1,154 research outputs found
Proof of finite surface code threshold for matching
The field of quantum computation currently lacks a formal proof of
experimental feasibility. Qubits are fragile and sophisticated quantum error
correction is required to achieve reliable quantum computation. The surface
code is a promising quantum error correction code, requiring only a physically
reasonable 2-D lattice of qubits with nearest neighbor interactions. However,
existing proofs that reliable quantum computation is possible using this code
assume the ability to measure four-body operators and, despite making this
difficult to realize assumption, require that the error rate of these operator
measurements is less than 10^-9, an unphysically low target. High error rates
have been proved tolerable only when assuming tunable interactions of strength
and error rate independent of distance, which is also unphysical. In this work,
given a 2-D lattice of qubits with only nearest neighbor two-qubit gates, and
single-qubit measurement, initialization, and unitary gates, all of which have
error rate p, we prove that arbitrarily reliable quantum computation is
possible provided p<7.4x10^-4, a target that many experiments have already
achieved. This closes a long-standing open problem, formally proving the
experimental feasibility of quantum computation under physically reasonable
assumptions.Comment: 5 pages, 4 figures, published versio
Simulations of aging and plastic deformation in polymer glasses
We study the effect of physical aging on the mechanical properties of a model
polymer glass using molecular dynamics simulations. The creep compliance is
determined simultaneously with the structural relaxation under a constant
uniaxial load below yield at constant temperature. The model successfully
captures universal features found experimentally in polymer glasses, including
signatures of mechanical rejuvenation. We analyze microscopic relaxation
timescales and show that they exhibit the same aging characteristics as the
macroscopic creep compliance. In addition, our model indicates that the entire
distribution of relaxation times scales identically with age. Despite large
changes in mobility, we observe comparatively little structural change except
for a weak logarithmic increase in the degree of short-range order that may be
correlated to an observed decrease in aging with increasing load.Comment: 9 pages, 12 figure
THE TRACES OF THE PAST: INFORMATIVE TOOLS FOR THE RECONSTRUCTION OF AURELIAN WALLS IN RIONE TESTACCIO
Abstract. Rome has a great cultural heritage, formed by the stratification of styles and political influences from different eras. The different eras and architectural styles that have defined the city in the two millennia of history, make each part unique in its kind. This succession of changes has by necessity led to the denial of some archaeologies that in past ages were pivotal points in the development of the ancient city. The research presented here is intended to analyze and reconstruct the archeology of the river stretch of the Aurelian Walls on the Lungotevere Testaccio partly disappeared from the architectural landscape of the city. The research was set in two main phases, the first based on the two-dimensional study of the lost fabric, focusing on the cartographic study and the digitization of them in the GIS environment. The second one still under development foresees the digitalization of the threedimensional elements detected and the insertion of these within the dedicated platforms.</p
INFORMATION MODELING AND LANDSCAPE: INTERVENTION METHODOLOGY FOR READING COMPLEX SYSTEMS
Abstract. When we talk about landscape and in particular landscape architecture, we refer to a living structure in continuous evolution and in clear contrast to the aesthetic and geometric immobility of the single architectural building. By landscape we mean a complex set of transformations of a historical and biological nature; the times of these components are very different, but they work in a single cycle and in symbiosis between them. This set is inseparable from what happens in the present, we must always think about who lives the reality and know how to interpret the different subjective perceptions of a space. The theme of landscape representation is a subject of difficult development, not only for the multiplicity of elements involved in a single system, but for the dynamism and continuous transformation of the element that one wants to study. The intrinsic multidisciplinarity in this field imposes different visions on the methodology to be used to understand and in the end represent. We must ask ourselves which is the problem in understanding how nowadays it is possible to develop a system capable of grouping the different needs that arise from the study of the landscape and which tools must be used in surveying and representation. To date, in the Italian context, the landscape project and its graphic representation is steady to the production of static images, realized with two-dimensional or three-dimensional digital drawing software, representing only the frames of reality, within the territory survey, or of future developments regarding projects. This methodology of representation imposes strong limits in the understanding of which systems and elements come into play when one enters into relationship with a living architecture.</p
Non-Gaussian fluctuations in stochastic models with absorbing barriers
The dynamics of a one-dimensional stochastic model is studied in presence of
an absorbing boundary. The distribution of fluctuations is analytically
characterized within the generalized van Kampen expansion, accounting for
higher order corrections beyond the conventional Gaussian approximation. The
theory is shown to successfully capture the non Gaussian traits of the sought
distribution returning an excellent agreement with the simulations, for {\it
all times} and arbitrarily {\it close} to the absorbing barrier. At large
times, a compact analytical solution for the distribution of fluctuations is
also obtained, bridging the gap with previous investigations, within the van
Kampen picture and without resorting to alternative strategies, as elsewhere
hypothesized.Comment: 2 figures, submitted to Phys. Rev. Let
Topological code Autotune
Many quantum systems are being investigated in the hope of building a
large-scale quantum computer. All of these systems suffer from decoherence,
resulting in errors during the execution of quantum gates. Quantum error
correction enables reliable quantum computation given unreliable hardware.
