20,102 research outputs found
Formation and Evolution of Binary Asteroids
Satellites of asteroids have been discovered in nearly every known small body
population, and a remarkable aspect of the known satellites is the diversity of
their properties. They tell a story of vast differences in formation and
evolution mechanisms that act as a function of size, distance from the Sun, and
the properties of their nebular environment at the beginning of Solar System
history and their dynamical environment over the next 4.5 Gyr. The mere
existence of these systems provides a laboratory to study numerous types of
physical processes acting on asteroids and their dynamics provide a valuable
probe of their physical properties otherwise possible only with spacecraft.
Advances in understanding the formation and evolution of binary systems have
been assisted by: 1) the growing catalog of known systems, increasing from 33
to nearly 250 between the Merline et al. (2002) Asteroids III chapter and now,
2) the detailed study and long-term monitoring of individual systems such as
1999 KW4 and 1996 FG3, 3) the discovery of new binary system morphologies and
triple systems, 4) and the discovery of unbound systems that appear to be
end-states of binary dynamical evolutionary paths.
Specifically for small bodies (diameter smaller than 10 km), these
observations and discoveries have motivated theoretical work finding that
thermal forces can efficiently drive the rotational disruption of small
asteroids. Long-term monitoring has allowed studies to constrain the system's
dynamical evolution by the combination of tides, thermal forces and rigid body
physics. The outliers and split pairs have pushed the theoretical work to
explore a wide range of evolutionary end-states.Comment: 42 pages, 4 figures, contribution to the Asteroids 4 boo
Tackling Anti-Social Behaviour: A Critical Review
Over the past decade, anti-social behaviour (henceforth referred to as ASB) has
become a focus of much policy-making and debate within central and local
government and the police. Clear definitions of ASB are lacking, but the term is
usually understood to refer to relatively minor criminal activity and non-criminal
ânuisanceâ behaviour that affects the social and/or physical environment of public or
semi-public places. The term ASB is frequently used synonymously with âdisorderâ,
and is sometimes associated with the concept of âincivilitiesâ.
Policy-makers and strategists, at national and local levels alike, reiterate that
problems of ASB can have a massively detrimental effect on neighbourhoods as a
whole, and on the lives of individuals. Hence strenuous and wide-ranging efforts are
being made to support, develop and implement schemes for tackling ASB â involving
a variety of enforcement and preventive measures
The effect of a random sampling interval on a sampled-data model of the human operator
Effect of random sampling interval on sampled data model of human operator in compensatory trackin
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Education as a Complex System: Conceptual and Methodological Implications
Education is a complex system, which has conceptual and methodological implications for education research and policy. In this article, an overview is first provided of the Complex Systems Conceptual Framework for Learning (CSCFL), which consists of a set of conceptual perspectives that are generally shared by educational complex systems, organized into two focus areas: collective behaviors of a system, and behaviors of individual agents in a system. Complexity and research methodologies for education are then considered, and it is observed that commonly used quantitative and qualitative techniques are generally appropriate for studying linear dynamics of educational systems. However, it is proposed that computational modeling approaches, being extensively used for studying nonlinear characteristics of complex systems in other fields, can provide a methodological complement to quantitative and qualitative education research approaches. Two research case studies of this approach are discussed. We conclude with a consideration of how viewing education as a complex system using complex systemsâ conceptual and methodological tools can help advance education research and also inform policy
New representation and a vacuum state for canonical quantum gravity
A new representation for canonical gravity and supergravity is presented,
which combines advantages of Ashtekar's and the Wheeler~DeWitt representation:
it has a nice geometric structure and the singular metric problem is absent. A
formal state functional can be given, which has some typical features of a
vacuum state in quantum field theory. It can be canonically transformed into
the metric representation. Transforming the constraints too, one recovers the
Wheeler~DeWitt equation up to an anomalous term. A modified Dirac quantization
is proposed to handle possible anomalies in the constraint algebra.Comment: 28 pages, LaTe
On the orientational ordering of long rods on a lattice
We argue that a system of straight rigid rods of length k on square lattice
with only hard-core interactions shows two phase transitions as a function of
density, rho, for k >= 7. The system undergoes a phase transition from the
low-density disordered phase to a nematic phase as rho is increased from 0, at
rho = rho_c1, and then again undergoes a reentrant phase transition from the
nematic phase to a disordered phase at rho = rho_c2 < 1.Comment: epl.cl
Comment on "Accelerated Detectors and Temperature in (Anti) de Sitter Spaces"
It is shown how the results of Deser and Levin on the response of accelerated
detectors in anti-de Sitter space can be understood from the same general
perspective as other thermality results in spacetimes with bifurcate Killing
horizons.Comment: 5 pages, LaTe
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