38,425 research outputs found

    On the Approximability and Hardness of the Minimum Connected Dominating Set with Routing Cost Constraint

    Full text link
    In the problem of minimum connected dominating set with routing cost constraint, we are given a graph G=(V,E)G=(V,E), and the goal is to find the smallest connected dominating set DD of GG such that, for any two non-adjacent vertices uu and vv in GG, the number of internal nodes on the shortest path between uu and vv in the subgraph of GG induced by DâˆȘ{u,v}D \cup \{u,v\} is at most α\alpha times that in GG. For general graphs, the only known previous approximability result is an O(log⁥n)O(\log n)-approximation algorithm (n=∣V∣n=|V|) for α=1\alpha = 1 by Ding et al. For any constant α>1\alpha > 1, we give an O(n1−1α(log⁥n)1α)O(n^{1-\frac{1}{\alpha}}(\log n)^{\frac{1}{\alpha}})-approximation algorithm. When α≄5\alpha \geq 5, we give an O(nlog⁥n)O(\sqrt{n}\log n)-approximation algorithm. Finally, we prove that, when α=2\alpha =2, unless NP⊆DTIME(npolylog⁥n)NP \subseteq DTIME(n^{poly\log n}), for any constant Ï”>0\epsilon > 0, the problem admits no polynomial-time 2log⁥1−ϔn2^{\log^{1-\epsilon}n}-approximation algorithm, improving upon the Ω(log⁥n)\Omega(\log n) bound by Du et al. (albeit under a stronger hardness assumption)

    D∗Dˉ∗D^*\bar D^* molecule interpretation of Zc(4025)Z_c(4025)

    Full text link
    We have used QCD sum rules to study the newly observed charged state Zc(4025)Z_c(4025) as a hidden-charm D∗Dˉ∗D^*\bar D^* molecular state with the quantum numbers IG(JP)=1+(1+)I^G(J^{P})=1^+(1^{+}). Using a D∗Dˉ∗D^*\bar D^* molecular interpolating current, we have calculated the two-point correlation function and the spectral density up to dimension eight at leading order in αs\alpha_s. The extracted mass is mX=(4.04±0.24)m_X=(4.04\pm0.24) GeV. This result is compatible with the observed mass of Zc(4025)Z_c(4025) within the errors, which implies a possible molecule interpretation of this new resonance. We also predict the mass of the corresponding hidden-bottom B∗Bˉ∗B^*\bar B^* molecular state: mZb=(9.98±0.21)m_{Z_b}=(9.98\pm0.21) GeV.Comment: 6 pages, 5 figures. Version appears in Eur. Phys. J.

    Factors affecting metal mobilisation during oxidation of sulphidic, sandy wetland substrates

    Get PDF
    Most metals accumulate as sulphides under anoxic conditions in wetland substrates, reducing their bioavailability due to the solubility of metal sulphides. However, upon oxidation of these sulphides when the substrate is occasionally oxidised, metals can be released from the solid phase to the pore water or overlaying surface water. This release can be affected by the presence of carbonates, organic matter and clay. We compared changes of Cd, Cu and Zn mobility (CaCl2 extraction) during oxidation of a carbonate-rich and a carbonate-poor sulphidic, sandy wetland substrate. In addition, we studied how clay with low and high cation sorption capacity (bentonite and kaolinite, respectively) and organic matter (peat) can counteract Cd, Cu and Zn release during oxidation of both carbonate-rich and carbonate-poor sulphidic sediments. CaCl2-extractability of Cu, a measure for its availability, is low in both carbonate-poor and carbonate-rich substrates, whereas its variability is high. The availability of Cd and Zn is much higher and increases when peat is supplied to carbonate-poor substrates. A strong reduction of Cd and Zn extractability is observed when clay is added to carbonate-poor substrates. This reduction depends on the clay type. Most observations could be explained taking into account pH differences between treatments, with kaolinite resulting in a lower pH in comparison to bentonite. These pH differences affect the presence and characteristics of dissolved organic carbon and the metal speciation, which in turns affects the interaction of metals with the solid soil phase. In carbonate-rich substrates, Cd and Zn availability is lower and the effects of peat and clay amendment are less clear. The latter can also be attributed to the high pH and lack of pH differences between treatments

