16,360 research outputs found
Correlated bursts and the role of memory range
Inhomogeneous temporal processes in natural and social phenomena have been
described by bursts that are rapidly occurring events within short time periods
alternating with long periods of low activity. In addition to the analysis of
heavy-tailed inter-event time distributions, higher-order correlations between
inter-event times, called correlated bursts, have been studied only recently.
As the possible mechanisms underlying such correlated bursts are far from being
fully understood, we devise a simple model for correlated bursts by using a
self-exciting point process with variable memory range. Here the probability
that a new event occurs is determined by a memory function that is the sum of
decaying memories of the past events. In order to incorporate the noise and/or
limited memory capacity of systems, we apply two memory loss mechanisms, namely
either fixed number or variable number of memories. By using theoretical
analysis and numerical simulations we find that excessive amount of memory
effect may lead to a Poissonian process, which implies that for memory effect
there exists an intermediate range that will generate correlated bursts of
magnitude comparable to empirical findings. Hence our results provide deeper
understanding of how long-range memory affects correlated bursts.Comment: 9 pages, 7 figure
Measuring the Hidden Aspects of Solar Magnetism
2008 marks the 100th anniversary of the discovery of astrophysical magnetic
fields, when George Ellery Hale recorded the Zeeman splitting of spectral lines
in sunspots. With the introduction of Babcock's photoelectric magnetograph it
soon became clear that the Sun's magnetic field outside sunspots is extremely
structured. The field strengths that were measured were found to get larger
when the spatial resolution was improved. It was therefore necessary to come up
with methods to go beyond the spatial resolution limit and diagnose the
intrinsic magnetic-field properties without dependence on the quality of the
telescope used. The line-ratio technique that was developed in the early 1970s
revealed a picture where most flux that we see in magnetograms originates in
highly bundled, kG fields with a tiny volume filling factor. This led to
interpretations in terms of discrete, strong-field magnetic flux tubes embedded
in a rather field-free medium, and a whole industry of flux tube models at
increasing levels of sophistication. This magnetic-field paradigm has now been
shattered with the advent of high-precision imaging polarimeters that allow us
to apply the so-called "Second Solar Spectrum" to diagnose aspects of solar
magnetism that have been hidden to Zeeman diagnostics. It is found that the
bulk of the photospheric volume is seething with intermediately strong, tangled
fields. In the new paradigm the field behaves like a fractal with a high degree
of self-similarity, spanning about 8 orders of magnitude in scale size, down to
scales of order 10 m.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Innovation and Nested Preferential Growth in Chess Playing Behavior
Complexity develops via the incorporation of innovative properties. Chess is
one of the most complex strategy games, where expert contenders exercise
decision making by imitating old games or introducing innovations. In this
work, we study innovation in chess by analyzing how different move sequences
are played at the population level. It is found that the probability of
exploring a new or innovative move decreases as a power law with the frequency
of the preceding move sequence. Chess players also exploit already known move
sequences according to their frequencies, following a preferential growth
mechanism. Furthermore, innovation in chess exhibits Heaps' law suggesting
similarities with the process of vocabulary growth. We propose a robust
generative mechanism based on nested Yule-Simon preferential growth processes
that reproduces the empirical observations. These results, supporting the
self-similar nature of innovations in chess are important in the context of
decision making in a competitive scenario, and extend the scope of relevant
findings recently discovered regarding the emergence of Zipf's law in chess.Comment: 8 pages, 4 figures, accepted for publication in Europhysics Letters
(EPL
Drug Prescription Pattern in a Nigerian Tertiary Hospital
Purpose: To evaluate the prescribing pattern of clinicians in the general outpatient unit of the Aminu Kano Teaching Hospital, Kano (AKTH),.Methods: This was a descriptive retrospective study conducted using 500 prescriptions made at the general outpatient unit of AKTH between April and July 2009.Results: A total of 497 prescriptions were successfully analyzed. The average number of drugs per encounter in the facility was 3.04. Generic prescribing was low at 42.7 % while antibiotic prescription was high at 34.4 %. Injections were prescribed in 4 % of encounters while 36.2, 19.1, 25.8 and 1 % of encounters had analgesics, antimalarials, antihypertensives and anxiolytics prescribed, respectively. Vitamins were prescribed in 9.7 % of encounters. Conclusion: Polypharmacy, low rate of generic prescriptions and overuse of antibiotics still remain a problem in health care facilities in Nigeria.. This calls for sustained interventional strategies and periodic audit at all levels of health care to avoid the negative consequences of inappropriate prescriptions.Keywords: Prescribing pattern, Generic drugs, Tertiary hospital, Essential drugs, Nigeri
Three-loop HTL gluon thermodynamics at intermediate coupling
We calculate the thermodynamic functions of pure-glue QCD to three-loop order
using the hard-thermal-loop perturbation theory (HTLpt) reorganization of
finite temperature quantum field theory. We show that at three-loop order
hard-thermal-loop perturbation theory is compatible with lattice results for
the pressure, energy density, and entropy down to temperatures .
