18,479 research outputs found
Nitrene Transfer Catalyzed by a Non-Heme Iron Enzyme and Enhanced by Non-Native Small-Molecule Cofactors
Transition-metal catalysis is a powerful tool for the construction of chemical bonds. Here we show that a non-heme iron enzyme can catalyze olefin aziridination and nitrene C–H insertion, and that these activities can be improved by directed evolution. The non-heme iron center allows for facile modification of the primary coordination sphere by addition of metal-coordinating molecules, enabling control over enzyme activity and selectivity using small molecules
On the inverse image of pattern classes under bubble sort
Let B be the operation of re-ordering a sequence by one pass of bubble sort.
We completely answer the question of when the inverse image of a principal
pattern class under B is a pattern class.Comment: 11 page
Canonical density matrix perturbation theory
Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev.
Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free energy
ensembles in tight-binding, Hartree-Fock or Kohn-Sham density functional
theory. The canonical density matrix perturbation theory can be used to
calculate temperature dependent response properties from the coupled perturbed
self-consistent field equations as in density functional perturbation theory.
The method is well suited to take advantage of sparse matrix algebra to achieve
linear scaling complexity in the computational cost as a function of system
size for sufficiently large non-metallic materials and metals at high
temperatures.Comment: 21 pages, 3 figure
Spin wave dispersion in La2CuO4
We calculate the antiferromagnetic spin wave dispersion in the half-filled
Hubbard model for a two-dimensional square lattice and find it to be in
excellent agreement with recent high-resolution inelastic neutron scattering
performed on La2CuO4 [Phys. Rev. Lett. 86, 5377 (2001)].Comment: typos correcte
Thermal state entanglement in harmonic lattices
We investigate the entanglement properties of thermal states of the harmonic
lattice in one, two and three dimensions. We establish the value of the
critical temperature for entanglement between neighbouring sites and give
physical reasons. Further sites are shown to be entangled only due to boundary
effects. Other forms of entanglement are addressed in the second part of the
paper by using the energy as witness of entanglement. We close with a
comprehensive diagram showing the different phases of entanglement versus
complete separability and propose techniques to swap and tune entanglement
experimentally.Comment: 9 pages, 4 figure
Susceptibility of the 2D S=1/2 Heisenberg antiferromagnet with an impurity
We use a quantum Monte Carlo method (stochastic series expansion) to study
the effects of a magnetic or nonmagnetic impurity on the magnetic
susceptibility of the two-dimensional Heisenberg antiferromagnet. At low
temperatures, we find a log-divergent contribution to the transverse
susceptibility. We also introduce an effective few-spin model that can
quantitatively capture the differences between magnetic and nonmagnetic
impurities at high and intermediate temperatures.Comment: 5 pages, 4 figures, v2: Updated data in figures, minor changes in
text, v3: Final version, cosmetic change
Interpretation of the ion mass spectra in the mass range 25-35 obtained in the inner coma of Halley's comet by the HIS-sensor of the Giotto IMS Experiment
The IMS-HIS double-focussing mass spectrometer that flew on the Giotto spacecraft covered the mass per charge range from 12 to 56 (AMU/e). By comparing flight data, calibration data, and results of model calculations of the ion population in the inner coma, the absolute mass scale is established, and ions in the mass range 25 to 35 are identified. Ions resulting from protonation of molecules with high proton affinity are relatively abundant, enabling us to estimate relative source strengths for H2CO, CH3OH, HCN, and H2S, providing for the first time a positive in situ measurement of methanol. Also, upper limits for NO and some hydrocarbons are derived
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