperature rise, and angular momentum increase through the cavity, given geometry parameters and the flow conditions at the interface between the cavity and primary flow path. This cavity model consists of two components, one that estimates the flow characteristics through the labyrinth seals and the other that predicts the transfer of momentum due to windage. A description of the one-dimensional model is given. The incorporation and use of the one-dimensional model in a multistage compressor primary flow analysis tool is described. The combination of this model and the primary flow solver was used to reliably simulate the significant impact on performance of the increase of hub seal leakage in a twelve-stage axial-flow compressor. Observed higher temperatures of the hub region fluid, different stage matching, and lower overall efficiencies and core flow than expected could be correctly linked to increased hub seal clearance with this new technique. The importance of including these leakage flows in compressor simulations is shown.
Dynamically Scaled Glottal Flow Through Symmetrically Oscillating Vocal Fold Models
NASA Astrophysics Data System (ADS)
Halvorson, Lori; Baitinger, Andrew; Sherman, Erica; Krane, Michael; Zhang, Lucy; Wei, Timothy
2011-11-01
Experimental results derived from DPIV measurements in a scaled up dynamic human vocal fold model are presented. The 10x scale vocal fold model is a new design that incorporates key features of vocal fold oscillatory motion. This includes coupling of down/upstream rocking as well as the oscillatory open/close motions. Experiments were dynamically scaled to examine a range of frequencies, 100 - 200 Hz, corresponding to the male and female voice. By using water as the working fluid, very high resolution, both spatial and temporal resolution, was achieved. Time resolved movies of flow through symmetrically oscillating vocal folds will be presented. Both individual realizations as well as phase-averaged data will be shown. Key features, such as randomness and development time of the Coanda effect, vortex shedding, and volume flow rate data will be shown. In this talk, effects associated with paralysis of one vocal fold will be discussed. This talk provides the baseline fluid dynamics for the vocal fold paralysis study presented in Sherman, et al. Supported by the NIH.
Modeling scattering from azimuthally symmetric bathymetric features using wavefield superposition.
Fawcett, John A
2007-12-01
In this paper, an approach for modeling the scattering from azimuthally symmetric bathymetric features is described. These features are useful models for small mounds and indentations on the seafloor at high frequencies and seamounts, shoals, and basins at low frequencies. A bathymetric feature can be considered as a compact closed region, with the same sound speed and density as one of the surrounding media. Using this approach, a number of numerical methods appropriate for a partially buried target or facet problem can be applied. This paper considers the use of wavefield superposition and because of the azimuthal symmetry, the three-dimensional solution to the scattering problem can be expressed as a Fourier sum of solutions to a set of two-dimensional scattering problems. In the case where the surrounding two half spaces have only a density contrast, a semianalytic coupled mode solution is derived. This provides a benchmark solution to scattering from a class of penetrable hemispherical bosses or indentations. The details and problems of the numerical implementation of the wavefield superposition method are described. Example computations using the method for a simple scattering feature on a seabed are presented for a wide band of frequencies. PMID:18247740
Spherically symmetric model atmospheres for late-type giant stars
NASA Astrophysics Data System (ADS)
Bennett, Philip Desmond
The ATHENA computer code was developed to model the extended atmospheres of late-type giant and supergiant stars. The atmospheres are assumed to be static, spherically symmetric and in radiative and hydrostatic equilibrium. Molecular line blanketing (for now) is handled using the simplifying assumption of mean opacity. The complete linearization method of Auer and Mihalas, adapted to spherical geometry, is used to solve the model system. The radiative transfer is solved by using variable Eddington factors to close the system of moment transfer equations, and the entire system of transfer equations plus constraints is solved efficiently by arrangement into the Rybicki block matrix form. The variable Eddington factors are calculated from the full angle-dependent formal solution of the radiative transfer problem using the impact parameter method of Hummer, Kunas. We were guided by the work of Mihalas and Hummer in their development of extended models of O stars, but our method differs in the choice of the independent variable. The radius depth scale used by Mihals and Hummer was found to fail because of the strongly temperature-dependent opacities of late-type atmospheres. Instead, we were able to achieve an exact linearization of the radius. This permitted the use of the numerically well-behaved column mass or optical depth scales. The resulting formulation is analogous to the plane-parallel complete linearization method and reduces to this method in the compact atmosphere limit. Models of M giants were calculated for Teff = 3000K and 3500K with opacities of the CN, TiO, and H2O molecules included, and the results were in general agreement with other published spherical models. These models were calculated assuming radiative equilibrium. The importance of convective energy transport was estimated by calculating the convective flux that would result from the temperature structure of the models. The standard local mixing length theory was used for this purpose
Chirally symmetric O(1/N{sub c}) corrections to the Nambu-Jona-Lasinio model
Dmitrasinovic, V.; Schulze, H.J.; Tegen, R.
1995-03-01
We develop an extended chirally symmetric self-consistent approximation scheme to the Nambu-Jona-Lasinio model, that corresponds to O(1/N{sub c}) corrections to the usual Hartree + random phase approximations. This scheme amounts to adding {open_quotes}meson cloud{close_quotes} contributions self-consistently to the quark self-energy and the meson polarization functions in a manner suggested by the weakly interacting nature of the quark and collective meson degrees of freedom of the NJL model in the large N{sub c} limit. We demonstrate explicitly that this scheme fulfills all the chiral symmetry theorems, namely the Goldstone theorem, the Goldberger-Treiman relation, and the conservation of the quark axial current. We explore the corrections to the quark self-energy and scalar condensate, as well as to the pion polarization function and the weak decay constant N{sub n}. The numerical evaluation of these corrections is presented and discussed. 23 refs., 14 figs., 2 tabs.
An analytical model of axial compressor off-design performance
Camp, T.R.; Horlock, J.H. . Whittle Lab.)
1994-07-01
An analysis is presented of the off-design performance of multistage axial-flow compressors. It is based on an analytical solution, valid for small perturbations in operating conditions from the design point, and provides an insight into the effects of choices made during the compressor design process on performance and off-design stage matching. It is shown that the mean design value of stage loading coefficient ([psi] = [Delta]h[sub 0]/U[sup 2]) has a dominant effect on off-design performance, whereas the stage-wise distribution of stage loading coefficient and the design value of flow coefficient have little influence. The powerful effects of variable stator vanes on stage-matching are also demonstrated and these results are shown to agree well with previous work. The slope of the working line of a gas turbine engine, overlaid on overall compressor characteristics, is shown to have a strong effect on the off-design stage-matching through the compressor. The model is also used to analyze design changes to the compressor geometry and to show how errors in estimates of annulus blockage, decided during the design process, have less effect on compressor performance than has previously been thought.
Charge radii in macroscopic-microscopic mass models of axial asymmetry
Iimura, H.; Buchinger, F.
2007-11-15
We show that the charge radii of axially asymmetric nuclei calculated in the frame of the finite-range droplet model are in better agreement with measured charge radii when axial asymmetry is taken into account. This improvement is mainly the result of a new set of ground-state quadrupole deformations {beta}{sub 2}, generated when masses are calculated including axial asymmetry, and to a much lesser degree due to the inclusion of the axial asymmetry in the calculation of the charge radii itself.
Symmetric bursting behaviors in the generalized FitzHugh-Nagumo model.
Abbasian, A H; Fallah, H; Razvan, M R
2013-08-01
In the current paper, we have investigated the generalized FitzHugh-Nagumo model. We have shown that symmetric bursting behaviors of different types could be observed in this model with an appropriate recovery term. A modified version of this system is used to construct bursting activities. Furthermore, we have shown some numerical examples of delayed Hopf bifurcation and canard phenomenon in the symmetric bursting of super-Hopf/homoclinic type near its super-Hopf and homoclinic bifurcations, respectively. PMID:23801268
A dimer PT -symmetric model simulated in GaAs/AlGaAs quantum wells
NASA Astrophysics Data System (ADS)
Meng, Li-Chen; Zhang, Wen-Jing; Liu, Jibing; Xie, Xiao-Tao
2016-05-01
We perform the possibility to generate a dimer PT -symmetric model based on a double lambda four-level system in GaAs/AlGaAs quantum wells with biexcitonic transitions. By presenting the detuning management and modulating the Rabi frequencies of the two strong coupling laser fields, we show that the PT -symmetric model can be realized by the spatial evolution of the weak probe laser and four-wave mixing (FWM)-generated field along the propagation direction. The two weak fields in our model may be used to simulate two laser propagating in two PT -symmetric parallel waveguides. The diffraction effect also can be studied in some conditions. Our scheme offers two advantages: the complex refractive index is controlled by the strong coupling fields; the symmetry energy exchange between a dimer PT -symmetric structure is guaranteed by the four-wave mixing process. The present investigation may provide research opportunities in optical experiments.
NASA Technical Reports Server (NTRS)
Holland, D. B.; Virgin, L. N.; Belvin, W. K.
2003-01-01
This paper presents a parameter study of the effect of boom axial loading on the global dynamics of a 2-meter solar sail scale model. The experimental model used is meant for building expertise in finite element analysis and experimental execution, not as a predecessor to any planned flight mission or particular design concept. The results here are to demonstrate the ability to predict and measure structural dynamics and mode shapes in the presence of axial loading.
Model-size reduction for the non-linear dynamic analysis of quasi-symmetric structures
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.; Peters, Jeanne M.
1987-01-01
A numerical technique is developed to reduce the size of models describing the nonlinear dynamic response of quasi-symmetric structures (i.e., structures with unsymmetric geometry). The response vectors of the structure are approximated by a linear combination of the symmetric and antisymmetric vectors at each time step. The mathematical formulation and numerical implementation of the method are described in detail, and results for a shallow laminated anisotropic panel of quadrilateral planform are presented in graphs and normalized contour plots.
Chiral quark model of nucleon spin-flavor structure with SU(3) and axial-U(1) breakings
Cheng, T.P.; Li, L.
1998-01-01
The chiral quark model with a nonet of Goldstone bosons can yield an adequate description of the observed proton flavor and spin structure. In a previous publication we have compared the results of an SU(3) symmetric calculation with the phenomenological findings based on experimental measurements and SU(3) symmetry relations. In this paper we discuss their SU(3) and axial U(1) breaking corrections. Our result demonstrates the broad consistency of the chiral quark model with the experimental observations of the proton spin-flavor structure. With two parameters, we obtain a very satifactory fit to the F/D ratios for the octet baryon masses and for their axial vector couplings, as well as the different quark flavor contributions to the proton spin. The result also can account for not only the light quark asymmetry {bar u}{minus}{bar d} but also the strange quark content {bar s} of the proton sea. SU(3) breaking is the key in reconciling the {bar s} value as measured in the neutrino charm production and that as deduced from the pion nucleon {sigma} term. {copyright} {ital 1997} {ital The American Physical Society}
Implementation of the manifest left-right symmetric model in FeynRules
NASA Astrophysics Data System (ADS)
Roitgrund, Aviad; Eilam, Gad; Bar-Shalom, Shaouly
2016-06-01
We present an implementation of the manifest left-right symmetric model in FeynRules. The different aspects of the model are briefly described alongside the corresponding elements of the model file. The model file is validated and can be easily translated to matrix element generators such as MadGraph5_aMC@NLO,CalcHEP, and Sherpa. The implementation of the left-right symmetric model is a useful step for studying new physics signals with the data generated at the LHC.
Model-size reduction for the analysis of symmetric structures with asymmetric boundary conditions
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.; Whitworth, Sandra L.
1987-01-01
A simple computational procedure is presented for reducing the size of the analysis model for a symmetric structure with asymmetric boundary conditions to that of the corresponding structure with symmetric boundary conditions. The procedure is based on approximating the asymmetric response of the structure by a linear combination of symmetric and antisymmetric global approximation vectors (or modes). The key elements of the procedure are (1) restructuring the governing finite-element equations to delineate the contributions to the symmetric and antisymmetric components of the asymmetric response, (2) successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite-element method is first used to generate a few global approximation vectors (or modes). Then the amplitudes of these modes are computed by using the Rayleigh-Ritz technique. The effectiveness of the computational procedure is demonstrated by means of numerical examples of linear static problems of shells, and its potential for solving nonlinear problems is discussed.
The Thirring interaction in the two-dimensional axial-current-pseudoscalar derivative coupling model
Belvedere, L.V. . E-mail: armflavio@if.uff.br
2006-12-15
We reexamine the two-dimensional model of massive fermions interacting with a massless pseudoscalar field via axial-current derivative coupling. The hidden Thirring interaction in the axial-derivative coupling model is exhibited compactly by performing a canonical field transformation on the Bose field algebra and the model is mapped into the Thirring model with an additional vector-current-scalar derivative interaction (Schroer-Thirring model). The Fermi field operator is rewritten in terms of the Mandelstam soliton operator coupled to a free massless scalar field. The charge sectors of the axial-derivative model are mapped into the charge sectors of the massive Thirring model. The complete bosonized version of the model is presented. The bosonized composite operators of the quantum Hamiltonian are obtained as the leading operators in the Wilson short distance expansions.
Stochastic modeling of cell growth with symmetric or asymmetric division.
Marantan, Andrew; Amir, Ariel
2016-07-01
We consider a class of biologically motivated stochastic processes in which a unicellular organism divides its resources (volume or damaged proteins, in particular) symmetrically or asymmetrically between its progeny. Assuming the final amount of the resource is controlled by a growth policy and subject to additive and multiplicative noise, we derive the recursive integral equation describing the evolution of the resource distribution over subsequent generations and use it to study the properties of stable resource distributions. We find conditions under which a unique stable resource distribution exists and calculate its moments for the class of affine linear growth policies. Moreover, we apply an asymptotic analysis to elucidate the conditions under which the stable distribution (when it exists) has a power-law tail. Finally, we use the results of this asymptotic analysis along with the moment equations to draw a stability phase diagram for the system that reveals the counterintuitive result that asymmetry serves to increase stability while at the same time widening the stable distribution. We also briefly discuss how cells can divide damaged proteins asymmetrically between their progeny as a form of damage control. In the appendixes, motivated by the asymmetric division of cell volume in Saccharomyces cerevisiae, we extend our results to the case wherein mother and daughter cells follow different growth policies. PMID:27575162
Stochastic modeling of cell growth with symmetric or asymmetric division
NASA Astrophysics Data System (ADS)
Marantan, Andrew; Amir, Ariel
2016-07-01
We consider a class of biologically motivated stochastic processes in which a unicellular organism divides its resources (volume or damaged proteins, in particular) symmetrically or asymmetrically between its progeny. Assuming the final amount of the resource is controlled by a growth policy and subject to additive and multiplicative noise, we derive the recursive integral equation describing the evolution of the resource distribution over subsequent generations and use it to study the properties of stable resource distributions. We find conditions under which a unique stable resource distribution exists and calculate its moments for the class of affine linear growth policies. Moreover, we apply an asymptotic analysis to elucidate the conditions under which the stable distribution (when it exists) has a power-law tail. Finally, we use the results of this asymptotic analysis along with the moment equations to draw a stability phase diagram for the system that reveals the counterintuitive result that asymmetry serves to increase stability while at the same time widening the stable distribution. We also briefly discuss how cells can divide damaged proteins asymmetrically between their progeny as a form of damage control. In the appendixes, motivated by the asymmetric division of cell volume in Saccharomyces cerevisiae, we extend our results to the case wherein mother and daughter cells follow different growth policies.
Duck, I. )
1993-04-01
Second-order radiative corrections to the nucleon axial vector coupling constant from gluon, pion, and sigma meson exchange are calculated in the chiral soliton quark model. Many apparent processes are found not to contribute. The soliton is elastically decoupled from meson radiative corrections which are dominated by a gluon exchange contribution equivalent to a gluonic hybrid component of the nucleon. A 30% radiative reduction of the axial coupling strength is indicated.
