28,357 research outputs found
System for computing operational probability equations
SCOPE system computes an expression relating the probability of system success to the probabilities of success of its components. It is especially designed for complex system reliability studies
Model Hamiltonian for strongly-correlated systems: Systematic, self-consistent, and unique construction
An interacting lattice model describing the subspace spanned by a set of
strongly-correlated bands is rigorously coupled to density functional theory to
enable ab initio calculations of geometric and topological material properties.
The strongly-correlated subspace is identified from the occupation number band
structure as opposed to a mean-field energy band structure. The self-consistent
solution of the many-body model Hamiltonian and a generalized Kohn-Sham
equation exactly incorporates momentum-dependent and crystal-symmetric
correlations into electronic structure calculations in a way that does not rely
on a separation of energy scales. Calculations for a multiorbital Hubbard model
demonstrate that the theory accurately reproduces the many-body polarization.Comment: 19 pages, 11 figure
Approximate formula for the macroscopic polarization including quantum fluctuations
The many-body Berry phase formula for the macroscopic polarization is
approximated by a sum of natural orbital geometric phases with fractional
occupation numbers accounting for the dominant correlation effects. This
reduced formula accurately reproduces the exact polarization in the
Rice-Mele-Hubbard model across the band insulator-Mott insulator transition. A
similar formula based on a one-body reduced Berry curvature accurately predicts
the interaction-induced quenching of Thouless topological charge pumping
Cooperative catalysis by silica-supported organic functional groups
Hybrid inorganicâorganic materials comprising organic functional groups tethered from silica surfaces are versatile, heterogeneous catalysts. Recent advances have led to the preparation of silica materials containing multiple, different functional groups that can show cooperative catalysis; that is, these functional groups can act together to provide catalytic activity and selectivity superior to what can be obtained from either monofunctional materials or homogeneous catalysts. This tutorial review discusses cooperative catalysis of silica-based catalytic materials, focusing on the cooperative action of acidâbase, acidâthiol, amineâurea, and imidazoleâalcoholâcarboxylate groups. Particular attention is given to the effect of the spatial arrangement of these organic groups and recent developments in the spatial organization of multiple groups on the silica surface
Sex Differences with Aging in the Fatigability of Dynamic Contractions
This study determined the sex difference with aging in fatigability of the elbow flexor muscles during a dynamic fatiguing task, and explored the associated mechanisms. We compared fatigability of the elbow flexor muscles in 18 young (20.2 ± 1 years: 9 men) and 36 old adults (73.5 ± 1 years: 16 men) during and in recovery from repeated dynamic contractions (~ 60°/s) with a load equivalent to 20% of maximal voluntary isometric contraction (MVIC) torque until failure. Transcranial magnetic stimulation (TMS) was used to assess supraspinal fatigue (an increase in the superimposed twitch, SIT) and the peak rate of muscle relaxation. Time to failure was briefer for the men than the women (6.1 ± 2.1 vs. 9.7 ± 5.5 min, respectively; P = 0.02) with no difference between young and old adults (7.2 ± 2.9 vs. 8.4 ± 5.2 min, respectively, P = 0.45) and no interaction (P \u3e 0.05). The relative decline in peak relaxation rate with fatigability was similar for young and old adults (P = 0.11), but greater for men than women (P = 0.046). Supraspinal fatigue increased for all groups and was associated with the time to failure (P \u3c 0.05). Regression analysis however, indicated that the time to failure was best predicted by the peak relaxation rate (baseline values and slowing with fatigability) (r2 = 0.55). Rate-limiting contractile mechanisms (e.g. excitationâcontraction coupling) were responsible for the increased fatigability of the elbow flexors of men compared with women for a dynamic fatiguing task of slow angular velocity, and this sex difference was maintained with aging. The age difference in fatigability for the dynamic task was diminished for both sexes relative to what is typically observed with isometric fatiguing contractions
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Gaining assurance in a voter-verifiable voting system
The literature on e-voting systems has many examples of discussion of the correctness of the computer and communication algorithms of such systems, as well as discussions of their vulnerabilities. However, a gap in the literature concerns the practical need (before adoption of a specific e-voting system) for a complete case demonstrating that the system as a whole has sufficiently high probability of exhibiting the desired properties when in use in an actual election. This paper discusses the problem of producing such a case, with reference to a specific system: a version of the PrĂȘt Ă Voter scheme for voter-verifiable e-voting. We show a possible organisation of a case in terms of four main requirements â accuracy, privacy, termination and âtrustednessââ and show some of the detailed organisation that such a case should have, the diverse kinds of evidence that needs to be gathered and some of the interesting difficulties that arise
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