A new proof of the flat wall theorem

We give an elementary and self-contained proof, and a numerical improvement, of a weaker form of the excluded clique minor theorem of Robertson and Seymour, the following. Let t,r >= 1 be integers, and let R = 49152t(24) (40t(2) +r). An r-wall is obtained from a 2r x r-grid by deleting every odd vertical edge in every odd row and every even vertical edge in every even row, then deleting the two resulting vertices of degree one, and finally subdividing edges arbitrarily. The vertices of degree two that existed before the subdivision are called the pegs of the r-wall. Let G be a graph with no Kt minor, and let W be an R-wall in G. We prove that there exist a set A subset of V(G) of size at most 12288t(24) and an r-subwall W' of W such that V(W') n A = 0 and W' is a flat wall in G A in the following sense. There exists a separation (X, Y) of G A such that X boolean AND Y is a subset of the vertex set of the cycle C' that bounds the outer face of W', V(W') subset of Y, every peg of W' belongs to X and the graph G[Y] can almost be drawn in the unit disk with the vertices X n Y drawn on the boundary of the disk in the order determined by C'. Here almost means that the assertion holds after repeatedly removing parts of the graph separated from X n Y by a cutset Z of size at most three, and adding all edges with both ends in Z. Our proof gives rise to an algorithm that runs in polynomial time even when r and t are part of the input instance. The proof is self-contained in the sense that it uses only results whose proofs can be found in textbooks. (C) 2017 The Authors. Published by Elsevier Inc

An exact characterization of tractable demand patterns for maximum disjoint path problems

We study the following general disjoint paths problem: given a supply graph G, a set T ⊆ V(G) of terminals, a demand graph H on the vertices T, and an integer k, the task is to find a set of k pairwise vertex-disjoint valid paths, where we say that a path of the supply graph G is valid if its endpoints are in T and adjacent in the demand graph H. For a class H of graphs, we denote by Maximum Disjoint ℋ-Paths the restriction of this problem when the demand graph H is assumed to be a member of ℋ. We study the fixed-parameter tractability of this family of problems, parameterized by k. Our main result is a complete characterization of the fixed-parameter tractable cases of Maximum Disjoint ℋ-Paths for every hereditary class ℋ of graphs: it turns out that complexity depends on the existence of large induced matchings and large induced skew bicliques in the demand graph H (a skew biclique is a bipartite graph on vertices a1, …, an, b1, …, bn with ai and bj being adjacent if and only if i ≤ j). Specifically, we prove the following classification for every hereditary class ℋ. If ℋ does not contain every matching and does not contain every skew biclique, then MAXIMUM Disjoint ℋ-Paths is FPT. If ℋ does not contain every matching, but contains every skew biclique, then MAXIMUM DISJOINT ℋ-Paths is W[1]-hard, admits an FPT approximation, and the valid paths satisfy an analog of the Erdös-Pósa property. If ℋ contains every matching, then MAXIMUM DISJOINT ℋ-Paths is W[1]-hard and the valid paths do not satisfy the analog of the Erdös-Pósa property

Knowledge and attitudes of family physicians coming to COPD continuing medical education

Barbara P Yawn, Peter C WollanOlmsted Medical Center, Research Department, Rochester, MN, USAPurpose: COPD remains under-recognized and under-treated. Much of early COPD care is given by primary care physicians but only when COPD is recognized. This survey explores the attitudes, beliefs, and knowledge related to COPD recognition, diagnosis, and treatment from family physicians and nurse practitioners (NPs) and physician assistants (PAs) working in primary care.Methods: We completed a survey of family physicians, and NPs/PAs attending one of three CME programs on five common chronic conditions including COPD.Results: Return rate was 62% (n = 284) including 178 physicians and 100 NPs/PAs. Fewer than half of the respondents reported knowledge of or use of COPD guidelines. The barriers to recognition and diagnosis of COPD they reported included the multiple morbidities of most COPD patients, failure of patients to report COPD symptoms, as well as lack of knowledge and inadequate training in COPD diagnosis and management. Three quarters (74%) of respondents reported use of spirometry to diagnose COPD but only 32% said they included reversibility assessment. COPD was incorrectly assessed as a disease primarily of men (78% of respondents) that appeared after age 60 (61%). Few respondents reported that they believed COPD treatment was useful or very useful for improving symptoms (15%) or decreasing exacerbations (3%) or that pulmonary rehabilitation was helpful (3%), but 13% reported they thought COPD treatment could extend longevity.Conclusions: Primary care physicians and NPs/PAs working in primary care continue to report lack of awareness and use of COPD guidelines, as well as correct information related to COPD epidemiology or potential benefits of available treatments including pulmonary rehabilitation. It is unlikely that diagnosis and management of COPD will improve in primary care until these knowledge gaps and discrepancies with published efficacy of therapy issues are addressed.Keywords: COPD treatment, diagnosis, management, patients, family physician