State variable model for unsteady two dimensional axial vortex flow with pressure relaxation
NASA Astrophysics Data System (ADS)
Abuharaz, Mazin Mohammed Elbakri
This research has utilized a state variable model for unsteady two dimensional axial vortex flows experiencing non-equilibrium pressure gradient forces. The model was developed successfully using perturbed radial and azimuthal momentum equations and a pressure Poisson's equations. Three main regions of the axial vortex flow were highlighted in this study including: a laminar core region, a non-equilibrium pressure envelope, and an outer potential vortex. Linear stability theory was utilized to formulate the model and the perturbation functions were assumed to be of the Fourier type. The flow parameters considered were the Reynolds numbers, ranging between 6,000 and 14,000, and a new non-equilibrium swirl parameter, Np determining the area of significant non-equilibrium pressure forces. Two other state variable parameters were imposed-complex frequency and associated azimuthal mode number. Perturbation outputs included primary Reynolds stress, radial and azimuthal velocity amplitudes, and radial pressure gradient amplitudes. Maximum perturbation growth occurred inside the non-equilibrium pressure zone between one and five core radii from the rotational axis, while the inner core remained laminar. The maximum amplitudes and critical radii depended on the four physical and state variable parameters. Increases in Np resulted in lower perturbation pressure gradient amplitudes, moving the critical radius closer to the vortex core, and expanding the non-equilibrium pressure zone. Increasing the frequency resulted in steady increases in the perturbation amplitudes until a particular dimensionless frequency was reached. Beyond that frequency, additional perturbation growth was insignificant or the amplitude decayed because of a high damping factor. Two types of azimuthal modes were unstable, the +/-½ modes inside the non-equilibrium pressure zone, causing the pressure gradient amplitudes to peak even though the azimuthal velocity profile remained stable, and +/- 1 helical
Axial form factors of the octet baryons in a covariant quark model
NASA Astrophysics Data System (ADS)
Ramalho, G.; Tsushima, K.
2016-07-01
We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q2. In our model the axial form factors GA(Q2) (axial-vector form factor) and GP(Q2) (induced pseudoscalar form factor) are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor gAq(Q2), and the induced pseudoscalar form factor gPq(Q2). The baryon wave functions are composed of a dominant S -state and a P -state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor gAq(Q2) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P -state mixture and the Q2 dependence of gPq(Q2), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime and use the low Q2 experimental data to estimate the meson cloud contributions for GA(Q2) and GP(Q2). Using the calibrated quark axial form factors and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors GA(Q2) and GP(Q2) of the octet baryons. The results are compared with the corresponding experimental data for GA(0 ) and with the estimates of baryon-meson models based on S U (6 ) symmetry.
Model independent extraction of the axial mass parameter in CCQE anti neutrino-nucleon scattering
NASA Astrophysics Data System (ADS)
Grebe, Heather
2013-10-01
Neutrino oscillation studies depend on a consistent value for the axial mass. For this reason, a model-independent extraction of this parameter from quasielastic (anti)neutrino-nucleon scattering data is vital. While most studies employ a model-dependent extraction using the dipole model of the axial form factor, we present a model-independent description using the z expansion of the axial form factor. Quasielastic antineutrino scattering data on C-12 from the MiniBooNE experiment are analyzed using this model-independent description. The value found, mA = 0 .85-0 . 06 + 0 . 13 +/- 0 . 13 GeV, differs significantly from the value utilized by the MiniBooNE Collaboration, mA = 1 . 35 GeV. Advisor: Dr. Gil Paz Wayne State Univerity.
Interaction of axial and oblique astigmatism in theoretical and physical eye models.
Liu, Tao; Thibos, Larry N
2016-09-01
The interaction between oblique and axial astigmatism was investigated analytically (generalized Coddington's equations) and numerically (ray tracing) for a theoretical eye model with a single refracting surface. A linear vector-summation rule for power vector descriptions of axial and oblique astigmatism was found to account for their interaction over the central 90° diameter of the visual field. This linear summation rule was further validated experimentally using a physical eye model measured with a laboratory scanning aberrometer. We then used the linear summation rule to evaluate the relative contributions of axial and oblique astigmatism to the total astigmatism measured across the central visual field. In the central visual field, axial astigmatism dominates because the oblique astigmatism is negligible near the optical axis. At intermediate eccentricities, axial and oblique astigmatism may have equal magnitude but orthogonal axes, which nullifies total astigmatism at two locations in the visual field. At more peripheral locations, oblique astigmatism dominates axial astigmatism, and the axes of total astigmatism become radially oriented, which is a trait of oblique astigmatism. When eccentricity is specified relative to a foveal line-of-sight that is displaced from the eye's optical axis, asymmetries in the visual field map of total astigmatism can be used to locate the optical axis empirically and to estimate the relative contributions of axial and oblique astigmatism at any retinal location, including the fovea. We anticipate the linear summation rule will benefit many topics in vision science (e.g., peripheral correction, emmetropization, meridional amblyopia) by providing improved understanding of how axial and oblique astigmatism interact to produce net astigmatism. PMID:27607493
Inflation in minimal left-right symmetric model with spontaneous D-parity breaking
Gong, Jinn-Ouk; Sahu, Narendra
2008-01-15
We present a simplest inflationary scenario in the minimal left-right symmetric model with spontaneous D-parity breaking, which is a well-motivated particle physics model for neutrino masses. This leads us to connect the observed anisotropies in the cosmic microwave background to the sub-eV neutrino masses. The baryon asymmetry via the leptogenesis route is also discussed briefly.
Chiral formulation for hyperKähler sigma-models on cotangent bundles of symmetric spaces
NASA Astrophysics Data System (ADS)
Kuzenko, Sergei M.; Novak, Joseph
2008-12-01
Starting with the projective-superspace off-shell formulation for four-dimensional Script N = 2 supersymmetric sigma-models on cotangent bundles of arbitrary Hermitian symmetric spaces, their on-shell description in terms of Script N = 1 chiral superfields is developed. In particular, we derive a universal representation for the hyperkähler potential in terms of the curvature of the symmetric base space. Within the tangent-bundle formulation for such sigma-models, completed recently in arXiv:0709.2633 and realized in terms of Script N = 1 chiral and complex linear superfields, we give a new universal formula for the superspace Lagrangian. A closed form expression is also derived for the Kähler potential of an arbitrary Hermitian symmetric space in Kähler normal coordinates.
A Symmetric Time-Varying Cluster Rate of Descent Model
NASA Technical Reports Server (NTRS)
Ray, Eric S.
2015-01-01
A model of the time-varying rate of descent of the Orion vehicle was developed based on the observed correlation between canopy projected area and drag coefficient. This initial version of the model assumes cluster symmetry and only varies the vertical component of velocity. The cluster fly-out angle is modeled as a series of sine waves based on flight test data. The projected area of each canopy is synchronized with the primary fly-out angle mode. The sudden loss of projected area during canopy collisions is modeled at minimum fly-out angles, leading to brief increases in rate of descent. The cluster geometry is converted to drag coefficient using empirically derived constants. A more complete model is under development, which computes the aerodynamic response of each canopy to its local incidence angle.
Effects of axial nonuniformity in modeling Q-switched lasers
Stone, D.H. )
1992-10-01
Generic Q-switched laser pulses are calculated using a point model and a traveling wave model. Results indicate that the point model approach commonly used in rate equation modeling is inadequate for large initial inversions, large internal losses, or large fractional outcoupling. The point model typically overestimates peak power and energy and distorts the pulse shape. A simple traveling wave model is developed which easily describes these cases. The optimum outcoupling to maximize peak power varies significantly between the two models. 9 refs.
Bhattacharya, Bhubanjyoti; Hill, Richard J.; Paz, Gil
2011-10-01
Quasielastic neutrino-nucleon scattering is a basic signal process for neutrino oscillation studies. At accelerator energies, the corresponding cross section is subject to significant uncertainty due to the poorly constrained axial-vector form factor of the nucleon. A model-independent description of the axial-vector form factor is presented. Data from the MiniBooNE experiment for quasielastic neutrino scattering on {sup 12}C are analyzed under the assumption of a definite nuclear model. The value of the axial mass parameter, m{sub A}=0.85{sub -0.07}{sup +0.22}{+-}0.09 GeV, is found to differ significantly from extractions based on traditional form factor models. Implications for future neutrino scattering and pion electroproduction measurements are discussed.
FAST Mast Structural Response to Axial Loading: Modeling and Verification
NASA Technical Reports Server (NTRS)
Knight, Norman F., Jr.; Elliott, Kenny B.; Templeton, Justin D.; Song, Kyongchan; Rayburn, Jeffery T.
2012-01-01
The International Space Station s solar array wing mast shadowing problem is the focus of this paper. A building-block approach to modeling and analysis is pursued for the primary structural components of the solar array wing mast structure. Starting with an ANSYS (Registered Trademark) finite element model, a verified MSC.Nastran (Trademark) model is established for a single longeron. This finite element model translation requires the conversion of several modeling and analysis features for the two structural analysis tools to produce comparable results for the single-longeron configuration. The model is then reconciled using test data. The resulting MSC.Nastran (Trademark) model is then extended to a single-bay configuration and verified using single-bay test data. Conversion of the MSC. Nastran (Trademark) single-bay model to Abaqus (Trademark) is also performed to simulate the elastic-plastic longeron buckling response of the single bay prior to folding.
NASA Astrophysics Data System (ADS)
Sahoo, Sharmistha; Zhang, Zhao; Teo, Jeffrey
Time reversal symmetric topological superconductors in three spatial dimensions carry gapless surface Majorana fermions. They are robust against any time reversal symmetric single-body perturbation weaker than the bulk energy gap. We mimic the massless surface Majorana's by coupled wire models in two spatial dimensions. We introduce explicit many-body interwire interactions that preserve time reversal symmetry and give energy gaps to all low energy degrees of freedom. The gapping 4-fermion interactions are constructed by interwire Kac-Moody current backscattering and rely on the fractionalization or conformal embedding of the Majorana wires.
Effects of f(R) Model on Dynamics of Axial Shear-Free Dissipative Fluids
NASA Astrophysics Data System (ADS)
Sharif, M.; Zunaira, Nasir
2016-04-01
We present a general analysis on non-static axial system with dissipative shear-free anisotropic fluid using polynomial inflationary f(R) model. We study the effects of dissipation on the dynamics of geodesic matter distribution. This leads the system either to rotation-free or expansion-free but not both simultaneously under geodesic condition. It is found that the system preserves its symmetry in both cases. For the rotation-free case, when there is no dissipation and Ricci scalar is constant, the axial system reduces to FRW universe model. This is exactly the same result obtained in general relativity.
Symmetric model of compressible granular mixtures with permeable interfaces
NASA Astrophysics Data System (ADS)
Saurel, Richard; Le Martelot, Sébastien; Tosello, Robert; Lapébie, Emmanuel
2014-12-01
Compressible granular materials are involved in many applications, some of them being related to energetic porous media. Gas permeation effects are important during their compaction stage, as well as their eventual chemical decomposition. Also, many situations involve porous media separated from pure fluids through two-phase interfaces. It is thus important to develop theoretical and numerical formulations to deal with granular materials in the presence of both two-phase interfaces and gas permeation effects. Similar topic was addressed for fluid mixtures and interfaces with the Discrete Equations Method (DEM) [R. Abgrall and R. Saurel, "Discrete equations for physical and numerical compressible multiphase mixtures," J. Comput. Phys. 186(2), 361-396 (2003)] but it seemed impossible to extend this approach to granular media as intergranular stress [K. K. Kuo, V. Yang, and B. B. Moore, "Intragranular stress, particle-wall friction and speed of sound in granular propellant beds," J. Ballist. 4(1), 697-730 (1980)] and associated configuration energy [J. B. Bdzil, R. Menikoff, S. F. Son, A. K. Kapila, and D. S. Stewart, "Two-phase modeling of deflagration-to-detonation transition in granular materials: A critical examination of modeling issues," Phys. Fluids 11, 378 (1999)] were present with significant effects. An approach to deal with fluid-porous media interfaces was derived in Saurel et al. ["Modelling dynamic and irreversible powder compaction," J. Fluid Mech. 664, 348-396 (2010)] but its validity was restricted to weak velocity disequilibrium only. Thanks to a deeper analysis, the DEM is successfully extended to granular media modelling in the present paper. It results in an enhanced version of the Baer and Nunziato ["A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials," Int. J. Multiphase Flow 12(6), 861-889 (1986)] model as symmetry of the formulation is now preserved. Several computational examples are
A symmetric approach to the massive nonlinear sigma model
Ferrari, Ruggero
2011-09-28
In the present study we extend to the massive case the procedure of divergences subtraction, previously introduced for the massless nonlinear sigma model (D = 4). Perturbative expansion in the number of loops is successfully constructed. The resulting theory depends on the Spontaneous Symmetry Breaking parameter v, on the mass m and on the radiative correction parameter Λ. Fermions are not considered in the present work. SU(2) Ⓧ SU(2) is the group used.
Modeling of recrystallization texture of aluminium: symmetric and asymmetric rolling
NASA Astrophysics Data System (ADS)
Wierzbanowski, K.; Kotra, M.; Wronski, M.; Sztwiertnia, K.; Wronski, S.; Lodini, A.
2015-04-01
In some metallic materials the dominating recrystallization mechanism can be described by the oriented growth behaviour. Phenomenological laws state that in selected materials only these nuclei grow intensively which have a given misorientation relation with the deformed matrix. This description is frequently verified in f.c.c. metals and generally reported misorientations correspond approximately to 400 rotation around the <111> axis. Basing on the above ideas the recrystallization model, including the compromise condition, was formulated and applied to the study of recrystallization textures of rolled polycrystalline aluminium.
A zonally symmetric model for volcanic influence upon atmospheric circulation
NASA Technical Reports Server (NTRS)
Schatten, K. H.; Mayr, H. G.; Harris, I.; Taylor, H. A., Jr.
1984-01-01
The effects of volcanic activity upon zonal wind flow in a model atmosphere are considered. A low latitude volcanic eruption could lower the tropospheric pole to equator temperature difference and thereby affect the atmospheric motions. When the temperature contrast decreases, the zonal wind velocities at high altitudes are reduced. To conserve angular momentum, the velocities in the lower atmosphere near the surface must increase, thus providing a momentum source for ocean currents. It is suggested that this momentum source may have played a role as a trigger for inducing the 1982-83 anomalous El Nino and possibly other climate changes.
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.
A new model for spherically symmetric anisotropic compact star
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Gupta, Y. K.; Dayanandan, Baiju; Ray, Saibal
2016-05-01
In this article we obtain a new anisotropic solution for Einstein's field equations of embedding class one metric. The solution represents realistic objects such as Her X-1 and RXJ 1856-37. We perform a detailed investigation of both objects by solving numerically the Einstein field equations with anisotropic pressure. The physical features of the parameters depend on the anisotropic factor i.e. if the anisotropy is zero everywhere inside the star then the density and pressures will become zero and the metric turns out to be flat. We report our results and compare with the above mentioned two compact objects as regards a number of key aspects: the central density, the surface density onset and the critical scaling behaviour, the effective mass and radius ratio, the anisotropization with isotropic initial conditions, adiabatic index and red shift. Along with this we have also made a comparison between the classical limit and theoretical model treatment of the compact objects. Finally we discuss the implications of our findings for the stability condition in a relativistic compact star.
