1,500 research outputs found
Lie Algebraic Similarity Transformed Hamiltonians for Lattice Model Systems
We present a class of Lie algebraic similarity transformations generated by
exponentials of two-body on-site hermitian operators whose Hausdorff series can
be summed exactly without truncation. The correlators are defined over the
entire lattice and include the Gutzwiller factor
, and two-site products of density
and spin
operators. The resulting non-hermitian many-body Hamiltonian can be solved in a
biorthogonal mean-field approach with polynomial computational cost. The
proposed similarity transformation generates locally weighted orbital
transformations of the reference determinant. Although the energy of the model
is unbound, projective equations in the spirit of coupled cluster theory lead
to well-defined solutions. The theory is tested on the 1D and 2D repulsive
Hubbard model where we find accurate results across all interaction strengths.Comment: The supplemental material is include
Composite fermion-boson mapping for fermionic lattice models
We present a mapping of elementary fermion operators onto a quadratic form of
composite fermionic and bosonic operators. The mapping is an exact isomorphism
as long as the physical constraint of one composite particle per cluster is
satisfied. This condition is treated on average in a composite particle
mean-field approach, which consists of an ansatz that decouples the composite
fermionic and bosonic sectors. The theory is tested on the one- and
two-dimensional Hubbard models. Using a Bogoliubov determinant for the
composite fermions and either a coherent or Bogoliubov state for the bosons, we
obtain a simple and accurate procedure for treating the Mott insulating phase
of the Hubbard model with mean-field computational cost
Tomography of the Reionization Epoch with Multifrequency CMB Observations
We study the constraints that future multifrequency Cosmic Microwave
Background (CMB) experiments will be able to set on the metal enrichment
history of the Inter Galactic Medium at the epoch of reionisation. We forecast
the signal to noise ratio for the detection of the signal introduced in the CMB
by resonant scattering off metals at the end of the Dark Ages. We take into
account systematics associated to inter-channel calibration, PSF reconstruction
errors and innacurate foreground removal. We develop an algorithm to optimally
extract the signal generated by metals during reionisation and to remove
accurately the contamination due to the thermal Sunyaev-Zel'dovich effect.
Although demanding levels of foreground characterisation and control of
systematics are required, they are very distinct from those encountered in
HI-21cm studies and CMB polarization, and this fact encourages the study of
resonant scattering off metals as an alternative way of conducting tomography
of the reionisation epoch. An ACT-like experiment with optimistic assumtions on
systematic effects, and looking at clean regions of the sky, can detect changes
of 3%-12% (95% c.l.) of the OIII abundance (with respect its solar value) in
the redshift range [12,22], for reionization redshift .
However, for , it can only set upper limits on NII abundance
increments of 60% its solar value in the redshift range [5.5,9],
(95% c.l.). These constraints assume that inter-channel calibration is accurate
down to one part in , which constitutes the most critical technical
requirement of this method, but still achievable with current technology.Comment: 10 pages, 2 figures, submitted to Astrophysical Journal. Comments are
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Colliding Pulse Mode-Locked Laser Diode using Multimode Interference Reflectors
We present a novel fully monolithic Colliding Pulse Mode-Locked Laser Diode (CPML) using Multimode Interference Reflectors (MMIRs) to create the laser resonator. We demonstrate experimentally for the first time to our knowledge the Colliding Pulse mode-locking of a laser using MMIRs by observation of the Optical Spectrum and by measuring the frequency spacing between the modes. This component is a promising candidate for Stable Millimeter-Wave Generation in ultra-wideband wireless communication links. Multimode Interference Reflectors are very versatile components that allow avoiding the required cleaved facets to operate
Document management practices in SMEs: An information management capability-based approach
Purpose: This research studied the current document management (DM) practices in small and medium-sized enterprises (SMEs) of a road freight transport sector in a South American city with the aim to determine strengths and challenges for improving information management. Design/methodology/approach: The study was conducted using a survey approach based on measuring information management capabilities (IMC) through the following main dimensions: perception about DM practices, DM policies and tools, IT usage, organizational climate, and problems related to document management. Findings: The main results from the work stated the challenges for these companies in adopting electronic document management systems (EDMS) and handling information effectively even though the business experience. Also, the study highlighted the top management commitment in terms of investments for IMC development. Nevertheless, this economic support tends to be not enough to afford the EDMS implementation.
Originality/value: Regarding the importance of information in road freight transport sector, this paper explored DM practices in a field in which no previous studies related to DM had been conducted and set the basis to make decisions to improve information management performance
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