3,767 research outputs found
The domination number and the least -eigenvalue
A vertex set of a graph is said to be a dominating set if every
vertex of is adjacent to at least a vertex in , and the
domination number (, for short) is the minimum cardinality
of all dominating sets of . For a graph, the least -eigenvalue is the
least eigenvalue of its signless Laplacian matrix. In this paper, for a
nonbipartite graph with both order and domination number , we show
that , and show that it contains a unicyclic spanning subgraph
with the same domination number . By investigating the relation between
the domination number and the least -eigenvalue of a graph, we minimize the
least -eigenvalue among all the nonbipartite graphs with given domination
number.Comment: 13 pages, 3 figure
Breaking a novel colour image encryption algorithm based on chaos
Recently, a colour image encryption algorithm based on chaos was proposed by
cascading two position permutation operations and one substitution operation,
which are all determined by some pseudo-random number sequences generated by
iterating the Logistic map. This paper evaluates the security level of the
encryption algorithm and finds that the position permutation-only part and the
substitution part can be separately broken with only and 2 chosen plain-images, respectively, where is the size of the
plain-image. Concise theoretical analyses are provided to support the
chosen-plaintext attack, which are verified by experimental results also.Comment: 5 pages, 1 figur
4-(4-Fluorophenyl)-2-oxo-1,2,5,6-tetrahydrobenzo[h]quinoline-3-carbonitrile
In the molecule of the title compound, C20H13FN2O, the fluorophenyl ring is oriented at a dihedral angle of 72.76 (3)° with respect to the fused benzene ring. In the crystal structure, intermolecular N—H⋯O, C—H⋯O and C—H⋯F interactions link the molecules into chains. π–π contacts between the quinoline and benzene rings [centroid–centroid distance = 3.918 (3) Å] may further stabilize the structure. A weak C—H⋯π interaction is also present. The O atom and two of the CH2 groups of the quinoline ring system are disordered over two positions. The O atom was refined with occupancies of 0.489 (17) and 0.511 (17), while C and H atoms were refined with occupancies of 0.435 (13) and 0.565 (13)
Spins of the supermassive black hole in M87: new constraints from TeV observations
The rapid TeV ray variability detected in the well-known nearby
radio galaxy M87 implies an extremely compact emission region (5-10
Schwarzschild radii) near the horizon of the supermassive black hole in the
galactic center. TeV photons are affected by dilution due to interaction with
the radiation field of the advection-dominated accretion flow (ADAF) around the
black hole, and can thus be used to probe the innermost regions around the
black hole. We calculate the optical depth of the ADAF radiation field to the
TeV photons and find it strongly depends on the spin of the black hole. We find
that transparent radii of 10 TeV photons are of and
for the maximally rotating and non-rotating black holes, respectively. With the
observations, the calculated transparent radii strongly suggest the black hole
is spinning fast in the galaxy. TeV photons could be used as a powerful
diagnostic for estimating black hole spins in galaxies in the future.Comment: 4 pages, 4 figures. to appear in ApJ
The CJT calculation in studying nuclear matter beyond mean field approximation
We have introduced a CJT calculation in studying nuclear matter beyond mean
field approximation. Based on the CJT formalism and using Walecka model, we
have derived a set of coupled Dyson equations of nucleons and mesons.
Neglecting the medium effects of the mesons, the usual MFT results could be
reproduced. The beyond MFT calculations have been performed by thermodynamic
consistently determining the meson effective masses and solving the coupled gap
equations for nucleons and mesons. The numerical results for the nucleon and
meson effective masses at finite temperature and chemical potential in nuclear
matter are discussed.Comment: 8 pages, 8 figure
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