1,847 research outputs found
Number of walks and degree powers in a graph
This note deals with the relationship between the total number of -walks
in a graph, and the sum of the -th powers of its vertex degrees. In
particular, it is shown that the the number of all -walks is upper bounded
by the sum of the -th powers of the degrees
Technical Note: Comparing and ranking soil drought indices performance over Europe, through remote-sensing of vegetation
In the past years there have been many attempts to produce and improve global soil-moisture datasets and drought indices. However, comparing and validating these various datasets is not straightforward. Here, interannual variations in drought indices are compared to interannual changes in vegetation, as captured by NDVI. By comparing the correlations of the different indices with NDVI we evaluated which drought index describes most realistically the actual changes in vegetation. Strong correlation between NDVI and the drought indices were found in areas that are classified as warm temperate climate with hot or warm dry summers. In these areas we ranked the PDSI, PSDI-SC, SPI3, and NSM indices, based on the interannual correlation with NDVI, and found that NSM outperformed the rest. Using this best performing index, and the ICA (Independent Component Analysis) technique, we analyzed the response of vegetation to temperature and soil-moisture stresses over Europe
Near-Perfect Correlation of the Resistance Components of Mesoscopic Samples at the Quantum Hall Regime
We study the four-terminal resistance fluctuations of mesoscopic samples near
the transition between the and the quantum Hall states. We
observe near-perfect correlations between the fluctuations of the longitudinal
and Hall components of the resistance. These correlated fluctuations appear in
a magnetic-field range for which the two-terminal resistance of the samples is
quantized. We discuss these findings in light of edge-state transport models of
the quantum Hall effect. We also show that our results lead to an ambiguity in
the determination of the width of quantum Hall transitions.Comment: As publishe
On commutativity based edge lean search
Exploring a graph through search is one of the most basic building blocks of various applications. In a setting with a huge state space, such as in testing and verification, optimizing the search may be crucial. We consider the problem of visiting all states in a graph where edges are generated by actions and the (reachable) states are not known in advance. Some of the actions may commute, i.e., they result in the same state for every order in which they are taken (this is the case when the actions are performed independently by different processes). We show how to use commutativity to achieve full coverage of the states while traversing considerably fewer edges
Two-Dimensional Electron Gas in InGaAs/InAlAs Quantum Wells
We designed and performed low temperature DC transport characterization
studies on two-dimensional electron gases confined in lattice-matched
InGaAs/InAlAs quantum wells grown by
molecular beam epitaxy on InP substrates. The nearly constant mobility for
samples with the setback distance larger than 50nm and the similarity between
the quantum and transport life-time suggest that the main scattering mechanism
is due to short range scattering, such as alloy scattering, with a scattering
rate of 2.2 ps. We also obtain the Fermi level at the
InGaAs/InAlAs surface to be 0.36eV above
the conduction band, when fitting our experimental densities with a
Poisson-Schr\"odinger model.Comment: Accepted in Applied Physics Letter
The Maximum-Level Vertex in an Arrangement of Lines
Let be a set of lines in the plane, not necessarily in general position. We present an efficient algorithm for finding all the vertices of the arrangement of maximum level, where the level of a vertex is the number of lines of that pass strictly below . The problem, posed in Exercise~8.13 in de Berg etal [BCKO08], appears to be much harder than it seems, as this vertex might not be on the upper envelope of the lines. We first assume that all the lines of are distinct, and distinguish between two cases, depending on whether or not the upper envelope of contains a bounded edge. In the former case, we show that the number of lines of that pass above any maximum level vertex is only . In the latter case, we establish a similar property that holds after we remove some of the lines that are incident to the single vertex of the upper envelope. We present algorithms that run, in both cases, in optimal time. We then consider the case where the lines of are not necessarily distinct. This setup is more challenging, and the best we have is an algorithm that computes all the maximum-level vertices in time . Finally, we consider a related combinatorial question for degenerate arrangements, where many lines may intersect in a single point, but all the lines are distinct: We bound the complexity of the weighted -level in such an arrangement, where the weight of a vertex is the number of lines that pass through the vertex. We show that the bound in this case is , which matches the corresponding bound for non-degenerate arrangements, and we use this bound in the analysis of one of our algorithms
Fluctuating Hall resistance defeats the quantized Hall insulator
Using the Chalker-Coddington network model as a drastically simplified, but
universal model of integer quantum Hall physics, we investigate the
plateau-to-insulator transition at strong magnetic field by means of a
real-space renormalization approach. Our results suggest that for a fully
quantum coherent situation, the quantized Hall insulator with R_H approx. h/e^2
is observed up to R_L ~25 h/e^2 when studying the most probable value of the
distribution function P(R_H). Upon further increasing R_L ->\infty the Hall
insulator with diverging Hall resistance R_H \propto R_L^kappa is seen. The
crossover between these two regimes depends on the precise nature of the
averaging procedure.Comment: major revision, discussion of averaging improved; 8 pages, 7 figures;
accepted for publication in EP
Beyond ‘witnessing’: children’s experiences of coercive control in domestic violence and abuse
Children’s experiences and voices are underrepresented in academic literature and professional practice around domestic violence and abuse. The project ‘Understanding Agency and Resistance Strategies’ addresses this absence, through direct engagement with children. We present an analysis from interviews with 21 children in the United Kingdom (12 girls and 9 boys, aged 8-18 years), about their experiences of domestic violence and abuse, and their responses to this violence. These interviews were analysed using interpretive interactionism. Three themes from this analysis are presented: a) ‘Children’s experiences of abusive control’, which explores children’s awareness of controlling behaviour by the adult perpetrator, their experience of that control, and its impact on them; b) ‘Constraint’, which explores how children experience the constraint associated with coercive control in situations of domestic violence, and c) ‘Children as agents’ which explores children’s strategies for managing controlling behaviour in their home and in family relationships. The paper argues that, in situations where violence and abuse occurs between adult intimate partners, children are significantly impacted, and can be reasonably described as victims of abusive control. Recognising children as direct victims of domestic violence and abuse would produce significant changes in the way professionals respond to them, by 1) recognising children’s experience of the impact of domestic violence and abuse; 2) recognising children’s agency, undermining the perception of them as passive ‘witnesses’ or ‘collateral damage’ in adult abusive encounters; and 3) strengthening professional responses to them as direct victims, not as passive witnesses to violence
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