7,994 research outputs found
Circumbinary disc survival during binary-single scattering: towards a dynamical model of the Orion BN/KL complex
The Orion BN/KL complex is the nearest site of ongoing high-mass star
formation. Recent proper motion observations provide convincing evidence of a
recent (about 500 years ago) dynamical interaction between two massive young
stellar objects in the region resulting in high velocities: the BN object and
radio Source I. At the same time, Source I is surrounded by a nearly edge-on
disc with radius ~50 au. These two observations taken together are puzzling: a
dynamical encounter between multiple stars naturally yields the proper motions,
but the survival of a disc is challenging to explain. In this paper we take the
first steps to numerically explore the preferred dynamical scenario of Goddi et
al., in which Source I is a binary that underwent a scattering encounter with
BN, in order to determine if a pre-existing disc can survive this encounter in
some form. Treating only gravitational forces, we are able to thoroughly and
efficiently cover a large range of encounter parameters. We find that disc
material can indeed survive a three-body scattering event if 1) the encounter
is close, i.e. BN's closest approach to Source I is comparable to Source I's
semi-major axis; and 2) the interplay of the three stars is of a short
duration. Furthermore, we are able to constrain the initial conditions that can
broadly produce the orientation of the present-day system's disc relative to
its velocity vector. To first order we can thus confirm the plausibility of the
scattering scenario of Goddi et al., and we have significantly constrained the
parameters and narrowed the focus of future, more complex and expensive
attempts to computationally model the complicated BN/KL region.Comment: MNRAS in pres
Attacking Group Protocols by Refuting Incorrect Inductive Conjectures
Automated tools for finding attacks on flawed security protocols often fail to deal adequately with group protocols. This is because the abstractions made to improve performance on fixed 2 or 3 party protocols either preclude the modelling of group protocols all together, or permit modelling only in a fixed scenario, which can prevent attacks from being discovered. This paper describes Coral, a tool for finding counterexamples to incorrect inductive conjectures, which we have used to model protocols for both group key agreement and group key management, without any restrictions on the scenario. We will show how we used Coral to discover 6 previously unknown attacks on 3 group protocols
Fock space relativistic coupled-Cluster calculations of Two-Valence Atoms
We have developed an all particle Fock-space relativistic coupled-cluster
method for two-valence atomic systems. We then describe a scheme to employ the
coupled-cluster wave function to calculate atomic properties. Based on these
developments we calculate the excitation energies, magnetic hyperfine constants
and electric dipole matrix elements of Sr, Ba and Yb. Further more, we
calculate the electric quadrupole HFS constants and the electric dipole matrix
elements of Sr, Ba and Yb. For these we use the one-valence
coupled-cluster wave functions obtained as an intermediate in the two-valence
calculations. We also calculate the magnetic dipole hyperfine constants of
Yb.Comment: 23 pages, 12 figures, 10 tables typos are corrected and some minor
modifications in some of the section
Integrating research with NHS clinical practice: Unwelcome intrusion or constructive triangulation?
When embarking on research into the effectiveness of psychoanalytic psychotherapy in the NHS or the application of psychoanalytic principles, researchers come up against a number of hurdles: many clinicians still see empirical research as antithetical or disruptive to the practice of psychoanalytic psychotherapy; psychoanalytic psychotherapy has previously fared poorly in evidence-based policy guidelines and this can discourage ambition, and there are technical problems of research design, measurement and standardization. Nevertheless, in a political climate which stresses service evaluation, measurable outcomes and empirical evidence, psychoanalytic psychotherapy must participate to survive. There may be gains from conducting research beyond simply meeting the requirement to provide evidence of effectiveness. Research may be viewed by some clinicians as an unwelcome intruder but it may have the potential to offer triangulation, the perspective of the 'third', and so strengthen the foundations of clinical practice and the development of psychoanalytic thought
A Woman\u27s Cry For Help: Why The United States Should Apply Germany\u27s Model Of Self-Defense For The Battered Woman
Domestic violence cuts across all social, economical, and political strata. In the United States a woman is beaten every fifteen seconds in her own home. In 1988, 1075 women were murdered by their spouse
Shape Coexistence and the Effective Nucleon-Nucleon Interaction
The phenomenon of shape coexistence is discussed within the self-consistent
Hartree-Fock method and the nuclear shell model. The occurrence of the
coexisting configurations with different intrinsic shapes is traced back to the
properties of the effective Hamiltonian.Comment: 40 pages (16 text, 24 figures). The file may also be retrieved at
http://csep2.phy.ornl.gov/theory_group/people/dean/shape_coex/shapes.htm
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