4,795 research outputs found
Coulomb field of an accelerated charge: physical and mathematical aspects
The Maxwell field equations relative to a uniformly accelerated frame, and
the variational principle from which they are obtained, are formulated in terms
of the technique of geometrical gauge invariant potentials. They refer to the
transverse magnetic (TM) and the transeverse electric (TE) modes. This gauge
invariant "2+2" decomposition is used to see how the Coulomb field of a charge,
static in an accelerated frame, has properties that suggest features of
electromagnetism which are different from those in an inertial frame. In
particular, (1) an illustrative calculation shows that the Larmor radiation
reaction equals the electrostatic attraction between the accelerated charge and
the charge induced on the surface whose history is the event horizon, and (2) a
spectral decomposition of the Coulomb potential in the accelerated frame
suggests the possibility that the distortive effects of this charge on the
Rindler vacuum are akin to those of a charge on a crystal lattice.Comment: 27 pages, PlainTex. Related papers available at
http://www.math.ohio-state.edu/~gerlac
Bellows flow-induced vibrations
Results of theoretical and experimental investigations of bellows typical of those found in space shuttle external tanks are presented. Correlation parameters are identified which generalize the alternating stress calculations cited in an earlier study. Alternating stress amplitudes and mean stress levels form the basis of a fatigue analysis incorporating seven ordinate charts for 347 stainless steel, alloy 21 6-9, and Inco 718. A crack propagation model is included with a program for computing bellows fatigue life. Two phase flow and material hardness properties are discussed
The Stern-Gerlach Experiment Revisited
The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment
of quantum physics providing evidence for several fundamental properties of
quantum systems. Based on today's knowledge we illustrate the different
benchmark results of the SGE for the development of modern quantum physics and
chemistry.
The SGE provided the first direct experimental evidence for angular momentum
quantization in the quantum world and thus also for the existence of
directional quantization of all angular momenta in the process of measurement.
It measured for the first time a ground state property of an atom, it produced
for the first time a `spin-polarized' atomic beam, it almost revealed the
electron spin. The SGE was the first fully successful molecular beam experiment
with high momentum-resolution by beam measurements in vacuum. This technique
provided a new kinematic microscope with which inner atomic or nuclear
properties could be investigated.
The original SGE is described together with early attempts by Einstein,
Ehrenfest, Heisenberg, and others to understand directional quantization in the
SGE. Heisenberg's and Einstein's proposals of an improved multi-stage SGE are
presented. The first realization of these proposals by Stern, Phipps, Frisch
and Segr\`e is described. The set-up suggested by Einstein can be considered an
anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which
the directional quantization process and possible interference effects of the
two different spin states are investigated.
In full agreement with the results of the new quantum theory directional
quantization appears as a general and universal feature of quantum
measurements. One experimental example for such directional quantization in
scattering processes is shown. Last not least, the early history of the
`almost' discovery of the electron spin in the SGE is revisited.Comment: 50pp, 17 fig
The profile of an emission line from relativistic outflows around a black hole
Recent observations show strong evidence for the presence of Doppler-shifted
emission lines in the spectrum of both black hole candidates and active
galactic nuclei. These lines are likely to originate from relativistic outflows
(or jets) in the vicinity of the central black hole. Consequently, the profile
of such a line should be distorted by strong gravitational effects near the
black hole, as well as special relativistic effects. In this paper, we present
results from a detailed study on how each process affects the observed line
profile. We found that the profile is sensitive to the intrinsic properties of
the jets (Lorentz factor, velocity profile, and emissivity law), as well as to
the spin of the black hole and the viewing angle (with respect to the axis of
the jets). More specifically, in the case of approaching jets, an intrisically
narrow line (blue-shifted) is seen as simply broadened at small viewing angles,
but it shows a doubly peaked profile at large viewing angles for extreme Kerr
black holes (due to the combination of gravitational focusing and Doppler
effects); the profile is always singly peaked for Schwarzschild black holes.
