PageRank in scale-free random graphs

We analyze the distribution of PageRank on a directed configuration model and show that as the size of the graph grows to infinity it can be closely approximated by the PageRank of the root node of an appropriately constructed tree. This tree approximation is in turn related to the solution of a linear stochastic fixed point equation that has been thoroughly studied in the recent literature

Application of Qualitative Methods in Health Research: An Overview

Qualitative research is type of formative research that includes specialized techniques for obtaining in-depth responses about what people think and how they feel. It is seen as the research that seeks answer to the questions in the real world. Qualitative researchers gather what they see, hear, read from people and places, from events and activities, with the purpose to learn about the community and to generate new understanding that can be used by the social world. Qualitative research have often been conducted to answer the question “why” rather than “what”. A purpose of qualitative research is the construction of new understanding. Here, we present an overview of application of qualitative methods in health research. We have discussed here the different types of qualitative methods and how we and others have used them in different settings/scenarios; sample size and sampling techniques; analysis of qualitative data; validity in qualitative research; and ethical issues

Role of (p)ppGpp in Viability and Biofilm Formation of Actinobacillus pleuropneumoniae S8.

Actinobacillus pleuropneumoniae is a Gram-negative bacterium and the cause of porcine pleuropneumonia. When the bacterium encounters nutritional starvation, the relA-dependent (p)ppGpp-mediated stringent response is activated. The modified nucleotides guanosine 5'-diphosphate 3'-diphosphate (ppGpp) and guanosine 5'-triphosphate 3'-diphosphate (pppGpp) are known to be signaling molecules in other prokaryotes. Here, to investigate the role of (p)ppGpp in A. pleuropneumoniae, we created a mutant A. pleuropneumoniae strain, S8ΔrelA, which lacks the (p)ppGpp-synthesizing enzyme RelA, and investigated its phenotype in vitro. S8ΔrelA did not survive after stationary phase (starvation condition) and grew exclusively as non-extended cells. Compared to the wild-type (WT) strain, the S8ΔrelA mutant had an increased ability to form a biofilm. Transcriptional profiles of early stationary phase cultures revealed that a total of 405 bacterial genes were differentially expressed (including 380 up-regulated and 25 down-regulated genes) in S8ΔrelA as compared with the WT strain. Most of the up-regulated genes are involved in ribosomal structure and biogenesis, amino acid transport and metabolism, translation cell wall/membrane/envelope biogenesis. The data indicate that (p)ppGpp coordinates the growth, viability, morphology, biofilm formation and metabolic ability of A. pleuropneumoniae in starvation conditions. Furthermore, S8ΔrelA could not use certain sugars nor produce urease which has been associated with the virulence of A. pleuropneumoniae, suggesting that (p)ppGpp may directly or indirectly affect the pathogenesis of A. pleuropneumoniae during the infection process. In summary, (p)ppGpp signaling represents an essential component of the regulatory network governing stress adaptation and virulence in A. pleuropneumoniae

Exploring spatial non‐stationarity in the social determinants of time to work

Social differences in time to work are a growing concern of transport planning, as they can increase the risk of social exclusion of some groups. Recent work has found that those differences tend to vary across the urban space. Geographic Weighted Regression models this variability by estimating relationships in each place, weighting data by distance to that place. This paper builds on this work by assuming that households and policy-makers make decisions over space by comparing places according to their function within the metropolitan space, regardless of their geographic proximity. The determinants of time to work then vary in the space defined by variables identifying that function. This procedure is applied to the case of the Lisbon Metropolitan Area at two moments in time. Higher times to work are associated with less-qualified populations, with the strength of the relationships generally increasing with centrality in relation to employment locations and dependence on jobs in the main metropolitan centre. The priority to investments in road transport in the period concerned extended the disadvantages to second-ring suburban areas

Multiple transport disadvantages: A cluster analysis of the socio-spatial distribution of levels of accessibility and pedestrian mobility in a metropolitan area.