Kumaresan, S; Yoganandan, N; Pintar, F A; Maiman, D J
1999-12-01
An anatomically accurate, three-dimensional, nonlinear finite element model of the human cervical spine was developed using computed tomography images and cryomicrotome sections. The detailed model included the cortical bone, cancellous core, endplate, lamina, pedicle, transverse processes and spinous processes of the vertebrae; the annulus fibrosus and nucleus pulposus of the intervertebral discs; the uncovertebral joints; the articular cartilage, the synovial fluid and synovial membrane of the facet joints; and the anterior and posterior longitudinal ligaments, interspinous ligaments, capsular ligaments and ligamentum flavum. The finite element model was validated with experimental results: force-displacement and localized strain responses of the vertebral body and lateral masses under pure compression, and varying eccentric anterior-compression and posterior-compression loading modes. This experimentally validated finite element model was used to study the biomechanics of the cervical spine intervertebral disc by quantifying the internal axial and shear forces resisted by the ventral, middle, and dorsal regions of the disc under the above axial and eccentric loading modes. Results indicated that higher axial forces (compared to shear forces) were transmitted through different regions of the disc under all loading modes. While the ventral region of the disc resisted higher variations in axial force, the dorsal region transmitted higher shear forces under all loading modes. These findings may offer an insight to better understand the biomechanical role of the human cervical spine intervertebral disc. PMID:10717549
Low-frequency intraseasonal variability in a zonally symmetric aquaplanet model
NASA Astrophysics Data System (ADS)
Das, Surajit; Sengupta, Debasis; Chakraborty, A.; Sukhatme, Jai; Murtugudde, Raghu
2016-04-01
We use the aquaplanet version of the community atmospheric model, with perpetual spring equinox forcing and zonally symmetric sea surface temperature (SST), to study tropical intraseasonal oscillations (ISOs). In the first two experiments, we specify zonally symmetric SST profiles that mimic observed climatological July and January SSTs as surface boundary conditions. In the January SST simulation, we find a zonal wavenumber 1 mode with dominant period of 60 days, moving east at about 6 m s-1. This mode, which resembles the Madden-Julian oscillation (MJO), is absent in the July SST case, although convectively coupled Kelvin waves are prominent in both experiments. To further investigate the influence of tropical SST on ISO and convectively coupled equatorial waves, we conduct experiments with idealised symmetric SST profiles having different widths of warm ocean centered at the equator. In the narrowest SST experiment, the variance of moist activity is predominantly in weather-scale Kelvin waves. When the latitudinal extent of warm SST is comparable to or larger than the equatorial Rossby radius, we find a dominant low frequency (50-80 days) eastward mode that resembles the MJO, as in the January SST experiment. We also find westward propagating waves with intraseasonal (30-120 days) periods and zonal wavenumber 1-3; the structure of these signals projects onto equatorially trapped Rossby waves with meridional mode numbers 1, 3 and 5, associated with convection that is symmetric about the equator. In addition, the model generates 30-80 days westward moving signals with zonal wavenumber 4-7, particularly in the narrow SST experiment. Although these waves are seen in the wavenumber-frequency spectra in the equatorial region, they have largest amplitude in the middle and high latitudes. Thus, our study shows that wider, meridionally symmetric SST profiles support a strong MJO-like eastward propagation, and even in an aquaplanet setting, westward propagating Rossby
Guendouz, Laouès; Aissani, Sarra; Marêché, Jean-François; Retournard, Alain; Marande, Pierre-Louis; Canet, Daniel
2013-01-01
The application of a weak static B0 magnetic field (less than 1 mT) may produce a well-defined splitting of the (14)N Quadrupole Resonance line when the electric field gradient tensor at the nitrogen nucleus level is of axial symmetry. It is theoretically shown and experimentally confirmed that the actual splitting (when it exists) as well as the line-shape and the signal intensity depends on three factors: (i) the amplitude of B0, (ii) the amplitude and pulse duration of the radio-frequency field, B1, used for detecting the NQR signal, and (iii) the relative orientation of B0 and B1. For instance, when B0 is parallel to B1 and regardless of the B0 value, the signal intensity is three times larger than when B0 is perpendicular to B1. This point is of some importance in practice since NQR measurements are almost always performed in the earth field. Moreover, in the course of this study, it has been recognized that important pieces of information regarding line-shape are contained in data points at the beginning of the free induction decay (fid) which, in practice, are eliminated for avoiding spurious signals due to probe ringing. It has been found that these data points can generally be retrieved by linear prediction (LP) procedures. As a further LP benefit, the signal intensity loss (by about a factor of three) is regained. PMID:24183810
Baryogenesis and asymmetric dark matter from the left-right mirror symmetric model
NASA Astrophysics Data System (ADS)
Yang, Wei-Min
2014-08-01
The paper suggests a left-right mirror symmetric model to account for the baryogenesis and asymmetric dark matter. The model can simultaneously accommodate the standard model, neutrino physics, matter-antimatter asymmetry and dark matter. In particular, it naturally and elegantly explains the origin of the baryon and dark matter asymmetries, and clearly gives the close interrelations of them. In addition, the model predicts a number of interesting results, e.g. that the cold dark matter neutrino mass is 3.1 times the proton mass. It is also feasible and promising to test the model in future experiments.
Three-dimensional model and simulation of vacuum arcs under axial magnetic fields
Wang Lijun; Jia Shenli; Zhou Xin; Wang Haijing; Shi Zongqian
2012-01-15
In this paper, a three-dimensional (3d) magneto-hydro-dynamic (MHD) model of axial magnetic field vacuum arcs (AMFVAs) is established. Based on this model, AMFVAs are simulated and analyzed. Three-dimensional spatial distributions of many important plasma parameters and electric characteristics in AMFVAs can be obtained, such as ion number density, ion temperature, electron temperature, plasma pressure, current densities along different directions (x, y, and z), ion velocities along different directions, electric fields strength along different directions, and so on. Simulation results show that there exist significant spiral-shaped rotational phenomena in the AMFVAs, this kind of rotational phenomenon also can be verified by the many related experiments (AMFVAs photographs, especially for stronger AMF strength). For current simulation results of AMFVAs, the maximal rotational velocity at anode side is about 1100 m/s. Radial electric field is increased from arc center to arc edge; axial electric field is decreased from cathode side to anode side. Radial electric field at arc edge can be larger than axial electric field. Azimuthal electric field in most regions is much smaller than radial and axial electric field, but it can reach about 1.19 kV/m. Radial magnetic field is the smallest one compared with other components, it reaches to maximum value at the position near to anode, it can influence arc characteristics.
Bowsher, J E; Tornai, M P; Peter, J; González Trotter, D E; Krol, A; Gilland, D R; Jaszczak, R J
2002-03-01
Reconstruction algorithms for transmission tomography have generally assumed that the photons reaching a particular detector bin at a particular angle originate from a single point source. In this paper, we highlight several cases of extended transmission sources, in which it may be useful to approach the estimation of attenuation coefficients as a problem involving multiple transmission point sources. Examined in detail is the case of a fixed transmission line source with a fan-beam collimator. This geometry can result in attenuation images that have significant axial blur. Herein it is also shown, empirically, that extended transmission sources can result in biased estimates of the average attenuation, and an explanation is proposed. The finite axial resolution of the transmission line source configuration is modeled within iterative reconstruction using an expectation-maximization algorithm that was previously derived for estimating attenuation coefficients from single photon emission computed tomography (SPECT) emission data. The same algorithm is applicable to both problems because both can be thought of as involving multiple transmission sources. It is shown that modeling axial blur within reconstruction removes the bias in the average estimated attenuation and substantially improves the axial resolution of attenuation images. PMID:11989845
Aissani, Sarra; Guendouz, Laouès; Marande, Pierre-Louis; Canet, Daniel
2015-01-01
As demonstrated before, the application of a weak static B0 magnetic field (less than 10 G) may produce definite effects on the ¹⁴N Quadrupole Resonance line when the electric field gradient tensor at the nitrogen nucleus level is of axial symmetry. Here, we address more precisely the problem of the relative orientation of the two magnetic fields (the static field and the radio-frequency field of the pure NQR experiment). For a field of 6G, the evolution of the signal intensity, as a function of this relative orientation, is in very good agreement with the theoretical predictions. There is in particular an intensity loss by a factor of three when going from the parallel configuration to the perpendicular configuration. By contrast, when dealing with a very weak magnetic field (as the earth field, around 0.5 G), this effect drops to ca. 1.5 in the case Hexamethylenetetramine (HMT).This is explained by the fact that the Zeeman shift (due to the very weak magnetic field) becomes comparable to the natural line-width. The latter can therefore be determined by accounting for this competition. Still in the case of HMT, the estimated natural line-width is half the observed line-width. The extra broadening is thus attributed to earth magnetic field. The latter constitutes therefore the main cause of the difference between the natural transverse relaxation time (T₂) and the transverse relaxation time derived from the observed line-width (T₂(⁎)). PMID:25910551
Phase diagram of the three-dimensional axial next-nearest-neighbor Ising model
NASA Astrophysics Data System (ADS)
Gendiar, A.; Nishino, T.
2005-01-01
The three-dimensional axial next-nearest-neighbor Ising model is studied by a modified tensor product variational approach. A global phase diagram is constructed with numerous commensurate and incommensurate magnetic phases. The devil’s stairs behavior for the model is confirmed. The wavelength of the spin modulated phases increases to infinity at the boundary with the ferromagnetic phase. Widths of the commensurate phases are considerably narrower than those calculated by mean-field approximations.
Gradient parameter and axial and field rays in the gradient-index crystalline lens model
NASA Astrophysics Data System (ADS)
Pérez, M. V.; Bao, C.; Flores-Arias, M. T.; Rama, M. A.; Gómez-Reino, C.
2003-09-01
Gradient-index models of the human lens have received wide attention in optometry and vision sciences for considering how changes in the refractive index profile with age and accommodation may affect refractive power. This paper uses the continuous asymmetric bi-elliptical model to determine gradient parameter and axial and field rays of the human lens in order to study the paraxial propagation of light through the crystalline lens of the eye.
Rare top quark decays in Alternative Left-Right Symmetric Models
Gaitan, R.; Miranda, O. G.; Cabral-Rosetti, L. G.
2007-06-19
We evaluate the flavor changing neutral currents (FCNC) decay t {yields} H0 + c in the context of Alternative Left-Right symmetric Models (ALRM) with extra isosinglet heavy fermions; the FCNC decays may place at tree level and are only supressed by the mixing between ordinary top and charm quarks. We also comment on the decay process t {yields} c + {gamma}, which involves radiative corrections.
An improved computer model for prediction of axial gas turbine performance losses
NASA Technical Reports Server (NTRS)
Jenkins, R. M.
1984-01-01
The calculation model performs a rapid preliminary pitchline optimization of axial gas turbine annular flowpath geometry, as well as an initial estimate of blade profile shapes, given only a minimum of thermodynamic cycle requirements. No geometric parameters need be specified. The following preliminary design data are determined: (1) the optimum flowpath geometry, within mechanical stress limits; (2) initial estimates of cascade blade shapes; and (3) predictions of expected turbine performance. The model uses an inverse calculation technique whereby blade profiles are generated by designing channels to yield a specified velocity distribution on the two walls. Velocity distributions are then used to calculate the cascade loss parameters. Calculated blade shapes are used primarily to determine whether the assumed velocity loadings are physically realistic. Model verification is accomplished by comparison of predicted turbine geometry and performance with an array of seven NASA single-stage axial gas turbine configurations.
Momentos centrados en sistemas estelares a simetria axial.
NASA Astrophysics Data System (ADS)
Sanz Subirana, J.; Juan Zornoza, J. M.; Català Poch, M. A.
Centered moments in the galactic plane have been analytically determined up to the fourth order for a non-stationary stellar system model with a distribution of peculiar velocities of the stars symmetric under point-axial transformations and equatorial plane reflexions. The obtained results explain satisfactorily the peculiar velocities distribution of the considered stellar samples in the solar neighborhood.
Symmetrizing the symmetrization postulate
NASA Astrophysics Data System (ADS)
York, Michael
2000-11-01
Reasonable requirements of (a) physical invariance under particle permutation and (b) physical completeness of state descriptions [1], enable us to deduce a Symmetric Permutation Rule(SPR): that by taking care with our state descriptions, it is always possible to construct state vectors (or wave functions) that are purely symmetric under pure permutation for all particles, regardless of type distinguishability or spin. The conventional exchange antisymmetry for two identical half-integer spin particles is shown to be due to a subtle interdependence in the individual state descriptions arising from an inherent geometrical asymmetry. For three or more such particles, however, antisymmetrization of the state vector for all pairs simultaneously is shown to be impossible and the SPR makes observably different predictions, although the usual pairwise exclusion rules are maintained. The usual caveat of fermion antisymmetrization—that composite integer spin particles (with fermionic constituents) behave only approximately like bosons—is no longer necessary.
Cylindrically symmetric models of gravitational collapse to black holes: A short review
NASA Astrophysics Data System (ADS)
Mena, Filipe C.
2015-07-01
We survey results about exact cylindrically symmetric models of gravitational collapse in General Relativity. We focus on models which result from the matching of two spacetimes having collapsing interiors which develop trapped surfaces and vacuum exteriors containing gravitational waves. We collect some theorems from the literature which help to decide a priori about eventual spacetime matchings. We revise, in more detail, some toy models which include some of the main mathematical and physical issues that arise in this context, and compute the gravitational energy flux through the matching boundary of a particular collapsing region. Along the way, we point out several interesting open problems.
Dimensional reduction of symmetric gauge fields, Higgs models, and spontaneous compactification
Volobuev, I.P.; Kubyshin, Y.A. ); Mourao, J.M. ); Rudolph, G. )
1989-05-01
Questions relating to the dimensional reduction of symmetric gauge fields in multidimensional spaces of the form {ital E}={ital M}{times}{ital G}/{ital H} are discussed. For such fields a general geometrical method of dimensional reduction and a method for calculating the potentials of the scalar fields of the reduced theory in the case of symmetric spaces {ital G}/{ital H} are presented systematically. The connection between dimensional reduction of gauge fields and the theory of spontaneous compactification and the physical interpretation of the solutions of this theory is traced in detail. Much attention is devoted to the application of the method of dimensional reduction to fermion matter fields and to the construction by this method of realistic models of the interactions of elementary particles in Minkowski space.
NASA Astrophysics Data System (ADS)
Kimura, Yusuke
2015-07-01
It has been understood that correlation functions of multi-trace operators in SYM can be neatly computed using the group algebra of symmetric groups or walled Brauer algebras. On the other hand, such algebras have been known to construct 2D topological field theories (TFTs). After reviewing the construction of 2D TFTs based on symmetric groups, we construct 2D TFTs based on walled Brauer algebras. In the construction, the introduction of a dual basis manifests a similarity between the two theories. We next construct a class of 2D field theories whose physical operators have the same symmetry as multi-trace operators constructed from some matrices. Such field theories correspond to non-commutative Frobenius algebras. A matrix structure arises as a consequence of the noncommutativity. Correlation functions of the Gaussian complex multi-matrix models can be translated into correlation functions of the two-dimensional field theories.
X-ray resonance scattering in a spherically symmetric coronal model
NASA Technical Reports Server (NTRS)
Haisch, B. M.; Claflin, E. S.
1985-01-01
In the solar corona the opacities of some of the prominent X-ray emission lines are on the order of tau of about I over typical coronal path lengths. A particular solution of the radiative transfer problem involving an extended, spherically symmetric coronal shell radiating isotropic, homogeneous emission in which single-scattering also takes place is presented and discussed. Within the context of this simplified model, it is found that scattered radiation is an important contribution to the total emergent resonance line flux and that for the He-like family of resonance (r), intercombination (i), and forbidden (f) lines, the ratio G = (f + i)/r would decrease as a function of optical depth for disk-center emission in an extended spherically symmetric corona.
NASA Astrophysics Data System (ADS)
Kirschner, O.; Ruprecht, A.; Riedelbauch, S.
2014-03-01
In hydropower plants the axial thrust bearing takes up the hydraulic axial thrust of the runner and, in case of vertical shafts, the entire weight of all rotating masses. The use of water lubricated bearings can eliminate the oil leakage risk possibly contaminating the environment. A complex flow is generated by the smaller film thickness due to the lower viscosity of water compared with oil. Measurements on a simplified hydrostatic axial trust bearing model were accomplished for validating CFD analysis of water lubricated bearings. In this simplified model, fixed pads are implemented and the width of the gap was enlarged to create a higher resolution in space for the measurements. Most parts of the model were manufactured from acrylic glass to get optical access for measurement with PIV. The focus of these measurements is on the flow within the space between two pads. Additional to the PIV- measurement, the pressure on the wall of the rotating disk is captured by pressure transducers. The model bearing measurement results are presented for varied operating conditions.
Plate fin heat exchanger model with axial conduction and variable properites
NASA Astrophysics Data System (ADS)
Hansen, Benjamin Jacob; White, Michael Joseph; Klebaner, Arkadiy
2012-06-01
Future superconduction radio frequency (SRF) cavities, as part of Project X at Fermilab,will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchanger are an effective option. However, at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numberical model that includes the effects of axial guide design decisions on heat exhanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters.
A mathematical model of the controlled axial flow divider for mobile machines
NASA Astrophysics Data System (ADS)
Mulyukin, V. L.; Karelin, D. L.; Belousov, A. M.
2016-06-01
The authors give a mathematical model of the axial adjustable flow divider allowing one to define the parameters of the feed pump and the hydraulic motor-wheels in the multi-circuit hydrostatic transmission of mobile machines, as well as for example built features that allows to clearly evaluate the mutual influence of the values of pressure and flow on all input and output circuits of the system.
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.
NASA Astrophysics Data System (ADS)
Reddy, D. R. K.; Raju, P.; Sobhanbabu, K.
2016-04-01
Five dimensional spherically symmetric space-time filled with two minimally interacting fields; matter and holographic dark energy components is investigated in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). To obtain a determinate solution of the highly non-linear field equations we have used (i) a relation between metric potentials and (ii) an equation of state which represents disordered radiation in five dimensional universe. The solution obtained represents a minimally interacting and radiating holographic dark energy model in five dimensional universe. Some physical and Kinematical properties of the model are, also, studied.
The symmetric six-vertex model and the Segre cubic threefold
NASA Astrophysics Data System (ADS)
Martins, M. J.
2015-08-01
In this paper we investigate the mathematical properties of the integrability of the symmetric six-vertex model towards the view of algebraic geometry. We show that the algebraic variety originated from Baxter’s commuting transfer method is birationally isomorphic to a ubiquitous threefold known as Segre cubic primal. This relation makes it possible to present the most generic solution for the Yang-Baxter triple associated to this lattice model. The respective R-matrix and Lax operators are parameterized by three independent affine spectral variables.
Discrete-vortex model for the symmetric-vortex flow on cones
NASA Technical Reports Server (NTRS)
Gainer, Thomas G.
