Indicators of hot fluid migration in sedimentary basins: evidence from the UK Atlantic Margin

Microthermometric, petrographic and isotopic methods have been used to detect evidence for hot fluid flow in Mesozoic and Tertiary sediments from the NW UK continental margin, West of Shetland. New data presented here show that temperatures are hotter by c. 40°C in Tertiary samples than in the underlying Jurassic and Cretaceous sediments in wells 204/28-1, 206/5-2, 208/27-1, especially in cements from samples as young as mid–upper Eocene in age. Paleocene samples can be discriminated from older (Jurassic and Cretaceous) and younger (Eocene) sandstones on the basis of silica cement morphology and cathodoluminescence zonation. Jurassic, Cretaceous and Eocene quartz cements show oscillatory zoning as a consequence of relatively slow burial cementation. In direct contrast, rapid precipitation of silica cements from the cooling of hot fluids has produced unzoned cements in all but one Paleocene sample. No evidence for unzoned quartz cements was noted in any pre-Paleocene or Eocene samples. The restriction of hot fluid inclusions and unzoned cements to the Paleocene and post-Paleocene is consistent with lateral focusing of hot fluids. Isotopic data from kaolinites indicate that these fluids are best represented by mixtures of Mesozoic or Tertiary meteoric waters and marine porewaters that have undergone isotopic alteration through interaction with volcanic material. Our results indicate that hot fluid flow occurred over a relatively long time-scale (i.e. several million years), which may have important consequences for the degradation of reservoired hydrocarbons in West of Shetland Paleocene plays

Improving gas sensing properties of graphene by introducing dopants and defects: a first-principles study

The interactions between four different graphenes (including pristine, B- or N-doped and defective graphenes) and small gas molecules (CO, NO, NO2 and NH3) were investigated by using density functional computations to exploit their potential applications as gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the graphene structure and the molecular adsorption configuration. All four gas molecules show much stronger adsorption on the doped or defective graphenes than that on the pristine graphene. The defective graphene shows the highest adsorption energy with CO, NO and NO2 molecules, while the B- doped graphene gives the tightest binding with NH3. Meanwhile, the strong interactions between the adsorbed molecules and the modified graphenes induce dramatic changes to graphene's electronic properties. The transport behavior of a gas sensor using B- doped graphene shows a sensitivity two orders of magnitude higher than that of pristine graphene. This work reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the appropriate dopant or defect

Tight Kernel Bounds for Problems on Graphs with Small Degeneracy

In this paper we consider kernelization for problems on d-degenerate graphs, i.e. graphs such that any subgraph contains a vertex of degree at most $d$. This graph class generalizes many classes of graphs for which effective kernelization is known to exist, e.g. planar graphs, H-minor free graphs, and H-topological-minor free graphs. We show that for several natural problems on d-degenerate graphs the best known kernelization upper bounds are essentially tight.Comment: Full version of ESA 201

Duality between quantum symmetric algebras

Using certain pairings of couples, we obtain a large class of two-sided non-degenerated graded Hopf pairings for quantum symmetric algebras.Comment: 15 pages. Letters in Math. Phy., to appear soo

Subset feedback vertex set is fixed parameter tractable

The classical Feedback Vertex Set problem asks, for a given undirected graph G and an integer k, to find a set of at most k vertices that hits all the cycles in the graph G. Feedback Vertex Set has attracted a large amount of research in the parameterized setting, and subsequent kernelization and fixed-parameter algorithms have been a rich source of ideas in the field. In this paper we consider a more general and difficult version of the problem, named Subset Feedback Vertex Set (SUBSET-FVS in short) where an instance comes additionally with a set S ? V of vertices, and we ask for a set of at most k vertices that hits all simple cycles passing through S. Because of its applications in circuit testing and genetic linkage analysis SUBSET-FVS was studied from the approximation algorithms perspective by Even et al. [SICOMP'00, SIDMA'00]. The question whether the SUBSET-FVS problem is fixed-parameter tractable was posed independently by Kawarabayashi and Saurabh in 2009. We answer this question affirmatively. We begin by showing that this problem is fixed-parameter tractable when parametrized by |S|. Next we present an algorithm which reduces the given instance to 2^k n^O(1) instances with the size of S bounded by O(k^3), using kernelization techniques such as the 2-Expansion Lemma, Menger's theorem and Gallai's theorem. These two facts allow us to give a 2^O(k log k) n^O(1) time algorithm solving the Subset Feedback Vertex Set problem, proving that it is indeed fixed-parameter tractable.Comment: full version of a paper presented at ICALP'1

Partitioning of phenanthrene by root cell walls and cell wall fractions of wheat (Triticum aestivum L.)

