For a fixed graph H, the reconfiguration problem for H‐colorings (ie, homomorphisms to H) asks: given a graph G and two H‐colorings φ and ψ of G, does there exist a sequence f0,…,fm of H‐colorings ...such that f0=φ, fm=ψ, and fi(u)fi+1(v)∈E(H) for every 0≤i<m and uv∈E(G)? If the graph G is loop‐free, then this is the equivalent to asking whether it possible to transform φ into ψ by changing the color of one vertex at a time such that all intermediate mappings are H‐colorings. In the affirmative, we say that φ reconfigures to ψ. Currently, the complexity of deciding whether an H‐coloring φ reconfigures to an H‐coloring ψ is only known when H is a clique, a circular clique, a C4‐free graph, or in a few other cases which are easily derived from these. We show that this problem is PSPACE‐complete when H is an odd wheel. An important notion in the study of reconfiguration problems for H‐colorings is that of a frozen H‐coloring; that is, an H‐coloring φ such that φ does not reconfigure to any H‐coloring ψ such that ψ≠φ. We obtain an explicit dichotomy theorem for the problem of deciding whether a given graph G admits a frozen H‐coloring. The hardness proof involves a reduction from a constraint satisfaction problem which is shown to be nondeterministic polynomial time NP‐complete by establishing the nonexistence of a certain type of polymorphism.
In the problem Mix(H) one is given a graph G and must decide if the Hom-graph Hom(G,H) is connected. We show that if H is a triangle-free reflexive graph with at least one cycle, Mix(H) is ...coNP-complete. The main part of this is a reduction to the problem NonFlat(H) for a simplicial complex H, in which one is given a simplicial complex G and must decide if there are any simplicial maps ϕ from G to H under which some 1-cycles of G maps to homologically nontrivial cycle of H. We show that for any reflexive graph H, if the clique complex H of H has a free, nontrivial homology group H1(H), then NonFlat(H) is NP-complete.
A fabrication technique using Al2O3-passivated local contacts was employed to produce narrow-bandgap CuInSe2 (CISe) photoabsorbers, which are well-suited as bottom cell materials in tandem devices. ...However, the performances of CISe cells with narrow bandgaps are impeded by the recombination of charge carriers, which reduces the open-circuit voltage (VOC). To overcome this limitation, an additional Al2O3 passivation layer was added to CISe solar cells. This enhanced the VOC while maintaining a spectral response of up to 1.0 eV, thereby boosting the photovoltaic conversion efficiency of the devices. Further, the Al2O3 passivation layer within the CISe absorber effectively mitigated the recombination of charge carriers, resulting in a substantial improvement in efficiency. Specifically, the Al2O3-passivated local contact hindered the charge-carrier recombination at the rear contact, leading to a marked increase in the VOC. Consequently, the overall photovoltaic conversion efficiency increased significantly from 10.4 % to 13 %. These results are expected to greatly further the development of CISe solar cells and achieve remarkable photovoltaic conversion efficiencies.
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•Improve VOC of CISe solar cells by implementing Al2O3 passivation layer.•Investigated Al2O3 passivation local contact effect in CISe light absorption layer.•Sample with Al2O3 passivation local contact exhibits strongly increased VOC.•Increased VOC can be attributed to reduced recombination at the back contact.•Photovoltaic conversion efficiency increases from 10.4 % to 13 %.
The predictive value of platelet-to-lymphocyte ratio (PLR) in acute illness is well known, but further evaluation is needed in traffic accident patients. PLR was significantly associated with an ...increased risk of in-hospital mortality in admitted adult traffic accident patients.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Let G be a digraph and B be a fixed reflexive digraph cycle. Given two homomorphisms ϕ,ϕ′:G→B, a walk from ϕ to ϕ′ in the Hom-graph Hom(G,B) corresponds to what is often called a reconfiguration ...sequence of the homomorphisms. Except in the case that B contains a 4-cycle, containing an oriented cycle of algebraic girth 0, we give a polynomial time algorithm that either finds a path between two given homomorphisms or discovers an obstruction certifying the non-existence of such a path.
Given a loop-free graph H, the reconfiguration problem for homomorphisms to H (also called H-colourings) asks: given two H-colourings f of g of a graph G, is it possible to transform f into g by a ...sequence of single-vertex colour changes such that every intermediate mapping is an H-colouring? This problem is known to be polynomial-time solvable for a wide variety of graphs H (e.g. all C4-free graphs) but only a handful of hard cases are known. We prove that this problem is PSPACE-complete whenever H is a K2,3-free quadrangulation of the 2-sphere (equivalently, the plane) which is not a 4-cycle. From this result, we deduce an analogous statement for non-bipartite K2,3-free quadrangulations of the projective plane. This include several interesting classes of graphs, such as odd wheels, for which the complexity was known, and 4-chromatic generalized Mycielski graphs, for which it was not.