1990-01-01
A relatively simple but accurate potential flow model was developed for studying the symmetric vortex flow on cones. The model is a modified version of the model first developed by Bryson, in which discrete vortices and straight-line feeding sheets were used to represent the flow field. It differs, however, in the zero-force condition used to position the vortices and determine their circulation strengths. The Bryson model imposed the condition that the net force on the feeding sheets and discrete vortices must be zero. The proposed model satisfies this zero-force condition by having the vortices move as free vortices, at a velocity equal to at the local crossflow velocity at their centers. When the free-vortex assumption is made, a solution is obtained in the form of two nonlinear algebraic equations that relate the vortex center coordinates and vortex strengths to the cone angle and angle of attack. The vortex center locations calculated using the model are in good agreement with experimental values. The cone normal forces as well as center locations are in good agreement with the vortex cloud method of calculating symmetric flow fields.
A model of unsteady spatially inhomogeneous flow in a radial-axial blade machine
NASA Astrophysics Data System (ADS)
Ambrozhevich, A. V.; Munshtukov, D. A.
A two-dimensional model of the gasdynamic process in a radial-axial blade machine is proposed which allows for the instantaneous local state of the field of flow parameters, changes in the set angles along the median profile line, profile losses, and centrifugal and Coriolis forces. The model also allows for the injection of cooling air and completion of fuel combustion in the flow. The model is equally applicable to turbines and compressors. The use of the method of singularities provides for a unified and relatively simple description of various factors affecting the flow and, therefore, for computational efficiency.
Double seesaw mechanism in a left-right symmetric model with TeV neutrinos
Almeida, F. M. L. Jr. de; Coutinho, Y. A.; Simoes, J. A. Martins; Ramalho, A. J.; Pinto, L. Ribeiro; Wulck, S.; Vale, M. A. B. do
2010-03-01
A left-right symmetric model is discussed with new mirror fermions and a Higgs sector with two doublets and neutral scalar singlets. The seesaw mechanism is generalized, including not only neutrino masses but also charged fermion masses. The spectrum of heavy neutrinos presents a second seesaw mass matrix and has neutrinos masses naturally in the TeV region. The model has very clear signatures for the new neutral vector gauge bosons. Two classes of models are discussed. New mirror neutrinos can be very light and a new Z{sup '} can be discriminated from other models by a very high invisible branching fraction. The other possibility is that mirror neutrinos can have masses naturally in the TeV region and can be produced through Z{sup '} decays into heavy neutrino pairs. Signatures and production processes for the model at the LHC energy are also presented.
Analysis of Growth and Decay Rates of the Axial Dipole in Geodynamo Models
NASA Astrophysics Data System (ADS)
Avery, M. S.; Constable, C.; Davies, C.; Gubbins, D.
2013-12-01
Observations of the Earth's magnetic field made at the surface reveal temporal variations in the field originating in the outer core. PADM2M is a reconstruction of the 0 to 2 Ma paleomagnetic axial dipole moment. Ziegler & Constable, 2011 showed that for periods longer than 25 kyr the rate of growth of the geomagnetic dipole is greater than its decay rate. This asymmetry is not limited to times when the field is reversing; this may be indicative of a key physical process of secular variation. To investigate the possible core processes underlying this observation we have analyzed a suite of numerical dynamo simulations, specifically the temporal variation of their axial dipole moments. We use the magnetic diffusion time to scale the simulations' nondimensional time, as this is more appropriate for the periods of interest here. An advantage to analyzing simulations is that they do not suffer from the same limitations in spatial and temporal resolution as the data; however, simulations cannot yet run with Earth-like rotational rates or diffusivities. All of our simulations span multiple diffusion times. We have chosen a broad range of simulations with different reversal regimes (dipole-dominated, non-reversing; dipole-dominated, reversing; multipolar, reversing) and with different heating modes (bottom, internal, or a combination of the two). For each simulation we conduct the same analysis that was applied to PADM2M. Families of smoothed axial dipole models are constructed using penalized smoothing splines as an effective low-pass filter to see at what timescales any asymmetry exist. The first derivatives of each axial dipole record are calculated in order to examine the rates of growth and decay. The results vary with the nature of the simulations. Further analysis is needed to determine what dynamo parameters, and related physical properties, determine the relative rates of growth and decay.
Connecting Dirac and Majorana neutrino mass matrices in the minimal left-right symmetric model.
Nemevšek, Miha; Senjanović, Goran; Tello, Vladimir
2013-04-12
Probing the origin of neutrino mass by disentangling the seesaw mechanism is one of the central issues of particle physics. We address it in the minimal left-right symmetric model and show how the knowledge of light and heavy neutrino masses and mixings suffices to determine their Dirac Yukawa couplings. This in turn allows one to make predictions for a number of high and low energy phenomena, such as decays of heavy neutrinos, neutrinoless double beta decay, electric dipole moments of charged leptons, and neutrino transition moments. We also discuss a way of reconstructing the neutrino Dirac Yukawa couplings at colliders such as the LHC. PMID:25167249
Magnetic moment of the majorana neutrino in the left-right symmetric model
Boyarkin, O. M. Boyarkina, G. G.
2013-04-15
Corrections to the neutrino magnetic dipole moment from the singly charged Higgs bosons h{sup ({+-})} and {delta}-tilde{sup (}{+-}) were calculated within the left-right symmetric model involving Majorana neutrinos. It is shown that, if the h{sup ({+-})} and {delta}-tilde{sup (}{+-}) bosons lie at the electroweak scale, the contributions from Higgs sector are commensurate with the contribution of charged gauge bosons or may even exceed it. The behavior of the neutrino flux inmatter and in amagnetic field was studied. It was found that resonance transitions between light and heavy neutrinos are forbidden.
Exact Solution of the Gauge Symmetric p-Spin Glass Model on a Complete Graph
NASA Astrophysics Data System (ADS)
Korada, Satish Babu; Macris, Nicolas
2009-07-01
We consider a gauge symmetric version of the p-spin glass model on a complete graph. The gauge symmetry guarantees the absence of replica symmetry breaking and allows to fully use the interpolation scheme of Guerra (Fields Inst. Commun. 30:161, 2001) to rigorously compute the free energy. In the case of pairwise interactions ( p=2), where we have a gauge symmetric version of the Sherrington-Kirkpatrick model, we get the free energy and magnetization for all values of external parameters. Our analysis also works for even p≥4 except in a range of parameters surrounding the phase transition line, and for odd p≥3 in a more restricted region. We also obtain concentration estimates for the magnetization and overlap parameter that play a crucial role in the proofs for odd p and justify the absence of replica symmetry breaking. Our initial motivation for considering this model came from problems related to communication over a noisy channel, and is briefly explained.
Next-to-minimal R-symmetric model: Dirac gaugino, Higgs mass and invisible width
NASA Astrophysics Data System (ADS)
Nakano, Hiroaki; Yoshikawa, Masaki
2016-03-01
We study a singlet extension of the minimal {U(1)}_R symmetric model, which shares the nice properties of Dirac gauginos and the R-symmetric Higgs sector. At the same time, a superpotential coupling of an R-charged singlet to the Higgs doublets can make a substantial contribution to the Higgs boson mass. We show that the 125 GeV Higgs boson is consistent with perturbative unification, even if the SUSY scale is as low as 1 TeV and if the D-term Higgs potential is suppressed, as is often the case in Dirac gauginos. The model also contains a light scalar and fermion, a pseudo-modulus and pseudo-goldstino: The former gets its mass mainly from SUSY-breaking soft terms, in addition to a small explicit R-symmetry breaking for the latter. We examine how the Higgs mass and width are affected by these light degrees of freedom. Specifically, we find that, depending on the parameters of R-charged Higgses, a pseudo-moduli lighter than half of the Standard Model Higgs boson mass is still allowed by the constraints from invisible decays of the Z and Higgs bosons. We also find that such a light scalar can reduce the Higgs boson mass, at most by a few percents.
Effects of CDTT model on the dynamical instability of cylindrically symmetric collapsing stars
Kausar, Hafiza Rizwana
2013-01-01
We assume cylindrically symmetric stars which begin collapsing by dissipating energy in the form of heat flux. We wish to study the effects of Carroll-Duvvuri-Trodden-Turner (CDTT) model, f(R) = R+σμ{sup 4}/R, on the range of dynamical instability. For this purpose, perturbation scheme is applied to all the metric functions, material functions and f(R) model to obtain the full set of dynamical equation which control the evolution of the physical variables at the surface of a star. It is found that instability limit involves adiabatic index Γ which depends on the density profile and immense terms of perturbed CDTT model. In addition, model is constrained by some requirement, e.g. positivity of physical quantities. We also reduce our results asymptotically as μ→0, being the GR results in both the Newtonian and post Newtonian regimes.
Hydrogen turbines for space power systems: A simplified axial flow gas turbine model
NASA Technical Reports Server (NTRS)
Hudson, Steven L.
1988-01-01
Hydrogen cooled, turbine powered space weapon systems require a relatively simple, but reasonably accurate hydrogen gas expansion turbine model. Such a simplified turbine model would require little computational time and allow incorporation into system level computer programs while providing reasonably accurate volume/mass estimates. This model would then allow optimization studies to be performed on multiparameter space power systems and provide improved turbine mass and size estimates for the various operating conditions (when compared to empirical and power law approaches). An axial flow gas expansion turbine model was developed for these reasons and is in use as a comparative bench mark in space power system studies at Sandia. The turbine model is based on fluid dynamic, thermodynamic, and material strength considerations, but is considered simplified because it does not account for design details such as boundary layer effects, shock waves, turbulence, stress concentrations, and seal leakage. Although the basic principles presented here apply to any gas or vapor axial flow turbine, hydrogen turbines are discussed because of their immense importance on space burst power platforms.
Study of lepton flavor violation in flavor symmetric models for lepton sector
NASA Astrophysics Data System (ADS)
Kobayashi, Tatsuo; Omura, Yuji; Takayama, Fumihiro; Yasuhara, Daiki
2015-10-01
Flavor symmetric model is one of the attractive Beyond Standard Models (BSMs) to reveal the flavor structure of the Standard Model (SM). A lot of efforts have been put into the model building and we find many kinds of flavor symmetries and setups are able to explain the observed fermion mass matrices. In this paper, we look for common predictions of physical observables among the ones in flavor symmetric models, and try to understand how to test flavor symmetry in experiments. Especially, we focus on the BSMs for leptons with extra Higgs SU(2) L doublets charged under flavor symmetry. In many flavor models for leptons, remnant symmetry is partially respected after the flavor symmetry breaking, and it controls well the Flavor Changing Neutral Currents (FCNCs) and suggests some crucial predictions against the flavor changing process, although the remnant symmetry is not respected in the full lagrangian. In fact, we see that τ - → e + μ - μ - ( μ + e - e -) and e + e - → τ + τ - ( μ - μ +) processes are the most important in the flavor models that the extra Higgs doublets belong to triplet representation of flavor symmetry. For instance, the stringent constraint from the μ → eγ process could be evaded according to the partial remnant symmetry. We also investigate the breaking effect of the remnant symmetry mediated by the Higgs scalars, and investigate the constraints from the flavor physics: the flavor violating τ and μ decays, the electric dipole moments, and the muon anomalous magnetic moment. We also discuss the correlation between FCNCs and nonzero θ 13, and point out the physical observables in the charged lepton sector to test the BSMs for the neutrino mixing.
Model-size reduction technique for the analysis of symmetric anisotropic structures
NASA Technical Reports Server (NTRS)
Noor, A. K.; Peters, J. M.
1985-01-01
A two-step computational procedure is presented for reducing the size of the analysis model for an anisotropic symmetric structure to that of the corresponding orthotropic structure. The key elements of the procedure are: (1) decomposition of the stiffness matrix into the sum of an orthotropic and nonorthotropic (anisotropic) parts; and (2) successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite element method is first used to generate few global approximation vectors (or modes). Then the amplitudes of these modes are computed by using the Rayleigh-Ritz technique. The global approximation vectors are selected to be the solution corresponding to zero nonorthotropic matrix and its various-order derivatives with respect to an anisotropic tracing parameter (identifying the nonorthotropic material coefficients). The size of the analysis model used in generating the global approximation vectors is identical to that of the corresponding orthotropic structure. The effectiveness of the proposed technique is demonstrated by means of numerical examples and its potential for solving other quasi-symmetric problems is discussed.
Axially Symmetric Brans-Dicke-Maxwell Solutions
NASA Astrophysics Data System (ADS)
Chatterjee, S.
1981-05-01
Following a method of John and Goswami new solutions of coupled Brans-Dicke-Maxwell theory are generated from Zipoy's solutions in oblate and prolate spheroidal coordinates for source-free gravitational field. All these solutions become Euclidean at infinity. The asymptotic behavior and the singularity of the solutions are discussed and a comparative study made with the corresponding Einstein-Maxwell solutions. The possibility of a very large red shift from the boundary of the spheroids is also discussed.
Axial and diffusion models of the laser pulse propagation in a highly-scattering medium
Tereshchenko, Sergei A; Danilov, Arsenii A; Podgaetskii, Vitalii M; Vorob'ev, Nikolai S
2004-06-30
The propagation of laser radiation through a layer of a highly-scattering medium (HSM) is considered on the basis of two theoretical models: a nonstationary axial (two-flux) model and a nonstationary diffusion model. Analytic expressions for the temporal distributions of the photons of an ultrashort laser pulse transmitted through the HSM are presented. Experimental temporal distributions are used to obtain the parameters of models corresponding to an HSM, to determine the theoretical temporal distributions, and to compare them with the experimental curves. These two theoretical models are compared quantitatively for the first time. Their advantages and drawbacks that must be considered in the development of HSM transmission optical tomography are pointed out. (light scattering)
Relaxed singular vectors, Jack symmetric functions and fractional level sl ˆ (2) models
NASA Astrophysics Data System (ADS)
Ridout, David; Wood, Simon
2015-05-01
The fractional level models are (logarithmic) conformal field theories associated with affine Kac-Moody (super)algebras at certain levels k ∈ Q. They are particularly noteworthy because of several longstanding difficulties that have only recently been resolved. Here, Wakimoto's free field realisation is combined with the theory of Jack symmetric functions to analyse the fractional level sl ˆ (2) models. The first main results are explicit formulae for the singular vectors of minimal grade in relaxed Wakimoto modules. These are closely related to the minimal grade singular vectors in relaxed (parabolic) Verma modules. Further results include an explicit presentation of Zhu's algebra and an elegant new proof of the classification of simple relaxed highest weight modules over the corresponding vertex operator algebra. These results suggest that generalisations to higher rank fractional level models are now within reach.
Inspiratory and expiratory steady flow analysis in a model symmetrically bifurcating airway.
Zhao, Y; Brunskill, C T; Lieber, B B
1997-02-01
Steady inspiratory and expiratory flow in a symmetrically bifurcating airway model was studied numerically using the finite element method (FIDAP). Flows of Reynolds number of 500 and 1000 during inspiration and a flow of Reynolds number of 500 during expiration were analyzed. Since the geometry of the bifurcation model used in this study is exactly the same as the model used in the experimental studies, the computed results were compared to the experimental findings. Results show that most of the important flow features that were observed in the experiment, such as the skewed velocity profiles in the daughter branches during inspiration and velocity peak in the parent tube during expiration, were captured in the numerical simulation. Quantitatively, the computed velocity profiles are in good agreement with the measured profiles. This comparison validates the computational simulations. PMID:9083849
Modeling Improvements and Users Manual for Axial-flow Turbine Off-design Computer Code AXOD
NASA Technical Reports Server (NTRS)
Glassman, Arthur J.
1994-01-01
An axial-flow turbine off-design performance computer code used for preliminary studies of gas turbine systems was modified and calibrated based on the experimental performance of large aircraft-type turbines. The flow- and loss-model modifications and calibrations are presented in this report. Comparisons are made between computed performances and experimental data for seven turbines over wide ranges of speed and pressure ratio. This report also serves as the users manual for the revised code, which is named AXOD.
Measurement of velocity deficit at the downstream of a 1:10 axial hydrokinetic turbine model
Gunawan, Budi; Neary, Vincent S; Hill, Craig; Chamorro, Leonardo
2012-01-01
Wake recovery constrains the downstream spacing and density of turbines that can be deployed in turbine farms and limits the amount of energy that can be produced at a hydrokinetic energy site. This study investigates the wake recovery at the downstream of a 1:10 axial flow turbine model using a pulse-to-pulse coherent Acoustic Doppler Profiler (ADP). In addition, turbine inflow and outflow velocities were measured for calculating the thrust on the turbine. The result shows that the depth-averaged longitudinal velocity recovers to 97% of the inflow velocity at 35 turbine diameter (D) downstream of the turbine.
