1,328 research outputs found
Orbital Optimization in the Density Matrix Renormalization Group, with applications to polyenes and \beta-carotene
In previous work we have shown that the Density Matrix Renormalization Group
(DMRG) enables near-exact calculations in active spaces much larger than are
possible with traditional Complete Active Space algorithms. Here, we implement
orbital optimisation with the Density Matrix Renormalization Group to further
allow the self-consistent improvement of the active orbitals, as is done in the
Complete Active Space Self-Consistent Field (CASSCF) method. We use our
resulting DMRGCASSCF method to study the low-lying excited states of the
all-trans polyenes up to C24H26 as well as \beta-carotene, correlating with
near-exact accuracy the optimised complete \pi-valence space with up to 24
active electrons and orbitals, and analyse our results in the light of the
recent discovery from Resonance Raman experiments of new optically dark states
in the spectrum.Comment: 16 pages, 8 figure
Phases of a two dimensional large N gauge theory on a torus
We consider two-dimensional large N gauge theory with D adjoint scalars on a
torus, which is obtained from a D+2 dimensional pure Yang-Mills theory on
T^{D+2} with D small radii. The two dimensional model has various phases
characterized by the holonomy of the gauge field around non-contractible cycles
of the 2-torus. We determine the phase boundaries and derive the order of the
phase transitions using a method, developed in an earlier work
(arxiv:0910.4526), which is nonperturbative in the 'tHooft coupling and uses a
1/D expansion. We embed our phase diagram in the more extensive phase structure
of the D+2 dimensional Yang-Mills theory and match with the picture of a
cascade of phase transitions found earlier in lattice calculations
(arxiv:0710.0098). We also propose a dual gravity system based on a
Scherk-Schwarz compactification of a D2 brane wrapped on a 3-torus and find a
phase structure which is similar to the phase diagram found in the gauge theory
calculation.Comment: 28 pages (+ 17 pages of appendix + 6 pages of ref.); 8 figures; (v2)
LaTeX Showkeys command deleted; (v3) refs and minor clarifications added;
emphasized the new proposal for applying holography to nonsupersymmetric
gauge theory; (v4) modified the arguments about holography; (v5) minor
corrections, version appeared in PR
Laser-Produced Heavy Ion Plasmas as Efficient Soft X-Ray Sources
We demonstrate extreme ultraviolet (EUV) and soft x-ray sources in the 2- to 7 -nm spectral region related to the beyond extreme ultraviolet (BEUV) question at 6.x nm and a water window source based on laser-produced high-Z plasmas. Strong emissions from multiply charged ions merge to produce intense unresolved transition array (UTA) toward extending below the carbon K-edge (4.37 nm). An outline of a microscope design for single-shot live- cell imaging is proposed based on a high-Z UTA plasma source, coupled to x-ray optics. We will discuss the progress and Z-scaling of UTA emission spectra to achieve lab-scale table-top, efficient, high-brightness high-Z plasma EUV-soft x-ray sources for in vivo bio-imaging applications
Monitoring active volcanoes: The geochemical approach
Shallow magmas located beneath active volcanoes release volatiles both
during eruptive activity and during inter-eruptive periods (passive degassing). The fluids in
active volcanic areas rise directly from magma, and their composition is characterized mainly
by H2O, CO2, SO2, H2S, HF and HCl (condensable gases), and by some non-condensable gases
(e.g. He, H2, N2, CO, CH4).
The chemical composition of fumarolic gases can reflect the pressure, temperature and
oxygen fugacity conditions of the deep magmatic source, provided that during their rise
towards the surface, the gases do not undergo re-equilibration processes [Giggenbach 1980,
Giggenbach 1996, Nuccio and Paonita 2001, Paonita et al. 2002]. As the equilibrium kinetics of
several chemical reactions is much slower than the rising velocities of the gases, the gas
molecular compositions often undergo quenching phenomena, so that the gases show
temperature and pressure equilibria higher than their outlet values.
The concentration of magmatic species or their molecular ratios can be determined by
means of direct sampling of fumarole gases or by using telemetric methods of observation.
The extensive parameters (mass output) of volcanic fluids, coupled with the intensive
parameters described before, provide basic and useful information for the formulation of
volcanic fluid degassing models [Italiano et al. 1997, Brusca et al. 2004, Inguaggiato et al. 2011].
The first step in the framework of the geochemical investigation of a volcanic system
aimed at surveillance is the chemical and isotopic characterization of the fluids, and the putting
forward of a geochemical model [Inguaggiato et al. 2011]; within this geochemical model, it is
possible to interpret the observed changes in any single investigated parameter. The
geochemical approach is to identify the following topics:
• The main end-members involved in the studied system;
• The possible type and degree of interaction processes: e.g. water-rock and gas-water interactions;
• The mixing among the individual end-members;
• The chemical and isotopic characterization of a possible hydrothermal system;
• The formulation of a geochemical model
Evidence for competition between the superconducting and the pseudogap state in (BiPb)_2(SrLa)_2CuO_{6+\delta} from muon-spin rotation experiments
The in-plane magnetic penetration depth \lambda_{ab} in optimally doped
(BiPb)_2(SrLa)_2CuO_{6+\delta} (OP Bi2201) was studied by means of muon-spin
rotation. The measurements of \lambda_{ab}^{-2}(T) are inconsistent with a
simple model of a d-wave order parameter and a uniform quasiparticle weight
around the Fermi surface. The data are well described assuming the angular gap
symmetry obtained in ARPES experiments [Phys. Rev. Lett {\bf 98}, 267004
(2007)], where it was shown that the superconducting gap in OP Bi2201 exists
only in segments of the Fermi surface near the nodes. We find that the
remaining parts of the Fermi surface, which are strongly affected by the
pseudogap state, do not contribute significantly to the superconducting
condensate. Our data provide evidence that high temperature superconductivity
and pseudogap behavior in cuprates are competing phenomena.Comment: 5 pages, 3 figure
Zero-field superfluid density in d-wave superconductor evaluated from the results of muon-spin-rotation experiments in the mixed state
We report on measurements of the in-plane magnetic penetration \lambda_{ab}
in the optimally doped cuprate superconductor (BiPb)_2(SrLa)_2CuO_6+\delta (OP
Bi2201) by means of muon-spin rotation (\muSR). We show that in unconventional
wave superconductors (like OP Bi2201), \muSR experiments conducted in
various magnetic fields allow to evaluate the zero-field magnetic penetration
depth \lambda_0, which relates to the zero-field superfluid density in terms of
\rho_s\propto\lambda_0^-2.Comment: 4 pages, 5 figure
Anisotropic Neutron Spin Resonance in Superconducting BaFeNiAs
We use polarized inelastic neutron scattering to show that the neutron spin
resonance below in superconducting BaFeNiAs (
K) is purely magnetic in origin. Our analysis further reveals that the
resonance peak near 7~meV only occurs for the planar response. This challenges
the common perception that the spin resonance in the pnictides is an isotropic
triplet excited state of the singlet Cooper pairs, as our results imply that
only the components of the triplet are involved
N-Soliton Solutions to a New (2 + 1) Dimensional Integrable Equation
We give explicitly N-soliton solutions of a new (2 + 1) dimensional equation,
. This equation is obtained by unifying two
directional generalization of the KdV equation, composing the closed ring with
the KP equation and Bogoyavlenskii-Schiff equation. We also find the Miura
transformation which yields the same ring in the corresponding modified
equations.Comment: 7 pages, uses ioplppt.st
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