41,260 research outputs found

### Fixed-Parameter Tractability of Token Jumping on Planar Graphs

Suppose that we are given two independent sets $I_0$ and $I_r$ of a graph
such that $|I_0| = |I_r|$, and imagine that a token is placed on each vertex in
$I_0$. The token jumping problem is to determine whether there exists a
sequence of independent sets which transforms $I_0$ into $I_r$ so that each
independent set in the sequence results from the previous one by moving exactly
one token to another vertex. This problem is known to be PSPACE-complete even
for planar graphs of maximum degree three, and W[1]-hard for general graphs
when parameterized by the number of tokens. In this paper, we present a
fixed-parameter algorithm for the token jumping problem on planar graphs, where
the parameter is only the number of tokens. Furthermore, the algorithm can be
modified so that it finds a shortest sequence for a yes-instance. The same
scheme of the algorithms can be applied to a wider class of graphs,
$K_{3,t}$-free graphs for any fixed integer $t \ge 3$, and it yields
fixed-parameter algorithms

### Nutritional characteristics of moon dust for soil microorganisms

Approximately 46% of the lunar sample (10084,151), 125.42 mg, was solubilized in 680 ml 0.01 M salicylic acid. Atomic absorption spectroscopic analysis of the solubilized lunar sample showed the following amount of metal ions: Ca, 3.1; Mg, 4.0; K, 0.09; Na, 0.67; Fe, 7.3; Mn, 1.6; Cu, Ni, Cr, less than 0.1 each. All are in ppm. Salicylic acid used to solubilize the lunar sample was highly inhibitory to the growth of mixed soil microbes. However, the mineral part of the lunar extract stimulated the growth. For optimal growth of the soil microbes the following nutrients must be added to the moon extract; sources of carbon, nitrogen, sulfur, phosphorus, and magnesium in addition to water

### Mediation of Supersymmetry Breaking via Anti-Generation Fields

In the context of the weakly coupled heterotic string, we propose a new model
of mediating supersymmetry breaking. The breakdown of supersymmetry in the
hidden sector is transmitted to anti-generation fields via gravitational
interactions. Subsequent transmission of the breaking to the MSSM sector occurs
via gauge interactions. It is shown that the mass spectra of superparticles are
phenomenologically viable.Comment: 8pages, LaTeX, 1 figure, final version to appear in Prog. Theor.
Phys. Vol.103, No.6 (2000

### Global modeling study of potentially bioavailable iron input from shipboard aerosol sources to the ocean

Iron (Fe) is an essential element for phytoplankton. The majority of iron is transported from arid and semiarid regions to the open ocean, but it is mainly in an insoluble form. Since most aquatic organisms can take up iron only in the dissolved form, aerosol iron solubility is a key factor that can influence the air-sea CO2 fluxes and thus climate. Field observations have shown relatively high iron solubility in aerosols influenced by combustion sources, but specific emissions sources and their contributions to deposition fluxes largely remain uncertain. Here, a global chemical transport model is used to investigate the effect of aerosol emissions from ship plumes on iron solubility in particles from the combustion and dust sources. The model results reveal that the oil combustion from shipping mainly contributes to high iron solubility (> 10%) at low iron loading (1-110 ng m-3) observed over the high latitude North Atlantic Ocean, rather than the other combustion sources from continental industrialized regions. Due to continuing growth in global shipping and no regulations regarding particles emissions over the open ocean, the input of potentially bioavailable iron from ship plumes is likely to increase during the next century. The model results suggest that deposition of soluble iron from ships in 2100 contributes 30-60% of the soluble iron deposition over the high latitude North Atlantic and North Pacific

### Reconfiguration of Dominating Sets

We explore a reconfiguration version of the dominating set problem, where a
dominating set in a graph $G$ is a set $S$ of vertices such that each vertex is
either in $S$ or has a neighbour in $S$. In a reconfiguration problem, the goal
is to determine whether there exists a sequence of feasible solutions
connecting given feasible solutions $s$ and $t$ such that each pair of
consecutive solutions is adjacent according to a specified adjacency relation.
Two dominating sets are adjacent if one can be formed from the other by the
addition or deletion of a single vertex.
For various values of $k$, we consider properties of $D_k(G)$, the graph
consisting of a vertex for each dominating set of size at most $k$ and edges
specified by the adjacency relation. Addressing an open question posed by Haas
and Seyffarth, we demonstrate that $D_{\Gamma(G)+1}(G)$ is not necessarily
connected, for $\Gamma(G)$ the maximum cardinality of a minimal dominating set
in $G$. The result holds even when graphs are constrained to be planar, of
bounded tree-width, or $b$-partite for $b \ge 3$. Moreover, we construct an
infinite family of graphs such that $D_{\gamma(G)+1}(G)$ has exponential
diameter, for $\gamma(G)$ the minimum size of a dominating set. On the positive
side, we show that $D_{n-m}(G)$ is connected and of linear diameter for any
graph $G$ on $n$ vertices having at least $m+1$ independent edges.Comment: 12 pages, 4 figure

### Reconfiguration on sparse graphs

A vertex-subset graph problem Q defines which subsets of the vertices of an
input graph are feasible solutions. A reconfiguration variant of a
vertex-subset problem asks, given two feasible solutions S and T of size k,
whether it is possible to transform S into T by a sequence of vertex additions
and deletions such that each intermediate set is also a feasible solution of
size bounded by k. We study reconfiguration variants of two classical
vertex-subset problems, namely Independent Set and Dominating Set. We denote
the former by ISR and the latter by DSR. Both ISR and DSR are PSPACE-complete
on graphs of bounded bandwidth and W[1]-hard parameterized by k on general
graphs. We show that ISR is fixed-parameter tractable parameterized by k when
the input graph is of bounded degeneracy or nowhere-dense. As a corollary, we
answer positively an open question concerning the parameterized complexity of
the problem on graphs of bounded treewidth. Moreover, our techniques generalize
recent results showing that ISR is fixed-parameter tractable on planar graphs
and graphs of bounded degree. For DSR, we show the problem fixed-parameter
tractable parameterized by k when the input graph does not contain large
bicliques, a class of graphs which includes graphs of bounded degeneracy and
nowhere-dense graphs

### Momentum-Dependent Hybridization Gap and dispersive in-gap state of The Kondo Semiconductor SmB6

We report the temperature-dependent three-dimensional angle-resolved
photoemission spectra of the Kondo semiconductor SmB$_6$. We found a difference
in the temperature dependence of the peaks at the X and $\Gamma$ points, due to
hybridization between the Sm 5d conduction band and the nearly localized Sm 4f
state. The peak intensity at the X point has the same temperature dependence as
the valence transition below 120 K, while that at the $\Gamma$ point is
consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This
suggests that the hybridization with the valence transition mainly occurs at
the X point, and the initial state of the magnetic excitation is located at the
$\Gamma$ point.Comment: 5 pages, 3 figure

### A numerical algorithm for optimal feedback gains in high dimensional LQR problems

A hybrid method for computing the feedback gains in linear quadratic regulator problems is proposed. The method, which combines the use of a Chandrasekhar type system with an iteration of the Newton-Kleinman form with variable acceleration parameter Smith schemes, is formulated so as to efficiently compute directly the feedback gains rather than solutions of an associated Riccati equation. The hybrid method is particularly appropriate when used with large dimensional systems such as those arising in approximating infinite dimensional (distributed parameter) control systems (e.g., those governed by delay-differential and partial differential equations). Computational advantage of the proposed algorithm over the standard eigenvector (Potter, Laub-Schur) based techniques are discussed and numerical evidence of the efficacy of our ideas presented

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