3,484 research outputs found
Seismic and solar performance of historical city. Urban form-based multicriteria analysis
The understanding of the global performance of a historical city is a complex balance
of several specific issues and requires a multi-disciplinary approach to face with actual urban
phenomena and challenges, such as the seismic risk and energy efficiency, that are strongly
influenced by urban form. This paper focuses on the potential of urban metrics and typological
indicators for describing the seismic vulnerability and the solar radiation availability of distinct
urban textures, and the correlation between the two aspects. Comparative analysis at fabric scale
was conducted on the historical centre of Rieti (Latium, Italy), to underline the main seismic and
solar indicators. In the last decade, we witnessed the spreading of urban scale assessment and
analysis tools, but seldom using an integrated approach to face the complexity of the historical
city. Relying on morpho-typological indicators, the proposed method characterizes the fabrics in
terms of seismic vulnerability and solar availability through a multicriteria analysis. The analysis
reveals substantial differences between fabrics using three groups of indicators: Plan, Space and
Analysis-oriented. Each group describes different features of the urban fabrics that affect seismic
and solar performance and suggests improvement strategies. The purpose is to support
policymaker and designer in the urban renovation process
Freezing distributed entanglement in spin chains
We show how to freeze distributed entanglement that has been created from the
natural dynamics of spin chain systems. The technique that we propose simply
requires single-qubit operations and isolates the entanglement in specific
qubits at the ends of branches. Such frozen entanglement provides a useful
resource, for example for teleportation or distributed quantum processing. The
scheme can be applied to a wide range of systems -- including actual spin
systems and alternative qubit embodiments in strings of quantum dots, molecules
or atoms.Comment: 5 pages, to appear in Phys. Rev. A (Rapid Communication
Mesoporous matrices for quantum computation with improved response through redundance
We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation. (c) 2007 American Institute of Physics
Comparing persistence diagrams through complex vectors
The natural pseudo-distance of spaces endowed with filtering functions is
precious for shape classification and retrieval; its optimal estimate coming
from persistence diagrams is the bottleneck distance, which unfortunately
suffers from combinatorial explosion. A possible algebraic representation of
persistence diagrams is offered by complex polynomials; since far polynomials
represent far persistence diagrams, a fast comparison of the coefficient
vectors can reduce the size of the database to be classified by the bottleneck
distance. This article explores experimentally three transformations from
diagrams to polynomials and three distances between the complex vectors of
coefficients.Comment: 11 pages, 4 figures, 2 table
Geometry induced entanglement transitions in nanostructures
We model quantum dot nanostructures using a one-dimensional system of two
interacting electrons. We show that strong and rapid variations may be induced
in the spatial entanglement by varying the nanostructure geometry. We
investigate the position-space information entropy as an indicator of the
entanglement in this system. We also consider the expectation value of the
Coulomb interaction and the ratio of this expectation to the expectation of the
confining potential and their link to the entanglement. We look at the first
derivative of the entanglement and the position-space information entropy to
infer information about a possible quantum phase transition.Comment: 3 pages, 2 figures, to appear in Journal of Applied Physic
Hubbard model as an approximation to the entanglement in nanostructures
We investigate how well the one-dimensional Hubbard model describes the entanglement of particles trapped in a string of quantum wells. We calculate the average single-site entanglement for two particles interacting via a contact interaction and consider the effect of varying the interaction strength and the interwell distance. We compare the results with the ones obtained within the one-dimensional Hubbard model with on-site interaction. We suggest an upper bound for the average single-site entanglement for two electrons in M wells and discuss analytical limits for very large repulsive and attractive interactions. We investigate how the interplay between interaction and potential shape in the quantum-well system dictates the position and size of the entanglement maxima and the agreement with the theoretical limits. Finally, we calculate the spatial entanglement for the quantum-well system and compare it to its average single-site entanglement
Entanglement and density-functional theory: testing approximations on Hooke's atom
We present two methods of calculating the spatial entanglement of an
interacting electron system within the framework of density-functional theory.
These methods are tested on the model system of Hooke's atom for which the
spatial entanglement can be calculated exactly. We analyse how the strength of
the confining potential affects the spatial entanglement and how accurately the
methods that we introduced reproduce the exact trends. We also compare the
results with the outcomes of standard first-order perturbation methods. The
accuracies of energies and densities when using these methods are also
considered.Comment: 14 pages with 18 figures; corrected typos, corrected expression for
first-order energy in section VI and consequently Fig.13, conclusions and
other results unaffecte
Effect of confinement potential geometry on entanglement in quantum dot-based nanostructures
We calculate the spatial entanglement between two electrons trapped in a
nanostructure for a broad class of confinement potentials, including single and
double quantum dots, and core-shell quantum dot structures.
By using a parametrized confinement potential, we are able to switch from one
structure to the others with continuity and to analyze how the entanglement is
influenced by the changes in the confinement geometry. We calculate the
many-body wave function by `exact' diagonalization of the time independent
Schr\"odinger equation. We discuss the relationship between the entanglement
and specific cuts of the wave function, and show that the wave function at a
single highly symmetric point could be a good indicator for the entanglement
content of the system. We analyze the counterintuitive relationship between
spatial entanglement and Coulomb interaction, which connects maxima (minima) of
the first to minima (maxima) of the latter. We introduce a potential quantum
phase transition which relates quantum states characterized by different
spatial topology. Finally we show that by varying shape, range and strength of
the confinement potential, it is possible to induce strong and rapid variations
of the entanglement between the two electrons. This property may be used to
tailor nanostructures according to the level of entanglement required by a
specific application.Comment: 10 pages, 8 figures and 1 tabl
A Tutorial on the Optimization of Amplify-and-Forward MIMO Relay Systems
The remarkable promise of multiple-input multiple-output (MIMO) wireless channels has motivated an intense research activity to characterize the theoretical and practical issues associated with the design of transmit (source) and receive (destination) processing matrices under different operating conditions. This activity was primarily focused on point-to-point (single-hop) communications but more recently there has been an extensive work on two-hop or multi-hop settings in which single or multiple relays are used to deliver the information from the source to the destination. The aim of this tutorial is to provide an up-to-date overview of the fundamental results and practical implementation issues of designing amplify-and-forward MIMO relay systems
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