33,641 research outputs found
LDA+Gutzwiller Method for Correlated Electron Systems
Combining the density functional theory (DFT) and the Gutzwiller variational
approach, a LDA+Gutzwiller method is developed to treat the correlated electron
systems from {\it ab-initio}. All variational parameters are self-consistently
determined from total energy minimization. The method is computationally
cheaper, yet the quasi-particle spectrum is well described through kinetic
energy renormalization. It can be applied equally to the systems from weakly
correlated metals to strongly correlated insulators. The calculated results for
SrVO, Fe, Ni and NiO, show dramatic improvement over LDA and LDA+U.Comment: 4 pages, 3 figures, 1 tabl
Bifurcation Boundary Conditions for Switching DC-DC Converters Under Constant On-Time Control
Sampled-data analysis and harmonic balance analysis are applied to analyze
switching DC-DC converters under constant on-time control. Design-oriented
boundary conditions for the period-doubling bifurcation and the saddle-node
bifurcation are derived. The required ramp slope to avoid the bifurcations and
the assigned pole locations associated with the ramp are also derived. The
derived boundary conditions are more general and accurate than those recently
obtained. Those recently obtained boundary conditions become special cases
under the general modeling approach presented in this paper. Different analyses
give different perspectives on the system dynamics and complement each other.
Under the sampled-data analysis, the boundary conditions are expressed in terms
of signal slopes and the ramp slope. Under the harmonic balance analysis, the
boundary conditions are expressed in terms of signal harmonics. The derived
boundary conditions are useful for a designer to design a converter to avoid
the occurrence of the period-doubling bifurcation and the saddle-node
bifurcation.Comment: Submitted to International Journal of Circuit Theory and Applications
on August 10, 2011; Manuscript ID: CTA-11-016
The Multiphase Intracluster Medium in Galaxy Groups Probed by the Lyman Alpha Forest
The case is made that the intracluster medium (ICM) in spiral-rich galaxy
groups today probably has undergone much slower evolution than that in
elliptical-rich groups and clusters. The environments of proto-clusters and
proto-groups at z > 2 are likely similar to spiral-rich group environments at
lower redshift. Therefore, like the ICM in spiral-rich groups today, the ICM in
proto-groups and proto-clusters at z > 2 is predicted to be significantly
multiphased. The QSO Lyman alpha forest in the vicinity of galaxies is an
effective probe of the ICM at a wide range of redshift. Two recent observations
of Lyman alpha absorption around galaxies by Adelberger et al. and by
Pascarelle et al are reconciled, and it is shown that observations support the
multiphase ICM scenario. Galaxy redshifts must be very accurate for such
studies to succeed. This scenario can also explain the lower metallicity and
lower hot gas fraction in groups.Comment: 4 pages, 1 figure, replaced with the version after proo
Evidence for the formation of a Mott state in potassium-intercalated pentacene
We investigate electronic transport through pentacene thin-films intercalated
with potassium. From temperature-dependent conductivity measurements we find
that potassium-intercalated pentacene shows metallic behavior in a broad range
of potassium concentrations. Surprisingly, the conductivity exhibits a
re-entrance into an insulating state when the potassium concentration is
increased past one atom per molecule. We analyze our observations theoretically
by means of electronic structure calculations, and we conclude that the
phenomenon originates from a Mott metal-insulator transition, driven by
electron-electron interactions.Comment: 8 pages, 6 figure
Measurements of the semileptonic decays B[overbar]âDâÎœ[overbar] and B[overbar]âD^*âÎœ[overbar] using a global fit to DXâÎœ[overbar] final states
Semileptonic B[overbar] decays to DXâÎœ[overbar](â=e or ÎŒ) are selected by reconstructing D^0â and D^+â combinations from a sample of 230Ă10^6 ΄(4S)âBB[overbar] decays recorded with the BABAR detector at the PEP-II e^+e^- collider at SLAC. A global fit to these samples in a three-dimensional space of kinematic variables is used to determine the branching fractions B(B^-âD^0âÎœ[overbar])=(2.34±0.03±0.13)% and B(B^-âD^(*0)âÎœ[overbar])=(5.40±0.02±0.21)% where the errors are statistical and systematic, respectively. The fit also determines form-factor parameters in a parametrization based on heavy quark effective theory, resulting in Ï_D^2=1.20±0.04±0.07 for B[overbar]âDâÎœ[overbar] and Ï_(D*)^2=1.22±0.02±0.07 for B[overbar]âD^*âÎœ[overbar]. These values are used to obtain the product of the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)| times the form factor at the zero recoil point for both B[overbar]âDâÎœ[overbar] decays, G(1)|V_(cb)|=(43.1±0.8±2.3)Ă10^(-3), and for B[overbar]âD^*âÎœ[overbar] decays, F(1)|V_(cb)|=(35.9±0.2±1.2)Ă10^(-3)
Inclusive Î_c^+ production in e^+e^- annihilations at âs=10.54ââGeV and in ΄(4S) decays
We present measurements of the total production rates and momentum distributions of the charmed baryon Î_c^+ in e^+e^-âhadrons at a center-of-mass energy of 10.54 GeV and in ΄(4S) decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in e^+e^-âcc[overbar] events, allowing direct studies of c-quark fragmentation. We measure a momentum distribution for Î_c^+ baryons that differs significantly from those measured previously for charmed mesons. Comparing with a number of models, we find none that can describe the distribution completely. We measure an average scaled momentum of =0.574±0.009 and a total rate of N_(Îc)^(qq[overbar]) =0.057±0.002(exp)±0.015(BF)ââÎ_c^+ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, pK^-Ï^+. In ΄(4S) decays we measure a total rate of N_(Îc)^΄=0.091±0.006(exp)±0.024(BF) per ΄(4S) decay, and find a much softer momentum distribution than expected from B decays into a Î_c^+ plus an antinucleon and one to three pions
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