Modeling the dynamical interaction between epidemics on overlay networks

Epidemics seldom occur as isolated phenomena. Typically, two or more viral agents spread within the same host population and may interact dynamically with each other. We present a general model where two viral agents interact via an immunity mechanism as they propagate simultaneously on two networks connecting the same set of nodes. Exploiting a correspondence between the propagation dynamics and a dynamical process performing progressive network generation, we develop an analytic approach that accurately captures the dynamical interaction between epidemics on overlay networks. The formalism allows for overlay networks with arbitrary joint degree distribution and overlap. To illustrate the versatility of our approach, we consider a hypothetical delayed intervention scenario in which an immunizing agent is disseminated in a host population to hinder the propagation of an undesirable agent (e.g. the spread of preventive information in the context of an emerging infectious disease).Comment: Accepted for publication in Phys. Rev. E. 15 pages, 7 figure

Brownian Dynamics of a Sphere Between Parallel Walls

We describe direct imaging measurements of a colloidal sphere's diffusion between two parallel surfaces. The dynamics of this deceptively simple hydrodynamically coupled system have proved difficult to analyze. Comparison with approximate formulations of a confined sphere's hydrodynamic mobility reveals good agreement with both a leading-order superposition approximation as well as a more general all-images stokeslet analysis.Comment: 4 pages, 3 figures, REVTeX with PostScript figure

Prescribing of Antipsychotic Medication in a Medicaid Population: Use of Polytherapy and Off-Label Dosages

OBJECTIVES: To describe the use of atypical antipsychotic medications in a Medicaid-enrolled population composed primarily of elderly and disabled patients. Our analyses focused upon the frequency of use of polytherapy with multiple antipsychotic medications and the prescribing of off-label dosages. METHODS: We conducted a cross-sectional retrospective analysis of oral antipsychotic medication use, as prescribed for this population in 2003. The unit of analysis was the patient. We determined the prevalence of use of each type of antipsychotic medication according to gender and age group and determined the extent of use of combination therapies with multiple oral antipsychotic medications. Using the dosage ranges described in the product labeling, we identified the percentage of patients prescribed in-range dosages, overall and for each atypical antipsychotic medication studied. Those identified as receiving out-of-range (off-label) dosages were further stratified by gender and age group. The statistical significance of differences between these proportions was assessed using the chi-square test. RESULTS: Of the 8,616 patients meeting our inclusion criteria, 7,748 (90%) received monotherapy with an oral antipsychotic medication and 868 patients (10%) received polytherapy with multiple oral antipsychotic medications. Approximately 2 of 3 patients receiving atypical antipsychotic medications were prescribed a dosage that was within the range recommended in the product labeling. Dosages lower than recommended in the product labeling were prescribed for 27% of patients receiving atypical antipsychotics, while 6% of patients received an above-range dosage. The frequency of patients receiving in-range dosages varied substantially among medications. Younger patients and male patients were more frequently prescribed above-range dosages while older patients and female patients were more frequently prescribed below-range dosages of these medications (P less than 0.001 for both findings). CONCLUSION: In this subpopulation of Medicaid enrollees who were prescribed antipsychotic medications, we found a 10% incidence of use of antipsychotic polytherapy and a 33% incidence of prescribing of dosages outside the range listed in the product labeling. These findings suggest that physicians commonly prescribe antipsychotic medications in a manner that differs from the recommendations described in the prescribing information. The off-label use of atypical antipsychotic medications raises important questions regarding the purpose and applicability of the product labeling and the role and ability of the pharmacist to provide information regarding the risks and benefits of therapy as commonly prescribed

A shadowing problem in the detection of overlapping communities: lifting the resolution limit through a cascading procedure

Community detection is the process of assigning nodes and links in significant communities (e.g. clusters, function modules) and its development has led to a better understanding of complex networks. When applied to sizable networks, we argue that most detection algorithms correctly identify prominent communities, but fail to do so across multiple scales. As a result, a significant fraction of the network is left uncharted. We show that this problem stems from larger or denser communities overshadowing smaller or sparser ones, and that this effect accounts for most of the undetected communities and unassigned links. We propose a generic cascading approach to community detection that circumvents the problem. Using real and artificial network datasets with three widely used community detection algorithms, we show how a simple cascading procedure allows for the detection of the missing communities. This work highlights a new detection limit of community structure, and we hope that our approach can inspire better community detection algorithms.Comment: 14 pages, 12 figures + supporting information (5 pages, 6 tables, 3 figures

Development and Delivery of a Quality Improvement Program to Reduce Antipsychotic Polytherapy

