2,771 research outputs found
Efficiency and persistence in models of adaptation
A cut-and-paste model which mimics a trial-and-error process of adaptation is
introduced and solved. The model, which can be thought of as a diffusion
process with memory, is characterized by two properties, efficiency and
persistence. We establish a link between these properties and determine two
transitions for each property, a percolation transition and a depinning
transition. If the adaptation process is iterated, the antipersistent state
becomes an attractor of the dynamics. Extensions to higher dimensions are
briefly discussed.Comment: 4 pages, 4 figures, submitted to publicatio
Collapse transition of a square-lattice polymer with next nearest-neighbor interaction
We study the collapse transition of a polymer on a square lattice with both
nearest-neighbor and next nearest-neighbor interactions, by calculating the
exact partition function zeros up to chain length 36. The transition behavior
is much more pronounced than that of the model with nearest-neighbor
interactions only. The crossover exponent and the transition temperature are
estimated from the scaling behavior of the first zeros with increasing chain
length. The results suggest that the model is of the same universality class as
the usual theta point described by the model with only nearest-neighbor
interaction.Comment: 14 pages, 5 figure
1-Methyl-2,4-bis(2-methoxyphenyl)-3-azabicyclo[3.3.1]nonan-9-one
The crystal structure of the title compound, C23H27NO3, shows that the compound exists in a chair–chair conformation with an equatorial disposition of 2-methoxyphenyl groups at an angle of 39.94 (3)° with respect to each other. An intermolecular N—H⋯π interaction is observed in the crystal packing
2,4-Bis(2-methylphenyl)-3-azabicyclo[3.3.1]nonan-9-one O-methyloxime
The molecule of the title compound, C23H28N2O, exists in a twin-chair conformation, with equatorial orientation of the ortho-tolyl groups on both sides of the secondary amino group. The title oxime compound and its ketone precursor 2,4-bis(2-methylphenyl)-3-azabicyclo[3.3.1]nonan-9-one exhibit similar stereochemistries, with the orientation of the o-tolyl rings almost identical in both compounds. In the title compound, the tolyl rings are at an angle of 23.77 (3)° with respect to one another; the angle in the precursor is 29.4 (1)° [Vijayalakshmi, Parthasarathi, Venkatraj & Jeyaraman (2000 ▶), Acta Cryst. C56, 1240–1241]. The cyclohexane ring and the oxime ether are disordered over two alternative orientations, with a refined site-occupancy ratio of 0.813 (2):0.186 (4). The crystal structure of the title compound is stabilized by intermolecular N—H⋯π interactions
2,4-Bis(4-propoxyphenyl)-3-azabicyclo[3.3.1]nonan-9-one
In the title compound, C26H33NO3, a crystallographic mirror plane bisects the molecule (two C atoms, one O atom and one N atom lie on the mirror plane). The molecule exists in a twin-chair conformation with equatorial orientations of the 4-propoxyphenyl groups. The dihedral angle between the 4-propoxyphenyl groups is 31.58 (3)°
Centrosome amplification fine tunes tubulin acetylation to differentially control intracellular organization
Exotic magnetism on the quasi-FCC lattices of the double perovskites LaNaBO (B Ru, Os)
We find evidence for long-range and short-range ( 70 \AA~at 4 K)
incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices
of the monoclinic double perovskites LaNaRuO and LaNaOsO
respectively. Incommensurate magnetic order on the FCC lattice has not been
predicted by mean field theory, but may arise via a delicate balance of
inequivalent nearest neighbour and next nearest neighbour exchange
interactions. In the Ru system with long-range order, inelastic neutron
scattering also reveals a spin gap 2.75 meV. Magnetic
anisotropy is generally minimized in the more familiar octahedrally-coordinated
systems, so the large gap observed for LaNaRuO may result from
the significantly enhanced value of spin-orbit coupling in this
material.Comment: 5 pages, 4 figure
Exact Partition Function Zeros of a Polymer on a Simple-Cubic Lattice
We study conformational transitions of a polymer on a simple-cubic lattice by
calculating the zeros of the exact partition function, up to chain length 24.
In the complex temperature plane, two loci of the partition function zeros are
found for longer chains, suggesting the existence of both the coil-globule
collapse transition and the melting-freezing transition. The locus
corresponding to coil-globule transition clearly approaches the real axis as
the chain length increases, and the transition temperature could be estimated
by finite-size scaling. The form of the logarithmic correction to the scaling
of the partition function zeros could also be obtained. The other locus does
not show clear scaling behavior, but a supplementary analysis of the specific
heat reveals a first-order-like pseudo-transition.Comment: 21 pages, 4 figure
Critical Exponents of the Four-State Potts Model
The critical exponents of the four-state Potts model are directly derived
from the exact expressions for the latent heat, the spontaneous magnetization,
and the correlation length at the transition temperature of the model.Comment: LaTex, 7 page
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