THE IMPEDANCE OF AN ANTENNA ABOVE A CIRCULAR GROUND PLATE LAID UPON A PLANE EARTH

1954 ◽  
Vol 32 (3) ◽  
pp. 205-222 ◽  
Author(s):  
G. Bekefi
Keyword(s):  
Wave Length ◽  
Variational Formula ◽  
Radial Electric Field ◽  
Theoretical Work ◽  
Approximate Theory ◽  
Conducting Plane ◽  
True Value ◽  
The Earth ◽  
Recent Theoretical Work ◽  
Ground Plate

Recent theoretical work by Storer, concerning the impedance of a vertical antenna in contact with a circular metal disk, is extended to include the case when the system is laid upon an imperfectly conducting plane earth. The expression for the impedance of the antenna is cast into a form which is stationary with respect to small variations (about the true value) of the unknown radial electric field over the surface of the earth. Numerical results are given for the case when the ground plate is sufficiently large as compared to the wave length of the radiation; the effect of variations in dielectric constant of the earth upon the impedance is shown. These calculations are compared to those obtained from the approximate theory of Monteath.A second variational formula for the antenna impedance is developed in terms of surface currents flowing in the metal ground plate. The application of this method becomes useful when the ground plate is not too large in comparison with the wave length.

The Relationship Between Electron-Only Magnetic Reconnection and Turbulence in Earth’s Magnetosheath

2020 ◽  
Author(s):  
Julia E. Stawarz ◽  
Jonathan P. Eastwood ◽  
Tai Phan ◽  
Imogen L. Gingell ◽  
Alfred Mallet ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Power Spectra ◽  
Theoretical Work ◽  
Small Scale ◽  
Current Sheets ◽  
The Earth ◽  
Recent Theoretical Work ◽  
Magnetospheric Multiscale ◽  
Scale Turbulence ◽  
The Relationship

<p>The Earth’s magnetosheath is filled with small-scale current sheets arising from turbulent dynamics in the plasma. Previous observations and simulations have provided evidence that such current sheets can be sites for magnetic reconnection. Recently, observations from the Magnetospheric Multiscale (MMS) mission have revealed that a novel form of “electron-only” reconnection can occur at these small-scale, turbulence-driven current sheets, in which ions do not appear to couple to the reconnected magnetic field to form ion jets. The presence of electron-only reconnection may facilitate dissipation of the turbulence, thereby influencing the partition of energy between ions and electrons, and can alter the nonlinear dynamics of the turbulence itself. In this study, we perform a survey of turbulent intervals in the Earth’s magnetosheath as observed by MMS in order to determine how common magnetic reconnection is in the turbulent magnetosheath and how it impacts the small-scale turbulent dynamics. The magnetic correlation length, which dictates the length of the turbulent current sheets, is short enough in most of the examined intervals for reconnection with reduced or absent ion jets to occur. Magnetic reconnection is found to be a common feature within these intervals, with a significant fraction of reconnecting current sheets showing evidence of sub-Alfvénic ion jets and super- Alfvénic electron jets, consistent with electron-only reconnection. Moreover, a subset of the intervals exhibit changes in the behavior of the small-scale magnetic power spectra, which may be related to the reconnecting current sheets. The results of the survey are compared with recent theoretical work on electron-only reconnection in turbulent plasmas.</p>

Directional Properties of Wireless Receiving Aerials

1928 ◽  
Vol 24 (4) ◽  
pp. 521-530 ◽  
Author(s):  
D. Burnett
Keyword(s):  
Wave Front ◽  
Incident Wave ◽  
Wave Length ◽  
Electric Vector ◽  
Approximate Theory ◽  
The Earth ◽  
Receiving Antenna

Equations have been given by Moullin to determine the current in a receiving antenna in wireless telegraphy and they have been discussed and extended by Colebrooke, who in particular considered the reception of a plane polarised wave with its electric vector vertical by an antenna which is partly vertical and partly horizontal. His result shows that the intensity of the received signal is independent of the orientation of the receiver. In practice, however, the incident wave front is not vertical, its tilt depending on the wave length and on the resistance of the earth, as shown by Zenneck, and the purpose of this paper is to investigate the effect of the orientation of a bent antenna in the reception of this type of wave. An approximate theory of the Beverage antenna is obtained by the same method.

