3,860 research outputs found
The gas temperature in the surface layers of protoplanetary disks
Models for the structure of protoplanetary disks have so far been based on
the assumption that the gas and the dust temperature are equal. The gas
temperature, an essential ingredient in the equations of hydrostatic
equilibrium of the disk, is then determined from a continuum radiative transfer
calculation, in which the continuum opacity is provided by the dust. It has
been long debated whether this assumption still holds in the surface layers of
the disk, where the dust infrared emission features are produced. In this paper
we compute the temperature of the gas in the surface layers of the disk in a
self-consistent manner. The gas temperature is determined from a
heating-cooling balance equation in which processes such as photoelectric
heating, dissociative heating, dust-gas thermal heat exchange and line cooling
are included. The abundances of the dominant cooling species such as CO, C, C+
and O are determined from a chemical network based on the atomic species H, He,
C, O, S, Mg, Si, Fe (Kamp & Bertoldi 2000). The underlying disk models to our
calculations are the models of Dullemond, van Zadelhoff & Natta (2002). We find
that in general the dust and gas temperature are equal to withing 10% for A_V
>~ 0.1, which is above the location of the `super-heated surface layer' in
which the dust emission features are produced (e.g. Chiang & Goldreich 1997).
High above the disk surface the gas temperature exceeds the dust temperature
and can can become -- in the presence of polycyclic aromatic hydrocarbons -- as
high as 600 K at a radius of 100 AU. This is a region where CO has fully
dissociated, but a significant fraction of hydrogen is still in molecular form.
The densities are still high enough for non-negligible H_2 emission to be
produced.....(see paper for full abstract)Comment: 28 pages, 8 figures, accepted for publication in Ap
Neogene plate tectonic reconstructions and geodynamics of North Island sedimentary basins: Implications for the petroleum systems
Although the modern Australia-Pacific plate boundary through New Zealand is relatively straight, there have been significant changes in its geometry during the Neogene. Within the North Island sector there has been a fundamental transition from an Alpine Fault translation/transpression regime to a Hikurangi margin subduction regime. This transition has been accompanied by the southward encroachment of the edge of the Pacific plate oceanic slab into Australia lithosphere, shortened and thickened along its eastern margin as a consequence of the prior Alpine Fault transpression, the process now operating in South Island. The response of the Australia lithosphere at the surface to the emplacement of the subducted slab at depth, has differed in the East Coast forearc region versus the foreland in western North Island, where the depth to the slab is greater and there has been a characteristic southward migration of depocentres pinned to the leading edge of the slab. The recent publication of new rotation parameters for relative motion of the Australia, Antarctic and Pacific plates, have provided key new data from which to plot the successive emplacement history of the Pacific slab beneath North Island, thus enabling the comparisons to be made with basin stratigraphy and geohistory. These data also constrain the age of subduction initiation at various points along the present trend of the Hikurangi Trough, identifying a younging of subduction initiation to the southwest. An implication of this younging direction is that the modern accretionÂŹary prism south of Cape Kidnappers can be no older than late Miocene (c. 11 Ma). The focus of this paper is on new ideas about the tectonic development of North Island and its basins, which have implications for hydrocarbon exploration
Ponderomotive manipulation of cold subwavelength plasmas
Ponderomotive forces (PFs) induced in cold subwavelength plasmas by an
externally applied electromagnetic wave are studied analytically. To this end,
the plasma is modeled as a sphere with a radially varying permittivity, and the
internal electric fields are calculated by solving the macroscopic Maxwell
equations using an expansion in Debye potentials. It is found that the PF is
directed opposite to the plasma density gradient, similarly to large-scale
plasmas. In case of a uniform density profile, a residual spherically symmetric
compressive PF is found, suggesting possibilities for contactless ponderomotive
manipulation of homogeneous subwavelength objects. The presence of a surface PF
on discontinuous plasma boundaries is derived. This force is essential for a
microscopic description of the radiation-plasma interaction consistent with
momentum conservation. It is shown that the PF integrated over the plasma
volume is equivalent to the radiation pressure exerted on the plasma by the
incident wave. The concept of radiative acceleration of subwavelength plasmas,
proposed earlier, is applied to ultracold plasmas. It is estimated that these
plasmas may be accelerated to keV ion energies, resulting in a neutralized beam
with a brightness comparable to that of current high-performance ion sources.Comment: 16 pages, 6 figure
Classical formulations of the electromagnetic self-force of extended charged bodies
