30,896 research outputs found
Quantal Density Functional Theory of Degenerate States
The treatment of degenerate states within Kohn-Sham density functional theory
(KS-DFT) is a problem of longstanding interest. We propose a solution to this
mapping from the interacting degenerate system to that of the noninteracting
fermion model whereby the equivalent density and energy are obtained via the
unifying physical framework of quantal density functional theory (Q-DFT). We
describe the Q-DFT of \textit{both} ground and excited degenerate states, and
for the cases of \textit{both} pure state and ensemble v-representable
densities. This then further provides a rigorous physical interpretation of the
density and bidensity energy functionals, and of their functional derivatives,
of the corresponding KS-DFT. We conclude with examples of the mappings within
Q-DFT.Comment: 10 pages. minor changes made. to appear in PR
Universal local pair correlations of Lieb-Liniger bosons at quantum criticality
The one-dimensional Lieb-Liniger Bose gas is a prototypical many-body system
featuring universal Tomonaga-Luttinger liquid (TLL) physics and free fermion
quantum criticality. We analytically calculate finite temperature local pair
correlations for the strong coupling Bose gas at quantum criticality using the
polylog function in the framework of the Yang-Yang thermodynamic equations. We
show that the local pair correlation has the universal value in the quantum critical regime, the TLL phase and the
quasi-classical region, where is the pressure per unit length rescaled by
the interaction energy with interaction
strength and linear density . This suggests the possibility to test
finite temperature local pair correlations for the TLL in the relativistic
dispersion regime and to probe quantum criticality with the local correlations
beyond the TLL phase. Furthermore, thermodynamic properties at high
temperatures are obtained by both high temperature and virial expansion of the
Yang-Yang thermodynamic equation.Comment: 8 pages, 6 figures, additional text and reference
Effective Field Theory of the Zero-Temperature Triangular-Lattice Antiferromagnet: A Monte Carlo Study
Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.Comment: 26 pages, 9 figure
Phosphorylation of conserved casein kinase sites regulates cAMP-response element-binding protein DNA binding in Drosophila
The Drosophila homolog of cAMP-response element-binding protein (CREB), dCREB2, exists with serine 231, equivalent to mammalian serine 133, in a predominantly phosphorylated state. Thus, unlike the mammalian protein, the primary regulation of dCREB2 may occur at a different step from serine 231 phosphorylation. Although bacterially expressed dCREB2 bound cAMP-response element sites, protein from Drosophila extracts was unable to do so unless treated with phosphatase. Phosphorylation of recombinant protein by casein kinase (CK) I or II, but not calcium-calmodulin kinase II or protein kinase A, inhibited DNA binding. Up to four conserved CK sites likely to be phosphorylated in vivo were responsible for this effect, and these sites were phosphorylated by a kinase present in Drosophila cell extracts that biochemically resembles CKII. We propose that the relative importance of different signaling pathways in regulating CREB activity may differ between Drosophila and mammals. In Drosophila, the dephosphorylation of CK sites appears to be the major regulatory step, while phosphorylation of serine 231 is necessary but secondary
Long range magnetic ordering in NaIrO
We report a combined experimental and theoretical investigation of the
magnetic structure of the honeycomb lattice magnet NaIrO, a strong
candidate for a realization of a gapless spin-liquid. Using resonant x-ray
magnetic scattering at the Ir L-edge, we find 3D long range
antiferromagnetic order below T=13.3 K. From the azimuthal dependence of
the magnetic Bragg peak, the ordered moment is determined to be predominantly
along the {\it a}-axis. Combining the experimental data with first principles
calculations, we propose that the most likely spin structure is a novel
"zig-zag" structure
Prediction of mechanical properties of β-SiAlON ceramics based on BP neural network
β-Si6-ZAlZOZN8-Z (0<Z≤2) ceramics with rod-like grain morphology were prepared by gas pressure sintering, and their mechanical properties (i.e., bulk density, hardness, fracture toughness, and flexural strength) were evaluated. A model to predict the mechanical properties of β-SiAlON ceramics was established by back propagation (BP) neural network, and the relationships between process parameters (i.e., Z-value and temperature) and mechanical properties were investigated. Results show that the model had good prediction accuracy and maximum relative error lower than 8 %. The model could reflect the complex nonlinear relationship between the process parameters and the mechanical properties of β-SiAlON ceramics. The model can provide an effective reference for optimizing the design of β-SiAlON ceramics
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