    Power Corrections in Charmless B Decays

    Full text link
    In this paper, we focus on the role of power corrections in QCD factorization(QCDF) method in charmless two-body nonleptonic BB meson decays. We use the ratio of the branching fraction of B+→π+K∗0B^+ \to \pi^+ K^{\ast 0} to that of B0→π−ρ+B^0 \to \pi^- \rho^+, for which the theoretical uncertainties are greatly reduced, to show clearly that the power corrections in charmless B decays are probably large. With other similar ratios considered, for example, for the B0→K−ρ+B^0 \to K^- \rho^+ decay, it is very likely that, among various sources of power corrections, annihilation topology plays an indispensable role at least for penguin dominated PV\rm PV channels. We also consider some selective ratios of direct CP asymmetries. Among these, we find that, if power corrections other than the chirally enhanced power corrections and annihilation topology were negligible, QCDF would predict the direct CP asymmetry of B→π+π−B \to \pi^+ \pi^- to be about 3 times larger than that of B→π±K∓B \to \pi^\pm K^\mp, with opposite sign. Experimentally any significant deviation from this prediction would suggest either new physics or possibly the importance of long-distance rescattering effects.Comment: references and note added, to appear in Phys. Rev.

    Orthopaedic referrals using a smartphone app: Uptake, response times and outcome

    Get PDF
    Background. It is well established that South Africa (SA) suffers an immense burden of violence and injuries. The responsibility of providing care for these injuries falls mainly on public health services, resulting in overloading of the health system. Prior to a recent intervention, the large burden had been exacerbated by limitations in the traditional referral system that highlighted the need for a better referral system. Vula’s smartphone app was introduced at Tygerberg Hospital in August 2016. This study evaluated the uptake, response times and outcomes using this app.Objectives. The main objectives of the study were to describe: (i) the number of referrals; (ii) referral response times; (iii) referring facilities; and (iv) referral outcomes. Secondary objectives were to: (i) evaluate whether the referral outcome pathway was appropriate; and (ii) assess professional conduct and evidence of upskilling.Methods. This retrospective, descriptive study investigated Vula app referrals to the Division of Orthopaedic Surgery at Tygerberg Hospital between 1 August 2016 and 31 March 2017. Vula was advertised to key facilities in the hospital’s referral network. All referrals to the division during the study period were systematically included in the analysis of operational outcomes, although some were excluded from the subsequent referral outcome analysis. Operational outcomes included the number of referrals, referring facilities and referral response times. Referral outcome analysis included the clinical diagnosis, referral pathway, whether the referral was used for upskilling and whether it was conducted in a professional manner.Results. A total of 2 275 referrals from 39 different facilities were received during the study period from 238 individual users; 50% of referrals received a response within 11 minutes, while a small percentage received no response. Clinical and demographic characteristics of 1 985 patients included in the referral outcome analysis indicated that the majority of trauma and emergency referrals involved males, with closed fractures being the most frequent clinical presentation. Although the most common referral outcome was immediate transfer, one-third of the patients were treated at the referring hospital with advice only.Conclusions. The large volume of orthopaedic referrals received through the Vula app suggests that Vula represents a successful alternative to traditional referral methods. Referrals managed by advice only could suggest that Vula facilitates some relief for the overburdened trauma services. Future research could further explore Vula’s role in strengthening the public health system, including interventions for high-volume referral areas and upskilling of referring health workers.

    q-Deforming Maps for Lie Group Covariant Heisenberg Algebras

    Get PDF
    We briefly summarize our systematic construction procedure of q-deforming maps for Lie group covariant Weyl or Clifford algebras.Comment: latex file, 4 pages. Contribution to the proceedings of the 5th Wigner Symposium. Slight modification

    Aborsie: ’n Juridiese, etiese en regsetiese vraagstuk

    Get PDF
    In die geledere van skokkende en onetiese dade in die menslike samelewing, beklee aborsie ’n besondere plek. Vir wetenskaplike doeleindes kan aborsie oor die algemeen gedefinieer word as die skeiding van of afdrywing uit die moederlyf van die „produk” van konsepsie, synde ’n fetus (Geldenhuys, 1974:11; O’Donovan 1975:2). ’n Verdere element van die definisie, wat die blote afdrywing van die vrug gewoonlik kwalifiseer, is dat die fetus, met betrekking tot nageboortelike lewe gesproke, nie lewensvatbaar moes gewees het nie. Met die byvoeging van hierdie element tot die eie definisie word tans egter vertoef ten einde eers die belangrike vraag wanneer lewe ontstaan, te beantwoord
    • 

    corecore