arXiv subjects

Robert W. Johnson

Publications and source records attributed to Robert W. Johnson.

At least 37 records · Page 2Linked to original sources

arXiv2010

Power law relating 10.7 cm flux to sunspot number

To investigate the relation between observations of the 10.7 cm flux and the international sunspot number so that a physical unit may be ascribed to historical records, both polynomial and power law models are developed giving the radio flux as a function of sunspot number and vice versa. Bayesian data analysis is used to estimate the model parameters and to discriminate between the models. The effect on the parameter uncertainty and on the relative evidence of normalizing the measure of fit is investigated. The power law giving flux as a function of sunspot number is found to be the most plausible model and may be used to estimate the radio flux from historical sunspot observations.

astro-ph.SR↗

arXiv2010

Fitting a sum of exponentials to lattice correlation functions using a non-uniform prior

Excited states are extracted from lattice correlation functions using a non-uniform prior on the model parameters. Models for both a single exponential and a sum of exponentials are considered, as well as an alternate model for the orthogonalization of the correlation functions. Results from an analysis of torelon and glueball operators indicate the Bayesian methodology compares well with the usual interpretation of effective mass tables produced by a variational procedure. Applications of the methodology are discussed.

hep-lat↗

arXiv2010

Effect of magnetization and magnetic field variation on stationary axisymmetric equilibrium

The inclusion of plasma magnetization in the equations of stationary equilibrium is derived, and its effect on the determination of axisymmetric equilibrium calculated. A factor of 2 on the pressure gradient arises in the equilibrium equation from the force felt by the dipole moment density. The algebraic and differential equation formulations are compared both with and without consideration of magnetization, revealing the effects of both magnetization and magnetic field variation on the equilibrium, which become more pronounced for high pressures in a weak external field. The equivalence of the magnetized equilibrium equation with the standard equilibrium equation in the limit of vanishing magnetization is demonstrated.

physics.plasm-ph↗

arXiv2010

Wavelets and Solar Magnetic Activity I: Wavelets on the Edge

The traditional continuous wavelet transform is plagued by the cone-of-influence, ie wavelets which extend past either end of a finite timeseries return transform coefficients which tend to decrease as more of the wavelet is truncated. These coefficients may be corrected simply by rescaling the remaining wavelet. The corrected wavelet transform displays no cone-of-influence and maintains reconstruction as either edge is approached. As an application and example, we present the corrected wavelet transform of the (derectified) yearly International Sunspot Number, R_i, as a measure of solar magnetic activity, and compare the yearly solar magnetic power with Oerlemans' glacial global temperature reconstruction.

physics.data-an↗

arXiv2010

Stationary axial plasma equilibrium in light of the magnetic polarization force

The standard equilibrium equation for magnetized plasma is extended to account for the magnetic polarization force. A factor of the pressure gradient arising from the magnetic decomposition of the Hall term survives the limit of vanishing magnetization and is canceled by a contribution from the magnetic polarization force, such that the proposed equation reduces to the standard form in the free current limit. Comparison of the solutions for an axially symmetric plasma column indicates agreement with the free current limit for vanishing magnetization and variation in the field and current profiles as the degree of magnetization increases.

physics.plasm-ph↗

arXiv2010

Modelling the electric field applied to a tokamak

The vector potential for the Ohmic heating coil system of a tokamak is obtained in semi-analytical form. Comparison is made to the potential of a simple, finite solenoid. In the quasi-static limit, the time rate of change of the potential determines the induced electromotive force through the Maxwell-Lodge effect. Discussion of the gauge constraint is included.

physics.class-ph↗

arXiv2010

Influence of solar magnetic activity on the North American temperature record

The effect of solar magnetic activity on the yearly mean average temperature is extracted from the historical record for much of North America. The level of solar activity is derived from the international sunspot number by the renormalized continuous wavelet transform using the Morlet basis to provide a running estimate of the power associated with the magnetic cycle. The solar activity gives the abscissa for a scatter plot of temperature for each station, from which the solar dependence and mean temperature are extracted. These parameters are then plotted against the latitude, longitude, and elevation for each station, revealing a dependence of their values on geophysical location. A mechanism to explain the latitudinal variation of the solar dependence is suggested.

