3,820 research outputs found
One-Dimensional Directed Sandpile Models and the Area under a Brownian Curve
We derive the steady state properties of a general directed ``sandpile''
model in one dimension. Using a central limit theorem for dependent random
variables we find the precise conditions for the model to belong to the
universality class of the Totally Asymmetric Oslo model, thereby identifying a
large universality class of directed sandpiles. We map the avalanche size to
the area under a Brownian curve with an absorbing boundary at the origin,
motivating us to solve this Brownian curve problem. Thus, we are able to
determine the moment generating function for the avalanche-size probability in
this universality class, explicitly calculating amplitudes of the leading order
terms.Comment: 24 pages, 5 figure
Area distribution and the average shape of a L\'evy bridge
We consider a one dimensional L\'evy bridge x_B of length n and index 0 <
\alpha < 2, i.e. a L\'evy random walk constrained to start and end at the
origin after n time steps, x_B(0) = x_B(n)=0. We compute the distribution
P_B(A,n) of the area A = \sum_{m=1}^n x_B(m) under such a L\'evy bridge and
show that, for large n, it has the scaling form P_B(A,n) \sim n^{-1-1/\alpha}
F_\alpha(A/n^{1+1/\alpha}), with the asymptotic behavior F_\alpha(Y) \sim
Y^{-2(1+\alpha)} for large Y. For \alpha=1, we obtain an explicit expression of
F_1(Y) in terms of elementary functions. We also compute the average profile <
\tilde x_B (m) > at time m of a L\'evy bridge with fixed area A. For large n
and large m and A, one finds the scaling form = n^{1/\alpha}
H_\alpha({m}/{n},{A}/{n^{1+1/\alpha}}), where at variance with Brownian bridge,
H_\alpha(X,Y) is a non trivial function of the rescaled time m/n and rescaled
area Y = A/n^{1+1/\alpha}. Our analytical results are verified by numerical
simulations.Comment: 21 pages, 4 Figure
Adapting to the digital age: a narrative approach
The article adopts a narrative inquiry approach to foreground informal learning and exposes a collection of stories from tutors about how they adapted comfortably to the digital age. We were concerned that despite substantial evidence that bringing about changes in pedagogic practices can be difficult, there is a gap in convincing approaches to help in this respect. In this context, this project takes a âbottom-upâ approach and synthesises several life-stories into a single persuasive narrative to support the process of adapting to digital change. The project foregrounds the small, every-day motivating moments, cultural features and environmental factors in people's diverse lives which may have contributed to their positive dispositions towards change in relation to technology enhanced learning. We expect that such narrative approaches could serve to support colleagues in other institutions to warm up to ever-changing technological advances
Maximum relative height of one-dimensional interfaces : from Rayleigh to Airy distribution
We introduce an alternative definition of the relative height h^\kappa(x) of
a one-dimensional fluctuating interface indexed by a continuously varying real
paramater 0 \leq \kappa \leq 1. It interpolates between the height relative to
the initial value (i.e. in x=0) when \kappa = 0 and the height relative to the
spatially averaged height for \kappa = 1. We compute exactly the distribution
P^\kappa(h_m,L) of the maximum h_m of these relative heights for systems of
finite size L and periodic boundary conditions. One finds that it takes the
scaling form P^\kappa(h_m,L) = L^{-1/2} f^\kappa (h_m L^{-1/2}) where the
scaling function f^\kappa(x) interpolates between the Rayleigh distribution for
\kappa=0 and the Airy distribution for \kappa=1, the latter being the
probability distribution of the area under a Brownian excursion over the unit
interval. For arbitrary \kappa, one finds that it is related to, albeit
different from, the distribution of the area restricted to the interval [0,
\kappa] under a Brownian excursion over the unit interval.Comment: 25 pages, 4 figure
Increased gravitational force reveals the mechanical, resonant nature of physiological tremor
Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head-to-foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system.This work was funded by a BBSRC Industry Interchange Award
to J.P.R.S. and R.F.R. C.J.O. was funded by BBSRC grant
BB/I00579X/1. C.A.V. was funded by AâMidex (Aix-Marseille
Initiative of Excellence
Appropriate use of elective coronary angiography in patients with suspected stable coronary artery disease
