Provenance Circuits for Trees and Treelike Instances (Extended Version)

Query evaluation in monadic second-order logic (MSO) is tractable on trees and treelike instances, even though it is hard for arbitrary instances. This tractability result has been extended to several tasks related to query evaluation, such as counting query results [3] or performing query evaluation on probabilistic trees [10]. These are two examples of the more general problem of computing augmented query output, that is referred to as provenance. This article presents a provenance framework for trees and treelike instances, by describing a linear-time construction of a circuit provenance representation for MSO queries. We show how this provenance can be connected to the usual definitions of semiring provenance on relational instances [20], even though we compute it in an unusual way, using tree automata; we do so via intrinsic definitions of provenance for general semirings, independent of the operational details of query evaluation. We show applications of this provenance to capture existing counting and probabilistic results on trees and treelike instances, and give novel consequences for probability evaluation.Comment: 48 pages. Presented at ICALP'1

Structurally Parameterized d-Scattered Set

In $d$-Scattered Set we are given an (edge-weighted) graph and are asked to select at least $k$ vertices, so that the distance between any pair is at least $d$, thus generalizing Independent Set. We provide upper and lower bounds on the complexity of this problem with respect to various standard graph parameters. In particular, we show the following: - For any $d\ge2$, an $O^*(d^{\textrm{tw}})$-time algorithm, where $\textrm{tw}$ is the treewidth of the input graph. - A tight SETH-based lower bound matching this algorithm's performance. These generalize known results for Independent Set. - $d$-Scattered Set is W[1]-hard parameterized by vertex cover (for edge-weighted graphs), or feedback vertex set (for unweighted graphs), even if $k$ is an additional parameter. - A single-exponential algorithm parameterized by vertex cover for unweighted graphs, complementing the above-mentioned hardness. - A $2^{O(\textrm{td}^2)}$-time algorithm parameterized by tree-depth ($\textrm{td}$), as well as a matching ETH-based lower bound, both for unweighted graphs. We complement these mostly negative results by providing an FPT approximation scheme parameterized by treewidth. In particular, we give an algorithm which, for any error parameter $\epsilon > 0$, runs in time $O^*((\textrm{tw}/\epsilon)^{O(\textrm{tw})})$ and returns a $d/(1+\epsilon)$-scattered set of size $k$, if a $d$-scattered set of the same size exists

Polynomial Kernels for Weighted Problems

Kernelization is a formalization of efficient preprocessing for NP-hard problems using the framework of parameterized complexity. Among open problems in kernelization it has been asked many times whether there are deterministic polynomial kernelizations for Subset Sum and Knapsack when parameterized by the number $n$ of items. We answer both questions affirmatively by using an algorithm for compressing numbers due to Frank and Tardos (Combinatorica 1987). This result had been first used by Marx and V\'egh (ICALP 2013) in the context of kernelization. We further illustrate its applicability by giving polynomial kernels also for weighted versions of several well-studied parameterized problems. Furthermore, when parameterized by the different item sizes we obtain a polynomial kernelization for Subset Sum and an exponential kernelization for Knapsack. Finally, we also obtain kernelization results for polynomial integer programs

An FPT 2-Approximation for Tree-Cut Decomposition

The tree-cut width of a graph is a graph parameter defined by Wollan [J. Comb. Theory, Ser. B, 110:47-66, 2015] with the help of tree-cut decompositions. In certain cases, tree-cut width appears to be more adequate than treewidth as an invariant that, when bounded, can accelerate the resolution of intractable problems. While designing algorithms for problems with bounded tree-cut width, it is important to have a parametrically tractable way to compute the exact value of this parameter or, at least, some constant approximation of it. In this paper we give a parameterized 2-approximation algorithm for the computation of tree-cut width; for an input $n$-vertex graph $G$ and an integer $w$, our algorithm either confirms that the tree-cut width of $G$ is more than $w$ or returns a tree-cut decomposition of $G$ certifying that its tree-cut width is at most $2w$, in time $2^{O(w^2\log w)} \cdot n^2$. Prior to this work, no constructive parameterized algorithms, even approximated ones, existed for computing the tree-cut width of a graph. As a consequence of the Graph Minors series by Robertson and Seymour, only the existence of a decision algorithm was known.Comment: 17 pages, 3 figure

Political Policing in Hong Kong

Modem states, democratic ones in particular, have grown to prefer the use of more subtle, or at least less visible, police surveillance to open confrontation in a courtroom, where the state itself may be scrutinised in public. Well-equipped national security agencies enable the state to respond to potential security threats before they mature. Hong Kong's political police unit, the Special Branch, was indispensable to Hong Kong's colonial political order. Although it was disbanded before the handover of Hong Kong to China in 1997, political policing and monitoring probably continue under the new legal order. This article examines the historical origin of political policing in Hong Kong, including the establishment of the Special Branch and its initial focus on communist activity in Hong Kong. It then traces the demise of the Special Branch prior to the handover, examines the role played by the Independent Commission Against Corruption, and explores the relevance of political policing to contemporary society.published_or_final_versio

Post-colonial careering and the discipline of geography: British geographers in Nigeria and the UK, 1945-1990

