8,315 research outputs found
Diameter Perfect Lee Codes
Lee codes have been intensively studied for more than 40 years. Interest in
these codes has been triggered by the Golomb-Welch conjecture on the existence
of the perfect error-correcting Lee codes. In this paper we deal with the
existence and enumeration of diameter perfect Lee codes. As main results we
determine all for which there exists a linear diameter-4 perfect Lee code
of word length over and prove that for each there are
uncountable many diameter-4 perfect Lee codes of word length over This
is in a strict contrast with perfect error-correcting Lee codes of word length
over \ as there is a unique such code for and its is
conjectured that this is always the case when is a prime. We produce
diameter perfect Lee codes by an algebraic construction that is based on a
group homomorphism. This will allow us to design an efficient algorithm for
their decoding. We hope that this construction will turn out to be useful far
beyond the scope of this paper
Accurate and efficient algorithm for Bader charge integration
We propose an efficient, accurate method to integrate the basins of
attraction of a smooth function defined on a general discrete grid, and apply
it to the Bader charge partitioning for the electron charge density. Starting
with the evolution of trajectories in space following the gradient of charge
density, we derive an expression for the fraction of space neighboring each
grid point that flows to its neighbors. This serves as the basis to compute the
fraction of each grid volume that belongs to a basin (Bader volume), and as a
weight for the discrete integration of functions over the Bader volume.
Compared with other grid-based algorithms, our approach is robust, more
computationally efficient with linear computational effort, accurate, and has
quadratic convergence. Moreover, it is straightforward to extend to non-uniform
grids, such as from a mesh-refinement approach, and can be used to both
identify basins of attraction of fixed points and integrate functions over the
basins.Comment: 19 pages, 8 figure
Creating partnerships for capacity building in developing countries - the experience of the World Bank
The authors discuss a variety of experiences in a number of transition, and developing countries to build institutional capacity for economics education. A flexible approach met with some success. The approach uses partnerships that combine the often different needs of a number of private donors, with the World Bank on the supply side. Much of the success was due to adopting each effort to the individual country situation. The authors also provide a brief summary of five academic institutions, and four research networks in Europe, Africa, Asia, and Latin America.Public Health Promotion,Health Monitoring&Evaluation,Agricultural Knowledge&Information Systems,Decentralization,ICT Policy and Strategies,ICT Policy and Strategies,Health Monitoring&Evaluation,Agricultural Knowledge&Information Systems,Tertiary Education,Scientific Research&Science Parks
The role of different negatively charged layers in Ca10(Fe1-xPtxAs)10(Pt3+yAs8) and superconductivity at 30 K in electron-doped (Ca0.8La0.2)10(FeAs)10(Pt3As8)
The recently discovered compounds Ca10(Fe1-xPtxAs)10(Pt3+yAs8) exhibit
superconductivity up to 38 K, and contain iron arsenide (FeAs) and platinum
arsenide (Pt3+yAs8) layers separated by layers of Ca atoms. We show that high
Tc's above 15 K only emerge if the iron-arsenide layers are at most free of
platinum-substitution (x \rightarrow 0) in contrast to recent reports. In fact
Pt-substitution is detrimental to higher Tc, which increases up to 38 K only by
charge doping of pure FeAs layers. We point out, that two different negatively
charged layers [(FeAs)10]n- and (Pt3+yAs8)m- compete for the electrons provided
by the Ca2+ ions, which is unique in the field of iron-based superconductors.
In the parent compound Ca10(FeAs)10(Pt3As8), no excess charge dopes the
FeAs-layer, and superconductivity has to be induced by Pt-substitution, albeit
below 15 K. In contrast, the additional Pt-atom in the Pt4As8layer shifts the
charge balance between the layers equivalent to charge doping by 0.2 electrons
per FeAs. Only in this case Tc raises to 38 K, but decreases again if
additionally platinum is substituted for iron. This charge doping scenario is
supported by our discovery of superconductivity at 30 K in the electron-doped
La-1038 compound (Ca0.8La0.2)10(FeAs)10(Pt3As8) without significant
Pt-substitution.Comment: 4 pages, 4 figure
Surface properties of the clean and Au/Pd covered FeO(111): a DFT and DFT+ study
The spin-density functional theory (DFT) and DFT+ with Hubbard term
accounting for on-site Coulomb interactions were applied to investigate
structure, stability, and electronic properties of different terminations of
the FeO(111) surface. All terminations of the ferrimagnetic
FeO(111) surface exhibit very large (up to 90%) relaxations of the
first four interlayer distances, decreasing with the oxide layer depth. Our
calculations predict the iron terminated surface to be most stable in a wide
range of the accessible values of the oxygen chemical potential. The adsorption
of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our
results show that Pd binds stronger than Au both to the Fe- and O-terminated
surface. DFT+ gives stronger bonding than DFT. The bonding of both
adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than
to the Fe-terminated surface
Chromogranin A in the pancreatic islet
Chromogranin A (CGA) is the major soluble protein within secretory vesicles of chromaffin cells. A polyclonal antiserum was raised against bovine CGA and characterized in two-dimensional immunoblots. Cellular and subcellular distribution of CGA in bovine pancreatic islet was investigated by immunocytochemistry. At the light microscopic level, CGA-like immunoreactivity was found in the same cells that react with antibodies against insulin, glucagon, and somatostatin. A minority of cells containing pancreatic polypeptide also showed faint immunostaining. At the ultrastructural level (protein A-gold technique), CGA-like immunoreactivity was confined exclusively to the secretory vesicles. Whereas the hormones were localized mainly in the central part of the secretory vesicles, CGA was present predominantly in the periphery. These findings indicate that a CGA-like protein is a regular constituent of the matrix of secretory vesicles in pancreatic endocrine cells
Characterization of hormone and protein release from alpha-toxin- permeabilized chromaffin cells in primary culture
Addition of Staphylococcus aureus alpha-toxin to adult bovine chromaffin cells maintained in primary culture causes permeabilization of cell membrane as shown by the release of intracellular 86Rb+. The alpha-toxin does not provoke a spontaneous release of either catecholamines or chromogranin A, a protein marker of the secretory granule, showing the integrity of the secretory vesicle membrane. However the addition of micromolar free Ca2+ concentration induced the co-release of noradrenaline and chromogranin A. In alpha-toxin-treated cells, the released chromogranin A could not be sedimented and lactate dehydrogenase was still associated within cells, which provides direct evidence that secretory product is liberated by exocytosis. By contrast, permeabilization of cells with digitonin caused a Ca2+- dependent but also a Ca2+-independent release of secretory product, a dramatic loss of lactate dehydrogenase, as well as release of secretory product in a sedimentable form. Ca2+-dependent exocytosis from alpha- toxin-permeabilized cells required Mg2+-ATP and did not occur in the presence of other nucleotides. Thus alpha-toxin is a convenient tool to permeabilize chromaffin cells, and has the advantage of keeping intracellular structures, specifically the exocytotic machinery, intact
Equivalent instances of the simple plant location problem
In this paper we deal with a pseudo-Boolean representation of the simple plant location problem. We define instances of this problem that are equivalent, in the sense that each feasible solution has the same goal function value in all such instances. We further define a collection of polytopes whose union describes the set of instances equivalent to a given instance. We use the concept of equivalence to develop a method by which we can extend the set of instances that we can solve using our knowledge of polynomially solvable special cases. We also present a new preprocessing rule that allows us to determine sites in which facilities will not be located in an optimal solution and thereby reduce the size of a problem instance.
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