1,513 research outputs found
Characteristics of Vehicular Traffic Flow at a Roundabout
We construct a stochastic cellular automata model for the description of
vehicular traffic at a roundabout designed at the intersection of two
perpendicular streets. The vehicular traffic is controlled by a self-organized
scheme in which traffic lights are absent. This controlling method incorporates
a yield-at-entry strategy for the approaching vehicles to the circulating
traffic flow in the roundabout. Vehicular dynamics is simulated within the
framework of the probabilistic cellular automata and the delay experienced by
the traffic at each individual street is evaluated for specified time
intervals. We discuss the impact of the geometrical properties of the
roundabout on the total delay. We compare our results with traffic-light
signalisation schemes, and obtain the critical traffic volume over which the
intersection is optimally controlled through traffic light signalisation
schemes.Comment: 10 pages, 17 eps figures. arXiv admin note: text overlap with
arXiv:cond-mat/040107
Characterising University WLANs within Eduroam Context
The eduroam initiative is assuming an ever growing relevance in providing a secure, worldwide roaming access within the university WLAN context. Although several studies have focused on educational WLAN traffic characterisation, the increasing variety of devices, mobility scenarios and user applications, motivate assessing the effective use of eduroam in order to sustain consistent network planning and deployment. Based on recent WLAN traffic traces collected at the University of Minho (Portugal) and University of Vigo (Spain), the present work contributes for identifying and characterising patterns of user behaviour regarding, for instance, the location and activity sector of users. The results of data analysis quantify the impact of network access location on the number of associated users, on the number and duration of sessions and corresponding traffic volumes. The results also illustrate to what extent users take advantage of mobility in the WLAN. Complementing the analysis on a monthly basis, a fine grain study of WLAN traffic is provided through the identification of users' behaviour and patterns in small timescales
Statistical mixing and aggregation in Feller diffusion
We consider Feller mean-reverting square-root diffusion, which has been
applied to model a wide variety of processes with linearly state-dependent
diffusion, such as stochastic volatility and interest rates in finance, and
neuronal and populations dynamics in natural sciences. We focus on the
statistical mixing (or superstatistical) process in which the parameter related
to the mean value can fluctuate - a plausible mechanism for the emergence of
heavy-tailed distributions. We obtain analytical results for the associated
probability density function (both stationary and time dependent), its
correlation structure and aggregation properties. Our results are applied to
explain the statistics of stock traded volume at different aggregation scales.Comment: 16 pages, 3 figures. To be published in Journal of Statistical
Mechanics: Theory and Experimen
Combining intensive practice nurse counselling or brief general practitioner advice with varenicline for smoking cessation in primary care: study protocol of a pragmatic randomized controlled trial
Introduction: Combining behavioural support and pharmacotherapy is most effective for smoking cessation and recommended in clinical guidelines. Despite that smoking cessation assistance from the general practitioner can be effective, dissemination of clinical practice guidelines and efforts on upskilling has not lead to the routine provision of smoking cessation advice among general practitioners. Intensive counselling from the practice nurse could contribute to better smoking cessation rates in primary care. However, the effectiveness of intensive counselling from a practice nurse versus usual care from a general practitioner in combination with varenicline is still unknown. Materials and methods: A pragmatic randomized controlled trial was conducted comparing: (a) intensive individual counselling delivered by a practice nurse and (b) brief advice delivered by a general practitioner; both groups received 12-weeks of open-label varenicline. A minimum of 272 adult daily smoking participants were recruited and treated in their routine primary care setting. The primary outcome was defined as prolonged abstinence from weeks 9 to 26, biochemically validated by exhaled carbon monoxide. Data was analysed blinded according to the intention-to-treat principle and participants with missing data on their smoking status at follow-up were counted as smokers. Secondary outcomes included: one-year prolonged abstinence, short-term incremental cost-effectiveness, medication adherence, and baseline predictors of successful smoking cessation. Discussion: This trial is the first to provide scientific evidence on the effectiveness, cost-effectiveness, and potential mechanisms of action of intensive practice nurse counselling combined with varenicline under real-life conditions. This paper explains the methodology of the trial and discusses the pragmatic and/or explanatory design aspects
Closed-Form Bayesian Inferences for the Logit Model via Polynomial Expansions
Articles in Marketing and choice literatures have demonstrated the need for
incorporating person-level heterogeneity into behavioral models (e.g., logit
models for multiple binary outcomes as studied here). However, the logit
likelihood extended with a population distribution of heterogeneity doesn't
yield closed-form inferences, and therefore numerical integration techniques
are relied upon (e.g., MCMC methods).
