35,300 research outputs found
Analyticity of the density of electronic wavefunctions
We prove that the electronic densities of atomic and molecular eigenfunctions
are real analytic in away from the nuclei.Comment: 19 page
kmos: A lattice kinetic Monte Carlo framework
Kinetic Monte Carlo (kMC) simulations have emerged as a key tool for
microkinetic modeling in heterogeneous catalysis and other materials
applications. Systems, where site-specificity of all elementary reactions
allows a mapping onto a lattice of discrete active sites, can be addressed
within the particularly efficient lattice kMC approach. To this end we describe
the versatile kmos software package, which offers a most user-friendly
implementation, execution, and evaluation of lattice kMC models of arbitrary
complexity in one- to three-dimensional lattice systems, involving multiple
active sites in periodic or aperiodic arrangements, as well as site-resolved
pairwise and higher-order lateral interactions. Conceptually, kmos achieves a
maximum runtime performance which is essentially independent of lattice size by
generating code for the efficiency-determining local update of available events
that is optimized for a defined kMC model. For this model definition and the
control of all runtime and evaluation aspects kmos offers a high-level
application programming interface. Usage proceeds interactively, via scripts,
or a graphical user interface, which visualizes the model geometry, the lattice
occupations and rates of selected elementary reactions, while allowing
on-the-fly changes of simulation parameters. We demonstrate the performance and
scaling of kmos with the application to kMC models for surface catalytic
processes, where for given operation conditions (temperature and partial
pressures of all reactants) central simulation outcomes are catalytic activity
and selectivities, surface composition, and mechanistic insight into the
occurrence of individual elementary processes in the reaction network.Comment: 21 pages, 12 figure
Blockwise SVD with error in the operator and application to blind deconvolution
We consider linear inverse problems in a nonparametric statistical framework.
Both the signal and the operator are unknown and subject to error measurements.
We establish minimax rates of convergence under squared error loss when the
operator admits a blockwise singular value decomposition (blockwise SVD) and
the smoothness of the signal is measured in a Sobolev sense. We construct a
nonlinear procedure adapting simultaneously to the unknown smoothness of both
the signal and the operator and achieving the optimal rate of convergence to
within logarithmic terms. When the noise level in the operator is dominant, by
taking full advantage of the blockwise SVD property, we demonstrate that the
block SVD procedure overperforms classical methods based on Galerkin projection
or nonlinear wavelet thresholding. We subsequently apply our abstract framework
to the specific case of blind deconvolution on the torus and on the sphere
An investigation of the aerodynamic characteristics of a new general aviation airfoil in flight
A low speed airfoil, the GA(W)-2, - a 13% thickness to chord ratio airfoil was evaluated. The wing of a Beech Sundowner was modified at by adding balsa ribs and covered with aluminum skin, to alter the existing airfoil shape to that of the GA(W)-2 airfoil. The aircraft was flown in a flight test program that gathered wing surface pressures and wake data from which the lift drag, and pitching moment of the airfoil could be determined. After the base line performance of the airfoil was measured, the drag due to surface irregularities such as steps, rivets and surface waviness was determined. The potential reduction of drag through the use of surface coatings such as KAPTON was also investigated
A system for production of defective interfering particles in the absence of infectious influenza A virus
<div><p>Influenza A virus (IAV) infection poses a serious health threat and novel antiviral strategies are needed. Defective interfering particles (DIPs) can be generated in IAV infected cells due to errors of the viral polymerase and may suppress spread of wild type (wt) virus. The antiviral activity of DIPs is exerted by a DI genomic RNA segment that usually contains a large deletion and suppresses amplification of wt segments, potentially by competing for cellular and viral resources. DI-244 is a naturally occurring prototypic segment 1-derived DI RNA in which most of the PB2 open reading frame has been deleted and which is currently developed for antiviral therapy. At present, coinfection with wt virus is required for production of DI-244 particles which raises concerns regarding biosafety and may complicate interpretation of research results. Here, we show that cocultures of 293T and MDCK cell lines stably expressing codon optimized PB2 allow production of DI-244 particles solely from plasmids and in the absence of helper virus. Moreover, we demonstrate that infectivity of these particles can be quantified using MDCK-PB2 cells. Finally, we report that the DI-244 particles produced in this novel system exert potent antiviral activity against H1N1 and H3N2 IAV but not against the unrelated vesicular stomatitis virus. This is the first report of DIP production in the absence of infectious IAV and may spur efforts to develop DIPs for antiviral therapy.</p></div
Differential regulation of Ota and Otb, two primary glycine betaine transporters in the methanogenic archaeon Methanosarcina mazei go1
Methanogenic archaea accumulate glycine betaine in response to hypersalinity, but the regulation of proteins involved, their mechanism of activation and regulation of the corresponding genes are largely unknown. Methanosarcina mazei differs from most other methanoarchaea in having two gene clusters both encoding a potential glycine betaine transporter, Ota and Otb. Western blot as well as quantitative real-time PCR revealed that Otb is not regulated by osmolarity. On the other hand, cellular levels of Ota increased with increasing salt concentrations. A maximum was reached at 300-500 m M NaCl. Ota concentrations reached a maximum 4 h after an osmotic upshock. Hyperosmolarity also caused an increase in cellular Ota concentrations. In addition to osmolarity Ota expression was regulated by the growth phase. Expression of Ota as well as transport of betaine was downregulated in the presence of glycine betaine. Copyright (c) 2007 S. Karger AG, Basel
Crystal water induced switching of magnetically active orbitals in CuCl2
The dehydration of CuCl2*2(H2O) to CuCl2 leads to a dramatic change in
magnetic behavior and ground state. Combining density functional electronic
structure and model calculations with thermodynamical measurements we reveal
the microscopic origin of this unexpected incident -- a crystal water driven
switching of the magnetically active orbitals. This switching results in a
fundamental change of the coupling regime from a three-dimensional
antiferromagnet to a quasi one-dimensional behavior. CuCl2 can be well
described as a frustrated J1-J2 Heisenberg chain with ferromagnetic exchange J1
and J2/J1 ~ -1.5 for which a helical ground state is predicted.Comment: 6 pages, 5 figures, 1 table (PRB, accepted
Impact of elasticity on the piezoresponse of adjacent ferroelectric domains investigated by scanning force microscopy
As a consequence of elasticity, mechanical deformations of crystals occur on
a length scale comparable to their thickness. This is exemplified by applying a
homogeneous electric field to a multi-domain ferroelectric crystal: as one
domain is expanding the adjacent ones are contracting, leading to clamping at
the domain boundaries. The piezomechanically driven surface corrugation of
micron-sized domain patterns in thick crystals using large-area top electrodes
is thus drastically suppressed, barely accessible by means of piezoresponse
force microscopy
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