For receding jets, however, the line profile becomes quite complicated owing to
complicated photon trajectories. To facilitate comparison with observations, we
searched a large parameter space to derive representative line profiles. We
show the results and discuss how to use emission lines as a potential tool for
probing the inner region of a black hole jet system.Comment: 16 pages in emulateapj style, 11 figure
Axial perturbations of general spherically symmetric spacetimes
The aim of this paper is to present a governing equation for first order
axial metric perturbations of general, not necessarily static, spherically
symmetric spacetimes. Under the non-restrictive assumption of axisymmetric
perturbations, the governing equation is shown to be a two-dimensional wave
equation where the wave function serves as a twist potential for the
axisymmetry generating Killing vector. This wave equation can be written in a
form which is formally a very simple generalization of the Regge-Wheeler
equation governing the axial perturbations of a Schwarzschild black hole, but
in general the equation is accompanied by a source term related to matter
perturbations. The case of a viscous fluid is studied in particular detail.Comment: 16 pages, no figures, minor correction
On the exciton binding energy in a quantum well
We consider a model describing the one-dimensional confinement of an exciton
in a symmetrical, rectangular quantum-well structure and derive upper and lower
bounds for the binding energy of the exciton. Based on these bounds, we
study the dependence of on the width of the confining potential with a
higher accuracy than previous reports. For an infinitely deep potential the
binding energy varies as expected from at large widths to at
small widths. For a finite potential, but without consideration of a mass
mismatch or a dielectric mismatch, we substantiate earlier results that the
binding energy approaches the value for both small and large widths,
having a characteristic peak for some intermediate size of the slab. Taking the
mismatch into account, this result will in general no longer be true. For the
specific case of a quantum-well
structure, however, and in contrast to previous findings, the peak structure is
shown to survive.Comment: 32 pages, ReVTeX, including 9 figure
Quantum Geometrodynamics I: Quantum-Driven Many-Fingered Time
The classical theory of gravity predicts its own demise -- singularities. We
therefore attempt to quantize gravitation, and present here a new approach to
the quantization of gravity wherein the concept of time is derived by imposing
the constraints as expectation-value equations over the true dynamical degrees
of freedom of the gravitational field -- a representation of the underlying
anisotropy of space. This self-consistent approach leads to qualitatively
different predictions than the Dirac and the ADM quantizations, and in
addition, our theory avoids the interpretational conundrums associated with the
problem of time in quantum gravity. We briefly describe the structure of our
functional equations, and apply our quantization technique to two examples so
as to illustrate the basic ideas of our approach.Comment: 11, (No Figures), (Typeset using RevTeX
Uniformly Accelerated Mirrors. Part 1: Mean Fluxes
The Davies-Fulling model describes the scattering of a massless field by a
moving mirror in 1+1 dimensions. When the mirror travels under uniform
acceleration, one encounters severe problems which are due to the infinite blue
shift effects associated with the horizons. On one hand, the Bogoliubov
coefficients are ill-defined and the total energy emitted diverges. On the
other hand, the instantaneous mean flux vanishes. To obtained well-defined
expressions we introduce an alternative model based on an action principle. The
usefulness of this model is to allow to switch on and off the interaction at
asymptotically large times. By an appropriate choice of the switching function,
we obtain analytical expressions for the scattering amplitudes and the fluxes
emitted by the mirror. When the coupling is constant, we recover the vanishing
flux. However it is now followed by transients which inevitably become singular
when the switching off is performed at late time. Our analysis reveals that the
scattering amplitudes (and the Bogoliubov coefficients) should be seen as
distributions and not as mere functions. Moreover, our regularized amplitudes
can be put in a one to one correspondence with the transition amplitudes of an
accelerated detector, thereby unifying the physics of uniformly accelerated
systems. In a forthcoming article, we shall use our scattering amplitudes to
analyze the quantum correlations amongst emitted particles which are also
ill-defined in the Davies-Fulling model in the presence of horizons.Comment: 23 pages, 7 postscript figure
Monitoring SO2 emission at the Soufriere Hills Volcano: implications for changes in erruptive conditions
FLWINinfo:eu-repo/semantics/publishe
Origin of Hawaiian Tholeiites: Trace Element Constraints
We report here geochemical studies of Hawaiian tholeiites and ultramafic xenoliths from Salt Lake Crater, Oahu. We focus attention on tholeiitic basalts that comprise the bulk of Hawaiian volcanoes. When the samples are screened to include only those lying neat the log-MgO (about 7 percent) end of olivine-control lines (Wright, 1971), tholeiites from individual volcanoes are remarkably uniform. On this basis, we show that, for tholeiites from six volcanoes, systematic geochemical differences exist that cannot be attributed to differentiation of these magmas from a common parental magma. Apparently there have been important differences in the processes of magma generation, source composition, or source mineral constitution.
Partial melting calculations based on REE contents emphasize these distinctions, but unique melting models are not presented. In these models, relative REE abundances in the source material is a major uncertainty. Nd isotopic studies of Hawaiian basalts require systematic differences in Sm/Nd for the source material of each volcano. Furthermore, the time-integrated Sm/Nd of the sources must be less than that in chondrites. REE analyses of Hawaiian garnet lherzolite xenoliths show that they have chondritic to light REE-enriched relative abundances with absolute contents (for light REE) about 3 to 8 times chondrites. These data obviously conflict with interpretations of the Nd isotopic data. Several possibilities follow: (1) the available xenoliths are not parental to tholeiite, (2) our simple interpretation of the Nd isotopic data is wrong, and (3) the source regions may have been invaded at geologically recent times by a light REE-enriched phase, in which case the xenoliths may represent the course material. If the xenoliths are characteristic of the source, partial melting calculations indicate that the tholeiites may be generated by 15 to 20 percent melting of garnet lherzolite and at the sane tune conform to constraints imposed by the REE and Ni contents and the partitioning of Fe and Mg between melts and residues. We propose that the primary tholeiitic magmas contain no more than about 12 percent MgO, and that erupted magmas probably fractionated less than 10 to 15 percent of olivine during ascent and storage in high-level chambers
- …