820 research outputs found
Developing the MTO Formalism
We review the simple linear muffin-tin orbital method in the atomic-spheres
approximation and a tight-binding representation (TB-LMTO-ASA method), and show
how it can be generalized to an accurate and robust Nth order muffin-tin
orbital (NMTO) method without increasing the size of the basis set and without
complicating the formalism. On the contrary, downfolding is now more efficient
and the formalism is simpler and closer to that of screened multiple-scattering
theory. The NMTO method allows one to solve the single-electron Schroedinger
equation for a MT-potential -in which the MT-wells may overlap- using basis
sets which are arbitrarily minimal. The substantial increase in accuracy over
the LMTO-ASA method is achieved by substitution of the energy-dependent partial
waves by so-called kinked partial waves, which have tails attached to them, and
by using these kinked partial waves at N+1 arbitrary energies to construct the
set of NMTOs. For N=1 and the two energies chosen infinitesimally close, the
NMTOs are simply the 3rd-generation LMTOs. Increasing N, widens the energy
window, inside which accurate results are obtained, and increases the range of
the orbitals, but it does not increase the size of the basis set and therefore
does not change the number of bands obtained. The price for reducing the size
of the basis set through downfolding, is a reduction in the number of bands
accounted for and -unless N is increased- a narrowing of the energy window
inside which these bands are accurate. A method for obtaining orthonormal NMTO
sets is given and several applications are presented.Comment: 85 pages, Latex2e, Springer style, to be published in: Lecture notes
in Physics, edited by H. Dreysse, (Springer Verlag
Third-Generation TB-LMTO
We describe the screened Korringa-Kohn-Rostoker (KKR) method and the
third-generation linear muffin-tin orbital (LMTO) method for solving the
single-particle Schroedinger equation for a MT potential. The simple and
popular formalism which previously resulted from the atomic-spheres
approximation (ASA) now holds in general, that is, it includes downfolding and
the combined correction. Downfolding to few-orbital, possibly short-ranged,
low-energy, and possibly orthonormal Hamiltonians now works exceedingly well,
as is demonstrated for a high-temperature superconductor. First-principles sp3
and sp3d5 TB Hamiltonians for the valence and lowest conduction bands of
silicon are derived. Finally, we prove that the new method treats overlap of
the potential wells correctly to leading order and we demonstrate how this can
be exploited to get rid of the empty spheres in the diamond structure.Comment: latex2e, 32 printed pages, Postscript figs, to be published in:
Tight-Binding Approach to Computational Materials Science, MRS Symposia
Proceedings No. 491 (MRS, Pittsburgh, 1998
Cultivating equality: delivering just and sustainable food systems in a changing climate
T
oday, the world faces a greater challenge perhaps than ever before:
tackling hunger and malnutrition in the face of climate change
and increasing natural resource scarcity. Civil society, governments,
researchers, donors, and the private sector are simultaneously debating
and collaborating to find solutions. But the dialogue is over-emphasizing
food production.
Improving yields is important, particularly in places where there is not
enough food or where food producers live in poverty. But simply producing
more is not enough to tackle hunger. Furthermore, acknowledging that
lack of food is not the sole cause of hunger is important. Inequality
shapes who has access to food and the resources to grow it and buy it.
It governs who eats first and who eats worst. Inequality determines who
can adapt more readily to a changing climate. Hunger and poverty are
not an accident â they are the result of social and economic injustice and
inequality at all levels, from household to global. The reality of inequality
is no truer for anyone than it is for women â half the worldâs population,
with far less than their fair share of the worldâs resources.
If we are to achieve the new Sustainable Development Goal of ending
hunger by 2030, we must address the underlying inequalities in food
systems. In a changing climate, agriculture and food systems must be
sustainable and productive â but our efforts cannot end there. They
must be profitable for those for whom it is a livelihood; they must be
equitable, to facilitate a level playing field in the market, to secure rights
to resources for food producers, and to ensure access to nutritious food for
all; they must be resilient to build the capacity of populations vulnerable
to economic shocks, political instability, and increasing, climate-induced
natural hazards to recover and still lift themselves out of poverty
Thiohalocapsa marina sp. nov., from an Indian marine aquaculture pond
A spherical-shaped, phototrophic, purple sulfur bacterium was isolated in pure culture from anoxic sediment in a marine aquaculture pond near Bheemli (India). Strain JA142T is Gram-negative and non-motile. It has a requirement for NaCl (optimum of 2â% and maximum of 6â% w/v NaCl). Intracellular photosynthetic membranes are of the vesicular type. In vivo absorption spectra indicate the presence of bacteriochlorophyll a and carotenoids of the okenone series as photosynthetic pigments. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain JA142T is related to halophilic purple sulfur bacteria of the genera Thiohalocapsa and Halochromatium, with the highest sequence similarity to Thiohalocapsa halophila DSM 6210T (97.5â%). Morphological and physiological characteristics differentiate strain JA142T from other species of the genera Halochromatium and Thiohalocapsa. Strain JA142T is sufficiently different from Thiohalocapsa halophila based on 16S rRNA gene sequence analysis and morphological and physiological characteristics to allow the proposal of a novel species, Thiohalocapsa marina sp. nov., with the type strain JA142T (=JCM 14780T =DSM 19078T).
The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain JA142T is AM491592.
A phase-contrast micrograph of cells of strain JA142T, whole-cell and acetone absorption spectra and 16S rRNA gene sequence-based neighbour-joining, maximum-likelihood, minimum-evolution and maximum-parsimony trees are available as supplementary material with the online version of this paper
Plasma exchange for primary autoimmune autonomic failure
We report on a patient with long-standing severe autonomic failure that affected his sympathetic and parasympathetic nervous systems. Antibodies against the ganglionic acetylcholine receptors were detected in the serum. Removal of the antibodies by means of plasma exchange resulted in a dramatic clinical improvement
Phylogeny of the Australian Solanum dioicum group using seven nuclear genes: Testing Symonâs fruit and seed dispersal hypotheses.
The dioecious and andromonoecious Solanum taxa (the âS. dioicum groupâ) of the Australian Monsoon Tropics have been the subject of phylogenetic and taxonomic study for decades, yet much of their basic biology is still unknown. This is especially true for plant-animal interactions, including the influence of fruit form and calyx morphology on seed dispersal. We combine field/greenhouse observations and specimen-based study with phylogenetic analysis of seven nuclear regions obtained via a microfluidic PCR-based enrichment strategy and high-throughput sequencing, and present the first species-tree hypothesis for the S. dioicum group. Our results suggest that epizoochorous trample burr seed dispersal (strongly linked to calyx accrescence) is far more common among Australian Solanum than previously thought and support the hypothesis that the combination of large fleshy fruits and endozoochorous dispersal represents a reversal in this study group. The general lack of direct evidence related to biotic dispersal (epizoochorous or endozoochorous) may be a function of declines and/or extinctions of vertebrate dispersers. Because of this, some taxa might now rely on secondary dispersal mechanisms (e.g. shakers, tumbleweeds, rafting) as a means to maintain current populations and establish new ones
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