Analytical modeling of the buffeting of a rod in axial flow. [PWR; BWR
Lin, W.H.; Wamsganss, M.W.
1981-12-01
Turbulent buffeting of a circular, flexible rod in axial flows is reported. The main excitation mechanisms are turbulent wall-pressure fluctuations and the motion-dependent force field caused by the rod motion. On the assumption that the turbulent wall-pressure fluctuations are independent of rod motion, a linear forced vibration model is proposed to compute the buffeting displacement of the rod with the aid of empirical constants determined from experimental measurements of wall-pressure fluctuations. Predicted and measured values of the root-mean-square rod displacement are shown to be in reasonably good agreement.
Scalar mesons in a linear sigma model with (axial-)vector mesons
Parganlija, D.; Kovacs, P.; Wolf, Gy.; Giacosa, F.; Rischke, D. H.
2013-03-25
The structure of the scalar mesons has been a subject of debate for many decades. In this work we look for qq states among the physical resonances using an extended Linear Sigma Model that contains scalar, pseudoscalar, vector, and axial-vector mesons both in the non-strange and strange sectors. We perform global fits of meson masses, decay widths and amplitudes in order to ascertain whether the scalar qq states are below or above 1 GeV. We find the scalar states above 1 GeV to be preferred as qq states.
GPS Modeling and Analysis. Summary of Research: GPS Satellite Axial Ratio Predictions
NASA Technical Reports Server (NTRS)
Axelrad, Penina; Reeh, Lisa
2002-01-01
This report outlines the algorithms developed at the Colorado Center for Astrodynamics Research to model yaw and predict the axial ratio as measured from a ground station. The algorithms are implemented in a collection of Matlab functions and scripts that read certain user input, such as ground station coordinates, the UTC time, and the desired GPS (Global Positioning System) satellites, and compute the above-mentioned parameters. The position information for the GPS satellites is obtained from Yuma almanac files corresponding to the prescribed date. The results are displayed graphically through time histories and azimuth-elevation plots.
3D shape analysis of the brain's third ventricle using a midplane encoded symmetric template model
Kim, Jaeil; Valdés Hernández, Maria del C.; Royle, Natalie A.; Maniega, Susana Muñoz; Aribisala, Benjamin S.; Gow, Alan J.; Bastin, Mark E.; Deary, Ian J.; Wardlaw, Joanna M.; Park, Jinah
2016-01-01
Background Structural changes of the brain's third ventricle have been acknowledged as an indicative measure of the brain atrophy progression in neurodegenerative and endocrinal diseases. To investigate the ventricular enlargement in relation to the atrophy of the surrounding structures, shape analysis is a promising approach. However, there are hurdles in modeling the third ventricle shape. First, it has topological variations across individuals due to the inter-thalamic adhesion. In addition, as an interhemispheric structure, it needs to be aligned to the midsagittal plane to assess its asymmetric and regional deformation. Method To address these issues, we propose a model-based shape assessment. Our template model of the third ventricle consists of a midplane and a symmetric mesh of generic shape. By mapping the template's midplane to the individuals’ brain midsagittal plane, we align the symmetric mesh on the midline of the brain before quantifying the third ventricle shape. To build the vertex-wise correspondence between the individual third ventricle and the template mesh, we employ a minimal-distortion surface deformation framework. In addition, to account for topological variations, we implement geometric constraints guiding the template mesh to have zero width where the inter-thalamic adhesion passes through, preventing vertices crossing between left and right walls of the third ventricle. The individual shapes are compared using a vertex-wise deformity from the symmetric template. Results Experiments on imaging and demographic data from a study of aging showed that our model was sensitive in assessing morphological differences between individuals in relation to brain volume (i.e. proxy for general brain atrophy), gender and the fluid intelligence at age 72. It also revealed that the proposed method can detect the regional and asymmetrical deformation unlike the conventional measures: volume (median 1.95 ml, IQR 0.96 ml) and width of the third
NASA Astrophysics Data System (ADS)
Kenkmann, Thomas; Hergarten, Stefan; Kuhn, Thomas; Wilk, Jakob
2016-08-01
Several models of shatter cone formation require a heterogeneity at the cone apex of high impedance mismatch to the surrounding bulk rock. This heterogeneity is the source of spherically expanding waves that interact with the planar shock front or the following release wave. While these models are capable of explaining the overall conical shape of shatter cones, they are not capable of explaining the subcone structure and the diverging and branching striations that characterize the surface of shatter cones and lead to the so-called horse-tailing effect. Here, we use the hierarchical arrangement of subcone ridges of shatter cone surfaces as key for understanding their formation. Tracing a single subcone ridge from its apex downward reveals that each ridge branches after some distance into two symmetrically equivalent subcone ridges. This pattern is repeated to form new branches. We propose that subcone ridges represent convex-curved fracture surfaces and their intersection corresponds to the bifurcation axis. The characteristic diverging striations are interpreted as the intersection lineations delimiting each subcone. Multiple symmetric crack branching is the result of rapid fracture propagation that may approach the Raleigh wave speed. We present a phenomenological model that fully constructs the shatter cone geometry to any order. The overall cone geometry including apex angle of the enveloping cone and the degree of concavity (horse-tailing) is largely governed by the convexity of the subcone ridges. Straight cones of various apical angles, constant slope, and constant bifurcation angles form if the subcone convexity is low (30°). Increasing subcone convexity leads to a stronger horse-tailing effect and the bifurcation angles increase with increasing distance from the enveloping cone apex. The model predicts possible triples of enveloping cone angle, bifurcation angle, and subcone angle. Measurements of these quantities on four shatter cones from different
Modeling the antisymmetric and symmetric stretching vibrational modes of aqueous carboxylate anions.
Sutton, Catherine C R; Franks, George V; da Silva, Gabriel
2015-01-01
The infrared spectra of six aqueous carboxylate anions have been calculated at the M05-2X/cc-pVTZ level of theory with the SMD solvent model, and validated against experimental data from the literature over the region of 1700 cm(-1) to 1250 cm(-1); this region corresponds to the stretching modes of the carboxylate group, and is often interrogated when probing bonding of carboxylates to other species and surfaces. The anions studied here were formate, acetate, oxalate, succinate, glutarate and citrate. For the lowest energy conformer of each anion, the carboxylate moiety antisymmetric stretching peak was predicted with a mean signed error of only 4 cm(-1) using the SMD solvent model, while the symmetric peak was slightly overestimated. Performing calculations in vacuum and scaling was found to generally over-predict the antisymmetric vibrational frequencies and under predict the symmetric peak. Different conformers of the same anion were found to have only slightly different spectra in the studied region and the inclusion of explicit water molecules was not found to significantly change the calculated spectra when the implicit solvent model is used. Overall, the use of density functional theory in conjunction with an implicit solvent model was found to result in infra-red spectra that are the best reproduction of the features found experimentally for the aqueous carboxylate ions in the important 1700 cm(-1) to 1250 cm(-1) region. The development of validated model chemistries for simulating the stretching modes of aqueous carboxylate ions will be valuable for future studies that investigate how carboxylate anions complex with multivalent metal cations and related species in solution. PMID:25048288
Spectral and transport properties of the PT-symmetric dimer model
NASA Astrophysics Data System (ADS)
Vázquez-Candanedo, O.; Izrailev, F. M.; Christodoulides, D. N.
2015-08-01
We study the scattering properties of the PT-symmetric tight-binding model with balanced gain and loss parameters. Our main interest is to establish the link between the spectral properties of scattering states and transport characteristics for the case of non-equal couplings between gain/loss sites. The analytical approach we have used allows one to reveal a quite unexpected role of this set-up in comparison with that of equal couplings. In particular, we demonstrate that for the exceptional points characterized by equal eigenvalues of the transfer matrix, the transmission coefficient can be different from one in contrast with the model with equal couplings. The analytical results are complemented by the numerical data.
Lepton flavor violating τ decays in the left-right symmetric model
NASA Astrophysics Data System (ADS)
Akeroyd, A. G.; Aoki, Mayumi; Okada, Yasuhiro
2007-07-01
The left-right symmetric extension of the standard model with Higgs isospin triplets can provide neutrino masses via a TeV scale seesaw mechanism. The doubly charged Higgs bosons HL±± and HR±± induce lepton flavor violating decays τ±→lll at tree level via a coupling which is related to the Maki-Nakagawa-Sakata matrix (VMNS). We study the magnitude and correlation of τ±→lll and μ→eγ with specific assumptions for the origin of the large mixing in VMNS while respecting the stringent bound for μ→eee. It is also shown that an angular asymmetry for τ±→lll is sensitive to the relative strength of the HL±± and HR±± mediated contributions and provides a means of distinguishing models with doubly charged Higgs bosons.
A two-dimensional (azimuthal-axial) particle-in-cell model of a Hall thruster
Coche, P.; Garrigues, L.
2014-02-15
We have developed a two-dimensional Particle-In-Cell model in the azimuthal and axial directions of the Hall thruster. A scaling method that consists to work at a lower plasma density to overcome constraints on time-step and grid-spacing is used. Calculations are able to reproduce the breathing mode due to a periodic depletion of neutral atoms without the introduction of a supplementary anomalous mechanism, as in fluid and hybrid models. Results show that during the increase of the discharge current, an electron-cyclotron drift instability (frequency in the range of MHz and wave number on the order of 3000 rad s{sup −1}) is formed in the region of the negative gradient of magnetic field. During the current decrease, an axial electric wave propagates from the channel toward the exhaust (whose frequency is on the order of 400 kHz) leading to a broadening of the ion energy distribution function. A discussion about the influence of the scaling method on the calculation results is also proposed.
Analysis Of Residence Time Distribution Of Fluid Flow By Axial Dispersion Model
Sugiharto; Su'ud, Zaki; Kurniadi, Rizal; Waris, Abdul; Abidin, Zainal
2010-12-23
Radioactive tracer {sup 82}Br in the form of KBr-82 with activity {+-} 1 mCi has been injected into steel pipeline to qualify the extent dispersion of water flowing inside it. Internal diameter of the pipe is 3 in. The water source was originated from water tank through which the water flow gravitically into the pipeline. Two collimated sodium iodide detectors were used in this experiment each of which was placed on the top of the pipeline at the distance of 8 and 11 m from injection point respectively. Residence time distribution (RTD) curves obtained from injection of tracer are elaborated numerically to find information of the fluid flow properties. The transit time of tracer calculated from the mean residence time (MRT) of each RTD curves is 14.9 s, therefore the flow velocity of the water is 0.2 m/s. The dispersion number, D/uL, for each RTD curve estimated by using axial dispersion model are 0.055 and 0.06 respectively. These calculations are performed after fitting the simulated axial dispersion model on the experiment curves. These results indicated that the extent of dispersion of water flowing in the pipeline is in the category of intermediate.
Analysis Of Residence Time Distribution Of Fluid Flow By Axial Dispersion Model
NASA Astrophysics Data System (ADS)
Sugiharto, Su'ud, Zaki; Kurniadi, Rizal; Waris, Abdul; Abidin, Zainal
2010-12-01
Radioactive tracer 82Br in the form of KBr-82 with activity ± 1 mCi has been injected into steel pipeline to qualify the extent dispersion of water flowing inside it. Internal diameter of the pipe is 3 in. The water source was originated from water tank through which the water flow gravitically into the pipeline. Two collimated sodium iodide detectors were used in this experiment each of which was placed on the top of the pipeline at the distance of 8 and 11 m from injection point respectively. Residence time distribution (RTD) curves obtained from injection of tracer are elaborated numerically to find information of the fluid flow properties. The transit time of tracer calculated from the mean residence time (MRT) of each RTD curves is 14.9 s, therefore the flow velocity of the water is 0.2 m/s. The dispersion number, D/uL, for each RTD curve estimated by using axial dispersion model are 0.055 and 0.06 respectively. These calculations are performed after fitting the simulated axial dispersion model on the experiment curves. These results indicated that the extent of dispersion of water flowing in the pipeline is in the category of intermediate.
NASA Astrophysics Data System (ADS)
Cifra, M.; Havelka, D.; Deriu, M. A.
2011-12-01
Microtubules are electrically polar structures fulfilling prerequisites for generation of oscillatory electric field in the kHz to GHz region. Energy supply for excitation of elasto-electrical vibrations in microtubules may be provided from GTP-hydrolysis; motor protein-microtubule interactions; and energy efflux from mitochondria. It recently was determined from anisotropic elastic network modeling of entire microtubules that the frequencies of microtubule longitudinal axial eigenmodes lie in the region of tens of GHz for the physiologically common microtubule lengths. We calculated electric field generated by axial longitudinal vibration modes of microtubule, which model is based on subnanometer precision of charge distribution. Due to elastoelectric nature of the vibrations, the vibration wavelength is million-fold shorter than that of the electromagnetic field in free space and the electric field around the microtubule manifests rich spatial structure with multiple minima. The dielectrophoretic force exerted by electric field on the surrounding molecules will influence the kinetics of reactions via change in the probability of the transport of charge and mass particles. The electric field generated by vibrations of electrically polar cellular structures is expected to play a role in biological self-organization.
Physically-based reduced order modelling of a uni-axial polysilicon MEMS accelerometer.
Ghisi, Aldo; Mariani, Stefano; Corigliano, Alberto; Zerbini, Sarah
2012-01-01
In this paper, the mechanical response of a commercial off-the-shelf, uni-axial polysilicon MEMS accelerometer subject to drops is numerically investigated. To speed up the calculations, a simplified physically-based (beams and plate), two degrees of freedom model of the movable parts of the sensor is adopted. The capability and the accuracy of the model are assessed against three-dimensional finite element simulations, and against outcomes of experiments on instrumented samples. It is shown that the reduced order model provides accurate outcomes as for the system dynamics. To also get rather accurate results in terms of stress fields within regions that are prone to fail upon high-g shocks, a correction factor is proposed by accounting for the local stress amplification induced by re-entrant corners. PMID:23202031
Physically-Based Reduced Order Modelling of a Uni-Axial Polysilicon MEMS Accelerometer
Ghisi, Aldo; Mariani, Stefano; Corigliano, Alberto; Zerbini, Sarah
2012-01-01
In this paper, the mechanical response of a commercial off-the-shelf, uni-axial polysilicon MEMS accelerometer subject to drops is numerically investigated. To speed up the calculations, a simplified physically-based (beams and plate), two degrees of freedom model of the movable parts of the sensor is adopted. The capability and the accuracy of the model are assessed against three-dimensional finite element simulations, and against outcomes of experiments on instrumented samples. It is shown that the reduced order model provides accurate outcomes as for the system dynamics. To also get rather accurate results in terms of stress fields within regions that are prone to fail upon high-g shocks, a correction factor is proposed by accounting for the local stress amplification induced by re-entrant corners. PMID:23202031
Interpretation of the Palumbo model of two axial rotators in the microscopic approach
Filippov, G.F.; Dotsenko, I.S.
1994-12-01
The nuclear model of two axial rotators is interpreted as a generalization of the Elliott SU{sub 3} model. The basis of the latter is extended to the basis of the tensor product SU{sub 3} x SU{sub 3}. For this purpose, the second-order Casimir operator of the SU{sub 3} group is constructed, and its eigenfunctions are found in the explicit form. The probabilities of the isoscalar and isovector M1 and E2 electromagnetic transitions between nuclear states with the quantum numbers ({lambda},{mu}) = (2n,0) and ({lambda},{mu}) = (2n-2,1) are calculated using the microscopic wave functions of the model. The calculated values of the transition probabilities and widths of levels for {sup 8}Be and {sup 20}Ne nuclei are compared with the experimental data. 17 refs., 5 tabs.
Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties
Hansen, B.J.; White, M.J.; Klebaner, A.; /Fermilab
2011-06-10
Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters. A numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger was developed and the effect of various design parameters on overall heat exchanger size was investigated. It was found that highly conductive metals should be avoided in the design of compact JT heat exchangers. For the geometry considered, the optimal conductivity is around 3.5 W/m-K and can range from 0.3-10 W/m-K without a large loss in performance. The model was implemented with an isenthalpic expansion process. Increasing the cold side inlet temperature from 2K to 2.2 K decreased the liquid fraction from 0.856 to 0.839 which corresponds to a 0.12 g/s increase in supercritical helium supply needed to maintain liquid level in the cooling bath. Lastly, it was found that the effectiveness increased when the heat load was below the design value. Therefore, the heat exchanger
Annoni, Jennifer; Gebraad, Pieter M. O.; Scholbrock, Andrew K.; Fleming, Paul A.; Wingerden, Jan-Willem van
2015-08-14
Wind turbines are typically operated to maximize their performance without considering the impact of wake effects on nearby turbines. Wind plant control concepts aim to increase overall wind plant performance by coordinating the operation of the turbines. This paper focuses on axial-induction-based wind plant control techniques, in which the generator torque or blade pitch degrees of freedom of the wind turbines are adjusted. The paper addresses discrepancies between a high-order wind plant model and an engineering wind plant model. Changes in the engineering model are proposed to better capture the effects of axial-induction-based control shown in the high-order model.