Our results suggest that HTLpt provides a systematic framework that can used to
calculate static and dynamic quantities for temperatures relevant at LHC.Comment: 24 pages, 13 figs. 2nd version: improved discussion and fixing typos.
Published in JHE
K. Sridhar Moorthy’s Theoretical Modelling in Marketing - A Review
Modelling has become a visible tool in many disciplines including marketing and several marketing models have been constructed. These models serve their pedagogical and practical purposes in some cases. However, among the marketing models so often cited is Moorthy‟s Theoretical Modelling in Marketing. This model is important, and hence this review once more, in that it offers a starting point, and in some cases the finishing line, for those who want to tread the pedestrian of modelling in marketing. But this is not the end; it also provides an explanation for those who want to know more about modelling in general by providing answers to some basic questions about the use of models. Our discussion here will certainly bring in many people who have been peeping into marketing modelling from behind the wall.Key words: Marketing, Modelling, Moorthy, Pedagogy, Theoretica
Interaction-induced Interlayer Charge Transfer in the Extreme Quantum Limit
An interacting bilayer electron system provides an extended platform to study
electron-electron interaction beyond single layers. We report here experiments
demonstrating that the layer densities of an asymmetric bilayer electron system
oscillate as a function of perpendicular magnetic field that quantizes the
energy levels. At intermediate fields, this interlayer charge transfer can be
well explained by the alignment of the Landau levels in the two layers. At the
highest fields where both layers reach the extreme quantum limit, however,
there is an anomalous, enhanced charge transfer to the majority layer.
Surprisingly, when the minority layer becomes extremely dilute, this charge
transfer slows down as the electrons in the minority layer condense into a
Wigner crystal. Furthermore, by examining the quantum capacitance of the dilute
layer at high fields, the screening induced by the composite fermions in an
adjacent layer is unveiled. The results highlight the influence of strong
interaction in interlayer charge transfer in the regime of very high fields and
low Landau level filling factors.Comment: Please see the formal version on PR
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Reflections on the Jesuit Mission to China
With the explosive growth of transnational dealings, professionals in developed countries have expanding opportunities to spread their particular ways of doing things around the world. However, missionary work, whether religious or secular, raises difficult questions about ends and means. What warrant do missionaries have for inducing others to act and believe as they do? What devices are permissible in the effort to bring about change in a host population? This working paper addresses some of these questions by reflecting on the Jesuit mission to China in the 17th century. The Jesuit mission was the first instance in the modern period of sustained missionary work by westerners in China, and it remains of enduring significance. By focusing on the “ethics of missionary work” in the Jesuit case, we draw some conclusions for 21st century would-be missionaries
Three-loop HTL QCD thermodynamics
The hard-thermal-loop perturbation theory (HTLpt) framework is used to
calculate the thermodynamic functions of a quark-gluon plasma to three-loop
order. This is the highest order accessible by finite temperature perturbation
theory applied to a non-Abelian gauge theory before the high-temperature
infrared catastrophe. All ultraviolet divergences are eliminated by
renormalization of the vacuum, the HTL mass parameters, and the strong coupling
constant. After choosing a prescription for the mass parameters, the three-loop
results for the pressure and trace anomaly are found to be in very good
agreement with recent lattice data down to , which are
temperatures accessible by current and forthcoming heavy-ion collision
experiments.Comment: 27 pages, 11 figures; corresponds with published version in JHE
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