5,982 research outputs found
MARKOV DIFFUSIONS IN COMOVING COORDINATES AND STOCHASTIC QUANTIZATION OF THE FREE RELATIVISTIC SPINLESS PARTICLE
We revisit the classical approach of comoving coordinates in relativistic
hydrodynamics and we give a constructive proof for their global existence under
suitable conditions which is proper for stochastic quantization. We show that
it is possible to assign stochastic kinematics for the free relativistic
spinless particle as a Markov diffusion globally defined on . Then
introducing dynamics by means of a stochastic variational principle with
Einstein's action, we are lead to positive-energy solutions of Klein-Gordon
equation. The procedure exhibits relativistic covariance properties.Comment: 31 pages + 1 figure available upon request; Plain REVTe
How does gas cool in DM halos?
In order to study the process of cooling in dark-matter (DM) halos and assess
how well simple models can represent it, we run a set of radiative SPH
hydrodynamical simulations of isolated halos, with gas sitting initially in
hydrostatic equilibrium within Navarro-Frenk-White (NFW) potential wells. [...]
After having assessed the numerical stability of the simulations, we compare
the resulting evolution of the cooled mass with the predictions of the
classical cooling model of White & Frenk and of the cooling model proposed in
the MORGANA code of galaxy formation. We find that the classical model predicts
fractions of cooled mass which, after about two central cooling times, are
about one order of magnitude smaller than those found in simulations. Although
this difference decreases with time, after 8 central cooling times, when
simulations are stopped, the difference still amounts to a factor of 2-3. We
ascribe this difference to the lack of validity of the assumption that a mass
shell takes one cooling time, as computed on the initial conditions, to cool to
very low temperature. [...] The MORGANA model [...] better agrees with the
cooled mass fraction found in the simulations, especially at early times, when
the density profile of the cooling gas is shallow. With the addition of the
simple assumption that the increase of the radius of the cooling region is
counteracted by a shrinking at the sound speed, the MORGANA model is also able
to reproduce for all simulations the evolution of the cooled mass fraction to
within 20-50 per cent, thereby providing a substantial improvement with respect
to the classical model. Finally, we provide a very simple fitting function
which accurately reproduces the cooling flow for the first ~10 central cooling
times. [Abridged]Comment: 15 pages, accepted by MNRA
A Teaching-Learning Framework for Materials Characterization
“Materials Characterization” is a broad discipline that plays a pivotal role in various scientific sectors and requires diversified training to provide learners with the necessary tools and skills for the investigation of materials’ structure, microstructure, and properties. This study puts forward a comprehensive framework aimed at providing undergraduate STEM students with a wide range of competencies for material characterization. These include acquiring the essential theoretical knowledge of key characterization methods, the ability to construct experimental plans, the skills needed for sample preparation, and the aptitude to generate, analyze, and interpret data. By combining various strategies and pedagogical tools, the framework aims to facilitate self-directed and self-determined learning, allowing students to shape their educational journey and explore areas of personal interest within the discipline. Furthermore, the framework incorporates diversified approaches aimed at developing research proficiency and the ability to communicate research outcomes, both within conference contexts and through report formats resembling publications. The findings demonstrate the promising prospect that undergraduate students have the capacity to acquire the methodologies of scientists and to produce work of comparable quality. This study testifies the considerable potential that lies in engaging enthusiastic and capable students in scientific research and fostering the early development of future researchers
Dynamical Generation of Noiseless Quantum Subsystems
We present control schemes for open quantum systems that combine decoupling
and universal control methods with coding procedures. By exploiting a general
algebraic approach, we show how appropriate encodings of quantum states result
in obtaining universal control over dynamically-generated noise-protected
subsystems with limited control resources. In particular, we provide an
efficient scheme for performing universal encoded quantum computation in a wide
class of systems subjected to linear non-Markovian quantum noise and supporting
Heisenberg-type internal Hamiltonians.Comment: 4 pages, no figures; REVTeX styl
Generalized Coherent States as Preferred States of Open Quantum Systems
We investigate the connection between quasi-classical (pointer) states and
generalized coherent states (GCSs) within an algebraic approach to Markovian
quantum systems (including bosons, spins, and fermions). We establish
conditions for the GCS set to become most robust by relating the rate of purity
loss to an invariant measure of uncertainty derived from quantum Fisher
information. We find that, for damped bosonic modes, the stability of canonical
coherent states is confirmed in a variety of scenarios, while for systems
described by (compact) Lie algebras stringent symmetry constraints must be
