3,216 research outputs found
International Cometary Explorer (ICE)
The primary mission objectives of the International Cometary Explorer (ICE) Comet Mission are to determine the composition and physical state of the Giacobini-Zinner Comet's nucleus; to determine the processes that governs the composition and distribution of neutral and ionized species in the cometary atmosphere; and to investigate the interaction between the solar wind and the cometary atmosphere. The spacecraft was in a halo orbit around the Sun-Earth libration point until it was moved 10 Jun. 1982 to the Earth's Geomagnetic Tail (GT). The spacecraft reached the GT in Jan. 1983 and remained there until Dec. 1983, at which time a lunar swing-by placed the spacecraft in a trajectory heliocentric orbit which encountered the comet Giacobini-Zinner in Sep. 1985. The spacecraft provided observations of solar wind upstream of Halley's Comet in 1986. Information is presented in tabular form and includes the following areas: Deep Space Network support, frequency assignments, telemetry, command, and tracking support responsibilities
Some Further Results for the Stationary Points and Dynamics of Supercooled Liquids
We present some new theoretical and computational results for the stationary
points of bulk systems. First we demonstrate how the potential energy surface
can be partitioned into catchment basins associated with every stationary point
using a combination of Newton-Raphson and eigenvector-following techniques.
Numerical results are presented for a 256-atom supercell representation of a
binary Lennard-Jones system. We then derive analytical formulae for the number
of stationary points as a function of both system size and the Hessian index,
using a framework based upon weakly interacting subsystems. This analysis
reveals a simple relation between the total number of stationary points, the
number of local minima, and the number of transition states connected on
average to each minimum. Finally we calculate two measures of localisation for
the displacements corresponding to Hessian eigenvectors in samples of
stationary points obtained from the Newton-Raphson-based geometry optimisation
scheme. Systematic differences are found between the properties of eigenvectors
corresponding to positive and negative Hessian eigenvalues, and localised
character is most pronounced for stationary points with low values of the
Hessian index.Comment: 16 pages, 2 figure
Comment on ``Quasisaddles as relevant points of the potential energy surface in the dynamics of supercooled liquids'' [J. Chem. Phys. 116, 10297 (2002); cond-mat/0203301]
Recently, the properties of supercooled liquids have been studied by mapping
instaneous configurations onto minima of the gradient squared. It was
originally suggested that this mapping would probe higher-order saddle points
of the potential energy surface. However, it was subsequently shown that the
majority of the minima of this function are only local minima and so do not
correspond to saddles. In this comment, we provide a critique of the suggestion
made by Angelani et al. [J. Chem. Phys. 116, 10297 (2002); cond-mat/0203301]
that although these minima are not true saddles, they are almost saddles (hence
the term quasisaddles). This issue has important implications for the
interpretation of the results obtained by this approach.Comment: 2 page
Structures, processes and governance in tax policy-making: an initial report
This report documents an international study of the tax policy-making process carried out under the auspices of the Oxford University Centre for Business Taxation (OUCBT).
The objective of the work was to make a comparative analysis of the structures, processes and governance in this important area of government activity, where there has been little work to date, and enable good practice to be identified.
We believe this study will help inform thinking among governments and other interested groups in both developed and developing countries; and provide them with benchmarks against which to measure their own arrangements and a methodology through which to do so. Good structures, processes and governance do not
automatically lead to good policy, but we believe getting these elements right will make the achievement of better policy outcomes more likely and reduce the risk of avoidable policy failures
Saddle Points and Dynamics of Lennard-Jones Clusters, Solids and Supercooled Liquids
The properties of higher-index saddle points have been invoked in recent
theories of the dynamics of supercooled liquids. Here we examine in detail a
mapping of configurations to saddle points using minimization of , which has been used in previous work to support these theories. The
examples we consider are a two-dimensional model energy surface and binary
Lennard-Jones liquids and solids. A shortcoming of the mapping is its failure
to divide the potential energy surface into basins of attraction surrounding
saddle points, because there are many minima of that do not
correspond to stationary points of the potential energy. In fact, most liquid
configurations are mapped to such points for the system we consider. We
therefore develop an alternative route to investigate higher-index saddle
points and obtain near complete distributions of saddles for small
Lennard-Jones clusters. The distribution of the number of stationary points as
a function of the index is found to be Gaussian, and the average energy
increases linearly with saddle point index in agreement with previous results
for bulk systems.Comment: 14 pages, 7 figure
Structural relaxation in Morse clusters: Energy landscapes
We perform a comprehensive survey of the potential energy landscapes of
13-atom Morse clusters, and describe how they can be characterized and
visualized. Our aim is to detail how the global features of the funnel-like
surface change with the range of the potential, and to relate these changes to
the dynamics of structural relaxation. We find that the landscape becomes
rougher and less steep as the range of the potential decreases, and that
relaxation paths to the global minimum become more complicated.Comment: 21 pages, 3 tables, 5 figure
Understanding fragility in supercooled Lennard-Jones mixtures. II. Potential energy surface
We numerically investigated the connection between isobaric fragility and the
properties of high-order stationary points of the potential energy surface in
different supercooled Lennard-Jones mixtures. The increase of effective
activation energies upon supercooling appears to be driven by the increase of
average potential energy barriers measured by the energy dependence of the
fraction of unstable modes. Such an increase is sharper, the more fragile is
the mixture. Correlations between fragility and other properties of high-order
stationary points, including the vibrational density of states and the
localization features of unstable modes, are also discussed.Comment: 13 pages, 13 figures, minor revisions, one figure adde
A concept for a fuel efficient flight planning aid for general aviation
A core equation for estimation of fuel burn from path profile data was developed. This equation was used as a necessary ingredient in a dynamic program to define a fuel efficient flight path. The resultant algorithm is oriented toward use by general aviation. The pilot provides a description of the desired ground track, standard aircraft parameters, and weather at selected waypoints. The algorithm then derives the fuel efficient altitudes and velocities at the waypoints
Non existence of a phase transition for the Penetrable Square Wells in one dimension
Penetrable Square Wells in one dimension were introduced for the first time
in [A. Santos et. al., Phys. Rev. E, 77, 051206 (2008)] as a paradigm for
ultra-soft colloids. Using the Kastner, Schreiber, and Schnetz theorem [M.
Kastner, Rev. Mod. Phys., 80, 167 (2008)] we give strong evidence for the
absence of any phase transition for this model. The argument can be generalized
to a large class of model fluids and complements the van Hove's theorem.Comment: 14 pages, 7 figures, 1 tabl
Coordination motifs and large-scale structural organization in atomic clusters
The structure of nanoclusters is complex to describe due to their
noncrystallinity, even though bonding and packing constraints limit the local
atomic arrangements to only a few types. A computational scheme is presented to
extract coordination motifs from sample atomic configurations. The method is
based on a clustering analysis of multipole moments for atoms in the first
coodination shell. Its power to capture large-scale structural properties is
demonstrated by scanning through the ground state of the Lennard-Jones and
C clusters collected at the Cambridge Cluster Database.Comment: 6 pages, 7 figure
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