We present here an alternative, closed-form Bayesian inferences for the logit
model, which we obtain by approximating the logit likelihood via a polynomial
expansion, and then positing a distribution of heterogeneity from a flexible
family that is now conjugate and integrable. For problems where the response
coefficients are independent, choosing the Gamma distribution leads to rapidly
convergent closed-form expansions; if there are correlations among the
coefficients one can still obtain rapidly convergent closed-form expansions by
positing a distribution of heterogeneity from a Multivariate Gamma
distribution. The solution then comes from the moment generating function of
the Multivariate Gamma distribution or in general from the multivariate
heterogeneity distribution assumed.
Closed-form Bayesian inferences, derivatives (useful for elasticity
calculations), population distribution parameter estimates (useful for
summarization) and starting values (useful for complicated algorithms) are
hence directly available. Two simulation studies demonstrate the efficacy of
our approach.Comment: 30 pages, 2 figures, corrected some typos. Appears in Quantitative
Marketing and Economics vol 4 (2006), no. 2, 173--20
Optimised Traffic Flow at a Single Intersection: Traffic Responsive signalisation
We propose a stochastic model for the intersection of two urban streets. The
vehicular traffic at the intersection is controlled by a set of traffic lights
which can be operated subject to fix-time as well as traffic adaptive schemes.
Vehicular dynamics is simulated within the framework of the probabilistic
cellular automata and the delay experienced by the traffic at each individual
street is evaluated for specified time intervals. Minimising the total delay of
both streets gives rise to the optimum signalisation of traffic lights. We
propose some traffic responsive signalisation algorithms which are based on the
concept of cut-off queue length and cut-off density.Comment: 10 pages, 11 eps figs, to appear in J. Phys.
Public attitudes towards healthcare policies promoting tobacco cessation in Germany: results from the representative German study on tobacco use (DEBRA study)
Objective The aim of this study was to assess
public acceptance of four possible healthcare policies
supporting tobacco dependence treatment in line with
the Framework Convention for Tobacco Control, Article 14
recommendations in Germany.
Design Cross-sectional household survey.
Setting Data were drawn from the German population
and collected through computer-assisted, face-to-face
interviews.
Participants Representative random sample of 2087
people (>14 years) from the German population.
Outcome measures Public acceptance was measured
regarding (1) treatment cost reimbursement, (2) standard
training for health professionals on offering cessation
treatment, and making cessation treatment a standard
part of care for smokers with (3) physical or (4) mental
disorders. Association characteristics with smoking status
and socio-economic status (SES) were assessed.
Results Support for all policies was high (50%–68%),
even among smokers (48%–66%). Ex-smokers and neversmokers were more likely to support standard training on
cessation for health professionals than current smokers
(OR 1.43, 95%CI 1.07 to 1.92; OR 1.43; 95%CI 1.14 to
1.79, respectively). Ex-smokers were also more likely
than current smokers to support cessation treatment for
smokers with mental disorders (OR 1.39, 95%CI 1.11
to 1.73). Men were less likely than women to support
cessation treatment for smokers with physical diseases
(OR 0.74, 95%CI 0.60 to 0.91) and free provision of
treatment (OR 0.80, 95%CI 0.66 to 0.97). Offering
cessation treatment to smokers with physical disorders
was generally more accepted than to those with mental
health issues.
Conclusions The majority of the German population
supports healthcare policies to improve the availability
and affordability of tobacco dependence treatment. Nonsmokers were more supportive than current smokers
of two of the four policies, but odds of support were
only about 40% higher. SES characteristics were not
consistently associated with public acceptance
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