3,407 research outputs found
A quantum violation of the second law?
An apparent violation of the second law of thermodynamics occurs when an atom
coupled to a zero-temperature bath, being necessarily in an excited state, is
used to extract work from the bath. Here the fallacy is that it takes work to
couple the atom to the bath and this work must exceed that obtained from the
atom. For the example of an oscillator coupled to a bath described by the
single relaxation time model, the mean oscillator energy and the minimum work
required to couple the oscillator to the bath are both calculated explicitly
and in closed form. It is shown that the minimum work always exceeds the mean
oscillator energy, so there is no violation of the second law
Balmer and Metal Absorption Feature Gradients in M32
Spectra from MDM Observatory are used to assess Lick/IDS feature strength
gradients inside the half-light radius of the compact Local Group elliptical
galaxy M32. All but a few (of 24 measured) indices show a statistically
significant gradient. Comparing with models, the index gradients indicate a
mean age and abundance gradient in the sense that the nucleus is a factor of
2.5 younger and a factor of 0.3 dex more metal-rich than at 1 effective radius.
This conclusion is only weakly dependent on which index combinations are used
and is robust to high accuracy. Stars near the M32 nucleus have a mean age and
heavy element abundance [M/H] of (4.7 Gyr, +0.02), judging from models by
Worthey with variable abundance ratios. This result has very small formal
random errors, although, of course, there is significant age-metallicity
degeneracy along an (age, abundance) line segment from (5.0 Gyr, 0.00) to (4.5
Gyr, +0.05). An abundance pattern of [C/M]=+0.077, [N/M]=-0.13, [Mg/M]=-0.18,
[Fe/M]~0.0, and [Na/M]=+0.12 is required to fit the feature data, with a
fitting precision of about 0.01 dex. Model uncertainties make the accuracies of
these values at least twice the magnitude of the precision. Forcing
scaled-solar abundances does not change the age very much, but it increases the
rms goodness of model-data fit by a factor of 3 and broadens the allowed range
of age to Gyr. The overall abundance pattern contrasts with larger
elliptical galaxies, in which all measurable lighter elements are enhanced
relative to iron and calcium.Comment: 23 pages, 9 figures, Astronomical Journal, in pres
Consistency of a Causal Theory of Radiative Reaction with the Optical Theorem
The Abraham-Lorentz-Dirac equation for a point electron, while suffering from
runaway solutions and an acausal response to external forces, is compatible
with the optical theorem. We show that a theory of radiative reaction that
allows for a finite charge distribution is not only causal and free of runaway
solutions, but is also consistent with the optical theorem and the standard
formula for the Rayleigh scattering cross section.Comment: 4 pages, 2 figure
Rotation and Spin in Physics
We delineate the role of rotation and spin in physics, discussing in order
Newtonian classical physics, special relativity, quantum mechanics, quantum
electrodynamics and general relativity. In the latter case, we discuss the
generalization of the Kepler formula to post-Newtonian order )
including spin effects and two-body effects. Experiments which verify the
theoretical results for general relativistic spin-orbit effects are discussed
as well as efforts being made to verify the spin-spin effects
Anomalous diffusion in quantum Brownian motion with colored noise
Anomalous diffusion is discussed in the context of quantum Brownian motion
with colored noise. It is shown that earlier results follow simply and directly
from the fluctuation-dissipation theorem. The limits on the long-time
dependence of anomalous diffusion are shown to be a consequence of the second
law of thermodynamics. The special case of an electron interacting with the
radiation field is discussed in detail. We apply our results to wave-packet
spreading
A multi-layer extension of the stochastic heat equation
Motivated by recent developments on solvable directed polymer models, we
define a 'multi-layer' extension of the stochastic heat equation involving
non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio
Nonlinear Excitations in Strongly-Coupled Fermi-Dirac Plasmas
In this paper we use the conventional quantum hydrodynamics (QHD) model in
combination with the Sagdeev pseudopotential method to explore the effects of
Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron
exchange and ion correlation on the large-amplitude nonlinear soliton dynamics
in Fermi-Dirac plasmas. It is found that in the presence of strong interactions
significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in
the two distinct regimes of nonrelativistic and relativistic degeneracies
exist. Furthermore, it is remarked that first-order corrections due to such
interactions (which are proportional to the fine-structure constant) are
significant on soliton dynamics in nonrelativistic plasma degeneracy regime
rather than relativistic one. In the relativistic degeneracy regime, however,
these effects become less important and the electron quantum-tunneling and
Pauli-exclusion dominate the nonlinear wave dynamics. Hence, application of
non-interacting Fermi-Dirac QHD model to study the nonlinear wave dynamics in
quantum plasmas such as compact stars is most appropriate for the relativistic
degeneracy regime
Quantum collapse in ground-state Fermi-Dirac-Landau plasmas
It is revealed that in a relativistically degenerate dense highly-magnetized
electron-ion plasma the effective quantum-potential due to the total
quantum-force acting on fermions may cancel-out causing a quantum transverse
collapse in the ground-state Fermi-Dirac-Landau (GSFDL) plasma. The condition
for the plasma transverse collapse is found to be restricted to the minimum
relativistic degeneracy parameter and minimum impressed magnetic field strength
values satisfied for many superdense astrophysical objects such as white dwarfs
and neutron stars. In such plasmas, the magnetization pressure is shown to
cancel the lateral electron degeneracy pressure counteracting the existing
gravitational pressure. Furthermore, using the Sagdeev pseudopotential method
in the framework of quantum magnetohydrodynamics (QMHD) model including spin
magnetization it is confirmed that the quantum pressure due to spin-orbit
polarization and the electron relativistic degeneracy has significant effects
on the existence criteria and the propagation of localized magnetosonic density
excitations in GSFDL plasmas. Current findings can have important implications
for the density excitations mechanism and gravitational collapse of the highly
magnetized astrophysical relativistically dense objects such as white-dwarfs,
neutron stars, magnetars and pulsars.Comment: To be Published in Journal Physics of Plasma
Intermittent magnetic field excitation by a turbulent flow of liquid sodium
The magnetic field measured in the Madison Dynamo Experiment shows
intermittent periods of growth when an axial magnetic field is applied. The
geometry of the intermittent field is consistent with the fastest growing
magnetic eigenmode predicted by kinematic dynamo theory using a laminar model
of the mean flow. Though the eigenmodes of the mean flow are decaying, it is
postulated that turbulent fluctuations of the velocity field change the flow
geometry such that the eigenmode growth rate is temporarily positive.
Therefore, it is expected that a characteristic of the onset of a turbulent
dynamo is magnetic intermittency.Comment: 5 pages, 7 figure
Orbital Ferromagnetism and Quantum Collapse in Stellar Plasmas
The possibility of quantum collapse and characteristics of nonlinear
localized excitations is examined in dense stars with Landau orbital
ferromagnetism in the framework of conventional quantum magnetohydrodynamics
(QMHD) model including Bohm force and spin-orbit polarization effects.
Employing the concepts of effective potential and Sagdeev pseudopotential, it
is confirmed that the quantum collapse and Landau orbital ferromagnetism
concepts are consistent with the magnetic field and mass-density range present
in some white dwarf stars. Furthermore, the value of ferromagnetic-field found
in this work is about the same order of magnitude as the values calculated
earlier. It is revealed that the magnetosonic nonlinear propagations can behave
much differently in the two distinct non-relativistic and relativistic
degeneracy regimes in a ferromagnetic dense astrophysical object. Current
findings should help to understand the origin of the most important mechanisms
such as gravitational collapse and the high magnetic field present in many
compact stars.Comment: To appear in journal Physics of Plasma
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