6,797 research outputs found
Entanglement scaling at first order phase transitions
First order quantum phase transitions (1QPTs) are signaled, in the
thermodynamic limit, by discontinuous changes in the ground state properties.
These discontinuities affect expectation values of observables, including
spatial correlations. When a 1QPT is crossed in the vicinity of a second order
one (2QPT), due to the correlation length divergence of the latter, the
corresponding ground state is modified and it becomes increasingly difficult to
determine the order of the transition when the size of the system is finite.
Here we show that, in such situations, it is possible to apply finite size
scaling to entanglement measures, as it has recently been done for the order
parameters and the energy gap, in order to recover the correct thermodynamic
limit. Such a finite size scaling can unambigously discriminate between first
and second order phase transitions in the vicinity of multricritical points
even when the singularities displayed by entanglement measures lead to
controversial results
Cloning transformations in spin networks without external control
In this paper we present an approach to quantum cloning with unmodulated spin
networks. The cloner is realized by a proper design of the network and a choice
of the coupling between the qubits. We show that in the case of phase covariant
cloner the XY coupling gives the best results. In the 1->2 cloning we find that
the value for the fidelity of the optimal cloner is achieved, and values
comparable to the optimal ones in the general N->M case can be attained. If a
suitable set of network symmetries are satisfied, the output fidelity of the
clones does not depend on the specific choice of the graph. We show that spin
network cloning is robust against the presence of static imperfections.
Moreover, in the presence of noise, it outperforms the conventional approach.
In this case the fidelity exceeds the corresponding value obtained by quantum
gates even for a very small amount of noise. Furthermore we show how to use
this method to clone qutrits and qudits. By means of the Heisenberg coupling it
is also possible to implement the universal cloner although in this case the
fidelity is 10% off that of the optimal cloner.Comment: 12 pages, 13 figures, published versio
Mathematics anxiety, working memory, and mathematics performance in secondary-school children
Mathematics anxiety (MA) has been defined as \u201ca feeling of tension and anxiety that interferes with the manipulation of numbers and the solving of math problems in a wide variety of ordinary life and academic situations\u201d. Previous studies have suggested that a notable proportion of children in primary and secondary school suffer from MA, which is negatively correlated with calculation skills. The processing efficiency and attentional control theories suggest that working memory (WM) also plays an important part in such anxious feelings.
The present study aimed to analyze the academic achievement and cognitive profiles of students with high math anxiety (HMA) and low math anxiety (LMA). Specifically, 32 students with HMA and 34 with LMA matched for age, gender, generalized anxiety, and vocabulary attending sixth to eighth grades were selected from a larger sample. The two groups were tested on reading decoding, reading comprehension, mathematics achievement, and on verbal short-term memory and WM. Our findings showed that HMA students were weak in several measures of mathematics achievement, but not in reading and writing skills, and that students with HMA reported lower scores on short-term memory and WM performances (with associated difficulties in inhibiting irrelevant information) than children with LMA. In addition, a logistic regression showed that weaknesses in inhibitory control and fact retrieval were the strongest variables for classifying children as having HMA or LMA
Guest editorial: Scientific seminar of the Italian Association of Transport Academicians (SIDT) 2019
Entanglement production by quantum error correction in the presence of correlated environment
We analyze the effect of a quantum error correcting code on the entanglement
of encoded logical qubits in the presence of a dephasing interaction with a
correlated environment. Such correlated reservoir introduces entanglement
between physical qubits. We show that for short times the quantum error
correction interprets such entanglement as errors and suppresses it. However
for longer time, although quantum error correction is no longer able to correct
errors, it enhances the rate of entanglement production due to the interaction
with the environment.Comment: 7 pages, 3 figures, published versio
Etude de l'efficacité d'un humain avec une canne
International audienceThis paper proposes a mathematical model of the walking with canes for an anthropomorphic biped with two identical legs with massless feet, two identical arms, and a torso. The walking is performed in the sagittal plane. The walking gait, which is cyclic, is composed of single support (SS) phases and impacts. The period of this cyclic walking is determined by the stride, because the motion of coupled arms is synchronized on this stride. The cane is considered massless. Thus in order to compare the walking with and without massless cane, the dynamic dynamic. Numerical tests show that the magnitude of the ground reaction in the stance foot is less with a massless-cane assistance than without one. Especially, the results prove that it is better to use canes with a handle
Risk factors for obstructive sleep apnea syndrome in children: state of the art
The obstructive sleep apnea syndrome (OSAS) represents only part of a large group of pathologies of variable entity called respiratory sleep disorders (RSD) which include simple snoring and increased upper airway resistance syndrome (UARS). Although the etiopathogenesis of adult OSAS is well known, many aspects of this syndrome in children are still debated. Its prevalence is about 2% in children from 2 to 8 years of age, mostly related to the size of the upper airways adenoid tissue. Several risk factors linked to the development of OSAS are typical of the pediatric age. The object of this paper is to analyze the state of the art on this specific topic, discussing its implications in terms of diagnosis and management
Stochastic dynamics beyond the weak coupling limit: thermalization
We discuss the structure and asymptotic long-time properties of coupled
equations for the moments of a Brownian particle's momentum derived
microscopically beyond the lowest approximation in the weak coupling parameter.
Generalized fluctuation-dissipation relations are derived and shown to ensure
convergence to thermal equilibrium at any order of perturbation theory.Comment: 6+ page
Role of miR-200c in myogenic differentiation impairment via p66Shc: implication in skeletal muscle regeneration of dystrophic mdx mice
Duchenne muscular dystrophy (DMD) is a genetic disease associated with mutations of Dystrophin gene that regulate myofiber integrity and muscle degeneration, characterized by oxidative stress increase. We previously published that reactive oxygen species (ROS) induce miR-200c that is responsible for apoptosis and senescence. Moreover, we demonstrated that miR-200c increases ROS production and phosphorylates p66Shc in Ser-36. p66Shc plays an important role in muscle differentiation; we previously showed that p66Shc(-/-) muscle satellite cells display lower oxidative stress levels and higher proliferation rate and differentiated faster than wild-type (wt) cells. Moreover, myogenic conversion, induced by MyoD overexpression, is more efficient in p66Shc(-/-) fibroblasts compared to wt cells. Herein, we report that miR-200c overexpression in cultured myoblasts impairs skeletal muscle differentiation. Further, its overexpression in differentiated myotubes decreases differentiation indexes. Moreover, anti-miR-200c treatment ameliorates myogenic differentiation. In keeping, we found that miR-200c and p66Shc Ser-36 phosphorylation increase in mdx muscles. In conclusion, miR-200c inhibits muscle differentiation, whereas its inhibition ameliorates differentiation and its expression levels are increased in mdx mice and in differentiated human myoblasts of DMD. Therefore, miR-200c might be responsible for muscle wasting and myotube loss, most probably via a p66Shc-dependent mechanism in a pathological disease such as DMD
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