3,521 research outputs found
Sulfur diagenesis in marine sediments
Bacterial sulfate reduction occurs in all marine sediments that contain organic matter. Aqueous sulfide (HS-, H2S), one of the initial products of bacterial sulfide reduction, is extremely reactive with iron bearing minerals: sulfur is fixed into sediments as iron sulfide (first FeS and then Fe2S2). A working definition is given of sulfur diagenesis in marine sediments. Controls and consequences of sulfate reduction rates in marine sediments are examined
A Closer Look at the Elementary Fermions
Although there have been many experimental and theoretical efforts to measure
and interpret small deviations from the standard model of particle physics, the
gap that the model leaves in understanding why there are only three generations
of elementary fermions, with hierarchical masses, has not received the
attention it deserves. I present here an attempt to fill this gap. Although our
findings are mostly only qualitative, they nevertheless may be of heuristic
value. Rules concerning the elementary fermions, some previously known and some
new, lead to a number of conclusions and questions that seem worth pursuing.
Some clarify the standard model, and others suggest possible modifications, the
implications of which are discussed.Comment: 8 page
Aharonov-Bohm Problem for Spin-One
The basic AB problem is to determine how an unshielded tube of magnetic flux
affects arbitrarily long-wavelength charged particles impinging on it.
For spin-1 at almost all the particles do not penetrate the tube, so the
interaction essentially is periodic in (AB effect). Below-threshold
bound states move freely only along the tube axis, and consequent induced
vacuum currents supplement rather than screen . For a pure magnetic
interaction the tube must be broader than the particle Compton wavelength,
i.e., only the nonrelativistic spin-1 AB problem exists.Comment: 15 pages, Late
Gauge Invariance and the Pauli-Villars Regulator in Lorentz- and CPT-Violating Electrodynamics
We examine the nonperturbative structure of the radiatively induced
Chern-Simons term in a Lorentz- and CPT-violating modification of QED. Although
the coefficient of the induced Chern-Simons term is in general undetermined,
the nonperturbative theory appears to generate a definite value. However, the
CPT-even radiative corrections in this same formulation of the theory generally
break gauge invariance. We show that gauge invariance may yet be preserved
through the use of a Pauli-Villars regulator, and, contrary to earlier
expectations, this regulator does not necessarily give rise to a vanishing
Chern-Simons term. Instead, two possible values of the Chern-Simons coefficient
are allowed, one zero and one nonzero. This formulation of the theory therefore
allows the coefficient to vanish naturally, in agreement with experimental
observations.Comment: 8 page
Local Casimir Energy For Solitons
Direct calculation of the one-loop contributions to the energy density of
bosonic and supersymmetric phi-to-the-fourth kinks exhibits: (1) Local mode
regularization. Requiring the mode density in the kink and the trivial sectors
to be equal at each point in space yields the anomalous part of the energy
density. (2) Phase space factorization. A striking position-momentum
factorization for reflectionless potentials gives the non-anomalous energy
density a simple relation to that for the bound state. For the supersymmetric
kink, our expression for the energy density (both the anomalous and
non-anomalous parts) agrees with the published central charge density, whose
anomalous part we also compute directly by point-splitting regularization.
Finally we show that, for a scalar field with arbitrary scalar background
potential in one space dimension, point-splitting regularization implies local
mode regularization of the Casimir energy density.Comment: 18 pages. Numerous new clarifications and additions, of which the
most important may be the direct derivation of local mode regularization from
point-splitting regularization for the bosonic kink in 1+1 dimension
Off-Diagonal Long-Range Order, Restricted Gauge Transformations, and Aharonov-Bohm Effect in Conductors
The Hamiltonian describing a conductor surrounding an external magnetic field
contains a nonvanishing vector potential in the volume accessible to the
electrons and nuclei of which the conductor is made. That vector potential
cannot be removed by a gauge transformation. Nevertheless, a macroscopic normal
conductor can experience no Aharonov-Bohm effect. That is proved by assuming
only that a normal conductor lacks off-diagonal long-range order (ODLRO). Then
by restricting the Hilbert space to density matrices which lack ODLRO, it is
possible to introduce a restricted gauge transformation that removes the
interaction of the conductor with the vector potential.Comment: Editing errors are corrected. One was slightly misleadin
Thermoelectric effects in quantum dots
We report a numerical renormalization-group study of the thermoelectric
effect in the single-electron transistor (SET) and side-coupled geometries. As
expected, the computed thermal conductance and thermopower curves show
signatures of the Kondo effect and of Fano interference. The thermopower curves
are also affected by particle-hole asymmetry.Comment: 8 pages with 3 figures; accepted for publication in Physica B
(special issue 'Strongly Correlated Electron Systems-SCES2008'
- …