If we instead consider graphs G and H with loops on every vertex (i.e. reflexive graphs), then the reconfiguration problem is defined in a similar way except that a vertex can only change its colour to a neighbour of its current colour. In this setting, we use similar ideas to show that the reconfiguration problem for H-colourings is PSPACE-complete whenever H is a reflexive K4-free triangulation of the 2-sphere which is not a reflexive triangle. This proof applies more generally to reflexive graphs which, roughly speaking, resemble a triangulation locally around a particular vertex. This provides the first graphs for which the reconfiguration problem is known to be PSPACE-complete for reflexive instances.
Recolouring reflexive digraphs Brewster, Richard C.; Lee, Jae-baek; Siggers, Mark
Discrete mathematics,
June 2018, 2018-06-00, Letnik:
341, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Given digraphs G and H, the colouring graph Col(G,H) has as its vertices all homomorphism of G to H. There is an arc ϕ→ϕ′ between two homomorphisms if they differ on exactly one vertex v, and if v ...has a loop we also require ϕ(v)→ϕ′(v). The recolouring problem asks if there is a path in Col(G,H) between given homomorphisms ϕ and ψ. We examine this problem in the case where G is a digraph and H is a reflexive, digraph cycle.
We show that for a reflexive digraph cycle H and a reflexive digraph G, the problem of determining whether there is a path between two maps in Col(G,H) can be solved in time polynomial in G. When G is not reflexive, we show the same except for certain digraph 4-cycles H.
Biodegradable poly(lactide-co-glycolide) (PLGA) has found widespread use in modern medical practice. However, the degradation rate of PLGA should be adjusted for specific biomedical applications such ...as tissue engineering, drug delivery, and surgical implantation. This study focused on the effect of electron beam radiation on nanofibrous PLGA mats in terms of physical properties and degradation behavior with cell proliferation. PLGA nanofiber mats were prepared by electrospinning, and electron beam was irradiated at doses of 50, 100, 150, 200, 250, and 300 kGy. PLGA mats showed dimensional integrity after electron beam irradiation without change of fiber diameter. The degradation behavior of a control PLGA nanofiber (0 kGy) and electron beam-irradiated PLGA nanofibers was analyzed by measuring the molecular weight, weight loss, change of chemical structure, and fibrous morphology. The molecular weight of the PLGA nanofibers decreased with increasing electron beam radiation dose. The mechanical properties of the PLGA nanofibrous mats were decreased with increasing electron beam irradiation dose. Cell proliferation behavior on all electron beam irradiated PLGA mats was similar to the control PLGA mats. Electron beam irradiation of PLGA nanofibrous mats is a potentially useful approach for modulating the biodegradation rate of tissue-specific nonwoven nanofibrous scaffolds, specifically for soft tissue engineering applications.
To determine the incidence of acute cerebral infarction or space occupying lesion (SOL) among patients with isolated vertigo or dizziness (IVD) and to evaluate the role of cerebellar function test ...(CFT) and D-dimer to discriminate ACI/SOL and non-ACI/SOL.
A retrospective study of consecutive emergency department (ED) patients with IVD during one year was conducted. ACI was based on the diffusion-weighted magnetic resonance imaging (DW-MRI), and SOL was based on the concurrent MRI sequences. A sensitivity analysis of CFT and D-dimer was also performed.
Among the 468 patients enrolled, 13 patients (2.8%) had ACI, 11 at cerebellum, 1 at occipital lobe, and 1 at centrum semiovale. Twenty-five patients (5.3%) had SOL. Aneurysm is most frequent (n = 7), followed by meningioma (n = 4) and venous anomaly (n = 4). In total, ACI/SOL was found in 8.1% (n = 38). Abnormal findings in finger-to-nose (FN), heel-to-shin (HTS), and rapid alternative movement (RAM) tests were significantly higher in ACI or ACI/SOL group, while gait disturbance, tandem gait abnormality, and Romberg's test were not. CFT sensitivities were low for ACI as well as for ACI/SOL, but specificities were high for ACI and ACI/SOL. D-dimer level showed a sensitivity of 100% at >0.18 mg/L for ACI and >0.15 mg/L for ACI/SOL. However, specificity was low at corresponding D-dimer level. Among the subgroup (n = 411) who did not show any abnormality in CFT, 9 patients (2.2%) had ACI, and 33 patients (8.0%) had ACI/SOL.
The present study reports a clinically significant incidence of ACI/SOL among ED patients with IVD. D-dimer showed high sensitive and low specificity, while CFT showed low sensitivity and high specificity.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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