The light-scattering Mueller matrices for Rayleigh and Rayleigh-Gans-Debye approximation

1990 ◽  
Vol 55 (12) ◽  
pp. 2889-2897
Author(s):  
Jaroslav Holoubek
Keyword(s):  
Light Scattering ◽  
Theoretical Work ◽  
Matrix Elements ◽  
Elastic Light Scattering ◽  
Yield Information ◽  
Recent Theoretical Work ◽  
Particle Parameters ◽  
Complete Set ◽  
Single Matrix ◽  
Scattering Matrix Elements

Recent theoretical work has shown that the complete set of polarized elastic light-scattering studies should yield information about scatterer structure that has so far hardly been utilized. We present here calculations of angular dependences of light-scattering matrix elements for spheres near the Rayleigh and Rayleigh-Gans-Debye limits. The significance of single matrix elements is documented on examples that show how different matrix elements respond to changes in particle parameters. It appears that in the small-particle limit (Rg/λ < 0.1) we do not loose much information by ignoring "large particle" observables.

scholarly journals Magnetospheric Structure of Rotation-Powered Neutron Stars

1992 ◽  
Vol 128 ◽  
pp. 56-77 ◽  
Author(s):  
Jonathan Arons
Keyword(s):  
Radio Emission ◽  
Gamma Radiation ◽  
Heavy Ions ◽  
Theoretical Work ◽  
Future Research ◽  
Observational Constraints ◽  
Polar Caps ◽  
Recent Theoretical Work ◽  
Density Flow ◽  
Promising Avenue

AbstractI survey recent theoretical work on the structure of the magnetospheres of rotation-powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research.

scholarly journals THE EXOTIC BARIUM BISMUTHATES

1996 ◽  
Vol 10 (08) ◽  
pp. 863-955 ◽  
Author(s):  
A. TARAPHDER ◽  
RAHUL PANDIT ◽  
H. R. KRISHNAMURTHY ◽  
T. V. RAMAKRISHNAN
Keyword(s):  
Bound States ◽  
Random Phase ◽  
Density Wave ◽  
Mean Field ◽  
Experimental Tests ◽  
Theoretical Work ◽  
Recent Theoretical Work ◽  
Effects Of Disorder ◽  
Exotic Physics ◽  
Transport Gaps

We review the remarkable properties, including superconductivity, charge-density-wave ordering and metal–insulator transitions, of lead- and potassium-doped barium bismuthate. We will discuss some of the early theoretical studies of these systems. Our recent theoretical work, on the negative-U, extended-Hubbard model for these systems, will also be described. Both the large- and intermediate-U regimes of this model were examined, using mean-field and random-phase approximations, particularly with a view to fitting various experimental properties of these bismuthates. On the basis of our studies, we point out possibilities for exotic physics in these systems. We also emphasize the different consequences of electronic and phonon-mediated mechanisms for the negative U. We show that, for an electronic mechanism, the semiconducting phases of these bismuthates must be unique, with their transport properties dominated by charge±2eCooperon bound states. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport and comment on the effects of disorder.

scholarly journals The length of coastlines in Ptolemy's Geography and in ancient periploi

2018 ◽  
Vol 9 (1) ◽  
pp. 9-24 ◽  
Author(s):  
Dmitry A. Shcheglov
Keyword(s):  
Caspian Sea ◽  
Simple Explanation ◽  
The Caspian Sea ◽  
The North ◽  
True Value ◽  
The Earth ◽  
Erroneous Estimate ◽  
Remarkable Agreement ◽  
East West

Abstract. The lengths of the coastlines in Ptolemy's Geography are compared with the corresponding values transmitted by other ancient sources, presumably based on some lost periploi (literally "voyages around or circumnavigations", a genre of ancient geographical literature describing coastal itineraries). The comparison reveals a remarkable agreement between them, suggesting that Ptolemy relied much more heavily on these or similar periploi than it used to be thought. Additionally, a possible impact of Ptolemy's erroneous estimate of the circumference of the Earth is investigated. It is argued that this error resulted in two interrelated distortions of the coastal outlines in Ptolemy's Geography. First, the north–south stretches of the coast that were tied to particular latitudes are shown compressed relative to the distances recorded in other sources in roughly the same proportion to which Ptolemy's circumference of the Earth is underestimated relative to the true value. Second, in several cases this compression is compensated by a proportional stretching of the adjacent east–west coastal segments. In particular, these findings suggest a simple explanation for the strange shape of the Caspian Sea in Ptolemy's Geography.

scholarly journals Landauer in the age of synthetic biology: energy consumption and information processing in biochemical networks

2015 ◽  
Author(s):  
Pankaj Mehta ◽  
Alex H Lang ◽  
David J Schwab
Keyword(s):  
Information Processing ◽  
Energy Consumption ◽  
Synthetic Biology ◽  
Protein Modification ◽  
Theoretical Work ◽  
Biochemical Networks ◽  
Fundamental Physics ◽  
Recent Theoretical Work ◽  
Cellular Circuits ◽  
Molecular Components