physics.data-an↗

arXiv2009

Edge Adapted Wavelets, Solar Magnetic Activity, and Climate Change

The continuous wavelet transform is adapted to account for signal truncation through renormalization and by modifying the shape of the analyzing window. Comparison is made of the instant and integrated wavelet power with previous algorithms. The edge adapted and renormalized admissible wavelet transforms are used to estimate the level of solar magnetic activity from the sunspot record. The solar activity is compared to Oerlemans' temperature reconstruction and to the Central England Temperature record. A correlation is seen for years between 1610 and 1990, followed by a strong deviation as the recently observed temperature increases.

physics.data-an↗

arXiv2009

Macroscopic electromagnetic stress tensor for ionized media

Following the arguments presented by Mansuripur [Opt. Express 16, 14821-14835 (2008)], we suggest a form for the macroscopic electromagnetic stress tensor appropriate for ionized media. The generalized Lorentz force includes the effects of polarization forces as well as those on the free charge and current densities. The resulting tensor is written in terms of the fields D, B, E, and H. Its expression for a fully ionized medium subject to an external electromagnetic field is discussed, as are the plasma conservation equations. An apparatus is suggested for its experimental discrimination.

physics.plasm-ph↗

arXiv2009

Non-stationary magnetized axially symmetric equilibrium from the fluid equations of motion

The equations of motion for a fully ionized hydrogenic plasma in applied coaxial electric and magnetic fields are analyzed, where the term for the Hall effect in the generalized Ohm's law equation picks up a factor of 1/2 relative to its usual expression. Magnetization of the medium is incorporated through the decomposition of the Hall term and the inclusion of the magnetization force, which is found to equal or exceed the gradient of the scalar pressure. A limit on the kinetic pressure obtains which corresponds to the usual limit of unity for a certain selection of parameters. Solutions of these equations for the free motion of the charges in the case of an infinite column with azimuthal symmetry are compared for various prescribed pressure profiles, where one finds that the profile near the outer edge plays an important role in the feasibility of the equilibrium.

physics.plasm-ph↗

arXiv2009

Enhanced Wavelet Analysis of Solar Magnetic Activity with Comparison to Global Temperature and the Central England Temperature Record

The continuous wavelet transform may be enhanced by deconvolution with the wavelet response function. After correcting for the cone-of-influence, the power spectral density of the solar magnetic record as given by the derectified yearly sunspot number is calculated, revealing a spectrum of odd harmonics of the fundamental Hale cycle, and the integrated instant power is compared to a reconstruction of global temperature in a normalized scatter plot displaying a positive correlation after the turn of the twentieth century. Comparison of the spectrum with that obtained from the Central England Temperature record suggests that some features are shared while others are not, and the scatter plot again indicates a possible correlation.

physics.data-an↗

arXiv2009

Comment on "Plasma ionization by annularly bounded helicon waves" [Phys . Plasmas 13, 063501 (2006)]

The neoclassical calculation of the helicon wave theory contains a fundamental flaw. Use is made of a proportional relationship between the magnetic field and its curl to derive the Helmholtz equation describing helicon wave propagation; however, by the fundamental theorem of Stokes, the curl of the magnetic field must be perpendicular to that portion of the field contributing to the local curl. Reexamination of the equations of motion indicates that only electromagnetic waves propagate through a stationary region of constant pressure in a fully ionized, neutral medium.

physics.plasm-ph↗

arXiv2008

On the application of Maxwell's theory to many-body systems, or why the resistive magnetohydrodynamic equations are not closed