Gas density detector for use in space

Gas density detector for meteoroid monitorin

Strain control of superlattice implies weak charge-lattice coupling in La0.5_{0.5}Ca0.5_{0.5}MnO3_3

We have recently argued that manganites do not possess stripes of charge order, implying that the electron-lattice coupling is weak [Phys Rev Lett \textbf{94} (2005) 097202]. Here we independently argue the same conclusion based on transmission electron microscopy measurements of a nanopatterned epitaxial film of La$_{0.5}$Ca$_{0.5}$MnO$_3$. In strain relaxed regions, the superlattice period is modified by 2-3% with respect to the parent lattice, suggesting that the two are not strongly tied.Comment: 4 pages, 4 figures It is now explained why the work provides evidence to support weak-coupling, and rule out charge orde

Dynamic Jahn-Teller Effect and Colossal Magnetoresistance in La1−xAxMnO3La_{1-x}A_xMnO_3

A model for $La_{1-x}Sr_xMnO_3$ which incorporates the physics of dynamic Jahn-Teller and double-exchange effects is presented and solved via a dynamical mean field approximation. In an intermediate coupling regime the interplay of these two effects is found to reproduce the behavior of the resistivity and magnetic transition temperature observed in $La_{1-x} Sr_x MnO_3$.Comment: 11 pages. Latex. Minor revisions, including improvement of discussion of state with frozen-in lattice distortion. Figures (available from [email protected]) unchange

Volume contraction at the Jahn-Teller transition of LaMnO3_3

We have studied the volume collapse of LaMnO$_3$ at the Jahn- Teller (JT) transition temperature T$_{JT}$=750 K which has recently been found in high temperature powder x- ray and neutron diffraction experiments. We construct a model Hamiltonian involving the pseudospin of Mn$^{3+}$ e$_g$ states, the staggered JT distortion and the volume strain coordinate. We show that the anharmonic coupling between these primary and secondary order parameters leads to the first order JT phase transition associated with a comparatively large reduction of the unit cell volume of $\Delta$V/V$\simeq$ 10$^{-2}$. We explain the temperature dependence of JT distortions and volume strain and discuss the volume change as function of the anharmonic coupling constant. A continuous change to a second order transition as function of model parameters is obtained. This behaviour is also observed under Ba doping.Comment: 5 pages, 4 figure

Do published guidelines for evaluation of Irritable Bowel Syndrome reflect practice?

BACKGROUND: The only US guidelines listed in the National Guideline Warehouse for the diagnosis of Irritable Bowel Syndrome (IBS) are the expert opinion guidelines published by The American Gastroenterology Association. Although the listed target audience of these guidelines includes family physicians and general internists, the care recommended in the guidelines has not been compared to actual primary care practice. This study was designed to compare expert opinion guidelines with the actual primary care provided and to assess outcomes in the 3 years following the IBS diagnosis. METHODS: This is a retrospective medical record review study using a random sample of incident IBS cases from all Olmsted County, Minnesota providers diagnosed between January 1, 1993 and December 31, 1995. Data was collected on all care and testing provided to the subjects as well as 3-year outcomes related to the IBS diagnosis. RESULTS: Of the 149 IBS patients, 99 were women and the mean age was 47.6 years. No patient had all of the diagnostic tests recommended in the guidelines. 42% had the basic blood tests of CBC and a chemistry panel. Sedimentation rate (2%) and serum thyroxine level (3%) were uncommon. Colon imaging studies were done in 41% including 74% of those over the age of 50. In the 3 years following the diagnosis, only one person had a change in diagnosis and no diagnoses of gastro-intestinal malignancies were made in the cohort. CONCLUSIONS: Primary care practice based diagnostic evaluations for IBS differ significantly from the specialty expert opinion-based guidelines. Implementation of the specialty guidelines in primary care practice would increase utilization with apparent limited improvement in diagnostic outcomes

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