A central goal of synthetic biology is to design sophisticated synthetic cellular circuits that can perform complex computations and information processing tasks in response to specific inputs. The tremendous advances in our ability to understand and manipulate cellular information processing networks raises several fundamental physics questions: How do the molecular components of cellu- lar circuits exploit energy consumption to improve information processing? Can one utilize ideas from thermodynamics to improve the design of synthetic cellular circuits and modules? Here, we summarize recent theoretical work addressing these questions. Energy consumption in cellular cir- cuits serves five basic purposes: (1) increasing specificity, (2) manipulating dynamics, (3) reducing variability, (4) amplifying signal, and (5) erasing memory. We demonstrate these ideas using several simple examples and discuss the implications of these theoretical ideas for the emerging field of synthetic biology. We conclude by discussing how it may be possible to overcome these limitations using “post-translational” synthetic biology that exploits reversible protein modification.

scholarly journals Mixed-polarity random-dot stereograms alter GABA and Glx concentration in the early visual cortex

2019 ◽  
Author(s):  
Reuben Rideaux ◽  
Nuno Goncalves ◽  
Andrew E Welchman
Keyword(s):  
Visual Cortex ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Dimensional Structure ◽  
Resonance Spectroscopy ◽  
Gaba Concentration ◽  
Recent Theoretical Work ◽  
Random Dot Stereograms ◽  
Mixed Polarity ◽  
Early Visual Cortex

ABSTRACTThe offset between images projected onto the left and right retinae (binocular disparity) provides a powerful cue to the three-dimensional structure of the environment. It was previously shown that depth judgements are better when images comprise both light and dark features, rather than only dark or only light elements. Since Harris and Parker (1995) discovered the “mixed-polarity benefit”, there has been limited evidence supporting their hypothesis that the benefit is due to separate bright and dark channels. Goncalves and Welchman (2017) observed that single- and mixed-polarity stereograms evoke different levels of positive and negative activity in a deep neural network trained on natural images to make depth judgements, which also showed the mixed-polarity benefit. Motivated by this discovery, here we seek to test the potential for changes in the balance of excitation and inhibition that are produced by viewing these stimuli. In particular, we use magnetic resonance spectroscopy to measure Glx and GABA concentration in the early visual cortex of adult humans while viewing single- and mixed-polarity random-dot stereograms (RDS). We find that observers’ Glx concentration is significantly higher while GABA concentration is significantly lower when viewing mixed-polarity RDS than when viewing single-polarity RDS. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents, consistent with recent theoretical work (Goncalves & Welchman, 2017).

scholarly journals Imaging Mueller matrix determination of transparent, unpolarizing samples using a classically entangled polarization state

2018 ◽  
Vol 64 (4) ◽  
pp. 407
Author(s):  
Jacqueline Isamar Muro-Ríos ◽  
R. Espinosa-Luna
Keyword(s):  
Open Space ◽  
Polarization State ◽  
Theoretical Work ◽  
Mueller Matrix ◽  
Experimental Setup ◽  
Wave Plate ◽  
Recent Theoretical Work ◽  
Study Results ◽  
Theoretical Proposal

Inspired in a recent theoretical work for the determination of the Mueller matrix, using as incidence a single classically entangled polarization state (F. Töppel et al., New J. Phys. 16 (2014) 073019), an experimental setup is proposed and tested.  The open space and two wave plate retarders are used as the transparent, nondepolarizing samples under study. Results show some experimental improvements are necessary in order to implement accurately the theoretical proposal in which this work is based.

scholarly journals Task-evoked pupil responses reflect internal belief states

2018 ◽  
Author(s):  
O. Colizoli ◽  
J.W. de Gee ◽  
A.E. Urai ◽  
T.H. Donner
Keyword(s):  
Pupil Diameter ◽  
Theoretical Work ◽  
Prediction Errors ◽  
Decision Confidence ◽  
Uncertain Evidence ◽  
Recent Theoretical Work ◽  
The Face ◽  
Belief States ◽  
State Of The Environment ◽  
Made In

AbstractPerceptual decisions about the state of the environment are often made in the face of uncertain evidence. Internal uncertainty signals are considered important regulators of learning and decision-making. A growing body of work has implicated the brain’s arousal systems in uncertainty signaling. Here, we found that two specific computational variables, postulated by recent theoretical work, evoke boosts of arousal at different times during a perceptual decision: decision confidence (the observer’s internally estimated probability that a choice was correct given the evidence) before feedback, and prediction errors (deviations from expected reward) after feedback. We monitored pupil diameter, a peripheral marker of central arousal state, while subjects performed a challenging perceptual choice task with a delayed monetary reward. We quantified evoked pupil responses during decision formation and after reward-linked feedback. During both intervals, decision difficulty and accuracy had interacting effects on pupil responses. Pupil responses negatively scaled with decision confidence prior to feedback and scaled with uncertainty-dependent prediction errors after feedback. This pattern of pupil responses during both intervals was in line with a model using the observer’s graded belief about choice accuracy to anticipate rewards and compute prediction errors. We conclude that pupil-linked arousal systems are modulated by internal belief states.

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