10,392 research outputs found
Fast Entropy Estimation for Natural Sequences
It is well known that to estimate the Shannon entropy for symbolic sequences
accurately requires a large number of samples. When some aspects of the data
are known it is plausible to attempt to use this to more efficiently compute
entropy. A number of methods having various assumptions have been proposed
which can be used to calculate entropy for small sample sizes. In this paper,
we examine this problem and propose a method for estimating the Shannon entropy
for a set of ranked symbolic natural events. Using a modified
Zipf-Mandelbrot-Li law and a new rank-based coincidence counting method, we
propose an efficient algorithm which enables the entropy to be estimated with
surprising accuracy using only a small number of samples. The algorithm is
tested on some natural sequences and shown to yield accurate results with very
small amounts of data
Resilience markers for safer systems and organisations
If computer systems are to be designed to foster resilient
performance it is important to be able to identify contributors to resilience. The
emerging practice of Resilience Engineering has identified that people are still a
primary source of resilience, and that the design of distributed systems should
provide ways of helping people and organisations to cope with complexity.
Although resilience has been identified as a desired property, researchers and
practitioners do not have a clear understanding of what manifestations of
resilience look like. This paper discusses some examples of strategies that
people can adopt that improve the resilience of a system. Critically, analysis
reveals that the generation of these strategies is only possible if the system
facilitates them. As an example, this paper discusses practices, such as
reflection, that are known to encourage resilient behavior in people. Reflection
allows systems to better prepare for oncoming demands. We show that
contributors to the practice of reflection manifest themselves at different levels
of abstraction: from individual strategies to practices in, for example, control
room environments. The analysis of interaction at these levels enables resilient
properties of a system to be ‘seen’, so that systems can be designed to explicitly
support them. We then present an analysis of resilience at an organisational
level within the nuclear domain. This highlights some of the challenges facing
the Resilience Engineering approach and the need for using a collective
language to articulate knowledge of resilient practices across domains
Precision Measurement Of The Neutron's Beta Asymmetry Using Ultra-Cold Neutrons
A measurement of A_β, the correlation between the electron momentum and neutron (n) spin (the beta asymmetry) in n beta-decay, together with the n lifetime, provides a method for extracting fundamental parameters for the charged-current weak interaction of the nucleon. In particular when combined with decay measurements, one can extract the V_(ud) element of the CKM matrix, a critical element in CKM unitarity tests. By using a new SD_2 super-thermal source at LANSCE, large fluxes of UCN (ultra-cold neutrons) are expected for the UCNA project. These UCN will be 100% polarized using a 7 T magnetic field, and directed into the β spectrometer. This approach, together with an expected large reduction in backgrounds, will result in an order of magnitude reduction in the critical systematic corrections associated with current n β-asymmetry measurements. This paper will give an overview of the UCNA Aβ measurement as well as an update on the status of the experiment
Exploring the importance of reflection in the control room
While currently difficult to measure or explicitly design for, evidence suggests that providing people
with opportunities to reflect on experience must be recognized and valued during safety-critical
work. We provide an insight into reflection as a mechanism that can help to maintain both individual
and team goals. In the control room, reflection can be task-based, critical for the 'smooth' day-to-day
operational performance of a socio-technical system, or can foster learning and organisational change
by enabling new understandings gained from experience. In this position paper we argue that
technology should be designed to support the reflective capacity of people. There are many
interaction designs and artefacts that aim to support problem-solving, but very few that support
self-reflection and group reflection. Traditional paradigms for safety-critical systems have focussed
on ensuring the functional correctness of designs, minimising the time to complete tasks, etc. Work
in the area of user experience design may be of increasing relevance when generating artefacts that
aim to encourage reflection
Elliptic Flow, Initial Eccentricity and Elliptic Flow fluctuations in Heavy Ion Collisions at RHIC
We present measurements of elliptic flow and event-by-event fluctuations
established by the PHOBOS experiment. Elliptic flow scaled by participant
eccentricity is found to be similar for both systems when collisions with the
same number of participants or the same particle area density are compared. The
agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence
that the matter is created in the initial stage of relativistic heavy ion
collisions with transverse granularity similar to that of the participant
nucleons. The event-by-event fluctuation results reveal that the initial
collision geometry is translated into the final state azimuthal particle
distribution, leading to an event-by-event proportionality between the observed
elliptic flow and initial eccentricity.Comment: To appear in the proceedings of the Lake Louise Winter Institute
2007. The proceedings of the institute will be published by World Scientifi
Metastability in Monte Carlo simulation of 2D Ising films and in Fe monolayer strips
Effective Curie temperatures measured in Fe monolayer strips agree reasonable
with computer sinulations of two-dimensional Ising model strips. The
simulations confirm the domain structure seen already by Albano et al.Comment: 3 pages, plain tex, 5 postscript figure
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