Comparative analysis of Bouc-Wen and Jiles-Atherton models under symmetric excitations
NASA Astrophysics Data System (ADS)
Laudani, Antonino; Fulginei, Francesco Riganti; Salvini, Alessandro
2014-02-01
The aim of the present paper is to validate the Bouc-Wen (BW) hysteresis model when it is applied to predict dynamic ferromagnetic loops. Indeed, although the Bouc-Wen model has had an increasing interest in last few years, it is usually adopted in mechanical and structural systems and very rarely for magnetic applications. Thus, for addressing this goal the Bouc-Wen model is compared with the dynamic Jiles-Atherton model that, instead, was ideated exactly for simulating magnetic hysteresis. The comparative analysis has involved saturated and symmetric hysteresis loops in ferromagnetic materials. In addition in order to identify the Bouc-Wen parameters a very effective recent heuristic, called Metric-Topological and Evolutionary Optimization (MeTEO) has been utilized. It is based on a hybridization of three meta-heuristics: the Flock-of-Starlings Optimization, the Particle Swarm Optimization and the Bacterial Chemotaxis Algorithm. Thanks to the specific properties of these heuristic, MeTEO allow us to achieve effective identification of such kind of models. Several hysteresis loops have been utilized for final validation tests with the aim to investigate if the BW model can follow the different hysteresis behaviors of both static (quasi-static) and dynamic cases.
Flow field visualization about external axial corners
NASA Technical Reports Server (NTRS)
Talcott, N. A., Jr.
1978-01-01
An experimental investigation was conducted to visualize the flow field about external axial corners. The investigation was initiated to provide answers to questions about the inviscid flow pattern for continuing numerical investigations. Symmetrical and asymmetrical corner models were tested at a Reynolds number per meter of 60,700,000. Oil-flow and vapor-screen photographs were taken for both models at angle of attack and yaw. The paper presents the results of the investigation in the form of oil-flow photographs and the surrounding shock wave location obtained from the vapor screens.
NASA Astrophysics Data System (ADS)
Fraternali, Fernando; Carpentieri, Gerardo; Amendola, Ada
2015-01-01
We study the geometrically nonlinear behavior of uniformly compressed tensegrity prisms through fully elastic and rigid-elastic models. The given models predict a variety of mechanical behaviors in the regime of large displacements, including an extreme stiffening-type response, already known in the literature, and a newly discovered, extreme softening behavior. The latter may lead to a snap buckling event producing an axial collapse of the structure. The switching from one mechanical regime to another depends on the aspect ratio of the structure, the magnitude of the applied prestress, and the material properties of the constituent elements. We discuss potential mechanical and acoustic applications of such behaviors, which are related to the design and manufacture of tensegrity lattices and innovative metamaterials.
Modelling of stiffness degradation due to cracking in laminates subjected to multi-axial loading.
Kashtalyan, M; Soutis, C
2016-07-13
The paper presents an analytical approach to predicting the effect of intra- and interlaminar cracking on residual stiffness properties of the laminate, which can be used in the post-initial failure analysis, taking full account of damage mode interaction. The approach is based on a two-dimensional shear lag stress analysis and the equivalent constraint model of the laminate with multiple damaged plies. The application of the approach to predicting degraded stiffness properties of multidirectional laminates under multi-axial loading is demonstrated on cross-ply glass/epoxy and carbon/epoxy laminates with transverse and longitudinal matrix cracks and crack-induced transverse and longitudinal delaminations. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'. PMID:27242290
Critical dynamics of the O(n)-symmetric relaxational models below the transition temperature
NASA Astrophysics Data System (ADS)
Täuber, U. C.; Schwabl, F.
1992-08-01
The critical dynamics of the O(n)-symmetric relaxational models with either nonconserved (model A) or conserved order parameter (model B) are studied below the transition temperature. As a consequence of Goldstone's theorem, the transverse modes are massless, implying infrared divergences in the theory along the entire coexistence curve. These Goldstone singularities can be treated within the field-theoretical formulation of the dynamical renormalization group by using the generalized regularization scheme as introduced by Amit and Goldschmidt, which has already been applied on the statics of the φ4 model below Tc by Lawrie. We extend the formalism in several respects: (i) we generalize it to dynamical phenomena, (ii) taking advantage of the fact that the theory is exactly treatable in the coexistence limit, we do not use the ɛ expansion; (iii) the flow equations are solved numerically, thus allowing for a detailed description of the crossover from the critical isotropic Heisenberg fixed point to the infrared-stable coexistence fixed point. We calculate the static susceptibilities as well as the dynamical correlation functions for models A and B within the complete crossover region, identifying the asymptotic coexistence anomalies and also a pronounced intermediate minimum of the effective critical exponents. Furthermore, the longitudinal dynamical correlation function GL(q,ω) displays an anomalous line shape.
A calculation model for primary intensity distributions from cylindrically symmetric x-ray lenses
NASA Astrophysics Data System (ADS)
Hristov, Dimitre; Maltz, Jonathan
2008-02-01
A calculation model for the quantitative prediction of primary intensity fluence distributions obtained by the Bragg diffraction focusing of kilovoltage radiation by cylindrical x-ray lenses is presented. The mathematical formalism describes primary intensity distributions from cylindrically-symmetric x-ray lenses, with a planar isotropic radiation source located in a plane perpendicular to the lens axis. The presence of attenuating medium inserted between the lens and the lens focus is accounted for by energy-dependent attenuation. The influence of radiation scattered within the media is ignored. Intensity patterns are modeled under the assumption that photons that are not interacting with the lens are blocked out at any point of interest. The main characteristics of the proposed calculation procedure are that (i) the application of vector formalism allows universal treatment of all cylindrical lenses without the need of explicit geometric constructs; (ii) intensity distributions resulting from x-ray diffraction are described by a 3D generalization of the mosaic spread concept; (iii) the calculation model can be immediately coupled to x-ray diffraction simulation packages such as XOP and Shadow. Numerical simulations based on this model are to facilitate the design of focused orthovoltage treatment (FOT) systems employing cylindrical x-ray lenses, by providing insight about the influence of the x-ray source and lens parameters on quantities of dosimetric interest to radiation therapy.
The Effect of Cumulus Momentum Mixing on the Development of a Symmetric Model Hurricane.
NASA Astrophysics Data System (ADS)
Challa, Malakondayya; Pfeffer, Richard L.
1984-04-01
The effect of the vertical transport of horizontal momentum by cumulus clouds on the development of a symmetric model hurricane is investigated. This is accomplished by using Sundqvist's symmetric hurricane model with parameterized cumulus friction. The scheme used to include cumulus friction in the model is essentially the same as that given by Stevens and Lindzen in 1978 and Lindzen in 1981. The results of two sets of numerical integrations are presented. In one, the initial wind and moisture distributions were derived from atmospheric observations in Atlantic intensifying cyclones as composited by McBride. In the other, the initial vortex was specified as that which corresponds to the linearly most unstable mode in Mak's 1980 linear analysis of the effect of cumulus friction on hurricane formation. Given each initial wind, temperature and moisture distribution, numerical integrations were performed with and without cumulus friction present in the model.With cumulus friction included, the growth rates of the initial disturbances and their final intensities are smaller than those obtained in the absence of cumulus friction. The Atlantic intensifying cyclone with cumulus friction reaches storm strength, whereas without cumulus friction it develops into a hurricane. In the second pair of numerical integrations with the initial vortex specified as described above, the model develops hurricanes with and without cumulus frictions, but the rate of intensification and final strength of the vortex are significantly smaller when cumulus friction is included. The damping effect of cumulus friction is attributed to the fact that the angular momentum transported from the lower into the upper troposphere by cumulus mixing is not fully replenished in the lower troposphere by the cumulus induced secondary (radial) circulation. This contrasts with the effect of the inward eddy flux of momentum, reported on previously, which was found to enhance the intensification of hurricanes
Botelho, L.C.L.
1985-03-15
We study a two-dimensional quantum field model with axial-vector-current--pseudoscalar derivative interaction using path-integral methods. We construct an effective Lagrangian by performing a chiral change in the fermionic variables leading to an exact solution of the model.
Effects of fluid viscoelasticity on the performance of an axial blood pump model.
Hu, Qi-Hui; Li, Jing-Yin; Zhang, Ming-Yuan
2012-01-01
An aqueous Xanthan gum solution (XGS) was used as blood analog fluid to explore the influence of fluid viscoelasticity on the performance of an axial blood pump model. For comparison, a 39 wt% Newtonian aqueous glycerin solution (GS), the common fluid in blood pump tests, was also used as a working fluid. The experimental results showed that a higher head curve was obtained using XGS in the pump than using GS. The heads of the XGS that were computed using the viscoelastic turbulence model agreed well with the measured data. In contrast, the standard k-ε turbulence model failed to provide satisfactory predictions for the XGS. The computational results revealed that in most parts of the pump model flow fields, the Reynolds shear stress values and turbulent dissipation rates of the XGS were all lower than those of the GS. The hemolysis index of the pump model using the XGS was calculated to be only one-third of that using the GS. PMID:22210649
Viscous throughflow modeling of axial compressor bladerows using a tangential blade force hypothesis
Gallimore, S.J.
1998-10-01
This paper describes the modeling of axial compressor blade rows in an axisymmetric viscous throughflow method. The basic method, which has been reported previously, includes the effects of spanwise mixing, using a turbulent diffusion model, and endwall shear within the throughflow calculation. The blades are modeled using a combination of existing two-dimensional blade performance predictions for loss and deviation away from the annulus walls and a novel approach using tangential blade forces in the endwall regions. Relatively simple assumptions about the behavior of the tangential static pressure force imposed by the blades allow the secondary deviations produced by tip clearance flows and the boundary layer flows at fixed blade ends to be calculated in the axisymmetric model. Additional losses are assigned in these regions based on the calculated deviations. The resulting method gives realistic radial distributions of loss and deviation across the whole span at both design and off-design operating conditions, providing a quick method of estimating the magnitudes of these effects in the preliminary design process. Results from the method are compared to measured data in low and high-speed compressors and multistage three-dimensional viscous CFD predictions.
NASA Technical Reports Server (NTRS)
Fanale, F. P.; Salvail, J. R.
1984-01-01
A generalized model for short period comets is developed which integrates in a fairly rigorous manner the isolation history of regions on rotating comets with specified axial orientation and the complex feedback processes involving heat, gas and dust transport, dust mantle development and coma opacity. Attention is focused on development, reconfiguration and partial or complete launching of dust mantles and the reciprocal effects of these three processes on ice surface temperature and gas and dust production. The dust mantle controls the H2O flux not only by its effect on the temperature at the ice interface but (dominantly) by its dynamic stability which strongly influences vapor diffusivity. The model includes the effects of latitude, rotation and spin axis orientation are included and applied to an initially homogeneous sphere of H2O ice and silicate using the orbital parameters of comet Encke. Numerous variations of the model, using combinations of grain size distribution, dust-to-ice ratio, latitude and spin axis orientation, are presented and discussed. Resulted for a similar nonrotating, constant Sun orientation models are also included.
Jarvis, Peter D; Sumner, Jeremy G
2016-08-01
We consider the continuous-time presentation of the strand symmetric phylogenetic substitution model (in which rate parameters are unchanged under nucleotide permutations given by Watson-Crick base conjugation). Algebraic analysis of the model's underlying structure as a matrix group leads to a change of basis where the rate generator matrix is given by a two-part block decomposition. We apply representation theoretic techniques and, for any (fixed) number of phylogenetic taxa L and polynomial degree D of interest, provide the means to classify and enumerate the associated Markov invariants. In particular, in the quadratic and cubic cases we prove there are precisely [Formula: see text] and [Formula: see text] linearly independent Markov invariants, respectively. Additionally, we give the explicit polynomial forms of the Markov invariants for (i) the quadratic case with any number of taxa L, and (ii) the cubic case in the special case of a three-taxon phylogenetic tree. We close by showing our results are of practical interest since the quadratic Markov invariants provide independent estimates of phylogenetic distances based on (i) substitution rates within Watson-Crick conjugate pairs, and (ii) substitution rates across conjugate base pairs. PMID:26660305
Flavor constraints on the Two Higgs Doublet Models of Z 2 symmetric and aligned types
NASA Astrophysics Data System (ADS)
Enomoto, Tetsuya; Watanabe, Ryoutaro
2016-05-01
We give a comprehensive study from flavor observables of π, K, D ( s), and B ( s) mesons for limiting the Two Higgs Doublet Models (2HDMs) with natural flavor conservation, namely, Z 2 symmetric (type I, II, X, Y) and aligned types of models. With use of updated theoretical predictions and experimental analyses of B → τν, D → μν, D s → τν, D s → μν, K → μν, π → μν, B s 0 → μ + μ -, B d 0 → μ + μ -, τ → Kν, τ → π ν, overline{B}to {X}_sγ , K- overline{K} mixing, {B}_d^0- {overline{B}}_d^0 mixing, and {B}_s^0- {overline{B}}_s^0 mixing, we obtain constraints on the parameters in the 2HDMs. To calculate the constraints, we pay attention to a determination of CKM matrix elements and re-fit them to experimental data so that new contributions from additional Higgs bosons do not affect the determination. As a result, we find that the charged Higgs boson mass less than around 490 GeV is ruled out from overline{B}to {X}_sγ in the type II and Y models, whereas large tan β is excluded from B s 0 → μ + μ - in the type II. We also see that severe constraints on the mass and couplings are put from overline{B}to {X}_sγ , B s 0 → μ + μ -, and {B}_s^0- {overline{B}}_s^0 in the aligned model. In addition, we discuss excesses of observables in the muon anomalous magnetic moment and the semi-tauonic B meson decays in the context of the 2HDM, and find that the aligned model can explain part of the excesses, compatible with the other constraints.
Ramond, P. . Dept. of Physics)
1993-01-01
The Wolfenstein parametrization is extended to the quark masses in the deep ultraviolet, and an algorithm to derive symmetric textures which are compatible with existing data is developed. It is found that there are only five such textures.
Ramond, P.
1993-04-01
The Wolfenstein parametrization is extended to the quark masses in the deep ultraviolet, and an algorithm to derive symmetric textures which are compatible with existing data is developed. It is found that there are only five such textures.
Park, Sung Hwan; Lee, Ji Min; Kim, Jong Shik
2013-01-01
An irregular performance of a mechanical-type constant power regulator is considered. In order to find the cause of an irregular discharge flow at the cut-off pressure area, modeling and numerical simulations are performed to observe dynamic behavior of internal parts of the constant power regulator system for a swashplate-type axial piston pump. The commercial numerical simulation software AMESim is applied to model the mechanical-type regulator with hydraulic pump and simulate the performance of it. The validity of the simulation model of the constant power regulator system is verified by comparing simulation results with experiments. In order to find the cause of the irregular performance of the mechanical-type constant power regulator system, the behavior of main components such as the spool, sleeve, and counterbalance piston is investigated using computer simulation. The shape modification of the counterbalance piston is proposed to improve the undesirable performance of the mechanical-type constant power regulator. The performance improvement is verified by computer simulation using AMESim software. PMID:24282389
Parametric modeling and stagger angle optimization of an axial flow fan
NASA Astrophysics Data System (ADS)
Li, M. X.; Zhang, C. H.; Liu, Y.; Y Zheng, S.
2013-12-01
Axial flow fans are widely used in every field of social production. Improving their efficiency is a sustained and urgent demand of domestic industry. The optimization of stagger angle is an important method to improve fan performance. Parametric modeling and calculation process automation are realized in this paper to improve optimization efficiency. Geometric modeling and mesh division are parameterized based on GAMBIT. Parameter setting and flow field calculation are completed in the batch mode of FLUENT. A control program is developed in Visual C++ to dominate the data exchange of mentioned software. It also extracts calculation results for optimization algorithm module (provided by Matlab) to generate directive optimization control parameters, which as feedback are transferred upwards to modeling module. The center line of the blade airfoil, based on CLARK y profile, is constructed by non-constant circulation and triangle discharge method. Stagger angles of six airfoil sections are optimized, to reduce the influence of inlet shock loss as well as gas leak in blade tip clearance and hub resistance at blade root. Finally an optimal solution is obtained, which meets the total pressure requirement under given conditions and improves total pressure efficiency by about 6%.
Alvarez, R.; Alves, L. L.