The concept of social justice is increasingly called upon in the assessment of the social and environmental sustainability of urban transport. This paper brings together two strands of the literature on this topic: the role of accessibility in social inclusion and the distribution of the environmental impacts of transport. Using the Lisbon Metropolitan Area as case study, we test if there are cumulative social inequalities in terms of accessibility and pedestrian mobility, considering that the latter depends on local environmental quality. We use GIS methods to estimate a series of neighbourhood-level indicators, such as private and public transport accessibility to jobs and urban facilities, community severance and pedestrian exposure to traffic noise. Neighbourhoods are then classified based on the scores of those indicators at two moments in time. We found six clusters. Accessibility increases and pedestrian mobility decreases as we move from the ‘main centre’ towards the ‘suburban’, ‘small centres’, ‘semi-rural’ and ‘rural’ clusters. A sixth cluster is labelled ‘multiple disadvantages’ and groups dispersed neighbourhoods that fare poorly in all indicators. The clusters are then characterized in terms of their socio-economic composition. We find that central areas usually have elderly populations, while rural areas and the “multiple disadvantaged” cluster tend to have low-qualified populations. We also test if disadvantages based on a neighbourhood’s location persist after accounting for the daily destinations and travel modes used by its population. We find that ‘multiple disadvantaged’ areas have the poorest scores in time to work, effects of congestion, and pedestrian noise exposures for commuters on the way to work. The main conclusion is that ‘hotspots’ of multiple transport-related disadvantages tend to have populations traditionally at risk of social exclusion. More emphasis should be put on locally-based interventions on and public participation methods in the definition of strategies for urban transport planning

On the Complexity of an Unregulated Traffic Crossing

The steady development of motor vehicle technology will enable cars of the near future to assume an ever increasing role in the decision making and control of the vehicle itself. In the foreseeable future, cars will have the ability to communicate with one another in order to better coordinate their motion. This motivates a number of interesting algorithmic problems. One of the most challenging aspects of traffic coordination involves traffic intersections. In this paper we consider two formulations of a simple and fundamental geometric optimization problem involving coordinating the motion of vehicles through an intersection. We are given a set of $n$ vehicles in the plane, each modeled as a unit length line segment that moves monotonically, either horizontally or vertically, subject to a maximum speed limit. Each vehicle is described by a start and goal position and a start time and deadline. The question is whether, subject to the speed limit, there exists a collision-free motion plan so that each vehicle travels from its start position to its goal position prior to its deadline. We present three results. We begin by showing that this problem is NP-complete with a reduction from 3-SAT. Second, we consider a constrained version in which cars traveling horizontally can alter their speeds while cars traveling vertically cannot. We present a simple algorithm that solves this problem in $O(n \log n)$ time. Finally, we provide a solution to the discrete version of the problem and prove its asymptotic optimality in terms of the maximum delay of a vehicle

The effect of Mg location on Co-Mg-Ru/γ-Al2O3 Fischer–Tropsch catalysts

© 2016 The Author(s) Published by the Royal Society. All rights reserved.The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer-Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3-xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3-xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3-xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-Time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature

On the Analysis of a Wave Energy Farm with Focus on Maintenance Operations

Wave energy has a promising technical potential that could contribute to the future energy mix. However, costs related to the deployment of wave energy converters (WECs) are still high compared to other technologies. In order to reduce these costs, two principle options are available, a reduction in cost and an increase in productivity. This paper presents a reliability-based computational tool to identify typical decision problems and to shed light on the complexity of optimising a wave power farm. The proposed tool is used to investigate productivity and availability of a wave energy farm during 10 years of operational life. A number of optimization possibilities to improve productivity, namely vessel choice, maintenance regime, failure rate and component redundancy, are then explored in order to assess their effectiveness. The paper quantifies the yield increase and provides a practical approach to evaluate the effectiveness of strategic and operational decision options. Results, in terms of the variations in productivity and availability of the farm, are analysed and discussed. Conclusions highlight the importance of reliability-centred simulations that consider the specific decision parameters throughout the operational life to find suitable solutions that increase the productivity and reduce the running cost for offshore farms.The work in this paper has been conducted within the multinational Initial Training Network (ITN) OceaNET, funded under the PEOPLE Programme (Marie Curie Actions) of European Union’s FP7. Mojo Maritime have provided access to Mermaid to support, and for integration with, this research