2,791 research outputs found
Transition Property For Cube-Free Words
We study cube-free words over arbitrary non-unary finite alphabets and prove
the following structural property: for every pair of -ary cube-free
words, if can be infinitely extended to the right and can be infinitely
extended to the left respecting the cube-freeness property, then there exists a
"transition" word over the same alphabet such that is cube free. The
crucial case is the case of the binary alphabet, analyzed in the central part
of the paper.
The obtained "transition property", together with the developed technique,
allowed us to solve cube-free versions of three old open problems by Restivo
and Salemi. Besides, it has some further implications for combinatorics on
words; e.g., it implies the existence of infinite cube-free words of very big
subword (factor) complexity.Comment: 14 pages, 5 figure
A national facilitation project to improve primary palliative care : impact of the Gold Standards Framework on process and self-ratings of quality
Background: Improving quality of end-of-life care is a key driver of UK policy. The Gold Standards Framework (GSF) for Palliative Care aims to strengthen primary palliative care through facilitating implementation of systematic clinical and organisational processes.
Objectives: To describe the general practices that participated in the GSF programme in 2003â5 and the changes in process and perception of quality that occurred in the year following entry into the programme, and to identify factors associated with the extent of change.
Methods: Participating practices completed a questionnaire at baseline and another approximately 12 months later. Data were derived from categorical questions about the implementation of 35 organisational and clinical processes, and self-rated assessments of quality, associated with palliative care provision.
Participants: 1305 practices (total registered population almost 10 million). Follow-up questionnaire completed by 955 (73.2%) practices (after mean (SD) 12.8 (2.8) months; median 13 months).
Findings: Mean increase in total number of processes implemented (maximum = 35) was 9.6 (95% CI 9.0 to 10.2; p<0.001; baseline: 15.7 (SD 6.4), follow-up: 25.2 (SD 5.2)). Extent of change was largest for practices with low baseline scores. Aspects of process related to coordination and communication showed the greatest change. All dimensions of quality improved following GSF implementation; change was highest for the "quality of palliative care for cancer patients" and "confidence in assessing, recording and addressing the physical and psychosocial areas of patient care".
Conclusion: Implementation of the GSF seems to have resulted in substantial improvements in process and quality of palliative care. Further research is required of the extent to which this has enhanced care (physical, practical and psychological outcomes) for patients and carers
Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study
Interference evaluation is crucial when deciding whether and how wireless
technologies should operate. In this paper we demonstrate the benefit of
risk-informed interference assessment to aid spectrum regulators in making
decisions, and to readily convey engineering insight. Our contributions are: we
apply, for the first time, risk assessment to a problem of inter-technology
spectrum sharing, i.e. Wi-Fi/LTE in the 5 GHz unlicensed band, and we
demonstrate that this method comprehensively quantifies the interference
impact. We perform simulations with our newly publicly-available tool and we
consider throughput degradation and fairness metrics to assess the risk for
different network densities, numbers of channels, and deployment scenarios. Our
results show that no regulatory intervention is needed to ensure harmonious
technical Wi-Fi/LTE coexistence: for the typically large number of channels
available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible,
rendering policy and engineering concerns largely moot. As an engineering
insight, Wi-Fi coexists better with itself in dense, but better with LTE, in
sparse deployments. Also, both main LTE-in-unlicensed variants coexist well
with Wi-Fi in general. For LTE intra-technology inter-operator coexistence,
both variants typically coexist well in the 5 GHz band, but for dense
deployments, implementing listen-before-talk causes less interference
LTE in Unlicensed Bands is neither Friend nor Foe to Wi-Fi
Proponents of deploying LTE in the 5 GHz band for providing additional
cellular network capacity have claimed that LTE would be a better neighbour to
Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the
debate, the Wi-Fi community has objected that LTE would be highly detrimental
to Wi-Fi network performance. However, there is a lack of transparent and
systematic engineering evidence supporting the contradicting claims of the two
camps, which is essential for ascertaining whether regulatory intervention is