BACKGROUND: Although antipsychotic polytherapy is considered appropriate in limited circumstances (e.g., during a brief “cross-titration” period when switching medications), its increasing prevalence indicates use beyond this limited scope. Despite absence of support in the medical literature and higher costs, antipsychotic polytherapy is common in the treatment of schizophrenia and related disorders. The highest utilization of antipsychotic polytherapy occurs on psychiatric inpatient units, and in 2008, the Joint Commission released the first set of 7 hospital-based inpatient psychiatric services (HBIPS) core measures, 2 of which assess antipsychotic polytherapy at time of discharge. OBJECTIVE: To describe the effect on antipsychotic polytherapy at time of discharge of a 2-part quality improvement program composed of educational seminars and prescriber-specific feedback provided to 11 psychiatrists in 4 acute inpatient psychiatric units in 2 hospitals. METHODS: In a regional academic health care system, we determined the prevalence of antipsychotic monotherapy and polytherapy at time of discharge for all patients discharged on standing antipsychotic medications during 3 periods: (a) a 3-month baseline period (August 2006 through October 2006); (b) in July 2007, after delivery of 4 educational luncheon seminars to 11 psychiatrists from November 2006 through June 2007; and (c) in June 2008, following the provision of monthly prescriber-specific audit feedback from August 2007 through June 2008. To prepare nurses for the change and address possible safety concerns, an educational module was delivered to the psychiatric nursing staff at “best practice” day lectures held in the first quarter of 2007. General themes in the educational presentations included literature-based reviews of (a) safety and efficacy of antipsychotic polytherapy, (b) medical risks of antipsychotic medications, (c) specific versus nonspecific effects of these medications, and (d) effectiveness of first- versus second-generation antipsychotic medications. The prescriber-specific audit feedback was provided in paper form and masked the identity of the other prescribers. The chief of service reviewed audit feedback individually with each psychiatrist on a quarterly basis. The primary outcome measure was the percentage of patients prescribed 2 or more antipsychotics at discharge. A secondary outcome measure was the percentage of patients prescribed 3 or more antipsychotics at discharge. Differences in the primary outcome measure, comparing (a) July 2007 with the baseline period and (b) June 2008 with July 2007, were analyzed using Fisher’s Exact tests. The Cochran-Armitage test for trend was used to assess the relationship between the primary outcome measure and the extent of the intervention, measured as the 3 time periods. For the secondary outcome measure, the Goodman-Kruskal gamma test for ordered categorical data was calculated to examine the association between the proportion of patients receiving 1, 2, or 3 or more antipsychotics at discharge and the 3 time periods. RESULTS: The percentage of patients prescribed 2 or more antipsychotics at discharge declined from 33.9% at baseline (132 of 389 patients), to 21.8% after delivery of the educational modules (44 of 202 patients, P = 0.002), and to 12.2% after audit feedback (18 of 147 patients, P = 0.023; Cochran-Armitage test for trend P \u3c 0.001). When antipsychotic use was classified as 1, 2, or 3 or more antipsychotic medications, more extensive intervention was associated with decreased combination use (Goodman-Kruskal gamma = 0.39, P \u3c 0.001). In the baseline period, 5.9% of patients were prescribed 3 or more antipsychotics at discharge. Following completion of the educational and audit components, respectively, the proportion of patients prescribed 3 or more antipsychotics declined to 2.5% and then to 0.0%. CONCLUSION: Educational modules presented to psychiatrists and nurses in group settings were associated with a decrease in the rate of prescribing 2 or more antipsychotics at discharge from acute psychiatric inpatient units. Addition of monthly audit feedback provided to psychiatrists was associated with further decreases

Near-wake analysis of actuator line method immersed in turbulent flow using large-eddy simulations

The interaction between wind turbines through their wakes is an important aspect of the conception and operation of a wind farm. Wakes are characterized by an elevated turbulence level and a noticeable velocity deficit, which causes a decrease in energy output and fatigue on downstream turbines. In order to gain a better understanding of this phenomenon this work uses large-eddy simulations together with an actuator line model and different ambient turbulence imposed as boundary conditions. This is achieved by using the Simulator fOr Wind Farm Applications (SOWFA) framework from the National Renewable Energy Laboratory (NREL) (USA), which is first validated against another popular Computational Fluid Dynamics (CFD) framework for wind energy, EllipSys3D, and then verified against the experimental results from the Model Experiment in Controlled Conditions (MEXICO) and New Model Experiment in Controlled Conditions (NEW MEXICO) wind tunnel experiments. By using the predicted torque as a global indicator, the optimal width of the distribution kernel for the actuator line is determined for different grid resolutions. Then, the rotor is immersed in homogeneous isotropic turbulence and a shear layer turbulence with different turbulence intensities, allowing us to determine how far downstream the effect of the distinct blades is discernible. This can be used as an indicator of the extents of the near wake for different flow conditions.</p

nonlinMIP contribution to CMIP6: model intercomparison project for non-linear mechanisms: physical basis, experimental design and analysis principles (v1.0)

nonlinMIP provides experiments that account for state-dependent regional and global climate responses. The experiments have two main applications: (1) to focus understanding of responses to CO2 forcing on states relevant to specific policy or scientific questions (e.g. change under low-forcing scenarios, the benefits of mitigation, or from past cold climates to the present day), or (2) to understand the state dependence (non-linearity) of climate change – i.e. why doubling the forcing may not double the response. State dependence (non-linearity) of responses can be large at regional scales, with important implications for understanding mechanisms and for general circulation model (GCM) emulation techniques (e.g. energy balance models and pattern-scaling methods). However, these processes are hard to explore using traditional experiments, which explains why they have had so little attention in previous studies. Some single model studies have established novel analysis principles and some physical mechanisms. There is now a need to explore robustness and uncertainty in such mechanisms across a range of models (point 2 above), and, more broadly, to focus work on understanding the response to CO2 on climate states relevant to specific policy/science questions (point 1). nonlinMIP addresses this using a simple, small set of CO2-forced experiments that are able to separate linear and non-linear mechanisms cleanly, with a good signal-to-noise ratio – while being demonstrably traceable to realistic transient scenarios. The design builds on the CMIP5 (Coupled Model Intercomparison Project Phase 5) and CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) protocols, and is centred around a suite of instantaneous atmospheric CO2 change experiments, with a ramp-up–ramp-down experiment to test traceability to gradual forcing scenarios. In all cases the models are intended to be used with CO2 concentrations rather than CO2 emissions as the input. The understanding gained will help interpret the spread in policy-relevant scenario projections. Here we outline the basic physical principles behind nonlinMIP, and the method of establishing traceability from abruptCO2 to gradual forcing experiments, before detailing the experimental design, and finally some analysis principles. The test of traceability from abruptCO2 to transient experiments is recommended as a standard analysis within the CMIP5 and CMIP6 DECK protocols