321 research outputs found
Barnes Hospital Record
https://digitalcommons.wustl.edu/bjc_barnes_record/1058/thumbnail.jp
Large-scale electronic structure theory for simulating nanostructure process
Fundamental theories and practical methods for large-scale electronic
structure calculations are given, in which the computational cost is
proportional to the system size. Accuracy controlling methods for microscopic
freedoms are focused on two practical solver methods, Krylov-subspace method
and generalized-Wannier-state method. A general theory called the
'multi-solver' scheme is also formulated, as a hybrid between different solver
methods. Practical examples are carried out in several insulating and metallic
systems with 10^3-10^5 atoms. All the theories provide general guiding
principles of constructing an optimal calculation for simulating nanostructure
processes, since a nanostructured system consists of several competitive
regions, such as bulk and surface regions, and the simulation is designed to
reproduce the competition with an optimal computational cost.Comment: 19 pages, 6 figures. To appear in J. Phys. Cond. Matt. A preprint PDF
file in better graphics is available at
http://fujimac.t.u-tokyo.ac.jp/lses/index_e.htm
De snuitkever Sitona cinerascens nieuw voor de fauna van Nederland
In deze bijdrage wordt Sitona cinerascens voor het eerst uit Nederland gemeld. Deze soort, die nergens in Europa algemeen voorkomt, is nu van drie locaties in het zuidwesten van ons land bekend. Er wordt kort ingegaan op de biologie van de soort en het voorkomen in Europ
Linear Algebraic Calculation of Green's function for Large-Scale Electronic Structure Theory
A linear algebraic method named the shifted
conjugate-orthogonal-conjugate-gradient method is introduced for large-scale
electronic structure calculation. The method gives an iterative solver
algorithm of the Green's function and the density matrix without calculating
eigenstates.The problem is reduced to independent linear equations at many
energy points and the calculation is actually carried out only for a single
energy point. The method is robust against the round-off error and the
calculation can reach the machine accuracy. With the observation of residual
vectors, the accuracy can be controlled, microscopically, independently for
each element of the Green's function, and dynamically, at each step in
dynamical simulations. The method is applied to both semiconductor and metal.Comment: 10 pages, 9 figures. To appear in Phys. Rev. B. A PDF file with
better graphics is available at http://fujimac.t.u-tokyo.ac.jp/lses
Hylis foveicollis (Coleoptera: Eucnemidae), een dood-houtkever nieuw voor de Nederlandse fauna
Hylis foveicollis is recorded for the first time from The Netherlands. This beetle is very rare throughout Europe, but it can lokally be found in large numbers under favourable conditions. The larvae develop in soft dead wood and probably feed on fung
Lattice field theory simulations of graphene
We discuss the Monte Carlo method of simulating lattice field theories as a
means of studying the low-energy effective theory of graphene. We also report
on simulational results obtained using the Metropolis and Hybrid Monte Carlo
methods for the chiral condensate, which is the order parameter for the
semimetal-insulator transition in graphene, induced by the Coulomb interaction
between the massless electronic quasiparticles. The critical coupling and the
associated exponents of this transition are determined by means of the
logarithmic derivative of the chiral condensate and an equation-of-state
analysis. A thorough discussion of finite-size effects is given, along with
several tests of our calculational framework. These results strengthen the case
for an insulating phase in suspended graphene, and indicate that the
semimetal-insulator transition is likely to be of second order, though
exhibiting neither classical critical exponents, nor the predicted phenomenon
of Miransky scaling.Comment: 14 pages, 7 figures. Published version freely available if accessed
via http://physics.aps.org/articles/v2/3
Krylov Subspace Method for Molecular Dynamics Simulation based on Large-Scale Electronic Structure Theory
For large scale electronic structure calculation, the Krylov subspace method
is introduced to calculate the one-body density matrix instead of the
eigenstates of given Hamiltonian. This method provides an efficient way to
extract the essential character of the Hamiltonian within a limited number of
basis set. Its validation is confirmed by the convergence property of the
density matrix within the subspace. The following quantities are calculated;
energy, force, density of states, and energy spectrum. Molecular dynamics
simulation of Si(001) surface reconstruction is examined as an example, and the
results reproduce the mechanism of asymmetric surface dimer.Comment: 7 pages, 3 figures; corrected typos; to be published in Journal of
the Phys. Soc. of Japa
Strengthening impact assessment: a call for integration and focus
We suggest that the impact assessment community has lost its way based on our observation that impact assessment is under attack because of a perceived lack of efficiency. Specifically, we contend that the proliferation of different impact assessment types creates separate silos of expertise and feeds arguments for not only a lack of efficiency but also a lack of effectiveness of the process through excessive specialisation and a lack of interdisciplinary practice. We propose that the solution is a return to the basics of impact assessment with a call for increased integration around the goal of sustainable development and focus through better scoping. We rehearse and rebut counter arguments covering silo-based expertise, advocacy, democracy, sustainability understanding and communication. We call on the impact assessment community to rise to the challenge of increasing integration and focus, and to engage in the debate about the means of strengthening impact assessment
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