The resistive magnetohydrodynamic (MHD) equations as usually defined in the quasineutral approximation refer to a system of 14 scalar equations in 14 scalar variables, hence are determined to be complete and soluble. These equations are a combination of Navier-Stokes and a subset of Maxwell's. However, one of the vector equations is actually an identity when viewed from the potential formulation of electrodynamics, hence does not determine any degrees of freedom. Only by reinstating Gauss's law does the system of equations become closed, allowing for the determination of both the current and mass flow velocity from the equations of motion. Results of a typical analysis of the proposed electromagnetic hydrodynamic model including the magnetization force are presented.

physics.plasm-ph↗

arXiv2008

On "the plasma approximation"

``The plasma approximation'' is, in the words of Pauli, ``not even wrong,'' as it expresses a disbelief in the symmetries of the underlying gauge field theory. The electrostatic field in question is divergenceful yet has no sources or sinks, thus breaking Lorentz covariance explicitly, and has no place in a self-consistent theory. Utilizing it leads to inconsistencies in the equation of motion and prevents a proper, field-theoretic treatment of condensed matter in the plasma state. By exposing the fallacy of replacing one of the field equations with one of the Bianchi identities, the applicability of Gauss' law to plasma physics is assured.

physics.plasm-ph↗

arXiv2008

Currents in a Tokamak

A self-consistent analysis of the currents in a tokamak yields the result that the parallel neutralizing current is given simply by the sum of currents commonly called the bootstrap current and the Pfirsch-Schlueter current. An expression is given relating the parallel and perpendicular pressure gradient induced species flow velocities to the total current.

physics.plasm-ph↗

arXiv2007

Non-Newtonian viscosity in magnetized plasma

The particle and momentum balance equations can be solved on concentric circular flux surfaces to determine the effective viscous drag present in a magnetized tokamak plasma in the low aspect ratio limit. An analysis is developed utilizing the first-order Fourier expansion of the poloidal variation of quantities on the flux surface akin to that by Stacey and Sigmar [Phys. Fluids, 28, 9 (1985)]. Expressions to determine the poloidal variations of density, poloidal velocity, toroidal velocity, radial electric field, poloidal electric field, and other radial profiles are presented in a multi-species setting. Using as input experimental data for the flux surface averaged profiles of density, temperature, toroidal current, toroidal momentum injection, and the poloidal and toroidal rotations of at least one species of ion, one may solve the equations numerically for the remaining profiles. The resultant effective viscosities are compared to those predicted by Stacey and Sigmar and Shaing, et al., [Nuclear Fusion, 25, 4 (1985)]. A velocity dependence of the effective viscosity is observed, indicating the presence of non-Newtonian fluid behavior in magnetized plasma.

physics.plasm-ph↗

arXiv2007

Viscosity and confinement in magnetized plasma

An alternative to the Braginskii decomposition is proposed, one rooted in treating the viscosity as a scalar quantity in a coordinate-free representation. With appropriate application to the rate-of-shear tensor, one may solve the neoclassical force density equations for its undetermined velocity dependence, as well as the radial and poloidal profiles mentioned in [R. W. Johnson, Phys. Plasmas, under review], using an improved poloidal expansion. The pseudoplastic behavior of magnetized plasma is again obtained, and the high viscosity solution is determined to be physical. A clear relationship between confinement mode and viscosity is observed, indicating a physical origin for transport barriers, pedestals, and other phenomena. The gyroviscous contribution is found to be an effect on the order of one one-thousandth of one percent of the dominant collisional viscosity.

physics.plasm-ph↗

arXiv2007

Improved Superlinks for Higher Spin Operators

Traditional smearing or blocking techniques serve well to increase the overlap of operators onto physical states but allow for links orientated only along lattice axes. Recent attempts to construct more general propagators have shown promise at resolving the higher spin states but still rely on iterative smearing. We present a new method of superlink construction which creates meared links from (sparse) matrix multiplications, allowing for gluonic propagation in arbitrary directions. As an application and example, we compute the positive-parity, even-spin glueball spectrum up to spin 6 for pure gauge SU(2) at beta = 6, L = 16, in D = 2+1 dimensions.

hep-lat↗