obeyed for the GCS set to be preferred. The relationship between GCSs,
minimum-uncertainty states, and decoherence-free subspaces is also elucidated.Comment: 5 pages, no figures; Significantly improved presentation, new
derivation of invariant uncertainty measure via quantum Fisher information
added
Experimental Implementation of a Concatenated Quantum Error-Correcting Code
Concatenated coding provides a general strategy to achieve the desired level
of noise protection in quantum information storage and transmission. We report
the implementation of a concatenated quantum error-correcting code able to
correct against phase errors with a strong correlated component. The experiment
was performed using liquid-state nuclear magnetic resonance techniques on a
four spin subsystem of labeled crotonic acid. Our results show that
concatenation between active and passive quantum error-correcting codes offers
a practical tool to handle realistic noise contributed by both independent and
correlated errors.Comment: 4 pages, 2 encapsulated eps figures. REVTeX4 styl
Constraints on upper crustal fluid circulation and seismogenesis from in-situ outcrop quantification of complex fault zone permeability
: The permeability of fault zones plays a significant role on the distribution of georesources and on seismogenesis in the brittle upper crust, where both natural and induced seismicity are often associated with fluid migration and overpressure. Detailed models of the permeability structure of fault zones are thus necessary to refine our understanding of natural fluid pathways and of the mechanisms leading to fluid compartmentalization and possible overpressure in the crust. Fault zones commonly contain complex internal architectures defined by the spatial juxtaposition of "brittle structural facies" (BSF), which progressively and continuously form and evolve during faulting and deformation. We present the first systematic in-situ outcrop permeability measurements from a range of BSFs from two architecturally complex fault zones in the Northern Apennines (Italy). A stark spatial heterogeneity of the present-day permeability (up to four orders of magnitude) even for tightly juxtaposed BSFs belonging to the same fault emerges as a key structural and hydraulic feature. Insights from this study allow us to better understand how complex fault architectures steer the 3D hydraulic structure of the brittle upper crust. Fault hydraulic properties, which may change through space but also in time during an orogenesis and/or individual seismic cycles, in turn steer the development of overpressured volumes, where fluid-induced seismogenesis may localize
Constraints on upper crustal fluid circulation and seismogenesis from in-situ outcrop quantification of complex fault zone permeability
The permeability of fault zones plays a significant role on the distribution of georesources and on seismogenesis in the brittle upper crust, where both natural and induced seismicity are often associated with fluid migration and overpressure. Detailed models of the permeability structure of fault zones are thus necessary to refine our understanding of natural fluid pathways and of the mechanisms leading to fluid compartmentalization and possible overpressure in the crust. Fault zones commonly contain complex internal architectures defined by the spatial juxtaposition of "brittle structural facies" (BSF), which progressively and continuously form and evolve during faulting and deformation. We present the first systematic in-situ outcrop permeability measurements from a range of BSFs from two architecturally complex fault zones in the Northern Apennines (Italy). A stark spatial heterogeneity of the present-day permeability (up to four orders of magnitude) even for tightly juxtaposed BSFs belonging to the same fault emerges as a key structural and hydraulic feature. Insights from this study allow us to better understand how complex fault architectures steer the 3D hydraulic structure of the brittle upper crust. Fault hydraulic properties, which may change through space but also in time during an orogenesis and/or individual seismic cycles, in turn steer the development of overpressured volumes, where fluid-induced seismogenesis may localize
Directional TGV-based image restoration under Poisson noise
We are interested in the restoration of noisy and blurry images where the texture mainly follows a single direction (i.e., directional images). Problems of this type arise, for example, in microscopy or computed tomography for carbon or glass fibres. In order to deal with these problems, the Directional Total Generalized Variation (DTGV) was developed by Kongskov et al. in 2017 and 2019, in the case of impulse and Gaussian noise. In this article we focus on images corrupted by Poisson noise, extending the DTGV regularization to image restoration models where the data fitting term is the generalized Kullback–Leibler divergence. We also propose a technique for the identifica-tion of the main texture direction, which improves upon the techniques used in the aforementioned work about DTGV. We solve the problem by an ADMM algorithm with proven convergence and subproblems that can be solved exactly at a low computational cost. Numerical results on both phantom and real images demonstrate the effectiveness of our approach
A Preliminary Study of Image Analysis for Parasite Detection on Honey Bees
International Conference Image Analysis and Recognition (ICIAR 2018, PĂłvoa de Varzim, Portugal
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