in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To
this end, we present a comprehensive coexistence study of Wi-Fi and
LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms
and a range of representative network densities and deployment scenarios. Our
results show that, typically, harmonious coexistence between Wi-Fi and LTE is
ensured by the large number of 5 GHz channels. For the worst-case scenario of
forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi -
when effective node density is low - but sometimes worse - when density is
high. We find that distributed interference coordination is only necessary to
prevent a "tragedy of the commons" in regimes where interference is very
likely. We also show that in practice it does not make a difference to the
incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as
long as one is in place. We therefore conclude that LTE is neither friend nor
foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic
engineering analysis exemplified by our case study is a best-practice approach
for supporting evidence-based rulemaking by the regulator.Comment: accepted for publication in IEEE Acces
A Pulsational Model for the Orthogonal Polarization Modes in Radio Pulsars
In an earlier paper, we introduced a model for pulsars in which non-radial
oscillations of high spherical degree (\el) aligned to the magnetic axis of a
spinning neutron star were able to reproduce subpulses like those observed in
single-pulse measurements of pulsar intensity. The model did not address
polarization, which is an integral part of pulsar emission. Observations show
that many pulsars emit radio waves that appear to be the superposition of two
linearly polarized emission modes with orthogonal polarization angles. In this
paper, we extend our model to incorporate linear polarization. As before, we
propose that pulsational displacements of stellar material modulate the pulsar
emission, but now we apply this modulation to a linearly-polarized mode of
emission, as might be produced by curvature radiation. We further introduce a
second polarization mode, orthogonal to the first, that is modulated by
pulsational velocities. We combine these modes in superposition to model the
observed Stokes parameters in radio pulsars.Comment: 19 pages, 4 figures accepted Ap
Peculiar behavior of the electrical resistivity of MnSi at the ferromagnetic phase transition
The electrical resistivity of a single crystal of MnSi was measured across
its ferromagnetic phase transition line at ambient and high pressures. Sharp
peaks of the temperature coefficient of resistivity characterize the transition
line. Analysis of these data shows that at pressures to ~0.35 GPa these peaks
have fine structure, revealing a shoulder at ~ 0.5 K above the peak. It is
symptomatic that this structure disappears at pressures higher than ~0.35 GPa,
which was identified earlier as a tricritical poin
Refraction in a pulsar magnetosphere - the effect of a variable emission height on pulse morphology
The Petrova (2000) model to calculate pulse profiles is extended to a
variable emission height model to make it physically self-consistent. In this
context variable means that the emission height is no longer considered to be
the same for different magnetic field lines. The pulse profiles calculated
using this new model seem to be less realistic due to a focusing effect and
cannot be used to fit (typical) multifrequency pulsar observations. Apart from
the focusing effect the general morphology of pulse profiles is not greatly
affected by introducing a variable emission height. Additional extensions of
the model will be needed to be able to fit observations, and several
suggestions are made.Comment: 7 pages, 5 figures, accepted to A&
Transition Property for -Power Free Languages with and Letters
In 1985, Restivo and Salemi presented a list of five problems concerning
power free languages. Problem states: Given -power-free words
and , decide whether there is a transition from to . Problem
states: Given -power-free words and , find a transition word
, if it exists.
Let denote an alphabet with letters. Let denote
the -power free language over the alphabet , where
is a rational number or a rational "number with ". If is a "number
with " then suppose and . If is "only" a
number then suppose and or and . We show
that: If is a right extendable word in and
is a left extendable word in then there is a
(transition) word such that . We also show a
construction of the word
Elastic properties of FeSi
Measurements of the sound velocities in a single crystal of FeSi were
performed in the temperature range 4-300 K. Elastic constants and
deviate from a quasiharmonic behavior at high temperature; whereas,
increases anomalously in the entire range of temperature, indicating a
change in the electron structure of this materia
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