152,888 research outputs found
A study of the research done on the gifted child from 1952 to the present day.
Thesis (Ed.M.)--Boston Universit
The origin of order in random matrices with symmetries
From Noether's theorem we know symmetries lead to conservation laws. What is
left to nature is the ordering of conserved quantities; for example, the
quantum numbers of the ground state. In physical systems the ground state is
generally associated with `low' quantum numbers and symmetric, low-dimensional
irreps, but there is no \textit{a priori} reason to expect this. By
constructing random matrices with nontrivial point-group symmetries, I find the
ground state is always dominated by extremal low-dimensional irreps. Going
further, I suggest this explains the dominance of J=0 g.s. even for random
two-body interactions.Comment: 5 figures; contribution to "Beauty in Physics" conference in honor of
Francesco Iachello, May 2012, Cocoyoc, Mexic
Tracing the evolution of nuclear forces under the similarity renormalization group
I examine the evolution of nuclear forces under the similarity
renormalization group (SRG) using traces of the many-body configuration-space
Hamiltonian. While SRG is often said to "soften" the nuclear interaction, I
provide numerical examples which paint a complementary point of view: the
primary effect of SRG, using the kinetic energy as the generator of the
evolution, is to shift downward the diagonal matrix elements in the model
space, while the off-diagonal elements undergo significantly smaller changes.
By employing traces, I argue that this is a very natural outcome as one
diagonalizes a matrix, and helps one to understand the success of SRG.Comment: 6 pages, 3 figures, 1 tabl
Why We Cannot (Yet) Ensure the Cybersecurity of Safety-Critical Systems
There is a growing threat to the cyber-security of safety-critical systems.
The introduction of Commercial Off The Shelf (COTS) software, including
Linux, specialist VOIP applications and Satellite Based Augmentation Systems
across the aviation, maritime, rail and power-generation infrastructures has created
common, vulnerabilities. In consequence, more people now possess the technical
skills required to identify and exploit vulnerabilities in safety-critical systems.
Arguably for the first time there is the potential for cross-modal attacks
leading to future ‘cyber storms’. This situation is compounded by the failure of
public-private partnerships to establish the cyber-security of safety critical applications.
The fiscal crisis has prevented governments from attracting and retaining
competent regulators at the intersection of safety and cyber-security. In particular,
we argue that superficial similarities between safety and security have led
to security policies that cannot be implemented in safety-critical systems. Existing
office-based security standards, such as the ISO27k series, cannot easily be integrated
with standards such as IEC61508 or ISO26262. Hybrid standards such as
IEC 62443 lack credible validation. There is an urgent need to move beyond
high-level policies and address the more detailed engineering challenges that
threaten the cyber-security of safety-critical systems. In particular, we consider
the ways in which cyber-security concerns undermine traditional forms of safety
engineering, for example by invalidating conventional forms of risk assessment.
We also summarise the ways in which safety concerns frustrate the deployment of
conventional mechanisms for cyber-security, including intrusion detection systems
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