Introduction: The American College of Cardiology Foundation (ACCF) with other professional societies developed appropriate use criteria (AUC) for diagnostic coronary angiography. This study aims to examine the appropriate use of elective coronary angiography for patients with suspected stable coronary artery disease in an Irish tertiary referral center. Methods: A retrospective chart review of all elective outpatient diagnostic coronary angiograms performed in Cork University Hospital in 2014 was carried out. Data on demographics, risk factors, clinical presentation, and prior non-invasive investigations were extracted. Each patient was evaluated according to the 2012 ACCF appropriate use criteria and classified as appropriate, uncertain, or inappropriate. Univariable and multivariable logistic regression analysis was performed to investigate the factors that predict patients undergoing appropriate diagnostic coronary angiography. Results: Of 417 elective outpatient diagnostic coronary angiograms, 259 (62%) were included in the analysis. Of these, 108 (42%) were classified as appropriate, 97 (37%) as uncertain, and 54 (21%) as inappropriate. In multivariable analysis, those with private health insurance were more likely to have an appropriate indication for coronary angiogram (OR 2.1, 95% CI 1.2â3.7) as were those with atrial fibrillation (OR 3.9, 95% CI 1.2â12.8). Ever smokers were less likely to have an appropriate indication for coronary angiogram than never smokers (OR 0.5, 95% CI 0.3â0.9). Conclusion: This is the first Irish study to evaluate the appropriate use of elective coronary angiography. Rates were similar to those of studies in other jurisdictions; however, there remains significant potential for quality improvement
Emotional intelligence in front-line/back-office employee relationships
PurposeâThis research undertakes a simultaneous assessment of interdependence in the behaviours of front-line and back-office employees and their joint effect on customer-related organizational performance. It also tests for a moderating influence of the emotional intelligence of front-line salespeople and back-office employees.
Design/methodology/approachâThe sample comprises 105 front-line sales employees and
77 back-office employees. The customer-related organizational performance data come from a U.K. business-to-business (B2B) electronics company. With these triadic data, this study uses partial least squares to estimate the measurement and structural models.
FindingsâSalespeopleâs customer orientation directly affects customer-related
organizational performance; the relationship is moderated by salespeopleâs emotional
intelligence. The emotional intelligence of salespeople also directly affects the customer directed citizenship behaviour of back-office employees. Furthermore, the emotional intelligence of back-office staff moderates the link between the emotional intelligence of salespeople and back-office staff citizenship behaviour. Back-office staff citizenship behaviour in turn affects customer-related organizational performance.
Originality/valueâThe emotions deployed by employees in interactions with customers
clearly shape customersâ perceptions of service quality, as well as employee-level
performance outcomes. But prior literature lacks insights into the simultaneous effects of front-line and back-office employee behaviour, especially in B2B settings. This article addresses these research gaps by investigating triadic relationshipsâamong back-office employees, front-line employees and customer outcomesâin a B2B setting, where they are of particular managerial interest
Assessment-schedule matching in unanchored indirect treatment comparisons of progression-free survival in cancer studies
Background
The timing of efficacy-related clinical events recorded at scheduled study visits in clinical trials are interval censored, with the interval duration pre-determined by the study protocol. Events may happen any time during that interval but can only be detected during a planned or unplanned visit. Disease progression in oncology is a notable example where the time to an event is affected by the schedule of visits within a study. This can become a source of bias when studies with varying assessment schedules are used in unanchored comparisons using methods such as matching-adjusted indirect comparisons.
Objective
We illustrate assessment-time bias (ATB) in a simulation study based on data from a recent study in second-line treatment for locally advanced or metastatic urothelial carcinoma, and present a method to adjust for differences in assessment schedule when comparing progression-free survival (PFS) against a competing treatment.
Methods
A multi-state model for death and progression was used to generate simulated death and progression times, from which PFS times were derived. PFS data were also generated for a hypothetical comparator treatment by applying a constant hazard ratio (HR) to the baseline treatment. Simulated PFS times for the two treatments were then aligned to different assessment schedules so that progression events were only observed at set visit times, and the data were analysed to assess the bias and standard error of estimates of HRs between two treatments with and without assessment-schedule matching (ASM).
Results
ATB is highly affected by the rate of the event at the first assessment time; in our examples, the bias ranged from 3 to 11% as the event rate increased. The proposed method relies on individual-level data from a study and attempts to adjust the timing of progression events to the comparatorâs schedule by shifting them forward or backward without altering the patientsâ actual follow-up time. The method removed the bias almost completely in all scenarios without affecting the precision of estimates of comparative effectiveness.
Conclusions
Considering the increasing use of unanchored comparative analyses for novel cancer treatments based on single-arm studies, the proposed method offers a relatively simple means of improving the accuracy of relative benefits of treatments on progression times
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