Several noncovariant formulations of the electromagnetic self-force of
extended charged bodies, as have been developed in the context of classical
models of charged particles, are compared. The mathematical equivalence of the
various dissimilar self-force expressions is demonstrated explicitly by
deriving these expressions directly from one another. The applicability of the
self-force formulations and their significance in the wider context of
classical charged particle models are discussed.Comment: 21 pages, 1 figur
Group Communication Patterns for High Performance Computing in Scala
We developed a Functional object-oriented Parallel framework (FooPar) for
high-level high-performance computing in Scala. Central to this framework are
Distributed Memory Parallel Data structures (DPDs), i.e., collections of data
distributed in a shared nothing system together with parallel operations on
these data. In this paper, we first present FooPar's architecture and the idea
of DPDs and group communications. Then, we show how DPDs can be implemented
elegantly and efficiently in Scala based on the Traversable/Builder pattern,
unifying Functional and Object-Oriented Programming. We prove the correctness
and safety of one communication algorithm and show how specification testing
(via ScalaCheck) can be used to bridge the gap between proof and
implementation. Furthermore, we show that the group communication operations of
FooPar outperform those of the MPJ Express open source MPI-bindings for Java,
both asymptotically and empirically. FooPar has already been shown to be
capable of achieving close-to-optimal performance for dense matrix-matrix
multiplication via JNI. In this article, we present results on a parallel
implementation of the Floyd-Warshall algorithm in FooPar, achieving more than
94 % efficiency compared to the serial version on a cluster using 100 cores for
matrices of dimension 38000 x 38000
Automated Termination Proofs for Logic Programs by Term Rewriting
There are two kinds of approaches for termination analysis of logic programs:
"transformational" and "direct" ones. Direct approaches prove termination
directly on the basis of the logic program. Transformational approaches
transform a logic program into a term rewrite system (TRS) and then analyze
termination of the resulting TRS instead. Thus, transformational approaches
make all methods previously developed for TRSs available for logic programs as
well. However, the applicability of most existing transformations is quite
restricted, as they can only be used for certain subclasses of logic programs.
(Most of them are restricted to well-moded programs.) In this paper we improve
these transformations such that they become applicable for any definite logic
program. To simulate the behavior of logic programs by TRSs, we slightly modify
the notion of rewriting by permitting infinite terms. We show that our
transformation results in TRSs which are indeed suitable for automated
termination analysis. In contrast to most other methods for termination of
logic programs, our technique is also sound for logic programming without occur
check, which is typically used in practice. We implemented our approach in the
termination prover AProVE and successfully evaluated it on a large collection
of examples.Comment: 49 page
The staircase method: integrals for periodic reductions of integrable lattice equations
We show, in full generality, that the staircase method provides integrals for
mappings, and correspondences, obtained as traveling wave reductions of
(systems of) integrable partial difference equations. We apply the staircase
method to a variety of equations, including the Korteweg-De Vries equation, the
five-point Bruschi-Calogero-Droghei equation, the QD-algorithm, and the
Boussinesq system. We show that, in all these cases, if the staircase method
provides r integrals for an n-dimensional mapping, with 2r<n, then one can
introduce q<= 2r variables, which reduce the dimension of the mapping from n to
q. These dimension-reducing variables are obtained as joint invariants of
k-symmetries of the mappings. Our results support the idea that often the
staircase method provides sufficiently many integrals for the periodic
reductions of integrable lattice equations to be completely integrable. We also
study reductions on other quad-graphs than the regular 2D lattice, and we prove
linear growth of the multi-valuedness of iterates of high-dimensional
correspondences obtained as reductions of the QD-algorithm.Comment: 40 pages, 23 Figure
Trickery, Treachery, Tyranny and Treason in Washington
Date unknownhttps://egrove.olemiss.edu/citizens_pamph/1081/thumbnail.jp
Involutivity of integrals for sine-Gordon, modified KdV and potential KdV maps
Closed form expressions in terms of multi-sums of products have been given in
\cite{Tranclosedform, KRQ} of integrals of sine-Gordon, modified Korteweg-de
Vries and potential Korteweg-de Vries maps obtained as so-called
-traveling wave reductions of the corresponding partial difference
equations. We prove the involutivity of these integrals with respect to
recently found symplectic structures for those maps. The proof is based on
explicit formulae for the Poisson brackets between multi-sums of products.Comment: 24 page
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