Few geographers wrote explicitly about decolonisation. Yet the ends of empires wrought substantial changes to the discipline of geography. It impacted the places studied, the approaches deemed appropriate, the sites of geographical knowledge production, the lecturing jobs available, and the shape and extent of transnational networks. Focusing on the ‘post-colonial careering’ of British geographers who worked at the university at Ibadan, Nigeria before returning to academic posts in UK geography departments, this paper explores the interconnections between academic careers, geographical knowledge and decolonisation. It argues that that we can understand these connections in three ways. First, geographers’ careers were shaped in important ways by decolonisation; second, these experiences in turn shaped the discipline of geography in the (post)colonial world and the UK; and third, geographers’ work at colonial universities and in Britain was not only influenced by, but was itself part of the process of decolonisation. The article contributes to understandings of decolonisation as registered, and actively produced, through academic research and careers, institutional development, and transnational networks. Uncovering the (post)colonial connections which shaped British geography in the post-war period broadens understandings of disciplinary history beyond those which focus on Anglo-American networks and offers opportunities to consider the lessons of these past disciplinary patterns and practices for contemporary geography

Magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO: first-principles calculations

The electronic structure and magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO have been investigated using first-principles methods. We show that the magnetic coupling between Gd or Nd ions in the nearest neighbor sites is ferromagnetic. The stability of the ferromagnetic coupling between Gd ions can be enhanced by appropriate electron doping into ZnO:Gd system and the room-temperature ferromagnetism can be achieved. However, for ZnO:Nd system, the ferromagnetism between Nd ions can be enhanced by appropriate holes doping into the sample. The room-temperature ferromagnetism can also be achieved in the \emph{n}-conducting ZnO:Nd sample. Our calculated results are in good agreement with the conclusions of the recent experiments. The effect of native defects (V$_{\rm{Zn}}$, V$_{\rm{O}}$) on the ferromagnetism is also discussed.Comment: 5 pages, 5 figure

What price a welcome? Understanding structure-agency in the delivery of respectful midwifery care in Uganda

Purpose – The purpose of this paper is to present the findings of research on mothers and midwives’ understanding of the concept of respectful care in the Ugandan public health settings. It focusses on one aspect of respect; namely communication that is perhaps least resource-dependent. The research found endemic levels of disrespect and tries to understand the reasons behind these organisational cultures and the role that governance could play in improving respect. Design/methodology/approach – The study involved a combination of in-depth qualitative interviews with mothers and midwives together with focus groups with a cohort of midwives registered for a degree. Findings – The findings highlight an alarming level of verbal abuse and poor communication that both deter women from attending public health facilities and, when they have to attend, reduces their willingness to disclose information about their health status. Respect is a major factor reducing the engagement of those women unable to afford private care, with health facilities in Uganda. Research limitations/implications – Access to quality care provided by skilled birth attendants (midwives) is known to be the major factor preventing improvements in maternal mortality and morbidity in low income settings. Although communication lies at the agency end of the structure-agency continuum, important aspects of governance contribute to high levels of disrespect. Originality/value – Whilst there is a lot of research on the concept of respectful care in high income settings applying this to the care environment in low resource settings is highly problematic. The findings presented here generate a more contextualised analysis generating important new insights which we hope will improve the quality of care in Uganda health facilities. Keywords: Leadership, Governance structures, Patient perspectives, Communication, Midwifery, Determinants of health Paper type Research pape

Edge Shear Flows and Particle Transport near the Density Limit in the HL-2A Tokamak

Edge shear flow and its effect on regulating turbulent transport have long been suspected to play an important role in plasmas operating near the Greenwald density limit $n_G$. In this study, equilibrium profiles as well as the turbulent particle flux and Reynolds stress across the separatrix in the HL-2A tokamak are examined as $n_G$ is approached in ohmic L-mode discharges. As the normalized line-averaged density $\bar{n}_e/n_G$ is raised, the shearing rate of the mean poloidal flow $\omega_{\rm sh}$ drops, and the turbulent drive for the low-frequency zonal flow (the Reynolds power $\mathcal{P}_{Re}$) collapses. Correspondingly, the turbulent particle transport increases drastically with increasing collision rates. The geodesic acoustic modes (GAMs) gain more energy from the ambient turbulence at higher densities, but have smaller shearing rate than low-frequency zonal flows. The increased density also introduces decreased adiabaticity which not only enhances the particle transport but is also related to a reduction in the eddy-tilting and the Reynolds power. Both effects may lead to the cooling of edge plasmas and therefore the onset of MHD instabilities that limit the plasma density

Human islet isolation and allotransplantation in 22 consecutive cases

This report provides our initial experience in islet isolation and intrahepatic allotransplantation in 21 patients. In group 1, 10 patients underwent combined liver-islet allotransplantation following upper-abdominal exenteration for cancer. In group 2, 4 patients received a combined liver-islet allograft for cirrhosis and diabetes. One patient had plasma C-peptide >3 pM and was therefore excluded from analysis. In group 3, 7 patients received 8 combined cadaveric kidney-islet grafts (one retransplant) for end-stage renal disease secondary to type 1 diabetes mellitus. The islets were separated by a modification of the automated method for human islet isolation and the preparations were infused into the portal vein. Immunosuppression was with FK506 (group 1) plus steroids (groups 2 and 3). Six patients in group 1 did not require insulin treatment for 5 to > 16 months. In groups 2 and 3 none of the patients became insulin-independent, although decreased insulin requirement and stabilization of diabetes were observed. Our results indicate that rejection is still a major factor limiting the clinical application of islet transplantation in patients with type 1 diabetes mellitus, although other factors such as steroid treatment may contribute to deteriorate islet engraftment and/or function. © 1992 by Williams and Wilkins