Plant cells have been reported to play an important role in the uptake of organic contaminants. This study was undertaken to provide an insight into the role of the root cell walls and their subfractions on sorption of phenanthrene to roots of wheat (Triticum aestivum L.). Root cell walls were isolated and further sequentially fractioned by removing pectin, hemicellulose one, and hemicellulose two. They were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state (13)C NMR. Root cell walls had a greater proportion of aromatic carbon and exhibited a lower polarity than the bulk roots. There was a stepwise increase in aromatic carbon content and a decrease in polarity following the sequential fractionation. The sorption affinity of phenanthrene increased gradually following the sequential extraction of root cells. A significant positive correlation between the sorption affinity K(OC) values and the aromatic carbon contents (r(2) = 0.896, p < 0.01) and a negative correlation between the sorption affinity K(OC) values and polarity ((O + N)/C) of root cell fractions (r(2) = 0.920, p < 0.01) were obtained. Improved modeling was achieved for phenanthrene sorption by involving the contribution of root cell walls as a source of root carbohydrates instead of using root lipids alone, which further confirms the significant contribution of root cell walls to phenanthrene sorption on wheat roots. The results provide evidence for the importance of the root cell walls in the partitioning of phenanthrene by plant roots

Initial-state parton shower kinematics for NLO event generators

We are developing a consistent method to combine tree-level event generators for hadron collision interactions with those including one additional QCD radiation from the initial-state partons, based on the limited leading-log (LLL) subtraction method, aiming at an application to NLO event generators. In this method, a boundary between non-radiative and radiative processes necessarily appears at the factorization scale (mu_F). The radiation effects are simulated using a parton shower (PS) in non-radiative processes. It is therefore crucial in our method to apply a PS which well reproduces the radiation activities evaluated from the matrix-element (ME) calculations for radiative processes. The PS activity depends on the applied kinematics model. In this paper we introduce two models for our simple initial-state leading-log PS: a model similar to the "old" PYTHIA-PS and a p_T-prefixed model motivated by ME calculations. PS simulations employing these models are tested using W-boson production at LHC as an example. Both simulations show a smooth matching to the LLL-subtracted W + 1 jet simulation in the p_T distribution of W bosons, and the summed p_T spectra are stable against a variation of mu_F, despite that the p_T-prefixed PS results in an apparently harder p_T spectrum.Comment: 10 pages, 6 figures; minor changes in the abstract and the text according to the comments from the refere

Open Problems in Parameterized and Exact Computation - IWPEC 2006

In September 2006, the Second International Workshop on Parameterized and Exact Computation was held in Zürich, Switzerland, as part of ALGO 2006. At the end of IWPEC 2006, a problem session was held. (Most of) the problems mentioned at this problem session, and some other problems, contributed by the participants of IWPEC 2006 are listed here

Onsager Relations and Hydrodynamic Balance Equations in 2D Quantum Wells

In this letter we clarify the role of heat flux in the hydrodynamic balance equations in 2D quantum wells, facilitating the formulation of an Onsager relation within the framework of this theory. We find that the Onsager relation is satisfied within the framework of the 2D hydrodynamic balance equation transport theory at sufficiently high density. The condition of high density is consonant with the requirement of strong electron-electron interactions for the validity of our balance equation formulation.Comment: 11 pages, RevTex, 4 postscript figures are avaliable upon reques

The spectrum of the random environment and localization of noise

We consider random walk on a mildly random environment on finite transitive d- regular graphs of increasing girth. After scaling and centering, the analytic spectrum of the transition matrix converges in distribution to a Gaussian noise. An interesting phenomenon occurs at d = 2: as the limit graph changes from a regular tree to the integers, the noise becomes localized.Comment: 18 pages, 1 figur