Unoptimized topological quantum error correction (TQEC), while still effective,
performs very suboptimally, especially at low error rates. Hand optimizing the
classical processing associated with a TQEC scheme for a specific system to
achieve better error tolerance can be extremely laborious. We describe a tool
Autotune capable of performing this optimization automatically, and give two
highly distinct examples of its use and extreme outperformance of unoptimized
TQEC. Autotune is designed to facilitate the precise study of real hardware
running TQEC with every quantum gate having a realistic, physics-based error
model.Comment: 13 pages, 17 figures, version accepted for publicatio
A Simulation of One Dimensional Contaminant Transport
In this note we present some simulations and some analytical solutions, in closed form, of the advection dispersion equation in one-dimensional domain. These solutions are obtained for not-conservative solutes by considering time-dependent, third type (Robin) boundary condition for first order reaction and linear equilibrium absorption. The Robin boundary condition models a combined production-decay function. The model is useful to describe sources as the contaminant release due to the failure of an underground pipelines or radioactive decay series. The developed analytical model gives rise to analytical solutions not present in the literature. Further, we remark that, for particular values of the rate constants involved in the model, our results furnish values which are in agreement with results present in the literature
Visualization of Coherent Destruction of Tunneling in an Optical Double Well System
We report on a direct visualization of coherent destruction of tunneling
(CDT) of light waves in a double well system which provides an optical analog
of quantum CDT as originally proposed by Grossmann, Dittrich, Jung, and Hanggi
[Phys. Rev. Lett. {\bf 67}, 516 (1991)]. The driven double well, realized by
two periodically-curved waveguides in an Er:Yb-doped glass, is designed so that
spatial light propagation exactly mimics the coherent space-time dynamics of
matter waves in a driven double-well potential governed by the Schr\"{o}dinger
equation. The fluorescence of Er ions is exploited to image the spatial
evolution of light in the two wells, clearly demonstrating suppression of light
tunneling for special ratios between frequency and amplitude of the driving
field.Comment: final versio
A clinical pilot study on the effect of the probiotic Lacticaseibacillus rhamnosus TOM 22.8 strain in women with vaginal dysbiosis
Lactobacilli with probiotic features play an essential role in maintaining a balanced vaginal microbiota and their administration has been suggested for the treatment and prevention of vaginal dysbiosis. The present study was aimed to in vitro and in vivo investigate the probiotic potential of the Lacticaseibacillus rhamnosus TOM 22.8 strain, isolated from the vaginal ecosystem of a healthy woman. For this purpose, safety and functional properties were in depth evaluated. The strain exhibited a broad spectrum of antagonistic activity against vaginal pathogens; adhesion capacity to both the vaginal VK2/E6E7 and the intestinal Caco-2 cells; anti-inflammatory and antioxidant activities, suggesting its promising probiotic features. In addition, an in vivo pilot-study was planned. Based on both clinical and microbiological parameters, the oral or vaginal strain administration, determined a significant pathogens reduction after 10 days of administration and a maintenance of eubiosis up to 30 days after the end of the treatment. Therefore, the L. rhamnosus TOM 22.8 strain can be proposed as valuable oral and/or vaginal treatment for vaginal dysbiosis
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