208,705 research outputs found
Fe/Ni ratio in the Ant Nebula Mz 3
We have analyzed the [Fe II] and [Ni II] emission lines in the bipolar
planetary nebula Mz~3. We find that the [Fe II] and [Ni II] lines arise
exclusively from the central regions. Fluorescence excitation in the formation
process of these lines is negligible for this low-excitation nebula. From the
[Fe II]/[Ni II] ratio, we obtain a higher Fe/Ni abundance ratio with respect to
the solar value. The current result provides further supporting evidence for Mz
3 as a symbiotic Mira.Comment: 2 pages, 1 figure, to be published in the Proceedings of the IAU
Symposium 234: Planetary Nebulae in Our Galaxy and Beyond, eds. M.J. Barlow,
R.H. Mende
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Supervisory Efficiency and Collusion in a Multiple-Agent Hierarchy
We analyze a principal-supervisor-two-agent hierarchy with inefficient supervision. The su-pervisor may collects a wrong signal on each agent’s unobservable effort level. When reportingto the principal, the supervisor can collude with one or both agents to manipulate the signalin exchange for a bribe. In contract design, we identify a new trade-off between the loss fromsupervisor-agent collusion and the risk from inefficient supervision: Although allowing collu-sion makes shirking more attractive to the agents, it brings in a benefit because it can “correct”an incorrect negative signal when the agent has exerted effort. Such collusive supervision savesrisk premiums that the principal has to pay for incentive provision. We characterize the princi-pal’s optimal contract choice among no-supervision, collusion-proof, and collusive-supervisioncontracts. We show that the collusive-supervision contract dominates when the supervisory ef-ficiency is at an intermediate level
Flexible protein folding by ant colony optimization
Protein structure prediction is one of the most challenging topics in bioinformatics.
As the protein structure is found to be closely related to its functions,
predicting the folding structure of a protein to judge its functions is meaningful to
the humanity. This chapter proposes a flexible ant colony (FAC) algorithm for solving
protein folding problems (PFPs) based on the hydrophobic-polar (HP) square lattice
model. Different from the previous ant algorithms for PFPs, the pheromones in the
proposed algorithm are placed on the arcs connecting adjacent squares in the lattice.
Such pheromone placement model is similar to the one used in the traveling salesmen
problems (TSPs), where pheromones are released on the arcs connecting the cities.
Moreover, the collaboration of effective heuristic and pheromone strategies greatly
enhances the performance of the algorithm so that the algorithm can achieve good
results without local search methods. By testing some benchmark two-dimensional
hydrophobic-polar (2D-HP) protein sequences, the performance shows that the proposed
algorithm is quite competitive compared with some other well-known methods
for solving the same protein folding problems
Effect of distribution of stickers along backbone on temperature-dependent structural properties in associative polymer solutions
Effect of distribution of stickers along the backbone on structural
properties in associating polymer solutions is studied using self-consistent
field lattice model. Only two inhomogeneous morphologies, i.e.,
microfluctuation homogenous (MFH) and micelle morphologies, are observed. If
the system is cooled, the solvent content within the aggregates decreases. When
the spacing of stickers along the backbone is increased the
temperature-dependent range of aggregation in MFH morphology and half-width of
specific heat peak for homogenous solutions-MFH transition increase, and the
symmetry of the peak decreases. However, with increasing spacing of stickers,
the above three corresponding quantities related to micelles behave
differently. It is demonstrated that the broad nature of the observed
transitions can be ascribed to the structural changes which accompany the
replacement of solvents in aggregates by polymer, which is consistent with the
experimental conclusion. It is found that different effect of spacing of
stickers on the two transitions can be interpreted in terms of intrachain and
interchain associations.Comment: 10 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1202.459
Possible and Molecular states in a chiral quark model
We perform a systematic study of the bound state problem of and
systems by using effective interaction in our chiral quark model.
Our results show that both the interactions of and states
are attractive, which consequently result in
and bound states.Comment: arXiv admin note: substantial text overlap with arXiv:1204.395
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