2007-05-15
This paper presents a two-dimensional electromagnetic model for a microwave (2.45 GHz) plasma reactor operated by an axial injection torch. The model solves Maxwell's equations, adopting a harmonic time description and considering the collision dispersion features of the plasma. Perfect-conductor boundary conditions are satisfied at the reactor walls, and absorbing boundary conditions are used at the open end of the coaxial waveguide powering the system. Simulations yield the distribution of the electromagnetic fields and the average power absorbed by the system for a given spatial profile of the plasma density (tailored from previous experimental measurements), with maximum values in the range 10{sup 14}-10{sup 15} cm{sup -3}. Model results reveal that the system exhibits features similar to those of an air-filled, one-end-shorted circular metal waveguide, supporting evanescent or oscillatory solutions for radial dimensions below or above a critical radius, respectively. Results also show that the fractional average power absorbed by the plasma is strongly influenced by the system dimensions, which play a major role in defining the geometry pattern of the electromagnetic field distribution. Simulations are used to provide general guidelines for device optimization.
Khan, Usman; Falconi, Christian
2014-01-01
Ideally, the design of high-performance micro-hotplates would require a large number of simulations because of the existence of many important design parameters as well as the possibly crucial effects of both spread and drift. However, the computational cost of FEM simulations, which are the only available tool for accurately predicting the temperature in micro-hotplates, is very high. As a result, micro-hotplate designers generally have no effective simulation-tools for the optimization. In order to circumvent these issues, here, we propose a model for practical circular-symmetric micro-hot-plates which takes advantage of modified Bessel functions, computationally efficient matrix-approach for considering the relevant boundary conditions, Taylor linearization for modeling the Joule heating and radiation losses, and external-region-segmentation strategy in order to accurately take into account radiation losses in the entire micro-hotplate. The proposed model is almost as accurate as FEM simulations and two to three orders of magnitude more computationally efficient (e.g., 45 s versus more than 8 h). The residual errors, which are mainly associated to the undesired heating in the electrical contacts, are small (e.g., few degrees Celsius for an 800 °C operating temperature) and, for important analyses, almost constant. Therefore, we also introduce a computationally-easy single-FEM-compensation strategy in order to reduce the residual errors to about 1 °C. As illustrative examples of the power of our approach, we report the systematic investigation of a spread in the membrane thermal conductivity and of combined variations of both ambient and bulk temperatures. Our model enables a much faster characterization of micro-hotplates and, thus, a much more effective optimization prior to fabrication. PMID:24763214
An Accurate and Computationally Efficient Model for Membrane-Type Circular-Symmetric Micro-Hotplates
Khan, Usman; Falconi, Christian
2014-01-01
Ideally, the design of high-performance micro-hotplates would require a large number of simulations because of the existence of many important design parameters as well as the possibly crucial effects of both spread and drift. However, the computational cost of FEM simulations, which are the only available tool for accurately predicting the temperature in micro-hotplates, is very high. As a result, micro-hotplate designers generally have no effective simulation-tools for the optimization. In order to circumvent these issues, here, we propose a model for practical circular-symmetric micro-hot-plates which takes advantage of modified Bessel functions, computationally efficient matrix-approach for considering the relevant boundary conditions, Taylor linearization for modeling the Joule heating and radiation losses, and external-region-segmentation strategy in order to accurately take into account radiation losses in the entire micro-hotplate. The proposed model is almost as accurate as FEM simulations and two to three orders of magnitude more computationally efficient (e.g., 45 s versus more than 8 h). The residual errors, which are mainly associated to the undesired heating in the electrical contacts, are small (e.g., few degrees Celsius for an 800 °C operating temperature) and, for important analyses, almost constant. Therefore, we also introduce a computationally-easy single-FEM-compensation strategy in order to reduce the residual errors to about 1 °C. As illustrative examples of the power of our approach, we report the systematic investigation of a spread in the membrane thermal conductivity and of combined variations of both ambient and bulk temperatures. Our model enables a much faster characterization of micro-hotplates and, thus, a much more effective optimization prior to fabrication. PMID:24763214
NASA Astrophysics Data System (ADS)
Xu, Limei; Buldyrev, Sergey V.; Angell, C. Austen; Stanley, H. Eugene
2006-09-01
Using molecular dynamics simulations, we study the Jagla model of a liquid which consists of particles interacting via a spherically symmetric two-scale potential with both repulsive and attractive ramps. This potential displays anomalies similar to those found in liquid water, namely expansion upon cooling and an increase of diffusivity upon compression, as well as a liquid-liquid (LL) phase transition in the region of the phase diagram accessible to simulations. The LL coexistence line, unlike in tetrahedrally coordinated liquids, has a positive slope, because of the Clapeyron relation, corresponding to the fact that the high density phase (HDL) is more ordered than low density phase (LDL). When we cool the system at constant pressure above the critical pressure, the thermodynamic properties rapidly change from those of LDL-like to those of HDL-like upon crossing the Widom line. The temperature dependence of the diffusivity also changes rapidly in the vicinity of the Widom line, namely the slope of the Arrhenius plot sharply increases upon entering the HDL domain. The properties of the glass transition are different in the two phases, suggesting that the less ordered phase is fragile, while the more ordered phase is strong, which is consistent with the behavior of tetrahedrally coordinated liquids such as water silica, silicon, and BeF2 .
Explaining the diphoton excess in alternative left-right symmetric model
NASA Astrophysics Data System (ADS)
Hati, Chandan
2016-04-01
We propose a possible explanation for the recent diphoton excess reported by ATLAS and CMS Collaborations at around a 750 GeV diphoton invariant mass within the framework of the E6-motivated alternative left-right symmetric model, which is capable of addressing the B decay anomalies in the flavor sector, the e e j j and e pTj j excesses reported by CMS in run 1 of the LHC, and high-scale leptogenesis. We find that gluon-gluon fusion can give the observed production rate of the 750 GeV resonance, n ˜, through a loop of scalar leptoquarks (h˜(c )) with a mass below a few TeV range, while n ˜ can subsequently decay into a γ γ final state via loops of h˜(c ) and E˜(c ). Interestingly, the slepton (E˜ (c )) loop can enhance the diphoton branching ratio significantly to successfully explain the observed cross section of the diphoton signal.
Theoretical constraints on masses of heavy particles in Left-Right symmetric models
NASA Astrophysics Data System (ADS)
Chakrabortty, J.; Gluza, J.; Jeliński, T.; Srivastava, T.
2016-08-01
Left-Right symmetric models with general gL ≠gR gauge couplings which include bidoublet and triplet scalar multiplets are studied. Possible scalar mass spectra are outlined by imposing Tree-Unitarity, and Vacuum Stability criteria and also using the bounds on neutral scalar masses MHFCNC which assure the absence of Flavour Changing Neutral Currents (FCNC). We are focusing on mass spectra relevant for the LHC analysis, i.e., the scalar masses are around TeV scale. As all non-standard heavy particle masses are related to the vacuum expectation value (VEV) of the right-handed triplet (vR), the combined effects of relevant Higgs potential parameters and MHFCNC regulate the lower limits of heavy gauge boson masses. The complete set of Renormalization Group Evolutions for all couplings are provided at the 1-loop level, including the mixing effects in the Yukawa sector. Most of the scalar couplings suffer from the Landau poles at the intermediate scale Q ∼106.5 GeV, which in general coincides with violation of the Tree-Unitarity bounds.
Higgs mass, superconnections, and the TeV-scale left-right symmetric model
NASA Astrophysics Data System (ADS)
Aydemir, Ufuk; Minic, Djordje; Sun, Chen; Takeuchi, Tatsu
2015-02-01
We discuss the physical implications of formulating the Standard Model (SM) in terms of the superconnection formalism involving the superalgebra s u (2 /1 ). In particular, we discuss the prediction of the Higgs mass according to the formalism and point out that it is ˜170 GeV , in clear disagreement with experiment. To remedy this problem, we extend the formalism to the superalgebra s u (2 /2 ), which extends the SM to the left-right symmetric model (LRSM) and accommodates a ˜126 GeV Higgs boson. Both the SM in the s u (2 /1 ) case and the LRSM in the s u (2 /2 ) case are argued to emerge at ˜4 TeV from an underlying theory in which the spacetime geometry is modified by the addition of a discrete extra dimension. The formulation of the exterior derivative in this model space suggests a deep connection between the modified geometry, which can be described in the language of noncommutative geometry, and the spontaneous breaking of the gauge symmetries. The implication is that spontaneous symmetry breaking could actually be geometric/quantum gravitational in nature. The nondecoupling phenomenon seen in the Higgs sector can then be reinterpreted in a new light as due to the mixing of low energy (SM) physics and high energy physics associated with quantum gravity, such as string theory. The phenomenology of a TeV scale LRSM is also discussed, and we argue that some exciting discoveries may await us at the LHC, and other near-future experiments.
NASA Technical Reports Server (NTRS)
Ratkiewicz, R.; Barnes, A.; Molvik, G. A.; Spreiter, J. R.; Stahara, S. S.; Cuzzi, Jeffery N. (Technical Monitor)
1995-01-01
Large-scale fluctuations in the solar wind plasma upstream of the heliospheric termination shock (TS) will cause inward and outward motions of the shock. Using numerical techniques, we extend an earlier strictly one-dimensional (planar) analytic gas dynamic model to spherical symmetry to investigate the features of global behavior of shock motion. Our starting point is to establish a steady numerical solution of the gasdynamic equations describing the interaction between the solar wind and the interstellar medium. We then introduce disturbances of the solar wind dynamic pressure at an inner boundary, and follow the subsequent evolution of the system, especially the motion of the termination shock. Our model solves spherically symmetric gasdynamic equations as an initial-boundary value problem. The equations in conservative form are solved using a fully implicit Total Variation Diminishing (TVD) upwind scheme with Roe-type Riemann solver. Boundary conditions are given by the solar wind parameters on an inner spherical boundary, where they are allowed to vary with time for unsteady calculations, and by a constant pressure (roughly simulating the effect of the local interstellar medium) on an outer boundary. We find that immediately after the interaction, the shock moves with speeds given by the earlier analogous analytic models. However, as the termination shock propagates it begins to slow down, seeking a new equilibrium position. In addition, the disturbance transmitted through the TS, either a shock or rarefaction wave, will encounter the heliopause boundary and be reflected back. The reflected signal will encounter the TS, causing it to oscillate. The phenomenon may be repeated for a number of reflections, resulting in a "ringing" of the outer heliosphere.
NASA Astrophysics Data System (ADS)
Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele
2016-02-01
An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.
Modeling of thermo-mechanical fatigue and damage in shape memory alloy axial actuators
NASA Astrophysics Data System (ADS)
Wheeler, Robert W.; Hartl, Darren J.; Chemisky, Yves; Lagoudas, Dimitris C.
2015-04-01
The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.
Finite element modelling of process-integrated powder coating by radial axial rolling of rings
Frischkorn, J.; Kebriaei, R.; Reese, S.; Moll, H.; Theisen, W.; Husmann, T.; Meier, H.
2011-05-04
The process-integrated powder coating by radial axial rolling of rings represents a new hybrid production technique applied in the manufacturing of large ring-shaped work pieces with functional layers. It is thought to break some limitations that come along with the hot isostatic pressing (HIP) which is used nowadays to apply the powdery layer material onto the rolled substrate ring. Within the new process the compaction of the layer material is integrated into the ring rolling and HIP becomes dispensable. Following this approach the rolling of such compound rings brings up some new challenges. The volume of a solid ring stays nearly constant during the rolling. This behaviour can be exploited to determine the infeed of the rollers needed to reach the desired ring shape. Since volume consistency cannot be guaranteed for the rolling of a compound ring the choice of appropriate infeed of the rollers is still an open question. This paper deals with the finite element (FE) simulation of this new process. First, the material model that is used to describe the compaction of the layer material is shortly reviewed. The main focus of the paper is then put on a parameterized FE ring rolling model that incorporates a control system in order to stabilize the process. Also the differences in the behaviour during the rolling stage between a compound and a solid ring will be discussed by means of simulation results.
NASA Astrophysics Data System (ADS)
Lozowski, E. P.; D'Amours, R.
1980-08-01
A model of spherical hailstone growth thermodynamics is presented, and used to examine the validity of the continuous growth and heat balance assumptions frequently employed in the `classical' hail growth models. The model is similar to the spherically symmetric model formulated by Macklin and Payne (1969), but solutions to the model equations are obtained by means of finite-difference numerical methods. In the model, we do not try to simulate the discrete accretion process of individual drops. Instead, we attempt to identify the implications of the discrete, time-dependent nature of the icing process, by examining the accretion of a thin uniform layer of supercooled water over the entire surface of the sphere. The heat transfer equations both with the air and within the hailstone axe then solved assuming radial symmetry. By the addition of several such layers, the finite growth of a spherical hailstone can be simulated. In the present paper, only growth in constant ambient conditions is considered. It is shown that there are large internal heat fluxes during the interval between the accretion of successive layers (typically 1 s), which cause the temperatures near the surface to oscillate several degrees above and below their time-mean value. Nevertheless, the time-averaged temperature over an accretion cycle is almost uniform throughout the hailstone and, when the environmental conditions are constant, is approximately equal to the equilibrium surface temperature predicted by the `classical' models. As the hailstone grows under constant environmental conditions, it continually adapts to the classical equilibrium temperature, warming up almost uniformly throughout. The time scale for this adjustment to a quasi-equilibrium state is found to be of the order of the internal diffusive time scale R2/k. It is speculated therefore that if the environmental conditions change slowly (over time scales large compared with R2/k) the hailstone thermodynamics will be adequately
Magné, Joëlle; Huneau, Jean-François; Borderie, Didier; Mathé, Véronique; Bos, Cécile; Mariotti, François
2015-09-01
Hyperhomocysteinemia induces vascular endothelial dysfunction, an early hallmark of atherogenesis. While higher levels of circulating asymmetric dimethylarginine (ADMA) and symmetric dimethyl arginine (SDMA), endogenous inhibitors of nitric oxide synthesis, have been associated with increased cardiovascular risk, the role that ADMA and SDMA play in the initiation of hyperhomocysteinemia-induced endothelial dysfunction remains still controversial. In the present study, we studied the changes of circulating ADMA and SDMA in a rat model of acutely hyperhomocysteinemia-induced endothelial dysfunction. In healthy rats, endothelium-related vascular reactivity (measured as acetylcholine-induced transient decrease in mean arterial blood pressure), plasma ADMA and SDMA, total plasma homocysteine (tHcy), cysteine and glutathione were measured before and 2, 4 and 6 h after methionine loading or vehicle. mRNA expression of hepatic dimethylarginine dimethylaminohydrolase-1 (DDAH1), a key protein responsible for ADMA metabolism, was measured 6 h after the methionine loading or the vehicle. Expectedly, methionine load induced a sustained increase in tHcy (up to 54.9 ± 1.9 µM) and a 30 % decrease in vascular reactivity compared to the baseline values. Plasma ADMA and SDMA decreased transiently after the methionine load. Hepatic mRNA expression of DDAH1, cathepsin D, and ubiquitin were significantly lower 6 h after the methionine load than after the vehicle. The absence of an elevation of circulating ADMA and SDMA in this model suggests that endothelial dysfunction induced by acute hyperhomocysteinemia cannot be explained by an up-regulation of protein arginine methyltransferases or a down-regulation of DDAH1. In experimental endothelial dysfunction induced by acute hyperhomocysteinemia, down-regulation of the proteasome is likely to dampen the release of ADMA and SDMA in the circulation. PMID:25792109
NASA Astrophysics Data System (ADS)
Kaneko, Y.; Shearer, P. M.
