THE CAPACITANCE MODEL FOR PERSISTENT CURRENTS IN MESOSCOPIC METAL RINGS

1994 ◽  
Vol 08 (19) ◽  
pp. 2593-2635 ◽  
Author(s):  
PETER KOPIETZ
Keyword(s):  
Energy Levels ◽  
Theoretical Work ◽  
Mean Free Path ◽  
Persistent Currents ◽  
Diffusive Regime ◽  
Metal Rings ◽  
Dependent Part ◽  
Recent Theoretical Work ◽  
Capacitance Model ◽  
Hartree Energy

We review recent theoretical work on persistent currents in mesoscopic normal-metal rings and present a detailed discussion the generalized capacitance model.20(a) This model provides a natural explanation for the surprisingly large experimentally observed currents in the diffusive regime. We pay particular attention to the problem of screening in a thin mesoscopic ring, and argue that screening corrections to the flux-dependent part of the Hartree energy are negligible provided the condition [Formula: see text] is satisfied. Here e2/C0 is the classical charging energy for adding one electron to the system, and [Formula: see text] is the average number of energy levels within an interval of width E c below the Fermi energy µ, where E c is the Thouless energy. This condition is equivalent with (k F l)(L⊥/L)2 ≪ 1 (where l is the elastic mean free path, L is the circumference and L⊥ is the transverse thickness of the ring), and shows that the ring geometry plays an important role. In thin rings the mesoscopic persistent current is universal in precisely the same sense as the variance of the conductance.

scholarly journals SPECTRAL CORRELATIONS IN DISORDERED MESOSCOPIC METALS AND THEIR RELEVANCE FOR PERSISTENT CURRENTS

1996 ◽  
Vol 10 (28) ◽  
pp. 1397-1406 ◽  
Author(s):  
AXEL VÖLKER ◽  
PETER KOPIETZ
Keyword(s):  
Energy Levels ◽  
Three Dimensional ◽  
Average Density ◽  
Electron Interaction ◽  
Energy Window ◽  
Persistent Currents ◽  
Dependent Part ◽  
The Difference ◽  
Aharonov Bohm ◽  
Grand Canonical

We use the Lanczos method to calculate the variance σ2(E, ϕ) of the number of energy levels in an energy window of width E below the Fermi energy for noninteracting disordered electrons on a thin three-dimensional ring threaded by an Aharonov–Bohm flux ϕ. We confirm numerically that for small E the flux-dependent part of σ2(E, ϕ) is well described by the Altshuler–Shklovskii-diagram involving two Cooperons. However, in the absence of electron–electron interactions this result cannot be extrapolated to energies E where the energy-dependence of the average density of states becomes significant. We discuss consequences for persistent currents and argue that for the calculation of the difference between the canonical- and grand canonical current it is crucial to take the electron–electron interaction into account.

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.

THE ANALOGUE OF THE AHARONOV–BOHM EFFECT FOR BOUND STATES FOR NEUTRAL PARTICLES

2011 ◽  
Vol 26 (18) ◽  
pp. 1331-1341 ◽  
Author(s):  
KNUT BAKKE ◽  
C. FURTADO
Keyword(s):  
Bound States ◽  
Neutral Particle ◽  
Energy Levels ◽  
Quantum Ring ◽  
Persistent Currents ◽  
One Dimensional ◽  
Neutral Particles ◽  
Quantum Flux ◽  
Bohm Effect ◽  
Aharonov Bohm

We study the analogue of the Aharonov–Bohm effect for bound states for a neutral particle with a permanent magnetic dipole moment interacting with an external field. We consider a neutral particle confined to moving between two coaxial cylinders and show the dependence of the energy levels on the Aharonov-Casher quantum flux. Moreover, we show that the same flux dependence of the bound states can be found when the neutral particle is confined to a one-dimensional quantum ring and a quantum dot, and we also calculate the persistent currents in each case.

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 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.

Effect of pressure on bubble size in dissolved air flotation

2002 ◽  
Vol 2 (5-6) ◽  
pp. 41-46 ◽  
Author(s):  
M. Han ◽  
Y. Park ◽  
J. Lee ◽  
J. Shim
Keyword(s):  
Bubble Size ◽  
Critical Pressure ◽  
Theoretical Work ◽  
Particle Sizes ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Recent Theoretical Work ◽  
Water And Wastewater ◽  
Air Flotation ◽  
Dissolved Air

Although dissolved air flotation (DAF) has been successfully adopted for water and wastewater treatment, the fundamental characteristics of the process have not been fully investigated. According to recent theoretical work on DAF, bubble size is one of the most important factors that affect the efficiency of the process, with better removal efficiency when the sizes of both bubbles and particles are similar. In this study, a newly developed particle counter method (PCM) was introduced to measure particle sizes. To confirm its usefulness, the results were compared with those from image analysis. Then, using PCM, the size of bubbles in DAF was measured under various pressure conditions which are known to affect the bubble size the most (from 2 to 6 atmospheres). The bubble size decreased as the pressure increased up to a pressure of 3.5 atmospheres. Above this critical pressure, the bubble size did not decrease with further increases in pressure. According to these experimental results, it is not only costly, but also unnecessary, to maintain a pressure above 3.5 atmospheres if the goal is only to generate smaller bubbles.

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