1,663 research outputs found
Graviton Propagators in Supergravity and Noncommutative Gauge Theory
We investigate the graviton propagator in the type IIB supergravity
background which is dual to 4 dimensional noncommutative gauge theory. We
assume that the boundary is located not at the infinity but at the
noncommutative scale where the string frame metric exhibits the maximum. We
argue that the Neumann boundary condition is the appropriate boundary condition
to be adopted at the boundary. We find that the graviton propagator behaves
just as that of the 4 dimensional massless graviton. On the other hand, the
non-analytic behaviors of the other Kaluza-Klein modes are not significantly
affected by the Neumann boundary condition.Comment: 19 page
Adaptive experimental design for one-qubit state estimation with finite data based on a statistical update criterion
We consider 1-qubit mixed quantum state estimation by adaptively updating
measurements according to previously obtained outcomes and measurement
settings. Updates are determined by the average-variance-optimality
(A-optimality) criterion, known in the classical theory of experimental design
and applied here to quantum state estimation. In general, A-optimization is a
nonlinear minimization problem; however, we find an analytic solution for
1-qubit state estimation using projective measurements, reducing computational
effort. We compare numerically two adaptive and two nonadaptive schemes for
finite data sets and show that the A-optimality criterion gives more precise
estimates than standard quantum tomography.Comment: 15 pages, 7 figure
Single-component quasicrystalline nanocrystal superlattices through flexible polygon tiling rule
Quasicrystalline superlattices (QC-SLs) generated from single-component colloidal building blocks have been predicted by computer simulations but are challenging to reproduce experimentally. We discovered that 10-fold QC-SLs could self-organize from truncated tetrahedral quantum dots with anisotropic patchiness. Transmission electron microscopy and tomography measurements allow structural reconstruction of the QC-SL from the nanoscale packing to the atomic-scale orientation alignments. The unique QC order leads to a tiling concept, the âflexible polygon tiling rule,â that replicates the experimental observations. The keys for the single-component QC-SL formation were identified to be the anisotropic shape and patchiness of the building blocks and the assembly microscopic environment. Our discovery may spur the creation of various superstructures using anisotropic objects through an enthalpy-driven route
Magnus Force in High Temperature Superconductivity and Berry Phase
In the topological framework of high temperature superconductivity we have
discussed the Magnus force acting on its vortices
Fontes de nitrogĂȘnio e tĂ©cnicas de propagação de mudas atuam na produtividade de erva-mate.
Avaliou-se a influĂȘncia de fontes de nitrogĂȘnio e tĂ©cnicas de propagação na produtividade de erva-mate. Em plantio realizado em 2005 em SĂŁo Mateus do Sul-PR (SMS), no espaçamento 1,2 x 3,0 m com mudas propagadas: por semente (procedĂȘncia SMS) e por miniestaquia (procedĂȘncias Bituruna, Cruz Machado e SMS). Em 2010, apĂłs a segunda colheita aplicou-se 130 kg ha-1 de nitrogĂȘnio na forma de nitrato de amĂŽnio, sulfato de amĂŽnio e ureia. Na colheita de 2012, com intervalo de 18 meses, quantificou-se a produtividade de erva-mate comercial, galho fino e galho grosso. A produtividade de todos os componentes avaliados foi influenciada pela interação entre fontes de N e procedĂȘncias. Conclui-se que a preferĂȘncia da erva-mate pela fonte de nitrogĂȘnio Ă© dependente do local de origem da cultura; a miniestaquia Ă© uma tĂ©cnica eficiente na propagação de erva-mate, recomendada para melhorar a produtividade da cultura
Asymptotic estimation theory for a finite dimensional pure state model
The optimization of measurement for n samples of pure sates are studied. The
error of the optimal measurement for n samples is asymptotically compared with
the one of the maximum likelihood estimators from n data given by the optimal
measurement for one sample.Comment: LaTeX, 23 pages, Doctoral Thesi
Hole dynamics in a quantum antiferromagnet beyond the retraceable path approximation
The one-hole spectral weight for two chains and two dimensional lattices is
studied numerically using a new method of analysis of the spectral function
within the Lanczos iteration scheme: the Lanczos spectra decoding method. This
technique is applied to the model for , directly in the
infinite size lattice. By a careful investigation of the first 13 Lanczos steps
and the first 26 ones for the two dimensional and the two chain cases
respectively, we get several new features of the one-hole spectral weight. A
sharp incoherent peak with a clear momentum dispersion is identified, together
with a second broad peak at higher energy. The spectral weight is finite up to
the Nagaoka energy where it vanishes in a non-analytic way. Thus the lowest
energy of one hole in a quantum antiferromagnet is degenerate with the Nagaoka
energy in the thermodynamic limit.Comment: RevTeX 3.0, SISSA preprint 156/93/CM/MB, 10 pages + postscript file
appended, contains more accurate calculations in Fig.
Variationnal study of ferromagnetism in the t1-t2 Hubbard chain
A one-dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping is studied variationally. This allows to exclude saturated
ferromagnetism for . The variational boundary has a minimum
at a ``critical density'' and diverges for .Comment: 5 pages, LateX and 1 postscript figure. To appear in Physica
Decay of Superconducting and Magnetic Correlations in One- and Two-Dimensional Hubbard Models
In a general class of one and two dimensional Hubbard models, we prove upper
bounds for the two-point correlation functions at finite temperatures for
electrons, for electron pairs, and for spins. The upper bounds decay
exponentially in one dimension, and with power laws in two dimensions. The
bounds rule out the possibility of the corresponding condensation of
superconducting electron pairs, and of the corresponding magnetic ordering. Our
method is general enough to cover other models such as the t-J model.Comment: LaTeX, 8 pages, no figures. A reference appeared after the
publication is adde
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