2014-12-01
Earthquake stress drops are often estimated from far-field body-wave spectra using measurements of seismic moment, corner frequency, and a specific theoretical model of rupture behavior. Perhaps, the most widely-used model is from Madariaga (1976), who performed finite-difference calculations for a singular crack radially expanding at a constant speed and showed that fc=kβ/afc = k beta/a, where fcfc is spherically averaged corner frequency, βbeta is the shear-wave speed, aa is the radius of the circular source, and kk = 0.32 and 0.21 for P and S waves, respectively, assuming the rupture speed VrVr = 0.9βbeta. Since stress in the Madariaga model is singular at the rupture front, the finite mesh size and smoothing procedures may have affected the resulting corner frequencies. Here we investigate the behavior of source spectra derived from dynamic models of radially expanding rupture with a cohesive zone that prevents a stress singularity at the rupture front. We find that in the small-scale yielding limit where the cohesive-zone size becomes much smaller than the source dimension, P- and S-wave corner frequencies of far-field body-wave spectra are systematically larger than those predicted by Madariaga (1976). In particular, the model with rupture speed VrVr = 0.9βbeta shows that kk = 0.38 for P waves and kk = 0.26 for S waves, which are 19 and 24 percent larger, respectively, than those of Madariaga (1976). Thus for these ruptures, the application of the Madariaga model overestimates stress drops by a factor of 1.7. We further address the validity of a standard assumption on a symmetrical circular source applied to real earthquakes. Our results suggest that up to a factor of two differences in the spherical average of corner frequencies are expected simply from the variability in source geometry and rupture styles, translating into a factor of eight differences in estimated stress drops. In addition, the large dependence of corner frequency on take-off angle
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NASA Astrophysics Data System (ADS)
Rama, María. Angeles; Pérez, María. Victoria; Bao, Carmen; Flores-Arias, María. Teresa; Gómez-Reino, Carlos
2005-05-01
Gradient-index (GRIN) models of the human lens have received wide attention in optometry and vision sciences for considering the effect of inhomogeneity of the refractive index on the optical properties of the lens. This paper uses the continuous asymmetric bi-elliptical model to determine analytically cardinal elements, magnifications and refractive power of the lens by the axial and field rays in order to study the paraxial light propagation through the human lens from its GRIN nature.
Critical exponents for a three-dimensional O([ital n])-symmetric model with [ital n][gt]3
Antonenko, S.A.; Sokolov, A.I. )
1995-03-01
Critical exponents for the three-dimensional O([ital n])-symmetric model with [ital n][gt]3 are estimated on the basis of six-loop renormalization-group (RG) expansions. A simple Pade-Borel technique is used for the resummation of the RG series and the Pade approximants [[ital L]/1] are shown to give rather good numerical results for all calculated quantities. For large [ital n], the fixed point location [ital g][sub [ital c
A simple model simulating a fan as a source of axial and circumferential body forces
Energy Science and Technology Software Center (ESTSC)
2002-07-01
This software can be used in a computational fluids dynamics (CFD) code to represent a fan as a source of axial and circumferential body forces. The combined software can be used effectively in car design analyses that involve many underhood thermal management simulations. FANMOD uses as input the rotational speed of the fan, geometric fan data, and the lift and drag coefficients of the blades, and predicts the body forces generated by the fan inmore » the axial and circumferential directions. These forces can be used as momentum forces in a CFD code to simulate the effect of the fan in an underhood thermal management simulation.« less
NASA Astrophysics Data System (ADS)
Magnucka-Blandzi, Ewa
2016-06-01
The study is devoted to stability of simply supported beam under axial compression. The beam is subjected to an axial load located at any point along the axis of the beam. The buckling problem has been desribed and solved mathematically. Critical loads have been calculated. In the particular case, the Euler's buckling load is obtained. Explicit solutions are given. The values of critical loads are collected in tables and shown in figure. The relation between the point of the load application and the critical load is presented.
Electrostatic mirror objective with eliminated spherical and axial chromatic aberrations.
Bimurzaev, Seitkerim B; Serikbaeva, Gulnur S; Yakushev, Evgeniy M
2003-01-01
Computational formulae for the coefficients of the third-order spherical aberration and the second-order axial chromatic aberration are presented for an axially symmetric electrostatic electron mirror. A technique for eliminating the high-order derivatives of the potential axial distribution in mirror systems from the integrands is described. Conditions for elimination of spherical and axial chromatic aberrations, either separately or simultaneously, are found for a three-electrode axially symmetric mirror composed of coaxial cylinders of the same diameter. A principal scheme of the transmission electron microscope, where an electrostatic electron mirror serves as its objective, is presented. PMID:14599097
Reactive control of subsonic axial fan noise in a duct.
Liu, Y; Choy, Y S; Huang, L; Cheng, L
2014-10-01
Suppressing the ducted fan noise at low frequencies without varying the flow capacity is still a technical challenge. This study examines a conceived device consisting of two tensioned membranes backed with cavities housing the axial fan for suppression of the sound radiation from the axial fan directly. The noise suppression is achieved by destructive interference between the sound fields from the axial fan of a dipole nature and sound radiation from the membrane via vibroacoustics coupling. A two-dimensional model with the flow effect is presented which allows the performance of the device to be explored analytically. The air flow influences the symmetrical behavior and excites the odd in vacuo mode response of the membrane due to kinematic coupling. Such an asymmetrical effect can be compromised with off-center alignment of the axial fan. Tension plays an important role to sustain the performance to revoke the deformation of the membrane during the axial fan operation. With the design of four appropriately tensioned membranes covered by a cylindrical cavity, the first and second blade passage frequencies of the axial fan can be reduced by at least 20 dB. The satisfactory agreement between experiment and theory demonstrates that its feasibility is practical. PMID:25324066
NASA Technical Reports Server (NTRS)
Chin, S.; Lan, C. Edward
1988-01-01
An inviscid discrete vortex model, with newly derived expressions for the tangential velocity imposed at the separation points, is used to investigate the symmetric and asymmetric vortex separation on cones and tangent ogives. The circumferential locations of separation are taken from experimental data. Based on a slender body theory, the resulting simultaneous nonlinear algebraic equations in a cross-flow plane are solved with Broyden's modified Newton-Raphson method. Total force coefficients are obtained through momentum principle with new expressions for nonconical flow. It is shown through the method of function deflation that multiple solutions exist at large enough angles of attack, even with symmetric separation points. These additional solutions are asymmetric in vortex separation and produce side force coefficients which agree well with data for cones and tangent ogives.
NASA Astrophysics Data System (ADS)
Penotti, Fabio E.; Cooper, David L.
2015-07-01
We examine the symmetry properties of spin-coupled (or full generalised valence bond) wavefunctions for C2H2 and N2. The symmetry-separated (σ,π) and bent-bond (ω) solutions are totally symmetric only in the D4h and D3h subgroups of D∞h, respectively. Two fairly different strategies are explored for imposing full cylindrical symmetry, with one of them (small nonorthogonal configuration interaction calculations involving rotated versions of the wavefunction) turning out to be somewhat preferable on energetic grounds to the other one (application of additional spin constraints to a single spatial configuration). It is also shown that mixing together the cylindrically symmetric symmetry-separated and bent-bond spin-coupled models leads to relatively small energy improvements unless the valence orbitals in each type of configuration are reoptimised.
Molecular Modeling of the Axial and Circumferential Elastic Moduli of Tubulin
Zeiger, A. S.; Layton, B. E.
2008-01-01
Microtubules play a number of important mechanical roles in almost all cell types in nearly all major phylogenetic trees. We have used a molecular mechanics approach to perform tensile tests on individual tubulin monomers and determined values for the axial and circumferential moduli for all currently known complete sequences. The axial elastic moduli, in vacuo, were found to be 1.25 GPa and 1.34 GPa for α- and β-bovine tubulin monomers. In the circumferential direction, these moduli were 378 MPa for α- and 460 MPa for β-structures. Using bovine tubulin as a template, 269 homologous tubulin structures were also subjected to simulated tensile loads yielding an average axial elastic modulus of 1.10 ± 0.14 GPa for α-tubulin structures and 1.39 ± 0.68 GPa for β-tubulin. Circumferentially the α- and β-moduli were 936 ± 216 MPa and 658 ± 134 MPa, respectively. Our primary finding is that that the axial elastic modulus of tubulin diminishes as the length of the monomer increases. However, in the circumferential direction, no correlation exists. These predicted anisotropies and scale dependencies may assist in interpreting the macroscale behavior of microtubules during mitosis or cell growth. Additionally, an intergenomic approach to investigating the mechanical properties of proteins may provide a way to elucidate the evolutionary mechanical constraints imposed by nature upon individual subcellular components. PMID:18621829
Soleimani, Effat; Mokhtari-Dizaji, Manijhe; Saberi, Hajir; Sharif-Kashani, Shervin
2016-08-01
Clarifying the complex interaction between mechanical and biological processes in healthy and diseased conditions requires constitutive models for arterial walls. In this study, a mathematical model for the displacement of the carotid artery wall in the longitudinal direction is defined providing a satisfactory representation of the axial stress applied to the arterial wall. The proposed model was applied to the carotid artery wall motion estimated from ultrasound image sequences of 10 healthy adults, and the axial stress waveform exerted on the artery wall was extracted. Consecutive ultrasonic images (30 frames per second) of the common carotid artery of 10 healthy subjects (age 44 ± 4 year) were recorded and transferred to a personal computer. Longitudinal displacement and acceleration were extracted from ultrasonic image processing using a block-matching algorithm. Furthermore, images were examined using a maximum gradient algorithm and time rate changes of the internal diameter and intima-media thickness were extracted. Finally, axial stress was estimated using an appropriate constitutive equation for thin-walled tubes. Performance of the proposed model was evaluated using goodness of fit between approximated and measured longitudinal displacement statistics. Values of goodness-of-fit statistics indicated high quality of fit for all investigated subjects with the mean adjusted R-square (0.86 ± 0.08) and root mean squared error (0.08 ± 0.04 mm). According to the results of the present study, maximum and minimum axial stresses exerted on the arterial wall are 1.7 ± 0.6 and -1.5 ± 0.5 kPa, respectively. These results reveal the potential of this technique to provide a new method to assess arterial stress from ultrasound images, overcoming the limitations of the finite element and other simulation techniques. PMID:26563198
Users manual and modeling improvements for axial turbine design and performance computer code TD2-2
NASA Technical Reports Server (NTRS)
Glassman, Arthur J.
1992-01-01
Computer code TD2 computes design point velocity diagrams and performance for multistage, multishaft, cooled or uncooled, axial flow turbines. This streamline analysis code was recently modified to upgrade modeling related to turbine cooling and to the internal loss correlation. These modifications are presented in this report along with descriptions of the code's expanded input and output. This report serves as the users manual for the upgraded code, which is named TD2-2.
Chai, Jee Won; Lee, Joon Woo; Kim, Su-Jin; Hong, Sung Hwan
2016-01-01
Objective To evaluate T2 relaxation time change using axial T2 mapping in a rabbit degenerated disc model and determine the most correlated variable with histologic score among T2 relaxation time, disc height index, and Pfirrmann grade. Materials and Methods Degenerated disc model was made in 4 lumbar discs of 11 rabbits (n = 44) by percutaneous annular puncture with various severities of an injury. Lumbar spine lateral radiograph, MR T2 sagittal scan and MR axial T2 mapping were obtained at baseline and 2 weeks and 4 weeks after the injury in 7 rabbits and at baseline and 2 weeks, 4 weeks, and 6 weeks after the injury in 4 rabbits. Generalized estimating equations were used for a longitudinal analysis of changes in T2 relaxation time in degenerated disc model. T2 relaxation time, disc height index and Pfirrmann grade were correlated with the histologic scoring of disc degeneration using Spearman's rho test. Results There was a significant difference in T2 relaxation time between uninjured and injured discs after annular puncture. Progressive decrease in T2 relaxation time was observed in injured discs throughout the study period. Lower T2 relaxation time was observed in the more severely injured discs. T2 relaxation time showed the strongest inverse correlation with the histologic score among the variables investigated (r = -0.811, p < 0.001). Conclusion T2 relaxation time measured with axial T2 mapping in degenerated discs is a potential method to assess disc degeneration. PMID:26798222
Cho, Edward Namkyu; Shin, Yong Hyeon; Yun, Ilgu
2014-11-07
A compact quantum correction model for a symmetric double gate (DG) metal-oxide-semiconductor field-effect transistor (MOSFET) is investigated. The compact quantum correction model is proposed from the concepts of the threshold voltage shift (ΔV{sub TH}{sup QM}) and the gate capacitance (C{sub g}) degradation. First of all, ΔV{sub TH}{sup QM} induced by quantum mechanical (QM) effects is modeled. The C{sub g} degradation is then modeled by introducing the inversion layer centroid. With ΔV{sub TH}{sup QM} and the C{sub g} degradation, the QM effects are implemented in previously reported classical model and a comparison between the proposed quantum correction model and numerical simulation results is presented. Based on the results, the proposed quantum correction model can be applicable to the compact model of DG MOSFET.
NASA Astrophysics Data System (ADS)
Radons, Günter
2008-06-01
The Preisach model with symmetric elementary hysteresis loops and uncorrelated input is treated analytically in detail. It is shown that the appearance of long-time tails in the output correlations is a quite general feature of this model. The exponent η of the algebraic decay t-η , which may take any positive value, is determined by the tails of the input and the Preisach density. We identify the system classes leading to identical algebraic tails. These results imply the occurrence of 1/f noise for a large class of hysteretic systems.
Karimi, Alireza; Navidbakhsh, Mahdi; Haghighatnama, Maedeh; Haghi, Afsaneh Motevalli
2015-01-01
The skin, being a multi-layered material, is responsible for protecting the human body from the mechanical, bacterial, and viral insults. The skin tissue may display different mechanical properties according to the anatomical locations of a body. However, these mechanical properties in different anatomical regions and at different loading directions (axial and circumferential) of the mice body to date have not been determined. In this study, the axial and circumferential loads were imposed on the mice skin samples. The elastic modulus and maximum stress of the skin tissues were measured before the failure occurred. The nonlinear mechanical behavior of the skin tissues was also computationally investigated through a suitable constitutive equation. Hyperelastic material model was calibrated using the experimental data. Regardless of the anatomic locations of the mice body, the results revealed significantly different mechanical properties in the axial and circumferential directions and, consequently, the mice skin tissue behaves like a pure anisotropic material. The highest elastic modulus was observed in the back skin under the circumferential direction (6.67 MPa), while the lowest one was seen in the abdomen skin under circumferential loading (0.80 MPa). The Ogden material model was narrowly captured the nonlinear mechanical response of the skin at different loading directions. The results help to understand the isotropic/anisotropic mechanical behavior of the skin tissue at different anatomical locations. They also have implications for a diversity of disciplines, i.e., dermatology, cosmetics industry, clinical decision making, and clinical intervention. PMID:25266627
NASA Technical Reports Server (NTRS)
Bozeman, Richard J., Jr. (Inventor); Akkerman, James W. (Inventor); Aber, Gregory S. (Inventor); VanDamm, George Arthur (Inventor); Bacak, James W. (Inventor); Svejkovsky, Paul A. (Inventor); Benkowski, Robert J. (Inventor)
1997-01-01
A rotary blood pump includes a pump housing for receiving a flow straightener, a rotor mounted on rotor bearings and having an inducer portion and an impeller portion, and a diffuser. The entrance angle, outlet angle, axial and radial clearances of blades associated with the flow straightener, inducer portion, impeller portion and diffuser are optimized to minimize hemolysis while maintaining pump efficiency. The rotor bearing includes a bearing chamber that is filled with cross-linked blood or other bio-compatible material. A back emf integrated circuit regulates rotor operation and a microcomputer may be used to control one or more back emf integrated circuits. A plurality of magnets are disposed in each of a plurality of impeller blades with a small air gap. A stator may be axially adjusted on the pump housing to absorb bearing load and maximize pump efficiency.
NASA Technical Reports Server (NTRS)
Betz, A
1944-01-01
Improvements, however, have been attained which permit a shortening of the structure without any impairment of the efficiency. The axial supercharger has a better efficiency and a simpler design than the radial supercharger. The relatively narrow range in which it operates satisfactorily should not be a very disturbing factor for practical flight problems. The length of this type of supercharger may be reduced considerably if some impairment in the efficiency is permitted.
NASA Astrophysics Data System (ADS)
Algar, C. K.
2015-12-01
Hydrogenotrophic methanogenesis is an important mode of metabolism in deep-sea hydrothermal vents. Diffuse vent fluids often show a depletion in hydrogen with a corresponding increase in methane relative to pure-mixing of end member fluid and seawater, and genomic surveys show an enrichment in genetic sequences associated with known methanogens. However, because we cannot directly sample the subseafloor habitat where these organisms are living, constraining the size and activity of these populations remains a challenge and limits our ability to quantify the role they play in vent biogeochemistry. Reactive-transport modeling may provide a useful tool for approaching this problem. Here we present a reactive-transport model describing methane production along the flow-path of hydrothermal fluid from its high temperature end-member to diffuse venting at the seafloor. The model is set up to reflect conditions at several diffuse vents in the Axial Seamount. The model describes the growth of the two dominant thermophilic methanogens, Methanothermococcus and Methanocaldococcus, observed at Axial seamount. Monod and Arrhenius constants for Methanothermococcus thermolithotrophicus and Methanocaldococcus jannaschii were obtained for the model using chemostat and bottle experiments at varying temperatures. The model is used to investigate the influence of different mixing regimes on the subseafloor populations of these methanogens. By varying the model flow path length and subseafloor cell concentrations, and fitting to observed hydrogen and methane concentrations in the venting fluid, the subseafloor biomass, fluid residence time, and methane production rate can be constrained.