2,662 research outputs found
Similarity of percolation thresholds on the hcp and fcc lattices
Extensive Monte-Carlo simulations were performed in order to determine the
precise values of the critical thresholds for site () and bond ()
percolation on the hcp lattice to compare with previous precise measuremens on
the fcc lattice. Also, exact enumeration of the hcp and fcc lattices was
performed and yielded generating functions and series for the zeroth, first,
and second moments of both lattices. When these series and the values of
are compared to those for the fcc lattice, it is apparent that the site
percolation thresholds are different; however, the bond percolation thresholds
are equal within error bars, and the series only differ slightly in the higher
order terms, suggesting the actual values are very close to each other, if not
identical.Comment: 10 pages, 4 figures, submitted to J. Stat. Phy
Why Worry about How Many Species and Their Loss?
We are astonishingly ignorant about how many species are alive on earth today, and even more ignorant about how many we can lose yet still maintain ecosystem services that humanity ultimately depends upon. Mora et al.'s paper is important in offering an imaginative new approach to assessing total species numbers, both on land and in the sea
Ideas in ecology
Journal ArticleThe word "ecology" means different things to different people. For example, during the last 25 years or so the word has been used to label attitudes, life-styles, consumer goods, political parties, and college courses. In the 1960s one university renamed its "Home Economics" course "Home Ecology." (But our own biology department reacted to the growing visibility of its conventional "Ecology" course by renaming it "Population Biology.") It is often said that Thoreau coined the word "ecology." He certainly ought to have done so, given the Rousseauesque yearnings that surround the word, and this may be why the myth lives on, even though it stems from a 1958 misreading of the word "geology" as "ecology" in one of his letters (James 1985). The German biologist Haeckel was actually the first to use the word "Oecologie," in 1866
Neutron Tunneling in 3He(3He,2p)4He
We investigate the possibility that in the astrophysically interesting energy range (i.e., well below the Coulomb barrier), the reaction 3He(3He,2p)4He proceeds predominantly by a neutron tunneling mechanism. Rough calculations of the magnitude and energy dependence of the total cross-section and of the shape of the proton differential cross-section are made on this basis. The results are in moderate agreement with recent experiments, and tend to justify a smooth extrapolation of these laboratory results down to the lower energies of astrophysical significance
Correlated interaction fluctuations in photosynthetic complexes
The functioning and efficiency of natural photosynthetic complexes is
strongly influenced by their embedding in a noisy protein environment, which
can even serve to enhance the transport efficiency. Interactions with the
environment induce fluctuations of the transition energies of and interactions
between the chlorophyll molecules, and due to the fact that different
fluctuations will partially be caused by the same environmental factors,
correlations between the various fluctuations will occur. We argue that
fluctuations of the interactions should in general not be neglected, as these
have a considerable impact on population transfer rates, decoherence rates and
the efficiency of photosynthetic complexes. Furthermore, while correlations
between transition energy fluctuations have been studied, we provide the first
quantitative study of the effect of correlations between interaction
fluctuations and transition energy fluctuations, and of correlations between
the various interaction fluctuations. It is shown that these additional
correlations typically lead to changes in interchromophore transfer rates,
population oscillations and can lead to a limited enhancement of the light
harvesting efficiency
Inverted orbital polarization in strained correlated oxide films
Manipulating the orbital occupation of valence electrons via epitaxial strain
in an effort to induce new functional properties requires considerations of how
changes in the local bonding environment affect the band structure at the Fermi
level. Using synchrotron radiation to measure the x-ray linear dichroism of
epitaxially strained films of the correlated oxide CaFeO3, we demonstrate that
the orbital polarization of the Fe valence electrons is opposite from
conventional understanding. Although the energetic ordering of the Fe 3d
orbitals is confirmed by multiplet ligand field theory analysis to be
consistent with previously reported strain-induced behavior, we find that the
nominally higher energy orbital is more populated than the lower. We ascribe
this inverted orbital polarization to an anisotropic bandwidth response to
strain in a compound with nearly filled bands. These findings provide an
important counterexample to the traditional understanding of strain-induced
orbital polarization and reveal a new method to engineer otherwise unachievable
orbital occupations in correlated oxides
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